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191.
To help understand factors that influence submarine fan deposition, we outline some of the principal sedimentary, tectonic,
and sea-level controls involved in deep-water sedimentation, give some data on the rates at which they operate, and evaluate
their probable effects. Three depositional end-member systems, two submarine fan types (elongate and radial), and a third
nonfan, slope-apron system result primarily from variations in sediment type and supply. Tectonic setting and local and global
sea-level changes further modify the nature of fan growth, the distribution of facies, and the resulting vertical stratigraphic
sequences.
Margin setting represents fan and/or source area 相似文献
192.
193.
Spectral Characteristics and Correction of Long-Term Eddy-Covariance Measurements Over Two Mixed Hardwood Forests in Non-Flat Terrain 总被引:1,自引:1,他引:0
Hong-Bing Su Hans Peter Schmid C. S. B. Grimmond Christoph S. Vogel Andrew J. Oliphant 《Boundary-Layer Meteorology》2004,110(2):213-253
We present turbulence spectra and cospectra derived from long-term eddy-covariancemeasurements (nearly 40,000 hourly data over three to four years) and the transferfunctions of closed-path infrared gas analyzers over two mixed hardwood forests inthe mid-western U.S.A. The measurement heights ranged from 1.3 to 2.1 times themean tree height, and peak vegetation area index (VAI) was 3.5 to 4.7; the topographyat both sites deviates from ideal flat terrain. The analysis follows the approach ofKaimal et al. (Quart. J. Roy. Meteorol. Soc.
98, 563–589, 1972) whose results were based upon 15 hours of measurements atthree heights in the Kansas experiment over flatter and smoother terrain. Both thespectral and cospectral constants and stability functions for normalizing and collapsingspectra and cospectra in the inertial subrange were found to be different from those ofKaimal et al. In unstable conditions, we found that an appropriate stabilityfunction for the non-dimensional dissipation of turbulent kinetic energy is of the form () = (1 - b-)-1/4 - c-, where representsthe non-dimensional stability parameter. In stable conditions, a non-linear functionGxy() = 1 + bxyc
xy (cxy < 1) was found to benecessary to collapse cospectra in the inertial subrange. The empirical cospectralmodels of Kaimal et al. were modified to fit the somewhat more (neutraland unstable) or less (stable) sharply peaked scalar cospectra observed over forestsusing the appropriate cospectral constants and non-linear stability functions. Theempirical coefficients in the stability functions and in the cospectral models varywith measurement height and seasonal changes in VAI. The seasonal differencesare generally larger at the Morgan Monroe State Forest site (greater peak VAI) andcloser to the canopy.The characteristics of transfer functions of the closed-path infrared gas analysersthrough long-tubes for CO2 and water vapour fluxes were studied empirically. This was done by fitting the ratio between normalized cospectra of CO2 or watervapour fluxes and those of sensible heat to the transfer function of a first-order sensor.The characteristic time constant for CO2 is much smaller than that for water vapour. The time constant for water vapour increases greatly with aging tubes. Three methods were used to estimate the flux attenuations and corrections; from June through August, the attenuations of CO2 fluxes are about 3–4% during the daytime and 6–10% at night on average. For the daytime latent heat flux (QE), the attenuations are foundto vary from less than 10% for newer tubes to over 20% for aged tubes. Correctionsto QE led to increases in the ratio (QH + QE)/(Q* - QG) by about 0.05 to0.19 (QH is sensible heat flux, Q* is net radiation and QG is soil heat flux),and thus are expected to have an important impact on the assessment of energy balanceclosure. 相似文献
194.
Schmidt H Bich Ha N Pfannkuche J Amann H Kronfeldt HD Kowalewska G 《Marine pollution bulletin》2004,49(3):229-234
The laboratory characterization of a field-operable surface-enhanced Raman scattering sensor (SERS optode) is presented for the detection of aromatic hydrocarbons in seawater. The sensor has been developed for deployment with a robust underwater spectrograph. To meet the demands of the harsh seawater application, sol-gel derived SERS substrates were used. The calibration curves of six PAHs were determined to be of Langmuir adsorption isotherm type with limits of detection ranging from the microg l(-1) to ng l(-1) level. The experimentally determined adsorption constants varied strongly with the molecular weight of the analytes and correlated with their solubility. A mixture of five PAHs dissolved in seawater was investigated to demonstrate the utility of this method for screening. Emphasis was put on the interference from suspended particulate matter (SPM). The Raman measurement with backscattering configuration was shown to be immune against turbidities up to 1000 NTU. The physico-chemical interference arising from adsorption by the sediment was measured on-line by adding sediment to a PAH-spiked solution. According to the calibration curve, the PAH concentration decrease corresponded to more than 98% of the analyte being scavenged by the sediment. 相似文献
195.
Michelle T. H. van Vliet Stephen Blenkinsop Aidan Burton Colin Harpham Hans Peter Broers Hayley J. Fowler 《Climatic change》2012,111(2):249-277
Regional or local scale hydrological impact studies require high resolution climate change scenarios which should incorporate
some assessment of uncertainties in future climate projections. This paper describes a method used to produce a multi-model
ensemble of multivariate weather simulations including spatial–temporal rainfall scenarios and single-site temperature and
potential evapotranspiration scenarios for hydrological impact assessment in the Dommel catchment (1,350 km2) in The Netherlands and Belgium. A multi-site stochastic rainfall model combined with a rainfall conditioned weather generator
have been used for the first time with the change factor approach to downscale projections of change derived from eight Regional
Climate Model (RCM) experiments for the SRES A2 emission scenario for the period 2071–2100. For winter, all downscaled scenarios
show an increase in mean daily precipitation (catchment average change of +9% to +40%) and typically an increase in the proportion
of wet days, while for summer a decrease in mean daily precipitation (−16% to −57%) and proportion of wet days is projected.
The range of projected mean temperature is 7.7°C to 9.1°C for winter and 19.9°C to 23.3°C for summer, relative to means for
the control period (1961–1990) of 3.8°C and 16.8°C, respectively. Mean annual potential evapotranspiration is projected to
increase by between +17% and +36%. The magnitude and seasonal distribution of changes in the downscaled climate change projections
are strongly influenced by the General Circulation Model (GCM) providing boundary conditions for the RCM experiments. Therefore,
a multi-model ensemble of climate change scenarios based on different RCMs and GCMs provides more robust estimates of precipitation,
temperature and evapotranspiration for hydrological impact assessments, at both regional and local scale. 相似文献
196.
Consistency of observed winter precipitation trends in northern Europe with regional climate change projections 总被引:1,自引:0,他引:1
Often it is claimed that the recent changes in northern European climate are at least partly anthropogenic even though a human
influence has not yet been successfully detected. Hence we investigate whether the recent changes are consistent with regional
climate change projections. Therefore, trends in winter (DJF) mean precipitation in northern Europe are compared to human
induced changes as predicted by a set of four regional climate model simulations. The patterns of recent trends and predicted
changes match reasonably well as indicated by pattern correlation and the similarity is very likely not random. However, the
model projections generally underestimate the recent change in winter precipitation. That is, the signal-to-noise ratio of
the anthropogenic precipitation change is either rather low or the presently used simulations are significantly flawed in
their ability to project changes into the future. European trends contain large signals related to the North Atlantic Oscillation
(NAO), of which a major unknown part may be unrelated to the anthropogenic signal. Therefore, we also examine the consistency
of recent and projected changes after subtracting the NAO signal in both the observations and in the projections. It turns
out that even after the removal of the NAO signal, the pattern of trends in the observations is similar to those projected
by the models. At the same time, the magnitude of the trends is considerably reduced and closer to the magnitude of the change
in the projections. 相似文献
197.
Jacqueline Flückiger Reto Knutti James W. C. White Hans Renssen 《Climate Dynamics》2008,31(6):633-645
Greenland ice cores, as well as many other paleo-archives from the northern hemisphere, recorded a series of 25 warm interstadial
events, the so-called Dansgaard-Oeschger (D-O) events, during the last glacial period. We use the three-dimensional coupled
global ocean–atmosphere–sea ice model ECBILT-CLIO and force it with freshwater input into the North Atlantic to simulate abrupt
glacial climate events, which we use as analogues for D-O events. We focus our analysis on the Northern Hemisphere. The simulated
events show large differences in the regional and seasonal distribution of the temperature and precipitation changes. While
the temperature changes in high northern latitudes and in the North Atlantic region are dominated by winter changes, the largest
temperature increases in most other land regions are seen in spring. Smallest changes over land are found during the summer
months. Our model simulations also demonstrate that the temperature and precipitation change patterns for different intensifications
of the Atlantic meridional overturning circulation are not linear. The extent of the transitions varies, and local non-linearities
influence the amplitude of the annual mean response as well as the response in different seasons. Implications for the interpretation
of paleo-records are discussed. 相似文献
198.
In order to understand the cometary plasma environment it is important to track the closely linked chemical reactions that dominate ion evolution. We used a coupled MHD ion-chemistry model to analyze previously unpublished Giotto High Intensity Ion Mass Spectrometer (HIS-IMS) data. In this way we study the major species, but we also try to match some minor species like the CHx and the NHx groups. Crucial for this match is the model used for the electrons since they are important for ion-electron recombination. To further improve our results we included an enhanced density of supersonic electrons in the ion pile-up region which increases the local electron impact ionization. In this paper we discuss the results for the following important ions: C+, CH+, CH+2, CH+3, N+, NH+, NH+2, NH+3, NH+4, O+, OH+, H2O+, H3O+, CO+, HCO+, H3CO+, and CH3OH+2. We also address the inner shock which is very distinctive in our MHD model as well as in the IMS data. It is located just inside the contact surface at approximately 4550 km. Comparisons of the ion bulk flow directions and velocities from our MHD model with the data measured by the HIS-IMS give indication for a solar wind magnetic field direction different from the standard Parker angle at Halley's position. Our ion-chemical network model results are in a good agreement with the experimental data. In order to achieve the presented results we included an additional short lived inner source for the C+, CH+, and CH+2 ions. Furthermore we performed our simulations with two different production rates to better match the measurements which is an indication for a change and/or an asymmetric pattern (e.g. jets) in the production rate during Giotto's fly-by at Halley's comet. 相似文献
199.
We present Monte Carlo simulations for the polarization of light reflected from planetary atmospheres. We investigate dependencies of intensity and polarization on three main parameters: single scattering albedo, optical depth of a scattering layer, and albedo of a Lambert surface underneath. The main scattering process considered is Rayleigh scattering, but isotropic scattering and enhanced forward scattering on haze particles are also investigated. We discuss disk integrated results for all phase angles and radial profiles of the limb polarization at opposition. These results are useful to interpret available limb polarization measurements of solar system planets and to predict the polarization of extra-solar planets as a preparation for VLT/SPHERE. Most favorable for a detection are planets with an optically thick Rayleigh-scattering layer. The limb polarization of Uranus and Neptune is especially sensitive to the vertically stratified methane mixing ratio. From limb polarization measurements constraints on the polarization at large phase angles can be set. 相似文献
200.