Distribution of Deep Near-Inertial Waves Observed in the Kuroshio Extension

Copyright©The Oceanographic Society of Japan/TERRAPUB/Springer Alford, 2003). Therefore, a study of the NIW energy transfer from the surface to the deep ocean around these western boundary current regions should consider the effect of strong background shear. Several studies have focused on how the background circulation affects the NIW propagation. Kunze (1985)’s theoretical treatment suggests that NIWs turn away from a jet when they approach its positive relative vorticity (ζ > 0) side, where the lowest frequency of freely-propagating NIWs increases from f to an effective f (feff = f + ζ/2 > f). It also suggests that NIWs can be trapped in a negative ζ region, where feff is lower than f thereby creating a waveguide. Furthermore, using a realistic numerical simulation, Zhai et al. (2004) show that the Gulf Stream can advect NIW energy away from its generation region. Observations demonstrate that trapping and amplifying of NIW energy occur in negative ζ regions, such as anticyclonic sides of fronts and anticyclonic eddies (e.g., Kunze and Sanford, 1984; Kunze et al., 1995; Shcherbina et al., 2003; Park and Watts, 2005; Morozov and Velarde, 2008). Studies using analytical and numerical models confirm that negative ζ regions can drain NIW energy to the deep ocean (e.g., Young and Jelloul, 1997; Lee and Niiler, 1998; Zhai et al., 2005b, 2007). Yet, in regions of strong background shear, such as the Gulf Stream and the Kuroshio Extension regions, observational Distribution of Deep Near-Inertial Waves Observed in the Kuroshio Extension