structure of the california coast ranges and san andreas fault at safod from seismic waveform inversion and reflection imaging 1 a seismic reflection and refraction survey across the san andreas fault saf near parkfield provides a detailed characterization of crustal structure across the location of the san andreas fault observatory at depth safod steep dip prestack migration and frequency domain acoustic waveform tomography were applied to obtain highly resolved images of the upper 5 km of the crust for 15 km on either side of the saf the resulting velocity model constrains the top of the salinian granite with great detail steep dip reflection seismic images show several strong amplitude vertical reflectors in the uppermost crust near safod that define an 2 km wide zone comprising the main saf and two or more local faults another prominent subvertical reflector at 2 4 km depth 9 km to the northeast of the saf marks the boundary between the franciscan terrane and the great valley sequence a deep seismic section of low resolution shows several reflectors in the salinian crust west of the saf two horizontal reflectors around 10 km depth correlate with strains of seismicity observed along strike of the saf they represent midcrustal shear zones partially decoupling the ductile lower crust from the brittle upper crust the deepest reflections from 25 km depth are interpreted as crust mantle boundary

gas hydrates off eastern canada velocity models from wide angle seismic profiles on the scotian slope abstract coincident single channel reflection and wide angle ocean bottom seismometer obs reflection refraction profiles were taken on the central continental slope off nova scotia in a region of possible gas hydrate occurrence as evidenced by recent identification of bottom simulating reflectors bsrs joint travel time inversions of wide angle reflections and refractions in the obs data result in three similar velocity models which all display anomalies consistent with the presence of gas hydrate and underlying free gas a high velocity zone hvz 60 120 m thick has velocity increases of 70 130 m s above a low velocity zone lvz 150 260 m thick where velocities decrease by 50 75 m s sensitivity analysis indicates that the refracted phase from the hvz offers better velocity resolution than the reflected phase from the top of the lvz comparison of synthetic seismograms for alternate models can further help to resolve details in the structure of the hvz and lvz layers depth migrations of the reflection profiles using the velocity models show that the depths of the velocity inversions and bsrs are consistent preliminary predictions of 2 6 bulk gas hydrate and

the vertical profile of wind and temperature in cyclones and anticyclones over the eastern two thirds of the united states a climatology abstract a climatological analysis based upon operational surface and upper air data from 1957 to 1994 of the wind and temperature profiles composited with respect to each quadrant of surface cyclones and anticyclones is presented for the eastern two thirds of the united states the cyclones and anticyclones are located via an objective procedure hodographs and soundings are also composited with respect to season geographic region time of day and for cyclones only intensity vertical profiles of the static stability parameter are composited with respect to season and quadrant for both cyclones and anticyclones the structures of mean cyclones and anticyclones are shown and discussed a diurnal variation in hodographs vertical shear is found which shows up in both cyclones and anticyclones as a rotation in the counterclockwise direction between 0000 and 1200 utc above the boundary layer the effect is greater in cyclones than in anticyclones this variation is hypothesized to be in part due to

a composite study of comma clouds and their association with severe weather over the great plains abstract sixty eight comma cloud systems over the great plains during two spring seasons were examined using satellite imagery and rawinsonde data composite soundings were produced for each of ten distinct parts of the comma cloud in order to describe quantitatively the atmospheric structure associated with wave cyclones that produced 585 severe weather events composite sectionals and soundings document the different kinematic and thermodynamic environment of each part of the comma cloud system relative wind isentropic analyses show air flow relative to the storm and provide additional evidence that the clear region intruding northward east of the cyclone center is an area of strong ascent of dry air with a previous history of subsidence stability computations from the mean soundings suggest that the most likely location for severe weather is near the central part of the comma tail in agreement with the tabulated severe weather reports a case study from 21 22 march 1981 is conducted to investigate

2d waveform tomography applied to long streamer mcs data from the scotian slope detailed velocity models of the earth s subsurface can be obtained through waveform tomography the accuracy of the long wavelength component of such velocity models which is the background velocity field is particularly sensitive to modeling low frequency refracted waves that have long paths through target structures thus field examples primarily have focused on the analysis of long offset wide angle data sets collected using autonomous receivers in which refractions arrive at significantly earlier times than reflections modern marine acquisition with long streamers now offers the ability to record refracted waves with high spatial density and uniform source both in shallow and deep water we used 2d multichannel seismic mcs data acquired with a 9 km long streamer over the scotian slope in water depths of 1600 m the refracted arrivals although mostly restricted to far offset receivers provided sufficient information to successfully invert for a high resolution background velocity field usin

crustal seismic imaging from multifold ocean bottom seismometer data by frequency domain full waveform tomography application to the eastern nankai trough 1 in offshore surveys the deep crust is generally investigated by traveltime tomography applied to sparse ocean bottom seismometer data the inferred velocity models are of limited resolution precluding a quantitative analysis of deep tectonic discontinuities if dense arrays of ocean bottom seismometers can be deployed the resulting data sets become amenable to full waveform processing which should lead to a significant improvement in the resolution of structures such acquisition and processing were achieved on the eastern nankai subduction zone full waveform inversion is entirely implemented in the frequency domain enabling efficient finite difference wave modeling and allowing to limit the inversion to a few discrete frequencies of increasing value such a hierarchical procedure defines a multiresolution approach to seismic imaging the data set was recorded by 93 instruments deployed along a 105 km long profile thirteen frequencies ranging from 3 to 15 hz were inverted sequentially wavelengths imaged by the full waveform inversion typically range between 0 5 and 8 km full waveform tomography reveals an intense compression in the upper prism and underlying backstop as evidenced by several thrusts the frontal ones still active corresponding to negative velocity anomalies the subducting paleo zenisu ridge is also reconstructed above which stands the decollement velocities in the upper mantle beneath the ridge are rather low 7 5 km s 1 suggesting partially serpentinized mantle beneath the ridge this paper demonstrates the feasibility of full waveform tomography based on dense ocean bottom seismometer data sets and its ability to quantitatively image the entire crust with a significantly improved resolution compared to what is usually achieved through traveltime tomography

evolution of seismic layer 2b across the juan de fuca ridge from hydrophone streamer 2 d traveltime tomography how oceanic crust evolves has important implications for understanding both subduction earthquake hazards and energy and mass exchange between the earth s interior and the oceans although considerable work has been done characterizing the evolution of seismic layer 2a there has been little analysis of the processes that affect layer 2b after formation here we present high resolution 2 d tomographic models of seismic layer 2b along 300 km long multichannel seismic transects crossing the endeavour northern symmetric and cleft segments of the juan de fuca ridge these models show that seismic layer 2b evolves rapidly following a different course than layer 2a the upper layer 2b velocities increase on average by 0 8 km s and reach a generally constant velocity of 5 2 0 3 km s within the first 0 5 myr after crustal formation this suggests that the strongest impact on layer 2b evolution may be that of mineral precipitation due to active hydrothermal circulation centered about the ridge crest and driven by the heat from the axial magma chamber variations in upper layer 2b velocity with age at time scales 0 5 ma show correlation about the ridge axis indicating that in the long term crustal accretion processes affect both sides of the ridge axis in a similar way below the 0 5 ma threshold differences in 2b velocity are likely imprinted during crustal formation or early crustal evolution layer 2b velocities at propagator wakes 5 0 0 2 km s where enhanced faulting and cracking are expected and at areas that coincide with extensional or transtensional faulting are on average slightly slower than in normal mature upper layer 2b analysis of the layer 2b velocities from areas where the hydrothermal patterns are known shows that the locations of current and paleohydrothermal discharge and recharge zones are marked by reduced and increased upper layer 2b velocities respectively additionally the distance between present up flow and down flow zones is related to the amount of sediment cover because as sediment cover increases and basement outcrops become covered direct pathways from the igneous basement through the seafloor are cut off forcing convective cells to find alternate paths

the sting at the end of the tail damaging winds associated with extratropical cyclones strong surface winds often accompany the low level jets that occur along the cold fronts of extratropical cyclones but there is evidence that the strongest surface winds occur in a distinctly different part of a certain class of cyclone the most damaging extratropical cyclones go through an evolution that involves the formation of a bent back front and cloud head separated from the main polar front cloud band by a dry slot when the cyclone attains its minimum central pressure the trailing tip of the cloud head bounding the bent back front forms a hook which goes on to encircle a seclusion of warm air the most damaging winds occur near the tip of this hook the sting at the end of the tail observations of the great storm of october 1987 in south east england are re examined in some detail to study this phenomenon the cloud head is shown to have a banded structure consistent with the existence of multiple mesoscale slantwise circulations air within these circulations leaves the hooked tip of the cloud head and enters the dry slot much faster than the rate of travel of the cloud head tip implying rapid evaporation and diabatic cooling immediately upwind of the area of damaging surface winds the circumstantial evidence from the observational study leads one to hypothesize that the mesoscale circulations and the associated evaporative heat sinks may play an active role in strengthening the damaging winds regardless of how important this role may be the evolution of the cloud pattern seen in satellite imagery is a useful tool for nowcasting the occurrence and location of the worst winds copyright 2004 royal meteorological society

origin evolution and finescale structure of the st valentine s day mesoscale gravity wave observed during storm fest part i origin and evolution abstract on 14 15 february 1992 a long lived mesoscale gravity wave was observed over the storm scale operational and research meteorology fronts experiment systems test observational network a precipitation band formed and intensified as the wave moved across kansas and missouri the disturbance was tracked for 14 h surface dual doppler radar and wind profiler analyses as well as isentropic analyses derived from a special rawinsonde network are used to examine the origin and evolution of this wave the wave originated at the leading edge of a dry air mass associated with downslope flow in the lee of the rockies the earliest surface pressure signatures of wave motion began as a dry air mass associated with the downslope flow ascended a warm front east of a lee cyclone a weak rainband developed simultaneously with the wave at the leading edge of the dry air mass the mesoscale gravity wave and convection remained tied to the leading edge of the advancing dry air mass during the first 8 10 h of

grain size stabilisation by dispersed graphite in a high grade quartz mylonite an example from naxos greece high grade quartz mylonites from naxos greece consist of alternating thin layers of pure quartz and quartz layers with 0 3 3 vol finely dispersed graphite particles graphite free layers are coarse grained 100 300 mm show undulose extinction subgrains lobate grain boundaries and have a strongly developed crystallographic preferred orientation in these layers dislocation flow is interpreted to be the dominant deformation mechanism in contrast graphite rich layers are fine grained 30 70 mm have equant quartz grain shapes and have a crystallographic preferred orientation that becomes progressively weaker with decreasing quartz grain size given the high temperature of deformation and the need for a c axis fabric destroying mechanism grain boundary sliding is interpreted to be important in these layers analysis shows an inverse relationship between quartz grain size and the graphite dispersion suggesting stabilization of quartz grain size by graphite particles graphite particles larger than 5 mm are concentrated along quartz boundaries suggesting that stabilisation only operates above a certain critical graphite particle size this study shows that a dispersed second phase such as graphite in a naturally deforming rock can inhibit grain boundary migration stabilise the grain size and enhance grain boundary sliding at the expense of dislocation flow q 2002 elsevier science ltd all rights reserved

quantitative imaging of complex structures from dense wide aperture seismic data by multiscale traveltime and waveform inversions a case study an integrated multiscale seismic imaging flow is applied to dense onshore wideaperture seismic data recorded in a complex geological setting thrust belt an initial p wave velocity macromodel is first developed by first arrival traveltime tomography this model is used as an initial guess for subsequent full waveform tomography which leads to greatly improved spatial resolution of the p wave velocity model however the application of full waveform tomography to the high frequency part of the source bandwidth is difficult due to the non linearity of this kind of method moreover it is computationally expensive at high frequencies since a finitedifference method is used to model the wave propagation hence full waveform tomography was complemented by asymptotic prestack depth migration to process the full source bandwidth and develop a sharp image of the short wavelengths the final traveltime tomography model and two smoothed versions of the final full waveform tomography model were used as a macromodel for the prestack depth migration in this study wide aperture multifold seismic data are used after specific preprocessing of the data 16 frequency components ranging from 5 4 hz to 20 hz were inverted in cascade by the full waveform tomography algorithm the full waveform tomography successfully imaged sw dipping structures previously identified as highresistivity bodies the relevance of the full waveform tomography models is demonstrated locally by comparison with a coincident vertical seismic profiling vsp log available on the profile the prestack depth migrated images inferred from the traveltime and the smoothed full waveform tomography macromodels are shown to be on the whole consistent with the final full waveform tomography model a more detailed analysis based on common image gather computations and local comparison with the vsp log revealed that the most accurate migrated sections are those obtained from the full waveform tomography macromodels a resolution analysis suggests that the asymptotic prestack depth migration successfully migrated the wideaperture components of the data allowing medium wavelengths in addition to the short wavelengths of the structure to be imaged

late cenozoic sea level changes and the onset of glaciation impact on continental slope progradation off eastern canada abstract late cenozoic sedimentation from four varied sites on the continental slopes off southeastern canada has been analysed using high resolution airgun multichannel seismic profiles supplemented with some single channel data biostratigraphic ties are available to exploratory wells at three of the sites uniform slow accumulation of hemipelagic sediments was locally terminated by the late miocene sea level lowering which is also reflected in changes in foraminiferan faunas on the continental shelf data are very limited for the early pliocene but suggest a return to slow hemipelagic sedimentation at the beginning of the late pliocene there was a change in sedimentation style marked by a several fold increase in accumulation rates and cutting of slope valleys this late pliocene cutting of slope valleys corresponds to the onset of late cenozoic growth of the laurentian fan and the initiation of turbidite sedimentation on the sohm abyssal plain although it corresponds to a time of sea level lowering the contrast with the late miocene lowstand indicates that there must also have been a change in sediment delivery to the coastline perhaps as a result of increased rainfall or development of valley glaciers high sedimentation rates continued into the early pleistocene but the extent of slope dissection by gullies increased gully cutting episodes alternated with sediment draping episodes throughout the southeastern canadian continental margin there was a change in sedimentation style in the middle pleistocene that resulted from extensive ice sheets crossing the continental shelf and delivering coarse sediment directly to the continental slope

multiscale seismic imaging of the eastern nankai trough by full waveform inversion 1 classical active seismic methods fail to sharply image the earth s deep crust we present the first crustal scale application of 2 d full waveform inversion based on dense ocean bottom seismic data to investigate the eastern nankai subduction system japan this approach allows to quantify seismic velocities up to an unprecedented degree of resolution results reveal compressive tectonic features within both the subducting oceanic crust and the backstop at depth velocity anomalies along major faults and structural discontinuities bring evidence for the presence of fluids and weakened material and also for a possible coseismic slip partitioning structure index terms 0902 exploration geophysics computational methods seismic 3025 marine geology and geophysics marine seismics 0935 8010 structural geology fractures and faults 8105 tectonophysics continental margins and sedimentary basins 1212 citation dessa j x s operto s kodaira a nakanishi g pascal j virieux and y kaneda 2004 multiscale seismic imaging of the eastern nankai trough by full waveform inversion geophys res lett 31 l18606 doi 10 1029 2004gl020453

mesoscale analysis of arc rainbands in a dry slot a series of almost concentric are shaped narrow rainbands was observed travelling at 140 km h 1 and producing severe wind gusts over parts of england their structure and environment have been analysed using radar and satellite imagery mesoscale model diagnostics surface observations and additional rawinsonde ascents obtained during the fronts and atlantic storm track experiment fastex the multiple rainband event is shown to have been associated with part of a dry intrusion characterized by a mesoscale vortex cold pool the event occurred within the dry slot region of a small frontal cyclone where the mesoscale pool of cold dry air was overrunning warm sector air continuous wind profiles from a uhf radar together with a well located rawinsonde at the epicentre of the arc rainbands showed that the major anomaly in the cold pool was an area of locally stronger winds 40 m s 1 at 800 hpa colocated with the temperature minimum at that level the observed orientation of the rainbands is explained in terms of the cold frontal structure at this level triggering ascent of the underlying warm moist air the multiple nature of the arc rainbands remains unexplained the possibilities of mesoscale gravity waves and conditional symmetric instability are both considered

high resolution observations of the trowal warm frontal region of two continental winter cyclones abstract this paper compares the structure of the trough of warm air aloft trowal warm frontal region of two continental wintertime cyclones the cyclones were observed over the central great lakes region during the lake induced convection experiment snowband dynamics project field campaign the cyclones had different origins with the first forming east of the colorado rockies and the second forming over the gulf of mexico they were associated with different upper level flow regimes one located just north of a nearly zonal jet and the other located just west of a nearly meridional jet both storms produced heavy swaths of snow across the states of illinois wisconsin and michigan high resolution observations of frontal structure were made during flights of the national center for atmospheric research electra aircraft using dropsondes and the electra doppler radar tail radar system the high resolution observations suggest a different arrangement of air masses in the trowal region compared with the

seismic evidence for large scale compositional heterogeneity of oceanic core complexes long lived detachment faults at mid ocean ridges exhume deep seated rocks to form oceanic core complexes occs using large offset 6 km multichannel seismic data we have derived two dimensional seismic tomography models for three of the best developed occs on the mid atlantic ridge our results show that large lateral variations in p wave velocity occur within the upper 0 5 1 7 km of the lithosphere we observe good correlations between velocity structure and lithology as documented by in situ geological samples and seafloor morphology and we use these correlations to show that gabbros are heterogeneously distributed as large tens to 100 km2 bodies within serpentinized peridotites neither the gabbros nor the serpentinites show any systematic distribution with respect to along isochron position within the enclosing spreading segment indicating that melt extraction from the mantle is not necessarily focused at segment centers as has been commonly inferred in the spreading direction gabbros are consistently present toward the terminations of the detachment faults this suggests enhanced magmatism during the late stage of occ formation due either to natural variability in the magmatic cycle or to decompression melting during footwall exhumation heat introduced into the rift valley by flow and crystallization of this melt could weaken the axial lithosphere and result in formation of new faults and it therefore may explain eventual abandonment of detachments that form occs detailed seismic studies of the kind described here when constrained by seafloor morphology and geological samples can distinguish between major lithological units such as volcanics gabbros and serpentinized peridotites at lateral scales of a few kilometers thus such studies have tremendous potential to elucidate the internal structure of the shallow lithosphere and to help us understand the tectonic and magmatic processes by which they were emplaced

seismic velocity structure at a gas hydrate reflector offshore western colombia from full waveform inversion seismic reflection profiles across many continental margins have imaged bottom simulating reflectors bsrs which have been interpreted as being formed at the base of a methane hydrate stability field such reflectors might arise either from an impedance contrast between high velocity partially hydrated sediments and water saturated sediments or from a contrast with partially gas saturated sediments these alternatives may be hard to distinguish by conventional amplitude versus offset or waveform modeling approaches here we investigate the origin of a high amplitude bsr in the accretionary wedge offshore of western colombia by seismic waveform inversion the inversion procedure consists of three steps firstly determination of root mean square velocities and hence estimates of the interval velocities between major reflectors by a global grid search for maximum normalized energy along elliptical trajectories in the intercept time slowness domain secondly determination of accurate interval velocities between these reflectors by a monte carlo search for maximum energy and thirdly a waveform fit in the frequency slowness domain using differential reflectivity seismograms and a conjugate gradient optimization algorithm to minimize the sample by sample waveform misfit between data and synthetic at two locations near a structural high we find a 30 m thick low velocity zone beneath the bsr with the properties of a partially gas saturated zone while at a third location where the bsr amplitude is lower we find no evidence for anomalously low velocities the preferential development of the bsr in structures that would tend to intercept fluid flow or migrating gas and the presence of free gas beneath the bsr indicate a mechanism of bsr formation in which free methane gas migrates upward into the hydrate stability field or is carried there in advecting pore water

three dimensional seismic refraction tomography a comparison of two methods applied to data from the faeroe basin this paper presents a comparison of two tomographic methods for determining three dimensional 3 d velocity structure from first arrival travel time data the first method is backprojection in which travel time residuals are distributed along their ray paths independently of all other rays the second method is regularized inversion in which a combination of data misfit and model roughness is minimized to provide the smoothest model appropriate for the data errors both methods are nonlinear in that a starting model is required and new ray paths are calculated at each iteration travel times are calculated using an efficient implementation of an existing method for solving the eikonal equation by finite differencing both inverse methods are applied to 3 d ocean bottom seismometer obs data collected in 1993 over the faeroe basin consisting of 53 479 travel times recorded at 29 obss this is one of the most densely spaced large scale 3 d seismic refraction experiments to date different starting models and values for the free parameters of each tomographic method are tested a new form of backprojection that converges more rapidly than similar methods compares favorably with regularized inversion but the latter method provides a simpler model for little additional computational expense when applied to the faeroe basin data bounds on two model features are assessed using regularized inversion with combined smoothness and flatness constraints an inversion of synthetic data corresponding to 100 data recovery from the real experiment shows a marked improvement in lateral resolution at deeper depths and demonstrates the potential of currently feasible 3 d refraction experiments to provide well resolved long wavelength velocity models the similarity of the final models derived from the two tomographic methods suggests that the results from the new form of backprojection can be relied on when limited computational resources rule out regularized inversion

observational synthesis of mesoscale structures within an explosively developing cyclone an observational case study is presented of a rapidly developing uk cyclone on 30 october 2000 to reveal the rich diversity of coexisting mesoscale structures in the vicinity of the cloud head dry slot and polar front cloud band the mesoscale structures include multiple rain bands due to upright convection originating in the boundary layer stacked slantwise convective circulations at middle levels cloud top striations due to upright convection originating at high levels above the polar front cloud band multiple sub structure within the cloud head and inertia gravity waves in the region of the tropopause fold the emphasis of the analysis synthesis is on the inter relationships between the various mesoscale structures issues raised by this study include i the interaction between upright and slantwise convection including the effects of evaporation in the dry slot ii the possible roles of inertia gravity waves and conditional symmetric instability in triggering organizing the dry slot convective rain bands and the sub structure within the cloud head and iii the relationship between the dry slot rain bands and the multiple structures within the cloud head this study is limited to documenting these relationships controlled experiments with high resolution mesoscale models will be required to establish cause and effect and to assess their importance copyright 2005 royal meteorological society

the relation of moist symmetric instability and upper level potential vorticity anomalies to the observed evolution of cloud heads the cloud head phenomenon has been known for some time as a precursor of rapid cyclogenesis based upon satellite imagery two stages of cloud head development are identified in this study that can be related to early and late stages of the associated cyclone weakly convex cloud heads emerge from the baroclinic zone at an early stage in cyclogenesis and strongly convex cloud heads develop in association with the rapid deepening of the cyclone trajectories are used to highlight the role of an upper level potential vorticity pv anomaly in the growth of the strongly convex cloud head and the main flow associated with the growth of the strongly convex cloud head is viewed using isentropic analysis the possible role of moist symmetric instability in the development of both weakly and strongly convex cloud heads is discussed and a new diagnostic for measuring the vertically integrated extent of realizable symmetric vrs instability based on the moist geostrophic pv is introduced royal meteorological society 2002 g j shutt s contribution is crown copyright

reexamining the cold conveyor belt abstract despite the popularity of the conveyor belt model for portraying the airflow through midlatitude cyclones questions arise as to the path of the cold conveyor belt the lower tropospheric airflow poleward of and underneath the warm front some studies beginning with carlson s analysis of the eastern u s cyclone of 5 december 1977 depict the cold conveyor belt moving westward reaching the northwest quadrant of the storm turning abruptly anticyclonically rising to jet level and departing the cyclone downstream hereafter the anticyclonic path other studies depict the cold conveyor belt reaching the northwest quadrant turning cyclonically around the low center and remaining in the lower troposphere the cyclonic path to clarify the path of the cold conveyor belt the present study reexamines carlson s analysis of the cold conveyor belt using an observational and mesoscale numerical modeling study of the 5 december 1977 cyclone this reexamination raises several previously unappreciated

dry intrusions lagrangian climatology and dynamical impact on the planetary boundary layer abstractdry air intrusions dis are dry deeply descending airstreams from the upper troposphere toward the planetary boundary layer pbl the significance of dis spans a variety of aspects including the interaction with convection extratropical cyclones and fronts the pbl and extreme surface weather here a lagrangian definition for di trajectories is used and applied to ecmwf interim reanalysis era interim data based on the criterion of a minimum descent of 400 hpa during 48 h a first global lagrangian climatology of di trajectories is compiled for the years 1979 2014 allowing quantitative understanding of the occurrence and variability of dis as well as the dynamical and thermodynamical interactions that determine their impact dis occur mainly in winter while traveling equatorward from 40 50 latitude dis typically reach the lower troposphere with maximum frequencies of 10 in winter in the storm track regions as well as over the mediterranean sea arabian sea and eastern north pa

mesoscale dynamics of the trowal and warm frontal regions of two continental winter cyclones abstract the dynamic and thermodynamic structure and associated frontal circulations within the trowal and warm frontal regions of two extratropical winter cyclones are examined using numerical simulations in each cyclone the warm moist airstream originating in the warm sector was found to bifurcate upon reaching the warm front one branch of the flow turned anticyclonically eastward corresponding to the warm conveyor belt while the second branch turned cyclonically westward becoming the trowal airstream the dynamic forcing of vertical motion within the two airstreams was investigated using the fifth generation pennsylvania state university national center for atmospheric research mesoscale model mm5 both from an analysis of the sawyer eliassen se equation in two dimensions and from complete model solutions shearing deformation associated with the jet stream and the low level cyclonic flow dominated confluent deformation near the trowal in both cases the shearing deformation was accompanied

reflection seismic waveform tomography 1 in seismic waveform tomography if using reflection data with limited source receiver offsets it is difficult to reconstruct the deep part of the subsurface velocity model we present two approaches to tackle this problem layer stripping and weighted updating in a layer stripping procedure we replace the top portion of seismic data with synthetics generated from the previous layer inversion and make the current inversion focus on the minimization of the data misfit corresponding to the deep part of the model to improve efficiency we use only sparsely sampled frequency data in the deeper layer inversions unlike the first layer inversion where we use densely sampled frequency data as usual the sparsely sampled frequencies together have the full wave number coverage for effective imaging combined use of dense and sparse sampling in frequency is a compromise between resolution and efficiency as it reduces the number of iterations needed in layer stripping inversion while still producing a good image in the second scheme we apply depth dependent weights to model updates in order to improve the convergence in an iterative solution the weighting is inversely proportional to the ray density variation along the depth and is mathematically equivalent to the application of an inverse hessian matrix which sharpens the gradient vector for model updating for real seismic data we transfer point source shot records to line source records by partial amplitude compensation and phase adjusting before inputting it to the waveform tomography we perform traveltime inversion to generate a reliable layered velocity model and then waveform tomography to produce a high resolution image of the subsurface model through frequency domain iteration