Impact of the Arctic amplification on midlatitudes atmospheric circulation and cold spells in winter using idealized numerical modelling

• Main Author: Jolly, Emilien
• Other Authors: Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Université Paris sciences et lettres, Fabio D'Andrea, Gwendal Rivière
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2020
• Subjects: Climat; Atmosphere; Dynamic; Atmosphère; Dynamique; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Arctic; Arctique*; Climate change
• Online Access: https://theses.hal.science/tel-03592535; https://theses.hal.science/tel-03592535/document; https://theses.hal.science/tel-03592535/file/Jolly_2020_These.pdf

The Arctic Amplification (AA) is a stronger atmospheric warming in the Arctic than in mid-latitudes, and its effects on atmospheric circulation are discussed. Its impact on Rossby waves and winter cold spells in mid-latitudes is analyzed using a 3-level dry quasi-geostrophic model on the sphere, with orography. First the study is conducted by comparing long simulations: one corresponds to the winter climatology of the last 30 years, and for the other one a AA pattern is added. It is build from a composite of the warmest winters in the Arctic. A spectral analysis shows a decrease in Rossby wave phase speed for the most energetic waves. This appears to be related to a jet narrowing and is accompanied by a moderate increase in low frequency variance at mid-latitudes, which may increase cold spells. This increase can compensate locally the warming in terms of the number of cold spells. Then, in a simplified framework, without zonal asymmetries, the impact of the jet width on the waves is more particularly studied. It appears that this narrowing can be a consequence of AA. It slows down the flow, with two consequences: a slowing down of the phase speed, through changes in the vorticity gradient; and a frequency shift of the variance from high frequency to low frequency. Finally, the variability of the AA pattern, and its consequences on this mecanism, are presented. The different ways of counting AA are permeable to the influences of the rest of climate change, which may have opposite influences. L’Amplification Arctique (AA) correspond au réchauffement atmosphérique plus fort dans l’Arctique qu’aux latitudes moyennes, et ses effets sur la circulation atmosphérique sont discutés. Son impact sur les ondes de Rossby et les vagues de froid en hiver aux latitudes moyennes est analysée en utilisant un modèle quasi-géostrophique sec à 3 niveaux sur la sphère, avec orographie. D’abord l’étude est menée en comparant des simulations longues : l’une correspond à la climatologie hivernale des 30 dernières années, et pour ...