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Harrison Nicholls (he/him)

Graduate student

Research theme

  • Astronomy and astrophysics

Sub department

  • Atmospheric, Oceanic and Planetary Physics

Research groups

  • Planetary Climate Dynamics
harrison.nicholls@physics.ox.ac.uk
Atmospheric Physics Clarendon Laboratory, room 113
nichollsh.github.io
  • About
  • Publications

Temperature–chemistry coupling in the evolution of gas giant atmospheres driven by stellar flares

Monthly Notices of the Royal Astronomical Society Oxford University Press 523:4 (2023) 5681-5702

Authors:

Harrison Nicholls, Olivia Venot

Abstract:

The effect of enhanced UV irradiation associated with stellar flares on the atmospheric composition and temperature of gas giant exoplanets was investigated. This was done using a 1D radiative-convective-chemical model with self-consistent feedback between the temperature and the non-equilibrium chemistry. It was found that flare-driven changes to chemical composition and temperature give rise to prolonged trends in evolution across a broad range of pressure levels and species. Allowing feedback between chemistry and temperature plays an important role in establishing the quiescent structure of these atmospheres, and determines their evolution due to flares. It was found that cooler planets are more susceptible to flares than warmer ones, seeing larger changes in composition and temperature, and that temperature–chemistry feedback modifies their evolution. Long-term exposure to flares changes the transmission spectra of gas giant atmospheres; these changes differed when the temperature structure was allowed to evolve self-consistently with the chemistry. Changes in spectral features due to the effects of flares on these atmospheres can be associated with changes in composition. The effects of flares on the atmospheres of sufficiently cool planets will impact observations made with JWST. It is necessary to use self-consistent models of temperature and chemistry in order to accurately capture the effects of flares on features in the transmission spectra of cooler gas giants, but this depends heavily on the radiation environment of the planet.
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Self-limited tidal heating and prolonged magma oceans in the L 98-59 system

(2025)

Authors:

Harrison Nicholls, Claire Marie Guimond, Hamish CFC Hay, Richard D Chatterjee, Tim Lichtenberg, Raymond T Pierrehumbert
Details from ArXiV

Impact of varying redox states on crystallization and atmospheric composition of rocky exoplanets.

Copernicus Publications (2025)

Authors:

Mariana Sastre, Tim Lichtenberg, Dan Bower, Harrison Nicholls, Inga Kamp
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Reliable Detections of Atmospheres on Rocky Exoplanets with Photometric JWST Phase Curves

The Astrophysical Journal Letters American Astronomical Society 978:2 (2025) l40

Authors:

Mark Hammond, Claire Marie Guimond, Tim Lichtenberg, Harrison Nicholls, Chloe Fisher, Rafael Luque, Tobias G Meier, Jake Taylor, Quentin Changeat, Lisa Dang, Hamish CFC Hay, Oliver Herbort, Johanna Teske
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Convective shutdown in the atmospheres of lava worlds

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 536:3 (2024) 2957-2971

Authors:

Harrison Nicholls, Raymond T Pierrehumbert, Tim Lichtenberg, Laurent Soucasse, Stef Smeets
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