Reaching Ground Level Research Articles

Spatial and energy distribution of muons inγ-induced air showers

The FLUKA Monte Carlo program is used to calculate the effects of hadroproduction by primary gamma rays incident upon the Earth's atmosphere; for the results presented in this paper, only primary angles at $0\ifmmode^\circ\else\textdegree\fi{}$ from zenith are considered. The FLUKA code is believed to be quite accurate in reproducing experimental photon hadroproduction data in the 1 GeV to 10 TeV energy range studied. The charged pions which are so produced can decay to muons with sufficient energy to reach ground level. The number of these muons and their radial and energy distribution are studied for incident gamma ray energies from 1 GeV to 10 TeV. The number of these muons is not negligible; they can, in certain circumstances, be used to study potential sources of gamma rays such as gamma ray bursts. It is found, for example, that a 10 TeV incident primary gamma ray produces, on average, 3.4 muons which reach ground level; the gamma ray energy which produces the maximum number of muons at ground level depends on the spectral index of the primary gamma spectrum, a constant which describes how the primary gamma flux rises with decreasing primary energy. For example, for a differential spectral index of 2.7, there is a broad maximum number of muons coming from $\ensuremath{\approx}30$ GeV primary gamma ray energy.

A field test of the quotient method for predicting risk to Microtus canicaudus in grasslands.

We used gray-tailed voles, Microtus canicaudus, as an experimental model species to field test a prediction of the Quotient Method (QM) for risk to small mammals of an insecticide in grasslands. In May 1997, we placed voles into 12 0.2-ha enclosures planted with a mixture of pasture grasses. In late July, we applied 1.55 kg/ha of the insecticide Guthion(R) 2S (azinphos-methyl) in three treatments: a control (all habitat sprayed with water), full spray (all of the habitat sprayed with Guthion 2S), and half-spray (one-half of the habitat sprayed with Guthion 2S and one half with water). Five replicates were used for the half-spray and control, and two replicates for the full-spray. The Guthion 2S treatment did not depress population size, growth rate, or survival of voles in half-spray or full-spray enclosures. Our results were inconsistent with the QM prediction for use of Guthion 2S in grass habitats. These results also differed from our previous studies in alfalfa habitats in which measurable responses were detected at the same application rate. The differences probably are due to the different types of vegetation between current and previous studies. The grass habitat in our enclosures was an average of 60 cm high and was very thick from ground level to about 40 cm. Much of the residue likely accumulated in the upper strata of vegetation and did not reach ground level at this application rate. Under the conditions of this study, voles were less affected in grassland habitat than they were in alfalfa habitat.

Ozone measurements in atmosphere and correlations with7Be in an Italian alpine valley

Since 1990 our Institute has been conducting7Be measurements in the atmosphere in order to use it as a tracer for air coming from the upper layers of the atmosphere and for the stratospheric ozone. In this paper we present the results on7Be measurements and ozone concentrations obtained with a one-year monitoring campaign carried out in Sondrio, an alpine twon in Northern Italy. For a few interesting events correlations between beryllium and ozone is observed.7Be reveals itself as a good marker which reaches ground level during particularly rare events such as stratospheric intrusions.

Ultraviolet Radiation and Plants: Burning Questions.

Plants use sunlight for photosynthesis and, as a consequence, are exposed to the ultraviolet (UV) radiation that is present in sunlight. UV radiation is generally divided into three classes: UV-C, UV-6, and UV-A. The UV-C region of the UV spectrum includes wavelengths below 280 nm; these highly energetic wavelengths are effectively absorbed by ozone in the stratosphere and, thus, are not present in sunlight at the earth’s surface. UV-C wavelengths will be removed from the light reaching the earth’s surface’so long as there is any ozone present (Caldwell et al., 1989). In contrast, UV radiation in the UV-B region, from 280 to 320 nm, does reach ground level. The UV-B portion of sunlight has received much attention in recent years because irradiation from this spectral region (especially 297 to 310 nm) will increase as the stratospheric ozone concentration decreases (Caldwell et al., 1989). Currently, ozone decreases result from chlorofluorocarbon contamination of the stratosphere (McFarland and Kaye, 1992). UV wavelengths from 320 to 390 nm, which make up the UV-A region of the spectrum, are not attenuated by ozone, so their fluence will be unaffected by ozone layer reduction. Like all living organisms, plants sense and respond to UV radiation, both the wavelengths present in sunlight (UV-A and UV-B) and the wavelengths below 280 nm (UV-C). AI1 types of UV radiation are known to damage various plant processes. Such damage can be classified into two categories: damage to DNA (which can cause heritable mutations) and damage to physiological processes. There has been much speculation about how increased UV radiation exposure will affect plants, but as yet, there are no definitive answers. In this review, I will discuss the kinds of damage that UV radiation can inflict on plants, the mechanisms plants use to perceive and respond to UV radiation, and the ecological relevance of UV light wavelengths that have been used in the experimental analysis of plant responses to UV radiation.

Ultraviolet radiation received in Antarctica in comparison with the Indian region

The decrease in atmospheric ozone over Antarctica during September–October 1987 implies enhanced u.v. radiation received at the ground in the region of the ozone hole. At the ozone hole in Antarctica the decrease in total ozone is enormous and sometimes the ozone level reaches as low as 120–130 DU, whereas the normal value of total ozone is around 300 DU. The decrease in ozone will not only increase u.v.B radiation several-fold but will also shift the cut-off wavelength to lower wavelengths. A model calculation for u.v.B radiation reaching ground level for different total ozone content (100–340 DU) has been carried out for several solar zenith angles appropriate to Indian as well as Antarctic stations. The u.v.B radiation received at Antarctica during the ozone-hole period are comparable to our equatorial stations over the summer period.

Ozone measurements and correlations with Be-7 in an Alpine Italian Valley

Abstract Our Institute since 1990 has been conducting Be-7 measurement in atmosphere in order to use it as a tracer for air coming from the open layers of the atmosphere and for the stratospheric ozone. In this paper we present the results on Be-7 and ozone concentrations obtained with a one year monitoring campaign carried out in Sondrio, an alpine town in Northern Italy. For a few interesting events correlation between beryllium and ozone is observed. Be-7 reveals itself as a good marker which reaches ground level during particularly rare events, such as stratospheric intrusions.

Les formes globales des plantes de sous-bois tropicaux et leur signification écologique

The understorey of tropical rainforests is characterized by a low energetic level and a uniform climate : low light intensity (1 % or less of the incident radiation reaches ground level), lack of wind, atmospheric humidity near saturation, and almost constant temperature. However, the many species of understorey plants display a great diversity of growth habits. This energy-poor environment implies economies in the elaboration of non assimilating organs such as roots and stems, whereas leaf blades tend to never overlap. Stem thickening is reduced, as cambial activity is low (in shrubby Dicots), or nil (in Ferns, Monocots, and herbaceous Dicots). This goes along with a low branching level and a single stem, either unique and perennial, or replaced by basal repetition from a collar-like zone. Contrary to what is usually said, orthotropic and plagiotropic stems are equally frequent in shaded environments. The present study deals with the arrangement of leaves on stems, the whole leafy surface of an individual plant composing its «assimilatory set ». In a tropical rainforest understorey plant, the form of this assimilatory set tends to remain almost the same throughout the life cycle of the individual, old leaves and stems being replaced by new ones. Field observations carried out all over the tropical World led the author to identify a limited number of elementary global forms of the assimilatory set of understorey plants. Some are simple geometric forms (discs, tori, cylinders, and cones) with an axial symmetry ; others (ovals and laminas) exhibit a helicoidal or a bilateral symmetry. Sheets and pendant elements are asymmetric forms. Twenty elementary global forms are described : stemless discs, elevated discs, cupola of discs, superposed discs, stemless sheaf tori, stemless crown tori, funnel shaped tori, ascending sheaf tori, elevated horizontal ovals, inclined ovals, horizontal creeping laminas, ascending oblique laminas, vertical appressed lami¬ nas, elevated horizontal laminas, superposed horizontal laminas, helices, cylinders, cones, pendant elements, and sheets. Each of these forms can be further divided, according to the variety of growth habits able to lead to the same global form. Exemples are given for each mode of elaboration of the various forms. The convergences in global forms between Ferns, Monocots, and Dicots are emphasized. The same global form can indeed be achieved by different growth habits. Reciprocally, the same growth habit can also lead to different global forms. The position of the sexual organs does not play any role in the elaboration of a global form, the latter corresponding to the way the plant takes the best possible advantage of its energy-poor environment. The preferential habitats of each elementary global forms are specified.

Construction Tender Competition for Two Railway Viaducts

The Neugut Viaduct begins at the small Sagentobel River, crosses a main road (Überlandstrasse) and the Glatt River and then divides before reaching ground level in an industrial area. The main bridge, which is approximately 920 m long, has two railway tracks both ramps being some 600 m in length, and an elevated approach of some 260 m. The Weidenholz Viaduct, starts at the edge of small wood at Aegert between Kriesbachstrasse and the six-lane Federal Highway N1, crosses the N1 at an acute angle and descends into an industrial area. It is appropriate to ask if the conditions in such railway viaducts as Neugut and Weidenholz, which did not create opportunities for important project variations, were such that a submission competition rather than a limited project competition or a fixed contract approach needed organising. The solutions proposed were interesting and diverse both financially and from the construction point of view; they offered the owner a true alternative.

Paleosuchus trigonatus Nests: Sources of Heat and Embryo Sex Ratios

All crocodilians which have been studied normally incubate their eggs at temperatures above 27 C (Magnusson et al., 1985). Sources of heat for nests include insolation, metabolic heat of embryos, and decomposition of vegetation included in the nest. Incubation temperatures affect the sex of hatchlings (Fergusson and Joanen, 1982, 1983; Webb et al., 1983a; Webb and Smith, 1984; Ferguson, 1985; Webb et al., 1987), post-hatching survival and growth under standardized conditions (Joanen et al., 1987), and influence the preferred temperatures of juveniles (Lang, 1987). Only two species of crocodilians, Paleosuchus trigonatus and Osteolaemus tetraspis, normally inhabit closed canopy rainforest far from large rivers and lakes. These species may face particular problems in maintaining their nests at the high and stable temperatures required by other species of crocodilians because insolation reaching ground level in rainforest may be only 0.5% that recorded outside the forest (Terborgh, 1985). Thermal relations of natural nests of 0. tetraspis have not been studied, but Magnusson et al. (1985) studied the temperatures in four nests of Paleosuchus trigonatus late in incubation. Based on these nests and nine abandoned nests from previous seasons they made the following predictions:

Unique series of increases in cosmic-ray intensity due to solar flares

THE second half of 1989 was the most prolific period of relativistic particle production by the Sun since continuous monitoring of cosmic-ray activity by neutron detectors was begun in 1957. Some of last year's events were among the largest bursts of particles observed throughout the last three solar cycles. Only when the particles released by the Sun during flares have energies greater than 0.5 gigaelectronvolt (GeV) are the secondary particles generated through interactions in the upper atmosphere able to reach ground level. Six different ground-level events were detected by the super neutron monitor in Calgary (geomagnetic latitude and longitude 51.08° N 245.91°, altitude 1,128 m, cut-off 1.07 GV) in the period July to October 1989. The intensity of energetic particle fluxes during these ground-level events is high enough to be a potential hazard, especially for passengers in aircraft at altitudes of 10 to 15 km.

Wind-Tunnel studies of variable stack heights for a low-profile building

An experimental wind-tunnel study of a proposed building with an exhaust stack was carried out. Smoke tracer techniques were employed to identify the wake and vortex shedding that was caused by the upstream edges or corners of the building. The data was used to determine a stack height required for the stack outlet to be free of the upstream wake effects. Additionally, smoke tracer experiments where smoke was emitted from the stack were conducted to identify the downwind dispersion of the smoke plume. Results from this data indicated if stack exhausts impacted upon the building roof or the downwind distance for the plume to reach ground level. An atmospheric wind tunnel was used to conduct the experiments. A 1:300 scale model of the building and its surroundings was placed in the tunnel and experiments were carried out to represent wind directions from the north, south, east, and west. Two different stack locations and three different stack heights were used in the experiments.

Diurnal variations in optical depth at Mars

Viking lander camera images of the Sun were used to compute atmospheric optical depth at the two sites over a period of 1 1 3 Martian years. The complete set of 1044 optical depth determinations is presented, with error estimates. Optical depths in the morning ( AM) are generally larger than in the afternoon ( PM). The AM-PM differences are ascribed to condensation of water into atmospheric ice aerosols at night and their evaporation in midday. A smoothed time series of these differences shows several seasonal peaks. These are simulated using a one-dimensional radiative-convective model that predicts Martian atmospheric temperature profiles. A calculation combining these profiles with water vapor measurement from the Mars atmospheric water detector (MAWD, on the Viking orbiters)is used to predict when diurnal variations of water condensation should occur. The model reproduces a majority of the observed peaks and shows the factors influencing the process. Diurnal variation of condensation is shown to peak when the latitude and season combine to warm the atmosphere to the optimum temperature, cool enough to condense vapor at night, and warm enough to cause evaporation at midday. The diurnal variation is enhanced by increased water vapor and is sometimes enhanced, sometimes diminished, by enhanced dust loading, depending on the other conditions. Often the model predicts condensation only at altitudes of 25 km or more, while at other times the condensation reaches ground level. Agreement between model and observations is also evident on a time scale of hours, when the data are available at more than two times in a single day.

Estimation of the natural background of ozone present at surface rural locations.

The natural background in the ozone concentration at rural locations in the United States and western Europe has been estimated by use of several approaches. The approaches utilized include the following: (1) historical trends in ozone concentration measurements, (2) recent ozone measurements at remote sites, (3) use of tracers of air originating in the stratosphere or upper troposphere and (4) results from applications of tropospheric photochemical models. While each of these approaches has its own limitations it appears that the natural background of ozone during the warmer months of the year is in the range of 10 to 20 ppb. Most of the ozone originating in the lower stratosphere or upper troposphere is lost by chemical or physical removal processes as well as undergoing dilution by air in the lower troposphere before reaching ground level rural locations. Lower tropospheric photochemical processes, those below 5 km, are likely to account for most of the ozone measured at rural locations during the warm...

The effect of nitrogen in spring on shoot number and leaf area of white clover in mixtures

AbstractSwards of perennial ryegrass/white clover were cut to 3 cm in March and allowed to regrow for approximately thirteen weeks. Half the swards received nitrogenous fertilizer at the time of cutting (+N treatment) while the other half received none (—N treatment).About four weeks after the application of treatments, the number of clover shoots in the — N treatment was significantly higher than that in the +N; at this stage total leaf area index on both treatments was low, but significantly greater in the + N. After 30 days, more light was reaching ground level in the — N treatments, and about 40 days after cutting there was between 17 and 50% more clover in the — N treatment than the +N.It is suggested that the inhibition of stolon branching with a consequent restriction in the rate of increase of clover leaf area is a major factor in the adverse effect of N fertilizer on clover.

An Eulerian model for scavenging of pollutants by raindrops

An Eulerian model for simulating the coupled processes of gas-phase depletion and aqueousphase accumulation of the pollutant species during a rain event has been formulated. The model is capable of taking into account any realistic vertical profile of pollutant species concentrations and time-dependent initial aqueous-phase concentrations at the cloud base. The model considers the processes of single species absorption and dissociation in the aqueous phase. The coupled partial differential equations constituting the model are discretized into a set of ordinary differential equations by using the Galerkin method with chapeau functions as the basis functions. These equations are solved to obtain the pollutant concentrations of the gas phase and raindrops as well as the pH of raindrops as a function of time and distance below cloud-base. Simulations are performed for scavenging of gaseous HNO 3, H 2O 2, SO 2, formaldehyde and NH 3. For the case of highly soluble HNO 3 and H 2O 2, raindrops are far from equilibrium with the gas phase and their capacity for absorption of these gases is undiminished even as they reach ground level. The gas-phase concentrations for these species decrease exponentially with time and the washout is determined primarily by the rain intensity and mass-transfer coefficient of the gaseous species to the raindrops. The pollutant species concentrations in raindrops are an almost linear function of the distance below the cloud base. For the simulation conditions considered in this study, the half-life periods of these gases for removal from the atmosphere range from 15 to 40 min. For SO 2 and formaldehyde, the aqueous-phase concentrations approach equilibrium as the drops fall to ground level and the gas-phase concentrations show large gradients in the vertical. Half-life periods for SO 2 range from 1.3 to 13 h depending on the initial raindrop pH and rain intensity. For formaldehyde, the half-life ranges from 19 to 63 min. Solubility of NH 3 is a strong function of the raindrop pH. As NH 3 is absorbed, the raindrop pH increases and NH 3 solubility decreases. For pre-acidified drops (pH = 4.6), ammonia solubility is very high and the drops are far from equilibrium with the gas phase throughout the falling period. The half-life for ammonia ranges from 11 min to over 3 h in our simulations.

Non-isothermal effects on SO 2 absorption by water droplets—II. Results and discussion

Presented results indicate that non-isothermal effects on SO 2 absorption by water droplets can be important in gas-absorption calculations and interpretation of ground level rain samples. For example, small droplets can desorb SO 2 before reaching ground level and in some cases these droplets can evaporate completely. The desorption of SO 2 can lead to a modest increase in droplet pH and, in effect, redistribute ambient SO 2 from higher to lower elevations.

The Impact of Stratospheric Ozone on Tropospheric Air Quality

A background of ozone (O3), principally of stratospheric origin, is present in the lower free troposphere. Typical mean O3 levels of 50 ppb, 40 ppb, and 30 ppb are encountered here in spring, summer, and fall, respectively. Maximum hourly O3 concentrations which are twice these mean values can be expected. Ozone from the free troposphere is routinely brought down to ground level under turbulent atmospheric conditions. Deep and rapid Intrusions of stratospheric air into the lower troposphere are associated with low-pressure troughs and occur regularly. In the mid troposphere, O3 levels as high as 300 ppb are found within these intrusions. Observational data showing these intrusions, containing high O3 concentrations, to directly reach ground level are currently lacking. Over the United States, an intrusion was present aloft on 8 9% of the days in 1978. The frequency, however, is somewhat reduced in summer and a northward movement is evident. During 1978, no intrusion occurred south of 30°N between June and August and none south of 40 °N in August. The hypothesis that low levels of stratospheric O3 produce disproportionately large amounts of O3 in the polluted atmosphere cannot be supported from currently known chemistry but should be studied further. The experimental technique involving a 7Be/O3 ratio to estimate the daily stratospheric component of ground level O3 is unverified and considered to be inadequate for air quality applications. Estimates resulting from such a technique are considered uncertain by a factor of more than three. Specially designed aircraft studies provide the best means to determine quantitatively the impact of stratospheric O3 on ground level air quality.

Determination of stratospheric ozone at ground level using 7Be/ozone ratios

The 7Be and O3 concentrations were measured and the 7Be/O3 ratios calculated for air particulates collected on several flights of two specially equipped commercial B747 jetliners between altitudes of 10 and 12 km and latitudes of 21° to 55° N. Upper tropospheric 7Be concentrations averaged about 520 pCi/10³m³, whereas the stratospheric average was about 4,700 pCi/10³m³. The 7Be/O3 ratio at 35° ‐ 42° N was determined to be 10.78 pCi/10³m³/ppbv for April‐June 1978. Concentrations of 7Be and O3 were also measured daily during June and July 1977 at Whiteface Mountain, New York. Daily variations in 7Be data indicated the arrival of a stratospheric air mass on June 15‐16. Comparison of 7Be concentrations show approximately a tenfold dilution of the stratospheric air during tropospheric descent. The 7Be/O3 ratio on June 15‐16 was 9.8 pCi/10³m³/ppbv within experimental error of the stratospheric value. This suggests that at least at times, stratospheric air, although diluted, reaches ground level without significant relative fractionation of 7Be and O3. Assuming this to be true on days when 7Be concentration is > 200 pCi/10³m³ (or ≥ 5% of the stratospheric value), we have determined the stratospheric ozone concentration at Whiteface Mountain to vary between 19 and 47 ppbv for summer months. Thus at a remote location such as Whiteface Mountain both stratospheric and the tropospheric sources play an important role.

On the effects of a sudden change in the albedo of the Earth

Acquisition by the upper atmosphere of some 1014 gm of cometary dust would have major implications on the Earth's climate. Pluvial activity would increase dramatically as temperature differences between sea and land widened. Global distribution of precipitation would be controlled by the density of the dust in the atmosphere; for a partially reflective blanket, a fraction of solar energy would still reach ground level creating new climatic zones. The totally undecomposed state of the interiors of Siberian Mammoths and the curious distribution, often uphill, of erratic boulders point to unbelievably sudden and severe conditions at the onset and possibly end of a glacial period. We suggest that a reflective blanket of particles could produce such conditions.

A laboratory study of dispersion from an elevated source within a modeled convective planetary boundary layer

Dispersion from an elevated source has been studied by means of a laboratory model of the convective planetary boundary layer. Results are presented in terms of a continuous point source located within a thermally convecting field and in the presence of a simulated uniform mean wind. Quantities measured in this study are nondimensionalized through the use of free-convection similarity scaling. From a source height of z s ∼- 0.24h , where h is the height of the convectively mixed layer, the average plume concentration maximum descends to ground level at a downstream distance x ∼- 0.4h/(w ∗U) , and remains there for a comparable distance before being carried high up into the mixed layer. (The convective velocity scale w ∗ divided by the mean wind U serves as a dimensionless stability parameter.) It is shown that a Gaussian plume formulation cannot adequately describe this evolving vertical concentration distribution. However, the Gaussian formulation provides an adequate estimate of the vertically-integrated cross-wind concentration distribution. The ground-level concentration field in the X-Y plane indicates that the mean plume first reaches ground level at x ∼- 0.15h/(w ∗U) and attains its maximum concentration near x ∼- 0.4h/( ∗/U) . Power-law formulations for the Gaussian diffusion parameters are made for small downstream distances.