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71.
The paper presents an approach towards a medium-term (decades) modelling of water levels and currents in a shallow tidal sea by means of combined hydrodynamic and neural network models. The two-dimensional version of the hydrodynamic model Delft3D, forced with realistic water level and wind fields, is used to produce a two-year-database of water levels and currents in the study area. The linear principal component analysis (PCA) of the results is performed to reveal dominating spatial patterns in the analyzed dataset and to significantly reduce the dimensionality of the data. It is shown that only a few principal components (PCs) are necessary to reconstruct the data with high accuracy (over 95% of the original variance). Feed-forward neural networks are set up and trained to effectively simulate the leading PCs based on water level and wind speed and direction time series in a single, arbitrarily chosen point in the study area. Assuming that the spatial modes resulting from the PCA are ‘universally’ applicable to the data from time periods not modelled with Delft3D, the trained neural networks can be used to very effectively and reliably simulate temporal and spatial variability of water levels and currents in the study area. The approach is shown to be able to accurately reproduce statistical distribution of water levels and currents in various locations inside the study area and thus can be viewed as a reliable complementary tool e.g., for computationally expensive hydrodynamic modelling. Finally, a detailed analysis of the leading PCs is performed to estimate the role of tidal forcing and wind (including its seasonal and annual variability) in shaping the water level and current climate in the study area. 相似文献
72.
Hongwu Xu Yusheng Zhao Sven C. Vogel Donald D. Hickmott Luke L. Daemen Monika A. Hartl 《Physics and Chemistry of Minerals》2010,37(2):73-82
The structure of deuterated jarosite, KFe3(SO4)2(OD)6, was investigated using time-of-flight neutron diffraction up to its dehydroxylation temperature. Rietveld analysis reveals
that with increasing temperature, its c dimension expands at a rate ~10 times greater than that for a. This anisotropy of thermal expansion is due to rapid increase in the thickness of the (001) sheet of [Fe(O,OH)6] octahedra and [SO4] tetrahedra with increasing temperature. Fitting of the measured cell volumes yields a coefficient of thermal expansion,
α = α0 + α1
T, where α0 = 1.01 × 10−4 K−1 and α1 = −1.15 × 10−7 K−2. On heating, the hydrogen bonds, O1···D–O3, through which the (001) octahedral–tetrahedral sheets are held together, become
weakened, as reflected by an increase in the D···O1 distance and a concomitant decrease in the O3–D distance with increasing
temperature. On further heating to 575 K, jarosite starts to decompose into nanocrystalline yavapaiite and hematite (as well
as water vapor), a direct result of the breaking of the hydrogen bonds that hold the jarosite structure together. 相似文献
73.
Eduard Bauerfeind Eva-Maria Nöthig Agnieszka Beszczynska Kirsten Fahl Lars Kaleschke Kathrin Kreker Michael Klages Thomas Soltwedel Christiane Lorenzen Jan Wegner 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(9):1471-1487
Since 2000 long-term measurements of vertical particle flux have been performed with moored sediment traps at the long-term observatory HAUSGARTEN in the eastern Fram Strait (79°N/4°E). The study area, which is seasonally covered with ice, is located in the confluence zone of the northward flowing warm saline Atlantic water with cold, low salinity water masses of Arctic origin. Current projections suggest that this area is particularly vulnerable to global warming. Total matter fluxes and components thereof (carbonate, particulate organic carbon and nitrogen, biogenic silica, biomarkers) revealed a bimodal seasonal pattern showing elevated sedimentation rates during May/June and August/September. Annual total matter flux (dry weight, DW) at ~300 m depth varied between 13 and 32 g m?2 a?1 during 2000 and 2005. Of this total flux 6–13% was due to CaCO3, 4–21% to refractory particulate organic carbon (POC), and 3–8% to biogenic particulate silica (bPSi). The annual flux of all biogenic components together was almost constant during the period studied (8.5–8.8 g m?2 a?1), although this varied from 27% to 67% of the total annual flux. The fraction was lowest in a year characterized by the longest duration of ice coverage (91 and 70 days for the calendar year and summer season, May–September, respectively). Biomarker analyses revealed that organic matter originating from marine sources was present in excess of terrigenious material in the sedimented matter throughout most of the study period. Fluxes of recognizable phyto- and protozooplankton cells amounted up to 60×106 m?2 d?1. Diatoms and coccolithophorids were the most abundant organisms. Diatoms, mainly pennate species, dominated during the first years of the investigation. A shift in the composition occurred during the last year when numbers of diatoms declined considerably, leading to a dominance of coccolithoporids. This was also reflected in a decrease in the sedimentation of bPSi. The sedimentation of biogenic matter, however, did not differ from the amount observed during the previous years. Among the larger organisms, pteropods at times contributed significantly to both the total matter and CaCO3, fluxes. 相似文献
74.
Volume, heat and salt transport by the West Spitsbergen Current 总被引:1,自引:0,他引:1
During the summer of 2000 (June-July) 14 CTD and ADCP transects perpendicular to the West Spitsbergen Current and along the western border of the Barents Sea were made. The measurements covered the area between 69° 43'and 80° N and 01° and 20° E. The main purpose was to follow changes in volume, heat and salt content of Atlantic Water (AW) on its way north. The strongest and most stable flow of AW was located along the continental slope where northward flowing currents exceeding 40 cm/sec were measured. A few weaker northward branches were also found to the west of the slope. South-directed currents were recorded between them and eddy-like mesoscale structures were commonly observed. Measured by vessel-mounted acoustic Doppler current profiler (VM-ADCP), the net northward transport of AW volume in the upper 136 m layer decreased from nearly 6 Sv at the southernmost transect to below 1 Sv at a latitude of 78° 50'N. Similarly, heat transport drops from about 173 TW to about 9 TW and relative salt transport (over 34.92 psu) from 980 × 103 kg/sec to 14 × 103 kg/sec. Transport in the southern direction prevails at the transect located between 79° 07'and 79° 30'N. The calculated baroclinic geostrophic transport of AW volume, heat and salt in the upper 1000 m layer behaves similarly. East-directed transport dominates at the Barents Sea boundary while westward flow prevails on the western side of the West Spitsbergen Current. 相似文献
75.
Monika Sester 《地球空间信息科学学报》2020,23(1):68-74
ABSTRACTThe increasing availability of devices to capture the position of moving objects (and other environmental information) leads to a very large amount and variety of mobility data. In order to obtain important information about the objects, their behavior or the environment of the objects, an automatic analysis is required. This article highlights current research questions in the context of the analysis of mobility data and presents them on the basis of work carried out at the Institute of Cartography and Geoinformatics (ikg) at Leibniz University of Hannover, Germany. A focus is put on the analysis and exploitation of information from Mobile Mapping vehicles. 相似文献
76.
77.
The relative intensities of anhysteretic remanent magnetization (RAM) and thermoramanent magnetization (TRM) are strongly dependent on grain size, blocking temperature and applied field, and are poorly predicted by existing theories. Analog techniques that substitute ARM for TRM probably yield adequate relative paleointensities in suites of mineralogically similar rocks, but they yield uncertain estimates of absolute paleointensity. 相似文献
78.
A transect of the St Marys River estuary from above the point of maximum salt wedge penetration to coastal salinities was
conducted in July 1999. None of the parameters examined—dissolved organic carbon (DOC) content, UV light absorbance at 254
nm, and Total Luminescence spectra—follow the rule of conservative mixing. The characteristics of the different molecular
size fractions of the St Marys River natural organic matter (NOM), as well as the results of a laboratory mixing experiment,
provided evidence that loss of larger molecular size compounds from riverine NOM may occur by coagulation at salinities up
to 10. An apparent gain of carbon in the lower estuary was attributed to exports from abundant coastal marshes in this area.
The Total Luminescence spectra of the riverine NOM can be described by two peaks, centered respectively around 340/445 nm,
and 230/430 nm Excitation/Emission Wavelength Pair (EEWP), which are characteristic of humic materials of aquatic origin.
The samples from the high salinity stations exhibit peaks at lower emission wavelength EEWP 320/424 nm, which can be considered
as marine humic-like material. The presence of amino acid-tryptophan like peaks were observed, with EEWP 300/350 nm in some
of the high salinity samples. This peak was of high relative fluorescence intensity. It is hypothesized that the intense biological
activity of the salt marsh and near coastal area is responsible for the carbon addition as well as the appearance of the highly
fluorescence amino acid-protein like material. 相似文献
79.
Abiotic typology of Polish lakes 总被引:3,自引:0,他引:3
According to the requirements of the Water Framework Directive 2000/60/EC, all member states of the EU have to establish the typology of their surface waterbodies. The typology is aimed at defining the type-specific reference conditions against which the ecological state of waters can be assessed. The abiotic typology of Polish lakes of an area greater than 50 ha was established based on morphometric, hydrographic and physico-chemical data taken from the Polish national monitoring dataset. The current dataset comprises 749 out of a total of 1042 lakes with an area greater than 50 ha in Poland. Lake types were identified based on a combination of abiotic characteristics of lakes specified in Annex II of the Water Framework Directive such as ecoregions, size, altitude, mean depth, geology and an additional factor – Schindler's ratio. Altogether 13 abiotic lake types were established. 相似文献
80.