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Release History and Transport Parameters of Relativistic Solar Electrons Inferred From Near-the-Sun In-situ Observations  

Neus Agueda   Submitted: 2016-09-22 07:29

We study four consecutive 300-800 keV electron events observed on 1980 May 28 by Helios-1, when the spacecraft was located at 0.31 AU from the Sun. We use two different techniques to extract the release time history of electrons at the Sun: (1) a data-driven method based on the assumption that particles conserve their magnetic moment as they propagate between the Sun and the spacecraft and (2) an inversion method that utilizes particle transport simulation results. Both methods make use of the particle angular distributions measured relative to the local direction of the magnetic field. The general characteristics of the release time profiles obtained by these two techniques are similar, especially during their rising phases. We find indications that the strength of the interplanetary scattering varies with the size of the solar parent event, suggesting that scattering processes are not necessarily an inherent property of the medium but are related to the amount of released particles at the Sun. We use the inferred release profiles to compute the expected intensities at 1 AU. In contrast to simultaneous near-Earth observations by IMP-8, our simulations predict the observation of four separate events at 1 AU. Processes that could contribute to the observation of one single time-extended event at 1 AU include (1) distinct magnetic connections of the spacecraft to the particle sources, (2) the spatio-temporal evolution of the particle sources, and (3) different particle transport conditions, including a variation of λr with radial distance and/or heliolongitude, as well as the possibility that electrons reached IMP-8 by diffusion perpendicular to the interplanetary magnetic field.

Authors: Agueda N. & Lario D.
Projects: None

Publication Status: Accepted
Last Modified: 2016-09-23 15:46
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Current Sheet Regulation of Solar Near-Relativistic Electron Injection Histories  

Neus Agueda   Submitted: 2013-01-28 04:57

We present a sample of three large near-relativistic (>50 keV) electron events observed in 2001 by both the ACE and the Ulysses spacecraft, when Ulysses was at high-northern latitudes (>60?) and close to 2 AU. Despite the large latitudinal distance between the two spacecraft, electrons injected near the Sun reached both heliospheric locations. All three events were associated with large solar flares, strong decametric type II radio burst and accompanied by wide (>212?) and fast (>1400 km s-1) coronal mass ejections (CMEs). We use advanced interplanetary transport simulations and make use of the directional intensities observed in-situ by the spacecraft, to infer the electron injection profile close to the Sun and the interplanetary transport conditions at both low and high latitudes. For the three selected events, we find similar interplanetary transport conditions at different heliolatitudes for a given event, with values of the mean free path ranging from 0.04 AU to 0.27 AU. We find differences in the injection profiles inferred for each spacecraft. We investigate the role that sector boundaries of the heliospheric current sheet (HCS) have on determining the characteristics of the electron injection profiles. Extended injection profiles, associated with coronal shocks, are found if the magnetic footpoints of the spacecraft lay in the same magnetic sector as the associated flare, while intermittent sparse injection episodes appear when the spacecraft footpoints are in the opposite sector or a wrap in the HCS bounded the CME structure.

Authors: N. Agueda, R. Vainio, S. Dalla, D. Lario, B. Sanahuja
Projects: ACE

Publication Status: Accepted
Last Modified: 2013-01-28 09:28
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A Database of >20 keV Electron Green's Functions of Interplanetary Transport at 1 AU  

Neus Agueda   Submitted: 2012-10-01 07:56

We use interplanetary transport simulations to compute a database of electron Green's functions, i.e., differential intensities resulting at the spacecraft position from an impulsive injection of energetic (>20 keV) electrons close to the Sun, for a large number of values of two standard interplanetary transport parameters: the scattering mean free path and the solar wind speed. The nominal energy channels of the ACE, STEREO, and Wind spacecraft have been used in the interplanetary transport simulations to conceive a unique tool for the study of near-relativistic electron events observed at 1 AU. In this paper, we quantify the characteristic times of the Green's functions (onset and peak time, rise and decay phase duration) as a function of the interplanetary transport conditions. We use the database to calculate the FWHM of the pitch-angle distributions at different times of the event and under different scattering conditions. This allows us to provide a first quantitative result that can be compared with observations, and to assess the validity of the frequently used term beam-like pitch-angle distribution.

Authors: Agueda N., Vainio R., Sanahuja B.
Projects: ACE,STEREO,Wind

Publication Status: ApJS, 202, 18, 2012
Last Modified: 2012-10-01 10:52
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Multi-spacecraft Study of the 8 November 2000 SEP Event: Electron Injection Histories 100 Degrees Apart  

Neus Agueda   Submitted: 2012-03-30 03:56

We present the analysis of a large solar near-relativistic electron event observed by the Ulysses and the ACE spacecraft on 8 November 2000, when Ulysses was located at a heliocentric distance of 2.4 AU and at a heliographic latitude of ∼80? S. We use a particle propagation model to infer the local interplanetary transport conditions and the injection histories of the near-relativistic electrons observed by both spacecraft. We find different local transport conditions for each set of observations. The inferred injection profiles for both spacecraft extend for several hours; but the injection at Ulysses was smaller and started later. The association with type II radio emission suggests that the heliospheric electrons were provided by coronal shock acceleration. An analysis of the in situ magnetic field and plasma measurements indicates that the global configuration of the heliosphere (disturbed by transient structures) could play a role in shaping the characteristics of solar energetic particle events observed from different locations.

Authors: N. Agueda, D. Lario, V. Ontiveros, E. Kilpua, B. Sanahuja and R. Vainio
Projects: None

Publication Status: In press
Last Modified: 2012-03-30 11:08
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Subject will be restored when possible  

Neus Agueda   Submitted: 2007-12-10 02:04

We present a Monte Carlo method to model the transport of solar nearrelativistic electrons in the interplanetary medium, including adiabatic focusing, pitch-angle dependent scattering, and solar wind effects. By taking into account the angular response of the LEFS60 telescope of the EPAM instrument on board the ACE spacecraft, we transform the simulated pitch-angle distributions into the sectored intensities measured by the telescope. The goal is to deconvolve the effects of the interplanetary transport in order to infer the underlying injection profile and the radial mean free path of the electrons. We apply the model to the near-relativistic electron event observed on 2000 May 1, associated with an impulsive X-ray flare, type III radio bursts, and a narrow fast CME. The deconvolved interplanetary transport conditions reveal a long radial mean free path of 0.9 AU and pitch-angle dependent scattering. The eight observed sectored intensities are fitted in detail for more than 90 min, except for a short period (∼12 min) right after the time of peak intensities. This discrepancy may suggest that the assumed scattering model performs more efficiently than the actual scattering processes at work. The resulting injection profile consists of two main components, an initial component lasting 2?3 min and probably related to a type III radio burst observed by WIND/WAVES at ∼10:21 UT, and a delayed component starting at the Sun around 10:35 UT with a typical injection decay time scale of ∼0.5 h. The delayed component may be related to the CME-driven shock.

Authors: N. Agueda, R. Vainio, D. Lario, and B. Sanahuja
Projects: None

Publication Status: ApJ (in press)
Last Modified: 2007-12-10 11:17
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Abstracts by Author
Release History and Transport Parameters of Relativistic Solar Electrons Inferred From Near-the-Sun In-situ Observations
Current Sheet Regulation of Solar Near-Relativistic Electron Injection Histories
A Database of >20 keV Electron Green's Functions of Interplanetary Transport at 1 AU
Multi-spacecraft Study of the 8 November 2000 SEP Event: Electron Injection Histories 100 Degrees Apart
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