Non-stationarity of the quasi-perpendicular bow shock: Comparison between Cluster observations and simulations

H. Comişel, M. Scholer, J. Soucek, S. Matsukiyo

    Research output: Contribution to journalArticle

    12 Citations (Scopus)

    Abstract

    We have performed full particle electromagnetic simulations of a quasi-perpendicular shock. The shock parameters have been chosen to be appropriate for the quasi-perpendicular Earth's bow shock observed by Cluster on 24 January 2001 (Lobzin et al., 2007). We have performed two simulations with different ion to electron mass ratio: run 1 with mi/me = 1840 and run 2 with mi/me = 100. In run 1 the growth rate of the modified two-stream instability (MTSI) is large enough to get excited during the reflection and upstream gyration of part of the incident solar wind ions. The waves due to the MTSI are on the whistler mode branch and have downstream directed phase velocities in the shock frame. The Poynting flux (and wave group velocity) far upstream in the foot is also directed in the downstream direction. However, in the density and magnetic field compression region of the overshoot the waves are refracted and the Poynting flux in the shock frame is directed upstream. The MTSI is suppressed in the low mass ratio run 2. The low mass ratio run shows more clearly the non-stationarity of the shock with a larger time scale of the order of an inverse ion gyrofrequency (Ωci): the magnetic field profile flattens and steepens with a period of ∼1.5Ωci-1. This non-stationarity is different from reformation seen in previous simulations of perpendicular or quasi-perpendicular shocks. Beginning with a sharp shock ramp the large electric field in the normal direction leads to high reflection rate of solar wind protons. As they propagate upstream, the ion bulk velocity decreases and the magnetic field increases in the foot, which results in a flattening of the magnetic field profile and in a decrease of the normal electric field. Subsequently the reflection rate decreases and the whole shock profile steepens again. Superimposed on this 'breathing' behavior are in the realistic mass ratio case the waves due to the MTSI. The simulations lead us to a re-interpretation of the 24 January 2001 bow shock observations reported by Lobzin et al. (2007). It is suggested that the high frequency waves observed in the magnetic field data are due to the MTSI and are not related to a nonlinear phase standing whistler. Different profiles at the different spacecraft are due to the non-stationary behavior on the larger time scale.

    Original languageEnglish
    Pages (from-to)263-274
    Number of pages12
    JournalAnnales Geophysicae
    Volume29
    Issue number2
    DOIs
    Publication statusPublished - Feb 11 2011

    Fingerprint

    bows
    shock
    magnetic field
    ion
    simulation
    mass ratios
    upstream
    electric field
    solar wind
    timescale
    wave group
    magnetic fields
    phase velocity
    profiles
    ions
    spacecraft
    compression
    comparison
    refracted waves
    gyrofrequency

    All Science Journal Classification (ASJC) codes

    • Astronomy and Astrophysics
    • Geology
    • Atmospheric Science
    • Earth and Planetary Sciences (miscellaneous)
    • Space and Planetary Science

    Cite this

    Non-stationarity of the quasi-perpendicular bow shock : Comparison between Cluster observations and simulations. / Comişel, H.; Scholer, M.; Soucek, J.; Matsukiyo, S.

    In: Annales Geophysicae, Vol. 29, No. 2, 11.02.2011, p. 263-274.

    Research output: Contribution to journalArticle

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