Asymmetric Baroclinic Response
to Tidal Forcing Along the Main Sill
of the Strait of Gibraltar Inferred
from Mooring Observations
Jesús García-Lafuente, Simone Sammartino,
José C. Sánchez-Garrido and Cristina Naranjo
Introduction
The Atlas of Internal Waves [1] highlights the Strait of Gibraltar as a region where
short-period, large-amplitude internal wave trains progressing into the Mediterranean Sea occur regularly throughout the year. Indeed they are renowned and
paradigmatic features of this area that have been known since long ago by fishermen and sailors navigating the Strait. They identified the tidal origin of the phenomenon that happens phase-locked with the barotropic tide (sea level oscillation)
and exhibits intensity quite well related to the spring-neap tidal cycle. Pioneer field
experiments carried out during the 1960s supported this empirical knowledge by
suggesting that the flow in the Strait does not move as a continuous or
smoothly-varying current, but as tidal-induced pulses [2, 3]. However, the severe
technical difficulties caused by the strong currents of the region, the safety
restrictions associated with the heavy maritime traffic, and the harsh meteorology,
prevented the acquisition of reliable in situ observations until the late 1960s [4].
The basic theory of internal wave generation and propagation involves the
combination of water stratification, bathymetry, and transcritical flows. These
conditions are often met in coastal regions such as continental shelves, inlets, fjords
and straits, where these waves are more frequently observed [1]. Wherever stratification, seabed irregularities or currents are enhanced, the generated internal wave
train will also be. Equally important is the angle of incidence of the flow with the
isobaths, normal incidence being the most favorable situation. The Strait of
Gibraltar has a year-round notable stratification (compared with the seasonal
stratification in other places of the ocean) due to the encounter of Mediterranean
and Atlantic waters. At the same time, the presence of the protruding sill of
J. García-Lafuente ( ✉ ) ⋅ S. Sammartino ⋅ J. C. Sánchez-Garrido ⋅ C. Naranjo
Physical Oceanography Group, University of Málaga, Málaga, Spain
e-mail: glafuente@ctima.uma.es
© Springer International Publishing AG, part of Springer Nature 2018
M. G. Velarde et al. (eds.), The Ocean in Motion, Springer Oceanography,
https://doi.org/10.1007/978-3-319-71934-4_14
193
to Tidal Forcing Along the Main Sill
of the Strait of Gibraltar Inferred
from Mooring Observations
Jesús García-Lafuente, Simone Sammartino,
José C. Sánchez-Garrido and Cristina Naranjo
Introduction
The Atlas of Internal Waves [1] highlights the Strait of Gibraltar as a region where
short-period, large-amplitude internal wave trains progressing into the Mediterranean Sea occur regularly throughout the year. Indeed they are renowned and
paradigmatic features of this area that have been known since long ago by fishermen and sailors navigating the Strait. They identified the tidal origin of the phenomenon that happens phase-locked with the barotropic tide (sea level oscillation)
and exhibits intensity quite well related to the spring-neap tidal cycle. Pioneer field
experiments carried out during the 1960s supported this empirical knowledge by
suggesting that the flow in the Strait does not move as a continuous or
smoothly-varying current, but as tidal-induced pulses [2, 3]. However, the severe
technical difficulties caused by the strong currents of the region, the safety
restrictions associated with the heavy maritime traffic, and the harsh meteorology,
prevented the acquisition of reliable in situ observations until the late 1960s [4].
The basic theory of internal wave generation and propagation involves the
combination of water stratification, bathymetry, and transcritical flows. These
conditions are often met in coastal regions such as continental shelves, inlets, fjords
and straits, where these waves are more frequently observed [1]. Wherever stratification, seabed irregularities or currents are enhanced, the generated internal wave
train will also be. Equally important is the angle of incidence of the flow with the
isobaths, normal incidence being the most favorable situation. The Strait of
Gibraltar has a year-round notable stratification (compared with the seasonal
stratification in other places of the ocean) due to the encounter of Mediterranean
and Atlantic waters. At the same time, the presence of the protruding sill of
J. García-Lafuente ( ✉ ) ⋅ S. Sammartino ⋅ J. C. Sánchez-Garrido ⋅ C. Naranjo
Physical Oceanography Group, University of Málaga, Málaga, Spain
e-mail: glafuente@ctima.uma.es
© Springer International Publishing AG, part of Springer Nature 2018
M. G. Velarde et al. (eds.), The Ocean in Motion, Springer Oceanography,
https://doi.org/10.1007/978-3-319-71934-4_14
193