circulations between mesoscale convective systems along a cold front abstract a frontal squall line that passed over the central united states on 14 15 june 1985 consisted of several primary mesoscale convective systems mcss with a prominent gap several hundred kilometers wide between two of them over central kansas and oklahoma an upper level jet streak crossed the front at right angles with the jet exit region centered in the gap surface upper air radar and satellite data are used to examine conditions contributing to this squall line gap all surface indicators e g a sharp wind shift line and strong low level moisture convergence pointed toward the development of new deep convection in the gap computations of vertical velocity using sounding data showed that the low level vertical motion was indeed upward there however strong subsidence existed aloft the demarcation between subsidence aloft and ascent at low levels was near the 0 c level where there was a concurrent inflow into the mcss a strong inversion existed near this level which effectively ca

a convective line with leading stratiform precipitation from bamex abstract on 31 may 2003 a front fed convective line with leading stratiform precipitation ffls was observed during the bow echo and mesoscale convective vortex experiment bamex the high resolution bamex measurements provided one of the first opportunities to thoroughly observe the characteristics of an ffls system the 31 may system had an overturning updraft during its early stages and produced leading stratiform precipitation as the system matured a jump updraft developed and the system began to produce trailing stratiform precipitation it appears that this transition was facilitated by a local decrease in the low level line perpendicular vertical wind shear over time as well as an increase in the surface cold pool s strength the bamex data further help to address the question of how ffls systems can be long lived when their inflow passes through the line leading precipitation preline soundings suggest a destabilization mechanism resulting from the vertical profile of cooling within the lea

momentum transport by a line of cumulonimbus abstract the vertical transport of horizontal momentum normal to a line of cumulonimbus observed during gate on 14 september 1974 is against the vertical momentum gradient contrary to the predictions of mixing length theory data from repeated aircraft passes normal to the line s axis at heights from 0 15 to 5 5 km are used to document the flux and determine its source the flux is concentrated in roughly a 25 km wide active zone just behind the leading edge of the line in kilometer scale convective updrafts accelerated upward by buoyancy and toward the rear of the line by mesoscale pressure forces the fall in mesoscale pressure from the leading edge to the rear of the active zone is mainly hydrostatic resulting from relatively high virtual temperatures and the 60 degree tilt of the leading edge from the vertical with the clouds at the surface well ahead of those aloft evaluation of the terms in the momentum flux generation equation confirms that the above process reflected by the velocity buoyan

formation of coastline features by large scale instabilities induced by high angle waves along shore sediment transport that is driven by waves is generally assumed to smooth a coastline this assumption is valid for small angles between the wave crest lines and the shore as has been demonstrated in shoreline models but when the angle between the waves and the shoreline is sufficiently large small perturbations to a straight shoreline will grow here we use a numerical model to investigate the implications of this instability mechanism for large scale morphology over long timescales our simulations show growth of coastline perturbations that interact with each other to produce large scale features that resemble various kinds of natural landforms including the capes and cuspate forelands observed along the carolina coast of southeastern north america wind and wave data from this area support our hypothesis that such an instability mechanism could be responsible for the formation of shoreline features at spatial scales up to hundreds of kilometres and temporal scales up to millennia

porosity evolution and crystallization driven fragmentation during weathering of andesite 1 a 10 m thick andesitic sill intrusion from the neuquen basin argentina shows spectacular examples of spheroidal weathering and liesegang banding the liesegang patterns demonstrate how andesite blocks initially cut out by a preweathering joint set are subdivided by fractures formed during the spheroidal weathering process the stresses that cause fracturing originate from the growth of ferrihydrite and calcite in the pore space of the andesite partly at the expense of original ilmenite amphibole and plagioclase the porosity evolution and fracture formation during progressive weathering was characterized by scanning electron microscopy studies x ray computed tomography and he and hg porosimetry fresh andesite has a porosity of approximately 8 and a major fraction 80 of the pore volume is composed of pores less than 10 m in diameter the extent of pore filling during weathering increases with pore size pores more than 100 m are almost completely filled by an intimate intergrowth of calcite and ferrihydrite whereas pores less than 10 m are filled less than 50 the fracturing associated with spheroidal weathering is caused by mineral growth in the largest pores which account for 10 20 of the total porosity the periodic precipitation of the weathering product to form liesegang bands indicates a significant supersaturation threshold before nucleation commences the increase in the weathering product growth rate with increasing size is therefore most likely due to higher nucleation probabilities in larger pores

a mathematical model of spit growth and barrier elongation application to fire island inlet usa and badreveln spit sweden a mathematical model of spit growth and barrier elongation adjacent to an inlet of arbitrary width supplied by sediment coming from longshore sediment transport was developed based on the spit growth model proposed by kraus 1999 the fundamental governing equation is the conservation equation for sand where the width of the spit is assumed constant during growth the portion of the longshore sediment transport feeding the spit has been estimated based on the ratio between the depth of the inlet channel and the depth of active longshore transport sediment transport from the channel due to the inlet flow as well as other sinks of sand e g dredging are taken into account measured data on spit elongation at fire island inlet united states and at badreveln spit sweden were used to validate the model the simulated results agree well with the measured data at both study sites where spit growth at fire island was restricted by the inlet flow and the growth at badreveln spit was unrestricted the model calculation for fire island inlet indicates that the dredging to maintain channel navigation is the major reason for the stable period observed from 1954 to 1994 at the fire island barrier the average annual net longshore transport rate at the eastern side of the fire island inlet obtained in this study was about 220 000 m 3 yr of which approximately 165 000 m 3 yr 75 of the net longshore transport is deposited in the inlet feeding the spit growth whereas the remaining portion 25 is bypassed downdrift through the ebb shoal complex c 2011 elsevier ltd all rights reserved less

microstructure and porosity evolution during experimental carbonation of a natural peridotite abstract carbonation experiments t 100 200 c pco2 14 6 19 4 mpa were performed under closed system conditions on a natural peridotite from almklovdalen w norway to investigate the microstructure and porosity evolution as a function of reaction progress the unreacted samples cubes of 2 5 3 cm3 were composed mainly of forsteritic olivine 80 90 vol clinochlore orthopyroxene amphibole and chromite initial porosities were on the order of 6 8 due to the presence of abundant inter and intragranular microfractures microstructural observations after 7 42 days of experimental treatment showed that olivine was by far the most reactive phase after 7 days at 100 c no carbonate products were formed but longer reaction times produced small amounts of magnesite on the surface and within the fracture network of the peridotite cubes increasing temperatures led to faster reactions and pore space filling by magnesite in addition replacement rims up to 50 m thick composed of magnesite and amorphous silica formed around individual olivine grains the replacement began with the formation of an amorphous silica layer that retained the shapes of the initial olivine grains this layer remained permeable during the reaction as it allowed further dissolution of the underlying olivine increasing extents of carbonation were accompanied by decreasing porosities and enhanced cementation of grain boundaries about 50 of the initial porosity was closed when carbonation reached about 10 the reacted samples showed no evidence of reaction induced cracking indicating that the carbonation reaction was self limiting in our experiments these results may have important implications for the efficiency of in situ co2 sequestration in peridotites

early growth of mesoscale convective complexes a meso β scale cycle of convective precipitation abstract the evolution of precipitation fields associated with several mesoscale convective complexes mccs has been inferred from radar reflectivity data in almost all cases examined including those described in the literature the system s convective ensemble undergoes a marked modulation in intensity on a meso time scale during the early growth stage of its meso scale life cycle this scale convective cycle is most evident in time series of volumetric precipitation rate due to convective echo and is characterized by a temporal maximum followed by a minimum 0 5 1 h later superimposed on an otherwise several hour monotonically increasing trend while the latter is due to a concurrent several hour increase in the areal extent of convective echo the scale perturbation is dominated by a modulation in intensity of the existing convective entities that the system constitutes at that stage of growth the scale cycle also marks the onset of a sustained increased growth rate of the mcc s s

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

interactions between a developing mesoscale convective system and its environment part i observational analysis this paper is the first in a two part series in which the interactions between a growing mesoscale convective system mcs and its surrounding environment are investigated the system studied here developed in northeastern colorado on 19 july 1993 and propagated into kansas as a long lived nocturnal mcs high resolution dual doppler and surface mesonet data collected from this system are discussed in part i while the results of a numerical simulation are discussed in part ii the observations show that organized mesoscale surface pressure and flow features appeared very early in the lifetime of this system long before the development of any trailing stratiform precipitation most of the stratiform anvil advected ahead of the convective line in the strong upper tropospheric westerlies in accordance with this most of the mid and upper tropospheric storm relative flow behind the line remained westerly or rear to front despite the westerlies the strongest flow perturbations with respect to the ambient winds developed to the rear of the line the structure of these perturbations was similar to the upper tropospheric front to rear and midtropospheric rear to front flows typically found in more mature leading line trailing stratiform systems the presence of these perturbations on the upwind side of the convective line indicates that gravity wave propagation was primarily responsible for their development

the relationship of surface pressure features to the precipitation and airflow structure of an intense midlatitude squall line abstract observations from the oklahoma kansas preliminary regional experiment for storm central ok pre storm have been used to document the surface pressure features accompanying an intense midlatitude squall line with trailing stratiform precipitation three well known features are observed a pre squall mesolow a squall mesohigh and a wake low particular attention is given to the wake low its life cycle and association with the trailing stratiform portion of the squall line during the formative stage the pressure field to the rear of the squall line mesohigh is relatively flat with only weak stratiform precipitation present as the squall line enters the developing to mature stages a pronounced wake low appears at the back edge of the surface stratiform precipitation area the squall line at this time is characterized by a strong rear inflow jet descending from the upper troposphere as far as 500 km behind the leading convective line to the lower troposphere just behind the line the trailin

summer surface flow characteristics over northeast colorado abstract surface wind data from the program for regional observing and forecasting services profs have been analyzed to investigate the diurnal wind flow pattern over the broad drainage are of the south platte river in northeast colorado a consistent diurnal pattern appears in monthly averages as well as on most undisturbed individual days and is similar to the classic descriptions of mountain valley wind flows it is observed that rather than occurring simultaneously at all elevations downslope to upslope and upslope to downslope surface flow transitions along the front range of northeast colorado begin near the foothills of the rocky mountains and propagate eastward across the plains during the summer months local confluence is found at midday along major east west ridges in the region e g cheyenne ridge and palmer lake divide consequently in addition to the north south continental divide these east west ridges are preferred regions for initial afternoon thunderstorm development the late a

paleowind 11 000 bp directions derived from lake spits in northern michigan we report on the characteristics of several previously unstudied late pleistocene spits in northern lower michigan each spit developed as strong waves eroded a headland or island within the main and or later stages of glacial lake algonquin most have ese to wnw orientations with prominent recurved hooks at their ends some are as long as 20 km sedimentologically the spits contain thick several meters or more sequences of sand and well rounded gravel we suggest that summertime winds during the spits formation 11 800 to 10 500 bp were both very strong and dominantly from the e and se based on the following data 1 their ese source or head of the spit to wnw orientation 2 the presence of steep wave cut bluffs on the east sides of the islands and headlands and 3 spit locations on the northeastern shore of michigan s lower peninsula coupled with their absence on the northwestern shore just 100 km away wind direction data provided by these spits agree with paleoclimatic models that suggest that the laurentide ice sheet had developed a strong anticyclonic circulation the near lack of archeological sites from this time period in the northern lower peninsula which was surrounded by lake algonquin at that time supports the notion that the climate of northern lower michigan was inhospitably cold and very windy in the late pleistocene

subarctic physicochemical weathering of serpentinized peridotite abstract frost weathering is effective in arctic and subarctic climate zones where chemical reactions are limited by the reduced availability of liquid water and the prevailing low temperature however small scale mineral dissolution reactions are nevertheless important for the generation of porosity by allowing infiltration of surface water with subsequent fracturing due to growth of ice and carbonate minerals here we combine textural and mineralogical observations in natural samples of partly serpentinized ultramafic rocks with a discrete element model describing the fracture mechanics of a solid when subject to pressure from the growth of ice and carbonate minerals in surface near fractures the mechanical model is coupled with a reaction diffusion model that describes an initial stage of brucite dissolution as observed during weathering of serpentinized harzburgites and dunites from the feragen ultramafic body fub se norway olivine and serpentine are effectively inert at relevant conditions and time scales whereas brucite dissolution produces well defined cm to dm thick weathering rinds with elevated porosity that allows influx of water brucite dissolution also increases the water saturation state with respect to hydrous mg carbonate minerals which are commonly found as infill in fractures in the fresh rock this suggests that fracture propagation is at least partly driven by carbonate precipitation dissolution of secondary carbonate minerals during favorable climatic conditions provides open space available for ice crystallization that drives fracturing during winter our model reproduces the observed cm scale meandering fractures that propagate into the fresh part of the rock as well as dm scale fractures that initiate the breakup of larger domains rock disintegration increases the reactive surface area and hence the rate of chemical weathering enhances transport of dissolved and particulate matter in the weathering fluid and facilitates co2 uptake by carbonate precipitation our observations have implications for element cycling and co2 sequestration in natural gravel and mine tailings

simulated convective lines with parallel stratiform precipitation part i an archetype for convection in along line shear abstract this article the first of two describing convective lines with parallel stratiform ps precipitation addresses the basic kinematic and precipitation features of these systems the ps mode appears to be the preferred organizational structure in environments with line parallel vertical wind shear this archetype for long lived convective systems has received relatively little attention to date and yet it is frequently implicated in flash flooding because it entails both the along line movement of hydrometeors and back building convective development as a reality check this paper presents conventional observations of the wind and reflectivity fields associated with an archetypal ps system from 2 may 1997 thereafter analyses of idealized numerical simulations serve as the basis for a more detailed investigation of ps systems internal structures and processes the observations and simulations suggest several unique aspects of the ps structure the environment s vertically sheared 3d wind prof

upscale evolution of mcss doppler radar analysis and analytical investigation abstract the development of two small mesoscale convective systems mcss in northeastern colorado is investigated via dual doppler radar analysis the first system developed from several initially isolated cumulonimbi which gradually coalesced into a minimal mcs with relatively little stratiform precipitation the second system developed more rapidly along an axis of convection and generated a more extensive and persistent stratiform echo and mcs cloud shield in both systems the volumetric precipitation rate exhibited an early meso scale convective cycle a maximum and subsequent minimum followed by reintensification into a modest mature stage this sequence is similar to that noted previously in the developing stage of larger mcss by mcanelly and cotton they speculated that the early meso convective cycle is a characteristic feature of development in many mcss that is dynamically linked to a rather abrupt transition toward mature stage structure this study presents kinematic evidence in suppo

in situ carbonation of peridotite for co2 storage the rate of natural carbonation of tectonically exposed mantle peridotite during weathering and low temperature alteration can be enhanced to develop a significant sink for atmospheric co2 natural carbonation of peridotite in the samail ophiolite an uplifted slice of oceanic crust and upper mantle in the sultanate of oman is surprisingly rapid carbonate veins in mantle peridotite in oman have an average 14c age of 26 000 years and are not 30 95 million years old as previously believed these data and reconnaissance mapping show that 104 to 105 tons per year of atmospheric co2 are converted to solid carbonate minerals via peridotite weathering in oman peridotite carbonation can be accelerated via drilling hydraulic fracture input of purified co2 at elevated pressure and in particular increased temperature at depth after an initial heating step co2 pumped at 25 or 30 c can be heated by exothermic carbonation reactions that sustain high temperature and rapid reaction rates at depth with little expenditure of energy in situ carbonation of peridotite could consume 1 billion tons of co2 per year in oman alone affording a low cost safe and permanent method to capture and store atmospheric co2

triple doppler analysis of a discretely propagating long lived high plains squall line abstract a nonsevere squall line that developed on 21 june 1993 along the northern foothills of the colorado rocky mountains is analyzed using a series of triple doppler analyses this squall line developed in a relatively dry environment characterized by weak low level but strong upper level vertical shear of the horizontal winds the drier thermodynamic profile as characterized by a higher lifting condensation level and weak low level shear resulted in convection forming not along but rather 7 10 km behind the leading edge of the shallow cold pool the strong upper level shear established a predominantly leading anvil this led to a suppression zone immediately ahead of the leading line which in turn resulted in a discrete mode of propagation of the squall line three different cycles were observed each cycle had a distinct line of convective cells that initiate intensify and then decay in each case the new cells developed 20 40 km out ahead of the decaying line of the previous cycle many studi

simulated convective lines with leading precipitation part i governing dynamics this article the first of two describing a study in which the authors used idealized numerical simulations to investigate convective lines with leading precipitation addresses the dynamics governing the systems structures and individual air parcels accelerations within them it appears that although unconventional systems with inflow passing through their line leading precipitation can be stable and long lived lower tropospheric inflowing air in the simulations ascends overturns in deep updrafts and subsequently carries its water content forward from the convective line where it gives rise to the leading precipitation region although relatively strong wind shear in the middle and upper troposphere accounts for a component of the downshear acceleration and hence overturning of air parcels in the simulated updrafts a mature system with leading precipitation also renders both persistent and periodic pressure anomalies that contribute just as much many of these accelerations which govern the overall system structure are largely transient and are lost when averaged over multiple convective cycles this article explains the dynamics that govern the transient updrafts and downdrafts within the systems including a precipitation cutoff mechanism that governs their multicellular periods

a numerical investigation of the organization and interaction of the convective and stratiform regions of tropical squall lines abstract a set of 13 two dimensional numerical simulations based on the 22 and 23 june soundings from the convectionprofonde tropicale in 1981 copt81 experiment in west africa is used to study the organization and interactionof the convective and stratiform regions of squall line type convective systems the initial wind profiles arecharacterized by the african easterly jet aej and the tropical easterly jet tej located at about 3 5 km and14 km respectively the physical processes that generate and maintain the mesoscale inflow at the rear of squall line type mesoscaleconvective systems are thereby examined horizontal potential temperature gradients generated by a combinationof latent heat release in the convective region and unsaturated mesoscale descent both modulated by evaporation cause a horizontal pressure gradient and generate horizontal line parallel vorticity the rear inflow is a consequenceof these processes the convective activity induces a significant upscale influence ahead of the

carbonation of ca bearing silicates the case of wollastonite experimental investigations and kinetic modeling abstract carbonation reactions of wollastonite have been investigated in experiments conducted at conditions relevant to geologic co 2 sequestration in subsurface environments t 90 c and pco 2 25 mpa experiments were performed in batch reactors on single mineral powders of selected grain size either in supercritical co 2 or in aqueous solutions with different alkalinities the main reaction products were calcite and amorphous silica calcite occurred either as a compact continuous coating of small crystals in the case of supercritical co 2 and in circum neutral ph aqueous solutions or as isolated larger crystals in acidic aqueous solutions measured extents of carbonation were faster in aqueous solutions than in supercritical co 2 extents of carbonation in aqueous acidic solutions were modelled using a geochemical code incorporating kinetic parameters for wollastonite dissolution and calcite precipitation taken from the literature comparison with experimental results shows that in aqueous solutions wollastonite dissolution is the rate limiting step of the carbonation reaction and that silica layers have only a minor passivation effect on the overall reaction rate in acidic solutions secondary calcite coating has only a minor effect on carbonation extent whereas the experimental data in circum neutral ph aqueous solutions are consistent with dissolution rates inhibited by the observed dense calcite coating a geochemical code incorporating a modified reactive surface model successfully accounted for this passivation effect the more efficient carbonation in acidic than in circum neutral ph solutions is thus ascribed to differences in microstructures of the secondary calcite layers due to differences in supersaturation states of calcite when its precipitation begins inhibitory effects of dense calcite coating are also invoked for limiting carbonation extents of wollastonite in supercritical co 2 secondary calcite precipitations are thus shown to play a major role both as coatings of reactive surfaces and by maintaining large undersaturation with respect to wollastonite dissolution

intense fracturing and fracture sealing induced by mineral growth in porous rocks article i nfo mineral precipitation in the pores of a rock may exert a force which is called crystallization pressure this process has been studied experimentally and results bring a new look on the way fractures may develop and seal in natural systems cylindrical core samples of porous limestone and sandstone were left for several weeks in contact with an aqueous solution saturated with sodium chloride at 30 or 45 c under axial normal stress in the range 0 02 0 26 mpa the fluid was allowed to rise in the core samples by capillary forces up to a controlled height where evaporation and precipitation occurred the uniaxial deformation of the samples was measured using high resolution displacement sensors the samples were characterized using computed x ray tomography allowing therefore imaging in 3d the intensity and localization of the damage two kinds of damage could be observed firstly small rock fragments were peeled from the sample surface secondly

formation of mesoscale lines of pirecipitation severe squall lines in oklahoma during the spring abstract four distinct kinds of severe mesoscale convective line development are identified in oklahoma during the spring based on the analysis of an 11 year period of reflectivity data from the national severe storms laboratory s 10 cm radar in norman oklahoma the primary classes of fine formation are broken line back building broken areal and embedded areal each is described in detail along with illustrative examples comparisons are made with other observations and with numerical model simulations the former two classes of line formation have been previously documented while the latter two have not only the broken areal squall line has been realistically simulated numerically the environment for each of the types of line development was determined from data from the standard national weather service surface and upper air networks and from special rawinsonde launches it was found that broken line formation tends to occur along cold fronts in a multicell environment while back building occur

control of alongshore oriented sand spits on the dynamics of a wave dominated coastal system holocene deposits northern gulf of lions france article the maguelone shore extends along the northern coast of the gulf of lions west of the rhone delta and east of high gradient coastal streams that have provided most of the clastic sediments to the gulf of lions margin since the early miocene this 10 km wide area is constituted by a small coastal watershed 15 km long in low lying carbonate hills a kilometre wide marsh a sandy beach barrier and a shoreface experiencing local low sedimentation rates this onshore offshore transition zone is a key area to understand the relationships between erosion by pass deposition and preservation processes unlike the neighbouring rhone deposits that display numerous thick deltaic sequences related to a continuous sediment flux the maguelone shore exhibits peculiar sedimentary bodies the analysis of about 250 km of new vhr seismic profiles acquired over the study area 9 short cores and outcrops data allowed us to determine the three dimensional high resolution geometry of the coastal system tracts from quaternary to present day this revealed dominant denudation processes in the upstream catchments associated with the formation of incised valleys during quaternary lowstands in addition this study investigates the erosion and deposition mechanisms controlled by littoral hydrodynamics that have been taken place on this shore since the last transgression in particular metre high and hundreds of metre long sandy bodies constructed by alongshore hydrodynamics were identified and their effect on the morphodynamics of the whole littoral system is discussed the maguelone shore can be used as an experimental study for onshore offshore dynamics under the influence of microtidal wave current hydrodynamics and very low river derived sediment flux during a eustatic cycle geometry of system tracts across flood plain to shoreface is usually considered to be controlled by relative sea level changes and is successfully analysed with 2d sequence stratigraphy cross shore models it is observed that in areas like the maguelone shore traditional sequence stratigraphy methods might not be fully relevant and need to integrate alongshore hydrodynamical processes

dissolution assisted pattern formation during olivine carbonation olivine and pyroxene bearing rocks in the oceanic crust react with hydrothermal fluids producing changes in the physical characteristics and behaviors of the altered rocks notably these reactions tend to increase solid volume reducing pore volume permeability and available reactive surface area yet entirely hydrated and or carbonated rocks are commonly observed in the field we investigate the evolution of porosity and permeability of fractured dunites reacted with co2 rich solutions in laboratory experiments the alteration of crack surfaces changes the mechanical and transport properties of the bulk samples analysis of three dimensional microstructural data shows that although precipitation of secondary minerals causes the total porosity of the sample to decrease an interconnected network of porosity is maintained through channelized dissolution and coupled carbonate precipitation the observed microstructure appears to be the result of chemo mechanical coupling which may provide a mechanism of porosity maintenance without the need to invoke reaction driven cracking

a cross shore model of barrier island migration over a compressible substrate abstract barrier islands that overlie a compressible substrate such as islands in deltaic environments or those that overlay mud or peat deposits load and consolidate the underlying subsurface through time the elevation and aerial extent of these islands are reduced making them more susceptible to future inundation and overwash sand washed over the island and onto back barrier marsh or into the bay or estuary begins the consolidation process on a previously non loaded substrate with time dependent consolidation as a function of the magnitude of the load duration of load and characteristics of the substrate the result is an increase in the overwash migration breaching and segmentation of these islands this research developed a two dimensional cross shore numerical model for evolution of a sandy barrier island that spans durations of years to decades as a function of erosion runup overwash migration and time dependent consolidation of the underlying substrate as a function of loading by the island the model was tested with field data and then applied to evaluate the effects of a compressible substrate on long term barrier island evolution results illustrate that barrier islands overlying a compressible substrate are more likely to have reduced dune elevation due to consolidation incur overall volumetric adjustment of the profile to fill in compressed regions outside the immediate footprint of the island and experience increased overwash and migration when the dune reaches a critical elevation with respect to the prevalent storm conditions

low froude number flow past three dimensional obstacles part i baroclinically generated lee vortices abstract we study the flow of a density stratified fluid past a three dimensional obstacle using a numerical model our special concern is the response of the fluid when the froude number is near or less than unity linear theory is inapplicable in this range of froude number and the present numerical solutions show the rich variety of phenomena that emerge in this essentially nonlinear flow regime two such phenomena which occupy parts i and ii of this study are the formation of a pair of vertically oriented vortices on the lee side and a zone of flow reversal on the windward side of the obstacle the ice vortices have been explained as a consequence of the separation of the viscous boundary layer from the obstacle however this boundary layer is absent by design in the present experiments and lee vortices still occur we argue that a vertical component of vorticity develops on the lee side owing to the tilting of horizontally oriented vorticity produced baroclinically as the isentropes deform in r

control of serpentinisation rate by reaction induced cracking abstract serpentinisation of mantle rocks requires the generation and maintenance of transport pathways for water the solid volume increase during serpentinisation can lead to stress build up and trigger cracking which ease fluid penetration into the rock the quantitative effect of this reaction induced cracking mechanism on reactive surface generation is poorly constrained thus hampering our ability to predict serpentinisation rate in geological environments here we use a combined approach with numerical modelling and observations in natural samples to provide estimates of serpentinisation rate at mid ocean ridges we develop a micromechanical model to quantify the propagation of serpentinisation induced cracks in olivine the maximum crystallisation pressure deduced from thermodynamic calculations reaches several hundreds of megapascals but does not necessary lead to crack propagation if the olivine grain is subjected to high compressive stresses the micromechanical model is then coupled to a simple geometrical model to predict reactive surface area formation during grain splitting and thus bulk reaction rate our model reproduces quantitatively experimental kinetic data and the typical mesh texture formed during serpentinisation we also compare the model results with olivine grain size distribution data obtained on natural serpentinised peridotites from the marum ophiolite and the papuan ultramafic belt papua new guinea the natural serpentinised peridotites show an increase of the number of olivine grains for a decrease of the mean grain size by one order of magnitude as reaction progresses from 5 to 40 these results are in agreement with our model predictions suggesting that reaction induced cracking controls the serpentinisation rate we use our model to estimate that at mid ocean ridges serpentinisation occurs up to 12 km depth and reaction induced cracking reduces the characteristic time of serpentinisation by one order of magnitude down to values comprised between 10 and 1000 yr the increase of effective pressure with depth also prevents cracking which positions the peak in serpentinisation rate at shallower depths 4 km above previous predictions

the role of silicate surfaces on calcite precipitation kinetics abstract the aim of this study is to illuminate how calcite precipitation depends on the identity and structure of the growth substrate calcite was precipitated at 25 c from supersaturated aqueous solutions in the presence of seeds of either calcite or one of six silicate materials augite enstatite labradorite olivine basaltic glass and peridotite rock calcite saturation was achieved by mixing a cacl2 rich aqueous solution with a nahco3 na2co3 aqueous buffer in mixed flow reactors containing 0 5 2 g of mineral rock or glass seeds this led to an inlet fluid calcite saturation index of 0 6 and a ph equal to 9 1 although the inlet fluid composition flow rate and temperature were identical for all experiments the onset of calcite precipitation depended on the identity of the seeds present in the reactor calcite precipitated instantaneously and at a constant rate in the presence of calcite grains calcite precipitated relatively rapidly on labradorite olivine enstatite and peridotite mainly composed of mg olivine surfaces but more slowly on augite and basaltic glass calcite precipitation rates however became independent of substrate identity and mass over time and all rates approach 10 9 68 0 08 mol s for 10 day long experiments and 10 9 21 0 2 mol s for 70 day long experiments scanning electron microscope images showed olivine enstatite and peridotite surfaces to be covered extensively with calcite coatings at the end of the experiments less calcite was found on labradorite and augite and the least on basaltic glass in all cases calcite precipitation occurs on the mineral rock or glass surfaces calcite precipitation on these surfaces however negligibly affects the dissolution rates of the silicate grains these results support ultramafic and basalt carbonation as a long term carbon storage strategy as calcite readily precipitates on the surfaces of minerals contained in these rocks without inhibiting their dissolution

a long lived mesoscale convective complex part ii evolution and structure of the mature complex abstract an eight day episode in august 1977 is described wherein 14 mesoscale convective complexes mccs developed in the central united states including one to the immediate ice of the rocky mountains on each day of the episode in part i of this article the daytime genesis of one of these systems was traced from its pre convective roots in the mountains of central colorado to its incipient mcc stage on the plains of eastern colorado in this paper its continued nocturnal development into a large mcc over kansas is followed satellite imagery shows that this system remained coherent for at least three days as it passed off the east coast and across the western atlantic ocean analysis is focused on the mature stage of this and a second mcc in the episode in order to compare their major dynamic features to those of similar midlatitude systems reported in the literature and also to previous studies of tropical mesoscale convective systems many of the important characteristics of midlatitude mccs fo

an observational analysis of a developing mesoscale convective complex abstract dual doppler radar surface mesonet satellite and upper air sounding data from the 1985 preliminary regional experiment for storm central field experiment are used to analyze the early growth stages of a mesoscale convective complex mcc that developed in the network on 3 june 1985 this mcc was characterized by a complex distribution of convective clusters and intervening stratiform echo as it grew from its initial stage to the typical meso scale cloud shield structure at its mature stage the mcc exhibited two very different states of organization as it grew the early state was characterized by a relatively weak and disorganized surface pressure pattern and a highly variable three dimensional mesoscale flow structure the later state was characterized by a well developed mesohigh wake low surface pressure pattern and more organized mososcale flow fields the evolution between these two regimes occurred about 1 h after the upper level cloud shield reached mcc proportions and manifested its

enhanced co2 mineral sequestration by cyclic hydraulic fracturing and si rich fluid infiltration into serpentinites at malentrata tuscany italy abstract the magnesite deposits of malentrata tuscany italy were derived from serpentinite silicification carbonation of the ligurian ophiolite and represent a natural analogue of in situ co 2 mineral sequestration carbonation of magnesium silicate minerals e g serpentine olivine at temperatures below 200 c is an exothermal process involving incorporation of carbon dioxide into stable carbonates e g magnesite dolomite serpentinites at malentrata were transformed to a brownish friable rock characterized by the occurrence of opal chromian montmorillonite fe rich magnesite and minor iron sulfides and oxides widespread lenses of cohesive rocks occur within the altered serpentines resulting from the complete silicification of the protolith the pervasive alteration of serpentinite was accompanied by the formation of a network of magnesite and dolomite veinlets and large magnesite dolomite veins along major structures field observations petrography and mineral chemistry define the following crystallization sequence in the major veins i early microgranular fe poor magnesite ii comb textured fe rich magnesite and dolomite cementing the early brecciated magnesite vein infill and iii late quartz chalcedony and rare opal in the cavities the mineral assemblage observed both in veins and in host rock is indicative of low temperature hydrothermal alteration driven by si and co 2 rich fluids under relatively low ph conditions pervasive and cyclic hydraulic fracturing maintained a high structural permeability during the whole hydrothermal event creating conduits for the input and output fluids the concomitant presence of co 2 and silica in the fluid enhanced the congruent dissolution of serpentine and hampered immediate carbonate deposition the mg bearing solutions were focused out of the reactor zone and promoted massive carbonate veining along the main structural discontinuities this two steps reaction dissolution of serpentinite followed by carbonate precipitation outside the reacting volume seems to be very efficient and provide new insights on in situ and ex situ induced mineral carbonation and its industrial applications

reaction induced fracturing during replacement processes replacement processes are common transformation mechanisms in minerals and rocks at a variety of conditions and scales the underlying mechanisms are in general poorly understood but both mechanical and chemical processes are thought to be important replacement of leucite kalsi2o6 by analcime naalsi2o6 h2o is common in silica poor igneous rocks a 10 increase in volume is associated with the replacement process and this generates stresses that eventually cause fracturing of the reacting leucite experimentally reacted leucite samples display characteristic fracturing patterns that include both spalling of concentric onion skin like layers near the reacting interface and the formation of cross cutting often hierarchically arranged sets of fractures that divide the remaining leucite into progressively smaller domains these structures may explain the patchy alteration patterns observed in natural leucite samples and similar so called mesh textures associated with the serpentinization of olivine grains during hydration of mafic or ultramafic rocks they are also strikingly similar to larger scale patterns formed during spheroidal weathering processes a simple discrete element model illustrates the mechanics that control the formation of such systems and shows how these replacement processes may be accelerated due to the generation of new reactive surface area by hierarchical fracturing processes

morphodynamics of intertidal bars in wave dominated coastal settings a review abstract intertidal bar systems are ubiquitous features on wave dominated beaches in coastal settings with a significant 1 m tidal range depending primarily on the wave conditions and the tidal range and to a lesser extent on the nearshore gradient they can assume a variety of forms slip face bars represent the most pronounced and dynamic intertidal bar morphology and are generally found on their own around the mean high tide level they usually form low on the intertidal beach after storm induced beach erosion and develop into a berm under prolonged calm wave conditions low amplitude ridges and sand waves represent multiple bar morphologies the bars occur across the entire intertidal profile and they remain present throughout the year multiple intertidal bars tend to be rather subdued and relatively static especially sand waves and their origin remains unclear the morphological response of intertidal bars to changing wave conditions is largely forced bars build up and migrate onshore under calm waves and are flattened and may migrate offshore during storms the morphological response is however significantly affected by relaxation time effects and morphological feedback particularly on beaches with multiple intertidal bars despite their morphological differences the intertidal bar types exhibit pronounced similarities in their morphodynamics sediment transport processes and morphological response are principally controlled by the tidal water levels on the beach because these together with the offshore wave energy level and the beach morphology determine the type intensity and duration of the wave processes operating on the cross shore profile it is the dominant importance of tidal water level variations and wave processes in shallow water depths swash and surf zone bores rather than wave height variability and deeper water wave processes breaking and shoaling waves that constitutes the main difference between intertidal and subtidal bar morphodynamics

spatially variable carbonation reactions in polycrystalline olivine abstract carbon dioxide co 2 injection into olivine rich mafic and ultramafic rocks is expected to result in the precipitation of divalent metal carbonate minerals permanently storing the co 2 underground previous experiments that used unconsolidated forsterite mg 2 sio 4 particles in experimental investigations of reactions with water and carbon dioxide have been useful for determining the identity rates of formation and spatial location of carbonate mineral reaction products however there remains a need for information regarding the influence of the internal pore structure and grain boundary surfaces on the extent and locations of these reactions in dense aggregates we conducted several experiments at 100 c and 100 bar co 2 using sintered san carlos olivine fo 90 and pure forsterite fo 100 cylinders and we documented the type and spatial distribution of the reaction products timing of carbonation was measured using in situ 13 c nmr spectroscopy without removing the sample from the reactor ex situ solid state nmr spectroscopy raman spectroscopy and electron microscopy were used to examine reacted samples and precipitates within 15 days magnesite is observed only on the surface of fo 90 after 53 and 102 days of reaction magnesite and amorphous silica are observed as a crust around the entire fo 100 cylinder and as isolated layers within the sample the spatial transition from an amorphous silica layer to the host fo 100 indicates that the development of amorphous silica did not impede further forsterite dissolution while earlier studies documented localized reactions at the grain scale the development of distinct zones of magnesite and amorphous silica suggest that divalent metal cations are mobile during carbonation of olivine grain boundaries pore structure and geochemical gradients strongly influence the locations of silicate mineral dissolution and carbonate mineral precipitation even in the absence of advective transport or confinement the clear spatial distribution of precipitates observed in this study indicates that carbonation in heterogeneous reservoirs may be strongly affected by grain scale microstructure

controls on rock weathering rates by reaction induced hierarchical fracturing abstract weathering of rocks takes place through complex processes involving an intimate coupling between mechanical disintegration of the rocks and interactions between the exposed rock surface the hydrosphere and the biosphere it is still poorly understood how this coupling affects weathering rates and patterns produced by weathering here we show that the observed spheroidal weathering patterns in basaltic intrusions dolerites in the karoo basin in south africa are created through volume expanding reactions which set up stresses that not only lead to spalling of spheroidal layers of rock but also drive a large scale hierarchical fracturing process by which the dolerite is continuously undergoing domain division the fracture processes generates new reactive surface area in a self accelerating manner thus providing a first order control on the total weathering rate

co2 sequestration and extreme mg depletion in serpentinized peridotite clasts from the devonian solund basin sw norway the conglomerates of the solund devonian basin of sw norway contain numerous locally up to 20 vol peridotitic clasts with concentric mm to 10 cm thick zones of varying red to black color the peridotite clasts show a clear alteration related textural evolution the least altered rocks are partly serpentinized peridotites showing a typical mesh texture with veins of serpentine magnesite and ni rich magnetite surrounding olivine fo91 relicts and its mg depleted clay like alteration product deweylite assemblage in the more advanced ophicarbonate stage the mesh cells contain calcite silica and are surrounded by talc in the final stage quartz calcite and hematite dominate the mineralogy and occur together with minor amounts of chromite talc cr chlorite and cr hydroandradite in tandem with this textural evolution is a decrease in mgo from 40 to 2 5 wt and a cao increase from 1 to 35 wt all peridotite clasts are characterized by high cr and ni concentrations the chemistry and the textural evolution show that the clasts formed by an extreme mg mobilization from the peridotite with development of secondary porosity and subsequent precipitation of calcite mgo removed from the clasts after burial is in part consumed by replacement reactions in the sediment matrix around the clasts where mg free minerals e g almandine are replaced by mg bearing minerals e g talc calculated apparent 87 sr 86 sr ratios of the clasts at 385 ma 0 7124 0 7139 corresponding to the inferred age of sediment deposition and incipient clast alteration indicate interaction with diagenetic basinal fluids we explain the reaction history as a three stage process involving a partial serpentinization of olivine in an oceanic environment b breakdown of olivine relicts to the deweylite assemblage resulting in mobilization of mgo under near surface conditions in a tropical devonian climate and c further mg mobilization and replacement of the deweylite assemblage by calcite and quartz after diagenesis sedimentary basins with abundant weathered peridotite represent potential sites for a permanent co2 storage by formation of calcite in a low temperature environment 2010 elsevier ltd all rights reserved

modelling the morphology of sandy spits abstract the shape dimensions and growth rate of an accumulating sandy spit is investigated by a theoretical and experimental study the idealised case of a spit growing without change of form under a constant wave forcing is considered the longshore wave driven sediment transport is taken to be dominant in the formation of the spit the shape of the spit is first described by an analytical one line model for the coastline development and by a simple littoral drift model the analytical model is valid for a spit with so large dimensions that quasi uniform conditions can be applied it is found that with this assumption the dimensions of the spit cannot be determined the width and shape of a finite spit is therefore determined from simulations with an area model for the wave driven current and sediment transport along the spit in this case the curvature effects from the spit on the longshore sediment transport inertia of the longshore current wave focussing are includes several solutions for a uniformly growing spit may exist and it is assumed that the fastest growing spit is the one to emerge the simulations indicate the width of the spit to be proportional to the width of the surf zone in experiments conducted in a wave tank an accumulating spit was formed at the down drift end of a uniform stretch of coast exposed to waves approaching at an angle the spit approached equilibrium dimensions when a constant wave climate was applied the radius of curvature of the spit varied according to the height of the incoming waves

reaction enhanced permeability during retrogressive metamorphism abstract retrogressive metamorphism is in most cases associated with influx of external fluids into igneous or metamorphic rocks with low to negligible initial permeabilities thus fluid migration is associated with some process that creates the necessary channels for migration one such mechanism is associated with the volume changes resulting from volatilization reactions petrographic studies of a partly serpentinized troctolite from the duluth complex in minnesota reveal how the increase in solid volume associated with hydration of olivine phenocrystals generates an extensive network of microfractures in the surrounding plagioclase dominated matrix this microfracture network allows hydrous fluids to penetrate further into the rock a 2 d spring network model illustrates how expanding polygons or non spherical grains in an elastically deforming matrix cause dilatant microfracturing and porosity generation even if the overall stresses are compressive the model emphasises how fluid infiltration may be promoted by stress heterogeneities set up by metamorphic reactions

forsterite dissolution and magnesite precipitation at conditions relevant for deep saline aquifer storage and sequestration of carbon dioxide the products of forsterite dissolution and the conditions favorable for magnesite precipitation have been investigated in experiments conducted at temperature and pressure conditions relevant to geologic carbon sequestration in deep saline aquifers although forsterite is not a common mineral in deep saline aquifers the experiments offer insights into the effects of relevant temperatures and pco2 levels on silicate mineral dissolution and subsequent carbonate precipitation mineral suspensions and aqueous solutions were reacted at 30 c and 95 c in batch reactors and at each temperature experiments were conducted with headspaces containing fixed pco2 values of 1 and 100 bar reaction products and progress were determined by elemental analysis of the dissolved phase geochemical modeling and analysis of the solid phase using scanning electron microscopy infrared spectroscopy and x ray diffraction the extent of forsterite dissolution increased with both increasing temperature and pco2 the release of mg and si from forsterite was stoichiometric but the si concentration was ultimately controlled by the solubility of amorphous silica during forsterite dissolution initiated in deionized water the aqueous solution reached supersaturated conditions with respect to magnesite however magnesite precipitation was not observed for reaction times of nearly four weeks magnesite precipitation was observed in a series of experiments with initial solution compositions that simulated extensive forsterite dissolution the precipitation of magnesite appears to be limited by the process of nucleation and nucleation requires a critical saturation index between 0 25 and 1 14 at 95 c and 100 bar pco2 magnesite precipitation is fastest in the presence of an initial magnesite seed although magnesite precipitates do form on the surfaces of forsterite particles the presence of the forsterite surface does not significantly accelerate magnesite precipitation relative to solid free systems

experimental evidence for chemo mechanical coupling during carbon mineralization in ultramafic rocks abstract storing carbon dioxide in the subsurface as carbonate minerals has the benefit of long term stability and immobility ultramafic rock formations have been suggested as a potential reservoir for this type of storage due to the availability of cations to react with dissolved carbon dioxide and the fast reaction rates associated with minerals common in ultramafic formations however the rapid reactions have the potential to couple with the mechanical and hydraulic behavior of the rocks and little is known about the extent and mechanisms of this coupling in this study we argue that the dissolution of primary minerals and the precipitation of secondary minerals along pre existing fractures in samples lead to reductions in both the apparent young s modulus and shear strength of aggregates accompanied by reduction in permeability hydrostatic and triaxial deformation experiments were run on dunite samples saturated with de ionized water and carbon dioxide rich solutions while stress strain permeability and pore fluid chemistry were monitored sample microstructures were examined after reaction and deformation using scanning electron microscopy sem the results show that channelized dissolution and carbonate mineral precipitation in the samples saturated with carbon dioxide rich solutions modify the structure of grain boundaries leading to the observed reductions in stiffness strength and permeability a geochemical model was run to help interpret fluid chemical data and we find that the apparent reaction rates in our experiments are faster than rates calculated from powder reactors suggesting mechanically enhanced reaction rates in conclusion we find that chemo mechanical coupling during carbon mineralization in dunites leads to substantial modification of mechanical and hydraulic behavior that needs to be accounted for in future modeling efforts of in situ carbon mineralization projects

seven doppler radar and in situ analysis of the 25 26 june 2015 kansas mcs during pecan abstractthis case study analyzes a nocturnal mesoscale convective system mcs that was observed on 25 26 june 2015 in northeastern kansas during the plains elevated convection at night pecan pro

the influence of convectively generated thermal forcing on the mesoscale circulation around squall lines abstract the dynamical processes that determine the kinematic and thermodynamic structure of the mesoscale region around 2d squall lines are examined using a series of numerical simulations the features that develop in a realistic reference simulation of a squall line with trailing stratiform precipitation are compared to the features generated by a steady thermal forcing in a dry simulation with no microphysical parameterization the thermal forcing in the dry simulation is a scaled and smoothed time average of the latent heat released and absorbed in and near the leading convective line in the reference simulation the mesoscale circulation in the dry simulation resembles the mesoscale circulation in the reference simulation and around real squall lines it includes an ascending front to rear flow a midlevel rear inflow a mesoscale up and downdraft an upper level rear to front flow ahead of the thermal forcing and an upper level cold anomaly to the rear of the thermal forcing it is also shown t

multiscale analysis of a mature mesoscale convective complex abstract a multiscale analysis reveals diverse atmospheric structure and processes within a mesoscale convective complex mcc observed during the oklahoma kansas preliminary regional experiment for storm central pre storm experiment this midlatitude system was the second in a series of four mccs that developed and traveled along a quasi stationary frontal zone over the central united states on 3 4 june 1985 objectively analyzed mesoscale upper air soundings encompassing the mcc are interpreted in tandem with more detailed dual doppler radar measurements that disclose the storm s internal airflow and precipitation structure the mature mcc is found to include a variety of local environments and associated weather ranging from tornadic thunderstorms to more linear convective bands and widespread chilling rains a corresponding spectrum of mesoscale ver6cw motion profiles is documented these findings are related to previous composite based portrayals of mccs as well as detailed case studies of simple

bathymetric control of holocene spit migration in a lacustrine environment wave processes are well known for developing spit systems in large or elongated lakes by inducing longshore sediment transport for spit migration while bathymetric interaction is less studied in

reaction assisted hierarchical fracturing during serpentinization abstract hierarchical fracture patterns are the result of a fracturing process that successively divides rocks into smaller domains in a 2d outcrop section such fracture patterns are characterized by four sided domains and t junctions where new fractures stop growing at right angles to pre existing fractures here we describe fracturing of mm to dm thick serpentinized orthopyroxenite dykes in a dunite matrix from the leka ophiolite complex in nord trondelag norway the fracturing process is driven by volume changes associated with the serpentinization of the dunites during this process the orthopyroxenite dykes are extended by the expanding dunite and undergo considerable fracturing the resulting fracture patterns are hierarchical the cumulative distributions of fracture lengths show a scaling behavior that lies between a log normal and power law fractal distribution this is consistent with a simple fragmentation model in which domains are divided according to a top hat distribution of new fracture positions within unfractured domains reaction assisted hierarchical fracturing is also likely to be responsible for other structures commonly observed in serpentinized ultramafic rocks including the mesh textures observed in individual olivine grains and the high abundance of rectangular domains at a wide range of scales this mechanism may provide first order controls on fluid migration rates in a wide variety of geological settings

dissolution of olivine during natural weathering abstract naturally weathered olivine occurring as phenocrysts in hawai ian volcanic rocks from several volcanic centers and regolith outcrop settings and as tectonized olivines from several metadunite bodies in the southern appalachian blue ridge are all similarly corroded by natural weathering conical funnel shaped etch pits occur as individual pits base to base pairs of cone shaped pits or en echelon arrays etch pit shapes and orientations in the smallest etch pit arrays visible in conventional scanning electron microscopy resemble even smaller features previously reported from transmission electron microscope investigations of olivine weathering etch pits occur in samples with chemical and or mineralogical evidence of weathering and or are associated with or proximal or directly connected to fractures or exposed outcrop surface and therefore are formed by weathering and not inherited from pre weathering aqueous alteration e g serpentinization iddingsitization of these parent rocks many etch pits are devoid of weathering products natural weathering of olivine is surface reaction limited similarity of corrosion forms from naturally weathered olivine from multiple igneous and metamorphic parent rock bodies suggests that olivine weathers in the same manner regardless of its specific crystallization recrystallization history eruption weathering exposure ages of the olivine s host rock and the local regolith history

the interface scale mechanism of reaction induced fracturing during serpentinization peridotite serpentinization has first order effects on geochemical and petrophysical processes in the lithosphere this process induces intensive fracturing generating fluid pathways to facilitate the hydration of vast amounts of originally impermeable rocks but the mechanism linking interfacial reaction processes with fracture propagation has not been understood by combining microstructural characteristics of olivine lizardite serpentinization with fundamental aspects of interface coupled dissolution precipitation and crack growth theory we propose a microstructurally consistent self propagating fracturing mechanism fracturing is driven by stress generated from the growth and transformation of a metastable amorphous proto serpentine phase where stress is localized within surface perturbations etch pits and coalesced etch pits that originate from the anisotropic dissolution of olivine water migration into fractures reiterates the process resulting in hierarchical olivine grain segmentation our results indicate that the advancement of serpentinization at the grain scale is independent of solid state diffusion and does not rely on external forces

phase transitions in the mgco2h2o system and the thermal decomposition of dypingite mg5 co3 4 oh 2 5h2o implications for geosequestration of carbon dioxide abstract the application of hydrated mg carbonates as co2 sequestering media is a pressing environmental challenge which requires a deep knowledge of the phase transitions occurring in the mg co2 h2o system as well as the thermal and structural stability of these phases in this paper we investigate the phase transition of nesquehonite mgco3 3h2o to dypingite mg5 co3 4 oh 2 5h2o occurring after an incubation of months and years in solution at ambient conditions however as the kinetics of this process resulted to be slow the phase transition of dypingite to hydromagnesite mg5 co3 4 oh 2 4h2o was investigated at non ambient conditions using in situ real time high resolution x ray powder diffraction moreover the thermal behaviour of dypingite and its decomposition have been also investigated with the aim to explore the appropriateness of this carbonate and the products of its decomposition as sinks of anthropogenic carbon dioxide the results suggest that the dypingite structure remains unaffected up to 438 k at temperature above this threshold dypingite transforms into hydromagnesite a further increase in temperature converts the well ordered hydromagnesite into a collapsed form at 528 k the heating of dypingite does not produce a loss of co2 as the intermediate phases have the same co2 mg molar ratio the final product of the heating is periclase mgo its nucleation occurs at temperature ranging from 573 to 663 k and it becomes the only phase in the temperature range 633 678 k these results highlighted that dypingite assures a stable storage of co2 in the conditions that prevail at the earth s surface moreover the transformation of dypingite in more thermodynamically stable hydromagnesite occurring without release of co2 enhances the safety of carbon dioxide disposal in solid form furthermore the observed volume changes during phase transitions which in turn could affect the porosity and permeability of the geological reservoir have been evaluated in order to improve the prediction of the safe and permanent storage of co2 in underground

the role of convectively generated rear inflow jets in the evolution of long lived mesoconvective systems abstract in this study the structure of convectively generated rear inflow jets and their role in the evolution of long lived mesoconvective systems are investigated through an analysis of idealized three dimensional simulations using a nonhydrostatic cloud model rear inflow jets are generated within these systems in response to the upshear tilting of the convective circulation as the horizontal buoyancy gradients along the back edge of the expanding system create a circulation that draws midlevel air in from the rear within this framework a wide range of rear inflow strengths and structures are produced depending on the magnitude of the ambient convective available potential energy cape and the vertical wind shear in general for environments characterized by weak to moderate vertical wind shear and weak to moderate cape the rear inflow jet descends and spreads along the surface well behind the leading edge of the gust front and the subsequent convective activity becomes weaker however for e

olivine dissolution rates a critical review abstract the dissolution rates of olivine have been considered by a plethora of studies in part due to its potential to aid in carbon storage and the ease in obtaining pure samples for laboratory experiments due to the relative simplicity of its dissolution mechanism most of these studies provide mutually consistent results such that a comparison of their rates can provide insight into the reactivity of silicate minerals as a whole olivine dissolution is controlled by the breaking of octahedral m2 oxygen bonds at or near the surface liberating adjoining sio44 tetrahedra to the aqueous fluid aqueous species that adsorb to these bonds apparently accelerate their destruction for example the absorption of h h2o and at some conditions selected aqueous organic species will increase olivine dissolution rates nevertheless other factors can slow olivine dissolution rates notably olivine dissolution rates are slowed by lowering the surface area exposed to the reactive aqueous fluid by for example the presence and or growth on these surfaces of either microbes or secondary phases the degree to which secondary phases decelerate rates depends on their ability to limit access of the reactive aqueous fluids to the olivine surface it seems likely that these surface area limiting processes are very significant in natural systems lowering olivine surface reactivity in many environments compared to rates measured on cleaned surfaces in the laboratory a survey of the literature suggests that the major factors influencing forsteritic olivine dissolution rates are 1 ph 2 water activity 3 temperature and 4 mineral fluid interfacial surface area evidence suggests that the effects of aqueous inorganic and organic species are relatively limited and may be attributed at least in part to their influence on aqueous solution ph moreover the observed decrease in rates due to the presence of secondary mineral coatings and or the presence of microbes can be attributed to their ability to decrease olivine surface area directly exposed to the reactive aqueous fluid as the reactivity of forsterite surfaces are spatially heterogeneous its surface area normalized rates will tend to decrease as it dissolves even in the absence of a mineral or bacterial coating each of these factors limits and or influences the application of forsterite dissolution to 1 enhanced weathering efforts 2 mineral carbonation and 3 the low temperature generation of hydrogen or hydrocarbons via the oxidation of its divalent iron

shoreline forms and deposits in gallocanta lake ne spain abstract the quaternary evolution of gallocanta lake central iberian chain spain is deduced from comparison between ancient deposits and present shoreline sedimentary forms present shoreline dynamics in the lake are controlled by persistent winds parallel to the long axis of the lake creating wave fronts at the shore and net longshore currents present lake level fluctuations lead to a shoreline progradation during periods of lowering and to a partial erosion of ancient deposits during periods of rising level quaternary deposits in the region are represented by stepped lacustrine terraces which reflect a greater extension of the lake in the past the sedimentological analysis of such deposits shows that their origin is linked to past lake level fluctuations short term e g seasonal to multi annual fluctuations would have led to the building of a single terrace level by shoreline progradation processes long term fluctuations related to regional climatic changes would have led to the present landscape of stepped terraces reflecting a progressive aridification of the area

large scale meteorological conditions associated with midlatitude mesoscale convective complexes abstract objective analyses of composited meteorological conditions attending ten mesoscale couvective complexes mcc reveal a number of distinctive characteristics and important interactions with the large scale environment the systems appear to be linked to eastward progression of a weak middle tropospheric short wave trough initial thunderstorms develop within a region of mesoscale convergence and lifting that is apparently forced primarily by low level warm advection the mcc system acquires mesoscale organization while it moves eastward ahead of the short wave trough diabatic heating eventually produces a system that is warm core in the middle troposphere and cold core in upper levels the mature mcc exhibits many similarities to tropical convective systems although it occurs within a considerably different large scale setting inflow within the lower half of the troposphere feeds convection within a region characterized by significant net upward mass flux and widespread precipitation thickne

washover fan and brackish bay sedimentation in the berriasian valanginian of bornholm denmark abstract the robbedale and jydegard formations berriasian valanginian of the danish island of bornholm represent a 100 m thick vertical sequence from shoreface foreshore and beach sands of a high energy coast through backbarrier flat bay margin pond and distal washover fan sand and clay brackish bay clay to fluvial sands the longevity of the backbarrier bay system c 10 myr thickness 100 m of the bay deposits and apparently stacked nature of the facies belts suggest a relatively stationary position of the individual subenvironments with only minor progradation this reflects strong tectonic control of the depositional system during an important phase of synsedimentary block faulting and wrenching along the tornquist zone the importance of washover fan sands in the backbarrier deposits and the lack of tidal indications in the whole sequence suggest a microtidal regime a system of migrating mud banks formed in shallow water on the landward side of the barrier the bay waters varied from almost fresh to brackish and anoxic conditions commonly occurred at the bottom adverse living conditions for most organisms in the bay caused seasonal possibly toxic dinoflagellate blooms resulting in mass mortality of infaunal bivalves bay margin ponds underwent periodic desiccation leading to mass mortality of freshwater gastropods as a general scenario it is envisaged that longshore currents redistributed bedload from a major delta and formed an extensive nw se barrier spit which partly enclosed a major bay to the ne the barrier was breached during heavy storms and the sand transported along the resulting washover channels was deposited on the backbarrier flat made up of the subaerial parts of coalescent washover fans enormous amounts of suspension load from the delta travelled further along the barrier to be deposited in the lee side bay

gravity waves compensating subsidence and detrainment around cumulus clouds abstract gravity waves play an important role in the redistribution of heat and moisture in a deep convecting cloud field we explore this role in a two dimensional numerical experiment on a simple moist convecting system consisting of an isolated long lasting nonprecipitating cloud in a calm atmosphere with no surface forcing the cloud develops a horizontally averaged density variation with height which is neutrally buoyant with respect to a moist adiabatic the buoyancy difference between the cloud and the undisturbed sounding produces circulations that can be understood as spreading gravity waves which adjust the environmental buoyancy to be equal to the cloud buoyancy by compensating subsidence unlike the circulations inside clouds this adjustment takes place without turbulent mixing hence the buoyancy adjustment time t1 during which the environment comes into rough buoyant equilibrium with the clouds is much shorter than the mixing time t2 which it takes a tracer initially concentrated at s

influence of amorphous silica layer formation on the dissolution rate of olivine at 90 c and elevated pco2 for mitigating against rising levels of atmospheric co2 carbonation of m2 bearing silicates has been proposed as a possible option for sequestering co2 over long time spans due to its rapid far from equilibrium dissolution rate and its widespread occurrence in mafic and ultramafic rocks olivine has been suggested as a potentially good candidate for achieving this goal although the efficacy of the carbonation reaction still needs to be assessed with this as a goal the present study aims at measuring the carbonation rate of san carlos olivine in batch experiments at 90 c and pco2 of 20 and 25 mpa when the reaction was initiated in pure water the kinetics of olivine dissolution was controlled by the degree of saturation of the bulk solution with respect to amorphous silica this yet unrecognized effect for olivine was responsible for a decrease of the dissolution rate by over two orders of magnitude in long term 45 days carbonation experiments with a high surface area to solution volume ratio sa v 24 600 m 1 the final composition of the solution was close to equilibrium with respect to sio2 am independent of the initial concentration of dissolved salts nacl and naclo4 ranging between 0 and 1 m and with an aqueous mg si ratio close to that of olivine no secondary phase other than a ubiquitous thin 40 nm si rich amorphous layer was observed these results are at odds with classic kinetic modeling of the process due to experimental uncertainties it was not possible to determine precisely the dissolution rate of olivine after 45 days but the long term alteration of olivine was indirectly estimated to be at least 4 orders of magnitude slower than predicted taken together these results suggest that the formation of amorphous silica layers plays an important role in controlling the rate of olivine dissolution by passivating the surface of olivine an effect which has yet to be quantified and incorporated into standard reactive transport codes

in situ sequestration of atmospheric co2 at low temperature and surface cracking of serpentinized peridotite in mine shafts abstract the investigation of carbonate formation at low temperature during weathering of ultramafic rocks has become increasingly important as it represents an analog study for a cost efficient carbon disposal strategy here we present new insight into carbonate formation under subarctic surface conditions obtained from extensively carbonated chromite mine shafts in the feragen ultramafic body e norway carbonation proceeded by formation of mm to cm thick carbonate surface coatings on the serpentinized peridotite host rock the surface coatings consist in most cases of pure lansfordite mgco 3 5h 2 o and sometimes nesquehonite mgco 3 3h 2 o heavy o and c isotopes are strongly enriched in the carbonate coatings relative to drip water samples from the mines and water samples from subaerial ponds the major element composition of the water samples reveal that infiltrating rainwater reacts rapidly with the peridotite mainly due to brucite dissolution within the mines discharging alkaline water forms thin films on walls and ceilings that evaporate upon circulation of cold dry air in mines with only one opening the carbonation is limited to the entrance area in mines with a more efficient air circulation due to multiple entrances carbonation is found throughout the mine evaporation of the mine water results in lansfordite saturation and precipitation and is accompanied by a rayleigh type distillation effect causing enrichment of the heavy c and o isotopes in the liquid from which the carbonates precipitate formation of the carbonate coatings involved fragmentation of the underlying serpentinite substrate fragmentation proceeded by subcritical cracking i e by a combination of substrate weakening due to brucite dissolution and stress build up due to lansfordite precipitation in fractures close to the surface reaction induced fracturing represents a positive feedback mechanism as it creates additional reactive surface area during the carbonation mining operations in the area ceased in the mid 1920s indicating that the described carbonation occurs on a time scale relevant for the disposal of anthropogenic co 2

interactions between a developing mesoscale convective system and its environment part ii numerical simulation the 19 july 1993 mesoscale convective system mcs discussed in part i was simulated using the regional atmospheric modeling system rams the model was initialized with variable physiographic and atmospheric data with the goal of reproducing the convective system and its four dimensional environment four telescopically nested moving grids allowed for horizontal grid spacings down to 1 67 km on the cloud resolving grid comparisons with the analysis show that the propagation evolution and structure of this mcs were well simulated the simulation is used to further investigate the interactions between this mcs and its surrounding environment in part i the doppler derived winds indicated that upshear westward propagating gravity waves left uppertropospheric front to rear and midtropospheric rear to front flow perturbations in their wake a similar flow structure developed in the simulated mcs and unlike the doppler results the low frequency waves that produced it were resolved in the data in the simulation much of the convectively generated temperature and momentum perturbations propagated westward with the waves leaving a warm wake in the clear air trailing the system although the gravity waves traveled rearward the perturbation flow in their wake was not strong enough to reverse the upper tropospheric storm relative winds thus most of the anvil condensate advected ahead of the convective line as the mcs encountered the low level jet the midtropospheric upward mass flux increased but gravity wave motions became less detectable the upper tropospheric anvil pushed westward into the strong flow as the system expanded into a characteristically oval shape temperature and momentum perturbations propagated rearward along with the anvil in a disturbance that resembled an advective outflow unlike the gravity waves this disturbance became almost stationary with respect to the ground and it retained its continuity through the rest of the simulation vertical cross sections indicate that a large slab of convectively processed air had detrained into the upper troposphere prior to this event much of the warm temperature anomalies generated within the convective towers either remained in the updrafts or propagated outward with the gravity waves early on individual updrafts were relatively erect and although condensate did detrain eastward in the forward anvil the temperature anomalies did not propagate with it in contrast convective updrafts associated with the expanding oval anvil disturbance were more continuous and they tilted strongly westward with height

experimental study of the carbonation of partially serpentinized and weathered peridotites abstract carbonation of partially serpentinized and weathered peridotites was studied experimentally under hydrothermal conditions t 200 c p co 2 130 180 bars experiments were performed in a closed system using whole rock drill core samples height 1 cm diameter 1 cm as starting material the initial samples were composed mainly of meshwork serpentine relicts of primary olivine and an olivine weathering product deweylite assemblage two types of solutions each with a total salt content corresponding to that of average seawater 35 g l dissolved salts were used 1 a na ca cl solution 12 5 g l cacl2 22 5 g l nacl and 2 a nacl solution 35 g l nacl after 15 25 days of experimental treatment the samples were partly covered with carbonates in addition noticeable carbonation reactions had occurred below the sample surfaces within zones with thicknesses up to 250 m in the na ca cl solution both the olivine relicts and the deweylite assemblage were partly replaced by calcite along the surrounding serpentine veins however the extent of calcitization was found to be considerably larger for the deweylite assemblage than for the olivine bulk fluid analyses show an increase in the mg and si concentrations with reaction time in the nacl solution the deweylite assemblage was partly dissolved resulting in large voids within the reaction zone in contrast the olivine was replaced by magnesite under the conditions of our experiments the meshwork serpentine was not reactive but aided fluid infiltration into the rock samples the experimentally produced microtextures closely resemble those found in natural examples our study elucidates the mechanisms by which carbonates form in ultramafic rocks under relatively high p co 2 t conditions and particularly in the presence of ca bearing aqueous solutions the existence of a serpentine meshtexture and the presence of weathering products formed from primary mg silicates may have significant beneficial effects on in situ co2 mineral sequestration in ultramafic rocks

frontal wave like evolution in some mesoscale convective complexes abstract in some mesoscale convective complexes mccs the convective regions assume a configuration that resembles a frontal wave while in other systems the configuration is not classifiable we examined the evolution of the internal structure and flow of two mccs that were part of an episode of systems that propagated along a stationary front and in which the convective activity evolved from a chaotic to a frontal wave like pattern the development of mesoscale vorticity and its possible relationship to the spatial patterns are explored each system developed two dissimilar convective bands that together formed an open wave pattern the greatest number of convective clusters and the greatest midlevel convergence and high level divergence were found in a core region the apex of the wave where the bands intersected the north south convective line was less enduring than the core convection or the cast west band it evolved from outflow boundaries of the early storms preceding the mesosystem a conce

experimental study of mg rich silicates carbonation at 400 and 500 c and 1 kbar the reactivity of olivines orthopyroxenes and serpentines chrysotile with co2 rich fluids was experimentally studied at 400 500 c and 1 kbar nacl levels of formation of solid carbonate phases were measured both by analysing the recovered gas phase and by step heating of the solid samples carbonation levels of several percents per hour from 3 to 57 in 4 h depending upon experimental conditions were measured with increasing efficiency in the order orthopyroxene chrysotile olivine in the case of olivine a positive impact of water fugacity and salinity on carbonation levels was evidenced microstructures of the samples showed that the carbonation reaction proceeded by dissolution precipitation a coupling between solid carbonate production mostly as magnesite and olivine serpentinisation was demonstrated isotopic compositions of carbon in gas phases and carbonates were measured they were found to be consistent with mass balance calculations additionally suggesting the existence of an accessory carbon bearing phase carrying negative 13c signatures this phase was identified by transmission electron microscopy as an ill ordered graphite phase which would account for about 15 of carbon mineral under these conditions

numerical study of an observed orogenic mesoscale convective system part 1 simulated genesis and comparison with observations abstract the interaction of topographically induced thermally and mechanically driven diurnal flow regimes in the lee of the rockies is shown to lead to the growth of a mesoscale convective system mcs an organic mcs observed during the 1977 combined south park area cumulus experiment and high plains experiment is numerically simulated with a two dimensional nonhydrostatic cloud model covering spatial scales of 1000 km in this numerical investigation meso meso and meso scales of motion are represented simultaneously as a result interesting features of cloud mesoscale interaction are predicted that cannot be represented in cloud parameterization frameworks based on the results of this simulation a six stage conceptual model of orogenic development is given

rear inflow in squall lines with trailing stratiform precipitation abstract the relative airflow and accompanying precipitation structure of squall lines trailed by mesoscale regions of stratiform rain are examined with emphasis on the occurrence of rear inflow i e the intrusion of environmental air into these storms across the trailing precipitation boundary three cases from kansas and oklahoma provide examples of strong rear inflow which crosses the back edge of the stratiform precipitation area at relative speeds exceeding 10 m s 1 the vertical profiles of relative flow at the trailing precipitation boundary of these three systems were remarkably similar with the rear inflow confined to a jet like layer centered at about 550 mb doppler radar data for two of these cases showed that the rear inflow jet occupied a continuous channel extending from middle levels at the back edge of the stratiform region to lower levels of the leading convective region where it merged with outflow from convective downdrafts to bolster the leading gust front strong front to rea

meso β scale characteristics of an episode of meso α scale convective complexes abstract a variety of meso scale 20 200 km 6 h convective complex mcc are described the analysis is based on a typical episode of mccs in the central united states thunderstorms in the mcc are generally well organized into meso scale convective features the larger mccs are typically preceded by several of these meso convective clusters or bands which tend to be aligned along linear meso scale features such as the eastern slope of the rockies or thermodynamic discontinuities evident in hourly surface or satellite data the intense development of these larger systems involves the growth merger and interaction of those meso convective feature located nearest the intersection of the meso axes along which they are aligned throughout the mature phase of the mcc multiple meso convective components may persist within the more uniform meso cloud shield as expanding regions of str

mesoscale organization of springtime rainstorms in oklahoma abstract radar reflectivity and raingage data obtained during six springtimes indicate the types of mesoscale organization that occur in association with major rain events in oklahoma at least 25 mm of rain in 24 h over an area exceeding 12 500 km2 in these storms the primary rain area is found to be a contiguous region of precipitation 10s to 100s of km in scale that consists partly of deep convection and partly of stratiform rain the patterns of rain formed by the convective and stratiform areas comprise a continuous spectrum of mesoscale structures about two thirds of the cases examined exhibited variations on the type of organization in which convective cells arranged in a moving line are followed by a region of stratiform rain storm organization was graded according to the degree to which it matched an idealized model of this leading line trailing stratiform structure the precipitation pattern was further graded according to whether its structure was relatively symmetric with respect to an a

reaction induced porosity and onset of low temperature carbonation in abyssal peridotites insights from 3d high resolution microtomography abstract in a drillcore sample of serpentinized harzburgite from the uppermost oceanic crust mid atlantic ridge odp leg 209 site 1270 we demonstrate using high resolution 3d microtomography that micron sized open cavities are present the development of porosity is interpreted to result from dissolution of brucite and or olivine petrographic observations indicate that voids are integrated in a network of carbonate veins the formation of which is linked to changing alkalinity in conjunction with dissolution reactions partial carbonate filling of pore spaces indicates that under static conditions low temperature carbonation leads to clogging of fluid pathways and thus to a reduction in permeability electron microprobe analyses show that the inner walls of open voids are lined with fe rich precipitates we propose that the iron in those phases was released by brucite or olivine dissolution and was subsequently oxidized and precipitated as ferric hydroxide thermodynamic computations show that this process may be a potential source of catabolic energy for microorganisms inhabiting serpentinites the proposed carbonation mechanism implies that carbonate precipitation may start soon after exposure of the abyssal peridotites when dissolution of brucite and weathering of olivine begin and continue until the phases become inaccessible to seawater predicting carbonation rates of abyssal peridotites will hence require understanding of permeability reactions

the wake low in a midlatitude mesoscale convective system having complex convective organization abstract an analysis has been carried out of the surface pressure field in a highly complex mesoscale convective system that occurred on 3 4 june 1985 during the oklahoma kansas preliminary regional expeximent for storm central ok pre storm during its mature stage the storm consisted of two primary intersecting convective bands approximately 200 km in length one oriented nie sw to the north and the other n s to the south with a stratiform precipitation region extending to the northwest of the bands stratifonn precipitation was weak to nonexistent in the southernmost portion of the storm although the organization of the storm was complex the surface pressure field resembled those associated with simpler quasi linear squall systems containing trading stratifom regions a mesohigh existed neat the convective line and a wake low was observed to the rear of the stratiform region a strong system relative descending rear inflow jet was observed in the northern part of the storm near the wake low

interactions between upper and lower tropospheric gravity waves on squall line structure and maintenance abstract using a simplified thermodynamic sounding and variable vertical wind shear we investigate the role of gravity waves on the structure and propagation of a simulated two dimensional squall line based on an observed squall line environment the modeled troposphere has been divided into three distinct thermodynamic layers these consist of an absolutely stable atmospheric boundary layer abl an elevated well mixed layer and an upper tropospheric layer of intermediate stability we find the mixed layer to have a dual role it has a reduced stability and thus provides abundant buoyancy for the convective scale updrafts and it provides an ideal layer to trap meso scale 20 200 km wave energy generated in the stable layers the generated waves thus have a significant and lasting impact on the simulation we also find this thermodynamic structure to be conducive to both strong surface wind perturbations and long lived squall lines experiments that vary the vertical wind shear profile demonstrate

structures and dynamics of quasi 2d mesoscale convective systems abstract recently three distinct archetypes for midlatitude linear mesoscale convective systems mcss have been identified this article focuses on the fundamentals of two of these archetypes convective lines with trailing stratiform ts precipitation and convective lines with leading stratiform ls precipitation both the ts and ls modes typically exhibit quasi 2d reflectivity patterns and quasi 2d environmental storm relative wind fields ongoing work has revealed that there are three common flow structures for these quasi 2d mcss front fed ts systems which are sustained by front to rear storm relative inflow as well as front fed ls and rear fed ls systems which are sustained by rear to front storm relative inflow this paper summarizes the observed structures of the front fed ts front fed ls and rear fed ls modes and then outlines an idealized numerical experiment in which these modes were simulated the authors analyze the basic simulated kinematic and microphysical structures and provid

gregarious tropical convection abstract a beat source with a vertical profile like that of observed tropical mesoscale convective systems mcss is shown to cause through inviscid gravity wave dynamics upward displacement at low levels in a mesoscale region surrounding the heating typical values are 10 30 area contraction at the surface everywhere within 270 km of the heating 6 h after it starts as a result conditions near an existing mcs but beyond the area of mcs outflow become more favorable for the development of additional convection this theory predicts that cloud clusters should be gregarious infrared satellite imagery confirms that almost half of the cold cloudiness observed in a month over the oceanic warm pool region was contributed by just 14 objectively defined multiday supercluters

fracture initiation during volume increasing reactions in rocks and applications for co2 sequestration abstract volume increasing processes in rocks can induce various types of fractures such as hierarchical domain division of the unreacted material and spalling of the reacted material the mechanism responsible for the selection of a particular fracture type is generally not known we study such deformations and fracture mechanisms in a simplified system with a range of numerical techniques and find that sharpness of reaction fronts and magnitude of volume increase are the main parameters controlling which fracture type forms spalling dominates when there is sharp reaction fronts and large magnitude of volume change otherwise we get mainly domain dividing fractures increasing reaction front sharpness and magnitude of volume change also increases the fracture density and we argue that the change in fracture density can be important for the viability of in situ co 2 sequestration in ultramafic rock

a severe frontal rainband part iii derived thermodynamic structure abstract pressure buoyancy and virtual potential temperature perturbations are calculated from wind fields derived from doppler radar data taken in a surface cold front the dynamics of the front are similar to a density current this hypothesis is also suggested by accompanying numerical simulations of cold air outflows the updraft at the leading edge of the cold air mass is maintained in conjunction with an upward directed pressure force the average maximum updraft is in excess of 7 m s 1 without any appreciable potential instability present in the undisturbed warm sector sounding the buoyancy and virtual potential temperature data reveal a front with a substantial fraction of the cooling taking place within the first 2 km of a frontal zone thus the aspect ratio width depth of the front even after the filtering associated with the interpolation and retrieval process is slightly less than one the frontogenesis for the shear in the along front wind and the thermal gradient are discussed the g

initiation and development of rear inflow within the 28 29 june 1989 north dakota mesoconvective system abstract five dual doppler analyses spanning a period of 1 5 h are used to document the initiation and development of rear inflow within a high plains squall line the squall line developed as part of the 28 29 june 1989 mesoconvective system that passed through the north dakota thunderstorm project observational network this storm was explosively initiated along a preexisting isolated gust front in an environment of much instability and weak upper air flow and moved within dual doppler coverage soon after its initiation the kinematic analyses were performed over a 90 min period as the squall line continued to develop and move to the east northeast the doppler analyses reveal that the rear inflow was initiated near the high reflectivity cores of the squall line within 20 min of the formation of the system with time the rear inflow expanded rearward increased in intensity and descended to near the surface behind the northern section of the squall line in regions where the squall line dissipated

forecasting implications of the 26 july 1985 northeastern colorado tornadic thunderstorm case abstract the case of a tornadic thunderstorm on 26 july 1985 in northeastern colorado is described from the synoptic to the thunderstorm scale utilizing a number of datasets some of which will become operational in the 1990s the available data included profilers doppler radar surface mesonet satellite and special soundings although the synoptic environment did not favor tornadic thunderstorms strong thunderstorms formed in localized area during a 2 h period in the afternoon and produced an 18 min tornado a number of events took place to produce the stronger then anticipated development including interaction among mesoscale outflow and stationary boundaries of particular importance was the change in the local environment along a stationary boundary known as the denver convergence vorticity zone special soundings taken near the stationary boundary revealed a deepening moist layer over time in association with the convergent wind field additional forcing from the collision of this boundary with o