Low-frequency Variations of the Deep Flow Southwest of the Tsugaru Straits

• Published in: Oceanography in Japan Vol. 10; no. 1; pp. 1 - 13
• Main Authors: Mori, Kosuke, Isoda, Yutaka, Murakami, Takashi, Ohtani, Kiyotaka
• Format: Journal Article
• Language: Japanese
• Published: The Oceanographic Society of Japan 2001
• Subjects: deep flow; eastern region of the Tsushima Straits; Japan sea; long term mooring observation; the Tsugaru Straits
• ISSN: 0916-8362; 2186-3105
• DOI: 10.5928/kaiyou.10.1

Form April 1994 to April 1995, we carried out direct current measurements southwest of the Tsugaru Straits with moored instruments at depths of 300m and 2, 100 m to investigate current variability of deep water below the Tsushima Warm Current. It was found that the deep current is very energetic with some low-frequency variations and a steady barotropic northward flow having a yearly mean speed of about 5 cm s-1. Velocity fluctuations were prominent in the upper and lower layers and occurred with three periods of 26∼30, 15∼18, and 10∼12 days. The variations with periods of 26∼30 and 10∼12 days are dominant throughout the year and correlated to local wind variations. The results of a barotropic model experiment forced by the wind stress suggest that the variation of 10∼12 days is caused by east-ward propagation of the topographic Rossby waves trapped on the west-east bottom slope. On the other hand, the variation of 15∼18 days appears to be baroclinic events associated with small meanders in July and August 1994.