V.G. Ledenev
Institite of Solar-Terrestrial Physics, Siberian Branch of the
Russian Academy of Sciences, Lermontov St. 126, Irkutsk 664033, Russia
High space resolution observations of solar radio emission U-bursts are not always explained on the base of the emission generation in the magnetic arch model, because in some cases the distance between sources corresponding to ascend and descent branches of the burst is less by an order of magnitude than the dimension of the magnetic arch which is connected with the burst source. Besides in the most cases the change of the polarization sense is not observed when the source moves from the one the burst branch to another one. On this basis we suggest a new model of U-burst generation, which takes into account inhomogeneity effects of the solar corona. It has been known, if electron beam moves in the direction of the plasma density decrease, the spectrum of excited plasma waves shifts to large wave numbers (to small phase velocities). This means that the spectrum of plasma waves concentrates nearby the distribution function border, which moves in the region of low velocities in the process of quasilinear relaxation. As plasma waves shifts in the region of large wave numbers, their frequency grows in accordance of the dispersion equation, which describes these waves. When the growth velocity of the plasma wave frequency exceeds the decrease velocity of the frequency due to a corona inhomogeneity, the branch with positive frequency drift appears on the dynamic spectrum of the radio emission. Executed calculations allow us to estimate a density and energy of electron beams generating U-bursts.