Formation process of the Kuroshio large meander in 2004

Abstract

Formation process of the 2004 Kuroshio large meander has been examined using a data assimilation and prediction system. The small meander southeast of Kyushu that occurred in December 2003 remains stationary until the next spring. The vorticity analysis indicates that this small meander is maintained by a balance between the advection and the bottom pressure torque on the continental slope. This balance is achieved as a result of reducing the advection by a westward propagating negative-temperature-anomaly originating in the wind stress field. The small meander starts moving eastward around May 2004, when an anticyclonic eddy east of the Tokara Strait is intensified by coalescing of two anticyclonic eddies. At that time, a deep-anticyclonic eddy is generated below the Kuroshio by a cross-frontal flow. The deep-anticyclonic eddy grows up during its eastward propagation. Then a southward flow in the eastern part of the eddy carries the Kuroshio path offshore, bringing about the large meander. The eddy energetic analysis indicates that baroclinic instability is essentially responsible for this large meander formation. The sensitivity analysis reveals that the small meander and the intensified anticyclonic eddy significantly affect the phase speed and the amplitude of the meander, respectively. It is also revealed that a slow phase speed and a large amplitude of the meander are regarded as conditions for the stationary large meander, which is also applicable to the past large meanders. In the 2004 large meander, these conditions coexist by the stationary small meander staying until the intensified anticyclonic eddy triggers baroclinic instability. Copyright 2008 by the American Geophysical Union.