A Model for the Alboran Sea Internal Solitary Waves

Abstract

The propagation into the Alboran Sea of the interface depression generated at the Strait of Gibraltar by the interaction of the semidiurnal tidal current with the main (Camarinal) sill is studied numerically by using a unidirectional model with two horizontal space dimensions. An initial waveform within the strait is determined whose evolution corresponds with the train of internal solitary waves detected in the Alboran Sea by means of current measurements at different depths, as described by Kinder. The agreement is good for two points located at about 45 km east of the strait, the first aligned with the strait axis and the second 20 km to the north. Moreover, the shape and amplitude of this initial condition are in agreement with a typical interface depression generated in the strait by the interaction of the tidal current with the sill. A series of numerical experiments with different initial conditions is also performed to study the sensitivity of the model results to changes in the initial internal wave, and the reason why solitary waves may or may not be observed in the western part of the Alboran Sea is thus clarified. In general the horizontal shape of the waves is similar to that shown in pictures taken by the Space Shuttle Challenger. A discrepancy between the numerical and the observed shape, i.e., the higher curvature of the waves in a beam aligned with the strait axis, is to be accounted for by the advection due to the Atlantic water inflow which is not modeled here. The present study helps to understand the observed connection between the weakening of the Atlantic water jet (and corresponding weakening of the Alboran Sea gyre) and the appearance of energetic internal solitary waves.