On the Linkage Between Rossby Wave Phase Speed, Atmospheric Blocking, and Arctic Amplification

• Published in: Geophysical Research Letters
• Main Authors: Riboldi, Jacopo, Lott, François, d'Andrea, Fabio, Rivière, Gwendal
• 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)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.STU.ME]Sciences of the Universe [physics]/Earth Sciences/Meteorology; Arctic
• Online Access: https://hal.science/hal-03013594; https://doi.org/10.1029/2020GL087796

International audience It has been hypothesized that enhanced Arctic warming with respect to midlatitudes, known as Arctic amplification, had led to a deceleration of eastward propagating Rossby waves, more frequent atmospheric blocking, and extreme weather in recent decades. We employ a novel, daily climatology of Rossby wave phase speed between March 1979 and November 2018, based on upper-level wind data, to test this hypothesis and describe phase speed variability. The diagnostic distinguishes between periods of enhanced or reduced eastward wave propagation and is related to the occurrence of blocking and extreme temperatures over midlatitudes. While remaining tied to the upper-level geopotential gradient, decadal trends in phase speed did not accompany the observed reduction in the low-level temperature gradient. These results confirm the link between low phase speeds and extreme temperature events, but indicate that Arctic amplification did not play a decisive role in modulating phase speed variability in recent decades. Plain Language Summary The Arctic is warming more rapidly than midlatitudes and the temperature difference between those regions is being reduced. As a result, it has been hypothesized that the jet stream will decrease in intensity and its meanders will move more slowly eastward, leading to more persistent or even extreme weather conditions. As the persistence of weather can substantially vary within and between seasons, assessing long-term changes is not trivial. To tackle this problem, we develop a "weather speedometer" and quantify the west-east displacements of jet meanders over Northern Hemisphere midlatitudes. This metric diagnoses whether jet meanders are on average propagating eastward (positive values), stagnating, or even retrogressing westward (negative values) on each day between March 1979 and November 2018. Using this metric, we confirm that low-speed periods are related to temperature extremes over northern midlatitudes. We also assess that there has not been an overall ...