Mykola Gordovskyy

Energetic electrons in the upper solar corona produce sources of radio emission observed at metric and deca-metric wavelengths. This emission provides unique diagnostic information about the characteristics of energetic electrons as well as the state of the coronal plasma. However, the sizes and shapes of these sources and their variation with frequency are not well understood. This is due to the relatively low spatial resolution and other effects, including ionospheric refraction and scattering.

We describe a novel empirical method for calibrating and interpreting solar imaging observations, accounting for instrumental and ionospheric effects. The method is based on observations of known compact radio sources in the same wavelength range. Using the developed method we derive the sizes and shapes of solar radio sources observed by the Low-Frequency Array (LOFAR) in the tied-array beam mode in the frequency range 30-45MHz. It is shown that in nine randomly selected events the source sizes range from about 3 to 20 arcminutes, and decrease with frequency. The corrected sizes and shapes of radio sources are in a good agreement with the results of numerical simulations of anisotropic radio-wave scattering in the solar corona.