Physical Processes Involved in the 1988 Drought and 1993 Floods in North America

Abstract

Abstract An analysis of the spring–summer 1988 drought and 1993 floods over North America reveals a reversal in the sign of anomalies in several fields. Large sea surface temperature anomalies of opposite signs existed in the tropical Pacific with strong La Nina conditions in 1988 and a mature El Nino in 1993. The distribution of tropical convection in the convergence zones and associated latent heating of the atmosphere were correspondingly altered, implying a large-scale switch in the anomalous tropical heating and forcing of extratropical quasi-stationary waves in the atmosphere, influencing the subtropical jet stream over the North Pacific and across North America. In 1988 the jet stream and the closely related storm track of high-frequency disturbances in the upper troposphere were displaced into Canada well north of the normal location—the farthest north of any year from 1979 to 1993. In 1993 a broader jet stream and the storm track were displaced well south of normal to a more springlike location a...