Hα filtergrams and GOES X-ray observations of four homologous flares of May 28, 1980 are analysed. The Hα data gave us information about the spatial structure of the flares. The X-ray data were used to determine the temperature of flare plasma and to investigate its time variations. We have found that the duration of the high plasma:temperature are approximalely equal for all the four analysed flares. The Hα-structure of these flares was complicated
nevertheless we have found only slight changes of the structure from flare to flare. These resulls suggest that a common reviving source of the energy release is responsible for all the four homologous flares. The individual flares are due to successive revivals of the energy source. The conditions of the energy flow along the magnetic field lines emerging from the energy source
determine which parts of the chromosphere are seen in the
Hα emission.
During the solar cycle minimum period, a period of a suddenly enhanced solar activity occurred in early February 198d. Two proton flares were observed during this period after a long period of a totally quiet solar activity (R = 0 on most days in the second half of December and in January). Other flares, various phenomena
accompanying proton flares, like type II and type IV radio bursts and a large Forbush deerease of cosmic ray intensity were observed as well as an extremely severe geomagnotic storm (Kp = 9) and strong disturbances in the Earth´s ionosphere (SIDs and ionospheric storm), Czechoslovak solar and geophysical observations for this period are presented and interpreted with the use of other observations. Special attention is given to the flares of February 4 (start 0732 and 1025 UT) and February 5 (start 0934 UT) because spectrohelioscopic observations from the Hurbanovo observatory are available for these events.
For five flares we have considered magnetic fields, measured in the flaring region and underlying sunspots. Main results:
a) magnetic field in flare is longitudinal, buf it is mainly transversal in fhe sunspol which the flare is situated on;
b) magnetic field strengths measured by Zeeman splitting of Ihe emission lines ol Fel, D1, and D-2 Nal, D3 Hel and Hα reach 1000-3000G, offen exeeeds ones determined by absorption lines in underlying sunspols;
e) it appears fhat in flare the magnetic field changes slowly wifh heighf, so far as its vaues estimated by emission lines of helium, hydrogen and metal are approximately equal.
We demonstrate that both in the global scale and in the scale of large and complex active regions the high flare activity is dosely related to the changes in the whole background magnetic field distribution. We found that the disturbances of the normal course of MALs during the years 1965 -1980 correlated with the maxima of flare activity and the mode of MALs distribution with the mean level of solar flare numbers. We showed that the development of activity during the last two ^submaxima of the 21st cycle of solar activity, especially the formation of the white-light flare region of April 1984, were parts of global processes in the solar atmosphere. They
were accompanied by a complete reorganization of the MALs patterns, background field sector structure and restructuralization of coronal holes. In both cases, in the global and in the local scales, we could follow the geophysical consequences of the entire reconstruction of global solar field amplified by the direct influence of many large flares.
We describe the course of events during the evolution of the 300 keV, 3B/M7 June 26, 1983, 14:07 UT flare, as observed at the Crimean Astrophysical Observatory. We show directly as they developed a/ preflare microprominence uprise (Fig. 1)
b/ emisslve-surge flare onset c/ flaring arch system during the maximum flare phase (Fig. 2) d/ flaring arch cooling, which dlffers from the proper "post-flare loops" phenomenon (Fig. 3). The maximum rate of the upward surge’s extension, along its
axis, was 360 km s-1.
Large two-ribbon flares are frequently accompanied by a system of (post)-flare loops, cooler structures being visible in several optical and UV lines. We investigate tlie non-LTE formation of hydrogen lines in stationary loop structures, taking into account the influence of macroscopic velocity flows along the loop. We demonstrate some diagnostically important effects on hydrogen Hα line and identify them using narrow-band Hα filtergrams. This diagnostics provides us with a reasonable description of physical conditions prevailing in the cool flare loops. However, we finally stress the importance of even more complex (and difficult)
radiation-hydrodynamical approach.
An attempt is presented to explain the large difference in the
intensity, frequency range and number of radio activity events
following the large flares in the two complex active regions of June
1982 (NOAA Nos. 3763 and 3776). The topology of their local magnetic
fields in relation to the global field is discussed as one of the main
factors causing this effect.