The highest portion is known as the Appleton layer, which lies above the Kennelly-Heaviside layers, and, at its upper reaches, it merges with the region of the Van Allen belts.  
Variation in its properties can stem from the amount of UV radiation received from the sun as well as effects of the earth's magnetic field.  The highest portion is known as the Appleton layer, which lies above the Kennelly-Heaviside layers, and, at its upper reaches, it merges with the region of the Van Allen belts.  FTP, identify this region where nitrogen and oxygen molecules interact with x-rays, the layer of the atmosphere that allows for long-distance radio communication because of charged particles.
Variation in its properties can stem from the amount of UV radiation received from the sun as well as effects of the earth's magnetic field.  
ionosphere