Seasonal and mesoscale variation in the surface temperature and salinity at the coastal and shelf region off Shikoku,Japan

A three-year-long time series of water temperature and salinity observed on a ferryboat in the shelf region off Shikoku Japan was analyzed, focusing on the phenomena with a time scale of more than one month. We found two remarkable fronts in the seasonal variations. One is the well-known Kii Channel Front. This front remains as a haline front in summer while a thermohaline front in winter. The other, which is formed near Cape Ashizuri-misaki, is newly found. Density gradient across the front in winter is in the opposite direction to that in summer. Next, focusing on phenomena with a shorter time scale, we found the simultaneous variation in water temperature over the observational region, the time scale of which is about three months. It has a good coherence with the variation in air temperature observed at the coast, which implies that this variation has something to do with a phenomenon including the atmospheric system. Warm water intrusion from the Kuroshio is also correlated with this variation. Short-period variations such as the eastward progression of warm water mass tend to be active when the simultaneous variation in water temperature is in the warming phase, i.e., water temperature is increasing.