Philander, S. G. H., 1981: The response of equatorial oceans to a relaxation of the trade winds. Journal of Physical Oceanography, 11 (2), 176-189.
Abstract: The trade winds over the central Pacific are observed to weaken several
months after the appearance of anomalously warm surface waters in the eastern
equatorial Pacific Ocean. The following results obtained with a numerical
model indicate how this relaxation of the winds affect the later stages
of El Niño. A weakening of the westward trade winds causes a zonal redistribution
of heat in the equatorial oceans and a warming of the eastern part of the
basin. The warming depends on the zonal extent of the region over which
the winds relax, and on the length of time T for which the winds relax.
As T increases the warming in the east increases until it asymtotes to a
maximum value when T exceeds the adjustment time of the basin (which is
~400 days in the case of the Pacific Ocean). Maximum heating is associated
with a permanent weakening of the winds, unless the winds reverse direction
and become eastward. Even weak eastward winds for a short period can cause
disproportionately large temperature increases (because of nonlinear mechanisms).
In the region where the winds relax, the heating is due to convergence
of surface waters on the equator, and advection by accelerating eastward
surface currents. As the time scale T increases, the acceleration becomes
less pronounced. East of the region where the winds relax, Kelvin waves
suppress the thermocline but leave the sea surface temperature unchanged
in linear models. In nonlinear models advection by eastward currents in
the wake of Kelvin waves can cause a warming, even at the surface. For winds
with a realistic spatial and temporal structure the identification of these
waves is difficult.