Evidence of a relation between El NIno and QBO, and for an El Nino in 1991–92

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Abstract

The possibility of a relation between El Nino and the quasi-biennial oscillation (QBO) in equatorial low stratosphere is investigated. Based on the 9 El Ninos and 16 quasi-biennial variations in 50 mb zonal wind at Singapore between 1954 and 1991, the sea-surface temperature (SST) in eastern equatorial Pacific has averaged nearly 0.5°C warmer one season after QBO east-wind maximum than 4–5 seasons before and after this maximum, but this difference in temperature is not statistically significant. Because of the difference in period of these oscillations (2 1/4 years on average in the case of the QBO, about 4 1/2 years on average in the case of El Nino), there can not be an El Nino associated with every QBO east-wind maximum, i.e., any relation between El Nino and QBO east-wind maximum has to “skip a beat” on occasion. This paper presents evidence for a pattern in this “skip”, such that an El Nino is associated with a QBO east-wind maximum except when the El Nino associated with the previous east-wind maximum was a major one and/or the SST maximum followed the previous east-wind maximum by a few seasons. On the basis of this pattern an El Nino would not have been expected in 1989 or 1990 (because the El Nino of 1987 was a major one) but would be expected in 1991 or 1992 in association with the QBO east-wind maximum projected to occur in the northern summer of 1992. Comparison with earlier “skips” shows that an El Nino would be most likely before the next east-wind maximum, or at the end of 1991. Because it would follow the aborted warm event of 1990, it probably would not be a major El Nino.

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