ABSTRACT

A multi-level model is applied to thesimulation of tidal currents and density field of Kagoshima Bay in summer. Tidal currents are calculated for tidal level of twelve hours(M2) given at the mouth of the bay. Heat flux is given by a constant value at sea surface, neglecting the diurnal changes. Numerical simulations are conducted in time marching from an initial state of the variables using a finite difference method. Time averaged values of 25th period of tidal oscillation from the initial state are taken as steady solutions. Distributions of the residual current, temperature, salinity and density thus obtained are compared with available observations. As an application of the present method, tidal simulations are presented for the past topography of Kagoshima Bay before the eruption in 1914, by which East Sakurajima Strait were blocked with lava. Distributions of temperature and salinity before the eruption were compared with those of present bay. Effects of East Sakurajima Strait on the physical environment are presented in graphics.

INTRODUCTION

Kagoshima Bay is a narrow bay, 75krn along the North-South and 20krn along the East-West. It is located at Southern edge of Kyushu. The size is almost same as Tokyo Bay but the topographic and the oceanographic characteristics are quite different. There is Sakurajima volcanic island at the interior of the bay and there is an oceanic basin of 400m in depth at the center of the bay. Before the great eruption of Sakurajima in 1914, there was a strait of 400m breadth and 70m depth. Since fish was found polluted by mercury in 1973 and the cultured fish were sometimes damaged by red tide, many investigations concerning the circulation of water and mass-transport in the bay have been done.

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