Kelvin-Helmholtz Instability of the CME Reconnection Outflow Layer in the Low Corona |
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Claire Foullon Submitted: 2013-09-26 10:37
New capabilities for studying the Sun allow us to image for the first time the magnetic Kelvin-Helmholtz (KH) instability developing at the surface of a fast coronal mass ejecta (CME) less than 150 Mm above the solar surface. We conduct a detailed observational investigation of this phenomenon, observed off the east solar limb on 2010 November 3, in the EUV with SDO/AIA. In conjunction with STEREO-B/EUVI, we derive the CME source surface position. We ascertain the timing and early evolution of the CME outflow leading to the instability onset. We perform image and spectral analysis, exploring the CME plasma structuring and its parabolic flow pattern. As we evaluate and validate the consistency of the observations with theoretical considerations and predictions, we take the view that the ejecta layer corresponds to a reconnection outflow layer surrounding the erupting flux rope, accounting for the timing, high temperature (~11.6 MK), and high flow shear (~680 km s?1) on the unstable CME northern flank and for the observed asymmetry between the CME flanks. From the irregular evolution of the CME flow pattern, we infer a shear gradient consistent with expected spatial flow variations across the KH-unstable flank. The KH phenomenon observed is tied to the first stage of a linked flare-CME event.
Authors: Foullon, C., Verwichte, E., Nykyri, K., Aschwanden, M.J., Hannah, I. G.
Projects: GOES X-rays ,RHESSI,SDO-AIA,SoHO-EIT,SoHO-MDI,SoHO-LASCO,STEREO
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Publication Status: ApJ Vol. 767 (2), article 170
Last Modified: 2013-09-30 10:00
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Plasmoid Releases in the Heliospheric Current Sheet and Associated Coronal Hole Boundary Layer Evolution |
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Claire Foullon Submitted: 2011-05-17 12:13
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: Foullon, C., Lavraud, B., Luhmann, J.G., Farrugia, C.J., Retinò, A., Simunac, K.D.C., Wardle, N.C., Galvin, A.B., Kucharek, H., Owen, C.J., Popecki, M., Opitz, A. and Sauvaud, J.-A.
Projects: SoHO-LASCO,STEREO
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Publication Status: ApJ (in press)
Last Modified: 2011-05-17 19:26
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From large-scale loops to the sites of dense flaring loops: preferential conditions for long-period pulsations in solar flares |
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Claire Foullon Submitted: 2010-06-06 07:43
Long-period quasi-periodic pulsations (QPPs) of solar flares are a class apart from shorter period events. By involving an external resonator, the mechanism they call upon differs from traditional QPP models, but has wider applications. We present a multi-wavelength analysis of spatially-resolved QPPs, with periods around 10 min, observed in the X-ray spectrum primarily at energies between 3 and 25 keV. Complementary observations obtained in Hα and radio emission in the kHz to GHz frequency range, together with an analysis of the X-ray plasma properties provide a comprehensive picture that is consistent with a dense flaring loop subject to periodic energisation and thermalisation. The QPPs obtained in Hα and Type III radio bursts, with similar periods as the QPPs in soft X-ray, have the longest periods ever reported for those types of datasets. We also report 1-2 GHz radio emission, concurrent with but unrestricted to the QPP time intervals, which is multi-structured at regularly separated narrowband frequencies and modulated with ~18-min periods. This radio emission can be attributed to the presence of multiple 'quiet' large-scale loops in the background corona. Large-scale but shorter inner loops below may act as preferential resonators for the QPPs. The observations support interpretations consistent with both inner and outer loops subject to fast kink magnetohydrodynamic waves. Finally, X-ray imaging indicates the presence of double loop-top sources in the flaring sites, which could be the particular signatures of the magnetically-linked inner loops. We discuss the preferential conditions and the driving mechanisms causing the repeated flaring.
Authors: Foullon, C., Fletcher, L., Hannah I.G., Verwichte, E., Cecconi, B., Nakariakov, V.M., Phillips K.J.H. and Tan, B.L.
Projects: RHESSI
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Publication Status: ApJ (accepted)
Last Modified: 2010-06-07 08:04
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Heliospheric Current Sheet Distortions from Adjacent Outflowing Transients: Multi-spacecraft Observations |
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Claire Foullon Submitted: 2009-11-02 03:09
The heliospheric current sheet (HCS) is a permanent solar wind feature, with well predicted Earth passages, but it can be structured and its main orientation can be highly distorted. We report new observations from 2 spacecraft in the solar wind (supported by observations from 3 spacecraft in the nightside magnetosheath), showing an evolution across the Sun-Earth line of large field reversals adjacent to the HCS. Contrary to a previously reported multi-spacecraft event, this case shows that the field inversion structure cannot be assumed to be well preserved and close to planar on the scale of the magnetospheric cross-section. However, both cases indicate the presence of field reversals in an away sector that is connected to the southern solar magnetic hemisphere but lies unexpectedly above a toward sector. Following the interpretation of the reversals as transient outflowing loops, associated initial flow deviations can be envisaged to account for the HCS deformations.
Authors: C. Foullon, B. Lavraud, C. J. Owen, A. N. Fazakerley and R.M. Skoug
Projects: None
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Publication Status: AIP Proc. 12th Solar Wind Conference, St. Malo, France, June 2009 (Refereed) accepted
Last Modified: 2009-11-02 07:54
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The Apparent Layered Structure of the Heliospheric Current Sheet: Multi-Spacecraft Observations |
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Claire Foullon Submitted: 2009-08-29 07:54
Multiple current sheet crossings are ubiquitous features of the solar wind associated with high-beta plasma sheets, notably during the passage of the heliospheric current sheet (HCS). As the HCS is being convected past near Earth, we attempt to resolve spatial scales and temporal variations of the apparent layered structure of the HCS, including adjacent large scale field reversals. We use several spacecraft for good spatial and cross-scale coverage, spanning 550 RE across and 900 RE along the Sun-Earth line: STEREO, ACE and Cluster. The multi-spacecraft magnetic and plasma observations within the leading edge of the sector boundary are consistent with (i) a broad multi-layered structure; (ii) occasional non-planar structures and Alfvénic fluctuations; (iii) various stages of transient outflowing loops formed by interchange reconnection. By comparison of the observations at each spacecraft, we obtain a synthesis of the evolution between the patterns of loops, and hence of the transient outflow evolution along the sector boundary. In particular, we present circumstantial evidence that a heat flux dropout, traditionally signalling disconnection, can arise from interchange reconnection and scattering. Moreover, the inter-spacecraft comparison eliminates ambiguities between interpretations of electron counterstreaming. Overall, the sector boundary layer remains, locally, a steady structure as it is convected in the solar wind across a radial heliospheric distance of 560-580 RE. However, non-planar structures on the Cluster spatial scale, as well as the variations in angular changes and transition durations on the broader scale, indicate that we are not following the evolution of single loops but more likely a bunch of loops with variable properties.
Authors: Foullon, C., Lavraud, B., Wardle, N.C., Owen, C.J., Kucharek, H., Fazakerley, A.N., Larson, D.E., Lucek, E., Luhmann, J.G., Opitz, A., Sauvaud, J.-A., Skoug, R.M.
Projects: STEREO
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Publication Status: Solar Physics (accepted)
Last Modified: 2009-08-31 08:22
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The Apparent Layered Structure of the Heliospheric Current Sheet: Multi-Spacecraft Observations |
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Claire Foullon Submitted: 2009-08-29 07:54
Multiple current sheet crossings are ubiquitous features of the solar wind associated with high-beta plasma sheets, notably during the passage of the heliospheric current sheet (HCS). As the HCS is being convected past near Earth, we attempt to resolve spatial scales and temporal variations of the apparent layered structure of the HCS, including adjacent large scale field reversals. We use several spacecraft for good spatial and cross-scale coverage, spanning 550 RE across and 900 RE along the Sun-Earth line: STEREO, ACE and Cluster. The multi-spacecraft magnetic and plasma observations within the leading edge of the sector boundary are consistent with (i) a broad multi-layered structure; (ii) occasional non-planar structures and Alfvénic fluctuations; (iii) various stages of transient outflowing loops formed by interchange reconnection. By comparison of the observations at each spacecraft, we obtain a synthesis of the evolution between the patterns of loops, and hence of the transient outflow evolution along the sector boundary. In particular, we present circumstantial evidence that a heat flux dropout, traditionally signalling disconnection, can arise from interchange reconnection and scattering. Moreover, the inter-spacecraft comparison eliminates ambiguities between interpretations of electron counterstreaming. Overall, the sector boundary layer remains, locally, a steady structure as it is convected in the solar wind across a radial heliospheric distance of 560-580 RE. However, non-planar structures on the Cluster spatial scale, as well as the variations in angular changes and transition durations on the broader scale, indicate that we are not following the evolution of single loops but more likely a bunch of loops with variable properties.
Authors: Foullon, C., Lavraud, B., Wardle, N.C., Owen, C.J., Kucharek, H., Fazakerley, A.N., Larson, D.E., Lucek, E., Luhmann, J.G., Opitz, A., Sauvaud, J.-A., Skoug, R.M.
Projects: STEREO
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Publication Status: Solar Physics (online first), DOI:10.1007/s11207-009-9452-4
Last Modified: 2009-09-28 09:47
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Ultra-long-period Oscillations in EUV Filaments near to Eruption: Two-wavelength Correlation and Seismology |
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Claire Foullon Submitted: 2009-06-05 08:00
We investigate whether or not ultra-long-period oscillations in EUV filaments can be related to their eruption. We report new observations of long-period (~ 10-30 h) oscillatory motions in an apparently quiescent filament as it crosses the solar disk, in a 12-minute-cadence SoHO/EIT 195? uninterrupted dataset. This dataset is chosen to explore characteristics of the filament oscillations depending on its eruptive behaviour, which is observed while the filament is still on the disk. The periods are found to increase in a near-stable regime prior to eruption. For the two sequences reported so far, we compare and link the EUV filament oscillations with pulsations in full-disk solar EUV irradiance from SoHO/CELIAS/SEM 304? flux measurements. In intervals with stationary periods, we find that the 304? pulsations and the 195? filament oscillations have similar periodicities, but are phase-shifted by about a quarter of period. The two-wavelength correlation serves to show that, when the filament is the dominant dynamical feature but can no longer be tracked on the disk, the full-disk irradiance may provide a mean to identify the period increase prior to the filament eruption. We use the periods thus obtained to estimate the height increase of filaments' suspending coronal magnetic field lines, based on a magnetohydrodynamical (MHD) wave interpretation of the oscillations. The results are consistent with changes in prominence heights detected off-limb and thus support the seismological tool employed. Other interpretations connected with thermal over-stability or MHD piston effect are possible. These theoretical predictions however do not explain the quarter-period shift between the two EUV-wavelength signals. In any case, the detected variations may provide a powerful diagnostic tool for the forecasting of prominence eruptions.
Authors: C. Foullon , E. Verwichte and V.M. Nakariakov
Projects: SoHO-EIT
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Publication Status: ApJ, accepted
Last Modified: 2009-06-05 08:01
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Multi-Spacecraft Study of the 21 January 2005 ICME: Evidence of Current Sheet Substructure Near the Periphery of a Strongly Expanding, Fast Magnetic Cloud |
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Claire Foullon Submitted: 2007-03-12 19:21
We examine the near-Earth Interplanetary Coronal Mass Ejection (ICME) apparently related to the intense Solar Energetic Particle (SEP) event of 20 January 2005. Our purpose is to contribute to the understanding of the macroscopic structure, evolution and dynamics of the solar corona and heliosphere. Using Cluster, ACE and Wind data in the solar wind, and Geotail data in the magnetosheath,
we perform a multi-spacecraft analysis of the ICME-driven shock, post-shock magnetic discontinuities and ejecta.
Traversals by the well-separated near-Earth spacecraft provide a coherent picture of the ICME geometry. Following the shock, the ICME sequence starts with a hot pileup, i.e., a sheath, followed by a fast ejecta characterised by a non-compressive density enhancement (NCDE), which is caused essentially by an enrichment in helium. The plasma and magnetic observations of the ejecta are consistent with the outskirts of a structure in strong expansion, consisting of nested magnetic loops still connected to the Sun. Within the leading edge of the ejecta, we establish the presence of a tilted current sheet substructure. An analysis of the observations suggests that the tilted current sheet is draped within the overlying cloud canopy, ahead of a magnetic cloud-like structure. The flux rope interpretation of this structure near L1, confirmed by observations
of the corresponding magnetic cloud, provided by Ulysses at 5.3 AU and away from the Sun-Earth line, indicate that the bulk of the cloud is in the north-west sector as seen from the Earth, with its axis nearly perpendicular to the ecliptic. This is consistent with the primary direction of travel of the fast halo-CME observed at the Sun. Moreover, the NCDE and helium enrichment are consistent with the position near the streamer belt of the flaring active region NOAA 10720 associated with the CME. However, differences between interplanetary and solar observations indicate a large rotation of the erupting filament and overlying arcade, which can be attributed to the flux rope being subject to the helical kink instability.
Authors: Foullon, C., Owen, C.J., Dasso, S., Green, L.M., Dandouras, I., Elliott, H.A., Fazakerley, A.N., Bogdanova, Y.V. and Crooker, N.U.
Projects: SoHO-EIT,SoHO-MDI,SoHO-LASCO,TRACE
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Publication Status: Solar Physics (in press DOI: 10.1007/s11207-007-0330-7)
Last Modified: 2007-06-11 12:42
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