Decadal variation in Earth's oblateness (J2) from satellite laser ranging data

Abstract

For four decades, satellite laser ranging has recorded the global nature of the long-wavelength hydrological mass redistributionwithin the Earth system,which results in significant variations in the Earth's dynamical oblateness, characterized by the second degree zonal geopotential spherical harmonic J2 (or C20). Analysis of the J2 time-series has shown a significant variation related to the strong El Niño-Southern Oscillation events with periods of 2-6 yr. In particular, the variation related to the powerful 2015-2016 El Niño that peaked during 2015 November- December was one of the strongest on record, comparable with the 1982-1983 and 1997-1998 events. In this study,we investigate further the hydrological mass transfer between atmosphere- ocean-land and their signature in the decadal variations of J2 with timescales of ~10 yr. We found that the ~6.4-yr variations can be accounted for by the atmosphere and ocean mass variations based on the improved Atmosphere-Ocean De-aliasing data, and the observed decadal variation in J2 correlates well with the decadal tropical variability characterized by the 5-yr running mean of the El Niño-Southern Oscillation Index, although existing physical models, especially the land water storage, are limited for the purpose of further studies of the excitation.