COMPUTATION OF SEISMOGRAMS AND ATMOSPHERIC OSCILLATIONS BY NORMAL-MODE SUMMATION FOR A SPHERICAL EARTH MODEL WITH REALISTIC ATMOSPHERE

We describe a theory to compute seismograms and atmospheric disturbanc es such as ionospheric oscillations or pressure variations in a realis tic spherical earth model with atmosphere. This theory is valid for a source located either in the solid earth or in the atmosphere. Solid e arth and atmospheric normal modes are computed for a radiation boundar y condition that models the dissipation of acoustic signals in the hig h atmosphere of the Earth, We show that the coupling between ground an d atmosphere occurs at a set of frequencies related to fundamentals an d harmonics of atmospheric modes. Spheroidal modes near these frequenc ies have up to 0.04 per cent of their energy in the atmosphere, and th us may be strongly excited by atmospheric sources. This theory can be used for more accurate modelling of the seismic data from meteoritic e vents or volcanic eruptions as well as for the analysis of barograms o r ionograms recorded after large earthquakes.