A Study of the Long Range Propagation of Infrasonic Waves in the Atmosphere

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  • Tahira Makoto
    Department of Earth Sciences, Aichi University of Education

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Other Title
  • 大気中におけるインフラソニック波の長距離伝播に関する研究
  • (II)熱圏ダクトの伝播における波形変化の数値的研究
  • (II) Numerical Study of the Waveform Deformation along Thermospheric Ray Paths

Abstract

Waveform deformation of volcanic infrasonic waves propagating long distances through thermospheric ducts is discussed. Ray tracing using a realistic atmospheric model including the vertical variation of temperature and mean wind has been performed. Burgers' equation, modified to include the effects of spreading of the sound wave, density stratification, and mean wind, is solved numerically along the computed ray paths to obtain the waveform deformation of the infrasonic waves propagating through the thermospheric duct. The effect of the caustic at or near the turning point is also taken into account.<br>This procedure has been applied to the infrasonic waves generated by the explosions of the volcano Sakurajima, and the waveforms expected to be observed at Kariya, 710km from the volcano have been computed. As a result, the characteristics of the waveform, amplitudes and frequencies computed for the rays reflected twice at the thermospheric level are in good agreement with the characteristics of the waves frequently observed at Kariya in summer season classified as type I in Tahira (1988). Those computed for the rays reflected three times explain well the observed nature of the waves of type III.

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