Abstract Kuroshio frontal eddies in the East China Sea (ECS) have been observed and investigated for a long time; however, the energetics of frontal eddy‐mean flow interactions remain unclear. In this study, we revisit the Kuroshio frontal eddies in the ECS from the perspective of the eddy energy budget using an eddy‐resolving ocean general circulation model (OGCM) named OFES2. By decomposing the variables into frontal eddy (5 <  T  < 20 days) and background components ( T  > 20 days), we diagnose each term in the eddy energy budget equation to examine their contributions and spatiotemporal variations. The results demonstrate that the frontal eddy energy increases downstream along the Kuroshio in the ECS, with high values in the upper 500 m. Baroclinic instability is the primary source of frontal eddy energy in the entire ECS Kuroshio region, while barotropic and shear instabilities also contribute to one‐third of the total energy conversion. In contrast, the work done by wind to eddy energy is insignificant. Further instability analysis suggests that these eddies can be generated either locally within the ECS or come from the upstream region east of Taiwan Island, with a faster growth rate in the ECS. The temporal variation of the frontal eddy energy is largely controlled by baroclinic instability, which is further modulated by the Kuroshio volume transport. The results of this study provide new insights into the Kuroshio frontal eddies, which may be extended to other western boundary current regions where the frontal eddies exist.

Abstract With the increasing sea surface temperature (SST) over the Kuroshio in the East China Sea (ECS), precipitation has significantly intensified during the mei-yu-baiu season over the last four decades. However, the extent to which changes in SST contributed to the intensified mei-yu-baiu precipitation remains unknown. Therefore, in this study, we aimed to quantify the contribution of Kuroshio warming to increased precipitation. We first simulated recent (2018–2022; RtRa) and past (1979–1983; HtHa) East Asian atmospheres for each June. Next, we conducted a set of sensitivity experiments (HtRa and RtHa) in which the SSTs used in the RtRa and HtHa were exchanged sequentially. The simulated precipitation averaged within the ECS–Kuroshio region increased by approximately 5.57 mm/day during the last four decades. Meanwhile, 37% (or 35% ± 14%) of that was mainly contributed by the SST increase over the ECS–Kuroshio. We revealed that the precipitation responded to ECS–Kuroshio warming through a combination of the following two mechanisms: 1. Intensified evaporation increased the equivalent potential temperature in the marine atmospheric boundary layer, which effectively destabilized the mid-to-upper troposphere and favored the development of local convection through the convective instability. 2. Increased SST and enhanced SST fronts over the ECS–Kuroshio intensified the near-surface wind convergence and upward movement by strengthening the near-surface low pressure that was anchored along the ECS–Kuroshio, which can amplify the convective activities.

Abstract Seasonal variations in wind stress impact the velocity of the upper layer of the Kuroshio current over the East China Sea (ECS-Kuroshio). The dynamics of this process, which involves vorticity adjustments in the baroclinic jet that is induced by local Ekman pumping over the jet, can be attributed to any of the wind stress components acting upon the jet: 1) wind stress relative to the sea surface current, 2) the along-stream wind stress component, which causes nonlinear Ekman pumping due to the effective Coriolis parameter, and 3) the wind stress curl over the jet. This study examines the contribution of these wind stress components to seasonal variability in the current velocity of the upper layer of the ECS-Kuroshio mainly using a satellite-based surface geostrophic-velocity time series and wind stress data. The results showed that the magnitude of the first and second wind stress components are comparable, but the third component is negligible. The rate of change in the surface speed of the ECS-Kuroshio current in response to seasonal variability in the along-stream wind stress was approximately 1.5–2.1 (m s⁻¹) per (N m⁻²). This rate of change is approximately 3–4 times as large as that obtained using a numerical model in a previous study, which did not consider the first and third components of wind stress. Consequently, our results showed that the response of the ECS-Kuroshio current speed to seasonal wind stress variability is influenced not only by the effect of nonlinear Ekman pumping, but also by the effect of wind stress relative to the surface current.

Abstract The El Niño‐Southern Oscillation (ENSO)‐related interannual variability of the Kuroshio in the East China Sea (ECS) was revisited based on reanalysis outputs during 1993–2018. Unlike the synchronized variations from 2006 to 2018, the period of 1993–2005 showed regional differences in how the ECS‐Kuroshio responded to ENSO events. Specifically, from the upstream region to the midway of the continental slope, the ECS‐Kuroshio exhibited distinct six‐year interannual modulation during 1993–2005. In contrast, downstream Kuroshio variability primarily followed a four‐year cycle, aligning with ENSO variability during the same period. Further analysis suggested that the sea surface height anomaly (SSHA) east of the Kerama Gap, near the midpoint of the Ryukyu Island chain, extended inside the ECS until the southern side of the Tokara Strait along the ECS‐Kuroshio path and was well correlated with the Kuroshio in the Tokara Strait during 1993–2005. The cause of this SSHA signal was attributed to forcing by ENSO‐related wind stress curl changes in the interior region. There was an obvious difference in the ENSO‐related atmospheric circulation before and after 2005. The wind stress curl pattern in the North Pacific during 1993–2005, characterized by a maximum in the Kerama Gap latitude band, shifted northward compared to that during 2006–2018. The relative northward shift of the ENSO‐related wind stress curl, which stimulates the long baroclinic Rossby wave propagating westward and arriving east of the Kerama Gap, affect the interannual variabilities of both the upstream and downstream Kuroshio.