Upper ocean responses in the central western equatorial Indian Ocean During the southwest monsoon season

Abstract

 Upper ocean (200 m) response under the pre-onset, and active regimes of southwest (SW) monsoonal forcing at 0°N. 60°E in the Indian Ocean was analysed utilising time series data collection during Indo-Soviet Monsoon Experiment, 1973 (ISMEX- 73). Oceanic response under the pre-onset domination of the wind stress momentum and onset domination of buoyancy flux (B₀) was apparent in shoaling/warming and deepening/cooling (12 m/0.5⁰ C in 4 days) of Mixed Layer Depth (MLD). The pre-onset increase was followed by an onset decrease in below layer thermohaline/density gradient and disappearance of Sub-surface Salinity Maximum (SSM). Corespondingly, MLD and its heat content (HC_MLD ) were more correlated to (B₀) and Q_N . Upper ocean response during active regime manifested in deepening/colling (20 m/1C in 6 days) of MLD under dominant production of turbulent kinetic energy by wind stress except for the convectively dominant mixing at the beginning and end. With reduction in below-layer thermohaline/density gradient and absence of SSM the correlations between MLD B₀ wind stress, Q_N and HC_MLD became insignificant due to increased advective flux during active regime. One dimensional simulation of mixed layer paramerters showed agreement.