Spectral Analysis of Solar Radio Type III Bursts from 20 kHz to 410 MHz
Résumé
We present the statistical analysis of the spectral response of solar radio type III bursts over the wide frequency range between 20 kHz and 410 MHz. For this purpose, we have used observations that were carried out using both spaced-based (Wind/Waves) and ground-based (Nan\c{c}ay Decameter Array and Nan\c{c}ay Radioheliograph) facilities. In order to compare the flux densities observed by the different instruments, we have calibrated the data and converted them to Solar Flux Units. This study found that type III bursts observed in the metric to hectometric wavelength range statistically exhibit a clear maximum radio flux density at around 2 MHz. In addition, using a simple empirical model we show that the median radio flux `S' of the studied dataset obeys the polynomial form $Y = 0.0497*x^3 - 1.6352*x^2 + 16.3033*x - 41.2399$, with $X=\ln{(F_\text{kHz})}$ and with $Y=\ln{(S_\text{SFU})}$. Using the Sittler and Guhathakurtha model for coronal streamers we have found that maximum of radio power falls in the range 4 to 10 $R_{\odot}$, depending on whether the type III emissions are assumed to be at the fundamental or the harmonic.
