Spectral peculiarities of strong solar bursts

We have investigated spectral features of strong radio burst emission for the 21st cycle of solar activity. The maximum daily radio fluxes in 8 frequency ranges are analyzed. For every year, the classification of these daily spectra is obtained by the cluster analysis method. We have shown that strong bursts are characterized by the stable shape of the mean radio emission spectra. For these bursts the total level of radio emission does not depend on the phase of the solar 11-yr cycle and varies with the quasi-period of 4 yr. The basic features of burst spectra can be explained by the gyrosynchrotron radiation of nonthermal electrons and plasma radiation at the second harmonic of plasma frequency. We supposed that in the generation region of centimetric emission, if the strength of the magnetic field B identical with 100G, 100 G, the number of microbursts can amount to (6-7) x 10 super(3) . In the generation region of decimetric emission, the energy of Langmuir waves changes as W sub(l) similar to n sub(e) super(0) super(.) super(4) .