發(fā)布時間：2018-05-11 23:30

  本文選題：熱帶氣旋生成 + 大尺度環(huán)流��； 參考：《南京大學》2017年碩士論文

【摘要】：夏季是西北太平洋地區(qū)熱帶氣旋(TC)生成較為活躍的季節(jié),其中8月份平均生成的TC頻數(shù)在所有月份里最多。本文從大尺度環(huán)流背景,MJO和赤道波動的位相和波動能量,赤道外Rossby波破碎和高層PV入侵等方面分析了 8月份的TC生成異常的成因。研究發(fā)現(xiàn)當西太地區(qū)8月份TC生成偏少(偏多)時,越赤道氣流和季風槽偏弱(偏強),對流層低層為反氣旋型(氣旋型)環(huán)流異常和大范圍的東風(西風)異常,中層的副熱帶高壓加強(減弱),而高層的南亞高壓和洋中槽偏弱(偏強),低層輻合和上層輻散的結(jié)合減弱(加強),東風(西風)切變偏強,對流層大氣的水汽偏干(偏濕),大尺度環(huán)流條件不利于(利于)濕對流活動和TC的生成。從統(tǒng)計上來看,E1Nifno或LaNinna與西太地區(qū)8月份TC生成的異常并沒有明顯的相關(guān)性。MJO和赤道波動整體的活躍(不活躍)位相,對西太地區(qū)8月份TC的生成具有一定的促進(抑制)作用。當8月份MJO處于活躍(不活躍)位相時,西太地區(qū)的對流層低層有氣旋性(反氣旋性)的環(huán)流異常和大范圍的西風(東風)異常,大尺度環(huán)流條件利于(不利于)低層輻合,對流活動發(fā)展和TC生成,TC的生成頻數(shù)偏多(偏少),且TC的生成位置相對集中(分散)。當8月份TC生成活躍時,赤道波動能量為大范圍的正異常,波動整體上偏活躍,且TC多數(shù)生成于赤道波動的對流活躍位相中;當8月份TC生成不活躍時,赤道波動能量為大范圍的負異常,即波動同期偏弱,且波動活躍區(qū)域向低緯度的ITCZ輻合區(qū)收縮,對擾動發(fā)展和TC生成的影響偏弱。當8月份的中部和西部太平洋地區(qū)的RWB發(fā)生頻率偏多(偏少)時,西太地區(qū)東部的對流層高層PV大值區(qū)向西發(fā)展(向東收縮),而西部的對流層偏暖區(qū)域向西收縮(向東發(fā)展)。東風切變偏弱(偏強),西風切變偏強(偏弱)且向西(東)偏移,西太東部的對流層水汽相對偏干(偏大),垂直運動減弱(增強),大尺度環(huán)流條件不利于(利于)對流發(fā)展和東部區(qū)域的TC生成。西太地區(qū)TC生成的頻數(shù)偏少(偏多),整體生成位置向西(東)偏移,且TC的整體強度偏小(偏大)。2014年8月份沒有TC形成,除了大尺度環(huán)流背景不利于TC生成外,熱帶擾動的數(shù)量同期偏少。熱帶擾動的發(fā)展處于MJO不活躍位相區(qū)中,對流活動和低層渦度的發(fā)展被抑制。同時赤道外高層的Rossby波破碎和PV入侵過程對熱帶擾動的發(fā)展也有重要的影響,其帶來的干冷空氣使得擾動中心附近的水汽偏干,垂直風切變增加,使得濕對流活動進一步受到抑制。受MJO和赤道波動的不活躍位相,以及赤道外高層RWB和PV入侵的共同影響,熱帶擾動的整體發(fā)展始終受到抑制,最終2014年8月份沒有TC生成。
[Abstract]:Summer is the most active season for TCC generation in the Northwest Pacific, and the average TC frequency in August is the highest in all months. In this paper, the causes of TC anomalies in August are analyzed in terms of the phase and energy of MJO and equatorial waves, the breakup of Rossby waves outside the equator and the high level PV intrusion in the large scale circulation background. It is found that the cross-equatorial flow and monsoon trough are weak (strong) in August, and the lower troposphere is an anticyclonic (cyclonic) circulation anomaly and a large-scale easterly (westerly) anomaly. The subtropical high in the middle layer is strengthened (weakened), while the South Asia high in the upper layer and the trough in the middle ocean are weak (strong), and the combination of convergence in the lower layer and divergence in the upper layer is weakened (strengthening, easterly (westerly) shear is stronger, In the tropospheric atmosphere, the water vapor is dry and the large scale circulation conditions are unfavorable to the wet convection activity and the generation of TC in the tropospheric atmosphere. Statistically speaking, there is no obvious correlation between E1Nifno or LaNinna and TC in August in Western Pacific region. MJO and the active (inactive) phase of equatorial fluctuation as a whole, which can promote (inhibit) the formation of TC in August in Western Pacific region. When MJO is active (inactive) in August, there are cyclonic (anticyclonic) circulation anomalies and westerly (easterly) anomalies in the lower troposphere of the Western Pacific region, and the large-scale circulation conditions are favorable (unfavorable) to the convergence of the lower troposphere. The development of convection activity and the formation frequency of TC are more and less, and the generation position of TC is relatively concentrated. When TC is active in August, the equatorial wave energy is positive anomaly in a wide range, the fluctuation is active on the whole, and most of TC is generated in the convective active phase of equatorial wave, and when TC is not active in August, The equatorial wave energy is a negative anomaly in a large range, that is, the fluctuation synchronization is weak, and the active fluctuation region shrinks to the ITCZ convergence region in the low latitude, which has a weak effect on the disturbance development and TC generation. When the frequency of RWB in the central and western Pacific regions in August is more or less, the high PV region of the upper troposphere in the eastern part of the Western Pacific region develops westward (contracting eastward), while the warm region of the western troposphere shrinks westward (eastward). The east wind shear is weak (strong), the west wind shear is strong (weak) and the west (east) is shifted to the west. The tropospheric water vapor in the eastern part of the western Pacific is relatively dry (larger and larger), the vertical motion is weakened (enhanced), and the large-scale circulation conditions are not conducive to the development of convection and the formation of TC in the eastern region. The frequency of TC generation in the Western Pacific region is relatively small (more or less), and the overall intensity of TC is smaller than that in August 2014, except that the large-scale circulation background is not conducive to the generation of TC, and the overall intensity of TC is relatively small (larger than that in August 2014), except that the large scale circulation background is not conducive to the generation of TC. The number of tropical disturbances is small in the same period. The development of tropical disturbances lies in the MJO inactive phase, and the convective activity and the development of the lower level vorticity are inhibited. At the same time, the breakup of Rossby waves and PV intrusion in the outer layer of the equator also have an important influence on the development of tropical disturbances. The dry cold air caused the water vapor in the vicinity of the disturbance center to be dry, and the vertical wind shear increased. The wet convection activity is further inhibited. Under the influence of the inactive phase of MJO and equatorial fluctuations, and the invasion of RWB and PV in the upper layer of the equator, the overall development of tropical disturbances is restrained all the time, and no TC is generated in August 2014.
【學位授予單位】：南京大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P444

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本文編號：1876139