AN EVALUATION OF DEEP CONVECTIVE MIXING IN THE GODDARD CHEMICAL-TRANSPORT MODEL USING INTERNATIONAL-SATELLITE-CLOUD-CLIMATOLOGY-PROJECT CLOUD PARAMETERS

The simulation of deep convective mixing in the Goddard Chemical Trans port Model (GCTM) is evaluated by comparing 1990-1992 distributions of upper tropospheric convective mass flux and cloud top pressure from t he Goddard Earth Observing System data assimilation system (GEOS-1 DAS ) with deep convective cloud fields from the International Satellite C loud Climatology Project (ISCCP). Deep convective mixing in the GCTM i s calculated using convective information from the GEOS-1 DAS. Therefo re errors introduced when deep convection is parameterized in the GEOS -1 DAS affect the distribution of trace gases in the GCTM. The locatio n of deep convective: mixing in the tropics is fairly well simulated, although its north-south extent is overestimated by >5 degrees. The fr equency of deep convective mixing also appears to be overestimated in the tropics, resulting in GCTM-calculated upper tropospheric concentra tions of carbon monoxide in the tropics that are larger and less varia ble than those observed. The spatial extent of deep convective mixing in the subtropics is overestimated at several locations including the Caribbean throughout the year and the South Pacific Convergence Zone d uring June-August. The extent of deep convection is underestimated ove r midlatitude marine storm tracks. DAS-calculated cloud top pressures differ from ISCCP cloud top pressures by less than one-half a GCTM lay er (35 hPa) at most longitudes in the tropics; however, cloud top pres sures are overestimated by more than 35 hPa (i.e., the vertical extent of deep convection is underestimated) over wintertime midlatitude sto rm tracks and the Indian Ocean and underestimated by more than 35 hPa at locations that include the Gulf of Mexico during December-February and central South America during June-August.