Properties of suprathermal electrons associated with discrete auroral arcs

Abstract

We report on the properties of suprathermal electrons observed over three discrete auroral arcs from a sounding rocket. By applying shifted kappa distributions and analyzing kappa parameters (density, temperature, and kappa), we found three novel characteristics to provide clues to understand the auroral acceleration mechanisms and magnetosphere‐ionosphere coupling processes. First, the auroral potential drop was proportional to the inverse square of kappa, consistent with previous theoretical investigations by Dors and Kletzing (). The observed dependency was slightly stronger than their calculations, suggesting additional contributions from nonlinear plasma processes. Second, the polytropic relation showed nonadiabatic (near isothermal) state of the source electrons. This can provide a restriction on the pressure balance issues in the plasma sheet convection. Third, there was a clear difference in the polytropic and kappa indices for the first arc as opposed to the second and the third arcs, suggesting different source locations in the plasma sheet for the precipitating electrons that cause these nearby arcs.

Using Kappa Distributions to Identify the Potential Energy

“…In the presence of a nonzero potential, the system is characterized by a phase space kappa distribution of a Hamiltonian (e.g., Livadiotis et al, ; Livadiotis, , , Chap. 3; some other examples of using specific potential energy in kappa distributions are Du, ; Hau & Fu, ; Ogasawara et al, ), …”

“…1; the reviews Pierrard & Lazar, 2010;Livadiotis & McComas, 2013a;Livadiotis, 2015a, and references therein). In the presence of a nonzero potential, the system is characterized by a phase space kappa distribution of a Hamiltonian (e.g., Livadiotis, 2015b, 2017; some other examples of using specific potential energy in kappa distributions are Du, 2004;Hau & Fu, 2007;Ogasawara et al, 2017),…”

On the Simplification of Statistical Mechanics for Space Plasmas

“…In the continuous description, the kappa distribution of particle velocity is written as: (for f kinetic degrees of freedom). The argument φ q , which is related with the entropy as shown in Equation (35), is given by:…”

“…Kappa distributions were employed to describe numerous space plasma populations in: (i) the inner heliosphere, including solar wind [1][2][3][4][5][6][7][8][9][10][11][12][13], solar spectra [14,15], solar corona [16][17][18][19], solar energetic particles [20,21], corotating interaction regions [22], and related solar flares [23][24][25][26]; (ii) the planetary magnetospheres including the magnetosheath [27,28], near the magnetopause [29], magnetotail [30], ring current [31], plasma sheet [32][33][34], ionosphere [35], magnetospheric substorms [36], magnetospheres of giant planets, such as Jovian [37,38], Saturnian [39][40][41], Uranian [42], Neptunian [43], magnetospheres of planetary moons, such as Io [44] and Enceladus [45], or cometary magnetospheres ...…”

Derivation of the entropic formula for the statistical mechanics of space plasmas

“…) Kappa distributions describe numerous space plasma populations. Several examples are the following: (i) the inner heliosphere, including solar wind (e.g., Maksimovic et al, 1997;Pierrard et al, 1999;Mann et al, 2002;Marsch, 2006;Zouganelis, 2008;Štverák et al, 2009;Livadiotis and McComas, 2013a;Yoon, 2014;Pierrard and Pieters, 2015;Pavlos et al, 2016), solar spectra (e.g., Dzifčáková and Dudík, 2013;Dzifčáková, et al, 2015), solar corona (e.g., Owocki and Scudder, 1983;Vocks et al, 2008;Lee et al, 2013;Cranmer, 2014), solar energetic particles (e.g., Xiao et al, 2008;Laming et al, 2013), corotating interaction regions (e.g., Chotoo et al, 2000), and related solar flares (e.g., Mann et al, 2009;Livadiotis and McComas, 2013b;Bian et al, 2014;Jeffrey et al, 2016); (ii) planetary magnetospheres, including magnetosheath (e.g., Formisano et al, 1973;Ogasawara et al, 2013), magnetopause (e.g., Ogasawara et al, 2015), magnetotail (e.g., Grabbe, 2000), ring current (e.g., Pisarenko et al, 2002), plasma sheet (e.g., Christon, 1987;Wang et al, 2003;Kletzing et al, 2003), magnetospheric substorms (e.g., Hapgood et al, 2011), aurora (e.g., Ogasawara et al, 2017), magnetospheres of giant planets, such as Jovian (e.g., Collier and Hamilton, 1995;…”