Double structure of the coastal front in the Kii Channel, Japan, during winter

<jats:p>Analysis of satellite thermal imagery showed that the coastal front in the Kii Channel, Japan, has a double structure that consists of the well‐known S‐shaped front and a newly found mouth front. The S‐shaped front is in a state of equilibrium as has been shown by previous numerical experiments, whereas the mouth front is produced as a direct response to the intermittent arrival of warm water from the Kuroshio. As was shown by a previous study, the warm water comes along the eastern or western coast, and the western path (the Geitou Branch) occurs less frequently than the eastern (the Kinan Branch). We found, however, that each appearance of the western path has a greater effect on the heat budget of the channel and the shape of the front than the eastern path does. The western path tends to produce a large temperature difference and to form a sharp mouth front which is often accompanied by tongue and outflowing structures. Both structures are produced by water intruding across the mouth front; the tongue structure by warm water intruding toward the coast, and the outflowing structure by cold water intruding toward the offshore region. The tongue structure is a transient process toward equilibrium, the S‐shaped front. A hypothetical model that shows how the tongue and outflowing structures are formed also is presented.</jats:p>