Evidence for Trapped Anomalous Cosmic Ray Oxygen Ions in the Inner Magnetosphere

A series of measurements of 5–30 MeV/nucleon oxygen ions made with track detector stacks on Cosmos satellites show isotropic angular distributions during solar energetic particle events. Solar-quiet times, on the other hand, have highly anisotropic distributions suggestive of a trapped-particle component. Detailed Monte Carlo simulations confirm this interpretation and allow us to measure the trapped and cosmic-ray contributions to the observed fluxes. Our data are fully consistent with anomalous cosmic-ray ions, rather than radial diffusion from the outer zone, as the source of the trapped particles

Observation of Energetic Trapped Oxygen Ions in the Inner Magnetosphere

We report on a series of measurements of 5-30 Me V /nuc oxygen ions made with trackdetector stacks on Cosmos satellites. We find that the angular distributions during solar energetic particle events are isotropic, while solar-quiet times show highly anisotropic distributions suggestive of a trapped particle component. Detailed Monte Carlo simulations confirm this interpretation and allow us to separate the trapped and cosmic ray contributions to the quiet-time fluxes. Our data appear fully consistent with trapping of anomalous cosmic ray ions as the source of the trapped particles but inconsistent with radial diffusion from the outer radiation zone

Anomalous Cosmic Ray Measurements in and outside the Magnetosphere: Implications for the Charge State

We report preliminary results from the Joint Study of the Charge State of the Anomalous Component, a cooperative project of the space agencies of the US and the USSR. The so-called "anomalous" cosmic ray component, including the elements He, N, 0, and Ne, as well as rarer species, is believed to represent a sample of neutral interstellar atoms that has been swept into the heliosphere, singly ionized, and then accelerated to energies as high as 60 MeV /nucleon. A key test of this theory is a direct verification that these energetic nuclei are indeed singly ionized. This prediction can be tested by comparing simultaneous measurements of the flux of anomalous cosmic rays made inside and outside the magnetosphere, using the geomagnetic field as a rigidity-dependent filter. Grigorov et al. have recently reported measurements of the flux of 10 MeV /nucleon C, N, and 0 nuclei made during 1986 to 1988 by a series of KOSMOS satellites flown in low Earth orbit. We have analyzed data from the same time periods from several instruments on IMP-8 and ICE, which were located outside the magnetosphere. We compare the 0 fluxes inside and outside the magnetosphere over this time period and examine the implications of these measurements for the charge state of anomalous cosmic rays

The Charge State of the Anomalous Component of Cosmic Rays

The ionic charge state of anomalous cosmic-ray oxygen has been determined by comparing measurements obtained inside the magnetosphere on a series of Cosmos satellite flights with simultaneous observations outside the magnetosphere from IMP 8 and ICE. We find a mean charge state of 0.9 ^(+0.3)_(-0.2) for ~10 MeV nucleon^(-1) anomalous oxygen, consistent with the model of Fisk, Kozlovsky, & Ramaty, in which the anomalous cosmic rays originate from the neutral component of the local interstellar medium. This same approach gives results consistent with a mean charge of +7 for solar energetic oxygen ions

Determining the charge states of solar energetic ions during large geomagnetic storms

We give a progress report on a new method of measuring the mean ionic charge states of solar energetic particles (SEPs) and apply this method to oxygen ions at energies of ∼10 MeV/nucleon. We compare simultaneous flux measurements inside and outside the magnetosphere to determine the geomagnetic transmission and use this result to find the corresponding mean ionic charge state. The key to this method is to determine the dependence of the geomagnetic transmission function on the mean ionic charge state of the ions. We report here the results of a new technique to calculate the geomagnetic transmission function, which attempts to account for the cutoff suppression caused by the geomagnetic activity which often accompanies SEP events