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71.
Dev Niyogi Hsin-I Chang Fei Chen Lianhong Gu Anil Kumar Surabi Menon Roger A. Pielke Sr. 《Natural Hazards》2007,42(2):345-359
Aerosols can affect the cloud-radiation feedback and the precipitation over the Indian monsoon region. In this paper, we propose
that another pathway by which aerosols can modulate the multi-scale aspect of Indian monsoons is by altering the land–atmosphere
interactions. The nonlinear feedbacks due to aerosol/diffuse radiation on coupled interactions over the Indian monsoon region
are studied by: (1) reviewing recent field measurements and modeling studies, (2) analyzing the MODIS and AERONET aerosol
optical depth datasets, and (3) diagnosing the results from sensitivity experiments using a mesoscale modeling system. The
results of this study suggest that the large magnitude of aerosol loading and its impact on land–atmosphere interactions can
significantly influence the mesoscale monsoonal characteristics in the Indo-Ganges Basin. 相似文献
72.
Uranium depositional controls at the Prairie Flats surficial uranium deposit, Summerland, British Columbia 总被引:1,自引:0,他引:1
A hydrological and geochemical investigation of the Prairie Flats surficial uranium deposit in Summerland, BC was undertaken to identify the principal controls on uranium deposition. A network of piezometers was installed and used to measure the hydraulic conductivities of the host sediments as well as the general flow direction and aqueous geochemistry of the resident groundwaters. Two hydrostratigraphic units were identified: a peat and clay unit overlying a sand and gravel unit. Measured hydraulic conductivities were on the order of 10-7 and 10-5 m/s, respectively, and the vertical hydraulic gradients indicate significant groundwater discharge upward into the peat and clay unit. Prairie Flats groundwaters are neutral to alkaline in pH, enriched in Ca2+ and HCO3-, and have dissolved uranium concentrations ranging from 10 to nearly 1,000 µg/l. Groundwater flow and geochemistry data were used to estimate the flux of uranium in groundwater at the site. A major fraction of the uranium is taken up by adsorption to organics. There is also evidence for subsequent desorption by the formation of soluble complexes with bicarbonate. Uranium that is not held by adsorption is most likely precipitated as uraninite, UO2(c). Reducing conditions in the peat and clay unit (Eh<0.1 V) relative to the underlying sand and gravel unit (Eh>0.2 V) may explain the high concentrations of uranium nearer ground surface. The current flux of uranium into the flats is significantly smaller than that calculated from the size and age of the deposit, which may be an indication of changing rates of deposition in response to varying climatic and hydrogeologic conditions over time. 相似文献
73.
74.
Roger A. Kuhnle 《地球表面变化过程与地形》1992,17(2):191-197
Bed load transport rates were measured with continuously recording pit samplers on two small gravel-bed streams in the Goodwin Creek Research Watershed, northern Mississippi, U.S.A. When transport samples were grouped according to whether the stage was rising or falling, significant differences in mean bed load transport rates were found at nearly all flow strengths. At higher flow strengths, mean bed load transport rates were greater during rising stages than during falling stages. The greater transport rates measured during rising stages may be caused by a lag in the formation and destruction of bed roughness elements. One of the streams also showed evidence for greater transport rates for low flows as the stage declined. This may be caused by differences in the stability of the bed material at the beginning and at the end of a transport event. 相似文献
75.
Near-infrared spectra, 0.65–2.5 μm, are presented for Tethys, Dione, Rhea, Iapetus, and Hyperion. Water ice absorptions at 2.0, 1.5, and 1.25 μm are seen in the spectra of all five objects (except the 1.25-μm band was not detected in spectra of Hyperion) and the weak 1.04-μm ice absorption is detected on the leading and trailing sides of Rhea, and the trailing side of Dione. Upper limits to the 1.04-μm ice band depth are <0.3% for the leading side of Dione; <0.7% for the leading side of Iapetus, and the trailing side of Tethys; <1% on the trailing side of Iapetus; and <5% on the leading side of Tethys. The leading-trailing side ice band depth differences on Saturn's satellites are similar to those for the Galilean satellites, indicating possible surface modification by magnetospheric charged particle bombardment. Limits are determined for the amount of particulates, trapped gases, and amonium hydroxide on the surface. The surfaces of Saturn's satellites (except the dark side of Iapetus) are nearly pure water ice, with probably less than about 1 wt% particulate minerals. The ice could be clathrates with as much as a few weight percent trapped gases. The upper limit of amonium hydroxide depends on the spectral data precision and varies from ~ 1 wt% NH3 for the leading side of Rhea to ~ 10 wt% NH3 for Dione. 相似文献
76.
Flare-associated soft X-ray bursts (8–12 Å) are examined for 283 events observed by OSO-III. These bursts are shown to be predominantly thermal in nature. Their time-profiles are roughly similar to those of the associated H flares, although the X-ray burst begins about two minutes earlier, on the average. The strength of the soft X-ray burst is directly related to the area and brilliance of the flare, the age and flare-richness of the associated plage, and the general level of solar activity at the time of the burst. The peak enhancements in the soft X-ray and H emission rates during flares are of the same order of magnitude, as are the total flare energies radiated at these wavelengths. We estimate that soft X-radiation accounts for up to 10% of a flare's total electromagnetic emission.NRC/NAS Resident Research Associate. 相似文献
77.
Roger Hayter 《The Professional geographer》1978,30(3):240-249
Based on interviews with corporate executives, this paper examines several decisions to locate pulp and paper mills in British Columbia during the 1960's and early 1970's. It emphasizes locational evaluations of regions, communities, and sites interpreted as parts of wider investment decision processes and longer-run corporate strategies. Relationships between initial locational decisions and post-locational assessments and adjustments are also identified. 相似文献
78.
In a previous paper, a semi-analytical solution for the long-term motion of Pluto was presented. The present paper contains: (1) a comparison of the present solution with the solution by Williams and Benson; (2) a discussion of the effect of the near resonance between Pluto and Uranus; and, (3) a calculation of the librational period of the eccentricity, inclination and perihelion.The semi-analytical solution is shown to agree very closely with the long-term solution for Pluto obtained by Williams and Benson using numerical integration of the averaged equations of motion. A small difference between the two solutions is attributed to neglecting the eccentricity and inclination of Neptune in the semi-analytical solution. 相似文献
79.
For petrological calculations, including geothermobarometry and the calculation of phase diagrams (for example, P–T petrogenetic grids and pseudosections), it is necessary to be able to express the activity–composition (a–x) relations of minerals, melt and fluid in multicomponent systems. Although the symmetric formalism—a macroscopic regular model approach to a–x relations—is an easy-to-formulate, general way of doing this, the energetic relationships are a symmetric function of composition. We allow asymmetric energetics to be accommodated via a simple extension to the symmetric formalism which turns it into a macroscopic van Laar formulation. We term this the asymmetric formalism (ASF). In the symmetric formalism, the a–x relations are specified by an interaction energy for each of the constituent binaries amongst the independent set of end members used to represent the phase. In the asymmetric formalism, there is additionally a "size parameter" for each of the end members in the independent set, with size parameter differences between end members accounting for asymmetry. In the case of fluid mixtures, for example, H2O–CO2, the volumes of the end members as a function of pressure and temperature serve as the size parameters, providing an excellent fit to the a–x relations. In the case of minerals and silicate liquid, the size parameters are empirical parameters to be determined along with the interaction energies as part of the calibration of the a–x relations. In this way, we determine the a–x relations for feldspars in the systems KAlSi3O8–NaAlSi3O8 and KAlSi3O8–NaAlSi3O8–CaAl2Si2O8, for carbonates in the system CaCO3–MgCO3, for melt in the melting relationships involving forsterite, protoenstatite and cristobalite in the system Mg2SiO4–SiO2, as well as for fluids in the system H2O–CO2. In each case the a–x relations allow the corresponding, experimentally determined phase diagrams to be reproduced faithfully. The asymmetric formalism provides a powerful and flexible way of handling a–x relations of complex phases in multicomponent systems for petrological calculations. 相似文献
80.
Rerouting the stakeholder express 总被引:1,自引:0,他引:1