1202 / 2024-09-20 16:52:40

Responses of the upper-ocean flow variability in different frequency bands to wind forcing changes

Oceanic submesoscale processes,inbalanced motions,wind forcing

Upper ocean flow variability is frequently measured using the relative vorticity and divergence metrics. In this work their responses to wind forcing changes and their relation in different frequency bands are investigated by comparing two numerical simulations of the Southern California Bight during a three-month winter season forced by two different meteorologic models. One simulation (NAM) receives weaker winds and the other (WRF) receives stronger winds. The results show that, within the upper ocean the WRF vorticity is notably elevated, whereas the

WRF divergence slightly changes and even weakens at certain depths. These two metrics are further decomposed into subtidal, diurnal, semi-diurnal and higher frequency components. Elevation of the WRF vorticity is primarily attributed to its subtidal and diurnal components. The WRF divergence subtidal and diurnal components also elevate within the upper ocean, whereas its semi-diurnal component weakens. In each frequency band the vorticity and divergence components are found to be linked by a vorticity growth time scale. The subtidal components have

the maximum time scale and slight elevation of the divergence component leads to much bigger increase of the vorticity component. The semi-diurnal components have much smaller time scale and weakening of the WRF divergence component barely affects the vorticity component.