Reflection of incident Equatorial Kelvin Waves from eastern basin boundaries which are not perpendicular to the Equator.

Abstract:

Reflection of incident equatorial Kelvin waves from eastern basin boundaries that are not perpendicular to the Equator.

Dennis W. Moore, PMEL, Seattle

Hristina Hristova, JIMAR and PMEL, Seattle

T.S.Durland, Oregon State University

Jay McCreary, University of Hawaii

The theory of linear equatorial waves shows that there is an intermediate frequency band between the highest frequency equatorial Rossby wave (with frequency approximately 0.3) and the lowest frequency equatorial gravity wave (with frequency approximately 1.7). Between these two frequencies the only free waves with real east-west wave number are the equatorial Kelvin wave, and the Yanai (or mixed Rossby-gravity) wave. We previously explored the partition of poleward-propagating, coastal-Kelvin wave energy propagating away from the equator on an eastern boundary when either an equatorial Kelvin wave or a Yanai wave is incident from the west. The coast need not be perpendicular to the equator. All the incident energy goes either north or south along the coast. None goes west along the equator.

We now extend the frequency range of the incident Kelvin wave so that it is possible to generate a long Rossby wave as part of the reflection off an eastern boundary which is not normal to the equator. So, for instance, an equatorial Kelvin wave with dimensionless frequency between 0.3 and 1.7 only produces poleward-propagating coastal waves at the eastern boundary. At a dimensionless frequency of 0.25, however, an incident equatorial Kelvin wave will produce a reflected long Rossby wave with a dimensionless wavenumber given by k = −1.75, with westward phase speed and group velocity, sending some energy back to the west along the equator. At the same time there is still coastal-wave energy propagating poleward on the eastern boundary. We explore the partition of energy between poleward-propagating coastal Kelvin waves and the westward-propagating, equatorial long Rossby wave.