Evidence and features of magnetospheric particle leakage on days 30–36, 1995: Wind, Geotail, and IMP 8 observations compared

Abstract

Simultaneous observations from the Geotail, IMP 8, and Wind spacecrafts during periods of energetic particle activity, studied previously far upstream from the Earth's bow shock, are used in this paper to resolve ambiguities between the leakage and Fermi models as the potential mechanism of such upstream events. CNO flux enhancements were observed at the current sheet (IMP 8 and Geotail), during intense substorm activity, before detection of a typical upstream Wind ion event rich in heavy ion species on day 31, 1995; the plasma sheet CNO flux enhancement was observed during times of a corotating interaction region with a seed population rich in CNO ion species. In addition, the features of energetic ion events observed on days 32–36, 1995, near the Earth's bow shock (Geotail and IMP 8) suggest that magnetospheric leakage of energetic particles is a much more likely source of the observed upstream ions than Fermi acceleration. Such features, observed during periods of high values of geomagnetic index Kp (3–5+), are the presence of upstream energetic electrons and ionospheric O+ ions, the dawn–dusk asymmetry of energetic ions and electrons, the anisotropic upstream ion distributions, the inverse energy dispersion of ion intensities, etc. A much higher percentage of electron‐associated ion events found near the magnetosphere/bow shock (Geotail) than in the far upstream region (Wind) suggests a rigidity‐dependent propagation in the upstream region. Furthermore, a systematic hardening of ion spectra over the whole energy range ∼0.05 to ∼1.00 MeV observed by IMP 8 near the bow shock suggests that the same particle distribution dominated the ion responses during the typical Wind event of day 34, 1995. The above results point out that the joint analysis of observations from all three spacecrafts can help to resolve a number of the ambiguities concerning the origin of upstream ion events on days 30–36, 1995, posed by the analysis of observations made by a distant spacecraft (Wind) alone.