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clear skies and at low surface temperatures. Many col-umnar crystals had complex inner structures that oftenwere asymmetric (figure 4). Nonuniform growth con-ditions under the extremely low temperatures probablyaccount for the complex shapes.

Electron microscopic examinations of pencil and tri-angle-shaped ice crystals revealed no detectable nucleus,which confirms that these crystals were formed by ho-mogeneous nucleation. On the other hand, the bulletcrystals, presumably formed in high clouds, had severalnuclei.

An upslope wind from the grid north was again con-firmed as the favored wind for the formation of ice crys-tals at South Pole Station.

This research has been supported by National ScienceFoundation grant DPP 76-23114.

ReferencesGonda, T., and T. Yamazaki. 1978. Morphology of ice droxtals

grown from supercooled water droplets. In Proceedings of the

4th International Conference on Vapor Growth and Epitaxy (July1978, Nagoya, Japan).

Hogan, A. W. 1976. Summer ice crystal precipitation at theSouth Pole. Journal of Atmospheric Sciences, 14: 246-49.

Kikuchi, K., and A. W. Hogan. 1976. Snow crystal observationin summer season at Amundsen-Scott Pole Station, Antarc-tica. Journal of the Faculty of Science ( Hokkaido University),series 7 (Geophysics), 5: 1-28.

Kuhn, M. 1968. Ice crystals and solar halo displays at PlateauStation, 1967. In ISAGE Symposium, pp. 298-302.

Magono, C., and C. W. Lee, 1966. Meteorological classificationof natural snow crystals.Journal of the Faculty of Science ( Hok-kaido University), series 7 (Geophysics), 2: 321-65.

Ohtake, T., 1971. Studies on Ice Fog. Environmental ProtectionAgency, Office of Air Programs, publication no. APTD-0626.

Ohtake, T., 1976. Ice crystals in the antarctic atmosphere. InProceedings of Ninth International Conference on Cloud Physics(26-30 July 1976, Boulder, Colorado), pp. 484-87.

Ohtake, T. 1978. Atmospheric ice crystals at the South Pole insummer. Antarctic Journal of the United States, 13(4): 174-75.

Shimizu, H. 1963. "Long prism" crystals observed in the pre-cipitation in Antarctica. Journal of Meteorological Society ofJa-pan, series 2, 41: 305-307.

Geophysical monitoring forclimatic change (GMcc)

LT. JOHN C. OSBORN JR., NOAA

Air Resources LaboratoryNational Oceanic and Atmospheric Administration

Boulder, Colorado 80303

From November 1977 to November 1978, theGeo-physical Monitoring for Climatic Change (GMcc) pro-gram continued operations at Amundsen-Scott (SouthPole) Station, one of the program's four baseline sta-tions. The purpose of the program is to measure traceconstituents of the atmosphere relevant to the study ofclimatic change and the anthropogenic impact on suchchange. South Pole operations in 1977-78 consisted oftaking continuous measurements of such parameters ascarbon dioxide, surface ozone, meteorology, solar radia-tion, and aerosols, as well as maintaining other discreteprograms and cooperating in other research efforts.

Continuous measurement activities included the fol-lowing:

1. Carbon dioxide. An infrared analyzer was used tocontinuously measure the atmospheric concentration ofcarbon dioxide (CO2). Twice monthly flask air sampleswere taken through theanalyzer sampling line for com-parison. Statistical analysis of the continuous data showedthat a weekly sampling could give representative data onthe CO2 trend at the South Pole. Consequently, in No-vember 1978, the continuous CO 2 analyzer was shut

down and a weekly hand-aspirated flask sampling rou-tine commenced. Continuous measurement of CO 2 isanticipated to resume in 1979 ' when the conversion ofstandard gases from CO2-in-N 2 to CO2-in-air is com-pleted.

During 1978, the annual mean South Pole CO2 con-centration was approximately 1.1 parts per million(ppm) greater than the annual mean for 1977. AtGMCC's Mauna Loa baseline station, the annual meanincrease detected was about 1.5 ppm. These changes arepart of the long-term increase observed worldwide. Theseasonal variation in concentration, marked by an earlywinter minimum and early summer maximum (Keelinget al., 1976), is very evident in figure 1.

334SPO 00 2 Monthly Concentrations

1975- 1978

09 H 9•' H- H •.

S•

-•.,H•- S

• ••S

3251975197619771978

Figure 1. GMCC South Pole provisional monthly mean car-bon dioxide (CO2) concentrations. Data either analyzed on,or corrected to, Boulder/GMcc lira 202 continuous analyser,and expressed in Scripps 1959 adjusted manometric index

scale.

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2. Surface ozone. Two instruments were used tomeasure ozone concentration. One is a photometer thatuses ultraviolet absorption by ozone. The other uses anelectrochemical concentration cell, with ozone as the ox-idant. The expected annual variation in concentration,with a summer minimum and winter maximum (Olt-mans and Komhyr, 1976), was observed during 1978.

3. Meteorology. Continuous measurements of winds,pressure, air and snow temperature, and atmosphericmoisture were made throughout the year. The wind andair temperature sensors were located on a tower 30 me-ters grid north of the clean air facility (CAF). The snowtemperature sensor was positioned between the towerand CAF. The pressure sensor was mounted inside thebuilding and the moisture monitor was attached to thegas-sampling stack.

The mean temperature for the period from Novem-ber 1977 to November 1978 was -49.4° C. This is 0.1°C less than the mean for the previous 20-year period ofSouth Pole Station existence. A 56-degree temperaturerange was observed during this year, with a maximumof -21° C on 3 January 1978 and a minimum of 770C on 17 September 1978. In five periods during thewinter, temperatures sank below -73.3° C (-100° F) formore than 12 hours at a time. Two of these, 19-20 Juneand 16-18 August, were also accompanied for a time bywinds of from 11 to 13 knots, creating wind chills downto -113° C.

4. Solar radiation. Austral summer continuous mea-surements were of direct and global irradiance. Directirradiance was obtained with a normal incidence pyr-heliometer mounted on a solar tracker. Global irradi-ance was measured with four pyranometers with quartz,GG-22, OG-1, and RG-8 hemispheric filters, and oneultraviolet pyranometer. In addition, discrete direct ir-radiance measurements were taken three times every 24hours on an unobscured sun using another pyrhelio-meter with a rotating filter wheel (quartz, OG-1, RG-2,RG-8). Figure 2 shows representative values.

5. Aerosols. Measurement activities consisted of mea-suring Aitken nuclei concentrations on a yearlong con-tinuous basis, three times every 24 hours, and intermit-tently, using three different instruments—one automaticand two manual condensation nuclei counters. Figure 3presents a time history of aerosol concentration trends.The characteristic temperature inversion, strong duringthe austral winter, allows surface aerosol depletion (Ho-gan and Bernard, 1978). Concentrations of less than 10nuclei per cubic centimeter were detected throughoutJune, July, and August 1978.

All measurements were carried out from the CAF, de-scribed by Peterson (1978). The GMCC measurement in-struments received ambient air from a dual samplingstack system, one stack being for gases and the other foraerosols. The intakes were 14 meters above the snowsurface, and lines ran from the stacks to the instruments.Flow rates from the gas stack were adjusted at the in-struments; laminar flow was maintained through theaerosol stack.

A centralized data acquisition system was used to re-ceive and record the inputs from the measuring instru-ments. The system consisted of a minicomputer, tapedrive, multiplexer digitizer, and cronolog clock. Analogsignals from the measurement instrumentation were

JanFebMa,AprMayJunJulAugSepOctNovDec

Figure 2. Normal Incident solar Irradiance values for clearsky conditions at South Pole. Hand held pyrhellometer mea-surements taken on days when sun clearly visible. Widescatter of data attributed to presence of Ice crystals on someof measurements days. Envelope describes upper limit ofmeasured lrradlances obtained for three-year period. Fordays when no Ice crystals were evident, scatter about meanof data Is approximately ±4.0% for values In the 90 to 105

mw per square centimeter range.

sent to the multiplexer for digitization and were re-corded on tape as 10-minute voltage sums and hourlyvalues in scientific units. Software controlled this processand made it possible to change scaling factors, initiatecalibrations, and check incoming voltages.

In addition to the measurement programs discussedabove, three discrete programs were maintained during1978. In one program, during the austral summer, ahand-held sunphotometer was used to take atmosphericturbidity measurements three times every 24 hourswhen the sun was not obscured by clouds.

The second program involved using a Dobson spec-trophotometer throughout the austral summer to meas-ure total atmospheric ozone. Observations were takenthree times every 24 hours, and quasi-simultaneouscomparisons of all observation types and wavelengthswere made whenever possible. In addition, focusedmoon observations were taken during the winter when-ever moonlight was strong enough to be detected byhigh instrument sensitivity. (South Pole Station is a partof the United States Dobson spectrophotometer net-work.)

3

SOUTH

2

POLE

11111111111111 H IllIIIIIliii I III I Hilillill I 111111 I 1111111974 1975 1976 1977 1978

Figure 3. Monthly geometric mean concentrations of Aitkennuclei for South Pole.

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The third program involved fluorocarbon analysis. Toanalyze F- i 1, F-12, and N 20, samples were drawn fromthe gas stack into 300-millimeter polished stainless steelcylinders. This was done bimonthly during the summerand monthly during the winter.

The GMCC program's South Pole Station is operatedby the Air Resources Laboratory of the National Oceanicand Atmospheric Administration (N0AA) with supportfrom the National Science Foundation. During the1977-78 yearlong season, the station was operated byJohn Osborn (physical scientist) and Larry Smith (elec-tronics engineer).

During 1977-78, the station's personnel also coop-erated in other research efforts, including projects ofthe Scripps Institute of Oceanography; U.S. Departmentof Energy; NOAA Atmospheric Physics and ChemistryLaboratory; Environmental Data and Information Serv-ice, University of California, San Diego; and the Arcticand Antarctic Research Institute, Leningrad, U.S.S.R.

For a review of all activities since 1972, see GMCC pro-gram summary reports 1-6. Besides data acquisition andachival work, the GMCC organization is actively involvedin atmospheric research. Data analysis and interpreta-tion and research publications within the organizationare part of the continuing work performed at the En-vironmental Research Laboratories, which are located inBoulder, Colorado.

References

Hanson, K. A., ed. 1978. Geophysical Monitoring for ClimaticChange. (Summary report no. 5, 1976.) Boulder, Colorado:

U. S. Department of Commerce, National Oceanic and At-mospheric Administration, Environmental Research Labo-ratories.

Hogan, A. W., and S. Barnard. 1978. Seasonal and frontalvariation in antarctic aerosol concentrations. Journal of Ap-plied Meteorology, 17(10): 1458-65.

Keeling, C. D., J . A. Adams, Jr., C. A. Ekdahl Jr., and P. R.Guenther. 1976. Atmospheric carbon dioxide variations atthe South Pole. Tellus, 28(6): 552-64.

Miller, J . M., ed. 1974. Geophysical Monitoringfor Climatic Change(Summary report no. 1, 1972.) Boulder, Colorado: U.S.Department of Commerce, National Oceanic and Atmos-pheric Administration, Environmental Research Laborato-ries.

Miller, J . M., ed. 1974. Geophysical Monitoringfor Climatic Change.(Summary report no. 2, 1973.) Boulder, Colorado: U.S.Department of Commerce, National Oceanic and Atmos-pheric Administration, Environmental Research Laborato-ries.

Miller, J . M., ed. 1975. Geophysical Monitoringfor Climatic Change.(Summary report no. 3, 1974.) Boulder, Colorado: U.S.Department of Commerce, National Oceanic and Atmos-pheric Administration, Environmental Research Laborato-ries.

Oltmans, S. J . , and W. D. Komhyr. 1976. Surface ozone inAntarctica. Journal of Geophysical Research, 81(30): 5359-64.

Peterson, J . T., ed. 1978. Geophysical Monitoring for ClimaticChange. (Summary report no. 6, 1977.) Boulder, Colorado:U.S. Department of Commerce, National Oceanic and At-mospheric Administration, Environmental Reserach Labo-ratories.

Watkins, J . A., ed. 1976. Geophysical Monitoring for ClimaticChange. (Summary report no. 4, 1975.) Boulder, Colorado:U.S. Department of Commerce, National Oceanic and At-mospheric Administration, Environmental Research Labo-ratories.

Lidar operations at PalmerStation

VERN N. SMILEY, BRUCE M. MORLEY, and JOSEPHA. WARBURTON

Desert Research InstituteAtmospheric Sciences CenterUniversity of Nevada System

Reno, Nevada 89506

In December 1977, we set up a two-channel dye laserlidar instrument at Palmer Station. The instrument re-corded data during the austral winter of 1978 and laterwas in operation for the austral winter of 1979. Theobjective of this program has been to determine the oc-currence and vertical profiles of ice crystals, water drops,and mixed-phase clouds at Palmer Station and to relatethese measurements to observed meteorological condi-tions.

The technique employed for ice/water discriminationis the measurement of depolarization in backscatter ofa polarized laser beam. We have employed this tech-nique previously in measurements at the South Pole(Smiley, Morley, and Whitcomb, 1976; Smiley et al.,1979; Smiley and Morley, 1979). Sassen (1978) giveslinear depolarization ratios for backscatter from varioustypes of ice particles: 0.03 to 0.5 for mixed-phase clouds;0.5 for pure ice crystal layers; 0.5 for snowflakes; 0.6for rimed particles; and 0.7 for graupel. The depolari-zation for pure spherical water drop clouds should bezero for single scattering.

In principle, ice and water can be discriminated inthese measurements. However, some complications canarise as a result of multiple scattering and crystal ori-entation. Multiple scattering causes depolarization indense water drop clouds; nevertheless, the multiple scat-tered radiation produces a spatial delay that shows upas a delayed non-zero depolarization. A high degree oforientation of crystals, plates in particular, can producevery small values of depolarization, possibly allowing anice layer to be mistaken for a water drop layer. We willstudy this phenomenon further in laboratory scatteringexperiments and also through lidar measurements incirrus in Nevada.

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