印度洋表面Stokes漂流对IOD事件的影响分析

Analysis of the Effects of Surface Stokes Drift in the Indian Ocean on IOD Events

  • 摘要: 波浪是影响海表面温度的重要因素。印度洋因其复杂的季风影响,波浪场也同样具有复杂的季节变化。为了进一步研究波浪对印度洋海表面温度的影响,本文利用ECMWF-ERA5发布的近40 a的月平均波浪参数、海表面温度(Sea Surface Temperature,SST)和表面Stokes漂流(Stokes drift)等再分析数据,采用EOF(Empirical Orthogonal Function)分析和相关性分析等方法,分析了印度洋表面Stokes漂流与IOD(Indian Ocean Dipole)事件的关系。首先单独分析了印度洋风浪和涌浪的空间分布特征,阿拉伯海风浪和涌浪的有效波高和波向受季风影响,季节性变化显著。纬向Stokes漂流的空间分布与风浪相似,受风带影响较大,而经向Stokes漂流则表现出了东边界强化的现象。进一步研究了印度洋纬向Stokes漂流与IOD事件的关系,二者的相关性可达到–0.8左右,并且结果显示:当+IOD事件或者−IOD事件发生,即热带印度洋出现SST异常时,纬向Stokes漂流诱导的波浪输运总是将冷水向暖水区域输运,从而达到调节东西印度洋SST的效果。因此,纬向Stokes漂流通过诱导东西向的水体输运可以加速IOD事件的衰退。

     

    Abstract: Surface wave plays an important role in affecting sea surface temperature. The wave field has complex seasonal variations due to the monsoon in the Indian Ocean. Reanalysis data of monthly mean wave parameters, sea surface temperature and surface Stokes drift in recent 40 years released by ECMWF-ERA5 and the EOF and correlation analysis are used to analyze the relationship between the surface Stokes drift and the IOD events. Firstly, the spatial distribution characteristics of wind waves and swells in the Indian Ocean are analyzed, and the results show that the significant wave height and mean wave direction of the wind waves and swells in the Arabian Sea are affected by the monsoon and exhibit significant seasonal variation. The spatial distribution of zonal surface Stokes drift is similar to that of wind waves, and both are greatly affected by wind bands, while the meridional surface Stokes drift exhibits strengthening along the east boundary. The relationship between the zonal Stokes drift and the IOD events is further investigated, and correlation coefficient between them can reach about −0.8. When +IOD events or −IOD events happen, or SST anomalies occur in the tropical Indian Ocean, the wave transport induced by the zonal Stokes drift always drives abnormal cold water to warmer region, playing an important role in regulating the SST in tropical Indian Ocean. Therefore, the zonal Stokes drift can accelerate the decaying of the IOD event by inducing the east-west water transport.

     

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