Potential impacts of aerosol–land–atmosphere interactions on the Indian monsoonal rainfall characteristics     

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   

Uranium depositional controls at the Prairie Flats surficial uranium deposit, Summerland, British Columbia   总被引：1，自引：0，他引：1  

Kathy Tixier  Roger Beckie 《Environmental Geology》2001,40(10):1242-1251

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, UO_2(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   

The initial cooling of pahoehoe flow lobes   总被引：1，自引：0，他引：1  

Laszlo Keszthelyi  Roger Denlinger 《Bulletin of Volcanology》1996,58(1):5-18

 In this paper we describe a new thermal model for the initial cooling of pahoehoe lava flows. The accurate modeling of this initial cooling is important for understanding the formation of the distinctive surface textures on pahoehoe lava flows as well as being the first step in modeling such key pahoehoe emplacement processes as lava flow inflation and lava tube formation. This model is constructed from the physical phenomena observed to control the initial cooling of pahoehoe flows and is not an empirical fit to field data. We find that the only significant processes are (a) heat loss by thermal radiation, (b) heat loss by atmospheric convection, (c) heat transport within the flow by conduction with temperature and porosity-dependent thermal properties, and (d) the release of latent heat during crystallization. The numerical model is better able to reproduce field measurements made in Hawai'i between 1989 and 1993 than other published thermal models. By adjusting one parameter at a time, the effect of each of the input parameters on the cooling rate was determined. We show that: (a) the surfaces of porous flows cool more quickly than the surfaces of dense flows, (b) the surface cooling is very sensitive to the efficiency of atmospheric convective cooling, and (c) changes in the glass forming tendency of the lava may have observable petrographic and thermal signatures. These model results provide a quantitative explanation for the recently observed relationship between the surface cooling rate of pahoehoe lobes and the porosity of those lobes (Jones 1992, 1993). The predicted sensitivity of cooling to atmospheric convection suggests a simple field experiment for verification, and the model provides a tool to begin studies of the dynamic crystallization of real lavas. Future versions of the model can also be made applicable to extraterrestrial, submarine, silicic, and pyroclastic flows. Received: 26 November 1994 / Accepted: 1 December 1995  相似文献   

Subsurface DC resistivity mapping: approximate 1-D interpretation     

Youcef Meheni  Roger Guérin  Yves Benderitter  Alain Tabbagh 《Journal of Applied Geophysics》1996,34(4):255-269

Resistivity prospecting is the main tool used to investigate the shallow structure of the ground. A series of new techniques for determining the 2-D and 3-D geometry of the ground is now finding increasing use, but the light and simple Wenner prospecting technique remains a practical and efficient tool for rapidly mapping lateral variations in resistivity. When the resistivity changes are smooth, 1-D modelling can be used to interpret the data, and the criteria governing this approximation can be defined from synthetic data generated by a 3-D slab-model. For a Wenner array, two quadripole configurations can be used, Normal and Dipole-Dipole. For these two configurations the width of the transition zone, the apparent anisotropy effect and the precision of the resistivity values recovered from 1-D inversion differ. However the simultaneous inversion of both sets of data gives better results than for either configuration by itself. Two examples illustrate that in geological contexts where the thickness of the weathered zone causes the changes in the apparent resistivity value, this parameter can be recovered from 1-D inversion.  相似文献   

The Use of Specific Capacity to Assess Transmissivity in Fractured-Rock Aquifers   总被引：6，自引：0，他引：6  

David Huntley  Roger Nommensen  Duane Steffey 《Ground water》1992,30(3):396-402

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Bed load transport during rising and falling stages on two small streams     

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   

Experimentally determined mineral-melt partition coefficients for Sc,Y and REE for olivine,orthopyroxene, pigeonite,magnetite and ilmenite   总被引：6，自引：0，他引：6  

Roger L. Nielsen  William E. Gallahan  Florence Newberger 《Contributions to Mineralogy and Petrology》1992,110(4):488-499

Our current lack of understanding of the partitioning behavior of Sc, Y and the REE (rare-earth elements) can be attributed directly to the lack of a sufficiently large or chemically diverse experimental data set. To address this problem, we conducted a series of experiments using several different natural composition lavas, doped with the elements of interest, as starting compositions. Microprobe analyses of orthopyroxene, pigeonite, olivine, magnetite, ilmenite and co-existing glasses in the experimental charges were used to calculate expressions that describe REE partitioning as a function of a variety of system parameters. Using expressions that represent mineral-melt reactions (versus element ratio distribution coefficients) it is possible to calculate terms that express low-Ca pyroxene-melt partitioning behavior and are independent of both pyroxene and melt composition. Compositional variations suggest that Sc substitution in olivine involves either a paired substitution with Al or, more commonly, with vacancies. The partitioning of Sc is dependent both on melt composition and temperature. Our experimentally determined olivine-melt REE Ds (partition coefficients) are similar to, but slightly higher than those reported by McKay (1986) and support their conclusions that olivines are strongly LREE depleted. Y and REE mineral/melt partition coefficients for magnetite range from 0.003 for La to 0.02 for Lu. Ilmenite partition coefficients range from 0.007 for La to 0.029 for Lu. These experimental values are two orders of magnitude lower than many of the published values determined by phenocryst/matrix separation techniques.  相似文献   

Role of Vertical Shafts in the Movement of Ground Water in Carbonate Aquifers     

Roger W. Brucker  John W. Hess  William B. White 《Ground water》1972,10(6):5-13

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Saturn's satellites: Nuar-infrared spectrophotometry (0.6–2.5 μm) of the leading and trailing sides and compositional implications     

Roger N. Clark  Robert H. Brown  Pamela D. Owensby  Alex Steele 《Icarus》1984,58(2):265-281

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   

Solar soft X-rays and solar activity     

Roger J. Thomas  Richard G. Teske 《Solar physics》1971,16(2):431-453

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