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.