3,042 research outputs found

    Large-eddy simulation of the up-slope boundary layer

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    Radiative heating in contrail cirrus

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    We developed an effective model (within our contrail cirrus prediction model, CoCiP) which computes the radiative heating rate in both the longwave and shortwave spectral ranges. The model parameterizes the impact of radiative heating on turbulent mixing and sublimation of ice particles in a thin cirrus layer

    Comparisons of cirrus cloud microphysical properties between polluted and pristine air

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    In this work, we analyze high-resolution (~200 m), in-situ observations from two global flight campaigns: 1) the HIAPER Pole-to-Pole Observations (HIPPO) global campaign in 2009-2011 funded by the US National Science Foundation (NSF), and 2) the Interhemispheric Differences In Cirrus Properties from Anthropogenic Emissions (INCA) campaign in 2000 funded by the European Union and participating research institutions. The HIPPO campaign observations were obtained over the North America continent and the central Pacific Ocean from 87ºN to 67ºS. During the INCA campaign, cirrus clouds were sampled with optical particle counters in the size range of about 1 to 800 m at midlatitudes, mainly over the Pacific west of Punta Arenas and over the North Atlantic west of Great Britain. We find that as CO concentration increases, the cirrus clouds tend to have smaller ice crystals (HIPPO data based on Fast-2DC ice probe > 87.5 µm), higher Nc of small particles (INCA data based on ice crystals > 3 µm measured by FSSP instrument), and slightly lower Nc for larger particles (HIPPO data Fast-2DC > 87.5 µm and INCA 2DC data for particles > 100 µm). These three features are consistent with each other, indicating that when there is stronger signature of anthropogenic emission, ice crystals would be more numerous and smaller

    Basin structure of optimization based state and parameter estimation

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    Most data based state and parameter estimation methods require suitable initial values or guesses to achieve convergence to the desired solution, which typically is a global minimum of some cost function. Unfortunately, however, other stable solutions (e.g., local minima) may exist and provide suboptimal or even wrong estimates. Here we demonstrate for a 9-dimensional Lorenz-96 model how to characterize the basin size of the global minimum when applying some particular optimization based estimation algorithm. We compare three different strategies for generating suitable initial guesses and we investigate the dependence of the solution on the given trajectory segment (underlying the measured time series). To address the question of how many state variables have to be measured for optimal performance, different types of multivariate time series are considered consisting of 1, 2, or 3 variables. Based on these time series the local observability of state variables and parameters of the Lorenz-96 model is investigated and confirmed using delay coordinates. This result is in good agreement with the observation that correct state and parameter estimation results are obtained if the optimization algorithm is initialized with initial guesses close to the true solution. In contrast, initialization with other exact solutions of the model equations (different from the true solution used to generate the time series) typically fails, i.e. the optimization procedure ends up in local minima different from the true solution. Initialization using random values in a box around the attractor exhibits success rates depending on the number of observables and the available time series (trajectory segment).Comment: 15 pages, 2 figure

    Neue Informationstechnologien und Flexible Arbeitssysteme: das NIFA-Panel im deutschen Maschinen- und Anlagenbau

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    Detection of 133^{133}Xe from the Fukushima nuclear power plant in the upper troposphere above Germany

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    After the accident in the Japanese Fukushima Dai-ichi nuclear power plant in March 2011 large amounts of radioactivity were released and distributed in the atmosphere. Among them were also radioactive noble gas isotopes which can be used as tracers to test global atmospheric circulation models. This work presents unique measurements of the radionuclide 133^{133}Xe from Fukushima in the upper troposphere above Germany. The measurements involve air sampling in a research jet aircraft followed by chromatographic xenon extraction and ultra-low background gas counting with miniaturized proportional counters. With this technique a detection limit of the order of 100 133^{133}Xe atoms in litre-scale air samples (corresponding to about 100 mBq/m3^3) is achievable. Our results provide proof that the 133^{133}Xe-rich ground level air layer from Fukushima was lifted up to the tropopause and distributed hemispherically. Moreover, comparisons with ground level air measurements indicate that the arrival of the radioactive plume at high altitude over Germany occurred several days before the ground level plume.Comment: 8 pages, 5 figure

    Experimental Test of the Influence of Propulsion Efficiency on Contrail Formation

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    According to a previously established thermodynamic theory, contrails are expected to form at a threshold temperature that increases with the overall efficiency of the aircraft propulsion. As a consequence, aircraft with modern engines, with higher overall efficiency, cause contrails over a larger range of cruise altitudes. To validate this theory, an experiment was performed in which contrail formation was observed behind two different fourengine jet aircraft with different engines flying wing by wing. Photographs document the existence of an altitude range in which the aircraft with high engine efficiency causes contrails whereas the other aircraft with lower engine efficiency causes none. For overall efficiencies of 0.23 and 0.31 and an ambient temperature lapse rate of 12 K km-1, the observed altitude difference is 80 m. This value would be larger (200m) in a standard atmosphere with smaller temperature lapse rate (6.5K km-1). In a standard atmosphere, an increase of overall efficiency from 0.3 to 0.5, which may be reached for future aircraft, would cause contrails at about 700 m lower altitude
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