Sound propagation in the sea near the Sanriku coast on 18 and 19 in July, 2007, and on 29 and 30 in January, 2010

Abstract

Structure of the sea and sound propagation in the sea near the Sanriku coast are analyzed on 18, 19 in July, 2007 (warm season), and on 29, 30 in January, 2010 (cold season). The Tsugaru warm current widely spreads near the Sanriku coast, other warm water masses are over the offshore sea of the coast, and the sea surface is warmed by the warm atmosphere on 18, 19 in July, 2007. The cold Oyashio water system lies under these warm water masses. The large water temperature difference makes it easy to form shadow zones in the warm water masses near the sea surface. If a sound source is settled in the cold Oyashio water system under the warm water masses, the sound is trapped in the sound channel formed near the Oyashio water system. Moreover, water temperature of 30m depth near the coast, though it is in the Tsugaru warm current domain, is relatively cold to make shadow zone in surrounding warmer domain of the Tsugaru warm current and in the other warmer water masses near the sea surface if a sound source is settled near the coast. The Tsugaru warm current was only 40 km wide near the Sanriku coast on 29, 30 in January, 2010. The Oyashio water system widely spread over the sea surface and the Coastal Oyashio water system occupied a part of the sea surface to form a surface duct.