HαMoreton waves observed on December 06, 2006

Abstract

Context. We present high temporal resolution observations of a Moreton wave event detected with the Hα Solar Telescope for Argentina (HASTA) in the Hα line 656.3 nm, on December 6, 2006. Aims. The aim is to contribute to the discussion about the nature and triggering mechanisms of Moreton wave events. Methods. We describe the HASTA telescope capabilities and the observational techniques. We carried out a detailed analysis to determine the flare onset, the radiant point location, the kinematics of the disturbance and the activation time of two distant filaments. We used a 2D reconstruction of the HASTA and corresponding TRACE observations, together with conventional techniques, to analyze the probable origin of the phenomenon. Results. The kinematic parameters and the probable onset time of the Moreton wave event are determined. A small-scale ejectum and the winking of two remote filaments are analyzed to discuss their relation with the Moreton disturbance. Conclusions. The analysis of the Moreton wave event favors the hypothesis that the phenomenon can be described as the chromospheric imprint of a single fast coronal shock triggered from a single source in association with a coronal mass ejection. Its onset time is concurrent with a Lorentz force peak measured in the photosphere, as stated by other authors. However, the existence of multiple shock waves that were generated almost simultaneously cannot be discarded.

Moreton and EUV Waves Associated with an X1.0 Flare and CME Ejection

“…In Hα, regions exhibiting double traces are noticeable (see features indicated by light-blue arrows in sectors 36 -39 of Figure 2a), suggesting the presence of more than a single coronal perturbation or a complex physical process that originates the differing chromospheric emissions. Other authors have suggested the presence of more than one Moreton-wavefront in the vicinity of an AR Francile et al, 2013). However, in our case the spatial separation between these two fronts is not large enough to conclude about their presence on a firm basis.…”

“…We estimate the kinematic characteristics of the Moreton wavefronts by fitting power-law curves (Warmuth et al, 2004a;Francile et al, 2013) for every sector of interest to the average spline obtained, as indicated above. These curves are suitable to fit smoothly kinematic trajectories with non-constant accelerations.…”

“…The parameters are calculated considering an RP located at the brightest flare kernel, i.e. not using an RP derived from tracing arcs of circumferences over the chromospheric Hα fronts as done by other authors (Warmuth et al, 2004a,b;Francile et al, 2013). Despite the differences between the methods of measurement, we consider that the values of the kinematic parameters (distances, speeds, and accelerations) should be similar far from the AR.…”

“…Following Vršnak and Cliver (2008), such coincidence cannot account for the necessary delay in the shock formation after the onset of the flare pressure pulse, given reasonable values of ambient Alfvén speed and piston expansion speed. Some authors have suggested that the launch of Moreton events precedes the flare impulsive phase (Veronig, Temmer, and Vršnak, 2008;Muhr et al, 2010), while others find a close temporal coincidence (Warmuth et al, 2004b;Francile et al, 2013), thus indicating that probably not all Moreton events are similar in this sense.…”

Large-scale Globally Propagating Coronal Waves

“…Warmuth et al, 2004a;Narukage et al, 2008;Muhr et al, 2010;Balasubramaniam et al, 2010;Warmuth, 2010;Asai et al, 2012;Francile et al, 2013). The initial velocities are in the range of 600 -1200 km s -1 and decline to ≈ 500 km s -1 before the Hα wave signatures vanish.…”