Search Publications
Newly Identified Properties of Surface Acoustic Power
Braun, D. C.; Schunker, H.
The cause of enhanced acoustic power surrounding active regions, known as the acoustic halo, is not as yet understood. We explore the properties of the enhanced acoustic power observed near disk center from 21 to 27 January 2002, including AR 9787. We find that i) there exists a strong correlation of the enhanced high-frequency power with magnetic…
The WHI Corona from Differential Emission Measure Tomography
Frazin, Richard A.; Huang, Zhenguang; Vásquez, Alberto M. +1 more
A three-dimensional (3D) tomographic reconstruction of the local differential emission measure (LDEM) of the global solar corona during the whole heliosphere interval (WHI, Carrington rotation CR 2068) is presented, based on STEREO/EUVI images. We determine the 3D distribution of the electron density, mean temperature, and temperature spread, in t…
Coronal Dimmings and the Early Phase of a CME Observed with STEREO and Hinode/EIS
Möstl, C.; Temmer, M.; Veronig, A. M. +2 more
We investigate the early phase of the 13 February 2009 coronal mass ejection (CME). Observations with the twin STEREO spacecraft in quadrature allow us to compare for the first time in one and the same event the temporal evolution of coronal EUV dimmings, observed simultaneously on-disk and above-the-limb. We find that these dimmings are synchroni…
Subsurface Velocity of Emerging and Decaying Active Regions
Howe, R.; Komm, R.; Hill, F.
We study the temporal variation of subsurface flows of 828 active regions and 977 quiet regions. The horizontal flows cover a range of depths from the surface to about 16 Mm and are determined by analyzing Global Oscillation Network Group high-resolution Doppler data with ring-diagram analyses. The vertical velocity component is derived from the d…
Simulation of the Unusual Solar Minimum with 3D SIP-CESE MHD Model by Comparison with Multi-Satellite Observations
Wu, S. T.; Feng, Xueshang; Zhang, Shaohua +2 more
The observations both near the Sun and in the heliosphere during the activity minimum between solar cycles 23 and 24 exhibit different phenomena from those typical of the previous solar minima. In this paper, we have chosen Carrington rotation 2070 in 2008 to investigate the properties of the background solar wind by using the three-dimensional (3…
Particle Acceleration and Propagation in Strong Flares without Major Solar Energetic Particle Events
Klein, K. -L.; Malandraki, O.; Trottet, G. +1 more
Solar energetic particles (SEPs) detected in space are statistically associated with flares and coronal mass ejections (CMEs). But it is not clear how these processes actually contribute to the acceleration and transport of the particles. The present work addresses the question why flares accompanied by intense soft X-ray bursts may not produce SE…
Nonlinear Force-Free Reconstruction of the Global Solar Magnetic Field: Methodology
Contopoulos, I.; Kalapotharakos, C.; Georgoulis, M. K.
We present a novel numerical method that allows the calculation of nonlinear force-free magnetostatic solutions above a boundary surface on which only the distribution of the normal magnetic field component is given. The method relies on the theory of force-free electrodynamics and applies directly to the reconstruction of the solar coronal magnet…
Constructing and Characterising Solar Structure Models for Computational Helioseismology
Moradi, H.; Gizon, L.; Schunker, H. +1 more
In local helioseismology, numerical simulations of wave propagation are useful to model the interaction of solar waves with perturbations to a background solar model. However, the solution to the linearised equations of motion include convective modes that can swamp the helioseismic waves that we are interested in. In this article, we construct ba…
A Snapshot of the Sun Near Solar Minimum: The Whole Heliosphere Interval
Galvin, Antoinette B.; de Toma, Giuliana; Welsch, Brian T. +22 more
We present an overview of the data and models collected for the Whole Heliosphere Interval, an international campaign to study the three-dimensional solar-heliospheric-planetary connected system near solar minimum. The data and models correspond to solar Carrington Rotation 2068 (20 March - 16 April 2008) extending from below the solar photosphere…
Characteristics of Type-II Radio Bursts Associated with Flares and CMEs
Vršnak, Bojan; Umapathy, S.; Vasanth, V. +1 more
We present a statistical study of the characteristics of type-II radio bursts observed in the metric (m) and deca-hectometer (DH) wavelength range during 1997-2008. The collected events are divided into two groups: Group I contains the events of m-type-II bursts with starting frequency ≥ 100 MHz, and group II contains the events with starting freq…