[7] The study of general characteristics of active regions generating proton flares is necessary for better understanding of the nature of proton flares. In this brief review, information on 19 active regions with increased flare activity observed on the Sun during the recent decades and accompanied by strong proton flares and geomagnetic effects (magnetic storms, aurora, and anomalous ionization in the Earth atmosphere) is considered. The delay of the proton fluxes near the Earth orbit relative to optical and X-ray photons is about 1-2 days depending on the heliographical longitude of the flare and the velocity of the ejected particles. The most energetic particles cover the distance to the Earth by 15-20 min. Proton events by their power may differ by 1.5 orders of magnitude and are often related to microwave bursts of II and IV types. In the analyzed events the maximum proton fluxes for the most powerful events were above 1000 pfu (up to 40,000 pfu where pfu is a proton flux unit: p cm-2 s-1 sr-1 ). For the rest of the events the flux values exceeded at 1 AU 100 pfu.
[8] During one passage over the solar disk, 11 X class flares were registered in one of the most productive AR considered. For the sake of comparison we present the data by Contarino et al. [2002], who analyzed flare activity in 2259 sunspot groups during the 5-year period from 1996 to 2001. During this period, 559 energetic events (including flares of the M and X classes) were registered. This means that there is less than 0.4 event per one group. If only flares of the X class are taken into account, the productivity of one AR is even less.
[9] Table 1 shows the data on the ARs: the observation date, the number of optical and X-ray flares, their maximum class, the number of flares of the X class, the proton flux with E> 10 MeV, and the corresponding class of the flare. The information on proton events was taken from SGD (Catalogue of solar proton events 1987-1996, Moscow 1998, available at http://umbra.nascom.nasa.gov/SEP/), and particular publications.
[10] All the considered ARs have a common feature in the magnetic field (MF) structure: there existed rather extended configuration of the d type. In 1966 it was still found that d configurations either precede or accompany all proton events [Warwick, 1966]. The term d configuration was introduced by Künzel [1960] and is used when the umbrae of opposite magnetic polarities are located in the common penumbra close to each other. Most often a small spot satellite emerges up in the same penumbra with the main spot, but d configuration can exist in groups of spots with the magnetic structure of the b, bg, and g types. Observations have shown that the highest activity takes place when the areas of the penumbra and umbrae of opposite polarity involved in the d configuration occupy considerable areas. It is known that the d and g configurations are the most flare active. Using the observations of 2789 AR during the 1989-1997 period, Sammis et al. [2000] showed that a relation between the power of X-ray flares and the structure of the magnetic field in the AR existed. Large ARs with the MF configuration of the bgd type are the most flare productive.
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