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1.
An ephemeral estuarine turbidity maximum (ETM) occurs at high water in the macrotidal Taf estuary (SW Wales, United Kingdom).
A new mechanism of ETM formation, due to resuspension and advection of material by flood tidal currents, is observed that
differs from classical mechanisms of gravitational circulation and tidal pumping. The flood tide advances across intertidal
sand flats in the main body of the estuary, progressively entraining material from the rippled sands. Resuspension creates,
a turbid front that has suspended sediment concentrations (SSC) of about 4,000 mg I−1 by the time it reaches its landward limit which is also the landward limit of salt penetration. This turbid body constitutes
the ETM. Deposition occurs at high slack water but the ETM retains SSC values up to 800 mg I−1, 1–2 orders of magnitude greater than ambient SSC values in the river and estuarine waters on either side. The ETM retreats
down the estuary during the ebb; some material is deposited thinly across emergent intertidal flats and some is flushed out
of the estuary. A new ETM is generated by the next flood tide. Both location and SSC of the ETM scale on Q/R3 where Q is tidal range and R is river discharge. The greatest expression of the ETM occurs when a spring tide coincides with
low river discharge. It does not form during high river discharge conditions and is poorly developed on neap tides. Particles
in the ETM have effective densities (120–160 kg m−3) that are 3–4 times less than those in the main part of the estuary at high water. High chlorophyll concentrations in the
ETM suggest that flocs probably originate from biological production in the estuary, including production on the intertidal
sand flats. 相似文献
2.
Mohd Zaki M. Amin Tanvir Islam Asnor M. Ishak 《Theoretical and Applied Climatology》2014,118(1-2):347-364
The authors have applied an automated regression-based statistical method, namely, the automated statistical downscaling (ASD) model, to downscale and project the precipitation climatology in an equatorial climate region (Peninsular Malaysia). Five precipitation indices are, principally, downscaled and projected: mean monthly values of precipitation (Mean), standard deviation (STD), 90th percentile of rain day amount, percentage of wet days (Wet-day), and maximum number of consecutive dry days (CDD). The predictors, National Centers for Environmental Prediction (NCEP) products, are taken from the daily series reanalysis data, while the global climate model (GCM) outputs are from the Hadley Centre Coupled Model, version 3 (HadCM3) in A2/B2 emission scenarios and Third-Generation Coupled Global Climate Model (CGCM3) in A2 emission scenario. Meanwhile, the predictand data are taken from the arithmetically averaged rain gauge information and used as a baseline data for the evaluation. The results reveal, from the calibration and validation periods spanning a period of 40 years (1961–2000), the ASD model is capable to downscale the precipitation with reasonable accuracy. Overall, during the validation period, the model simulations with the NCEP predictors produce mean monthly precipitation of 6.18–6.20 mm/day (root mean squared error 0.78 and 0.82 mm/day), interpolated, respectively, on HadCM3 and CGCM3 grids, in contrast to 6.00 mm/day as observation. Nevertheless, the model suffers to perform reasonably well at the time of extreme precipitation and summer time, more specifically to generate the CDD and STD indices. The future projections of precipitation (2011–2099) exhibit that there would be an increase in the precipitation amount and frequency in most of the months. Taking the 1961–2000 timeline as the base period, overall, the annual mean precipitation would indicate a surplus projection by nearly 14~18 % under both GCM output cases (HadCM3 A2/B2 scenarios and CGCM3 A2 scenario). According to the model simulation, the September–November periods might be the more significant months projecting the increment of the precipitation amount around over 50 %, while the precipitation deficit would be seen in March–May periods. 相似文献
3.
Sustainable water resources management require scientifically sound information on precipitation, as it plays a key role in hydrological responses in a catchment. In recent years, mesoscale weather models in conjunction with hydrological models have gained great attention as they can provide high‐resolution downscaled weather variables. Many cumulus parameterization schemes (CPSs) have been developed and incorporated into three‐dimensional Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR) mesoscale model 5 (MM5). This study has performed a comprehensive evaluation of four CPSs (the Anthes–Kuo, Grell, Betts–Miller and Kain–Fritsch93 schemes) to identify how their inclusion influences the mesoscale model's precipitation estimation capabilities. The study has also compared these four CPSs in terms of variability in rainfall estimation at various horizontal and vertical levels. For this purpose, the MM5 was nested down to resolution of 81 km for Domain 1 (domain span 21 × 81 km) and 3 km for Domain 4 (domain span 16 × 3 km), respectively, with vertical resolutions at 23, 40 and 53 vertical levels. The study was carried out at the Brue catchment in Southwest England using both the ERA‐40 reanalysis data and the land‐based observation data. The performances of four CPs were evaluated in terms of their ability to simulate the amount of cumulative rainfall in 4 months in 1995 representing the four seasonal months, namely, January (winter), March (spring), July (summer) and October (autumn). It is observed that the Anthes–Kuo scheme has produced inferior precipitation values during spring and autumn seasons while simulations during winter and summer were consistently good. The Betts–Miller scheme has produced some reasonable results, particularly at the small‐scale domain (3 km grid size) during winter and summer. The KF2 scheme was the best scheme for the larger‐scale (81 km grid size) domain during winter season at both 23 and 53 vertical levels. This scheme tended to underestimate rainfall for other seasons including the small‐scale domain (3 km grid size) in the mesoscale. The Grell scheme was the best scheme in simulating rainfall rates, and was found to be superior to other three schemes with consistently better results in all four seasons and in different domain scales. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
4.
5.
Nurul Hawani Idris Mohamad Jahidi Osman Kasturi Devi Kanniah Nurul Hazrina Idris Mohamad Hafis Izran Ishak 《制图学和地理信息科学》2017,44(2):113-127
ABSTRACTWeb 2.0 and the proliferation of built-in Global Positioning System (GPS) on smartphones have influenced the increase of geo-crowdsourcing activities in a number of different contexts. The aim of this paper is to evaluate the performance of indigenous people’s use of mobile collection applications that are embedded in a smartphone to facilitate ecotourism asset mapping. In order to achieve this, field usability testing was conducted where structured observational method was used to assess the performance. The findings indicate majority of them can complete the data entry tasks using mobile data collection. The performance of data entries using radio button, icons, camera and audio methods were identified as better than free text and drop-down list methods. There was a correlation between the level of education with the ability of using radio button, drop-down list and image icon as data entry methods. The paper also discusses the extent of local knowledge relating to ecotourism within the community. The findings should be useful in the understanding of the design of mobile geo-crowdsourcing tools for use within other contexts that focus on data collection by semiliterate and indigenous groups. 相似文献
6.
Regional flood frequency analysis (RFFA) is often used in hydrology to estimate flood quantiles when there is a limitation
of at-site recorded flood data. One of the commonly used RFFA methods is the index flood method, which is based on the assumptions
that a region satisfies criterion of simple scaling and it can be treated homogeneous. Another RFFA method is quantile regression
technique where prediction equations are developed for flood quantiles of interest as function of catchment characteristics.
In this paper, the scaling property of regional floods in New South Wales (NSW) State in Australia is investigated. The results
indicate that the annual maximum floods in NSW satisfy a simple scaling assumption. The application of a heterogeneity test,
however, reveals that NSW flood data set does not satisfy the criteria for a homogeneous region. Finally, a set of prediction
equations are developed for NSW using quantile regression technique; an independent test shows that these equations can provide
reasonably accurate design flood estimates with a median relative error of about 27%. 相似文献
7.
Drainage sampling for uranium in the Torrington district, New South Wales, Australia 总被引:1,自引:0,他引:1
A brief orientation study has been conducted to evaluate the use of drainage geochemical sampling for U in the granitic and forested terrain of the Torrington district of northeastern New South Wales. Anomalous U levels are present in both stream sediments and waters draining a known W prospect containing accessory U. The U dispersion is affected by interrelated environmental factors such as catchment physiography and the organic content of the stream sediments. The influence of organic content on U level in stream sediments is most significant. Variation in sediment organic content is related to accumulation of vegetal organic debris and charcoal in stream channels by sheetwashing of sparsely covered forest floors particularly in catchments of high topographic relief. The U is apparently absorbed onto the organic material from ephemerally flowing stream waters. Temporal variations in U content of stream sediment are indicated which necessitate careful consideration in planning and interpreting the results of a survey in this environment. 相似文献
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9.
A new independent limit on the cosmological constant/dark energy from the relativistic bending of light by Galaxies and clusters of Galaxies 总被引:1,自引:0,他引:1
M. Ishak W. Rindler † J. Dossett J. Moldenhauer C. Allison 《Monthly notices of the Royal Astronomical Society》2008,388(3):1279-1283
We derive new limits on the value of the cosmological constant, Λ, based on the Einstein bending of light by systems where the lens is a distant galaxy or a cluster of galaxies. We use an amended lens equation in which the contribution of Λ to the Einstein deflection angle is taken into account and use observations of Einstein radii around several lens systems. We use in our calculations a Schwarzschild–de Sitter vacuole exactly matched into a Friedmann–Robertson–Walker background and show that a Λ-contribution term appears in the deflection angle within the lens equation. We find that the contribution of the Λ-term to the bending angle is larger than the second-order term for many lens systems. Using these observations of bending angles, we derive new limits on the value of Λ. These limits constitute the best observational upper bound on Λ after cosmological constraints and are only two orders of magnitude away from the value determined by those cosmological constraints. 相似文献