Interaction between the trigger meander of the Kuroshio and the abyssal anticyclone over Koshu Seamount as seen in the reanalysis data

Abstract

[1] The JCOPE (Japan Coastal Ocean Predictability Experiment) reanalysis data is analyzed to examine the transition from the non-large meander path to the large meander path of the Kuroshio that occurred in 2004. It was preceded by the generation of “trigger meander” off the southeastern coast of Kyushu, which then propagated eastward. After passing Cape Shiono-misaki, the trigger meander amplified rapidly over Koshu Seamount (located about 200 km to the south of Cape Shiono-misaki) where the accompanying abyssal anticyclone was significantly enhanced. Strong downwelling occurred upstream of the meander trough where the abyssal anticyclone crossed the Kuroshio, causing the vertical vortex stretching (shrinking) in the upper (lower) ocean; the resulting enhanced abyssal anticyclone further amplified the meander trough in the upper ocean. All of these features agree well with the model results suggesting the importance of baroclinic instability over Koshu Seamount in the formation of the large meander path.