Ionization Growth at Sunrise in the E-F Region of the Ionosphere

ABSTRACT

Observations of h'(f) curves have been made at frequent intervals near the gyrofrequency at sunrise. A sensitive receiving system consisting of a Cossor ionosonde and an aerial array of 40 dipoles was used. The sensitivity of the system was high enough to record continuously the extraordinary mode reflections from the F-layer down to 1·7 Mc/s. Some very interesting sunrise effects, well before the ground sunrise, on the group heights of the extraordinary mode reflections near 2 Mc/s. have been observed. Following the sunrise effect multiple stratifications in the region between E and F layers have been recorded. The observed sunrise effect on the group heights is studied in the light of theories of layer formation in a region of linear scale-height gradient for grazing incidence of solar radiation. It is shown that the effect is due to photoionization. Sunrise layers of ionization have been computed using recent rocket data of ionizing radiations and ionized constituents in this region. Using these with models of night-time ionization distribution, empirical n(h) profiles have been derived. It is shown that the multiple stratifications may be observed especially at sunrise depending upon the actual night-time distribution.