Dawn‐to‐dusk evolution of air turbulence,temperature and sensible and latent heat fluxes above a forest canopy: Concepts,model and field comparisons

Abstract

Dawn‐to‐dusk evolution of air turbulence, sensible heat and latent heat above a forest during cloud‐free or near‐cloud‐free summer conditions is modelled by way of a system of differential equations. Temperatures in and above the canopy, near canopy‐top wind velocities, early morning leaf moisture (dew) and afternoon canopy ventilation (i.e. heat released from the canopy and from below the canopy) are included in the mathematical treatment. Computed results are compared with field data for atmospheric temperature and wind speed profiles up to 1200 m, within‐canopy temperature, and canopy‐level radiation, turbulent fluxes and wind speeds. Data were collected at a central New Brunswick mixed‐wood forest site dominated by spruce (Picea spp. ) and shade‐tolerant hardwoods for four representative summer days. It was found that the effective canopy temperature was not only affected by insolation, but also by the extent of canopy ventilation and the amount of dew on the foliage. The growth of the mixing layer was affected by canopy ventilation and by above‐canopy wind speeds. Model calculations closely simulated the meteorological observations.     

A contribution to the crystal chemistry of the voltaite group: solid solutions, Mössbauer and infrared spectra, and anomalous anisotropy

Voltaite is a mineral of fumaroles, solfatares, coal-fire gas vents, and acid-mine drainage systems. The nominal composition is K₂Fe₅ ²⁺Fe₃ ³⁺Al(SO₄)₁₂·18H₂O and the nominal symmetry is cubic, $Fd\overline{3}c$ . The tetragonal (I4₁/acd) superstructure of voltaite is known as the mineral pertlikite. In this study, we investigated 22 synthetic voltaite samples in which Fe²⁺ was partially or completely replaced by Mg, Zn, Mn, or Cd, by single-crystal and powder X-ray diffraction (both in-house and synchrotron). Two samples contained NH₄ ⁺ instead of K⁺. The structure of voltaite is based on a framework defined by kröhnkite-like heteropolyhedral chains which host both M³⁺ and M²⁺ in octahedral coordination. Unit cell dimensions of the end-members scale almost linearly with the size of M²⁺. In the Fe²⁺-Mg-Zn solid solutions, the Fe²⁺-Mg and Fe²⁺-Zn solutions are linear (ideal) in terms of their lattice-parameter variations. The Mg-Zn solid solution, however, is strongly non-ideal. A detailed analysis of the topology of the chains showed that this behavior originates in expansion and contraction of individual M²⁺-O bonds within the chains. In the Mg-Zn solid solution, some of the M²⁺-O bonds expand while none contract. In the other solid solutions, expansion of some M²⁺-O bonds is always compensated by contraction of the other ones. Parts of the nominally cubic crystals are optically anisotropic and their symmetry is found to be tetragonal by single crystal X-ray diffraction measurements. The coexistence of cubic and tetragonal sectors within a single crystal without any detectable difference in their chemical composition is difficult to explain in terms of growth of such composite crystals. Mössbauer and infrared spectra collected on our synthetic crystals conform with previously published data.     

A new approach to quantification of metamorphism using ultra-small and small angle neutron scattering

In this paper we report the results of a study using small angle and ultra-small angle neutron scattering techniques (SANS and USANS) to examine the evolution of carbonates during contact metamorphism. Data were obtained from samples collected along two transects in the metamorphosed Hueco limestone at the Marble Canyon, Texas, contact aureole. These samples were collected from the igneous contact out to ∼1700 m. Scattering curves obtained from these samples show mass fractal behavior at low scattering vectors, and surface fractal behavior at high scattering vectors. Significant changes are observed in the surface and mass fractal dimensions as well as the correlation lengths (pore and grain sizes), surface area to volume ratio and surface Gibbs Free energy as a function of distance, including regions of the aureole outside the range of classic metamorphic petrology. A change from mass-fractal to non-fractal behavior is observed at larger scales near the outer boundary of the aureole that implies significant reorganization of pore distributions early in the metamorphic history. Surface fractal results suggest significant smoothing of grain boundaries, coupled with changes in pore sizes. A section of the scattering curve with a slope less than −4 appears at low-Q in metamorphosed samples, which is not present in unmetamorphosed samples. A strong spike in the surface area to volume ratio is observed in rocks near the mapped metamorphic limit, which is associated with reaction of small amounts of organic material to graphite. It may also represent an increase in pore volume or permeability, suggesting that a high permeability zone forms at the boundary of the aureole and moves outwards as metamorphism progresses. Neutron scattering data also correlate well with transmission electron microscopic (TEM) observations, which show formation of micro- and nanopores and microfractures during metamorphism. The scattering data are, however, quantifiable for a bulk rock in a manner that is difficult to achieve using high-resolution imaging (e.g. TEM). Thus, neutron scattering techniques provide a new approach to the analysis and study of metamorphism.     

AustroMars and PolAres: Measuring forward contamination during Mars-analogue missions

The search for life on Mars is one of the most ambitious scientific challenges in astrobiology. Although the surface of the planet is generally believed to be hostile to life, habitats embedded in the subsurface water repositories might harbor diminutive traces of extant or even extant life requiring advanced analytical capabilities. At the same time, hardware (including a human crew) delivered from Earth introduces the inherent risk of contaminating the very samples to be investigated for tracers of life and as such might compromise the pristinity of the sample leading to a false-positive detection. Deep subsurface drilling activities are considered to be one of the most promising sampling techniques, but require extensive infrastructure and technologies yet to be developed and increase the probability of such a forward contamination. AustroMars and PolAres are two Mars-analogue research programmes conducted by the Austrian Space Forum to investigate the contamination vectors of human Mars surface activities. Using fluorescent microspherules and non-pathogenic bacteria, an analysis strategy to quantify the bioload transfer rates and its field application in a Mars-analogue setting is described.     

Relation of the jet in M 87 to nearby galaxies in the virgo cluster

The massive and active galaxies in the core of the Virgo Cluster were shown in 1968 to be aligned on either side of M 87, along the direction of the jet and counter-jet. Recent observations confirm the significance of this alignment by showing that the brightest X-ray sources, including additional large galaxies, define the same line. Detailed X-ray maps of M 86 show that this galaxy, which is part of the alignment, is probably blown by a wind from M 87 due to its close alignment with the jet. But the large radio E galaxy, M 84, which is 1.4 degrees away from M 87, andexactly along the line of the jet, is shown by the compression of its X-ray isophotes to be actually moving out along the line of the jet. This evidence furnishes rather spectacular support for the earlier conclusion that M 84 had originated as a proto-galaxy within M 87 and had been ejected out along the line of the jet. Alexander von Humboldt Senior Scientist awardee at the Max-Planck-Institut für Astrophysik, Garching, FRG.     

Climate Protection Strategies: International Allocation and Distribution Effects

In international climate policy discussions, one of the centralissues for medium- to long run climate protection strategiesis the uncertainty about the costs and the distributional effectsof specific unilateral or multilateral emission reductions. Thispaper looks at the world-wide effects of climate protection strategieson the allocation of resources, on economic growth in differentregions, and on the regional welfare effects. The analysis isbased on a global recursively dynamic, multi-region, multi-sectorcomputable general equilibrium model parameterized accordingto the ICLIPS (Integrated Assessment of Climate Protection Strategies)integrated assessment model. The simulations show that nationalclimate policies will have important international repercussions.It is therefore important to consider international allocationeffects in the analysis of national climate protection strategies.The welfare costs of greenhouse gas emission reductions risemore than proportionally with lower emission targets. The analysisof the carbon leakage rate indicates that most of the leakagerapidly disappears if emission reduction moves towards an efficientdistribution of emission targets.     

Barium partitioning in coccoliths of Emiliania huxleyi

The coccolithophore Emiliania huxleyi was grown in seawater under different Ba concentrations. The relationship of coccolith Ba/Ca ratio and seawater Ba/Ca ratio was found to be linear. The linear regression yields the apparent Ba exchange coefficient of 0.10. Our data support a recently proposed generic model (Langer G., Gussone N., Nehrke G., Riebesell U., Eisenhauer A., Kuhnert H., Rost B., Trimborn S., and Thoms S. (2006) Coccolith strontium to calcium ratios in Emiliania huxleyi: the dependence on seawater strontium and calcium concentrations. Limnol. Oceanogr.51, 310-320.) developed for explaining apparent exchange coefficients of metabolically inert divalent trace metals, such as Sr, in E. huxleyi. This model represents the first approach combining cell physiological processes and data from inorganic precipitation experiments, which quantitatively explains coccolith apparent Sr and Ba exchange coefficients.