Abstract
ABSTRACTMultisource satellite remote sensing data have been used to analyze the strong upwelling event off the southern coast of Sri Lanka in 2013 and its relationship with Indian Ocean dipole (IOD) events. The upwelling area in 2013 is 5.7 times larger than that in a normal year and lasts from June to August, with the peaks of the cooling anomaly reaching −1.5°C and the positive chlorophyll a concentration anomaly exceeding 3.1 mg m−3. In 2013, the negative unseasonable IOD (IODJJA) event enhances the southwest monsoon, while the blocking of the monsoon wind by the island results in a stronger westerly/northwesterly wind stress off the southern coast of Sri Lanka and a weaker westerly/northwesterly wind stress over the eastern Sri Lanka waters. This causes stronger offshore transport and positive Ekman pumping off the southern coast, forming a strong upwelling event there. Further analysis indicates that the interannual variability of the upwelling, as represented by a newly constructed index based on satellite observations, is primarily caused by the variations of local wind associated with the IOD. The upwelling off the southern coast of Sri Lanka weakens (strengthens) in the positive (negative) IOD years. However, an analysis based on 21 IOD events during 1982–2019 demonstrates that the effects of the three types of IOD events, including IODJJA, prolonged IOD (IODLONG), and normal IOD (IODSON), on the upwelling are different. Compared to the IODSON events, the IODJJA and IODLONG events tend to have stronger influences due to their earlier developing phases.
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