Occurrence and Evolution of Mesoscale Thermodynamic Phenomena in the Northern Part of the East Sea (Japan Sea) Derived from Satellite Altimeter Data

Abstract

Based on satellite measurements and oceanic reanalysis data, it has been possible to investigate the spatiotemporal variability of the mesoscale phenomena in the northern part of the East Sea (NES) where direct observations of currents and hydrographical conditions are scarce. For the first time, this study identifies the detailed spatiotemporal structure of the mesoscale features in the NES and the mechanism of its occurrence and evolution, which have important consequences on the distribution of the intermediate water masses in the East Sea. Here, we show that mesoscale thermodynamic phenomena in the northwestern region of the East Sea are characterized by a dipole structure associated with positive and negative sea surface height anomalies. These result in a strong thermal gradient between the seasonally non-persistent anomalies, which emerge and strengthen during late fall and early winter. In contrast to the previous finding of the relationship between winter monsoon winds and mesoscale features in the NES, we found that this relationship is crucial only to the emergence of the mesoscale phenomena. Consequently, we present a new perspective on the evolution mechanism of the mesoscale features in the NES. Of direct significance to the present study, thermohaline transport into the northwestern region of the East Sea regulates the strengthening and weakening of mesoscale features in the NES. Wind forcing may contribute to the emergence of the mesoscale features in the NES and then the intensification of the mesoscale activities is attributed to the intrusion of warm and fresh surface water advected from the southern part of the East Sea.

Mesoscale Dynamics and Eddy Heat Transport in the Japan/East Sea from 1990 to 2010: A Model-Based Analysis

“…These features of the mesoscale dynamics and spatial structure of currents are similar to those reproduced by ARGOS trajectories along the eastern coast of North Korea [59] and consist of a change in the velocity direction from southward to northward in this region of the JES [69]. From autumn to winter, the high EKE (1.5-2.5 × 10 3 J m −2 ) in the southwestern and northwestern JES is in a good agreement with the results of [70], where the authors revealed intensification of the mesoscale phenomenon associated with the dipole structure eastward the Peter the Great Bay. The authors declared that the leading factor of this structure is associated with the heat and freshwater transport from the southwestern JES by currents.…”

“…We estimated the heat transport from the southwestern to northern JES and showed that the heat transport along the western JES boundary was induced by mesoscale eddies propagating polewards along this boundary. In this region, the eddy heat transport reaches ∼ 10 13 W (Figure 18), which is an order of magnitude lower than estimated in [70]. Note that in the northwestern JES, the mechanism of the mesoscale dynamics' generation is the baroclinic instability of the basin-scale circulation, which was not considered in the study mentioned above.…”

“…Since the zMEHT is very small at the latitude of the Korea/Tsushima Strait, we suggest that the heat redistribution from basin-scale currents to the mesoscale dynamics takes place mainly in the JES, and one of the primary mechanisms of this is the instability of basin-scale currents in the JES. When studying the JES climate variability, the East Sea Intermediate Water (ESIW) is considered as a marker for this variability [70]. This water is characterized by high temperature, low salinity, and a high concentration of dissolved oxygen [73].…”

“…This water is characterized by high temperature, low salinity, and a high concentration of dissolved oxygen [73]. Kim et al [70] suggested that the generation of the ESIW is associated with mesoscale eddies. According to our investigation, the JES mesoscale dynamics is responsible for not only the intensive meridional eddy heat transport, but also eddy salt transport.…”