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Waiting time distribution of solar energetic particle events modeled with a non-stationary Poisson process  

Chuan Li   Submitted: 2014-08-15 01:06

We present a study of the waiting time distributions (WTDs) of solar energetic particle (SEP) events observed with the spacecraft WIND and GOES. Both the WTDs of solar electron events (SEEs) and solar proton events (SPEs) display a power-law tail ~ Δ t-\gamma. The SEEs display a broken power-law WTD. The power-law index is \gamma1 = 0.99 for the short waiting times (<70 hours) and \gamma2 = 1.92 for large waiting times (>100 hours). The break of the WTD of SEEs is probably due to the modulation of the corotating interaction regions (CIRs). The power-law index \gamma ~ 1.82 is derived for the WTD of SPEs that is consistent with the WTD of type II radio bursts, indicating a close relationship between the shock wave and the production of energetic protons. The WTDs of SEP events can be modeled with a non-stationary Poisson process which was proposed to understand the waiting time statistics of solar flares (Wheatland 2000; Aschwanden & McTiernan 2010). We generalize the method and find that, if the SEP event rate \lambda = 1/Δ t varies as the time distribution of event rate f(\lambda) = A \lambda- α exp(-β \lambda), the time-dependent Poisson distribution can produce a power-law tail WTD ~ Δ t α - 3, where 0 ≤ α < 2.

Authors: Chuan Li, Sijia Zhong, Linghua Wang, Wei Su, and Cheng Fang
Projects: None

Publication Status: Accepted for publication in ApJ Letters
Last Modified: 2014-08-20 09:47
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Coronal magnetic topology and the production of solar impulsive energetic electrons  

Chuan Li   Submitted: 2013-07-18 04:54

We investigate two candidate solar sources or active regions (ARs) in association with a solar impulsive energetic electron (SIEE) event on 2002 October 20. The solar particle release (SPR) times of SIEEs are derived by using their velocity dispersion with consideration of the instrumental effect. It is found that there are double electron injections at the Sun. The low-energy (<13 keV) electron injection coincides with a C6.6 flare in AR10154 and is accompanied with prominent type III radio bursts rather than a stronger M1.8 flare in AR10160. The M1.8 flare produces, however, faint type III radio bursts. Electrons of ~25 to ~300 keV are released ~9 min later when a jet-like CME travels to ~2.6 solar radii. We further examine the coronal magnetic configurations above the two ARs based on the potential field source surface (PFSS) model. It is found that open field lines, rooted in AR10154 and well connected to the Earth, provide escaping channels for energetic electrons. Only a small portion of magnetic fields are opened above AR10160, being responsible for the faint type III radio bursts. These lines are, however, not well connected, making it impossible for SIEEs detection by near-Earth spacecraft. The results appear to establish a physical link between coronal magnetic topology, formation of type III radio bursts, and production of SIEEs.

Authors: C. Li, L. P. Sun, X. Y. Wang, and Y. Dai
Projects: None

Publication Status: A&A letters, accepted
Last Modified: 2013-07-18 18:46
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ELECTRON AND PROTON ACCELERATION DURING THE FIRST GROUND LEVEL ENHANCEMENT EVENT OF SOLAR CYCLE 24  

Chuan Li   Submitted: 2013-05-22 19:21

High-energy particles were recorded by near-Earth spacecraft and ground-based neutron monitors (NMs) on 2012 May 17. This event was the first ground level enhancement (GLE) of solar cycle 24. In this study, we try to identify the acceleration source(s) of solar energetic particles by combining in situ particle measurements from the WIND/ 3DP, GOES 13, and solar cosmic rays registered by several NMs, as well as remote-sensing solar observations from SDO/AIA, SOHO/LASCO, and RHESSI. We derive the interplanetary magnetic field (IMF) path length (1.25 ± 0.05 AU) and solar particle release time (01:29 ± 00:01 UT) of the first arriving electrons by using their velocity dispersion and taking into account contamination effects. We found that the electron impulsive injection phase, indicated by the dramatic change in the spectral index, is consistent with flare non-thermal emission and type III radio bursts. Based on the potential field source surface concept, modeling of the open-field lines rooted in the active region has been performed to provide escape channels for flare-accelerated electrons. Meanwhile, relativistic protons are found to be released ~10 minutes later than the electrons, assuming their scatter-free travel along the same IMF path length. Combining multi-wavelength imaging data of the prominence eruption and coronal mass ejection (CME), we obtain evidence that GLE protons, with an estimated kinetic energy of ~1.12 GeV, are probably accelerated by the CME-driven shock when it travels to ~3.07 solar radii. The time-of-maximum spectrum of protons is typical for shock wave acceleration.

Authors: Li, C., Firoz, K. A., Sun, L. P., Miroshnichenko, L. I.
Projects: None

Publication Status: ApJ, 770, 34, 2013
Last Modified: 2013-05-23 16:18
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BIDIRECTIONAL FLUXES OF NEARLY RELATIVISTIC ELECTRONS DURING THE ONSET OF SOLAR ENERGETIC PARTICLE EVENTS  

Chuan Li   Submitted: 2013-05-22 19:16

We report intensity and anisotropy measurements of energetic electrons in the energy range of ∼27?∼500 keV as observed with the Wind and Advanced Composition Explorer (ACE) spacecraft in 2000 June for several solar energetic particle (SEP) events. The solar sources of the SEP events are inferred from observations from the Solar and Heliospheric Observatory spacecraft. All of the events originate from the western limb active regions (ARs), which are well connected by interplanetary magnetic field (IMF) lines linking the Sun to near-Earth space. The observations on board Wind show bimodal pitch angle distributions (PADs), whereas ACE shows PADs with one peak, as is usually observed for impulsive injection of electrons at the Sun. During the time of observations, Wind was located, upstream of the Earth's bow shock in the dawn-noon sector, at distances of ∼40?∼80 RE from the Earth, and we infer that it was magnetically connected to the quasi-parallel bow shock. Meanwhile, ACE, orbiting the Sun?Earth libration point L1, was not connected to the bow shock. The electron intensity?time profiles and the energy spectra show that the backstreaming electrons observed at Wind are not of magnetospheric origin. The observations suggest rather that the bidirectional electron fluxes are due to reflection or scattering by an obstacle located at a distance of less than ∼150 RE in the anti-sunward direction, which is compatible with the obstacle being the Earth's bow shock or magnetosheath.

Authors: Sun, L. P. and Li, C.
Projects: None

Publication Status: ApJ, 765, 99, 2013
Last Modified: 2013-05-23 16:17
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Coronal jets, magnetic topologies, and the production of interplanetary electron streams  

Chuan Li   Submitted: 2011-06-17 13:24

We investigate the acceleration source of the impulsive solar energetic particle (SEP) events on 2007 January 24. Combining the in situ electron measurements and remote-sensing solar observations, as well as the calculated magnetic fields obtained from a potential-field source-surface model, we demonstrate that the jets associated with the hard X-ray flares and type-III radio bursts, rather than the slow and partial coronal mass ejections, are closely related to the production of interplanetary electron streams. The jets, originated from the well-connected active region (AR 10939) whose magnetic polarity structure favors the eruption, are observed to be forming in a coronal site, extending to a few solar radii, and having a good temporal correlation with the electron solar release. The open-field lines near the jet site are rooted in a negative polarity, along which energetic particles escape from the flaring AR to the near-Earth space, consistent with the in situ electron pitch angle distribution. The analysis enables us to propose a coronal magnetic topology relating the impulsive SEP events to their solar source.


Authors: Li, C., Matthews, S. A., van Driel-Gesztelyi, L., Sun, J., and Owen, C. J.
Projects: None

Publication Status: ApJ, 735, 43
Last Modified: 2011-06-18 06:54
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Major electron events and coronal magnetic configurations of the related solar active regions  

Chuan Li   Submitted: 2011-06-15 03:48

A statistical survey of 26 major electron events during the period 2002 February through the end of solar cycle 23 is presented. We have obtained electron solar onset times and the peak flux spectra for each event by fitting to a power-law spectrum truncated by an exponential high-energy tail, i.e., f(E) sim E<sup>-delta </sup>e<sup>-E/E<sub>0</sub></sup>. We also derived the coronal magnetic configurations of the related solar active regions (ARs) from the potential-field source-surface model. It is found that (1) 10 of the 11 well-connected open field-line events are prompt events whose solar onset times coincide with the maxima of flare emission and 13 of the 14 closed field-line events are delayed events. (2) A not-well-connected open field-line event and one of the closed field-line events are prompt events, they are both associated with large-scale coronal disturbances or dimming. (3) An averaged harder spectrum is found in open field-line events compared with the closed ones. Specifically, the averaged spectral index ? is of 1.6 ± 0.3 in open field-line events and of 2.0 ± 0.4 in closed ones. The spectra of three closed field-line events show infinite rollover energies E 0. These correlations clearly establish a significant link between the coronal magnetic field-line topology and the escape of charged particles from the flaring ARs into interplanetary space during the major solar energetic particle events.


Authors: Li, C., Owen, C. J., Matthews, S. A., Dai, Y., and Tang, Y. H.
Projects: None

Publication Status: ApJL, 720, L36
Last Modified: 2011-06-15 12:26
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Solar source of energetic particles in interplanetary space during the 2006 December 13 event  

Chuan Li   Submitted: 2009-07-17 05:20

An X3.4 solar are and a fast halo coronal mass ejection (CME) occurred on 2006 December 13, accompanied by a high flux of energetic particles recorded both in near-Earth space and at ground level. Our purpose is to provide evidence of flare acceleration in a major solar energetic particle (SEP) event. We first present observations from ACE/EPAM, GOES, and the Apatity neutron monitor. It is found that the initial particle release time coincides with the flare emission and that the spectrum becomes softer and the anisotropy becomes weaker during particle injection, indicating that the acceleration source changes from a confined coronal site to a widespread interplanetary CME-driven shock. We then describe a comprehensive study of the associated flare active region. By use of imaging data from HINODE/SOT and SOHO/MDI magnetogram, we infer the flare magnetic reconnection rate in the form of the magnetic flux change rate. This correlates in time with the microwave emission, indicating a physical link between the flare magnetic reconnection and the acceleration of nonthermal particles. Combining radio spectrograph data from Huairou/NOAC, Culgoora/IPS, Learmonth/RSTN, and WAVES/WIND leads to a continuous and longlasting radio burst extending from a few GHz down to several kHz. Based on the photospheric vector magnetogram from Huairou/NOAC and the nonlinear force free field (NFFF) reconstruction method, we derive the 3D magnetic fi eld confi guration shortly after the eruption. Furthermore, we also compute coronal fi eld lines extending to a few solar radii using a potential- field source-surface (PFSS) model. Both the so-called type III-l burst and the magnetic field configuration suggest that open-fi eld lines extend from the are active region into interplanetary space, allowing the accelerated and charged particles escape.

Authors: C. Li, Y. Dai, J. -C. Vial, C. J. Owen, S. A. Matthews, Y. H. Tang, C. Fang, and A. N. Fazakerley
Projects:

Publication Status: A&A, in press
Last Modified: 2009-08-26 01:54
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Solar source of energetic particles in interplanetary space during the 2006 December 13 event  

Chuan Li   Submitted: 2009-07-17 05:20

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: C. Li, Y. Dai, J. -C. Vial, C. J. Owen, S. A. Matthews, Y. H. Tang, C. Fang, and A. N. Fazakerley
Projects: None

Publication Status: A&A, 503, 1013
Last Modified: 2011-06-15 03:51
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Flare magnetic reconnection and relativistic particles in the 2003 October 28 event  

Chuan Li   Submitted: 2007-06-26 02:33

An X17.2 solar flare occurred on 2003 October 28, accompanied by multi-wavelength emissions and a high flux of relativistic particles observed at 1AU. We present the analytic results of the TRACE, SOHO, RHESSI, ACE, GOES, hard X-ray (INTEGRAL satellite), radio (Onderejov radio telescope), and neutron monitor data. It is found that the inferred magnetic reconnection electric field correlates well with the hard X-ray, gamma-ray, and neutron emission at the Sun. Thus the flare's magnetic reconnection probably makes a crucial contribution to the prompt relativistic particles, which could be detected at 1 AU. Since the neutrons were emitted a few minutes before the injection of protons and electrons, we propose a magnetic-field evolution configuration to explain this delay. We do not exclude the effect of CME-driven shock, which probably plays an important role in the delayed gradual phase of solar energetic particles.

Authors: C. Li, Y. H. Tang, Y. Dai, C. Fang, and J. -C. Vial
Projects: None

Publication Status: Accepted by A&A
Last Modified: 2007-06-26 09:08
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The acceleration characteristics of solar energetic particles in the 2000 July 14 event  

Chuan Li   Submitted: 2006-09-14 21:29

In large gradual solar energetic particle (SEP) events, especially the ground-level enhancement (GLE) events, where and how energetic particles are accelerated is still a problem. By using imaging data from TRACE, Yohkoh/HXT, SOHO/MDI and SOHO/EIT, along with the data from the GOES, Apatity NM, and SOHO/LASCO CME catalog, the evolution of the X5.7 two-ribbon flare and the associated SEP event on 14 July 2000 are studied. It is found that the magnetic reconnection in this event consists of two parts, and the induced electric field Erec is temporally correlated with the evolution of hard X-ray and gamma-ray emission. In particular, the first hard X-ray and gamma-ray emission peak occurred at 10:22 UT, corresponding to the magnetic reconnection in the western part of the flare ribbons and the maximum Erec of 9.5 V/cm; the second emission peak at 10:27 UT, corresponding to the eastern part and the maximum Erec of 13.0 V/cm. We also analyze the SEP injection profiles as functions of time and CME-height, and find two-component injection which may result from different acceleration mechanisms. A reasonable conclusion is that reconnection electric field makes a crucial contribution to the acceleration of relativistic particles and to the impulsive component of the large gradual SEP event, while CME-driven shocks play a dominant role in the gradual component.

Authors: C. Li, Y. H. Tang, Y. Dai, W. G. Zong, & C. Fang
Projects: None

Publication Status: A&A (in press)
Last Modified: 2006-09-18 17:51
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The acceleration characteristics of solar energetic particles in the 2000 July 14 event  

Chuan Li   Submitted: 2006-09-14 21:29

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: C. Li, Y. H. Tang, Y. Dai, W. G. Zong, & C. Fang
Projects:

Publication Status: A&A, 461, 1115
Last Modified: 2011-06-15 15:19
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Abstracts by Author
Waiting time distribution of solar energetic particle events modeled with a non-stationary Poisson process
Coronal magnetic topology and the production of solar impulsive energetic electrons
ELECTRON AND PROTON ACCELERATION DURING THE FIRST GROUND LEVEL ENHANCEMENT EVENT OF SOLAR CYCLE 24
BIDIRECTIONAL FLUXES OF NEARLY RELATIVISTIC ELECTRONS DURING THE ONSET OF SOLAR ENERGETIC PARTICLE EVENTS
Coronal jets, magnetic topologies, and the production of interplanetary electron streams
Major electron events and coronal magnetic configurations of the related solar active regions
Solar source of energetic particles in interplanetary space during the 2006 December 13 event
Solar source of energetic particles in interplanetary space during the 2006 December 13 event
Flare magnetic reconnection and relativistic particles in the 2003 October 28 event
The acceleration characteristics of solar energetic particles in the 2000 July 14 event
The acceleration characteristics of solar energetic particles in the 2000 July 14 event

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