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Oscillation of solar radio emission at coronal acoustic cut-off frequency by T. Zaqarashvili et al.

25 Jul 2017, 11:03 UTC
Oscillation of solar radio emission at coronal acoustic cut-off frequency  by T. Zaqarashvili et al.
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Recent SECCHI COR2 observations on board the STEREO-A spacecraft have detected density structures at a distance of 2.5-15 R$_{\odot}$ propagating with periodicity of about 90 minutes (Viall and Vourlidas 2015). The authors suggested that the density structures probably formed in the lower corona. We analyzed radio emission at the frequencies of 8–32 MHz, which correspond to a distance of about 1.5–2.5 R$_{\odot}$ according to the Baumbach-Allen model of coronal electron density. The radio observation allowed us to search for the periodicity source at heights lower than the COR2 FOV.
Figure 1. Dynamic spectrum of radio emission observed by URAN-2 on August 1, 2011.
Observations and data analysis
Large Ukrainian radio telescope URAN-2 observed a type IV radio burst in the frequency range of 8-32 MHz during the time interval 08:15-11:00 UT on August 1, 2011 (Figure 1).
Figure 2. Wavelet spectrum of radio emission intensity at 15 MHz during 5:00–14:00 UT.
We use a wavelet analysis to find oscillations of the radio emission intensity at four different frequencies: 15 MHz, 20 MHz, 25 MHz, and 30 MHz (Figure 2 displays the wavelet spectrum at 15 MHz). The most powerful period on the wavelet spectrum is located at about 80 ...

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