TWP-ICE global atmospheric model intercomparison: Convection responsiveness and resolution impact

Results are presented from an intercomparison of atmospheric general circulation model (AGCM) simulations of tropical convection during the Tropical Warm Pool-International Cloud Experiment (TWP-ICE). The distinct cloud properties, precipitation, radiation, and vertical diabatic heating profiles associated with three different monsoon regimes (wet, dry, and break) from available observations are used to evaluate 9 AGCM forecasts initialized daily from realistic global analyses. All models captured well the evolution of large-scale circulation and thermodynamic fields, but cloud properties differed substantially among models. Compared with the relatively well simulated top-heavy heating structures during the wet and break period, most models had difficulty in depicting the bottom-heavy heating profiles associated with cumulus congestus during the dry period. The best performing models during this period were the ones whose convection scheme was most responsive to the free tropospheric humidity. Compared with the large impact of cloud and convective parameterizations on model cloud and precipitation characteristics, resolution has relatively minor impact on simulated cloud properties. However, one feature that was influenced by resolution in several models was the diurnal cycle of precipitation. Peaking at a different time from convective precipitation, large-scale precipitation generally increases in high resolution forecasts and modulates the total precipitation diurnal cycle. Overall, the study emphasizes the need for convection parameterizations that are more responsive to environmental conditions as well as the substantial diversity among large-scale cloud and precipitation schemes in current AGCMs. This experiment has demonstrated itself to be a very useful test bed for those developing cloud and convection schemes for AGCMs.