Other
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsh22c..07h&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SH22C-07
Other
7859 Transport Processes, 2104 Cosmic Rays, 2114 Energetic Particles, Heliospheric (7514)
Scientific paper
The motion of the Voyager 1 & 2 spacecraft through the outer heliosphere during the 1994 to 1999 period provides the opportunity to probe the spatial variations of anomalous cosmic ray (ACR) intensities during an A > 0 solar minimum phase (i.e., with positive heliomagnetic polarity). Applying a "quasi-local" method to determine spatial intensity gradients, we find that the radial gradients of 0.6- to 40-MeV/nucleon ACRs at this time are positive, and larger as particle rigidity decreases. Additionally, the bulk features of the ACR recovery that took place during this period can be reproduced with a surprisingly simple drift-free transport model indicating, for instance, that the observed exponential growth of the lower-rigidity ACR intensities is primarily due to the motion of the Voyager spacecraft through sizeable radial intensity gradients, in quantitative agreement with the first result of the quasi-local gradient (QLG) method. Interpretation of our transport model and the more sophisticated modeling of other scientists supports the second result of the QLG method, that ACRs with rigidities below ~2 GV have significant negative latitudinal gradients, and small positive gradients at higher rigidities. In the outer heliosphere, 2 GV appears to correspond to the ACR rigidity below which the estimated drift velocity is small compared to the solar wind speed. We explore the interpretation that the relative lack of drift effects for lower-rigidity ACRs permits other phenomena, such as the positive latitudinal gradient of the solar wind velocity, to cause the negative latitudinal intensity gradients we have observed.
Hamilton Douglas C.
Hill Matthew E.
Krimigis Stamatios M.
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