Low-frequency variability of the separated western boundary current in response to a seasonal wind stress in a 2.5-layer model with outcropping

Abstract

International audienc

Western boundary circulation and coastal sea-level variability in Northern Hemisphere oceans

“…In the Pacific, anomalous wind stress curl triggers westward-propagating baroclinic jet-trapped Rossby waves that shift the jet meridionally (Sasaki et al, 2013;Sasaki and Schneider, 2011a;Sugimoto and Hanawa, 2009;Ceballos et al, 2009). A similar mechanism has been proposed for the Atlantic (Sasaki and Schneider, 2011b;Sirven et al, 2015). Sasaki et al (2014) hypothesized that the incoming jet-trapped Rossby waves, which are responsible for the extensions' shifts, break on the western boundary and propagate equatorwards as Kelvin or other coastally trapped waves, linking the extension variability to coastal sea level.…”

“…However, diverse behaviours have been found in models, with some supporting this paradigm (Zhang and Vallis, 2007;Zhang, 2008;Sanchez-Franks and Zhang, 2015) and some finding the opposite: an enhanced AMOC and northward-shifted GSNW (De Coetlogon et al, 2006;Kwon and Frankignoul, 2014). Alternatively, as in the Pacific with the KE, the Gulf Stream Extension has been linked to the mechanism of remote wind stress curl forcing the westward propagation of large-scale jet undulations (Sasaki and Schneider, 2011b;Sirven et al, 2015). Finally, Andres et al (2013) highlighted the fact that the coastal sea level on the large shelf north of Cape Hatteras was in agreement with the location of the Gulf Stream Extension west of 69 • W and suggested that the shelf transport pushes the Gulf Stream, whereas Ezer et al (2013) hypothesized that a more inertial Gulf Stream south of the separation point may "overshoot" to the north when leaving the coastline at 35 • N and control, at least to some extent, the location of the extension.…”

“…These jet-trapped waves are possible thanks to the sharp gradient of relative vorticity induced by WBC extensions comparable to or greater than the meridional gradient of planetary vorticity within the mid-latitude band. Hence, the jet-trapped waves are essentially Rossby waves, but they propagate in the waveguide formed by the WBC extension, which allow their meridional narrowing as they progress westward and their southwestward propagation in the Atlantic (Sasaki et al, 2013;Sasaki and Schneider, 2011a, b;Sirven et al, 2015). It is, however, important to note that, in the Atlantic, the lateral shifts of the Gulf Stream Extension have been more often linked with the DWBC and the NRG.…”