a buoyancy flux driven cyclonic gyre in the labrador sea abstract the generation mechanism for a wintertime cyclonic gyre in the western labrador sea first observed by clarke and gascard is studied by using simple theoretical models it is shown that atmospheric cooling which occurs during outbreaks of cold dry continental air can be localized by air modification induced by oceanic heat and water vapor transport the resulting scale of cooling is comparable to the cross shore scale of the observed gyre the density structure of the underlying water mass is then altered by this localized cooling and also by horizontal mixing the model results compare reasonably well with observations finally it is demonstrated that the observed gyre may be generated when the new density structure adjusts itself to geostrophic equilibrium

an ice ocean coupled model an ice model an ocean model and a method of coupling the models are described the ice model is a synthesis with variations and extensions of previous modeling ideas ice thickness concentration velocity and internal energy are prognostic variables the ice thermodynamics are represented by temperatures at the snow surface ice surface the interior and the bottom surface melting and freezing rates are calculated at the ice atmosphere ice ocean and atmosphere ocean interfaces a prescribed portion of summer meltwater can be stored on the surface and refrozen in the fall the ocean model includes a second moment turbulence closure submodel and enables one to solve for oceanic heat flux the interfacial stress and subsurface properties in this paper the model is applied to one dimensional simulations but the equations are cited in a form for implementation by two and three dimensional models in a companion paper kantha and mellor this issue the model is used for two dimensional vertical plane simulations in the bering sea several one dimensional sensitivity studies are performed in the case where the ice model is decoupled from the ocean here the oceanic heat flux and sea surface temperature are prescribed constants the studies reveal the role and sensitivity of surface trapped meltwater ice concentration and ice divergence with the coupled ice ocean model the seasonally varying oceanic heat flux and mixed layer properties are determined by the model some comparisons with observations in the central arctic ocean are possible the role of the molecular sublayer immediately adjacent to the ice is examined frazi ice production is related to the large disparity in the molecular diffusivities for temperature and salinity the mixed layer model contains empirical constants which are known from turbulence data the molecular sublayer parameterization requires one empirical parameter b which is uncertain but from this study is assuredly greater than zero the value implicit in previous models the ice model requires the empirical parameters ci f and ci u to quantitatively account for freezing or melting processes in open leads their values are also uncertain but we present reasoning and sensitivity studies to suggest specific values finally an empirical parameter g is introduced it is the ratio of the value of the ice thickness used to represent average ice volume in the dynamic and thermodynamic equations to the value of the thickness needed in the heat conduction equation estimates of g are made from observed thickness distribution functions sensitivity studies show it to be an important parameter

stress orientation inferred from shear wave splitting in basement rock at cajon pass s waves generated by mode conversion of p waves from surface compressional sources and recorded by oriented geophones at depths between 1300 and 1820 meters in the cajon pass scientific drillhole arrive at higher apparent velocities when polarized along the direction n70 e than when polarized in the orthogonal direction the observed polarization dependent velocities are consistent with seismic anisotropy due to in situ fractures or cracks that are preferen tially aligned n70 e subnormal to the san andreas fault this result is consistent with the maximum principal horizontal stress direction at cajon pass also being subnormal to the san andreas fault

field measurement of radial solute transport in fractured rock the results of a tracer experiment conducted in a single fracture are interpreted using a semianalytical model which accounts for advective dispersion matrix diffusion mixing in the test zones and for tortuosity the experiment was conducted using a conservative tracer which was injected into a steady divergent flow field arrival of tracer was monitored in an array of 13 boreholes intersecting the fracture over a square area of approximately 30 m on a side the arrival of tracer was detected in 11 of the 13 boreholes simulation of the transport process suggests that matrix diffusion may play a significant role in the migration of solutes contrary to previously published results the relative influence of advective dispersion was found to be increasingly diminished with increasing scale fracture apertures determined from the results of the tracer experiment were found to be in general agreement with apertures calculated from independent hydraulic tests the individual advective processes that contribute to advective dispersion remain unresolved on the basis of this experiment

seasonal ice extent on the northeast newfoundland shelf over the northeast newfoundland shelf the main source of ice is advection from the north by winds and currents using historical ice charts it is shown that the advance of ice is limited by ice melt throughout the winter months when the ocean provides the only source of heat part of which is lost to the atmosphere and part of which goes to melting ice following techniques developed by maykut 1978 1982 the vertical growth of sea ice south of 55 n is examined in terms of the net heat loss from the ocean fw and the conductive heat flux fc through the ice to the atmosphere fc is estimated by assuming a linear temperature gradient through the ice from the freezing point of seawater at the underside of the ice to the surface temperature calculated by solving the radiation balance at the ice surface using monthly climatological data the flux fw is estimated from monthly averaged temperature profiles from station 27 off st john s newfoundland in the south and from historical data from the labrador shelf in the north the results suggest that in the north over bare ice growth of approximately 1 cm d might be sustained off hopedale 55 n for december through march while in the south off st john s an estimated melt rate of 5 cm d can be sustained throughout the winter months growth rates are strongly dependent on the depth of snow cover and the fraction of open water the flux fw reaches 250 w m 2 at station 27 in january and it is suggested that much of this heat is derived from summertime heating when the whole of the northeast newfoundland shelf is ice free

roughness of natural fault surfaces the roughness of fault surfaces is important in the mechanics of fault slip and could play a role in determining whether sliding occurs via earthquakes or fault creep we have made preliminary measurements of the power spectral density of several fault surfaces over the wavelength range from 10 5 to 1 m using field and laboratory scale profilimeters the fault surfaces are strongly anisotropic profiles parallel to the slip direction have amplitudes about one order of magnitude lower than those perpendicular to the slip direction over most of the wavelength interval measured fault roughness perpendicular to the slip direction is similar to the roughness of natural joints the greater smoothness in the slip direction presumably represents wear resulting from slip combining our data with previous measurements of the roughness spectrum of the san andreas fault shows that fault surfaces are fractal over nearly eleven orders of magnitude in wavelength

physical and numerical studies of a fracture system model physical and numerical studies of transient flow in a model of discretely fractured rock are presented the physical model is a thermal analogue to fractured media flow consisting of idealized disc shaped fractures the numerical model is used to predict the behavior of the physical model the use of different insulating materials to encase the physical model allows the effects of differing leakage magnitudes to be examined a procedure for determining appropriate leakage parameters is documented these parameters are used in forward analysis to predict the thermal response of the physical model knowledge of the leakage parameters and of the temporal variation of boundary conditions are shown to be essential to an accurate prediction favorable agreement is illustrated between numerical and physical results the physical model provides a data source for the benchmarking of alternative numerical algorithms

a coupled ice ocean modeling study of the northwest atlantic ocean 1 a coupled ice ocean modeling system is developed for the northwest atlantic ocean based on the second version of the los alamos sea ice model and a regional ocean circulation model the coupled ice ocean system differs from other coupled systems for the same region mainly in two ways first the semi prognostic method suggested by sheng et al 2001 is used in the ocean component this method adjusts the momentum equation of the ocean component to reduce drift of the modeled ocean state allowing us to carry out a multiyear simulation second the sea ice component uses the elastic viscous plastic ice rheology developed by hunke and dukowicz 1997 and winton s 2000 three layer thermodynamics the coupled system is forced by climatological monthly mean atmospheric forcing at the atmosphere ocean atmosphere ice interface and oceanic forcing at the model open boundaries the system is integrated for 3 years model results from the third year compare favorably with the observations in the region the coupled system reproduces reasonably well the phase and magnitude of the annual cycle of sea ice we demonstrate the effect of the ice heat capacity previously unaccounted for in earlier model results of this region in delaying the springtime sea ice melt on the labrador and newfoundland shelves

coupled sea ice ocean state estimation in the labrador sea and baffin bay sea ice variability in the labrador sea is of climatic interest because of its relationship to deep convection mode water formation and the north atlantic atmospheric circulation historically quantifying the relationship between sea ice and ocean variability has been difficultbecause ofin situ observation paucity and technical challenges associated with synthesizing observations with numerical models here the relationship between ice and ocean variability is explored by analyzing new estimates of the ocean ice state in the northwest north atlantic the estimates are syntheses of in situ and satellite hydrographic and ice data with a regional 1 38 coupled ocean sea ice model the synthesis of sea ice data is achieved with an improved adjoint of a thermodynamicicemodel modelanddataaremadeconsistent inaleastsquaressense byiterativelyadjustingcontrol variables including ocean initial and lateral boundary conditions and the atmospheric state to minimize an uncertainty weighted model data misfit cost function the utility of the state estimate is demonstrated in an analysis of energy and buoyancy budgets in the marginal ice zone miz in mid march the system achieves a state of quasi equilibrium during which net ice growth and melt approaches zero newly formed ice diverges from coastal areas and converges via wind and ocean forcing in the miz the convergence of ice mass in the miz is ablated primarily by turbulent ocean ice enthalpy fluxes the primary source of the enthalpy required for sustained miz ice ablation is the sensible heat reservoir of the subtropical origin subsurface waters

convection in groundwater below an evaporating salt lake 1 onset of instability convective groundwater motion can be generated in aquifers beneath and adjacent to saline lakes such motions strongly control the subsurface distribution of salts the formation of saline minerals and the distribution of contaminants that may be disposed of in the saline lake in particular schemes to use saline lakes as evaporation basins for irrigation waste waters must consider the groundwater dynamics associated with convection the convection is driven by the evaporative concentration of salts at the land surface leading to an unstable distribution of density however the evaporative groundwater discharge can dynamically stabilize this saline boundary layer and inhibit convection in this work we investigate the nature and onset of convection for a range of boundary conditions typically found in saline lakes processes involved in the accumulation of salt at the surface of a groundwater discharge zone and in the gravitational instability of the near surface groundwater are considered results of theoretical stability analysis are applied through laboratory and numerical experimentation to the more complex geometries typically found in the field these comparisons indicate that for large saline lakes the stability of the saline boundary layer can be parameterized by traditional rayleigh criteria in which the aquifer permeability and the evaporation rate from the lake bed are principal controlling factors for typical saline lake environments convection will dominate in sediments whose permeability exceeds approximately 10 14 m2 below this threshold permeability the boundary layer should be stabilized by the evaporative flux resulting in the accumulation of salts and evaporites at the land surface these results provide insight into the predictive behavior of groundwater dynamics and solute distributions in many natural systems

a model of sea ice and the upper ocean mixed layer off labrador an existing dynamic thermodynamic ice model is coupled to an existing bulk mixed layer model of the upper ocean the model is applied to the seasonal evolution of ice in the marginal ice zone off labrador ocean currents are prescribed daily atmospheric observations are used as forcing the coupled model simulates the growth phase of ice and the evolution of the upper ocean temperature and salinity reasonably well the results show that mixed layer deepening can account for the offshore ice extent the southern extent of ice is influenced more by the meridional gradients in atmospheric heat flux and in ocean heat content lateral advection within the ocean is important in determining the southern ice extent

multiply polarized shear wave vsps from the cajon pass drillhole a 3 component vsp data set was acquired in the cajon pass drillhole with a multiply polarized shear wave source and a conventional p wave source producing a 9 component data set the vsp data show effects on the full wavefield from the sediment granite interface mode converted waves are identified with significant scattering of s wave energy from the leading p wavefront hodographs are used to display s wave particle motions in two dimensions shear wave splitting is observed in the hodographs the shear wave particle motion is used to infer anisotropy orientation with respect to the local strike of the san andreas fault stress induced fracturing is assumed to be a possible cause of the shear wave splitting a variation of particle motion orientation with depth is observed implying a variation in anisotropy orientation as a function of depth

a field example of measuring hydrodynamic dispersion in a single fracture a field example of measuring the dispersive properties of a single fracture in fractured plutonic rock is presented the experimental technique involves injecting a slug of conservative tracer into a steady groundwater flow field established between a pumping and recharging borehole and monitoring the tracer breakthrough by sampling the withdrawal water directly the breakthrough curves from two experiments were analyzed with a model which describes the flow field geometry either analytically or numerically and solves for hydrodynamic dispersion analytically a longitudinal dispersivity of 1 40 m was estimated by fitting the model to each set of field data the magnitude of the dispersion was determined to be independent of dispersive effects created by flow through the borehole instrumentation and thought to be purely hydrodynamic in nature

the formation of labrador sea water part i large scale processes abstract data obtained in the western labrador sea during march 1976 by hudson are analysed to show that new labrador sea water was being formed at this time on the basis of hydrographic and moored current meter data it is hypothesized that a 200 km scale cyclonic gyre forms in winter in the western labrador sea and that this gyre retains the developing deep mixed layers in this general area long enough for the transformation to labrador sea water to take place using a model it is demonstrated that water columns found along the western boundary of the labrador sea can be modified by cooling evaporation and mixing to form deep mixed layers with the properties of labrador sea water approximately 105 km3 of new labrador sea water was formed in 1976 an estimate that is consistent with earlier estimates of mean annual production rates this water 2 9 c 34 84 is some 0 6 c cooler and 0 06 fresher than that defined by lazier 1973 from his data collected in 1966 the variation of labrador sea water

contaminant transport in a single fracture periodic boundary and flow conditions the effects of time periodic inlet contaminant concentration and groundwater flow velocity on contaminant transport in a single planar fracture imbedded in a relatively impermeable rock matrix are investigated the calculations show that the contaminant propagates as a damped traveling wave into the matrix and along the fracture if longitudinal dispersion is neglected penetration of the wave into the matrix and fracture depends upon the input frequency as under uniform flow conditions a daily oscillation penetrates into the matrix and fracture approximately 1 cm and 1 m respectively an annual oscillation penetrates approximately 10 cm and tens of meters for the matrix and fracture respectively these results depend upon physical properties of the rock matrix and fracture and upon the flow velocity because longitudinal dispersion acts to further damp the amplitude of the traveling waves these results give maximum penetration distances for the waves if the flow velocity also has a small time periodic component the downstream contaminant oscillations are virtually unchanged unless the inlet condition and flow have the same frequency in this case a dc transport of contaminant transport occurs that may have an amplitude as large as one half of the magnitude of the velocity oscillation these results indicate that in the absence of resonance negligible error occurs in treating contaminant transport using mean inlet and flow conditions rather than more realistic time varying ones observations of oscillations however can be used to provide useful information on rock and fracture transport properties such as d and d

the local effects of groundwater pumpage within a fault influenced groundwater basin ash meadows nye county nevada u s a abstract large scale groundwater pumpage and water level decline data are used in a preliminary attempt to identify the hydraulic connection between several wells and devils hole a small pond in nye county nevada u s a results indicate that despite the discontinuous nature of the local aquifers many wells have good hydraulic connection with devils hole hydraulic connection between the wells and devils hole exhibits a complex spatial variability typical of carbonate terrane zones or directions of minimal hydraulic connection may result from fault controlled structural discontinuities zones or directions of enhanced hydraulic connection point to the presence of large scale groundwater flow through fractures or conduits the orientation of waterbearing fractures or conduits inferred from this study is qualitatively consistent with the major orientation of local and regional structural features

a coupled one dimensional sea ice ocean model a prognostic one dimensional mixed layer pycnocline model describing the vertical structure of the upper ocean is coupled to a thermodynamic sea ice model the coupled prognostic model is compared with the more usual sea ice model overlying a fixed mixed layer with constant oceanic heat flux and is then applied to investigate the effect of temporal and regional variations of the entrained oceanic heat flux on the sea ice cover in both polar regions in the southern ocean a standard simulation is compared with two perturbation experiments which both describe the occurrence of a polynya in the arctic ocean the effect of possible soviet river diversions is investigated finally the response of the coupled model to paleoclimatic forcing and boundary conditions is presented

diffusion in the matrix of granitic rock field test in the stripa mine three field experiments in granitic rock were performed at 360 m depth in a mine to investigate diffusion in the undisturbed rock matrix the results from all three experiments showed that tracers had migrated through the disturbed zone close to the injection hole and a distance into the undisturbed rock matrix these results show that it is possible for dissolved compounds to migrate into the rock matrix in its natural stress environment diffusivities and hydraulic conductivities obtained in this in situ experiment compare well with those obtained in laboratory experiments

assessing the validity of the channel model of fracture aperture under field conditions in recent investigations of fluid and solute movement in discrete fractures spatial heterogeneity of the fracture aperture has been conceptualized as a series of noninterconnecting constant aperture flow paths or channels two methods of estimating the distribution of the aperture sizes are presented using information from a single hole pumping test and a radially converging tracer test the first method uses the transmissivity of the fracture and mean arrival time of the tracer while the second method uses the mean and variance of the solute arrival time if the fracture can be conceptualized as a series of nonintersecting flow paths of constant aperture the two methods should yield identical estimates for the parameters of the distribution the validity of the channel model can be assessed by comparing the parameters of the distribution that are estimated by the two methods this technique was demonstrated using hydraulic and tracer tests conducted in a discrete areally extensive horizontal fracture in the silurian dolomite in the northeastern illinois a lognormal and a truncated gamma distribution were used to describe the distribution of constant aperture flow paths the lognormal distribution could not reproduce the abrupt rising limb and maximum rate of mass arrival that characterized the tracer tests the gamma distribution more accurately predicted the shape of the breakthrough curves however the two methods of estimating the parameters of the distribution provided significantly different estimates of the variances of the aperture sizes the mean aperture as estimated by the two methods was similar the difference in the variance of the aperture as estimated by the two methods indicates that alternative conceptual models of aperture heterogeneity are required to more accurately describe both fluid and solute movement in this field situation

sea ice winter convection and the temperature minimum layer in the southern ocean the structure of the near surface waters in the southern ocean poleward of the antarctic polar front but away from continental margins is investigated with a three dimensional time dependent numerical model which resolves the annual sea ice cycle the growth and decay of the ice field is predicted using one of semtner s 1976 thermodynamic ice models in terms of specified atmospheric data and computed thermohaline characteristics of the ocean layers the ice field is found to be sensitive to the lateral advection of heat by the oceanic circulation as well as vertical heat transports due to deep winter convection the model treats the temperature minimum layer in the southern ocean as the remnant of a deep winter mixed layer which becomes capped by surface heating and precipitation in summer the predicted thermohaline characteristics of the temperature minimum layer and the surface mixed layer are in good agreement with observations finally the annual air sea heat exchange predicted by the model is discussed the model s predicted area averaged heat loss experienced by the ocean south of the atlantic polar front is much smaller than was previously estimated this is attributed to errors in the southern region of the model domain it is suggestedmore that models which include the interactions between sea ice and surface deep and bottom waters along the continental margins are needed to investigate this region less

analytical models of slug tests in the present paper attempts are made to develop solutions to various models of slug tests that may be applicable in analyzing the results of such tests where existing solutions are inadequate various geometries that may be encountered in heterogeneous systems such as fractured rocks are considered solutions are presented for linear flow radial flow with boundaries two layer and concentric composite models with different flow geometries between the inner and outer region solutions are obtained in laplace space and inverted back to real space numerically type curves are presented for each solution analyses of the type curves and derivative response curves reveal that many curves have unique shapes only for certain combination of the flow parameters and the distance other sets of type curves are similar in shape although log log plots and derivative plots may emphasize some features that may not be apparent in semilog plots these results show that slug tests suffer problems of nonuniqueness to a greater extent than other well tests

growth of contact area between rough surfaces under normal stress the contact area between deforming rough surfaces in marble alabaster and quartz was measured from thin sections of surfaces bonded under load with low viscosity resin epoxy the marble and alabaster samples had contact areas that increased with stress at an accelerating rate this result suggests that the strength of the asperity contacts decreased progressively during the deformation following some form of strain weakening relationship this conclusion is supported by petrographic observation of the thin sections that indicate that much of the deformation was cataclastic with minor twinning of calcite and kinking of gypsum in the case of the quartz the observed contact area was small and increased approximately linearly with normal stress only the irreversible cataclastic deformation was observed however strain induced birefringence and cracking of the epoxy not observed with the other rocks suggests that significant elastic deformation occurred but recovered during unloading

an approximate solution for one dimensional absorption in unsaturated porous media the boundary layer or integral method was used to derivea closed form approximate solution for one dimensional absorption ofwater in an unsaturated porous medium whose characteristic curves are ofthe van genuchten type in this approach an assumed saturation profile issubstituted into the governing equation and integrated from the boundaryout to the wetting front this yields closed form solutions for the frontlocation and the instantaneous liquid flux of the boundary the accuracyof this solution in predicting the flux as determined by comparison withnumerical solutions utilizing a boltzmann type transformation is alwayswithin 15 percent for any value of the initial saturation as an exampleof the use of this approximate solution saturation profiles werecalculated for absorption into the topopah spring volcanic tuff at yuccamountain nevada the site of the proposed nuclear wasterepository

evaluation of electromagnetic tomography to map in situ water in heated welded tuff an experiment was conducted in the g tunnel complex at the nevada test site to evaluate geotomography as a possible candidate for in situ monitoring of moisture content near a heater in densely welded tuff alterant tomographs of electromagnetic permittivity at 200 mhz were made of the densely welded tuff in two planes near a heater which was used to simulate the thermal load of a nuclear waste container when the 1 kw heater was turned on the tomographs indicated a rapid and strong drying adjacent to the heater moisture loss was not symmetric about the heater but seemed to be strongly influenced by heterogeneity in the rock mass the linear character of many tomographic features and their spatial correlation with fractures mapped in boreholes are evidence that drying was most rapid along certain fractures when the heater was turned off an increase in moisture content occurred around the heater and along the dry fractures however this process is much slower and the magnitude of the moisture increase much smaller than the changes observed during heating of the rock the interpretation of the tomographs is preliminary until they can be processed without the restrictive assumption of straight ray paths for the signals through the highly heterogeneous rock mass however from these preliminary results we conclude that geotomography can provide useful moisture content information near a heater in densely welded tuff this conclusion is based on the fact that the experiment results and their interpretation are self consistent and in good agreement with behavior expected of the heated rock mass

a study of thermally induced convection near a high level nuclear waste repository in partially saturated fractured tuff we present simple estimates for velocities of buoyancy driven flow of liquid and gas phases near a hypothetical high level nuclear waste repository in partially saturated fractured tuff these estimates indicate that gas phase convection could take place with appreciable velocity of the order of 20 m year while liquid convection is expected to be very slow of the order of 0 1 mm year detailed numerical simulations using an effective continuum approximation to represent fracture effects confirm these estimates and demonstrate a sensitivity of gas convection to the strength of binary diffusion

testing a coupled ice mixed layer model under subarctic conditions abstract a one dimensional oceanic mixed layer model has been coupled with a thermodynamic sea ice model in order to study the seasonal cycle of ice ocean interaction in the subarctic ocean the ice thickness is assumed constant and only variations of ice compactness under the effect of the atmospheric and oceanic heat fluxes are considered the mixed layer model allows prediction of the rate of entrainment mainly as the result of the penetrative buoyancy driven convection both heat and salt conservation equations are included so that the respective efficiency with regard to vertical mixing of brine rejection below the ice and intense surface cooling in open water can be compared the model has been run for ten years on a zonal vertical section across the greenland sea the annual entrainment retreat cycle of the mixed layer is well reproduced with maximum depths occurring in late winter even down to the bottom at some locations near the ice edge surface cooling is found to be a more efficient mecha

scale dependence of continuum models for fractured basalts numerical simulations are carried out to determine the scale above which an equivalent porous medium epm model can be used to represent flow through the dense interiors of fractured basalts steady laminar flow is assumed to occur through the interconnected network of conduits formed by the intersecting column defining fracture patterns of the basalt dense interiors the basalt rock matrix is considered to be impermeable a porous medium equivalence is established in terms of fluid darcian fluxes a polar plot for the equivalent hydraulic conductivity is used to test whether a given fractured basalt system can be approximated as an epm for interconnected colonnade network models of filled or unfilled fractures with uniform apertures and a column diameter of 1 m epm models are appropriate at a length scale of approximately 6 times the column diameter for network models of filled or unfilled fractures with a lognormal aperture b millimeters distribution mean in b 1 945 and ln b 0 896 epm models can be justified at length scales of approximately 22 and 27 times the column diameter respectively the computed equivalent k values for clay filled fractures compare favorably with the field measured data this suggests that a model comprised of an interconnected network of filled fractures may not be an unlikely representation of flow through the dense interiors at the small scales considered in this study several limitations of the study are noted

fracture characterization by means of attenuation and generation of tube waves in fractured crystalline rock at mirror lake new hampshire results are presented from experiments carried out in conjunction with the u s geological survey at the hubbard brook experimental forest near mirror lake new hampshire the study focuses on our ability to obtain orientation and transmissivity estimates of naturally occurring fractures the collected data set includes a four offset hydrophone vertical seismic profile full waveform acoustic logs at 5 15 and 34 khz borehole televiewer temperature resistivity and self potential logs and borehole to borehole pump test data borehole televiewer and other geophysical logs indicate that permeable fractures intersect the mirror lake boreholes at numerous depths but less than half of these fractures appear to have significant permeability beyond the annulus of drilling disturbance on the basis of acoustic waveform log analysis the vertical seismic profiling vsp data indicate a single major permeable fracture near a depth of 44 m corresponding to one of the most permeable fractures identified in the acoustic waveform log analysis vsp data also indicate a somewhat less permeable fracture at 220 m and possible fractures at depths of 103 and 135 m all correspond to major permeable fractures in the acoustic waveform data set pump test data confirm the presence of a hydraulic connection between the mirror lake boreholes through a shallow dipping zone of permeability at 44 m in depth effective fracture apertures calculated from modeled transmissivities correspond to those estimated for the largest fractures indicated on acoustic waveform logs but are over an order of magnitude larger than effective apertures calculated from tube waves in the vsp data set this discrepancy is attributed to the effect of fracture stiffness a new model is presented to account for the mechanical strength of asperities in resisting fracture closure during the passage of seismic waves during the generation of vsps

matching a field tracer test with some simple models simple models of fluid flow and dispersion in a porous rock matrix are compared and used to match the results of tracer tests at the wairakei new zealand geothermal field it is found that models which allow transient diffusion from fractures into the surrounding rock matrix give a better match to test results than either a model which allows only longitudinal dispersion or a pseudo steady state double porosity model for some tests a model which includes two fractures is required to match the field data

laboratory and simulation studies of solute transport in fracture networks physical and numerical fracture network models have been used to analyze the transport of conservative solutes in systems of parallel sided fractures the processes controlling dispersion in fracture systems that are explicitly simulated by the numerical model are 1 development of a velocity profile within individual fractures 2 transverse molecular diffusion between streamlines both within fractures and at fracture junctions and 3 advection with the bulk fluid through a system of fractures with a range of hydraulic gradients and apertures the first two processes referred to as microdispersion are often assumed to be secondary to the third referred to as macrodispersion the validity of this assumption is however highly dependent on the hydrodynamics of the system under consideration data collected from a physical model of a fracture network are used to validate a numerical model that explicitly simulates all three transport processes the numerical model is then used to evaluate the relevance of microdispersion processes in a system where macrodispersion is significant

rb sr chronology and crystal chemistry of celadonites from the parana continental tholeiites brazil abstract celadonites from the parana flood basalts have been dated by internal rb sr isochrons using the ammonium acetate leaching technique previously used by hart and staudigel 1986 for celadonites from dsdp holes the residues after leaching have very high 87rb 86sr ratios 18 7 1900 and very radiogenic 87sr 86sr 0 73 2 96 electron microprobe analyses show that potassium and thus also presumably rubidium became enriched in these minerals during the transformation of a proto celadonite smectite phase into celadonite our leaching experiment suggests that radiogenic 17sr and rubidium are very resistant to chemical fractionation during leaching and thus may have remained in closed system for rb sr chronology ages varying from 107 1 to 81 1 ma have been obtained at two different sites one on high ti basalts in the northern parana basin and the other on low ti basalts in the southern basin these ages are significantly younger than the eruption of the flood basalts 127 137 ma and in this respect are in good agreement with results obtained on celadonites from oceanic ridges initial 87sr 86sr ratios are distinctly higher in the celadonites than in the host basalts probably due to contamination by radiogenic strontium transported by the hydrothermal fluids our results suggest that mineralogy and isotopic composition are different in celadonites from the northern and southern parana basins although this needs to be confirmed on a larger dataset

on a test case for density dependent groundwater flow and solute transport models the salt lake problem like any other computer model density dependent mathematical groundwater models must be verified to ascertain that they accurately represent the physics implied by a governing set of equations very few test cases for density dependent groundwater numerical models exist as such there is still a need for new and more robust tests of these modeling codes in this paper a numerical model of an idealized evaporating salt lake is produced using the two dimensional density dependent saturated unsaturated transport sutra model the results of which are compared with an equivalent laboratory hele shaw cell system developed by wooding et al 1997a b evaporation results in dense brine overlying less dense fluid which is hydrodynamically unstable and leads to downward convection of salt fingers or plumes a comparison of experimental and numerical plume growth shows good spatial and temporal agreement the numerically generated plume pattern is sensitive to changes in random noise level applied just below the evaporation surface that serves as a trigger for the growth of instabilities experimental plume patterns were best matched with a noise level corresponding to 1 of the total salinity difference between boundary layer and background fluid concentrations at saturation in a second comparison the stream function based finite difference model described by wooding et al 1997a b which differs significantly in principle from sutra is shown after revision to give good spatial and temporal agreement with experimental results this test for density dependent groundwater models appears to be the most comprehensive and detailed available to date

some anomalous features of flow and solute transport arising from fracture aperture variability model fractures with variable apertures are generated by a statistical method and water flow and tracer transport in these fractures are calculated tracer injection and collection are simulated for parallel and convergent flow fields the impact of the use of different injection flow rates and the different locations of injection and collection points are studied the results show that the transport time dispersion and the so called mass balance fracture aperture are very sensitive to the location of the injection point and the injection flow rate these anomalous effects appear to be consistent with observations in several recent field experiments the implications of the calculated results on the analysis of tracer tests are discussed it is concluded that because of the stochastic nature of variable fracture apertures and their permeabilities a point tracer test in a fracture is not sufficient to characterize the properties of the fracture dispersivities and apertures calculated from different tracer tests in the same fracture may vary by orders of magnitude depending on the flow rate and the location of the injection however a line injection of tracer averaged over a series of adjacent points may avoid some of these problems

dispersion in tracer flow in fractured geothermal systems interpretation of tracer tests is commonly based on the analysis of flow through a porous medium in geothermal reservoirs however the principal permeability arises from fractures and a porous medium approach is not applicable the dispersion of tracer material flowing in a fracture is shown to be dominated by molecular diffusion across the fracture a mechanism known as taylor dispersion for typical values of reservoir parameters this transverse diffusion will obliterate any transverse tracer concentration gradients caused by the velocity profile across the fracture the effective dispersivity is found to be a function of fracture aperture mean flow velocity and molecular diffusivity and is orders of magnitude greater than for porous medium flow typically peclet numbers are anticipated to lie between orders 1 and 100 and field results confirm this range

hydrographic preconditioning for seasonal sea ice anomalies in the labrador sea abstractthis study investigates the hydrographic processes involved in setting the maximum wintertime sea ice si extent in the labrador sea and baffin bay the analysis is based on an ocean and sea ice state estimate covering the summer to summer 1996 97 annual cycle the estimate is a synthesis of in situ and satellite hydrographic and ice data with a regional coupled ocean sea ice model si advective processes are first demonstrated to be required to reproduce the observed ice extent with advection the marginal ice zone miz location stabilizes where ice melt balances ice mass convergence a quasi equilibrium condition achieved via the convergence of warm subtropical origin subsurface waters into the mixed layer seaward of the miz an analysis of ocean surface buoyancy fluxes reveals a critical role of low salinity upper ocean 100 m anomalies for the advancement of si seaward of the arctic water irminger water thermohaline front anomalous low salinity waters slow the rate of buoyancy loss driv

dispersed fluid flow in fractured reservoirs an analysis of tracer determined residence time distributions a methodology for analyzing the internal flow characteristics of a fractured geothermal reservoir using tracer determined residence time distribution curves is outlined emphasis is placed on comparison of the statistical quantities obtained from the tracer curves of different reservoirs or of the same reservoir under different conditions in this way model independent information may be used unambiguously to construct empirical reservoir performance correlations downhole measurements of the tracer response exiting from discrete fracture zones permit further characterization of reservoir fluid flow behavior tracer experiments conducted in prototype hot dry rock geothermal reservoirs in fractured rock are examined using these statistically based data analysis methods

spatially varying hydraulic and solute transport characteristics of a fractured till determined by field tracer tests funen denmark a natural gradient tracer test that simulated one dimensional flow was conducted in a large 4 m 4 8 m surface area isolated block of fractured till in funen denmark to determine both bulk and spatially distributed hydraulic properties hydraulic conductivity based on free flow tests was higher in the upper 2 5 m 5 81 10 5 m s 1 than in the upper 4 m 8 00 10 6 m s 1 of till indicating the more highly fractured and bioturbated nature of the upper part of the till chloride was introduced at the surface of the block as nacl solution 490 mg l 1 cl and breakthrough of cl was monitored in 13 horizontal screens at depths of 2 5 and 4 m arrival times of half of the input cl concentrations c c0 0 5 ranged about sevenfold among various screens at each sampling depth 5 35 hours at 2 5 m and 11 68 hours at 4 m chloride breakthrough data for the two depths were fitted to both an equivalent porous media epm model based on the convective dispersive equation and a discrete fracture model these results indicate differences in transport characteristics of the till with depth at the 2 5 m depth the epm model fit the initial part of the breakthrough curves quite well for most samplers but did not predict the long tails adequately the converse was generally true for the discrete fracture model thus it appears that transport in the upper 2 5 m of till is controlled by a complex interconnected system of fractures and macropores field measurements of fractures and macropores at this site substantiate these results at the 4 m depth the discrete fracture model described solute transport in all samplers better than the epm model indicating that vertical fracture flow dominates in the lower portion of the block fracture apertures and spacings were estimated based on the cubic law and fitting the breakthrough data to the discrete fracture model fitted fracture spacings at the 4 m depth 0 025 0 08 m were slightly smaller than the minimum spacing 0 09 m mapped in the field calculated apertures at the 4 m depth were large compared with other studies and ranged from 65 to 127 m average value of 94 m

a two dimensional coupled ice ocean model of the bering sea marginal ice zone a two dimensional coupled ice ocean model has been formulated and applied to the wintertime bering sea marginal ice zone the oceanic component is a multilevel model that incorporates second moment closure for turbulent mixing in the water column the ice cover is modeled as a viscous plastic continuum melting at the ice ocean interface is computed using well known lawof the wall concepts in a turbulent boundary layer with particular attention to the disparate momentum and scalar transfer resistance coefficients over rough walls the thermodynamic and dynamical interactions between the ocean and the ice cover and the energy balances at the air ice and air sea interfaces are modeled according to the companion paper mellor and kantha this issue the model incorporates barotropic tides both diurnal and semidiurnal for application to the bering shelf double diffusive fluxes across the interface between the colder fresher layer beneath the melting ice and the warmer more saline water underneath are prescribed from laboratory data on double diffusive convection during winter sea ice in the central bering sea is transported toward the shelf break by off ice winds where it encounters northward flowing warmer north pacific waters and melts it is this situation to which the two dimensional model has been applied by neglecting all variations in the along ice edge direction the water conditions downstream of the ice edge the ice conditions upstream and the wind stress are the primary inputs to the model the model simulates transition from ice covered to open ocean conditions and the associated ice edge front and the two layer circulation underneath the ice cover sensitivity studies indicate that the density structure and the circulation beneath the ice and the position of the ice edge are rather sensitive to the parameters affecting the dynamics and the thermodynamics of the coupled ice ocean system even small changes in the relevant parameters can cause a substantial retreat or advance of the ice edge which may help explain why marginal ice zones are such dynamically active regions

on thermohydrologic conditions near high level nuclear wastes emplaced in partially saturated fractured tuff 2 effective continuum approximation this paper presents an effective continuum approximation for modeling of fluid and heat flow in fractured porous media the approximation is based on the thermohydrologic behavior observed in detailed simulations with explicit consideration of fracture effects see the companion paper part 1 the crucial concept in the development of an effective continuum approximation is the notion of local thermodynamic equilibrium between rock matrix and fractures where applicable it provides a substantial simplification of the description of fluid and heat flow in fractured porous media we derive formulas for effective continuum characteristic curves relative permeabilities and capillary pressures in terms of the properties of fracture and matrix continua respectively numerical simulations demonstrate that under favorable conditions the effective continuum approximation closely matches predictions obtained from an explicit modeling of fracture effects it is also demonstrated that the approximation breaks down under unfavorable conditions very tight rock matrix a simple criterion for the applicability of an effective continuum approximation is derived from consideration of diffusive processes a quantitative evaluation shows the criterion to be consistent with results of our numerical simulations

on thermohydrologic conditions near high level nuclear wastes emplaced in partially saturated fractured tuff 1 simulation studies with explicit consideration of fracture effects we have performed modeling studies on the simultaneous transport of heat liquid water vapor and air in partially saturated fractured porous rock formation parameters were chosen as representative of the potential nuclear waste repository site in the topopah spring unit of the yucca mountain tuffs the presence of fractures makes the transport problem very complex both in terms of flow geometry and physics the numerical simulator used for our flow calculations takes into account most of the physical effects believed to be important in multiphase fluid and heat flow it has provisions for handling the extreme nonlinearities that arise in phase transitions component disappearances and capillary discontinuities at fracture faces we model a region around an infinite linear string of nuclear waste canisters taking into account both the discrete fractures and the porous matrix thermohydrologic conditions in the vicinity of the waste packages are found to depend strongly on relative permeability and capillary pressure characteristics of the fractures which are unknown at the present time if liquid held on the rough walls of drained fractures is assumed to be mobile strong heat pipe effects are predicted under these conditions the host rock will remain in two phase conditions right up to the emplacement hole and formation temperatures will peak near 100 c if it is assumed that liquid cannot move along drained fractures the region surrounding the waste packages is predicted to dry up and formation temperatures will rise beyond 200 c a substantial fraction of waste heat can be removed if emplacement holes are left open and ventilated as opposed to backfilled and sealed emplacement conditions comparing our model predictions with observations from in situ heater experiments reported by zimmerman and coworkers some intriguing similarities are noted however for a quantitative evaluation additional carefully controlled laboratory and field experiments will be needed

investigation of the hydraulic connection between the upper storage reservoir and the underground powerhouse in the hongping pumped storage hydroelectric powerstation field tracer tests in fractured rocks were performed to investigate the hydraulic connection between the upper storage reservoir and the underground powerhouse in the hongping pumped hydroelectric storage powerstation hphsp data from tracer measurement points indicated the appearance of multiple peak values during the course of tracer migration which revealed multiple water pathways in fractured aquifers owing to the development and intersection of fractures and faults also complex hydrogeological structural systems were proposed according to geological data from borehole logs and outcrops seen in the exploration adit these structures revealed the different permeability and strong heterogeneity of the fractured media and can therefore explain the existence of a concentrated water conducting passage from the upper storage reservoir to the underground powerhouse multiple peak values in the field tests were examined using a laboratory cross fracture experiment involving tracer migration and numerical simulation based on transition probability according to the observed data and the numerical results the laboratory model and simulation method can capture the characteristics of groundwater flow and tracer migration in fractured rocks

space time variation of mixed layer properties heat and salt fluxes and ice melt in the newfoundland marginal ice zone oceanographic data collected in the newfoundland marginal ice zone in march 1992 are analyzed to study the variation of mixed layer properties across the ice zone the mixed layer depth decreases from 80 m in the interior of the pack ice to 25 m at the eastern ice edge over a distance of 120 km in the open ocean without ice cover the depth is considerably greater 150 200 m the temperature under the pack ice is near freezing a sharp increase in both the temperature and salinity occurs across the ice edge the variation of the mixed layer properties is simulated by integrating a one dimensional bulk mixed layer model coupled to sea ice from november 1991 to march 1992 the initial ocean conditions are obtained from an objective analysis of archived data of november 1991 the forcings are 6 hourly meteorological data from the european centre for medium range weather forecasts ice concentration and thickness are treated as prescribed functions of time extracted from daily ice maps since ice in the area is not locally formed the model simulation is in good agreement with the observations from the model results a detailed analysis of the roles of wind stress ice melt surface cooling and shortwave radiation in the water mass transformation of the upper ocean is carried out there are large differences in the melt rate and water ice heat flux between the times when ice enters the shelf and after the water has been cooled by the ice to near freezing 15 20 cm d 1 and 500 700 wm 2 and 0 2 cm a 1 and 20 50 wm 2 respectively a large portion of the heat in the water column is expended for ice melting from january to march calculations that use surface data such as surface wind and sea surface temperature without considering ice melt can underestimate the net ocean to air heat flux especially at the eastern ice edge in march

response of two phase fluids to fracture configurations within submarine hydrothermal systems submarine hydrothermal systems at mid ocean ridges evolve within a region of brittle deformation overlying a region of ductile deformation the interplay between brittle and ductile modes of deformation and the geometry of fracture systems within the brittle zone can exert a significant influence on fluid flow especially under conditions leading to aqueous two phase separation within the brittle region fractures vary between large conduits directly open to the seafloor and small veins and microcracks with constricted or indirect connections to the seafloor in the ductile region fluids may be trapped under near lithostatic pressure while fluids within throughgoing veins in the brittle region will experience hydrostatic pressure in a narrow transition zone between these two extremes a steep pore fluid pressure gradient must exist in the brittle region itself fluid pressures will vary between lithostatic and hydrostatic as fluid occupies interstices varying from isolated pores through tortuous microcracks to channels directly connected to the main upflow conduits a hydrostatic gradient modified by the decreased density of hot fluid and the effects of the flow itself should be applicable in major conduits open to the seafloor fluctuating pressure conditions in the transition zone may induce phase changes in a fluid remaining at constant depth as a result of the large volume increase that accompanies two phase separation a two phase fluid must either accelerate upward or exert an increased pressure on its surroundings possibly leading to enhanced fracturing the fracture configuration will also affect the behavior of the mixed fluid after phase separation a two phase fluid experiencing rapid turbulent flow in a large open conduit is more likely to remain a well mixed suspension of vapor and liquid whereas a two phase mixture in a constricted branching series of channels moving more slowly in a laminar flow regime is more likely to undergo physical isolation of the phases leading to venting of a vapor phase and retention of a saline brine phase at depth we propose a possible configuration for the fracture pattern within a submarine hydrothermal system consisting of a feeder zone comprised of anastomozing microcracks and veinlets progressively increasing in diameter and decreasing in abundance feeding into a main upflow stockwork zone in which flow directly to the surface takes place in relatively large unconstricted conduits fluid movement within a feeder zone may be modified by capillary flow tortuous channelways disconnected fractures blocking of cracks by mineral deposition and opening of new fractures

a model study of upper ocean sea ice interactions abstract a thermodynamic sea ice model including leads has been coupled to a one dimensional oceanic mixed layer model in order to investigate the upper ocean sea ice interactions the oceanic heat flux at the base of the ice layer fb is predicted not imposed assuming a thermodynamic equilibrium between the bottom of the ice and the water just below for testing of the model the annual cycle of the arctic sea ice and upper ocean is simulated along longitude 169 5 w the model produces a realistic evolution of the sea ice thickness and extent and of the upper mean salinity and temperature profiles the major deficiencies in the simulation are linked to the absence of ocean and ice dynamics the modeled value of fb is far from being constant below thin ice it can be larger than 5 w m 2 due to the important fraction of the solar irradiance that is transmitted through the ice absorbed in the mixed layer and then returned to the ice below the thicker perennial sea ice fb takes values between 0 and

a review of sea ice and ocean modeling relevant to the labrador and newfoundland shelves numerical and analytical models of sea ice and ocean circulation are reviewed from a viewpoint of their application to the labrador and newfoundland shelves seasonal variabilities of sea ice and ocean circulation have not been reported in numerical models the difficulty comes from the importance of both stratification and bottom topography sea ice should be included for seasonal cycle calculations individual mechanisms of variabilities with time scales ranging from a day to a month have been studied extensively using various models so that the coupling of these models will make it possible to test the predictability of sea ice and ocean circulation the data collected during limex 87 and 89 provide verification of the models