Regional Advection Perturbations in an Irrigated Desert (RAPID) experiment     

H. A. R. De Bruin  O. K. Hartogensis  R. G. Allen  J. W. J. L. Kramer 《Theoretical and Applied Climatology》2005,80(2-4):143-152

Summary The RAPID field experiment took place in August–September 1999 at a site 25km south of Twin Falls, Idaho, USA. The experiment concerned micrometeorological observations over extensive, well-irrigated fields covered with the fast-growing crop alfalfa. During daytime, on a number of days the sensible heat flux was negative and the latent heat flux exceeded net radiation. The energy required for the latent heat flux to be larger than net radiation has to be advected from elsewhere. As the fields were large, we refer to this process as regional advection. Local advection, on the other hand, refers to advection effects, where the wet to dry transition is on a field scale. Evidence is presented that the RAPID data are subject to regional advection conditions.A simple model, based on Penman-Monteith, is derived that describes the regional-advection case rather well. The influence of wind speed under those conditions is illustrated using data and the model. The correlation coefficients between temperature and horizontal wind component appear to be good indicators for advection.  相似文献   

Age,petrogenesis and metamorphism of the syn-collisional Prøven Igneous Complex,West Greenland     

K.?ThraneEmail author  J.?Baker  J.?Connelly  A.?Nutman 《Contributions to Mineralogy and Petrology》2005,149(5):541-555

The Paleoproterozoic Prøven Igneous Complex (PIC) in West Greenland extends from ca. 72°15 to 73°10N, approximately 500 km north of the subduction-related intrusive complex in the core of the +1100 km wide, asymmetric collisional Nagssugtoqidian-Rinkian Orogen. A new U-Pb SHRIMP age for the PIC of 1869±9 Ma indicates that it intruded synchronously with the main collisional phase of the orogen into the passive margin side of the collision. Sm-Nd and Lu-Hf isotopic and A-type geochemical signatures are compatible with its derivation from melted Archean lower crustal material contaminated to varying degrees by pelitic sedimentary rocks of the Karrat Group. The timing, petrogenesis and position of the PIC within the orogen support a model of collisionally induced delamination of the mantle lithosphere following initial collision. Upwelling asthenospheric mantle replacing the partially or completely detached mantle lithosphere caused widespread partial melting of lower crust that resulted in the areally extensive (~ 250,000 km²) Cumberland-Prøven intrusive complexes of Baffin Island and West Greenland. Emplacement of the PIC at 1.87 Ga caused a high-temperature low- to medium-pressure metamorphic aureole that contrasts the regional, overprinting higher-pressure amphibolite facies metamorphism. The consequent high-temperature garnet-orthopyroxene-biotite-bearing assemblages occurring within the margin of the intrusion in the aureole are attributed to the intrusion event. Garnet-controlled Sm-Nd and Lu-Hf ages of 1.82–1.80 Ga require efficient diffusion of these elements during orogenic reheating at this time. This age range overlaps the post-collisional, north–south shortening in the Nagssugtoqidian Orogen to the south and serves to confirm the recently proposed genetic link between these two orogens. These new data infer that garnet-controlled isochrons based on the Lu-Hf and Sm-Nd systems cannot date high-grade events in slowly cooled or significantly reheated terrains in rocks possessing other phases that close at low temperatures.  相似文献   

Importance of the vadose zone in analyses of unconfined aquifer tests   总被引：5，自引：0，他引：5  

Moench AF 《Ground water》2004,42(2):223-233

Analytical models commonly used to interpret unconfined aquifer tests have been based on upper-boundary (water table) conditions that do not adequately address effects of time-varying drainage from the vadose zone. As a result, measured and simulated drawdown data may not agree and hydraulic parameters may be inaccurately estimated. A 72-hour aquifer test conducted in Cape Cod, Massachusetts, in a slightly heterogeneous, coarse-grained, glacial outwash deposit was found to be a good candidate for testing models with different upper-boundary conditions. In general, under the commonly invoked assumption of instantaneous drainage, measured and simulated drawdowns were found to agree with one another only at late time and early time. In the intermediate-time range, because of delayed drainage, measured drawdowns always exceeded simulated values, most noticeably in piezometers located near the water table. To reduce these discrepancies, an analytical model was developed that can fully account for time-varying drainage given that the aquifer is not strongly heterogeneous. The approach is flexible as the model, which makes use of empirical relations, does not constrain drainage to follow any particular functional relation. By this approach, measured and simulated drawdowns agree over the complete time range, and the estimated parameters are consistent with prior studies and with what is known about the aquifer geometry, stratigraphy, and composition. By properly accounting for vadose zone drainage, it was found that realistic estimates of all hydraulic parameters, including specific yield, could be obtained with or without the use of late-time data.  相似文献   

The 3.4–3.5 Ga São José do Campestre massif, NE Brazil: remnants of the oldest crust in South America     

E. L. Dantas  W. R. Van Schmus  P. C. Hackspacher  A. H. Fetter  B. B. de Brito Neves  U. Cordani  A. P. Nutman  I. S. Williams 《Precambrian Research》2004,130(1-4):113-137

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Potential field extrapolation using three components of a solar vector magnetogram with a finite field of view     

G. Allen Gary 《Solar physics》1996,163(1):43-64

The potential magnetic field from a finite planar boundary is extrapolated into the upper hemisphere using information from all three magnetic field components. The method determines, first, the transverse field associated with the observed normal magnetic intensity. Then by subtraction, the method determines the associated transverse magnetic field observed in the interior (i.e., in the field of view) of the magnetogram which is due to the normal flux exterior to the field of view of the magnetogram. Inverting this information gives an approximation to the exterior normal flux. The combination of the observed normal flux of the interior and the approximation of the exterior normal flux is employed to calculate the potential field. The formulation of the problem results in an ill-posed integral inversion problem in which a regularized solution is obtained using the singular value decomposition (SVD) technique in conjunction with an appropriate Tikhonov-Phillips filter. The technique can be applied to correcting potential field calculations which are influenced by out-of-view fluxes, e.g., for a high spatial resolution vector magnetogram with a small field of view in which there is no supporting exterior data. The problem studied is also important in providing a regularized solution of the Cauchy potential problem. The method provides a much larger range of convergence than the method of Gary and Musielak (1992), and, in fact, is stable in the total upper hemisphere.The U.S. Government right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.  相似文献   

Vivianite auto-oxidation     

Allen R. Pratt 《Physics and Chemistry of Minerals》1997,25(1):24-27

Vivianite, Fe₃(PO₄)₂×8?H₂O, (010) surfaces cleaved in an N₂ gas atmosphere are examined using X-ray photoelectron spectroscopy (XPS). Quantitative evaluation of Fe(2p ₃₂) and O(1s) spectra show cleaved surfaces are partly oxidized. Ferric hydroxide is identified as an oxidation product. An auto-reduction-oxidation mechanism involving rupture of hydrogen bonds between the H₂O ligands which hold together the sheet structure of vivianite is proposed.  相似文献   

FACTORS INFLUENCING LONGEVITY OF AERIAL PHOTOGRAPHIC PRODUCTS ON ARCHIVAL STORAGE     

M. Edge  N. S. Allen 《The Photogrammetric Record》1992,14(80):207-218

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Simulation of steady-state flow in three-dimensional fracture networks using the boundary-element method     

Allen M. Shapiro  Johan Andersson 《Advances in water resources》1985,8(3):106-110

An efficient method for simulating steady-state flow in three-dimensional fracture networks is formulated with the use of the boundary-element method. The host rock is considered to be impervious, and the fractures can be of any orientation and areal extent. The fractures are treated as surfaces where fluid movement is essentially two-dimensional. Fracture intersections are regarded as one-dimensional fluid conduits. Hence, the three-dimensional geometric characteristics of the fracture geometry is retained in solutions of coupled sets of one- and two-dimentional equations. Use of the boundary-element method to evaluate the fluid responses in the fractures precludes the need to internally discretize the areal extent of the fractures.  相似文献   

DISCUSSION OF "Classification of Ground-Water Systems of the United States," by Ralph C. Heath, July-August 1982 issue, v. 20, no. 4, pp. 393–401     

Allen F. Agnew 《Ground water》1982,20(6):748-748

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Implications of frequency-domain inversion of earthquake ground motions for resolving the space-time dependence of slip on an extended fault   总被引：1，自引：0，他引：1  

Allen H. Olson  John G. Anderson 《Geophysical Journal International》1988,94(3):443-455

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