VISSR Atmospheric Sounder (VAS) Simulation Experiment for a Severe Storm Environment

Abstract

The GOES satellites launched in the 1980's are carrying an instrument called the VISSR Atmospheric Sounder (VAS), which is designed to provide temperature and moisture profile-sounding capability for mesoscale weather systems. As a controlled study of this capability, VAS radiance fields are simulated for pre-thunderstorm environments in Oklahoma to demonstrate three points: 1) significant moisture gradients can be seen directly in images of the VAS channels, 2) temperature and moisture profiles can be retrieved from VAS radiances with sufficient accuracy to delineate the major features of a severe storm environment, and 3) the quality of VAS mesoscale soundings improve with conditioning by local weather statistics. Even though the simulated VAS soundings have the usual limitations in absolute accuracy, gradient strength and vertical resolution (especially in the lower tropospheric moisture retrievals), it is still possible to retrieve mesoscale regions of potential instability from the synthetic VAS radiances for a mostly clear pre-thunderstorm environment. The rms tropospheric profile errors are ±1°C and ±25% in temperature and mixing ratio, respectively. The results represent the optimum retrievability of mesoscale information from VAS radiances without the use of ancillary data. The simulations suggest that VAS data will yield the best soundings when a human being classifies the scene, picks relatively clear areas for retrieval, and applies a ?local? statistical database to resolve the ambiguities of satellite observations in favor of the most probable atmospheric structure.