2026-04-13T13:30:03Zhttps://recercat.cat/oai/request

oai:recercat.cat:2117/3975952026-02-04T07:19:05Zcom_2072_1033col_2072_452950

00925njm 22002777a 4500 dc Polkova, Iuliia author Swingedouw, Didier author Hermanson, Leon author Koehl, Armin author Stammer, Detlef author Ortega Montilla, Pablo author Bilbao, Roberto author 2023 Due to large northward transports of heat, the Atlantic Ocean circulation is strongly affecting the climate of various regions. Its internal variability has been shown to be predictable decades ahead within climate models, providing the hope that synchronizing ocean circulation with observations can improve decadal predictions, notably of the North Atlantic subpolar gyre (SPG). Climate predictions require a starting point which is a reconstruction of the past climate. This is usually done with data assimilation methods that blend available observations and climate model states together. There is no unique method to derive initial conditions. Moreover, initialization can be implemented with full-field observations or their anomalies superimposed on the model's climatology to avoid strong drifts in predictions. How critical ocean circulation drifts (following the initialization step) are for prediction skill has not been assessed yet. We analyze this possible connection using the dataset of twelve prediction systems from the World Meteorological Organization Lead Centre for Annual-to-Decadal Climate Prediction. We find a wide variety of initial errors for the Atlantic meridional overturning circulation (AMOC) related to a dynamically imbalanced AMOC cell leading to strongly displaced or multiple maxima in the overturning structures. This likely results in a blend of model drift and initial shock. We identify that the AMOC initialization influences the quality of SPG predictions. When predictions show a large initial error in their AMOC, they usually have low skill for predicting internal variability of the SPG for a time horizon of 6-10 years. Full-field initialized predictions with low AMOC drift show better prediction skill of the SPG than those with a large AMOC drift. Nevertheless, while the anomaly-initialized predictions do not experience large drifts, they show low SPG skill when skill also present in historical runs is removed using a residual correlation metric. Thus, reducing initial shock and model biases for the ocean circulation in prediction systems might help to improve their SPG prediction beyond 5 years. Climate predictions could also benefit from quality-check procedure for assimilation/initialization because currently the research groups only reveal problems in initialization once the set of predictions has been completed, which is an expensive effort. The author(s) declare financial support was received for the research, authorship, and/or publication of this article. Funding for IP was provided by the Deutsche Forschungsgemeinschaft, Project number 436413914. LH and DSm were supported by the Met Office Hadley Centre Climate Programme funded by BEIS and Defra. IB was supported by the Trond Mohn Foundation (Grant BFS2018TMT01; Bjerknes Climate Prediction Unit) and the Research Council of Norway (Grant 309562; Climate Futures). PA, DN, HP, and MK acknowledge funding from the European Union's Horizon Europe Research and Innovation Programme through the ASPECT project under grant agreement No 101081460. DSw received financial support from the French government in the framework of the University of Bordeaux's IdEx Investments for the Future program / RRI Tackling Global Change. DSw also acknowledges funding from UKRI Decadal project (MR/W009641/1). RM would like to acknowledge funding support from CSIRO DCFP (Decadal Climate Forecasting Project). HT and TK were supported by MEXT program for the advanced studies of climate change projection (SENTAN) Grant Number JPMXD0722680395. Peer Reviewed "Article signat per 26 autors/es: Iuliia Polkova, Didier Swingedouw, Leon Hermanson, Armin Köhl, Detlef Stammer, Doug Smith, Jürgen Kröger, Ingo Bethke, Xiaosong Yang, Liping Zhang, Dario Nicolì, Panos J. Athanasiadis, Pasha Karami, Klaus Pankatz, Holger Pohlmann, Bo Wu, Roberto Bilbao, Pablo Ortega, Shuting Yang, Reinel Sospedra-Alfonso, William Merryfield, Takahito Kataoka, Hiroaki Tatebe, Yukiko Imada, Masayohi Ishii, Richard J. Matear" Postprint (published version) Àrees temàtiques de la UPC::Enginyeria agroalimentària::Ciències de la terra i de la vida::Climatologia i meteorologia Ocean-atmosphere interaction. Weather forecasting Atlantic meridional overturning circulation Subpolar gyre Decadal Predictions Prediction skill Initialization shock Initial conditions Data assimilation Internal variability Frontiers Simulació per ordinador Initialization shock in the ocean circulation reduces skill in decadal predictions of the North Atlantic subpolar gyre