Mixed layer temperature balance in the eastern Indian Ocean during the 2006 Indian Ocean dipole

Abstract

An anomalous climate mode, the positive Indian Ocean dipole (IOD), occurred in 2006 with the anomalous sea surface temperature (SST) distribution in the tropical Indian Ocean. Using various types of observational data, we investigated the temperature variation in the surface mixed layer in the eastern Indian Ocean to clarify the processes that produced the anomalous SST variation in 2006. Analysis was conducted at an intraseasonal time scale and focused on a location (5°S, 95°E) where in situ measurements by the Triangle Trans‐Ocean Buoy Network were available. Temporal changes in the mixed layer temperature were obtained from the buoy data. Air‐sea heat fluxes and horizontal heat advection were estimated from the buoy data, satellite‐based data, and reanalysis products. Heat balance analysis demonstrated that air‐sea heat fluxes and horizontal heat advection mainly accounted for the mixed layer temperature variation. The results indicate that the relative importance of the heat fluxes and horizontal heat advections changed remarkably with the onset of the IOD. During January to mid‐May 2006, before the onset of the IOD, the temperature variation was mainly explained by the net surface heat flux at an intraseasonal time scale. During the IOD in late August to November 2006, the northwestward horizontal temperature gradient and the surface current produced large horizontal heat advection that exceeded the contribution of surface heat fluxes. These results confirm the importance of oceanic processes in the evolution of the IOD, and the heat balance analysis would be a fundamental example in validating model outputs for the Indian Ocean.