Sensitivity of a Model Shelfbreak Front to the Parameterization of Vertical Mixing

Abstract

Recent observations have suggested that the trapped-front model of Chapman and Lentz is consistent with some aspects of the shelfbreak front in the Middle Atlantic Bight. The sensitivity of the model to the parameterization of vertical mixing is examined to determine which model features are robust and potentially observable and which are variable and less reliable. The basic frontal trapping mechanism, frontal location, surface intensified frontal jet with weak flow at the bottom, and detachment of the bottom boundary layer at the shoreward edge of the foot of the front are all insensitive to the parameterization of vertical mixing. On the other hand, the frontal shape and width and the cross-frontal circulation and momentum balances within the front change dramatically with the parameterization of vertical mixing. Constant mixing coefficients produce strong vertical mixing within the front, which results in steady shoreward flow in the bottom boundary layer there. Mixing coefficients that depend on the local stratification and shear produce weak vertical mixing within the front, which allows oscillating currents that may be frontal-trapped waves.