EWM 26: Pathways to dissipation of near-inertial waves in the presence ... by Pascale Lelong

Pathways to dissipation of near-inertial waves in the presence of mesoscale eddies by Pascale Lelong (NorthWest Research Associates) We examine the life cycle of wind-generated, near-inertial internal waves with a suite of nested high resolution simulations spanning a range of scales from hundreds of kilometers to a few meters. The outer domain encompasses a region that includes the Sidra Gyre, a semi-permanent anticyclone located off the coast of Libya, while the innermost domain moves with the eddy core and is limited to the region at the base of Sidra. The coordinated nested simulations produce a dynamically-coupled flow field consisting of mesoscale eddies, subme soscale filaments, near-inertial and higher frequency internal waves, shear-driven instabilities, and nearly isotropic turbulent motions below the Ozmidov scale, allowing for a comprehensive detailed study of dynamical processes from the meso- to turbulent scales in a realistic ocean setting. Our one-way nesting approach reproduces energy cascades tracked from wind-forced near-inertial waves in the surface mixed layer, through refraction and trapping in a baroclinic anticyclone, downward propagation into the pycnocline, critical-layer amplification and ultimately to shear instability, yielding insight unattainable with stand-alone simulations. We examine the possible pathways to dissipation as the waves and address the fundamental question of how near-inertial internal waves lead to diapycnal mixing: Do near-inertial waves break and directly produce small scale, isotropic turbulence or is there an intermediate transition to large-scale anisotropic turbulence on the path to isotropy and dissipation?