MODFLOW 2000 head uncertainty,a first-order second moment method   总被引：1，自引：0，他引：1  

Glasgow HS  Fortney MD  Lee J  Graettinger AJ  Reeves HW 《Ground water》2003,41(3):342-350

A computationally efficient method to estimate the variance and covariance in piezometric head results computed through MODFLOW 2000 using a first-order second moment (FOSM) approach is presented. This methodology employs a first-order Taylor series expansion to combine model sensitivity with uncertainty in geologic data. MODFLOW 2000 is used to calculate both the ground water head and the sensitivity of head to changes in input data. From a limited number of samples, geologic data are extrapolated and their associated uncertainties are computed through a conditional probability calculation. Combining the spatially related sensitivity and input uncertainty produces the variance-covariance matrix, the diagonal of which is used to yield the standard deviation in MODFLOW 2000 head. The variance in piezometric head can be used for calibrating the model, estimating confidence intervals, directing exploration, and evaluating the reliability of a design. A case study illustrates the approach, where aquifer transmissivity is the spatially related uncertain geologic input data. The FOSM methodology is shown to be applicable for calculating output uncertainty for (1) spatially related input and output data, and (2) multiple input parameters (transmissivity and recharge).  相似文献   

EUV observations of the chromospheric network     

E. M. Reeves  W. H. Parkinson 《Solar physics》1972,24(1):113-117

Extreme ultraviolet observations of a quiet region of the Sun on August 18, 1969, with the Harvard spectroheliometer on OSO 6 indicate that the chromospheric network can be observed in lines of the chromosphere and transition region (T = 8.4 × 10⁵ K) with almost identical structure. At coronal heights, the network changes but some residual structure can still be discerned in Mgx and perhaps Sixii (T = 2.3 × 10⁶ K), although there is little or no evidence remaining in Fexvi (T = = 3.5 × 10⁶ K).  相似文献   

Estimating Rainfall Recharge and Soil Water Residence Times in Pukekohe, New Zealand, by Combining Geophysical, Chemical, and Isotopic Methods   总被引：1，自引：0，他引：1  

Michael R. Rosen  John Bright  Peter Carran  Michael K. Stewart  Robert Reeves 《Ground water》1999,37(6):836-844

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Late Quaternary secular variation of geomagnetic declination in western New York     

William J. Brennan  Mark J. Hamilton  Richard K. Kilbury  Richard L. Reeves  Laura J. Covert 《Earth and Planetary Science Letters》1984,70(2):363-372

A secular variation record of the geomagnetic declination has been obtained from glaciolacustrine varved clays and postglacial sediments, sampled both from outcrop and from piston cores from Lake Ontario. It appears to be uninterrupted and covers the interval 14,000 years B.P. (¹⁴C) to the present. The record for the interval 14,000–12,300 years B.P. consists of true declination and was obtained from samples collected from outcrop. The record for the interval 12,500 + years B.P. to the present consists of relative declination and was obtained from piston cores. The secular variation record is internally consistent and is compatible with the chronology of events known to have occurred during and following the deglaciation of western New York. Use of the record for magnetic correlation within the study area is demonstrated.  相似文献   

Stone movement on hillslopes in the Mojave Desert,California: A 16-year record   总被引：1，自引：0，他引：1  

Athol D. Abrahams  Anthony J. Parsons  Ronald U. Cooke  Richard W. Reeves 《地球表面变化过程与地形》1984,9(4):365-370

Previous research has shown that either hydraulic action or creep may be the dominant process transporting coarse debris down hillslopes in the American Southwest. This study analyses the movement over 16 years of painted stones on two hillslopes in the central Mojave Desert to ascertain which of these two processes dominate in this region. The distance moved (M) is found to be directly related to length of overland flow (X) and hillslope gradient (S), and inversely related to particle size (D). The fact that M is more highly correlated with X than with S suggests that hydraulic action rather than creep is the dominant process. It is concluded that this is probably the case over most of the Mojave and Sonoran Deserts on slopes up to at least 24°, and that it is only at higher elevations where winters are more severe that creep may become dominant.  相似文献   

Radar observations of auroral zone flows during a multiple-onset substorm   总被引：1，自引：0，他引：1  

J. P. Morelli  R. J. Bunting  S. W. H. Cowley  C. J. Farrugia  M. P. Freeman  E. Friis-Christensen  G. O. L. Jones  M. Lester  R. V. Lewis  H. Lühr  D. Orr  M. Pinnock  G. D. Reeves  P. J. S. Williams  T. K. Yeoman 《Annales Geophysicae》1995,13(11):1144-1163

We present an analysis of ground magnetic field, ionospheric flow, geosynchronous particle, and interplanetary data during a multiple-onset substorm on 12 April 1988. Our principal results concern the modulations of the ionospheric flow which occur during the impulsive electrojet activations associated with each onset. During the first hour of the disturbance these take place every \sim12.5 min and involve the formation of a new intense westward current filament in the premidnight sector, just poleward of the preexisting extended current system driven by the large-scale flow. These filaments are \sim1 h MLT wide (\sim600 km), and initially expand poleward to a width of \sim300 km before contracting equatorward and coalescing with the preexisting current, generally leaving the latter enhanced in magnitude and/or expanded in latitude. Within the impulsive electrojets the flow is found to be suppressed to values 50–100 m s⁻¹ or less during the first few minutes, before surging equatorward at 0.5-1.0 km s⁻¹ during the phase of rapid coalescence. The implication is that the precipitation-induced Hall conductivity within the impulsive electrojet initially rises to exceed \sim100 mho, before decaying over a few minutes. This value compares with Hall conductivities of \sim20 mho in the quasi-steady current regions, and a few mho or less in the regions poleward of the electrojets and in the preonset ionosphere. Preliminary evidence has also been found that the flow surges propagate from midnight to the morning sector where they are associated with arrested equatorward motion or poleward contractions of the current system. These observations are discussed in terms of present theoretical paradigms of the global behaviour of fields and flows which occur during substorms.  相似文献   

Geophysical evidence for a failed Jurassic rift and triple junction in Kenya     

C.V. Reeves  F.M. Karanja  I.N. MacLeod 《Earth and Planetary Science Letters》1987,81(2-3)

The interpretation of new and pre-existing aeromagnetic survey data for Kenya, in conjunction with published gravity data, indicates the existence of a palaeo-triple junction of Jurassic age in eastern Kenya. Two arms, represented by the Mombasa coast and the Somali coast respectively, developed into a part of the Indian Ocean. The third arm, which is now concealed by a cover of Quaternary sediments and volcanic rocks, remains as a rifted, sediment-filled trough extending at least as far northwest as the presently active East Africa Rift in Lake Turkana. It has a remarkable similarity, both in scale and geometry, with the Benue Trough of the Niger Delta. As with the Niger Delta, the present Kenyan coastline is not indicative of the true continental margin, as extensive sedimentation has occurred beyond the continental edge in the region of the triple junction since dispersal. Delineation of the true continental margin from aeromagnetic evidence allows pre-drift Madagascar to be re-assembled in closer proximity to the coast than indicated in many reconstructions though the geological evidence supporting this pre-drift position is still controversial.  相似文献   

TRACE and Yohkoh Observations of High-Temperature Plasma in a Two-Ribbon Limb Flare     

Warren HP  Bookbinder JA  Forbes TG  Golub L  Hudson HS  Reeves K  Warshall A 《The Astrophysical journal》1999,527(2):L121-L124

The ability of the Transition Region and Coronal Explorer (TRACE) to image solar plasma over a wide range of temperatures (Te approximately 104-107 K) at high spatial resolution (0&farcs;5 pixels) makes it a unique instrument for observing solar flares. We present TRACE and Yohkoh observations of an M2.4 two-ribbon flare that began on 1999 July 25 at about 13:08 UT. We observe impulsive footpoint brightenings that are followed by the formation of high-temperature plasma (Te greater, similar10 MK) in the corona. After an interval of about 1300 s, cooler loops (Te<2 MK) form below the hot plasma. Thus, the evolution of the event supports the qualitative aspects of the standard reconnection model of solar flares. The TRACE and Yohkoh data show that the bulk of the flare emission is at or below 10 MK. The TRACE data are also consistent with the Yohkoh observations of hotter plasma (Te approximately 15-20 MK) existing at the top of the arcade. The cooling time inferred from these observations is consistent with a hybrid cooling time based on thermal conduction and radiative cooling.  相似文献   

Fractionation of platinum group elements in upper mantle: Evidence from peridotite xenoliths from Wangqing     

Yigang Xu  B. Orberger  S. J. Reeves 《中国科学D辑(英文版)》1998,41(4):354-361

The peridotite xenoliths from Wangqing display a downward-concave PGE pattern with Pt at maximum due to Pt-Pd fractionation, which is different from the flat or negatively sloped patterns commonly observed for worldwide peridotite xenoliths and massifs. Taking into account the difference in partition coefficients of Pt and Pd between alloy and sulfide melt, it is suggested that some of the Wangqing peridotites must have been equilibrated with a melt in which alloy and sulfide coexisted. Segregation of Pt-rich alloy from Pd-sulfide melts due to density contrast and extraction of residual melts without sulfide saturation resulted in the fractionation of Pt from Pd. Project supported by the Ministry of Human Affairs and a part of an international collaboration program between the Chinese Academy of Sciences and Centre National de Recherche Scientifique (CNRS, France), and Australian Institute of Nuclear Sciences and Engineering (AINSE) grant to SJR.  相似文献   

Geological remote sensing in aerospace and time. Introduction     

Reeves  Colin V. 《Geologie en Mijnbouw》1998,77(2):113-116

Geologie en Mijnbouw - The more one considers the earth sciences these days, the more one realises that any view that falls short of global runs the risk of being short-sighted. This article...  相似文献