南海海表温时空演变与南海夏季风爆发早晚相关性初探

利用我国近海1986-2008年间的海温再分析资料,分析了南海海温异常的时空变化,重点揭示了南海夏季风爆发前后(4-6月)南海表层海温异常的时空演变特征,并探讨了其与南海夏季风爆发早晚的相关关系。结果显示,南海夏季风爆发前后南海表层海温异常存在一个显著时空演变模态,4月南海全域海表温度异常几呈负位相态势,其中正值信号首先出现于巴拉望岛以西海域,随后逐步向西向北扩展,5月南海大部已被海表温异常正位相控制,6月南海表层海温异常完成负-正位相转换。分析表明,南海表层海温异常时空演变的年际差异与南海夏季风爆发的早晚存在显著相关。综合已有研究认为,南海海表温异常时空演变所形成的季节内尺度的热力差异(主要包含演进趋势、速度和幅度等)可能是影响南海夏季风爆发早晚的一个重要因子,据此建立了海表温温差异常指标,其对南海夏季风爆发早晚具有较好的反映能力。此外,南海海表温异常时空演变与南海暖池的变化紧密关联。相关分析还发现,南海夏季风爆发前期南海暖池与印度洋暖池的海表温差异常存在显著正相关关系,而与西太平洋暖池为负相关关系。南海海表温异常季节内演变在印-太暖池区海表热力格局及差异形成背景下或可通过影响大尺度经向和纬向环流而引发南海夏季风爆发早晚之年际异常。

The relation between the spatial-temporal evolution of SST in the South China Sea and the earlier or later onset of the South China Sea summer monsoon

Spatio-temporal variations of the sea temperature anomaly in the South China Sea (SCS) were investigated based on the reanalysis dataset of China seas from 1986 to 2003. With focus on the evolution of the sea surface temperature anomaly(SSTA) before and after (during April to Jun) the onset of the SCS summer monsoon (SCSSM), its relation with the occasion of the SCSSM onsets was discussed. The results show that, there exists a significant evolution mode on seasonal scale, in which the positive SSTA develops firstly near the sea area west of Palawan in April, and extends rapidly westward and northward in May when the positive SSTA controls the most part of the SCS, and then the SSTA in the SCS achieves a negative-positive phase transition in June. The analysis indicates that, the interannual difference of the SSTA evolution mode was associated significantly with the earlier or later onset of the SCSSM. Synthesizing with the previous studies, it is considered that the anomalous thermal evolution (including trends,speed,magnitude) on intra-seasonal scale in the sea surface of the SCS could be one of important factors to impact earlier and later onset of the SCSSM. According to this, the author established a temperature difference index based on the SSTA evolution in the SCS, which reflects well to the earlier and later onset of the SCSSM. In addition, the evolution of the SSTA can be related closely with the variation of the SCS warm pool (SCSWP). It is found that the SST difference (April-May) anomaly of the SCSWP during the period before the onset of the SCSSM was striking of positive correlation with that of the Indian Ocean warm pool (IOWP), while evident negative relation with that of the Western Pacific warm pool (WPWP). Under the background of formation of the surface thermal pattern and contrast in Indio-Pacific warm pool regions, the anomalous intra-seasonal evolution of the SSTA in the SCS is expected to give rise to the interannual difference of the SCSSM onset (earlier or later) through the thermal effect on the large scale of meridional and zonal atmospheric current anomalies.