A theoretical reason to expect inviscid western boundary currents in realistic oceans |
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| Institution: | 1. Department of Marine Environmental Informatics, National Taiwan Ocean University, Keelung, Taiwan;2. Institute of Oceanography, National Taiwan University, Taipei, Taiwan;3. Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, Japan;1. School of Science, Guizhou Minzu University, Guiyang 550025, China;2. Collaborative Innovation Center of Biomass Energy, Henan Agricultural University, Zhengzhou 450002, Henan Province, China;1. Universidad Autónoma del Estado de Hidalgo, Academic Area of Chemistry, Carretera Pachuca-Tulancingo Km. 4.5, Mineral de la Reforma, Hgo, Mexico;2. Universidad Andrés Bello, Departamento de Ciencias Químicas, Facultad de Ciencias Exactas, Sede Concepción, Autopista Concepción-Talcahuano 7100, Talcahuano, Chile;3. Universidad Bernardo O Higgins, Laboratorio de Bionanotecnología, General Gana 1780, Santiago, Chile;4. Laboratorio Virtual NANOCOSMOS, Centro de Investigación en Materiales Avanzados, Chihuahua, Miguel de Cervantes 120, Complejo Industrial Chihuahua, Chih 31136, Mexico;1. Puertos del Estado, 28041 Madrid, Spain;2. ICM-CSIC, 08003 Barcelona, Spain;3. IMEDEA-CSIC, 07190 Esporles, Spain;4. Autoridad Portuaria Bahía de Algeciras, 11207 Algeciras, Spain;1. St. Petersburg State University, 7–9, Universitetskaya nab., St. Petersburg 199034, Russia;2. NIERSC, Nansen International Environmental and Remote Sensing Centre, 14th line, 7, St. Petersburg 199034, Russia;3. Arctic and Antarctic Research Institute, Bering str., 38, St. Petersburg 199397, Russia;4. Pacific Oceanological Institute of the Russian Academy of Sciences, 43 Baltiiskaya St., 690041 Vladivostok, Russia;1. Dhirubhai Ambani Institute of Information and Communication Technology, Gandhinagar 382007, Gujarat, India;2. Max-Planck Institut für Physik Komplexer Systeme, Nöthnitzer Str. 38, Dresden, D-01187, Germany;3. Condensed Matter Physics Division, Saha Institute of Nuclear Physics, Calcutta 700064, India |
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| Abstract: | The conventional picture of an ocean gyre, based on an ocean with vertical sidewalls, assumes a balance between an input of vorticity by wind stress curl, and a viscous flux of vorticity through the boundary at the same latitude, resulting from a viscous western boundary current which may be significantly modified by nonlinear terms. Potential interactions with topography are also commonly acknowledged as a possible complicating factor. In this idealized picture, the zonal momentum balance is taken to be geostrophic, as numerous model analyses confirm. A theoretical argument is given here which shows that, in an ocean with sloping sidewalls, this geostrophic balance results in bottom pressure torques which balance the wind stress curl at each latitude. This removes the requirement for a viscous western boundary current at each latitude suggesting that the dynamics within a western boundary current may be essentially inviscid. While inviscid western boundary currents have already been found in certain idealized systems, and in one set of diagnostics from an eddy permitting model, the generality of the argument presented here gives a strong reason to believe that these are not special cases. Inviscid western boundary currents are in fact the rule, and the vertical sidewall case is an unrealistic exception. |
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