CoAuthors

Shuiming Chen Chen (University of Hawaii, USA); Niklas Schneider (University of Hawaii, USA)

Rather than a single and continuous boundary current outflow, long-term satellite observations reveal that the Oyashio Extension (OE) in the North Pacific subarctic gyre is comprised of two independent, northeast-southwest slanted, front systems. With a mean latitude along 40N, the western OE front exists primarily west of 153E and is a continuation of the subarctic gyre western boundary current. The eastern OE front, also appearing along 40N, is located between 153E and 170E, whose entity is disconnected from its western counterpart. During 1982-2016, both of the OE fronts exhibit prominent decadal fluctuations, although their signals show little contemporaneous correlation. An upper ocean temperature budget analysis based on satellite altimetry data and the ECCO2 state estimate reveals that the advective temperature flux convergence plays a critical role in determining the low-frequency temperature changes relating to the OE fronts. Specifically, the western OE front variability is controlled by the decadal mesoscale eddy modulations in the upstream Kuroshio Extension (KE). An enhanced eddy activity increases the poleward heat transport and works to strengthen the western OE front. The eastern OE front variability, on the other hand, is dictated by both the meridional shift of the KE position and the circulation intensity change immediately north of the eastern OE. Different baroclinic adjustment speeds for the KE and OE are found to cause the in-phase changes between these latter two processes.