Improvements to the equatorial Pacific cold
tongue in an OGCM: possible implications for the NCEP GODAS and CFS
Kris Karnauskas
ESSIC
Abstract:
A reduced
gravity OGCM of the tropical Pacific Ocean is used to determine the
improvements to the simulated equatorial Pacific cold tongue region
through choices in horizontal resolution and coastline geometry,
particularly the Galápagos Islands. Four simulations are
performed, forced by identical climatological forcing. Results are
compared between model grids with and without the Galápagos
Islands, with coarse and fine resolutions. It is found that a more
realistic treatment of the Galápagos Islands results in a
complete termination of the Equatorial Undercurrent (EUC), which leads
to improvements in the simulated spatial structure of the cold tongue,
in addition to a basin-wide warming of up to 2°C in the central
Pacific. The termination of the EUC is directly responsible for the
improvements east of the Galápagos Islands, and for the
basin-wide reduction of the tropical cold bias through dynamical and
surface heat flux adjustments.
It is thought that such an improvement will have a considerable impact
on the ability of coupled ocean-atmosphere and ocean-ecosystem models
to produce realistic clouds, precipitation, and biological activity in
the tropical Pacific Ocean. It is clear that the effects of the
Galápagos Islands on the Pacific Ocean beginning with equatorial
currents cannot be ignored on the annualmean. The next logical step is
to exploit these effects on interannual variability and the
implications for the predictability of the couple ocean-atmosphere
system. In particular, the potential benefits to the predictive skill
of, for example, future iterations of the NCEP GODAS and CFS by
implementing the Galápagos Islands at sufficient resolution
should be given serious consideration.