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Multiyear Subinertial and Seasonal Eulerian Current Observations near the Florida Big Bend Coast

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  • 1 Department of Earth, Ocean and Atmospheric Science, The Florida State University, Tallahassee, Florida
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Abstract

Multiyear in situ Eulerian acoustic Doppler current profiler measurements were obtained at 5-, 10-, and 19-m depths off the Big Bend coast, and in 19 m off the Florida Peninsula to the south. Analysis on subinertial time scales, dominated by weatherband frequencies, led to the following conclusions. At the 19-m Big Bend site (K-Tower), consistent with coastally trapped wave (CTW) theory, the along-isobath flow is not proportional to the local along-isobath wind stress, but rather to the alongshore wind stress to the south along the west Florida shelf (WFS). At the southern 19-m site, consistent with previous work, the along-isobath flow is driven by , but is weakened by an alongshore pressure gradient brake. Via CTW dynamics this brake is due to the abrupt “end” of the WFS at the Florida Keys. By contrast, along-isobath flow at the shallow 5-m site is driven by the local wind in a constant stress turbulent frictional layer. Because of the freshwater flux near the coast, density usually increases seaward. This leads to a strong asymmetry in the cross-isobath frictional bottom boundary layer (BBL) flow when the subinertial along-isobath flow direction changes. In one case the BBL flow is shoreward and gravitationally stable while, in the other, the BBL flow is gravitationally unstable as less dense water is forced under more dense water. Seasonal changes in the seaward horizontal density gradient also shear the seasonal along-isobath flow via thermal wind dynamics.

Corresponding author address: Allan J. Clarke, Department of Earth, Ocean and Atmospheric Science, The Florida State University, 433A Oceanography/Statistics Building, 117 North Woodward Avenue, P.O. Box 3064320, Tallahassee, FL 32306-4320. E-mail: aclarke@fsu.edu

Abstract

Multiyear in situ Eulerian acoustic Doppler current profiler measurements were obtained at 5-, 10-, and 19-m depths off the Big Bend coast, and in 19 m off the Florida Peninsula to the south. Analysis on subinertial time scales, dominated by weatherband frequencies, led to the following conclusions. At the 19-m Big Bend site (K-Tower), consistent with coastally trapped wave (CTW) theory, the along-isobath flow is not proportional to the local along-isobath wind stress, but rather to the alongshore wind stress to the south along the west Florida shelf (WFS). At the southern 19-m site, consistent with previous work, the along-isobath flow is driven by , but is weakened by an alongshore pressure gradient brake. Via CTW dynamics this brake is due to the abrupt “end” of the WFS at the Florida Keys. By contrast, along-isobath flow at the shallow 5-m site is driven by the local wind in a constant stress turbulent frictional layer. Because of the freshwater flux near the coast, density usually increases seaward. This leads to a strong asymmetry in the cross-isobath frictional bottom boundary layer (BBL) flow when the subinertial along-isobath flow direction changes. In one case the BBL flow is shoreward and gravitationally stable while, in the other, the BBL flow is gravitationally unstable as less dense water is forced under more dense water. Seasonal changes in the seaward horizontal density gradient also shear the seasonal along-isobath flow via thermal wind dynamics.

Corresponding author address: Allan J. Clarke, Department of Earth, Ocean and Atmospheric Science, The Florida State University, 433A Oceanography/Statistics Building, 117 North Woodward Avenue, P.O. Box 3064320, Tallahassee, FL 32306-4320. E-mail: aclarke@fsu.edu
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