Rossby Wave Driven Eulerian Mean Flows Along Non-Zonal Barriers, with Application to the Hawaiian Ridge

Abstract

We show that the reflection of baroclinic Rossby waves from a non-zonal barrier generates a Eulerian mean flow along the barrier. In order to produce a mean current of realistic magnitude, friction (in the form of Rayleigh damping) has to be incorporated into the theory. However, the wave-induced mean flow still exists in the absence of friction; the key requirement for mean flow production is the non-zonality of the reflecting wall. The theory is applied to the Hawaiian Ridge where the incident Rossby wave field is known for the 5° square 20?25°N, 155?160°W (Magaard, 1983). The mean flow produced by this incident wave field consists of 1) a narrow eastward coastal jet ?20 km wide, and 2) a band-structured flow of alternating directions beyond the coastal jet. The width of each band in 2) is ?50 km, and the envelope of the current oscillations decreases (from a maximum surface value of ?0.75 m s?1) exponentially with distance from the Hawaiian Ridge. In the region between the western side of Maui and the eastern side of Hawaii (a span of ?300 km), the structure of the predicted current system agree fairly well with the surface flow field found in White's (1983) recent analysis of historical hydrographic and XBT data.