Atmospheric pressure and gravity

Abstract

S U M M A R YGravity Green's functions for a column load of a model atmosphere on a spherical, elastic Earth are presented and they are used to evaluate the contribution of global atmospheric pressure variations to local gravity. The Green's functions are found to be relatively insensitive to the details of the model atmosphere, but they are dependent on the temperature at the base of the column, and on the relative height difference between the base of the column and the gravity station. The total signal that global pressure systems contribute to gravity is about 30 pgal, of which about 90 per cent is produced by the atmosphere within 50 km of the gravity station. A zone between 50 and 1000 km from the gravity station contributes a couple of pgal, as does the remainder of the globe. This pattern, the coherence scale of pressure fluctuations, the time and spatial scales appropriate to the hydrostatic approximation, and the distance of the gravity station from the oceans, suggest a division of the globe into local, regional, and global zones. Data requirements, processing details, and the reliability of the computed signal are different in each zone. The local zone is within about 50 km of the gravity station. Within this zone pressure changes rapidly in time, but is spatially coherent, so that hourly observations of pressure and temperature at the gravity site alone are sufficient to compute an accurate correction, except when a front is passing through. The regional zone extends from the edge of the local zone to between several hundred and a thousand kilometres. The signal from this zone is small and is only weakly coherent with the signal from the central zone, so that a rather sparse array of hourly samples of pressure and temperature are required. The gravity signal from the global zone can reach about a pgal. It varies on a time-scale of days, and is influenced by the response of the oceans to pressure variations. Previously reported observations that the admittance between local pressure and gravity residuals depends on epoch, frequency, or site, are most probably due to incorrect modelling. A proper local, regional, temperature, and global correction can adequately account for the gravity signal from the atmosphere to within a few tens of ngal in the diurnal band, and about 100ngal in the days to seasonal band, except during extreme weather conditions. The application of the local correction lowers the power spectral density of the gravity residuals in every band from seasonal to hourly. The regional, global, and temperature corrections lower the residual noise in the seasonal and synoptic bands, but are not consistently effective at periods less than about half a day.

Gravity field variations from superconducting gravimeters for GRACE validation

“…The attraction effect is removed by a 3D-modelling up to a spherical distance of 5° (Neumeyer et al, 2004(Neumeyer et al, , 2006aAbe et al, 2009;Klügel and Wziontek, 2009). For the remaining parts of the Earth's surface the reduction is based on surface pressure (Merriam, 1992), which is used as well for the reduction of the atmospheric loading. Not applied up to now are reductions with respect to the nontidal ocean mass redistribution, which are presently suffering from uncertainties due to a rough grid , and the ocean pole tide effect, which is with < 2 nm/s² at European SG sites smaller than the uncertainties of other long-period signals (Chen et al, 2008).…”

Time series of superconducting gravimeters and water storage variations from the global hydrology model WGHM

“…While several proven methods exist to reduce atmospheric effects reaching from simple barometric admittance to three-dimensional modeling based on operational weather models (Warburton and Goodkind, 1977, Merriam, 1992, Kroner and Jentzsch, 1999, Neumeyer et al, 2004, Klügel and Wziontek, 2009, the contribution of hydrological variations is much more difficult to describe. Initially treated as a disturbing effect in the analysis of the Earth and ocean tides and the interpretation of long-term gravity changes, this signal is considered today as valuable information to quantify mass changes of the system Earth, to verify and improve models describing such processes or to supplement and validate other time-variable gravity field observations, e.g.…”

An Experimental Gravimetric Result for the Revival of Corpuscular Theory.

“…L'enceinte est également scellée pour l'isoler des effets de variation de pression (poussée d'Archimède). On rapporte pour ce type d'appareil une influence de la pression atmosphérique de moins de 0.4 μgal/milibar [8].…”