Dynamical effects on the global distribution of thermospheric atomic oxygen

Abstract

This numerical study of dynamical effects on the global distribution of atomic oxygen in the thermosphere makes use of a three‐component model of upper atmospheric dynamics which treats the gases N2, O2, and O coupled together by collisions. This model simultaneously treats diurnal and seasonal variations of the distributions of these gases. Specific comparisons of hydrostatic computations with those taking into account wind‐induced departures from hydrostatic equilibrium show that none of these gases can be considered to be in hydrostatic equilibrium below ∼200 km. Global scale winds are shown to cause the observed winter enhancement of atomic oxygen in the lower thermosphere. Comparison of the model results with observational data shows generally good agreement.

The effect of breaking gravity waves on the dynamics and chemical composition of the mesosphere and lower thermosphere

“…Transport by advection is not negligible, however, particularly above 100 km. During solstice the thermospheric circulation provides rapid meridional flow from the summer to the winter hemispheres, resulting in increased atomic oxygen densities in the winter lower thermosphere near 120 km, in agreement with observations [see, e.g., Kasting and Roble, 1981;Straus and Christopher, 1979 thermosphere and mesosphere must include photochemical production and loss (particularly near 70-80 km, where the photochemical destruction rate becomes very large), advection by the mean meridional circulation, and small-scale diffusion. The latter two are expected to vary significantly with season and latitude as a result of the dissipation of gravity waves.…”

The perturbed neutral circulation in the vicinity of a symmetric stable auroral arc

“…The most unstable wave has L • 1.6Lc and a growth rate of cz • 0.4U/(2Y). Early in the simu- Mayr, 1977' Mayr and Volland, 1972' Straus and Christopher, 1979. Granting the great simplicity of the segmented tanh model, it appears that shearing instabilities might result in unstable perturbations achieving significant amplitude in 1 hour.…”

The zonally averaged circulation, temperature, and compositional structure of the lower thermosphere and variations with geomagnetic activity

“…Dickinson et al [1981] calculated the zonally averaged structure determined by the NCAR thermospheric general circulation model (TGCM) and found good agreement with results obtained from these two-dimensional zonal average studies. The compositional response of the thermosphere above about 150 km has been investigated by many authors [e.g., Volland and Mayr, 1971;Mayr and Volland, 1972a, 1974Hays et al, 1973;Mayr and Hedin, 1977;Hinton, 1978;Philbrick et al, 1977;Pr61ss, 1977Pr61ss, , 1981 Reber and Hedin, 1974;Taeusch and Hinton, 1975;Taeusch, 1977;Straus and Christopher, 1979;Porter et al, 1981;Hedin et al, 1981]. These studies show that at F region heights during geomagnetic disturbances the heavier constituents increase and the lighter constituents decrease in concentration at high latitudes in response to auroral Joule and particle heating.…”