Magnetotail Fast Flow Occurrence Rate and Dawn-Dusk Asymmetry at X_GSM ∼ -60 R_E

Area of Science:

• Space Physics
• Plasma Physics
• Geophysics

Background:

• Plasma sheet fast flows are key transporters of mass, flux, and energy in Earth's magnetotail.
• Previous studies were limited to regions closer to Earth (within -60 Earth radii) due to observational constraints.

Purpose of the Study:

• To statistically investigate the characteristics of earthward and tailward plasma flows at approximately 60 Earth radii downtail.
• To understand the spatial distribution and symmetry of magnetic reconnection in the magnetotail.

Main Methods:

• Utilized 5 years (2011-2015) of data from the ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moons Interaction with the Sun) mission.
• Analyzed flow velocities and directions, distinguishing between earthward, tailward, and convective flows.
• Correlated flow characteristics with geomagnetic activity levels (AL index).

Main Results:

• A significant fraction of observed fast flows (43-56%) are directed earthward at 60 Earth radii, indicating reconnection is probable on both near-Earth and midtail sides.
• Tailward convective flows exhibit a duskward asymmetry (over 60%), while earthward flows are symmetric during low activity and duskward asymmetric during high activity.
• The dawn-dusk asymmetry of flows becomes more pronounced downtail during high geomagnetic activity.

Conclusions:

• Magnetic reconnection occurs with similar probability on either side of 60 Earth radii downtail.
• The observed asymmetries in plasma flows are consistent with the asymmetric nature of tail reconnection, particularly during strong substorms.
• Near-Earth reconnection may favor the dusk sector, while midtail reconnection exhibits symmetry during weak substorms and duskward asymmetry during strong substorms.