structural characterization of natural loess and remolded loess under triaxial tests this paper characterizes the microstructural evolution of saturated natural loess from a site in jingyang china during triaxial test along two stress paths for comparison the same soil in remolded state is also characterized mercury intrusion porosimetry mip scanning electron microscopy sem and environmental scanning electron microscopy esem were used for the microstructure investigation results show that the microstructure of natural loess is similar to that of remolded loess before the consolidated undrained cu triaxial tests including conventional triaxial compression ctc test and reduced triaxial compression rtc test on the contrary their microstructures are different after the tests deeper examination shows that loading led to a significant change of inter aggregate pores without modifying the intra aggregate pores in addition the volume of inter aggregate pores after the rtc test is greater than that after the ctc test under the same consolidation stress the microstructure features of natural and remolded loess after the tests are further used to analyze the macro mechanical behavior for better understanding the relationship between them the results show that it is the cementation bonds of which breakage is influenced by stress path and confining pressure that play important roles in the strength and deformation behavior

experimental behaviour of compacted marls jurassic marls from abadia portugal were used in the construction of some motorway embankments large fragments of this evolving material remained after the construction process and their degradation was of concern because of the expected change of the engineering properties of the compacted material the material exhibits a very complex behaviour which is difficult to reproduce with existing constitutive models for unsaturated structured materials this paper focuses on understanding and providing data on the interaction between the pure marls rock and the aggregate behaviour it presents the main results of tests performed to characterise the hydro mechanical behaviour of compacted marls in specimens prepared with different grading size distributions and subjected to oedometer tests where both stress and suction changes were applied the experimental data obtained were analysed considering the presence of fragments and their degradation the marl matrix was characterised to complete the existing

mercury intrusion and permeability of louiseville clay several theories have been proposed to correlate the permeability hydraulic conductivity with the pore size distribution of soils and it seemed interesting to determine if these theories could be applied to natural clays for this purpose permeability and mercury intrusion porosimetry tests were performed on a champlain sea clay for both intact and remoulded conditions after compression of the specimens to strains varying from 0 to 42 the results show that for either intact or remoulded soil conditions there is a relationship between the pore size parameters and the permeability of the clay however there is no unique relationship for both intact and remoulded clays and for the silt and clay considered in previous studies consequently mercury intrusion porosimetry alone cannot be usepto evaluate the permeability of soils in general plusieurs thkories ont ctc proposces pour corrcler la permiabilite conductivitk hydraulique avec la distribution des grosseurs de pore des sols et il a semblc intiressant de verifier si ces theories pourraient 2tre appliquees aux argiles naturelles a cette fin des essais de permcabilitc et de porosimctrie a intrusion de mercure okt ctc rcaliscs sur l argile de la mer champlain dans des conditions tant intactes que remanikes apris la compression des specimens a des dcformations variant de 0 a 42 les rcsultats demontrent que pour des conditions soit intactes ou remanices il existe une relation entre les paramitres de grosseur de pore et la permcabilitc de l argile cependant il n existe pas de relation unique pour les argiles tant intactes que remanices et pour le limon et l argile ctudics antkrieurement en conscquence la porosimctrie a intrusion de mercure ne peut pas a elle seule tre utilisce pour cvaluer la permcabilitc des sols en general mots clds permcabilitc argile porosimctrie a intrusion de mercure structure traduit par la rcdaction

ice and debris in the fretted terrain mars viking moderate and high resolution images along the northern highland margin were studied monoscopically and stereoscopically to contribute to an understanding of the development of fretted terrain results suport the hypothesis that the fretting process involved flow facilitated by interstitial ice the process apparently continued for a long period of time and debris apron formation shaped the fretted terrain in the past as well as the present interstitial ice in debris aprons is most likely derived from ground ice obtained by sapping or scarp collapse debris aprons could have been removed by sublimation if they consisted mostly of ice or by deflation if they consisted mostly of debris to remove the debris wind erosion was either very intense early in martian history or was intermittent perhaps owing to climatic cycles the location of debris aprons in two midlatitudinal belts can be attributed to atmospheric conditions that permit ice to remain in the ground at moderate depth in those latitudes and climatic factors that permit temperatures to be warm enough for ice to flow channels have minimum gradients of 5 8 m km which permits flowing ice to deform by dislocation creep at exceedingly low strain rates alternately ice charged debris may have been buoyed by brines by analogy with the fretted channels ice could have flowed through the outflow channels if the atmospheric pressure was somewhat higher in the past and permitted ice to exist in the equatorial area

lightning in the anvils of supercell thunderstorms abstractthis study uses data from the oklahoma lightning mapping array ok lma the national lightning detection network and the norman oklahoma koun prototype weather surveillance radar 1988 doppler wsr 88d radar to examine the evolution and structure of lightning in the anvils of supercell storms as they relate to storm dynamics and microphysics several supercell storms within the domain of the ok lma were examined to determine whether they had lightning in the anvil region and if so the time and location of the initiation of the anvil flashes were determined every warm season supercell storm had some flashes that were initiated in or near the stronger reflectivities of the parent storm and propagated 40 70 km downstream to penetrate well into the anvil some supercell storms also had flashes that were initiated within the anvil itself 40 100 km beyond the closest 30 dbz contour of the storm these flashes were typically initiated in one of three locations 1 coincident with a local reflec

modification of the dichotomy boundary on mars by amazonian mid latitude regional glaciation 1 restoration of the dichotomy boundary to its original position to assess its origin requires a thorough knowledge of processes responsible for its degradation and retreat the unique fretted terrain located along the deuteronilus protonilus mensae northern mid latitude portion of the boundary has been long held to provide clues to dichotomy degradation processes we use new spacecraft data to show that fretted valleys display a multitude of characteristics typical of integrated valley glacial systems on earth multiple theater headed alcove like accumulation areas sharp arete like ridges typical of glacial erosion converging patterns of downslope valley flow valley lineation patterns typical of folding and shear wrap around features indicative of flow around obstacles and broad piedmont like lobes as the valley fill extends out into the northern lowlands the single integrated system containing these features covers about 30 000 km2 and is one of dozens of fretted valleys along the dichotomy boundary in this region these relationships suggest that the boundary area was subjected to very large scale regional glaciation during the amazonian recognition and documentation of this important late stage process provides information critical to reconstructing the original dichotomy boundary

investigation of land subsidence with the combination of distributed fiber optic sensing techniques and microstructure analysis of soils abstract land subsidence is a global phenomenon caused by a variety of factors and there are still many challenges in land subsidence monitoring the results of an investigation of land subsidence using the combination of distributed fiber optic sensing dfos techniques and microstructure analysis of soil are here presented two dfos techniques brillouin optical time domain reflectometry botdr and fiber bragg grating fbg were developed in two boreholes namely gm03 and sz01 in su xi chang area china to monitor movement of strata crossed by the borehole and pore pressure in some specific strata scanning electron microscope sem and mercury intrusion porosimetry mip were employed to quantify and characterize the microstructures of undisturbed soils from the boreholes based on the botdr monitoring results the annual levels of land subsidence in gm03 and sz01 are 1 2 mm and 2 9 mm respectively and the movement history of strata were clearly tracked for both boreholes the main contributors to subsidence are two aquitards ad2 and ad3 that exist adjacent to the second aquifer af2 the results obtained by fbg based sensors indicate good agreement with botdr and it confirms that the deformation of aquifer is significantly controlled by pore pressure sem images were analyzed with pore particle and crack analysis system pcas three statistical parameters including average form factor ffavg fractal dimension df and area probability distribution index b were used to describe the geometric characteristics of pores it is found that larger average form factor larger fractal dimension and higher proportion of large pores in soil microstructures favors land subsidence mip results confirm that area probability distribution index can be used for the estimation of strata compression potential in land subsidence investigations

wetting of compacted clays under laterally restrained conditions initial state overburden pressure and mineralogy compacted clay fills are generally placed at the optimum value of water content and immediately after placement they are unsaturated wetting might subsequently occur due for example to rainfall infiltration which can cause volumetric deformation of the fill either swell or collapse with associated loss of shear strength and structural integrity if swelling takes place under partially restrained deformation due for example to the presence of a buried rigid structure or a retaining wall additional stresses will develop in the soil and these can be detrimental to the stability of walling elements and other building assets factors such as dry density overburden pressure compaction water content and type of clay are known to influence the development of stresses this paper investigates these factors by means of an advanced stress path testing programme performed on four different clays with different mineralogy index properties and geological histories specimens of kaolin clay london clay be

mars global surveyor observations of martian fretted terrain the martian fretted terrain between latitudes 30 and 50 n and between 315 and 360 w has been reexamined in light of new mars orbiter camera moc and mars orbiter laser altimeter mola data from mars global surveyor much of the terrain in the 30 50 latitude belt in both hemispheres has a characteristic stippled or pitted texture at moc 1 5 m scale the texture appears to result from partial removal of a formerly smooth thin deposit as a result of sublimation and deflation a complex history of deposition and exhumation is indicated by remnants of a former thicker cover of layered deposits in some hollows and on some slopes particularly those facing the pole are smooth textured deposits outlined by an outward facing escarpment throughout the study area are numerous escarpments with debris flows at their base the escarpments typically have slopes in the 20 30 range at the base of the escarpment is commonly a deposit with striae oriented at right angles to the escarpment outside this deposit is the main debris apron with a surface that typically slopes 2 3 and complex surface textures suggestive of compression sublimation and deflation the presence of undeformed impact craters indicates that the debris flows are no longer forming fretted valleys contain lineated fill and are poorly graded they likely form from fluvial valleys that were initially like those elsewhere on the planet but were subsequently widened and filled by the same mass wasting processes that formed the debris aprons slope reversals indicate that downvalley flow of the lineated fill is minor the ubiquitous presence of breaks in slope formed by mass wasting and the complex surface textures that result from mass wasting deflation and sublimation decreases the recognizability of the shorelines formerly proposed for this area

duration and extent of large electric fields in a thunderstorm anvil cloud after the last lightning 1 a series of balloon electric field e soundings and time correlated radar scans through the balloon locations are used to examine the evolution of charge and reflectivity inside a dissipating thunderstorm anvil the soundings cover a 75 min period during and after the final lightning flash in distant convection the first sounding measured large e magnitudes maximum 65 kv m 1 and significant charge densities of both polarities maximum 2 5 nc m 3 within and screening the anvil little change in the maximum e values occurred in the 30 min between the first and third soundings although altitudes and densities of some charge regions decreased with time maximum 0 6 nc m 3 screening charge regions were observed in close coincidence with 12 dbz radar reflectivity contours and interior positive charge was found in the reflectivity maxima of both anvil decks the fourth sounding ascended through visible but optically less dense cloud and no enhanced e values were detected overall the data indicate the interior positive charge region of the main anvil contained about 150 c and covered at least 250 km2 nearly 30 min after the last lightning flash potentially hazardous e values of 30 35 kv m 1 were measured at 9 9 10 2 km altitude a common jet aircraft cruising altitude more than 20 km away from and 32 min after the final lightning flash about 50 min after the last flash the main positive charge region contained an estimated 50 c and potentially hazardous e values associated with the anvil extended over at least 220 km2

evolution of microstructure in compacted london clay during wetting and loading the influence of fabric on mechanical behaviour is explicitly considered in some of the current constitutive models for unsaturated soils these are based on assumptions regarding the interaction b

electric fields cloud microphysics and reflectivity in anvils of florida thunderstorms into the interior electric fields very frequently increased abruptly from 1 to 10 kv m 1 even though the particle concentrations and radar reflectivity increased smoothly the abrupt increase in field usually occurred when the aircraft entered regions with a reflectivity of 10 15 dbz we suggest that the abrupt increase in electric field was because the charge advection from the convective core did not occur across the entire breadth of the anvil and because the advection of charge was not constant in time also some long lived anvils showed enhancement of electric field and reflectivity far downwind of the convective core screening layers were not detected near the edges of the anvils comparisons of electric field magnitude with particle concentration or reflectivity for a combined data set that included all anvil measurements showed a threshold behavior when the average reflectivity such as in a 3 km cube was less than approximately 5 dbz the electric field magnitude was 3 kv m 1 based on these

global statistics of lightning in anvil and stratiform regions over the tropics and subtropics observed by the tropical rainfall measuring mission 1 the statistics of lighting in the anvil and stratiform regions of convective systems are summarized from tropical rainfall measuring mission trmm satellite observations from 1998 to 2009 the locations of lightning flashes in convective systems are determined by combining three dimensional precipitation radar pr observations with lightning flash center locations from lightning imaging sensor observations the geographical distributions of flashes in the anvil and stratiform regions of thunderstorms over the tropics and subtropics are presented flashes in stratiform regions are found to account for 5 6 of all lightning flashes observed within the trmm pr swath while flashes in nonraining anvil regions made up another 5 5 of the sample diurnally flashes in anvil regions peak earlier than flashes in stratiform regions 15 30 lt as opposed to 17 30 lt seasonal and regional variations of these flashes are discussed features in pr observations that likely contribute to charge separation are identified as contiguous areas with 6 km echoes exceeding 30 dbz lightning flashes are then assigned to one of these features by the nearest neighbor method convective properties of features linked with lightning in stratiform and nonraining anvil regions are then analyzed we find that features associated with lightning flashes in anvil regions are relatively weak and occur in small systems composed of a single convective region while flashes in the stratiform regions are also relatively weak but more likely occur in multicell systems about 15 of features with lightning are associated with at least one stratiform or anvil flash

study of the structure of a sensitive champlain clay and of its evolution during consolidation scanning electron microscopy and mercury intrusion porosimetry are used in parallel to identify the structure of a medium sensitivity champlain clay the clay structure is observed firstly on intact remolded and oven dried soils and secondly on soils consolidated at various levels in one dimensional compression both methods of investigation reveal for the intact soil the existence of an aggregated structure characterized by an interaggregate and an intra aggregate porosity remolding affects interaggregate links but does not destroy aggregates the observation of clay structure at various levels of one dimensional compression shows that the collapse of the structure is progressive the largest interaggregate pores being the first affected as the consolidation proceeds smaller and smaller pores are affected for a given pressure increment only the largest existing pores are affected a structure anisotropy has been seen to develop with increasing compression the scanning electron microscope and the me

collapsibility composition and microstructure of loess in china the collapse potential mineralogy microstructure and particle morphology of a loess from the loess plateau china were characterized by double oedometer testing x ray diffraction scanning ele

ageing effects in a compacted bentonite a microstructure approach it is suspected that the as compacted state of heavily compacted clays used as possible engineered barriers for nuclear waste disposal is time dependent and that further change may occur in the material even at constant water content and density this paper presents an investigation of the time dependent microstructure changes of an mx80 clay bentonite compacted at various dry densities and water contents microstructure investigation is based on mercury intrusion pore size distribution measurements and scanning electron microscopy sem results obtained by other researchers by using x ray diffraction at low angles are also used statically compacted samples of mx80 were kept at constant volume and water content for various periods of time 1 30 and 90 days prior to mercury intrusion and sem micro structure investigation a significant change in micro structure with time was observed characterised by a decrease in the inter aggregate porosity and an increase in the very thin porosity not intruded by

lightning initiation in the anvils of two supercell storms 1 previous studies of lightning in anvil clouds have reported that flashes began in or near the storm core and propagated downwind into the anvil it had been thought that flashes could not be initiated far downwind in the anvil because anvil charge was thought to be produced mainly in the storm s deep updraft and to decrease with distance into the anvil here we report observations of the in cloud development of lightning flashes in the anvils of two supercell storms including the first observations of flashes that began in the anvil 30 100 km from the cores of the storms and propagated upwind back toward the cores interaction between charge regions in the two converging anvils of adjoining storms appeared to cause some of the distant flash initiations but a local charging mechanism in the anvil likely also contributed to the flash initiations all flashes that struck ground beneath the distant anvil transferred negative charge to ground instead of the positive charge usually transferred to ground there an apparent consequence of the parent storm having an inverted polarity electrical structure

swelling phenomena and effective stress in compacted expansive clays the central aim of this paper is to discuss the applicability of the effective stress principle as defined by terzaghi total stress minus pore water pressure to predict the behaviour of expansive

geomorphic evidence for former lobate debris aprons at low latitudes on mars indicators of the martian paleoclimate 1 circumferential depressions enclosing mesas and plateaus in the northern kasei valles and in the tartarus colles regions of mars are interpreted as indicators of the former extent of lobate debris aprons thought to be mixtures of ice and clastic particles these former lobate debris aprons existed about 1 ga ago and were embayed by lavas or other flow deposits after the lobate debris aprons had been removed by sublimation and deflation topographic depressions with a depth of 50 m and a width of several kilometers were left behind between the mesa or plateau scarp and the solidified flow materials these depressions or moats are located equatorward of 30 at significantly lower latitudes than generally observed for occurrences of modern intact lobate debris aprons this observation provides evidence that the paleoclimate at that time was different than today probably due to a higher averaged obliquity of the planet s rotational axis

an experimental study on the compaction and collapsible behaviour of a flood defence embankment fill with renewed interest in the performance of flood embankments globally it is important that the performance of fills in conditions similar to as constructed are scrutinised the fill material investigated in this study was sampled from flood embankments located along the bengawan solo river in east java indonesia the recurrent history of overtopping and stability issues in these embankments provided the motivation for developing a better understanding of the behaviour of this compacted fill under different loading and wetting conditions the site investigation revealed that the embankment fill was compacted at low dry densities and that there was local variation in the dry densities determined a detailed study highlighted that at low compactive efforts this fill material exhibits an irregular double peak compaction curve which can be explained by the tendency of this fill to form aggregates on wetting to cover different plausible operational conditions of these embankments saturated and unsaturated compression oedometer tests and one dimensional collapse tests were performed under different initial conditions specimens compacted at conditions similar to as constructed exhibited significant collapse deformation up to 13 6 on wetting evolution of the microstructure during loading and wetting paths was investigated using mip and esem a physically based framework proposed by romero 2013 was used to explain the changes in the macroscale collapse behaviour observed in the oedometer tests based on the evolution of microporosity using this model the evolution of the microporosity with dry density and water content was presented this microstructural approach could be used as a tool for specifying appropriate compaction conditions for earthworks where fill material is susceptible to volumetric collapse

pore size distribution of a compacted silty soil after compaction saturation and loading soil microstructure is an important feature that controls soil behaviour at the macroscale this microstructure depends on the sample preparation method and evolves during saturation and loading this paper investigates the effects of compaction water content drying techniques adopted prior to performing porosimetry saturation and loading on the evolution of the microstructure of a silty soil mercury intrusion porosimetry is used to obtain the pore size distribution at different states of soil presenting single and double porosity it is observed that in presence of aggregates obtained from a compaction on the dry side of optimum the bimodal pore size distribution is not significantly affected by the saturation process at zero stress this feature of behaviour is quite specific to low plasticity silty soil conversely loading under saturated conditions has a more significant effect on the pore size distribution this bimodal distribution converges into a single mode of pore size when the stress is

mechanical behaviour of heavily compacted bentonite under high suction changes the paper reports the results of an experimental study carried out on a bentonite compacted to a dry density of up to 1 7 mg m3 a high value for this type of soil the soil fabric has been studied using a variety of techniques revealing a clear bimodal pore distribution that corresponds to two distinct structural levels a microstructural one and a macrostructural one the main testing programme has been performed using oedometers especially designed to apply a very large range of suctions by applying the axis translation technique using nitrogen as the gas fluid it has been possible to reach suctions up to 15 mpa the higher suction range has been achieved by applying a controlled atmosphere where the relative humidity has been fixed by a solution of sulphuric acid or salts in this way suctions up to 550 mpa could be reached the maximum vertical stress that could be applied in the apparatus was 10 mpa two types of test have been carried out a tests in which a combination of loading paths at constant suction and drying wetting paths at constant load were applied b swelling tests under constant volume conditions in order to determine the swelling pressure and the stress path followed during wetting the results of the experimental programme are examined taking into account the role of the soil fabric in controlling observed mechanical behaviour in addition the results of the laboratory tests are reproduced and interpreted using a generalised plasticity model that considers explicitly the interaction between macrostructure and microstructure in this way it is possible to achieve a more complete understanding of the mechanisms that underlie observed behaviour and in particular the interplay between the two structural levels

a framework for the behaviour of unsaturated expansive clays the paper presents a framework for describing the mechanical behaviour of unsaturated expansive clays it is an extension of an existing formulation developed for unsaturated soils of low activity the extended framework is based on the distinction within the material of a microstructural level where the basic swelling of the active minerals takes place and a macrostructural level responsible for major structural rearrangements by adopting simple assumptions concerning the coupling between the two levels it is possible to reproduce major features of the behaviour of unsaturated expansive clays some selected qualitative comparisons between model predictions and experimental results reported in the literature are presented despite the simplified hypotheses made a very encouraging agreement is obtained key words capillarity clay model unsaturation suction expansive soils

small lightning flashes from shallow electrical storms on jupiter lightning flashes have been observed by a number of missions that visited or flew by jupiter over the past several decades imagery led to a flash rate estimate of about 4 10 3 flashes per square kilometre per year refs 1 2 the spatial extent of voyager flashes was estimated to be about 30 kilometres half width at half maximum intensity hwhm but the camera was unlikely to have detected the dim outer edges of the flashes given its weak response to the brightest spectral line of jovian lightning emission the 656 3 nanometre h line of atomic hydrogen1 3 6 the spatial resolution of some cameras allowed investigators to confirm 22 flashes with hwhm greater than 42 kilometres and to estimate one with an hwhm of 37 to 45 kilometres refs 1 7 9 these flashes with optical energies comparable to terrestrial superbolts of 0 02 1 6 1010 joules have been interpreted as tracers of moist convection originating near the 5 bar level of jupiter s atmosphere assuming photon scattering from points beneath the clouds 1 3 7 8 10 12 previous observations of lightning have been limited by camera sensitivity distance from jupiter and long exposures about 680 milliseconds to 85 seconds meaning that some measurements were probably superimposed flashes reported as one1 2 7 9 10 13 here we report optical observations of lightning flashes by the juno spacecraft with energies of approximately 105 108 joules flash durations as short as 5 4 milliseconds and inter flash separations of tens of milliseconds with typical terrestrial energies the flash rate is about 6 1 10 2 flashes per square kilometre per year more than an order of magnitude greater than hitherto seen several flashes are of such small spatial extent that they must originate above the 2 bar level where there is no liquid water14 15 this implies that multiple mechanisms for generating lightning on jupiter need to be considered for a full understanding of the planet s atmospheric convection and composition small lightning flashes detected on jupiter by juno have shallow origins above the 2 bar level of jupiter s atmosphere where temperatures are too low for liquid water to exist

wettability decay in an oil contaminated waste mineral mixture with dry wet cycles the dependency of soil particle wettability on soil water content implies that soils subjected to drying wetting cycles become wettable with wetting and water repellent with drying while this has been demonstrated widely the results are contradictory when water repellent soils are subjected to a sequence of cycles added to this past wettability measurements were seldom done in batches of samples collected from the field at natural or dry water contents with little appreciation that slight particle size variations different drying wetting histories and fabric as required by different wettability measurement methods may alter the results this note presents soil particle wettability soil water content relations by means of an index test following staged drying and wetting paths over a period of 8 months for an untreated oil contaminated anthropogenic soil a mixture of slag coal particles fly ash and mineral particles from barry docks uk a site formally used for oil storage which is to be remediated and redeveloped for housing the results revealed a decrease in the water repellency and increasing mineralization and bacterial activity with the wetting and drying cycles

work input analysis for soils with double porosity and application to the hydromechanical modeling of unsaturated expansive clays a mechanical approach for unsaturated expansive soils considering double porosity has been developed based on the porous media theory in this approach the adsorbed and the capillary water as well as the micropores and macropores are two distinct phases an interaggregate stress considered as the work conjugate of the macrostructural strain increment has been defined both physicochemical and capillary effects of the pore water have been introduced at the macroscopic level other work conjugate variables relevant for the constitutive modeling of double porosity unsaturated media have also been identified consisting of the modified suction as conjugate of the increment of the macrostructural degree of saturation and the microstructural effective stress as conjugate of the microstructural volumetric strain increment a hydromechanical model for unsaturated expansive clays taking into account the interaction between the micro and the macrostructures in expansive clays can thus be built based on the bou

observations and numerical simulations of the origin and development of very large snowflakes abstract the canadian atlantic storms program casp ii field experiment was conducted near st john s newfoundland canada during january march 1992 and it focused on the nature of winter storms analyses of casp ii aircraft surface satellite and radar observations collected during an intensive study of the origin and development of 9 mm h 1 precipitation containing 4 5 cm diameter snowflakes are compared in this article with results of the mm5 mesoscale and mitchell microphysical models mm5 simulations of the thermal kinematic and bulk microphysical fields were in good agreement with the observations this comparison provided the basis for extending the spatial and temporal scales of the aircraft observations to a larger scale domain using the model results the mitchell analytical numerical model was used to improve the understanding of the microphysical processes that led to the development of the very large snowflakes a synthesis of results using the different techniques leads to the co

electric field measurements within a severe thunderstorm anvil the anvil cloud of a supercell severe storm in central oklahoma was penetrated by two free balloons carrying corona probes to measure electric fields the two balloons passed through the portion of the anvil upstream of the precipitation core and provided information on the charge concentrations and vertical thicknesses of the electric charge regions within the cloud the trajectories of the balloons relative to the storm were horizontally separated by approximately 35 km providing information on the horizontal extent of the charge regions contrary to the general assumption that anvil interiors are positively charged the results of the two flights indicate that extensive regions of both net positive and negative charge were present in the interior of the anvil net positive charge was observed in both balloon flights in the lower portion of the anvil interior the vertical thickness of the positive charge region was measured in each flight to be 1 6 and 2 3 km respectively a charge concentration of 0 2 nc m 3 was estimated from one of the flights net negative charge was observed by both balloons in the upper portion of the anvil interior the vertical thickness and charge concentration of the negative charge region were estimated from one flight to be 3 2 km and 0 1 nc m 3 respectively screening charge layers were identified at the upper and lower boundaries of the anvil with a typical thickness of a few hundred meters which is an order of magnitude greater than that calculated in a previous model we propose a conceptual model of the development of anvil charge regions based on our balloon measurements and previous observations of anvil dynamics in this model we suggest that the thicknesses of the anvil screening layers increase with distance from the precipitation core of the storm owing to turbulent mixing near the cloud boundaries and differences in the sedimentation rates of the cloud particles negative charge in the upper portion of the anvil interior results from the expansion of the upper negative screening layer into lower levels of the anvil cloud

a discussion of the application of mercury intrusion porosimetry for the investigation of soils including an evaluation of its use to estimate volume change in compacted clayey soils

effect of compaction water content on the strength of cement stabilized rammed earth materials current guidelines suggest that stabilized rammed earth materials be compacted at their optimum water content to achieve their maximum strength although this is true for traditional rammed earth

a microstructure based elastoplastic model to describe the behaviour of a compacted clayey silt in isotropic and triaxial compression the paper focuses on the hydromechanical behaviour of an unsaturated compacted clayey silt accounting for fabric changes induced by drying wetting cycles occurring at low stress levels the respon

debris flow origin for the simud tiu deposit on mars a late hesperian smooth plains deposit on mars interpreted as a debris flow extends more than 2000 km from hydraotes chaos through simud and tiu valles and into chryse planitia the simud tiu deposit widens out to 1000 km and embays streamlined landforms and knobs made up of sedimentary and perhaps volcanic deposits that were carved by earlier channeling activity morphologic features of the simud tiu deposit observed in viking and pathfinder images are generally consistent with a debris flow origin but some of the deposit s salient features are not readily explained by catastrophic flooding or ice flow internal depressions appear to be bounded by linear scarps along flow margins where differential shearing may have occurred and in areas where flow spreading may have produced zones of extensional breakup and thinning within the flow possible flow lobes within the deposit may have formed by successive flow surges within the flow unit the pathfinder landing site is on the simud tiu deposit and the observations there are consistent with debris flow the low longitudinal ridges at the site may have formed by clast interactions as the flow ground to a halt imbricated planar rocks on the ridges such as in the rock garden also may have been emplaced by debris or ice flow however stream energy calculations at ares vallis and channel geology indicate that flooding probably was incapable of emplacing the meter size boulders observed at the pathfinder site dewatering of pressurized zones in the debris flow or underlying material may be responsible for mud eruptions that formed a couple of patches of low pancakelike shields up to 5 km in diameter and for probable water flows that formed two small rille channels a few kilometers long local irregular grooves may be cracks that resulted from later desiccation and contraction of the flow material the debris flow unit apparently coalesced from outflows of water fluidized debris originating from beneath chaotic and hummocky terrains within and along the margins of simud and tiu valles the deposit is onlapped from the north by another flow deposit originating from acidalia planitia if the simud tiu debris flow had entered a standing body of water a turbidity current may have arisen from the debris flow and then backflowed over the debris flow to account for the acidalia deposit

an insight into the water retention properties of compacted clayey soils experimental data from different testing methodologies on different compacted clayey soils with dominant bimodal pore size distribution are presented and analysed to provide a comprehensive picture of the evolution of the aggregated fabric along hydraulic and mechanical paths fabric changes are analysed both from the porous network viewpoint by means of careful mercury intrusion porosimetry investigation and from the soil skeleton viewpoint by quantifying swelling and shrinkage of the aggregates in an environmental scanning electron microscopy study the consequences of the aggregated fabric evolution on the water retention properties of compacted soils are analysed and discussed a new model for water retention domain is proposed which introduces a dependence of the intra aggregate pore volume on water content the model succeeds in tracking correctly the evolution of the hydraulic state of the different soils investigated along generalised hydromechanical paths the proposed approach brings to l

the extension of lightning flashes from thunderstorms near cape canaveral florida the horizontal distance that intracloud ic and cloud to ground cg lightning flashes extend from thunderstorms is presented for warm season nonsevere storms near cape canaveral fl the warning decision support system integrated information wdss ii software allowed us to ingest display and make distance calculations using radar reflectivity data from nearby national weather service offices and lightning information from the national lightning detection network and the local lightning detection and ranging network the flash distances were determined manually using a measuring tool within wdss ii six categories of flashes were investigated a cg flashes measured from the edge of the convective core 30 dbz to the ground strike location that is beneath the attached anvil b cg bolt from the blue flashes measured from cloud edge 0 dbz to the ground strike point that contains only 0 dbz overhead c cg bolt from the blue flashes as in category b but measured from the edge of the precipitation 18 dbz d ic flashes that exit a portion of the cloud that is not an anvil measured from cloud edge 0 dbz e ic flashes within anvils measured from the edge of convective precipitation 30 dbz to the termination point within the anvil and f ic flashes exiting the edge 0 dbz of anvils results for each category are presented in the forms of frequency distributions of distances and their cumulative frequency distributions

collapsibility composition and microfabric of the coastal zone loess around the bohai sea china abstract coastal loess is a special loess deposit that is distributed around the bohai sea the primary objective of this study was to investigate the physical index mineralogical characteristics and collapse potential of coastal loess the secondary objective was to survey the effect of fine silt particles particle size 5 10 m 6 64 7 64 on the collapse process we tested the specific gravity moisture content dry density atterberg limits grain size distribution mineralogy and collapsibility characteristics in a laboratory generated scanning electron microscopy sem images and performed mercury intrusion porosometry mip tests the results of this investigation indicated that coastal loess has a moderately severe collapse potential the collapsibility coefficient decreases with an increase in the initial water content it initially increases and then decreases with an increase in vertical pressure as revealed by the mip test the collapse produces a smaller porosity and the middle pores are primarily responsible for the collapse the relationship of the collapsibility coefficient and particles with a diameter 7 64 have the same tendency in terms of their effect on collapse these results and analyses are important to improve the engineering construction safety in coastal zone loess areas and achieve a better understanding of loess properties compared with loess from a typical loess paleosol section

evidence for recent climate change on mars from the identification of youthful near surface ground ice ground ice in the crust and soil may be one of the largest reservoirs of water on mars1 2 3 near surface ground ice is predicted to be stable at latitudes higher than 40 ref 4 where a number of geomorphologic features indicative of viscous creep and hence ground ice have been observed5 mid latitude soils have also been implicated as a water ice reservoir6 the capacity of which is predicted to vary on a 100 000 year timescale owing to orbitally driven variations in climate7 it is uncertain however whether near surface ground ice currently exists at these latitudes and how it is changing with time here we report observational evidence for a mid latitude reservoir of near surface water ice occupying the pore space of soils the thickness of the ice occupied soil reservoir 1 10 m and its distribution in the 30 to 60 latitude bands indicate a reservoir of 1 5 6 0 104 km3 equivalent to a global layer of water 10 40 cm thick we infer that the reservoir was created during the last phase of high orbital obliquity less than 100 000 years ago and is now being diminished