Turbulence in the solar wind
| Quand ? |
Le 13/10/2025, de 11:00 à 12:00 |
|---|---|
| Où ? | Salle Condorcet |
| S'adresser à | Nicolas Plihon |
| Participants |
Olga Alexandrova |
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Solar wind is an excellent laboratory to study astrophysical plasma turbulence in a wide range of scales. Here, the plasma is very rarefied: the mean free path is of the order of 1 astronomical unit (au). Nevertheless, since the beginning of the space research, a turbulent cascade is observed at sub-collisional scales. The nature of the cascade and its dissipation are still under debate: is it plasma waves turbulence with resonant damping as dissipation mechanism, or a hydro-like strong turbulence? One of the inherent properties of a strong turbulence is intermittency, which is due to presence of coherent structures. Coherent structures are high amplitude events localized in space and living longer than any random fluctuation. Considering solar wind at 1 au, we find different types of structures, such as current sheets and Alfven vortices in fast solar wind (>500 km/s) and compressive vortices, magnetic holes, solitons and shocks in slow wind (~300 km/s). Their scale goes from fluid (MHD) to kinetic ion (~100 km) and electron (~1 km) scales. Closer to the Sun, from ~10 to 35 solar radii, signatures of intermittent events are also observed with NASA/Parker Solar Probe mission. A statistical study at 0.17 au shows presence of embedded coherent structures from MHD down to kinetic scales. Alfven vortices appear dominant at all scales and seems to be an important building bloc of solar wind turbulence. Regarding dissipation of electromagnetic cascade in the solar wind, we show spectral curvature at scales around the electron Larmor radius, indicating that this scale plays a role of the dissipation scale in nearly collisionless plasma.