A comparative study of dipolarization fronts at MMS and Cluster.

Area of Science:

• Space Physics
• Magnetospheric Physics
• Plasma Physics

Background:

• Dipolarization fronts (DFs) are transient structures in planetary magnetospheres.
• Understanding DF dynamics is crucial for magnetospheric energy transport.
• Previous studies lacked comprehensive statistical analysis of DF velocities and properties.

Purpose of the Study:

• To statistically analyze the velocities and characteristics of dipolarization fronts.
• To compare DF properties observed by the MMS and Cluster spacecraft at different radial distances.
• To investigate the relationship between DF velocity and the magnetic field strength ahead of the fronts.

Main Methods:

• Utilized magnetic field data from the Magnetospheric Multiscale (MMS) and Cluster spacecraft.
• Assumed a semicircular cross-section for DFs and modeled their propulsion by magnetic tension.
• Employed multispacecraft observations to determine DF velocities and properties.

Main Results:

• Approximately 75% of DFs propagate earthward, while 25% move tailward.
• MMS, at closer radial distances (below 12 RE), observed faster DFs (∼57% > 150 km/s) compared to Cluster (∼35% below 20 RE).
• Higher DF velocities correlate with increased magnetic field (B) values ahead of the fronts, indicative of magnetic flux pileup.

Conclusions:

• DFs exhibit variable flux transport rates, increasing closer to Earth.
• The observed correlation between DF velocity and upstream magnetic field strength supports a 'snow plow' mechanism.
• These findings enhance our understanding of energy and flux transport within the Earth's magnetotail.