Seasonal Effects on Distributions of Minor Neutral Constituents in the Mesosphere and Lower Thermosphere

Abstract

Calculations have been made of the diurnal variations in minor neutral constituents in the mesosphere and lower thermosphere for the condition of 60 ø latitude, summer and winter, using the method developed by the authors [Shimazaki and Laird, 1970]. The excited molecular oxygen O•.(x/x•) has been added and the effects of absorption of Schumann-Runge bands have been taken into account. The results show significant seasonal differences, which may be interpreted mainly in terms of the difference of penetration of solar radiation and the duration of sunlit hours. However, the comparison of the observed seasonal and diurnal variations in the airglow emissions from hydroxyl, atomic oxygen (5577 A), and O•.(x/x•) with those calculated from models suggests that effects of large-scale meridional circulation (horizontal and vertical transports) may be important in explaining these observations. It is shown that the concentration of the constituents whose main loss mechanism is recombination with atomic oxygen decreases sharply above ~80 km. These constituents include OH, HO2, H•.Oe, and NO•. (nighttime) and the extension of this general theory may explain the sudden decrease observed by rockets in the water-cluster ion concentration above ~80 km. Ion-neutral chemistry should be important in explaining an observed increase in [NO] above •85 km.x Paper presented at COSPAR Symposium on D-and E-Region profiles and diurnal variations of the different constituents. Moreover, the model was not appropriate for extensive comparison with observations, because most rocket and satellite observations have been made at middle or high latitudes and at seasons other than equinoxes.To obtain a better understanding of the effects of photodissociation, chemical reactions, and dynamical (eddy diffusion) processes, and also to make more realistic comparisons, we have made model calculations for the latitude of 60 ø for summer and winter. It is well known that the mesophere is much warmer in winter than in summer, whereas the temperature in the thermosphere and stratosphere is greater in summer than in winter. Corresponding to this difference in the temperature structure, summer and winter should have different density variations with height, affecting the absorption of solar radiation energy. The chemical reaction coefficients for some reactions are sensitive to temperature changes, and the upper atmosphere is known to be more turbulent in winter than in summer. Thus, examination 24 SHIMAZAKI AND LAIRD of the difference between the summer and winter models could be useful in identifying the effects of photodissociation, chemical reactions, and eddy diffusion. There are major North American missile ranges at Ft. Churchill (59øN), Wallops Island (38øN), White Sands (32øN), and Eglin (30øN) from which rockets making observations that can be compared with our model have been or could be flown. Our calculations should be directly comparable to rocket observations made at Ft. Churchill and should be comparable, after suitable allowance for probable...

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

“…In order to reproduce experimental data between 70 and 80 km during high solar activity, higher NO concentrations between 70 and 80 km are required than during low solar activity, in agreement with both theoretical models of NO (e.g. Shimazaki and Laird, 1972) and experimental data (HALOE). Figure 7 shows how experimental and modeled electron density profiles respond to season changes.…”

“…2a are used as input parameters into the theoretical model of the D-region. The O profiles 1 and 2 at altitudes between 60 and 85 km are taken from the models by Zadorozhny (1982) and Shimazaki and Laird (1972). The O profile above 85 km is taken from the MSIS-2000 neutral atmosphere model.…”

The role of atomic oxygen concentration in the ionization balance of the lower ionosphere during solar proton events

“…Turbulent diffusion resulting from the breaking of gravity waves acts as a transport mechanism responsible for strong mixing and dissipative processes. Thus the atomic oxygen is strongly controlled by both photochemical and dynamical processes (downward and meridional transports, turbulence, molecular and eddy diffusions) (Shimazaki and Laird, 1972;Keneshea et al, 1972;Thomas and Bowman, 1972;Maharaj-Sharma and Shepherd, 2004;Russell et al, 2004Russell et al, , 2005Murray and Plane, 2005). These processes are expected to lead to substantial changes in the atomic oxygen concentration.…”

“…These profiles reflect the minimum and maximum values of [O] given by different diffusivephotochemical models for daytime quiet conditions. The O(h)-profile number 1 is taken from the model by Shimazaki and Laird (1972). The O(h)-profile 2 at altitudes less than 80 km is taken from the model by Zadorozhny (1982) and at altitudes above 80 km from the MSIS-2000 neutral atmosphere model (Hedin, 1991).…”

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

“…1 by curves 1-3 (Shimazaki and Laird, 1972;Rodrigo et al, 1986;Thomas and Bowman, 1985). Deviations in the concentration of ozone between O 3 -profiles 1-3 can be explained by differences in accounting for solar radiation intensity in different wavelength ranges, in absorption cross sections, in values of eddy diffusion coefficient, in concentration of atomic oxygen and other species, in rate constants of reactions and in other factors applied in the model studies.…”