Comparison of two-dimensional cloud resolving model simulations with shipboard radar observations during TOGA COARE

West Pacific warm pool cloud physical and radiative properties simulated for a 32-day period using the National Center for Atmopsheric Research (NCAR) two-dimensional cloud-resolving model (CRM) are rigorously compared to shipboard radar data observations. The radar data were obtained using the Massachusetts Institute of Technology (MIT) and Tropical Ocean-Global Atmosphere (TOGA) C-band Doppler radars on board the R/V Vickers and PRC Xianyanghong (PRC #5) respectively, as operated during the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean-Atmopshere Response Experiment (COARE). Cloud simulations were carried out during the period 5 December 1992 to 5 January 1993.

Comparisons were performed using several different analysis techniques. Diurnal hourly-mean rainfall rates were used to test how well the model simulated the early morning and late afternoon rainfall maxima. Percent frequency distributions of rainfall rate were computed to determine how well the model simulated the distribution of rainfall rates throughout the period. Model mixing ratio values were used to derive reflectivities for a more direct comparison to the observed reflectivity values. These derived reflectivity fields were then compared using cumulative frequency by altitude diagrams (CFAD). After a convective and stratiform partitioning scheme was applied to the reflectivity data, an analysis of the modality of the maximum convective column height of the 30 dBZ contour was performed.

Results indicate that the ice microphysical parameterizations were too simple and thus unusable to accurately simulate the ice phase processes. Model-derived reflectivity values near and below the melting layer were much too high as a result of the erroneous simulation of the ice phase processes and liquid precipitation in the warmer region below. The CRM did simulate the general patterns observed in the radar data rather well. In addition, results of the comparison showed good agreement in the diurnal cycle of rainfall rates over the entire period.