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Spatial and temporal variations of the january circumpolar vortex over the northern hemisphere
Author(s) -
Davis Robert E.,
Benkovic Stephanie R.
Publication year - 1994
Publication title -
international journal of climatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.58
H-Index - 166
eISSN - 1097-0088
pISSN - 0899-8418
DOI - 10.1002/joc.3370140406
Subject(s) - teleconnection , circumpolar star , climatology , northern hemisphere , principal component analysis , polar vortex , geology , vortex , southern hemisphere , latitude , common spatial pattern , geography , geodesy , oceanography , meteorology , el niño southern oscillation , mathematics , statistics , troposphere
Temporal and spatial variations of the Northern Hemisphere's circumpolar vortex are analysed for each January from 1947 to 1990. Our data set is developed by digitizing the 546‐dam isoheight from 50‐kPa charts and recording the latitude of this contour at each 10° meridian. Principal components analysis is applied to the resulting 699‐day by 36‐variable matrix to examine the temporal and spatial evolution of the circumpolar vortex. The first principal component is comparable to the Pacific‐North America (PNA) teleconnection pattern. Over the 44 Januarys analysed, the frequency of the positive phase of the PNA pattern has increased. Principal component 2 is similar to the Eurasian pattern and varies between axially asymmetric zonal flow and a three‐wave pattern centred over the pole. The asymmetric pattern, which is characterized by higher heights over western Europe and Scandinavia, has increased in frequency over the study period. With the third principal component, which is similar to the East Atlantic teleconnection pattern, the strength of the Icelandic Low varies markedly. Time series of scores on the third component indicate that 50‐kPa heights over the North Atlantic are lower over the past 20 years. The fourth principal component is related to vortex area. The northern vortex has occupied a more expanded position since the mid‐1960s. These first four principal components explain half of the total variance in the data. In toto , these results indicate that the January circumpolar vortex has expanded over the past two decades. Most of the expansion has occurred in the vicinity of the Aleutian Low and has produced increased meridional flow throughout much of the Western Hemisphere. This circulation change could account for the observed increased occurrence of warm air masses in winter over eastern Alaska and western Canada, increased cyclone occurrence in the north‐western Atlantic, and both the increased frequency of Arctic outbreaks and declining temperatures in the south‐eastern USA. The overall vortex expansion is contrary to general circulation model forecasts that predict a decrease in the meridional temperature gradient of the Northern Hemisphere as trace‐gas concentrations increase.