The ENSO signal in the polar stratosphere is of practical interest because of its possible effects on surface weather and climate through the North Atlantic Oscillation. It has been suggested that major El Ninos may produce unusually cold winters in Europe, and that the stratosphere may play a role in this effect. Some models predict that El Nino should produce warming in the Arctic stratosphere in winter, but a significant signal has often been hard to find in the real world, in part because of the short length of the temperature records used and the confounding influence of the quasi-biennial oscillation (QBO).

Most recent work on this topic uses reanalysis results rather than actual observations. Using radiosonde data instead of reanalyses, we find a significant ENSO warming signal in the Arctic winter stratosphere extending as low as 300 mb, as well as a significant cooling response in the tropical stratosphere. Like the stratospheric ENSO signal found in models, the observed Arctic winter signal of more than 4 K is largely confined to February, and is not seen in winters when the quasi-biennial oscillation is in the easterly wind phase. Correlations between ENSO and 100 mb Arctic temperatures in winter are around 0.4 after removal of the effect of the QBO. Our results support the claim that the effect of ENSO on winter stratospheric temperatures in the Arctic may be comparable in size to that of the QBO.