the life cycle of baroclinic eddies in a storm track environment abstract the life cycle of baroclinic eddies in a controlled storm track environment has been examined by means of long model integrations on a hemisphere a time lagged regression that captures disturbances with large meridional velocities has been applied to the meteorological variables this regressed solution is used to describe the life cycle of the baroclinic eddies the eddies grow as expected by strong poleward heat fluxes at low levels in regions of strong surface baroclinicity at the entrance of the storm track in a manner similar to that of charney modes as the eddies evolve into a nonlinear regime they grow deeper by fluxing energy upward and the characteristic westward tilt exhibited in the vorticity vanishes by rotating into a meridional tilt in which the lower level cyclonic vorticity center moves poleward and the upper level center moves equatorward this rather classical picture of baroclinic evolution is radically modified by the simultaneous development of an upper level eddy downs

diagnosis of the downstream ridging associated with extratropical transition using short term ensemble forecasts abstract the dynamical mechanisms that led to downstream ridging during the extratropical transition et of typhoons tokage and nabi are evaluated using data drawn from a cycling ensemble kalman filter coupled with the weather research and forecasting model wrf during both transitions the ensemble covariances indicate that the 350 k potential vorticity pv at the apex of the ridge which is used to define the ridge structure is proportional to the amount of precipitation along the baroclinic zone to the northeast of the tropical cyclone tc and at some times to the upper tropospheric divergence above the tropical cyclone multivariate regression calculations indicate that the frontal precipitation has the largest impact on the ridge amplitude and area during tokage s transition while the tc divergence has roughly equal impact during some times of nabi s transition the amount of precipitation along the baroclinic zone is modulated by the lower tropospheric frontogenesis and moisture flux on the

mountain torque events at the tibetan plateau the interaction of large scale wave systems with the tibetan plateau tp is investigated by regressing pressure potential temperature winds precipitation and selected fluxes in winter onto the three components toi of this massif s mountain torque on the basis of the 40 yr ecmwf reanalysis era 40 data events with respect to the equatorial greenwich axis of the global angular momentum exhibit by far the largest torques to1 which essentially represent north south pressure differences across the tp the axial torque to3 peaks when the surface pressure is high at the eastern slope of the tp the torque to2 with respect to the 90 e axis is closely related to to3 with to2 to3 the maximum minimum of to1 tends to occur about 1 day earlier than the minimum maximum of to2 all torque events are initiated by equivalent barotropic perturbations moving eastward along the northern rim of the tp in general the initial depression for example forms a southward protruding extension at the eastern slope of the tp and a new high grows near japan later the perturbation near japan moves eastward in to2 events but extends northward in to1 events these flow developments cannot be explained by theories of topographic instability the observed vertical motion at the lee slope is at best partly consistent with theories of linear quasigeostrophic wave motion along mountain slopes these findings lead the authors to test the eventual usefulness of linear theories by fitting the linear terms of a novel statistical equation for the potential temperature to the observed changes of and the torque to the observations this test indicates that the evolving regression patterns of can be explained by linear terms at least in specific domains in turn pressure tendency regressions at a selected level can be calculated on the basis of the linear tendencies above that level the formation of the lee trough appears to be mainly caused by horizontal warm air advection along the slopes but changes of the potential temperature above the height of the tp also contribute significantly to the pressure changes in the lee cold air advection aloft strengthens the japan high turbulent transports appear to be mainly responsible for the decay of the perturbations but data accuracy problems impede the analysis in particular the noisiness of the vertical motion fields affects the skill of the linear calculations

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

ageostrophic geopotential fluxes in downstream and upstream development of baroclinic waves abstract with the use of a simple primitive equation model it is demonstrated that the convergence divergence of ageostrophic geopotential fluxes can be a major source sink of kinetic energy for both downstream and upstream development of baroclinic waves and can play a dominant role during the early stages of wave development it is also shown that both surface friction and effects lead to an asymmetry in the upstream versus downstream development with downstream development much stronger a total group velocity is defined based on ageostrophic fluxes and its relationship to the rate of wave packet spreading and to convective and absolute instability is discussed

wave packets and life cycles of troughs in the upper troposphere examples from the southern hemisphere summer season of 1984 85 abstract in this paper reanalysis data for the southern hemisphere summer season of 1984 85 produced by the european centre for medium range weather forecasts have been analyzed to examine wave packets and life cycles of baroclinic waves a semiobjective algorithm has been devised to track wave packets it is found that the perturbations in the upper troposphere are dominated by wave packets some of these wave packets can be tracked for several weeks during which they can make up to two trips around the latitude circle the energy life cycles of waves that make up several of these wave packets were analyzed and apart from the incipient waves that started the wave packets most of the subsequent wave development was found to be dominated by convergence and divergence of energy fluxes rather than due to baroclinic or barotropic conversions demonstrating that these wave packets are indeed coherent entities that propagate due to downstream development or dispersion the energy life cycle of the most

observational constraints on the cloud thermodynamic phase in midlatitude storms the conditions under which supercooled liquid water gradually gives way to ice in the mixed phase regions of clouds are still poorly understood and may be an important source of cloud feedback uncertainty in general circulation model projections of long term climate change two winters of cloud phase discrimination cloud top temperature sea surface temperature and precipitation from several satellite datasets the nasa terra and aqua moderate resolution imaging spectroradiometer and the tropical rainfall measuring mission for the north atlantic and pacific ocean basins are analyzed to better understand these processes reanalysis surface pressures and vertical velocities are used in combination with a synoptic storm tracking algorithm to define storm tracks create composite storm dynamical and cloud patterns and examine changes in storm characteristics over their life cycles characteristically different storm cloud patterns exist in the atlantic and pacific and on the west and east sides of each ocean basin this appears to be related to the different spatial patterns of sea surface temperature in the two ocean basins glaciation occurs at very warm temperatures in the high thick heavily precipitating clouds typical of frontal ascent regions except where vertical velocities are strongest similar to previous field experiments outside frontal regions however where clouds are shallower supercooled water exists at lower cloud top temperatures this analysis is the first large scale assessment of cloud phase and its relation to dynamics on climatologically representative time scales it provides a potentially powerful benchmark for the design and evaluation of mixed phase process parameterizations in general circulation models and suggests that assumptions made in some existing models may negatively bias their cloud feedback estimates

mechanical controls on the deformation of continents at convergent margins abstract spatial variations in the rigidity of continental plates expressed in terms of an effective elastic thickness t e can have a profound influence on the style of deformation of ocean continent convergent margins depending on the spatial distribution of t e strains related to plate boundary forces can become concentrated where t e is small we calculate t e and t e anisotropy in western canada by using and comparing the wavelet and multitaper coherence methods in addition to a nearly stepwise change in t e from the cordillera to the craton we show that weak axes of t e anisotropy are parallel with most compressive directions of horizontal stress components and fast axes of upper mantle seismic anisotropy maxima in the magnitude of t e anisotropy are spatially correlated with the locations of most earthquakes and the locations and directions of maxima in electrical anisotropy and conductivity the pattern of brittle failure and seismicity is explained as a response to plate boundary forces acting on a plate of variable rigidity and is expected to induce the observed mechanical anisotropy and enhance the flow of crustal fluids resulting in locally high electrical conductivities our combined results thus suggest for the first time that the elastic properties of continental lithosphere have a leading order influence on the deformation and evolution of convergent plate boundaries

far upstream precursors of heavy precipitation events on the alpine south side this study examines the upper level flow pattern that foreshadows the comparatively frequent co occurrence of heavy precipitation events on the alpine south side together with potential vorticity pv streamers aloft over western europe it is hypothesized that each streamer is itself preceded by a dynamically distinctive and a thermodynamically active flow associated with the space time development and the ultimate breaking over europe of synoptic scale rossby waves the ecmwf european centre for medium range weather forecasts era 40 dataset is used to examine the nature of a streamer s coherent precursor pattern by deriving seasonal composites of refined hovmoller diagrams the upper level pattern of the pv and its gradient and mid tropospheric diabatic heating for the autumn and winter seasons the composites reveal a significant and coherent wave packet precursor signal in the pv field that can be traced back 1 week to the central and eastern pacific contemporaneously the coherent signatures in the composite pv gradient field and diabatic heating fields are conducive to triggering and or supporting the wave signal and also contribute to subsequent downstream wave breaking in spring the composite precursor pv signal appears over and propagates eastward from the atlantic basin and its limited zonal extent is attributed to the lack of a coherent pv waveguide in summer the signal appears essentially in situ in the hovmoller analysis but extends across the atlantic basin in the pv composite results an indication is also provided of the extent to which the composite characteristics are evident in two individual events and note is made of the study s implications for medium range forecasting copyright 2008 royal meteorological society

dynamics of rossby wave packets in a quantitative potential vorticity potential temperature framework abstractrossby wave packets rwps have been associated with increased atmospheric predictability but also with the growth and propagation of forecast uncertainty to address the important question of under which conditions rwps imply high and low predictability a potential vorticity potential temperature pv framework is introduced to diagnose rwp dynamics finite amplitude rwps along the midlatitude waveguide are considered and are represented by the synoptic scale wavelike undulations of the tropopause the evolution of rwps is examined by the amplitude evolution of the individual troughs and ridges troughs and ridges are identified as pv anomalies on levels intersecting the midlatitude tropopause by partitioning the pv tendency equation individual contributions to the amplitude evolution are identified a novel aspect is that the important role of the divergent flow and the diabatic pv modification is quantified explicitly arguably prominent upper tropospheric divergent flow is associated

baroclinic development in observations and nasa gsfc general circulation models abstract comparative diagnostic analyses of developing synoptic scale baroclinic disturbances in ncep ncar reanalyses and the nasa ncar nascar and aries nasa s seasonal to interannual prediction project nsipp general circulation model simulations are performed in particular lag composite analyses of wintertime cyclonic and anticyclonic events occurring in the north pacific and north atlantic storm tracks are constructed to pursue a synoptic and dynamic characterization of eddy development the data are also seasonally stratified to study aspects of the north pacific midwinter suppression phenomenon winter averaged results indicate that the model simulated events are generally too weak in amplitude particularly in the upper troposphere for the north pacific storm track model simulated events are also anomalously distended in the meridional direction the existing model biases in eddy structure and magnitude lead to anomalously weak baroclinic energy conversions for both cyclonic and anticycloni

southern hemisphere summertime rossby waves and weather in the australian region motivated by recent studies on the significant summertime weather patterns in the australian region the life cycle of summertime transient rossby wave packets in the southern hemisphere is investigated the strength of the interaction between the wave packets and the jet i is defined by the advection of potential vorticity by the divergent part of the wind on the 350 k isentropic surface the magnitude of i is used as the basis for time lagged composites in distinct regions sw chile sw africa over the indian ocean sw australia and over the w pacific the interaction is strongest on the stratospheric side of the jet core although in each case cyclogenesis from a pre existing disturbance in the upper troposphere precedes the generation of the rossby wave packets there are two types of interaction with the jet in the sw chile sw africa and indian ocean cases extratropical cyclogenesis and the associated convection lies on the poleward side of the jet and hence i is positive in the sw australia and w pacific cases extratropical cyclogenesis occurs 3 days earlier than the others and i is negative as it describes the interaction of a downstream propagating rossby wave packet with the subtropical jet in all cases as the cyclones develop the wave activity propagates from low levels to the upper levels of the troposphere and then downstream and equatorwards towards higher values of refractive index the equatorward refraction of the sw australia and w pacific wave packets is accompanied by enhanced tropical convection in the warm conveyor belt of the advancing front

crustal anisotropy in a subduction zone forearc northern cascadia s wave splitting analyses using low frequency earthquake templates at three component stations across southern vancouver island and northern washington indicate the presence of a heterogeneous distribution of crustal anisotropy in the north american plate for southern vancouver island we investigate contributions to anisotropy from the leech river complex a terrane composed of strongly foliated phyllites and schists with steeply dipping foliations striking east west fast directions across mainland southern vancouver island are subparallel to the dominant leech river complex foliation direction east to west increases in delay times and small scale azimuthal variations in fast directions indicate heterogeneous anisotropy we test azimuthally anisotropic leech river complex models constrained by previous geological and seismic reflection studies through forward modeling using 3 d spectral element method simulations the preferred model of a north northeast shallowly dipping wedge of leech river complex material with varying orientation of anisotropy terminating at midcrustal levels explains the splitting observations at a majority of southern vancouver island stations for stations where anisotropic leech river complex models do not recreate observations fast directions are subparallel to local estimates of maximum compressive horizontal stress suggesting that fluid filled cracks could be a source of anisotropy we assert that the leech river complex is the primary source of crustal anisotropy beneath southern vancouver island not cracks as suggested by prior studies fast directions at stations on northern washington exhibit variations with azimuth and incidence angle suggesting complex anisotropy interpreted as due to a combination of cracks and preferred mineral orientation of metamorphosed slates of the olympic core rocks these slates may also underlay stations on southern vancouver island and represent another source of anisotropy

impacts of northern tibetan plateau on east asian summer rainfall via modulating midlatitude transient eddies roles of the tibetan plateau tp in forming and changing the seasonal asian climate system have been widely explored however little is known about modulation effects of the tp on extratropical transient eddies tes and subsequent synoptic responses of the east asian rainfall in this study the community atmospheres model version 5 1 coupled with a slab ocean model is employed to highlight the important role of the tp in regulating the upper tropospheric transient wave train comparison between sensitivity experiments with and without the tp shows that the northern tp excites a strong anomalous anticyclone which shifts the upper level east asian westerly jet northward and helps transfer barotropic and baroclinic energy from the mean flow to the synoptic te flow the transient wave train is primarily shifted northward by northern tp and is forced to propagate southeastward along the eastern flank of the tp until reaching eastern china before the strengthening of monsoonal southerlies the tp modulated transient wave train cools the troposphere which decreases the static stability over northern china meanwhile the associated anomalous warm advection induces ascending motion leading to excessive rainfall by releasing unstable energy as the southerly strengthens due to the southeastward propagation of the wave train anomalous heavy rainfall subsequently appears over eastern china from north to south which increases day to day rainfall variation in this region additionally occurrence of this upper tropospheric transient wave train associated with low level southerly peak is substantially increased by northern tp

evaluation of anisotropy by shear wave splitting the polarizations of three component shear wavetrains carry unique information about the internal structure of the rock through which they pass specifically commonly observed shear wave splitting may contain information about the orientation of crack distributions this information cannot usually be recovered from shear waves recorded at the free surface because of interference with the interaction of the shear wave with the surface even for nearly vertical incidence however shear wave splitting in synthetic three component vertical seismic profiles in some cases may be interpreted directly in terms of the direction of strike of vertical cracks because the human eye is not skilled at identifying the phase relationships between three component seismograms played out conventionally as parallel time series the polarizations are displayed in orthogonal sections of the particle displacements to facilitate recognition and evaluation of the shear wave splitting estimating the orientations of cracks an

characteristics of wave packets in the upper troposphere part i northern hemisphere winter abstract gridded data produced by the ecmwf reanalysis project have been analyzed to document the properties of wave packets in the northern hemisphere winter midlatitude upper troposphere based on results from earlier investigations 300 hpa meridional wind variations were chosen for analysis wave packet envelopes were also defined by performing complex demodulation on the wind data the properties of the wave packets are mainly illustrated using time lagged one point correlation maps performed both on and wave packet envelopes the results show that over most regions in the northern hemisphere winter with the exception of the deep tropics and near the aleutian low medium scale waves dominant wavenumber 5 8 exhibit the characteristics of downstream development and occur within wave trains that propagate with eastward group velocities much faster than the phase speeds of individual phases of the waves their group velocity is highly correlated with the local time mean 200 400 hpa wind while the

simulation and projection of circulations associated with atmospheric rivers along the north american northeast coast abstracttorrential rainfall occurring along the north american northeast coast nanc in summer and autumn is accompanied by strong atmospheric rivers ars which efficiently transport abundant mo

structure and evolution of baroclinic waves as inferred from regression analysis abstract the structure of transient disturbances with periods shorter than a week is documented an the basis of one point regression maps and longitude height sections derived from the national meteorological center nmc operational analyses for nine winter seasons the reference time series for the regression coefficients is highpass filtered normalized 500 mb height at a grid point in the pacific stormtrack the field variables that were regreesed on the reference time series were not filtered the regression statistics yield quantitative estimates of the amplitudes of the high frequency fluctuations in the geopotential height temperature wind ageostrophic wind vorticity divergence vertical velocity and outgoing longwave radiation fields the observed high frequency fluctuations exhibit a vertical and meridional structure suggestive of baroclinic waves evolving through the mature phase of their life cycle most of the results are in qualitative agreement with previous studies but the ageostrop

on the dynamics of a storm track abstract an idealized primitive equation model is used to determine the factors controlling the dynamics and maintenance of eddy activity in a storm track the results show that localized regions of enhanced baroclinicity do not necessarily lead to localization of eddy activity by studying the energetics of the storm track it is shown that while baroclinic conversion does indeed correlate with the region of maximum baroclinicity it is the downstream radiation of energy through the ageostrophic geopotential fluxes which acts as a trigger for the development and maintenance of eddy activity over less baroclinic regions extending the region of eddy activity much further downstream from the region of high baroclinicity examples of eddy life cycles are given that show that convergence and divergence of ageostrophic fluxes can dominate baroclinic and barotropic conversion especially in regions with weak baroclinicity factors that may limit the zonal extent of a storm track are discussed evidence of down

shear wave polarizations near the north anatolian fault iii observations of temporal changes summary almost all shear waves from local earthquakes recorded on closely spaced three component seismometer networks deployed near the north anatolian fault turkey in two experiments in 1979 and 1980 display shear wave splitting the observations are consistent with the presence of eda extensive dilatancy anisotropy distributions of fluid filled cracks and microcracks aligned by the regional stress field temporal changes in the stress field which may occur before an earthquake may modify the geometry and possibly the orientation of the eda microcracks and lead to corresponding changes in the behaviour of the split shear waves a third experiment was undertaken in 1984 to investigate eda further and to search for possible temporal variations of the polarization of the leading split shear wave and the time delay between split shear waves observations indicate that the polarization alignments which are parallel to the strike of the parallel vertical eda cracks are unaltered between 1979 and 1984 implying that the direction of the regional stress field has not changed significantly temporal changes in the stress field are more likely to cause changes in the crack density and or aspect ratio which would result in a corresponding change in time delay between the split shear waves we examine observations of time delay in relation to their propagation path with respect to the crack geometry since it is then possible to separate the effects of changes in crack density and changes in aspect ratio with this procedure a small temporal variation of time delays is found between 1979 and 1984 consistent with a decrease in crack density and consequently a relaxation of stress in this time period no evidence was found for any observable variation of time delay over a six month observation span in 1984 we suggest that analysis of repeated shear wave vsps offers a technique for monitoring stress changes before earthquakes

wrf hindcasts of cold front passages over the arm eastern north atlantic site a sensitivity study abstractthe present study explores the ability of the weather research and forecasting wrf model to accurately reproduce the passage of extratropical cold fronts at the doe arm eastern north atlantic ena observation site on the azores an analysis of three case studies is performed in which the impact of the wrf domain size position of the model boundary relative to the ena site grid spacing and spectral nudging conditions are explored the results from these case studies indicate that model biases in the timing and duration of cold front passages change with the distance between the model domain boundary and the ena site for these three cases if the western model boundary is farther than 1500 km from the site the front becomes too meridional and fails to reach the site making 1000 or 1500 km the optimal distances in contrast integrations with small distances e g 500 km between the site and domain boundaries have inadequate spatial spinup i e the domain is too small for the model to pr

an energetic view of the relation between the mediterranean storm track and the north atlantic oscillation the time tendency equation of eddy kinetic energy eke includes some important forcing terms such as baroclinic conversion bcc barotropic conversion btc and energy flux this article compares the ensemble mean distribution of these forcing terms as well as the baroclinic generation bcg term in critical positive and critical negative months of the north atlantic oscillation nao focusing on the mediterranean and middle east regions results show that all the computed terms attain larger values and all the extrema are stronger in the positive phase the energy flux vectors point to energy transfer from the west of the atlantic and north of europe to the mediterranean region with the transfer being weaker in the positive phase there is energy flux divergence over the central region of the mediterranean sea which is more extensive in the positive phase relative to the negative phase the energy flux divergence leads to a radiation source in this region the direction of the energy flux vectors then indicates that the energy radiated from the central mediterranean region is transferred southeastward leading to an energy flux convergence over the red sea and the northeast of africa this convergence is stronger and more extensive in the positive phase which may be responsible for the observed larger value of the upper level eddy kinetic energy in the positive phase the patterns of the bcg and bcc together with the energy flux convergence suggest that while the mediterranean storm track is affected by the north atlantic storm track more strongly in the negative phase it acts as an independent centre of action by radiating energy southeastward in the positive phase copyright 2011 royal meteorological society

current tectonics of northern cascadia from a decade of gps measurements 1 global positioning system gps measurements to study regional deformation were initiated in northern cascadia in the late 1980s and early 1990s on the basis of a decade of gps data we derive a crustal velocity field for nw washington sw british columbia the permanent and campaign gps velocities are defined with respect to north america in the itrf2000 reference frame velocity uncertainties are estimated using a model of time series noise spectra this new velocity field is the basis for interpretation of the tectonics of the northern cascadia subduction system gps velocities are interpreted in terms of interseismic loading of the megathrust using different coupling models our data confirm that the upper part of the megathrust is nearly fully locked an exponential model for the downdip transition zone gives slightly better agreement with the data compared to the common linear transition the landward decrease of forearc strain loading is smaller than predicted by any of the current subduction interseismic models this could be a consequence of a small 0 3 mm yr long term motion of the southern vancouver island forearc with respect to north america or of a concentration of interseismic strain across the elastically weaker cascadia volcanic arc in northern vancouver island our velocity field supports the existence of an independent explorer microplate currently underthrusting underneath north america at least up to brooks peninsula further north gps velocities indicate transient and or permanent deformation of northernmost vancouver island related to the interaction with the explorer microplate and possibly with the queen charlotte transform margin

interactions of north pacific tropical midlatitude and polar disturbances resulting in linked extreme weather events over north america in october 2007 abstractthis study uses observations and model reanalyses to examine the multiscale processes associated with four high impact extreme weather events ewes over north america during late october 2007 the ewes consisted of wind driven wildfires in california prolonged anomalous cold conditions in mexico linked to two cold surges heavy rainfall in the eastern united states and severe flood producing heavy rainfall in southern mexico the ewes involved a pronounced large scale flow reconfiguration across the north pacific and north america in conjunction with the formation of a high amplitude rossby wave train the flow reconfiguration involved perturbations to the north pacific jet stream linked to polar midlatitude and tropical disturbances including three tropopause level polar disturbances originating over northeastern asia transient extratropical cyclones a diabatic rossby vortex and western north pacific tropical cyclone kajiki eulerian and lagrangian diagnostics indicate that ridge amplifi

crustal velocity structure in the eastern insular and southernmost coast belts canadian cordillera seismic refraction data recorded along a 330 km cross strike profile through the eastern insular and southernmost coast belts of the canadian cordillera are interpreted using an iterative combination of traveltime inversion and amplitude forward modelling the resultant model is characterized by large lateral variations in velocity the most significant of these variations is a decrease in upper and middle crustal velocities to the east of the surface trace of the harrison fault which likely represents the transition from crust of the insular superterrane to that of the intermontane superterrane this interpretation is consistent with some present geological models that place the possible probable location of the suture between the two superterranes less than 20 km east of the harrison fault velocities at the base of the upper crust average 6 4 and 6 2 km s west and east of the fault respectively mid crustal velocities average 6 6 6 9 km s to the west and 6 35 6 45 km s to the east of the fault low

continental crust anisotropy measurements from tectonic tremor in cascadia we present new observations of crustal anisotropy in the southern cascadia forearc from tectonic tremor the abundance of tremor activity in oregon and northern california during slow slip events offers an enormous amount of information with which to measure and analyze anisotropy in the upper brittle continental crust to accomplish this we performed analyses of wave polarization and shear wave splitting of tectonic tremor signals using three component broadband seismic stations the splitting times range between 0 11 and 0 32 s and are consistent with typical values observed in the continental crust fast polarization azimuths are in general margin parallel and trend n s which parallels the azimuths of the maximum compressive stresses observed in this region this pattern is likely to be controlled by the stress field comparatively the anisotropic structure of fast directions observed in the northern section of the cascadia margin is oblique with respect to the southern section of cascadia which in general trends e w and is mainly controlled by active faulting and geological structures source distribution analysis using a bivariate normal distribution that expresses the distribution of tremors in a preferred direction shows that in northern california and oregon the population of tremors tends to distribute parallel to fast polarization azimuths and maximum compressive stresses suggesting that both tremor propagation and anisotropy are influenced by the stress field results show that the anisotropy reflects an active tectonic process that involves the northward movement of the oregon block which is rotating as a rigid body in northern cascadia previous results of anisotropy show that the crust is undergoing a shortening process due to velocity differences between the oregon block and the north america plate which is moving more slowly with respect to the oregon block making it clash against vancouver island

the role of hydrous phases in the formation of trench parallel anisotropy evidence from rayleigh waves in cascadia 1 the cause of seismic anisotropy exhibiting trench parallel fast directions in subduction systems has been the subject of significant recent research we provide new constraints on the contributions of hydrous phases to seismic anisotropy from an unusually well localized region of trench parallel fast directions in rayleigh wave phase velocities near the cascade arc at 45 to 66 s periods we constrain the location of the anisotropic material to within or directly above the oceanic plate using the depth sensitivity of rayleigh waves as a function of frequency and the accurate slab imaging available for cascadia from scattered wave studies we infer that the likely source of trench parallel anisotropy is either a thin layer of sheared hydrous material directly above the slab or hydrated outer rise faults in the upper part of the subducting plate similar contributions to trench parallel anisotropy from hydrous phases are likely stronger in other subduction zones

the north atlantic oscillation response to large scale atmospheric anomalies in the northeastern pacific abstractingredients in the north pacific flow influencing rossby wave breakings in the north atlantic and the intraseasonal variations of the north atlantic oscillation nao are investigated using both reanalysis data and a three level quasigeostrophic model on the sphere first a long term run is shown to reproduce the observed relationship between the nature of the synoptic wave breaking and the phase of the nao furthermore a large scale low frequency ridge anomaly is identified in the northeastern pacific in the days prior to the maximum of the positive nao phase both in the reanalysis and in the model a large scale northeastern pacific trough anomaly is observed during the negative nao phase but does not systematically precede it then short term linear and nonlinear simulations are performed to understand how the large scale ridge anomaly can act as a precursor of the positive nao phase the numerical setup allows for analysis of the propagation of synoptic waves in the eastern pacific in the p

seismic evidence for rotating mantle flow around subducting slab edge associated with oceanic microplate capture tectonic plate reorganization at a subduction zone edge is a fundamental process that controls oceanic plate fragmentation and capture however the various factors responsible for these processes remain elusive we characterize seismic anisotropy of the upper mantle in the explorer region at the northern limit of the cascadia subduction zone from teleseismic shear wave splitting measurements our results show that the mantle flow field beneath the explorer slab is rotating anticlockwise from the convergence parallel motion between the juan de fuca and the north america plates re aligning itself with the transcurrent motion between the pacific and north america plates we propose that oceanic microplate fragmentation is driven by slab stretching thus reorganizing the mantle flow around the slab edge and further contributing to slab weakening and increase in buoyancy eventually leading to cessation of subduction and microplate capture

a siberian precursor to midwinter intraseasonal variability in the north pacific storm track 1 an observational diagnostic analysis is performed to study variations in the behavior of upper tropospheric rossby waves prior to intraseasonal variability in the north pacific storm track the research is motivated from considerations of the midwinter suppression of the north pacific storm track during midwinter strong upper tropospheric cyclone events in the north pacific storm track are preceded 7 days by a large scale cyclonic circulation anomaly located over siberia the siberian precursor anomaly is found to be strongly linked to one of the primary modes of upper tropospheric intraseasonal variability over asia more generally this asian mode is determined to provide a substantial modulation in the structure and amplitude of the north pacific storm track at lead times of 5 to 8 days this downstream influence is concentrated during midwinter and is likely related to intraseasonal variations in the east asian winter monsoon

stress directions and shear wave anisotropy observations from local earthquakes in southeastern sicily italy the spatial distribution of 414 earthquakes 1 0 m l 4 6 recorded from 1994 to 2002 in southeastern sicily italy has been analyzed the seismicity generally coincides with mapped plio quaternary faults including the north north west south southeast striking offshore fault system which is the most important tectonic structure of the area for the best located events we computed 70 focal mechanisms by combining p wave polarities with s wave polarizations a predom inance of strike slip and normal faults was observed focal mechanisms were then inverted for stress tensor parameters by using the algorithm of gephart and forsyth the results highlighted a region governed mainly by a north northwest south south east to northwest southeast compressional stress regime moreover anisotropy anal ysis of shear waves showed a polarization of fast s waves coherently aligned with this stress direction a finer scale analysis of the stress tensor evidenced three regions characterized by slightly differing orientation of the greatest principal stress axis r1 the eastern sector displays a nearly horizontal r1 trending northwest southeast the central sector is affected by a low dip north northwest south southeast r1 whereas in the western sector a north northwest south southeast oriented r1 with a higher dip angle was detected finally the comparison of the spatial distribution of seismicity occurring during 1994 2002 with locations of previous instrumental earthquakes and larger m 5 0 historical events showed that the seismicity patterns are persistent

northern hemisphere rossby wave initiation events on the extratropical jet a climatological analysis abstracta climatology of rossby wave initiation rwi events on the northern hemisphere mid latitude jet is compiled by applying an objective rwi identification algorithm to the era interim re analysis dataset in winter rwi events occur most frequently over the northwestern pacific and less often over the north atlantic in summer the total number of rwi events is lower than in winter and the north pacific rwi region shifts towards the tibetan plateau composite analysis of the large scale flow prior to during and after winter north pacific rwi events shows an upstream wave train propagating across asia on the arctic waveguide prior to rwi the composite wave forms on a relatively weak zonal jet streak exhibits a baroclinic structure and is strongly amplified by latent heat release in the warm conveyor belt of a deepening surface cyclone moreover the wave forms in a region of large scale upper level deformation upstream of a pre existing ridge further active tropical convection affects the longit

the impact of wave packets propagating across asia on pacific cyclone development abstract in this paper ecmwf 40 yr reanalysis data have been examined to study the influence of upper level wave packets propagating across asia into the pacific on surface cyclone development over the pacific previous studies have shown that in winter wave packets propagate across asia over two branches a northern branch over siberia and a southern branch along the subtropical jet across southern asia results presented here show that subsequent to the presence of wave packets on either branch the frequency of occurrence of deep cyclones defined as cyclones with central pressure below 960 hpa as well as explosively deepening cyclones those with a deepening rate of 1 bergeron or more are significantly enhanced this enhancement also clearly follows the wave packet eastward as it propagates across the pacific wave packets from the two branches are found to interfere with each other such that if wave packets of the appropriate configuration are present on both the northern and southern branch s

olivine fabric transitions and shear wave anisotropy in the ryukyu subduction system recent shear wave splitting measurements from the fore arc region of the ryukyu subduction system show large magnitude 0 3 1 6 s trenchparallel splitting in both local and teleseismic phases the similarity of splitting parameters associated with shallow local s and teleseismic phases suggests that the source of anisotropy is located in the fore arc mantle one explanation for this pattern of shear wave splitting involves a transition from commonly observed high temperature olivine fabrics with flow parallel seismically fast directions to a flow normal b type olivine fabric in the cold fore arc mantle of the ryukyu wedge we test the b type fabric hypothesis by comparing observed splitting parameters to those predicted from geodynamic models that incorporate olivine fabric development the distribution of olivine fabric is calculated with high resolution thermomechanical models of the ryukyu subduction zone that include realistic slab geometry and an experimentally based wet olivine rheology we conclude that b type fabric can explain the magnitude and trench parallel orientation of deep local s phases that sample the core of the forearc mantle however our calculations show that b type fabric alone cannot account for large magnitude trench parallel splitting associated with teleseismic phases that sample the shallow tip of the fore arc mantle alternative models for trench parallel teleseismic splitting in the shallow tip of the fore arc mantle involve the addition of crustal or slab anisotropy and highly anisotropic foliated antigorite serpentinite 2008 elsevier b v all rights reserved

simplified analysis of horizontal stresses in a buttressed forearc sliver at an oblique subduction zone forearc slivers are commonly present at obliquely convergent margins such slivers are often buttressed at their leading edges but no quantitative model of the buttress effect exists i consider the horizontal stresses in a buttressed sliver using a simple plan view two dimensional elastic model the driving force created by the subducting plate is approximated by a body force in the direction of plate convergence an airy stress function solution relates the stress field to the boundary and body forces that allows the relative importance of different forces driving and resisting the sliver to be evaluated oblique subduction can easily cause arc parallel compression in the buttressed sliver especially near the leading edge because the arc parallel component of the driving force by the subducting plate is integrated over a much larger distance than its arc normal component for the southwest kuril arc the stress field predicted by the simple model agrees with that inferred from geological structures it is possible that the model can also explain the stress field of the cascadia forearc as constrained by earthquake focal mechanisms and in situ stress measurements

a decade of shear wave splitting in the earth s crust what does it mean what use can we make of it and what should we do next it is 10 years since shear wave splitting throught to be diagnostic of some form of seismic anisotropy was first positively identified in the earth s crust from the beginning it was argued that the splitting was probably associated with the presence of stress aligned cracks inclusions in the crust and that this would provide the opportunity for monitoring the in situ geometry of cracks and stress in a variety of different circumstances and in a variety of different applications

rossby wave packets on the midlatitude waveguide a review abstractrossby wave packets rwps are rossby waves for which the amplitude has a local maximum and decays to smaller values at larger distances this review focuses on upper tropospheric transient rwps along the midlatitude jet stream their central characteristic is the propagation in the zonal direction as well as the transfer of wave energy from one individual trough or ridge to its downstream neighbor a process called downstream development these rwps sometimes act as long range precursors to extreme weather and presumably have an influence on the predictability of midlatitude weather systems the paper reviews research progress in this area with an emphasis on developments during the last 15 years the current state of knowledge is summarized including a discussion of the rwp life cycle as well as rossby waveguides recent progress in the dynamical understanding of rwps has been based in part on the development of diagnostic methods these methods include algorithms to identify and track rwps

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

case for very low coupling stress on the cascadia ssubduction fault a fundamental problem in plate tectonics is the shear strength of major plate boundary faults this translates to the question whether the generally observed small earthquake stress drops of 3 10 mpa on major faults release most of the accumulated stress or only a small fraction of it there is strong evidence that the san andreas fault a major transform plate boundary is weak 20 mpa shear resistance it is not yet clear whether subduction thrust faults are also weak we present two types of evidence from the northern cascadia subduction zone that indicate very low coupling shear stress on that plate interface and hence very low strength of the subduction thrust fault comparable to that estimated for the san andreas fault first the well defined surface heat flow and heat generation allow negligible frictional heating on the plate interface the average shear stress on the fault must thus be very low over a time scale of a few million years second focal mechanism solutions for small crustal earthquakes in the southern vancouver island area indicate that the horizontal stress in the direction of plate convergence has a similar magnitude to the vertical stress this inferred stress state requires the present tectonic stress coupled across the subduction thrust fault to be very low one explanation for the weakness of the fault is the presence of near lithostatic pore fluid pressure in the region of the fault zone for which there is independent evidence the conclusion of a weak subduction thrust fault does not conflict with geodetic observations of contemporary surface deformation which indicate that the fault is currently locked accumulating strain energy toward a future great earthquake the surface deformation responds to the small 20 mpa temporal changes of the stress field associated with the subduction earthquake cycle this transient stress is superimposed on the larger background regional stress field in which the maximum compression is parallel to the margin the weakness of the cascadia subduction thrust fault and the unusual stress state of the forearc region have important implications for earthquake hazards for example a subduction earthquake may induce large strike slip earthquakes in the forearc that affect a large area

a case study of downstream baroclinic development over the north pacific ocean part ii diagnoses of eddy energy and wave activity the sequential development of a western and then an eastern north pacific cyclone is examined in terms of eddy energy and a phase independent wave activity based on the propagation of both a contiguous wave activity center and eddy energy the development of the western cyclone appears to influence its downstream neighbor a quantitative comparison of these two diagnoses is made in terms of group velocity and only minor differences are found during much of the initial evolution it is only once the tropopause undulations lose their wavelike appearance at which point application of the group velocity concept itself becomes quite tenuous that the downstream propagation of eddy energy seems faster than that of wave activity conventional methods of tracking this wave packet are also briefly discussed

vertical structure of midlatitude analysis and forecast errors abstract the dominant vertical structures for analysis and forecast errors are estimated in midlatitudes using a small ensemble of operational analyses errors for fixed locations in the central north pacific and eastern north america are selected for comparing errors in regions with relatively low and high observation density respectively results for these fixed locations are compared with results for zonal wavenumber 9 which provides a representative sample of baroclinic waves this study focuses on deviations from the ensemble mean for meridional wind and temperature at 40 n these quantities are chosen for simplicity and because they capture dynamical and thermodynamical aspects of midlatitude baroclinic waves results for the meridional wind show that analysis and forecast errors share the same dominant vertical structure as the analyses this structure peaks near the tropopause and decays smoothly toward small values in the middle and lower troposphere the dominant vertical structure for analysi

seismicity and stress tensor inversion in the central washington cascade mountains abstract tectonic stress in the pacific northwest washington is dominated by a n s major compressive axis 1 and a minor compressive axis 3 which varies from e w to near vertical some variations in this pattern occur in different parts of the region in this study we used 550 earthquakes in the central washington cascade mountains to study in detail the uniformity of the stress tensor in this volcanic arc earthquakes from the pacific northwest seismograph network pnsn catalog were divided into several subsets based on epicentral and depth groupings and stress tensor inversions using the gephart and forsyth technique were computed for each group as in previous similar studies the maximum compressive stress axis 1 is nearly horizontal and trending n s to nne ssw in all but one subset shallower events directly under mount rainier have a near vertical 1 for other subsets the minimum compressive stress axis 3 deviates from vertical to horizontal for different groups of events in particular events in the depth range of 10 to 14 km in the western rainier seismic zone wrsz have near vertical 3 direction whereas other depth ranges in this area show a near horizontal e w 3 orientation we hypothesize that the change in orientation of 3 in the 10 to 14 km depth range in the wrsz may be due to the influence of the nearby mount rainier magmatic system independent evidence for magma at this depth comes in the form of a few deep long period lp events

variations in sks splitting across western canada measurements of sks splitting parameters have been made at stations of the canadian national seismograph network for events over the period 1993 mid1994 here we report on results obtained from western stations in the northern cordillera the alignment of polarization directions with major transcurrent fault systems suggests that the crust and upper mantle are being deformed coherently splitting parameters in the southern cordillera however are oriented approximately perpendicular to the strike of major tectonic features notably the cascadia subduction zone this contrast in the character of fast polarization directions between the southern and northern cordillera is thought to reflect the change in the tectonic style of the adjacent plate margin from convergent along the southern b c coast to transform north of the triple junction one plausible explanation is that upper mantle anisotropy in the southern region is due primarily to mantle flow perpendicular to the margin involving upwelling at the juan de fuca ridge subduction along the coast and associated back arc asthenospheric flow beneath the b c interior

anisotropic structures of oceanic slab and mantle wedge in a deep low frequency tremor zone beneath the kii peninsula sw japan 1 anisotropy is an important feature of elastic wave propagation in the earth and can arise from a variety of ordered architectures such as fractures with preferential alignments or preferred crystal orientations we studied the regional variations in shear wave anisotropy around a deep low frequency earthquake lfe zone beneath the kii peninsula sw japan using waveforms of local earthquakes observed by a dense linear array along the lfe zone the fast directions of polarization are subparallel to the strike of the margin for both crustal and intraslab earthquakes the delay time of the split shear waves in intraslab earthquakes is larger than that in crustal earthquakes and shows a down dip variation across the lfe zone this indicates that anisotropy exists in the mantle wedge and in the lower crust and or oceanic slab we explain the observed delay time of 0 015 0 045 s by suggesting that the mantle wedge consists of a deformed 1 15 km thick serpentine layer if the mantle wedge is completely serpentinized in addition to high fluid pressures within the oceanic crust the sheared serpentine layer may be a key factor driving lfes in subduction zones

developing wave packets in the north pacific storm track developing wave packets in the western north pacific storm track are diagnosed observationally an abrupt upstream edge to baroclinic wave activity over the western north pacific facilitates comparisons between the observational results and previous theoretical predictions on the spatiotemporal evolution of an impulse disturbance results show that surface cyclogenesis events are preceded by a sharply peaked wave packet that originates poleward of the himalaya plateau and develops rapidly across the north pacific to north america composite wave packet structure is broadly consistent with linear theory for idealized models such as eady s the longitude height structure of the mature packet reveals deep growing waves with horizontal wavelengths of approximately 4000 km near the packet peak downstream from the peak amplitude decays exponentially and wavelength decreases approximately linearly to about 2500 3000 km at the leading edge meridional potential vorticity gradients are concentrated near the tropopause in contrast to linear theory the packets show an abrupt upstream edge and no evidence of upstream development as the packet travels through the along stream variations of the pacific jet stream the packet peak and leading edge group velocity vary these accelerations change the packet length and suggest that the pacific jet may act to focus the packets a sample of north atlantic storm track events reveals similar results and suggests that the atlantic storm track is often seeded by wave packets that originate over the western north pacific ocean in contrast atlantic packets refract equatorward and become trapped on the subtropical jet to the south of himalaya plateau suggesting perhaps less potential for seeding disturbances in the pacific storm track

tropical transition of an unnamed high latitude tropical cyclone over the eastern north pacific abstractin early november 2006 an unnamed tropical cyclone tc formed via the tropical transition tt process at 42 n over the eastern north pacific an extratropical cyclone ec developing downstream of a thinning upper tropospheric trough over the eastern north pacific served as the precursor disturbance that would ultimately undergo tt the tt of the unnamed tc was extremely unusual occurring over 16 c sea surface temperatures in a portion of the eastern north pacific basin historically devoid of tc activity this paper 1 identifies the upper and lower tropospheric features linked to the formation of the ec that transitions into the unnamed tc 2 provides a synoptic overview of the features and processes associated with the unnamed tc s tt and 3 discusses the landfall of the weakening cyclone along the west coast of north america as observed in previous studies of tt the precursor ec progresses through the life cycle of a marine extratropical frontal cyclone developing a bent back warm fr

comparison of wave packets associated with extratropical transition and winter cyclones abstractdifferences in the development of wave packets associated with midlatitude cyclones and the extratropical transition et of tropical cyclones in the western north pacific wnp and atlantic basins are diagnosed observationally by compositing climate forecast system reanalysis cfsr data over a 32 yr period and applying the null hypothesis of no difference in the development structure propagation or downstream extent while the development of midlatitude cyclones during the fall august october and winter november march amplifies a preexisting wave packet moving through the midlatitude storm track et is associated with the quasi stationary amplification of the midlatitude flow the et cases involving the interaction of the decaying tc with a preexisting midlatitude trough are associated with a greater downstream amplitude and longer lasting downstream response than et cases that do not involve the interaction with a trough in the wnp et wave packets have greater amplitude than those asso

shear wave splitting above the subducting juan de fuca plate shear wave splitting observed in three component broadband recordings of local earthquakes near southern vancouver island british columbia provide the first constraints on shear wave anisotropy in the continental crust above the subducting juan de fuca plate waveforms of 22 shallow earthquakes 15 30 km depth and 16 deep earthquakes 40 60 km depth were examined for shear wave splitting the fast polarization direction is well defined at 312 19 for the deep earthquakes and 293 27 for the shallow earthquakes these fast polarization directions are approximately parallel to the continental margin and coincide with the orientation of the pressure axes of small crustal earthquakes in this region interpreting this polarization pattern in terms of the extensive dilatancy anisotropy model indicates a margin parallel compressive stress regime comparing the average time delays between the fast and slow shear waves for the deep earthquakes 0 32 s and the shallow earthquakes 0 20 s suggests that the source of the seismic anisotropy is stronger in the upper 20 km of the continental crust here the average differential shear wave anisotropy is estimated at 2 3 these observations support the theory of weak coupling between the downgoing juan de fuca plate and the overlying north america plate as the principal stress is perpendicular to the direction of subduction and the s wave splitting above the subducting plate is nearly perpendicular to the sks splitting direction in the upper mantle beneath the subducting plate

influence of the background state on rossby wave propagation into the great lakes region based on observations and model simulations abstractthe authors investigate the relationship between hydrology in the great lakes basin namely overlake precipitation and transient rossby waves using the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data and historical output from phase 3 of the coupled model intercomparison project cmip3 the preferred path of observed rossby wave trains associated with overlake precipitation on lake superior depends strongly on season and appears to be related to the time mean upper level flow during summer and fall the northern hemisphere extratropical jet is relatively narrow and acts as a waveguide such that rossby wave trains traversing the great lakes region travel along the extratropical pacific and atlantic jets during other months the pacific jet is relatively broad which allows more wave activity originating in the tropics to penetrate into the midlatitudes and influence lake superior precipitation analysis is extended to cmip3 mod

absolute and convective instability of the african easterly jet abstractthe stability of the african easterly jet aej is examined using idealized numerical simulations it is found that a zonally homogeneous representation of the aej can support absolute instability in the form of african easterly waves aews this finding is verified through a local energy budget which demonstrates the presence of both upstream and downstream energy fluxes these energy fluxes allow unstable wave packets to spread upstream and downstream relative to their initial point of excitation this finding is further verified by showing that the ground relative group velocity of these wave packets has both eastward and westward components in contrast with normal mode instability theory which emphasizes wave growth through energy extraction from the basic state the life cycle of the simulated aews is strongly governed by energy fluxes convergent fluxes at the beginning of the aew storm track generate new aews whereas divergent fluxes at the end of the storm track lead to their decay i

a regional study of shear wave splitting above the cascadia subduction zone margin parallel crustal stress recordings of local earthquakes from 16 three component broadband seismic stations in southwestern british columbia washington and northern oregon are used to study regional variations of shear wave anisotropy in the north american plate above the subducting juan de fuca plate there is evidence for shear wave splitting at all sites with good agreement of fast polarization directions and travel time delays at adjacent stations most stations exhibit fast directions parallel to the strike of the margin with anisotropy of 1 2 these fast polarization directions are consistent with earthquake focal mechanisms and borehole stress studies indicating that the observed anisotropy is likely due to crustal stresses i e extensive dilatancy anisotropy theory the margin parallel stresses may be due to oblique subduction of the juan de fuca plate however at the station closest to the coast ozb the fast direction shows a more margin normal orientation that may be associated with the proximity of the locked portion of the underlying subduction thrust fault

a subducted oceanic ridge influencing the nankai megathrust earthquake rupture megathrust earthquake rupture is highly influenced by seafloor bathymetric features such as oceanic fracture zones seamounts and ridges in convergent plate margins where these features subduct recent seismic reflection and refraction data reveal a trough parallel subducted oceanic ridge that is attached to the descending philippine sea plate beneath the accretionary wedge of the overriding eurasian plate in the eastern nankai trough subduction zone consisting of the tonankai and tokai segments the seismic survey data confirm the existence of subducted paleo zenisu ridge that was suggested by just magnetic data and as a result expands its distribution to the west the newly constrained subducted ridge that spans the two segments is estimated to be a maximum of 2 5 km high 20 30 km wide and 200 km long spatial mapping of the ridge shows that it is located roughly at the seaward edge of the coseismic rupture zone of the 1944 tonankai earthquake m 8 1 this ridge appears to be in close contact with the seaward end of the rigid backstop in the tonankai segment both the spatial correlation and the ridge backstop collision geometry suggest that the subducted ridge might be strongly mechanically coupled and may thus play a significant role as a seaward barrier inhibiting the 1944 earthquake rupture from propagating farther seaward

evidence for shallow and pervasive seismic anisotropy in the wellington region new zealand the shear waves of local earthquakes were recorded during a 5 month deployment of seven three component digital seismographs on the wellington peninsula new zealand the seismographs were spaced an average of less than 5 km apart and over 300 local earthquakes were recorded with phase arrivals within the shear wave window a significant number 37 of the earthquakes recorded showed clear evidence of shear wave splitting identifiable fast and slow shear wave arrivals with similar pulse shapes consistent polarization directions at particular stations were also observed even when poor signal to noise ratio or scattering meant that no slow shear wave arrival could be identified however there were large station to station differences in the polarization directions correcting for the observed shear wave splitting improved the fit between the measured shear wave polarizations and those calculated assuming a double couple focal mechanism the cause of the observed shear wave splitting is therefore most likely to be seismic anisotropy large station to station differences in the polarization alignments ranging from 61 24 to 137 18 suggest that most anisotropy is confined to the top 2 3 km of the crust however there is evidence from one station for a small amount of pervasive anisotropy if such a trend existed on the other stations it could not be identified because of the large scatter in the data points the measured delay times between split shear waves vary from 0 02 to 0 22 s with a mean value of 0 1 0 06 s this translates to a near surface shear wave velocity anisotropy of about 10 with up to 2 pervasive anisotropy possible throughout the crust this data set indicates that extensive dilatancy anisotropy cannot be the sole cause of crustal seismic anisotropy and that foliations in the rock fabric and the fracture zones of active faults may also be important there is no evidence for temporal change in the shear wave splitting parameters during the period of the experiment

synopsis sfb 108 stress and stress release in the lithosphere1 abstract stress and stress release in the lithosphere has been studied within a collaborative research centre at karlsruhe university sfb 108 as special contribution from germany to the international lithosphere program ilp this synopsis is an outline of the research results obtained by the sfb 108 as presented in this special volume of tectonophysics it starts with a summary of ideas on stress and stress release in the lithosphere which guided the sfb 108 at its beginning in 1981 it is followed by a review of strategy in cooperative research on rift systems world stress map and the scales of structure of the continental lithosphere from crust to mantle the main observations are then summarized and connections are made between key results from the various disciplines to obtain new views in lithospheric tectonics finally we address open questions and perspectives for future research the research addressed various styles of continental rifting from the afro arabian rift system to the central european rift system with the rhinegraben and the grabens in the french massif central as outstanding features a number of critical parameters such as thickness heat flow rheology composition strength of the crust and of the lithospheric mantle and the influence of active mantle plumes were identified and classified together they strongly influence the style of rifting petrophysical modelling of integrated information on seismic velocities composition and temperature from xenolith analysis density gravity and topography provided essential constraints on plume lithosphere interaction in the french massif central and also in the kenya rift the rhinegraben and its variscan environment offered the opportunity to study different concepts of upper and lower crust including the occurrence of deep crustal earthquakes and the role of an alpine detachment a special concern of the sfb 108 was the distribution of dimensions of heterogeneities in the lithosphere and its relation to the scales of their generating processes the crust mantle boundary was recognized as a major change in scales of heterogeneities by deep seismic sounding dss methods applied to the lower crust and the lithospheric mantle the study of the tectonic stress in western europe revealed that the crust is in frictional equilibrium down to midcrustal levels and is also decoupled from the mantle allowing adjustive motions of blocks and independent subduction in the foreland of the alps this decoupling is achieved in a thin and hot lithosphere driven by mid atlantic ridge push and alpine continent continent collision it is described in a quantitative dynamic model of crust mantle decoupling the sfb 108 has shown that earth scientists have to rediscover the importance of pattern recognition if complex influences are to be recognized

type b cyclogenesis in a zonally varying flow abstract it is hypothesized that surface cyclogenesis in the northern hemisphere storm track regions can be described by the structural modification of baroclinic wave packets traversing a zonally varying flow field we test this hypothesis using a linear quasigeostrophic model with a zonally varying basic state and zonally varying ekman layer eddy viscosity at midchannel the basic state consists of a region of strong low level baroclinicity and weak ekman dissipation surrounded by regions of weak low level baroclinicity strong ekman dissipation and enhanced low level static stability eigenanalyses and initial value integrations support this model of type b cyclogenesis the results can be summarized as follows 1 a disturbance initiated upstream of the midchannel baroclinic zone rapidly evolves into a wave packet with maximum amplitude near the tropopause the wave packet undergoes a structural modification upon entering the low level baroclinic zone developing maximum amplitude at the surface t

the annual cycle of northern hemisphere storm tracks part ii regional detail abstractin part i of this study the annual cycle of the northern hemisphere storm tracks was investigated using feature tracking and eulerian variance based diagnostics applied to both the vortici

characteristics of wave packets in the upper troposphere part ii seasonal and hemispheric variations abstract gridded 300 hpa meridional wind data produced by the ecmwf reanalysis project were analyzed to document the seasonal and hemispheric variations in the properties of upper tropospheric wave packets the properties of the wave packets are mainly illustrated using time lagged one point correlation maps performed on based on indices that show the coherence of wave propagation as well as examination of correlation maps schematic waveguides were constructed for the summer and winter seasons of both hemispheres along which waves preferentially propagate with greatest coherence in the summers the waveguides basically follow the position of the midlatitude jets in the northern hemisphere winter the primary waveguide follows the subtropical jet over southern asia into the pacific but there is a secondary branch running across russia joining the primary waveguide near the entrance to the pacific storm track over the atlantic the waveguide passes east southeastward toward north africa then bac

split from slip and schist crustal anisotropy beneath northern cascadia from non volcanic tremor 1 polarization and splitting analyses of minute long windows of non volcanic tremor at 3 component stations in the vicinity of southern vancouver island provide new evidence for the presence of anisotropy within the crustal portion of the north american plate beneath cascadia as reported previously tremor particle motions are predominantly horizontal and inferred to manifest an upgoing wavefield composed primarily of s waves under this assumption estimates of incidence angle and back azimuth can be deduced from orientation of the smallest principle direction of motion when subjected to standard s wave splitting analysis most stations yield systematic and reproducible fast polarization directions estimates of original polarization direction are more scattered and splitting times often exhibit multimodal distributions numerical simulations wherein band limited synthetic seismograms comprising contributions from multiple sources are analyzed for splitting neatly reproduce these characteristics and thereby provide a framework for interpretation a number of stations in our study sit astride the san juan fault which based on reflection studies dips approximately 60 to 70 to the north underlying these stations is the leech river complex consisting of strongly foliated greenschist facies phyllites with steeply dipping foliations striking parallel to fast polarization directions of split s waves detailed laboratory velocity measurements at elevated pressures show that as little as 2 to 3 km of vertically dipping leech river phyllite are required to produce the observed splitting these phyllites have some of the highest s wave anisotropies measured to date and are part of a once continuous belt of anisotropic crust extending over 2000 km along the western north american coast from southern vancouver island to southwest alaska

the role of the central asian mountains on the midwinter suppression of north pacific storminess abstractthe role of the central asian mountains on north pacific storminess is examined using an atmospheric general circulation model by varying the height and the areas of the mountains a series of model integrations show that the presence of the central asian mountains suppresses the north pacific storminess by 20 30 during boreal winter their impact on storminess is found to be small during other seasons the mountains amplify stationary waves and effectively weaken the high frequency transient eddy kinetic energy in boreal winter two main causes of the reduced storminess are diagnosed first the decrease in storminess appears to be associated with a weakening of downstream eddy development the mountains disorganize the zonal coherency of wave packets and refract them more equatorward as the zonal traveling distance of wave packets gets substantially shorter downstream eddy development gets weaker second the central asian mountains suppress the global baroclinic energy conversion the decre

a comparison of the downstream predictability associated with et and baroclinic cyclones abstractthe impact of the extratropical transition et of tropical cyclones and baroclinic cyclogenesis in the western north pacific wnp atlantic and southern indian ocean sio basins on the predictability of the downstream midlatitude flow is assessed using 30 years of cases from the global ensemble forecast system gefs reforecast version 2 in all three basins et is associated with statistically larger 500 hpa geopotential height forecast standard deviation sd compared to the forecast climatology the higher sd values originate from where the tc enters the midlatitudes and spread downstream at the group velocity of the associated wave packet of the three basins wnp et is associated with the largest amplitude and longest lasting sd anomalies forecasts initialized 2 4 days prior to the onset of et have larger sd anomalies compared to forecasts initialized during or after the onset of et by contrast the region of positive sd anomaly associated with winter baroclinic cyclones is confined to

interaction of north atlantic baroclinic wave packets and the mediterranean storm track observational studies show that the main energy source for developing cyclones is due to downstream radiation from existing upstream disturbances this process is involved in the propagation of coherent wave packets linking the north atlantic and mediterranean storm tracks in winter to understand the link the rossby wave packets have been analyzed for the winter season 2004 05 by means of wave envelope energetic and wave activity diagnostics two specifically selected cases are presented one with clear propagation of the wave packet to the mediterranean region from the north atlantic storm track and the other with zonal propagation of the wave packets along the central latitude of the north atlantic storm track the dynamical effects leading to the distinct propagation characteristics of the two cases are discussed it is shown that the two cases make clear impacts on the horizontal flux of wave activity across a domain surrounding the mediterranean storm track