| Rainstorm is one of the most frequent disastrous weathers in China,but in the extremely arid area of southern Xinjiang,the occurrence of heavy rain needs not only enough water vapor,but also cooperates with local terrain features and underlying surface features,meanwhile,land-atmosphere interaction also plays an important role in the occurrence and development of heavy rainfall.In this paper,the synoptic situation,water vapor source budget and trigger mechanism of a rainstorm in southern Xinjiang basin are preliminarily discussed by using FNL,ERA5 reanalysis data,automatic meteorological station observation data and FY-2G radiation brightness temperature data.Afterwards,parameterization scheme is applied to the WRF model in order to carry out sensitivity analysis of the land surface process during the rainstorm process,then the influence that the land-atmosphere interaction imposed on the rainstorm is discussed.Based on the optimal parameterization scheme of land surface process,the terrain sensitivity experiment is carried out to study the effect of topographic height on rainstorm.The main conclusions are as follows:The persistent heavy precipitation in southern Xinjiang which occurred under the background of the large-scale circulation with two-body distribution of South Asia high,was caused by the joint action of 200 h Pa upper southwest jet,the vortex of Balkhash Lake on 500 h Pa,Iran high pressure ridge,700 h Pa shear line and surface convergence line.The water vapor of the rainstorm mainly comes from the Atlantic Ocean,the Black Sea,the Li / Aral Sea,the Arabian Sea and the Bay of Bengal,and reaches the southern Xinjiang basin along the northwest,west and southwest paths.Water vapor is mainly delivered from the upper troposphere of the southern boundary and the lower and upper troposphere of the northern boundary to the southern Xinjiang basin,and is discharged in the lower and upper troposphere of the eastern boundary.The mesoscale convergence line caused by the high topography in the south of southern Xinjiang is an important trigger system for this heavy precipitation.The water vapor brought by the northwest air flow to the north of the convergence line accumulates in front of the mountain,and under the action of topographic uplift and the promotion of the convergence line,unstable energy is released,resulting in the generation and development of the convective system,causing heavy precipitation in the southern Xinjiang basin.The occurrence of heavy precipitation is sensitive to land surface processes,and the simulation effect changes along with different land surface schemes.TS scores show that the simulation effect of RUC scheme is obviously better than that of SLAB and NOAH scheme,and the simulation effect of SLAB is most trivial among the other two.The distribution and variation of sensible and latent heat fluxes are strongly relevant to land surface schemes.The sensible and latent heat fluxes simulated by different schemes are distinct,besides,latent heat flux contributes more to precipitation and owns greater relevance with heavy precipitation than sensible heat flux.The wind field and humidity conditions near the ground are not sensitive to the selection of land surface scheme in the model.The large topography of the plateau has an obvious impact on the reinforcement of the heavy precipitation,and the topographic height is also related to the rain belt and the magnitude of precipitation.Within a certain range of topographic height,the increase of topographic height leads to the growth of precipitation.The topography of the plateau influences the precipitation by affecting the delivery of water vapor and the distribution of wind field.The topographic height could have an impact on the vertical circulation,and the topographic dynamic forcing shall enhance the vertical circulation,so that the vertical velocity increases,and the ascending motion extends to a higher height,moreover,the vertical motion is the strongest at the maximum slope of the terrain. |
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