Interannual variation of the southern limit in the Yellow Sea Bottom Cold Water and its causes

- The southern limit of the YSBCW shows a pronounced inter-annual variability.
- The variation is closely related to the SST in winter and the wind stress.
- The SST in winter is mainly determined by the air temperature and wind speed.

The Yellow Sea Bottom Cold Water (YSBCW) occupies a wide region below the Yellow Sea (YS) thermocline in summer. The southern limit of the YSBCW shows pronounced interannual variability. A regional ocean model with realistic forcing was used to identify the structure of the YSBCW and to investigate the causes of its interannual variability from 1981 to 2010. Sea surface temperature (SST) in winter is strongly correlated with the southern limit of the YSBCW in summer. The correlation coefficient between the August southern limit and the February SST is − 0.884. This result suggests that cold SST is associated with the increased southern limit in the following summer. Linear regression suggests that the southern limit increases by about 55 km when the SST in February decreases by 1 °C. The southern limits are more extended to the south in August than in June in some years despite surface heating. The difference in southern limits between June and August is positively correlated with the summer southerly wind stress with a correlation coefficient of 0.529. The contribution of SST in winter on the southern limit of the YSBCW in summer is larger than the wind stress in summer. The SST in winter is mainly determined by the air temperature and wind speed in winter. The other factor affecting winter SST is the previous year's bottom water temperature. The winter SST is significantly correlated with the bottom water temperature in previous year. The southern limit of the YSBCW in the observed data in the limited area has relatively weak correlation with the winter SST and summer southerly wind stress possibly due to observation error and uncertainty of the reanalysis wind.