Kinetic features of explosive energy conversion and dissipation in magnetotail dipolarizations
Abstract
The Earth's magnetosphere is a unique natural laboratory of fully collisionless plasmas. Its magnetotail is particularly significant because it accumulates the energy of the solar wind/ magnetosphere interaction and then releases it in the form of substorms, pseudobreakups, bursty bulk flows and dipolarization fronts. The Magnetospheric MultiScale (MMS) mission provides for the first time a critical opportunity to investigate energy conversion in these dipolarization processes in collisionless plasmas, because it enables measurements of 3D vectors of electric and magnetic fields, ion and electron bulk flow velocities, pressure tensor components, and, crucially, their spatial derivatives. However, dissipation in collisionless plasmas cannot be described by the standard resistive MHD parameter, the Joule heating rate, because that fluid parameter cannot distinguish between ion and electron dissipation. Here, using 3D PIC simulations of the magnetotail current sheet, we describe plasma dissipation accompanying tail dipolarization in terms of new kinetic measures different for ions and electrons: the pressure dilatation, as well as the double contraction of deviatoric pressure tensor and traceless strain-rate tensor. Simulations show signatures of dissipation both near new X-lines and near dipolarization fronts, which may form before the magnetic topology change. Dissipation patterns are different for ions and electrons and they reveal characteristic striation features on the scales of the lower hybrid drift instability. We also discuss manifestations of these theoretically predicted features in MMS observations.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E3164S