Inter‐Annual Variations of the Westward Shift of Yellow Sea Warm Current Controlled by Local Wind Stress Curl

Abstract

The Yellow Sea Warm Current (YSWC) transports water from the East China Sea to the Bohai Sea and exhibits a typical westward shifting pathway in winter. Previous studies have attributed this westward shift to changes in local wind stress, defining the YSWC axis by using the warm water tongue from the sea surface temperature (SST). Here we re‐examine the westward shift of the YSWC by defining its pathway dynamically. We use the observed position of the maximum SST along section 35°N and calculate the YSWC pathway from horizontal stream function in a high‐resolution Regional Ocean Modeling System (ROMS) simulation of the East China Sea from 1979 to 2020. It is found that in most years the westward shifted YSWC lies near the 70 m isobath just as the warm tongue axis, but in some years it is closer to the center Yellow Sea, lying near the deep trough. Contrary to previous studies we find no significant correlation between the inter‐annual variability of the shift and the meridional or zonal components of local wind stress in our simulation. Instead, we find that potential vorticity (PV) input by the depth‐averaged wind stress curl dominates the inter‐annual variability of YSWC's westward shift. These changes in PV originate from the realistic wind stress curl in the model that includes spatial inhomogeneity.

The Critical Role of Thermal Stratification Associated With the Yellow Sea Cold Water Mass in Modulating Winter Sea Surface Temperature

“…This study further enriches our understanding of the transition process from stratification to vertical homogeneity in the water temperature structure of the YS during early winter. Combining the findings of Wan and Ma (2022), this study further shows that it is because the formation of the YSWT is not controlled by the YS Warm Current, the inter‐annual variations of the YSWT and the YS Warm Current exhibit significant difference. Moreover, this study underscores the limitations associated with inferring the flow field structure of the YS during winter solely based on the spatial distribution of SST, emphasizing the potential for substantial inaccuracies.…”

“…(2022) based on in‐situ observations conducted in 2009. The vertical temperature structure along the 35°N section was further examined, which is a typical section for studying the spatiotemporal variations of the YSWT (e.g., Song et al., 2009; Wan & Ma, 2022). The core of the YSWT along the 35°N section was situated around 121.5°E, with a mean temperature of approximately 12.8°C.…”

“…While there are several explanations and interpretations, the formation of the YSWT has predominantly been attributed to the influence of the YS Warm Current (Z. Liu et al., 2021). However, a recent study by Wan and Ma (2022) revealed the contrasting inter‐annual variations between the main axis of the YSWT and the YS Warm Current, challenging the notion of using the YSWT as an indicator of the YS Warm Current. The inter‐annual variation of the YS Warm Current pathway was more significant and was controlled by depth‐averaged wind stress.…”