Identifying Magnetotail Jet Front Signatures in a 3D + 3V Global Hybrid-Vlasov Simulation

Abstract

Magnetic reconnection in Earth's magnetotail is thought to create bursty bulk flows (BBFs), short-lived plasma bulk velocity enhancements in the magnetotail's central plasma sheet (CPS) region. Closely related to BBFs are dipolarization fronts (DFs), sudden increases in $B_z$, the magnetic field component aligned with Earth's magnetic dipole axis. BBFs are involved in, for example, transport of energy and mass, and DFs contribute to for instance energy conversion processes and plasma acceleration. Both phenomena increase magnetic flux transport in the magnetotail. We demonstrate novel methods of identifying BBFs and DFs in 3D global magnetospheric simulations and present results for multiple case studies. We search for BBFs and DFs in a simulation conducted using the 3D global magnetospheric hybrid-Vlasov code Vlasiator. DFs are identified using a $B_z$ time derivative threshold, whereas BBFs are defined based on a velocity threshold. The tailward DF (anti-DF) identification criteria are fulfilled by tailward-propagating flux ropes, while earthward-propagating DFs are mostly seen in finger-like structures of high earthward bulk velocity alongside BBFs. We show that detections of fast flows meeting the BBF criteria in virtual spacecraft time series also originate due to moving reconnection locations and movement of the current sheet within the CPS region, while the reconnection outflow stays roughly constant. The results show that rapid $B_z$ variations in the simulation have multiple sources, and similar satellite measurements of BBFs can arise from different physical phenomena. Our findings may help with interpreting satellite observations in the magnetotail.