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我国东部极端降水变化特征及成因分析

Variation Characteristics of Extreme Precipitation over the East of China and the Reason Analysis

【作者】 王苗

【导师】 郭品文;

【作者基本信息】 南京信息工程大学 , 气象学, 2011, 硕士

【摘要】 本文首先利用我国东部地区392个站点的逐日降水资料集对近50年东部地区极端降水基本变化特征进行研究,其次就ENSO对极端降水的季节影响加以分析,并初步运用湿位涡理论探讨了可能成因,最后以1948-1976年和1977-2008年两个阶段作为研究子时段,利用NECP/NCAR再分析资料重点讨论了前后两个阶段我国东部地区的大气湿位涡差异及稳定度状况,并分析了水汽输送、垂直运动状况,且从大气对流层顶温度变化的角度出发探讨了造成前后两阶段大气稳定度差异的原因,得出以下主要结论:(1)我国东部地区极端降水气候平均分布呈现从东南沿海到西北内陆方向减少的态势,在各个年代又各有差异;近50年极端降水量、极端降水量占降水量比例、极端降水次数和极端降水强度长期变化趋势在北方均主要表现为减小的趋势,在南方四个要素则呈现一致增大的趋势;华北地区和长江中下游地区的四个要素在70年代末80年代初均发生了“类似于突变”,且两个区域年平均降水量“类似于突变点”均出现在1976年,即以1976年为界,北方地区由前期的湿状态转为后期的干状态,干旱几率加大,而南方地区则由干转湿,降水增多,容易形成大范围洪涝;(2)ENSO暖、冷年极端降水对比显著区域主要在华北东部地区,暖年和冷年当年夏季该地区分别对应着极端降水的负、正距平区;在暖年次年,夏季和春季分布形有相似之处,北方呈现正距平,南方分布形势较为复杂,江南地区也有极端降水大值区;次年秋季,极端降水正距平区主要分布在北方;次年冬季,整个东部地区以极端降水负距平为主,冷年次年四季极端降水基本呈相反的分布形势;对应的MPV场在暖、冷年当年可以较好的反映出华北地区大气性质的变化,而在低纬度地区还不能作为很好预测极端降水分布情况的依据;(3)湿位涡有“南减北增”的趋势,对流稳定度在前后两个阶段发生了显著改变,低层对流稳定度距平在后一阶段的分布形势呈现为“南负北正”型,与前一阶段相反,南方趋于对流不稳定,北方趋于对流稳定;中纬度地区斜压稳定度在前期呈现低层负距平高层正距平的分布型,在后期则为低层正距平高层负距平的分布型,整个东部地区低层斜压稳定度都有趋于增大的趋势;在中层,相比起前一阶段,后期呈现“南负北正”显著对比分布型,即南方地区趋于斜压不稳定,北方地区则呈现斜压稳定的形势,大气性质的南北显著变化是我国东部地区极端降水呈现“南增北减”的变化趋势一个重要原因;(4)1976年之后,到达华北地区的水汽量显著减少;前后两个阶段的垂直环流以35。N为界,东部低纬地区由下沉运动变为上升运动,而高纬地区由上升运动变为下沉运动;高纬度地区300hPa层次在1976年之后表现为温度负距平场中心,使得我国东部地区高空热力性质产生差异,进而影响了对流稳定度的变化;同时高层的温度降低使得冷中心南北两侧西风分量相应的加大和减小,斜压稳定度相应的出现减弱和增强的变化趋势。

【Abstract】 By using the daily rain data of 392 stations of the Eastern China, the characteristics of extreme precipitation of the Eastern China during the recent 50 years are analyzed firstly. Then the response characteristics of the extreme rainfall over eastern China in different seasons to the ENSO are studied. In addition we utilize the theory of moist potential vorticity(MPV) to investigate the possible reason. At last, by dividing the research time into 1948-1976 and 1977-2008, the differences of moist potential vorticity(MPV) and the atmospheric stability of the two periods are focusly discussed based on the NECP/NCAR reanalyzed data. The mositure flux and the vertical motion are also analyzed. From the point of the cooling of the air in the middle and upper troposphere, we inquire into the reasons of the differences of the atmospheric stability during the two periods. The main results are as follows:1)The extreme precipitation over the Eastern China exhibits more along the southeast and less in northwest inland, but different in each decade:The count、its percentage of the total rain、the frequency and the intensity of the extreme precipitation all decreased in North China while increased in South China. The four factors of the North China and lower reaches of the Yangtze River take a change which is similar to the mutation form the late 1970s to the early 1980s and the precipitation pattern changes in 1976.That means the rainfall over the North China transform into dry state while the South China coverts into wet state;2)The extreme rainfall differs significantly over the east area of the Northern China in the warm and cold years. In the spring and summer of the following year of El Nino, it has nearly the same distribution that the north exhibits more and the south exhibits a complex distribution that there is a great value over the south area of the Yangtze River valley; In the autumn of the following year, construct to the spring and the summer. The big value is main over the northern region; in the winter, it mainly has less. However, it presents an adverse distribution pattern in the following year of La Nina; The corresponding MPV can well reflect the atmospheric stability of the north area, especially Northern China but not perfectly in the Low-latitude region; 3)The MPV exhibits a reduction in the North China and a growth in the South China. The convective stability changes significantly in the two stages and shows less in the south and more in the north in the next stage on the lower level. That is to say that the south area tends to be convectively unstable and the North China tends to be convectively stable; The baroclinic stability of the middle latitude shows minus departure on the lower level in the former stage and reversedly in the latter stage. The baroclinic stability of the whole east area takes on a increasing tendency; On the middle level it shows less in the south and more in the north in the next stage That means that the south area tends to be baroclinicly unstable and the North China tends to be baroclinicly stable. The variation of the atmospheric property is a main reason for the change trend of the extreme precipitation over Eastern China;4)The moisture reaching the North China deceased remarkably after 1976.The low latitude changes from downward movement to upward movement and the high latitude changes contrarily; The temperature shows minus after 1976 on the 300hPa level over the high latitudes,which leads to the difference of the thermal properties and then affects the convective stability; Meanwhile the temperature decreasing makes the west wind increase in the south and decrease in the north respectively and the baroclinic stability weakens and strengthens accordingly.

【关键词】 极端降水湿位涡稳定度
【Key words】 Extreme precipitationMoist potential vorticityStability
  • 【分类号】P426.6
  • 【下载频次】331
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