北上台风"黑格比"残余环流对上海地区暴雨的增幅机理分析OA

Based on the hourly precipitation data fused from national automatic weather stations and CMORPH,the best track data of tropical cyclones,the minute-level observation data of airport automatic weather stations and ERA-5 reanalysis data,the influence mechanism of the decaying typhoon"Hagupit"on the strong precipitation in the southern rear airspace of Shanghai on August 5,2020 was explored.The results show that:(1)Different from the previous precipitation areas of northward-moving typhoons which were mainly located near the typhoon eye wall,on the right side of the typhoon's forward direction and in the convergence area where it met the cold air from the north(the left side of the typhoon's forward direction),this strong precipitation process was the second stage of strong precipitation that occurred in the Shanghai airspace 400 km south of the typhoon center after the typhoon moved northward and decayed,rather than the main precipitation of the typhoon.The strong precipitation formed in a favorable environment where the mid-to-high latitude trough and the subtropical high remained stable.After the westward extension of the subtropical high,the pressure gradient between it and the trough strengthened,resulting in the development of a low-level jet and providing sufficient water vapor.With the cyclonic convergence on the left side,the initial upward movement in the middle and lower layers in the Shanghai airspace was established.(2)Meanwhile,after the typhoon moved northward,it merged into the mid-to-high latitude trough.The airspace over Shanghai was situated ahead of the mid-latitude trough and to the south of the upper-level jet exit region,thereby establishing a north-to-south horizontal configuration consisting of the upper-level jet,the typhoon,and the low-level jet.With the southward folding and extension of the tropopause in the upper-level jet exit region,the tropopause folding indicated the existence of Rossby wave breaking.The positive anomalous potential vorticity was transported downward to form downward-propagating wave energy,connecting with the positive anomalous potential vorticity in the middle and lower layers,prompting a significant enhancement of the westerly and northwesterly winds on the south side of the typhoon.The dry and cold air in the middle and upper layers was transmitted downward and merged with the warm and moist southerly airflow of the low-level jet.The convective instability energy was released,prompting the enhancement of the upward movement in the middle and lower layers,providing favorable conditions for the enhancement of the precipitation intensity in the lower layer of this region.(3)The high anomalous potential vorticity triggered upward movement on its lower right side,prompting the development of upward movement in the middle and upper layers of Shanghai.Superimposed on the middle and low-level upward movement in the convergence area on the left side of the low-level jet,a strong upward movement throughout the troposphere was formed,which in turn led to the enhancement of the precipitation intensity on the rear side during the period when the typhoon moved northward and went out to sea.