E region

E region, ionospheric region that generally extends from an altitude of 90 km (60 miles) to about 160 km (100 miles). As in the D region (70–90 km), the ionization is primarily molecular—i.e., resulting from the splitting of neutral molecules—oxygen (O₂) and nitrogen (N₂)—into electrons and positively charged molecules. Unlike that of the D region, the ionization of the E region remains at night, though it is considerably diminished. The E region was responsible for the reflections involved in Marconi’s original transatlantic radio communication in 1902. The ionization density is typically 10⁵ electrons per cubic centimetre during the day. Intermittent patches of stronger ionization are sometimes observed at the same general altitude.