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Evaluation of cumulus cloud – radiation interaction effects on air quality –relevant meteorological variables from WRF, from a regional climate perspective
Herwehe, J., Kiran Alapaty, T. Otte, Chris Nolte, AND R. Bullock. Evaluation of cumulus cloud – radiation interaction effects on air quality –relevant meteorological variables from WRF, from a regional climate perspective. Presented at 12th Annual CMAS Conference, Chapel Hill, NC, October 28 - 30, 2013.
The National Exposure Research Laboratory (NERL) Atmospheric Modeling and Analysis Division (AMAD) conducts research in support of EPA mission to protect human health and the environment. AMAD research program is engaged in developing and evaluating predictive atmospheric models on all spatial and temporal scales for forecasting the air quality and for assessing changes in air quality and air pollutant exposures, as affected by changes in ecosystem management and regulatory decisions. AMAD is responsible for providing a sound scientific and technical basis for regulatory policies based on air quality models to improve ambient air quality. The models developed by AMAD are being used by EPA, NOAA, and the air pollution community in understanding and forecasting not only the magnitude of the air pollution problem, but also in developing emission control policies and regulations for air quality improvements
Aware only of the resolved, grid-scale clouds, the Weather Research & Forecasting model (WRF) does not consider the interactions between subgrid-scale convective clouds and radiation. One consequence of this omission may be WRF’s overestimation of surface precipitation during summer. To address this problem, our regional climate modeling group at the U.S. EPA modified WRF to provide feedbacks from the Kain-Fritsch (KF) convection parameterization to the Rapid Radiative Transfer Model – Global (RRTMG) radiation schemes in order to allow the subgrid cumulus clouds, along with the resolved clouds, to affect both shortwave and longwave radiative processes (Alapaty et al., Geophys. Res. Lett., 2012). We implemented this cumulus cloud – radiation connection in a recent release of WRF (Version 3.5) and used it to simulate a multiyear period over the contiguous U.S. The purpose of this study is to perform an initial evaluation of the effects on air quality-relevant meteorological variables when including the cumulus cloud – radiation interactions in regional climate simulations. The focus of this evaluation will be on temporally- and regionally-averaged analyses of parameters such as 2-meter temperature (for biogenic emissions, reaction rates), 10-meter wind speed and planetary boundary layer height (to gauge ventilation), specific humidity (important in particulate matter processes), cloud fraction (which affects photolysis and aqueous chemistry), precipitation (a sink for PM), and, possibly other quantities, such as the frequency of frontal passages, for example. For users of the Community Multiscale Air Quality modeling system (CMAQ), this study should provide some indication of the changes and potential improvements expected in WRF-driven CMAQ air quality predictions when including subgrid-scale cloud effects on radiation.