Air-sea interactions associated with internal oceanic variability in the tropics

High mean SSTs in the tropics are often associated with high frequency variabilities in the winds. Typically, such high frequency winds are attributed to the atmospheric internal variability due to their scales and energetics. The oceans are considered sluggish and incapable of producing such intrinsic internal variabilities. An OGCM coupled to an advective atmospheric mixed layer is forced with climatoligcal winds to produce a hundred years of oceanic circulation fields and SSTs. Detailed analyses shows that the SST anomalies associated with the nonlinearties and mesoscale variabilities in the tropical oceans are significant and often as large as the interannual SST anomalies in the Atlantic and Indian Oceans. Basic instabilities such as the barotropically driven tropical instability waves contribute significantly to the mixed layer heat budget and unlike baroclinic instabilities, these do not necessarily transport heat from one part of the ocean to the other but gain heat from the atmosphere through gradients in the air temperature and humidity. Such internal variabilities in the tropical Atlantic may play a role in controlling the slow-frequency variability of the ITCZ and hence the meridional mode. In the high mean SST reigons of tropical Indian Ocean, multiple recirculating regions and the highly nonlinear currents forced by the reversing monsoonal forcing generate SST anomalies that can significantly affect the strong intraseasonal variability of the region. Secular SST trends in the Indian Ocean are related to the MJO activity index and also found to impact the NAO and the North Pacific variabilities. While tropical instability waves in the tropical Pacific are known to contribute to the cold-tongue heat budget, the role of the atmospheric vs. oceanic heat transport anomalies associated with them are not as obvious when heat fluxes are not interactive with SSTs. The biological feedbacks during boreal spring months are also affected by the oceanic internal variability which has implications for the annual cycle and the phase-locking of the ENSO cycle. Details of the analyses of air-sea interactions associated with the internal variabilities of the tropical oceans will be discussed.