anatomy of north pacific decadal variability abstract a systematic analysis of north pacific decadal variability in a full physics coupled ocean atmosphere model is executed the model is an updated and improved version of the coupled model studied by latif and barnett evidence is sought for determining the details of the mechanism responsible for the enhanced variance of some variables at 20 30 yr timescales the possible mechanisms include a midlatitude gyre ocean atmosphere feedback loop stochastic forcing remote forcing or sampling error decadal variability in the model is expressed most prominently in anomalies of upper ocean streamfunction sea surface temperature sst and latent surface heat flux in the kuroshio oyashio extension koe region off japan the decadal signal off japan is initiated by changes in strength and position of the aleutian low the atmospheric perturbations excite sst anomalies in the central and eastern north pacific with opposing signs and canonical structure the atmospheric perturbations also change the ekm

enhanced linkage between eurasian winter and spring dominant modes of atmospheric interannual variability since the early 1990s abstractthe present study reveals a marked enhancement in the relationship between eurasian winter and spring atmospheric interannual variability since the early 1990s specifically the dominant mode of winter eurasian 500 hpa geopotential height anomalies with same sign anomalies over southern europe and east asia and opposite sign anomalies over north central eurasia is largely maintained to the following spring after the early 1990s but not before the early 1990s the maintenance of the dominant atmospheric circulation anomaly pattern after the early 1990s is associated with a triple sea surface temperature sst anomaly pattern in the north atlantic that is sustained from winter to the subsequent spring this triple sst anomaly pattern triggers an atmospheric wave train over the north atlantic through eurasia during winter through spring atmospheric model experiments verify the role of the triple sst anomaly in maintaining the eurasian atmospheric circulation anomalies by contrast before the ea

mantle flow in subduction systems the subslab flow field and implications for mantle dynamics 1 the character of the mantle flow field in subduction zones remains poorly understood despite its importance for our understanding of subduction dynamics in particular little attention has been paid to mantle flow beneath subducting slabs in order to identify processes that make first order contributions to the global pattern of subslab mantle flow we have compiled shear wave splitting measurements from subduction zones worldwide from previously published studies and estimated average splitting parameters for the subslab region globally the subslab region is overwhelmingly dominated by trench parallel fast splitting directions we tested for relationships between splitting delay time a measure of the strength of anisotropy and parameters that are indicators of tectonic processes such as trench migration velocity convergence velocity and obliquity age of subducting lithosphere and slab dip curvature seismicity and thickness we used several different plate motion models to describe plate and trench motions and evaluated the differences among the models we find that only one parameter namely the trench migration velocity in a pacific hot spot reference frame appears to correlate well with the strength of the subslab splitting signal this finding supports a model in which the mantle beneath subducting slabs is dominated by three dimensional flow induced by trench migration we explore several implications of our model for various aspects of mantle dynamics including the choice of a suitable reference frame s for mantle flow the existence of a thin decoupling zone between slabs and the subslab mantle and consequences for mass transfer between the upper and lower mantle

midlatitude atmosphere ocean interaction during el nino part i the north pacific ocean abstract atmosphere ocean experiments are experiments are used to investigate the formation of sea surface temperature sst anomalies in the north pacific ocean during fall and winter of the el nino year experiments in which the ncar community climate model ccm surface fields am used to force a mixed layer ocean model in the north pacific no air sea feedback are compared to simulations in which the ccm and north pacific ocean model are coupled anomalies in the atmosphere and the north pacific ocean during el nino are obtained from the difference between simulations with and without prescribed warm sst anomalies in the tropical pacific in both the forced and coupled experiments the anomaly pattern resembles a composite of the actual sst anomaly field during el nino warm ssts develop along the cost of north america and cold ssts form in the central pacific in the coupled simulations air sea interaction results in a 25 to 50 reduction in the magnitude of the sst and mixed layer depth anomalies

development of a dynamics based statistical prediction model for the changma onset abstractthe timing of the changma onset has high impacts on the korean peninsula yet its seasonal prediction remains a great challenge because the changma undergoes various influences from the tropics subtropics and midlatitudes in this study a dynamics based statistical prediction model for the changma onset is proposed this model utilizes three predictors of slowly varying sea surface temperature anomalies sstas over the northern tropical central pacific the north atlantic and the north pacific occurring in the preceding spring season sstas associated with each predictor persist until june and have an effect on the changma onset by inducing an anticyclonic anomaly to the southeast of the korean peninsula earlier than the climatological changma onset date the persisting negative sstas over the northern tropical central pacific and accompanying anomalous trade winds induce enhanced convection over the far western tropical pacific in turn these induce a cyclonic anomaly over the south china s

the structure of the sumatran fault revealed by local seismicity the combination of the sunda megathrust and the strike slip sumatran fault sf represents a type example of slip partitioning however superimposed on the sf are geometrical irregularities that disrupt the local strain field the largest such feature is in central sumatra where the sf splits into two fault strands up to 35 km apart a dense local network was installed along a 350 km section around this bifurcation registering 1016 crustal events between april 2008 and february 2009 528 of these events with magnitudes between 1 1 and 6 0 were located using the double difference relative location method these relative hypocentre locations reveal several new features about the crustal structure of the sf northwest and southeast of the bifurcation where the sf has only one fault strand seismicity is strongly focused below the surface trace indicating a vertical fault that is seismogenic to 15 km depth by contrast intense seismicity is observed within the bifurcation displaying streaks in plan and cross section that indicate a complex system of faults bisecting the bifurcation in combination with analysis of topography and focal mechanisms we propose that the bifurcation is a strike slip duplex system with complex faulting between the two main fault branches

atmosphere ocean relationship in the midlatitude north pacific seasonal dependence and east west contrast 1 the present study documents the relationship between the surface heat flux and sea surface temperature sst and estimates the contribution of different processes to sst changes in the midlatitude north pacific it is found that the atmosphere ocean relationship displays pronounced differences between winter and summer and between the western and central basins of the north pacific in the western basin the shortwave radiation change associated with a positive cloud sst feedback is a dominant factor for the development of sst anomalies in boreal summer in boreal winter surface latent heat flux anomalies develop in response to sst and in turn damp the sst anomalies the meridional advection induced by anomalous geostrophic currents near the coast and by anomalous ekman currents away from the coast has important contributions to the sst changes in the central basin the latent heat flux change is a dominant factor for the development of sst anomalies and the shortwave radiation mainly responds passively to sst anomalies in boreal summer both latent heat flux and meridional advection contribute to the sst changes in boreal winter the wind changes over the north pacific play an important role for the sst changes both in winter and summer through their impacts on cloud surface wind speed advection of atmospheric boundary layer moisture and ekman transport citation wu r and j l kinter iii 2010 atmosphere ocean relationship in the midlatitude north pacific seasonal dependence and east west contrast j geophys res 115 d06101 doi 10 1029 2009jd012579

interdecadal thermocline variability in the north pacific for 1958 97 a gcm simulation an ocean general circulation model is forced with the ncep reanalysis wind stress for 1958 97 to understand mechanisms of ocean subsurface variability with relatively high horizontal 1 83 18 and vertical 41 levels resolutions the model produces mode waters on a range of density surfaces in the western central and eastern north pacific in qualitative agreement with observations these mode waters appear as a thermostad or a region of weak stratification in the upper thermocline as they flow southward from their formation regions in the kuroshio and its extension in the model subsurface temperature variability in the central subtropical gyre reaches a maximum within the thermostad in contrast to what might be expected from the linear baroclinic rossby wave theory this variance maximum is associated with the longitudinal shift in the path of mode waters in particular deepened mixed layer and accelerated eastward currents in the kuroshio extension by wind changes in the mid 1970s act cooperatively to move the central mode waters toward the east causing large subsurface temperature anomalies besides the local maximum in the central north pacific subtropical gyre two additional maxima of the subsurface anomaly are identified in the northwestern and southern parts of the gyre respectively among these subsurface anomaly centers the one in the northwestern north pacific has a strong effect on the model sea surface temperature suggesting that the kuroshio and its extension are a key region to decadal interdecadal ocean atmosphere interaction finally possible effects of atmospheric thermal forcing are discussed

a rotated eof analysis of global sea surface temperature variability with interannual and interdecadal scales abstract spatiotemporal variability of preferred global scale sea surface temperature anomaly patterns is documented applying a varimax rotated empirical orthogonal function r eof analysis to monthly mean sst anomalies the present study focuses especially on the interdecadal variability of leading r eof modes it is first found that temporal variability of r eof1 has a quasi periodicity of 2 5 years and coincides quite well with the occurrence of the enso event hence this mode can be identified with the enso mode and distinguished from the other modes dominated by interdecadal variability the authors find that r eof2 typically shows the dominance of interdecadal variability and signals of the enso phenomenon are removed this mode is characterized by increasing indian ocean sst and decreasing central north pacific sst around 40 50 n in the recent ten or more years a further indication is that both r eof3 and r eof4 which show the dominance of interdecadal variability are fundamentally regarded a

effects of northern and southern components of the east asian winter monsoon variability on sst changes in the western north pacific the present study investigates the impacts of the two components of the east asian winter monsoon eawm variability on sea surface temperature sst changes in the western north pacific when the eawm is stronger than normal significant negative sst anomalies form in the east asian marginal seas and subtropical western north pacific and persist from winter to the following spring it is found that winter spring sst anomalies in the yellow sea and the japan sea have a close association with the northern component of the eawm variability whereas the southern component has a large impact on sst changes in subtropical western north pacific the two components induce sst anomalies through both surface heat flux and oceanic advection changes the surface latent heat flux is predominantly responsible for sst changes the oceanic advection has a secondary contribution to the sst change in subtropical western north pacific associated with the northern component and in the japan sea associated with the southern component the surface latent heat flux anomalies associated with the northern component are induced through changes in both wind speed and sea air humidity difference and those associated with the southern component are induced mainly through changes in sea air humidity difference north of 20 n the sst anomalies induced by the northern component are mostly independent of el nino southern oscillation enso while enso has a large effect on the sst anomalies in open oceanic regions the southern component has a dominant contribution independent of enso to the sst anomalies in the marginal seas

a strengthened impact of november arctic oscillation on subsequent tropical pacific sea surface temperature variation since the late 1970s the connection between november arctic oscillation ao and the following spring summer tropical pacific sea surface temperature sst experienced a pronounced enhancement around the late 1970s the connection was weak before but strong after the late 1970s the present study investigates the plausible reasons for the connection change after the late 1970s significant anomalous cyclone appears over subtropical north pacific and pronounced anomalous westerly winds occur over tropical western pacific in the positive phase of november ao as such november ao could exert a significant influence on the subsequent spring summer tropical pacific sst variation by contrast before the late 1970s anomalous cyclone and associated anomalous westerly winds to its south are weak and shift northward thereby the connection between november ao and tropical pacific sst is weak further analyses suggest that the interdecadal change in the anomalous cyclone over the subtropical north pacific may be related to the change in the november ao s pacific component and the strength of feedback of synoptic scale eddy to mean flow specifically after the late 1970s november ao s pacific component displays a zonally elongated structure which is favorable for the formation of easterly wind anomalies over the mid latitude north pacific and related wave mean flow interaction in addition feedback of synoptic eddy to mean flow is enhanced after the late 1970s which is partly related to the intensification of the north pacific storm track this may also contribute to enhancement of the anomalous cyclone over the subtropical pacific

simulation of the response of the north pacific ocean to the anomalous atmospheric circulation associated with el nino during el nino events when positive sea surface temperature sst anomalies form in the equatorial pacific sst anomalies also tend to develop in the north pacific this study attempts to model and explain the large scale features of the observed sst anomaly field in the north pacific during the fall and winter of the el nino year the experiment design consists of a mixed layer ocean model of the north pacific which is forced by atmospheric surface fields from two sets of community climate model ccm integrations the el nino set with prescribed positive sst anomalies in the tropical pacific and the control set which is obtained from an extended ccm integration with prescribed climatological ssts the response of the midlatitude ocean to atmospheric surface fields associated with el nino is obtained by compositing each set of model integrations el nino and control and then taking the difference between the composites the ocean model is able to reproduce the general features of the observed midlatitude sst anomaly pattern warm water in the northeast pacific and an elliptically shaped cold pool in the central pacific in these regions a large fraction of the temperature anomalies are significant at the 95 level as indicated by a two tailed t test the ocean temperature anomalies simulated by the model are primarily caused by changes in the sensible and latent heat flux and to a lesser extent the longwave radiation flux entrainment of cold water from below the mixed layer also influences ocean temperatures however the entrainment anomaly pattern has a complex spatial structure which does not always coincide with the simulated mixed layer temperature anomalies

wind driven shifts in the latitude of the kuroshio oyashio extension and generation of sst anomalies on decadal timescales abstract the causes of decadal variations of north pacific sea surface temperatures ssts are examined using a hindcast performed with an ocean general circulation model thermodynamically coupled to an atmospheric mixed layer model ogcm aml model and forced by the time history of observed surface winds the shift in north pacific ocean climate that occurred around 1976 77 is focused on since this is the best observed example available after the 1976 77 shift the aleutian low deepened and moved to the southeast of its previous position this placed anomalous cyclonic flow over the north pacific the sst response as simulated by the ocean model consisted of two components a fast and local part and a delayed and remote part in the central pacific stronger westerlies cool the ocean by increased equatorward ekman drift here the dynamical cooling is sufficiently large that the surface fluxes damp the sst anomaly this ekman response is fast and local and cools the ssts beginning in 1977 and persistin

shear wave anisotropy in the crust mantle wedge and subducting pacific slab under northeast japan to study the anisotropic structure beneath northeast ne japan we made 4366 shear wave splitting measurements using high quality seismograms of many earthquakes occurring in the crust and the subducting pacific slab our results provide important new information on the s wave anisotropy in the upper crust lower crust mantle wedge and subducting pacific slab in the upper crust the anisotropy is mainly caused by the stress aligned fluid saturated microcracks the measured delay times dts increase to 0 10 s at 10 11 km depth the fast velocity directions fvds are parallel to either the tectonic stress or the strike of active faults the maximum dts for the low frequency earthquakes near the moho are 0 15 0 17 s suggesting strong anisotropy at the base of the crust or in the uppermost mantle the measurements for the intermediate depth earthquakes in the pacific slab show dominant e w trench normal fvds in the back arc area and n s trench parallel fvds in the fore arc area the trench normal fvds in the back arc area are caused by the corner flow in the mantle wedge as a result of the subduction of the pacific plate the maximum dts for the slab earthquakes reach 0 30 0 32 s at 100 km depth but only half of the total dts are produced in the mantle wedge the small dts in the mantle wedge may result from an isotropic or weak anisotropic zone in the middle of the mantle wedge in the fore arc the dominant trench parallel fvds for the slab earthquakes are consistent with those for the upper crust earthquakes and 80 of the total dts can be accounted for by the anisotropy in the crust in the subducting pacific slab the trench parallel fvds may reflect either the original fossil anisotropy in the pacific plate when the plate was produced in the mid ocean ridge or the preferred orientations of the crystals and cracks in the upper part of the subducting slab

precessional forced extratropical north pacific mode and associated atmospheric dynamics using transient accelerated simulations of the community climate system model version 3 and an earth system model of intermediate complexity as well as equilibrium experiments of the community earth system model we identified a response of the extratropical air ocean coupled system to the precessional insolation changes at orbital timescales and named this extratropical response pattern as the north pacific mode npm corresponding to the increased decreased boreal winter summer insolation at 22 ka relative to 10 8 ka the npm is characterized by a western warm eastern cold seesaw pattern of sea surface temperature sst over the extratropical north pacific from november to april a weakened winter aleutian low and an anomalous anticyclonic circulation throughout the troposphere this feature forms a barotropic warm ridge response of tropospheric temperature and geopotential height to the precessional insolation at the surface rainfall increases over east asia and the northwest pacific which indicates a weakened east asian winter monsoon while drier conditions appear over the northeast pacific and the western coasts of north america associated with a negative phase of npm is a weaker warming over the equatorial pacific during winter the increased winter insolation at precessional band not only induces the in phase sst warming over the northwest pacific and the tropical pacific but also explains those extratropical atmospheric changes associated with npm the latter might be associated with the warm sst induced tropospheric downstream ridge response through transient eddy activities besides the vital role of air ocean interactions the decreased summer insolation is also essential to the zonal sst seesaw of npm at precessional band

relative contribution of enso and east asian winter monsoon to the south china sea sst anomalies during enso decaying years present study investigates respective contributions of el nino southern oscillation enso and east asian winter monsoon eawm to two periods of sea surface temperature sst anomalies in the south china sea scs one subsequent to the enso mature phase and the other in the following summer during 1982 2010 it is found that the sst anomalies in the first period are related to the eawm and the enso impact independent of eawm is weak which differs from previous studies the sst anomalies in the second period are mainly due to the enso effect a heat budget analysis shows that changes in shortwave radiation and wind related surface latent heat flux as well as horizontal advections are the processes leading to the eawm related sst anomalies in the first period the enso related sst anomalies in the second period are contributed by shortwave radiation and latent heat flux anomalies as well as meridional advection and vertical upwelling processes near the southeast coast of indochina peninsula the enso contribution to the scs sst anomalies in the first period is larger before than after the late 1970s this is attributed to an earlier development of enso events that is followed by larger equatorial central and eastern pacific sst anomalies in boreal summer and subsequently larger north indian ocean sst anomalies around october consequently anomalous surface anticyclone over the scs is stronger leading to larger surface heat flux anomalies and thus a larger sst increase around october before than after the late 1970s

modeling anisotropy and plate driven flow in the tonga subduction zone back arc the goal of this study is to determine whether shear wave splitting observed in subduction zone back arc regions the tonga subduction zone in particular can be quantitatively modeled with flow in the back arc mantle driven by the motions of the subducting slab and the upper back arc plate we calculated two dimensional mantle flow models using known tonga plate motions as boundary conditions and assuming a range of uniform and variable viscosity structures shear wave splitting was predicted for the anisotropy due to lattice preferred orientation lpo of olivine and orthopyroxene in the flow model finite strain fields the predicted shear wave splitting provides a good match to the fast directions parallel to the azimuth of subducting plate motion and splitting times 0 5 1 5 s observed in tonga both for models where lpo anisotropy develops everywhere above 410 km and for models where lpo anisotropy is confined to regions of relatively high stress if lpo anisotropy does develop over the entire upper 410 km of the mantle the strength of anistropy induced by a given amount of shear strain must be relatively weak 4 for shear strains of 1 5 with a maximum value of 6 for very large strains the splitting observations are comparably fit by a wide range of different viscosity models anisotropy due to melt filled cracks aligned by stresses in the back arc flow models predicts fast directions roughly normal to observed values and thus cannot alone explain the observed splitting

distinguishing interannual variations of the northern and southern modes of the east asian winter monsoon abstractthe east asian winter monsoon eawm related climate anomalies have shown large year to year variations in both the intensity and the meridional extent the present study distinguishes the interannual variations of the low latitude and mid to high latitude components of the eawm to gain a better understanding of the characteristics and factors for the eawm variability through composite analysis based on two indices representing the northern and southern components modes of the eawm variability the present study clearly reveals features unique to the northern and southern mode the northern mode is associated with changes in the mid to high latitude circulation systems including the siberian high the aleutian low the east asian trough and the east asian westerly jet stream whereas the southern mode is closely related to circulation changes over the global tropics the north atlantic and north america a strong northern mode is accompanied by positive negative and positive surface temp

anisotropic structure under a back arc spreading region the taupo volcanic zone new zealand 1 we investigate anisotropy surrounding a continental back arc spreading region the central volcanic region cvr in the north island of new zealand and present a simple method for spatial averaging to examine heterogeneous anisotropy s phases from local earthquakes yield consistent trench parallel fast directions in the southern compressional region but varied directions in the northern extensional region in the forearc east of the cvr is nearly trench parallel suggesting shear in the mantle or trench parallel flow in the western cvr local phases from 50 to 80 km depth give parallel to extension 120 and phases from 150 to 220 km depth yield similar 150 these results suggest asthenospheric flow with olivine a axes oriented in the extension direction down to 100 150 km depth in the eastern cvr local phases show mixed suggesting that it is a transition between the western cvr and the forearc trench parallel for shallow local events within the cvr may be caused by fluid filled cracks trench parallel for deeper local events and for sks phases can be explained by standard olivine fabrics developed by lithospheric shearing by trench parallel flow and by fossil anisotropy in the subducting oceanic lithosphere alternatively in the cvr they could be caused in part by hydrous minerals at the slab mantle upper interface which could cause olivine a axes to orient parallel to the trench due to a maximum shear stress oriented perpendicular to the trench along the slab we suggest that trench perpendicular flow in the extensional region helps to drive fluids away from the slab while in the compressional region trench parallel flow fails to distribute the fluids explaining the location of changes in geophysical properties

seismic characterization of mantle flow in subduction systems can we resolve a hydrated mantle wedge this study provides new constraints on the resolvability of mantle flow in subduction zone settings as inferred by observations of seismic anisotropy we are motivated by the broad range of shear wave splitting observations in subduction systems that suggest complex flow geometries changes in the deformation state of mantle minerals or a combination of both while shear wave splitting fast polarization directions are typically interpreted as a proxy for flow or maximum finite extension experimental studies suggest that olivine slip systems change under higher stress and hydration states conditions likely appropriate for subduction systems in this study we predict shear wave splitting as a result of mantle silicate lattice preferred orientation development in steady state two dimensional mantle flow models using a textural development theory that incorporates the combined effects of intracrystalline slip and dynamic recrystallization we utilize the resulting textures to predict shear wave splitting for populations of seismic raypaths traversing the model within the subduction zone mantle wedge the results of our study demonstrate that combined observations of variations in fast polarization directions and splitting times make it possible to resolve a shift from anhydrous to hydrous mantle insubduction zone settings provided very good sampling of the mantle wedge our models are generally consistent with observed splitting variations for several subduction zones with dense data sampling including tonga japan and kamchatka the implications of our work suggest that provided adequate data sampling shear wave splitting measurements can provide the necessary information to evaluate potential competing effects between variations in mantle flow direction and changes in the stress and hydration states of subduction zone mantle wedges

seismic anisotropy in the sumatra subduction zone an important tool for understanding deformation occurring within a subduction zone is the measurement of seismic anisotropy through observations of shear wave splitting sws in sumatra two temporary seismic networks were deployed between december 2007 and february 2009 covering the fore arc between the fore arc islands to the back arc we use sks and local sws measurements to determine the type amount and location of anisotropy local sws measurements from the fore arc islands exhibit trench parallel fast directions which can be attributed to shape preferred orientation of cracks fractures in the overriding sediments in the sumatran fault region the predominant fast direction is fault trench parallel while in the back arc region it is trench perpendicular the trench perpendicular measurements exhibit a positive correlation between delay time and raypath length in the mantle wedge while the fault parallel measurements are similar to the fault parallel fast directions observed for two crustal events at the sumatran fault this suggests that there are two layers of anisotropy one due to entrained flow within the mantle wedge and a second layer within the overriding crust due to the shear strain caused by the sumatran fault sks splitting results show a nnw sse fast direction with delay times of 0 8 3 0 s the fast directions are approximately parallel to the absolute plate motion of the subducting indo australian plate the small delay times exhibited by the local sws 0 05 0 45 s in combination with the large sks delay times suggest that the anisotropy generating the teleseismic sws is dominated by entrained flow in the asthenosphere below the slab

predicting western north pacific ocean climate abstract it is shown that wintertime sea surface temperature anomalies in the confluence region of the kuroshio oyashio currents in the western north pacific can be skillfully predicted at lead times of up to 3 yr the predictions are based on the history of the wind stress over the north pacific and oceanic rossby wave dynamics the predictions may be exploitable in fisheries research and other ecological applications

azimuthal anisotropy in the earth from observations of sks at geoscope and nars broadband stations abstract we have analyzed observations of low frequency sks waves recorded on horizontal components at several broadband stations of the geoscope and nars arrays splitting of sks is consistently observed and in good agreement with a hypothesis of azimuthal anisotropy due to transverse anisotropy with a horizontal axis in the upper mantle beneath the receivers we have designed an inversion method which takes advantage of observations made simultaneously at different azimuths and which permits us to obtain estimates of the direction of fast axis of anisotropy as well as the time delay between the orthogonal quasi shear waves in general the directions of fast velocity obtained both for stations around the atlantic and around the pacific appear to be related to directions of past and present plate motions

seismic anisotropy and mantle flow seismic anisotropy in the mantle is primarily due to deformation induced lattice preferred orientation lpo of olivine crystals the aim of this paper is to better understand how such lpo is produced by flow and to learn whether observations of seismic anisotropy can be used to infer the local direction of flow within the mantle the basis of the work is a two dimensional theory which describes how lpo evolves during an arbitrary time dependent deformation ribe 1989 i investigate the evolution of lpo beneath ocean ridges above subducted slabs and in thermal convective flows the ocean ridge model predicts that the seismic anisotropy produced at a fast spreading ridge should be greater in magnitude than that produced at a slow spreading ridge and that the fast axis should be more nearly horizontal the subduction zone model predicts that strong seismic anisotropy should be produced above subducted slabs with the fast axis aligned with the slab regardless of the subduction angle the evolution of lpo in typical convective flows is extremely complex and depends strongly on such factors as the mode of heating and the surface boundary conditions in general there is no simple relation between the lpo and the local flow direction in any of the models considered the attempt to use seismic anisotropy to map flow patterns on a global scale is therefore probably unwarranted however the lpo does become aligned with the flow direction when the flow is a progressive simple shear such a flow occurs in limited portions of the mantle beneath the lithosphere at a fast spreading ridge above subducted slabs and in boundary layers beneath rigid surfaces such as continents observations of seismic anisotropy may therefore indicate the sense of shear at shallow depths in the mantle

seismic anisotropy beneath the lower half of the north island new zealand teleseismic scs and sks events recorded on nine broadband seismograph stations have been used to investigate seismic anisotropy beneath the lower half of the north island new zealand this area lies above the hikurangi subduction zone and the array provides ray paths which sample the mantle both above and below the slab shear wave splitting measurements give similar fast polarizations and delay times at each station the average sks fast polarization is approximately ne sw subparallel to the strike of subduction and the major geological features with an average sks delay time of 1 6 0 1 s this lack of variation in splitting parameters suggests that similar fast polarizations are found in both the mantle wedge and the subslab mantle the anisotropy in the lithospheric portion of the mantle wedge is most likely caused by the preferred orientation of olivine due to the shear deformation associated with oblique convergence any anisotropy in the slab is probably due to fossil mineral alignment anisotropy in the asthenosphere is most likely caused by the preferred orientation of olivine due to asthenospheric flow the similar ne sw fast polarizations found in the asthenosphere both above and below the slab suggest that the mantle flow is in a trench parallel direction in both regions

interdecadal indian ocean basin mode driven by interdecadal pacific oscillation a season dependent growth mechanism abstractthe interdecadal variability of basinwide sea surface temperature anomalies sstas in the tropical indian ocean tio referred to as the interdecadal indian ocean basin mode id iobm is

shear wave splitting beneath western united states in relation to plate tectonics we have examined shear wave splitting in teleseismic shear waves from 26 broadband stations in the western united states fast polarization directions and delay times t show spatial variations that are coherent within geologic provinces stations located near the san andreas fault show clear evidence for fault parallel anisotropy in the crust and upper mantle 115 125 km thickness this can be explained by the finite strain associated with the relative plate motion between the north american and pacific plates the lateral extent of this strain field is probably narrow to the west because stations 55 km west of the san andreas fault do not show fault parallel anisotropy in southern california station lac located 80 km east of the san andreas fault shows large fault parallel anisotropy this suggests that the pacific north american plate boundary in the mantle might be displaced to the east in southern california a deeper e w oriented fast direction of anisotropy underlies the fault parallel anisotropic layer in the vicinity of the san andreas fault an e w fast feature is also present beneath the western basin and range and the foothills of the sierra nevada although local variations are present the magnitude of delay times suggests that this feature resides in the asthenosphere we interpret this feature as the asthenospheric flow in the slabless window left behind the farallon plate the flow induced anisotropy may partially be frozen in at shallow depths station orv is located near the southern edge of the gorda slab where no anisotropy is detected the absence of anisotropy at this location could therefore mark a boundary between farallon associated flow and regions where e w oriented asthenospheric flow did not occur the lack of evidence for ne sw fast orientation within the walker lane shear belt of western nevada suggests that this crustal feature does not extend into the mantle or that is not as well developed as that beneath the san andreas fault stations located over the young subducting gorda plate mark a change in the fast direction to nearly ne sw this direction aligns well with the maximum compressive stress direction in the overlying north american plate and the ne sw directed internal shearing of the gorda plate the anisotropic thicknesses calculated from delay times suggest roughly double that expected for purely lithospheric contributions this implies that the anisotropic thickness may include some of the asthenosphere alternatively using a higher anisotropy of 8 can bring thicknesses in line with other measures of lithospheric thicknesses the correspondence between the fast directions and the present plate tectonic deformations suggest that mapping upper mantle deformation through seismic anisotropy is a viable method and that asthenospheric flow may be a significant contributor to seismic anisotropy

seismic anisotropy of the pacific slab and mantle wedge beneath the japanese islands 1 the mantle beneath the japanese islands is complex because of subduction of the pacific and philippine sea plates and the deformation associated with it detection of seismic anisotropy should be useful for understanding the processes occurring in such mantle here we resolve seismic anisotropy of the mantle wedge from that of the underlying subducted pacific slab using a large number of measurements of shear wave splitting for a family of core reflected shear phases scs sscs scs2 and sscs2 the anisotropy of the mantle wedge changes sharply across the volcanic front on the pacific side of the volcanic front a vertically propagating shear wave is polarized with the fast direction approximately parallel to the trench whereas on the back arc side it is polarized with the fast direction approximately parallel to the plate convergence direction the pacific slab is uniformly anisotropic with the nnw fast direction consistent with the paleospreading direction of the northwestern pacific seafloor the preferential alignment of anisotropic crystals frozen in the plate at the time of its formation appears to be preserved down to depths beyond 400 km within the slab

interannual variability of the kuroshio extension system and its impact on the wintertime sst field altimetry data from the first 7 yr topex poseidon t p mission october 1992 september 1999 are analyzed to investigate the interannual variability in regions of the kuroshio extension and its southern recirculation gyre large scale interannual changes of the kuroshio extension system are characterized by the oscillation between an elongated state and a contracted state in the elongated state the kuroshio extension has a larger eastward surface transport a greater zonal penetration and a more northerly zonal mean path all these characteristics are closely connected to the presence of an intense zonally elongated southern recirculation gyre in its contracted state the kuroshio extension has a smaller eastward surface transport a more southerly mean path and is accompanied by a weaker southern recirculation gyre during the t p period the kuroshio extension changed from the elongated state in 1992 93 to the contracted state in 1996 97 and back to the elongated state since late 1997 in addition to these large scale changes the mesoscale eddy field also exhibited prominent interannual changes in the kuroshio extension region in the upstream region between the izu ridge and the shatsky rise the eddy kinetic energy level was generally low while the kuroshio extension was in its elongated state and high while in the contracted state downstream of the shatsky rise on the other hand the eke level was high low when the kuroshio extension was in the elongated contracted state the large scale interannual changes in the kuroshio extension system have a significant impact on the regional wintertime sst anomaly field the warm cold wintertime sst anomalies tend to persist in years when the kuroshio extension is in its elongated contracted state a diagnostic analysis of the surface ocean heat balance indicates that the nonseasonal geostrophic advection by the ocean circulation works to reduce increase the wintertime sst anomalies when the kuroshio extension changes from an elongated contracted state to a contracted elongated state the sst anomalies associated with the large scale changes of the kuroshio extension have an area averaged peak topeak amplitude of 18c and appear independent of the interannual sst changes in the tropical pacific ocean

sea surface temperature anomalies planetary waves and air sea feedback in the middle latitudes the mechanisms that contribute to the generation and damping of large scale mid latitude sea surface temperature sst anomalies are discussed the sst anomalies reflect primarily the response of the upper ocean to the changes in air sea fluxes that are associated with daily weather fluctuations heat flux forcing is dominant in the lower middle latitudes while wind driven entrainment may be most effective in the high latitudes advection by anomalous ekman current is generally less important and ekman pumping is negligible the sst anomalies decay in part because of entrainment effects associated with mixed layer deepening and oceanic mixing and in part because of heat exchanges with the atmosphere the three approaches commonly used to model the evolution of sst anomalies are reviewed case studies based on monthly or seasonal anomaly maps of the large scale sst and atmospheric anomalies numerical simulations with one dimensional mixed layer models and stochastic forcing models we stress the similarities in the different approaches and discuss their main advantages and limitations the response of the atmosphere to mid latitude sst anomalies is considered first we discuss the poorly known relationship between sst anomalies and diabatic heating using a crude assumption for the air sea coupling we consider a two layer quasi geostrophic channel model and discuss the stationary wave response to sst anomaly forcing and the resulting air sea feedback it is found that the back interaction of the sst anomalies onto the atmosphere causes a weak sst anomaly damping at large scales and a strong one at small scales the air sea coupling should also act as an eastward propagator for the sst anomalies the response of more realistic linear wave models to prescribed diabatic heating is then reviewed and it is suggested that realistic mid latitude sst anomalies have a weak influence on the atmospheric circulation corresponding to changes in the geopotential height of 10 30 m at most this order of magnitude is consistent with the results of general circulation model experiments and with the limited climate predictability associated with mid latitude sst anomalies

spatial patterns of atmosphere ocean interaction in the northern winter abstract the variability of monthly mean sea surface temperature sst anomalies over the extratropical north atlantic and pacific and its relation to atmospheric circulation anomalies over the northern hemisphere during wintertime is investigated by applying eigenvector analysis to a 39 year dataset and correlating the time series of the resulting expansion coefficients with the hemispheric 500 mb height and sea level pressure fields in agreement with previous studies the simultaneous correlation between the tone series of the expansion coefficient of the first empirical orthogonal function eof 1 of north pacific sea surface temperature sst and the hemispheric 500 mb height field resembles the pacific north american pattern and the corresponding pattern for atlantic sst resembles the north atlantic oscillation in the vicinity of the conters of action of thew patterns the sst fluctuations associated with these modes explain on the order of half the variance of 500 mb height and slightly less of

global climatology of near inertial current characteristics from lagrangian observations 1 satellite tracked surface drifter data from 1999 2006 are used to compute global climatology of inertial current characteristics at seasonal scales the global mean near inertial current amplitude at 15m depth is 10 cm s 1 corresponding to mixed layer inertial energies of 300 j m 2 the southern ocean and the western north pacific and atlantic oceans are the most energetic in the near inertial frequency band whereas weaker inertial activity is observed in the subtropical and eastern boundary regions in every ocean basin inertial activity is higher during fall and winter associated with maximum storms activity and deeper mixed layers this study also shows that the mixed layer model developed by r t pollard and r c millard 1970 and forced by the qscat ncep blended wind product is too energetic in the tropics and not enough at high latitudes these discrepancies could question the previous estimates of the wind work to inertial motions based on those simulations