The Simulation of Effect of Topographic Slope, Aspect and Shading over the Eastern Slope of Tibet Plateau

The radiation budget can be quit variable in mountain areas due to topography effects on exchange between local hydrology and heat. The topography factors, including slope angle, aspect, shading, and terrain high, cannot be ignored in meteorological studies of complex terrain. The slope and aspect can change the incoming shortwave radiation by changing the zenith angle, while the shading effects belong to nonlocal topographic features often happening in rugged landscapes can change the diffuse radiation. While such topography factors are available in model, the simulation of radiation balance can be improved. The eastern slope of Tibet Plateau(ESTP) and Sichuan Basin(SB) have complex terrain which includes the greatly varying slope angle and terrain high. There are also some weather systems being relative to its special terrain are important for the local population and agriculture. Taking into account improving numerical weather predictive capabilities and research for the Tibet Plateau, it is imperative to consider those topography effects. \\ In this work, the short wave radiation effects of slope angle, aspect and shading(ESAS) of the ESTP are assessed through a precipitation case. The model Weather Research and Forecasting (WRFV3.5) was used to conduct the control and sensitive tests to simulate the case happed during Aug 16-17 in 2012 in which it is clear in the daytime and rainy at night. The simulations have 3 domains with model resolution 50, 10, 2 km and geography data resolution 10, 10, 2 arc-m, and Only the simulation results of the finest domains will be compared and analyzed. The ESAS is included in the finest domain of sensitive test but not in the control test. \\ The results show that slope angle and aspect results in shortwave radiative forcing on surface higher than 20 and -32 Wm-2 in the daytime. The spatial distribution of the forcing is relative to the corresponding terrain slope angle and aspect: the large slope angle for high forcing and the small slopes for low forcing, the west aspect for negative forcing and the east aspect for positive forcing. The shading effect makes the changes of net shortwave radiation flux at surface over the ESTP shift southeasterly toward the SB and the shifting starts after 13 Beijing Time. Fig 1 describes the distributions of the short wave radiative forcing(a) deduced by slope angle and aspect and the changes of the short wave radiation flux(b) cased by ESAS. It shows that the distribution of radiation flux changes shifting to the SCB is still similar with slope angle and aspect of ESTP like the forcing. The distributions of changes of various heat flux(latent heat, sensitive heat and ground heat) at surface and ground temperature in daytime agree greatly with the short wave radiation flux changes: they all have an own high values belt like the adjacence of the TP and SCB in the SCB. The changes of heat flux at night distribute with familiar features but declining extent as those in daytime. A high values belt of the changes of latent heat flux at surface always appears in the SCB both in daytime and at night. It can be concluded that the impact of net shortwave radiation flux changes due to the ESAS on various heat flux at surface will continue at night. Both of the changes of vapor water mixing ratio and wind field have the distribution pattern with a high values belt similar to variations of latent heat flux in the corresponding time. Their high values belts are more alike at night. The increase(decrease) of latent heat flux can improve(reduce) the wind speed. \\ The precipitation of control simulation has the approximate rain belt comparing with observation data. But the northern of the simulated band extends to Northeast and the intensity is higher, while the precipitation is more scattered in the south. In sensitive simulation adding the ESAS, the location of band doesn't change but the intensity decreases and is lower than observation. Moreover, the number of high rain center in north of band in the sensitive test is 3 that is more closer to observation compared to 1 in the control test. The distribution of changes of precipitation is consistent with that of water vapor and wind field. \\ This study shows that considering the ESAS in model can make thermal and hydrology budget closer to observations over the ESTP. To simulating the local weather systems more reasonable it is necessary to present more detailed terrain slope.