| Water Mass Exchange Between the Main Basin and Shiozu Bay |
| I. OKAMOTO and S. ENDOH |
| Physical Processes in a Large Lake : Lake Biwa, Japan. AGU., 31-42, 1995 |
| Shiozu Bay is the largest bay in Lake Biwa situated at the northern end of the main basin. Water mass exchanges between the main basin and Shiozu Bay are largely attributed to two kinds of internal oscillations, to a surface seiche and to wind-driven vertical circulation. The first internal oscillation was a standing wave in the bay on the thermocline (internal seiche). The period was 24 hours in the summer season and was often developed due to resonance with a daily wind. The exchange volume was estimated by using well defined temperature oscillations recorded simultaneously at two different water depths. The volume was 1.4 x 108m3 equivalent to 22% of all bay water per half period. The coefficient of horizontal diffusion driven by this oscillatory motion was estimated at 2.1 - 4.1 x 105cm2 s-1. The second internal oscillation occurred originally in a similar way as the first oscillation. Power spectra show the peaks in temperature and current velocity recorded simultaneously in summer at a period of about 1 day (1st oscillation) and about 2 days (2nd oscillation). A characteristic feature of the internal oscillation was that the flowing water mass in the upper layer, above the thermocline, was always compensated by the counter-flowing water mass of the lower layer. Strong northerly winds forced the warm surface layers from the bay causing an inflowing and upwelling of cold deep main basin water. This resulted in a water mass exchange of 45% of total bay water. |