Laboratory experiments have been carried out to investigate the uptake of sulfur dioxide by water drops containing heavy metal ions where the metal ions serve as catalysts to oxidise the taken up S(IV) into S(VI). During the gas uptake the drops were freely suspended at their terminal velocity in the airstream of the Mainz vertical wind tunnel. Two series of experiments were carried out, one with large millimeter size water drops containing manganese or iron ions, and the other with small water drops containing manganese ions and having radii in hundreds of micron size range. The experimental results were compared against model computations using the Kronig–Brink model and the fully mixed model, modified for the case that heavy metal ions present in the liquid phase act as catalysts for the oxidising process. The results of the model calculations show that there are only small differences between the predicted gas uptake according to the two models. In addition it was found that the experimental obtained results from the uptake of SO2 by water drops containing heavy metal ions for both, large and small water drops did agree with the model results. 相似文献
The physical processes of raindrop impact and water flow on the leaves and branches of selected tropical tree species were examined under laboratory conditions using simulated rainfall. Inclined branches were found to be particularly efficient in detaining impacting water droplets. This efficiency in raindrop detention increases linearly as a function of branch inclination on branches that are initially dry. On branches that have been thoroughly wetted, this increase in raindrop detention with branch inclination is best expressed as a logarithmic function. At branch inclinations of 60° above the horizontal, the quantity of branchflow was found to be > 80 per cent of the total quantity of impacting rainfall, indicating that < 20 per cent was lost to rainsplash. The strong positive relationship between branchflow and branch inclination explains why trees with large projected areas of steeply inclined upthrust branches have significant quantities of intercepted water draining from their branches and trunks under heavy rainfall conditions. This drainage from the woody frame of trees influences surficial processes by generating both stemflow and large throughfall droplets. 相似文献
Streamers were injected into a large population of small droplets, of radii about 20 m, confined to a given region of pre-determined shape on a photographic film, and situated in a gap between which a variable electric field can be applied. Results showed that the droplet region behaves like a dipole discharging from both ends if its inclination to the electric field is less than 45° and the field is not less than –230 kV/m at atmospheric pressure.We deduced that streamer intensification will occur at relatively low fields if there exists pockets of large number density of small droplets. 相似文献
Forest canopies present irregular surfaces that alter both the quantity and spatiotemporal variability of precipitation inputs. The drop size distribution (DSD) of rainfall varies with rainfall event characteristics and is altered substantially by the forest stand properties. Yet, the influence of two major European tree species, European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H. Karst), on throughfall DSD is largely unknown. In order to assess the impact of these two species with differing canopy structures on throughfall DSD, two optical disdrometers, one above and one below the canopy of each European beech and Norway spruce, measured DSD of both incident rainfall and throughfall over 2 months at a 10‐s resolution. Fractions of different throughfall categories were analysed for single‐precipitation events of different intensities. While penetrating the canopies, clear shifts in drop size and temporal distributions of incoming rainfall were observed. Beech and spruce, however, had different DSD, behaved differently in their effect on diameter volume percentiles as well as width of drop spectrum. The maximum drop sizes under beech were higher than under spruce. The mean ± standard deviation of the median volume drops size (D50) over all rain events was 2.7 ± 0.28 mm for beech and 0.80 ± 0.04 mm for spruce, respectively. In general, there was a high‐DSD variability within events indicating varying amounts of the different throughfall fractions. These findings help to better understand the effects of different tree species on rainfall partitioning processes and small‐scale variations in subcanopy rainfall inputs, thereby demonstrating the need for further research in high‐resolution spatial and temporal properties of rainfall and throughfall. 相似文献
On March 16–17, 2008, a sea fog occurred in Dianbai in the west of Guangdong Province and was accompanied by a high-pressure synoptic system. Using comprehensive observation datasets, this study analyzes the evolution of liquid water content during this sea fog and investigates the relationships between liquid water content and the average diameters and count densities of fog droplets, air temperature, wind speed and turbulence exchanges. The main results are presented as follows. (1) The sea fog showed a quasi-periodic oscillation characteristic, i.e., it developed, disappeared and then developed again. (2) During the sea fog, the number of fog droplets changed significantly while the changes in average diameter of the fog droplets were relatively small. The development and disappearance of the sea fog correlated significantly with the fog droplet numbers. (3) The air-cooling mechanism played a significant role in sea fog formation and development. However, the influences of this mechanism were not evident during fog persistence. (4) During sea fog formation, weak turbulence exchanges were helpful for fog formation. During sea fog development and persistence, liquid water content increased when turbulence exchanges weakened, and vice versa. The changes in turbulence exchanges were closely related to the quasi-periodic oscillations observed in sea fog presence. 相似文献
This paper describes the internal organisation of two diatremes (Águas Emendadas and Neuzinha) and one small breccia-filled conduit (Tigre) in the central portion of the Late Cretaceous Goiás Alkaline Province (GAP), central Brazil, and explores the criteria for facies recognition. The GAP kamafugitic diatremes are emplaced into Carboniferous sandstones of the Aquidauana Formation, at the northern margin of the Paraná Basin. They are usually elliptical structures, not longer than 900 m, filled with breccia and partially covered by thin kamafugitic to basanitic lava flows. The breccias are dominated by juvenile pyroclasts, with subordinate amounts of cognate fragments and xenoliths. In addition to variations in ash and lapilli proportions, juvenile fragment types may be used to discriminate genetic processes and the corresponding pyroclastic deposits.
An extensive field, textural and compositional dataset was analysed by multivariate statistical techniques. Combined with field observations, this allowed us to define a set of facies for kamafugitic diatremes, and, more importantly, to understand the internal structure of the studied bodies and to cross-correlate them. Seven distinct facies were recognised. The Fluidised Conduit Facies (FCF) represents high-energy, strongly fluidised but only moderately fragmented systems. It occurs in a confined environment, and is typical of deeper parts of the conduit, before the actual diatreme level is reached by the ascending fluidised magma. Large amounts of spinning droplets are formed within this region. The Fluidised Conduit–Diatreme Facies (FCDF) is characteristic of intermediate depths in the conduit, where highly fluidised and highly fragmented systems produce large amounts of ash. Spinning droplets decrease in abundance, ordinary juvenile fragments become very common, and xenoliths from the country rock in the immediate vicinity of the diatreme are present. The Fluidised Fragmented Facies (FFF) and the Magmatic Fluidised Facies (MFF) produce very heterogeneous deposits that dominate the shallower part of the system, making up most of the diatreme-filling materials. The Fluidised Fragmented Facies can be distinguished by much higher degrees of fluidisation, fragmentation and system energy. It occupies the internal part of the diatreme and is characterised by the common presence of tuff pockets, tuff fragments, and accretionary and armoured lapilli. The Magmatic Fluidised Facies typically occupies the outer portion of the diatreme and can be distinguished from the Fluidised Fragmented Facies by the dominance of lapilli over ash and by the presence of abundant wrapped fragments. The Magmatic Facies (MF) and the Coherent Magmatic Facies (CMF) are volumetrically subordinate and represent late stages, when less fluidised and less fragmented material, or even coherent magma erupts relatively passively, in the aftermath of the main explosive stage that generated the diatreme. The Border Facies is defined by the increased abundance of material from the immediate country rock. At Águas Emendadas and Neuzinha this facies is marked by the presence of fragments of peperite-like rock, formed by the interaction of the fluidised magma with friable sandstone. 相似文献