Numerical simulation of pollutant dispersion in a small valley under conditions with supercritical Richardson numbers

The numerical drainage wind model of Wonget al. (1987) is used together with a Lagrangian particle model in the simulation of carbon monoxide (CO) dispersion within a small urban valley in Edmonton, Alberta, Canada. The conditions studied are those of strong static stability when vertical mixing is suppressed. These are conditions with the Richardson number exceeding its critical value (hereafter referred to as supercritical conditions). Observations showed that under such conditions, vertical turbulence is suppressed but horizontal turbulence still exists. The effects of turbulence in the dispersion and transport of pollutants under such conditions are small. However, in the present simulation, a simple turbulence parameterization based on observations is used for supercritical conditions. Some field experiments were performed and the observations are compared with model results. For a location downwind of the CO source, two peaks can be observed during the course of the drainage flow regime. The model results suggest that these represent an initial flux from the drainage flow and a second flux later from drainage wind recirculation. Another main feature of the model-predicted concentration field is zones of maximum concentration at and above the valley floor. There is a drainage wind cell on each side of the valley slope and the cells are effectively decoupled from the prevailing wind above. The present modelling results show that when the prevailing wind exists before the development of the drainage wind, it can be instrumental in transporting CO from one drainage wind cell to the other. Otherwise, the CO released within one drainage wind cell is well contained.     

The Younger Dryas and the Sea of Ancient Ice

We propose that prior to the Younger Dryas period, the Arctic Ocean supported extremely thick multi-year fast ice overlain by superimposed ice and firn. We re-introduce the historical term paleocrystic ice to describe this. The ice was independent of continental (glacier) ice and formed a massive floating body trapped within the almost closed Arctic Basin, when sea-level was lower during the last glacial maximum. As sea-level rose and the Barents Sea Shelf became deglaciated, the volume of warm Atlantic water entering the Arctic Ocean increased, as did the corresponding egress, driving the paleocrystic ice towards Fram Strait. New evidence shows that Bering Strait was resubmerged around the same time, providing further dynamical forcing of the ice as the Transpolar Drift became established. Additional freshwater entered the Arctic Basin from Siberia and North America, from proglacial lakes and meltwater derived from the Laurentide Ice Sheet. Collectively, these forces drove large volumes of thick paleocrystic ice and relatively fresh water from the Arctic Ocean into the Greenland Sea, shutting down deepwater formation and creating conditions conducive for extensive sea-ice to form and persist as far south as 60°N. We propose that the forcing responsible for the Younger Dryas cold episode was thus the result of extremely thick sea-ice being driven from the Arctic Ocean, dampening or shutting off the thermohaline circulation, as sea-level rose and Atlantic and Pacific waters entered the Arctic Basin. This hypothesis focuses attention on the potential role of Arctic sea-ice in causing the Younger Dryas episode, but does not preclude other factors that may also have played a role.     

Electric field measurements in solar flares

Meaurements of solar flare spectra have allowed the electric field strengths in two flares to be determined, using the Inglis-Teller formula. Further, an independently estimated value for the electron density has allowed the two components of this field, that is, the interionic component and the external component that arises, for example, through plasma instabilities, to be separately extracted. External electric field strengths 0.5 kV cm^–1 for a limb flare and 1.3 kV cm^–1 for a white-light flare are found. Estimates of electric fields strengths generated by the resistive magnetic tearing instability indicate that this process could account for a significant part of the electric field if pre-existing magnetic field strengths in the flaring regions are characterized by a few kilogauss. Other plasma processes probably contribute measurably as well.Operated by the Association of Universities for Research in Astronomy, Inc., under contract NSF AST84-18716 with the National Science Foundation.     

The Ideology of U.S. Agriculture: How Are Integrated Management Approaches Envisioned?

The ease and affordability of the herbicide glyphosate and the development of glyphosate tolerant crops has encouraged a simplified weed management system in the U.S. However, the overuse of this technological package in recent years has led to an explosion in the number of herbicide resistant weeds and a decrease in the effectiveness of glyphosate. In addition to this bio-chemical problem, many growers appear to be stuck within a farming ideology that focuses on a reduction in time/labor, an increase in profitability and a vision of ever-increasing efficiencies of scale. This may prevent them from conceptualizing and implementing solutions that fall outside of a simple herbicide application plan. The objective of this paper is to begin describing the current ideology of industrial corn and soybean farmers in the United States, as well as how this ideology contributes to farmers’ resistance to complex weed management strategies.     

A brave new (virtual) world: distributed searches, relevance scoring and facets

Our ability to deal with complex systems has improved through information system research which includes improved modeling (both data and system), the use of semantics and advances in distributed computing. The past decade has seen an explosion in the amount and variety of geosciences data and the emergence of true open data repositories through which scientists can freely access this data. Those data are found in thousands of repositories located around the world. Virtual observatories have been created to address the challenge of helping scientists search those repositories to find and access the required data. This challenge is been addressed by using technologies such as the Internet (with ample connectivity and bandwidth), the Web, cheap computing power, cheap storage and standards for critical components. Many scientific disciplines are developing virtual observatories. Yet some of the most compelling science questions cross multiple domains. While semantics can provide cross domain reasoning, often the first step in answering a question is determining what resources are available which may be relevant to a topic. The topic can be expressed as simple phrases or word sequences. Using a common relevance scoring method at all locations can enable a federated search across loosely coupled providers. The results of which can be organized into facets to aid the user in selecting the most promising resources with which to pursue the scientific investigation. We describe an approach to developing and deploying relevance scoring methods and faceted results in this brave new (virtual) world. We have found that a scoring method which considers both the presence of terms and the proximity of these terms relative to the order of the terms in the query improves the assessment of relevance. We call this Term Presence-Proximity (TPP) scoring and describe a method for calculating a normalized score. TPP scoring compares favorably with other scoring approaches.     

Recent Trends In Laurentian Great Lakes Ice Cover

A 39-winter (1963–2001) record of annual maximum ice concentration (AMIC), the maximum fraction of lake surface area covered by ice each year, is analyzed for each Great Lake. Lake Erie has the largest median AMIC (94%) followed by Lakes Superior (80%), Huron(63%), Michigan (33%), and Ontario (21%). The frequency distributionof AMICs is negatively skewed for Lakes Superior and Erie and positively skewed for Lakes Michigan and Ontario. Temporal and spatial patterns of typical and extreme AMICs is presented within the context of long-term average air temperatures and lake bathymetry. The variation of spatially averaged ice concentration with discrete depth ranges are discussed for each lake for the upper and lower end of the typical range of AMIC values. In general, ice concentration decreases with increasing depth ranges for a given winter. A decrease in the gradient of ice concentration with depths was also observed with an increase in the AMIC from winter 1983 to winter 1984. A temporal trend in the AMICs supports the hypothesis of three ice cover regimes over the past 39 winters. Approximately 44% of the highest quartile (10 highest) AMICs for the Great Lakes occurred during the 6-winter period:1977–1982 providing evidence of a higher ice cover regime during thisperiod relative to the 14 winters before them (1963–1976) and the 19 winters after them (1983–2001). Winter 1998 established new low AMIC extremes,and the AMIC averaged over the 1998–2001 winters is the lowest for theperiod of record on four of the five Great Lakes. These recent trends taken together are noteworthy as they may be harbingers of a period of even lower AMICs in the 21st Century.     

Nonlinear shear mass participation factor (rd) for cyclic shear stress ratio evaluation

Most methods for assessment of in situ seismic soil liquefaction potential require evaluation of the earthquake-induced cyclic shear stress ratio (CSR). Estimates of the in situ CSR can be developed directly, using dynamic response analyses, but it is common in ‘simplified’ analysis methods to develop estimates of the in situ CSR using empirical relationships. Unfortunately, the most widely used existing empirical relationships are based on limited response analyses and do not take full advantage of current knowledge of factors affecting this response problem. As a result, they are both biased and unnecessarily imprecise. This paper presents the results of a relatively comprehensive suite of site response studies (2153 site response analyses), performed using carefully selected suites of site conditions and input time histories, to provide an improved basis for development of estimates of in situ CSR using the r_d-approach. The resulting empirical correlations, developed using the Bayesian updating method, provide a much improved basis for simplified empirical evaluation of CSR as a function of (1) depth; (2) earthquake magnitude; (3) intensity of shaking; and (4) site stiffness.     

Documentation of soil conditions at liquefaction and non-liquefaction sites from 1999 Chi–Chi (Taiwan) earthquake

The 1999 Chi–Chi, Taiwan, earthquake provides case histories of ground failure and non-ground failure that are valuable to the ongoing development of liquefaction susceptibility, triggering and surface manifestation models because the data occupy sparsely populated parameter spaces (i.e. high cyclic stress ratio and high fines content with low to moderate soil plasticity). In this paper, we document results from several large site investigation programs conducted in Nantou, Wufeng and Yuanlin, Taiwan. The seismic performance of the investigated sites include non-ground failure building and free-field sites, building sites with partial foundation bearing failures, free-field lateral spread sites, and free-field level ground sites with sediment boils. Field and laboratory investigation protocols for the sites are described, including cone penetration testing (some with pore pressure and shear wave velocity measurements) and rotary wash borings with standard penetration testing (including energy measurements). Implications of the SPT energy measurements with respect to established guidelines for the estimation of SPT energy ratio (including short rod corrections) are presented. Finally, data for three example sites are shown that illustrate potential applications of the data set, and which also demonstrate a condition where existing liquefaction analysis procedures fail to predict the observed field performance.