Numerical simulation of the transient response of the Kuroshio leading to the large meander formation south of Japan

Abstract

Figure 1). After the small meander passes Cape Shiono-misaki, it slows down and rapidly amplifies in -1 month so that the Kuroshio loops back west of the Izu-Ogasawara Ridge. Then the sharpness of the meander trough gradually relaxes and the LM path is attained. The small meander generated off the southeastern coast of Kyushu is therefore often called the "trigger meander" [Solomon, 1978]. Although the generation of a small meander off the southeastern coast of Kyushu is observed in winter or early spring almost every year, the rapid amplification of the trigger meander leading to the formation of the LM path was observed only five times (1959, 1975, 1981, 1986, and 1989) since the monitoring of the Kuroshio path variation became possible based on observational data -50 years ago.By analyzing the time series of sea level difference between Naze and Nishino-omote (see Figure 1) from 1965 to 1992, Kawabe [1995] showed that the Kuroshio current velocity through the Tokara Strait once increased before the trigger meander was formed and, except for 1975, the trigger meander was generated in -1 month, during which period the increased Kuroshio current velocity was relaxing. Although a number of numerical studies have been carried out to reproduce the bimodal features of the Kuroshio by using inflow-outflow re-

Decay mechanism of the 2004/05 Kuroshio large meander

“…Observational studies using satellite altimetry have suggested that the small meander southeast of Kyushu is generated as a result of interaction between the Kuroshio and a mesoscale eddy propagating westward from the Kuroshio recirculation region Hanawa, 2001, 2003;Mitsudera et al, 2001;Kamachi et al, 2004]. The mechanism of the subsequent evolution of the small meander into the large meander have been investigated by recent modeling studies [Endoh and Hibiya, 2001;Miyazawa et al, 2004;Tsujino et al, 2006]. They have suggested that baroclinic instability is essentially responsible for the large meander formation.…”

The Kuroshio large meander formation in 2004 analyzed by an eddy‐resolving ocean forecast system

“…[22] Previous modeling studies [Hurlburt et al, 1996;Endoh and Hibiya, 2001;Miyazawa et al, 2004Miyazawa et al, , 2005aTsujino et al, 2006] have suggested that the Kuroshio large meander is generated through the baroclinic instability that occurs southeast of the Kii Peninsula. From this viewpoint, we examined both the horizontal and vertical distributions For example, in the wTM (wt05) case, negative SSHA (e.g., ÀSSHA(i, j)) at 29°-34°N, 130°-134°E on 8 May 2004 was changed to the same spatial pattern of positive sign with half amplitude (e.g., (0.5) SSHA(i, j)).…”

“…[15] Previous modeling and observational studies have suggested that the trigger meander southeast of the Kyushu Island [e.g., Solomon, 1978;Endoh and Hibiya, 2001] and mesoscale eddies [e.g., Ebuchi and Hanawa, 2003;Miyazawa et al, 2004Miyazawa et al, , 2005a [16] To identify key factors responsible for the large meander growth southeast of the Kii Peninsula in July 2004, we conducted three sensitivity experiments with the amplitude of each factor weakened in the initial conditions: weak trigger meander, weak anticyclonic eddy, and weak cyclonic eddy (hereafter wTM, wAE, and wCE, respectively). Table 1 (on 8 May 2004) indicates that the trigger meander was weakened in the wTM case, that the cyclonic eddy disappeared in the wCE case, and that the anticyclonic eddy was weakened in the wAE case.…”

“…The rate of change of the vorticity was determined using the following equation [e.g., Endoh and Hibiya, 2001;Masumoto, 2004]:…”

“…Some observational studies suggested that these mesoscale eddies play important roles in the Kuroshio path variation south of Japan [Book et al, 2002;Ebuchi and Hanawa, 2003]. Recent modeling studies also suggested that an interaction between the Kuroshio and the mesoscale eddy south of Japan triggers the transition from the nonlarge meander to the large meander [Akitomo and Kurogi, 2001;Endoh and Hibiya, 2001;Tsujino et al, 2006]. In fact, our preliminary model experiment showed that anticyclonic eddies activated in the subtropical frontal region may affect the Kuroshio path variation south of Japan through their downstream movement along the Kuroshio in the East China Sea [Miyazawa et al, 2004].…”