SM036-03
Kinetic instabilities in the shock transition region and magnetic reconnection in the Earth’s quasi-parallel bow shock

Monday, 14 December 2020: 19:08
Virtual
Naoki Bessho1,2, Li-Jen Chen3, Shan Wang1,3, Jonathan Ng4, Michael Hesse5 and Lynn B Wilson III6, (1)University of Maryland College Park, College Park, MD, United States, (2)NASA Goddard Space Flight Center, Greenbelt, United States, (3)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (4)University of Maryland College Park; NASA Goddard Space Flight Center, College Park, MD, United States, (5)University of Bergen, Space Plasma Physics Group, Bergen, Norway, (6)NASA Goddard Space Flight Center, Heliospheric Physics Laboratory, Code 672, Greenbelt, MD, United States
Recorded Presentation
Abstract:
In the Earth’s bow shock, a variety of waves can be excited by instabilities due to interactions between reflected ions and incident particles, and large-amplitude electromagnetic waves can result in producing current sheets. Space observations, including NASA’s Magnetospheric Multiscale (MMS), show that there are many current sheets in the shock transition region and the downstream region, and some of them show signatures of magnetic reconnection, which is a rapid energy release process from magnetic energy to particles’ energy. Reconnection may play an important role to heat and accelerate particles in the shock.

We study kinetic instabilities in the shock transition region that drive magnetic reconnection in quasi-parallel shocks, by means of 2-D particle-in-cell simulations with parameters similar to the Earth’s bow shock. In a high Alfven Mach number shock, we identify two types of waves: a long-wavelength mode whose wavelength is a few ion skin depths, and a short-wavelength mode whose wavelength is smaller than the ion skin depth. The former is a right-handed wave propagating toward the shock in the plasma rest frame, obliquely to the magnetic field, and due to a non-resonant ion-ion beam instability. The latter is a right-handed wave in the plasma rest frame, excited by a secondary instability due to electron beams accelerated by the electric field in the long-wavelength mode.

Magnetic reconnection is driven by these two types of waves, where magnetic field lines are bent and two opposite directional magnetic field lines contact together. The size of magnetic fluctuations due to the short-wavelength mode is on the order of ion skin depth or less. As a result, electron-only reconnection can occur, where electrons participate in reconnection but ions pass through the region without interacting with such small-scale structures.

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