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Analysis of Chorus Wave Power on Burst‐Mode Timescales During the Van Allen Probes Era.

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Title: Analysis of Chorus Wave Power on Burst‐Mode Timescales During the Van Allen Probes Era.
Authors: Black, R.1,2 (AUTHOR) rb894@exeter.ac.uk, Allanson, O.1,3 (AUTHOR), Meredith, N. P.2 (AUTHOR), Hillier, A.4 (AUTHOR), Hartley, D. P.5 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. May2026, Vol. 131 Issue 5, p1-30. 30p.
Subject Terms: Radiation belts, Electromagnetic waves, Plasma physics, Magnetospheric physics
Abstract: Interactions between whistler‐mode chorus waves and electrons are a key driver of dynamics in Earth's radiation belts. These global dynamics are often described using Fokker‐Planck diffusion models. Whilst, in many cases, such models effectively describe the large scale changes within the region, they often rely upon spatially and temporally averaged representations of the wave properties. However, observations have shown that whistler‐mode chorus can display large sub‐second powers that challenge model assumptions and potentially give rise to non‐diffusive processes. Here, we investigate the power of whistler‐mode chorus on sub‐second timescales using the high‐resolution data capture mode on the Van Allen Probes' Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS). We show that peak chorus power on sub‐second timescales is regularly larger than the corresponding spacecraft "survey" power by over a factor of 100. The work also explores the magnetospheric conditions under which the largest sub‐second power variability of chorus waves is observed, and we find that trends vary across different chorus frequency bands. Notably, the largest powers are observed in the lower‐band frequency range during active conditions and between 21:00–12:00 MLT, where >46% $\%$ of burst samples contain an instantaneous wave intensity that exceeds 2.25×104pT2 $2.25\times 1{0}^{4}\ p{T}^{2}$. Further, binning the lower‐band power by the ratio of plasma‐to‐gyrofrequency separates the waves into two distinct low and high variability populations. The results quantify sub‐second wave power variability that may influence energetic electron dynamics not currently captured in time‐averaged wave models. Plain Language Summary: Whistler‐mode chorus is an electromagnetic emission excited in Earth's magnetosphere that can interact with electrons in the outer radiation belt. Through such interactions, electrons can be accelerated, or scattered into the atmosphere. Over long timescales, the resulting global changes in the electron population are typically modeled as a diffusive process. The wave power spectrum is a key input to these models. However, spacecraft measurements show that chorus wave power can be intense and highly variable on short timescales. These features may not be captured in traditional wave statistics due to a variety of spatial and temporal averaging. Such intense and rapidly varying waves may also violate assumptions required for the diffusive framework, and can instead result in interactions with distinct particle responses. Using high‐resolution spacecraft data, we show that maximum chorus wave powers on short timescales can be orders of magnitude larger than those inferred from averaged spacecraft surveys. Under certain magnetospheric conditions, we also identify a population of waves for which up to half may violate assumptions in current radiation belt modeling. Our study motivates further work to investigate how the short‐timescale variability of chorus wave power could affect modeling of wave‐particle interactions. Key Points: Sub‐second chorus wave power in different frequency bands are investigated using the EMFISIS burst‐ and survey‐mode dataLower‐band power was largest during active times (AE > 300 nT) whilst power variability peaked at low fpe/fce ${f}_{pe}/{f}_{ce}$ (<5) across all activitiesLarge ratios of maximum burst‐to‐survey power were observed in lower‐band at low fpe/fce ${f}_{pe}/{f}_{ce}$ (<5), and upper‐band over all conditions [ABSTRACT FROM AUTHOR]
Copyright of Journal of Geophysical Research. Space Physics is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Analysis of Chorus Wave Power on Burst‐Mode Timescales During the Van Allen Probes Era.
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  Data: Interactions between whistler‐mode chorus waves and electrons are a key driver of dynamics in Earth&#39;s radiation belts. These global dynamics are often described using Fokker‐Planck diffusion models. Whilst, in many cases, such models effectively describe the large scale changes within the region, they often rely upon spatially and temporally averaged representations of the wave properties. However, observations have shown that whistler‐mode chorus can display large sub‐second powers that challenge model assumptions and potentially give rise to non‐diffusive processes. Here, we investigate the power of whistler‐mode chorus on sub‐second timescales using the high‐resolution data capture mode on the Van Allen Probes&#39; Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS). We show that peak chorus power on sub‐second timescales is regularly larger than the corresponding spacecraft &quot;survey&quot; power by over a factor of 100. The work also explores the magnetospheric conditions under which the largest sub‐second power variability of chorus waves is observed, and we find that trends vary across different chorus frequency bands. Notably, the largest powers are observed in the lower‐band frequency range during active conditions and between 21:00–12:00 MLT, where &gt;46% $\%$ of burst samples contain an instantaneous wave intensity that exceeds 2.25&#215;104pT2 $2.25\times 1{0}^{4}\ p{T}^{2}$. Further, binning the lower‐band power by the ratio of plasma‐to‐gyrofrequency separates the waves into two distinct low and high variability populations. The results quantify sub‐second wave power variability that may influence energetic electron dynamics not currently captured in time‐averaged wave models. Plain Language Summary: Whistler‐mode chorus is an electromagnetic emission excited in Earth&#39;s magnetosphere that can interact with electrons in the outer radiation belt. Through such interactions, electrons can be accelerated, or scattered into the atmosphere. Over long timescales, the resulting global changes in the electron population are typically modeled as a diffusive process. The wave power spectrum is a key input to these models. However, spacecraft measurements show that chorus wave power can be intense and highly variable on short timescales. These features may not be captured in traditional wave statistics due to a variety of spatial and temporal averaging. Such intense and rapidly varying waves may also violate assumptions required for the diffusive framework, and can instead result in interactions with distinct particle responses. Using high‐resolution spacecraft data, we show that maximum chorus wave powers on short timescales can be orders of magnitude larger than those inferred from averaged spacecraft surveys. Under certain magnetospheric conditions, we also identify a population of waves for which up to half may violate assumptions in current radiation belt modeling. Our study motivates further work to investigate how the short‐timescale variability of chorus wave power could affect modeling of wave‐particle interactions. Key Points: Sub‐second chorus wave power in different frequency bands are investigated using the EMFISIS burst‐ and survey‐mode dataLower‐band power was largest during active times (AE &gt; 300 nT) whilst power variability peaked at low fpe/fce ${f}_{pe}/{f}_{ce}$ (&lt;5) across all activitiesLarge ratios of maximum burst‐to‐survey power were observed in lower‐band at low fpe/fce ${f}_{pe}/{f}_{ce}$ (&lt;5), and upper‐band over all conditions [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
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  Data: &lt;i&gt;Copyright of Journal of Geophysical Research. Space Physics is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder&#39;s express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.&lt;/i&gt; (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
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        Value: 10.1029/2026JA035082
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      – Code: eng
        Text: English
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        Type: general
      – SubjectFull: Electromagnetic waves
        Type: general
      – SubjectFull: Plasma physics
        Type: general
      – SubjectFull: Magnetospheric physics
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      – TitleFull: Analysis of Chorus Wave Power on Burst‐Mode Timescales During the Van Allen Probes Era.
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              Text: May2026
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