Articles | Volume 12, issue 1
https://doi.org/10.5194/os-12-137-2016
https://doi.org/10.5194/os-12-137-2016
Research article
 | 
18 Jan 2016
Research article |  | 18 Jan 2016

Temporal evolution of the momentum balance terms and frictional adjustment observed over the inner shelf during a storm

M. Grifoll, A. L. Aretxabaleta, J. L. Pelegrí, and M. Espino

Abstract. We investigate the rapidly changing equilibrium between the momentum sources and sinks during the passage of a single two-peak storm over the Catalan inner shelf (NW Mediterranean Sea). Velocity measurements at 24 m water depth are taken as representative of the inner shelf, and the cross-shelf variability is explored with measurements at 50 m water depth. During both wind pulses, the flow accelerated at 24 m until shortly after the wind maxima, when the bottom stress was able to compensate for the wind stress. Concurrently, the sea level also responded, with the pressure-gradient force opposing the wind stress. Before, during and after the second wind pulse, there were velocity fluctuations with both super- and sub-inertial periods likely associated with transient coastal waves. Throughout the storm, the Coriolis force and wave radiation stresses were relatively unimportant in the along-shelf momentum balance. The frictional adjustment timescale was around 10 h, consistent with the e-folding time obtained from bottom drag parameterizations. The momentum evolution at 50 m showed a larger influence of the Coriolis force at the expense of a decreased frictional relevance, typical in the transition from the inner to the mid-shelf.

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Short summary
We investigate the rapidly changing equilibrium between the momentum sources and sinks during the passage of a single two-peak storm over the Catalan inner shelf (NW Mediterranean Sea). At 24m water depth, a primary momentum balance between acceleration, pressure gradient and frictional forces (surface and bottom) is established. The frictional adjustment timescale was around 10h, consistent with the e-folding time obtained from bottom drag parameterizations.