Radar and electrical characteristics of convection observed during MCTEX

The Maritime Continent Thunderstorm Experiment (MCTEX) was conducted over the Tiwi Islands 50-100 km north of Darwin, Australia, during November-December 1995. Two MCTEX cases are presented in this study. First, the convective evolution is summarised, including the processes by which shallow precipitating cumulus clouds evolved into electrically active, deep convection. Using multiparameter radar (C-band; 5.3 cm) estimates, the history of precipitation-sized ice and liquid water is compared to lightning-flash rates. In this context, the non-inductive graupel-ice particle charging theory is evaluated. For both case study days, the first deep convection was anchored to the leeward coast sea-breeze front. First, shallow precipitating cells originating from the island interior created evaporatively cooled pools that focused surface convergence along their perimeter. Rapid convective development ensued as these cool pools approached the sea-breeze front, triggering higher order cloud mergers along the sea-breeze front. This vigorous deep convection produced an extensive cold pool with convection persisting along its western edge where the environmental wind shear enabled more vertically oriented updraughts. The temporal evolution of mixed-phase graupel mass was compared to lightning-flash rates. Lightning was detected only after convective cells produced significant quantities of millimeter-sized ice particles. Lightning was not detected in predominately warm-rain cells. Furthermore, fluctuations in graupel mass were correlated with fluctuations in lightning-flash rates. Cloud-to-ground lightning was found to be closely tied to the mixed-phase graupel mass, consistent with the non-inductive graupel-ice particle charging theory. Polarimetric radar estimates also suggested that graupel formed as raindrops were lofted above the freezing level by convective updraughts.