An investigation of the ionospheric D region at sunrise, 3, time variations of negative-ion and electron densities

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⁻, O3⁻, 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 NO2⁻ + 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 night-time D-layer ledge of electron density. The 98 and 94° VLF radio propagation effects are explicable on the basis of this model.