Active auroral arc powered by accelerated electrons from very high altitudes

Area of Science:

• Space Physics
• Atmospheric Science
• Plasma Physics

Background:

• Auroral arcs are caused by energetic electrons colliding with atmospheric atoms.
• Electron acceleration typically occurs near the ionosphere, a few thousand kilometers above Earth.
• The precise altitude of this acceleration has remained uncertain.

Purpose of the Study:

• To determine the highest altitude at which electrons are accelerated to form auroral arcs.
• To investigate the spatial extent of the electron acceleration region responsible for auroras.

Main Methods:

• Utilized high-angular resolution electron data from the Arase satellite in the magnetosphere.
• Correlated satellite observations with ground-based all-sky imager data of auroral displays.
• Analyzed electron properties and dynamics during active auroral arc events.

Main Results:

• Demonstrated that electrons powering active auroral arcs are accelerated at altitudes exceeding 30,000 km.
• Observed electron acceleration characteristics consistent with known processes but at significantly higher altitudes.
• Identified the dominant auroral acceleration region extending far into the magnetosphere.

Conclusions:

• The primary region for auroral electron acceleration extends much higher than previously thought, reaching well into the magnetosphere.
• This discovery implies that unknown magnetospheric processes are responsible for generating the electric fields that accelerate electrons for auroras.
• Challenges existing models of aurora formation and highlights the need for further investigation into magnetospheric physics.