Numerical dissipation strongly affects the equatorial jet speed in simulations of hot Jupiter atmospheres

ABSTRACT Hot Jupiters are tidally locked gaseous exoplanets with atmospheric circulations dominated by a super-rotating equatorial jet. Their global circulation is often studied simulations in 3D general models (GCMs). Energy builds up at the smallest scales these and must be dissipated. Many use ‘hyperdiffusion’ for this, which applies tendency to prognostic variables based on high-order Laplacian operator. This removes unrealistic unstable build-up of energy small scales, ideally does not affect large-scale circulation. In this study, we show that hyperdiffusion can fact hot Jupiters. These planets have large velocity gradients, so produce momentum may largest scales. We analyse four different parameters GCM THOR. zonal budget as strongly physical forcing. The slows down spreads out jet, reducing its speed more than $50{{\ \rm per\ cent}}$ some levels. from GCMs MITgcm Exo-FMS compare effects their dissipation methods. drag jet due reduced using weaker coefficient, higher resolution, or order diffusion. aim provide basis study investigate ‘real’ shows need examine long-held modelling assumptions when studying novel exoplanets.