9:15 AM - 9:30 AM
[ACG49-02] Kuroshio Large Meander and its interaction with path variability of the Kuroshio Extension: Insights from a long-term simulation of an eddy-resolving CESM
★Invited Papers
Keywords:Kuroshio Large Meander, Kuroshio Extension, North Pacific, eddy-resolving coupled general circulation model
The Kuroshio Large Meander (LM) is a characteristic, southward deflection of the Kuroshio off the southern coast of Japan, which can endure for months to years. It exerts substantial effects on regional oceanic and atmospheric conditions, as well as marine ecosystems. The ongoing LM event that began in 2017 has become the longest on record, coinciding with a remarkable northward migration of the Kuroshio Extension (KE). Despite their importances, the processes controlling LM duration and its relationship with the KE remain insufficiently understood, partly due to the limited instrumental records.
This study examines the path variability of the Kuroshio and KE using a 520-year simulation of an eddy-resolving Community Earth System Model (CESM). The model successfully replicates observed path variations, including LM occurrences and meridional shifts of the KE. Obtained results indicate that net Kuroshio transport, accounting for the countercurrents, generally decrease during LM periods, consistent with observations. When simulated LM events are classified into long- and short-duration types to delve into the processes contributing to their persistence, the KE tends to migrate northward during long LM events, whereas it remains in a more southern position during short LM events. As the KE is situated further south, westward-propagating mesoscale disturbances from the KE can more easily reach the LM region, inducing a return to a non-LM path and terminating LM events. Further classification of long LM events into those with and without a northward shift of the KE highlights contrasting initiation processes. The former is associated with the eastward propagation of a small trigger meander near Kyushu and an anticyclonic anomaly to its east Conversely, the latter are initiated by the westward propagation of a southward meander near the Izu Ridge or in the KE region.
This study examines the path variability of the Kuroshio and KE using a 520-year simulation of an eddy-resolving Community Earth System Model (CESM). The model successfully replicates observed path variations, including LM occurrences and meridional shifts of the KE. Obtained results indicate that net Kuroshio transport, accounting for the countercurrents, generally decrease during LM periods, consistent with observations. When simulated LM events are classified into long- and short-duration types to delve into the processes contributing to their persistence, the KE tends to migrate northward during long LM events, whereas it remains in a more southern position during short LM events. As the KE is situated further south, westward-propagating mesoscale disturbances from the KE can more easily reach the LM region, inducing a return to a non-LM path and terminating LM events. Further classification of long LM events into those with and without a northward shift of the KE highlights contrasting initiation processes. The former is associated with the eastward propagation of a small trigger meander near Kyushu and an anticyclonic anomaly to its east Conversely, the latter are initiated by the westward propagation of a southward meander near the Izu Ridge or in the KE region.