Atmospheric Reanalysis datasets provide temporally consistent, physically based reconstructions of the Earth’s atmosphere, yet their coverage rarely extends before the nineteenth century due to the scarcity of direct observations. To overcome this limitation, we present the concept and initial realization of the Millennium Atmospheric Reanalysis, a framework that integrates both natural isotope proxies and anthropogenic documentary records within a data assimilation system. The first component, Isotopic Proxy Data Assimilation, employs an ensemble-based offline assimilation of multi-proxy δ¹⁸O archives—including tree rings, speleothems, corals, and ice cores—from the dod2k compilation. Using isotope-enabled coupled climate models (MPI-ESM-wiso and iCESM), we reconstruct global fields of temperature, precipitation, and drought indices (scPDSI, SPEI) for the past two millennia. The reconstructions reproduce observed interannual to centennial variability with high skill during the instrumental period, particularly in tropical and monsoon regions.

The second component, Old Weather Data Assimilation, applies an online data assimilation of descriptive weather diaries—converted to total cloud cover values—to reproduce subdaily meteorological variations over Japan during 1802–1841. The assimilated results successfully reproduce observed temporal patterns of precipitation, solar radiation, and near-surface temperature anomalies, including the Tenpō famine (1832–1837). Together, these complementary approaches establish the methodological foundation for a continuous, high-resolution atmospheric reanalysis spanning the Common Era. The resulting dataset will enable validation of paleoclimate simulations, enhance understanding of climate–society linkages (e.g., the 14^th-century « Great Transition »), and provide a new perspective for integrating proxy, historical, and model-based evidence into coherent climate reconstructions.

Pr. Kei Yoshimura, IIS Chiba Experimental Station, The University of Tokyo, Japan.

Contact

En présentiel
Observatoire de Paris, 77 avenue Denfert-Rochereau, Salle Danjon
Veuillez réserver auprès de  si vous êtes extérieur à l’Observatoire

Zoom
https://cnrs.zoom.us/j/97838365122?pwd=QiYNWf2PKxlCvH67GoMhg9bbYqX7A7.1