A high-quality monthly total cloud amount dataset for Australia

A high-quality monthly total cloud amount dataset for 165 stations has been developed for monitoring and assessing long-term trends in cloud cover over Australia. The dataset is based on visual 9 a.m. and 3 p.m. observations of total cloud amount, with most records starting around 1957. The quality control process involved examination of historical station metadata, together with an objective statistical test comparing candidate and reference cloud series. Individual cloud series were also compared against rainfall and diurnal temperature range series from the same site, and individual cloud series from neighboring sites. Adjustments for inhomogeneities caused by relocations and changes in observers were applied, as well as adjustments for biases caused by the shift to daylight saving time in the summer months. Analysis of these data reveals that the Australian mean annual total cloud amount is characterised by high year-to-year variability and shows a weak, statistically non-significant increase over the 1957–2007 period. A more pronounced, but also non-significant, decrease from 1977 to 2007 is evident. A strong positive correlation is found between all-Australian averages of cloud amount and rainfall, while a strong negative correlation is found between mean cloud amount and diurnal temperature range. Patterns of annual and seasonal trends in cloud amount are in general agreement with rainfall changes across Australia, however the high-quality cloud network is too coarse to fully capture topographic influences. Nevertheless, the broadscale consistency between patterns of cloud and rainfall variations indicates that the new total cloud amount dataset is able to adequately describe the broadscale patterns of change over Australia. Favourable simple comparisons between surface and satellite measures of cloudiness suggest that satellites may ultimately provide the means for monitoring long-term changes in cloud over Australia. However, due to the relative shortness and homogeneity problems of the satellite record, a robust network of surface cloud observations will be required for many years to come.     

In Situ Destruction of Perchlorate and Nitrate Using Gaseous Electron Donor Injection Technology

Perchlorate and nitrate in vadose‐zone soil can be continuing sources of groundwater contamination and technologies for remediation of these sources are limited. Gaseous electron donor injection technology (GEDIT) is an in situ approach that was demonstrated at a site in California. A mixture of hydrogen, carbon dioxide, liquefied petroleum gas (LPG), and nitrogen was injected into the vadose zone over a period of 5 months followed by 3 months of LPG alone. Perchlorate and nitrate plus nitrite nitrogen concentrations were reduced by over 90% and both were capable of being reduced to nondetectable concentrations. Hydrogen was required for perchlorate destruction, although concentrations as low as 0.5% were effective. Hydrogen was not required for nitrate destruction. Contaminant destruction was observed in both fine‐grained and coarse‐grained soils ranging from clay to gravel. Hydrogen was an effective electron donor because of its low molecular weight and high diffusivity which likely promoted its penetration into low‐permeability formations. Contaminant destruction was also observed in moisture contents ranging from 6.8% to 36% demonstrating that GEDIT was effective in low‐ and high‐moisture soils. The radius of influence (ROI) for perchlorate destruction was approximately 3.0 to 4.6 m while that for nitrate was greater than 17 m. The ROI was limited by use of a single injection location. Use of a grid injection system is anticipated to greatly increase efficiency. This research represents the first demonstration of GEDIT for treatment of contaminants in the vadose zone.     

A Simplified Approach to Bridge Substructure Design

Strut-and-tie modeling is an analysis and design tool for reinforced concrete elements in which it may be assumed that internal stresses are transferred through a truss mechanism. The tensile ties and compressive struts serve as truss members connected by nodal zones. The internal truss idealized by the strut-and-tie model implicitly account for the distribution of both flexure and shear. In 1998, the AASHTO LRFD Bridge Specifications (1998) incorporated the strut-and-tie modeling procedure for the analysis and design of deep reinforced concrete members where sectional design approaches are not valid. In most instances, hammerhead piers can be defined as deep reinforced concrete members and therefore, should be designed using the strut-and-tie modeling approach. However, most bridge designers have not embraced the strut-and-tie model due to the unfamiliarity with the design procedure, the inability to check the truss model??s validity (without laboratory tests or a finite element model), and the time it takes to complete the strut-and-tie model analysis and design. Therefore, with the formulation of a well-defined strut-and-tie modeling procedure, practicing engineers will become more comfortable with the design method and employ the method more often and more consistently. This paper presents a uniform design procedure for employing strut-and-tie modeling for hammerhead piers that can be readily utilized by practicing engineers. Additionally, a comparison between the strut-and-tie method and standard sectional design practices will be performed for a typical hammerhead pier.     

Origin of high Zn contents in Jurassic limestone of the Jura mountain range and the Burgundy: evidence from Zn speciation and distribution

In order to better understand the origin and enrichment mechanisms leading to elevated Zn concentrations in Jurassic limestone of the Jura mountain range (JMR) and the Burgundy (B), we investigated four locations of Bajocian age (JMR: Lausen–Schleifenberg, Gurnigel; B: Vergisson–Davayé, Lucy-le-Bois) and two locations of Oxfordian age (JMR: Dornach, Pichoux) for their Zn distribution and speciation. Measurements of the acid-extractable and bulk Zn contents showed that Zn is stratigraphically and spatially heterogeneously distributed, in association with permeable carbonate levels. Up to 3,580 and 207 mg/kg Zn was detected in Bajocian and Oxfordian limestone, respectively, with numerous limestone samples having Zn contents above 50 mg/kg. Using X-ray absorption near edge structure spectroscopy and micro-X-ray fluorescence spectrometry, the speciation and micro-scale distribution of Zn was investigated for selected limestone samples. In Bajocian limestone sphalerite and/or Zn-substituted goethite and a minor fraction of Zn-bearing carbonates were identified. In contrast, Zn-bearing carbonates (Zn-substituted calcite and hydrozincite) were accounting for most of the total Zn in Oxfordian limestone. The micro-scale distribution of Zn for Bajocian and Oxfordian limestone was however similar with localized Zn-rich zones in the limestone cement and at the rim of oolites. The stratigraphic sporadicity and microscale heterogeneity of the Zn distribution together with the Zn speciation results point to a hydrothermal origin of Zn. Occurence of Zn-goethite is probably linked to the oxidative transformation of framboidal pyrite and hydrothermal sphalerite in contact with meteoritic waters. Difference in speciation between Bajocian limestone and Oxfordian limestone may be related to differences in rock permeability and/or to various hydrothermal events. Isotopic dating of the different mineralizations will be needed to decipher differences in Zn speciation and the precise chronology of hydrothermal episodes.     

Physiological effects of hypercapnia in the deep-sea bivalve Acesta excavata (Fabricius, 1779) (Bivalvia; Limidae)

The option of storing CO₂ in subsea rock formations to mitigate future increases in atmospheric CO₂ may induce problems for animals in the deep sea. In the present study the deep-sea bivalve Acesta excavata was subjected to environmental hypercapnia (pHSW 6.35, PCO₂ = 33,000 μatm) corresponding to conditions reported from natural CO₂ seeps. Effects on acid–base status and metabolic rate were related to time of exposure and subsequent recovery. During exposure there was an uncompensated drop in both hemolymph and intracellular pH. Intracellular pH returned to control values, while extracellular pH remained significantly lower during recovery. Intracellular non-bicarbonate buffering capacity of the posterior adductor muscle of hypercapnic animals was significantly lower than control values, but this was not the case for the remaining tissues analyzed. Oxygen consumption initially dropped by 60%, but then increased during the final stages of exposure, which may suggest a higher tolerance to hypercapnia than expected for a deep-living species.     

A SF6 tracer study of horizontal mixing in Lake Constance

Horizontal mixing processes in the hypolimnion of the western part of Lake Constance are studied by measuring the dispersion of a sulfur hexafluoride (SF₆) tracer plume. Only 1 liter gaseous SF₆ (STP) was released at a central hypolimnic depth of 60 m in August 1990. Over a period of 3 months the horizontal dispersion of the tracer plume was measured by 19 surveys using a new, vertically integrating sampling device. The observed horizontal dispersion is marked by strong storm-induced stirring events. Nevertheless mean turbulent diffusion coefficients for the whole period can be computed. They rise about linear from 0.7 10⁵ cm²/s to 3.0 10⁵ cm²/s with the distance from the western end of the lake. For the hypolimnion of Überlingersee, a sill-separated basin in the western part of Lake Constance, a simple budget model gives an exchange time of 67 ± 6 days with the main basin (Obersee).     

The impact of decadal fluctuations in mean precipitation and temperature on runoff: A sensitivity study over the United States

The nature of climate variability is such that decadal fluctuations in average temperature (up to 1 °C annually or 2 °C seasonally) and precipitation (approximately 10% annually), have occurred in most areas of the United States during the modern climate record (the last 60 years). The impact of these fluctuations on runoff was investigated, using data from 82 streams across the United States that had minimal human interference in natural flows. The effects of recent temperature fluctuations on streamflow are minimal, but the impact of relatively small fluctuations in precipitation (about 10%) are often amplified by a factor of two or more, depending on basin and climate characteristics. This result is particularly significant with respect to predicted changes in temperature due to the greenhouse effect. It appears that without reliable predictions of precipitation changes across drainage basins, little confidence can be placed in hypothesized effects of the warming on annual runoff.     

The 1991 eruption of Hekla,Iceland

The eruption that started in the Hekla volcano in South Iceland on 17 January 1991, and came to an end on 11 March, produced mainly andesitic lava. This lava covers 23 km² and has an estimated volume of 0.15 km³. This is the third eruption in only 20 years, whereas the average repose period since 1104 is 55 years. Earthquakes, as well as a strain pulse recorded by borehole strainmeters, occurred less than half an hour before the start of the eruption. The initial plinian phase was very short-lived, producing a total of only 0.02 km³ of tephra. The eruption cloud attained 11.5 km in height in only 10 min, but it became detached from the volcano a few hours later. Several fissures were active during the first day of the eruption, including a part of the summit fissure. By the second day, however, the activity was already essentially limited to that segment of the principal fissure where the main crater subsequently formed. The average effusion rate during the first two days of the eruption was about 800 m³ s^–1. After this peak, the effusion rate declined rapidly to 10–20 m³ s^–1, then more slowly to 1 m³ s^–1, and remained at 1–12 m³ s^–1 until the end of the eruption. Site observations near the main crater suggest that the intensity of the volcanic tremor varied directly with the force of the eruption. A notable rise in the fluorine concentration of riverwater in the vicinity of the eruptive fissures occurred on the 5th day of the eruption, but it levelled off on the 6th day and then remained essentially constant. The volume and initial silica content of the lava and tephra, the explosivity and effusion rate during the earliest stage of the eruption, as well as the magnitude attained by the associated earthquakes, support earlier suggestions that these parameters are positively related to the length of the preceeding repose period. The chemical difference between the eruptive material of Hekla itself and the lavas erupted in its vicinity can be explained in terms of a density-stratified magma reservoir located at the bottom of the crust. We propose that the shape of this reservoir, its location at the west margin of a propagating rift, and its association with a crustal weakness, all contribute to the high eruption frequency of Hekla.