[A-OS18] Kuroshio Large Meander

[AOS18-06] Why has the 2017 Kuroshio large meander lasted so long?

*Norihisa Usui¹, Nariaki Hirose¹, Yosuke Fujii¹, Nadao Kohno¹ (1.Meteorological Research Institute)

Keywords:Kuroshio large meander, Kuroshio transport, Wind stress

The Kuroshio large meander (KLM) occurred in the end of August 2017 for the first time in 12 years. It is still maintained in February 2021, although it became unstable and a cyclonic eddy was detached in the late 2020. The duration of the 2017 KLM exceeds three years, which is the second longest after the KLM in 1975-1980. Former studies have suggested that duration of the KLM is correlated with the Kuroshio transport and a lower transport leads to a longer duration of the KLM. In fact, the observed Kuroshio transport south of Japan has been relatively low since 2017, when the current KLM was formed. The Kuroshio transport diagnosed by a 1.5-layer reduced gravity model driven by the wind stress field of the atmospheric reanalysis also shows a low transport state, suggesting that the low Kuroshio transport caused by the wind stress field in the North Pacific is a possible cause for the long duration of the 2017 KLM. Former studies have also pointed out that the Kuroshio transport increased when past large meanders such as KLMs in 1975-1980 and 2004-2005 decayed. There is currently no signal in the wind stress field to significantly increase the Kuroshio transport. In the presentation, we would like to discuss the characteristics of the wind stress fields in the North Pacific leading to the low Kuroshio transport and their relation to climate indices.