EXOS-D Observations of Thermal Ion Energy Distributions in Transverse Ion Energization Regions

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The Suprathermal ion Mass Spectrometer (SMS) on EXOS-D frequently observed the energy distributions of both thermal and suprathermal ions in and near Transverse Ion Energization (TIE) regions. TIE frequently occurs at low energies (<20 eV) near the dayside cusp or auroral regions at high altitude (>2000 km) over a latitudinal range less than ∼50 km. In TIE regions, all (major and minor) ion species are energized to approximately the same energy perpendicular to the local magnetic field and expand outward along the magnetic field line forming conical ion distributions. Therefore, a TIE region is characterized by the occurrence of ion conics peaking at 90° pitch angles. From the measured thermal ion energy distributions, we estimated the ion velocity parallel and perpendicular to the magnetic field, density and temperature for the individual species in and near TIE regions. We found that the TIE occurs in the velocity shear region between eastward and westward plasma convection. In the dayside region, field-aligned flow of light (H<SUP>+</SUP> and He<SUP>+</SUP>) ions is often observed equatorward of the TIE region; the characteristic of this flow is consistent with classical polar wind. In contrast, poleward of the TIE region, O<SUP>+</SUP> is often a major component of the polar wind flow.


  • Earth, Planets and Space  

    Earth, Planets and Space 47(11), 1161-1169, 1995-11 

    Society of Geomagnetism and Earth, Planetary and Space Sciences

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