Reply to ‘‘Comments on ‘On the Steadiness of Separating Meandering Currents’’’

The authors thank Nof et al. for their comments on the authors’ paper ‘‘On the steadiness of separating meandering currents.’’ The authors’ paper was motivated by a series of papers by Nof et al. Under a certain set of conditions (reduced gravity, steady state, no meridional velocity at outflow, and parallel outflow), Nof et al. showed that a separating and retroflecting frictionless current cannot be steady because of a momentum imbalance. The main conclusion of the authors’ paper was that they agree with the Nof et al. result that a momentum imbalance exists and extended the proof to all possible configurations of retroflecting currents, even including friction. The authors’ results point to a new mechanism for the generation of variability in the ocean that is not related to dynamical instability of the flow. The main claim in the comments is that the authors incorrectly argued in the appendix that the steadystate solutions presented by Nof et al. in several papers fulfill the extra constraint u2 5g9h. In the original paper, the authors showed that it follows from the geostrophic assumption stated implicitly in all these Nof et al. papers, because the flow is assumed to be parallel. Nof et al. now argue that the flow is only approximately geostrophic in all Nof et al. papers. The authors show in this reply that for steady weakly meandering outflows approximate geostrophy does lead to a momentum imbalance paradox as Nof et al. claim. However, for a steady strongly meandering outflow, approximate geostrophy is not enough and one has to use the method explored by van Leeuwen and De Ruijter to derive a momentum imbalance paradox.