SPREADING AND INTERMITTENT STRUCTURE OF THE UPSTREAM BOUNDARY OF PLANETARY MAGNETIC FORESHOCKS

The fast particles in the electron foreshocks propagate along the magn etic field lines, so that the effect of low frequency magnetic fluctua tions is to create both a broadening and a fine structure of the fores hock upstream boundary. This is studied by means of a 3-D numerical si mulation of turbulent magnetic fields. Applications to Venus, Earth, a nd Mars magnetic foreshocks are done. It is found that a spacecraft ca n be magnetically connected to the bow shock even when it is upstream of the nominal magnetic foreshock boundary, and that the mixing of mag netic field lines can give an explanation for the broadband bursty ele ctrostatic noise observed within the electron foreshock.