Non-linear and non-stationary hydroclimate variability in France and the Euro-Atlantic area

• Main Author: Fossa, Manuel
• Other Authors: Morphodynamique Continentale et Côtière (M2C), Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rouen Normandie (UNIROUEN), Normandie Université (NU)-Centre National de la Recherche Scientifique (CNRS), Normandie Université, Nicolas Massei, Benoît Laignel
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2020
• Subjects: Atmospheric circulation; Climatology; Hydrology; Nonlinear systems; Signal processing; Non-linearity; Non-stationarity; Hydroclimate variability; Circulation atmosphérique; Climatologie; Hydrologie; Systèmes non-linéaires; Traitement du signal; Non-linéarité; Non-stationarité; Variabilité hydroclimatique; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; North Atlantic
• Online Access: https://tel.archives-ouvertes.fr/tel-02934594; https://tel.archives-ouvertes.fr/tel-02934594/document; https://tel.archives-ouvertes.fr/tel-02934594/file/manuelfossa.pdf

The works presented in this thesis explore the non-linearity and non-stationarity aspects of the hydroclimate system in France and the Euro-Atlantique area. In part I, «Spatio-temporal scales of hydroclimate variability in France», classifications of precipitation, temperature and discharge time series of 152 watersheds were established, based on non-linear and non-stationary characteristics. In particular, we based our classifications on spectral contents and cross-scale, phase-phase, phase-amplitude interactions. Results show clear homogeneous regions for each variable, but with complex spectral content and cross-scale interactions. Part II, « Spatiotemporal of local and large-scale climate variability», we studied how the watershed modulation altered the spectral correlation between local climate (precipitation, temperature) and discharge. We then studied the large-scale atmospheric patterns linked to discharge, with a combined spatial and temporal spectral analysis. Results show than temperature is the main driver of discharge at the annual scale, but precipitation is the main driver for other time scales. The large scale atmospheric patterns linked to discharge were shown to be time scale dependent and heavily modulated from West to east, with interacting atmospheric components shifting the main time scales of spectral correlation with discharge. Finally, Part III « North Atlantic atmospheric circulation dynamics», introduces a new conjecture linking the geometrical theory of the extremal length (a conformal invariant) and conservative atomspheric systems, such as the North Atlantic atmospheric circulation. We have shown that the time invariance of the extremal length implies conservation in mechanical energy within the atmospheric system, and that the increase/decrease of invariance induces mechanical energy losses/gains. The application of the theory to the North Atlantic atmospheric circulation, shows that depending on the time scale, the dynamics are vastly different, ranging for asymptotically stable ...