Comparison of the ENSO-Related Interannual Variability of the ECS-Kuroshio Before and After 2005

Abstract

The El Niño-Southern Oscillation (ENSO)-related interannual variability of the Kuroshio in the East China Sea (ECS) was revisited based on reanalysis outputs during 1993–2018. Unlike the synchronized variations from 2006 to 2018, the period of 1993–2005 showed regional differences in how the ECS-Kuroshio responded to ENSO events. Specifically, from the upstream region to the midway of the continental slope, the ECS-Kuroshio exhibited distinct six-year interannual modulation during 1993–2005. In contrast, downstream Kuroshio variability primarily followed a four-year cycle, aligning with ENSO variability during the same period. Further analysis suggested that the sea surface height anomaly (SSHA) east of the Kerama Gap, near the midpoint of the Ryukyu Island chain, extended inside the ECS until the southern side of the Tokara Strait along the ECS-Kuroshio path and was well correlated with the Kuroshio in the Tokara Strait during 1993–2005. The cause of this SSHA signal was attributed to forcing by ENSO-related wind stress curl changes in the interior region. There was an obvious difference in the ENSO-related atmospheric circulation before and after 2005. The wind stress curl pattern in the North Pacific during 1993–2005, characterized by a maximum in the Kerama Gap latitude band, shifted northward compared to that during 2006–2018. The relative northward shift of the ENSO-related wind stress curl, which stimulates the long baroclinic Rossby wave propagating westward and arriving east of the Kerama Gap, affect the interannual variabilities of both the upstream and downstream Kuroshio.