[A-OS16] Coastal ocean circulation and material cycle

[AOS16-06] Material Transport processes off the Japan mainland influenced by the Kuroshio and coastal topography investigated with particle tracking simulations

*Junpei Sakon¹, Eiji Masunaga¹, Yusuke Uchiyama² (1.Ibaraki University, 2.Kobe University)

Keywords:Numerical simulations, Particle tracking model, Kuroshio, Diffusion

Numerous phenomena, such as, the Kuroshio, eddies, tides internal waves largely influence ocean dynamics resulting in complicated physical structures off the Japan mainland. Field observations of detailed complicated physical structures are difficult to obtain due to technical issues. This study investigated mass transport and dispersion processes off the southeast Japan mainland using a double-nested high-resolution Reginal Ocean Modeling System (ROMS) with a Lagrange particle tracking simulations. Particles were released at the all horizontal grid points of the ROMS domain, total 674 × 802 grid points. Approximately 3.79 × 10⁵ particles were released over two periods, the summer and winter seasons. Time evolutions of the particle-to-particle distance are computed by pairs of two particles defined by initial locations of particles. A pair of two particles are the nearest two particles in the north-south or east-west direction. The distance between the pair particles tends to long around large eddies and near the Kuroshio due to strain effects. Although particles in the coastal regions are left around the initially released regions, the particle-to-particle distance increases in the coastal regions.
Furthermore, released particles are categorized to six groups to evaluate regional transport processes (coastal upstream and downstream, Kuroshio upstream and downstream, and offshore upstream and downstream). The major and minor axes of particle dispersions are estimated based on the two-dimensional variance analysis. The ratio between the major and minor directions, and the major axis direction are compared for the separated six regions. A seasonal comparison shows that the dispersion coefficient in the offshore is approximately ten times higher in winter than that in summer. The dispersion coefficient shows similar values along the major and minor axes in the offshore regions, which implies isotropic eddy-induced particle transport in horizontally. On the other hand, the major axis dispersion, roughly the east-west direction, is approximately one order higher along the Kuroshio and coastal regions than the minor axis dispersion. This result suggests that the magnitude of dispersion highly depends on large scale strain motions.