Browsing by Subject "hybrid-Vlasov simulation"

The Sun's corona is constantly releasing a stream of charged particles known as the solar wind. When the solar wind interacts with Earth's magnetic field, it drags the field lines forming a magnetic tail behind Earth. This magnetotail hosts a process called magnetic reconnection, which converts magnetic energy into plasma heating, plasma kinetic energy and particle acceleration. Reconnection occurs at magnetic structures called X-lines. Magnetic reconnection is thought to be responsible for creating bursty bulk flows (BBFs), short-lived plasma velocity increases in the magnetotail's central plasma sheet region. In satellite measurements, BBFs are seen as minute-timescale velocity increases along Earth-Sun direction. Closely related to BBFs are dipolarization fronts (DFs), sudden increases in $B_z$, the magnetic field component aligned with Earth’s magnetic dipole axis. Despite their short timescales, both phenomena greatly affect the energy distribution and flux transport within the magnetotail. The three-dimensional nature of BBFs and DFs is studied using Vlasiator, a simulation code utilizing a hybrid-Vlasov approach where ions are modelled using distribution functions and electrons are treated as a charge-neutralizing fluid. DFs are identified using a magnetic field 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. DFs moving away from Earth are found at magnetic islands that form between multiple X-lines, while DFs moving earthward are mostly seen in finger-like structures of high earthward velocity. BBFs matching satellite observations are also seen at the same structures. Events registered as BBFs in simulated satellite measurements also originate from other sources, including magnetic reconnection at multiple X-lines, movement of reconnecting X-lines and vertical movement of a current sheet within the central plasma sheet. Most DFs are accompanied by velocity increases, but BBFs often result in only small magnetic field enhancements. The results imply that there are multiple different types of dipolarization fronts, and similar satellite measurements of bursty bulk flows can arise from different physical phenomena. The certainty of the results is reduced by low magnetic field variations in the simulation compared to spacecraft measurements and a small DF dataset. The findings may still help with interpreting satellite observations in the magnetotail.