Assembling Proterozoic Australia: Inside out or outside in?     

Chris Clark  David E. Kelsey  Martin Hand 《Gondwana Research》2007,11(4):575-576

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High-Resolution Forecast Models of Water Vapor Over Mountains: Comparison With MERIS and Meteosat Data     

Min Zhu Wadge  G. Holley  R.J. James  I.N. Clark  P.A. Changgui Wang Woodage  M.J. 《Geoscience and Remote Sensing Letters, IEEE》2007,4(3):401-405

Propagation delay due to variable tropospheric water vapor (WV) is one of the most intractable problems for radar interferometry, particularly over mountains. The WV field can be simulated by an atmospheric model, and the difference between the two fields is used to correct the radar interferogram. Here, we report our use of the U.K. Met Office Unified Model in a nested mode to produce high-resolution forecast fields for the 3-km-high Mount Etna volcano. The simulated precipitable-water field is validated against that retrieved from the Medium-Resolution Imaging Spectrometer (MERIS) radiometer on the Envisat satellite, which has a resolution of 300 m. Two case studies, one from winter (November 24, 2004) and one from summer (June 25, 2005), show that the mismatch between the model and the MERIS fields ( rms = 1.1 and 1.6 mm, respectively) is small. One of the main potential sources of error in the models is the timing of the WV field simulation. We show that long-wavelength upper tropospheric troughs of low WV could be identified in both the model output and Meteosat WV imagery for the November 24, 2004 case and used to choose the best time of model output.  相似文献   

Three-dimensional simulations of air flow and momentum transfer in partially harvested forests     

Terry L. Clark  Stephen J. Mitchell 《Boundary-Layer Meteorology》2007,125(3):505-524

In order to predict wind loading on trees (canopy height h) in partially harvested forests, it is necessary to characterize air flow and momentum transfer in progressively more complex patterns where groups of trees (or aggregates) are retained. In this study, we used large-eddy simulation to explore the effects of aggregate size, inter-aggregate spacing, and the ratio between the aggregate size and inter-aggregate spacing on air flow and momentum transfer. Forty-five grid points across an aggregate were needed to achieve an adequate level of turbulence. Using grid sizes of h/15 throughout was too viscous for the smaller aggregates. Vertical and horizontal flow deflection by the leading aggregates sheltered some of the downstream aggregates to varying degrees where turbulence increased for subsequent rows. The number of rows of protected aggregates decreased as aggregate dimensions and the space between aggregates increased. A theoretical treatment of time-dependent wind is presented for the lead aggregate and a simulation case is presented for the case of a gust of reduced wind passing through the aggregate pattern. The leading aggregate responded with decreasing moment for decreasing ambient wind speed as predicted by theory. However, downwind aggregates experienced substantial increases in bending moment. The overall results of the disruptive aspects of time dependence agrees with arguments regarding the role of irrotational (potential) flow to this problem. Our treatment of retention pattern design is only a first step and further research suggestions are presented.  相似文献   

The equatorial disc of the Be star X Persei     

Telting  Waters  Roche  Boogert  Clark  de Martino  & Persi 《Monthly notices of the Royal Astronomical Society》1998,296(4):785-799

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No refuge in the zoo     

R.B. Clark 《Marine pollution bulletin》1978,9(3):58-59

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Tanker wrecks and the human element     

R.B. Clark 《Marine pollution bulletin》1978,9(5):113-114

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Predicted relative sea-level changes (18,000 years B.P. to present) caused by late-glacial retreat of the Antarctic Ice Sheet     

James A. Clark  Craig S. Lingle 《Quaternary Research》1979,11(3):279-298

Predictions of global changes in relative sea level caused by retreat of the Antarctic Ice Sheet from its 18,000 yr B.P. maximum to its present size are calculated numerically. When combined with the global predictions of relative sea-level change resulting from retreat of the Northern Hemisphere ice sheets, the results may be compared directly to observations of sea-level change on the Antarctic continent as well as at distant localities. The comparison of predictions to the few observations of sea-level change on Antarctica supports the view that the Antarctic Ice Sheet was larger 18,000 years ago than at present. The contribution of the Antarctic Ice Sheet to the total eustatic sea-level rise is assumed to be 25 m (25% of the assumed total eustatic rise). If as little as 0.7 m of this 25-m rise occurred between 5000 yr B.P. and the present, few mid-oceanic islands would emerge. If the Antarctic Ice Sheet attained its present dimensions by 6000 yr B.P., however, and if the volume of the ocean has remained constant for the past 5000 years, numerous islands throughout the Southern Hemisphere would emerge. It is suggested that a thorough study of Pacific islands, believed by some to have slightly emerged shorelines of Holocene age, would yield useful information about ocean volume changes during the past 5000 years, and hence on the glacial history of the Antarctic Ice Sheet.  相似文献   

Atmospheric effects in the remote sensing of phytoplankton pigments   总被引：3，自引：0，他引：3  

Howard R. Gordon  Dennis K. Clark 《Boundary-Layer Meteorology》1980,18(3):299-313

We investigate the accuracy with which relevant atmospheric parameters must be estimated to derive phytoplankton pigment concentrations (chlorophyll a plus phaeophytin a ) of a given accuracy from measurements of the ocean's apparent spectral radiance at satellite altitudes. The analysis is limited to an instrument having the characteristics of the Coastal Zone Color Scanner scheduled to orbit the Earth on NIMBUS-G. A phytoplankton pigment algorithm is developed which relates the pigment concentration (C) to the three ratios of upwelling radiance just beneath the sea surface which can be formed from the wavelengths () 440, 520 and 550 nm. The pigment algorithm explains from 94 to 98% of the variance in log₁₀ C over three orders of magnitude in pigment concentration. This is combined with solutions to the radiative transfer equation to simulate the ocean's apparent spectral radiance at satellite altitudes as a function of C and the optical properties of the aerosol, the optical depth of which is assumed to be proportioned to ^-n . A specific atmospheric correction algorithm, based on the assumption that the ocean is totally absorbing at 670 nm, is then applied to the simulated spectral radiance, from which the pigment concentration is derived. Comparison between the true and derived values of C show that: (1) n is considerably more important than the actual aerosol optical thickness; (2) for C 0299-1 0.2 g l^-1 acceptable concentrations can be determined as long as n is not overestimated; (3) as C increases, the accuracy with which n must be estimated, for a given relative accuracy in C, also increases; and (4) for C greater than about 0.5 g 1^-1, the radiance at 440 nm becomes essentially useless in determining C. The computations also suggest that if separate pigment algorithms are used for C 1gl^-1 and C 1 gl^-1, accuracies considerably better than ±± in log C can be obtained for C 1 g l^-1 with only a coarse estimate of n, while for C 10 gl^-1, this accuracy can be achieved only with very good estimates of n.Contribution No. 387 from the NOAA/ERL Pacific Environmental Laboratory.On leave from Department of Physics, University of Miami, Coral Gables, Florida.  相似文献   

Some methods for statistical analysis of multimodal distributions and their application to grain-size data   总被引：1，自引：0，他引：1  

Malcolm W. Clark 《Mathematical Geology》1976,8(3):267-282

Some of the methods used in the resolution of mixed normal distributions are discussed under three headings: analytical, graphical, and numerical methods. Attention is given to their applicability in the analysis of grain-size data as derived from sieving. Comparisons are made by applying several methods to published data. It is concluded that the numerical methods offer most scope, especially the method of nonlinear least squares. Some analyses of beach sediments, using this method, are presented. The adoption of a convention for the number of individuals in the sample increases ease of interpretation.  相似文献   

Geochronology and petrochemistry of Easter and Sala y Gomez Islands: implications for the origin of the Sala y Gomez Ridge     

James G. Clark  Jack Dymond 《Journal of Volcanology and Geothermal Research》1977,2(1):29-48

Easter and Sala y Gomez Islands lie along the Sala y Gomez Ridge, a broad zone of high topography and scattered seamounts extending east-southeast from the East Pacific Rise. K-Ar ages and major element abundances of volcanic rocks from these islands are used to test the fixed melting spot hypothesis for the origin of this feature. Poike volcano, the oldest center on Easter Island, was constructed in two episodes, occurring at 2.5 and 0.9 m.y. ago. Eruptive activity on Sala y Gomez was nearly contemporaneous with the earliest volcanism on Easter Island. No migration of volcanism with time is apparent along the Sala y Gomez Ridge. Basaltic rocks from Easter Island have tholeiitic affinities, while those dredged from the base of Sala y Gomez belong to an alkali olivine basalt series. Differences in basalt chemistry suggest that the volcanic rocks from the two islands formed from magmas that equilibrated at different pressures, and a model is presented which relates the character of the erupted liquids to magma segregation at the base of a progressively thickening lithosphere. The islands and seamounts comprising the Sala y Gomez Ridge do not fall on a small circle about the Nazca-mantle pole of absolute motion. Available evidence, therefore, does not support a fixed melting spot origin for Easter Island, Sala y Gomez, and the Sala y Gomez Ridge. Rather, it appears that the Sala y Gomez Ridge formed along a leaky fracture zone, and in response to a major re-orientation of spreading centers in this area.  相似文献