Stratospheric Temperature Variations in Autumn—Northern and Southern Hemispheres Compared

SIGMUND FRITZ National Environmental Satellite Service, NOAA, Suitland, Md.

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RAYMOND M. McINTURFF National Weather Service, NOAA, Hillcrest Heights, Md.

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Abstract

The Satellite Infrared Spectrometer onboard Nimbus 3 has a 5 cm−1 spectral interval centered at 669.3 cm−1 (15µm). The stratosphere contributes nearly all the outgoing terrestrial radiation at this frequency, and, consequently, the observed radiances provide a measure of a weighted mean temperature of the upper 100 mb of air. Maps of the 669.3 cm−1 channel radiances indicate layer-mean stratospheric temperature patterns. Such patterns are studied for both the Northern Hemisphere and the Southern Hemisphere, mainly for the periods of transition from summertime to wintertime circulation regimes. The periods under consideration are of special interest because pockets of warm air remain in spite of the seasonal cooling due to decreasing solar radiation over each hemisphere. Changes in location and intensity of both cold and warm areas are described. The principal region of high radiance (warm air) over the Northern Hemisphere, traditionally associated with the Aleutian anticyclone, was found to be mainly over Siberia. A corresponding warm region over the Southern Hemisphere was found, and its mean position during the transition period is only 25° of longitude farther to the west. Possible explanations for these positions are discussed.

Abstract

The Satellite Infrared Spectrometer onboard Nimbus 3 has a 5 cm−1 spectral interval centered at 669.3 cm−1 (15µm). The stratosphere contributes nearly all the outgoing terrestrial radiation at this frequency, and, consequently, the observed radiances provide a measure of a weighted mean temperature of the upper 100 mb of air. Maps of the 669.3 cm−1 channel radiances indicate layer-mean stratospheric temperature patterns. Such patterns are studied for both the Northern Hemisphere and the Southern Hemisphere, mainly for the periods of transition from summertime to wintertime circulation regimes. The periods under consideration are of special interest because pockets of warm air remain in spite of the seasonal cooling due to decreasing solar radiation over each hemisphere. Changes in location and intensity of both cold and warm areas are described. The principal region of high radiance (warm air) over the Northern Hemisphere, traditionally associated with the Aleutian anticyclone, was found to be mainly over Siberia. A corresponding warm region over the Southern Hemisphere was found, and its mean position during the transition period is only 25° of longitude farther to the west. Possible explanations for these positions are discussed.

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