17 Sep (CLIM) Xueke Li, Extreme Weather/Climate

Xueke Li, University of Pennsylvania 

Title: Planetary Wave Resonance and Midlatitude Weather Extremes: Toward Better Understanding of the Phenomenon 

Time: Wed, 17 Sep, 1:30pm 

Location: Horizon Hall, Room 4014 or via Zoom (for Zoom link, email xdu5@gmu.edu) 

Host: Xiaojing Du 

ABSTRACT: Climate change is increasing the frequency and severity of boreal summer weather extremes, from heatwaves to floods, to droughts and wildfires. Many of these events are inextricably linked to anomalous behavior of the jet stream and meanders therein tied to Rossby or planetary waves. A key mechanism underlying this connection is quasi-resonant amplification (QRA), in which planetary waves become trapped and amplified, contributing to persistent extreme events. Yet the impact climate change is having on QRA remains elusive, owing to the rarity of real-world realizations of the phenomenon and its inadequate representation in current-generation climate models, which struggle to resolve nonlinear interactions among physical drivers across scales. 

Using extended reanalysis and observational datasets, I show that planetary wave resonance events have tripled since the mid-20th century. Climate projections further indicate that these events are likely to increase substantially in the future, and likely play a significantly greater role in both current and future-projected extreme weather events than is evident in current-generation climate models. These lines of evidence suggest that anthropogenic warming is altering background conditions in ways that favor more resonant events. My work has identified multiple surface forcing pathways, including: (1) El Niño–Southern Oscillation (ENSO) events; (2) land–atmosphere interactions; and (3) aerosol-induced Arctic de-amplification. However, the precise role of each forcing in initiating, sustaining, or disrupting the conditions for resonance occurrence remains uncertain, meriting further investigation.