[A-CG36] Extratropical oceans and atmosphere

[ACG36-06] Extreme northward meander of the Kuroshio Extension in 2023 in an eddying OGCM

*Masami Nonaka¹, Shoichiro Kido¹ (1.Application Laboratory, Japan Agency for Marine-Earth Science and Technology)

Keywords:Kuroshio Extension, meandering, eddying ocean GCM, oceanic intrinsic variability

In 2023, an extreme northward meander of the Kuroshio Extension was observed in its upstream region. Such anomalous meander induced warm sea surface temperature anomalies (SSTAs) to the east of northern Japan, and it was found that the warm SSTAs affected surface air temperature aloft, inducing the record-breaking hot summer over northern Japan. In the present study, we investigate possible mechanisms of the extreme northward meander based on ensemble hindcast simulation with an eddying OGCM, JCOPE-FGO, with 10 ensemble members with slightly different initial conditions on January 1^st, 1993. Several ensemble members represent the extreme northward meander in 2023 closely resembling the observed one, while others displayed a significantly weaker northward meander. In this particular model, the probability of the extreme northward meander is higher in the 2020s. This is associated with the northward shift of the ensemble mean of the axis of the Kuroshio Extension from the late 2010s. The model results suggest that oceanic intrinsic variability of the Kuroshio Extension in addition to the atmospheric-driven northward shift of the Kuroshio Extension induced the extreme northward meander in 2023.