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1.
This paper is designed to bring to the attention the fact that the effect of focusing of solar energetic particles is always essential as compared with scattering, no matter how small the value of the mean free path may be. That is why, an ordinary (focusing-free) diffusion approach can not be applied to the solar cosmic ray transport. In the case of high-energy solar particles, the focused diffusion is demonstrated to lead to a power law decay of energetic particle intensity much like an ordinary diffusion. However, the power law index of the decay is renormalized by the focusing. 相似文献
2.
E. Riihonen J. Torsti A. Anttila J. Kuusela M. Lumme E. Valtonen 《Annales Geophysicae》1996,14(5):503-509
The HED particle detector of the ERNE experiment to be flown on the SOHO spacecraft is unique compared to the earlier space-born detectors in its high directional resolution (better than 2°, depending on the track inclination). Despite the fixed view cone due to the three-axis stabilization of the spacecraft, the good angular and temporal resolution of the detector provides a new kind of opportunity for monitoring in detail the development of the anisotropies pertaining, for example, to the onset of SEP events, or passage of shock fronts related to gradual events. In order to optimize the measurement parameters, we have made a preflight simulation study of the HED anisotropy measurement capabilities. The purpose was to prove the feasibility of the selected measurement method and find the physical limits for the HED anisotropy detection. The results show HED to be capable of detecting both strong anisotropies related to impulsive events, and smoother anisotropies associated with gradual events. 相似文献
3.
This paper presents an integrated analysis of GOES 6, 7 and neutron monitor observations of solar cosmic-ray event following the 1990 May 24 solar flare. We have used a model which includes particle injection at the Sun and at the interplanetary shock front and particle propagation through the interplanetary medium. The model does not attempt to simulate the physical processes of coronal transport and shock acceleration, therefore the injections at the Sun and at the shock are represented by source functions in the particle transport equation. By fitting anisotropy and angle-average intensity profiles of high-energy (>30 MeV) protons as derived from the model to the ones observed by neutron monitors and at GOES 6 and 7, we have determined the parameters of particle transport, the injection rate and spectrum at the source. We have made a direct fit of uncorrected GOES data with both primary and secondary proton channels taken into account.The 1990 May 24–26 energetic proton event had a double-peaked temporal structure at energies 100 MeV. The Moreton (shock) wave nearby the flare core was seen clearly before the first injection of accelerated particles into the interplanetary medium. Some (correlated with this shock) acceleration mechanism which operates in the solar corona at a height up to one solar radius is regarded as a source of the first (prompt) increase in GOES and neutron monitor counting rates. The proton injection spectrum during this increase is found to be hard (spectral index 1.6) at lower energies ( 30 MeV) with a rapid steepening above 300 MeV. Large values of the mean free path ( 1.8 AU for 1 GV protons in the vicinity of the Earth) led to a high anisotropy of arriving protons. The second (delayed) proton increase was presumably produced by acceleration/injection of particles by an interplanetary shock wave at height of 10 solar radii. Our analysis of the 1990 May 24–26 event is in favour of the general idea that a number of components of energetic particles may be produced while the flare process develops towards larger spatial/temporal scales.Visiting Associate from St. Petersburg State Technical University, St. Petersburg 195251, Russia. 相似文献
4.
J. L. Bertaux E. Kyrölä E. Quémerais R. Pellinen R. Lallement W. Schmidt M. Berthé E. Dimarellis J. P. Goutail C. Taulemesse C. Bernard G. Leppelmeier T. Summanen H. Hannula H. Huomo V. Kehlä S. Korpela K. Leppälä E. Strömmer J. Torsti K. Viherkanto J. F. Hochedez G. Chretiennot R. Peyroux T. Holzer 《Solar physics》1995,162(1-2):403-439
On board the SOHO spacecraft poised at L1 Lagrange point, the SWAN instrument is mainly devoted to the measurement of large scale structures of the solar wind, and in particular the distribution with heliographic latitude of the solar wind mass flux. This is obtained from an intensity map of the sky Lyman emission, which reflects the shape of the ionization cavity carved in the flow of interstellar H atoms by the solar wind. The methodology, inversion procedure and related complications are described. The subject of latitude variation of the solar wind is shortly reviewed: earlier Lyman results from Prognoz in 1976 are confirmed by Ulysses. The importance of the actual value of the solar wind mass flux for the equation of dynamics in a polar coronal hole is stressed. The instrument is composed of one electronic unit commanding two identical Sensor Units, each of them allowing to map a full hemisphere with a resolution of 1°, thanks to a two-mirrors periscope system. The design is described in some details, and the rationale for choice between several variants are discussed. A hydrogen absorption cell is used to measure the shape of the interplanetary Lyman line and other Lyman emissions. Other types of observations are also discussed : the geocorona, comets (old and new), the solar corona, and a possible signature of the heliopause. The connexion with some other SOHO instruments, in particular LASCO, UVCS, SUMER, is briefly discussed. 相似文献
5.
Monte Carlo simulations of interplanetary transport are employed to study adiabatic energy losses of solar protons during
propagation in the interplanetary medium. We consider four models. The first model is based on the diffusion-convection equation.
Three other models employ the focused transport approach. In the focused transport models, we simulate elastic scattering
in the local solar wind frame and magnetic focusing. We adopt three methods to treat scattering. In two models, we simulate
a pitch-angle diffusion as successive isotropic or anisotropic small-angle scatterings. The third model treats large-angle
scatterings as numerous small-chance isotropizations. The deduced intensity–time profiles are compared with each other, with
Monte Carlo solutions to the diffusion-convection equation, and with results of the finite-difference scheme by Ruffolo (1995).
A numerical agreement of our Monte Carlo simulations with results of the finite-difference scheme is good. For the period
shortly after the maximum intensity time, including deceleration can increase the decay rate of the near-Earth intensity essentially
more than would be expected based on advection from higher momenta. We, however, find that the excess in the exponential-decay
rate is time dependent. Being averaged over a reasonably long period, the decay rate of the near-Earth intensity turns out
to be close to that expected based on diffusion, convection, and advection from higher momenta. We highlight a variance of
the near-Earth energy which is not small in comparison with the energy lost. It leads to blurring of any fine details in the
accelerated particle spectra. We study the impact of realistic spatial dependencies of the mean free path on adiabatic deceleration
and on the near-Earth intensity magnitude. We find that this impact is essential whenever adiabatic deceleration itself is
important. It is also found that the initial angular distribution of particles near the Sun can markedly affect MeV-proton
energy losses and intensities observed at 1 AU. Computations invoked during the study are described in detail. 相似文献
6.
Energetic Particle Fluxes during the Bastille Day Solar Eruption 总被引：2，自引：0，他引：2
We report on our observations of solar energetic particle fluxes of p, He, C, O, Ne, Mg, Si, and Fe ions measured by the Energetic and Relativistic Nucleon and Electron (ERNE) experiment associated
with the Bastille Day solar flare and coronal mass ejection (CME) on 14 July 2000. We observed two clear maxima of the Fe/O
ratio at the energies 8.5–15 MeV nucl−1. The first Fe/O maximum occurred ∼ 3 hours after the beginning of the particle event, and the second maximum ∼ 22 hours after
the first one at the arrival of the shock associated with the Bastille Day eruption. We also observed a change in the energy
spectrum of oxygen concurrent with a change in the direction of the interplanetary magnetic field at the start of the second
enhancement of the Fe/O ratio. We propose an interpretation of the particle event where observed interplanetary particle fluxes
are associated with two different particle sources near the Sun and in interplanetary space. We suggest that heavy ions observed
during the first period of the Fe/O enhancement were released when a coronal shock reached a magnetic foot point connected
to 1 AU. The second maximum of Fe/O occurred when spacecraft encountered Fe-rich material stored in magnetic field flux tubes
early in the event and was possibly reaccelerated by the interplanetary shock. 相似文献
7.
Kocharov L. G. Torsti J. Tang F. Zirin H. Kovaltsov G. A. Usoskin I. G. 《Solar physics》1997,172(1-2):271-278
This paper demonstrates the important interplanetary manifestation of strongly tilted magnetic fields at the flare site. We start with analysis of Big Bear Solar Observatory (BBSO) observations of magnetic structures at sites of two flares responsible for >100 MeV neutron events. Based on these observations, a model of neutron production is considered. This model takes into account the observed large tilt of magnetic field lines at footpoints of flare magnetic loops. Results of the new calculations are compared with both previous calculations and observations. The tilt of magnetic field lines at the flare site is proved to be the most important parameter limiting anisotropy of high-energy secondary emission in solar flares. 相似文献
8.
Torsti J. Valtonen E. Anttila A. Vainio R. Mäkelä P. Riihonen E. Teittinen M. 《Solar physics》1997,170(1):193-204
The energy spectra of the anomalous components of helium, nitrogen and oxygen have been measured by the ERNE experiment on board the SOHO spacecraft. During February 28–April 30, 1996, the maximum intensity of anomalous helium was found to be 3.8 × 10-5 cm-2 sr-1 s-1 (MeV nucl-1)-1 in the energy range 10–15 MeV nucl-1. During the period January 26–April 30, 1996, the maximum oxygen intensity was 1.2 × 10-5 cm-2 sr-1 s-1 (MeV nucl-1)-1 at 4–7 MeV nucl-1, and the maximum nitrogen intensity 1.7 × 10-6 cm-2 sr-1 s-1 (MeV nucl-1)-1 at 4–9 MeV nucl-1. These peak intensities are at the same level as two solar cycles ago in 1977, but significantly higher than in 1986. This gives observational evidence for a 22-year solar modulation cycle. A noteworthy point is that the spectra of anomalous nitrogen and oxygen appear to be somewhat broader than in 1977. 相似文献
9.
A joint analysis of neutron monitor and GOES data is performed to study the production of high-energy neutrons at the Sun. The main objects of the research are the spectrum of >50 MeV neutrons and a possible spectrum of primary (interacting) protons which produced those neutrons during the major 1990 May 24 solar flare. Different possible scenarios of the neutron production are presented. The high magnitude of the 1990 May 24 neutron event provided an opportunity to detect neutron decay protons of higher energies than ever before. We compare predictions of the proposed models of neutron production with the observations of protons on board GOES 6 and 7. It is shown that the precursor in high-energy GOES channels observed during 20:55–21:09 UT can be naturally explained as originating from decay of neutrons in the interplanetary medium. The ratio of counting rates observed in different GOES channels can ensure the selection of the model parameters.The set of experimental data can be explained in the framework of a scenario which assumes the existence of two components of interacting protons in the flare. A hard spectrum component (the first component) generates neutrons during a short time while the interaction of the second (soft spectrum) component lasts longer. Alternative scenarios are found to be of lesser likelihood. The intensity-time profile of neutron - decay protons as predicted in the framework of the two-component exponential model of neutron production (Kocharov et al., 1994a) is in an agreement with the proton profiles observed on board GOES. We compare the deduced characteristics of interacting high-energy protons with the characteristics of protons escaping into the interplanetary medium. It is shown that, in the 100–1000 MeV range, the spectrum of the second component of interacting protons was close to the spectrum of the prompt component of interplanetary protons. However, it is most likely that, at 300 MeV, the interacting proton spectrum was slightly softer than the spectrum of interplanetary protons. An analysis of gamma-ray emission is required to deduce the spectrum of interacting protons below 100 MeV and above 1 GeV. 相似文献
10.
Torsti J. Valtonen E. Kocharov L. G. Vainio R. Riihonen E. Anttila A. Laitinen T. Teittinen M. Kuusela J. 《Solar physics》1997,170(1):179-191
The energetic particle instrument ERNE on-board SOHO started its observations on December 15, 1995. The low-energy sensor of ERNE, LED, is capable of measuring particles in the energy range from 1 to 10 MeV nucl-1. From the beginning of the year 1996 until May 22, 1996, LED-observations included four energetic particle events above threshold intensities. An energetic particle event caused by a corotating interaction region that accelerated protons upto 10 MeV, was observed during January 20–25. Another similar particle event occured on May 6–12. The events were separated by four solar rotation periods. They had similar time profiles, but the one in May had a harder spectrum and a lower intensity level. The 4He-to-proton ratios were in accordance with the solar wind value. Energetic particles observed during April 22–23 and May 14–17 were accelerated at the Sun. The first one was apparently an outcome from an active region observed on the west limb by telescopes on-board SOHO. Protons were detected at energies from 1 to 10 MeV. For this event, the4He-to-proton ratio in the range 1.5–5 MeV nucl-1 was 3%. No 3He ions were detected. The period of May 14–15 was, in contrast, extremely 3He-rich: it had a3He-to-proton ratio of 1.5 ± 0.6 and a 3He-to- 4He ratio as high as 8. The period of May 14–17 comprised at least three individual, one-day-long events. The first two events were 3He-rich, while the last one seemed to have a normal composition. 相似文献