Exploration of the solar corona by high resolution solar decametric observations

Current state of knowledge of high resolution observations at decameter wavelengths of the quiet Sun, the slowly varying component (SVC), type I to V bursts, and noise storms is summarized. These observations were interpreted to yield important physical parameters of the solar corona and the dynamical processes around 2R from the photosphere, where transition from closed to open field lines takes place and the solar wind builds up. The decametric noise bursts were classified into BF-type bursts that show variation of intensity with frequency and time, and decametric-type III bursts. The angular sizes of noise storm sources are discussed by taking into consideration refraction and scattering effects. An attempt is made to give the phenomenology of all the known varieties of decametric bursts in this review. Available polarization information of decametric continuum and bursts is summarized. Recent simultaneous satellite and ground-based observations of decametric solar bursts show that their intensities are deeply modulated by scintillations in the Earth's ionosphere. Salient features of various models and theories of the metric and decametric noise storms proposed are examined, and a more satisfactory model is suggested, which explains the BF-type bursts and conventional noise storm bursts at decametric wavelengths, invoking the induced scattering process for 1 -> t conversion. Suggestions are made for additional solar decametric studies from the ground-based and satelliteborne experiments.