Revision of convection, radiation and cloud schemes in the ECMWF integrated forecasting system

Abstract

Revisions to the convection, radiation and cloud schemes recently introduced into the European Centre for Medium‐Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS) are described, together with discussion of their impact upon model performance. Seasonal simulations with observed sea surface temperatures (SSTs) for June/July/August 1987 and December/January/February 1987/88 with a low‐resolution (T63) version of the model are used to assess the impact of the revised schemes, concentrating upon tropical climate and variability. While the revisions improve the physical basis of the schemes, and each improves aspects of the seasonal climate, overall improvement does not result until the changes are combined. Biases in simulated temperature and top‐of‐atmosphere and surface energy budgets are reduced, leading to a substantial decrease of an equatorial SST cold bias in coupled ocean‐atmosphere simulations used in seasonal forecasting. At higher resolution (T213) changes to temperature and wind fields are similar to those found in seasonal simulations, with little impact upon medium‐range forecast performance in mid latitudes, although these forecasts proved a more critical test of the impact of the schemes upon mid‐latitude flows. The paper demonstrates the methodology used in the development of parametrizations of physical processes at ECMWF, and points to the need to balance parametrization improvements especially between schemes which are highly interactive.