Observations of the longitudinal spread of solar energetic particle events in solar cycle 24
With the twin STEREO spacecraft, significantly separated from L1-based satellites such as ACE, simultaneous multi-point measurements of solar energetic particle (SEP) events can be made for H-Fe ions from a few hundred keV/nuc to over 100 MeV/nuc and for electrons from tens to hundreds of keV. These observations allow studies of the longitudinal characteristics of SEP events to advance beyond statistical analysis of single point measurements. Although there have been few large SEP events thus far in cycle 24, there have been a number of smaller events that have been detected by more than one spacecraft. The composition of these SEP events, as indicated by the H/He and Fe/O abundance ratios, shows a dependence on longitudinal distance from the solar source in some events, at times with ratios varying by an order of magnitude. However, these variations are not organized by either the speed or width of the associated coronal mass ejections.
Additional Information© 2012 American Institute of Physics. This work was funded by NASA under grants NNX08AI11G and NNX10AQ68G at Caltech, NNX10AT75G at JHUAPL, and subcontracts SA2715-26309 from UC Berkeley (NASA contract NAS5-03131) and N00173-10-1-G010 from NRL. The STEREO/SEPT project is supported under grant 50 OC 0902 by the German Bundesministerium für Wirtschaft through the Deutsches Zentrum für Luft und Raumfahrt (DLR). We thank Nariaki Nitta for useful discussions regarding solar source identifications. We used data from the CME catalog generated and maintained at the CDAW Data Center by NASA and The Catholic University of America in cooperation with NRL and from the CACTus CME catalog, generated and maintained by the SIDC at the Royal Observatory of Belgium.
Published - APC000103.pdf