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.

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