Large-scale coronal waves and shocks

The most energetic and violent processes in our solar system are solar flares and coronal mass ejections (CMEs). Flares represent an explosive release of energy, previously stored in complex magnetic fields associated with sunspots, on time scales of minutes to hours, in the form of high-energetic particles, plasma heating and flows. CMEs are huge amounts of magnetized plasma expelled into interplanetary space with hundreds to thousands of km/s, occasionally heading towards Earth. Flares, CMEs and their associated phenomena are the main cause for major perturbations of our "space weather". CME/flare events are frequently associated with large-scale large-amplitude waves and shocks in the solar corona. Coronal waves and their associated dimmings belong to the clearest evidence for large-scale magnetic field reconfigurations associated with the onset of earth-directed halo CMEs, which are otherwise difficult to assess but are of severe importance for space-weather disturbances at Earth. Coronal waves, which have been first imaged by the Extreme-ultraviolet Imaging Telescope (EIT) onboard Solar and Heliospheric Observatory (SOHO; ESA/NASA) about ten years ago, are a quite controversial subject in solar physics, regarding a) their nature (waves? no waves at all?), b) their driver (flares? CMEs? magnetic field line restructuring?), and c) their relation to wave-like signatures observed in the chromosphere ("Moreton waves"). Until recently, the data available were severely hampered by time cadences much too low to catch the kinematics and dynamics of these phenomena, which would be necessary to solve the controversy. These limitations are now overcome by the EUVI (Extreme UltraViolet Imager) instruments on the twin Solar TErrestrial RElations Observatory (STEREO; NASA) spacecraft launched in October 2006, which regularly image the Sun (from two different perspectives, ahead and behind Earth) in the extreme ultraviolet wavelength range with high time cadence. Thus, it is for the first time possible to really study the dynamics of coronal waves. The principal aim of our project is to use these unprecedented data (combined with a variety of other space-based and ground-based observations) to perform comprehensive statistical as well as detailed case studies of the main observational characteristics, underlying nature and initiation of large-scale waves and shocks observed in the solar corona, their relation to flares and CMEs, as well as their relation to Moreton waves observed in the chromosphere.

The most energetic and violent processes in our solar system are solar flares and coronal mass ejections (CMEs). Flares represent an explosive release of energy, previously stored in complex magnetic fields associated with sunspots, on time scales of minutes to hours, in the form of high-energetic particles, plasma heating and flows. CMEs are huge amounts of magnetized plasma expelled into interplanetary space with hundreds to thousands of km/s, occasionally heading towards Earth. Flares, CMEs and their associated phenomena are the main cause for major perturbations of our "space weather". CME/flare events are frequently associated with large-scale large-amplitude waves and shocks in the solar corona. Coronal waves and their associated dimmings belong to the clearest evidence for large-scale magnetic field reconfigurations associated with the onset of earth-directed halo CMEs, which are otherwise difficult to assess but are of severe importance for space-weather disturbances at Earth. Coronal waves, which have been first imaged by the Extreme-ultraviolet Imaging Telescope (EIT) onboard Solar and Heliospheric Observatory (SOHO; ESA/NASA) about ten years ago, are a quite controversial subject in solar physics, regarding a) their nature (waves? no waves at all?), b) their driver (flares? CMEs? magnetic field line restructuring?), and c) their relation to wave-like signatures observed in the chromosphere ("Moreton waves"). Until recently, the data available were severely hampered by time cadences much too low to catch the kinematics and dynamics of these phenomena, which would be necessary to solve the controversy. These limitations are now overcome by the EUVI (Extreme UltraViolet Imager) instruments on the twin Solar TErrestrial RElations Observatory (STEREO; NASA) spacecraft launched in October 2006, which regularly image the Sun (from two different perspectives, ahead and behind Earth) in the extreme ultraviolet wavelength range with high time cadence. Thus, it is for the first time possible to really study the dynamics of coronal waves. The principal aim of our project is to use these unprecedented data (combined with a variety of other space-based and ground-based observations) to perform comprehensive statistical as well as detailed case studies of the main observational characteristics, underlying nature and initiation of large-scale waves and shocks observed in the solar corona, their relation to flares and CMEs, as well as their relation to Moreton waves observed in the chromosphere.