Simulation of the improved parameterization scheme for snow radiation effect over the Tibetan Plateau on the impact of summer rainfall in China

Abstract The radiation effect of snow cover on the Tibetan Plateau (TP) impacts East Asia's weather and climate by affecting the local energy balance. Given the overestimation of snow cover on the TP in the model, the Noah with Multiparameterization options (Noah-MP) surface model was used in the Weather Research and Forecasting Model (WRF) to modify the fresh snow density scheme and soil texture on the TP to improve the model's simulation of snow-related parameters. Then further analyze the impact of the improved scheme on the summer rainfall simulation in China. The results show significant snow cover on the TP in winter 2012, with average surface albedo and snow cover fraction (SCF) of 0.32 and 34.30%, respectively. The WRF control experiment (CTL) overestimates the surface albedo and SCF of the TP, with a simulated average winter albedo of 0.54. The simulated SCF improved by 8% in the experiment with modified fresh snow density and soil texture on the TP (FSD) compared to the CTL. Larger snow cover in winter on the TP leads to excessive rainfall in Southern China and less precipitation in the mid-lower reaches of the Yangtze River in the summer of 2012. Compared with the observed rainfall, the deviations in South China, North China, and Yellow River basins in China simulated by the WRF FSD are significantly reduced. The spatial correlation coefficient between the observed-based and WRF-simulated rainfall increases from 0.76 in CTL to 0.88 in FSD. The simulated snow cover on the TP in the improved WRF experiment is smaller than that in the CTL, causing a decrease in surface albedo and an increase in sensible heat flux. The continued melting of snow leads to an increase in latent heat flux, a decrease in sensible heat flux, and a weakening of diabatic heating. The diabatic heating changes on the TP in the improved experiment further enhanced the westerly jet in the jet exit area. The low-level anticyclonic circulation from the South China Sea to the Bay of Bengal is also anomalous, affecting the water vapor transport processes. The results illustrated and emphasized that improving the simulation of snow accumulation and melting processes on the TP contributes to improving rainfall simulation in the mid-lower reaches of the Yangtze River in climate models.