Atmospheric blocking is a key feature of mid-latitude weather. It is defined as a flow configuration, in which a quasi-stationary anticyclonic circulation anomaly disrupts the prevailing westerly flow. This pattern is often linked to various weather extremes. Despite its importance, blocking mechanisms are not fully understood. Accurately representing blocking in climate models is still challenging, and weather forecasting models struggle to predict the onset and duration of blocking. This thesis aims to enhance the understanding of blocking mechanisms and their links to temperature extremes by exploring three aspects:

(i) The contribution of dry and moist processes to blocking circulation: Using a dry General circualtion model whose climatology is close to the reanalyses, I showed blocking events have similar characteristics in the model and the reanalyses but are rarer in the model. It means there is no specific property of blocking that cannot be simulated by the dry model.

(ii) Heatwaves and Blocking: This study explores the link between temporally evolving heatwaves and atmospheric blocking using a quasi-Lagrangian framework. It highlights how blocking characteristics are linked to heatwave occurrences and their properties.

(iii) Gulf Stream and Blocking Dynamics: Using ECMWF-IFS sensitivity experiments, this study examines how surface latent heat fluxes from the Gulf Stream influence blocking formation and maintenance.

Lieu
École normale supérieure – PSL
24 rue Lhomond – aile Erasme
Salle Claude Froidevaux – E314

Visio
https://cnrs.zoom.us/j/94005611526?pwd=EbGxaTSpRLJcfNlSUweagJWZo3M7wA.1

• Fabio D’ANDREA, Président du jury (École normale supérieure – PSL)
• Olivia ROMPPAINEN-MARTIUS, Rapportrice (University of Bern)
• Stephan PFAHL, Rapporteur (Institut für Meteorologie)
• Camille LI, Examinatrice (University of Bergen)
• Paolo DAVINI, Examinateur (CNR-ISAC)
• Gwendal RIVIÈRE, Directeur de thèse (CNRS-LMD)
• Sébastien FROMANG, Directeur de thèse (CEA)