Semidiurnal frequency of the fields of the Arctic ice rarefaction and compression from the MTVZA-GYa satellite radiometer data

The spatiotemporal variability is considered ofthe field of ice rarefaction and compression in the Arctic due to the passage of semidiurnal tidal waves. A simplified method is developed for identification of such fields on the maps of the scattering index (SI) of ice computed from the MTVZA-GYa radiometer data. It is demonstrated that the low and high values of ice SI are ob served at tidal rarefactions and compressions, respectively. The analysis of the maps of extreme values of SI observed in overlapping semidiurnal and diurnal MTVZA-GYa measurements corroborated the existence of semidiurnal periodicity of alternating fields of the Arctic ice rarefaction and compression and revealed no variability in ice SI in the areas where tidal wave phases converge (there the convergence amplitude is minimum).     

Studying the effects of vortices flowing around seamounts on ice properties from satellite microwave data

The changes are considered in the computation and map representation of the scattering index (SI) of thick first-year ice identified from the MTVZA-GYa radiometer data. For the first time improved ice SI maps enabled detecting the zones of the low values of sea ice SI which were steadily formed in the same areas over the Lomonosov and Gakkel ridges. It is demonstrated that the intense local ice drift formed under the influence of the vortices flowing around seamounts, may be a reason for the formation of such zones. The cases are considered when the zones of the low values of ice SI were of synoptic scale (up to 1200 km) and could have been the result of the independent influence of the vortices flowing around seamounts and strong surface wind. The utility of new SI maps is noted for monitoring the areas where the vortices flowing around seamounts may considerably modify propeties of the sea ice cover.     

Identification of the age and compression areas of sea ice from the AMSU satellite microwave radiometer data

A physical substantiation of the new quantitative index of sea ice scattering (Bukharov index) computed from the all-weather AMSU satellite radiometer data is considered. A high sensitivity of the scattering index to the age, thickness, and hummocking of ice in the areas of its compression is demonstrated. The daily maps of the sea ice scattering index in the Arctic are plotted. The analysis of maps enabled to reveal a new phenomenon, a steady existence of various-scale areas of short-range deformations of the sea ice in the Arctic. A new technique is proposed of the identification of age, relative thickness, and compression areas of ice using the maps of minimum and maximum values of the scattering index.     

A year-round monitoring of sea ice properties from the AMSU satellite microwave radiometer data

A new approach to the year-round daily monitoring of sea ice properties based on the multispectral measurements of the AMSU satellite radiometer is considered. It is revealed that the increase in the values of the sea ice scattering index and its anomalously high variability are observed during the warm period of the year. The analysis of main reasons influencing the variations of the sea ice scattering index in different seasons is carried out. The recommendations are proposed on the identification of ice properties on the maps of the sea ice scattering index plotted for the warm, cold, and transition periods.     

Quantifying Arctic contributions to climate predictability in a regional coupled ocean-ice-atmosphere model

The relative importance of regional processes inside the Arctic climate system and the large scale atmospheric circulation for Arctic interannual climate variability has been estimated with the help of a regional Arctic coupled ocean-ice-atmosphere model. The study focuses on sea ice and surface climate during the 1980s and 1990s. Simulations agree reasonably well with observations. Correlations between the winter North Atlantic Oscillation index and the summer Arctic sea ice thickness and summer sea ice extent are found. Spread of sea ice extent within an ensemble of model runs can be associated with a surface pressure gradient between the Nordic Seas and the Kara Sea. Trends in the sea ice thickness field are widely significant and can formally be attributed to large scale forcing outside the Arctic model domain. Concerning predictability, results indicate that the variability generated by the external forcing is more important in most regions than the internally generated variability. However, both are in the same order of magnitude. Local areas such as the Northern Greenland coast together with Fram Straits and parts of the Greenland Sea show a strong importance of internally generated variability, which is associated with wind direction variability due to interaction with atmospheric dynamics on the Greenland ice sheet. High predictability of sea ice extent is supported by north-easterly winds from the Arctic Ocean to Scandinavia.     

Analysis of interrelation between the scattering index of sea ice and its properties

Analyzed is the interrelation between the properties of the sea ice, its scattering index at the frequencies of 23 and 31 GHz, and the brightness temperature computed from the multispectral measurements with the AMSU radiometer. Within the frameworks of the simplified model representations, the quantitative estimates are obtained of the influence of the ice thickness, ice concentration, and presence of inhomogeneities in the emitting layer and snow cover on the ice surface on the ice scattering index values. It is demonstrated that the scattering on the dislocations formed near the surface of ice at its bend and compression can be the main reason for the rapid change in the scattering index of one-year and old ice observed in different seasons. The results of the analysis corroborated the validity of applying the scattering index for the revelation of the areas of deformation and hummocking of sea ice, as well as for the estimation of the age and thickness of thin and young ice.     

Effects of variability of sea ice transport through the Fram Strait on the intensity of the Atlantic deep circulation

Results from an ice-ocean coupled model are used to investigate the impact of long-term variability in sea ice transport at the Fram Strait on the intensity of the Atlantic deep circulation. An increase (or decrease) in sea ice transport through the Fram Strait leads to a stronger (or weaker) deep circulation in the Atlantic. Change in the sea ice transport is accompanied by a salinity anomaly in the surface layer of the Arctic Ocean. Such an anomaly could inversely affect the Atlantic circulation once it reaches deep water formation regions. If the Canadian Archipelago is closed, the anomaly is subsequently transported through the Fram Strait, and counters the initial changes in the Atlantic deep circulation. On the other hand, if the Canadian Archipelago is open, some of the anomaly is transported to the Canadian Archipelago, and the initial change in the Atlantic deep circulation persists. In the Arctic Ocean basin, the time scale and path of the salinity anomalys propagation depends on the large-scale flow at the surface of the Arctic Ocean. Our results suggest that the salinity anomaly transport and its propagation pathway out of the Arctic Ocean are important determinants of the role of sea ice transport variability through the Fram Strait in controlling the intensity of the Atlantic deep circulation.     

Variability of Fram Strait sea ice export: causes, impacts and feedbacks in a coupled climate model

Analyses of a 500-year control integration of the global coupled atmosphere–sea ice–ocean model ECHAM5.0/MPI-OM show a high variability in the ice export through Fram Strait on interannual to decadal timescales. This variability is mainly determined by variations in the sea level pressure gradient across Fram Strait and thus geostrophic wind stress. Ice thickness anomalies, formed at the Siberian coast and in the Chukchi Sea, propagate across the Arctic to Fram Strait and contribute to the variability of the ice export on a timescale of about 9 years. Large anomalies of the ice export through Fram Strait cause fresh water signals, which reach the Labrador Sea after 1–2 years and lead to significant changes in the deep convection. The associated anomalies in ice cover and ocean heat release have a significant impact on air temperature in the Labrador Sea and on the large-scale atmospheric circulation. This affects the sea ice transport and distribution in the Arctic again. Sensitivity studies, simulating the effect of large ice exports through Fram Strait, show that the isolated effect of a prescribed ice/fresh water anomaly is very important for the climate variability in the Labrador Sea. Thus, the ice export through Fram Strait can be used for predictability of Labrador Sea climate up to 2 years in advance.     

Regional Arctic sea ice variations as predictor for winter climate conditions

Seasonal prediction skill of winter mid and high northern latitudes climate from sea ice variations in eight different Arctic regions is analyzed using detrended ERA-interim data and satellite sea ice data for the period 1980–2013. We find significant correlations between ice areas in both September and November and winter sea level pressure, air temperature and precipitation. The prediction skill is improved when using November sea ice conditions as predictor compared to September. This is particularly true for predicting winter NAO-like patterns and blocking situations in the Euro-Atlantic area. We find that sea ice variations in Barents Sea seem to be most important for the sign of the following winter NAO—negative after low ice—but amplitude and extension of the patterns are modulated by Greenland and Labrador Seas ice areas. November ice variability in the Greenland Sea provides the best prediction skill for central and western European temperature and ice variations in the Laptev/East Siberian Seas have the largest impact on the blocking number in the Euro-Atlantic region. Over North America, prediction skill is largest using September ice areas from the Pacific Arctic sector as predictor. Composite analyses of high and low regional autumn ice conditions reveal that the atmospheric response is not entirely linear suggesting changing predictive skill dependent on sign and amplitude of the anomaly. The results confirm the importance of realistic sea ice initial conditions for seasonal forecasts. However, correlations do seldom exceed 0.6 indicating that Arctic sea ice variations can only explain a part of winter climate variations in northern mid and high latitudes.     

Time-dependence of sea-ice concentration and multiyear ice fraction in the Arctic Basin

The time variation of the sea-ice concentration and multiyear ice fraction within the pack ice in the Arctic Basin is examined, using microwave images of sea ice recently acquired by the Nimbus-5 spacecraft and the NASA CV-990 airborne laboratory. The images used for these studies were constructed from data acquired from the Electrically Scanned Microwave Radiometer (ESMR) which records radiation from earth and its atmosphere at a wavelength of 1.55 cm. Data are analyzed for four seasons during 1973–1975 to illustrate some basic differences in the properties of the sea ice during those times. Spacecraft data are compared with corresponding NASA CV-990 airborne laboratory data obtained over wide areas in the Arctic Basin during the Main Arctic Ice Dynamics Joint Experiment (1975) to illustrate the applicability of passive-microwave remote sensing for monitoring the time dependence of sea-ice concentration (divergence). These observations indicate significant variations in the sea-ice concentration in the spring, late fall and early winter. In addition, deep in the interior of the Arctic polar sea-ice pack, heretofore unobserved large areas, several hundred kilometers in extent, of sea-ice concentrations as low as 50% are indicated.     

Consequences of change and variability in sea ice on marine ecosystem and biogeochemical processes during the 2007–2008 Canadian International Polar Year program

Change and variability in the timing and magnitude of sea ice geophysical and thermodynamic state have consequences on many aspects of the arctic marine system. The changes in both the geophysical and thermodynamic state, and in particular the timing of the development of these states, have consequences throughout the marine system. In this paper we review the ??consequences?? of change in sea ice state on primary productivity, marine mammal habitats, and sea ice as a medium for storage and transport of contaminants and carbon exchange across the ocean-sea-ice-atmosphere interface based upon results from the International Polar Year. Pertinent results include: 1) conditions along ice edges can bring deep nutrient-rich ??pacific?? waters into nutrient-poor surface waters along the arctic coast, affecting local food webs; 2) both sea ice thermodynamic and dynamic processes ultimately affect ringed seal/polar bear habitats by controlling the timing, location and amount of surface deformation required for ringed seal and polar bear preferred habitat 3) the ice edges bordering open waters of flaw leads are areas of high biological production and are observed to be important beluga habitat. 4) exchange of climate-active gases, including CO₂, is extremely active in sea ice environments, and the overall question of whether the Arctic Ocean is (or will be) a source or sink for CO₂ will be dependent on the balance of competing climate-change feedbacks.     

A Nine-layer Atmospheric General Circulation Model and Its Performance

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Influence of coupling on atmosphere, sea ice and ocean regional models in the Ross Sea sector, Antarctica

Air–sea ice–ocean interactions in the Ross Sea sector form dense waters that feed the global thermohaline circulation. In this paper, we develop the new limited-area ocean–sea ice–atmosphere coupled model TANGO to simulate the Ross Sea sector. TANGO is built up by coupling the atmospheric limited-area model MAR to a regional configuration of the ocean–sea ice model NEMO. A method is then developed to identify the mechanisms by which local coupling affects the simulations. TANGO is shown to simulate realistic sea ice properties and atmospheric surface temperatures. These skills are mostly related to the skills of the stand alone atmospheric and oceanic models used to build TANGO. Nonetheless, air temperatures over ocean and winter sea ice thickness are found to be slightly improved in coupled simulations as compared to standard stand alone ones. Local atmosphere ocean feedbacks over the open ocean are found to significantly influence ocean temperature and salinity. In a stand alone ocean configuration, the dry and cold air produces an ocean cooling through sensible and latent heat loss. In a coupled configuration, the atmosphere is in turn moistened and warmed by the ocean; sensible and latent heat loss is therefore reduced as compared to the stand alone simulations. The atmosphere is found to be less sensitive to local feedbacks than the ocean. Effects of local feedbacks are increased in the coastal area because of the presence of sea ice. It is suggested that slow heat conduction within sea ice could amplify the feedbacks. These local feedbacks result in less sea ice production in polynyas in coupled mode, with a subsequent reduction in deep water formation.     

Sea ice in the Barents Sea: seasonal to interannual variability and climate feedbacks in a global coupled model

Sea ice variability in the Barents Sea and its impact on climate are analyzed using a 465-year control integration of a global coupled atmosphere–ocean–sea ice model. Sensitivity simulations are performed to investigate the response to an isolated sea ice anomaly in the Barents Sea. The interannual variability of sea ice volume in the Barents Sea is mainly determined by variations in sea ice import into Barents Sea from the Central Arctic. This import is primarily driven by the local wind field. Horizontal oceanic heat transport into the Barents Sea is of minor importance for interannual sea ice variations but is important on longer time scales. Events with strong positive sea ice anomalies in the Barents Sea are due to accumulation of sea ice by enhanced sea ice imports and related NAO-like pressure conditions in the years before the event. Sea ice volume and concentration stay above normal in the Barents Sea for about 2 years after an event. This strongly increases the albedo and reduces the ocean heat release to the atmosphere. Consequently, air temperature is much colder than usual in the Barents Sea and surrounding areas. Precipitation is decreased and sea level pressure in the Barents Sea is anomalously high. The large-scale atmospheric response is limited with the main impact being a reduced pressure over Scandinavia in the year after a large ice volume occurs in the Barents Sea. Furthermore, high sea ice volume in the Barents Sea leads to increased sea ice melting and hence reduced surface salinity. Generally, the climate response is smallest in summer and largest in winter and spring.     

A Model Study of the Relationship between Sea-Ice Variability and Surface and Intermediate Water Mass Properties in the Labrador Sea

Sea ice plays an important role in the variability of the Labrador Sea especially in its most western part adjacent to an important region of deep convection. Winter-to-winter re-emergence and propagation of both sea-ice concentration (SIC) and sea surface temperature anomalies have been observed following years of high SIC in this region. They have potentially important links to water mass properties and freshwater and heat transports in the subpolar North Atlantic. This article builds on the results of two precursor papers and presents results from a coupled sea-ice–ocean model study of the interannual variability of sea ice in the Labrador Sea. The relationships between SIC and water column properties in the subpolar North Atlantic are assessed. Winters with high SIC and strong surface cooling are found to be conducive to intensified convection. Surface and mid-depth temperature and salinity anomalies are observed in the Labrador Sea and the northwestern North Atlantic during winters with anomalous Labrador Sea SIC. These anomalies are found to propagate along the major circulation patterns in the subpolar North Atlantic and to persist for up to three years.     

Climate fluctuations of the Weddell Sea and its surroundings in a transient climate change scenario

The response of the Weddell Sea and Antarctic Peninsula to anthropogenic forcing simulated by a global climate model is analyzed. The model, despite its low resolution, is able to capture several aspects of the observed regional pattern of climate change. A strong warming and depletion of the sea ice cover in the western Weddell Sea contrasts with a slight cooling and a sea-ice extension in the eastern Weddell Sea. This simulated long-term climate change is modulated by interdecadal variability but also affected by some abrupt regional changes in the oceanic mixed layer depth. Between 1960 and 2030 a reorganization of the deep convection activity in the Weddell Sea sustains the opposition between the eastern and western Weddell Sea. The deep convection collapses in the western Weddell Sea in the 2030s. The sea ice retreat trend is then followed by an increase of the sea ice cover in the western Weddell Sea. In the eastern Weddell Sea another abrupt collapse of the deep convection activity occurs around 2080. This event is followed by a rapid cooling and sea ice extension during the next 20 years. Most of the surface changes are associated with large-scale atmospheric circulation changes that project on the dominant mode of natural variability but also with oceanic convection and circulation changes.     

The demise of Arctic sea ice during stabilisation at high greenhouse gas concentrations

A climate model experiment was conducted using the HadCM3 climate model and a scenario in which the atmospheric CO₂ concentration was increased over 70 years from pre-industrial concentrations to 4 times this level and then stabilised for more than a 1,000 years. During the period of stabilisation the global atmospheric surface temperatures continued to rise as the deep oceans adjusted towards a new equilibrium. However, even after 1,000 years this new equilibrium had not been reached. During the first 600 years, Arctic and Antarctic winter sea ice thickness and area covered declined with a significant impact on the global radiation budget. After this period the area of the Arctic covered by sea ice entered a 150 years period during which time it underwent a series of oscillations. Following the oscillation the centre of the Arctic basin became ice free throughout the year. A sensitivity experiment demonstrates that although the sea ice extent can be greatly reduced through the artificial heating of the mixed layer, prior to the onset of the oscillatory phase the ice recovers over 15 years. Understanding the causes of this oscillatory phase may elucidate the mechanisms of variability in the Arctic in the present climate and in future policy relevant scenarios. We have investigated the atmospheric and oceanic forcing on the ice during the oscillatory phase, and find that the behaviour is linked to a redistribution of Arctic Ocean heat stores.     

STUDY ON SEA ICE WITH GMS REAL-TIME DATA

By use of GMS-4 infrared brightness temperature and visible albedo data from January toFebruary in 1995,the method for extracting of sea ice parameters is developed.The digital remotesensing picture is obtained on Liaodong Bay.Based on the difference in physical properties betweenice and water,a criterion distinguishing ice from water is set up.Ice thickness has been calculatedaccording to the relationship between ice thickness and brightness as well as albedo.Iceconcentration is retrieved due to the difference on albedo between ice and water.The resultsindicate that the accuracy of ice-water distinguishing is 84.8%,the errors of ice thickness and iceconcentration are 3.8 cm and 22%,respectively.     

STUDY ON SEA ICE WITH GMS REAL-TIME DATA*

By use of GMS-4 infrared brightness temperature and visible albedo data from January to February in 1995,the method for extracting of sea ice parameters is developed.The digital remote sensing picture is obtained on Liaodong Bay.Based on the difference in physical properties between ice and water,a criterion distinguishing ice from water is set up.Ice thickness has been calculated according to the relationship between ice thickness and brightness as well as albedo.Ice concentration is retrieved due to the difference on albedo between ice and water.The results indicate that the accuracy of ice-water distinguishing is 84.8%,the errors of ice thickness and ice concentration are 3.8 cm and 22%,respectively.     

The Response of Arctic Sea Ice to Global Change

The sea ice-covered polar oceans have received wider attention recently for two reasons. Firstly, the global conveyor belt circulation of the ocean is believed to be forced in the North and South Atlantic through deep water formation, which to a large degree is controlled by the variations of the sea ice margin and especially by the sea ice export to lower latitudes. Secondly, CO₂ response experiments with coupled climate models show an enhanced warming in polar regions for increased concentrations of atmospheric greenhouse gases. Whether this large response in high latitudes is due to real physical feedback processes or to unrealistic simplifications of the sea ice model component remains to be determined. Coupled climate models generally use thermodynamic sea ice models or sea ice models with oversimplified dynamics schemes. Realistic dynamic-thermodynamic sea ice models are presently implemented only at a few modeling centers. Sensitivity experiments with thermodynamic and dynamic-thermodynamic sea ice models show that the more sophisticated models are less sensitive to perturbations of the atmospheric and oceanic boundary conditions. Because of the importance of the role of sea ice in mediating between atmosphere and ocean an improved representation of sea ice in global climate models is required. This paper discusses present sea ice modeling as well as the sensitivity of the sea ice cover to changes in the atmospheric boundary conditions. These numerical experiments indicate that the sea ice follows a smooth response function: sea ice thickness and export change by 2% of the mean value per 1 Wm^-2 change of the radiative forcing.