Gamma instability in an inhomogeneous environment and salt-fingering staircase trapping: Determining the step size

Abstract

For mid-latitude salt-fingering staircases in the oceans, the staircase step-sizes are always observed to be smaller at vertical positions of relatively higher background gradients than at vertical positions characterized by relatively lower gradients. We extend the gamma instability theory of Radko (2003) to a system with inhomogeneous background gradients for temperature and salinity to explain this observed trend. On the basis of our three-dimensional turbulence analyses and mean-field model simulation, we successfully explain the origins of such step-size differences and test our proposed mechanism against the historical staircase data recorded in the Tyrrhenian Basin.