A Striking Example of the Atmosphere's Leading Traveling Pattern

Abstract

Conventional and complex empirical orthogonal function (EOF) techniques show that for at least four months during the fall and winter of 1979/80 a large-amplitude, large-scale, traveling flow anomaly existed in the troposphere and stratosphere. This feature evolved in a cyclic manner, exhibiting an average period of about 23 days. Its phase propagation was toward the west, while its amplitude was concentrated in a broad envelope centered over Canada. The phenomenon was equivalent barotropic in the troposphere and increased in amplitude with altitude. It represented about 25% of the variance of geopotential heights in the troposphere and stratosphere for the months of November through March. The meridional and zonal structure of the zonal wavenumber one component of the traveling anomaly is similar to that of the theoretical 16-day wave. However, it is distinct from that theoretical mode in that its period is longer and, in the troposphere, zonal wave two makes a large contribution to its structure. Complex EOF analysis of many years of wintertime daily flow maps suggests that the long-lived traveling feature of 1979/80 is simply a striking example of the leading traveling pattern in the troposphere/stratosphere during the northern winter. Except for an isolated peak at about 25 days, this leading complex EOF has a red temporal spectrum.