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Improving High-resolution Weather Forecasts using the Weather Research and Forecasting (WRF) Model with Upgraded Kain-Fritsch Cumulus Scheme
Citation:
Zheng, Y., Kiran Alapaty, A. Kumar, AND D. Niyogi. Improving High-resolution Weather Forecasts using the Weather Research and Forecasting (WRF) Model with Upgraded Kain-Fritsch Cumulus Scheme. Presented at AGU Fall Meeting, San Franciso, CA, December 09 - 13, 2013.
Impact/Purpose:
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
Description:
High-resolution weather forecasting is affected by many aspects, i.e. model initial conditions, subgrid-scale cumulus convection and cloud microphysics schemes. Recent 12km grid studies using the Weather Research and Forecasting (WRF) model have identified the importance of incorporating subgrid-scale cloud-radiation interactions using the Kain-Fritsch (KF) and Rapid Radiation Transfer Model, Global schemes. However, it is still unclear to what extent the KF convection scheme could be modified to improve high resolution precipitation forecasts with the WRF model. In this numerical study, we have made several changes to the KF scheme (i.e. inclusion of subgrid-scale cloud radiation interactions, a dynamic adjustment timescale, cloud updraft mass fluxes impact on grid-scale vertical velocity and a LCL-based entrainment methodology). These science updates introduce scale dependency for some of these parameters in KF scheme and makes the upgraded KF scheme usable at 9km and 3km grid resolutions in the WRF-ARW 3.4.1. The WRF model convection forecast experiments are performed over US Southern Great Plains in 2002 summer, during which the International H2O Project (IHOP 2002) measurements are used for model forecast validations. The evaluation also uses MET tool which is widely used for model performances to provide some statistical verification. Results indicate that (1) the initial conditions play a key role in the high resolution weather forecasting; and (2) our modified KF scheme is able to alleviate the excessive precipitation in 9km resolution and improve the precipitation forecasts in 3km resolution simulations.