华南夏季持续性强降水的低频特征及影响因子分析

发布时间：2018-08-01 08:49

【摘要】：利用1982-2011年夏季5-8月中国气象观测站点逐日降水资料、NCEP/NCAR全球再分析日平均资料、NOAA逐日向外长波辐射OLR资料集和海表温度SST数据、以及澳大利亚气象局的RMM-MJO(Real-time Multivariate MJO)指数等,通过选取低频降水事件的方法,考察了华南夏季12-30d持续性强降水的基本统计特征,然后利用位相合成的方法分析了华南夏季持续性强降水期间伴随的低频大气环流形势以及低频信号的来源和传播情况,同时也分析了低频海气耦合过程、热带MJO(Madden-Julian Oscillation)的传播活动对华南夏季12-30d持续性强降水的影响及途径。主要结论如下:(1)华南夏季降水具有显著的12-30d低频振荡特征,降水量和降水强度的大值区集中分布在华南的东南部沿海地区。持续性强降水事件的持续天数范围为3-6天,其中以持续3-4天的事件居多,持续4天的事件的降水量占总低频降水事件降水量的比重最大。前汛期末期(6月)是华南夏季12-30d持续性强降水最易发生的时段。持续性强降水期间的雨带自东南沿海向西北内陆推进。(2)在华南夏季12-30d持续性强降水发生期间,华南及邻近海域低层受到强大的低频气旋式环流控制,低频上升运动显著,而南海-菲律宾海一带则是强的低频反气旋式环流,其西侧向北的低频水汽输送不断将孟加拉湾北部和南海的水汽送至华南及邻近海域进行辐合上升。低层的低频信号来源于热带西太平洋和南海-菲律宾海一带低频振荡的西北向传播,同时伴随着西太平洋副热带高压明显的西伸北扩和东撤收缩的低频变化过程。而在高层,当持续性强降水发生时,华南北侧(22°-45°N,95°-130°E)区域强大的低频气旋式环流和孟加拉湾-南海一带的低频反气旋式环流相互配合,使华南高层处于强大的辐散场中,从而加强了低层的辐合与低频上升运动,造成持续性强降水的增强与维持。高层的低频信号来源于包含异常气旋和反气旋的低频Rossby波列的东南向传播。(3)在低频降水的整个过程中,伴随着低层低频环流的演变,海表温度异常(SSTA)也发生了明显的低频变化,且海表温度的演变与低层大气环流场的演变呈现近π/2的位相差,即存在低频海气相互作用。低频大气环流异常能够通过云辐射和热通量过程改变低频SSTA,而由大气强迫的低频SSTA能够通过影响低层大气的稳定性来对大气施加明显的反馈作用,该低频海气耦合过程有利于大气低层的低频信号不断向华南地区传播,从而影响华南夏季12-30d持续性强降水的发生、发展与结束。(4)热带强MJO的传播活动对华南夏季12-30d持续性强降水存在明显的调制作用。当MJO对流活跃中心位于热带印度洋时(即强MJO的第1-3位相),所伴随的大气异常环流场有利于华南夏季12-30d持续性强降水的发生。尤其在强MJO的第1位相,西太平洋副热带高压西伸北扩,热带西太平洋上空出现显著的位势高度正异常,并伴有强大的异常反气旋式环流,其西北侧强盛的异常西南风控制着整个华南地区低层,造成最强烈的向华南地区的西南风水汽输送,华南地区出现明显的水汽异常辐合和显著的上升运动,对流强烈发展,导致华南夏季12-30d持续性强降水发生在强MJO第1位相的天数最多,该位相是最有利于华南夏季12-30d持续性强降水发生的位相。当MJO对流活跃中心进入西太平洋后(即强MJO的第5-7位相),所产生的大气异常环流场不利于华南夏季12-30d持续性强降水的发生,特别是在强MJO的第7位相,异常环流型与第1位相基本相反,华南夏季12-30d持续性强降水发生在强MJO第7位相的天数最少。
[Abstract]:Using the daily precipitation data of the China Meteorological Observation Station in the summer of 1982-2011 years, the daily mean data of NCEP/NCAR global reanalysis, the OLR data set by NOAA and the SST data of the sea surface temperature, and the RMM-MJO (Real-time Multivariate MJO) index of the Australian Bureau of meteorology, and the method of selecting low frequency precipitation events, are investigated. The basic statistical characteristics of the persistent strong precipitation of 12-30d in Southern China in summer are analyzed. Then the low frequency atmospheric circulation and the source and propagation of low frequency signals are analyzed with the method of phase synthesis in the summer of Southern China, and the low frequency sea air coupling process and the tropical MJO (Madden-Julian Oscillation) are also analyzed. The main conclusions are as follows: (1) the summer precipitation in Southern China has the characteristics of significant 12-30d low frequency oscillation, and the large value area of precipitation and precipitation intensity is concentrated in the southeast coastal areas of Southern China. The duration of persistent strong water drop events is 3-6 days, which is held in Southern China. The last 3-4 days of events are most, the precipitation of the last 4 days of the event accounts for the largest proportion of the total low frequency precipitation event precipitation. The end period of the pre flood period (June) is the most likely time period for the persistent strong precipitation of 12-30d in summer in Southern China. The rain belt during the persistent strong rainfall is promoted from the southeast coast to the northwest inland. (2) the persistent strong precipitation of 12-30d in summer in the summer of Southern China. During the period, the low floor of Southern China and its adjacent sea area is controlled by a strong low-frequency cyclonic circulation, the low frequency rising movement is significant, while the South China Sea and the Philippines sea is a strong low-frequency anticyclone circulation, and the northward low frequency water vapor transport to the north of the west side of the West Bengal and the South China Sea continuously converge to the Southern China and the adjacent sea area. Low frequency signals are derived from the northwestward propagation of low frequency oscillations in the tropical western Pacific and the South China Sea and the Philippines sea, along with the low frequency variation of the Western Pacific subtropical high in the West extension and eastward contraction. At the high level, when the persistent strong precipitation occurs, the north side of Southern China (22 -45 N, 95 -130 E) is strong. The large low-frequency cyclonic circulation and the low frequency anticyclonic circulation in the bay of Bengal - South China Sea make the Southern China high rise in the strong divergence field, thus strengthening the low level convergence and low frequency rising movement, resulting in the enhancement and maintenance of persistent strong precipitation. The low frequency signal of the high rise is derived from the low frequency of cyclone and anticyclone. (3) in the whole process of low frequency precipitation, (3) in the whole process of low frequency precipitation, with the evolution of low frequency circulation, the sea surface temperature anomaly (SSTA) also has obvious low frequency changes, and the evolution of sea surface temperature and the evolution of the low atmospheric ring flow field present the near PI /2 phase difference, that is, the low frequency sea air interaction. Low frequency atmospheric ring. The flow anomaly can change the low frequency SSTA through the process of cloud radiation and heat flux, and the low frequency SSTA that is forced by the atmosphere can exert a significant feedback effect on the atmosphere by affecting the stability of the lower atmosphere. The low frequency sea air coupling process is beneficial to the low frequency signals of the lower atmosphere to spread to the Southern China region, thus affecting the summer 12-30d in Southern China. The occurrence, development and end of persistent strong precipitation. (4) the propagation of tropical strong MJO has a distinct modulation effect on the persistent strong precipitation of 12-30d in Southern China in summer. When the MJO convective active center is located in the tropical India ocean (that is, the 1-3 phase of strong MJO), the accompanying atmospheric anomalous annular flow field is beneficial to the persistent strong precipitation of 12-30d in Southern China in summer. Especially in the first phase of the strong MJO, the West Pacific subtropical high extends north and extends northward, and there is a significant positive anomaly over the western tropical Pacific Ocean, with a strong anomalous anticyclone circulation, and the strong anomalous southwest wind in the northwest side controls the low level of the whole Southern China region, causing the strongest southwestern Fengshui to the Southern China region. In Southern China area, there is obvious anomalous water vapor convergence and significant rising movement in Southern China area. Convection develops strongly, which leads to the largest number of strong MJO first phases in the summer of Southern China in summer, which is the most favorable phase for Southern China's summer 12-30d persistent strong descending water, when MJO convection center enters West Taiping. After ocean (that is, the 5-7 phase of strong MJO), the anomalous atmospheric circulation field produced is not conducive to the occurrence of persistent strong precipitation of 12-30d in Southern China in summer, especially in the seventh phase of strong MJO, and the anomalous circulation pattern is basically opposite to the first phase. In summer, the number of days of persistent strong precipitation of 12-30d in the strong MJO seventh phases is the least.
【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】：P426.6

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