Northern hemisphere cold air outbreaks are more likely to be severe during weak polar vortex conditions

Jinlong Huang,Wenshou Tian,Peter Hitchcock,Amanda C Maycock,Christine M Mckenna

doi:10.1038/s43247-021-00215-6

Jinlong Huang, Wenshou Tian + Show 3 more

Open Access

https://doi.org/10.1038/s43247-021-00215-6

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Abstract

Severe cold air outbreaks have significant impacts on human health, energy use, agriculture, and transportation. Anomalous behavior of the Arctic stratospheric polar vortex provides an important source of subseasonal-to-seasonal predictability of Northern Hemisphere cold air outbreaks. Here, through reanalysis data for the period 1958–2019 and climate model simulations for preindustrial conditions, we show that weak stratospheric polar vortex conditions increase the risk of severe cold air outbreaks in mid-latitude East Asia by 100%, in contrast to only 40% for moderate cold air outbreaks. Such a disproportionate increase is also found in Europe, with an elevated risk persisting more than three weeks. By analysing the stream of polar cold air mass, we show that the polar vortex affects severe cold air outbreaks by modifying the inter-hemispheric transport of cold air mass. Using a novel method to assess Granger causality, we show that the polar vortex provides predictive information regarding severe cold air outbreaks over multiple regions in the Northern Hemisphere, which may help with mitigating their impact.

Highlights

Severe cold air outbreaks have significant impacts on human health, energy use, agriculture, and transportation
Our analysis reveals that weak polar vortex conditions are associated with a disproportionate increase in the simultaneous occurrence of severe cold air outbreaks (CAOs) in multiple regions of the northern extratropics in a reanalysis dataset, as compared to moderate CAOs (Fig. 1)
Through a combination of reanalysis data and state-of-the-art climate models, we provide corroborative evidence that weak polar vortex conditions in the lower stratosphere substantially increase the risk of severe CAOs over most continental regions of the northern extratropics

Summary

Introduction

Severe cold air outbreaks have significant impacts on human health, energy use, agriculture, and transportation. Anomalous behavior of the Arctic stratospheric polar vortex provides an important source of subseasonal-to-seasonal predictability of Northern Hemisphere cold air outbreaks. Through reanalysis data for the period 1958–2019 and climate model simulations for preindustrial conditions, we show that weak stratospheric polar vortex conditions increase the risk of severe cold air outbreaks in mid-latitude East Asia by 100%, in contrast to only 40% for moderate cold air outbreaks Such a disproportionate increase is found in Europe, with an elevated risk persisting more than three weeks. This leads to an excess of cold air in high latitudes of Europe and East Asia and sheds light on the spatial and temporal response of CAOs following anomalous stratospheric conditions

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