Polarimetric radar analysis of convection in northwestern Mexico

The over-arching goal of the North American Monsoon Experiment (NAME) is to improve prediction of warm-season rainfall over North America, and especially over the southwestern portion of the U.S. where summer rains are forced by the North American Monsoon (NAM). For NAME, a comprehensive network of instrumentation was deployed during summer 2004 in order to document the variability of precipitation across the Sierra Madre Occidental (SMO) and adjacent coastal plain and Gulf of California (GoC), regions central to supplying moisture to the NAM and generating rain over the southwestern U.S. This report focuses on analysis of the ground-based radar observations collected by the S-Pol radar, an S-Band polarimetric Doppler radar operated by the National Center for Atmospheric Research (NCAR) during the NAME Enhanced Observing Period (EOP), which occurred during July-August 2004. The main dataset for the presented analyses consists of 3-D Cartesian grids, which include all major polarimetric variables (reflectivity, differential reflectivity, specific differential phase, linear depolarization ratio, and correlation coefficient) as well as fuzzy-logic-based hydrometeor identification.

Statistical and case study analyses of the S-Pol radar 3-D dataset are being done in order to extract the salient organizational characteristics and microphysical processes from precipitating systems (convective and mesoscale) in the NAME region. The dataset is being analyzed to derive statistics for warm rain vs. ice-based precipitation, and properties of the rain drop size distributions (DSDs), evaluated as functions of topography and diurnal cycle. In addition, mean statistics on the vertical reflectivity profile and microphysical structures are being computed and analyzed as functions of topography and diurnal cycle. The ultimate goal of this work is to understand, and to describe via a conceptual model (or perhaps models in the case of substantial heterogeneity), the microphysical characteristics of convection in the NAME region.