Analytic expressions for ULF wave radiation belt radial diffusion coefficients

Area of Science:

• Space Physics
• Plasma Physics
• Geophysics

Background:

• Radiation belts are crucial regions of energetic charged particles trapped by Earth's magnetic field.
• Understanding particle dynamics, particularly radial diffusion, is key to predicting radiation belt behavior.
• ULF and chorus waves are significant drivers of radiation belt dynamics.

Purpose of the Study:

• To derive and present analytic expressions for ULF wave-driven radial diffusion coefficients.
• To incorporate these coefficients into global radiation belt transport models.
• To validate the new coefficients against observational data and assess their predictive capability.

Main Methods:

• Derived diffusion coefficients from statistical ULF wave power, electric field power (from ground magnetometers), and compressional magnetic field power (from in situ measurements).
• Developed 1-D radial diffusion simulations using CRRES-observed energy spectra and empirical chorus wave loss terms.
• Compared simulation results with CRRES observations of differential electron flux.

Main Results:

• Analytic expressions for radial diffusion coefficients as a function of L and Kp were established.
• Diffusion coefficients were found to be largely independent of particle energy.
• 1-D model simulations showed excellent agreement with CRRES observations of 0.976 MeV electron flux.

Conclusions:

• The derived analytic expressions for radial diffusion coefficients are crucial for accurate radiation belt modeling.
• The electric field diffusion coefficient is dominant over the magnetic diffusion coefficient.
• Models driven by geomagnetic indices like Kp show significant promise for space radiation belt specification.