Source of the dayside cusp aurora.

Area of Science:

• Space Physics
• Auroral Physics
• Magnetospheric Physics

Background:

• Monochromatic all-sky imagers in Antarctica monitor auroral activity.
• The Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission studies magnetospheric dynamics.

Purpose of the Study:

• To investigate the origin of dayside cusp aurora using coordinated satellite and ground-based observations.
• To determine the relationship between magnetopause crossings and ionospheric auroral emissions.

Main Methods:

• Coordinated observations from Antarctic imagers and THEMIS satellites.
• Magnetic field and plasma density measurements from THEMIS.
• Ionospheric mapping using the Tsyganenko-96 field model.

Main Results:

• Dayside cusp aurora (630 nm) is confirmed to be on open field lines, originating from magnetosheath precipitation.
• Structured N2+ (427.8 nm) emissions indicate particle acceleration.
• Magnetosheath particle energy and density correlate with N2+ emission intensity.
• Dispersive Alfvén waves are the likely electron acceleration mechanism.

Conclusions:

• Dayside cusp aurora is a direct consequence of magnetosheath particle precipitation onto open field lines.
• Particle acceleration, likely by dispersive Alfvén waves, is crucial for generating observed auroral emissions.
• A distinct hard-electron precipitation zone at lower latitudes originates within the magnetosphere.