夏季北印度洋-西太平洋表层和深层海温的季节内变率及其对大气低频振荡的响应

The northern Indian Ocean–western North Pacific is the dominant domain where the "21st-Century Maritime Silk Road" involves, and it is also the key area where the boreal summer atmospheric intraseasonal oscillation (BSISO) is the most active. The BSISO is an equatorial eastward-propagating atmospheric wave in the form of a coupled anomalous convection-circulation system, with northward-migrating components in the Asian summer monsoon region, which interacts constantly with the underlying oceans, thus significantly affecting the oceanic environment and meteorological condition in the northern Indian Ocean–western North Pacific. However, the marine meteorological prediction on intraseasonal timescales is the great difficulty for current climate models. Actually, the forecasting skill and performance of the models will be improved only if the characteristics and cause of the intraseasonal variability of the coupled atmosphere-ocean system are well understood. Therefore, this proposal is to investigate the spatial distributions and temporal evolutions of the intraseasonal variability of the sea surface temperature (SST) and oceanic temperature in the the northern Indian Ocean–western Pacific using multi-source observational oceanic data. Based on the case studies and composite analyses, the physical processes will be explored for the intraseasonal SST anomalies relating to the heat and momentum exchanges at the air-sea interface. Also examined are the relationships of the intraseasonal SST anomalies with the horizontal and vertical propagations of deep oceanic temperature anomalies. Finally, the formation mechanisms for intraseasonal variations of ocean temperatures will be validated through numerical simulations from the perspective of the BSISO forcing.

北印度洋–西太平洋是“21世纪海上丝绸之路”涵盖的核心海域、也是北半球夏季大气低频振荡(BSISO)最为活跃的区域。BSISO是一种在亚洲夏季风区即向东又向北传播的行星尺度异常对流-环流耦合的大气波动，它不断地与下垫面的海洋相互作用，因而强烈地影响着北印度洋–西太平洋海域的海洋环境和气象状况。然而，季节内尺度的海洋气象预测是当今气候系统动力模式预报的难点。只有弄清海气系统季节内变率的规律和成因，才能有效提高模式性能和预报水平，满足“一带一路”战略需求。因此，本项目拟利用多源海洋观测和再分析资料，揭示北印度洋–西太平洋海域表层温海（SST）和深层海温的季节内变化的空间分布和演变规律；基于SST季节内振荡典型个例和合成分析，探究SST异常信号与海-气界面热量、动量交换的物理过程、与深层海温异常信号水平和垂直传播的关系；从BSISO强迫海洋的角度，通过数值模拟揭示海温季节内变率形成的物理机制。

北印度洋–西太平洋是北半球夏季大气季节内振荡（BSISO）最为活跃的区域。BSISO是一种在亚洲夏季风区即向东又向北传播的行星尺度对流-环流耦合的大气波动，它不断地与下垫面的海洋相互作用，从而引起北印度洋–西太平洋海域海水温度和环流的季节内变化。然而，季节内尺度的海洋气象预测是当今动力模式预报的难点。本项目因而聚焦于海表温度（SST）和深层海温的季节内变率，从大气强迫海洋的角度，揭示北印度洋–西太平洋海域海温季节内变化的时空演变规律。. 项目组通过四年的努力探究，完成了研究计划和目标，取得一系列创新性成果。. 1）揭示出整个北印度洋至西北太平洋海域SST和深层海温对北半球夏季亚洲季风区30–60天大气BSISO响应的基本规律。BSISO自赤道印度洋向东和向北传播过程中分别于南海、西北太平洋、孟加拉湾北部和阿拉伯海西部强迫出几个显著的SST季节内振荡中心。海盆尺度的SST正（负）异常主要发生在局地抑制（活跃）对流位相，且SST最大正（负）异常滞后于最强对流异常的位相差是BSISO的1/4周期。深层海温季节内振荡的最大振幅出现在温跃层附近，且显著振荡信号可向下传播到至少1000米深处。因各海盆的地形和侧边界不同，SST和深层海温振荡的振幅、传播特征及其热力和动力强迫因素也随海盆的不同而不同。. 2）揭示出南海和西北太平洋关键区表层和深层海温季节内变率的时空演变及其强迫因素的相对贡献。对于南海，BSISO有关的海表净热通量对季节内SST局地变化的贡献达到60%，而海洋的垂直夹卷的贡献也超过了30%。对于西北太平洋区，温跃层附近的海温异常在经向上呈偶极型分布。. 3）揭示出孟加拉湾和阿拉伯海关键区表层和深层海温季节内变率的时空演变以及上层海洋温度平流与海洋波动对SST变率的相对贡献。孟加拉湾北部SST季节内变率中心的形成不仅取决于局地风应力异常的强迫而且受到BSISO有关的赤道风应力强迫的海洋Kelvin波动和Rossby波动的远程影响。阿拉伯海西部的显著SST季节内振荡中心主要取决于BSISO表面风速异常和风应力旋度异常。