Variations of summer water-mass structure in Toyama bay coastal-zone are investigated using CTD data and a second moment turbulent closure model (Mellor and Yamada, 1974) forced by windstress, heat flux and freshwater flux in summer (July to September). Forcing fluxes, wind stress, heat flux, and freshwater flux are obtained from the appropriate daily observational data using a bulk method. Daily mean heat fluxes extremely over estimate surface temperature in the model. However, the heat flux in the time interval of one hour is able to reproduce nearly the actual ocean temperature. Then it is found that the daily changing heat flux and wind stress are crucial to form summer ocean stratification in Toyama bay. In the numerical experiments in summer from 2004 to 2009, the outstanding characteristics of stratifying and mixing process against the forcing are captured and are similar to observational results for each year. Wind stress, heat flux, and freshwater flux play an important role in stratifying and/or mixing surface water mass from surface to 50 m. In particular, the experiments are carried out for four cases of different freshwater input during severe rainfall in July, 2006 and following to August-September. As a result, for the case of increasing river runoff the low salinity layer develops prominently and affects the stratification and mixing of the coastal-zone mass water in Toyama bay.

The meander of Kuroshio southeast of Kyushu is well known as Kuroshio small meander. Many previous studies pointed out the impact of mesoscale eddies in generating of Kuroshio small meander. Accordingly, we investigated the relationship between Kuroshio small meander and mesoscale eddies defined by a winding-angle method. First, examining the frequency of Kuroshio small meander, we showed that Kuroshio small meanders having a relatively large spatiotemporal scale occurred 16 times from 1993 to 2006. Second, from the tracks of an eddy in the Kuroshio recirculation region, we found that a relatively large-scale meander tends to occur when an anticyclonic (cyclonic) eddy is located in the southern (eastern) region southeast of Kyushu. Therefore, we conclude that the location of a mesoscale eddy near Kyushu is important for the development of Kuroshio small meander. We showed that a mesoscale eddy approaching to east coast of Taiwan is the generating factor of Kuroshio small meander. Furthermore, we found that a relatively large-scale meander does not occur when the Kuroshio axis is located south of 32°N off Omaezaki.