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副热带大气季节内振荡对东亚夏季旱涝的影响研究 【作者】韩荣青 【导师】李维京; 董敏

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副热带大气季节内振荡对东亚夏季旱涝的影响研究

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【作者】韩荣青导师李维京; 董敏水利论文3j:c:Y9\R1l`i
【作者基本信息】南京信息工程大学,气象学,2006年,博士水利论文9K;gc rU C+YzZ

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(k p)Y)J-p D"}0【中文摘要】 本文利用1958-2002年的NCEP/NCAR再分析资料、1951-2000年中国687站24h降水量资料,及1979-2004年CMAP降水资料,通过动力诊断分析与时空谱分析相结合的方法,展开了北太平洋副热带-中纬度大气低频振荡影响东亚旱涝的研究,主要结论如下:(1)降水量的季节变率在东亚(110.0-140.0E,22.5-45.0N)和东北太平洋(160.0W-115.0W,22.5-45.0)呈反位相分布,东北太平洋降水在冬、夏存在很大的季节变率,即冬湿夏干。发现在北太平洋副热带,经向风的纬向传播在冬、夏季明显地反向,加之纬向风在冬、夏季反向,因此认为在东亚-北太平洋的副热带地区,存在一个纬向振荡的季风系统,它与经典的东亚季风系统有着密切的联系,从全球来看大西洋东部到地中海一带也存在着类似的气候特征。通过分析其机制指出,夏季在东亚-西太平洋地区相对角动量(东、西风AAM)转换以低层东风AAM通过上升运动转换为高层AAM为特征,在东北太平洋为高层西风AAM通过下沉运动转换为低层东风AAM;而冬季这两个区域的相对AAM转换恰好相反;从而揭示了相对AAM转换随季节变化的纬向振荡所造...更多成的前述特殊的季风气候形态的机理。(2)全球从赤道到中纬度,经向风的季节内振荡在副热带大气中所占比重最大,在热带最低。在北太平洋副热带的大气低层,经向风季节内振荡(ISO)沿纬圈向西传播的强或弱,是同一纬带上东亚夏季风区降水偏多或偏少的强信号。对1958 -2000年夏季情况的分析表明,位于不同纬带上的东亚季风区(由南向北分为4个区域),所有涝的年份里,无论当年东亚季风强弱与否,同一纬带上太平洋经向风ISO沿纬圈向西传播较强;在绝大多数旱的年份里,与之相反,同一纬带上太平洋经向风ISO向西传播较弱或中断。进一步分析发现,经向风ISO的纬向传播对应着大气经向型环流的移动,向西传播影响东亚夏季风区降水的ISO有来自中东太平洋低纬度东风气流中的低频波(如副热带东风带中的ISO的演变);也有来自中高纬度阿拉斯加湾及鄂霍次克海一带低频低压(如洋中槽)和高压(如阻塞高压和东北太平洋高压)向南向西的频散。因此东亚夏季旱涝不但与热带季风有关,而且与中东太平洋副热带东风带中的ISO向西传播、中高纬度长波调整时低频扰动向西的不连续后退密切相关。(3)东亚-太平洋地区东风角动量(AAM)主要分布在对流层下层,而西风AAM主要分布在对流层中高层。夏季在东亚-西太平洋副热带地区东风AAM通过上升运动转换为西风AAM,在东北太平洋副热带西风AAM通过下沉运动转换为东风AAM。分析表明,北太平洋约30°N以南的副热带和以北的中纬度地区,对流层低层经向风ISO纬向  还原水利论文SS\6B8G9r|

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【英文摘要】 The relationships between the precipitation of Eastern Asia (20° -45°N, 110°-135°E) and the 30-60-day intraseasonal oscillations (ISO) over the boreal Pacificduring the summer and its mechanism are studied in the paper. The daily wind andheight fields of NCEP/NCAR reanalysis data and the 24h precipitation data of China687 stations during 1958-2002, and the pentad precipitation of CMAP/NOAA from 1979to 2004, are all analyzed by the Space-time filter analysis. The study resultsare presented as follows:(1) The paper discovers that the zonal propagating directions of the meridionalwind over subtropical North Pacific are reverse with the seasonal shift fromsummer to winter, and then the seasonal variability calculated from monthlyCMAP Precipitation Data for the Northeastern Pacific (160.0W-115.0W,22.5-45.0) is a considerable and significant value, and varies against theseasonal variability of Eastern Asia (110.0-140.0E, 22.5-45.0N). Moreover thezonal wind also presents the reverse changes o...更多ver the subtropical NorthPacific in turn between summer and winter so the zonally seasonal oscillationsexist between the Eastern Asia and the northeastern Pacific and the climateof the northeastern Pacific may be able to call the unusual monsoon climate.The paper makes clear the dynamic reasons of the unusual monsoon climateemploying the theories of the exchanges between westerly and easterly angularmomentum and the mean vertical circulation of Asian-Pacific region. Inadditional to the similar climate also exists in the region from the easternAtlantic to Mediterranean Sea, the thermal causes of the zonal distributionof the traditional and unusual monsoon in the subtropics of the NorthernHemisphere are probably the “quadruplet heating pattern” in summers, and“reversed quadruplet heating pattern” in winter.(2) The proportion for the meridional wind ISO in the subtropical atmosphere isstrikingly bigger than the one in tropics, which is distinct from the ISO ofthe zonal wind and height. The analysis results, from every drought and floodsummer for 4 different regions of East Asia respectively during 1958-2000,showed that the precipitation amount in the East Asian summer monsoon regionis well correlated to the westward propagation of 30-60-day ISO via the northcentral-eastern Pacific, and depends little on the intensity changes of theEast Asian summer monsoon. And the westward ISO is usually the low-frequencycyclones and anticyclones from the Bay of Alaska in northeastern Pacific andthe Okhotsk in the northwestern Pacific of mid-high latitudes, and the ISOevolution in subtropical easterlies. In mid-high latitude the phenomena arerelated to the westward propagating mid-ocean trough and block high backingoff. Therefore the westward propagating ISO from the north central-easternPacific to East Asia are indispensable for sufficient rainfall occurring inEast Asia in summer, which is resulted from long-wave adjustment process inthe mid-high latitudes and ISO evolving in tropical easterlies.(3) It is found that the mainly relative atmospheric angular momentum (AAM) ofeasterly wind distributes in the low-level troposphere while the main AAM ofwesterly wind distributes in the mid-high levels troposphere from Eastern Asiato the northeastern Pacific. And the easterly AAM convert into the westerlyAAM through the ascending airflow in the subtropical western Pacific whilethe reverse process takes place by the falling airflow in the northeasternPacific. Then it is found that the interannual anomaly mechanism for the zonalpropagations of the meridional wind ISO at 850hPa pressure level over thesubtropical North Pacific(about the south of 30°N) is quite different fromthe one over mid-latitude North Pacific. In the subtropical North Pacific,the strongly (weakly) interannual changes for the westwards propagations ofthe meridional wind ISO are caused by the strongly (weakly) interannualchanges for the relative AAM conversion occurred in the western Pacific (theone through the ascending airflow), and the cross-spectrum analyses showedthat the meridional wind ISO is lagging about 1-18d behind the one of therelative AAM in the subtropics from Eastern Asia to the northwestern Pacific;while the causes of the interannual anomalies for the zonal propagations ISOover the mid-latitude North Pacific are closely interconnected with thelong-wave adjustment process in the mid-high latitudes, e.g. the westwardpropagating mid-ocean trough and block high backing off, etc.(4) The anomalies of the easterly and westerly AAM took on the teleconnectionpattern, i .e. the western Pacific pattern (WP) and the Pacific North-Americapattern (PNA), and the easterly AAM transferring to westerly AAM wouldoccurred easily at negative SLP zones(heating regions) for the region fromthe eastern Asia to the mid-Pacific. And then the convections and westwardpropagations of ISO were enhanced and maintained by the AAM conversions inthe western Pacific, while the strong convections always happened to theoverlapped regions of negative SLP anomalies and the edge of westerly-AAManomalies center. On the contrary, the strong convections and activewestward propagations of ISO would be not occurred without the anomaliesconversions of the easterly AAM to the westerly AAM from the eastern Asiato the mid Pacific. Then E-P fluxes no latitudinal mean is analyzed alongthe path of the teleconnection pattern, which helps to confirm theaforementioned conclusions again.  还原水利论文!`4Lukr\eb4Y

1cn5?Boh C s(|7I0【中文关键词】 时空谱分析; ISO纬向传播; 东亚旱涝; 相对AAM; 季风; 纬向的季节振荡
~:s#R3n;|0【英文关键词】 Space-Time spectral analysis; ISO zonal propagations; floods and droughts in Eastern Asia; relative AAM exchange; Monsoon; zonal oscillations in season水利论文w#PU H@3JH
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