平塚観測塔に現れる黒潮による８０日周期潮位変動と急激な水温変化

Abstract

The tidal data analysis from 1989 to 1994 in Hiratsuka revealed that the long period variation of sea level was influenced by variability of the Kuroshio, which flows in the neighborhood of the southern part of Sagami Bay. The spectral analysis for the Hiratsuka tidal data showed strong well-separated spectral peaks with typical time scales of 1 year, 80 days, 50 days, 33 days, and 24 days. The variability of 80 days is induced by the mesoscale variation of the Kuroshio and propagates from the southern part: Hachijyo and Miyake islands. The sea level affected by the variation with this period rises as the Kuroshio approaches to the Nojimazaki, to the Irozaki and vice versa. This result suggests that the oceanic conditions of Sagami Bay are affected from down stream side of the Kuroshio. In particular, when the Kuroshio front approaches to the Nojimazaki in wrinter, the rapid temperature rise occurs: the sea level rises rapidly before the rapid rise of the temperature. In this case, the strong westward currents were observed in Hiratsuka. This phenomena developed to the Kyuu-Chou, which damaged the Yellowtail fixed nets, in January 9, 1994. When the Kuroshio front is away from the Nojimazaki in summer, the sea level falls with the fall of the temperature. These phenomena may propagate to Hiratsuka as the Kelvin waves and may play an important role for the mixing in Sagami Bay.