Effect of the Yellow Sea warm current fronts on the westward shift of the Yellow Sea warm tongue in winter

Based on long-term and high resolution NOAA/NASA AVHRR Pathfinder SST data and applying new indices, the present study gives a quantitative description of the pattern and interannual variation of the westward shift of the warm tongue (WSWT) relative to the bathymetric trough of the Yellow Sea (YS), which was only qualitatively mentioned in the previous works. The thermal fronts associated with the warm tongue are also accurately determined using a newly presented front-detection method. A new mechanism on the WSWT is presented according to the significant physical relations between the WSWT and fronts. The originally northward flowing YS warm current (YSWC) source water is prevented by the front on its northern side (YF-N), which resides in the east-west direction and across the entrance of the YS trough, from advancing further northward along the YS trough. Instead, the warm water is induced to flow westward along the front and connect with the northward flowing compensating flow in the interior YS, forming the entire westward shifted YS warm tongue. Observations confirm the above hypothesis by revealing the fact that when the northern front moves more southward or becomes stronger, the WSWT enhances. The other local dynamics, such as the wind in the YS and the YSWC itself, do not directly influence the WSWT; however, they do modulate it through determining the position and strength of the YF-N.