What are the dominant effect and frequency range for a sky wave?

The dominant effect for a sky wave is refraction, which occurs as the radio waves travel through different layers of the atmosphere, particularly the ionosphere. Refraction causes the waves to bend back towards the Earth, allowing them to be received at greater distances than would be possible with line-of-sight transmissions.

The frequency range associated with sky waves is from 300 kHz to 30 MHz. This frequency band allows for effective propagation via the ionosphere, making it suitable for long-range communications such as HF (high frequency) radio transmissions. Waves in this range can reflect off the ionosphere, enabling transmission beyond the horizon, which is essential for various forms of communication, especially in military operations and during times when terrestrial communication may be compromised.

In contrast, the other answers reference effects and frequency bands that do not appropriately characterize the behavior of sky waves.