【作者】 杨玮；

【导师】 何金海； 王盘兴；

【作者基本信息】 南京信息工程大学 ， 气象学， 2013， 博士

【摘要】 本文用NCEP/NCAR再分析资料、中国160站资料、CMAP和ERSST资料,通过理论分析和统计动力诊断方法,围绕“副热带西风急流异常的气候效应及成因”这一主题,以两种副热带西风急流指数的定义和计算为切入点,分析了它们的气候及异常特征,发现它们存在明显的季节变化和年际变化,与北半球区域气候异常关系密切。在此基础上,重点讨论了副热带西风急流与角动量输送、热带SST、平均经圈环流之间的联系,揭示了急流异常的成因,对北半球冬季副热带西风急流取得了较系统和较深入的认识。主要结论为：1)根据两种不同经度范围纬向平均[u]图的分布,定义了北半球副热带西风急流(J,0～360°)和亚洲副热带西风急流(JA,70～145°E)两种大尺度环流系统,建立了冬季季、月J、JA的64年(1948-2011)环流指数(强度P、中心位置C(φc、pc))序列,它们对急流位置的描述是二维的,包含了急流中心的南北位置和高、低空位置。2)通过强度指数和位置指数对J、JA的描述,可见J、JA稳定存在于整个冬季,中心位于30°N、200hPa附近。其气候特征为：J(JA)在12月最弱,2月(1月)达最强；季内中心位置不断南移,而垂直方向则表现为高、低空不断振荡。季、月J、JA强度异常的年际变化趋势基本一致,J的强度以年际尺度振荡周期为主,而JA除此之外还存在10～20a周期的年代际振荡。J、JA中心位置在1970’s初期前偏南偏高,之后偏北偏低；J、JA中心位置均存在10a及以下周期,且J年代际振荡较JA显著。3)J、JA与北半球气候异常显著相关,J(JA)强度与气温(T)、降水(R)的显著相关区主要在西半球(东半球)。J(JA)的强度与T、R的相关明显强(弱)于其中心位置,且它们与T的相关均明显强于与R的相关。特别地,JA与中国气候异常显著相关,故在我国冬季气候异常分析及短期预测研究中,用JA指数更为合理。JA强年,我国除西南外的大部分区域气温偏低(尤以长江以南地区为主),华北、华中和华东降水偏少(尤以华北为主)；JA中心位置异常年,显著相关区成片出现在一定地理区域。4)12-2月,全域西风角动量从热带东风带向中高纬西风带的经向输送主要发生在中低纬度；强度冬季强于夏季,北半球季节差异大于南半球。全域u角动量强经向输送主要在中低纬对流层上部和冬半球高纬平流层进行,J位于角动量强向极输送中心高纬一侧的输送辐合区中；北半球冬季J主要由平均经圈环流输送及其辐合维持,其次由大小相当的定常波和瞬变涡输送及其辐合维持。另外,Hadley环流将热带东风带地面的全域Ω角动量向上、向副热带纬度输送,是两半球东西风及J维持的主要原因；Hadley环流对Ω角动量的输送以及伴随的u角动量的转换,有利于热带对流层中东西风带界面随高度增加向赤道倾斜,并在对流层顶关于赤道不对称。5)局域西风角动量的经向和垂直输送特征与全域类似,不同的是,局域西风角动量还涉及到西、东边界上的纬向输送。在JA的维持中,局域u角动量的经向输送及其辐合作正贡献,纬向和垂直输送作负贡献,它们的平衡是JA维持的环流原因；JA大部分区域为纬向净输出,西、东边界上的平均纬向环流及它们和定常波的相互作用是主要的。另外,局域Hadley环流对亚洲区域热带对流层东西风带界面结构特征的形成起关键作用,该交界面关于赤道准对称。6)北半球冬季急流搜索区u角动量输送辐合的异常增强使J增强、JA减弱,并伴有J中心位置北抬、上升和JA的南移；且J的u角动量异常输送主要由定常波与瞬变涡输送分量引起,JA的u角动量异常输送则由平均纬向环流与定常波相互作用以及纬向定常波分量引起。热带海洋SST异常与J、JA异常的相关显著。强El Nino (La Nina)年,北半球Hadley环流偏强(弱)、中心偏南(北),亚洲Hadley环流偏弱(强)、Ferrel环流偏强(弱),导致J的异常加强(减弱)、中心偏南(北)和JA的偏南偏高(偏北偏低)。更多还原

【Abstract】 Based on the NCEP/NCAR reanalysis dataset, the observation data of160-stations in China, CMAP and ERSST dataset, this paper focuses on the theme of "climatic effects of the subtropical westerly jet anomalies and its causes" by using the theoretical analysis and diagnostic methods of statistics and dynamics. The starting point for analyses is the definition and calculation of indices of the two subtropical westerly jets. The climatic and anomalous features of these indices are analyzed and found that there are obvious seasonal and interannual variability, and they are closely related to the regional climate anomalies in Northern Hemisphere. On this basis, the relationship between the subtropical westerly jet stream and angular momentum transport, tropical SST, the mean meridional circulation are discussed. The cause of the jet stream anomaly is revealed. The systematic and in-depth understanding of subtropical westerly jet stream in Northern hemisphere winter is obtained. The main conclusions are as follows:1) The two large-scale circulation systems, northern hemisphere subtropical westerly jet stream (J,0～360°) and Asian subtropical westerly jet stream (JA,70～145°E), are defined by zonal average distributions of [u] in two different longitude range. The64-year seasonal and monthly series of the circulation indices (intensity P, central position C (φc, pc)) of J and JA in winter are established. The jets’positions described by them are two-dimensional, including the meridional and vertical position of the jet stream center.2) From the description of J and JA by intensity index and position index, it can be found that J and JA exist throughout the winter with their center near30°N,200hPa. J (JA) is the weakest in December and up to the strongest in February (January). During the winter, the centers constantly move southward and oscillate between high and low level of the vertical direction. The interannual variations of the seasonal and monthly intensity anomalies of J and JA are consistent. J has the interannual scale oscillation mainly. Besides this, JA has the10-20a-period interdecadel oscillation. The central positions of J and JA are higher and southerly before the early of1970’s, lower and northerly after that with the period of≤10a. J’s interdecadel oscillation is more significant than JA.3) J and JA are significantly associated with the climate anomalies of the Northern Hemisphere. The significant correlation region between J (JA) intensity and temperature (T), precipitation (R) is mainly in the Western Hemisphere (Eastern Hemisphere). The correlation between J (JA) intensity and T, R is obviously stronger (weaker) than its central position. Their correlation with T is distinctly bigger than R. In particular, JA has the significant correlation with China climate anomalies. So in the research of winter climate anomalies analyses and the short-term climate prediction in China, the index of JA is more reasonable. In the stronger JA years, most of China except the southwest has the lower temperature (especially in the area to the south of the Yangtze River) and the northern, central and eastern China has the less precipitation (especially in northern China). In the years of JA central location anomalies, the significant correlation area appears analogous in a certain geographical area.4) From December to February, westerly angular momentum transport meridionally from tropical easterlies to extratropical westerlies in northern winter, which intensity in winter is stronger than summer. The seasonal difference in the northern hemisphere is greater than the southern hemisphere. The strong meridional transportation of global u angular momentum is at upper troposphere of the middle and low latitudes and the high latitude stratosphere in winter hemisphere. J is in the transportation convergence zone to the high latitude side of strong angular momentum poleward transportation center. During the northern hemisphere winter, J is maintained by the average meridional circulation transportation and its convergence mainly, and then is preserved by the equivalent steady wave, transient eddy transportation and its convergence. In addition, Hadley circulation transports the global Ω angular momentum at the ground of the tropical easterlies upward and poleward to the subtropical latitudes. This is the main reason that the easterlies and westerlies in the two hemispheres and J maintain. The transportation of Ω angular momentum by Hadley circulation and the accompanying transformation of u angular momentum contribute to equatorward inclining the interface of the easterlies and westerlies in the tropical troposphere with the increase of height and the asymmetry about the equator in the tropopause.5) The meridional and vertical transportation characteristics of local westerly angular momentum are similar to the global situation with the difference that the local westerly angular momentum is related with the zonal transportation at the west and east boundary. During the maintenance of JA, the meridional transportation of local u angular momentum and its convergence has the positive contribution, but the zonal and vertical transportation has the negative contribution. Their balance is the circulation reason of the maintenance of JA. JA has the zonal net export in most area. The main compent is the average zonal circulation and its interaction with the steady wave. Otherwise, local Hadley circulation plays a key role on the interface structure formation of the easterlies and westerlies in Asian regional tropical troposphere. The interface is quasi-symmetric about the equator.6) In the jet stream search area of northern hemisphere winter, the abnormal increase of u angular momentum transportation convergence enhances J and weakens JA, accompanying the northward and upward movement of the J’s central position and the southward movement of JA. The u angular momentum anomaly transportation of J is caused by the transportation components of the steady wave and transient eddy, while J is caused by the interaction between the average zonal circulation and the steady wave, and the component of the zonal steady wave. The SST anomalies in the tropical ocean are significantly related with the anomaly of J and JA. In the years of strong El Nino (La Nina), Hadley circulation in northern hemisphere is stronger (weaker) and its central position is southward (northward), but Hadley circulation in Asia is weaker (stronger) and Ferrel circulation is stronger (weaker). This situation can lead to the stronger (weaker) J, its central position moves southward (northward) and JA moves southward and higher (northward and lower).更多还原