The impact of precipitating ice and snow on the radiation balance in global climate models

Climate models often ignore the radiative impact of precipitating hydrometeors. CloudSat retrievals provide the first means to distinguish between cloud versus precipitating ice mass and characterize its vertical structure. With this information, radiative transfer calculations are performed to examine the impact of excluding precipitating ice on atmospheric radiative fluxes and heating rates. The preliminary results show that such exclusion can result in underestimates of the reflective shortwave flux at the top of the atmosphere (TOA) and overestimates of the downwelling surface shortwave and emitted TOA longwave flux, with the differences being about 5–10 Wm−2 in the most convective and rainfall intensive areas and greatest for the TOA longwave flux. There are also considerable differences (∼10–25%) in the vertical profiles of shortwave and longwave heating, resulting in an overestimation (∼up to 10%) of the integrated column cooling. The implications of these results are that models that exclude these ice components are achieving TOA radiation balance through compensating errors as well as possibly introducing biases in atmospheric circulations.