Abstract
The off-shelf region between 16.0 degrees and 16.5 degrees N in the southern Red Sea is identified as a new hotspot for the occurrence of oceanic internal solitary waves. Satellite observations reveal trains of solitons that, surprisingly, appear to propagate from the center of the Red Sea, where it is deepest, toward the continental shelf, but they do not survive as coherent structures over the shelf. These solitons are characterized by coherent crest lengths exceeding 80 km and crest-to-crest distances of more than 2 km, compatible with signatures of large-amplitude solitary waves. Despite the fact that these Red Sea solitons have large amplitudes, they appear to be generated by very weak surface tides. Tidal current velocity is only about 5 cm s(-1) over the shelf, much weaker than over other ocean shelves where similar solitary waves have been reported. The appearance of these waves over this particular geographical stretch suggests generation by a locally amplified internal tide on the main pycnocline. We consider three possible explanations for soliton generation in the Red Sea: interfacial tide resonance, local generation by internal tidal beams generated at the shelf breaks, and local generation by internal tidal beams generated at the shelf breaks but first amplified by repeated focusing reflections.
Highlights
We investigate the generation mechanisms of internal solitary waves (ISWs) observed in the Red Sea
It is important to stress that the ISWs observed in the synthetic aperture radar (SAR) images exhibit large-amplitude signals
The SAR image contrasts produced by the Red Sea ISWs shown in Figure 3b are comparable, and quite close, to SAR image contrasts seen in other regions where very powerful ISWs have been documented
Summary
Internal waves occur in a limited region, situated between the Saso Islands (S) to the east and the Dahlak Marine Park Islands (D) to the west This location coincides with one of the widest zones of the southern Red Sea where the surface tides are strongest, but only slightly stronger than anywhere else in the Red Sea. This location coincides with one of the widest zones of the southern Red Sea where the surface tides are strongest, but only slightly stronger than anywhere else in the Red Sea These tidal currents are very weak compared to other continental shelves where ISWs are usually observed.
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