MMS Observations of Narrow-Band Quasi-Parallel Whistler Waves in the Flow Braking Region in Near-Earth Magnetotail

Abstract

This paper presents an analysis of wave activity recorded by the MMS satellites during a prolonged dipolarization in the near magnetotail (XGSM ~ –17 RE). It was found that multiple narrow-band, quasi-parallel whistler wave bursts were observed behind the leading front of dipolarization, during the phase of growth of the magnetic field’s BZ component. The durations of wave bursts were ~1–15 s, and the characteristic frequencies ranged from ~0.1 to 0.8 fc (fc is the electron gyrofrequency). Based on a detailed analysis of a single wave burst, it was found that the frequency corresponding to the maximum value of a linear increment of quasi-parallel whistler waves was close in magnitude to the observed frequency, which indicates the possibility of satellite location close to the source of waves. We also demonstrated that, in the case under discussion, the electrons with pitch angles of 125°–135° and energies of ~3–12 keV made a largest contribution to the increment of whistler waves. These observations have shown that, during dipolarizations, the thermal and suprathermal electron populations are most effectively involved in resonant interaction with whistler waves.