The growth over sunrise of the C and D layers of the ionosphere is investigated for a model which includes: the negative ion species O−, O2−, O3−, O4−, NO2−, NO3−, CO3−, and CO4−; ion-pair production by galactic cosmic rays, precipitated electrons, photoionization of NO by scattered Lyman-α radiation, and the photoionization of NO and O2(1Δ) by direct solar radiation; the photodetachment of most of the negative ions; and the time variations of all these parameters. It is found that the inclusion of the reaction NO3− + O → NO2 + O2− with a rate constant of 5×10−14 cm3 sec−1 in combination with fast electron-ion recombination (α ∼ 10−5 cm3 sec−1) can accurately reproduce both the development of the C layer at sunrise and the correct magnitude and form for the D-layer development. The photodetachment of NO3− is not a suitable alternate source of sunrise electrons because of the large electron affinity of NO3. The photodetachment of lower-affinity negative ions, such as hydrated species, could replace the NO3− + O → NO2 + O2− reaction if indeed the presunrise mesospheric ions are predominantly hydrated. The dominant ions in the present scheme are NO3−, CO4−, and CO3−. Atomic oxygen greatly limits the quantity of negative ions above 75 km at all times of the day by associative detachment and is responsible for the nighttime D-layer ledge of electron density. The 98 and 94° VLF radio propagation effects are explicable on the basis of this model.
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