Long-Term Variations of the Kuroshio Extension Path in Winter: Meridional Movement and Path State Change

摘要

As an indicator of the Kuroshio Extension (KB) path, the KE northern boundary (KENB) was detected based on the position of the strong winter sea surface temperature (SST) gradient between 142 degrees and 155 degrees E, using high spatial resolution satellite-derived SST for the 30 winters (January to March) from 1982 to 2011. The KE path showed meridional movement with a period of 10-15 yr and an amplitude of about 2 degrees latitude. The changes in latitudinal position of the KE path were initiated by a north-south shift of the Aleutian low (AL). Negative wind stress curl anomalies around 35 degrees N in the eastern North Pacific associated with a northward shift of the AL induced a deepening of the main thermocline depth, and then this deepening signal propagated westward, reaching the KE region after about 3 yr, where it caused the KB path to move northward. The path state of the KB (straight path/convoluted path) modulated on a time scale of 8-12 yr, but this was not significantly correlated with the meridional movement of the KB path. The anticyclonic eddies containing warm-salty water that detached northward from the convoluted KE exerted a strong influence on oceanic conditions in the Kuroshio-Oyashio Confluence (KOC) region. The changes in path state of the KE were related to the path of the Kuroshio south of Japan over the long term; a convoluted (straight) KE path was associated with the Kuroshio taking the offshore nonlarge (nearshore nonlarge or typical large) meander path