Dynamical Links between the Decadal Variability of the Oyashio and Kuroshio Extensions

Shuiming Chen, University of Hawaii at Manoa, Honolulu, HI, United States, Bo Qiu, Univ Hawaii Manoa, Honolulu, HI, United States and Niklas Schneider, Univ Hawaii, Honolulu, HI, United States
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 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. Lack of contemporaneous
correlation between the decadal western and eastern OE variability is
found to be related to the interaction of meridionally migrating KE
jet with the Shatsky Rise near 159E.