The causes of Arctic surface air temperature rise and the corresponding sea ice decline in the early 20th century are still a matter of debate. One hypothesis, considering the major contribution of the internal variability to the early warming event, is the leading one. This study aims to assess the contributions of the Northern Hemisphere’s leading natural variability modes to winter temperature changes in the Arctic during 20th century. Two methodologies were compared to remove externally forced signals from Arctic SAT observations—linear detrending and subtracting the multi-model ensemble mean, thereby isolating internal variability. The study introduces a novel perspective on regional evaluation across four equal-area Arctic sectors (European, Asian, Pacific, and North Atlantic), uncovering a heterogeneous spatial pattern of the Arctic SAT modulation by climate indices. Statistical analysis reveals northern extratropical modes explain 66% (median) of total variance, with dominance of AMO index in HadCRUT5 detrended observations and only 30% with PDO index prominent in observations-CMIP6 residuals. It is revealed that forced-signal removal data outperforms the detrending procedure in isolating unforced internal dynamics. AMO’s susceptibility to external forcings like greenhouse gases/aerosols is also underscored by the results of the study. Future directions advocate dynamic approaches like large initial-condition ensembles prescribing sea surface temperature/sea ice or isolating modes for causal attribution beyond statistical links.

This study investigates seasonal changes in near-surface wind speeds in the Arctic using the regional climate model (RCM) simulations with RCA4 driven by four global climate models (GCMs) CMIP5 under Representative Concentration Pathways (RCP) 4.5 and 8.5 scenarios. In addition, the RCM RCA-GUESS (RCA4 with interactive vegetation dynamics) is used to investigate the role of biogeophysical feedbacks in modulating near-surface wind speeds under different RCP scenarios. Our results show that the reduction in ocean surface roughness induced by sea-ice reduction leads to a projected increase in near-surface wind speeds over the Arctic Ocean, with the most pronounced effects occurring in autumn and winter. Overall, the projected changes in near-surface wind speeds from the RCM are consistent with the changes from the forcing GCMs though the RCM simulations show larger amplitude changes compared to the GCMs. The expansion of vegetation on land increases surface roughness and alters atmospheric circulation by modifying static stability and the land-sea temperature contrast, leading to changes in near-surface wind speeds. Specifically, wind speeds decrease over continental regions but increase over parts of the Arctic Ocean. This study emphasizes that interactive vegetation dynamics significantly influence changes in land surface properties and near-surface wind speeds. These processes should be incorporated into Earth system models to enhance the accuracy of future climate projections.

Based on the ERA5 reanalysis data for the period 1979-2021, the authors have quantified the seasonal and regional connections between significant wave heights and changes in cyclone activity in the atmosphere of the Northern Hemisphere. The contribution of extratropical cyclones to the formation of the corresponding features and variations of sea waves is evaluated. The maxima of the extreme sea wave occurrence frequency in winter and summer corresponds to sea areas with an increased frequency of cyclones, in particular, over the Pacific and Atlantic oceans. It has been found that the contribution of extratropical cyclones to the generation of significant wave heights reaches 70% in winter and 50% in summer. The largest contribution is associated with intense cyclones: 90% in winter and 40% in summer.

The study presents the classification of cyclones according to the region of origin and track in the Euro-Atlantic sector. The cyclones have been identified according to the ERA5 reanalysis data. Their seasonal frequency, travel speed, size, and central pressure have been quantified, and their trends have been revealed. Mean and maximum total precipitation associated with the distinguished types of cyclones over the territory of Europe is determined. It is shown that the frequency of the North Atlantic cyclones in the recent 40 years has decreased in winter, summer, and autumn and increased in spring. It has been revealed, that the frequency of the southern cyclones insignificantly decreases in summer and increases in winter. A decrease in minimum central pressure for some types of the North Atlantic cyclones occurs in winter and summer. There is an increase in maximum total precipitation in winter due to the North Atlantic cyclones and in summer due to the southern cyclones. The number of days with cyclonic precipitation decreases for all types of cyclones.

Using the statistical properties of the solution of the Fokker–Planck–Kolmogorov equation (FPK) for velocities and coordinates and using the vortex identification method, quantitative estimates of the distributions of various characteristics of cyclones and anticyclones (including lifetime, wind speed, size, characteristic forcing, and kinetic energy) depending on their intensity have been obtained. The calculations are based on ERA5 reanalysis data for the period 2010–2021. The vortex lifetimes estimated using the FPK correspond to the lifetimes obtained using the vortex identification method, and the theoretical distribution of cyclones by intensity practically coincides with those observed. The characteristics of vortices during their life cycle are also investigated. In general, all the characteristics of cyclones analyzed increase with their intensification. However, for intense anticyclones, the increase is not as pronounced as for cyclones.

We obtained quantitative estimates of the spatial and seasonal features of the characteristics of anticyclones in the atmosphere of the Northern Hemisphere and their changes in recent decades using the ERA5 reanalysis data (1979–2021). A high correlation between the interannual variations of the mean seasonal recurrence of anticyclones and surface temperature over extensive regions in the extratropical latitudes of the Northern Hemisphere was noted. According to the obtained estimates, up to 60% of the interannual variance of surface temperature in winter and summer is associated with variations of the mean seasonal recurrence of anticyclones, and up to 50% with variations of intense winter and summer anticyclones.

The Arctic has warmed more than twice the rate of the entire globe. To quantify possible climate change effects, we calculate wind energy potentials from a multi-model ensemble of Arctic-CORDEX. For this, we analyze future changes of wind power density (WPD) using an eleven-member multi-model ensemble. Impacts are estimated for two periods (2020-2049 and 2070-2099) of the 21st century under a high emission scenario (RCP8.5). The multi-model mean reveals an increase of seasonal WPD over the Arctic in the future decades. WPD variability across a range of temporal scales is projected to increase over the Arctic. The signal amplifies by the end of 21st century. Future changes in the frequency of wind speeds at 100 m not useable for wind energy production (wind speeds below 4 m/s or above 25 m/s) has been analyzed. The RCM ensemble simulates a more frequent occurrence of 100 m non-usable wind speeds for the wind-turbines over Scandinavia and selected land areas in Alaska, northern Russia and Canada. In contrast, non-usable wind speeds decrease over large parts of Eastern Siberia and in northern Alaska. Thus, our results indicate increased potential of the Arctic for the development and production of wind energy. Bias corrected and not corrected near-surface wind speed and WPD changes have been compared with each other. It has been found that both show the same sign of future change, but differ in magnitude of these changes. The role of sea-ice retreat and vegetation expansion in the Arctic in future on near-surface wind speed variability has been also assessed. Surface roughness through sea-ice and vegetation changes may significantly impact on WPD variability in the Arctic.

We obtained quantitative estimates of seasonal and regional features and changes in cyclone activity in the atmosphere of the Northern Hemisphere and determined the contribution of extratropical cyclones to the formation of corresponding features and changes in the surface wind, using ERA5 reanalysis data for recent decades (1979–2021). According to these estimates, the contribution of extratropical cyclones to surface wind speeds in the regions of their high occurrence reaches 60% in winter and 50% in summer. The strongest contribution is related to intense cyclones: about 60% in winter and about 25% in summer.

The study addresses the question, if Arctic sea ice decline is the main driver of observed changes in terms of Arctic-midlatitude linkages during winter. We discuss, if the increase of global sea surface temperatures plays an additional role. A set of four model sensitivity experiments with different sea ice and sea surface temperature boundary conditions is analyzed and compared to observed changes in reanalysis data. A detection of atmospheric circulation regimes is performed. These regimes are evaluated for their cyclone and blocking characteristics and their changes in frequency during winter to reveal tropospheric changes induced by the change of boundary conditions. Furthermore, the impacts on the large-scale circulation up into the stratosphere are investigated. The results show that the impact from sea surface temperature changes is generally stronger than the impact of sea ice concentration changes alone. However, in particular in terms of the startospheric pathway, the combined impact of sea ice and sea surface temperature changes reproduces findings from the reanalysis best.For early winter, the observed increase in atmospheric blocking in the region between Scandinavia and the Ural are primarily induced by the changes in sea surface temperatures. Nevertheless, the impacts on the stratospheric circulation in terms of a weakened polar vortex, are only observed if sea ice is reduced and sea surface temperatures are increased. Late winter impacts are more inconsistent in the model sensitivity study, but slightly improved when both components of forcing are changed. In this context, we further identify a discrepancy in the model to reproduce the weakening of the stratospheric polar vortex through blocking induced upward propagation of planetary waves.

Quantitative estimates are obtained for regional features of the frequency distribution of extreme temperature, precipitation, and wind anomalies in the winter months in the Northern Hemisphere extratropical zone, associated with atmospheric circulation regimes (henceforth regimes) in the Euro-Atlantic sector. Using k-means cluster analysis for the daily geopotential height fields from the ERA5 reanalysis for 1979–2021, four most characteristic winter atmospheric circulation regimes are identified in the Euro-Atlantic sector corresponding to the North Atlantic Oscillation (NAO) in the positive (NAO+) and negative (NAO−) phases, Scandinavian blocking (SCAND), and the regime with anomalously high pressure over the North Atlantic and low pressure over Europe (ATL). Trends in the frequency of occurrence and in structures of regimes are analyzed. The NAO+ and NAO− regimes turned out to be asymmetrical in spatial structure with significantly different frequencies of occurrence (33

Changes in wind energy resources in high latitudes of the Northern Hemisphere are quantitatively assessed based on ERA5 reanalysis data for 1979–2021. The wind energy potential (WEP) is estimated during the analysis. According to the ERA5 reanalysis data, the WEP noticeably increases over the Greenland, Norwegian, Barents, Kara, and Chukchi Seas and European Russia in winter and over the Kara and Norwegian Seas in spring under the modern climate regime. A general increase in the WEP is observed along the Arctic coast, in particular, over its Russian sector in summer and autumn. These changes in the WEP correlate quite well with the retreat of sea ice in the Arctic and with the leaf area index, which characterizes the roughness of the underlying surface, in high latitudes of the Northern Hemisphere. An increase in the part of the year when wind generators are capable of operating in the Russian Arctic makes the region quite promising for the use and development of wind power under current climate change.

We quantified the seasonal/regional patterns and changes in cyclone activity in the atmosphere of the Northern Hemisphere and determined the contribution of extratropical cyclones to the formation of corresponding patterns and precipitation changes. It is ascertained that the contribution of extratropical cyclones to the total amount of precipitation exceeds 60% on the whole; for regions with a high cyclone frequency, it attains 75% in winter and 65% in summer. Intense cyclones contribute the most: 60% in winter and 35% in summer.

Cyclone events in the Arctic strongly affect both atmospheric variables, such as wind, air temperature and clouds, and surface variables, including sea ice concentration (SIC) and turbulent heat fluxes. However, despite the progress via recent statistical studies, the overall impact of cyclones on Arctic weather, sea ice, and feedback processes between them is not quantitatively well known. In this study we built up on previous publications and present further details on cyclone impacts on Arctic sea ice in winter by covering a wider range of timescales than before and evaluating our results separately for three different marginal seas of the Arctic Ocean. Hereby we make use of the ERA5 reanalysis and a storm tracking algorithm to analyze the temporal evolution of SIC up to two weeks around the occurrence of each cyclone and compare it with a non-cyclone reference state. The results show an initial decrease in SIC associated with the occurrence of a cyclone for the Barents and Kara Seas, which is balanced by an increase during the following days. On the contrary, in the Greenland Sea SIC remains lower after a cyclone event for the whole analyzed time period. For all the marginal seas considered, the impact of cyclones on sea ice is intensified, if SIC at a grid cell is low and if the intensity of a cyclone is high. Ongoing work consists of providing more details about the mechanisms responsible for the identified regional differences in cyclone influence on sea ice.

Quantitative estimates of changes in wind energy resources in the Arctic were obtained using the RCA4 regional climate model under the RCP4.5 and RCP8.5 climate change scenarios for 2006-2099. The wind power density proportional to cubic wind speed was analyzed. The procedure for the model near-surface wind speed bias correction using ERA5 data as a reference with subsequent extrapolation of wind speed to the turbine height was applied to estimate the wind power density (WPD). According to the RCA4 simulations for the 21st century under both anthropogenic forcing scenarios, a noticeable increase in the WPD was noted, in particular, over the Barents, Kara, and Chukchi seas in winter. In summer, a general increase in the WPD is manifested over the Arctic Ocean. The changes are more significant under the RCP8.5 scenario with high anthropogenic forcing for the 21st century. According to model projections, an increase in the interdaily WPD variations does not generally lead to the deviations of wind speed to the values at which the operation of wind generators is unfeasible.

Arctic cyclones, as a prevalent feature in the coupled dynamics of the Arctic climate system, have large impacts on the atmospheric transport of heat and moisture and deformation and drifting of sea ice. Previous studies based on historical and future simulations with climate models suggest that Arctic cyclogenesis is affected by the Arctic amplification of global warming, for instance, a growing land-sea thermal contrast. We thus hypothesize that biogeophysical feedbacks (BF) over the land, here mainly referring to the albedo-induced warming in spring and evaporative cooling in summer, may have the potential to significantly change cyclone activity in the Arctic. Based on a regional Earth system model (RCA-GUESS) which couples a dynamic vegetation model and a regional atmospheric model and an algorithm of cyclone detection and tracking, this study assesses for the first time the impacts of BF on the characteristics of Arctic cyclones under three IPCC Representative Concentration Pathways scenarios (i.e. RCP2.6, RCP4.5 and RCP8.5). Our analysis focuses on the spring- and summer time periods, since previous studies showed BF are the most pronounced in these seasons. We find that BF induced by changes in surface heat fluxes lead to changes in land-sea thermal contrast and atmospheric stability. This, in turn, noticeably changes the atmospheric baroclinicity and, thus, leads to a change of cyclone activity in the Arctic, in particular to the increase of cyclone frequency over the Arctic Ocean in spring. This study highlights the importance of accounting for BF in the prediction of Arctic cyclones and the role of circulation in the Arctic regional Earth system.

Climate change in the Arctic is embedded in the global climate system leading to phenomenon like Arctic Amplification and linkages to the mid-latitudes. A major forcing emerges from changed surface conditions like declining sea ice cover (SIC) and rising sea surface temperatures (SST). We performed time-slice model experiments with the global atmosphere-only model ECHAM6 and changed SIC and SST to either high or low states, respectively. These experiments are compared to reanalysis data and analysed aiming at a separation between the influences of SIC and SST, while focusing on linkages between the Arctic and mid-latitudes in winter. We identify five significant regimes in the Atlantic-Eurasian sector with the k-means clustering method. The regimes include different blocking patterns, situation with strong low pressure influence and the North Atlantic Oscillation in its two phases. Their frequency of occurrence is discussed for winter months. In the reanalysis we observe an increase of blocking patterns in early winter of the most recent decades. This is reproduced by our experiments with increased SST, where blocking becomes more dominant overall. In late winter, an increased frequency of occurrence of the North Atlantic Oscillation in its negative phase is observed. This and the overall temporal behaviour of regimes in recent years is best represented if SST and SIC are changed to their more recent state simultaneously. Therefore, our results suggest that increased SSTs and reduced SIC together act on observed linkages between polar regions and mid-latitudes.

The impact of sea ice concentration (SIC) changes in the Nordic Seas on the winter cyclone activity in the Nordic Seas is analyzed in 10-member ensemble simulations with the coupled Arctic atmosphere-ocean-sea ice model HIRHAM-NAOSIM for the 1979–2016 period. The analysis reveals that anomalously low SIC in the Nordic Seas leads to decrease in vertical atmospheric static stability, and thus may result in favorable conditions for cyclogenesis in the Nordic Seas. Our analysis also shows a statistically significant increase of cyclone frequency over the Nordic Seas under conditions of the low SIC regime.

The impact of the Atlantic water inflow (AW inflow) into the Barents Sea on the regional cyclone activity in winter is analyzed in 10 ensemble simulations with the coupled Arctic atmosphere-ocean-sea ice model HIRHAM-NAOSIM for the 1979–2016 period. The model shows a statistically robust connection between AW inflow and climate variability in the Barents Sea. The analysis reveals that anomalously high AW inflow leads to changed baroclinicity in the lower troposphere via changed static stability and wind shear, and thus favorable conditions for cyclogenesis in the Barents/Kara Seas. The frequency of occurrence of cyclones, but particularly of intense cyclones, is increased over the Barents Sea. Furthermore, the cyclones in the Barents Sea become larger (increased radius) and stronger (increased intensity) in response to an increased AW inflow into the Barents Sea, compared to years of anomalously low AW inflow.The authors acknowledge the support by the Russian-German project funded by the Federal Ministry of Education and Research of Germany and Ministry of Science and Higher Education of the Russian Federation (grant 05.616.21.0109 (RFMEFI61619X0109)).

In this study, we evaluated the climatology and interannual variability of marine coldair outbreaks (MCAOs) in the Russian Arctic marginal seas (from the Barents to Chukchi seas). We used a simple index for identifying MCAOs based on the vertical potential temperature gradient between the sea surface and the 800 hPa level. We calculated the index using 6-hourly Era-Interim data for the 1979-2018 period. Given the index, we evaluated spatial and temporal variability of weak, medium, and strong MCAOs frequency as well as their dependence on seaice concentration using non-parametric tests. The most intense MCAOs were found in the Barents and Kara seas. The annual cycle maximum for the western Russian Arctic (WRA) were found in wintertime, while it was revealed in mid-late autumn for the eastern Russian Arctic (ERA). In the WRA, we found a statistically significant decrease in amount of strong MCAOs in winter and late autumn and a general strengthening of MCAOs in spring. Meanwhile, over the ERA region, increase of moderate and weak cold-air intrusions during October and November was revealed.

Changes in the characteristics of cyclone activity (frequency, depth and size) in the Arctic are analyzed based on simulations with state-of-the-art regional climate models (RCMs) from the Arctic-CORDEX initiative and global climate models (GCMs) from CMIP5 under the Representative Concentration Pathway (RCP) 8.5 scenario. Most of RCMs show an increase of cyclone frequency in winter (DJF) and a decrease in summer (JJA) to the end of the 21st century. However, in one half of the RCMs, cyclones become weaker and substantially smaller in winter and deeper and larger in summer. RCMs as well as GCMs show an increase of cyclone frequency over the Baffin Bay, Barents Sea, north of Greenland, Canadian Archipelago, and a decrease over the Nordic Seas, Kara and Beaufort Seas and over the sub-arctic continental regions in winter. In summer, the models simulate an increase of cyclone frequency over the Central Arctic and Greenland Sea and a decrease over the Norwegian and Kara Seas by the end of the 21st century. The decrease is also found over the high-latitude continental areas, in particular, over east Siberia and Alaska. The sensitivity of the RCMs' projections to the boundary conditions and model physics is estimated. In general, different lateral boundary conditions from the GCMs have larger effects on the simulated RCM projections than the differences in RCMs' setup and/or physics.