Rapid Magnetotail Reconfiguration and Ion‐Scale Wave Activity at Mercury

Abstract

Mercury's magnetosphere is an extremely dynamic environment, where substorm‐like activity, including dipolarization fronts and particle acceleration, periodically disrupts the stability and radial extent of the closed field line region. The common narrowband ∼1 Hz waves at Mercury, near the local proton gyrofrequency are preferentially observed on closed field lines during quieter intervals, but their relationship to magnetospheric dynamics remains poorly understood. Here, we combine MESSENGER data sets of ∼1 Hz wave activity and dipolarization fronts to investigate whether newly closed field lines can sustain wave growth. We find that ∼1 Hz waves on the nightside are systematically absent during orbits with dipolarization intervals and typically confined within 1.3 R _M , compared to greater downtail extents during quiet intervals. The results indicate that ∼1 Hz waves require long‐lived, stable closed field lines to grow; therefore, when they are observed, they can serve as diagnostics of Mercury's magnetospheric state, establishing a clear connection between field‐line history, magnetospheric dynamics, and wave occurrence in Mercury's magnetotail.