The Role of an Intense Jet in the Tsugaru Strait in the Formation of the Outflow Gyre Revealed Using High-Frequency Radar Data

The seasonal features of the eastward jet through the Tsugaru Strait was investigated using surface velocity data between 2014 and 2019 obtained from high-frequency radar located in the eastern part of the strait, as well as data obtained from repeated shipboard observations from 2009 to 2019. The potential-vorticity-front-model was used, and the volume transport of low potential vorticity (PV) water and the intensity of the PV gap at the front in the eastern part of the strait were estimated from these data. The influence of these parameters on the seasonal flow pattern of the Tsugaru Warm Current out to the Pacific Ocean (the summer/autumn "gyre mode" or winter/spring "coastal mode") was examined. The distribution of the parameters was consistent with the theoretical understanding, showing that in addition to the volume transport, an increase in the local PV gap can also contribute to the development of the gyre.