Hot Jupiter atmospheric flows at high resolution

Abstract

ABSTRACT Global circulation models (GCMs) of atmospheric flows are now routinely used to interpret observational data on hot Jupiters. Localized ‘equatorial β-plane’ simulations have revealed that a barotropic (horizontal shear) instability of the equatorial jet appears at horizontal resolutions beyond those typically achieved in global models; this instability could limit wind speeds and lead to increased atmospheric variability. To address this possibility, we adapt the computationally efficient, pseudo-spectral PlaSim GCM, originally designed for Earth studies, to model hot Jupiter atmospheric flows and validate it on a reference benchmark. We then present high-resolution global models of HD209458b, with horizontal resolutions of T85 (128×256) and T127 (192×384). The barotropic instability phenomenology found in β-plane simulations is not reproduced in these global models, despite comparably high meridional resolutions. Nevertheless, high-resolution models do exhibit additional flow variability on long time-scales (of the order of 100 planet days or more), which is absent from the lower resolution models. It manifests as a breakdown of the north–south symmetry of the equatorial wind. By post-processing the atmospheric flows at various resolutions (assuming a cloud-free situation), we show that the stronger flow variability achieved at high resolution does not translate into noticeably stronger dayside infrared flux variability. More generally, our results suggest that high horizontal resolutions are not required to capture the key features of hot Jupiter atmospheric flows.