A method for estimating deep, depth independent current variability is described. The procedure uses XBT derived dynamic heights to remove the near surface signal from altimetric sea surface height (SSH). The difference between SSH and dynamic height is operationally defined as barotropic height (BRT). Currents are obtained from BRT slopes using the geostrophic balance. The method requires the variability below the deepest XBT measurement to be small. Results are restricted to temporal variability, as geoid uncertainties in the SSH data render absolute current estimations impossible. The technique is originally developed for use in the Atlantic Western Boundary Current (WBC). Comprehensive verification of the methodology requires simultaneous SSH, XBT and current meter measurements. There are no available Atlantic data sets that meet these requisites. The alternative is to use synthetic data from the CLIPPER Atlantic model (1=6o resolution). Correlation (r) between estimated and modelled near bottom velocities in WBC areas of interest vary from 0.7 to 0.8. Further tests are conducted with observed data from the Shikoku Basin boundary current in southern Japan, where the method is capable of reproducing the directly measured near bottom current variability (r = 0:6). The procedure is also tested using north Pacific (5o ¡ 55oN) data from the OCCAM model. Correlations between model derived and BRT estimated velocities are around r = 0:7 for the Shikoku Basin northern boundary and for the Pacific WBC. Values reach r = 0:9 in large areas of the basin's interior, specially over smooth topography. The above method is used to generate time series of the barotropic variability in two areas of the Atlantic Western Boundary. One site is located at 38oN, inshore of the Gulf Stream. The other is at 8oS, off the Brazilian coast. Both series are a approximately 6 years long. Empirical Orthogonal Function analysis results conducted on SSH and sea surface temperature data are used to confirm the feasibility of applying the method in the chosen South Atlantic area. Currents are compared to scatterometer derived local along-shore wind stress and basin wide wind stress curl. In both areas, current variability is significantly correlated to basin averaged wind stress curl and and also to local along-shore wind stress. The relationship between currents and wind curl is coherent with the WBC response to interior Sverdrup flow. We propose that local wind stress exerts control over the flow by divergence of the Ekman flow at the coast. In the north, the variability is dominated by interannual oscillations of the wind curl. The effects of the local stress are secondary and have annual frequency. Both wind stress curl and along-shore wind are significantly correlated to the currents on the southern site, but the local effect appears to be the dominant forcing. The main observed results are confirmed by data from a numerical model with 1=6o horizontal resolution. / A Dissertation Submitted to the Department of Oceanography in Partial FulfiLlment of the Requirements for the Degree of Doctor of Philosophy. / Spring Semester, 2004. / November 7, 2003. / TOPEX, Atlantic, Western Boundary, Variability / Includes bibliographical references. / Georges L. Weatherly, Professor Directing Thesis; Steven L. Blumsack, Outside Committee Member; William M. Landing, Committee Member; Doron Nof, Committee Member; James O'Brien, Committee Member; Kevin Speer, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_180545 |
| Contributors | Montengro, Alvaro (authoraut), Weatherly, Georges L. (professor directing thesis), Blumsack, Steven L. (outside committee member), Landing, William M. (committee member), Nof, Doron (committee member), O'Brien, James (committee member), Speer, Kevin (committee member), Department of Earth, Ocean and Atmospheric Sciences (degree granting department), Florida State University (degree granting institution) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource, computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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