The effect of internal gravity waves on cloud evolution in sub-stellar atmospheres

Parent, Amy; Falconer, Ruth E.; Lee, Elspeth K. H.; Meyer, Karen; Stark, Craig R.

doi:10.1051/0004-6361/201937063

Cited by 3 publications

(3 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, the dynamics and global atmospheric circulation will impose wind shear that could affect convection as well as gravity-wave generation and vertical propagation (Frits & Alexander 2003). Such gravity waves could impact the condensation and nucleation of species condensing at higher altitudes (Parent et al 2020).…”

Section: Discussionmentioning

confidence: 99%

Cloud-convection Feedback in Brown Dwarf Atmospheres

Lefèvre¹,

Tan²,

Lee

et al. 2022

ApJ

View full text Add to dashboard Cite

Numerous observational evidence has suggested the presence of active meteorology in the atmospheres of brown dwarfs. A near-infrared brightness variability has been observed. Clouds have a major role in shaping the thermal structure and spectral properties of these atmospheres. The mechanism of such variability is still unclear, and neither 1D nor global circulation models can fully study this topic due to resolution. In this study, a convective-resolving model is coupled to gray-band radiative transfer in order to study the coupling between the convective atmosphere and the variability of clouds over a large temperature range with a domain of several hundred kilometers. Six types of clouds are considered, with microphysics including settling. The clouds are radiatively active through the Rosseland mean coefficient. Radiative cloud feedback can drive spontaneous atmospheric variability in both temperature and cloud structure, as modeled for the first time in three dimensions. Silicate clouds have the most effect on the thermal structure with the generation of a secondary convective layer in some cases, depending on the assumed particle size. Iron and aluminum clouds also have a substantial impact on the atmosphere. Thermal spectra were computed, and we find the strongest effect of the clouds is the smoothing of spectral features at optical wavelengths. Compared to observed L and T dwarfs on the color–magnitude diagram, the simulated atmospheres are redder for most of the cases. Simulations with the presence of cloud holes are closer to observations.

show abstract

Section: Discussionmentioning

confidence: 99%

Cloud-convection Feedback in Brown Dwarf Atmospheres

Lefèvre¹,

Tan²,

Lee

et al. 2022

ApJ

View full text Add to dashboard Cite

show abstract

“…However, the dynamics and global atmospheric circulation will impose wind shear that could affect convection as well as gravity waves generation and vertical propagation (Frits & Alexander, 2003). Such gravity waves could impact the condensation and nucleation of species condensing at higher altitudes (Parent et al, 2020). The heat capacity of H/He is set constant in the model, while the temperature varies by several thousands of kelvin over the vertical.…”

Section: Discussionmentioning

confidence: 99%

Cloud-convection feedback in brown dwarfs atmosphere

Lefèvre,

Tan,

Lee

et al. 2022

Preprint

View full text Add to dashboard Cite

Numerous observational evidence has suggested the presence of active meteorology in the atmospheres of brown dwarfs. A near-infrared brightness variability has been observed. Clouds have a major role in shaping the thermal structure and spectral properties of these atmospheres. The mechanism of such variability is still unclear and both 1D and global circulation model cannot fully study this topics due to resolution. In this study, a convective resolving model is coupled to grey-band radiative transfer in order to study the coupling between the convective atmosphere and the variability of clouds over a large temperature range with a domain of several hundreds of kilometers. Six types of clouds are considered, with microphysics including settling. The clouds are radiatively active using Rosseland mean coefficient. Radiative cloud feedback can drive spontaneous atmospheric variability in both temperature and cloud structure, as modeled for the first time in three dimensions. Silicate clouds have the most effect of the thermal structure with the generation of a secondary convective layer in some cases, depending on the assumed particle size. Iron and Aluminum clouds also have a substantial impact on the atmosphere. Thermal spectra were computed, and we find the strongest effect of clouds is the smoothing of spectral features at optical wavelengths. Compared to observed L and T dwarfs on color-magnitude diagram, the simulated atmospheres are redder for most of the cases. The simulations with the presence of cloud holes are closer to the observations.

show abstract

“…For a range of magnetic field strengths of B ≈ 10 −3 − 0.1 T, the cyclotron period is P ≈ 1 hrs−1 mins. Other atmospheric processes occur on the following timescales (Helling & Casewell 2014): wave propagation (0.3−3 s); large-scale convection 20 min−3.5 hrs); gravitational settling (15 mins−8 months); diffusive eddy mixing (3 hrs−3 yrs); and, buoyancy oscillations (10−10 3 s) (Parent et al 2020). In comparison, the magnetic field alignment of charged dust grains is possible since it occurs on a shorter timescale than other notable atmospheric processes, with the exception of wave phenomena.…”

Section: Introductionmentioning

confidence: 99%

Evolution of spheroidal dust in electrically active sub-stellar atmospheres

Stark

Diver

2020

A&A

Self Cite

View full text Add to dashboard Cite

Context. Understanding the source of sub-stellar polarimetric observations in the optical and near-infrared is key to characterising sub-stellar objects and developing potential diagnostics for determining properties of their atmosphere. Differential scattering from a population of aligned, non-spherical dust grains is a potential source of polarization that could be used to determine geometric properties of the dust clouds. Aims. This paper addresses the problem of spheroidal growth of dust grains in electrically-activated sub-stellar atmospheres. It presents the novel application of a mechanism whereby non-spherical, elongated dust grains can be grown via plasma deposition as a consequence of the surface electric field effects of charged dust grains. Methods. We numerically solve the differential equations governing the spheroidal growth of charged dust grains via plasma deposition as a result of surface electric field effects in order to determine how the dust eccentricity and the dust particle eccentricity distribution function evolve with time. From these results we determine the effect of spheroidal dust on the observed linear polarization. Results. Numerical solutions show that e ≈ 0.94 defines a watershed eccentricity, where the eccentricity of grains with an initial eccentricity less than (greater than) this value decreases (increases) and spherical (spheroidal) growth occurs. This produces a characteristic bimodal eccentricity distribution function yielding a fractional change in the observed linear polarization of up to ≈ 0.1 corresponding to dust grains of maximal eccentricity at wavelengths of ≈ 1µm, consistent with the near infrared observational window. Order of magnitude calculations indicate that a population of aligned, spheroidal dust grains can produce degrees of polarization P ≈ O(10 −2 − 1%) consistent with observed polarization signatures. Conclusions. The results presented here are relevant to the growth of non-spherical, irregularly-shaped dust grains of general geometry where non-uniform surface electric field effects of charged dust grains are significant. The model described in this paper may also be applicable to polarization from galactic dust and dust growth in magnetically confined plasmas.

show abstract

The effect of internal gravity waves on cloud evolution in sub-stellar atmospheres

Cited by 3 publications

References 39 publications

Cloud-convection Feedback in Brown Dwarf Atmospheres

Cloud-convection Feedback in Brown Dwarf Atmospheres

Cloud-convection feedback in brown dwarfs atmosphere

Evolution of spheroidal dust in electrically active sub-stellar atmospheres

Contact Info

Product

Resources

About