Characterisation and Simulation of the Multiscaling Properties of the Energy-Containing Scales of Horizontal Surface-Layer Winds   总被引：1，自引：1，他引：0  

Michael K. Lauren  Merab Menabde  Alan W. Seed  Geoffrey L. Austin 《Boundary-Layer Meteorology》1999,90(1):21-46

The multiscaling statistics of atmospheric surface-layer winds at low wavenumbers above farmland and in the lee of a mountain range were examined using a hot-wire and lightweight cup anemometer. It was found that the horizontal velocity spectra could be broken into high and low-wavenumber regimes according to the parameters given by this analysis. The low-wavenumber end of the spectrum possessed a spectral slope parameter that varied between values of 0.8 and 1.35 at the farmland site during the period of the experiment, and the high-wavenumber end – corresponding to the inertial range – possessed a spectral slope slightly greater than -5/3. The larger values for this parameter for the low-wavenumber end appeared to coincide with unstable conditions. In the lee of the mountain range, the low-wavenumber spectral slope parameter was larger still, at 1.45. The low-wavenumber signals over farmland were much less intermittent than inertial-range signals, but in the lee of the mountain range the intermittency increased. From this analysis, it was shown that the statistical properties of the recorded wind signal could be reproduced using a bounded random multiplicative cascade. The model was successfully used to simulate the wind velocity field directly, rather than simulating the energy dissipation field. Since the spectral slope parameter for low wavenumbers appeared to be a function of atmospheric stability, the method presented is a simple way of generating wind signals characteristic of a variety of atmospheric conditions.  相似文献   

Advances in automatic interpolation for real-time mapping     

Gregoire Dubois 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(5):597-599

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Sedimentological and palaeoenvironmental study from Waregi Hill in the Hiwegi Formation (early Miocene) on Rusinga Island,Lake Victoria,Kenya     

Lauren A. Michel  Thomas Lehmann  Kieran P. Mcnulty  Steven G. Driese  Holly Dunsworth  David L. Fox  William E.H. Harcourt-Smith  Kirsten Jenkins  Daniel J. Peppe 《Sedimentology》2020,67(7):3567-3594

Palaeontological deposits on Rusinga Island, Lake Victoria, Kenya, provide a rich record of floral and faunal evolution in the early Neogene of East Africa. Yet, despite a wealth of available fossil material, previous palaeoenvironmental reconstructions from Rusinga have resulted in widely divergent results, ranging from closed forest to open woodland environments. Presented here is a detailed study of the sedimentology and fauna of the early Miocene Hiwegi Formation at Waregi Hill on Rusinga Island, Kenya. New sedimentological analyses demonstrate that the Hiwegi Formation records an environmental transition from the bottom to the top of the formation. Lower in the Hiwegi Formation, satin-spar calcite after gypsum in siltstone deposits are interpreted as evidence for open hypersaline lakes. Moving up-section, carbonate deposits – interpreted previously as evidence of aridity – are actually diagenetic calcite cements, which preserve root systems of trees, suggesting a more closed environment; further up-section, the uppermost palaeosol layer contains abundant root traces and tree-stump casts, previously reported as evidence of a closed-canopy forest. These newly interpreted environmental differences are reflected by differences in faunal composition and abundance data from Hiwegi Formation fossil sites R1 and R3. Taken together, this work suggests that divergent palaeoenvironmental reconstructions in previous studies may have been informed by time-averaging across multiple environments. Further, results demonstrate that during the early Miocene local or regional habitat heterogeneity already existed. Rusinga’s Hiwegi Formation varied both spatially and temporally, which challenges the interpretation that a broad forested environment stretched across the African continent during the early Neogene, transitioning later to predominately open landscapes that characterize the region today. This result has important implications for interpretations of the selective pressures faced by early Miocene fauna, including Rusinga Island’s well-preserved fossil primates.  相似文献   

Laboratory and numerical studies of wave damping by emergent and near-emergent wetland vegetation   总被引：3，自引：0，他引：3  

Lauren N. Augustin  Jennifer L. Irish  Patrick Lynett 《Coastal Engineering》2009

Wetlands protect mainland areas from erosion and damage by damping waves. Yet, this critical role of wetland is not fully understood at present, and a means for reliably determining wave damping by vegetation in engineering practice is not yet available. Laboratory experiments were conducted to measure wave attenuation resulting from synthetic emergent and nearly emergent wetland vegetation under a range of wave conditions and plant stem densities. The laboratory data were analyzed using linear wave theory to quantify bulk drag coefficients and with a nonlinear Boussinesq model to determine numerical friction factors to better represent wetland vegetation in engineering analysis.  相似文献   

Runoff sensitivity to snow depletion curve representation within a continental scale hydrologic model     

Graham A. Sexstone  Jessica M. Driscoll  Lauren E. Hay  John C. Hammond  Theodore B. Barnhart 《水文研究》2020,34(11):2365-2380

The spatial variability of snow water equivalent (SWE) can exert a strong influence on the timing and magnitude of snowmelt delivery to a watershed. Therefore, the representation of sub-grid or sub-watershed snow variability in hydrologic models is important for accurately simulating snowmelt dynamics and runoff response. The U.S. Geological Survey National Hydrologic Model infrastructure with the precipitation-runoff modelling system (NHM-PRMS) represents the sub-grid variability of SWE with snow depletion curves (SDCs), which relate snow-covered area to watershed-mean SWE during the snowmelt period. The main objective of this research was to evaluate the sensitivity of simulated runoff to SDC representation within the NHM-PRMS across the continental United States (CONUS). SDCs for the model experiment were derived assuming a range of SWE coefficient of variation values and a lognormal probability distribution function. The NHM-PRMS was simulated at a daily time step for each SDC over a 14-year period. Results highlight that increasing the sub-grid snow variability (by changing the SDC) resulted in a consistently slower snowmelt rate and longer snowmelt duration when averaged across the hydrologic response unit scale. Simulated runoff was also found to be sensitive to SDC representation, as decreases in simulated snowmelt rate by 1 mm day⁻¹ resulted in decreases in runoff ratio by 1.8% on average in snow-dominated regions of the CONUS. Simulated decreases in runoff associated with slower snowmelt rates were approximately inversely proportional to increases in simulated evapotranspiration. High snow persistence and peak SWE:annual precipitation combined with a water-limited dryness index was associated with the greatest runoff sensitivity to changing snowmelt. Results from this study highlight the importance of carefully parameterizing SDCs for hydrologic modelling. Furthermore, improving model representation of snowmelt input variability and its relation to runoff generation processes is shown to be an important consideration for future modelling applications.  相似文献   

Sensitivity analysis of hydraulic conductivity and Manning's n parameters lead to new method to scale effective hydraulic conductivity across model resolutions     

Lauren M. Foster  Reed M. Maxwell 《水文研究》2019,33(3):332-349

Hydrological modelling is an important tool for research, policy, and management, but uncertainty remains about parameters transferability from field observations made at small scale to models at the catchment scale and larger. This uncertainty compels the need to develop parameter relationships that are translatable across scale. In this study, we compare the changes to modelled processes as resolution is coarsened from 100‐m to 1‐km in a topographically complex, 255‐km² Colorado River headwater catchment. We conducted a sensitivity analysis for hydraulic conductivity (K) and Manning's n parameters across four orders of magnitude. Results showed that K acts as a moderator between surface and subsurface contributions to streamflow, whereas n moderates the duration of high intensity, infiltration‐excess flow. The parametric sensitivity analysis informed development of a new method to scale effective hydraulic conductivity across modelling resolutions in order to compensate for the loss of topographic gradients as resolution is coarsened. A similar mathematical relationship between n and lateral resolution changes was not found, possibly because n is also sensitive to time discretization. This research provides an approach to translate hydraulic conductivity parameters from a calibrated coarse model to higher resolutions where the number of simulations are limited by computational demand.  相似文献   

Radarclinometry of the sand seas of Africa’s Namibia and Saturn’s moon Titan     

Catherine D. Neish  Ralph D. Lorenz  Lauren C. Wye 《Icarus》2010,208(1):385-394

Radarclinometry is a powerful technique for estimating heights of landforms in synthetic aperture radar (SAR) images of planetary surfaces. In particular, it has been used to estimate heights of dunes in the sand seas of Saturn’s moon Titan (Lorenz, R.D., and 39 colleagues [2006]. Science 312, 724-727). In this work, we verify the technique by comparing dune heights derived from radarclinometry to known topography of dune fields in the Namib sand sea of western Africa. We compared results from three different image grid spacings, and found that 350 m/pixel (the same spacing at which the Cassini RADAR data was processed) is sufficient to determine dune height for dunes of similar morphometry to those of the Namib sand sea. At this grid spacing, height estimates derived from radarclinometry are largely representative of, though may underestimate by as much as 30%, or overestimate by as much as 40%, true dune height. Applying the technique to three regions on Titan, we estimate dune heights of 45-180 m, and dune spacings of 2.3-3.3 km. Obtaining accurate heights of Titan’s dunes will help to constrain the total organic inventory on Titan.  相似文献   

Stellar population and kinematic profiles in spiral bulges and discs: population synthesis of integrated spectra     

Lauren A. MacArthur  J. Jesús González  Stéphane Courteau 《Monthly notices of the Royal Astronomical Society》2009,395(1):28-63

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Molting as a mechanism of depuration of metals in the fiddler crab, Uca pugnax     

Bergey LL  Weis JS 《Marine environmental research》2007,64(5):556-562

Metal distributions in the exoskeleton and soft tissues of the fiddler crab, Uca pugnax, were examined during intermolt and immediate postmolt to determine if distribution of the metals changed prior to molting and to determine if molting is a feasible mechanism to depurate metals. Fiddler crabs were collected from two locations in New Jersey, a highly contaminated site and a relatively clean environment. The crabs from the contaminated site had higher concentrations of metals in their soft tissues for Cu, significantly higher concentrations of Pb in their soft tissues and carapace, but did not have any significant differences in concentrations of Zn in comparison to their conspecifics from the relatively clean site during intermolt. Crabs from the contaminated site has significantly higher levels of Cu, Pb, and Zn in both their soft tissues and exuvia immediately after molting. Crabs from both sites shifted copper and zinc from the carapace into the soft tissues prior to molting. Lead distribution shifted from the soft tissues to the exoskeleton prior to molting in the population from the contaminated site but shifted from the exoskeleton into the soft tissues for the relatively clean site. Average percent of the total body burden eliminated during the molting process for the highly contaminated site varied with each metal, 12% Cu, 76% Pb, and 22% Zn. Average percent of the total body burden eliminated during molting process for the relatively clean site also varied with each metal and was significantly lower than the conspecifics from the contaminated site, 3% Cu, 56% Pb, and 8% Zn. Molting can reduce overall body burdens significantly and is a feasible mechanism to depurate lead.  相似文献   

Nutrient dynamics in an alpine headwater stream: use of continuous water quality sensors to examine responses to wildfire and precipitation events          下载免费PDF全文

Lauren R. Sherson  David J. Van Horn  Jesus D. Gomez‐Velez  Laura J. Crossey  Clifford N. Dahm 《水文研究》2015,29(14):3193-3207

Stream water quality can change substantively during diurnal cycles, discrete flow events, and seasonal time scales. In this study, we assessed event responses in surface water nutrient concentrations and biogeochemical parameters through the deployment of continuous water quality sensors from March to October 2011 in the East Fork Jemez River, located in northern New Mexico, USA. Events included two pre‐fire non‐monsoonal precipitation events in April, four post‐fire precipitation events in August and September (associated with monsoonal thunderstorms), and two post‐fire non‐monsoonal precipitation events in October. The six post‐fire events occurred after the Las Conchas wildfire burned a significant portion of the contributing watershed (36%) beginning in June 2011. Surface water nitrate (NO₃? N) concentrations increased by an average of 50% after pre‐fire and post‐fire non‐monsoonal precipitation events and were associated with small increases in turbidity (up to 15 NTU). Beginning 1 month after the start of the large regional wildfire, monsoonal precipitation events resulted in large multi‐day increases in dissolved NO₃? N (6 × background levels), dissolved phosphate (100 × background levels), specific conductance (5 × background levels), and turbidity (>100 × background levels). These periods also corresponded with substantial sags in dissolved oxygen (<4 mg l^?1) and pH (<6.5). The short duration and rapid rates of change during many of these flow events, particularly following wildfire, highlight the importance of continuous water quality monitoring to quantify the timing and magnitude of event responses in streams and to examine large water quality excursions linked to catchment disturbance. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献