Physics – Plasma Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsh43a1815d&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SH43A-1815
Physics
Plasma Physics
[7514] Solar Physics, Astrophysics, And Astronomy / Energetic Particles, [7859] Space Plasma Physics / Transport Processes
Scientific paper
It takes from a few minutes to hours for solar energetic particles to transport from the Sun to Earth. Because the speed of particle transport and scattering are energy dependent, the instantaneous spectrum of solar energetic particles rapidly varies over the time scale of an event. As a result, we typically look at their event-integrated spectrum, in order to infer the spectral properties of source particles and to minimize time dependent variations. Observed event-integrated spectrum often shows a joint double power-law distribution with a smaller spectral slope at lower energies. The energy at the spectral break or roll-over depends on the charge-to-mass ratio of particles (Mewaldt et al., 2006; Tylka et al., 2000). We have used a stochastic model of solar energetic particle transport (Zhang et al., 2009) in a 3-dimensional Parker magnetic field to study the event-integrated solar energetic particle spectrum. With this model we can study how the event-integrated spectra at different locations in the inner heliosphere, particularly at Earth or at Mars orbit, depend on the properties of particle transport in the interplanetary medium. Our model results show the event-integrated spectrum still has an approximate power-law distribution but the spectral index is smaller than that of source particles injected at the Sun. At high energies, the event-integrated spectra show a gradual roll-over to steeper spectral slopes. The value of the roll-over energy and observed spectral index depends on the spectrum of injected particles and on the radial distance. In addition, we will show how the event-integrated spectrum is affected by interplanetary transport coefficients.
Diaz I.
Rassoul Hamid K.
Zhang Minghui
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