Observation of an MHD Alfvén vortex in the slow solar wind

Authors Organisations
  • Owen Roberts(Author)
    European Space Research and Technology Centre (ESTEC)
  • Xing Li(Author)
  • O. Alexandrova(Author)
    LESIA - Observatoire de Paris
  • Bo Li(Author)
    Shandong University
Type Article
Original languageEnglish
Pages (from-to)3870-3881
JournalJournal of Geophysical Research
Volume121
Issue number5
Early online date05 May 2016
DOI
Publication statusPublished - 15 Jun 2016
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Abstract

In the solar wind, magnetic field power spectra usually show several power-laws. In this paper, magnetic field data from the Cluster mission during an undisturbed interval of slow solar wind is analyzed at 0.28Hz, near the spectral break point between the ion inertial and dissipation/dispersion ranges. Assuming Taylor's frozen-in condition, it corresponds to a proton kinetic scale of kvA/Ωp∼0.38, where vA and Ωp are the Alfv\'en speed and proton angular gyrofrequency, respectively. Data show that the Cluster spacecraft passed through a series of wavepackets. A strong isolated wavepacket is found to be in accordance with the four Cluster satellites crossing an Alfv\'en vortex, a nonlinear solution to the incompressible MHD equations. A strong agreement is seen between the data from four satellites and a model vortex with a radius of the order of 40 times the local proton gyro-radii. The polarization at different spacecraft is compared and is found to agree with the vortex model, whereas it cannot be explained solely by the linear plane wave approach