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OVALIE: Oceanic intrinsic Variability versus Atmospheric forced variabiLIty of sea level changE



Living Planet Fellowship research project carried out by William Llovel and Alice Carret.

Global mean sea level rise is one of the most direct consequences of actual global warming. Since the beginning of the 20th century, global mean sea level experiences an unabated increase of 1.1-1.9 mm.yr-1 recorded by tide gauges. Based on satellite altimetry and since 1993, global mean sea level rises at a higher rate of 3 mm.yr-1. This higher rate denotes a possible acceleration in this global rise. Actual global mean sea level rise mainly reflects global ocean warming (through thermal expansion of sea water) and land ice melt (from Greenland, Antarctica and mountain glaciers).
Monitoring precisely these climate variables is mandatory to better understand processes at work under current global warming and to validate climate models used for projections. Careful investigations of these observations jointly with state-of-the-art numerical simulations have also helped for interpreting these changes and underlying mechanisms. Some of these joint observational/numerical investigations have demonstrated that the evolution of the ocean in the turbulent regions has a stochastic character even over interannual to multidecadal periods. This stochastic character of the ocean is known as intrinsic variability. This latter is poorly known in the global ocean despite its recently acknowledged contribution to the oceanic variability. Thus, this intrinsic variability may bias our interpretation of low-frequency variability of the ocean. One barely knows the temporal and spatial signature of the intrinsic variability, the precise footprints of this intrinsic variability as a function of depth and its signature on observations. Furthermore, we do not have enough knowledge on how this intrinsic variability contributes to the recent regional sea level change and its contributions such as temperature, salinity and mass changes.
Therefore, the atmospheric evolution may force a variety of long-term oceanic variability. This means that the most accurate satellite/in situ observations can describe the atmospheric forced variability along with the chaotic ocean intrinsic changes.
The OVALIE project proposes to scientifically investigate and partition the respective contribution of the atmospheric forced variability versus the oceanic intrinsic variability for the sea level observations (satellite data -based on Topex/Poseidon, Jason 1-2-3, ERS1, ERS2, ENVISAT, Altika and GRACE- and in situ measurements –based on Argo floats and other in situ measurements).

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