Magnetosphere Seminars

Magnetospheric Multiscale Observations of Magnetic Reconnection in the Earth’s Magnetosheath

Speaker:Rick Wilder [LASP]
Date:Tuesday, Nov 06, 2018
Location:LASP Space Science Building, room N100 (1st floor)

Seminar Abstract:

In 2015, NASA launched the Magnetospheric Multiscale (MMS) mission to study magnetic reconnection in the Earth’s magnetosphere, especially at the electron scale. Although the main focus of the first phase of the mission was on the dayside magnetopause, MMS has also encountered reconnection diffusion region events in the region of shocked solar wind that flows past the earth, known as the “magnetosheath.” Magnetosheath events are important because the reconnection is often symmetric and laminar. Additionally, the reconnecting current sheets are carried rapidly past the spacecraft by the magnetosheath flow. This makes the events simple to study compared to those at the magnetopause, which has highly variable motion. We will show several examples of diffusion region events observed in the magnetosheath, where the reconnecting magnetic fields have varying shear angles between them. We find that at low magnetic shear angle (anti-parallel reconnection), the electrons are agyrotropic, and the bulk of the energy conversion is due to electric fields and currents perpendicular to the background magnetic field. As the shear angle increases, magnetic reconnection quickly becomes dominated by parallel electric fields and currents, with the agyrotropy becoming less apparent. Additionally, in regions where the magnetosheath is turbulent, we will show magnetic reconnection events with an extremely high shear angle that appear to only affect the electrons. This “electron only” reconnection may be important for understanding the collisionless dissipation of energy in turbulence.