Abstract We address the unsolved question of how foreshock field-aligned beam (FAB) parallel temperatures are produced. Studies including numerical simulations and recent observations have indicated that shocks can be nonstationary and include embedded spatial structures with varied scales. As a first step towards assessing the impact of such variability on backstreaming ions, we examine how a randomly distributed shock normal direction will affect FAB parallel velocity (v ∥) distributions. Assuming that the FABs are produced in a quasi-adiabatic reflection process at the shock, we derive a probability distribution function for v ∥. These derived distributions exhibit second, third and fourth order moments that agree well with the observations for a large range of reflection efficiencies δ, and depend strongly upon the average angle between the magnetic field and the shock normal θ Bn0. Best agreement is obtained for fluctuations of the normal orientation of a few degrees about a nominal direction. The derived model predicts a strong correlation between the shock geometry (θ Bn0) and the moments of the parallel velocity distribution, but with stronger tails extending to higher values of θ Bn0, a trend opposite to the observations.


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    Title :

    Effect of Shock Normal Orientation Fluctuations on Field-Aligned Beam Distributions


    Contributors:
    Meziane, K. (author) / Hamza, A. M. (author) / Wilber, M. (author) / Lee, M. A. (author) / Mazelle, C. (author) / Lucek, E. A. (author) / Hada, T. (author) / Markowitch, A. (author)


    Publication date :

    2009-10-30


    Size :

    14 pages





    Type of media :

    Article/Chapter (Book)


    Type of material :

    Electronic Resource


    Language :

    English




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