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Accueil > A propos du LPP > Communication > Actualités archivées > 2023 > Ripples at the surface of the terrestrial bow-shock when the solar wind blows at high Mach numbers

Ripples at the surface of the terrestrial bow-shock when the solar wind blows at high Mach numbers

Toutes les versions de cet article : [English] [français]

The Sun continuously emits charged particles, mainly protons and electrons, flowing out at supermagnetosonic speed : this is the solar wind. Because of its high speed, its interaction with the terrestrial magnetic field generates a shock wave, traditionally called bow-shock, standing in front of the planet. Shaped as a gigantic paraboloid umbrella, the bow-shock plays the important role of shielding Earth’s environment from the direct penetration of solar energetic particles by diverting them away from it.

In a recent paper in Journal of Atmospheric and Solar-Terrestrial Physics, E. Cazzola, in post-doc in the space plasma team at LPP and his collaborators have simulated the bow-shock in steady conditions taking into account the presence of an interplanetary magnetic field perpendicular to the direction of the Sun, as well as perpendicular to the incident solar wind. While the bow-shock surface is smooth for slow solar winds, E. Cazzola et al. have observed that ripples appear at its surface for large solar wind speeds. These ripples are elongated in the direction perpendicular to the interplanetary magnetic field and propagate from the nose of the bow shock towards the flanks as shown in the figure.

Distribution du champ magnétique à la surface du choc d'étrave à l'état stationnaire

Different processes can be responsible for the generation and propagation of waves at small or large scales et the shock surface. Thanks to the 3D hybrid formalism here adopted (the ions are treated as individual particles, the electrons as a fluid), E. Cazzola et al. have suggested that they could be generated by a mechanism based on the ions dynamics, called shock reformation. Briefly, the bow-shock forms a barrier reflecting part of the incident flow. The direction of the interplanetary magnetic field, tangent to the surface at the nose, contributes to efficiently accumulate reflected particles upstream the shock front. A new shock front thus starts to grow ahead the previous one, prior to being pushed back by the flow to the initial equilibrium position. This cyclic back and forth motion of the bow-shock surface near its nose initiates a surface wave which then propagates away from the nose along the bow-shock’s flanks.

Further details can be found in :
Cazzola, E., Fontaine, D., & Savoini, P. (2023). On the 3D global dynamics of terrestrial bow-shock rippling in a quasi-perpendicular interaction with steady solar wind. Journal of Atmospheric and Solar-Terrestrial Physics, 246, 106053,
https://doi.org/10.1016/j.jastp.2023.106053.

Contacts at LPP : Emanuele Cazzola, Dominique Fontaine and Philippe Savoini, « space plasmas » team

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