Search

The current management focus for many of British Columbia's grasslands is on sustaining their high natural and economic values in light of concerns over climate change and spread of exotic species. To that end, scientific information on plant community--soil--topographic relationships is required to assist with the often complex decisions that managers face. We collected data on vegetation, topography, and soil properties at 38 sites over a range of elevation zones and aspects at Lac du Bois Grasslands Provincial Park near Kamloops, British Columbia. Cluster analysis of the vegetation data validated the current three-zonal system used for grazing management but indicated that boundaries between adjacent plant communities are interspersed according to aspect. Principal component analysis (PCA) of environmental variables identified a gradient from the less productive, lower grasslands (higher soil bulk density, bare soil, coarse fragment content), to the more productive, upper grasslands (higher litter cover, total soil C and aggregate stability). Projection of six exotic species functional groups into the PCA-environment space showed significant associations of winter annuals with the lower grasslands, versus perennials (both clonal reproducers and seed bankers) with the upper grasslands. Our analysis showed promise in identifying fine-scale linkages between plant community patterns and key environmental factors. This approach may be useful as part of a proactive management plan for maintaining the health of British Columbia grasslands. Key words: grassland plant communities, exotic species functional groups, principal component analysis, soil-topographic gradients, climate change. La gestion de plusieurs prairies de Colombie-Britannique se concentre sur la durabilite de leurs fortes valeurs naturelles et economiques a la lumiere des inquietudes soulevees par le changement climatique et la dissemination d'especes exotiques. A cette fin, une information scientifique relative aux relations entre la communaute vegetale, le sol et la topographie est necessaire afin de soutenir la prise de decisions souvent complexes a laquelle le gestionnaire doit faire face. Les auteurs ont recueilli des donnees sur la vegetation, la topographie et les proprietes du sol de 38 sites ?i travers un eventail de zones d'elevation et d'orientation dans le Lac du Bois Grasslands Provincial Park pres de Kamloops (Colombie-Britannique). L'analyse des grappes des donnees de la vegetation validait le systeme actuel a trois zones utilise dans la gestion du paturage, mais elle indiquait que les frontieres entre les communautes de plantes adjacentes sont disseminees en fonction de l'orientation. L'analyse en composantes principales (ACP) des variables environnementales a identifie un gradient des prairies moins productives plus basses (densite de masse du sol plus elevee, sol nu, contenu en fragments grossiers) vers les prairies plus productives plus elevees (couvert de litiere plus eleve, C total du sol, stabilite des agregats). La projection de six groupes fonctionnels d'especes exotiques dans l'ACP--espace environnemental a revele des associations significatives entre les annuelles d'hiver et les prairies plus basses, comparativement aux vivaces (reproducteurs clonaux et banques de semences) et les prairies plus elevees. L'analyse des auteurs s'annonce prometteuse pour identifier les liens a echelle fine entre les patrons des communautes vegetales et les facteurs environnementaux cles. Cette approche peut etre utile dans le contexte d'un plan de gestion proactif afin de maintenir la sante des prairies en Colombie-Britannique. [Traduit par la Redaction] Mots-cles : communautes vegetales des prairies, groupes fonctionnels d'especes exotiques, analyse en composantes principales, gradients sol-topographie, changement climatique., Introduction The grasslands of British Columbia (B.C.) are an asset to the province's biodiversity, economy, natural beauty, and recreation. Their conservation value for numerous endangered plant and animal species and [...]

The aim of this study was to qualitatively and quantitatively characterize the optic surface topography of unworn hydrogel contact lenses (CLs) using atomic force microscopy (AFM) analysis and methods of modern metrology. The CLs used in this study were vifilcon A (Focus® Monthly Toric Visitint® model, CIBA Vision Corp.). AFM analysis was performed in Tapping Mode™ in an aqueous environment. The surface roughness analysis was based on six quantitative statistical parameters: arithmetic mean deviation of the surface ([S.sub.a]), root mean square deviation of the surface ([S.sub.q]), skewness of the topography height distribution ([S.sub.sk]), kurtosis of the topography height distribution ([S.sub.ku]), 10-point average of the absolute heights ([S.sub.z]), and vertical distance between highest peak and lowest surface point ([S.sub.t]). These parameters were determined across different square areas (1,4, 9, 16, and 25 µ[m.sup,2]). The surface roughness parameter values were found to be dependent on the examined surface area. The values of [S.sub.a], [S.sub.q], |[S.sub.sk]|, [S.sub.z], and [S.sub.t] parameters increase with the increasing size of the scanning area, an opposite effect of that observed for the [S.sub.ku] parameter values. The proposed methodology might potentially have implications for the future testing of contact lens hydrophilic polymers. POLYM. ENG. SCI., 53:2141-2150, 2013. @ 2013 Society of Plastics Engineers, INTRODUCTION Digital image analysis and mathematical morphology is broadly used in many areas, including material science, medicine, and biology (1-3). In material science, the microstructure of machined surface topography, as [...]

Low-density polyethylene (LDPE) modified by atmospheric dielectric surface barrier discharge plasma in oxygen was investigated to improve surface properties and adhesion of LDPE to more polar polymers. The process of plasma modification was investigated using several methods--surface energy measurements, Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance (FTIR-ATR), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM). The surface energy of LDPE increased significantly after activation by oxygen barrier plasma even at very short time of modification. The FTIR-ATR spectra manifested the presence of carbonyl functional groups on the surface of polymer pretreated by oxygen barrier plasma. It was shown by SEM, and AFM, that the topography of modified LDPE was significantly changed and the surface of modified polymer exhibited higher roughness in comparison with unmodified polymer. The surface energy of treated LDPE diminished in the course of ageing especially during the first 10 days after modification by barrier plasma. Hydrophilicity of the modified LDPE surface was stabilized by photochemical post-functionalization with 2,2,6,6-tetramethyl-piperidin-4-yl-diazoacetate. POLYM. ENG. SCI., 53:516-523, 2013. © 2012 Society of Plastics Engineers, INTRODUCTION Polyethylene exhibits many valuable bulk properties, but it has low surface energy (1, 2) which causes its poor dyeability and bondability. The modification and/or activation is necessary for improving [...]

Researchers in several continents have found that agriculture began not in major river valleys but up in the hills, where early farmers tended crops on alluvial fans and improved irrigation by building earth barriers across them. Here the authors reveal a similar process in the hills of Baluchistan and Khyber Pakhtunkhwa, where early farming villages overlook the plains of the Punjab and Sindh, heartland of the later Indus civilisation. Today this is a troubled border zone, with difficult access on the ground, but our researchers make exemplary use of satellite survey to map the villages in their specific local environments. Keywords: South Asia, early villages, environment, topography, agriculture, Introduction The topographical and environmental contexts of the earliest settlement sites in South Asia are critical factors for understanding the origins and spread of village-based farming. The specific locations of [...]

The famous Celtic site of Entremont, well known for its head cult and warrior statues, is a heritage gem of southern France. This naturally inhibits further excavation there, bur the authors show just how much can be achieved through an integrated package of remote mapping techniques. Their exemplary methodology produced more than a high resolution plan of the unexcavated part of the site; this type of integrated procedure generates ground-breaking research, without breaking any ground. Here the investigation mobilised arguments for pre-urban monuments, and the activities, enclosures, entrances and circulation of the oppidum. Keywords: France, Entremont, Late Iron Age (third to second century BC), topographic survey, geophysical survey, GPR, oppidum, urbanism, Introduction The degree to which urbanisation in the indigenous societies of temperate Europe was a direct reflection of Mediterranean prototypes is a recurrent question in Iron Age studies. The organisation [...]

The placoid scales, or denticles, of the external epidermis of elasmobranchs are well known as a hard protective coat over the skin to reduce abrasion or as elements lo reduce hydrodynamic drag. However, the structure and function of denticles within the oral cavity is uncertain. Using stereological and scanning electron microscopy, this study examines the structure and distribution of oral denticles in a range of elasmobranchs. Of the batoids analyzed, only members of the Rhinobatidae possessed oral denticles, with no denticles found in the members sampled in the Gymnuridae or Dasyatidae. In contrast, oral denticles were located in all the selachians examined, except for members of the Orectolobidae. Within the selachians, the denticles of the Carcharhinidae have a grooved surface and a central spine, which is angled toward the posterior of the mouth. These denticular adaptations are beneficial to reduce hydro-dynamic drag, an advantage for these free-swimming species with ram ventilation. Alternatively, members of the Hemiscyllidae have broad bulbous denticles that often overlap, providing a hard surface to protect the epithelium from abrasion during the consumption of hard-bodied prey. The distribution and high number of oral denticles appears to spatially compromise the capacity for oral (taste) papillae to populate the oropharyngeal cavity but provides increased friction and grip on prey items as they are manipulated within the mouth., Introduction The epidermis of teirrestrial vertebrates has a protective outer layer of dead keratinized cells, whereas the protective outer layer of most fishes consists of living cells that form scales [...]

[1] Geochronology of fluvial deposits can be used to characterize provenance, the paleotopography of sediment source regions, and the development of regional drainage systems. We present U-Pb and (U-Th)/He ages of detrital zircon grains from Eocene gravels preserved in several paleoriver systems along the western flank of the central and northern Sierra Nevada. These ages allow us to trace the sourcing of detritus in paleorivers and to constrain the evolution of the Sierra Nevada range front. U-Pb zircon age distributions are bimodal, with a dominant peak between 1 10 and 95 Ma and smaller but significant peaks in the Middle to Late Jurassic, matching the predominant ages of the Sierra Nevada batholith. A small fraction (

Industrially ground surfaces often have a characteristic surface topography known as chatter marks. The surface finishing is mainly monitored by optical measurement techniques. In this work, the monitoring of an industrial belt grinding process with a light scattering sensor is presented. Although this technique is primarily applied for parametric surface roughness analysis, here it is shown that it enables also the measurement of the surface topography, i.e., the chatter marks occurring during the belt grinding process. In particular, it is proven that the light scattering method is appropriate to measure online the topography of chatter marks. Furthermore, the frequency analysis of the data reveals that the wavelength of chatter marks strongly depends on process parameters, such as the grinding speed. OCIS codes: 120.3940, 290.5880.

A new scanning electrochemical microscopy (SECM) tip positioning method that allows surface topography and activity to be resolved simultaneously and independently is presented. The tip, controlled by a piezoelectric positioner operated in closed loop, is oscillated normal to the substrate surface. Changes in the oscillation amplitude, caused by the intermittent contact (IC) of the tip with the substrate surface, are used as a feedback signal to control the tip height. The method is illustrated with amperometric feedback approach curve measurements to inert (insulating) and active (conducting) substrates using 12.5 and 1 [micro]m radii Pt disk electrodes. Imaging of gold bands on a glass substrate demonstrates the capabilities for simultaneous topography and activity mapping. The prospect for using IC methodology more widely with other types of tips is highlighted briefly. 10.1021/ac101099e

The theory of conductive heat transfer cannot explain different attenuations of the daily amplitude of peat temperatures (Ts) in hummocks (detectable below the 20-cm depth) and hollows (disappearing above the 10+ cm depth). Large readily drained macropores in the upper fibric peat determine a large air permeability and hence may enhance heat transfer by air convection in porous media, driven by temperature gradients between hummock sides and interiors. In this study, the ecosys model was used to simulate a peat thermal regime at Mer Bleue peatland, Ontario, Canada. It was hypothesized that adding the air-convective heat transfer to conductive plus water-convective heat transfers would improve simulations of [T.sub.S]. The results for [T.sub.S], ground heat fluxes, G, and sensible heat fluxes, H, modeled with and without air-convective heat transfer were tested with continuous hourly measurements from 2000 to 2004 using thermocouples, heat flux plates, and eddy covariance. Simulated air-convective heat transfer caused an average increase in 6' and a corresponding decrease in H of ~20 W [m.sup.-2] from the simulated conductive plus water-convective heat transfer. Hastened soil warming in hummocks resulted in better agreement between measured and simulated hummock [T.sub.S] values with (RMSD of 2.23[degrees]C) than without air-convective heat (RMSD of 2.54[degrees]C). Enhanced hummock [T.sub.S] caused an indirect increase in hollow Ts in the model with (RMSD of 1.68[degrees]C) compared to without airoconvective heat (RMSD of 1.82[degrees]C). Our results suggest that air convection is probably an important mechanism of heat transfer in peat hummocks and should be included in peatland biogeochemical models. doi: 10.2136/sssaj2009.0288

At finer scales, raindrops are the sources of the onset of soil erosion. Understanding the effects of raindrops at the decimeter scale is useful for soil erosion prediction, understanding erosion principles, and deriving erosion control management practices. The objective of this study was to develop and test a physically based model to predict the effect of raindrop erosion on soil microtopogeaphy and identify the parameters that can be experimentally measured. The model has three parameters: (i) detachment rate [mu] ~ (9.0 [+ or -] 4.0) x [10.sup.-2] kg [m.sup.-2][mm,sup.-1], (ii) average projection distance). [lambda] 0.15 [+ or -] 0.05 m, and (iii) a dimensionless anisotropy coefficient [delta] 3 [+ or -] 1, which expresses the slope dependency of [lambda] and [mu]. Variation in soil height caused by raindrop erosion followed a diffusion-type equation with a source term. Under uniform conditions of soil and rainfall, the model simplifies into a basic diffusion equation. Under the homogeneous bare soil condition, soil surface roughness is predicted by an exponential decay model. Under nonuniform conditions, when sparse perennial vegetation protects the soil locally from raindrop impact (a common surface feature in semiarid areas), the model predicts that small mounds of 2 to 30 cm in height can develop underneath the cover. On a horizontal surface, the mound height asymptotically tends to a limit. On sloping areas, however, mounds are predicted to develop faster, higher, and to be asymmetric. Under both flat and sloping terrain, model predictions were found consistent with published data and models, with the noticeable improvement that the model parameters can be measured by laboratory experiments. doi: 10.2136/sssaj2009.0063

The Colorado Plateau of the southwestern United States is characterized by a bowl-shaped high elevation, late Neogene--Quaternary magmatism at its edge, large gradients in seismic wave velocity across its margins, and relatively low lithospheric seismic wave velocities. We explain these observations by edge-driven convection following rehydration of Colorado Plateau lithosphere. A rapidly emplaced Cenozoic step in lithosphere thickness between the Colorado Plateau and adjacent extended Rio Grande rift and Basin and Range province causes small-scale convection in the asthenosphere. A lithospheric drip below the plateau is removing lithosphere material from the edge that is heated and metasomatized, resulting in magmatism. Edge-driven convection also drives margin uplift, giving the plateau its characteristic bowl shape. The edge-driven convection model shows good consistency with features resolved by seismic tomography. doi: 10.1130/G31031.1

The individual components of the slope-parallel surface radiation balance were measured in and around Arizona's Meteor Crater to investigate the effects of topography on the radiation balance. The crater basin has a diameter of 1.2 km and a depth of 170 m. The observations cover the crater floor, the crater rim, four sites on the inner sidewalls on an east-west transect, and two sites outside the crater. Interpretation of the role of topography on radiation differences among the sites on a representative clear day is facilitated by the unique symmetric crater topography. The shortwave radiation balance was affected by the topographic effects of terrain exposure, terrain shading, and terrain reflections, and by surface albedo variations. Terrain exposure caused a site on the steeper upper eastern sidewall of the crater to receive 6% more daily integrated shortwave energy than a site on the lower part of the same slope. Terrain shading had a larger effect on the lower slopes than on the upper slopes. At the lower western slope site the daily total was reduced by 6%. Measurements indicate a diffuse radiation enhancement due to sidewall reflections. The longwave radiation balance was affected by counterradiation from the crater sidewalls and by reduced emissions due to the formation of a nighttime temperature inversion. The total nighttime longwave energy loss at the crater floor was 72% of the loss observed at the crater rim. DOI: 10.1175/2010JAMC2353.1

Fault scarps represent the most obvious expression of tectonic activity at the Earth's surface. Studies on scarp morphology place constraints on fault kinematics and scarp-degradation processes, and were often based on geomorphic dating techniques. Fault scarps exposed in areas of simple topography facilitate data acquisition and interpretation, whereas little work bad been done where fault scarps are superimposed on complex, dissected topography. Fault scarps developed in complex topography are commonly observed along flower structures and at tips of strike-slip faults. Such structures are important elements for evaluating the evolution and linking of strike-slip fault systems, and appear to be scale-independent from several meters to hundreds of kilometers. We examined the detailed meter- to hundred meter--scale structure and surface expression of a flank of one fault scarp--bounded pressure ridge (Rex Hills flower structure) by combining field mapping with high-resolution digital elevation model (DEM) analysis. Based on terrestrial laser scanning we generated a detailed DEM and extracted high-resolution topographic cross sections, which enabled us to identify fault scarps and to determine their relative ages and geometry. Our study site is located on the transpressional left-bend between the Pahrump and Amargosa segments of the dextral Stateline fault system. The topography is characterized by alternating valleys and ridges (each ~100 m long, relief of ~4 m). We observed the following: the southern Rex Hills slope exhibits three fault scarps related to three reverse fault branches; the basal scarp (scarp 1) is most continuous, and exhibits five segments, the upper two scarps (scarps 2 and 3) are less continuous. Furthermore, fault scarps exposed on ridge crests are more numerous (up to four to five scarps), and smaller (~5 m high); valleys often exhibit single large (>10 m high), smoothed scarps. To easily detect differences between the scarps, we evaluated the height and slope angle of the scarps using topographic cross sections. Our analysis indicates that scarp shape is influenced by fault dip, lithology, and degradation processes resulting in large scatter and broad overlap in scarp-height--slope-angle space. The analysis further indicates that scarp degradation is stronger in the valleys, and that the preservation potential of small, individual fault scarps is therefore greater on the ridge crests. We compared our fault-scarp data with published, calibrated data yielding an age of-2 ka for the Rex Hills scarps consistent with an earlier finding. This suggests that the scarp shape mainly reflects progressive degradation since the most recent surface rupture. Our approach of analyzing high-resolution topographic data of closely spaced fault scarps is promising especially when combined with subsurface data as well as geochronological and paleoseismic data, and it provides a basic scheme for analyzing scarp populations in a complex topographic region. Despite the absence of subsurface data, our approach allowed the study of complex high-resolution fault-scarp morphologies across a flower structure for the first time. doi: 10.1130/B26536.1

Incidents of chute cutoff are pervasive along many meandering rivers worldwide, but the process is seldom incorporated into theoretical analyses of planform evolution, partly due to the paucity of observations describing its physical controls. Here, we describe a mechanism of chute cutoff that may be prevalent along large meandering rivers with uniform floodplain topography. The mechanism occurs independently of sudden changes in conveyance capacity, such as those caused by natural dams, and instead, it is initiated during a flood by the incision of an embayment. The embayment is typically located almost a channel width upstream of the entrance to the meander that undergoes cutoff, and subsequent floods extend the embayment downstream until a chute is formed. Using sequences of historical aerial photos of the Sacramento River in California, USA, we found that embayments formed where channel curvature was greatest, or where the channel most tightly curved away from the downstream flow path. Embayments formed only within those portions of the floodplain that were lightly vegetated by grasses or crops. We develop a simple physical model that describes the environmental conditions that can lead to embayment formation. The model considers the role of floodplain vegetation in preventing chute incision and in part explains why chute cutoff is prevalent along some meandering rivers but not others. doi: 10.1130/B26560.1

Cordilleran orogenic systems such as the Andes are controlled by shortening rates, climatically-controlled erosion rates, and, in some cases, eclogite production and delamination. All of these processes are coupled, however, making it difficult to uniquely determine the relative importance of each process and the feedbacks among them. In this paper we develop a mass-balanced numerical model that couples an actively-shortening orogen and crustal root with eclogite production, delamination, and climatically controlled erosion. The model provides a first-order quantification of the sources (shortening) and sinks (erosion and eclogite production and delamination) of crustal volume during the Cenozoic in the Andes as a function of latitude and time. Given reasonable estimates for the rates of eclogite production and the threshold size of the eclogitic root required for delamination, the model suggests that, in the central Andes between 5[degrees]S and 32[degrees]S, the orogen has grown to a sufficient height to produce and maintain eclogite, which in turn has promoted delamination in the lower crust and mantle. In this region, climatically controlled erosion rates influence the size of the orogen through two separate mechanisms: by exporting mass via surface processes and by controlling the lithostatic pressure in the lower crust, which modulates the rates of eclogite production and/or delamination. To the north and south of the central Andes, relatively low shortening rates and high precipitation and erosion rates have slowed eclogite production such that delamination likely has not occurred during the Cenozoic. doi: 10.1130/G30755.1

Previous work with Mars general circulation models (MGCMs) has shown that the north south slope in Martian topography causes asymmetries in the Hadley cells at equinox and in the annual average. To quantitatively solve for the latitude of the dividing streamline and poleward boundaries of the cells, the Hadley cell model of Lindzen and Hou was modified to include topography. The model was thermally forced by Newtonian relaxation to an equilibrium temperature profile calculated with daily averaged solar forcing at constant season. Two sets of equilibrium temperatures were considered that either contained the effects of convection or did not. When convective effects were allowed, the presence of the slope component shifted the dividing streamline upslope, qualitatively similar to a change in season in Lindzen and Hou's original (flat) model. The modified model also confirmed that the geometrical effects of the slope are much smaller than the thermal effects of the slope on the radiative--convective equilibrium temperature aloft. The results are compared to a simple MGCM forced by Newtonian relaxation to the same equilibrium temperature profiles, and the two models agree except at the winter pole near solstice. The simple MGCM results for radiative convective forcing also show an asymmetry between the strengths of the Hadley cells at the northern summer and northern winter solstices. The Hadley cell weakens with increasing slope steepness at northern summer solstice but has little effect on the strength at northern winter solstice. DOI: 10.1175/2009JAS3130.1

We reconstruct ancient temperature and elevation gradients across the early Eocene (52-49 Ma) northern Sierra Nevada (California, United States) using organic molecular proxies that record atmospheric and ground-level effects of topography. Paleoelevation was determined by reconstructing the change in the hydrogen isotopic composition of precipitation ([DELTA][delta][D.sub.precip]) and mean annual temperature ([DELTA][T.sub.GDGT]) (glycerol dialkyl glycerol tetraethers) from the isotopic composition of fossil angiosperm leaf n-alkanes and the distribution of microbially produced soil tetraethers preserved in leaf-bearing sediments. Organic molecular data produce equivalent range-scale ([delta][D.sub.n-alkane]) and channel ([T.sub.GDGT]) paleoelevation estimates that show the northern Sierra Nevada was a warm (>6-8[degrees]C warmer than modern), high-elevation (>2 km), and moderate-to low-relief landscape at the Eocene Climatic Optimum. Modern northern Sierra Nevada topography likely reflects post-Paleocene reduction of mean surface elevation and late Cenozoic increases in relief. doi: 10.1130/G30215.1

Gap dynamics in temperate, late-suceessional forests influence important riparian functions, including organic matter recruitment and light environments over streams. However, controls on gap dynamics specific to riparian forests are poorly understood. We hypothesized that (i) gaps are larger and more frequent nearer streams, (ii.) gaps cluster at within-stand scales, and (iii) tree damage type and gap fraction vary among riparian landforms. All gaps within four 6-9 ha plots in riparian old-growth eastern hemlock (Tsuga canadensis (L.) Carriere) - northern hardwood forest in the Adirondack Mountains. New York, USA, were mapped and measured. We recorded species, damage type, and diameter at breast height for gapmakers and dominant perimeter trees. Spatial distribution was assessed with Ripley's K. Spatial autocorrelation in gap area and tree damage type were assessed using Moran's I. Linear regression analysis defined relationships between proximity to streams and gap area and frequency. Expanded gap fraction ranged from 28.3% to 47.6%. Gaps were randomly distributed at scales ≤25 m and clustered at scales of 63-122 m. Distribution patterns were not consistent at other scales. Convergent and divergent landforms significantly influenced gap fraction, tree damage type, and species distributions. Positive correlations between convergent topography and gap area suggest an interaction between low-order riparian landforms and gap formation dynamics in late-suceessional forests. Resume: La dynamique des trouees dans les forets temperees en fin de succession influence d'importantes fonctions riveraines. dont le recrutement de matiere organique et 1'environnement lumineux au dessus des cours d'eau. Cependant, les facteurs qui controlent la dynamique des trouees propre aux forets riveraines sont peu compris. Nous avons pose les hypotheses suivantes: (i) les trouees sont plus grandes et plus frequentes pres des cours d'eau. (ii) les trouees sont regroupees a une echelle plus petite que celle du peuplement et (iii) le type de dommages aux arbres et l'ouverture du couvert varient parmi les reliefs riverains. Nous avons cartographic et mesure toutes les trouees a l'interieur de parcelles de six a neuf ha etablies dans une vieille foret riveraine dominee par la pruche (Tsuga canadensis (L.) Carriere) et les feuillus nordiques et situee dans les montagnes Adirondack de l'Etat de New York, aux Etats-Unis. Nous avons note l'espece, le type de dommages et le DHP des arbres a l'origine d'une trouee et des arbres dominants en peripheric La distribution spatiale a ete estimee a l'aide du coefficient K de Ripley. L'autoeorrelation spatiale dans la trouee et le type de dommages aux arbres ont ete estimes a l'aide du coefficient I de Moran. Une analyse de regression lineaire a ete utilisee pour etablir les relations entre la proximite des cours d'eau et la superficie ainsi que la frequence des trouees. L'ouverture expansee du couvert variait de 28,3 % a 47,6 %. Les trouees etaient aleatoirement distribuees a des echelles allant jusqu' a 25 m et regroupees a des echelles variant de 63 a 122 m. Les patrons de distribution n' etaient pas coherents a d'autres echelles. Les reliefs convergents et divergent influencaient significativement l'ouverture du couvert, le type de dommages aux arbres et la distribution des especes. Des correlations positives entre la topographic convergente et la superficie des trouees indique qu'il y a une interaction entre les reliefs riverains de rang inferieur et la dynamique de formation des trouees dans les forets en fin de succession. [Traduit par la Redaction], Introduction Old-growth forests in northeastern North America provide important ecological and riparian functions. Compared with younger forest stands, old-growth northern hardwoods generally have more and larger canopy gaps, greater densities [...]

We address the measurement and correction of fan distortion in optical coherence tomography (OCT). This effect arises from the scanning system configuration and prevents one, in general, from obtaining quantitative topographic data from OCT. Computer simulations allowed us to quantify the effect and evaluate its dependence on the scanning mirror separation and design of the collimating lens, as well as to estimate the optimal axial position of that lens to minimize the fan distortion. We also developed a numerical algorithm based on 3-D ray propagation for the correction of the residual fan distortion. The effect was studied experimentally using a custom developed time-domain OCT in a Michelson configuration provided with a confocal channel, and the accuracy of the fan distortion correction algorithm tested on samples of known dimensions (flat surfaces and spherical lenses). With a proper calibration of the system with use of an onfocal channel, this algorithm makes it possible for time-domain OCT devices to be used as topographers. OCIS codes: 110.4500, 120.6650, 120.4640, 110.6880, 330.7327, 330.4300.

We obtained spatially extensive canopy height measurements using airborne remote sensing to characterize the structure and dynamics of a tropical rain forest landscape. Light detection and ranging (LiDAR) is a remote-sensing technology that acquires measurements of canopy height and ground elevation. By recording the return time of laser pulses emitted by aircraft-mounted sensors, LiDAR systems quantify the structure and geometry of individual trees and canopy height and enable estimation of the vertical and horizontal distribution of biomass using millions of accurate height measurements. This data set contains 127 849 839 records from 128 square kilometers of tropical wet forest in the Atlantic lowlands of Costa Rica (mean sampling density is 1.99 observations/[m.sup.2]). The study area includes all 16 square kilometers of mixed-land-use forest at the La Selva Biological Station and the lower flanks of Braulio Carrillo National Park. It contains a mosaic of historical and contemporary land use that is representative of contemporary tropical forest landscapes. Field studies demonstrated that LiDAR measurements were precise and accurate throughout the topographic and structural conditions at the site. Each record includes: easting and northing mapped coordinates (UTM Zone 16 North), height above ground (m), interpolated ground elevation (m), and six remote-sensing descriptors (point classification, the return number, the number of returns for the given pulse, intensity, scan angle, and the time of emission of the laser pulse). The data can be applied to a wide range of questions in basic and applied science, and are a valuable resource from a well-studied tropical rain forest for teaching and education. They also provide a quantitative baseline against which future conditions can be assessed. Key words: biomass,' carbon; Costa Rica; Jbrest structure; landscape; La Selva Biological Station; LiDAR; light detection and ranging; Neotropics; remote sensing; sustainability.

Field properties--topography, hydraulic resistance, and infiltration--play an important role in the performance of surface irrigation systems, and appropriate characterizations of these are required as data input to simulation or design software. The EWRI/ASCE Task Committee on Soil and Crop Hydraulic Properties has been charged with preparing a guide for practitioners faced with such data entry. The result is this special section of the Journal of Irrigation and Drainage Engineering in which this paper is the first in the series presented. It describes the characteristics of these field properties and notes a series of caveats to be considered when dealing with them in the course of analyses or designs of surface irrigation systems. DOI: 10.1061/(ASCE)IR.1943-4774.0000119 CE Database subject headings: Channel beds; Hydraulic roughness; Infiltration; Surface irrigation.

In geoid computation, effects of real three-dimensional topographic masses on the Earth's gravity field must be accurately quantified and, in the Stokes-Helmert scheme, replaced with effects of those masses condensed on the geoid. The most comprehensive modern schemes for evaluation of topographical effects account for terrain effects, use a spherical model of topography, and incorporate two-dimensionally varying models of topographical mass density. In this contribution, we employ a three-dimensionally varying model of topographical density. We use Newton's integration to determine the direct topographical effect (DTE) on gravity and primary indirect topographical effect (PITE) on gravity potential. Lastly, we apply Stokes' integration to calculate the DTE, PITE, and secondary indirect topographical effect (SITE) on geoidal height. We focus here on validation of our results and demonstration of our software's capabilities. We present results for the simple geometrical shape of a disc under various rotations and for the anomalous density of lake waters. Effects on geoidal height for these simulations reach centimetre level, up to 2.2 cm in magnitude. For a simulation of the effects of neglected mass anomalies of the lakes, we find results reaching 0.8 cm in magnitude. We examine the behavior of our results as calculated using various step sizes for numerical integration and by comparing numerical results with analytical results for the specific case of a disc. These results suggest that the maximum percent error of our results is about 23.5% for the DTE on gravity and 7.6% for the PITE on gravity potential. Dans le calcul d'un geoide, les effets de masses topographiques reelles tri-dimensionnelles sur le champ de gravite terrestre doivent etre quantifies adequatement et, selon la methode de Stokes-Helmert, ces effets doivent etre remplaces par les effets de ces masses condensees sur le geoide. Les methodes modernes les plus completes pour l'evaluation des effets topographiques tiennent compte des effets du terrain, utilisent un modele spherique de topographie et incorporent des modeles de topographie masse-densite variant dans deux dimensions. Dans cet article, nous utilisons un modele de densite topographique variant dans trois dimensions. Nous utilisons l'integration de Newton pour determiner l'effet topographique direct << DTE >> sur la gravite et l'effet topographique primaire indirect << PITE >> sur le potentiel gravimetrique. Finalement, nous appliquons l'integration de Stokes pour calculer le DTE, le PITE et l'effet topographique indirect secondaire << SITE >> sur l'ondulation du geoide. Nous mettons l'accent ici sur la validation de nos resultats et sur la demonstration des capacites de notre logiciel. Nous presentons les resultats pour la simple forme geometrique d'un disque sous diverses rotations et pour la densite anormale des eaux de lacs. Les effets sur l'ondulation du geoide de ces simulations atteignent le niveau du centimetre, jusqu'a une amplitude de 2,2 cm. Pour une simulation des effets des anomalies de masse negligees des lacs, nous obtenons des resultats qui atteignent une amplitude de 0,8 cm. Nous examinons le comportement de nos resultats tels que calcules en utilisant divers increments pour l'integration numerique et en comparant les resultats numeriques aux resultats analytiques pour le cas specifique d'un disque. Le pourcentage maximum d'erreur de nos resultats serait d'environ 23,5 % pour le DTE sur la gravite et de 7,6 % pour le PITE sur le potentiel gravimetrique. [Traduit par la Redaction], Introduction The geoid, an equipotential surface approximating mean sea level, is a common reference surface for height systems. It is given by its vertical separation from a reference geocentric biaxial [...]

A review of seven studies addressing soil flux related to manual hoeing and weeding in Asia and Africa indicates that tillage erosion from hand-held implements on steep hillslopes can alter topography and influence the distribution of soil and nutrients within fields. Soil flux resulting from manual tillage increases with slope in a near-linear fashion until the slope angle approaches the angle of repose for displaced aggregates. On steeper slope gradients, the increase in soil flux is nonlinear because displaced clods roll, bounce, or slide relatively long distances downslope before coming to rest or breaking down. Because of this ravel-like transport process, soil flux is modeled most appropriately across a wide range of gradients as a nonlinear process. A modified nonlinear ravel model predicted soil fluxes in the reviewed studies better than a linear model, but it was not superior to a general exponential model. Additional field studies are needed to increase the basic understanding and predictability of soil erosion by manual tillage on steep slopes, as this activity is still practiced in many areas of the world.

Corneal topography estimation that is based on the Placido disk principle relies on good quality of precorneal tear film and sufficiently wide eyelid (palpebral) aperture to avoid reflections from eyelashes. However, in practice, these conditions are not always fulfilled resulting in missing regions, smaller corneal coverage, and subsequently poorer estimates of corneal topography. Our aim was to enhance the standard operating range of a Placido disk videokeratoscope to obtain reliable corneal topography estimates in patients with poor tear film quality, such as encountered in those diagnosed with dry eye, and with narrower palpebral apertures as in the case of Asian subjects. This was achieved by incorporating in the instrument's own topography estimation algorithm an image processing technique that comprises a polar-domain adaptive filter and a morphological closing operator. The experimental results from measurements of test surfaces and real corneas showed that the incorporation of the proposed technique results in better estimates of corneal topography, and, in many cases, to a significant increase in the estimated coverage area making such an enhanced videokeratoscope a better tool for clinicians. Index Terms--Adaptive filtering, cornea, keratrometry, tear film.

Increases in atmospheric C have resulted in concerns about global warming and interest in finding the means to sequester atmospheric C through land management strategies. The purposes of this study were to: (i) compare changes in mineral soil C after a 30-yr interval, and (ii) examine the potential roles of soil N, soil texture, and topography in these changes. The Camp Branch watershed is a second-growth, oak-dominated, mixed hardwood forest on the Cumberland Plateau in central Tennessee. In July 1976, soil samples were collected at permanently identified points and archived. These points were resampled in July 2006 and both the archived and new samples of the 0- to 10-cm increment of the mineral soil were analyzed for C and N. Comparisons revealed that the changes in C and N were distinct to each of the eight soil series occurring on the site. Comparison of 2006 samples to 1976 samples indicated that changes in C concentration ranged from -13.1 to 12.0%. Changes in C mass ranged from -11.3 to 8.3%. Increases in C were most closely associated with increases in the C/total N ratio. The change in C was positively correlated with the change in exchangeable inorganic N ([r.sup.2] = 0.31, P< 0.0001). An overstory inventory indicated a decline in oak domination and site-specific changes in basal area, density, and stand age. Since regression analysis revealed that the change in C was riot predicted by topographic factors or soil texture, we speculate that changes in forest covet influenced the changes in mineral soil C.

The small helical protein BBL has been shown to fold and unfold in the absence of a free energy barrier according to a battery of quantitative criteria in equilibrium experiments, including probe-dependent equilibrium unfolding, complex coupling between denaturing agents, characteristic DSC thermogram, gradual melting of secondary structure, and heterogeneous atom-by-atom unfolding behaviors spanning the entire unfolding process. Here, we present the results of nanosecond T-jump experiments probing backbone structure by IR and end-to-end distance by FRET. The folding dynamics observed with these two probes are both exponential with common relaxation times but have large differences in amplitude following their probe-dependent equilibrium unfolding. The quantitative analysis of amplitude and relaxation time data for both probes shows that BBL folding dynamics are fully consistent with the one-state folding scenario and incompatible with alternative models involving one or several barrier crossing events. At 333 K, the relaxation time for BBL is 1.3 [micro]s, in agreement with previous folding speed limit estimates. However, late folding events at room temperature are an order of magnitude slower (20 [micro]s), indicating a relatively rough underlying energy landscape. Our results in BBL expose the dynamic features of one-state folding and chart the intrinsic time-scales for conformational motions along the folding process. Interestingly, the simple self-averaging folding dynamics of BBL are the exact dynamic properties required in molecular rheostats, thus supporting a biological role for one-state folding. downhill folding | folding landscape | landscape topography | protein dynamics

Systematic optimization of the tooth contact pattern under load is an open problem in the design of spiral bevel and hypoid gears. In order to enhance its shape and position, gear engineers have been assisted by numerical tools based on trial-and-error approaches, and/or they have been relying on the expertise of skilled operators. The present paper proposes a fully automatic procedure to optimize the loaded tooth contact pattern, with the advantage of eventually reducing design time and cost. The main problem was split into two identification subproblems: first, to identify the ease-off topography capable of optimizing the contact pattern; second, to identify the machine-tool setting variations required to obtain such ease-off modifications. Both of them were formulated and solved as unconstrained nonlinear optimization problems. In addition, an original strategy to quickly approximate the tooth contact pattern under load was conceived. The results obtained were very satisfactory in terms of accuracy, robustness, and computational speed. They also suggest that the time required to optimize the contact pattern can be significantly reduced compared with typical time frames. A sound mathematical framework ensures results independent of the practitioner's subjective decision-making process. By defining a proper objective function, the proposed method can also be applied to affect other contact properties, such as to improve the motion graph or to decrease the sensitivity of the transmission to assembly errors. Furthermore, it can be easily adapted to any gear drive by virtue of its systematic and versatile nature. [DOI: 10.1115/1.3013844]

We present a detailed analysis of the airborne passive microwave remote-sensing data that were collected at a broad range of microwave bands and at a high spatial resolution during the 2002 and 2003 National Aeronautics and Space Administration Cold Land Processes Experiment (CLPX). An accurate measurement of snowpack properties using passive microwave observations requires the detailed knowledge of the relationship between snowpack geophysical parameters and the upwelling polarimetric brightness signature. The principle microwave instrument used for the CLPX was the polarimetric scanning radiometer (PSR), which provided ~100-m resolution maps of the snow emissivity at all Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) bands during several intensive observation periods over the Colorado Rocky Mountains. The observed conditions included drought, normal snowpack, and spring snowmelt. The PSR and related ground-based observations of snowpack properties made during the 2002 and 2003 CLPX campaigns provide a comprehensive high-resolution passive microwave data set. Results show that the high-resolution PSR data exhibit emissivity modes that are similar to those observed in the historical data sets, and that the empirical relationships between the emissivity and the snow water equivalent (SWE), after the effects of macrovegetation are removed, closely match those found in the past theoretical studies. The use of the 89-GHz channel in the empirical relationships provides improved accuracy under dry snow conditions and a small SWE; however, the variability of the SWE--emissivity relationships increases with an increasing SWE. A summary of the observed relationships between the emissivity spectra of snow and snowpack properties is presented. Comparison of the total water content from the AMSR-E and PSR observations shows that the satellite measurements underestimated the total volume of water storage from airborne observations on the average by a factor of five. Index Terms--Airborne polarimetric scanning radiometer (PSR), beam polarization correction, georegistration, microwave emissivity, passive microwave remote sensing, retrieval algorithm development, snowpack, snow water equivalent (SWE), topography, validation.

The Colorado Plateau contains Late Cretaceous marine strata that are at a mean elevation of ~2 km. The timing and amount of uplift since the Cretaceous has generated considerable debate. With the exception of a few studies, topography supported by vertical stresses generated by viscous flow in the mantle has not been explicitly considered to contribute to the elevation of this region. Herein we compute the viscous flow beneath North America that is driven by density anomalies inferred from joint seismic-geodynamic modeling. We find that the Colorado Plateau overlies a strong mantle upwelling that is coupled to the sinking Farallon slab, currently beneath the eastern United States. Consequently, the Colorado Plateau is currently a focused dynamic topography high within the western U.S. Cordillera. Moreover, this strong upwelling impacts the base of the lithosphere at an oblique angle east of the plateau directly below the Rio Grande Rift. We attribute this flow as being responsible for some of the recent magmatic activity along the Jemez lineament as well as contributing to the recent rifting process in the Rio Grande Rift valley. Keywords: Colorado Plateau, Rio Grande Rift, mantle convection, dynamic topography, uplift rates.

In this paper, we evaluate the additive effects of topography, soil nonlinearity, and soil-structure interaction (SSI) along the crest of an idealized 40 m high cliff-type topographic feature with slope inclination 30[degrees], where excessive damage was observed during the Athens 1999 earthquake. The objective of this paper is to investigate the relative contribution of topographic amplification, and kinematic SSI as a function of the incident motion frequency content and geotechnical site conditions for a surface and fin embedded structure located at the cliff crest. For this purpose, we perform elastic parametric and nonlinear site-specific two-dimensional finite element simulations using three profiles and six input motions. We illustrate the role of SSI in altering the response at the location of peak topographic amplification potential behind the crest, the effects of incident motion incoherency on the transient structural response, and the beneficial contribution of structural embedment. We finally suggest that empirical models for base-slab averaging of shallow foundations, developed as a function of site conditions, structural dimensions and center line location, could be combined with topographic amplification factors to predict realistic design spectra for structures located on irregular topographic features. DOI: 10.1061/(ASCE) 1090-0241 (2007) 133:11(1414) CE Database subject headings: Topography, Slopes; Kinematics; Soil-structure interaction.

Shallow orographic convection embedded in an unstable cap cloud can organize into convective bands. Previous research has highlighted the important role of small-amplitude topographic variations in triggering and organizing banded convection. Here, the underlying dynamical mechanisms are systematically investigated by conducting three-dimensional simulations of moist flows past a two-dimensional mountain ridge using a cloud-resolving numerical model. Most simulations address a sheared environment to account for the observed wind profiles. Results confirm that small-amplitude topographic variations can enhance the development of embedded convection and anchor quasi-stationary convective bands to a fixed location in space. The resulting precipitation patterns exhibit tremendous spatial variability, since regions receiving heavy rainfall can be only kilometers away from regions receiving little or no rain. In addition, the presence of banded convection has important repercussions on the area-mean precipitation amounts. For the experimental setup here, the gravity wave response to small-amplitude topographic variations close to the upstream edge of the cap cloud (which is forced by the larger-scale topography) is found to be the dominant triggering mechanism. Small-scale variations in the underlying topography are found to force the location and spacing of convective bands over a wide range of scales. Further, a self-sufficient mode of unsteady banded convection is investigated that does not dependent on external perturbations and is able to propagate against the mean flow. Finally, the sensitivity of model simulations of banded convection with respect to horizontal computational resolution is investigated. Consistent with predictions from a linear stability analysis, convective bands of increasingly smaller scales arc favored as the horizontal resolution is increased. However, small-amplitude topographic roughness is found to trigger banded convection and to control the spacing and location of the resulting bands. Thereby, the robustness of numerical simulations with respect to an increase in horizontal resolution is increased in the presence of topographic variations.

A fractal dimension and a fractal roughness parameter are usually used to characterize a fractal surface. For a fractal-regular surface, a fractal domain length is also included. Such a formulation is based on an approximation using a constant value of the fractal scaling parameter that represents the ratio of the spatial frequencies of adjacent harmonic components in the Weierstrass-Mandelbrot (W-M)function. Although there were some reasons for assuming a constant value of 1.5 for the fractal scaling parameter, it is still left more or less arbitrary, to adopt this assumption in fractal modeling of solid contact. In the present study, the fractal scaling parameter was treated as a variable rather than a constant by using a form of the W-M function with randomized phases based on a random walk formulation. A simple numerical scheme with clear graphical interpretation was developed to determine the value of the fractal scaling parameter. The fractal dimension, fractal roughness parameter, and fractal scaling parameter were all recovered with reasonable accuracy from numerically generated surface profiles. [DOI: 10.1115/1.2768617] Keywords: fractal, surface characterization, rough surface, topography, contact mechanics

The eigenvalue-eigenvector-based approach for understanding the scattering mechanisms of polarimetric synthetic aperture radar (POLSAR) data leads to noisy classification results due to arbitrarily fixed zone boundaries in the H/[bar.[alpha]] plane. In this paper, a new classification scheme that can address the inherent vagueness of class boundaries in the H/[bar.[alpha]] plane was tested in order to improve the unsupervised classification of the microwave scattering mechanism by introducing concepts related to fuzzy sets. A 2-D fuzzy membership function was developed for the fuzzification of the 2-D H/[bar.[alpha]] plane. The proposed fuzzy H/[bar.[alpha]] classifier is composed of three steps: fuzzification of the H/[bar.[alpha]] plane, iterative refinement of membership degrees using the c-means algorithm, and defuzzification for the final decision process. The performance of this new approach for the L-band NASA/Jet Propulsion Laboratory's Airborne SAR data obtained during the PACRIM-II experiment was shown to be consistently improved. This new classification technique can be applied to POLSAR data without any a priori information. The fuzzification of the zone boundaries can be further applied to the interpretation of the POLSAR data, e.g., multifrequency classification, retrieval of bio-and geophysical parameters, etc. In order to propose another implementation of the fuzzy boundary representation, we exploited the combination of the H/[bar.[alpha]] state space and anisotropy information. Index Terms--Fuzzy sets, radar polarimetry, target decomposition, terrain classification.

Farms and forests dominate the rural landscape of the northern New England states of Maine, New Hampshire and Vermont, among the most heavily forested states in the US. However, we know little about the stewardship of farm woodlots and their contributions to the whole farm system, despite region-wide increases in farm forest acreage. Using a mail survey, this study found that almost half of respondents had a written management plan for their forestland, most of which had been written by a forester, and approximately three-quarters took an active role in the management of their woodlots. Farm woodlot harvesting and management contributed over 7% of total farm income. Variables such as respondent's state of residence, age, education and type of farm were investigated in order to better understand farmers' forest stewardship behavior. Implications for effective outreach to farm forest owners are offered. Key words: farm woodlot, farm forest, forest stewardship

Constraining the topography of the inner-core boundary is important for studies of core-mantle coupling and the generation of the geodynamo. We present evidence for significant temporal variability in the amplitude of the inner core reflected phase PKiKP for an exceptionally high-quality earthquake doublet, observed postcritically at the short-period Yellowknife seismic array (YK), which occurred in the South Sandwich islands within a 10-year interval (1993/2003). This observation, complemented by data from several other doublets, indicates the presence of topography at the inner-core boundary, with a horizontal wavelength on the order of 10 km. Such topography could be sustained by small-scale convection at the top of the inner core and is compatible with a rate of super rotation of the inner core of [approximately equal to] 0.1-0.15[degrees] per year. in the absence of inner-core rotation, decadal scale temporal changes in the innercore boundary topography would provide an upper bound on the viscosity at the top of the inner core. PKiKP | super rotation | doublet

Research on automatic identification of impact craters on Mars and other planetary bodies has concentrated on detecting them from imagery data. We present a novel approach to crater detection that utilizes digital topography data instead of images. Craters are delineated by topographic curvature. Thresholding maps of curvature transforms topographic data into a binary image, from which craters are identified using a combination of segmentation and detection algorithms. We apply our method to a large and technically demanding test site and compare the results to the existing catalog of manually identified craters. Our algorithm finds many small craters not listed in the manual catalog, but it fails to detect heavily degraded craters. A detailed quality assessment of the algorithm is presented. The topography-based crater-detection algorithm offers a relatively simple and ready-to-use tool for identification and characterization of fresh impact craters with an adequate performance for the immediate application to Martian geomorphology. Index Terms--Automated extraction of features, craters, digital topography, Mars, object recognition, segmentation.

[1] We investigate numerically the evolution of crustal and lithospheric thickness, thermal structure, topography, and strain rate of the Tibetan Plateau through time, using the thin viscous sheet approach. We show that lithospheric mantle must have been removed from beneath Tibet to explain the present surface elevation and lack of regional surface slope. In the absence of this removal, the modeled topography reaches a maximum elevation of

Data from three micronetworks with eddy correlation data and three additional micronetworks without eddy correlation data are analyzed to study the spatial variability of surface air temperature in complex terrain. A simple similarity relationship is constructed to relate the spatial variation of air temperature along the slope to the thermal forcing and mixing. Mixing is not included in present empirical formulations of the surface air temperature distribution in complex terrain. The development of surface temperature gradients along the slope, resulting from surface heating or cooling, is bounded by a maximum (or saturated) value, where a further increase of temperature gradients is restricted by redistribution of heat by thermally driven slope circulations. Although much of the spatial variation of the surface air temperature is governed by complex three-dimensionality and surface vegetation, a relatively simple relationship is able to account for much of the diurnal and day-to-day variation of the spatial distribution of air temperature. This relationship requires information on the surface heat flux and friction velocity over a reference surface. Required generalizations of the relationship are outlined before it can be applied to an arbitrary site.

This paper is an extension of a theoretical study by Luo on the effect of large-scale land sea contrast (LSC) topography on the formation of an eddy-driven blocking. It is found that the topography term can be included explicitly in the blocking evolution equation because of the inclusion of the higher-order wave topography interaction. Although the blocking flow cannot be excited purely by the LSC topography, the LSC topography is found to be capable of enhancing the amplification of the dipole component in a blocking flow associated with upstream synoptic-scale eddies. In this case, a strong omega-type blocking high can be driven by the joint action of synoptic-scale eddies and LSC topography. This seems to provide an explanation of a difference in blocking intensity between the Northern and Southern Hemispheres. The most important finding of this paper is that in the presence of LSC topography the double jets that appear during the onset of an eddy-driven dipole block collapse into a strong single westerly jet that is within the south side of an omega-type blocking high, which is different from the result predicted by the theoretical model proposed in Luo's previous work.

Numerical simulations are conducted of geostrophically balanced flow over an isolated mountain cut by a horizontal gap. The relative importance of the along-gap synoptic-scale pressure gradient and terrain-induced mesoscale circulations for the generation of gap winds was examined by changing the direction of the synoptic-scale wind relative to the topography. In all cases, the forcing associated with mesoscale circulations generated by the mountain was at least as significant as the synoptic-scale pressure gradient. In the cases where a component of the large-scale flow was directed perpendicular to the ridge, the dynamics were dominated by either the vertical momentum fluxes due to mountain lee waves or by mesoscale pressure gradients associated with upstream blocking or lee troughing. Mesoscale circulations were also important when the large-scale flow was parallel to the ridge because surface friction turned the low-level winds toward the high pressure side of the ridge, partially blocking the flow and enhancing the along-gap pressure gradient. The flow in the interior of a very long uniform gap was also simulated for a case with the synoptic-scale winds parallel to the ridge so that the synoptic-scale pressure gradient was down the gap. The flow in the interior of the long gap was not horizontal and not in a simple dynamical balance between acceleration, the pressure gradient force, and surface friction. Even the flow in the lowest 150 m was gradually subsiding. Subsidence and lateral momentum flux convergence at low levels near the center of the gap were important contributors to the mass and along-gap momentum budgets.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.06.015 Byline: Andrew F. Cheng, Andrew J. Dombard Keywords: Comets; nucleus; Geological processes; Geophysics Abstract: Three Jupiter family comets have now been observed by spacecraft with the surprising result that these comets lack unambiguous impact craters. Large-scale topography generally appears to be softened on these comets, although sharp topography is preserved at small scales. We find that viscous relaxation of water ice may explain these observations, given reasonable assumptions about ice grain size and temperatures attained in the interiors. We suggest that both the shapes and the cratering records of Jupiter family comets may be substantially modified and no longer reflect cometary formation processes or collisional evolution in the Kuiper Belt. Author Affiliation: The Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723, USA Article History: Received 11 May 2006

An enhanced National Center for Atmospheric Research (NCAR) integrated sounding system (ISS) was deployed as part of the Vertical Transport and Mixing (VTMX) field experiment, which took place in October of 2000. The enhanced ISS was set up at the southern terminus of the Great Salt Lake Valley just north of a gap in the Traverse Range (TR), which separates the Great Salt Lake and Utah Lake basins. This location was chosen to sample the dynamic and thermodynamic properties of the flow as it passes over the TR separating the two basins. The enhanced ISS allowed for near-continuous sampling of the nocturnal boundary layer (NBL) and low-level winds associated with drainage flow through the gap in the TR. Diurnally varying winds were observed at the NCAR site on days characterized by weak synoptic forcing and limited cloud cover. A down-valley jet (DVJ) was observed on about 50% of the nights during VTMX, with the maximum winds usually occurring within 150 m of the surface. The DVJ was associated with abrupt warming at low levels as a result of downward mixing and vertical transport of warm air from the inversion layer above. Several processes were observed to contribute to vertical transport and mixing at the NCAR site. Pulses in the strength of the DVJ contributed to vertical transport by creating localized areas of low-level convergence. Gravity waves and Kelvin-Helmholtz waves, which facilitated vertical [nixing near the surface and atop the DVJ, were observed with a sodar and an aerosol backscatter lidar that were deployed as part of the enhanced ISS. The nonlocal nature of the processes responsible for generating turbulence in strongly stratified surface layers in complex terrain confounds surface flux parameterizations typically used in mesoscale models that rely on Monin Obukhov similarity theory. This finding has major implications for modeling NBL structure and drainage flows in regions of complex terrain.

In this paper, a framework for smoothing gridlike digital terrain elevation data, which achieves a fair shape by means of minimizing an energy functional, is presented. The minimization is performed under the side condition of hard constraints, which comes from available horizontal and vertical accuracy bounds in the standard elevation specification. In this paper, the framework is introduced, and the suitability of this method for the tasks of accuracy-constrained smoothing, feature-preserving smoothing, and filling of data voids is demonstrated. Index Terms--Digital terrain elevation data (DTED), fair polyline networks, guaranteed error bounds, surface smoothing, terrain compression, terrain visualization, topography preserving.

The Rheic Ocean is widely believed to have formed in the Late Cambrian-Early Ordovician as a result of the drift of peri-Gondwanan terranes, such as Avalonia and Carolina, from the northern margin of Gondwana, and to have been consumed in the Devonian Carboniferous by continent-continent collision during the formation of Pangea. Other peri-Gondwanan terranes (e.g., Armorica, Ossa-Morena, northwest Iberia, Saxo-Thuringia, Moldanubia) remained along the Gondwanan margin at the time of Rheic Ocean formation. Differences in the Neoproterozoic histories of these peri-Gondwanan terranes suggest the location of the Rheic Ocean rift may have been inherited from Neoproterozoic lithospheric structures formed by the accretion and dispersal of periGondwanan terranes along the northern Gondwanan margin prior to Rheic Ocean opening. Avalonia and Carolina have Sm-Nd isotopic characteristics indicative of recycling of a juvenile ca. 1 Ga source, and they were accreted to the northern Gondwanan margin prior to voluminous late Neoproterozoic arc magmatism. In contrast, Sm-Nd isotopic characteristics of most other peri-Gondwanan terranes closely match those of Eburnian basement, suggesting they reflect recycling of ancient (2 Ga) West African crust. The basements of terranes initially rifted from Gondwana to form the Rheic Ocean were those that had previously accreted during Neoproterozoic orogenesis, suggesting the rift was located near the suture between the accreted terranes and cratonic northern Gondwana. Opening of the Rheic Ocean coincided with the onset of subduction beneath the Laurentian margin in its predecessor, the Iapetus Ocean, suggesting geodynamic linkages between the destruction of the Iapetus Ocean and the creation of the Rheic Ocean. Keywords: Pangea, Rheic Ocean, Neoproterozoic suture, Sm-Nd data, terranes.

Summer precipitation over the central United States depends strongly on the strength of the Great Plains low-level jet (LLJ). The Geophysical Fluid Dynamics Laboratory's new generation of the atmospheric general circulation model (GCM) and the linear and nonlinear stationary wave models are used in this study to examine the role of North American topography in maintaining the Great Plains summer mean LLJ and precipitation. Atmospheric GCM experiments were first performed with and without the North American topography and with prescribed climatological sea surface temperatures. Results show that the Great Plains LLJ disappears completely in the experiment when the North American topography is removed, while the summer seasonal mean LLJ is well simulated in the experiment with full earth topography. In the absence of the North American topography, the summer precipitation is significantly reduced over the central United States and increased along the Gulf States and northeast Mexico. Linear and nonlinear stationary wave models are used to determine the physical mechanisms through which the North American topography maintains the Great Plains time mean LLJ. Possible mechanisms include the physical blocking of the topography and the induced flow over and around the mountains, the thermal effect due to the elevation of the topography, and the transient thermal and vorticity forcing due to the modification of transient eddy activities in the presence of the topography. The linear and nonlinear model results indicate that the dominant mechanism for maintaining the time mean Great Plains LLJ is through the nonlinear effect of the trade wind along the southern flank of the North Atlantic subtropical high encountering the east slope of the Sierra Oriental and causing the flow to turn northward. As the flow turns north along the east slope of the North American topography, it obtains anticyclonic shear vorticity and thus the LLJ. The effect of the thermal forcing is negligible, while the effect of transient forcing is only important in extending the jet farther northward and eastward. The results suggest that variations in the strength of the North Atlantic subtropical anticyclone and the associated trade wind over the Caribbean Sea and the Gulf of Mexico may be important for understanding the interannualvariation of the Great Plains LLJ and U.S. precipitation.

New seismic observations of crustal structure along the Juan de Fuca Ridge indicate that the axial rift topography reflects magma-induced deformation rather than alternating phases of magmatism and tectonic extension, as previously proposed. Contrary to predictions of the episodic models, crustal magma bodies are imaged beneath portions of all ridge segments surveyed at average depths of 2.1-2.6 km. The shallow rift valley or axial graben associated with each Juan de Fuca segment is ~50-200 m deep and 1-8 km wide and is well correlated with a magma body in the subsurface. Analysis of graben dimensions (height and width) shows that the axial graben narrows and graben height diminishes where the magma body disappears, rather than deepening and broadening, as expected for rift topography due to tectonic extension. We propose an evolutionary model of axial topography that emphasizes the contribution of dike intrusion to subsidence and fault slip at the seafloor. In this model an evolving axial topography results from feedbacks between the rheology of the crust above a magma sill and dike intrusion, rather than episodic magma delivery from the mantle. Keywords: Juan de Fuca Ridge, magma chambers, dikes, faulting, spreading centers.