Simulated effects of land immersion on regional arid climate: a case study of the pre-Saharan playa of Chott el-Jerid (south of Tunisia)

The potential effects on the regional climate induced by partially immersing the arid pre-Saharan playa basin of Chott el-Jerid (south of Tunisia) are investigated by comparing two multi-year (1991–2011) sets of numerical simulations each consisting of ten-member ensemble and performed using the WRF regional climate model. The first WRF ensemble is performed under current land use and land cover, while the second is carried out after introducing a virtual large and shallow surface water reservoir (a lake) in Chott el-Jerid. The most pronounced effects generated by the artificial lake are circumscribed over its surface and slightly spread downwind to the other parts of the Chott. The lake has a clear moderating effect on near-surface air temperatures by increasing (decreasing) the wintertime (summertime) air temperatures. Sensible heat fluxes are remarkably increased in winter and decreased in summer over the lake following the temperature gradient between the lake surface and the overlying atmosphere. Latent heat fluxes, moisture convergence, and water vapor mixing ratio are increased over the lake throughout the year, especially in winter. The lake also induces domain-wide decreased (increased) surface pressures and land (lake) breeze circulation in winter (summer). Simulated rainfall amounts are most increased over the lake in winter likely because of an enhanced atmospheric instability, while they slightly decrease in summer.     

Local Agenda 21 and Barriers to Sustainability at the Local Government Level in Victoria,Australia

At the 1992 Rio 'Earth Summit', Australia joined other nations in committing to processes leading to the formulation of 'Local Agenda 21s' (LA21s) by 1996. Subsequently, in the latter year, Whittaker carried out a national survey of local government authorities to evaluate what progress had been made. Whittaker's conclusion was that progress in Australia had been slow, but ten 'leading-edge' Victorian councils were identified through a self-reporting process. In this paper we discuss the concept of LA21, analyse in closer detail the 'progress' that has been made in the ten Victorian councils, and discuss some of the broader forces that, we argue, have made LA21 formulation increasingly difficult, particularly in the state of Victoria in the recent past.     

Experimental evidence for an ascending microflow of geogas in the ground

A microflow of free ascending gas has been observed in 26 out of 30 tested boreholes at three different sites. The flow rates vary between 60 × 10⁻⁴ and 4 cm³/min m² horizontally projected borehole area. Sampling has been made in ground boreholes as well as in holes drilled downwards from the lowest levels in two mines. The composition of the gas varies considerably. The main components of the gas are nitrogen, argon, oxygen and methane. Traces of heavier hydrocarbons are observed. At the site of the ground holes, only traces of methane are observed. In all sampled holes the existence of free oxygen is observed. The nitrogen/argon quotient is close to the atmospheric quotient in all sampled holes, indicating a partly atmospheric origin of the gas. The existence of methane and traces of heavier hydrocarbons indicates the existence of a second source.     

A model for multiphase flow and transport in porous media including a phenomenological approach to account for deformation—a model concept and its validation within a code intercomparison study

Multiphase flow processes in unsaturated cohesive soils are often affected by deformation due to swelling and shrinking as a result of varying water contents. This paper presents a model concept which is denoted ‘phenomenological’ in terms of the processes responsible for soil deformation, since the effects of deformation on flow and transport are only considered by constitutive relations that allow an adaptation of the hydraulic properties. This new model is validated in a detailed intercomparison study with two state-of-the-art models that are capable of explicitly describing the processes relevant for the deformation. A ‘numerical experiment’ with a state-of-the-art reference model is used to produce ‘measurement data’ for an inverse-modelling-based estimation of the model input parameters for the phenomenological concept.     

Climate during the last glacial maximum in the Wasatch and southern Uinta Mountains inferred from glacier modeling

Recent improvements in understanding glacial extents and chronologies in the Wasatch and Uinta Mountains and other mountain ranges in the western U.S. call for a more detailed approach to using glacier reconstructions to infer paleoclimates than commonly applied AAR-ELA-ÄT methods. A coupled 2-D mass balance and ice-flow numerical modeling approach developed by [Plummer, M.A., Phillips, F.M., 2003. A 2-D numerical model of snow/ice energy balance and ice flow for paleoclimatic interpretation of glacial geomorphic features. Quaternary Science Reviews 22, 1389–1406] allows exploration of the combined effects of temperature, precipitation, shortwave radiation and many secondary parameters on past ice extents in alpine settings. We apply this approach to the Little Cottonwood Canyon in the Wasatch Mountains and the Lake Fork and Yellowstone Canyons in the south-central Uinta Mountains. Results of modeling experiments indicate that the Little Cottonwood glacier required more precipitation during the local Last Glacial Maximum (LGM) than glaciers in the Uinta Mountains, assuming lapse rates were similar to modern. Model results suggest that if temperatures in the Wasatch Mountains and Uinta Mountains were  6 °C to 7 °C colder than modern, corresponding precipitation changes were  3 to 2× modern in Little Cottonwood Canyon and  2 to 1× modern in Lake Fork and Yellowstone Canyons. Greater amounts of precipitation in the Little Cottonwood Canyon likely reflect moisture derived from the surface of Lake Bonneville, and the lake may have also affected the mass balance of glaciers in the Uinta Mountains.     

A model for oxygen and sulfur isotope fractionation in sulfate during bacterial sulfate reduction processes

We present a model of bacterial sulfate reduction that includes equations describing the fractionation relationship between the sulfur and the oxygen isotope composition of residual sulfate (δ³⁴S_{SO4_residual}, δ¹⁸O_{SO4_residual}) and the amount of residual sulfate. The model is based exclusively on oxygen isotope exchange between cell-internal sulfur compounds and ambient water as the dominating mechanism controlling oxygen isotope fractionation processes. We show that our model explains δ³⁴S_{SO4_residual} vs. δ¹⁸O_{SO4_residual} patterns observed from natural environments and from laboratory experiments, whereas other models, favoring kinetic isotope fractionation processes as dominant process, fail to explain many (but not all) observed δ³⁴S_{SO4_residual} vs. δ¹⁸O_{SO4_residual} patterns. Moreover, we show that a “typical” δ³⁴S_{SO4_residual} vs. δ¹⁸O_{SO4_residual} slope does not exist. We postulate that measurements of δ³⁴S_{SO4_residual} and δ¹⁸O_{SO4_residual} can be used as a tool to determine cell-specific sulfate reduction rates, oxygen isotope exchange rates, and equilibrium oxygen isotope exchange factors. Data from culture experiments are used to determine the range of sulfur isotope fractionation factors in which a simplified set of equations can be used. Numerical examples demonstrate the application of the equations. We postulate that, during denitrification, the oxygen isotope effects in residual nitrate are also the result of oxygen isotope exchange with ambient water. Consequently, the equations for the relationship between δ³⁴S_{SO4_residual}, δ¹⁸O_{SO4_residual}, and the amount of residual sulfate could be modified and used to calculate the fractionation-relationship between δ¹⁵N_{NO3_residual}, δ¹⁸O_{NO3_residual}, and the amount of residual nitrate during denitrification.     

The antiferromagnetic-paramagnetic transition in αFe2O3 in the single prism approximation of the cluster variation method

The single prism approximation SPA of the cluster variation method has been used to model the antiferromagnetic-paramagnetic transition in hematite. This calculation yields insight into the accuracy of the SPA and other approximate methods for modeling order-disorder phenomena. Published values of the magnetic coupling constants were used to calculate the Néel temperature, sublattice magnetization, and magnetic specific heat. The calculated Néel temperature is found to be 1.21 times the observed value, as compared to 1.36 times observed for a mean field theory approximation, an improvement that reflects the superior treatment of configurational entropy in the SPA. Qualitative to semiquantitative agreement is obtained between observed and calculated values for sublattice magnetization and magnetic specific heat; however we find that previously published values for the magnetic specific heat are too large by a factor of two.     

26Al‐26Mg isotope systematics of the first solids in the early solar system

High‐precision bulk aluminum‐magnesium isotope measurements of calcium‐aluminum‐rich inclusions (CAIs) from CV carbonaceous chondrites in several laboratories define a bulk ²⁶Al‐²⁶Mg isochron with an inferred initial ²⁶Al/²⁷Al ratio of approximately 5.25 × 10^?5, named the canonical ratio. Nonigneous CV CAIs yield well‐defined internal ²⁶Al‐²⁶Mg isochrons consistent with the canonical value. These observations indicate that the canonical ²⁶Al/²⁷Al ratio records initial Al/Mg fractionation by evaporation and condensation in the CV CAI‐forming region. The internal isochrons of igneous CV CAIs show a range of inferred initial ²⁶Al/²⁷Al ratios, (4.2–5.2) × 10^?5, indicating that CAI melting continued for at least 0.2 Ma after formation of their precursors. A similar range of initial ²⁶Al/²⁷Al ratios is also obtained from the internal isochrons of many CAIs (igneous and nonigneous) in other groups of carbonaceous chondrites. Some CAIs and refractory grains (corundum and hibonite) from unmetamorphosed or weakly metamorphosed chondrites, including CVs, are significantly depleted in ²⁶Al. At least some of these refractory objects may have formed prior to injection of ²⁶Al into the protosolar molecular cloud and its subsequent homogenization in the protoplanetary disk. Bulk aluminum and magnesium‐isotope measurements of various types of chondrites plot along the bulk CV CAI isochron, suggesting homogeneous distribution of ²⁶Al and magnesium isotopes in the protoplanetary disk after an epoch of CAI formation. The inferred initial ²⁶Al/²⁷Al ratios of chondrules indicate that most chondrules formed 1–3 Ma after CAIs with the canonical ²⁶Al/²⁷Al ratio.     

Orbit Determination of Binary Asteroids

In addition to the detection of an asteroid moon or a binary asteroid, the knowledge of the satellite’s true orbit is of high importance to derive fundamental physical parameters of the binary system such as its mass and to shed light on its possible formation history and dynamical evolution (prograde/retrograde orbit, large/small eccentricity or inclination, etc.). A new methodology for preliminary orbit determination of binary asteroids – and visual binaries in general – is proposed. It is based on Thiele–Innes method combined with a ‘trial and error’ Monte-Carlo technique. This method provides the full set of solutions (bundle of orbits, with the 7 orbital elements) even for a reduced number of observations. The mass is a direct by-product of this orbit determination, from which one can next infer the bulk-density and porosity. In addition to the bundle of orbits, the method provides the marginal probability densities of the foreseen parameters. Such error analysis – since it avoids linear approximation – can be of importance for the prediction of the satellite’s position in the plane-of-sky during future stellar occultations or subsequent observations, but also for the analysis of the orbit’s secular evolution. After briefly describing the method, we present the algorithm and its application to some practical cases, with particular emphasis on asteroids binaries and applications on orbital evolution.