Variations of Midlatitude Transient Dynamics Associated with ENSO

The winter response of the atmosphere to El Nino events in the Pacific is studied both from a 14-year integration of the Center for Ocean–Land–Atmosphere GCM using observed SSTs from January 1979 to February 1993 and from the corresponding analyses of ECMWF. Emphasis is put on the shift in the high-frequency transients that define the Pacific storm track during warm events. Warm and normal ensembles are defined on the basis of the GCM’s diabatic heating field in the tropical Pacific, which falls in one of two states. During the winters of 1982/83, 1986/87, and 1991/92, the heating averaged between 6°S and 6°N lies in the range of 100–200 W m−2 all the way across the basin. The remaining 10 “normal” years all show no large tropical diabatic heating anomalies in the mid or eastern Pacific. The difference between warm and normal ensembles for the mean fields of zonal wind u and height z indicates an eastward and equatorward extension of the midlatitude Pacific jet, associated with a similar extensio...