Observed intraseasonal thermocline variability in the Bay of Bengal

The time series of temperature data obtained from moored buoys deployed at 8 degrees N, 12 degrees N, and 15 degrees N along 90 degrees E in the Bay of Bengal (BoB) shows a persistent intraseasonal variability on 30-120 day time scale in three distinct periods 30-70 day, near 90 day, and near 120 day in the thermocline region. The standard deviation of moored buoy temperature data shows that half of the variability in the thermocline region is contributed from the 30-120 day variability. The relative contribution of local Ekman pumping velocity and remote wind forcing from equatorial Indian Ocean (EIO) to the intraseasonal thermocline variability in the BoB is examined using satellite-derived sea surface height anomaly (SSHA), wind and depths of 23 degrees isotherm (D23, proxy for thermocline depth) derived from moored buoys temperature data. The analysis shows that large amplitude intraseasonal oscillations of thermoclineparticularly the near 90 day and 120 day variabilitycould not be explained by local Ekman pumping velocity alone. The SSHA, D23, and wind fields reveal that the first and second baroclinic mode Kelvin and Rossby waves, which are generated remotely by winds from the EIO and eastern BoB, can significantly influence the thermocline variability in the BoB. The near 90 day and 120 day thermocline variability is driven primarily by the variability of equatorial zonal wind stress. While the 30-70 day thermocline variability is affected most by interior Ekman pumping over the Bay, it also appears to be influenced by zonal wind stress in the EIO and alongshore wind stress in the eastern BoB.