びわ湖の水の流動に関する数値実験的研究 ―主として1層2次元モデルについて―

Abstract

In order to understand the water motion in Lake Biwa-ko, numerical experiments have beenperformed. Lake Biwa-ko is divided into 25 x 65 square meshes of which intervals are 1 km.Nonlinear hydrodynamic equations for this two-dimensional one-layer model are numerically in-tegrated by giving the wind stress as the external force, the effects of the bottom stress and theCoriolis' force being taken into account.The south-west wind blowing uniformly over the whole lake with the speed of 5 in/sec hasbeen given, and the elevations of water surface and velocities at 30 points in the lake have beenpunched out at every 5 minutes. The frequency spectra of amplitude and velocity obtained byFourier analysis about these 296 digital data at each point give the characters of longitudinal seichesin Lake Biwa-ko. The periods of these seiches thus obtained are of 255. 5, 79. 8 and 69. 1 minutes, and these oscillations correspond uni-, bi- and tn-nodal seiches in Lake Biwa-ko respectively. Onthe other hand, it is shown that the cyclonic lake currents appear in the north basin in the case ofthe southerly wind. Some results about the distribution of the elevation of water surface and aboutthe effects of the nonlinear terms and the Coriolis' term are also mensioned.