3:15 PM - 3:30 PM
[ACG37-10] Evolution and mechanism of the positive Indian Ocean Dipole event in 2012
Evolution and mechanism of a peculiar positive Indian Ocean Dipole (IOD) event that occurred in 2012 are examined. In contrast to the normal IOD event, which starts to develop in late boreal spring, peaks in fall, and decays in winter, the 2012 IOD event was initiated in July, peaked in August, and decayed quickly in fall. Although the normal IOD event is associated with shallower thermocline in the eastern equatorial Indian Ocean, it was deeper than normal in 2012 and this may have delayed the onset of the IOD in this year. For quantitative discussions, mixed layer temperature balance of the eastern pole of the IOD is calculated using outputs from an ocean general circulation model. In agreement with past studies, negative sea surface temperature anomalies in the eastern pole are generated mainly owing to anomalous cooling by the vertical terms (i.e. entrainment and turbulent vertical diffusion) during the normal IOD. However, anomalous cooling by the surface heat flux term played the dominant role in the development of the eastern pole in 2012, and the vertical terms opposed the anomalous cooling. The anomalous cooling by the surface heat flux term is due to stronger cooling by latent heat flux. Also, warming of the surface mixed layer by the climatological shortwave radiation was suppressed owing to deeper mixed layer.