As simulated with the MHI oceanic model (Shapiro, 1998), surface gradient currents in the entire Japan Sea strengthen (weaken) in late summer (winter), with the highest (lowest) velocity in August (February), in line with altimetry data (Morimoto and Yanagi, 2001). The simulated patterns of the surface circulation are in line with those derived from satellite imagery (Nikitin and Kharchenko, 2002). In particular, a northern meander of the East Korean Warm Current is simulated near the North Korea coast in October, caused by local anticyclonic wind stress curl. The simulated deep circulation is geostrophic and reaches the highest (lowest) velocity in April (November), after 2 to 3 months of the extreme surface velocity.
This study investigates characteristics of water temperature variations in the middle reaches of the Shinano River. Attention is given to the impact of a hydropower plant on downstream water temperature daily regime. Peculiar diurnal variation of water temperature appears immediately downstream of the power plant. At a different site, 17 km downstream of the power plant, thermal anomaly manifests in a different form that is designated herein as in-stream tropic night.