Exploring the Effects of Active Magnetic Drag in a GCM of the Ultra-Hot Jupiter WASP-76b

TL;DR

This study models the impact of spatially varying magnetic drag on the atmospheric circulation of ultra-hot Jupiter WASP-76b, revealing significant effects on observable phase curves and emphasizing the importance of detailed magnetic treatments.

Contribution

It introduces a locally calculated active magnetic drag approach in a GCM for WASP-76b, improving upon previous uniform drag models and highlighting the spatial dependence of magnetic effects.

Findings

Magnetic effects are strongest in the upper atmosphere.

Magnetic drag reduces hotspot offset and increases flux contrast.

Models suggest a magnetic field of at least 3 G for WASP-76b.

Abstract

Ultra-hot Jupiters represent an exciting avenue for testing extreme physics and observing atmospheric circulation regimes not found in our solar system. Their high temperatures result in thermally ionized particles embedded in atmospheric winds interacting with the planet's interior magnetic field by generating current and experiencing bulk Lorentz force drag. Previous treatments of magnetic drag in 3D General Circulation Models (GCMs) of ultra-hot Jupiters have mostly been uniform drag timescales applied evenly throughout the planet, which neglects the strong spatial dependence of these magnetic effects. In this work, we apply our locally calculated active magnetic drag treatment in a GCM of the planet WASP-76b. We find the effects of this treatment to be most pronounced in the planet's upper atmosphere, where strong differences between the day and night side circulation are present. These circulation effects alter the resulting phase curves by reducing the hotspot offset and increasing the day-night flux contrast. We compare our models to Spitzer phase curves which imply a magnetic field of at least 3 G for the planet. We additionally contrast our results to uniform drag timescale models. This work highlights the need for more careful treatment of magnetic effects in atmospheric models of hot gas giants.