Radiative impacts of precipitating hydrometeors on atmosphere circulation features in weather and climate models

Climate models such as those used in the Intergovernmental Panel on Climate Change (IPCC) assessments, often ignore the radiative impacts of precipitating hydrometeors (e.g., rain, snow) due in part to the perception that the combination of their limited spatial extent, short lifetime and large particle radii make them incapable of having a tangible radiative impact on the atmosphere. Moreover, the limited observations of the amount of precipitating hydrometeor mass in the atmosphere makes the validation of radiative impact calculation difficult. Because of these factors, global models ignore the radiative processes associated with falling hydrometeors and only consider the “suspended” water in radiation calculations. As a result, such models are likely achieving top of atmosphere (TOA) agreement with observations through compensating errors which however introduce atmospheric circulation, hydrometeors, precipitation and land/sea surface temperatures biases. By using the ice particle size distribution parameters estimated by the CloudSat retrieval algorithm, CloudSat retrievals of ice water content provide one of the first comprehensive means to estimate the amount of precipitating ice mass in the atmosphere and characterize its vertical structure.

We perform a series of sensitivity tests in order to examine the global scale differences arising from exclusion/inclusion of the precipitating hydrometeors for radiation calculations on atmospheric radiative fluxes and heating rates, as well as surface precipitation and dynamics using ECMWF IFS, GSFC/GEOS5, a cloud resolving GCM-fvMMF. We also examine regional impacts using the WRF model.

These results will demonstrate the usefulness of considering both suspended and precipitating atmospheric water mass to evaluate and constrain model representations of cloud-radiative processes and feedbacks.