Atmospheric blocking is the most common cause of extreme weather conditions. In the present paper, model data are used to investigate the relationship between the Arctic Oscillation index and the characteristics of atmospheric blocking. The dependence of the duration and intensity of blocking on the index (or phase) of the principal mode during its initial period is estimated. A typical blocking episode is considered, and it is shown that increased values of integral regional enstrophy can be an indicator of the change in the dynamic regime.

With the help of numerical modeling and reanalysis data, interactions between the components of the climate system in the Arctic under the conditions of climate warming have been studied. When analyzing the data and results of numerical experiments, the method of expanding fields of state characteristics in terms of empirical orthogonal functions was used. Trends in the atmospheric impact on the ocean–ice system during the warming period and their relationship with trends in future warming projections under the most severe RCP 8.5 scenario in the CMIP-5 project are identified. In addition, numerical modeling revealed a 44-year periodicity in the interaction between the Arctic Ocean circulation and the heat content of the Atlantic water layer: this can be associated with the Atlantic meridional overturning circulation.

The characteristics of eddy mass transport are estimated depending on the values of the parameters of a large-scale flow that forms under the conditions of the shelf seas in the Arctic. For this, the results of numerical simulation of the Kara Sea with a horizontal resolution permitting the development of mesoscale eddies are used. The multiple realizations of eddy mass flux resulting from a numerical experiment are considered as a statistical sample and are analyzed using methods of sensitivity study and clustering of sample elements. Functional dependencies are obtained that are closest to the simulated distributions of quantities. These expressions make it possible, within the framework of large-scale models, to evaluate the characteristics of the cross-isobathic eddy mass transport in the diffusion approximation with a counter-gradient flux. Numerical experiments using the SibCIOM model showed that areas along the Fram branch of the Atlantic waters trajectory in the Arctic as well as the shelf of the East Siberian and Laptev seas with adjacent deep water areas are most sensitive to the proposed parametrization of eddy exchanges. Accounting for counter-gradient eddy fluxes turned out to be less important.

Numerical modeling is one of the leading research tools for the climate problems. Among numerical models, researchers use, in particular, coupled models, that are numerical models describing more than one climate component dynamics and their interactions. The simulation results with such models depend on the way how these interactions are configured. Therefore, a proper configuration of the exchanges is crucial. The software called a “coupler” is often used to configure these interactions. The coupler is most helpful if the model components are independent of each other modules, their number exceeds two, and they have their own computational grid and time integration step. Key functions of the coupler are managing data exchange between models, setting up synchronous interaction between them based on the time integration step, and interpolating data from one model’s computational grid to the other model’s grid. Additional functions can also be implemented, e.g., fluxes computation between model components, data assimilation, working with the file system, etc. The coupler has one crucial feature: if there is a set of different models of climate system components, one can construct new coupled models by coupling various subsets of these components with coupler. This paper gives an overview of the SCM (SibCIOM Coupling Module) coupler we first developed for the model SibCIOM (Siberian Coupled Ice and Ocean Model). The description of this coupler has not been published before. The SCM coupler is a separate module to which the main climate system model component, such as atmospheric, oceanic, sea ice and land components, can be attached. Additional functions of this coupler include computation of atmosphere-to-ocean and atmosphere-to-ice fluxes and ocean and sea ice state correction using a tidal model. This paper also gives examples of two models constructed with the SCM coupler.

This work considers a series of numerical experiments to identify the direct role of the sea ice reduction process in forming climatic trends in the northern hemisphere. We used two more or less independent mechanisms of ice reduction. The first is traditionally associated with increasing the concentration of carbon dioxide in the atmosphere from the historic level of 360 ppm to the level corresponding to the maximum concentration in implementing the mildest scenario RCP 2.6 - 450 ppm. Due to this growth, the average air temperature in the Arctic increases, and, by this, the ice volume decreases. The second mechanism is associated with a decrease in the reflectivity of ice and snow. As a result, the amount of solar radiation absorbed by the ice increases while the ice volume decreases. We assume that comparing the results of these two experiments allows us to judge the direct role of ice reduction, regardless of the reasons that caused this reduction.

From September 2019 to September 2020, the sea-level atmospheric pressure over the Beaufort Gyre region (BGR) was reduced relative to climatology and a well pronounced cyclonic circulation forcing of sea ice and ocean lasted more than eight months. This resulted in the following: increased sea ice area in 2020 relative to 2019; periodic reversals of sea ice drift from anticyclonic to cyclonic; the formation of an unusual donut-shaped sea ice cover pattern (in August-September 2020); upwelling in the central BGR with a reduction of freshwater content by ~1000 km3; downwelling along the periphery of the BGR; changes in the intensity and trajectories of freshwater fluxes from the Mackenzie river and Bering Strait and fresh water contributions to the BGR freshwater content; unusual warming of the Pacific water layer in the northern BGR; and biogeochemical changes driven by ocean circulation and water mass redistribution. Numerical modeling is used to better understand the causes and consequences of the observed changes. Sea-level atmospheric pressure from NCAR/NCEP reanalysis, sea ice concentration and ice motion from NSIDC, altimetry based sea surface heights from Technical University of Denmark, and hydrographic data from the Beaufort Gyre project and USCGC Healy expeditions are used in the study.

Numerical models develop with development of computational technique, and this development can include either creation of new models, or modification, improvement of existing ones. Modifications can concern both mathematical part, for example, change of numerical schemes, parameterization of various physical processes, and technical part, for example, adaptation of algorithms for use on other computer systems or parallelization of algorithms. The paper considers the issue of optimization of parallel computations for the ice and ocean model SibCIOM. Optimization consists in constructing a mesh partitioning for which the nodes are evenly distributed across the computational cores and the time spent on exchanges is minimal. The METIS package is used to implement such a mesh partitioning. A conceptual description of the implementation of exchange processes for such partitioning is presented.

We used a satellite-derived global daily sea surface temperature (SST) dataset with resolution 0.25 × 0.25∘ to analyze interannual changes in the Arctic Shelf seas from 2000 to 2020 and to reveal extreme events in SST distribution. Results show that the second decade of the 21st century for the Siberian Arctic seas turned significantly warmer than the first decade, and the increase in SST in the Arctic seas could be considered in terms of marine heatwaves. Analyzing the spatial distribution of heatwaves and their characteristics, we showed that from 2018 to 2020, the surface warming extended to the northern deep-water region of the Laptev Sea 75∘ to 81∘N. To reveal the most important forcing for the northward extension of the marine heatwaves, we used three-dimensional numerical modeling of the Arctic Ocean based on a sea-ice and ocean model forced by the NCEP/NCAR Reanalysis. The simulation of the Arctic Ocean variability from 2000 to 2020 showed marine heatwaves and their increasing intensity in the northern region of the Kara and Laptev seas, closely connected to the disappearance of ice cover. A series of numerical experiments on the sensitivity of the model showed that the main factors affecting the Arctic sea-ice loss and the formation of anomalous temperature north of the Siberian Arctic seas are equally the thermal and dynamic effects of the atmosphere. Numerical modeling allows us to examine the impact of other physical mechanisms as well. Among them were the state of the ocean and winter sea ice, the formation of fast ice polynias and riverine heat influx.

As a result of the analysis of the NOAA surface temperature observational data (Huang et al., 2020), the periods corresponding to "marine heatwaves" in the northeastern Pacific Ocean (2013-2019) were identified. Marine heatwaves were defined as exceeding the 90th percentile threshold. The same analysis of the temperature in the Bering Strait's immediate vicinity showed anomalously warm waters in the same years. Analysis of the pressure field, which forms the atmosphere's dynamic state and affects the water circulation system of the Bering Sea, allowed us to assume the inflow of anomalously warm Pacific waters into the Chukchi Sea. To analyze the North Pacific heatwaves' consequences for the Arctic Ocean, we carried out two numerical experiments using the regional ocean and sea ice model SibCIOM (Golubeva et al., 2018) and NCEP/NCAR atmospheric reanalysis data (Kalnay et al., 1996). The first numerical experiment was carried out to calculate hydrodynamic and ice fields from January 2000 to November 2020 (Experiment 1). On the Arctic and the Pacific Ocean boundary in the Bering Strait, we used the monthly average climatic values ​​of the transport, temperature, and salinity of waters coming from the Pacific Ocean. Experiment 2 was carried out from 2014 to November 2020. The calculated values ​​of hydrological and ice characteristics obtained in Experiment 1 were used as the initial state for this experiment. In contrast to Experiment 1, a heat flux exceeding the average climatic values ​​was set at the Bering Strait in Experiment 2. Its assignment was provided by using temperature values ​​from observational data in the Bering Strait vicinity (Huang et al., 2020). Comparison of monthly average hydrological and ice fields obtained in two numerical experiments and analysis of numerical results showed that an increase in the temperature of the Pacific waters entering the Arctic shelf through the Bering Strait leads to an increase in the heat content of the Chukchi Sea waters, heat transfer by currents in the surface and subsurface layers, a gradual increase in the heat content of the Beaufort Sea, and the reduction of Arctic ice cover. The increase in heat content in Experiment 2 for the Beaufort Sea was obtained in both the upper 50-meter and 250-meter layers. The research is supported by the Russian Science Foundation, grant №. 19-17-00154.

The amplified warming of the Arctic is one of several factors influencing atmospheric dynamics. In this work, we consider a series of numerical experiments to identify the role of Arctic sea ice reduction in affecting climate trends in the Northern Hemisphere. With this aim in mind, we use two independent mechanisms of ice reduction. The first is traditionally associated with increasing the concentration of carbon dioxide in the atmosphere from the historic level of 360 ppm to 450 ppm and 600 ppm. This growth increases air temperature and decreases the ice volume. The second mechanism is associated with a reduction in the reflectivity of ice and snow. We assume that comparing the results of these two experiments allows us to judge the direct role of ice reduction. The most prominent consequences of ice reduction, as a result, are the weakening of temperature gradient at the tropopause level in mid-latitudes; the slower zonal wind at 50–60∘ N; intensification of wave activity in Europe, Western America, and Chukotka; and its weakening in the south of Siberia and Kazakhstan. We also consider how climate change may alter regimes such as blocking and stationary Rossby waves. The study used the INM-CM48 climate system model.

The impact of increasing Greenland freshwater discharge on the subpolar North Atlantic (SPNA) remains unknown as there are uncertainties associated with the time scales of the Greenland freshwater anomaly (GFWA) in the SPNA. Results from numerical simulations tracking GFWA and an analytical approach are employed to estimate the response time suggesting a decadal time scale (13 years) required for the SPNA to adjust for increasing GFWA. Analytical solutions obtained for a long-lasting increase of freshwater discharge show a non-steady state response of the SPNA with increasing content of the GFWA. In contrast, solutions for a short-lived pulse of freshwater demonstrate different responses of the SPNA with a rapid increase of freshwater in the domain followed by an exponential decay after the pulse has passed. Derived theoretical relation between time scales show that residence time scales are time-dependent for a non-steady state case and asymptote the response time scale with time. Residence time of the GFWA deduced from Lagrangian experiments is close to and smaller than the response time, in agreement with the theory. The Lagrangian analysis shows dependence of the residence time on the entrance route of the GFWA and on the depth. The fraction of the GFWA exported through Davis Strait has limited impact on the interior basins, whereas the fraction entering the SPNA from the southwest Greenland shelf spreads into the interior regions. In both cases, the residence time of the GFWA increases with depth demonstrating long persistence of the freshwater anomaly in the subsurface layers.

A simple method is proposed for identifying mesoscale eddies in the results of numerical modeling. The method uses extrema in distributions of the sea level elevation as eddy markers. By using the method, we analyze statistics of mesoscale eddies resulting from SibPOM numerical simulations in the Eurasian sector of the Arctic marginal seas. The results of using this method show that the number of cyclonic eddies slightly exceeds the number of anticyclonic eddies, but the excess is only 2-3%. Also, we demonstrate that a significant number of eddies arise under the ice cover. The number of such eddies increases significantly in winter. This fact indicates that the convection caused by salt rejection during freezing plays an essential role in their formation. The numerical modeling results confirm the phenomenon of active eddy generation in the ice edge zone. Besides, the results show that in the near-edge zone, a more significant number of eddies are formed from the icy side adjacent to the edge, and not from the ice-free side. The periods of seawater freezing and ice melting, accompanied by corresponding displacements in the ice edge, produce eddies different in nature. The number of eddies in the marginal ice zone has two seasonal maxima corresponding to these two periods.

A coupled ice-ocean model forced by atmospheric reanalysis data is used to examine a change in the bottom layer of the Laptev Sea on a scale of several decades. The model shows that since the mid-1980s there has been a warming of bottom waters in the shelf region. Analyzing values of bottom temperature averaged over a decade, we show that since 2005 the intensity of warming of the bottom layer has increased. The main reason for this is disappearance of ice cover in summer accompanied by an influx of heat into the surface layer of the sea. Also, an essential factor is the dynamic state of the atmosphere. The intensification of surface currents due to wind action promotes mixing of waters and heat transfer to the bottom layer of the sea. The heat anomalies entering the near-bottom layer of the sea during the autumn cooling could exist during the winter period.

The paper investigates the role of atmospheric circulation in the surface layer in forming the Arctic ice structure. For the analysis, the empirical orthogonal function (EOF) method of decomposition of the surface wind field is used, and the reaction of ice to changes in the principal components of leading EOF modes is investigated using statistical methods. Analyzing the rate of ice change in the Arctic associated with the Arctic ocean oscillation mode, we concluded that this mode’s variability leads to the formation of a seesaw in the ice field between two regions. From the one side, it is the region of the central deep-water part of the Arctic, including the East Siberian Sea, and from the other side, it is all other marginal seas. The second (“dipole”) mode is most associated with an increase/decrease in the ice thickness at the Arctic exit through the Fram Strait, as well as the formation of the so-called “ice factory” in the coastal region of the Beaufort Sea in the positive phase of this mode. There is also a significant relationship between the variability of third mode and the arrival of Atlantic waters with a high heat content into the Arctic through the Barents opening, which creates preconditions for ice formation in this region.

A study is presented on integral variability in Arctic Ocean characteristics, such as the volume transport and the heat content of the Atlantic water (AW) layer, obtained as results of numerical simulations using a model, SibCIOM. On the basis of an EOF decomposition three non-degenerate modes are obtained for the integral stream function and three modes for the heat content of the AW layer in the Arctic. Considering the cross-correlations of the EOF principal components a 44-yr cycle is obtained. It relates the cyclonic circulation mode in the Arctic and the second mode of AW heat content, associated with the AW warming in the area of the Beaufort Gyre. The Atlantic Multi-decadal Oscillation (AMO) statistically can act as a source of such a cycle, however, the thus obtained correlation is at the limit of the admissible significance, and the period of AMO oscillations is 1.5-2 times longer. In our opinion, a relationship with fluctuations in the Atlatic Meridional Overturning Circulation (AMOC) seems to be more plausible. However, no understanding of the role of these two mid-latitude and polar processes in relation to what extent they act as a cause or a consequence has yet been established in this study.

The role of the ocean in the response of the climate system to an increase in the atmospheric CO2 concentration is investigated by using a system of numerical models, ICMMG-PlaSim. The results of this study are summarized as follows: a) the ocean, to some extent (up to 20%), contributes to the increase in the annual mean state and to the decrease in the amplitude of seasonal oscillations (by 2-3%), which ultimately leads to insignificant changes in the summer period and to a significant mitigation of winter, b) the ocean stabilizes the annual mean state of the Arctic oscillation, making it practically unchanged with increasing CO2 concentration but, at the same time, contributes to the significant increase in the amplitude of the seasonal cycle of this oscillation, c) the ocean enhances the temperature (or thermal) component of the seasonal variation associated with the appearance of additional areas freed from ice cover, with an additional average increase in the temperature of the atmosphere at the ice edge. Besides, the ocean enhances the seasonal oscillations of this component, so that the summer manifestations become much stronger, d) our tests have revealed that the role of the Arctic dipole under global warming is insignificant. These conclusions, though, may undergo significant changes under a more detailed consideration of carbon cycles in the atmosphere, ocean, and land.

AbstractContinental runoff is one of the major sources of the Arctic freshwater budget. As is generally known, it influences water column stratification and maintains Arctic halocline, which isolates the sea ice and the cold, fresh upper layer from the warmer, saltier Atlantic waters of the Arctic Ocean. An increase in river runoff was observed in recent years. It is suggested that this will have an impact on Arctic water mass transformations. However, few details are known regarding river freshwater export to the Central Arctic Basin. It is assumed that river water pathways in vast shelf seas and deep basins are closely related to atmospheric variability. In this study, we use three-dimensional coupled regional ocean-ice model simulations forced by atmospheric reanalysis data to investigate the change in Siberian rivers freshwater pathways in the Arctic Ocean due to the variability of atmospheric dynamics. A numerical experiment with an increasing runoff of the largest Siberian rivers is carried out. The consequences of adding freshwater to particular regions of the Arctic Ocean are analysed.

Purpose.Considered are the processes of dense bottom water formation in winter in the region of the Novaya Zemlya northwestern coast, its further propagation (cascading) towards the St. Anna trough and then to the open ocean.The goal of the paper is to show that the process of such propagation is closely related to generation of the mesoscale eddies.Methods and Results.The data of available measurements indicate only some residual forms of such a movement, since they cover mainly a summer season.Numerical study was carried out using the system of the nested models SibCIOM and SibPOM.In course of the numerical experiments it became possible to show the system capability in describing the water bottom structure and to reproduce the process of bottom water propagation in details.Analysis of the above-mentioned process has revealed energy conversion of the available potential energy of a regular motion into the potential energy of eddy formations.The eddy structures' ageostrophicity, in its turn, contributes to the accelerated advancement of dense shelf waters downard along the sloping bottom.Conclusions.One of the important features of cascading is that at the initial stage, it is accompanied by active generation of the mesoscale eddy structures.Both processes interact energetically and contribute to increase of heat and mass exchange between the shelf and the open ocean.Proper description of this exchange is a prerequisite for successful modeling of the intermediate and deep water thermodynamics in the Arctic Ocean.