J. Clim. 11:3309-3319
Abstract
To study the dynamics that may lead to decadal oscillations
in the
North Pacific a simple coupled model is developed. The
ocean is based
on the linear, potential-vorticity equation for baroclinic
planetary waves. The atmosphere is reduced to a non-local wind response
to
thermocline depth anomalies. The wind stress has
a spatially fixed structure
and its amplitde depends on the thermocline perturbation at one location
or in
a predefined index region.
Such a simple coupled model produces decadal oscillations for suitable
parameter choices. For realistic wind stress patterns, the patterns
of oceanic
variability are similar to those observed. It is determined by
the speed of long
Rossby waves at the coupling latitude. The period of the oscillation
is rather
insensitive to the coupling strength and amounts to approximately twice
the time the
Rossby wave needs to travel from the center of the wind stress curl
anomaly to the
coupling location.
A stochastic component to the atmospheric forcing is incorporated by
white noise added to the feedback. With such a forcing,
typical oceanic spectra become red with a broad peak at decadal time
scales superimposed.