Large-Scale Temperature Changes in the Stratosphere Observed from Nimbus III

Abstract

The radiances in the CO₂ band centered at 669.3 cm⁻¹ (15 μ), measured by the satellite infrared spectrometer on Nimbus III, are examined. These radiances are a measure of a weighted mean temperature of approximately the upper 100 mb of the atmosphere. A new result shows that stratospheric warmings in the winter hemisphere are accompanied by simultaneous coolings in the stratosphere of the tropics and the summer hemisphere. These out-of-phase changes of stratospheric temperature may be explained by heat transfer changes caused by variations of the meridional circulation and large-scale eddies. The out-of-phase relationship in stratospheric temperature is evident in the radiances when averaged around latitude circles, although the changes observed on certain dates do not occur at all longitudes. The isotherms in the stratosphere tend to be more nearly circumpolar on a day with minimum radiance. On a day when the warming reached its maximum, the higher radiances occur only in one part of the latitude zone. Widespread cooling in the tropics takes place while the warming progresses in the winter hemisphere, and eventually it occurs at all longitudes in a broad latitudinal zone in the tropics and the summer hemisphere. The atmosphere seems to act like a standing wave in which the amplitude of the temperature changes are larger in the middle and high latitudes of the winter hemisphere than in the tropics and summer hemisphere. The nodal point moved somewhat with the season, between about 25–45S, during the Southern Hemisphere winter. Radiance data also show the seasonal trend of stratospheric temperature from 8ON to 80S. The expected seasonal variation is found in middle and high latitudes; however, the winter radiances at 80S are not as cold in relation to the winter radiances at 8ON as might be expected from climatological temperatures up to 30 mb.