Stratosphere-Troposphere Coupling of Extreme Stratospheric Wave Activity and the Linkage to Cold Events over North America

Extreme stratospheric events have been suggested to be connected to surface temperature anomalies, but some key processes are not well understood. Here we will present several dynamic aspects on the linkage between extreme stratospheric variability and cold events over North America in observations and climate models. First, in contrast to persistent weather regimes associated with the zonally symmetric weakening of a polar vortex, more robust and widespread cooling over North America is found to follow a displacement of the polar vortex due to strong planetary wave activity. Particularly, extreme stratospheric wave events are accompanied by intraseasonal fluctuations between warm and cold spells over North America, with strong wave events followed by an increased risk of surface cold extremes 5-25 days later. Moreover, the dynamic links between extreme stratospheric wave activity and surface anomalies are attributed to changes in the vertical structure of wave coupling. Weak wave events show a wave structure of westward tilt with increasing altitude, while strong wave events feature a shift from westward tilt to eastward tilt during their life cycle. An examination of CMIP6 models shows that models with a degraded representation of stratospheric wave structure exhibit biases in the troposphere during an extreme stratospheric wave event. Finally, we will explore the representation of the relation between stratospheric variability and surface anomalies with a linear inverse model (LIM). As the dynamic modes in a LIM are associated with different eigenvalues or timescales, this provides a dynamic mode interpretation for stratosphere-troposphere coupling and their associated surface anomalies.

Ding, X., Chen, G., Zhang, P., Domeisen, D. I. V., & Orbe, C. (2023). Extreme stratospheric wave activity as harbingers of cold events over North America. Communications Earth & Environment, 4(1), 187. https://doi.org/10.1038/s43247-023-00845-y

Ding, X., Chen, G., & Ma, W. (2023). Stratosphere‐Troposphere Coupling of Extreme Stratospheric Wave Activity in CMIP6 Models. Journal of Geophysical Research: Atmospheres, 128(16). https://doi.org/10.1029/2023JD038811