Extreme vertical drafts and the modulation of local energy dissipation in stratified geophysical flows

Stratified geophysical flows can develop extreme events in the form of bursts in the temperature and in the vertical velocity, resulting from the interplay of gravity waves and turbulent motions, through a mechanism producing the amplification of the fields in a range of the governing parameters of geophysical interest (Feraco et al., EPL 2018, 2021). Performing direct numerical simulations of the Boussinesq equations with Froude numbers observable in geophysical scenarios, we show how these structures - which appear intermittently in space and time - do generate patches of turbulence and enhance kinetic and potential energy dissipation (Marino et al., PRF 2022). Here we show as well that due to the emergence of extreme vertical velocity drafts in stratified geophysical fluids, roughly 10% of the domain flow can account for up to 50% of the global volume dissipation. This evidence provides a possible explanation for the observed variability of the local energy dissipation in the bulk of oceanic flows and the modulation of its probability distribution function, reminiscent of estimates based on global models (Pearson & Fox-Kemper, PRL 2018).

Bibliography:

Pearson & Fox-Kemper, PRL, 2018, Vol. 120, p.094501.

Feraco et al., EPL, 2018, Vol. 123 (4), p.44002.

Feraco et al., EPL, 2021, Vol. 135, p. 14001.

Marino et al. PRF, 2022, Vol. 7, p.033801.