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.