Modelling suppressed and active convection: Comparisons between three global atmospheric models

The Met Office Unified Model, the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System and the National Center for Atmospheric Research (NCAR) Community Atmosphere Model 3 were used to compare simulations of suppressed and active convection by global atmospheric models (GAMs) in the Tropical West Pacific. The case used it three-week period selected from the Tropical Ocean and Global Atmosphere-Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE). The global models were initialized from ERA-40 on each day of the case and the 12-36 h forecasts were concatenated together to create a continuous sequence of forecasts. One active and two Suppressed subperiods were identified and used to examine the behaviour of the models within different convective regimes. All the GAMs were able to clearly distinguish between the Suppressed and active regimes in terms of precipitation rate, precipitable water and radiative fluxes, and they all produced strong deep convection during the most active period. However, there were significant differences in the behaviour of the GAMs convection parametrizations during the most suppressed period. There was good agreement in the long-wave radiative fluxes where the GAMs were in good agreement in terms of convective activity, but there was less agreement in the short-wave fluxes, with the biggest differences being in the most active period. Throughout, there were large differences in the relative proportion of convective and large-scale precipitation produced by the GAMs. By making comparisons with reference data in the form of observations, reanalyses and cloud-resolving models, several issues that were specific to individual GAMs are identified and discussed. Copyright (C) Royal Meteorological Society and Crown Copyright, 2008