Wintertime temperature extremes in the high Arctic: drivers, statistics and implications for the mid-latitudes

Temperature extremes in the high Arctic have made the headlines in recent years, with wintertime warm spells approaching 0 &#176;C at the North Pole. In the first part of this presentation, I will outline some salient large-scale and synoptic atmospheric drivers of wintertime warm and cold spells in the high Arctic. The warm spells are systematically associated with a large-scale circulation pattern that creates a natural pathway for extreme moisture intrusions from the Atlantic sector into the Arctic. Anomalies in the distribution of synoptic cyclones then favour a deep penetration of these intrusions across the Arctic basin. The large-scale circulation pattern associated with the warm spells further favours the advection of cold air across central-northern Eurasia. On the contrary, cold Arctic extremes are associated with a persistent low-pressure system over the pole. This effectively isolates the high latitudes from mid-latitude air masses, favouring an intense radiative cooling of the polar region. In the second part of the presentation, I will discuss return times of the wintertime warm spells, using a novel approach grounded in extreme value theory. This approach explicitly takes into account the spatial structure of the moisture intrusions driving the temperature extremes, and I will try to convince you that it provides a more realistic set of estimates than conventional return-time algorithms.

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On the Drivers of Wintertime Temperature Extremes in the High Arctic

Journal of Climate ◽

10.1175/jcli-d-17-0386.1 ◽

2018 ◽

Vol 31 (4) ◽

pp. 1597-1618 ◽

Cited By ~ 27

Author(s):

Gabriele Messori ◽

Cian Woods ◽

Rodrigo Caballero

Keyword(s):

Large Scale ◽

Arctic Basin ◽

High Arctic ◽

The Arctic ◽

Height Anomaly ◽

Northern Eurasia ◽

Deep Penetration ◽

Pressure System ◽

Reanalysis Dataset ◽

Atlantic Sector

The salient features and drivers of wintertime warm and cold spells in the high Arctic are investigated. The analysis is based on the European Centre for Medium-Range Weather Forecasts interim reanalysis dataset. It is found that the warm spells are systematically associated with an intense sea level pressure and geopotential height anomaly dipole, displaying a low over the Arctic basin and a high over northern Eurasia. This configuration creates a natural pathway for extreme moisture influx episodes from the Atlantic sector into the Arctic (herein termed moisture intrusions). Anomalous cyclone frequency at the pole (largely attributable to local cyclogenesis) then favors a deep penetration of these intrusions across the Arctic basin. The large-scale circulation pattern associated with the warm spells further favors the advection of cold air across Siberia, leading to the so-called warm Arctic–cold Eurasia pattern previously discussed in the literature. On the contrary, cold Arctic extremes are associated with a severely reduced frequency of moisture intrusions and a persistent low pressure system over the pole. This effectively isolates the high latitudes from midlatitude air masses, favoring an intense radiative cooling of the polar region.

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A Diagnostic Model of the Nordic Seas and Arctic Ocean Circulation: Quantifying the Effects of a Variable Bottom Density along a Sloping Topography

Journal of Physical Oceanography ◽

10.1175/2008jpo3862.1 ◽

2008 ◽

Vol 38 (12) ◽

pp. 2685-2703 ◽

Cited By ~ 14

Author(s):

Signe Aaboe ◽

Ole Anders Nøst

Keyword(s):

Arctic Ocean ◽

Ocean Circulation ◽

Large Scale ◽

The Arctic ◽

Diagnostic Model ◽

Large Scale Circulation ◽

Nordic Seas ◽

Variable Bottom ◽

Canadian Basin ◽

Baroclinic Transport

Abstract A linear diagnostic model, solving for the time-mean large-scale circulation in the Nordic seas and Arctic Ocean, is presented. Solutions on depth contours that close within the Nordic seas and Arctic Ocean are found from vorticity balances integrated over the areas enclosed by the contours. Climatological data for wind stress and hydrography are used as input to the model, and the bottom geostrophic flow is assumed to follow depth contours. Comparison against velocity observations shows that the simplified dynamics in the model capture many aspects of the large-scale circulation. Special attention is given to the dynamical effects of an along-isobath varying bottom density, which leads to a transformation between barotropic and baroclinic transport. Along the continental slope, enclosing both the Nordic seas and Arctic Ocean, the along-slope barotropic transport has a maximum in the Nordic seas and a minimum in the Canadian Basin with a difference of 9 Sv (1 Sv ≡ 106 m3 s−1) between the two. This is caused by the relatively lower bottom densities in the Canadian Basin compared to the Nordic seas and suggests that most of the barotropic transport entering the Arctic Ocean through the Fram Strait is transformed to baroclinic transport. A conversion from barotropic to baroclinic flow may be highly important for the slope–basin exchange in the Nordic seas and Arctic Ocean. The model has obvious shortcomings due to its simplicity. However, the simplified physics and the agreement with observations make this model an excellent framework for understanding the large-scale circulation in the Nordic seas and Arctic Ocean.

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Ocean carbon storage uniquely linked to ocean heat

10.5194/egusphere-egu21-13595 ◽

2021 ◽

Author(s):

Ben Bronselaer ◽

Laure Zanna

Keyword(s):

Carbon Storage ◽

Large Scale ◽

Climate Models ◽

Circulation Pattern ◽

Secondary Importance ◽

Large Scale Circulation ◽

Excess Carbon ◽

Excess Heat ◽

Surface Ocean ◽

Ocean Carbon

As the climate warms due to greenhouse gas emissions, the ocean absorbs excess heat and carbon. The patterns of ocean excess heat and carbon storage appear tightly linked when the large-scale circulation is fixed. This unique link is not shared with any other ocean tracer, such as Chlorofluorocarbons (CFCs). At the same time, ocean excess carbon storage patterns are mostly unchanged whether the large-scale circulation is free to evolve, or fixed to the pre-industrial circulation pattern, as the climate warms. Here, we interpret the reason for this behavior by breaking ocean carbon storage into two parts: uptake of atmospheric anomalies by the surface ocean, and subsequent internal storage by the ocean&#8217;s circulation. We show that the patterns of surface ocean carbon anomalies are dictated by mean state biogeochemical properties and therefore mostly unchanged by circulation changes. Furthermore, surface biogeochemical properties are strongly shaped by the ocean temperature, providing a link between ocean heat and carbon uptake. CFCs on the hand, lack chemical buffering and therefore the patterns of CFC storage do not correlate with heat as much as carbon patterns do. The patterns of surface anomalies ultimately explain most of the differences in how temperature, carbon and CFCs are stored by the ocean, while changes in internal pathways are of secondary importance. Furthermore, the ratio of total ocean carbon and heat storage is roughly constant across warming scenarios and climate models, which might have further implications for relating ocean carbon storage to important climate metrics, such as the transient response to cumulative emissions.

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Linkage of Arctic Sea Ice and Energy Transport

10.5194/egusphere-egu21-2057 ◽

2021 ◽

Author(s):

Ines Höschel ◽

Dörthe Handorf ◽

Christoph Jacobi ◽

Johannes Quaas

Keyword(s):

Sea Ice ◽

Large Scale ◽

Energy Transport ◽

Arctic Sea Ice ◽

The Arctic ◽

Moist Static Energy ◽

Large Scale Circulation ◽

Arctic Sea ◽

Rossby Wave Propagation ◽

Static Energy

The loss of Arctic sea ice as a consequence of global warming is changing the forcing of the atmospheric large-scale circulation. &#160;Areas not covered with sea ice anymore may act as an additional heat source. &#160;Associated changes in Rossby wave propagation can initiate tropospheric and stratospheric pathways of Arctic - Mid-latitude linkages.&#160; These pathways have the potential to impact on the large-scale energy transport into the Arctic.&#160; On the other hand, studies show that the large-scale circulation contributes to Arctic warming by poleward transport of moist static energy. This presentation shows results from research within the Transregional Collaborative Research Center &#8220;ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)3&#8221; funded by the Deutsche Forschungsgemeinschaft.&#160; Using the ERA interim and ERA5 reanalyses the meridional moist static energy transport during high ice and low ice periods is compared. &#160;The investigation discriminates between contributions from planetary and synoptic scale.&#160; Special emphasis is put on the seasonality of the modulations of the large-scale energy transport.

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Large-scale circulation associated with moisture intrusions into the Arctic during winter

Geophysical Research Letters ◽

10.1002/grl.50912 ◽

2013 ◽

Vol 40 (17) ◽

pp. 4717-4721 ◽

Cited By ~ 124

Author(s):

Cian Woods ◽

Rodrigo Caballero ◽

Gunilla Svensson

Keyword(s):

Large Scale ◽

The Arctic ◽

Large Scale Circulation

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Energetics of the Western Hemisphere Circulation Pattern

Journal of Climate ◽

10.1175/jcli-d-19-0211.1 ◽

2019 ◽

Vol 32 (22) ◽

pp. 7857-7870 ◽

Cited By ~ 1

Author(s):

Xin Tan ◽

Ming Bao ◽

Xuejuan Ren

Keyword(s):

North Atlantic ◽

Large Scale ◽

Low Frequency ◽

Lower Troposphere ◽

Circulation Pattern ◽

Western Hemisphere ◽

Self Organizing Maps ◽

Atlantic Sector ◽

The North ◽

Energy Maintenance

Abstract The Western Hemisphere (WH) circulation pattern, identified by self-organizing maps cluster analysis, is a low-frequency atmospheric regime that influences the fluctuations of large-scale circulation over the North Pacific–North American–North Atlantic areas. The reanalysis datasets from ECMWF are used to estimate the energetics of the WH pattern in this study. The composite results based on monthly WH events reveal that the kinetic energy (KE) associated with the WH pattern is maintained through the barotropic conversion from the climatological-mean westerlies, mainly in the Atlantic jet exit regions. The KE could also be gained through the barotropic feedback forcing from transient eddies. The corresponding baroclinic conversion of available potential energy (APE) from the climatological-mean state, which contributes most efficiently to the energy maintenance of the WH pattern, is obvious in the middle and lower troposphere, owing to the thermal contrast of the colder continent and warmer ocean over the North America–North Atlantic sector. The baroclinic conversion associated with the heat flux on the climatological temperature gradient is consistent with the southwestward-tilting height anomalies from 850 to 500 hPa. The baroclinic feedback from transient eddies contributes negatively to the energy conversion and destroys the maintenance of the WH pattern.

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The Robustness of Midlatitude Weather Pattern Changes due to Arctic Sea Ice Loss

Journal of Climate ◽

10.1175/jcli-d-16-0167.1 ◽

2016 ◽

Vol 29 (21) ◽

pp. 7831-7849 ◽

Cited By ~ 34

Author(s):

Hans W. Chen ◽

Fuqing Zhang ◽

Richard B. Alley

Keyword(s):

Sea Ice ◽

Large Scale ◽

Coupled System ◽

Circulation Pattern ◽

Ice Cover ◽

Arctic Sea Ice ◽

The Arctic ◽

Intrinsic Variability ◽

Arctic Sea ◽

Arctic Sea Ice Loss

Abstract The significance and robustness of the link between Arctic sea ice loss and changes in midlatitude weather patterns is investigated through a series of model simulations from the Community Atmosphere Model, version 5.3, with systematically perturbed sea ice cover in the Arctic. Using a large ensemble of 10 sea ice scenarios and 550 simulations, it is found that prescribed Arctic sea ice anomalies produce statistically significant changes for certain metrics of the midlatitude circulation but not for others. Furthermore, the significant midlatitude circulation changes do not scale linearly with the sea ice anomalies and are not present in all scenarios, indicating that the remote atmospheric response to reduced Arctic sea ice can be statistically significant under certain conditions but is generally nonrobust. Shifts in the Northern Hemisphere polar jet stream and changes in the meridional extent of upper-level large-scale waves due to the sea ice perturbations are generally small and not clearly distinguished from intrinsic variability. Reduced Arctic sea ice may favor a circulation pattern that resembles the negative phase of the Arctic Oscillation and may increase the risk of cold outbreaks in eastern Asia by almost 50%, but this response is found in only half of the scenarios with negative sea ice anomalies. In eastern North America the frequency of extreme cold events decreases almost linearly with decreasing sea ice cover. This study’s finding of frequent significant anomalies without a robust linear response suggests interactions between variability and persistence in the coupled system, which may contribute to the lack of convergence among studies of Arctic influences on midlatitude circulation.

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Greenland accumulation and its connection to the large-scale atmospheric circulation in ERA-Interim and paleo-climate simulations

Climate of the Past Discussions ◽

10.5194/cpd-9-3825-2013 ◽

2013 ◽

Vol 9 (4) ◽

pp. 3825-3870

Author(s):

N. Merz ◽

C. C. Raible ◽

H. Fischer ◽

V. Varma ◽

M. Prange ◽

...

Keyword(s):

Atmospheric Circulation ◽

Large Scale ◽

Ice Core ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Circulation Pattern ◽

Local Flow ◽

Large Scale Circulation ◽

Circulation Patterns ◽

Local Accumulation

Abstract. Accumulation and aerosol chemistry records from Greenland ice cores offer the potential to reconstruct variability in Northern Hemisphere atmospheric circulation over the last millennia. However, an important prerequisite for a reconstruction is the stable relationship between local accumulation at the ice core site with the respective circulation pattern throughout the reconstruction period. We address this stability issue by using a comprehensive climate model and performing time-slice simulations for the present, the pre-industrial, the early Holocene and the last glacial maximum (LGM). The relationships between accumulation, precipitation and atmospheric circulation are investigated on on various time-scales. The analysis shows that the relationship between local accumulation on the Greenland ice sheet and the large-scale circulation undergoes a significant seasonal cycle. As the weights of the individual seasons change, annual mean accumulation variability is not necessarily related to the same atmospheric circulation patterns during the different climate states. Within a season, local Greenland accumulation variability is indeed linked to a consistent circulation pattern, which is observed for all studied climate periods, even for the LGM, however these circulation patterns are specific for different regions on the Greenland ice sheet. The simulated impact of orbital forcing and changes in the ice-sheet topography on accumulation exhibits strong spatial variability emphasizing that accumulation records from different ice core sites cannot be expected to look alike since they include a distinct local signature. Accumulation changes between different climate periods are dominated by changes in the amount of snowfall and are driven by both thermodynamic and dynamic factors. The thermodynamic impact determines the strength of the hydrological cycle, and warmer temperatures are generally accompanied by an increase in Greenland precipitation. Dynamical drivers of accumulation changes are the large-scale circulation and the local orography having a distinct influence on the local flow characteristic and hence the amount of precipitation deposited in any Greenland region.

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Trend in temperature extreme indices over Mongolia and associated large-scale circulations

10.21203/rs.3.rs-133487/v1 ◽

2020 ◽

Author(s):

Baljinnyam Nyamjantsan ◽

Changhyun Yoo

Keyword(s):

Large Scale ◽

Extreme Temperature ◽

The Arctic ◽

Gobi Desert ◽

Temperature Extremes ◽

Temperature Extreme ◽

East Atlantic ◽

Rate Of Increase ◽

June July ◽

Extreme Indices

Abstract Employing the percentile-based indices, TN10p, TX10p, TN90p, and TX90p during 1961–2018, we evaluate temporal and spatial trends in extreme temperature at 54 stations over Mongolia. Statically significant changes in temperature extremes in the warm (TN90p and TX90p) and cool indices (TN10p and TX10p) are found. The rate of increase in the number of warm nights and days are respectively 1.5 and 1.9 days decade− 1, while the cool nights and days show a declining trend of -0.8 and − 1.5 days decade− 1, respectively. Despite the fact that the trends are most vigorous during June-July-August, seasonal variations can be seen. Also, spatial distributions of the trends reveal weakest magnitudes in Gobi Desert, while strongest in the west and north of Mongolia. The large-scale atmospheric circulations account for changes in the temperature extreme indices. The East Atlantic, East Atlantic/western Russian, and Scandinavian patterns, and the Arctic Oscillation is found to contribute the most to the interannual variation in the temperature extremes.

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Moisture origin as a driver of temporal variabilities of the water vapour isotopic composition in the Lena River Delta, Siberia

10.5194/acp-2019-942 ◽

2020 ◽

Cited By ~ 1

Author(s):

Jean-Louis Bonne ◽

Hanno Meyer ◽

Melanie Behrens ◽

Julia Boike ◽

Sepp Kipfstuhl ◽

...

Keyword(s):

Isotopic Composition ◽

Water Vapour ◽

Hydrological Cycle ◽

Diurnal Variations ◽

The Arctic ◽

Northern Eurasia ◽

Research Station ◽

Atlantic Sector ◽

Moisture Sources ◽

Lena Delta

Abstract. In the context of the Arctic amplification of climate change affecting the regional atmospheric hydrological cycle, it is crucial to characterize the present-day’s moisture sources of the Arctic. The isotopic composition is an important tool to enhance our understanding of the drivers of the hydrological cycle, due to the different molecular characteristics of water stable isotopes during phase change. This study introduces two years of continuous in situ water vapour and precipitation isotopic observations conducted since July 2015 in the east-Siberian Lena delta, at the research station on the Samoylov Island. The vapour isotopic signals are dominated by variations at the seasonal and synoptic time scales. Diurnal variations of the vapour isotopic signals are masked by synoptic variations, indicating low variations of the amplitude of local sources at the diurnal scale in winter, summer and autumn. Low amplitude diurnal variations in spring may indicate exchange of moisture between the atmosphere and the snow-covered surface. Moisture sources diagnostics based on semi-Lagrangian backward trajectories reveal that different air mass origins have contrasted contributions to the moisture budget of the Lena delta region. At the seasonal scale, the distance from the net moisture sources to the arrival site strongly varies. During the coldest months, no contribution from local secondary evaporation is observed. Variations of the vapour isotopic composition during the cold season on synoptic time scale are strongly related to moisture source regions and variations in the atmospheric transport: warm and isotopically-enriched moist air is linked with fast transport from the Atlantic sector; while dry and cold air with isotopically-depleted moisture is generally associated to air masses moving slowly over northern Eurasia.

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