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<p>We investigate the occurrence characteristics and amplitude-frequency relationships of Pc5 ultra-low frequency (ULF) waves (1.67–6.7 mHz) using 30 years of GOES magnetic field data (1995–2025) from GOES-8 to GOES-18. An enhanced CLEAN algorithm, employing iterative Hanning peak model fitting and subtraction, identified 27,279 radial, 26,145 azimuthal, and 31,259 parallel wave events in the Mean Field-Aligned coordinate system. Radial and parallel waves exhibit peak amplitudes between 9–15 MLT, driven by solar wind dynamic pressure, while azimuthal and parallel components dominate in the 15–21 MLT sector, consistent with Kelvin-Helmholtz instability. Strong power-law relationships (<InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_20474_Article_IEq1.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="72" /> </InlineMediaObject> <EquationSource Format="TEX">\(R^2 \ge 0.85\)</EquationSource> </InlineEquation>) between amplitude and frequency are observed for radial and azimuthal components in dawn and dusk sectors, with weaker correlations for the parallel component (<InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_20474_Article_IEq2.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="72" /> </InlineMediaObject> <EquationSource Format="TEX">\(R^2 \le 0.24\)</EquationSource> </InlineEquation>). These relationships vary with solar wind conditions, with radial components showing robust power-law fits under strong and moderate conditions (<InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_20474_Article_IEq3.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="72" /> </InlineMediaObject> <EquationSource Format="TEX">\(R^2 \ge 0.93\)</EquationSource> </InlineEquation>). ULF wave occurrence rates peak during solar maxima, correlating strongly with solar wind parameters (<InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_20474_Article_IEq4.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="72" /> </InlineMediaObject> <EquationSource Format="TEX">\(R^2 \ge 0.73\)</EquationSource> </InlineEquation>), and exhibit quasi-biennial oscillations (QBOs)–short-term (1.5–4 year) modulations linked to solar dynamo processes. High-pass filtered data show strong correlations with dynamic pressure (<InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_20474_Article_IEq1.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="72" /> </InlineMediaObject> <EquationSource Format="TEX">\(R^2 \ge 0.85\)</EquationSource> </InlineEquation>). These findings resolve discrepancies in prior studies, highlighting the interplay of solar cycle, QBOs, and MLT-dependent drivers in Pc5 ULF wave dynamics, with implications for radiation belt dynamics and space weather forecasting.</p>

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Occurrence characteristics and amplitude-frequency relationship of the Pc5 ULF waves from 3 decades of GOES data

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  • 发表日期：

    2025年10月21日

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  • Fadil Inceoglu,
  • Paul T. M. Loto’aniu

摘要

We investigate the occurrence characteristics and amplitude-frequency relationships of Pc5 ultra-low frequency (ULF) waves (1.67–6.7 mHz) using 30 years of GOES magnetic field data (1995–2025) from GOES-8 to GOES-18. An enhanced CLEAN algorithm, employing iterative Hanning peak model fitting and subtraction, identified 27,279 radial, 26,145 azimuthal, and 31,259 parallel wave events in the Mean Field-Aligned coordinate system. Radial and parallel waves exhibit peak amplitudes between 9–15 MLT, driven by solar wind dynamic pressure, while azimuthal and parallel components dominate in the 15–21 MLT sector, consistent with Kelvin-Helmholtz instability. Strong power-law relationships ( \(R^2 \ge 0.85\) ) between amplitude and frequency are observed for radial and azimuthal components in dawn and dusk sectors, with weaker correlations for the parallel component ( \(R^2 \le 0.24\) ). These relationships vary with solar wind conditions, with radial components showing robust power-law fits under strong and moderate conditions ( \(R^2 \ge 0.93\) ). ULF wave occurrence rates peak during solar maxima, correlating strongly with solar wind parameters ( \(R^2 \ge 0.73\) ), and exhibit quasi-biennial oscillations (QBOs)–short-term (1.5–4 year) modulations linked to solar dynamo processes. High-pass filtered data show strong correlations with dynamic pressure ( \(R^2 \ge 0.85\) ). These findings resolve discrepancies in prior studies, highlighting the interplay of solar cycle, QBOs, and MLT-dependent drivers in Pc5 ULF wave dynamics, with implications for radiation belt dynamics and space weather forecasting.