  Through the process of thermal ionization, intense stellar irradiation
renders Hot Jupiter atmospheres electrically conductive. Simultaneously,
lateral variability in the irradiation drives the global circulation with peak
wind speeds of order ~ km/s. In turn, the interactions between the atmospheric
flows and the background magnetic field give rise to Lorentz forces that can
act to perturb the flow away from its purely hydrodynamical counterpart. Using
analytical theory and numerical simulations, here we show that significant
deviations away from axisymmetric circulation are unstable in presence of a
non-negligible axisymmetric magnetic field. Specifically, our results suggest
that dayside-to-nightside flows, often obtained within the context of
three-dimensional circulation models, only exist on objects with anomalously
low magnetic fields, while the majority of highly irradiated exoplanetary
atmospheres are entirely dominated by zonal jets.
