observations of planetary boundary layer structure in the eastern equatorial pacific abstract atmospheric soundings were collected from a research ship in the eastern equatorial pacific to determine the kinematic and thermodynamic structure of the planetary boundary layer pbl in the vicinity of a strong front in sea surface temperature sst these observations have been used to test the hypothesis proposed by wallace et al and hayes et al that the low level wind shear was enhanced on the cold side of the front because of greater static stability the pbl structure was analyzed from a transect along 110 w from 10 n to 5 s with a focus on the 500 m deep atmospheric mixed layer as defined with respect to virtual potential temperature v significant mixed layer variability was found due to diurnal and other effects but there were systematic differences in mean structure as a function of latitude the mixed layer was neutrally stratified over warm water between 6 5 n and 1 5 n and was slightly stably stratified over the cooler water between 1 n and 2 s the mean total vertical wind

an experimental study of the relationship between joint spacing and layer thickness abstract two methods for measuring joint spacing are described and compared the area method is a constant for a given outcrop area and is not affected by joint distribution within that area in contrast the line method depends on the location of the linear traverse two kinds of joint sets are distinguished on bedding surfaces 1 a poorly developed set represents the early stages of development when typical joint lengths are less than typical spacing 2 a well developed set represents later stages when lengths are much greater than spacing the area method is applicable to both poorly and well developed sets whereas the line method produces inconsistent results for poorly developed joint sets surface textures on many joints indicate point fracture origins and propagation parallel to bedding whereas most numerical model studies of spacing assume linear origins and propagation perpendicular to bedding the laboratory experiments described in this paper do not suffer from these restrictions an important concept confirmed during these experiments is fracture saturation when the applied strain reaches a certain value fracture spacing stops evolving and remains nearly constant these fracture sets are well developed spacing at saturation is a function of layer thickness but is independent of strain whereas spacing before saturation varies strongly with applied strain thus plotting spacing vs thickness and comparing the slopes of lines fit to such data for poorly developed joint sets in different layers is unlikely to be a diagnostic test for differences in material properties on the other hand spacing may be a sensitive indicator of strain for layers with poorly developed joint sets assessing fracture saturation is a lirst order consideration when gathering spacing data

the distribution of the mid to lower crustal low velocity zone beneath the northeastern tibetan plateau revealed from ambient noise tomography we collected continuous seismic data recorded between 2007 and 2010 by 208 broadband stations from the chinese provincial digital seismic networks a seismic collaborative experiment of northern tibet and the northeastern tibet seismic experiment cross correlations of vertical component records are computed to extract the rayleigh wave empirical green s functions group and phase velocities are then constructed from the empirical green s functions in 8 to 50 s period at periods 25 s more than 10 lower velocities are imaged beneath the qaidam basin and high velocities are observed beneath the nonbasin regions at periods 30 s up to 10 lower velocities are imaged in the qiangtang and songpan ganze terranes from these group and phase velocity maps a three dimensional 3 d vsv model of the crust is derived the model shows that the qiangtang and songpan ganze terranes have a very thick crust with a prominent low velocity zone lvz in the middle crust the lvz thins out in the vicinity of the eastern kunlun mountains providing a new constraint on the mode of deformation across the tibetan plateau the northwestern qilian orogen where receiver functions reveal a moho deeper than the surrounding areas also features a relatively weak midcrustal lvz which we interpret as an intracrustal response associated with the shortening between the north china craton and the tibetan plateau

quasi lagrangian large eddy simulations of cross equatorial flow in the east pacific atmospheric boundary layer using a large eddy simulation les the atmospheric boundary layer abl is numerically modeled along 958w from 88 st o 48n during boreal autumn and compared to observations from the east pacific investigation of climate processes in the coupled ocean atmosphere system epic 2001 since the local abl winds are predominantly southerly in this season a quasi lagrangian forcing is used in which the abl air column is forced as if it were advecting northward with the mean september october 2001 meridional wind across the equatorial cold tongue and the rapidly warming ssts to the north pressure gradients and large scale zonal advective tendencies are prescribed as a function of latitude where possible observations from the epic 2001 experiment are used for forcing and for comparison with model results the abl s modeled vertical structure accords with the conceptual model of wallace et al and agrees well with observations surface stability accounts for the minimum in surface wind over the equatorial cold tongue and the maximum over the warm water to the north stability of the lower abl over the cold tongue allows a jet to accelerate at about 500 m height relatively uncoupled to the frictional surface layer vertical mixing over the warm water to the north distributes this momentum to the surface additional simulations were performed to explore the modeled abl s sensitivity to pressure gradients zonal advection free tropospheric humidity and initial conditions the model abl was robust changing the forcings resulted in little change in the modeled structure the strongest sensitivity was of stratocumulus clouds over the cold tongue to cloud top radiative cooling once formed at the southern edge of the cold tongue modeled stratocumulus clouds demonstrate a remarkable ability to maintain themselves over the cold tongue in the absence of surface fluxes by radiative cooling at their tops the persistence of thin stratocumulus clouds in this lagrangian model suggests that horizontal advection of condensate might be an important process in determining cloudiness over the cold tongue

modelling stress dependent permeability in fractured rock including effects of propagating and bending fractures the influence of in situ stresses on flow processes in fractured rock is investigated using a novel modelling approach the combined finite discrete element method femdem is used to model the deformation of a fractured rock mass the fracture wall displacements and aperture changes are modelled in response to uniaxial and biaxial stress states the resultant changes in flow properties of the rock mass are investigated using the complex systems modelling platform csmp csmp is used to model single phase flow through fractures with variable aperture and a permeable rock matrix the study is based on a geological outcrop mapping of a low density fracture pattern that includes the realism of intersections bends and segmented features by applying far field boundary stresses to a square region geologically important phenomena are modelled including fracture dependent stress heterogeneity the re activation of pre existing fractures i e opening closing and shearing the propagation of new fractures and the development of fault zones flow anisotropy is investigated under various applied stresses and matrix permeabilities in situ stress conditions that encourage a closing of fractures together with a more pervasive matrix dominated flow are identified these are compared with conditions supporting more localised flow where fractures are prone to dilatational shearing and can be more easily exploited by fluids the natural fracture geometries modelled in this work are not perfectly straight promoting fracture segments that dilate as they shear we have demonstrated the introduction of several realistic processes that have an influence on natural systems fractures can propagate with wing cracks there is the potential for new fractures to connect with existing fractures thus increasing the connectivity and flow blocks can rotate when bounded by fractures bent fractures lead to locally different aperture development highly heterogeneous stress distributions emerge naturally results presented in this work provide a mechanically rigorous demonstration that a change in the stress state can cause reactivation of pre existing fractures and channelling of flow in critically stressed fractures

estimating flow heterogeneity in natural fracture systems abstract examples of small to medium scale fault systems have been mapped in jurassic sedimentary rocks in north somerset england these examples include contractional and dilational strike slip oversteps as well as normal faults these maps form the basis of calculations performed to investigate heterogeneity in natural fracture systems with the aim of predicting fluid flow localisation in different fault styles as there is no way to measure fracture aperture directly we use vein thickness to represent an integrated flow path or palaeo aperture from which we derive a representation of the flow distribution three different methods are used to estimate flow heterogeneity based on 1 fracture density the ratio of fracture length to area 2 fracture aperture fracture porosity and 3 hydraulic conductance fracture permeability normalised to the pressure gradient and fluid properties our results show that fracture density and hydraulic conductance are poorly correlated and that fracture density does not fully represent the natural heterogeneity of fracture systems fracture aperture and hydraulic conductance indicate stronger degrees of flow localisation different types of structures also seem to display characteristic and predictable patterns of heterogeneity normal fault systems show the highest magnitude of localisation along the faults rather than in the relay ramps while contractional and dilational strike slip systems show very strong localisation in the faults and oversteps respectively in all cases the amount of damage in the oversteps can modify such patterns of heterogeneity

imaging 3 d fracture networks around boreholes a new method has been developed for building and visualizing three dimensional 3 d subsurface natural fracture networks in rocks surrounding boreholes using image logs such as cast emi fmi fms rosi and others the method correlates fracture patterns with different stages of fracture network development for individual sets of fractures and extrapolates fracture density and connectivity from one dimension 1 d in boreholes to 3 d in the surrounding rocks the application of this work is 3 d visualizations of fracture distributions in volumes close to the boreholes for well planning reservoir scale fracture model building reservoir flow simulation and hydraulic fracture control

the concept of joint saturation and its application two of the major joint driving mechanisms are joint normal stretching and poroelastic shrinkage and these lead to joint sets commonly associated with structural bending and natural hydraulic fracturing respectively regardless of joint driving mechanism joint infilling is a nonhomogeneous poisson process in the presence of stress shadows through probability modeling we show that in all cases joint spacing is best fit with gamma distributions the shape parameter of the best fit gamma distribution to joint spacing data is a quantitative means to assess the extent of saturation which is represented in a new parameter the joint saturation ratio jsr to test the utility of jsr we call upon published structural bending joint data elk basin lilstock and rives plate bending experiment the shape parameters for these well developed structural bending joints are equal to around three corresponding to a jsr of approximately 30p using the same analysis on the spacing of natural hydraulic fractures collected from outcrops in the gas prone devonian sections of the appalachian basin we find that natural hydraulic fractures differ in two aspects from structural bending joints first the joint spacing is proportional to bed thickness in bedded rocks but not in gas shale sections second the joint saturation of natural hydraulic fractures is generally lower than in well developed structural bending joints thus the jsr is a means to distinguish the joint driving mechanism and to represent joint saturation level independent of bed thickness effects it can be used to distinguish natural fractures from drilling induced fractures and to improve the fracture network modeling

onset of the somali jet in the arabian sea during june 1997 the national aeronautics and space administration scatterometer surface wind vectors are used to describe the rapid onset of the somali jet throughout the arabian sea in june 1997 the time of somali jet onset varied over the arabian sea with june 17 18 the average time the somali jet appeared first in the western arabian sea expanded over 2 weeks to encompass the arabian sea and produced a threefold increase in surface wind convergence in the eastern arabian sea the onset time of the 12 m s 1 isotach preceded by 3 4 days the onset of monsoon rainfall in goa for somali jet wind speeds above 10 m s 1 the 2 day 1 1 sea surface temperature decreased 0 5 c per 1 m s 1 increase in collocated wind speed the somali jet created a north south distribution of ekman pumping and suction in the central arabian sea to enhance the eastward surface current by 0 1 m s 1 the somali jet doubled the southward ekman transport across the southern boundary of the arabian sea in june 1997 when the most intense el nino episode of the century was in its onset phase the southward ekman transport across the southern boundary of the arabian sea was one half that observed since 1992

the influence of sea surface temperature on surface wind in the eastern equatorial pacific weekly to monthly variability abstract temporal correlations between near equatorial surface wind and sea surface temperatures sst at 11 w in the eastern pacific ocean are investigated using data from an array of moored sensors between 5 n and 5 s the signature of tropical instability waves with periods of 20 30 days is apparent in time series of sst and both the meridional and zonal wind components results indicate the existence of a band of pronounced horizontal divergence in the surface wind field associated with the large meridional sst gradient equatorial front normally located just north of the equator perturbations of the equatorial front by the instability waves induce fluctuations in the overlying winds evidence of the air sea coupling is stronger in time series of the meridional gradients of wind and sst than between time series of the variables themselves the meridional differencing serves as a high pass filter in the space domain which removes planetary scale wind fluctuations that are unrelated to the local sst

air sea interaction effects in the lower troposphere across the north wall of the gulf stream abstract significant atmospheric and oceanographic differences have often been observed in the regions lying on either side of the north wall of the gulf stream satellite visible range sensors have revealed changes in reflectivity across the gulf stream believed to be due to changes in sea state that are related to these atmospheric and oceanic differences in addition lines of low level cloud paralleling the edge of the gulf stream have been observed to persist in satellite imagery for several days at a time anomalous radar propagation also has been noted to occur in these same regions in an attempt to document the interrelation of these phenomena the lower atmosphere over the north wall of the gulf stream was studied on two separate occasions sea state photography and measurements of sea surface temperature air temperature dew point temperature and atmospheric pressure were made by an instrumented rp 3a aircraft flying at various altitudes from the gulf stream across the north wall and onto

estimating average fracture spacing in subsurface rock knowledge of the spacing of fractures in reservoir rocks i e the distance between parallel fractures in a subsurface joint set can lead to a better understanding of the production characteristics of a reservoir and serve to quantify the relative degree of deformation in subsurface rocks in this paper i present a new method for estimating the spacing of subsurface fractures this new method is easy to use from the standpoint of both data collection and data analysis the average fracture spacing method can be applied with boreholes of any orientation relative to a fracture set the method is especially powerful when it is used for the relatively common case of a borehole nearly parallel to a fracture set e g vertical borehole intersecting vertical fractures average fracture spacing is estimated from an analytical solution based on observed borehole fracture intersections and observed fracture porosity the only data required are the dimensions of the core or imaged borehole and the total height of all sampled fractures because the likelihood of intersecting fractures increases when a well is deviated perpendicular to the fractures of a set fracture reservoirs commonly are candidates for deviated boreholes an informed decision on borehole deviation requires predicting the fracture intersection frequency as a function of both deviation magnitude and direction a new method based on probabilities of borehole fracture intersections uses spacing and height data from subsurface joint like fractures and the borehole diameter to predict fracture intersection frequencies for all possible well deviations fracture intersection frequency solutions are presented with respect to a conventional geographic reference frame thus simplifying even the most complex three dimentional situations

inter well scale natural fracture geometry and permeability variations in low deformation carbonate rocks regional natural fracture networks often show variations on a scale below that captured by seismic reflection data this variability is not considered in most reservoir models but likely impacts uncertainties in permeability we quantify this uncertainty using a database of 13 000 fractures in nine outcrops digitised in the carbonate jandaira formation potiguar basin brazil distance between outcrops is on average 11 km with a minimum of 300 m which is comparable to the distance between wells in naturally fractured reservoirs in between outcrops significant variations exist in orientation intensity length and topology using discrete fracture matrix flow models we model the permeability of each deterministic pattern and find that small changes in geometry and topology result in permeability variations that are not captured by connectivity based analyses such as percolation probabilities particularly when the matrix is permeable the permeability variations associated with subseismic scale fracture variability are not captured in conventional stochastic models but can be captured using deterministic outcrop models with flow through discrete fractures the deterministic models provide a permeability range associated with subseismic fracture variability that can be assigned to grid cells of fractured reservoir flow models as an alternative to assuming constant permeability in the absence of subseismic scale deformation

the hydraulics of an evolving upwelling jet flowing around a cape upwelling jets flow alongshore in approximate geostrophic balance with the onshore pressure gradient induced by coastal upwelling observations of such jets have shown that they often move offshore downstream of capes leaving a pool of upwelled water inshore comparisons are made between this behavior and the hydraulic transition of a potential vorticity conserving coastal current as it passes a topographic anomaly at which it is exactly critical to long coastal trapped waves an analytic 1 5 layer model of coastal hydraulics with constant potential vorticity in each layer predicts flow fields i e jet separation in critical situations that resemble observations when scales approximate cape blanco on the oregon coast separation occurs at a jet transport of around 0 76 3 106 m3 s21 similar to observed transports time dependent semigeostrophic calculations suggest that during an upwelling season the jet would evolve from a weak flow which was subcritical everywhere and symmetric about the cape to an exactly critical state that made a transition from subcritical to supercritical structure at the head of the cape the predicted flow field at critical transition consists of a narrow upwelling jet upstream of the cape that moves offshore and broadens at the cape this critical state would be accompanied by a downstream jump back to subcritical conditions further upwelling favorable winds would lead to transient waves that propagated upstream and downstream modifying the upstream and downstream conditions and restoring criticality thus the head of the cape exerts hydraulic control on the flow and prevents the jet transport from increasing above its critical level inherent in the hydraulic approach is the assumption that alongshore scales are large for realistic alongshore scales solutions modified by coastline curvature suggest that the convexity of the head of a cape slightly inhibits the transition to a strongly upwelled downstream state by increasing the required critical transport in the presence of topographic features with finite alongshore scale the hydraulic approach can be used to construct a flow field although this flow field has an inherent error arising from the implicit assumptions regarding scales estimation of this error for topography representing cape blanco suggests that in places the cape is rather abrupt for hydraulic theory to be valid

three dimensional magnetotelluric imaging of the se gonghe basin implication for the orogenic uplift in the northeastern margin of the tibetan plateau abstract to better understand the upper crustal shortening and orogenic uplift in the northeastern margin of the tibetan plateau we have utilized magnetotelluric mt data at 116 sites along two lines around the se gonghe basin to determine a three dimensional 3d resistivity model by a 3d mt inversion package modem our resistivity model reveals a significant feature of step discontinuities between high and low resistivity blocks at different depths in the upper and middle crust these discontinuities correspond well with the sharp topography variations thus showing clear tendencies to be the thrust faults beneath the gonghe basin responsible for the formation of gonghe nan shan ghns thrust belt our 3d resistivity model also shows a large higher resistivity body at depths of 3 10 km located beneath the hot springs around the basin we interpreted this anomaly as resistive granite body which acts as hot dry rocks hdrs to generate heat for the hot springs on the surface our results also reveal a pronounced conductive layer at depths of 10 25 km in the middle upper crust which is most likely caused by partial melting for heating the above hdrs this high conductivity layer would behave in a ductile regime near the bottom of the high resistivity body and act as a decollement for the crustal shortening and deformation in the northeastern margin of the tibetan plateau

satellite measurements reveal persistent small scale features in ocean winds four year averages of 25 kilometer resolution measurements of near surface wind speed and direction over the global ocean from the quikscat satellite radar scatterometer reveal the existence of surprisingly persistent small scale features in the dynamically and thermodynamically important curl and divergence of the wind stress air sea interaction over sea surface temperature fronts throughout the world ocean is evident in both the curl and divergence fields as are the influences of islands and coastal mountains ocean currents such as the gulf stream generate distinctive patterns in the curl field these previously unresolved features have important implications for oceanographic and air sea interaction research

ocean atmosphere covariability in the western arabian sea abstract the western arabian sea exhibits strong spatial variability in sea surface temperature sst during the southwest monsoon with changes in sst that can exceed 5 c over 200 km exploration of satellite based and in situ data shows a strong connection between mesoscale sst features and changes in the atmospheric boundary layer the fundamental relationship is that of weak strong wind velocities overlying cold warm sst features there are also coherent changes in other near surface meteorological parameters such as the air sea temperature difference and relative humidity indicating changes in the stability of the planetary boundary layer over the mesoscale sst features these relationships are similar to those recently reported over the equatorial pacific tropical instability wave region this observed covariability of atmospheric boundary layer structure and sst results in variations of the surface heat and moisture fluxes latent heat flux is modified by changes in relative humidity principa

on the coupling of wind stress and sea surface temperature a simple quasi equilibrium analytical model is used to explore hypotheses related to observed spatial correlations between sea surface temperatures and wind stress on horizontal scales of 50 500 km it is argued that a plausible contributor to the observed correlations is the approximate linear relationship between the surface wind stress and stress boundary layer depth under conditions in which the stress boundary layer has come into approximate equilibrium with steady free atmospheric forcing warmer sea surface temperature is associated with deeper boundary layers and stronger wind stress while colder temperature is associated with shallower boundary layers and weaker wind stress two interpretations of a previous hypothesis involving the downward mixing of horizontal momentum are discussed and it is argued that neither is appropriate for the warm to cold transition or quasi equilibrium conditions while one may be appropriate for the cold to warm transition solutions of a turbulent large eddy simulation numerical model illustrate some of the processes represented in the analytical model a dimensionless ratio a is introduced to measure the relative influence of lateral momentum advection and local surface stress on the boundary layer wind profile it is argued that when a 1 and under conditions in which the thermodynamically induced lateral pressure gradients are small the boundary layer depth effect will dominate lateral advection and control the surface stress

local and remote atmospheric response to tropical instability waves a global view from space a la nina took place in the equatorial pacific in 1999 and strong tropical instability waves tiws developed causing large meanders of a sea surface temperature sst front between the equator and 3 n high resolution satellite measurements are used to describe the variability of sst surface wind velocity column integrated water vapor cloud liquid water and precipitation associated with these strong tiws in 1999 coherent ocean atmosphere patterns emerge in both the pacific and atlantic revealing rich regional characteristics in the far eastern pacific southeasterly trades strengthen weaken over positive negative sst anomalies apparently due to enhanced reduced mixing with high speed winds aloft in the central pacific we find evidence that sst induced sea level pressure changes also contribute substantially to wind fluctuations similar sst wind covariability also exists in the southern hemisphere along 2 s but the wind variability induced by unit sst anomaly is much larger than that north of the equator in the central pacific where the equatorial front is broad the northern sst pattern has a large meridional scale and reaches as far north as 6 n further to the north in the intertropical convergence zone itcz where local sst anomalies are small significant variability is found in clouds and precipitation which is further correlated with surface wind convergence in the atlantic tiw signals in sst are strongly trapped near the equator but they induce significant remote response in the itcz which takes a more southern position than its pacific counterpart and thus more susceptible to tiw influence

detection of widespread fluids in the tibetan crust by magnetotelluric studies magnetotelluric exploration has shown that the middle and lower crust is anomalously conductive across most of the north to south width of the tibetan plateau the integrated conductivity conductance of the tibetan crust ranges from 3000 to greater than 20 000 siemens in contrast stable continental regions typically exhibit conductances from 20 to 1000 siemens averaging 100 siemens such pervasively high conductance suggests that partial melt and or aqueous fluids are widespread within the tibetan crust in southern tibet the high conductivity layer is at a depth of 15 to 20 kilometers and is probably due to partial melt and aqueous fluids in the crust in northern tibet the conductive layer is at 30 to 40 kilometers and is due to partial melting zones of fluid may represent weaker areas that could accommodate deformation and lower crustal flow

air sea interaction over the upwelling region of the somali coast 1 during the southwest monsoon two upwelling cells are established along the somali coast around 4 n 5 n and 10 n the sea surface temperatures ssts over these regions can fall to about 22 c on average during this time using satellite derived data the covariability in wind and sst is examined for the months of june august 2005 a particularly strong upwelling season in july 2005 when a strong localized upwelling event occurred near 4 n 5 n the somali jet which establishes itself along the coast during june august was found to have oscillated at a frequency of about 4 8 weeks high covariability in mesoscale winds and ssts were found over the upwelling region the observed covariability of wind and ssts is argued to be the result of sst modulation of the atmospheric stability such that over warm temperatures the unstable atmosphere brings down high winds and over cold temperatures the stable atmosphere decelerates the surface winds these sst induced changes in the lower atmosphere lead to changes in wind stress divergence and a dipole in wind stress curl across the cold filament with negative positive curl upstream downstream of the cold tongue

a geometrically based method for predicting stress induced fracture aperture and flow in discrete fracture networks modeling of fluid flow in naturally fractured reservoirs is often done through modeling and upscaling of discrete fracture networks dfns the two dimensional fracture geometry required for dfns is obtained from subsurface and outcropping analog data however these data provide little information on subsurface fracture aperture which is essential for quantifying porosity and permeability apertures are difficult to obtain from either outcropping or subsurface data and are therefore often based on fracture size or scaling relationships but these do not consider the orientation and spatial distribution of fractures with respect to the in situ stress field using finite element simulations mechanical aperture can be modeled explicitly but because changes in fracture geometry require renewed meshing and simulating this approach is not easily integrated into subsurface dfn modeling workflows we present a geometrically based method for calculating the shear induced hydraulic aperture that is an aperture of up to 0 5 mm 0 02 in that can result from shear displacement along irregular fracture walls the geometrically based method does not require numerical simulations but it can instead be directly applied to dfns using the fracture orientation and spacing distributions in combination with an estimate of the regional stress tensor and orientation the frequency distribution of hydraulic aperture from the geometrically based method is compared with finite element models constructed from five real fracture networks digitized from outcropping pavements these networks cover a wide range of possible geometries and spatial distributions the geometrically based method predicts the average hydraulic aperture and equivalent permeability of fractured porous media with error margins of less than 5

variability in satellite winds over the benguela upwelling system during 1999 2000 1 wind stress variability over the benguela upwelling system is considered using 16 months 01 august 1999 to 29 november 2000 of satellite derived quikscat wind data variability is investigated using a type of artificial neural network the self organizing map som and a wavelet analysis the som and wavelet analysis are applied to an extracted data set to find that the system may be divided into six discrete wind regimes the wavelet power spectra for these wind regions span a range of frequencies from 4 to 64 days with each region appearing to contain distinct periodicities to the north 10 23 5 s the majority of the power occurs during austral winter with a 4 16 day periodicity further investigation of national centers for environmental prediction reanalysis outgoing longwave radiation data indicates that the winter intensification of wind stress off the angolan coast is linked with convective activity over equatorial west africa the summer activity appears to be linked with the intensification of the angolan heat low convective activity over the congo basin appears to impact upon wind stress variability off the angolan coast throughout the year farther south 24 35 s the majority of the power occurs in the summer here a bimodal distribution occurs with peaks of 4 12 and 25 50 days the southernmost regions appear to be forced at higher frequencies by both midlatitude cyclones austral winter and mesoscale coastal lows austral summer at lower frequencies eastward propagating periodic wind events that originate over eastern south america appear to be important to the forcing of wind stress over the southern benguela

comparison of deterministic with stochastic fracture models in water flooding numerical simulations determination of multiphase flow properties considering the variation of fracture patterns i e number of fracture sets their orientation length distribution spacing and in situ aperture remains a key challenge in reservoirs in reservoir engineering one way is by studying outcrop analogs with comparable petrophysical properties and a similar geological history and incorporating these data into model building discretization and numerical simulation the limitation of directly incorporating attributes measured on outcrops is that this method is error prone because of postburial processes mineralized fracture vein attributes are good candidates to use as analogs for open fractures formed under in situ conditions to establish the relationship between fracture length and aperture and help to reveal the conditions at the time of their formation and to quantify fracture induced porosity in rock masses vein attributes determined from scan lines and window samples were combined to condition the stochastic generation of fractures using the discrete fracture network code fracman comparison of water breakthrough time and oil saturation at breakthrough was then determined by applying a constant pressure gradient for each realization to simulate water flooding numerical simulation using the combined finite element finite volume method the different stochastic realizations were compared with discrete fracture and matrix models and we show how the uncertainty in these fracture attributes affects multiphase flow behavior in naturally fractured rocks uncertainty in quantifying these attributes has a profound impact for predicting the oil recovery and water breakthrough time based on limited information from boreholes

intraseasonal variability of the low level jet stream of the asian summer monsoon abstract the strong cross equatorial low level jet stream llj with its core around 850 hpa of the asian summer monsoon june september is found to have large intraseasonal variability during the monsoon onset over kerala india and during break monsoon periods when the convective heating of the atmosphere is over the low latitudes of the indian ocean the axis of the llj is oriented southeastward over the eastern arabian sea and it flows east between sri lanka and the equator and there is no llj through peninsular india this affects the transport of moisture produced over the indian ocean to peninsular india and the bay of bengal in contrast during active monsoon periods when there is an east west band of strong convective heating in the latitudes 10 20 n from about longitude 70 to about 120 e the llj axis passes from the central arabian sea eastward through peninsular india and it provides moisture for the increased convection in the bay of bengal and for the monsoon depressions forming there

distinct influence of air sea interactions mediated by mesoscale sea surface temperature and surface current in the arabian sea abstractduring the southwest monsoons the arabian sea as develops highly energetic mesoscale variability associated with the somali current sc great whirl gw and cold filaments cf the resultant high amplitude anomalies and gradients of sea surface temperature sst and surface currents modify the wind stress triggering the so called mesoscale coupled feedbacks this study uses a high resolution regional coupled model with a novel coupling procedure that separates spatial scales of the air sea coupling to show that sst and surface currents are coupled to the atmosphere at distinct spatial scales exerting distinct dynamic influences the effect of mesoscale sst wind interaction is manifested most strongly in wind work and ekman pumping over the gw primarily affecting the position of gw and the separation latitude of the sc if this effect is suppressed enhanced wind work and a weakened ekman pumping dipole cause the gw to extend northeastward delaying the sc separation by 1 current wind i

on the dynamics of the east african jet iii arabian sea branch abstract barotropic simulations of the east african jet are extended to include the arabian sea branch of the flow and to allow for flow over the mountains of africa large scale mass source sink forcing present to the east of the model orography drives the low level circulation many features of the southeast trades cross equatorial flow and southwest monsoon are simulated among them are the separation of the jet from the african highlands a wind speed maximum over the arabian sea and a reinforcement of the southwest monsoon by the arabian northerlies splitting of the jet over the arabian sea is not simulated starting from a state of rest a well developed southwest monsoon is achieved in a week of simulated time inclusion of a prescribed southern hemisphere midlatitude disturbance excites a significant response in the cross equatorial flow even though flow is permitted over the african mountains downstream the surges excite a response over both the arabian sea and the bay of bengal the bay r

evaluation of the representative elementary volume rev of a fractured geothermal sandstone reservoir the objective of this study is to evaluate a representative elementary volume rev in a fractured geothermal sandstone reservoir in germany using the discrete fracture network dfn model approach due to the lack of in situ data from the deep geothermal reservoir field measurements of outcrop reservoir analogues were conducted to get a quantitative description of the dfn field measurements reveal that the geometry of the dfn is largely influenced by the lithological layering e g relationship between joint spacing and bed thickness thus dfn models have to be completed individually for each layer since each bed is distinct compared to its neighbouring beds various dfns were generated using statistical derived fracture input data the two dimensional universal distinct element code udec was used for fracture flow simulations in order to determine the minimum rev the equivalent average conductivity tensors were obtained with increasing block size plots of conductivity tensor coefficients versus block size exhibit only minor variation of the hydraulic properties with increasing block size hence an rev size of 10 m 10 m could be determined for all studied stochastically derived discrete fracture networks

adjustment of the marine atmospheric boundary layer to the large scale bend in the california coast 1 observations of the surface wind field off the u s west coast were made from satellite by the sea surface microwave imager ssm i during june 1994 and june 1996 the coast bends inward 28 at 40 n latitude northerly wind speeds are high within a region that extends far south and offshore of this bend bounded on the east by the california coast on average the high speed wind zone extends 250 km from shore and 800 km alongcoast long coast perpendicular aircraft transects show that moving onshore the depth of the mabl decreases the northerly wind speed increases and the froude number increases a network of oceanographic buoys records the surface wind speed direction and pressure from six buoy pressure measurements the geostrophic wind vector was computed to represent the synoptic flow over the oregon northern california coastal waters the satellite surface wind fields were composited by the direction of the buoy geostrophic background wind the predominant direction is 210 180 a high speed region extends south of the bend for directions in the 0 180 range moving counterclockwise which corresponds to a downcoast component of the pressure gradient for directions between 180 and 0 flow splits at the bend and the region of highest winds is found to its north and offshore a high speed region south of the bend was present in 65 of the satellite wind maps as well as in the june averages the flow s response to coastal promontories such as point arena is nested within this broad zone of fast thin likely supercritical flow

the influence of sea surface temperature on surface wind in the eastern equatorial pacific seasonal and interannual variability abstract the climate of the eastern pacific exhibits a pronounced equatorial asymmetry boundary layer air originating in the southern hemisphere trades crosses the equator and flows into the intertropical convergence zone itcz whose southern limit is nearly always located at least 4 to the north of the equator the sea surface temperature sst distribution is characterized by a prominent cold tongue centered 1 s a strong frontal zone centered 2 n and a warm eastward current centered near 5 n the surface wind field exhibits a pronounced horizontal divergence as the air flows northward across the oceanic frontal zone these features vary in strength in response to the annual cycle and the el nino southern oscillation phenomenon the northward cross equatorial surface winds the cold tongue and the frontal zone all tend to be strongest during the cold season july through november during the cold season of the coldest years when the cold tongue is most prominent the cross equatorial flow t

fracture density in the deep subsurface techniques with application to point arguello oil field because monterey formation reservoirs rely on fractures joints for permeability quantitative information on fracture spacing is important to exploration strategies and for understanding reservoir behavior density of joints in cores of four wells from the point arguello reservoir has been determined with a new probability based method and these subsurface joint densities are compared with joint densities measured at nearby outcrops my measure of joint density is the fracture spacing index which is the slope of the trend of layer thickness to joint spacing a single set of extension joints that strike parallel to bedding dip predominates at outcrops likewise the cores contain a single set of extension joints perpendicular to the anticline axis and parallel to present day maximum horizontal compressive stress in core and at outcrop the only lithologic control on joint density is between nonjointed mudstone and harder more brittle jointed rocks within each well the fracture spacing index is the same for all hard rocks though it varies between wells in the reservoir joint density relates to structural position the most densely jointed strata fracture spacing index 0 45 are from the hinge of a minor anticline where its plunge steepens a less steeply plunging anticlinal nose has lower joint density fracture spacing index 0 30 the lowest joint density fracture spacing index 0 095 and 0 12 is in cores from gently dipping areas at outcrops in various structural settings the fracture spacing index is the same approximately 1 29 in chert dolostone and porcelanite and siliceous shale these rocks may be saturated with joints so that differences in brittle strain due to local structural variations have been overwhelmed as joints continued to form during unroofing of these strata chert looks more fractured than other lithologies because of thin bedding fracture spacing index is used to compute such parameters as fracture porosity and volume of fractures that directly contact the well bore these parameters may be important when trying to model the behavior of a petroleum reservoir or when trying to assess the feasibility of strongly deviating wells to improve the performance of a fracture reservoir

structural controls of fracture orientations intensity and connectivity teton anticline sawtooth range montana the teton anticline is a multiple hinge anticline containing fractured mississippian devonian carbonates in the frontal part of the sawtooth range in montana the structure serves as a good surface analog for fracture patterns and connectivities within subsurface folded carbonate reservoirs the primary fracture sets are longitudinal and transverse relative to the axis of the fold although two additional oblique sets are also present the length and density of the longitudinal fracture sets are strongly controlled by position relative to multiple hinges the transverse fractures are related to changes in fold plunge and exhibit less variation in fracture density fracture connectivity is dependent on the number of fracture sets their orientations and dispersions and the densities of the fracture sets the connectivity is measured using two parameters the fractional connected area fca which represents the fraction of the total sample area that is connected by fractures and the distribution of clusters of different sizes in any given area because the longitudinal fractures represent the dominant fracture set and also show the most variation with structural position the fracture connectivity as measured by both the fcas and the distribution of cluster sizes is greater in the vicinity of the fold hinges the results and approaches used in the study have some important implications for subsurface folded fractured carbonate reservoirs the analysis of sparsely distributed fracture data from wells must be integrated with an understanding of the controls of the macroscopic structure on fracture parameters to effectively simulate fracture patterns and connectivities around subsurface structures

fracture distribution along an upper jurassic carbonate ramp ne spain abstract understanding the distribution of natural fractures in sedimentary systems is of high relevance for the exploration and production of fluids in the subsurface this study focuses on a kimmeridgian mixed siliciclastic carbonate ramp system which is part of the jurassic limestones outcropping in the northeastern iberian chain the study area is located north of the ricla village fifty kilometers southwest of zaragoza the outcrop stretches over six kilometers in length it allows for recording detailed fracture patterns and facies variations a gis based software package digifract is used to measure and digitize fractures in vertical outcrops fracture orientation measurements obtained from vertical and horizontal outcrops are used to create a conceptual three dimensional image of the fracture distribution of the mixed ramp system the fracture data are processed by integrating outcrop logs and sample data obtained from thin sections and rock property analysis the continuous facies belts of the shallow low angle ramp system show limited lateral variations the studied sediments are subdivided in four main facies tracts ft s ft 1 bioclastic siltstones ft 2 alternating sandy limestones and marls ft 3 cross bedded and channelled oolitic bioclastic sand and grainstones and ft 4 coralgal float to mudstones with eventites measured fracture orientations of the vertical and horizontal outcrops are identical throughout the entire exposure two main fracture sets are identified the first set set 1 has a n s direction and the second set set 2 has a ne sw direction the lateral homogeneity of the sedimentary system thus facies layer thickness and slope angle can be translated to the observed fracture patterns within one single facies belt fractures tend to behave the same in the proximal middle and distal part of the ramp system however vertical facies variations are an important factor for the measured vertical fracture heterogeneity fine grained mud supported facies correspond to periods of a sea level highstand coarse grained cemented facies on the other hand are related to a sea level lowstand the physical contrast of the sediments caused by sea level fluctuations forces fractures to solely concentrate in the brittle layers fracture density and termination patterns observed on this ramp stand in contrast to fracture geometries observed in flat topped carbonate platforms lateral facies heterogeneity and platform anatomy of flat topped carbonate platforms are key parameters for the eventual fracture distribution for the studied mixed ramp type system the vertical facies variations are key parameter

numerical simulation of boundary layer structure and cross equatorial flow in the eastern pacific abstract recent observations from spaceborne microwave sensors have revealed detailed structure of the surface flow over the equatorial eastern pacific in the boreal fall season a marked acceleration of surface wind across the northern sea surface temperature sst front of the cold tongue is a prominent feature of the regional climate previous studies have attributed the acceleration to the effect of enhanced momentum mixing over the warmer waters a high resolution numerical model is used to examine the cross frontal flow adjustment in a comprehensive comparison the model agrees well with many observed features of cross equatorial flow and boundary layer structure from satellite tropical atmosphere ocean tao moorings and the recent eastern pacific investigation of climate processes epic campaign in particular the model simulates the acceleration across the sst front and the change from a stable to unstable boundary layer analysis of the model momentum budget indicates that the hydrostatic

arabian sea surface winds and ocean transports determined from ers 1 scatterometer satellite scatterometer wind velocity measurements are a new source of data for studies of seasonal to interannual ocean atmosphere interactions in the arabian sea where the largest and steadiest wind speeds occur in northern summer three satellite wind velocity data products named cmod4 fd and ifr2 all created from radar backscatter measured by the first european remote sensing satellite ers 1 were compared to moored buoy wind measurements recorded in the central arabian sea during october 1994 to october 1995 orthogonal regression analysis of 74 collocations indicated ifr2 winds were more representative of buoy winds compared to cmod4 and fd ifr2 winds during 1995 are described including the time of monsoon onset and the path of the somali jet monthly mean vertical transport across the bottom of the ekman layer of the arabian sea north of 8 n meridional ekman transport along 8 5 n and sverdrup transport along 8 5 n were computed with ifr2 data from may 1992 to may 1996 during the 1992 1995 june september southwest monsoon upwelling into the ekman layer of the arabian sea occurred at a mean rate of 3 4 sv 1 sv 106 m3 s 1 which was one third smaller than the volume transport exiting within the ekman layer across the southern boundary of the arabian sea and the southward sverdrup transport was 15 sv during the 1992 1996 december march northeast monsoon nearly 5 sv sank below the bottom of the ekman layer 4 sv entered the arabian sea in the ekman layer and the sverdrup transport was negligible year to year transport variations were small

the 30 50 day mode at 850 mb during monex abstract the analyzed wind field at 850 mb during the summer monsoon experiment monex is subjected to a time series analysis to confirm the existence of a peak in the time range of 30 50 days having established that this study presents a mapping of the motion field for this time scale in this short paper we illustrate the steady meridional propagation of a train of troughs and ridges that seem to form near the equator and dissipate near the himalayas the meridional scale of this mode is around 300 km and its meridional speed of propagation is 0 75 latitude per day the amplitude of the wind for this mode is around 3 6 m s 1 the salient contributions here are the mapping and the demonstration of a very regular behavior of this mode its existence is here noted from a period well before the onset of monsoon i e from early may to late july three major storms during monex were noted to form within the trough line of this system and the period of major cessation of rains over the indian subconti

microseismicity constrained discrete fracture network models for stimulated reservoir simulation abstractthe effectiveness of hydraulic fracture stimulation in low permeability reservoirs was evaluated by mapping microseismic events related to rock fracturing the geometry of stage by stage event point sets were used to infer fracture orientation particularly in the case where events line up along an azimuth or have a planar distribution in three dimensions locations of microseismic events may have a higher degree of uncertainty when there is a low signal to noise ratio either due to low magnitude or to propagation effects low signal to noise events are not as accurately located in the reservoir or may fall below the detectability limit so that the extent of fracture stimulated reservoir may be underestimated in the bakken formation of the williston basin we combined geologic analysis with process based and stochastic fracture modeling to build multiple possible discrete fracture network dfn model realizations we then integrated the geologic model with production data and numerical simul

coefficients for sea surface wind stress heat flux and wind profiles as a function of wind speed and temperature surface layer coefficients for wind profiles wind stress and heat flux in typical open sea conditions are briefly reviewed businger dyer flux gradient relationships and a charnock wind stress formula fit the empirical data and are dimensionally consistent these have been solved by an iterative method and the results are presented in a tabular form suitable for climatological calculations from marine wind and temperature data

supercritical marine layer flow along a smoothly varying coastline abstract a model for hydraulically supercritical atmospheric marine layer flow along a smoothly varying coastline is formulated and solved numerically the model is motivated by a recent comparison of code observations to a simple hydraulic theory which suggested the presence of an expansion fan and a compression jump downstream of topographic features the marine layer is modeled as a homogeneous rotating fluid layer decelerated by surface friction and forced by imposed upper level pressure gradients the equations are solved by a characteristic based gridpoint scheme the results indicate that the expansion fan is a robust feature that persists under most conditions in the present more realistic model but is dramatically altered in structure by the presence of friction while the jump may weaken rapidly offshore due mainly to offshore variations of the layer height upstream of the jump the agreement between observations and model predictions is good enough to suggest that a first order description of

the impact of in situ stress and outcrop based fracture geometry on hydraulic aperture and upscaled permeability in fractured reservoirs abstract aperture has a controlling impact on porosity and permeability and is a source of uncertainty in modeling of naturally fractured reservoirs this uncertainty results from difficulties in accurately quantifying aperture in the subsurface and from a limited fundamental understanding of the mechanical and diagenetic processes that control aperture in the absence of cement bridges and high pore pressure fractures in the subsurface are generally considered to be closed however experimental work outcrop analyses and subsurface data show that some fractures remain open and that aperture varies even along a single fracture however most fracture flow models consider constant apertures for fractures we create a stress dependent heterogeneous aperture by combining finite element modeling of discrete fracture networks with an empirical aperture model using a modeling approach that considers fractures explicitly we quantify equivalent permeability i e combined matrix and stress dependent fracture flow fracture networks extracted from a large outcropping pavement form the basis of these models the results show that the angle between fracture strike and 1 has a controlling impact on aperture and permeability where hydraulic opening is maximum for an angle of 15 at this angle the fracture experiences a minor amount of shear displacement that allows the fracture to remain open even when fluid pressure is lower than the local normal stress averaging the heterogeneous aperture to scale up permeability probably results in an underestimation of flow indicating the need to incorporate full aperture distributions rather than simplified aperture models in reservoir scale flow models

toward a quantitative definition of mechanical units new techniques and results from an outcropping deep water turbidite succession tanqua karoo basin south africa the physical properties of reservoirs are strongly influenced by distributed fracture fields outcrop studies are commonly used to determine them but have provided unsatisfactory results because the definition of mechanical units i e groups of layers displaying homogeneous fracture patterns is difficult and typically conducted in a qualitative manner we have developed a systematic methodology to acquire and process fracture patterns in outcrops and to define their relation with stratigraphy we dedicate particular attention to the vertical distribution of fractures in a sedimentary succession commonly composed of layers of different thicknesses and compositions the method makes full use of geographic information system technologies and allows for direct digital acquisition in the field leading to time efficient acquisition data are processed with a newly developed routine that permits an objective description of the changes of fracture characteristics along the stratigraphy of the outcrop the operator is then able to define the most suitable fracture stratigraphy the integration of results from different outcrops is thought to provide a tool for predicting fracture distributions in subsurface target areas

formation and growth of extensional fracture sets naturally occurring extension fractures including some joints and veins form sets consisting of numerous subparallel fractures each with well defined ends in order to correctly interpret these fractures in the field it is necessary to determine which factors control the geometries of fracture sets this requires consideration of the conditions leading to both the initiation and the cessation of fracture propagation a fracture begins to propagate when the crack extension force reaches a critical value which is a property of the rock and of environmental conditions after propagation initiates the crack extension force varies owing to 1 increase in crack length 2 change in remote strain 3 elastic interaction with nearby cracks 4 change in internal fluid pressure and 5 stress relaxation due to growth of cracks in the surrounding rock each fracture continues to propagate as long as its crack extension force exceeds the critical value and terminates when this condition is no longer met neglecting fluid effects the final geometry of the fracture set is a function of the remote strain history and the initial crack geometry which can be characterized by the initial crack density for low initial densities large increases in crack length occur with little or no increase in remote strain however for large initial densities crack lengths increase only if the applied strain increases this analysis is used to estimate the variation in remote strain during formation of a fracture set in granitic rock from observations of the final fracture geometry

observations of coupling between surface wind stress and sea surface temperature in the eastern tropical pacific satellite measurements of surface wind stress from the quikscat scatterometer and sea surface temperature sst from the tropical rainfall measuring mission microwave imager are analyzed for the three month period 21 july 20 october 1999 to investigate ocean atmosphere coupling in the eastern tropical pacific oceanic tropical instability waves tiws with periods of 20 40 days and wavelengths of 1000 2000 km perturb the sst fronts that bracket both sides of the equatorial cold tongue which is centered near 1 8s to the east of 1308w these perturbations are characterized by cusp shaped features that propagate systematically westward on both sides of the equator the space time structures of these sst perturbations are reproduced with remarkable detail in the surface wind stress field the wind stress divergence is shown to be linearly related to the downwind component of the sst gradient with a response on the south side of the cold tongue that is about twice that on the north side the wind stress curl is linearly related to the crosswind component of the sst gradient with a response that is approximately half that of the wind stress divergence response to the downwind sst gradient the perturbed sst and wind stress fields propagate synchronously westward with the tiws this close coupling between sst and wind stress supports the wallace et al hypothesis that surface winds vary in response to sst modification of atmospheric boundary layer stability