Predictability of Stratified Turbulence

In the study of geophysical fluid dynamics, predictability still stands in the foreground of interest as one of the primary challenges. Following Lorenz's pioneering framework, several results from homogeneous and isotropic turbulence have suggested that flows with many scales of motion present limited predictability due to the inevitable contamination of error from small to large scales, even if initially confined to small scales. In this work, we investigate the predictability of freely decaying stratified turbulence, which is representative of small-scale geophysical turbulence where Coriolis effects are weak. Predictability of stratified turbulence is studied using direct numerical simulations by analyzing the error growth in pairs of realizations of velocity fields departing from almost indiscernible initial conditions. Previous studies have indicated that the finite range of predictability is determined by to the slope of the flow's kinetic energy spectrum. In stratified turbulence, the shape of the energy spectrum depends on the buoyancy Reynolds number, as long as it is not too large. We perform a comparative analysis of spectra and perturbation upscale growth behaviour in different regimes of stratified turbulence from large to unitary order of buoyancy Reynolds number.