Studies on Annual and Interannual Variations of Oceanic Thermal Domes

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We studied both annual and interannual variations of oceanic thermal domes in the Pacific and the Atlantic. In particular, the Costa Rica Dome, the Mindanao Dome, the Angola Dome and the Guinea (Dakar) Dome are analysed in detail using several high-resolution ocean general circulation models. The Costa Rica Dome was also investigated utilizing the cruise of R/V Kaiyo-maru in January 1992. During the cruise both hydrographic (ADCP,XBT,CTD, water sampling) and meteorological observations were conducted. The following is the main outcome of the present research program. 1) We analyzed the model sensitivity to the surface heat and momentum fluxes and the effects of small islands using the Indo-Pacific model. It is found that the transport of low-latitude western boundary currents is much affected by those flux conditions. Also,even a small island can affect seriously surrounding oceanic conditions if it is located in strong currents. 2) An Indo-Pacific ocean model demonstrates that the sea … More sonal Costa Rica Dome cannot be generated well in some years like 1981 and 1983 because of lack of elements of formation due to basin-scale ocean-atmosphere variabilities. The model also shows an ability to capture several interesting synoptic events. For example, the Geosat altimetry data shows that an unusually strong anticyclone was generated in the Gulf of Tehuantepec in October, 1987 and then moved westward keeping its identity. The eddy was traced for a certain period by the EPOCS drifter 6858. This interesting event is clearly resolved in the model forced by the ECMWF winds but the simulated eddy strength (estimated by rotation speed and dynamic height anomaly) is one half of the observed one. This is mostly due the winds that are too weak, particularly in terms of the curl of the stress. 3) A general ocean circulation model for the Atlantic Ocean is used to analyze the seasonal variations in the Guinea Dome and Angola Dome regions. Model results are the following. The model Guinea Dome is cooled from June trough October due to active divergence of the heat transport, although the cooling rate is partly counteracted by the surface heating. The cooling is mostly related to the intensified positive curl of the local wind which converges into the ITCZ migrating northward during the boreal summer and fall. The coastal Guinea region experiences heating twice a year due to propagation of coastal downwelling Kelvin waves. The model Angola Dome is cooled from March through September. The horizontal divergence of the heat transport associated with the cold subsurface SECC(or SEUC) always tends to cool the Angola Dome. During the austral summer,however,the surface warming cancels the above current- induced cooling. The coastal Angola region is also much affected by the poleward propagation of the coastal downwelling Kelvin waves from the tropics twice a year. The generation of the downwelling Kelvin waves is due to the semiannual intensification of the westerly compone Less