印度洋热含量在南海夏季风爆发中的作用

The impact of springtime heat content in the Indian Ocean on the South China Sea summer monsoon onset

利用Scripps海洋研究所0—400m上层海洋热含量资料和美国环境监测中心/国家大气研究中心(National Centers for Environmental Prediction/National Center for Atmospheric Research,NCEP/NCAR)的再分析资料,运用经验正交分解(empirical orthogonal function,EOF)等统计方法,研究在有ENSO影响和去除ENSO影响的情况下,前期春季印度洋热含量如何影响南海夏季风爆发。结果表明,在没有扣除ENSO信号的情况下,热带印度洋热含量EOF分解第一模态呈东西相反变化的空间分布。印度洋东部热含量为正(负)异常、西部为负(正)异常时,南海夏季风爆发较早(晚),印度洋上层热含量主要通过影响热带印度洋上空大气的垂直运动和高低层辐散辐合,进而影响季风纬向环流的强弱,来影响南海夏季风爆发的早晚。在扣除ENSO信号的情况下,印度洋热含量CEOF(conditional EOF)第一模态的空间分布类似于EOF第一模态的空间分布;第二模态表现为除小部分海区外,热带印度洋热含量呈一致变化的海盆模态。这两个模态对南海夏季风爆发的作用表现出不确定性。

The impact of springtime heat content in the Indian Ocean on the South China Sea （SCS） summer monsoon onset is investigated using Empirical Orthogonal Function （EOF）. The author uses 0-400 m upper-ocean heat content data from the Scripps Institution of Oceanography and meteorological data from the National Centers for Environmental Prediction/National Center for Atmospheric Research （NCEP/NCAR）. The results show that under the influence of E1 Nino-Southern Oscillation （ENSO） EOF1 of the heat content has a pattern of sea-saw variation between the eastern and western Indian Ocean. When the heat content is positively anomalous in the eastern Indian Ocean and negatively anomalous in the western Indian Ocean, the SCS summer monsoon has an early onset; otherwise the onset is delayed. The mechanism is that the heat content pattern in the Indian Ocean affects the vertical movement and divergence field of upper and lower atmosphere over the tropical Indian Ocean as well as the strength of zonal wind, leading to early or late onset of the SCS summer monsoon. The spatial pattern of conditional EOF1 （CEOF1） of the heat content is similar to that of EOF1, while the spatial pattern of CEOF2 displays a uniform pattern except for a small region. The relative importance of the two modes gives uncertainty of their influence on the SCS summer monsoon onset.