E-Print Archive

There are 3784 abstracts currently viewable.


Search:

Advanced Search
Options
Main Page Add New E-Print Submitter
Information
Feedback
News Help/FAQ About Preferences
Manage Key Phrase
Notification
Why does the apparent mass of a coronal mass ejection increase?  

Li Feng   Submitted: 2015-09-15 08:46

Mass is one of the most fundamental parameters characterizing the dynamics of a coronal mass ejection (CME). It has been found that CME apparent mass measured from the brightness enhancement in coronagraph images shows an increasing trend during its evolution in the corona. However, the physics behind it is not clear. Does the apparent mass gain come from the mass outflow from the dimming regions in the low corona, or from the pileup of the solar wind plasma around the CME when it propagates outwards from the Sun? We analyzed the mass evolution of six CME events. Their mass can increase by a factor of 1.6 to 3.2 from 4 to 15 Rs in the field of view (FOV) of the coronagraph on board the Solar Terrestrial Relations Observatory (STEREO). Over the distance about 7 to 15 Rs, where the coronagraph occulting effect can be negligible, the mass can increase by a factor of 1.3 to 1.7. We adopted the `snow-plough' model to calculate the mass contribution of the piled-up solar wind in the height range from about 7 to 15 Rs. For 2/3 of the events, the solar wind pileup is not sufficient to explain the measured mass increase. In the height range from about 7 to 15 Rs, the ratio of the modeled to the measured mass increase is roughly larger than 0.55. Although the ratios are believed to be overestimated, the result gives evidence that the solar wind pileup probably makes a non-negligible contribution to the mass increase. It is not clear yet whether the solar wind pileup is a major contributor to the final mass derived from coronagraph observations. However, our study suggests that the solar wind pileup plays increasingly important role in the mass increase as a CME moves further away from the Sun.

Authors: Feng, Li; Wang, Yuming; Shen, Fang; Shen, Chenglong; Inhester, Bernd; Lu, Lei; Gan, Weiqun
Projects: None

Publication Status: accepted by ApJ
Last Modified: 2015-09-16 13:50
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Radial Flow Pattern of a Slow Coronal Mass Ejection  

Li Feng   Submitted: 2015-09-15 08:44

Height?time plots of the leading edge of coronal mass ejections (CMEs) have often been used to study CME kinematics. We propose a new method to analyze the CME kinematics in more detail by determining the radial mass transport process throughout the entire CME. Thus, our method is able to estimate not only the speed of the CME front but also the radial flow speed inside the CME. We have applied this method to a slow CME with an average leading edge speed of about 480 km s-1. In the Lagrangian frame, the speeds of the individual CME mass elements stay almost constant within 2 and 15 RS, the range over which we analyzed the CME. Hence, we have no evidence of net radial forces acting on parts of the CME in this range or of a pile up of mass ahead of the CME. We find evidence that the leading edge trajectory obtained by tie-pointing may gradually lag behind the Lagrangian front-side trajectories derived from our analysis. Our results also allow a much more precise estimate of the CME energy. Compared with conventional estimates using the CME total mass and leading edge motion, we find that the latter may overestimate the kinetic energy and the gravitational potential energy.

Authors: Feng, Li; Inhester, Bernd; Gan, Weiqun
Projects: None

Publication Status: The Astrophysical Journal, Volume 805, Issue 2, article id. 113, 9 pp. (2015).
Last Modified: 2015-09-16 13:50
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Kelvin-Helmholtz instability of a coronal streamer  

Li Feng   Submitted: 2013-07-21 20:23

The shear-flow-driven instability can play an important role in energy transfer processes in coronal plasma. We present for the first time the observation of a kink-like oscillation of a streamer probably caused by the streaming kink mode Kelvin-Helmholtz instability. The wave-like behavior of the streamer was observed by Large Angle and Spectrometric Coronagraph Experiment (LASCO) C2 and C3 aboard SOlar and Heliospheric Observatory (SOHO). The observed wave had a period of about 70 to 80 minutes, and its wavelength increased from 2 Rsun to 3 Rsun in about 1.5 hours. The phase speeds of its crests and troughs decreased from 406 pm 20 to 356 pm 31 kms-1 during the event. Within the same heliocentric range, the wave amplitude also appeared to increase with time. We attribute the phenomena to the MHD Kelvin-Helmholtz instability which occur at a neutral sheet in a fluid wake. The free energy driving the instability is supplied by the sheared flow and sheared magnetic field across the streamer plane. The plasma properties of the local environment of the streamer were estimated from the phase speed and instability threshold criteria.

Authors: Li Feng, Bernd Inhester, Weiqun Gan
Projects: None

Publication Status: ApJ, accepted
Last Modified: 2013-07-22 09:24
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Magnetic Energy Partition between the CME and Flare from AR 11283  

Li Feng   Submitted: 2013-01-16 07:04

On 6 September 2011, an X-class flare and a halo CME as observed from the Earth were erupted from the same active region AR 11283. The magnetic energy partition between them has been investigated. SDO/HMI vector magnetograms were used to obtain the coronal magnetic field with the nonlinear force-free field (NLFFF) extrapolation method. The free magnetic energies before and after the flare were calculated to estimate the released energy available to power the flare and the CME. For the flare energetics, thermal and nonthermal energies were derived using the RHESSI and GOES data. To obtain the radiative output, SDO/EVE data in the 0.1-37 nm waveband were utilized. We have reconstructed the three dimensional (3D) periphery of the CME from the coronagraph images observed by STEREO-A, B, and SOHO. The mass calculations were then based on a more precise Thomson scattering geometry. The subsequent estimate of the kinetic and potential energies of the CME took advantage of the more accurate mass, and the height and speed in a 3D frame. The released free magnetic energy resulting from the NLFFF model is about 6.4 ? 1031 ergs, which has a possible upper limit of 1.8 ? 1032 ergs. The thermal and nonthermal energies are lower than the radiative output of 2.2 ? 1031 ergs from SDO/EVE for this event. The total radiation covering the whole solar spectrum is probably a few times larger. The sum of the kinetic and potential energy of the CME could go up to 6.5x1031 ergs. Therefore, the free energy is able to power the flare and the CME in AR 11283. Within the uncertainty, the flare and the CME may consume similar amount of free energy.

Authors: L. Feng, T. Wiegelmann, Y. Su, B. Inhester, Y.P. Li, X.D. Sun, W.Q. Gan
Projects: SDO-AIA,SDO-HMI,SDO-EVE,STEREO

Publication Status: ApJ, in press
Last Modified: 2013-01-16 07:37
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Morphological evolution of a 3D CME cloud reconstructed from three viewpoints  

Li Feng   Submitted: 2012-03-15 19:41

The propagation properties of coronal mass ejections (CMEs) are crucial to predict its geomagnetic effect. A newly developed three dimensional (3D) mask fitting reconstruction method using coronagraph images from three viewpoints has been described and applied to the CME ejected on August 7, 2010. The CME's 3D localisation, real shape and morphological evolution are presented. Due to its interaction with the ambient solar wind, the morphology of this CME changed significantly in the early phase of evolution. Two hours after its initiation, it was expanding almost self-similarly. CME's 3D localisation is quite helpful to link remote sensing observations to in situ measurements. The investigated CME was propagating to Venus with its flank just touching STEREO B. Its corresponding ICME in the interplanetary space shows a possible signature of a magnetic cloud with a preceding shock in VEX observations, while from STEREO B only a shock is observed. We have calculated three principle axes for the reconstructed 3D CME cloud. The orientation of the major axis is in general consistent with the orientation of a filament (polarity inversion line) observed by SDO/AIA and SDO/HMI. The flux rope axis derived by the MVA analysis from VEX indicates a radial-directed axis orientation. It might be that locally only the leg of the flux rope passed through VEX. The height and speed profiles from the Sun to Venus are obtained. We find that the CME speed possibly had been adjusted to the speed of the ambient solar wind flow after leaving COR2 field of view and before arriving Venus. A southward deflection of the CME from the source region is found from the trajectory of the CME geometric center. We attribute it to the influence of the coronal hole where the fast solar wind emanated from.

Authors: L. Feng, B. Inhester, Y. Wei, W.Q. Gan, T.L. Zhang, M.Y. Wang
Projects: STEREO

Publication Status: ApJ, accepted
Last Modified: 2012-03-19 14:14
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Particle kinetic analysis of a polar jet from SECCHI COR data  

Li Feng   Submitted: 2011-12-12 23:12

Aims. We analyze coronagraph observations of a polar jet observed by the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) instrument suite onboard the Solar TErrestrial RElations Observatory (STEREO) spacecraft. Methods. In our analysis we compare the brightness distribution of the jet in white-light coronagraph images with a dedicated kinetic particle model. We obtain a consistent estimate of the time that the jet was launched from the solar surface and an approximate initial velocity distribution in the jet source. The method also allows us to check the consistency of the kinetic model. In this first application, we consider only gravity as the dominant force on the jet particles along the magnetic field. Results. We find that the kinetic model explains the observed brightness evolution well. The derived initiation time is consistent with the jet observations by the EUVI telescope at various wavelengths. The initial particle velocity distribution is fitted by Maxwellian distributions and we find deviations of the high energy tail from the Maxwellian distributions. We estimate the jet's total electron content to have a mass between 3.2 imes 1014 and 1.8 imes 1015 g. Mapping the integrated particle number along the jet trajectory to its source region and assuming a typical source region size, we obtain an initial electron density between 8 imes 109 and 5 imes 1010 cm-3 that is characteristic for the lower corona or the upper chromosphere. The total kinetic energy of all particles in the jet source region amounts from 2.1 imes 1028 to 2.4 imes 1029 erg.

Authors: L. Feng, B. Inhester, J. de Patoul, T. Wiegelmann, W.Q. Gan
Projects: STEREO

Publication Status: A&A, in press
Last Modified: 2011-12-13 14:37
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Stereoscopic polar plume reconstructions from STEREO/SECCHI images  

Li Feng   Submitted: 2009-08-25 11:00

We present stereoscopic reconstructions of the location and inclination of polar plumes of two data sets based on the two simultaneously recorded images taken by the EUVI telescopes in the SECCHI instrument package onboard the Solar TErrestrial RElations Observatory spacecraft. The 10 plumes investigated show a superradial expansion in the coronal hole in three dimensions (3D) which is consistent with the two-dimensional results. Their deviations from the local meridian planes are rather smallwith an average of 6.◦47. By comparing the reconstructed plumes with a dipole field with its axis along the solar rotation axis, it is found that plumes are inclined more horizontally than the dipole field. The lower the latitude is, the larger is the deviation from the dipole field. The relationship between plumes and bright points has been investigated and they are not always associated. For the first data set, based on the 3D height of plumes and the electron density derived from SUMER/SOHO Si viii line pair, we found that electron densities along the plumes decrease with height above the solar surface. The temperature obtained from the density scale height is 1.6?1.8 times larger than the temperature obtained from Mg ix line ratios. We attribute this discrepancy to a deviation of the electron and the ion temperatures. Finally, we have found that the outflow speeds studied in the O vi line in the plumes corrected by the angle between the line of sight and the plume orientation are quite smallwith amaximum of 10 km s-1. It is unlikely that plumes are a dominant contributor to the fast solarwind.

Authors: L. Feng, B. Inhester, S. K. Solanki, K. Wilhelm, T. Wiegelmann, B. Podlipnik, R. A. Howard, S. P. Plunkett, J.P. Wuelser, W.Q. Gan
Projects: STEREO

Publication Status: ApJ, 2009, 700, 292
Last Modified: 2009-08-26 09:21
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Subject will be restored when possible  

Li Feng   Submitted: 2007-11-09 07:09

We present the first reconstruction of the three-dimensional shape of magnetic loops in an active region from two different vantage points based on simultaneously recorded images. The images were taken by the two EUVI telescopes of the SECCHI instrument onboard the recently launched STEREO spacecraft when the heliocentric separation of the two space probes was 12 degrees. We demostrate that these data allow to obtain a reliable three-dimensional reconstruction of sufficiently bright loops. The result is compared with field lines derived from a coronal magnetic field model extrapolated from a photospheric magnetogram recorded nearly simultaneously by SOHO/MDI. We attribute discrepancies between reconstructed loops and extrapolated field lines to the inadequacy of the linear force-free field model used for the extrapolation.

Authors: L. Feng, B. Inhester, S. Solanki, T. Wiegelmann, B. Podlipnik, R.A. Howard, J._P. Wuelser
Projects: STEREO

Publication Status: ApJL, accepted
Last Modified: 2007-11-09 07:53
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Magnetic Stereoscopy of Coronal Loops in NOAA 8891  

Li Feng   Submitted: 2007-06-04 03:19

The Solar TErrestrial RElations Observatory (STEREO) requires powerful tools for the three-dimensional (3D) reconstruction of the solar corona. Here we test such a program with data from SOHO and TRACE. By taking advantage of solar rotation, a newly developed stereoscopy tool for the reconstruction of coronal loops is applied to the solar active region NOAA 8891 observed from 1 March to 2 March 2000. The stereoscopic reconstruction is composed of three steps. First, we identify loop structures in two TRACE images observed from two vantage viewpoints approximately 17 degrees apart, which corresponds to observations made about 30 hours apart. In the second step, we extrapolate the magnetic field in the corona with the linear force-free field model from the photospheric line-of-sight SOHO/MDI data. Finally, combining the extrapolated field lines and one-dimensional loop curves from two different viewpoints, we obtain the 3D loop structures with the magnetic stereoscopy tool. We demonstrate that by including the magnetic modeling this tool is more powerful than pure geometrical stereoscopy, especially in resolving the ambiguities generated by classical stereoscopy. This work will be applied to the STEREO mission in the near future.

Authors: L. Feng , T. Wiegelmann, B. Inhester, S. Solanki, W. Q. Gan and P. Ruan
Projects: STEREO

Publication Status: Solar Physics (2007), 241:235-249
Last Modified: 2007-06-04 14:37
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 


Key
Go to main E-Print pageGo to main E-Print page.
Download PreprintDownload Preprint.
Submitter's HomepageSubmitters Homepage.
Edit EntryEdit Entry.
Delete AbstractDelete abstract.

Abstracts by Author
Why does the apparent mass of a coronal mass ejection increase?
Radial Flow Pattern of a Slow Coronal Mass Ejection
Kelvin-Helmholtz instability of a coronal streamer
Magnetic Energy Partition between the CME and Flare from AR 11283
Morphological evolution of a 3D CME cloud reconstructed from three viewpoints
Particle kinetic analysis of a polar jet from SECCHI COR data
Stereoscopic polar plume reconstructions from STEREO/SECCHI images
Subject will be restored when possible
Magnetic Stereoscopy of Coronal Loops in NOAA 8891

Related Pages
MSU Solar Physics.
Max Millennium Science Mail Archive.
Max Millennium Message of the Day Mail Archive.
Max Millennium Flare Catalog

Archive Maintainer
Alisdair Davey



© 2003 Solar Physics Group - Montana State University