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91.
P. B. Storebø T. Bjorvatten K. Hønn»shagen A. Lillegraven C. D. Jones C. J. P. Van Buijtenen 《Boundary-Layer Meteorology》1983,26(2):127-139
Unipolar air ions released into the wind constitute a tracer which can be measured with high resolution. An ion source produces a cloud with homogeneous charge density, insensitive to source strength, dependent on time since formation only. It is well suited for tracing concentration changes due to turbulence, less suited for cloud size tracing. A tight array of 8 sensors has been used to examine turbulently dispersed ions. High-resolution records are presented and discussed. The highest concentrations measured could be undiluted source material. The frequency distribution within a plume did not differ from that in a multitude of puffs. The distribution seems to be log-normal with a geometric standard deviation of about 2.45. The time resolution used corresponds to volume resolutions of 40, 225, and 650 cm3. Sample size had no apparent effect. 相似文献
92.
Low frequency electrostatic waves are studied in magnetized plasmas with an electron temperature which varies with position in a direction perpendicular to the magnetic field. For wave frequencies below the ion cyclotron frequency, the waves need not follow any definite dispersion relation. Instead a band of phase velocities is allowed, with a range of variation depending on the maximum and minimum values of the electron temperature. Simple model equations are obtained for the general case which can be solved to give the spatial variation of a harmonically time varying potential. A simple analytical model for the phenomenon is presented and the results are supported by numerical simulations carried out in a 2.5-dimensional particle-in-cell numerical simulation. We find that when the electron temperature is striated along B0 and low frequency waves (ci) are excited in this environment, then the intensity of these low frequency waves will be striated in a manner following the electron temperature striations. High frequency ion acoustic waves (ci) will on the other hand have a spatially more uniform intensity distribution. 相似文献
93.
Herak Marijan Herak Davorka Markušić Snježana Ivančić Ines 《Studia Geophysica et Geodaetica》2001,45(3):251-266
The rate of aftershock occurrence after the M6 Ston-Slano (Croatia) earthquake is modeled as the Epidemic Type Aftershock Sequence (ETAS). Increase of the modeled cumulative number of aftershocks with time was fitted to observations by the least-squares criterion using the combined grid-search and Monte-Carlo approach. This enabled not only the estimation of the most probable ETAS parameters, but also the determination of their confidence limits, as well as the estimation of the bias between them. It has been found that the bias is significant for some of the parameter pairs, regardless of the threshold magnitude assumed. Residual analyses revealed that all strong aftershocks (M
L
4.5) occurred during the periods of normal to high aftershock activity. There were two periods of quiescence in the sequence, both of which were followed by a strong aftershock. 相似文献
94.
Iodine contents of soils developed over the major rock formations of the northern zone of the Eastern Pontide Tectonic Belt
(Northeastern Turkey) have been investigated with respect to soil-parent rock relationship, effect of topography, elevation,
and climate to construe its effect on the health of the local population. Samples were collected from the A and B horizons
of the soils developed over the major stratigraphic units constituting the eastern Pontides, including the Lower Basic Complex
of Jurassic-Lower Cretaceous age, the Berdiga limestone (Jurassic-lower Cretaceous), the Dagbasi granitoid (Upper Cretaceous),
volcano-sedimentary sequence of Upper Cretaceous age, ore-bearing and barren dacites of Upper Cretaceous age, and Neogene
alkaline basalts. Chemical analyses of soil samples indicate significantly lower iodine abundances for all the soils studied
(5–28 ppm) in comparison to the average abundance of iodine in analogous soils of other parts of the world (22–93 ppm). The
concentration of iodine in soils developed over the same geologic formation decrease with increasing elevation. In certain
cases, this decrease may reach up to 70%. Goiter is highly common throughout this region in Turkey. The results of this study
suggest that the iodine deficiency of region’s soils may be a principal underlying cause for this area of Turkey being an
endemic goiter region. 相似文献
95.
96.
The regional ocean model system (ROMS) is used to downscale a 26-year period of the twentieth century 20C3M experiment from
the global coupled Bergen climate model (BCM) for the North Sea. Compared to an observational-based climatology, BCM have
good results on the mean temperature, except for too low winter temperature. This is connected to a too weak inflow of Atlantic
water. The downscaling gives added value to the BCM results by providing regional details, doubling the Atlantic inflow, and
improving the mean winter temperature. For mean salinity, BCM has values very close to the climatology, whereas the downscaling
becomes too fresh. The downscaling, however, improves the sea surface salinity, the vertical structure, and the Norwegian
Coastal Current. It is concluded that the downscaling procedure as presented here is a suitable tool for assessing the future
Atlantic inflow and sea temperature in the North Sea based on a global climate projection. 相似文献
97.
介绍散射伽玛能谱测井仪的组成工作原理、探测系统、探测技术、数据采集、处理及传输技术,能谱探测电路、数据采集电路及编制实时数据采集程序。并针对散射伽玛能谱测井在解决复杂岩性地层地质问题,确定空隙度、解释煤层气、裂隙带等方面的独具特点以及在煤田地质勘探中开展散射伽能谱测井的必要性进行了讨论。 相似文献
98.
Arctic ecosystems could provide a substantial positive feedback to global climate change if warming stimulates below-ground CO2 release by enhancing decomposition of bulk soil organic matter reserves.Ecosystem respiration during winter is important in this context because CO2 release from snow-covered tundra soils is a substantial component of annual net carbon (C) balance, and because global climate models predict that the most rapid rises in regional air temperature will occur in the Arctic during winter. In this manipulative field study, the relative contributions of plant and bulk soil organic matter C pools to ecosystem CO2 production in mid-winter were investigated. We measured CO2 efflux rates in Swedish sub-arctic heath tundra from control plots and from plots that had been clipped in the previous growing season to disrupt plant activity. Respiration derived from recently-fixed plant C (i.e., plant respiration, and respiration associated with rhizosphere exudates and decomposition of fresh litter) was the principal source of CO2 efflux, while respiration associated with decomposition of bulk soil organic matter was low, and appeared relatively insensitive to temperature. These results suggest that warmer mid-winter temperatures in the Arctic may have a much greater impact on the cycling of recently-fixed, plant-associated C pools than on the depletion of tundra bulk soil C reserves, and consequently that there is a low potential for significant initial feedbacks from arctic ecosystems to climate change during mid-winter. 相似文献
99.
In this study, turbulent heat flux data from two sites within the Baltic Sea are compared with estimates from two models. The main focus is on the latent heat flux. The measuring sites are located on small islands close to the islands of Bornholm and Gotland. Both sites have a wide wind direction sector with undisturbed over-water fetch. Mean parameters and direct fluxes were measured on masts during May to December 1998.The two models used in this study are the regional-scale atmospheric model HIRLAM and the ocean model PROBE-Baltic. It is shown that both models overestimate the sensible and latent heat fluxes. The overestimation can, to a large extent, be explained by errors in the air-water temperature and humidity differences. From comparing observed and modelled data, the estimated 8-month mean errors in temperature and humidity are up to 1 °C and 1 g kg-1, respectively. The mean errors in the sensible and latent heat fluxes for the same period are approximately 15 and 30 W m-2, respectively.Bulk transfer coefficients used for calculating heat and humidity fluxes at the surface were shown to agree rather well with the measurements, at least for the unstable data. For stable stratification, the scatter in data is generally large, and it appears that the bulk formulation chosen overestimates turbulent heat fluxes. 相似文献
100.
Douglas D. Walker Björn Gylling Anders Ström Jan-Olof Selroos 《Hydrogeology Journal》2001,9(5):419-431
Safety Report 1997 (SR 97) of the Swedish Nuclear Fuel and Waste Management Company is a comprehensive performance assessment
of three hypothetical radioactive waste repositories in Sweden. It includes hydrogeologic studies (data compilation, parameter
synthesis, and groundwater flow modeling) to determine groundwater flow and the associated uncertainties for the three sites.
This report reviews and compares the hydrogeologic characterization programs, the site characteristics, and the groundwater
flow models used in the SR 97 performance assessment. Although differences in site-characterization programs tend to mask
differences in site characteristics, the sites do have notable differences that affect the results of the performance assessment.
The effects of model uncertainties evaluated by the variant cases appear to be smaller than the variability of results for
the base case (best estimate of site conditions) of each site.
Electronic Publication 相似文献