A Reexamination of the Northern Hemisphere Sea Level Pressure Variability by the Independent Component Analysis

The results of the empirical orthogonal function (EOF) analysis applied to the sea-level pressure (SLP) variability in the extratropical Northern Hemisphere is reexamined from viewpoint of statistical independence. For this purpose, “Independent Component Analysis” is introduced, whose effectiveness is demonstrated in its application to a set of simple hypothetical models. While its application to stratospheric variability confirms the relevance of the EOF analysis, its application to the SLP suggests that the two leading components of the EOF analysis are likely superpositions of two statistically independent signals. One of them represents a seesaw-like relationship in the intensities between the surface Aleutian and Icelandic lows, and the other is characterized by a significant long-term trend with the cold ocean-warm land pattern.