【作者】 祝丽娟；

【导师】 王亚非；

【作者基本信息】 中国气象科学研究院 ， 气象学， 2011， 硕士

【摘要】 本文以探索热带气旋活动规律为主要目标,利用1949-2009年的台风年鉴和NCEP/NCAR再分析资料等分析了南海范围季节内振荡特征及其与南海热带气旋活动之间的关系。针对南海区域创建了一个新的能表示MJO活动的指数,分析了该指数对南海热带气旋活动规律的指示及对应的大气环流特征。其次验证了区域气候模式RegCM3.0对南海范围季节内振荡特征的模拟能力,并运行了基于侧边界信号的数值试验来探讨影响南海范围季节振荡强弱的信号来源。全文主要结论包括:(1)首先针对南海地区创建了一个新U指数,经验证该指数能够较好的描述南海地区MJO的具体特征;(2)利用U指数把MJO活动划分了8个位相,发现其位相变化和南海地区热带气旋活动有很好的对应关系,其中U指数的不活跃期(第4-6位相)对应南海生成气旋和登陆气旋均明显减少,而活跃期(第7-3位相)情况刚好相反;(3)合成分析表明,指数的活跃期时南海地区对应负OLR异常(强对流)和气旋式切变,同时副热带高压强度较弱,东退明显,为气旋生成发展创造有利的大尺度环境场。活跃期以第2位相特征最明显,强度最强;不活跃期则抑制对流及气旋发展,以第6位相表现最强。说明热带MJO东传时,伴随对流中心位置的东移,南海地区对应不同的气旋活动特征;(4)把U指数与广义的CPC-MJO指数进行比较,发现CPC-MJO120指数对南海地区最有代表性,且其与U指数相关性是存在大概一个的时间位相差。此外,CPC-MJO120指数不能清楚地判明南海地区气旋活动归属于活跃与否两类,从反面证明了U指数对于表征南海地区的优越性;(5)进一步从积云对流能源供应的角度来探讨气旋发展,发现加热中心、强对流中心及水汽通量散度配合一致。活跃位相整层热源的垂直剖面均反映南海对应强上升运动和中层加热;不活跃位相则情况相反。热带气旋发展也依赖加热的垂直分布。活跃位相的加热峰值高度正好对应对流系统的发展期,适合气旋发展。因此,热带MJO东传会影响南海地区加热配置,从而影响热带气旋活动;(6)数值试验结果表明,相对于南海范围内部信号,外部的信号传入起了很重要的作用。来自北边和西边的季节内振荡信号的传入对南海范围季节内振荡强弱影响最大,尤其是北边信号。推测是中高纬度振荡向低纬传播和源于印度洋的季节内振荡的东传对南海地区30-60天尺度的振荡影响最大。更多还原

【Abstract】 In order to study the tropical cyclone (TC) activity, the characteristics of intra-seasonal oscillation (MJO) over the South China Sea (SCS) was examined to discuss the relationship between the MJO and cyclones over the SCS by using the tropical cyclones data from year 1949 to 2009 and NCEP/NCAR reanalysis data et al. A new index named U index was created to describe the MJO activity over the SCS. The filtered time series of the zonal wind at 850hPa was divided into 8 phases. The tropical cyclone activity and atmospheric circulation features were studied according to the phase variation. In addition, the oscillation simulation ability of the regional climate model was tested and three groups of sensitive simulation tests were carried out to find out the most influential signal based on the lateral boundaries.The main conclusions are as follows: (1) The new U index was able to describe the MJO activity over the SCS effectively; (2) The MJO process was divided into 8 phases using the U index. The phase variation was found to be in accordance with the tropical cyclone activity over the SCS with less TC formation and landfall during inactive period (phase 4-6) while the situation was quite contrary during active period (phase 7-3); (3) The composite analysis indicated that there were negative OLR anomaly (strong convection), weak subtropical high and cyclonic shear during active MJO period, which created a favorable circumstance for TC generation. The majority of TC genesis locations came from the Northwestern Pacific and the TC from the SCS also increased evidently. The phase 2 and 6, regarded as the representation of the most active and inactive period of U index respectively, had the most significant characteristics of each period. Therefore TC activity was quite different accompany with the eastward propagation of convective centers of MJO; (4) The U index was found to have a phase deviation with the CPC-MJO index. As the CPC-MJO120 index had the highest correlation coefficient with other three indexes, it was treated as the deputy of the index to represent the SCS. The CPC-MJO index was found to be incapable of grouping the TC activity over the SCS into two main classes, although phase 3 and 7, as the delegation of the most active and inactive period, revealed such a tendency to some extent; (5) Convection was of great importance both for MJO and TC grow up. The composite analysis of the horizontal and vertical convective heating distribution according to different MJO phases was studied. The results showed that in different phases, the heating source was quite different. In combination with the convergence and divergence of the moisture transport fluxes, the modulation of TC activity by MJO can be revealed effectively from the energy aspect. Thus, the U index was more suitable for describing the MJO propagation eastward over the SCS and the wind at 850hPa corresponded well with the MJO phases as well; (6) Numerical simulation results showed that the intraseasonal oscillation signal comes from the north and west boundaries have the most influential impact on the MJO intensity over the South China sea, especially that from the north. It is supposed to be the propagation of the intraseasonal oscillation from the middle-high latitude to the low-latitude and the eastward propagation from the India ocean to the South China sea.更多还原