transient development in confluent and diffluent flow abstract explaining the growth of disturbances superimposed on mean flows is a central problem in meteorology most widely studied models of the development process involve perturbations to shear flows with shear restricted to the meridional direction recently the importance of zonal variation of the mean flow was recognized and the study of shear flows extended to include zonal variation in shear these studies found that the eigenfunctions associated with unstable modes in the simple shear problem are highly sensitive to zonal variation of the mean flow however there also exists another mechanism for development in a zonally inhomogeneous flow field transient growth not associated with exponential instability properly configured perturbations exhibit transient growth in deformation fields associated with regions of confluence and diffluence at rates comparable to development in shear flow in this work analytic solution of the linear initial value problem for the barotropic vorticity equation in de

deltaic sedimentation in an unstable tectonic environment the lower limestone group lower carboniferous of east fife scotland the lower limestone group which outcrops extensively on the east coast of fife southeast scotland consists of interbedded sandstones siltstones and claystones with occasional coal seams and limestone beds several of the coals have been mined economically in the past the sequence was deposited in a shallow water deltaic setting three facies associations have been distinguished 1 laminated claystones and marine bioclastic limestones which were deposited in prodelta and marine shelf environments 2 crudely coarsening upward sandstone units interpreted as delta front deposits of fluvially dominated though wave influenced shallow water deltas and 3 interbedded clastic sedimentary rocks and coals deposited in delta plain environments the sequence as a whole accumulated by repeated progradation and abandonment of deltaic complexes palaeosol profiles of four types are superbly preserved within the delta plain facies association these are 1 organic soils peats now coal seams 2 gley palaeosols which formed in persistently waterlogged conditions 3 freely drained soils which formed on a quartz sand rich substrate and 4 similar profiles formed by free drainage through variable substrates and involving b horizon accumulation of concretionary iron oxides compound palaeosols are common deposition of the lower limestone group was influenced by the tectonic and volcanic instability of the fife area during visean times frequent seismic events centred on active fault lines caused local uplift of parts of the normally waterlogged delta plain environment allowing the formation of well drained soils peats coals were best developed and least affected by oxidation in an elongate fault bounded zone of enhanced subsidence

simulated life cycles of persistent anticyclonic anomalies over the north pacific role of synoptic scale eddies abstract this study examines the role of synoptic scale eddies during the development of persistent anticyclonic height anomalies over the central north pacific in a general circulation model under perpetual january conditions the gcm replicates the basic characteristics of the evolution of the anomaly patterns found in observations the life cycle is characterized by the rapid establishment of the major anomaly center and considerably longer maintenance and decay phases which include the development of downstream anomaly centers the simulation also shows a realistic evolution of synoptic scale activity beginning with enhanced activity off the east coast of asia prior to onset followed by a northward shift of the pacific storm track which lasts throughout the maintenance phase the initial enhancement of synoptic scale eddy activity is associated with a large scale cyclonic anomaly that develops over siberia several days prior to the onset of the main anticyclonic anomaly over the central north pacif

measured anisotropy in pierre shale the five elastic coefficients which characterize a transversely isotropic medium have been measured for the pierre shale the first arrival times deduced from two closely spaced vertical seismic profiles provide values of magnitude and direction of the phase velocity at a given depth for different locations of the sources from these velocities we can estimate the five elastic coefficients by assuming that the p and sv wave velocities have only a small dependence on the angle of propagation on the other hand it is shown that the accuracy in the difference between the directions of propagation and particle motion is not sufficient to determine the anisotropy this work was industrially sponsored through the integrated geophysics project

seismic anisotropy in sedimentary rocks part 1 a single plug laboratory method a single plug method for measuring seismic velocities and transverse isotropy in rocks has been rigorously validated and laboratory tested the method requires only one sample to measure the velocities needed to derive the five independent elastic constants for transversely isotropic materials in this method piezoelectric transducers are fitted to the top bottom and sides of the cylindrical sample laboratory velocity and anisotropy can be measured as functions of pressure temperature fluid saturation and fluid displacement because this method uses a horizontal core plug that has much higher permeability than a vertical core plug it is especially suitable for low permeability shale measurements it reduces the sample preparation and velocity measurement time by more than two thirds

determining formation shear wave transverse isotropy from borehole stoneley wave measurements many rocks exhibit transversely isotropic ti characteristics for determining the ti property using acoustic logging stoneley waves are the only borehole wave mode that has a significant sensitivity to ti effects especially when the formation is acoustically slow compared to the borehole fluid this study describes a method for deriving the formation shear wave ti parameter from the stoneley wave data acquired by a logging tool it is shown that the presence of the tool in the borehole can substantially affect the stoneley wave propagation fortunately for low frequency stoneley waves the tool effect can be satisfactorily modeled using an effective modulus regardless of the actual structure of the tool the modulus can be determined from a calibration procedure in the inversion processing of the stoneley wave data the stoneley wave slowness is related to the weighted average of the wave s dispersion curve over the frequency range occupied by the wave spectrum this provides a fast method for the inversion as a processing example this method has been applied to estimate the shear wave ti parameter profile for the lewis shale formation in braggs wyoming the resulting profile delineates the shear wave anisotropy magnitude and variation for this shale formation

the dynamics of large scale cyclogenesis over the north pacific ocean abstract earlier studies of persistent large scale flow anomalies have been extended with the aim of identifying the primary mechanisms for persistent anomaly development in this study the focus is on wintertime cases of persistent cyclonic flow anomalies over the north pacific these cases are typically manifested by an abnormally intense cyclonic circulation extending over the north pacific basin an unusually strong and eastward extended east asian jet and a well defined pacific north american teleconnection pattern we have conducted extensive diagnostic analyses in order to determine the mechanisms responsible for development in particular these diagnostics examine the processes influencing the time evolution of eddy potential enstrophy and potential vorticity anomalies the cases are preceded by a buildup of anomalously high potential vorticity air at upper levels over eastern asia this high potential vorticity air is initially advected eastward in association with synoptic scale cyclogenesis

variability of the observed midlatitude storm tracks in relation to low frequency changes in the circulation pattern abstract the principal modes of month to month variability of the wintertime storm tracks over the north pacific and north atlantic are identified by empirical orthogonal function analysis of the root mean square statistics of bandpass 2 5 6 day filtered geopotential height data for 19 yr one of the two leading modes depicts fluctuations in the level of synoptic scale activity without any noticeable spatial displacement of the storm track axes whereas the other mode is associated with meridional shifts of the storm tracks from their time averaged positions higher order modes are indicative of diversion or truncation of cyclone tracks in particular geographical regions it is demonstrated that the leading storm track modes are linked to some of the best known monthly averaged teleconnection patterns the dipolar western pacific and western atlantic patterns for the monthly mean flow are seen to be accompanied by marked changes in the intensity of the storm tracks over the western oceans whereas the m

life cycles of persistent anomalies ii the development of persistent negative height anomalies over the north pacific ocean abstract the present study extends our previous work on the life cycles of persistent anomalies by providing more comprehensive analyses of the synoptic and dynamical characteristics associated with the developments of the anomalies we focus here on the developments of major cases of persistent negative height anomalies over the extratropical central north pacific pac region during wintertime these ewes are generally manifested at the surface by an anomalously intense and eastward displaced aleutian low and at upper levels by an abnormally strong zonal jet that extends across most of the western and central pacific at midlatitudes the associated flow anomalies usually resemble particularly strong realizations of the pacific north american pna teleconnection pattern the large scale flow anomalies are typically preceded by a buildup of anomalously cold air over asia and an intensification of the upper level jet over southeastern asia and the fox western pacific a few days prior to the larger scal

sonic logging in deviated boreholes penetrating an anisotropic formation laboratory study development of deepwater fields requires drilling deviated or horizontal wells many formations are highly anisotropic that is the p and s wave velocities vary with propagation direction sonic logs acquired in these wells need to be corrected for anisotropy effects before the logs can be used in formation evaluation and seismic applications in this study we use a laboratory model made of an orthorhombic phenolite block to study acoustic logging in deviated wells we first measure the qp qsv and sh wave group velocities by using body waves at angles of 0 15 30 45 60 75 and 90 relative to the slowest p wave principal axis of the phenolite block we then drill holes at the same angles in the block we record monopole and dipole sonic waveforms in these holes and extract the qp qsv sh and stoneley wave velocities by using the slowness time semblance method the velocities measured through the use of monopole logging and dipole logging vary with borehole deviations we find that an equivalent transversely isotropic ti model can fit the measured qp qsv and stoneley wave velocities very well the s wave velocities at low to medium borehole deviations can be used to differentiate an orthorhombic material from a ti one

seismic anisotropy of fractured rock a simple method for including the effects of geologically realistic fractures on the seismic propagation through fractured rocks can be obtained by writing the effective compliance tensor of the fractured rock as the sum of the compliance tensor of the unfractured background rock and the compliance tensors for each set of parallel fractures or aligned fractures the compliance tensor of each fracture set is derivable from a second rank fracture compliance tensor for a rotationally symmetric set of fractures the fracture compliance tensor depends on only two fracture compliances one controlling fracture compliance normal the other tangential to the plane of the fractures the stiffness tensor which is more useful in the consideration of elastic wave propagation through rocks can then be obtained by inversion the components of the excess fracture compliance tensor represent the maximum amount of information that can be obtained from seismic data if the background rock is isotropic and the normal a

simulation and interpretation of sonic waveforms in high angle and horizontal wells abstractwe have developed a new method to process and interpret sonic waveforms acquired in high angle ha and horizontal hz wells in the vicinity of layer boundaries numerical simulations are examined for ha hz fluid filled borehole models in which sonic tools with monopole and dipole sources operate across a horizontal bed boundary in hard and soft formations simulations are performed with a 3d time domain finite difference method assuming a sonic logging tool in which each receiver station consists of eight azimuthal receivers instead of conventional processing for monopole and dipole waveforms which takes the average and difference respectively of waveforms acquired with azimuthal receivers we analyze the waveforms acquired individually by each azimuthal receiver for dipole sources we refer to the dispersive signals recorded by individual receivers as pseudo flexural waves and we first process them with a weighted spectral semblance method to obtain the frequency dispersion curves we t

image mispositioning due to dipping ti media a physical seismic modeling study a scaled physical model was constructed to investigate the magnitudes of imaging errors incurred by the use of isotropic processing code when there is seismic velocity anisotropy present in the dipping overburden the model consists of a block of transversely isotropic ti phenolic material with the ti axis of symmetry dipping at an angle of 45 its scaled thickness is 1500 m and it is intended to simulate the dipping clastic sequences found in many fold thrust belts a piece of isotropic plexiglas affixed to the underside of the anisotropic block has a step function in it to simulate a target reef edge or fault the anisotropy parameters of the material are 0 1 and e 0 24 on zero offset data the imaged position of the target is shifted laterally 320 m in the updip direction of the beds whereas on time and depth migrated multichannel sections the shift is 300 m the lateral shift is offset dependent with the amount of shift in any common midpoint gather decreasing from 320 m on the near off

piecewise tendency diagnosis of dynamical processes governing the development of an upper tropospheric mobile trough abstract the intensification and evolution of midlatitude upper tropospheric mobile troughs may be viewed in terms of the isentropic advection and deformation of the tropopause potential vorticity gradient the potential vorticity viewpoint allows one to qualitatively assess observed events in the context of existing theories of mobile trough genesis such as baroclinic instability or downstream development in order to quantitatively determine the role of distinct dynamical process the method of piecewise tendency diagnosis or ptd is developed ptd is an extension of piecewise potential vorticity inversion applied to height tendencies with the forcing terms in the quasigeostrophic height tendency equation partitioned into potential vorticity advection associated with distinct dynamical processes a particular case of mobile trough genesis which occurred during 1 4 december 1980 over north america is diagnosed using ptd although about 20 of the intensification of the trough was due to superposition

barotropic wave propagation and instability and atmospheric teleconnection patterns abstract a global barotropic model linearized about the 300 mb climatological mean january flow is perturbed by applying a series of localized forcings distributed throughout the tropics and subtropics structures which resemble the observed pacific north american and east atlantic teleconnection patterns noted by wallace and gutzler 1981 tend to recur in the responses similar patterns are found to result from the dispersion of isolated initial perturbations placed at a variety of locations in the tropics and midlatitudes it is shown that these structures are related to the most rapidly growing mode associated with barotropic instability of the zonally varying climatological basic state in the absence of damping this mode has an e folding time of about a week and a period close to 50 days in localized regions the instantaneous growth rates can be competitive with those of baroclinic instability these episodes of rapid local barotropic growth are interspersed with intervals in which the local

persistent anomalies of the extratropical northern hemisphere wintertime circulation structure abstract in a previous study of the extratropical northern hemisphere wintertime circulation significant variations were described in the occurrence of anomalies that persist beyond the durations associated with synoptic scale variability persistent anomalies the present study extends that work by identifying the typical structures of persistent anomalies focusing on whether persistent occur in certain key regions the central north pacific pac the eastern north atlantic atl and the northern soviet union nsu are related to recurrent large scale flow patterns for each region detailed comparisons are provided of the flow patterns associated with persistent positive and negative anomaly cases and with the patterns obtained in other observations and theoretical studies of persistent phenomena the results provide evidence for the recurrence of certain preferred anomaly patterns to a first approximation the composite anomaly patterns of the positive and negative cases for a region can be de

an empirical method for estimation of anisotropic parameters in clastic rocks clastic sediments particularly shale exhibit transverse isotropic properties with the symmetric axis perpendicular to bedding vti these anisotropic rock properties are important in seismic imaging prestack seismic analysis and reservoir characterization laboratory tests are the main techniques used in measuring rock anisotropic properties vertical seismic profiling vsp and seismic refraction are the in situ techniques used to determine anisotropic parameters all of these methods provide significant insight to the anisotropic properties of the subsurface however limitations exist in the applications of these methods because of cost issues and restrictions on the number of measurements that can be conducted therefore new techniques that are cost effective easy to use and able to measure continuous anisotropic profiles are desirable this paper describes a methodology which involves the use of conventional rock properties to derive anisotropic rock properties

a unified three dimensional instability theory of the onset of blocking and cyclogenesis abstract the instability characteristics of three dimensional flow typical of the northern hemisphere average winter troposphere are examined in a two layer spherical quasigeostrophic model the properties of the four fastest growing small amplitude disturbances that develop on the basic state have been analyzed for three cases case 1 2a and 3 having increasingly larger static stability parameters for case 1 the fastest growing disturbance mode which is propagating eastward rather rapidly has a monopole cyclogenesis structure with maximum amplitudes slightly downstream of the jetstream maxima in the pacific ocean and off the cast coast of north america comparisons of streamfunctions squared and momentum and heat fluxes with bandpass filtered observations for transient eddies which pick out the developing storms are quite reasonable considering that a two layer model is used and the contributions from individual linear modes are considered for case 2a the fastest growing mode has large scale hi

seismic anisotropy of shales the seismic properties and preferred clay mineral orientation of a suite of shales are investigated using laboratory velocity measurements as a function of confining pressure x ray diffraction techniques and electron microprobe backscatter bse imaging the velocity measurements indicate that these shales are transversely isotropic with the main symmetry axis perpendicular to bedding anisotropy at elevated pressures caused mainly by preferred orientation of clays illite parallel to bedding ranges from 20 vp and 19 vs for a sample of new albany shale to 30 vp and 35 vs for a sample of chattanooga shale the degree of clay mineral alignment in the shales is constrained by orientation indices produced using simple x ray diffraction techniques a strong positive correlation is found between the degree of preferred orientation as expressed in the orientation indices and seismic anisotropy bse images of the shale fabrics confirm in a qualitative manner the results of the x ray study to investigate wave propagation in the shales elastic constants of each sample are calculated and used to produce phase and group wave velocity surfaces which describe variation in velocity as a function of angle to the bedding normal the calculated velocity surfaces constrained by independent velocity measurements display a lack of shear wave splitting at near normal incidence in even the most anisotropic shales for the highly anisotropic chattanooga shales group velocity surfaces differ significantly from corresponding phase velocity surfaces

piecewise tendency diagnosis of weather regime transitions abstract piecewise tendency diagnosis ptd is extended and employed to study the dynamics of weather regime transitions originally developed for adiabatic and inviscid quasigeostrophic flow on a beta plane ptd partitions local geopotential tendencies into a linear combination of dynamically meaningful source terms within a potential vorticity pv framework here ptd is amended to account for spherical geometry diabatic heating and ageostrophic processes and is then used to identify the primary mechanisms responsible for northern hemisphere weather regime transitions height tendency patterns obtained by summing the contributions of individual ptd forcing terms correspond very well to actual height tendencies composite ptd analyses reveal that linear pv advections provide the largest dynamical forcing for the weather regime development over the north pacific specifically linear baroclinic growth provides the primary forcing while barotropic deformation of pv anomalies provides a secondary contrib

anisotropy correction for deviated well sonic logs application to seismic well tie borehole sonic logs acquired in deviated wells penetrating the hrz and colville shales in the niakuk field in alaska s north slope are seen to be significantly faster than vertical well logs these differences are attributed to shale anisotropy an iterative inversion scheme was created to invert for shale anisotropy parameters using multiple wells penetrating shale sections at different angles the inversion involves fitting the sonic log data at a range of borehole angles to the compressional wave group velocity surface the result is an estimate of the anisotropy parameters e and and the vertical p wave velocity the results show that the shales are strongly anisotropic with compressional wave anisotropy thomsen s parameter e on the order of 40 and the anisotropy parameter relates vertical velocity to short offset nmo velocity around 10 this large anisotropy can affect seismic imaging avo and time depth calculations a procedure was created to estimate the anisotropy corrected vertical s

hydraulic stimulation of natural fractures as revealed by induced microearthquakes carthage cotton valley gas field east texas we produced a high resolution microseismic image of a hydraulic fracture stimulation in the carthage cotton valley gas field of east texas we improved the precision of microseismic event locations four fold over initial locations by manually repicking the traveltimes in a spatial sequence allowing us to visually correlate waveforms of adjacent sources the new locations show vertical containment within individual targeted sands suggesting little or no hydraulic communication between the discrete perforation intervals simultaneously treated within an 80 m section treatment i e fracture zone lengths inferred from event locations are about 200 m greater at the shallow perforation intervals than at the deeper intervals the highest quality locations indicate fracture zone widths as narrow as 6 m similarity of adjacent source waveforms along with systematic changes of phase amplitude ratios and polarities indicate fairly uniform source mechanisms fracture plane orientation and sense of slip over

elastic wave propagation in a fluid filled borehole and synthetic acoustic logs the propagation and dispersion characteristics of guided waves in a fluid filled borehole are studied using dispersion curves and modeling full wave acoustic logs by synthetic microseismograms the dispersion characteristics of the pseudo rayleigh reflected and stoneley waves in a borehole with and without a tool in the center are compared effects of different tool properties are calculated the effect of a rigid tool is to make the effective borehole radius smaller as an approximation dispersion characteristics of the guided waves in a borehole with a tool can be calculated as a purely fluid filled borehole with a smaller effective radius theoretical waveforms microseismograms of elastic waves propagating in a borehole are calculated using a discrete wavenumber integration with an appropriate choice of parameters our results look similar to the acoustic waveforms recorded in a limestone and a shale formation several factors affect the shape of an acoustic log microseismogram the effective rad

the speed of a tube wave the low frequency tube wave speed is given explicitly for a variety of borehole environments the presence of a logging tool the effects of casing and bore eccentricity are considered the results are all relatively simple and indicate that the speed decreases in the presence of a tool or borehole eccentricity the speed increases in the presence of casing as long as the casing shear modulus exceeds that of the formation

experimental laboratory determination of the dynamic elastic properties of wet drained shales the ultrasonic anisotropic elastic properties of drained saturated shales were measured as a function of confining pressure two shales were characterized in this study a jurassic outcrop shale retrieved under the sea in a saturated state and a kimmeridge clay shale cut from a north sea borehole both shales were highly anisotropic both texturally as revealed by scanning electron microscopy analysis and elastically as measured ultrasonically in the laboratory the strongest anisotropy was seen in the kimmeridge clay shale where up to 38 compressional wave anisotropy thomsen s parameter e and up to 58 shear wave anisotropy thomsen s parameter were observed in addition for both shales e and were found to decrease as a function of increasing confining pressure with the pore pressure drained to atmosphere while the anellipticity deviation of the slowness surfaces from ellipses was found to be positive and decreased as a function of increasing confining pressure accompanying these changes in elastic properties was a decrease in porosity with increasing confining pressure from 10 5 to 8 5 for the jurassic shale the decrease in overall anisotropy of the shales with increasing confining pressure was found to be consistent with theoretical modeling of shale properties where the shale anisotropy and anellipticity were predicted to decrease as a function of decreasing fluid filled porosity