Propagation of acoustic-gravity waves in the atmosphere

Abstract

Abstract. ]Komogeneous wave guide theory is used to derive dispersion curves, vertical pressure distributions, and synthetic baregrams for atmospheric waves. A complicated mode structure is found involving both gravity and acoustic waves. Various models of the atmosphere are studied to explore seasonal and geographic effects on pulse propagation. The influence of different zones in the atmosphere on the character of the baregrams is studied. It is found that the first arriving waves are controlled by the properties of the lower atmospheric channel. Comparison of theoretical results and experimental data from large thermonuclear explosions is made in the time an,d frequency domains, and the following conclusions are reached: (1) The major features on baregrams are due to dispersion; (2) superposition of severM modes is needed to explain observed features; (3) scatter of d•t• outside the range permitted by extreme atmospheric models shows the influence of winds for Ax; wind effects and higher modes are less important for A• waves. A discussion is included on atmospheric terminations and how these affect dispersion curves.

Theoretical Prediction of Acoustic-Gravity Pressure Waveforms Generated by Large Explosions in the Atmosphere

“…If the top of the atmosphere is adjacent to a rigid surface or is bounded by a free surface, then there is nowhere for energy to leak and there are no leaking modes. On the other hand, as was originally observed by Press and Harkrider (1962), if the uppermost region of the atmosphere is taken as an isothermal half-space, then there are certain regions of the k vs. w ( for fixed e ) plane (with k and w real) in which the dispersion curves for non-leaking modes cannot penetrate. If a mode's dispersion curve apparently terminates at the edge of such a region, then it would seem that the extension of the mode into such a region would be a leaky mode.…”

A Least-Squares Procedure for Direct Estimation of Azimuth and Velocity of a Propagating Wave

“…It is interesting to note that the pronounced group velocity minima predicted by Press and Harkrider (1962) the SWAP group velocity is about two percent higher than the seismoprint ridge line indicates.. This is probably due to mode interference, i.e., to energy interference in the i\arrow-band filter outputs, to which the SWAP procedure is known to be sensitive (see Archambeau and Flinn, 1965).…”

Low-Frequency Atmospheric Gravity Waves from Vertical Tectonic Deformation During Two Recent Chilean Megathrust Events: the 2010 Maule (Mw8.8), and 2014 Iquique (Mw8.2) Earthquakes

“…Although somewhat modified models, such as CIRA [23], MISISE [24], and NRL-C2Z [25] have been presented to date, we refer to the US standard structure as a more global scale structure to discuss lower frequency waves. For the ARDC standard atmosphere, the phase and group velocities of several acoustic and gravity modes have been calculated [26,27], where the air density is assumed to decrease exponentially with altitude. In addition, Harkrider [22] atmosphere to a point source and a receiver both located on the ground surface, by approximating the above thermal structure by 39 horizontally stratified, isothermal layers terminated either with the isothermal half-space or with the free surface at an altitude of 220 km.…”