The Frequency of Occurrence of Pre-Flare Fluctuations in Microwave Radiation of Active Regions

Geomagnetism and Aeronomy, Springer, Switzerland. 2023. Vol. 63. No. 7. P. 916–919.

Abramov-Maximov V. E., I. A. Bakunina

We present a study of the frequency of occurrence of quasi-periodic fluctuations (QPFs) of microwave
radiation from solar active regions at the pre-flare stage. We used correlation curves obtained with the
Nobeyama Radioheliograph (NoRH). We analyzed 529 flares of classes X, M, and C (according to the GOES
classification). In a significant number of considered events (approximately 75% of the powerful flares and
50% of the weaker flares), preflare fluctuations of microwave radiation with a duration of up to ten pulses are
observed. The character of preflare fluctuations is different in different cases. In some cases, almost harmonic
oscillations are observed. In most cases, the fluctuations are sporadic and look like a sequence of weak
flares. It is possible that the nature of the preflare QPFs is different in different cases.

Keywords: микроволновое излучение, солнечные вспышки, solar flares, microwave emission, quasi-periodic pulsations of microwave emission, квазипериодические колебания микроволнового излучения