SOUND PROPAGATION IN THE ATMOSPHERE 
pressed the hill on which the Seismological Laboratory 
is located. The waves are probably of the type dis- 
cussed theoretically by Pekeris [23]. 
If the source of the sound is not at the surface of the 
earth, sound paths can easily be constructed by using 
equations (10) to (17). For a source in the tropopause, 
the rays follow patterns similar to those constructed by 
Ewing [7] for the “tropopause” in the ocean. 
PROBLEMS FOR FURTHER RESEARCH 
Results concerning the following problems would aid 
most in the interpretation and use of recorded sound 
Waves passing through the atmosphere: 
1. Determination of the velocity and absorption of 
sound waves in rarified air at pressures down to 0.01 mb. 
2. Effect of wind at various levels up to 100 km on 
sound propagation. (Some authors probably overesti- 
mate such effects, others underestimate them.) 
3. Effects of the wind component perpendicular to 
the direction of the sound propagation. 
4. Determination of additional travel-time curves 
for sound waves refracted in the stratosphere (a) in 
various latitudes, (b) their annual period, (c) their 
diurnal period (no clear period has been found), (d) 
correlation of results under (a) to (c) with periodicities 
of ozone content in the “‘ozonosphere.”’ 
5. Change in frequencies prevailing in sound waves 
with distance from the source; effects of selective ab- 
sorption. 
6. Indications of dispersion of sound waves under 
various conditions. (Present experiments do not indi- 
cate dispersion.) 
7. Theory of free pressure waves in the atmosphere; 
extension of the theory of Pekeris [23] to other models, 
considering the most recent data on temperature in 
the stratosphere and in the ionosphere. 
8. Properties of sound waves refracted at levels near 
100 km [4] and of free pressure waves [12, p. 329]. 
9. Natural pressure waves in the atmosphere in vari- 
ous latitudes, on islands, near coasts, and far inland 
(including use of tripartite stations with base lengths 
of about 14 of the wave length of the waves to be studied, 
see Fig. 7); causes of such waves [13] and their possible 
use in weather forecasting. 
REFERENCES 
1. Avanasorr, J. V., SNAvety, B. L., and Brown, J., “A 
New Instrument for Subsonic Frequency Measurements”’ 
(abstract). J. acoust. Soc. Amer., 20: 222-223 (1948). 
2. Bairp, H. F., and BANWELL, C. J., “Recording of Air-Pres- 
sure Oscillations Associated with Microseisms at Christ- 
church.” N. Z. J. Sci. Tech., 21: 314B-329B (1940). 
3. Benrorr, H., and Gurensere, B., ‘‘Waves and Currents 
Recorded by Electromagnetic Barographs.”’ Bull. Amer. 
meteor. Soc., 20: 421-426 (1939). 
4. Cox, EH. F., ‘“‘Abnormal Audibility Zones in Long Distance 
Propagation through the Atmosphere.” J. acoust. Soc. 
Amer., 21: 6-16 (1949). Correction, zbid., p. 501. 
5. —— and others, ‘‘Upper-Atmosphere Temperatures from 
Helgoland Big Bang.” J. Meteor., 6: 300-311 (1949). 
6. Empen, R., ‘‘Beitrige zur Thermodynamik der Atmos- 
phare.”’ Meteor. Z., 35: 18-29, 74-81, 114-123 (1918). 
7. Ewine, M., and Worze1, J. L., ‘“Long Range Sound Trans- 
10. 
11. 
12. 
13. 
14. 
15. 
16. 
WW 
18. 
19. 
20. 
21. 
22. 
23. 
24. 
25. 
26. 
27. 
28. 
29. 
30. 
375 
mission.’’ Geol. Soc. Amer., Mem. No. 27 (1948). (See p. 
19) 
. GUTENBERG, B., ‘‘Propagation of Sound Waves in the At- 
mosphere.”’ J. acoust. Soc. Amer., 14: 151-155 (1942). 
“Die dynamische Vergrésserung von Schallregis- 
trierinstrumenten fiir andauernde Sinuswellen.” Beitr. 
Geophys., 26: 34-36 (1930). 
— “Die Schallausbreitung in der Atmosphire,’’ Hand- 
buch der Geophysik, Bd. 9, SS. 89-145. Berlin, G. Born- 
trager, 1932. 
— ‘Die Schallgeschwindigkeit in den untersten Schich- 
ten der Atmosphire.” Z. Geophys., 2: 101-106 (1926). 
— “Interpretation of Records Obtained from the New 
Mexico Atomic Bomb Test, July 16, 1945.” Bull. seism. 
Soc. Amer., 36: 327-330 (1946). 
— and Bentorr, H., ‘“‘Atmospheric-Pressure Waves 
near Pasadena.” Trans. Amer. geophys. Un., 22: 424-426 
(1941). 
GuTENBERG, B., and RicuTeEr, C., ‘‘Pseudoseisms Caused 
by Abnormal Audibility of Gunfire in California.” 
Beitr. Geophys., 31: 155-157 (1931). 
Harpy, H. C., Teurarr, D., and Pretemeter, W. H., ‘‘The 
Velocity of Sound in Air.”’ J. acoust. Soc. Amer., 13: 
226-233 (1942). 
HerRGESELL, H., und Ducxert, P., ‘‘Die Ergebnisse der 
Sprengungen zu Forschungszwecken in Deutschland 
vom 1. April 1923 bis zum 30. September 1926.” Arb. 
preuss. aero. Obs., Wiss. Abh., Bd. 16 (B), 55 SS. (1927). 
Hereromz, G., “‘Uber das Benndorfsche Problem der Fort- 
pflanzungsgeschwindigkeit der Erdbebenstrahlen.’”’ Phys. 
Z., 8: 145-147 (1907). 
Koéuzmr, J., “Die Schallausbreitung in der Atmosphire 
und die dussere Hérbarkeitszone.”’ Meteor. Z., 42: 457— 
463 (1925). 
Metsser, O., ‘“‘Der Hinfallswinkel des anormalen Luft- 
schalls.’’ Z. Geophys., 3: 285-292 (1927). 
Morr, H., ‘“‘Ueber den Einfluss der meteorologischen 
Zustainde der Troposphare auf die Ausbildung der anor- 
malen Schallzone.’’ Ann. schweiz. meteor. Zent-Anst., 
Anhang, 36 SS. (1918). (With bibliography) 
Natrona Apyisory CoMMITTEE For AnRONAUTICS, J'enta- 
tive Tables for the Properties of the Upper Atmosphere, 
prepared by C. N. Warrretp, Washington, D. C., 1946. 
Nava ResearcuH Laporatory, RockretT-SonDE RESEARCH 
Section, Curves of Temperature vs. Altitude over White 
Sands, New Mexico. 1948. 
Pexenis, C. L., ‘“‘The Propagation of a Pulse in the Atmos- 
phere. Part II.’’ Phys. Rev., 73: 145-154 (1948). 
Pernter, J. M., ‘Der Krakatau-Ausbruch und seine 
Folge-Erscheinungen.”’ Meteor. Z., 6: 329-339, 409-418, 
447-466 (1889). 
Quieter, T. H., ‘‘An Experimental Determination of the 
Velocity of Sound in Dry CO2-Free Air and Methane at 
Temperatures below the Ice Point.’”’ Phys. Rev., 67: 298- 
303 (1945). 
ScuropineeEr, E., “Zur Akustik der Atmosphire.’’ Phys. 
Z., 18: 445-453 (1917). 
Scuuuze, G.-A., “Luftseismik”’ in Naturforschung und 
Medizin in Deutschland 1939-1946 (FIAT Rev.). Wies- 
baden, Dieterich, 1948. (See Vol. 18, Pt. 2, pp. 66-71) 
Wercener, A., “Akustik der Atmosphiire’” in Muiller- 
Pouillet’s Lehrbuch der Physik, Bd. 11. Braunschweig, 
Vieweg, 1928. (See pp. 171-198) 
“Die dussere Hérbarkeitszone.’’ Z. Geophys., 1: 297- 
314 (1925). 
Wuirete, F. J. W., ‘‘The High Temperature of the Upper 
Atmosphere as an Explanation of Zones of Audibility.”’ 
Nature, 111: 187 (1923). 
