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An Investigation of the Ionospheric D Region at Sunrise: 3, Time Variations of Negative-Ion and Electron Densities


  • R. P. Turco,

  • C. F. Sechrist Jr.


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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