Relative changes in consistency of winter surface air temperature during ENSO events across western Canada

Previous studies established a connection between El Niño–Southern Oscillation (ENSO) and winter surface air temperature (SAT) in western Canada. This paper compares the year-to-year variation of winter SAT across the region under ENSO and ENSO-free (neutral) conditions. The comparison is based on the ratio of the difference between the standard deviation (σ) of mean monthly ENSO SAT signals and σ of mean monthly ENSO-free signal to σ of the mean monthly ENSO-free SAT. The signal is defined as the difference between mean monthly temperature during ENSO and the mean monthly ENSO-free SAT. During El Niño December and February, SAT variability is lower by 13 and 18 percent, respectively, than in an equivalent ENSO-free period. In January, variability under El Niño is 24 percent higher than its ENSO-free counterpart. During La Niña, decrease in variability is observed during all three months by 3, 21 and 24 percent from December through February, respectively. The lower variability experienced in five of the six ENSO months underscores greater winter SAT consistency during ENSO. Variability difference is lowest along the Pacific Coast and highest in the Prairies. Except in January under El Niño, those areas, which normally experience SAT variability higher than the regional average (mostly the Prairies), achieve greater temperature stability (reduced variability) during ENSO. January variability is higher in the Prairies during El Niño. In general, in western Canada, SAT regimes look more similar under ENSO than they do under ENSO-free conditions. ENSO tends to stabilise winter temperatures more effectively in the Prairies than it does along the coast.