Correspondences

What is linked, what is not

Each arc joins two phenomena tested on this site. Green and animated: clear link (correlation significant at 5 % after correcting for autocorrelation, or a response outside chance in an event study). Grey: inconclusive test. A statistical link alone does not establish causation.

Clear link
Inconclusive

Hypotheses tested

Clear links

correlation p < 0.05 or epochs outside chance

Causation demonstrated

a correlation demonstrates none

Arc width from |r| of the stored result; several tests between the same phenomena are drawn as stacked arcs.

Hypothesis tested: A positive NAO strengthens the westerlies and shifts the storm track north-east: more storms over the British Isles, the North Sea and Scandinavia, fewer to the south (Hurrell, 1995; Donat et al., 2010). Two signs are predicted: positive in the north, negative or null in the south.

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Method and sources

NAO: NOAA CPC monthly index, mean of December, January and February; a winter is named after the year of its January. Storms: sum of the ERA5 daily severity index (Leckebusch et al., 2008) over the same days, north and south of 50° N, 25° W–40° E.

Pearson correlation with log(1 + index), as the index is very skewed (a few storms make a winter), with the Spearman rank correlation alongside; effective size from the autocorrelation, 2-winter block bootstrap interval. The verdict is on the north, where the expected sign is positive; the south is a control of opposite sign.

Reading this result

Northern Europe follows the NAO: winters of strongly positive NAO (1989/90, 1992/93, 2014/15, 2019/20) are also stormy winters. The south responds little or the other way, as the shift of the storm track predicts. Yet the NAO explains only part of the differences from one winter to the next: a single storm is enough to make a severe winter, and winters of neutral NAO can have some. Correlation is not causation: common factors (seasons, cycles, trends) or coincidence can produce it. The p-values account for autocorrelation (effective n) but not for preprocessing choices; the confidence interval comes from a block bootstrap. The limits of the source data apply.

SOURCES OF THIS PAGE

North Atlantic Oscillation index (NOAA CPC): NOAA CPC, monthly North Atlantic Oscillation index (rotated PCA of 500 hPa height anomalies, 1950–). · source page ↗
Licence : U.S. Government work, public domain · retrieved on Oct 23, 2026 · SHA-256 1d4c1cdcc5d0…
ERA5 daily maximum 10 m wind gust over Europe and the north-east Atlantic (Copernicus C3S): Hersbach, H., Bell, B., Berrisford, P., et al. (2020). The ERA5 global reanalysis. Quarterly Journal of the Royal Meteorological Society, 146, 1999–2049. Copernicus Climate Change Service, ERA5 post-processed daily statistics on single levels from 1940 to present, Climate Data Store. · doi:10.1002/qj.3803 · source page ↗
Licence : Copernicus licence (CC BY 4.0 compatible): free use with attribution; contains modified Copernicus Climate Change Service information
Hurrell (1995): Hurrell, J. W. (1995). Decadal trends in the North Atlantic Oscillation: regional temperatures and precipitation. Science, 269(5224), 676–679. · doi:10.1126/science.269.5224.676
Licence : Published literature; cited
Donat et al. (2010): Donat, M. G., Leckebusch, G. C., Pinto, J. G., & Ulbrich, U. (2010). Examination of wind storms over Central Europe with respect to circulation weather types and NAO phases. International Journal of Climatology, 30(9), 1289–1300. · doi:10.1002/joc.1982
Licence : Published literature; cited
Pinto et al. (2012): Pinto, J. G., & Raible, C. C. (2012). Past and recent changes in the North Atlantic oscillation. WIREs Climate Change, 3(1), 79–90. · doi:10.1002/wcc.150
Licence : Published literature; cited
Leckebusch et al. (2008): Leckebusch, G. C., Renggli, D., & Ulbrich, U. (2008). Development and application of an objective storm severity measure for the Northeast Atlantic region. Meteorologische Zeitschrift, 17(5), 575–587. · doi:10.1127/0941-2948/2008/0323
Licence : Published literature; cited
Hersbach et al. (2020): Hersbach, H., Bell, B., Berrisford, P., Hirahara, S., Horányi, A., et al. (2020). The ERA5 global reanalysis. Quarterly Journal of the Royal Meteorological Society, 146(730), 1999–2049. · doi:10.1002/qj.3803
Licence : Published literature; cited

NAO and European windstorms The North Atlantic Oscillation shifts storms northwards

What is linked, what is not