Broadband Electrostatic Waves Behind Dipolarization Front: Observations and Analyses

Abstract

Using high-resolution MMS data, we report the observations of broadband electrostatic waves associated with parallel electron temperature anisotropy ( 𝐴𝐴 𝐴𝐴𝑒𝑒‖ > 𝐴𝐴𝑒𝑒⟂ ) 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 𝐴𝐴 𝐴𝐴= 𝐹𝐹‖∕𝐹𝐹⟂ − 1 , where 𝐴𝐴 𝐴𝐴 is phase space densities at each energy. By performing correlation analyses between parallel flux anisotropies ( 𝐴𝐴 𝐴𝐴𝐴𝐴 ) and power spectral densities (PSDs) of these waves, we find that: (a)𝐴𝐴 𝐴𝐴𝐴𝐴 in 0.8-20 keV are positively correlated with the parallel electric field fluctuations in 50-3,000 Hz; (b) 𝐴𝐴 𝐴𝐴𝐴𝐴 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.Plain Language Summary Dipolarization fronts (DFs), the leading edge of the earthward high speed plasma jets in the Earth's magnetotail, are characterized by a sudden increase of northward magnetic field. It plays crucial roles in global flux transport and energy conversion during substorm. Behind DFs, there are various plasma waves related to the electron temperature anisotropies. For example, the whistler waves excited by perpendicular electron temperature anisotropy have been widely observed. However, few studies on the relationship between parallel electron temperature anisotropy and waves are reported behind DFs. In this study, using MMS data, we report the observations of broadband electrostatic waves associated with parallel electron temperature anisotropy behind a DF, and quantitatively investigate the correlation between parallel electron anisotropies and power spectral densities of these waves.

Retracted: New Types of Electron Pitch Angle Distributions on Mars: Funnel and Skirt Distributions

“…S. Fu et al, , 2013W. D. Fu et al, 2022;Guo, Fu, Cao, Yu, et al, 2021;He et al, 2022;Liu et al, 2019;Wang et al, 2019;Yu et al, 2022), however, the physical processes corresponding to these distributions in Martian system may be more complex due to the chaotic space environment of Mars (e.g., Artemyev et al, 2017;Bertucci et al, 2003;Fedorov et al, 2006;Wang et al, 2020;Weber et al, 2019).…”

Dipolarization Fronts in Cold‐Dense and Hot‐Tenuous Plasma Sheet Conditions: A Comparative Study

“…We can fit the high‐energy (>100 eV) electron distributions by using the Maxwellian models with [ N e , T e ] = [1.8 cm −3 , 174 eV] in omni direction, [1.7 cm −3 , 182 eV] in perpendicular direction, and [2.0 cm −3 , 173 eV] in parallel direction (see the blue dashed lines in Figures 3a–3c). Therefore, we can identify the low‐energy electrons (<100 eV), and high‐energy electrons (>100 eV) in this FPR as the cold population and thermal population, respectively, following previous studies (H. S.Fu et al., 2020a; H. S. Fu, Xu, Vaivads, & Khotyaintsev, 2019; Guo, Fu, Cao, Fan, et al., 2021; Guo, Fu, Cao, Yu, et al., 2021; Zhao et al., 2019). Clearly, the thermal population of FPR in CDPS manifested perpendicular temperature anisotropy ( T e ⊥ > T e // ), while the cold population manifested temperature isotropy, and the direct comparison of electron PSD in perpendicular and parallel direction showed the same results (Figure 4d).…”

“…S. Fu et al, 2014aH. S. Fu et al, , 2020bGrigorenko et al, 2020;Guo, Fu, Cao, Yu, et al, 2021;Hwang et al, 2014;Khotyaintsev et al, 2011;D. X. Pan et al, 2018;Yang et al, 2017;M.…”

Direct Evidence of Interchange Instabilities at Dipolarization Fronts

“…DFs are tangential discontinuity with typical thickness comparable to the ion inertial length (e.g., Fu et al., 2012b; Xu et al., 2018) and separate the hot and tenuous plasma from the ambient cold and dense plasma in the magnetotail (e.g., Fu et al., 2012a, 2012b, Fu, Cao, et al., 2013; Runov et al., 2009; Sergeev et al., 2009; Sitnov et al., 2009; Xu et al., 2019). Consequently, the strong gradient of fields and particles at the DFs provide free energy source for the excitement and development of various types of instabilities, such as magnetohydrodynamic (MHD) interchange instabilities (ICI) at MHD scale (e.g., Guzdar et al., 2010; Lapenta & Bettarini, 2011), kinetic interchange instabilities at ion/sub‐ion scales (e.g., Lin et al., 2014; Pritchett & Coroniti, 2010, 2013; Pritchett & Lu, 2018; Pritchett et al., 2014), anisotropy instabilities (e.g., Fu, Cao, Cully, et al., 2014; Fu, Cao, Zhima, et al., 2014; Fu, Chen, et al., 2020; Grigorenko et al., 2020; Guo et al., 2021; Huang et al., 2012; Khotyaintsev et al., 2011; Liu et al., 2017; Zhou et al., 2014), streaming instabilities (e.g., Hwang et al., 2014; Liu, Vaivads, 2019; Yang et al., 2017), and lower hybrid drift instabilities (e.g., Divin et al., 2015; Khotyaintsev et al., 2011; Liu, Fu, Vaivads, 2018; Pan et al., 2018). The PIC simulations shows that the kinetic ICI at DF can lead to the interpenetration of the hot and tenuous plasma and ambient cold and dense plasma and cause the planar surface of DF to become rippled, resulting in perturbations of the magnetic field, density, and electron flow at the front (Pritchett & Coroniti, 2010, Pritchett et al., 2014; Shustov et al., 2019).…”