skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Self-similar expansion of solar coronal mass ejections: Implications for Lorentz self-force driving

Abstract

We examine the propagation of several coronal mass ejections (CMEs) with well-observed flux rope signatures in the field of view of the SECCHI coronagraphs on board the STEREO satellites using the graduated cylindrical shell fitting method of Thernisien et al. We find that the manner in which they propagate is approximately self-similar; i.e., the ratio (κ) of the flux rope minor radius to its major radius remains approximately constant with time. We use this observation of self-similarity to draw conclusions regarding the local pitch angle (γ) of the flux rope magnetic field and the misalignment angle (χ) between the current density J and the magnetic field B. Our results suggest that the magnetic field and current configurations inside flux ropes deviate substantially from a force-free state in typical coronagraph fields of view, validating the idea of CMEs being driven by Lorentz self-forces.

Authors:
; ;  [1];  [2]
  1. Indian Institute of Science Education and Research, Dr. Homi Bhabha Road, Pashan, Pune 411008 (India)
  2. Space Science Division, Naval Research Laboratory, 4555 Overlook Avenue, SW Washington, DC 20375 (United States)
Publication Date:
OSTI Identifier:
22365487
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 790; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; APPROXIMATIONS; CURRENT DENSITY; CYLINDRICAL CONFIGURATION; EXPANSION; INCLINATION; LORENTZ FORCE; MAGNETIC FIELDS; MASS; SATELLITES; STELLAR CORONAE; SUN

Citation Formats

Subramanian, Prasad, Arunbabu, K. P., Mauriya, Adwiteey, and Vourlidas, Angelos, E-mail: p.subramanian@iiserpune.ac.in. Self-similar expansion of solar coronal mass ejections: Implications for Lorentz self-force driving. United States: N. p., 2014. Web. doi:10.1088/0004-637X/790/2/125.
Subramanian, Prasad, Arunbabu, K. P., Mauriya, Adwiteey, & Vourlidas, Angelos, E-mail: p.subramanian@iiserpune.ac.in. Self-similar expansion of solar coronal mass ejections: Implications for Lorentz self-force driving. United States. doi:10.1088/0004-637X/790/2/125.
Subramanian, Prasad, Arunbabu, K. P., Mauriya, Adwiteey, and Vourlidas, Angelos, E-mail: p.subramanian@iiserpune.ac.in. Fri . "Self-similar expansion of solar coronal mass ejections: Implications for Lorentz self-force driving". United States. doi:10.1088/0004-637X/790/2/125.
@article{osti_22365487,
title = {Self-similar expansion of solar coronal mass ejections: Implications for Lorentz self-force driving},
author = {Subramanian, Prasad and Arunbabu, K. P. and Mauriya, Adwiteey and Vourlidas, Angelos, E-mail: p.subramanian@iiserpune.ac.in},
abstractNote = {We examine the propagation of several coronal mass ejections (CMEs) with well-observed flux rope signatures in the field of view of the SECCHI coronagraphs on board the STEREO satellites using the graduated cylindrical shell fitting method of Thernisien et al. We find that the manner in which they propagate is approximately self-similar; i.e., the ratio (κ) of the flux rope minor radius to its major radius remains approximately constant with time. We use this observation of self-similarity to draw conclusions regarding the local pitch angle (γ) of the flux rope magnetic field and the misalignment angle (χ) between the current density J and the magnetic field B. Our results suggest that the magnetic field and current configurations inside flux ropes deviate substantially from a force-free state in typical coronagraph fields of view, validating the idea of CMEs being driven by Lorentz self-forces.},
doi = {10.1088/0004-637X/790/2/125},
journal = {Astrophysical Journal},
number = 2,
volume = 790,
place = {United States},
year = {Fri Aug 01 00:00:00 EDT 2014},
month = {Fri Aug 01 00:00:00 EDT 2014}
}
  • In this paper, we investigate the solar cycle variation of coronal null points and magnetic breakout configurations in spherical geometry, using a combination of magnetic flux transport and potential field source surface models. Within the simulations, a total of 2843 coronal null points and breakout configurations are found over two solar cycles. It is found that the number of coronal nulls present at any time varies cyclically throughout the solar cycle, in phase with the flux emergence rate. At cycle maximum, peak values of 15-17 coronal nulls per day are found. No significant variation in the number of nulls ismore » found from the rising to the declining phase. This indicates that the magnetic breakout model is applicable throughout both phases of the solar cycle. In addition, it is shown that when the simulations are used to construct synoptic data sets, such as those produced by Kitt Peak, the number of coronal nulls drops by a factor of 1/6. The vast majority of the coronal nulls are found to lie above the active latitudes and are the result of the complex nature of the underlying active region fields. Only 8% of the coronal nulls are found to be connected to the global dipole. Another interesting feature is that 18% of coronal nulls are found to lie above the equator due to cross-equatorial interactions between bipoles lying in the northern and southern hemispheres. As the majority of coronal nulls form above active latitudes, their average radial extent is found to be in the low corona below 1.25 R {sub sun} (175, 000 km above the photosphere). Through considering the underlying photospheric flux, it is found that 71% of coronal nulls are produced though quadrupolar flux distributions resulting from bipoles in the same hemisphere interacting. When the number of coronal nulls present in each rotation is compared to the number of bipoles emerging, a wide scatter is found. The ratio of coronal nulls to emerging bipoles is found to be approximately 1/3. Overall, the spatio-temporal evolution of coronal nulls is found to follow the typical solar butterfly diagram and is in qualitative agreement with the observed time dependence of coronal mass ejection source-region locations.« less
  • The authors have investigated the importance of the form of the driving mechanism in MHD simulations of coronal mass ejections. Previous authors have performed simulations using a thermal driving mechanism, and have found that this mechanism cannot reproduce the observed features of mass ejections unless an elaborate model of the initial corona is used. They have devised a model simulation problem and have found that the use of a simple form for the initial corona, with an upward moving parcel of cold, dense plasma as the driving mechanism, can produce results that are consistent with many of the features observedmore » by coronagraphs. Their results imply that the nature of the driving mechanism may play an important role in determining the dynamical evolution of mass ejections.« less
  • We present a method for measuring electrical currents enclosed by flux rope structures that are ejected within solar coronal mass ejections (CMEs). Such currents are responsible for providing the Lorentz self-force that propels CMEs. Our estimates for the driving current are based on measurements of the propelling force obtained using data from the LASCO coronagraphs aboard the SOHO satellite. We find that upper limits on the currents enclosed by CMEs are typically around 10{sup 10} A. We estimate that the magnetic flux enclosed by the CMEs in the LASCO field of view is a few times 10{sup 21} Mx.
  • The authors describe a set of solar coronal mass ejection (CME) events where coincident data sets from both X ray and white light instruments have been made available through deliberate planning. Using these they have been able to put tight limits on possible descriptions of the typical sequence of events, and these they relate to interpretations of models involving flares and CMEs. The findings confirm recent suggestions that CME onsets precede any related flare activity and that the associated flaring commonly lies to one side of the CME span. The CME launch appears to be associated with minor X raymore » (flare precursor) activity. Although this scenario has been previously discussed (see Harrison, 1986, and references therein), the abundance of flare and CME models which are not compatible with this picture demands that confirmation be sought using programs such as this.« less
  • We develop an empirical model to estimate mass-loss rates via coronal mass ejections (CMEs) for solar-type pre-main-sequence (PMS) stars. Our method estimates the CME mass-loss rate from the observed energies of PMS X-ray flares, using our empirically determined relationship between solar X-ray flare energy and CME mass: log (M {sub CME}[g]) = 0.63 Multiplication-Sign log (E {sub flare}[erg]) - 2.57. Using masses determined for the largest flaring magnetic structures observed on PMS stars, we suggest that this solar-calibrated relationship may hold over 10 orders of magnitude in flare energy and 7 orders of magnitude in CME mass. The total CMEmore » mass-loss rate we calculate for typical solar-type PMS stars is in the range 10{sup -12}-10{sup -9} M {sub Sun} yr{sup -1}. We then use these CME mass-loss rate estimates to infer the attendant angular momentum loss leading up to the main sequence. Assuming that the CME outflow rate for a typical {approx}1 M {sub Sun} T Tauri star is <10{sup -10} M {sub Sun} yr{sup -1}, the resulting spin-down torque is too small during the first {approx}1 Myr to counteract the stellar spin-up due to contraction and accretion. However, if the CME mass-loss rate is {approx}> 10{sup -10} M {sub Sun} yr{sup -1}, as permitted by our calculations, then the CME spin-down torque may influence the stellar spin evolution after an age of a few Myr.« less