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| Titel |
Radio seismology of the outer solar corona |
| VerfasserIn |
Teimuraz Zaqarashvili, Valentin Melnik, Anatoliy Brazhenko, Mykhaylo Panchenko, Alexander Konovalenko, Vladimir Dorovskyy, Helmut Rucker |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250088747
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| Publikation (Nr.) |
 EGU/EGU2014-2891.pdf |
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| Zusammenfassung |
| Observed oscillations of coronal loops in extreme ultraviolet (EUV) lines have been
successfully used to estimate plasma parameters in the inner corona (< 0.2R0, where R0 is
the solar radius). However, coronal seismology in EUV lines fails for higher altitudes because
of rapid decrease in line intensity. We aim to use radio observations to estimate the plasma
parameters of the outer solar corona (> 0.2R0). We used the large Ukrainian radio telescope
URAN-2 to observe type IV radio bursts at the frequency range of 8-32 MHz during the
time interval of 09:50-12:30 UT on April 14, 2011. The burst was connected to
C2.3 flare, which occurred in AR 11190 during 09:38-09:49 UT. The dynamic
spectrum of radio emission shows clear quasi-periodic variations in the emission
intensity at almost all frequencies. Wavelet analysis at four different frequencies
(29 MHz, 25 MHz, 22 MHz, and 14 MHz) shows the quasi-periodic variation of
emission intensity with periods of ~ 34 min and ~ 23 min. The periodic variations
can be explained by the first and second harmonics of vertical kink oscillation of
transequatorial coronal loops, which were excited by the same flare. The apex of
transequatorial loops may reach up to 1.2 R0 altitude. We derive and solve the dispersion
relation of trapped magnetohydrodynamic (MHD) oscillations in a longitudinally
inhomogeneous magnetic slab. The analysis shows that a thin (with width to length ratio of
0.1), dense (with the ratio of internal and external densities of ≥ 20) magnetic
slab with weak longitudinal inhomogeneity may trap the observed oscillations.
Seismologically estimated Alfvén speed inside the loop at the height of ~ 1 R0 is ~
1000 km s-1. The magnetic field strength at this height is estimated as ~ 0.9 G.
Extrapolation of magnetic field strength to the inner corona gives ~ 10 G at the height
of 0.1 R0. Radio observations can be successfully used for the sounding of the
outer solar corona, where EUV observations of coronal loops fail. Therefore, radio
seismology of the outer solar corona is complementary to EUV seismology of the inner
corona.
The research leading to these results has received funding from the Austrian
“Fonds zur Förderung der wissenschaftlichen Forschung” under project P24740-N27. |
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