Characteristic Patterns of Variability of Sea Level Pressure in the Northern Hemisphere

Abstract

Abstract Seasonal and annual mean sea level pressures for the Northern Hemisphere have been analyzed to determine the dominant modes of interannual and longer period variability using monthly sea level pressure analyses as revised by Trenberth and Paolino (1980). Empirical orthogonal function (EOF) analysis is used to reveal the modes which explain most of the variance for the period 1925–77. In winter, Kutzbach's (1970) EOF 1 for January remains the dominant mode and a closely related pattern dominates all seasons and the annual means. Although there are differences in detail in each season, the dominant mode is basically a high-latitude zonal-index-type pattern with departures in pressure at high latitudes corresponding to anomalies of opposite sign in low latitudes. EOF 1 is linked to the North Atlantic Oscillation, but the north–south fluctuations in mass also occur in the Pacific and, to a lesser extent, elsewhere. Time series associated with this pattern have highly significant spectral peaks at the...