Polar lows in the Northern Hemisphere: influence of the large-scale environment, its variability and its changes with climate change

• Main Author: Mallet, Paul-Etienne
• Other Authors: Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École des Ponts ParisTech (ENPC)-École polytechnique (X)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Ecole Polytechnique X, Chantal Claud([e-mail])
• Format: Thesis
• Language: French
• Published: HAL CCSD 2013
• Subjects: extreme events; climate change; polar lows; événements extrêmes; changement climatique; geo; envir; Gulf of Alaska; Pacific; Labrador Sea; Nordic Seas; North Atlantic; Alaska
• Online Access: https://pastel.archives-ouvertes.fr/pastel-00932363/file/These_PEM_small_.pdf; https://pastel.archives-ouvertes.fr/pastel-00932363

Polar lows (PLs) are intense meso-cyclones forming in winter at hight latitudes over open water. Despite their low spatial and temporal extension, they are particularly dangerous, being associated with strong winds and heavy snowfall, causing very low visibility and high waves. The purpose of this thesis is to study the impact of climate variability on their outbreak, and in particular to make an assessment of their evolution with climate change. Firsly, large-scale environment leading to development of Pls is determined using all available homogeneous PLs observations. Geopotential height at 500 hPa, the temperature difference between the surface of the ocean and 500 hPa, wind and temperature near the surface, and the potential vorticity (PV) at 300 hPa present significant anomaly patterns over large areas centrerd over PL genesis zones. The focus is done on the Nordic Seas for which there is a wide and homogeneous climatology of Pls, although other regions of the Northern Hemisphere are also studied (Labrador Sea, Gulf of Alaska .). Pls develop after a certain build-up, the outbreak day been marked by strong wind and PV intensification. Significant disparities between the different formation areas indicate some heterogeneity in the relative influence of formation mechanisms. A second part is devoted to study the influence of climate variability on Pls. Two approaches to this variability are then considered: the teleconnection patterns over the North Pacific and weather regimes over the North Atlantic and Europe. Teleconnection patterns based on the idea that the atmospheric variability can be described by variations in the intensity of specific large-scale, persistent and recurrent patterns. For each North Pacific area, the study of the relationship between these patterns and key variables for Pls formation highlight respective influences of each teleconnection patterns on Pls development. The idea behind the concept of weather regimes is that the atmospheric circulation variability can be described as an ...