Assessment of VAS Soundings in the Analysis of a Preconvective Environment

Abstract

Retrievals from the VISSR Atmospheric Sounder (VAS) an combined with conventional data to assess the impact of geosynchronous satellite soundings upon the analysis of a pre-convective environment over the central United States on 13 July 1981. VAS retrievals of temperature, dewpoint, equivalent potential temperature, precipitable water, and lifted index are derived with 30 km resolution at 3 hour intervals. When VAS fields are combined with analyses from conventional data sources regions with convective instability are more clearly delineated prior to the rapid development of the thunderstorms. The retrievals differentiate isolated areas in which most air extends throughout the lower troposphere (and are therefore more conducive for the development of deep convective storms) from those regions where moisture is confined to a thin layer near the earth's surface (where convection is less likely to occur). The analyses of the VAS retrievals identify significant spatial gradients and temporal changes in the thermal and moisture fields, especially in the regions between radiosonde observations. The detailed analyses also point to limitations in using VAS data. Even with nearly optimal conditions for passive remote sounding (generally clew skies, minimal orographic effects, and a rapidly changing moisture field), the VAS retrievals were still degraded in some regions by small clouds which are unresolved in the infrared imagery. These analyses, however, demonstrate that the geosynchronous VAS can be used in a case study mode to produce high-resolution spatial and temporal measurements that are useful for the quantitative analysis of a cloud-free pre-convective environment.