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  • 1
    Publication Date: 2017-01-20
    Description: This study deals with observations and simulations of the evolution of coastal polynias focusing on the Ronne Polynia. We compare differences in polynia extent and ice drift patterns derived from satellite radar images and from simulations with the Finite Element Sea Ice Ocean Model, employing three atmospheric forcing data sets that differ in spatial and temporal resolution. Two polynia events are analyzed, one from austral summer and one from late fall 2008. The open water area in the polynia is of similar size in the satellite images and in the model simulations, but its temporal evolution differs depending on katabatic winds being resolved in the atmospheric forcing data sets. Modeled ice drift is slower than the observed and reveals greater turning angles relative to the wind direction in many cases. For the summer event, model results obtained with high-resolution forcing are closer to the drift field derived from radar imagery than those from coarse resolution forcing. For the late fall event, none of the forcing data yields outstanding results. Our study demonstrates that a dense (1–3 km) model grid and atmospheric forcing provided at high spatial resolution ( 〈 50 km) are critical to correctly simulate coastal polynias with a coupled sea-ice ocean model.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 2
    Publication Date: 2016-11-29
    Description: Mesoscale model simulations were conducted for the Weddell Sea region for the autumn and winter periods of 2008 using a high-resolution, limited-area, non-hydrostatic atmospheric model. A sea ice–ocean model was run with enhanced horizontal resolution and high-resolution forcing data of the atmospheric model. Daily passive thermal and microwave satellite data was used to derive the polynya area in the Weddell Sea region. The focus of the study is on the formation of polynyas in the coastal region of Coats Land, which is strongly affected by katabatic flows. The polynya areas deduced from two independent remote sensing methods and data sources show good agreement, while the results of the sea ice simulation show some weaknesses. Linkages between the pressure gradient force composed of a katabatic and a synoptic component, offshore wind regimes and polynya area are identified. It is shown that the downslope surface offshore wind component of Coats Land is the main forcing factor for polynya dynamics, which is mainly steered by the offshore pressure gradient force, where the katabatic force is the dominant term. We find that the synoptic pressure gradient is opposed to the katabatic force during major katabatic wind events.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 3
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 4
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 5
    Publication Date: 2019-12-03
    Description: In the early 1980s, Germany started a new era of modern Antarctic research. The Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) was founded and important research platforms such as the German permanent station in Antarctica, today called Neumayer III, and the research icebreaker Polarstern were installed. The research primarily focused on the Atlantic sector of the Southern Ocean. In parallel, the German National Science Foundation (Deutsche Forschungsgemeinschaft DFG) started a Priority Program ‘Antarctic Research’ (since 2003 called SPP-1158) to foster and intensify the cooperation between scientists from different German universities and the AWI as well as other institutes involved in polar research. Here, we review the main findings in meteorology and oceanography of the last decade, funded by the priority program. The paper presents field observations and modelling efforts, extending from the stratosphere to the deep ocean. The research spans a large range of temporal and spatial scales, including the interaction of both climate components. In particular, radiative processes, the interaction of the changing ozone layer with large-scale atmospheric circulations, and changes in the sea ice cover are discussed. Climate and weather forecast models provide an insight into the water cycle and the climate change signals associated with synoptic cyclones. Investigations of the atmospheric boundary layer focus on the interaction between atmosphere, sea ice, and ocean in the vicinity of polynyas and leads. The chapters dedicated to polar oceanography review the interaction between the ocean and ice shelves with regard to the freshwater input and discuss the changes in water mass characteristics, ventilation and formation rates, crucial for the deepest limb of the global, climate relevant meridional overturning circulation. They also highlight the associated storage of anthropogenic carbon as well as the cycling of carbon, nutrients, and trace metals in the ocean with special emphasis on the Weddell Sea.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 6
    Publication Date: 2014-04-04
    Description: Dense shelf water is an essential ingredient to the formation of Antarctic Bottom Water (AABW). It is formed on the continental shelves surrounding Antarctica, when freezing rates are sufficiently high to push ocean salinity to values of 34.65 and higher. Coastal polynyas, where the ice is driven away from the coastline, maintain the highest freezing rates in Antarctic winter. Since the Weddell Sea is considered the most productive source region of AABW, we investigate the dense water formation on the continental shelves of the southwestern Weddell Sea, with a focus on the role of coastal polynyas, using the Finite Element Sea ice-Ocean Model (FESOM), a primitive-equation, hydrostatic ocean model coupled with a dynamic-thermodynamic sea ice model. The horizontal resolution of the global, unstructured mesh is up to 3 km at the southwestern Weddell Sea coastline; in vertical direction the mesh features 37 depth levels (resolution increases toward the surface). The model was initialized on 01/01/1980 with data from the Polar Hydrographic Climatology and forced with NCEP/NCAR Reanalysis data. The 20-year period 1990-2009 is used for analysis. Our results indicate that in an average year, the polynya freezing rates of 9 cm/d cause a seasonal variation in salinity of 0.3 psu under the Ronne polynya and result in the production of dense shelf water, which leaves the continental shelf (outlined by the 700 m isobath in this study) at a long-term mean volume flux of 5.2 Sv. Some of this water contributes to the formation of Weddell Sea Deep/Bottom Water, but a large fraction is diluted by mixing with ambient water and leaves the Weddell Sea at intermediate levels.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 7
    Publication Date: 2016-11-29
    Description: The development of coastal polynyas, areas of enhanced heat flux and sea ice production, strongly depends on atmospheric conditions. In Antarctica, measurements are scarce and models are essential for the investigation of polynyas. A robust quantification of polynya exchange processes in simulations relies on a realistic representation of atmospheric conditions in the forcing dataset. The sensitivity of simulated coastal polynyas in the south-western Weddell Sea to the atmospheric forcing is investigated with the Finite-Element Sea ice-Ocean Model (FESOM) using daily NCEP/NCAR reanalysis data (NCEP), 6 hourly Global Model Europe (GME) data and two different hourly datasets from the high-resolution Consortium for Small-Scale Modelling (COSMO) model. Results are compared for April to August 2007–09. The two coarse-scale datasets often produce the extremes of the data range, while the finer-scale forcings yield results closer to the median. The GME experiment features the strongest winds and, therefore, the greatest polynya activity, especially over the eastern continental shelf. This results in higher volume and export of High Salinity Shelf Water than in the NCEP and COSMO runs. The largest discrepancies between simulations occur for 2008, probably due to differing representations of the ENSO pattern at high southern latitudes. The results suggest that the large-scale wind field is of primary importance for polynya development.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 8
    Publication Date: 2014-12-11
    Description: Radical environmental changes are forecasted to occur in the Shelf areas of the Siberian Arctic during this century. The Laptev polynyas play a key role due to their impact on ice production and related feedback processes in the ocean and atmosphere. Observations and model studies have been performed within the BMBF founded project "Polynya systems face changes" (2007-2010) which is embedded in the IPY-project "Complex Investigations of Seasonal Cycle in the Arctic Seas". Four automatic weather stations which were installed along the fast ice edge in April 2008 reveal that the GME analyses (Global Model of Deutscher Wetterdienst) describe the synoptic conditions accurately (e.g. absolute error of wind speed between 0.2 and 0.5 ms-1 and correlation coefficients between 0.8 and 0.9). Thus, these analyses are an excellent data set for nesting meso-scale atmosphere models and forcing ocean models. Realistic and artificial case studies are presented with the non-hydrostatic atmospheric model COSMO (Consortium for Small-scale Modeling, Deutscher Wetterdienst) and the Finite Element Sea Ice Ocean Model (FESOM, Alfred Wegener Institute) on a grid with a horizontal resolution of 5km. These simulations show that the polynyas modify the atmosphere till a height of several kilometers. Furthermore, an accurate simulation of ice surface temperature is essential to quantify ice production realistically. The highest ice production rate was simulated for a cyclone case at the end of December 2007, whereas ice production is marginal for the April 2008 polynya cases.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 9
    Publication Date: 2014-12-09
    Description: Global Change and its predicted key impact on the Arctic bring the Laptev Sea to the centre of climate-related polar research. This Shelf Sea is known as being a highly productive area for the formation of new ice throughout the winter season. A main part of the ice production occurs in flaw polynyas which appear recurrently at the edge of the fast ice surrounding the coastal zones during wintertime. This work attempts to provide a method to reliably estimate the ice production in the Laptev Sea polynyas from model result s of the numerical weather prediction model COSMO. Our modeling approach contains the use of COSMO with 15 and 5 km horizontal resolution nested in global GME/ERA-Interim data to calculate ice production in polynyas. To account for realistic polynya representation polynya area is prescribed to the COSMO model by daily AMSR-E satellite data. The potential volume ice production is calculated from atmospheric net radiation fluxes. In contrast to preceding studies our new COSMO-based method takes into account the effect of polynyas on the atmosphere. Over open water, warmer 2m temperatures (COSMO in comparison to NCEP) lead to lower ice production. Over thin ice, surface temperature depends on air temperature and reduced air surface temperature gradients cause lower heat fluxes and less ice production than over open water. As warm-biased NCEP values are balancing the effects of our improvements the comparison of ice production retrieval based on NCEP data with our results show minor total differences only. Both methods are leading to results in same order of magnitude if the polynya is assumed to be covered with 10cm of thin-ice. This supports the thesis that either of them leads to feasible ice production values if thin ice within the polynya is accounted for in the calculation. In case of an open water polynya, however, our study underlines the impact of the atmospheric data on the ice production. Thus we conclude that it is of major importance to choose a validated ice thickness parameterization for the model.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 10
    Publication Date: 2016-01-07
    Description: The interaction between polynyas and the atmospheric boundary layer is examined in the Laptev Sea using the regional, non-hydrostatic Consortium for Small-scale Modelling (COSMO) atmosphere model. A thermodynamic sea-ice model is used to consider the response of sea-ice surface temperature to idealized atmospheric forcing. The idealized regimes represent atmospheric conditions that are typical for the Laptev Sea region. Cold wintertime conditions are investigated with sea-iceocean temperature differences of up to 40 K. The Laptev Sea flaw polynyas strongly modify the atmospheric boundary layer. Convectively mixed layers reach heights of up to 1200 m above the polynyas with temperature anomalies of more than 5 K. Horizontal transport of heat expands to areas more than 500 km downstream of the polynyas. Strong wind regimes lead to a more shallow mixed layer with strong near-surface modifications, while weaker wind regimes show a deeper, well-mixed convective boundary layer. Shallow mesoscale circulations occur in the vicinity of ice-free and thin-ice covered polynyas. They are forced by large turbulent and radiative heat fluxes from the surface of up to 789 W m-2, strong low-level thermally induced convergence and cold air flow from the orographic structure of the Taimyr Peninsula in the western Laptev Sea region. Based on the surface energy balance we derive potential sea-ice production rates between 8 and 25 cm d-1. These production rates are mainly determined by whether the polynyas are ice-free or covered by thin ice and by the wind strength.
    Type: Article , PeerReviewed
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