Numerical investigation of an oceanic resonant regime induced by hurricane winds |
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| Authors: | Guillaume Samson Hervé Giordani Guy Caniaux Frank Roux |
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| Institution: | (1) Centre National de Recherches Météorologiques, Groupe d’étude de l’Atmosphère Météorologique, Météo-France, CNRS, 42 avenue Gaspard Coriolis, 31057 Toulouse Cedex 01, France;(2) Laboratoire de l’Atmosphère et des Cyclones, Université de La Réunion, Météo-France, CNRS, 15 avenue René Cassin, 97715 Saint-Denis Cedex 09, France;(3) Laboratoire d’Aérologie, Université Toulouse 3, CNRS, 14 avenue Edouard Belin, 31400 Toulouse, France |
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| Abstract: | The oceanic mixed layer (OML) response to an idealized hurricane with different propagation speeds is investigated using a
two-layer reduced gravity ocean model. First, the model performances are examined with respect to available observations relative
to Hurricane Frances (2004). Then, 11 idealized simulations are performed with a Holland (Mon Weather Rev 108(8):1212–1218,
1980) symmetric wind profile as surface forcing with storm propagation speeds ranging from 2 to 12 m s−1. By varying this parameter, the phasing between atmospheric and oceanic scales is modified. Consequently, it leads to different
momentum exchanges between the hurricane and the OML and to various oceanic responses. The present study determines how OML
momentum and heat budgets depend on this parameter. The kinetic energy flux due to surface wind stress is found to strongly
depend on the propagation speed and on the cross-track distance from the hurricane center. A resonant regime between surface
winds and near-inertial currents is clearly identified. This regime maximizes locally the energy flux into the OML. For fast-moving
hurricanes (>6 m s−1), the ratio of kinetic energy converted into turbulence depends only on the wind stress energy input. For slow-moving hurricanes
(<6 m s−1), the upwelling induced by current divergence enhances this conversion by shallowing the OML depth. Regarding the thermodynamic
response, two regimes are identified with respect to the propagation speed. For slow-moving hurricanes, the upwelling combined
with a sharp temperature gradient at the OML base formed in the leading part of the storm maximizes the oceanic heat loss.
For fast propagation speeds, the resonance mechanism sets up the cold wake on the right side of the hurricane track. These
results suggest that the propagation speed is a parameter as important as the surface wind speed to accurately describe the
oceanic response to a moving hurricane. |
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| Keywords: | Air– sea interactions Oceanic mixed layer Hurricane propagation speed Entrainment parameterization Upwelling Resonant regime Near-inertial currents |
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