This paper presents analyses of the finescale structure of convection in the comma head of two continental winter cyclones and a 16-storm climatology analyzing the distribution of lightning within the comma head. A case study of a deep cyclone is presented illustrating how upper-tropospheric dry air associated with the dryslot can intrude over moistGulf air, creating two zones of precipitation within the comma head: a northern zone characterized by deep stratiform clouds topped by generating cells and a southern zone marked by elevated convection.Lightning,when it occurred, originated fromthe elevated convection.Asecond case study of a cutoff low is presented to examine the relationship between lightning flashes and wintertime convection. Updrafts within convective cells in both storms approached 6-8ms-1, and convective available potential energy in the cell environment reached approximately 50-250 J kg-1. Radar measurements obtained in convective updraft regions showed enhanced spectral width within the temperature range from -10° to -20°C, while microphysical measurements showed the simultaneous presence of graupel, ice particles, and supercooled water at the same temperatures, together supporting noninductive charging as an important charging mechanism in these storms. A climatology of lightning flashes across the comma head of 16 winter cyclones shows that lightning flashes commonly occur on the southern side of the commahead where dry-slot air ismore likely to overrun lower-level moist air. Over 90% of the cloud-to-ground flashes had negative polarity, suggesting the cells were not strongly sheared aloft. About 55%of the flashes were associated with cloud-to-ground flashes while 45%were in-cloud flashes.
|Original language||English (US)|
|Number of pages||24|
|Journal||Journal of the Atmospheric Sciences|
|State||Published - May 2014|
ASJC Scopus subject areas
- Atmospheric Science