The PIRATE OST/ST project

• Main Author: Penduff, Thierry
• Other Authors: Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Observatoire des Sciences de l'Univers de Grenoble (Fédération OSUG)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP), Université Grenoble Alpes (UGA)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2020
• Subjects: [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; Sea ice
• Online Access: https://hal.science/hal-04549910; https://hal.science/hal-04549910v1/document; https://hal.science/hal-04549910v1/file/PIRATE_PENDUFF.pdf

International audience The main goal of the PIRATE (Probabilistic InteRpretation of Altimeter & in-siTu obsErvations) OST/ST project is to study the intrinsic vs extrinsic sources of the ocean variability observed by altimeter and in-situ. We consider real observations and the OCCIPUT ensemble of ocean/sea-ice simulations to disentangle and characterize 2 components of the oceanic variability for several variables, focusing on interannual-to-decadal timescales: the first component is the Atmospherically Forced Variability (AFV) that is directly driven by the fluctuating atmospheric forcing; the second component is the Chaotic Intrinsic Variability (CIV) that is spontaneously generated by the eddying ocean, whose phase is random, and is independent of the phase of the atmospheric variability.In PIRATE, we have disentangled the extrinsic and intrinsic sources of ocean variability in 2 ways. [1] we have first split the total model variability into AFV and CIV from simple and classical ensemble statistics: the fluctuations of the ensemble mean were used to estimate and characterize the AFV, and the deviations of each member around this ensemble mean provided us with the CIV. [2] Then we have acknowledged that this pragmatic, usual splitting of the variability into both components is not consistent with the Dynamical Systems Theory (DST): we have thus developed more mathematically-consistent diagnostics to characterize the sea level variability, now properly seen as an ocean-driven CIV modulated by the atmospheric variability throughout the integration.The first method allowed us to confirm that the imprint of the interannual-to-decadal CIV on many observed variables (sea level, Ocean Heat Content, Atlantic Overturning, etc) can be as strong as the imprint of the AFV in several eddy-active regions: these CIV-related random low-frequency fluctuations cannot be neglected when interpreting the global ocean simulated or observed variability. We also showed that CIV may hamper in several regions the detection and ...