Characterization of Sea level Changes along the Louisiana/Florida Shelf Using High Frequency (HF) Radar Data and Sea level Measurements
Date of Award
Doctor of Philosophy (PhD)
Ocean Science and Engineering
In this dissertation, three sea level studies in the Mississippi Bight (MSB) have been conducted. The first is an investigation into why VDatum, the vertical datum transformation tool of NOAA, has large errors in the western side of the MSB. The second is an estimation of the subinertial (>2 day timescale) shape of sea level over the high frequency radar (HFR) coverage in the MSB and to what extent it is in geostrophic balance. The third study examines the relative contribution of different mechanims to the subinertial sea level in the HFR coverage area. For the first study, NOAA hypothesized that the errors were due to subsidence, but it was found that errors in range (~0.23 m) and in absolute tidal datums levels (0.15 to -0.41 m) were present and it was shown that imperfections in the tidal models and Topography of the Sea Surface could be responsible in these errors, respectively. The second study was aimed to provide mapped sea level estimates over the MSB, other than the gridded sea level estimates derived from coarse resolution satellite altimetry data. In the study, it was determined that the subinertial sea surface topography was predominately in geostrophic balance as Coriolis force was dominant in momentum balance except for few instances (0.01%) when Rossby number >0.1. The resulting subinertial sea level anomalies were validated using sea level observations from an offshore buoy and Setinel-3 along-track satellite altimeter data. The estimated root mean square difference of <0.04 m indicated a good agreement of the reconstructed sea level anomalies with independent observations. Analysis of the empirical orthogonal function showed that the first two modes explained majority of the variance in the sea level anomalies. In the third study, three mechanisms (wind-stress, Loop Current (LC) influence and freshwater discharge) were investigated to understand their contribution to the estimated patterns in the sea level gradient. Wind-stress was found to have the most influence in the patterns of the sea level gradient. While there was no indication of significant influence from freshwater discharge, it was revealed that the LC remotely influenced the patterns in sea level changes.
2022, Uchenna Chizaram Nwankwo
nwankwo, uchenna, "Characterization of Sea level Changes along the Louisiana/Florida Shelf Using High Frequency (HF) Radar Data and Sea level Measurements" (2022). Dissertations. 1987.
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