亚非夏季风系统的气候特征及其年代际变率研究

发布时间：2018-01-12 01:18

本文关键词：亚非夏季风系统的气候特征及其年代际变率研究　出处：《中国气象科学研究院》2017年博士论文　论文类型：学位论文

【摘要】：亚非夏季风是一个横跨北非、南亚和东亚的带状行星尺度系统,其强弱与位置异常能够影响大范围跨地区的旱涝分布。对亚非夏季风系统年代际变化的研究和归因具有十分重要的科学意义和应用价值,本文利用再分析数据和CMIP5模式数据,揭示了亚非夏季风系统的结构特征,重点分析了近百年亚非夏季风年代际变率特征及成因;并探讨了中等排放情景下未来亚非夏季风降水的可能变化,加深对气候变化背景下的季风演变过程和机理的理解。本论文得到的结论如下:(1)亚非夏季风系统具有完整的大尺度季风雨带。北非萨赫勒地区、南亚以及东亚(中国黄淮至华北地区)降水呈现出一致变化。多种变量(降水极大值区、低层风场辐合区和OLR极小值区)清晰地表征了亚非夏季风系统的带状分布特征。定义的亚非夏季风强度指数和位置指数,能够准确直观的刻画亚非夏季风系统的整体性的变化特征。(2)近百年亚非夏季风的年代际变率的主模态:北非萨赫勒地区、南亚以及东亚地区(中国黄淮至华北地区)降水呈现出一致型增加或减少。亚非夏季风降水经历了三次年代际转折:第一次出现在1920年前后,亚非夏季风降水由少转多;北非萨赫勒地区、南亚地区与中国东部地区的降水同步增多。第二次年代际转折出现在1960s年代末期,亚非夏季风降水由多转少;北非萨赫勒地区、南亚地区与中国东部地区降水同步减少。第三次年代际转折出现在1990s年代后期,北非萨赫勒和中国东部季风雨带加强和北移。(3)亚非夏季风降水年代际变化的原因。亚非夏季风年代际主模态受到AMO的调制。在1920s至1950s年代,AMO处于正位相,亚非夏季风降水偏多;在1960s至1980年代,AMO处于负位相,亚非夏季风降水减少。在AMO负位相和PDO正位相阶段,亚非夏季风经历了 1960s至1980s年代的少雨期,对流层中层存在遥相关波列,两个主要的负中心位于地中海和东亚北部,主要的正中心位于欧洲中部。在北非地区,对流层高层的气旋性环流与低层为反气旋性环流耦合,导致下沉气流发展,不利于发生降水。在东亚的黄淮地区,对流层高层受气旋性环流控制,不利于发生降水。(4)近三十年来,在AMO冷位相转暖位相条件下,亚非夏季风降水在20世纪90年代中后期的第三次年代际转折及其机制。从1990s年代后期开始,中国东部季风区主雨带呈现出加强和北移的变化,主雨带到达江淮-黄淮地区。北非萨赫勒地区变湿,降水由少转多。萨赫勒地区和我国黄淮地区降水呈同相变化(增多)原因在于欧亚与北非的大气环流在温、压、风三个方面对AMO暖位相呈现出显著的耦合响应。AMO暖位相在对流层上层激发出气旋与反气旋相间的东传的Rossby波列。这个波列中,位于北非上空的反气旋与北非地区地面的热低压相辐合,增强了在萨赫勒地区的上升运动。同时,在东亚地区上空也存在一个反气旋与黄淮地区地面气压场上的低压相辐合,进而加强了中国黄淮地区的上升运动,导致了萨赫勒地区和东亚黄淮地区一致的降水增强。(5)AMO暖位相对亚非夏季风系统结构的调制作用。亚非夏季风的结构特征主要体现为低层西风与高层东风。低层,来自北方的三股冷空气与来自赤道的几内亚湾偏西风、索马里越赤道气流、孟加拉湾西南风的汇合,形成三个冷暖空气的交汇区。AMO暖位相下,对流层上层温度变暖导致了高层热带东风急流不断加强北进。对流层上层变暖导致热带东风急流在入口区(东亚分支)和出口区(北非分支)风速的同步加强。高空热带东风急流的这种同步变化,分别激发并加强了急流入口区和出口区非地转次级环流,引起急流入口区右侧(黄淮地区)和出口区左侧(萨赫勒)的上升运动与降水同步增多。(6)多模式集合平均预估中等排放情景下,未来亚非夏季风降水整体上呈增加趋势,雨带北移,且存在着阶段性变化。在21世纪后期(2070s～2099s),亚非夏季风区将进入一个全面多雨期。未来百年,亚非夏季风降水增加与北移的特征受到自然变率和人类活动所致的全球变暖的共同影响,但在本世纪后半期,人类活动的影响更为明显。
[Abstract]:Asian African summer monsoon is a zonal planetary scale systems across North Africa, South Asia and East Asia, and the abnormal distribution of the intensity and position can affect a wide range across the region. It has an important scientific significance and application value of the research and the Asian African summer monsoon interdecadal change attribution, reanalysis data and CMIP5 data using this model and reveals the structural features of the Asian African summer monsoon system, focuses on the analysis of nearly a hundred years of summer monsoon interdecadal variability characteristics and causes; and discusses the secondary emission scenarios may change the Asian African summer monsoon precipitation, to deepen under the background of climate change in the monsoon evolution process and mechanism of the understanding of the conclusions. Are as follows: (1) summer monsoon system complete with large scale monsoon rain belt. The Sahel, South Asia and East Asia (China Huang Huai to the North China area) showed favorable precipitation Change. Many variables (maximum precipitation area, low wind convergence zone and OLR minimum area) clear characterization of the zonal distribution of Afro Asian summer monsoon system. Summer monsoon intensity index and the index position of the definition of integrity can accurately describe the variation characteristics of summer monsoon system. (2) the main mode of nearly a hundred years of summer monsoon interdecadal variability: Sahel, South Asia and East Asia (China Huang Huai to the North China area) precipitation showed identical type of increase or decrease. Summer monsoon rainfall experienced three interdecadal turning: for the first time in 1920 before and after the summer monsoon the precipitation from less turn; Sahel, South Asia and Eastern Chinese precipitation increased second times. Synchronous interdecadal appeared in 1960s in the late summer monsoon precipitation by around North Africa; SA Heller region, South Asia Area and precipitation in the east coastal region of Chinese simultaneously reduced. Third times interdecadal appeared in 1990s in the late 1960s, Sahel and North Africa China Eastern monsoon rain belt northward and strengthen. (3) the reason of interannual change summer monsoon precipitation in summer monsoon. The decadal main modal by AMO modulation. In 1920s to 1950s in AMO. In its positive phase, Asian African summer monsoon rainfall in 1960s; to 1980s, AMO in the negative phase, reduce the summer monsoon precipitation. In AMO negative and PDO positive phase, Asian African summer monsoon experienced less rainfall 1960s to 1980s in the middle troposphere are teleconection, two is located in the center of the main negative the Mediterranean Sea and the northern East Asia, is a major center located in Central Europe. In North Africa, upper tropospheric cyclonic circulation and the low level anticyclonic circulation coupling caused subsidence development, is not conducive to the occurrence of drop The water in East Asia. The Huang Huai area, the upper troposphere by cyclone circulation control, is not conducive to the occurrence of precipitation. (4) in the past thirty years, in the cold phase of AMO warm phase under the condition of summer monsoon precipitation in late 1990s third interdecadal and its mechanism. Starting from 1990s in the late 1990s, the main rain belt in Eastern the monsoon region China showing changes and strengthening northward, the main rain belt arrived Huang Huai Jianghuai area. Sahel wet precipitation from less. Turn the Sahel and China's Huang Huai area precipitation has a phase change (increase) in the atmospheric circulation in Eurasia and North Africa in the temperature, pressure, wind three aspects of AMO warm phase showed a significant coupling response of.AMO warm phase excitation cyclone and anticyclone and the eastward propagation of the Rossby wave in the upper troposphere. This wave, located in North Africa over the ground anticyclone and North Africa hot Low voltage phase convergence, enhances the upward movement in the Sahel region. At the same time, in the East Asian region over there is an anti cyclone and ground pressure in Huang Huai area on the field of low convergence, and strengthen the Huang Huai area Chinese upward movement, led to enhanced precipitation in the Sahel area and East Asia Huang Huai consistent. (5) AMO a relatively warm summer monsoon system structure modulation. Structural characteristics of summer monsoon is mainly reflected in low level and high level. The Lower East West, from the north and three cold air from the Gulf of Guinea equatorial westerly, the cross equatorial flow over the bay of Bengal, Southwest wind convergence, forming three warm and cold air the intersection area of.AMO warm phase, the upper troposphere temperature warming tall tropical easterly jet strengthened north. The upper troposphere warming of the tropical easterly jet in the entrance area (East Branch) And the exit area (North African branch) strengthen the wind speed. The synchronous change of high-altitude tropical easterly jet, respectively, to stimulate and strengthen the jet entrance and exit areas of ageostrophic secondary circulation, the right of the entrance region (Huang Huai) on the left and exit area (Sahel) ascending motion and precipitation synchronization (6 increase. The multi model ensemble prediction) secondary emission scenario, the future of the Asian African summer monsoon precipitation showed an increasing trend on the whole, the rain belt northward, and there is a phase change. In the late twenty-first Century (2070s ~ 2099s), the Asian African summer monsoon region will enter a comprehensive multi period. In the next century, Asian African summer monsoon and precipitation increase North features affected by global warming caused by human activities and the natural rate, but in the second half of this century, the influence of human activity is more obvious.

【学位授予单位】：中国气象科学研究院
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P425.42

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