Broadband Electrostatic Waves Behind Dipolarization Front: Observations and Analyses

Using high-resolution MMS data, we report the observations of broadband electrostatic waves associated with parallel electron temperature anisotropy (Te parallel to>Te perpendicular to ${T}_{e{\Vert} } > {T}_{e\perp }$) behind a dipolarization front (DF). These electrostatic waves include electrostatic solitary waves and electron cyclotron waves. To quantify electron anisotropy, we define the parallel flux anisotropy parameter Q=F parallel to/F perpendicular to-1 $Q={F}_{{\Vert} }/{F}_{\perp }-1$, where F $F$ is phase space densities at each energy. By performing correlation analyses between parallel flux anisotropies (Qs $Qs$) and power spectral densities (PSDs) of these waves, we find that: (a) Qs $Qs$ in 0.8-20 keV are positively correlated with the parallel electric field fluctuations in 50-3,000 Hz; (b) Qs $Qs$ in 0.8-20 keV are positively correlated with perpendicular electric field fluctuations in all frequency ranges; (c) the correlation between parallel flux anisotropies and perpendicular electric field fluctuations is more significant in this case. We also discuss the possibility of electron firehose instability and wave-particle interactions. Our study promotes the understanding of the properties and dynamics of DFs.