Dynamics of the neutral gas in the thermosphere for small Rossby number motions

Abstract

Equations describing the motions of the neutral gas in the thermosphere are formulated, nondimensionalized, and expanded in Rossby number. Adiabatic warming and cooling by vertical motions is comparable to the variable component of diabatic heating and can account for the large departures of observed diurnal and meridional temperature variations from the values predicted by one‐dimensional diabatic models. To illustrate the application of the theory to the dynamics of the thermospheric diurnal oscillation, a series of numerical experiments, assuming a two‐dimensional zonal strip, has been carried out. Ion drag was neglected, and consequently the horizontal motion amplitudes (∼700 m/sec) were unrealistically large. A steady diurnal oscillation in agreement with the observed diurnal bulge was obtained after an ad hoc reduction of the adiabatic heating by a factor of 4. Vertical motions shifted the phase of maximum temperature to a time three hours earlier than that obtained in the absence of motions.

A Consideration on the Tidal Wave Transmission through the Ionized Atmosphere

“…The excitation of wind motion in the thermosphere has recently been discussed by Volland (1966) and Dickinson et al (1968). They are mainly concerned with heating by the solar radiation absorbed in the thermosphere.…”

A two-component model of the diurnal variations in the thermospheric composition

“…This aspect of the energetics has been the basis for Harris and Priester's (1962) one dimensional model of the diurnal variations in the thermosphere. However, a second and not less important energy train goes through the global circulation (Dickinson et al, 1968;Volland and Mayr, 1970) which is significantly affected by ion collisions and thus by the ion density. In this mechanism, which is explicitly neglected in one dimensional models, energy is exchanged between day and night through adiabatic expansion and contraction and this in turn affects the temperature and the thermospheric composition.…”

Wave dynamics in the thermosphere: I: Tidal motion

“…A more basic approach is to calculate the wind velocity for a given energy input. Dickinson et al (1968) followed this line and discussed the motions of the neutral gas excited in the thermosphere by the solar UV and EUV input as given by Mahoney (1966). The solar EUV responsible for the heating was identified with absorption in the Schuman-Runge continuum, for wavelengths equal to or shorter than that of the first ionization potential of O2 and the Lyman a line.…”

“…Although the model was unrealistically simple and the wind velocity was found to be as unreasonably large as 700 m/sec at 400 km due to neglect of the ion drag, the result was significant in showing the maximum (temperature) variation to come three hours earlier than in the absence of motions; the motions were suggested to be the second heat source called by Harris and Priester (1965). The considerations by Dickinson et al (1968) were based on the following assumption: at the lower boundary of the thermosphere, usually taken as 120 km, no hydrodynamic energy flux exists, an assumption which implies no coupling of the thermosphere with the lower atmosphere. The question arises whether that assumption is realistic.…”