The Super El Niño–Polar Vortex Paradox QBO Modulation and a Testable Hypothesis for Winter 2026/27

Mehmet Can TANYERI

The absence of major midwinter sudden stratospheric warmings (SSWs) during the three strongest El Niño winters in the instrumental record—1982/83, 1997/98, and 2015/16—poses an open question at the high-amplitude end of the canonical ENSO–stratosphere pathway. Motivated by the exceptionally strong El Niño developing in 2026, this study re-examines that relationship using publicly available ONI, NAO, AO, and QBO indices (1951–2026) together with major SSW event statistics derived from the NOAA SSW Compendium (1958–2024). Three results emerge. First, the ENSO–NAO relationship shows contrasting intraseasonal tendencies: a positive association in November–December (r = +0.21) and a negative association in January–March (r = −0.12). Although the individual confidence intervals include zero, a paired bootstrap indicates a non-zero difference between the two periods (Δr = 0.33; 95% CI: 0.08–0.56), while the full-winter mean largely obscures this structure. Second, the QBO signal is weak in seasonal-mean surface correlations but clearer in event statistics: the probability of at least one major SSW is approximately 1.7 times higher during easterly-QBO than westerly-QBO winters (risk ratio 1.71; 95% CI: 0.99–2.96; Fisher p = 0.071), with this contrast substantially reduced during El Niño winters. Third, all three super El Niño winters defined by ONI ≥ +2.0 occurred under westerly-QBO conditions and lacked a major midwinter SSW. Given the sample size (n = 3), this pattern is treated as a testable hypothesis rather than evidence of causation. The evolving 2026/27 winter therefore provides a prospectively defined observational test of competing QBO-modulation and nonlinear ENSO–stratosphere explanations, with implications for downward coupling, intraseasonal NAO evolution, and eastern Mediterranean winter circulation.