Numerical study of the cloud seeding effects

The microphysical model with the bulk water parameterization is applied to simulated both contact and deposition nucleation as well as the imersion freezing for unseeded cases and the cases immediately after seeding performed for the cold continental Cb clouds with small cloud droplets. The injection of agent AgI is performed in temperature region between –8°C and –12°C. The four groups of sensitivity experiments are executed.

An assessment of global and regional climate change based on the EH5OM climate model ensemble

An analysis of climate change for global domain and for the European/Mediterranean region between the two periods, 1961–1990 (representing the twentieth century or “present” climate) and 2041–2070 (representing future climate), from the three-member ensemble of the EH5OM climate model under the IPCC A2 scenario was performed. Ensemble averages for winter and summer seasons were considered, but also intra-ensemble variations and the change of interannual variability between the two periods. First, model systematic errors are assessed because they could be closely related to uncertainties in climate change. A strengthening of westerlies (zonalization) over the northern Europe is associated with an erroneous increase in MSLP over the southern Europe. This increase in MSLP is related to a (partial) suppression of summer convective precipitation. Global warming in future climate is relatively uniform in the upper troposphere and it is associated with a 10% wind increase in the subtropical jet cores. However, spatial irregularities in the low-level temperature signal single out some regions as particularly sensitive to climate change. For Europe, the largest near-surface temperature increase in winter is found over its north-eastern part (more than 3°C), and the largest summer warming (over 3.5°C) is over south Europe. For south Europe, the increase in temperature averages is almost an order of magnitude larger than the increase in interannual variability. The magnitude of the warming is larger than the model systematic error, and the spread among the three model realisations is much smaller than the magnitude of climate change. This further supports the significance of estimated future temperature change. However, this is not the case for precipitation, implying therefore larger uncertainties for precipitation than for temperature in future climate projections.     

Cluster analysis of tropical cyclone tracks in the Southern Hemisphere

A probabilistic clustering method is used to describe various aspects of tropical cyclone (TC) tracks in the Southern Hemisphere, for the period 1969–2008. A total of 7 clusters are examined: three in the South Indian Ocean, three in the Australian Region, and one in the South Pacific Ocean. Large-scale environmental variables related to TC genesis in each cluster are explored, including sea surface temperature, low-level relative vorticity, deep-layer vertical wind shear, outgoing longwave radiation, El Niño-Southern Oscillation (ENSO) and the Madden-Julian Oscillation (MJO). Composite maps, constructed 2 days prior to genesis, show some of these to be significant precursors to TC formation—most prominently, westerly wind anomalies equatorward of the main development regions. Clusters are also evaluated with respect to their genesis location, seasonality, mean peak intensity, track duration, landfall location, and intensity at landfall. ENSO is found to play a significant role in modulating annual frequency and mean genesis location in three of the seven clusters (two in the South Indian Ocean and one in the Pacific). The ENSO-modulating effect on genesis frequency is caused primarily by changes in low-level zonal flow between the equator and 10°S, and associated relative vorticity changes in the main development regions. ENSO also has a significant effect on mean genesis location in three clusters, with TCs forming further equatorward (poleward) during El Niño (La Niña) in addition to large shifts in mean longitude. The MJO has a strong influence on TC genesis in all clusters, though the amount modulation is found to be sensitive to the definition of the MJO.     

Analysis of the Saharan dust regional transport

Summary The Balkan Peninsula is situated in the impact zone of Saharan dust storms. The case of Saharan dust transport to Belgrade in the period of 14–17 April 1994 is analyzed using the Eta model for synoptic and meso scale processes. Air back trajectories are calculated at six model levels from 434 up to 5129m with horizontal grid resolutions of 1°×1° and 10×10. Following cyclonic circulation the dust was picked up from North Africa, and transported over Mediterranean. Simultaneously, according to the analysis of the three lowest trajectories, transport of trace metals from Macedonia and southern Serbia by the Koshava wind might be dominant in the observed episode. Turbulent flow enhanced the coagulation process of initially clean dust particles with particles containing Pb and Cd. The coagulation and scavenging processes below and in clouds increased deposition rates of Pb and Cd in Belgrade in the course of wet removal, and consequently trough resuspension processes. Dry deposition samples contained characteristic particles up to 30µm in diameter with Fe content of 11 to 15 atomic% and significant ratio Si/Fe of 3 to 5, determined for selected single particles by the SEM/EDX method. Following dry and wet deposition of Cd and Pb, a residual effect of dustfall is noticed throughout the vegetational period.     

Fluctuations and trends of annual precipitation in different climatic regions of Croatia

Summary Secular series of annual precipitation over Croatia have been studied at three stations representing the different climatic regions of Croatia: Osijek (continental precipitation climate), Zagreb-Gri (continental precipitation climate with maritime influence) and Crikvenica (maritime precipitation climate).The time series analysis has been deduced by using a quick test for stationarity according to Schönwiese and Malcher, moving average filters, the Mann-Kendall rank statistic, and a progressive test for trend according to Sneyers. From this analysis, the stationarity in time series of annual precipitation totals is stated over the entire interval at all locations except for a very short interval during the first decade of the twentieth century over the continental lowland (Osijek). A generally decreasing trend is present over the entire interval, but is statistically significant only in the continental lowland (Osijek).With 4 Figures     

Physical properties and the chemical composition of sphalerites from Yugoslavia

Chemical and spectral analyses are given for 16 sphalerites from Yugoslavia. Since they were formed under various conditions the content of Fe and other metals (Mn and Cd especially) varies widely. The relation between the dimensions of elementary cell and the molar percent of FeS in the sphalerites of Yugoslavia shows only slight differences from Vegard's rule. The indices of refraction and reflectivity as well as dispersion for the wavelengths 440, 460, 480, 500, 540, 580, 620, and 660 nm were measured. For the wavelengths mentioned, diagrams are given showing the relation between reflectivity and microhardness of sphalerite and its chemical composition.

---

Zusammenfassung Für 16 jugoslawische Zinkblenden wurde die chemische Zusammensetzung und spektralanalytisch der Gehalt an Spurenelementen ermittelt. Da die Zinkblenden unter sehr verschiedenen Bedingungen entstanden, schwankt ihr Gehalt an Fe und anderen Metallen, besonders Mn und Cd stark. Die Verhältnisse zwischen der Größe der Elementarzelle und den Molprozenten von FeS zeigen nur geringe Abweichungen von der Vegard-Regel. Für die Wellenlängen 440, 460, 480, 500, 540, 580, 620 und 660 nm wurden Refraktionsindices, Absorptionskoeffizient und Reflexionsvermögen ermittelt. Die Beziehungen zwischen Reflexionsvermögen, Mikrohärte und chemischer Zusammensetzung werden in Diagrammen dargestellt.

     

Synthesis and characterization of high-pressure and high-temperature sphene (CaTiSiO5)

Sphene (CaTiSiO₅), a calcium titanosilicate ceramic has been prepared from a powder mixture of CaCO₃, TiO₂ and SiO₂ using vibro-milling for homogenization and activation of precursors. During the high-pressure and high-temperature synthesis (HPS) process at 4 GPa and 1,200 °C, sphene undergoes into phase transition, from room-temperature phase P2₁ /a to high-temperature phase A2/a. Evidence of that structural phase transition is given in this paper using infrared, Raman spectroscopy and X-ray powder diffraction. Rietveld refinement was employed to get the structural information of the synthesized powder. The most important structural change due to phase transition, the disappearance of the characteristic out-of-center distortion of the Ti atom and moving to the center of octahedra, was confirmed. HPS is an effective method for producing full-dense ceramics without any additives. Reduction of particle size occurred during high-pressure compaction. Microstructure and particle size of both phases were analyzed by scanning electron microscopy.     

Recrystallization mechanisms of fergusonite from metamict mineral precursors

The metamict state and recrystallization of fergusonite in metamict natural samples were studied by thermal methods (TGA-DTA), X-ray powder diffraction (XRD), Raman spectroscopy (RS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and electron microprobe (EPMA). Two metamict mineral samples of fergusonite were investigated in order to identify the original premetamict crystal structure and to identify recrystallization mechanisms. The TEM data and RS provided evidence on the partial preservation of the original structure in the investigated minerals, which are X-ray amorphous. It was shown that fergusonite could recrystallize from a metamict mineral with original fergusonite structure or from metamictized pyrochlore, which was altered before or after metamictization. Two recrystallization mechanisms were recognized: (a) epitaxial growth occurring at the boundary between preserved premetamict structure fragments and completely metamictized areas, and (b) nucleation-crystal growth mechanism occurring in completely amorphous areas of the minerals, and resulting in recrystallization of the original mineral as well as in the crystallization of a new mineral with a modified chemical composition as compared to the initial matrix.     

The effect of coherency stress on the mechanism of the reaction albite+K+⇌K-feldspar+Na+ and on the mechanical state of the resulting feldspar

Coherency stress and coherency strain energy generated by Na⁺?K⁺ ion exchange in alkali feldspars are calculated using an isotropic model, and deformation of single crystals of alkali feldspars exposed to molten alkali chlorides at \(P_{H_2 O} \) < 1 bar is described. Coherency stress in alkali feldspars can reach 10–20 kb. When it is large, partial relaxation by fracture and/or plastic deformation takes place under anhydrous conditions, but temporary build-up of stress is unavoidable even under hydrothermal conditions. Because of coherency strain energy, a thin layer of an end-member alkali feldspar produced by cation exchange on a grain of the other end-member alkali feldspar would be unstable with respect to dissolution. Therefore, under hydrothermal conditions one end-member alkali feldspar replaces the other by dissolution and precipitation. The mechanism of the reaction $$Na_x K_{1 - x} AlSi_3 O_{8_{(feld.)} } + yK^ + \rightleftharpoons Na_{x - y} K_{1 + y - x} AlSi_3 O_{8_{(feld.)} } + yNa^ + $$ is primarily controlled by \(P_{H_2 O} \) and by ΔK/(Na + K), the difference between the equilibrium value and the initial value of the atomic K/(Na + K) ratio of the feldspar. When ¦ΔK/(Na + K)¦ is small, the reaction proceeds by cation exchange. When ¦ΔK/(Na + K)¦ is large, cation exchange still occurs if \(P_{H_2 O} \) is very low, but under hydrothermal conditions replacement by dissolution and precipitation occurs.     

Rotation axes of asteroids: Results for 14 objects

In this paper results of determinations of the rotation axis direction (as given by ecliptic coordinates of its intersection with geocentric celestial sphere) for 14 asteroids are presented for which a sufficient number of good observations are available. The calculation is performed by using the improved amplitude-magnitude method developed by V. Zappalà, M. Di Martino, P. Farinella, and P. Paolicchi (1983, In Asteroids, Comets, Meteors, pp. 73–76). Additionally, an improvement of the method is described regarding a weighting procedure. Whenever possible, the results are compared with already existing data, coming from other methods (mainly from photometric astrometry). In general, very good agreement was found, which can be considered as strongly encouraging for further application of the adopted procedure. Some preliminary approaches for a statistical investigation are given.