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An Extreme Solar Event of 20 January 2005: Properties of the Flare and the Origin of Energetic Particles
Kurt, V. G.; Grechnev, V. V.; Chertok, I. M. +9 more
The famous extreme solar and particle event of 20 January 2005 is analyzed from two perspectives. Firstly, using multi-spectral data, we study temporal, spectral, and spatial features of the main phase of the flare, when the strongest emissions from microwaves up to 200 MeV gamma-rays were observed. Secondly, we relate our results to a long-standi…
Helioseismology of Sunspots: Confronting Observations with Three-Dimensional MHD Simulations of Wave Propagation
Duvall, T. L., Jr.; Gizon, L.; Cameron, R.
The propagation of solar waves through the sunspot of AR 9787 is observed by using temporal cross-correlations of SOHO/MDI Dopplergrams. We then use three-dimensional MHD numerical simulations to compute the propagation of wave packets through self-similar magnetohydrostatic sunspot models. The simulations are set up in such a way as to allow a co…
First Imaging of Coronal Mass Ejections in the Heliosphere Viewed from Outside the Sun Earth Line
Howard, Russell A.; Bewsher, Danielle; Davis, Christopher J. +13 more
We show for the first time images of solar coronal mass ejections (CMEs) viewed using the Heliospheric Imager (HI) instrument aboard the NASA STEREO spacecraft. The HI instruments are wide-angle imaging systems designed to detect CMEs in the heliosphere, in particular, for the first time, observing the propagation of such events along the Sun - Ea…
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…