No abstract

We present the first observation of a solar impulsive electron event spanning the entire solar wind‐suprathermal particle energy range (few eV to hundreds of keV), obtained with the 3‐D Plasma and Energetic Particle experiment on the WIND spacecraft. The electron energy spectrum fits to a power‐law ∼ E−3 from ∼40 keV down to a peak at ≲ 1 keV, with significant flux detected down to ∼0.5 keV. Since the range of such low energy electrons in ionized hydrogen is much less than the column density of the corona, they must be accelerated high, ∼1 R⊙ (solar radius) above the photosphere, for typical active coronal density models.

On a rapid inward pass through the subsolar magnetosheath (MSH) and magnetopause (MP), the WIND spacecraft initially encountered a moderately‐compressed low‐magnetic shear MP (at a radial distance of 8.6 RE), followed by multiple crossings of a high‐shear MP (at 8.2 RE). The large shear resulted from a southward turning of the external MSH field. Strong magnetic field pile‐up, a plasma depletion layer (PDL), and plasma flow acceleration and rotation to become more perpendicular to the local magnetic field were observed in the MSH on approach to the low‐shear MP. At the high‐shear MP, magnetic reconnection flows were detected, and there are some indications that plasma depletion effects were weak or absent in the adjacent MSH. We attribute the changes in the MP and MSH properties to the sudden rotation of the MSH field direction. In essence, the structure of the MP regions under the unusually high solar wind ram pressure condition in this case does not seem to be qualitatively different from that observed under more typical (less compressed) conditions. Also similar to previous observations, the mirror mode is marginally unstable in the MSH proper, but is stable in the PDL. In this region, the proton temperature anisotropy is inversely correlated with βp∥. Finally, the electron distributions are observed to be anisotropic (Te⟂/Te∥ ∼1.3) throughout the entire MSH.

No abstract

During the first year of operation, the WIND spacecraft followed a complicated orbit which took it from the Earth to the upstream libration point and back again. During this time, a considerable number of upstream particle events were observed all the way out to the libration point. These events are typically of short duration (a few tens of minutes) and up until now have only been seen in the energetic protons (at energies of a few tens of keV, but extending up to several hundreds of keV). We present here new observations from the Three‐dimensional (3D) plasma and energetic particle experiment on the WIND spacecraft of these upstream events, with particular emphasis on the uniqueness of the observations from this instrument: energy spectra measured over the range from a few keV to several hundreds of keV, and complete three‐dimensional angular distributions covering the same range of energies. We present here for the first time a complete spectrum of these ions extending from a few eV to a few MeV. This spectrum, with a turnover at one or two keV, shows that the bulk of the energy density of the upstream ions is at around 1 keV. These are most likely the particles responsible for the low‐frequency waves which are usually seen accompanying upstream events.