The Research On The Relationship Between Tibetan Plateau Vortex And Low-frequency Oscillation

There are many unique weather system over the Tibetan Plateau, andTibetanPlateau Vortex (TPV) itself is representative of the low-value weather systems,and its generation, development and eastward propagation are often accompanied withprecipitation, strong winds, thunderstorms and other weather processes, resulting in aseries of extremeweather events over the Tibetan Plateau and the Sichuan-Chongqingregions downstream of the plateau which is one of the major styles of extremeweatherevents in those areas. Some TPVs, which move from the plateau to the east and developstrong could even affect a wide range of China’s eastern region. Thus the research onmechanisms ofthe occurrence, development and eastward propagation of TPV and itsprediction methods is pretty significant.In this paper, we explored the tropical MJOmodulation onTPV and revealedthe mechanismsof the formation of TPV in thebackground of the climate change, and we got the following main conclusions:(1)By the statistical analysis of data setof the MICAPS TPV,we found that thenumber of TPV generated in summer,the number of TPV generated inevery monthfromJune to August, the each number of TPV generated ineastern, western and centralregions andthe each number of TPV moving out of the Plateau vortex, not moving outof the Plateau vortex numbershowed a downward trend.The number of TPV generatedin June, the number of the eastward shift TPV andthe number of the central TPVshoweddownward trend.The largest number of TPV is generated in June, July is in thesecond,and August is the last. The strongest interannual fluctuation of TPV is July,August is the second, and June is the last.The number of TPV generated ineasternregions of the Tibetan Plateauis the largest, and the interannual fluctuation is thestrongest too, TPV generated inthe central regions is the second, and TPV generatedinthe westernregions is the last.(2) By the statistical analysis of data setof the NCEP TPV, we found that thenumber of TPV generated in summer, the number of TPV generated in every monthfrom June to August, the each number of TPV generated in eastern, western regions andthe each number of TPV not moving out of the Plateau vortex number showed a increasing trend.The number of TPV generated in June, the number of the eastward shiftTPV and the number of the central TPV showed downward trend.The largest number ofTPV is generated in June, July is in the second,and August is the last. The strongestinterannual fluctuation of TPV is June, July is the second, and August is the smooth.The number of TPV generated in central regions of the Tibetan Plateauis the largest, andthe interannual fluctuation is the strongest too, TPV generated in the western regions isthe second, and TPV generated in the eastern regions is the last.(3)The results show that MJO plays an important role on Tibetan Plateau Vortex,the number of Plateau Vortex generated in Active period of MJO is three times than thatin weak period. During MJO active period, the number of the Plateau vortex is moreduring phase1and phase2while less during phase3and phase7.With the Synthesis ofphase1and phase7respectively, We discover that the synthetic fieldsof allmeteorological elements on phase1show apparent factors which conducive to thegeneration of the Plateau vortex, but it’s opposite on phase7.(4)During the strong (weak) MJO period, the Tibetan Plateau is in control of alow-frequency low-pressure cyclone (high-pressure anticyclone) system, thus theatmospheric circulation conditions over the plateau are conducive (not conducive) to thegeneration of TPV.(5)The number of TPV is significantly influenced by the atmosphericcirculation.When the number of TPV is larger, the climatology of western Tibetan Highis weak, and the whole climatology of Tibetan High is strong; However, the wholeclimatology of Tibetan High is weak in the year which the number of TPV is smaller.(6)When the year TPV happened more, the propagation of atmospheric lowfrequency fluctuation in500hPa is from the south side of Tibetan Plateau to northward,and also the propagation of atmospheric low frequency fluctuation in500hPa is fromthe south side of Tibetan Plateau to the Indian Ocean during May to the earlier10daysin July. From the middle of July to August, the propagation of atmospheric lowfrequency fluctuation is from Siberia to the Plateau, and a strong atmospheric lowfrequency fluctuation generated over the Iranian Plateau,and propagated to the TibetanPlateau over the low reaches,however,there also have a strong propagation ofatmospheric low frequency fluctuation from Western Pacific to the Tibetan Plateau;When the year TPV happened less, the propagation of atmospheric low frequencyfluctuation from Plateau to Siberia is significant,the first and second propagations caneven to the Indian Ocean during May to the earlier10days in July; From the middle of July to August,the low frequency fluctuation generated in bay of Bengal moved to theSiberia regions, at the same time,there is a propagation from Iranian Plateau to TibetanPlateau,but the strength of propagations in less TPV years is weaker than in more TPVyears,also the propagation from Eastern Pacific to Tibetan Plateau is not clear.(7)When the less TPV years, the low frequency fluctuation of summer zonal andmeridional wind over Tibetan Plateau is stronger than which in more TPV years, and thezonal and meridional wind show a distribution of reverse phase,which include3timestransitions from positive to negative.