Science Seminars

The Temperature Anisotropy Regulation in the Earth’s Magnetosheath: MMS Observations and PIC Simulations

Speaker: Narges Ahmadi (LASP)
Date: Thursday, Nov 29, 2018
Time: 4:00 PM
Location: SPSC W120

Seminar Abstract:

The proton mirror mode is one of the most prevalent instabilities found behind the shocks of celestial bodies, such as comets, planets, and stars. Near Earth, the quasi-perpendicular bow shock heats protons in the direction perpendicular to the magnetic field, creating a temperature anisotropy that generates mirror mode structures in the downstream region. Mirror modes form as compressional peaks or holes along the background magnetic field and they compete with proton cyclotron waves to consume the free energy in the magnetosheath. In late stages of their evolution, mirror mode structures take the form of magnetic holes that trap particles via the mirror force.The Magnetospheric Multiscale mission has observed electron whistler waves at the center and at the edges of mirror mode magnetic holes. We examine the growth mechanisms of these whistler waves and their interaction with the host magnetic hole. In the observations, as magnetic holes develop and get deeper, an electron population gets trapped and develops a temperature anisotropy favorable for whistler waves to be generated. To investigate this process, we used expanding box particle-in-cell simulations to produce the mirror instability, which then evolve into magnetic holes. The simulation shows that whistler waves can be generated at the center and edges of magnetic holes, which reproduces the primary features of the MMS observations. Our research into the cross-scale energy coupling within mirror mode waves elucidates how energy flow occurs between waves and plasma and how it can cascade from ion to electron scales.​