GEOPHYSICAL RESEARCH LETTERS, VOL. 22, NO. 20, PAGES 2733-2736, OCTOBER 15, 1995 Preliminaryresults from POAM II: Stratospheric ozone at high northern latitudes C.E. Randall, 1D.W. Rusch, • R.M. Bevilacqua, 2J. Lumpe, 3T.L. Ainsworth? D. Debrestian, 3 M. Fromm? S.S. Krigman, 3 J.S. Hornstein, 2 E.P. Shettle, 2 J.J.Olivero, 4 and R.T. Clancy 5 Abstract. We present results from the first 18 months of measurements by the Polar Ozone and Aerosol Measurement experiment (POAM l'I) in the northernhemisphere. POAM II was launched on 25 September 1993, onboard the SPOT-3 satellite into a sun-synchronous polar orbit. The results pre- sented here spana latitude rangefrom about 55 ø to 71 ø, and an altitude range from about 18 to 35 km. Our resultscompare well with SAGE II data from 1986 to 1991. The observed vari- ability in the zonally-averaged ozone retrievals is due to a convolution of the true seasonal variation in ozone with the seasonal variation in latitude of the POAM II measurements. The seasonal variations in ozone at different altitudes reflect a transition between summer-time photochemical and dynamical control around 25 km. The longitudinal variation in ozone densities correlates well with the position of the measurement with respectto the polar vortex. Mixing ratios inside the vor- tex duringthe wintersof 1993-1994 and 1994-1995 are indica- tive of enhanced descent within the vortex, as well as other dynamical processes and possibly chemicaldepletion. Introduction In this paperwe present preliminary results from the POAM II (Polar Ozone and Aerosol Measurement) instrument onboard the SPOT-3 satellite. This satellite was launched on 25 September 1993, into a sun-synchronous 98ø-inclination orbit at an altitude of 833 kin. POAM II is a solar occultation device, and is described in detail by W. Glaccum et al. ("The Polar Ozone and Aerosol Measurement(POAM II) Instrument", sub- mitted to J. Geophys. Res., 1995). Briefly, the instrument consists of nine optical channels ranging in wavelengthfrom 353 nm to 1059 nm, with a 0.01o by 0.75ø field of view. The narrow aspect of the field of view is orientedperpendicular to the horizon and translates to a vertical resolution of about 1 km on the Earth's limb. Occultation measurements are made 14 times per day in each hemisphere. Longitudes of successive occultation events are separated by approximately 25.4 ø, so eachday a circle of lati- l Laboratory forAtmospheric and Space Physics, University of Colorado,Boulder 2 Naval Research laboratory, Washington 3CPI, Fairfax 4ERAU,Daytona Beach sSpace Science Institute, Boulder Copyright 1995 by theAmerican Geophysical Union. Paper number 95GL02649 0094-853 4/95/95 GL-0264 9503.00 tudeis covered in each hemisphere. The latitude of the observa- tions varies slowly throughout the year. Solar extinctionis monitored as the sun "rises" in the northern hemisphere, and as it "sets" in the southern hemisphere. The slant path trans- mission profiles thus obtained are invertedto obtaindensity profiles of 0 3, H20 andNO 2, aerosol extinction profries, and temperature profiles [Bevilacqua et al., 1995].Altitude profiles are interpolated onto potential temperature grids using NationalMeteorological Center(NMC) pressure and tempera- ture data. Mixing ratios are presently calculated using total densities derived from NMC data. Here we discuss only the northern hemisphere observations from November 1993 through March 1995, whichrange in lat- itude from about 55 ø to 71 ø. We concentrate on retrievals of ozone density at altitudes between about 18 and 35 km. Preliminary results from the southern hemisphere, where POAM trackedthe dissipation of the Antarcticozone hole in 70 I.I I I I I I.I I I.L..I. I I I I ........ '......"' Lot 1.2 ,'. •' , 0.8 '•'i" ':" .' "• 1120 3.0• :•, .•,•. , • .1 • • ß • ß "". ' ' . 850 2.0 ' ,' . . .. 4.0 '•, ß 2.0 8.o . soo • '" .,i . o N d M M d S N d M Figure l. POAM II ozone densities in the Northern hemi- sphere for potential temperatures of015200 K_• 1 650 K, 850 K and 1120 K. Densities are in units of 1 cm. Tickmarks on the horizontal axis denote months, beginning with November 1993. POAM II measurement latitudes are plotted in the top panel. 2733