MESOSPHERIC TEMPERATURE INVERSIONS AS SEEN BY ISAMS IN DECEMBER 1991

A large number of mesospheric temperature inversion layers have been o bserved locally in recent decades, notably by the network of French li dars. It is shown in this paper that the Improved Stratospheric and Me sospheric Sounder on board the Upper Atmosphere Research Satellite is able to detect the presence of temperature inversions, and thus allows the study of their occurrence and characteristics on a global scale. During December 1991, inversions of large amplitude (greater than 20 K ) are seen almost every day, especially in mid latitudes, with extent varying typically from 10(5) to 10(6) km(2). Several particularly larg e inversions were observed at the end of the month. Their correlation with assimilated stratospheric winds is consistent with the interpreta tion that gravity waves propagate unfiltered through the stratosphere in the regions of strong winds, and break in the mesosphere.