Ground-based Observations of the Solar Sources of Space Weather

Monitoring of the Sun and its activity is a task of growing importance in the frame of space weather research and awareness. Major space weather disturbances at Earth have their origin in energetic outbursts from the Sun: solar flares, coronal mass ejections and associated solar energetic particles. In this review we discuss the importance and complementarity of ground-based and space-based observations for space weather studies. The main focus is drawn on ground-based observations in the visible range of the spectrum, in particular in the diagnostically manifold H alpha spectral line, which enables us to detect and study solar flares, filaments (prominences), filament (prominence) eruptions, and Moreton waves. Existing H alpha networks such as the GONG and the Global High-Resolution H alpha Network are discussed. As an example of solar observations from space weather research to operations, we present the system of real-time detection of H alpha flares and filaments established at Kanzelhohe Observatory (KSO; Austria) in the frame of the space weather segment of the ESA Space Situational Awareness programme (swe. ssa. esa. int). An evaluation of the system, which is continuously running since July 2013 is provided, covering an evaluation period of almost 2.5 years. During this period, KSO provided 3020 hours of real-time H alpha observations at the ESA SWE portal. In total, 824 H alpha flares were detected and classified by the real-time detection system, including 174 events of H alpha importance class 1 and larger. For the total sample of events, 95 % of the automatically determined flare peak times lie within 5 min of the values given in the official optical flares reports (by NOAA and KSO), and 76 % of the start times. The heliographic positions determined are better than 5. The probability of detection of flares of importance 1 or larger is 95 %, with a false alarm rate of 16 %. These numbers confirm the high potential of automatic flare detection and alerting from ground-based observatories.