The inter-annual variability of the Yellow Sea Warm Current surface axis and its influencing factors

Abstract

Based on the Pathfinder sea surface temperature (PFSST), the surface axis and its pattern of the Yellow Sea Warm Current (YSWC) are discussed. A structure of double-warm-tongue is found in February and it varies in different years. Two indexes are calculated to represent the westward shift (WSI) and northward extension (NEI) of the warm water in the Yellow Sea (YS). Wavelet analysis illustrates that the WSI and NEI have prominent periods of 3–6 years and 3–4 years, respectively. The Empirical Orthogonal Function (EOF) decomposition is applied to the winter wind stress curl and the Kuroshio Current (KC) transport, which are believed to play important roles in forcing the variability of the YSWC surface axis. Statistics shows that the WSI is significantly related with the second EOF mode of the wind stress curl in February, which may force the YSWC surface axis moving westward and maintaining the double warm tongues because of its opposite curl in the YSWC domain. The first EOF mode of wind stress curl in January is propitious for inducing the warm tongue in the YS to advance more northward. Hence, the wind stress curls both in January and in February could force variations of the YSWC surface axis; however, the effect of the January wind stress curl is relatively weaker than that of the February. The relationship between the NEI and the KC transport is remarkable, and it seems that the stronger KC supplies more power to push the YSWC northward against the southward wind.