Abstract

Contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth, referred to as teleconnections in this paper, are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the Northern Hemisphere winter, with time scales on the order of a month or longer. A review of existing literature on the subject reveals the existence of at least four such patterns: the North Atlantic and North Pacific Oscillations identified by Walker and Bliss (1932). a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes, first noted by Lorenz (1951), and what we will refer to as the Pacific/North American pattern, which has been known to operational long-range forecasters in this country since the 1950's.

A data set consisting of NMC monthly mean sea level pressure and 500 mb height analyses for a 15-year period is used as a basis for calculating the temporal correlation coefficients between all possible pairs of grid points. An objective method is used to identify and describe the strongest teleconnection patterns in this correlation matrix. The five leading patterns are compared with, and found to bear some similarity to, the leading eigenvectors of the correlation matrix. Certain of the above calculations are repeated on an independent data set in order to test the reproducibility of the patterns.

The North Atlantic Oscillation and the Pacific/North American patterns are strongly evident in both data acts. The former is associated with fluctuations in the strength of the climatological mean jet stream over the western Atlantic. The Pacific/North American pattern includes a north–south seesaw in the central Pacific somewhat reminiscent of the North Pacific Oscillation mentioned by Walker and Bliss (1932) and Bjerknes (1969), together with centers of action over western Canada and the southeastern United States. Several other teleconnection patterns are revealed by the analysis of the primary data set, but are not found to be as reproducible in the independent data set.

The sea level pressure statistics are dominated by negative correlations between the polar region and temperature latitudes, whereas the 500 mb statistics are dominated by patterns of a more regional scale, which display a nearly equivalent barotropic structure with amplitudes increasing with height. Most of the regional patterns have only one or two well-defined centers of action at the earth's surface, but at mid-tropospheric levels they are more wavelike in appearance and characterized by multiple centers of action; at these levels their structure resembles that of forced stationary wakes on a sphere.

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