Physical boundaries of Intrathermocline Ulleung Eddies in the East/Japan Sea

A new eddy detection algorithm is developed based on the particle tracking experiment (PTE) to determine the spatial extent of the Intrathermocline Ulleung Eddies (IUE) in the East/Japan Sea (EJS). The new eddy detection method enables us to identify three regions of interests: the IUE, transitional regions between the IUE and mean currents, and mean current regions around IUE. The estimated spatial boundary of the IUE is expressed as least square fitted elliptic characteristics from February to September, 2015. Accordingly, we could obtain three main results after analyzing the IUE: (1) the center and the highest sea level height of the IUE are not co-located, suggesting that the IUE is sustained by potential vorticity through the relative vorticity in response to bathymetry changes; (2) the highest sea level is always anchored around Ulleung Island, which is associated with the relatively high Chlorophyll concentration (Chl) around the edge of the IUE; and (3) the shape of the IUE is strongly influenced by the current systems in the Ulleung Basin. Furthermore, the semi-major and semi-minor axes, and its ratios are determined as well as the mean areas and the highest sea surface height of the IUE to understand the spatio-temporal characteristics of the IUE and the dominant frequencies on it.