The coupling of acoustic‐gravity waves in the main atmosphere to acoustic waves characteristic of individual minor species in the atmosphere is postulated. Such coupling would exist as a result of resonances in the response of the minor species and its likelihood depends on the mass of the atmospheric particle relative to the major species mass, the diffusion of the minor species and the direction of propagation of the main disturbance. These minor species disturbances may explain some AE‐C measurements in the thermosphere, and could possibly play a role in the distribution of minor species and their chemistry in the mesosphere.
The response of ionization to a gravity wave moving through the ionosphere is studied. Hydrodynamic equations are used, and local thermodynamic equilibrium is imposed for simplicity. The treatment involves a perturbation analysis, and the background medium is assumed to be time stationary, horizontally stratified, and known. It is shown that ionization may be locally resonant at each level for certain frequencies and directions, for which condition neutral and ionized particles are considered closely or critically coupled. The phase direction for this critical coupling is always downward in the absence of a magnetic field. A magnetic field results in two resonant directions for the same frequency, and these directions are mostly downward. Observed TID's associated with gravity waves may be indicative of such resonances. It is also noted that strong coupling may occur to neutral acoustic waves at high altitudes. Previous investigations restrict their use of momentum equations to the diffusion equation. The analysis also shows that such restrictions result in the neglect of terms arising from momentum transport due to any background ambipolar diffusion velocity and wave motion. These terms are mostly relevant at higher altitudes.
An elastic cantilever is used for the measurement of the mass of a small quantity, by measuring the shifted resonant frequency when the unknown mass is attached to the free end of the cantilever. The measurements of resonant frequencies of the cantilever with and without an attached mass should allow the calculation of mass. An optical glass fibre is used as the cantilever and is excited by an acoustic wave. The resonant frequency of the optical glass-fibre cantilever is determined by measuring the maximum displacement by optical means while the exciting frequency is swept. Since the optical glass-fibre is chemically stable, this system can be used to measure a chemically active viscous fluid as well as small soft materials because it is easy to attach these materials to the end of the glass fibre without any glue joint. The experimental results obtained by this method for small masses (10-300 mu g) are in good agreement with those measured by the commercially available microbalance.
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