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Accueil > A propos du LPP > Communication > Actualités archivées > 2025 > A new approach to investigate turbulent wave processes in the solar wind

A new approach to investigate turbulent wave processes in the solar wind

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Interactions between energetic electron beams and coronal/solar wind plasmas are at the origin of various processes of turbulent waves’ transformations and electromagnetic radiation during solar radio bursts of types II and III. The properties of electrostatic wave turbulence excited by electron beams in randomly inhomogeneous and weakly magnetized solar wind plasmas can be evidenced by studying the statistics of Langmuir and upper-hybrid waves’ electric fields’ amplitudes. This can provide key information on linear and nonlinear processes developing in turbulent plasmas. Nowadays, modern spacecraft such as Solar Orbiter and Parker Solar Probe provide the unique opportunity to study the characteristics of electric field distributions directly using the waveforms measured in the solar wind.


Panel (a) : β-distributions of the PDFs of ∣𝐸∣ and log∣𝐸∣² as a function of the square of skewness (β1) and the kurtosis (β2), for waveforms provided by the RPW-TDS receiver on board Solar Orbiter, with the sampling rate 262 kHz (January 17, 2023). Contour boundaries of the β-distributions obtained using waveforms provided by a simulation performed in a randomly inhomogeneous and magnetized plasma with Δ𝑁 = 0.025 and Ω = 0.01 are superimposed ; black and cyan contours correspond to the β-distributions of the PDFs of log∣𝐸∣² and ∣𝐸∣, respectively.
Panel (b) : Example of PDFs measured by Solar Orbiter (green dots) and calculated by the simulation (red lines) at positions in the (β1,β2)-diagram in (a) indicated by a black dot (log∣𝐸∣²) and a black star (∣𝐸∣), respectively (see legend).

In the present work, we study the statistical properties of beam-driven upper-hybrid wave turbulence in the solar wind by focusing on the probability density functions (PDFs) of electric field amplitudes |E|. For the first time, high-resolution and long-term 2D particle-in-cell simulations are carried out to analyze correlations between the skewness (degree of anisotropy) and the kurtosis (degree of flatness) of the PDFs of |E| and log|E|2, for various intensities of the plasma magnetization ratio Ω=ωc/ωp and average levels of random density fluctuations ΔN. Electric field distributions log |E|2 and |E| are shown to be in good agreement with typical distributions obtained from the Time Domain Sampler subunit installed on the Solar Orbiter spacecraft. Results demonstrate the promising potential of this method for investigating wave turbulent processes in plasmas, as well as for detecting and classifying interesting events in satellite datasets.

We would like to thank the Smilei development team for their code and support, as well as the Solar Orbiter RPW and TDS teams for their observations.

Reference : Statistical properties of beam-driven upper-hybrid wave turbulence in the solar wind, V. Annenkov, C. Krafft, A. Volokitin, P. Savoini, A&A 699 L6 (2025), https://doi.org/10.1051/0004-6361/202555087

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CNRS Ecole Polytechnique Sorbonne Université Université Paris-Saclay Observatoire de Paris
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