ИСТИНА

The modern satellite observations of flare arcades in solar flares demon- strate a consistent increase in the brightness of individual coronal loops. We have solved the problem of the small perturbations stability of a homogeneous longitudinal reconnecting current layer in the MHD approximation. The suppression of the plasma thermal conductivity by the magnetic field inside the current layer provides an instability. The instability increases in a radiative cooling time scale of the plasma in the linear phase. A periodic structure of hot and cold fibers arranged transversely to the direction of the electric current are formed as a result of the instability. The proposed mechanism of the thermal instability can be useful for an explanation of the consistent increase in the brightness of individual coronal loops in solar flares.