Clear evidence for the sign-reversal of the pressure admittance to gravity near 3 mHz

The influence of the atmosphere on gravity measurements by Newtonian attraction and vertical displacements due to surface loading is well known and studied especially at frequencies below 1 mHz. Less work has been done at the higher seismic frequencies where inertial effects come into play. The sensor mass of a vertical accelerometer responds to several forces caused by the atmosphere, on global, regional and local scales. For the seismic frequencies the atmosphere above the observation site has the largest influence. A simple “Gedankenexperiment” demonstrates that the gravitational effect on one hand and the free air and inertial effects due to deformation on the other have opposite sign. Since the inertial effect is strongly frequency-dependent there should be a crossover-frequency where the pressure admittance to gravity changes sign. Simple analytical models clearly show this property near frequencies of a few mHz and are used here to amplify the variance reduction of the gravity residuals. The crossover-frequency depends on the properties of the models of the atmospheric phenomena and the elasticity of the Earth’s crust. Therefore in reality it must be expected to vary in time and space.We show one extremely clear example of this sign-reversal detected in the gravity data from the superconducting gravimeter GWR-C025 in Vienna among other examples which demonstrate the reality of this effect.