Search Publications
Modeling of Flux Rope Coronal Mass Ejections
Howard, R. A.; Vourlidas, A.; Thernisien, A. F. R.
We present a forward-modeling technique for flux rope-like CMEs using an empirically defined model of a flux rope, the graduated cylindrical shell (GCS). To compare it with white-light coronagraph observations, we assume an electron distribution through the GCS and derive synthetic images in total and polarized brightness for various projections o…
A Statistical Study of Main and Residual Accelerations of Coronal Mass Ejections
Zhang, J.; Dere, K. P.
In this paper we present the results of a statistical study of the accelerations of coronal mass ejections (CMEs). A CME usually undergoes a multiphased kinematic evolution, with a main acceleration phase characterized by a rapid increase of CME velocity in the inner corona, followed by a relatively smooth propagation phase characterized by a cons…
Solar Differential Rotation Influenced by Latitudinal Entropy Variations in the Tachocline
Toomre, Juri; Brun, Allan Sacha; Miesch, Mark S.
Three-dimensional simulations of solar convection in spherical shells are used to evaluate the differential rotation that results as thermal boundary conditions are varied. In some simulations a latitudinal entropy variation is imposed at the lower boundary in order to take into account the coupling between the convective envelope and the radiativ…
A Model for Spectral and Compositional Variability at High Energies in Large, Gradual Solar Particle Events
Lee, Martin A.; Tylka, Allan J.
Shocks driven by fast coronal mass ejections (CMEs) are generally believed to be the dominant accelerators in large, gradual solar energetic particle (SEP) events. A key challenge for this notion has been the highly variable spectral and compositional characteristics of these events above a few tens of MeV per nucleon. We have recently proposed th…
Magnetoacoustic Portals and the Basal Heating of the Solar Chromosphere
McIntosh, Scott W.; Cacciani, Alessandro; Armstrong, James D. +3 more
We show that inclined magnetic field lines at the boundaries of large-scale convective cells (supergranules) provide ``portals'' through which low-frequency (<5 mHz) magnetoacoustic waves can propagate into the solar chromosphere. The energy flux carried by these waves at a height of 400 km above the solar surface is found to be a factor of 4 g…
The Proper Treatment of Coronal Mass Ejection Brightness: A New Methodology and Implications for Observations
Vourlidas, Angelos; Howard, Russell A.
With the complement of coronagraphs and imagers in the SECCHI suite, we will follow a coronal mass ejection (CME) continuously from the Sun to Earth for the first time. The comparison, however, of the CME emission among the various instruments is not as easy as one might think. This is because the telescopes record the Thomson-scattered emission f…
Different Power-Law Indices in the Frequency Distributions of Flares with and without Coronal Mass Ejections
Howard, R. A.; Gopalswamy, N.; Yashiro, S. +1 more
We investigated the frequency distributions of flares with and without coronal mass ejections (CMEs) as a function of flare parameters (peak flux, fluence, and duration of soft X-ray flares). We used CMEs observed by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) mission and soft X-ray …
Coronal Holes, Jets, and the Origin of 3He-rich Particle Events
Pick, M.; Mason, G. M.; Wang, Y. -M.
Using magnetograph measurements, coronal field extrapolations, and imaging observations, we investigate the solar origins of 25 3He-rich particle events from the period 1997-2003. In essentially every case we find that the source of the impulsive solar energetic particles (SEPs) lies next to a coronal hole containing Earth-directed open…
The Calm before the Storm: The Link between Quiescent Cavities and Coronal Mass Ejections
de Toma, G.; Gibson, S. E.; Burkepile, J. +2 more
Determining the state of the corona prior to CMEs is crucial to understanding and ultimately predicting solar eruptions. A common and compelling feature of CMEs is their three-part morphology, as seen in white-light observations of a bright expanding loop, followed by a relatively dark cavity, and finally a bright core associated with an erupting …
Forward Modeling of the Corona of the Sun and Solar-like Stars: From a Three-dimensional Magnetohydrodynamic Model to Synthetic Extreme-Ultraviolet Spectra
Peter, Hardi; Gudiksen, Boris V.; Nordlund, Åke
A forward model is described in which we synthesize spectra from an ab initio three-dimensional MHD simulation of an outer stellar atmosphere, where the coronal heating is based on braiding of magnetic flux due to photospheric footpoint motions. We discuss the validity of assumptions such as ionization equilibrium and investigate the applicability…