The primary task of the Debrecen Heliophysical Observatory (DHO) has been the most detailed, reliable, and precise documentation of the solar photospheric activity since 1958. This long-term effort resulted in various solar catalogs based on ground-based and space-borne observations. A series of sunspot databases and on-line tools were compiled at DHO: the Debrecen Photoheliographic Data (DPD, 1974-), the dataset based on the Michelson Doppler Imager (MDI) of the Solar and Heliospheric Observatory (SOHO) called SOHO/MDI-Debrecen Data (SDD, 1996(SDD, -2010, and the dataset based on the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO) called SDO/HMI-Debrecen Data (HMIDD, 2010-). User-friendly web-presentations and on-line tools were developed to visualize and search data. As a last step of compilation, the revised version of Greenwich Photoheliographic Results (GPR, 1874(GPR, -1976 catalog was converted to DPD format, and a homogeneous sunspot database covering more than 140 years was created. The database of images for the GPR era was completed with the full-disc drawings of the Hungarian historical observatoriesÓgyalla and Kalocsa and with the polarity drawings of Mount Wilson Observatory. We describe the main characteristics of the available data and on-line tools.
The forecast method introduced by Korsós et al. (2014) is generalised from the horizontal magnetic gradient (G M ), defined between two opposite polarity spots, to all spots within an appropriately defined region close to the magnetic neutral line of an active region. This novel approach is not limited to searching for the largest G M of two single spots as in previous methods. Instead, the preflare conditions of the evolution of spot groups is captured by the introduction of the weighted horizontal magnetic gradient, or W G M . This new proxy enables the potential of forecasting flares stronger than M5. The improved capability includes (i) the prediction of flare onset time and (ii) an assessment whether a flare is followed by another event within about 18 hours. The prediction of onset time is found to be more accurate here. A linear relationship is established between the duration of converging motion and the time elapsed from the moment of closest position to that of the flare onset of opposite polarity spot groups. The other promising relationship is between the maximum of the W G M prior to flaring and the value of W G M at the moment of the initial flare onset in the case of multipleflaring. We found that when the W G M decreases by about 54%, then there is no second flare. If, however, when the W G M decreases less than 42%, then there will be likely a follow-up flare stronger than M5. This new capability may be useful for an automated flare prediction tool.
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