Kuroshio Meanders in the East China Sea

Abstract

An array of seven inverted echo sounders was moored along and across the Kuroshio in the East China Sea for more than one year. The data from this array show evidence of energetic meanders with periods of 7, 11, and 16 days. The respective phase velocities of these meanders are 28, 20, and 17 km day Ϫ1 downstream. The 7-and 16-day waves are intermittent, but the 11-day waves are present throughout the deployment. The instability responsible for these waves is investigated with a spectral numerical model applied to a background state representing the Kuroshio in this region. The fastest-growing instability from the model has e-folding growth time of 2 days, period of 12 days, and phase velocity of 18 km day Ϫ1 downstream. It appears to be a close representation of the 11-day wave seen in the observational data. Such a model has been previously used to represent meanders in the Gulf Stream at similar latitudes off the east coast of the United States. The Kuroshio meanders have approximately half the phase velocity and twice the period of the Gulf Stream meanders. To investigate the reasons for these differences, the flow and topography of the model background state were varied. The slower phase velocity and longer period of the Kuroshio meanders appear to be consequences of the deeper shelf and lower transport, with a modifying effect due to the difference in cross-shelf positioning of the current core (more over-the-shelf in the case of the Kuroshio).

Short-term fluctuations south of Japan and their relationship with the Kuroshio path: 8- to 36-day fluctuations

“…Frontal waves of similar frequencies have been reported in other coastal areas in Japan: in the East China Sea (Sugimoto et al 1988;Qiu et al 1990;James et al 1999), in the Tokara Strait (Qiu et al 1990;Maeda et al 1993;Feng et al 2000), south of Shikoku (Awaji et al 1991), near the separation point of the Kuroshio to the Kuroshio Extension (Itoh and Sugimoto 2008), and in the Kuroshio Extension (Tracey et al 2012). Frontal wave disturbances have been also found in the Gulf Stream (Lee and Atkinson 1983;Tracey and Watts 1986;Oey 1988;Savidge 2004).…”

Mean Structure and Variability of the Kuroshio from Northeastern Taiwan to Southwestern Japan

“…In the East China Sea and south of Japan, Kuroshio transport, velocity structure, and position exhibit temporal variability at scales ranging from high-frequency frontal meanders, to seasonal variations in Kuroshio intrusions onto the shelf, to interannual transport variability, to multiyear path shifts of the Kuroshio south of Japan (Kawabe, 1995(Kawabe, , 2005James et al, 1999;Andres et al, 2011). Variability at eddy time scales (~100-day period) is particularly pronounced and often swamps any interannual signals or an annual cycle Zhang et al, 2001;Andres et al, 2008b).…”

“…Cross-isobath exchange in the East China Sea can be associated with Kuroshio frontal meanders (James et al, 1999) and with so-called small and large Kuroshio intrusions onto the shallow shelf Vélez-Belchí et al, 2013). Observations from long-term ADCP measurements at the Taiwan and Korea/Tsushima Straits suggest there is about 1.2 Sv of net transport onto the shallow East China Sea shelf from the Kuroshio (Jan et al, 2006;Isobe, 2008), but net flow onto the shelf has also been inferred to be as high as 3.0 Sv in the fall (Teague et al, 2003).…”

“…This exchange may be at least partially responsible for dramatic temperature increases on the East China Sea shelf: reconstructions of global sea surface temperatures (SSTs) suggest that the Kuroshio (and other subtropical western boundary currents) have warmed more rapidly than the global average rate of SST increase over the last century (Wu et al, 2012), and the neighboring East China Sea shelf is also a region of intense SST increase (see their Figure 1). Cross-isobath exchange in the East China Sea can be associated with Kuroshio frontal meanders (James et al, 1999) and with so-called small and large Kuroshio intrusions onto the shallow shelf Vélez-Belchí et al, 2013). Observations from long-term ADCP measurements at the Taiwan and Korea/Tsushima Straits suggest there is about 1.2 Sv of net transport onto the shallow East China Sea shelf from the Kuroshio (Jan et al, 2006;Isobe, 2008), but net flow onto the shelf has also been inferred to be as high as 3.0 Sv in the fall (Teague et al, 2003).…”

“…These persistent 11-day period meanders have wavelengths of about 210 km and propagate downstream at 20 km day −1 . The Kuroshio frontal meanders are related to baroclinic instability (James et al, 1999) and may be excited near abrupt changes in bottom slope (Isobe and Beardsley, 2006). These meanders drive cross-shelf exchange by drawing low-salinity shelf waters into the subsurface Kuroshio (Isobe et al, 2004).…”