Interannual variability in the barrier layer and forcing mechanism in the eastern equatorial Indian Ocean and Bay of Bengal

Interannual variability (IAV) in the barrier layer thickness (BLT) and forcing mechanisms in the eastern equatorial Indian Ocean (EEIO) and Bay of Bengal (BoB) are examined using monthly Argo data sets during 2002–2017. The BLT during November–January (NDJ) in the EEIO shows strong IAV, which is associated with the Indian Ocean dipole mode (IOD), with the IOD leading the BLT by two months. During the negative IOD phase, the westerly wind anomalies driving the downwelling Kelvin waves increase the isothermal layer depth (ILD). Moreover, the variability in the mixed layer depth (MLD) is complex. Affected by the Wyrtki jet, the MLD presents negative anomalies west of 85°E and strong positive anomalies between 85°E and 93°E. Therefore, the BLT shows positive anomalies except between 86°E and 92°E in the EEIO. Additionally, the IAV in the BLT during December–February (DJF) in the BoB is also investigated. In the eastern and northeastern BoB, the IAV in the BLT is remotely forced by equatorial zonal wind stress anomalies associated with the El Niño-Southern Oscillation (ENSO). In the western BoB, the regional surface wind forcing-related ENSO modulates the BLT variations.