Variations In Surface Conditions Research Articles

Using ADEOS/POLDER data to reduce angular variability of NOAA/AVHRR reflectances

Time series of National Oceanic and Atmospheric Administration (NOAA)/Advanced Very High Resolution Radiometer (AVHRR) Global Area Coverage (GAC) data, collected daily over two 50-km targets during March–June 1997 in Hungary, were corrected for angular effects using coincident multiangle Polarization and Directionality of the Earth's Reflectance (POLDER) Level-2 Land Surface data products. The POLDER data used consisted of narrow-band 0.67- and 0.765-μm reflectances corrected for ozone and water vapor absorption and Rayleigh scattering effects. The AVHRR visible (0.55–0.75 μm) and near-IR (0.68–1.05 μm) data were converted to reflectances, screened for clouds, and corrected for the same atmospheric effects as the POLDER data. Neither POLDER nor AVHRR data were corrected for aerosol effects. POLDER reflectances were used to derive bidirectional reflectance distribution function (BRDF) for each 6-km 2 POLDER grid box. The BRDFs were normalized to the near-nadir values at 45° solar zenith angle, resulting in the anisotropic factors, which were derived for each month for each grid box. Thus, seasonal variability of local anisotropy for each POLDER grid box in the target areas was established. The anisotropic factors were then applied to the AVHRR/GAC visible and near-IR reflectances mapped into the POLDER grid. The anisotropy-corrected AVHRR reflectances exhibit less fluctuation than the original uncorrected values, thus, facilitating the interpretation of short-term variability in surface conditions. Application of the POLDER BRDFs to AVHRR data is especially advantageous for processing AVHRR temporal composites because of the scarce angular statistics in the areas of frequent clouds, which hampers derivation of BRDFs from AVHRR data itself. Assuming that the local BRDF does not substantially vary from year to year, this approach could be extended to data from the growing seasons of other years. Ultimately, the multiyear time series could be corrected so that the variability, related to angular effects, inherent to AVHRR time series, is reduced. The current approach suggests a paradigm for a synergistic use of TERRA/EOS Multiangle Imaging SpectroRadiometer (MISR)/MODerate resolution Imaging Spectrometer (MODIS) data stream.

Are biodiversity ‘hotspots’ correlated with current ecoclimatic stability? A pilot study using the NOAA-AVHRR remote sensing data

The GAC (Global Area Coverage) by the NOAA-AVHRR satellites represents an excellent data set for studying global and regional patterns of variations in surface conditions driven in part by climatic variation. In this pilot study we examined whether biodiversity ‘hotspots’, defined from peak concentrations of neoendemics as well as geographically relict forms, differ in ecoclimatic stability from surrounding areas under present-day climatic conditions. Coefficients of variation of the ratio between brightness surface temperature (Ts) and the Normalized Difference Vegetation Index (NDVI) based upon 10 years' monthly composited scenes of tropical Africa revealed distinctive geographical patterns of interannual variability in surface conditions. Regions with a predominance of old species are characterized by spatial uniformity in the ecoclimatic variability, while regions where rapidly radiating groups dominate are spatially complex in this respect. However, the exact ‘hotspots’, with peak concentrations of endemic species, are characterized by a local reduction in ecoclimatic variability, or placement on the boundary to a stable region. This relationship was supported statistically by comparing ecoclimatic profiles across montane forests representing ‘hotspots’, and those of other montane forests. It is suggested that, because of interactions between prevailing atmospheric flows, topography and vegetation, the impact of extreme weather is moderated locally. The correlation between current stability and aggregates of neoendemics as well as old relics indicate that local moderation of climatic extremes persist through shifting climatic periods, permitting populations of unique species to survive in these places. The results are used to identify study sites for better ground truthing and for paleoclimatological studies which may be useful for more thorough studies of these relationships.

Comparative influence of land and sea surfaces on the Sahelian drought: a numerical study

Abstract. The aim of this work is to compare the relative impact of land and sea surface anomalies on Sahel rainfall and to describe the associated anomalies in the atmospheric general circulation. This sensitivity study was done with the Météo-France climate model: ARPEGE. The sensitivity to land surface conditions consists of changes in the management of water and heat exchanges by vegetation cover and bare soil. The sensitivity to ocean surfaces consists in forcing the lower boundary of the model with worldwide composite sea surface temperature (SST) anomalies obtained from the difference between 4 dry Sahel years and 4 wet Sahel years observed since 1970. For each case, the spatiotemporal variability of the simulated rainfall anomaly and changes in the modelled tropical easterly jet (TEJ) and African easterly jet (AEJ) are discussed. The global changes in land surface evaporation have caused a rainfall deficit over the Sahel and over the Guinea Coast. No significant changes in the simulated TEJ and an enhancement of the AEJ are found; at the surface, the energy budget and the hydrological cycle are substantially modified. On the other hand, SST anomalies induce a negative rainfall anomaly over the Sahel and a positive rainfall anomaly to the south of this area. The rainfall deficit due to those anomalies is consistent with previous diagnostic and sensitivity studies. The TEJ is weaker and the AEJ is stronger than in the reference. The composite impact of SST and land surfaces anomalies is also analyzed: the simulated rainfall anomaly is similar to the observed mean African drought patterns. This work suggests that large-scale variations of surface conditions may have a substantial influence on Sahel rainfall and shows the importance of land surface parameterization in climate change modelling. In addition, it points out the interest in accurately considering the land and sea surfaces conditions in sensitivity studies on Sahel rainfall.

Basin‐scale solar irradiance estimates in semiarid regions using GOES 7

Semiarid regions exhibit large temporal and spatial variability in surface conditions and, therefore, pose a challenge for estimating components of the surface energy budget. In particular, it is difficult to estimate the evapotranspiration component of the hydrological cycle. Because evapotranspiration is strongly controlled by absorbed solar radiation, an attempt has been made here to evaluate the accuracy at which the downward shortwave irradiance (SW ↓) can be estimated from satellites on basin scale. It was demonstrated that even under highly variable cloud conditions, satellite estimates of SW ↓ daily means were within 10% of measured values, while 5‐day means were within 3% of measured values. Such accuracies are of relevance for hydrological modeling at watershed and basin scales.

Effect of monoline process on hard disk properties

Monoline process or integrated production system in hard disk fabrication was studied. Properties of hard disks depend on the time between processes because of alternating their surface conditions. In batch process, disks should be kept in a certain hours between processes untill the variation of surface conditions are saturated to avoid property deviations. In monoline process, disk properties will kept uniformly from disk to disk, because the periodical treatments give constant surface conditions. In some means, it should be called a dynamic process.

Recent warming in southeastern Zaire (Central Africa) inferred from disturbed geothermal gradients

Several temperature-depth profiles measured in Kasai and in Shaba provinces of Zaire using mining exploration boreholes exhibit a significant negative temperature gradient near the surface. This anomalous curvature which extends to 100–200 m depth could reflect the effect of variations in surface conditions. Applying the theory of heat conduction in a semi-infinite homogeneous medium, these profiles indicate a surface warming by 3–4°C. This warming is related to the effect of the environmental changes associated with the mining exploitation and the urbanization during the last 40–90 years.

Recent warming in southeastern Zaire (Central Africa) inferred from disturbed geothermal gradients

Several temperature-depth profiles measured in Kasai and in Shaba provinces of Zaire using mining exploration boreholes exhibit a significant negative temperature gradient near the surface. This anomalous curvature which extends to 100–200 m depth could reflect the effect of variations in surface conditions. Applying the theory of heat conduction in a semi-infinite homogeneous medium, these profiles indicate a surface warming by 3–4°C. This warming is related to the effect of the environmental changes associated with the mining exploitation and the urbanization during the last 40–90 years.

Role of native oxide in the activation of implanted Si in GaAs

We have investigated the effect of oxygen plasma treatment on GaAs surface prior to plasma enhanced chemical vapor deposition of silicon nitride cap on the activation efficiency of implanted Si in GaAs. The oxygen plasma treatment improved the activation efficiency by ∼35% over (1:10) NH4OH:H2O treatment. In addition, the oxygen plasma treated samples had uniform sheet resistance across the wafer with minimum wafer-to-wafer variations. X-ray photoelectron spectroscopy analysis of oxygen plasma treated GaAs surface indicated the formation of ∼25-Å-thick oxide layer consisting of Ga2O3, As2O3, As2O5, and elemental As. During the activation anneal, the arsenic-containing oxides react with the GaAs substrate to form Ga2O3 and elemental As which increases the probability that the implanted Si incorporates in the Ga sites over the As sites, and thereby improves the activation efficiency. This surface related mechanism suggests that the variation in activation efficiency is mostly attributed to variation in surface conditions, and may explain the wide variety of reported values of activation efficiency. The higher and uniform activation efficiency for high Si implants improved the wafer scale variation of ohmic contact resistance to n+-GaAs.

Improvement in the Activation Efficiency of Implanted Si in GaAs using Oxygen Plasma Pretreatment

ABSTRACTWe have investigated the effect of GaAs surface conditions prior to plasma enhanced chemical vapor deposition of a silicon nitride cap on the activation efficiency of implanted Si in GaAs. The oxygen plasma treatment improved the activation efficiency of implanted Si by ∼35% over (1:10) NH4OH:H2O treatment. X-ray photoelectron spectroscopy (XPS) analysis of the oxygen plasma treated GaAs surface indicated the formation of ∼25Å thick oxide layer consisting of Ga2O3, As2O3, As2O5 and elemental As. During the activation anneal, the arsenic-containing oxides react with the GaAs substrate to form Ga2O3 and elemental As. The presence of excess As between the GaAs and the nitride cap film increases the probability that the implanted Si incorporates in the Ga sites over the As sites, and thereby improves the activation efficiency. This surface-related mechanism suggests that the variation in activation efficiency is mostly attributed to variation in surface conditions, and may explain the wide variety of reported values of activation efficiency.

Development of an accelerated abrasion test apparatus with a standardized testing procedure

Depending on the nature of the working environment, the abrasive wear of concrete floor slabs can range from scratching or scuffing to impact and local crushing. To assess abrasion resistance it is, therefore, necessary to have a versatile apparatus. This investigation describes the development of a basic apparatus with three modes of action and a standardized testing procedure, for assessing the abrasion resistance of concrete slabs in the industrial environment. It consisted of a rotating plate carrying a total load of 65 kg so that it was sufficiently portable for both laboratory and site testing. Three different types of abrasion head—(a) revolving pads, (b) rolling wheels, (c) dressing wheels—could be fixed to the plate so that the effects of different modes of wear could be assessed. The abrasion resistance is expressed in terms of the depth of the groove produced by 15 min of abrasion. A laboratory programme was undertaken to assess the apparatus and test method. The factors examined included the methods of assessing the abrasive wear, the duration of the test, the minimum number of tests to reliably assess the abrasion resistance, the relative performance of the three types of test head and the mechanism(s) by which each head abraded the concrete surface. Consequently a standardized procedure was developed which was found to be sensitive to variations in surface conditions. This has the additional advantages of simulating service conditions and of being repeatable, easy to follow and with the cost and time of testing not being excessive.

Variation in the Apparent Coefficient of Friction of Wheat on Galvanized Steel

ABSTRACT TESTS were conducted with five different samples of galvanized steel to determine the variability that exists in the coefficient of friction of wheat on galvanized steel surfaces as a function of pressure and number of trials and to analyze the variation in surface conditions of the galvanized steel surface before and after use. It was determined that the coefficient of friction decreased with both pressure and the number of trials. This variation in the coefficient of friction is believed to be caused by a deposition of waxy paraffin coating on the galvanized surface as the test blades were pulled through the grain sample. Tests conducted with antidynamic tubes within a model bin supported the idea that the coefficient of friction varies with both pressure and the number of times the grain comes in contact with the galvanized surface.

Investigation of summer synoptic climate controls on the mass balance of Meighen Ice Cap

Abstract The Meighen Ice Cap synoptic climate classification system, developed from the study of six years of summer meteorological and glaciological observations, appears to account for significant variations in the energy‐ and mass‐balance climates of the ice cap. In relating the summer frequency of the three synoptic types to fourteen years of mass‐balance measurements, it was found that variations in surface conditions, solar angle and type of precipitation could be accounted for by the relative sequence of synoptic types. Further it was shown that the types could be represented by the position of the dominant 500‐mb cold Low influencing Meighen Island, thus providing a link between the mass balance and the general circulation. Dominance of the winter pattern of a 500‐mb Low in the Hudson Bay –Baffin Island region throughout the summer season is capable of maintaining Meighen Ice Cap at its present size. A shift of the 500‐mb Low from the winter position directly to the Beaufort Sea or adjoining Polar...

Variability of surface conditions in the West African Upwelling: Rebert, J. P., 1978. Doc. scient. Cent. Rech. océanogr., Dakar-Thiaroye, 67(100): 27 pp

Variability of surface conditions in the West African Upwelling: Rebert, J. P., 1978. Doc. scient. Cent. Rech. océanogr., Dakar-Thiaroye, 67(100): 27 pp

Supersonic viscous flow over cones at large angles of attack

Numerical solutions for the flow field about cones with nose angles of up to 30° at angles of attack up to 50° for a range of Reynolds numbers and wall temperature ratios are presented. The solutions obtained permit interaction between the inviscid region and the boundary layer on the body through the displacement-thickness effect. The solutions are valid throughout the flow field except in the region adjacent to the leeward line of symmetry. Comparisons are made with experimental results and other numerical solutions. Detailed flow structure and the variation of surface conditions with cone angle, incidence, Reynolds number and wall temperature are indicated. The numerical methods used for the inviscid flow equations are Telenin's method and the method of characteristics, while a modified form of the method of integral relations is applied to the boundary-layer equations.

Second-Harmonic Radiation from Metal Surfaces

A calculation is performed of the second-harmonic radiation generated by the reflection of incident radiation from a metal surface in a model that considers only plasma effects and neglects periodic lattice structure in the metallic bulk and any form of surface roughness. The radiation is due to three kinds of currents: one localized to within a few angstroms of the surface and parallel to it, another also localized at the surface but normal to it, and a bulk current in the skin-depth region of the incident light, a region several hundred angstroms thick. Previous expressions for the normal surface current are found to be incorrect, and a new expression is derived. The second-harmonic radiation due to the surface currents is sensitive to surface conditions, while the contribution of the bulk current is only weakly sensitive to them. Theoretical estimates suggest that changes in the radiation intensity with variation in surface condition are caused primarily by changes in the parallel surface currents due to variations in surface scattering. In the course of this investigation general relationships and explicit forms for the second-order response of an isotropic electron gas are given.

Apparatus for Studying Friction and Sliding Electrical Contacts

Apparatus for the study of friction and sliding electrical contacts is described in detail. The equipment is designed for precise atmospheric control, a feature proven to be essential in any study of sliding contact phenomena. Examples are given of the type of results obtained with this apparatus when used in frictional studies. The kinetic friction is recorded by a sensitive strain gauge system which indicates transient effects, due to the variations in surface conditions, within a single revolution of the test cylinder under the rider.

Physiography of the Prairies and North-Eastern Australia

THE much-debated problem why the prairies of the United States are treeless is, according to an article by Mr. B. Shimek in the Bulletin of the State University of Iowa, new series, No. 35, essentially one for the botanist, since, despite variation in surface-conditions, there is comparative uniformity in the flora throughout the area. Summarising the available evidence, the author concludes that exposure to evaporation, as determined by temperature, wind, and topography, is the primary factor in the development of the treeless condition, and that the flora persists in the exposed areas because of its xerophytic character. On the other hand, rainfall and drainage, although important as determining the amount of moisture in air and soil, are only a secondary factor, as they may be equal in the forested and treeless areas; while the nature of the soil and the geological formation affect the matter only so far as they induce conservation of water. Prairie-fires were an effect rather than a cause, and when they did act in the latter sense were but local, while seed-dispersal, although accounting for the growth of plants, will not explain the origin and presence of the flora as a whole. Finally, such agencies as the bison and the action of the sea do not enter into the problem at all.