On the Observational Properties of the Decameter Striae

© 2018 International Union of Radio Science URSI. In the paper we present the preliminary results of analysis of the solar Type IIIb bursts properties observed on June 14, 2012. Namely the parameters of their fine structure known as striae are studied in the continuous frequency band 8 - 32 MHz. It is shown that durations and instantaneous frequency bandwidths depend on the observing frequency. Notably, bandwidth increases and duration decreases with the frequency. The comparative analysis of the decameter spikes and striae is also performed.status: publishe

Decameter U-burst Harmonic Pair from a High Loop

© 2014, Springer Science+Business Media Dordrecht. The results of the first observations of solar sporadic radio emission within 10 – 70 MHz by the Giant Ukrainian Radio Telescope (GURT) are presented and discussed. Observations in such a wide range of frequencies considerably facilitate the registration of harmonic pairs. The solar U-burst harmonic pair observed on 8 August 2012 is analyzed. The burst key features were determined. Among them, the time delay between the fundamental and harmonic emissions was of special interest. The fundamental emission was delayed for 7 s with respect to the harmonic emission. A model for explaining the occurrence of such a delay is proposed, in which the emission source is located inside a magnetic loop containing plasma of increased density. In this case, the delay appears due to the difference in group velocities of electromagnetic waves at the fundamental and the harmonic frequencies.status: publishe

Solar Decameter Spikes

We analyze and discuss the properties of decameter spikes observed in July - August 2002 by the UTR-2 radio telescope. These bursts have a short duration (about one second) and occur in a narrow frequency bandwidth (50 - 70 kHz). They are chaotically located in the dynamic spectrum. Decameter spikes are weak bursts: their fluxes do not exceed 200 - 300 s.f.u. An interesting feature of these spikes is the observed linear increase of the frequency bandwidth with frequency. This dependence can be explained in the framework of the plasma mechanism that causes the radio emission, taking into account that Langmuir waves are generated by fast electrons within a narrow angle θ≈13 {ring operator} - 18 {ring operator} along the direction of the electron propagation. In the present article we consider the problem of the short lifetime of decameter spikes and discuss why electrons generate plasma waves in limited regions. © 2013 Springer Science+Business Media Dordrecht.status: publishe

Fine and Superfine Structure of the Decameter-Hectometer Type II Burst on 7 June 2011

© 2015, Springer Science+Business Media Dordrecht. The characteristics of a type II burst with a herringbone structure observed both with ground-based radio telescopes (UTR-2 and URAN-2) and space-borne spectrometers (STEREO-A and B) are discussed. The burst was recorded on 7 June 2011 in the frequency band 3 – 33 MHz. It was characterized by extremely rich fine structure. Statistical analysis of more than 300 herringbone sub-bursts constituting the burst was performed separately for the positively (reverse) and negatively (forward) drifting sub-bursts. The sense and the degree of circular polarization of the herringbone sub-bursts were measured in a wide frequency band (16 – 32 MHz). A second-order fine frequency structure of the herringbone sub-bursts was observed and studied for the first time. Using STEREO/COR1 and SOHO/LASCO-C2 images, we determined the direction and radial speed of the coronal mass ejection responsible for the studied type II burst. The possible location of the type II burst source on the flank of the shock was found.Published in Solar Physics. The final publication is available at http://link.springer.com/article/10.1007%2Fs11207-015-0725-9status: publishe

The Storm of Decameter Spikes During the Event of 14 June 2012

© 2015, Springer Science+Business Media Dordrecht. An event on 14 June 2012, observed with the radio telescopes UTR-2 (Kharkov, Ukraine), URAN-2 (Poltava, Ukraine), and NDA (Nançay, France) during a joint Summer campaign, is analyzed and discussed. The high solar activity resulted in a storm of spikes, and a storm of Type III bursts, Type IIIb bursts, and a Type IV burst observed in the decameter band. During the observed time interval, the average flux of radio emission changed twice. Using spikes as a tool for diagnostics of plasma parameters, we followed variations of the coronal temperature and the coronal magnetic field in the observed time interval. Thus, in frames of the model described in this article the observed decameter spikes’ durations of 0.3 – 1 seconds correspond to the coronal plasma temperatures of ≈0.1–0.6×106K{\approx}\, 0.1\,\mbox{--}\,0.6 \times10^{6}~\mbox{K}. At the same time the spikes’ frequency bandwidths of 25 – 80 kHz give us the magnetic-field value of about 2 G.status: publishe