Effect of Moisture on Attraction Force in Beach Sand

Beach sands located above the sea water level exist in an unsaturated, rather than a fully saturated or dry state. Within the unsaturated zone, a steep excavated surface can be sustained for some unknown but finite time, and some slopes may remain stable for extended time periods due to capillary forces. These observations clearly indicate small but nonzero values for attraction strength (tensile strength and cohesion) in unsaturated beach sands, especially apparent but not confined to settings where there are low stress levels. Thus, experiments were carried out to quantify the magnitude of attraction strength in moist sands (D_r = 30%) and to examine the variation of these values as a function of moisture content and presence of a small amount of fines. Tensile strength, which is significantly different from zero, increases with increasing moisture content and fines. However, the influences of fines on the tensile strength are substantially dependent on the water content. Apparent cohesion strength is also identified in moist sands. A simple relationship between tensile strength and apparent cohesion is proposed using the obtained data. This study would help to further understand the phenomenon of stability of beach sands.     

Influence of biological and environmental factors on hepatic steroid and xenobiotic metabolism in fish: interaction with PCB and β-naphthoflavone

The degree of induction of hepatic cytochrome P-450 monooxygenases in fish by various chemicals may vary owing to many factors such as sex, sexual maturity, age, season and environmental temperature. In the present investigation the influences of gonadal steroids and water temperature on the inductive response were studied. The data indicate that gonadal steroids and water temperature modulate the response of the cytochrome P-450 system in rainbow trout to PCB and β-naphthoflavone.     

Modelling the Baltic Sea ocean climate on centennial time scale: temperature and sea ice

This study considers the possible use of different kinds of forcing datasets in Baltic Sea ocean climate modelling on centennial time scales, in particular for the past half millennium. We demonstrate that high-quality station data of the past century and gridded multi-proxy reconstructions for the past 500 years can be used with great success but with various levels of detail. We also demonstrate that output data from the state-of-the-art global climate model EcHo-G are not suitable for modelling the Baltic Sea ocean climate. Two climate properties were studied: the annual maximum ice extent (MIB) and the vertically and horizontally integrated annual water temperature. Centennial time scale results indicate that the seventeenth and nineteenth centuries were the coldest centuries, while the 1690s were the coldest decade and 1695 the coldest year in the last 500 years. The results also indicate that the twentieth century was the warmest century with the least MIB of the last 500 years. On a decadal time scale, the 1990s, 1930s and 1730s were the warmest decades and comparable in terms of both water temperature and MIB. The year 1989 had the minimum observed MIB of only 52,000 km², implying that the Baltic Sea has been partly ice covered in all winters of the past half millennium. Even though different climate forcing mechanisms may operate on the climate system today compared to over the last half millennium, this study cannot clearly state that the region is experiencing climate change outside the natural limits of the past 500 years.     

Soil-precipitation feedbacks during the South American Monsoon as simulated by a regional climate model

We summarize the recent progress in regional climate modeling in South America with the Rossby Centre regional atmospheric climate model (RCA3-E), with emphasis on soil moisture processes. A series of climatological integrations using a continental scale domain nested in reanalysis data were carried out for the initial and mature stages of the South American Monsoon System (SAMS) of 1993–92 and were analyzed on seasonal and monthly timescales. The role of including a spatially varying soil depth, which extends to 8 m in tropical forest, was evaluated against the standard constant soil depth of the model of about 2 m, through two five member ensemble simulations. The influence of the soil depth was relatively weak, with both beneficial and detrimental effects on the simulation of the seasonal mean rainfall. Secondly, two ensembles that differ in their initial state of soil moisture were prepared to study the influence of anomalously dry and wet soil moisture initial conditions on the intraseasonal development of the SAMS. In these simulations the austral winter soil moisture initial condition has a strong influence on wet season rainfall over feed back upon the monsoon, not only over the Amazon region but in subtropical South America as well. Finally, we calculated the soil moisture–precipitation coupling strength through comparing a ten member ensemble forced by the same space–time series of soil moisture fields with an ensemble with interactive soil moisture. Coupling strength is defined as the degree to which the prescribed boundary conditions affect some atmospheric quantity in a climate model, in this context a quantification of the fraction of atmospheric variability that can be ascribed to soil moisture anomalies. La Plata Basin appears as a region where the precipitation is partly controlled by soil moisture, especially in November and January. The continental convective monsoon regions and subtropical South America appears as a region with relatively high coupling strength during the mature phase of monsoon development.     

Phase partitioning of aerosol particles in clouds at Kleiner Feldberg

The partitioning of aerosol particles between cloud droplets and interstitial air by number and volume was determined both in terms of an integral value and as a function of size for clouds on Mt. Kleiner Feldberg (825 m asl), in the Taunus Mountains north-west of Frankfurt am Main, Germany. Differences in the integral values and the size dependent partitioning between two periods during the campaign were observed. Higher number and volume concentrations of aerosol particles in the accumulation mode were observed during Period II compared to Period I. In Period I on average 87±11% (±one standard deviation) and 73±7% of the accumulation mode volume and number were incorporated into cloud droplets. For Period II the corresponding fractions were 42±6% and 12±2% in one cloud event and 64±4% and 18±2% in another cloud event. The size dependent partitioning as a function of time was studied in Period II and found to have little variation. The major processes influencing the partitioning were found to be nucleation scavenging and entrainment.     

Computer modelling of clouds at Kleiner Feldberg

The airflow, cloud microphysics and gas- and aqueous-phase chemistry on Kleiner Feldberg have been modelled for the case study of the evening of 1 November 1990, in order to calculate parameters that are not easily measured in the cloud and thus to aid the interpretation of the GCE experimental data-set. An airflow model has been used to produce the updraught over complex terrain for the cloud model, with some care required to ensure realistic modelling of the strong stable stratification of the atmosphere. An extensive set of measurements has been made self-consistent and used to calculate gas and aerosol input parameters for the model. A typical run of the cloud model has calculated a peak supersaturation of 0.55% which occurs about 20 s after entering cloud where the updraught is 0.6 m s^–1. This figure has been used to calculate the efficiency with which aerosol particles were scavenged; it is higher than that calculated by other methods, and produces a cloud with slightly too many droplets. A broad cloud droplet size spectrum has been produced by varying the model inputs to simulate turbulent mixing and fluctuations in cloud parameters in space and time, and the ability of mixing processes near cloud-base to produce a lower peak supersaturation is discussed. The scavenging of soluble gases by cloud droplets has been observed and departures from Henry's Law in bulk cloud-water samples seen to be caused by variation of pH across the droplet spectrum and the inability of diffusion to adjust initial distributions of highly soluble substances across the spectrum in the time available. Aqueous-phase chemistry has been found to play a minor role in the cloud as modelled, but circumstances in which these processes would be more important are identified.     

NaCl Aerosol Particle Hygroscopicity Dependence on Mixing with Organic Compounds

Organic compounds in the atmosphere can influence the activation, growth and lifetimes of haze, fog and cloud droplets by changing the condensation and evaporation rates of liquid water by these aqueous aerosol particles. Depending on the nature and properties of the organic compounds, the change can be to enhance or reduce these rates. In this paper we used a tandem differential mobility analyzer (TDMA) to examine the effect of tetracosane, octanoic acid, and lauric acid on the hygroscopic properties of NaCl aerosol particles at relative humidities (RH) between 30 and 95%. These organic compounds have been identified in ambient aerosol particle samples. A slight lowering of the deliquescence relative humidity (DRH) and suppression of hygroscopic growth for the NaCl-organic compound mixtures were observed when compared to pure NaCl particles. The growth of pure NaCl particles was 2.25 in diameter at 85% RH while the growth of the mixed particles was 1.3 to 1.7 in particle diameter at 85% RH with organic mass fraction of 30–50%. This shows that these organic compounds have to be present in rather large mass fractions to effect the hygroscopic behavior to a similar degree observed for ambient aerosol during field measurements. Despite the mixing of the organic material with NaCl, hysteresis was observed for decreasing RH histories, suggesting the formation of metastable droplets. These laboratory results are strikingly similar to ambient field results. For example, if the total organic mass fraction of the particles is between 0.30 and 0.50, the particle growth at 85% RH is about a factor of 1.4 for the laboratory and field measurements. Such reduction in growth compared to the pure inorganic salt is in contradiction to speculations concerning significant effects by organic compounds on cloud condensation nuclei and thus formation on clouds.     

Sixty year10Be record from Greenland and Antarctica

We report in this study the distribution of¹⁰Be in the top 40 m of the Renland ice core (East Greenland) and in a 30 m long core from DML (Dronning Maud Land, Antarctica) for the period 1931–1988. The two sites show differences in¹⁰Be content, the Antarctica site showing smaller variance and a lower average¹⁰Be annual flux. Similarly, the average accumulation rate (cm water equivalent year⁻¹) is higher in the Renland relative to DML. The variability in accumulation (precipitation) rates seems to explain part of the difference in¹⁰Be flux between the two polar sites. Cyclic fluctuations of¹⁰Be flux correlate with the 11-year sunspot number and cosmic ray intensity than with the aa index (perturbation of the geomagnetic activity by the solar wind). Our data corroborate¹⁰Be cyclic fluctuation pattern from the Dye 3 ice core and confirm a promising potential for correlation of global and local events.     

Hygroscopicity of pre-existing particle distribution and formation of cloud droplets: a model study

The effects of the hygroscopicity of a pre-existing particle distribution and condensation of nitric acid on cloud droplet formation were studied by using an air parcel and multicomponent condensation model. The pre-existing particle distribution used is a bimodal distribution in which the particles are assumed to be internally mixed, i.e. they are composed partly from ammonium nitrate salt and partly from some insoluble substance. The mean diameters of the distributions and the mass fraction of soluble salt were varied in the simulations. Generally, the number of activated cloud droplets was found to be increased, when the initial mass fraction of salt (i.e. the initial amount of salt) was increased. However, the effects of increased initial amount of salt on the cloud droplet formation were not straightforward in all cases studied. The effects of the condensing hygroscopic substance, with initial nitric acid concentrations of 0.1, 1.0 and 10.0 ppbv on the activation of cloud droplets were also studied. The number of activated droplets increased when the initial concentration of nitric acid was increased.