English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

Available Potential Energy (APE) dissipation plays a central role in thedescription of mixing in turbulent stratified fluids. The dominant paradigm isthat it converts APE into background gravitational potential energy ${\rmGPE}_r$, and that the APE thus converted can be infinitely recycled back intoAPE by external buoyancy fluxes such as high-latitude cooling in the oceans. Inthis paper, we argue that such a paradigm is unphysical, because its corollaryis that APE dissipation is neither truly dissipative nor irreversible, whilealso violating energy conservation in more subtle ways. In this paper, we provefrom first principles that in reality, APE dissipation is a form of Jouleheating, which --- like viscous dissipation --- can only increase ${\rm GPE}_r$via locally expanding the fluid parcels, a tiny effect. ${\rm GPE}_r$ thusprimarily increases at the expense of the exergy of the stratification, asubcomponent of the background internal energy, regardless of whether the flowis laminar or turbulent. The results greatly clarify the energetics ofmechanically- and buoyancy-driven circulations. As a side benefit, our resultsyield a new physical principle justifying why turbulent mixing tends tohomogenise the fluid's materially conserved variables rather than relax thefluid towards thermodynamic equilibrium.

APE dissipation is a form of Joule heating. It is irreversible, not reversible