atmospheric rotors and severe turbulence in a long deep valley abstractthe conceptual model of an atmospheric rotor is reexamined in the context of a valley using data from the terrain induced rotor experiment t rex conducted in 2006 in the southern sierra nevada and owens valley california all t rex cases with strong mountain wave activity have been investigated and four of them iops 1 4 6 and 13 are presented in detail their analysis reveals a rich variety of rotorlike turbulent flow structures that may form in the valley during periods of strong cross mountain winds typical flow scenarios in the valley include elevated turbulence zones downslope flow separation at a valley inversion turbulent interaction of in valley westerlies and along valley flows and highly transient mountain waves and rotors the scenarios can be related to different stages of the passage of midlatitude frontal systems across the region the observations from owens valley show that the elements of the classic rotor concept are modulated and at times almost completely offset

spectral analysis of ground penetrating radar response to thin sedimentary layers 1 ground penetrating radar gpr systems utilized in studies of sedimentary deposits generate wavelengths tens of centimeters that are commonly much longer than the thickness of bedding often millimeters to centimeters within the target strata where this is the case radar profiles represent interference patterns simple models of radar response to sequences of thin beds such as those found in coastal deposits show potentially detectable spectral shifts toward higher frequencies in radar returns spectral analysis of radar data over barrier beach deposits at waites island south carolina shows that returns from packages with heavy mineral laminations are shifted toward higher frequencies relative to returns from more isolated contacts such spectral shifts may be useful as an indicator of fine scale layering on radar profiles

variations in the age of arctic sea ice and summer sea ice extent 1 three of the past six summers have exhibited record low sea ice extent on the arctic ocean these minima may have been dynamically induced by changes in the surface winds based on results of a simple model that keeps track of the age of ice as it moves about on the arctic ocean we show that the areal coverage of thick multi year ice decreased precipitously during 1989 1990 when the arctic oscillation was in an extreme high index state and has remained low since that time under these conditions younger thinner ice anomalies recirculate back to the alaskan coast more quickly decreasing the time that new ice has to ridge and thicken before returning for another melt season during the 2002 and 2003 summers this anomalously younger thinner ice was advected into alaskan coastal waters where extensive melting was observed even though temperatures were locally colder than normal the age of sea ice explains more than half of the variance in summer sea ice extent

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones viii a model for the seeder feeder process in warm frontal rainbands abstract previous field studies have indicated that warm frontal rainbands form when ice particles from a seeder cloud grow as they fall through a lower level feeder cloud in this paper we present results from a parameterized numerical model of the growth processes that can lead to the enhancement of precipitation in a seeder feeder type situation the model is applied to two types of warm frontal rainbands in the first type 1 situation the vertical air motions are typical of those associated with slow widespread lifting in the vicinity of warm fronts in the second type 2 situation the vertical air motions are stronger and more characteristic of the mesoscale the model simulations show that in the type 1 situations the growth of the seed ice crystals within the feeder zone is due to vapor deposition the feeder zone in this case is slightly sub saturated with respect to water due to the presence of the seed crystals in regions where the feeder zone is not seeded from aloft snow cryst

radar reflections from sedimentary structures in the vadose zone ground penetrating radar gpr is a suitable technique for imaging sedimentary structures in the vadose zone because small texture related capillary pressure variations lead to changes in water content and electromagnetic properties to study exactly how gpr reflections are generated by sedimentary structures gpr profiles of an aeolian sedimentary succession are combined with measurements of textural electromagnetic and water retention characteristics from a trench time domain reflectometry indicates that small variations in texture in the high angle dune sediment are associated with changes in water content synthetic modelling shows that these changes cause clear gpr reflections in an experimental approach to estimate the radar response of structures below the wave resolution i e features smaller than 4 variations in grain size distribution and porosity in a thin section were used to reconstruct water retention curves and impedance models of the thinly layered sediment synthetic radar records calculated from the impedance models show that reflections from the studied subcentimetre scale structures are composites of interfering signals although these low amplitude interfering signals will commonly be overprinted by more prominent reflections they may cause reflection patterns that change with frequency and do not represent primary bedding

mountain waves over mont blanc influence of a stagnant boundary layer abstract a stationary mountain wave embedded in southwesterly flow over mont blanc in the alps was observed simultaneously by three research aircraft and three types of remote sensing gps dropsondes airborne light detecting and ranging lidar and rapid scan satellite imagery these observations provide a basis for testing linear and nonlinear theories of how mountain waves over complex terrain are controlled by the ambient wind profile especially the effects of a low level stagnant layer and the jet stream aloft the layer of blocked flow near the ground reduced the amplitude of the wave generation the strong wind and weak stability in the upper troposphere forced the wave into a decaying evanescent state in spite of this evanescent condition no lee waves were observed the authors resolve this paradox by demonstrating that the stagnant layer below 3 km played an additional role it was able to absorb downward reflected waves preventing the formation of a resonant cavity linear theory inclu

trade off of elastic structure and q in interpretations of seismic attenuation the quality factor q is an important phenomenological parameter measured from seismic or laboratory seismic data and representing wave energy dissipation rate however depending on the types of measurements and models or assumptions about the elastic structure several types of qs exist such as intrinsic and scattering qs coda q and apparent qs observed from wavefield fluctuations we consider three general types of elastic structures that are commonly encountered in seismology 1 shapes and dimensions of rock specimens in laboratory studies 2 geometric spreading or scattering in body surface and coda wave studies and 3 reflectivity on fine layering in reflection seismic studies for each of these types the measured q strongly trades off with the inherently limited knowledge about the respective elastic structure for the third of the above types the trade off is examined quantitatively in this paper for a layered sequence of reflectors e g an oil or gas reservoir or a hydrothermal zone reflection amplitudes and phases vary with frequency which is analogous to a reflection from a contrast in attenuation we demonstrate a quantitative equivalence between phase shifted reflections from anelastic zones and reflections from elastic layering reflections from the top of an elastic layer followed by weaker reflections from its bottom can appear as resulting from a low q within or above this layer this apparent q can be frequency independent or dependent according to the pattern of thin layering due to the layering the interpreted q can be positive or negative and it can depend on source receiver offsets therefore estimating q values from frequency dependent or phase shifted reflection amplitudes always requires additional geologic or rock physics constraints such as sparseness and or randomness of reflectors the absence of attenuation in certain layers or specific physical mechanisms of attenuation similar conclusions about the necessity of extremely detailed models of the elastic structure apply to other types of q measurements

alaska landfast sea ice links with bathymetry and atmospheric circulation 1 using radarsat synthetic aperture radar sar imagery of northern alaska and northwestern canada we calculated a mean climatology of the annual landfast ice cycle for the period 1996 2004 we also present the monthly minimum mean and maximum landfast ice extents throughout the study area these data reveal where and when the landfast is most stable and which sections of the coast are susceptible to midseason breakout events stabilization of landfast ice is strongly related to the advance of the seaward landfast ice edge slie into waters around 18 m deep isobaths near this depth are a good approximation for midseason landfast ice extent comparison with work from the 1970s suggests a reduced presence of landfast ice in this region of the arctic due to later formation and earlier breakup this will likely lead to an increase in coastal erosion and may also have profound effects upon subsistence activities which are intimately linked to the timing of marine mammal migration patterns interannually landfast ice formation correlates with the incursion of pack ice into coastal waters suggesting that the later mean date of formation in recent years may be related to the increasingly northward location of the perennial sea ice edge the timing of breakup correlates well with onset of thawing air temperatures analysis of regional data shows a multidecadal trend toward earlier thaw onset which suggests that the observed change in breakup dates may be part of a longer term trend

subduction megathrust heterogeneity characterized from 3d seismic data megathrust roughness and structural complexity are thought to be controls on earthquake slip at subduction zones because they result in heterogeneity in shear strength and resolved stress however because active megathrust faults are difficult to observe the causes and scales of complexity are largely unknown here we measured the in situ properties of the megathrust of the middle america subduction zone in a three dimensional seismic reflection volume to determine how fault properties vary we quantify spatial variability in the megathrust roughness overburden and rock physical properties heterogeneity in the megathrust roughness exists at length scales of a few kilometres because the megathrust is dissected by active lower plate normal faults which offset the megathrust and renewed fault roughness spatial variations in the rock physical properties at the plate interface are characterized by correlation length scales of hundreds of metres frontal prism taper historical seismicity and the variation in earthquake stress drop values local to the megathrust are all affected by the heterogeneity at these length scales both geometric and rheological complexities may therefore control the mechanical behaviour of the subduction plate interface which includes earthquake rupture characteristics geometric and rheological complexities may control the mechanical behaviour of megathrusts according to an analysis of the heterogeneity in roughness and rock properties of the middle america megathrust from 3d seismic reflection data

valuable lessons from acquiring 3d seismic for coal seam gas coalbed methane cbm or coal seam gas csg is being developed on a basinwide scale primarily as feedstock for three new liquefied natural gas lng facilities on the east coast of australia a recent 3d seismic survey acquired specifically for csg in the surat and bowen basins shows that although structural detail of the reservoir is a valuable tool deriving other information for reservoir characterization from thinly bedded coals requires a thorough investigation of the effects of high reflectivity thin beds although work continues to progress the results so far suggest that 3d seismic surveys can provide information for improved reservoir characterization

arctic sea ice variability in the context of recent atmospheric circulation trends abstract forty years 1958 97 of reanalysis products and corresponding sea ice concentration data are used to document arctic sea ice variability and its association with surface air temperature sat and sea level pressure slp throughout the northern hemisphere extratropics the dominant mode of winter january march sea ice variability exhibits out of phase fluctuations between the western and eastern north atlantic together with a weaker dipole in the north pacific the time series of this mode has a high winter to winter autocorrelation 0 69 and is dominated by decadal scale variations and a longer term trend of diminishing ice cover east of greenland and increasing ice cover west of greenland associated with the dominant pattern of winter sea ice variability are large scale changes in sat and slp that closely resemble the north atlantic oscillation the associated sat and surface sensible and latent heat flux anomalies are largest over the portions of the marginal sea ice zone in which the tr

foehn cold pool interactions in the inn valley during piano iop2 a case study is presented of a south foehn emanating from the wipp valley austria which encountered a cold air pool cap in the inn valley near the city of innsbruck the analysis is based on data collected during the second intensive observation period of the penetration and interruption of alpine foehn piano field experiment foehn was initiated on 3 november 2017 by an eastward moving trough and terminated in the afternoon of 5 november 2017 by a cold front passage on two occasions reversed foehn flow deflected at the mountain ridge north of innsbruck penetrated to the bottom of the inn valley the first breakthrough occurred in the afternoon of 4 november 2017 it was transient and locally limited to the northwest of the city the second final breakthrough occurred in the morning of 5 november 2017 and was recorded by all surface stations in the vicinity of innsbruck it started with a foehn air intrusion to the northeast of innsbruck and continued with the westward propagation of the foehn cap boundary along the valley subsequently observed northerly winds above the city were caused by an atmospheric rotor a few hours later and prior to the cold front passage the cap pushed back and lifted the foehn air from the ground during both nights shear flow instabilities formed at the foehn cap interface which resulted in turbulent heating of the cap and cooling of the foehn however this turbulent heating cooling was partly compensated by other mechanisms especially in the presence of strong spatial cap heterogeneity during the second night heating in the cap was most likely overcompensated by negative horizontal temperature advection

influences of the sierra nevada on intermountain cold front evolution abstractrecent studies indicate that strong cold fronts develop frequently downstream of the sierra nevada over the intermountain west to help ascertain why this paper examines the influence of the sierra nevada on the rapidly developing intermountain cold front of 25 march 2006 comparison of a weather research and forecasting wrf model control simulation with a simulation in which the height of the sierra nevada is restricted to 1500 m roughly the elevation of the valleys and basins of the intermountain west shows that the interaction of southwesterly prefrontal flow with the formidable southern high sierra produces a leeward orographic warm anomaly that enhances the cross front temperature contrast several processes generate this orographic warm anomaly including flow modification by the sierra nevada i e windward blocking of low level pacific air leeward subsidence and increased southerly flow from the mojave desert and lower colorado river basin into the intermountain west diabatic hea

relating the hydraulic properties of a fractured rock mass to seismic attributes theory and numerical experiments numerical experiments are conducted to establish how the properties of a seismic signal are related to the hydraulic properties of a fractured rock mass a hybridized reflectivity method is developed and used to compute a 1d synthetic seismogram for a geologic section which consists of a series of layers with one of the layers consisting of fractures seismic attributes notably instantaneous amplitude frequency and bandwidth are computed for a reflected seismic energy from a fractured zone with known distribution of fracture parameters fracture length aperture and spacing the permeability of the fractured zone is computed using a discrete fracture model the synthetic seismogram is computed using the modified displacement discontinuity model mdd which accounts for fracture opening and finite lengths of fractures a significant correlation is established between the seismic attributes and fractured rock mass permeability all the seismic attributes tend to increase with increase in permeability the correlation is significant enough to establish a meaningful empirical relation between seismic attributes and fracture permeability

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

shear wave reflection profiling for near surface lignite exploration we present the results of a shear wave reflection experiment and in situ measurements in opencast lignite exploration near surface coal seams have lower shear wave velocities 200 m s and lower densities than sand and clay layers due to strong reflection coefficients a shear wave reflection survey provides a powerful tool in lignite prospecting due to shorter seismic wavelengths shear waves will yield a higher resolution of shallow subsurface structure than compressional waves low shear wave velocities and strong lateral velocity variations however require a dense data acquisition in the field the variation of stacking velocities can exceed 15 within a profile length of 300 m the different steps in processing and interpretation of results are described with actual records the final cmp stack shows steep angle fault zones with maximum dislocations of 20 m within a coal seam

complex dielectric permittivity measurements from ground penetrating radar data to estimate snow liquid water content in the pendular regime 1 monitoring the snow water equivalent swe is critical to effective management of water resources in many parts of the world that depend on the mountain snowpack for water storage there are currently no methods to remotely sense swe with accuracy over large lateral distances in the steep and often forested terrain of mountain basins previous studies have shown that measurements of ground penetrating radar gpr velocity can provide accurate estimates of swe in dry snow introduction of liquid water into the snowpack results in a three phase system that cannot be accurately characterized with gpr velocity alone we show that measuring the frequency dependent gpr signal attenuation and velocity provides a direct estimate of the complex dielectric permittivity because the imaginary component is a function only of liquid water content we can utilize both the real and imaginary components of the permittivity to estimate liquid water content snow density and swe using existing empirical relationships that are valid in the pendular regime we tested this new method at two field sites and found that the estimates were accurate to within 12 of gravimetric methods in both a moist and a dry snowpack gpr has the potential to provide swe estimates across large lateral distances over a broad range of snow conditions

detection and resolution of thin layers a model seismic study1 the detection and resolution of a thin layer closely situated above a high impedance basement are predominantly determined by both the frequency content of the incident seismic wavelet and the existence of the nearby high impedance bedrock the separation of the thin layer and the basement arrivals is investigated depending on the low frequency content of the wavelet the high frequency content of the wavelet is kept constant the initial wavelet spectrum with low frequencies has a rectangular shape all wavelets used have zero phase characteristics numerical and analogue seismic modelling techniques are used the study is based on the geology of the pachangchi sandstone in west taiwan firstly the resolution of a thin layer between two half spaces is examined by applying the ricker and de voogd den rooijen criteria the lack of low frequency components of the incident seismic wavelet reduces the shortest true two way traveltime by about 20 in addition low frequency components of the wavelet diminish the deviation between true and apparent two way traveltime by about 65 for layer thicknesses in the transition from a thick to a thin layer the second step deals with the influence of a high impedance basement just below a thin layer on the detection and resolution of that thin layer reflected signal energies and apparent two way traveltimes are considered the reflected signal energy depends on the low frequency content of the incident wavelet the layer s thickness and the distance between the basement and the layer this applies only to layers with thicknesses less than or equal to one third of the mean wavelength in the layer and a distance to basement in the range of one to one half of the mean wavelength in the rock material between layer and basement the minimum thin layer thickness resolvable decreases with increasing distance to the basement i e for a layer thickness of one third of the mean wavelength in the layer the relative error of the two way traveltime increases from 5 to 30 if the distance is reduced from one to one half of the mean wavelength in the material between the basement and the thin layer finally a combination of vertical seismic profiling and downward continuation techniques is presented as a preprocessing procedure to prepare realistic data for the detection and resolution investigation

another look at downslope windstorms part i the development of analogs to supercritical flow in an infinitely deep continuously stratified fluid abstract numerical simulations are conducted to examine the role played by different amplification mechanisms in the development of large amplitude mountain waves it is shown that when the static stability has a two layer structure the nonlinear response can differ significantly from the solution to the equivalent linear problem when the parameter nh u is as small as 0 3 in the cases where the nonlinear waves are much larger than their linear counterparts the highest stability is found in the lower layer and the flow resembles a hydraulic jump simulations of the 11 january 1972 boulder windstorm are presented which suggest that the transition to supercritical flow forced by the presence of a low level inversion plays an essential role in triggering the windstorm the similarities between breaking waves and nonbreaking waves which undergo a transition to supercritical flow are discussed

some aspects of the effect of surface friction on flows over mountains the effect of surface friction on flow over mountains in stratified fluids is investigated using a two dimensional version of the naval research laboratory s non hydrostatic coupled ocean atmosphere mesoscale prediction system coamps without surface friction flow over a mountain attains a maximum speed at the surface on the lee slope with surface friction the flow speed vanishes at the surface and reaches a maximum near the top of the boundary layer bl corresponding to this wind distribution is a shallow layer of very large vertical wind shear beneath the jet maximum and a weaker but deeper sheared layer elsewhere this strong shear generates maximum turbulent kinetic energy tke at the jet maximum region meanwhile the buoyancy effect associated with the mountain gravity wave inhibits the production of the tke above the jet maximum region the combined effects of shear and buoyancy lead to a very shallow bl on the lee slope in general surface friction reduces the amplitude of mountain gravity waves comparison of the flow fields with the outline of the bl height indicates that flow characteristics correspond closely to the distribution of the bl height it is hypothesized that the reduction in mountain wave amplitude in the presence of surface friction is due to the reduction in the slope of the bl height as compared to the terrain height for narrower and or higher mountains the bl height exhibits a secondary peak on the lee side that further modifies the wave simulations using the bl height as a solid mountain without surface friction confirm that characteristics of flow over the mountain are associated with the distribution of bl height rather than the terrain height field as the non dimensional mountain height increases the magnitude of the effect of surface friction decreases due to decreasing bl depth on the lee side with the result that the bl height profile becomes closer to the terrain height field the effect of surface friction on asymmetric mountains is also investigated without surface friction the pressure drag shows distinctive reduction with a secondary peak on the downstream side but the effect is less when the secondary peak is on the upstream side with surface friction all three mountains have similar pressure drag corresponding to their similar bl height profiles copyright 2003 royal meteorological society

seismic modeling of an early jurassic drowned carbonate platform djebel bou dahar high atlas morocco 1 along the southern margin of the high atlas of morocco early jurassic carbonate platforms developed in a transtensional rifted basin one of these platforms was the djebel bou dahar platform which grew to a vertical relief of 500 m drowned and was onlapped by deep marine sediments exceptional outcrops allowed detailed lithologic models of the platform to be made with a resolution of a few meters we constructed a geometric model from building blocks comprising particular rock types we estimated p wave velocities and bulk densities of these lithologies from hand specimens and we assumed these properties to be homogeneous and invariant throughout the building blocks we constructed time sections of reflectivity from vertical incidence and image ray migration techniques these time sections were convolved with 25 to 200 hz ricker wavelets to produce synthetic seismic sections large scale features such as the platform and the drowning unconformity were resolved regardless of the frequencies and modeling techniques used broad low frequency wavelets resulted in profiles with apparent truncation of bedding and basinward shifts in the point of onlap smaller scale features such as reef knolls and sand bodies at the platform margin were poorly resolved at frequencies up to 50 hz however we inferred the existence and location of these smaller features from the disturbance and distortion of other reflections this distortion is most obvious in image ray migration modeling because of the refraction of rays through the small scale features geometric effects caused lateral amplitude variations due to wavelet interference along the unconformity reflection where no petrophysical changes were modeled the seismic models of the djebel bou dahar in its present stage may be good analogs for seismic lines of deeply buried carbonate platforms to make a comparison with real seismic lines of less deeply buried platforms possible we reconstructed both the geometry and petrophysical properties and the subsequent seismic modeling of the djebel bou dahar carbonate platform as it was prior to the onset of deep burial at this stage impedance contrasts were at their maximum this study clearly demonstrates the significance of modeling the seismic response of a detailed outcrop based stratigraphic model and shows that seismic modeling of specific sequence stratigraphy can reveal what features are likely to be resolved under ideal conditions and what pitfalls may await the interpreter

diurnal variation of downslope winds in owens valley during the sierra rotor experiment abstract the impact of diurnal forcing on a downslope wind event that occurred in owens valley in california during the sierra rotors project srp in the spring of 2004 has been examined based on observational analysis and diagnosis of numerical simulations the observations indicate that while the upstream flow was characterized by persistent westerlies at and above the mountaintop level the cross valley winds in owens valley exhibited strong diurnal variation the numerical simulations using the coupled ocean atmosphere mesoscale prediction system coamps capture many of the observed salient features and indicate that the in valley flow evolved among three states during a diurnal cycle before sunrise moderate downslope winds were confined to the western slope of owens valley shallow penetration state surface heating after sunrise weakened the downslope winds and mountain waves and eventually led to the decoupling of the well mixed valley air from the westerlies aloft around local noon decoupled

identification of shallow water flow sands by vp vs inversion of conventional 3d seismic data shallow water flow swf from overpressured unconsolidated uncemented sands is a high profile hazard in deep water drilling thus accurate predrill seismic prediction of swf sands is an important practical problem laboratory measurements show high seismic compressional to shear velocity vp vs ratios in swf sands thus vp vs anomalies produced by elastic seismic inversion can provide a quantitative identification of swf sands before drilling three 3d common angle aperture prestack time migrated data sets from the garden banks area of the gulf of mexico are inverted simultaneously for vp vs two wells provide constraints high vp vs values are observed in a known swf zone in shell deepwater development s well gb920 1 in kerr mcgee oil gas corporation s well gb877 1 vp vs anomalies match well with independent predrill swf sand predictions based on geologic information and seismic amplitudes high vp vs anomalies 9 are used to identify potential swf sands away from the wells we conclude that

effects of inversion height and surface heat flux on downslope windstorms abstractsimulations are presented focusing on the role of temperature inversions in controlling the formation and strength of downslope wind storms three mechanisms are examined depending on the relative height of the inversion with respect to the mountain and the stability of vertically propagating mountain waves for low level inversions flows are generated that closely resemble a reduced gravity shallow water hydraulic response with a large vertical displacement of the inversion on the lee side of the mountain for higher level inversion cases simulated flows more closely followed a stratified hydraulic behavior with the inversion acting as a rigid reflective lid in the third mechanism downslope winds were forced by a self induced critical layer located below the inversion height the presence of the inversion in this case had little effect on the resulting downslope winds observations made on the falkland islands show that downslope windstorms may preferentially occur in early morning even withou

on the spatiotemporal behavior of sea ice concentration anomalies in the northern hemisphere 1 reduction in the aerial extent and thickness of sea ice in the northern hemisphere is an important element in understanding how the arctic responds to global scale climate variability and change previous studies have demonstrated a significant reduction in minimum sea ice extent serreze et al 2003 with record reduction in 2005 observational studies attribute this phenomenon to variations in sea level pressure and large scale atmospheric teleconnection patterns such as the northern annular mode nam deser et al 2000 serreze et al 2003 in this study we examine variations in sea ice in the context of spatiotemporal variability of sea ice concentration sic anomalies in the northern hemisphere during the onset of ice formation examined in particular are timescales associated with coherent regions of persistence in an e folding time spatial distribution efsd annual variations of weekly sic anomalies are studied and spatial relations between positive and negative sic anomalies are explored on a hemispheric scale the results from this investigation demonstrate coherent sic persistence patterns throughout the northern hemisphere with timescales ranging from 3 to 7 weeks spatial correspondence between negative trends in sic anomalies and the efsd suggests that the same mechanism may be responsible for both increased ice reduction and persistence in this region examination of spatial coherence in sic anomalies indicates that maximum sic anomalies prevail near the kara sea beaufort sea and chukchi sea regions during late summer early fall from 1979 to 2004 a latitudinal assessment at 80 70 and 60 n indicates a poleward shift and retreat in sic anomalies while also underlining the decadal shift in variability often attributed to the nam

a link between fram strait sea ice export and atmospheric planetary wave phase 1 a link is found between the variability of fram strait sea ice export and the phase of zonal wave 1 in slp for the period 1958 1997 previous studies have found that the link between ice export through fram strait and the nao is inconsistent over time scales longer than the last two decades inconsistent and low correlations are also found between fram strait ice export and the ao index the phase of zonal wave 1 explains 60 70 of the simulated ice export variance after the removal of two anomalous phases in 1966 and 1967 unlike the nao and ao links these high variances are consistent for both the first and second halves of the 40 year period this consistency is attributed to the sensitivity of wave 1 phase to the presence of secondary low pressure systems in the barents sea that serve to drive arctic sea ice southward through fram strait

greenland sea odden sea ice feature intra annual and interannual variability the odden is a large sea ice feature that forms in the east greenland sea that may protrude eastward to 5 e from the main sea ice pack at about 8 w between 73 and 77 n it generally forms at the beginning of the winter season and can cover 300 000 km2 throughout the winter the outer edge of the odden may advance and retreat by several hundred kilometers on timescales of a few days to weeks satellite passive microwave observations from 1978 through 1995 provide a continuous record of the spatial and temporal variations of this extremely dynamic phenomenon aircraft synthetic aperture radar satellite passive microwave and ship observations in the odden show that the odden consists of new ice types rather than older ice types advected eastward from the main pack the 17 year record shows both strong interannual and intra annual variations in odden extent and temporal behavior for example in 1983 the odden was weak in 1984 the odden did not occur and in 1985 the odden returned late in the season an analysis of the ice area and extent time series derived from the satellite passive microwave observations along with meteorological data from the international arctic buoy program iabp determined the meteorological forcing associated with odden growth maintenance and decay the key meteorological parameters that are related to the rapid ice formation and decay associated with the odden are in order of importance air temperature wind speed and wind direction oceanographic parameters must play an important role in controlling odden formation but it is not yet possible to quantify this role because of a lack of long term oceanographic observations

deep convection in the irminger sea forced by the greenland tip jet open ocean deep convection one of the processes by which deep waters of the world s oceans are formed is restricted to a small number of locations for example the mediterranean and labrador seas recently the southwest irminger sea has been suggested as an additional location for open ocean deep convection the deep water formed in the irminger sea has the characteristic temperature and salinity of the water mass that fills the mid depth north atlantic ocean which had been believed to be formed entirely in the labrador basin here we show that the most likely cause of the convection in the irminger sea is a low level atmospheric jet known as the greenland tip jet which forms periodically in the lee of cape farewell greenland and is associated with elevated heat flux and strong wind stress curl using a history of tip jet events derived from meteorological land station data and a regional oceanic numerical model we demonstrate that deep convection can occur in this region when the north atlantic oscillation index is high which is consistent with observations this mechanism of convection in the irminger sea differs significantly from those known to operate in the labrador and mediterranean seas

on horizontal wind gradient variability from the stratosphere to the lower troposphere in the arctic 1 previous studies have demonstrated changes in vertical wind shear in recent decades with implications for upward propagating planetary waves the stratospheric polar vortex and tracer transport changes in vertical wind shear combined with horizontal gradients have also been shown to contribute to an increase in vertical gradients in tracer fields with important implications for vertical transport in order to explore the extent to which changes in vertical wind shear are reflected in changes to horizontal stirring we examine horizontal wind gradient fields from the stratosphere to the lower troposphere from 1979 to 2006 studied in particular are the spatial and temporal properties and trends for relative vorticity divergence strain and the okubo weiss criterion which monitors the competition between strain and vorticity dominated fields to illustrate how horizontal wind gradients have changed over the last several decades the results from this investigation show negative vorticity and strain anomalies during winter following 1998 associated with an increase in sudden stratospheric warmings and perturbations to the polar vortex noted in recent years spatial distributions for relative vorticity and strain fields exhibit coherent structures near the tropopause and middle stratosphere during fall and winter which are captured by the okubo weiss fields trend analyses highlight statistically significant trends in relative vorticity and okubo weiss fields during winter the results from this investigation demonstrate that statistically significant trends exist from the stratosphere to the lower troposphere it is hypothesized that the coupling from the lower troposphere to the upper atmosphere will be important in the development of our understanding of the response of sea ice concentrations to climate variability and change

on the diurnal variation of mountain waves abstract the diurnal variation of mountain waves and wave drag associated with flow past mesoscale ridges has been examined using the coupled ocean atmosphere mesoscale prediction system coamps and an analytical boundary layer bl model the wave drag exhibits substantial diurnal variation in response to the change in the atmospheric bl characteristics such as the bl depth shape factor and stability during daytime a convective bl develops characterized by a shallow shear layer near the surface and a deep well mixed layer aloft both of which tend to decrease the wave drag as a result the convective bl could significantly weaken mountain waves and reduce the momentum flux by up to 90 near the surface the flow pattern resembles a potential flow with a surface wind maximum located near the ridge crest during nighttime a shallow stable bl develops and the modulation of wave drag by the stable nocturnal bl is governed by the bl froude number fr if the bl flow is supercritical the drag incr

an intercomparison of model predicted wave breaking for the 11 january 1972 boulder windstorm abstract two dimensional simulations of the 11 january 1972 boulder colorado windstorm obtained from 11 diverse nonhydrostatic models are intercompared with special emphasis on the turbulent breakdown of topographically forced gravity waves as part of the preparation for the mesoscale alpine programme field phase the sounding used to initialize the models is more representative of the actual lower stratosphere than those applied in previous simulations upper level breaking is predicted by all models in comparable horizontal locations and vertical layers which suggests that gravity wave breaking may be quite predictable in some circumstances characteristics of the breaking include the following pronounced turbulence in the 13 16 km and 18 20 km layers positioned beneath a critical level near 21 km a well defined upstream tilt with height and enhancement of upper level breaking superpositioned above the low level hydraulic jump sensitivity experiments indicate that the structure of the wave bre

analysis and interpretation of seismic data from thin reservoirs northwest java basin indonesia a detailed analysis and interpretation is performed of a 2 d seismic line over a sequence of thin reservoirs in the upper cibulakan formation in the northwest java basin most well sites in this area are selected to be structures near fault zones as faults are assumed to be the main hydrocarbon migration paths amplitude variation with offset analysis is little used because of contamination by thin layer tuning effects attribute analysis impedance inversion and full wavefield modeling suggest that gas reservoirs are detectable even when they are less than their tuning thickness as they correspond to acoustic impedance anomalies and low instantaneous frequency the presence of hydrocarbons can also be detected by anomalous behavior in crossplots of acoustic impedance versus density and p wave velocity sandstone reservoirs show low velocity and low impedance two dimensional p velocity and density distributions resulting from impedance inversion produce synthetic elastic common source gathers that disp

the sundowner winds experiment swex pilot study understanding downslope windstorms in the santa ynez mountains santa barbara california abstractsundowner winds are downslope gusty winds often observed on the southern slopes of the santa ynez mountains sym in coastal santa barbara sb california they typically peak near sunset

the katla volcanic system imaged using local earthquakes recorded with a temporary seismic network katla is one of the most active subglacial volcanoes in iceland a temporary seismic network was operated on and around katla for 2 5 years a subset of similar to 800 analyzed local earthquakes cl

vertical resolution of a seismic survey in stratigraphic sequences less than 100 m deep in southeastern kansas a 400 m long 12 fold high resolution common depth point cdp reflection seismic profile was acquired across shallow converging pennsylvanian strata in the independence area of southeastern kansas one of the principal objectives was to determine practical vertical resolution limits in an excellent shallow seismic data area with borehole control the dominant frequency of the cdp stacked data is in excess of 150 hz based on peak to peak measurements interference phenomena observed on stacked seismic data incorporated with models derived from log and drill hole information suggest a practical vertical resolution limit of about 7 m or one third of the dominant wavelength this practical resolution is slightly less than the predicted theoretical resolution limit of 5 m based on the generally accepted one quarter wavelength axiom these data suggest conventional rules of thumb describing resolution potential are not accurate when reflectors on shallow narrow bandwidth data converge rapidly across horizo

evaluation of direct hydrocarbon indicators through comparison of compressional and shear wave seismic data a case study of the myrnam gas field alberta shear waves differ from compressional waves in that their velocity is not significantly affected by changes in the fluid content of a rock because of this relationship a gas related compressional wave bright spot or direct hydrocarbon indicator will have no comparable shear wave anomaly in contrast a lithology related compressional wave anomaly will have a corresponding shear wave anomaly thus it is possible to use shear wave seismic data to evaluate compressional wave direct hydrocarbon indicators this case study presents data from myrnam alberta which exhibit the relationship between compressional and shear wave seismic data over a gas reservoir and a low velocity coal

recent changes in arctic sea ice the interplay between ice dynamics and thermodynamics abstract it is well established that periods of high north atlantic oscillation nao index are characterized by a weakening of the surface high pressure and surface anticyclone in the beaufort sea and the intensification of the cyclonic circulation in the eastern arctic ocean the response of arctic sea ice to these atmospheric changes has been studied with a thickness distribution sea ice model coupled to an ocean model during a period of high nao 1989 96 the model shows a substantial reduction of ice advection into the eastern arctic from the canada basin and an increase of ice export through fram strait both of which tend to deplete thick ice in the eastern arctic ocean and enhance it in the western arctic in an uneven dipolar pattern we call the east west arctic anomaly pattern ewaap from the period 1979 88 with a lower nao index to the period 1988 96 with a high nao index the simulated ice volume in the eastern arctic drops by about a quarter while that in the western arctic increases by

a record minimum arctic sea ice extent and area in 2002 1 arctic sea ice extent and area in september 2002 reached their lowest levels recorded since 1978 these conditions likely resulted from 1 anomalous warm southerly winds in spring advecting ice poleward from the siberian coast 2 persistent low pressure and high temperatures over the arctic ocean in summer promoting ice divergence and rapid melt

post rift flood basalt like volcanism on the newfoundland basin nonvolcanic margin the u event mapped with spectral decomposition abstract diabase sills emplaced at less than 5 km depth presently 7 km are imaged throughout the newfoundland basin as an extraordinarily high amplitude package of seismic reflections historically referred to as the u event the sills are extensive covering roughly 20 000 km2 and represent a post rift voluminous magmatic episode along an otherwise nonvolcanic rifted margin spectral decomposition is used to estimate a total magmatic volume at roughly 1000 2000 km3 on an individual basis the major sills are comparable to flows in flood basalt volcanic environments a proposed mechanism for generating these large volumes of magma which are also very limited in time to perhaps only two major intrusive episodes 2 sills is the approach of the canary and madeira hot spots suppressed volcanism while the hot spots traveled under full thickness continental lithosphere of newfoundland resulted in a local accumulation of magma which was suddenly released when the hot spots approached thinned lithosphere at the eastern edge of the grand banks the emplacement of the sills anticipated the arrival of the hot spots geographically

vertical resolution of thick beds thin beds and thin bed cyclothems resolution has two common definitions the first of these relates to determination of the position of a reflector in time or space resolution by this definition is inversely related to pulse width or sharpness of the wavelet and potentially directly related to bandwidth of the frequency spectrum the second definition of resolution relates to determination of the spacing of close features such as thin beds this type of resolution is determined by the rayleigh criterion which inversely relates resolution to wavelength resolution of thin beds improves with shorter wavelength or higher frequency in comparison to the rayleigh criterion the ricker and widess criteria improve the resolution potential of thin beds but they rely on models of the reflectors and require that the beds be isolated it is a long established and widely accepted axiom that the best wavelets contain bandwidths of at least a couple of octaves this results in wavelets with reduced side lobes and ringiness a more easily interpret

the present state of seismic data acquisition one view seismic data acquisition in the mid 1980s is briefly reviewed in terms of hardware the trend has been toward an increased number of data channels in both land and marine applications this has led to the development of digital telemetry systems positioning systems particularly for marine work have made use of artificial satellites the perceived need for s wave information has led to development of s wave sources such as the horizontal vibrator s waves in a few cases have been used to validate hydrocarbon indicators on seismic records there has been a distinct trend toward three dimensional 3 d seismic recording both on land and at sea and for both exploration and production applications

seismic attributes a historical perspective a seismic attribute is a quantitative measure of a seismic characteristic of interest analysis of attributes has been integral to reflection seismic interpretation since the 1930s when geophysicists started to pick traveltimes to coherent reflections on seismic field records there are now more than 50 distinct seismic attributes calculated from seismic data and applied to the interpretation of geologic structure stratigraphy and rock pore fluid properties the evolution of seismic attributes is closely linked to advances in computer technology as examples the advent of digital recording in the 1960s produced improved measurements of seismic amplitude and pointed out the correlation between hydrocarbon pore fluids and strong amplitudes bright spots the introduction of color printers in the early 1970s allowed color displays of reflection strength frequency phase and interval velocity to be overlain routinely on black and white seismic records interpretation workstations in the 1980s provided

diminished amplitude reflections fadeout in bermuda rise stratification abstract single and multichannel deep tow seismic records collected on the southwestern bermuda rise reveal areas within the acoustic layering where the intensity of reflectors fade or even disappear over lateral distances of 20 60 m the fadeouts are conspicuously present in a highly stratified interval consisting of lower to middle eocene siliceous turbidites and thin cherty layers interbedded with hemipelagic pelagic clays and oozes acoustic scattering at rough interfaces gas pockets and changes in geoacoustic properties do not readily account for the diminished amplitudes of the reflections detailed examination of the wave coda from selected fadeout areas reveal changes in reflector geometry due to faulting of the sediments strong reflections within the stratified sequence are thought to result from the thin high impedance chert beds that occur within the turbidite layers secondary reflections multiples generated by the hard chert interfaces are thought to interact constructively with primary reflections to generate strong interference reflections but also destructively to cause fadeouts where the faulting has changed the layer configuration alternatively the fadeouts may result from the dissolution of chert beds due to the upward migration of silica deficient pore fluids along faults and fractures in response to excess pore pressures

response of sea ice to the arctic oscillation abstract data collected by the international arctic buoy programme from 1979 to 1998 are analyzed to obtain statistics of sea level pressure slp and sea ice motion sim the annual and seasonal mean fields agree with those obtained in previous studies of arctic climatology the data show a 3 hpa decrease in decadal mean slp over the central arctic ocean between 1979 88 and 1989 98 this decrease in slp drives a cyclonic trend in sim which resembles the structure of the arctic oscillation ao regression maps of sim during the wintertime january march ao index show 1 an increase in ice advection away from the coast of the east siberian and laptev seas which should have the effect of producing more new thin ice in the coastal flaw leads 2 a decrease in ice advection from the western arctic into the eastern arctic and 3 a slight increase in ice advection out of the arctic through fram strait taken together these changes suggest that at least part of the thinning of sea ice recently observed ov

investigation of upstream boundary layer influence on mountain wave breaking and lee wave rotors using a large eddy simulation abstract interactions between a turbulent boundary layer and nonlinear mountain waves are explored using a large eddy simulation model simulations of a self induced critical layer which develop a stagnation layer and a strong leeside surface jet are considered over time wave breaking in the stagnation region forces strong turbulence that influences the formation and structure of downstream leeside rotors shear production is an important source of turbulence in the stagnation zone and along the interface between the stagnation zone and surface jet as well as along the rotor edges buoyancy perturbations act as a source of turbulence in the stagnation zone but are shown to inhibit turbulence generation on the edges of the stagnation zone surface heating is shown to have a strong influence on the strength of downslope winds and the formation of leeside rotors in cases with no heating a series of rotor circulations develops capped by a region of increased winds weak heating disrupts this system an

application of amplitude spectrum and genetic inversion to determine shaly facies distribution a case study murzuq basin libya late ordovician glacial deposits of the mamuniyat formation are the main oil reservoir in the murzuq basin in libya autopicking the strong reflection at the base of the silurian shales can be used to map the top of the mamuniyat reservoir in the area where it is in direct contact with the silurian shales however in areas where the bir tlacsin formation a mud prone unit is between the silurian shales and the mamuniyat reservoir the top of the mamuniyat is difficult to pick because the units juxtaposed across the boundary are too similar to produce a strong reflection defining the bir tlacsin facies is important because it impacts hydrocarbon accumulation and migration to predict the distribution of the shaly facies of bir tlacsin and enhance mapping of the top mamuniyat reservoir we utilized a continuous wavelet transform to identify the distinctive thickness of the hot shale and bir tlacsin units we also used genetic inversion to distinguish the bulk density of the bir tlacsin facies a 64 hz frequency gave good time resolution to the amplitude spectrum and was used to predict the facies distribution of the bir tlacsin in contrast the 24 hz frequency showed good frequency resolution of the amplitude spectrum and was used to estimate the temporal thickness of the non reservoir unit of bir tlacsin and hot shale that estimate was then used to modify the autopick horizon for the base of the silurian reflector to approximate the top of the mamuniyat reservoir because of the large density contrast between the shaly facies of the bir tlacsin and the underlying and overlying units inverted density also provides a way to predict the distribution of the bir tlacsin through estimated temporal thickness and to enhance mapping of the top mamuniyat reservoir through mapping the base of the inverted density of the bir tlacsin a comparison between mapping of the top reservoir using spectral decomposition and inverted density with respect to autopick shows that both methods improved the top of the mamuniyat reservoir mapping prediction of the presence of bir tlacsin and improved accuracy of the top of the mamuniyat reservoir mapping reduce the risk of drilling the shaly facies of bir tlacsin and provide a better estimate of the reservoir reserve

turbulence characteristics in an elevated shear layer over owens valley abstract characteristics of turbulence in the lower and middle troposphere over owens valley have been examined using aircraft in situ measurements obtained from the terrain induced rotor experiment the two events analyzed in this study are characterized by a deep turbulent layer from the valley floor up to the midtroposphere associated with the interaction between trapped waves and an elevated shear layer kelvin helmholtz kh instability develops above the mountaintop level and often along the wave crests where the richardson number is reduced the turbulence induced by kh instability is characterized by a progressive downscale energy cascade a well defined inertial subrange up to 1 km and large eddies with vertical to horizontal aspect ratios less than unity the turbulence below the mountaintop level is largely shear induced associated with wave steepening and breaking and is more isotropic evaluation of structure functions indicates that while the turbulence energy cascade is predominately dow

wave breaking induced surface wakes and jets observed during a bora event 1 an observational and modeling study of a bora event that occurred during the field phase of the mesoscale alpine programme is presented research aircraft in situ measurements and airborne remote sensing observations indicate the presence of strong low level wave breaking and alternating surface wakes and jets along the croatian coastline over the adriatic sea the observed features are well captured by a high resolution coamps simulation analysis of the observations and modeling results indicate that the long extending wakes above the boundary layer are induced by dissipation associated with the low level wave breaking which locally tends to accelerate the boundary layer flow beneath the breaking farther downstream of the high peaks a hydraulic jump occurs in the boundary layer which creates surface wakes downstream of lower terrain passes the boundary layer flow stays strong resembling supercritical flow

complex seismic trace analysis of thin beds displays of complex trace attributes can help to define thin beds in seismic sections if the wavelet in a section is zero phase low impedance strata whose thicknesses are of the order of half the peak to peak period of the dominant seismic energy show up as anomalously high amplitude zones on instantaneous amplitude sections these anomalies result from the well known amplitude tuning effect which occurs when reflection coefficients of opposite polarity a half period apart are convolved with a seismic wavelet as the layers thin to a quarter period of the dominant seismic energy thinning is revealed by an anomalous increase in instantaneous frequency this behavior results from the less well known but equally important phenomenon of frequency tuning by beds which thin laterally instantaneous frequency reaches an anomalously high value when bed thickness is about a quarter period and remains high as the bed continues to thin in this paper complex trace analysis is applied to a synthetic model of a we

seismic response and construction of seaward dipping wedges of flood basalts voring volcanic margin geological and geophysical data from the 900 m of volcanic basement drilled at ocean drilling program site 642 provide the framework for studying seismic properties of huge extrusive constructions on volcanic margins the main part of the drilled section corresponding to a prominent seaward dipping reflector sequence consists of subaerially emplaced tholeiitic basalt flows and thin interbedded sediments the basalts exhibit a characteristic velocity and density lava flow distribution reflecting changing porosity pore aspect ratio distribution and alteration stacks of laterally continuous basalt flows appear to have thin layer transverse isotropic properties for typical wavelengths in multichannel seismic data vertical seismic profiling and average sonic log velocities are similar 3 77 km s and 3 88 km s respectively while comparable refraction velocities are 10 20 higher synthetic seismogram modeling based on downhole logs shows that basement reflectors originate from interference and tuning effects of numerous basalt flow and interbedded sediment interfaces though the most continuous reflectors are related to thick flows seismic models based on the characteristic velocity and density basalt flow distributions and site 642 stratigraphy show that reflector truncation and onlap may be caused by seismic interference phenomena in a sequence of landward thinning flows the base of the dipping reflector sequence reflector k correlates with flows in the lower part of upper series basalts while the transition from basaltic to underlying dacitic andesitic lavas correlates with a locally defined reflector a model for the breakup related volcanism includes 1 prebreakup dacitic andesitic volcanism 2 early breakup basaltic volcanism infilling the prebreakup relief 3 main breakup stage with intense focused volcanism large subsidence and lava pounding and 4 late breakup volcanism during a period of decreased subsidence and local off axis activity

wind driven shelf basin exchange on an arctic shelf the joint roles of ice cover extent and shelf break bathymetry 1 the efficiency of shelf basin exchange sbe in polar regions during summer is strongly moderated by the location of the ice edge relative to underlying topography numerical model calculations suggest that upwelling favorable winds generate very little sbe so long as the ice edge remains shoreward of the shelf break but an abrupt onset of shelf break upwelling takes place when the ice edge retreats beyond the shelf break a climatology 1968 2000 of ice conditions from the canadian shelf of the beaufort sea shows large interannual variability in ice edge extent and duration of ice free conditions in summer similarly available hydrographic data reflect a corresponding variability in water mass properties under scenarios of climate warming associated with greenhouse gas build up both the extent and duration of summer melt back are predicted to increase and this may have dramatic impacts on sbe and biological productivity

meteorological forcing of sea ice concentrations in the southern beaufort sea over the period 1979 to 2000 1 northern hemisphere sea ice areal extent and perhaps thickness have shown a detectable reduction over the past several decades this situation is particularly apparent in the southern beaufort sea the region encompassing the mackenzie shelf the cape bathurst polynya and the canada basin mobile pack ice all occur in a region referred to here as the canadian arctic shelf exchange study area cases in this paper we present results from an analysis of atmosphere sea ice and ocean coupling over the period 1979 to 2000 as a means of setting a physical science context for the cases research network operating over the period 2001 2005 results show that the cape bathurst polynya complex can be considered as a recurrent polynya particularly the flaw leads associated with the early opening of the polynya the polynya appears to be a consequence of the beaufort sea gyre acting like an ice bridge and a series of flaw leads creating conditions conducive to oceanic upwelling the sea ice average areal extent has been decreasing in this region over the period 1979 to 2000 large regional reductions are found i north of the yukon and alaska coasts in the region between the canada basin pack ice and the landfast sea ice and 2 at the eastern limit of the cape bathurst polynya in amundsen gulf the meteorological forcing of sea ice anomalies occurs through a full range of timescales and space scales at hemispheric scales a statistical cross correlation analysis between weekly sea ice concentration anomalies and the arctic oscillation accounts for a maximum of about 25 percent of the explained variance and show a surprising spatial coherence in correlation magnitudes both within the study area and northward along the canadian archipelago coast at local scales positive and negative concentration anomaly periods can be explained through local scale advective processes associated with regional scale sea level pressure 500 hpa geopotential heights and surface temperature anomalies

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

mechanisms of up valley winds abstract the basic physical mechanisms governing the daytime evolution of up valley winds in mountain valleys are investigated using a series of numerical simulations of thermally driven flow over idealized three dimensional topography the three dimensional topography used in this study is composed of two two dimensional topographies one a slope connecting a plain with a plateau and the other a valley with a horizontal floor the present two dimensional simulations of the valley flow agree with results of previous investigations in that the heated sidewalls produce upslope flows that require a compensating subsidence in the valley core bringing down potentially warmer air from the stable free atmosphere in the context of the three dimensional valley plain simulations the authors find that this subsidence heating in the valley core is the main contributor to the valley plain temperature contrast which under the hydrostatic approximation is the main contributor to the valley plain pressure differe

tuning effect and interference reflections from thin beds and coal seams the ricker and widess criteria of resolving thin beds are established and widely accepted axioms analysis of tuning effects from an isolated thinning bed is commonly used in estimating the thickness of a thin bed however frequency and amplitude tuning effects may also result from a sequence of thin beds depending on the thicknesses acoustic properties and the relative location of thin beds in space tuning effects from interference reflections can sometimes deform the seismic wavelet and cause complex waveforms coal seams as thin as 1 20 of the predominant wavelength can produce reflections and these reflections may be a composite of primary and multiple reflections interference reflections from two closely spaced coal seams were recorded and used to interpret a seam anomaly roll that may create adverse conditions for longwall mining the seismic data and computer model results correlated with findings of several boreholes

experimental study of acoustic anisotropy and birefringence in dry and saturated fontainebleau sandstone the velocities of ultrasonic p sh and sv waves have been measured in two perpendicular directions in samples of fontainebleau sandstone as received or thermally cracked dry or saturated under uniaxial stress we have investigated the effect of cracking saturation and uniaxial stress on the velocity of p and s waves in two orthogonal directions anisotropy and the velocity of s waves with two orthogonal polarizations in each direction of propagation birefringence the effect of cracking saturation and uniaxial stress on poisson s ratio has also been investigated the velocity anisotropy is larger for s waves than for p waves and practically disappears in saturated samples birefringence is attenuated in saturated samples inversion of the results using crampin s model gives values of the crack densities in three directions in qualitative agreement with the state of cracking observed by scanning electron microscopy in particular the crack density is found to be near zero in sandstones with r

observations and numerical simulations of subrotor vortices during t rex high resolution observations from scanning doppler and aerosol lidars wind profiler radars as well as surface and aircraft measurements during the terrain induced rotor experiment t rex provide the first comprehensive documentation of small scale intense vortices associated with atmospheric rotors that form in the lee of mountainous terrain although rotors are already recognized as potential hazards for aircraft it is proposed that these small scale vortices or subrotors are the most dangerous features because of strong wind shear and the transient nature of the vortices a life cycle of a subrotor event is captured by scanning doppler and aerosol lidars over a 5 min period the lidars depict an amplifying vortex with a characteristic length scale of 500 1000 m that overturns and intensifies to a maximum spanwise vorticity greater than 0 2 s 1 radar wind profiler observations document a series of vortices characterized by updraft downdraft couplets and regions of enhanced reversed flow that are generated in a layer of strong vertical wind shear and subcritical richardson number the observations and numerical simulations reveal that turbulent subrotors occur most frequently along the leading edge of an elevated sheet of horizontal vorticity that is a manifestation of boundary layer shear and separation along the lee slopes as the subrotors break from the vortex sheet intensification occurs through vortex stretching and in some cases tilting processes related to three dimensional turbulent mixing the subrotors and ambient vortex sheet are shown to intensify through a modest increase in the upstream inversion strength which illustrates the predictability challenges for the turbulent characterization of rotors

processing modelling and predicting time lapse effects of overpressured fluid injection in a fractured reservoir summary time lapse seismology is important for monitoring subsurface pressure changes and fluid movements in producing hydrocarbon reservoirs we analyse two 4 d 3c onshore surveys from vacuum field new mexico usa where the reservoir of interest is a fractured dolomite in phase vi a time lapse survey was acquired before and after a pilot tertiary recovery programme of overpressured co2 injection which altered the fluid composition and the pore fluid pressure phase vii was a similar time lapse survey in the same location but with a different lowerpressure injection regime applying a processing sequence to the phase vi data preserving normal incidence shearwave anisotropy time delays and polarization and maximizing repeatability interval time analysis of the reservoir interval shows a significant 10 per cent change in shear wave velocity anisotropy and 3 per cent decrease in the p wave interval velocities a 1 d model incorporating both saturation and pressure changes is matched to the data the saturation changes have little effect on the seismic velocities there are two main causes of the time lapse changes any change in pore fluid pressures modifies crack aspect ratios additionally when there are overpressures as there are in phase vi there is a 90 change in maximum impedance directions and the leading faster split shear wave instead of being parallel to the crack face as it is for low pore fluid pressures becomes orthogonal to the crack face the anisotropic poro elasticity ape model of the evolution of microcracked rock calculates the evolution of cracked rock to changing conditions ape modelling shows that at high overburden pressures only nearly vertical cracks to which normal incidence p waves are less sensitive than s waves remain open as the pore fluid pressure increases ape modelling matches the observed time lapse effects almost exactly demonstrating that shear wave anisotropy is a highly sensitive diagnostic of pore fluid pressure changes in fractured reservoirs in this comparatively limited analysis ape modelling of fluid injection at known pressure correctly predicted the changes in seismic response particularly the shear wave splitting induced by the high pressure co2 injection in the phase vii survey ape modelling also successfully predicted the response to the lower pressure injection using the same phase vi model of the cracked reservoir the underlying reason for this remarkable predictability of fluid saturated reservoir rocks is the critical nature and high crack density of the fluid saturated cracks and microcracks in the reservoir rock which makes cracked reservoirs critical systems

seismic interpretation of carbonate depositional environments most seismic stratigraphic or seismic lithologic interpretations have been applied to clastic depositional systems because of their unique sedimentologic and mineralogic characteristics carbonate rocks are more difficult to study using seismic data increased knowledge of carbonate deposits and their petrophysical parameters and higher quality geophysical tools now permit a better understanding of carbonate rocks using seismic images in this paper seismic facies of carbonate rocks are characterized step by step from the basin to the supratidal environment 1 pelagic deposits shales and micritic limestone layers exhibit continuous parallel reflections with an apparently high frequency chalk deposits display continuous high amplitude reflections at the top and base with an internal reflection free zone 2 talus deposits are characterized by discontinuous oblique reflections of high amplitude carbonate debris flow generates chaotic reflections with hummocky surfaces channels exhibit erosional truncations 3 reef barriers are mound shaped biogenic deposits that display marginal onlapping reflections overlying reflections drape the reefs and underlying reflections exhibit pull up or pull down effects hyperbolic diffractions also may occur 4 platform border sands are mound shaped oblique reflections of moderately high amplitude 5 inner shelf strata are characterized by parallel continuous reflections typically displaying low frequency patch reefs may be distinguished within the inner shelf system mound shape drape of overlying reflections velocity anomalies and spurious events 6 where dolomitized the intertidal to supratidal facies exhibit a marbled zone a practically reflection free zone with a few discontinuous reflections diagenetic events such as paleokarst zones may be delineated using special analyses involving amplitude offset variations the study of carbonate depositional environments and petrophysical characteristics provides a more complete geologic insight including relative changes in sea level within a sedimentary basin such studies are fundamental in analyzing carbonate reservoirs and their paleogeographic settings

design and field experiments of a ground penetrating radar for mars exploration 1 we developed a wideband low power lightweight prototype ground penetrating radar gpr for subsurface exploration for mars the transmitter and receiver subsystems were constructed using a commercially available radio frequency rf and digital integrated circuits connectorized components and evaluation boards the transmit receive system antennas laptop controller and batteries are all accommodated on a 2 5 m sled field experiments were conducted in kansas and alaska the experiments in kansas tested the operation of the system the primary objective of the alaska experiments was to investigate the ability of a gpr to detect and distinguish between subsurface deposits of ice and ice cemented soils the investigation depths of these experiments ranged from 1 m to 30 m and the subsurface geology included near surface thaw discontinuous permafrost water saturated soils and lenses of pure ice dielectric contrasts within the ground were detected with near meter resolution however identifying the geologic context of an interface was difficult due to ambiguities associated with reflection data these investigations demonstrate some of the difficulties associated with inverting reflection data to obtain dielectric properties of the subsurface fortunately previous geophysical investigations such as drilled cores and seismic surveys helped to constrain the geology and numerical simulations provided an additional resource for the interpretations on mars additional geological context will be limited and numerical simulations will become extremely important for data interpretation due to these difficulties we demonstrate in one experiment how dielectric information can be obtained directly from bistatic measurements with a fixed transmitter and mobile receiver finally a comparison with a commercially available geophysical survey systems inc gssi radar system is presented and we discuss how the system can be modified and improved for future exploration on mars

large amplitude mountain wave breaking over greenland abstract a large amplitude mountain wave generated by strong southwesterly flow over southern greenland was observed during the fronts and atlantic storm track experiment fastex on 29 january 1997 by the noaa g iv research aircraft dropwindsondes deployed every 50 km and flight level data depict a vertically propagating large amplitude wave with deep convectively unstable layers potential temperature perturbations of 25 k that deformed the tropopause and lower stratosphere and a vertical velocity maximum of nearly 10 m s 1 in the stratosphere the wave breaking was associated with a large vertical flux of horizontal momentum and dominated by quasi isotropic turbulence the coupled ocean atmosphere mesoscale prediction system coamps nonhydrostatic model with four nested grid meshes with a minimum resolution of 1 7 km accurately simulates the amplitude location and timing of the mountain wave and turbulent breakdown finescale low velocity plumes that resemble wakelike structures emanate from highl

feasibility of cdp seismic reflection to image structures in a 220 m deep 3 m thick coal zone near palau coahuila mexico the common depth point cdp seismic reflection method was used to delineate subsurface structure in a 3 m thick 220 m deep coal zone in the palau area of coahuila mexico an extensive series of walkaway noise tests was performed to optimize recording parameters and equipment reflection events can be interpreted from depths of approximately 100 to 300 m on cdp stacked seismic sections the seismic data allow accurate identification of the horizontal location of the structure responsible for a drill discovered 3 m difference in coal zone depth between boreholes 150 m apart the reflection method can discriminate folding with wavelengths in excess of 20 m and faulting with offset greater than 2 m at this site

shear wave reflectivity anisotropies poisson s ratios and densities of a southern appalachian paleozoic sedimentary sequence abstract the physical properties of a sequence of paleozoic sedimentary rocks have been examined in detail with an emphasis on laboratory measurements of density shear wave velocity shear wave splitting and vp vs ratios seismic properties of 147 cores from 49 rock samples collected from the thorn hill sedimentary sequence of eastern tennessee are examined in terms of implications for future seismic studies in the southern appalachians the shear wave velocities of these rocks are strongly influenced by the relatively high shear wave velocity of quartz shear wave velocity anisotropy is present in most of the lithologic groups it is highest in the shales while being almost insignificant in the dolostones the related phenomenon of shear wave splitting occurs to some degree in all of the lithologies studied and at high pressures originates from mineral orientation splitting due to preferred mineral orientation is most prominent in the shales but also is significant in some of the carbonates compressional to shear velocity vp vs ratios of approximately 1 82 dolostones and 1 95 limestones effectively characterize the carbonates while other lithologies display wider ranges of vp vs primarily due to the influence of accessory minerals such as quartz densities of the sample suite range from 2 34 g cm3 shale to 2 86 g cm3 dolostone using average data for each lithologic group to calculate normal incidence reflection coefficients significant differences in the shear and compressional reflectivity of hypothetical interfaces are found normal incidence shear and compressional wave synthetic seismograms approximating the subsurface reflectivity of the entire thorn hill section indicate that three zones of high amplitude reflections would be seen on reflection records obtained over this 3327 m thick sequence overall the shear and compressional synthetics are similar in appearance differences are seen at some interfaces in the mississippian devonian interval which are more reflective to shear waves and in the ordovician martinsburg formation which appears more reflective to compressional waves

shallow seismic reflection in a mine gallery abstract the technique of seismic reflection was used to survey the mineral deposits in a copper mine exploiting the sulfide minerals galena pyrite and chalcopyrite this approach required the adaptation of seismic reflection techniques to the specific features of the mine which are thin mineral bearing layers variable thickness of overlying strata and innaccessible rock faces field measurements were made according to a four fold multiple coverage after an initial survey we were able to develop a model that allowed the evaluation of the optimal offset based on synthetic traces deconvolution considerably improved the procedure together with the definition and the ability to determine the depth of the upper contact of the mineral deposit finally the application of complex traces analysis mainly of instantaneous amplitude permitted us to specify the degree of continuity in the mineral horizon under survey

gravity wave breaking over the central alps role of complex terrain abstract the characteristics of gravity waves excited by the complex terrain of the central alps during the intensive observational period iop 8 of the mesoscale alpine programme map is studied through the analysis of aircraft in situ measurements gps dropsondes radiosondes airborne lidar data and numerical simulations mountain wave breaking occurred over the central alps on 21 october 1999 associated with wind shear wind turning and a critical level with richardson number less than unity just above the flight level 5 7 km of the research aircraft ncar electra the electra flew two repeated transverses across the otztaler alpen during which localized turbulence was sampled the observed maximum vertical motion was 9 m s 1 corresponding to a turbulent kinetic energy tke maximum of 10 5 m2 s 2 spectrum analysis indicates an inertia subrange up to 5 km wavelength and multiple energy containing spikes corresponding to a wide range of wavelengths manual analysis of gps dropsonde data indic

using surface pressure variations to categorize diurnal valley circulations experiments in owens valley abstract harmonic analysis has been applied to data from nearly 1000 automatic surface observation system asos stations over the united states to extract diurnal pressure signals the largest diurnal pressure amplitudes 200 pa and the earliest phases 0600 lst for surface pressure maximum were found for stations located within deep mountain valleys in the western united states the origin of these unique characteristics of valley pressure signals is examined with a detailed study of owens valley california analysis of observational data from the terrain induced rotor experiment t rex project shows that the ratio of the valley surface pressure to temperature amplitude can be used to estimate the daily maximum mixed layer depth h on days with strong westerly winds above the valley the mixed layer is found to be shallower than on quiescent days because of a flushing effect in the upper parts of the valley idealized two dimensional weather research and forecasting model simulations were used to

arctic climate and atmospheric planetary waves analysis of a fifty year record 1946 1995 of monthly averaged sea level pressure data provides a link between the phases of planetary scale sea level pressure waves and arctic ocean and ice variability results of this analysis show 1 a breakdown of the dominant wave 1 pattern in the late 1960 s 2 shifts in the mean phase of waves 1 and 2 since this breakdown 3 an eastward shift in the phases of both waves 1 and 2 during the years of simulated cyclonic arctic ocean circulation relative to their phases during the years of anticyclonic circulation 4 a strong decadal variability of wave phase associated with simulated arctic ocean circulation changes finally the arctic atmospheric circulation patterns that emerge when waves 1 and 2 are in their extreme eastern and western positions suggest an alternative approach for determining significant forcing patterns of sea ice and high latitude variability

seismic attribute based characterization of coalbed methane reservoirs an example from the fruitland formation san juan basin new mexico the fruitland formation of the san juan basin is the largest producer of coalbed methane in the world production patterns vary from one well to another throughout the basin reflecting factors such as coal thickness and fracture and cleat density in this study we integrated conventional p wave three dimensional 3 d seismic and well data to investigate geological controls on production from a thick continuous coal seam in the lower part of the fruitland formation our objective was to show the potential of using 3 d seismic data to predict coal thickness as well as the distribution and orientation of subtle structures that may be associated with enhanced permeability zones to do this we first derived a seismic attribute based model that predicts coal thickness we then used curvature attributes derived from seismic horizons to detect subtle structural features that might be associated with zones of enhanced permeability production data show that the best producing wells are associated with seismically definable structural features and thick coal although other factors e g completion practices and coal type affect coalbed methane production our results suggest that conventional 3 d seismic data integrated with wire line logs and production data are useful for characterizing coalbed methane reservoirs

modeling studies of interference reflections in thin layered media bounded by coal seams high resolution seismic data collected over a major u s coal basin indicated potential complex problems associated with interference reflections these problems differed from those normally encountered in the exploration of oil and gas because of differences in the geologic boundary conditions modeling studies were conducted to investigate the effects of overlapping primary reflections and the composite reflection that result from stacking individual wavelets a modified empirical formula of lindseth s linear relationship between acoustic impedance and velocity is used to extrapolate velocity information from density logs to provide appropriate geophysical properties for modeling the synthetic seismograms generated from density and synthetic sonic logs correlated well with the processed seismic data a 150 hz ricker wavelet is used to convolve with the computer models and the models showed that certain anomalous composite reflections result from the superposition of overlapping primary reflections de

intrabasement reflections of the ontong java plateau implications for plateau construction 1 the early cretaceous ontong java plateau ojp in the western equatorial pacific earth s most voluminous large igneous province lip is characterized by intrabasement seismic reflections to investigate the nature of such reflections we have analyzed new and all older multichannel seismic mcs reflection data from the ojp using an instantaneous phase velocity analysis technique and synthetic seismograms intrabasement reflections are most prevalent on the main ojp especially on its crest on mcs data the reflections 1 are semicontinuous and subparallel to the top of igneous basement 2 in places have the opposite phase of seafloor reflections and 3 have an average frequency of 20 hz we calculate synthetic seismograms using impedance contrasts between massive lava and pillow lava flows obtained from downhole logs at ojp scientific drill sites and show that these lithologies can produce intrabasement reflections similar to those observed in the mcs data alternatively to evaluate the possibility of sediment sedimentary rock interbeds causing the intrabasement reflections we use published early cretaceous sedimentation rates determined from ojp drill sites and published estimates for the duration of massive ojp volcanism to calculate a range of possible sedimentary interbed thicknesses the range proves to be below the detection limit of the mcs data therefore we conclude that the intrabasement reflections arise from alternating relatively thin lava flows produced at low effusion rates and relatively thick massive flows generated at high effusion rates both originating from vents and fissures on the ojp probably on its crest

on sea ice concentration anomaly coherence in the southern beaufort sea 1 the circumpolar flaw lead polynya system is a region of enhanced biological productivity and for significant portions of the annual cycle dominates the exchange of energy and mass across the ocean sea ice atmosphere osa interface we investigate the nature of sea ice concentration sic anomalies for spatial and temporal statistical persistence within a portion of this flaw lead system we find such a structure in the shelf break zone between amundsen gulf and the canada basin ncep ncar reanalysis data is used to determine the potential roles of oceanic and atmospheric forcing in creating and maintaining this observed coherence in the sic anomalies results suggest that the coherence pattern is consistent over the instrumental record 1979 to 2000 although it changes in shape and extent between years the forcing mechanisms creating this coherence in sic anomalies appear to be tied to surface wind driven upwelling in the shelf break areas of the southern beaufort sea sbs