North Atlantic Oscillation, East Atlantic pattern and jet variability since 1685

2020 ◽  
Author(s):  
Javier Mellado-Cano ◽  
David Barriopedro ◽  
Ricardo García-Herrera ◽  
Ricardo Trigo ◽  
Armand Hernández
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Jet Stream ◽  
East Atlantic ◽  
East Atlantic Pattern ◽  
The North ◽  
The North Atlantic ◽  
Jet Variability ◽  
Instrumental Records

<p>Instrumental records of the leading patterns of variability are short, hampering a proper characterization of the atmospheric circulation beyond the mid-19<sup>th</sup> century. In this work, recently published in Mellado-Cano et al. (2019), we present the longest (1685-2014) observational-based records of winter NAO and East Atlantic (EA) indices as well as estimates of the North Atlantic eddy-driven jet stream for the same period. They are inferred from wind direction observations over the English Channel assembled in monthly indices of the persistence of the wind in the four cardinal directions. Our NAO and EA series are significantly correlated with traditional indices, showing comparable skill to that obtained between some instrumental indices, and capture their main signatures on European temperature and precipitation.</p><p>By identifying winters with different combinations of NAO/EA phases in the 20<sup>th</sup> century, our results highlight the additional role of EA in shaping the North Atlantic action centers and the European climate responses to NAO. The joint effects of NAO and EA cause European surface climate anomalies that can substantially differ from their canonical signatures, meaning that a proper characterization of regional climates cannot be achieved by the NAO alone. The EA interference with the NAO signal is stronger in precipitation than in temperature and affects areas with strong responses to NAO such as Greenland and the western Mediterranean.</p><p>The time series display large variability from interannual to multidecadal time scales, with e.g. positive (negative) EA (NAO) phases dominating before 1750 (during much of the 19<sup>th</sup> century). The last three centuries uncover multidecadal periods characterized by specific NAO/EA states and substantial variability in the North Atlantic jet stream, thus providing new evidences of the dynamics behind some outstanding periods. Transitions in the NAO/EA phase space have been recurrent and pin down long-lasting anomalies, such as the displacement of the North Atlantic action centers in the late 20<sup>th</sup> century, besides some disagreements between historical NAO indices.</p><p>Mellado-Cano, J., D. Barriopedro, R. García-Herrera, R.M. Trigo, 2019: Examining the North Atlantic Oscillation, East Atlantic pattern and jet variability since 1685. Journal of Climate. doi: https://doi.org/10.1175/JCLI-D-19-0135.1</p>

scholarly journals Monthly Rainfall Signatures of the North Atlantic Oscillation and East Atlantic Pattern in Great Britain

Atmosphere ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 1533
Author(s):  
Harry West ◽  
Nevil Quinn ◽  
Michael Horswell
Keyword(s):  
Great Britain ◽  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Monthly Rainfall ◽  
East Atlantic ◽  
East Atlantic Pattern ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation ◽  
Regional Rainfall

Atmospheric-oceanic circulations (teleconnections) have an important influence on regional climate. In Great Britain, the North Atlantic Oscillation (NAO) has long been understood as the leading mode of climate variability, and its phase and magnitude have been found to influence regional rainfall in previous research. The East Atlantic Pattern (EA) is also increasingly recognised as being a secondary influence on European climate. In this study we use high resolution gridded rainfall and Standardised Precipitation Index (SPI) time series data for Great Britain to map the monthly rainfall signatures of the NAO and EA over the period January 1950–December 2015. Our analyses show that the influence of the two teleconnections varies in space and time with distinctive monthly signatures observed in both average rainfall/SPI-1 values and incidences of wet/dry extremes. In the winter months the NAO has a strong influence on rainfall and extremes in the north-western regions. Meanwhile, in the southern and central regions stronger EA-rainfall relationships are present. In the summer months opposing positive/negative phases of the NAO and EA result in stronger wet/dry signatures which are more spatially consistent. Our findings suggest that both the NAO and EA have a prominent influence on regional rainfall distribution and volume in Great Britain, which in turn has implications for the use of teleconnection forecasts in water management Decemberision making. We conclude that accounting for both NAO and EA influences will lead to an enhanced understanding of both historic and future spatial distribution of monthly precipitation.

scholarly journals Examining the North Atlantic Oscillation, East Atlantic Pattern, and Jet Variability since 1685

2019 ◽  
Vol 32 (19) ◽  
pp. 6285-6298 ◽  
Author(s):  
Javier Mellado-Cano ◽  
David Barriopedro ◽  
Ricardo García-Herrera ◽  
Ricardo M. Trigo ◽  
Armand Hernández
Keyword(s):  
Nineteenth Century ◽  
Twentieth Century ◽  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Jet Stream ◽  
East Atlantic ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract Recent studies have stressed the key role of the east Atlantic (EA) pattern and its interactions with the North Atlantic Oscillation (NAO) in Euro-Atlantic climate variability. However, instrumental records of these leading patterns of variability are short, hampering a proper characterization of the atmospheric circulation beyond the mid-nineteenth century. In this work, we present the longest (1685–2014) observational-based records of winter NAO and EA indices as well as estimates of the North Atlantic eddy-driven jet stream speed and latitude for the same period. The time series display large variability from interannual to multidecadal time scales, with, for example, positive (negative) EA (NAO) phases dominating before 1750 (during much of the nineteenth century). By identifying winters with different combinations of NAO/EA phases in the twentieth century, our results highlight the additional role of EA in shaping the North Atlantic action centers and the European climate responses to NAO. The EA interference with the NAO signal is stronger in precipitation than in temperature and affects areas with strong responses to NAO such as Greenland and the western Mediterranean, which prevents simplistic relationships of natural proxies with NAO. The last three centuries uncover multidecadal periods dominated by specific NAO/EA states and substantial interannual-to-centennial variability in the North Atlantic jet stream, thus providing new evidence of the dynamics behind some outstanding periods. Transitions in the NAO/EA phase space have been recurrent and pin down long-lasting anomalies, such as the displacement of the North Atlantic action centers in the late twentieth century, besides some disagreements between NAO indices.

scholarly journals Are the Winters 2010 and 2012 Archetypes Exhibiting Extreme Opposite Behavior of the North Atlantic Jet Stream?*

2013 ◽  
Vol 141 (10) ◽  
pp. 3626-3640 ◽  
Author(s):  
João A. Santos ◽  
Tim Woollings ◽  
Joaquim G. Pinto
Keyword(s):  
North Atlantic ◽  
Jet Stream ◽  
Climate Conditions ◽  
Rossby Wave Breaking ◽  
The North ◽  
Westerly Jet ◽  
Opposite Behavior ◽  
The North Atlantic ◽  
Jet Variability ◽  
North Atlantic Jet

Abstract The atmospheric circulation over the North Atlantic–European sector experienced exceptional but highly contrasting conditions in the recent 2010 and 2012 winters (November–March, with the year dated by the relevant January). Evidence is given for the remarkably different locations of the eddy-driven westerly jet over the North Atlantic. In the 2010 winter the maximum of the jet stream was systematically between 30° and 40°N (south jet regime), whereas in the 2012 winter it was predominantly located around 55°N (north jet regime). These jet features underline the occurrence of either weak flow (2010) or strong and persistent ridges throughout the troposphere (2012). This is confirmed by the very different occurrence of blocking systems over the North Atlantic, associated with episodes of strong cyclonic (anticyclonic) Rossby wave breaking in 2010 (2012) winter. These dynamical features underlie strong precipitation and temperature anomalies over parts of Europe, with detrimental impacts on many socioeconomic sectors. Despite the highly contrasting atmospheric states, mid- and high-latitude boundary conditions do not reveal strong differences in these two winters. The two winters were associated with opposite ENSO phases, but there is no causal evidence of a remote forcing from the Pacific sea surface temperatures. Finally, the exceptionality of the two winters is demonstrated in relation to the last 140 years. It is suggested that these winters may be seen as archetypes of North Atlantic jet variability under current climate conditions.

scholarly journals Cyclones causing wind storms in the Mediterranean: characteristics, trends and links to large-scale patterns

2010 ◽  
Vol 10 (7) ◽  
pp. 1379-1391 ◽  
Author(s):  
K. M. Nissen ◽  
G. C. Leckebusch ◽  
J. G. Pinto ◽  
D. Renggli ◽  
S. Ulbrich ◽  
...  
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Positive Phase ◽  
East Atlantic ◽  
The North ◽  
The North Atlantic ◽  
Wind Storms ◽  
The Mediterranean ◽  
Wind Events ◽  
The North Atlantic Oscillation

Abstract. A climatology of cyclones with a focus on their relation to wind storm tracks in the Mediterranean region (MR) is presented. Trends in the frequency of cyclones and wind storms, as well as variations associated with the North Atlantic Oscillation (NAO), the East Atlantic/West Russian (EAWR) and the Scandinavian variability pattern (SCAND) are discussed. The study is based on the ERA40 reanalysis dataset. Wind storm tracks are identified by tracking clusters of adjacent grid boxes characterised by extremely high local wind speeds. The wind track is assigned to a cyclone track independently identified with an objective scheme. Areas with high wind activity – quantified by extreme wind tracks – are typically located south of the Golf of Genoa, south of Cyprus, southeast of Sicily and west of the Iberian Peninsula. About 69% of the wind storms are caused by cyclones located in the Mediterranean region, while the remaining 31% can be attributed to North Atlantic or Northern European cyclones. The North Atlantic Oscillation, the East Atlantic/West Russian pattern and the Scandinavian pattern all influence the amount and spatial distribution of wind inducing cyclones and wind events in the MR. The strongest signals exist for the NAO and the EAWR pattern, which are both associated with an increase in the number of organised strong wind events in the eastern MR during their positive phase. On the other hand, the storm numbers decrease over the western MR for the positive phase of the NAO and over the central MR during the positive phase of the EAWR pattern. The positive phase of the Scandinavian pattern is associated with a decrease in the number of winter wind storms over most of the MR. A third of the trends in the number of wind storms and wind producing cyclones during the winter season of the ERA40 period may be attributed to the variability of the North Atlantic Oscillation.

The Summer North Atlantic Oscillation: Past, Present, and Future

2009 ◽  
Vol 22 (5) ◽  
pp. 1082-1103 ◽  
Author(s):  
Chris K. Folland ◽  
Jeff Knight ◽  
Hans W. Linderholm ◽  
David Fereday ◽  
Sarah Ineson ◽  
...  
Keyword(s):  
North Atlantic Oscillation ◽  
Time Scales ◽  
North Atlantic ◽  
Southern Oscillation ◽  
Storm Track ◽  
Summer Drought ◽  
Summer Climate ◽  
The North ◽  
The North Atlantic ◽  
Instrumental Records

Abstract Summer climate in the North Atlantic–European sector possesses a principal pattern of year-to-year variability that is the parallel to the well-known North Atlantic Oscillation in winter. This summer North Atlantic Oscillation (SNAO) is defined here as the first empirical orthogonal function (EOF) of observed summertime extratropical North Atlantic pressure at mean sea level. It is shown to be characterized by a more northerly location and smaller spatial scale than its winter counterpart. The SNAO is also detected by cluster analysis and has a near-equivalent barotropic structure on daily and monthly time scales. Although of lesser amplitude than its wintertime counterpart, the SNAO exerts a strong influence on northern European rainfall, temperature, and cloudiness through changes in the position of the North Atlantic storm track. It is, therefore, of key importance in generating summer climate extremes, including flooding, drought, and heat stress in northwestern Europe. The El Niño–Southern Oscillation (ENSO) phenomenon is known to influence summertime European climate; however, interannual variations of the SNAO are only weakly influenced by ENSO. On interdecadal time scales, both modeling and observational results indicate that SNAO variations are partly related to the Atlantic multidecadal oscillation. It is shown that SNAO variations extend far back in time, as evidenced by reconstructions of SNAO variations back to 1706 using tree-ring records. Very long instrumental records, such as central England temperature, are used to validate the reconstruction. Finally, two climate models are shown to simulate the present-day SNAO and predict a trend toward a more positive index phase in the future under increasing greenhouse gas concentrations. This implies the long-term likelihood of increased summer drought for northwestern Europe.

North Atlantic Oscillation

2017 ◽  
Author(s):  
Edward Hanna ◽  
Thomas E. Cropper
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Climate Models ◽  
Global Climate ◽  
Global Climate Models ◽  
The Arctic ◽  
Energy Output ◽  
Jet Stream ◽  
The North ◽  
The North Atlantic

Many variations in the weather in the European and North Atlantic regions are linked with changes in the North Atlantic Oscillation (NAO). The NAO is measured using a south-minus-north index of atmospheric surface pressure variation across the North Atlantic and is closely connected with changes in the North Atlantic atmospheric polar jet stream and wider changes in atmospheric circulation. The physical, human, and biological impacts of NAO changes extend well beyond weather and climate, with major economic, social, and environmental effects. The NAO index based on barometric pressure records now extends as far back as 1850, based on recent work. Although there are few significant overall trends in monthly or seasonal NAO (i.e., for the whole record), there are many shorter-term multidecadal variations. A prominent increase in the NAO between the 1960s and 1990s was widely noted in previous work and was thought to be related to human-induced greenhouse gas forcing. However, since then this trend has reversed, with a significant decrease in the summer NAO since the 1990s and a striking increase in variability of the winter—especially December—NAO that has resulted in four of the six highest and two of the five lowest NAO Decembers occurring during 2004–2015 in the 116-year record, with accompanying more variable year-to-year winter weather conditions over the United Kingdom. These NAO changes are related to an increasing trend in the Greenland Blocking Index (GBI; equals high pressure over Greenland) in summer and a significantly more variable GBI in December. Such NAO and related jet stream and blocking changes are not generally present in the current generation of global climate models, although recent process studies offer insights into their possible causes. Several plausible climate forcings and feedbacks, including changes in the sun’s energy output and the Arctic amplification of global warming with accompanying reductions in sea ice, may help explain the recent NAO changes. Recent research also suggests significant skill in being able to make seasonal NAO predictions and therefore long-range weather forecasts for up to several months ahead for northwest Europe. However, global climate models remain unclear on longer-term NAO predictions for the remainder of the 21st century.

Split

Jet Stream ◽  
2019 ◽  
pp. 137-148
Author(s):  
Tim Woollings
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Hadley Cell ◽  
The North ◽  
Weather And Climate ◽  
Climate Patterns ◽  
The North Atlantic ◽  
Jet Variability ◽  
The North Atlantic Oscillation ◽  
Jet Structure

Over the North Atlantic the eddy-driven jet stream finally separates from the subtropical jet, forming a split jet structure. Free from the steady influence of the Hadley cell, the northern jet is highly variable and its shifts and meanders affect weather and climate patterns around much of the hemisphere. This chapter introduces the North Atlantic Oscillation, the dominant pattern of jet variability, giving an overview of its history and impacts.

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