Numerical simulation of double warm tongues related to the bifurcation of the Yellow Sea warm current

Abstract

A recurrence of double warm tongues structure (DWTS) in the Yellow Sea has been revealed by recent observational studies. Here, this paper proposes a quantitative definition of the DWTS using Empirical Orthogonal Function (EOF) analysis of sea surface temperature (SST) based on a high-resolution Regional Ocean Modeling System (ROMS) simulation from 1985 to 2009. Moreover, heat and dynamic balance analyses are applied to examine the contribution of the bifurcation of Yellow Sea Warm Current (YSWC) to the formation of DWTS. Numerical results indicate that the second EOF mode in our study region manifests obvious distinctions between double warm tongues and single warm tongue patterns. The DWTS coexists with the bifurcation of YSWC, the eastern branch current flowing right over the Yellow Sea trough and the western major current flowing along the 50–70m isobaths. A remarkable heat advection along the Yellow Sea trough is responsible for the forming and maintaining of eastern warm tongue. The eastern branch current is driven by sea surface height (SSH) pressure gradient related to the adjustment of winter winds in the Yellow Sea, which is indicated by a close correlation coefficient between the DWTS and the curl of depth-averaged wind stress.