Content area
Full Text
Abstract: This paper demonstrates that an annular mode can be constructed from the combination of the North Atlantic Oscillation (NAO) and the Pacific/North American (PNA) patterns. The quasi-annularity, meridional dipole and vertical barotropy of the constructed annular mode resemble those of the Atlantic Oscillation (AO) pattern. It is also a dominant mode in terms of the variance contribution. Moreover, its temporal correlation with the AO is quite strong. This new annular mode has the advantage over the AO in that it incorporates a large portion of the PNA and makes the center of action in the Pacific stronger and more physically relevant than that of the AO. Or, more generally, it may be regarded as a physical mode unlike the AO. The results of this study also indicate the NAO-PNA perspective contains most of the information of the AO, whereas the AO perspective only contains about half of the information of the NAO-PNA. Consequently, the NAO-PNA perspective is regarded by the authors to be more comprehensive than that of the AO.
Key words: annular mode; NAO-PNA perspective; AO
CLC number: P434 Document code: A doi: 10.3969/j.issn.1006-8775.2010.01.009
(ProQuest: ... denotes formulae omitted.)
The Arctic Oscillation (AO), the North Atlantic Oscillation (NAO) and the Pacific-North American pattern (PNA) are the three most prominent modes of the winter climate variability of the Northern Hemisphere extra-tropics (Thompson and Wallace[6,7], Wallace[11], Walker and Bliss[9], Wallace and Gutzler[10]). The AO, also known as the Northern Hemisphere Annular Mode (NAM), is usually regarded as a result of wave-zonal interaction on the hemispheric scale. This wave-zonal interaction is particularly characterized by 1) the interaction between the synoptic eddy and the North Atlantic jet in the troposphere, 2) the interaction between the synoptic eddy and the Northern Pacific jet, and 3) the interaction between upward-propagating quasi-stationary waves and the polar vortex in the stratosphere. Point 3) to some extent depends on points 1) and 2), so only the former two points are the most basic. On these issues, one can refer to a review by Thompson, Lee and Baldwin[8]. Generally, the AO, represented by the leading Empirical Orthogonal Function (EOF) of monthly mean sea surface pressure (SLP), does have two centers of action over both of the ocean basins. However, the following facts...