Severe Storm Observations Using the Microwave Sounding Unit

Abstract

The microwave sounding unit (MSU) aboard the NOAA polar orbiting satellites contains four channels in the oxygen band, at 50.30, 53.74, 54.96 and 57.95 GHz, which receive thermal radiation originating primarily from four regions ranging from the surface to the lower stratosphere. This study focuses on the measurements obtained for a convective storm over the central United States beginning 12 April 1979. Temperature and precipitation effects are examined by comparing the MSU measurements with “clear column” brightness temperatures computed from radiosonde data. Decreases of up to 12 K from clear column values in the 53.74 GHz brightness temperature field identify precipitation regions. Measurements in the nonprecipitating areas correspond to temperatures near the 700 mb level where the channel has its maximum response. The 54.96 GHz upper tropospheric sounding channel (peaking near 300 mb) displays up to a 2 K decrease at the storm center, compared to neighboring measurements. This decrease around the storm center agrees with clear column values and is attributed to temperature changes due to evaporative cooling around the 1 50 mb tropopause level. For the 57.95 GHz stratosphere sounding channel (peaking near 90 mb) the measurements also compare well with the radiosonde data, although the measurements mainly reflect large-scale temperature variations rather than any local storm features. In addition to providing atmospheric data, the MSU detects surface temperature and emissivity variations in the most transparent channel at 50.30 GHz. By combining the “window” channel with the 53.74 6Hz channel, temperature effects are minimized and surface emissivity is derived in nonprecipitating areas. The emissivity measurements are useful for displaying the wet ground in the clearer areas behind the advancing storm system.