Modons on tidally synchronized extrasolar planets

Abstract

ABSTRACT We investigate modons on tidally synchronized extrasolar planet atmospheres. Modons are dynamic, coherent flow structures composed of a pair of storms with opposite signs of vorticity. Modons are important because they can divert flows and lead to recognizable weather patterns. On synchronized planets, powered by the intense irradiation from the host star, large modons reach planetary-scale in size and exhibit quasi-periodic life-cycles – chaotically moving around the planet, breaking and reforming many times over long durations (e.g. thousands of planet days). Additionally, the modons transport and mix planetary-scale patches of hot and cold air around the planet, leading to high-amplitude and quasi-periodic signatures in the disc-averaged temperature flux. Hence, they induce variations of the ‘hotspot’ longitude to either side of the planet’s substellar point – consistent with observations at different epochs. The variability behaviour in our simulations broadly underscores the importance of accurately capturing vortex dynamics in extrasolar planet atmosphere modelling, particularly in understanding current observations.