Bottom pressure change associated with the 2004–2005 large meander of the Kuroshio south of Japan

2018 ◽  
Vol 68 (7) ◽  
pp. 847-865 ◽  
Author(s):  
Akira Nagano ◽  
Takuya Hasegawa ◽  
Hiroyuki Matsumoto ◽  
Keisuke Ariyoshi
Keyword(s):  
Pressure Change ◽  
Bottom Pressure ◽  
Large Meander ◽  
South Of Japan ◽  
The Kuroshio

scholarly journals Seafloor Pressure Change Excited at the Northwest Corner of the Shikoku Basin by the Formation of the Kuroshio Large-Meander in September 2017

2021 ◽  
Vol 8 ◽  
Author(s):  
Akira Nagano ◽  
Yusuke Yamashita ◽  
Keisuke Ariyoshi ◽  
Takuya Hasegawa ◽  
Hiroyuki Matsumoto ◽  
...  
Keyword(s):  
Continental Slope ◽  
Crustal Deformation ◽  
Pressure Change ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Large Meander ◽  
Shikoku Basin ◽  
Current Path ◽  
Seafloor Pressure ◽  
The Kuroshio

The Kuroshio takes a greatly southward displaced path called a large-meander (LM) path off the southern coast of Japan on interannual to decadal time scales. The transition of the current path from a non-large-meander path to an LM path is the most salient ocean current variation south of Japan. The change in pressure on the seafloor due to the formation of the LM path in September 2017 is of critical importance to understand the dynamics of the LM path and to distinguish the change due to the Kuroshio path variation from changes due to crustal deformation. Hence, we examined the seafloor pressure across the continental slope off the eastern coast of Kyushu for the period March 2014 to April 2019. The pressure and its cross-slope gradient over the continental slope shallower than 3,000 m beneath near the Kuroshio are invariable. As a mesoscale current path disturbance, called a small meander, passed over the observation stations, the pressure decreased by approximately 0.1 dbar on the continental slope deeper than 3000 m and was kept low until the end of the observation period (April 2019). The pressure decrease is consistent with the changes in sea surface height and subsurface water density and is caused by the baroclinic enhancement of the Shikoku Basin local recirculation. This seafloor pressure change implies a strengthening of the deep southwestward current, possibly as a part of a deep cyclonic circulation in the Shikoku Basin. The present study demonstrated that, in addition to altimetric sea surface height data, hydrographic data are useful to distinguish the ocean variation in seafloor pressure from the variation due to crustal deformation, and vice versa.

scholarly journals Subtropical Mode Water Variability in a Climatologically Forced Model in the Northwestern Pacific Ocean

2012 ◽  
Vol 42 (1) ◽  
pp. 126-140 ◽  
Author(s):  
Elizabeth M. Douglass ◽  
Steven R. Jayne ◽  
Synte Peacock ◽  
Frank O. Bryan ◽  
Mathew E. Maltrud
Keyword(s):  
Pacific Ocean ◽  
Mixed Layer Depth ◽  
Northwestern Pacific ◽  
Northwestern Pacific Ocean ◽  
Large Meander ◽  
The West ◽  
Mode Water ◽  
Subtropical Mode Water ◽  
South Of Japan ◽  
The Kuroshio

Abstract A climatologically forced high-resolution model is used to examine variability of subtropical mode water (STMW) in the northwestern Pacific Ocean. Despite the use of annually repeating atmospheric forcing, significant interannual to decadal variability is evident in the volume, temperature, and age of STMW formed in the region. This long time-scale variability is intrinsic to the ocean. The formation and characteristics of STMW are comparable to those observed in nature. STMW is found to be cooler, denser, and shallower in the east than in the west, but time variations in these properties are generally correlated across the full water mass. Formation is found to occur south of the Kuroshio Extension, and after formation STMW is advected westward, as shown by the transport streamfunction. The ideal age and chlorofluorocarbon tracers are used to analyze the life cycle of STMW. Over the full model run, the average age of STMW is found to be 4.1 yr, but there is strong geographical variation in this, from an average age of 3.0 yr in the east to 4.9 yr in the west. This is further evidence that STMW is formed in the east and travels to the west. This is qualitatively confirmed through simulated dye experiments known as transit-time distributions. Changes in STMW formation are correlated with a large meander in the path of the Kuroshio south of Japan. In the model, the large meander inhibits STMW formation just south of Japan, but the export of water with low potential vorticity leads to formation of STMW in the east and an overall increase in volume. This is correlated with an increase in the outcrop area of STMW. Mixed layer depth, on the other hand, is found to be uncorrelated with the volume of STMW.

scholarly journals Effects of Koshu Seamount on the Development of Baroclinic Instability Leading to the Kuroshio Large Meander

2017 ◽  
Vol 47 (10) ◽  
pp. 2563-2576 ◽  
Author(s):  
Yuki Tanaka ◽  
Toshiyuki Hibiya
Keyword(s):  
Lower Layer ◽  
Bottom Topography ◽  
Baroclinic Instability ◽  
Northern Slope ◽  
Large Meander ◽  
Resonant Coupling ◽  
Small Meander ◽  
South Of Japan ◽  
Rapid Amplification ◽  
The Kuroshio

AbstractThe Kuroshio south of Japan shows bimodal path fluctuations between the large meander (LM) path and the nonlarge meander (NLM) path. The transition from the NLM path to the LM path is triggered by a small meander generated off southwestern Japan. The small meander first propagates eastward (downstream) along the Kuroshio and then rapidly amplifies over Koshu Seamount, located about 200 km south of Japan, leading to the formation of the LM path of the Kuroshio. Although Koshu Seamount is essential for the rapid amplification of the small meander, the underlying physical mechanism is not fully understood. In this study, the role of Koshu Seamount is revisited using a two-layer quasi-geostrophic model that takes into account the effects of bottom topography. Numerical experiments show that the transition from the NLM path to the LM path can be successfully reproduced only when bottom topography mimicking Koshu Seamount is incorporated. In this case, the upper-layer meander trough is rapidly amplified together with a lower-layer anticyclone by baroclinic instability during their passage over the northern slope of Koshu Seamount. A linear stability analysis shows that baroclinic instability over a seamount is caused by resonant coupling between the upper-layer Rossby wave in the eastward background flow and the lower-layer seamount-trapped wave during their eastward propagation over the northern slope of the seamount. The spatial scale and structure of this baroclinically unstable mode are close to those of the numerically reproduced small meander in its early amplification stage over the seamount.

Characteristics of an atypical large-meander path of the Kuroshio current south of Japan formed in September 2017

2018 ◽  
Vol 40 (4) ◽  
pp. 525-539 ◽  
Author(s):  
Akira Nagano ◽  
Yusuke Yamashita ◽  
Takuya Hasegawa ◽  
Keisuke Ariyoshi ◽  
Hiroyuki Matsumoto ◽  
...  
Keyword(s):  
Kuroshio Current ◽  
Large Meander ◽  
South Of Japan ◽  
The Kuroshio

scholarly journals The Effect of Koshu Seamount on the Formation of the Kuroshio Large Meander South of Japan

2011 ◽  
Vol 41 (9) ◽  
pp. 1624-1629 ◽  
Author(s):  
Takahiro Endoh ◽  
Hiroyuki Tsujino ◽  
Toshiyuki Hibiya
Keyword(s):  
Stability Analysis ◽  
Numerical Model ◽  
Water Depth ◽  
Baroclinic Instability ◽  
Model Output ◽  
Northern Slope ◽  
Large Meander ◽  
Kuroshio Large Meander ◽  
South Of Japan ◽  
The Kuroshio

Abstract Using an inflow–outflow numerical model, the authors demonstrate that the existence of Koshu Seamount, located about 200 km to the south of Cape Shiono-misaki, is essential in creating the large meander (LM) of the Kuroshio. When Koshu Seamount is completely smoothed out, the meander trough propagates away without being amplified to form the LM. In contrast, nearly the same LM as in the case with full topography is formed when the foot of Koshu Seamount remains without being smoothed out and also when the foot of Koshu Seamount is filled in so that the upper part of Koshu Seamount remains. A linear stability analysis applied to the model output shows that the Kuroshio becomes baroclinically most unstable when the water depth decreases offshoreward. The authors therefore conclude that the enhancement of baroclinic instability over the northern slope of Koshu Seamount is a prerequisite to the formation of the LM.

Sign in / Sign up

Export Citation Format

Share Document