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Time Evolution of Elemental Ratios in Solar Energetic Particles Events

Zelina, P. and Dalla, S. and Cohen, C. M. S. and Mewaldt, R. A. (2017) Time Evolution of Elemental Ratios in Solar Energetic Particles Events. Astrophysical Journal, 835 (1). Art. No. 71. ISSN 0004-637X. doi:10.3847/1538-4357/aa5274.

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Heavy ion ratio abundances in solar energetic particle (SEP) events, e.g., Fe/O, often exhibit decreases over time. Using particle instruments on the Advanced Composition Explorer, Solar and Heliospheric Observatory and Solar Terrestrial Relations Observatory spacecraft, we analyzed heavy ion data from 4 SEP events taking place between 2006 December and 2014 December. We constructed 36 different ionic pairs and studied their time evolution in each event. We quantified the temporal behavior of abundant SEP ratios by fitting the data to derive a decay time constant B. We also considered the ratio of ionic mass-to-charge for each pair, the S value given, e.g., for Fe/O by S_(Fe/O) = (M/Q)_(Fe)(M/Q)_O. We found that the temporal behavior of SEP ratios is ordered by the value of S: ratios with S > 1 showed decreases over time (i.e., B > 0) and those with S > 1 showed increases (B > 0). We plotted B as a function of S and observed a clear monotonic dependence: ratios with a large S decayed at a higher rate. A prominent discontinuity at S = 2.0 (corresponding to He/H) was found in three of the four events, suggesting anomalous behavior of protons. The X/H ratios often show an initial increase followed by a decrease, and decay at a slower rate. We discuss possible causes of the observed B versus S trends within current understanding of SEP propagation.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Cohen, C. M. S.0000-0002-0978-8127
Mewaldt, R. A.0000-0003-2178-9111
Additional Information:© 2017 American Astronomical Society. Received 2016 October 17. Accepted 2016 December 5. Published 2017 January 19. We thank the instrument teams of ACE/SIS, STEREO/LET, STEREO/HET and SOHO/ERNE for providing Level 2 data, made publicly available through ACE and STEREO Science Centers, and the Space Research Laboratory at the University of Turku. P.Z. acknowledges support from the JHI at the University of Central Lancashire through a PhD studentship. S.D. acknowledges support from the UK Science and Technology Facilities Council (STFC) (grant ST/M00760X/1) and the Leverhulme Trust (grant RPG-2015-094). The work at Caltech was supported by the National Science Foundation grant NSF-1156004, NASA grants NNX13A66G and subcontract 00008864 of NNX15AG09G. Facilities: ACE - Advanced Composition Explorer satellite, GOES - Geostationary Operational Environmetal Satellite, SOHO - Solar Heliospheric Observatory satellite, STEREO - NASA's Solar Terrestrial Relations Observatory.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)ST/M00760X/1
Leverhulme TrustRPG-2015-094
Subject Keywords:Sun: abundances; Sun: heliosphere; Sun: particle emission
Issue or Number:1
Record Number:CaltechAUTHORS:20170125-152407803
Persistent URL:
Official Citation:P. Zelina et al 2017 ApJ 835 71
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:73739
Deposited On:25 Jan 2017 23:48
Last Modified:11 Nov 2021 05:21

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