西北太平洋地区八月份热带气旋生成异常的机理分析

发布时间：2018-05-11 23:30

本文选题：热带气旋生成 + 大尺度环流　；参考：《南京大学》2017年硕士论文

【摘要】：夏季是西北太平洋地区热带气旋(TC)生成较为活跃的季节,其中8月份平均生成的TC频数在所有月份里最多。本文从大尺度环流背景,MJO和赤道波动的位相和波动能量,赤道外Rossby波破碎和高层PV入侵等方面分析了 8月份的TC生成异常的成因。研究发现当西太地区8月份TC生成偏少(偏多)时,越赤道气流和季风槽偏弱(偏强),对流层低层为反气旋型(气旋型)环流异常和大范围的东风(西风)异常,中层的副热带高压加强(减弱),而高层的南亚高压和洋中槽偏弱(偏强),低层辐合和上层辐散的结合减弱(加强),东风(西风)切变偏强,对流层大气的水汽偏干(偏湿),大尺度环流条件不利于(利于)湿对流活动和TC的生成。从统计上来看,E1Nifno或LaNinna与西太地区8月份TC生成的异常并没有明显的相关性。MJO和赤道波动整体的活跃(不活跃)位相,对西太地区8月份TC的生成具有一定的促进(抑制)作用。当8月份MJO处于活跃(不活跃)位相时,西太地区的对流层低层有气旋性(反气旋性)的环流异常和大范围的西风(东风)异常,大尺度环流条件利于(不利于)低层辐合,对流活动发展和TC生成,TC的生成频数偏多(偏少),且TC的生成位置相对集中(分散)。当8月份TC生成活跃时,赤道波动能量为大范围的正异常,波动整体上偏活跃,且TC多数生成于赤道波动的对流活跃位相中;当8月份TC生成不活跃时,赤道波动能量为大范围的负异常,即波动同期偏弱,且波动活跃区域向低纬度的ITCZ辐合区收缩,对扰动发展和TC生成的影响偏弱。当8月份的中部和西部太平洋地区的RWB发生频率偏多(偏少)时,西太地区东部的对流层高层PV大值区向西发展(向东收缩),而西部的对流层偏暖区域向西收缩(向东发展)。东风切变偏弱(偏强),西风切变偏强(偏弱)且向西(东)偏移,西太东部的对流层水汽相对偏干(偏大),垂直运动减弱(增强),大尺度环流条件不利于(利于)对流发展和东部区域的TC生成。西太地区TC生成的频数偏少(偏多),整体生成位置向西(东)偏移,且TC的整体强度偏小(偏大)。2014年8月份没有TC形成,除了大尺度环流背景不利于TC生成外,热带扰动的数量同期偏少。热带扰动的发展处于MJO不活跃位相区中,对流活动和低层涡度的发展被抑制。同时赤道外高层的Rossby波破碎和PV入侵过程对热带扰动的发展也有重要的影响,其带来的干冷空气使得扰动中心附近的水汽偏干,垂直风切变增加,使得湿对流活动进一步受到抑制。受MJO和赤道波动的不活跃位相,以及赤道外高层RWB和PV入侵的共同影响,热带扰动的整体发展始终受到抑制,最终2014年8月份没有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.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P444

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