Role of Barystatic Sea Level Change in Global Mass Conservation and Its Excitation to Length-Of-Day Variations

Abstract

Barystatic sea level stores excess water mass from the atmosphere and land to maintain global mass conservations within the Earth system. Besides the secular contribution to global sea-level rise, changes in barystatic sea level also play an important role in mass-induced length-of-day (LOD) variations over a few years or shorter periods. Compared to barystatic sea level changes deduced from the geophysical models, Gravity Recovery and Climate Experiment and GRACE follow-on (GRACE/GFO) measurements provide actual observed ocean mass changes. Here, we investigate short-term both seasonal (annual and semiannual) and non-seasonal LOD variations caused by mass redistribution using GRACE/GFO mass estimates and effective angular momentum (EAM) products, particularly quantitatively assessing the excitation from the barystatic sea level. Note that correcting the problem of global mass non-conservation is necessary for GRACE/GFO mass estimates in both spherical harmonic and mascon solutions to calculate the LOD excitation accurately. LOD mass term contributions derived from GRACE/GFO mass estimates considering global mass conservation show high consistency with satellite laser ranging results and are much closer to geodetic LOD observations than EAM products at seasonal and non-seasonal time scales. The barystatic sea level exhibits the most significant amplitude in mass-induced LOD variations, compensating for most land hydrological excitation, but shows no clear correlation with the atmosphere. Due to slight fluctuations in cryospheric effects and the substantial compensatory action of the barystatic sea level, differences in the land hydrological excitation do not lead to significant deviations in the total LOD mass term between EAM products and GRACE/GFO mass estimates.