Michael B. Meyer, G. Garland Lala, -82: A Cooperative Field Study and James E. Jiusto1 Atmospheric Sciences Research Center of Radiation Fog State University of New York at Albany Albany, NY 12222

Abstract

The Physics Section of the Atmospheric Sciences Research Center-State University of New York at Albany conducted a coop- erative field study (FOG-82) during the of 1982 as part of an ongoing radiation-fog research program. A computer-controlled data-acquisition system consisting of sophisticated soil, surface, and boundary-layer sensors, as well as contemporary aerosol and drop- let probes was developed. These data are being used to address a var- iety of critical problems related to radiation-fog evolution. Scientists from 10 universities and research laboratories partici- pated in portions of FOG-82. Research objectives included studies of fog mesoscale , radiation studies, low-level water budget, vertical fog structure, fog supersaturation, condensation nuclei, and fog-water chemistry, as well as radiation-fog life cycles. A comprehensive description of the FOG-82 program and objectives is presented.

FIG . 1. Monthly heavy-fog (visibility, V less than or equal to 1/4 1. Introduction mile) [solid line] and heavy-fog-duration [dashed line] frequency for Albany, New York, 1970-79. The Section of the Atmospheric Sciences Re- search Center-State University of New York at Albany (ASRC-SUNY) has been involved in fog research for many years, concentrating on the understanding of fog-evolution processes through field measurements and numerical fog modeling. Additional work has been done in fog (synoptic) . A climatological survey of National Service heavy- fog observations (1970-79) at Albany, New York, reveals a distinct "fog " during the autumn months (Fig. 1). During September and October an average of four to five heavy-fog (visual range less than or equal to 400 m) events, each lasting some two to four hours, can be expected to occur. Relying on this seasonal dependence of fog frequency, an extensive cooperative field study of radiation fog (FOG- 82) was conducted at the Albany County Airport, Albany, New York, from 7 September to 7 November 1982 (Fig. 2). This program produced much data which has become the focal point of ongoing research and data analysis. FIG. 2. Aerial view of the FOG-82 field site at the Albany County Airport, Albany, New York (photo by Anne Marie Pitaniello).

2. Field program objectives

The ASRC-SUNY radiation-fog-measurement program has of basic surface-layer variables and aerosol characteristics in evolved from a "bare bones" study involving measurements the early to mid 1970s to a complex integration of soil, sur- face, and boundary-layer sensors, as well as state-of-the-art probes to more accurately detail fog microphysical processes

1 and aerosol behavior. Along with this gradual strengthening This paper is dedicated to the memory of Dr. James E. Jiusto of the field program over the past decade has come a neces- who passed away 5 October 1983. sary increase in computing and analytical power. Thus, a © 1986 American Meteorological Society more-comprehensive approach for addressing the many re-

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FIG. 3. FOG-82 instrumentation and measurement system.

maining mysteries of fog evolution is now possible. The bution, as well as the vertical evolution of fog and sed- primary research objectives for FOG-82 are summarized imentation flux of fog water, will be examined. below. 5) Develop a 10.6-/zm infrared-transmission system which allows us to test the full range of applicability of the unique relationship between infrared extinction and 1) Understand the development of the surface-layer struc- LWC (Chylek, 1978; Pinnick et al., 1979) in real envi- ture under conditions of strong nocturnal cooling and ronmental conditions. low wind speed and provide data to assess the relative 6) Continue emphasis on fog forecasting and modeling roles of radiative and turbulent transport involved with through study of radiation-fog climatology and surface radiation-fog formation. synoptic patterns conducive to heavy-fog formation 2) Monitor vertical development of the nocturnal bound- (Meyer and Jiusto, 1982) and use of field-study data for ary layer using balloon profiles of temperature, mois- initialization and verification of a numerical model of ture, and wind to better define the thermodynamic radiation-fog formation (Lala et al., 1975). conditions within this layer. 7) Foster cooperative research with scientists from 10 3) Define mesoscale influences from information on the universities and research laboratories who have partic- horizontal fields of temperature, moisture, wind, and ipated in portions of the field program, supporting stud- pressure from a dense mesonetwork to aid in determin- ies in the areas of fog mesoscale meteorology, fog- ing the importance of local flow regimes (terrain ef- water chemistry, condensation nuclei, low-level water fects, advection) and spatial inhomogeneities (cold budget, visible and infrared radiation, vertical fog pockets, moisture sources) in radiation-fog mechanisms. structure, and fog supersaturation. 4) Determine radiation-fog microphysical properties from measurements of aerosol and droplet-size spectra, liq- uid-water content (LWC) and atmospheric extinction and thus study the development and intensity of radia- 3. Experimental design tion at various phases in their life cycles. Vertical variations in the sensitive relationship of extinction to During the mid 1970s small-scale studies of fog formation fog LWC and characteristics of the droplet-size distri- were begun by the ASRC-SUNY Cloud Physics Section.

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These initial studies involved selected measurements of sur- not uncommon at low levels (approximately 100-200 m) face-layer thermodynamic variables, wind speed, visual shortly after sunset. Also, operations during fog periods were range, and fog-droplet-size distributions. Most of the mea- restricted by the Federal Aviation Administration to those surements were made manually with some data recorded with times when aircraft in the area were not making instrument analog recorders. With a growing appreciation for the com- landings. plexity of the problem of fog formation came the desire to The tethered-balloon soundings were augmented by peri- expand the measurement program both in scale and resolu- odic releases of a radiosonde-type instrument (AIR, Inc. Air- tion. The development of a digital data system controlled by sonde) carried by a free balloon. This system provided a microcomputer allowed for the increased volume of data to temperature, humidity, and pressure data from the surface to be recorded in a format that would facilitate future analysis. a level of about 500 mb. Data from this instrument was tele- Further refinement of the program, as well as the addition of metered to the same ground station used for tethered-bal- several droplet spectrometers capable of producing data at loon data. high rates, led to the development of an integrated data- The NCAR (National Center for Atmospheric Research) acquisition system with extensive real-time analysis capabili- PAM (Portable Automated Mesonet) system was made avail- ties. Figure 3 gives an overview of the layout of the instru- able for the duration of FOG-82 to help address objective 3. mentation and measurement system with signal lines and Our mesonetwork of 25 surface weather stations continu- sampling intervals indicated. ously recorded temperature, humidity, and pressure at the two-meter level, wind speed and direction at a four-meter height and rainfall within a 12-km radius of the airport base a. Instrumentation and measurements site. Station spacings were between 2 and 7 km. 1) Surface and boundary layer Air temperature and humidity were measured at logarithmi- 2) Fog microphysics cally spaced intervals (0.1-16 m) with in-house-designed Fog-microphysics data consist of measurements of fog and psychrometers utilizing transistor thermometers installed in haze droplet-size distributions, fog LWC, and atmospheric concentric stainless-steel aspirated shields. This arrangement optical extinction. Size-spectra measurements were made minimizes radiation errors under nocturnal conditions. Sim- with a Particle Measuring System (PMS) FSSP-100 droplet ilar temperature sensors were placed at logarithmically spectrometer. This instrument is capable of operating in any spaced levels in the soil to a depth of 0.5 m. Wind measure- of four overlapping size ranges covering from 0.5 to 47 mi- ments, important in the determination of the turbulent struc- crons diameter. LWC and optical extinction can be derived ture, were made with sensitive Gill propeller anemometers at through integration of droplet mass and area spectra, respec- four logarithmically spaced levels between 1 and 16 m. Also tively. During FOG-82, two FSSP-lOOs were used at the sur- of importance in understanding the development of the sur- face and the 10-meter level. face layer is the profile of net longwave radiation. Ventilated Another system to determine fog LWC was designed Funk-type (Swissteco) radiometers were installed at the 1-, around a 10.6-jum wavelength C02 laser operating over a 4-, and 16-m levels to provide information on the longwave folded 30-m path. Transmission measurements were made fluxes and estimates of cooling due to longwave-radiative- with a ratiometric pyroelectric radiometer referenced to the flux divergence. This array of automated measurements was laser output. This approach reduced the influence of vari- augmented by manual observations of soil moisture content ations in the laser output due to inherent instability and as determined by conductivity measurements, as well as dew temperature sensitivity and made possible measurements deposition as indicated by the mass of water collected on flat over a wide range of water contents (0.01 to 1.0 g • m 3). These plates. These data provide a basic description of the meteoro- measurements were augmented by periodic high-volume fil- logical conditions in the surface layer and serve as inputs for ter samples which were used to measure water content the calculation of surface-layer heat, moisture, and radiation gravimetrically. budgets. Also included in the fog microphysics instrumentation Early in the fog program it was realized that data restricted were forward-scatter visibility meters (AEG-Telefunken to surface-layer variables were insufficient to fully under- MS04, Wright & Wright Fog-15, EG&G 207) which fur- stand the processes leading to fog formation and that mea- nished data on optical extinction by aerosol particles and fog surement capabilities had to be extended to higher levels. drops. In addition to these surface measurements, one visibil- During the last two years (1981, 1982) of the program this ity instrument was located at a height of 10 m to provide in- problem was addressed by the addition of a tethered-balloon formation on the origin of fog formation as well as the height sounding system (AIR, Inc. Tethersonde). This instrument dependence of extinction in fog and haze. consists of a balloon-borne instrument package which tele- meters data on temperature, humidity, pressure, and winds 3) Aerosols to a ground-based receiving station. The ground station pro- vides real-time data processing as well as data storage on mag- Small-particle concentrations were measured with a contin- netic tape for subsequent analysis. uous-flow condensation-nucleus counter (TSI Inc. TSI-3020) While providing an opportunity to measure profiles (and and their size distribution was measured with an electrical- therefore vertical fog structure) to an elevation of 400 m, the mobility analyzer (TSI Inc. TSI-3030) over the size range system was not without limitations. Balloon operations were from 0.01 to 1.0 jum diameter. Information on soluble par- prohibited when wind speeds exceeded 7 m • s"1, which was ticles was obtained from measurements of the cloud-conden-

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TABLE 1. FOG-82 contributing participants.

Individuals f~ield program Objectives Group I-Indirect involvement (Equipment)

NCAR Fred Brock (P) Mesoscale meteorology— Boulder, CO 80307 Steve Semmer (P) horizontal and time variations John Militzer (P) (PAM system) Colorado State University Steve Cox (I) Radiation studies—visible Fort Collins, CO 80523 Steve Ackerman (P) and infrared (infrared Chris Johnson-Pasqua (P) spectrometer; radiometers) ARVIN/CALSPAN Corp. Roland Pilie (P) Low-level water-budget study Environmental Systems Department Eugene Mack (P) (dewplates, HiVol (LWC) Buffalo, NY 14221 Bruce Wattle (P) samplers) James Hanley (P) U.S. Army Atmospheric Sciences Lab Mel Heaps (I) Loan of PMS optical particle White Sands Missile Range, NM 88002 Robert Olsen (I) counters; Vertical Fog Structure Naval Research Lab Hermann Gerber (P) Supersaturation study: I.R. Washington, D.C. 20375 scattering (saturation hygrometer: I.R. scatter probe) Desert Research Institute James Hudson (P) Haze and cloud-condensation- University of Nevada, Reno, NV 89506 nuclei study (haze chamber; CCN counter)

U.S. Department Commerce John DeLuisi (I) Loan of net radiometers NOAA-ERL, Boulder, CO 80302 Institute of Technology Michael Hoffman (I) Fog-water chemistry (water Environmental Engineering Science Jed Waldman (P) collector, wet chemistry Pasadena, CA 91125 Daniel Jacobs (P) analyzers Istituto FISBAT Sandro Fuzzi (P) Fog-water chemistry Consiglio Nazionale Delle Richerche (CNR) Bologna, Italy

ASRC-SUNY (Chemistry Section) Ray Castillo (P) Fog-water chemistry (water Albany, NY 12222 Volker Mohnen (I) collector, pH and ion constituent analysis) water chemistry, mesoscale analysis (pH, conductivity probes; ion analyzer) sation-nucleus supersaturation spectrum using an automated log-signal processing system was developed to provide the light-scattering cloud-condensation-nucleus counter (Lala, necessary scaling and filtering of signals prior to sampling. 1981). Measurement of the spectrum over the range from Following the analog-signal conditioning system were two 0.25 to 1.0 percent supersaturation was controlled by a dedi- analog to digital converters which, on command from the cated microcomputer system. Additional measurements of computer, sampled the analog signals and converted them to the total small-particle concentration were made manually digital form for further processing under the control of the with an expansion-type condensation-nucleus counter (Gard- computer. This organization provided an efficient means of ner Associates). converting analog signals at the required rates while main- taining the necessary accuracy and resolution. Other instruments used in this study, such as the PMS drop- b. Data-acquisition system let-spectrometer system, produced data reports in digital In order to organize the variety of sensor outputs from in- form. For digital inputs, the role of the computer system was struments used during FOG-82 into a structured digital data to accept the data and provide scaling and reformatting be- base and provide for instrument control and real-time analy- fore storing the reports. These instruments operated inde- sis, a data-acquisition system was developed using a PDP- pendently of the main system and generated data reports on 11/23 (Digital Equipment Corp.) microcomputer. The pri- their own schedule. To accommodate this mode of operation mary purpose of the system was the collection of data in the computer-system software was designed to acquire data digital form from all instruments with subsequent storage from a number of sources concurrently. onto magnetic media. Dedicated software and hardware In addition to the data-acquisition and control tasks, the were developed to satisfy these requirements and to provide computer system also incorporated real-time analysis capa- the user with real-time displays of data during the experiment. bilities. This feature was implemented through a set of user- The majority of the sensor outputs (48 signals) were analog callable analysis routines that produced reports on a selected voltages which required sampling and conversion to digital set of data. Reports included information in the form of form before processing by the computer. A specialized ana- scaled measurements as well as derived quantities. This in-

Unauthenticated | Downloaded 10/06/21 08:06 AM UTC Bulletin American Meteorological Society 829 formation was helpful to the user in monitoring the progress lected ranged, depending on the variations of LWC, from 0.5 of the experiment as well as in verifying instrument and com- to 12 ml per sample. A few 60-minute samples were collected puter-system operation. In addition to its vital role in mon- in the stages of fog formation or dissipation, but most of the itoring experimental conditions and in assuring data quality, samples were collected in 10 to 30 min. real-time-analysis software formed the basis of post-experi- The sample pH was measured directly in the field. A flat- ment data verification and analysis programs. end pH probe was used for the smallest samples. They were then refrigerated and the chemical analyses were performed within a few days. Anions (CP, F", Br", NO3, SOf, NHl) were determined by ion chromatography. The cations (Na+, 4. Contributing participants K+, Ca2+, Mg2+) and trace metals (Mn, Cu, Fe) were deter- mined by atomic absorption. Field programs of a broad scope require the efforts of many During the course of the sampling program, Hi-Vol aero- individuals with differing interests. FOG-82 has been partic- sol filter samples were collected. The suspended particulate ularly successful due to the ingenuity and hard work of all matter (TSP) was determined by weighing. The filters were involved. Moreover, the variety of participants brought to then leached with water at room temperature. The resulting the project a broad range of research interests which com- solution was filtered and the soluble fraction of TSP was de- plimented our own efforts and stimulated us all. A discussion termined. The filtered solution was then analyzed for the of each group's research objectives and equipment follows. same constituents as for fog-water samples. These work goals have been summarized from more lengthy preliminary reports. Table 1 lists those individuals from out- side the ASRC-SUNY Cloud Physics Section who contrib- c. Environmental Engineering Science—California Institute uted to the FOG-82 project through either participation in of Technology (D. J. Jacob and J. M. Waldman) the field or some important indirect role. FOG-82 provided a unique opportunity to study the chemi- cal composition of fog water with the help of extensive data a. National Center for Atmospheric Research {J. W. Militzer) on the major physical and meteorological parameters of The PAM-I system was designed and built by NCAR for the relevance to the droplet chemistry. sole purpose of supporting the scientific community in its ef- Fog water was collected at the 1.4-m level using a rotating- arm collector (RAC), which was modified from an original forts to collect and analyze surface-array weather data -1 (Brock and Govind, 1977). Since the first field project in design reported by Mack and Pilie (1975). Up to 2 ml • min of fog water was collected during dense fog and 0.1 to 1.0 1975, PAM has been utilized for a variety of investigations -1 including , , squall lines, sea breezes, re- ml • min during lighter fog. Based on calibration tests in a gional and, in this study, the formation of radia- cloud chamber using mechanically-generated droplets and a tion fog (Hess, 1985). Specifically, PAM-I was used to study laser optical particle counter (Jacob et al., 1982), the Caltech mesoscale influences and local flow regimes (see Objective 3). RAC was determined to have a lower size cutoff of approxi- mately 8 yum. While it is likely that the smaller droplets are b. Istituto FISBA T— C. N. R., Bologna, Italy (5. Fuzzi) and more concentrated, the bulk of the liquid water in fogs is con- ASRC-SUNY (R. A. Castillo) tributed by droplets larger than 8 jum. However, this size cut- off may lead to a slight underestimation of solute mass in fog. Studies on the chemistry of the atmospheric liquid phase For each sample, measurement of pH and separation of (cloud, fog, and ) have been given increased im- preserved aliquots were generally completed within 20 min- portance in recent years. The acidity of precipitation and the utes after collection. The samples were stored on ice until wet acid deposition is a major environmental issue. Wet dep- they could be brought to the laboratory for complete analy- osition occurs by fog as well. The amount of water deposited sis. In this case, more than two weeks passed between collec- by fog drip (interception by foliage) can be compared to tion and analysis. Major cations were determined by flame that of a light rainfall, so that the associated acid deposition atomic absorption spectroscopy and major anions by ion can be significant. Moreover, the fog water deposited by chromatography. Ammonium ion was determined by the wind-driven interception or settling of the largest drops on phenolhypochlorite method. A complete description of our surfaces can enhance the damaging effect of substances pre- analytical methods is given by Munger et al. (1983). Rain- viously deposited by dry deposition (Wisniewski, 1982). water collected in Albany was analyzed for major ionic com- Also, in some areas fog occurs more frequently than rain. ponents similarly to fog water. Few studies have been published on the chemistry of fog water, and generally only average chemical data have been d. Arvin/Calspan Advanced Technology Center (B. J. Wattle, presented. Studies on fog chemistry have only recently con- E. J. Mack, R. J. Pilie, J T. Hanley) sidered the connection between fog-droplet microphysics and chemical composition (Waldman et al., 1982; Fuzzi et Under Contract No. DAAG29-83-C-0022 with the Army al., 1983). During FOG-82, some collections of fog water Research Office, Calspan conducted a limited investigation were made during the month of October for the purpose of of the influence of vegetation on the low-level water budget chemical analysis. in fog. The objective of this field study was to explore the role Fog water was collected with a screen impactor. Sampling of vegetation as a sink for liquid water in fog through deposi- was started when the fog LWC, from the ASRC-SUNY mea- tion, precipitation, and impaction processes, and as a pos- surements, increased to 0.01 g • m-3. The amount of water col- sible source of water that (through re-evaporation) could be

Unauthenticated | Downloaded 10/06/21 08:06 AM UTC 830 Vol. 67, No. 7, July 1986 instrumental in prolonging a fog. This effort was a continua- proximately 1.5 m. Two Campbell Scientific Model CR-21 tion and expansion of past Calspan studies of dew deposition Data Loggers were used to acquire and store the radiation and fog-water collection on vegetation. data on a conventional cassette tape recorder which at a lat- Calspan instrumentation was set up in a slight depression ter date was played back through an interface for quantita- near equipment of other participants in FOG-82. Grass tive computer processing. height where our dew and fog-water deposition measure- The radiation sensors consisted of two (upwelling and ments were obtained, varied from approximately 15 cm in downwelling) pyranometers (Eppley Precision Spectral Pyra- mowed areas to approximately 75 cm in natural, tall grass. nometer) with WG7 outer hemispheres (0.3 to 2.8 /xm band- Calspan instrumentation comprised high-volume filter pass), two pyranometers with RG8 outer hemispheres (0.7 to samplers for LWC and "dew scales" in a variety of configu- 2.8 /jim bandpass), and two pyrgeometers (modified Eppley rations for surface water-deposition measurements. Precision Spectral Pyrgeometer) with silicon hemispheric Four versions of dew-deposition/fog-water-collection domes (4 to 50 jum bandpass). scales were used. One of these dew scales was a conventional During the experiment air was circulated over the domes dewplate consisting of a 0.05 m2 aluminum plate painted to inhibit the formation of dew. The dome temperature was with flat-black Rustoleum (emissivity = 0.92) to closely monitored by a single precision bead thermistor attached to simulate the radiative characteristics of moist, green vegeta- the inside of the silicon hemisphere. The sink temperature tion. This same device, with a freshly prepared surface, was was determined from a bead thermistor attached to the hous- used to obtain the dew-deposition measurements previously ing as close to the cold junction as possible. The pyrgeometers reported by Calspan (Mack and Pilie, 1973 and Pilie et al., were calibrated by heating the dome and then facing the pyr- 1975). Also, two model meadow grass plots were constructed geometer into a conical cavity blackbody of large thermal on 0.05 m2 plastic bases and mounted on separated dew-scale mass with a known temperature. arrangements to simulate, respectively, short (approximately 18 cm) and tall (approximately 61 cm) meadow grass. These f. Desert Research Institute—University of Nevada simulated meadows were fabricated by removing the grass (J. G. Hudson) from 0.05 m2 of natural meadow, drying it in fine sand to pre- serve the natural shape of each blade, reassembling it be- The relationship between fog condensation nuclei (FCN) tween strips of styrofoam to cover the 0.05 m2 dewplate and and fog droplets has been established by nearly simultaneous painting with the same black paint as the dewplate. Finally, a measurements of the input FCN spectrum to a fog and the modified dewplate with a styrofoam pad, identical to the fog-droplet spectrum (Hudson, 1980). When the number of base plates of the grass plots was used to provide a "control" fog droplets was matched with the FCN spectra an effective measurement for the grass plots and in order to quantify the supersaturation, Seif, was inferred. Although the investiga- amount of water collected by the base alone. tion represented an important development in fog physics, Calspan's observations began at 1800 EDT each evening, the relationship between FCN and droplets was based on cir- at which time the dew scales were zeroed and the LWC cumstantial evidence since there was no way to determine samplers were prepared. Data were obtained thereafter by that the droplets had actually nucleated on the particles with reading the dew scales at one-hour intervals and occasionally the lowest critical supersaturations, Sc. more frequently in rapidly changing conditions. Careful The significant aspect of the in-fog measurements made notes documenting , wind conditions, ground- during FOG-82 is that fog droplets were removed from some fog occurrence, and other meteorological events were also of the samples. The difference in spectral shape and number recorded to augment data provided by the ASRC-SUNY concentration between interstitial cloud condensation nuclei datanet. Results from analyses of these data are available in a (CCN) and the out-of-fog or total in-fog CCN measurements technical report: Wattle et al., 1984. was the subject of this work. CCN were measured with a con- tinuous-flow diffusion chamber (Hudson and Squires, 1976) and an isothermal haze chamber (Hudson, 1980). e. Department of —Colorado State University (S. A. Ackerman, C. Johnson-Pasqua, S. K. Cox) g. Naval Research Laboratory (H. Gerber) The formation, structure, and dissipation of fog is a complex interaction of radiative transfer, turbulence, and thermo- The NRL saturation hygrometer, which is capable of pre- dynamic processes, and is dependent on the geographic locale cisely measuring relative humidity in a range centered at 100 and the micro-, meso-, and synoptic-scale conditions. The percent, was brought to the FOG-82 project for several rea- Colorado State University (CSU) measurements included sons. Increased experience with this hygrometer in the field the upward and downward radiative fluxes of three spectral was required to better establish its operating characteristics regions (0.3-2.8 /JLm, 0.7-2.8 /xm and 4.0-50.0 /JLm). such as accuracy and stability, since to date only limited mea- The instrumentation package used during FOG-82 was a surements have been made in fog (Gerber, 1981, 1982). radiative boundary-layer system designed and fabricated by Another objective was to study the nature of the fine-scale the Department of Atmospheric Science at CSU. The system structure of humidity in radiation fog. A third objective was has demonstrated a high degree of reliability in such harsh to utilize the humidity data with the comprehensive set of environments as the Saudi Arabian desert. other microphysical and meteorological measurements to Upwelling and down welling solar radiation were measured get a better understanding of the physical processes respon- in the three different wavelength regions at a height of ap- sible for the formation of radiation fogs.

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The saturation hygrometer is described in detail by Gerber that infrared (10.6 jum) extinction is directly proportional to (1980). It consists essentially of a thermally thin mirror on LWC (from droplet diameters generally less than 28 jum). In- which a dew deposit is monitored optically. The exchange of itial results tend to confirm that infrared extinction methods water vapor with the dew droplets is a controlled process (ver- are capable of producing reasonable measurements with sus the uncontrolled process for the standard dew-point hy- high time resolution in the field environment. grometer) in that presized salt nuclei situated on the hydro- phobic mirror act as condensation sites for the dew. This prevents uncontrolled condensation on portions of the mir- 6. Future Plans ror devoid of nuclei and gives a predictable and reproducible response of the hygrometer to changes in ambient relative The next phase of effort, now underway, is aimed at quantify- humidity. ing physical mechanisms involved, computing fluxes, heat, The measurements were made 1.5 meters above the and water budgets, and refining the numerical model and ground. An HP-85 data-logging system digitized and re- forecasting techniques. A lengthy analysis period is envi- corded data at a rate of one set of measurements every three sioned to fully exploit the wealth of data obtained and to col- seconds or less. laborate with project participants and others on relevant studies of mutual interest. Interested researchers should con- tact the authors regarding data availability. 5. Preliminary Results Several enhancements to our fog-measurement program are currently undergoing development and testing. These A variety of fog (and haze) intensities of varying duration include were encountered during FOG-82. On 10 occasions (out of 1) Use of high-speed measurements from the FSSP drop- 27 experiments conducted) heavy radiation fog formed. The let spectrometer, sonic anemometers, a krypton hy- 1982 fog season was representative of the local fog climatol- grometer and a fast heat sensor to determine fluxes of ogy presented earlier, with 22 hours of measurements made heat, momentum, moisture, and fog water with a high during heavy-fog conditions. This section briefly summa- degree of time resolution. rizes some of the preliminary results emerging from FOG-82. 2) Incorporate a cloud-droplet spectrometer (PMS OAP- The life cycle of a radiation fog has been observed to en- 230X) to add large- (10-300 ^m diameter) droplet siz- compass as many as five distinct stages of evolution, sun- ing capabilities. down, conditioning, mature fog, sunrise, and dissipation 3) Develop and refine an isothermal haze chamber to pro- phase (Lala et al., 1982; Jiusto et al., 1983). Some evidence vide additional information on active nuclei in the suggests that turbulence and associated vertical mixing can lower end of the CCN supersaturation spectrum (less prevent, promote, or intensify radiation fog depending on than 0.25 percent). the fog-evolution stage. Modification effects of local heat 4) Work with available lidar systems for determining fog and moisture advection may also play an important role in levels and motion. the onset and intensity of the fog. 5) Institute aerial and time-lapse photography capabili- A question of considerable interest in the study of fog proc- ties to help define local influences on fog development. esses is the vertical distribution of fog microphysical parame- ters such as LWC, visual range, and drop-size distribution. In addition, the feasibility of obtaining and siting on In the "conditioning stage" when patches of fog occur they acoustic sounder system for in-depth study of turbulent are mainly surface phenomena and usually appear only at structure is being addressed. and below the 1.5-m level. The majority of cases studied thus far have shown a trend of higher LWC aloft (10 m) early in Acknowledgments. The ASRC-SUNY FOG-82 project was spon- the fog, with a reversal of this trend during dissipation. It was sored by the National Science Foundation (NSF Grant ATM8022208) observed that some fogs seem to form aloft initially and mix and the United States Army Research Office (ARO Contract downward. Two explanations of fog occurring aloft seem DAAG-29-81-K-0019). We are grateful to the following individuals likely: first that the fog actually formed in an elevated layer who made invaluable contributions: Mark Kornfein, John Sicker, Kenneth Webster, Dolores Leonard, Mark Solomon, James Theimer, and second, that the fog formed elsewhere and, due to the and Andrew Landor. local flow regime, advected over the field site. Nearby water A field program of the type described requires the cooperation of bodies and low-lying grassy fields are apparently often a pre- many people. We are thankful to a number of airport officials, in ferred site of fog formation. particular to Mr. John Masko, Albany County Airport manager; Mr. Edward Deitz, FAA Flight Service Section chief; Mr. Eugene The drop sizes in our inland radiation fogs can be substan- Bryant and Mr. Donald Schultz, FAA Air Traffic Control chiefs. We tially larger than previously believed. They occasionally ap- also appreciate the efforts of Mr. William Wilson and Mr. Bud Van- proach sizes thought to be more commonly encountered in Dyke of the Latham Town Water district. coastal advection fogs. Drops over 35 microns in diameter are not uncommon, and in one case drops were noted by observers. Also indicated is that LWC can approach or References exceed 0.5 g • m~3 which is much higher than the oft-quoted 3 value of 0.1 g-m" (Jiusto, 1974). Brock, F. V., and P. K. Govind, 1977: Portable automated mesonet As an alternative to the spectral-integration method for in operation. J. Appl. Meteor., 16, 299-310. determining fog LWC, an infrared laser transmissometer Chylek, P., 1978: Extinction and liquid water content of fogs and was designed to implement Chylek's (1978) theoretical result . J. Atmos. Sci., 35, 296-300.

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Fuzzi, S., G. Orsi, and M. Mariotti, 1983: Radiation fog liquid water of radiation fog formation on four consecutive nights. Proc. of acidity at a field station in the Po Valley. J. Aerosol Sci., 14, Conf. on Cloud Physics, AMS, 15-18 November, Chicago, IL, 135-318. 9-11. Gerber, H., 1980: A saturation hygrometer for measurement of rela- Mack, E. J. and R. J. Pilie, 1973: The Microstructure of Radiation Fog tive humidity between 95 and 105%. J. Atmos. Sci., 19,1196-1208. at Travis Air Force Base. Calspan Report No. CJ-5076-M-7,73 pp. , 1981: Microstructure of a radiation fog. J. Atmos. Sci., 38, (available from Calspan Corporation, Buffalo, NY 14225.) 454-458. , and , 1975: Fog Water Collector, U.S. Patent No. 3889532. , 1982: Nature of fog nuclei from measurements of relative hu- Meyer, M. B. and J. E. Jiusto, 1982: Radiation-fog intensities asso- midity. Idojaras, 86, 175-178. ciated with surface synoptic patterns at Albany, New York. Proc. Hess, W. N., 1985: NCAR and the Universities. Bull. Amer. Meteor. of 9 th Conf. on and Analysis, AMS, 28 June-1 Soc., 66, 515-529. July 1982, Seattle, WA, 469-473. Hudson, J. G., 1980: Relationship between fog condensation nuclei Munger, J. W., D. J. Jacob, J. M. Waldman and M. R. Hoffman, and fog microstructure. J. Atmos. Sci., 37, 1854-1867. 1983: Fog water chemistry in an urban atmosphere. J. Geophys. , and P. Squires, 1976: An improved continuous flow diffusion Res., 88, 5109-5121. cloud chamber. J. Appl. Meteor., 15, 776-782. Pilie, R. J., E. J. Mack, W. C. Kocmond, C. W. Rogers, and W. J. Jacob, D. J., R. C. Flagan, J. M. Waldman, and M. R. Hoffman, Eadie, 1975: The Life Cycle of Valley Fog. Part I: Micrometeoro- 1982: Design and calibration of rotating arm collectors for am- logical Characteristics. J. Appl. Meteor., 14, 347-363. bient fog sampling. Proc. 4th International Conference on Precipi- Pinnick, R. G., S. G. Jennings, P. Chylek, and H. J. Auvermann, tation Scavenging, Dry Deposition and Resuspension, 29 Nov.-3 1979: Verification of a linear relation between IR extinction, ab- Dec., Santa Monica, CA, Elsevier, Netherlands Publ., 125-136. sorption and liquid water content of fogs. J. Atmos. Sci., 36, Jiusto, J. E., 1974: Remarks on visibility in fog. J. Appl. Meteor., 13, 1577-1586. 608-610. Waldman, J. M., J. W. Munger, D. J. Jacob, R. C. Flanagan, J. J. , and G. G. Lala, 1983: The Fog project—1982. Proc. of 9th Morgan, and M. R. Hoffman, 1982: Chemical composition of acid Conf. on Aerospace and Aeronautical Meteorology, AMS, 6-9 June fog. Science, 218, 677-680. 1983, Omaha, NE, 95-98. Wattle, B. J., E. J. Mack, R. J. Pilie, and J. T. Hanley, 1984: The Role Lala, G. G., 1981: An automatic light scattering CCN counter. of Vegetation in the Low-Level Water Budget in Fog. Calspan Re- Rech. Atmos., 15, 259-262. port 7096-M-l, 33 pp. (available from Calspan Corp., Buffalo, NY , E. Mandel, and J. E. Jiusto, 1975: A numerical evaluation of 14225.) radiation fog variables. J. Atmos. Sci., 32, 720-728. Wisniewski, J., 1982: The potential acidity associated with dews, , J. E. Jiusto, M. B. Meyer, and M. Kornfein, 1982: Mechanisms frosts and fogs. Water, Air Soil Pollut., 17, 361-377. • announcements1

Video Cassette Recording of Droughts NC 28801. Those who are interested in obtaining a copy for Available loan should contact their librarian, who should then request Monthly Palmer Hydrological Drought Indices (PHDI) across the tape from the NCDC library. The VCR can be copied, if the contiguous United States have been depicted and described desired. Currently, three copies of 1/2" VHS tape and two during the years 1895 through 1983 on a video cassette re- copies of 3/4" VHS tape are available for loan. cording (VCR). The PHDI is delineated by seven intensities varying from dark brown for extreme drought to deep blue for extreme wetness. The spatial resolution is substate scale (cli- Explosive-Cyclogenesis Program Planned mate divisions). The PHDI and the color scheme are described A research program to study explosive cyclogenesis of Atlantic by the narration as well as the movement, intensity, and du- is being planned by the Office of Naval Research ration of the major droughts and wet spells of the 20th century. and a team of universities and other meteorological and ocean- The VCR graphically illustrates the varying time and space ographic research organizations. The goals of the Experiment scales of drought in the United States from the pulsating na- on Rapidly Intensifying in the Atlantic (ERICA) are ture of the four major drought episodes of the 1930s to the to develop an understanding of the fundamental physical proc- very wet period of the early and mid 1970s. esses in the atmosphere that lead to explosive cyclogenesis at The VCR is recommended to those with an interest in the sea; identify measurable precursors that can be used for accu- scope, magnitude, and migration of drought in the United States rate operational dynamical meteorological forecast-model pre- during the last 89 years. It is well suited for classroom pres- dictions; and determine the minimum set of these observables entation with a length of 22 minutes. necessary for accurate forecasts of intense cyclogenesis at sea. The VCR is available on interlibrary loan from the National Multiyear program efforts, including numerical modeling re- Climatic Data Center (NCDC), Federal Building, Asheville, search, will benefit from the related (Genesis of Atlantic Lows Experiment) and CASP (Canadian Atlantic Storms Pro- gram) field-measurement episodes recently completed in Jan- 1 Notice of registration deadlines for meetings, workshops, uary-March 1986. The field-intensive measurement phase for and seminars, deadlines for submittal of abstracts or papers to ERICA is scheduled in the North Atlantic (centered approxi- be presented at meetings, and deadlines for grants, proposals, awards, nominations, and fellowships must be received at least three months before deadline dates.—News Ed. (continued on page 855)

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