Research On The Influence System And Water Vapor Transport Characteristics Of Sudden Rainstorm In The Sichuan Basin

Based on the precipitation data from national meteorological stations in Sichuan Province over the past ten years(2010-2019),the temporal and spatial distribution of sudden rainstorms in climate scale over Sichuan mountainous regions are studied,and accordingly two sudden rainstorm events occurred around the Sichuan Basin are fully analyzed including its influencing systems and dynamic impact factors by using the data of ERA5 reanalysis.Then,the transport characteristics and budget of water vapor during the two processes are analyzed based on Euler's method.Finally,the trajectory of the two processes is simulated,the contribution of each moisture source to the moisture transportation is quantitatively analyzed,the characteristics of moisture transportation revealed by the two methods are compare by introducing the HYSPLIT model based on the Lagrangian method and.The main conclusions are as follows :(1)The two high-frequency areas of sudden rainstorm events over Sichuan mountainous regions are in the western Sichuan Basin along the mountains and in the northern Sichuan Basin along the mountains.Average rainfall and duration,the peak of rainfall and rainfall intensity are positively correlated.July is the month with the highest frequency of sudden rainstorm events,mainly concentrated in the western Sichuan basin along the mountains and the average rainfall is relatively high.The frequency is also relatively high in June and August,mostly concentrated in the western Sichuan basin along the mountains and southern Sichuan mountainous regions,in which the western Sichuan basin along the mountains is prone to sudden heavy rain events with strong rain and short duration in August.The frequency is the lowest in May and September,and the regions are mostly distributed in mountainous area of the northern Sichuan basin and the western Sichuan basin along the mountains.(2)Sudden rainstorms in the northeastern Sichuan basin and the southwestern Sichuan basin occurred under the background of the low trough in 500 h Pa moving to east,the Western Pacific subtropical high which extends to west.The difference is that the dynamic triggering condition of the rainstorm in the northeastern Sichuan basin is the low-level jet.The large-scale SWLJ and the meso-micro scale low-level jet in mountainous terrain built a dynamical coupling of the positive vorticity column and strong divergence column in low-level.The triggering factor of sudden rainstorm is the low-level shear line.The two streams of north cold air and southeastward warm-moist flow form a shear line in lower level,which makes the rainstorm area to be such dynamic structure characteristics of positive vorticity and strong convergence.The Qin-Ba mountainous and the Tibetan Plateau are the enhancement factor in the process of rainstorm in the northeastern Sichuan basin,while they are the Daliang Mountain and the Hengduan Mountain in rainstorm of the southwestern Sichuan basin.(3)The transport of water vapor in the rainstorm over the northeastern Sichuan basin and the rainstorm over the southwestern Sichuan basin is mainly based on the north-south meridional transportation.The water vapor inpour in the two process both from the south and east boundaries,and the intensity of the water vapor transport at850 h Pa is stronger than that at 700 h Pa.The difference is mainly on the south boundary.The integral layer of the south boundary in the rainstorm over the the southwestern Sichuan bought vapor in,while it is only the mid-upper layer in the rainstorm over the the southwestern Sichuan.(4)There are four main sources of water vapor in the northeastern Sichuan basin,of which the South China Sea-East China Sea has the highest contribution,accounting for 42.6% of the moisture transportation,followed by the Arabian Sea-India Peninsula(25.9%),the Middle East at the third position,it is 17.1%,the Bay of Bengal region has the lowest contribution(14.4%).The main moisture sources of rainstorm in the southwestern Sichuan basin are the Arabian Sea– the Bay of Bengal,West Asia,South China Sea,East China Sea,and Eurasia,accounting for 40.6%,11.8%,20.3%,13.2%and 14.1% of the total moisture transport,respectively.The moisture from the East China Sea has a greater contribution in the rainstorm over the northeastern Sichuan basin,and the Arabian Sea-the Bay of Bengal contributes more in the rainstorm over the southwestern Sichuan basin.(5)the air parcel will continuously experience the process of water loss and water absorption when air parcel is transported from the source to the target area.In general,the air particle gain moisture in the sea surface,while the air particle loss moisture in the land.The moisture changes of the transport trajectories are affected by the topography,especially the high mountains around the Sichuan Basin.Compared with the Euler method,the Lagrangian method can capture the spatial-temporal characteristics of three-dimension of water vapor transportation,what's more,it can also provide the moving path of moisture and quantitatively distinguish the contribution of each moisture source to the precipitation.