Possible Causes of Anomalies in Seasonal Mean Circulation Patterns during the 1982–83 El Niño Event

Abstract

For six consecutive seasons around the 1982?83 El Niño event the relation between observed anomalies in atmospheric circulation patterns and anomalies in various forcing mechanisms is diagnosed. A linear model is used in an attempt to simulate atmospheric anomalies as a stationary response to observed anomalies in tropical diabatic heating, mountain and transient eddy effects. The response to forcing by transient eddies is large for all seasons and is significantly correlated with observed anomalies. To what extent observed anomalous transient eddy activity is related to anomalous conditions at the earth?s surface can not be deduced from these experiments. The midlatitude effect of tropical heating are found to be small oven during the mature phase of the 1982?83 warming event. However these results are critically dependent on the exact location of the zero wind line. The effect of the orography caused by observed anomalies in zonal mean westerly winds is small in general. In one season, when El Niño is at its maximum, the effect is comparable in magnitude to that of the transient eddies.