(collaboration with J. Pedlosky)
The interaction of equatorial Rossby waves with a western
boundary perforated with one or more narrow gaps is
investigated using a shallow water numerical model and
supporting theory. It is found that very little of the
incident energy flux is reflected into eastward propagating
equatorial Kelvin waves provided that at least one gap
is located within approximately a deformation radius of the
equator. Due to the circulation theorem around an island,
the existence of a second gap off the equator reduces the
reflection of short Rossby waves and enhances the transmission
of the incident energy into the western basin. The westward
energy transmitted past the easternmost island is further reduced
upon encountering islands to the west, even if these islands are
located entirely within the "shadow" of the easternmost island.
A series of calculations was carried out in which westward propagating
waves were generated by a patch of zonal wind stress in the middle of
the Pacific Ocean. The amount of energy reflected into eastward
propagating Kelvin waves was strongly dependent on the duration and
meridional length scale of the forcing. For forcing events that last
2 years and have a meridional length scale of 700 km, the reflection
is 37% of the incident energy flux, very close to that predicted
by the theories of Clarke (1991, JGR-Oceans) and du Penhoat and Cane
(1991, JGR-Oceans). However, wind events of shorter duration or
smaller meridional length scale produce considerably less reflection.
For parameters typical of ENSO (1 year duration, 400 km meridional
scale) we find 23% reflection. This suggests that winds must be
of sufficient duration and meridional length scale to sustain
This work has been generously supported through grants from the
National Science Foundation and the Office of Naval Research.
Recent manuscript on these subjects :
Pedlosky, J. and M. A. Spall, 2005. Reflection and transmission of
equatorial Rossby waves. Journal of Physical
Oceanography , 35, 363-373.
An animation of a Rossby wave impinging on a western boundary with a gap :
Rossby wave movie , (use browser Back button to end).
An animation of a Kelvin wave impinging on an eastern boundary with a gap :
Kelvin wave movie , (use browser Back button to end).