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  • Author or Editor: U. O. Farrukh x
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G. S. Kent, C. R. Trepte, U. O. Farrukh, and M. P. McCormick

Abstract

Aerosol extinction data obtained by the Stratospheric Aerosol Measurement II (SAM II) satellite instrument during the 1979/80 Northern Hemisphere winter season have been analyzed in relation to the cyclonic polar vortex. A synoptic approach has been employed to study the behavior of aerosol extinction ratio and optical depth between altitudes of 8 and 30 km as a tracer of mean atmospheric motions in and near the polar vortex. As the polar vortex intensifies, a gradient of extinction ratio is established across the polar-night jet stream, which is associated with subsidence within the vortex. Maximum subsidence occurs at the center of the vortex. Calculated descent rates relative to isentropic surfaces are of the order of 8 × 10−4 m s−1 near 20 km, at the center of the vortex between September and December. Below an altitude of 14 km, taken as the base of the vortex, and outside the vortex, horizontal movements occur freely, masking any systematic vertical motions. Extinction enhancements by polar stratospheric clouds and changes produced by sudden warmings in the second half of winter have prevented a similar study for this period. An estimate of the aerosol mass transferred downward through the base of the vortex for the entire season is 7000 tonnes. Comparison of the inferred stratospheric motions with earlier studies using radioactive tracers shows good agreement.

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G. S. Kent, U. O. Farrukh, P. H. Wang, and A. Deepak

Abstract

The SAGE-I and SAM-II satellite sensors were designed to measure, with global coverage, the 1 μm extinction produced by the stratospheric aerosol. In the absence of high altitude clouds, similar measurements may be made for the free tropospheric aerosol. Median extinction values at middle and high latitudes in the Northern Hemisphere, for altitudes between 5 and 10 km, are found to be one-half to one order of magnitude greater than values at corresponding latitudes in the Southern Hemisphere. In addition, a seasonal increase by a factor of 1.5–2 was observed in both hemispheres, in 1979–80, in local spring and summer. Following major volcanic eruptions, a long-lived enhancement of the aerosol extinction is observed for altitudes above 5 km.

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