We report on observed nocturnal profiles, in which an inversion layer is located at the core of a low-level jet, bounded between two well-mixed layers. High-resolution vertical profiles were collected during a field campaign in a small plain in the Israeli desert (Negev), distant 100 km from the eastern shore of the Mediterranean Sea. During the evening hours, the synoptic flow, superposed on the late sea breeze, forms a low-level jet characterized by a maximum wind speed of 12 ms−1 at an altitude of 150 m above the ground. The strong wind shear at the jet maximum generates downward heat fluxes that act against the nocturnal ground cooling. As a result, the typical ground-based nocturnal inversion is “elevated” towards the jet centre, hence a typical early morning thermal profile is observed a few hours after sunset. Since the jet is advected into the region, its formation does not depend on the presence of a surface nocturnal inversion layer to decouple the jet from surface friction. On the contrary, here the advected low-level jet acts to hinder the formation of such an inversion. These unusual temperature and wind profiles are expected to affect near-ground dispersion processes. 相似文献
Laminated sediments in Lake Ohau, Mackenzie Basin, New Zealand, offer a potential high‐resolution climate record for the past 17 kyr. Such records are particularly important due to the relative paucity of detailed palaeoclimate data from the Southern Hemisphere mid‐latitudes. This paper presents outcomes of a study of the sedimentation processes of this temperate lake setting. Hydrometeorological, limnological and sedimentological data were collected over a 14 month period between 2011 and 2013. These data indicate that seasonality in the hydrometeorological system in combination with internal lake dynamics drives a distinct seasonal pattern of sediment dispersal and deposition on a basin‐wide scale. Sedimentary layers that accumulate proximal to the lake inflow at the northern end of the lake form in response to discrete inflow events throughout the year and display an event stratigraphy. In contrast, seasonal change in the lake system controls accumulation of light (winter) and dark (summer) laminations at the distal end of the lake, resulting in the preservation of varves. This study documents the key processes influencing sediment deposition throughout Lake Ohau and provides fundamental data for generating a high‐resolution palaeoclimate record from this temperate lake. 相似文献
In this paper, we describe the ray-tracing code used to calculate the signatures of quasi-linear voids in front of, and on, the last scattering surface. The spherically symmetric, general relativistic, Lagrangian fluid equations are integrated in time along with the geodesic equations. The voids are partially filled and are surrounded by either cold dark matter or interacting fluid with a small amount of pressure. In order to obtain accurate results using smaller arrays, a non-uniform grid is employed. 相似文献
This article presents the results of a study of the relationship between rainfall and Normalized Difference Vegetation Index (NDVI) in East Africa and the Sahel. Monthly data for the years 1982 to 1985 have been analyzed. We have evaluated NDVI-rainfall relationships by vegetation type, using the major formations described by White (1983). In the article, a comparison of the differential response of vegetation growth to rainfall in the two study regions is emphasized. The most important conclusions of our research are as follows:
The spatial patterns of annually-integrated NDVI closely reflect mean annual rainfall.
There is a good relationship between rainfall variations and NDVI on seasonal and interannual time scales for areas where mean annual rainfall ranges from approximately 200 to 1200 mm.
In most cases, NDVI is best correlated with the rainfall total for the concurrent plus two antecedent months; the correlation is better in the Sahel than in East Africa.
The ratios of NDVI to rainfall are considerably higher in East Africa than in the Sahel.
Mean annually-integrated NDVI is linearly related to mean annual rainfall in the Sahel. In East Africa the relationship is approximately log-linear; above some threshold value of rainfall, NDVI values level off and vary minimally with rainfall.
Two possible explanations of this last conclusion are suggested: above this threshold, rainfall is no longer the limiting factor in vegetation growth and/or NDVI is not a good indicator of vegetation growth. The latter is a likely possibility since NDVI directly reflects photosynthetic activity and becomes a poor indicator of biomass (i.e., growth) as high canopy densities are reached. The NDVI-rainfall relationship for East Africa is markedly similar to the relationship between NDVI and Leaf Area Index demonstrated by Sellers (1985) and Asrar et al. (1984). 相似文献
Degradation of dissolved chlorinated solvents using granular iron is an established in situ technology. This paper reports on investigations into mixing iron and bentonite with contaminated soil for in situ containment and degradation of dense nonaqueous phase liquid source zones. In the laboratory, hypovials containing soil, water, bentonite, iron, and free-phase trichloroethene (TCE) were assembled. Periodic measurement of TCE, chloride, and degradation products showed progressive degradation of TCE to nondetectable levels. Subsequently, a demonstration was conducted at Canadian Forces Base Borden near Alliston, Ontario, Canada, where, in 1991, a portion of the surficial aquifer was isolated and free-phase tetrachloroethene (PCE) was introduced. Using a drill rig equipped with large-diameter mixing blades, three mixed zones were prepared containing 0%, 5%, and 10% granular iron by volume. The bentonite was added to serve as a lubricant to facilitate injection of the iron and to isolate the contaminated zone. Analysis of core samples showed reasonably uniform distributions of iron through the mixed zones. Monitoring over a 13-month period following installation showed, relative to the control, a decline in PCE concentrations to virtually nondetectable values. Reaction rates in the laboratory tests were similar to those reported in the literature, while the rate in the field test was substantially lower. The lower rate may be a consequence of mass transfer limitations under the static conditions of the field test. Results indicate that mixing iron and bentonite into source zones may be an effective means of source-zone remediation, with the particular advantage of being relatively immune to effects of geologic heterogeneity. 相似文献
Musky Bay in Lac Courte Oreilles, Wisconsin, USA, is currently eutrophic. This large, shallow bay of an oligotrophic lake possesses the densest aquatic plant growth and a floating algal mat. Paleoecological reconstructions encompassing the last 130 years, were based on multiproxy analyses of sediment cores from three coring sites, two within the bay and one in the lake itself. These data were compared to historical records of the construction and expansion of two commercial cranberry bogs and shoreline residential homes to identify temporal and causal relations of eutrophication. The proxies investigated included: minor and trace elements; biogenic silica; and the diatom community. Post-depositional diagenesis of organic carbon, nitrogen, and phosphorus in the upper 30 cm of the core obscured records of historical ambient nutrient concentrations in the bay obviating their usefulness for this purpose. In contrast, calcium, magnesium, and potassium concentration profiles appeared to reflect runoff of soil amendments applied to the cranberry bogs and aerial fertilizer spraying over the eastern bog adjacent to Musky Bay. The increase in aluminum content since about 1930 coincided with the historical trend in shoreland development and construction of the original commercial cranberry farm. The biogenic silica profile recorded a steady increase of nutrients to Musky Bay over the last several decades. Stratigraphic changes in the diatom community indicated that nutrient input began to increase in the 1940s and accelerated in the mid-1990s with the onset of a noxious floating algal mat. The diatom community indicates the bay has possessed a significant macrophyte community for at least the last 200 years, but increased nutrient input was manifested by a change in the composition, and an increase in the density of the epiphytic diatom community. Cranberry farming appeared to be the major source of nutrients because the diatom community changes occurred prior to the significant increase in residential housing. 相似文献
The Pan-Canadian Framework on Clean Growth and Climate Change is designed to put Canada on track to meet its Paris commitments. A key pillar of the plan is the introduction of a pan-Canadian carbon price by the end of 2018. However, four Canadian provinces, nearly 85% of the Canadian economy and population, have already implemented carbon pricing systems. British Columbia (BC) has a carbon tax. Alberta is transitioning from an output-based allocation system for industrial emitters to a hybrid system combining a carbon levy and refined output-based system. Québec and Ontario have implemented cap-and-trade systems, linked to California. Recognizing these existing systems, rather than impose a single carbon pricing mechanism, the Pan-Canadian Approach to Carbon Pricing gives provinces and territories the flexibility to adopt a carbon tax, a hybrid system, or a cap-and-trade system. To address concerns relating to ‘fairness’ and equivalency of carbon price, a federal carbon pricing benchmark establishes criteria relating to minimum ‘common scope’ and ‘increases in stringency’ that provincial and territorial carbon pricing systems must meet. This article explores the design features of the existing Alberta, BC, Ontario and Québec carbon pricing systems, and considers how the benchmark affects stringency and addresses equivalency of carbon price across these different systems.
Key policy insights
Canada is taking advantage of its federal structure of government to introduce a minimum pan-Canadian carbon price of $10/tCO2e in 2018, rising by $10/year to $50/tCO2e in 2022.
Rather than imposing a uniform pricing mechanism, the Canadian federal government is recognizing existing subnational carbon pricing mechanisms with very different design features – BC’s carbon tax, Québec and Ontario’s cap-and-trade systems, and Alberta’s hybrid system – to deliver the pan-Canadian carbon price.
In order to deliver a minimum level of increasing stringency and to address issues of equivalency of carbon price across sub-national jurisdictions, the federal government is in the early stages of implementing a federal carbon-pricing benchmark.
The lessons learned from the Canadian experience will be relevant to harmonizing carbon pricing systems across both other federal jurisdictions and countries.
The spatial distributions of lead, arsenic, and copper(Pb, As, and Cu, respectively) in surface snow along the transect from the Zhongshan Station to Dome A, East Antarctica, are presented. The mean concentrations of Pb, As, and Cu are1.04±1.56 pg/g, 0.39±0.08 pg/g, and 11.2±14.4 pg/g, respectively. It is estimated that anthropogenic contributions are dominant for Pb, As, and Cu. Spatially, Pb concentrations show an exponentially decreasing trend from the coast inland, while a moderate decreasing trend is observed for Cu concentrations in the coastal area(below 2,000 m above sea level(a.s.l.)).In the intermediate area(2,000–3,000 m a.s.l.), the concentrations and enrichment factors of all these elements show high variability due to the complicated characteristics of climate and environment. On the inland plateau(above 3,000 m a.s.l.),the high concentrations of As and Pb are induced by high deposition efficiency, the existence of polar stratospheric precipitation, and the different fraction deposition to East Antarctica. The extremely high concentrations with maximum values of9.59 pg/g and 69.9 pg/g for Pb and Cu, respectively, are suggested to result mainly from local human activities at the station. Our results suggest that source, transport pathway, and deposition pattern, rather than distance from the coast or altitude, lead to the spatial distributions of Pb, As, and Cu; and it is further confirmed by spatial variations of the three metals deposited over the whole continent of Antarctica. 相似文献