Stability and dynamics of convection in dry salt lakes

Lasser, J., Ernst, M. and Goehring, L. ORCID: 0000-0002-3858-7295, 2021. Stability and dynamics of convection in dry salt lakes. Journal of Fluid Mechanics, 917: A14. ISSN 0022-1120

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Dry lakes covered with a salt crust organised into beautifully patterned networks of narrow ridges are common in arid regions. Here, we consider the initial instability and the ultimate fate of buoyancy-driven convection that could lead to such patterns. Specifically, we look at convection in a deep porous medium with a constant throughflow boundary condition on a horizontal surface, which resembles the situation found below an evaporating salt lake. The system is scaled to have only one free parameter, the Rayleigh number, which characterises the relative driving force for convection. We then solve the resulting linear stability problem for the onset of convection. Further exploring the nonlinear regime of this model with pseudo-spectral numerical methods, we demonstrate how the growth of small downwelling plumes is itself unstable to coarsening, as the system develops into a dynamic steady state. In this mature state we show how the typical speeds and length scales of the convective plumes scale with forcing conditions, and the Rayleigh number. Interestingly, a robust length scale emerges for the pattern wavelength, which is largely independent of the driving parameters. Finally, we introduce a spatially inhomogeneous boundary condition – a modulated evaporation rate – to mimic any feedback between a growing salt crust and the evaporation over the dry salt lake. We show how this boundary condition can introduce phase locking of the downwelling plumes below sites of low evaporation, such as at the ridges of salt polygons.

Item Type: Journal article
Publication Title: Journal of Fluid Mechanics
Creators: Lasser, J., Ernst, M. and Goehring, L.
Publisher: Cambridge University Press
Date: 25 June 2021
Volume: 917
ISSN: 0022-1120
Divisions: Schools > School of Science and Technology
Record created by: Jonathan Gallacher
Date Added: 04 May 2021 10:59
Last Modified: 23 Oct 2021 03:00

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