The recent warming of the Arctic causes degradation of permafrost, release of greenhouse gases due to the decomposition of previously frozen organic matter, increase in the area and diversity of vegetation, and decrease of in the bearing capacity of permafrost soils. In this regard, the evolution of the seasonally thawed soil layer is of particular interest. The paper presents the results of comprehensive studies of energy exchange processes in the atmospheric surface layer and the upper layer of permafrost, carried out in 2016–2020 at the Research Station “Ice Base Mys Baranova” (Bolshevik Island, Severnaya Zemlya Archipelago), supplemented by the results of model calculations of seasonally thawed depth (STD) dynamics. The study examines the role of surface snow albedo decreases due to short-term intrusions of warm air masses, leading to the intensification of snow melting and soil surface heating due to increase in absorbed incoming solar radiation, is analyzed. A version of the Leibenson model, validated by data of observations, is used for assessing the role of landscape factors and meteorological conditions in the dynamics of STD. Despite the simplified formulation of the problem and the approximate assignment of heat and mass transfer of soil properties in the area under study, the model results could be considered satisfactory, and proposed approach can be used for assessing the state of STD.

Low-level jets (LLJs) are important features in the Arctic climate system. The forecast of LLJs in polar regions is highly relevant for logistic operations, particularly for aircrafts, as well as for wind energy and air pollution transport. LLJs were investigated during 2014/15 at the Tiksi observatory in the Laptev Sea region. Besides the routine synoptic observations, data from a meteorological tower and SODAR (Sound Detection And Ranging) data were available from October 2014 to September 2015. The SODAR yields vertical profiles of the wind speed and wind direction with a vertical resolution of 10 m and a temporal resolution of 20 min (height range 30-550 m). These measurements were used to evaluate simulations performed with the regional climate model CCLM with 5 km resolution, which was run with nesting in ERA5 data in a forecast mode.CCLM simulations agreed well with near-surface and SODAR observations and represented the LLJ structures very well. However, SODAR measurements were mostly limited to wind speeds <12 m/s since the echo was typically too weak for higher winds. The CCLM data showed that LLJs occur frequently for wind speeds being too high for the SODAR. Although SODAR wind profiles are limited in range and have a lot of gaps, they represent a valuable data set for model verification. However, a full picture of the LLJ events could be obtained only with the model data. The simulations showed that LLJs at Tiksi occur in about 70% of all profiles. When only LLJs in the range of the SODAR and with wind speeds of less than 10m/s were considered, only about 20% of all profiles showed LLJs, which was the same amount as found in the SODAR profiles. LLJs with at least 3 h duration were simulated for the same days as the observations in about 80% of all cases.

Представлены результаты десятилетних измерений сезонного оттаивания грунта на северном побережье о. Большевик (арх. Северная Земля). Экспериментальные данные дополнены оценками динамики толщины сезонноталого слоя (СТС), выполненными по данным наблюдений в приземном слое атмосферы с помощью варианта известной модели Лейбензона. The report presents the results of a decade of measurements of seasonal soil thawing on the northern coast of Bolshievik Island (Severnaya Zemlya archipelago). The experimental data are complemented by estimates of the dynamics of the thickness of the seasonally thawed layer (STL), obtained from observations in the surface layer of the atmosphere using a variant of the well-known Leibenson model.

Measurements of the atmospheric boundary layer (ABL) structure were performed for three years (October 2017–August 2020) at the Russian observatory “Ice Base Cape Baranova” (79.280° N, 101.620° E) using SODAR (Sound Detection And Ranging). These measurements were part of the YOPP (Year of Polar Prediction) project “Boundary layer measurements in the high Arctic” (CATS_BL). ABL measurements and near-surface observations were used for verification of the regional climate model COSMO-CLM (CCLM) with a 5 km resolution for 2017–2020. The SODAR showed a topographical channeling effect for the wind field in the lowest 100 m. The verification of the CCLM with near-surface data of the observatory showed good agreement. The comparison with SODAR data showed a positive bias for the wind speed of about 1.0-1.5 m/s. The CCLM data showed the frequent presence of low-level jets (LLJs) associated with the topographic channeling. Although SODAR wind profiles are limited in range and have a lot of gaps, they represent a valuable data set for model verification. However, a full picture of the ABL structure and the climatology of channeling events could be obtained only with the model data. LLJs were detected in 37% of all profiles and most LLJs were associated with channeling, particularly LLJs with a jet speed ≥15 m/s (which were 29% of all LLJs). The analysis of the simulated 10m wind field showed that the 99%-tile of the wind speed reached 18 m/s and clearly showed a dipole structure of channeled wind at both exits of Shokalsky Strait. The climatology of channeling events showed that this dipole structure was caused by the frequent occurrence of channeling at both exits. Channeling events lasting at least 12 h occurred on about 62 days per year at both exits.

Large stores of carbon frozen in the Arctic as permafrost are under threat of thawing as temperatures in the Arctic increase at a rate four times that of the global mean. This study uses recent atmospheric data from the North Slope of Alaska and Northeast Siberia to provide the most up-to-date assessment of emissions and trends from these two major high-latitude regions.We use two methods to quantify emissions and assess trends across different seasons: 1) Using 35 years of data from Barrow, Alaska, a wind sector method that quantifies trends in emissions by calculating concentration enhancements over background using wind direction to identify the land sector (first used in Sweeney et al., 2016), and 2) using Barrow data and recent data from three Siberian stations, an inversion method with the high-resolution atmospheric transport model NAME that quantifies both emissions and trends from these regions. We use results from these two approaches to quantify the temperature sensitivity (Q10) of soils based on correlations between surface air and ground temperatures with methane emissions.With the inclusion of atmospheric concentration data after 2015, we now show that land emissions from the North Slope of Alaska have been increasing since 2000, reflecting a change from previous analyses, which showed no significant increase in summertime methane emissions between 1986-2014 (Sweeney et al., 2016). We find significant emissions from the late shoulder season (Autumn-Winter), which has historically been undermeasured and underrepresented in models and emissions inventories, in this region of Alaska as well as two North-eastern Siberian locations, the Taymyr Peninsula and the East Siberian Lowlands. We show that emissions during this late-season have been growing over the past two decades at a rate similar to summer-time emissions.Our results based on long-term atmospheric data can be used to show that important change is happening in the Arctic, with an increasing emissions trend and the presence of late shoulder season emissions.

Measurements of the atmospheric boundary layer (ABL) structure were performed for three years (October 2017–August 2020) at the Russian observatory “Ice Base Cape Baranova” (79.280° N, 101.620° E) using SODAR (Sound Detection And Ranging). These measurements were part of the YOPP (Year of Polar Prediction) project “Boundary layer measurements in the high Arctic” (CATS_BL) within the scope of a joint German–Russian project. In addition to SODAR-derived vertical profiles of wind speed and direction, a suite of complementary measurements at the observatory was available. ABL measurements were used for verification of the regional climate model COSMO-CLM (CCLM) with a 5 km resolution for 2017–2020. The CCLM was run with nesting in ERA5 data in a forecast mode for the measurement period. SODAR measurements were mostly limited to wind speeds <12 m/s since the signal was often lost for higher winds. The SODAR data showed a topographical channeling effect for the wind field in the lowest 100 m and some low-level jets (LLJs). The verification of the CCLM with near-surface data of the observatory showed good agreement for the wind and a negative bias for the 2 m temperature. The comparison with SODAR data showed a positive bias for the wind speed of about 1 m/s below 100 m, which increased to 1.5 m/s for higher levels. In contrast to the SODAR data, the CCLM data showed the frequent presence of LLJs associated with the topographic channeling in Shokalsky Strait. Although SODAR wind profiles are limited in range and have a lot of gaps, they represent a valuable data set for model verification. However, a full picture of the ABL structure and the climatology of channeling events could be obtained only with the model data. The climatological evaluation showed that the wind field at Cape Baranova was not only influenced by direct topographic channeling under conditions of southerly winds through the Shokalsky Strait but also by channeling through a mountain gap for westerly winds. LLJs were detected in 37% of all profiles and most LLJs were associated with channeling, particularly LLJs with a jet speed ≥ 15 m/s (which were 29% of all LLJs). The analysis of the simulated 10 m wind field showed that the 99%-tile of the wind speed reached 18 m/s and clearly showed a dipole structure of channeled wind at both exits of Shokalsky Strait. The climatology of channeling events showed that this dipole structure was caused by the frequent occurrence of channeling at both exits. Channeling events lasting at least 12 h occurred on about 62 days per year at both exits of Shokalsky Strait.

The estimates of seasonal and interannual variability of surface heat balance components on the Bolshevik Island, Severnaya Zemlya archipelago for period from September 2013 to December 2021 are presented. It is shown that seasonal variability of turbulent sensible and latent heat fluxes is fundamentally different. In winter turbulent sensible heat flux H is directed to the surface due to longwave radiative cooling. In summer H, due to strong heating of surface with low albedo by solar radiation, is directed into atmosphere and reaches up to 25% of incoming short-wave radiation. In opposite turbulent latent heat flux LE in winter is directed from the snow-covered surface to the atmosphere, but its values do not exceed 10% of H. In summer variability of soil surface moisture during the snowless period and the relatively high air humidity determined variable, but mainly from the underlying surface to the atmosphere direction of LE. Data about thermal regime of the soil active layer and the characteristics of surface energy balance allow us to draw a conclusion about the reasons for the abnormally warm state of soil upper layer and extremal permafrost thawing in 2020. It is shown that the timing and intensity of thawing were associated with changes in all components of the surface heat balance, with the main changes occurring in the intensity of incoming long-wave radiation, caused by synoptic processes in troposphere, and absorption of incoming short-wave radiation, determined by earlier onset of snow melting and, accordingly, decrease in surface albedo.

Abstract. Arctic tundra is facing unprecedented warming, resulting in shifts in the vegetation, thaw regimes, and potentially in the ecosystem-atmosphere exchange of carbon (C). The estimates of regional carbon dioxide (CO2) and methane (CH4) budgets, however, are highly uncertain. We measured CO2 and CH4 fluxes, vegetation composition and leaf area index (LAI), thaw depth, and soil wetness in Tiksi (71° N, 128° E), a heterogeneous site located within the prostrate dwarf-shrub tundra zone in northeastern Siberia. Using the closed chamber method, we determined net ecosystem exchange (NEE) of CO2, dark ecosystem respiration (ER), ecosystem gross photosynthesis (Pg), and CH4 fluxes during the growing season. We applied a previously developed high-spatial-resolution land-cover map over an m area of 35.8 km2. Among the land-cover types varying from barrens to dwarf-shrub tundra and tundra wetlands, the light-saturated NEE and Pg scaled with the LAI of vascular plants. Thus, the graminoid-dominated tundra wetlands, with high LAI and the deepest thaw depth, had the highest light-saturated NEE and Pg (up to −21 (uptake) and 28 mmol m−2 h−1, respectively) and were disproportionately important for the summertime CO2 sequestration on a landscape scale. Dry tundra, including the dwarf-shrub-dominated vegetation and only sparsely vegetated lichen tundra, had only small CO2 exchange rates. While tundra wetlands were sources of CH4, lichen tundra, including bare ground habitats, consumed atmospheric CH4 at a substantial rate. On a landscape scale, the consumption by lichen tundra and barrens could offset ca. 10 % of the CH4 emissions. We acknowledge the uncertainty involved in spatial extrapolations due to a small number of replicates per land-cover type. This study, however, highlights the need for distinguishing different land-cover types including the dry tundra habitats to account for their consumption of the atmospheric CH4 when estimating tundra C-exchange on a larger spatial scale.

In 2014/2015 a one-year field campaign at the Tiksi observatory in the Laptev Sea area was carried out using Sound Detection and Ranging/Radio Acoustic Sounding System (SODAR/RASS) measurements to investigate the atmospheric boundary layer (ABL) with a focus on low-level jets (LLJ) during the winter season. In addition to SODAR/RASS-derived vertical profiles of temperature, wind speed and direction, a suite of complementary measurements at the Tiksi observatory was available. Data of a regional atmospheric model were used to put the local data into the synoptic context. Two case studies of LLJ events are presented. The statistics of LLJs for six months show that in about 23% of all profiles LLJs were present with a mean jet speed and height of about 7 m/s and 240 m, respectively. In 3.4% of all profiles LLJs exceeding 10 m/s occurred. The main driving mechanism for LLJs seems to be the baroclinicity, since no inertial oscillations were found. LLJs with heights below 200 m are likely influenced by local topography.

In the paper, we present the results of an analysis of ceilometer measurements at North Pole (NP) drifting station 37, 39, and 40. The frequencies of the total cloud amount (in tenth) = TCA and the cloud base heights (CBHs) are calculated for the period of the polar night. A comparison of the cloud-cover score according to the ceilometer data with the visual observation data showed good agreement. However, the value of the correlation coefficient depends on the interpretation of the ceilometer data. In general, a bimodal distribution of the cloud-cover score with the highest frequency of clear sky and overcast clouds are characteristic for indicated stations. The analysis of the frequency of the CBH showed that the most characteristic CBHs are below 600 m. In November, cloud heights in the range of 1000–2000 m are also observed, while their frequency decreases during the winter. Cloudiness during the polar night is characterized by a strong positive radiative forcing, which has a warming effect on the surface temperature of ice and air. However, cloud radiative forcing, as well as the cloudiness frequency and its effect on the temperature regime, varies significantly from station to station. These differences may become the subject of further research on the interrelation of cloud characteristics with other processes in the Arctic climate system. These statistical estimates significantly supplement the available data on the cloud cover of the Central Arctic.

The paper presents the results of theverification of ERA-Interim and ERA5 reanalyses data on surface airtemperature obtained from drifting buoys, ground-based weather stations,and, for the first time, from measurements at the North Pole driftingstations. The North Pole station data were not assimilated in thereanalyses, which provides a rare opportunity for independentvalidation. The comparison with data of the North Pole drifting stationsrevealed that bias for the cold season in the Arctic basin is 2.25°С forERA-Interim and 3.92°С for ERA5, respectively. The comparison with dataof drifting buoys allows us to speculate about the cause of such largeerrors in the reanalyses. Some buoys were installed from the air-basedplatform. In this case, the temperature sensor of the buoy waspotentially buried in the snow cover that shielded it from the coldatmosphere and contributed to the heating due to the heat flux from theunderlying layer of sea water. The assimilation of such data could beone of the reasons for the overestimation of air temperature overdrifting ice in the both reanalysis.

Investigations of active soil layer on the Research station “Ice Base Cape Baranova’’ had been started in February 2016 after installation on the meteorological site sensors of Finnish Meteorological Institute: thermochain with IKES PT00 temperature sensors at depths of 20, 40, 60, 80 and 100 cm, soil heat flux sensor HFP, and two ThetaProbe type ML3 soil moisture sensors. Based on the results of measurements annual cycle of soil temperature changes was revealed with amplitudes 10 - 15 ° C less than the amplitudes of surface air layer temperature (Ta) and especially the temperature of the soil upper surface (Tsrad), in great degree determined by short-wave radiation heating and long-wave radiation cooling. Approximation by linear fittings shows average rates of increase Ta - 0.4°C/year, Тsrad - 0.3°C/year, and temperatures of active soil layer - 0.2°C/year. The data on thermal regime of active soil layer and characteristics of energy exchange in atmospheric surface layer make it possible to draw the conclusion about the reason for the abnormally warm state of the upper meter soil layer in summer 2020, despite in March during the whole period under study active soil layer was the warmest in 2017. Comparison in temperatures of the underlying surface and characteristics of surface heat balance during period under study showed that in 2020 the temperature of the soil surface at the end of May for a short time reached the temperature of snow melting. It is happened 25 days earlier than in 2017 as well as other years and led to radical decrease in surface albedo, sharp increase of heat flux to the underlying surface, and increased duration of active soil layer heating. Additionally, permafrost thawing studies using a manual contact method were carried out on the special site, organized according to CALM standards. These studies showed significant variety of soil active layer thicknesses in the relatively small area (~0.12 km2), which indicates significant spatial variability of microrelief, structure and thermophysical properties of soil, as well as vegetation, typical for Arctic desert. Calculations carried out with version of the well-known thermodynamic Leibenzon model for various parameterizations of vegetation and soil properties partly described peculiarities of spatial variability of observed thawing depths.

The parameterization of ocean/sea-ice/atmosphere interaction processes is a challenge for regional climate models (RCMs) of the Arctic, particularly for wintertime conditions, when small fractions of thin ice or open water cause strong modifications of the boundary layer. Thus, the treatment of sea ice and sub-grid flux parameterizations in RCMs is of crucial importance. However, verification data sets over sea ice for wintertime conditions are rare. In the present paper, data of the ship-based experiment Transarktika 2019 during the end of the Arctic winter for thick one-year ice conditions are presented. The data are used for the verification of the regional climate model COSMO-CLM (CCLM). In addition, Moderate Resolution Imaging Spectroradiometer (MODIS) data are used for the comparison of ice surface temperature (IST) simulations of the CCLM sea ice model. CCLM is used in a forecast mode (nested in ERA5) for the Norwegian and Barents Seas with 5 km resolution and is run with different configurations of the sea ice model and sub-grid flux parameterizations. The use of a new set of parameterizations yields improved results for the comparisons with in-situ data. Comparisons with MODIS IST allow for a verification over large areas and show also a good performance of CCLM. The comparison with twice-daily radiosonde ascents during Transarktika 2019, hourly microwave water vapor measurements of first 5 km in the atmosphere and hourly temperature profiler data show a very good representation of the temperature, humidity and wind structure of the whole troposphere for CCLM.

The study of the carbon isotope composition of atmospheric aerosol in the Arctic zone is of great importance for the pyrogenic carbon sources identification. Atmospheric aerosol samples were collected in the Arctic at the research station Ice Base Cape Baranov (the Severnaya Zemlya archipelago) from April 2018 to November 2019 and at Barentsburg (the Svalbard archipelago) from December 2018 to July 2019 and from November 2019 to February 2020. The carbon isotope composition (δ13C value) was determined in aerosol samples to identify the sources of carbonaceous aerosols. For Ice Base Cape Baranov the average δ13C value (–27.5±0.5%) of total carbon of the winter (2018-2019) aerosols lower than the average δ13C value (–26.8±0.8%) of the spring-summer (2019) aerosols. The average δ13С values of the atmospheric aerosols in Barentsburg showed that the δ13С value was –26.9‰ in winter, the δ13С value was –26.3‰ and – 26.1‰ in spring and summer, respectively. The increased δ13C values in spring and summer (2019) at the Ice Base Cape Baranov can likely be explained by the input of soot aerosol, the source of which is boreal forest fires at the Krasnoyarsk Region and the Republic of Sakha. According to the backward trajectories of the air masses, the transfer of soot particles to Barentsburg was carried out from Europe, North America and over the Arctic Ocean, and to the Severnaya Zemlya from the continental part of Krasnoyarsk Region and the Republic of Sakha.

We discuss the measurements of aerosol optical depth (AOD) of the atmosphere and aerosol (NA) and black carbon (MBC) concentrations in 2018-2019 at two Arctic stations: Barentsburg (Archipelago Spitsbergen) and “Cape Baranov” (Archipelago Severnaya Zemlya). The average aerosol characteristics at “Cape Baranov” had been: AOD (0.5 μm) = 0.11, NA = 5.24 cm-3, MBC = 47 ng/m3 in 2019; and AOD (0.5 μm) = 0.07, MBC = 68 ng/m3 in 2018. The aerosol characteristics in Barentsburg, on the average, have larger values: AOD (0.5 μm) = 0.12, NA = 6.09 cm-3, MBC = 91 ng/m3 in 2019; and AOD (0.5 μm) = 0.087, NA = 6.54 cm-3, MBC = 109 ng/m3 in 2018.

The Arctic region is one of the main areas of greenhouse gases sources due to large amount of biomass, carbon stocks in the soil and extensive wetlands. Large resources of previously inactive organic carbon may take part in atmospheric chemical reactions under melting permafrost conditions. In this case, carbon dioxide concentrations will increase in the atmosphere. Since 2015 Arctic and Antarctic Research Institute in cooperation with Finnish Meteorological Institute have been measuring the continuous concentrations of water vapor, methane, carbon dioxide and carbon monoxide at Research Station "Ice Base Cape Baranova" (79° 18´ N, 101° 48´ E, 30 m asl.) using cavity ringdown spectroscopy (CRDS) analyzer Picarro G2401. The sampling inlet is located at 10 m height.Data preprocessing consists of deleting values obtained during power failures and 2 minutes after calibration. The values for wind directions corresponding to the transfer from diesel power station (90 - 145 °) and for wind speeds less than 3 m/s were also discarded because in this case polluted air may be distributed over the station homogeneously. After that data were adjusted taking into account the nearest calibration values by linear interpolation. The archive of carbon dioxide concentrations data averaged over each hour from October 2015 to December 2019 was used for further analysis.CO2 time series are characterized by a pronounced annual variation with concentration decreasing in summer months. The absorption by sea phytoplankton in the absence of sea ice cover causes the annual variability of carbon dioxide. Besides, the predominant presence of stable stratification of the atmospheric surface layer throughout the polar night contributes to accumulation of the gas in the surface layer in winter. The annual amplitude is 18–20 ppm approximately, which is consistent with the data of Alert and Barrow polar stations.The analysis of the dependence of registered concentration distribution on the wind direction shows that the highest values are observed during the air-mass transfer from the south-western and northern directions. If the first case can be explained by the anthropogenic impact and presence of extensive wetlands in the summer, the reason for the second one requires a more detailed analysis. Applying the HYSPLIT trajectory model for cases of elevated values of greenhouse gas concentrations did not allow us to obtain an unambiguous answer. Although elevated values were observed, as a rule, when air masses transferred from the regions of Norilsk, Yamal, the Kola Peninsula, and Lena estuary, however, there were cases of elevated concentrations during the transfer of air masses from the Arctic Ocean. This may be due to the action of any local sources, but their detection requires additional data analysis. The work had been executed in frame of CNTP Roshydromet 1.5.3.3.

Based on the data of meteorological observations, executed in 2013-2019 at Research Station “Ice base Cape Baranova” (RS) and original algorithm, taken into account accuracy of measurements and footprints, the components of surface heat budget are calculated. It is shown that in winter due to radiation cooling turbulent sensible heat flux (H) directs to underlying surface. In summer H due to radiation heating of surface with low albedo directs to atmosphere and reaches 25% of the incoming short-wave radiation. The turbulent latent heat flux (LE) in winter directs to atmosphere. Its value is not more than 10% of H. During summer LE has no predominant direction. Comprehensive monitoring carried out at RS since 2013 allowed to examine the role of large-scale processes in the polar atmosphere and hydrosphere on the formation of local climate in the region. In 2016, 2018 and 2019 sea ice cover of the Barents and Kara Seas in October, the month of active freezing of active soil layer, occupied the minimal area starting 1978 year (http://wdc.aari.ru/datasets/d0042/). This circumstance along with peculiarities of circulation processes in the atmosphere had led to anomalous of temperature and humidity regimes of lower troposphere. These years monthly mean air temperature up to 700 hPa was about -4 °C compared to -7 - -11 °C in 2013 - 2015 and 2017. In 2016 the lower troposphere was warmer by 2 - 3 °C and specific humidity in atmospheric boundary layer was 30–60% higher its values in 2013–2015 and 2017. Even in 2018, when the area of open water adjacent to the Severnaya Zemlya archipelago was significantly larger than in 2016, specific humidity at altitudes up to 3 km was 4-12 percents less. In 2016 monthly mean wind speed, mainly of southwestern direction, reached maximum value, more than 7 m/s. It led to weakening of atmospheric surface layer stratification (z/L <0.2). The air specific humidity significantly increased also, up to 3.0 and 2.7 g /kg at 2 meters and at z0 . Long-wave radiation fluxes increased by more than 15 – 20 W/m2. Same time due to increase of underlying surface temperature, its long-wave radiation cooling, which was not compensated by the increase of incoming long-wave radiation increased up to -27 W/m2. H, directed to the underlying surface, increased to 10 W/m2 and LE, directed to atmosphere, increased almost 2 times, up to 12 W/m2. As a result of multidirectional changes of heat fluxes, defining surface heat balance, its value in October 2016 (-31.6 W/m2) was comparable to calculated for other years. The most probable explanation of the revealed features of atmospheric boundary and surface layers in October 2016 are the absence of sea ice cover in the waters, adjacent to the archipelago, prevented cooling of atmosphere, and strong zonal component of the wind velocity, caused the transfer of warm and moist air masses of Atlantic origin into the study area. The work had been done under financial support of the Ministry of Science and Higher Education of the Russian Federation (project no. RFMEFI61619X0108).