Short meridional scale anomalies in the lower stratosphere and upper troposphere
Short meridional scale anomalies (SMSA) in the lower stratospheric temperature field were recently discovered by Stanford and Short (1981) in the analyses of Microwave Sounding Unit (MSU) channel 4 data. Newman and Stanford (1983) further elucidated the properties of these anomalies, and their work is duplicated herein;It is shown that 1000-3000 km meridional scale anomalies with 10,000-40,000 km zonal scales exist in the MSU channel 4 data, and the existence of these anomalies is independent of the analysis scheme. Additionally, these anomalies are observed in TIROS-N satellite MSU channel 3 data, as well as Nimbus 6 satellite Scanning Microwave Sounder (SCAMS) data. The atmospheric origin of the SMSA is established through the correlation of MSU channel 4 brightness temperatures with brightness temperatures simulated from European Centre for Medium Range Weather Forecasting (ECMWF) analyses, National Meteorological Center (NMC) analyses, and radiosonde data. These conventional data simulations correlate well with the MSU channel 4 data. The independence of the conventional and satellite data establishes that the SMSA are not due to instrumental effects;The horizontal, vertical, and time structure of the SMSA are studied using both satellite and conventional data. The SMSA exist in both hemispheres, have zonal scales of 10,000 to 40,000 km, and are strongest in the mid-latitudes. The vertical SMSA temperature structure shows maxima in the lower stratosphere and upper troposphere with a node between these maxima in the 200 to 400 mb region. The SMSA are not regularly propagating features. They are found to be episodic, with an episode lasting from 1 to 3 weeks;In addition to the temperature structure, the SMSA are also found in the zonal wind, meridional wind, geopotential heights, and possibly the low-level cloud data. Heat and momentum fluxes are investigated, and it is found that the fluxes due to the SMSA are not the most important parts of the total heat and momentum flux budgets. However, the portions due to the SMSA are not inconsequential. Finally, a possible forcing mechanism due to secondary effects of baroclinic instabilities is outlined for the SMSA.