Passage VII

In the ionosphere (the atmosphere between 50 km and 2,000 km above Earth's surface), gaseous atoms and molecules lose electrons and become ions when struck by energetic solar radiation (X-rays and ultraviolet radiation). The figure shows the electron density, in free electrons/cm³, for a portion of the ionosphere above a 45°N latitude location. The electron density and the specific ions present in the D, E, and F layers of the ionosphere are important in the long-distance transmission of high frequency radio signals. Electron density varies between daytime and nighttime as well as between maximum sunspot count and minimum sunspot count.