3-minute oscillations at wavelength 1.76 cm in 1992–2006
Pulkovo Astronomical Observatory, 196140 Saint Petersburg, Russia e-mail: firstname.lastname@example.org
2 University of Turku, Tuorla Observatory, 21500 Piikkiö, Finland e-mail: email@example.com
Accepted: 31 May 2008
Context. We discuss variations of polarized radio emission using the correlation data obtained with the Nobeyama Radioheliograph at 1.76 cm wavelength. We focus on the radio 3-min oscillations.
Aims. We consider the daily averaged correlation data with right and the left hand circular polarizations in order to study how the power spectrum and the basic periods of the 3-min oscillations changed during 1992–2006.
Methods. We use spectral analysis to obtain the power spectrum of oscillations, excluding the solar flares.
Results. It was found that oscillations with a period of about 3 min occur during all phases of the solar activity cycle when at least one sunspot is present on the solar disk, and that there is a linear correlation between the strength of the 3-min oscillations and the monthly mean of the sunspot areas. The basic period of these oscillations changes, beginning from 150–160 s to 170–180 s with the level of solar activity. Also, we found that there is a linear correlation between the basic period and the monthly mean of the sunspot areas.
Key words: Sun: radio radiation / Sun: oscillations
© ESO, 2008