Improving Simulations of Convective Systems from TRMM LBA: Easterly and Westerly Regimes

• DOI: 10.1175/jas3879.1
• Publication Date: 2007-04-16T19:48:27Z
• Authors: S. Lang; W-K. Tao; J. Simpson; R. Cifelli; S. Rutledge; W. Olson; J. Halverson
• Keywords: Graupel; Squall line; Free convective layer; Cloud physics

Abstract The 3D Goddard Cumulus Ensemble model is used to simulate two convective events observed during the Tropical Rainfall Measuring Mission Large-Scale Biosphere–Atmosphere (TRMM LBA) experiment in Brazil. These epitomized type of systems that formed distinctly different environments TRMM LBA. 26 January 1999 squall line within a sheared low-level easterly wind flow. On 23 February 1999, convection developed weak westerly flow, resulting weakly organized, less intense convection. Initial simulations captured basic organization and intensity each event. However, improvements resolution microphysics produced better as compared observations. More realistic diurnal growth was achieved by lowering horizontal grid spacing from 1000 250 m. This gradual transition shallow deep occurred over span hours opposed an abrupt appearance Eliminating dry graupel bulk scheme effectively removed unrealistic presence high-density ice simulated anvil. comparisons with radar reflectivity data using contoured-frequency-with-altitude diagrams (CFADs) revealed snow contents were too large. excessive reduced primarily collection efficiency cloud water resulted further agreement transfer cloud-sized particles precipitation-sized appears be efficient original scheme. Overall, these changes lead more precipitation model. artifacts due inability one-moment allow for size sorting, such rain evaporation, also found but could not resolved without moving two-moment or bin As result, rainfall histograms underestimated occurrence high rates radar-based histograms. Nevertheless, improved signature should latent heating retrievals result both convective–stratiform separation well physically hydrometeor structures radiance calculations.