scholarly journals A possibility of large scale intrusions generation in the Arctic Ocean under stable-stable stratification: an analytical consideration

2016 ◽  
Author(s):  
Natalia Kuzmina
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Arctic Basin ◽  
Stable Stratification ◽  
Velocity Shear ◽  
The Arctic ◽  
Vertical Diffusion ◽  
Linear Shear ◽  
Dimensional Instability ◽  
Thermohaline Stratification

Abstract. Some analytical solutions are found for the problem of three-dimensional instability of a weak geostrophic flow with linear velocity shear taking into account vertical diffusion of buoyancy. The analysis is based on the potential vorticity equation in a long-wave approximation when the horizontal scale of disturbances is taken to be much larger than the local baroclinic Rossby radius. It is hypothesized that the solutions found can be applied to describe stable and unstable disturbances on a planetary scale with respect, especially, to the Arctic Basin, where weak baroclinic fronts with typical temporal variability periods of the order of several years or more are observed and the beta-effect is negligible. Stable (decaying with time) solutions describe disturbances that, in contrast to the Rossby waves, can propagate to both the west and east, depending on the sign of the linear shear of geostrophic velocity. The unstable (growing with time) solutions are applied to describe large-scale intrusions at baroclinic fronts under the stable–stable thermohaline stratification observed in the upper layer of the Polar Deep Water in the Eurasian Basin. The proposed description of intrusive layering can be considered as a possible alternative to the mechanism of interleaving due to the differential mixing.

scholarly journals Generation of large-scale intrusions at baroclinic fronts: an analytical consideration with a reference to the Arctic Ocean

Ocean Science ◽  
2016 ◽  
Vol 12 (6) ◽  
pp. 1269-1277 ◽  
Author(s):  
Natalia Kuzmina
Keyword(s):  
Arctic Ocean ◽  
Large Scale ◽  
Velocity Shear ◽  
The Arctic ◽  
Vertical Diffusion ◽  
Planetary Scale ◽  
The Arctic Ocean ◽  
Linear Shear ◽  
Long Wave Approximation ◽  
Thermohaline Stratification

Abstract. Analytical solutions are found for the problem of instability of a weak geostrophic flow with linear velocity shear accounting for vertical diffusion of buoyancy. The analysis is based on the potential-vorticity equation in a long-wave approximation when the horizontal scale of disturbances is considered much larger than the local baroclinic Rossby radius. It is hypothesized that the solutions found can be applied to describe stable and unstable disturbances of the planetary scale with respect, in particular, to the Arctic Ocean, where weak baroclinic fronts with typical temporal variability periods on the order of several years or more have been observed and the β effect is negligible. Stable (decaying with time) solutions describe disturbances that, in contrast to the Rossby waves, can propagate to both the west and east, depending on the sign of the linear shear of geostrophic velocity. The unstable (growing with time) solutions are applied to explain the formation of large-scale intrusions at baroclinic fronts under the stable–stable thermohaline stratification observed in the upper layer of the Polar Deep Water in the Eurasian Basin. The suggested mechanism of formation of intrusions can be considered a possible alternative to the mechanism of interleaving at the baroclinic fronts due to the differential mixing.

scholarly journals NUMERICAL SIMULATION OF ARCTIC HALOCLINE FORMATION

2020 ◽  
Vol 4 (1) ◽  
pp. 83-90
Author(s):  
Marina A. Tarkhanova ◽  
Elena N. Golubeva
Keyword(s):  
River Flow ◽  
Three Dimensional ◽  
Arctic Basin ◽  
The Arctic ◽  
Atmospheric Effects ◽  
Main Attention ◽  
The Past ◽  
Model Distribution ◽  
Arctic Ice ◽  
Thermohaline Stratification

This paper discusses issues related to the analysis of the Arctic halocline state over the past decades. Observational data show that the layer of halocline in the Arctic Ocean significantly changed in the last 40 years, which may affect the Arctic ice cover. For the study we used a three-dimensional ocean and sea ice numerical model developed at the ICMMG SB RAS. The main attention was devoted to the analysis of the model distribution of water salinity in the upper 250-meter layer and its variability. Based on numerical experiments on the sensitivity of thermohaline stratification to variations in atmospheric effects and the intensity of river flow, we identified areas of the Arctic basin in which the variability of the Arctic halocline was the most pronounced.

scholarly journals Description of the perturbations of oceanic geostrophic currents with linear vertical velocity shear taking into account friction and diffusion of density

2019 ◽  
Vol 55 (2) ◽  
pp. 73-85
Author(s):  
N. P. Kuzmina ◽  
S. L. Skorokhodov ◽  
N. V. Zhurbas ◽  
D. A. Lyzhkov
Keyword(s):  
Vertical Velocity ◽  
Maximum Flow ◽  
Arctic Basin ◽  
Stable Stratification ◽  
Short Wave ◽  
Velocity Shear ◽  
The Arctic ◽  
Mesoscale Structures ◽  
Wide Range ◽  
Geostrophic Flows

A spectral problem of Orr-Sommerfeld type for describing stable and unstable disturbances of oceanic geostrophic flows with linear vertical velocity shear is considered. Calculations of eigenvalues, increments of growth rate of unstable modes, and eigenfunctions of the fastest growing disturbances are presented. It is found that the instability of the flow is observed over a wide range of horizontal scales: in addition to long-wave perturbations with a phase velocity exceeding the maximum flow velocity and perturbations with scales of the Rossby radius, short-wave modes with scales much smaller than the Rossby radius (sub-mesoscale structures) exist. The results of the model are used to describe intrusions in the Arctic basin, which are observed under conditions of absolutely stable stratification.

scholarly journals Arctic sea ice thickness loss determined using subsurface, aircraft, and satellite observations

2015 ◽  
Vol 9 (1) ◽  
pp. 269-283 ◽  
Author(s):  
R. Lindsay ◽  
A. Schweiger
Keyword(s):  
Sea Ice ◽  
Large Scale ◽  
Spatial Scales ◽  
Arctic Basin ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Ice Thickness ◽  
Spatial And Temporal Variability ◽  
Sampling Errors ◽  
Sea Ice Thickness

Abstract. Sea ice thickness is a fundamental climate state variable that provides an integrated measure of changes in the high-latitude energy balance. However, observations of mean ice thickness have been sparse in time and space, making the construction of observation-based time series difficult. Moreover, different groups use a variety of methods and processing procedures to measure ice thickness, and each observational source likely has different and poorly characterized measurement and sampling errors. Observational sources used in this study include upward-looking sonars mounted on submarines or moorings, electromagnetic sensors on helicopters or aircraft, and lidar or radar altimeters on airplanes or satellites. Here we use a curve-fitting approach to determine the large-scale spatial and temporal variability of the ice thickness as well as the mean differences between the observation systems, using over 3000 estimates of the ice thickness. The thickness estimates are measured over spatial scales of approximately 50 km or time scales of 1 month, and the primary time period analyzed is 2000–2012 when the modern mix of observations is available. Good agreement is found between five of the systems, within 0.15 m, while systematic differences of up to 0.5 m are found for three others compared to the five. The trend in annual mean ice thickness over the Arctic Basin is −0.58 ± 0.07 m decade−1 over the period 2000–2012. Applying our method to the period 1975–2012 for the central Arctic Basin where we have sufficient data (the SCICEX box), we find that the annual mean ice thickness has decreased from 3.59 m in 1975 to 1.25 m in 2012, a 65% reduction. This is nearly double the 36% decline reported by an earlier study. These results provide additional direct observational evidence of substantial sea ice losses found in model analyses.

Eddy statistics validation of an ORCA12 ocean and sea ice model for the Arctic with satellite data

2020 ◽  
Author(s):  
Stefanie Rynders ◽  
Yevgeny Akesenov ◽  
Igor Kozlov
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Large Scale ◽  
Mixed Layer Depth ◽  
Three Dimensional ◽  
The Arctic ◽  
The European Union ◽  
Boundary Current ◽  
Horizon 2020 ◽  
The Uk

<p>As sea ice and ocean models are moving to higher resolution it becomes possible to permit eddy formation even in the Arctic Ocean. Eddies can affect the three dimensional ocean state through causing mixing and even ventilation of subsurface ocean layers if they are deep enough. To ensure models have the potential to simulate the density structure correctly it is therefore necessary to start doing model validation of not only the large scale ocean state, but also of the eddy field. Eddy statistics for the Arctic are available from satellite for the Western Arctic Ocean and the Fram Strait, in particular on number, size and cyclonicity of eddies for open ocean versus ice covered sites. These are compared to a NEMO-LIM 1/12 degree sea ice and ocean simulation (resolution 2-5km), upon which the model based statistics are expanded to the whole Arctic. In the model it is also possible to examine the depth structure of eddies, allowing to generate size vs. depth statistics. This, together with climatological mixed layer depth, provides a first estimate to get satellite-based information on mixing from eddies in the Arctic. We also map the maximum depth of eddies, to examine ventilation and identify sites with especially deep eddies, for instance at the boundary current. Acknowledgements: Grant NE/R000654/1 “Towards a Marginal Sea Ice Cover” funded by the UK Natural Research Council (NERC) and the UK-Russia Arctic bursaries program funded by the United Kingdom’s Department for Business, Energy and Industrial Strategy. The study is also supported from the project “The Advective Pathways of nutrients and key Ecological substances in the Arctic (APEAR)” (grant NE/R012865/1) funded by the Joint UK NERC/German Federal Ministry of Education and Research Changing Arctic Ocean Programme. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 821926 (IMMERSE). IK acknowledges the support from RFBR grant No 18-35-20078.</p>

scholarly journals Influence of Atlantic inflow on the freshwater content in the upper layer of the Arctic basin

2019 ◽  
Vol 65 (4) ◽  
pp. 363-388
Author(s):  
G. V. Alekseev ◽  
A. V. Pnyushkov ◽  
A. V. Smirnov ◽  
A. E. Vyazilova ◽  
N. I. Glok
Keyword(s):  
Fresh Water ◽  
Large Scale ◽  
Barents Sea ◽  
Lower Boundary ◽  
Arctic Basin ◽  
Water Layer ◽  
Atlantic Water ◽  
Water Masses ◽  
The Arctic ◽  
The North

Inter-decadal changes in the water layer of Atlantic origin and freshwater content (FWC) in the upper 100 m layer were traced jointly to assess the influence of inflows from the Atlantic on FWC changes based on oceanographic observations in the Arctic Basin for the 1960s – 2010s. For this assessment, we used oceanographic data collected at the Arctic and Antarctic Research Institute (AARI) and the International Arctic Research Center (IARC). The AARI data for the decades of 1960s – 1990s were obtained mainly at the North Pole drifting ice camps, in high-latitude aerial surveys in the 1970s, as well as in ship-based expeditions in the 1990s. The IARC database contains oceanographic measurements acquired using modern CTD (Conductivity – Temperature – Depth) systems starting from the 2000s. For the reconstruction of decadal fields of the depths of the upper and lower 0 °С isotherms and FWC in the 0–100 m layer in the periods with a relatively small number of observations (1970s – 1990s), we used a climatic regression method based on the conservativeness of the large-scale structure of water masses in the Arctic Basin. Decadal fields with higher data coverage were built using the DIVAnd algorithm. Both methods showed almost identical results when compared.  The results demonstrated that the upper boundary of the Atlantic water (AW) layer, identified with the depth of zero isotherm, raised everywhere by several tens of meters in 1990s – 2010s, when compared to its position before the start of warming in the 1970s. The lower boundary of the AW layer, also determined by the depth of zero isotherm, became deeper. Such displacements of the layer boundaries indicate an increase in the volume of water in the Arctic Basin coming not only through the Fram Strait, but also through the Barents Sea. As a result, the balance of water masses was disturbed and its restoration had to occur due to the reduction of the volume of the upper most dynamic freshened layer. Accordingly, the content of fresh water in this layer should decrease. Our results confirmed that FWC in the 0–100 m layer has decreased to 2 m in the Eurasian part of the Arctic Basin to the west of 180° E in the 1990s. In contrast, the FWC to the east of 180° E and closer to the shores of Alaska and the Canadian archipelago has increased. These opposite tendencies have been intensified in the 2000s and the 2010s. A spatial correlation between distributions of the FWC and the positions of the upper AW boundary over different decades confirms a close relationship between both distributions. The influence of fresh water inflow is manifested as an increase in water storage in the Canadian Basin and the Beaufort Gyre in the 1990s – 2010s. The response of water temperature changes from the tropical Atlantic to the Arctic Basin was traced, suggesting not only the influence of SST at low latitudes on changes in FWC, but indicating the distant tropical impact on Arctic processes. 

Understanding the variability of the Eddy Kinetic Energy in the Arctic Ocean.

2021 ◽  
Author(s):  
Camille Lique ◽  
Heather Regan ◽  
Gianluca Meneghello ◽  
Claude Talandier
Keyword(s):  
Kinetic Energy ◽  
Arctic Ocean ◽  
Time Scales ◽  
Large Scale ◽  
Small Deformation ◽  
Arctic Basin ◽  
Temporal Variations ◽  
Eddy Kinetic Energy ◽  
The Arctic ◽  
The Arctic Ocean

<p>Mesoscale activity in the Arctic Ocean remains largely unexplored, owing primarily to the challenges of i) observing eddies in this ice-covered region and ii) modelling at such small deformation radius. In this talk, we will use results from a simulation performed with a high-resolution, eddy resolving model to investigate the spatial and temporal variations of the eddy kinetic energy (EKE) in the Arctic Basin. On average and in contrast to the typical open ocean conditions, the levels of mean and eddy kinetic energy are of the same order of magnitude, and EKE is intensified along the boundary and in the subsurface. On long time scales (interannual to decadal), EKE levels do not respond as expected to changes in the large scale circulation. This can be exemplified when looking at the spin up of the gyre that occurred in response to a strong surface input of momentum in 2007-2008. On seasonal time scales, the estimation of a Lorenz energy cycle allows us to investigate the drivers behind the peculiarities of the EKE field, and to understand the relative roles played by the atmospheric forcing for them.</p><p> </p>

scholarly journals Interannual characteristics of an 80 km resolution diagnostic Arctic ice–ocean model

1991 ◽  
Vol 15 ◽  
pp. 155-162 ◽  
Author(s):  
John E. Ries ◽  
William D. Hibler
Keyword(s):  
Ocean Circulation ◽  
Large Scale ◽  
Eddy Viscosity ◽  
Barents Sea ◽  
Arctic Basin ◽  
Ocean Model ◽  
The Arctic ◽  
Atmospheric Forcing ◽  
Ice Edge ◽  
Arctic Ice

Seasonal simulations with large-scale coupled ice–ocean models have reproduced many features of the ice and ocean circulation of the Arctic Ocean and the Greenland and Norwegian seas (e.g. Hibler and Bryan, 1987; Semtner, 1987). However, the crude resolution and high lateral eddy viscosity used by these models prevent the simulation of many of the smaller-scale seasonal features and tend to produce sluggish circulation. Similarly, the use of a single year’s atmospheric forcing prevents the simulation of features on an interannual time-scale. As an initial step towards addressing these issues, an 80 km diagnostic Arctic ice–ocean model is constructed and integrated over a three-year period using daily atmospheric forcing to drive the model. To examine the effect of topographic resolution and eddy viscosity on model results, similar simulations were performed with a 160 km-resolution model. The results of these simulations are compared with one another, with buoy drift in the Arctic Basin, and with observed ice-edge variations. The model results proved most sensitive to changes in horizontal resolution. The 80 km results provided a more realistic and robust circulation in most areas of the Arctic and improved the modelled ice edge in the Barents Sea, while also successfully simulating the interannual variation in the region. Although it performed better than the 160 km model, the 80 km model still produced too large an ice extent in the Greenland Sea. No significant improvement in the ice-edge prediction was observed by varying the lateral eddy viscosity. The results indicate that problems remain in the vertical resolution in shallow regions, in treating penetrative convection, and in the simulation of inflow into the Arctic Basin through the Fram Strait.

scholarly journals Large-Scale Patterns of Snow Melt on Arctic Sea Ice Mapped from Meteorological Satellite Imagery

1987 ◽  
Vol 9 ◽  
pp. 200-205 ◽  
Author(s):  
G. Scharfen ◽  
R.G. Barry ◽  
D.A. Robinson ◽  
G. Kukla ◽  
M.C Serreze
Keyword(s):  
Large Scale ◽  
Surface Albedo ◽  
Late Summer ◽  
Arctic Basin ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Snow Melt ◽  
Ice Surface ◽  
Air Temperatures ◽  
Ice Concentration

The seasonal progression of snow melt on the Arctic pack ice is mapped from satellite shortwave imagery (0.4–1.1 micrometers) for four spring/summer seasons (1977, 1979, 1984 and 1985). This provides the first detailed information on the temporal change of the ice surface albedo in summer and of its year-to-year variability. The average surface albedo of the Arctic Basin for the years investigated falls from between 0.75 and 0.80 in early May to between 0.35 and 0.45 in late July and early August. In the central Arctic, where ice concentration remains high and ponding on the ice is limited, the July albedo ranges from 0.50 to 0.60. Overall, melt progresses poleward from the Kara and Barents Seas and from the southern Beaufort and Chukchi Seas, with the melt fronts meeting on the American side of the Pole. There are substantial year-to-year differences in the timing, duration and extent of the melt interval. The progression of melt in May and June of the earliest melt year (1977) was about 3 weeks ahead of the latest year (1979). By late July, the central Arctic was essentially snow free in 1977 and 1979, but more than 50% snow covered in 1984. Although limited in extent, our data base suggests relationships between snow melt and Arctic surface air temperatures in spring, spring cloudiness and the extent of late summer ice.

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