Cole, Kelly Lynne (2008-08). Low-frequency variability of currents in the deepwater eastern Gulf of Mexico. Master's Thesis. Thesis uri icon

abstract

  • Vertical structure of the low frequency horizontal currents at the northern edge of the Loop Current during eddy shedding events is observed using concurrent hydrographic, moored, and satellite altimetry data from 2005. Dynamic modes are calculated at three deep (~3000 m), full water-column moorings in the eastern Gulf of Mexico. Time-series of the barotropic and first two baroclinic modes are found using a least squares minimization that fits theoretically derived modes to observed moored velocity data. EOF analyses show that the majority of observed variance is explained by a surface-trapped mode that is highly coherent with the temporal amplitudes of the first baroclinic mode, and a lower, but significant percentage of variance is captured in bottom-intensified modes. Amplitudes of the second empirical mode indicate that currents are more coherent in the ocean interior approaching the Loop Current, as more variance is explained by this mode at the southernmost mooring near the Loop Current. A dynamic mode decomposition of the horizontal currents reveals that the barotropic and first baroclinic modes exhibit low frequency variability and eddy time scales of 10 - 40 days. Second baroclinic mode amplitudes show higher frequency variability and shorter time scales. A model utility test for the least squares fit of modeled to observed velocity shows that the second baroclinic mode is useful to the statistical model during 50 - 85 % of the mooring deployment, and is particularly necessary to the model when cyclonic features are present in the study area. The importance of the second baroclinic mode to the model increases significantly closer to the Loop Current. High-speed currents associated with the Loop Current and anticyclones stimulate a strong first baroclinic response, but the second baroclinic mode amplitudes are found to be similar in magnitude to the first baroclinic mode amplitudes at times. This happens episodically and could be an indication of higher order dynamics related to frontal eddies or Loop Current eddy shedding.
  • Vertical structure of the low frequency horizontal currents at the northern edge of
    the Loop Current during eddy shedding events is observed using concurrent
    hydrographic, moored, and satellite altimetry data from 2005. Dynamic modes are
    calculated at three deep (~3000 m), full water-column moorings in the eastern Gulf of
    Mexico. Time-series of the barotropic and first two baroclinic modes are found using a
    least squares minimization that fits theoretically derived modes to observed moored
    velocity data.
    EOF analyses show that the majority of observed variance is explained by a
    surface-trapped mode that is highly coherent with the temporal amplitudes of the first
    baroclinic mode, and a lower, but significant percentage of variance is captured in
    bottom-intensified modes. Amplitudes of the second empirical mode indicate that
    currents are more coherent in the ocean interior approaching the Loop Current, as more
    variance is explained by this mode at the southernmost mooring near the Loop Current.
    A dynamic mode decomposition of the horizontal currents reveals that the
    barotropic and first baroclinic modes exhibit low frequency variability and eddy time scales of 10 - 40 days. Second baroclinic mode amplitudes show higher frequency
    variability and shorter time scales. A model utility test for the least squares fit of
    modeled to observed velocity shows that the second baroclinic mode is useful to the
    statistical model during 50 - 85 % of the mooring deployment, and is particularly
    necessary to the model when cyclonic features are present in the study area. The
    importance of the second baroclinic mode to the model increases significantly closer to
    the Loop Current.
    High-speed currents associated with the Loop Current and anticyclones stimulate
    a strong first baroclinic response, but the second baroclinic mode amplitudes are found
    to be similar in magnitude to the first baroclinic mode amplitudes at times. This happens
    episodically and could be an indication of higher order dynamics related to frontal eddies
    or Loop Current eddy shedding.

publication date

  • August 2008