Explicit and parameterized realizations of convective cloud systems in TOGA COARE

Convection and cloud processes are examined in a hierarchy of two-dimension al numerical realizations of cloud systems observed during the 19-26 Decemb er 1992 period of the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosp here Response Experiment. The hierarchy consists of cloud-resolving simulat ions at a 2-km resolution, and two sets of 15-km resolution simulations; on e attempts to treat convection explicitly and the other parameterizes conve ction using the Kain-Fritsch scheme. The Kain-Fritsch parameterization shows reasonable results but shortcomings are found in comparison with the cloud-resolving model. (i) The entraining plumes in the parameterization excessively overshoot the tropopause, which produces a cold bias mostly through adiabatic cooling. The attendant moist ure detrainment over-produces cirrus cloud. (ii) Because parameterized down drafts detrain at the lowest level they generate a surface cold bias. (iii) The scheme fails to represent the trimodal convection (cumulonimbus reachi ng the tropopause, cumulus congestus around the melting level, and shallow convection regimes) realized by the cloud-resolving simulation and also see n in observations. The lack of shallow convection and cumulus congestus lea ds to an overprediction of the low-level moisture. (iv) The simulations are sensitive to the magnitude of moisture feedback from the convective parame terization to the grid scale but less sensitive to whether the moisture is in vapor or condensed phase. These deficiencies are mostly a consequence of the single-plume model that represents updrafts and downdrafts in the parameterization scheme, along wi th the lack of a shallow convection scheme. A more realistic model of entra inment and detrainment that reduces overshoot and represents the cumulus co ngestus is required. Realistic downdraft detrainment and relative humidity are needed to improve the downdraft parameterization and alleviate the surf ace temperature bias.