Atmospheric dispersion in the arctic: Winter-time boundary-layer measurements

The winter-time arctic atmospheric boundary layer was investigated with micrometeorological and SF₆ tracer measurements collected in Prudhoe Bay, Alaska. The flat, snow-covered tundra surface at this site generates a very small (0.03 cm) surface roughness. The relatively warm maritime air mass originating over the nearby, partially frozen Beaufort Sea is cooled at the tundra surface resulting in strong (4 to 30 °C · (100 m)^-1) temperature inversions with light winds and a persistent weak (1 to 2 °C · (100 m)^-1) surface inversion with wind speeds up to 17 m s^-1. The absence of any diurnal atmospheric stability pattern during the study was due to the very limited solar insolation. Vertical profiles were measured with a multi-level mast from 1 to 17 m and with a Doppler acoustic sounder from 60 to 450 m. With high wind speeds, stable layers below 17 m and above 300 m were typically separated by a layer of neutral stability. Turbulence statistics and spectra calculated at a height of 33 m are similar to measurements reported for non-arctic, open terrain sites and indicate that the production of turbulence is primarily due to wind shear. The distribution of wind direction recorded at 1 Hz was frequently non-Gaussian for 1-hr periods but was always Gaussian for 5-min periods. We also observed non-Gaussian hourly averaged crosswind concentration profiles and assume that they can be modeled by calculating sequential short-term concentrations, using the 5-min standard deviation of horizontal wind direction fluctuations () to estimate a horizontal dispersion coefficient ( _y ), and constructing hourly concentrations by averaging the short-term results. Non-Gaussian hourly crosswind distributions are not unique to the arctic and can be observed at most field sites. A weak correlation between horizontal ( _v ) and vertical ( _w ) turbulence observed for both 1-hr and 5-min periods indicates that a single stability classification method is not sufficient to determine both vertical and horizontal dispersion at this site. An estimate of the vertical dispersion coefficient, _z , could be based on or a stability classification parameter which includes vertical thermal and wind shear effects (e.g., Monin-Obukhov length, L).     

Sediment yield in South Africa — A preliminary geographical analysis

The study examines the spatial relationships between sediment yield and 15 independent environmental variables in 54 catchments in South Africa. Rooseboom's (1978) data on the sediment yield from the catchments were standardized for a single time period. Bivariate regression analyses reveal no simple relationships. Multivariate regression analyses conducted for the whole and various sub-areas of South Africa indicate that latitude and longitude are the primary variables affecting spatial variations in sediment yield. This may be as a result of latitude and longitude being surrogate variables reflecting variation in other environmental variables (e. g. geology, vegetation). Within the sub-areas, 43.4% to 97.8% of the variation in sediment yield is explained by the combined variation in a number of different environmental variables. This study highlights a need for the collection and analysis of more sediment yield data, which would allow the analyses to be refined, to predict sediment yields from ungauged catchments in South Africa.     

Urban Seismic Risk Evaluation: A Holistic Approach

Risk has been defined, for management purposes, as the potential economic, social and environmental consequences of hazardous events that may occur in a specified period of time. However, in the past, the concept of risk has been defined in a fragmentary way in many cases, according to each scientific discipline involved in its appraisal. From the perspective of this article, risk requires a multidisciplinary evaluation that takes into account not only the expected physical damage, the number and type of casualties or economic losses, but also the conditions related to social fragility and lack of resilience conditions, which favour the second order effects (indirect effects) when a hazard event strikes an urban centre. The proposed general method of urban risk evaluation is multi hazard and holistic, that is, an integrated and comprehensive approach to guide decision-making. The evaluation of the potential physical damage (hard approach) as the result of the convolution of hazard and physical vulnerability of buildings and infrastructure is the first step of this method. Subsequently, a set of social context conditions that aggravate the physical effects are also considered (soft approach). In the method here proposed, the holistic risk evaluation is based on urban risk indicators. According to this procedure, a physical risk index is obtained, for each unit of analysis, from existing loss scenarios, whereas the total risk index is obtained by factoring the former index by an impact factor or aggravating coefficient, based on variables associated with the socio-economic conditions of each unit of analysis. Finally, the proposed method is applied in its single hazard form to the holistic seismic risk evaluation for the cities of Bogota (Colombia) and Barcelona (Spain).     

Nullarbor 018: A new L6 chondrite from Australia

Abstract— A new meteorite find from the Nullarbor Plain in Australia was studied using optical, SEM, and electron microprobe techniques. The meteorite, Nullarbor 018, is an orthodox L6 chondrite that experienced minor-to-moderate alteration of metal during terrestrial weathering (grade A–B to B). During weathering, troilite was preferentially altered, and roughly 20% of the original complement of S in the meteorite was removed. Shock metamorphic effects corresponding to shock stage S4 (or shock facies d) are found, including the presence of some diaplectic feldspar (maskelynite). The meteorite is not obviously paired with other finds from the Nullarbor region, but the possibility that it is paired cannot be excluded.     

Saturn's satellites: Nuar-infrared spectrophotometry (0.6–2.5 μm) of the leading and trailing sides and compositional implications

Near-infrared spectra, 0.65–2.5 μm, are presented for Tethys, Dione, Rhea, Iapetus, and Hyperion. Water ice absorptions at 2.0, 1.5, and 1.25 μm are seen in the spectra of all five objects (except the 1.25-μm band was not detected in spectra of Hyperion) and the weak 1.04-μm ice absorption is detected on the leading and trailing sides of Rhea, and the trailing side of Dione. Upper limits to the 1.04-μm ice band depth are <0.3% for the leading side of Dione; <0.7% for the leading side of Iapetus, and the trailing side of Tethys; <1% on the trailing side of Iapetus; and <5% on the leading side of Tethys. The leading-trailing side ice band depth differences on Saturn's satellites are similar to those for the Galilean satellites, indicating possible surface modification by magnetospheric charged particle bombardment. Limits are determined for the amount of particulates, trapped gases, and amonium hydroxide on the surface. The surfaces of Saturn's satellites (except the dark side of Iapetus) are nearly pure water ice, with probably less than about 1 wt% particulate minerals. The ice could be clathrates with as much as a few weight percent trapped gases. The upper limit of amonium hydroxide depends on the spectral data precision and varies from ～ 1 wt% NH₃ for the leading side of Rhea to ～ 10 wt% NH₃ for Dione.     

Lithium isotope fractionation in the southern Cascadia subduction zone

We present lithium (Li) abundances and isotope compositions for a suite of anhydrous olivine tholeiites (HAOTs) and hydrous basalt-andesitic (BA) lavas from the Mt. Shasta and Medicine Lake regions, California. The values of δ⁷Li vary from + 0.9‰ to + 6.4‰ and correlate inversely with distance from the trench. These data are consistent with continuous isotope fractionation of Li during dehydration of the subducted oceanic lithosphere, an interpretation corroborated by uniformly high pre-eruptive H₂O contents in basaltic andesites accompanied by high Li, Rb, Sr, Ba and Pb abundances. The subduction-derived component that was added to these hydrous magmas is shown to be very similar beneath both Mt. Shasta and Medicine Lake volcanoes despite characteristically distinct Li isotope compositions in the magmas themselves. More evolved andesites and dacites from Mt. Shasta have δ⁷Li from + 2.8 to + 6.9‰ which is identical with the range obtained for HAOTs and BA lavas from Mt. Shasta. Therefore, Li isotopes do not provide evidence for any other crustal component admixed to Mt. Shasta andesites or dacites during magmatic differentiation and magma mixing in the crust.     

Maquiladora Myths: Locational and Structural Change in Mexico's Export Manufacturing Industry

Trends in location, labor force, and procurement practices in maquiladoras are examined using recent data sources. A growing proportion of maquiladoras are selecting interior locations, south of the borderlands. Once dominated by young women, the labor force is rapidly approaching gender parity. While far below prevailing rates in the United States, maquiladora wages are comparable with equivalent manufacturing sectors in Mexico. Majority ownership of maquiladoras is split almost evenly between Mexico and the U.S., however, maquiladoras have failed to develop domestic sources of materials and parts and remain dependent on imported material inputs. As the North American Free Trade Agreement is phased in, the regulatory environment of maquiladoras will change but their role as low cost assembly specialists will persist.