Stratospheric dayside-to-nightside circulation responsible for nightside ozone hotspots on tidally-locked exoplanets

Interpreting atmospheric spectra of exoplanets requires understanding the underlying atmospheric physics and chemistry. Studies have previously shown that for tidally locked, Earth-like exoplanets that orbit M-dwarf stars, photochemistry supports a highly structured 3-D ozone distribution, including a stratospheric ozone layer. We use a 3-D coupled Climate-Chemistry model (CCM), the Met Office Unified Model with the UK Chemistry and Aerosol framework, to describe the atmosphere of Proxima Centauri b. The chemical network includes the Chapman ozone reactions and the hydrogen oxide and nitrogen oxide catalytic cycles. We find that ozone is mainly produced on the dayside of the planet, initiated by the incoming stellar radiation. The ozone is then advected to the nightside, where it descends at the locations of permanent Rossby gyres that result in localised ozone hotspots. We will show that a stratospheric dayside-to-nightside circulation drives this nightside ozone distribution. This finding illustrates the 3-D nature of exoplanetary atmospheres and the potential impact on spectroscopic observations.