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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. Source

Fabian K.,Geological Survey of Norway | Leonhardt R.,Zentralanstalt fur Meteorologie und Geodynamik
Earth and Planetary Science Letters | Year: 2010

A recent proposal of a multiple-specimen technique promises to be a viable alternative to the classical Thellier-Thellier method of absolute paleointensity determination. However, to exploit the full potential of the multiple-specimen approach, a thorough understanding of its theoretical foundation, and a detailed experimental verification of its implicit assumptions is required. Here, the validity of the multiple-specimen technique is studied on a collection of synthetic samples covering grain sizes ranging from single domain (SD) over intermediate pseudo-single domain (PSD), to multidomain (MD). The experimental data indicate that the multiple-specimen method in its present form systematically overestimates paleointensity for intermediate PSD to MD particle sizes. This finding is investigated theoretically by a statistical theory of weak-field thermoremanence, and quantified by a phenomenological thermoremanence model. Based on this theoretical framework, and on the new experimental evidence, an extended version of the multiple-specimen technique is designed, which is more reliable in the critical domain-state range. The new measurement scheme improves normalization, and quantifies the PSD and MD overestimate, which then can even be corrected for. Furthermore, the proposed measurement scheme includes a thermal repeat measurement to assess the effect of alteration upon the accuracy of the final paleointensity result. The new technique is verified experimentally for the synthetic samples investigated. © 2010 Elsevier B.V. Source

Balzarini A.,RSE SpA | Pirovano G.,RSE SpA | Zabkar R.,University of Ljubljana | Curci G.,University of LAquila | 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. Source

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. Source

Lang M.N.,Zentralanstalt fur Meteorologie und Geodynamik | Gohm A.,University of Innsbruck
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. Source

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