Observation of Whistler Mode Waves Inside Mirror Mode Structures in the Earth's Outer Magnetosphere

Abstract

AbstractWhistler mode waves are commonly observed inside mirror mode structures (MM‐Ss) in the magnetosheath. Although MM‐Ss have also been detected in the magnetosphere, there is no statistical study investigating the properties of whistler mode waves inside MM‐Ss. Using Magnetospheric Multiscale (MMS) satellites, our present study identifies and statistically analyzes whistler mode waves detected inside MM‐Ss in the Earth's magnetosphere. Both the observational evidence (bidirectional propagation) and theoretical analyses suggest that whistler mode waves are excited in the low‐magnetic‐field regions of MM‐Ss. Statistical results indicate that whistler mode waves are frequently observed inside the MM‐Ss in the dusk sector. Most of these waves (>70%) are in the frequency range of 0.1–0.4 fce and have amplitudes less than ∼50 pT. Moreover, most of them are observed to propagate in the direction both parallel and antiparallel to the background magnetic field, and their wave normal angles are typically less than ∼40°. Our study analyzes the properties and generation of whistler mode waves inside MM‐Ss and reveals that MM‐Ss are a possible source region in the Earth's magnetosphere. Therefore, our study provides new insight into the properties of whistler mode waves inside MM‐Ss which are pervasive in space plasmas.