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
|
 
 
|
|
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
|
 
 
|
|
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 x 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
|
 
 
|
|
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
|
 
 
|
|
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
|
 
 
|
|
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
|
 
 
|
|
|
Key
|
 | Go to main E-Print page. |
 | Download Preprint. |
 | Submitters Homepage. |
 | Edit Entry. |
 | Delete abstract. |
|
|
|