Relation between Lee-eddy Generation behind a Peninsula and Spatiotemporal Perturbation of the Coastal-current found in Wakasa Bay, Japan

Yosuke Igeta, Japan Sea National Fishseries Research Institute, Niigata, Japan, Shoko Abe, Fisheries Research Agency, Yokohama, Japan, Atsushi Kaneda, Fukui Prefectural University, Faculty of Marine Bioscience, Fukui, Japan, Kenichi Fukudome, National Institute of Technology, Toyama college, Toyama, Japan, Yutaka Kunmaki, Kyoto Prefectural Agriculture, Forestry and Fisheries Technology Center, Japan and Alexander E Yankovsky, University of South Carolina Columbia, Columbia, SC, United States
Abstract:
Generation of coastal lee-eddy (LE) behind a peninsula due to amplification/arrival of coastal boundary current (CBC) was investigated by using current data obtained from moored and shipboard ADCP in and around Wakasa Bay (WB) off the Japanese coast in the Japan Sea. The WB with 100km along-shelf and 40km cross-shelf scales is located over continental shelf shallower than 200m, including Tango Peninsula (TP) with length 20km at its western boundary region. Since coastal branch of Tsushima Warm Current (CBTWC), eastward CBC, flows just off the WB, the LE is known to be generated downstream TP and grow as anticyclonic eddy in WB intermittently. However, generation conditions for the core of the anticyclonic lee eddy remain unexplained. We adopted LE event in the summer-fall of 2013 reported by previous study as analysis period to focus on relation between location of the axis of the CBTWC and generation of core of the LE. After current with the coast on the right had been amplified, current observed at tip of the TP reversed its alongshore direction. This implies a detachment of the CBTWC from the TP coast because of the generation of the core of LE behind the TP tip. From shipboard ADCP data obtained just upstream from the LE -generation point, axis of the coastal current found 20km off the tip of the TP coast was confirmed to approach the tip after the generation of the core of eddy. The approach was accompanied by intrusion of the low salinity water <34psu in the surface layer. Based on the observations, we hypothesize that the low salinity water intrusion strengthened a stratification condition around the coast, which made the current path arrive at coast. Before LSW event, current axis of the CBTWC might have moved offshore because of a surface-to-bottom density front establishing. Possibility of the LE-generation mechanism above was confirmed by numerical experiment with realistic bottom topography and simplified CBC using the ROMS.
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