| The plateau monsoon is a weather system between the plateau and the surrounding areas formed by the thermal difference.Plateau vortex is a unique weather system created by the dynamic,thermal and large topography of the plateau.In this paper,the climatic characteristics of the plateau monsoon were studied and analyzed by using the data of the European central era-interim reanalysis,and the establishment and retreat time of the plateau summer monsoon as well as the reasons were calculated.The seasonal oscillation of the plateau monsoon was studied and analyzed by using wavelet analysis.The data set for the objective identification of vortex on the qinghai-tibet plateau was used to compare and analyze the characteristics of strong and weak summer monsoon wind,source area,path,frequency,intensity,cooling and warming properties,area and duration of vortex on the plateau,and the influence mechanism was discussed.The main research results are as follows:(1)the plateau monsoon is strongest in summer,followed by spring,autumn and winter.Plateau monsoon oscillation characteristics: quasi-four,six years,and in 2002,2003,these periodic oscillation characteristics are most obvious.The 6th pentad of march is the establishment time of plateau summer monsoon,while the 4th pentad and5 th pentad of October are the retreat time of plateau summer monsoon.(2)the plateau monsoon is mainly caused by the thermal difference between winter and summer.In the lower layer,there is an obvious thermal low-pressure center on the plateau,and the plateau summer monsoon blows to the main body from all sides.There is an obvious positive divergence center in the main area of the upper level,and the plateau summer monsoon blows around from the main body of the plateau.(3)periodic oscillation characteristics of the plateau vortex: quasi-four-year periodic oscillation in spring;In summer,quasi-triennial periodic oscillation;In autumn,quasi-six-year periodic oscillation;In winter,quasi-triennial and quasi-six-year periodic oscillations occur.The frequency of the warm vortex and the moving low vortex on the plateau have quasi-four-year periodic oscillation.(4)in the main body of the plateau,the plateau monsoon intensity is in direct proportion to the plateau vortex generation frequency.The plateau vortex generates a high hairband at 30on-36 on,80oe-93 oe.The annual average frequency of the formation of the plateau vortex in the strong monsoon years,the number of eastward shifts and the annual average frequency of the formation of the plateau vortex in the east of the plateau are all more than those in the weak monsoon years.In strong years,the circulation situation field and dynamic field are conducive to maintaining the strong convergent updraft,and the abundant water vapor is continuously transported to the central part of the plateau,which is conducive to the formation of the plateau vortex(5)in the initial stage,the intensity of plateau vortex is sensitive to the perception of monsoon strength,but in the development process,due to the strong latent heat area on the east side of the plateau,which is conducive to the eastward movement of the plateau vortex in the whole process,the gap between them becomes smaller.The sensible heat in strong monsoon years is greater than that in weak monsoon years.In addition,due to the strong sensible heat in the central and western parts of the plateau in strong monsoon years,most plateau vortexes with high intensity were born in the central and western parts of the plateau,and the intensity of plateau vortexes was relatively strong at the beginning.(6)whether in strong or weak years,the plateau vortex with a longer life history tends to draw closer to the west of the plateau,and the proportion of plateau vortex with a long life history in weak monsoon years is higher than that in weak monsoon years.In weak monsoon years,the range of cold advection is relatively large.Therefore,the proportion of plateau vortex with long life history in weak monsoon years is more than that in strong monsoon years. |
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