Classification, seasonality and persistence of low-frequency atmospheric circulation patterns

The seasonality and persistence of the major modes of interannual variability in the low-frequency atmospheric circulation were studied using orthogonally rotated principle component analysis (RPCA) of Northern Hemisphere 1-month mean 700 mb heights. The twice-daily data for the 1950-1984 period were used. Winter results are similar to those of other recent RPCA and teleconnection studies. The strongest summer pattern is the North Atlantic Oscillation, which is also the strongest winter pattern; it systematically contracts northward in summer and expands southward in winter, being the only pattern found for every month of the year. The robustness of the RPCA results was examined through consistency with results of other studies and of adjacent month solutions within this study, as well as by replicating the results using 3-month and 10-day means of 700-mb height. It is concluded that the RPCA method provides a physically meaningful and statistically stable product with the simplicity of teleconnection patterns but with superior pattern choice and depiction.