Regionalizing the impacts of wind and wave-induced currents on surface
ocean dynamics: a long-term variability analysis in the Mediterranean
Sea
Abstract
Effects of wind and waves on the surface dynamics of the Mediterranean
Sea are assessed using a modified Ekman model including a
Stokes-Coriolis force in the momentum equation. Using 25 years of
observations, we documented intermittent but recurrent episodes during
which Ekman and Stokes currents substantially modulate the total
mesoscale dynamics by two non-exclusive mechanisms: (i) by providing a
vigorous input of momentum (e.g. where regional winds are stronger)
and/or (ii) by opposing forces to the main direction of the geostrophic
component. To properly characterize the occurrence and variability of
these dynamical regimes we perform an objective classification combining
self-organizing maps (SOM) and wavelet coherence analyses. It allows
proposing a new regional classification of the Mediterranean Sea based
on the respective contributions of wind, wave and geostrophic components
to the total mesoscale surface dynamics. We found that the effects of
wind and waves are more prominent in the northwestern Mediterranean,
while the southwestern and eastern basins are mainly dominated by the
geostrophic component. The resulting temporal variability patterns show
a strong seasonal signal and cycles of 5 - 6 years in the total kinetic
energy arising from both geostrophic and ageostrophic components.
Moreover, the whole basin, specially the regions characterized by strong
wind- and wave- induced currents, shows a characteristic period of
variability at $5$ years. That can be related with climate modes of
variability. Regional trends in the geostrophic and ageostrophic
currents shows an intensification of 0.058 +-1.43 10^-5 cm/s per
year.