Simulation Of The Effects Of Complex Terrain On Local And Downstream Cloud Precipitation Characteristics In Summer On The Qinghai-Tibet Platea

The complex topography of the Tibetan Plateau(TP)has a fundamental role in regulating the formation and maintenance of the South Asian Summer Monsoon(SASM).The complex terrain in different regions of the TP has different impacts on the SASM,affecting the cloud and precipitation characteristics of the SASM on the TP and influencing the strength of the monsoon’s downstream propagation.In this study,the Weather Research and Forecasting(WRF)model was used to investigate the individual and collective effects of terrain uplift in different parts of the TP on regional climate change,and to explore the mechanism by which increased complexity of the TP terrain affects the monsoon’s advancement and water vapor balance,using high-resolution terrain elevation data.The results show that:(1)The uplift of the southern slope of the TP plays a positive role in maintaining and developing the South Asian high pressure system(SAH),which is favorable for maintaining the water vapor supply of the SASM’s northern branch.At the same time,the southern slope of the TP is conducive to the production and development of the anomalous circulation system in the mid-latitude troposphere,promoting the downward transmission of water vapor and convective clouds.The TP’s local heating effect is favorable for lifting and forming convective clouds and precipitation,while the upper atmosphere of the troposphere warms due to nonadiabatic heating.Water vapor from the TP mainly flows towards China’s central and eastern regions(CEC),and the sensitive region of the TP(98°-105°E,25°-32.5°N)affects the water vapor transport path.Removing the sensitive region of the TP is conducive to increasing precipitation and convective clouds in southeastern China(SEC).(2)Removing the uplift of the TP terrain is conducive to the abnormal divergence of water vapor in the northern mid-latitude TP,which contributes more water vapor to the abnormal convergence in northeastern China.The dynamic anomalies of the mid-latitude and low-latitude systems are in a confrontational state,resulting in low efficiency of precipitation and convective cloud generation,a weakening of the monsoon’s landward advancement,and a southward shift of the rainfall belt.(3)With the increase of the resolution of the complex terrain of the TP in the model,the increase in terrain resistance weakens the westerly belt and increases the meridional wind,forming a new geostrophic balance.The model generally overestimates surface wind speed,but the increase in resolution of the complex terrain and the better resolution of processes related to non-uniform surface forcing correct the overestimation of wind speed,and the correction of wind speed caused by increasing the horizontal resolution is more obvious.(4)With the increase of the resolution of the complex terrain of the TP in the model,both the near-surface flow and updraft components of the slope flow on the southern slope of the TP show a decreasing trend,reducing low-level water vapor,and leaving more water vapor in the form of terrain-driven precipitation at the front edge and low-altitude uplift zone of the southern slope of the TP.The release of latent heat from precipitation and the effect of terrain strengthen the SAH,enhancing the TP’s ability to capture water vapor from the northern branch of the SASM,and indirectly promoting the transport of more water vapor to the TP.(5)Compared with changing the resolution of terrain data,changing the horizontal resolution of the model has a greater impact on the smoothing effect of complex terrain on water vapor transport.At higher horizontal resolutions,the differences in highland water vapor transport caused by increasing the resolution of terrain data are more pronounced.