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Days Elapsed Between Collection and Analysis Figure 3. The effect of sample storage on mixing ratios of HCFC-22 in flasks from the South Pole and Cape Grim. The plotted residuals were obtained from a linear fit to the data at each station. A mean atmospheric mixing ratio of 95 ppt was determined for HCFC-22 during 1992 at the South Pole. Similar mixing ratios were observed at the South Pole and Cape Grim, suggesting that the mixing ratio of HCFC-22 is fairly constant in the Southern Hemisphere below 40 0 S. Finally, comparisons between results from the South Pole and Cape Grim suggest that HCFC-22 is stable in both dry and wet flask samples for extended periods. We thank the National Science Foundation and B. Mendonca for logistical support, and we thank personnel involved with flask sampling at both the South Pole and Cape Grim. This work was supported in part by the Atmospheric Chemistry Project of NOAA's Climate and Global Change Program.

trations. Nature, 359(6394), 403-405. Elkins, J.W., T.M. Thompson, T.H. Swanson, J.H. Butler, B.D. Hall, S.O. Cummings, D.A. Fisher, and A.G. Raffo. 1993. Decrease in the growth rates of atmospheric chlorofluorocarbons 11 and 12. Nature, 364(6440), 780-783. Fraser, P.J., S. Penkett, M. Gunson, R. Weiss, and F.S. Rowland. In press. NASA report on concentrations, lifetimes, and trends of CFCs, halons and related species. Washington, D.C.: U.S. Government Printing Office. Midgley, P.M. and D.A. Fisher. 1993. The production and release to the atmosphere of chlorodifluoromethane (HCFC-22). Atmospheric Environment, 27A(14), 2215-2223. Montzka, S.A., J.W. Elkins, J.H. Butler, T.M. Thompson, W.T. Sturges, T.H. Swanson, R.C. Myers, T.M. Gilpin, T.J. Baring, S.O. Cummings, G.A. Holcomb, J.M. Lobert, and B.D. Hall. 1992. Nitrous oxide and halocarbons division (chapter 5). In E.E. Ferguson and R. Rossen (Eds.), Summary report 1991: Climate Monitoring and Diagnostic Laboratory (Vol. 20). Boulder, Colorado: NOAA Climate Monitoring and Diagnostics Laboratory. Montzka, S.A., R.C. Myers, J.H. Butler, J.W. Elkins, and S.O. Cummings. 1993. Global tropospheric distribution and calibration scale of HCFC-22. Geophysical Research Letters, 20(8), 703-706. Montzka, S.A., M.R. Nowick, R.C. Myers, J.W. Elkins, J.H. Butler, S.O. Cummings, P.J. Fraser, and L.W. Porter. In press. NOAA/CMDL chlorodifluoromethane (HCFC-22) observations at Cape Grim.

Baseline 91. Rasmussen, R.A., and M.A.K. Khalil. 1983. Rare trace gases at the South Pole. Antarctic Journal of the U.S., 18(5), 250-252. Rinsland, C.P., D.W. Johnson, A. Goldman, and J.S. Levine. 1989. Evidence for a decline in the atmospheric accumulation rate of CHC1F2 (CFC-22). Nature, 337(6207), 535-537. Solomon, S., M. Mills, L.E. Heidt, W.H. Pollock, and A.F. Tuck. 1992. On the evaluation of ozone depletion potentials. Journal of Geophysical Research, 97(D1), 825-842. Steele, L.P., P.J. Fraser, R.A. Rasmussen, M.A.K. Khalil, T.J. Conway, A.J. Crawford, R.H. Gammon, K.A. Masarie, and K.W. Thoning. 1987. The global distribution of methane in the troposphere. Journal ofAtmospheric Chemistry, 5(2), 125-171. UNEP (United Nations Environmental Program). 1987. Montreal protocol to reduce substances that deplete the ozone layer report (final report). New York: UNEP. Zander, R., M.R. Gunson, C.B. Farmer, C.P. Rinsland, F.W. Irion, and E. Mahieu. 1992. The 1985 chlorine and fluorine inventories in the stratosphere based on ATMOS observations at 30 0 north latitude. Journal ofAtmospheric Chemistry, 15(2), 171-186.

References Butler, J.H., J.W. Elkins, B.D. Hall, S.O. Cummings, and S.A. Montzka. 1992. A decrease in the growth rates of atmospheric halon concen-

Atmospheric longwave radiation spectrum and near-surface atmospheric temperature profiles at South Pole Station VON P. WALDEN and STEPHEN

G. WARREN, Geophysics Program, University of Washington, Seattle, Washington 98195

radiation spectrum coincident with the state of the atmosphere for use in our climate studies at the University of Washington. The data set spans the full year from 14 January 1992 through 14 January 1993. We are attempting to determine the controls of the longwave radiation budget on the antarctic plateau and to offer spectral measurements for use in testing atmospheric radiation models and radiation codes in climate models.

he antarctic atmosphere is the coldest and driest on T Earth. The downward clear-sky emission to the ice sheet in winter averages about 75 watts per square meter, that is, less than half that for the subarctic winter standard atmosphere (figure 1 and the table). In a collaborative effort at South Pole Station with Frank J. Murcray and Renate Heuberger of the University of Denver, we have compiled a data set of surface-based measurements of the downward

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Wavelength, m

Approximate fluxes for different spectral regions (Wm-2)a

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Primary Spectral Antarctic Subarctic emitters region (cm-1)a winter winter Carbon dioxide 550-800 25 53 Water (window) 800-950,1100-1200 2 3 Ozone 950-1100 2 4 Methane, 1200-1375 2 7 nitrous oxide Water 0-550,1375-2500 48 109 Total (0-2500) 79 176

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a Units:

"W rn- 2 " denotes Watts per square meter. "cm-1" denotes wavenumber or inverse centimeter.

The downward infrared spectral radiance [6-17 micrometers (.tm)] was measured throughout the year using the University of Denver's Fourier-transform interferometer. Over 500 spectra were obtained, about half under cloud-free conditions. Broadband longwave irradiance was measured with an Eppley pyrgeometer. Coincident vertical profiles of temperature, ozone, and water vapor were obtained from routine radiosonde launches by the South Pole Weather Office and ozonesonde launches by the National Oceanic and Atmospheric Administration (NOAA). On a few occasions, NOAA launched a frost-point hygrometer which yields more accurate water vapor profiles above 500 millibars than do the routine Weather Office sondes [Oltmans (NOAA) personal communication]. Cloud information is available from visual observations, supplemented by measurements from a laser ceilometer and by photographs during the sunlit months. Good temporal coverage from the laser ceilometer is available for April, June, mid-to-late August, September, and early October. The possibility of using the ceilometer data to infer cloud base height and cloud optical depth is being investigated. Sizes and shapes of atmospheric ice crystals, cloud particles, and blowing snow are being studied by photomicroscopy, from which size distributions will be derived. Parts of the infrared spectrum are sensitive to the atmospheric temperature profile in the lowest 200 meters (m), where in winter a strong temperature gradient is usually found. The radiosonde carried by a rapidly rising balloon does not measure these temperatures accurately because the response time of its thermistor is about 6-8 seconds (s). To quantify this error, in collaboration with the South Pole Weather Office, we flew a radiosonde on a tethered kite on nine occasions in August and September 1992, immediately prior to the routine launch of the same sonde. The kite was stopped at specified levels long enough for the pressure and temperature sensors to equilibrate. The response time for the thermistor was determined independently by moving the radiosonde from a warm room into the cold air and measuring its temperature as it equilibrated. The typical e-folding

600 800 1000 1200 1400 1600 Wavenumber, cm1

Figure 1. Downward infrared spectra at the Earth's surface, under clear sky, from three different terrestrial atmospheres. The antarctic winter spectrum was measured at South Pole Station on 21 May 1992. The subarctic winter and tropical spectra are model simulations using MODTRAN. (The tropical spectrum is included for visual comparison only.) The viewing zenith angle is 600; spectral resolution is 1 inverse centimeter (cm- 1 ). Radiance is in milliwatts per square meter per steradian per inverse centimeter. response time of 6-8 s explains the radiosonde temperature error of a few degrees we observed between the kite and the balloon (figure 2). The relatively warm temperature reported as the second reading from the radiosonde balloon flight is probably due to releasing the sonde immediately after bringing it out of a warm room. This value is actually the first value reported by the sonde, but in the data stream sent out to the global telecommunications network a value is added to the beginning, which comes from the 2-m thermometer upwind of the station (-63°C, in this case). We will use this information to develop a method for correction of the radiosonde temperature profiles throughout the winter. The infrared radiation measurements are being summarized by defining several spectral regions where different gases are the major emitters. The table shows an example of the approximate total irradiance in each of these regions for a clear-sky case for the antarctic winter compared with calculations for the subarctic winter using MODTRAN2 (Berk, Bern-

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stein, and Robertson 1989). Seasonal cycles of the radiation in these spectral bands yield information on the controls of the longwave radiation budget throughout the year, the strong surface-based temperature inversion playing a major role in the spectral regions of carbon dioxide and water vapor. Radiation model simulations using various spectral and vertical resolutions are being compared to the downward spectral radiance measurements. Selected well-calibrated radiance spectra with coincident vertical profiles of atmospheric constituents for clear-sky scenes will be offered as case studies for the Intercomparison of Radiation Codes used in Climate Models (ICRCCM) (Ellingson, Ellis, and Fels 1991). We would like to thank Kitt Hughes and Bob Koney of the South Pole Weather Office for their help in the radiosonde thermistor experiments. This research was supported by National Science Foundation grant OPP 91-20380.

3000

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References -65 -60 -55 -50 45 40

Berk, A., L.S. Bernstein, and D.C. Robertson. 1989. MODTRAN: A moderate resolution model for LOWTRAN 7 (AFGL-TR-89-0122). Hanscom AFB, Massachusetts: Air Force Geophysics Laboratory. Ellingson, R.G., J. Ellis, and S. Fels. 1991. The intercomparison of radiation codes used in climate models: Long wave results. Journal of Geophysical Research, 96(D5), 8929-8953. Oltmans, S. 1993. Personal communication.

Temperature, C

Figure 2. Temperature profiles from a radiosonde on a tethered kite and on a routine balloon launch from 28 August 1992 at South Pole Station. Also included is the 2-m air temperature that is inserted as the lowest temperature in the South Pole Weather Office radiosonde profile.

Relative elevations of meteorological facilities at South Pole Station STEPHEN G. WARREN, Department ofAtmospheric Sciences, University of Washington, Seattle, Washington 98195 MICHAEL STARBUCK, U.S. Geological Survey, Mid-Continent Mapping Center, Rolla, Missouri 65401 CARL GROENEVELD, Climate Monitoring and Diagnostics Laboratory, National Oceanic and Atmospheric Administration, Environmental Research Laboratories, Boulder, Colorado 80303

every year as the surface snow accumulates and rises against the meteorological towers. The heights of instruments of the Weather Office (radiosonde launching deck, 2-m thermometers, and barometer) were surveyed by Michael Starbuck and Stephen Warren on 5-8 October 1992, relative to benchmarks established by the U.S. Geological Survey (USGS). The heights of the laser ceilometer on the Clean Air Facility and thermometers on the 23-rn meteorological walk-up tower were surveyed by Carl Groeneveld and Stephen Warren on 22 November 1992. The locations of these instruments are indicated in the figure. The surveys employed a standard leveling technique and obtained relative elevations to within 2 centimeters (cm), which are shown in the table. In a personal communication, Jerry Mullins of USGS told us that

e near-surface climate of the antarctic plateau is characterized in winter by a strong temperature inversion. Temperature-dependent processes can, therefore, vary over vertical distances of only a few meters, for example, the formation of diamond-dust ice crystals and the atmospheric emission of infrared radiation. At South Pole Station in the winter of 1992, the air at 21 meters (m) height was usually 3-4°C warmer than at 2 m height and, on occasion, was as much as 19 degrees warmer. Detailed information about the temperature profile near the surface is needed to interpret the measured infrared radiation spectra and to evaluate the turbulent heat fluxes. At South Pole Station this profile can be obtained from radiosonde launches, together with temperature measurements at the snow surface, at the standard reporting height 2 m above the surface, and near the top of the 23-rn meteorological tower. The height of the radiosonde-launching deck has changed since its installation in the summer of 1974-1975, relative to the 2-rn thermometers that are raised

the 1991 elevation at South Pole Doppler Benchmark "Ken Murphy" is 2833.51 m. This is an estimated value based on the

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