A Simulation Study On The Influence Of The Topography Of The Greater Khingan Mountains And Changbai Mountains On The Summer Climate In Northeast China

Northeast China is an important grain production area,and the summer climate variation has a significant impact on the grain production over the region.Therefore,it is of great scientific and practical significance to carry out research on the mechanism of the summer climate variation over Northeast China.Previous related researches have paid more attention on the effects of the climate system internal variability and external forcing,but less attention has been paid on the climate effects of the Northeast China terrains.Therefore,this thesis uses the regional numerical model of WRF-ARW(V3.9)to study the impacts of the two major terrains of the Greater Khingan Range(GKR)and Changbai Mountain(CM)on the summer climate over Northeast China by designing several sets of terrain sensitivity experiments.The main conclusions are drawn as follows:(1)Compared with the observation,the simulation of the WRF-ARW(V3.9)model driven by the ERA-Interim reanalysis at a horizontal spacing of 15 km shows cold-bias and wet-bias in Northeast China.But in general,the WRF-ARW(V3.9)model has a good ability to simulate the summer climate and atmospheric circulation over Northeast China.It can reproduce the spatial distribution characteristics of summer precipitation,temperature,water vapor and atmospheric circulations over Northeast China.Therefore,the WRF-ARW(V3.9)model is suitable for the simulation study of climate change over Northeast China.(2)The terrains of the GKR and CM can significantly influence the Northeast China summer precipitation.Relative to the control run precipitation,the uplift of the GKR leads to a precipitation increase of about 30% over the region from the GKR eastern slope to the Songnen Plain and a decrease of about 24% over the region from the GKR western slope to eastern Mongolia.The uplift of the CM causes a precipitation increase of about 26% over the region from the CM southern slope to the Korean Peninsula and a decrease of about 22% over the region from the CM northern slope to the Sanjiang Plain.The two mountains influence the precipitation mainly through the terrain's blocking effect and dynamic uplift effect.These effects strengthen(weaken)the precipitation over the windward(leeward)slope.Compared to the individual effects of the two mountains,the combined effect of the GKR and CM weakens the response of summer precipitation to the terrain over the GKR eastern slope to the Songnen Plain,the GKR western slope to eastern Mongolia and CM southern slope to the Korean Peninsula.However,over the Sanjiang Plain,the combined effect of the two mountains enhances the response of precipitation there.(3)The uplift of the GKR and CM can significantly influence the summer surface air temperature(SAT)over Northeast China.Subtracting the air temperature changes caused by the terrain uplift with a temperature lapse rate of 0.60?/100 m,the GKR can still cause an additional SAT decrease by about 1.03? over the region from the GKR eastern slope to the Songnen Plain and an addition SAT increase by about 0.50? over the region from the GKR western slope to eastern Mongolia.The uplift of CM can lead to an additional SAT decrease by about 0.35? over the region from the CM southern slope to the Korean Peninsula and an addition decrease by about 0.22? over the region from the CM northern slope to the Sanjiang Plain.Over most parts of Northeast China,the combined effects of the two mountains have an enhanced effect(off-set effect)on summer SAT over the warming(cooling)regions caused by the individual terrain.when the two terrains coexist,the SAT over the region from the GKR eastern slope to the Songnen Plain is decreased further by about 0.56?,the SAT over the region from the GKR western slope to eastern Mongolia is increased by about 0.61?,the SAT over the region from the CM southern slope to the Korean Peninsula is decreased by about0.31?,and the SAT over the region from the CM northern slope to the Sanjiang Plain is decreased by about 0.19?.The changes in surface net heat flux is consistent with that of SAT over Northeast China.Over the significant cooling(warming)regions influenced by the GKR,the changes in sensible heat flux(shortwave radiation and sensible heat flux)have major contribution to that of surface net heat flux.Over the significant cooling regions influenced by the CM,the changes in sensible heat flux and latent heat flux have major contribution to that of surface net heat flux.