Initial Fe/O Enhancements in Large, Gradual, Solar Energetic Particle Events: Observations from Wind and Ulysses

Tylka, A. J.; Malandraki, O.; Dorrian, Gareth; Ko, Yuan‐Kuen; Marsden, R. G.; Ng, C. K.; Tranquille, C.

doi:10.1007/s11207-012-0064-z

Cited by 33 publications

(39 citation statements)

References 49 publications

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“…Fe scatters less than C or O at constant velocity, for example, and high-energy particles less than those at low energy, so we see relatively Fe-rich SEPs with hard energy spectra early in events and Fe-poor SEPs with softer spectra later. Tylka et al (2012) (Reames et al, 1997;Reames, Ng, and Berdichevsky, 2001;Reames, 2000;Reames and Ng, 2004). Abundances of the elements, measured over a large number of gradual SEP events using LEMT, have not been reported previously.…”

Section: Introductionmentioning

confidence: 89%

“…We will see that the scattering mean free path depends upon a small power of a particle's magnetic rigidity, or momentum per unit charge (Parker, 1963;Ng, Reames, and Tylka, 2003;Tylka et al, 2012). This makes scattering depend upon both A/Q and velocity and is a principal cause of the abundance variations observed by Meyer (1985) and by Breneman and Stone (1985).…”

Section: Introductionmentioning

confidence: 90%

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Element Abundances in Solar Energetic Particles and the Solar Corona

Reames

2013

Sol Phys

103

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Section: Introductionmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 90%

Element Abundances in Solar Energetic Particles and the Solar Corona

Reames

2013

Sol Phys

103

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“…However, Event 9 has an even larger e/p ratio (∼4400). Ng et al 1999;Tylka et al 2013. ) In fact, relative to the gradual-SEP average value, the event-integrated Fe/O ratios in these three energy ranges are 2.46 ± 0.05, 1.36 ± 0.10, and 1.30 ± 0.19, respectively.…”

Section: Appendixmentioning

confidence: 99%

“…The elemental ratios in these events also show some transient structure near the start of the event, when particle intensities are low. This initial temporal structure is likely the result of rigidity-dependent interplanetary transport, which can arise when an ion's charge-to-mass ratio is different from that of oxygen (Tylka et al , 2013Ng et al 1999Ng et al , 2003Mason et al 2006). Although these transport distortions are seen in some of our events, they are present for too few hours to compromise our general characterization of the elemental composition.…”

Section: Notesmentioning

confidence: 99%

Source Regions of the Interplanetary Magnetic Field and Variability in Heavy-Ion Elemental Composition in Gradual Solar Energetic Particle Events

Tylka

et al. 2013

ApJ

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Gradual solar energetic particle (SEP) events are those in which ions are accelerated to their observed energies by interactions with a shock driven by a fast coronal mass ejection (CME). Previous studies have shown that much of the observed event-to-event variability can be understood in terms of shock speed and evolution in the shock-normal angle. However, an equally important factor, particularly for the elemental composition, is the origin of the suprathermal seed particles upon which the shock acts. To tackle this issue, we (1) use observed solar-wind speed, magnetograms, and the potential-field source-surface model to map the Sun-L1 interplanetary magnetic field (IMF) line back to its source region on the Sun at the time of the SEP observations and (2) then look for a correlation between SEP composition (as measured by Wind and Advanced Composition Explorer at ∼2-30 MeV nucleon −1 ) and characteristics of the identified IMF source regions. The study is based on 24 SEP events, identified as a statistically significant increase in ∼20 MeV protons and occurring in 1998 and 2003-2006, when the rate of newly emergent solar magnetic flux and CMEs was lower than in solar-maximum years, and the field-line tracing is therefore more likely to be successful. We find that the gradual SEP Fe/O is correlated with the field strength at the IMF source, with the largest enhancements occurring when the footpoint field is strong due to the nearby presence of an active region (AR). In these cases, other elemental ratios show a strong charge-to-mass (q/M) ordering (at least on average), similar to that found in impulsive events. Such results lead us to suggest that magnetic reconnection in footpoint regions near ARs bias the heavy-ion composition of suprathermal seed ions by processes qualitatively similar to those that produce larger heavy-ion enhancements in impulsive SEP events. To address potential technical concerns about our analysis, we also discuss efforts to exclude impulsive SEP events from our event sample.

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“…These include the possibility of strong longitudinal variations in the seed population composition sampled by different portions of an interplanetary shock and the effects of particle transport on the SEP composition evaluated at a common energy. Studies of the latter was recently performed by [14,15] and it was found that transport can have a significant influence on observed SEP composition. Such possible transport effects will be examined in a future study of the temporal evolution of the Fe/O ratios in these events.…”

Section: Discussionmentioning

confidence: 99%

Solar energetic particle characteristics and their dependence on longitude in solar cycle 24

Cohen¹,

Mason²,

Mewaldt³

et al. 2013

AIP Conference Proceedings

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Abstract. In previous solar cycles, most studies examining the longitude dependence of solar energetic particle (SEP) event characteristics (such as composition and spectral hardness) have involved statistical analysis of single-point measurements. With the significant separation between the two STEREO and near-Earth spacecraft during solar cycle 24, these SEP characteristics can be examined simultaneously from multiple vantage points. Using SEP measurements from sensors on STEREO and ACE, we have examined the longitude dependence of the Fe/O abundance ratio at 10 MeV/nuc and the oxygen spectral index for energies above 10 MeV/nuc. Longitudinal patterns were sought that support or refute the scenarios put forth by Tylka et al. and Cane et al. to explain the Fe-enriched large SEP events of cycle 23. Unfortunately few Fe-enriched events have occurred in cycle 24 and their longitudinal behavior is not entirely consistent with either of the proposed scenarios.

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Initial Fe/O Enhancements in Large, Gradual, Solar Energetic Particle Events: Observations from Wind and Ulysses

Cited by 33 publications

References 49 publications

Element Abundances in Solar Energetic Particles and the Solar Corona

Element Abundances in Solar Energetic Particles and the Solar Corona

Source Regions of the Interplanetary Magnetic Field and Variability in Heavy-Ion Elemental Composition in Gradual Solar Energetic Particle Events

Solar energetic particle characteristics and their dependence on longitude in solar cycle 24

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