Relation of Satellite-Based Thunderstorm Intensity to Radar-Estimated Rainfall

Abstract

Quantitative observations of thunderstorms in the midwest United States made with short-interval (5 min) geosynchronous satellite data are examined in relation to concurrent digital radar observations for one case study over a limited area. Individual thunderstorms are defined in the satellite infrared (IR) data by the location of relative minima in the equivalent blackbody temperature (TBB) field. In a large majority of cases, these satellite-defined thunderstorms coincide with individual radar echoes. This agreement allows comparison of digital satellite and radar data for individual thunderstorms. The evolution of individual thunderstorms in terms of radar echo and satellite-observed cloud features is examined. An examination of a number of storms indicated that the first low-level radar echo (18 dBZ) appeared when the satellite observed cloud-top minimum TBB had a mean of 246 K (7.4 km). As the storms evolve, larger reflectivities appear as the cloud tops penetrate upward to colder temperatures. Larger reflectivity values (>50 dBZ) begin as the storms approach and penetrate the tropopause. Maximum radar reflectivity is shown to be correlated with satellite-based estimates of thunderstorm intensity. Thunderstorm top ascent rates in the 235-240 K (?8.8 km) region indicate the intensity of the initial storm updraft and are correlated with the maximum storm reflectivity with weak cells (-dTBB/dt of 1 K min?1) having maximum reflectivity of 30?40 dBZ and strong cells (3?4 K min?1) having echoes of ≥50 dBZ. The minimum TBB observed during the lifetime of the storm (Tmin), indicative of maximum storm top height, is also correlated to maximum storm rainfall. Storms with tops colder (higher) than the tropopause (212 K) have the highest rainfall rates in the severe storm situation examined here. The parameter Tmin is also very well related to maximum volume rain rate as estimated from the radar data. Storms observed to reach temperatures lower than the tropopause temperature had volume rain rates of the order 103 m3 s?1, compared to 102 m3 s?1 for weaker storms.