Abstract

Purpose: The overview of the scientifi c papers devoted to the study of the solar decameter radio emission with the world’s largest UTR-2 radio telescope (Ukraine) published for the last 50 years. Design/methodology/approach: The study and analysis of the scientifi c papers on both sporadic and quiet (thermal) radiation of the Sun recorded with the UTR-2 radio telescope at the decameter wavelength range. Findings: The most signifi cant observational and theoretical results of the solar radio emission studies obtained at the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine for the last 50 years are given. Conclusions: For the fi rst time, at frequencies below 30 MHz, the Type II bursts, Type IV bursts, S-bursts, drift pairs and spikes have been recorded. The dependences of these bursts parameters on frequency within the frequency band of 9 to 30 MHz were obtained. The models of their generation and propagation were suggested. Moreover, for the fi rst time the fi ne time-frequency structures of the Type III bursts, Type II bursts, Type IV bursts, U- and J-bursts, S-bursts, and drift pairs have been observed due to the high sensitivity and high time-frequency resolutions of the UTR-2 radio telescope. The super-fi ne structure of Type II bursts with a “herringbone” structure was identifi ed, which has never been observed before. New types of bursts were discovered: “caterpillar” bursts, “dog-leg” bursts, Type III bursts with decay, Type III bursts with changing drift rate sign, Type III-like bursts, Jb- and Ub-bursts, etc. An interpretation of the unusually high drift rates and drift rates with alternating signs of the Type III-like bursts was suggested. Based on the dependence of spike durations on frequency, the coronal plasma temperature profi le at the heliocentric heights of 1.5–3RS was determined. Usage of the heliographic and interferometric methods gave the possibility to start studies of the spatial characteristics – sizes and locations of the bursts emission sources. Thus, it was shown that at the decameter band, the Type III burst durations were defi ned by the emission source linear sizes, whereas the spike durations were governed by the collision times in the source plasma. It was experimentally proved that the effective brightness temperatures of the sources of solar sporadic radio emission at the decameter band may reach values of 1014–1015 K. In addition, it was found that the radii of the quiet Sun at frequencies 20 and 25 MHz are close to the distances from the Sun at which the local plasma frequency is equal to the corresponding observed frequency of radio emission in the Baumbach–Allen model. Key words: UTR-2; Sun; decameter radio emission; radio bursts; corona

Highlights

  • Solar observations with the UTR-2 radio telescope (Ukraine) have begun right after its commissioning in 1970

  • Before 2000, all observations were made at a limited number of fixed frequencies, typically at 25, 20, 16, 12.5, and 6.25 MHz. This fact significantly narrowed down a variety of studied events mainly to Type III bursts, drift pairs and thermal radio emission of the Sun

  • The possibility to observe the Sun in the heliographic mode allowed to determine the spatial characteristics of the received radio emission sources – their angular sizes and locations in the corona

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Summary

Introduction

Solar observations with the UTR-2 radio telescope (Ukraine) have begun right after its commissioning in 1970. A number of events, such as Type II and Type IV bursts, U- and J-bursts, S-bursts and spikes as well as their fine structure were first observed at the frequency below 30 MHz. Carrying out the observations in an interferometric mode by using some separate sections of the UTR-2 radio telescope opens new possibilities in studying the events occurring in the corona at distances of 1.5 3RS (RS is the solar radius). Exploration of the Solar Decameter Radio Emission with the UTR-2 Radio Telescope. The main results obtained from observations of the solar radio emission with the UTR-2 radio telescope for the last 50 years are presented

Type III Bursts
Type IIIb–IIId Bursts
U- and J-Bursts
Type II Bursts
Type IV Bursts
Drift Pairs
Spikes
10. Unusual Bursts
Findings
11. Quiet Sun
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