Internal Solitary Waves System in the Mozambique Channel

Abstract

Satellite images of the Mozambique Channel (MC), collected by Synthetic Aperture Radars (SARs) from the Envisat and European Remote Sensing (ERS) satellites, reveal sea surface signatures of oceanic Internal Solitary Waves (ISWs). The MC has been expected to be a major hotspot for the generation of Internal Tides (ITs) in the ocean. New results now show that the Sofala bank (or shelf, located near 20 degrees S, 36 degrees E) is indeed a strong and previously unknown source for the generation of ITs and ISWs. The hotspot region is located between 20 and 21 degrees S, where the barotropic tidal forcing and tidal transports are highest in the area, due to the particular nature of the bathymetry there. Two distinct types of ISWs are observed to travel offshore, away from the shelf-break, and their possible generation mechanisms are discussed. Mode 2 ISWs propagating in MC are also observed in SAR imagery. It is discussed that they may be generated by a tidal beam impinging the thermocline from below, in a similar process to some of the Mode 1 ISWs generated off the Sofala bank. ISW refraction patterns, often observed in SAR imagery in MC are presented, and a particular example is shown where ISWs and eddy-like features are seen to interact. The influence of these rotating features in the refraction patterns is briefly discussed. Finally, it is shown that large-scale atmospheric gravity waves of solitary-like form are also frequently observed in the region, and thus care must be taken when discriminating oceanic and atmospheric ISW signatures in SAR images, if a correct interpretation is to be made.