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).
