By means of the algorithm presented in Part I of this study, the temporal course H(t) and the daily mean H of the sensible heat flux H can be determined from measurements of the thermodynamic surface temperature (as a function of time) and from a one-time-of-day air temperature observation. Inaddition to these temperatures, one needs estimates of daily mean wind speed,of the roughness lengths of momentum and heat transfer, and of the displacementheight. In Part I, the algorithm was derived for areas with homogeneous surfaces,i.e., with uniform surface temperature, and the method was verified with measurements taken during several field campaigns. The root mean square error for the temperature difference between surface and air, in the comparison between measurement and model, amounted to one or two kelvin, and the error of H was 10 to 25 per cent. The method can be used to determine the sensible heat flux from measurements of surface temperatures by satellites, but can also be applied to ground based measurements.In Part II, the procedure is generalized for areas that consist of various surface types (sub-regions) with different surface temperatures, and can be usedwhen only a few (at least one) air temperature measurements per day are available over only one of the different sub-regions. This generalization should allow improvements to the estimates for H(t) by means of temperature measurements from, e.g., NOAA/AVHRR or LANDSAT/TM, taking into account the heterogeneity of the area contained in one METEOSAT pixel. Criteria are given as to whether effective (areal mean) surface temperatures and roughness lengths may be used for the computation of H or if the above mentioned generalized procedure has to be applied. The new algorithm is verified by measurements sampled during the field campaigns EFEDA 91 (Spain) and HIBE 89 (Hildesheimer Börde in Germany), and by using synthetic data (due to the lack of measured data) for one further combined surfacetype [soil and water (lakes)]. 相似文献
We develop a parameterisation for the effective roughness length of terrain that consists of a repeating sequence of patches, in which each patch is composed of strips of two roughness types. A numerical model with second-order closure in the turbulent stress is developed and used to show that: (i) the normalised Reynolds stress develops as a self-similar profile; (ii) the mixing-length parameterisation is a good first-order approximation to the Reynolds stress. These findings are used to characterise the blending layer, where the stress adjusts smoothly from its local surface value to its effective value aloft. Previous studies have assumed that this adjustment occurs abruptly at a single level, often called the blending height. The blending layer is shown to be characterised by height scales that arise naturally in linear models of surface layer flow over roughness changes, and calculations with the numerical model show that these height scales remain appropriate in the nonlinear regime. This concept of the blending layer allows the development of a new parameterisation of the effective roughness length, which gives values for the effective roughness length that are shown to compare well with both atmospheric measurements and values determined from the second-order model. 相似文献
The Evaporation at Grid/Pixel Scale (EVA_GRIPS) project was realised in order to determine the area-averaged evaporation over a heterogeneous land surface at the scale of a grid box of a regional numerical weather prediction or climate model, and at the scale of a pixel of a satellite image. EVA_GRIPS combined surface-based and airborne measurements, satellite data analysis, and numerical modelling activities. A mesoscale field experiment, LITFASS-2003, was carried out in the heterogeneous landscape around the Meteorological Observatory Lindenberg (MOL) of the German Meteorological Service in May and June, 2003. The experiment was embedded in the comprehensive, operational measurement program of the MOL. Experimental determination of surface fluxes on a variety of spatial scales was achieved by employing micrometeorological flux stations, scintillometers, a combination of ground-based remote sensing instruments, and the Helipod, a turbulence probe carried by a helicopter. Surface energy fluxes were also derived from satellite data. Modelling work included the use of different Soil–Vegetation–Atmosphere Transfer schemes, a large-eddy simulation model and three mesoscale atmospheric models. The paper gives an overview on the background of EVA_GRIPS, and on the measurements and meteorological conditions during LITFASS-2003. A few general results are discussed. 相似文献
Modern and known-age Pleistocene fluvial sediments were investigated by optical dating of quartz to test the suitability of the approach for dating deposits from the deeply incised Middle Rhine Valley. Samples from modern flood sediments revealed skewed distributions indicating different residual levels of equivalent dose (De) within the different aliquots. Nevertheless, a substantial number of aliquots from the modern deposits reflect De values close to zero. For the Pleistocene samples, optical ages are in general consistent with age control given by the presence of the Laacher See Tephra and radiocarbon dating. However, some samples overestimate the known age by a few thousand years when using the arithmetic mean. This is apparently explained by including aliquots in the determination of mean De where the optical signal was incompletely bleached at deposition. The most difficult issue in this context is identifying a suitable approach that can distinguish between the variability of De due to partial bleaching and microdosimetry. However, even when considering these limitations it appears that optical dating will by a quite suitable method to date Pleistocene sediments from such a complex fluvial environment, especially when focusing on a precision scale beyond a few thousand years. 相似文献
An ESR experimental study of artificial optical bleaching of sedimentary quartz has shown that the aluminum center was maximally bleached after a 6-month illumination equivalent to natural light. This duration seems too long to apply in natural conditions. Nevertheless, the measurement of the ESR intensity of aluminum centers in quartz extracted from modern sediments and deposited in sandy bars shows that the maximum bleaching has effectively been reached.
In order to determine the relationship between the bleaching and the distance covered by a quartz grain in a river, samples were collected along the Creuse River (France) from its spring to about 170 km downstream, where maximum bleaching levels were observed in previous studies. The ESR intensities of the aluminum and titanium centers in quartz were measured, using X-band spectroscopy, before and after artificial bleaching. The difference measured between these sub-samples shows that the maximum bleaching level is obtained in the course of the first kilometer. Hence, the assumption that ESR dating of fluvial sediment is based on the optical bleaching was validated. 相似文献
Sediments attributed to flooding events of River Danube concerning the bleaching of the optical stimulated luminescence (OSL) signal were investigated. It is demonstrated that the OSL signal in both quartz and feldspar is not completely but differentially bleached in the sediment grains. Partial bleaching of the samples is clearly indicated by the scatter of equivalent dose determined for several individual single aliquots. It is also shown that residual ages in feldspars are significantly higher than those calculated for quartz. It is furthermore demonstrated that analysing measurement-time dependent equivalent dose estimates is not a suitable method to identify partial bleaching in the investigated sediment grains. However, the transport and deposition process of the investigated samples was probably disturbed by an artificial input of sediment, and this case study may thus not be representative of undisturbed high flood events in the past. 相似文献
Studies on the coral reefs of the South China Sea (SCS) was the theme of the 6th Session of the 3rd Conference on Earth System Science (CESS) in Shanghai, 2014. This session discussed the most recent study developments on the SCS coral reefs, including coral reefs’ responses to global changes, coral reefs’ records on past climatic variations, and the activities about constructions and oil gas explorations in the coral reefs areas of the SCS. Disturbed by intensive anthropogenic activities and global climate warming, coral reefs in the SCS have declined dramatically, reflecting the up to 80% decrease of living coral cover and many areas having less than 20% of living coral cover. Geochemical data of SCS coral skeletons clearly show that since the Industry Revolution, the pollution situation of the SCS have dramatically increased and the seawater pH values have been continuously lowering, i.e. oceanic acidification. All these environmental phenomenon are further stressing the healthy development of the coral reef ecosystem in the SCS. Meanwhile, the poor coral reef ecosystems in the SCS are facing more anthropogenic disturbances such as coastal developments and engineering constructions. Obviously, the SCS coral reefs will be faced with more environmental challenges in the coming future. We therefore suggest that the policy makers should realize the extreme importance and the fragile of the coral reef ecosystems, and scientifically and with great cautions design construction project when in coral reef areas. We initiated the concept of “green engineering” for future developments in coral reef areas. Coral reefs are widely spreading in the whole SCS, and most of them developed since Miocene. Variations in coral reef structures provide good future oil-gas exploration. Because the SCS coral reefs have a long-developing history and a wide spatial distribution, they provide great potential in recording past environmental changes. 相似文献
Two parameterisation schemes for the turbulent surface fluxes and drag coefficients over the Arctic marginal sea-ice zone
(MIZ) are (further) developed, and their results are compared with each other. Although the schemes are based on different
principles (flux averaging and parameter averaging), the resulting drag coefficients differ only slightly in the case of neutral
and stable stratification. For unstable stratification and sea-ice conditions being typical for the north-eastern Fram Strait,
the drag coefficients resulting from the parameter-averaging concept are 5–10% larger than those of the flux-averaging concept.
At a sea-ice concentration of 45%, the parameter-averaging method overestimates the heat fluxes by a factor of 1.2. An inclusion
in the schemes of form drag caused by floe edges and ridges has a much larger effect on the drag coefficient, and on the momentum
fluxes, than the choice between the parameter-averaging or flux-averaging methods. Based on sensitivity studies with the flux-averaging
scheme, a simple formula for the effective drag coefficient above the Arctic MIZ is derived. It reduces the computational
costs of the more complex parameterisations and could also be used in larger scale models. With this simple formula, the effective
drag coefficient can be calculated as a function of the sea-ice concentration and skin drag coefficients for water and ice
floes. The results obtained with this parameterisation differ only slightly from those using the more complex schemes. Finally,
it is shown that in the MIZ, drag coefficients for sea-ice models may differ significantly from the effective drag coefficients
used in atmospheric models. 相似文献
The effect of parametric uncertainty in recharge rate and spatial variability of hydraulic conductivity upon free-surface flow is investigated in a stochastic framework. We examine the three-dimensional free-surface gravitational flow problem for sloped mean uniform flow in a randomly heterogeneous porous medium under the influence of random recharge. We develop analytic solutions for the variance of free-surface position, head, and specific discharge on the free surface. Additionally, we obtain semi-analytic solutions for the statistical moments of head and specific discharge beneath the free-surface. Statistical moments are derived using a first-order approximation and then compared with their parallel in an unbounded medium. The effect of recharge mean and variability on the statistical moments is analyzed. Results can be applied to more complex flows, slowly varying in the mean. 相似文献