Electron Energy Partition across Interplanetary Shocks. I. Methodology and Data Product

Area of Science:

• Space Physics
• Plasma Physics
• Astrophysics

Background:

• Electron velocity distribution functions (VDFs) are crucial for understanding plasma behavior in space.
• Interplanetary (IP) shocks are significant events that accelerate particles and modify plasma properties.
• Previous models often used bi-Maxwellian functions to describe electron distributions.

Purpose of the Study:

• To statistically analyze electron VDFs near IP shocks using the Wind spacecraft data.
• To compare the fitting accuracy of different VDF models, specifically self-similar versus bi-Maxwellian, for core electron populations.
• To quantify the parameters of these distributions and their implications for particle scattering.

Main Methods:

• Analyzed 15,314 electron VDFs within ±2 hours of 52 IP shocks observed by the Wind spacecraft.
• Fitted VDFs to a sum of three model functions: cold dense core, hot tenuous halo, and field-aligned beam/strahl.
• Investigated bi-kappa, symmetric/asymmetric bi-self-similar, and bi-Maxwellian models for the core component.

Main Results:

• Self-similar VDF models provided a better fit for core electrons than bi-Maxwellian models under all conditions studied.
• Bi-kappa VDFs were found to be optimal for both halo and beam/strahl components.
• Provided quartile ranges for kappa exponents (κ_ec, κ_eh, κ_eb) and self-similar exponents (s_ec, p_ec, q_ec).

Conclusions:

• The deviation of self-similar distributions from Maxwellian distributions indicates inelastic particle scattering.
• This study is the first to statistically demonstrate the superiority of self-similar VDFs for core electrons near IP shocks.
• The findings offer insights into particle scattering mechanisms and plasma turbulence in the heliosphere.