| In this paper,the daily precipitation data of W est C hina from 2020 stations provided by the N ational M eteorological Information C enter of C hina M eteorological A dministration,the re-analysis data of E R A 5,and the SST data of H adley C enter were used to analyze the basic climatic characteristics of precipitation in late summer and early autumn in W est C hina(W C)during 1961-2021,and the related characteristics of atmospheric circulation and SST.F urthermore,the temporal and spatial characteristics of the heavy precipitation in A ugust 2020 were analyzed,and its relationship with large-scale circulation and sea temperature was discussed.The main conclusions are as follows:(1)From 1961 to 2021,the precipitation in late summer and early autumn in W est C hina increased from northwest to southeast,with high values in Sichuan B asin and low values in high altitudes.The continuous heavy precipitation in W est China in August 2020 set the highest rainfall record since records began in 1961.There were three consecutive heavy precipitation processes during August 11-18,23-24 and 30-31,with a total of 161 stations exceeding the historical average level of precipitation.(2)F avorable circulation was sustained during A ugust;W C was positioned between two anomalous high pressure centers over the T ibetan Plateau and S ea of Japan and an anomalous low-pressure center over M ongolia located on its north side,which created a stable and long trough and formed a low-pressure center over W C.At 200 hPa,the E ast A sian subtropical westerly jet(EAJS)was much stronger than average and southward,and the S outh A sian H igh(SAH)was strong and extended eastward to 150°E.A t 500 hPa,the western P acific subtropical high(WPSH)was westward and exceptionally strong,which helped abundant water vapor reach the southeastern part of W C and provided favorable dynamic and thermodynamic conditions for precipitation in this region.In addition,the eastward extension of the SAH promotes the westward extension of W PSH,which collectively enhanced the precipitation in W C.A t 850 hP a,the low-level jet corresponding to the west-extending subtropical high from the Sea of Japan to WC further enhanced and guided the water vapor transport to W C.In addition,the M ei-Yu front over the Y angtze R iver B asin in June and July strengthened the northwestward spread of diabatic heating,transient energy,and wave activity fluxes,which likely influenced the large-scale circulation factors and reinforced the precipitation in W C in A ugust 2020.At the same time,there is a significant positive correlation between the western Pacific SST and the extreme precipitation in W C,indicating that the western Pacific SST affects the heavy precipitation in late summer and early autumn in W C by regulating the circulation.(3)The disturbed wind field showed that there was southerly wind over W C on the day of the rainstorm,which reached its strongest on the day of the heavy precipitation,and the position of the disturbed shear line corresponded to the position of the heavy precipitation.T he vorticity equation was used to diagnose and analyze the heavy precipitation process.It was found that the increase of horizontal relative vorticity advection at low level in the heavy precipitation area resulted in the increase of local vorticity,which led to the strengthening of cyclonic circulation and convergence.Therefore,it is believed that the relative vorticity advection term plays a major role in the heavy precipitation process and is the main dynamic condition for the occurrence and development of rainfall. |
PDF Full Text Request