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I. Tolstoy and P. Pan

Abstract

Two- and four-layer models of the atmosphere up to heights of about 500 km allow a systematic and fairly accurate account of the far-field properties of guided internal and surface gravity waves having periods >10 min. Simple formulae and numerical results are given for a variety of models allowing one to determine the importance of such effects as compressibility, free vs rigid boundaries, layering, and the earth's rotation. The importance of coupling effects similar to those occurring in layered acoustic and electromagnetic waveguides is emphasized. It is also shown, in the period pass-band between 10 and 200 min, that there is in all models a difference between surface and internal wave group velocities of sufficient magnitude to preclude confusion in the travel times of these modes. It is also stressed that the layer of atmosphere between altitudes of 110 and 150 km, in which the Väisälä frequency may exceed the acoustic cut-off frequency, plays a critical role in determining the amplitude of the ground-level pressure perturbations associated with the passage of a surface gravity wave. This amplitude is sensitive to the precise laws of atmospheric stratification as well as to wind sheer fields at these heights. It is shown that our assumptions concerning the nature of the “effective free surface” of the atmosphere are at least consistent with the damping of 15 min period, 600 m sec−1 pressure waves observed in connection with large nuclear explosions in 1967 and 1968.

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I. Tolstoy and T. J. Herron

Abstract

It is shown, given perturbations of the jet stream wind system similar to those reported from balloon and aircraft studies, that it is possible to calculate ground level pressure fluctuations. Using a density stratified model of the troposphere and a constant gravity field, and assuming the jet stream to act as a traveling disturbance, a simple linear model predicts the correct order of magnitude and power spectra for microbarographic fluctuations in the 5–60 min period range.

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I. Tolstoy and T. J. Herron

Abstract

Atmospheric gravity waves excited by nuclear explosions were recorded on several occasions during the period 1967–68, on a large aperture (250 km × 200 km) array of long-period microbarographs (1–60 min period pass-band) in the New York-New jersey area. The spectrum of these waves peaks near a period of 15 min and their average group velocity (∼600 m sec−1), their dispersion and attenuation conform to theoretical predictions, for the surface mode.

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T. J. Herron and I. Tolstoy

Abstract

A major portion of atmospheric pressure fluctuations in the 30–90 min period range was observed to move across a small array of microbarographs with speeds and directions that correlate with jet stream winds. Measured speeds (10–50 m sec−1) and periods, with plane wave assumptions, yield wavelengths of the order of 100 km. The pressure fluctuations were observed, however, to decorrelate in much less than one wavelength, implying that they are not free waves, but more likely are disturbances dragged along by the tropopause winds.

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