| Short-time heavy rainfall is the main severe convective disastrous weather affecting Northwest China,which is easy to cause geological disasters,such as mountain torrents and debris flows.The precipitation statistics in recent years show that the intensity and frequency of precipitation in Northwest China have increased significantly since the 1960 s.Lanzhou is located in the valley between the mountain range at the edge of the Tibetan Plateau and the Loess Plateau,and has unique valley topography.At the same time,it is also located in the transition zone between the dry and the wet climate,which is a sensitive area for land-atmosphere interaction.But existing studies have mainly classified heavy precipitation statistically according to different large-scale circulation situations and water vapor sources.There are few studies about the influence of related land surface processes on intense precipitation.Therefore,this paper deeply studies the internal structure,organization and development of two convection systems in Lanzhou based on high-resolution observations and refined numerical prediction products,in order to study the influence of land surface patterns with different complexity on the simulation of heavy rainfall in Lanzhou area.In this paper,two intense precipitation events in Lanzhou area under different weather background are selected:(1)local intense precipitation in April 19,2018 under the high-altitude low trough type background;(2)local short-term thermal convective precipitation in September 22,2020 under the weak weather scale background.We use the Weather Research and Forecasting coupled with the land surface models NOAH,CLM4 and RUC to investigate the effects of different land surface models on precipitation simulations,and to investigate the intrinsic causes of the differences in strong precipitation simulations in terms of land-atmosphere interactions.(1)The simulation results of local heavy precipitation on April 19,2018 show that the simulated convection initiation is close to the observation because the RUC land surface model can reasonably simulate stronger surface sensible heat flux and horizontal transport of water vapor in Lanzhou before precipitation occurs,which provides the necessary water vapor and thermodynamic conditions for convection initiation.(2)The numerical simulation results of local short-duration thermal convection in September 22 2020 show that the CLM4 simulation surface latent heat flux is high,which transports water vapor into the boundary layer through local convergent upward motion and enhances convective system development,thus reasonably reproducing this local intense precipitation process.In addition,the energy transport distribution of CLM4 is consistent with the distribution of urban land types in Lanzhou.Compared with CLM4,the surface latent heat flux is lower and the sensible heat release to the atmosphere is larger simulated by NOAH,especially in urban areas.In conclusion,difference with sensible and latent heat flux distribution by varies land surface process parameterization schemes,results the transport of water vapor from surface to the boundary layer and the spatial temporal evolution of boundary layer differently,ultimately affects the time and the location of convective initiation.Therefore,the choice of parameterization scheme for the land surface process has a great impact on the simulation of local intense convective precipitation in the Lanzhou area.The results of the paper have implications for improving the understanding of the mechanisms of land-atmosphere interactions on the occurrence and development of heavy rainfall and its forecasting. |
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