... IONOSPHERIC DATA IN THE INTERACTIVE SPIDR SYSTEM . ... The Ionosphere The ionosphere is that part of the upper atmosphere where free electrons occur in sufficient density to have an appreciable influence on the propagation of radio frequency electromagnetic waves. ... These regions may be further divided into several regularly occurring layers, such as F1 or F2. ... E Region: The region between about 95 and 150km above the Earth that marks the height of the regular daytime E layer. ...