Large-scale EUV waves: dynamics, driver and plasma properties

Solar flares and coronal mass ejections (CMEs) are the most energetic eruptions in the solar system. They are driven by the strong magnetic fields in sunspots, and are frequently accompanied by large-scale large-amplitude waves and shocks in the solar atmosphere. Large-scale disturbances propagating through the solar corona have been first imaged by the Extreme-Ultraviolet Imaging Telescope (EIT) onboard the ESA/NASA Solar and Heliospheric Observatory (SOHO) about 15 years ago. They have attracted much attention due to their association with Earth-directed geo-effective halo CMEs, but they were also the source of a substantial controversy in the solar physics community as regards their physical interpretation. In this project, we will make use of the unprecedented observational data that are available nowadays via a fleet of scientific spacecraft dedicated to solar and heliospheric observations to address the following aims: - Using the ultrahigh-cadence multi-band imaging from the Atmospheric Imaging Assembly (AIA) onboard NASA`s recent Solar Dynamics Observatory (SDO), we will study the fine structure, wave characteristics, and dynamics of EUV waves as well as their initiation in relation to the impulsive CME expansion. - Important plasma diagnostics of EUV waves (density, temperature, plasma motions at the wave front), which are still outstanding, will be studied through dedicated observing campaigns of the Extreme-Ultraviolet Imaging Spectrometer (EIS) onboard the Japanese Hinode mission combined with SDO/AIA high-cadence imaging. - The relation of coronal EUV waves to chromospheric Moreton waves will be analyzed by combining high-cadence EUV imaging by SDO/AIA with high-cadence imaging in the wings of the Halpha spectral line from ground-based observatories. To this aim we will develop a new Halpha wing telescope system at Kanzelhöhe Observatory of the University of Graz. - We will systematically study the association of EUV waves with solar energetic particle events measured in-situ at multiple platforms in the heliosphere. The outcome of this study may provide a basis for better forecasting of particle events at Earth from solar observations.

Flares and coronal mass ejections from our Sun are the most energetic phenomena in our solar system, and can lead to strong disturbances of our space weather. They are caused by strong magnetic field concentrations in sunspots, and they are often associated by large-scale disturbances in the solar atmosphere. In this project, we showed in observations from various NASA and ESA satellites like SDO, STEREO, SOHO and Proba 2 as well as in numerical simulations that these large-scale disturbances are fast magneto-acoustic waves of high amplitudes, propagating through the solar corona. We also showed that the associated chromospheric Moreton waves can only be initiated in cases where the coronal wave has very high amplitude and develops into a shock wave. On the other hand, the acceleration of solar energetic particle reaching Earth seems not to be related to these large-scale waves. Finally, for better observations of Moreton waves a new telescope was developed and installed at Kanzelhöhe Observatory for Solar and Environmental Research that observes the full Sun simultaneously in the wings of the Halpha spectral line of neutral hydrogen.