Identifying magnetotail jet fronts in a 6D global hybrid-Vlasov simulation

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. Both phenomena affect energy distribution and flux transport in the magnetotail.

We demonstrate novel methods of identifying BBFs and DFs in a 3D global magnetospheric simulation and present results for multiple case studies. BBFs and DFs are searched for in a simulation conducted using Vlasiator, a global magnetospheric hybrid-Vlasov code where ions are modeled using distribution functions and electrons are treated as a charge-neutralizing fluid. DFs are identified using a magnetic field time derivative threshold dB_z /dt > 0.35 nT/s. BBFs are defined based on a velocity threshold, and they are studied on a case-by-case basis. Tailward DFs (anti-dipolarization fronts) are found at magnetic islands, while earthward DFs are mostly seen in finger-like structures of high earthward bulk velocity alongside BBFs. Signatures registered as BBFs in spacecraft view also originate due to moving reconnection locations and movement of the current sheet within the CPS 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. The findings may help with interpreting satellite observations in the magnetotail.