Coherent Modes of Northern Hemisphere Wind Extremes and Their Links to Global Large-Scale Drivers

We investigate the spatially coherent modes of storminess over the Northern Hemisphere (NH) land regions during 1940–2023. Locally, stormy days are defined by us as local exceedances of the 95th-percentile of wind speed anomalies derived from ERA5 reanalysis data. Applying a Principal Component Analysis (PCA) to seasonal (ONDJFM) local storm indices reveals a leading mode of hemispheric variability characterised by a north–south dipole structure. 

Regions north of 50° N (Europe–Asia) fluctuate coherently, in opposite phase to those farther south. 
Correlation analyses between the principal component time series and global spatial fields of sea surface temperature (SST), mean sea level pressure (MSLP), and skin temperature (i.e. surface temperature at radiative equilibrium; SKT) identify teleconnections to the North Atlantic Oscillation (NAO) and Pacific SST anomalies, indicating that known climate modes modulate storm synchrony.

To explore physical causality between SKT and storminess modes related to the atmospheric response to SKT anomalies, the relevant patterns of SKT identified in the SKT–storm correlation analysis were used to drive the ACE2 climate emulator. The ACE2 emulator is a recently released artificial-intelligence emulator trained with ERA5 reanalysis. The emulator experiments reproduce the observed storm variability pattern and yield a split jet-stream response with both poleward and equatorward branches. 

These results provide causal evidence that coherent large-scale patterns of seasonal storminess exist and that large-scale surface temperature gradients can excite those coherent patterns of hemispheric storm variability.

Our findings bridge statistical climate variability with physical processes, offering a framework for understanding how continental storm risks respond to changes in global surface temperature.