Impact of Changes in Radiation Parameterization on Model Medium-range and Monthly Forecasting

A comparison of two radiation parameterization schemes has been carried out in the T106 Medium-range NWP model and the National Climate Center’s climate model T63. The radiation scheme used for the control integration in the two models at present was the original ECMWF operational radiation scheme (OPE), and the new radiation scheme (NEW) was the version that became operational on May 2, 1989 in ECMWF. Results indicate that OPE overestimates the short-wave water absorptivity, which leads to too large short-wave atmospheric absorption and too small downward short-wave radiation at the surface; OPE also underestimates the long-wave radiative cooling and the outgoing long-wave radiation at the top of atmosphere (OLR). In NEW the radiative energy available at the surface and an overall cooling of the troposphere increase; large turbulent heat fluxes are generated; the convective activity is enhanced; and the precipitation clearly increases. The warm temperature bias in the stratosphere in OPE is corrected. The operational parallel statistical test indicates a more pronounced improvement to the medium-range forecast of 4—7 days.