Planetary Rotation Effects on Ionospheric Electrodynamics With Closed-Field, Magnetospherically Unforced Polar Caps: Earth-Parameterized Simulations With Implications for Jupiter and Saturn

Abstract

Ionospheric electrodynamics are classically governed by magnetic topology, with solar wind driving two-cell convection in open polar regions and neutral wind dynamo prevailing at closed lower latitudes. However, it remains unclear whether this paradigm applies to fast-rotating planets or Earth's state with extremely weak upstream conditions, where polar regions become largely closed. Global Earth-based simulations under closed-field, magnetospherically unforced polar cap conditions predict that the neutral wind dynamo generates a one-cell convection pattern in polar regions, a fundamental departure from the magnetospherically driven two-cell structure. The convection direction is primarily controlled by the pressure gradient from neutral temperature distributions and the Coriolis force, forming counterclockwise flow around high-latitude cold regions and clockwise around low-latitude warm regions in the Northern Hemisphere. Furthermore, faster planetary rotation suppresses dynamo efficiency through Coriolis-induced wind deceleration. These results establish a theoretical baseline for planetary atmospheric ion-neutral coupling without imposed magnetospheric forcing.