Reaching Ground Level Research Articles

Density scaling approximation for Monte-Carlo simulations of radioactive plumes

The release of radioactive gas into the atmosphere can diffuse into large volumes of air downwind from the point of release. The extent of radioactivity can cover thousands of cubic meters of air. For such large volumes, the weather models used to predict the down-wind distribution of the plume and the radiation transport models used to predict the radiation reaching ground-level from the plume can take tens of hours of computer time on multi-node institutional High-Performance Computing facilities.In this paper we focus on the radiation transport aspect of plume modeling. We describe a phenomenological method for approximating the amounts of radiation that reach ground level from large volumes of a static radioactive plume that can be calculated on a stand-alone personal computer in much shorter computation times than those usually needed for such large volume evaluations. We refer to this method as the Density Scaling Approximation (DSA). Its ability to approximate ground-level count rates of large plumes comes from using a small-plume volume with a scaled-up value of air density to simulate the same number of scatterings that occur during transport in larger plume volumes at normal air density.We demonstrate the DSA by using a 100 m-diameter air-filled hemispherical dome geometry with a uniform volumetric activity of 135Xe gas throughout the air-filled volume. The DSA for a larger dome diameter is obtained by evaluating the 100 m dome with an air density scaled up by the linear ratio of the larger diameter to the 100 m diameter. We find that this approximation works well for dome diameters up to 1200 m – the largest diameter studied and a size more than sufficient for accounting for all the radiation from 135Xe. Moreover, most of our DSA results can be calculated over 500 times faster than corresponding full-sized geometry with normal air density.To help evaluate the accuracy of the DSA and gain insight into how well it can reproduce different regions of the spectra, we use three, easily understood regions of interest to compare the DSA results to the full-sized geometry at normal air density results. These regions are the full-energy peak, the region of single-Compton scattering, and the region of multiple-Compton scattering. We show how the dominance of the Compton scattering mechanism determines this division and thus provides insight into how Compton scattering is manifested in spectra from photon scattering through air in general, and how well the DSA approximation works.

Heat exposure variations and mitigation in a densely populated neighborhood during a hot day: Towards a people-oriented approach to urban climate management

Climate change and increasing urbanization call for the effective adaptation of cities to extreme heat. To improve the applicability of the research, sophisticated computational fluid dynamics models are being developed to capture the complexity of climate in a real urban environment, while a human-oriented paradigm is emerging concurrently. In this paper we present a synergy of these approaches by analyzing outdoor thermal exposure on five different pedestrian routes in Prague-Dejvice (Czech Republic), employing the PALM modeling system and realistic use-cases. Our simulations reveal important spatio-temporal variability in the Universal Thermal Climate Index (UTCI) in the urban neighborhood. Our findings particularly emphasize the negative effect of open spaces, such as gaps between buildings and shorter buildings, on the thermal exposure of pedestrians. These configurations allow more direct irradiation to reach ground level, while the other adverse climatic characteristics of midrise/highrise developments are largely preserved. The effect of urban greenery is quite variable during the day. Trees can reduce UTCI by up to 10 °C, but this strongly depends on the location (e.g., distance from neighboring buildings). Irrigated grass reduces UTCI by about 1.8 °C, but dried grass has little heat mitigation effect. In conclusion, our results suggest that expert-based knowledge together with sophisticated and fine-scale models can identify effective heat stress reduction measures without draconian changes to, or investments in, the urban environment.

Reintroduced megaherbivores indirectly shape small-mammal responses to moonlight.

Moonlight structures activity patterns of many nocturnal species. Bright moonlight often limits the activity of nocturnal prey, but dense vegetation weakens this effect. Using 8years of live-trapping data, we asked whether reintroduced megaherbivores (Bison bison) indirectly altered moonlight avoidance by small mammals in tallgrass prairies. In plots with bison, plants intercepted 20% less light, allowing more moonlight to reach ground level. During nights with no moonlight, Peromyscus maniculatus activity was similar in plots with and without bison. During nights with peak moonlight, P. maniculatus activity was four times greater in plots without bison compared to plots with bison. Conversely, Microtus ochrogaster activity was twice as great during full moons compared to new moons, but only in plots with bison. We also equipped a subset of traps with temperature sensors to estimate trap-entry time. Although M. ochrogaster was more active on bright nights, most activity occurred before moonrise or after moonset, avoiding periods of bright moonlight. We conclude that megaherbivores play an unappreciated but important indirect role in tallgrass prairies by inducing behavioral shifts in other animal species. Because overlap in activity patterns can predict the likelihood of predator-prey encounters, such activity shifts have important implications for trophic interactions throughout restored prairie food webs. Additional work to understand interspecific and intraspecific variation in response to moonlight may improve efforts to forecast changes in community assembly due to restoration and land-use change.

Insights into rainfall undercatch for differing raingauge rim heights

Abstract The measurement of rainfall has a long history, but despite its apparent simplicity it is difficult to quantify accurately. The common installation of raingauges with rims above the ground surface results in a difference between the rainfall caught and the amount reaching ground level, termed undercatch. The UK standard installation of raingauges is for their rim to be sited at 0.305 m above the ground; however, the use of weighing gauges installed at a minimum rim height of 1 m has increased in recent years. The installation of these weighing raingauges raises complex questions of homogeneity in rainfall data across space and time. Here, we investigate the impact of these changes using field trials of commonly deployed UK raingauges at a site in south-east England. This paper discusses the results of the trial, exploring the variation in and potential drivers of undercatch with differing gauge sitings. With varying standards for gauge heights around the world and new rainfall measurement technologies coming to the market all the time, improved understanding of undercatch is needed to inform evolving operational practices and explore the possibility of developing catch correction algorithms to remove arising inhomogeneity in precipitation datasets.

Global gene expression analysis in etiolated and de-etiolated seedlings in conifers.

Plant life cycle begins with germination of seed below the ground. This is followed by seedling’s development in the dark: skotomorphogenesis; and then a light-mediated growth: photomorphogenesis. After germination, hypocotyl grows rapidly to reach the sun, which involves elongation of shoot at the expense of root and cotyledons. Upon reaching ground level, seedling gets exposed to sunlight following a switch from the etiolated (skotomorphogenesis) to the de-etiolated (photomorphogenesis) stage, involving a series of molecular and physiological changes. Gymnosperms have evolved very differently and adopted diverse strategies as compared to angiosperms; with regards to response to light quality, conifers display a very mild high-irradiance response as compared to angiosperms. Absence of apical hook and synthesis of chlorophyll during skotomorphogenesis are two typical features in gymnosperms which differentiate them from angiosperms (dicots). Information regarding etiolation and de-etiolation processes are well understood in angiosperms, but these mechanisms are less explored in conifer species. It is, therefore, interesting to know how similar these processes are in conifers as compared to angiosperms. We performed a global expression analysis (RNA sequencing) on etiolated and de-etiolated seedlings of two economically important conifer species in Sweden to review the differentially expressed genes associated with the two processes. Based on the results, we propose that high levels of HY5 in conifers under DARK condition coupled with expression of few other genes associated with de-etiolation in angiosperms e.g. SPA, DET1 (lower expression under DARK) and CRY1 (higher expression under DARK), leads to partial expression of photomorphogenic genes in the DARK phenotype in conifers as displayed by absence of apical hook, opening of cotyledons and synthesis of chlorophyll.

An experimental investigation and scaling analysis on flame sag of pool fire in cross flow

Flame sag, a phenomenon observed as flame sinks downwards along the leeward sidewall, occurs for a pool fire having its rim above the ground in cross flows. Few data or investigations of this phenomenon have been reported in the literature. In the present study, the length of flame sag measured from the lowest point of sunk flame to the pool rim; as well as the critical speed of the cross flow under which the lowest point of sunk flame reaches the ground level (namely flame sag length equaling sidewall height), were quantified. Experiments were carried out by employing square quartz sand box pool fires with dimensions in the range of 10–20 cm for various cross flow air speeds, heat release rates and pool rim heights. Propane is used as the fuel. The results showed that the length of the flame sag increased with the increasing of the fire source heat release rate. And it also increased with the increasing of the air speed of the cross flow. However, the flame sag length decreased with increasing pool size. The critical air speed of the cross flow at which the flame sag reached the ground increased with increasing pool size and rim height, meanwhile decreased with increasing heat release rate. A scaling analysis for the interaction physics of the fuel flow near the base with the cross flow, and the total buoyant flow (heat release rate) of the fire with the cross flow, was provided to characterize the flame sag behavior. Two dimensionless quantities(ρa-ρf)gDρaUw2, Q̇/DgρacpTaUw3, namely an inverse Froude number for the base and an inverse Froude number for the interaction of total buoyancy of the fire with cross flow, were derived from the analysis with a new length scale found as ξL=ρaUw2(ρa-ρf)g. The data of flame sag length, as well as the critical value of the cross flow speed for flame sag reaching ground level, were shown to correlate well to the proposed dimensionless quantities.

Quantifying street tree regulating ecosystem services using Google Street View

The urban heat island is a particular challenge for tropical cities, which receive year-round high inputs of solar radiation. Plants can help mitigate elevated urban temperatures by providing shade and increasing evaporative cooling, although the resulting increase in humidity may negatively affect thermal comfort. Street trees offer particular potential for cooling urban microclimates, as well as providing other ecosystem services, because they can be integrated within dense urban street networks. However, we have little quantitative information about the role of street trees in providing regulating ecosystem services in tropical cities. In this study, we analysed hemispherical photographs extracted from Google Street View to quantify the proportion of green canopy coverage at 50m intervals across more than 80% of Singapore’s road network. Canopy coverage data were then used to estimate the proportion of annual radiation that would be blocked from reaching ground level by the canopy. Across all locations, a median of 13% of the annual diffuse and direct solar radiation was shaded, and over 70% of this shading effect was due to the tree canopy. There was significant variation between different urban landuse types, with trees providing more shade in parks and low-density low-rise areas than in industrial and higher-density residential areas. Mapping the provision of street tree ecosystem services could help to prioritise areas for new planting by identifying streets or street sections with low shading. The approach developed in this article could be readily applied to quantify the proportion of canopy coverage and proportion of solar radiation shaded across other tropical cities. The method may also be applicable in temperate cities if Google Street View photographs were collected during the growing season.

Results of a study of Cypripedium in several regions of Siberia (Russia)

This study of populations of Cypripedium calceolus L., Cypripedium macranthon Sw. and their hybrid Cypripedium ventricosum Sw. in several regions of Siberia was carried out in 2009–2014. Isolated and mixed populations of the two species and their hybrid were surveyed. In sympatric populations, C. macranthon is most common in the central part and those of C. calceolus prevail in the western part of the range. Mature vegetative and/or reproductive shoots were present but vegetative reproduction was clearly most important in most of the populations investigated. Five colour variations were recorded for C. ventricosum. All species benefit from the increase in the intensity of light reaching ground level in forests after ground fires in spring destroy young trees and undergrowth. Vegetative reproduction and the size of the plants increases in burnt areas. Important factors determining the size and the ontogenetic structure of Cypripedium populations are: the duration of the growing season, the ecological conditions, the activities of pollinators and the relationships among the three species in sympatric populations.

Monitoring 7Be and tritium in rainwater in Daejeon, Korea and its significance

We investigated the concentrations of beryllium-7 and tritium in rainwater along with sodium concentration in the region of Daejeon, Korea for 7 months. The results demonstrate that 7Be in rainwater is inversely proportional to the amount of sodium present and proportional to the rainfall. Also, it was observed that tritium reaches ground level about a month later than 7Be. This study will guide prospective geological research applications associated with cosmogenic nuclides especially in rainwater for the Korean region.

Non-native and native shrubs have differing impacts on species diversity and composition of associated plant communities

The spread of non-native plants has been depicted as a serious threat to biodiversity. However, it remains unclear whether the indigenousness of the invading plant plays a marked role for the ecological consequences of an invasion as few studies have compared the ecological impacts of non-native shrubs with structurally or functionally comparable native shrubs. We studied patches of introduced and native shrubs to assess whether there are general differences in plant species composition or biomass between patches formed by non-native versus native shrubs. The indigenousness of the shrub (non-native vs. native) did not explain the variation in soil nutrients, neither the production of shoot biomass or allocation of growth to different parts of the shoot. The amount of light reaching ground level did not differ between patches of a non-native and a native shrub. However, species richness and biomass of herbaceous plants were lower in patches of non-native than native shrubs and the amount of litter was higher below non-native than native shrubs. Our results suggest that the indigenousness of the patch-forming plant may be an important factor for the diversity and composition of associated herbaceous vegetation. Based on our results, resource availability (light and nutrients) is not a sufficient explanation for the negative effects of non-native shrubs on plant communities. Further research is needed to investigate whether alternative explanations, such as the novelty of the toxic compounds produced by non-native plants, can explain the differences we observed.

TeV ASTROPHYSICS WITH THE MILAGRO AND HAWC OBSERVATORIES

Ground-based gamma-ray astronomy has historically implemented two dramatically different techniques. One method employs Imaging Atmospheric Cherenkov Telescope(s) (IACT) that detect the Cherenkov light generated in the atmosphere by extensive air showers. The other method employs particle detectors that directly detect the particles that reach ground level — known as Extensive Air Shower (EAS) arrays. Until recently, the IACT method had been the only technique to yield solid detections of TeV gamma-ray sources. Utilizing water Chernkov technology, Milagro, was the first EAS array to discover new gamma-ray sources and demonstrated the power of and need for an all-sky high duty cycle instrument in the TeV energy regime. The transient nature of many TeV sources, the enormous number of potential sources, and the existence of TeV sources that encompass large angular areas all point to the need for an all-sky, high duty-factor instrument with even greater sensitivity than Milagro. The High Altitude Water Cherenkov (HAWC) Observatory will be over an order of magnitude more sensitive than Milagro. In this paper we will discuss the results from Milagro and the design of the HAWC instrument and its experimental sensitivity.

Effect of Flare Stack Radiation on the Mixing Height over Olorunsogo Area of Ogun State, Nigeria

Mixed layer depth, Solar and flare stack radiations, Atmospheric boundary layer Abstract: Mixing of chemical species released from pollution sources occurs at certain heights in the atmospheric boundary layer of the troposphere. Within this height, mixing of materials occurs due to convective heat transport and mechanical (wind) actions. The mixed layer height can be estimated by analyzing measured meteorological parameters. In this study, the parameterization of meteorological variables based on established mathematical models were used to compute mixed layer height over Olorunsogo in Ogun State, Nigeria. The vertical extent through which pollutants mix occurs was described in a height-temperature profile for both the day time and nocturnal characteristics. The mixing depths were computed for two locations comprising one area with gas flaring operation present and another with no flare stack present. The findings of this study revealed that mixed layer depth for the location without flaring activities, day time ranged between 1200m and 1400m, and at night time as well as early morning ranged between 150m and 400m. In contrast with the location where gas flaring occurred, mixing height ranged between 9280m and 9310m for day time and between 9100m and 9180m for nocturnal period. In addition, it was observed that pollution trapped below the flare during the day, experience rapid vertical motion due to outgoing long wave radiation (OLR) from the surface. While above the flare a vertical motion coupled with dispersion occurs under lapse rate for pollutants, but remained trapped at the inversion layer. At night time, pollutants around the flare advect vertically and experience rapid vertical dispersed motion and after going through the flare are trapped at the inversion layer. Hence most submicron sized particulate matter hardly reaches ground level over areas where gas flaring operations occur except entrainments in wet depositions predominantly through rainfall.

Research Spotlight: Auroral emissions reach ground level

Earth's auroral electrons radiate some of their energy in radio waves. Theories of the mechanism for emission of this radiation, known as auroral kilometric radiation (AKR), suggest that this radiation propagates away from Earth and cannot be detected at ground level. However, LaBelle and Anderson present the first evidence that AKR does penetrate to ground level. On three occasions in July 2004 the researchers detected radio emissions that appeared to be AKR at the South Pole Station in Antarctica. They compared these emissions with AKR emissions detected simultaneously by the U.S.‐Japanese Geotail satellite and found that they had the same frequency structure, suggesting that the emissions detected at ground level were indeed AKR. (Geophysical Research Letters, doi:10.1029/2010GL046411, 2011)

Flow and pollution transport during Wagerup 2006: a case study

As part of a broader field campaign dubbed Wagerup 2006, a case study was carried out to determine the overnight pollution transport mechanisms and flow characteristics near Wagerup, Western Australia. The ambient conditions were characterized by stable stratification with little synoptic influence in the lower boundary layer. An elevated jet intrusion originating on a nearby escarpment slope was found to induce sufficient mixing causing elevated pollution plumes to reach ground level. Onset of mixing was accurately predicted by non-linear critical Richardson number estimates obtained in previous laboratory work. The increase in ground level temperatures brought about by shear induced mixing later prompted a sea-breeze like gravity current that was completely blocked by the escarpment and as a result pollutants were trapped against the escarpment slope. A notable side effect of the topographic blocking was the subsequent steady 360° rotation of ground level winds within an area of influence described by the Rossby deformation radius. Copyright © 2009 Royal Meteorological Society

New method to measure the attenuation of hadrons in extensive air showers

Extensive air showers are generated through interactions of high-energy cosmic rays impinging the Earth’s atmosphere. A new method is described to infer the attenuation of hadrons in air showers. The numbers of electrons and muons, registered with the scintillator array of the KASCADE experiment, are used to estimate the energy of the shower inducing primary particle. A large hadron calorimeter is used to measure the hadronic energy reaching observation level. The ratio of energy reaching ground level to the energy of the primary particle is used to derive an attenuation length of hadrons in air showers. In the energy range from 106 to 3×107 GeV the attenuation length obtained increases from 170 to 210 g/cm2. The experimental results are compared to predictions of simulations based on contemporary high-energy interaction models.Received 27 March 2009DOI:https://doi.org/10.1103/PhysRevD.80.022002©2009 American Physical Society

Entry Trajectory Model with Thermomechanical Breakup

a most probable cutplane. The detailed geometric and inertial modules have been coded to generate fragments of a general shape and size. The iteration over debris fragments includes complete thermal ablation and mechanical disintegration by centrifugal stresses. As soon as new debris is generated, its state vector and geometry is fed back to the dynamics and aerothermal loads modules, and simulation is performed over the next time interval. Only the largest surviving fragment is tracked for long-term simulation, whereas the other fragments are tracked for a prespecified duration. When a fragment is either completely ablated/disintegrated or reaches ground level, its simulation is ended. Hence, the scheme results in a complete simulation of the entry trajectory with en route debris shedding events until either ground impact or complete ablation and mechanical disintegration. Sample trajectory simulations for an entry capsule representative of deboost from a circular (or elliptical) orbit are considered. A dispersion analysis based on variations in the entry conditions has been conducted and its effect on the probable debris field is calculated. The speed and flight-path angle have the largest effect on downrange dispersion, whereas the heading angle affects cross-range dispersion the most. Increase in the object’s entry mass (assumed nominally distributed) has a negligible effect on the debris field, whereas a 10% decrease in the mass causes an appreciable variation in debris dispersion.

Twentieth-Century (Light-)Blues - The Cambridge History of Twentieth-Century Music, edited by Nicholas Cook and Anthony Pople. Cambridge: Cambridge University Press, 2004. xviii + 818 pp. ISBN 0 521 66256 7.

Twentieth-Century (Light-)Blues - The Cambridge History of Twentieth-Century Music, edited by Nicholas Cook and Anthony Pople. Cambridge: Cambridge University Press, 2004. xviii + 818 pp. ISBN 0 521 66256 7. - Volume 130 Issue 2

The impact of atmospheric pollution on vitamin D status of infants and toddlers in Delhi, India

Aims: To compare the vitamin D status of 34 children, 9–24 months old, living in an area of Delhi renowned for high levels of atmospheric pollution (Mori Gate), with a...

Long-term ozone and UV variations at Thessaloniki, Greece

Total columnar ozone has been decreasing over middle latitudes (20°–60°) between 1979 and December 2000 at rates of about 4% in winter/spring and about 2% per decade in the summer. Total ozone trends through 1997 and through 2000 differ only over the middle and high latitudes of the northern hemisphere. This long-term trend was interrupted by periods of enhanced volcanic activity, which resulted to significant ozone losses (more than 5% per year) following large volcanic eruptions (El Chichon in 1982 and particularly Mt Pinatubo in 1991). Linked to the ozone decrease are well-documented global increases of the harmful UV-B solar radiation levels reaching ground level. Through 1997 the erythemal dose over middle latitudes in clear skies was increasing at rates exceeding 5% per decade while the solar UV irradiance at the lower wavelengths was increasing by more than 10% per decade, partly enhanced by the decrease of air pollutants such as sulfur dioxide in the case of Thessaloniki. However, evidence is presented in this study that during the last decade (1990–2001) over Thessaloniki, the ozone trend was smaller the order of −1.5% per decade. Also the associated increasing trends in the erythemal dose and at 305 nm are smaller not exceeding +2% and +4% per decade respectively under clear skies. The long-term UV variability has a QBO component, which cannot be overlooked, even in comparison with the amplitude of the annual cycle.

The surface UV-B irradiation in the Arctic: observations at the Polish polar station, Hornsund (77°N,15°E), 1996–1997

Measurements of the UV-B radiation reaching ground level at the Polish polar station, Hornsund (Svalbard, 77° N , 15°30′E, 11 m a.s.l.), have been carried out since February 1996 by means of a temperature stabilized Robertson–Berger-type meter. The seasonal pattern of UV dose and UV index, and factors affecting the UV-B level there are studied for the period March–October of 1996 and 1997. The quality of the UV measurements is assured by comparisons of the instrument readings with those calculated from a radiative transfer model under clear-sky conditions. A statistical method is proposed to examine the year-to-year drift of the instrument readings. The maximum value of UV daily dose and UV index are found in late spring of 10.2 MED (1 MED=210 J eff m −2) and 2.5, respectively. The maximum UV irradiance at the midnight is ≅4 mW eff m −2 . The seasonal pattern of UV daily dose appears to be asymmetric relative to the summer solstice. All-weather UV measurements taken in early spring provided much higher (≅50%) UV irradiances than the corresponding measurements in late summer because of larger ground albedo and atmospheric transparency (due to smaller cloud/aerosol optical depth) in early spring. Depletion of total ozone is not the only source of the UV trend over Arctic. It is found that long-term (1965–1997) changes in the cloud cover over southern Svalbard had significant impact on the UV level there.