Global mean and local sea level budget from updated observations andresiduals analysis (SLBC_cci+ project)

The closure of the Sea Level Budget (SLB) at monthly, yearly, and interannual scales, with the utmost precision, remains a fundamental challenge in modern physical oceanography. Firstly, this closure is crucial to assert that all major contributors to sea level variability are accurately identified and quantified. Secondly, it serves as a valuable means for cross-validating complex global observation systems, such as the Argo in-situ network, satellite gravimetry missions GRACE/GRACE-FO, and the satellite altimetry constellation, while closely monitoring their performances. Thirdly, this closure proves to be an effective approach for testing the consistency of various observed variables within the climate system, including sea level, ocean temperature and salinity, ocean mass, land ice melt, and changes in land water storage, in accordance with conservation laws, notably those governing mass and energy.

In this presentation, we will share the latest results obtained for the sea level budget, including 1) an up-to-date estimate of the global mean budget closure from 1993 to 2022; 2) advancements in the analysis of regional patterns of each component of the budget, as well as of the budget residuals, allowing the identification of regions where the SLB does not close, with a focus on the North Atlantic and the Arctic Ocean where the residuals are significantly high. When and where the SLB closes, we can interpret the causes of the total sea level variations. The analysis at regional scales allows us to assess the relative importance of the individual components all over the oceans. When the SLB does not close, we investigate in each component the potential errors causing non-closure (e.g., in-situ data sampling, geocenter correction in gravimetric data) and how potential inconsistencies in their processing can impact large-scale patterns (e.g., geocenter and atmosphere corrections).

Future works will address questions related to the structural deficiency of the observing system, inconsistent effective resolution across different observing subsystems (in-situ data, satellite gravimetry, and satellite altimetry), potential measurement errors in a single observing subsystem, and the isolation of errors in terms of time and space. To address these questions, we will assess an SLB using synthetic components derived from oceanic models. This novel approach will enable us to estimate the spatial and temporal resolutions inherent in each observation, thereby enhancing the estimation of their respective uncertainties. We will also analyse the signature of internal climate variability on sea level budget components interannual changes, by using state-of-the-art model simulations and reanalyses.

This work is performed within the framework of the Sea Level Budget Closure Climate Change Initiative (SLBC_cci+) programme of the European Space Agency (ESA).