Airborne Radar Measurements of Vertical Air Motion in the Comma Head of Winter Cyclones

Understanding processes in the comma head of winter cyclones is important due to the high impact weather within the comma head. Improved knowledge will allow better interpretation of observations and improved simulation of cold season extratropical cyclones. Data from the 2009-2010 Profiling of Winter Storms (PLOWS) project are utilized here to determine how the radar observations of mesoscale structures relate to the comma head as a whole.

This study utilizes data collected by the airborne University of Wyoming Cloud Radar (WCR) aboard the NCAR/NSF C-130 in the comma head of three cyclones observed during PLOWS. The high 30 m resolution of the WCR allows the detection of mesoscale circulations such as the several kilometer deep convective updrafts of up to 5 ms^-1 within the upper level dry intrusion, as well as the smaller scale cloud top generating cells with horizontal sizes ranging from 0.5 to 1.5 km and vertical motions in excess of 1 m s^-1. In this presentation, we use contoured frequency by altitude diagrams (CFADs) to show distributions of vertical radial velocity measured by the WCR and to relate the measured vertical radial velocities to vertical air motion. Data from the operational Rapid Update Cycle (RUC) model is used in conjunction with WCR data to show how reduced stability above the warm front leads to the growth of the deep convection within the dry intrusion, and to cloud top generating cells. We relate the transverse frontogenesis circulation to the WCR observed larger scale precipitation morphology. Finally, we show that much of the precipitation outside of the dry slot convection and the generating cells is falling near its terminal velocity, indicating a lack of significant broad-scale vertical motion within the stratiform regions.