Short Meridional Scale Anomalies in the Lower Stratosphere and Upper Troposphere

Abstract

Short-meridional scale anomalies (SMSA) in the lower stratospheric temperature field have been discovered in the analyses of Microwave Sounding Unit channel 4 data. In this paper, we investigate the time scales of these features, their presence in the u-wind, v-wind, and geopotential, and the heat and momentum fluxes resulting from the SMSA. The SMSA are not regularly propagating features. Latitudinal movement occurs in both northern and southern directions. Both eastward movement and stationarity are observed in the zonal direction. The anomalies are episodic, with an episode lasting from 1 to 3 weeks. They require a few days to grow, persist from a few days to two weeks, and then decay over a period of a few days. In addition to the temperature structure, SMSA are found in the zonal wind, meridional wind, and geopotential heights. The SMSA heat fluxes are small. The SMSA momentum fluxes, both the self momentum flux and that caused by interaction with other scales, are found to be substantial. The meridional gradient of these momentum fluxes constitutes an appreciable acceleration of the zonal mean wind. Finally, it is suggested that the SMSA are possibly caused by secondary effects of baroclinic disturbances.