Search Publications
Investigation of Quasi-periodic Solar Oscillations in Sunspots Based on SOHO/MDI Magnetograms
Riehokainen, A.; Kallunki, J.
In this work we study quasi-periodic solar oscillations in sunspots, based on the variation of the amplitude of the magnetic field strength and the variation of the sunspot area. We investigate long-period oscillations between three minutes and ten hours. The magnetic field synoptic maps were obtained from the SOHO/MDI. Wavelet (Morlet), global wa…
Vorticity of Subsurface Flows of Emerging and Decaying Active Regions
Howe, R.; Komm, R.; Hill, F.
We study the temporal variation of the vorticity of subsurface flows of 828 active regions and 977 quiet regions. The vorticity of these flows is derived from measured subsurface velocities. The horizontal flows are determined by analyzing high-resolution Global Oscillation Network Group Doppler data with ring-diagram analysis covering a range of …
Magnetic Connectivity Between Active Regions 10987, 10988, and 10989 by Means of Nonlinear Force-Free Field Extrapolation
Inhester, B.; Wiegelmann, T.; Tadesse, Tilaye +1 more
Extrapolation codes for modelling the magnetic field in the corona in Cartesian geometry do not take the curvature of the Sun's surface into account and can only be applied to relatively small areas, e.g., a single active region. We apply a method for nonlinear force-free coronal magnetic field modelling of photospheric vector magnetograms in sphe…
Non-thermal "Burst-on-Tail" of Long-Duration Solar Event on 26 October 2003
Struminsky, A.; Zimovets, I.
Observations of a rare long-duration solar event of GOES class X1.2 from 26 October 2003 are presented. This event showed a pronounced burst of hard X-ray and microwave emission, which was extremely delayed (> 60 min) with respect to the main impulsive phase and did not have any significant response visible in soft X-ray emission. We refer to t…
Correlations Between CME Parameters and Sunspot Activity
Du, Zhanle
Smoothed monthly mean coronal mass ejection (CME) parameters (speed, acceleration, central position angle, angular width, mass, and kinetic energy) for Cycle 23 are cross-analyzed, showing that there is a high correlation between most of them. The CME acceleration (a) is highly correlated with the reciprocal of its mass (M), with a correlation coe…
Kinematics and Flare Properties of Radio-Loud CMEs
Prakash, O.; Shanmugaraju, A.; Umapathy, S. +1 more
A detailed analysis of the characteristics of coronal mass ejections (CMEs) and flares associated with decameter-hectometer wavelength type-II radio bursts (hereafter DH-type-II radio bursts, DH-CMEs or radio-loud CMEs) observed in the period 1997 - 2008 is presented. A sample of 61 limb events is divided into two populations based on the residual…
Coronal Diagnostics from Narrowband Images Around 30.4 nm
Andretta, V.; Del Zanna, G.; Telloni, D.
Images taken in the band centered at 30.4 nm are routinely used to map the radiance of the He II Ly α line on the solar disk. That line is one of the strongest, if not the strongest, line in the EUV observed in the solar spectrum, and one of the few lines in that wavelength range providing information on the upper chromosphere or lower transition …
Velocity Characteristics of Rotating Sunspots
Alexander, D.; Zhu, C.; Tian, L.
A statistical study is carried out to investigate the detailed relationship between rotating sunspots and the emergence of magnetic flux tubes. This paper presents the velocity characteristics of 132 sunspots in 95 solar active regions. The rotational characteristics of the sunspots are calculated from successive SOHO/MDI magnetograms by applying …
The Evolution of Sunspot Magnetic Fields Associated with a Solar Flare
Gallagher, Peter T.; Murray, Sophie A.; Bloomfield, D. Shaun
Solar flares occur due to the sudden release of energy stored in active-region magnetic fields. To date, the precursors to flaring are still not fully understood, although there is evidence that flaring is related to changes in the topology or complexity of an active-region's magnetic field. Here, the evolution of the magnetic field in active regi…
Long-Term Variation of the Corona in Quiet Regions
Mariska, J. T.; Kamio, S.
Using Hinode EUV Imaging Spectrometer (EIS) spectra recorded daily at Sun center from the end of 2006 to early 2011, we studied the long-term evolution of the quiet corona. The light curves of the higher temperature emission lines exhibit larger variations in sync with the solar activity cycle while the cooler lines show reduced modulation. Our st…