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Oceanographic Factors
Published in Ronald C. Chaney, Marine Geology and Geotechnology of the South China Sea and Taiwan Strait, 2020
The individual currents that comprise a specific oceanic gyre do not flow at the same speeds. Currents along the western margins of ocean basins are considerably swifter and narrower than their counterparts on the eastern side. An example of this effect is the velocity of the Gulf Stream approaches 9 km/h, while the Canary Current flows south along the European coast at less than 1 km/h (Parker, 1985). This western intensification of gyre currents results from a balance between several factors that affect the surface currents. These include the increasing magnitude of the Coriolis effect with latitude, latitudinal variations of wind strength and direction, and friction between the water currents and contiguous land masses. These factors cause the topographic highs of the oceanic highs of the oceanic gyres to be offset to the west as shown schematically in Figure 3.15. The western boundary currents move faster than those on the eastern side because a constant volume of water is squeezed into a narrower band along the western margins of the ocean basins.
Chapter 1: Physical Processes
Published in Gunnar Kullenberg, Pollutant Transfer and Transport in the Sea, 1982
Gunnar Kullenberg, Gunnar Kullenberg
With the general circulation we understand the large scale, more or less permanent oceanic current systems driven by the combined action of wind and thermohaline forcing. The essentially wind-driven circulation of the upper layer has a similar appearance in all the oceans. There is a strong east-west asymmetry with the strongest currents at the western boundaries of the ocean. Such western boundary currents are the Gulf Stream in the North Atlantic, the Kuroshio in the North Pacific, the Agulhas Current in the South Indian Ocean and the East Australian Current in the South Pacific. These currents transport water poleward, with velocities in the range 100 to 200 cms–1 which has been transferred towards the west with the broad zonal flow in the north and south equatorial currents. Around 40° latitude the western boundary currents change to more zonal eastward flow. There is generally no pronounced currents at the eastern side, but rather slow equatorward flows feeding the equatorial currents. Thus so-called subtropical circulation gyres are formed71 with an anticyclonic sense of rotation. The reason for the western asymmetry is to be found in the combined action of friction and the variation of the Coriolis (rotational) effect with latitude.72 At higher latitudes there is a tendency towards a cyclonic gyre with intensified flow towards the equator along the western boundaries; examples are the East Greenland Current and the Falkland Current. The circulation reaches at least about 1000 m depth. At 800 m in the North Atlantic the circulation is very similar to the surface motion,73,74 although the mean velocities are smaller, generally less than 30 cms–1.
Ocean–Atmosphere Interactions
Published in Yeqiao Wang, Atmosphere and Climate, 2020
Direct measurements of air-sea flux are few, limited both in time and in space. These measurements of air-sea fluxes are important, however, for developing, calibrating, and verifying the estimated air- sea flux from parameterization schemes.[8,9] The parameterization schemes for air-sea fluxes use state variables of the atmosphere and the ocean (e.g., wind speed, temperatures, humidity) to estimate the fluxes. A commonly used parameterization scheme for air-sea fluxes is the "bulk-aerodynamic" formula. This is based on the premise that wind stress is proportional to the mean wind shear computed between surface and 10 m above surface, and sensible heat flux and latent heat flux are proportional to the vertical temperature and moisture gradients computed between surface and 2 m above surface. As a result, air-sea fluxes have been computed globally and regionally from a variety of analyzed and regionally observed or analyzed atmospheric and oceanic states leading to a number of air-sea flux intercomparison studies.[10-12] These intercomparisons provide insight into the uncertainty of estimating air-sea fluxes as well as revealing salient differences in the state variables used in the parameterization scheme. For example, Smith et al.[10] found that in many regions of the planet the differences in surface air temperature and humidity amongst nine different products of air-sea fluxes had a more significant impact than the differences in the surface air wind speed (at 10 m) on the differences in the air-sea fluxes. Climatologically, large values of sensible heat flux are observed in the winter along the western boundary currents of the middle-latitude oceans, when cold continental air passes over the warm ocean currents (e.g., Gulf Stream). In the tropics and in the sub-tropical eastern oceans, the sensible heat flux is usually small. In the former region, climatologically, the wind speeds and the vertical temperature gradients between the surface and 2 m above the surface are weak. In the sub-tropical eastern oceans, with prevalence of upwelling, the SSTs are relatively cold leading to generally smaller sensible heat flux. The latent heat flux is observed climatologically to be large everywhere in the global oceans relative to the sensible heat flux, with exceptions over polar oceans in the winter season. The ratio of sensible to latent heat flux, called the Bowen ratio, has a latitudinal gradient with a higher (smaller) ratio displayed
Detailed investigation of the three-dimensional structure of a mesoscale cold eddy in the Kuroshio extension region*
Published in Journal of Operational Oceanography, 2018
Chen Xi, Hu Dong, Mao Ke-feng, Li Yan
The Kuroshio Current is one of the major western boundary currents in the global ocean. It carries momentum and heat northward from the tropics to midlatitude regions. After separating from the coast of Japan at around 35°N, it flows zonally into the North Pacific Ocean with a zonal jet called the Kuroshio Extension (KE). The mean path of the upstream KE is characterised by the presence of two quasi-stationary meanders with their ridges located at 144° and 150°E, respectively. Near 159°E, the KE jet encounters the Shatsky Rise where it often bifurcates: the main body of the jet continues eastward, and a secondary branch tends to move northeastward to 40°N where it joins the Subarctic Current (e.g. Mizuno and White 1983; Niiler et al. 2003). With the eastward transport enhanced by the neighbouring recirculation gyres, the KE region (KER) has long been recognised as rich in large-amplitude meanders and energetic shedding eddies (e.g. Yasuda et al. 1992; Joyce et al. 2001). It is one of the regions with the most active mesoscale eddies within the North Pacific Ocean (Qiu and Chen 2010) and eddies in this region are characterised by large amplitudes, high degrees of nonlinearity (Chelton et al. 2011), and may persist for periods ranging from several months to more than one year. Baroclinicity of the Kuroshio Current serves as the source of energy for the mesoscale eddies (Qiu and Chen 2010). In turn, the region’s eddies perform the important role of regulating the form and temporal changes of KER’s oceanic jet streams (Waterman et al. 2011), and they are important factors for the generation of subtropical mode water in the North Pacific Ocean (Qiu et al. 2007; Nishikawa et al. 2010).
Copernicus Marine Service Ocean State Report
Published in Journal of Operational Oceanography, 2018
Karina von Schuckmann, Pierre-Yves Le Traon, Neville Smith, Ananda Pascual, Pierre Brasseur, Katja Fennel, Samy Djavidnia, Signe Aaboe, Enrique Alvarez Fanjul, Emmanuelle Autret, Lars Axell, Roland Aznar, Mario Benincasa, Abderahim Bentamy, Fredrik Boberg, Romain Bourdallé-Badie, Bruno Buongiorno Nardelli, Vittorio E. Brando, Clément Bricaud, Lars-Anders Breivik, Robert J.W. Brewin, Arthur Capet, Adrien Ceschin, Stefania Ciliberti, Gianpiero Cossarini, Marta de Alfonso, Alvaro de Pascual Collar, Jos de Kloe, Julie Deshayes, Charles Desportes, Marie Drévillon, Yann Drillet, Riccardo Droghei, Clotilde Dubois, Owen Embury, Hélène Etienne, Claudia Fratianni, Jesús García Lafuente, Marcos Garcia Sotillo, Gilles Garric, Florent Gasparin, Riccardo Gerin, Simon Good, Jérome Gourrion, Marilaure Grégoire, Eric Greiner, Stéphanie Guinehut, Elodie Gutknecht, Fabrice Hernandez, Olga Hernandez, Jacob Høyer, Laura Jackson, Simon Jandt, Simon Josey, Mélanie Juza, John Kennedy, Zoi Kokkini, Gerasimos Korres, Mariliis Kõuts, Priidik Lagemaa, Thomas Lavergne, Bernard le Cann, Jean-François Legeais, Benedicte Lemieux-Dudon, Bruno Levier, Vidar Lien, Ilja Maljutenko, Fernando Manzano, Marta Marcos, Veselka Marinova, Simona Masina, Elena Mauri, Michael Mayer, Angelique Melet, Frédéric Mélin, Benoit Meyssignac, Maeva Monier, Malte Müller, Sandrine Mulet, Cristina Naranjo, Giulio Notarstefano, Aurélien Paulmier, Begoña Pérez Gomez, Irene Pérez Gonzalez, Elisaveta Peneva, Coralie Perruche, K. Andrew Peterson, Nadia Pinardi, Andrea Pisano, Silvia Pardo, Pierre-Marie Poulain, Roshin P. Raj, Urmas Raudsepp, Michaelis Ravdas, Rebecca Reid, Marie-Hélène Rio, Stefano Salon, Annette Samuelsen, Michela Sammartino, Simone Sammartino, Anne Britt Sandø, Rosalia Santoleri, Shubha Sathyendranath, Jun She, Simona Simoncelli, Cosimo Solidoro, Ad Stoffelen, Andrea Storto, Tanguy Szerkely, Susanne Tamm, Steffen Tietsche, Jonathan Tinker, Joaquín Tintore, Ana Trindade, Daphne van Zanten, Luc Vandenbulcke, Anton Verhoef, Nathalie Verbrugge, Lena Viktorsson, Karina von Schuckmann, Sarah L. Wakelin, Anna Zacharioudaki, Hao Zuo
Strong poleward Western Boundary Currents are present in the world’s major ocean basins, which compensate for the wind-driven equatorward transport in the ocean subtropical gyres (Imawaki et al., 2013). The Kuroshio in the North Pacific Ocean, the Gulf Stream in the North Atlantic, the Agulhas Current in the Indian Ocean can be distinguished on Figure 1.6.1 of Section 1.6, where 1993–2014 climatological velocity reach more than 1 m/s In the East Australian Current in the South Pacific, and the Brazil Current in the South Atlantic, climatological velocities are of the order of 50 cm/s.