Frontal circulation and westward transversal current at the Yellow Sea entrance in winter

Abstract

During the wintertime monsoon, a tongue‐shaped thermohaline front is established at the Yellow Sea (YS) entrance where the Cheju Warm Current (CWC) water, originating in the Kuroshio, and the YS cold water meet. The frontal circulation as well as the frontal structure has been investigated by analyzing comprehensive conductivity‐temperature‐density data, float tracks, current data, and wind data. The front develops by the westward advance of the CWC water, but it is bounded by the shallow Changjiang Banks (CB) that acts like a stopper in the deep part of the YS entrance. The northern part of the tongue‐shaped front displays a wave‐like motion of 20 km in amplitude and 80 km in wavelength and isotherms, isohalines, and isopycnals are declined downward toward the north. The geostrophic current field indicates formation of a cyclonic circulation along the front which consists of a westward transversal current (TC) along 34°N and a southeastward outflow along the 50 m isobath of the CB. The westward trajectories of floats along the northern front support existence of the TC and a superposition of float tracks evidences cyclonic frontal circulation. The new observational findings of the TC and the cyclonic circulation do not match the classical paradigm of a northerly wind‐driven circulation which consists of the northward inflow through the central trough and the southward outflow on the coastal sides. The cyclonic turning of the cold water around the warm tongue stands in contrast with the anticyclonic rounding of the warm CWC water around Jeju‐do.