# Collaborative Research: GEM--Quantifying the Contribution of Off-Equatorial Ultra-Low Frequency (ULF) Waves on Radial Diffusion in the Radiation Belts

> **NSF 01002324DB NSF RESEARCH & RELATED ACTIVIT** · Regents of the University of Michigan - Ann Arbor (MI) · $118,893

## Abstract

Electromagnetic waves with frequencies in the ultra-low frequency (ULF) range are known to be among the leading causes of radial diffusion and transport of energetic electrons in Earth's radiation belts.   The frequencies of ULF waves overlap with the range of drift frequencies of energetic electrons as they circle the Earth, leading to resonant interactions.  Numerous expressions have been derived to quantitatively describe radial diffusion so that they can be incorporated into global models of radiation belt electrons.  However, most expressions of the radial diffusion rates are derived only for equatorially mirroring electrons and are based on estimates of the power of ULF waves that are obtained either from spacecraft close to the equatorial plane or from the ground.  Recent studies using the Van Allen Probes and Arase have shown that the wave power in magnetic fluctuations is significantly enhanced away from the magnetic equator, consistent with models simulating the natural modes of oscillation of magnetospheric field lines.  This has significant implications for the estimation of radial diffusion rates, as higher pitch angle electrons will experience considerably higher ULF wave fluctuations than equatorial electrons.  This project will derive the magnetic and electric field wave powers and incorporate them into the 3D test particle simulations to estimate the diffusion coefficient.  The novel, pitch-angle-dependent diffusion rates will be introduced to a global model

## Key facts

- **NSF award ID:** 2534683
- **Awardee organization:** Regents of the University of Michigan - Ann Arbor (MI)
- **SAM.gov UEI:** GNJ7BBP73WE9
- **PI:** Weichao Tu
- **Primary program:** 01002324DB NSF RESEARCH & RELATED ACTIVIT
- **All programs:** EXP PROG TO STIM COMP RES
- **Estimated total:** $118,893
- **Funds obligated:** $118,893
- **Transaction type:** Standard Grant
- **Period:** 09/01/2025 → 05/31/2027

## Primary source

NSF Award Search: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2534683

## Citation

> US National Science Foundation, Award 2534683, Collaborative Research: GEM--Quantifying the Contribution of Off-Equatorial Ultra-Low Frequency (ULF) Waves on Radial Diffusion in the Radiation Belts. Retrieved via AI Analytics 2026-06-06 from https://api.ai-analytics.org/grant/nsf/2534683. Licensed CC0.

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