Non‐Tidal Oceanic Contribution to the Variation of the Earth's Oblateness

Abstract

AbstractCox and Chao obtained time series of the Earth's dynamic oblateness J2 by analyzing Satellite Laser Ranging data for 25 years and found that since 1997/1998, the J2 variation shows dramatical abnormal changes after removing seasonal signals. The long‐term change of J2 before 1996 can be well explained by the theory of mantle rebound since the last ice age but the change since 1997/1998 is inconsistent with the theory. It was suspected that the abnormal change was the result of geophysical fluid motions and the atmosphere has been excluded as a possible source. In this study, we investigate two ocean general circulation models to conclude that the mass transfer within the oceans, specifically within the Pacific ocean, contributes to at least part of the observed variation since 1997/1998. The identification of geophysical source helps verify the SLR results of Cox and Chao. Different from previous work on the interpretation of J2 variation, our study uses two ocean models and the altimetry data from TOPEX/Poseidon for model validation. Our conclusion is that part of the observed abnormal J2 variation since 1997/1998 may be from variations of steric effects, which are the result of thermal and saline variations, and might not be easily discerned from the sea surface height variations observed with the T/P altimetry.