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Injection of solar energetic particles into both loop legs of a magnetic cloud  

Nina Dresing   Submitted: 2016-01-06 09:49

Context. Each of the two Solar TErrestrial RElations Observatory (STEREO) spacecraft carries a Solar Electron and Proton Telescope (SEPT) which measures electrons and protons. Anisotropy observations are provided in four viewing directions: along the nominal magnetic field Parker spiral in the ecliptic towards the Sun (SUN) and away from the Sun (Anti-Sun / ASUN), and towards the north (NORTH) and south (SOUTH). The solar energetic particle (SEP) event on 7 November 2013 was observed by both STEREO spacecraft, which were longitudinally separated by 68? at that time. While STEREO A observed the expected characteristics of an SEP event at a well-connected position, STEREO B detected a very anisotropic bi-directional distribution of near-relativistic electrons and was situated inside a magnetic-cloud-like structure during the early phase of the event. Aims. We examine the source of the bi-directional SEP distribution at STEREO B. On the one hand this distribution could be caused by a double injection into both loop legs of the magnetic cloud (MC). On the other hand, a mirroring scenario where the incident beam is reflected in the opposite loop leg could be the reason. Furthermore, the energetic electron observations are used to probe the magnetic structure inside the magnetic cloud. Methods. We investigate in situ plasma and magnetic field observations and show that STEREO B was embedded in an MC-like structure ejected three days earlier on 4 November from the same active region. We apply a Graduated Cylindrical Shell (GCS) model to the coronagraph observations from three viewpoints as well as the Global Magnetic Cloud (GMC) model to the in situ measurements at STEREO B to determine the orientation and topology of the MC close to the Sun and at 1 AU. We also estimate the path lengths of the electrons propagating through the MC to estimate the amount of magnetic field line winding inside the structure. Results. The relative intensity and timing of the energetic electron increases in the different SEPT telescopes at STEREO B strongly suggest that the bi-directional electron distribution is formed by SEP injections in both loop legs of the MC separately instead of by mirroring farther away beyond the STEREO orbit. Observations by the Nancay Hadioheliograph (NRH) of two distinct radio sources during the SEP injection further support the above scenario. The determined electron path lengths are around 50% longer than the estimated lengths of the loop legs of the MC itself (based on the GCS model) suggesting that the amount of field line winding is moderate.

Authors: Nina Dresing, Raúl Gómez-Herrero, Bernd Heber, Miguel Angel Hidalgo, Andreas Klassen, Manuela Temmer, Astrid Veronig
Projects: STEREO

Publication Status: accepted, in press
Last Modified: 2016-01-06 10:48
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Statistical survey of widely spread out solar electron events observed with STEREO and ACE with special attention to anisotropies  

Nina Dresing   Submitted: 2014-07-08 04:57

Context. In February 2011, the two STEREO spacecrafts reached a separation of 180 degrees in longitude, offering a complete view of the Sun for the first time ever. When the full Sun surface is visible, source active regions of solar energetic particle (SEP) events can be identified unambiguously. STEREO, in combination with near-Earth observatories such as ACE or SOHO, provides three well separated viewpoints, which build an unprecedented platform from which to investigate the longitudinal variations of SEP events. Aims. We show an ensemble of SEP events that were observed between 2009 and mid-2013 by at least two spacecrafts and show a remarkably wide particle spread in longitude (wide-spread events). The main selection criterion for these events was a longitudinal separation of at least 80 degrees between active region and spacecraft magnetic footpoint for the widest separated spacecraft. We investigate the events statistically in terms of peak intensities, onset delays, and rise times, and determine the spread of the longitudinal events, which is the range filled by SEPs during the events. Energetic electron anisotropies are investigated to distinguish the source and transport mechanisms that lead to the observed wide particle spreads. Methods. According to the anisotropy distributions, we divided the events into three classes depending on different source and transport scenarios. One potential mechanism for wide-spread events is efficient perpendicular transport in the interplanetary medium that competes with another scenario, which is a wide particle spread that occurs close to the Sun. In the latter case, the observations at 1 AU during the early phase of the events are expected to show significant anisotropies because of the wide injection range at the Sun and particle-focusing during the outward propagation, while in the first case only low anisotropies are anticipated. Results. We find events for both of these scenarios in our sample that match the expected observations and even different events that do not agree with the scenarios. We conclude that probably both an extended source region at the Sun and perpendicular transport in the interplanetary medium are involved for most of these wide-spread events.

Authors: N. Dresing, R. Gómez-Herrero, B. Heber, A. Klassen, O. Malandraki , W. Dr?ge , and Y. Kartavykh
Projects: STEREO

Publication Status: published
Last Modified: 2014-07-08 11:56
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The large longitudinal spread of solar energetic particles during the January 17, 2010 solar event  

Nina Dresing   Submitted: 2012-06-08 02:03

We investigate multi-spacecraft observations of the January 17, 2010 solar energetic particle event. Energetic electrons and protons have been observed over a remarkable large longitudinal range at the two STEREO spacecraft and SOHO suggesting a longitudinal spread of nearly 360 degrees at 1,AU. The flaring active region, which was on the backside of the Sun as seen from Earth, was separated by more than 100 degrees in longitude from the magnetic footpoints of each of the three spacecraft. The event is characterized by strongly delayed energetic particle onsets with respect to the flare and only small or no anisotropies in the intensity measurements at all three locations. The presence of a coronal shock is evidenced by the observation of a type II radio burst from the Earth and STEREO~B. In order to describe the observations in terms of particle transport in the interplanetary medium, including perpendicular diffusion, a 1D model describing the propagation along a magnetic field line (model 1) (Droege, 2003) and the 3D propagation model (model 2) by (Droege et al., 2010) including perpendicular diffusion in the interplanetary medium have been applied, respectively. While both models are capable of reproducing the observations, model 1 requires injection functions at the Sun of several hours. Model 2, which includes lateral transport in the solar wind, reveals high values for the ratio of perpendicular to parallel diffusion. Because we do not find evidence for unusual long injection functions at the Sun we favor a scenario with strong perpendicular transport in the interplanetary medium as explanation for the observations.

Authors: N. Dresing, R.Gomez-Herrero, A. Klassen, B. Heber, Y. Kartavykh, W. Droege
Projects: ACE,GONG,SoHO-EIT,STEREO

Publication Status: accepted
Last Modified: 2012-06-28 04:02
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The large longitudinal spread of solar energetic particles during the January 17, 2010 solar event  

Nina Dresing   Submitted: 2012-06-08 02:03

We investigate multi-spacecraft observations of the January 17, 2010 solar energetic particle event. Energetic electrons and protons have been observed over a remarkable large longitudinal range at the two STEREO spacecraft and SOHO suggesting a longitudinal spread of nearly 360 degrees at 1,AU. The flaring active region, which was on the backside of the Sun as seen from Earth, was separated by more than 100 degrees in longitude from the magnetic footpoints of each of the three spacecraft. The event is characterized by strongly delayed energetic particle onsets with respect to the flare and only small or no anisotropies in the intensity measurements at all three locations. The presence of a coronal shock is evidenced by the observation of a type II radio burst from the Earth and STEREO~B. In order to describe the observations in terms of particle transport in the interplanetary medium, including perpendicular diffusion, a 1D model describing the propagation along a magnetic field line (model 1) (Dr''oge, 2003) and the 3D propagation model (model 2) by (Dr''oge et al., 2010) including perpendicular diffusion in the interplanetary medium have been applied, respectively. While both models are capable of reproducing the observations, model 1 requires injection functions at the Sun of several hours. Model 2, which includes lateral transport in the solar wind, reveals high values for the ratio of perpendicular to parallel diffusion. Because we do not find evidence for unusual long injection functions at the Sun we favor a scenario with strong perpendicular transport in the interplanetary medium as explanation for the observations.

Authors: N. Dresing, R.G{'o}mez-Herrero, A. Klassen, B. Heber, Y. Kartavykh, W. Dr{"o}ge
Projects: ACE,GONG,SoHO-EIT,STEREO

Publication Status: accepted
Last Modified: 2012-06-28 04:01
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The large longitudinal spread of solar energetic particles during the January 17, 2010 solar event  

Nina Dresing   Submitted: 2012-06-08 02:03

We investigate multi-spacecraft observations of the January 17, 2010 solar energetic particle event. Energetic electrons and protons have been observed over a remarkable large longitudinal range at the two STEREO spacecraft and SOHO suggesting a longitudinal spread of nearly 360 degrees at 1,AU. The flaring active region, which was on the backside of the Sun as seen from Earth, was separated by more than 100 degrees in longitude from the magnetic footpoints of each of the three spacecraft. The event is characterized by strongly delayed energetic particle onsets with respect to the flare and only small or no anisotropies in the intensity measurements at all three locations. The presence of a coronal shock is evidenced by the observation of a type II radio burst from the Earth and STEREO~B. In order to describe the observations in terms of particle transport in the interplanetary medium, including perpendicular diffusion, a 1D model describing the propagation along a magnetic field line (model 1) (Dr''oge, 2003) and the 3D propagation model (model 2) by (Dr''oge et al., 2010) including perpendicular diffusion in the interplanetary medium have been applied, respectively. While both models are capable of reproducing the observations, model 1 requires injection functions at the Sun of several hours. Model 2, which includes lateral transport in the solar wind, reveals high values for the ratio of perpendicular to parallel diffusion. Because we do not find evidence for unusual long injection functions at the Sun we favor a scenario with strong perpendicular transport in the interplanetary medium as explanation for the observations.

Authors: N. Dresing, R.G'omez-Herrero, A. Klassen, B. Heber, Y. Kartavykh, W. Dr"oge
Projects: ACE,GONG,SoHO-EIT,STEREO

Publication Status: accepted
Last Modified: 2012-06-28 04:00
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The large longitudinal spread of solar energetic particles during the January 17, 2010 solar event  

Nina Dresing   Submitted: 2012-06-08 02:03

We investigate multi-spacecraft observations of the January 17, 2010 solar energetic particle event. Energetic electrons and protons have been observed over a remarkable large longitudinal range at the two STEREO spacecraft and SOHO suggesting a longitudinal spread of nearly 360 degrees at 1,AU. The flaring active region, which was on the backside of the Sun as seen from Earth, was separated by more than 100 degrees in longitude from the magnetic footpoints of each of the three spacecraft. The event is characterized by strongly delayed energetic particle onsets with respect to the flare and only small or no anisotropies in the intensity measurements at all three locations. The presence of a coronal shock is evidenced by the observation of a type II radio burst from the Earth and STEREO~B. In order to describe the observations in terms of particle transport in the interplanetary medium, including perpendicular diffusion, a 1D model describing the propagation along a magnetic field line (model 1) (Dr?ge, 2003) and the 3D propagation model (model 2) by (Dr?ge et al., 2010) including perpendicular diffusion in the interplanetary medium have been applied, respectively. While both models are capable of reproducing the observations, model 1 requires injection functions at the Sun of several hours. Model 2, which includes lateral transport in the solar wind, reveals high values for the ratio of perpendicular to parallel diffusion. Because we do not find evidence for unusual long injection functions at the Sun we favor a scenario with strong perpendicular transport in the interplanetary medium as explanation for the observations.

Authors: N. Dresing, R.Gomez-Herrero, A. Klassen, B. Heber, Y. Kartavykh, W. Dr?ge
Projects: ACE,GONG,SoHO-EIT,STEREO

Publication Status: accepted
Last Modified: 2012-06-28 03:59
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Abstracts by Author
Injection of solar energetic particles into both loop legs of a magnetic cloud
Statistical survey of widely spread out solar electron events observed with STEREO and ACE with special attention to anisotropies
The large longitudinal spread of solar energetic particles during the January 17, 2010 solar event
The large longitudinal spread of solar energetic particles during the January 17, 2010 solar event
The large longitudinal spread of solar energetic particles during the January 17, 2010 solar event
The large longitudinal spread of solar energetic particles during the January 17, 2010 solar event

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