can mesoscale models reproduce meandering motions the influence of meandering flow on dispersion of pollutants is frequently underrepresented in dispersion models in terms of measurements meandering is primarily associated with time scales between the turbulence and the applied averaging time which is usually 1 h the related spatial scales thus range roughly from 10 2 to 10 4 m referred to here as submesoscales as the state of the art mesoscale models should be capable of reproducing flow features on scales larger than the turbulence and as the meandering generating mechanisms are not fully understood yet it is useful to examine if the mesoscale models can reproduce meandering for that purpose the wrf chem model at 1 3 km horizontal resolution is used to simulate a weak wind night during the cases99 experiment the measurements are used for detailed model verification the model with its typical set up fails to reproduce the variability at submesoscales and the locus of the under representation is traced to too strong horizontal diffusion reducing or removing the model diffusion allows the appearance of the submeso variability whose spectral properties and the resulting plume behaviour agree well with the measurements the linear correlation between the simulations with reproduced variability and the measurements is low as is the case between two simulations with only slightly different set up the conclusion is that mesoscale models are able to reproduce the strength of variability and the effects of meandering but only with reduced or removed horizontal diffusion the question arises whether it is possible to obtain a linear correlation i e to correctly reproduce individual modes at these scales at all copyright c 2010 royal meteorological society

dynamical aspects of wintertime cold air pools in an alpine valley system this study presents high resolution numerical simulations in order to examine the dynamical mechanisms controlling the persistence of wintertime cold air pools in an alpine valley system first a case study of a cold pool episode is conducted the formation of which was related to the passage of a warm front north of the alps while the preexisting cold air was rapidly advected away in the alpine foreland a persistent cold pool was maintained in the inner alpine part of the valley system associated with sustained horizontal temperature differences of up to 10 k over a distance of 30 km the case study is complemented by a series of semi idealized simulations combining realistic topography with idealized large scale flow conditions these simulations consider a range of different ambient wind directions in order to investigate their impact on the cold pool persistence the results indicate that the most important dynamical mechanism controlling the persistence of cold air pools in deep alpine valleys is cold air drainage toward the alpine foreland the preferred direction for such a drainage flow is down the pressure gradient imposed by the geostrophically balanced ambient flow thus for a given valley geometry and a given strength of the ambient flow the probability for persistent cold air pools mainly depends on the ambient wind direction if the direction of the imposed pressure gradient matches a sufficiently wide connection to the foreland a valley or a low pass then a drainage flow will lead to a rapid removal of the cold air however the presence of pronounced lateral constrictions in the connecting valley may strongly reduce the drainage efficiency cold pool erosion by turbulent vertical mixing seems to play a comparatively minor role in deep valley systems as considered in this study

forty years of ttg research abstract ttgs tonalite trondhjemite granodiorite are one of the archetypical lithologies of archaean cratons since their original description in the 1970s they have been the subject of many studies and discussions relating to archaean geology in this paper we review the ideas concepts and arguments brought forward in these 40 years and try to address some open questions both old and new the late 1960s and the 1970s mark the appearance of grey gneisses ttg in the scientific literature during this period most work was focused on the identification and description of this suite and the recognition that it is a typical archaean lithology ttgs were already recognised as generated by melting of mafic rocks this was corroborated during the next decade when detailed geochemical ttg studies allowed us to constrain their petrogenesis melting of garnet bearing metamafic rocks and to conclude that they must have been generated by archaean geodynamic processes distinct from their modern counterparts however the geodynamic debate raged for the following 30 years as many distinct tectonic scenarios can be imagined all resulting in the melting of mafic rocks in the garnet stability field the 1990s were dominated by experimental petrology work a wealth of independent studies demonstrated that melting of amphibolites as well as of mafic eclogites can give rise to ttg liquids whether amphibolitic or eclogitic conditions are more likely is still an ongoing debate from 1990s onwards one of the key questions became the comparison with modern adakites as originally defined these arc lavas are reasonably close equivalents to archaean ttgs pending issues largely revolve around definitions as the name ttg has now been applied to most archaean plutonic rocks whether sodic or potassic irrespective of their hree contents this leads to a large range of petrogenetic and tectonic scenarios a fair number of which may well have operated concurrently but are applicable only to some of the rocks lumped together in the ever broadening ttg bin

archaean lode gold deposits in africa crustal setting metallogenesis and cratonization abstract archaean rocks in africa are preserved in seven important tectonic and physiographic terranes the zimbabwe craton the kaapvaal craton of south africa the tanzanian shield the north zaire massif which extends westwards into the central african republic the kasai angola massif of southern zaire the atlantic rise of cameroun gabon and congo extending southwards to the malanje strip of northern angola the guinea rise of guinea sierra leone and liberia and the reguibat rise of mauritania morocco and northwest algeria dilational vein and brittle to ductile shear zone mineralization is common in the zimbabwe craton distribution of the gold being controlled by the permeability characteristics of the hydrothermal conduits and by the competence and chemistry of the wallrocks within the kaapvaal craton the barberton greenstone belt has the highest productivity with a marked concentration of lode type mineralization at or near the tectonized contact between the basalt dominated onverwacht group and the metasediments of the fig tree group smaller lode gold deposits are also present in the greenstone belts of the central and northern kaapvaal craton the more important being the stibnite gold mineralization that accompanied late brittle deformation of carbonatized high mg basalts in the murchison greenstone belt the archaean basement and supracrustal sequences of the guinea rise the reguibat rise the atlantic rise and the kasai angola massif are dominated by medium and high grade metamorphic rocks and with the exception of small greenschist facies sequences in central sierra leone the guinea rise are mostly devoid of gold mineralization however vein type gold lodes are more numerous in the low metamorphic grade greenstone belts of the north zaire massif and the tanzanian shield the important gold producing terranes are characterized by a complex tectonic history of strike slip and reverse dip slip shearing the productive lodes commonly being hosted by second or higher order shear zones these shear zones demonstrate an important component of late reverse dip slip activation or reactivation which provided optimum conditions for crustal de watering during prograde metamorphism and emplacement of tonalitic magmas the stratigraphic sequences and tectonic evolution are generally compatible with but do not unequivocally demonstrate cordilleran type accretionary regimes a link between gold metallogeny and the tectonothermal events that preceded and ultimately culminated in cratonization is commonly evident however cratonization in africa in a broad sense was diachronous ranging from ca 3 0 ga in the barberton greenstone belt through ca 2 6 2 5 ga in the zimbabwe and tanzanian cratons to the ca 2 0 ga eburnean event of west africa the latter contributing to the important gold mineralization of southwest ghana this multiplicity of tectonothermal events and the evidence for higher and more persistent crustal heat fluxes in the early precambrian terranes of west and equatorial africa have important ramifications for crustal evolution metallogeny and gold exploration

mesoscale impacts of explicit numerical diffusion in a convection permitting model abstractin convection permitting simulations the spectrum of resolved motions is truncated near scales where convection is active an energy gap between resolved and unresolved motions does not exist such that the upscale and downscale fluxes of energy across the spectrum are affected by the representation of turbulence as well as implicit and explicit numerical diffusion in the current study a systematic analysis is undertaken of the role of explicit numerical diffusion in simulations of diurnal convection over a large alpine region using the consortium for small scale modeling cosmo mesoscale model results are explored by using energy spectra and by diagnosing the physical and dynamical contributions to the bulk mesoscale heat budget in addition a linear analytical model is employed to assess different formulations of numerical diffusion consistent with previous studies the authors find that diffusion may strongly affect the energy spectrum and the formation of precipitation besides the d

worldwide initiation of holocene marine deltas by deceleration of sea level rise radiocarbon dated deltaic sequences of holocene age from different parts of the world began to accumulate within a restricted time range from about 8500 to 6500 years ago evaluation of major delta processes indicates that deceleration in sea level rise was the key factor in holocene delta formation within many deltas there is as much as a 2000 year age range between basal deposits in seaward and landward cores this age difference records the progressive landward migration of near mean sea level depositional environments during the lower to mid holocene establishment of a chronostratigraphic framework for holocene delta development provides a fundamental global baseline for distinguishing sea level change from vertical land motion by tectonism and isostasy and for evaluating rates of future marine incursion into low lying deltas

constraints on the origin of archean trondhjemites based on phase relationships of nuk gneiss with h2o at 15 kbar we report the t x h2o phase relations for the trondhjemitic nuk gneiss which comprises the principal component of the second phase of archean 3 0 2 8 by igneous activity in the godthab region of southwestern greenland a pressure of 15 kbar was chosen to place constraints on possible protoliths for trondhjemitic melts at lower crustal depths under h2o saturated conditions a melting interval of 135 c separates the solidus at 610 c from the liquidus at 745 c h2o saturation at 15 kbar occurs at approximately 15 5 wt h2o the h2o undersaturated liquidus extends along a curved path from 745 c at 15 5 wt h2o to 1100 c at 2 h2o lower h2o contents were not investigated at low h2o contents 7 mafic residues consisting of some combination of hb ga ep and bi are possible and could correspond to amphibolitic source rocks at lower melt h2o contents 5 possible residues consist of na pl qz ga and could correspond to an earlier generation of tonalitic trondhjemitic rocks however such residues would not impart the highly fractionated ree patterns characteristic of archean trondhjemites if a first generation of tonalitic trondhjemitic melts was generated by higher pressure partial fusion of eclogite and emplaced at 55 km depth it would crystallize to an assemblage consisting almost entirely of na pl qz with highly fractionated ree patterns these rocks in turn could be partially melted to yield a second generation of trondhjemites which would inherit the highly fractionated ree patterns because neigher pl nor qz is capable of significantly fractionating hree from lree

major and trace element geochemistry of the archaean ntem plutonic complex south cameroon petrogenesis and crustal evolution the ntem complex crops out in south cameroon and belongs to the congo craton it corresponds to a 2 8 ga basement which in the northern part is made up of plutonic rocks 1 charnockites and 2 soo tonalites both have similar compositions and define a typical tonalite trondhjemite and granodiorite ttg suite the study of isotopes isr major elements and ree allows us to propose a petrogenetic model that may summarized as follows 1 1 partial melting of the mantle gave rise to tholeiites 2 2 tholeiites transformed into garnet bearing amphibolites underwent partial fusion thus generating the parental magma of the ttg suite 3 3 fractional crystallization mainly of hornblende and plagioclase produced the differentiated ttg suite this scheme is typical of archaean ttg suites and is supposed to have occurred in a subduction like geodynamic environment where because of the high archaean geothermal gradients the subducted oceanic crust underwent fusion before dehydration operated it is also possible to show that the ttg suite was not emplaced during the granulite facies metamorphism but that this occurred later affecting only some parts of the basement consequently the ntem complex appears to be an archaean high grade terrane where the granulitic assemblages may be early proterozoic in age characteristic that seems to be more widespread among archaean high grade terranes

the impact of lee side stratification on the spatial distribution of orographic precipitation numerical simulations are presented in order to investigate the effect of the lee side stratification on the spillover of orographic precipitation the simulations are conducted with idealized topography as well as with idealized large scale flow conditions and consider both moist neutral and convectively unstable situations strong lee side static stability is achieved by creating a basin enclosed by four mountain ridges that is filled with a cold air pool sensitivity tests are also performed with a plateau topography representing the limit of an infinitely stable cold air pool it is found that the presence a cold air pool in the lee of a mountain ridge greatly increases the precipitation spillover because the cold pool suppresses the lee side downslope air motion that otherwise leads to a rapid evaporation of the precipitation the maximum fractional enhancement of the lee side precipitation ranges between one order of magnitude in a convectively unstable environment and two orders of magnitude in a nonconvective one however the largest absolute values are found in the convective cases because convective cells decay more slowly than stratiform precipitation in all simulations with a lee side cold pool the precipitation decay in the lee of the mountain tends to be approximately exponential sensitivity experiments indicate that the lee side precipitation enhancement due to a cold pool depends only weakly on the height and the width of the mountain the precipitation on the upstream side of the mountain also tends to be enhanced by a lee side cold pool due to a change of the gravity wave pattern however this side effect is comparatively small never exceeding a factor of three in the cases tested in this study a notable precipitation enhancement over the mountain crest is found for low mountains only copyright 2005 royal meteorological society

the granite problem as exposed in the southern snake range nevada a geochemically and mineralogically diverse group of granitoids is present within an area of 900 km2 in the southern snake range of eastern nevada the granitoids exposed range in age from jurassic through cretaceous to oligocene and include two calcic intrusions two different types of two mica granites and aplites the younger intrusions appear to have been emplaced at progressively more shallow depths all of these granitoid types are represented elsewhere in the eastern great basin but the southern snake range is distinguished by the grouping of all these types within a relatively small area

upb and smn edvidence for eburnian and pan african high grade metamorphism in cratonic rocks of southern cameroon abstract u pb analyses of zircons and sm nd mineral and whole rock analyses of samples from southern cameroon document three distinct rock forming or high grade metamorphic events 2900 ma 2050 ma and 600 ma zircons from the ebolowa charnockite in southern cameroon yield an age of 2896 7 ma consistent with published rb sr total rock data for the region sm nd crustal formation ages for these rocks are 3000 ma indicating that the granitoids and ntem series gneisses in the north end of the congo craton formed 2900 ma ago and do not contain major contributions from older archean crust a second metamorphic event of eburnian age is identified from re equilibration of sm and nd in gneisses and metadolerites of the ntem complex at 2050 ma zircons from the younger nyong series gneisses are a complex mixture of cores and overgrowths the overgrowths in most cases formed during a high grade metamorphic event between 2100 and 2000 ma and clearly postdate the ebolowa charnockite the ages of the cores are not precisely known but we believe most represent detrital zircons from 2900 ma protoliths sm nd crustal formation ages for samples of the nyong series gneisses are generally 2500 to 2900 ma indicating that their precursors were apparently derived mainly from the archean craton with variable amounts of younger component sm nd garnet total rock isochrons for metamorphosed mafic rocks in the nyong series yield ages of 2050 ma and zircons from one of them yield an upper intercept age of 2037 10 ma further documenting the existence of a major event with magmatism and charnockitization at 2000 to 2100 ma we interpret the nyong series metasedimentary gneisses as post 2900 ma cratonic cover that was deformed and metamorphosed during the 2000 to 2100 ma eburnian orogeny we cannot define precise limits on the ages of sedimentation preliminary data on metamorphosed intrusive rocks associated with the yaounde series yield u pb concordant ages around 620 ma consistent with sm nd garnet whole rock ages from the same series this dates the pan african tectono metamorphic activity in the southern end mobile belt the pan african lower intercepts of zircons and sm nd garnet whole rock ages from thnyong series are the consequences of this event which is further represented by a 590 ma zircon age from a late syenitic pluton results from cameroon are consistent with recent results from the western part of the congo craton farther south and from the northeastern part of the sao francisco craton in brazil one interpretation of these results is that the congo and sao francisco cratons were joined during the ebumian trans amazonian orogeny 2100 ma and are bordered to the north by a late mesoproterozoic rift basin that was closed during the pan african brasiliano orogeny 600 ma

orographic gravity waves close to the nonhydrostatic limit of vertical propagation abstract orographic gravity waves excited by a narrow mountain ridge are investigated with the aid of numerical simulations when the nondimensional mountain half width na u is around 1 n a and u being the brunt vaisala frequency the dimensional half width and the ambient wind speed respectively only part of the gravity wave spectrum excited by the mountain is able to propagate vertically in this case linear theory as well as numerical simulations with low mountains show two wind maxima one at the mountain crest and one in the lee of the mountain as na u is reduced below 1 the wind maximum in the lee weakens and moves farther downstream and the maximum at the crest intensifies rapidly with decreasing na u simulations in which a gap with a level axis is embedded in the mountain ridge demonstrate that the wind perturbations along the gap axis are qualitatively similar to those over the adjacent mountain ridge however their magnitude is substantially lower and the tendency to form a wind max

fohn in the rhine valley during map a review of its multiscale dynamics in complex valley geometry this paper summarizes the findings of seven years of research on fohn conducted within the project fohn in the rhine valley during map form of the mesoscale alpine programme map it starts with a brief historical review of fohn research in the alps reaching back to the middle of the 19th century afterwards it provides an overview of the experimental and numerical challenges identified before the map field experiment and summarizes the key findings made during map in observation simulation and theory we specifically address the role of the upstream and cross alpine flow structure on fohn at a local scale and the processes driving fohn propagation in the rhine valley the crucial importance of interactions between the fohn and cold air pools frequently filling the lower rhine valley is highlighted in addition the dynamics of a low level flow splitting occurring at a valley bifurcation between the rhine valley and the seez valley are examined the advances in numerical modelling and forecasting of fohn events in the rhine valley are also underlined finally we discuss the main differences between fohn dynamics in the rhine valley area and in the wipp inn valley region and point out some open research questions needing further investigation copyright 2007 royal meteorological society

interaction between dynamics and cloud microphysics in orographic precipitation enhancement a high resolution modeling study of two north alpine heavy precipitation events abstract interactions of atmospheric dynamics and cloud microphysics with the alpine orography are investigated for two north alpine heavy precipitation cases 20 22 may 1999 and 22 23 august 2005 both cases were related to a deep cyclone propagating slowly eastward along the alps advecting moist air of mediterranean origin toward the northern side of the alps a validation against high resolution rain gauge data reveals that the average model bias is below 15 in the region of interest but there is a tendency to systematically underestimate very heavy precipitation a scale decomposition of the discrepancies between model and observations reveals that errors on the meso scale contribute at least as much to the total model error as discrepancies on the meso scale on the scale of single mountain ridges and valleys the formation of precipitation maxima at valley locations is investigated with particular emphasis on a region in which a valley receives systematically more precipitation than the adj

transport of terrestrial organic carbon to the oceans by rivers re estimating flux and burial rates this study re estimates one important component in the global carbon cycle the modern global fluviatile organic carbon discharge and burial rates according to these results approximately 430 1012 g of terrestrial organic carbon are transported to the ocean in modern times this amount is higher than the latest estimates but takes into account new data from oceania not previously considered in global flux studies however only the minor amount of 10 or approximately 43 1012 gc year 1 is most likely buried in marine sediments this amount is similar to the burial of marine organic carbon in the coastal ocean 55 1012 gc year 1 adding both estimates gives approximately 100 1012 gc year 1 which is the value calculated by berner 1982 for terrestrial deltaic shelf sediments however the results in this study suggest that on a global scale the organic carbon content in coastal ocean sediments is not solely of terrestrial origin but a mixture of nearly equal amounts of marine and terrestrial organic carbon the major part of the terrestrial organic carbon that enters the ocean by rivers approximately 400 1012 gc year 1 seems to be either a remineralised in the ocean whereas the mechanism by which the terrestrial organic carbon is oxidised in the ocean are unknown or b is dispersed throughout the oceans and accumulates in pelagic sediments

diurnal circulation of the bolivian altiplano part ii theoretical and model investigations abstract the first step in the evolution of the diurnal circulation of grand plateaus is the matutinal buildup of inflow through mountain passes connecting the lowlands with the plateau proper maximum inward transport is attained in the afternoon corresponding observations at the bolivian altiplano are described in the first part of this paper here both a linear model and the fifth generation pennsylvania state university ncar mesoscale model mm5 are used to better understand the dynamics of this process first discussed is the solution to the linear sea breeze problem where a heated fluid layer is restricted to the half plane x 0 rapidly moving barotropic modes lead to surface pressure fall in the heated half plane and to pressure rise for x 0 slow baroclinic modes describe the horizontally expanding inflow toward the heated layer near the ground with return flow aloft this basic structure of the response carries over to more complicated topographies where a heated plateau with vertical side

activity of the yoro fault system determined from coseismic subsidence events recorded in the holocene delta sequence of the nobi plain central japan the holocene delta sequence of the nobi plain central japan records coseismic subsidence in the western part of the plain caused during the past 6000 years by movement on the yoro fault we identified four episodes of upward fining deposition and increasing electrical conductivity in delta front deposits that occurred 600 200 1300 900 4200 3800 and 5600 4700 years ago suggesting that episodes of sea level rise interrupted progradation of the kiso river delta considering the general trend of relative sea level fall during the middle to late holocene under the influence of eustasy and hydroisostasy the temporal correspondence of rises of relative sea level with activity on the yoro fault suggests they reflect coseismic subsidence due to yoro fault activity the timing of the coseismic subsidence events identified in this study also corresponds with that of previously reported faulting events at the kuwana fault to the south of the yoro fault these results are consistent with the previous interpretation that the yoro and kuwana faults comprise a behavioral segment within the yoro fault system our off fault paleoseismic study shows that coseismic subsidence events detected in holocene delta sequences can provide further evidence of faulting events inferred from the on fault paleoseismic studies

petrogenesis of juvenile type birimian paleoproterozoic granitoids in central cote d ivoire west africa geochemistry and geochronology abstract the birimian paleoproterozoic granitoids of central cote d ivoire are associated either with greenstone belts or with basin sedimentary rocks field data indicate two stages of granitoid emplacement which according to singlezircon and monazite 207 pb 206 pb age determinations occurred within a short period of time the first generation of granitoids 2123 2108 ma intruded and metamorphosed the greenstone belts whereas the second generation 2108 2097 ma intruded and metamorphosed the sedimentary pile and subordinate andesitic volcanic rocks of the bandama basin unconformably overlying the greenstone belts geochemical and isotopic data show that the various granitoids belong to four magmatic groups 1 sodic calc alkaline nacg 2 potassic calc alkaline kcg 3 peraluminous alg and 4 alkaline alkg all the granitoids show juvenile features with mantle like low initial sr isotopic compositions 0 700 0 702 and positive epsilon nd values 1 5 2 7 these data indicate that a the nacg may have formed by partial melting of a garnet amphibolite crust b the kcg and alkg derived from partial melting of crustal mafic to intermediate metaigneous rocks and c the alg epsilon nd 1 5 represent infracrustal melting of young sialic igneous materials during a regional crustal shortening in a transcurrent tectonic context sm nd model ages 2 25 2 4 ga preclude the existence of an archean crust reworked in the birimian magmas an underplating model is discussed

archaean plate tectonics revisited 1 heat flow spreading rate and the age of subducting oceanic lithosphere and their effects on the origin and evolution of continents a simple model which relates the rate of seafloor creation and the age of the oceanic lithosphere at subduction to the rate of continental accretion can successfully explain the apparent differences between archaean and phanerozoic terrains in terms of plate tectonics the model has been derived using the following parameters 1 the spreading rate at mid ocean ridges 2 the age of the oceanic lithosphere at the time of subduction 3 the area age distribution of the seafloor 4 the continental surface area as a fraction of the total surface area of the earth and 5 the erosion rate of continents as a function of continental surface area and the total number of continental masses observations in phanerozoic terranes suggest that there are profound differences in the nature and volume of subduction zone igneous activity depending upon the age of the oceanic lithosphere being subducted and the nature of the overriding plate that is either continental or oceanic the subduction of young oceanic lithosphere less than 50 m y old which is thermally buoyant appears to result in a reduced volume of igneous activity most of the igneous activity caused by subduction of young oceanic lithosphere is either siliceous plutonism or bimodal tholeiitic rhyolitic volcanism when very young lithosphere is being subducted 50 m y old appears to result in greater volumes of igneous activity including the eruption of andesitic magmas thus andesites could only begin to be abundant in the rock record when older oceanic lithosphere began to be subducted our model predicts that as the earth aged and as heat flow from the interior of the earth diminished the proportion of old oceanic lithosphere being subducted increased fundamentally changing the nature of subduction zone igneous activity and the rate of continental accretion if the subduction of old oceanic lithosphere results in an 8 10 times greater volume of subduction zone magmatism our model predicts or explains all of the following observed features of earth history 1 archaean terranes appear to record two periods of rapid continental accretion between 3 8 and 3 5 b y ago and between 3 1 and 2 6 b y ago 2 there are very few differences and many marked similarities between rocks from archaean terranes and equivalent rocks from phanerozoic terranes 3 the total continental area appears to have remained essentially constant for the past 2 b y 4 archaean andesites are comparatively rare and the relative abundances of mafic and siliceous rocks appear to change during the archaean and the proterozoic with siliceous volcanics becoming proportionately more abundant in the geologic record with time 5 plutonic tonalites and trondhjemites appear to have been relatively much more abundant during the archaean plate tectonics is thus shown to have evolved over time due to a gradually decreasing rate of creation of oceanic lithosphere meaning that archaean tectonics and phanerozoic tectonics are but two points on an evolutionary continuum

role of a thin komatiite rich oceanic crust in the archean plate tectonic process in the archean tectonic regime the time available for oceanic lithosphere to cool on its journey from ridge to convergent plate boundary was far less than at present under these conditions only an inherently dense lithosphere could have acquired the negative buoyancy necessary for it to subduct at this time plate tectonics could have operated only if 1 the oceanic crust was rich in komatiite lava and 2 the thickness of this crust was not much greater than the thickness of modern oceanic crust

prediction of clouds and rain using a z coordinate nonhydrostatic model abstract the most common option for numerical models of the atmosphere is to use model layers following the surface of the earth using a terrain following vertical coordinate the present paper investigates the forecast of clouds and precipitation using the z coordinate nonhydrostatic version of the lokalmodell lm z this model uses model layers that are parallel to the surface of the sphere and consequently intersect the orography physical processes are computed on a special grid allowing adequate grid spacing even over high mountains in other respects the model is identical to the nonhydrostatic terrain following version of the lm which in a number of european countries is used for operational mesoscale forecasting the terrain following version of the lm lm tf is used for comparison with the forecasts of the lm z terrain following coordinates are accurate when the orography is shallow and smooth while z coordinate models need not satisfy this condition because the condition of smooth orogra

carbon storage in a holocene deltaic sequence an example from the nobi plain central japan abstract we estimated the rate of accumulation and total amount of organic carbon oc stored in holocene sediments of the nobi plain of central japan by analyzing 2701 existing borehole sections and 218 14c ages reconstructing the three dimensional stratigraphic architecture of the delta system calculating the volume of sediments in the delta and using oc contents measured from sediments from eight boreholes on the plain we calculated that a total of 167 tg of oc was stored in deltaic deposits on the plain during the past 6000 years a dramatic increase in the amount of stored oc since 1000 cal bp is probably a combined result of increases in sediment supply to the delta in response to human activities in the drainage basin and expansion of the area of subaerial delta as a result of progradation oc accumulation rates for the nobi plain during the past 6000 years ranged from 15 3 to 37 5 g m 2 y 1 which are comparable to rates obtained from other holocene delta and to rates from floodplain and lake systems with higher oc contents in their sediments the higher sedimentation rates of the deltaic deposits compensates for their lower oc contents

mantle convection and early crustal evolution abstract the existence of peridotitic komatiites in the archaean suggests that the archaean mantle was significantly hotter than the modern mantle this evidence is contradicted by estimates of archaean continental geothermal gradients based on the pressure and temperature recorded in metamorphic rocks which suggest that there is no marked difference between archaean and modern continental geothermal gradients numerical modelling shows that small changes in the mantle temperature can have an important influence on convection if the average temperature of the upper mantle is increased by 200 c convection within the mantle becomes chaotic and an upper mantle partial melt zone encircles the globe the crust formed during this period will be komatiitic in composition but will be unstable and will be mixed back into the mantle by subduction later when the mantle temperature falls to 100 c above its present level the upper mantle partial melt zone contracts away from subduction areas it is suggested that the first primitive felsic magmas were generated at subduction zones the appearance of these magmas at 3 8 ga permitted the formation of buoyant continents and eventually led to crustal thickening as a consequence of this thickening the proto continents consisting of a bimodal suite of basalts and sodic granodiorites contained two types of latent energy 1 radioactive energy held in elements such as th k and u and 2 potential energy resulting from the elevation of the continents above sea level the potential energy of the continents led to sedimentation the increase in the rate of sedimentation during the archaean resulted from increased crustal buoyancy at the same time heat released by radioactive elements in the deep crust built up under the insulating blanket of the upper crust this caused a major metamorphic metasomatic and crustal melting event which produced the potassic granites of the late archaean once the radioactive elements had been removed from the lower crust that region of the continent become tectonically stable the proterozoic shelf sediments were deposited at the margins of these stable cratons convection models of the archaean mantle show hot diapirs rising from the boundary layer above the core mantle interface we suggest that these diapirs began to melt at a depth of 450 km giving rise to komatiitic magmas this model requires the average temperature of the archaean upper mantle to be 100 c above that of the modern mantle the similarity between archaean and modern continental geothermal gradients can be explained if archaean continents formed above subduction zones raising the temperature of the archaean mantle by 100 c 1 halves the thickness of the oceanic lithosphere 2 increases the oceanic geothermal gradient at the mid point of a convection cell 3 decreases the viscosity of the mantle by at least an order of magnitude the combination of these effects produces a marked decrease in the strength of the archaean lithosphere and mantle thus the form of archaean tectonics can be expected to have been very different from modern tectonics

three dimensional cut cell modelling for high resolution atmospheric simulations owing to the recent rapid development of computer technology the resolution of atmospheric numerical models has increased substantially with the use of next generation supercomputers atmospheric simulations using horizontal grid intervals of o 100 m or less will gain popularity at such high resolution more of the steep gradients in mountainous terrain will be resolved which may result in large truncation errors in those models using terrain following coordinates in this study a new three dimensional 3d cartesian coordinate non hydrostatic atmospheric model is developed a cut cell representation of topography based on finite volume discretization is combined with a cell merging approach in which small cut cells are merged with neighbouring cells either vertically or horizontally in addition a block structured mesh refinement technique is introduced to achieve a variable resolution on the model grid with the finest resolution occurring close to the terrain surface the model successfully reproduces a flow over a 3d bell shaped hill that shows a good agreement with the flow predicted by the linear theory the ability of the model to simulate flows over steep terrain is demonstrated using a hemisphere shaped hill the advantage of a locally refined grid around the hill with cut cells at the terrain surface is also demonstrated the model reproduces smooth mountain waves propagating over varying grid resolution without introducing large errors associated with the change of mesh resolution at the same time the model shows a good scalability on the locally refined grid

gap flows results from the mesoscale alpine programme an overview of advances in the observation modelling forecasting and understanding of flows through gaps achieved in the mesoscale alpine programme is given gaps are lateral constrictions of topography level gaps often combined with vertical terrain changes passes of the possible flow configurations only an asymmetric one relatively deep and slow upstream accelerating and thinning downstream which connects two different reservoirs on each side of the gap is examined the flow is strongly nonlinear making hydraulics reduced gravity shallow water theory rather than linear theory the simplest conceptual model to describe gap flow results from idealized topographical and flow conditions are presented together with gap flows through a pass in the central alpine wipp valley for a given depth of the upstream reservoir the gap controls the mass flux through it and marks the transition from a subcritical flow state upstream to a supercritical one downstream which eventually adjusts to the downstream reservoir in a hydraulic jump three gap flow prototypes were found a classical layer one with neutral stratification and a capping inversion and two with a continuous stratification for which a special analytical self similar hydraulic solution exists in all three cases a deepening wedge of nearly mixed and stagnant air forms on top of the gap flow plunging down from the pass the descent causes a warming and relative drying of the air making gap flows a special case of fohn topographical variations smaller than the gap scale cause additional hydraulic jumps flow separation vorticity banners gravity waves and interactions with cold pools turbulent friction cannot be neglected the climatological frequency of gap flows depends on the establishment of two different reservoirs and reaches 20 for the wipp valley copyright 2007 royal meteorological society

a carbon storage perspective on alluvial sediment storage in the rhine catchment abstract floodplains are important sinks in terms of the sediment and carbon flux in fluvial systems despite the large amount of detailed geomorphological studies which include measurements on total organic carbon little is known of the coupling of long term carbon and sediment flux and on the amount of carbon storage in floodplains therefore the influence of the sedimentary facies in fluvial systems was investigated based on a statistical analysis of 1948 organic carbon measurements in different parts of the rhine catchment the analysis allows to develop a conceptual carbon budget model of fluvial systems which was coupled with a holocene alluvial sediment budget to estimate the holocene sequestration rates of carbon storage in floodplains averaged over the rhine catchment the sedimentary carbon sequestration ranges between 3 4 to 25 4 g m 2 yr 1 with more reasonable values between 5 3 to 17 7 g m 2 yr 1 compared to the recent particulate carbon export these values are in the same order of magnitude but somewhat smaller indicating that approximately the same amount of the exported carbon may be stored in floodplains however compared to sedimentary carbon sequestration rates obtained elsewhere the presented values are at the lower limit corresponding to the lower mean holocene soil erosion and floodplain accumulation rates

holocene floodplain sediment storage and hillslope erosion within the rhine catchment the response of fluvial systems to land use and climate change varies depending on catchment size while forcing response mechanisms of small catchments are reasonably well understood the response of larger drainage basins is less clear in particular the impact of land use and climate change on the rhine system is poorly understood because of the catchment size 185 000 km 2 and the long history of human cultivation which started approximately 7500 years ago a sediment budget is calculated to specify the amount of alluvial sediment that was deposited during the holocene and to estimate long term soil erosion rates the results suggest that 599 14 10 9 t of holocene alluvial sediment is stored in the non alpine part of the rhine catchment south and central germany eastern france the netherlands about 50 of holocene alluvial sediment is deposited along the trunk valley and the delta upper rhine lower rhine coastal plain while the rest is stored along the tributary valleys the floodplain sediment storage corresponds to a mean erosion rate of 0 559 0 16 t ha per yr 38 59 10 7 mm kyr across the rhine catchment outside the alps this holocene averaged estimate amounts for sediments that were delivered to the channel network and is at the lower limit of erosion rates from other studies of different methodology

sediment and carbon storages in the yahagi river delta during the holocene central japan abstract we estimated stored sediment and carbon during the holocene for each layer of the yahagi river delta central japan and discussed the provenance of stored carbon to estimate the bulk density and the carbon content of each layer we collected two 30 m deep undisturbed cores the volume of each layer was calculated using arcview 3d analyst although the volume ratio of each layer to the total volume was calculated to be 9 5 for the top mud layer 34 9 for the upper sand layer 32 8 for the middle mud layer and 22 9 for the lower sand layer the mass ratio of each layer to the total mass was calculated to be 8 5 40 9 25 2 and 25 4 respectively and the stored carbon ratio in each layer to the total stored carbon was 20 4 4 7 55 9 and 18 9 respectively these results suggest that the top mud and middle mud layers have a significant role as a place for carbon sequestration during postglacial time total stored carbon in the study area of only 92 1 km 2 was estimated at 26 tg c which is equivalent to 0 003 of atmospheric carbon this suggests that deltas on the globe have accumulated a massive amount of carbon during the evolution the inorganic carbon ratio to total carbon reached more than 45 around the boundary between the middle mud and lower sand layers the increasing trend in the c org n total ratio accompanied with a decrease in 13 c from the bottom to the top horizon in the middle mud layer indicates a gradual increase in terrestrial organic matter contribution the relative proportion of terrestrially derived materials decreases with increasing distance seaward

dynamics of the foehn mechanism in the mcmurdo dry valleys of antarctica from polar wrf foehn events over the mcmurdo dry valleys mdvs the largest ice free region of antarctica promote glacial melt that supports biological activity in the lakes streams rocks and soils although mdvs foehn events are known to depend upon the synoptic scale circulation the physical processes responsible for foehn events are unknown a polar optimized version of the weather research and forecasting model polar wrf is used for a case study of a representative summer foehn event from 29 december 2006 to 1 january 2007 in order to identify and explain the mdvs foehn mechanism pressure differences across an elevated mountain gap upstream of the mdvs provide forcing for southerly flow into the western upvalley entrance of the mdvs complex terrain over the elevated gap and the mdvs leads to mountain wave effects such as leeside acceleration hydraulic jumps wave breaking and critical layers these mountain wave effects depend on the ambient geostrophic wind direction pressure driven channelling then brings the warm dry foehn air downvalley to eastern mdv sites brief easterly intrusions of maritime air into the eastern mdvs during foehn events previously have been attributed to either a sea breeze effect in summer or local cold pooling effects in winter in this particular case the easterly intrusions result from blocking effects of nearby ross island and the adjacent antarctic coast temperature variability during the summer foehn event which is important for meltwater production and biological activity when it exceeds 0 c primarily depends on the source airmass rather than differences in foehn dynamics

proterozoic links between the borborema province ne brazil and the central african fold belt the congo cc and the sao francisco sfc cratons were joined at about 2 05 ga northern parts of palaeoproterozoic basement subsequently underwent extension at about 1 ga forming intracratonic basins neoproterozoic metasedimentary rocks in these basins yield detrital zircons as young as 630 ma the brasiliano and pan african c 620 580 ma assembly of west gondwana extensively altered this system the sergipano domain occurs north of the sfc and the comparable yaoundedomain occurs north of the cc crust north of the sergipano domain com prises the pernambuco alagoas peal domain the ne sw striking tchollire banyo fault in cameroon may extend southwestwards between the peal and sergipano domains defining northern limits of abundant sfc cc basement the adamawa yadedomain in africa does not appear to extend into brazil the transverse domain of brazil is a collage of palaeoproterozoic crustal blocks the 1 0 ga cariris velhos orogen cvo late neoproterozoic basins and brasi liano granites the cvo extends ene for more than 700 km in brazil but eastern continuation into africa has not been identified north of the transverse domain contiguous c 2 15 ga gneisses comprise basement of rio grande do norte and cearadomains which continue eastwards into western nigeria and western sahara

large eddy simulation over complex terrain using an improved immersed boundary method in the weather research and forecasting model abstractthe weather research and forecasting wrf model is increasingly being used for higher resolution atmospheric simulations over complex terrain with increased resolution resolved terrain s

alpine gravity waves lessons from map regarding mountain wave generation and breaking the two month special observing period of the mesoscale alpine programme map in autumn 1999 included a variety of complex mountain wave events seven wave events were carefully analyzed compared with numerical models and described in published papers these detailed investigations revealed some common dynamical elements i e the importance of low level processes involving the slow moving boundary layer low level wind shear causing either wave absorption or decoupling spilling upstream blocking and latent heat release based on these studies it is clear that any quantitative prediction of mountain wave generation must take full account of these lower troposphere processes the newest numerical models show significant skill in simulating these effects using these models the climatology of waves over the alps can be studied copyright 2007 royal meteorological society

applying horizontal diffusion on pressure surface to mesoscale models on terrain following coordinates abstract the national centers for environmental prediction regional spectral model and mesoscale spectral model ncep rsm msm use a spectral computation on perturbation the perturbation is defined as a deviation between rsm msm forecast value and their outer model or analysis value on model sigma coordinate surfaces the horizontal diffusion used in the models applies perturbation diffusion in spectral space on model sigma coordinate surfaces however because of the large difference between rsm msm and their outer model or analysis terrains the perturbation on sigma surfaces could be large over steep mountain areas as horizontal resolution increases this large perturbation could introduce systematical error due to artificial vertical mixing from horizontal diffusion on sigma surface for variables with strong vertical stratification such as temperature and humidity this nonnegligible error would eventually ruin the forecast and simulation results over mountain areas in high resolution modeling to a

ree geochemistry and isotopic data of archean silicic volcanics and granitoids from the pilbara block western australia implications for the early crustal evolution eighteen silicic volcanic rocks of the warrawoona group and ten associated plutonic rocks from the pilbara block western australia have been chosen for geochemical and isotopic studies silicic volcanics of the unsb upper member of north star basalt are dated at 3 56 3 57 by both the rb sr and the sm nd methods the respective 1 initial isotopic composition values are 0 7005 5 sr and 0 50810 39 nd this age is consistent with the stratigraphic interpretation that the talgatalga subgroup in which the north star basalt occupies the lowermost position is overlain by the duffer formation whose age was earlier established at 3 45 by the zircon u pb method the new rb sr data on six silicic lava samples from the duffer formation yield an isochron of 3 23 0 28 2v though imprecise this age agrees with the zircon age within error limits rb sr ages of 2 3 2 4 obtained for the panorama rocks and the wyman formation do not correspond to their initial eruption ages chemical arguments suggest that these ages represent the time of metasomatism associated with the widespread thermal event in this region about 2 3 2 4 ago geochemically most of these analyzed rocks volcanic and plutonic are of tonalite trondhjemitegranodiorite ttg composition a typical feature found in many other archean terrains they generally show fractionated ree patterns except the panorama formation rocks furthermore the wyman formation rhyolites and the post tectonic adamellites show significant negative eu anomalies suggesting a similar mode of magma generation and a probable genetic link theoretical considerations suggest that most of these ttg rocks could have been generated by partial melting of amphibolitic or basaltic sources followed by fractional crystallization although the archean granitic gneisses often possess mantle like isr values the trace element data indicate that they could not have been derived by direct melting of upper mantle materials the immediate tectonic implication is that in any archean terrain the formation of na rich continental crust of ttg suite must be preceded by the presence of basaltic crust the occurrence of this basaltic crust is a matter of controversy such crust might have been totally destroyed by repeated melting processes or its remnants are now represented by some of the mafic ultramafic enclaves within the tonalite trondhjemite batholiths

evolution in composition of granitic rocks controlled by time dependent changes in petrogenetic processes examples from the archaean of eastern finland abstract the grey gneisses of eastern finland form the basement on which the archaean greenstone belts were developed they are composed of tonalites trondhjemites and granodiorites ttg emplaced during two distinct magmatic episodes at 2 86 ga kivijarvi gneisses and 2 65 ga naavala petrogenetic models based on trace element behaviour indicate that the ttg are ultimately derived from the mantle by a mechanism involving two stages 1 1 melting of the mantle to form a tholeiitic crust and 2 2 re melting of these tholeiites transformed into garnet amphibolites to yield ttg rocks the low yb contents of archaean ttg are explained by the influence of residual garnet and hornblende in the source rocks involved in magma genesis after 2 5 ga the role of these minerals becomes progressively less important and this is interpreted in terms of a cooling earth model at present the subducted oceanic crust is relatively cold and the geothermal gradient at its interface with the overlying mantle wedge is low in addition the descending lithospheric slab undergoes dehydration before partial melting is able to occur and the liberated fluids pass upward into the mantle wedge or base of the continental crust where partial melting may begin these magmas have calc alkaline affinities and have equilibrated with residual olivine and pyroxene in the source consequently the liquids derived from partial melting have high yb contents during the archaean subducted oceanic crust was relatively hot and the geothermal gradients in the interface zone with the mantle were high c 20 25 c km 1 thus partial melting of the subducted oceanic material was possible at temperatures between 650 and 700 c before dehydration would take place residual phases in the source would include garnet and hornblende thus explaining the low yb contents of the ttg association it is concluded that there has been a change in the site of cale alkaline magma genesis since archaean times

crustal growth in the mesoarchean plutonic belt from the memve ele area ntem complex southwestern cameroon evidence of early earth transpressional tectonics abstract the mesoarchean crust of the plutonic belt of the memve ele area lies in the southwestern part of the ntem complex ntc cameroon emplacement of these rocks resulted from both gravity and tectonic driven vertical flow perpendicular to the direction of shortening at the time of partial melting and magmatic accretion such deformation patterns suggest the occurrence of a long lived hot orogen and may explain a nearly isobaric retrograde pressure temperature p t path recorded within high t low to medium p metamorphic rocks however in the memve ele shear zone msz a metamorphic gradient runs from granulite to green schist facies structural analysis reveals four continuous ductile deformations the first stage is characterized by the emplacement of dome and basin structures the second stage is marked by coeval diapiric movements and a transpressional shear zone the third stage is marked by both transpressional and lateral flow regimes and the last stage is marked by horizontal constrictional strain these features indicate that the mesoarchean crust is affected by a long lived horizontal shortening deformation d1 d3 coeval with vertical movements in which concentric cleavages occur around domes thus the studied area can be considered as exemplifying an early earth style tectonics the structural patterns in the msz contain zone of high strain rocks belonging to the deep and shallow mid crusts that have recorded transpressional tectonics the compressional strain regime in which results coeval steep to shallow dipping structural features and dome and basin geometries associated to msz activities contributed to maintaining a stable crustal thickness in the memve ele area during mesoarchean orogeny

nonhydrostatic atmospheric modeling using a combined cartesian grid abstract a new method for representing topography on a cartesian grid is applied to a two dimensional nonhydrostatic atmospheric model to achieve highly precise simulations over steep terrain the shaved cell method based on finite volume discretization is used along with a cell combining approach in which small cut cells are combined with neighboring cells either vertically or horizontally a unique staggered arrangement of variables enables quite simple computations of momentum equations by avoiding the evaluation of surface pressure and reducing the computational cost of combining cells for the velocity variables the method successfully reproduces flows over a wide range of slopes including steep slopes where significant errors are observed in a model using conventional terrain following coordinates the advantage of horizontal cell combination on extremely steep slopes is also demonstrated

numerical simulations of the 12 13 august 2002 flooding event in eastern germany in this paper high resolution numerical simulations of the 12 13 august 2002 flooding event in eastern germany are presented the simulations are performed with the penn state national center for atmospheric research mesoscale model mm5 in a four domain configuration with a finest horizontal resolution of 1 km sensitivity experiments are performed with coarser resolutions 3 and 9 km with different cloud microphysical parametrizations and with a different date of initialization moreover tests with i km resolution but the smoothed topography of the 9 km runs are conducted in order to isolate the contribution of the model topography to the differences between the 1 km runs and the 9 km runs the results show that the high resolution runs reproduce the observed structure of the precipitation field very well in particular the location of the rainfall maximum is correct to within 15 km the quantitative agreement between model results and observations is fairly good in regions with light to moderate rain but large amounts of precipitation tend to be underpredicted for observed 36 hour rainfall accumulations exceeding 200 mm the negative bias typically ranges between 15 and 30 with fairly little dependence on the microphysical parametrization in the coarser resolved runs the bias at high precipitation amounts becomes even more pronounced and it is found that this behaviour is not only due to the fact that a coarser resolution is associated with a smoother topography this indicates a systematic deficiency in the microphysical parametrizations limiting their ability to simulate heavy precipitation

archean granulite gneisses from eastern hebei province china rare earth geochemistry and tectonic implications the granulite gneisses and their retrograded products of the qianxi group from eastern hebei province china have been investigated for their isotope and trace element geochemistry a consistent age of about 2 5 ae has been obtained by the rb sr and sm nd whole rock isochron methods in agreement with the zircon u pb data pidgeon 1980 d y liu unpubl geochemical arguments from initial isotopic ratios isr and ind and elemental distribution patterns have led us to conclude that this age of about 2 5 ae represents the time of granulite facies metamorphism which must have followed closely the primary emplacement of their protoliths previous claims for early archean ages 3 5 ae of these granulites are not substantiated the mineral isotope systematics register an important thermal event at about 1 7 ae roughly corresponding to the time of the widespread luliang orogeny ma and wu 1981 or chungtiao movement huang 1978

numerical simulations of the foehn in the rhine valley on 24 october 1999 map iop 10 abstract this paper presents numerical simulations of the map iop 10 foehn case 24 october 1999 for the lower alpine rhine valley which was one of the two target areas selected for foehn observations the simulations have been performed with a modified version of the fifth generation pennsylvania state university ncar mesoscale model mm5 most importantly the horizontal diffusion of temperature and the mixing ratios of water vapor and cloud water is computed truly horizontally rather than along the model surfaces as is the case in the original mm5 in the rhine valley the foehn case under consideration was characterized by a complex and rapidly changing flow field in the early morning the foehn was restricted to the upper parts of the valley while a cold air pool was present in the lower parts and around the exit toward lake constance during the following hours the cold air pool was gradually eroded and the foehn reached lake constance around noon only 3 h later a shallow cold front passing f

three dimensional idealized simulations of barrier jets along the southeast coast of alaska abstract three dimensional idealized simulations using the fifth generation pennsylvania state university ncar mesoscale model mm5 down to 6 km grid spacing were performed in order to understand how different ambient conditions wind speed and direction stability and inland cold pool and terrain characteristics impact barrier jets along the southeastern alaskan coast the broad inland terrain of western north america is important in alaskan jet development since it rotates the impinging flow cyclonically more coast parallel well upstream of the coast thus favoring more low level flow blocking while also adding momentum and width to the barrier jet near the steep coastal terrain the largest wind speed enhancement factor 1 9 2 0 in the terrain parallel direction relative to the ambient onshore directed wind speed occurs at relatively low froude numbers fr 0 3 0 4 these low froude numbers are associated with 10 15 m s 1 ambient wind speeds and wind directions orientated 30 45 from terra

major and trace element geochemistry and crustal evolution of archaean granodioritic rocks from eastern finland in the eastern part of central finland vast areas of granodioritic gneisses surround the ca 2 65 ga greenstone belts these granodioritic gneisses can be divided into two chronological and lithological units 1 grey gneisses 2 86 ga old with a typical archaean ttg tonalite trondhjemite granodiorite composition 2 augen gneisses 2 51 ga old with a granodioritic to granitic composition the sr and nd isotopic data preclude derivation of the grey gneisses from very much older continental material the highly fractionated ree distribution patterns la yb n 37 103 with few or no eu anomalies militate against a direct mantle origin the data suggest that the grey gneisses have most likely been derived by partial melting of short lived basaltic crustal material garnet bearing amphibolite it is estimated that the basaltic protoliths were separated from a mantle source no more than 150 ma before the melting such an early basaltic crust might have been completely destroyed or might have left some remnants which are now represented by mafic inclusions in the grey gneisses the augen gneisses have a relatively high isr value 0 705 which suggests an origin by recycling of pre existing crustal material grey gneisses their ree patterns are less fractionated than those of the grey gneisses and sometimes have negative eu anomalies using the sr isotopic and trace element data a model calculation suggests that the augen gneisses could have been derived by partial melting 50 of mixed protoliths with ttg greenstone belt volcanics in a proportion of 70 30 by volume followed by fractional crystallisation

an improved method for computing horizontal diffusion in a sigma coordinate model and its application to simulations over mountainous topography abstract a set of modifications is presented to reduce the unphysical impact of horizontal diffusion in numerical models with a terrain following sigma coordinate system at model levels sufficiently far away from the ground vertical interpolation is used to compute diffusion truly horizontally when the coordinate surfaces are sloping close to the ground where truly horizontal computation of diffusion is not everywhere possible without intersecting the topography a combination of one sided truly horizontal diffusion and orography adjusted diffusion along the sigma surfaces is used for most of the variables the latter means that the diffusion coefficient is reduced strongly when the grid points involved in the computation of horizontal diffusion are located at greatly different heights for temperature one sided horizontal diffusion is not used because it damps the slope wind circulation in an unphysical way however a temperature gradient correction is applied to the terrain following part of the t

topographic effects on radiation in the wrf model with the immersed boundary method implementation validation and application to complex terrain abstracttopographic effects on radiation including both topographic shading and slope effects are included in the weather research and forecasting wrf model and here they are made compatible w

cooling by melting precipitation in alpine valleys an idealized numerical modelling study in this study cooling by melting precipitation in alpine valleys is investigated this phenomenon can occur if the initial freezing level is sufficiently far below the crest height of the surrounding mountain ridges so that the air mass in the valley can become decoupled from the environmental flow in this case the latent heat required for melting the falling snow is continuously removed from the valley air until the snowline reaches the valley bottom an analytical heat budget calculation indicates that the reduction of the air volume related to the mountains encompassing a valley significantly reduces the amount of precipitation needed to cool the air in a valley compared to a plain region however the impact of this so called volume effect on the precipitation amounts is smaller than the geometrical volume factor frequently considered in the context of valley wind circulations numerical simulations with a highly idealized two dimensional model indicate an even smaller volume effect which might be partly due to numerical inaccuracies we also examined the impact of an air mass exchange between the upper part of the valley atmosphere and the environment it is found that the warm air advection resulting from this air mass exchange induces a bifurcation in the temperature evolution of the valley atmosphere if the temperature advection exceeds a certain threshold value depending on the precipitation intensity and on the height of the initial freezing level no significant cooling is obtained for weaker advective warming the valley atmosphere is cooled and the freezing level eventually reaches the valley bottom if the precipitation lasts long enough the transition zone between the two regimes is fairly narrow implying that forecasting real events of cooling by melting is subject to a large uncertainty our results also suggest that resolving the turbulent eddies that form below the melting layer is important for realizing the volume effect which implies that mesoscale numerical models with parametrized turbulence will systematically underestimate the cooling effect in alpine valleys copyright 2006 royal meteorological society

an immersed boundary method enabling large eddy simulations of flow over complex terrain in the wrf model abstractthis paper describes a three dimensional immersed boundary method ibm that facilitates the explicit resolution of complex terrain within the weather research and forecasting wrf model two interpolation methods trilinear and inverse distance weighting idw are used at the core of the ibm algorithm this work expands on the previous two dimensional ibm algorithm of lundquist et al which uses bilinear interpolation simulations of flow over a three dimensional hill are performed with wrf s native terrain following coordinate and with both ib methods comparisons of flow fields from the three simulations show excellent agreement indicating that both ib methods produce accurate results idw proves more adept at handling highly complex urban terrain where the trilinear interpolation algorithm fails this capability is demonstrated by using the idw core to model flow in oklahoma city oklahoma from intensive observation period 3 iop3 of the joint urban 2003 field campaign flow in oklahoma c

geochemistry of precambrian gneisses relevance for the evolution of the east antarctic shield archaean granulite facies orthogneisses of the napier complex in enderby land metamorphosed 3070 maago comprise two chemically distinct suites the more abundant mainly of tonalitic to granodioritic composition shows strong y depletion explicable by hydrous partial melting of a garnet bearing source garnet amphibolite or possibly eclogite it apparently represents new continental crust other gneisses predominantly of trondhjemitic to granitic s s composition do not show y depletion and have higher tio2 zr nb la ce and ga al and lower cao sr and mg mg total fe they probably originated by relatively dry melting of predominantly felsic crystal rocks both suites show evidence for loss of rb relative to k th and u during metamorphism late archaean 2800 ma amphibolite facies gneisses of macrobertson land are of undepleted type and may be representative of a higher crustal level than those of enderby land late proterozoic 1000 ma granulite facies gneisses of enderby land rayner complex are to a large extent remetamorphosed napier complex rocks of igneous derivation in contrast gneisses of similar age in macrobertson land include a much higher proportion derived either directly or by partial melting from sedimentary protoliths

high accuracy synchronism for seismic reflectors and 14c ages holocene prodelta succession of the kiso river central japan abstract horizons at 500 yr intervals for the past 6000 years can be inferred in two cores drilled along a high resolution seismic line in the prodelta of the kiso river ise bay central japan these horizon ages clearly indicate that a given seismic reflection line in the profile is isochronous synchronism between ages and reflectors in the succession is especially distinct for the interval from 5000 to 2500 yr bp despite the reflectors having inclined planes and having the same ages at different depths these data indicate that the kiso river delta prograded to form a downlap surface before the maximum flooding stage of the post glacial relative sea level rise at about 6000 yr bp delta progradation beginning late in the transgressive stage was caused by the flow of large amounts of sediment into this steep river that is part of the active japanese volcanic arc

the thermal circulation of a grand plateau sensitivity to the height width and shape of the plateau abstract idealized numerical simulations are presented to investigate the sensitivity of the thermal plateau circulation to the plateau height width and the presence of a mountain ridge encompassing the plateau the study concentrates on plateaus surrounded by land with the same surface properties so that the topography is the only source of differential heating for low plateaus it is found that the strength of the plateau circulation increases with the plateau height because the excess heating of the plateau increases with its height the plateau circulation reaches its maximum strength for plateau heights similar to the mixed layer depth over the surrounding lowlands for even higher plateaus the depth of the circulation decreases whereas the peak intensity exhibits little change the plateau height also controls the temporal evolution of the plateau circulation for low plateaus low level inflow is primarily found during the night because convection cells forming over the lateral slopes prevent a

evaluating implementations of the immersed boundary method in the weather research and forecasting model abstractthe terrain following coordinate system used by many atmospheric models can cause numerical instabilities due to discretization errors as resolved terrain slopes increase and the grid becom

reconstruction of holocene environmental changes in the kiso ibi nagara compound river delta nobi plain central japan by diatom analyses of drilling cores abstract holocene environmental changes were reconstructed by analyzing diatom assemblages from sediment cores ym kzn nk and mc from the nobi plain central japan five diatom assemblage zones were identified 1 at the beginning of the holocene freshwater species were dominant 2 then marine and brackish marine species increased indicating transgression 3 in the middle holocene proportions of marine and brackish marine species became almost constant with marine species dominant 4 marine species began to be replaced by freshwater species indicating marine regression as a result of delta progradation and 5 freshwater species again became dominant these diatom assemblages correlate with previously defined lithological units zones 1 and 2 with unit b fluvial to coastal plain zone 3 with unit c inner bay or prodelta zone 4 mainly with unit d1 delta front slope and zone 5 with units d2 delta front platform and e delta plain and flood plain although the shoreline migrated landward transgression faster than it migrated seaward regression transgressive diatom assemblage changes decrease in marine brackish water species took up to 1000 years whereas regressive changes required only a few hundred years diatom analysis is useful for reconstructing not only holocene sea level changes and sedimentary environments but also local geographic effects

thermally driven flows at an asymmetric valley exit observations and model studies at the lech valley exit the summertime thermal circulation in the region of an asymmetric valley exit is investigated by means of observations and high resolution model simulations the northeastward oriented alpine lech valley opening into the bavarian alpine foreland has an eastern slope exceeding the western slope by about 15 km northerly winds along the eastern slope are frequently observed reaching substantial strength during fair weather conditions a field experiment has been conducted to explore this phenomenon and to pinpoint the connection of the northeasterly flow to the lech valley wind circulation numerical simulations have also been carried out to support the interpretation of the observations it is found that the northerlies owe their existence to the dominantly easterly flow along the foothills of the alps which is partly induced by the alpine heat low but may be strengthened by favorable synoptic conditions examples for both situations will be discussed the diurnal flow in the lech valley has little obvious impact on these northeasterlies on days with moderate synoptic easterly flow a wake is present on the lee of the eastern slope of the exit region accompanied by a shear zone along the edge of the wake this shear zone is forced southward during the daytime because of thermally initiated pressure gradients between the alpine foreland and the alps leading to sudden wind changes in the exit area at the time of its passage

the impact of upstream blocking drainage flow and the geostrophic pressure gradient on the persistence of cold air pools idealized numerical simulations are performed to investigate dynamical mechanisms affecting the persistence of cold air pools in basins and valleys the first orography type considered is a shallow elongated basin located upstream of a mountain ridge for sensitivity tests the mountain ridge is removed the second type is a basin embedded in a plateau like mountain ridge in part of the simulations this basin has an outflow towards the lee side plain so as to assess the impact of the drainage flow the large scale flow is taken to be in geostrophic balance in the standard setting it is perpendicular to the basin and the ridge the main effect of a large scale pressure gradient is to induce a circulation within a cold air pool until the upper boundary of the cold pool is inclined such as to compensate for the ambient pressure gradient the cold air accumulates where the ambient pressure is lowest for a shallow basin this means that part of the cold air may be lost due to advection out of the basin the upstream influence of a mountain ridge in the lee of a shallow basin is found to be twofold it tends to deflect the low level flow towards the lower pressure leading to an additional ridge parallel force on the cold air pool on the other hand the absolute wind speed is reduced diminishing the turbulent mixing near the top of the cold pool the simulations show that the first effect prevails for ridge normal flow while second effect may dominate for other flow directions drainage flow out of a valley is found to be very important as it promotes the penetration of warm air into valleys very effectively it may cause a cold pool in a deep valley to disappear more quickly than a cold pool in a shallow basin sensitivity tests show that the persistence of a cold pool depends on its depth on its vertically integrated heat deficit and on the maximum heat deficit at the bottom of the cold pool copyright 2003 royal meteorological society

a new model to simulate the martian mesoscale and microscale atmospheric circulation validation and first results 1 the laboratoire de meteorologie dynamique lmd mesoscale model is a new versatile simulator of the martian atmosphere and environment at horizontal scales ranging from hundreds of kilometers to tens of meters the model combines the national centers for environmental prediction ncep national center for atmospheric research ncar fully compressible nonhydrostatic advanced research weather research and forecasting arw wrf dynamical core adapted to mars with the lmd general circulation model gcm comprehensive set of physical parameterizations for the martian dust co2 water and photochemistry cycles since lmd gcm large scale simulations are also used to drive the mesoscale model at the boundaries of the chosen domain of interest a high level of downscaling consistency is reached to define the initial state and the atmosphere at the domain boundaries a specific hybrid vertical interpolation from the coarse resolution gcm fields to the high resolution mesoscale domain is used to ensure the stability and the physical relevancy of the simulations used in synoptic scale mode with a cyclic domain wrapped around the planet the mesoscale model correctly replicates the main large scale thermal structure and the zonally propagating waves the model diagnostics of the near surface pressure wind and temperature daily cycles in chryse planitia are in accordance with the viking and pathfinder measurements afternoon gustiness at the respective landing sites is adequately accounted for on the condition that convective adjustment is turned off in the mesoscale simulations on the rims of valles marineris intense daytime anabatic 30 m s 1 and nighttime katabatic 40 m s 1 winds are predicted within the canyon corridors topographical channeling can amplify the wind a few kilometers above the ground especially during the night through large eddy simulations in gusev crater the model describes the mixing layer growth during the afternoon and the associated dynamics convective motions overlying gravity waves and dust devil like vortices modeled temperature profiles are in satisfactory agreement with the miniature thermal emission spectrometer mini tes measurements the ability of the model to transport tracers at regional scales is exemplified by the model s prediction for the altitude of the tharsis topographical water ice clouds in the afternoon finally a nighttime warm ring at the base of olympus mons is identified in the simulations resulting from adiabatic warming by the intense downslope winds along the flanks of the volcano the surface temperature enhancement reaches 20 k throughout the night such a phenomenon may have adversely affected the thermal inertia derivations in the region

accumulation of organic carbon in five brazilian lakes during the holocene abstract a comparative study was made of organic carbon accumulation in five lacustrine environments in brazil large open water lake ponds with floating meadows and marshes the most representative cores were used to calculate the accumulation of total organic carbon toc in the sediment over the past 12 000 cal years bp carbon accumulation rates were determined using the toc concentration sediment in situ density 14 c calibrated ages and the interpolated sedimentation rate cm year 1 or sediment accumulation rate g m 2 year 1 the c n ratio and microscopic observations were used to characterise the sedimentary organic matter recent toc accumulation in the lakes was estimated at 7 41 g m 2 year 1 by averaging the last 500 years this variation roughly correlated with the present day ratio of watershed area vs lake area indicating that nutrient input is important for the modern accumulation of organic matter the accumulation rates were greatest in lakes with floating macrophytes the largest lake dom helvecio with a strong thermal stratification low primary production and low carbon accumulation had relatively well preserved organic matter when its low watershed area lake area ratio was considered the general increase in carbon accumulation during the holocene followed the expansion of lakes and the development of a wetter climate due to a growing penetration of the atlantic and amazonian wet air mass over brazil driven by insolation changes this change in carbon accumulation was not controlled by the higher water and nutrient inputs alone more organic matter was decomposed when lake levels were low at the beginning of the holocene some lakes were also influenced by higher inputs of allochthonous organic matter during the early and middle holocene these inputs included high concentrations of charcoal fragments lake morphology and its changes as the lake level rose as well as the nature of primary producers strongly influenced the carbon accumulation rates our understanding of how climate changes are linked to changes in the lacustrine environment should not be based on measuring organic matter alone but requires a good description of the organic matter and other limnological parameters

quantitative analysis of land transformation in a holocene delta an example from the tama river lowland central japan abstract human activities such as the expansion of agricultural and urban land use on subaerial deltas and landfilling of subaqueous deltas have large impacts on holocene deltas here we quantified the volume of the holocene deltaic deposits in the tama river lowland located in the tokyo metropolitan area by analyzing 3872 existing borehole sections using gis and evaluated artificial land transformation the total volume of deltaic deposits accumulated during the past 9000 years was estimated to be 3925 106 m3 of which artificially deformed near surface material ad 676 106 m3 occupies approximately 17 this ratio is much larger than that in the nobi plain 4 6 in the nagoya metropolitan area suggesting that the impact of anthropogenic disturbance on the delta has been greater in tokyo than in the nagoya metropolitan area approximately 71 of ad is distributed in the seaward area where landfills were created mainly after the taisho period 1912 1926 the source of the ad is considered to be dredged soil construction waste soil and mountain sand the remaining 29 of ad occurred in the landward area floodplain and delta plain and likely originates from the in situ disturbed sediments of the delta plain and floodplain in addition to earth fill the seaward ad deposits including redeposition by dredging within the delta accumulated at a rate of 4 79 106 m3 year which is much higher than that of the accumulation of natural deltaic deposits during the holocene 0 36 106 m3 year this clearly shows that anthropogenic forcing has become a strong influence on geomorphological and sedimentological processes within the delta

geochemical evolution of archaean granulite facies gneisses in the vestfold block and comparisons with other archaean gneiss complexes in the east antarctic shield the vestfold block like other archaean cratons in east antarctica and elsewhere consists predominantly of felsic orthogneiss mossel and crooked lake gneisses with subordinate mafic granulite tryne metavolcanics and paragneiss chelnok supracrustals two major periods of continental crust formation are represented the mossel gneiss metamorphosed about 3 000 ma ago is mainly of tonalitic composition and is similar to much of the roughly coeval napier complex in enderby land the crooked lake gneiss was emplaced under high grade conditions about 2 450 ma ago and comprises a high proportion of more potassic rocks monzodioritic and monzonitic suites as well as tonalite and minor gabbro and diorite both mossel and crooked lake gneisses are depleted in y and have moderate to high sr ce y and ti y consistent with melting of a mafic source subducted hydrated oceanic crust leaving major residual hornblende garnet most crooked lake gneisses are more enriched in incompatible elements p sr la ce and particularly rb ba and k than mossel gneisses suggesting derivation from a more enriched mafic source the vestfold block contains few orthogneisses derived by melting of older felsic crustal rocks in marked contrast to the archaean napier complex and in particular southern prince charles mountains both mossel and crooked lake tonalites are strongly depleted in rb k th and u and have very low rb sr and high k rb more potassic orthogneisses are depleted in th u and to lesser extents rb tryne metavolcanics are depleted in th and rb but appear to have been enriched in k and probably na possibly during early low grade alteration

petrogenesis of archaean trondhjemites tonalites and granodiorites from eastern finland major and trace element geochemistry

sediment facies and holocene deposition rate of near coastal fluvial systems an example from the nobi plain japan abstract floodplains are a major component of present near coastal fluvial systems that have evolved in response to postglacial changes in climate and sea level knowledge of sedimentary facies and deposition rates on a centennial to millennial time scale is required for considering floodplain evolution two cores ap1 and ap2 were acquired from an abandoned channel of the ibi river and its natural levee on the nobi plain central japan sediment facies analysis electrical conductivity and radiocarbon dating of borehole samples showed that in both cores organic rich dark gray floodbasin mud overlies deltaic deposits dating to after approximately 3200 years calibrated radiocarbon age cal bp in relation to delta progradation the accumulation of floodbasin mud continued at the both sites until about 400 cal bp around 400 cal bp the mud was eroded by the overlying channel sand and gravel at ap1 and was covered by fine grained natural levee deposits at ap2 with an abrupt contact this timing is concordant with the historical record of avulsion of the ibi river during the keicho era ad 1596 1615 averaged aggradation rates at the ap1 and ap2 sites were approximately 2 2 and 3 2 mm yr respectively faulting related subsidence along the western edge of the plain has influenced these rates by creating accommodation averaged deposition rates differed greatly between the floodbasin and the levee suggesting that rapid aggradation of the natural levee also occurred on a centennial to millennial scale these empirical data may be useful for testing models of the architecture and evolution of near coastal fluvial systems

lewisian gneiss geochemistry and archaean crustal development models abstract the geochemistry of lewisian amphibolite facies gneisses from northwest scotland is described with particular reference to the rare earth elements ree and compared with the geochemistry of lewisian granulite facies gneisses the results show that there are no significant differences between laxfordian amphibolite facies and scourian granulite facies gneisses in terms of ree and other immobile trace elements at equivalent silica levels although the mobile radioactive heat producing elements k rb th u are significantly lower in the granulites in both types the basic gneisses have moderately fractionated ree patterns while the intermediate and acid gneisses have strongly fractionated ree patterns with low heavy ree abundances and decreasing levels of total ree with increasing sio 2 the most silicic gneisses develop large positive europium anomalies these gross chemical similarities between gneisses from intermediate amphibolite facies and lower granulite facies crustal levels constrain models for the evolution of the archaean crust the depletion of k rb cs th and u in granulites but not other incompatible trace elements cannot be explained by magmatic processes the positive eu anomaly in the more siliceous gneisses of both facies is a function of the primary processes of crustal generation and not secondary processes such as intracrustal melting or fractional crystallisation fractionation of radioactive heat producing elements from other trace elements is a result of granulite facies metamorphism with these elements being removed by an active fluid phase the apparent lack of partial melting in lower crustal granulites suggests a model for archaean crustal growth largely through underplating by primary tonalitic magmas

origin and evolution of the late precambrian high grade yaounde gneisses cameroon abstract the yaounde series is composed of low to high grade garnet bearing schists and gneisses belonging to the pan african north equatorial fold belt the high grade rocks consist of kyanite garnet gneisses and garnet plagioclase gneisses containing layers of calcsilicate rocks marbles quartzites and magnetite rich orthopyroxenites the chemical patterns of these rocks are those of a sedimentary sequence of shales and greywackes and minor dolomite rocks dolomitic marls evaporitic beds quartzites and iron rich sediments some volcanogenic greywackes may have been of alkaline affinity this sequence was probably deposited in shallow water near shore semi barred conditions which can be related either to an intracontinental distensive environment or to a passive margin at the northern edge of the congo craton the yaounde gneisses were deformed during two main tectonic phases the first phase d1 is marked by a layering s0 s1 resulting from tectonic transposition the second one d2 corresponds to tangential tectonics with isoclinal folds and flat lying shear zones associated with a s2 schistosity and a l2 lineation a third phase late d2 is marked by the development of low temperature mylonitic shears scarce wrench faults indicate later e w compression the d1 d2 transition is characterized by the emplacement of mafic and ultramafic rocks and by the development of high pressure granulite facies conditions t 750 800 c p 10 12 kbar these peak metamorphic conditions triggered a widespread migmatization dated at 565 22 ma and coeval with the d2 event the gradual decrease of the metamorphic conditions toward the south and the existence of a syn d2 retrograde inverse metamorphic gradient suggest that the overall structure of the yaounde series is a large tectonic nappe thrust onto the congo craton a geotectonic scheme for the north equatorial fold belt is discussed