Can measurements of sea level and Earth's gravity field constrain estimates of the global water/energy cycle fluxes ?
Event: 2020 Ocean Surface Topography Science Team Meeting (virtual)
Session: Science I: Climate data records for understanding the causes of global and regional sea level variability and change
Presentation type: Type Forum
For more than 25 years, the scientific community, space agencies and oceanographic agencies have established a global observing system to estimate precisely sea level changes and their contributions. The objective was to produce observations sufficiently precise to determine the variations in sea level in response to climate change and to assess their impacts and the associated risks for coastal populations and ecosystems. This observation system, made up of satellite altimetry (Topex, Jason and Sentinel), space gravimetry (GRACE and GRACE-FO) and in situ measurements of ocean temperature (Argo, XBT, CTD), acquired with time such a maturity, that it allows today to determine the variations of sea level and its contributions with an almost global coverage, a monthly resolution and a stability of <± 0.4mm.yr-1 (90%CL) over periods > 20 years. This level of precision and reliability is now sufficient to place constraints on the estimates of fluxes in the global water and energy cycle. In this presentation, I propose to show how measurements of sea level, gravimetry and ocean temperature (with their associated uncertainties) today make it possible to constrain the planet's water and energy top of the atmosphere balance and surface balance. We use the ocean heat content changes (OHC) estimated from sea level changes corrected for the ocean mass changes to constrain a-posteriori the global estimates of the water energy fluxes. We follow the approach of the NASA NEWS project (L’Ecuyer et al. 2015) in which available estimates of the water energy fluxes are brought together in a variational framework and the OHC constraint is imposed a-posteriori along with the constraint from the energy and water conservation laws. With the variational framework, the estimates of the water energy fluxes are adjusted within their error bars to respect the constraints from OHC and the conservation laws. This leads to a reassessment of the global radiative fluxes over 2005-2015 that are consistent with current estimates of sea level rise and changes in ocean mass.