Figure 8.

Characteristic radio frequencies in the solar atmosphere. The middle corona includes a critical region where the transition of radio-emission mechanisms occurs. The dark-pink box marks the nominal range of the middle corona (≈ 1.5 – 6 ${\mathrm{R}}_{\odot }$) and the light-pink box marks an extended range taking into account the highly structured and dynamic nature of the corona. The corresponding frequencies that are relevant to radio observations of the middle-corona range from < 10 MHz to ≈ 1 GHz. (Adapted from Figure 4.1 in Gary and Hurford (2004) with permission.)