【作者】 孙双文；

【导师】 魏皓； 兰健；

【作者基本信息】 中国海洋大学 ， 物理海洋学， 2010， 博士

【摘要】 印度洋偶极子(IOD)是发生在热带印度洋上的海气耦合事件,是年际尺度上热带印度洋变化的主要模态之一,同时也是全球气候系统年际变化的重要组成部分,其发生对周边乃至全球的气候有显著影响。探讨IOD事件的发生机制和发展过程及东、西极之间的联系对全球气候变化的研究有重要意义。本文使用HadISST、SODA等数据资料,较全面的分析了IOD期间热带印度洋海表面温度(SST)及温跃层深度的变化规律。并使用HYCOM模拟的结果进行混合层热收支分析,研究了混合层温度的变化与各海洋动力、热力过程的联系。分析了IOD期间流场的异常情况及其对IOD发展的作用。并通过一系列数值实验,对风场、热通量场,及印度洋不同区域的大气强迫场各自在IOD东、西极发展中所起的作用进行了评价。主要结论如下：一、IOD期间SST及温跃层深度的变化规律。西极SST的正异常3-4月开始发展,并可维持较长时间,其增暖以赤道以南部分为主。东极SST负异常9-10月达到峰值,随后经历了一个迅速的增暖过程,SST转化为显著的正异常。IOD东、西极SSTA的变化均与nino3.4指数呈正相关关系,东、西极SSTA的变化也为正相关。东、西极温跃层深度的变化为明显的负相关关系,且东极的变化提前西极两个月左右。二、应用混合层热收支分析,评价了独立及伴随El Nino发生的两类IOD事件中与海表面热通量、水平、垂向对流过程所起的作用。结果表明,独立IOD事件具有开始及达到峰值的时间提前,以东极的温度异常为主,消衰后不出现海盆一致增暖现象的特点。原因是1、独立IOD事件中风场异常出现较早,导致动力过程造成的东极降温的时间提前；2、伴随El Nino发生的IOD事件中,西极的增暖受垂向对流过程与海表面热通量正异常的共同影响。独立IOD事件中海表面热通量正异常很弱,且由于东风异常出现及结束的时间较早,因此动力过程不能继续对西极起到加温的作用,导致西极没有出现显著的增暖；3、伴随El Nino发生的IOD事件后期,海表面热通量的正异常不论强度还是作用区域都远远大于独立IOD事件,为东极的反弹提供了能量。且独立IOD事件中由于反弹的时间出现较早,此时沿岸动力过程造成的降温作用仍然存在,削弱了热通量带来的增暖作用。三、对IOD期间流场异常及流场EOF分解的结果表明,流场异常10月份前发展缓慢,10月显著增大,11月流场异常最强,这是与风场的变化相联系的。在两类IOD事件中,流场异常在三维空间中的分布和发展变化具有很强的一致性。各断面流场异常的EOF分解的第一模态均为与IOD事件相联系的模态。第一模态的时间系数在IOD年,包括发生独立IOD事件的年份,均出现了显著的峰值。可见,热带印度洋的流场的异常主要是受IOD事件控制的,而非受El Nino的影响。四、通过使用不同大气强迫场进行驱动的数值实验表明,仅用风场异常能够基本模拟出IOD的发展,但在东极SSTA的反弹及西极增暖延长的过程中,热通量扮演着比风场更重要的角色。在独立发生及伴随El Nino发生的两类IOD事件中,西极SSTA强度的差别主要是海表面热通量场的不同导致的。风场异常的过早结束和热通量场没有出现正异常是1994年西极没有出现明显异常的根本原因。东印度洋的SSTA信号可以通过Rossby波的西传影响到西印度洋,但东、西极SSTA主要是在当地强迫场的影响下产生和发展,相关性较弱。其中西极长时间增暖的现象也主要是西印度洋局地强迫产生的。与SSTA的变化不同,东、西极的温跃层深度异常总是同时发展的,表现出明显的偶极子型分布,具有相互诱导的关系。不论在中东印度洋还是西印度洋风场的强迫下,温跃层深度异常的分布趋势是大致一致的。东印度洋的强迫场对IOD期间的温跃层深度变化的影响大于西印度洋。更多还原

【Abstract】 The Indian Ocean Dipole (IOD) is an air-sea coupled phenomenon. On the interannual time scale, it is one of the dominant modes in the tropical Indian Ocean. The IOD is considered as an important mechanism for the changes in the tropical Indian Ocean and global climate due to its significant impact on the climate of both the surrounding and remote regions. Understandings of the mechanisms of IOD have important significance on studies of climate change.Interannual variations in the surface and subsurface tropical Indian Ocean are studied using HadISST and SODA datasets. The relative role of ocean dynamics and surface heat flux in the initiation and development of the IOD is investigated by analyzing results from a general circulation ocean model (HYCOM).A series of experiments are conducted to assess the relative importance of the eastern and western Indian Ocean forcing fields in driving the IOD.The anomalous ocean circulation during IOD is also studied. The main conclusions are as follows:1.The surface and subsurface variations of the tropical Indian Ocean during IOD events are significantly different. A prominent characteristic of the eastern pole is the SSTA rebound after a cooling process, which does not take place at the subsurface layer. In the western pole, the surface anomalies last longer than the subsurface anomalies.The subsurface anomalies are strongly correlated with ENSO, while the relationship between the surface anomalies and ENSO is much weaker. The subsurface anomalies of the two poles are negatively correlated while they are positively correlated at the surface layer.2.The mixed layer heat budget analysis indicates that the vertical advection and the surface heat flux are both important to the western warming. In IOD years without El Nino,the positive heat flux anomalies are not obvious, and the vertical advection persists shorter than in the years that IOD co-occurred with El Nino.So the western warming is not evident in these years.The development of eastern cooling is mainly caused by vertical advection, the cooling begins earlier in IOD years without El Nino. As the IOD decays, the eastern pole begins to warm up.It is primarily induced by anomalous surface heat flux. In IOD years without El Nino, the surface heat flux anomalies are weaker. Also the eastern pole begins to warm in September, when the vertical advection caused cooling is still strong, so the eastern rebound in IOD years without El Nino is much weaker than IOD years with El Nino.3.The EOF analysis is applied to ocean circulation anomalies in several vertical sections of the tropical Indian Ocean. The results indicate that the first modes of anomalous current in these sections are all determined by IOD events. The influence of El Nino is relatively weaker.4.Ttest runs are performed to assess the relative importance of eastern and western Indian Ocean forcing fields in driving the IOD. In these runs the interannual variability of all atmospheric forcing fields are separately suppressed in the western and eastern tropical Indian Ocean. The results indicate that the SST anomalies of the eastern and western pole are mainly determined by local forcing fields.The long persistence warming of the western pole can mainly be attributed to local forcing. Different form the SST, the thermocline depth variations in the eastern and western Indian Ocean has the characteristic of entirety. The western deepening and eastern shoaling always happen together. Both the eastern and western forcing test runs can trigger this pattern.更多还原