Initial Time Dependence of Abundances in Solar Energetic Particle Events     

Reames DV  Ng CK  Tylka AJ 《The Astrophysical journal》2000,531(1):L83-L86

We compare the initial behavior of Fe/O and He/H abundance ratios and their relationship to the evolution of the proton energy spectra in "small" and "large" gradual solar energetic particle (SEP) events. The results are qualitatively consistent with the behavior predicted by the theory of Ng et al. published in 1999. He/H ratios that initially rise with time are a signature of scattering by non-Kolmogorov Alfvén wave spectra generated by intense beams of shock-accelerated protons streaming outward in large gradual SEP events.  相似文献   

Gamma-Ray Line Observations of the 2000 July 14 Flare and SEP Impact on the Earth     

Share  G.H.  Murphy  R.J.  Tylka  A.J.  Schwartz  R.A.  Yoshimori  M.  Suga  K.  Nakayama  S.  Takeda  H. 《Solar physics》2001,204(1-2):41-53

The HXS and GRS detectors on Yohkoh observed the 14 July 2000, X5.7 flare, beginning at ∼ 10:20 UT, ∼ 4 min before the peak in soft X-rays. The hard X-rays and γ-rays peaked ∼ 3 min later at ∼ 10:27 UT. Solar γ-ray emission lasted until ∼ 10:40 UT. Impact of high-energy ions at the Sun is revealed by the γ-ray lines from neutron capture, annihilation radiation and de-excitation that are visible above the bremsstrahlung continuum. From measurement of these lines we find that the flare-averaged spectrum of accelerated protons is consistent with a power law ge10 MeV with index 3.14±0.15 and flux 1.1×10³² protons MeV⁻¹ at 10 MeV. We estimate that there were ∼1.5×10³⁰ erg in accelerated ions if the power law extended without a break down to 1 MeV; this is about 1% of the energy in electrons > 20 keV from measurements of the hard X-rays. We find no evidence for spectral hardening in the hard X-rays that has been suggested as a predictor for the occurrence of solar energetic particle (SEP) events. This was the third largest proton event above 10 MeV since 1976. The GRS and HXS also observed γ-ray lines and continuum produced by the impact of SEP on the Earth's atmosphere beginning about 13 UT on 14 July. These measurements show that the SEP spectrum softened considerably over the next 24 hours. We compare these measurements with proton measurements in space.  相似文献   

Fluence Ordering of Solar Energetic Proton Events Using Cosmogenic Radionuclide Data     

G. A. Kovaltsov  I. G. Usoskin  E. W. Cliver  W. F. Dietrich  A. J. Tylka 《Solar physics》2014,289(12):4691-4700

While data on the cosmogenic isotopes ¹⁴C and ¹⁰Be made it possible to evaluate extreme solar proton events (SPEs) in the past, their relation to standard parameters quantifying the SPE strengths, viz. the integrated fluence of protons with energy above 30 MeV, F ₃₀, is ambiguous and strongly depends on the assumed shape of the energy spectrum. Here we propose a new index, the integral fluence of an SPE above 200 MeV, F ₂₀₀, which is related to the production of the cosmogenic isotopes ¹⁴C and ¹⁰Be in the Earth atmosphere, independently of the assumptions on the energy spectrum of the event. The F ₂₀₀ fluence is reconstructed from past cosmogenic isotope data, which provides an assessment of the occurrence probability density function for extreme SPEs. In particular, we evaluate that extreme SPEs with F ₂₀₀>10¹⁰ cm^?2 occur no more frequently than once per 10?–?15 kyr.  相似文献   

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

Allan J. Tylka  Olga E. Malandraki  Gareth Dorrian  Yuan-Kuen Ko  Richard G. Marsden  Chee K. Ng  Cecil Tranquille 《Solar physics》2013,285(1-2):251-267

Shocks driven by fast coronal mass ejections (CMEs) are the dominant particle accelerators in large, “gradual” solar energetic particle (SEP) events. In these events, the event-integrated value of the iron-to-oxygen ratio (Fe/O) is typically ～?0.1, at least at energies of a few MeV/nucleon. However, at the start of some gradual events, when intensities are low and growing, initially Fe/O is ～?1. This value is also characteristic of small, “impulsive” SEP events, in which particle acceleration is due to magnetic reconnection. These observations suggested that SEPs in gradual events also include a direct contribution from the flare that accompanied the CME launch. If correct, this interpretation is of critical importance: it indicates a clear path to interplanetary space for particles from the reconnection region beneath the CME. A key issue for the flare origin is “magnetic connectedness”, i.e., proximity of the flare site to the solar footpoint of the observer’s magnetic field line. We present two large gradual events observed in 2001 by Wind at L1 and by Ulysses, when it was located at >?60^° heliolatitude and beyond 1.6 AU. In these events, transient Fe/O enhancements at 5?–?10 MeV/nucleon were seen at both spacecraft, even though one or both is not “well-connected” to the flare. These observations demonstrate that an initial Fe/O enhancement cannot be cited as evidence for a direct flare component. Instead, initial Fe/O enhancements are better understood as a transport effect, driven by the different mass-to-charge ratios of Fe and O. We further demonstrate that the time-constant of the roughly exponential decay of the Fe/O ratio scales as R ², where R is the observer’s radial distance from the Sun. This behavior is consistent with radial diffusion. These observations thus also provide a potential constraint on models in which SEPs reach high heliolatitudes by cross-field diffusion.  相似文献   

Spatial Distribution of Solar Energetic Particles in the Inner Heliosphere     

Donald V. Reames  Chee K. Ng  Allan J. Tylka 《Solar physics》2013,285(1-2):233-250

We study the spatial distribution of solar energetic particles (SEPs) throughout the inner heliosphere during six large SEP events from the period 1977 through 1979, as deduced from observations on the Helios 1 and 2, IMP 7 and 8, ISEE 3, and Voyager 1 and 2 spacecraft. Evidence of intensity maxima associated with the expanding shock wave is commonly seen along its central and western flanks, although the region of peak acceleration or “nose” of the shock is sometimes highly localized in longitude. In one event (1 January 1978) a sharp peak in 20?–?30 MeV proton intensities is seen more strongly by Voyager at ～?2 AU than it is by spacecraft at nearby longitudes at ～?1 AU. Large spatial regions, or “reservoirs,” often exist behind the shocks with spatially uniform SEP intensities and invariant spectra that decrease adiabatically with time as their containment volume expands. Reservoirs are seen to sweep past 0.3 AU and can extend out many AU. Boundaries of the reservoirs can vary with time and with particle velocity, rather than rigidity. In one case, a second shock wave from the Sun reaccelerates protons that retain the same hard spectrum as protons in the reservoir from the preceding SEP event. Thus reservoirs can provide not only seed particles but also a “seed spectrum” with a spectral shape that is unchanged by a weaker second shock.  相似文献