【作者】 周晓霞；

【导师】 王盘兴； 丁一汇；

【作者基本信息】 南京信息工程大学 ， 应用气象学， 2007， 博士

【摘要】 利用NCEP／NCAR再分析资料和中国气象台站气温和降水观测资料，讨论了亚洲夏季风区水汽通量场的时空特征及其与中国降水的关系，主要结论如下：1亚洲季风区夏季为强大的水汽汇，东亚大陆和印度季风区均有强的辐合中心。亚洲季风区在赤道以北有很强的西风输送。对于纬向平均的经向输送，亚洲季风区向北的水汽通量在赤道地区最大，约为全球平均的2倍。5-7月来自印度季风区的水汽输送持续加强，而6-7月来自西太平洋的偏东水汽输送发展到极盛。亚洲季风区不论在纬向和经向输送上，都表现了其独特性。2东亚季风区水汽输送路径和源地因季节而不同，中国南方冬春季水汽主要来自副热带和中纬西风的输送，副热带西风输送在春季最强。春末至夏初则以热带西风输送为主，在夏季，热带西风水汽通量最强，中高纬度西风水汽输送也达到最强，二者季节变化同位相，7月达到极值，此时中高纬度西风水汽通量仅为热带西风水汽通量的1／4左右。3华北汛期降水有明显的年际和年代际变化，与通过南边界和西边界的水汽相关较好，特别是在年代际尺度上，均有准17年的周期。但90年代以后，准11年的周期可能更为重要。70年代中期突变之后，季风气流比西风带输送减弱得更剧烈，使得西风带水汽输送对华北汛期降水的作用相对增大。水汽收支分析表明，南边界的水汽变化对旱涝起着主导作用。4水汽通量和中国东部地区夏季降水存在多时间尺度变化及相关关系。对年代际尺度，华北地区和长江中下游地区的降水与水汽通量场的相关最为显著。在年际尺度上，水汽通量场和降水均有2-3年的显著周期。水汽通量场与江淮流域和黄河流域以及江南大部的降水有密切关系。对30-60天季节变化部分，均表现出明显的准40天周期振荡。SVD前两个模态描述了长江及江南地区、长江以北到山东半岛地区降水与水汽输送有显著的正相关关系。第三模态主要反映了华南及东部沿海异常降水时的水汽输送特征，它与台风活动密切相关。5夏季华南地区水分内循环最强，华北次之，江淮地区最弱。在干季蒸发的作用尤其重要，特别是冬季，蒸发一方面要补偿辐散流出的水汽，一方面也是降水的水汽来源。水汽输送的分析表明，平均流和瞬变波造成的水汽辐合辐散几乎反位相。瞬变波总是沿平均水汽梯度方向输送水汽，从而维持不同纬度间大气的水汽平衡。瞬变输送活跃区位置和强度有明显的季节变化，各季节都以经向输送为主。在各区域雨季时期，平均环流的输送对水汽辐合起了决定作用，而瞬变波常引起水汽辐散。在降水较少的季节，平均环流的作用显著减小，瞬变输送的作用相对增大。对于华北地区，夏季水汽主要来自平均流引起的辐合，大部分月份(7-8月除外)水汽输送由瞬变波完成。6中国大暴雨时期个例分析表明，不同区域强降水过程，异常水汽来源不同。华北地区主要来自副热带西太平洋，长江中下游和华南地区主要来自孟加拉湾和南海。对华北地区强降水过程，区域水汽通量的经向输送相对较强，对长江流域和华南地区的强降水，区域水汽通量的纬向输送相对更明显，此时由北边界输出的水汽大大减少，南边界水汽流入的增大导致的经向辐合加强是降水量增大的主要原因。更多还原

【Abstract】 Based on the 1948-2005 NCEP/NCAR reanalysis data and the station observationsof precipitation and temperature of China from 1951-2005, the features of Asiansummer monsoon and their relations with the rainfall in China are investigated, themain results from this study are as follows:1)The Asian summer monsoon region is a major moisture sink in summer with twoconvergent centers in East Asian and Indian summer monsoon region, respectively.The prominent westerly moisture transfer north of the Equator over Asian summermonsoon region is in reverse with other places of similar geographic latitudes, and thezonally averaged meridional moisture transfer across the equator is around 2 timeslarger than that averaged along the equator. The southwest moisture transport fromIndian monsoon increases from May to July, and the southwest transport from thewestern Pacific enhances from June to July.2)The moisture transports from various latitudes in East Asian summer monsoonchange with season. In winter and spring, moisture primarily comes from subtropicaland mid-latitude westerlies in South China, the subtropical westerly moisture flux isstrongest in spring. From the end of spring to summer, the tropical westerly fluxreinforced greatly with its peak in July, while the magnitude of the mid-high latidudewesterly moisture flux is only about a quarter of the tropical westerly flux.3)The rainy season rainfall of North China bears obvious interannual andinterdecadal variabilities, and have good agreement with moisture influx from itssouth and west boundaries, particularly on interdecadal time scale, a 17-year period isevident throughout 1951-2005. But the 11-year period is more conspicuous after1990’s. The rapid weakening of moisture transport by monsoonal currents andmid-latitude westerlies occurred in the middle of 1970’s, and the former, which holdthe keys of the rainfall in North China, decreased more drasticly than the latter.4) Close relationship between summer moisture transfer and rainfall in the east partof China is revealed on multi-scale. For the interdecadal time scale, the North China,as well as Changjiang River basin appear significant correlation with the distributionof moisture flux. As to the interannual time scale, the moisture flux and rainfall bothhave a 2-3year period. The moisture flux closely relate to the rainfall inChangjiang-Huaihe River valley, the Huanghe River valley and the most part of southof Changjiang River. On the 30～60-day time scale, a 40-day period is discoveredexplicitly. The three SVD leading modes demonstrate the relationship between moisture transport and summer rainfall in China, specifically the third modeillustrates the effect of typhoon activities on the rainfall in coastal areas of China.5)Water balance estimate indicates that in summer, water recycling is mostvigorous over South China, then the North China, and most inactive inChangjiang-Huaihe River valley. During non-rainy season, especially in winter, thenet moisture convergence is mainly a result of evaporation offsetting the moisturedivergence in the regions, which provides moisture for the rainfall during the season.Evidence also shows that the moisture transfer by the mean flow and that by transienteddy are out of phase in annual cycle. The intensive belt of transient eddy flux shiftswith season, and characterized by distinct meridional transport. In rainy season, themean flow moisture transport is decisively responsible for the regional water vaporconvergence, in contrast, the transient eddies play an opposite role to the mean flow.As for non-rainy season, the transient moisture transfer becomes relatively crucial.6)Calculations of the violent rainfall cases in different regions demonstrate that theanomalous moisture essential for the rainfall comes from different sources. For thecase of 1963, the anomalous moisture is chiefly from the subtropical western Pacific,and the regional meridional transport is dominant. While for the cases in theChangjiang River valley and South China, the anomalous moisture sources are Bay ofBengal and the South China Sea, and the zonal moisture transport is noticeable. Thegrowth of the meridional moisture convergence caused by the influx across thesouthern boundary principally accounts for the augmentation of the rainfall in eachregion.更多还原