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Geometric Triangulation of Imaging Observations to Track Coronal Mass Ejections Continuously Out to 1 AU  

Ying Liu   Submitted: 2010-01-08 15:20

We describe a geometric triangulation technique, based on time-elongation maps constructed from imaging observations, to track coronal mass ejections (CMEs) continuously in the heliosphere and predict their impact on the Earth. Taking advantage of stereoscopic imaging observations from STEREO, this technique can determine the propagation direction and radial distance of CMEs from their birth in the corona all the way to 1 AU. The efficacy of the method is demonstrated by its application to the 2008 December 12 CME, which manifests as a magnetic cloud (MC) from in situ measurements at the Earth. The predicted arrival time and radial velocity at the Earth are well confirmed by the in situ observations around the MC. Our method reveals non-radial motions and velocity changes of the CME over large distances in the heliosphere. It also associates the flux-rope structure measured in situ with the dark cavity of the CME in imaging observations. Implementation of the technique, which is expected to be a routine possibility in the future, may indicate a substantial advance in CME studies as well as space weather forecasting.

Authors: Ying Liu, Jackie A. Davies, Janet G. Luhmann, Angelos Vourlidas, Stuart D. Bale, Robert P. Lin
Projects: STEREO

Publication Status: Accepted for publication in ApJ Letters
Last Modified: 2010-01-09 08:18
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Coronal Mass Ejections and Global Coronal Magnetic Field Reconfiguration  

Ying Liu   Submitted: 2009-10-29 00:18

We investigate the role of coronal mass ejections (CMEs) in the global coronal magnetic field reconfiguration, a debate that has lasted for about two decades. Key evidence of the coronal field restructuring during the 2007 December 31 CME is provided by combining imaging observations from widely separated spacecraft with the potential-field source-surface (PFSS) model, thanks to the extraordinarily quiet Sun at the present solar minimum. The helmet streamer, previously disrupted by the CME, re-forms but is displaced southward permanently; the preexisting heliospheric plasma sheet (HPS) is also disrupted as evidenced by the concave-outward shape of the CME. The south polar coronal hole shrinks considerably. Plasma blobs moving outward along the newly formed HPS suggest the occurrence of magnetic reconnection between the fields blown open by the CME and the ambient adjacent open fields. A streamer-like structure is also observed in the wake of the CME and interpreted as a plasma sheet where the thin post-CME current sheet is embedded. These results are important for understanding the coronal field evolution over a solar cycle as well as the complete picture of CME initiation and propagation.

Authors: Liu, Y., J. G. Luhmann, R. P. Lin, S. D. Bale, A. Vourlidas, and G. J. D. Petrie
Projects: STEREO

Publication Status: 2009, Astrophys. J. Lett., 698, L51
Last Modified: 2009-10-29 10:11
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Relationship Between a Coronal Mass Ejection-Driven Shock and a Coronal Metric Type II Burst  

Ying Liu   Submitted: 2009-10-29 00:11

It has been an intense matter of debate whether coronal metric type II bursts are generated by coronal mass ejection (CME)-driven shocks or flare blast waves. Using unprecedented high-cadence observations from STEREO/SECCHI, we investigate the relationship between a metric type II event and a shock driven by the 2007 December 31 CME. The existence of the CME-driven shock is indicated by the remote deflection of coronal structures, which is in good timing with the metric type II burst. The CME speed is about 600 km s-1 when the metric type II burst occurs, much larger than the Alfvén speed of 419?489 km s-1 determined from band splitting of the type II burst. A causal relationship is well established between the metric and decametric?hectometric type II bursts. The shock height?time curve determined from the type II bands is also consistent with the shock propagation obtained from the streamer deflection. These results provide unambiguous evidence that the metric type II burst is caused by the CME-driven shock.

Authors: Liu, Y., J. G. Luhmann, S. D. Bale, and R. P. Lin
Projects: STEREO

Publication Status: 2009, Astrophys. J. Lett., 691, L151
Last Modified: 2009-10-29 10:11
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Subject will be restored when possible  

Ying Liu   Submitted: 2008-04-28 14:50

We examine the upstream meridional deflection flows of interplanetary coronal mass ejections (ICMEs) in an effort to investigate their cross-sectional shape and the magnetic field orientation in their sheath regions. Eight out of 11 magnetic clouds (MCs) near solar minimum identified for the curvature study are concave outward as indicated by the elevation angle of the MC normal with respect to the solar equatorial plane; an inverse correlation is observed between the meridional deflection flow and the spacecraft latitude for these concave-outward MCs, which suggests that the upstream plasma is deflected toward the equatorial plane. MHD simulations, however, show that the meridional deflection flow moves poleward for a concave-outward CME. The poleward flow deflection is observed only ahead of convex-outward MCs. Possibilities leading to this discrepancy are discussed. The deflection flow speed in sheath regions of ICMEs increases with the ICME speed relative to the ambient solar wind, which together with the coupling between the meridional magnetic field and deflection flow yields a positive linear correlation between the sheath meridional field and the ICME relative speed. This empirical relationship could predict the sheath meridional field based on the observed CME speed, which may be useful for space weather forecasting as ICME sheaths are often geoeffective. Implications of the deflection flows and ICME curvature are also discussed in terms of magnetic reconnection and particle acceleration in ICME sheaths.

Authors: Y. Liu, W. B. Manchester IV, J. D. Richardson, J. G. Luhmann, R. P. Lin, and S. D. Bale
Projects: None

Publication Status: Accepted for publication in JGR - Space Physics
Last Modified: 2008-04-28 15:51
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Subject will be restored when possible  

Ying Liu   Submitted: 2008-04-28 14:50

We examine the upstream meridional deflection flows of interplanetary coronal mass ejections (ICMEs) in an effort to investigate their cross-sectional shape and the magnetic field orientation in their sheath regions. Eight out of 11 magnetic clouds (MCs) near solar minimum identified for the curvature study are concave outward as indicated by the elevation angle of the MC normal with respect to the solar equatorial plane; an inverse correlation is observed between the meridional deflection flow and the spacecraft latitude for these concave-outward MCs, which suggests that the upstream plasma is deflected toward the equatorial plane. MHD simulations, however, show that the meridional deflection flow moves poleward for a concave-outward CME. The poleward flow deflection is observed only ahead of convex-outward MCs. Possibilities leading to this discrepancy are discussed. The deflection flow speed in sheath regions of ICMEs increases with the ICME speed relative to the ambient solar wind, which together with the coupling between the meridional magnetic field and deflection flow yields a positive linear correlation between the sheath meridional field and the ICME relative speed. This empirical relationship could predict the sheath meridional field based on the observed CME speed, which may be useful for space weather forecasting as ICME sheaths are often geoeffective. Implications of the deflection flows and ICME curvature are also discussed in terms of magnetic reconnection and particle acceleration in ICME sheaths.

Authors: Y. Liu, W. B. Manchester IV, J. D. Richardson, J. G. Luhmann, R. P. Lin, and S. D. Bale
Projects:

Publication Status: 2008, J. Geophys. Res., 113, A00B03, doi:10.1029/2007JA012996
Last Modified: 2008-09-23 21:09
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Deflection flows ahead of ICMEs as an indicator of curvature and geoeffectiveness  

Ying Liu   Submitted: 2008-04-28 14:50

We examine the upstream meridional deflection flows of interplanetary coronal mass ejections (ICMEs) in an effort to investigate their cross-sectional shape and the magnetic field orientation in their sheath regions. Eight out of 11 magnetic clouds (MCs) near solar minimum identified for the curvature study are concave outward as indicated by the elevation angle of the MC normal with respect to the solar equatorial plane; an inverse correlation is observed between the meridional deflection flow and the spacecraft latitude for these concave-outward MCs, which suggests that the upstream plasma is deflected toward the equatorial plane. MHD simulations, however, show that the meridional deflection flow moves poleward for a concave-outward CME. The poleward flow deflection is observed only ahead of convex-outward MCs. Possibilities leading to this discrepancy are discussed. The deflection flow speed in sheath regions of ICMEs increases with the ICME speed relative to the ambient solar wind, which together with the coupling between the meridional magnetic field and deflection flow yields a positive linear correlation between the sheath meridional field and the ICME relative speed. This empirical relationship could predict the sheath meridional field based on the observed CME speed, which may be useful for space weather forecasting as ICME sheaths are often geoeffective. Implications of the deflection flows and ICME curvature are also discussed in terms of magnetic reconnection and particle acceleration in ICME sheaths.

Authors: Y. Liu, W. B. Manchester IV, J. D. Richardson, J. G. Luhmann, R. P. Lin, and S. D. Bale
Projects:

Publication Status: 2008, J. Geophys. Res., 113, A00B03, doi:10.1029/2007JA012996
Last Modified: 2008-09-23 21:07
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Subject will be restored when possible  

Ying Liu   Submitted: 2008-04-10 15:11

We describe a method with which to measure the magnetic field orientation of coronal mass ejections (CMEs) using Faraday rotation (FR). Two basic FR profiles, Gaussian-shaped with a single polarity or N-shaped with polarity reversals, are produced by a radio source occulted by a moving flux rope, depending on its orientation. These curves are consistent with Helios observations, providing evidence for the flux rope geometry of CMEs. Many background radio sources can map CMEs in FR onto the sky. We demonstrate with a simple flux rope that the magnetic field orientation and helicity of the flux rope can be determined 2?3 days before it reaches the Earth, which is of crucial importance for space weather forecasting. An FR calculation based on global magnetohydrodynamic (MHD) simulations of CMEs in a background heliosphere shows that FR mapping can also resolve a CME geometry that curves back to the Sun. We discuss implementation of the method using data from the Mileura Widefield Array (MWA).

Authors: Y. Liu, W. B. Manchester IV, J. C. Kasper, J. D. Richardson, and J. W. Belcher
Projects: None

Publication Status: The Astrophysical Journal, 665:1439?1447, 2007 August 20
Last Modified: 2008-09-23 21:10
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Ying Liu   Submitted: 2008-04-10 15:02

The biggest halo coronal mass ejection (CME) since the Halloween storm in 2003, which occurred on 13 December 2006, is studied in terms of its solar source and heliospheric consequences. The CME is accompanied by an X3.4 flare, EUV dimmings and coronal waves. It generated significant space weather effects such as an interplanetary shock, radio bursts, major solar energetic particle (SEP) events, and a magnetic cloud (MC) detected by a fleet of spacecraft including STEREO, ACE, Wind and Ulysses. Reconstruction of the MC with the Grad-Shafranov (GS) method yields an axis orientation oblique to the flare ribbons. Observations of the SEP intensities and anisotropies show that the particles can be trapped, deflected and reaccelerated by the large-scale transient structures. The CME preceding shock is observed at both the Earth and Ulysses when they are separated by 74circ in latitude and 117circ in longitude, the largest shock extent ever detected. The shock arrival time at Ulysses is well predicted by an MHD model which can propagate the 1 AU data outward. The CME/shock is tracked remarkably well from the Sun all the way to Ulysses by coronagraph images, type II frequency drift, in situ measurements and the MHD model. These results reveal a technique which combines MHD propagation of the solar wind and type II emissions to predict the shock arrival time at the Earth, a signal advance for space weather forecasting especially when in situ data are available from the Solar Orbiter and Sentinels.

Authors: Y. Liu, J. G. Luhmann, P. C. Schroeder, L. Wang, Y. Li, R. P. Lin, S. D. Bale, R. Muller-Mellin, M. H. Acuna, and J.-A. Sauvaud
Projects: STEREO

Publication Status: Submitted to ApJ
Last Modified: 2008-04-16 05:32
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A comprehensive view of the 2006 December 13 CME: From the Sun to interplanetary space  

Ying Liu   Submitted: 2008-04-10 15:02

The biggest halo coronal mass ejection (CME) since the Halloween storm in 2003, which occurred on 2006 December 13, is studied in terms of its solar source and heliospheric consequences. The CME is accompanied by an X3.4 flare, EUV dimmings and coronal waves. It generated significant space weather effects such as an interplanetary shock, radio bursts, major solar energetic particle (SEP) events, and a magnetic cloud (MC) detected by a fleet of spacecraft including STEREO, ACE, Wind and Ulysses. Reconstruction of the MC with the Grad-Shafranov (GS) method yields an axis orientation oblique to the flare ribbons. Observations of the SEP intensities and anisotropies show that the particles can be trapped, deflected and reaccelerated by the large-scale transient structures. The CME-driven shock is observed at both the Earth and Ulysses when they are separated by 74circ in latitude and 117circ in longitude, the largest shock extent ever detected. The ejecta seems missed at Ulysses. The shock arrival time at Ulysses is well predicted by an MHD model which can propagate the 1 AU data outward. The CME/shock is tracked remarkably well from the Sun all the way to Ulysses by coronagraph images, type II frequency drift, in situ measurements and the MHD model. These results reveal a technique which combines MHD propagation of the solar wind and type II emissions to predict the shock arrival time at the Earth, a significant advance for space weather forecasting especially when in situ data are available from the Solar Orbiter and Sentinels.

Authors: Y. Liu, J. G. Luhmann, R. Muller-Mellin, P. C. Schroeder, L. Wang, R. P. Lin, S. D. Bale, Y. Li, M. H. Acuna, and J.-A. Sauvaud
Projects: SoHO-EIT,SoHO-LASCO,STEREO

Publication Status: 2008, ApJ, in press
Last Modified: 2008-09-23 21:10
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Ying Liu   Submitted: 2008-04-10 14:52

Coronal mass ejections (CMEs) are often assumed to be magnetic flux ropes, but direct proof has been lacking. A key feature, resulting from the translational symmetry of a flux rope, is that the total transverse pressure as well as the axial magnetic field has the same functional form over the vector potential along any crossing of the flux rope. We test this feature (and hence the flux-rope structure) by reconstructing the 2007 May 22 magnetic cloud (MC) observed at STEREO B, Wind/ACE, and possibly STEREO A with the Grad-Shafranov (GS) method. The model output from reconstruction at STEREO B agrees fairly well with the magnetic field and thermal pressure observed at ACE/Wind; the separation between STEREO B and ACE/Wind is about 0.06 AU, almost half of the MC radial width. For the first time, we reproduce observations at one spacecraft with data from another well-separated spacecraft, which provides compelling evidence for the flux-rope geometry and is of importance for understanding CME initiation and propagation. We also discuss the global configuration of the MC at different spacecraft on the basis of the reconstruction results.

Authors: Y. Liu, J. G. Luhmann, K. E. J. Huttunen, R. P. Lin, S. D. Bale, C. T. Russell, and A. B. Galvin
Projects: STEREO

Publication Status: The Astrophysical Journal, 677:L133?L136, 2008 April 20
Last Modified: 2008-09-23 21:10
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Abstracts by Author
Geometric Triangulation of Imaging Observations to Track Coronal Mass Ejections Continuously Out to 1 AU
Coronal Mass Ejections and Global Coronal Magnetic Field Reconfiguration
Relationship Between a Coronal Mass Ejection-Driven Shock and a Coronal Metric Type II Burst
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Subject will be restored when possible
Deflection flows ahead of ICMEs as an indicator of curvature and geoeffectiveness
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A comprehensive view of the 2006 December 13 CME: From the Sun to interplanetary space
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