A Comparison of Parameters of 3-minute and 5-minute Oscillations in Sunspots from Synchronous Microwave and Optical Observations

V.E. Abramov-Maximov1, G.B. Gelfreikh1, N.I. Kobanov2, K. Shibasaki3

1Central Astronomical Observatory at Pulkovo, St.-Petersburg, Russia
2Institute of Solar Terrestrial Physics, Irkutsk, Russia
3Nobeyama Solar Radio Observatory, Minamisaku, Nagano, Japan


The observations of 3 and 5 minute oscillations in sunspots present information on propagation of MHD waves in the magnetic tubes of sunspots. In this report we present a comparison of wavelet spectra of radio flux oscillations at λ = 1.76 cm with oscillations of longitude component of the velocity at the chromosphere in sunspot umbra and penumbra in some active regions. We use observations for 23 days on 2004 and 2005.

The radio maps of the sun obtained with the Nobeyama Radio Heliograph at wavelength of 1.76 m were used. The spatial resolution of the radio data was about 10-15 arcsec and 10 sec cadence. On the radio maps sunspot-associated sources were identified and calculated time profiles of their maximum brightness temperatures for each radio source. These presented information on oscillations of plasma parameter (in the regions with magnetic field B = 2000 Gs) at the level of the chromosphere-corona transition region. The optical observations were carried out at Sayan observatory. These data included information on longitude component of the magnetic field at the photosphere (line Fe I 6569 A) and longitude component of the velocity at the chromosphere (line Hα was used).

Comparing the wavelet diagrams covering the same periods of observation at radio and optics has shown that some zugs of time profiles are very similar in both kinds of observations (similar oscillation frequencies and their drifts, variations in amplitudes), however, some significant differences were also registered. The best similarity in optical and radio oscillations was found on August 18, 2004, when the AR was near the center of the solar disk. The phase shifts between the two kinds of observations reflecting the propagation of the MHD waves were also analyzed.