Signs of Preparation of Solar Flares in the Microwave Range

We present a study of the spatial distribution of quasi-periodic oscillations (QPOs) of microwave emission in three solar active regions before flares. The following events are considered: SOL2011-09-06T01:50M5.3, SOL2011-09-25T02:33M4.4, and SOL2012-07-08T04:19C6.6. Daily observations on the Nobeyama Radioheliograph at a frequency of 17 GHz are used. In all three cases, pre-flare trains of the QPOs of microwave emission are detected. The length of the trains is 3–4 pulses. In all cases, the most strongly detected oscillations manifested themselves in a compact zone in an active region coinciding with the region of maximum microwave emission brightness during the flare.