The observation of radio, X-ray and Hα emission from substellar objects indicates the presence of plasma regions and associated high-energy processes in their surrounding envelopes. This paper numerically simulates and characterises Critical Velocity Ionisation, a potential ionisation process, that can efficiently generate plasma as a result of neutral gas flows interacting with seed magnetized plasmas. By coupling a Gas-MHD interactions code (to simulate the ionisation mechanism) with a substellar global circulation model (to provide the required gas flows) we quantify the spatial extent of the resulting plasma regions, their degree of ionisation and their lifetime for a typical substellar atmosphere. It is found that the typical average ionisation fraction reached at equilibrium (where the ionisation and recombination rates are equal and opposite) ranges from 10-5 to 10-8, at pressures between 10-1 and 10-3 bar, with a trend of increasing ionisation fraction with decreasing atmospheric pressure. The ionisation fractions reached as a result of Critical Velocity Ionisation are sufficient to allow magnetic fields to couple to gas flows in the atmosphere.
|Number of pages||8|
|Early online date||17 Dec 2019|
|Publication status||Published - 17 Dec 2019|
- Brown dwarfs
- Extrasolar gas giants
- Astrophysical fluid dynamics
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Critical velocity ionisation in substellar atmospheres
Wilson, A. (Creator), Dobbs-Dixon, I. (Creator), Diver, D. A. (Creator) & Stark, C. (Creator), University of Glasgow, 17 Dec 2019