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  • 1
    In: Meteorologische Zeitschrift, April 2011, Vol.20(2), pp.91-93
    Keywords: Apennines
    ISSN: 0941-2948
    E-ISSN: 16101227
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  • 2
    In: Meteorologische Zeitschrift, April 2011, Vol.20(2), pp.173-184
    Description: In a previous study the authors developed and optimized tools for 4 -dimensional variational assimilation ( 4 DVAR) of Global Positioning System (GPS) ground-based Slant Total Delay (STD) data in the framework of the Mesoscale Model 5 (MM5) system. In this study, advantage is taken from the parallel implementation of 4DVAR and the availability of STD data processed at the Helmholtz Centre Potsdam, German Research Centre for Geosciences (GFZ), providing data for a large and continuously operating network of groundbased receivers in Germany. The results of two long-term assimilation experiments are presented. The first assimilation experiment, performed over a period of two weeks (1-14 August 2007), shows that the impact in STD observation space of an independent network of GPS receivers is positive. After the assimilation window the impact is decreasing with time, lasting in average for 12 h. The second assimilation experiment, performed over a period of one month (1-31 August 2007), indicates that the impact on the precipitation forecast is weak but positive. German In einer vorangegangenen Studie entwickelten und optimierten die Autoren Werkzeuge zur 4-Dimensionalen Variationalen Assimilation (4DVAR) von boden-gestützten Global Positioning System (GPS) Slant Total Delay (STD) Daten im Rahmen des Mesoskaligen Modells 5 (MM5). In dieser Studie, ziehen wir Vorteil aus der parallelen Implementierung der 4 DVAR und der Verfügbarkeit von STD Daten, die am GFZ Potsdam für ein großes und kontinuierlich operierendes Netzwerk von boden-gestützten Empfängern in Deutschland abgeleitet werden. Die Resultate von zwei Langzeitassimilationsexperimenten werden gezeigt. Das erste Experiment, über eine Periode von zwei Wochen (1-14 August 2007), zeigt, dass der Impakt im STD Beobachtungsraum eines unabhäangigen Netzwerks von Empfäangern positiv ist. Nach dem Assimilationsfenster nimmt der Impakt ab und häalt im Mittel für 12 Stunden an. Das zweite Assimilationsexperiment, üuber eine Periode von einem Monat (1-31 August 2007), zeigt, dass der Impakt in der Niederschlagsvorhersage schwach aber positiv ist
    Keywords: Apennines
    ISSN: 0941-2948
    E-ISSN: 16101227
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  • 3
    Language: English
    In: Atmospheric Environment, 2011, Vol.45(16), pp.2795-2802
    Description: The physical and chemical properties of aerosols emitted from a livestock farm were determined by a novel approach which combines high-resolution lidar measurements (0.33 s, 30 m) with simulations of a microphysics–chemistry–transport model. This first of two companion papers describes the scanning lidar measurements of optical particle properties. The lidar system employed laser radiation at a wavelength of 355 nm with a power of 9 W and a pulse repetition rate of 30 Hz. The laser beam was expanded before transmission to the atmosphere so that it became eye-safe at distances 〉270 m to the lidar. The elastic backscatter signal was detected with a resolution of 0.033 s and 3 m. A receiving telescope with a primary-mirror diameter of 40 cm was used. For this system, we developed a novel method for two-dimensional retrievals of the particle backscatter coefficient. With this set up and approach, the lidar was able to identify the aerosol plume up to a range of ∼2.5 km from the source, a farm in northern Germany, in daytime. The measurements confirm that the optical particle properties of the emission plume vary largely with distance from the source and that the maximum particle backscatter coefficient is found away from the source. Within a close-to-horizontal scan (elevation angle of 2.3°), we found a mean particle backscatter coefficient of 1.5·10  m  sr inside the plume between 1.5 and 2.0 km distance from the source. Subtraction of the mean particle backscatter coefficient of the background aerosol present in this case (4.1·10  m  sr ) yields a particle backscatter coefficient of the livestock aerosols of 1.1·10  m  sr . The limited extend of the plume is revealed with the scanning lidar: Scans with a slightly higher elevation angle of 4.8° did not pick up the plume.
    Keywords: Livestock Aerosols ; Aerosol–Optical Properties ; Scanning Lidar ; Engineering ; Environmental Sciences
    ISSN: 1352-2310
    E-ISSN: 1873-2844
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  • 4
    Language: English
    In: Atmospheric Environment, 2011, Vol.45(17), pp.2981-2990
    Description: A new high-resolution microphysics–chemistry-transport model (LES-AOP) was developed and applied for the investigation of aerosol transformation and transport in the vicinity of a livestock facility in northern Germany (PLUS1 field campaign). The model is an extension of a Large-Eddy Simulation (LES) model. The PLUS1 field campaign included the first deployment of the new eye-safe scanning aerosol lidar system of the University of Hohenheim. In a combined approach, model and lidar results were used to characterise a faint aerosol source. The farm plume structure was investigated and the absolute value of its particle backscatter coefficient was determined. Aerosol optical properties were predicted on spatial and temporal resolutions below 100 m and 1 min, upon initialisation by measured meteorological and size-resolved particulate matter mass concentration and composition data. Faint aerosol plumes corresponding to a particle backscatter coefficient down to 10  sr  m were measured and realistically simulated. Budget-related quantities such as the emission flux and change of the particulate matter mass, were estimated from model results and ground measurements.
    Keywords: Large-Eddy Simulation ; Aerosol Physical Modelling ; Agricultural Aerosol Source ; Aerosol Optical Properties ; Lidar Signal ; Engineering ; Environmental Sciences
    ISSN: 1352-2310
    E-ISSN: 1873-2844
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  • 5
    Language: English
    In: Boundary-Layer Meteorology, 2010, Vol.136(2), pp.253-284
    Description: High-resolution water vapour measurements made by the Atmospheric Radiation Measurement (ARM) Raman lidar operated at the Southern Great Plains Climate Research Facility site near Lamont, Oklahoma, U.S.A. are presented. Using a 2-h measurement period for the convective boundary layer (CBL) on 13 September 2005, with temporal and spatial resolutions of 10 s and 75 m, respectively, spectral and autocovariance analyses of water vapour mixing ratio time series are performed. It is demonstrated that the major part of the inertial subrange was detected and that the integral scale was significantly larger than the time resolution. Consequently, the major part of the turbulent fluctuations was resolved. Different methods to retrieve noise error profiles yield consistent results and compare well with noise profiles estimated using Poisson statistics of the Raman lidar signals. Integral scale, mixing-ratio variance, skewness, and kurtosis profiles were determined including error bars with respect to statistical and sampling errors. The integral scale ranges between 70 and 130 s at the top of the CBL. Within the CBL, up to the third order, noise errors are significantly smaller than sampling errors and the absolute values of turbulent variables, respectively. The mixing-ratio variance profile rises monotonically from ≈0.07 to ≈3.7 g 2  kg −2 in the entrainment zone. The skewness is nearly zero up to 0.6  z / z i , becomes −1 around 0.7–0.8  z / z i , crosses zero at about 0.95  z / z i , and reaches about 1.7 at 1.1  z / z i (here, z is the height and z i is the CBL depth). The noise errors are too large to derive fourth-order moments with sufficient accuracy. Consequently, to the best of our knowledge, the ARM Raman lidar is the first water vapour Raman lidar with demonstrated capability to retrieve profiles of turbulent variables up to the third order during daytime throughout the atmospheric CBL.
    Keywords: Boundary-layer turbulence ; Convective boundary layer ; Raman lidar ; Turbulence statistics
    ISSN: 0006-8314
    E-ISSN: 1573-1472
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  • 6
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 17 September 2019, Vol.116(38), pp.18841-18847
    Description: Large-scale afforestation is increasingly being considered as a negative emissions method for sequestering large quantities of atmospheric CO At the same time, regional weather modification methods, like cloud seeding, are being used to counteract increasing water scarcity in arid regions. Large-scale sustainable desert agroforestry plantations can contribute to climate change mitigation and can also be used to modify regional climate, particularly rainfall. Climate impacts from plantations need to be well understood before considering implementation. Typically, impact studies are attempted at continental or global scales and use coarse-resolution models, which suffer from severe systematic errors. This is highly problematic because decision makers should only countenance geoengineering schemes like global afforestation if impacts are understood on the regional scale. We posit the necessity of using high-resolution regional models with sophisticated representations of land-atmosphere feedback and vegetation. This approach allows for studying desert plantations and the process chain leading to climate modification. We demonstrate that large-scale plantations enhance regional clouds and rainfall and derive an index for predicting plantation impacts. Thus, desert plantations represent a unique environmental solution via predictable regional weather modification and carbon storage.
    Keywords: Desert Plantations ; Rainfall Enhancement ; Weather Modification
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 7
    Language: English
    In: Meteorologische Zeitschrift, 01 February 2013, Vol.22(1), pp.3-4
    Keywords: Meteorology & Climatology
    ISSN: 0941-2948
    E-ISSN: 1610-1227
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  • 8
    Language: English
    In: Meteorologische Zeitschrift, 01 June 2014, Vol.23(1), pp.79-102
    Description: The impact of assimilating radar radial velocities and reflectivities from the French and German radar network on nowcasting to short-range quantitative precipitation forecasting (SRQPF) was investigated during COPS IOP10. For this purpose, the Weather Research and Forecasting (WRF) model was applied in a convection permitting configuration and a resolution of 3.6 km covering Central Europe. Four different experiments were carried out to study the influence of assimilating 3-dimensional radar data by employing the first developed convection permitting WRF rapid update cycle (RUC) with a 3-h cycle interval over Central Europe. For the control experiment, only conventional observations were selected for assimilation. For the other experiments, radar radial velocities and reflectivities were added. Additionally, the reflectivity operator was slightly modified to study the influence of a smaller lower boundary for the rain water mixing ratio. The results show a positive impact on SRQPF over Eastern France when applying radar radial velocities in addition to conventional observations and Global Positioning System Zenith Total Delay (GPS-ZTD). Radial velocities reduce the overestimation of 3-h precipitation compared to the control experiment without radar data. The bias and RMSE show an improvement of about 10 % respectively. When applying also radar reflectivities in addition, the 3-h precipitation bias is reduced by about 50 % compared to the assimilation of radial velocities only. The frequency bias for different precipitation thresholds now shows values 〈1$〈1$. This is possibly related to the different microphysics schemes in the forecast model and the applied moisture partitioning scheme in the 3DVAR due to its simplicity. The experiment with a modified reflectivity operator shows no improvement compared to the original version. The results demonstrate the great potential of assimilating radar data using variational techniques on the convection-permitting scale.
    Keywords: 3dvar ; Wrf ; Radar Data ; Convection Permitting ; Cops ; Nowcasting ; Meteorology & Climatology
    ISSN: 0941-2948
    E-ISSN: 1610-1227
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  • 9
    Language: English
    In: Journal of Applied Meteorology and Climatology, 2013, Vol.52(10), pp.2312-2327
    Description: ABSTRACT Soil water content (SWC) depends on and affects the energy flux partitioning at the land–atmosphere interface. Above all, the latent heat flux is limited by the SWC of the root zone on one hand and radiation on the other. Therefore, SWC is a key variable in the climate system. In this study, the performance of the Weather Research and Forecasting model coupled with the Noah land surface model (WRF-Noah) system in a climate hindcast simulation from 1990 to 2008 is evaluated with respect to SWC versus two reanalysis datasets for Europe during 2007 and 2008 with in situ soil moisture observations from southern France. When compared with the in situ observations, WRF-Noah generally reproduces the SWC annual cycle while the reanalysis SWCs do not. The biases in areal mean WRF-Noah SWCs relate to biases in precipitation and evapotranspiration in a cropland environment. The spatial patterns and temporal variability of the seasonal mean SWCs from the WRF-Noah simulations and from the two reanalyses correspond well, while absolute values differ significantly, especially at the regional scale.
    Keywords: Prediction ; Temporal Variations ; Annual Variations ; Energy Transfer ; Evapotranspiration ; Climatology ; Water Content ; Weather Forecasting ; Heat Transfer ; Climate Models ; Radiation ; Numerical Simulations ; Energy Flux ; Evapotranspiration ; Climatology ; Precipitation ; Latent Heat Flux ; Soil Moisture ; Data Reanalysis ; Weather ; Spatial Distribution ; Rainfall ; Simulation ; Evapotranspiration ; Water Content ; Soil ; Agricultural Land ; Sulfur Dioxide ; Energy ; Climatology ; Meteorology ; Soil Moisture ; Seasonal Variations ; Weather ; Variability ; Radiation ; Climates ; Climatology ; Precipitation ; Soil Water ; Fluctuations ; Model Studies ; Weather ; Variability ; Radiation ; Climates ; Climatology ; Precipitation ; Soil Water ; Fluctuations ; Model Studies ; France ; Renewable Resources-Terrestrial ; Evaporation/Evapotranspiration (556.13) ; Water Resources and Supplies ; Groundwater ; Regional Studies, Expeditions and Data Reports;
    ISSN: 15588424
    E-ISSN: 15588432
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  • 10
    Language: English
    In: Applied optics, 01 November 2011, Vol.50(31), pp.5921-37
    Description: Differential absorption lidar (DIAL) is a unique technique for profiling water vapor from the ground up to the lower stratosphere. For accurate measurements, the DIAL laser transmitter has to meet stringent requirements. These include high average power (up to 10 W) and high single-shot pulse energy, a spectral purity 〉99.9%, a frequency instability 〈60 MHz rms, and narrow spectral bandwidth (single-mode, 〈160 MHz). We describe extensive modeling efforts to optimize the resonator design of a Ti:sapphire ring laser in these respects. The simulations were made for the wavelength range of 820 nm, which is optimum for ground-based observations, and for both stable and unstable resonator configurations. The simulator consists of four modules: (1) a thermal module for determining the thermal lensing of the Brewster-cut Ti:sapphire crystal collinear pumped from both ends with a high-power, frequency-doubled Nd:YAG laser; (2) a module for calculating the in-cavity beam propagations for stable and unstable resonators; (3) a performance module for simulating the pumping efficiency and the laser pulse energy; and (4) a spectral module for simulating injection seeding and the spectral properties of the laser radiation including spectral impurity. Both a stable and an unstable Ti:sapphire laser resonator were designed for delivering an average power of 10 W at a pulse repetition frequency of 250 Hz with a pulse length of approximately 40 ns, satisfying all spectral requirements. Although the unstable resonator design is more complex to align and has a higher lasing threshold, it yields similar efficiency and higher spectral purity at higher overall mode volume, which is promising for long-term routine operations.
    Keywords: Semiconductor Lasers -- Properties ; Semiconductor Lasers -- Composition ; Sapphires -- Optical Properties;
    ISSN: 1559128X
    E-ISSN: 1539-4522
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