Measurements of east Tushima Current in winter and estimation of its seasonal variability

Abstract

The Tushima Current in the east channel was measured in a site of the strong current between Tushima and Iki Islands for 43 days of the winter in 1986. The primary results are: First, it was highly barotropic and flowed northeastward with a mean speed of about 20 cm sec−1. Second, it was decelerated by northeast winds rather than by northwest winds in a frequency range of 0.3 and 0.4 cpd. Third, the scale analysis showed that the Tushima Current is approximately in geostrophic balance. The best empirical relationship between the measured Tushima Current and cross-channel adjusted sea level difference is given by $$V = 3.0(\Delta \eta _{K - I} - 65.5cm),$$ whereV (cm sec−1) andΔη K−I (cm) denote the northeast current component and the adjusted sea level difference between the average of three tidal stations (Moji, Hakata, and Sasebo) and Izuhara. Finally, the annual variation of the Tushima Current estimated from coastal sea level data during the past 19 years using the above formula showed a much weaker seasonal change in the east strait than in the Korea Strait.