Langmuir and Upper Hybrid Waves Behind Dipolarization Fronts

Abstract Dipolarization fronts (DFs), ion‐scale magnetic‐dipolar transients in the magnetotail, are favorable regions for the generation of various types of plasma waves, which are important for energy transport and dissipation in the magnetosphere. The plasma waves hitherto reported near the DFs are typically low‐frequency (lower than electron cyclotron frequency) modes. Here, we report MMS observations of high‐frequency waves, including Langmuir and upper hybrid waves near the electron plasma frequency, inside flux pileup regions behind the DFs. Using MMS high‐cadence data, we revealed that the Langmuir waves were possibly generated by local electron beams and rapidly thermalized the beams, and the upper hybrid waves, which were associated with perpendicularly anisotropic electrons, may propagate from other regions. These waves can drive localized energy transfer and accelerate local electrons at a rate of ∼1.5 eV/s, indicating that the high‐frequency waves can play a role in wave‐particle energy transfer near the DFs.