Article

Space Science Reviews

, Volume 126, Issue 1, pp 239-266

First online:

IMF Direction Derived from Cycloid-Like Ion Distributions Observed by Mars Express

  • M. YamauchiAffiliated withSwedish Institute of Space Physics Email author 
  • , Y. FutaanaAffiliated withSwedish Institute of Space PhysicsInstitute of Space and Astronautical Science
  • , A. FedorovAffiliated withCentre d’Etude Spatiale des Rayonnements
  • , E. DubininAffiliated withMax-Planck-Institut für Sonnensystemforschung
  • , R. LundinAffiliated withSwedish Institute of Space Physics
  • , J.-A. SauvaudAffiliated withCentre d’Etude Spatiale des Rayonnements
  • , D. WinninghamAffiliated withSouthwest Research Institute
  • , R. FrahmAffiliated withSouthwest Research Institute
  • , S. BarabashAffiliated withSwedish Institute of Space Physics
    • , M. HolmstromAffiliated withSwedish Institute of Space Physics
    • , J. WochAffiliated withMax-Planck-Institut für Sonnensystemforschung
    • , M. FraenzAffiliated withMax-Planck-Institut für Sonnensystemforschung
    • , E. BudnikAffiliated withCentre d’Etude Spatiale des Rayonnements
    • , H. BorgAffiliated withSwedish Institute of Space Physics
    • , J. R. SharberAffiliated withSouthwest Research Institute
    • , A. J. CoatesAffiliated withMullard Space Science Laboratory, University College London
    • , Y. SoobiahAffiliated withMullard Space Science Laboratory, University College London
    • , H. KoskinenAffiliated withFinnish Meteorological InstituteDepartment of Physical Sciences, University of Helsinki
    • , E. KallioAffiliated withFinnish Meteorological Institute
    • , K. AsamuraAffiliated withInstitute of Space and Astronautical Science
    • , H. HayakawaAffiliated withInstitute of Space and Astronautical Science
    • , C. CurtisAffiliated withDepartment of Physics, University of Arizona
    • , K. C. HsiehAffiliated withDepartment of Physics, University of Arizona
    • , B. R. SandelAffiliated withLunar and Planetary Lab, University of Arizona
    • , M. GrandeAffiliated withRutherford Appleton Laboratory
    • , A. GrigorievAffiliated withSwedish Institute of Space Physics
    • , P. WurzAffiliated withUniversity of Bern, Physikalisches Institut
    • , S. OrsiniAffiliated withInstituto di Fisica dello Spazio Interplanetari
    • , P. BrandtAffiliated withApplied Physics Laboratory, Johns Hopkins University
    • , S. Mckenna-LawlerAffiliated withSpace Technology Ltd., National University of Ireland
    • , J. KozyraAffiliated withSpace Physics Research Lab., University of Michigan
    • , J. LuhmannAffiliated withSpace Science Lab., University of California in Berkeley

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Abstract

Although the Mars Express (MEX) does not carry a magnetometer, it is in principle possible to derive the interplanetary magnetic field (IMF) orientation from the three dimensional velocity distribution of pick-up ions measured by the Ion Mass Analyser (IMA) on board MEX because pick-up ions' orbits, in velocity phase space, are expected to gyrate around the IMF when the IMF is relatively uniform on a scale larger than the proton gyroradius. During bow shock outbound crossings, MEX often observed cycloid distributions (two dimensional partial ring distributions in velocity phase space) of protons in a narrow channel of the IMA detector (only one azimuth for many polar angles). We show two such examples. Three different methods are used to derive the IMF orientation from the observed cycloid distributions. One method is intuitive (intuitive method), while the others derive the minimum variance direction of the velocity vectors for the observed ring ions. These velocity vectors are selected either manually (manual method) or automatically using simple filters (automatic method). While the intuitive method and the manual method provide similar IMF orientations by which the observed cycloid distribution is well arranged into a partial circle (representing gyration) and constant parallel velocity, the automatic method failed to arrange the data to the degree of the manual method, yielding about a 30° offset in the estimated IMF direction. The uncertainty of the derived IMF orientation is strongly affected by the instrument resolution. The source population for these ring distributions is most likely newly ionized hydrogen atoms, which are picked up by the solar wind.

Keywords

IMF Mars ion gyration pick-up process