Influences of Continental Monsoons and Air–Sea Coupling on the Climate of the Equatorial Pacific

Abstract

An air?sea?land coupled model of intermediate complexity was used to reveal the important roles of air?sea coupling and adjacent continental monsoons (i.e., American monsoons and Asian?Australian monsoons) on the annual cycle and mean state of the equatorial Pacific. Excluding the effects of adjacent continental monsoons, the simulated mean SST in the western Pacific displays a warm bias; the SST seasonal cycle exhibits an erroneous, dominant annual component in the western Pacific, and insufficient strength and a 2-month phase delay in the equatorial eastern Pacific. The air?sea coupling alone cannot sustain the full strength of the annual marches of the ITCZ/cold tongue complex. This is because the diabatic heating associated with the ITCZ rainfall generates both a southerly and a westerly component to its equatorward side; while the southerly cools the cold tongue establishing a positive feedback to enhance the ITCZ, and the equatorial westerly favors cold tongue warming inducing a negative feedback that offsets the effect of the southerly component. Including the influences from the adjacent continental monsoons significantly improves the simulations of the mean state and annual cycle of the equatorial Pacific. The Asian?Australian monsoons are found to improve the mean SST through enhancing the strength of the trades and to yield a correct semiannual cycle of surface wind speed and SST in the equatorial western Pacific. However, they have little influence on the annual cycle in the eastern Pacific SST. In contrast, the South American monsoon exerts profound impacts on the annual variations of the southeast trades and SST in the eastern Pacific, but not the mean SST. The Colombian and North American continental monsoons have little impact on the annual cycle of SST in the cold tongue.