Laboratory simulation of diffusion in contaminated marine sediments

Wastes from offshore oil drilling activities are often discharged to the marine environment. Solid wastes that settle onto the bottom sediment may pose a health threat to marine organisms and eventually to man through the food chain. We need to understand their fate in order to predict the chemical concentration levels and life-times in the sediment and adjoining aquatic boundary layer. A laboratory simulation of selected in-bed processes that addresses contaminant leaching from the sediment is proposed. The process chosen for simulation in this study is the coupled desorption-diffusion of contaminants from the bed to the water column. A simple mathematical model of the process is also proposed. Preliminary results using organic chemicals for both the simulation and the model are presented. The results suggest that the experimental procedure represents a good way of estimating the diffusive leaching rates of hydrophobic compounds from contaminated sediments.     

Modeling the dynamics of the land-sea breeze circulation for air quality modeling

Conventional atmospheric dispersion and air quality models require that the wind field be known with a higher resolution than is currently available from field monitoring stations in most coastal areas. In this paper, a numerical model is developed to predict the wind flow field during the land-sea breeze. The form and assumptions and method of solution of the model are described. The model output is compared to atmospheric data taken from a field study conducted in the Santa Barbara Channel and Ventura-Oxnard plain in southern California.     

Characterizing the distribution of observed precipitation and runoff over the continental United States

This paper describes the development of a comprehensive geographic database of historical precipitation and runoff measurements for the conterminous U.S. The database is used in a spatial analysis to characterize large scale precipitation and runoff patterns and to assess the utility and limitations of using historical hydro-meteorological data for providing spatially distributed precipitation estimates at regional and continental scales. Long-term annual average precipitation (P) and runoff (Q) surfaces (geographically referenced, digital representations of a continuous spatial distribution) generated from interpolation of point measurements are used in a distributed water balance calculation to check the reliability of precipitation estimates. The resulting input-output values (P- Q) illustrate the deficiency (sparse distribution and low elevation bias) of historical precipitation measurements in the mountainous western U.S. where snowmelt is an important component of the annual runoff. The incorporation of high elevation snow measurements into the precipitation record significantly improves the water balance estimates in some areas and enhances the utility of historical data for providing spatially distributed precipitation estimates in topographically diverse regions. Regions where the use of historical precipitation data may be most limited for precipitation estimation are identified and alternatives to the use of interpolated historical data for precipitation estimation across large heterogenous regions are suggested. The research establishes a database for continental scale studies and provides direction for the successful development of spatially distributed regional scale water balance models.     

Transient climatic response to an increase of greenhouse gases

The physical factors governing the transient climatic response to an increase of greenhouse gases are discussed, reasons for remaining uncertainties are identified, and recent climate modelling results are briefly summarized. The relevance of the transient response, and of uncertainties in the transient response, to questions such as the applicability of equilibrium climate model simulations to a gradual greenhouse gas increase, the verification of model projections, rates of climatic change, and the impacts of preventative strategies for dealing with the buildup of greenhouse gases is also discussed.     

Flow and transport modeling in the sea-breeze part II: Flow model application and pollutant transport

A modifiedE- non-hydrostatic model with non-equilibrium level 2.5 closure was applied to the flow and pollutant dynamics in the sea-breeze. The model predicts key observed characteristics of the sea-breeze, such as midday slowing of inland penetration, fast and deep inland penetration in late afternoon, and detachment of the sea-breeze from the feeding flow in early evening. In late evening when the turbulent mixing over the land subsides due to the surface cooling, a frontal density current is formed and the predicted structure is in good agreement with observations and laboratory experiments of density currents. Turbulent mixing over the land is a key parameter that controls midday slowing and late afternoon frontal development.The calculated thermal internal boundary layer and fumigation of an elevated line source show good agreement with observations and similarity theory. Calculations suggest that the residual plume aloft over the sea returns onshore at ground level during the afternoon sea-breeze and has a large impact on ground-level concentrations during the following day.     

Guest editorial: the 2001 UK census: remarkable resource or bygone legacy of the 'pencil and paper era'?

National censuses are expensive. They are conducted infrequently. They collect information that some feel infringes their human rights, and people are required by law to complete them. The outputs are not perfect, and in some situations may be misleading. Some suggest that censuses hark back to a period when regularly collected administrative data were not available. These are some of the views held about national censuses. Why, then, would others argue that they are an essential resource? In this paper, we consider some of the pros and cons of conducting national censuses, before introducing a series of papers that draw on early data available from the 2001 UK census. We argue that these papers, and the wealth of research that will be conducted in the future with 2001 census data, make a strong case for supporting the compulsory collection of personal information about the 'entire' population every ten years.     

The effects of hydrogen bonding on the shear viscosity of liquid water

As one of the fundamental physical properties of fluids, viscosity is considered to be the result of intermolecular forces and molecular momentum exchange. In this paper, we assume that hydrogen bonds, as the dominant intermolecular force, dominate the shear viscosity of liquid water and a relationship between the shear viscosity and hydrogen bonding is developed using dimensional analysis,which is further validated by computational chemistry methods. Water, methanol and ethanol are taken as examples to illustrate shear viscosity accounting for intermolecular forces and momentum exchange and their temperature dependence as a result of molecular thermal motions. The calculated shear viscosity of water is consistent with experimental data, which supports the idea that we can use the conceptual model to reveal the nature of shear viscosity.