Nonlinear multiscale interactions and internal dynamics underlying a typical eddy-shedding event at Luzon Strait

Abstract

Eddy‐shedding is a highly nonlinear process that presents a major challenge in geophysical fluid dynamics. Using the newly developed localized multiscale energy and vorticity analysis (MS‐EVA), this study investigates an observed typical warm eddy‐shedding event as the Kuroshio passes the Luzon Strait, in order to gain insight into the underlying internal dynamics. Through multiscale window transform (MWT), it is found that the loop‐form Kuroshio intrusion into the South China Sea (SCS) is not a transient feature, but a quasi‐equilibrium state of the system. A mesoscale reconstruction reveals that the eddy does not have its origin at the intrusion path, but comes from the Northwest Pacific. It propagates westward, preceded by a cyclonic (cold) eddy, through the Kuroshio into the SCS. As the eddy pair runs across the main current, the cold one weakens and the warm one intensifies through a mixed instability. In its development, another cold eddy is generated to its southeast, which also experiences a mixed instability. It develops rapidly and cuts the warm eddy off the stream. Both the warm and cold eddies then propagate westward in the form of a Rossby wave (first baroclinic mode). As the eddies approach the Dongsha Islands, they experience another baroclinic instability, accompanied by a sudden accumulation of eddy available potential energy. This part of potential energy is converted to eddy kinetic energy through buoyancy conversion, and is afterward transferred back to the large‐scale field through inverse cascading, greatly reducing the intensity of the eddy and eventually leading to its demise.

Hydrological and Biogeochemical Controls on Absorption and Fluorescence of Dissolved Organic Matter in the Northern South China Sea

“…A small vertical gradient of CDOM and FDOM in the upper 100 m of the warm eddy suggested a greater mixed layer depth and lower biological productivity than the SCS no eddy region, indicating that the warm eddy was formed by the intrusion of the Kuroshio Current. Previous studies by physical oceanographers suggest that warm eddies near the Luzon Strait can be separated from the adjacent Kuroshio Current (Jia & Liu, ; Zhao, Liang, & Gan, ). Our results provide optical data to support this assumption, suggesting that the optical properties of CDOM should be helpful in the study of active marginal sea‐open ocean interactions in the Luzon Strait.…”

Wind Forced Variability in Eddy Formation, Eddy Shedding, and the Separation of the East Australian Current

“…While beyond the scope of this paper, an interesting extension would refine the size of the local surface forcing (i.e., spatially modify the forcing area from VARY‐LOCAL) and qualify the importance of remote higher‐period variability (>5 day means). In addition, the change in eddy shedding behavior would benefit from a more detailed energetics analysis (e.g., Kang & Curchitser, ; Jouanno et al, ; Munday & Zhai, ; Zhao et al, ; Zhong et al, ).…”

Three-Dimensional Structure and Interannual Variability of the Kuroshio Loop Current in the Northeastern South China Sea

“…For the Kuroshio intrusion into the SCS, the occurrence of KLC only accounts for less than 20% of the total intrusion state (Nan et al 2011). With respect to the Luzon Strait transport, it has a sandwich structure in vertical and only its upper-layer component is partially contributed by the Kuroshio intrusion (Tian et al 2006;Zhang et al 2015;Gan et al 2016). As such, the interannual variability of the KLC and its modulation mechanism are to a large degree unclear at present.…”