UNIVERSITY OF WASHINGTON
DEPARTMENT OF ATMOSPHERIC SCIENCES
SEATTLE, WASHINGTON 98105
CONTRIBUTIONS FROM
THE CLOUD PHYSICS LABORATORY
Field Research in Cloud Physics in the
Olympic Mountains, Winter 1967-68
by
P. V. Hobbs, W. D. Scott, D. A. Burrows,
L. F. Radke and J. D. Locatelli
SEPTEMBER 1968 i
ABSTRACT
A field program in cloud physics was carried out at the research station in the Olympic Mountains from January 22 to
March 31, 1968. During this period measurements were made of cloud condensation nuclei, ice nuclei, Aitken particles, light scattering coefficient of the air, ozone, and airborne sodium- containing particles. Observations were also made of the types and concentrations of ice and water particles in the clouds that formed at station level. On a number of occasions simul- taneous measurements were obtained of the atmospheric electric field, the net charges on precipitation particles, and the charges that these particles communicated to an ice surface with which they collided. 11
TABLE OF CONTENTS Page
Abstract
List of Figures ^y
List of Tables vn
Introduction 1
SECTION 1 SYNOPTIC MEASUREMENTS 5
SECTION 2 CLOUD CONDENSATION NUCLEI, LIGHT SCATTERING COEFFICIENT, SODIUM-CONTAINING PARTICLES, AND AITKEN NUCLEI MEASUREMENTS 8
2.1 Cloud condensation nuclei 8 2.2 Light scattering measurements 18 2.3 Sodium-containing particles 23 2.4 Aitken nuclei 30
SECTION 3 ICE NUCLEI AND OZONE MEASUREMENTS 32
3.1 Locations 32 3.2 Instrumentation 34 3.3 Comparison between ice nucleus counts in the Olympic Mountains and in Seattle 36 3.4 The effect on the concentrations of ice nuclei in the Olympics of the transport of air from the Puget Sound and Seattle 36 3.5 The effects of snowfall on the concentration of ice nuclei and ozone 52 3.6 The effect of fronts on the concentrations of ice nuclei and ozone 54 3.7 Increases in ice nucleus concentration accompanying westerly flow 55 3.8 Twelve-hour average variations in ice nucleus counts and ozone 56
SECTION 4 CLOUD AND PRECIPITATION PARTICLES 64
4.1 Types of particles 64 4.2 Liquid water content 64 4.3 Concentrations of ice particles 65
SECTION 5 ELECTRICAL MEASUREMENTS 69
5.1 Charging of an ice sphere moving through natural snowfall 69 5.2 Electrical charges on individual ice particles in the air 81 Ill
5. 3 Individual charges received by a surface exposed to natural cloud and precipitation particles 101 APPENDICES
Appendix A 106
Appendix B 115
Appendix C 127
REFERENCES 135
ACKNOWLEDGMENTS 137 IV
LIST OF FIGURES
Figure
Fig. 1 Location of the Olympic Mountains. 2
Fig. 2 Schematic diagram of the automatic cloud condensation nucleus counter. 9
Fig. 3 Concentrations of cloud condensation nuclei at 1% supersaturation and light scattering coefficient b during March 28, 1968. 12 s Fig. 4 Concentrations of cloud condensation nuclei at 1% supersaturation and light scattering coefficient b during March 29, 1968. 13 S Fig. 5 Twelve-hour variations in cloud condensation nuclei counts and light scattering coefficient b during s February. 15
Fig. 6 Twelve-hour variations in cloud condensation nuclei counts and light scattering coefficient b during s March. 16
Fig. 7 Concentration of cloud condensation nuclei at 1% supersaturation during February 7, 1968. 17
Fig. 8 Concentration of cloud condensation nuclei at 1Z supersaturation and light scattering coefficient b during March 26, 1968. s 19 Fig. 9 Variations of concentration of cloud condensation nuclei with supersaturation in different types of air mass. 20
Fig. 10 Diurnal variation in light scattering coefficient b for February 13, 1968. 24 S Fig. 11 Flame spectrometer. 26
Fig. 12 Size spectra of sodium-containing particles in the air measured on March 13, 1968. 29
Fig. 13 Location of ice nucleus counter and ozone recorder in the Olympics. 33
Fig. 14 Location of ice nucleus counter at the University of Washington. 35
Fig. 15 Average ice-nucleus spectra curves for the Olympic Mountains and Seattle. 37 v
Page
Synoptic, Ice Nuclei, and Ozone Data for Olympic 40 Mountains (Blue Glacier). (Key to Figures 16-26 found in Table 1. )
41
42
43
44
45
46
47
48
49
50
Variations in ice nucleus count in the Olympic Mountains on March 28, 1968. 53
Twelve-hour averages of Synoptic, Ice Nuclei, and 58 Ozone Data for Olympic Mountains (Blue Glacier). (Key to Figures 28-29 found in Table 2. )
59
Concentrations of ice particles and ice nuclei. 6P
Net charge on rotating ice sphere and atmospheric electric field (March 14). 71
Net charge on rotating ice sphere and atmospheric electric field (March 14). 72
Net charge on rotating ice sphere and atmospheric electric field (March 15). 73
Net charge on rotating ice sphere and atmospheric electric field (March 15). 74
Net charge on rotating ice sphere and atmospheric electric field (March 15). 75 VI
Figure Page
Fig. 36 Net charge on rotating ice sphere and atmospheric electric field (March 15). 76
Fig. 37 Free charge on ice sphere as a function of velocity of sphere through the air. (Data from Runs 10, 11 and 12, March 15). 79
Fig. 38 Charge on ice sphere as a function of velocity of sphere through the air. (Data from Run 13, March 16). 80
Fig. 39 Ratio of number of positive to number of negative charges. 98
Fig. 40 Log-probability plots for positive charge on particles. 99
Fig. 41 Log-probability plots for negative charges on particles. 100 vii
LIST OF TABLES
Key to Figures 16-26. Synoptic, Ice Nuclei and Ozone Data for Olympic Mountains (Blue Glacier)
Key to Figures 28-29. Twelve-hour averages of Synoptic, Ice Nuclei and Ozone Data for Olympic Mountains (Blue Glacier)
Concentrations of ice particles.
Tables 4-11 are the results of measurements of electrical charges on individual ice particles in the air.
Tables 12-13 are the results of experiments of the individual charges received by a surface exposed to natural cloud and precipitation par- ticles. 1
INTRODUCTION
The University of Washington's research station in the Olympic Moun- tains is situated at an altitude of 2025 meters above mean sea level and is about 2-1/2 km NNE of Mt. Olympus (Fig. 1). Mt. Olympus (2430 m) is the highest peak on the Olympic Peninsula. The peninsula itself is the first mountainous area encountered by storms that move in from the Pacific
Ocean. Consequently, precipitation on the western slopes of the peninsula is (150 high to 200 inches per year), while in the rainshadow area some 50 km to the northeast of Mt. Olympus the precipitation falls to as low as 17 inches per year.
The research station provides an ideal site for many types of cloud and physics meteorological investigations. For example, since the area to the west and southwest of Mt. Olympus is virtually free of towns and other human habitation, the air that flows over the station in the pre-
vailing westerly or southwesterly airstreams is comparatively free of
man-made contaminants and may be considered to be unmodified maritime air. In easterly flows, on the other hand, the air is continental in character. Measurements of the concentrations and types of particulates in the air for these two distinct cases can provide valuable information on some of the basic differences between maritime and continental air masses. Another factor which has proved to be of considerable value is the location of the research station on an isolated ridge, with the land falling off steeply to valleys on the west and east sides; on clear days the Pacific Ocean may be seen from the research station. Moreover, in addition to the orographic clouds that commonly form over the mountains, isolated cumulus clouds often build up in the valleys which surround the 124 122 120
124 122 120
Fig. I Location of the Olympic Mountains. 3
station and it is possible to study the life-histories of these clouds
and investigate the effects that they have on measurements being made at
the research station. Wave clouds in the lee of Mt. Olympus are also
common. In winter ice crystal clouds, supercooled clouds, and mixed
clouds often extend down to ground level in the neighborhood of the sta-
tion. This makes it possible to carry out in-cloud measurements and experiments at the station.
The cloud physics group at the University of Washington first car-
ried out a field program at the research station in the Olympic Mountains
during the winter of 1965-66 (see Hobbs et al. 1966) A longer and much more detailed program was carried out from January 22 to March 31, 1968, and it is with this program that the present report is concerned. The main purpose of this report is to give a general description of the meas- urements that were taken, to present examples of some of the experimental results, and to point out a few of the interesting facts that have al- ready emerged from a preliminary analysis of the data. Theories and speculations have been kept to a minimum. More detailed accounts of several aspects of the work will be submitted for publication in the near future.
For convenience the report has been divided into the following five sections:
Section 1: Synoptic measurements
Section 2: Cloud condensation nuclei, light scattering coefficient,
sodium-containing particles, and Aitken nuclei measure-
ments
Section 3: Ice nuclei and ozone measurements 4
Section 4: Cloud and precipitation particles
Section 5: Electrical measurements SECTION 1
SYNOPTIC MEASUREMENTS
Regular synoptic measurements of wet and dry bulb temperatures, maximum and minimum temperatures, wind speed and direction, total miles of wind past the station, and cloud and weather conditions were made daily at 0900, 1200, 1500, 1800 and 2100 throughout the program. In addition, wet and dry bulb temperatures and wind speed and direction were recorded automatically on a digital printer during certain periods.
A summary of the principal features of the weather exoerienced at the research station is given below.
The weather during the program was quite variable. The coldest period occurred during the last week of January following the passage of a cold front on the 25t*">. The lowest temperature, -1F, was recorded on the morning of the 28^.
From January 30 until February 4, several weather disturbances moved rapidly past the station bringing heavy snow as well as somewhat warmer weather. From the 5th through the 16th of February the weather was dominated by high pressure and an easterly flow. This produced twelve days of sunshine and warm weather. The temperature reached 49F on February 6.
On February 17 a new series of weather disturbances began to move in, these lasted through February 25 and brought much snow and rain.
Three days of sunshine from February 26 through 28 brought the warmest weather of the program: the temperature reached 51F on February 28.
Starting on February 29 until about March 18, the weather was gen- erally unsettled with frequent disturbances and heavy precipitation. 6
During the first f.. days of . te^per.tur. was often ^ above free- ing and heavy rains ... experienced. Aft., about March 5 the tempera- ture dropped and precipitation was In the form of snow. On March 18 the weather cleared and remained ouite pleasant until March ,2 when a new frontal disturbance again approached the station. Th. weather re.ain.d Cloudy ith freouent periods of snow though March ,9. ifh the passage of a cold front on March 29 th. te.peratur. dropped sharply, clearing during the night resulted in a low of 7F recorded on the coming of March 30.
Th. features experienced during the program were generally w.r- "er than usual for the ti.e of year. The ..an te^erature for the .ntir. period was about 26F. For Februarypphw.-*^,, the4.1, Bean temperature was about 32F and for March the ean temperature was about 24F. The snowfall for the period was rather belo. nor^l, expecially for the month of February. Curing February about ,2 inches of snowfall was recorded while for March the snowfall .s ,e inches. The total snowfall for the entire program was about 136 inch.3. The period of greatest snowfall was fro. March 11 to March 16 wh.n ,2 inches of snowfall was recorded in five days. Bu. to th. usual probl.ms of .aking reliable snow measurements in th. mountains, the readings ouot.d above should be con- sidered as minimum values. The winds accompanying storm systems were often ouite strong and wind gusts near 100 mph were observed on several occasions. The strongest sustained wind of about . minute duration measured at an observation time was from the west at ,5 mph. This occurred at 0900 hour. on March 3 as part of the last gasp of a dying occluded f^t. Preceding another oc- 7
eluded front a 67 mph west wind was recorded on February 3. The highest
average wind speed for a 12-hour period was 42 mph recorded from 2100
February 18 to 0900 February 19 and also from 0900 to 2100 February 22.
For the 24-hour period from 0900 March 26 to 0900 March 27 the wind speed averaged 38 mph, and for the 36-hour period from 0900 March 26 to 2100
March 27, the wind speed averaged 36 mph. The periods of high wind usually preceded occluded fronts moving in from the Pacific Ocean. The strongest winds of a storm were often accompanied by pressure oscillations. During a period of very strong wind gusts, the pressure would drop abruptly by about a millibar and then rise rapidly again, but not as abruptly as it fell. The wind would then slowly taper off for a period of about 15 min- utes to one hour until the next series of strong gusts began. This be- havior apparently reflects the mesoscale structure of the storm systems, particularly occluded fronts. 8
SECTION 2
CLOUD CONDENSATION NUCLEI, LIGHT SCATTERING COEFFICIENT,
SODIUM-CONTAINING PARTICLES, AND AITKEN NUCLEI MEASUREMENTS
2.1 Cloud condensation nuclei
The concentrations of cloud condensation nuclei (CCN) in the air
were measured on a continual basis during most of the program using the
automatic instrument invented by Radke and Hobbs (1968). This instrument
consists of a large thermal diffusion chamber, an optical sensor, and an
electronic read-out system (Fig. 2). Samples of air are automatically
drawn into the thermal diffusion chamber at any desired intervals of time
down to about 100 sec. Water vapor begins to condense on those conden-
sation nuclei in the air which are active at the maximum supersaturation
in the chamber, and within a short period of time the droplets form a
mono-dispersed cloud. The light scattering coefficient of the cloud of
droplets in a central portion of the chamber is automatically measured at
a given time after the air enters the chamber by means of an integrating
nephelometer (Charlson et al. 1967). The light scattering coefficient
is related in a simple way to the concentration and the size of the drop-
lets in the monodispersed cloud. Since the sizes of the droplets that
form in the chamber have been determined previously as a function of time,
the reading of the nephelometer can be converted to give the concentra-
tion of droplets in the cloud. This number is recorded either on a digi- tal printer or on strip chart. It is important to realize that in this
instrument the scattering from the suspended particulates in the air, which is also recorded by the nephelometer, is generally very much less than the scattering from the water droplets. For example, an order of Somple outlet
>-^-Sompletti pump V.^ ,/ [Sequencer
Somple inlet
Fig. 2 Schematic diagram of the automatic cloud condensation nucleus counter. 10 magnitude change in the background scattering from the particulates (which occurs only rarely) is equivalent to a change of just 5 CCN cm"
To reduce sampling any local particulates that might have originated from the station, the air was drawn through a vertical stack 6 inches in diameter and 40 ft. high. Fresh samples of air were drawn into the cham- ber every 100 sec. and 10 to 15 measurements were taken on each sample during the few seconds that the droplets were at a known size. Unless stated otherwise, the concentrations of CCN described in this report are those activated at supersaturation of 1 per cent.
The variations that were observed in the concentrations of CCN can be divided into short-term and long-term variations. The short-term variations occurred over time intervals of the order of hours and were' connected with changes in the local meteorological conditions The long- term variations included diurnal cycles, changes that could be related to whether maritime or continental air masses dominated the weather pattern, and changes due to variations in wind direction. Three-hourly average values for all of the CCN measurements that were obtained are plotted in
Appendix A.
In unstable conditions the short-term variations could be surpris- ingly large, the CCN count varying by as much as 200 to 300 per cent in periods of 30 minutes. The most striking short-term variations occurred with the buildup or evaporation of cumulus clouds upwind in the valleys lying to the west of the station. When the clouds were growing up to altitudes equal to and higher than that of the station, the CCN count would decrease sharply. Conversely, when the clouds were dissipating the
CCN count would increase. These observations indicate that growing clouds 11
absorb (and also probably generate) large numbers of CCN and that these
particles are left behind in the clear air when the clouds evaporate
Some good examples of these short variations occurred on March 28
and 29 (Figs. 3 and 4) Heavy snowfall during the night and morning of
the 28 resulted in very low CCN counts from midnight to about 0600
hours. At about 0600 hours the CCN count started to rise. It stopped
snowing and began to clear at 0830 hours, and between 0830 and .1030 the
CCN count rose from about 25 to 160 cm"3. Shortly after the peak at 1030
another bank of cumulus cloud developed to the west and the CCN count
fell to about the value at midday. This rather dramatic decrease in CCN
count occurred even though the station itself was clear of cloud. The
smaller variations which were measured between midday and about 2100 hours are typical of those which occur in unstable conditions. Similar variations in CCN count were observed on March 29. The maximum reading at 1030, and the secondary maxima at other times, all coincided with halts in precipitation and local clearing of cloud upwind of the station.
It is interesting to note that although precipitation from convective clouds upwind could cause the concentration of CCN active at 1 per cent _g supersaturation to fall to less than 10 cm the effect of precipitation from orographic clouds upwind was much less dramatic.
The most interesting long-term variations in CCN counts were obser- ved during an extended period of fine weather in early February, and a shorter period of stormy weather in late March. During the period Feb- ruary 6 to 17 the weather was dominated by a stationary high pressure system NE of the station located in south central British Columbia; the winds were mainly from the east and north-east, and the weather was verv 12
Light scattering coefficient bq(units of 10 m') Q o oo r*- O O Q O O O O 0 c\j q oo b0 c ,c M o 1) <0 w fc Q. M d. 'O C 00 0 10 i-l 01 <-' '0 M C en 0 ^C m a) h u e w u ^s 0 U o o o o o o o o o o o o o mild and sunny. During this period there was a marked diurnal variation in CCN count which was particularly evident when the measurements were averaged over 12 hour periods (Fig. 5), the count was generally low from 0000 to 1200 hours and significantly higher from 1200 to 2400 hours. From March 26 to 29 the station was dominated by a westerly airstream, and the weather was unpleasant with frequent periods of snow and fog. The average concentration of CCN during this period was only half that during the period February 6 to 17. Moreover, the diurnal variations were exactly opposite to those described above, with higher counts from 0000 to 1200 hours and lower counts from 1200 to 2400 hours (Fig. 6) The long-term variations in CCN counts described above appear to be explicable as follows. Firstly, the higher average counts in the easter- ly airstream compared to those in the westerly airstream is no doubt due to the greater particulate content of continental air compared to mari- time air. An interesting example of this effect is seen in the measure- ments taken during the evening of February 7 (Fig. 7) On this occasion an inversion layer was below the level of the station, but whilst the wind was from the east the CCN count was fairly high. Between 1800 and 2200 hours the wind was from the south and the CCN count dropped to 20 cm"3, This change in count probably reflected the difference in the particulate contents of continental air from the east and modified maritime air from the south. The diurnal variations in count during the period February 6 to 17, which showed higher counts from 1200 to 2400 than from 0000 to 1200 hours, appeared to be associated with convective activity which lifted lower level air from the surrounding valleys up to the station during the afternoons. In fact, during this period, a thin blue haze 15 220 CCN at 1% averaged over 12-hr. periods 200 Light- scattering coefficient b averaged over 12-hr. periods. (N. B. Each point on graph placed at 180 beginning of 12 -hr. period 160 ? 140 <-) 120 *- ^0 | l00 0 >- ^E 40 2 20 I*., ^,, Y)rf '^"-p'y^O-0?'? 0^0?^ .-^O ^. ^ .^^4, P, ? <'.X^, 0 ^ .L--L --1 -L_J....jJO^ 3 5 7 9 13 15 17 19 21 23 25 27 29 Day of Month Fig. 5 Twelve-hour variations in cloud condensation nuclei counts and light scattering coefficient b during February. 16 13 15 17 19 21 23 25 27 29 31 Day of Month Fig. 6 Twelve-hour variations in cloud condensation nuclei counts and light scattering coefficient b during March. 09 12 15 Local Time (hrs) Fig. 7 Concentration of cloud condensation nuclei at .1% super.a^r^nn during Febru.':rv /, 1968. 1 8 could usually be seen in the valleys and this often increased in height as the day progressed. It seems very likely that the diurnal variations observed during the period March 26 to 29, when the station was dominated by a westerly air- stream, were due to the fact that convective precipitation was much more frequent after rather than before midday. Consequently, the CCN were precipitated-out during the afternoons. A good example of this occurred on March 26 (Fig. 8) when it started to snow just before midday and the CCN count dropped by about a factor of four between midday and 1330; the count remained low and variable throughout the afternoon. Finally, reference is made to Fig. 9 which shows the results of measurements of the concentrations of CCN active at different supersatur- ations under different synoptic conditions. It can be seen from these results that in the one case where the air could be clearly designated as continental in origin, the CCN counts were significantly higher than for the maritime or modified maritime air. It should be pointed out that a key factor in our ability to relate some of the variations in CCN count to local and larger-scale synoptic conditions was the unique location of the research station. Thus, it was possible to identify situations under which the station was dominated by maritime or continental air, moreover, the situation of the station on a high isolated ridge surrounded by deep valleys permitted excellent sur- veyance of the development of local clouds. 2.2 Light scattering measurements The total light scattering coefficient b of the air (including sus- 5 ponded particulates but excluding ice or water particles) was measured 09 12 15 Local Time (hrs ) Fig. 8 Concentration of cloud condensation nuclei at 1% supersaturation and light scattering coefficient b during March 26-, 1968. 20 lOOOr A 1700 Morch 23. Wind W 12mph a 1300 March 25. Wind Snowing. Maritime air. Variable ESE 3 mph. Light snow. Transitional 0900 March 23. Wind SE 3mph. maritime- Snowing. Modified maritime air. continental air. 1200 Feb. l5. Wind E 15 mph Clear. Continental air. Supersaturation (%) Fig. 9 Variations of concentration of cloud condensation nuclei with supersaturation in different types of air mass. 21 for a period of about fifty days using an integrating nephelometer (Ahl- quist and Charlson, 1966). The air samples were drawn through the same vertical stack, forty feet in height, that was used for the CCN measure- ments. The objectives of these measurements were (1) to provide back- ground readings for the CCN measurements, (2) to attempt to relate vari- ations in bg to changes in the meteorological conditions, (3) to see if there was a correlation between bg and the concentration of CCN in the air, and (4) to estimate the total mass of particulates in the air and the visual range of the atmosphere. The results obtained, as they relate to each of the above objectives, will be discussed in turn. The integrating nephelometer used for determining bg was about one- hundred times more sensitive than that used in the automatic CCN chamber. The measured value of bg ranged from 2.8 x 10~5 to 8.0 x 10~5 m~1. The lower value represents essentially Rayleigh scattering by air molecules alone, and the upper value is typical of that obtained in the cleanest urban air. The values of bg measured at the research station were such that scattering from air molecules and suspended dry particulates in the automatic CCN chamber was always a small fraction of the scattering from the water droplets that formed on active condensation nuclei in the cham- ber. During periods when precipitation was not the falling values of bs were comparatively high, particularly when the wind was from the east. Precipitation caused significant reductions in bg. The diurnal variations noted in CCN were also seen in bg but to a lesser degree. For example, during the period February 6 to 17 (Fig. 5) the values of b were S lower from 0000 to 1200 hours than from 1200 to 2400 hours, while the reverse 22 trend was noted during the period March 26 to 29 (Fig. 6). Fig. 10 (February 13) and Fig. 8 (March 26) show representative days during these two periods. The reasons for these trends are no doubt the same as those already suggested to explain the diurnal variations in CCN. The influ- ence of growing clouds upwind of the station acting as a sink for par- ticulates and evaporating clouds acting as a source, was observed also in the measurements of bg. For example, on March 28 (Fig. 3) b was fairly low and steady in magnitude during the night and early morning when it was snowing and there was thick cloud over the station. However, when it stopped snowing and began to clear up between about 0830 to 1030 hours, the magnitude of bg rose sharply and reached a peak at 1030 hours. Shortly after this time another bank of cumulus developed to the west and bg fell sharply even though the station itself remained clear of cloud. A similar behavior was observed in the CCN count (Fig. 3) By combining the simultaneous measurements of bg and CCN counts during the period 0830 to 1030 hours on March 28, an upper limit can be deduced for the size of the unwetted CCN particles active at 1 per cent supersaturation. bs inc- reased by about 3 x 10-5 m~1 between 0900 and 1030 hours on March 28, and at the same time the concentration of CCN increased by about 100 cm"3. If we assume that the increase in bg was due only to those particles which caused the increase in CCN count, it can easily be shown that the "equivalent monodispersed" radius of these particles was about 0.2 mic- rons The correlation coefficients between b_ and the CCN count are listed in Appendix B. When both these variables are smoothed by taking 3-hourly averages, the daily correlation coefficient sometimes rises to as high as 23 0.7. In addition, as we have seen above, many of the more dramatic changes in b and CCN count occurred simultaneously. The magnitude of the light scattering coefficient due to the suspen- ded particulates in the air (bg) appears to be related in a unique manner to the total mass m of particulates in the air by the relationship: m 3.1 x 105 b*s where, m is in u gm~3 and bg in m~1 (Charlson et al. 1967). Using this relationship, the average value for the total mass of suspended dry par- ticulates in the air during periods of fine weather and easterly flow was Q found to be 4.6 u gm~ and for periods of unsettled weather (westerly flow) it was 3.1 u gnT3. The lower value for the unsettled weather ref- lects both the cleaner westerly air from the Pacific Ocean and the scaven- ging of particulates by precipitation. The total light scattering coef- ficient bg is related to the visual range L of the atmosphere by the for- mula (Middleton, 1963) 3>9 L ^ The maximum ^ steady value of bg that was recorded at the research station was 8.0 x 10" m~ which corresponds to a minimum visual range of 50 km. It should be noted that this visual range deduced in this manner does not take into account any reduction in visibility due to ice or water in the form of clouds or precipitation particles. 2.3 Sodium-containing particles The concentrations of sodium-containing particles in the air were measured at 0900, 1200, 1500, 1800 and 2100 hours each day for a period of about one month using a modified version of the familiar sodium flame 09 12 15 Local Time (hrs) Fig. 10 Diurnal variation in light scattering coefficient b,, for February 13, 1968. 25 spectrometer (Soudain, 1951; Vonnegut and Neubauer, 1953; Woodcock and Spencer, 1957). The principle of this device is that sodium-containing particles which are drawn into a flame will emit bright yellow flashes, and these flashes may be counted electronically by a photomultiplier tube which views the flame through a filter which transmits only the sodium D lines. It should be noted that since nearly all of the sodium compounds which occur in the atmosphere are highly soluble, a particle which con- tains a reasonable mass of sodium will probably serve as a good cloud condensation nucleus. A sketch of the flame spectrometer which we used is shown in Fig. 11. It consisted of a small filtered acetylene burner which drew in air at an appropriate rate (2 liter min"1) to ensure proper burning. The air was sampled in such a way that the loss of small particles by impaction was minimized, but cloud droplets or ice particles were not sampled. The flame was viewed through a 5228 A narrow-band pass (10 X) filter by an IP22 photomultiplier. The a.c. coupled output from the photomultiplier, which consisted of a series of pulses of different amplitudes, was recor- ded on a high speed pen recorder. From the number of pulses that were detected in a given period of time, and the known rate at which the air was drawn into the flame, the concentration of particles in the air which contained sodium could be deduced. The device gave zero count when oper- ated in a clean room. Three-hourly averages of the sodium-containing particle (SCP) counts are shown in Appendix A. The time variations in SCP count over the order of minutes was small unless the local meteorological conditions were changing rapidly. In common with the CCN count and b s the SCP count 26 IP22 Photo- High multiplier tube speed pen recorder High pressure acetylene inlet ^g* 11 Flame spectrometer. 27 decreased markedly when cumulus clouds were growing upwind and increased when the clouds evaporated. Precipitation decreased the SCP count. How- ever, unlike the CCN count, the SCP count decreased significantly when orographic clouds were building up in the vicinity of the station. One of the more interesting variations in SCP count (and CCN count) occurred during the passage through the station of a weak occluded front from the west on March 1. The sequence of events was as follows. On February 28 there was an easterly flow and the weather was sunny. The CCN count increased during the day from about 60 to 150 cm"3 at 1 per cent supersaturation, b was fairly high at 6.5 x and S 10~5 m"1, the SCP count was steady at about 10 per liter. February 29 was sunny during the morning, but the cloud amount and the relative humidity increased in the afternoon. The wind at the station was light SW until 1600 hours and then shifted to WSW and increased to 20 to 30 mph. The weather maps in- dicated that the flow was shifting slowly from an easterly to a southerly between 1000 and 1300 hours on the 29th. The CCN count continued to rise until about 1030 on the 29th when it reached a peak value. The SCP count also increased during the 291 although at a somewhat slower rate than the CCN count, and reached a peak of 150 per liter at 1800 hours. At 1830 hours on February 29, both the SCP count and the CCN count fell sharply with the onset of precipitation. The occluded front went through the station between 0100 and 0500 hours on March 1, light SW winds and moderate snowfall continued through March 1 and the SCP count (10 per liter), CCN count (60 cm" ), and b (3 x 10~- m ^ ), all remained low. S A number of interesting features are illustrated in the case de- scribed above. For example, the SCP count as well as the CCN count 28 increased with increasing easterly flow from the continent (this was verified from the wind trajectories and by the increasing values of b ) s but the SCP count did not peak until the wind had shifted so as to advect maritime air. This indicates that the ocean was a larger source of sodium- containing particles than the land lying to the east of the station. Another interesting example occurred on March 13. The station had been in cloud and the snowfall nearly continuous for two days. The wind was strong and from the SW, and the SCP count less than 20 per liter. At about 0900 hours on March 13 the snow stopped and a few breaks appeared in the cloud. Simultaneously the SCP count increased to 150-200 per liter (Fig. 12a). At 1100 hours the station was again immersed in cloud. The size-spectrum of SCP measured at 1200 hours (Fig. 12b) was quite distinct from that at 0900 hours, in particular there was a marked decrease in the number of larger particles. It started to snow in the early afternoon and continued for the remainder of the day; at 1500 hours the SCP count was about 40 per liter. The SCP counts measured at 1800 and 2100 hours (Figs. 12c and d) were much lower than at 0900 and 1200 hours, but the size-spectra at 1800 and 2100 were similar to that at 0900 hours. The magnitudes of the signals from the photomultiplier tube of a flame spectrometer are dependent on the amounts of sodium in the parti- cles that traverse the flame. Previous workers who have used the flame spectrometer have not calibrated for size, but have used the instrument only as a counter of sodium-containing particles. The primary design requirement in order that a size-calibration be possible, is that all of the particles in the air that is drawn into the flame traverse . 5.540' (a) 0900 hours (c) 1800 hours i Snow not falling Light snow C Q. Concentration of sodium-containing Concentration of sodium-containing B oi30 particles 155 per liter particles 16 per liter '6 g40 (b) 1200 hours (d) 2100 hours 5g Snowing Light snow Concentration of sodium-containing Concentration of sodium-containing 1 &30 particles 120 per liter particles = 22 per 1 1 liter 520a o s >0 Kv 0 Q. 1 g^m 5 10 15 20 25 0 5 10 15 20 25 30 Voltage output from PM tube Voltage output from PM tube 'jd [02.05 35 45 5.5--7^5--- .6 1.0 2.05 3.5 45 5.5--^5" Equivalent diameter (microns) Equivalent diameter (microns) of sodium chloride particles of sodium chloride particles Fig. 12 Size spectra of sodium containing particles in the air measured on March 13, 1968. 30 approximately the same temperature profile. In our instrument this requirement was approached by mixing the air with the combustion gases prior to the point at which they entered the flame, and by maintaining a smooth laiinar flame. Preliminary size-calibration of this instrument has been carried out at the University of Washington by Pueschel (private coanminication, 1968) using sodium chloride particles of known sizes. This calibration is indicated on the horizontal scales in Fig. 12. 2.4 Aitken nuclei The concentrations of Aitken nuclei in the air were measured daily at 0900, 1200, 1500, 1800 and 2100 hours during the whole program using a Gardner Associates Type CN expansion chamber. Since the air was sam- pled just a few feet above ground level, some of the measurements that were obtained were affected by local sources of particulates generated by the research station itself. Whenever possible the measurements were taken upwind of the station in order to reduce this uncertainty. The measured concentrations of Aitken nuclei ranged from less than 100 cm (obtained many times in westerly and south-westerly air flows) 500 cm"3 in easterly winds, and 100 cm"3 in westerly winds. Similar variations were observed in the concentration of Aitken nuclei with meteorological conditions to those which have been described for CCN, bg and SCP. For example, on March 28 snow had been falling during the night and early morning, but it stopped snowing and began to cleay at 0830 hours. At about 1030 hours another bank of cumulus cloud developed to the west of the station, although the station itself re- mained clear of cloud. These variations in conditions were reflected in 31 the concentration of Aitken nuclei which rose from less than 100 cm"3 at 0900 hours on March 28 to 400 cm-3 at 1200 hours, and fell again to 100 cm"3 at 1500 and 1800 hours. Also, as we have seen in 2.3, the SCP count rose steadily during the day of February 29, reached a peak value at 1800 hours, and fell sharply at 1830 hours with the onset of precipitation. The Aitken nuclei counts showed similar variations, at 1200 hours on the 29th the concentration was 1,000 cm"3, at 1800 hours it was 20,000 cm"3, and at 2100 hours 10,000 cm"3. The correlations between the concentrations of Aitken nuclei and the various other par- ticulates that were monitored are given in Appendix B. 32 SECTION 3 ICE NUCLEI AND OZONE MEASUREMENTS The concentrations of ice nuclei in the air active at -21C, and the concentrations of ozone, were measured continually from January 25 to March 29 at the Olympic Mountains research station. The temperature spectra of the ice nuclei were measured at midday whenever possible. To determine whether the concentrations of ice nuclei in the Olymoics dif- fered from those in Seattle, simultaneous measurements of ice nuclei were also made at the University of Washington in Seattle. In conjunc- tion with these measurements, simultaneous measurements of the concen- trations of ice nuclei were made by Dr. Ohtake at Fairbanks, 'Alaska, and bv members of the University of Hawaii's Cloud Physics Laboratory at Hilo, Hawaii. However, in this report we will confine our attention to the measurements made in the Olympic Mountains and Seattle. 3.1 Locations The location of the Olympic Mountains research station is shown in Fig. 1 and in greater detail in Fig. 13. Even thouph the station is at an altitude of 2025 meters (approx. 800 mb pressure) the origin of the air that reaches the station will not, of course, be exclusively from this level. Thus air moving towards the station from lower levels in the at- mosphere will often rise up over the Olympic Mountains. However, on those days when the atmosphere is very stable, air below the level of the station may not be able to penetrate the inversion level and reach the station. When the wind speed is slight at the lower levels and greater around the 800 mb level, the air reaching the station is more representative of the free air at the 800 mb level than it is on days 33 Fig. 13 Location of ice nucleus counter and ozone recorder in the Olympic Mountains. 3'4 when the wind speed is greater in the lower levels. The major source of man-made pollution affecting the station is probably the Seattle-Tacoma industrial complex which lies about 60 miles ESE of the station. On days when there is not a westerly flow of clean air from the Pacific, pollution from Seattle and Tacoma tends to collect in the Puget Sound basin. The ice nucleus counter at the University of Washington in Seattle was located on the roof of a twelve story apartment building (Terry Hall) Al- though this counter was in a typical city environment, SW and S winds from the downtown area of Seattle (and also from the city of Tacoma) carried significantly more city pollution than did winds from the east (Fig. 14) 3.2 Instrumentation The concentrations of ice nuclei in the air were measured with the NCAR acoustical ice nucleus counter (Steele et al. 1967) The micro- phones and the printers used with each of the instruments were calibra- ted at the University of Washington before the beginning of the program in order to ensure that they had the same sensitivity to similar signals from the acoustical sensor. Air was drawn into the chambers at a rate of 10 liter min"1, and the total number of ice nuclei detected in each half-hour was totalized and printed out on strip-paper together with the time and date of the measurement. To ensure a uniform and dense cloud of water droplets in the chamber, the salt solution aerosol generators were operated at all times. The chamber was normally held at a tempera- ture of -21C, but whenever possible additional measurements were taken at -15C and -10C between noon and 1 p.m. The concentration of ozone in the air at the Olympic Mountains re- search station was measured using a modified version of the Brewer-Mast 35 Fig. 14 Location of the ice nucleus counter at the University of Washington. 36 electrochemical ozone analyzer (Mast and Saunders, 1962) This instru- ment depends on the oxidation of potassium-iodide in the air, the mass of oxidant entering the detector in unit time is proportional to the cur- rent generated by the reaction. It should be noted that it is tacitly assumed that the oxidant is in the form of ozone. This is probably a good assumption for the relatively uncontaminated air in the Olympic Mountains. However, during those periods when air from the Seattle- Tacoma industrial complex was reaching the station, oxidants may have been present in forms other than ozone. 3.3 Comparison between ice nucleus counts in the Olympic Mountains and in Seattle Average ice-nucleus spectra curves for the Olympic Mountains (Blue Glacier) and Seattle (Terry Hall) were obtained by averaging the half- hour totals of ice nuclei at -10, -15, and -21C as measured at midday throughout the period of the program (Fig. 15). Two important differences can be seen between the two spectra. Firstly, the ice-nucleus counts in Seattle were greater than those in the Olympics, particularly at warmer temperatures. Secondly, the ice- nucleus spectra curve for Seattle shows a distinct "hook" at higher tem- peratures, whereas, the curve for the Olympics is approximately a straight line on the semi-log plot. It would appear from these results that the City of Seattle is act- ing as a source of ice nuclei and that many of these particles are effec- tive at temperatures above about -15C. 3.4 The effect on the concentrations of ice nuclei in the Olympics of the transport of air from the Puget Sound and Seattle 37 100 Olympic Mountains ( Blue Glacier) Seattle ( Terry Hall) o *s 10 ^ o o 0 0 (/) 3 JU 0 3 0. 0 -5 -10 15 -20 -25 Temperature (C) Fig. 15 Average ice-nucleus spectra curves for the Olympic Mountains and Seattle. 38 Three hour averages of the concentrations of ice nuclei and ozone, together with synoptic data, for the Blue Glacier station during the period January 25 to March 29, 1968 are shown in Figs. 16 through 26. The key to these figures is contained in Table 1. In this section we point out some of the variations in the concentrations of ice nuclei measured at the Blue Glacier which appeared to be due to the transport of air from the city of Seattle to the Olympic Mountains. The concentrations of ice nuclei measured during the period February 8-13 ( Figs. 18 and 19) and on February 15 (Fig, 19) showed a diurnal oscillation in which the ice nucleus counts were higher in the afternoons than in the mornings. The explanation for these oscillations appears to lie in the synoptic situation. Following the buildup of high pressure over the region which commenced on February 2, the skies were clear and the winds easterly on February 7. The ice nucleus count during the morning of February 8 was about 50 per 100 liters of air. The radiosonde sounding taken at Quillayute airport at 0400 hours on February 8 showed light NE winds at the surface and a very stable lapse rate extending 2,000 ft. (950 mb) above the surface, with S and SE winds at the level of the Blue Glacier station. Due to the extreme stability of the atmos- phere at this time it was very unlikely that air from the Puget-Sound region and Seattle could have reached the Blue Glacier during the morning of February 8. However, by about 1600 hours on February 8 the ice nucleus count had risen to about 1 per liter of air. The radiosonde sounding for February 8 showed that the stability of the air had de- creased markedly and that the transport of air from the Seattle area to Ice nucleus counts refer to -21C unless otherwise stated. 39 Table 1 Key to Figures 16 26 Synoptic, Ice Nuclei and Ozone Data for Olympic Mountains (Blue Glacier) The fol lowing information is contained on Figures 16 26. --Oz 3-hour average of concentration of ozone in parts per hundred mi ion of ai r (pphm) (From 1/2 hour values) --IN-3-hour average of ice nuclei per 300 ters of ai r (from 1/2 hour totals) Both of the above were computed at 0000, 0300, 0600, 0900, 1200, 1500, 1800, and 2100, as the middle of the 3-hour average period plotted on the graph. ~~~RH'~"- Relative humidi ty in per cent. --T-- Ai r temperature (F) The above two were recorded from a wet and dry bulb thermo- meter in a standard meteorological instrument shack at the same time as wind speed and di rection, etc. P-- Barometric pressure in mi ibars at station, averaged over 0300-0900, 0900-1500, 1500-2100, 2100-0300; and recorded at 0000, 0600, 1200, and 1800. Interpolated values. 0 Total cloud cover in lOth's. (e.g. (^ 5/10) Q Wind di rection and speed in mi les per hour. (e.g./ N.E. at 25 mph) Cloud type and weather (at time of observation) Ac al tocumulus s snow e.g. Lk ight snow Cb cumulonimbus L ight Bs blowing snow Ci ci rrus M moderate VLs very ight snow Cs ci rrostratus B blowing Sc stratocumulus V very F fog Wind di rection only, taken from the 3-hourly synoptic surface maps as typical surface wind for N.W. Washington at time shown. (e.g. N.E.) X' Indicates ^a radiosonde sounding for Qui layute Ai rport, Wash. plotted at this time. --RH-- 45r ---RH 810 -RH 40 v . 35 S800F V^HV /RH-'91/ fBO ^ "^ S 30 $70 | 25 790 ^ cr> -^ 8 e60 20 ^^-P =----p ---p-i50 '^lS^5 "- 780 $40 ^-----P-^^^ ---^ ^T "-^T^ .5 10 /^-^T^o30 //^-^ ^ 5 : ---\^ \s ^ ^20 : ^ 10 l-* A O-i /t^ ^^l 06 12 18 06 12 18 06 12 18 06 12 18 06 12 18 March 14 March 15 March 16 March 17 March 18 Figure 24 06 12 18 06 12 18 00 06 12 18 00 06 12 18 00 06 12 18 00 March 19 March 20 March 21 March 22 March 23 Figure 25 F F F F F s s s s s Bs Bs Bs Bs + + ^^-w/ 1^+ M f ^///^-^ Wm +^'t Occlusion Dying f\ Occlusion Wind convergence / Cold front over from NW occlusion \ from NW in upper Puget / Seattle fromNNW ^ \ from W Sound-NW. lower / / \ Puget Sound-SW IN .N / N ^ -4-01 -^4]' ^LN ^ ^ ^"^ ^~0z 18 00 06 12 18 00 06 12 18 00 06 12 18 00 06 12 18 00 06 12 March 24 March 25 March 26 March 27 March 28 March 29 Figure 26 the Blue Glacier was quite possible. Two noints -should he notic---'; j'n this example. Firstly, the diurnal changes in thf thermal struct-., ^'; the atmosphere observed on February 8 arc typicaJ of winter condit ns namely, the surface temperature reaches a minimum qt about R400 heir's and the stability is a maximum, and the surface temperature is a maximum at about 1500 hours at which time there is a maximum instability. Sec ondly, the increase in ice nucleus counts in the afternoon was accompan- ied by 15 mph SE winds at the research station, and conditions were fa- vourable for the transport of polluted air from Seattle to the Olympic Mountains. Since we have seen already that the concentrations of ice nuclei in Seattle are generally significantly higher than the concentra- tions in the Olympic Mountains (Fig. 15) it seems reasonable to conclude- that the increase in ice nucleus counts at the Blue Glacier during the afternoon of February 8 was due to the transport of ice nuclei from the Seattle area. Further evidence to support this conclusion was found by examining the relationship between ice nucleus counts and the synoptic situations on other occasions. Basically the same diurnal changes in static stability, wind direc- tion, and ice nucleus counts described above occurred from February 8 to 15. However, beginning on February 11 a low pressure system started to develop off the coast of Western Washington and clear air from the Pa- cific began to be advected to the Olympic ?'.-;'intains. This caused a gen- eral decrease in the ice nucleus count from February 11 to 13 (Fig. 1) By February 15 the low pressure center had dissipated, and the winds .-'t the level of the station were E to SE. The ccundings at Ouillayute on this day showed that the ^same diurnaJ pattern of stability as was obser .-- 52 ed from February 8 to 13 had been reestablished and the ice nuclei counts were again higher in the afternoon than in the morning (Fig. 19) This cycle was not repeated on February 16 since an incoming cyclonic storm from the Pacific disrupted the synoptic pattern. The diurnal variations in ozone during the period February 8 to 16 show generally higher concentrations in the mornings than in the after- noons. This effect is fairly well known, and is due to the upward trans- port of air which is fairly low in ozone from lower regions of the atmos- phere during the afternoons. This result, therefore, lends support to the argument that air from the Puget Sound basin was being transported up to the Blue Glacier in the afternoons during the period February 8 to 16. 3.5 The effects of snowfall on the concentrations of ice nuclei and ozone On several occasions the measurements of ice nuclei in the air indi- cated that the concentrations decreased in the presence of snowfall and fog and increased when it stopped snowing and the cloud or fog cleared. For example, on February 4 (Fig. 17) it started to snow at about 1500 hours and the concentrations of ice nuclei decreased from 40 to 30 per 300 liters of air between 1500 and 1800 hours. It stopped snowing at about 1800 hours and the ice nucleus count recovered to 40/300 L by 2100 hours. A similar case occurred on March 28 (Fig. 27) During the early morning it was snowing and overcast, but it stopped snowing and the cloud began to dissipate between about 0830 and 1030 hours. This clear- ing was accompanied by a rise in ice nucleus count from about 30/300 L at 0900 hours to a maximum of 213/300 L at about 1000 hours. Shortly after 1030 hours, another bank of cumulus developed to the west, and the 09 12 15 T ime (hr) Fig. 27 Variations in ice nucleus count in the Olympic Mountains on March 28, 1968. 54 ice nucleus count dropped sharply. It is interesting to note that simi- lar variations in cloud condensation nuclei and the light scattering coefficient were observed on March 28 (Fig. 3) The concentrations of ozone in the air also decreased in snowfall, presumably due to its absorption by the snow. 3.6 The effect of fronts on the concentrations of ice nuclei and ozone Most of the fronts which passed over the Olympic Mountains station during the program were occluded, had a general north-south orientation, and moved from west to east. Consequently, when a front was to the west of the station, air was carried from the Puget Sound basin to the sta- tion, and after the front had passed over the station the air was from the west. Although the surface winds did not always show this change, the higher level winds in the radiosonde soundings and the winds at the station generally exhibited a pronounced shift. A nice example of this change in wind direction, and the effect that it had on the ice nucleus count, can be seen during the period from 1200 hours on January 30 to 0000 hours on January 31 (Fig. 17). Although the United States Weather Bureau synoptic map did not show the passage of a front through the station during this period, the shift of the sur- face wind from SE to SW, the fall and subsequent rise in pressure, and the violent wind on the morning of January 31, indicate that a front did indeed pass over the station. The fall in pressure commenced at about 1800 hours on January 30 when the surface wind shifted to SE. At this time the ice nucleus count increased sharply and reached a peak of 60/300 L at 0000 hours on January 31. By 0600 hours on January 31 the wind had returned to SW and the ice nucleus count had fallen to 10/300 L. 55 As we have mentioned previously, the increase in ice nucleus count with the south-easterly winds appeared to be due to the transportation of polluted air to the station from the Puget Sound basin. A fairly dramatic response to the passage of an occluded air front occurred in the ozone level on February 17 (Fig. 20). The front went through between 1200 and 1500 hours. The concentration of ozone began to fall at about 0900 and it reached a minimum at about 1500 hours. It then increased somewhat more slowly and recovered to just below the 0900 hour level by 0000 hours on February 18. The decrease in ozone was prob- due ably to its absorption by the precipitation and clouds which accom- panied the passage of the front. -3-7 Increases in ice nucleus concentration accompanying westerly flow During the program there were some periods of stormy weather with W and SW winds in which the ice nucleus count increased to almost the lev- els observed when polluted air from the Puget Sound basin was reaching the station. These periods can be divided into two categories: (1) those occasions on which even with a strong W or SW wind at the station there was a possibility of the transport of polluted air from the south to the station and (2) those occasions on which it appeared that only clean air from the Pacific Ocean could be reaching the station. An example of the first category occurred on March 26 (Fig. 26). A dying occluded front passed over the station between 0900 and 1200 hours but the wind at the station remained SW all day. The wind speed and ice nucleus count increased in magnitude, reaching a maximum around 1500 hours. The radiosonde sounding for 0400 hours on March 26 showed a low k The cities and industries of Hoquium and Aberdeen lie south of the station (Fig. 13) 56 level inversion, light winds, and clouds below the level of the station. The situation, therefore, was not conducive to the transfer of lower air up to the station. The 1600 hour sounding on March 26 showed a SW wind at the Blue Glacier but to the west of the station the surface winds were S at 20 mph. Hence, surface air from the south was being transported up to higher levels to the west of the station, and from there it could have been transported to the station on the SW winds. This hypothesis is con- firmed by the fact that the sounding for 0400 hours on March 27 showed that the winds at the station were still from the SW but the S winds to the west of the station had decreased significantly, and the ice nucleus count was again low (Fig. 26) An example of the second category occurred on March 14 (Fig. 24) when the ice nucleus count was of the order 100/300 L at 1600 hours. The radiosonde soundings for 1600 hours show SW winds from the surface up to 500 mb, which seems to exclude any local pollution effects. Hence, the reason for the high ice nucleus counts on occasions such as this remains unexplained. 3.8 Twelve hour average variations in ice nucleus counts and ozone The 12-hour averages for the concentrations of ice nuclei and ozone throughout the program are shown in Figs. 28 and 29. The key to these figures is shown in Table 2. Some of the more important variations are described below. 1. January 25-29 (Fig. 28) This period was characterized by the coldest temperatures during the program, high relative humidity, and low air pressure. On January 25 and 26, the ice nucleus count was fairly high (about 40/300 L), but de- 57 Table 2 Key to Figures 28-29 Twelve-hour Averages of Synoptic, Ice Nuclei and Ozone Data for Olympic Mountains (Blue Glacier) The fol lowing information is contained on Figures 28-29. --02- 12-hour averages of concentration of ozone in parts per hundred mi ion of ai r (pphm) --IN- 12-hour averages of ice nuclei per 300 ters of ai r -RH- 12-hour averages of relative humidi ty in per cent T- 12-hour averages of ai r temperature (F) P-- 2^-hour averages of station pressure (mb) Interpolated values Wind speed, di rection, and cloud cover best describing the period 0900 2100. ^ 25 mph from SW, completely (ex. ft ^r overcast V Variable wind 200 o I 180 <^ 1^ 0 A vP^ <^^J^3^ t 8 1 o ^140 w 0 o 's IN " ^I I Q.-S) CM o' 3 c c w o 120 "'.S 0 ^ w " 60 *5 5 40 IN E ' ^^ -o^IN-^ ^A-t-^N 25 2627 28 29 30 31 2 4 6 7 8 9 10 12 13 14 15 16 17 18 19 20 21 24 25 26 27 28 29 January 1968 February 1968 ^ Figure 28 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 21 22 23 2425 26 27 28 March 1968 Figure 29 60 creased to 10 to 15/300 L after a cold front from the north passed through the station on the 26 The passage of the front was followed by clearing skies and NE winds but the pressure failed to build up over the station. The winds subsequently shifted to the south, it became in- creasingly cloudy and warmer, and the ice nucleus count oscillated be- tween 10 to 20/300 L. 2. January 29-February 2 (Fig. 28) Rising pressure and temperature, cloudy skies, snow and blowing snow, and strong SW to W winds typified this period. Starting at about 15/300 L, the ice nucleus count increased to 40/300 L. The count then decreased to about 15/300 L in the strong westerly winds from January 31 to February 2. 3. February 6-16 (Fig. 28) After the passage of a cold front from the NW on February 3, a high pressure area developed over the region and this gave rise to NE-SE winds, warm temperatures, low relative humidities, and clear weather. The ice nucleus count was generally high from February 9 to February 12, but with higher values in the afternoons than in the mornings. The concentration of ozone, on the other hand, followed the reverse pattern with lower concentrations in the afternoons than in the mornings. More- over, from February 9 to 12 the ice nucleus count showed a general de- crease, while the concentration of ozone tended to increase. On February 13 a low pressure center developed off the Pacific coast, the relative humidity increased and the temperature decreased. The ice nucleus count decreased during the morning of the 13th but the concentration of ozone peaked during this twelve hour period. By Feb- 61 ruary 15 the pressure had the recovered, temperature was rising and the relative humidity had fallen sharply. The pattern of an increase in ice nucleus count during the afternoon was reestablished, although there was very little difference in the twelve hour averages for ozone in the morn- ings and afternoons. t. February 16-25 (Fig. 28) Excluding February 17 the average ice nucleus counts observed during this period were less than 10/300 L, the lowest which was observed during the program The average concentrations of ozone during this period were also the lowest for the month of February. The weather was generally stormy with the passage of three occluded fronts bringing snow five days out of seven, temperatures around freezing, high relative humidity, and winds predominately fro. the south and west. It is interesting to note that during the periods when the occluded fronts passed on the 17th ^ 21st, the ice nucleus counts increased while the concentration of ozone fell. 5. February 26-28 (Fig. 28) Rising temperatures (reaching close to 20F above freezing) clear skies, lowering humidity, increasing ice nucleus counts and ozone con- centration, are typical of this period. An occluded front which dissi- pated off the Pacific Coast caused little or no shift in the wind at the surface, but at the level of the research station (800 mb) the winds shifted from ESE on February 26-27 to SW on February 28. 6' March 7-March 9 (Fig. 29) This was a period of rising pressure and temperature, progressively clearer days, falling relative humidity, and light variable winds. Dur- 62 ing this period the ice nucleus counter was not operating. The concen- tration of ozone increased up to the afternoon of March 9 when it de- creased sharply. 7. March 9-18 (Fig. 29) Temperatures averaged below 25F, it snowed seven days out of ten, skies were almost continuously overcast, and the winds were from the south and west gusting up to 65 mph. Three fronts passed through the station during this period. The ice nucleus count showed a dramatic increase from the 14 to the 16 March, the 12-hour average increasing from 20/300 L to 200/300 L. Although the ozone data were not complete it appears that the twelve averages for the concentration of ozone followed the same trend as the ice nucleus count, which is contrary to the results obtained during other periods of ice nucleus count (e.g. February 9-15) On March 18, the pressure was rising, the winds veered round to the NW, the temperature dropped, and the ice nucleus count fell to the more normal value of about 40/300 L. 8. March 19-23 (Fig. 29) The pressure and temperature continued to rise until the 20th with winds from the SE and W and partially clearing skies. During the after- noon of March 20 the ice nucleus count doubled and the concentration of ozone also increased. On the morning of the 21st the ice nucleus count fell again but the amount of ozone remained high. 9. March 23-29 (Fig. 29) Two points should be noticed during this period. Firstly, the 12- hour average ice nucleus count increased after the passage of an occlu- sion from the west on the 26th. Secondly, the subsequent drop in ice 63 nucleus count after the occlusion from the NW had passed and the winds shifted from SW to W. 64 SECTION 4 CLOUD AND PRECIPITATION PARTICLES 4.1 Types of particles The types and sizes of the cloud and precipitation particles were sampled at station level using slide replicas. Glass microscope slides (3" x I") coated with a 2 per cent solution of fonnvar in ethylene di- chloride were used for this purpose. A brief description of the parti- cles that were collected on each of the slides is given in Appendix C. 4.2 Liquid water content The liquid water content and effective droplet diameter of the supercooled clouds that formed around the station were measured on two occasions using the multi-cylinder method (dark, 1946). The first measurement was made between 0915 and 1500 hours on Feb- ruary 1. During this period the air temperature was -5C, the station was immersed in cloud, and the visibility was less than one-half a mile. The liquid water content was found to be 0.028 g m~3 and the effective cloud droplet diameter was 18 microns. The second measurement was taken on 2 February between 1730 and 2100 hours. An occlusion had passed through the station at 1200 hours, and the winds were from 10 to 30 mph from the west. The air temperature was -5C at 1500 and decreased to -6C at 2100. The skies were overcast and the visibility about 200 yards. On this occasion the liquid water content was 0.04 g m~3 and the effective droplet diameter 10.5 microns. It should be noted that on neither of these two occasions was the method sufficiently sensitive to determine the cloud droplet size distribution from the milti-cylinder measurements. 65 4.3 Concentrations of ice particles The concentrations of ice particles in the air were estimated on a number of occasions in the following way. A solid black cylinder, 1 foot in length and 1-1/2 inches in diameter, was dipped into a mixture con- sisting of 1 part of 1% fonnvar solution and 10 parts of ordinary rubber solution. This mixture was sufficiently sticky to retain all of the ice particles that landed on it and it also replicated the crystals. The coated cylinder was then held at arm's length and rotated several times in a horizontal plane through the air. The number of ice particles col- lected on the forward-facing half of the cylinder was counted visually, and the concentration of ice particles in the air estimated from this measurement and the known volume of air through which the cylinder had been rotated. Measurements were never taken in winds which were suffi- ciently strong to produce blowing snow. The collision efficiencies of the ice particles with the cylinder were assumed to be unity, so the estimated concentrations were probably on the low side. Simultaneous measurements were made at the station of the concentrations of ice nu- cleus count with temperature using the NCAR ice nucleus counter. From these measurements the number of effective ice nuclei at the temperature of the cloud top could be estimated. The NCAR counter generally gives readings which are 16 to 52 per cent lower than those obtained with a mixing chamber (Steele et al. 1967) however, this relatively small correction was ignored. The cloud top temperatures were estimated from the regular radiosonde measurements taken at the Weather Bureau Station at Quillayute Airport (47 57' N, 124 33' W) which is about 20 miles due west of the research station. The habits of the ice crystals 66 collected at the station provided a check on these temperatures. The results of the measurements are summarized in Table 3 and Fig. 30. The first important point which emerges from the observations is that sig- nificant concentrations of ice particles (= 1 to 10 liter"1) can exist in clouds which have cloud top temperatures as high as -4C. Secondly, the concentrations of ice particles in the air on different occasions were from one to four orders of magnitude greater than the estimated concen- trations of effective ice nuclei at the cloud tops. These results confirm the belief that some very effective mechanisms must exist in clouds for the multiplying of the number of ice particles. The results in Fig. 30 show also that the concentrations of ice particles in the air, and the ratio of ice particles to ice nuclei, decrease with decreasing cloud top temperature. Since the growth of ice crystals from the vapor phase be- comes increasingly important as the temperature of the cloud decreases, observations shown in Fig. 30 suggest that the freezing of supercooled cloud droplets is responsible for the high ratio of ice particles to ice nuclei at the higher temperatures. TABLE 3 Estimated number Ratio of con- Date and Estimated of ice nuclei Number of centration of Types of ice par- time of temperature of per cm0 effective ice particles ice particles tides collected observation cloud top (C) at cloud top per cm3 to ice nuclei on slides March 7 -6 2. 3 x 10~6 1. 7 x 10-2 7.4 x 10 Long columns 1630 Hexagonal platec March 9 -12 4. 3 x 10-6 3.0 x 10-4 6. 9 x 10 Irregular particles 2100 Hexagonal plates Frozen drops Dendrites (rare) 2 March 10 -12 1. 8 x 10~5 3.0 x 10-3 1.7 x 10 Long rimed columns 1015 Irregular particles Frozen drops 3 March 13 -6 2.4 x 10~6 3.0 x 10-3 1. 3 x 10 Irregular particles 1300 Frozen drops 3 March 15 -11 1.0 x 10~5 6.0 x 10-3 6.0 x 10 Long, thin rimed columns 1745 Irregular particles March 17 -16 2.0 x 10~5 9.0 x 10-4 4. 5 x 10 Dendrites; columns 1110 Irregular particles 2 March 22 -12 5. 5 x 10~6 6. 0 x 10-4 1.1 x 10 Needles; columns 1750 Irregular particles March 22 -12 5.5 x 10-6 5. 0 x 10-4 9. 0 x 10 Needles; columns 1805 Irregular particles 2 March 22 -12 5.5 x 10-6 2.0 x 10-3 3. 7 x 10 Rimed and capped columns 1940 (some long and fragile) March 23 -5 2.2 x 10-6 7. 0 x 10"3 3.2 x 103 0900 March 25 -4 2. 0 x 10-6 8. 0 x 10-3 4. 0 x 103 1425 68 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20 -22 -24 -26 Estimoted temperature of cloud top (C) Fig. 30 Concentrations of ice particles and ice nuclei 69 SECTION 5 ELECTRICAL MEASUREMENTS Several theories of charge generation in clouds and thunderstorms ascribe the charging to the collison of cloud particles with hailstones falling through the cloud. During the past three years we have carried out a series of field measurements in a number of different locations with the objectives of determining the conditions under which an ice surface receives significant charge when it is exposed to a stream of cloud and precipitation particles, measuring the magnitudes of these charges, and elucidating the principal mechanisms by which the charge is generated. Some of the results of this work have been described by Hobbs and Burrows (1966) Burrows et al. (1967a, b) and Scott and Hobbs (1968a, b). In this section we describe the results of further elec- trical measurements which were carried out in -5-1 G^rg^ng of an ice sphere moving through natural snowfall An ice sphere, 2.5 cm in diameter, was rotated in a horizontal plane through falling snow at velocities ranging from 8 to 20 m sec"1. The net charge acquired the by sphere was recorded on every revolution by allow- ing the sphere to pass through an induction can with a small slit in its side. Charges down to 10"3 esu could be measured in this way. Simul- taneous measurements were taken of the atmospheric electric field and 70 the precipitation current, and the types and sizes of ice particles in the air were observed by taking slide replicas. This experiment, there- fore, was similar to that conducted by Burrows et al. (1967a, b) at Yellowstone Park in January 1967. However, due to the use of a greatly improved field meter, in the experiments described below we are able to observe the relationship between the charge acquired by the ice sphere and the direction and magnitude of the atmospheric electric field in much greater detail than was possible for the measurements obtained in Yellowstone. The experiment was performed on three separate days. On the first day (March 14, Figs. 31-32) the air temperature was -6C and the snowfall consisted of single needles and hollow columns, some of which were lightly rimed. The electric field was quite large and varied rapidly between about -1 * +15 and +95 volt cm The charges acquired h(y the ice sphere as it whirled through the snowfall were always negative, but the magnitude fluc- tuated rapidly between about -1 to -6.5 esu. Although these fluctuations had about the same frequency as the fluctuations in the electric field they did not appear to be directly correlated with the field. The second series of measurements were taken on March 15 (Figs. 33 to 36). The air temperature was -6C and there was a light but steady fall of lightly rimed aggregates of needle and column crystals from a layer of altostratus cloud. However, during the last run in this series (No. 12), stellar crystals and plates predominated. During the first run (No. 9) there was an abrupt reversal in the sign of the atmospheric electric field (+4.5 to -3.5 volt cm" ) in a time interval of about * Positive sign denotes a downward directed electric field. IUU A .. / \ 1\ !\ 80 / , / / \ -K / \ ,\ '1 / \ / \ / \ / \ / ^ / / \ // s'. \ / \ \ / ^ / \ / f 60 V \ \ "-" \ / E x / \ \ 0 \. / \ / \ i 40 \ .--v '-y \ / -0 \' \ / tf , .0 6 v^^ ~. -4 \^ 0 w /^/ -60 "V Velocity of Velocity of Velocity of Velocity of -6 5 = ^ sphere 16.6m sec sphere 17.7m sec sphere 17.0m sec"' sphere = 9.6m sec"' 2250 2235 2240 2245 2250 22 54 Local Time (hrs) 31 Net charge on rotating ice sphere and atmospheric electric field (March 14). /\ A / "-. /l A A / ,"\ \ / \ / \ / 60 \/ V \/ Atmospheric electric field \ / 20 \ \ / Net charge on ice sphere \; v <- Velocity of sphere ------I_____ 2315 Local Time (hrs) Fig. 32 Net charge on rotating Ice sphere and atmospheric electric field (March C.\J Atmospheric electric field E Net charge on ice sphere 16 Bound charge Q^on ice sphere due to electric field (CL= b + cE ) N.B. Electric field meter not working properly at all T" 12 times during this period. E 0 8 V ---.-.... -= 4 \ ..- 0 ------\ ^,^* \ ,^^^^^, 'h- v "^ "5 / ^^te^* 1 0 y 'x"^ -'''" ,0 Run 9 ^ ^ ^^ 1-4 ^^^j^^ A^^ f ^ ^^'" (0 ^ 0 /^ \ f^^ E < -8 |<-><->|<->[t---->|<-(<->|<-->|<->| -12 8.8 14.4 19.1 8.2 15.5 17.8 12.3 20.2 *-Velocity of sphere(m sec-') -16 810 1815 1820 1825 1830 18 33 Fig. Net charge on rotating ice sphere and atmospheric electric field (March 15). SJ 16 Atmospheric electric field Net charge on ice sphere V12 0 "o a ^^''~"\ -<"*'~. *.-.--^.--" .--"~'--. ^^ """' ^u ^^.----^ .S ^*~'~^' 4 ^-^^^^ 0.4 -0 *h> 0.2 "5 0 5 o Run 10 *C -0.2 0 ^-4 \^^A^/^--A^ (0 -0.4 0 E r------*\*--*T---^\*-*1 -0.6 5 -8 Velocity of sphere (m sec"')-* 15.0 17.5 8.3 17.6 -0.8 5 -12 -1C Fig. 34' Net charge on-rotating ice sphere and atmospheric electric field (March 15). Atmospheric electric field Net charge on ice sphere Tg l2 U 3? ^.-- fl 3 ^ ^--^ (A U > U 0.2 S -5 0 a. ^J (0 _o Run II 'k. A) w -0.4 ^0 0 E 0> 5 -8 17.3 8.5 15.0 18.8 8.6 19.4 16. 8 <- Velocity of sphere (m sec-') -0.85-0.6^ -16 2200 2205 2210 2215 2220 2224 Local Time hrs Fig. 35 Net charge on rotating ice sphere and atmospheric electric field (March 15). <;u 16 Atmospheric electric field Net charge on ice sphere "E 12 u .-^ / 0 / / 8 /" -^'-^/ ^o / --,^ -V / Si ^ s -^ 3 \ ^ ^'^ ^ ^' (A ^ 4 --^./^ ~~'^-..--~~ "^^^ 0.4 S. *Z!.a u 0.2 J o 0 Run 12 0 w y 4) \-~^^----'^ Vw-^Sj^S^ -0.2 . "S. -4 (A -0.4 o 0 |<-----> <-->1<---?.| E 17.5 8. 5 19.9 <- Velocity of sphere (m sec"') -0.6 ? 5 0 -8 -c -0.8 u -12 -ifi 2225 2230 2235 2240 2245 2249 Local Time (hrs) Fig. 36 Net charge on rotating ice sphere and atmospheric electric field (March 15). 77 2-1/2 minutes, and this was accompanied by a simultaneous change in the sign of the charge on the sphere (-0.35 to +0.25 esu). It can be shown that since the ice sphere is better connected to the ground through the experimental apparatus than it is to the air, the ice sphere will acquire a bound charge which, in general, will be propor- tional in magnitude and opposite in sign to the atmospheric electric field. In Run 9 (Fig. 33) the atmospheric electric field varied slowly but definitely and the charge on the ice sphere appeared to be controlled mainly by the electric field. In this case the net charge probably con- sisted mainly of bound charge. The bound charge Q. is given by an expression of the form, Q^ = b + cE where, E is the atmospheric electric field and b and c are constants. The "best-fit" relationship of this kind to th6 measured data of Run 9 is indicated in Fig. 33. It can be seen that in this case the bound charge follows very closely the measured value of the net charge (except for a brief period around 1815 hours when the speed of the sphere was 19.1 m sec" and the charging of the sphere due to collisions with ice particles became important). In Runs 10, 11 and 12 (Figs. 34-36) the atmospheric electric field and the snowfall were both very steady; in these cases the relationship between the net charge on the sphere, the velocity of the sphere, and the atmospheric electric field is Q -0.0075 v -0.032 E -0.02 where, Q is the net charge on the ice sphere in esu, E the electric field in volt cm" and v the velocity of the ice sphere through the air in 78 m sec" The last two terms on the right hand side of this expression represent the bound charge. The first term on the right hand side is the contribution to the net charge due to the particles in the air colliding with the sphere; we will call this the "free charge" on the sphere. The free charge as a function of the velocity of the sphere is plotted in Fig. 37. It should be noted that the above expression is to be expected if the charge communicated to the sphere per particle col- lision is independent of both the velocity of the impact and the charge on the sphere. The coefficient of the first term in the above expression for Q is equal to the product of the charge acquired by the sphere per unit path length due to collisions with particles in the air and the time constant for conduction between the sphere and the ground through the experimental apparatus. For our apparatus the time constant was about 6 seconds. Hence, the average charge acquired by the ice sphere per cm of path length through the air due to collisions with snow particles was approxi- mately -1 x 10" esu. For an ice sphere 2.5 cm in diameter, a snow particle concentration in the air of 10~2 to 10~3 cm"3, and a constant collision efficiency equal to unity, the average charge communicated to the ice sphere per snow particle collision would have been -2 x 10~3 to _4 -2 x 10 esu. This range of values is in good agreement with those obtained by Scott and Hobbs (1968) who measured the charge per particle collision by a direct method. On March 16 measurements were made in a supercooled cloud at -5.5C (Fig. 38, Run 13) The cloud was fairly thin and it dissipated towards the end of the run. The charge on the sphere initially increased in 0. 2 O. Run 10 X Run o Run 12 0 3 -0 &-0.2 v> c 0 a> -0.3 o ^0 "5 -o.4 0) 4> k. U. -0.5 -0.6 0 4 6 8 10 12 14 16 18 20 22 24 Velocity of sphere (m sec"1) Fig. 37 Free on charge ice sphere as a function of velocity of sphere through the air (Data from runs 10, 11 and 12, March 15) 20.------ 16 Atmospheric electric field Net charge on ice sphere f*12 Bound charge on ice sphere due to electric field E u ft ^^.-.^ > 0 ^^ ^.<. .^^'""^' o~ -.-" '^---^"---.-.^ ^ '*- ^^ ; 4 --- u o y S> Run 3 ^-4 (A 0 v1^^^"--?^",^ ^^^ E ^ 5 -16 I^U 1005 1010 1015 1020 102 Fig. 38 Charge on ice sphere as a function of velocity of sphere through the air. (Data from Run 13, March 16). 81 magnitude from -0.18 to -0.26 esu, but when the cloud dissipated the charge on the ice sphere at the end of the run was entirely bound charge, then the bound charge is as shown in Fig. 38. It can be seen that as the cloud dissipated the charge on the ice sphere changed from positive with respect to the bound charge to negative. As the final traces of the cloud disappeared the charge decreased to the bound charge value. This change in sign of the charging just before the cloud dissipated is quite interest- ing. The negative charging which occurred at the boundary between the cloud and the clear air suggests that the charging may have been due to the ice sphere acquiring the charges of the cloud droplets as they col- lided with and froze on to the ice sphere. Reiter (1964) has observed in the Alps that stable, layer clouds in a positive potential gradient acquire a negative charge layer at their lower boundary and a positive charge layer at their uppermost boundary due to the change in ionic conductivity which occurs in the boundary layers. The charges come from ions in the clear air moving toward the cloud in the potential gradient. At or just inside the edge of the cloud they are captured by cloud droplets and are no longer able to move in the potential gradient. In stable clouds this boundary layer may be quite thin. The electric field trace in Fig. 38 also confirms this idea. Just as the charging current became negative, the positive electric field began to decrease and continued to decrease after the cloud had dissipated. This behaviour would be expected if a thin layer of negative space charge moved from below the station to above the station during the period when negative charging was occurring. S'2 Electrical charges on individual ice particles in the air The electrical charges on individual ice particles falling through 82 the air were measured by allowing the particles to pass through an induction ring (2.5 cm in diameter) connected to an electronic circuit which would detect charge down to 10~5 esu. The induction ring was placed inside a large metal container at a distance of about 2 cm from a hole, slightly smaller than the diameter of the induction ring, which was situated at the head of a conical nose on the container. The con- tainer could be used in either a vertical or horizontal position. In the vertical position some of the ice particles in the air would fall directly through the hole and the induction ring. In order to reduce the effects of the wind when the container was used in the vertical position it was fitted with a large wind shield. When the wind was sufficiently strong that the ice particles had an appreciable hori- zontal velocity, the metal container was placed in the horizontal position. In some cases the nose of the container was kept pointed into the wind by placing it on a small platform which was rotated by a servo-mechanism responding to a wind vane. In some cases the ice particles were drawn into the hole and through the induction ring by operating a vacuum cleaner connected to the other end of the metal container. There were no significant differences between the vertical arid horizontal arrangements when the vacuum cleaner was not used. But when the vacuum cleaner was turned on more large charges were measured. Measurements were obtained on eight separate occasions on three different days. The results are listed in Tables 4 to 11. 83 TABLE 4 February 17, 1968. 1038 to 1042 hours. Temperature -1C. Wind SE 25 mph. Light snowfall of aggregates of needles and hollow columns, some cloud droplets up to 20 microns in diameter also present. Electric field -10 V cm Magnitude of Charge Number of Particles 3 (in units of 10 esu) Positively charged Negatively charged 1.0 15 21 1.5 23 12 2.0 2.5 57 56 3.0 4.5 40 32 5.0 6.5 27 6 7.0 10.5 12 10 11.0 14.5 2 3 15.0 20.0 3 0 20.5 25.0 4 0 > 25 0 0 Totals 183 140 ^0 Mean positive charge +4 x 10 esu Mean negative charge -1 x 10" esu -3 Net mean charge per particle +1 x 10" esu 84 TABLE 5 February 17, 1968. 1106 to 1130 hours. Temperature -1.5C. Wind SSE 25 mph. Light snowfall of aggregates of needles, hollow columns and plates, some cloud droplets up to 30 50 microns diameter. Part (a) -1 1107 1111 hours. Electric field -20 V cm" Magnitude of Charge Number of Particles (in units of 10 esu) Positively charged Negatively charged 1.0 1.25 10 4 1.5 1.75 12 10 2.0 2.75 25 21 3.0 4.5 42 36 5.0 6.5 49 29 7.0 10.5 52 11 11.0 14.5 32 6 15.0 20.0 21 0 20.5 25.0 9 0 > 25 29 2 Totals 281 119 Mean positive charge +1 x 10 esu Mean negative charge -5 x 10" esu -3 Net mean charge per particle +6 x 10" esu 85 TABLE 5 Part (b) 1121 1123 hours. Electric field changing from -20V cm"1 to 3.5 V cm"1 Magnitude of Charge Number of Particles (in units of 10" esu) Positively charged Negatively charged 1.0 1.25 6 4 1.5 1.75 5 8 2.0 2.5 14 10 3.0 4.5 30 12 5.0 6.5 28 10 7.0 10. 5 28 10 11.0 14. 5 21 0 15.0 20.0 27 3 20.5 25.0 8 0 > 25 33 1 Totals 210 58 Mean positive charge = +1 x 10~2 esu Mean negative charge -5 x 10~3 esu Net mean charge per particle +9 x 10~3 esu 86 TABLE 5 Part (c) 1123 1126 hours. Electric field changing from +3.5 to +25 V cm Magnitude of Charge Number of Particles 3 (in units of 10 esu) Positively charged Negatively charged 0.5 0.75 0 3 1.0 1.25 8 6 1.5 1.75 6 6 2.0 2.75 12 20 3.0 4.75 23 29 5.0 6.75 18 27 7.0 10.75 31 37 11.0 14.5 17 10 15.0 20.0 10 7 20.5 25.0 4 3 > 25 31 10 Totals 160 158 -2 Mean positive charge +1 x 10 esu _3 Mean negative charge -8 x 10 esu -3 Net mean charge per particle = +2 x 10 esu 87 TABLE 6 February 17, 1968. 1714 to 1721 hours. Temperature -5C. Light snow and fog. Electric field +30 V cm Magnitude of Charge Number of Particles 3 (in units of 10 esu) Positively charged Negatively charged 0.5 0.75 6 18 1.0 1.25 9 20 1. 5 1.75 10 17 2.0 2.75 18 25 3.0 4.75 28 24 5.0 6.75 11 16 7.0 10.75 11 11 11.0 14.5 5 5 15.0 20.0 3 1 20.5 25.0 2 0 > 25 3 0 Totals 106 135 _g Mean positive charge +5 x 10 esu Mean negative charge -5 x 10~ esu _4 Net mean charge per particle -8 x 10 esu 88 TABLE 7 February 17, 1968. 1954 to 2013 hours. Temperature -1C. Light snow and fog. Part (a) 1956 1959 hours. Electric field changing from -18 to +21 V cm"1. Magnitude of Charge Number of Particles 3 (in units of 10 esu) Positively charged Negatively charged 0.5 0.75 6 2 1.0 1.25 12 8 1.5 1.75 3 15 2.0 2.75 13 15 3.0 4.75 16 16 5.0 6.5 11 14 7.0 10.75 10 13 11.0 14.5 4 7 15.0 20.0 3 7 20.5 25.5 4 3 > 25 2 10 Totals 84 110 -3 Mean positive charge +6 x 10 esu Mean negative charge -8 x 10 esu Net mean charge per particle = -2 x 10" esu 90 TABLE 8 February 17, 1968. 2015 to 2031 hours. Temperture -1C. Light snowfall of aggregates of needles, capped columns and a few plates. Part (a) 2015 2018 hours. Electric field changing from -3 to 6.5 V cm"1. Magnitude of Charge Number of Particles (in units of 10 esu) Positively charged Negatively charged 0.20 0.25 2 2 0.30 0.35 3 4 0.40 0.50 5 12 0.60 0.95 8 25 1.0 1.3 9 19 1.1 2.15 7 12 2.2 2.9 4 16 3. 0 4.0 5 5 4.1 5.0 3 5 > 5.0 10 20 Totals 56 120 Mean positive charge +2 x 10 esu _3 Mean negative charge -2 x 10 esu -4 Net mean charge per particle -8 x 10 esu 89 TABLE 7 Part (b) -1 1959 2000 hours. Electric field +21V cm Magnitude of Charge Number of Particles 3 (in units of 10 esu) Positively charged Negatively charged 0.75 3 4 1.0 1.25 12 8 1.5 2.25 8 20 2.5 3.25 3 6 3.5 5.25 6 8 5.5 7.25 7 13 7.5 10.0 4 0 10.25 12.5 2 5 > 12.5 6 8 Totals 51 72 Mean positive charge +5 x 10 esu Mean negative charge -5 x 10 esu -4 Net mean charge per particle -8 x 10 esu 91 TABLE 8 Part (b) 2018 2019 hours. Electric field +6 V cm"1. Magnitude of Charge Number of Particles -3 (in units of 10 esu) Positively charged Negatively charged 0.5 6 5 0.75 1 7 1.0 1.25 5 8 1.5 2.25 8 15 2.5 3.25 0 6 3.5 5.25 5 2 5.5 7.25 0 0 7.5 10.0 0 0 10.25 12.5 0 3 > 12.5 0 1 Totals 25 47 Mean positive charge = +2 x 10" esu -3 Mean negative charge = -3 x 10" esu <3 Net mean charge per particle = -1 x 10" esu 92 TABLE 8 Part (c) 2019 2020 hours. Electric field +5 V cm"1. Magnitude of Charge Number of Particles -3 (in units of 10 esu) Positively charged Negatively charged 0.20 5 4 0.30 5 4 0.4 0.5 7 13 0.6 0.9 8 19 1.0 1.3 5 10 1.4 2.1 4 12 2.2 2.9 6 3 3.0 4.0 2 4 4.1 5.0 2 1 > 5.0 5 12 Totals 49 82 Mean positive charge = +2 x 10" esu Mean negative charge -2 x 10~ esu Net mean charge per particle = -5 x 10" esu 93 TABLE 9 March 7, 1968. 1640 to 1645 hours. Temperature -6C. Wind SW 10 mph, Light snowfall of aggregates of columns and small plates, a few small cloud droplets. Magnitude of Charge Number of Particles 3 (in units of 10 esu) Positively charged Negatively charged ^ 0.1 21 31 0.15 3 3 0.2 0.3 43 54 0.4 0.6 29 29 0.7 1.2 22 32 1.3 2.5 10 25 2.6 5.0 9 4 > 5.0 6 0 Totals 143 178 -3 Mean positive charge +1 x 10 esu -4 Mean negative charge -7 x 10 esu Net mean charge per particle +4 x 10 esu 94 TABLE 10 March 29, 1968. 1134 to 1139 hours Temperature -9.5C. Wind NW 10 mph. Light snow and fog. Electric field +28 V cm Magnitude of Charge Number of Particles 3 (in units of 10 esu) Positively charged Negatively charged < 0.5 31 43 0.5 0.75 10 19 1.0 1.25 26 32 1.5 1.75 18 24 2.0 2.75 22 40 3.0 4.75 33 38 5.0 7.75 11 16 8.0 10.75 7 6 11.0 14.75 5 7 15.0 19.75 4 4 20.0 25.0 3 2 > 25 2 13 Totals 172 244 Mean positive charge +4 x 10 esu Mean negative charge -4 x 10 esu -3 Net mean charge per particle -1 x 10 esu 95 TABLE 11 March 29, 1968. 1444 to 1454 hours. Temperature -10.3C. Wind WNW 17 mph. Light snow and fog. Part (a) 1444 1446 hours. Electric field 84 V cm"1. Magnitude of Charge Number of Particles 3 (in units of 10 esu) Positively charged Negatively charged < 2.5 13 25 2.5 3.75 4 2 5.0 6.25 19 19 7.5 8.75 15 9 10.0 13.75 11 12 15. 0 23.75 6 13 25.0 38.75 5 6 40.0 53.75 3 0 55.0 73.75 2 1 75.0 98.75 1 1 100.0 125.0 0 0 > 125 0 0 Totals 79 88 Mean positive charge 1 x 10" esu _o Mean negative charge -1 x 10 esu Net mean charge per particle +4 x 10~ esu 96 TABLE 11 Part (b) 1446 1449 hours. Electric field + 66 V cm"1. Magnitude of Charge Number of Particles -3 (in units of 10 esu) Positively charged Negatively charged < 0.5 6 5 0.5 0.75 1 1 1.0 1.25 17 17 1.5 1.75 20 6 2.0 2.75 29 28 3.0 4.75 33 28 5.0 7.75 26 24 8.0 10.75 14 10 11.0 14.75 10 4 15.0 19.75 5 3 20.0 25.5 1 0 > 25 3 8 Totals 165 134 Mean positive charge +5 x 10~ esu -3 Mean negative charge -6 x 10" esu -4 Net mean charge per particle +3 x 10" esu 97 A number of interesting relationships can be found in the results contained in the above tables. Firstly, the mirror image relationship between the sign of the electric field and the sign of the net charge carried by the particles in the air is generally upheld. However, there are several interesting exceptions to this rule, the most glaring of which are those shown in Tables 5 and U where the electric fields are large and positive and the net charges per particle are still posi- tive. The results shown in Table 5, Parts (b) and (c), illustrate the influence of the electric field on the charge spectra. The electric field changed from -20 to +3.5 V cm" near the conclusion of Part (b) and in Part (c) the field increased from +3.5 to +25 V cm~^-; this was accompanied by a large increase in the relative number of negatively charged particles in Part (c) as well as an increase in the magnitude of the mean negative charge, although the net mean charge per particle still remained positive in sign in Part (c). Considering all of the results contained in Tables 4 to 11, there are nearly equal numbers of positive and negative charges. Thus of a total of 3654 measured charges, the number of positive charges exceeded the number of negative charges by only 126. However, for charges of magnitude less than 2.5 x 10 esu, the number of particles carrying a negative charge was 988 and the number carrying a positive charge was 743. While for charges of magnitude greater than 2.5 x 10 esu, the positively charged particles outnumbered the negatively charged par- ticles by 1147 to 776 (Fig. 39). The positive and negative charge distributions are plotted on log-probability paper in Figs. 40 and 41. It can be seen that in some cases the results tend to lie on straight 98 100[- w o 3 u s 0> 0) o 10 w x 0a x x a x x g .Ol x 5 x x ,0 x ^ a:^ O.|l------I---1--L .0 10 100 Magnitude of charge on porticlesdn units of lO^esu) Fig. 39 Ratio of number of positive to number of negative charges. 99 10-I Run x Run 2 o Run 3 A Run 4 a Run 5 + Run 6 Run 7 Run 8 -2 10 o 0. 0 0 a> > -^1 E !0 (A 0 Q. 10 2 5 10 15 20 30 40 50 60 70 80 90 95 98 Per cent of particles with charges less than Q Fig. 40 Log-probability plots for posit ive change on particles. 100 2 5 10 15 20 30 40 50 60 70 80 90 95 98 Per cent of particles with charges less than Q Fig. 41 Log-probability plots for negative charges on particles. 101 lines which indicates a log-normal distribution of charges. It should Q be noted that in general charges less than about 2.5 x 10~ esu do not have a significant effect on the net mean charge oer particle. If the charges greater in magnitude than 2.5 x 10" esu are studied, it is found that the predominant sign of the charge is temperature dependent. At temperatures around -1C the very large positive charges outnumber the negative charges of comparable magnitude by about 4.5 to 1. However, for temperatures near -10C the very large negative charges outnumber the positive charges by 2 to 1. If it is assumed that the larger charges are carried on the larger particles at temperatures around -10C it would be possible for gravitational separation of the snow particles in the cloud to lead to a positive charge center in the upper part of the cloud and a negative charge center in the lower part. Although the measurements described here were not made in thunderclouds the clouds were generally convective in nature and of sufficient size to be classified as cumulus congestus. For example in the clouds in which measurements were taken from 1444 to 1454 hours on March 29 (Table 11) the field was 84 V cm so that charge separation within the cloud must have taken place in this case. 5.3. Individual charges received by a surface exposed to natura1 cloud and precipitation particles On two occasions simultaneous measurements were obtained of the charges on individual particles in the air and the charges that these particles communicated to a hemispherical surface with which they collided. The purpose of these measurements was to obtain more de- tailed information on the mechanism by which a surface is charged 102 when ice particles in the air collide with it. The measurements were made by placing the hemispherical surface about 1 cm behind the induc- tion ring which has been described in the last section. The individual charges communicated to the hemispherical surface by particles which passed through the ring and collided with the surface were measured using the electrometer described by Scott and Hobbs (1968b). In one case the hemispherical surface consisted of copper, and in the other case the copper was covered with a thin layer of ice. It should be noted that in these experiments the hemispherical surface was situated inside a metal container, so the atmospheric electric field was excluded from the region where the particles were colliding with the surface. The results of the experiments are shown in Tables 12 and 13. It can be seen from the above Tables that the mean charges on the particles in the air (measured with the induction ring) are closely correlated with the mean charges communicated to the hemispheres. In the case of the copper hemisphere (Table 12) the mean positive and the mean negative charges received by the hemisphere were 0.05 of the mean positive and the mean negative charges respectively on the particles in -4 the air; the net mean charge per particle in the air was only +7 x 10 esu and the net mean charge communicated to the hemisphere was essentially zero. For the ice coated hemisphere (Table 13), the mean positive and the mean negative charges received by the hemisphere were 0.1 of the mean positive and the mean negative charges respectively on the particles in the air; the net mean charge per particle in the air was -6 x 10" ^ esu and the net mean charge communicated to the hemisphere was -2 x 10" esu. It is interesting to note, however, that when the individual TABLE 12 March 22, 1968. 1400 hours. Temperature -2C. Wind SSW 15 mph. Light snowfall of heavily rimed aggregates of needles and columns. Station below cloud base. Electric field +2V cm"^- decreasing to zero. Charges on Particles (Induction ring) Charges communicated to copper hemisphere Magnitude of Number of Particles Magnitude of Number of Particles charges (in units Positively Negatively charges (in units Positively Negatively 3 of i0~3 esu) Charged Charged of 10 esu) Charged Charged 0. 5 7 7 < 0.12 0 0 1.0 4 10 0.12 1 1 1. 5 3 8 0.24 3 5 2 2.5 9 11 0..36 1 5 3 4. 5 7 8 0.48 0.60 4 9 5 7.5 6 3 0.72 1.08 10 21 8 10. 5 2 1 1.20 1.80 4 7 11 14.5 1 0 1.92 2. 52 5 7 15 19.5 1 0 2.64 3.48 1 4 20 25 0 1 3.60 4.68 3 2 > 25 2 0 4.80 6.00 5 0 > 6.00 1 2 Totals 47 54 Totals 38 63 -4 Mean positive charge +4 x 10 esu Mean positive charge +2 x 10" esu _4 Mean negative charge -2 x 10 esu Mean negative charge -1 x 10 esu Net mean charge per particle +7 x 10 esu Net mean charge per particle 0 TABLE 13 March 28, 1968. 1319 to 1323 hours. Temperature -5C. Wind W 12 mph. Light snow and fog. Electric field +9 V cm'1. Charges on Particles (Induction ring) Charges communicated to ice covered hemisphere Magnitude of Number of Particles Magnitude of Number of Particles charges (in units Positively Negatively charges (in units Positively Negatively 3 3 of 10 esu) Charged Charged of 10 esu) Charged Charged 2.5 1 9 < 1.2 0 0 5 7 18 1.2 0 0 7.5 1 19 2.4 0 0 10 12.5 3 26 3.6 1 16 15 22.5 6 19 4.8- 6.0 1 33 25 32.5 3 4 7.2 10.8 0 41 35 52.5 0 4 12.0 15.6 0 11 55 72.5 0 0 16.8 25.2 2 10 75 100 1 0 26.4 34.8 0 4 102.5 125 0 0 36.0 48.0 0 1 > 125 0 0 49.2 60.0 0 0 > 60.0 0 2 Totals 27 105 Totals 4 128 Mean positive charge +1 x 10 esu Mean positive charge +1 x 10 esu _9 Mean negative charge -1 x 10 esu Mean negative charge -1 x 10 esu Net mean charge per particle -6 x 10~3 esu Net mean charge per particle -4 x 10"^ esu 105 particles were investigated in most cases there appeared to be little correlation between the charge on a particle in the air and the charge that the particle communicated to the hemispherical surface. For ex- ample, in the case of the results shown in Table 13, the average charge transferred to the hemisphere by particles having a charge greater than +3 x 10" esu was -1.5 x 10" esu, while for particles having a charge less than -3 x 10 esu the average charge transferred was +0.6 x 10~4 esu. Therefore, for these large particles the direct transfer of the charges on the particles to the hemisphre was not the predominant mechanism for the charging of the latter. In this case, mechanical fragmentation of the particles on colliding with the ice sphere could have been an important charging mechanism. 106 APPENDIX A The following eight graphs show measurements of concentrations of cloud condensation nuclei light scattering coefficient, and concentra- tions of sodium-containing particles obtained at the Mount Olympus Research Station during the period February 5 March 31, 1968. Key. Concentration of cloud condensation nuclei (CCN) at 1 per cent superaturation. Light scattering coefficient (b ). s 0 Concentration of sodium-containing particles (SCP), 280 260 2^0 220 200 180 160 1^0 120 100 80 60 ^0 20 February ^ 5 6 9 10 280 260 2^0 220 200 180 160 JL- 1^0 o 0 120 100 80 60 40 20 February 12 13 1^ 15 16 17 iW 260 2^0 8 220 200 7 180 160 6 A 1AO z ^E- t-1 T -t- 0 0 120 5 -X 100 ja V/ ;' 80 < ^ 60 / ^0 3 <--' -^ 20 " 0 2 February 18 19 20 21 22 23 lh February 25 26 27 28 29 30 31 280 3 260 2k0 8 220 200 7 180 0 0 160 6 1AO / 0 ^0 120 o - r m 0 5 0 ^ 00 -0 100 % <9 o /WJ 0 " 80 ^ r\ /"'s o / V ^ 60 ^ /' ^ / ^ ^10 ' ^ 3 20 / ^ 0 n 2 13 14 15 16 March 2A 25 26 27 28 29 30 115 APPENDIX B CORRELATION COEFFICIENTS The following tables show the weekly and daily correlation coeffi- cients between some of the measured variables. The following abbrevia- tions have been used: CCNC = Cloud condensation nucleus count b = Light scattering coefficient 5 INC = Ice nucleus count ANC = Aitken nucleus count WS = Wind speed TO = Total oxidant SCPC Sodium-containing particle count The number in the parentheses after each correlation coefficient gives the number of data points on which the correlation is based. The following conclusions can be drawn from these results. 1. The correlation between the CCNC and b is nearly always positive and the weekly correlation coefficients are generally significant at the 99% confidence level. 2. The correlation between the CCNC and INC, while significant on some occasions is not consistently either positive or negative. 3. The correlation between the CCNC and ANC is usually positive, although the confidence level is not high due to the small number of samples of ANC. 4. The weekly correlation coefficients between CCNC and SCPC are always positive. 5. Apart from one exception, b and TO are negatively correlated. 5 116 6. There is a strong negative correlation between b and s WS; however, the confidence level is low due to small number of samples of WS. 7. There is a tendency for the SCPC and ANC to be positively correlated but confidence level is low due to small number of samples of ANC. 117 JANUARY 24 27 CCNC b INC ANC WS TO WEEK Sun. Mon. Tues. ^ Wed. Thurs. Fri. Sat. WEEK Sun. Mon. INC Tues. Wed. Thurs. Fri. Sat. WEEK Sun. Mon. ANC Tues. Wed. Thurs. Fri. Sat. WEEK .38 (10) Sun. Mon. WS Tues. Wed. Thurs. Fri. -.34 (4) Sat. -.73 (S) WEEK Sun. Mon. TO Tues. Wed. Thurs. Fri. Sat. WEEK Sun. Mon. SCPC Tues. Wed. Thurs. Fri. Sat. 118 JANUARY 28 FEBRUARY 3 CCNC b INC ANC WS TO WEEK Sun. Hon. b Tues. s Wed. Thurs. Fri. Sat. WEEK Sun. Mon. INC Tues. Wed. Thurs. Fri. Sat. WEEK .06 (11) Sun. Mon. .57 (4) ANC Tues. -.75 (3) Wed. Thurs. Fri. Sat. WEEK .24 (15) -.26 (23) Sun. .70 (3) -.63 (4) Mon. -1.00 (3) +.07 (4) WS Tues. -.78 (3) .85 (5) Wed. -.60 (4) Thurs. -.94 (4) Fri. -.08 (3) Sat. WEEK Sun. Mon. TO Tues. Wed. Thurs. Fri. Sat. WEEK Sun. Mon. SCPC Tues. Wed. Thurs. Fri. Sat. 119 FEBRUARY 4 10 CCNC b INC ANC WS TO WEEK Sun. Mon. b s Tues. Wed. Thurs. Fri. Sat. WEEK .14 (73) Sun. Mon. INC Tues. Wed. .36 (9) Thurs. -.37 (24) Fri. .24 (22) Sat. .sa n -n WEEK .29 (7) -.70 (3) Sun. Mon. ANC Tues. Wed. Thurs. .28 (3) -.89 (3) Fri. .98 (3) Sat. WEEK -.05 (33) .28 (16) -.68 (11) Sun. Mon. .68 (4) WS Tues. 86 (5) Wed. 1.00 (3) Thurs. .50 (7) -.34 (5) -.73 (5) Fri. .38 (7) -.97 (4) Sat. .?IR (7) .99 f4) WEEK -.38 (168) -.20 (77) -.69 (11) .77 (33) Sun. Mon. TO Tues. .20 (25) .92 (5) -.23 (8) Wed. -.81 (36) -.28 (9) -.27 (5) Thurs. .40 (38) -.16 (25) -.34 (5) .83 (9) Fri. -.08 -.56 (22) -.97 (4) .93 (8) Sat. .38 (W) --';U CIK) .69 (3) WEEK Sun. Mon. SCPC Tues. Wed. Thurs. Fri. Sat. 120 FEBRUARY 11 17 CCNC b INC ANC WS TO WEEK .33(174) Sun. Mon. .14 (49) Tues. .44 (49) Wed. .62 (33) Thurs. -.02 (43) Fri. Sat. WEEK .14(172) .16(100) Sun. .66 (23) Mon. -.34 (22) -.40 (22) Tues. .30 (41) .40 (41) Wed. Thurs. -.14 (33) .60 (37) Fri. .61 (20) Sat. .34 (33) WEEK -.19 (12) .18 (11) -.33 (6) Sun. Mon. -.44 (3) .45 (3) Tues. Wed. Thurs. .99 (4) .59 (5) .58 (3) Fri. Sat. WEEK -.44 (29) -.63 (22) -.28 (21) .16 (16) Sun. -.37 (3) -.70 (5) Mon. -.37 (7) -.26 (7) -.66 (3) Tues. .27 (6) -.38 (6) .31 (5) Wed. -.83 (3) -.34 (4) Thurs. -.92 (4) .24 (5) -.83 (3) -.66 (5) Fri. -1.00 (4) .57 (4) Sat. .92 (4) -.17 (3) WEEK .08(206) -.50(140) .22(199) .36 (14) -.18 (29) Sun. .27 (24) .33 (44) .29 (6) Mon. 30 (28) -.60 (28) -.47 (21) -.90 (3) Tues. .43 (24) -.81 (20) -.95 (19) Wed. -.74 (33) -.40 (44) -.43 (5) Thurs. .04 (43) -.49 (48) -.58 (37) .44 (5) -.62 (5) Fri. -.59 (21) -.28 (40) 87 (4) -.43 (6) Sat. -.02 (37) -.41 (38) .53 (4) WEEK Sun. Mon. Tues. Wed. Thurs. Fri. Sat. 121 FEBRUARY 18 24 CCNC INC ANC WS TO WEEK Sun. Mon. b Tues. s Wed. Thurs. Fri. Sat. WEEK -.65 (9) -.33 (51) Sun. -.65 (9) Mon. INC Tues. -.13 (14) Wed. .40 (29) Thurs. Fri. Sat. -.38 WEEK .13 (7) -.22 (13) Sun. .95 (4) Mon. ANC Tues. .94 (4) Wed. -.23 (4) Thurs. Fri. Sat. WEEK -.82 (7) -.37 (13) -.13 (32) Sun. .75 (4) .92 (4) Mon. -.33 (4) WS Tues. -.91 (4) -.94 (5) Wed. -.84 (4) .27 (5) Thurs. -.84 (5) Fri. .00 (5) Sat. .43 (4) WEEK -.16 (22) .45 (66) -.27 (88) .67 (13) -.54 (14) Sun. -.16 (22) -.33 (13) Mon. TO Tues. .58 (16) .23 (39) .55 (5) -.67 (5) Wed. .27 (39) -.14 (29) -.74 (5) -.35 (5) Thurs. Fri. Sat. -.14 (11) -.08 (7) WEEK Sun. Mon. SCPC Tues. Wed. Thurs Fri Sat. 122 FEBRUARY 25 MARCH 2 CCNC INC ANC WS TO WEEK .42(123) Sun. b Mon. .34 (8) s Tues. .25 (24) Wed. -.36 (13) Thurs. -.62 (32) Fri. .54 (46) Sat. WEEK .42 (60) .36(111) Sun. -.16 (43) Mon. .70 (5) -.25 (28) INC Tues .38 (37) -.01 (28) Wed. .69 (12) -.15 (12) Thurs. Fri. Sat. 81 (6) WEEK .25 (15) .63 (21) .60 (15) Sun. -.61 (4) .28 (5) Mon. .79 (5) -.21 (3) ANC Tues. .15 (5) .46 (5) Wed. .77 (5) Thurs. Fri. .76 (4) .98 (4) Sat. WEEK .52 (34) .21 (34) -.04 (18) .25 (26) Sun. -.74 (4) .50 (5) 36 (5) Mon. .95 (4) 1.00 (3) WS Tues. -.56 (7) -.61 (4) .37 (7) .59 (5) Wed. .16 (4) -.35 (7) .18 (5) Thurs. -.70 (8) .36 (7) Fri. .25 (9) .27 (8) .50 (4) Sat. 14 (5) WEEK -.16(114) -.11(186) .26(127) .33 (19) -.15 (28) Sun. .21 (43) -.30 (46) .95 (5) .02 (5) Mon. -.56 (8) .60 (8) -.31 (28) 71 (5) .91 (4) TO Tues. -.12 (34) -.14 (22) .20 (38) -.95 (5) -.56 (6) Wed. .62 (14) -.23 (3) .61 (15 Thurs. 37 (34) -.08 (47) -.19 (8) Fri. -.21 (24) -.05 (24) -.96 (4) Sat. WEEK .^8 (22) .19 (21) -.47 (R) 35 (5) .81 (10) -.35 ri8) Sun. Mon. SCPC Tues. -.96 (3) -1.00 .99 (3) Wed. 36 (4) Thurs. 87 (10) .61 (10) 1.00 (3) -.18 (10) Fri. -.34 (5) -.18 (6) .49 (4) -.82 (4) Sat. 85 (3) MARCH 3 9 CCNC INC ANC WS TO WEEK .09 (53 Sun. .04 (22] Mon. .29 (14) b Tues. s Wed. Thurs. Fri. Sat. .54 (17) WEEK -.23 (25) .80 (14) Sun. Mon. INC Tues. Wed. Thurs. Fri. Sat. --73 (7S) .80 (14) WEEK .45 (13) -.56 (4) .42 (7) Sun. .95 (4) Mon. ANC Tues. .26 (4) Wed. Thurs. .50 (3) Fri. Sat. .47 (4) .53 (3) WEEK .04 (22) -.43 (8) -.17 (7) .62 (23) Sun. -.68 (8) -.52 (5) -.48 (4) Mon. .24. (5) WS Tues. .55 (5) .46 (5) Wed. .99 (3) Thurs. -.29 (3) -.27 (5) Fri. Sat. -.36 (5) .99 (3) .41 (3) WEEK .19 (39) -.66 (12) -.05 (47) -.14 (14) .13 (16) Sun. .10 (4) Mon. TO Tues. Wed. .74 (7) .29 (4) Thurs. .42 (16) -.15 (5) .69 (5) Fri. -.73 (11) -.10 (5) .56 (5) Sat. -.59 f32) -.66 fl2) .00 do) -.81 f3) -.27 f4) WEEK .12 (11) -.26 (5) .40 (8) .58 (14) .16 (14) -.48 (14) Sun. -.20 (4) -.18 (3) Mon. SCPC Tues. Wed. Thurs. .34 (4) .98 (4) -.84 (4) -.47 (5) Fri. .76 (3) .20 (3) -.28 (5 Sat. -.97 (4) -.60 (4) .21 (4) .57 (3) -.97 (4) 124 MARCH 10 16 CCNC INC ANC WS TO WEEK .09(132) Sun. -.24 (38) Mon. -.01 (32) b Tues. s Wed. Thurs. .62 (5) Fri. .48 (11) Sat. -.02 (47) WEEK .20 (98) .05(210) Sun. .17 (22) .10 (33) Mon. .23 (20) .35 (33) INC Tues. .18 (33) Wed. -.32 (28) Thurs. -.70 (10) .57 (31) Fri. .29 (19) .21 (24) Sat. -. 32 (28) -.71 0^ WEEK .17 (13) .30 (27) .21 (24) Sun. .99 (3) .34 (5) 86 (4) Mon. .94 (3) -.81 (5) -.45 (3) ANC Tues. -.74 (3) Wed. -.99 (3) Thurs. 1.00 (3) Fri. .99 (3) -.27 (3) Sat. -Q1 (<.) -.71 (5) .21 (5) WEEK .39 (15) .27 (31) .19 (26) .19 (29) Sun. .96 (4) -.39 (6) 38 (4) .72 (4) Mon. .33 (4) .40 (6) -.80 (3) .84 (4) WS Tues. .20 (5) .60 (3) .44 (3) Wed. -1.00 (3) .99 (3) .94 (4) Thurs -.28 (3) 32 (5) .42 (5) Fri. -.77 (3) 1.00 (3) -.64 (5) Sat. .32 (5) -.43 (5) .52 (5) .16 (4) WEEK .19 (68) .18(152) .21(105) .22 (30) -.21 (36) Sun. .62 (32) -.35 (43) .34 (13) 82 (5) .16 (6) Mon. -.42 (6) -.32 (22) 32 (17) -1.00 (3) .91 (3) TO Tues -.34 (40) -.32 (24) -.97 (3) -.15 (4) Wed. .03 (11) -.40 (11) Thurs. .06 (11) -.86 (12) -.08 (24) -.68 (4) -.36 (4) Fri. -.67 (10) -.38 (13) -.12 (21) -.50 (3) 1.00 (3) Sat. -.06 (10) 34 (12) .44 (9) WEEK .22 (10) -.06 (26) .36 (23) .37 (19) -.56 (19) .22 (19) Sun. .70 (4) -.94 (3) .99 (4) -.38 (3) .00 (4) Mon. .16 (3) -.74 (3) SCPC Tues -.74 (3) -.30 (3) Wed. .39 (4) -.15 (5) -.92 (4) -.74 (5) .00 (4) Thurs. .51 (4) .24 (4) 3 (3) Fri. 88 (3) .96 (4) -.46 (4) Sat. .28 (5) -.36 (5) .72 (5) .82 (4) -.55 (3) 125 MARCH 17 23 CCNC INC ANC WS TO WEEK--- .30(197) Sun. Mon. b Tues. s .03 (19) Wed. .72 (43) Thurs. .52 (49) Fri. .58 (45) Sat. -.26 (41) WEEK--- .26(155) -.27(223) Sun. .38 (30) Mon. -.22 (30) INC Tues. Wed. -.22 (36) -.13 (42) Thurs. -.29 (42) -.12 (42) Fri. .30 (40) .48 (38) Sat. -.02 (37) 33 r3Q) WEEK--- .60 (21) -.30 (33) .21 (24 Sun. -1.41 (3) -.41 (4) Mon. .72 (4) ANC Tues. -.45 (5) Wed. -1.00 (4) -.84 (5) .37 (4) Thurs. -.60 (5) -.51 (5) -.51 (5) Fri. .85 (5) .21 (5) -.22 (4) Sat. -97 (^\ -.88 (6) .84 f.S) WEEK -.26 (36) -.08 (49) .08 (36) -.22 (34) Sun. .49 (3) .31 (4) -.95 (5) Mon. .38 (5) .48 (4) WS Tues. -.10 (5) -.49 (5) Wed. -.58 (7) -.61 (8) .33 (6) .57 (5) Thurs. .126(11) .33 (11) 33 (9) -.59 (5) Fri. -.56 (10) .10 (10) .64 (9) -.81 (5) Sat. .63 (6) -.71 (7) .77 (6) -.65 (5) WEEK--- .26(179) -.25(276) .26(185) .77 (25) .34 (40) Sun. .19 (9) -.48 (9) Mon. -.69 (48) -.08 (29) -.57 (4) .48 (5) TO Tues. .19 (19) -.08 (49) -.44 (5) .34 (5) Wed. -.69 (43) -.64 (49) .23 (42) -.02 (5) .70 (8) Thurs. -.25 (49) -.43 (49) .19 (42) -.22 (5) -.13 (11) Fri. .49 (47) .40 (45) -.03 (39) .34 (4) -.09 (10) Sat. .16 (21) -.47 (25) .25 (22) WEEK .34 (26) .54 (42) .21 (27) .65 (30) .13 (31) .62 (34) Sun. .48 (4) .32 (5) .48 (5) -.79 (5) Mon. .89 (5) 1.00 (3) .68 (3) -.14 (5) SCOC Tues. .83 (5) .48 (10) 37 (4) -.94 (4) .24 (10) Wed. -.64 (4) -.59 (5) .99 (4) .25 (5) 80 (5) .92 (5) Thurs. -.97 (6) -.43 (6) .48 (6) .68 (5) -.23 (5) .63 (6) Fri. .92 (7) .87 (7) .87 (6) .67 (5) -.30 (6) .96 (R) Sat. .78 (4) .55 (5) .97 (4) .16 (3) -.26 (3) MARCH 24 30 CCNC INC ANC WS TO WEEK .29(219) Sun. .26 (46) Mon. -.27 (36) b Tues. .66 (49) s Wed. -.49 (39) Thurs .57 (49) Fri. Sat. WEEK .20(181) .28(192) Sun. .20 (39) .25 (41) Mon. .30 (24) -.56 (26) INC Tues. -.18 (39) -.11 (39) Wed. -.33 (37) .06 (44) Thurs. .67 (42) .64 (42) Fri. Sat. WEEK -.22 (24) .28 (22) .17 (14) Sun. -.86 (3) .23 (4) -.98 (3) Mon. -.58 (4) .69 (4) ANC Tues -.55 (5) -.26 (5) .66 (3) Wed. -.17 (3) .62 (5) .99 (4) Thurs. -.76 (4) .71 (4) Fri. ? -.36 (5) Sat. T WEEK -.43 (44) -.21 (37) .33 (23) -.20 (24) Sun. -.70 (8) -.57 (9) -.12 (6) .24 (4) Mon. .51 (7) .38 (8) 86 (3) -.70 (4) WS Tues. -.32 (7) -.10 (7) -.19 (5) .76 (4) Wed. .11 (3) .63 (5) .26 (4) .56 (4) Thurs -.67 (8) -.28 (8) 88 (5) .00 (3) Fri. 7 (11) Sat. .16 .49 (5) WEEK .12(131) -.18(121) -.17(101) -.54 (13) .45 (21) Sun. -.16 (15) -.08 (16) -.29 (141 -.81 (4) .11 (6) Mon. .18 (22) -.40 (24) .64 (16) 85 (3) .60 (5) TO Tues. -.43 (19) -.10 (19) 32 (IP) 37 (3) Wed. .41 (19) .08 (29) -.42 (25) -.37 (U) .45 (4) Thurs -.36 (33) -.46 (33) -.40 (30) Fri ) .06 (23) Sat. J WEEK .07 (26) .44 (22) 17 (15 .65 (15) -.52 (19) .24 (i,u) Sun. -.32 (4) -.07 (5) 80 ~; ^ -.18 (3) -.21 (4) .nn f3) Mon. -.94 (4) -.18 ;5) 39 (3) 1.00 (" SCPC Tues. .18 (5) 81 (5) -.95 (3) -.17 (4) -.36 (5) Wed. -.87 (3) .76 (4) .94 (4) -.70 (3) Thurs. -.3U (3) -1.00 (3) .29 (3) .20 (3) Fri. .17 (7) -.72 (3) (3) Sat. .35 APPENDIX C SLIDE REPLICAS Time and Approximate Sizes Slide Number Date Types of Particles of Particles (mm) 1-1 1615 Irregular oarticles (common) 0.9 Feb. 2 Rimed hollow prisms (fairly common) 0.7 Hexagonal plates (rare) 0.5 Aggregates of hexagonal plates 1-2 1615 " Feb. 2 1-3 1700 Hollow prisms (common) 0.2 to 0.6 Feb. 2 Irregular particles Hexagonal plates (rare) 1-4 1030 Hollow prisms (common) 0.3 Feb. 17 Irregular particles (common) 1.0 Hexagonal plates 0.3 1-5 1100 Irregular particles (common) 1.0 Feb. 17 Columns (common) 0.3 Hexagonal plates (rare) 0.2 1-6 1115 Columns (common) 1.0 Feb. 17 Irregular particles (common) 0.3 Hexagonal plates (rare) 0.2 128 Time and Approximate Slide Number Sizes Date Types of Particles of Particles (mm) 1-7 1130 Columns (common) 0.3 Feb. 17 Irregular particles (common) 1.0 Drops (few) 0.2 1-8 2020 Irregular particles (common) 1 .0 Feb. 17 Columns Capped columns Drops (few) 0.5 1-9 2025 Irregular aggregates (common) 1 .0 Feb. 17 Drops (common) 0.07 1-10 2030 Capped columns (common) 0.4 Feb. 17 Irregular particles 1 .0 1-13 2045 Irregular particles (common) 1 .0 Feb. 17 Drops (few) 0.06 Columns (few) 0.5 Ice pellets (few) 0.2 1-15 1630 Columns 0.3 March 7 1-16 2100 Irregular particles 0.2 March 9 Hexagonal plates 0.4 Drops 0.3 Time and Approximate Sizes Slide Number Date Types of Particles of Particles (mm) 1-17 2145 Irregular particles (common) 0.4 March 9 Drops Hexagonal plates (few) Columns (few) 1-18 1030 Irregular rimed particles (common) March 10 Drops 0.2 Columns (common) 0.3 to 1.2 1-19 2245 Columns (common) March 11 Hexagonal plates Irregular particles 1-20 2045 Irregular particles (common) March 12 Columns 1-21 1305 Irregular particles (common) 1.0 March 13 Drops (common) 0.5 Rimed columns (rare) 1-22 2245 Irregular particles (common) 1 .0 March 14 Columns (common) 1.0 Drops (rare) 0.05 1-23 2250 March 14 130 Time and Approximate Sizes Slide Number Date Types of Particles of Particles (mm) 1-24 2255 Irregular particles (common) 0.5 to 1 March 14 Columns (rare) 1.0 Needles (rare) 1.0 Hexagonal plates (rare) 1-25 2260 Irregular particles (common) Small March 14 Columns Hexagonal plates (rare) O.B Drops 0.04 to 0.3 1-26 1740 Rimed columns (common) 0. 1 to 1 March 15 Irregular particles (rare) 1-27 1815 Rimed columns (common) 0.1 March 15 Irregular particles (few) 1-28 1828 Capped columns (common) 0.4 March 15 Stellar crystals (rare) 0.8 Irregular aggregat"s (fairly common) 1.0 1-29 2150 Badly frosted March 15 Some irregular (common) 1.3 to 2.0 1-30 2230 Badly frosted March 15 Columns (few) 0.7 Irregular (common) 1. 3 to 2.0 131 Time and Approximate S i ze s Slide Number Date Types of Particles of Particles (mm) 1-31 2230 Hexagonal plates (rare) 1.2 March 15 Columns (rare) 0.8 Steliars (several) 1.5 Irregular (few) 1.0 1.5- "^ 1-32 1115 Broken stellars (few) 0.9 March 17 Irregular (common) 0.3 1-33 1415 Broken stellars (several) 0.9 March 22 Irregular (common) 4.7 1-34 1417 Needles (common) 0.01 March 22 Irregular (several) 0.3 to 1.5 1-35 1805 Needles (common) 0.1 to 0.4 March 22 Irregular columns (rare) 1.0 Irregular (few) 0.2 to 1.5 1-36 1805 Needles (several) 0.3 March 22 Columns (rare) 1.0 Irregular (few) 0.4 to 1.0 1-37 1930 Columns (common) 0.4 March 22 Capped columns (common) 1.0 Rimed columns (common) 1.0 Aggregates of columns (few) 2.5 Irregular (few) 0.8 132 Time and Approximate Sizes Slide Number Date Types of ~jt"-" ParticlesLj.i-j.ca of Particles (mm) 1-38 1930 Needles (several) 0.6 March 22 Capped columns (several) 0.4 to 1.0 Rimed columns (several) 0.6 to 1.2 Irregular (several) 1.0 1-39 2025 Frosted March 22 1-40 2030 Hollow columns (few) 0.4 March 22 Rimed columns (common) 0.6 Needles (common) 0.3 Irregular (several) 0.2 to 1.5 1-41 2035 Hollow columns (common) 0.3 March 22 Rimed columns (several) 0.9 Capped columns (several) 0.4 Needles (common) 0.2 Irregular (several) 1.0 1-42 2045 Rimed columns (common) 0.4 March 22 Needles (common) 0.2 to 0.6 1-43 2055 Rimed columns (common) 0. 5 to 1.6 March 22 Ueedles (common) 0.2 Irregular (several) 0.7 to 1.0 133 Time and Approximate Sizes Slide Number Date Types of Particles of Particles (mm) 1-44 2110 Badly frosted March 22 Melted 1-45 1215 Slide broken after exposure March 23 1-46 1505 Rimed columns (common) 1.7 March 23 Capped columns (common) 1.0 Hollow columns (several) 0.8 to 1.0 Broken plates (few) 1.5 to 2.0 1-47 1935 Rimed columns (common) 1.7 March 24 Hollow columns (common) 0.9 Aggregates of plates (few) 1.2 Plates (several) 0.9 Needles (common) 0.3 1-48 1940 Rimed columns (common) 1.3 March 24 Needles (common) 0.3 Broken plates (several) 0.4 to 0.9 Broken stellars (several) 1.8 1-49 1945 Rimed columns (several) 1.4 March 24 Needles (common) 0.3 Broken stellars (few) 0.9 Broken plates (few) 0.3 to 1.0 134 Time and Approximate Sizes Slide Number Date Types of Particles of Particles (mm) 1-50 1950 Rimed columns (several) 1.0 March 24 Capped columns (several) 1.0 Columns (several) 1.0 Broken stellars (common) 1.0 to 1.5 Needles (common) 0.3 1-51 1955 Rimed columns (several) 0.3 to 1.5 March 24 Needles (common) 0.3 Broken stellars (several) 1.8 1-52 2000 Broken plates (common) 0.3 to 0.9 March 24 Broken stellars (few) 0.8 Rimed columns (few) 1.0 Needles (common) 0.2 135 REFERENCES Ahlquist, N. C. and R. J. Charlson, "A new instrument for evaluating the visual quality of air." Paper presented at annual meeting of PNW Intern. Section of the Air Pollution Control Assoc. Seattle, 1966. Burrows, D. A. , W. D. Scott, and P. V. Hobbs, "The charging of ice spheres due to collisions with snowflakes," Yellowstone Field Report No. 7, SUNY, 1967a. Burrows, D. A. P. V. Hobbs, and W. D. Scott, "Factors affecting the electric charge acquired by an ice sphere moving through natural snowfall," Ross Gunn Memorial Issue, Hon. Weather Rev. 95, 878, 1967b. Charlson, R. J. , H. Horvath, and R. F. Pueschel, "The direct measurement of atmospheric light scattering coefficient for studies of visibility and pollution," Atmos. Environ. , 1, 469, 1967. dark, V. F. "The multi-cylinder method," Mt. Washington Observatory, Monthly Research Bulletin, 2, No. 6, 1946. Hobbs, P. V. , and D. A. Burrows, "The electrification of an ice sphere moving through natural clouds," J. of the Atmos. Sci. 23, 757, 1966. Hobbs, P. V. , W. D. Scott, J. E. Dye, and D. A. Burrows, "Preliminary re- port on a field research program carried out in the Olympic Mountains of Washington State," Contributions from the Cloud Physics Laboratory, University of Washington, Seattle, April 1966. Mast, G. M. , and E. E. Saunders, "Research and development of instrumenta- tion for ozone sensing," I.S.A. Trans. 1(4), 325, 1962. Middle-ton, W. E. K. , Vision through the atmosphere, University of Toronto Press, Toronto, 1963. Radke, L. F. and P. V. Hobbs, "An automatic cloud condensation nucleus counter," Proc. of Intern. Conf. on Cloud Physics Toronto, August 1968. Reiter, R. Felder, Strome und Aerosole in der unteren Troposphare. Verlag Dr. Steinkopff, Darmstadt, 1964. Scott, W, D. and P. V. Hobbs, "The charging of ice surfaces exposed to natural ice particles," Proc. of Intern. Conf. on Cloud Physics, Toronto, August 1968a. Scott, W. D. and P. V. Hobbs, "The spectra of charging events due to the collision of natural ice particles with an ice surface," Quart. J. Roy. Met. Soc. 1968b (in press). Soudain, R. "Realisation d'un compteur automatic de nayaux de clorine de sodium," J. Sci. de la Met. 3, 137, 1951. Steele, R.L. C.P. Edwards, L. 0. Grant, and G. Langer, "A calibration of the NCAR Acoustical Ice Nucleus Counter," J. Appl. Met. 6, 1097, 1967. Vonnegut, B. and R. L. Neubauer, "Counting sodium containing particles in the atmosphere by their spectral emission in a hydrogen flame," Bull. Amer. Met. Soc. 34, 163, 1953. Woodcock, A. H. and A. T. Spencer, "An airborne flame photometer and its use in the scanning of marine atmospheres for sea salt particles," J. Met. 14, 437, 1957. 137 ACKNOWLEDGMENTS Help was received from many people during the course of this program. In particular, thanks are due to J. Pinnons, W. Mach, R. Smith, B. Ryan, and A. Alkezweeny for assistance in collecting and analysing the measure- ments; to R. Charlson and J. Kelly for the loan of an integrating nephelom- eter and a Brewer-Mast electrochemical analyser, respectively; to Mr. B. Gale, Superintendent of the Olympic National Park, and his staff for their helpful cooperation; and to Mrs. D. Carey and Mrs. P. Yenser for typing the manuscript and preparing the diagrams. The principal source of support for this program was Grant GA 780 from the Atmospheric Sciences Section of the National Science Foundation. Support for the work described in 2 was received from the U.S. Dept. of Interior, Office of Atmospheric Water Resources Contract 14-06-D-5970 with the State of Washington, Dept. of Water Resources. The U.S.-Japan Cooperative Program (NSF Grant GF 285) provided partial support for the ice nucleus measurements.