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Hamburg, Germany

The Deutscher Wetterdienst, German pronunciation: , commonly abbreviated as DWD, , residing in Offenbach am Main, Germany, is a scientific agency that monitors weather and meteorological conditions over Germany and offers weather services for the general public as well as specific services for e.g. nautical, aviational or agricultural purposes. Organizationally, it lies within the Federal Ministry of Transport, Building and Urban Affairs . The DWDs main task is to warn against weather-related dangers, as well as monitoring and rating changes in the German climate. The organization runs atmospheric models on their own supercomputer to help in the task of weather forecasting. The DWD is also responsible for running the national clime archive and runs one of the biggest libraries worldwide that is specialized on weather and climate. Wikipedia.

Extended logistic regression has been shown to be a method well suited to calibrating precipitation forecasts from medium-range ensemble prediction systems. The extension of the logistic regression unifies the separate predictive equations for each threshold, introducing the predictive threshold as part of the predictors. Mutually consistent probabilities and a reduction in the total number of regression parameters to be evaluated are part of the benefits of the extendedapproach. However, considering the predictive threshold as the only ''unification'' predictor constrains the regression parameters associated with the primary predictors to be constant with the threshold. To alleviate the rigidity of the extended scheme, interaction terms are introduced in the unified predictive equation. Within the framework of the convection-permitting Germanfocused Consortium for Small-Scale Modeling ensemble prediction system (COSMO-DE-EPS), it is shown that extended logistic regression, applied to short-range precipitation forecasts with the ensemble mean as the primary predictor, improves the performance of the system. Interaction effects are first illustrated through the analysis of regression parameters and then the positive impact on the calibrated forecasts of the new extended logistic regression scheme, including interaction terms, is shown using quantitative and qualitative measures of reliability and sharpness. © 2013 American Meteorological Society. Source

Reichardt J.,German Weather Service
Journal of Atmospheric and Oceanic Technology

A spectrometer for height-resolved measurements of the Raman backscatter-coefficient spectrum of water in its gaseous and condensed phases is presented. The spectrometer is fiber coupled to the far-range receiver of the Raman Lidar for Atmospheric Moisture Sensing (RAMSES) of the German Meteorological Service and consists of a Czerny-Turner spectrograph (500-mm focal length) and a 32-channel single-photon-counting detection system based on a multianode photomultiplier. During a typical measurement (transmitter wavelength of 355 nm), the spectrum between 385 and 410nm is recorded with a spectral resolution of 0.79 nm; the vertical resolution is 15m and the height range is 15 km. The techniques outlined are those that are applied to calibrate the spectrum measurement and to monitor fluorescence by atmospheric aerosols that have the potential to interfere with the water observation. For the first time, Raman spectra of liquid-water, mixedphase, and cirrus clouds are reported, and their temperature dependence is investigated by means of band decomposition. The spectrum-integrated condensed-water Raman backscatter coefficient strongly depends on cloud particle volume, but it is not tightly correlated with the cloud optical properties (particle extinction and backscatter coefficient), which implies that retrieval of cloud water content from optical proxies is likely impossible. Aerosol measurements are also discussed. Depending on type, aerosols may show no backscattering in the spectrometer range at all, or a featureless spectrum that stems quite likely from fluorescence. Finally, the example of a cloud forming in an aerosol layer demonstrates that the new instrument not only opens up new perspectives in cloud research but also contributes to studies of cloud-aerosol interaction. © 2014 American Meteorological Society. Source

To extend the numerical stability limit over steep slopes, a truly horizontal pressure-gradient discretization based on the ideas formulated by Mahrer in the 1980s has been developed. Conventionally, the pressure gradient is evaluated in the terrain-following coordinate system, which necessitates a metric correction term that is prone to numerical instability if the height difference between adjacent grid points is much larger than the vertical layer spacing. The alternative way pursued here is to reconstruct the pressure gradient at auxiliary points lying at the same height as the target point on which the velocity is defined. This is accomplished via a second-order Taylor-series expansion in this work, using the hydrostatic approximation to transform the second derivatives into first derivatives to facilitate second-order accurate discretization in the presence of strong vertical grid stretching. Moreover, a reformulated lower boundary condition is used that avoids the extrapolation of vertical derivatives evaluated in potentially very thin layers. A sequence of tests at varying degrees of idealization reveals that the truly horizontal pressure-gradient discretization improves numerical stability over steep slopes for a wide range of horizontal mesh sizes, ranging from a few hundreds of meters to tens of kilometers. In addition, tests initialized with an atmosphere at rest reveal that the spurious circulations developing over steep mountains are usually smaller than for the conventional discretization even in configurations for which the latter does not suffer from stability problems. ©2012 American Meteorological Society. Source

For atmospheric simulation models with resolutions from about 10 km to the subkilometer cloud-resolving scale, the complete nonhydrostatic compressible Euler equations are often used. An important integration technique for them is the time-splitting (or split explicit) method. This article presents a comprehensive numerical stability analysis of Runge-Kutta (RK)-based partial time-splitting schemes. To this purpose a linearized two-dimensional (2D) compressible Euler system containing advection (as the slow process), sound, and gravity wave terms (as fast processes) is considered. These processes are the most important ones in limiting stability. First, the detailed stability properties are discussed with regard to several off-centering weights for each fast process described by horizontally explicit, vertically implicit schemes. Then the stability properties of the temporally and spatially discretized three-stage RK scheme for the complete 2D Euler equations and their stabilization (e.g., by divergence damping) are discussed. The main goal is to find optimal values for all of the occurring numerical parameters to guarantee stability in operational model applications. Furthermore, formal orders of temporal truncation errors for the time-splitting schemes are calculated. With the same methodology, two alternatives to the three-stage RK method, a so-called RK3-TVD method, and a new four-stage, second-order RK method are inspected. © 2010 American Meteorological Society. Source

Huld T.,European Commission - Joint Research Center Ispra | Muller R.,German Weather Service | Gambardella A.,European Commission - Joint Research Center Ispra
Solar Energy

The Photovoltaic Geographical Information System (PVGIS) is a web application for the estimation of the performance of photovoltaic (PV) systems in Europe and Africa, which has become widely used by the PV community in Europe. We here present the results of adapting the solar radiation data calculated from satellite data in the Climate Monitoring Satellite Application Facility (CM-SAF) to PVGIS. The CM-SAF solar radiation database is characterized by very low overall bias and shows good accuracy at validation sites. The application to PVGIS brings important improvements relative to the existing solar radiation databases within PVGIS. © 2012 . Source

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