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Observing small scale Alfvénic turbulence around 0.2 AU

Abstract:

Recent results obtained from the analysis of interplanetary observations recorded by Helios 2 within the inner heliosphere showed, for the first time, that the Probability Distribution Function (PDF) of magnetic field vector fluctuations, within the MHD frequency range of turbulence, can be remarkably well fitted by a double lognormal. These two components of the total PDF have been ascribed to Alfvénic fluctuations and advected structures. Since this analysis was carried on using only magnetic field data because of low time resolution of plasma measurements, we lack of a sure proof of the Alfvénic nature of those fluctuations that we believe contribute to one of the two lognormals. Moreover, we still don't know whether the advected structures forming the second lognormal are locally generated by the turbulent evolution of the fluctuations or they rather come from the source regions of the wind where they reflect the complicate topology of the magnetic field. Remote sensing and high time resolution in-situ observations performed by Solar Orbiter at the perihelion, during the corotation phase, would certainly amplify the results already reached by Helios and would eventually give an answer to these problems.