Decadal sea‐level variability along the coast of Japan in response to ocean circulation changes

Abstract

[1] Decadal sea-level variability along the coast of Japan and its relation to large-scale ocean circulation changes from 1993 to 2010 was investigated using tide-gauge and satellite-derived sea-level data. A singular value decomposition (SVD) analysis is performed between coastal sea levels of Japan and sea levels in the western North Pacific. The first SVD mode reveals that the northward shifts of the Kuroshio Extension (KE) jet and the Kuroshio southeast of Japan accompany the coastal sea-level rise in the early 2000s and 2010, and their southward shifts accompany the coastal sea-level fall in the late 1990s and the late 2000s. The shifts of the KE jet are induced by westward propagating Rossby wave from the eastern North Pacific, which is concentrated along the KE jet axis as jettrapped Rossby waves. The resulting sea-level changes along the coast of Japan show a strong spatial contrast. The sea-level fluctuation is quite large along the southeastern coast of Japan that is under the direct influence of the jet-trapped Rossby waves, and also large in the western coast of Japan, probably due to coastal waves that are excited by the incoming Rossby waves, but is small north of the KE jet latitude. Hence, the nature of the wave trapped by the KE jet produces an ''active zone'' and a ''shadow zone'' of coastal sea-level variability of Japan. Our results indicate that the correct representation of western boundary currents is necessary for reliable prediction of future coastal sea-level changes.Citation: Sasaki, Y. N., S. Minobe, and Y. Miura (2014), Decadal sea-level variability along the coast of Japan in response to ocean circulation changes,

Forcing Factors Affecting Sea Level Changes at the Coast

“…As for the case of the Gulf Stream, interannual to decadal fluctuations of the KuE can have large impacts on coastal sea level variability. Sasaki et al (2014) have researched sea level variability along the coasts of Japan, primarily on decadal timescales. The first empirical orthogonal function (EOF) mode of sea level variability in the KuE region had previously been shown to describe well the meridional displacements of the KuE on decadal timescales (e.g., Taguchi et al 2007).…”

“…The first empirical orthogonal function (EOF) mode of sea level variability in the KuE region had previously been shown to describe well the meridional displacements of the KuE on decadal timescales (e.g., Taguchi et al 2007). Sasaki et al (2014) found that northward shifts of the KuE jet and the Kuroshio Current southeast of Japan are accompanied by higher sea levels at the coast. The decadal variability of the KuE latitude is mainly induced by westward-propagating, wind-forced Rossby waves from the eastern North Pacific (Qiu and Chen 2005;Yasuda and Sakurai 2006).…”

“…This is because any windinduced Rossby waves will be trapped along the KuE axis (Sasaki et al 2013). Hence, the area north of the KuE becomes a shadow zone which an incoming Rossby wave does not enter (Sasaki et al 2014). Instead, a wind-forced coastal wave is one of the causes of interannual coastal sea level variability north of the KuE (e.g., Nakanowatari and Ohshima 2014).…”

“…Sea level anomalies of ~30 cm were observed that resulted from the passage of coastal trapped waves induced by short-term fluctuations of the Kuroshio around 34°N, 140°E. Sasaki et al (2014) stress the importance of understanding the dynamical reasons for such variability in order to reliably predict future sea level changes. In a later modelling study of Japan sea level variability over 1906, Sasaki et al (2017 further pointed to the need to understand natural variability on decadal timescales for understanding future regional sea level change.…”

Wind- versus Eddy-Forced Regional Sea Level Trends and Variability in the North Pacific Ocean

“…With regard to the regional sea level changes in the extratropical North Pacific, the lowfrequency changes in the surface wind stress field have also been considered a main driver in determining the regional sea level trends and variability in the western subarctic gyre, the Alaska gyre, the Kuroshio Extension, and off the North America continent (e.g., Qiu 2002;Cummins and Lagerloef 2004;Qiu and Chen 2005;Yasuda and Sakurai 2006;Bromirski et al 2011;Sasaki et al 2014). It is worth emphasizing that away from the coastal orography, the surface wind stress field has generally large spatial scales.…”