The Effect of the Australian-Maritime Continents on the Indian Ocean Dipole Mode in an Idealized Coupled General Circulation Model

抄録

This paper investigates the effect of the Australian-maritime continents on the Indian Ocean Dipole (IOD) mode by using a coupled general circulation model (CGCM) under an idealized land—sea configuration. In such idealized CGCM experiments, the presence of the Australian-maritime continents increases the amplitude of the IOD between July and September. To determine the possible mechanisms associated with IOD enhancement by the Australian-maritime continents, the mean state during the boreal summer (austral winter) was compared from model runs both with, and without, the Australian-maritime continents. The presence of the Australian-maritime continents reduces rainfall during the austral winter, and generates an easterly (westerly) wind anomaly over the equatorial Indian Ocean (Pacific). These conditions are favorable for the development of a cooler SST and shallower thermocline, and hence enhance IOD amplitude through the thermocline feedback. In addition, a linear baroclinic model (LBM) experiment showed that the negative heating caused by the reduced rainfall over the Australian-maritime continents generates a significant easterly (westerly) wind anomaly over the equatorial Indian Ocean (Pacific) through the Matsuno—Gill response.