Schematic illustration of the lower location of the HFC sources of the type II burst with respect to the LFC sources observed at the same frequency. Panel a) corresponds to an instant t₁, which is before the instant t₂ (t₂ > t₁) of panel b). Solar surface is depicted by thick black line with inclined ticks on the right. Thick dashed arc-like line shows the shock wave front. Light and dark grey ellipses represent the LFC and HFC sources, respectively. Horizontal arrow shows the direction of their movement. Levels of constant plasma density are shown by vertical straight dashed and dotted lines. Corresponding plasma densities are marked by n₁, , n₂, with and n₁ > n₂. Corresponding second harmonic of plasma frequencies, at which the LFC and HFC sources are emitted, are marked by f₁ and f₂, with f₁ > f₂.