Precursors of solar flares in the microwave range
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Abstract
We present a study of the spatial distribution of quasiperiodic oscillations of microwave emission in two active regions before M-class flares. We have studied two events: NOAA 11283 on September 6 and NOAA 11302 on September 25, 2011. We used the Nobeyama Radioheliograph (NoRH) daily observations at a frequency of 17 GHz. In both cases we found the preflare wave trains of brightness temperature oscillations of microwave emission in active regions. The duration of wave trains is about 3–4 oscillation cycles. We found that the source of oscillations was a compact zone in the active region, which coincides with the area of maximum brightness during a flare.
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