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Laboratory for Atmospheric and Space Physics


Anomalous Cosmic Rays

  • Discovery of the precise location of trapped ACRs in the magnetosphere.
  • Measurement of the elemental composition of trapped ACRs, including C,N,O, and Ne.
  • Discovery that the trapped anomalous cosmic rays are the dominant component of high energy (> 10 MeV) ions heavier than He in the magnetosphere.
  • Determination that ACR nitrogen, oxygen and neon are singly charged.
  • Determination that the upper limit of ACR O2+ is less than ~10% of the total ACR oxygen, thus limiting acceleration time scales in the heliosphere.
  • Discovery that the interplanetary spectrum of anomalous oxygen extends to at least 100 MeV/nuc implying that the ACR acceleration mechanism (termination shock?) accelerates particles to at least 1.6 GeV.
  • Discovery (in collaboration with Voyager, Ulysses, and Pioneer spacecraft) that the ACR intensity increases with heliolatitude during the 1993 approach to solar minimum, in contrast to the opposite
    behaviour observed at the previous solar minimum; this confirms predictions of one class of particle transport theories which include particle drift.
  • Discovery (in collaboration with Voyager, Ulysses, and Pioneer spacecraft) that the radial gradients of ACR are much smaller in the current solar minimum than during the previous solar minimum in 1987.

Solar Energetic Particles

  • Determination of “normal” solar system isotopic abundances for Ne and Mg in the large solar particle events of Oct/Nov 1993.
  • Excesses (factor ~4) of neutron rich isotopes of Ne and Mg in 3He-rich solar particle events
  • Demonstration that high-energy (> 1 MeV/nuc) heavy ions in the large solar particle events of late 1992 were partially ionized charge states, similar to those reported previously for energies near 1 MeV/nuc, with the exception of Fe, which had a significantly lower ionization state.
  • Demonstration that the energy spectra of impulsive 3He-rich events routinely extend to > 10 MeV/nuc

Magnetospheric Physics

  • Discovery that magnetospheric electrons are globally accelerated in association with the impact of high speed solar wind streams.
  • Evidence for deep dielectric charging as a likely cause of the Jan 1994 Anik spacecraft anomalies.
  • Discovery that remnants of relativistic electron belt generated by the 24 Mar 1991 interplanetary shock persisted into 1993.
  • Discovery that the inner radiation belt at L=1.2 is composed roughly of equal amounts of 3He and 4He at 10 MeV/nuc.
  • Discovery of high-energy (~15-55 MeV/nuc) deuterium trapped in the magnetosphere.
  • Discovery that relativistic electron precipitation routinely has temporal structure at the time scale of the bounce period.

Middle Atmosphere Physics

  • Discovery that electron flux variations at SAMPEX altitudes are well correlated with solar wind variations, providing a solar-magnetosphere-middle atmosphere coupling.
  • Demonstration that the primary relativistic electron flux inputs into the middle atmosphere occur in the range 3.5<L<5.5, corresponding to subauroral latitudes.
  • Discovery that relativistic electron energy inputs into the middle atmosphere are asymmetric between the northern and southern hemispheres, with the largest inputs occurring in the southern hemisphere. Within each hemisphere, there are preferred longitudes for the energy inputs.
  • Indication that relativistic precipitating electrons provide a significant source of odd nitrogen to the middle atmosphere and can affect middle atmospheric ozone.