Extreme ultraviolet and X-ray emission of solar flares as observed from the CORONAS-F spacecraft in 2001-2003

The results of measuring UV radiation onboard the CORONAS-F spacecraft during solar flares in 2001-2003 are considered. Some conclusions from the analysis of variations of solar-flare emission in several spectral intervals, namely, in soft X-rays, in the 10- to 130-nm range, and in the band near 120 nm, are discussed. The data were obtained by the VUSS-L and SUFR instruments. Time and energy characteristics of flares recorded onboard the CORONAS-F spacecraft are compared to the GOES measurements in the interval 0.1-0.8 nm and to the SOHO measurements of UV radiation in the 26- to 34-nm band. In particular, it is demonstrated that UV radiation is generated several (1-10) minutes before X-ray emission for most flares considered in the study. It is shown that the energy of flare emission in the extreme ultraviolet is usually not greater than similar to 10% of its preflare level and that energy fluxes in different wavelength ranges are related by a power law. Such an analysis makes it possible to better understand the mechanism of flare development.