Small-scale high-temperature structures in flare regions

When analyzing YOHKOH/SXT, HXT (soft and hard X-ray) images of solar flares against the background of plasma with a temperature T similar or equal to 6 MK, we detected localized (with minimum observed sizes of approximate to 2000 km) high-temperature structures (HTSs) with T approximate to (20-50) M K with a complex spatial-temporal dynamics. Quasi-stationary, stable HTSs f orm a chain of hot cores that encircles the flare region and coincides with the magnetic loop. No structures are seen in the emission measure. We reac hed conclusions about the reduced heat conductivity (a factor of similar to 10(3) lower than the classical isotropic one) and high thermal insulation of HTSs. The flare plasma becomes collisionless in the hottest HTSs (T > 20 MK). We confirm the previously investigated idea of spatial heat localizat ion in the solar atmosphere in the form of HTSs during flare heating with a volume nonlocalized source. Based on localized soliton solutions of a nonl inear heat conduction equation with a generalized flare-heating source of a potential form including radiative cooling, we discuss the nature of HTSs. (C) 2001 MAIK "Nauka/Interperiodica".