Average night-time electron density profiles between 87 and 115 km derived from absorption measurements at 10 fixed frequencies from 250 to 1000 kHz at Tsumeb (19°S)

Abstract

Results of absorption measurements carried out in 1964 at Tsumeb, S.W.A., at 10 fixed frequencies between 250 and 1000 kHz are presented and interpreted by theory. The calculations yielded the night-time E-region (87–115 km) average electron-density profiles of the background ionization (averages over 14 nights), in which various Es-layers were embedded. The electron density N decreased continuously with time t after sunset in the entire height range. The corresponding recombination coefficients α, defined by the equation dN/ dt = − αN 2, decreased from 9 × 10 −8 cm 3/sec at 87.5 km to 6 × 10 −9 cm 3/sec at 115 km. At heights ranging from 87.5 to 97 km α was proportional to atmospheric pressure. Different recombination coefficients were obtained for the two periods from 1800 to 2400 hr and from 0000 to 0600 hr. All these results suggest that different physical processes occur in the night-time E-region depending not only on height but also on time.