Evidence of Langmuir/$\mathcal{Z}$-mode Wave Decay into $\mathcal{Z}$-mode Electromagnetic Radiation in the Solar Wind
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| Format: | Preprint |
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2026
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| _version_ | 1866908788862222336 |
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| author | Polanco-Rodríguez, F. J. Krafft, C. Savoini, P. |
| author_facet | Polanco-Rodríguez, F. J. Krafft, C. Savoini, P. |
| contents | The nonlinear decay of Langmuir/$\mathcal{Z}$-mode waves into electromagnetic $\mathcal{Z}$-mode wave radiation at the plasma frequency is observed for the first time in the solar wind. This finding was enabled by the unprecedented high-resolution electric and magnetic field measurements provided by the Radio Plasma Waves (RPW) instrument aboard the Solar Orbiter spacecraft, which encountered an electron beam associated with a Type III radio burst. The decay process is definitively identified through multiple lines of evidence: satisfaction of frequency and wavevector resonance conditions, strong phase coherence and temporal coincidence between the interacting waves, exclusion of competing mechanisms, and full agreement with theoretical predictions. Particle-in-cell simulations, conducted under close beam-plasma conditions, successfully reproduce the key features of the observations. Notably, they suggest that the wave packet observed by Solar Orbiter may be trapped within an extended, nearly flat-bottomed density well, where the decay process is not overcome by wave scattering on random density fluctuations and subsequent mode conversion effects. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2601_18495 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Evidence of Langmuir/$\mathcal{Z}$-mode Wave Decay into $\mathcal{Z}$-mode Electromagnetic Radiation in the Solar Wind Polanco-Rodríguez, F. J. Krafft, C. Savoini, P. Plasma Physics The nonlinear decay of Langmuir/$\mathcal{Z}$-mode waves into electromagnetic $\mathcal{Z}$-mode wave radiation at the plasma frequency is observed for the first time in the solar wind. This finding was enabled by the unprecedented high-resolution electric and magnetic field measurements provided by the Radio Plasma Waves (RPW) instrument aboard the Solar Orbiter spacecraft, which encountered an electron beam associated with a Type III radio burst. The decay process is definitively identified through multiple lines of evidence: satisfaction of frequency and wavevector resonance conditions, strong phase coherence and temporal coincidence between the interacting waves, exclusion of competing mechanisms, and full agreement with theoretical predictions. Particle-in-cell simulations, conducted under close beam-plasma conditions, successfully reproduce the key features of the observations. Notably, they suggest that the wave packet observed by Solar Orbiter may be trapped within an extended, nearly flat-bottomed density well, where the decay process is not overcome by wave scattering on random density fluctuations and subsequent mode conversion effects. |
| title | Evidence of Langmuir/$\mathcal{Z}$-mode Wave Decay into $\mathcal{Z}$-mode Electromagnetic Radiation in the Solar Wind |
| topic | Plasma Physics |
| url | https://arxiv.org/abs/2601.18495 |