Corrections for Wind-Speed Errors from Sodar and Lidar in Complex Terrain     

Stuart Bradley  Yvette Perrott  Paul Behrens  Andy Oldroyd 《Boundary-Layer Meteorology》2012,143(1):37-48

The quality of lidar and sodar wind estimates is generally judged through comparisons with mast-mounted instruments, and the resulting regressions. Evaluation of the relative merits of lidars versus sodars is complicated by the fact that lidars are generally placed close to a mast whereas sodars are generally placed some distance from a mast so that acoustic reflections off the mast are reduced. This leads to the two technologies, lidar and sodar, not being compared in similar situations. Differences arising from the two geometries can be expected to be larger in complex terrain, where the wind regime can vary significantly spatially. The current work explores these differences in moderately complex terrain. Lidar–mast comparisons are performed with the lidar close to an 80 m mast, and sodar–mast comparisons performed with the sodar 300 m from the mast. Systematic variations in estimated wind speed are found to occur with height, consistent with predictions from a simple flow model. When the lidar was moved to the sodar location, further from the mast, there were significant changes in the estimated wind speeds and a reduction in correlation with the mast-based wind speeds, as expected. However, the correlation between collocated lidar and sodar winds was high. This finding emphasizes that any comparison of two remote sensing instruments needs to be through similar experiments, and that differences in accuracy often reported for the lidar and sodar technologies are likely to be contaminated due to poor comparison configurations. A method was devised to simulate the sodar being collocated with the mast, by using the lidar–sodar measurements and the lidar–mast measurements. It was found that there was then no statistically detectable difference between lidar–mast regressions and sodar–mast regressions for the particular lidar and sodar tested. Both remote sensing instruments were also found to be good estimators of Weibull parameters, as compared with those derived from mast data. The conclusion is that the sodar measured the winds above the sodar with a similar accuracy to the lidar measuring winds above the lidar.  相似文献   

Water diffusion in Mount Changbai peralkaline rhyolitic melt     

Haoyue Wang  Zhengjiu Xu  Harald Behrens  Youxue Zhang 《Contributions to Mineralogy and Petrology》2009,158(4):471-484

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Diffusive transport of water in porous feldspars from granitic saprolites: In situ experiments using FTIR spectroscopy     

A.V. Simonyan  H. Behrens  S. Dultz 《Geochimica et cosmochimica acta》2009,73(23):639-452

A novel experimental cell was developed for in situ measurements of transport phenomena in porous media using Fourier-Transform Infrared (FTIR) Spectroscopy. The technique was employed at ambient pressure in the temperatures range of 11–44 °C to study the H₂O → D₂O exchange between water-saturated weathered feldspars (bulk porosity of 5–19 vol% for feldspar) from granitic saprolites and a surrounding aqueous liquid. Such measurements are an important step for understanding internal weathering reactions of feldspars in soils and aquifers. Effective diffusion coefficients D_eff for water in water-saturated porous feldspars were determined assuming one-dimensional diffusion in a quasi-homogeneous medium. The values of D_eff vary from 7.2 × 10⁻¹⁰ to 1.9 × 10⁻¹¹ m²/s and are 1–2 orders of magnitude lower than the diffusion coefficients (D) of protons and molecular H₂O in liquid water. The activation energy for the H₂O → D₂O exchange process in porous feldspars ranges from 7.8 to 18.8 kJ/mol.The results imply that the effective diffusivity of water is mainly controlled by physical properties of the feldspars like porosity, pore connectivity, pore geometry and distribution. Perthitic feldspars with homogeneous pore distribution in the albitic lamellas have diffusional tortuosity factors X = D/D_eff between 3 and 10 while alkali feldspars with inhomogeneously distributed and disconnected pores have much higher X values up to 129. Diffusion anisotropy has been verified for a vein perthite with diffusion perpendicular to the lamellas being faster by 0.3–0.5 log units than within the lamellas. It has to be emphasized that the study is based only on few selected feldspars, including perthitic feldspar, and additional work on samples with different weathering stages is needed to test the importance of the different parameters controlling diffusive transport in the pore system.  相似文献   

Water diffusion in dacitic melt     

Huaiwei Ni  Harald Behrens 《Geochimica et cosmochimica acta》2009,73(12):3642-3655

H₂O diffusion in dacitic melt was investigated at 0.48-0.95 GPa and 786-893 K in a piston-cylinder apparatus. The diffusion couple design was used, in which a nominally dry dacitic glass makes one half and is juxtaposed with a hydrous dacitic glass containing up to ∼8 wt.% total water (H₂O_t). H₂O concentration profiles were measured on quenched glasses with infrared microspectroscopy. The H₂O diffusivity in dacite increases rapidly with water content under experimental conditions, similar to previous measurements at the same temperature but at pressure <0.15 GPa. However, compared with the low-pressure data, H₂O diffusion at high pressure is systematically slower. H₂O diffusion profiles in dacite can be modeled by assuming molecular H₂O (H₂O_m) is the diffusing species. Total H₂O diffusivity D_H2Ot within 786-1798 K, 0-1 GPa, and 0-8 wt.% H₂O_t can be expressed as: where D_H2Ot is in m²/s, T is temperature in K, P is pressure in GPa, K = exp(1.49 − 2634/T) is the equilibrium constant of speciation reaction (H₂O_m+O?2OH) in the melt, X = C/18.015/[C/18.015 + (100 − C)/33.82], C is wt.% of H₂O_t, and 18.015 and 33.82 g/mol correspond to the molar masses of H₂O and anhydrous dacite on a single oxygen basis. Compared to H₂O diffusion in rhyolite, diffusivity in dacite is lower at intermediate temperatures but higher at superliquidus temperatures. This general H₂O diffusivity expression can be applied to a broad range of geological conditions, including both magma chamber processes and volcanic eruption dynamics from conduit to the surface.  相似文献   

Pressure dependence of viscosity of rhyolitic melts     

Hejiu Hui  Youxue Zhang  Piero Del Gaudio  Harald Behrens 《Geochimica et cosmochimica acta》2009,73(12):3680-3693

Viscosity of silicate melts is a critical property for understanding volcanic and igneous processes in the Earth. We investigate the pressure effect on the viscosity of rhyolitic melts using two methods: indirect viscosity inference from hydrous species reaction in melts using a piston cylinder at pressures up to 2.8 GPa and direct viscosity measurement by parallel-plate creep viscometer in an internally-heated pressure vessel at pressures up to 0.4 GPa. Comparison of viscosities of a rhyolitic melt with 0.8 wt% water at 0.4 GPa shows that both methods give consistent results. In the indirect method, viscosities of hydrous rhyolitic melts were inferred based on the kinetics of hydrous species reaction in the melt upon cooling (i.e., the equivalence of rheologically defined glass transition temperature and chemically defined apparent equilibrium temperature). The cooling experiments were carried out in a piston-cylinder apparatus using hydrous rhyolitic samples with 0.8-4 wt% water. Cooling rates of the kinetic experiments varied from 0.1 K/s to 100 K/s; hence the range of viscosity inferred from this method covers 3 orders of magnitude. The data from this method show that viscosity increases with increasing pressure from 1 GPa to 3 GPa for hydrous rhyolitic melts with water content ?0.8 wt% in the high viscosity range. We also measured viscosity of rhyolitic melt with 0.13 wt% water using the parallel-plate viscometer at pressures 0.2 and 0.4 GPa in an internally-heated pressure vessel. The data show that viscosity of rhyolitic melt with 0.13 wt% water decreases with increasing pressure. Combining our new data with literature data, we develop a viscosity model of rhyolitic melts as a function of temperature, pressure and water content.  相似文献   

Meltwater discharge during the Holocene from the Wilkes subglacial basin revealed by beryllium isotope analysis of marine sediments     

Bethany Behrens  Yosuke Miyairi  Adam D. Sproson  Masako Yamane  Yusuke Yokoyama 《第四纪科学杂志》2019,34(8):603-608

Understanding Antarctic Ice Sheet dynamics related to global climate change is of scientific and societal interest as the future behaviour of the ice sheet under the currently changing climate is unknown. We present beryllium‐10 (¹⁰Be) analysis of a high‐resolution marine sediment core from the Adélie Basin near the eastern Wilkes Land margin, which is susceptible to marine ice sheet instability due to the low‐lying nature and down‐sloping trough of the Wilkes Subglacial Basin. Combined with a newly constructed age model using compound specific radiocarbon dates, the data reveal three events associated with high meteoric ¹⁰Be at ca. ~10 ka, ca. ~6.5 ka and from ca. ~4 ka. We interpret these high meteoric ¹⁰Be events to be derived from the deposition of ¹⁰Be released from the ice sheet during meltwater discharge. In particular, the shift to higher meteoric ¹⁰Be concentration at~4 ka may correspond to changes in climate patterns at this time. Copyright © 2019 John Wiley & Sons, Ltd.  相似文献   

Introduction     

Gualtiero Badin  Jörn Behrens  Christian Franzke  Jens Rademacher 《地球物理与天体物理流体动力学》2019,113(5-6):425-427

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The dependence of the partitioning of iron and europium between plagioclase and hydrous tonalitic melt on oxygen fugacity   总被引：1，自引：0，他引：1  

Max Wilke  Harald Behrens 《Contributions to Mineralogy and Petrology》1999,137(1-2):102-114

The dependence of iron and europium partitioning between plagioclase and melt on oxygen fugacity was studied in the system SiO₂(Qz)—NaAlSi₃O₈(Ab)—CaAl₂Si₂O₈(An)—H₂O. Experiments were performed at 500 MPa and 850 °C/750 °C under water saturated conditions. The oxygen fugacity was varied in the log f _O2-range from −7.27 to −15.78. To work at the most reducing conditions the classical double-capsule technique was modified. The sample and a C—O—H bearing sensor capsule were placed next to each other within a BN jacket to minimise loss of hydrogen to the vessel atmosphere. By this setup redox conditions slightly more reducing than the FeO—Fe₃O₄ buffer could be maintained even in 96 h runs. Raman spectra showed that the BN was modified by reaction with hydrogen resulting in a low hydrogen permeability. The partition coefficients determined for Eu at 850 °C and 500 MPa vary from 0.095 at conditions of the Cu—Cu₂O buffer to 1.81 at the most reducing conditions (C—O—H sensor). In the same f _O2 interval the partition coefficient for Fe varies from 0.55 at oxidising conditions to 0.08 at the most reducing conditions. The partitioning of Sm, which was added as a reference for a trivalent REE, does not vary with the oxygen fugacity, yielding an average value for D = 0.07. Lowering the temperature to 750 °C for a given f _O2 decreases the partition coefficient of Eu and increases that of Fe. Comparison with published data at 1 atm and at higher temperatures shows that both temperature and composition of the melt have strong effects on the partitioning behaviour. As the change of the partition coefficients in the geologically relevant f _O2 range is quite strong, element partitioning of Eu and Fe might be used to estimate redox conditions for the genesis of igneous rocks. Furthermore, by modelling the partitioning data it is possible to extract information about the redox state of the melt. Resulting ferric-ferrous ratios show significant differences from those predicted by empirical models. Received: 14 October 1998 / Received: 5 March 1999  相似文献   

Development of an ensemble prediction system for ocean surface waves in a coastal area     

Arno Behrens 《Ocean Dynamics》2015,65(4):469-486

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Electrical conductivity of H-bearing orthopyroxene single crystals measured with impedance spectroscopy     

Elke Schlechter  Roland Stalder  Harald Behrens 《Physics and Chemistry of Minerals》2012,39(7):531-541

In this study, the electrical conductivity of synthetic and natural orthopyroxene single crystals containing various amounts of hydrogen and cation impurities (i.e., Al, Fe) was investigated using impedance spectroscopy. A new cell was developed to measure conductivities of submillimeter-sized oriented single crystals with impedances up to 10¹⁰?Ohm. In contrast to previous studies on olivine and orthopyroxene, results from this study do not show a simple correlation of the concentration of protons and the electrical conductivity. Instead, the electrical conductivity appears to be a complex function of iron content, hydrogen content, crystal orientation and concentration of other impurity cations and shows similar activation energies to hydrogen diffusion. Model calculations considering proton conduction rather exclude than suggest orthopyroxene as responsible phase for high-conductivity regions in the Earth’s upper mantle.  相似文献