A COMPARISON OF WSR-88D REFLECTIVITIES, SSM I BRIGHTNESS TEMPERATURES, AND LIGHTNING FOR MESOSCALE CONVECTIVE SYSTEMS IN TEXAS .1. RADAR REFLECTIVITY AND LIGHTNING/

This is the first part of a two part study. Part I compares radar data from the League City, Texas, WSR-88D and cloud-to-ground (CG) lightni ng data for a set of eight mesoscale convective systems (MCSs), which occur al various stages of development along the upper Texas gulf coas t. Vertical profiles of radar reflectivity (VPRR) as well as plan view s and vertical cross sections are constructed to characterize the stru cture and relative strength of each MCS. The VPRR are also compared wi th similar profiles from tropical oceanic MCSs. The data show that in all cases the majority of negative CG lightning flashes are located ne ar high-reflectivity convective cores (>35 dBZ) in the mixed-phase reg ion (0 degrees C less than or equal to T greater than or equal to -20 degrees C). Growing or mature MCSs typically had larger negative flash counts and higher percentages of negative lightning (>80%) associated with convective cores than MCSs al later stages of their life cycle. Comparison of the median VPRR for the various MCSs showed that althoug h each case had high-reflectivity cores (45-55 dBZ) in the lowest 2-3 km, the more electrically active MCSs were characterized by smaller re flectivity lapse rates (decrease of reflectivity with height) in mixed -phase region than the cores in the remaining systems. Based on existi ng theories of charge separation, the observation of high negative fla sh counts coincident with convective cores having small reflectivity l apse rates in the mixed phase region is consistent with the presence o f large ice particles aloft. Positive CG flashes were mostly located i n low reflectivity (less than 30 dBZ near the -10 degrees C level) str atiform regions, independent of MCS life cycle stage or VPRR type. Sev eral cases with reports of large hail also had high positive flash den sities associated with high reflectivity cores. Part II of this study compares 85-GHz brightness temperatures from the Special Sensor Microw ave/Imager to lightning data for the same set of MCSs in Part I. Resul ts from both parts of this study strongly suggest that the presence of large ice particles aloft is the common linkage between MCSs with lig htning, with high radar reflectivity aloft, and large 85-GHz temperatu re depressions.