EGU24-8235, updated on 08 Mar 2024
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Observations of internal wave generation in Madeira island 

Jesus Reis1,2,3, Juan Gomiz-Pascual1, Álvaro Peliz2, Rui Caldeira2,3, and Miguel Bruno1
Jesus Reis et al.
  • 1University of Cádiz, Cadiz, Spain
  • 2Instituto Dom Luiz, Faculty of Sciences of the University of Lisbon, Lisbon, Portugal
  • 3Oceanic Observatory of Madeira, ARDITI, Madeira, Portugal

There is a considerable number of coastal regions where the interaction of barotropic tidal currents with the stratified water column over seamounts or sill topographies generates large amplitude internal waves. An example of this is the internal bores generated around the main sill of the Strait of Gibraltar. It is known that the vertical mixing induced by these phenomena induces a relevant biological response in both the generation place and remote areas. The present work analyses the generation of this kind of internal waves in the northern half of the submarine ridge between Madeira and the Desertas Islands (Portugal). Here, the interaction of a rather intense barotropic tidal current with the stratified water column and the abrupt ridge topography leads to the creation of hydraulic jumps that evolve into internal bores and solitons, which radiate outwards from the sill. These bores can be formed at both sides of the sill (eastern and western sides) in synchrony with the barotropic flow direction. The hydraulic jump that gives rise to the internal waves is generated after supercritical conditions are established over the sill (internal Froude number, Fr >1). While supercritical conditions prevail, the internal bore stands trapped on the downstream side of the sill. With the weakening of the barotropic current, the supercritical conditions are lost (Fr <1), and the internal bore and subsequent solitons are released from the sill. Internal bores formed on the western side of the sill have greater amplitudes than those formed on the eastern side, and it seems to be related to the different orientations of the barotropic current concerning the longitudinal axis of the sill depending on the flow being eastward or westward. A smaller hydraulic jump is also formed during the eastward phase of the barotropic tidal current. This study is the first to document the internal wave activity in the SE of Madeira Island. It combines data from satellite images, in-situ campaigns, and moored instruments to allow the observation of the hydraulic conditions before, during, and after the generation events. Estimates of the vertical mixing using Richardson number and energy fluxes calculations helped identify internal wave events.

How to cite: Reis, J., Gomiz-Pascual, J., Peliz, Á., Caldeira, R., and Bruno, M.: Observations of internal wave generation in Madeira island , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8235,, 2024.