Search Publications
Relationship between Rotating Sunspots and Flares
Zhang, Hongqi; Liu, Jihong; Zhang, Yin
Active Region (AR) NOAA 10486 was a super AR in the declining phase of solar cycle 23. Dominated by the rapidly rotating positive polarity of an extensive δ sunspot, it produced several powerful flare-CMEs. We study the evolution and properties of the rotational motion of the major poles of positive polarities and estimate the accumulated helicity…
Topological Departures from Translational Invariance along a Filament Observed by THEMIS
Aulanier, G.; Bommier, V.; Schmieder, B. +2 more
We study the topology of the 3D magnetic field in a filament channel to address the following questions: Is a filament always formed in a single flux tube? How does the photospheric magnetic field lead to filament interruptions and to feet formation? What is the relation between feet-related field lines and the parasitic polarities? What can topol…
The Global Solar Magnetic Field Through a Full Sunspot Cycle: Observations and Model Results
Liu, Yang; Schrijver, Carolus J.
Based on 11 years of SOHO/MDI observations from the cycle minimum in 1997 to the next minimum around 2008, we compare observed and modeled axial dipole moments to better understand the large-scale transport properties of magnetic flux in the solar photosphere. The absolute value of the axial dipole moment in 2008 is less than half that in the corr…
Automated McIntosh-Based Classification of Sunspot Groups Using MDI Images
Colak, T.; Qahwaji, R.
This paper presents a hybrid system for automatic detection and McIntosh-based classification of sunspot groups on SOHO/MDI white-light images using active-region data extracted from SOHO/MDI magnetogram images. After sunspots are detected from MDI white-light images they are grouped/clustered using MDI magnetogram images. By integrating image-pro…
Subsurface Meridional Circulation in the Active Belts
Howe, R.; Komm, R.; Hill, F. +2 more
Temporal variations of the subsurface meridional flow with the solar cycle have been reported by several authors. The measurements are typically averaged over periods of time during which surface magnetic activity existed in the regions where the velocities are calculated. The present work examines the possible contamination of these measurements …
Can We Improve the Preprocessing of Photospheric Vector Magnetograms by the Inclusion of Chromospheric Observations?
Schrijver, C. J.; Wiegelmann, T.; Metcalf, T. R. +2 more
The solar magnetic field is key to understanding the physical processes in the solar atmosphere. Nonlinear force-free codes have been shown to be useful in extrapolating the coronal field upward from underlying vector boundary data. However, we can only measure the magnetic field vector routinely with high accuracy in the photosphere, and unfortun…
Automatic Detection and Classification of Coronal Holes and Filaments Based on EUV and Magnetogram Observations of the Solar Disk
Habbal, Shadia Rifai; Scholl, Isabelle F.
A new method for the automated detection of coronal holes and filaments on the solar disk is presented. The starting point is coronal images taken by the Extreme Ultraviolet Telescope on the Solar and Heliospheric Observatory (SOHO/EIT) in the Fe IX/X 171 Å, Fe XII 195 Å, and He II 304 Å extreme ultraviolet (EUV) lines and the corresponding full-d…
Three-Dimensional Reconstruction of Two Solar Coronal Mass Ejections Using the STEREO Spacecraft
Howard, Timothy A.; Tappin, S. James
Previous attempts to produce three-dimensional (3-D) reconstructions of coronal mass ejections (CMEs) have required either modeling efforts or comparisons with secondary associated eruptions near the solar surface. This is because coronagraphs are only able to produce sky-plane-projected images of CMEs and it has hence been impossible to overcome …
A Flare-Generated Shock during a Coronal Mass Ejection on 24 December 1996
Magdalenić, J.; Temmer, M.; Vršnak, B. +3 more
We present a multiwavelength study of the large-scale coronal disturbances associated with the CME - flare event recorded on 24 December 1996. The kinematics of the shock wave signature, the type II radio burst, is analyzed and compared with the flare evolution and the CME kinematics. We employ radio dynamic spectra, position of the Nançay Radiohe…
Observation and Modeling of the Solar-Cycle Variation of the Meridional Flow
Gizon, Laurent; Rempel, Matthias
We present independent observations of the solar-cycle variation of flows near the solar surface and at a depth of about 60 Mm, in the latitude range ± 45°. We show that the time-varying components of the meridional flow at these two depths have opposite sign, whereas the time-varying components of the zonal flow are in phase. This is in agreement…