Investigation of the Influences of Cloud Microphysics on WRF-Solar Solar Irradiance with a New Microphysics Parameterization

Abstract:

Limited understanding of microphysical processes and inadequate parameterizations in the numerical weather prediction models result in a major challenge to accurately forecast solar irradiance in cloudy conditions. This study focuses on the influences of cloud microphysical properties on solar irradiance. First, a new microphysics parameterization developed at the Brookhaven National Laboratory will be implemented into the state of art Weather Research and Forecast model designed for solar radiation simulation and forecasting (WRF-Solar). Compared to the commonly used microphysics scheme, the BNL scheme explicitly considers the effect of relative dispersion of cloud droplet size distribution on the effective radius and autoconversion process. Second, the BNL scheme will be tested in different cloud regimes (shallow cumulus v.s. stratocumulus) against the measurements at the DOE’s ARM SGP site. Comparison with the default Thompson aerosol aware scheme will also be made to identify the model improvements in cloud properties and solar irradiance. Third, the response of solar irradiance to different cloud microphysical properties will be investigated using the new scheme to better understand the causes of the resulted solar irradiance in the model. The results will provide physical insight into the improvement of solar irradiance forecast in cloudy conditions.