Abstract
We report on evidence for the generation of an ultra-low frequency plasma wave by the drift-mirror plasma instability in the dynamic plasma environment of Earth's inner magnetosphere. The plasma measurements are obtained from the Radiation Belt Storm Probes Ion Composition Experiment onboard NASA's Van Allen Probes Satellites. We show that the measured wave-particle interactions are driven by the drift-mirror instability. Theoretical analysis of the data demonstrates that the drift-mirror mode plasma instability condition is well satisfied. We also demonstrate, for the first time, that the measured wave growth rate agrees well with the predicted linear theory growth rate. Hence, the in-situ space plasma observations and theoretical analysis demonstrate that local generation of ultra-low frequency and high amplitude plasma waves can occur in the high beta plasma conditions of Earth's inner magnetosphere.
Highlights
The drift-mirror (DM) plasma instability[1] and its significance for fundamental plasma physics have been discussed for several decades
We report on evidence for the generation of an ultra-low frequency plasma wave by the drift-mirror plasma instability in the dynamic plasma environment of Earth’s inner magnetosphere
The in-situ space plasma observations and theoretical analysis demonstrate that local generation of ultra-low frequency and high amplitude plasma waves can occur in the high beta plasma conditions of Earth’s inner magnetosphere
Summary
The drift-mirror (DM) plasma instability[1] and its significance for fundamental plasma physics have been discussed for several decades. We report conclusive evidence of the generation of a DM mode in the high beta plasma environment of Earth’s inner magnetosphere using data from NASA’s Van Allen Probes. Past studies have often observed wave-particle characteristics generally consistent with the DM instability, such as anticorrelations between wave and plasma pressure, but those satellite observations (in Earth’s inner magnetosphere) have generally failed to satisfy the instability condition and the wave growth rate has never been directly measured and corroborated. The conditions under which the mode is established in the deep inner magnetosphere have significant implications in ring current dynamics, because ULF modes can be involved with particle energization and diffusion.[1,6,9] Importantly, these results provide fundamental information on the physics of high beta plasmas that can only be obtained with modern in-situ measurements.
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