Variability in atmospheric circulation and moisture flux over the Arctic

Abstract. Time series of monthly, seasonal and annual mean air temperature, precipitation, snow cover duration and specific runoff of rivers in Estonia are analysed for detecting of trends and regime shifts during 1951–2015. Trend analysis is realised using the Mann–Kendall test and regime shifts are detected with the Rodionov test (sequential t-test analysis of regime shifts). The results from Estonia are related to trends and regime shifts in time series of indices of large-scale atmospheric circulation. Annual mean air temperature has significantly increased at all 12 stations by 0.3–0.4 K decade−1. The warming trend was detected in all seasons but with the higher magnitude in spring and winter. Snow cover duration has decreased in Estonia by 3–4 days decade−1. Changes in precipitation are not clear and uniform due to their very high spatial and temporal variability. The most significant increase in precipitation was observed during the cold half-year, from November to March and also in June. A time series of specific runoff measured at 21 stations had significant seasonal changes during the study period. Winter values have increased by 0.4–0.9 L s−1 km−2 decade−1, while stronger changes are typical for western Estonia and weaker changes for eastern Estonia. At the same time, specific runoff in April and May have notably decreased indicating the shift of the runoff maximum to the earlier time, i.e. from April to March. Air temperature, precipitation, snow cover duration and specific runoff of rivers are highly correlated in winter determined by the large-scale atmospheric circulation. Correlation coefficients between the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) indices reflecting the intensity of westerlies, and the studied variables were 0.5–0.8. The main result of the analysis of regime shifts was the detection of coherent shifts for air temperature, snow cover duration and specific runoff in the late 1980s, mostly since the winter of 1988/1989, which are, in turn, synchronous with the shifts in winter circulation. For example, runoff abruptly increased in January, February and March but decreased in April. Regime shifts in annual specific runoff correspond to the alternation of wet and dry periods. A dry period started in 1964 or 1963, a wet period in 1978 and the next dry period at the beginning of the 21st century.

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Different responses of Central Asian precipitation to strong and weak El Niño events

Journal of Climate ◽

10.1175/jcli-d-21-0238.1 ◽

2021 ◽

pp. 1-60

Keyword(s):

Soil Moisture ◽

Central Asia ◽

El Niño ◽

El Nino ◽

Moisture Flux ◽

The Arctic ◽

Central Asian ◽

El Niño Events ◽

Sst Anomalies ◽

El Nino Events

Abstract The present study investigated impacts of strong and weak El Niño events on Central Asian precipitation variability from El Niño developing years to decaying years. It is found that strong El Niño events persistently enhance Central Asian precipitation from the mature winter to decaying summer. Large warm sea surface temperature (SST) anomalies in the tropical central-eastern Pacific induce anomalous upper-level divergence and updraft over Central Asia through large-scale convergence and divergence in the mature winter and decaying spring. Meanwhile, the associated wind anomalies induce anomalous eastward and northeastward moisture flux from the North Atlantic and Arabian Sea to Central Asia. Both anomalous ascent and moisture flux convergence favor above-normal precipitation over Central Asia in the mature winter and decaying spring. The El Niño events induced Central Asian precipitation anomalies are extended to the decaying summer due to the role of soil moisture. Increased rainfall in winter and spring enhances soil moisture in the following summer, which in turn, contributes to more precipitation in summer through modulating regional evaporation. During weak El Niño events, significant wet anomalies are only seen in the developing autumn, which result from anomalous southeastward moisture flux from the Arctic Ocean, and the abnormal signals are weak in the other seasons. The different responses of Central Asian precipitation to strong and weak El Niño events may be attributed to the difference in intensity of tropical SST anomalies between the two types of events.

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Impacts of large-scale atmospheric circulation changes due to winter sea-ice retreat on Black Carbon transport and deposition to the Arctic

10.5194/acp-2016-1007 ◽

2016 ◽

Author(s):

Luca Pozzoli ◽

Srdan Dobricic ◽

Simone Russo ◽

Elisabetta Vignati

Keyword(s):

Sea Ice ◽

Atmospheric Circulation ◽

North Atlantic ◽

Large Scale ◽

Southern Oscillation ◽

The Arctic ◽

The North ◽

Ice Retreat ◽

The North Atlantic Oscillation ◽

Sea Ice Retreat

Abstract. Winter warming and sea ice retreat observed in the Arctic in the last decades determine changes of large scale atmospheric circulation pattern that may impact as well the transport of black carbon (BC) to the Arctic and its deposition on the sea ice, with possible feedbacks on the regional and global climate forcing. In this study we developed and applied a new statistical algorithm, based on the Maximum Likelihood Estimate approach, to determine how the changes of three large scale weather patterns (the North Atlantic Oscillation, the Scandinavian Blocking, and the El Nino-Southern Oscillation), associated with winter increasing temperatures and sea ice retreat in the Arctic, impact the transport of BC to the Arctic and its deposition. We found that the three atmospheric patterns together determine a decreasing winter deposition trend of BC between 1980 and 2015 in the Eastern Arctic while they increase BC deposition in the Western Arctic. The increasing trend is mainly due to the more frequent occurrences of stable high pressure systems (atmospheric blocking) near Scandinavia favouring the transport in the lower troposphere of BC from Europe and North Atlantic directly into to the Arctic. The North Atlantic Oscillation has a smaller impact on BC deposition in the Arctic, but determines an increasing BC atmospheric load over the entire Arctic Ocean with increasing BC concentrations in the upper troposphere. The El Nino-Southern Oscillation does not influence significantly the transport and deposition of BC to the Arctic. The results show that changes in atmospheric circulation due to polar atmospheric warming and reduced winter sea ice significantly impacted BC transport and deposition. The anthropogenic emission reductions applied in the last decades were, therefore, crucial to counterbalance the most likely trend of increasing BC pollution in the Arctic.

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Increase in Aerosol Black Carbon in the 2000s over Ny-Ålesund in the Summer

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-15-0009.1 ◽

2015 ◽

Vol 73 (1) ◽

pp. 251-262 ◽

Cited By ~ 2

Author(s):

Liqi Chen ◽

Wei Li ◽

Jianqiong Zhan ◽

Jianjun Wang ◽

Yuanhui Zhang ◽

...

Keyword(s):

Temporal Variation ◽

Black Carbon ◽

Atmospheric Circulation ◽

Yellow River ◽

The Arctic ◽

Radiative Energy ◽

Back Trajectory ◽

Significant Implication ◽

Svalbard Archipelago ◽

Local Emissions

Abstract To investigate the concentrations, sources, and temporal variations of atmospheric black carbon (BC) in the summer Arctic, routine ground-level observations of BC by optical absorption were made in the summer from 2005 to 2008 at the Chinese Arctic “Yellow River” Station (78°55′N, 11°56′E) at Ny-Ålesund on the island of Spitsbergen in the Svalbard Archipelago. Methods of the ensemble empirical-mode decomposition analysis and back-trajectory analysis were employed to assess temporal variation embedded in the BC datasets and airmass transport patterns. The 10th-percentile and median values of BC concentrations were 7.2 and 14.6 ng m−3, respectively, and hourly average BC concentrations ranged from 2.5 to 54.6 ng m−3. A gradual increase was found by 4 ng m−3 a−1. This increase was not seen in the Zeppelin Station and it seemed to contrast with the prevalent conception of generally decreasing BC concentration since 1989 in the Arctic. Factors responsible for this increase such as changes in emissions and atmospheric transport were taken into consideration. The result indicated that BC from local emissions was mostly responsible for the observed increase from 2005 to 2008. BC temporal variation in the summer was controlled by the atmospheric circulation, which presented a significant 6–14-day variation and coherent with 1–3- and 2–5-day and longer cycle variation. Although the atmospheric circulation changes from 2005 to 2008, there was not a marked trend in long-range transportation of BC. This study suggested that local emissions might have significant implication for the regional radiative energy balance at Ny-Ålesund.

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The Impact of Regional Arctic Sea Ice Loss on Atmospheric Circulation and the NAO

Journal of Climate ◽

10.1175/jcli-d-15-0315.1 ◽

2016 ◽

Vol 29 (2) ◽

pp. 889-902 ◽

Cited By ~ 51

Author(s):

Rasmus A. Pedersen ◽

Ivana Cvijanovic ◽

Peter L. Langen ◽

Bo M. Vinther

Keyword(s):

Sea Ice ◽

Atmospheric Circulation ◽

General Circulation ◽

Ice Cover ◽

Arctic Sea Ice ◽

The Arctic ◽

Near Surface ◽

Arctic Sea ◽

The Impact ◽

Sea Ice Reduction

Abstract Reduction of the Arctic sea ice cover can affect the atmospheric circulation and thus impact the climate beyond the Arctic. The atmospheric response may, however, vary with the geographical location of sea ice loss. The atmospheric sensitivity to the location of sea ice loss is studied using a general circulation model in a configuration that allows combination of a prescribed sea ice cover and an active mixed layer ocean. This hybrid setup makes it possible to simulate the isolated impact of sea ice loss and provides a more complete response compared to experiments with fixed sea surface temperatures. Three investigated sea ice scenarios with ice loss in different regions all exhibit substantial near-surface warming, which peaks over the area of ice loss. The maximum warming is found during winter, delayed compared to the maximum sea ice reduction. The wintertime response of the midlatitude atmospheric circulation shows a nonuniform sensitivity to the location of sea ice reduction. While all three scenarios exhibit decreased zonal winds related to high-latitude geopotential height increases, the magnitudes and locations of the anomalies vary between the simulations. Investigation of the North Atlantic Oscillation reveals a high sensitivity to the location of the ice loss. The northern center of action exhibits clear shifts in response to the different sea ice reductions. Sea ice loss in the Atlantic and Pacific sectors of the Arctic cause westward and eastward shifts, respectively.

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Atmospheric transport of persistent semi-volatile organic chemicals to the Arctic and cold condensation in the mid-troposphere – Part 2: 3-D modeling of episodic atmospheric transport

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-7315-2010 ◽

2010 ◽

Vol 10 (15) ◽

pp. 7315-7324 ◽

Cited By ~ 11

Author(s):

L. Zhang ◽

J. Ma ◽

C. Tian ◽

Y. Li ◽

H. Hung

Keyword(s):

Atmospheric Circulation ◽

Atmospheric Transport ◽

The Arctic ◽

Organic Chemicals ◽

High Latitudes ◽

Volatile Organic ◽

Volatile Organic Chemicals ◽

Cold Condensation ◽

Condensation Effect ◽

Modeling Study

Abstract. Two 3-dimensional global atmospheric transport models for persistent organic pollutants (POPs) have been employed to investigate the association between the large-scale atmospheric motions and poleward transports of persistent semi-volatile organic chemicals (SVOCs). We examine the modeled daily air concentration of α- and γ-hexachlorocyclohexane (HCH) over a period from 1997 through 1999 during which a number of episodic atmospheric transport events were detected in this modeling study. These events provide modeling evidence for improving the interpretation on the cold condensation effect and poleward atmospheric transport of SVOCs in the mid-troposphere. Two episodic transport events of γ-HCH (lindane) to the high Arctic (80–90° N), one from Asian and another from Eurasian sources, are reported in this paper. Both events suggest that the episodic atmospheric transports occurring in the mid-troposphere (e.g. from 3000 m to 5500 m height) are driven by atmospheric horizontal and vertical motions. The association of the transport events with atmospheric circulation is briefly discussed. Strong southerly winds, forced by the evolution of two semi-permanent high pressure systems over mid-high latitudes in the Northern Hemisphere, play an important role in the long-range transport (LRT) of HCHs to the high latitudes from its sources. Being consistent with the cold condensation effect and poleward atmospheric transport in a mean meridional atmospheric circulation simulated by a 2-D atmospheric transport model, as reported by the first part of this study, this modeling study indicates that cold condensation is likely occurring more intensively in the mid-troposphere where rapid declining air temperature results in condensed phase of the chemical over and near its source regions and where stronger winds convey the chemical more rapidly to the polar region during the episodic poleward atmospheric transport events.

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Quantification of the Arctic Sea Ice‐Driven Atmospheric Circulation Variability in Coordinated Large Ensemble Simulations

Geophysical Research Letters ◽

10.1029/2019gl085397 ◽

2020 ◽

Vol 47 (1) ◽

Cited By ~ 1

Author(s):

Yu‐Chiao Liang ◽

Young‐Oh Kwon ◽

Claude Frankignoul ◽

Gokhan Danabasoglu ◽

Stephen Yeager ◽

...

Keyword(s):

Sea Ice ◽

Atmospheric Circulation ◽

Arctic Sea Ice ◽

The Arctic ◽

Large Ensemble ◽

Ensemble Simulations ◽

Arctic Sea

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Late Twenty-First-Century Changes in the Midlatitude Atmospheric Circulation in the CESM Large Ensemble

Journal of Climate ◽

10.1175/jcli-d-16-0340.1 ◽

2017 ◽

Vol 30 (15) ◽

pp. 5943-5960 ◽

Cited By ~ 21

Author(s):

Y. Peings ◽

J. Cattiaux ◽

S. Vavrus ◽

Gudrun Magnusdottir

Keyword(s):

Atmospheric Circulation ◽

Extreme Temperature ◽

Internal Variability ◽

First Century ◽

The Arctic ◽

Arctic Amplification ◽

Large Ensemble ◽

Longitudinal Sector ◽

Twenty First Century ◽

Projected Changes

Projected changes in the midlatitude atmospheric circulation at the end of the twenty-first century are investigated using coupled ocean–atmosphere simulations from the Community Earth System Model Large Ensemble (CESM-LENS). Different metrics are used to describe the response of the midlatitude atmospheric dynamics in 40 ensemble members covering the 1920–2100 period. Contrasted responses are identified depending on the season and longitudinal sector that are considered. In winter, a slowdown of the zonal flow and an increase in waviness is found over North America, while the European sector exhibits a reinforced westerly flow and decreased waviness. Extreme temperature events in midlatitudes are more sensitive to thermodynamical than dynamical changes, and a general decrease in the intensity of wintertime cold spells is found. Analyses of individual ensemble members reveal a large spread in circulation changes due to internal variability. Causes for this spread are found to be tied to the Arctic amplification in the Pacific–North American sector and to the polar stratosphere in the North Atlantic. A competition mechanism is also discussed between the midlatitude response to polar versus tropical changes. While the upper-tropospheric tropical warming pushes the jet stream poleward, in winter, Arctic amplification and the weaker polar vortex exert an opposite effect. This competition results in a narrowing of the jet path in the midlatitudes, leading to decreased/unchanged waviness/blockings. This interpretation somewhat reconciles conflicting results between the hypothesized effect of Arctic amplification and projected changes in midlatitude flow characteristics. This study also illustrates that further understanding of regional processes is critical for anticipating changes in the midlatitude dynamics.

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Recent summer Arctic atmospheric circulation anomalies in a historical perspective

The Cryosphere ◽

10.5194/tc-9-53-2015 ◽

2015 ◽

Vol 9 (1) ◽

pp. 53-64 ◽

Cited By ~ 21

Author(s):

A. Belleflamme ◽

X. Fettweis ◽

M. Erpicum

Keyword(s):

Atmospheric Circulation ◽

Greenland Ice Sheet ◽

Arctic Region ◽

Reanalysis Data ◽

Circulation Type ◽

Arctic Sea Ice ◽

The Arctic ◽

Pressure Area ◽

Circulation Anomalies ◽

The Arctic Region

Abstract. A significant increase in the summertime occurrence of a high pressure area over the Beaufort Sea, the Canadian Arctic Archipelago, and Greenland has been observed since the beginning of the 2000s, and particularly between 2007 and 2012. These circulation anomalies are likely partly responsible for the enhanced Greenland ice sheet melt as well as the Arctic sea ice loss observed since 2007. Therefore, it is interesting to analyse whether similar conditions might have happened since the late 19th century over the Arctic region. We have used an atmospheric circulation type classification based on daily mean sea level pressure and 500 hPa geopotential height data from five reanalysis data sets (ERA-Interim, ERA-40, NCEP/NCAR, ERA-20C, and 20CRv2) to put the recent circulation anomalies in perspective with the atmospheric circulation variability since 1871. We found that circulation conditions similar to 2007–2012 have occurred in the past, despite a higher uncertainty of the reconstructed circulation before 1940. For example, only ERA-20C shows circulation anomalies that could explain the 1920–1930 summertime Greenland warming, in contrast to 20CRv2. While the recent anomalies exceed by a factor of 2 the interannual variability of the atmospheric circulation of the Arctic region, their origin (natural variability or global warming) remains debatable.

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