Effect of coastal-trapped waves on the synoptic variations of the Yellow Sea Warm Current during winter

Significant short-term fluctuations of the Yellow Sea Warm Current (YSWC) at several days' time scale were observed in the Yellow Sea (YS) during winter of 2006-2007. Observations indicated that the synoptic fluctuations of the YSWC appear to be associated with low-frequency sea level variations. By analyzing direct current measurements, sea level elevations and results from a regional ocean model, this study characterizes the variation of the YSWC at synoptic time scale and examines its connection with propagation of coastal-trapped waves during winter. The model captures the observed short-term fluctuations of the YSWC at several days' periods and suggests a close relation between coastal-trapped waves and the YSWC variability. The YSWC is intensified (weakened) when the westward sea level-related barotropic pressure gradient is enhanced (diminished) due to the propagation of coastal-trapped waves. Model experiments with idealized periodic surface forcing further identify the important role of the coastal-trapped waves on adjusting the strength of the YSWC. The model results also suggest that the propagation of coastal-trapped waves contribute to the intermittent northwestward intrusion of Cheju Warm Current (CWC) in the frontal region northwest of Cheju. Generation and propagation of the coastal-trapped waves give rise to the westward barotropic pressure gradient in the YS entrance, which periodically pumps the CWC water into the YS interior west of Cheju.