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Journal ArticleDOI

Classification, seasonality and persistence of low-frequency atmospheric circulation patterns

01 Jun 1987-Monthly Weather Review (American Meteorological Society)-Vol. 115, Iss: 6, pp 1083-1126
TL;DR: In this article, Orthogonally rotated principle component analysis (RPCA) was used to identify and describe the seasonality and persistence of the major modes of interannual variability.
Abstract: Orthogonally rotated principle component analysis (RPCA) of Northern Hemisphere 1-month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability. The analysis is detailed and comprehensive, in that 1) a high resolution, approximately equal-area 358-point grid is used for the virtually maximum possible 35-year period of record, 2) a positive bias in the NMC data base in the early 1950s in the subtropics is largely eliminated for the first time, and 3) homogeneous, separate analyses of each month of the year are carried out, detailing the mouth-to-month changes in the dominant circulation patterns. Winter results are similar to those of other recent RPCA and teleconnection studies except that some less obvious patterns are identified and further detail of the better-known patterns is provided. Two north-south dipole patterns are found over the Pacific Ocean (West Pacific Oscillation and East Pacific pattern) and over the Atla...

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Journal ArticleDOI
04 Aug 1995-Science
TL;DR: An evaluation of the atmospheric moisture budget reveals coherent large-scale changes since 1980 that are linked to recent dry conditions over southern Europe and the Mediterranean, whereas northern Europe and parts of Scandinavia have generally experienced wetter than normal conditions.
Abstract: Greenland ice-core data have revealed large decadal climate variations over the North Atlantic that can be related to a major source of low-frequency variability, the North Atlantic Oscillation. Over the past decade, the Oscillation has remained in one extreme phase during the winters, contributing significantly to the recent wintertime warmth across Europe and to cold conditions in the northwest Atlantic. An evaluation of the atmospheric moisture budget reveals coherent large-scale changes since 1980 that are linked to recent dry conditions over southern Europe and the Mediterranean, whereas northern Europe and parts of Scandinavia have generally experienced wetter than normal conditions.

7,593 citations

Journal ArticleDOI
TL;DR: In this paper, the authors compare the structure of the interannual variability associated with the ENSO cycle and documents its time history back to 1900, using the leading EOFs of the SST anomaly and anomaly deviation fields in various domains and the associated expansion coefficient (or principal component) time series, which are used to construct global regression maps of SST, sea level pressure (SLP), and a number of related variables.
Abstract: A number of recent studies have reported an ENSO-like EOF mode in the global sea surface temperature (SST) field, whose time variability is marked by an abrupt change toward a warmer tropical eastern Pacific and a colder extratropical central North Pacific in 1976‐77. The present study compares this pattern with the structure of the interannual variability associated with the ENSO cycle and documents its time history back to 1900. The analysis is primarily based on the leading EOFs of the SST anomaly and ‘‘anomaly deviation’’ fields in various domains and the associated expansion coefficient (or principal component) time series, which are used to construct global regression maps of SST, sea level pressure (SLP), and a number of related variables. The use of ‘‘anomaly deviations’’ (i.e., departures of local SST anomalies from the concurrent global-mean SST anomaly) reduces the influence of global-mean SST trends upon the structure of the EOFs and their expansion coefficient time series. An important auxiliary time series used in this study is a ‘‘Southern Oscillation index’’ based on marine surface observations. By means of several different analysis techniques, the time variability of the leading EOF of the global SST field is separated into two components: one identified with the ‘‘ENSO cycle-related’’ variability on the interannual timescale, and the other a linearly independent ‘‘residual’’ comprising all the interdecadal variability in the record. The two components exhibit rather similar spatial signatures in the global SST, SLP, and wind stress fields. The SST signature in the residual variability is less equatorially confined in the eastern Pacific and it is relatively more prominent over the extratropical North Pacific. The corresponding SLP signature is also stronger over the extratropical North Pacific, and its counterpart in the cold season 500-mb height field more closely resembles the PNA pattern. The amplitude time series of the ENSO-like pattern in the residual variability reflects the above-mentioned shift in 1976‐77, as well as a number of other prominent features, including a shift of opposite polarity during the 1940s.

2,409 citations


Cites background from "Classification, seasonality and per..."

  • ...…resembles the most prominent mode of internal variability of the Northern Hemisphere wintertime geopotential height field (Wallace and Gutzler 1981; Barnston and Livezey 1987; Kushnir and Wallace 1989) and the leading mode of coupled variability of the extratropical Pacific SST and Northern…...

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Journal ArticleDOI
TL;DR: The changes over the North Pacific have been well documented and have contributed to increases in temperatures across Alaska and much of western North America and to decreases in sea surface temperatures over the central North Pacific as mentioned in this paper.
Abstract: Large changes in the wintertime atmospheric circulation have occurred over the past two decades over the ocean basins of the Northern Hemisphere, and these changes have had a profound effect on regional distributions of surface temperature and precipitation. The changes over the North Pacific have been well documented and have contributed to increases in temperatures across Alaska and much of western North America and to decreases in sea surface temperatures over the central North Pacific. The variations over the North Atlantic are related to changes in the North Atlantic Oscillation (NAO). Over the past 130 years, the NAO has exhibited considerable variability at quasi-biennial and quasi-decadal time scales, and the latter have become especially pronounced the second half of this century. Since 1980, the NAO has tended to remain in one extreme phase and has accounted for a substantial part of the observed wintertime surface warming over Europe and downstream over Eurasia and cooling in the northwest Atlantic. Anomalies in precipitation, including dry wintertime conditions over southern Europe and the Mediterranean and wetter-than-normal conditions over northern Europe and Scandinavia since 1980, are also linked to the behavior of the NAO. Changes in the monthly mean flow over the Atlantic are accompanied by a northward shift in the storm tracks and associated synoptic eddy activity, and these changes help to reinforce and maintain the anomalous mean circulation in the upper troposphere. It is important that studies of trends in local climate records, such as those from high elevation sites, recognize the presence of strong regional patterns of change associated with phenomena like the NAO.

1,830 citations


Cites background from "Classification, seasonality and per..."

  • ...The difference high minus low NAO index values shows a clear shift in [80] storm track activity with statistically significant enhanced variance over the North Atlantic and northern Europe and reduced activity over the subtropical Atlantic....

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  • ...The similarity between the departure pattern of temperature (Figure 6) and the decadal anomalies over the North Atlantic and surrounding landmasses (Figure 1a) is striking and suggests that the recent temperature anomalies over these regions are strongly related to the persistent and exceptionally strong positive phase of the NAO index since the early 1980s....

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  • ...Interannual and longer time-scale changes in the atmospheric circulation and lower tropospheric temperatures during winter over the North Atlantic and adjacent land areas do not appear to be strongly influenced by tropical SST variability (e.g., Barnett, 1985; Kumar et al., 1994; Graham et al., 1994; Lau and Nath, 1994)....

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  • ...Changes in Storm Tracks and Their Effects on the Mean Flow Changes in the mean circulation patterns over the North Atlantic are accompanied by pronounced shifts in the storm tracks and associated synoptic eddy activity (Rogers, 1990; Hurrell, 1995b; Rogers and Mosley-Thompson, 1995)....

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  • ...Although it is evident throughout the year, it is most pronounced during winter and accounts for more than one-third of the total variance of the SLP field over the North Atlantic (Figure 4, see also Wallace and Gutzler, 1981; Barnston and Livezey, 1987)....

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Journal ArticleDOI
TL;DR: Early instrumental pressure measurements from Gibraltar and the Reykjavik area of Iceland have been used to extend to 1821 the homogeneous pressure series at the two locations In winter the two sites are located close to the centres of action that comprise the North Atlantic Oscillation (NAO) as mentioned in this paper.
Abstract: Early instrumental pressure measurements from Gibraltar and the Reykjavik area of Iceland have been used to extend to 1821 the homogeneous pressure series at the two locations In winter the two sites are located close to the centres of action that comprise the North Atlantic Oscillation (NAO). The extended 'winter half-year' record of the NAO enables recent changes in the record to be placed in the context of the period 1823-1996 The period since the early 1970s is the most prolonged positive phase of the oscillation and the late 1980s and early 1990s is the period with the highest values (strongest westerlies) The winter of 1995-1996 marked a dramatic switch in the index, with the change from 1994-1995 being the greatest change recorded from one year to the next since the series began in 1923. (The extended Gibraltar and Reykjavik monthly pressures and the NAO series can be found on the Climatic Research Unit home page. www.cru.uea-ac.uk.

1,717 citations

Book ChapterDOI
TL;DR: The North Atlantic Oscillation (NAO) is one of the most prominent and recurrent patterns of atmospheric circulation variability as discussed by the authors, and it dictates climate variability from the eastern seaboard of the United States to Siberia and from the Arctic to the subtropical Atlantic, especially during boreal winter.
Abstract: The North Atlantic Oscillation (NAO) is one of the most prominent and recurrent patterns of atmospheric circulation variability. It dictates climate variability from the eastern seaboard of the United States to Siberia and from the Arctic to the subtropical Atlantic, especially during boreal winter, so variations in the NAO are important to society and for the environment. Understanding the processes that govern this variability is, therefore, of high priority, especially in the context of global climate change. This review, aimed at a scientifically diverse audience, provides general background material for the other chapters in the monograph, and it synthesizes some of their central points. It begins with a description of the spatial structure of climate and climate variability, including how the NAO relates to other prominent patterns of atmospheric circulation variability. There is no unique way to define the spatial structure of the NAO, or thus its temporal evolution, but several common approaches are illustrated. The relationship between the NAO and variations in surface temperature, storms and precipitation, and thus the economy, as well as the ocean and ecosystem responses to NAO variability, are described. Although the NAO is a mode of variability internal to the atmosphere, indices of it exhibit decadal variability and trends. That not all of its variability can be attributed to intraseasonal stochastic atmospheric processes points to a role for external forcings and, perhaps, a small but useful amount of predictability. The surface, stratospheric and anthropogenic processes that may influence the phase and amplitude of the NAO are reviewed.

1,712 citations


Cites background or result from "Classification, seasonality and per..."

  • ...The NAO is the only teleconnection pattern evident throughout the year in the NH [ Barnston and Livezey , 1987 ] ....

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  • ..., Barnston and Livezey , 1987 ; Kushnir and Wallace , 1989 ] ....

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  • ...…the boreal winter months ; however , throughout the year the leading pattern of variability is characterized by a surface pressure dipole , and thus may be viewed as the NAO , although the spatial pattern is not stationary [ Barnston and Livezey , 1987 ; Hurrell and van Loon , 1997 ; Portis et al ....

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  • ...…correspond to the negative and positive phases of the NAO , while the third and fourth regimes display a strong anticyclonic ridge and trough , respectively , off western Europe and bear some resemblance to the EA teleconnection pattern [ Wallace and Gutzler , 1981 ; Barnston and Livezey , 1987 ] ....

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  • ...The second EOF , which resembles the East Atlantic ( EA ) pattern during the winter and spring months [ Wallace and Gutzler , 1981 ; Barnston and Livezey , 1987 ] , generally accounts for about 15% of the total SLP variance ( not shown ) ....

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