Cavanaugh, N. R., M. J. DeFlorio, T. A. O'Brien, A. J. Miller and W. D. Collins, 2016:
Uncorrelated versus independent: Pacific sea surface temperature
variability and the El Nino Southern Oscillation
Monthly Weather Review, sub judice.
Abstract.
We quantitatively demonstrate that non-Gaussianity leads to tail dependence
in the leading principal components (PCs) of Pacific SSTs. We then examine
the independent components (ICs) of Pacific SSTs. Our analysis suggests
the existence of three predominant, statistically independent modes, each of
which resembles the canonical El Nino structure. The IC1 spatial pattern is
nearly identical to the PC1 spatial pattern, suggesting an alternative statistical
definition of the El Nino mode. Unlike PC1, however, IC1 is strongly skewed
and heavy-tailed, consistent with the observed skewness of SST anomalies.
We examine the transient statistics of IC1 in a large GCM ensemble forced
with historical and projected greenhouse gas forcing. Our results do not indicate
additional strengthening in El Nino variability, despite the fact that observed
probabilities of El Nino events have roughly doubled over the 20th
century.
Preprint (pdf)