Circular,Stationary Profiles Emerging in Unidirectional Abrasion

Models of moving interfaces, especially those with stable soliton-like behavior, are of central importance in many areas of physics, for example, surface growth models, chemical waves, and more. Here described for the first time in a realistic geophysical context is a partial differential equation model of bedrock abrasion by unidirectional impacts generalizing earlier pioneering work on pebble shapes by Bloore who treated isotropic impacts (Bloore in Math. Geol. 9:113–122, 1977). The result is a simple geometrical partial differential equation exhibiting circular arcs as solitary wave profiles. The latter seem to be the first known analytic solutions on Bloore-type models. Solitonic behavior, although familiar in many areas of physics, appears not to have been encountered in the geophysical literature. Not only are the existence and stability of these stationary, traveling shapes demonstrated here by numerical experiments based on finite difference approximations, but it is also shown that the results received here are consistent with recent laboratory experiments. The simulations within show that, depending on initial profile shape and other parameters, these circular profiles may evolve via long transients, which in a geological setting, may appear as noncircular stationary profiles.     

Circulation of the Venus upper mesosphere/lower thermosphere: Doppler wind measurements from 2001–2009 inferior conjunction,sub-millimeter CO absorption line observations

Sub-millimeter ¹²CO (346 GHz) and ¹³CO (330 GHz) line absorptions, formed within the mesospheric to lower thermospheric altitude (70–120 km) region of the Venus atmosphere, have been mapped across the nightside disk of Venus during 2001–2009 inferior conjunctions, employing the James Clerk Maxwell Telescope (JCMT). Radiative transfer analysis of these thermal line absorptions supports temperature and CO mixing profile retrievals, as described in a companion paper (Clancy et al., 2012). Here, we consider the analysis of the sharp line absorption cores of these CO spectra in terms of accurate Doppler wind profile measurements at 95–115 km altitudes versus local time (～8 pm–4 am) and latitude (～60N–60S). These Doppler wind measurements support determinations of the nightside zonal and subsolar-to-antisolar (SSAS) circulation components over a variety of timescales. The average behavior fitted from 21 retrieved maps of ¹²CO Doppler winds (obtained over hourly, daily, weekly, and interannual intervals) indicates stronger average zonal (85 m/s retrograde) versus SSAS (65 m/s) circulation at the 1 μbar pressure (108–110 km altitude) level. However, the absolute and relative magnitudes of these circulation components exhibit extreme variability over daily to weekly timescales. Furthermore, the individual Doppler wind measurements within each nightside mapping observation generally show significant deviations (20–50 m/s, averaged over 5000 km horizontal scales) from the simple zonal/SSAS solution, with distinct local time and latitudinal characters that are also time variable. These large scale residual circulations contribute 30–70% of the observed nightside Doppler winds at any given time, and may be most responsible for global variations in nightside lower thermospheric trace composition and temperatures, as coincidentally retrieved CO abundance and temperature distributions do not correlate with solution retrograde zonal and SSAS winds (see companion paper, Clancy et al., 2012). Limited comparisons of these nightside submillimeter results with dayside infrared Doppler wind measurements suggest distinct dayside versus nightside circulations, in terms of zonal winds in particular. Combined ¹²CO and ¹³CO Doppler wind mapping observations obtained since 2004 indicate that the average zonal and SSAS wind components increase by 50–100% between altitudes of 100 and 115 km. If gravity waves originating from the cloud levels are responsible for the extension of zonal winds into the thermosphere (Alexander, M.J. [1992]. Geophys. Res. Lett. 19, 2207–2210), such waves deposit substantial momentum (i.e., break) in the lower nightside thermosphere.     

Single element and competitive sorption of copper, zinc and lead onto a Luvisol profile

The sorption parameters of Cu, Zn and Pb are related to the composition of the different genetic horizons of a Luvisol profile in batch sorption experiments. The affinities of metals towards the soil samples from different horizons followed the same sequence, e.g. Pb≥C>>Zn. By far the highest metal retention was found in the C_k horizon due to the alkaline conditions. It is followed by the A horizon with its high organic matter content, while the lowest sorption capacity was found in the Bt horizon. In the horizons free of carbonate, primarily Pb and Cu were immobilized. The studied soil can be characterized by high amount of organic matter, clay accumulation horizon, as well as calcareous subsoil. This kind of profile development makes soils able to immobilize a significant metal pollution.     

Distribution and sorption of potentially toxic metals in four forest soils from Hungary

Metals of natural and anthropogenic origin behave differently in soils mostly due to their different mobility. In this study, sequential extractions and batch sorption experiments were performed to relate the fractionation of native Ni, Cu, Zn and Pb to the sorption properties of added metals in four soils with contrasting physiochemical characteristics. A significant effect due to sample composition on both the mobility and sorption characteristics of these metals was found. The efficiency of soil components in metal immobilization was in the order of carbonate > organic matter > swelling clay minerals. The partitioning of native metals together with the information gained through the sorption isotherms allows a deeper insight on the fate and behavior of metals in soils with various compositions.     

Distribution of brine in grain boundaries during static recrystallization in wet, synthetic halite: insight from broad ion beam sectioning and SEM observation at cryogenic temperature

We report observations from room temperature static recrystallization experiments (annealing times from minutes to year) of cold-pressed, synthetic, coarse-grained, wet sodium chloride, prepared by broad ion beam polishing and SEM observations at cryogenic temperature to observe directly the brine in grain boundaries. At all stages of annealing, the majority of the brine in the samples is connected in 2D sections along grain boundaries. Another part of the brine is in isolated brine inclusion arrays along grain boundaries and in brine inclusions left behind by migrating brine-filled grain boundaries. Most of these boundaries are mobile because the aggregate is coarsening. We interpret that the boundaries without observable brine films (<15 nm) and brine inclusion arrays are healed and immobile. Evolution of grain boundary structure involves three major processes. First, dissolution on one side of the grain boundary and precipitation on the other side, resulting in grain boundary migration. Second, the development of facets formed by low-index crystallographic planes of the grains bounding the grain boundary brine. When both sides of a grain boundary are able to develop low-index facets in a thick brine film, the resulting impingement boundary is interpreted to be immobile and may prevent the new grain from migrating into a deformed neighbor. When one side of a faceted boundary consists of low-index crystallographic planes and the other side passively follows this faceted shape along irrational surfaces, the boundary is mobile. Third, the healing of grain boundary brine films, producing solid–solid grain boundaries without resolvable brine films.     

The Mechanics of Rocking Stones: Equilibria on Separated Scales

Rocking stones, balanced in counter-intuitive positions, have always intrigued geologists. In our paper, we explain this phenomenon based on high-precision scans of pebbles which exhibit similar behavior. We construct their convex hull and the heteroclinic graph carrying their equilibrium points. By systematic simplification of the arising Morse–Smale complex in a one-parameter process, we demonstrate that equilibria occur typically in highly localized groups (flocks), the number of the latter being reliably observed and determined by hand experiments. Both local and global (micro and macro) equilibria can be either stable or unstable. Most commonly, rocks and pebbles are balanced on stable local equilibria belonging to stable flocks. However, it is possible to balance a convex body on a stable local equilibrium belonging to an unstable flock and this is the intriguing mechanical scenario corresponding to rocking stones. Since outside observers can only reliably perceive flocks, the last described situation will appear counter-intuitive. A comparison between computer experiments and hand experiments reveals that the latter are consistent, that is, the flocks can be reliably counted and the pebble classification system proposed in our previous work is robustly applicable. We also find an interesting logarithmic relationship between the flatness of pebbles and the average number of global equilibrium points, indicating a close relationship between classical shape categories and the new classification system.     

Geochemical,mineralogical and magnetic characteristics of vertical dust deposition in urban environment

Studies on composition and distribution of dust deposition are necessary for the risk assessment of dust to atmospheric quality. We studied the vertical distribution pattern of dust and metal (Cu, Fe, Pb, Zn) deposition up to 33 m height in urban environment. Integrated geochemical, mineralogical and magnetic study of the seasonally sampled dust helped to specify our knowledge on the use of magnetic susceptibility for tracking its deposition. Harmful dust and metal deposition may occur even at great heights and at the low-traffic side of buildings. Re-suspension of local surface materials dominates the dust deposition primarily in summer and spring due to weather conditions, and it may overwrite the influence of recent anthropogenic activities on dust composition. The accepted air-flow models should be modified by taking the local conditions (weather, morphology, etc.) into account. All studied metals showed strong enrichment in the dust and could be characterized by similar vertical deposition pattern to dust. The total susceptibility was found to be much more useful proxy for tracking dust and metal deposition than mass-specific susceptibility. Using the former, potential errors arising from sampling practice of settled dust could be eliminated. The most important heavy-metal-bearing phases were iron oxides and clay minerals. Their different behavior during the dust deposition is reflected by the vertical metal distribution patterns. Clay minerals originate primarily from re-suspension and may be one of the most important sources of potentially mobile heavy metals in such materials.     

Upper limits for H2SO4 in the mesosphere of Venus

Rapid temporal variability of SO₂ and SO in the Venus 85–100 km mesosphere (Sandor, B.J., Clancy, R.T., Moriarty-Schieven G.H. [2007]. Bull. Am. Astron. Soc. 39, 503; Sandor, B.J., Clancy, R.T., Moriarty-Schieven, G.H., Mills, F.P. [2010]. Icarus 208, 49–60) requires in situ sources and sinks for these molecules. While many loss mechanisms are recognized, no process for in situ production is known. Observational investigations to find, or constrain other potential sulfur reservoirs offer one method toward understanding the applicable photochemistry. Here, we report upper limits for gas-phase H₂SO₄ (sulfuric acid) abundances in Venus’ 85–100 km upper mesosphere, derived from 16 ground-based sub-mm spectroscopic observations in the period 2004–2008. Unlike the ubiquitous sulfuric acid solid/liquid aerosol, the gas phase would be photochemically active, potentially both source and sink for SO and SO₂. H₂SO₄ is retrieved from sub-mm lines located in the same bandpass as the SO₂ and SO lines described by Sandor et al. (Sandor, B.J., Clancy, R.T., Moriarty-Schieven, G.H., Mills, F.P. [2010]. Icarus 208, 49–60). H₂SO₄ upper limits reported here are thus simultaneous and spatially coincident with measurements of SO₂ and SO, providing for analysis of the three sulfur species collectively. The average H₂SO₄ abundance over 16 observations is 1 ± 2 ppb (i.e. <3 ppb). Upper limits for individual observations range from 3 to 44 ppb, where quality of the observing weather is the dominant constraint on measurement precision. The sum of H₂SO₄, SO₂ and SO varies widely. In one comparison, the sum [H₂SO₄ + SO₂ + SO] measured on one date differs by 10-σ from the sum measured 2 months later. We conclude that upper mesospheric sulfur atoms are not conserved among the three molecules, that H₂SO₄ is not a significant sulfur reservoir for balancing the observed variations of [SO₂ + SO], and is not relevant to the (still unknown) photochemistry responsible for observed behavior of SO₂ and SO. Having ruled out H₂SO₄, we infer that elemental sulfur is the most probable candidate for the needed third reservoir.     

Factors triggering landslide occurrence on the Zemun loess plateau,Belgrade area,Serbia

Among the numerous factors that trigger landslide events, the anthropogenic impact caused by inadequate planning and faulty land use in urban areas is increasing. The Zemun settlement on the northern outskirts of Belgrade has experienced a number of landslides in the last three decades, endangering buildings and roads, and claiming human lives, particularly in the case of the 2010/2011 landslides. Selected meteorological parameters were used to calculate rainfall erosivity indices such as Precipitation Concentration Index and Modified Fournier Index over the period 1991–2015. Drought indices, Lang aridity index and Palfai Drought Index were calculated as well. Mann–Kendall trend test was applied to identify potential rising and/or declining trends both in meteorological parameters and calculated indices. Trend analysis of the annual and seasonal scales yielded a statistically significant trend in the spring time series. Stable arid and pronounced drought conditions were recorded. The modified Fournier index based on monthly mean values yields moderate aggressiveness, with several extreme values indicating very high erosivity classes, especially for 2010/2011. The geological substrate is predominantly loess and hence highly susceptible to erosion and slope failure when climatological conditions are suitable. Accelerated urbanization at the end of the last century reduced vegetation cover, intensified pressure on the vertical loess slope, and lacked suitable rain drainage systems so that surface-water runoff was directed into the porous loess, thereby endangering slope stability. We proposed a geomorphic model to describe the nature of the erosional processes on the loess cliffs of the Zemun loess plateau. Results from this study have implications for mitigation strategies.     

A post-IR IRSL chronology and dust mass accumulation rates of the Nosak loess-palaeosol sequence in northeastern Serbia

In the Middle Danube Basin, Quaternary deposits are widely distributed in the Vojvodina region where they cover about 95% of the area. Major research during the last two decades has been focused on loess deposits in the Vojvodina region. During this period, loess in the Vojvodina region has become one of the most important Pleistocene European continental climatic and environmental records. Here we present the dating results of 15 samples taken from the Nosak loess-palaeosol sequence in northeastern Serbia in order to establish a chronology over the last three glacial–interglacial cycles. We use the pIRIR₂₉₀ signal of the 4–11 μm polymineral grains. The calculated ages are within the error limits partially consistent with the proposed multi-millennial chronostratigraphy for Serbian loess. The average mass accumulation rate for the last three glacial–interglacial cycles is 265 g m⁻² a⁻¹, which is in agreement with the values of most sites in the Carpathian Basin. Our results indicate a highly variable deposition rate of loess, especially during the MIS 3 and MIS 6 stages, which is contrary to most studies conducted in Serbia where linear sedimentation rates were assumed.