P42 Understanding cloud-top precipitation generating cells through high resolution modeling studies

Keeler, Jason M., University of Illinois (U of I) and National Center for Atmospheric Research (NCAR), Brian F. Jewett, Bob M. Rauber, Greg M. McFarquhar, U of I, Roy M. Rasmussen, Greg Thompson, Lulin Xue, and Changhai Liu, National Center for Atmospheric Research

A thorough understanding of the dynamics that modulate the development, maintenance, structure, and kinematics of cloud-top precipitation generating cells is crucial to understanding heavy snowfall in winter cyclones. These cells are hypothesized to be responsible for the initial generation of precipitation particles, which then undergo aggregation, accretion, and diffusional growth as they fall through stable frontal layers to the surface. Generating cells were ubiquitous in high-resolution remote sensing and in-situ observations made during the 2009-2010 Profiling of Winter Storms (PLOWS) field campaign. Observations from the Wyoming Cloud Radar (WCR) aboard the NSF/NCAR C-130, paired with thermodynamic analyses, indicate that generating cells have bases above stable frontal layers and tops at the tropopause. Such cells were observed in all 13 PLOWS IOPs with NSF/NCAR C-130 flight legs, and were sampled extensively atop the warm frontal and comma-head regions of these cyclones. Observed generating cell dimensions were ~0.75 – 1.5 km wide and ~1.5 – 2.0 km deep, with maximum vertical velocities of approximately +/- 3 m s-1.

Given the small horizontal and vertical dimensions of generating cells, simulations aimed at understanding their physics require modeling on the LES scale. This poster will discuss case study and planned ultra-high-resolution (50 m horizontal grid spacing) idealized Weather Research and Forecasting (WRF) simulations aimed at identifying the mechanisms that modulate the development and kinematics of generating cells. A unique aspect of this study is the wealth of data to which model output can be compared, ranging from atmospheric profiles (rawinsondes, X-band radar, 915 MHz profilers, and WCR) to in-cloud measurements of hydrometeor size distributions and mass contents. Careful selection of the vertical environmental profile, settings for domain boundaries, spacing of model vertical levels, and issues regarding microphysical and radiation treatments will be discussed.