Prototype LAAS Architecture Design Considerations     

Boris S. Pervan  Samuel P. Pullen  David G. Lawrence  Konstantin Gromov  Jock Christie  Guttorm Opshaug  Vicky Lu  Ping-Ya Ko  Per Enge  Bradford W. Parkinson 《GPS Solutions》1998,2(1):49-61

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An annual cycle of vegetation in a GCM. Part II: global impacts on climate and hydrology     

D. M. Lawrence  J. M. Slingo 《Climate Dynamics》2004,22(2-3):107-122

The Met Office Hadley Centre Unified Model (HadAM3) with the tiled version of the Met Office Surface Exchange Scheme (MOSES2) land surface scheme is used to assess the impact of a comprehensive imposed vegetation annual cycle on global climate and hydrology. Two 25-year numerical experiments are completed: the first with structural vegetation characteristics (Leaf Area Index, LAI, canopy height, canopy water capacity, canopy heat capacity, albedo) held at annual mean values, the second with realistic seasonally varying vegetation characteristics. It is found that the seasonalities of latent heat flux and surface temperature are widely affected. The difference in latent heat flux between experiments is proportional to the difference in LAI. Summer growing season surface temperatures are between 1 and 4 K lower in the phenology experiment over a majority of grid points with a significant vegetation annual cycle. During winter, midlatitude surface temperatures are also cooler due to brighter surface albedo over low LAI surfaces whereas during the dry season in the tropics, characterized by dormant vegetation, surface temperatures are slightly warmer due to reduced transpiration. Precipitation is not as systematically affected as surface temperature by a vegetation annual cycle, but enhanced growing season precipitation rates are seen in regions where the latent heat flux (evaporation) difference is large. Differences between experiments in evapotranspiration, soil moisture storage, the timing of soil thaw, and canopy interception generate regional perturbations to surface and sub-surface runoff annual cycles in the model.  相似文献   

Unusual sedimentary deposits on the SE side of Stromboli volcano, Italy: products of a tsunami caused by the ca. 5000 years BP Sciara del Fuoco collapse?     

Lawrence H. Tanner  Sonia Calvari 《Journal of Volcanology and Geothermal Research》2004,137(4):329-340

The role of sector collapse in the generation of catastrophic volcanigenic tsunami has become well understood only recently, in part because of the problems in the preservation and recognition of tsunami deposits. Tinti et al. [Tinti, S., Bortolucci, E., Romagnoli, C., 2000. Computer simulations of tsunamis due to sector collapse at Stromboli, Italy. J. Volcanol. Geotherm. Res. 96, 103–128] modeled a tsunami produced by the c. 5,000 years BP collapse of the Sciara del Fuoco on the island volcano Stromboli. Although deposits associated with this event are generally lacking on the island, volcaniclastic breccias on the SE side of the island extending to an elevation above 120 m a.s.l. may have been generated by this tsunami. Deposits above 100 m are dominated by coarse breccias comprising disorganized, poorly sorted, nonbedded, angular to subangular lava blocks in a matrix of finer pyroclastic debris. These breccias are interpreted as a water-induced mass flow, possibly a noncohesive debris flow, generated as colluvial material on steep slopes was remobilized by the return flow of the tsunami wave, the run-up of which reached an elevation exceeding 120 m a.s.l. Finer breccias of subrounded to rounded lava blocks cropping out at 15 m a.s.l. are similar to modern high-energy beach deposits and are interpreted as beach material redeposited by the advancing tsunami wave. The location of these deposits matches the predicted location of the maximum tsunami wave amplitude as calculated by modeling studies of Tinti et al. [Tinti, S., Bortolucci, E., Romagnoli, C., 2000. Computer simulations of tsunamis due to sector collapse at Stromboli, Italy. J. Volcanol. Geotherm. Res. 96, 103–128]. Whereas the identification and modeling of paleo-tsunami events is typically based on the observation of the sedimentary deposits of the tsunami run-up, return flow may be equally or more important in controlling patterns of sedimentation.  相似文献   

Comparison of Five Eulerian Air Pollution Forecasting Systems for the Summer of 1999 Using the German Ozone Monitoring Data     

Stefan Tilmes  JØrgen Brandt  Frode FlatØy  Robert Bergström  Johannes Flemming  Joakim Langner  Jesper H. Christensen  Lise M. Frohn  Øystein Hov  Ingo Jacobsen  Eberthard Reimer  Rainer Stern  Jörg Zimmermann 《Journal of Atmospheric Chemistry》2002,42(1):91-121

Eulerian state-of-the-art air pollution forecasting systems on the European scale are operated routinely by several countries in Europe. DWD and FUB, both Germany, NERI, Denmark, NILU, Norway, and SMHI, Sweden, operate some of these systems. To apply such modeling systems, e.g. for regulatory purposes according to new EU directives, an evaluation and comparison of the model systems is fundamental in order to assess their reliability. One step in this direction is presented in this study: The model forecasts from all five systems have been compared to measurements of ground level ozone in Germany. The outstanding point in this investigation is the availability of a huge amount of data – from forecasts by the different model systems and from observations. This allows for a thorough interpretation of the findings and assures the significance of the observed features. Data from more than 300 measurement stations for a 5-month period (May–September 1999) of the German monitoring networks have been used in this comparison. Different spatial and temporal statistical parameters were applied in the evaluation. Generally, it was found that the most comprehensive models gave the best results. However, the less comprehensive and computational cheaper models also produced good results. The extensive comparison made it possible to point out weak points in the different models and to describe the individual model behavior for a full summer period in a climatological sense. The comparison also gave valuable information for an assessment of individual measurement stations and complete monitoring networks in terms of the representativeness of the observation data.  相似文献   

Pore pressure during metamorphism of carbonate rock: effect of volumetric properties of H<Subscript>2</Subscript>O–CO<Subscript>2</Subscript> mixtures     

Theodore C. Labotka  Lawrence M. Anovitz  James G. Blencoe 《Contributions to Mineralogy and Petrology》2002,144(3):305-313

The molar volume of mixtures of CO₂ and H₂O is a strong function of the fluid composition. Both CO₂ and H₂O participate in the metamorphism of carbonate rocks, resulting in a change in the fluid composition during reaction. One of the effects of the change in composition is the increase in pore-fluid pressure with only small increases in extent of reaction, ;. Pressure calculated from the volumetric properties of CO₂-H₂O mixtures at 400 °C increases greatly with small increases of ; but drops at greater values because of the increase in pore volume as a result of (V_solid. The pore pressure increase at small values of ;, though, readily exceeds the reported tensile strength of carbonate rocks, and the rock cannot sustain significant reaction without fracturing. The result of a small amount of reaction is a fractured rock with increased permeability, which promotes fluid transport.  相似文献   

Transcontinental profile of recent vertical crustal movements     

M.B. Lawrence  L.D. Brown 《Tectonophysics》1979,52(1-4)

A transcontinental profile of vertical crustal movement from San Diego, California, to Meldrim (Savannah), Georgia, has been assembled from precise leveling data of the National Geodetic Survey. Assuming constant movement during the time interval between leveling and releveling surveys, rates of movement have been plotted. The overall rate of movement of the East Coast relative to the West Coast derived from leveling is opposite in sign to the corresponding rate from tide gauges at San Diego and Savannah. Though this discrepancy is within the acceptable limits of normal random error associated with leveling measurements, it may also result in part from unavoidable uncertainties at the connection points between the various segments. In the absence of deterministic evidence on the source of the discrepancy, a least-squares adjustment was performed to distribute this difference in the overall trend through the profile. Apart from this trend, the western end of the profile is dominated by pronounced subsidence (rates 10 cm/yr) owing to water withdrawal and associated consolidation of alluvial sediments. With the exception of these movements, rates of vertical movement of the eastern and western United States are similar, suggesting that if such measurements represent significant tectonic activity, this activity may not be confined to the western United States. Movements are correlated with topography only in the peninsular ranges of California. Although these apparent elevation changes may reflect actual ground movement, this correlation may also result from systematic leveling errors. Comparison with gravity, depth to basement and depth to Moho shows no correlation.  相似文献   

Importance of alteration of volcanic material in the sediments of deep sea drilling site 323: chemistry, 18O16O and 87Sr86Sr     

J.R. Lawrence  J.I. Drever  T.F. Anderson  H.K. Brueckner 《Geochimica et cosmochimica acta》1979,43(4):573-588

A downhole decrease in ¹⁸O, Mg²⁺ and K⁺, an increase in Ca²⁺ and a low ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio of 0.7067 in the pore fluids of DSDP site 323 were caused principally by the alteration of volcanic material. These chemical and isotopic patterns were produced by the alteration, in order of decreasing importance of: a 60-m thick basal layer of volcanic ash; the underlying basalts; and igneous components in the 640-m thick upper sequence composed largely of terrigenous material. A significant portion of the alteration of the ash in the basal sequence must have occurred before the deposition of the upper sediments, perhaps under the influence of advecting solutions. The rest of the alteration occurred during the deposition of the thick upper sediments. Mass balance considerations and the low δ¹⁸O values of most of the alteration products suggest that much of the later alteration occurred progressively over the last 13 Myr. The principal alteration products were smectite, potassium feldspar, clinoptilolite and calcite.  相似文献   

Sulphide neomagmas and highly metamorphosed sulphide deposits     

L. J. Lawrence 《Mineralium Deposita》1967,2(1):5-10

Orebodies that have undergone high grade regional metamorphism sometimes exhibit features which appear to be metamorphic counterparts of certain magmatic-hydrothermal mineralization. These include ore bearing metapegmatites, metahydrothermal veins and metadeuteric veins and vugs. These mineral facies are completely contained within the metamorphosed orebody the ore minerals of which invariably exhibit textures resulting from annealing recrystallization. Intrusive relationships between metapegmatite, metahydrothermal veins, etc., and the orebody are evident. — Experimental work on certain sulphide systems indicates that partial melting may occur at temperatures around 700 °C, i.e., at the sillimanite grade of metamorphism. Thus a sulphide neomagma may develop along the lines of anatexis. — These aspects are considered with respect to the lead—zinc orebody at Broken Hill, New South Wales.

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Zusammenfassung Erzkörper, die hochgradiger Regionalmetamorphose unterworfen waren, zeigen manchmal Charakterzüge, welche denjenigen gewisser magmatisch-hydrothermaler Vererzungen gleichgestellt werden können. Diese Beispiele umfassen erzführende Metapegmatite, metahydrothermale Adern und metadeuterische Adern und Drusen. Diese Mineralfolgen sind beschränkt auf den metamorphosierten Erzkörper, dessen Erzmineralien dann jeweils Erzgefüge zeigen, die durch Rekristallisation entstanden sind. Intrusive Beziehungen zwischen den Metapegmatiten, den metahydrothermalen Adern usw. und dem Erzkörper sind offensichtlich. — Experimentelle Untersuchungen gewisser Sulfidsysteme deuten darauf hin, daß partielles Schmelzen bei Temperaturen um 700 °C möglich ist; also in dem Sillimanitbereich der Metamorphose. In dieser Weise ist es möglich, daß ein Sulfidneomagma sich in der Art einer Anatexis entwickeln kann. — Diese Probleme werden in bezug auf den Blei-Zink-Erzkörper in Broken Hill, New South Wales, Australien, diskutiert.

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An algorithm for the computer arrangement of reactions about invariant points     

Lawrence M. Barron  B. Jane Barron 《Contributions to Mineralogy and Petrology》1977,62(1):103-107

A computerised algorithm is used to arrange fluid-absent reactions about invariant points in P—T space for an end-member model of blueschist facies metamorphism at Port Macquarie, N.S.W., consisting of the nine phases quartz, albite, jadeite, lawsonite, zoisite, paragonite, glaucophane, pyrope and chlorite. Inspection of the print-out (a table of reaction take-off angles for each invariant point) indicates that this multisystem consists of two mutually exclusive sets of invariant points; lawsonite-absent, paragonite-absent and glaucophane-absent versus the other six. The algorithm is completely general for any two intensive variables and can treat solid solution minerals or degeneracy in reactions/invariant points.Terms ABS(X) Absolute value of X - A(J) Slope of reaction J in degrees - V(J) Denominator variable in the slope fraction for reaction J - R(K, J) Reaction coefficient of phase K in reaction J - S(K, J) Stability pointer for phase K in reaction J, in degrees - SGN (X) Library function: =–1 when X<0; =+1 when X0 - B(Q) Correct take-off angle for the Q-absent reaction in degrees  相似文献   

Some thermodynamic properties of the Berman and Brown model for CaO-Al₂O₃-SiO₂     

Lawrence M. Barron 《Geochimica et cosmochimica acta》1986,50(12):2727-2733

The and (1984) excess free energy model (B&B) is extremely convenient to use in modelling multicomponent solutions. However, spinodal calculations reveal that their calibration of this model for CaO-Al₂O₃-SiO₂ produces liquation tielines that do not appear to be in agreement with experimental work. In addition, their calibration contains some strongly negative excess entropy parameters and these permit a most unusual inverted liquation field to start at approximately >2115°C, wt% (SiO₂, Al₂O₃, CaO) = (70, 16, 14). This inverted field expands rapidly to cover most of the ternary for T> 2300°C and continues to expand at all higher temperatures. The Berman and Brown calibration for this system carries these negative excess entropies of mixing because the solution model is very strongly asymmetric as a result of the use of normal oxide mole weights in modelling the configurational entropy of mixing. A suggestion is made for a fairly natural restriction on the relative sizes of empirical models for excess versus configurational entropy.

Expressions are presented for the general consolute condition (all solution models) and for the second and third partials of the B&B G^x model.  相似文献