Solar Flare Recognition and Analysis

The Sun, our nearest star, changes its appearance in manifold ways, following an approximately 11 year cycle. Among the most violent phenomena of solar activity are solar flares, which represent an explosive energy release in the solar atmosphere on the time scale of minutes. Due to the direct influence of the high energetic particles, accelerated during large flare events, near the Earth`s environment, flares are a main cause for perturbations of the space weather, which denotes the conditions on the Sun and in the solar wind, the Earth`s magnetosphere, ionosphere, and thermosphere that can influence the performance and reliability of ground-based and space-based technological systems and can endanger human life. The objective of the proposed project is to set up a system, which automatically and in quasi real- time recognizes the onset of a flare and follows its evolution. For this purpose the H-alpha observing instrumentation at the Kanzelhöhe Solar Observatory, Austria, will be utilized, which performs full-disk H-alpha observations of the Sun with an acquisition rate of 1 minute on a daily basis. From such an automatic image analysis system we can profit in several ways: 1) The application of the software to the actually grabbed H-alpha full-disk images provides an automatic and quasi real-time description of solar activity. Moreover, the quasi-real time detection of the onset of a flare will be used as a trigger for even higher cadence observations, providing us with a very high time resolution imaging of the flare dynamics. 2) The same software can also be applied to already existing H-alpha images in the Kanzelhöhe data archive, providing a general survey and analysis on the occurrence of solar flares. Moreover, it offers an easy access to statistical as well as multi-wavelength studies of flares. 3) Recently the "Global High-Resolution H-alpha Network" has been established between the Big Bear Solar Observatory (U.S.A.), the Yunnan Astronomical Observatory (China) and the Kanzelhöhe Solar Observatory, which is a coordinated round-the-clock network of full-disk observations of the Sun in H-alpha with a time cadence of 1 image per minute and a spatial resolution of 1" per pixel. Since all three observatories use a similar observing equipment and the same data post-processing routines, the proposed flare recognition system can be easily applied also to the Big Bear and Yunnan data, which enables us to follow the evolution of solar flares in exceptional long (in the optimum case: uninterrupted) image time series.

The present project was aimed to set up new as well as to enhance existing programs for solar flare monitoring and recognition at the Kanzelhöhe Solar Observatory (KSO) which is affiliated to the Institute of Physics of the University of Graz, Austria, and to study the physics of these high-energetic events. Solar flares and coronal mass ejections are the driver for the so-called space weather which can affect the Earth environment by a variety of phenomena (highly energetic particles, shock waves, enhanced radiation, etc.) and are in particular a hazard to highly technological systems in space, for instance telecommunication satellites. Any attempts to model and predict the space weather conditions have to rely on the physical understanding of these events on the Sun as well as their coupling to the interplanetary medium. One important task is thus the regular observation and analysis of solar flares and CMEs on the Sun. During this project the time cadence of full-disk imaging in the H-alpha spectral line at KSO (with a spatial resolution of 2.2 arcsec/pixel) was enhanced from >1 min to a regular (i.e. 7 days a week) high cadence observing mode of 5 sec. These data provide an important basis for space weather studies and provide also important ground-based support for satellite missions dedicated to studies of the Sun, as e.g. the NASA/ESA SOHO satellite, NASA`s RHESSI mission as well as future missions such as STEREO and Solar B. Furthermore, the Kanzelhöhe H imaging capabilities were significantly extended and improved by implementing automatic flare observations also in the blue and red wings of the H-alpha spectral line, which is in particular useful for the study of mass motions and wave phenomena. During this project new insight into the origin and propagation of waves associated with solar flare/CME events was gained. It was shown that at least for some waves there is evidence that the flare (pressure pulse) is the driver and not the CME expansion. Moreover, for the first time flare waves have been identified in metric-range radio images which is important since it offers new diagnostic information that can provide us with better insight into the physical conditions in the disturbance itself. An important finding of the project was also the discovery of coronal thick-target hard X-ray sources. Such thick target hard X-ray sources have been observed for the first time with the RHESSI instrument and are a challenge to the standard scenario of magnetic reconnection in solar flares.