What makes radiocommunication out to 200 km possible at lower HF frequencies during the daytime?

At lower HF frequencies (such as the 160-metre and 80-metre bands), ground wave propagation is highly effective and can cover distances out to roughly 200 km depending on terrain and conductivity. During the daytime, the D layer of the ionosphere becomes heavily ionized by the sun and absorbs lower frequency sky waves, making 'skip' or sky-wave communication practically impossible over these moderate distances. Therefore, the reliable signal heard out to 200 km is primarily the ground wave, which follows the Earth's contour without relying on the ionosphere. Distractors like tropospheric ducting and space waves typically apply to VHF and UHF frequencies rather than the lower HF bands.