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.
Highlights
Oceanic mesoscale features impact on the overlying atmosphere through thermodynamic processes, which are driven by the sea surface temperature (SST) anomalies associated with the oceanic mesoscale field [1,2,3,4,5]
Besides the large basin-wide cyclonic circulation, the mesoscale features in the northwestern region of the East Sea (ES) are characterized by a dipole mode associated with warm and cold eddies, resulting in a strong thermal gradient between the seasonally non-persistent eddies, which emerged and strengthened during late fall and early winter
Previous studies show that the mesoscale phenomena in the northern part of the East Sea (NES) may be closely related to a dipole of wind stress curl to the south of Vladivostok in winter
Summary
Oceanic mesoscale features impact on the overlying atmosphere through thermodynamic processes, which are driven by the sea surface temperature (SST) anomalies associated with the oceanic mesoscale field [1,2,3,4,5]. Empirical orthogonal function (EOF) analysis of sea surface height (SSH) measured by satellite altimetry was used in Kim and Yoon [33] to investigate the upper layer circulation in the NES. They showed that it is characterized by a basin-wide cyclonic circulation, which has significant semi-annual variations strengthening in summer and winter. Mesoscale features besides the basin-wide cyclonic circulation in the NES were reported by several researchers [34,35,36,37,38] Based on observations, they showed an anticyclonic eddy that induces a northward coastal current reversal along the North Korean coast and a northwestern thermal front (NWTF) south of Vladivostok during wintertime. For the first time, the mechanism of its occurrence and evolution is investigated using continuous observations over a long period (i.e., 1993–2017)
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