A Numerical Simulation Of Mountain-plain Breeze Circulation In Eastern Chengdu

In this paper,WRF(V3.9)is used to simulate the mountain-plain breeze circulation in eastern Chengdu(Longquan mountain)under clean and polluted atmospheric conditions.The structure and evolution of the mountain-plain breeze circulation are discussed as purpose.Besides,the influence of AOD on the mountain-plain breeze circulation in a heavy pollution event on 7 December 2016 is examined by conducting a sensitivity experiment in which the AOD value is reduced.The Longquan mountain is fairly long from north to south,comparatively narrow from east to west and low in height.Result shows that a distinct mountain-plain breeze is predicted under clean atmospheric condition on 1 October 2016.During the daytime,the plain breeze can last for 5-7 hours,but the plain breeze circulation is easily covered by turbulent movement.Under polluted atmospheric condition on 7December 2016,intense ground inversion exists,causing uncommon surface temperature distribution between the mountain and plain area.The cross-mountain downslope wind circulation occurs in the late morning and at night due to the imbalance of radiation and the dynamic forcing of background wind.It behaves stronger in the late morning and weaker at night.Plain breeze circulation begins after noon when a distinct horizontal potential temperature gradient appears between the mountain and plain areas,and reaches its maximum at 15:00 LST with a horizontal stretch of 3 to 4 times of the mountain width,a vertical stretch of 1.2 km,and a maximum vertical velocity of 0.6 m/s.While it lasts shorter compared to the plain breeze on 1 October 2016,only for 4-5 hours.It ends at around 17:00 LST,and gradually converts into mountain plain breeze circulation afterwards.In both cases(clear and polluted cases),the cross-mountain downslope breeze circulation and mountain-plain breeze circulation vary greatly in the north-south direction due to the heterogeneity of the mountain terrain.The terrain of the northern part of the mountain is higher and wider compared to the middle and south part.The cross-mountain downslope breeze is stronger in the southern part of the mountain.The plain breeze circulation in the middle and southern part is easily covered by vigorous turbulences.In the northern part,on the contrary,there exists a intensive and long-lasting plain breeze circulation.After reducing the AOD in the sensitivity experiment of polluted case,the solar radiation an heat flux increase.The difference of sensible heat flux between mountain and plain also increase.The boundary layer rises higher and lasts longer.Plain breeze circulation in the middle and southern part is more ambiguous due to amplified turbulence;while in the northern part,it is enhanced and prolonged due to the elevated planetary boundary layer.