High frequency temporal earth gravity variations detected by GRACE satellites

High frequency temporal gravity changes on sub-monthly time scales are caused by Earth's mass transport primarily originating from tidal and nontidal atmospheric and oceanic motions. Exploitation of precise GRACE satellite-to-satellite ranging measurements now makes it possible to monitor these changes on a global scale with a moderate spatial resolution. Thus, a time series of daily 10 × 10 Earth gravity models has been produced for the time span from July 2 to September 30, 2003. The solid Earth, oceanic and atmospheric tidal forces are accounted for during data processing, while variations in the gravitational potential produced by non-tidal atmosphere and ocean mass transport are omitted in the apriori force models. The recovered gravity changes are then compared to non-tidal model predictions. It is found that the agreement varies with the degree and order of the gravity harmonics. Generally, the recovered harmonics are highly correlated with the models for low order coefficients but the agreement degrades when the order becomes larger. Our results prove that GRACE is able to trace geophysical signals at short time scales, and that GRACE data can be useful to validate model predicted large-scale mass transports. Once we are able to separate tidal and nontidal signals for a longer time span, daily gravity recovery might also prove to be useful to study gravity changes taking place at sub-monthly time scales, such as oceanic tides.