ALBERT

Description: This paper presents an altimetric method for ocean monitoring by remote sensing. It uses carrier observations of reflected GNSS signals. The method is illustrated in a simulation study and applied to a long term experiment yielding an ocean tide spectrum. The altimetric concept is based on residual observations of Doppler frequency. A linear relation between Doppler residuals f0 and height departures ΔH from the surface level is derived. In contrast to existing phase-based methods which are constrained by smooth ocean conditions, the frequency-based retrieval here described holds good for rougher ocean conditions. Two retrievals of Doppler residuals are distinguished: Tracking Retrieval and Spectral Retrieval. A simulation study investigates the performance of Spectral Retrieval for a rough ocean surface with a noise-like sea level deviation ξ(t). Simulation settings were adjusted to reflection events in coastal experiments with an elevation range of [5…15] deg. In this range Tracking Retrieval tolerates a surface standard deviation σξ 〈 5 cm, whereas Spectral Retrieval tolerates σξ ≤ 30 cm. These limits correspond to significant wave heights of 20 cm for Tracking Retrieval and 1.2 m for Spectral Retrieval. The simulation results are confirmed by applying the altimetric method to the experimental data. The recovery of continuous phase tracks in experimental data is onerous and Tracking Retrieval only works for a period of smooth ocean conditions (162 events). By contrast, Spectral Retrieval yields altimetric estimates throughout the whole experiment (2607 events). The altimetric time series extends over more than 60 days and results in a tide spectrum that resolves diurnal (K1) and semidiurnal (M2, S2) constituents. The formal precision for these estimates lies in the decimeter range.

Description: We analyze horizontal transport from midlatitudes into the tropics (in-mixing) and its impact on seasonal variations of ozone, carbon monoxide and water vapor in the Tropical Tropopause Layer (TTL). For this purpose, we use three-dimensional backward trajectories, driven by ECMWF ERA-Interim winds, and a conceptual one-dimensional model of the chemical composition of the TTL. We find that the fraction of in-mixed midlatitude air shows an annual cycle with maximum during NH summer, resulting from the superposition of two inversely phased annual cycles for in-mixing from the NH and SH, respectively. In-mixing is driven by the monsoonal upper-level anticyclonic circulations. This circulation pattern is dominated by the Southeast Asian summer monsoon and, correspondingly, in-mixing shows an annual cycle. The impact of in-mixing on TTL mixing ratios depends on the in-mixed fraction of midlatitude air and on the meridional gradient of the particular species. For CO the meridional gradient and consequently the effect of in-mixing is weak. For water vapor, in-mixing effects are negligible. For ozone, the meridional gradient is large and the contribution of in-mixing to the ozone maximum during NH summer is about 50%. This in-mixing contribution is not sensitive to the tropical ascent velocity, which is about 40% too fast in ERA-Interim. As photochemically produced ozone in the TTL shows no distinct summer maximum, the ozone annual anomaly in the upper TTL turns out to be mainly forced by in-mixing of ozone-rich extratropical air during NH summer.

Description: Industrial crystallization processes are frequently bound to the application of additives. Additives can modify the crystal morphology. Computer methods allow a precise prediction of the crystal modifications induced by additives. The effect of water as additive molecule on crystal morphology predictions by means of molecular dynamics (MD) is insufficiently explored. This work focuses on the prediction of the crystal habit of benzoic acid in the presence of three-site water. The selection of the temperature control algorithm – the thermostat – applied in MD simulations is highlighted for water. Significant modifications in the crystal morphology can be observed. The given data allow a decision for a certain thermostat in advance. If a fast equilibration is required, the Direct Velocity Scale thermostat should be used. However, for a precise prediction of the morphology, the Nosé temperature control algorithm is recommended. Computer methods allow a precise prediction of the crystal modifications induced by additives. This work focuses on the prediction of the crystal habit of benzoic acid in the presence of three-site water. The selection of the temperature control algorithm, the thermostat, applied in molecular dynamics simulations is highlighted for water.

Description: The crystal growth process is modeled considering the concentration of solvent and solute in the solution. Molecular dynamics (MD) is performed to model the solvent effect on crystal morphology. Molecular modeling is used as tool to estimate the face growth rates of a crystal. Investigations on the liquid phase (solution), the phase separation, and the resulting solid phase (crystal) are conducted. The commercial software Materials Studio 4.0 is applied to build a layered system consisting of solution (liquid phase) and crystal surface (solid phase). The data allow predicting the crystal morphology in the presence of a solvent. The achieved predictions are in good agreement with experimental results, here presented for benzoic acid. Modeling of a solvent mixture at realistic concentration levels is investigated for reliable morphology prediction. By means of specialized software, a solution is modeled and the crystal growth process is analyzed in molecular dynamics. Molecular modeling data of crystalline benzoic acid in an aqueous solution are presented as a case study.

Description: The adjustment of parameterized gravity waves associated with model convection and finer vertical resolution has made possible the generation of the quasi-biennial oscillation (QBO) in two GISS models, GCMAM III and a climate/middle atmosphere version of Model E2. Both extend from the surface to 0.002 hPa, with 2°x2.5° resolution and 102 layers. Many realistic features of the QBO are simulated, including magnitude and variability of its period and amplitude. The period itself is affected by the magnitude of parameterized convective gravity wave momentum fluxes, and interactive ozone (which also affects the QBO amplitude and variability), among other forcings. Although varying SSTs affect the parameterized momentum fluxes, neither aspect is responsible for the modeled variation in QBO period. Both the parameterized and resolved waves act to produce the respective easterly and westerly wind descent, although their effect is offset in altitude at each level. The modeled and observed QBO influences on tracers in the stratosphere, such as ozone, methane and water vapor are also discussed. Due to the link between the gravity wave parameterization and the models' convection, and the dependence on the ozone field, the models may also be used to investigate how the QBO may vary with climate change.

Description: Nature Geoscience 7, 326 (2014). doi:10.1038/ngeo2154 Authors: S. Abiven, M. W. I. Schmidt & J. Lehmann Biochar has been heralded as a solution to a number of agricultural and environmental ills. To get the most benefit from its application, environmental and social circumstances should both be considered.

Description: Questions Is there a spatial pattern in the community structure (stem densities, species richness and species composition) of trees and shrubs during more than 100 yr of heathland to forest succession? To what extent is community structure influenced by land-use history and distance to seed sources? Do these effects change in time? Location A 350-ha heathland (Nørholm) in southwest Denmark was abandoned in 1895 and left for free succession. Prior to abandonment the heathland was under traditional management for centuries. Method Trees and shrubs were recorded and measured in ten surveys spanning 91 yr (1921–2012). In the first nine surveys, complete censuses were used, whereas 116 randomly placed plots (10-m radius) were used in the most recent survey. We used mixed models and different multivariate techniques (non-metric multidimensional scaling and permutational multivariate ANOVA) to analyse spatio-temporal patterns in stem densities, species richness and species composition and the effects of land-use history and distance to seed sources. Results Tree and shrub densities increased exponentially over time and were consistently lower at longer distance from seed sources. Land-use history affected the rate of increase in tree densities, with lower encroachment rates at previously cultivated soils. Initially, species richness increased rapidly but leveled off in later successional stages. Richness was marginally higher at areas closer to seed sources, whereas it was not affected by land-use history. The succession showed a shift from early to mid-successional species over time; but distance to seed source determined which species were colonizing at early stages. Conclusion Distance to seed source and land-use history can differentially affect the structure and spatial patterns of developing forest communities. Although both factors had long-lasting effects on rates of colonization, the spatial patterns of colonization and species composition were mainly determined by distance to seed sources. The importance of distance to seed sources became less over time, suggesting that dispersal is a stronger driver at early stages. After more than a century since abandonment, forest covers 〈30% of the area, indicating that lack of heathland management did not strongly promote tree colonization at this site. Over more than 100 yr of spontaneous heathland to forest succession, distance to seed sources and land-use history had different effects on the community structure of colonizers. Slower colonization rates at formerly cultivated areas were indirectly determined by higher nutrient availability. Dispersal from seed sources had more widespread effects on community structure, albeit more strongly at early stages.

Description: [1]  This paper presents an altimetric method for ocean monitoring by remote sensing. It uses carrier observations of reflected GNSS signals. The method is illustrated in a simulation study and applied to a long term experiment yielding an ocean tide spectrum. The altimetric concept is based on residual observations of Doppler frequency. A linear relation between Doppler residuals f 0 and height departures Δ H from the surface level is derived. In contrast to existing phase-based methods which are constrained by smooth ocean conditions, the frequency-based retrieval here described holds good for rougher ocean conditions. Two retrievals of Doppler residuals are distinguished: Tracking Retrieval and Spectral Retrieval. A simulation study investigates the performance of Spectral Retrieval for a rough ocean surface with a noise-like sea level deviation ξ ( t ). Simulation settings were adjusted to reflection events in coastal experiments with an elevation range of [5…15] deg. In this range Tracking Retrieval tolerates a surface standard deviation σ ξ 〈 5 cm, whereas Spectral Retrieval tolerates σ ξ ≤ 30 cm. These limits correspond to significant wave heights of 20 cm for Tracking Retrieval and 1.2 m for Spectral Retrieval. The simulation results are confirmed by applying the altimetric method to the experimental data. The recovery of continuous phase tracks in experimental data is onerous and Tracking Retrieval only works for a period of smooth ocean conditions (162 events). By contrast, Spectral Retrieval yields altimetric estimates throughout the whole experiment (2607 events). The altimetric time series extends over more than 60 days and results in a tide spectrum that resolves diurnal (K1) and semidiurnal (M2, S2) constituents. The formal precision for these estimates lies in the decimeter range.

Description: [1]  The retreat of Arctic sea-ice has led to renewed calls to exploit Arctic shipping routes. The diversion of ship traffic through the Arctic will shorten shipping routes and possibly reduce global shipping emissions. However, deposition of black carbon (BC) aerosol emitted by additional Arctic ships could cause a reduction in the albedo of snow and ice, accelerating snow-melt and sea-ice loss. Here, we use recently compiled Arctic shipping emission inventories for 2004 and 2050 together with a global aerosol model to quantify the contribution of future Arctic shipping to high-latitude BC deposition. Our results show that Arctic shipping in 2050 will contribute less than 1% to the total BC deposition north of 60° due to the much greater relative contribution of BC transported from non-shipping sources at lower-latitudes. We suggest that regulation of the Arctic shipping industry will be an insufficient control on high-latitude BC deposition.

Description: Article The origin of high-temperature superconductivity in iron-based materials remains a challenging task to solve, but the concept of orbital differentiation of the charge carriers may be a crucial ingredient to the answer. Here, the authors identify an orbital-selective metal–insulator transition and the opening of a gap in the material Rb 1−x Fe 2−y Se 2 . Nature Communications doi: 10.1038/ncomms4202 Authors: Zhe Wang, M. Schmidt, J. Fischer, V. Tsurkan, M. Greger, D. Vollhardt, A. Loidl, J. Deisenhofer