Mathematics – Logic
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsh21d..10e&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SH21D-10
Mathematics
Logic
7514 Energetic Particles (2114), 7536 Solar Activity Cycle (2162), 7867 Wave/Particle Interactions
Scientific paper
Electrons of cosmic ray energies (a few MeV and above) pose many fascinating puzzles in the physics of the heliosphere. Spectra of solar electrons are intimately related to the altitude of parent flares in the solar atmosphere, yet the reason for this is completely unknown. Below 30 MeV, electrons escaping from the Jovian magnetosphere dominate the inner heliosphere. Until observations of positrons are available, it will probably not be known whether true cosmic ray electrons of this energy propagate to the inner heliosphere. Because of their non power law spectrum, and the non central location of Jupiter, Jovian electrons themselves provide a unique tool to study particle propagation in the heliosphere. Above a few hundred MeV, electrons in the heliosphere are clearly cosmic, as indicated by the presence of positrons. Many of the considerations related to isotope abundances of nuclei apply to electrons and positrons as well, but with an important difference, namely the opposite charge sign of positrons and electrons. Differences in their behavior result from phenomena like gradient and curvature drifts that are in turn diagnostic of the large scale symmetry of the solar wind magnetic field. Very little is actually known about electrons at intermediate energies except that they show a persistent negative spectral index reminiscent of the anomalous component. But unlike the anomalous component, these electrons show comparatively little variation with solar activity, and the relation of what variation is observed to solar magnetic polarity is undetermined. Since these electrons move much faster than nuclei of comparable rigidity, their interaction with dynamically evolving waves and turbulence in the solar wind can be quite different from that of nuclei, and in fact can result in dramatically larger diffusion coefficients. Anomalously large diffusion coefficients have indeed been the classic, phenomenological explanation for the negative spectral index of the low energy electrons. It is also possible that this spectrum signals a component of electrons accelerated in the same process that produces the anomalous nuclei. Starting from a seed population at Jovian energies, the energy gain required is that expected for singly charged particles drifting in the termination shock. Much work remains to be done in this energy range, and making progress requires new and systematic observations of electrons and positrons.
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