Microphysical Structure of Generating Cells atop Comma-Head Clouds within Winter Cyclones

The microphysical structure of cloud-top convective generating cells at temperatures between -10 and -55°C across the comma head of 11 continental cyclones was determined using data collected by the W-band University of Wyoming Cloud Radar and in-situ instrumentation aboard the NSF/NCAR C-130 during the 2009-10 Profiling of Winter Storms (PLOWS) project.

Ice particle number concentrations averaged 1.9 times larger inside generating cells compared to outside, and derived ice water contents and median mass diameters averaged 2.2 and 1.1 times larger in cells. Supercooled water was directly measured at temperatures of -31.5°C and above, within and between generating cells. The median and 95^th percentile liquid water content increased from ~0.09 to 0.12 g m^-3 and from 0.14 to 0.28 g m^-3, respectively, as temperature approached -10°C.

The enhanced concentrations in cells are consistent with greater ice production in convective updrafts, with the increases in mass and diameter demonstrating that generating cells provide environments favorable for enhanced particle growth. The impact of water saturation and supercooled water in the cells was evident in particle imagery, with rapid particle growth by diffusion and sometimes riming apparent in addition to aggregational growth. Turbulent mixing acted to lessen the observed differences between the cells and surrounding regions with supercooled water observed both within and between cells, similar habits within and between cells, and the appearance of rimed particles even in ice-phase conditions. Results will be presented for a case study observed on 15 Feb. 2010 and for statistical analyses of the entire PLOWS data set.