Internal wave transmission through a thermohaline staircase

Sutherland, Bruce

doi:10.1103/physrevfluids.1.013701

Cited by 20 publications

(30 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The free modes were found to differ from those of a continuously stratified medium, with those waves with wavelengths that are comparable with a step-size being affected the most. The transmission of internal waves through a density staircase in a similar Cartesian model was studied by Sutherland (2016), who adopted the "traditional approximation" to incorporate rotation (this assumes that the buoyancy force dominates the Coriolis acceleration in the direction of stratification, thereby disallowing inertial waves), and subsequently André et al (2017) studied the free modes and transmission of internal and inertial waves in a local model that included the full Coriolis acceleration at any latitude in a planet. The density staircase was found to strongly affect the transmission of waves through such a region in a frequency and wavelength-dependent manner.…”

Section: Introductionmentioning

confidence: 99%

Wave propagation in semiconvective regions of giant planets

Pontin

Barker

Hollerbach

et al. 2020

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

Recent observations of Jupiter and Saturn suggest that heavy elements may be diluted in the gaseous envelope, providing a compositional gradient that could stabilise ordinary convection and produce a stably-stratified layer near the core of these planets. This region could consist of semi-convective layers with a staircase-like density profile, which have multiple convective zones separated by thin stably-stratified interfaces, as a result of double-diffusive convection. These layers could have important effects on wave propagation and tidal dissipation that have not been fully explored. We analyse the effects of these layers on the propagation and transmission of internal waves within giant planets, extending prior work in a local Cartesian model. We adopt a simplified global Boussinesq planetary model in which we explore the internal waves in a non-rotating spherical body. We begin by studying the free modes of a region containing semi-convective layers. We then analyse the transmission of internal waves through such a region. The free modes depend strongly on the staircase properties, and consist of modes with both internal and interfacial gravity wave-like behaviour. We determine the frequency shifts of these waves as a function of the number of steps to explore their potential to probe planetary internal structures. We also find that wave transmission is strongly affected by the presence of a staircase. Very large-wavelength waves are transmitted efficiently, but small-scale waves are only transmitted if they are resonant with one of the free modes. The effective size of the core is therefore larger for non-resonant modes.

show abstract

Section: Introductionmentioning

confidence: 99%

Wave propagation in semiconvective regions of giant planets

Pontin

Barker

Hollerbach

et al. 2020

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

show abstract

“…Belyaev et al (2015) derived the dispersion relation for the free modes of a staircase, showed that regions of layered semi-convection could sustain g-modes, and considered the effects of rotation at the pole and at the equator. Sutherland (2016) studied the transmission of an incident internal wave upon a density staircase embedded in a stably stratified medium under the traditional approximation, which consists of neglecting the horizontal component of the rotation vector in the Coriolis acceleration. Finally, André et al (2017;hereafter Paper I) have generalised both of these previous studies by analysing the effects of rotation including the full Coriolis acceleration at any latitude, and studied its effects on the free modes of a density staircase and on the transmission of incident waves.…”

Section: Introductionmentioning

confidence: 99%

Layered semi-convection and tides in giant planet interiors

André

Mathis

Barker

2019

A&A

View full text Add to dashboard Cite

Context. Recent Juno observations have suggested that the heavy elements in Jupiter could be diluted throughout a large fraction of its gaseous envelope, providing a stabilising compositional gradient over an extended region of the planet. This could trigger layered semi-convection, which, in the context of giant planets more generally, may explain Saturn’s luminosity excess and play a role in causing the abnormally large radii of some hot Jupiters. In giant planet interiors, it could take the form of density staircases, which are convective layers separated by thin stably stratified interfaces. In addition, the efficiency of tidal dissipation is known to depend strongly on the planetary internal structure. Aims. We aim to study the resulting tidal dissipation when internal waves are excited in a region of layered semi-convection by tidal gravitational forcing due to other bodies (such as moons in giant planet systems, or stars in hot Jupiter systems). Methods. We adopt a local Cartesian model with a background layered density profile subjected to an imposed tidal forcing, and we compute the viscous and thermal dissipation rates numerically. We consider two sets of boundary conditions in the vertical direction: periodic boundaries and impenetrable, stress-free boundaries, with periodic conditions in the horizontal directions in each case. These models are appropriate for studying the forcing of short-wavelength tidal waves in part of a region of layered semi-convection, and in an extended envelope containing layered semi-convection, respectively. Results. We find that the rates of tidal dissipation can be enhanced in a region of layered semi-convection compared to a uniformly convective medium, where the latter corresponds with the usual assumption adopted in giant planet interior models. In particular, a region of layered semi-convection possesses a richer set of resonances, allowing enhanced dissipation for a wider range of tidal frequencies. The details of these results significantly depend on the structural properties of the layered semi-convective regions. Conclusions. Layered semi-convection could contribute towards explaining the high tidal dissipation rates observed in Jupiter and Saturn, which have not yet been fully explained by theory. Further work is required to explore the efficiency of this mechanism in global models.

show abstract

“…Some numerical and theoretical studies suggest that a water column with a layered stratification limits internal wave activity (Ghaemsaidi et al., ; Sutherland, ) and could, therefore, maintain low shear and turbulent levels. A double‐diffusive staircase might serve as a filtering function transmitting only internal waves with specific properties.…”

Section: Discussionmentioning

confidence: 99%

The Regulation of Sea Ice Thickness by Double‐Diffusive Processes in the Ross Gyre

Bebieva

Speer

2019

JGR Oceans

View full text Add to dashboard Cite

New fine‐scale observations from the central Ross Gyre reveal the presence of double‐diffusive staircase structures underlying the surface mixed layer. These structures are persistent over seasons, with more developed mixed layers within the double‐diffusive staircase in winter months. The sensitivity of the ice formation rate with respect to mixing processes within the main pycnocline (double‐diffusive versus purely turbulent mixing) is investigated with the 1‐D model. A scenario with purely turbulent mixing results in significant underestimates of sea ice thickness. However, a scenario when double‐diffusive mixing operates in the presence of weak shear yields plausible ranges for sea ice thickness that agrees well with the observations. The model results and observations suggest a peculiar feedback mechanism that promotes the self‐maintenance of double‐diffusive staircases. Suppression of the vertical heat fluxes due to the presence of a double‐diffusive staircase, compared to purely turbulent case, allows Upper Circumpolar Deep Water to be more exposed to surface buoyancy fluxes. Our results shed light on the process—double diffusion—that might account for estimated rates of winter water mass transformation in the central Ross Gyre.

show abstract

Internal wave transmission through a thermohaline staircase

Cited by 20 publications

References 24 publications

Wave propagation in semiconvective regions of giant planets

Wave propagation in semiconvective regions of giant planets

Layered semi-convection and tides in giant planet interiors

The Regulation of Sea Ice Thickness by Double‐Diffusive Processes in the Ross Gyre

Contact Info

Product

Resources

About