Physical Oceanography, Vol.
NORTH ATLANTIC OSCILLATION: DESCRIPTION, MECHANISMS,
AND INFLUENCE ON THE EURASIAN CLIMATE
A. B. Polonskii,
D. V. Basharin,
E. N. Voskresenskaya,
and S. Worley
The present work is devoted to the characteristic of the North-Atlantic Oscillation and the analy-
sis of the state-of-the-art of this problem. In the survey section of the work, we deal with the fol-
lowing issues: the definition of the North Atlantic and Arctic Oscillations, their interaction with
oceanic processes, and their influence on the variations of climate in Eurasia. In addition, by us-
ing the COADS (Comprehensive Ocean Atmosphere Data Set) data and the data on the dis-
charge of European and Asian rivers, we establish some new original results. It is confirmed that
the anomalies of the sea-surface temperature are consequences of the integral response of the
ocean to the preceding atmospheric actions and that the spectra of these anomalies are character-
ized by the presence of significant peaks within the band of periods of
yr. These periods
correspond to inherent oceanic variability. The atmospheric response manifests itself in the form
of abnormal conditions over the catchment areas of European and Asian rivers, which leads to
oscillations of their discharges. As a result of the intensification of the North Atlantic Oscillation
and the displacement of the centers of action of the atmosphere in the 60–90s of the previous
century, the influence of this oscillation on the climatic conditions in the European-Asian region
became more intense.
Introduction. Basic Definitions
The general atmospheric circulation in the North Atlantic is characterized by the following basic specific
features : Trade winds are located between the region of high pressure at subtropical latitudes (Azores High)
and the region of low pressure in the vicinity of the intratropical convergence zone [ITCZ (tropical depression)].
The drop of pressure between these zones characterizes the intensity of trade winds. Due to the asymmetry of
the distribution of land area over the Globe, the subtropical regions of high pressure in the Northern and South-
ern Hemispheres and the zone of tropical depression are located asymmetrically about the equator. In the Atlan-
tic Ocean, these centers of atmospheric action (CAA) are shifted northward (by several degrees). Moreover, the
indicated shift is more pronounced in the east part of the Atlantic than in its west part. As a result, on the aver-
age (over a year), the axis of the ITCZ is located in the Northern Hemisphere. It is inclined to latitudinal circles
and, thus, lies between
15°W. West winds are predominant to
the north of the Azores High and up to about
a region of low pressure is formed near Iceland
(Iceland Low). The gradient of pressure between the Azores High and Iceland Low specifies the intensity of
west transfer at mid latitudes and weather over the European continent. The change in the direction of zonal at-
mospheric circulation from eastward in tropics to westward at middle latitudes is caused by the instability of the
Hadley cell at mid latitudes. This instability leads to the development of cyclones and anticyclones in which the
wind velocity is much higher than the velocity of the mean flow. The North-Atlantic cyclones traveling in the
northeast direction prove to be especially intense. They carry relatively warm and humid air from the regions of
the Atlantic close to the Gulf Stream and North-Atlantic Current to Europe and form, at middle latitudes, the
predominant westerly over the European continent .
Marine Hydrophysical Institute, Ukrainian Academy of Sciences, Sevastopol.
USA National Center of Atmospheric Research (NCAR), Boulder, CO, USA.
Translated from Morskoi Gidrofizicheskii Zhurnal, No.
42–59, March–April, 2004. Original article submitted February 4, 2003;
revision submitted February 11, 2003.
96 0928-5105/04/1402–0096 © 2004 Plenum Publishing Corporation