Rectified flow in a stratified coastal ocean

Abstract

An idealized numerical model is used to explore the generation of mean flows by oscillating wind forcing in a stratified coastal ocean with no alongshore variability, i.e., where neither barotropic nor baroclinic instability is a factor. On the inner shelf, where surface-to-bottom mixing occurs, a mean cross-shelf flow develops, as examined by Castelao et al. (2010), and the present results suggest that this flow can remain two-dimensional if there is a nonzero cross-shelf density gradient. Offshore of the inner shelf, where the water column is stratified, a mean alongshore flow develops in the direction opposite to coastal-trapped wave propagation. This flow is associated with cross-shelf density gradients that are set up by the asymmetry between onshore and offshore flow in the bottom boundary layer. Both forms of rectified flow (cross-shelf and alongshore) are sensitive to the presence of surface heating, and the rectifications can be readily masked by the effect of a steady alongshore wind stress.

The Summer Heat Balance of the Oregon Inner Shelf Over 2 Decades: Intraseasonal Variability

“…Additionally, during light winds, as well as at times under downwelling‐favorable winds, there was evidence of an upwelling‐type across‐shelf circulation with offshore currents in the surface layer (e.g., Figure 9m). Previous studies have identified upwelling‐type circulations due to vertical thermal wind shear driven by an across‐shelf density gradient that overcomes the wind‐driven shear during light or downwelling‐favorable winds (e.g., Brink, 2018; Chen & Chen, 2017). This leads to a reversal in the stress profile and hence the across‐shelf circulation driven by the stress divergence.…”

“…Local along‐shelf pressure gradients may also be caused by time‐varying processes such as coastal‐trapped waves. An across‐shelf density gradient resulting from warmer temperatures in the shallower water close to the coast can also induce an across‐shelf upwelling‐type circulation and heat flux (Brink, 2018; Chen & Chen, 2017). This component of the Ekman circulation is referred to as the turbulent thermal wind balance (Gula et al., 2014; Wenegrat & McPhaden, 2016).…”