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

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.