Resonant planetary waves contributed to Pacific Northwest Heat Dome event of 2021

The team of researchers, including Michael Mann from the University of Pennsylvania and Stefan Rahmstorf from PIK, demonstrates how the phenomenon of resonant planetary wave amplification literally prepared the ground for the Pacific Northwest Heat Dome event of summer 2021, thus making it such a record-shattering event. The unprecedented extreme heat wave, with temperatures exceeding 47 °C in Portland, led to hundreds of excess deaths, extensive crop damage, numerous wildfires and more. The authors of the paper find that, prior to the heat incident, an extended resonant planetary wave configuration caused a soil moisture deficit which amplified lower atmospheric warming, due to the missing cooling effect of evaporation of soil moisture, and made this event so extreme.

Vladimir Petoukhov's groundbreaking theory from 2013 describes the mechanism for quasi-resonant amplification of planetary waves, also called Rossby-waves, in the jet stream, which is not yet well captured in current climate models. The theory illuminates the connection between resonant phenomena and the occurrence of synchronous extreme weather events across the northern hemisphere. Neglecting such preconditioning feedback mechanisms in climate model analyses could potentially lead to the likelihood or severity of extreme heat waves being underestimated in the future, the authors warn.