Modulations of North American and European Weather Variability and Extremes by Interdecadal Variability of the Atmospheric Circulation over the North Atlantic Sector

AbstractThe dominant mode of wintertime interdecadal covariability between subseasonal surface air temperature (SAT) variability and midtropospheric circulation over the North Atlantic sector is identified through maximum covariance analysis applied to century-long reanalysis data. This mode highlights a tendency for subseasonal temperature variability over Europe and eastern North America to be enhanced during decades when the negative phase of the North Atlantic Oscillation (NAO) prevails. This interdecadal NAO is characterized by a stationary Rossby wave train that originates from the subtropical Atlantic, propagates northward into the subpolar Atlantic, and finally refracts toward Europe and the Middle East. A decadal increase in precipitation in the subtropics under the enhanced supply of heat and moisture from the Gulf Stream and its surroundings appears to act as a source for this wave train. The influence of the interdecadal NAO on subseasonal SAT variability is explained primarily by the modulated efficiency of baroclinic conversion of available potential energy from the background atmospheric flow to subseasonal eddies. The combination of enhanced subseasonal variability and low winter-mean temperature anomalies associated with the negative phase of the interdecadal NAO increases the frequency of cold extremes affecting Europe and the eastern United States.

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North Hemispheric winter air temperature variability and its linkage to North Pacific and North Atlantic SST modes?

10.5194/egusphere-egu2020-16 ◽

2020 ◽

Author(s):

Binhe Luo ◽

Dehai Luo ◽

Aiguo Dai ◽

Lixin Wu

Keyword(s):

North America ◽

Air Temperature ◽

North Atlantic ◽

North Pacific ◽

Wave Train ◽

Surface Air Temperature ◽

Eastern North America ◽

The North ◽

The North Atlantic ◽

The North Pacific

Winter surface air temperature (SAT) over North America exhibits pronounced variability on sub-seasonal-to-interdecadal timescales, but its causes are not fully understood. Here observational and reanalysis data from 1950-2017 are analyzed to investigate these causes. Detrended daily SAT data reveals a known warm-west/cold-east (WWCE) dipole over midlatitude North America and a cold-north/warm-south (CNWS) dipole over eastern North America. It is found that while the North Pacific blocking (PB) is important for the WWCE and CNWS dipoles, they also depend on the phase of the North Atlantic Oscillation (NAO). When a negative-phase NAO (NAO-) concurs with PB, the WWCE dipole is enhanced (compared with the PB alone case) and it also leads to a warm north/cold south dipole anomaly in eastern North America; but when PB occurs with a positive-phase NAO (NAO+), the WWCE dipole weakens and the CNWS dipole is enhanced. In particular, the WWCE dipole is favored by a combination of eastward-displaced PB and NAO- that form a negative Arctic Oscillation. Furthermore, a WWCE dipole can form over midlatitude North America when PB occurs together with southward-displaced NAO+.The PB events concurring with NAO- (NAO+) and SAT WWCE (CNWS) dipole are favored by the El Nio-like (La Nia-like) SST mode, though related to the North Atlantic warm-cold-warm (cold-warm-cold) SST tripole pattern. It is also found that the North Pacific mode tends to enhance the WWCE SAT dipole through increasing PB-NAO- events and producing the WWCE SAT dipole component related to the PB-NAO+ events because the PB and NAO+ form a more zonal wave train in this case.

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The AMV phase-dependence of the connection between February NAO and March surface air temperature over the Tibetan Plateau

10.5194/egusphere-egu21-9879 ◽

2021 ◽

Author(s):

Jingyi Li ◽

Fei Li ◽

Shengping He ◽

Huijun Wang ◽

Yvan J Orsolini

Keyword(s):

Tibetan Plateau ◽

Air Temperature ◽

Rossby Wave ◽

North Atlantic ◽

Wave Train ◽

Surface Air Temperature ◽

The Tibetan Plateau ◽

The North ◽

Rossby Wave Train ◽

The North Atlantic

The Tibetan Plateau (TP), referred to as the &#8220;Asian water tower&#8221;, contains one of the largest land ice masses on Earth. The local glacier shrinkage and frozen-water storage are strongly affected by variations in surface air temperature over the TP (TPSAT), especially in springtime. This study reveals a distinct out-of-phase connection between the February North Atlantic Oscillation (NAO) and March TPSAT, which is non-stationary and regulated by the warm phase of the Atlantic Multidecadal Variability (AMV+). The results show that during the AMV+, the negative phase of the NAO persists from February to March, and is accompanied by a quasi-stationary Rossby wave train trapped along a northward-shifted subtropical westerly jet stream across Eurasia, inducing an anomalous adiabatic descent that warms the TP. However, during the cold phase of the AMV, the negative NAO does not persist into March. The Rossby wave train propagates along the well-separated polar and subtropical westerly jets, and the NAO&#8722;TPSAT connection is broken. Further investigation suggests that the enhanced synoptic eddy and low-frequency flow (SELF) interaction over the North Atlantic in February and March during the AMV+, caused by the enhanced and southward-shifted storm track, help maintain the NAO anomaly pattern via positive eddy feedback. This study provides a new detailed perspective on the decadal variability of the North Atlantic&#8722;TP connections in late winter&#8722;early spring.

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The Record-Breaking High Temperature over Europe in June of 2019

Atmosphere ◽

10.3390/atmos11050524 ◽

2020 ◽

Vol 11 (5) ◽

pp. 524 ◽

Cited By ~ 1

Author(s):

Wei Zhao ◽

Ningfang Zhou ◽

Shangfeng Chen

Keyword(s):

High Temperature ◽

North Atlantic ◽

Wave Train ◽

Surface Air Temperature ◽

Shortwave Radiation ◽

The North ◽

Atmospheric Wave ◽

Local Soil ◽

Anomalous Anticyclone ◽

The North Atlantic

Observational and reanalysis data show that the surface air temperature (SAT) over most parts of Europe in June of 2019 broke the highest temperature on record. In this study, we investigate the factors for the formation of this record-breaking high temperature over Europe, focusing on the role of atmospheric circulation anomalies. A strong anomalous anticyclone appeared over Europe, with a quasi-barotropic vertical structure. On one hand, the downward motion anomalies associated with this anomalous anticyclone led to less cloud cover and an increase in downward shortwave radiation, which contributed to the SAT warming over Europe. On the other hand, southerly wind anomalies to the west side of the anomalous anticyclone also resulted in SAT warming via carrying warmer and wetter air northward from lower latitudes. The formation of the anticyclonic anomaly over Europe in June of 2019 was closely related to an atmospheric wave train propagating eastward from the mid-high latitudes of the North Atlantic to Eurasia. The atmospheric wave train over the North Atlantic–Eurasia region is suggested to be mainly related to the Atlantic–Eurasia teleconnection pattern. Further analysis indicates that a decrease in the local soil moisture over Europe may also have escalated the surface temperature warming through a positive land–atmosphere feedback.

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On the Extratropical Influence of Variations of the Upper-Tropospheric Equatorial Zonal-Mean Zonal Wind during Boreal Winter

Journal of Climate ◽

10.1175/jcli-d-14-00185.1 ◽

2014 ◽

Vol 28 (1) ◽

pp. 168-185 ◽

Cited By ~ 4

Author(s):

Gereon Gollan ◽

Richard J. Greatbatch

Keyword(s):

Time Series ◽

North Atlantic ◽

Zonal Wind ◽

North Pacific ◽

Wave Train ◽

Reanalysis Data ◽

Boreal Winter ◽

Quasi Biennial Oscillation ◽

The North ◽

The North Atlantic

Abstract Variations in the global tropospheric zonal-mean zonal wind [U] during boreal winter are investigated using rotated empirical orthogonal functions applied to monthly means. The first two modes correspond to the northern and southern annular mode and modes 3 and 4 represent variability in the tropics. One is related to El Niño–Southern Oscillation and the other has variability that is highly correlated with the time series of [U] at 150 hPa between 5°N and 5°S [U150]E and is related to activity of the Madden–Julian oscillation. The extratropical response to [U150]E is investigated using linear regressions of 500-hPa geopotential height onto the [U150]E time series. Use is made of reanalysis data and of the ensemble mean output from a relaxation experiment using the European Centre for Medium-Range Weather Forecasts model in which the tropical atmosphere is relaxed toward reanalysis data. The regression analysis reveals that a shift of the Aleutian low and a wave train across the North Atlantic are associated with [U150]E. It is found that the subtropical waveguides and the link between the North Pacific and North Atlantic are stronger during the easterly phase of [U150]E. The wave train over the North Atlantic is associated with Rossby wave sources over the subtropical North Pacific and North America. Finally, it is shown that a linear combination of both [U150]E and the quasi-biennial oscillation in the lower stratosphere can explain the circulation anomalies of the anomalously cold European winter of 1962/63 when both were in an extreme easterly phase.

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Enhanced Linkage between Eurasian Winter and Spring Dominant Modes of Atmospheric Interannual Variability since the Early 1990s

Journal of Climate ◽

10.1175/jcli-d-17-0525.1 ◽

2018 ◽

Vol 31 (9) ◽

pp. 3575-3595 ◽

Cited By ~ 16

Author(s):

Shangfeng Chen ◽

Renguang Wu ◽

Wen Chen ◽

Shuailei Yao

Keyword(s):

Interannual Variability ◽

Atmospheric Circulation ◽

North Atlantic ◽

Wave Train ◽

Seasonal Prediction ◽

Dominant Mode ◽

The North ◽

Anomaly Pattern ◽

Sst Anomaly ◽

The North Atlantic

The present study reveals a marked enhancement in the relationship between Eurasian winter and spring atmospheric interannual variability since the early 1990s. Specifically, the dominant mode of winter Eurasian 500-hPa geopotential height anomalies, with same-sign anomalies over southern Europe and East Asia and opposite-sign anomalies over north-central Eurasia, is largely maintained to the following spring after the early 1990s, but not before the early 1990s. The maintenance of the dominant atmospheric circulation anomaly pattern after the early 1990s is associated with a triple sea surface temperature (SST) anomaly pattern in the North Atlantic that is sustained from winter to the subsequent spring. This triple SST anomaly pattern triggers an atmospheric wave train over the North Atlantic through Eurasia during winter through spring. Atmospheric model experiments verify the role of the triple SST anomaly in maintaining the Eurasian atmospheric circulation anomalies. By contrast, before the early 1990s, marked SST anomalies related to the winter dominant mode only occur in the tropical North Atlantic during winter and they disappear during the following spring. The triple SST anomaly pattern after the early 1990s forms in response to a meridional atmospheric dipole over the North Atlantic induced by a La Niña–like cooling over tropical Pacific, and its maintenance into the following spring may be via a positive air–sea interaction process over the North Atlantic. Results of this analysis suggest a potential source for the seasonal prediction of the Eurasian spring climate.

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On the Predictability of the Winter Euro-Atlantic Climate: Lagged Influence of Autumn Arctic Sea Ice

Journal of Climate ◽

10.1175/jcli-d-14-00472.1 ◽

2015 ◽

Vol 28 (13) ◽

pp. 5195-5216 ◽

Cited By ~ 43

Author(s):

J. García-Serrano ◽

C. Frankignoul ◽

G. Gastineau ◽

A. de la Cámara

Keyword(s):

Sea Ice ◽

North Atlantic ◽

Wave Train ◽

Surface Air Temperature ◽

Arctic Sea Ice ◽

Prediction Skill ◽

Sea Ice Concentration ◽

Atlantic Sector ◽

Empirical Prediction ◽

The North

Abstract Satellite-derived sea ice concentration (SIC) and reanalyzed atmospheric data are used to explore the predictability of the winter Euro-Atlantic climate resulting from autumn SIC variability over the Barents–Kara Seas region (SIC/BK). The period of study is 1979/80–2012/13. Maximum covariance analyses show that the leading predictand is indistinguishable from the North Atlantic Oscillation (NAO). The leading covariability mode between September SIC/BK and winter North Atlantic–European sea level pressure (SLP) is not significant, indicating that no empirical prediction skill can be achieved. The leading covariability mode with either October or November SIC/BK is moderately significant (significance levels <10%), and both predictor fields yield a cross-validated NAO correlation of 0.3, suggesting some empirical prediction skill of the winter NAO index, with sea ice reduction in the Barents–Kara Seas being accompanied by a negative NAO phase in winter. However, only November SIC/BK provides significant cross-validated skill of winter SLP, surface air temperature, and precipitation anomalies over the Euro-Atlantic sector, namely in southwestern Europe. Statistical analysis suggests that November SIC/BK anomalies are associated with a Rossby wave train–like anomaly across Eurasia that affects vertical wave activity modulating the stratospheric vortex strength, which is then followed by downward propagation of anomalies that impact transient-eddy activity in the upper troposphere, helping to settle and maintain the NAO-like pattern at surface. This stratospheric pathway is not detected when using October SIC/BK anomalies. Hence, only November SIC/BK, with a one-month lead time, could be considered as a potential source of regional predictability.

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Recent climatic variations in the North Atlantic sector

Deep Sea Research Part B Oceanographic Literature Review ◽

10.1016/0198-0254(85)92723-2 ◽

1985 ◽

Vol 32 (9) ◽

pp. 735

Keyword(s):

North Atlantic ◽

Atlantic Sector ◽

Climatic Variations ◽

The North ◽

The North Atlantic

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The North Atlantic Ocean as a Modulator of Vegetation Greening/Browning in the Northern High Latitudes?

10.5194/egusphere-egu21-15595 ◽

2021 ◽

Author(s):

Leonard F. Borchert ◽

Alexander J. Winkler

Keyword(s):

Climate Variability ◽

North Atlantic ◽

North Atlantic Ocean ◽

Internal Variability ◽

Dominant Mode ◽

High Latitudes ◽

Model Simulations ◽

Internal Climate Variability ◽

The North ◽

The North Atlantic

Vegetation in the northern high latitudes shows a characteristic pattern of persistent changes as documented by multi-decadal satellite observations. The prevailing explanation that these mainly increasing trends (greening) are a consequence of external CO2 forcing, i.e., due to the ubiquitous effect of CO2-induced fertilization and/or warming of temperature-limited ecosystems, however does not explain why some areas also show decreasing trends of vegetation cover (browning). We propose here to consider the dominant mode of multi-decadal internal climate variability in the north Atlantic region, the Atlantic Multidecadal Variability (AMV), as the missing link in the explanation of greening and browning trend patterns in the northern high latitudes. Such a link would also imply potential for decadal predictions of ecosystem changes in the northern high latitudes.An analysis of observational and reanalysis data sets for the period 1979-2019 shows that locations characterized by greening trends largely coincide with warming summer temperature and increasing precipitation. Wherever either cooling or decreasing precipitation occurs, browning trends are observed over this period. These precipitation and temperature patterns are significantly correlated with a North Atlantic sea surface temperature index that represents the AMV signal, indicating its role in modulating greening/browning trend patterns in the northern high latitudes.Using two large ensembles of coupled Earth system model simulations (100 members of MPI-ESM-LR Grand Ensemble and 32 members of the IPSL-CM6A-LR Large Ensemble), we separate the greening/browning pattern caused by external CO2 forcing from that caused by internal climate variability associated with the AMV. These sets of model simulations enable a clean separation of the externally forced signal from internal variability. While the greening and browning patterns in the simulations do not agree with observations in terms of magnitude and location, we find consistent internally generated greening/browning patterns in both models caused by changes in temperature and precipitation linked to the AMV signal. These greening/browning trend patterns are of the same magnitude as those caused by the external forcing alone. Our work therefore shows that internally-generated changes of vegetation in the northern lands, driven by AMV, are potentially as large as those caused by external CO2 forcing. We thus argue that the observed pattern of greening/browning in the northern high latitudes could originate from the combined effect of rising CO2 as well as the AMV.

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New Miocene Monachinae from the Western Shore of the Chesapeake Bay (Maryland, USA)

Vestnik Zoologii ◽

10.1515/vzoo-2017-0029 ◽

2017 ◽

Vol 51 (3) ◽

pp. 221-242 ◽

Cited By ~ 5

Author(s):

S. J. Rahmat ◽

I. A. Koretsky ◽

J. E. Osborne ◽

A. A. Alford

Keyword(s):

North Atlantic ◽

Fish Fauna ◽

Eastern United States ◽

Aquatic Life ◽

Low Salinity ◽

The North ◽

Early Oligocene ◽

The Family ◽

Western Shore ◽

The North Atlantic

Abstract The Family Phocidae includes four subfamilies (Phocinae, Monachinae, Cystophorinae, and Devinophocinae) consisting of mediumto large-sized mammals that possess distinctive adaptations to semi-aquatic life. In the Miocene of the Chesapeake Group, only two subfamilies of the Family Phocidae were identified: Phocinae and Monachinae. Leptophoca, a representative of the subfamily Phocinae, appears on the eastern shore of the North Atlantic around 16 million years ago. Recently, two new monachine species, the larger Terranectes magnus (n. gen., n. sp.) and the medium-sized T. parvus (n. sp.), were recorded in the Upper Miocene of the Chesapeake Group in the Eastover Formation (7.0–6.0 Ma) and St. Marys Formation (10.0-8.0 Ma). These two distinct subfamilies of seals indicate a well-marked divergence between phocines and monachines, much earlier than 18 million years ago, as previously suggested. The Eastover Formation was deposited in a shallow embayment that covered southern Maryland, the coastal plain of Virginia, and the northeastern corner of North Carolina. The geologically older St. Marys Formation represents a tide-influenced coastal environment, with low-salinity estuaries. There was a sharp temperature decrease in the Late Miocene, indicated by a shift to a cooler-water fish fauna during St. Marys time. The Eastover Formation reflects warmer waters with relatively strong currents, significant shoals, barriers, and varied depths. Fossil evidence of earlier seals suggests that phocids originated in the North Atlantic and otarioids in the North Pacific. True seals diverged from ancient Carnivora in the early Oligocene (or earlier) in the Paratethyan / Mediterranean Basins, spread widely during the Middle Miocene and crossed westward across the Atlantic Ocean, before dispersing in the eastern United States by the Early Pliocene.

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The concurrence of Atmospheric Rivers and explosive cyclogenesis in the North Atlantic and North Pacific basins

10.5194/esd-2017-76 ◽

2017 ◽

Author(s):

Jorge Eiras-Barca ◽

Alexandre M. Ramos ◽

Joaquim G. Pinto ◽

Ricardo M. Trigo ◽

Margarida L. R. Liberato ◽

...

Keyword(s):

North Atlantic ◽

North Pacific ◽

Reanalysis Data ◽

Water Vapour Flux ◽

Atmospheric Rivers ◽

The North ◽

Explosive Cyclones ◽

The North Atlantic ◽

Characteristic Features ◽

Western Side

Abstract. The explosive cyclogenesis of extra-tropical cyclones and the occurrence of atmospheric rivers are characteristic features of baroclinic atmospheres, and are both closely related to extreme hydrometeorological events in the mid-latitudes, particularly on coastal areas on the western side of the continents. The potential role of atmospheric rivers in the explosive cyclone deepening has been previously analysed for selected case studies, but a general assessment from the climatological perspective is still missing. Using ERA-Interim reanalysis data for 1979–2011, we analyse the concurrence of atmospheric rivers and explosive cyclogenesis over the North Atlantic and North Pacific Basins for the extended winter months (ONDJFM). Atmospheric rivers are identified for almost 80 % of explosive deepening cyclones. For non-explosive cyclones, atmospheric rivers are found only in roughly 40 % of the cases. The analysis of the time evolution of the high values of water vapour flux associated with the atmospheric river during the cyclone development phase leads us to hypothesize that the identified relationship is the fingerprint of a mechanism that raises the odds of an explosive cyclogenesis occurrence and not merely a statistical relationship. This insight can be helpful for the predictability of high impact weather associated with explosive cyclones and atmospheric rivers.

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