P44  Introducing Subgrid-Scale Cloud Feedbacks to Radiation in WRF

Alapaty, Kiran, Jerold Herwehe, Chris Nolte, Russ Bullock, Tanya Otte, Megan Mallard, United States Environmental Protection Agency,  Jimy Dudhia, NCAR, and Jack Kain, NOAA/NSSL

The Atmospheric Modeling and Analysis Division at EPA is advancing the science of the cloud-aerosol-radiation (CAR) interactions by continued development of integrated modeling systems for meteorology/climate (such as the Weather Research & Forecasting model, WRF) and air quality (the Community Multiscale Air Quality model, CMAQ).  In these models, when used at coarse spatial resolutions (e.g., 36 km grid cells), convective cumulus clouds are modeled as subgrid-scale clouds.  Thus, in order to achieve full CAR interactions of cumulus clouds with aerosols and radiation, cumulus cloud parameterizations need to be linked with radiation and aerosol processes.  As a first step, our research group has implemented a cloudiness formulation that is widely used in GCMs (e.g., CAM5) to account for the effects on radiation of the cumulus clouds from WRFÕs Kain-Fritsch (KF) scheme.  Following the CAM5 methodology, we first estimate 3-D cloud fraction associated with the KF clouds. Then, estimated grid-scale cloudiness and associated condensate are adjusted such that the total cloud fraction does not exceed unity.  These respective parameters are then passed to a radiation scheme (RRTMG) to affect the short- and long-wave radiative processes.  Two simulations for a one-week period ending July 30, 2010 were performed using WRF v3.3.1.  For the first simulation, standard WRF code was used (Base case), while the second simulation (Modified case) used updated codes to account for subgrid cloud-radiation feedbacks.  Preliminary results from the seven-day simulations indicate simulated cloud fractions in the Modified case compare favorably with the GOES-derived cloud fractions.  Also, other results from the Modified case, such as insolation, 2-m temperature and water vapor mixing ratio, and precipitation are closer to respective observations obtained from SURFRAD data, hourly surface observations, and NOAA/AHPS precipitation analyses.  To further assess the impact of the cloud-radiation feedbacks from a seasonal climate perspective, we have performed two additional 3-year simulations, again with and without subgrid cloud-radiation feedbacks.  Preliminary results obtained from the seven-day simulations as well as those from the seasonal simulations will be presented.