科研之友
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摘要
The Indian Ocean equatorial undercurrent (EUC) is an important part of the equatorial current system and plays a vital role in Indian Ocean mass transport and heat exchange. Based on the SODA 3.4.2 ocean reanalysis data, we studied the three-dimensional spatial structure of the EUC in the Indian Ocean and its interannual variability, and the relationship between the EUC and Indian Ocean dipole (IOD) on the interannual timescale. Results show that the climatological Indian Ocean EUC usually appears in late winter and early spring from February to April and late summer and early autumn from August to October, and displays a symmetric zonal current anomaly distribution over the equator. Semiannual variation of the EUC is primarily attributed to the eastward subsurface zonal pressure gradient force (PGF) that is driven by the equatorial easterly wind. On the interannual scale, the structure and intensity of the EUC in the Indian Ocean is significantly regulated by the IOD. During the positive IOD developing years, the Indian Ocean EUC occurs almost a whole year, and its intensity increases in spring and weakens in summer. The EUC finally reaches the peak amplitude, and its core is slightly moved southward to the equator during the mature of positive IOD. Dynamic diagnosis reveals that, the eastward subsurface PGF in the equatorial central Indian Ocean dominates the interannual variability of the Indian Ocean EUC and is an important proxy of the interannual variation of the EUC. Therefore, IOD mainly affects the Indian Ocean subsurface PGF via the positive feedback mechanism of the wind-thermocline-sea surface temperature anomalies, and further modulates the interannual variation of EUC. Meanwhile, the enhanced EUC can compensate the upwelling in the equatorial eastern Indian Ocean and further maintain the IOD.
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单位中国科学院大学; 热带海洋环境国家重点实验室
