Ionospheric Reflections from Heights Below the E Region

The pulse method of radio sounding has been used at 1.75 Mc/s to detect low ionospheric regions whose voltage reflection coefficient exceeds 4 × 10?6. Observations from February to July 1955 have revealed reflections, from 95 km vertical height and of day-time occurrence only, which are believed to originate in the lower E region. A region with a lower boundary predominantly at 85 km has been found to exist continuously, and previous suggestions as to its meteor origin are queried. A series of complex partial reflections have been detected during day-time only down to 53 km, with significant heights near 75, 67, and 55 km. The occurrence and strength of these lower reflections increases markedly during winter.