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

Abstract

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.