Coherent events at ion scales in the inner Heliosphere: \textit{Parker Solar Probe} observations during the first Encounter

Abstract

\textit{Parker Solar Probe} has shown the ubiquitous presence of strong magnetic field deflections, namely switchbacks, during its first perihelion where it was embedded in a highly Alfvénic slow stream. Here, we study the turbulent magnetic fluctuations around ion scales in three intervals characterized by a different switchback activity, identified by the behaviour of the magnetic field radial component, $B_r$. \textit{Quiet} ($B_r$ does not show significant fluctuations), \textit{weak} ($B_r$ has strong fluctuations but no reversals) and \textit{strong} ($B_r$ has full reversals) periods show a different behaviour also for ion quantities and Alfvénicity. However, the spectral analysis shows that each stream is characterized by the typical Kolmogorov/Kraichnan power law in the inertial range, followed by a break around the characteristic ion scales. This frequency range is characterized by strong intermittent activity, with the presence of non-compressive coherent structures, such as current sheets and vortex-like structures, and wave packets, identified as ion cyclotron modes. Although, all these intermittent events have been detected in the three periods, they have a different influence in each of them. Current sheets are dominant in the \textit{strong} period, wave packets are the most common in the \textit{quiet} interval; while, in the \textit{weak} period, a mixture of vortices and wave packets is observed. This work provides an insight into the heating problem in collisionless plasmas, fitting in the context of the new solar missions, and, especially for \textit{Solar Orbiter}, which will allow an accurate magnetic connectivity analysis, to link the presence of different intermittent events to the source region.

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Cited by in corpus (9)

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