The Long Period Oscillations of Microwave Emission of Solar Active Regions by Observations on NoRH and SSRT

I.A. Bakunina1, S.V. Lesovoy2, K. Shibasaki3, A.A. Solovjev4, Yu.V. Tikhomirov1, V.L. Bakunin5

1Radiophysical Research Institute (NIRFI), Nizhny Novgorod, Russia
2Institute of Solar-Terrestrial Physics RAS SB, Irkutsk, Russia
3Nobeyama Solar Radio Observatory, Minamisaku, Nagano, Japan
4Central Astronomical Observatory at Pulkovo, St.Petersburg, Russia
5Institute of Applied Physics RAS, Nizhny Novgorod, Russia

Quasi-periodic long-term oscillations of the solar flux radio emission have being studied since 1974 (Stix, Sowyer, Pustilnik, Kobrin and others). New radio telescopes, for example, Nobeyama Radio Heliograph (NoRH) opened new possibilities for studying oscillations of solar radio emission due to high spatial resolution (Gelfreikh, Nagovitsyn, 2006).

We present the first results of studying and comparison of the parameters of quasi-periodic long-term oscillations of microwave emission of the large (> 0.7) sunspots simultaneously on both radioheliographs - NoRH (17 GHz) and Siberian Solar Radio Telescope (SSRT) (5.7 GHz) with 1 minute cadence. Radioheliographs have been working with the large time overlap (over 4 hours) and have the spatial resolution 10 arcsec (NoRH) and 20 arcsec (SSRT).

On the radio maps sunspot-associated sources were identified and time profiles of their maximum brightness temperatures and circular polarization degree for each radio source were calculated. We found out that: 1) long period oscillations are surely observed on both frequencies and have pulse group (zugs) character; 2) periods of the long-term oscillations on both 17 and 5.7 GHz are in the range of 20 - 150 min; 3) amplitudes of oscillations are three or more times greater on 17 GHz than on 5.7 GHz - this result comes to an agreement with our model calculations of cyclotron emission maximum brightness temperatures with dipole or virtual monopole simulation of a magnetic field above sunspot.