Solar Radio Astronomy

According to their timescale, emission from the Sun can be divided into three types. There is the slowly varying emission which changes on a timescale of 11 years and follows the solar cycle. A more rapidly varying radiation on timescale of weeks, known as quiescent emission, is related to the occurrence of active regions. Last but not least is the very abrupt emission produced by solar activity such as flares and coronal mass ejections on timescales of second to hours. All three kinds of behavior can also be observed at radio wavelength, each being produced mostly by different mechanisms. At microwave and millimeter wavelengths, the quiet Sun emission, which varies on 11 years timescale, is due to thermal bremsstrahlung. Nevertheless, the quiescent radio emission has a strong contribution from thermal gyro‐resonance especially at microwaves, whereas thermal bremsstrahlung dominates the millimetric and submillimetric waves. On the other hand, gyro‐synchrotron radiation from non‐thermal electrons is the main mechanism producing the flare emission at wavelengths shorter than cm, whereas the metric and decimetric emission from radio burst are due to coherent plasma radiation. Especial emphasis will be given to the newest findings in solar radio astronomy by the Solar Group at CRAAM. These results were obtained mainly from two radio telescopes: the Submillimeter Solar Telescope (SST) operating at 212 and 405 GHz and the Nobeyama Radio Heliograph (NoRH) at 17 and 34 GHz.