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Ocean Surface Topography from Space
Caption for SSH-SST Indian Ocean Animation

by: Claire Perigaud

This animation illustrates the strong climatic anomalies that took place in the Indian Ocean in 1997-1998-1999.

In winter 1997/98, sea level was significantly lower than usual in the eastern equatorial Indian Ocean including along Indonesia, and significantly higher in the western Indian Ocean including along Kenya. A year later, the situation is reversed with high sea level in the East, low in the West. These sea level anomalies are associated with strong atmospheric anomalies: it rained way more than usual over Kenya in 1998 and way more than usual over Indonesia in 1999.

These patterns of opposite signs between what is happenning in the East and what is happenning in the West of the Indian Ocean correspond to extrema of the Indian Ocean dipole oscillations (Saji et al., Nature, 401, 360-363, 1999; Webster et al., Nature, 401, 356-360, 1999).

This animation illustrates well that sea level anomalies (SLA) significantly differ from the sea surface temperature anomalies (SSTA). Although it is generally true that a sea level rise corresponds to an ocean warming, it is normal that SLA and SSTA do not perfectly match each other.

Variations of subsurface temperature have a signature in SLA whereas SSTA show the changes at the surface only. Thus, the eastern equatorial Indian Ocean, which is a pool of warm waters, has a mean thermocline relatively deep and the thermocline shoaling induced by the equatorial easterlies in 1997/98 has a negligible cooling impact on the SSTA whereas it corresponds to a strong 20 cm drop of SLA. In the western Indian Ocean, the cooling impact of the thermocline shoaling in 1998/99 can be seen in the SSTA too, but even then and there, SLA and SSTA patterns do not match well each other. This is because SLA primarily corresponds to wind and ocean dynamics, whereas SSTA primarily corresponds to surface mixing and air-sea heat fluxes.

See GLOBAL SSH-SST Animation caption for more details.

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