4:00 PM - 4:15 PM
[MIS24-03] Bottom pressure variation associated with 2004-2005 Kuroshio large meander south of Japan
Keywords:Kuroshio, Large meander, Bottom pressure, Inverted Echo Sounder, Seismic observing system
Off the southern coast of Japan, a Kuroshio large meander occurred in late July 2004 and continued to exist until about August 2005. Before the formation of the large-meander (LM) path, a Kuroshio path disturbance, called a small meander, occurred to the southeast of Kyushu. The propagation and development of the small meander were observed by bottom pressure sensors installed on inverted echo sounders (PIES) off Ashizuri-misaki and a seismic observing system off Muroto-misaki. The variations in bottom pressure, sea surface height (SSH), and the PIES-derived geopotential distance were examined focusing on the formation of the LM path. The bottom pressure was found to be depressed presumably due to a deep cyclonic eddy associated with the small meander, and this depression led the SSH depression by up to about two months. The phase shift between the surface and deep layers was significantly greater than those of other small meanders that did not develop into large meanders. This is evidence that baroclinic instability is an important process for the development to the large meander. After the formation of the LM path, the bottom pressure beneath the Kuroshio increased with a lag of about two months behind the SSH elevation. The high bottom pressure continued until about February 2005 when the LM path began to decay. The bottom pressure increase suggests that due to the stronger near-bottom current in the LM period than the non-LM period, the topographic steering is effective in the LM period and stabilizes the path. This is consistent with the fact that no small meanders occurred in the early LM period from late July 2004 to early February 2005.