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Electron Kinetic Entropy across Quasi-Perpendicular Shocks
Martin Lindberg1, Andris Vaivads1, Savvas Raptis1
1Space and Plasma Physics, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, 114 28 Stockholm, Sweden.
Entropy (Basel, Switzerland)
|June 24, 2022
Summary
Researchers analyzed Magnetospheric Multiscale (MMS) data to understand electron kinetic entropy changes across Earth's bow shock. Findings show entropy increases at the shock, influenced by electron temperature and plasma beta, yielding an average adiabatic index of 1.64.
Area of Science:
- Space Physics
- Plasma Physics
- Astrophysics
Background:
- Earth's quasi-perpendicular bow shock is a critical magnetospheric boundary.
- Understanding particle behavior, like electron kinetic entropy, is key to shock dynamics.
Purpose of the Study:
- To investigate electron kinetic entropy per particle (Se) changes across Earth's bow shock using Magnetospheric Multiscale (MMS) data.
- To determine the relationship between entropy changes and shock conditions.
- To calculate the effective adiabatic index of electrons.
Main Methods:
- Analysis of 22 MMS bow shock crossings with calibrated electron distribution functions.
- Correction for spacecraft potential, secondary electrons, low-energy gaps, and plasma density.
- Correlation of entropy change (ΔSe) with electron temperature change (ΔTe) and upstream electron plasma beta (βe).
Main Results:
- All shock crossings showed a positive or zero increase in electron kinetic entropy (ΔSe).
- ΔSe strongly depends on ΔTe and βe, with larger ΔTe and smaller βe correlating with larger ΔSe.
- The average effective adiabatic index for electrons was determined to be ⟨γe⟩=1.64±0.07.
Conclusions:
- Electron kinetic entropy consistently increases across the quasi-perpendicular bow shock.
- Electron temperature and plasma beta are significant factors influencing entropy changes.
- The study provides a quantitative measure of electron adiabatic behavior at the bow shock.
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