Diurnal variations of odd nitrogen and ionic densities in the mesosphere and lower thermosphere: Simultaneous solution of photochemical-diffusive equations

Abstract

Diurnal variations of number densities of oxygen, nitrogen, hydrogen, carbon, and ionic minor constituents in the mesosphere and lower thermosphere are investigated using the simultaneous solution of photochemical‐diffusive equations. Special account is taken of the mutual coupling of nitrogen compounds with ions. Quantum yield of N(²D) production in the dissociative recombination of NO+ and the photodissociation of N2, which are the main sources of NO in the lower thermosphere, must be ≳0.5 in order to reproduce the NO density around 100 km deduced from γ band airglow measurements. The NO density shows no substantial diurnal variation between the heights of 75 and 110 km and shows the day‐to‐night variation of a factor of greater than 2 above 120 km, whereas NO changes almost completely into NO2 at night below ∼70 km. The calculated NO density is smaller than that observed in the height range of 60–80 km, although it explains the observed electron density according to currently known ion chemistry. A larger rate coefficient recently measured for the conversion of NO+ into NO+·N2, which eventually will be hydrated to NO+·H2O, can be used to adequately model the height where the dominant ion changes from hydrated ions to NO+. Disagreement of the calculated atomic oxygen density profiles with the observed ones in the lower thermosphere is discussed in connection with the eddy diffusion coefficient and the solar flux. Dynamical transport of atomic oxygen such as the general circulation may be invoked to resolve this disagreement.

Electron density profiles in the quiet lower ionosphere based on the results of modeling and experimental data

“…Experimental data demonstrate the dependence of NO number density on latitude, solar activity and season (Grossmann et al, 1985;Siskind and Rusch, 1992;Siskind et al, 1997Siskind et al, , 1998. Theoretical studies have revealed the processes controlling photochemical sources and sinks of nitric oxide (Ogawa and Shimazaki, 1975;Siskind et al, 1997Siskind et al, , 1998. The reactions that are responsible for production of odd nitrogen, i.e.…”

“…nitrogen oxide and atomic nitrogen, in the lower thermosphere, are summarized in Table 1. (Ogawa and Shimazaki, 1975;Marov et al, 1996;DeMore et al, 1994;Sander et al, 2003).…”

“…Examples of nitric oxide number density profiles during the daytime (solar zenith angle below 90 • ) retrieved from photochemical models 1, 1a, 1b, 1c, 1d (Solomon et al, 1982) and experimental measurements 2 (Ogawa and Shimazaki, 1975), 2a, 2b (Siskind et al, 1998), 3a, 3b (Meira, 1971.…”

The influence of ozone concentration on the lower ionosphere – modelling and measurements during the 29–30 October 2003 solar proton event

“…The height distribution of the O 3 -density in the mesosphere, its seasonal and diurnal variations and the secondary peak have been explained by theoretical investigations and by modelling Laird, 1970, 1972;Ogawa and Shimazaki, 1975;Swider et al, 1978;Keneshea et al, 1979;Thomas and Bowman, 1985;Rodrigo et al, 1986;Sandor et al, 1997;Marsh et al, 2003;Jackman et al, 1995Jackman et al, , 2005. The primary chemical production mechanism for odd oxygen in the thermosphere and mesosphere is photodissociation of molecular oxygen.…”

“…2. Input values for nitric oxide (curve 1, Verronen et al, 2002) and atomic oxygen: curve 2 is for the autumn season (Swider et al, 1978) and curve 3 is for winter daytime concentrations at altitudes below 70 km accordingly to the investigation results by Ogawa and Shimazaki (1975). .…”