Deterministic chaos in modulated multi-cell drifts of localized lower-hybrid oscillations excited by high-frequency waves in the ionosphere
<p>The prominent broad upshifted maximum (BUM) feature in electromagnetic emissions stimulated by powerful high-frequency radio waves in the ionosphere exhibits an exponential spectrum for pump frequencies near a harmonic of the ionospheric electron gyro frequency. Exponential power spectra ar...
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-06-01
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| Series: | Annales Geophysicae |
| Online Access: | https://angeo.copernicus.org/articles/43/319/2025/angeo-43-319-2025.pdf |
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| Summary: | <p>The prominent broad upshifted maximum (BUM) feature in electromagnetic emissions stimulated by powerful high-frequency radio waves in the ionosphere exhibits an exponential spectrum for pump frequencies near a harmonic of the ionospheric electron gyro frequency. Exponential power spectra are a characteristic of deterministic chaos. In the present treatment, a two-fluid model is derived for lower-hybrid (LH) oscillations driven by parametric interaction of the electromagnetic pump field, the electron Bernstein mode, and the upper-hybrid mode, as previously proposed to interpret the BUM. In two-dimensional geometry across the geomagnetic field, LH oscillations localized in cylindrical density depletions are associated with multi-cell plasma drift patterns. The numerical simulations show that topological modulations of the drift can give rise to approximately Lorentzian-shaped pulses in the LH time signal. For parameter values typical of the ionospheric experiments, the exponential power spectrum of the Lorentzian pulses has a slope that is consistent with the slope of the BUM spectrum. The BUM spectral structure is therefore attributed to deterministic chaos in LH dynamics.</p> |
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| ISSN: | 0992-7689 1432-0576 |