ANALYSIS ON ASYMMERIC PRECIPITATION OFTHE STRONG TYPHOON NESAT (1117) BEFOREAND AFTER LANDING ON HAINAN ISLAND

ZHOU Hai-bo; BAI Ai-juan; CAI Qin-bo

doi:10.16032/j.issn.1004-4965.2017.03.010

Abstract：Using the NCEP 1 °×1 o reanalysis data,satellite data,this paper takes the strong typhoon Nesat in 2011 for example to analyze the precipitation characteristics of the typhoon before and after landing on Hainan Island,and the asymmetry characteristics of TBB,humidity,horizontal wind speed and vertical velocity surrounding the typhoon on the left and right sides of the path,and discuss the possible causes of precipitation distribution from the aspect of the distribution of spatial structure.The results are showed as follows.Before and after landing on Hainan Island,the precipitation distribution of typhoon Nesat showed significant asymmetry,and heavy rainfall mainly concentrated on the left side of the path.In addition to relatively symmetricaltemperature anomalies,other physical quantities surrounding the typhoon showed significant asymmetry in the following points:(1) TBB.The intensity of strong convective clouds was greater,its range on the left side was larger than on the right side;(2) Moisture.The range of wet area on the left side was larger than on the right side;(3) Horizontal wind field.The maximum wind speed on the right side were stronger than on the left side when the typhoon was at sea and landed,especially when the typhoon landed maximum wind speed difference between the sides was up to 20rn/s;the range of equal maximum wind speed on the right side was wider than on the left side before and after the landing of the typhoon;(4) Vertical velocity.Upward motion on the left side was stronger than on the right side,especially vertical rising velocity on the left side was-2.4 Pa/s stronger than on the right side when the typhoon landed.By comparing the distribution of the above physicswith the distribution of precipitation,we found that humidity may be one reason for the asymmetric distribution of precipitation,and the vertical speed may be the main reason for asymmetric precipitation of typhoon Nesat.From the vertical wind shear,we further explored the role of the formation mechanism of asymmetric typhoon precipitation and found that the heavy rainfall was concentrated in the shear direction and along the left side before and after the typhoon landed on Hainan Island.Vertical wind shear can better explain the strong vertical upward movement and heavy precipitation area on the left side of the path.In addition,Hainan Island terrain conditions also led to a significant increase in typhoon precipitation in the western part of theisland during the landing of typhoon Nesat.