Influence Of Large-scale Circulation On The Precipitation Distribution Of Extratropical Transitional Tropical Cyclones

Based on the data of reanalysis data,rainfall data from TRMM(Tropical Rainfall Measuring Mission)and RSMC Best-track database,this paper analyze statistically the asymmetric characteristics of precipitation distribution of extratropical transitional tropical cyclones in China from 1998 to 2013 at first.Then,the paper make a comparative study on the Impact of large-scale circulation on the LOC-type(Left of center)and ROCtype(Right of center)precipitation distribution,and numerical simulation experiments were carried out to study possible mechanism of subtropical high and trough-ridge system impacting the precipitation distribution of extropical transitional TCs,The main contents and conclusions are as follows:(1)During the 16 years of statistics,there are 62 cases of the extratropical transitional TCs appear to show significant phenomenon of rainfall asymmetry.About 62.9% of them are LOC-type precipitation distribution,which is usually accompanied by the northward jump and strengthen or southward retreat and weaken of the subtropical high.ROC-type precipitation distribution accounts for 37.09%,and none of them would appear in the process of the subtropical high northward jumping and strengthening.(2)Before the Usagi transformed into an extratropical cyclone,there is a strong deep trough in the high latitude area,and a cold front on the north side of the TC.cold air from high level spread downward to the south,enhancing the low-level disturbance,along with the front edge lifting effect causing precipitation to concentrated on the left side of the moving path.The meridional to zonal circulation adjustment during the ET process is the main reason for the LOC precipitation characteristic becomes more significant.(3)During the ET process of Ewiniar,the subtropical high is propelling northward and retreating eastward while weakening.The upstream is a straight westerly wind,and the downstream is a strong ridge of high pressure.Precipitation occurs on the stronger side of the warm and humid air downstream,and the ET prossess is slower.At the same time,there is a positive feedback effect between the precipitation and the warm front.The low-level layer in the precipitation area is stable and the high-level layer is unstable.Before the front water vapor rises,it enters the unstable layer and causes strong precipitation.The northerly subtropical high is the main cause of ROC-type precipitation during ET prosses of Ewiniar,and the decrease of subtropical high intensity is the main reason why the ROC precipitation characteristics are weakening.The conclusions of this paper are beneficial to deepening the understanding of the causes and evolution mechanism of the asymmetric precipitation characteristics of extropical transitional TCs.