variations of the east asian jet stream and asian pacific american winter climate anomalies in this study the authors apply the ncep ncar reanalysis and other observations to depict the association of the asian pacific american climate with the east asian jet stream eajs with an emphasis on boreal winter seasons and on interannual timescales they analyze the variations of the eajs and their relationships with el nino southern oscillation enso and extratropical north pacific sea surface temperature sst and assess the relative connections of the eajs and enso to the anomalies of atmospheric circulation surface temperature and precipitation in the asian pacific american region it is found that the eajs is coupled to a teleconnection pattern spanning the entire asian pacific american region with the strongest signals over east asia and the western pacific this pattern differs significantly from that associated with enso which influences the earth s climate extensively with a strongest impact on the climate over the central pacific and east a strong eajs is associated with an intensification of the weather and climate systems in asia and over the pacific such as deepening of the east asian trough and the aleutian low and strengthening of the east asian winter monsoon it is linked to colder and drier conditions in east asia and stronger convection over the tropical asia australia sector compared with enso the eajs seems to link to the climate signals of asia and the pacific more strongly an intensified eajs is also associated with anomalies of temperature and precipitation in north america due to the related changes in stationary wave patterns while the eajs does not strongly link to the tropical central eastern pacific sst it is significantly associated with the extratropical north pacific sst more specifically the second most dominant mode of the empirical orthogonal function analysis of the sst in addition a strong weak eajs seems to follow a large small meridional gradient of the western pacific sst associated with warming cooling in the tropics subtropics and cooling warming in the extratropics

ionospheric electron density inversion for global navigation satellite systems radio occultation using aided abel inversions the abel inversion of ionospheric electron density profiles with the assumption of spherical symmetry applied for radio occultation soundings could introduce a greater systematic error or sometimes artifacts if the occultation rays trespass regions with larger horizontal gradients in electron density the aided abel inversions have been proposed by considering the asymmetry ratio derived from ionospheric total electron content tec or peak density nmf2 of reconstructed observation maps since knowledge of the horizontal asymmetry in ambient ionospheric density could mitigate the inversion error here we propose a new aided abel inversion using three dimensional time dependent electron density ne based on the climatological maps constructed from previous observations as it has an advantage of providing altitudinal information on the horizontal asymmetry improvement of proposed ne aided abel inversion and comparisons with electron density profiles inverted from the nmf2 and tec aided inversions are studied using observation system simulation experiment osse comparison results show that all three aided abel inversions improve the ionospheric profiling by mitigating the artificial plasma caves and negative electron density in the daytime e region the equatorial ionization anomaly crests in the f region become more distinct the statistical results show that the ne aided abel inversion has less mean and rmse of error percentage above 250 km altitudes and the performances for all aided abel inversions are similar below 250 km altitudes

observations of global ionospheric responses to the 2009 stratospheric sudden warming event by formosat 3 cosmic 1 the global ionospheric response to a stratospheric sudden warming ssw is studied using three dimensional electron density maps derived from radio occultation observations of formosat 3 cosmic during the 2009 ssw periods results show that the ionospheric electron density at eia crests exhibit a morning early afternoon increase followed by an afternoon decrease and an evening increase indicative of a semidiurnal component during the ssw period which is consistent with recent studies the latitude altitude electron density slice maps show that the ssw related modifications of the equatorial plasma fountain interact with the existing summer to winter neutral winds and resulting in a north south asymmetry the global ionospheric response shows a clear longitudinal dependence in the equatorial plasma fountain enhancement during morning early afternoon inferred from the duration of the equatorial ionization anomaly eia enhancement following the enhancement prominent global eia reductions resulting from the equatorial plasma fountain weakening in the afternoon sector are seen the ionospheric response to the 2009 ssw event is also compared with the usual seasonal variation during january february 2007 instead of showing the electron density increase in the northern hemisphere and decrease in the southern hemisphere as the usual seasonal variation does the ssw period ionosphere shows prominent global electron density reductions in the afternoon period during the 2009 ssw event

imaging diffraction points using the local image matrices generated in prestack migration energy angle distributions in the local image matrix which is a function of local incident and receiving angles at a subsurface point are different for a planar reflector and a diffraction point the former exhibits a linear distribution along a certain dip direction whereas the latter shows a scattered distribution in the entire matrix therefore the singular values of the local image matrix in the local angle domain indicate the energy distribution along different dip directions the difference between the auto and crosscorrelation coefficients of the sets of singular values between adjacent image points can be used to distinguish these two types of targets and obtain prestack images which contain only diffraction points using three synthetic examples we found that the method can effectively image diffraction points seismic images of diffraction points may provide important information about geological discontinuities and diffraction points can be taken as secondary sources for potential applications in imaging subsalt structures which are poorly illuminated by primary waves

ionospheric annual anomaly new insights to the physical mechanisms the ionospheric annual anomaly or nonseasonal anomaly of the ionosphere is characterized by globally increased ionization in december solstice than in june solstice though this phenomenon was reported several decades ago the causal mechanisms have not been fully understood till today in this paper the f2 layer peak electron density nmf2 data from formosa satellite 3 constellation observing system for meteorology ionosphere and climate radio occultation observations during the low solar activity year 2009 were systematically analyzed to investigate the physical mechanisms responsible for annual anomaly and its local time latitudinal and longitudinal variability it is found that the annual anomaly is primarily dominant at southern hemisphere at all local times with significant enhancements at equatorial ionization anomaly crest latitudes during noon to afternoon hours and at high latitudes during nighttimes the annual anomaly in northern hemisphere occurs with relatively smaller magnitudes and confined only to morning to early afternoon hours 08 14 lt this study brings out the important roles of effective neutral winds due to the geomagnetic field configuration and the offset between geomagnetic equator and subsolar point for the enhanced plasma density in the southern hemisphere during december that majorly contributes to the ionospheric annual anomaly these results provide new insights to the responsible mechanisms behind the ionospheric annual anomaly and its local time latitudinal and longitudinal variation

artificial plasma cave in the low latitude ionosphere results from the radio occultation inversion of the formosat 3 cosmic previous studies report unexpected electron density reductions termed plasmacaves located underneath the equatorial ionization anomaly eia crests a radiooccultation ro observation simulation experiment has been built to evaluate possiblebiases introduced by the spherical symmetry assumption in the standard abel roinversion processes the experiment simulates the electron density profiles andreconstructs the plasma structure of the eia at low latitudes where the horizontal gradientis most significant the reconstruction shows that artificial plasma caves are createdunderneath the eia crests along with three density enhancements in adjacent latitudes theartifact appears mainly below 250 km altitudes and becomes pronounced when theeias are well developed above that altitude the two eia features in the original truth model the international reference ionosphere iri 2007 and in the inversion are similar but the inversion reconstructs less distinct eia crests with underestimation of the electrondensity a simple correction has been introduced by multiplying the ratio between thetruth and inversion with actual formosat 3 cosmic observations this initialcorrection shows that the artificial plasma caves are mitigated results also reveal that thero technique is not suitable to detect or rule out possible existence of the plasma caves

longitudinal variations in the f region ionosphere and the topside ionosphere plasmasphere observations and model simulations 1 constellation observing system for meteorology ionosphere and climate cosmic observations of the total electron content tec above and below 800 km are used to study the local time and seasonal variation of longitude structures in both the f region ionosphere as well as the topside ionosphere and plasmasphere the cosmic observations reveal the presence of distinct longitude variations in the topside ionosphere plasmasphere tec and these further exhibit a seasonal and local time dependence the predominant feature observed at all local times in the topside ionosphere plasmasphere tec is a substantial maximum minimum during northern hemisphere winter summer around 300 360 geographic longitude around equinox at a fixed local time a wave 4 variation in longitude prevails in the daytime f region tec as well as the topside ionosphere plasmasphere tec the wave 4 variation in longitude persists into the nighttime in the f region however the nighttime topside ionosphere plasmasphere tec exhibits two maxima in longitude the cosmic observations clearly reveal the presence of substantial longitude variations in the f region and topside ionosphere plasmasphere and to elucidate the source of the longitude variations results are presented based on the coupling between the global ionosphere plasmasphere model and the thermosphere ionosphere electrodynamics general circulation model the model simulations demonstrate that the orientation of the geomagnetic field plays a fundamental role in generating significant longitude variations in the topside ionosphere plasmasphere but does not considerably influence longitude variations in the f region ionosphere the model results further confirm that nonmigrating tides are the primary mechanism for generating longitude variations in the f region ionosphere the coupled model additionally demonstrates that nonmigrating tides are also of considerable importance for the generation of longitude variations in the topside ionosphere plasmasphere tec

on the maintenance and initiation of the intraseasonal oscillation in the ncep ncar reanalysis and in the gla and ukmo amip simulations in this study satellite derived outgoing longwave radiation olr and the reanalysis from the national centers for environmental prediction national center for atmospheric research are used as verification data in a study of intraseasonal variability in the goddard laboratory for atmospheres gla and the united kingdom meteorological office ukmo atmospheric general circulation models these models simulated the most realistic intraseasonal oscillations io of the 15 atmospheric model intercomparison project models previously analyzed during the active phase of the intraseasonal oscillation convection is observed to migrate from the indian ocean to the western central pacific ocean and into the south pacific convergence zone spcz the simulated convection particularly in the gla model is most realistic over the western central pacific ocean and the spcz in the reanalysis the baroclinic structure of the io is evident in the eddy stream function and eastward migration of the anticyclone cyclone pairs occurs in conjunction with the eastward development of convection both the gla and ukmo models exhibit a baroclinic structure on intraseasonal time scales the gla model is more realistic than the ukmo model at simulating the eastward migration of the anticyclone cyclone pairs when the convection is active over the western central pacific in the ukmo model the main heating is located off the equator which contributes to the irregular structures seen in this model on intraseasonal time scales the maintenance and initiation of the intraseasonal oscillation has also been investigated analysis of the latent heat flux indicates that evaporative wind feedback is not the dominant mechanism for promoting the eastward propagation of the intraseasonal oscillation since evaporation to the west of the convection dominants the data suggest a wave cisk conditional instability of the secondkind type mechanism although the contribution by frictional convergence is not apparent in the gla model enhanced evaporation tends to develop in place over the west pacific warm pool while in the ukmo simulation westward propagation of enhanced evaporation is evident it is suggested that lack of an interactive ocean may be associated with the models systematic failure to simulate the eastward transition of convection from the indian ocean into the western pacific ocean this hypothesis is based upon the examination of observed sea surface temperature sst and its relationship to the active phase of the intraseasonal oscillation which indicates that the io may evolve as a coupled ocean atmosphere mode the eastward propagation of convection appears to be related to the gradient of sst with above normal sst to the east of the convection maintaining the eastward evolution and decreasing sst near the western portion of the convective envelope being associated with the cessation of convection

ionospheric plasma caves under the equatorial ionization anomaly 1 this paper reports the existence of plasma caves minima in the electron density located at 5 10 to the magnetic equator in the bottomside ionosphere based on electron densities simulations from the international reference ionosphere iri 2007 and clear evidences given by plasma density and drift measurements of the dynamic explorer 2 de 2 satellite during 1981 1983 the iri simulations suggest plasma caves as daytime features 08 00 19 00 lt length of 18 158 km in the longitudinal direction that range from thee region up to about 300 km altitude with 10 or 1100 km width in the latitudinal direction in situ measurements of the ion and electron densities probed by the de 2 confirm the existence of the plasma caves at low altitudes of the eia ionosphere the unexpected downward and upward or weakly and strongly upward ion drifts at the magnetic equator and the two off equators seem to play an important role responsible for the plasma cave formation

estimates of the precision of gps radio occultations from the cosmic formosat 3 mission 1 the constellation observing system for meteorology ionosphere and climate cosmic formosa satellite 3 formosat 3 is a six satellite radio occultation mission that was launched in mid april 2006 the close proximity of the cosmic satellites provides a unique opportunity to estimate the precision of the radio occultation remote sensing technique from closely collocated occultations 10 km separation of tangent points the rms difference of refractivity between 10 and 20 km altitude is less than 0 2 which is approximately twice better than previous estimates obtained from champ and sac c collocated occultations apparently due to smaller separation of the occultation pairs and due to parallel occultation planes in the lower troposphere the maximal rms is 0 8 at 2 km altitude and decreases abruptly to 0 2 between 6 and 8 km altitude the rms difference of electron density in the ionosphere between 150 and 500 km altitude for collocated occultations is about 103 cm 3

poststack velocity analysis by separation and imaging of seismic diffractions small geologic features manifest themselves in seismic data in the form of diffracted waves which are fundamentally different from seismic reflections using two field data examples and one synthetic example we demonstrate the possibility of separating seismic diffractions in the data and imaging them with optimally chosen migration velocities our criteria for separating reflection and diffraction events are the smoothness and continuity of local event slopes that correspond to reflection events for optimal focusing we develop the local varimax measure the objectives of this work are velocity analysis implemented in the poststack domain and high resolution imaging of small scale heterogeneities our examples demonstrate the effectiveness of the proposed method for high resolution imaging of such geologic features as faults channels and salt boundaries

poststack diffraction imaging using reverse time migration abstract we propose a method for imaging small scale diffraction objects in complex environments in which kirchhoff based approaches may fail the proposed method is based on a separation between the specular reflection and diffraction components of the total wavefield in the migrated surface angle domain reverse time migration was utilized to produce the common image gathers this approach provides stable and robust results in cases of complex velocity models the separation is based on the fact that in surface angle common image gathers reflection events are focused at positions that correspond to the apparent dip angle of the reflectors whereas diffracted events are distributed over a wide range of angles the high resolution radon based procedure is used to efficiently separate the reflection and diffraction wavefields in this study we consider poststack diffraction imaging the advantages of working in the poststack domain are its numerical efficiency and the reduced computational time the numerical results show that the proposed method is able to image diffraction objects in complex environments the application of the method to a real seismic dataset illustrates the capability of the approach to extract diffractions

3 d seismic attributes using a semblance based coherency algorithm seismic coherency is a measure of lateral changes in the seismic response caused by variation in structure stratigraphy lithology porosity and the presence of hydrocarbons unlike shaded relief maps that allow 3 d visualization of faults and channels from horizon picks seismic coherency operates on the seismic data itself and is therefore unencumbered by interpreter or automatic picker biases we present a more robust multitrace semblance based coherency algorithm that allows us to analyze data of lesser quality than our original three trace cross correlation based algorithm this second generation semblance based coherency algorithm provides improved vertical resolution over our original zero mean crosscorrelation algorithm resulting in reduced mixing of overlying or underlying stratigraphic features in general we analyze stratigraphic features using as narrow a temporal analysis window as possible typically determined by the highest usable frequency in the input seismic data in the limit one may confidently apply our new semblance based algorithm to a one sample thick seismic volume extracted along a conventionally picked stratigraphic horizon corresponding to a peak or trough whose amplitudes lie sufficiently above the ambient seismic noise in contrast near vertical structural features such as faults are better enhanced when using a longer temporal analysis window corresponding to the lowest usable frequency in the input data the calculation of reflector dip azimuth throughout the data volume allows us to generalize the calculation of conventional complex trace attributes including envelope phase frequency and bandwidth to the calculation of complex reflector attributes generated by slant stacking the input data along the reflector dip within the coherency analysis window these more robust complex reflector attribute cubes can be combined with coherency and dip azimuth cubes using conventional geostatistical clustering and segmentation algorithms to provide an integrated multiattribute analysis

seismic modelling for geological fractures based on knowledge of a commutative group calculation of the rock stiffness and on some geophysical assumptions the simplest fractured medium may be regarded as a fracture embedded in an isotropic background medium and the fracture interface can be simulated as a linear slip interface that satisfies nonwelded contact boundary conditions the kinematic displacements are discontinuous across the interface whereas the dynamic stresses are continuous across the interface the finite difference method with boundary conditions explicitly imposed is advantageous for modelling wave propagation in fractured discontinuous media that are described by the elastic equation of motion and nonwelded contact boundary conditions in this paper finite difference schemes for horizontally vertically and orthogonally fractured media are derived when the fracture interfaces are aligned with the boundaries of the finite difference grid the new finite difference schemes explicitly have an additional part that is different from the conventional second order finite difference scheme and that directly describes the contributions of the fracture to the wave equation of motion in the fractured medium the numerical seismograms presented to first order show that the new finite difference scheme is accurate and stable and agrees well with the results of previously published finite difference schemes the coates and schoenberg method the results of the new finite difference schemes show how the amplitude of the reflection produced by the fracture varies with the fracture compliances later comparisons with the reflection coefficients indicate that the reflection coefficients of the fracture are frequency dependent whereas the reflection coefficients of the impedance contrast interface are frequency independent in addition the numerical seismograms show that the reflections of the fractured medium are equal to the reflections of the background medium plus the reflections of the fracture in the elastic fractured medium this article is protected by copyright all rights reserved

enhancing the detection of small coal structures by seismic diffraction imaging abstract faults are the most important geological structures that need to be detected in any modern underground coal mining project even a fault with a throw of a few metres can create safety issues and lead to costly delays in mine production while seismic surveys are usually successful at locating faults with throws greater than 5 10 m reliable techniques for resolving more subtle faults dykes and other minor features are yet to be developed in seismic data there are two types of seismic energy signatures that can be used for subsurface imaging specular reflections and diffractions specular reflections are created by relatively smooth surfaces between layers of differing impedance contrasts such as at coal rock interfaces specular reflections are used in conventional seismic reflection surveys diffractions are generated by local discontinuities caused by surface roughness faults dykes and fractures in this paper we describe the use of a moving average error filter which along with a process of reflection event flattening for accommodation of dips and undulations of coal seam reflections can be used to effectively extract diffraction signals from post stack reflection seismic data by identifying diffractions small faults and other minor features that are elusive using conventional seismic reflection processing can be detected suggesting that diffraction imaging may be a superior method to seismic reflection imaging both synthetic and real 2d and 3d coal seismic data are used to illustrate the feasibility of diffraction imaging for small fault detection it is demonstrated from synthetic examples that the extracted diffractions can be used to detect faults with a throw of 1 m while a real data example shows that it is possible to detect igneous dykes with widths of just 4 m

reverse time migration migration of stacked or zero offset sections is based on deriving the wave amplitude in space from wave field observations at the surface conventionally this calculation has been carried out through a depth extrapolation we examine the alternative of carrying out the migration through a reverse time extrapolation this approach may offer improvements over existing migration methods especially in cases of steeply dipping structures with strong velocity contrasts this migration method is tested using appropriate synthetic data sets

field aligned neutral wind bias correction scheme for global ionospheric modeling at midlatitudes by assimilating formosat 3 cosmic hmf2 data under geomagnetically quiet conditions this study demonstrates the usage of a data assimilation procedure which ingests the formosat 3 cosmic f3 c hmf2 observations to correct the model wind biases to enhance the capability of the new global ionosphere plasmasphere electrodynamics ipe model under geomagnetically quiet conditions the ipe model is built upon the field line interhemispheric plasma model with a realistic geomagnetic field model and empirical model drivers the hmf2 observed by the f3 c radio occultation technique is utilized to adjust global thermospheric field aligned neutral winds i e a component of the thermospheric neutral wind parallel to the magnetic field at midlatitudes according to a linear relationship between time differentials of the field aligned wind and hmf2 the adjusted winds are further applied to drive the ipe model the comparison of the modeled electron density with the observations of f3 c and ground based gps receivers at the 2012 march equinox suggests that the modeled electron density can be significantly improved in the midlatitude regions of the southern hemisphere if the wind correction scheme is applied moreover the f3 c observation the ipe model and the wind bias correction scheme are applied to study the 2012 southern hemisphere midlatitude summer nighttime anomaly southern msna weddell sea anomaly wsa event at december solstice for examining the role of the neutral winds in controlling the longitudinal variation of the southern msna wsa behavior with the help of the wind bias correction scheme the ipe model better tracks the f3 c observed eastward movement of the southern msna wsa feature the apparent eastward movement of the southern msna wsa features in the local time coordinate is primarily caused by the longitudinal variation in the declination angle of the geomagnetic field that controls the field aligned projection of both geographic meridional and zonal components of the neutral wind both the ipe simulations and the f3 c observations show the significant longitudinal variation in the speed of the eastward movement of the southern msna wsa

simulations of persistent north pacific circulation anomalies and interhemispheric teleconnections abstract evidence is presented from a composite analysis of a 14 year general circulation model simulation that persistent north pacific pnp circulation anomalies during boreal winter are part of a larger scale meridional development extending into the tropics and the southern hemisphere lagged composites suggest that the development is initiated over the tropical pacific by anomalous convection characterized by an east west dipole structure centered at the date line one to two weeks prior to the extratropical onset time relatively weak wave trains extending from the region of anomalous convection into the extratropics appear to set the stage for the subsequent rapid development of the pnp anomalies after onset the pnp anomalies extend into the tropics and enhance moisture transports that tend to supply moisture to and thus reinforce the associated tropical precipitation anomalies the mature stage is characterized by a strong coupling between hemispheres including twin low level cyclonic a

contributions of downstream eddy development to the teleconnection between enso and the atmospheric circulation over the north atlantic abstractthe spatiotemporal evolution of various meteorological phenomena associated with el nino southern oscillation enso in the north pacific north american north atlantic sector is examined using both ncep ncar reanalyses and output from a 2000 yr integration of a global coupled climate model particular attention is devoted to the implications of downstream eddy developments on the relationship between enso and the atmospheric circulation over the north atlantic the el nino related persistent events are characterized by a strengthened pacific subtropical jet stream and an equatorward shifted storm track over the north pacific the wave packets that populate the storm tracks travel eastward through downstream development the barotropic forcing of the embedded synoptic scale eddies is conducive to the formation of a flow that resembles the negative phase of the north atlantic oscillation nao the more frequent and higher persistence of those episodes during el nino winters contribute to the prevale

diffraction imaging by prestack reverse time migration in the dip angle domain prestack image volumes may be decomposed into specular and non specular parts by filters defined in the dip angle domain for space shift extended image volumes the dip angle decomposition is derived via local radon transform in depth and midpoint coordinates followed by an averaging over space shifts we propose to employ prestack space shift extended reverse time migration and dip angle decomposition for imaging small scale structural elements considered as seismic diffractors in models with arbitrary complexity a suitable design of a specularity filter in the dip angle domain rejects the dominant reflectors and enhances diffractors and other non specular image content the filter exploits a clear discrimination in dip between specular reflections and diffractions the former are stationary at the specular dip whereas the latter are non stationary without a preferred dip direction while the filtered image volume features other than the diffractor images for example noise and truncation artifacts are also present synthetic and field data examples suggest that diffractors tend to dominate and are readily recognizable averaging over space shifts in the filter construction makes the reflectors rejection robust against migration velocity errors another consequence of the space shift extension and its angle domain transforms is the possibility of exploring the image in a multiple set of common image gathers the filtered diffractions may be analyzed simultaneously in space shift scattering angle and dip angle image gathers by means of a single migration job the deliverables of our method obviously enrich the processed material on the interpreter s desk we expect them to further supplement our understanding of the earth s interior this article is protected by copyright all rights reserved

post stack velocity analysis in the dip angle domain using diffractions interval velocity analysis in complex geological areas is often considered as an unresolved problem a novel approach to improve the velocity analysis process is to perform the analysis in a non conventional domain and to use seismic events that are usually ignored during standard data processing and imaging in this study a method to analyse diffraction data for migration velocity analysis in the time or depth domain is presented the method is based on the clear distinction between diffractions and reflections in the post migration dip angle domain the attractive possibility to perform the analysis using only stacked data as an input is demonstrated on synthetic and real data examples

diffraction imaging by focusing defocusing an outlook on seismic superresolution diffractions always need more advertising it is true that conventional seismic processing and migration are usually successful in using specular reflections to estimate subsurface velocities and reconstruct the geometry and strength of continuous and pronounced reflectors however correct identification of geological discontinuities such as faults pinch outs and small size scattering objects is one of the main objectives of seismic interpretation the seismic response from these structural elements is encoded in diffractions and diffractions are essentially lost during the conventional processing migration sequence hence we advocate a diffraction based data oriented approach to enhance image resolution as opposed to the traditional image oriented techniques which operate on the image after processing and migration even more it can be shown that at least in principle processing of diffractions can lead to superresolution and the recovery of details smaller than the seismic wavelength the so called reflection stack is capable of effectively separating diffracted and reflected energy on a prestack shot gather by focusing the reflection to a point while the diffraction remains unfocused over a large area muting the reflection focus and defocusing the residual wavefield result in a shot gather that contains mostly diffractions diffraction imaging applies the classical isotropic diffraction stack to these diffraction shot gathers this focusingmuting defocusing approach can successfully image faults small size scattering objects and diffracting edges it can be implemented both in model independent and modeldependent contexts the resulting diffraction images can greatly assist the interpreter when used as a standard supplement to full wave images

3d seismic characterization of fractures in a dipping layer using the double beam method the characterization of natural and induced fractures in terms of fracture orientation fracture spacing or density and fracture compliance is critical in reservoir development given the multiscale nature of the fracture distribution the commonly used effective anisotropy assumption may not be valid the recently proposed double beam method to characterize the fractured reservoir has the potential to invert for the spatially dependent fracture network information for a horizontal reservoir layer however the inverted results can be biased if the fractured reservoir layer is dipping as a result it is essential to estimate and include the dip angle information of reservoir layers in applying the double beam method we used forward modeling to demonstrate the bias and proposed a new method to correct for the error caused by the reservoir layer dip angle for a dipping layer our new method can correctly invert for the fracture parameters including the fracture orientation and fracture spacing

diffraction imaging in depth high resolution imaging is of great value to an interpreter for instance to enable identification of small scale faults and to locate formation pinch out positions standard approaches to obtain high resolution information such as coherency analysis and structure oriented filters derive attributes from stacked migrated images since they are image driven these techniques are sensitive to artifacts due to an inadequate migration velocity in fact the attribute derivation is not based on the physics of wave propagation diffracted waves on the other hand have been recognized as physically reliable carriers of high or even super resolution structural information however high resolution information encoded in diffractions is generally lost during the conventional processing sequence indeed migration kernels in current migration algorithms are biased against diffractions we propose here methods for a diffraction based data oriented approach to image resolution we also demonstrate the different behaviour of diffractions compared to specular reflections and how this can be leveraged to assess characteristics of subsurface features in this way a rough surface such as a fault plane or unconformity may be distinguishable on a diffraction image and not on a traditional reflection image we outline some characteristic properties of diffractions and diffraction imaging and present two novel approaches to diffraction imaging in the depth domain the first technique is based on reflection focusing in the depth domain and subsequent filtering of reflections from prestack data the second technique modifies the migration kernel and consists of a reverse application of stationary phase migration to suppress contributions from specular reflections to the diffraction image both techniques are proposed as a complement to conventional full wave pre stack depth migration and both assume the existence of an accurate migration velocity

analysis of ionospheric electron density distribution from gps met occultations the authors present results from analysis of gps met occultation data obtained from the university corporation for atmospheric research database they have used high rate occultation data to study the performance of an earlier 4d ionospheric electron content model obtained tomographically with the use of the gps constellation with satisfactory results in addition they have processed ucar level one medium rate occultation data by using the gipsy package to obtain aligned phases under the assumption of local spherical symmetry this phase information has been processed to yield ray path bending angles through doppler shift analysis which have then been used to yield profiles of electronic density via the abel transform these profiles give important information for preparing future tomographic work although the limitations imposed by the working assumptions in this approach cannot be ignored

green s function implementation of common offset wave equation migration common offset migration is extremely important in the context of migration velocity analysis mva since it generates geologically interpretable migrated images however only a wave equation based migration handles multipathing of energy in contrast to the popular kirchhoff migration with first arrival traveltimes we have combined the superior treatment of multipathing of energy by wave equation based migration with the advantages of the common offset domain for mva by implementing wave equation migration algorithms via the use of finite difference green s functions with this technique we are able to apply wave equation migration in measurement configurations that are usually considered to be of the realm of kirchhoff migration in particular wave equation migration of common offset sections becomes feasible the application of our wave equation common offset migration algorithm to the marmousi data set confirms the large increase in interpretability of individual migrated sections for about twice

negative ionospheric storm coincident with de 1 observed thermospheric disturbance on october 14 1981 the de 1 far ultraviolet fuv imaging instrument recorded a large thermospheric disturbance over europe and russia on october 14 1981 during a geomagnetic storm commencing near the end of the previous day the disturbance is quantified in terms of o n2 the column density ratio referenced to a fixed depth in n2 the ratio is derived from de 1 dayglow observations with a filter whose signal transmission is dominated by o i 130 4 nm emission within the disturbed region o n2 is less than that in surrounding regions with minimum values being more than a factor of 2 smaller than undisturbed values images of o n2 are compared to ground based ionosonde data from 13 sites some within and others outside of the disturbed region the data are in the form of nmax the maximum electron density which in the presence of an f2 layer is equivalent to nmf2 the data exhibit negative ionospheric storm effects reduced nmax within the disturbed region and normal behavior elsewhere the degree of correlation between o n2 and nmax suggests that the approximate geographical extent of dayside regions experiencing negative ionospheric storm effects can be determined from global fuv imaging of the disturbed and surrounding regions the analysis is extended to the following day to address the recovery of the disturbed region the o n2 ratio has returned to undisturbed values except in a smaller disturbance region containing weak reductions in o n2 this is either a remnant of the strong disturbance from the day before or a newly formed disturbance from substorm activity several hours prior to the new observations only the ionosonde sites within this region recorded values of nmax below their monthly median values

double crests of peak height in the equatorial ionospheric f2 layer observed by cosmic for the first time we report daytime double crests of peak height hmf2 in the f2 layer based on the constellation observing system for meteorology ionosphere and climate cosmic observations during 2007 2014 evident double crests of hmf2 occurred at around 10 geomagnetic latitude with a trough over the magnetic equator at low solar activity and at march equinox this phenomenon is referred to as an equatorial height anomaly eha of the ionospheric f2 layer the double crests became less obvious at september equinox and disappeared at solstices at solstices only one crest was observed in the summer hemisphere which is probably associated with transequatorial neutral winds in addition the double eha crests generally take place during 10 00 14 00 local times our results indicate that the eha favors the conditions of strong vertical plasma drifts and weak transequatorial neutral winds during low solar activity the eha feature is reproduced by the thermosphere ionosphere electrodynamics global circulation model at march equinox and low solar activity

the statistics and horizontal structure of anomalous weather regimes in the community climate model abstract the statistics horizontal structure and linear barotropic dynamics of anomalous weather regimes are evaluated in a 15 winter integration of the ncar community climate model ccm2 statistical and ensemble analyses of simulated regimes are contrasted with parallel analyses derived from ncep ncar reanalyses the ccm2 replicates much of the structure of observed frequency distributions for anomalous weather regimes over the north pacific and north atlantic regions the main differences are a northward shift and longitudinal broadening of the north pacific frequency maximum and a weakening and southward shift of the north atlantic maximum ensemble analyses reveal that simulated north pacific regimes attain a more isotropic horizontal anomaly structure than observed cases which are zonally elongated the e vector diagnoses indicate that north pacific cases in the ccm2 are also associated with much weaker local barotropic energy conversions from the climatological mean flow this is partly due to

the ionospheric midlatitude trough observed by formosat 3 cosmic during solar minimum 1 this paper for the first time reports global three dimensional 3 d structures of the ionospheric midlatitude trough using electron density profiles derived from the gps radio occultation experiment on board formosat 3 cosmic f3 c satellites during the solar minimum period february 2008 to january 2009 results show that the midlatitude trough extends from dusk to dawn in all four seasons and is most pronounced in the winter hemisphere the troughs in the two hemispheres are asymmetric where the trough in the northern hemisphere is more evident and stronger than that in the southern hemisphere during the equinoctial seasons in general the trough minimum position shows a high low high latitudinal variation with magnetic local time and occurs at lower latitudes under higher magnetic activity on the other hand the midlatitude trough structures become more complex in the southern hemisphere because of the nighttime plasma density enhancement of the weddell sea anomaly our results demonstrate that the new data set of gps radio occultation by f3 c is useful to probe the global 3 d electron density structures of the midlatitude trough

equatorial windows and barriers for stationary rossby wave propagation abstractrossby waves can cross the equator and connect the northern hemisphere nh and southern hemisphere sh or be blocked in the vicinity of the equator this work explores the windows and ba

motions of the equatorial ionization anomaly crests imaged by formosat 3 cosmic 1 the equatorial ionization anomaly eia structures and evolutions are imaged using radio occultation observation of the newly launched formosat 3 cosmic f3 c satellite constellation three dimensional ionospheric images provide unprecedented detail of the eia structure globally this paper presents images of the eia structures during july august 2006 and discusses the development and subsidence of the eia clear seasonal asymmetries in both ionospheric electron density and layer height are observed two dimensional cross section maps at a meridian provide dynamic variations and motions of the northern and southern eia crests results suggest that in addition to the asymmetric neutral composition effect interactions between the summer to winter transequatorial neutral winds and strength of the equatorial plasma fountain effect play important roles in producing asymmetric development of the eia crests as imaged by the f3 c

separation and imaging of seismic diffractions using migrated dip angle gathers abstractcommon reflection angle migration can produce migrated gathers either in the scattering angle domain or in the dip angle domain the latter reveals a clear distinction between reflection and diffraction events we derived analytical expressions for events in the dip angle domain and found that the shape difference can be used for reflection diffraction separation we defined reflection and diffraction models in the radon space the radon transform allowed us to isolate diffractions from reflections and noise the separation procedure can be performed after either time migration or depth migration synthetic and real data examples confirmed the validity of this technique

ionospheric f2 region perturbed by the 25 april 2015 nepal earthquake seismic waves can be detected in the earth s atmosphere and ionosphere however their impacts on ionospheric electron density ne structures near the altitude of peak ne hmf2 have not yet been fully determined due to the lack of sufficient observations sampled in the vertical direction here we apply a ground based global positioning system gps receiving network in asia as well as the space based gps occultation experiment on board the formosat 3 cosmic f3 c satellite to vertically scan the ionospheric ne structures which were perturbed by the magnitude mw7 8 nepal earthquake that occurred on 25 april 2015 the f3 c altitudinal ne profiles show that the nepal earthquake induced air perturbations penetrate into the ionosphere at supersonic speeds of approximately 800 m s and change the ne structure by 10 near hmf2 the vertical scale of the ne perturbation is 150 km while the hmf2 is uplifted by more than 30 km within 1 min those results reveal that the earthquake induced ground displacement should be considered as a significant force that perturbs the vertical ne structure of the ionosphere