[A-CG32] 中緯度大気海洋相互作用

[ACG32-P14] Submesoscale Restratification in the Kuroshio Extension Region Modify the Wintertime NPSTMW Formation and Destruction Along Outcropping Buoyancy Fronts

*Travis Prochko¹、Yukio Masumoto¹ (1.University of Tokyo)

The Kuroshio Extension region exerts a great influence on the formation and variability of the North Pacific Subtropical Mode Water (NPSTMW), both on seasonal and longer time scales. Specifically, strong fronts, mixed layer variation, and associated surface heat loss in the winter season are important components of the seasonal NPSTMW formation and destruction process, with both meso- and submeso-scale processes contributing to this cycle. In this study, the seasonal variability of NPSTMW and the connection between this variability and winter-time submesoscale processes are investigated using the submesoscale-permitting (1/30^o) North Pacific Ocean model for the Earth Simulator (NP-OFES) for the year 2002. Although only a single year, the simulation captures the standard NPSTMW seasonal cycle: (i) formation throughout November-March, (ii) isolation during March-June, and (iii) dissipation from June-November. In late winter (February-March), submesoscale are active along strong buoyancy fronts extending through the whole mixed layer, characterized by a vertical flux of buoyancy which restratifies the mixed-layer along the fronts, often corresponding to the edges of the isopycnal outcrop regions associated with NPSTMW formation by air-sea buoyancy fluxes. In these regions, submesoscale vertical flux of buoyancy and increase of mean potential vorticity (PV) modulate the NPSTMW in two ways compared to the surrounding NPSTMW regions (weak fronts or horizontal buoyancy gradient): (1) a shift of the overall NPSTMW PV to higher values, often above the 2x10^-10 (m^-1s^-1) “low PV” boundary set by observation and (2) by shifting the change in the sign of the PV gradient down by ~50m. Furthermore, when compared to the equivalent 1/10^o NP-OFES simulation, the NPSTMW in the 1/30^o simulation the mean potential density is slightly lighter (~-0.1kgm^-3). These findings suggest that although the overall mode water volume is comparable between the two eddy-resolving and submesoscale-permitting models, the composition (in terms of potential density and PV profile) is influenced by submesoscale activity along the outcropping regions.