The electron density in the lower ionosphere

Abstract

Abstract The amplitudes of the partial reflections obtained from heights between 60 and 120 km, on frequencies of 720 and 1420 kc/s, wore measured over a period of 2 years. The results indicate a mean electron density in the D -region 1·8 times greater than the values reported by other workers. This difference is caused by an increase of four times in the D -region ionization over the last sunspot cycle. The anomalous absorption in winter is caused by an increase of about 80 per cent in the ionization at heights below 90 km. An increase of the order of 500 electrons/cm 3 , at heights down to 60 km, is responsible for radio fade-outs. Some total reflections were obtained from a height of 90 km at noon, indicating a density of 20,000 electrons/cm 3 and a gradient of 10,000 electrons/cm 3 per km at this height. Total reflections from this 90 km layer were also obtained near sunset, and showed a very rapid increase in height immediately after ground sunset. Reflections obtained from clouds of ionization at night indicate gradients of up to 10,000 electrons/cm 3 per km at heights of 80–115 km.