Role of Tropical Easterly Jet and IOD on Chlorophyll-a Variability over South Eastern Arabian Sea

The present study aimed to understand the Tropical Easterly Jet (TEJ) stream and Indian Ocean Dipole mode (IOD) impact on Chlorophyll-a (Chl-a) variability in the summer monsoon season over the South East Arabian Sea (SEAS). The study utilized the high-resolution (4km) Chl-a observations from the MODIS-Aqua, wind profiles from ERA5, and Sea Surface Temperature (SST) from OISSTv2 for the period 2003–2023. The study finds that the strength of the TEJ in the upper troposphere (200–100 hPa) and the IOD Index significantly influence the Chl-a concentration over the SEAS. The strong/weak TEJ winds along with negative/positive IOD conditions enhanced the surface westerly/easterly wind anomalies over West Coast of India (WCI), Southern Tip of India (STI), and Eastern Equatorial Indian Ocean (EEIO), and created a favorable/unfavorable condition (upwelling/downwelling) for anomalous Chl-a concentration over SEAS. The analysis also finds that the unprecedented positive/negative Chl-a blooms in 2010, 2016, 2020, and 2022 (2012, 2015, and 2019) were associated with either strong/weak TEJ, negative/positive IOD conditions, or a combination of both over the SEAS. The composite analysis shows that the Ekman Pumping Velocity (EPV) was positive/negative and the sea surface height anomalies (SSHA) were negative/positive during the strong/weak TEJ conditions, which supports the upwelling/downwelling conditions over the SEAS. The study emphasizes that apart from local wind effects, strong/weak TEJ and negative/positive IOD induced strong westerly/easterly wind anomalies near WCI, STI, Sri Lanka, and the EEIO region, triggering the coastal Kelvin and Rossby waves and pathways for anomalous positive/negative Chl-a blooms over the SEAS.