Clearly the polar stratospheric cloud layer at 15 kilometers ismeasured by both the lidar and particle counter. Comparisonsof the lidar scattering ratio with the scattering ratio calculatedfrom particle-counter measurements has provided informationon the shape and composition of polar stratospheric cloud par-ticles (Deshler et al. 1991).

J. Hereford, S. Gabriel, and K. Hofmann were at McMurdofrom 22 August to 3 November, and T. Deshler from 22 Augustto 5 October. This work was supported by the National ScienceFoundation grant DPP 87-15913. The lidar measurements werefunded by the Italian Antarctic Program under the FAADRgrant. A. Adriani, G. Gobbi, S. Ugazio, and M. Viterbini wereat McMurdo from 21 August to 14 October 1990.

References

Deshler, T., D.J. Hofmann, J.V. Hereford, and C.B. Sutter. 1990. Ozoneand temperature profiles over McMurdo Station, Antarctica, in thespring of 1989. Geophysical Research Letters, 17, 151-154.

Deshler, T., and D.J. Hofmann. 1991. Ozone profiles at McMurdo Sta-tion, Antarctica, the austral spring of 1990. Geophysical Research Letters,18, 657-660.

Deshler, T., A. Adriani, D.J. Hofmann, and G.E Gobbi. 1991. Evidencefor denitrification in the 1990 Antarctic spring stratosphere: II Lidarand aerosol measurements. Geophysical Research Letters, 18, 1999-2002.

Gobbi, G.E. T. Deshler, A. Adriani, and D.J. Hofmann. 1991. Evidencefor denitrification in the 1990 Antarctic spring stratosphere: 1. Lidarand temperature measurements. Geophysical Research Letters, 18, 1995-1998.

Hanson, D., and K. Mauersberger. 1988. Laboratory studies of thenitric acid trihydrate: Implications for the polar stratosphere. Geo-physical Research Letters, 15, 855-858.

Hofmann, D.J., J.W. Harder, J.M. Rosen, J.V. Hereford, and J.R. Car-penter. 1989. Ozone profile measurements at McMurdo Station, Ant-arctica, during the spring of 1987 Journal Geophysical Research, 94,16,527-16,536.

Hofmann, D.J., S.J. Oltmans, and T. Deshler. 1991. Simultaneous bal-loonborne measurements of stratospheric water vapor and ozone inthe polar regions. Geophysical Research Letters, 18, 1011-1014.

Solomon, S. 1990. Progress towards a quantitative understanding ofAntarctic ozone depletion. Nature, 347, 347-354.

A study of polarstratospheric clouds

at the South Pole

J.M. ROSEN and N.T. KJOME

Department of Physics and AstronomyUniversity of Wyoming

Laramie, Wyoming 82071

S.J. OLTMANS

National Oceanic and Atmospheric Adminst rationClimate Monitoring and Diagnostics Laboratory

Boulder Colorado 80303

This paper describes research performed during austral win-ter 1990 taking balloonborne measurements of polar strato-spheric clouds and frost point in the nighttime stratosphereover Amundsen-Scott South Pole Station. Scientists believe thatpolar stratospheric clouds help establish conditions for ozonedestruction by removing nitric acid from the vapor phase andby providing a surface on which chlorine compounds can beactivated. Since polar stratospheric clouds form only at rela-tively low temperatures, the South Pole clearly is one of themost auspicious sites to study these clouds: the lowest strato-spheric temperatures, as well as significant ozone depletion,occur there.

A newly developed balloonborne instrument, a backscatter-sonde, was used to obtain the polar stratospheric cloud profiles.This instrument, described by Rosen and Kjome (1991a), hasbeen used to study polar stratospheric clouds in the north polar

vortex (Rosen, Oltmans, and Evans 1989) as well as to monitorstratospheric aerosols at midlatitude. The data product gener-ated by the backscattersonde is similar to that produced by lidarsystems. A balloonborne frost-point sensor with a successfulrecord in the Arctic and Antarctic also was used in this project(Rosen et al. 1988; Rosen, Oltmans, and Evans 1989; Rosen,Kjome, and Oltmans 1990).

The 1990 effort resulted in fewer soundings than initiallyanticipated, but in general, the program was successful. Majorfindings were published by Rosen and Kjome (1991b).

Preliminary results obtained with the frost-point sensorshowed that the entire troposphere and stratosphere inside thevortex become saturated as the atmosphere gradually cools.From combined frost-point and backscattersonde results, wecan deduce that continued cooling in winter causes not onlyextensive polar stratospheric cloud formation but also signifi-cant dehydration and denitrification in the stratosphere. Theextent to which dehydration and denitrification are exported tohigher latitudes is an important question and needs to be ad-dressed by soundings from other locations.

A second effort was carried out at the South Pole in australwinter 1991. Research was conducted to obtain more extensivedata on water vapor and polar stratospheric cloud developmentat selected critical periods. Soundings during initial polar strat-ospheric formation in May will define the necessary conditionsfor type I and type II polar stratospheric clouds. Monitoringcharacteristic low winter stratospheric frost points duringspring warming and final stages of the winter vortex provideda measure of the permeability of the vortex "bottle."

This work was supported by the National Science Foundationunder grant DPP 88-16563. Fred Schrom and Carl Groeneveldwere primarily responsible for instrument preparation andlaunching of the balloons at Amundsen-Scott Station. Theywere assisted by David Ayers and Kitt Hughes. Their effortsare greatly appreciated.

244 ANTARCTIC JOURNAL

References

Rosen, J.M, D.J. Hofman, J.R. Carpenter, and J.W. Harder. 1988. Bal-loon borne antarctic frost point measurements and their impact onpolar stratospheric cloud theories. Geophysical Research Letters, 15,859-862.

Rosen, J.M., S.J. Oltmans, and W.EJ. Evans. 1989. Balloon borne ob-servations of PSCs, frost point, ozone and nitric acid in the northpolar vortex. Geophysical Research Letters, 8, 791-794.

Rosen, J.M., NT. Kjome, and S.J. Oltmans. 1990. Observation of back-scatter, particle concentration and frost point in north polar vortexstratospheric clouds. Geophysical Research Letters, 17, 1271-1274.

Rosen, J.M., and N.T. Kjome. 1991a. Backscattersonde: A new instru-ment for atmospheric aerosol research. Applied Optics, 30, 1552-1561.

Rosen, J.M., and N.T. Kjome. 1991b. Balloon borne observations ofbackscatter, frost point and ozone in polar stratospheric clouds at thesouth pole. Geophysical Research Letters, 18, 171-174.

Lidar measurementsof the middle atmosphere

at South Pole

RICHARD L. COLLINS, DANIEL C. SENFT,and CHESTER S. GARDNER

Department of Electrical and Computer EngineeringUniversity of Illinois at Urbana-Champaign

Urbana, Illinois 61801

RAY W. SLITER

U.S. Geological SurveyMenlo Park, California 94025

The antarctic ozone hole has generated much interest in thecomposition and dynamics of the antarctic middle atmosphere.Ground-based measurements from the interior of the continentin winter are rare. In this article, we present lidar measure-ments of polar stratospheric clouds and mesospheric sodiumprofiles made on 25 June 1990 at the South Pole.

The University of Illinois at Urbana-Champaign (UIUC) so-dium lidar was installed at the Amundsen-Scott South PoleStation in December 1989. The lidar is composed of a flashlamp-pumped tunable dye laser that is tuned to 589 nanometers anda receiving system based on a 35-centimeter Cassegrain tele-scope. The system configuration was developed in 1986 for anairborne lidar campaign. Because the receiving system includesan astronomical-quality telescope and narrowband etalon fil-ters, the lidar can make measurements during both the day andnight. The etalon subsystem and its controller were designedby Fred Roessler and John Harlander from the University ofWisconsin. Although the UIUC sodium lidar does not includea large telescope nor the latest in laser technology, it is a ruggedand reliable system capable of measuring aerosol, stratospherictemperature, and mesospheric sodium profiles. Figure 1 showsthe total integrated photocount profile for 25 June 1990. Theprofile shows enhanced scattering from polar stratosphericclouds between 15 and 25 kilometers. Molecular scattering de-cays with altitude up to 65 kilometers. Resonant scattering fromthe sodium layer is evident from 75 to 110 kilometers.

Gardner, Sen,ft, and Collins installed the system at SouthPole during December 1989, and Collins wintered over to op-erate the system, with assistance from Sliter, through October

1990. The lidar was operated during cloud-free conditions, from17 December 1989 until 28 October 1990. A total of 420 hoursof lidar measurements were obtained.

Polar stratospheric clouds first formed in the last 10 days ofMay. Initially these clouds formed in thin layers about 1 kilo-meter thick close to an altitude of 22 kilometers. By mid-June,polar stratospheric clouds had formed distinct layers 1-3 kilo-meters thick over the entire 12-28 kilometer altitude region.This structure is illustrated in figure 2, with backscatter profilesplotted at 30-minute intervals over a 15-hour period. The finevertical structure evident on 25 June is typical of that observedthroughout the austral winter until September. Little change inthis vertical structure can be seen over the 14-hour observationperiod, indicating that the clouds, as they are moved overheadby advection, cover a wide horizontal expanse. By mid-Septem-ber, with the return of sunlight to the antarctic stratosphereand rising temperatures, the polar stratospheric clouds dissi-pated. Thin, broken polar stratospheric clouds were observeduntil mid-October.

Previous observations of the sodium layer have been limitedto interferometric, and lidar studies at Syowa station (69°S). Thesodium column abundance of approximately 6 x 10 atoms persquare centimeter is typical of that observed at Syowa in 1985(Nomura et al. 1987), but lower than that observed at Svalbard(78°N) in January 1987 (Gardner, Senft, and Kwon 1988) and atUrbana (40°N) over a 6-year period (1980-1986) (Gardner et al.1986). The height of the layer centroid, approximately 89 kilo-

University of Illinois South Pole Na Lidar25 June 1990

120

100

- 80

.604.,

4., 40

20

10 10 31o41o510 Total photocounts

Figure 1. Total lidar photocount profile 25 June 1990. Scatteringfrom polar stratospheric clouds, the neutral atmosphere, and me-sospheric sodium are evident. (km denotes kilometer.)

1991 REVIEW 245