Negative turbulent production during flow reversal in a stratified oscillating boundary layer on a sloping bottom

Three-dimensional direct numerical simulations are performed to model an internal tidal beam at near-critical slope, and the phase dependence of turbulent processes is investigated. Convective instability leads to density overturns that originate in the upper flank of the beam and span the beam width of 6 m during flow reversal from downslope to upslope boundary motion. During this flow reversal event, negative turbulent production is observed signaling energy transfer from velocity fluctuations to the mean flow. In this note, we explain the mechanism underlying negative production.