Spikes and Striae as a Fine Structure of the Solar Decameter Radiation

The present thesis is devoted to observations and analysis of fine structured solar radio burstsat decameter wavelengths. The observations of the Sun exploit the entire electromagnetic spectrum including its optical, radio, X-ray, gamma ranges, etc. Among these the observations in the radio range turns out to be an important tool for the remote determination of the solar coronal parameters and the processes that occur in it at different heights.The decameter range takes a special place in the whole spectrum of the solar radio emission. The decameter radiation originates in the less dense regions of the solar corona at the heights 1.5 − 3.5 solar radii,which are practically inaccessible for investigation by the optical methods. In these regions the corona is very inhomogeneous which results in a wide variety of solar finestructured radio bursts. Such bursts are rare in the hectometer and kilometer wavelength ranges. Studying the parameters of these bursts yields a possibility for remote diagnostics of those inhomogeneities, both in the plasma and in the magnetic field. Furthermore, the decameter wavelength range is the longest wavelength range that is accessible for observations from the Earth. The data analyzed in the present thesis were obtained with some of the largest decameter radio telescopes UTR-2, URAN-2 and NDA. The high sensitivity and resolution of the equipment enabled us to register and analyze the fine structured solar radio bursts such as spikes and chains of striae also known as Type IIIb bursts. The thesis consists of five Chapters in which different parameters of the decameter spikes and striae are obtained and discussed. In Chapter 1 the necessary background information about the Sun, a brief history of the first observations of solar sporadic radio emission and the obtained results, as well as a classification of solar radio bursts are presented. In Chapter 2 a short description is provided of the radio telescopes and the relevant back-ends used for the observations of the solar sporadic radio emission in the decameter range. In Chapters 3 and 4 an overview of the results regarding spike bursts observed in different frequency ranges is given. The main parameters of the decameter spikes (their duration, bandwidth, and flux) and their dependencies on the frequency in the continuous band have been obtained. In Chapter 5 the analysis of type IIIb bursts and also their fine structure stria-bursts, observed with the UTR-2 radio telescope in the frequency range 8 – 30 MHz, is provided. The main parameters of type IIIb bursts, such as their drift rates and the number of stria-bursts forming it, are presented. The parameters of the stria-bursts (duration, bandwidth, and flux) are also analyzed in this chapter. The results obtained in the present thesis show and prove the importance of observations of the solar sporadic radiation at decameter wavelengths. The study and analysis of this radiation is very important tool for the remote determination of the solar atmosphere parameters and processes occurring in it at various heights.nrpages: 134status: publishe