Explanation:

The ionosphere is composed of three main parts, named for obscure historical reasons: the D, E, and F regions . The electron density is highest in the upper, or F region . The F region exists during both daytime and nighttime. During the day it is ionized by solar radiation, during the night by cosmic rays. The D region disappears during the night compared to the daytime, and the E region becomes weakened. The ionosphere has major importance to us because, among other functions, it influences radio propagation to distant places on the Earth, and between satellites and Earth.