Accurately specifying storm-time ULF wave radial diffusion in the radiation belts

TL;DR

This paper develops improved models for ULF wave-driven radial diffusion in the radiation belts by statistically analyzing 11 years of ground-based magnetometer data, highlighting the importance of Dst and Kp parameters.

Contribution

It introduces a combined Dst and Kp parameterization for ULF wave power, enhancing the accuracy of storm-time radial diffusion models in the radiation belts.

Findings

Kp is the best single parameter for ULF wave power specification.

High energy tails in ULF wave power are linked to Dst during storms.

Two-parameter models outperform single-variable models in representing radial diffusion.

Abstract

Ultra-low frequency (ULF) waves can contribute to the transport, acceleration and loss of electrons in the radiation belts through inward and outward diffusion. However, the most appropriate parameters to use to specify the ULF wave diffusion rates are unknown. Empirical representations of diffusion coefficients often use Kp; however, specifications using ULF wave power offer an improved physics-based approach. We use 11 years of ground-based magnetometer array measurements to statistically parameterise the ULF wave power with Kp, solar wind speed, solar wind dynamic pressure and Dst. We find Kp is the best single parameter to specify the statistical ULF wave power driving radial diffusion. Significantly, remarkable high energy tails exist in the ULF wave power distributions when expressed as a function of Dst. Two parameter ULF wave power specifications using Dst as well as Kp provide a better statistical representation of storm-time radial diffusion than any single variable alone.