Time filter

Source Type

Sillmann J.,University of Victoria | Sillmann J.,Max Planck Institute for Meteorology | Mischa M.C.,Federal Office of Meteorology and Climatology | Kallache M.,French Climate and Environment Sciences Laboratory | And 2 more authors.
Journal of Climate | Year: 2011

North Atlantic atmospheric blocking conditions explain part of the winter climate variability in Europe, being associated with anomalous cold winter temperatures. In this study, the generalized extreme value (GEV) distribution is fitted to monthly minima of European winter 6-hourly minimum temperatures from the ECHAM5/MPI-OM global climate model simulations and the ECMWF reanalysis product known as ERA- 40, with an indicator for atmospheric blocking conditions being used as covariate. It is demonstrated that relating the location and scale parameter of the GEV distribution to atmospheric blocking improves the fit to extreme minimum temperatures in large areas of Europe. The climate model simulations agree reasonably with ERA-40 in the present climate (1961-2000). Under the influence of atmospheric blocking, a decrease in the 0.95th quantiles of extreme minimum temperatures can be distinguished. This cooling effect of atmospheric blocking is, however, diminished in future climate simulations because of a shift in blocking location, and thus reduces the chances of very cold winters in northeastern parts of Europe. © 2011 American Meteorological Society.

Staedler Y.M.,University of Vienna | Masson D.,Federal Office of Meteorology and Climatology | Schonenberger J.,University of Vienna
PLoS ONE | Year: 2013

Computed tomography remains strongly underused in plant sciences despite its high potential in delivering detailed 3D phenotypical information because of the low X-ray absorption of most plant tissues. Existing protocols to study soft tissues display poor performance, especially when compared to those used on animals. More efficient protocols to study plant material are therefore needed. Flowers of Arabidopsis thaliana and Marcgravia caudata were immersed in a selection of contrasting agents used to treat samples for transmission electron microscopy. Grayscale values for floral tissues and background were measured as a function of time. Contrast was quantified via a contrast index. The thick buds of Marcgravia were scanned to determine which contrasting agents best penetrate thick tissues. The highest contrast increase with cytoplasm-rich tissues was obtained with phosphotungstate, whereas osmium tetroxide and bismuth tatrate displayed the highest contrast increase with vacuolated tissues. Phosphotungstate also displayed the best sample penetration. Furthermore, infiltration with phosphotungstate allowed imaging of all plants parts at a high resolution of 3 μm, which approaches the maximum resolution of our equipment: 1.5 μm. The high affinity of phosphotungstate for vasculature, cytoplasm-rich tissue, and pollen causes these tissues to absorb more X-rays than the surrounding tissues, which, in turn, makes these tissues appear brighter on the scan data. Tissues with different brightness can then be virtually dissected from each other by selecting the bracket of grayscale to be visualized. Promising directions for the future include in silico phenotyping and developmental studies of plant inner parts (e.g., ovules, vasculature, pollen, and cell nuclei) via virtual dissection as well as correlations of quantitative phenotypes with omics datasets. Therefore, this work represents a crucial improvement of previous methods, allowing new directions of research to be undertaken in areas ranging from morphology to systems biology. © 2013 Staedler et al.

Weigel A.P.,Federal Office of Meteorology and Climatology | Mason S.J.,Columbia University
Monthly Weather Review | Year: 2011

This article refers to the study of Mason and Weigel, where the generalized discrimination scoreDhas been introduced. This score quantifies whether a set of observed outcomes can be correctly discriminated by the corresponding forecasts (i.e., it is a measure of the skill attribute of discrimination). Because of its generic definition, D can be adapted to essentially all relevant verification contexts, ranging from simple yes-no forecasts of binary outcomes to probabilistic forecasts of continuous variables. For most of these cases, Mason and Weigel have derived expressions forD, many of which have turned out to be equivalent to scores that are already known under different names. However, no guidance was provided on how to calculate D for ensemble forecasts. This gap is aggravated by the fact that there are currently very few measures of forecast quality that could be directly applied to ensemble forecasts without requiring that probabilities be derived from the ensemble members prior to verification. This study seeks to close this gap. A definition is proposed of how ensemble forecasts can be ranked; the ranks of the ensemble forecasts can then be used as a basis for attempting to discriminate between corresponding observations. Given this definition, formulations of D are derived that are directly applicable to ensemble forecasts. © 2011 American Meteorological Society.

Peyraud L.,Federal Office of Meteorology and Climatology
Weather and Forecasting | Year: 2013

On the afternoon of 18 July 2005, a particularly intense supercell thunderstorm struck the Lake Geneva region of Switzerland. The storm initiated just southwest of Lyon, France, and tracked over 300km toward the northeast before losing its supercell characteristics in the Swiss Alpine foothills around the town of Interlaken. During its 3-h lifespan, the storm's forward translation averaged 60-80kmh-1. At the height of its severity, this supercell was responsible for hail the size of golf balls, a microburst with measured wind gusts of up to 160kmh-1, and two confirmed tornadoes. Miraculously, nobody was killed nor seriously injured. However, the material losses were considerable, including ravaged vineyards, damage to buildings and vehicles, and sections of forests that were completely destroyed. A postevent analysis was undertaken utilizing radar imagery/algorithms, satellite images, lightning and surface data, eyewitness reports, and a damage survey. This case provides a unique look at a supercell evolving within an Alpine environment and helps confirm prior research concerning certain storm features and signatures that have been observed in North American Great Plains supercells and elsewhere. Concerning tornadogenesis, this paper helps confirm via observations and simulations hypotheses proposed in several previous papers that low-level wind flow modified through channeling by mountains can periodically provide a locally favorable wind shear environment for tornadogenesis. For this particular case, inflow winds that channeled around mountain features appear to have been instrumental in the formation of the second tornado, since important topographical obstacles prevented any significant low-level gradient wind shear from operating on the eastern end of Lake Geneva, where this tornado occurred. © 2013 American Meteorological Society.

Weigel A.P.,Federal Office of Meteorology and Climatology | Knutti R.,ETH Zurich | Liniger M.A.,Federal Office of Meteorology and Climatology | Appenzeller C.,Federal Office of Meteorology and Climatology
Journal of Climate | Year: 2010

Multimodel combination is a pragmatic approach to estimating model uncertainties and to making climate projections more reliable. The simplest way of constructing a multimodel is to give one vote to each model ("equal weighting'), while more sophisticated approaches suggest applying model weights according to some measure of performance ("optimum weighting"). In this study, a simple conceptual model of climate change projections is introduced and applied to discuss the effects of model weighting in more generic terms. The results confirm that equally weighted multimodels on average outperform the single models, and that projection errors can in principle be further reduced by optimum weighting. However, this not only requires accurate knowledge of the single model skill, but the relative contributions of the joint model error and unpredictable noise also need to be known to avoid biased weights. If weights are applied that do not appropriately represent the true underlying uncertainties, weighted multimodels perform on average worse than equally weighted ones, which is a scenario that is not unlikely, given that at present there is no consensus on how skill-based weights can be obtained. Particularly when internal variability is large, more information may be lost by inappropriate weighting than could potentially be gained by optimum weighting. These results indicate that for many applications equal weighting may be the safer and more transparent way to combine models. However, also within the presented framework eliminating models from an ensemble can be justified if they are known to lack key mechanisms that are indispensable for meaningful climate projections. © 2010 American Meteorological Society.

Lohnert U.,University of Cologne | Maier O.,Federal Office of Meteorology and Climatology
Atmospheric Measurement Techniques | Year: 2012

The motivation of this study is to verify theoretical expectations placed on ground-based microwave radiometer (MWR) techniques and to confirm whether they are suitable for supporting key missions of national weather services, such as timely and accurate weather advisories and warnings. We evaluate reliability and accuracy of atmospheric temperature profiles retrieved continuously by the microwave profiler system HATPRO (Humidity And Temperature PROfiler) operated at the aerological station of Payerne (MeteoSwiss) in the time period August 2006-December 2009. Assessment is performed by comparing temperatures from the radiometer against temperature measurements from a radiosonde accounting for a total of 2107 quality-controlled all-season cases. In the evaluated time period, the MWR delivered reliable temperature profiles in 86% of all-weather conditions on a temporal resolution of 12-13 min. Random differences between MWR and radiosonde are down to 0.5 K in the lower boundary layer and increase to 1.7 K at 4 km height. The differences observed between MWR and radiosonde in the lower boundary layer are similar to the differences observed between the radiosonde and another in-situ sensor located on a close-by 30 m tower. Temperature retrievals from above 4 km contain less than 5% of the total information content of the measurements, which makes clear that this technique is mainly suited for continuous observations in the boundary layer. Systematic temperature differences are also observed throughout the retrieved profile and can account for up to ±0.5 K. These errors are due to offsets in the measurements of the microwave radiances that have been corrected for in data post-processing and lead to nearly bias-free overall temperature retrievals. Different reasons for the radiance offsets are discussed, but cannot be unambiguously determined retrospectively. Monitoring and, if necessary, corrections for radiance offsets as well as a real-time rigorous automated data quality control are mandatory for microwave profiler systems that are designated for operational temperature profiling. In the analysis of a subset of different atmospheric situations, it is shown that lifted inversions and data quality during precipitation present the largest challenges for operational MWR temperature profiling. © 2012 Author(s). CC Attribution 3.0 License.

Scherrer S.C.,Federal Office of Meteorology and Climatology | Appenzeller C.,Federal Office of Meteorology and Climatology
International Journal of Climatology | Year: 2014

The occurrence of fog and low stratus (FLS) clouds is a common phenomenon over the Swiss plateau during the winter half years. Classical fog observations using horizontal visibility are of limited use for climatological analyses of persistent FLS situations. We present a simple method for determining long climatological series of days with FLS lasting at least a half or a full daylight day. The method relies solely on high quality relative sunshine duration measurements at two stations, a Plateau station below or within the FLS layer (e.g. Zürich/Fluntern) and a nearby peak station above the FLS layer (e.g. Säntis). The analysis for the period 1901-2012 shows that full day FLS are a typical phenomenon of the months November to January, whereas the half day FLS also often occur in October and February. There is substantial interannual and decadal variability. The total number of Zürich full FLS days varies between 4 and 31d (mean: 17d) and between 10 and 49d (mean: 28d) for at least a half FLS days in the September to March period. The foggiest decade in the 1901-2012 record was 1984-1993; the least foggy decade was 1999-2008 with roughly 40-45% less FLS occurrence than only 15years before. In the most recent years a return towards the climatological mean can be observed. The long term data series does not show any significant long-term trends for the occurrence of full nor for half day FLS events. The reconstructed FLS occurrence is well correlated with the number of days with cold air pooling. They show very similar decadal variability and long term trends. © 2013 Royal Meteorological Society.

Frei T.,Federal Office of Meteorology and Climatology
Meteorological Applications | Year: 2010

National Meteorological Services provide meteorological data, information, forecasts and various related products, which are important for the smooth functioning of many aspects in economy, administration and society. The merit of meteorological services cannot be deduced directly from the consumption of services. Rather, it emerges from the improvement of decisions by economic stakeholders thanks to weather and climate information. These services are purchased by users in order to be able to offer optimally or demand a certain service or, with respect to security, these services aim at helping to prevent damage from extreme events. A rough estimate for a number of selected sectors shows that benefits from weather services in Switzerland are in the region of hundreds of millions Swiss Francs (1 Swiss Franc ∼ {currency sign}0.66, US$0.83 as at 2008). This pilot study shows that it is not possible to estimate one single figure representing the overall benefit from weather services in a country. Concerning the economic sector, a benefit analysis should therefore concentrate on those subsectors where weather services are particularly relevant, i.e. agriculture, construction, energy, insurance, telecommunication, tourism, transport, logistics and water availability. Analysis of benefits from climate data is of particular interest to MeteoSwiss since the Federal Office is the main source for climate data in Switzerland. Climate data form the basis on which climate change and possible climate threats can be detected. This study estimates for the first time the socio-economic benefits of meteorological and climatic information in Switzerland as a small developed European country and gives an outlook of how a further study might be designed. © 2009 Royal Meteorological Society.

Lapillonne X.,ETH Zurich | Fuhrer O.,Federal Office of Meteorology and Climatology
Parallel Processing Letters | Year: 2014

For many scientific applications, Graphics Processing Units (GPUs) can be an interesting alternative to conventional CPUs as they can deliver higher memory bandwidth and computing power. While it is conceivable to re-write the most execution time intensive parts using a low-level API for accelerator programming, it may not be feasible to do it for the entire application. But, having only selected parts of the application running on the GPU requires repetitively transferring data between the GPU and the host CPU, which may lead to a serious performance penalty. In this paper we assess the potential of compiler directives, based on the OpenACC standard, for porting large parts of code and thus achieving a full GPU implementation. As an illustrative and relevant example, we consider the climate and numerical weather prediction code COSMO (Consortium for Small Scale Modeling) and focus on the physical parametrizations, a part of the code which describes all physical processes not accounted for by the fundamental equations of atmospheric motion. We show, by porting three of the dominant parametrization schemes, the radiation, microphysics and turbulence parametrizations, that compiler directives are an efficient tool both in terms of final execution time as well as implementation effort. Compiler directives enable to port large sections of the existing code with minor modifications while still allowing for further optimizations for the most performance critical parts. With the example of the radiation parametrization, which contains the solution of a block tri-diagonal linear system, the required code modifications and key optimizations are discussed in detail. Performance tests for the three physical parametrizations show a speedup of between 3× and 7× for execution time obtained on a GPU and on a multi-core CPU of an equivalent generation. © 2014 World Scientific Publishing Company.

News Article | December 28, 2015
Site: www.reuters.com

Clear skies and dry ground have seen the Alpine nation end the year 3.4 degrees Celsius above the long-term historical average for December, a climatologist for the Federal Office of Meteorology and Climatology (MeteoSwiss) said on Monday. "There's no doubt about it," Stephan Bader said. "It's the warmest December in our recorded measurements dating back to 1864 - clearly. And it's especially pronounced at higher altitudes." The dry warmth and slopes bereft of snow have hurt resort owners and ski lift operators, who are already contending with Switzerland's strong currency discouraging foreign visitors. MeteoSwiss earlier this month said it expected 2015 to break the annual record for the third time in just a handful of years. Globally, this year will be the warmest on record and 2016 could be even warmer due to the El Niño weather pattern, the World Meteorological Organization said last month. It warned that inaction on climate change could see global average temperatures rise by 6 degrees Celsius or more.

Loading Federal Office of Meteorology and Climatology collaborators
Loading Federal Office of Meteorology and Climatology collaborators