Decadal to Multidecadal Variability of the Western North Pacific Subtropical Front and Countercurrent

Abstract

The subtropical countercurrent (STCC) is a shallow, eastward jet against the wind-driven westward mean circulation in the Subtropical gyre (

Long‐Term Decreasing of Sea Level Along Latitude of the Luzon Strait During 1993–2020: Surface Versus Subsurface Perspectives

“…During the late winter to early spring, water mass in the mixed layer will subduct into the subsurface ocean and stored in the thermocline as the mode water (Hanawa & Talley, 2001; Masuzawa, 1969; Wu et al., 2021). Subsequently, the mode water propagates southwestward riding on the thermocline circulation to the subtropical western Pacific Ocean (Liu & Hu, 2007; Wu & Xu, 2023; Wu et al., 2022) and arrives at the subtropical front region (Figure 7a). The subtropical front is located in the east of Luzon Strait, extending from 125° to 170°E, where it is also the STCC region with strong vertical velocity shear and high EKE.…”

“…While these previous studies highlight the importance of surface forcing, such as wind or buoyancy forcing, recent studies (e.g., Wu et al., 2022; Xu et al., 2022) propose the importance of subsurface forcing from the mode water. It is found that the mode water can carry the anomalous signals from its formation region, propagate southwestward along the thermocline circulation and affect the STCC in about 5 years later (Wu et al., 2022). Since the thickness anomaly of mode water could change the tilt of thermocline and further contribute to the vertical velocity shear (Kobashi et al., 2021), this provides another possibility that the mode water may force the STCC region (i.e., the latitudinal band along the Luzon Strait of 18°–22°N, 125°–170°E) from subsurface and generate the observed decreasing trend of sea level and EKE.…”

“…Previous authors only propose that the surface wind forcing by low‐frequency climate modes, such as the Pacific Decadal Oscillation, may induce the eddy‐forcing changes or the EKE decreasing during 1992–2013. While these previous studies highlight the importance of surface forcing, such as wind or buoyancy forcing, recent studies (e.g., Wu et al., 2022; Xu et al., 2022) propose the importance of subsurface forcing from the mode water. It is found that the mode water can carry the anomalous signals from its formation region, propagate southwestward along the thermocline circulation and affect the STCC in about 5 years later (Wu et al., 2022).…”

“…The sea surface temperature (SST) front in this region also contributes to the growth of eddies (Chang & Oey, 2014; Kobashi & Xie, 2012; Qiu et al., 2014). The eddies propagate westward and approach the Kuroshio east of Luzon in months to years, depending on the location at which the eddies are formed, and affect the Kuroshio (Chang et al., 2015; Lien et al., 2014) and EKE variability near the western boundary (Wu & Gan, 2023; Wu et al., 2022). Furthermore, they produce significant influences on the estimation of the interannual variability of the Kuroshio transport (Huang et al., 2023).…”

Relative importance of global warming, the IPO, and the AMO in surface air temperature and terrestrial precipitation

“…The results are consistent with the findings of Sun et al (2017), who suggested that the SST variability over the western tropical Pacific can largely be explained by the AMO. Wu et al (2022) demonstrated that the SST variability over the western tropical Pacific is controlled by the AMO through the variability of the subtropical mode water. This is verified in the present study via information flow whereby the variability of SAT over the northwestern Pacific can be explained by the AMO, especially west of the Mariana Trench.…”