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Coastal Flows Driven by Alongshore Density Gradients

Ross VennellJoint Program, MIT/WHOI

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Paola Malanotte-RizzoliMassachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, Center for Meteorology and Physical Oceanography, Cambridge, MA 02139

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Abstract

In this note we study the effect of an alongshore density gradient in driving the near-coastal circulation and determining the direction of the alongshore flow. We revisit and extend the results obtained by Malanotte-Rizzoli and Bergamasco (MRB) using the same simple analytical model but changing the longshore density distribution and examining the full solution, not only its far-field behavior as done by MRB. We find as a new result that the near-coastal flow is profoundly modified when passing from monotonic, northward increasing density profiles, the case studied by MRB, to double-ramp profiles with a density maximum. In particular, the reversal of the density gradient north of its maximum is a necessary condition for the creation of a strong southward flowing coastal cell. This cell does not exist when the density increases monotonically northward. The examples shown, even though idealized compare well both in flow direction and in order of magnitude with what is observed in winter in the northern Adriatic sea.

Abstract

In this note we study the effect of an alongshore density gradient in driving the near-coastal circulation and determining the direction of the alongshore flow. We revisit and extend the results obtained by Malanotte-Rizzoli and Bergamasco (MRB) using the same simple analytical model but changing the longshore density distribution and examining the full solution, not only its far-field behavior as done by MRB. We find as a new result that the near-coastal flow is profoundly modified when passing from monotonic, northward increasing density profiles, the case studied by MRB, to double-ramp profiles with a density maximum. In particular, the reversal of the density gradient north of its maximum is a necessary condition for the creation of a strong southward flowing coastal cell. This cell does not exist when the density increases monotonically northward. The examples shown, even though idealized compare well both in flow direction and in order of magnitude with what is observed in winter in the northern Adriatic sea.

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