Evaluation of Interannual Simulations and Indian Ocean Dipole Events During 2000–2014 from a Basin Scale General Circulation Model

Abstract

Interannual simulations performed using an eddy-permitting ocean general circulation model (OGCM) for years 2000–2014 were validated against buoy measurements over the Indian Ocean (IO). Model-simulated fields were evaluated extensively using multiple statistical metrics to quantify the quality of model in reproducing variability in oceanic surface and subsurface features. The model-simulated sea surface temperature (SST) at different moored buoy locations exhibits high (close to + 0.9) correlation coefficient (R) with the ranges of standard deviation (SD) of simulated SST consistent with the corresponding buoy observations. The root mean square difference (RMSD) estimated between the buoy and simulated SST was found to be less than 0.6 °C at most of the buoy locations. The model-simulated subsurface temperature profile, including the thermocline, resembled good agreement with the buoy profiles. Intraseasonal and interannual variability of 20 °C isotherm (D20) was simulated reasonably well as observed at the respective buoy locations. Mean error in surface currents was low; however, the meridional component from model simulations showed a better agreement (RMSD < 0.25 m/s) with the observations as compared to zonal components (< 0.4 m/s) for the periods of buoy data availability. The Dipole Mode Index (DMI) derived from simulated SST reproduces the positive/negative Indian Ocean Dipole (IOD) events that occurred during the simulation period. Interannual variability in temperature, currents and oceanic mixed layer depth was analyzed in response to IOD events. The anomalies in equatorial currents were found to affect the strength of coastal currents along the Indian coastlines. Model simulations showed the enhanced (suppressed) coastal upwelling process along the Sumatra coast that leads to anomalous cooling (warming) off the Sumatra coast during the positive (negative) IOD events.