Effects of symmetric instability in the Kuroshio Extension region in winter

Abstract

Submesoscale symmetric instability (SI) in the ocean surface mixed layer (SML) plays a significant role in the forward energy cascade and vertical material transports. Due to its small spatial scales of typically less than 1 km, SI is not resolved by current climate ocean models and most regional models. This work investigates the SI effects in the Kuroshio Extension (KE) region by using a SI parameterization scheme implemented in the Coastal and Regional Ocean Community Model (CROCO). Compared to a SI-lacking model at the same spatial resolution of 500 m, a SI-parameterized model more closely resembles an ultra-high resolution (20 m) non-hydrostatic model that is intended to resolve SI directly on the basis of evaluating the energy source of SI: geostrophic shear production. As SI restratifies the SML, the SI-parameterized model simulates a shallower SML depth in the KE region compared to the SI-lacking one, which is closer to the observed state. The potential vorticity is also modulated and a reduction of negative PV is found due to the parameterized SI. The results here demonstrate the capability of the SI scheme in the representation of the SI impacts and an improvement in the simulation of the KE.