1269 / 2024-09-20 21:38:39

Attribution of upper gyre's variability in the Bay of Bengal through Indian Ocean climate modes

BOB; Indian Ocean climate modes; land-sea-atmosphere interaction

The Bay of Bengal (BOB) is a marginal sea of Northern Indian Ocean, which is heavily influenced by the monsoon. Satellite observations showed that the seasonal oceanic gyre of BOB and the summertime offshore jet extended from Western Boundary Currents (WBC) has significant inter-annual variability. In addition to the well-known Indian Ocean Dipole (IOD) mode, the newly identified climate mode of the Indian Ocean, Indian Ocean Tripole (IOT) mode, has also received attention in recent years. However, its impact on BOB circulation have not been illustrated enough yet. This study investigates the impacts of boreal autumn matured IOD and summer matured IOT on BOB circulation based on analyses of the merged satellite observation products and the output of a 1.5 layer reduced-gravity numerical model. Numerical experiments indicate that the influence of IOT on the WBC is evident in spring and IOD has more extensive influence in summer season compared to IOT. Analyses also indicate that the upper seawater warming during boreal spring led to the development of land-sea breeze over the western BOB, which is helpful to force the western boundary offshore jet to higher latitude. It is also demonstrated that under the circumstance of offshore jet shift northward, gyres' response in the northern BOB mainly contribute to IOD mode related wind anomaly, the response near the western boundary mainly contribute to IOT mode. Our study contributes to better understanding of land-sea-atmosphere interaction in the BOB.