Arctic cyclones are extratropical cyclones of a few thousands of kilometers traveling in the Arctic region. They play a major role in Arctic weather and climate and are at the heart of this thesis. Most of them are similar to midlatitude cyclones in their structure and mechanisms, but some summer Arctic cyclones distinguish by being long or having a cold core temperature. In this PhD thesis, a new cyclone phase space is first developed as a tool to identify and characterize cold-core cyclones. A second part of the work focuses on long summer Arctic cyclones, particularly coming from the Eurasian continent. It reveals a transition towards a cold-core structure, as the cyclone moves over sea ice, due to diabatic and frictional processes. Finally, we explore the representation of Arctic cyclones in a climate model with different resolutions. Cyclone structures are better represented at higher resolution, but their number is overestimated on the continents, particularly in winter.

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

Visio
https://visio.numerique.gouv.fr/rei-uzlp-cne

Reviewers: Suzanne Gray (University of Reading) & Heini Wernli (ETH Zürich)
Examiners: Freddy Bouchet (LMD, CNRS), Jennifer Catto (University of Exeter) & Camille Li (CFI, University of Bergen)
Supervisors: Gwendal Rivière (LMD, CNRS) & Sébastien Fromang (LSCE, CEA)