On the nature of microwave pulsations from solar active regions

Heading: 
Astronomy and Astrophysics
1Gelfreikh, GB, 2Tsap, YT, 1Kopylova, YG, 2Tsvetkov, LI, 3Goldvarg, TB, 1Nagovitsin, YA, 2Yurovsky, YF, 2Budzinovskaya, IA
1Main Astronomical Observatory of the Russian Academy of Sciences, St. Petersburg, Russia
2Scientific-Research Institute «Crimean Astrophysical Observatory» of the Ministry for Education and Science of Ukraine, Nauchny, Crimea, Ukraine
3B.B. Gorodovikova Kalmyk State University, Elista, Republic of Kalmykia, Russia
Kosm. nauka tehnol. 2003, 9 ;(5-6):136-139
https://doi.org/10.15407/knit2003.05.136
Publication Language: Russian
Abstract: 
On the basis of observed data obtained with the radio telescope RT-22 of the Crimean Astrophysical Observatory at 8.6 and 15.4 GHz the quasi-periodic variations of microwave radiation from solar active regions with periods less then 10 min are investigated. The revealed oscillations with periods of 10–40s we connected with the Alfven disturbances. It was established that acoustic modes with periods less than 1 min strongly dissipate in lower corona due to the thermal conductivity. Within the framework of the homogeneous model the influence of acoustic and Alfven oscillations on the thermal mechanisms of microwave radiation is analyzed. The probable sources of the coronal heating are discussed.
Keywords: microwave pulsations, solar active regions, Sun's corona
Full text (PDF)
 
References: 
1. Gelfreich G. B., Goldvarg T. B., Kopylova Yu. G., et al. On the variations of microwave and decemetre radiation in the active regions of the solar atmosphere. In: Solar activity and cosmic rays after the sign inversion of the polar magnetic field of the Sun: Proc. Intern. Conf., 127—132 (GAO RAN, St.-Petersburg, 2002) [in Russian].
2. Zhelezniakov V. V. Electromagnetic waves in space plasma: Generation and propagation, 432 p. (Nauka, Moscow, 1977) [in Russian].
3. Priest E. R. Solar Magneto-hydrodynamics, 589 p. (Mir, Moscow, 1985) [in Russian].
4. De Pontieu, Martens P. C., Hudson H. S. Chromospheric damping of Alfven waves. Astrophys. J., 558 (2), 859—871 (2001).
https://doi.org/10.1086/322408
5. Gordon B. E., Hollweg J. V. Collisional damping of surface waves in the solar corona. Astrophys. J., 266 (1), 373—382 (1983).
https://doi.org/10.1086/160785
6. Nindos A., Alissandrakis C. E., Gelfreikh G. B., et al. Spatially resolved microwave oscillations above a sunspot. Astron. and Astrophys., 386 (2), 658—673 (2002).
https://doi.org/10.1051/0004-6361:20020252
7. Rudawy P., Phillips K. J. H., Read P., et al. Search for short period coronal plasma oscillations: SECIS results from 1999 and 2001 total eclipse. In: Solar Variability From Core to Outer Frontiers: Proc. 10th European Solar Physics Meeting, 967—970 (Prague, 2002).
8. Shibasaki K. Microwave detection of umbral oscillations in NOAA active region 8156: diagnostics of temperature minimum in sunspot. Astrophys. J., 550 (2), 1113— 1118 (2001).
https://doi.org/10.1086/319820

9. Williams D. R., Phillips K. J. H, Rudawy P., et al. High-frequency oscillations in a solar active region coronal loop. Mon. Notic. Roy. Astron. Soc., 326, 428—436 (2001).
https://doi.org/10.1046/j.1365-8711.2001.04491.x