Fluid-Kinetic Variations in the Storm-Time Inner Magnetosphere

Area of Science:

• Space Physics
• Plasma Physics
• Geophysics

Background:

• Earth's inner magnetosphere is characterized by a dipolar field, while the plasma sheet exhibits stretched magnetic field lines.
• Storm-time variations in electromagnetic fields occur at the interface of these distinct magnetospheric regions.
• Understanding these variations is crucial for comprehending energy transfer and particle dynamics during geomagnetic storms.

Purpose of the Study:

• To decompose storm-time broadband electromagnetic field variations into fundamental fluid-kinetic and wave modes.
• To analyze the spectral characteristics and spatial structures of these wave modes.
• To investigate potential coupling or conversion mechanisms between different wave modes.

Main Methods:

• Decomposition of electromagnetic field variations using model eigen-vectors.
• Analysis of full Van Allen Probes fields measurements.
• Examination of wave properties across a broad spectrum of scales, including the kinetic range.

Main Results:

• Storm-time variations are a superposition of dispersive Alfvén waves, including fast and slow modes.
• Significant spectral energy densities are observed across various scales, extending into the kinetic range.
• Wave structures are often filamentary, lacking a distinct perpendicular propagation direction, and exhibit coinciding phase speeds for fast and Alfvénic modes.

Conclusions:

• The observed field variations are complex, composed of a broad spectrum of wave modes.
• Mode coupling or conversion is suggested by the coinciding parallel phase speeds of fast and Alfvénic waves.
• These findings enhance our understanding of magnetospheric dynamics during geomagnetic storms.