Excitation of normal modes by atmospheric turbulence: Source of long-period seismic noise

Abstract

Turbulent atmosphere can exert force on the solid Earth by the Reynolds stress, which can in principle generate motions of the solid Earth. Using a stochastic formulation and the Kolmogorov picture of isotropic turbulence, an expression for normal-mode excitation by atmospheric turbulence is derived. The final analytical formula for average acceleration contains the average convective velocity of atmosphere as the only practical parameter in the theory. Comparison with IDA gravimeter data shows that long-period noise below 3 mHz, which is ubiquitous in all good signal-to-noise ratio (S/N) records, can be explained by an average atmospheric convective velocity of 6.5 m s-1. While this is somewhat larger than the value expected for a simplified atmospheric model (4 m s-1), its proximity in value as well as its frequency dependence strongly support the view that the cause of long-period noise is atmospheric turbulence.