Remote-sensing observations of filament formation along the almeria-oran front

Two sequences of daily NOAA AVHRR thermal images of the Almeria-Oran front in the Western Mediterranean are presented. Unstable filamentary features (''filaments'' herein) are observed on the front, having length scales comparable to that of the front itself, and growing and decaying on a timescale of a few days. The process of initiation of the filaments is observed to be variable, although as these features develop, their appearances tend to converge. All the filaments are eventually advected onto, and subsumed within the Algerian coastal current. It is suggested that variations in the flow in the Eastern Alboran Gyre are responsible for the initiation of the filaments, and that the interaction of the same gyral flow with the lateral topography of the southern Spanish coast is responsible for one mode of initiation as well as for other features associated with the front: A second mode of initiation appears to be associated with a deformation of the frontal interface unconnected with the coastal topography. The flow regime in the Algerian Basin close to the front appears to play a role in the distortion and suppression of the filaments. Measurements of the wavelengths, growth rates and phase speeds of the filaments are presented, and these indicate that, in general, their growth rate is greater than their rate of decay, and that their phase speeds tend to be greater during the diminution phase than during the growth phase. Comparisons of these parameters with those derived from a theoretical model of an isolated surface front are generally favourable.