Effects of wave-induced vertical Reynolds stress on upper-ocean momentum transfer over the Scotian Shelf during extreme weather events

Abstract

The effects of wave-induced vertical Reynolds stress (WIVRS) on the upper-ocean momentum transfer over the Scotian Shelf (ScS) are examined using a coupled wave-circulation modeling system during two extreme storm events: Hurricane Earl and Winter Storm Echo. The effects of WIVRS are specified in the circulation model using the wave pressure-slope stress ( τP) suggested by Mellor (2013). The inclusion of τP enhances the downward momentum transfer within the surface layer when the storm passes overhead associated with strong vertical gradients of τP, leading to relatively weak vertical shears of horizontal currents and thus weak turbulent Reynolds stress (τT) in the upper-ocean layer. This in turn weakens the vertical momentum transfer to deeper water through τT just after the storm passage. The reduced downward momentum transfer after the storm due to the inclusion of τP is found to be in better agreements with both the ADCP observations and the HF-radar observations. The ADCP observations show a relatively slow decay of upper-ocean currents, and the HF-radar observations show relatively strong clockwise-rotating near-inertial surface currents over the offshore area of the ScS just after the storm passage. The model results also demonstrate that the effects of τP are more pronounced during Hurricane Earl due to deeper penetration depths of τP associated with stronger winds (up to 33 m/s) than those during Winter Storm Echo (wind speeds up to 25 m/s).