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Widhalm B.,Zentralanstalt fur Meteorologie und Geodynamik | Bartsch A.,Zentralanstalt fur Meteorologie und Geodynamik | Bartsch A.,Vienna University of Technology | Leibman M.,Russian Academy of Sciences | Khomutov A.,Russian Academy of Sciences
Cryosphere | Year: 2017

The active layer above the permafrost, which seasonally thaws during summer, is an important parameter for monitoring the state of permafrost. Its thickness is typically measured locally, but a range of methods which utilize information from satellite data exist. Mostly, the normalized difference vegetation index (NDVI) obtained from optical satellite data is used as a proxy. The applicability has been demonstrated mostly for shallow depths of active-layer thickness (ALT) below approximately 70 cm. Some permafrost areas including central Yamal are, however, characterized by larger ALT. Surface properties including vegetation structure are also represented by microwave backscatter intensity. So far, the potential of such data for estimating ALT has not been explored. We therefore investigated the relationship between ALT and X-band synthetic aperture radar (SAR) backscatter of TerraSAR-X (averages for 10 x10m window) in order to examine the possibility of delineating ALT with continuous and larger spatial coverage in this area and compare it to the already-established method of using NDVI from Landsat (30 m). Our results show that the mutual dependency of ALT and TerraSAR-X backscatter on land cover types suggests a connection of both parameters. A range of 5 dB can be observed for an ALT range of 100 cm (40-140 cm), and an R2 of 0.66 has been determined over the calibration sites. An increase of ALT with increasing backscatter can be determined. The root mean square error (RMSE) over a comparably heterogeneous validation site with maximum ALT of >150 cm is 20 cm. Deviations are larger for measurement locations with mixed vegetation types (especially partial coverage by cryptogam crust) with respect to the spatial resolution of the satellite data. © Author(s) 2017.


Balzarini A.,RSE SpA | Pirovano G.,RSE SpA | Zabkar R.,University of Ljubljana | Curci G.,University of L'Aquila | And 5 more authors.
Atmospheric Environment | Year: 2015

In the framework of the AQMEII initiative WRF-Chem has been applied over Europe adopting two chemical configurations for the calendar year 2010. The first one employed the RADM2 gas-phase chemistry and MADE/SORGAM aerosol module, while the second one implemented the CBM-Z gaseous parameterization and MOSAIC aerosol chemistry. Configurations shared the same domain, meteorological setups and input data. The Comparison demonstrated that CBM-Z has a more efficient ozone-NO titration than RADM2 in regions with sufficiently high levels of NOx and VOCs. At the same time, CBM-Z is found to have a more effective NO2 + OH reaction. The parameterization of the relative humidity of deliquescence point has a strong impact on HNO3 and NO3 concentrations over Europe, particularly over the sea. The MADE approach showed to be more efficient than MOSAIC. Differently, particulate sulfate and SO2 ground concentrations proved to be more influenced by the heterogeneous SO2 cloud oxidation. PM10 and PM2.5 have shown similar results for MOSAIC and MADE/SORGAM, even though some differences were found in the dust and sea salt size partitioning between modes and bins. Indeed, in MADE the sea salt was distributed only in the coarse fraction, while the dust emissions were distributed mainly in the fine fraction. Finally, different chemical mechanisms give different Aerosol Optical Depths (AOD). WRF-Chem is found to under predict the AODs in both configurations because of the misrepresentation of the dust coarse particle, as shown by the analysis of the relationship between the Angström exponent and the AOD bias. Differently, when the AOD is dominated by fine particles, the differences in model performance are more evident, with MADE/SORGAM generally performing better than MOSAIC. Indeed the higher availability of both sulfate and nitrate has a significant influence on reconstruction of the AOD estimations. This paper shows the great importance of chemical mechanisms in both gaseous and aerosols predictions, as well as in the calculation of aerosol optical properties. © 2014 Elsevier Ltd.


Lang M.N.,Zentralanstalt fur Meteorologie und Geodynamik | Gohm A.,University of Innsbruck | Wagner J.S.,German Aerospace Center
Atmospheric Chemistry and Physics | Year: 2015

Idealized large-eddy simulations were performed to investigate the impact of different mountain geometries on daytime pollution transport by thermally driven winds. The main objective was to determine interactions between plain-to-mountain and slope wind systems, and their influence on the pollution distribution over complex terrain. For this purpose, tracer analyses were conducted over a quasi-two-dimensional mountain range with embedded valleys bordered by ridges with different crest heights and a flat foreland in cross-mountain direction. The valley depth was varied systematically. It was found that different flow regimes develop dependent on the valley floor height. In the case of elevated valley floors, the plain-to-mountain wind descends into the potentially warmer valley and replaces the opposing upslope wind. This superimposed plain-to-mountain wind increases the pollution transport towards the main ridge by an additional 20 % compared to the regime with a deep valley. Due to mountain and advective venting, the vertical exchange is 3.6 times higher over complex terrain than over a flat plain. However, the calculated vertical exchange is strongly sensitive to the definition of the convective boundary layer height. In summary, the impact of the terrain geometry on the mechanisms of pollution transport confirms the necessity to account for topographic effects in future boundary layer parameterization schemes. © Author(s) 2015.


Schnepp E.,University of Leoben | Leonhardt R.,Zentralanstalt fur Meteorologie und Geodynamik | Korte M.,German Research Center for Geosciences | Klett-Drechsel J.,KERAMIK UM
Geophysical Journal International | Year: 2016

Palaeomagnetic data obtained from archaeological materials are used for reconstructions of the Earth's magnetic field of the past millennia. While many studies tested the reliability of this recorder for palaeointensity only a few studies did this for direction. The study presents an archaeomagnetic and rock magnetic investigation applied to an experimental pottery kiln, which was operated in 2003 to produce stone ware. This kind of high-quality pottery needs a temperature of at least 1160 °C. Shortly before heating of the kiln direct absolute measurements of the absolute geomagnetic field vector have been carried out close to it. After cooling of the kiln 24 oriented palaeomagnetic samples have been taken. Although Curie temperatures are about 580 °C, that is the typical temperature for magnetite, thermal as well as alternating field demagnetisations reveal also a considerable amount of hematite as magnetic carrier. This mixture of magnetite and hematite is dominated by pseudo-single domain grains. Demagnetisation removed in some cases weak secondary components, but in most cases the specimens carried a single component thermoremanent magnetisation. The mean characteristic remanent magnetisation direction agrees on 95 per cent confidence level with the directly measured field direction. Archaeointensity was obtained from five specimens with the Thellier-Coe method and with the multiple-specimen palaeointensity domain-state corrected method. Six of these specimens also provided a result of the Dekkers-Böhnel method, which overestimated the archaeointensity by about 9 per cent compared to the direct value, while after correction for fraction the value agrees very well. For the multiple-specimen palaeointensity domain-state corrected method only fractions between 25 and 75 per cent have been used and specimens showing alteration have been excluded. Above 450 °C many specimens showed alteration of the magnetic grains. Because median destructive temperatures were often above this value in most cases the fraction was less than 50 per cent. Nevertheless the obtained intensity (48.48 ± 0.24 μ) is on 95 per cent confidence level in agreement with the direct observation. Behaviour of the specimens during the Thellier-experiments was not ideal because of narrow unblocking temperature spectra and alteration. Nevertheless, the obtained mean archaeointensity is also in agreement with the direct field observation. Here the relative palaeointensity error is about 6 per cent and very high compared the multiple-specimen palaeointensity domain-state corrected method. The investigation demonstrates that a pottery kiln can provide a very precise estimate of the ancient geomagnetic field vector. © The Authors 2016.


Schneider S.,Zentralanstalt fur Meteorologie und Geodynamik | Wang Y.,Zentralanstalt fur Meteorologie und Geodynamik | Wagner W.,Vienna University of Technology | Mahfouf J.-F.,Meteo - France
Monthly Weather Review | Year: 2014

In this study, remotely sensed soil moisture data from the Advanced Scatterometer (ASCAT) on board the Meteorological Operational (MetOp) series of satellites are assimilated in the regional forecasting model, Aire Limitée Adaptation Dynamique Développement International (ALADIN-Austria), using a simplified extended Kalman filter. A pointwise bias correction method is applied to the ASCAT data as well as quality flags prepared by the data provider. The ASCAT assimilation case study is performed over central Europe during a 1-month period in July 2009. Forecasts of those assimilation experiments are compared to the control run provided by the operational ALADIN version of the Austrian Met Service, Zentralanstalt für Meteorologie und Geodynamik (ZAMG). Forecasts are furthermore verified versus in situ data. For a single-day case study the ability of the approach to improve precipitation forecast quality in the presence of high impact weather is demonstrated. Results show that 1) based on a one station in situ data evaluation, soil moisture analysis is improved, compared to the operational analysis, when ASCAT soil moisture data is assimilated; 2) pointwise bias correction of the satellite data is beneficial for forecast quality; 3) screen level parameter forecasts can be slightly improved as a result of this approach; and 4) convective precipitation forecast is improved over flatland for the investigation period while over mountainous regions the impact is neutral. © 2014 American Meteorological Society.


Mestre O.,Institute Of Mathematiques Of Toulouse | Gruber C.,Zentralanstalt fur Meteorologie und Geodynamik | Prieur C.M.,Joseph Fourier University | Caussinus H.,University Paul Sabatier | Jourdain S.,Direction de la Climatologie
Journal of Applied Meteorology and Climatology | Year: 2011

One major concern of climate change is the possible rise of temperature extreme events, in terms of occurrence and intensity. To study this phenomenon, reliable daily series are required, for instance to compute dailybased indices: high-order quantiles, annual extrema, number of days exceeding thresholds, and so on. Because observed series are likely to be affected by changes in the measurement conditions, adapted homogenization procedures are required. Although a very large number of procedures have been proposed for adjustment of observed series at amonthly time scale, fewhave been proposed for adjustment of daily temperature series. This article proposes a newadjustmentmethod for temperature series at a daily time scale. This method, called spline daily homogenization (SPLIDHOM), relies on an indirect nonlinear regression method. Estimation of the regression functions is performed by cubic smoothing splines. This method is able to adjust the mean of the series aswell as high-order quantiles andmoments of the series. When usingwell-correlated series, SPLIDHOM improves the results of two widely usedmethods, as a result of an optimal selection of the smoothing parameter. Applications to the Toulouse, France, temperature series are shown as a real example. © 2011 American Meteorological Society.


Bergstedt H.,University of Salzburg | Bartsch A.,Zentralanstalt fur Meteorologie und Geodynamik
European Space Agency, (Special Publication) ESA SP | Year: 2016

Surface status (freeze/thaw) can be derived using microwave sensors. Two data products (C-Band, based on Metop ASCAT and ENVISAR ASAR GM) were compared in a spatial and temporal sense. The datasets have been separately published as an outcome of the DUE Permafrost project. The comparison reveals an importance of good temporal resolution of both data sets. The results show differences between the data sets especially in regions of complex topography as well as during the transitional periods with different intensity during spring and autumn. The results suggest an added value of the integration of SAR and scatterometer data with a special focus on mountainous areas, lake rich regions and transitional periods with a separate view on thaw and freeze back.


Schoner W.,Zentralanstalt fur Meteorologie und Geodynamik | Bohm R.,Zentralanstalt fur Meteorologie und Geodynamik | Auer I.,Zentralanstalt fur Meteorologie und Geodynamik
Theoretical and Applied Climatology | Year: 2012

Mountain observatories around the world are unique sites for monitoring and investigating variations, trends, forcings and feedbacks in the climate system, which are of utmost interest for understanding global climate change. From the small number of these research platforms, Sonnblick Observatory (Austrian Alps) stands out because of its long time series dating back to 1886 at an elevation of 3,100 m a. s. l. The paper describes the contribution of mountain observatories to climatology by the example of Sonnblick Observatory. The observatory's scientific evolution is summarised, starting from the original idea of upper air atmospheric measurements to its recent role as an atmospheric background station and interdisciplinary research site. © 2012 Springer-Verlag.


Baumann-Stanzer K.,Zentralanstalt fur Meteorologie und Geodynamik | Stenzel S.,Zentralanstalt fur Meteorologie und Geodynamik
Meteorologische Zeitschrift | Year: 2011

In case of an accidental release of toxic gases the emergency responders need fast information about the affected area and the maximum impact. Hazard distances calculated with the models MET, ALOHA, BREEZE, TRACE and SAMS for scenarios with chlorine, ammoniac and butane releases are compared in this study. The variations of the model results are measures for uncertainties in source estimation and dispersion calculation. Model runs for different wind speeds, atmospheric stability and roughness lengths indicate the model sensitivity to these input parameters. In-situ measurements at two urban near-traffic sites are compared to results of the Integrated Nowcasting through Comprehensive Analysis (INCA) in order to quantify uncertainties in the meteorological input. The hazard zone estimates from the models vary up to a factor of 4 due to different input requirements as well as due to different internal model assumptions. None of the models is found to be 'more conservative' than the others in all scenarios. INCA wind-speeds are correlated to in-situ observations at two urban sites in Vienna with a factor of 0.89. The standard deviations of the normal error distribution are 0.8 ms-1 in wind speed, on the scale of 50 degrees in wind direction, up to 4°C in air temperature and up to 10 % in relative humidity. The observed air temperature and humidity are well reproduced by INCA with correlation coefficients of 0.96 to 0.99. INCA is therefore found to give a good representation of the local meteorological conditions. Besides of real-time data, the INCA-short range forecast for the following hours may support the action planning of the first responders. © by Gebrüder Borntraeger 2011.


Maurer C.,Zentralanstalt fur Meteorologie und Geodynamik | Hammerl C.,Zentralanstalt fur Meteorologie und Geodynamik | Koch E.,Zentralanstalt fur Meteorologie und Geodynamik | Hammerl T.,Zentralanstalt fur Meteorologie und Geodynamik | Pokorny E.,Zentralanstalt fur Meteorologie und Geodynamik
Theoretical and Applied Climatology | Year: 2011

The detection and quantification of extreme weather conditions in the past are important for correctly assessing the significance of today's extremes especially in the context of climate change. We specified extreme years by a synopsis of phenological data, temperature reconstructions and measurements and descriptive documentary sources starting in the 16th century. The spatial scale investigated is regional to interregional, covering Austria, Switzerland and north-eastern France. Thus, we defined a list of 36 extreme years (1536-2007), where two or more of several parameters (grape harvest data and/or mean temperatures) available at that time exceeded the two-sigma threshold with regard to a reference period of 105 years. In Western Europe, there were extreme spring to early summer temperatures and/or exceptional phenological observations on all three locations in 1542, 1718, 1811, 1822, 2003, 2006 and 2007. As only grape harvest data are on hand, our phenological dates can only indicate anomalous temperature conditions during spring and early summer, i. e. mean temperatures which significantly correlate to these phenological records. In addition to these data, we used independent documentary sources from the municipal archives of Retz, a town in Lower Austria, for affirming or amending these results. © 2011 The Author(s).

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