FACILITIES FOR NO. 4 SUMMER 1967

^v!SA I IONAI. CENTER /OR. ATM OSPH ERIC . * £ 5 E A R

J*-??'''- ' . ’ * " . 7 ' FACILITIES FOR atmospheric research No. 4 Summer 1967

FACILITIES FOR ATMOSPHERIC RESEARCH is published for the NCAR Facilities Laboratory, Daniel F. Rex, Director.

Assistant to theD irector is Charles A. Palmer, Jr. Divisions o f the Facilities Laboratory and their heads are:

NCAR RESEARCH AVIATION FACILITY-- John W. Hinkelman, Jr. DESIGN AND PROTOTYPE DEVELOPMENT FACILITY — Stig A. Rossby SCIENTIFIC BALLOON FACILITY—Alvin L. Morris PROGRAM ON APPLICATIONS ANALYSIS Thomas W. Bilhorn COMPUTING FACILITY--John M. Gary GLOBAL ATMOSPHERIC MEASUREMENTS PROGRAM — Vincent E. Lally FIELD OBSERVING FACILITY— Williams. Lanterman. Jr.

NCAR is operated by the non-profit Univer­ sity Corporation for Atmospheric Research (UCAR), and is sponsored by the National Ballooning Science Foundation. The members of UCAR are 23 U.S. universities with graduate pro­ 5 A Simple Balloon Ranging System grams in the atmospheric sciences or re­ lated fields. 9 FA A Rule Changes on Balloon Flight 10 Space Simulation Chambers Editor: Paul M. Sears Reporters: Halka Chronic. Ronald Cox 22 Stonehenge Launch Technique Art: William E. Hemphill Production:Bob L. Wyatt Aviation

National Center for Atmospheric Research 12 Techniques for Study of Mountain Waves Box 1470 Boulder, Colorado 80302 26 NCAR Ice Nucleus Counter

Field Observation Published quarterly Second class postage paid at Boulder, Colorado 2 Instrumenting the Sea Breeze Project 6 Troposcatter Study of the Atm osphere UCAR Member Universities University of Alaska University of Arizona Comprehensive Programs University of California 17 Hail Suppression in the USSR University of Chicago Colorado State University 24 Lessons from the Line Islands University of Colorado Cornell University University of Denver Florida State University University of Hawaii The Johns Hopkins University Massachusetts Institute of Technology University of Michigan University of Minnesota New York University University of Oklahoma Pennsylvania State University Saint Louis University Texas A and M University University of Texas Cover : Texas Coastline and Gulf of Mexico, looking north from Gemini V. University of Utah An article beginning on page 2 describes a project to study sea University of Washington University of Wisconsin breeze along the Texas Gulf Coast. Instrumenting the Sea Breeze Project

During the last three years Uni­ versity of Texas atmospheric scien­ tists have been studying the detailed mechanisms which drive the sea breezes along the Texas Gulf coast. The great variety of changes in space and time which characterizes these breezes has required careful system­ atizing of field instrumentation tech­ niques. Mere numbers of instruments are not sufficient; only when properly scaled to the events to be measured can the instruments reveal what occurs inside the sea breeze and on its fringes. The originators of the Sea Breeze Project and its chief investigators are Amos Eddy and K. H. Jehn, pro­ fessors of meteorology at the Uni­ versity of Texas in Austin. Other members of the University’s Atmos­ pheric Science Group have assisted the research or conducted separate experiments related to it. The N a­ tional Science Foundation (NSF) is supporting the overall project. In the summer of 1965 a pilot study was carried out to determine how clearly the sea-breeze phenom­ enon can be distinguished from the larger circulatory features super­ The study area prior to relocating some stations for summer 1967 experiments. imposed upon it. Using only basic meteorological equipment — thermo­ graph, hygrograph, sling psychrom-Statistical Model eral theoretical models now exist, eter, anemometer and vane, and pilot the most plausible being a two- balloons —the study found clear evi­ Typically, and rather consistently, dimensional model proposed in 1961 dence that the Gulf breeze extends distracting stratus layers and un­ by Mariano Estoque at the Univer­ 15 to 25 mi inland, where tempera­ balanced land-sea temperatures are sity of Hawaii. The Sea Breeze Proj­ tures and humidity contrast sharply absent during June, giving the best ect will seek to verify Estoque’s with readings farther inland, and chances for all the circulatory phases model experimentally, and to extend fluctuate with the wind in the lowest of the sea breeze to develop. Data it to three dimensions. The expanded layers. The promising results of the from the concentrated periods of model will consider the entire range 1965 pilot study have led to an ex­ observation each June, together with of heat and energy transfers to and tensive program, which started in data from other year-round observa­ from the sea breeze, and energy con­ 1966 and is scheduled to last until at tions, will ultimately supply sufficientversions within it, thus deriving a least 1969, including periods of in­ detail to represent the sea breeze in balanced energy budget for the whole tensive activity during each June. a statistical-dynamical model. Sev­ system.

2 Observational Network

Along a stretch of the Texas Gulf coastline between Port Arthur and Galveston, more than a dozen sta­ tions have been established since the project began; each is assigned specific observational duties. Some stations are several miles inland, others are offshore, aboard tideland oil rigs. Key stations are directly on the beach. During intensive observa­ tion periods research aircraft and radiosondes extend the data-gather- ing network vertically, allowing the sampling of a volume of air about Texas Gulf Coast as seen from Gemini V. 120 by 40 mi, by 20,000 ft deep. The study area has a straight, even The 1967 Program The Atmospheric Science Group coastline, no islands or reefs off­ itself supplied most of the surface shore, and exceedingly fiat terrain Toward the end of May of this meteorological instrumentation, in­ for several miles inland. This simple year, the Field Observing Facility cluding various wind detectors, psy- topography makes it easier to char­ began transporting to the Texas chrometers, microbarographs, and acterize the basic parameters of the coast and installing at the field sites raingages, and supportive electrical study. During peak periods of experi­two power generators, fifteen GMQ- equipment and vehicles. Radio equip­ mentation this summer and last, 12 wind systems, eight MRI me­ ment at each station and in four Shell Oil Company provided boat chanical weather stations, four 400- vehicles kept field workers informed transportation to the offshore plat­ MHz radiosonde receivers, and two of each other’s progress and needs. forms, and the U.S. Coast Guard 22-channel data-acquisition system The U.S. Weather Bureau lent nu­ assured standby evacuation facilities commutators. NCAR staff members merous sensing instruments, and in the event of severe storm warn­ remained at the sites for the peak issued daily weather reports to the ings. Important assistance was also period of data gathering to keep all project when requested. The project provided by the Standard Oil Com­ systems running smoothly. also maintained its own general pany of Texas. Two NCAR Queen Air 80 re­ weather forecasting facilities in the In June 1966 and again in 1967 search aircraft sampled a three- field. NCAR provided major assistance to dimensional array of temperature, the project by supplying ground in­pressure, humidity and wind vari­ strumentation and other field sup­ ables during one week in mid-June. Scale Analysis port equipment, two instrumented During a peak 30-hr period, at least aircraft for the mid-June weeks of one aircraft was aloft at all times. Unless the equipment of such a round-the-clock data taking, and Doppler radar measurements during project is properly situated, many computer facilities for data conver­ the flights showed the extent to features of the sea breeze, or their sion. NCAR Facilities Laboratory which onshore and offshore winds true dimensions, might easily elude support had been requested by the followed the deflecting effects of the the sensors. The project has there­ Atmospheric Science Group in the earth’s rotation. The Airborne Re­ fore dealt systematically with the fall of 1965 as a part of its N SF search Instrumentation System fact that the various physically re­ research proposal. Staff members of (ARIS) on board the Queen Airs re­ lated phenomena of the breeze occur, NCAR’s Field Observing Facility corded sensor data on analog mag­ and undergo change, on differing and the Research Aviation Facility netic tapes. These records, along scales of space and time. The answer consulted several times with the with all data from ground sensors to what constitutes statistically valid project scientists before operations which could be recorded on magnetic data must come from the system began in 1966 and 1967, to outline tape, are presently being converted itself. the specific needs which NCAR to digital form by NCAR’s Control The proper use of each instrument could fulfill. Data 6600 computer. requires a determination of just what

3 density and frequency of measure­ parameters in the critical beach area. pling of the microscale. A slightly ments will suffice to represent accur­ The importance of the scaling tech­ shorter tower was erected in the surf ately the parameter in question, nique is evident in measurements of zone to measure corresponding through scale analysis —a method­ energy fluxes. Heat transfer in the boundary layer conditions over the ology derived from statistical prin­ circulating sea breeze, for example, water. An instrument package con­ ciples. Instrument pairs, separated must be measured on different scales taining a Gill bi-vane anemometer by selected distances, record their at the air-water interface and aloft. and wet and dry thermocouples was data on analog tape. After conver­ Failure to regard the differing scales attached to the larger tower at two sion into digital form the power would seriously disrupt calculations levels; it recorded wind, tempera­ spectra of these signals are analyzed of the energy budget. ture, and wet-bulb readings onto five for statistical information on the ex­ simultaneous channels of tape. Ten­ tent to which each instrument of the tative results from the sensors lo­ pair “sensed” the parameter. A Energy Exchanges cated on the towers indicate that in series of relocations of the instru­ daytime, land influences outweigh ment pairs in subsequent field experi­ Two general magnitudes of events those of the Gulf up to about 20 or ments finally gives the optimum delineate the sea breeze and make 30 ft above ground, while at the placements, spacings, and observa­ corresponding demands on instru­ higher levels measured by the tower, tional frequencies necessary to mentation: a microscale in which sea-breeze effects become dominant. represent the parameter. energy is taken from its sources — Such determinations are vital to principally water and land surfaces — In a satisfactory sea-breeze model, the whole experiment, for once they and a mesoscale in which energy is total input and output of energies are solidly established and the data dynamically converted into the var­ must agree, and a major aim of the stations appropriately relocated, the ious components within the sea observing program will be to secure data gathered pertain directly to the breeze itself. Measurements of data for the overall energy budget of statistical requirements of the sea- energy exchange at the microscale the sea-breeze phenomenon. Air­ breeze model. For this reason, the level required locating sensors at borne equipment was used this sum­ emphasis this past June was upon various levels above the water and mer to make indirect measurements scaling instruments and their loca­ land surfaces, up to about 100 ft. In related to the latent heat of the sys­ tions in the field to obtain average this summer’s field phase a vertical tem. Latent heat taken up as water space and time distributions for each profile device was shuttled up and vapor must correlate with total mass parameter. Instruments were grouped down a 105-ft tower standing about lost from the system as rain. Meas­ both parallel and transversely to the 200 ft back from the beach, to pro­ urements of cloud moisture, made shore, to seek a good resolution of vide detailed time and space sam­ with liquid water meters and drop-

D ay time portion o f the sea breeze cycle with sche­ matic representation o f the energy budget.

4 size-distribution samplers, provided standard devices. Scaling techniques cision; the data stations will be information about the total latent often involved using different makes moved about to bring each sensor heat involved in the updraft portion of instruments in the pair placements, to its best location. In proportion of the sea-breeze cycle. The instru­ providing a check of their sensitivi­ to the growing acuteness of the net­ ments, mounted in the NCAR air­ ties. Microscale heat flux between work, data gathering for use in de­ craft, were operated by a University land or water surfaces and the atmos­ signing the statistical sea-breeze of Texas Atmospheric Science phere required instruments capable model will increase. Scale analysis Group member. of measuring velocity and tempera­ of the mesoscale is already well ture on the same sensor, a feature along; and details of the microscale only recently available in some com­ will be significantly clearer once this Other Equipment mercial instruments. A Beckman & summer’s field returns are in. As the Whitley heat meter located just be­ sea-breeze model begins to take Commercially available equipment low the soil surface measured heat shape, data will be generalized to performed most of the basic meas­ flux to and from the earth; nearby, equations of heat, energy and urements for the project, once the 1 m above the ground surface, a motion. The mesoscale will assume needed instrument capabilities had Middleton net radiometer measured quantitative definition, and data from been determined by scale analysis. the net radiant energy exchange. the microscale will dictate the bound­ Surface conditions of pressure, tem­ ary limits of its equations. The de­ perature, humidity and wind, and tailed mechanisms of the sea breeze, most aspects of mesoscale heat Conclusion whose most dramatic features man transfer, water vapor formation, and has always known, should ultimately kinetic energy relationships in the Gradually each portion of the in­ be shown in their relation to the boundary layer, were recorded on strument network should gain pre­ breeze phenomenon as a whole.

A Simple Balloon Ranging System

A simple electronic balloon rang­ modulate a 250-MHz FM/FM te­ pointing accuracy is obtained by ing system has been developed by lemetry transmitter. At the ground rotating the antenna system to null Raven Industries, Inc., of Sioux station the audio signal is again de­ the pointing error. A selsyn system Falls, South Dakota, which adds tected from the telemetry signal and provides azimuth readout on a me­ only a minimum of balloon-borne a phase comparison is made between chanical counter. electronic equipment to that normally the transmitted and the received During a recent test at the NCAR used for scientific balloon flight signal. A digital phase meter is used Flight Station at Palestine, Texas, support. for phase measurements where 1° of range and azimuth from the Raven The system utilizes the free space phase shift represents 1 n mi of range. system were compared with data propagation delay characteristics The azimuth of the balloon from from an M-33 radar set. The max­ of a two-way radio signal from the the ground station is measured by imum azimuthal error was 1.9° at 50 ground station to the balloon. An using the directional characteristics n mi and the largest range error was audio signal with a wavelength of of two antennas. The antenna system 1 n mi. Raven engineers believe 360 n mi modulates a 150-MHz consists of two high-gain vertically accuracy of the system can be im­ transmitter which is normally used polarized yagi antennas, horizontally proved by mechanical and electrical for communicating with recovery skewed so that the main-pattern refinements of the design and in­ vehicles and tracking aircraft, and lobes intersect at the half-power stallation. for transmitting command signals to points. The antennas are alternately the balloon system. This audio signal switched to the telemetry receiver, The ranging system is being used is extracted from the command re­ and a visual azimuth error is indicated this summer forthe ON R flight series ceiver on the balloon and used to on an oscilloscope. High-resolution at Ft. Churchill, Manitoba, Canada.

5 Troposcatter Study of the Atmosphere

Douglas H. Sargeant, University of Wisconsin

About two decades ago radio CEDAR RAPIDS, experimenters were surprised to dis­ IOWA cover that ultra-high-frequency radio waves could be consistently propa­ gated well beyond the horizon by using high-powered, sensitive equip­ ment developed during the wartime radar effort. These microwaves are not reflected by the ionosphere, and do not travel well along the ground. They would thus be “shadowed” by the earth and lost into space, were it not for inhomogeneities of the tropo­ sphere which scatter them forward in a curved path around the earth. This phenomenon, called trans­ horizon tropospheric forward scatter propagation, or “troposcatter,” makes possible highly reliable com­ munications systems such as tele­ phone links between Florida and Puerto Rico. Many troposcatter sys­ tems are also in use in Vietnam. Despite numerous practical appli­ cations and a rich history of experi­ mental and theoretical research, a pheric structure, motion, and fluxes. scatterers which contributes to the certain mystery still surrounds many The primary structural feature which received signal produces a doppler physical details of troposcatter prop­produces troposcatter is refractive spectrum of frequencies which de­ agation. Meteorologists and elec­ index inhomogeneity, caused by pro­ pends on the locations, speeds, and trical engineers at the University of nounced temperature and humidity strengths of the various scatterers. Wisconsin and the Collins Radio gradients in the atmosphere. Al­ Time variations of signal* charac­ Company are collaborating on a re­ though scales of a few meters or less teristics result from changes in re­ search program which provides a define the principal “scatterers,” fractive index structures, brought novel combination of radio and regions of large gradient are often about by transport of mass, heat, and meteorological measurements de­ organized into extended horizontal moisture. In the absence of appreci­ signed to clarify the troposcatter layers. able horizontal advection, boundary mechanism and to lay a foundation The troposphere normally appearsfluxes at the ground constitute the for remote atmospheric probing “rough” or “blobby” to the radio principal sources for these changes. techniques. waves, so that motion of the scatter­ These general arguments do not Troposcatter signal characteris­ ing regions with the wind creates explain exactly how troposcatter tics depend upon, and can potentially doppler shifts in frequency of the signals depend on important meteor­ provide information about atmos­ radio waves. The entire array of ological variables. The problem in troposcatter probing is to isolate the In practice, a 960-MHz signal is Some 85 sets of vertical profiles of multitude of possible effects, and to transmitted from CCRF to UW, the lowest few kilometers have been establish useful relationships be­ where one-way amplitude and phase reduced using the NCAR Control tween signal characteristics and me­ measurements are made by using a Data 6600 computing system, and teorological variables. After hypo­ second stable clock. A special phase- are presently being analyzed in de­ thetical propagation mechanisms lock transponder is used which tail. Measurements of pressure, tem­ have been formulated, the next step allows the received signal to be re­ perature, dewpoint, refractivity, is experiments providing simultan­ transmitted at 810 MHz back to speed, and drift angle were included. eous observations of the pertinent CCRF without loss of phase co­ Micrometeorological measure­ radio and meteorological variables. herence. Continuous recordings are ments sufficient to determine the sur­ The design, execution, and interpre­ made on magnetic tape and on strip face heat budget were made at the tation of such experiments have been charts. ground at both radio terminals and the objectives of the program des­ near mid-path. Sensors and automat­ cribed here. Meteorological Measurement ic digital data-logging systems espe­ System cially designed for this purpose were Radio Measurement System employed. Analysis of these data It is impossible to define in detail yields estimates of vertical fluxes of The experiments make use of a the state of the entire portion of sensible heat and moisture. propagation link extending about atmosphere traversed by the radio 230 km between the University of waves, so it was necessary to select Wisconsin (UW) terminal near Madi­ meteorological measurements which Results son, Wisconsin, and the Collins Com­ appeared likely on physical grounds munications Research Facility to be related to the signal character­ (CCRF) near Cedar Rapids, Iowa. istics. As we noted, structure, mo­ Some of the most interesting re­ Figure 1 illustrates the pertinent tion, and boundary fluxes should all sults involve the previously unavail­ geometry of some experiments des­ be important. able phase data. To facilitate inter­ cribed below. Large (30-ft) dish Only the gross horizontal and ver­ pretation, it is helpful to visualize antennas define 2.5° beams which tical structure can be determined the following geometry. To a first intersect to form a so-called “com­ from normal Weather Bureau data. approximation, all scatterers which mon volume.” It is usually assumed Radiosondes, some modified to carry give equal total ray-path length (or that the principal scattering phenom­ radiometers, have been flown at mid­ phase) lie on an ellipse which has the ena which redirect radio energy from path at 4- to 6-hr intervals to further radio terminals as foci. Thus to each one beam into the other occur within define the vertical structure. Pibals path length or phase there corre­ the common volume. have been flown at 30-min to 1-hr in­ sponds a long, thin, ellipsoidal sur­ This radio measurement system tervals to secure wind data. Since face of revolution which has the determines the phase of the radio relatively fine-structured vertical fea­ straight (chordal) line between the signal, in addition to its amplitude, tures are important to the radio radio terminals as an axis. Any indi­ which has been extensively studied waves, and since a large horizontal vidual scatterer moving in the atmos­ by others. Because phase is directly extent is involved, instrumented air­ phere creates a doppler shift in the related to path length and doppler craft have also been used. In early radio signal proportional to the rate shifts, interpretation is greatly facili­ experiments a University of Wis­ at which it crosses surfaces of equal tated. The phase system resolves consin Cessna 310 was used, and in increment in phase or path length. 0.01 cycles of the propagated wave later experiments the NCAR Re­ Scatterers moving parallel to the whose frequehcy is near 1 GHz (109 search Aviation Facility provided propagation link axis are essentially cps). This resolution is equivalent to a Queen Air A80. These latter flights, moving along a constant-phase sur­ a relative time measurement of 1 which included direct radio refrac- face, and create negligible doppler part in 1011 between the two termi­ tivity measurements using a Thomp- shift. The motions which create nals. Although such measurements son-Vetter cavity refractometer doppler shifts are conveniently vis­ are at the limit of independent clock owned by ESSA of Boulder, con­ ualized on a transverse cross section stabilities, they can be accomplished stituted one of the early “shake- of the ellipsoids, such as that shown by sending a phase-coherent signal down” utilizations of the ARIS data- in Fig. 2. The concentric circles are round-trip, so that only one inde­ acquisition system developed by drawn for equal increments in path pendent clock is involved. the NCAR Aviation Facility. length in a mid-path plane.

7 GREAT CIRCLE DEPARTURE (km)

F i g . 2

A straightforward calculation shows that a scatterer at position (y, z) relative to the chordal axis (Fig. 2) and moving with velocity com­ ponents (v, w) would create a dop- 2 pier shift fd given by fd = - — (vy + AQ wz) where X is the radio wavelength and 2d is the station separation. Since the horizontal cross-path wind- speed, v, normally greatly exceeds the vertical motion, the second term can usually be neglected. Thus the doppler shift is proportional to the cross-path windspeed and to the dis­ tance of a scatterer from the great- 1 0 5 6 CST Sa = 0.0° circle plane. All scatterers upwind of the great circle are shortening the path length and create a higher frequency. 17.12 IT Scatterers downwind of the great circle create a lower frequency. When the antennas are pointed syn­ chronously in azimuth away from the great circle, as shown in Fig. 1, one of these two sets of scatterers predominates. Figure 3 gives a sample of strip-chart record show­ ing the phase at two antenna azi­ muths. The doppler shift is equal to the slope of the trace, which is seen piece-wise because the phase- measuring device is reset every time 1316 CST 0 a = -l. O ° its selected range is exceeded. F i g . .? f

In several experiments the anten­ nas were pointed successively at various azimuth angles from the

3.0 l 1 l l | r" i i -t iiii iiii ]l 11 1 great circle. A typical result for 5- min average doppler shifts is shown ® in Fig. 4. The slope of the curve is 2.0 related to the scatterer velocity, and SYNCHRONOUS BEAM OFFSET SEPTEMBER 28, 1966 the shape of the curve depends upon the relative strengths of the various 1.0 ® scatterers within the antenna beams. >- « <_> Z Additional information is available UJ 0.0 59 « from the spectrum of doppler shifts; 3 • ® o ® ® only the average doppler shift is plotted here. 1.0 ® Such measurements appear to justify a hope that important infor­ a. ® O 2.0 mation regarding tropospheric struc­ ture and motions can be extracted from troposcatter signals. The equa­ 3.0 tion suggests that by using very ® narrow antenna beams (so that y can be held effectively to zero), vertical .1 . 1 iiii iiii iiii iiii i 2.0 S. I.0S. 0.0 1.0 N. 2.ON. motions can be observed directly by this sensitive technique. These and ANTENNA POINTING ANGLE (DEG ) FROM GREAT CIRCLE Fig. 4 other possibilities suggested by the continuing analysis of the wealth of data now available are being pur­ sued with much anticipation.

Federal Airways Authority Rule Changes on Flight of Balloons

The Federal Airways Authority required. Also, at least two methods, present an echo to surface radar recently made significant changes in systems, devices, or combinations operating in the 200 to 2700 MHz regulations for flights of unmanned thereof that function independently frequency range. This requirement free balloons. The new regulations, of each other must be available to is also completely new. effective 28 April 1967, require that terminate the flight of the balloon each unmanned free balloon which is envelope. No requirement for ter­ The changes were made to en­ subject to the regulations be equip­ minating the flight of the envelope hance safety in the air by minimizing ped with at least two payload cut- was contained in previous regula­ the chances of a balloon becoming a down systems or devices that operate tions. Finally, the balloon envelope derelict and by ensuring that a bal­ independently of each other. Pre­ must be equipped with a radar- loon can be tracked even after its viously only one such device was reflective device or material that will electrical power is depleted.

9 ORGANIZATION LOCATION SIZE

AEROJET-GENERAL Azusa, Calif. 8’D x 151L Space Simulation Laboratory 8.5’ D x 8.2’L

AVCO CORPORATION Wilmington, Mass. 8’D x 10'L Research and Advance 5’D Sphere Development

BALL BROTHERS Boulder, Colo. 10'D x 15'L

! BEECH AIRCRAFT, INC. Boulder, Colo. 6'D x 9’ L 4'D x 4'L

B E LL AEROSYSTEMS COMPANY Buffalo, N. Y. 5'D x 8'L

B E LL TELEPHONE LABORATORIES Whippany, N .J. 4.5’D x 7’L 7.5’D x 12*L

BEMCO, INC. Pacoima, Calif. 7’L x 5’W x 7’H

BENDIX CORPORATION Ann Arbor, Mich. 20'D x 27’L S p ace Systems Division 4’D x 4'L BOEING COMPANY Seattle, Wash. 3.5’D x 5’L S im u lation DAYTON T.[BR0WN,| INC. Bohemia, Long Island, N.Y. 5’D x 5’ L DOUGLAS AIR C R AFT COMPANY Santa Monica, Calif. 4’D Sphere 5’ L x 5’W x 5’H

C h a m b e rs Huntington Beach, Calif. 36.5’ D Sphere 5'D x 6’H 10’D x 12* L

FAIRCHILD CAMERA AND Syosset, Long Island, N.Y. 4'D x 8.3’L INSTRUMENT CORPORATION 13' L x 15'W x 14'H Space and Defense Systems

GARRETT CORPORATION Torrance, Calif. 15’D x 23’H Scientists preparing balloon ex­ AiResearch Manufacturing 7’D x 38'L

periments sometimes wish to check GENERAL DYNAMICS San Diego, Calif. 12’D x 19’L Astronautics Division 12'D x 19’L their equipment on the ground under Dynamics Laboratory 5’D x 10’L conditions as near as possible to 5’D x 4'L GENERAL ELECTRIC Valley Forge, Pa. 28'D Sphere those to be encountered during flight. 30’D x 30’H 8’D x 10'L It is usually not difficult to find small 10*D x 24’ L vacuum chambers, but chambers GENERAL MOTORS CORPORATION Indianapolis, Ind. 5.5'D x 8’L Allison Speedway Division large enough to hold complete GRUMMAN AIR C R AFT Bethpage, N. Y. ‘ 4’D x 8'L 15’D x 20’ H balloon-borne experiments may not 22’D Sphere

be readily available. The locations of HUGHES AIRCRAFT El Segundo, Calif. 6’D x 8.5’H some of the larger chambers in the Space Systems Division 14’D x 36’H Research Laboratory Malibu, Calif. 5’D x 15'L U.S. are listed in the accompanying 4’D x 10’L 9’D x 18'L table. Dimensions and orientation of IN TERNATION AL BUSINESS Oswego, N. Y. 6’D x 8’ L cylindrical chambers are indicated MACHINES Space Guidance Center by diameter, D, and length, L. or JOHNS HOPKINS UNIVERSITY Si 1 ver Spring, Md. 6’D x 7’L height, H, of the cylinder. Spherical Applied Physics Laboratory 7’D x 9’L 3’D x 5‘ L

chambers are identified, and di­ LEAR SIEGLER, INC. Grand Rapids, Mich. 6’D x 6’ L Instrument Division ameter, D. is given. Width, W, Environmental Test Laboratory

height, H, and length, L, are all given LING-TEMCO-VOUGHT, INC. Dallas, Tex. 10'D x 10'L when the chamber is rectangular. Astronautics Division LITTON INDUSTRIES Beverly Hills, Calif. 7’D x 14’L One chamber is a truncated cone: Electronic Equipment 3’D x l l ’ L two diameters and the height are LOCKHEED AIRCRAFT Burbank, Calif. 9.5’D x 8.5'H CORPORATION (Rye Canyon) given. Lockheed-California Company Lockheed Missiles and Space Sunnyvale, Calif. 12' D x 17’ L A more complete listing of Company 18’D x 20’ L 3.8’D x 9'H chambers is given in C a ta lo g o f Truncated Cone

Space Simulation Vacuum Cham­ MARTIN MARIETTA CORPORATION Middle River, Md. 4'D x 5'L bers, published by the Aerospace Martin Space Systems Division Me DONNELL AIRCRAFT St. Louis, Mo. 30'D x 36'L Industries Association of America, 18’D x 30'L 8'D x 12'L Inc., ATC Report No. ARTC-38, 5.5'D x 10’L 4’D Sphere June, 1964. Only chambers larger 3.5'D x 8.3'L 35'L x 14'W x 14'H than 3' x 3' x 3' are listed. Copies of NATIONAL RESEARCH Cambridge, Mass. 3.5’D x 4.5’L CORPORATION the catalog may be obtained by writ­ Space Vacuum Laboratory ing to: Contract Research Division NORTH AMERICAN AVIATION Canoga Park, Calif. 3'D x 5’ L National Standards Association, Inc. Atomics International Division 1321 14th Street. N. W. Washington. D.C. 20005

10 ORGANIZATION LOCATION SIZE

Los Angeles Division El Segundo, Calif 19’D x 17’L 15’D x 22'L 5’D x 6’ L 3’D x 4'L

Rocketdyne Division Canoga Park, Calif. 4’D x 6’ L

Space and Information Downey, Calif. 6‘D x 14’L Systems Division 5'D x 7'L 3’D x 4'L

NORTHROP CORPORATION Hawthorne, Calif. 12'D x 15'L Northrop Space Laboratories 5’D x 7’ L

Norair Division Hawthorne, Calif. 57.5'D Sphere

Nortronics Division Palos Verdes, Calif. 4'D x 5'L

PHILCO CORPORATION Palo Alto, Calif. 8.5'D x 9’ L Western Development Laboratories 7'D x 7'L 4'D x 5'L Aeronutronic Division Newport Beach, Calif. 8'D x 27'L

PITTSBURGH-DES MOINES STEEL Pittsburgh, Pa. 8'D x 8'L COMPANY Neville Island Research Center

RADIO CORPORATION OF AMERICA Lancaster, Pa. 6'D x 5'L 6'D x 5’ L

Princeton, N. J. 26'D x 20'H 5.5'D x 10'L 4'D x 5'L

REPUBLIC AVIATION Farmingdale, N. Y. 13'D x 20'L 8’D x 15’L

SANDIA CORPORATION Albuquerque, N. M. 4'D x 9'L | 6’D x 10'L

1 SPACE TECHNOLOGY Redondo Beach, Calif. 28'D Sphere LABORATORIES 7'D x 12' L 6'D x 8'L

UNITED AIRCRAFT CORPORATION Eost Hartford, Conn. 4.5'D x 5.5'L Pratt and Whitney Aircraft Division 6'D x 6'L

UNIVERSITY OF SOUTHERN Los Angeles, Calif. 9'D x 20'L CALIFORNIA

WYLE LABORATORIES El Segundo, Calif. 4'D x 4'H

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

Ames Research Center Moffett Field, Calif. 4'D x 5’L

Goddard Space Flight Center Greenbelt, Md. 28’D x 40'L 12’D x 15'H 8'D x 8'L 8'D x 8'L

Jet Propulsion Laboratories Pasadena, Calif. 25'D x 25'L 7'D x 14'L

Langley Research Center Langley Station, 8’D x 15'L Hampton, Va. 7.5’D x 10.5'L 6.5'D x 8.5'L 7'D x 7'L 5'D x 5'L

Lewis Research Center Cleveland, Ohio 30'D x 100'L 25'D x 70’L 15'D x 60’ L 6’D x 10’H 5’D x 16’L 4.5'D x 6'H 100'D x 120'H

Manned Spacecraft Center Houston, Tex. 55’D x 90'H (Clear Lake) 4'D x 6'L 6'D x 6’H

Marshall Space Flight Center Huntsvil le, Ala. 4'D x 6’L 6'D x 9'H 15'D x 20’H UNITED STATES AIR FORCE

Arnold Engineering Development Arnold Air Force 35'D x 65'H Station, Tenn. 18’D x 29'L 7'D x 12'L

Aero Propulsion Laboratory Wright-Patterson Air 23'D x 27'H Force Base, Ohio 8.5'D x 25’ L 6'D x 9'L

Avionics Laboratory Wright-Patterson Air 8'D x 12'L Force Base, Ohio

Flight Dynamics Laboratory Wright-Patterson Air 3’D x 4’L Force Base, Ohio 4’D x 5’L

Rocket Propulsion Laboratory Edwards Air Force Base, 30’D Sphere Calif. 8’D x 5'H UNITED STATES NAVY

Naval Missile Center Pt. Mugu, Col if. 10’D x 20’L Techniques for the Study of Mountain Waves

Severe and often damaging foot­ tems aloft, and at the ground surface. Superpressure Balloons hill winds are a common winter Techniques are now in preparation occurrence along the eastern slope to penetrate the 2,000- to 3,000-ft in­ Two major techniques have been of the Colorado Rockies. While termediate region, which so far has employed for measuring the wave these winds, which at times attain been almost inaccessible. flow aloft. It seemed, in view of speeds of over 120 mph, are cer­ Anemometers supplied by available methods suggested by tainly related to the familiar moun­ NCAR’s Field Observing Facility D. R. Booker and L. W. Cooper tain “chinook,” their exceptional have been carefully located to meas­ (J. Appl. Meterol. 4 (1), 122-129, violence seems due to influences ure representative ground conditions. 1965) and others, that superpressure from oscillating wind layers above, Anemometer stations are several balloons, floating at a constant den­ known as mountain lee waves, which miles apart in a region extending sity level would reveal the exact occasionally dip to the ground from near the divide down to a point vertical and horizontal courses of surface. several miles east of the foothills. the lee waves. An NCAR balloon NCAR interest in the various Lee waves form as winds pass launching van, manned by a team manifestations of atmospheric tur­ over a mountain barrier, the waves from Western Scientific Services of bulence includes both theoretical then forming peaks and troughs Fort Collins, Colo., was engaged by and observational studies of moun­ downwind, in rows parallel to the the project last winter, and was dis­ tain waves. One detailed study, mountain crest. The anemometers patched to a Middle Park launching headed by Douglas Lilly of the reveal the extent to which surface site west of the continental divide Laboratory of the Atmospheric wind fluctuations reflect the rise and during conditions of probable wave Sciences, is currently in progress, fall of the waves overhead. Data activity. The logistical difficulties of seeking to learn how the mountain taken so far show wind speed getting crew and supplies over near­ waves, flowing eastward from the maxima at points parallel to the ly 150 mi of mountain roads to the 13,000-ft continental divide, are able mountain range, thus verifying the launching site on short notice some­ to produce exceptionally strong supposition that such a relationship times prevented launchings during winds at the ground surface, par­ exists. Anemometer data are, of periods of high winds. Consequently, ticularly at the point where the course, subject to changing wind pat­ balloon flights could not always mountains give way to the plains. terns imposed by terrain features, supply data during periods of great­ Field observations have included but sufficient quantities of data will est interest to the experiment. measurements within the wave sys­ lessen this uncertainty. Numerous balloon flights suc­

12 Aircraft flight path along 211° VOR hearing.

ceeded, however, in tracing impor­ considered, to a first approximation, Apart from logistical difficulties tant details of the mountain wave as a neutral air trajectory tracer. involved in arriving at the launching form and flow. Their most important A radio transponder weighing 82 site, balloon launching operations contribution has been in distinguish­ gm was suspended 20 ft below the proceeded extremely well. The ing waves of fairly consistent pro­ ballast —a distance which minimized meteorological conditions which portions from waves of higher ve­ pendulum effects. X-band radar favored the formation of mountain locity which plunge from an initial emissions from an M-33 radar instal­ waves east of the divide generally crest to the foot of the mountains lation on Gunbarrel Hill east of the brought mild winds, moderate tem­ with scarcely any subsequent re­ mountains activated the transponder, peratures and overcast to the west­ covery of a wave-like appearance. which relayed back a 400-MHz sig­ ern slope. Launching was relatively Pillow-shaped, 0.75-cu m Mylar nal. The balloon’s flight could thus easy, and the initial ascent was not balloons were inflated with helium at be traced from the M-33 installation. particularly hazardous to the bal­ the launching site and ballasted to The entire balloon assembly was loons. A typical feature of the same produce zero net buoyancy at the towed aloft to altitudes between meteorological circumstances, how­ desired flight altitudes. The high 16,000 and 23,000 ft by a 100-gm ever, was the banking of the overcast modulus of elasticity of Mylar film rubber balloon at a rate of several into a heavy cap cloud surrounding makes it the best-suited material, hundred feet per minute, and re­ the divide. Here the balloons often because increased pressure causes leased by a timed fuse. The fuse was met trouble. Many were lost even almost no perceptible change in the a variation of one suggested by before being released by their timed balloon’s volume. A superpressure Booker and Cooper, and was as­ fuses. Some radar trackings showed balloon displaced above or below its sembled for the present project by balloons falling to the ground at equilibrium floating level becomes the NCAR Scientific Balloon Fa­ rates as high as 2000 ft/min. Such heavier or lighter than the displaced cility. A length of internally burn­ catastrophic plunges could have re­ air and, therefore, attempts to return ing dynamite fuse was attached by a sulted from powerful downdrafts, to the equilibrium level. Booker and section of pyrotechnic igniter fuse but the majority of failures occurred Cooper showed, however, that in to the tow line. The dynamite fuse when a cap cloud was present, indi­ strong mountain wave conditions the burned at 8 to 10 ft/sec, allowing a cating that icing conditions —super­ restoring terminal velocity was small simple calculation of the length cooled water freezing quickly on the compared to the vertical speed of needed to sever the tow line at the balloon film —were responsible the air, so that the balloon could be specified altitude. instead.

13 Aircraft Motion in Waves

The uncertainty of balloon per­ formance and unexpectedly high unit costs led last February to the replace­ ment of balloons by powered aircraft for the remainder of the w inter’s test­ ing. Commercial and research pilots have frequently noted the general qualitative effects of mountain waves on aircraft. A pilot flying through such a wave system normally —or instinctively —raises the aircraft’s nose and gives added power when in a downdraft, and lowers the nose when he encounters an updraft. He thus attempts to hold constant alti­ tude. Many pilots have remarked up­ on the drastic loss of altitude which can occur if there is not sufficient power reserve to equal the occasion­ ally severe losses of airspeed. If, however, the aircraft is not re­ strained from following the upward and downward motions of the waves, its flight path provides a moderately accurate measure of the wave activity. The present project used this principle to obtain quantitative data on the waves. On days chosen for flight into the waves, the Research Aviation Fa­ cility’s Queen Air 80 aircraft flew three round-trip traverses between a point 10 mi east of the Denver VOR monitor and a point 55 mi west of it, on a magnetic VOR bearing of 277. The pilot first “set up” the flight at its easternmost point by gaining the desired altitude and then adjusting the craft to constant power and con­ stant attitude; he then flew into the waves, maintaining the magnetic bearing of 277. NCAR pilots re­ marked upon the peculiar sensation of flying through the waves at con­ stant power, but later came to find waves easier to negotiate when lost or gained altitude was not corrected. On each mission the Queen Air made two passes back and forth over the continental divide at 25,000, 20,000 and 16,000 ft. Clouds often

14 15 divide may provide a partial solution. A more promising possibility is wire chaff dropped from above and traced by radar as winds carry it along. Fine aluminum wires cut to one-fourth the wavelength of X-band (3-cm) radar, reflect back a large white blotch on the radar receiver, charac­ teristic of the motion and distribu­ tion of the chaff. A radar frequency of 9 GHz will be employed. R. M. Lhermitte of the Envi­ ronmental Science Services Adminis­ tration (ESSA) also has suggested use of ground-based doppler radar to track streams of chaff launched from west of the divide. The doppler radar would be capable of directly measur­ ing the velocity of the chaff in the direction of the beam and thus pro­ vide a three-dimensional measure­ ment of wave activity. Field experiments will continue through the summer on a small scale and will gain momentum next winter as mountain wave activity increases. Balloons may continue to provide data in favorable circumstances. More airplane flights into the wave region are planned, and experiments At constant power setting, vertical motions of the aircraft are induced withby the wire chaff are currently in mountain waves. Upwind flight path is exactly out of phase, downwind progress. path in phase with the wave flow. Lilly has pointed out that many aspects of mountain wave activity and its relation to severe ground hid the ground, and icing conditions along the flight line. Taken together, wind storms should be explored, and were frequent. The 16,000-ft level, the parameters measured show ac­ that the availability of NCAR facili­ just 3,000 ft above the mountain curately the structure and dimen­ ties in a region of pronounced wave range, contained the strongest tur­ sions of the wave flow at the activity might invite participation by bulence, the pilots reported. altitudes flown. Wave amplitudes outside investigators. Inquiries may As the aircraft responded to ver­ ranged from one thousand to several be directed to: tical changes in air motion, the Air­ thousand feet, and wavelengths from craft Research Instrumentation Sys­ 6 to 10 mi. According to Lilly, the tem (ARIS) constantly recorded Queen Air 80, properly flown, can pressure changes with respect to obtain most of the measurements the time. This record showed the project needs, to within about 3,000 changes in altitude with time caused ft of the ground surface. Douglas K. Lilly by vertical wind components. Dop­ National Center for pler radar recorded ground speed, Atmospheric Research airspeed, horizontal wind com­ Chaff Possibilities Box 1470 ponents and drift. A project scientist rode during the flights to operate the Measurements closer to the ground Boulder, Colorado 80302 research instruments, while the pilots require more expendable equipment, made separate altitude and tempera­ of course. Slow-lift balloons re­ ture readings at various checkpoints leased along the lee side (east) of the

16 #

Hail Suppression in the USSR

Guy Goyer, NCAR

A report by G. K. Sulakvelidze, then, the hail suppression technique decreases to the top of the cloud entitled “Results of the Caucasus that was developed; and, finally, the (Fig. 1). This vertical wind can reach Anti-Hail Expedition of 1965,” de­ results of the program and the con­ as much as 30 m/sec in very large scribes in some detail recent work on clusions that we may draw from it in mature thunderstorms. hail suppression carried out by three relation to hail suppression research The temperature at the maximum groups in the USSR —the High in the U.S. updraft level was found to be a Mountain Geophysical Institute, the critical factor in determining the Central Aerological Observatory, Mapping the Updraft Profile formation of rain, hail, or snow. If and the Institute of Geophysics of the maximum updraft velocity Georgia. We have known about the The first stage of the Soviet pro­ occurs at a temperature above, say, Soviet hail suppression program forgram was to determine the vertical 5°C (i.e., below the 5°C level), all some time, but up to now we have profile of the wind field in the storm. you can get from such a cloud is rain; had virtually no numerical data with This mapping of the updraft was car­ between -5°C and -20°C you will which to assess the validity of the ried out by using radar to track small get large hail, because under these results claimed. However, the Sulak­ balloons fitted with corner reflectors. conditions a few of the cloud drop­ velidze report provides many facts It was found that the updraft at the lets freeze and give rise to a small and figures, and its overall coherence ground is not a single thermal, but number of large stones; and if the is impressive; it shows convincingly that there are several thermals feed­ temperature is lower than -20°C, a the correlation between laboratory ing into the cloud, which combine in large number of droplets freeze and work, theoretical work, field observa­ the middle of the cloud to form a give rise to small hailstones or snow. tions, and the hail suppression pro­ single vertical updraft. It was also Thus, it appeared that the two prime ject itself. In this article I shall dis­ found that the vertical velocity in factors relating to hail formation m cuss, first, the hailstorm model on the cloud itself is an almost linear were the maximum updraft velocity which the Soviet program was based, function of height above cloud base and the temperature at which this and how that model was verified; up to a certain maximum, and then maximum occurs.

17 tion. it appeared that a radar reflec­ tivity of between 1 x 10~7 cm-1 and 4 x 10-7 cm-1 corresponded to large- droplet rain or soft hail, and a reflectivity greater than 4 x 10-7 cm-1 corresponded to damaging hail. Confident that they had the “threshold value” of radar reflec­ tivity needed to identify a hail center in a cloud, next season the Soviet scientists went to a lower altitude, in the farming region, to verify their findings. However, here they found that the threshold value derived from the high-altitude studies occasionally corresponded to rain, and not to hail, at the ground. Sulakvelidze postu­ lated that this must be due to the fact that, whereas the freezing level in the earlier studies had been about 1 km above ground level, here it was 4 or 5 km and the hail had base. melted on the way down. A subse­ quent laboratory and theoretical pro­ Accumulation Zone Concept updraft is trapped in a closed cycle gram confirmed this hypothesis: it of events: as it grows, it will rise and was found that hailstones of 1.5 to A consideration of the trajectory fall, and then shatter into fragments 2 cm in diameter melt completely in of water droplets in such a wind field which, in turn, are carried upward falling 4 or 5 km through an atmos­ led to the concept that droplets rising and grow into larger droplets ... and phere warmer than 0°C. above the level of maximum updraft so on. Under these conditions, an The cross-sectional area of the form an accumulation zone of liquid accumulation zone builds up above accumulation zone at the threshold supercooled water, located slightly the level of maximum updraft. The reflectivity was determined from the above the wind maximum (as shown liquid water content in this zone may radar picture to be about 3 or 4 km2, in Fig. 1). The argument runs as be as high as 30 gm/m3, as compared which agreed well with the area of follows. Water droplets carried into with 3 or 4 gm/m3 at the base of the the hailswath at the ground after the cloud by the updraft coalesce cloud. If the maximum updraft is less making due correction for the with other droplets, and grow larger than 10 m/sec, no accumulation zone spreading effect of the wind. This as they rise to higher levels. But, as is formed, and all droplets can fall meant that the volume of the we have seen, once past the level of and evaporate or produce virga. accumulation zone at the threshold maximum velocity, the updraft was about 10 km3 in most cases (with gradually decreases toward the top a maximum of, perhaps, 30 km3). of the cloud. Therefore, each grow­ Detecting the Accumulation Zone ing droplet will rise to a level at which the updraft is just sufficient to The next step was to go into the Measuring Hail Size in the Cloud support it. As the droplet continues field and determine by radar if, in to grow it must fall to a level of fact, there was an accumulation zone At this stage, it was obvious that greater updraft, and it would con­ as proposed in the model. Then, an effective hail suppression pro­ tinue to grow and fall were it not for given a detectable accumulation gram would require more than the the fact that falling droplets disinte­ zone, some correlation was needed ability to detect the mere presence of grate when they reach a diameter of between the radar reflectivity of the hail in a cloud: the size of the hail about 6 mm. Thus, if the updraft zone and hail or rain at the ground. would have to be known to a fair maximum is greater than 10 m/sec — Field operations began on a 7000-ft degree of accuracy. Consequently, a the terminal velocity of a 6-mm drop­ mountain peak where the frequency radar technique was developed let—any droplet carried up into the of hailstorms was reasonably high, which was able to provide a contin­ region above the level of maximum and after several months of observa­ uous indication, in real time, of the

18 diameter of the hailstones in the Final Model to reduce its damaging effects. The cloud. This technique was based on microphysical principle upon which the fact that the radar reflectivity Figure 2 is an idealized picture of the Soviet suppression efforts were of a body of hailstones is much more the final hailstorm model upon which based was that of seeding to in­ strongly dependent upon their size the Soviet program was based. The crease the number of hail embryos. than upon their number: in fact, the figure shows the vertical velocity The total liquid water content of a intensity of the return signal is distribution as a function of height, given cloud is-fixed in the sense that proportional to the sixth power of the temperature gradient through the it is a function of the updraft. If the the radius of the stones, as compared cloud, the liquid water content, and number of natural nuclei is small, with the first power of the number. the growth of the hailstone as a each may grow into a large hailstone; By determining the volume of the function of its trajectory through the but if the number of nuclei is in­ accumulation zone by radar, and cloud. As it moves toward the top of creased, each will receive a smaller then counting the number of hail­ the cloud, the hail embryo is travel­ share of the available water and thus stones at the ground, it was found ing at high speed in a medium of com­ grow to a smaller size. These smaller that the concentration of hailstones paratively low liquid water content; hailstones may either melt on the in the cloud varied between 0.1 and on the way down, it is falling slowly way down or, if they reach the 10 per m3. Since the number is not against an increasing updraft and ground, cause less damage than critical, the average value of one spends a long time in a region of would larger ones. If, for example, stone per m3 is sufficiently accurate highly concentrated supercooled you increase the number of hail for deriving the size of the hailstones water. Thus, according to the model, embryos from 5 to 500 per m3, the from the reflectivity of the accumula­ the hailstone grows very slowly on resulting hailstones will be about tion zone. In order to be able to the way up and very rapidly on the one quarter of the radius of the nat­ measure the diameter of hailstones way down. ural hailstones that would have over a continuous range between 1 grown in the unseeded cloud. Since and 4 cm, the Soviets adopted a dual­ the impact energy of a hailstone wavelength radar system operating Suppression Principle varies as the fourth power of its at 3.2 and 10 cm. They claim that the radius, such a reduction in size would hail as measured at the ground is Having developed a detailed hail­ mean a considerable reduction in within 35 per cent of the size calcu­ storm model, the next task was to damage. lated from the radar measurements, find an efficient way to suppress the after correction for melting. hail —either to stop it completely or Seeding Agent

Silver iodide, which has been widely used in cloud-seeding experi­ ments in the U.S. and elsewhere, was chosen as the principal seeding agent. (Lead iodide was also used in some cases.) One of the key findings of the Soviet program was that the effectiveness of silver iodide as a seeding agent is strongly dependent upon the temperature at which it is generated. It was discovered that if the silver iodide crystals are gener­ ated at or below -6°C, then they will nucleate (grow ice crystals) at that temperature; but, if they are gener­ ated at above — 6°C, they will not nucleate until the temperature reaches — 13°C. This tem perature requirement, along with the need for Fig. 2 Growth of a hailstone (radius r) for typical distributions of temperature timeliness T, and accuracy of delivery, liquid-water content q, and vertical velocity v. The equilibrium thickness ruled of the out the possibility of using a liquid-water layer on the hailstone is denoted by h,,q. ground-based seeding technique.

19 AREA RADAR YEAR GUNS PROJECTILES PERSONNEL EXPERIMENTS 0 0 0 ’s ACRES (DUAL) Table 1 Growth of the Soviet hail 1961 75 1 1 44 30 20 suppression program. The 1962 75 1 1 132 30 35 operational phase began in 1963 2 25 1 1 146 30 20 1964. 1964 1150 8 17 1020 2 8 5 2 0 3 1965 1215 15 20 2888 475 366

YEAR REFERENCE PROTECTED REFERENCE/PROTECTED

1959-63 6.7 6.8 1.0 4.0 7.0 0.6 30.0 19.0 1.6 Entire Expedition 8.0 8.0 1.0 Table 2 1963 — 0 _ Ratio of damaged area to 1964 6.0 6.0 1.0 total cultivated area (per 3.0 0.6 5.0 cent). 49.0 3.0 16.4 Entire Expedition 9.0 5.0 1.8 1965 19.0 2.3 8.3 20.0 6.0 3.3 20.0 8.0 2.5 Entire Expedition 19.4 3.2 6.1

Suppression Technique servers in both areas to measure the mate to be made of the maximum up­ hailswath and the crop damage. The draft velocity, the temperature at the In the course of determining the construction of the shell has not maximum updraft, and the maximum threshold reflectivity, it was found been revealed; all that is known is size of hailstone that would develop that the rate of change of reflectivity that it normally contains 100 gm of in the untreated cloud. On the basis of the accumulation zone in a hail­ silver iodide, and generates about of five years’ experience in different storm was very rapid — in a matter of 1013 nuclei per gm at — 10°C. The areas of the USSR, the Soviets claim minutes, the reflectivity would go early tests were carried out with to be able to forecast the occur­ from a low value to the threshold regular anti-aircraft shells which, of rence of hail at the ground with 90 corresponding to hail. This meant course, scattered metal fragments all per cent accuracy. The immediate that the seeding method would have over the countryside. Consequently, short-term forecast is provided by to be very fast, as well as accurate. A a non-splintering shell was developed the dual-wavelength radar, which technique was subsequently devel­ — after two years’ work and an not only locates the accumulation oped by which silver iodide crystals expenditure of about $300,000 zone in the cloud, but also indicates could be delivered directly to the (264,000 rubles). the size of the hailstones as they de­ accumulation zone by an explosive velop. When the meteorologist in shell fired from an anti-aircraft gun. Forecasting Procedure charge of the operation is satisfied The basic field unit in the Soviet that conditions in the accumulation program comprised one dual-wave­ A long-range forecast alerts the zone are right for seeding, the shell length radar and four guns, protect­ gun crews on days when hail is is fired into the cloud. In practice, ing an area of about 400 sq mi. The likely. The local stratification of the seeding action has had to be carried protected area was usually sur­ atmosphere is determined from out within 5 min of locating the rounded by a control area, with ob­ radiosonde data, which allow an esti­ accumulation zone.

20 8 Program Results

COI— Tables 1 and 2, and Fig. 3 give Z CONTROL some indication of the results of the LU AREA 2 6 Soviet hail suppression program up>- < to 1965. Table 1 shows the growth 0- of the program from 1961 to 1965. PROTECTED X The number of people indicated in \ A R EA < 4 the table is based on a staff of 25 at 0£ H each radar station and 5 at each gun to CO site. Figure 3 is a typical Soviet in­ o surance data graph for the years o 1961, 1962, and 1964. It shows that < 2 in 1964 (when the operational pro­ 1— gram started) insurance payments in o the protected area dropped almost to zero, whereas in the control area they remained at more or less the 1961 1962 1963 1964 same level as the previous year. Table 2 shows the ratio of damaged area to total cultivated area. All we Fig. 3 Typical Soviet insurance data for the years 1961, 1962, and 1964. know about the economics of the 1965 project is that it cost about Conclusions parently, they would have had much $900,000 (810,000 rubles), including better results in many cases, had it the development of the shell which, The general impression given by not been for lack of shells and “ FAA- as mentioned earlier, cost about the report is that Sulakvelidze’s type” restrictions on firing. $300,000. So the one-year effort, group has developed a very success­ I feel that there are some important without the cost of the shell, amount­ ful hail suppression technique, but lessons to be learned from this re­ ed to about $600,000 for protecting that this method is not universally port in relation to hail suppression an area of about 2000 sq mi —i.e., the accepted in the USSR. There is a research in the U.S. The Soviet fore­ cost of protection was around 70^ rival group which favors rocket seed­ casting methods are similar to ours per acre. ing of the whole cloud, and the in many respects, and forecasting is In a recent article published in the report indicates that Soviet scientists a prime area in which advances must USSR (E. K. Fedorov, 1966: “Pur­ are generally looking for better ways be made before undertaking any sub­ poses and perspectives of the to suppress hail. For example, therestantial hail suppression program. hydrometeorological service,” M e­ were 29 tests of a technique in which We should certainly attempt to teorology and Hydrometeorology the warm part of the cloud was verify the Sulakvelidze hailstorm 6), it was reported that the present seeded with condensation nuclei and model — to see if it is applicable to the hail suppression program in the surface-active agents while, at the U.S. climate and how it might be im­ Caucasus, covering 6000 km2, costs same time, the supercooled part of proved. This limited objective could about 1 per cent of the total agri­ the cloud was seeded with the regu­ be achieved at a reasonable cost. If cultural product of that area, and lar nucleating agent. This method it turns out that the model is well- that the program would be profitable evidently was successful enough to founded, I think we should then even if the crop damage were re­ be recommended for large-scale tests carry out a large-scale test of the duced by only 10 per cent. It is in 1966 —about which no informa­ Soviet suppression technique. How­ claimed that evaluation of the data tion has yet been published. Other ever, there is nothing in the Sulakve­ for 1964-1965 shows that, during this experiments have been carried out to lidze report to indicate that we period, the damage was reduced to modify the weather system at an should drop our current, broad- 75-80 per cent below normal. The earlier stage of development, e.g., based hail modification research; on article goes on to say that if the 1966 seeding the squall line. One thing is the contrary, there is every indica­ results confirm those of 1964-1965, certain: there are serious problems tion that the recent Soviet efforts are the hail suppression network will be connected with using guns. One just a step —albeit a substantial one enlarged to cover an area of around problem the Soviets had was with — in the direction of effective and 40,000 to 50,000 km2. their equivalent of the FAA. Ap­ practical hail suppression.

21 STONEHENGE Launch. Technique

Jack M. Angevine and John W. Sparkman, Jr., NCAR

A small but growing number of balloon-borne experiments require heavy yet delicate scientific pay­ loads. Such experiments are par­ ticularly vulnerable at launch, when in an astronomical experiment, for example, an impact may jar the tele­ scope out of alignment and cause long and costly downtime for repair. These experiments have created the need for improved launch techniques which reduce the possibility of dam­ age by isolating the payload from the rest of the balloon train until the moment of launch, and then assuring a smooth transfer of load to the bal­ loon. Surface winds are the greatest obstacle to making a reliable launch, and methods of handling heavy, deli­ cate loads should ideally be able to cope with winds up to 15 mph, with means of realigning with wind im­ mediately prior to launch. The NCAR Scientific Ballooning Facil­ ity has considered and tested a variety of possible launch methods to meet these requirements. The most attractive method to emerge has been termed the “Stonehenge Stonehenge anchor array and bridle system. Launch.”

22 Credit : University of California Space Sciences laboratory The heavy-duty dual balloon sys­ tem developed for the Stratoscope program appears to provide ade­ quate flight reliability for the heaviest payloads currently being flown. The Stonehenge Launch is based on use of such a dual system. A number of anchor points are spaced equally around the circumference of a circle, with the payload in the center. A bridle, consisting of two equal- length cables, is attached to two anchor points downwind from the payload, and the free ends are fixed to the load line at a common point. The geometry of the bridle and length of the load line can be arranged so that the load line re­ mains slack when the main balloon lies horizontal during inflation. Dur­ ing erection of the balloon train the apex of the bridle moves toward and directly over the payload. When this point is reached, the lift is divided between the bridle and the load line. The mainstay may be released at any subsequent time during erection, and then the bridle cables are released when the payload is airborne. In a series of tests the mainstay was released at various points along the path of the launch balloon. The procedure which appeared most re­ liable (while providing acceptable payload acceleration) was to release Stonehenge Test Launch of 10,000-lb load by University of California the mainstay when the lift was and G. T. Schjeldahl Company, in a NASA-sponsored research project. divided nearly equally between load line and bridle. The complete circle of anchor cable is then transferred to one of tem and one helium supply. Al­ points allows a variety of bridle con­ the new set of anchor points. By though the launch procedure is figurations. and permits alignment reverse movement of the winch ve­ straightforward, this flexibility per­ for any wind direction. If the wind hicle the other side of the bridle can mits repeated training and testing of changes direction after start of in­ likewise be relocated. This pro­ a particular configuration at rela­ flation and prior to launch, the cedure usually requires less than 10 tively low cost. bridle can be reoriented when the min. The simplicity of the Stonehenge launch balloon is elevated enough A number of launch tests have method and equipment make it for the bridle to be well clear of the been made with payloads varying adaptable to any location having payload, and while the load line is from 850 to 10,000 lb. Results indi­ sufficient operating surface. Through still slack. When changing orienta­ cate that launches can be made con­ variations of the anchor array and tion at this stage, the mainstay winch sistently with payload accelerations bridle the method can be adapted to vehicle is moved on its circle until below 0.65 g. any single-unit payload configura­ the complete bridle load is trans­ The Stonehenge method allows a tion. and the actual payload need ferred to one bridle line, while the launch to be practiced realistically not be involved with the launch until other line becomes slack. The slack many times, using one balloon sys­ minutes prior to flight.

23 (

Lessons From the Line Islands

During March and April field costs, with some additional support parties representing about two dozen being provided by the National research organizations, universities, Science Foundation. It is difficult to and military and other government set precise dollar values on the ser­ agencies established bases on the vices contributed by the various Line Islands, a group of small atolls cooperating organizations, but they 1000 to 1500 mi south of Hawaii, to were major and substantial. conduct a major meteorological field experiment. From the Islands them­ On 5 May participants in the selves, and from ships and aircraft in Experiment met in Honolulu to re­ the vicinity, they collected the most view their experiences and to see comprehensive set of meteorological what lessons could be drawn from data ever obtained in the tropics. this hastily organized effort, for the The Experiment was organized to benefit of future experiments which secure basic data on the tropics, may be carried out in other remote taking particular advantage of areas. Quite understandably, the pictures from NASA’s ATS-1 satel­ most pointed comments related to lite, in synchronous orbit nearly over the great desirability of having more the Line Islands. Of necessity it was time to plan the work. Scientists organized with little lead time. The stressed the importance of always exercise was coordinated by NCAR, keeping uppermost the scientific ob­ which also underwrote the direct jectives of such an experiment. They

24 also noted that scientific procedures, communications systems. Obvi­ ment and of changes in these aims. by their very nature, require much ously, it is best to move into space (Indeed, participants in general felt leeway for changing plans in mid­ that is already set up and functioning, that morale and cooperation are best stream, and urged that support if possible. maintained when all participants are people approach their jobs with the Participants pointed out that it is informed of any changes in plans.) prospect of having to cope with manyimportant to build or rehabilitate Safe load limits for light research spur-of-the-moment changes in pro­ living quarters and have them ready aircraft were sometimes approached, gram during the course of a field for use before the scientific and ob­ suggesting that future field experi­ experiment. serving people move in. However, ments might use heavier research Support people nevertheless calledsome scientists should be brought in aircraft. A standby plane for search for more exact planning by scientists, as soon as possible, to advise in and rescue should be available at all where possible. Representatives of siting and setting up the observing times that logistic or research craft military groups which took part in equipment. are in the air. Professional navigators the Experiment noted that some es­ Participants in the Line Islands should be used in remote oceanic sentials are simply not amenable to Experiment learned by bitter experi­ areas, along with more powerful shortcuts: it often takes several ence the importance of having homing devices and associated air­ months after plans are firm to get the adequate time to label all packages craft instrumentation. necessary clearances for military of equipment and supplies as to con­ Support groups felt that their cooperation. (And it was quite clear tents and destination. Time was also people were overworked, and sug­ that such cooperation was essential needed but lacking for careful load­ gested a one-third increase in to the success of the recent Experi­ ing of the barge so that first neces­ numbers. The scientific groups also ment.) One participant proposed an sities—particularly those needed for felt that more people would have affiliation of government and non­ unloading and building —could be been appropriate, as recreation and government organizations to handle available first. Some sort of time and rest times were almost unavailable future large programs, with a groupbudget network planning, such as because of the heavy workload im­ like NCAR or ESSA as coordinator. Program Evaluation and Review posed by the observing schedule. Much of the discussion concerned Technique (PERT) or the Critical Weekend visitors created special advance surveys of experimental Path Method (CPM), was strongly problems and often strained the al­ areas. Last November, two months recommended, and should be used ready overtaxed facilities. before the Line Islands Experiment starting at an early stage of an experi­ The effects of salt spray on instru­ got underway, a party of a dozen per­ ment, to provide estimates of time ments had been underestimated and sons visited the Islands and made an and cost for logistics activities. (In the scientists felt that further efforts extensive survey of conditions to be the Experiment, such procedures to protect instruments would be well encountered there. The work of the were followed in detail in the roll-up advised. survey party greatly eased the prob­operations.) The need for a staff doctor was lems of moving the Experiment staff Professional planners and contrac­ recognized before the field work into the Islands and of setting up and tors familiar with the area to be began, and the doctor was taken in conducting the observing program. occupied should be sought out and during the first week of actual opera­ In view of the relatively brief dura­ employed. In the Line Islands, tions. In spite of the tropical environ­ tion of such experiments, it is weekly supply flights were needed to ment and some doubts as to water particularly important that surveysustain the Experiment. The logistics supply, the health of the group re­ parties not be misled by the apparent people thought that more careful mained excellent. availability of housing, office, and planning by the scientists would Although participants brought out laboratory space. Each field situa­ make it possible to do with less fre­ these many ways in which the pro­ tion must be judged by its particular quent flights. gram could have been improved, the needs, and both the suitability and Communications were sufficient to overall scientific goals of the Line the location of existing buildings meet basic needs of the Experiment, Islands Experiment were hand­ must be evaluated in terms of the but could have been improved, par­ somely attained. Each group ful­ aims of the project. Sometimes it will ticularly between remote groups and filled its responsibilities and all were be appropriate to fix up old buildings;headquarters, between various pleased with the results. The success at other times new ones will be the groups on each island, and with air­ of this pilot program was due in large only solution. Advance surveys craft. The logistics people felt they part to the versatility and adaptability should consider thoroughly the could have functioned better if they of the many individuals involved, and effects of decay and neglect, es­ had been kept completely informed to their ability to apply hard work pecially of vital power, water, and of the scientific aims of the Experi­ and ingenuity to the tasks at hand.

25 NCAR Ice Nucleus Counter

AEROSOL

2.5cm DIA h

The ability to detect and count ice The acoustic particle counter. MICROPHONE nuclei is essential to many studies in Tests with cigarette smoke indi­ cloud physics. NCAR scientists cate that air drawn through the have designed an automatic, portable capillary moves by laminarflow, ice nucleus counter which detects and that laminar flow extends a short distance beyond the exit and counts ice nuclei in the field or in of the capillary before meeting the laboratory, and which is now the turbulent flow in the exit manufactured commercially by E. section. When a particle leaves Bollay Associates, Inc., of Boulder. the capillary, it induces a mo­ CAPILLARY mentary change from laminar to turbulent flow in the exit jet Unexplained Clicks and apparently produces a shock wave, which moves UP­ The counter is based on an as yet PARTICLE STREAM at slightly more than unexplained phenomenon: under the speed of sound and pro­ 2.5cm DIA proper design conditions, airborne duces an audible click. particles moving rapidly through a narrow passage produce a sound when they leave the passage. Al­ though the exact cause of the sound is unknown—some sort of low pres­ sure shock wave appears to produce a noise pulse —the phenomenon was put to work by Gerhard Langer of NCAR in 1963, in an effort to count dust particles. Langer, while working for the Illinois Institute of Tech­ nology, had observed that the sound produced by a vacuum cleaner in­ creased when aerosol particles

26 100ml FLASK passed through it, so he experimented end the capillary expands abruptly. an airborne particle of lint from the to find a way to separate the sounds Air drawn through the tube moves tissue leaves the capillary. produced by individual particles. rapidly through the capillary, and Similar experiments conducted slows down suddenly when it leaves earlier in France and the United the capillary. Acoustic Sensor Design States had been unsuccessful. Langer Langer created airborne “dust” for made and tested a large number of his experiments by the simple Further testing with varying tube glass sensors, varying their diam­ expedient of crumpling a piece of and capillary diameters and lengths eters, shapes, and sizes until he cleansing tissue in front of the en­ of approach and exit sections indi­ found an efficient basic design: a trance tube. Near the point of expan­ cated optimum dimensions for glass tube is gradually confined like sion at the capillary exit a sound —an separation and detection of particles. a funnel into a capillary; at its other audible click —is produced each time Capillaries 1.5 to 3.0 mm in diameter

NCAR ice nucleus counter with rate computer and digital printer.

COMPRESSOR WATER LINE TO HUMIDIFIER

CLOUD CHAMBER CONTROL PANEL

RATE COMPUTER

SENSOR

27 were found to be best with practical results, were mostly large and im­ us counters. It has also proved its airflow rates. The signal increases in mobile; a portable, automatic, con­ reliability up to 15,000 ft. Above strength and in signal-to-noise ratio tinuous counter was greatly to be that altitude the signal-to-noise ratio with increasing diameter of the desired. is not adequate in a noisy aircraft capillary, but as the capillary di­ environment, and a sensor with a ameter increases the size of the mix­ larger capillary (and therefore a ing chamber must also be increased. The NCAR Counter larger cooling chamber) must be used The entrance and exit sections to attain an audible signal. Also, should be at least 2 cm in diameter A unit containing the sensor and a above 15,000 ft the low air density to reduce noise from turbulence. cloud chamber, in which incoming allows many ice crystals to settle Speed of airflow and shape of exit air could be humidified and super­ out of the airstream to the bottom of are critical for successful operation cooled, was built at NCAR. A con­ the mixing chamber, where they are of the counter. Although the exit tinuous air sample, humidified if not counted. must be fairly abrupt, the sound is necessary, can be drawn into the produced only if the capillary rounds cold chamber to form an artificial smoothly into the widened exit por­ cloud. Ice crystals nucleated in it Use of the Counter tion of the tube — the transition must are allowed to grow for about 1 min not be sharp or rough. Pressure before being drawn through a counter NCAR ice nucleus counters have should drop approximately 18 cmattached at the lower end of the mix­ been employed to measure diffusion Hg. Too long a capillary weakens the ing and cooling chamber. Problems of artificial ice nuclei in cloud- signal —the optimum length is 5 to of spurious counts produced by ice seeding experiments. Both airborne 10 cm. crystals which grow on the walls of and truck-mounted units were used the chamber are prevented with a in a study of this type, in coopera­ polyurethane foam liner, kept satu­ tion with E. Bollay Associates and Counting Ice Nuclei rated with glycol. in conjunction with their weather The sensor used in the NCAR modification test program along the Langer was aware of the potential counter is a 2.5-cm glass tube in the Park Range (Colorado) for the of a device that could count dust entrance and exit tubes. The capillary Bureau of Reclamation. Airborne particles larger than 5 p. in diameter is 1.5 mm in diameter, 6 cm long. A and surface-based counters are also without interference from a back­ microphone attached above the being used by the University of ground of smaller particles. Roscoe sensor’s capillary tube converts each Wyoming in a test program seeding Braham, of the University of Chi­ acoustic signal into an electrical im­ the cap cloud over Elk Mountain, cago, suggested that the number of pulse and relays it to an electronic Wyoming, and by the National Re­ ice crystals present in supercooled computer designed by C. P. Edwards search Council of Canada in hail clouds could be ascertained with an of E. Bollay Associates. The com­ suppression studies. A counter is airborne acoustic sensor, since it puter automatically senses changes aboard the ESSA ship O cea n o ­ could distinguish the crystals from in count rate and selects an optimum grapher on her current world voyage. smaller cloud droplets. New roles meter scale for recording the count; Rosinski is using one of the for the counter — measuring the the scales correspond to 10, 100, counters in field projects designed number of natural ice nuclei in clouds 1000, and 10,000 counts/min with to determine the origin of ice nuclei, and in the atmosphere, and tracing air flowing at 10 liters/min. Signals some of which may be extraterres­ silver iodide plumes —soon became are counted during 2-min periods trial and may enter the troposphere apparent to Langer and to Jan Rosin- when the signal frequency is low, but by way of the jet stream. The equip­ ski, also of NCAR. By passing an in successively shorter periods when ment can also be used to track air­ air sample through a moist, super­ the frequency increases. Data are flow in buildings, the air being cooled chamber, artificial clouds traced automatically on a paper strip “tagged” with silver iodide smoke. could be made in which ice crystals chart. The acoustic sensor by itself can be would form around ice nuclei in the The NCAR counter has recently used to monitor particles in a clean air sample. The crystals could then been calibrated with a mixing room. NCAR aircraft have also be counted, revealing the number of chamber and the National Science carried the ice nucleus counter to ice nuclei present in the air. Previous Foundation/Colorado State Univer­ trace dispersion of some of the in­ ice nucleus counters, none of which sity isothermal cloud chamber, both dustrial contaminants -in the Denver- could give continuous and immediate previously used as laboratory nucle­ Boulder area.

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