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A new approach to understanding fluid mixing in process-study models of stratified fluids

Lookup NU author(s): Dr Samuel Hartharn-EvansORCiD, Dr Magda CarrORCiD



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Copyright © 2024 Samuel George Hartharn-Evans et al. While well-established energy-based methods of quantifying diapycnal mixing in process-study numerical models are often used to provide information about when mixing occurs, and how much mixing has occurred, describing how and where this mixing has taken place remains a challenge. Moreover, methods based on sorting the density field struggle when the model is under-resolved and when there is uncertainty as to the definition of the reference density when bathymetry is present. Here, an alternative method of understanding mixing is proposed. Paired histograms of user-selected variables (which we abbreviate USPs (user-controlled scatter plots)) are employed to identify mixing fluid and are then used to display regions of fluid in physical space that are undergoing mixing. This paper presents two case studies showcasing this method: shoaling internal solitary waves and a shear instability in cold water influenced by the nonlinearity of the equation of state. For the first case, the USP method identifies differences in the mixing processes associated with different internal solitary wave breaking types, including differences in the horizontal extent and advection of mixed fluid. For the second case, the method is used to identify how density and passive tracers are mixed within the core of the asymmetric cold-water Kelvin-Helmholtz instability.

Publication metadata

Author(s): Hartharn-Evans SG, Stastna M, Carr M

Publication type: Article

Publication status: Published

Journal: Nonlinear Processes in Geophysics

Year: 2024

Volume: 31

Issue: 1

Pages: 61-74

Online publication date: 30/01/2024

Acceptance date: 17/12/2023

Date deposited: 20/02/2024

ISSN (print): 1023-5809

ISSN (electronic): 1607-7946

Publisher: Copernicus Publications


DOI: 10.5194/npg-31-61-2024


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Funder referenceFunder name
NE/S007512/1Natural Environment Research Council (NERC)
Natural Sciences and Engineering Research Council of Canada