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On the gradients of ACR oxygen at intermediate heliocentric distances: Ulysses/Soho results

  • Authors: Marsden, R. G.; Sanderson, T. R.; Tranquille, C.; Trattner, K. J.; Anttila, A.; Torsti, J.
  • Publication: Advances in Space Research, Volume 23, Issue 3, p. 531-534, 1999
  • Statistical study
  • ADS link
  • Abstract: During 1997 and up to the present time, the heliocentric position of the Ulysses spacecraft has changed only slowly in distance and latitude, being close to the equator at a distance of ~5 AU. This period provides an excellent opportunity to observe the evolution of the Anomalous Cosmic Ray (ACR) spectrum at a location intermediate between 1 AU and the outer heliosphere. We present ACR observations in the energy range ~3 to 30 MeV/nucleon made using the COSPIN/LET instrument on board Ulysses and the ERNE experiment on SOHO at 1 AU. Based on these observations, which cover a latitude range of ~0° to 20° with respect to the heliographic equator, we find a radial gradient Gr of 18.0±2.4 %/AU and a latitudinal gradient Gλ of 0.6±0.1 %/deg for ACR oxygen at 10 MeV/n, with corresponding values of 25.0±3.0 %/AU and 0.9±0.1 %/deg at 5.5 MeV/n.

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