Dynamics of atmospheric multi-scale systems: A low-order model perspective

Public defence of Oisin Hamilton's doctoral thesis

The weather in the midlatitudes displays low frequency variability (LFV), or long term repetitions, over time spans much longer than the usual two week forecasting horizon. This LFV originates from internal variability as well as couplings, or interactions, between the atmosphere and other components of the climate system. This thesis studies this variability using reduced order models, which aim to distil the core dynamics of the atmosphere.

In particular, atmospheric blocking - or persistent weather patterns made up of high pressure systems - is studied from a dynamical systems perspective. This links particular atmospheric behaviour with specific structures in state space. Using specific unstable solutions to the system, we provide an explanation as to why we observe persistent weather patterns in the model. This method is also found to provide information about the onset and decay of these weather systems.  Through implementing a non-linear radiation scheme we find that multiple climate states can exist in reduced order coupled models. Lastly, we study how energy is transferred between scales in the atmosphere, to better understand the deficiencies of low order atmosphere models.

This thesis introduces a number of reduced order models that are used to investigate the dynamics of the atmosphere, revealing the richness and diversity of the dynamical behaviours. These findings could guide future studies, using more accurate climate, models on the emergence of LFV, and on how different components of the climate system interact.

Jury members : 

Prof. Michel Crucifix (UCLouvain) (Supervisor)
Dr. Stéphane Vannitsem (RMIB) (Supervisor) 
Prof. Qiuzhen Yin (UCLouvain) (Chairperson) 
Prof. François Massonnet (UCLouvain) (Secretary)
Dr. Jonathan Demaeyer (RMIB) 
Prof. Dr. Ulrike Feudel (University of Oldenburg)
Prof. Valerio Lucarini (University of Leicester)