Magnetohydrodynamical Torsional Oscillations from Thermoresistive Instability in Hot Jupiters
Hot Jupiter atmospheres may be subject to a thermoresistive instability where an increase in the electrical conductivity due to ohmic heating results in runaway of the atmospheric temperature. We introduce a simplified one-dimensional model of the equatorial substellar region of a hot Jupiter that i...
| Main Authors: | , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2023-01-01
|
| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/ad0968 |
| _version_ | 1827595232229720064 |
|---|---|
| author | Raphaël Hardy Paul Charbonneau Andrew Cumming |
| author_facet | Raphaël Hardy Paul Charbonneau Andrew Cumming |
| author_sort | Raphaël Hardy |
| collection | DOAJ |
| description | Hot Jupiter atmospheres may be subject to a thermoresistive instability where an increase in the electrical conductivity due to ohmic heating results in runaway of the atmospheric temperature. We introduce a simplified one-dimensional model of the equatorial substellar region of a hot Jupiter that includes the temperature dependence and time dependence of the electrical conductivity, as well as the dynamical back-reaction of the magnetic field on the flow. This model extends our previous one-zone model to include the radial structure of the atmosphere. Spatial gradients of electrical conductivity strongly modify the radial profile of Alfvénic oscillations, leading to steepening and downward transport of magnetic field, enhancing dissipation at depth. We find unstable solutions that lead to self-sustained oscillations for equilibrium temperatures in the range T _eq ≈ 1000–1200 K and radial magnetic field strength in the range ≈10–100 G. For a given set of parameters, self-sustained oscillations occur in a narrow range of equilibrium temperatures that allow the magnetic Reynolds number to alternate between large and small values during an oscillation cycle. With our simplified geometry, outside of this temperature window the system reaches a steady state in which the effect of the magnetic field can be approximated as a magnetic drag term. Our results show that thermoresistive instability is a possible source of variability in magnetized hot Jupiters at colder temperatures and emphasize the importance of including the temperature dependence of electrical conductivity in models of atmospheric dynamics. |
| first_indexed | 2024-03-09T02:50:44Z |
| format | Article |
| id | doaj.art-e79194bc5f4b45248550e71826c5e9a7 |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-09T02:50:44Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-e79194bc5f4b45248550e71826c5e9a72023-12-05T13:23:58ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-0195914110.3847/1538-4357/ad0968Magnetohydrodynamical Torsional Oscillations from Thermoresistive Instability in Hot JupitersRaphaël Hardy0https://orcid.org/0000-0002-2599-6225Paul Charbonneau1https://orcid.org/0000-0003-1618-3924Andrew Cumming2https://orcid.org/0000-0002-6335-0169Département de Physique, Université de Montréal , Montréal, QC H3C 3J7, Canada ; raphael.hardy@umontreal.ca; Department of Physics and Trottier Space Institute, McGill University , Montréal, QC H3A 2T8, Canada; Institut de Recherche sur les Exoplanètes (iREx), Université de Montréal , Montréal, QC H3C 3J7, CanadaDépartement de Physique, Université de Montréal , Montréal, QC H3C 3J7, Canada ; raphael.hardy@umontreal.caDepartment of Physics and Trottier Space Institute, McGill University , Montréal, QC H3A 2T8, Canada; Institut de Recherche sur les Exoplanètes (iREx), Université de Montréal , Montréal, QC H3C 3J7, CanadaHot Jupiter atmospheres may be subject to a thermoresistive instability where an increase in the electrical conductivity due to ohmic heating results in runaway of the atmospheric temperature. We introduce a simplified one-dimensional model of the equatorial substellar region of a hot Jupiter that includes the temperature dependence and time dependence of the electrical conductivity, as well as the dynamical back-reaction of the magnetic field on the flow. This model extends our previous one-zone model to include the radial structure of the atmosphere. Spatial gradients of electrical conductivity strongly modify the radial profile of Alfvénic oscillations, leading to steepening and downward transport of magnetic field, enhancing dissipation at depth. We find unstable solutions that lead to self-sustained oscillations for equilibrium temperatures in the range T _eq ≈ 1000–1200 K and radial magnetic field strength in the range ≈10–100 G. For a given set of parameters, self-sustained oscillations occur in a narrow range of equilibrium temperatures that allow the magnetic Reynolds number to alternate between large and small values during an oscillation cycle. With our simplified geometry, outside of this temperature window the system reaches a steady state in which the effect of the magnetic field can be approximated as a magnetic drag term. Our results show that thermoresistive instability is a possible source of variability in magnetized hot Jupiters at colder temperatures and emphasize the importance of including the temperature dependence of electrical conductivity in models of atmospheric dynamics.https://doi.org/10.3847/1538-4357/ad0968Astrophysical fluid dynamicsMagnetohydrodynamicsExoplanet atmospheric variabilityExoplanet atmospheric dynamics |
| spellingShingle | Raphaël Hardy Paul Charbonneau Andrew Cumming Magnetohydrodynamical Torsional Oscillations from Thermoresistive Instability in Hot Jupiters The Astrophysical Journal Astrophysical fluid dynamics Magnetohydrodynamics Exoplanet atmospheric variability Exoplanet atmospheric dynamics |
| title | Magnetohydrodynamical Torsional Oscillations from Thermoresistive Instability in Hot Jupiters |
| title_full | Magnetohydrodynamical Torsional Oscillations from Thermoresistive Instability in Hot Jupiters |
| title_fullStr | Magnetohydrodynamical Torsional Oscillations from Thermoresistive Instability in Hot Jupiters |
| title_full_unstemmed | Magnetohydrodynamical Torsional Oscillations from Thermoresistive Instability in Hot Jupiters |
| title_short | Magnetohydrodynamical Torsional Oscillations from Thermoresistive Instability in Hot Jupiters |
| title_sort | magnetohydrodynamical torsional oscillations from thermoresistive instability in hot jupiters |
| topic | Astrophysical fluid dynamics Magnetohydrodynamics Exoplanet atmospheric variability Exoplanet atmospheric dynamics |
| url | https://doi.org/10.3847/1538-4357/ad0968 |
| work_keys_str_mv | AT raphaelhardy magnetohydrodynamicaltorsionaloscillationsfromthermoresistiveinstabilityinhotjupiters AT paulcharbonneau magnetohydrodynamicaltorsionaloscillationsfromthermoresistiveinstabilityinhotjupiters AT andrewcumming magnetohydrodynamicaltorsionaloscillationsfromthermoresistiveinstabilityinhotjupiters |