What causes ionosphere to change between day and night?
The angle of the sun rays on the ionosphere. For example, all radio amateurs working on long and medium frequencies will tell you that, at sunset or sunrise, you’ll get the best conditions for trans-continental transmissions. The different layers of the ionosphere and how they are affected by the sun rays is a complex science but, it is what e.g. enabled me to “talk” to New Zealand from my home in Norway: on the other side of the earth. What I still don’t know is if my signals were received from over the North Pole, or the South Pole. Sometimes, the propagations are so good that you hear an echo: You receive signals from both sides!
