Monitoring of Saharan dust fallout on Crete and its contribution to soil formation   总被引：3，自引：0，他引：3  

TOMAS NIHLÉN  JAN O. MATTSSON  ERS RAPP  CHRISOULA GAGAOUDAKI  GEORGES KORNAROS  JOHN PAPAGEORGIOU 《Tellus. Series B, Chemical and physical meteorology》1995,47(3):365-374

  相似文献   

A three-dimensional,iterative mapping procedure for the implementation of an ionosphere-magnetosphere anisotropic Ohm’s law boundary condition in global magnetohydrodynamic simulations     

Michael L. Goodman 《Annales Geophysicae》1995,13(8):843-853

The mathematical formulation of an iterative procedure for the numerical implementation of an ionosphere-magnetosphere (IM) anisotropic Ohm’s law boundary condition is presented. The procedure may be used in global magnetohydrodynamic (MHD) simulations of the magnetosphere. The basic form of the boundary condition is well known, but a well-defined, simple, explicit method for implementing it in an MHD code has not been presented previously. The boundary condition relates the ionospheric electric field to the magnetic field-aligned current density driven through the ionosphere by the magnetospheric convection electric field, which is orthogonal to the magnetic field B, and maps down into the ionosphere along equipotential magnetic field lines. The source of this electric field is the flow of the solar wind orthogonal to B. The electric field and current density in the ionosphere are connected through an anisotropic conductivity tensor which involves the Hall, Pedersen, and parallel conductivities. Only the height-integrated Hall and Pedersen conductivities (conductances) appear in the final form of the boundary condition, and are assumed to be known functions of position on the spherical surface R=R₁ representing the boundary between the ionosphere and magnetosphere. The implementation presented consists of an iterative mapping of the electrostatic potential , the gradient of which gives the electric field, and the field-aligned current density between the IM boundary at R=R₁ and the inner boundary of an MHD code which is taken to be at R₂>R₁. Given the field-aligned current density on R=R₂, as computed by the MHD simulation, it is mapped down to R=R₁ where it is used to compute by solving the equation that is the IM Ohm’s law boundary condition. Then is mapped out to R=R₂, where it is used to update the electric field and the component of velocity perpendicular to B. The updated electric field and perpendicular velocity serve as new boundary conditions for the MHD simulation which is then used to compute a new field-aligned current density. This process is iterated at each time step. The required Hall and Pedersen conductances may be determined by any method of choice, and may be specified anew at each time step. In this sense the coupling between the ionosphere and magnetosphere may be taken into account in a self-consistent manner.  相似文献   

Organic Acid Derivatization Techniques Applied to Petroleum Hydrocarbon Transformations in Subsurface Environments     

Michael J. Barcelona  Jie Lu  Daniel M. Tomczak 《Ground Water Monitoring & Remediation》1995,15(2):114-124

Evidence for the natural microbial remediation of subsurface fuel contamination situations should include identification and analysis of transformation or degradation products. In this way. u mass balance between fuel constituents and end products may be approached to monitor cleanup progress. Application of advanced organic acid metabolite derivatization techniques to several known sites of organic compounds and fuel mixture contamination provide valuable information on the pathways and progress of microbial transformation. Good correlation between observed metabolites and transformation pathways of aromatic fuel constituents were observed at the sites.  相似文献   

X-ray fluorescence spectrometry for field analysis of metals in marine sediments   总被引：1，自引：0，他引：1  

M. O. Stallard  S. E. Apitz  C. A. Dooley 《Marine pollution bulletin》1995,31(4-12)

The accuracy, precision and performance of a field-portable X-ray fluorescence (XRF) spectrometer was evaluated for the determination of metals in marine sediments both in the laboratory and, more importantly, on board a small research vessel. The XRF performed with minimal problems on board the survey vessel and provided precise, near-real-time determination of metals at levels indicative of contamination in samples obtained by sediment grabs. Analytical results obtained on the wet, bulk samples in the field and on the dry, homogenized samples in the laboratory were comparable.  相似文献   

Effective barometric admittance and gravity residuals   总被引：1，自引：0，他引：1  

D. J. Crossley  O. G. Jensen  J. Hinderer 《Physics of the Earth and Planetary Interiors》1995,90(3-4)

In the analysis of surface gravity signals that may originate from the Earth's core, the step of correcting for the atmospheric pressure fluctuations is one that must be done carefully. We apply two techniques for determining the local, or effective, barometric admittance function between simultaneous observations of surface gravity and pressure. The first is a frequency domain fit that computes the admittance on a band-by-band basis. Using data from both the Canadian and French superconducting gravimeters we determined that the magnitude of the local, or background, admittance increases smoothly and monotonically from about 0.2 μgal mbar⁻¹ at long periods (> 10 days) to about 0.35 μgal mbar⁻¹ at frequencies greater than 3 cycles per day (c.p.d.); the phase lag is within a few degrees of 180°. By comparison, the effective admittances of the large-scale harmonics of the solar heating tide (S₁---S₇) are much smaller, between 0.1 and 0.3 μgal mbar⁻¹, for most of the harmonics of a day. In the second approach we fit a symmetrical time domain admittance function having lengths between 1 and 19 h using both a standard least-squares fit to a white noise residual and a new, and clearly superior, fit assuming a brown noise residual. Both time and frequency domain approaches give comparable results and contribute to a significant lowering of the residual level in non-tidal bands.  相似文献   

Geology and eruptive history of the Rabaul Caldera area, Papua New Guinea     

I. A. Nairn  C. O. Mckee  B. Talai  C. P. Wood 《Journal of Volcanology and Geothermal Research》1995,69(3-4)

Rabaul Caldera is the most recently active (1937–1943) of four adjoining volcanic centres aligned north-south through the northern extremity of eastern New Britain. Geological mapping after the 1983–1985 Rabaul seismic and deformation crisis has partially revealed a long and complex eruption history dominated by numerous explosive eruptions, the largest accompanied by caldera collapse. The oldest exposed eruptives are the basaltic pre-caldera cone Tovanumbatir Lavas K/Ar dated at 0.5 Ma. The dacitic Rabaul Quarry Lavas exposed in the caldera wall and K/Ar dated at 0.19 Ma, are overlain by a sequence of dacitic and andesitic pyroclastic flow and fall deposits. Uplifted coral reef limestones, interbedded within the pyroclastic sequence on the northeast coast, suggest that explosive eruptions in the Rabaul area had commenced prior to the 0.125 Ma last interglacial high sea level stand. The pyroclastic sequence includes the large Boroi Ignimbrites and Malaguna Pyroclastics both ⁴⁰Ar/³⁹Ar dated at about 0.1 Ma, and the Barge Tunnel Ignimbrite ⁴⁰Ar/³⁹Ar dated at around 0.04 Ma. Few reliable ages exist for the many younger eruptives. These include Holocene ignimbrites of the latest caldera-forming eruptions—the Raluan Pyroclastics variously dated (¹⁴C) at either about 3500 or 7000 yr B.P., and the ca. 1400 yr B.P. Rabaul Pyroclastics. At least eight intracaldera eruptions have occurred since the 1400 yr B.P. collapse, building small pyroclastic and lava cones within the caldera.A major erosional episode is evident as a widespread unconformity in the upper pyroclastic stratigraphy at Rabaul. Lacking relevant radiometric ages, this episode is assumed to have occurred during last glaciation low sea levels and is here arbitarily dated at ca. ?20 ka. At least five, possibly nine, significant ignimbrite eruptions have occurred at Rabaul during the last ?20 ka. The new eruptive history differs considerably from that previously published, which considered ignimbrite eruption and caldera collapse to have first occurred at 3500 yr B.P.Rabaul volcanism has been dominated by two main types: (a) basaltic and basaltic andesite cone building eruptions; and (b) dacitic, and rarely andesitic or rhyolitic, plinian/ignimbrite eruptions of both high- and low-aspect ratio types. The 1400 yr B.P. Rabaul Ignimbrite is a type example of a low-aspect ratio, high-energy, and potentially very damaging eruption. Fine vitric ash deposits, common in the Rabaul pyroclastic sequence, demonstrate the frequent modification of eruptions by external water probably related to early caldera lakes or bays. Interbedding of these fine ashes with plinian pumice lapilli beds suggests that many early eruptions occurred from multiple vents, located in both wet and dry areas.  相似文献   

Watermass structure and current system in the Western Indian Ocean during August, 1985     

A. Suryanarayana  G. V. Reddy  T. Pankajakshan  G. S. Michael  J. S. Sastry  N. Bahulayan 《Ocean Dynamics》1987,40(5):234-234

  相似文献   

The inverse gravimetric problem: Existence,uniqueness and stability of the solution     

Ctirad Matyska  Reviewers O. Man  Reviewers M. Burda 《Studia Geophysica et Geodaetica》1987,31(3):252-257

Summary The paper is concerned with the mathematical properties of the density distribution within the Earth obtained by inverting of the external gravity field, provided an Earth's reference density model, used as the initial guess, is available. The method of regularization, which proves the existence, the uniqueness and the stability of the solution, which is nearest the initial guess in the L ² norm, is described.

---

nua m¶rt; uauu ¶rt;am a¶rt;au ¶rt; aumau n u uma, m uma aaa a an¶rt;u nmmu . mm m¶rt; n¶rt;maum m amu u, m ¶rt;a, mu u uu aa u.

  相似文献   

Micro-scale modelling in the study of plume evolution in heterogeneous media     

E. O. Frind  E. A. Sudicky  S. L. Schellenberg 《Stochastic Environmental Research and Risk Assessment (SERRA)》1987,1(4):263-279

The migration of contaminants in heterogeneous aquifers involves dispersive processes that act at different scales. The interaction of these processes as a plume evolves can be studied by micro-scale modelling whereby two scales, a local- or micro-scale and an aquifer- or macro-scale, are covered simultaneously. Local-scale dispersive processes are represented through the local dispersion coefficient in the transport equation, while large-scale dispersion due to heterogeneities is represented through the resolution of the flow field and the diffusive exchange between streamtubes. The micro-scale model provides both the high degree of resolution compatible with local-scale processes, and the extent required for the approach to asymptotic conditions, using grids of up to a million nodal points. The model is based on the dual potential-streamfunction formulation for flow, and the transport problem is formulated in a natural coordinate system provided by the flownet. Simulations can be used to verify stochastic theories of dispersion, without the restrictive assumptions inherent in the theory. For the two-dimensional case, results indicate convergence of the effective dispersivity to the theoretical macrodispersivity value. Convergence takes place within a travel distance of about 50 correlation lengths of the hydraulic conductivity field. However, the approach taken to asymptotic conditions, as well as the macrodispersivity value, may differ for different realizations of the same medium. The influence of early-time events such as plume splitting on the asymptotic convergence remains to be investigated.  相似文献   

Archean inheritance in zircon from late Paleozoic granites from the Avalon zone of southeastern New England: an African connection     

R.E. Zartman  O. Don Hermes 《Earth and Planetary Science Letters》1987,82(3-4)

In southeastern New England the Narragansett Pier Granite locally intrudes Carboniferous metasedimentary rocks of the Narragansett basin, and yields a monazite UPb Permian emplacement age of 273 ± 2Ma. Zircon from the Narragansett Pier Granite contains a minor but detectable amount of an older, inherited component, and shows modern loss of lead. Zircon from the late-stage, aplitic Westerly Granite exhibits a more pronounced lead inheritance —permitting the inherited component to be identified as Late Archean. Such old relict zircon has not been previously recognized in Proterozoic to Paleozoic igneous rocks in New England, and may be restricted to late Paleozoic rocks of the Avalon zone. We suggest that the Archean crustal component reflects an African connection, in which old Archean crust was underplated to the Avalon zone microplate in the late Paleozoic during collision of Gondwanaland with Avalonia.  相似文献