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1.
VOLKER GREWE MARTIN DAMERIS RALF HEIN ROBERT SAUSEN BENEDIKT STEIL 《Tellus. Series B, Chemical and physical meteorology》2001,53(2):103-121
The development of the future atmospheric chemical composition is investigated with respect to NO y and O3 by means of the off‐line coupled dynamic‐chemical general circulation model ECHAM3/CHEM. Two time slice experiments have been performed for the years 1992 and 2015, which include changes in sea surface temperatures, greenhouse gas concentrations, emissions of CFCs, NO x and other species, i.e., the 2015 simulation accounts for changes in chemically relevant emissions and for a climate change and its impact on air chemistry. The 2015 simulation clearly shows a global increase in ozone except for large areas of the lower stratosphere, where no significant changes or even decreases in the ozone concentration are found. For a better understanding of the importance of (A) emissions like NO x and CFCs, (B) future changes of air temperature and water vapour concentration, and (C) other dynamical parameters, like precipitation and changes in the circulation, diabatic circulation, stratosphere‐troposphere‐exchange, the simulation of the future atmosphere has been performed stepwise. This method requires a climate‐chemistry model without interactive coupling of chemical species. Model results show that the direct effect of emissions (A) plays a major rôle for the composition of the future atmosphere, but they also clearly show that climate change (B and C) has a significant impact and strongly reduces the NO y and ozone concentration in the lower stratosphere. 相似文献
2.
In the Sila massif of northern Calabria a continuous sectionis exposed through a segment of a Hercynian deep continentalcrust, which has been interpreted by previous workers as a stackof basement nappes (‘Monte Gariglione Complex’).The section consists essentially of metapelitic migmatites andsubordinate metabasites and marbles, which were metamorphosedat medium-pressure–high-temperature granulite-facies conditions.A continuous metamorphic gradient through the exposed segmentcan be deduced from the systematic change in the compositionsof ferromagnesian minerals in divariant metapelitic assemblages.This gradient is partly supported by conventional geothermobarometryand by applying the TWEEQU method. However, peak-metamorphicconditions are better defined by dehydration melting reactions,which reveal 相似文献
3.
GERNOT ARP CHRISTIAN OSTERTAG‐HENNING SELÇÜK YÜCEKENT JOACHIM REITNER VOLKER THIEL 《Sedimentology》2008,55(5):1227-1251
Fossil stromatolites may reveal information about their hydrochemical palaeoenvironment, provided that assignment to a specific microbial community and a corresponding biogeochemical mechanism of formation can be made. Tithonian stromatolites of the Münder Formation at Thüste, north Germany, have traditionally been considered as formed by intertidal cyanobacterial communities. However, thin sections of the stromatolites show elongated angular traces of former gypsum crystals in a dense arrangement, but no algal or cyanobacterial filament traces. Moreover, high Fe2+ and Mn2+ contents, oxygen‐isotope and sulphur‐isotope ratios of carbonate‐bound sulphates, and sulphurized hydrocarbon biomarkers of the stromatolitic carbonate indicate that CaCO3 precipitation occurred near the oxic–anoxic interface as a result of intensive bacterial sulphur cycling rather than photosynthetic activity. Furthermore, anaerobic oxidation of methane by Archaea may have driven CaCO3 precipitation in deeper parts of the biofilm community, as reflected by high concentrations of squalane with a strongly negative δ13C in conjunction with evaporite pseudomorphs showing extremely low δ13CCarb ratios. Consequently, the Thüste stromatolites are now interpreted as having initially formed by gypsum impregnation of biofilms. Subsequently, early Mg‐calcitic calcitization within the biofilms occurred because of combined bacterial iron, manganese and sulphate reduction, with an increasing contribution of anaerobic oxidation of methane with depth. This model plausibly explains the prominent preservation of signals derived from oxygen‐independent metabolic pathways, whereas virtually no geochemical record exists for an aerobic community that may, nevertheless, have prevailed at the stromatolite surface. Photic‐zone stromatolites with a prominent signal of anaerobic oxidation of methane may be common in, and indicative of, oxygen‐depleted sulphate‐bearing environments with high rates of methane production, conditions that possibly were fulfilled at the Archaean to Proterozoic transition. 相似文献
4.
States of maximum entropy production in a one-dimensional vertical model with convective adjustment 总被引：2，自引：0，他引：2
We investigate the hypothesis that the atmosphere is constrained to maximize its entropy production by using a one-dimensional (1-D) vertical model. We prescribe the lapse rate in the convective layer as that of the standard troposphere. The assumption that convection sustains a critical lapse rate was absent in previous studies, which focused on the vertical distribution of climatic variables, since such a convective adjustment reduces the degrees of freedom of the system and may prevent the application of the maximum entropy production (MEP) principle. This is not the case in the radiative-convective model (RCM) developed here, since we accept a discontinuity of temperatures at the surface similar to that adopted in many RCMs.
For current conditions, the MEP state gives a difference between the ground temperature and the air temperature at the surface ≈10 K. In comparison, conventional RCMs obtain a discontinuity ≈2K only. However, the surface boundary layer velocity in the MEP state appears reasonable (≈m s−1 ). Moreover, although the convective flux at the surface in MEP states is almost uniform in optically thick atmospheres, it reaches a maximum value for an optical thickness similar to current conditions. This additional result may support the maximum convection hypothesis suggested by Paltridge (1978 ). 相似文献
For current conditions, the MEP state gives a difference between the ground temperature and the air temperature at the surface ≈10 K. In comparison, conventional RCMs obtain a discontinuity ≈2K only. However, the surface boundary layer velocity in the MEP state appears reasonable (≈m s
5.
6.
Suspension and calibration of a sediment trap 总被引：5，自引：0，他引：5
By Lars Håkanson 《Aquatic Sciences - Research Across Boundaries》1984,46(1):171-175
The aim of this technical note is to introduce a new, simple construction of a buoy-carried, suspended sediment trap that
meets given demands concerning design (geometry of vessels) and stability during the registration period. The device is based
on a ball-and-socket joint in the center and two Plexiglas cylinders (D=5cm, H=30cm) on PVC plastic arms. The suspension consists
of only three parts. To determine the optimal construction, the apparatus has been calibrated in a circulating flume at various
water velocities. 相似文献
7.
一个地方下月的雨量,能不能从当地上月天气演变的结果所记录下来的各种气象要素的数值来推测呢?现在这篇报告的目的就想解答这个问题。关於这方面的研究,以前早有人注意,例如竺可桢教授研究过冬天温度与夏季雨量的关系, 相似文献
8.
The evolution of identical twin errors from an atmospheric general circulation model is studied in the linear range (small errors) through intermediate times and the approach to saturation. Between forecast day 1 and 7, the normalized error variance in the tropics is similar to that at higher latitudes. After that, tropical errors grow more slowly. The predictability time τ taken for tropical errors to reach half their saturation values is larger than that for mid-latitudes, especially for the planetary waves, thus implying greater potential predictability in the tropics.
The discrepancy between mid-latitude and tropical τ is more pronounced at 850 hPa than at 200 hPa, is largest for the planetary waves, and is more pronounced for errors arising from wave phase differences (than from wave amplitude differences).
The spectra of the error in 200 hPa zonal wind show that for forecast times up to about 5 d, the tropical error peaks at much shorter scales than the mid-latitude errors, but that subsequently tropical and mid-latitude error spectra look increasingly similar.
The difference between upper and lower level tropical τ may be due to the greater influence of mid-latitudes at the upper levels. 相似文献
The discrepancy between mid-latitude and tropical τ is more pronounced at 850 hPa than at 200 hPa, is largest for the planetary waves, and is more pronounced for errors arising from wave phase differences (than from wave amplitude differences).
The spectra of the error in 200 hPa zonal wind show that for forecast times up to about 5 d, the tropical error peaks at much shorter scales than the mid-latitude errors, but that subsequently tropical and mid-latitude error spectra look increasingly similar.
The difference between upper and lower level tropical τ may be due to the greater influence of mid-latitudes at the upper levels. 相似文献
9.
Common parametrization models for cloud microphysical processes use condensate mass density and/or particle number density as prognostic properties. However, other moments of the particle size distribution can likewise be chosen for prediction. This study deals with parametrization models with one and two, respectively, prognostic moments for the sedimentation of drop ensembles. The spectral resolving model defines the reference solution.
The evolution of the vertical profiles of liquid water content, drop number density and rain rate strongly depend on the choice of the prognostic moments in the parametrization models. In models with a single prognostic moment, its vertical profile is copied by all other moments. The moment of most physical pertinence is recommended for prediction. In models with two prognostic moments, the vertical profiles of all moments differ. The orders of the prognostic moments should be chosen close to the order of moments of highest relevance. Otherwise large errors occur. For example, comparison of modelled versus observed radar reflectivity (6th moment with respect to diameter) does not tell much about the quality of other properties if reflectivity is diagnosed from for example, number density and mass density. Furthermore, mass conservation is fulfilled only if mass density is forecasted. 相似文献
The evolution of the vertical profiles of liquid water content, drop number density and rain rate strongly depend on the choice of the prognostic moments in the parametrization models. In models with a single prognostic moment, its vertical profile is copied by all other moments. The moment of most physical pertinence is recommended for prediction. In models with two prognostic moments, the vertical profiles of all moments differ. The orders of the prognostic moments should be chosen close to the order of moments of highest relevance. Otherwise large errors occur. For example, comparison of modelled versus observed radar reflectivity (6th moment with respect to diameter) does not tell much about the quality of other properties if reflectivity is diagnosed from for example, number density and mass density. Furthermore, mass conservation is fulfilled only if mass density is forecasted. 相似文献
10.