Vertical Structure of Wintertime Teleconnection Patterns

Abstract

Orthogonal rotated principal component analysis of the wintertime, Northern Hemisphere, 5-day mean sea level pressure field yielded five modes which are of some dynamical interest. One can be identified with the well-known North Atlantic Oscillation and another with the Pacific/North American pattern. Three of the other modes are highly baroclinic in the sense that their sea level pressure patterns and their associated 500 mb height patterns are different in shape and opposite in polarity over substantial areas. These more baroclinic patterns attain their largest amplitudes in the vicinity of the Himalayas and Rockies. Their spatial patterns evolve very differently in the lower and middle troposphere: the sea level pressure patterns exhibit a distinctive eastward and/or equatorward phase propagation, parallel to contours of surface elevation, along the northern and/or eastern side of the mountain ranges, while the corresponding 500 mb patterns evolve in a manner consistent with the concept of Rossby wave dispersion. It is hypothesized that the phase propagation of the sea level pressure pattern is due, in part, to the equivalent-beta effect responsible for the terrain slope. These highly baroclinic patterns appear to be associated with the low-temporal correlations between 1000 and 500 mb height and for the deep equatorward penetration of wintertime cold air outbreaks observed along the lee slopes of the major mountain ranges.