Arctic Warming Research Articles

The weakening AMOC under extreme climate change

Changes in the Atlantic Meridional Overturning Circulation (AMOC) in the quadrupled CO2 experiments conducted under the sixth Coupled Model Intercomparison Project (CMIP6) are examined. Increased CO2 triggers extensive Arctic warming, causing widespread melting of sea ice. The resulting freshwater spreads southward, first from the Labrador Sea and then the Nordic Seas, and proceeds along the eastern coast of North America. The freshwater enters the subpolar gyre north of the separated Gulf Stream, the North Atlantic Current. This decreases the density gradient across the current and the current weakens in response, reducing the inflow to the deepwater production regions. The AMOC cell weakens in tandem, first near the North Atlantic Current and then spreading to higher and lower latitudes. This contrasts with the common perception that freshwater caps the convection regions, stifling deepwater production; rather, it is the inflow to the subpolar gyre that is suppressed. Changes in surface temperature have a much weaker effect, and there are no consistent changes in local or remote wind forcing among the models. Thus an increase in freshwater discharge, primarily from the Labrador Sea, is the precursor to AMOC weakening in these simulations.

Asymmetric impacts of surface thaw onset change on seasonal vegetation growth in Arctic permafrost

AbstractAimChanges in surface thaw onset in Arctic permafrost can regulate terrestrial ecosystem dynamics. Permafrost surface thaw onset has advanced significantly because of strong Arctic warming. However, surface thaw onset change effects on vegetation during the different growing season stages remain unclear.LocationArctic and subarctic permafrost region.Time Period1982–2016.Major Taxa StudiedArctic vegetation.MethodsThis study investigated surface thaw onset change effects on vegetation growth in the Arctic permafrost region by analysing the relationships between surface thaw onset dates and vegetation indices obtained via satellite remote sensing from 1982 to 2016.ResultsThe leaf area index (LAI) from April to June was negatively correlated (−0.16 area‐averaged partial correlation coefficient) with surface‐thawed dates in over 78.6% of the Arctic permafrost region, and the LAI from August to October was positively correlated (0.17 area‐averaged partial correlation coefficient) with surface‐thawed dates in over 79.9% of the Arctic permafrost region. These distinct relationships suggest that earlier thaw onset may have a positive effect on vegetation growth during the early stage of the growing season. However, earlier thaw onset can limit vegetation growth during the late stage of the growing season. The different relationships between surface thaw onset and LAI can be explained by moisture availability. This difference occurred because 67.3% of the Arctic permafrost region was more constrained by temperature during the early stage of the growing season, therefore, the earlier thaw onset alleviated this temperature constraint and benefited vegetation growth. During the late stage of the growing season, 47.7% of the Arctic permafrost region was more constrained by moisture.Main ConclusionsOur results suggest that surface thaw onset change effects on vegetation vary by period, and this difference requires careful consideration when predicting ecosystem changes in permafrost regions.

Interannual variation of the Warm Arctic–Cold Eurasia pattern modulated by Ural blocking and the North Atlantic Oscillation under changing sea ice conditions

Together with rapid Arctic warming and sea ice decline, especially over the Barents–Kara seas (BKS), extreme cold winters have occurred frequently in mid-latitudes, particularly in Central Eurasia. A pattern with two distinct winter temperature anomalies centered over the BKS and Central Eurasia is known as the Warm Arctic–Cold Eurasia (WACE) pattern. The impacts of sea ice loss over the BKS and internal atmospheric variability on past WACE formation remain under discussion mainly due to the large internal atmospheric variability in the mid-latitudes. This study analyzed a large-ensemble historical experiment prescribing observed sea ice condition to investigate the role of internal atmospheric variability in the observed interannual variation of the WACE pattern. Comparison of ensemble members suggests that internal atmospheric variability is important for regulating the magnitude of the WACE pattern. Besides the strong effect of local sea ice loss, winter temperature over the BKS increases due to warm advection driven by the Ural blocking and positive phase of the North Atlantic Oscillation. A decrease in winter temperature over Central Eurasia is mainly attributable to the cold advection enhanced by Ural blocking rather than the remote effect of sea ice decline over the BKS. Our study reveals the importance of internal atmospheric variability in elucidating the observed interannual variation of the WACE pattern.

Leading role of outer-Arctic circulation transport in AMOC response to global warming over a century

Using the Alfred Wegener Institute Climate Model (AWI-CM 1.1 LR), we explored how Arctic and extra-Arctic warming affect the response of Atlantic meridional overturning circulation (AMOC) to quadruple carbon dioxide (4 × CO2) forcing. The results suggest that AMOC weakening is mainly affected by circulation adjustment caused by extra-Arctic warming, while Arctic warming has a limited local impact and a relatively small contribution to AMOC weakening. Due to the warming outside the Arctic, the increase in northward advective heat transport dominates the weakening of deep convection in Nordic Seas. While in the Labrador Sea, the decrease in advection heat transport is compensated by a more significant decrease in ocean heat loss to the atmosphere, leading to an enhancement of the upper ocean stratification. Besides, the weakening of deep convection associated with AMOC response under global warming is more pronounced in Nordic Seas than in Labrador Sea.

Contrasting Deep and Shallow Winter Warming over the Barents–Kara Seas on the Intraseasonal Time Scale

Abstract The vertical structure of Arctic warming is of great importance and attracts increasing attention. This study defines two types of Arctic warming events (deep versus shallow) according to their temperature profiles averaged over the Barents–Kara Seas (BKS), and thereupon compares their characteristics and examines their difference in generation through thermodynamic diagnoses. A deep Arctic warming event—characterized by significant bottom-heavy warming extending from the surface into the middle-to-upper troposphere—emanates from the east of Greenland and then moves downstream toward the BKS primarily through zonal temperature advection. The peak day of deep warming event lags that of the precipitation and resultant diabatic heating over southeast Greenland by about four days, suggesting that the middle-to-high tropospheric BKS warming is likely triggered by the enhanced upstream convection at the North Atlantic high latitudes. In contrast, a shallow warming event—manifested by warming confined within the lower troposphere—is preceded by the meridional advection of warm air from inland Eurasia. These anomalous southerlies over Eurasian lands during shallow warming events are related to the eastward extension of the deepened Icelandic low. During deep warming events, the in situ reinforcement of the Icelandic low favors abundant moisture transport interplaying with the southeast Greenland terrain, leading to intense precipitation and latent heat release there. Both deep and shallow warming events are accompanied by Eurasian cooling, but the corresponding cooling of the deep warming event is profoundly stronger. Further, intraseasonal deep Arctic warming events could explain nearly half of the winter-mean change in the warm Arctic–cold Eurasia anomaly. Significance Statement Divergent conclusions on whether Arctic warming is influencing the midlatitudes impede a clear understanding of the warm Arctic–cold Eurasia (WACE) phenomenon. Recent findings that on the interannual or longer time scales, Eurasian cooling tends to occur in the presence of deep rather than shallow Arctic warming have attracted increasing concern regarding the vertical structure of Arctic warming. On this basis, here we classify intraseasonal Arctic warming events into deep and shallow groups and contrast them from various aspects. Emerging near eastern Greenland and associated with upstream convection activities, intraseasonal deep Arctic warming events are accompanied by significant Eurasian cooling, largely determining the seasonal-mean WACE condition. However, caused by meridional temperature advection from Eurasian lands, shallow warming events less correlate with Eurasian cooling.

Современные проблемы коренных малочисленных народов российской Арктики в условиях климатических изменений

The article describes the current problems of small indigenous peoples of the Russian Arctic in the context of climate change, the main of which are: the food problem, the problem of transport accessi-bility, the problem of economic activity and the problem of health. Because of global warming due to the increase in the average annual temperature, there is a high probability that the above-mentioned problems will only increase and significantly affect all life support systems of small indigenous peoples of the Russian Arctic. The article uses analysis and synthesis, induction and deduction to show the interconnection and mutual influence of the existing problems on the economic activity and health of small indigenous peoples in the conditions of climate change in the Arctic. In order to solve the current problems of the Russian Arctic indigenous minorities in the context of climate change, the following is required: 1) development of laws, strategies and/or state programs for the protection of indigenous peoples to minimize the adverse effects of climate change by sectors (reindeer herding, fishing, hunting and gathering); 2) creation of a system for assessing the impact of climate change on the economic activity and health of indigenous peoples; 3) participation of indigenous peoples in environmental monitoring and implementation of environmental projects in the Arctic.

No detectable trend in mid-latitude cold extremes during the recent period of Arctic amplification

It is widely accepted that Arctic amplification—accelerated Arctic warming—will increasingly moderate cold air outbreaks to the mid-latitudes. Yet, an increasing number of recent studies also argue that Arctic amplification can contribute to more severe winter weather. Here we show that the temperature of cold extremes across the United States east of the Rockies, Northeast Asia and Europe have remained nearly constant over recent decades, in clear contrast to a robust Arctic warming trend. Analysis of trends in the frequency and magnitude of cold extremes is mixed across the US and Asia but with a clearer decreasing trend in occurrence across Europe, especially Southern Europe. This divergence between robust Arctic warming and no detectable trends in mid-latitude cold extremes highlights the need for a better understanding of the physical links between Arctic amplification and mid-latitude cold extremes.

Arctic warming drives striking twenty-first century ecosystem shifts in Great Slave Lake (Subarctic Canada), North America's deepest lake.

Great Slave Lake (GSL), one of the world's largest and deepest lakes, has undergone an aquatic ecosystem transformation in response to twenty-first-century accelerated Arctic warming that is unparalleled in at least the past two centuries. Algal remains from four high-resolution palaeolimnological records retrieved from the West Basin provide baseline limnological data that we compared with historical phycological surveys undertaken on GSL between the 1940s and 1990s. We document the rapid restructuring of algal community composition ca 2000 CE that is consistent with recent increases in regional air temperature and declines in ice cover and wind speed, that collectively altered habitats for aquatic biota. This new limnological regime initiated the first observation of scaled chrysophytes and favoured the rapid proliferation of small planktonic cyclotelloid diatoms which replaced the long-established dominance of large filamentous Aulacoseira islandica in West Basin sedimentary records. Such abrupt transformations in the primary producers of this socioecologically valuable 'northern Great Lake' may have widespread implications for the entire food web with unknown consequences for aquatic ecosystem functioning and fisheries, which First Nations, Métis and other northern communities depend upon, pointing to the need for new studies.

Current-climate sea ice amount and seasonality as constraints for future Arctic amplification

The recent Arctic sea ice loss is a key driver of the amplified surface warming in the northern high latitudes, and simultaneously a major source of uncertainty in model projections of Arctic climate change. Previous work has shown that the spread in model predictions of future Arctic amplification (AA) can be traced back to the inter-model spread in simulated long-term sea ice loss. We demonstrate that the strength of future AA is further linked to the current climate’s, observable sea ice state across the multi-model ensemble of the 6th Coupled Model Intercomparison Project (CMIP6). The implication is that the sea-ice climatology sets the stage for long-term changes through the 21st century, which mediate the degree by which Arctic warming is amplified with respect to global warming. We determine that a lower base-climate sea ice extent and sea ice concentration (SIC) in CMIP6 models enable stronger ice melt in both future climate and during the seasonal cycle. In particular, models with lower Arctic-mean SIC project stronger future ice loss and a more intense seasonal cycle in ice melt and growth. Both processes systemically link to a larger future AA across climate models. These results are manifested by the role of climate feedbacks that have been widely identified as major drivers of AA. We show in particular that models with low base-climate SIC predict a systematically stronger warming contribution through both sea-ice albedo feedback and temperature feedbacks in the future, as compared to models with high SIC. From our derived linear regressions in conjunction with observations, we estimate a 21st-century AA over sea ice of 2.47–3.34 with respect to global warming. Lastly, from the tight relationship between base-climate SIC and the projected timing of an ice-free September, we predict a seasonally ice-free Arctic by mid-century under a high-emission scenario.

Priorities and limitations of development of international scientific cooperation of circumpolar countries in the field of sustainable development of the Arctic

Aim. To identify priorities and limitations of the development of international scientific cooperation of circumpolar countries in the field of sustainable development of the Arctic.Tasks. To characterize circumpolar countries with identification of their natural, climatic and socio-economic features; to assess the impact of climate change on the sustainable development of circumpolar countries; to identify priorities for the development of international scientific cooperation in the field of sustainable development of the Arctic in the context of climate change; to identify the features of Arctic policy of circumpolar countries in modern conditions.Methods. The methodology of the presented study was developed based on its goal and the set scientific objectives. Arctic climate change is assessed by comparing a set of indicators for the period from 1971 to the present. The key priorities of the state Arctic policies of circumpolar countries are identified on the basis of the analysis of their political and program documents. The priorities for the development of international cooperation in the field of sustainable development of the Arctic are identified on the basis of the author’s works and correlated with the opinion of authoritative Arctic researchers.Results. The conducted research has shown that the rapid climate change in the Arctic has become the main challenge of natural origin to the sustainable development of circumpolar countries. The following priorities of scientific research within the framework of international cooperation of circumpolar countries in the field of sustainable development of the Arctic have been identified: first, comprehensive study of natural, anthropogenic, socio-economic processes in the Arctic; second, thorough documentation of the identified features; third, creation of a unified international database reflecting the ecological, economic, and social state of the Arctic territories; fourth, comprehensive modeling and assessment of the impact of climate change on the sustainable development of the Arctic; third, creation of a single international database reflecting the ecological, economic, and social state of the Arctic territories; third, creation of a single international database reflecting the ecological, economic, and social state of the Arctic territories; fourth, comprehensive modeling and assessment of the impact of climate change in the Arctic.Conclusions. The climate challenge of sustainable development of the Arctic territories can only be met through individual and joint efforts of all circumpolar countries. Initially, the national strategies of the circumpolar countries were based on a common aspiration: to work through close cooperation, including scientific cooperation, with international partners to achieve the common goal of creating a peaceful, economically successful and sustainable future for the Arctic. The exclusion of the Russian Federation (RF) from international scientific cooperation on issues of environmental management in the context of climate change repeatedly increases the risks of sustainable development of the Arctic territories.

The Effect of Arctic Sea‐Ice Loss on Extratropical Cyclones

AbstractTaking advantage of the Polar Amplification Model Intercomparison Project simulations and using a Lagrangian objective feature tracking algorithm, we determine the response of extratropical cyclones to sea‐ice loss and consequent weakening of the equator‐to‐pole near‐surface temperature gradient. The wintertime storm tracks are found to shift equatorward in the North Atlantic and over Europe, and eastward in the North Pacific. In both regions, cyclones become weaker and slower, particularly on the poleward flank of the storm tracks. On average, there are fewer individual cyclones in the extratropics each winter, they last longer, are weaker, and travel more slowly. These changes are greatest over the Arctic, but still statistically significant in midlatitudes despite being small compared to internal variability. Inter‐model spread in cyclone responses are not strongly correlated with that in Arctic warming or Arctic amplification. Little change in summertime cyclones is found.

Quantifying exchangeable base cations in permafrost: a reserve of nutrients about to thaw

Abstract. Permafrost ecosystems are limited in nutrients for vegetation development and constrain the biological activity to the active layer. Upon Arctic warming, permafrost thaw exposes large amounts of soil organic carbon (SOC) to decomposition and minerals to weathering but also releases organic and mineral soil material that may directly influence the soil exchange properties (cation exchange capacity, CEC, and base saturation, BS). The soil exchange properties are key for nutrient base cation supply (Ca2+, K+, Mg2+, and Na+) for vegetation growth and development. In this study, we investigate the distributions of soil exchange properties within Arctic tundra permafrost soils at Eight Mile Lake (Interior Alaska, USA) because they will dictate the potential reservoir of newly thawed nutrients and thereby influence soil biological activity and vegetation nutrient sources. Our results highlight much lower CEC density in surface horizons (∼9400 cmolc m−3) than in the mineral horizons of the active layer (∼16 000 cmolc m−3) or in permafrost soil horizons (∼12 000 cmolc m−3). Together, with the overall increase in CEC density with depth and the overall increase in BS (percentage of CEC occupied by exchangeable base cations Ca2+, K+, Mg2+, and Na+) with depth (from ∼19 % in organic surface horizons to 62 % in permafrost soil horizons), the total exchangeable base cation density (Ca2+, K+, Mg2+, and Na+ in g m−3) is up to 5 times higher in the permafrost than in the active layer. More specifically, the exchangeable base cation density in the 20 cm upper part of permafrost about to thaw is ∼850 g m−3 for Caexch, 45 g m−3 for Kexch, 200 g m−3 for Mgexch, and 150 g m−3 for Naexch. This estimate is needed for future ecosystem prediction models to provide constraints on the size of the reservoir in exchangeable nutrients (Ca, K, Mg, and Na) about to thaw. All data described in this paper are stored in Dataverse, the online repository of Université catholique de Louvain, and are accessible through the following DOI: https://doi.org/10.14428/DVN/FQVMEP (Mauclet et al., 2022b).

Robust and perfectible constraints on human-induced Arctic amplification

The Arctic near-surface warming is much faster than its global counterpart. Yet, this Arctic amplification occurs a rate that is season, model and forcing-dependent. The present study aims at using temperature observations and reanalyses to constrain the projections of Arctic climate during the November-to-March season. Results show that the recently observed four-fold warming ratio is not entirely due to a human influence, and will decrease with increasing radiative forcings. Global versus regional temperature observations lead to complementary constraints on the projections. When Arctic amplification is defined as the additional polar warming relative to global warming, model uncertainties are narrowed by 30% after constraint. Similar results are obtained for projected changes in the Arctic sea ice extent (40%) and when using sea ice concentration and polar temperature observations to constrain the projected polar warming (37%), thereby confirming the key role of sea ice as a positive but model-dependent surface feedback.

Arctic warming by abundant fine sea salt aerosols from blowing snow

The Arctic warms nearly four times faster than the global average, and aerosols play an increasingly important role in Arctic climate change. In the Arctic, sea salt is a major aerosol component in terms of mass concentration during winter and spring. However, the mechanisms of sea salt aerosol production remain unclear. Sea salt aerosols are typically thought to be relatively large in size but low in number concentration, implying that their influence on cloud condensation nuclei population and cloud properties is generally minor. Here we present observational evidence of abundant sea salt aerosol production from blowing snow in the central Arctic. Blowing snow was observed more than 20% of the time from November to April. The sublimation of blowing snow generates high concentrations of fine-mode sea salt aerosol (diameter below 300 nm), enhancing cloud condensation nuclei concentrations up to tenfold above background levels. Using a global chemical transport model, we estimate that from November to April north of 70° N, sea salt aerosol produced from blowing snow accounts for about 27.6% of the total particle number, and the sea salt aerosol increases the longwave emissivity of clouds, leading to a calculated surface warming of +2.30 W m−2 under cloudy sky conditions.

Tonga volcanic eruption triggered anomalous Arctic warming in early 2022

On 15 January 2022, the submarine volcano on Hunga Tonga-Hunga Ha'apai Island erupted and injected a small amount of SO2 but an unprecedent amount of water vapor into the stratosphere. The impact of Tonga eruption on climate was dynamically simulated using a fully coupled climate prediction system FIO-CPS v2.0 by considering both SO2 and water vapor injections into the stratosphere, which is the first attempt to incorporate the volcanic water vapor injection in a climate prediction system to evaluate its effect on surface climate response. Model results indicated that the surface air temperature (SAT) over the Arctic region was significantly warmer in early 2022 as a response to the co-injection of SO2 and water vapor from Tonga eruption, although its effect on global mean SAT was found to be insignificant. In February 2022, the average warming anomaly in the Arctic area reached up to 1.1 °C, with zonal mean warming of 2.0 °C near the North Pole. The Tonga eruptions induced anomalous heat transport which primarily contributed to the Arctic warming in February. However, it had a cooling effect on the Arctic area in January and March. In addition to heat transport, the eruption also triggered anomalous northward transport of water vapor. This led to an increase in the water vapor content, which further enhanced the downward longwave radiation and cloud-radiative feedback over the Arctic region, ultimately contributing to the Arctic SAT warming in early 2022. In the simulation only SO2 injection was considered without water vapor injection, the pattern of SAT response showed warming over the Eurasian continent and cooling in the north over Arctic Ocean, which is opposite to that in the simulation with co-injection of SO2 and water vapor. This indicated that volcanic water vapor injection of Tonga eruption played a dominant role in the Arctic warming. Consequently, submarine volcano should receive more attention due to its potential climate effects, especially when it involves significant water vapor releases.

Role of Horizontal Heat Advection in Arctic Surface Warming During Early Spring

AbstractReanalysis data and numerical model are employed to uncover the mechanisms of spring (March–April) Arctic surface warming. Different from other seasons, little additional solar radiation absorption or seasonal heat storage release contributes to Arctic surface warming in spring. Both observation and numerical results suggest that horizontal heat advection dominates Arctic surface air warming. However, horizontal advection originates from lower latitudes instead of local energy redistribution as in other seasons. Furthermore, Arctic warming weakens the meridional potential vorticity gradient, which strengthens the synoptic atmospheric blocking event. As a result, more warm (cold) air is transported to higher (lower) latitudes along the edge of high pressure, which is an accumulation of atmospheric blocking events. The results suggest that anomalous meridional heat transport plays more important roles in Arctic surface warming when the anomalous radiative forcing is weak. Without being absorbed by the ocean, additional available energy induces strong Arctic springtime surface warming.

The Effect of Temperature on the Distribution of Zoonotic Pathogens in Livestock and Wildlife Populations: A Systematic Review

Background. Evidence for the impact of climate change on the distribution of zoonoses has largely focussed on the burden in humans and is lacking information on the effect of temperature on nonvectorborne zoonoses that are transmitted indirectly through contaminated environments. We present a systematic literature review on the impact of temperature on the distribution of zoonotic pathogens in mammalian livestock and wildlife populations, with a focus on nonvectorborne zoonoses that can be spread through air, water, food, and soil. Methods. We systematically searched PubMed, Scopus, and Web of Science, as well as grey literature, and screened titles, abstracts, and full text. English, peer-reviewed, and full text studies were included if they: focused on temperature; considered incursion, distributional burden or risk; and focused on a zoonotic pathogen in livestock and/or wildlife populations of mammalian vertebrates that can be transmitted through indirect pathways without a nonmammalian and nonvertebrate intermediate host. Results. Temperature was an important determinant of zoonoses distribution across all 17 studies included in the final review, with 11 studies finding a positive association. The majority of studies focused on parasites (7) and bacteria (9) and were conducted in the northern hemisphere. Two studies provided future climate projections that identified areas of increasing prevalence and expanded risk for pathogens that were already established. However, no studies specifically investigated the risk of zoonotic incursion with increasing temperature. Few studies explored how local variations in temperature and urbanisation interact with distal changes like Arctic warming to affect the distribution and spread of nonvectorborne pathogens through food, water, and soil. Conclusions. The review’s findings point to the value of a One Health approach to biosecurity that builds on the interconnected relationship between human, animal, plant, and environmental health. Such research is urgently needed to inform the prioritisation and risk assessment of zoonoses more comprehensively in a rapidly changing climate.

The Marginal Ice Zone as a dominant source region of atmospheric mercury during central Arctic summertime

Atmospheric gaseous elemental mercury (GEM) concentrations in the Arctic exhibit a clear summertime maximum, while the origin of this peak is still a matter of debate in the community. Based on summertime observations during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition and a modeling approach, we further investigate the sources of atmospheric Hg in the central Arctic. Simulations with a generalized additive model (GAM) show that long-range transport of anthropogenic and terrestrial Hg from lower latitudes is a minor contribution (~2%), and more than 50% of the explained GEM variability is caused by oceanic evasion. A potential source contribution function (PSCF) analysis further shows that oceanic evasion is not significant throughout the ice-covered central Arctic Ocean but mainly occurs in the Marginal Ice Zone (MIZ) due to the specific environmental conditions in that region. Our results suggest that this regional process could be the leading contributor to the observed summertime GEM maximum. In the context of rapid Arctic warming and the observed increase in width of the MIZ, oceanic Hg evasion may become more significant and strengthen the role of the central Arctic Ocean as a summertime source of atmospheric Hg.

Contribution of the tropical sea surface temperature in the Arctic tropospheric warming during 1979–2013

The contribution of the tropical sea surface temperature in the Arctic tropospheric warming during 1979–2013 was studied through simulations using the CAM6-Nor atmospheric general circulation model. Results showed that the tropical sea surface temperature explained about 30%–40% of the autumn warming and the January warming in the historical simulation. This implies that the tropical sea surface temperature could have been one of the main drivers of Arctic winter tropospheric warming between 1979 and 2013. The tropical sea surface temperature impacts generally came from a combination of the effects of the tropical central-eastern Pacific, the tropical Indo-western Pacific, and the tropical Atlantic, except for the January warming below 850 hPa, which was dominated by the tropical Indo-western Pacific impacts.

Impacts of the extratropical North Pacific on boreal summer Arctic circulation

A distinct characteristic of the Arctic summer atmospheric circulation is the anomalous anticyclonic circulation centered over the Arctic Ocean associated with significant Arctic warming. Previous studies have related the underlying mechanisms to the earlier spring Eurasian snowmelt and the tropical Pacific forcing. Here, the authors show that the Arctic summer anomalous anticyclonic circulation is significantly related to the extratropical North Pacific sea surface temperature anomalies (SSTAs) in spring, indicating a teleconnection from the extratropical North Pacific to the Arctic. The SSTA pattern is characterized by warm anomalies in the midlatitudes of the extratropical North Pacific surrounded by significant cold anomalies, resembling the negative phase of the Pacific Decadal Oscillation (PDO) but without significant signals in the tropics (referred to as the negative PDO-like pattern). This negative PDO-like pattern in May can stimulate a Rossby wave propagating from the Bering Sea to the Arctic and lead to an anomalous Arctic anticyclone which can be sustained during summer. Meanwhile, the negative PDO-like pattern can persist to summer and induce an anomalous surface low pressure over the Bering Sea in summer. This anomalous surface low causes anomalous rising motions and induces upper-level divergence anomalies which further intensify the summer Arctic anticyclone. The upper-level tropospheric Arctic anticyclone can force anomalous adiabatic descent over the Arctic and sub-Arctic, leading to significant adiabatic heating in the Arctic. As a result, a significant warming emerges over the Arctic with the center located in the middle troposphere. The connection between the negative PDO-like SSTAs and the summer Arctic anticyclone has been confirmed by numerical experiments.