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: When the quasi-biennial oscillation (QBO) is in its easterly phase, planetary waves are steered towards the pole and brake the vortex more: the winter is more disturbed, with more sudden warmings. This is the Holton and Tan (1980) relation, found in observations but not in every decade (Anstey and Shepherd, 2014).

No data imported yet. Run: php bin/console --no-debug app:analysis:compute qbo-vortex

Method and sources

QBO: equatorial zonal wind at 30 hPa (NOAA PSL), mean of October and November. Vortex: zonal-mean zonal wind at 60° N and 10 hPa from NASA’s MERRA-2/GEOS analyses, mean of the following December to February. One point per winter since 1979/80. Lag fixed in advance; Pearson, effective sample size of Bretherton et al., 3-year block bootstrap; test repeated after removing variations longer than 21 years. The classic test uses the QBO at 40–50 hPa; only the 30 hPa series is imported here.

Reading this result

The expected link shows: r ≈ 0.4, as clear after removing trends. In the third of winters with the most easterly QBO, the vortex averages about 25 m/s, against about 35 m/s in the most westerly third. An easterly QBO does not force a sudden warming, though: it raises its odds, and the relation varies with decades and solar activity. 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

Quasi-biennial oscillation, 30 hPa equatorial zonal wind (NOAA PSL): NOAA PSL climate index QBO: zonal-mean zonal wind at 30 hPa at the equator from the NCEP/NCAR reanalysis (Kalnay, E., et al., 1996, Bull. Amer. Meteor. Soc., 77, 437–471). · doi:10.1175/1520-0477(1996)077<0437:TNYRP>2.0.CO;2 · source page ↗
Licence : U.S. Government work, public domain; cite NOAA PSL and the NCEP/NCAR reanalysis (Kalnay et al., 1996) · retrieved on Oct 25, 2026 · SHA-256 2d06ed3d14b2…
Northern stratosphere: polar vortex, polar-cap temperature and wave heat flux, daily (NASA GSFC, MERRA-2 and GEOS FP): NASA GSFC Atmospheric Chemistry and Dynamics Laboratory, Annual Meteorological Statistics (Northern Hemisphere), from MERRA-2 (Gelaro, R., et al., 2017, Journal of Climate, 30, 5419–5454) and GEOS FP. · doi:10.1175/JCLI-D-16-0758.1 · source page ↗
Licence : NASA data, no restriction on use (NASA Earth science data policy); cite MERRA-2 (Gelaro et al., 2017). The GEOS forecasts are experimental and given for research · retrieved on Nov 2, 2026 · SHA-256 7df51d62c772…
Holton et al. (1980): Holton, J. R., & Tan, H.-C. (1980). The influence of the equatorial quasi-biennial oscillation on the global circulation at 50 mb. Journal of the Atmospheric Sciences, 37(10), 2200–2208. · doi:10.1175/1520-0469(1980)037<2200:TIOTEQ>2.0.CO;2
Licence : Published literature; cited
Anstey et al. (2014): Anstey, J. A., & Shepherd, T. G. (2014). High-latitude influence of the quasi-biennial oscillation. Quarterly Journal of the Royal Meteorological Society, 140(678), 1–21. · doi:10.1002/qj.2132
Licence : Published literature; cited

QBO and the polar vortex When the equatorial stratospheric wind blows from the east, is the following winter’s polar vortex weaker?

What is linked, what is not