Low‐energy solar electrons and ions observed at Ulysses February‐April, 1991: The inner heliosphere as a particle reservoir

Roelof, E. C.; Gold, R. E.; Simnett, G. M.; Tappin, S. J.; Armstrong, T. P.; Lanzerotti, L. J.

doi:10.1029/92gl01312

Cited by 113 publications

(84 citation statements)

References 5 publications

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“…The transit time for a 63 keV electron with zero-degree pitch-angle along an ideal spiral to 2.5 AU (i.e., a curvilinear distance of 3.3 AU for a solar wind velocity of 650 km/s) is one hour. Roelof et al (1992) state that the reason the rise is nearly velocity dispersionless with a near-constant spectrum is that the transit times for these particles are considerably shorter than the rise time of 3.1 h. Thus, the electrons easily populate the¯ux tube to 2.5 AU faster than their rate of injection. On March 23, Ulysses was located at a distance of 2.5 AU from the Sun, and the Ulysses footpoint mapped back to a longitude of ~W60°on the Sun as viewed from the Earth.…”

Section: Discussionmentioning

confidence: 99%

Probing the magnetic topology of coronal mass ejections by means of Ulysses/HI-SCALE energetic particle observations

2000

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Abstract. In this work, solar¯are energetic particlē uxes (E e ³ 42 keV) observed by the HI-SCALE instrument onboard Ulysses, a spacecraft that is probing the heliosphere in 3-D, are utilized as diagnostics of the large-scale structure and topology of the interplanetary magnetic ®eld (IMF) embedded within two well-identi®ed interplanetary coronal mass ejection (ICME) structures. On the basis of the energetic solar¯are particle observations ®rm conclusions are drawn on whether the detected ICMEs have been detached from the solar corona or are still magnetically anchored to it when they arrive at 2.5 AU. From the development of the angular distributions of the particle intensities, we have inferred that portions of the ICMEs studied consisted of both open and closed magnetic ®eld lines. Both ICMEs present a ®lamentary structure comprising magnetic ®laments with distinct electron anisotropy characteristics. Subsequently, we studied the evolution of the anisotropies of the energetic electrons along the magnetic ®eld loop-like structure of one ICME and computed the characteristic decay time of the anisotropy which is a measure of the amount of scattering that the trapped electron population underwent after injection at the Sun.

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Section: Discussionmentioning

confidence: 99%

Probing the magnetic topology of coronal mass ejections by means of Ulysses/HI-SCALE energetic particle observations

2000

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“…Previous observational studies (e.g. Anderson et al 1995;Roelof et al 1992;Bieber et al 2002;Tan et al 2009) have provided evidence of the presence of discrete solar windinterplanetary magnetic field structures beyond 1 AU, which are able to reflect SEPs back to the inner heliosphere. The present study provides another example in which the electron propagation is influenced by a similar structure.…”

Section: Discussionmentioning

confidence: 99%

Solar near-relativistic electron observations as a proof of a back-scatter region beyond 1 AU during the 2000 February 18 event

Agueda

Vainio

Lario

2010

A&A

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Aims. We study the near-relativistic (NR; >30 keV) electron event observed on 2000 February 18 by near-Earth spacecraft. Previous works have explained this event by assuming that the propagation of NR electrons is essentially "scatter-free" at heliocentric radial distances r < 1 AU, and that beyond 1 AU particles are "back-scattered" by magnetic field irregularities. Methods. Our aim is to re-visit this interplanetary propagation scenario and infer the injection profile at the Sun by fitting the electron directional intensities observed by the Advanced Composition Explorer. Results. We use a Monte Carlo transport model to explore this approach. We assume that the interplanetary magnetic field is an Archimedean spiral and that the interplanetary transport of NR electrons is characterized by a large radial mean free path (λ r > 0.5 AU) and anisotropic pitch-angle scattering for r < 1 AU, and a small radial mean free path (λ r < 0.5 AU) and isotropic scattering in the back-scatter region. Conclusions. The event cannot be explained without assuming a back-scatter region beyond 1 AU. The best fit is obtained by assuming λ r = 3.2 AU in the inner heliosphere and a back-scatter region characterized by a small mean free path λ r = 0.2 AU located beyond 1.2 AU.

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“…Helios 1 encounters the event near central meridian and observes a peak in the 3-6 MeV proton intensity near the shock passage time. The intensities at the other s/c, after reaching a peak, begin to track closely those seen at Helios 1 after they enter the socalled 'reservoir' region (see also McKibben 1972;Roelof et al 1992) in which the intensities and energy spectra are nearly identical. These results indicate that only a small number of particles can leak out of the reservoir.…”

Section: Multi-spacecraft Observations Of Sep Eventsmentioning

confidence: 65%

“…These results indicate that only a small number of particles can leak out of the reservoir. Observations have provided strong evidence for the location of magnetic 'barriers' in space beyond 1 AU and their role in determining the decay phase of SEP events and the establishment and maintenance of particle reservoirs in the heliosphere (Roelof et al 1992(Roelof et al , 2012aSarris and Malandraki 2003;Tan et al 2012). Reames et al (1996) also considered that the decay phase of the SEP events consists of particles propagating between the converging magnetic field near the Sun and a moving shell of strong scattering formed downstream of the distant traveling shocks.…”

Section: Multi-spacecraft Observations Of Sep Eventsmentioning

confidence: 99%

Solar Energetic Particles and Space Weather: Science and Applications

Malandraki

Crosby

2017

Astrophysics and Space Science Library

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This chapter provides an overview on solar energetic particles (SEPs) and their association to space weather, both from the scientific as well as from the applications perspective. A historical overview is presented on how SEPs were discovered in the 1940s and how our understanding has increased and evolved since then. Current state-of-the-art based on unique measurements obtained in the 3-dimensional heliosphere (e.g. by the Ulysses, ACE, STEREO spacecraft) and their analysis is also presented. Key open questions on SEP research expected to be answered in view of future missions that will explore the solar corona and inner heliosphere are highlighted. This is followed by an introduction to why SEPs are studied, describing the risks that SEP events pose on technology and human health. Mitigation strategies for solar radiation storms as well as examples of current SEP forecasting systems are reviewed, in context of the two novel real-time SEP forecasting tools developed within the EU H2020 HESPERIA project.

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Low‐energy solar electrons and ions observed at Ulysses February‐April, 1991: The inner heliosphere as a particle reservoir

Cited by 113 publications

References 5 publications

Probing the magnetic topology of coronal mass ejections by means of Ulysses/HI-SCALE energetic particle observations

Probing the magnetic topology of coronal mass ejections by means of Ulysses/HI-SCALE energetic particle observations

Solar near-relativistic electron observations as a proof of a back-scatter region beyond 1 AU during the 2000 February 18 event

Solar Energetic Particles and Space Weather: Science and Applications

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