Climatic implications of cirque distribution in the Romanian Carpathians: palaeowind directions during glacial periods

The many glacial cirques in the mountains of Romania indicate the distribution of former glacier sources, related to former climates as well as to topography. In the Transylvanian Alps (Southern Carpathians) cirque floors rise eastward at 0.714 m km⁻¹, and cirque aspects tend ENE, confirming the importance of winds from some westerly direction. There is a contrast between two neighbouring ranges: the Făgăraş, where the favoured aspect of cirques is ENE, and the Iezer, where the tendency is stronger and to NNE. This can be explained by the Iezer Mountains being sheltered by the Făgăraş, which implies precipitation‐bearing winds from north of west at times of mountain glaciation. Palaeoglaciation levels also suggest winds from north of west, which is consistent with aeolian evidence from Pleistocene dunes, yardangs and loess features in the plains of Hungary and southwestern Romania. In northern Romania (including Ukrainian Maramureş) the influence of west winds was important, but sufficient only to give a northeastward tendency in cirque aspects. This gave stronger asymmetry than in the Transylvanian Alps, as the northward (solar radiation incidence) tendency in these marginally glaciated mountains was less diluted by wind effects. Cirque floors in northern Romania are lower also in northeast‐facing cirques. In general, cirque aspects result from several factors and the mean tendency is not downwind, but is displaced from poleward by wind and by minor effects. Copyright © 2010 John Wiley & Sons, Ltd.     

Possible soil tension controls on the isotopic equilibrium fractionation factor for evaporation from soil

The stable isotopes of hydrogen and oxygen (δ²H and δ¹⁸O) are useful conservative tracers for tracking the movement of water in soil. But although the tracking of water infiltrating through the soil profile and its movement as run‐off and groundwater recharge are well developed, water movement through the soil can also include evaporative fractionation. Soil water fractionation factors have, until now, been largely empirical. Unlike open water evaporation where temperature, humidity, and vapour pressure gradient define fractionation, soil water evaporation includes fractionation by soil matrix effects. These effects are still poorly characterized. Here, we present preliminary results from a simple laboratory experiment with four soil admixtures with grain sizes that range from sand to silt and clay. Our results show that soil tension seems to control the isotope fractionation of resident soil water. The relationship between soil tension and equilibrium fractionation appears to be independent of soil texture and appears well supported by thermodynamic theory. Although these results are preliminary, they suggest that future work should go after soil tension effects as a possible explanatory factor of soil water and water vapour fractionation.     

Halogens in tektites and impact glasses

Abstract— Impact glasses, tektites and some related basement rocks were analyzed for F, Cl, Br and I. The tektite and impact glasses show similar abundance patterns within the groups. Muong Nong-type tektites indicate that the halogens have been depleted in the order I > Br > Cl > F in their melt under oxidizing conditions. For Darwin Glass selective volatilization of F from the melt is a major depleting process. Cl, Br and I are lost to a lesser extent.     

Nonlinearity effects on resonant absorption of surface Alfvén waves in incompressible plasmas

The resonant absorption of small amplitude surface Alfvén waves is studied in nonlinear incompressible MHD for a viscous and resistive plasma. The reductive perturbation method is used to obtain the equation that governs the spatial and temporal behaviour of small amplitude nonlinear surface Alfvén waves. Numerical solutions to this equation are obtained under the initial condition that att = 0 the spatial variation is purely sinusoidal. The numerical results show that nonlinearity accelerates the wave damping due to resonant absorption. Resonant absorption is a more efficient wave damping mechanism than can be anticipated on the basis of linear theory.     

Resonant behaviour of MHD waves on magnetic flux tubes

The resonances that appear in the linear compressible MHD formulation of waves are studied for equilibrium states with flow. The conservation laws and the jump conditions across the resonance point are determined for 1D cylindrical plasmas. For equilibrium states with straight magnetic field lines and flow along the field lines the conserved quantity is the Eulerian perturbation of total pressure. Curvature of the magnetic field lines and/or velocity field lines leads to more complicated conservation laws. Rewritten in terms of the displacement components in the magnetic surfaces parallel and perpendicular to the magnetic field lines, the conservation laws simply state that the waves are dominated by the parallel motions for the modified slow resonance and by the perpendicular motions for the modified Alfvén resonance.The conservation laws and the jump conditions are then used for studying surface waves in cylindrical plasmas. These waves are characterized by resonances and have complex eigenfrequencies when the classic true discontinuity is replaced by a nonuniform layer. A thin non-uniform layer is considered here in an attempt to obtain analytical results. An important result related to earlier work by Hollweg et al. (1990) for incompressible planar plasmas is found for equilibrium states with straight magnetic field lines and straight velocity field lines. For these equilibrium states the incompressible and compressible surface waves have the same frequencies at least in the long wavelength limit and there is an exact correspondence with the planar case. As a consequence, the conclusions formulated by Hollweg et al. still hold for the straight cylindrical case. The effects of curvature are subsequently considered.     

SYMPOSIUM ON EVAPORATION / SYMPOSIUM SUR L'ÉVAPORATION

SUMMARY

The geographical transposition of the results obtained from representative and experimental watersheds is a matter of regressions based upon geomorphological caracteristics of these watersheds. Therefore, the lumped model for the transformation of precipitations into runoff, generally used for small sized basins, must be simplified and standardized in order to be defined, in any case, by the same parameters. Moreover, the elements of the hydrograph, especially the base time, are to be determined by a very strict processus providing with “consistent” estimates. These new necessary conditions lead to see again the methods used till now for scientific purposes in operating the data from small watersheds, to the so-called “standard hydrograph”.