arXiv subjects

A. M. Veronig

Publications and source records attributed to A. M. Veronig.

58 records · Page 4Linked to original sources

arXiv2009

Analytic modeling of the Moreton wave kinematics

The issue whether Moreton waves are flare-ignited or CME-driven, or a combination of both, is still a matter of debate. We develop an analytical model describing the evolution of a large-amplitude coronal wave emitted by the expansion of a circular source surface in order to mimic the evolution of a Moreton wave. The model results are confronted with observations of a strong Moreton wave observed in association with the X3.8/3B flare/CME event from January 17, 2005. Using different input parameters for the expansion of the source region, either derived from the real CME observations (assuming that the upward moving CME drives the wave), or synthetically generated scenarios (expanding flare region, lateral expansion of the CME flanks), we calculate the kinematics of the associated Moreton wave signature. Those model input parameters are determined which fit the observed Moreton wave kinematics best. Using the measured kinematics of the upward moving CME as the model input, we are not able to reproduce the observed Moreton wave kinematics. The observations of the Moreton wave can be reproduced only by applying a strong and impulsive acceleration for the source region expansion acting in a piston mechanism scenario. Based on these results we propose that the expansion of the flaring region or the lateral expansion of the CME flanks is more likely the driver of the Moreton wave than the upward moving CME front.

astro-ph.SR↗

arXiv2009

STEREO quadrature observations of the 3D structure and driver of a global coronal wave

We present the first observations of a global coronal wave ("EIT wave") from the two Solar Terrestrial Relations Observatory (STEREO) satellites in quadra- ture. The wave's initiation site was at the disk center in STEREO-B and precisely on the limb in STEREO-A. These unprecedented observations from the STEREO Extreme Ultraviolet Imaging (EUVI) instruments enable us to gain insight into the wave's kinematics, initiation and 3D structure. The wave propagates globally over the whole solar hemisphere visible to STEREO-B with a constant velocity of 263+/-16 km/s. From the two STEREO observations we derive a height of the wave in the range of 80-100 Mm. Comparison of the wave kinematics with the early phase of the erupting CME structure indicates that the wave is initiated by the CME lateral expansion, and then propagates freely with a velocity close to the fast magnetosonic speed in the quiet solar corona.

astro-ph.SR↗

arXiv2007

Large amplitude oscillatory motion along a solar filament

Large amplitude oscillations of solar filaments is a phenomenon known for more than half a century. Recently, a new mode of oscillations, characterized by periodical plasma motions along the filament axis, was discovered. We analyze such an event, recorded on 23 January 2002 in Big Bear Solar Observatory H$α$ filtergrams, in order to infer the triggering mechanism and the nature of the restoring force. Motion along the filament axis of a distinct buldge-like feature was traced, to quantify the kinematics of the oscillatory motion. The data were fitted by a damped sine function, to estimate the basic parameters of the oscillations. In order to identify the triggering mechanism, morphological changes in the vicinity of the filament were analyzed. The observed oscillations of the plasma along the filament was characterized by an initial displacement of 24 Mm, initial velocity amplitude of 51 km/s, period of 50 min, and damping time of 115 min. We interpret the trigger in terms of poloidal magnetic flux injection by magnetic reconnection at one of the filament legs. The restoring force is caused by the magnetic pressure gradient along the filament axis. The period of oscillations, derived from the linearized equation of motion (harmonic oscillator) can be expressed as $P=π\sqrt{2}L/v_{Aϕ}\approx4.4L/v_{Aϕ}$, where $v_{Aϕ} =B_{\phi0}/\sqrt{μ_0ρ}$ represents the Alfvén speed based on the equilibrium poloidal field $B_{\phi0}$. Combination of our measurements with some previous observations of the same kind of oscillations shows a good agreement with the proposed interpretation.

astro-ph↗

arXiv2006

RHESSI Results -- Time For a Rethink?

Hard X-rays and gamma-rays are the most direct signatures of energetic electrons and ions in the sun's atmosphere which is optically thin at these energies and their radiation involves no coherent processes. Being collisional they are complementary to gyro-radiation in probing atmospheric density as opposed to magnetic field and the electrons are primarily 10--100 keV in energy, complementing the (>100 keV) electrons likely responsible for microwave bursts. The pioneering results of the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) are raising the first new major questions concerning solar energetic particles in many years. Some highlights of these results are discussed -- primarily around RHESSI topics on which the authors have had direct research involvement -- particularly when they are raising the need for re-thinking of entrenched ideas. Results and issues are broadly divided into discoveries in the spatial, temporal and spectral domains, with the main emphasis on flare hard X-rays/fast electrons but touching also on gamma-rays/ions, non-flare emissions, and the relationship to radio bursts.

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