Diagnosis And Numerical Simulation Of Rainstorm Under The Background Of A Deformation Field

Rainstorm under the background of the deformation field occurred in northern Henan from the night of 8 July 2016 to the next morning.We studied the process from the perspective of potential vorticity.In this paper,WRF 3.8 is used to carry out detailed numerical simulation of the wind field,temperature field and precipitation of the rainstorm in northern Henan on July 9,2016,and then the terrain sensitivity test is carried out on the formation of the Taihang Mountain terrain.WRFDA 3.8 was used to perform three-dimensional variational assimilation of ground data in order to improve the simulation level.Finally,the role of the deformation field and terrain in this heavy rain is summarized.To sum up,the main contents of this study are as follows:(1)The results show that as the northwest high potential vorticity and cold air move to the southeast the potential vorticity values in the north of Henan increase gradually with the formation of the deformation field from 20:00 on 8 July to 08:00 on 9 July.The cold air brought by the high potential vorticity meets the warm air brought by the typhoon and subtropical high pressure,which makes the convective instability develop and causes strong precipitation.When the potential vorticity in northern Henan has decreased and the cold air,typhoon and the warm wet air have weakened,the precipitation attenuates consequently at 02:00 on 9 July.The north of Henan Province shows a high potential vorticity of 1 PVU at 400-600 h Pa,and the strong convergence of water vapor from 850 h Pa to surface increases.The maximum value is at 900 h Pa in front of Taihang Mountain during 02:00 to 08:00 on 9 July.The dynamic terrain force strengthens the convergence of water vapor.Secondary circulation forms from southeastern Shanxi to the rainstorm area of northern Henan at 113.5-116°E at 400 h Pa.The rising branch of the secondary circulation triggers the release of unstable energy,while the rising branch of the circulation corresponds to the rainstorm area of northern Henan.Finally,the deformation in north of Henan increase gradually from 20:00 on 8 July to 08:00 on 9 July resulting in enhanced water vapor convergence,which is also one of main causes of the rainstorm formation.The potential vorticity diagnosis shows that the dynamic effect of the horizontal potential vorticity advection results in an increase in the positional potential vorticity at 08:00 on the 9th,while the vertical transport and latent heat are negative contributions.(2)The results show that the simulated wind field roughly simulates the deformation field in the NCEP wind field,and the low vortex and shear line that are not present in the NCEP wind field are simulated in the north of Henan.The simulated rain belt position is basically the same as the actual situation.The range of heavy rain is small.In the topographic sensitivity experiment,after reducing the terrain height of Taihang Mountain,the shear line and low vortex position on the wind field changed significantly,the precipitation in the north of Henan decreased significantly,and the precipitation on the leeward slope of Taihang Mountain increased.After the assimilation of ground data,the simulation level of precipitation and wind field is significantly improved.In summary,the simulation results show that the deformation field causes the wind field and water vapor to converge in the rainstorm area,and the topographic dynamic forced uplift is an important reason for the formation of this precipitation.(3)The deformation field caused a low vortex at 700 h Pa,and a shear line appeared on the ground.The wind field and water vapor were converged in the upper part of the rainstorm area,and the topographical force forced uplift was an important reason for the formation of this precipitation.