Deterministic chaos in modulated multi-cell drifts of localized lower-hybrid oscillations excited by high-frequency waves in the ionosphere.
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| Title: | Deterministic chaos in modulated multi-cell drifts of localized lower-hybrid oscillations excited by high-frequency waves in the ionosphere. |
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| Authors: | Leyser, Thomas B.1 (AUTHOR) thomas.leyser@irfu.se |
| Source: | Annales Geophysicae (ANGEO) (09927689). 2025, Vol. 43 Issue 1, p319-329. 11p. |
| Subject Terms: | *Geomagnetism, *Shortwave radio, *Electromagnetic interactions, *Radio waves, *Frequency spectra |
| Abstract: | 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. [ABSTRACT FROM AUTHOR] |
| Database: | Energy & Power Source |
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| Abstract: | 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. [ABSTRACT FROM AUTHOR] |
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| ISSN: | 09927689 |
| DOI: | 10.5194/angeo-43-319-2025 |
