Injection and Interplanetary Transport of Near‐Relativistic Electrons: Modeling the Impulsive Event on 2000 May 1

J. Space Weather Space Clim.

Gómez-Herrero

et al. 2017

-We study two consecutive solar near-relativistic (>50 keV) electron events observed on 2014 August 1 by both STEREO spacecraft with a longitudinal separation of only about 35°. The events were unambiguously associated with a solar source location and not accompanied by type II radio bursts or coronal mass ejections. Despite their close location, the two spacecraft were embedded in different solar wind streams and the electron intensities observed by the two STEREOs showed clear differences in onset times, peak intensities and pitch-angle distributions. The apparently better connected spacecraft, STEREO B, observed a smaller and more isotropic intensity increase and a later event onset time than STEREO A. Since the interplanetary transport conditions of solar energetic particles (SEPs) have a direct influence on the characteristics of the observed temporal profiles and the particle anisotropies at the spacecraft location, our aim is to understand if the observations on 2014 August 1 could be explained by different interplanetary transport conditions along each flux tube connecting the spacecraft with the solar source. For that purpose, we use a Monte Carlo interplanetary transport model combined with an inversion procedure to fit the in-situ observations of the two near-relativistic multi-spacecraft electron events. This allows us to obtain the injection profiles at the Sun and infer the transport conditions, which are characterized by the electron radial mean free path, l r . We obtain an almost simultaneous release of electrons for both spacecraft in both events. The release is consistent with the timing and duration of the type III radio burst emission and it is larger for STEREO B, the better connected spacecraft. In addition, we obtain different transport conditions in different solar wind streams. We find that the stream in which STEREO B was embedded was more diffusive (l r = 0.1AU for Event I and l r = 0.06AU for Event II) than the stream in which STEREO A was embedded (l r = 0.31AU for Event I and l r = 0.37AU for Event II). These different transport regimes are sufficient to explain the early onset for the worse connected spacecraft, STEREO A, and the observation of larger and more anisotropic intensities.

Section: Modelingmentioning

confidence: 99%

Interplanetary transport of solar near-relativistic electrons on 2014 August 1 over a narrow range of heliolongitudes

Pacheco

J. Space Weather Space Clim.

Gómez-Herrero

et al. 2017

“…We simulate the interplanetary transport of SEPs injected at the root of an Archimedean spiral magnetic field line using the Monte Carlo technique (Agueda et al 2008). The model includes particle streaming along the magnetic field lines, pitch-angle focusing by the diverging IMF, pitch-angle scattering by magnetic fluctuations, adiabatic deceleration resulting from the interplay of scattering and focusing, and solar wind convection (Kocharov et al 1998;Vainio et al 2000).…”

Section: Interplanetary Transport Modelmentioning

confidence: 99%

“…We infer the interplanetary transport conditions and the injection time profile at the Sun from a set of in-situ measured sectored intensities by using the inversion technique presented in Agueda et al (2008) and Agueda et al (2009b). By taking the angular response of the sectors scanned by the LEFS60 telescope into account, it is possible to transform the simulated PADs into sectored intensities measured by the telescope (Agueda et al 2008).…”

Section: Fitting Techniquementioning

confidence: 99%

See 1 more Smart Citation

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

Vainio

Lario

2010

A&A

Self Cite

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.

“…This equation may take additional effects into account that arise, for example, from the spatial variation in the guiding magnetic field. A lot of work has been done in simulating this transport by numerically solving Fokker-Planck equations that include different effects, such as adiabatic focusing, adiabatic cooling or perpendicular diffusion, assuming different types of magnetic turbulence that lead to different shapes of the diffusion coefficients (for review see Dröge & Kartavykh 2009;Dröge et al 2010;Dröge 2003;Agueda et al 2008;Qin et al 2004;Ruffolo 1995).…”

Section: Introductionmentioning

confidence: 99%

A diffusive description of the focused transport of solar energetic particles

Artmann

Schlickeiser

et al. 2011

A&A

Self Cite

The transport of solar energetic charged particles along the interplanetary magnetic field in the ecliptic plane of the sun can be described roughly by a one-dimensional diffusion equation. Large-scale spatial variations of the guide magnetic field can be taken into account by adding an additional term to the diffusion equation that includes the effect of adiabatic focusing. We solve this equation analytically by assuming a point-like particle injection in time and space and a spatial power-law dependence for the focusing length and the spatial diffusion coefficient. We infer the intensity-and anisotropy-time profiles of solar energetic particles from this solution. Through these the influence of different assumptions for the diffusion parameters can be seen in a mathematically closed form. The comparison of calculated and measured intensity-and anisotropy-time profiles, which are a powerful diagnostic tool for interplanetary particle transport, gives information about the large-scale spatial dependence of the focusing length and the diffusion coefficient. For an exceptionally large solar energetic particle event, which did occur on 2001 April 15, we fit the 27−512 keV electron intensities and anisotropies observed by the Wind spacecraft using the theoretically derived profiles. We find a linear spatial dependence of the mean free path along the guiding magnetic field. We also find the mean free path to be energy independent, which supports the theory of "velocity-dependent diffusion". This means that the intensity profiles for the discussed energies exhibit the same shape if they are plotted against the traveled distance and not against the time. In this case the profiles differ only in their maximum values and we can determine the energy spectra of the solar flare electrons out of the scaling factor we need to fit the data. The derived spectra exhibits a power-law dependence ∝E −3 kin in an energy range from ∼50 keV to ∼500 keV.