skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Joint Ne/O and Fe/O Analysis to Diagnose Large Solar Energetic Particle Events during Solar Cycle 23

Abstract

We have examined 29 large solar energetic particle (SEP) events with the peak proton intensity J {sub pp}(>60 MeV) > 1 pfu during solar cycle 23. The emphasis of our examination is put on a joint analysis of Ne/O and Fe/O data in the energy range (3–40 MeV nucleon{sup −1}) covered by Wind /Low-Energy Matrix Telescope and ACE /Solar Isotope Spectrometer sensors in order to differentiate between the Fe-poor and Fe-rich events that emerged from the coronal mass ejection driven shock acceleration process. An improved ion ratio calculation is carried out by rebinning ion intensity data into the form of equal bin widths in the logarithmic energy scale. Through the analysis we find that the variability of Ne/O and Fe/O ratios can be used to investigate the accelerating shock properties. In particular, the high-energy Ne/O ratio is well correlated with the source plasma temperature of SEPs.

Authors:
;  [1];  [2]
  1. Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
  2. IAASARS, National Observatory of Athens, GR-15236, Penteli (Greece)
Publication Date:
OSTI Identifier:
22663921
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 835; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; CONCENTRATION RATIO; DIAGNOSIS; ELECTRON TEMPERATURE; EMISSION; HELIOSPHERE; ION TEMPERATURE; IONS; IRON; MASS; MEV RANGE; NEON; OXYGEN; PLASMA; PROTONS; SENSORS; SOLAR CYCLE; SPECTROMETERS; SUN; TELESCOPES

Citation Formats

Tan, Lun C., Shao, Xi, and Malandraki, Olga E., E-mail: ltan@umd.edu. Joint Ne/O and Fe/O Analysis to Diagnose Large Solar Energetic Particle Events during Solar Cycle 23. United States: N. p., 2017. Web. doi:10.3847/1538-4357/835/2/192.
Tan, Lun C., Shao, Xi, & Malandraki, Olga E., E-mail: ltan@umd.edu. Joint Ne/O and Fe/O Analysis to Diagnose Large Solar Energetic Particle Events during Solar Cycle 23. United States. doi:10.3847/1538-4357/835/2/192.
Tan, Lun C., Shao, Xi, and Malandraki, Olga E., E-mail: ltan@umd.edu. Wed . "Joint Ne/O and Fe/O Analysis to Diagnose Large Solar Energetic Particle Events during Solar Cycle 23". United States. doi:10.3847/1538-4357/835/2/192.
@article{osti_22663921,
title = {Joint Ne/O and Fe/O Analysis to Diagnose Large Solar Energetic Particle Events during Solar Cycle 23},
author = {Tan, Lun C. and Shao, Xi and Malandraki, Olga E., E-mail: ltan@umd.edu},
abstractNote = {We have examined 29 large solar energetic particle (SEP) events with the peak proton intensity J {sub pp}(>60 MeV) > 1 pfu during solar cycle 23. The emphasis of our examination is put on a joint analysis of Ne/O and Fe/O data in the energy range (3–40 MeV nucleon{sup −1}) covered by Wind /Low-Energy Matrix Telescope and ACE /Solar Isotope Spectrometer sensors in order to differentiate between the Fe-poor and Fe-rich events that emerged from the coronal mass ejection driven shock acceleration process. An improved ion ratio calculation is carried out by rebinning ion intensity data into the form of equal bin widths in the logarithmic energy scale. Through the analysis we find that the variability of Ne/O and Fe/O ratios can be used to investigate the accelerating shock properties. In particular, the high-energy Ne/O ratio is well correlated with the source plasma temperature of SEPs.},
doi = {10.3847/1538-4357/835/2/192},
journal = {Astrophysical Journal},
number = 2,
volume = 835,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}
  • The effects of scatter-dominated interplanetary transport on the spectral properties of the differential fluence of large gradual solar energetic particle (SEP) events are investigated analytically. The model assumes for simplicity radial constant solar wind and radial magnetic field. The radial diffusion coefficient is calculated with quasilinear theory by assuming a spectrum of Alfvén waves propagating parallel to the magnetic field. Cross-field transport is neglected. The model takes into consideration several essential features of gradual event transport: nearly isotropic ion distributions, adiabatic deceleration in a divergent solar wind, and particle radial scattering mean free paths increasing with energy. Assuming an impulsivemore » and spherically symmetric injection of SEPs with a power-law spectrum near the Sun, the predicted differential fluence spectrum exhibits at 1 AU three distinctive power laws for different energy domains. The model naturally reproduces the spectral features of the double power-law proton differential fluence spectra that tend to be observed in extremely large SEP events. We select nine western ground-level events (GLEs) out of the 16 GLEs during Solar Cycle 23 and fit the observed double power-law spectra to the analytical predictions. The compression ratio of the accelerating shock wave, the power-law index of the ambient wave intensity, and the proton radial scattering mean free path are determined for the nine GLEs. The derived parameters are generally in agreement with the characteristic values expected for large gradual SEP events.« less
  • Energetic particles in large solar energetic particle (SEP) events are a major concern for space weather. Recently, Li et al. proposed a 'twin-CME' scenario for ground-level events. Here we extend that study to large SEP events in solar cycle 23. Depending on whether preceding coronal mass ejections (CMEs) within 9 hr exist and whether ions >10 MeV nucleon{sup -1} exceed 10 pfu, we categorize fast CMEs with speed >900 km s{sup -1} and width >60 Degree-Sign from the western hemisphere source regions into four groups: groups I and II are 'twin' and single CMEs that lead to large SEPs; groupsmore » III and IV are 'twin' and single CMEs that do not lead to large SEPs. The major findings of this paper are: first, large SEP events tend to be 'twin-CME' events. Of 59 western large SEP events in solar cycle 23, 43 are 'twin-CME' (group I) events and 16 are single-CME (group II) events. Second, not all 'twin CMEs' produced large SEPs: 28 twin CMEs did not produce large SEPs (group III events). Some of them produced excesses of particles up to a few MeV nucleon{sup -1}. Third, there were 39 single fast CMEs that did not produce SEPs (group IV events). Some of these also showed an excess of particles up to a few MeV nucleon{sup -1}. For all four groups of events, we perform statistical analyses on properties such as the angular width, the speed, the existence of accompanying metric type II radio bursts, and the associated flare class for the main CMEs and the preceding CMEs.« less
  • Since the field-line mixing model of Giacalone et al. suggests that ion dropouts cannot happen in the “gradual” solar energetic particle (SEP) event because of the large size of the particle source region in the event, the observational evidence of ion dropouts in the gradual SEP event should challenge the model. We have searched for the presence of ion dropouts in the gradual SEP event during solar cycle 23. From 10 SEP events the synchronized occurrence of ion and electron dropouts is identified in 12 periods. Our main observational facts, including the mean width of electron–ion dropout periods being consistentmore » with the solar wind correlation scale, during the dropout period the dominance of the slab turbulence component and the enhanced turbulence power parallel to the mean magnetic field, and the ion gyroradius dependence of the edge steepness in dropout periods, are all in support of the solar wind turbulence origin of dropout events. Also, our observation indicates that a wide longitude distribution of SEP events could be due to the increase of slab turbulence fraction with the increased longitude distance from the flare-associated active region.« less
  • We have surveyed ∼0.1–100 MeV nucleon{sup −1} O and Fe fluence spectra during 46 isolated, large gradual SEP events observed at ACE during solar cycles 23 and 24. Most SEP spectra are well represented by the four-parameter Band function with a normalization constant, low-energy spectral slope, high-energy spectral slope, and break energy. The O and Fe spectral slopes are similar and most spectra steepen above the break energy, probably due to common acceleration and transport processes affecting different ion species. SEP spectra above the break energies depend on the origin of the seed population; larger contributions of suprathermal flare materialmore » result in higher Fe/O ratios and flatter spectra at higher energies. SEP events with steeper O spectra at low energies and higher break energies are associated with slower coronal mass ejections (CMEs), while those associated with fast (>2000 km s{sup −1}) CMEs and ground level enhancements have harder or flatter spectra at low and high energies, and O break energies between ∼1 and 10 MeV nucleon{sup −1}. The latter events are enriched in {sup 3}He and higher-energy Fe, and have Fe spectra that rollover at significantly lower energies compared with O, probably because Fe ions with smaller Q/M ratios can escape from the distant shock more easily than O ions with larger Q/M ratios. We conclude that SEP spectral properties result from many complex and competing effects, namely Q/M-dependent scattering, shock properties, and the origin of the seed populations, all of which must be taken into account to develop a comprehensive picture of CME-driven shock acceleration of large gradual SEP events.« less
  • The time-intensity profile of large solar energetic particle (SEP) event is well organized by solar longitude as observed at Earth orbit. This is mostly due to different magnetic connection to the shock that is associated with large SEP event propagates from the Sun to the heliosphere. Earlier studies have shown event averaged heavy ion abundance ratios can also vary as a function of solar longitude. It was found that the Fe/O ratio for high energy particle (>10 MeV/nucleon) is higher for those western magnetically well connected events compare to the eastern events as observed at L1 by the Advanced Composition Explorermore » (ACE) spacecraft. In this paper, we examined the low energy (∼1 MeV/nucleon) heavy ions in 110 isolated SEP events from 2009 to the end of 2014. In addition, the optical and radio signatures for all of our events are identified and when data are available we also located the associated coronal mass ejection (CME) data. Our survey shows a higher Fe/O ratio at events in the well-connected region, while there are no corrections between the event averaged elemental composition with the associated coronal mass ejection speed. This is inconsistent with the higher energy results, but inline with other recent low-energy measurements.« less