The significance of equatorial westerlies

In all three tropical oceans there are regions of shallow lower tropospheric westerlies located in the summer hemisphere poleward of cross-equatorial flow. They may be found in the summer and winter in the Indian Ocean and in the boreal summer hemisphere of the eastern Pacific and Atlantic oceans. These westerlies are often mistaken physically as the result of Coriolis turning but they are decidedly sub-geostrophic in nature and associated string cross-equatorial pressure gradients and the deepest convection of the ITCZ. They are regions of strong inertially instability and, as a result, highly disturbed and are source regions of equatorial waves. Of particular interest is their role in ocean-atmosphere interaction. For example, they enhance stress curl to shallow the thermocline in the southern Indian Ocean producing what has been described as a climatically sensitive region. We examine the physical nature of the class of instabilities that produce equatorial westerlies and their coupled ocean-atmosphere character. We are particularly interested the possible low-frequency modulation of these instabilities and its role in the formation of the MJO in the Indian Ocean sector and the modulation of the summer and winter monsoon.