Chapter 14
Internal Solitary Waves System in the
Mozambique Channel
Jorge M. Magalhaes, José C. B. da Silva and Adrian L. New
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
◦ S, 36
◦ 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
◦ 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.
J. M. Magalhaes () · J. C. B. da Silva
Department of Geosciences, Environment, and Spatial Planning,
Interdisciplinary Centre of Marine and Environmental Research, CIMAR,
Porto, Portugal
e-mail: jmagalhaes@fc.ul.pt
Also at: Faculty of Sciences, University of Porto, Porto, Portugal
A. L. New
Marine Systems Modelling Group, National Oceanography Centre,
Southampton, Southampton, UK
V. Barale, M. Gade (eds.), Remote Sensing of the African Seas,
263
DOI 10.1007/978-94-017-8008-7_14,
© Springer Science+Business Media Dordrecht 2014
Internal Solitary Waves System in the
Mozambique Channel
Jorge M. Magalhaes, José C. B. da Silva and Adrian L. New
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
◦ S, 36
◦ 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
◦ 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.
J. M. Magalhaes () · J. C. B. da Silva
Department of Geosciences, Environment, and Spatial Planning,
Interdisciplinary Centre of Marine and Environmental Research, CIMAR,
Porto, Portugal
e-mail: jmagalhaes@fc.ul.pt
Also at: Faculty of Sciences, University of Porto, Porto, Portugal
A. L. New
Marine Systems Modelling Group, National Oceanography Centre,
Southampton, Southampton, UK
V. Barale, M. Gade (eds.), Remote Sensing of the African Seas,
263
DOI 10.1007/978-94-017-8008-7_14,
© Springer Science+Business Media Dordrecht 2014