【作者】 张岚；

【导师】 徐海明； 杜岩；

【作者基本信息】 南京信息工程大学 ， 气象学， 2012， 硕士

【摘要】 南印度洋偶极子是南印度洋存在的一种偶极型海温异常现象,在年际和年代际尺度上均有十分明显的表现。但目前有关印度洋海气相互作用的研究主要集中在热带印度洋地区,针对南印度洋地区的工作相对比较少。本文利用逐月OISST和ERSST资料以及NCEP2表面风场等资料探讨了南印度洋偶极子的结构特征、形成原因及其与ENSO的关系以及年代变化特征,得出以下主要结论：(1)印度洋海温变率最强的地区位于副热带南印度洋,其年际海温变化最显著的特征就是海温呈现西南-东北向的偶极型分布,称为南印度洋偶极子(SIOD)。南印度洋偶极子在11月开始出现,对应有两个明显的冷暖中心,次年2月达到极值,然后在4-6月份消亡。SIOD的形成主要是风场、潜热通量和短波辐射通量起作用,但混合层深度异常加厚或变浅也有助于SIOD的形成。另外,SIOD的形成和南极绕极环流过程在某种程度上联系在一起。南印度洋500hPa位势高度场、850hPa风场和海平面气压与SST偶极子模态可以看作是南半球海气耦合绕极模态的一部分。(2)近30年资料表明,SIOD在北半球冬春季出现,次年2-3月份达到盛期,超前ENSO9-10个月,且具有季节锁相特征。在70年代中期的年代际气候突变后,SIOD与ENSO的关系显著增强,正南印度洋偶极子(PSIOD)事件之后一般都有El nino事件发生,负南印度洋偶极子(NSIOD)事件之后都有La nina事件发生。1-3月份发生PSIOD,且其前期冬季11-12月份(NDJ)发生La Nina事件的情况下,SIOD东西两极冷暖中心异常偏北,尤其东边一极冷中心的位置明显较其他年份偏向西北,且东南风异常偏强,赤道印度洋有西风异常向东传播。1-3月份发生NSIOD,且其前期冬季NDJ发生El nino事件的情况与之类似。ENSO事件会对SIOD的强度和位置造成一定影响。(3) SIOD具有明显的年代际变化特征。SIOD在六七十年代强度较强,而SIOD指数与Nino3.4NDJ指数的相关均在七十年代末气候突变以后显著增强,东西两极与Nino3.4NDJ(0)指数的相关均在八十年代以后增强,东边一极与Nino3.4NDJ指数呈现负相关。SIOD和ENSO关系的增强可能与太平洋年代际振荡(Pacific Decadal Oscillation)和全球变暖有关。另外,由于ENSO与热带印度洋偶极子(IOD)的关系在70年代中期之后增强,SIOD和IOD关系也相应增强。值得注意的是,在八十年代末以后,SIOD东边一极分裂出两个中心,致使SIOD呈现三极分布的形势。更多还原

【Abstract】 Southern Indian Ocean Dipole is significant dipolelike sea sueface temperature (SST) pattern in the Southern Indian Ocean. It is robust in the interannual and interdecadal time scale, and distinguished difference from the SST dipole in the tropical Indian Ocean. However, most previous researches focused on dipole in the tropical region of Indian Ocean, seldom work paid attention to the Southern region. Using monthly OISST、ERSST and NCEP2reanalysis, the characteristics and evolution of SIOD, and its interdecadal variations and correlation with ENSO are investigated in this study. The mainly results are as follows:(1)The variance analysis of the Indian Ocean sea surface temperature (SST) indicates that a strong dipole oscillation occurs in the Southern Indian Ocean, so called Southern Indian Ocean Dipole(SIOD). Usually, SIOD develops in November, peaks in February and decays in April-June of the next year. Wind, latent heat flux and shortwave radiation flux play an important role in the formation of SIOD. Besides, the change of the mixed layer depth contributes to the formation of SIOD. Further study indicated that the formation of SIOD is associated with the Antarctic Circumpolar process. Moreover, SIOD as well as the corresponding sea level pressure,500hPa geopotential height field and850hPa wind field over Southern Indian Ocean can be regarded as part of the southern hemisphere circumpolar modes of coupled ocean-atmosphere.(2)In recent three decades, SIOD are phase-locked to the austral summer season, preceding the El Nino signal by9toll months. Furthermore, El Nino events usually occur after positive SIOD (PSIOD), while La Nina events occur after negative SIOD (NSIOD).When PSIOD events occur in January to March and at the same time La Nina events occur in the previous winter, the two poles of SIOD will be exceptionally northerly. Particularly the location of the cold center will deflect obviously to north-west than other years, the southeast wind anomalies stronger, and westerly anomalies will propagate eastward in the equatorial Indian Ocean, Vice versa the situation of NSIOD occur in January to March and at the same time El Nino events occur in the previous winter. ENSO events will exert a certain impact on the strength and location of SIOD.(3)SIOD exhibits interdecadal variations in the longer time-scale. The intensities of SIOD are strongest in the1960s and1970s, but it’s relationship with ENSO is enhanced after mid1970s, the inter-decadal abrupt climate change. This enhance may be related to the Pacific Decadal Oscillation (PDO) and global warming. The east pole and Nino3.4NDJ index presents the inverse correlation. Furthermore, the relationship between SIOD and IOD also increase correspondingly because of the relationship of ENSO and IOD enhanced after the mid-1970s. It is worth noting that the east pole of SIOD splits into two centers after the end of1980s, resulting in three poles distribution of SIOD.更多还原