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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Boundary layer meteorology 93 (1999), S. 75-116 
    ISSN: 1573-1472
    Keywords: Aircraft study ; Arctic boundary layer ; Downslope winds ; Katabatic wind
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The aircraft-based experiment KABEG‘97 (Katabatic wind and boundary-layer front experiment around Greenland) was performed in April/May 1997. During the experiment, surface stations were installed at five positions on the ice sheet and in the tundra near Kangerlussuaq, West Greenland. A total of nine katabatic wind flights were performed during quite different synoptic situations and surface conditions, and low-level jets with wind speeds up to 25m s-1 were measured under strong synoptic forcing of the katabatic wind system. The KABEG data represent a unique data set for the investigation of katabatic winds. For the first time, high-resolution and accurate aircraft measurements can be used to investigate the three-dimensional structure of the katabatic wind system for a variety of synoptic situations. Surface station data show that a pronounced daily cycle of the near-surface wind is present for almost all days due to the nighttime development of the katabatic wind. In a detailed case study the stably-stratified boundary layer over the ice and the complex boundary-layer structure in the transition zone ice/tundra are investigated. The katabatic wind system is found to extend about 10 km over the tundra area and is associated with strong wind convergence and gravity waves. The investigation of the boundary-layer dynamics using the concept of a two-layer katabatic wind model yields the results that the katabatic flow is always a ‘shooting’ flow and that the ‘pure katabatic’ force is the main driving mechanism for the flow regime, although a considerable influence of the large-scale synoptic forcing is found as well.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2015-03-13
    Type: Article , PeerReviewed
    Format: text
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  • 3
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    Schweizerbarth
    In:  Meteorologische Zeitschrift, 17 (5). pp. 589-601.
    Publication Date: 2015-04-15
    Description: Polar regions offer the opportunity to study many processes under strongly simplified conditions ('natural laboratory'). For example, the plateau areas of the polar ice sheets represent areas with an almost ideal homogeneous surface over a scale of several 100 km, which are extraordinary suited for studies of the stable boundary layer (SBL). In coastal areas we find often a transition of the SBL to a convective boundary layer (CBL) over polynyas, which allows for near-ideal studies of internal boundary layers. The sea ice areas in polar regions are another example for natural laboratory conditions, since they represent large areas with well-defined heterogeneities of two surface types. The present review shows examples of how the polar areas can be used as a natural laboratory for field experiments in the Arctic and Antarctic with a focus on the work performed by German research groups.
    Type: Article , PeerReviewed
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  • 4
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    Springer
    In:  Boundary-Layer Meteorology, 124 (3). pp. 361-381.
    Publication Date: 2017-12-31
    Description: The experiment IGLOS (Investigation of the Greenland Boundary Layer Over Summit) was conducted in June and July 2002 in the central plateau of the Greenland inland ice. The German research aircraft Polar2, equipped with the turbulence measurement system Meteopod, was used to investigate turbulence and radiation flux profiles near research station “Summit Camp”. Aircraft measurements are combined with measurements of radiation fluxes and turbulent quantities made from a 50 m tower at Summit Camp operated by Eidgenössische Technische Hochschule (ETH) Zürich. During all six flight missions, well-developed stable boundary layers were found. Even in high-wind conditions, the surface inversion thickness did not exceed roughly 100 m. The turbulent height of the stable boundary layer (SBL) was found to be much smaller than the surface inversion thickness. Above the surface layer, significant turbulent fluxes occurred only intermittently in intervals on the order of a few kilometres. Turbulent event fraction in the upper SBL shows the same dependence on gradient Richardson number as reported for near-surface measurements. Clear-air longwave radiation divergence was always found to contribute significantly to the SBL heat budget. In low-wind cases, radiative cooling even turned out to be dominant.
    Type: Article , PeerReviewed
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  • 5
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    International Glaciological Society
    In:  Annals of Glaciology, 56 (69). pp. 29-37.
    Publication Date: 2015-03-13
    Description: Polynyas and leads are key elements of the wintertime Arctic sea-ice cover. They play a crucial role in surface heat loss, potential ice formation and consequently in the seasonal sea-ice budget. While polynyas are generally sufficiently large to be observed with passive microwave satellite sensors, the monitoring of narrow leads requires the use of data at a higher spatial resolution. We apply and evaluate different lead segmentation techniques based on sea-ice surface temperatures as measured by the Moderate Resolution Imaging Spectroradiometer (MODIS). Daily lead composite maps indicate the presence of cloud artifacts that arise from ambiguities in the segmentation process and shortcomings in the MODIS cloud mask. A fuzzy cloud artifact filter is hence implemented to mitigate these effects and the associated potential misclassification of leads. The filter is adjusted with reference data from thermal infrared image sequences, and applied to daily MODIS data from January to April 2008. The daily lead product can be used to deduct the structure and dynamics of wintertime sea-ice leads and to assess seasonal divergence patterns of the Arctic Ocean.
    Type: Article , PeerReviewed
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  • 6
    Publication Date: 2016-02-23
    Type: Article , PeerReviewed
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  • 7
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    Schweizerbarth
    In:  Meteorologische Zeitschrift, 25 (5). pp. 543-562.
    Publication Date: 2019-05-31
    Description: The simulation of extremes using climate models is still a challenging task. Currently, the model grid horizontal resolution of state-of-the art regional climate models (RCMs) is about 11–25 km, which may still be too coarse to represent local extremes realistically. In this study we use dynamically downscaled ERA-40 reanalysis data of the RCM COSMO-CLM at 18 km resolution, downscale it dynamically further to 4.5 km and finally to 1.3 km to investigate the impact of the horizontal resolution on extremes. Extremes are estimated as return levels for the 2, 5 and 10‑year return periods using ‘peaks-over-threshold’ (POT) models. Daily return levels are calculated for precipitation and maximum 2 m temperature in summer as well as precipitation and 2 m minimum temperature in winter. The results show that CCLM is able to capture the spatial and temporal structure of the observed extremes, except for summer precipitation extremes. Furthermore, the spatial variability of the return levels increases with resolution. This effect is more distinct in case of temperature extremes due to a higher correlation with the better resolved orography. This dependency increases with increasing horizontal resolution. In comparison to observations, the spatial variability of temperature extremes is better simulated at a resolution of 1.3 km, but the return levels are cold-biased in summer and warm-biased in winter. Regarding precipitation, the spatial variability improves as well, although the return levels were slightly overestimated in summer by all CCLM simulations. In summary, the results indicate that an increase of the horizontal resolution of CCLM does have a significant effect on the simulation of extremes and that impact models and assessment studies may benefit from such high-resolution model output.
    Type: Article , PeerReviewed
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  • 8
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    Springer
    In:  In: Arctic Climate Change : the ACSYS Decade and Beyond. , ed. by Lemke, P. and Jacobi, H. W. Atmospheric and oceanographic sciences library : ASTL, 43 . Springer, Dordrecht, The Netherlands, pp. 279-324. ISBN 978-94-007-2026-8
    Publication Date: 2018-01-19
    Type: Book chapter , NonPeerReviewed
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  • 9
    Publication Date: 2023-03-09
    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 Research 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.
    Type: Article , PeerReviewed
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