Principal Components of the North American Summer Temperature Field and the Antecedent Oceanic and Atmospheric Conditions

Abstract

The first two principal components of the North American summer temperature field are examined in reference to the antecedent oceanic and atmospheric conditions of the Northern Hemisphere, and are shown to have considerable prognostic value. The planetary scale circulation associated with the thermal field over the western tropical Pacific and the ocean-atmosphere interaction over the central North Pacific-Aleutian region appear to be important in determining the summer surface temperature pattern over North America.
The examination of the cross-correlation patterns and their temporal variations indicates that the anomalous SST fields in the North Pacific in the preceding seasons are closely related to the temperature field in North America in the following summer. The negative anomalous departures in the central North Pacific SST precede the high first component of the North America summer temperature field, and the positive departures precede the low first component. For the dominance of the first component in the mid-western United States, this directly infers the predictability of the summer temperature in the region. The signal of anomalous SST departures appears early in the preceding fall, reaches its maximum in the winter and spring, and diminishes toward the summer. An El Nino mode is also detected for the North American summer temperature, indicating the impact of ENSO on the general circulation beyond the winter half of the year.