closed mesoscale cellular convection driven by cloud top radiative cooling abstract closed mesoscale cellular convection mcc consists of mesoscale cloud patches separated by narrow clear regions strong radiative cooling occurs at the cloud top in this study a dry two dimensional boussinesq model is used to study the effects of cloud top cooling on convection wide updrafts and narrow downdrafts are used to indicate the asymmetric circulations associated with the mesoscale cloud patches linear analysis of the model indicates only that the longest waves are most unstable and gives no indication of asymmetric convection cells in the linear convective regime a weakly nonlinear analysis suggests the presence of downdrafts that are narrower than the updrafts but this effect is not very pronounced for reasonable values of parameters fully nonlinear numerical simulations show that strong cloud top cooling can generate highly asymmetric mesoscale cells corresponding to closed mcc nonlinear processes play essential roles in generating and maintaining closed mcc the effects of cl

effect of shear displacement on the hydraulic conductivity of a fracture abstract the effect of shear displacement inclined relative to macroscopic water flow on the hydraulic conductivity of a rock fracture was estimated using synthetic fractures that reproduce a tensile fracture in granite the results showed that the hydraulic aperture normalized by the mean aperture increased with the angle between the directions of shear displacement and macroscopic water flow according to a sinusoidal function of twice the angle formulae were established to estimate the hydraulic aperture of the fracture as a function of the mean aperture the standard deviation of the initial aperture the shear displacement and the angle between the shear displacement and macroscopic water flow based on results obtained in both this work and previous work but neglecting scale effects by assuming the mechanical properties of the fracture based on experimental results for granite but neglecting scale effects the hydraulic conductivity of the fracture with an arbitrary direction under a given state of stress 1 29 mpa 2 25 mpa and 3 13 5 mpa was estimated for macroscopic water flow in the directions of both 1 and 2 when the contour map of the transmissivity of the fracture is plotted on a stereonet of the normal direction of the fracture in the principal axes of stress there is a ridge line of the local maximum of transmissivity in the circumferential direction and the inclination angle of the ridge from the 3 axis decreases with shear displacement since shear dilation increases with both a decrease in normal stress and an increase in shear displacement furthermore for the condition of stress given in this study the transmissivity for macroscopic water flow in the direction of 1 is maximum for a fracture with a normal direction within the 2 3 plane while that in the direction of 2 is maximum for a fracture with a normal direction within the 1 3 plane

laboratory investigation of nonlinear flow characteristics in rough fractures during shear process abstract to understand the influence of shear behavior on the transporting properties of fluid through a single fracture splitting fractures were made in the laboratory and shear flow tests were carried out under constant normal load conditions the applied normal stress is in the range of 0 5 3 0 mpa before the physical test the fracture s morphology is measured for identification of the roughness at each shear step we performed 5 8 high precise hydraulic tests with different hydraulic gradient the relationship between pressure gradient and volume flow rate demonstrates to be nonlinear and fits very well with forchheimer s and izbash s laws the linear and nonlinear coefficients in forchheimer s law are quite sensitive to shear deformation closure or dilation experienced 1 2 and 1 3 orders of magnitude reduction during shear respectively an empirical equation is proposed to quantify the relationship between linear coefficient and nonlinear coefficient based on the experimental observations the two coefficients in izbash s law are quantified the m value is in the range between 1 06 and 1 41 and the value experiences a reduction of 1 2 orders of magnitude during shear in addition the studied critical reynolds number exhibits a decreasing and increasing variation corresponding to shear contraction and shear dilation of rock fracture for all the cases in this study the critical reynolds number ranges between 1 5 and 13 0

development of a shear flow test apparatus and determination of coupled properties for a single rock joint abstract a new laboratory technique for coupled shear flow tests of rock joints was developed and used to investigate the coupled effect of joint shear deformation and dilatancy on hydraulic conductivity of rock joints this technique was used to carry out coupled shear flow tests with an artificial created granite joint sample under constant normal loads and up to residual shear deformations of 20 mm the hydraulic conductivity was estimated by using a finite difference method and an approximate equation assuming the cubic law the shear flow testing results revealed that the change of hydraulic conductivity is approximately similar to that of the dilatancy of a joint the hydraulic conductivity increases rapidly by about 1 2 1 6 orders of magnitude for the first 5 mm of shear displacement after passing the residual shear stress the hydraulic conductivity becomes gradually a constant value with increasing shear displacement on the other hand the hydraulic conductivity after shearing is about one order of magnitude larger than that prior to shearing shear flow coupling characteristics obtained from these tests have a consistent trend with barton s model prediction during the initial shear process however increasing deviation between measured and predicted hydraulic conductivity of rock joint samples has been observed with increasing shear displacement

fluid flow through rough fractures in rocks i high resolution aperture determinations abstract full characterisation of rough fracture surfaces and the resulting variable apertures is an important step in the drive towards an improved understanding of the factors which control fluid flow through rocks a number of surface profiling techniques exist such as needle or laser profiling however these techniques are difficult and time consuming to apply to the total area of a fracture because they involve measuring a large number of parallel profiles which are then difficult to align accurately hence although a single profile may have high resolution in the z direction and the direction of the profile the fracture surface has a much lower resolution due to alignment errors we have developed and improved considerably a previously existing optical concept for obtaining the topography of a fracture surface where the information about surface heights is measured simultaneously the method relies on the construction of high fidelity transparent models of the fracture surface which are imaged while covered with dyed and undyed water the resulting images are converted to topography by a simple calibration procedure that makes use of the lambert beer law this method utilises in house optiprof software which provides considerably more control over the imaging process than previous attempts at optical profiling we have applied the technique to a range of rock fractures and test pieces and have found the technique to work reliably with lateral resolutions of 15 m and a vertical resolution of 15 m although all these could be improved by increasing the pixel count and the bit depth of the camera respectively

mercury s albedo from mariner 10 implications for the presence of ferrous iron mariner 10 clear filter 490 nm images of mercury were recalibrated and photometrically normalized to produce a mosaic of nearly an entire hemisphere of the planet albedo contrasts are slightly larger than seen in the lunar highlands excluding maria variegations indicative of compositional differences include diffuse low albedo units often overlain by smooth plains the high albedo smooth plains of borealis planitia and high albedo enigmatic crater floor deposits a higher level of contrast between immature crater ejecta and average mature material on mercury compared to the moon is consistent with a more intense space weathering environment on mercury that results in a more mature regolith immature lunar highlands materials are 1 5 times higher in reflectance than analogous immature mercurian materials immature materials of the same composition would have the same reflectance on both bodies thus this observation requires that mercury s crust contains a significant darkening agent either opaque minerals or ferrous iron bearing silicates in abundances significantly higher than those of the lunar highlands if the darkening agent is opaque minerals e g ilmenite or ulvospinel mercury s crust may contain significant ferrous iron and yet not exhibit a 1 m absorption band

experimental and numerical study of the geometrical and hydraulic characteristics of a single rock fracture during shear abstract coupled shear flow tests were conducted on two artificial rock fractures with natural rock fracture characteristics under constant normal loading boundary conditions numerical simulations using the 3 d navier stokes equations taking account of the inertial effects of fluid were conducted using the void space geometry models obtained from the coupled shear flow tests the test and numerical simulation results show that the evolutions of geometrical and hydraulic characteristics of rock fracture exhibit a three stage behavior transmissivity of a certain void space geometry within a fracture is related to the reynolds number of fluid flow due to the inertial effects of fluid which can be represented by the navier stokes equations but cannot be represented by some simplified equations such as the cubic law the reynolds equation or the stokes equations the mechanical aperture is usually larger than the hydraulic aperture back calculated from measured flow rate and the difference between them is found strongly related to the geometrical characteristics of the fractures a mathematical equation is proposed to describe the relation between hydraulic aperture and mechanical aperture by means of the ratio of the standard deviation of local mechanical aperture to its mean value the standard deviation of local slope of fracture surface and reynolds number

submillimeter scale topography of the lunar regolith we have applied computer stereophotogrammetry to apollo lunar surface closeup camera alscc pictures of the lunar surface to construct the first ever digital topographic relief maps of undisturbed lunar soil over spatial scales from 85 m to 8 5 cm using elevation histograms fractal analysis and hapke s photometric roughness model we show that apollo 14 fra mauro imbrium ejecta is rougher than average apollo 11 mare tranquilitatis and apollo 12 oceanus procellarum mare surfaces at submillimeter to decimeter size scales we confirm the early result of k lumme et al 1985 earth moon planets33 19 29 that the cumulative distribution of elevations for lunar soil is typically well described by gaussian statistics however cumulative distributions are insensitive to asymmetries in the shapes of elevation histograms of 11 discrete elevation histograms we measured about half exhibit significant deviations from gaussian behavior we also confirm lumme et al s finding that the roughnesses of all lunar surfaces increase with decreasing size scale we further show that the scale dependence of roughness is well represented by fractal statistics the rates of change of roughness with size scale represented by fractal dimension d are remarkably similar among terrians after correcting for the contribution of large scale roughness our average value of d 2 31 0 06 falls within the range 2 0 d 2 4 reported from lunar radar studies the amplitude of roughness which we characterize with the rms slope angle at 1 mm scale varies significantly among terrains for lunar mare the average rms slope angle is 16 4 3 and that for fra mauro regolith is 25 1 by comparison to radar data we suggest that the roughness of fra mauro imbrium ejecta regolith is similar to that of lunar highland terrains we find that the gaussian slope distribution assumed in b w hapke s model 1984 icarus59 41 59 adequately describes typical lunar regolith surfaces a revised form of hapke s equation that models realistic particle phase functions and the coherent backscatter opposition effect was fitted to disk resolved lunar photometric observations and yields estimates of 27 1 for highland and 24 1 for mare regolith these values of as well as the implied relative highland mare photometric roughness ratio are best matched in our elevation data by the cummulative contributions of surface topography covering all scales greater than 0 1 mm less than 5 of the photometrically detected roughness of lunar regolith is contributed by surface relief at scales larger than 8 cm this conclusion implies that values of derived from whole disk and disk resolved photometry respectively may be taken to represent the same physical quantity in addition particulate samples used in goniophotometric measurements should not be assumed to be photometrically smooth i e 0 as is often done in laboratory applications of hapke s photometric model the predicted photometric roughness at size scales of 0 1 mm and less significantly exceed photometric estimates and suggests that there exists a measurable size scale below which topographic relief either is not photometrically detectable or is not represented in the hapke model as macroscopic roughness

multi scale approach to invasion percolation of rock fracture networks summary a multi scale scheme for the invasion percolation of rock fracture networks with heterogeneous fracture aperture fields is proposed inside fractures fluid transport is calculated on the finest scale and found to be localized in channels as a consequence of the aperture field the channel network is characterized and reduced to a vectorized artificial channel network acn different realizations of acns are used to systematically calculate efficient apertures for fluid transport inside differently sized fractures as well as fracture intersection and entry properties typical situations in fracture networks are parameterized by fracture inclination flow path length along the fracture and intersection lengths in the entrance and outlet zones of fractures using these scaling relations obtained from the finer scales we simulate the invasion process of immiscible fluids into saturated discrete fracture networks which were studied in previous works

airborne observations of turbulence mixing and gravity waves in the tropopause region 1 in situ observations of small scale dynamics and compositional structure in the tropopause region are presented the measurements were made aboard the grob egrett high altitude research aircraft above aberystwyth wales in the summer of 2000 the observations presented here show evidence of mixing of ozone and water vapor in a patch of intense turbulence just above the tropopause this turbulence is shown to be the result of wind shear above a tropospheric jet stream the value of the vertical eddy diffusion coefficient in this turbulence is estimated to be 0 9 m2 s 1 it is also shown that wavelike perturbations superimposed on the overall tracer structure can be accounted for by a gravity wave

ct scanning and flow measurements of shale fractures after multiple shearing events abstract a shearing apparatus was used in conjunction with a hassler style core holder to incrementally shear fractured shale cores while maintaining various confining pressures computed tomography scans were performed after each shearing event and were used to obtain information on evolving fracture geometry fracture transmissivity was measured after each shearing event to understand the hydrodynamic response to the evolving fracture structure the digital fracture volumes were used to perform laminar single phase flow simulations local cubic law with a tapered plate correction model to qualitatively examine small scale flow path variations within the altered fractures fractures were found to generally increase in aperture after several shear slip events with corresponding transmissivity increases lower confining pressure resulted in a fracture more prone to episodic mechanical failure and sudden changes in transmissivity conversely higher confining pressures resulted in a system where after an initial setting of the fracture surfaces changes to the fracture geometry and transmissivity occurred gradually flow paths within the fractures are largely controlled by the location and evolution of zero aperture locations a reduction in the number of primary flow pathways through the fracture and an increase in their width was observed during all shearing tests

numerical simulation of shear induced flow anisotropy and scale dependent aperture and transmissivity evolution of rock fracture replicas fluid flow anisotropy in a single rock fracture during a shear process is an important issue in rock mechanics and is investigated in this paper using fem modelling considering evolutions of apert

microphysical properties of convectively generated fall streaks within the stratiform comma head region of continental winter cyclones abstractthis paper presents analyses of the microphysical structure of comma head stratiform precipitation in 14 continental cyclones focusing on fall streaks of hydrometeors produced by cloud top convective generating cells data were obtained at temperatures between 4 and 45 c using in situ instrumentation and the w band university of wyoming cloud radar all operated aboard the national science foundation national center for atmospheric research c 130 analyses are presented first for a case study of one cyclone followed by statistical analyses of the full dataset using radar based objective classifications the statistical percentile number concentrations averaged 1 9 times larger within the fall streaks compared to the regions between them and the corresponding ice water content and median mass diameter values averaged 2 2 and 1 1 times larger ice phase conditions were predominant within the stratiform precipitation with deposition and aggregation the primary ice growth mechanisms no distinc

instability characteristics of radar derived mesoscale organization modes within cool season precipitation near portland oregon abstractthe instability characteristics associated with different radar derived mesoscale organization modes are examined using six cool seasons of operational scanning radar data near portland oregon and operational sounding data from salem oregon additionally several years of microwave rain radar ka band vertically pointing radar data from portland and merwin washington are used to characterize the nature and occurrence of generating cells and fall streaks the combination of a new metric convective stratiform intermittency with the classification of radar reflectivity maps into convective and stratiform precipitation types was applied to periods when the freezing level was 1 4 km altitude this method distinguishes periods with embedded convective within stratiform mesoscale organization from those that were mostly convective or mostly stratiform mesoscale organization occurs in a continuum of states with predominantly stratiform structure occurring most frequently generating cells in the s

resolved hapke parameter maps of the moon we derived spatially resolved near global hapke photometric parameter maps of the moon from 21 months of lunar reconnaissance orbiter camera lroc wide angle camera wac multispectral observations using a novel tile by tile method 1 latitude by 1 longitude bins the derived six parameters w b c bs0 hs and p for each tile were used to normalize the observed reflectance standard angles i g 60 e 0 instead of the traditional angles i g 30 e 0 within each tile resulting in accurate normalization optimized for the local photometric response each pixel in the seven color near global mosaic 70 s to 70 n and 0 e to 360 e was computed by the median of normalized reflectance from large numbers of repeated observations uv 50 and visible 126 on average the derived mosaic exhibits no significant artifacts with latitude or along the tile boundaries demonstrating the quality of the normalization procedure the derived hapke parameter maps reveal regional photometric response variations across the lunar surface the b c henyey greenstein double lobed phase function parameters maps demonstrate decreased backscattering in the maria relative to the highlands except 321 nm band probably due to the higher content of both smfe submicron iron and ilmenite in the interiors of back scattering agglutinates in the maria the hs angular width of shadow hiding opposition effect map exhibits relatively lower values in the maria than the highlands and slightly higher values for immature highland crater ejecta possibly related to the variation in a grain size distribution of regolith

elevated potential instability in the comma head distribution and development abstractthe development of elevated potential instability within the comma head of a continental winter cyclone over the north central united states is examined using a 63 h weather research and forecasting wrf model simulation the simulation is first compared to the observed cyclone the distribution of most unstable convective available potential energy mucape within the comma head is then analyzed the region with positive mucape was based from 2 to 4 km altitude with mucape values up to 93 j kg 1 backward trajectories from five sublayers within the region of elevated convection in the comma head were calculated to investigate how elevated potential instability developed air in the lowest sublayer the source air for convective cells originated 63 h earlier near baja california at elevations between 2 25 and 2 75 km altitude air atop the layer where convection occurred originated at altitudes between 9 25 and 9 75 km in the arctic 5000 km away from the origin of air in the lowest sublayer

dynamics of cloud top generating cells in winter cyclones part iii shear and convective organization abstractcloud top generating cells gcs are a common feature atop stratiform clouds within the comma head of winter cyclones the dynamics of cloud top gcs are investigated using very high resolution idealized wrf model simulations to examine the role of shear in modulating the structure and intensity of gcs simulations were run for the same combinations of radiative forcing and instability as in part ii of this series but with six different shear profiles ranging from 0 to 10 m s 1 km 1 within the layer encompassing the gcs the primary role of shear was to modulate the organization of gcs which organized as closed convective cells in simulations with radiative forcing and no shear in simulations with shear and radiative forcing gcs organized in linear streets parallel to the wind no gcs developed in the initially stable simulations with no radiative forcing in the initially unstable and neutral simulations with no radiative forcing or shear gcs were exceptionally weak with no clear organization

vertical velocity and physical structure of generating cells and convection in the comma head region of continental winter cyclones abstractthe vertical motion and physical structure of elevated convection and generating cells within the comma heads of three continental winter cyclones are investigated using the wyoming w band cloud radar mounted on the national science foundation national center for atmospheric research nsf ncar c 130 supplemented by analyses from the rapid update cycle model and weather surveillance radar 1988 doppler wsr 88d data the cyclones followed three distinct archetypical tracks and were typical of those producing winter weather in the midwestern united states in two of the cyclones dry air in the middle and upper troposphere behind the pacific cold front intruded over moist gulf of mexico air at lower altitudes within the comma head separating the comma head into two zones elevated convection in the southern zone extended from the cold frontal surface to the tropopause the stronger convective updrafts ranged from 2 to 7 m s 1 and downdrafts ranged from 2 to 6 m s 1 the horizontal scale of the

relative rates of optical maturation of regolith on mercury and the moon 1 quantifying relative differences in regolith optical maturation rates is critical to interpreting multispectral reflectance measurements of airless bodies in this study normalized reflectance measurements of crater ejecta blankets and rays are used as indicators of the relative state of regolith maturation on mercury and the moon as well as for a comparison of surface reflectance characterization of craters with high reflectance ejecta from lunar reconnaissance orbiter camera and mercury dual imaging system orbital mosaics indicates that the optical maturation rate is up to 4 times faster on mercury than on the moon observations also show that there are fewer immature craters per unit area on mercury than on the moon and suggest a younger average age for mercurian rayed craters than for lunar rayed craters a comparison of crustal reflectance of immature material yields a ratio of 1 9 0 4 for the average photometrically normalized reflectance of lunar material to that of mercurian material the difference in reflectance is attributed primarily to differences in composition between the lunar highlands and average surface material on mercury the new observations of immature craters per unit area and surface reflectance of immature materials are consistent with previous proposals that regolith maturation rates are faster on mercury than the moon and but here we quantify the relative rate from empirical observations for the first time

testing the relation between uv vis color and tio2 content of the lunar maria reflectance spectroscopy is important for placing lunar samples into a regional and global geologic context to this end the ultraviolet visible uv vis color ratio used to estimate the tio2 composition of mature mare basalts has been one of the most widely used spectral parameters in lunar exploration we examine the correlation between uv vis color and tio2 content using a combination of clementine lunar prospector and sample data to document the extent to which color is dependent upon tio2 examination of the remotely sensed data reveals that the correlation between uv vis ratio and tio2 composition is best represented by a sigmoidal trend rather than the canonical linear or curvilinear correlation with this information we are then able to evaluate between two models that propose different explanations for the relationship between uv vis color and tio2 the first model attributes the correlation between tio2 and uv vis color to spectrally neutral opaques i e ilmenite while the other emphasizes the effect of fe ti charge transfer in lunar glasses and dual scattering mechanisms between high and low ti basalts we do not find evidence in the spectral data to support the occurrence of fe ti charge transfer in lunar glass as the principal cause for color in high ti basalts the data also do not substantiate the existence of different scattering mechanisms e g volume v surface scattering between high and low tio2 basalts instead our analyses substantiate that the spectral effects of ilmenite exhibit a major influence over the uv vis ratio by including sample data we find that in addition to ilemenite tio2 content factors such as feo content ilmenite grain size modal abundance of plagioclase and the olivine to pyroxene ratio in a mare soils can influence the uv vis continuum these findings point to promising avenues of research that future uv vis spectral techniques can exploit in order to yield more accurate tio2 estimates and potentially additional petrologic information

fault s hydraulic diffusivity enhancement during injection induced fault reactivation application of pore pressure diffusion inversions to laboratory injection experiments in situ observations of fluid induced fault slip reactivation as well as the analysis of induced seismicity have demonstrated the complexity of fluid fault interactions under geological conditions if fluid flow commonly reactivates faults in the form of aseismic slip or earthquakes the resulting shear deformation causes strong modifications of the hydraulic properties in this context the relationship between slip front and fluid front on deep faults remains not fully understood in this study we investigate shear induced fluid flow and hydraulic diffusivity enhancement during fracture shearing in the laboratory we use a series of injection reactivation tests conducted under triaxial conditions at different confining pressures 30 60 and 95 mpa the evolution of the fluid pressure along the saw cut andesite rock sample was monitored by two pressure sensors at two opposite locations of the experimental fault we estimate the history of the effective hydraulic diffusivity and its associated uncertainties governing the experimental fault using the pressure history at two points on the fault for this we develop a deterministic and a probabilistic inversion procedure which is able to reproduce the experimental data for a wide time range of the different experiments in this study the hydraulic diffusivity increases by one order of magnitude through the injection experiment hydraulic diffusivity changes are mainly governed by the reduction of the effective normal stress acting on the fault plane with a second order effect of the shear slip

photometrically corrected global infrared mosaics of enceladus new implications for its spectral diversity and geological activity between 2004 and 2017 spectral observations have been gathered by the visual and infrared mapping spectrometer vims on board cassini brown et al 2004 during 23 enceladus close encounters in addition to more distant surveys the objective of the present study is to produce a global hyperspectral mosaic of the complete vims data set of enceladus in order to highlight spectral variations among the different geological units this requires the selection of the best observations in terms of spatial resolution and illumination conditions we have carried out a detailed investigation of the photometric behavior at several key wavelengths 1 35 1 5 1 65 1 8 2 0 2 25 2 55 and 3 6 m characteristics of the infrared spectra of water ice we propose a new photometric function based on the model of shkuratov et al 2011 when combined corrected mosaics at different wavelengths reveal heterogeneous areas in particular in the terrains surrounding the tiger stripes on the south pole and in the northern hemisphere around 30 n 90 w those areas appear mainly correlated to tectonized units indicating an endogenous origin potentially driven by seafloor hotspots

three dimensional flow measurements in rock fractures nuclear magnetic resonance imaging is applied to measure flow patterns in natural water saturated rough walled rock fractures from three dimensional water density and velocity vector images the fracture morphology and flow patterns are determined the parabolic nature and asymmetry of the velocity profiles and thus the accuracy of local cubic law flow rate predictions vary greatly this depends on the degree of wall roughness particularly complex flow patterns are found in one sample which contains a sharp fracture wall discontinuity a power law for the flow rate versus aperture for the low flow region was found without considering the hydraulic gradients

characterization of major discontinuities from borehole cores of the black consolidated marl formation of draix french alps a quantitative description of rock discontinuities present in subsurface cores that were drilled down to 20 m in the marls of the laval and moulin catchments near draix france is presented three kinds of discontinuities are studied those fully open those open but filled with clay rich material and those sealed with calcite with a laser profiler the topography of facing sides of typical discontinuities was measured with a normal resolution of 1 m the probability distribution of the elevation of each surface are obtained and shown to be normal possible self affine scaling invariance of the topography were explored the mineralogical content of an interface between the marl bulk and the embedded calcite vein is also investigated using x ray computed tomography implication of this study for water transport in such discontinuities is addressed in a companion paper in the same issue copyright 2011 john wiley sons ltd

experimental study of the hydro mechanical behavior of rock joints using a parallel plate model containing contact areas and artificial fractures in recent years geological disposal of radioactive wastes is considered to be the most promising option which requires the understanding of the coupled mechanical hydraulic and thermal properties of the host rock masses and rock fractures the hydro mechanical behavior and properties of rock fractures are usually determined by laboratory experiments on fracture specimens that serve as the basic building block of the constitutive models of fractured rock masses laboratory testing of rock fractures involve a number of technical issues that may have significant impacts on the reliability and applicability of the testing results chief among them are the quantitative estimation of the evolutions of hydraulic transmissivity fields of fractures during shear under different normal constraint conditions and the sealing techniques when fluid flow during shear is involved in this study a new shear flow testing apparatus with specially designed fluid sealing techniques for rock fractures were developed under constant normal load cnl or constant normal stiffness cns constraint the topographical data of all fracture specimens were measured before testing to constitute the geometrical models for simulating the change of mechanical aperture distributions during shearing a number of shear flow coupling tests were carried out on three kinds of rock fracture specimens to evaluate the influence of morphological properties of rock fractures on their hydro mechanical behaviour some empirical relations were proposed to evaluate the effects of contact area and surface roughness on the behavior of fluid flow through rock fractures

space weathering from mercury to the asteroid belt the variety of evidence bearing on the nature of space weathering is reviewed the effects of space weathering include spectral darkening reddening and subdued absorption bands and the distinctive magnetic electron spin resonance caused by single domain metallic iron particles ever since the apollo missions two paradigms have dominated the thinking of the planetary science community concerning space weathering 1 the optical effects are caused by impact vitrified glass in agglutinates and 2 the submicroscopic metallic iron results from the reduction of ferrous iron by the impact melting of minerals whose surfaces have been saturated with hydrogen from the solar wind however studies carried out since the apollo program showed that both of these paradigms are invalid a hypothesis first suggested by the author and his colleagues 26 years ago but not generally accepted at that time now appears to be essentially correct both the optical and magnetic effects are caused by metallic iron particles smaller than the wavelength in ubiquitous vapor deposited coatings on soil particle surfaces and inside agglutinates the vapor is generated by both solar wind sputtering and micrometeorite impact vaporization and injected preferentially downward into the porous regolith the iron is reduced by a physical process the selective loss of oxygen that occurs during deposition of the vapor and does not require heating melting or a reducing environment a mathematical theory that describes the optical effects of the submicroscopic iron quantitatively is derived and applied to the regoliths of the moon mercury and an s asteroid

mapping the feo and tio2 content of the lunar surface with multispectral imagery the derivation of quantitative elemental concentrations from multispectral imaging of the moon has long been a goal of lunar remote sensing concentration maps at the spatial resolutions available from the recent clementine mission would provide a revolutionary new tool for understanding the origin and evolution of the lunar crust lucey et al 1995 presented a method for extracting the concentration of fe from multispectral imaging of the moon this paper examines and quantifies important aspects ofthat technique left unexamined by lucey et al which had the potential to severely limit its utility these aspects include the effects of maturity grain size mineralogy shading due to topography and the presence of glass we also present a new algorithm for derivation of tio2 from multispectral imaging of both mare and highland units we find that both techniques are only weakly sensitive to maturity and that they have about 1 wt accuracy based on examination of the spectral properties and compositions of resolved lunar sampling stations presented by blewett et al 1997 we also discuss these findings in the context of two contrasting views of the effect of composition on lunar spectral properties presented by pieters and coworkers and hapke and coworkers we find the view of hapke and coworkers to be more consistent with our observations using a global mosaic of clementine multispectral data and these element derivation algorithms we find that the global modal abundance of feo is 4 5 wt 1 wt and the global modal abundance of tio2 is 0 45 wt 1 wt

application of multiple photometric models to disk resolved measurements of mercury s surface insights into mercury s regolith characteristics abstract photometric analyses are used to standardize images obtained at a variety of illumination and viewing conditions to a common geometry for the construction of maps or mosaics and for comparison with spectral measurements acquired in the laboratory many models exist that can be used to model photometric behavior two of the most commonly use models those of hapke and kaasalainen shkuratov are compared for their ability to standardize messenger images of mercury analysis of the modeling results shows that photometric corrections using the kaasalainen shkuratov model provides significantly less contrast between images acquired at large differences in emission angle the contrast seen between images acquired at large differences in either incidence and phase angle is smaller with the hapke model based corrections but not significantly better than that provided by the kaasalainen shkuratov model photometric studies are also used to infer scattering properties of the surface regolith the quantitative correlation between photometric model parameters and surface properties is questionable but laboratory studies do indicate general correlations and trends between parameters and sample properties that allow for comparisons between surfaces based on photometric modeling based on comparisons with the moon and several asteroids that have been observed by spacecraft the photometric analyses presented here are interpreted to indicate that mercury s regolith is smoother on micrometer scales and has a narrower particle size distribution with a lower mean particle size than lunar regolith grain structures of regolith particles from mercury are inferred to be different than those of the moon or those asteroids observed to date mercury s regolith may contain a component compositionally distinct from lunar regolith

microphysical properties and radar polarimetric features within a warm front abstracton 21 january 2009 the warm front of an extensive low pressure system affected u k weather in this work macroscopic and microphysical characteristics of this warm front are investigated using in situ optical array probes temperatures sensors and radiosondes and s band polarimetric radar data from the aerosol properties processes and influences on the earth s climate clouds project the warm front was associated with a warm conveyor belt a zone of wind speeds of up to 26 m s 1 which played a key role in the formation of extensive mixed phase cloud mass by ascending significant liquid water lwc 0 22 g m 3 at a level 3 km and creating an ideal environment at temperatures 5 c for ice multiplication then generating cells which formed in the unstable and sheared layer above the warm conveyor belt influenced the structure of the stratiform cloud layer dividing it into two types of elongated and slanted ice fall streaks one depicted by large zdr values and the other by large zh

analysis of the messenger mascs photometric targets part ii photometric variability between geomorphological units abstract this study examines the level of structural uniformity within mercury s regolith as a function of geomorphological unit using two categories of photometric models hapke versus kaasalainen shkuratov the variation between and within similar geomorphological units are examined with the mercury atmosphere and surface composition spectrometer mascs photometry sequence data sets the results show evidence for variations in the spectral and photometric scattering properties both within similar geomorphological units and between different geomorphological units the ejecta and cratering units show the largest differences between the modeling results each indicating variations in different properties the results for the intercrater materials smooth materials and dark materials show consistent results between both models the variations include possible differences in grain structures regolith compaction and surface roughness on micron to millimeter scales

stability and charging characteristics of the comma head region of continental winter cyclones abstractthis paper presents analyses of the finescale structure of convection in the comma head of two continental winter cyclones and a 16 storm climatology analyzing the distribution of lightning within the comma head a case study of a deep cyclone is presented illustrating how upper tropospheric dry air associated with the dry slot can intrude over moist gulf air creating two zones of precipitation within the comma head a northern zone characterized by deep stratiform clouds topped by generating cells and a southern zone marked by elevated convection lightning when it occurred originated from the elevated convection a second case study of a cutoff low is presented to examine the relationship between lightning flashes and wintertime convection updrafts within convective cells in both storms approached 6 8 m s 1 and convective available potential energy in the cell environment reached approximately 50 250 j kg 1 radar measurements obtained in convective updraft regions showed enhanced spectral

photometric properties of phobos surface materials from viking images abstract clear filter viking images and an accurate numerical model of the shape of phobos have been used to determine this satellite s photometric properties a global average hapke function derived from disk resolved data confirms previous indications that phobos has a strong opposition surge photometrically corrected images were mosaicked into an albedo map most of the resulting normal reflectances are in the range 0 06 0 10 and the brightest region on phobos is the northeast rim of the crater stickney the portion of that rim with the highest concentration of grooves globally there are three albedo classes reasonably separated geographically 1 bright material is to the east and south of stickney corresponding approximately to the locations on phobos having the highest bluest visible near ir ratio murchie et al 1991 2 the darkest material is to stickney s west correlating with material having an intermediate visible nir ratio murchie et al s bluish gray unit 3 intermediate albedo material dominates the anti stickney hemisphere corresponding to material with a lower visible nir ratio murchie et al s reddish gray unit a search for variations in phase behavior across phobos surface shows few such effects overall limited to isolated areas 1 stickney s floor darkens with increasing phase faster than average phobos this crater floor is both slightly more backscattering and significantly rougher than the global average the latter effect may be related to the slumping hinted at in low resolution images of stickney 2 we confirm that in many cases the contrast between the bright rims of small craters and grooves and their surroundings drops noticeably with increasing phase phase angles in use 10 50 however these bright rims overall display a diversity of photometric behavior and are the most heterogeneous areas on phobos in terms of regolith properties 3 we confirm that dark deposits in the floors of smaller craters darken faster with increasing phase than their surroundings cf goguen et al 1978 and find that these deposits are more backscattering than average phobos isolated regions with unusual phase behavior occur on phobos but not on deimos thomas et al 1996 the variable photometric properties of phobos isolated craters and grooves and the association of global albedo features with stickney reinforce interpretations that phobos regolith is emplaced and modified by discrete cratering events and is not mixed horizontally by extensive downslope creep as is apparently the case on deimos

the structure of radiatively driven convection in stratocumulus data from a series of five research flights in marine stratocumulus are used to investigate the structure of radiatively driven free convective layers conditional sampling methods are used to determine the properties of the primary convective elements negatively buoyant downdraughts the turbulent velocity data are also subjected to spectral analysis and the turbulent kinetic energy tke balance is evaluated for each case results from each case are found to be very similar if scaled using appropriate mixed layer quantities downdraughts are selected using a criterion based on vertical velocity the distributions of their intersected widths at cloud top and the velocity spectra are consistent with downdraughts occupying narrow regions 0 1 0 15 h wide h being the mean mixed layer depth around the periphery of larger regular 0 5 h 0 75 h diameter updraughts as suggested by cellular patterns observed in the cloud tops downdraughts are found to carry over half of the total turbulent fluxes of heat and water substance within cloud and also transport variance down the mean gradients their thermodynamic properties are consistent with their containing a small fraction of air from above cloud top although their negative buoyancy is almost entirely due to the incorporation of radiatively cooled air the properties of the downdraughts near cloud top suggest they are formed primarily as a result of the local horizontal convergence of upwelling motions constrained by the inversion while being cooled radiatively these quasi horizontal motions scour the base of the inversion incorporating some drier air before being forced downwards in relatively narrow zones comparisons with other convective layers over land or sea suggest that convection in stratocumulus proceeds with a greater mass flux and correspondingly reduced differences between convective elements and the environment possibly reflecting the improved ventilation possible at an inversion interface compared with much rougher surfaces the tke balance divides into three main regions and is consistent with the interpretations given above the pressure transport is implied to be the largest source term close to cloud top comparisons with model results reveal some important differences

global photometric properties of asteroid 4 vesta observed with dawn framing camera abstract dawn spacecraft orbited vesta for more than one year and collected a huge volume of multispectral high resolution data in the visible wavelengths with the framing camera we present a detailed disk integrated and disk resolved photometric analysis using the framing camera images with the minnaert model and the hapke model and report our results about the global photometric properties of vesta the photometric properties of vesta show weak or no dependence on wavelengths except for the albedo at 554 nm the global average geometric albedo of vesta is 0 38 0 04 and the bond albedo range is 0 20 0 02 the bolometric bond albedo is 0 18 0 01 the phase function of vesta is similar to those of s type asteroids vesta s surface shows a single peaked albedo distribution with a full width half max 17 relative to the global average this width is much smaller than the full range of albedos from 0 55 to 2 global average in localized bright and dark areas of a few tens of km in sizes and is probably a consequence of significant regolith mixing on the global scale rheasilvia basin is 10 brighter than the global average the phase reddening of vesta measured from dawn framing camera images is comparable or slightly stronger than that of eros as measured by the near earth asteroid rendezvous mission but weaker than previous measurements based on ground based observations of vesta and laboratory measurements of hed meteorites the photometric behaviors of vesta are best described by the hapke model and the akimov disk function when compared with the minnaert model lommel seeliger model and lommel seeliger lambertian model the traditional approach for photometric correction is validated for vesta for 99 of its surface where reflectance is within 30 of global average

vertical cloud structure in a midlatitude cyclone from a 94 ghz radar abstract the vertical structure of clouds associated with a developing midlatitude cyclone was studied using a 94 ghz cloud radar accompanied by a host of other surface based instruments and rawinsondes a thickening cirrostratus deck was observed as the storm approached as the storm drew near low level moisture advection increased and a drizzle producing stratus deck quickly developed a rather lengthy period of light to occasionally moderate rain accompanied the passage of the storm when the storm pulled away to the northeast and the rain ended the character of the stratus deck changed markedly with no drizzle production evident other cloud features observed included generating cells and their resultant fallstreaks and an eye that apparently accompanied the passage of a negatively tilted upper level trough as evidenced by measurements from a 50 mhz wind profiler located near the cloud radar rawinsonde measurements showed that the cloud radar also traced the descent of the melting layer satel

the role of cloud top generating cells and boundary layer circulations in the finescale radar structure of a winter cyclone over the great lakes abstractdata from airborne w band radar are used in conjunction with thermodynamic fields from the weather research and forecasting model and air parcel back trajectories from the hysplit model to investigate the finescale reflectivity vertical motion and airmass structure of the comma head of a winter cyclone in the vicinity of the great lakes cloud top generating cells formed along an upper level frontal boundary vertically separating dry air which 48 h earlier was located in the upper troposphere over south central canada from moist air which was located in the lower troposphere over the southeast united states the stronger updrafts within the generating cells had vertical velocities ranging from 1 to 3 m s 1 the generating cells were important to precipitation production within the comma head precipitation trails formed within the generating cells could sometimes be followed to the boundary layer before merging boundary layer air beneath the cyclone s comma head exhibited convective circulati

near photometry of asteroid 253 mathilde abstract near s multispectral imager msi recorded over 300 images of asteroid 253 mathilde during a flyby on june 27 1997 images were acquired at 0 70 m at solar phase angles from 40 to 136 these data combined with telescopic observations at phase angles from 1 to 16 were used to derive a photometric model for mathilde the photometric properties of mathilde were then compared with those of similar small bodies we find that 1 mathilde has a geometric albedo of 0 047 0 005 at 0 55 m making it the darkest minor planet yet observed by spacecraft 2 mathilde is remarkably homogeneous in reflectance across the surface normal reflectance ranges from 0 041 to 0 053 a distribution at the low end of the range of reflectance measurements of carbonaceous chondrites 0 03 0 11 and in the middle of the range of albedo measurements of c type asteroids 0 03 0 06 3 typical reflectance contrasts on mathilde occur at the level of 6 from the mean as compared to phobos which exhibits variation at the level of 20 from the mean 4 as a whole mathilde is more backscattering than phobos and mathilde may have a less porous regolith or a different distribution of regolith grain sizes than phobos

anisotropy of flow in a fracture undergoing shear and its relationship to the direction of shearing and injection pressure abstract the work presented deal with the effects of shear direction and injection flow rate on the directional anisotropy of the flow for a given normal stress also is related to these effects the evolution of the intrinsic transmissivity of the fracture in relation to the shear direction and tangenital displacements particularly for small displacements tests are performed on mortar replicas of a natural fracture so that the fracture roughness and void space geometry are the same for each test three shear directions are defined these tests results show that the evolution of the intrinsic transmissivity of a fracture depends on the shear direction particularly for small displacements less than 0 5 mm and that shearing induces noticeable modifications in flow direction

planetary regolith surface analogs optimized determination of hapke parameters using multi angular spectro imaging laboratory data this work presents a method for a determination of the global set of parameters involved in hapke s model for planetary surface analogs when dealing with a set of angular conditions representative of the usual range of observation in planetary exploration for spaceborne optical instruments the present approach is founded on a genetic algorithm the whole set of hapke parameters is treated simultaneously without any a priori assumptions it limits the risk of meeting a local extreme and the stability and repeatability of the determination are improved moreover it requires less computational time than a monte carlo routine as a demonstration using multi angular measurements acquired by a new laboratory wide field multispectral imaging facility parameter values for various grain sizes and material compositions of planetary regolith surface analogs are derived and their potential wavelength dependence is studied the results coherent with the literature validate all the steps in our methodology we focus our interest in the understanding of the physical meaning of hapke s parameters in particular of the parameter of the shadowing function for macroscopic roughness it appears that the features smaller than the centimeter scale contribute predominantly to the photometric effect related to the rocky aspect of planetary soil surfaces the parameter may thus be mainly considered as an integral of the roughness properties in the submillimetric centimetric range indeed the most representative case for describing natural regolith surface lies in texture classes in the millimeter range not involving necessarily a high macroscopic roughness with large surface slopes at hundreds of meters scale these findings strengthen the case that depends on both the grain size and the material geological properties

abundance and distribution of iron on the moon the abundance and distribution of iron on the moon is derived from a near global data set from clementine the determined iron content of the lunar highlands crust 3 percent iron by weight supports the hypothesis that much of the lunar crust was derived from a magma ocean the iron content of lower crustal material exposed by the south pole aitken impact basin on the lunar farside is higher 7 to 8 percent by weight and consistent with a basaltic composition this composition supports earlier evidence that the lunar crust becomes more mafic with depth the data also suggest that the bulk composition of the moon differs from that of the earth9s mantle this difference excludes models for lunar origin that require the earth and moon to have the same compositions such as fission and coaccretion and favors giant impact and capture

vertically pointing airborne doppler radar observations of kelvin helmholtz billows abstract a train of kelvin helmholtz billows in a deep stratiform cloud over a mountain range is documented using data from a high resolution vertically pointing airborne doppler radar the billows had a spacing of 2 2 5 km and a small aspect ratio the formation and decay of the billows appear to be related to flow acceleration over a mountain

surface textural properties of icy satellites a comparison between europa and rhea abstract solar phase curves for rhea are presented using new telescopic opposition data along with voyager imaging observations two viable solutions were found to hapke s model 1986 icarus 67 264 280 which was used to describe this phase curve the porosity derived from the model s opposition parameters show that the optically active portion of rhea s regolith has a porosity between 80 and 95 which is slightly lower than the porosity seen on europa and higher than the porosity measured for the moon using similar methods the macroscopic roughness is comparable to that measured by verbiscer and veverka 1989 icarus 82 336 353 for rhea the single particle scattering functions found in this study are predominantly forward scattering which contradicts the results of verbiscer and veverka 1989

mesoscale shallow convection in the atmosphere this paper is a review of the observational experimental theoretical and numerical studies of mesoscale shallow convection msc in the atmosphere typically msc is 1 to 2 km deep has a horizontal length scale of a few to a few tens of kilometers and takes distinctive planforms linear and hexagonal the former is called a cloud street roll or band while the latter is called mesoscale cellular convection mcc comprising three dimensional cells msc is characterized by its shape horizontal extent convective depth and aspect ratio the latter is the ratio of the horizontal extent to that in the vertical for cells the horizontal extent is their diameter whereas for rolls it is their spacing rolls usually align along or at angles of up to 10 from the mean horizontal wind of the convective layer with lengths from 20 to 200 km widths from 2 to 10 km and convective depths from 2 to 3 km the typical value of aspect ratio ranges from 2 to 20 rolls may occur over both water surface and land surfaces mesoscale convective cells may be divided into two types open and closed open cell circulation has downward motion and clear sky in the cell center surrounded by cloud associated with upward motion closed cells have the opposite circulation both types of cell have diameters ranging from 10 to 40 km and aspect ratios of 5 to 50 and both occur in a convective layer with a depth of about 1 to 3 km both the magnitude and direction of horizontal wind in the convective layer change little with height msc results from a complex and incompletely understood mix of processes these processes are outlined and their interplay is examined through a review of theoretical and laboratory analyses and numerical modeling of msc

direct measurement of contact area and stress dependence of anisotropic flow through rock fracture with heterogeneous aperture distribution abstract direct measurement of a contact area using pressure sensitive film was performed for artificially generated granite tensile fractures with different shear displacements of 2 3 and 5 mm and at various normal stresses of up to approximately 100 mpa to clarify the relationship between anisotropic flow and normal stress in a rock fracture with shear displacement aperture distributions with contact areas were then numerically generated using fracture surface geometry data and anisotropic flow was evaluated through a bi directional flow simulation the directional distributions of contacting asperities in the fracture plane were clearly observed for every given condition and the contacting asperities tended to align in the direction perpendicular to shear displacement generally the contact area increased and the anisotropic distribution was enhanced with increasing normal stress however the contact areas for 3 mm shear displacement were less stress dependent anisotropic flow with higher permeability in the perpendicular direction was always observed for aperture distributions with an anisotropic distribution of the contacting asperities flow paths created in the aperture distributions seemed less tortuous in the perpendicular direction due to the distribution of the contacting asperities the anisotropic flow was enhanced with increasing normal stress to the fracture and was more evident for the smaller shear displacements of 2 mm due to the high sensitivity of the contact area to the normal stress the results suggested that the anisotropic flow was likely for a wide range of normal stresses and correspondingly at varying depths in the earth s crust at which anisotropic flow was enhanced with increasing normal stress based on the stress dependence of the contact area in addition the stress dependent anisotropic flow is expected for much higher normal stresses because complete fracture closure with 100 contact area may be unexpected under the crustal stress conditions at depths of several to ten thousand meters

permeability anisotropy induced by the shear displacement of rough fracture walls 1 the permeability anisotropy that results from a shear displacement between the complementary self affine walls of a rough fracture is investigated experiments in which a dyed fluid radially injected into a transparent fracture displaces a transparent one are presented a clear anisotropy is observed in the presence of shear displacements and allows us to estimate the ratio of the permeabilities for flows parallel and perpendicular to a simple model which accounts for the development of channels perpendicular to qualitatively explains these results and predicts a permeability decreasing increasing linearly with the variance of the aperture field for flow parallel perpendicular to the shear displacement these predictions are then compared to the results of numerical simulations performed using a lattice boltzmann technique and to the anisotropies measured in displacement experiments

ponded deposits on asteroid 433 eros in late january 2001 the near shoemaker spacecraft performed low altitude passes over the surface of 433 eros coordinated observations of the asteroid surface were obtained at submeter resolution by the near laser rangefinder and the multispectral imager this paper presents three independent coordinated observations of a 90 m pond adjacent to a granular debris flow including the highest resolution altimetric measurements of ponded deposits on eros the ponded deposits appear to have been emplaced by fluid like motion of dry asteroidal regolith a simple model of seismic agitation from impacts is developed to account for pond formation on eros the model predicts that ponds should form readily on eros but not on the moon where ponds are not observed the model also suggests that the absence of observable ponds in the largest craters of eros as well as on phobos and deimos may be related to regolith depth

numerical investigation of geometrical and hydraulic properties in a single rock fracture during shear displacement with the navier stokes equations extensive research has shown that fluid flow through rock fractures is greatly influenced by surface roughness for a single rock fracture the roughness of the upper and bottom surfaces is the same in the initial condition and then its deformation occurs with normal stress and shear stress imposed on the natural rock previous researchers have paid considerable attention to describing the roughness of the single fracture and its effects on fluid flow however few studies have explained the fluid flow with shear displacement and the direction of the fluid flow velocity field in this work a more detailed 2d numerical model was developed using a laser scanner system with a spacing grid of 0 1 mm to investigate the influence of shear displacement accurately the comsol multiphase codes were applied by applying the navier stokes equations the results of the procedure for shear displacement simulation illustrate the distribution of the absolute velocity and pressure drop under the constant pressure gradient the velocities predicted at the vertical profiles of the inlet were similar to the parabolic velocity curve defined by the cubic laws the mean mechanical aperture was usually larger than the hydraulic aperture from the measured flow rates and a devised empirical equation was proposed to describe the relationship between the mechanical aperture and the hydraulic aperture values the recirculation zones observed in directional fluid flow during shear explain the anisotropy of roughness of a single fracture and the phenomenon argues the applicability of local cubic laws which overestimate the total fluid flow rate

anisotropy in capillary invasion and fluid flow through induced sandstone and shale fractures abstract understanding the physics of flows in a single fracture is the basis for modeling subsurface transport problems in fractured media capillary pressure curve and equivalent aperture have been accepted as tools for characterizing capillary invasion and single phase flow in a single fracture numerical modeling is used to determine the capillary pressure curve and the equivalent aperture for different flow directions in sandstone and shale fractures invasion percolation method is used to model the invasion process of dense non aqueous phase liquid in a water saturated sandstone fracture from different directions finite element method is applied to model the flows of brine and electric current in the fractures along different directions the numerical results are calibrated against the experimental data including capillary pressure measurement and single phase flow tests in the fractures results from the invasion percolation modeling show that the capillary pressure curve is independent of invasion direction the study on the flows of brine and electric current in the fractures illustrates that the sandstone fracture displays a higher anisotropy in hydraulic and electrical conductivities than the shale fracture furthermore it is found that the anisotropy is correlated with the directional roughness harmonic mean and range of fracture aperture

oberon color photometry from voyager and its geological implications abstract three primary terrains are exposed at the surface of oberon average cratered terrain bright crater rays and prominent dark deposits often seen on but not restricted to crater floors we have applied hapke s 1986 icarus 67 264 280 photometric model to voyager imaging and earth based observations to determine photometric properties and colors of oberon s terrains and compare the results with those for the other uranian satellites all terrains on oberon exhibit photometric roughnesses 21 that are lunar like and similar to average global photometric roughnesses of titania and umbriel the asymmetry factors are backscattering for all terrains 0 35 g 0 20 and fall within the observed range for other uranian satellites at visual wavelengths g becomes more backscattering with decreasing single scattering albedo 0 25 0 0 61 the brightest materials on oberon are relatively neutral in color typical of materials covering other uranian satellites but the violet clear and green clear albedo ratios for the darkest terrains on oberon are atypically large for uranian satellites the variation can be modeled in terms of a binary mixture of low albedo and high albedo materials having slightly different colors oberon s leading hemisphere is dominantly covered with dark surface materials identical in color to dark deposits on crater floors while materials on the trailing hemisphere are richer in a spectrally neutral icy component with dark materials occurring in small irregular patches bright ray craters appear to have excavated into a relatively cleaner spectrally neutral icy crust dark materials at the surface may be effusive flood deposits a dark layer below the icy crust which is more exposed on the leading hemisphere due to preferential erosion by impacts or possibly exogenic in origin

testing the hapke photometric model improved inversion and the porosity correction abstract in conjunction with a companion paper shepard m k helfenstein p 2011 icarus submitted for publication we derive test and apply a detailed approach for visualizing the phase angle dependence of light scattering in particulate soils from both whole disk and disk resolved observations to reduce the number of model parameters and provide stronger constraints on model fits we combine hapke s hapke b 2008 icarus 195 918 926 recent correction for effects of porosity with his hapke b 1986 icarus 67 264 280 model of the shadow hiding opposition effect we further develop our method as a tool for least squares fitting of hapke s model to photometric data finally we present an improved method for estimating uncertainties in retrieved values of hapke model parameters we perform a preliminary test of the model on spectrogoniometric measurements from three selected laboratory samples from shepard and helfenstein shepard m k helfenstein p 2007 j geophys res 112 e03001 17 our preliminary suite of test samples is too small and selective to permit the drawing of general conclusions however our results suggest that hapke s porosity correction improves the fidelity of fits to samples composed of low and moderate albedo particles and may allow for more reliable retrieval of porosity estimates in these materials however we find preliminary evidence that in high albedo surfaces the effects of porosity may be difficult to detect

photometric diversity of terrains on triton voyager disk resolved images of triton in the violet 0 41 m and green 0 56 m wavelengths have been analyzed to derive the photometric characteristics of terrains on triton similar conclusions are found using two distinct but related definitions of photometric units one based on color ratio and albedo properties a s mcewen 1990 geophys res lett 17 1765 1768 the other on albedo and brightness ratios at different phase angles cf p lee et al 1992 icarus 99 82 97 a significant diversity of photometric behavior much broader than that discovered so far on any other icy satellite occurs among triton s terrains remarkably differences in photometric behavior do not correlate well with geologic terrain boundaries defined on the basis of surface morphology this suggests that in most cases photometric properties on triton are controlled by thin deposits superposed on underlying geologic units single scattering albedus are 0 98 or higher and asymmetry factors range from 0 35 to 0 45 for most units the most distinct scattering behavior is exhibited by the reddish northern units already identified as the anomalously scattering region asr by lee et al which scatters light almost isotropically with g 0 04 in part due to the effects of triton s clouds and haze it is difficult to constrain the value of hapke s macroscopic roughness parameter precisely for triton or to map differences in among the different photometric terrains however our study shows that triton must be relatively smooth with less than 15 20 and suggests that a value of 14 is appropriate the differences in photometric characteristics lead to significantly different phase angle behavior for the various terrains for example a terrain e g the asr that appears dark relative to another at low phase angles will reverse its contrast become relatively brighter at larger phase angles the photometric parameters have been used to calculate hemispherical albedos for the units and to infer likely surface temperatures based on these results we determine that all but the most southerly regions south of the equator of the reddish northern terrains are likely to have been covered with deposits of nitrogen frost at the time of the voyager flyby in agreement with the suggestion from the photometry that these units are overlain by a thin veneer of material

the improve 1 storm of 1 2 february 2001 part ii cloud structures and the growth of precipitation abstract on 1 2 february 2001 a strong cyclonic storm system developed over the northeastern pacific ocean and moved onto the washington coast this storm was one of several that were documented during the first field phase of the improvement of microphysical parameterization through observational verification experiment improve in the 1 2 february case soundings and wind profiler measurements showed that a wide cold frontal rainband was coincident with the leading edge of an upper level cold front in a classical warm occlusion ground based radar observations revealed the presence of subbands within the wide cold frontal rainband and two layers of precipitation generating cells within this rainband one at 5 7 km msl and the other at 9 10 km msl the lower layer of generating cells produced fallstreaks that were traced from the cells down to the radar bright band at 2 km msl observations suggest a connection between the subbands and the lower layer of generating cells a research aircraft equipped

distinctive space weathering on vesta from regolith mixing processes whereas space weathering of some airless bodies such as the moon occurs through the accumulation on regolith of nanophase metallic particles spectroscopic data show that space weathering of the asteroid vesta occurs through the small scale mixing of diverse surface components which gradually generates locally homogenized upper regolith between 16 july 2011 and 5 september 2012 nasa s space probe dawn was orbiting vesta a protoplanet thought to have survived virtually intact since an early phase of solar system formation in this issue of nature two groups report on the encounter carle pieters and co workers find that space weathering on vesta has followed a different course from that observed on the moon and on itokawa the asteroid sampled in an earth return mission on vesta weathering involved fine scale regolith soil mixing that has removed clear traces of recent impact deposits there are no signs of the nanophase metallic particle deposits seen on the moon and itokawa thomas mccord and co authors describe two main types of material on vesta s surface bright and dark the bright material may be uncontaminated indigenous vesta basaltic soil with the darker material derived from low albedo impactors dawn has now moved on and is due to rendezvous with the protoplanet ceres in february 2015 the surface of the asteroid vesta has prominent near infrared absorption bands characteristic of a range of pyroxenes confirming a direct link to the basaltic howardite eucrite diogenite class of meteorites1 2 3 processes active in the space environment produce space weathering products that substantially weaken or mask such diagnostic absorption on airless bodies observed elsewhere4 5 and it has long been a mystery why vesta s absorption bands are so strong analyses of soil samples from both the moon6 and the asteroid itokawa7 determined that nanophase metallic particles commonly nanophase iron accumulate on the rims of regolith grains with time accounting for an observed optical degradation these nanophase particles believed to be related to solar wind and micrometeoroid bombardment processes leave unique spectroscopic signatures that can be measured remotely8 9 10 but require sufficient spatial resolution to discern the geologic context and history of the surface which has not been achieved for vesta until now here we report that vesta shows its own form of space weathering which is quite different from that of other airless bodies visited no evidence is detected on vesta for accumulation of lunar like nanophase iron on regolith particles even though distinct material exposed at several fresh craters becomes gradually masked and fades into the background as the craters age instead spectroscopic data reveal that on vesta a locally homogenized upper regolith is generated with time through small scale mixing of diverse surface components

flow enhancement of a rough fracture we study experimentally and numerically the permeability of a rough fracture at laboratory scale when viscous forces are dominating low reynolds number the experimental setup includes a granite fracture surface 10 10 cm opened in mode i it allows a continuous opening of the fracture parallel to its mean plane the fracture roughness is measured and characterized in terms of self affine heterogeneities its isotropy is checked the departure from the cubic law is measured as a function of the aperture opening for mean separations between 4 0 and 10 3 mm and the pressure drop orientation by rotating the fracture by 90 degrees a strongly anisotropic hydraulic behavior is observed and results from the geometrical heterogeneities that exist up to the fracture macro scale

polarimetric doppler radar observations of kelvin helmholtz waves in a winter storm abstractkelvin helmholtz waves were observed by the twin lakes oklahoma ktlx weather surveillance radar 1988 doppler wsr 88d the norman oklahoma koun polarimetric wsr 88d and the polarimetric collaborative adaptive sensing of the atmosphere casa radars on 30 november 2006 during a winter storm in central oklahoma the life cycle and structure of the waves are analyzed from the radar data and the nearby atmospheric conditions are examined the initial perturbations associated with the waves are first evident only in the radars radial velocity fields as the waves mature perturbations become discernable in the reflectivity factor z and spectrum width sw fields of both radars and in the differential reflectivity zdr and to a lesser extent the cross correlation coefficient hv fields of koun as the waves break and begin to dissipate the perturbations subside a dual doppler analysis is synthesized to examine the kinematic structure of the waves and to relate the polarimetric observation

lunar iron and titanium abundance algorithms based on final processing of clementine ultraviolet visible images the clementine mission to the moon returned global imaging data collected by the ultraviolet visible uvvis camera this data set is now in a final state of calibration and a five band multispectral digital image model dim of the lunar surface will soon be available to the science community we have used observations of the lunar sample return sites and stations extracted from the final dim in conjunction with compositional information for returned lunar soils to revise our previously published algorithms for the spectral determination of the feo and tio2 content of the lunar surface the algorithms successfully normalize the effects of space weathering so that composition may be determined without regard to a surface s state of maturity these algorithms permit anyone with access to the standard archived dim to construct high spatial resolution maps of feo and tio2 abundance such maps will be of great utility in a variety of lunar geologic studies

integrated spectral analysis of mare soils and craters applications to eastern nearside basalts abstract high spatial resolution clementine images are examined to measure the reflectance properties of small and optically immature mare craters that have sampled discrete compositional units the spectral properties of these relatively crystalline mare materials are compared to associated mature soils to determine the effects of space weathering on specific basalt types space weathering is observed to alter the optical properties of distinct lunar basalt units in a systematic manner allowing compositional distinctions to be recognized across maturity states ultraviolet visible reflectance properties of mare basalts are sensitive to titanium content but are relatively independent of maturity state and demonstrate only a slight reddening as regoliths mature to soils other compositional distinctions between basalt types are identified by differences in albedo and band strength of ferrous minerals that are maintained over a full range of maturity states immature deposits within large craters are compared to the spectral properties of well defined mare units to examine the composition of buried materials when craters excavate through the mare highland contamination is readily identified as a mixing relation between mafic and feldspathic lithologies the approach presented here provides new information on the composition and stratigraphy of several nearside mare deposits including the identification of thin low iron and very low titanium basalts in lacus somniorum and more iron rich low titanium basalts in eastern mare frigoris

reflectance and color variations on mercury regolith processes and compositional heterogeneity multispectral images of mercury obtained by the messenger spacecraft reveal that its surface has an overall relatively low reflectance with three large scale units identified on the basis of reflectance and slope 0 4 to 1 0 micrometer a higher reflectance relatively red material occurs as a distinct class of smooth plains that were likely emplaced volcanically a lower reflectance material with a lesser spectral slope may represent a distinct crustal component enriched in opaque minerals possibly more common at depth a spectrally intermediate terrain probably forms most of the upper crust three other spectrally distinct but spatially restricted units include fresh crater ejecta less affected by space weathering than other surface materials high reflectance deposits seen in some crater floors and moderately high reflectance relatively reddish material associated with rimless depressions

dispersion of solids in fracturing flows of yield stress fluids solids dispersion is an important part of hydraulic fracturing both in helping to understand phenomena such as tip screen out and spreading of the pad and in new process variations such as cyclic pumping of proppant whereas many frac fluids have low viscosity e g slickwater others transport proppant through increased viscosity in this context one method for influencing both dispersion and solids carrying capacity is to use a yield stress fluid as the frac fluid we propose a model framework for this scenario and analyse one of the simplifications a key effect of including a yield stress is to focus high shear rates near the fracture walls in typical fracturing flows this results in a large variation in shear rates across the fracture in using shear thinning viscous frac fluids flows may vary significantly on the particle scale from stokesian behaviour to inertial behaviour across the width of the fracture equally according to the flow rates hele shaw style models give way at higher reynolds number to those in which inertia must be considered we develop a model framework able to include this range of flows while still representing a significant simplification over fully three dimensional computations in relatively straight fractures and for fluids of moderate rheology this simplifies into a one dimensional model that predicts the solids concentration along a streamline within the fracture we use this model to make estimates of the streamwise dispersion in various relevant scenarios this model framework also predicts the transverse distributions of the solid volume fraction and velocity profiles as well as their evolutions along the flow part

impact induced thermal effects in the lunar and mercurian regoliths while the moon and mercury are similar objects in a geomorphologic sense they also possess important differences particularly in the context of small scale impact phenomena not only is the surface of mercury notably hotter than that of the moon but the impact flux is also more intense at mercury due to higher impact velocities and a greater spatial density of micrometeoroids by extrapolating the terrestrial micrometeoroid flux to the moon and mercury it is found that the impact rate at mercury is 5 5 times greater and the mean impact velocity more than 60 percent higher than at the moon a model of impact melting and vaporization applied to the lunar and mercurian environments indicates that almost 14 times more impact melt and over 20 times more vapor are generated per unit time in the mercurian regolith although the surface temperature plays a role in determining the melt and vapor volumes the difference in impact velocity appears to be markedly more important average craters formed by identical projectiles under the two velocity distributions on the two planets should be very similar in size because differences in the kinetic energy of the average impactors will be offset by the differences in gravitational acceleration as a result variations in regolith mixing should depend more on the actual impact rates than on disparities in excavated volumes each average impact on mercury however will produce more than twice as much impact melt as its lunar counterpart introducing more glass into the mercurian regolith although substantial quantities of impact vapor are produced on both planets mixing of the regolith should occur quickly enough in each case to spread the deposited vapor over large surface areas the resulting vapor coatings should be negligibly small for most purposes a much larger agglutinate population should exist on mercury and individual agglutinates should be similar to those of the lunar highlands reflectance spectra and visual albedos indicate that the mercurian crust possesses relatively small quantities of fe perhaps similar to those of apollo 16 light and dark matrix breccias laboratory studies have demonstrated that as the magnetic fractions which are correlated with agglutinate abundances of soils derived from these breccias increase the differences in 0 565 mm visible light reflectivity between the soils diminish should the regional variations in fe content of the mercurian crust be similar to those of these apollo 16 samples then the intense agglutination environment could account for the lack of optical contrast across the mercurian surface at the same time the very large fraction of impact glass in the regolith would imply that most pyroxenes have been fused and incorporated into these glasses seriously attenuating the fe2 crystal field absorption near 0 9 mm supporting this picture are the most recently published spectral observations of mercury which provide little or no evidence of such an absorption feature

mimas photometric roughness and albedo map voyager imaging observations of mimas between 6 and 132 in phase angle provide sufficient data to model such surface characteristics as large scale roughness and directional scattering properties we have analyzed disk integrated and disk resolved voyager clear filter 0 48 m photometric data using a modified version of hapke s 1986 icarus 67 264 280 equation which accommodates anisotropic multiple scattering since near opposition observations are limited we assume mimas has a rhea like opposition surge with angular width h 0 066 and amplitude bo 0 55 we find a single scattering albedo o 0 951 0 002 a henyey greenstein asymmetry parameter g 0 213 0 005 and a macroscopic roughness parameter 30 1 the photometric roughness is greater than those derived in a similar manner from other bright icy satellite surfaces though comparable to the 30 determined for mimas by buratti 1985 icarus 61 208 217 who applied the hapke theory and the 30 25 found by mcewen 1987 personal communication who used fits to the minnaert k parameter to evaluate we find a geometric albedo pv 0 69 0 05 and phase integral q 0 78 0 05 corresponding to a spherical albedo a pvq 0 54 0 1 and a mean opposition magnitude vo 12 62 0 07 our photometric analysis is summarized in terms of an albedo map which reproduces the satellite s observed lightcurve and indicates that normal reflectance range from 0 64 on the leading hemisphere to 0 74 on the trailing one reflectances at extreme southern latitudes are a few percent higher than those at corresponding northern latitudes though in general the equatorial latitudes are brighter than the polar regions the photometric properties show no variation across the surface or relation to any particular terrain type

disk resolved photometric analysis of european terrains abstract using hapke s photometric model we examined the photometric textures of a representative subset of the geologic units on europa defined by lucchitta and soderblom 1982 satellites of jupiter pp 521 555 university of arizona press tucson the individual units studied possess the same small mean photometric slope angle as that found by domingue et al 1991 icarus 90 30 42 for the entire disk with one major exception the particles composing the surfaces of most of the units have similar scattering properties however the single particle scattering functions of the two bright plains regions examined are very different from each other and from the other units if the bright plains units are geologically younger than the other units an aging process that affects the single particle phase functions and albedos is inferred in our previous study we concluded that the disk integrated photometric properties of europa could not be explained adequately by ion bombardment however a new study on the effects of ion irradiation on the optical properties of materials sack et al 1991 j geophys res e 96 2 17535 17539 renders this conclusion invalid

lunar swirls examining crustal magnetic anomalies and space weathering trends 1 we have used multispectral images from clementine and data from lunar prospector s magnetometer to conduct a survey of lunar crustal magnetic anomalies prominent lunar swirls and lesser known swirl markings to provide new information on the nature of swirls and their association with magnetic anomalies we find that all swirls and swirl like albedo patterns are associated with areas of magnetized crust but not all areas of magnetized crust are colocated with swirl like albedo anomalies all observed swirls exhibit spectral characteristics similar to immature material and generally have slightly lower feo values compared with their surroundings as determined with a multispectral iron mapping method we discuss these results in relation to the various hypotheses for swirl formation the comet impact hypothesis for lunar swirls would not predict a difference in the spectrally determined feo content between swirls and nearby ordinary surfaces the compositional difference could be explained as a consequence of 1 magnetic shielding of the surface from the solar wind which could produce anomalous space weathering little darkening with limited reddening and potentially alter the predictions of the multispectral iron mapping algorithm while the compositional contrast could be enhanced by delivery of lower feo ejecta from outside the swirl and 2 accumulation of fine plagioclase rich dust moving under the influence of electric fields induced by solar wind interactions with a magnetic anomaly therefore we cannot at present clearly distinguish between the solar wind shielding and electrostatic dust accumulation models for swirl formation we describe future measurements that could contribute to solution of the puzzle of swirl origin

a novel three dimensional discrete fracture network model for investigating the role of aperture heterogeneity on fluid flow through fractured rock masses abstract effect of anisotropic aperture on the hydraulic properties of single rock fractures has been systematically investigated yet the aperture variability of individual fractures in 3d discrete fracture networks dfns is commonly negligible by using parallel plate fractures the present study proposed a 3d dfn model with fractures having heterogeneous apertures to estimate the influence of fracture variability on fluid flow in total a set of 1280 3d models with increasing fracture densities and fracture lengths are generated and the fluid flow through the models is simulated using a developed numerical code the influences of aperture heterogeneity and network topology on the flow pattern and permeability of 3d dfns are estimated the results show that the network topology provides a first order frame of geometrical connectivity and the heterogeneous aperture further allows the flow to select some most transmissive channels within these connected fractures the dfn model with identical apertures generates a large number of medium flow rate regions whereas the dfn model with fractures having heterogeneous apertures results in extremely low and high flow rate regions the permeability ratio of the two models is widely spread in terms of a small variation in the average mechanical aperture as a result of strong dependence on the aperture distribution the average permeability ratio increases significantly first and then approaches to 1 0 with increasing the average mechanical aperture this allows for the definition of a critical mechanical aperture above which the permeability can be properly predicted using the dfn model with fractures having identical apertures and below which the permeability is much altered by the aperture variability and the dfn model with fractures having heterogeneous apertures should be employed

mercury s global color mosaic an update from messenger s orbital observations abstract we report an update to the photometric correction used to produce global color mosaics of mercury derived from an analysis of photometric observations acquired during the orbital phase of messenger s primary mission comparisons between versions of the color mosaic produced with photometric corrections derived from flyby and orbital data indicate that areas imaged at high incidence and emission angles 50 are better standardized to a common illumination and viewing geometry with the orbit derived corrections seams between images taken at very different illumination geometries however are still present at visually detectable levels further improvements to the photometric correction await updates to the radiometric calibration that will enable data retrieval over a larger range of photometric angles

galileo photometry of asteroid 243 ida galileo imaging observations over phase angles 19 5 to 109 8 are combined with near opposition earth based data to derive the photometric properties of ida to first order these properties are uniform over the surface and well modeled at 0 55 m by hapke parameters 0 0 22 h 0 020 b0 1 5 g 0 33 and 18 with corresponding geometric albedop 0 21 0 030 01and bond albedoab 0 081 0 0170 008 ida s photometric properties are more similar to those of average s asteroids p helfenstein and j veverka 1989 asteroids ii univ of arizona press tucson than are those of 951 gaspra two primary color units are identified on ida terrain a exhibits a spectrum with relatively shallower 1 m absorption and a relatively steeper red spectral slope than average ida while terrain b has a deeper 1 m absorption and a less steep red slope the average photometric properties of ida and terrain a are similar while those of terrain b differ mostly in having a slightly higher value of 0 0 22 versus 0 21 suggesting that terrain b consists of slightly brighter more transparent regolith particles galileo observations of ida s satellite dactyl over phase angles 19 5 to 47 6 suggest photometric characteristics similar to those of ida the major difference being dactyl s slightly lower albedo 0 20 compared to 0 21