Radial Diffusion Driven by Spatially Localized ULF Waves in the Earth's Magnetosphere

TL;DR

This study introduces a new model for radial diffusion driven by localized ULF waves in Earth's magnetosphere, showing that wave localization significantly impacts particle transport efficiency.

Contribution

It presents the first quasi-linear radial diffusion coefficient that accounts for MLT localization of ULF waves, highlighting the importance of wave localization in particle transport.

Findings

Localized ULF waves can enhance radial diffusion by 10-25%.

Diffusion efficiency varies with the extent of wave localization.

Waves covering more than 30% of MLT have similar effects as uniform waves.

Abstract

Ultra-Low Frequency (ULF) waves are critical drivers of particle acceleration and loss in the Earth's magnetosphere. While statistical models of ULF-induced radial transport have traditionally assumed that the waves are uniformly distributed across magnetic local time (MLT), decades of observational evidence show significant MLT localization of ULF waves in the Earth's magnetosphere. This study presents, for the first time, a quasi-linear radial diffusion coefficient accounting for localized ULF waves. We demonstrate that even though quasi-linear radial diffusion is averaged over drift orbits, MLT localization significantly alters the efficiency of particle transport. Our results reveal that when ULF waves cover more than 30\% of the MLT, the radial diffusion efficiency is comparable to that of uniform wave distributions. However, when ULF waves are confined within 10\% of the drift orbit, the diffusion coefficient is enhanced by 10 to 25\%, indicating that narrowly localized ULF waves are efficient drivers of radial transport.