The Climate Characteristics Of The Southwest Vortex And Its Relationship With The Sichuan And Chongqing Rainstorm

Based on the MICAPS data, the NCEP/NCAR reanalysis data and precipitationdata, using Empirical orthogonal function (EOF), the Morlet wavelet, correlation andcomposition analysis and other statistical analysis methods, to analyze the temporal andspatial variation of the frequency of the Southwest Vortex characteristics and discussthe correlation of the southwest vortex frequency and the rainstorm in Sichuan andChongqing. In addition, three new diagnosis methods use to analyze the raincharacteristics in Sichuan and Chongqing. The conclusions can summarize as follows:i Statistical study of the Southwest Vortexi) Different research discrimination standards of the Southwest Vortex in commonis that refer to a specific region of the eastern Tibetan Plateau700hPa pressuresurface of the closed cyclonic.ii) An annual average of the low vortex number is99.Inter-annual variation of theSouthwest Vortex: the vortex frequency in the1980s is more than the average,vortex numbers began less than normal from1988. In the1990s the vortexnumber has significantly reduced, after2000the number of vortex has rebound.iii) Monthly variation of the Southwest Vortex: June is the most frequency monththat the vortex appears, An average of10.1. February and December, the numberof vortex appears at least, An average of7.3. General vortex is more frequent insummer and less appears in winter. The appearance of vortex has obviouslyseasonal variations.iv) The Southwest Vortex is generated in the Sichuan Kowloon and the basin andthe junction area between them.ii Research on the correlation of the Southwest Vortex and the rainstorm in Sichuanand Chongqing.i) The best correlation area between the Southwest Vortex and the rainstorm is justlocated in the region that the vortex always moved. The region is in the southeastof Sichuan and southwest of Chongqing. The eastward shift of the vortex maythe important factor that leads the precipitation regions in southeastern of Sichuan and southwest of Chongqing.ii) During1999to2001, changes in precipitation and the number of vortex have thesame trends in Sichuan and Chongqing. After2002, the trends were different.iii) Southwest Vortex movement may be the main factor that leads the increases inprecipitation of Sichuan-Chongqing region in May and June. But it did littlework in July, August and September. That may be associated with seasonchanges or atmospheric circulation or other factors.iii Diagnosis research on rainstorm of Sichuan-Chongqing region that affected by theSouthwest Vortexi) The positive high value center area of moist potential vorticity in "z" coordinate(Pm), convective vorticity vector (CVV) and wet vorticity vector (MVV)corresponding to the time of occurrence of heavy precipitation. If the positivevalue enhance and the contour become intensively, the precipitation will bestrengthen.ii) On the850hPa horizontal distribution, the positive high value center of CVV andMVV region located the occurrence of heavy precipitation. But different withM.Th. heavy precipitation appears in the junction of.positive and negativevalues of Pained the contour is intensive.iii) In the vertical structure of the storm center, the high and the low level of Pm,CVV and MVV showed a consistent positive value distribution. In the low levelof CVV and MVV, there have positive high value center and contour intensiveband.iv) Moist potential vorticity in "p" coordinate(MPV) can decompose intopositive-pressure moist potential vorticity(MPV1) and baroclinic moist potentialvorticity(MPV2).When high and low level of MPV1have the positive andnegative stacking configuration, it is a favorable situation for the development ofa heavy rain occurs. Strong precipitation area is in the junction of positive andnegative values of MPV1.If the value of MPV2increase, it will lead thedevelopment of vertical vorticity. And benefit for stimulating the movement ofconvection and increase the intensity of precipitation.v) Moist potential vorticity in "p" coordinate (MPV) has the most widely used inthe heavy rain and it diagnoses effectively. CVV and MVV are seldom used inthe rainstorm; they have the similar characteristics when diagnose the rainstorm.However, in the order of magnitude the MVV far less than The CVV.vi) The regional average of the moist potential vorticity vertical integration [Pm] and the regional average of the wet vorticity vector vertical integration [MVV]have positive high correlation coefficient with6-hours accumulated precipitation.The correlation between the regional average of the convective vorticity vectorvertical integration [CVV] and the6-hours accumulated precipitation is lowerthan [Pm] and [MVV].When the [Pm] and [MVV] have the maximum, thechanges in precipitation becoming more significant. Heavy rain can happeneasily.