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The region of the ionosphere in which the E layer tends to form. The region lies between 60 and 90 miles (100–150 km). The region reflects electromagnetic energy from 100 kHz to 30 MHz and plays an important role in long-distance radio communications. The E layer is subdivided into two or more layers, and these are then designated as E1, E2, etc. Patchy and intermittent clouds of fairly high ionization, known as sporadic E layers, also form in the same general region. See E layer.