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  • Articles  (61)
  • 2010-2014  (59)
  • 1955-1959  (2)
  • Geosciences  (61)
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  • Articles  (61)
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  • 1
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    A single column model ensemble approach applied to the twp-ice experiment (2013)
    Wiley
    Details
    Publication Date: 2013-05-02
    Description: [1]  Single column models (SCM) are useful testbeds for investigating the parameterisation schemes of numerical weather prediction and climate models. The usefulness of SCM simulations are limited, however, by the accuracy of the best-estimate large-scale observations prescribed. Errors estimating the observations will result in uncertainty in modelled simulations. One method to address the modelled uncertainty is to simulate an ensemble where the ensemble members span observational uncertainty. This study first derives an ensemble of large-scale data for the Tropical Warm Pool International Cloud Experiment (TWP-ICE) based on an estimate of a possible source of error in the best-estimate product. This data is then used to carry out simulations with 11SCM and 2 cloud-resolving models (CRM). Best-estimate simulations are also performed. All models show that moisture-related variables are close to observations and there are limited differences between the best-estimate and ensemble mean values. The models, however, show different sensitivities to changes in the forcing particularly when weakly forced. The ensemble simulations highlight important differences in the surface evaporation term of the moisture budget between the SCM and CRM. Differences are also apparent between the models in the ensemble mean vertical structure of cloud variables whilst for each model cloud properties are relatively insensitive to forcing. The ensemble is further used to investigate cloud variables and precipitation and identifies differences between CRM and SCM particularly for relationships involving ice. This study highlights the additional analysis that can be performed using ensemble simulations and hence enables a more complete model investigationcompared to using the more traditional single best-estimate simulation only.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Effectiveness of GNSS Spoofing Countermeasure Based on Receiver CNR Measurements (2012)
    Hindawi
    Details
    Publication Date: 2012-07-18
    Description: A perceived emerging threat to GNSS receivers is posed by a spoofing transmitter that emulates authentic signals but with randomized code phase and Doppler over a small range. Such spoofing signals can result in large navigational solution errors that are passed onto the unsuspecting user with potentially dire consequences. In this paper, a simple and readily implementable processing rule based on CNR estimates of the correlation peaks of the despread GNSS signals is developed expressly for reducing the effectiveness of such a spoofer threat. Consequently, a comprehensive statistical analysis is given to evaluate the effectiveness of the proposed technique in various LOS and NLOS environments. It is demonstrated that the proposed receiver processing is highly effective in both line-of-sight and multipath propagation conditions.
    Print ISSN: 1687-5990
    Electronic ISSN: 1687-6008
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Published by Hindawi
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  • 3
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    Nearshore chlorophyll-a events and wave-driven transport (2011)
    Wiley
    Details
    Publication Date: 2011-01-21
    Description: Continuous records of temperature and chlorophyll-a [chl-a] fluorescence were used to characterize phytoplankton variability at two shallow intertidal stations on the northern California coast. Chl-a records from spring and summer 2007 and 2008 were characterized by distinct peaks persisting for 1.5 to five days. These peaks represent bloom events, which often coincided between the two sites even though they are separated by ∼150 km. Blooms did not appear to be directly forced by individual upwelling episodes. While some events were associated with reversals of upwelling-favorable winds, there was a stronger relationship between chl-a peaks and peaks in surface swell height. This relationship was dominant in spring and early summer, but no longer evident by July. We suggest that these nearshore chl-a peaks are an accumulation of phytoplankton caused by convergence of onshore wave transport against the impermeable coastal boundary. Scaling arguments show this mechanism to be consistent with observed chl-a increase rates. This mechanism has not been previously considered as a forcing for blooms at rocky coasts, and it may have significant implications for understanding coastal productivity, larval dispersal, and nearshore water quality.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Parameterizing correlations between hydrometeor species in mixed-phase Arctic clouds (2011)
    Wiley
    Details
    Publication Date: 2011-08-16
    Description: Mixed-phase Arctic clouds, like other clouds, contain small-scale variability in hydrometeor fields, such as cloud water or snow mixing ratio. This variability may be worth parameterizing in coarse-resolution numerical models. In particular, for modeling multispecies processes such as accretion and aggregation, it would be useful to parameterize subgrid correlations among hydrometeor species. However, one difficulty is that there exist many hydrometeor species and many microphysical processes, leading to complexity and computational expense. Existing lower and upper bounds on linear correlation coefficients are too loose to serve directly as a method to predict subgrid correlations. Therefore, this paper proposes an alternative method that begins with the spherical parameterization framework of Pinheiro and Bates (1996), which expresses the correlation matrix in terms of its Cholesky factorization. The values of the elements of the Cholesky matrix are populated here using a “cSigma” parameterization that we introduce based on the aforementioned bounds on correlations. The method has three advantages: (1) the computational expense is tolerable; (2) the correlations are, by construction, guaranteed to be consistent with each other; and (3) the methodology is fairly general and hence may be applicable to other problems. The method is tested noninteractively using simulations of three Arctic mixed-phase cloud cases from two field experiments: the Indirect and Semi-Direct Aerosol Campaign and the Mixed-Phase Arctic Cloud Experiment. Benchmark simulations are performed using a large-eddy simulation (LES) model that includes a bin microphysical scheme. The correlations estimated by the new method satisfactorily approximate the correlations produced by the LES.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Global Warming Potentials and Radiative Efficiencies of Halocarbons and Related Compounds: A Comprehensive Review (2013)
    Wiley
    Details
    Publication Date: 2013-04-25
    Description: [1]  In the mid-1970s it was recognized that, as well as being substances that deplete stratospheric ozone, chlorofluorocarbons (CFCs) were strong greenhouse gases that could have substantial impacts on radiative forcing of climate change. Around a decade later, this group of radiatively active compounds was expanded to include a large number of replacements for ozone-depleting substances such as chlorocarbons, hydrochlorocarbons, hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), bromofluorocarbons, and bromochlorofluorocarbons. [2]  This paper systematically reviews the published literature concerning the radiative efficiencies (REs) of CFCs, bromofluorocarbons and bromochlorofluorocarbons (halons), HCFCs, HFCs, PFCs, SF 6 , NF 3 , and related halogen containing compounds. In addition we provide a comprehensive and self-consistent set of new calculations of REs and global warming potentials (GWPs) for these compounds, mostly employing atmospheric lifetimes taken from the available literature. We also present Global Temperature change Potentials (GTPs) for selected gases. Infrared absorption spectra used in the RE calculations were taken from databases and individual studies, and from experimental and ab initio computational studies. Evaluations of REs and GWPs are presented for more than 200 compounds. Our calculations yield REs significantly (〉 5%) different from those in the Intergovernmental Panel on Climate Change Fourth Assessment Report (AR4) for 49 compounds. We present new RE values for more than 100 gases which were not included in AR4. A widely-used simple method to calculate REs and GWPs from absorption spectra and atmospheric lifetimes is assessed and updated. This is the most comprehensive review of the radiative efficiencies and global warming potentials of halogenated compounds performed to date.
    Print ISSN: 8755-1209
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    GNSS Spoofing Detection Based on Signal Power Measurements: Statistical Analysis (2013)
    Hindawi
    Details
    Publication Date: 2013-01-22
    Description: A threat to GNSS receivers is posed by a spoofing transmitter that emulates authentic signals but with randomized code phase and Doppler values over a small range. Such spoofing signals can result in large navigational solution errors that are passed onto the unsuspecting user with potentially dire consequences. An effective spoofing detection technique is developed in this paper, based on signal power measurements and that can be readily applied to present consumer grade GNSS receivers with minimal firmware changes. An extensive statistical analysis is carried out based on formulating a multihypothesis detection problem. Expressions are developed to devise a set of thresholds required for signal detection and identification. The detection processing methods developed are further manipulated to exploit incidental antenna motion arising from user interaction with a GNSS handheld receiver to further enhance the detection performance of the proposed algorithm. The statistical analysis supports the effectiveness of the proposed spoofing detection technique under various multipath conditions.
    Print ISSN: 1687-5990
    Electronic ISSN: 1687-6008
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Published by Hindawi
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  • 7
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    Effectiveness of GNSS Spoofing Countermeasure Based on Receiver CNR Measurements (2013)
    Hindawi
    Details
    Publication Date: 2013-01-22
    Description: A perceived emerging threat to GNSS receivers is posed by a spoofing transmitter that emulates authentic signals but with randomized code phase and Doppler over a small range. Such spoofing signals can result in large navigational solution errors that are passed onto the unsuspecting user with potentially dire consequences. In this paper, a simple and readily implementable processing rule based on CNR estimates of the correlation peaks of the despread GNSS signals is developed expressly for reducing the effectiveness of such a spoofer threat. Consequently, a comprehensive statistical analysis is given to evaluate the effectiveness of the proposed technique in various LOS and NLOS environments. It is demonstrated that the proposed receiver processing is highly effective in both line-of-sight and multipath propagation conditions.
    Print ISSN: 1687-5990
    Electronic ISSN: 1687-6008
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Published by Hindawi
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  • 8
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    GNSS Spoofing Detection Based on Signal Power Measurements: Statistical Analysis (2012)
    Hindawi
    Details
    Publication Date: 2012-11-07
    Description: A threat to GNSS receivers is posed by a spoofing transmitter that emulates authentic signals but with randomized code phase and Doppler values over a small range. Such spoofing signals can result in large navigational solution errors that are passed onto the unsuspecting user with potentially dire consequences. An effective spoofing detection technique is developed in this paper, based on signal power measurements and that can be readily applied to present consumer grade GNSS receivers with minimal firmware changes. An extensive statistical analysis is carried out based on formulating a multihypothesis detection problem. Expressions are developed to devise a set of thresholds required for signal detection and identification. The detection processing methods developed are further manipulated to exploit incidental antenna motion arising from user interaction with a GNSS handheld receiver to further enhance the detection performance of the proposed algorithm. The statistical analysis supports the effectiveness of the proposed spoofing detection technique under various multipath conditions.
    Print ISSN: 1687-5990
    Electronic ISSN: 1687-6008
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Published by Hindawi
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  • 9
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    Comparing Plume Characteristics Inferred from Cross-Borehole Geophysical Data (2012)
    Soil Science Society of America (SSSA)
    Details
    Publication Date: 2012-11-28
    Description: We compare results of three cross-borehole geophysical approaches for imaging tracer migration arising from a point injection of water in the unsaturated zone: three-dimensional electrical resistivity tomography (ERT), two-dimensional ground-penetrating radar (GPR) tomography and quasi-three-dimensional GPR tomography. In the studied field experiment, a tracer was injected for a period of 5 d and was monitored both during injection and for 5 d during the subsequent redistribution. The three methods show similar characteristics of the plume development and movement, which has a strong lateral component and slow vertical migration. In addition to revealing the main tracer plume, two-dimensional GPR and the quasi-three-dimensional GPR results show development of secondary plumes at depth, which are not captured by the three-dimensional ERT due to lack of resolution. The flow patterns are compared to geological information from a coring obtained at the site and it is concluded that the diversion of water in the lateral direction can be caused by a few thin layers of contrasting geological composition. Mass balance calculations based on moment analysis of the moisture content changes reveal that two-dimensional and quasi-three-dimensional GPR results show similar results and that three-dimensional ERT underestimate the amount of tracer substantially. Our results further show that the analysis volume as well as threshold value for moisture content increase has significant impact on computed mass recovery. The choice of threshold value, in particular, should be method-dependent and needs to be considered carefully if the results of the moment calculations are to be used in constraining hydrological models.
    Electronic ISSN: 1539-1663
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Soil Science Society of America (SSSA)
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  • 10
    Electronic Resource
    Electronic Resource
    Gleichgewichts – und Wachstumsformen von Kristallen by B. Honigmann (1959)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 12 (1959), S. 614-614 
    Details
    ISSN: 0001-5520
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0365110X59001827
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    Paper (German National Licenses)
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