南海上层热含量年际变化的南北差异及其与ENSO的关联

The South China Sea (SCS),located at the Indo-Pacific Warm Pool Centre, is an important part of the Western Pacific-Indian Ocean heat reservoir. The variability of the upper layer ocean heat content (OHC) in the SCS may have great impacts, not only on the local atmospheric circulation, but also on the formation of tropical cyclone, the onset of monsoon and the variations of weather and climate in the Southern China. Preliminary analysis revealed that during ENSO period, interannual variation of OHC in the SCS has a significant regional differences, that is, on interannual scale variations of OHC in the Northern and the Southern part are in antiphase, but the mechanism is unclear. Based on previous researches, history observations, satellite remote sensing and the reanalysis dataset, this work tends to reveal the spatial-temporal variability of the upper ocean heat content and its response to ENSO, with main focus on North-South differences features of this response in the SCS. A systematic study on how ENSO affects on the variability of the upper ocean heat content in the SCS by atmospheric and oceanic processes and on North-South differences of OHC is firstly performed.Then the numerical sensitivity experiments are further conducted using regional numerical ocean models to isolate the effects of atmospheric and oceanic processes on interannual variability and regional differences of upper layer heat content in the SCS. Through this research, the regional differences of upper layer heat content in the South China Sea and its response to ENSO are clarified. The dynamic and thermodynamic factors that cause these differences are then understood, which will provide an important scientific basis for us to enhance the simulation and prediction of regional climate variabilty in the South China Sea.

南海地处印-太暖池中心，是联系西太平洋-印度洋暖池系统的重要组成部分。南海上层热含量的变异不仅对局地大气环流，而且对台风形成、季风爆发及我国南方天气和气候异常有重要影响。已有研究表明，ENSO期间南海上层热含量的年际变化具有显著的区域性差异，具体表现为南部和北部热含量在年际尺度上呈反位相变化，但机制尚不太清楚。本项目拟在前人研究的基础上，利用历史观测、卫星遥感和再分析资料分析南海上层热含量的年际变化及其对ENSO响应的南北差异；探讨ENSO在南海海区引起大气和海洋过程的变异及其对南海上层热含量南北演变差异的可能影响；在此基础上，进一步采用海洋数值模式，以敏感性试验为手段，辨识大气和海洋过程对南北部海域热含量年际变化的影响。通过研究，明确南海上层热含量年际变化及其对ENSO响应的区域性差异，理解导致这种差异的热力和动力学成因，为提升南海区域性气候模拟和预测水平提供科学依据。

南海地处印-太暖池中心，是联系西太平洋-印度洋暖池系统的重要组成部分。南海上层热含量的变异不仅对局地大气环流，而且对台风形成、季风爆发及我国南方天气和气候异常有重要影响。本项目利用历史观测、卫星遥感和再分析资料对比分析了南海1993-2006年的上层海洋热含量的变化。七套资料计算得到的南海上层海洋热含量的年循环比较一致，但年际变化却有显著差异。对比了1998、2005-2008年若干航次与各套资料相应时段的温度结构，发现Ishii、OFES、CORA以及AIPO1.0的结果与实测更为一致；在 ENSO 期间，南海热含量变化在南海北部和南部呈现出不同演变特征；进一步研究表明，ENSO引起的风异常在南海南北部的差异是导致该热含量异常的主要原因。海水的热盐度变化是一个相互补偿的过程，热变化同时引起盐度变化。客观分析数据EN4以及 OFES模式结果显示南海表层海水盐度在1993-2014年有淡化趋势，最显著区域位于吕宋岛以西和南海南部。盐度收支分析表明，淡水强迫在吕宋岛以西海域起主要贡献，而水平平流输运主导南海西部的表层盐度变化；吕宋岛以西表层盐度的降低与近年来沃克环流加强引起的夏季强降雨增加有关。受PDO的影响，吕宋以东海域次表层水体同样呈现显著的淡化趋势。