The ionosphere is a region of the atmosphere ranging from 65 km above the Earth's surface to its outer edge at an altitude of 500 km. This region has an abundance of ions that were formed from incoming solar ultraviolet radiation. The ions reflect radio waves back to Earth. During the day, the ion layer is lower in the atmosphere due to the Sun's radiation. At night, the layer moves up higher in the atmosphere. This helps radio waves, especially AM radio, to be reflected over longer distances across the Earth. The ionosphere is affected by solar flares and the 11-year sunspot cycle. The years of maximum activity in the sunspot cycle suppress the ionosphere. Auroras are also formed when these charged particles reach the Earth and interact with the magnetic field.

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