Local Ground Level Research Articles

Hybrid Forecasting of Wind for Air Pollution Dispersion over Complex Terrain

In case of an unplanned emission event from a nuclear power plant, the local population can be protected more efficiently when valid atmospheric dispersion model results are available. Atmospheric dispersion models use local meteorological variables as inputs. When atmospheric dispersion in the future is being predicted, a forecast of the local meteorological variables is needed. The most important variable in atmospheric dispersion modelling is wind, and accurately predicting ground level winds presents a challenge to numerical weather prediction models. We therefore develop hybrid models for forecasting local ground level wind at a single location where the terrain is complex and the average wind is weak and fluctuating. Wind speed and direction are modelled as west-east and south-north wind components. Each model is composed of a numerical weather prediction model and a Gaussian process statistical model that uses numerical weather predictions as some of its inputs and is trained on historical data to predict the output component. The most advanced Gaussian process models studied are of Gaussian process nonlinear autoregressive model with exogenous input (GPNARX) type. In addition to numerical weather predictions, they also use local meteorological variables, including the output variable, as their inputs. Numerical weather prediction results based on large scale information and fundamental knowledge of the system are thus supplemented by local measurements that better reflect the effects of local topography and land use. The models are tested by prediction and simulation. The wind components predicted by more advanced models are more accurate than raw or post-processed numerical weather prediction results. As an example, a model predicting 2D wind vector 1.5 h in advance achieves a NRMSE of 0.214 if it uses all the immediately available information. This is better than both the persistence model with NRMSE of 0.188 and post-processed NWP with NRMSE of 0.164. This demonstrates that hybrid modelling provides the best weather information for short-term and medium-term atmospheric dispersion forecasting. While the method is motivated by nuclear emission sources, it could also be applied to other pollution.

Investigation of sonic boom waveforms and metrics at elevated receiver locations

Microphones used for aircraft noise measurements are sometimes positioned above local ground level, for example to accommodate environmental protection or to comply with certification regulations. Acoustic waves reflected from the ground can interfere with waves propagating directly to elevated receivers. A modeling study was conducted of sonic boom waveforms received at ground level versus at elevated positions, using source characteristics for an early X-59 low-boom aircraft configuration (C609) and a variety of atmospheric conditions. Ground impedance effects from different ground cover types were also considered. Among several acoustic metrics, it was found that perceived level of loudness (PL) and A-weighted sound exposure level were in general the most sensitive to differences due to receiver position. Location within the boom carpet also affected receiver levels based on the angle between the incoming ray and the ground: the difference between metrics at ground and elevated receivers was generally higher at undertrack locations where that angle was largest. Depending on atmospheric conditions and receiver location within the carpet, predicted PL at an elevated receiver was lower than the level at the ground by up to 5.0 dB for a receiver height of 4 ft and 2.2 dB lower for a 1.6-ft receiver.

New European Wind Atlas: The Østerild balconies experiment

One of the main objectives of the New European Wind Atlas (NEWA) project is to carry out large scale field experiments at a high spatial and temporal resolution, and provide a significant upgrade to the experimental databases currently available. The Østerild balconies experiment aimed at collecting measurements over a relatively flat and semi-forested terrain to quantify the effect of various terrain features on the mean wind field. The experiment was performed at the Østerild test station for large wind turbines in Northern Denmark, from April to August 2016. The two 250 m meteorological towers available at the test site were equipped with balconies, first at 50 m above local ground level, later raised to 200 m. Scanning lidars were placed on each of the balconies, performing horizontal scans over 90° arcs with an east or west orientation depending on the incoming wind direction. The purpose of this study is to describe i) the new filtering method applied to the data, ii) the wind field reconstruction and the iii) utilisation of the derived wind fields to examine the imprint of surface heterogeneity on the mean wind flow. Cloud point data from aerial lidar scans were used to accurately derive the terrain and tree height. The mean wind flow patterns appeared to be heavily influenced by the terrain characteristics at the height of 50 m above ground level.

Searching for the effects of the May-June 2012 Emilia seismic sequence (northern Italy): medium-depth deformation structures at the periphery of the epicentral area

<p>In 2012, a seismic sequence occurred in the lowlands of the Emilia-Romagna Region (northern Italy), between the borders of the Modena, Ferrara and Bologna Provinces. It consisted of seven mainshocks (5.9 > Ml > 5) that were recorded between May 20 and 29, 2012 [INGV 2012a] and 2,200 minor earthquakes [INGV 2012b]. An interferometric analysis [Bignami et al. 2012, Salvi et al. 2012, this volume] highlighted three main deformation areas, each of which was 12 km wide (from S to N) and 10 km to 20 km long in an ESE-WNW to E-W direction, thus affecting an area of about 600 km2 (Figure 1). Field and aerial geological surveys recorded numerous surficial effects, such as: (i) sediment liquefaction [Crespellani et al. 2012]; (ii) localized ground fissures resembling surficial faulting [Fioravante and Giretti 2012] (Figure 2); (iii) groundwater levels rising up to 400 cm above the local ground level in phreatic wells during the mainshocks (lower values were observed in confined aquifers); and (iv) dormancy of previously known sinkholes [Borgatti et al. 2010, Cremonini 2010a, and references therein]. Some of the observed surface phenomena were previously recorded as coseismic effects during the earthquakes of Ferrara (1570) and Argenta (1624) [Boschi et al. 1995, Galli 2000], together with the early rising of the water level of the Po River in the Stellata section. […]</p>

The relation between intraocular pressure change and plasma natriuretic peptide under simulated hypobaric conditions

Purpose:To ascertain whether the changes in intraocular pressure (IOP) that occur during hypobaric hypoxic exposure are related to plasma N-terminal pro-brain natriuretic peptide (BNP) levels.Materials and Methods:The study group comprised 26 healthy participants (all male, mean age 23.1 years). IOP was measured at local ground level, (792 m above sea level), then while in a chamber providing hypobaric hypoxic conditions (the subjects were exposed to a pressure equivalent to 9144 m for 1-3 min), and again after exit from the chamber. In each condition, the mean of three consecutive measurements of IOP was calculated for each eye. For BNP measurements, blood samples were drawn before the participants entered the chamber and just after they left the chamber.Results:IOP during hypobaric hypoxic exposure (18.00 ± 3.70 mmHg) was significantly greater than that before (15.66 ± 2.10 mmHg, P < 0.001) or after (16.10 ± 2.63 mmHg, P = 0.001) the exposure. IOP levels before and after the exposure were not significantly different (P = 0.136). Plasma BNP levels measured before and after exposure to hypobaric hypoxic conditions were not significantly different (P = 0.462).Conclusion:Plasma BNP levels did not change after short-term hypobaric hypoxic exposure, while the IOP increased. This increase may have been caused by some other systemic factors. As the hypobaric hypoxic conditions were reversed, IOP decreased to normal levels.

Age-Related Differences in Central Corneal Thickness Alterations Caused by Short-Term Hypobaric Hypoxia

To assess the effect of short-term hypobaric hypoxic exposure on central corneal thickness (CCT) in healthy participants in 2 different age groups. Seventy eyes in 35 healthy men were investigated. Twenty participants (mean age 22.8 +/- 0.6 years) comprised 1 group, and 15 (mean age 32.1 +/- 2.8 years) comprised another group. CCT was measured via ultrasound pachymetry initially at local ground level (792 m above sea level), then during short-term hypobaric hypoxic exposure (equivalent to 9144 m altitude), and then again under ground level conditions. The mean of 10 consecutive CCT measurements in each eye under each set of conditions was used in statistical analysis. In the younger group, initial CCT was 561.5 +/- 36.1 microm. This increased to 562.3 +/- 36.7 microm under hypobaric hypoxic conditions, and after the return to local ground level conditions, CCT decreased to 560.1 +/- 34.5 microm. CCT values under hypobaric hypoxic conditions were not significantly different from those measured before or afterward (P > 0.05). In the older group, initial CCT was 566.0 +/- 33.7 microm. This increased to 576.9 +/- 28.5 microm under hypobaric hypoxic conditions, and after the return to local ground level conditions, CCT decreased to 567.9 +/- 33.3 microm. In the older group, CCT values under hypobaric hypoxic conditions were significantly greater than those measured initially (P < 0.001) or afterward (P < 0.01). In both age groups, initial CCT did not differ significantly from final CCT (P > 0.05). Short-term hypobaric hypoxic exposure increased CCT significantly in the older age group, whereas it yielded a nonsignificant minor increase in the younger age group.

Two Decades of Regular Observations of 14CO2 and 13CO2 Content in Atmospheric Carbon Dioxide in Central Europe: Long-Term Changes of Regional Anthropogenic Fossil CO2 Emissions

Time series are presented of radiocarbon and 13C contents in atmospheric carbon dioxide over eastern Europe (southern Poland), covering the periods 1983–1994 and 2000–2004. The carbon isotope composition was measured in biweekly composite samples of atmospheric CO2, collected about 20 m above the local ground level. The data for 2 observational sites are presented: i) city of Kraków (50°04′N, 19°55′E; 220 m asl; for 1983–1994 and 2000–2004); and ii) Kasprowy Wierch, Tatra Mountains (49°14′N, 19°56′E; 1989 m asl; for 2000–2004). The latter site is considered a regional reference station, relatively free of anthropogenic influences. During the period 1983–1994, observations in the Kraków area revealed a gradual decrease of 14C content with a broad minimum around 1991 and a small increase by about 10% in the subsequent years. δ13C also changes with time, showing a decreasing trend from approximately −9.6% in 1983, with a slope of −0.02%/yr. The observed trends for both isotopes coincide well with a substantial reduction of coal consumption in Poland and partial replacement of coal by natural gas, especially in urban regions. After 2000, the δ13C slightly increases, reaching a mean value of −10% in 2004, while Δ14C is below the reference level by ∼3.5%. Observations at Kasprowy Wierch (regional reference station) also reflect a diminishing input of fossil carbon into the regional atmosphere. The fossil component in atmospheric CO2, calculated with the aid of 14C data available for the 2 study periods, shows a reduction of anthropogenic input by a factor of 2, which is confirmed by annual statistics of coal consumption.

A compact quantum-cascade laser based spectrometer for monitoring the concentrations of methane and nitrous oxide in the troposphere

A spectrometer, based on the frequency down-chirped radiation from a pulsed quantum-cascade laser, capable of detecting fluctuations in local ground level methane and nitrous oxide concentrations over a time scale of minutes, is presented. The applicability of this instrument to low-level atmospheric detection is demonstrated through sampling gases in two locations.

Field validation of a semi-continuous method for aerosol black carbon (aethalometer) and temporal patterns of summertime hourly black carbon measurements in southwestern PA

Two methods for measuring aerosol elemental carbon (EC) are compared. Three-hour integrated carbon samples were collected on quartz filters during the summer of 1990 in Uniontown, PA, primarily during episodes of elevated particulate pollution levels. These samples were analyzed for EC and organic carbon (OC) using a thermo/optical reflectance (TOR) method. Aerosol black carbon (BC) was measured using an Aethalometer, a semi-continuous optical absorption method. The optical attenuation factor for ambient BC was supplied by the instrument manufacturer. Three-hour average concentrations were calculated from the semi-continuous BC measurements to temporally match the EC/OC integrated quartz filter samples. BC and EC concentrations are highly correlated over the study period ( R 2=0.925). The regression equation is BC (μg m -3)=0.95 (±0.04) EC−0.2 (±0.4). The means of 3 h average measurements for EC and BC are 2.3 and 2.0 μg m -3, respectively, average concentrations of EC and BC ranged from 0.6 to 9.4 and 0.5 to 9.0 μg m -3 respectively. TOR OC and EC concentrations were not highly correlated ( R 2=0.22). The mean OC/EC ratio was 1.85. The 10-week Aethalometer hourly dataset was analyzed for daily and weekly temporal patterns. A strong diurnal BC pattern was observed, with peaks occurring between 7 a.m. and 9 a.m. local time. This is consistent with the increase in emissions from ground level combustion sources in the morning, coupled with poor dispersion before daytime vertical mixing is established. There was also some indication of a day-of-week effect on BC concentrations, attributed to activity of local ground level anthropogenic sources. Comparison of BC concentrations with co-located measurements of coefficient of haze in a separate field study in Philadelphia, PA, during the summer of 1992 showed good correlation between the two measurements ( R 2=0.82).

Wind-driven upwelling off the Namaqualand coast of South Africa in spring 1980

Sea surface temperature was monitored off the Namaqualand coast of South Africa (29–32°S, 16–18°E) during the spring of 1980 by aerial radiation thermometry. The aircraft flew a grid pattern extending 30 km inland and about 100 km offshore. Wind data were obtained from aircraft drift measurements at 152 m above sea or local ground level. A time series of wind information from a coastal station in the centre of the study area showed a longshore wind direction (170°) with a slight onshore component due to the prevalence of seabreezes. The South Atlantic high-pressure cell and equatorward wind flow became established during October 1980. However, in November a persistent upper-air trough caused wind reversals affecting the distribution of sea surface temperature. Upwelling off Namaqualand is typically confined to the coastal strip, but with a broad plume of cold water extending offshore near 30°S. The location of the minima in sea surface temperature is attributed to the proximity of a southerly wind maximum...

Urban path-loss characteristics at 820 MHz

Results are presented of UHF propagation measurements conducted at 820 MHz in urban Philadelphia. The Philadelphia tests departed from previous path-loss measurements in that emphasis was placed on transmission from relatively low land-site antennas at heights of 40-70 feet above local ground level. Composite path-loss statistics have been derived for transmissions from five separate locations covering local environments considered typical of an urban area. This paper describes the measurement configuration, summarizes the data processing techniques, and presents results of the analysis.

A Note on Stratigraphy at Memphis

In volume XI of this journal Christine Lilyquist published a short account of the ''Middle King dom (or more likely, as she herself argues, First Intermediate Period) cemetery discovered accidentally at Memphis in 1954 and excavated by the Department of Antiquities.1 In March 1975 I paid a brief visit to the site in the company of Abdulla Sayed Mahmoud of the Department of Antiquities, who is preparing a more detailed account of this work. The observations which I made on the context should be regarded as a supplement to Dr. Lilyquist's article; to carry them much further would amount to beginning a fresh survey of Memphis, though this is badly needed. A small number of diagnostic sherds were drawn on the spot and are illustrated here (fig. 1); Mr. Abdulla Sayed very kindly supplied me with the photograph for pl. I. It may be recalled that the burial chambers so far uncovered seem all to be part of one large multiple tomb, probably within one enclosure wall, of a type known elsewhere at this time. One of the excavation photographs shows that, on the east side of the relatively small total area excavated, the eastern wall of this communal tomb was exposed, and, lying in front of it, a row of offeringtables at something like three meters below the present average ground level. In pl. I this east wall of the tomb is towards the right side of the photograph, running away from the viewer. The heap of rough stones piled up against it serves now to protect one of the two funerary stelae found in position in the wall and left standing. The offering-tables were in a row occupying the ground beyond, which has since been partly buried again by an accumulation of earth. The discovery of the offering-tables was of great importance, for it indicated directly where the local ground level was at the time when the tomb was made, and that, as a consequence, most of the burial chambers were at the then ground level. A close parallel to this situation is provided by a large tomb excavated by the Antiquities Department in 1961 at Tell Basta.2 However, beneath this level, as Dr. Lilyquist notes,3 there appear to have been at least two more chambers, and these were presumably truly subterranean, cut into the local ground level beneath the main mass of the communal tomb. In the absence of a detailed contour plan of Memphis, or of a series of spot heights, it is difficult to relate with any precision this particular Middle Kingdom ground level to the floor levels of the nearby New Kingdom shrines and temples, but all would seem to be not far from the present water-table, which provides a rough-and-ready common horizon. Thus the lower burial chambers of the tomb are now partly filled with damp earth to suggest that the water table is not far beneath, and this is the case with the nearby small temple of Hathor Nebet-Hetepet,4 whilst the floors of the great Ptah temple and of the very ruined temple of Rameses II behind the Museum housing the famous colossus are now actually under water. It thus seems likely that the tomb was built on ground which was, if anything, slightly above the level which was used as the floor for the adjacent New Kingdom temples. It is evident from the north and south sides of the cutting in which the tomb lies exposed that the site had been covered by one or more strata of ancient debris. On the north side (pl. I) it can be seen that, when this debris began to accumulate, the roof of the tomb was in ruins and the rubbish