Simulated Multiscale Variations in the Western Tropical Pacific: The Mindanao Dome Revisited

Abstract

Using a high-resolution OGCM result, multiscale variations of the Mindanao Dome (MD) are discussed. The MD is generated by local Ekman upwelling as the positive curl of the Asian winter monsoon increases over the western tropical Pacific, as discussed in the literature. It is shown, however, that the MD decays owing to the Pacific basinwide annual cycle; the warm anomaly that propagates from the eastern tropical Pacific plays an important role in the attenuation of the MD. Also, the negative wind stress curl associated with the northward shift of the ITCZ in the eastern Pacific and the easterly component of the trade winds in the central Pacific strengthens the warm anomaly. The interannual variation of the MD is governed by variations in both the Ekman upwelling forced locally and the downwelling forced remotely in the east. At its northern fringe, the MD is attenuated by the westward propagating warm eddies on the North Equatorial Current, which are triggered by a negative wind stress curl and amplified through a baroclinic conversion process. This suggests the importance of oceanic internal variabilities in discussing climate variations in the tropical western Pacific.