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| Paper: |
The Charge-to-Mass Dependence of SEP Fluences Over Wide Longitudes |
| Volume: |
484, Outstanding Problems in Heliophysics: From Coronal Heating to the Edge of the Heliosphere |
| Page: |
24 |
| Authors: |
Cohen, C. M. S.; Mewaldt, R. A.; Mason, G. M. |
| Abstract: |
Accurate characterization of the transport of energetic particles throughout the inner heliosphere is important for the
planning of space missions and the development and testing of space weather forecasting tools. How particles are
distributed in both radius and longitude during a solar energetic particle (SEP) event has been the subject of a number
of studies. Initially these studies were performed through statistical analysis of single-spacecraft measurements of
many different SEP events. Later multi-spacecraft observations of individual events were examined, most notably using
data from Helios and, very recently, MESSENGER. Currently by combining measurements from near-Earth spacecraft and the
twin STEREO spacecraft, particle distributions can be examined as a function of longitude separately from radial
dependences. Additionally, while previous studies concentrated on protons and electrons, the SEP sensors on STEREO and
ACE allow heavy ions to be examined as well. We have analyzed 5 large SEP events in 2011 and 2012 that were clearly
observed by both STEREOs and ACE and determined the longitudinal distribution of the event-integrated fluences for H,
He, O at 3.6-5 MeV/nuc and for H, He, O, and Fe at 0.32-0.45 MeV/nuc. We find no consistent charge-to-mass dependence in
the longitudinal distributions at either energy suggesting rigidity is not a controlling factor in the particle spread
in longitude. We find that typically lower energy ions have a wider longitudinal spread than higher energy ions suggesting
a velocity dependence. Both of these results are consistent with the possibility that magnetic field
line meandering and/or co-rotation is a primary means of longitudinally transporting particles. |
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