Stability and Charging Characteristics of the Comma-head Region of Continental Winter Cyclones

This paper presented radar analyses of the fine-scale structure of convection within the comma-head of continental winter cyclones, and a 16 storm climatology analyzing the distribution of lightning across the cyclone's comma-head. The work, based on detailed measurements from the Profiling of Winter Storms campaign, uses data from the University of Wyoming Cloud Radar, the University of Alabama 915 MHz profiler, and two sounding Systems, supplemented by measurements from the National Lightning Detection Network. The analyses show that upper tropospheric dry air associated with a cyclone's dry slot can intrude over the warm front of strong cyclones, creating two zones of precipitation within the comma head, a northern zone characterized by deep stratiform clouds and capped by cloud top generating cells, and a southern zone marked by elevated convection. Lightning, when it occurs, appears to originate from the elevated convection within the southern zone. Updrafts within the convective cells in the southern zone can approach 6-8 m s-1, and convective available potential energy measured in the environment of the cells can reach ~50-250 J Kg-1. Microphysical measurements within the convective updrafts showed the simultaneous presence of graupel, ice particles, and supercooled water within the temperature range 10°C to 20°C, supporting non-inductive charging as an important mechanism charging these winter storms. Over 90% of the cloud-to-ground discharges in the 16 winter cyclones were negative polarity, suggesting the cells were not strongly sheared aloft. About 55% of the flashes were associated with cloud-to-ground strikes while 45% were in-cloud discharges.