PROPAGATION AND DISPERSION OF ATMOSPHERIC WAVE-PACKETS AROUND A SPHERICAL GLOBE

In this work we investigate the propagation of atmospheric waves in a spherical geometry. The monochromatic wave solution in a spherical atm osphere is found first. The dispersion relations of acoustic-gravity w aves and Lamb waves are found to approximate to the well-known results obtained in the flat earth case in a broad region away from the sourc e and its antipode. In the source and its antipodal regions the horizo ntal phase velocity is found to vary. The spherical geometry mandates the horizontal wavenumber to assume discrete values with a separation equal to the reciprocal of the earth radius. With the monochromatic so lutions obtained as a basis, both Lamb wave packets and gravity wave p ackets in a source-free atmosphere are discussed. By using the well-kn own Poisson's formula the global propagation of a wave packet in a sph erical geometry can be described as bouncing of waves between a starti ng area and its antipodal region. Some comparisons of the theoretical results with observational data, especially those acquired in the afte rmath of the eruption of Mount St. Helens, 18 May 1980, are made.