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  • 1
    Online-Ressource
    Online-Ressource
    Imaging of firn isochrones across an Antarctic ice rise and implications for patterns of snow accumulation rate
    International Glaciological Society ; 2004
    In:  Journal of Glaciology Vol. 50, No. 170 ( 2004), p. 413-418
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 50, No. 170 ( 2004), p. 413-418
    Kurzfassung: It has been an underlying assumption in many studies that near-surface layers imaged by ground-penetrating radar (GPR) can be interpreted as depositional markers or isochrones. It has been shown that GPR layers can be approximately reproduced from the measured electrical properties of ice, but these material layers are generally narrower and more closely spaced than can be resolved by typical GPR systems operating in the range 50−400 MHz. Thus GPR layers should be interpreted as interference patterns produced from closely spaced and potentially discontinuous material layers, and should not be assumed to be interpretable as precise markers of isochrones. We present 100 MHz GPR data from Lyddan Ice Rise, Antarctica, in which near-surface ( 〈 50 m deep) layers are clearly imaged. The growth of the undulations in these layers with depth is approximately linear, implying that, rather than resulting from a pattern of vertical strain rate, they do correspond to some pattern of snowfall variation. Furthermore, comparison of the GPR layers with snow-stake measurements suggests that around 80% of the rms variability in mean annual accumulation is present in the GPR layers. The observations suggest that, at least in this case, the GPR layers do approximate isochrones, and that patterns of snow accumulation over Lyddan Ice Rise are dominated by extremely persistent spatial variations with only a small residual spatial variability. If this condition is shown to be widely applicable it may reduce the period required for measurements of surface elevation change to be taken as significant indications of mass imbalance.
    Materialart: Online-Ressource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/172756504781829882
    Sprache: Englisch
    Verlag: International Glaciological Society
    Publikationsdatum: 2004
    ZDB Id: 2140541-4
    SSG: 14
    Standort Signatur Einschränkungen Verfügbarkeit
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    Online-Ressource
  • 2
    Online-Ressource
    Online-Ressource
    An Autonomous Doppler Sodar Wind Profiling System
    American Meteorological Society ; 2005
    In:  Journal of Atmospheric and Oceanic Technology Vol. 22, No. 9 ( 2005-09-01), p. 1309-1325
    Details
    In: Journal of Atmospheric and Oceanic Technology, American Meteorological Society, Vol. 22, No. 9 ( 2005-09-01), p. 1309-1325
    Kurzfassung: An autonomous Doppler sodar wind profiling system has been designed, built, tested, and then deployed for 2 years at a remote site in Coats Land, Antarctica. The system is designed around a commercially available phased-array sodar (a Scintec flat-array sodar, FAS64) and powered from five modular power system units. Each power unit comprises two batteries, two photovoltaic solar panels, and two vertical axis wind generators, plus charging control and isolation circuitry. The sodar’s main processing unit is located at the antenna, but is controlled from a manned research station 50 km distant, in real time, by a line-of-sight UHF radio link. Data from an integral automatic weather station (AWS) are also transmitted over the radio link, allowing meteorologically informed decisions on whether or not to operate the Doppler sodar. Over the 2-yr experiment dozens of sounding episodes, lasting from a few hours to a few days, were obtained. Successful soundings were obtained in temperatures down to −33°C, and wind speeds up to 12 m s−1. In general, the wind data quality was good, but the range was disappointing, probably as a result of the strongly stable atmospheric conditions that were experienced. The wind profiling system that is described has been used to obtain the first remote wintertime observations of katabatic winds over the Antarctic continent.
    Materialart: Online-Ressource
    ISSN: 1520-0426 , 0739-0572
    URL: Article
    DOI: 10.1175/JTECH1779.1
    Sprache: Englisch
    Verlag: American Meteorological Society
    Publikationsdatum: 2005
    ZDB Id: 2021720-1
    ZDB Id: 48441-6
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    Online-Ressource
    Online-Ressource
    In situ measurements of cloud microphysics and aerosol over coastal Antarctica during the MAC campaign
    Copernicus GmbH ; 2017
    In:  Atmospheric Chemistry and Physics Vol. 17, No. 21 ( 2017-11-06), p. 13049-13070
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 17, No. 21 ( 2017-11-06), p. 13049-13070
    Kurzfassung: Abstract. During austral summer 2015, the Microphysics of Antarctic Clouds (MAC) field campaign collected unique and detailed airborne and ground-based in situ measurements of cloud and aerosol properties over coastal Antarctica and the Weddell Sea. This paper presents the first results from the experiment and discusses the key processes important in this region, which is critical to predicting future climate change. The sampling was predominantly of stratus clouds, at temperatures between −20 and 0 °C. These clouds were dominated by supercooled liquid water droplets, which had a median concentration of 113 cm−3 and an interquartile range of 86 cm−3. Both cloud liquid water content and effective radius increased closer to cloud top. The cloud droplet effective radius increased from 4 ± 2 µm near cloud base to 8 ± 3 µm near cloud top. Cloud ice particle concentrations were highly variable with the ice tending to occur in small, isolated patches. Below approximately 1000 m, glaciated cloud regions were more common at higher temperatures; however, the clouds were still predominantly liquid throughout. When ice was present at temperatures higher than −10 °C, secondary ice production most likely through the Hallett–Mossop mechanism led to ice concentrations 1 to 3 orders of magnitude higher than the number predicted by commonly used primary ice nucleation parameterisations. The drivers of the ice crystal variability are investigated. No clear dependence on the droplet size distribution was found. The source of first ice in the clouds remains uncertain but may include contributions from biogenic particles, blowing snow or other surface ice production mechanisms. The concentration of large aerosols (diameters 0.5 to 1.6 µm) decreased with altitude and were depleted in air masses that originated over the Antarctic continent compared to those more heavily influenced by the Southern Ocean and sea ice regions. The dominant aerosol in the region was hygroscopic in nature, with the hygroscopicity parameter κ having a median value for the campaign of 0.66 (interquartile range of 0.38). This is consistent with other remote marine locations that are dominated by sea salt/sulfate.
    Materialart: Online-Ressource
    ISSN: 1680-7324
    URL: Article
    URL: Article
    DOI: 10.5194/acp-17-13049-2017
    DOI: 10.5194/acp-17-13049-2017-supplement
    Sprache: Englisch
    Verlag: Copernicus GmbH
    Publikationsdatum: 2017
    ZDB Id: 2092549-9
    ZDB Id: 2069847-1
    Standort Signatur Einschränkungen Verfügbarkeit
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    Online-Ressource
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