Global oscillatory modes in high-end climate modeling and reanalyses

• Published in: Climate Dynamics
• Main Authors: Feliks, Yizhak, Small, Justin, Ghil, Michael
• Other Authors: Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: Climatic oscillations; Interannual variability; Solar cycle; Synchronization; [SDU]Sciences of the Universe [physics]; [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology; Labrador Sea; North Atlantic
• Online Access: https://insu.hal.science/insu-03726931; https://insu.hal.science/insu-03726931/document; https://insu.hal.science/insu-03726931/file/Feliks2021_Article_GlobalOscillatoryModesInHigh-e-2.pdf; https://doi.org/10.1007/s00382-021-05872-z

International audience Interannual oscillatory modes, atmospheric and oceanic, are present in several large regions of the globe. We examine here low-frequency variability (LFV) over the entire globe in the Community Earth System Model (CESM) and in the NCEP-NCAR and ECMWF ERA5 reanalyses. Multichannel singular spectrum analysis (MSSA) is applied to these three datasets. In the fully coupled CESM1.1 model, with its resolution of 0.1 ×0.1 degrees in the ocean and 0.25 ×0.25 degrees in the atmosphere, the fields analyzed are surface temperatures, sea level pressures and the 200-hPa geopotential. The simulation is 100-year long and the last 66 yr are used in the analysis. The two statistically significant periodicities in this IPCC-class model are 11 and 3.4 year. In the NCEP-NCAR reanalysis, the fields of sea level pressure and of 200-hPa geopotential are analyzed at the available resolution of 2.5 ×2.5 degrees over the 68-years interval 1949-2016. Oscillations with periods of 12 and 3.6 years are found to be statistically significant in this dataset. In the ECMWF ERA5 reanalysis, the 200-hPa geopotential field was analyzed at its resolution of 0.25 ×0.25 degrees over the 71-years interval 1950-2020. Oscillations with periods of 10 and 3.6 years are found to be statistically significant in this third dataset. The spatio-temporal patterns of the oscillations in the three datasets are quite similar. The spatial pattern of these global oscillations over the North Pacific and North Atlantic resemble the Pacific Decadal Oscillation and the LFV found in the Gulf Stream region and Labrador Sea, respectively. We speculate that such regional oscillations are synchronized over the globe, thus yielding the global oscillatory modes found herein, and discuss the potential role of the 11-year solar-irradiance cycle in this synchronization. The robustness of the two global modes, with their 10-12 and 3.4-3.6 years periodicities, also suggests potential contributions to predictability at 1-3 years horizons.