Circular currents in the north basin of Lake Biwa (II) - Comparisons between observed current and geostrophic current.

In order to determine the validity of applying a geostrophic relationship to the circular currents in Lake Biwa, a series of quasi-simultaneous observations of currents and water temperature were carried out. The current measurements were made using the drifters with cross-board placed at several depths. The vertical profiles of water temperature were measured by a bathythermograph at four points about 500 m away from the current station. The comparisons between the directly measured current and estimated geostrophic current show that the geostrophic approximation is not so valid for the current observed at a specified time and space. On the other hand, the current averaged over a time long enough to cancel the effect of the slowest internal wave, can serve as the baroclinic geostrophic current including the centrifugal force.