In this study, we found an inherent numerical error in the ice microphysics processes of WDM6 and corrected it by re-driving the theoretical formula. We found that the correction has improved monsoon precipitation distribution over East Asia in the WRF regional climate simulation.
The WDM6 is one of the widely used microphysics schemes in the Weather Research and Forecasting (WRF) Model, which predicts the mixing ratio and number concentration of cloud droplets and rain. The WRF is also the most widely used numerical model in weather and climate. The revised WDM6 code will be implemented to WRF, thus the result of this study could be applicable to any research that uses WRF and WDM6 in the future.
The major characteristics of ice microphysics in Weather Research and Forecasting (WRF) Double-Moment 6-class (WDM6) bulk-type cloud microphysics originate from the diagnosed ice number concentration, which is a function of the cloud-ice mixing ratio. In this study, we correct numerical errors in ice microphysics processes of the WDM6, in which the cloud-ice shape is assumed as single bullets, and examine the impact on regional climate simulations. By rederiving the relationships between cloud microphysics characteristics, including the one linking the cloud-ice mixing ratio and number concentration, we remove numerical errors intrinsic to the description of cloud-ice characteristics in the original WDM6 microphysics scheme. The revised WDM6 is tested using a WRF framework for regional climate simulations over the East Asian region. We find that our correction to the WDM6 improves the model’s performance in capturing the observed distribution of the monsoon rain band.