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Southern Oscillation Processes and the North Atlantic
and Arctic Oscillations
I. I. Mokhova and D. A. Smirnovb
a Oboukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Pyzhevskii per. 3, Moscow, 119017 Russia
e-mail: mokhov@ifaran.ru
b Institute of Radio Engineering and Electronics (Saratov Branch), Russian Academy of Sciences,
Zelenaya ul. 38, Saratov, 410019 Russia
e-mail: smirnovda@info.sgu.ru
Received November 9, 2005
Abstract—On the basis of the nonlinear techniques for the estimation of coupling between oscillatory systems
from time series, we investigate the dynamics of climatic modes characterizing global and Northern Hemi-
sphere (NH) processes. The North Atlantic Oscillation (NAO) and Arctic Oscillation indices and the El Niño–
Southern Oscillation (ENSO) indices are analyzed in terms of the most reliable data from 1950 through 2004
and earlier data since the 19th century. These indices characterize changes in NH atmospheric pressure (specif-
ically, sea-level pressure in the North Atlantic and NH extratropical latitudes as a whole) and in equatorial
Pacific sea-surface temperature and sea-level pressure to which the strongest variations of global surface tem-
perature and global climate on interannual time scales and of regional climatic anomalies in the NH are linked.
The methods used are based on phase-dynamics modeling and nonlinear prediction models (a nonlinear version
of Granger causality). From both methods and various ENSO indices, the inference about the ENSO effect on
the NAO during the latter half of the 20th century and in the early 21st century is made with confidence prob-
ability of at least 0.95. The influence is characterized by a time delay of about two years. No inverse influence
is found with a similar degree of reliability. Results of estimating the coupling between the ENSO and the NAO
depend on the type of index that is used to describe the NAO. The ENSO effect on the NAO is detected with
sufficient confidence when the NAO index is chosen to be a larger scale characteristic. However, when a more
local index of the NAO is used, no statistically significant coupling to the ENSO is found. Increasing the length
of the analyzed ENSO and NAO series (over more than 100 yr) does not lead to any more reliable detection of
coupling. Analysis of the data for different time intervals during 1950–2004 has revealed a strengthening of the
ENSO effect on the NAO, although this inference is not reliable.
DOI: 10.1134/S0001433806050069
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