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J. F. Potter

Abstract

Corrections for anisotropic scattering in a cloudy medium are added to a synthetic spectrum analysis by Belton, Hunten and Goody of CO2 bands and a water vapor line in the spectrum of Venus. It is found that to a good approximation the introduction of anisotropic scattering merely renormalizes the theoretical curves so that the corrections can be applied without recalculating the synthetic spectra. Since the line shapes and relative intensities are unaltered, derived pressures and temperatures remain the same. The corrected results indicate that the scattering mean free path in the Cytherian clouds resembles that for terrestrial cirrus clouds and that there is at least 20 times too little water vapor present to be in equilibrium with a water or ice cloud.

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A. E. Roche, J. B. Kumer, J. L. Mergenthaler, R. W. Nightingale, W. G. Uplinger, G. A. Ely, J. F. Potter, D. J. Wuebbles, P. S. Connell, and D. E. Kinnison

Abstract

This paper discusses simultaneous measurements of stratospheric CIONO2, HNO3, temperature, and aerosol extinction coefficient by the Cryogenic Limb Array Etalon Spectrometer (CLAES) on the NASA Upper Atmosphere Research Satellite (UARS), obtained over the period 9 January 1992 through 23 April 1993. The discussion concentrates on the stratosphere region near 21 km of particular interest to heterogeneously driven ozone depletion. For periods between 12 June and 1 September 1992 at latitudes poleward of about 60°S, when temperatures were below type I polar stratospheric cloud (PSC) formation thresholds throughout the lower stratosphere, CLAES observed high levels of PSCs coincident with highly depleted fields of both HNO3 and CIONO2. By 17 September, the incidence of PSCs had greatly diminished in the lower stratosphere, but both CIONO2 and HNO3 remained highly depleted. These observations are consistent with the removal of gaseous HNO3 through the formation of nitric acid trihydrate (NAT) particles and the removal of CIONO2 through heterogeneous reactions on the particle surfaces. They also suggest substantial denitrification of the lower Antarctic vortex through sedimentation of PSC particles. In the Northern Hemisphere winter of 1992/93 far fewer PSCs were observed in the Arctic lower-stratosphere vortex, which had shorter periods and more localized regions of cold temperatures. Both HNO3 and CIONO2 maintained much higher levels inside the Arctic vortex than those seen in the Antarctic throughout the winter/spring period. Following 28 February 1993 when Arctic vortex temperatures rose above 195 K, CIONO2 was observed in large quantities [>2.1 ppbv near 21 km] inside the vortex. The persistence of relatively high levels of HNO3 inside the Arctic spring vortex compared with the low levels seen in the Antarctic spring vortex suggest a much lower level of denitrification in the Arctic.

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