Research on the Effects of Improvement of Land Surface Subgrid Topographic Parameterization on Regional Temperature and Precipitation Simulation in Western China

The land surface as the underlying of the atmosphere provides lower boundary conditions for atmospheric model. Topography plays a crucial role in the accuracy of the model results. Current most land surface models use the same atmospheric forcing in subgrid units within the same model grid, and does not consider the influence of subgrid topography on atmospheric forcing, which would impact the simulation of meteorological elements and land-atmosphere interactions. In this paper, the modification of Land Surface Subgrid Topographic Parameterization(LSSTP) is proposed, the input atmospheric forcing is revised according to its relationship with the subgrid's terrain height in the NOAH LSM and then it was introduced into the WRF(Weather Research and Forecasting) model for numerical experiments. Three groups of numerical simulation test were conducted to investigate the effects of this improvement on the simulation results of the WRF model. The results show that: The new LSSTP introduced in this paper has clearly improved the simulation of the surface 2m air temperature above the Tianshan Mountains, the Kunlun Mountains, and the southern Qinghai-Tibet Plateau. But the new LSSTP shows little improvement on precipitation simulation. However, the test with higher resolution has simulated the precipitation well. The improvement is due to the fact that the test with higher resolution has been refined on both land and atmospheric grids, while the new LSSTP only considers the effects of land subgrids. The simulation results of the temperature of the new LSSTP are improved by revising surface upward long-wave flux and the surface sensible heat flux, while the test with higher resolution has simultaneously refined the grids of atmosphere and land, the improvement of precipitation and temperature simulation is achieved by comprehensively changing the surface energy balance. In addition, we also simulated a cold wave process and a heat wave process, and the new LSSTP can simulate these processes well.