## What fraction of a Kelvin wave incident on a narrow strait is transmitted?

Helen L. Johnson and Chris Garrett, *Journal of Physical Oceanography*,
**36**, 945-954.

**Abstract**

Parameters governing the fraction of a Kelvin wave
transmitted through a narrow gap or channel include time-dependence,
nonlinearity, friction and strait geometry, yet only limited regions
of this parameter space have been explored. Linear inviscid models
(which neglect advective and frictional terms in the momentum
equations) predict that 100% of the volume flux of a low-frequency
Kelvin wave or steady boundary current incident on a narrow strait is
transmitted, even when the strait width becomes infinitely small.
Here the nonlinear, inviscid, flat bottom problem is considered, and
it is shown that, provided the geometry varies slowly, the quasi-steady
solution can be found in the rotating-hydraulics literature.
In the narrow channel limit the fraction transmitted can be
approximated by a simple prediction based on non-rotating hydraulics.
Unless an incoming Kelvin wave has a large amplitude in comparison with the
background layer depth the strait width must be considerably smaller
than the deformation radius before it limits the volume flux passing
through. Results also show that a Kelvin wave of given volume flux
will squeeze through a narrower gap if it is pushed rather than
pulled.

This manuscript is available as a PDF file.