Plasma rest frame distributions of suprathermal ions in the Earth's foreshock region

We present rest frame ion distributions computed from three‐dimensional observations of upstream suprathermal ions gained by the University of Iowa Quadrispherical Lepedea on ISEE‐1. The observations are for a single inbound, midmorning pass starting upstream from the ion foreshock and continuing across the quasiparallel bow shock into the magnetosheath. The crossing of the ion foreshock boundary is marked by a several minute burst of ions of temperature 100–200 eV moving along the IMF away from the bow shock at 500 km/s relative to the solar wind. The observation of these ‘reflected’ ions is followed by an extended interval of ‘diffuse’ ions of temperatures 2‐3 keV flowing at ∼250 km/s relative to the solar wind and persisting until the bow shock is crossed. The diffuse ion β has a value of approximately 6 in the region of the suprathermal ions, exceeding the normal thermal ion β of the solar wind by roughly an order of magnitude. Both types of suprathermal ions constitute roughly 2% of the total ion density and carry a parallel heat flux of ∼2 × 10 −2 ergs cm −2 s −1 . When integrated over an assumed 10 × 10 R E bow shock emission area, this implies an upstream dissipation that may approach 10 17 to 10 18 ergs/s, comparable to a modest substorm.

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