Role of Arctic sea ice decline on the mid-latitude climate : atmospheric teleconnections

• Main Author: Chripko, Svenya
• Other Authors: Climat, Environnement, Couplages et Incertitudes Toulouse (CECI), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Paul Sabatier - Toulouse III, Rym Msadek, Emilia Sanchez-Gomez
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2020
• Subjects: Arctic sea ice; Mid-latitudes; Teleconnections; Atmospheric circulation; Atmospheric variability; Arctic oscillation; Climate models; Glace de mer arctique; Moyennes latitudes; Téléconnexions; Circulation atmosphérique; Variabilité atmosphérique; Oscillation arctique; Modèles climatiques; [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology; Arctic; albedo; Arctique*; Sea ice
• Online Access: https://theses.hal.science/tel-03611295; https://theses.hal.science/tel-03611295/document; https://theses.hal.science/tel-03611295/file/2020TOU30314b.pdf

The Arctic has been warming twice as fast as the whole globe since the preindustrial era: this phenomenon is known as Arctic amplification. Arctic amplification and associated Arctic sea ice decline can affect the climate locally. It has also been shown to affect the large-scale atmospheric circulation beyond the Arctic, yielding changes in the mid-latitude climate. However, the mechanisms beneath this linkage are still poorly understood. The objective of this thesis is to bring more insight into these mechanisms. For that purpose, we have defined and run sensitivity experiments that allow to isolate the effect of Arctic sea ice decline from other climate forcings. In these experiments, which have been done with the CNRM-CM6 climate model using different horizontal resolutions, sea ice albedo is reduced to the ocean value, leading to an increase in absorbed solar radiation and a reduction of sea ice especially in summer. We first evaluate the model mean state and its representation of Arctic-to-mid-latitude linkages. This analysis suggests that increasing the horizontal resolution in the atmosphere and ocean generally leads to more realistic mean climate conditions in the Northern Hemisphere. We further show that linkages between atmospheric and sea ice variability are consistent between the model and the observations. These results indicate that Arctic sea ice influence on the atmosphere is hardly detectable in observations and in free-running models because of the large internal variability, which stresses the need to properly isolate this link using dedicated sensitivity experiments. Secondly, we focus on the rapid atmospheric response during autumn and winter, when Arctic amplification is maximum. Using a dynamical adjustment method based on a regional reconstruction of circulation analogs, the mechanisms of the regional temperature response are investigated. We show that the sea-ice-induced warming over North America and Europe can be explained by : (i) cyclonic changes in circulation that favor warm air ...