Large‐scale energy budget of impulsive magnetic reconnection: Theory and simulation

• Published in: Journal of geophysical research. Space physics 2017-03, Vol.122 (3), p.3212-3231
• Main Authors: Kiehas, S. A., Volkonskaya, N. N., Semenov, V. S., Erkaev, N. V., Kubyshkin, I. V., Zaitsev, I. V.
• Format: Article
• Language: English
• Subjects: Balances (scales); Budgeting; Budgets; Compressibility; Compressing; Computational fluid dynamics; Computer simulation; Direct power generation; Energy; Energy balance; Energy budget; Energy budgets; Energy conversion efficiency; Energy management; Kinetic energy; Kinetics; Magnetic fields; Magnetic Reconnection; Magnetic Storms; Magnetic Storms and Substorms; Magnetohydrodynamics; Magnetospheric Physics; Mathematical analysis; Mathematical models; Natural Hazards; Numerical simulations; Outflow; Plasma; plasma physics; Solar Physics, Astrophysics, and Astronomy; Space Plasma Physics; Space Weather; Substorms; Thermal energy; Time dependence; Wakes
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1002/2016JA023169

We evaluate the large‐scale energy budget of magnetic reconnection utilizing an analytical time‐dependent impulsive reconnection model and a numerical 2‐D MHD simulation. With the generalization to compressible plasma, we can investigate changes in the thermal, kinetic, and magnetic energies. We study these changes in three different regions: (a) the region defined by the outflowing plasma (outflow region, OR), (b) the region of compressed magnetic fields above/below the OR (traveling compression region, TCR), and (c) the region trailing the OR and TCR (wake). For incompressible plasma, we find that the decrease inside the OR is compensated by the increase in kinetic energy. However, for the general compressible case, the decrease in magnetic energy inside the OR is not sufficient to explain the increase in thermal and kinetic energy. Hence, energy from other regions needs to be considered. We find that the decrease in thermal and magnetic energy in the wake, together with the decrease in magnetic energy inside the OR, is sufficient to feed the increase in kinetic and thermal energies in the OR and the increase in magnetic and thermal energies inside the TCR. That way, the energy budget is balanced, but consequently, not all magnetic energy is converted into kinetic and thermal energies of the OR. Instead, a certain fraction gets transfered into the TCR. As an upper limit of the efficiency of reconnection (magnetic energy → kinetic energy) we find ηeff=1/2. A numerical simulation is used to include a finite thickness of the current sheet, which shows the importance of the pressure gradient inside the OR for the conversion of kinetic energy into thermal energy. Key Points Grad P inside plasma outflow region reduces kinetic energy and enhances thermal energy Wake region and TCR must be considered for full energy balance Reconnection acts as a refrigerator