【作者】 于波；

【导师】 管兆勇；

【作者基本信息】 南京信息工程大学 ， 气象学， 2013， 博士

【摘要】 使用再分析和观测资料、利用大气环流模式FrAM1.0输出资料,就IOD对亚澳季风环流结构和东亚夏季气候变动的影响进行了多角度的研究,得到主要结论如下：(1)IOD对夏季(6-8月)的印度季风、南亚高压、东北亚对流层上空环流变动产生显著影响,且IOD可通过多种途径影响东北亚对流层环流异常。1994年的IOD事件可导致6-8月南亚高压西部加强,且扰动通过沿着亚洲急流的向东传播影响到东北亚上空异常反气旋环流的形成与变化。东北亚地区[120°E-145。E,35°N-45°N]的这一异常反气旋环流具有相当正压结构,其变化与低值位涡的东传和积累、与大气质量的异常堆积均存在内在联系。另外,提出了局地三圈环流分解方法,并利用新的方法计算了1994年的局地经圈和纬圈环流。结果表明,1994年IOD事件可以引起显著的纬圈和经圈环流异常。通过长期的观测数据分析和利用AGCM进行数值模拟研究,证明了7-8月东亚夏季气候和季风环流确实可受到印度洋偶极子的影响。在正印度洋偶极子事件发生年份,东亚部分地区包括中国东部和东北部、日本部分地区和韩国夏季可能遭受异常的干旱和高温。正IOD导致了日本、中国东北部及东部部分地区上空出现反气旋环流异常,从而引起这些区域夏季气候异常干旱。由IOD诱发的西太平洋和中国南方地区上空气旋性环流异常减弱了来自孟加拉湾、南海和西太平洋的偏南季风,减弱了来自热带地区的水汽输送。然而,正IOD年份该气旋性环流异常却可引起夏季风期间中国华南地区降水偏多。在pDM事件发生期间,东亚地区异常偏热的夏季气候可能是异常动力加热的结果。在日本和鄂霍茨克海地区,正的温度平流异常起主导作用,平衡了异常的非绝热冷却和由于微弱上升运动造成的异常冷却,从而引起并利于维持这些地区夏季异常高温。在中国东部地区,下沉运动起主导作用,由此引起的异常动力增温抵消了由于水汽凝结减少而产生的非绝热冷却和负的温度水平平流异常。正IOD事件中,异常的相对涡度平流在对流层不同等压面上平衡了异常的行星涡度平流,这致使鄂霍茨克海和由太平洋西北部到日本东北部地区上空形成了具有相当正压结构的反气旋异常环流。IOD SSTA引起了地中海-撒哈拉和里海地区环流的异常变化。从热带西印度洋辐散的无旋异常风场在连接IOD和地中海-撒哈拉及里海地区上空环流变化之间的关系中起到关键作用。从印度洋偶极子西极区向外流出的辐散气流和IOD引起的青藏高原上空的异常辐散气流影响了温带环流变化。地中海-撒哈拉、印度西部区域和青藏高原上空的扰动可影响到东亚地区7-8月份环流的异常变化。沿着西风带急流,Rossby波能量的向东传播在连接欧洲和东亚区域起到重要作用。通过来自索马里向东经孟加拉湾和中国南部地区直至日本岛附近的对流层低层西风气流,正IOD事件期间的扰动波能可传播至东亚上空并导致东亚上空季风环流异常。因此,东亚地区可被视为一个独特区域：在正的IOD事件中,IOD可通过对流层高层的西风波导将欧亚大陆与东亚连接起来,并通过对流层低层波导将热带印度洋和孟加拉湾与东亚连接了起来。如此IOD影响东亚地区季风活动和夏季气候异常是通过这一“三角形”遥相关进行的。(2)模式试验结果表明了IOD可对夏季季风环流的正压/斜压特征产生显著影响,强的纬向风切变向偶极子较暖的一极位移。季风是海陆热力差异造成的,季风环流具有显著的斜压特征。通过利用一个T42L28大气环流模式对IOD影响季风环流变化的数值试验,可以得到印度洋偶极子型海温异常对季风环流正压／斜压特征的显著影响。结果表明：印度洋偶极子型海温异常可以引起印度尼西亚、非洲大陆以及印度次大陆地区夏季降水异常,这种降水异常联系于异常的感热和潜热加热而造成的异常辐合辐散运动。因为偶极子型海温异常强迫改变了季风区温度场分布,热带地区大气的斜压环流和斜压性强弱随之改变。强的纬向风切变向偶极子较暖的一极位移。试验结果还表明,IOD事件可引起热带外环流异常,且不论是正偶极子型强迫或负偶极子型强迫,西太平洋暖池和东亚地区的大气环流均出现异常。然而,在正偶极子试验和负偶极子试验中,环流的异常型并不显著反相。(3)研究发现1O1D的频繁发生可显著影响ENSO和IOV的年际联系,造成ENSO-IOV关系的显著的年代际改变。利用观测和再分析资料进行的研究表明,ENSO和IOV(印度洋变率)的年际变化联系发生了显著的年代际改变。热带印度洋各变量与ENSO各指数之间的相关关系在1871-1999年研究时段内具有明显的年代际变化。在20世纪50年代和70年代ENSO-IOV关系较紧密,而在20世纪60年代和1980年之后两者关系较弱。热带印度洋SSTA的EOF1为具有海盆尺度的单极模态,其解释了20世纪50年代和70年代各自总体方差的60%以上,且该两个时段内EOF1与ENSO各指数呈高相关。当IOV-ENSO关系较弱时,印度洋偶极子事件发生更加频繁。EOF分析已表明,具有偶极结构的EOF2仅解释这些时期IOSSTA总方差的10%。然而,在1960-1969年和1980-1997年期间,由EOF1解释的方差下降相对显著。EOF1时间系数与ENSO指数之间的相关在这两个时段显著减小。20世纪50年代和70年代期间,当ENSO-IOV关系紧密时,海表附近异常风场中显示出环澳大利亚环流,而在20世纪60年代和1980-1997年期间,当EOF2模态重要性增大,EOF1模态与ENSO各指数相关关系较弱时,该环流在南印度洋上空出现断裂。环澳大利亚环流可被看作在水平面上横跨太平洋和印度洋之间的大气桥,它不同于处于纬向垂直剖面上的Walker环流大气桥。EOF分析和其他分析部分地证实,在阿拉弗拉海区域纬向风异常是ENSO和IOD现象的重要指示参数。在El Nino时期,盛行正的纬向风异常,而在强的正IOD事件期间或之前,盛行负的或弱的纬向风异常。这与El Nino或IOD事件发生时东南印度洋和印度尼西亚区域异常的海平面气压分布一致。更多还原

【Abstract】 By using the observational data, the reanalysis data and the output data of atmosphere general circulation model FrAM1.0, the influence of the Indian Ocean dipole (IOD) on Asian-Australian monsoon circulation structure and East Asian climate change in summer were studied from multi-angles. The main results were as follows:(1) The Indian Ocean dipole (IOD) significantly affected the Indian monsoon, the south Asia high and the atmospheric circulation in the upper troposphere over Northeast Asia during the summer (June-August). The IOD also influenced atmospheric circulation anomaly in the troposphere over Northeast Asia through multiple ways.The IOD event in1994can lead to the strengthening of the western South Asia High in June-August and the atmosphere disturbance spread eastward along the Asian jet, which affected the formation and variation of the anomalous anticyclonic circulation over Northeast Asia([120°E-145°E,35°N-45°N]). The variation of this anomalous anticyclonic circulation with the equivalent barotropic structure was intrinsically related to the accumulation and the eastern-spread of the lower potential vorticity and the abnormal accumulation of air quality. In addition, the three cells circulation decomposition method was proposed, by which the local meridional and zonal circulation of1994were calculated. The results showed that the IOD event in1994can cause significant zonal and meridional circulation anomalies.Analysis of observational data and numerical simulation studies of AGCM demonstrated that the East Asian summer monsoon circulation and climate during July-August were affected by the IOD.In the years of positive Indian Ocean dipole event, parts of East Asia including the eastern and northeastern parts of China, Japan and Korea may suffer from abnormally hot and dry summer. The positive IOD resulted in the anomalous anticyclone over Japan and the eastern and northeastern part of China, causing abnormally dry summer in these regions. The anomalous cyclonic circulation over the southern part of China and the western Pacific induced by the IOD weakened the monsoonal southward wind from the Bay of Bengal, the South China Sea, and the tropical Western Pacific, preventing the subtropical East Asia from receiving the normal water vapor from the tropical regions. However, the cyclonic circulation anomalies in the positive IOD year can cause more precipitation over South China than normal during the summer monsoon.During the positive IOD events, the anomalous dynamic heating was responsible for the abnormally hot summer Over East Asia. Over Japan and the Sea of Okhotsk, the dominant anomalous positive horizontal advection of temperature balanced the abnormal non-adiabatic cooling and the abnormal cooling caused by weak upward motion, causing and maintaining these unusually high temperatures in summer. Over the eastern part of China, the dominant sinking motion caused constant power warming to offset the non-adiabatic cooling and the anomalous negative horizontal advection of temperature due to the reduced condensation.During the positive IOD events, the anomalous relative vorticity advection balanced the anomalous planetary vorticity advection in various isobaric surfaces of the troposphere, leading to the formation of anomalous anticyclonic circulation with the equivalent barotropic structure over the Sea of Okhotsk and the region from northwestern part of Pacific Ocean to northeastern part of Japan.The IOD SSTA caused abnormal changes of circulation in the Mediterranean-Sahara and the Caspian Sea region. The divergent irrotational anomalous wind field from the tropical western Indian Ocean played a key role in the relationship between the IOD and circulation variation over the Mediterranean-Sahara and the Caspian Sea regions. The temperate circulation change was affected by the divergent flow outward from West polar region of the Indian Ocean Dipole and the abnormal divergent flow due to the IOD over the Tibetan Plateau.The abnormal change of circulation in East Asia during July-August was affected by the disturbance over the Mediterranean-Sahara region, the western part of India and the Qinghai-Tibet Plateau. The eastern spread of Rossby wave energy played an important role in connecting Europe and East Asia along the westerly jet. Through the westerly flow in the lower troposphere coming from Somalia, the Bay of Bengal and the southern part of China, until to the Japanese island, the disturbance wave energy during the positive IOD event can spread over to East Asia and led to the abnormal monsoon circulation over East Asia. Thus, East Asia can be seen as a unique area. In a positive IOD event, the IOD connected Eurasia and East Asia by westerly flow in the higher troposphere and connected Indian Ocean and Bay of Bengal and East Asia by westerly flow in lower troposphere. So the IOD affected the activities of the monsoon and the summer climate anomaly in East Asia through the "triangle" teleconnection.(2) The results of data experiments showed that both the barotropic and baroclinic structures of the monsoon circulation were significantly affected by the IOD. The stronger vertical shear of the zonal wind moved to the warming pole of the dipole.Monsoon is caused by land-sea thermal contrast and the monsoon circulation is characterized by the significant baroclinicity. The response of the monsoon circulation to the tropical Indian Ocean Dipole was studied by using the Atmospheric General Circulation Model (AGCM) T42L28and the data experiments. Both the barotropic and baroclinic structures of the monsoon circulation were significantly affected by the Indian Ocean dipole (IOD) sea surface temperature anomalies (SSTA). The IOD was able to induce anomalous changes in surface fluxes of both the sensible heat and latent heat causing the anomalous divergence in the troposphere, and hence forth resulting in the anomalous rainfall in Indonesia, the African continent and the Indian subcontinent. The IOD SST anomalies forced the atmosphere to change its temperature spatial distributions, which induced the modifications of the monsoon circulation baroclinicity. Both the barotropic and baroclinic structures of the monsoon circulation were hence to change. The stronger vertical shear of the zonal wind moved to the warming pole of the dipole.Further more, the IOD SSTA was able to change the circulations not only in the tropical region but also in the extra tropics. Whether positive or negative, the dipole mode forcing brought about an unusual atmospheric circulation over the warm pool of the West Pacific and the East-Asian region, and excited an anomalous wave train over the middle latitudes. However, the anomalous types were not obviously reversed each other.(3) The study showed that the frequent occurrence of the IOD can significantly affect the interannual connection between ENSO and IOV, resulting in significant decadal variation of ENSO-IOV relationship.The research using observational data and reanalysis data showed that the significant decadal variation was found in interannual connection between ENSO and IOV. The relationship between the tropical Indian Ocean variables and the ENSO indices had significant decadal variation in the study period from1871to1999. The relationship between ENSO and10V was closer in the1950s and1970s, but weaker in the1960s and after1980s. The EOF1of tropical Indian Ocean SSTA was unipolar mode with basin scale, interpreting more than60%of the population variance in1950s and1970s. In these two periods, EOF1and the ENSO indices showed high correlation.When the IOV-ENSO relationship was weak, the Indian Ocean Dipole events occurred more frequently. EOF analysis showed that, EOF2with a dipole structure only explained10%of the total variance of OSSTA during these periods. However, the variance explained by EOF1decreased significantly in the periods of1960-1969and1980-1997. The correlation between the time coefficients of EOF1and ENSO indices significantly reduced in these two periods.In1950s and1970s, the abnormal wind field near the sea surface showed circulation around Australia when the IOV-ENSO relationship was closer. While in the1960s and the period of1980-1997, this circulation broken over the southern Indian Ocean when the importance of EOF2modal increased and the correlation between EOF1and ENSO indices was weak. The circulation around Australia was considered to be the atmospheric bridge across the Pacific and the Indian Ocean in the horizontal plane, which was different from the Walker circulation atmospheric bridge in the zonal vertical plane.The EOF analysis and others partially confirmed that the zonal wind anomaly in the Alafula Sea region was an important indicating parameter of ENSO and IOD phenomenon. During the El Nino period, the positive zonal wind anomaly was prevailing. While during or before the strong positive IOD events, the negative or weak zonal wind anomaly was prevailing. This was consistent with the distribution of the anomalous sea level pressure over southeast Indian Ocean and Indonesia when the El Nino or IOD event happened.更多还原