lateral heterogeneity and azimuthal anisotropy in the north atlantic determined from ss s differential travel times to explore upper mantle heterogeneity beneath the north atlantic we have measured 70 ss s differential travel times using the waveform cross correlation method both the two way preliminary reference earth model prem and j b jeffreys bullen residuals exhibit a maximum variation of 17 s ranging from 10 to 7 and 9 to 8 s respectively the lack of correlation between ss s and s residuals along with the strong correlation between ss s and ss residuals suggests that ss s differential travel times eliminate source and receiver effects and sample the upper mantle anomalies near the ss bounce points without being strongly affected by lower mantle heterogeneities we find evidence for a strong local anomaly in the north atlantic residuals for bounce points immediately to the north of the azores gibraltar plate boundary average about 4 s faster than for the bounce points to the south of the boundary we infer that this velocity contrast exists in the lithosphere and continues below a depth of 200 km a series of linear multiple regression experiments demonstrate that variation in velocity with increasing age of the seafloor and azimuthal anisotropy are both significant contributors to the prem and j b residuals assuming that travel time delays are a linear function of the square root of the seafloor age we find the coefficient for age to be about 1 0 s m y this is smaller than but not significantly different from the corresponding slope for the s delays of intraplate earthquakes in the atlantic reported by j d duschenes and s c solomon 1977 and favors the presence of small amounts of water e g 0 1 in the upper mantle in modeling anisotropy we carry out an experiment using synthetic seismograms to examine the shear wave splitting phenomena in the anisotropic medium and investigate three possible forms for sh wave delay as a function of azimuth sinusoidal variations as a function of 2 4 and a combination of 4 predominant and 2 that mimics the delay expected in olivine crystals when the axis is aligned horizontally our regression models strongly prefer the predominance of a 4 to a 2 variation and the last type of anisotropy explains our data best from the preferred anisotropy model the olivine axis or the upper mantle shearing flow is inferred to be oriented n s the magnitude of the azimuthal variation suggests that anisotropy extends over a depth range of several hundred kilometers in the upper mantle

the shear wave velocity gradient at the base of the mantle the relative amplitudes and travel have been directed toward obtaining global times of scs and s phases are utilized to place averages and the degree of lateral variation in constraints on the shear wave velocity gradient d properties remains an open question above the core mantle boundary a previously a conflicting result was found by mitchell and reported long period scsh sh amplitude ratio helmberger 1973 who utilized the relative minimum in the distance range 65 o to 70 o is shown amplitudes and timing of long period scs and s to be a localized feature apparently produced by phases to constrain the s wave velocity gradient an amplitude anomaly in the direct s phase and in d they found a minimum in the scsh sh therefore need not reflect the velocity gradient amplitude ratio near 68 o which was attributed to at the base of the mantle the amplitude ratios low amplitudes of the scs arrivals unable to that are free of this anomaly are consistent with explain this feature by models with negative or calculations for the jb model or models with mild near zero shear velocity gradients in d they positive or negative velocity gradients in the proposed models with positive s wave velocity lowermost 200 km of the mantle scsv arrivals gradients above the cmb these positive are particularly sensitive to the shear velocity gradients extended over 40 to 70 km above the structure just above the core mantle boundary core reaching velocities at the cmb as high as the apparent arrival time of the peak of scsv is 7 6 to 7 8 km s these models can explain the as much as 4 sreater than that of scsh in the observed amplitude ratio behavior as well as an distance range 75 v to 80 o for sea of okhotsk apparent difference observed in the arrival times events recorded in north america this can be of transversely and radially polarized scs explained by interference effects produced by a mitchell and helmberger also proposed a low q localized high velocity layer or strong positive zone in d or finite outer core rigidity to s wave velocity gradient in the lowermost 20 km explain the baseline of the scsh sh amplitude of the mantle a velocity increase of about 5 ratios while the majority of their data was for is required to explain the observed shift between deep south american events recorded in north scsv and scsh this thin high velocity layer america they did analyze one deep sea of okhotsk varies laterally as it is not observed in event for which the radial and transverse scs similar data from argentine events refined arrival times were not different which suggested estimates of the outermost core p velocity lateral variations in the d velocity structure structure are obtained by modeling sks signals in in this paper we extend the analysis of scs the distance range 75 o to 85 o s

mineralogy and composition of the upper mantle seismic velocities are calculated for two petrological models of the upper mantle an olivine rich assemblage pyrolite and a garnet clinopyroxene rich olivine bearing assemblage piclogite these are compared with recent seismic profiles for various tectonic provinces the shield data is most consistent with a cold olivine and orthopyroxene rich lid the seismic lithosphere extending to 150 km followed by a high temperature gradient and or a change in mineralogy that serves to decrease the velocity from 200 to 400 km the velocities follow a 1400 c adiabat the rise tectonic mantle is much slower presumably hotter and is likely to be above the solidus to depths of at least 300 km the high v p v s ratio of the lower oceanic lithosphere in the western pacific is most consistent with eclogite

ship observations and numerical simulation of the marine atmospheric boundary layer over the spring oceanic front in the northwestern south china sea the response of the marine atmospheric boundary layer mabl structure to an oceanic front is analyzed using global positioning system gps sounding data obtained during a survey in the northwestern south china sea nscs over a period of about 1 week in april 2013 the weather research and forecasting wrf model is used to further examine the thermodynamical mechanisms of the mabl s response to the front the wrf model successfully simulates the change in the mabl structure across the front which agrees well with the observations the spatially high pass filtered fields of sea surface temperature sst and 10 m neutral equivalent wind from the wrf model simulation show a tight positive coupling between the sst and surface winds near the front meanwhile the sst front works as a damping zone to reduce the enhancement of wind blowing from the warm to the cold side of the front in the lower boundary layer analysis of the momentum budget shows that the most active and significant term affecting horizontal momentum over the frontal zone is the adjustment of the pressure gradient it is found that the front in the nscs is wide enough for slowly moving air parcels to be affected by the change in underlying sst the different thermal structure upwind and downwind of the front causes a baroclinic adjustment of the perturbation pressure from the surface to the midlayer of the mabl which dominates the change in the wind profile across the front

an apparent double planed benioff zone beneath northern chile resulting from misidentification of reflected phases epicenters of intermediate depth events located by the isc taken together with focal depths determined from the reflected phase pp define a double planed seismic zone beneath northern chile and northwestern argentina the lower zone of seismicity however is the result of a systematic misidentification of sp as pp at many north american seismograph stations the lower seismic plane consists of 14 earthquakes located between 22 and 24 5 s that occurred between 1964 and 1984 depths calculated from pp arrival times reported to the isc are heavily biased by the abundance of reports from high gain stations in western north america reports from these stations place the lower zone events at 125 150 km depth 35 45 km below the main wadati benioff zone short period seismograms produced by the lower zone earthquakes at north american stations show only one clear reflected phase following p which is often incorrectly identified as pp our identification of this phase as sp results in a shallower depth determination that is in agreement with pp and sp arrival time reports from stations in africa and southern europe the absence of a strong pp phase from north american records for the 14 events can be explained by the proximity of its take off angle to a nodal plane on the focal sphere the majority of intermediate depth events in the region lie in the upper plane these earthquakes do produce recognizable pp phases hence no clear evidence exists for a double planed seismic zone in this region

satellite measurements reveal persistent small scale features in ocean winds four year averages of 25 kilometer resolution measurements of near surface wind speed and direction over the global ocean from the quikscat satellite radar scatterometer reveal the existence of surprisingly persistent small scale features in the dynamically and thermodynamically important curl and divergence of the wind stress air sea interaction over sea surface temperature fronts throughout the world ocean is evident in both the curl and divergence fields as are the influences of islands and coastal mountains ocean currents such as the gulf stream generate distinctive patterns in the curl field these previously unresolved features have important implications for oceanographic and air sea interaction research

local and remote atmospheric response to tropical instability waves a global view from space a la nina took place in the equatorial pacific in 1999 and strong tropical instability waves tiws developed causing large meanders of a sea surface temperature sst front between the equator and 3 n high resolution satellite measurements are used to describe the variability of sst surface wind velocity column integrated water vapor cloud liquid water and precipitation associated with these strong tiws in 1999 coherent ocean atmosphere patterns emerge in both the pacific and atlantic revealing rich regional characteristics in the far eastern pacific southeasterly trades strengthen weaken over positive negative sst anomalies apparently due to enhanced reduced mixing with high speed winds aloft in the central pacific we find evidence that sst induced sea level pressure changes also contribute substantially to wind fluctuations similar sst wind covariability also exists in the southern hemisphere along 2 s but the wind variability induced by unit sst anomaly is much larger than that north of the equator in the central pacific where the equatorial front is broad the northern sst pattern has a large meridional scale and reaches as far north as 6 n further to the north in the intertropical convergence zone itcz where local sst anomalies are small significant variability is found in clouds and precipitation which is further correlated with surface wind convergence in the atlantic tiw signals in sst are strongly trapped near the equator but they induce significant remote response in the itcz which takes a more southern position than its pacific counterpart and thus more susceptible to tiw influence

role of the gulf stream and kuroshio oyashio systems in large scale atmosphere ocean interaction a review abstract ocean atmosphere interaction over the northern hemisphere western boundary current wbc regions i e the gulf stream kuroshio oyashio and their extensions is reviewed with an emphasis on their role in basin scale climate variability sst anomalies exhibit considerable variance on interannual to decadal time scales in these regions low frequency sst variability is primarily driven by basin scale wind stress curl variability via the oceanic rossby wave adjustment of the gyre scale circulation that modulates the latitude and strength of the wbc related oceanic fronts rectification of the variability by mesoscale eddies reemergence of the anomalies from the preceding winter and tropical remote forcing also play important roles in driving and maintaining the low frequency variability in these regions in the gulf stream region interaction with the deep western boundary current also likely influences the low frequency variability surface heat fluxes damp the low frequency sst anomalies ove

anisotropy and shear velocity heterogeneities in the upper mantle long period surface waves are used to map lateral heterogeneities of velocity and anisotropy in the upper mantle the dispersion curves are expanded in spherical harmonics up to degree 6 and inverted to find the depth structure the data are corrected for the effect of surface layers and both love and rayleigh waves are used shear wave velocity and shear polarization anisotropy can be resolved down to a depth of about 450 km the shear wave velocity distribution to 200 km depth correlates with surface tectonics except in a few anomalous regions below that depth the correlation vanishes cold subducted material shows up weakly at 350 km as fast s wave anomalies in the transition region a large scale pattern appears with fast mantle in the south atlantic s anisotropy at 200 km can resolve uprising or downwelling currents under some ridges and subduction zones the pacific shows a nw se fabric

ocean frontal effects on the vertical development of clouds over the western north pacific in situ and satellite observations abstract a suite of shipboard and satellite observations are analyzed and synthesized to investigate the three dimensional structure of clouds and influences from sea surface temperature fronts over the western north pacific sharp transitions are observed across the kuroshio extension ke front in the marine atmospheric boundary layer mabl and its clouds the ocean s influence appears to extend beyond the mabl with higher cloud tops in altitude along the ke front than the surroundings in winter intense turbulent heat release from the ocean takes place on the southern flank of the ke front where the cloud top penetrates above the mabl and reaches the midtroposphere in this band of high cloud tops frequent lightning activity is observed the results of this study suggest a sea level pressure mechanism for which the temperature gradient in the mabl induces strong surface wind convergence on the southern flank of the ke front deepening the clouds there in early summer sea fog frequently occurs on

worldwide variations in the attenuative properties of the upper mantle as determined from spectral studies of short period body waves abstract a worldwide study of short period teleseismic body wave spectra shows that the high frequency falloff rates of spectra are correlated with the tectonic type of the source and receiver regions and with source depth the data indicate in a consistent manner that the main cause for such variations is the lateral variation of q in the upper mantle as well as change of q with depth using the internal consistency checks provided by redundancies in the data set other effects such as crustal site dependent distortion of the spectra source effects and instrument non linearity can be ruled out as significant factors influencing the t estimates obtained the results indicate high attenuation in the upper mantle under tectonic regions and new oceans long period regional attenuation studies indicate similar variations in mantle q among the types of regions mentioned but yield significantly lower q estimates in all areas the short and long period attenuation results can be reconciled only by assuming a frequency dependent q that increases with frequency along all types of paths such that the relative differences in q along various types of paths retain the same sign over the short and long period bands

anisotropic models of the upper mantle long period rayleigh wave and love wave dispersion data particularly for oceanic areas have not been simultaneously satisfied by an isotropic structure in this paper available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy anelastic dispersion sphericity and gravity we assume that the surface wave data represents an azimuthal average of actual velocities thus we can treat the mantle as transversely isotropic the resulting models for average earth average ocean and oceanic regions divided according to the age of the ocean floor are quite different from previous results which ignore the above effects the models show a low velocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studies the correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggestive for most of the earth sh sv in the vicinity of the low velocity zone neat the east pacific rise however sv sh at depth consistent with ascending flow anisotropy is as important as temperature in causing radial and lateral variations in velocity the models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age this layer defines the lid or seismic lithosphere in the pacific the lid thickens with age to a maximum thickness of 50 km this thickness is comparable to the thickness of the elastic lithosphere the lid thickness is thinner than derived using isotropic or pseudo isotropic procedures a new model for average earth is obtained which includes a thin lid this model extends the fit of a prem type model to shorter period surface waves

the p wave upper mantle structure beneath an active spreading centre the gulf of california summary detailed analysis of short period travel time dt d and wave form data reveals the upper mantle structure beneath an oceanic ridge to depths of 900 km more than 1400 digital seismograms from earthquakes in mexico and central america recorded at scarlet yield 1753 travel times and 58 direct measurements of dt d as well as high quality stable waveforms the 29 events combine to form a continuous record section from 9 to 40 with an average station spacing of less than 5 km first the travel times are inverted using the tau method of bessonova et al the resultant model is adjusted to agree with the experimental p values further constraints arise from the observed relative amplitudes of mantle phases which are modelled by trial and error using wkbj synthetic seismograms chapman wiggins model gca which is appropriate for western mexico north of 20 latitude is similar to existing upper mantle models for shield tectonic continental and arc trench regimes below 400 km but differs significantly in the upper 350 km gca velocities are very low in this depth range the model catches up with the others with a very large velocity gradient from 225 to 390 km this well resolved feature is consistent with the shear wave model tna for western north america of grand helmberger the abundant data from 20 to 30 control the detailed shape of the 660 km discontinuity very large velocity gradients lie both above 620 660 km and below 661 680km a 2 8 per cent velocity change

subducted slabs and the geoid constraints on mantle rheology and flow geoid anomalies are primarily the result of the density contrasts driving mantle convection and plate motion the total geoid anomaly resulting from a given density contrast in a convecting earth is affected by the mass anomalies associated with the flow induced deformation of the upper surface and internal compositional boundaries as well as by the density contrast itself these boundary deformations and hence the total gravity field depend on the radial distribution of effective viscosity if the internal density contrasts can be estimated as is the case for subducted slabs useful constraints can be placed on the depth and on the variation of viscosity with depth of the convecting system the degree 4 9 components of the observed long wavelength geoid are highly correlated with those predicted by a density model for seismically active subducted slabs the positive sign of the correlation requires that the effective viscosity increases with depth by a factor of 30 or more the amplitude of the correlation cannot be explained by the density contrasts associated with just the seismically active parts of subducted slabs however the amplitude can be explained if the density contrasts associated with subduction extend into the lower mantle or if old lithosphere is piled up at the base of the upper mantle beneath subduction zones to a thickness in excess of 350 km over horizontal distances of thousands of kilometers mantlewide convection in a mantle that has a viscosity increasing with depth provides a simple explanation of the long wavelength geoid anomalies over subduction zones

a method for the near source anisotropy by the pair event inversion of rayleigh wave radiation patterns summary a novel method is proposed for retrieving the 3 d orientation of axes of symmetry of near source anisotropy by a non linear inversion of observed radiation patterns of seismic displacement spectra of rayleigh waves if faulting is generated within an anisotropic source region body force equivalents for the faulting are in general not a double couple but the sum of three orthogonal dipole forces kosevich kawasaki tanimoto as a result of the third dipole force radiation patterns of rayleigh waves are deformed the deformation amounting to several per cent of those for an isotropic source medium the non linear inversion is carried out to find the optimum fault plane solutions giving the minimum square residual between observed and theoretical radiation patterns in some period range in order to remove effects of heterogeneity along propagation paths a pair event scheme is involved in the inversion which denotes taking spectral amplitude ratios and differential phases of the seismic displacement spectra of the pair events having close hypocentres and different fault plane solutions the uniqueness of the fault plane solutions of the non linear inversion is afforded a proof by the monte carlo experiment the non linear inversion is repeated for some possible types of symmetry of the near source orthotropic anisotropy due to the preferred orientation of olivine crystals as mantle materials square residuals thus obtained are compared with each other to see which orientation gives the minimum the method is applied to pair events which occurred in the anomalous mantle beneath the mid atlantic ridge this leads to a discovery that one type of symmetry of the preferred orientations with a b and c axes aligned vertical parallel to and perpendicular to the trend n11e of the ridge axis respectively is most likely existing in the anomalous mantle

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

cloud response to the meandering kuroshio extension front abstracta unique set of observations on board research vessel r v mirai in april 2010 captured a striking cloud hole over a cold meander of the kuroshio extension ke east of japan as corroborated by atmospheric soundings ceilometer shipboard radiation data and satellite cloud images distinct differences were also observed between the warm meander farther to the north and warm water south of the ke the atmosphere is highly unstable over the warm meander promoting a well mixed marine atmospheric boundary layer mabl and a layer of solid stratocumulus clouds capped by a strong inversion over the warm water south of the ke mabl deepens and is decoupled from the ocean surface scattered cumulus clouds develop as captured by rapid variations in ceilometer derived cloud base the results show that the meandering ke front affects the entire mabl and the clouds such atmospheric response can potentially intensify the baroclinicity in the lower atmosphere

radiosonde observational evidence of the impact of an extremely cold sst spot on a mesoscale anticyclone radiosondes were launched in august 2006 from a research vessel above a spot around the kuril islands between the north pacific and the okhotsk sea characterized by an extremely cold sea surface temperature sst and a large horizontal temperature gradient caused by strong tidal mixing because this cold sst was caused solely by this oceanic process the observed data chiefly reflect the oceanic influence on the atmosphere in this area where the summertime sst is typically lower than in other seas in the same latitude belt a minimum sst of 2 c and a horizontal gradient of 7 c 10 km were observed in august 2006 during the cruise the area was covered by a layer of fog up to about 1000 m thick the following observations reveal the presence of an atmospheric mesoscale anticyclone and a cold dome caused by ocean cooling of the atmosphere the wind direction over the cold spot and the strong gradient region was northeasterly below the altitude of about 500 m in contrast to the southwesterly geostrophic wind and the area of northeasterly wind was characterized by a cold air mass and a high pressure anomaly this ageostrophic wind distribution indicates mesoscale anticyclonic circulation below 500 m the fog layer was also thinner in the northeasterly wind area than in other areas suggesting vertical dry air advection i e a subsidence associated with the mesoscale anticyclone in addition our observational results suggest that the pressure adjustment mechanism can explain this mesoscale circulation

constraints from core reflections on mantle q and density at the core boundary amplitudes and periods of the phases pcp and pcs provide valuable constraints on the mean values of the damping parameter q in the mantle and on the density jump at the mantle core boundary the method is to compare pcp and pcs pulses at a station from the same earthquake to the first order for small to moderate angular distances the two travel paths differ only in the p and s upward legs measurements of clear wave pulses at berkeley and jamestown stations were obtained for earthquakes giving reflections under both continental and oceanic areas amplitude ratios were formed after allowances for geometric spreading the results of comparisons with plausible earth models confirm a density jump at the mantle core boundary of 1 7 the average mantle q estimates under both continental and ocean regions is 650 340 in agreement with results of others from surface waves the best match between the observations and theoretical models occurs when q is assumed to increase with frequency like with also increasing with frequency correlations between observations and model values yield 0 4 1 0 under the oceanic region and 0 3 1 0 under the continental region for wave periods 1 5 seconds the average mantle cut off period 0 5 m 0 7 is consistent with an earlier estimate of sipkin and jordan

an investigation of the regional variations and frequency dependence of anelastic attenuation in the mantle under the united states in the 0 5 4 hz band summary studies of teleseismic p and s wave amplitudes and spectra in the 0 5 4 hz band show large variations in the attenuative properties of the upper mantle under the united states the data indicate that attenuation is greatest under the south western united states including but not confined to the basin and range province the lowest attenuation prevails under the north central shield regions the north eastern part of the country consisting of new england and possibly including a larger area along the eastern seaboard is characterized by moderate attenuation in the mantle the level of the high frequency energy in short period seismic waves and the differences between q values derived from short and long period data indicate that q is frequency dependent the form of frequency dependence of t compatible with the data in the 0 5 4 hz range does not allow a rapid decrease of t with increasing frequency rather it supports a gradual decrease covering the broader 0 1 4 hz range the curves of t versus frequency for shield to shield and mixed shield to western united states type paths are parallel with an average difference of 0 2 s in t in the short period band but may diverge towards the long period band for both curves t p is below 1 s for shield to shield paths t p must be below 0 5 s at 1 hz

double seismic zone in tonga the clear evidence of a double seismic zone beneath japan1 2 has led seismologists to search for other such zones elsewhere because they have been found in few other areas3 6 double seismic zones are thought to be rare and to depend strongly on a peculiar combination of external conditions such as age of the descending slab and the convergence rate 7 we report here a new double seismic zone which has been found beneath the tonga arc8 where the stress state in the subducting slab has been described as strongly down dip compressional7 9 10 this discovery suggests that the double seismic zone is a general feature of subducting slabs and may be found in many other subduction zones

lateral heterogeneity and azimuthal anisotropy of the upper mantle love and rayleigh waves 100 250 s the lateral heterogeneity and apparent anisotropy of the upper mantle are studied by measuring rayleigh and love wave phase velocities in the period range 100 250 s spherical harmonic descriptions of the lateral heterogeneity are obtained for order and degree up to 1 m 10 slow regions are evident at the east pacific rise northeast africa tibet tasman sea southwestern north america and triple junctions in the northern atlantic and indian oceans fast regions occur in australia western pacific and the southern atlantic these features are also found by a completely different analysis based on the backus gilbert method the backus gilbert method also shows that the obtained phase velocities are averaged values within an area of about 2000 km radius and the errors are about 1 of the phase velocity in the zeroth order spherically symmetric earth inversion for azimuthal dependence shows that for low angular order the fast phase velocity directions seem to correlate well with the plate motion vectors however resolution analysis by the backus gilbert method shows that the current data do not have enough resolution for everywhere on the globe only a few regions currently have adequate azimuthal coverage thus confirmation of the above correlation requires a more complete data set

sea level pressure minimum along the kuroshio and its extension abstractatmospheric effects of sea surface temperature sst fronts along the kuroshio and kuroshio extension k ke are investigated by examining spatial characteristics of the climatological sea level pressure slp surface winds and surface heat flux q fields based on an in situ observation dataset a hydrostatic effect of the sst front is observed during the northwesterly monsoon characterized by a westward extending low slp wedge trough slightly south of the peak in q along the k ke ageostrophic surface westerlies crossing slp isobars toward a trough center are found north of the low slp wedge apparently because of the eastward acceleration by the vertical mixing effect this feature of the ageostrophic winds is less pronounced south of it a north south asymmetry arising as vertical mixing accelerates decelerates eastward ageostrophic winds north south of it while the slp trough near the sst front is found nearly year round except for summer its meridional location seasonally migrates pr

kuroshio extension variability and forcing of the pacific decadal oscillations responses and potential feedback abstract a forcing mechanism is sought for the large scale circulation changes in the kuroshio extension region of the western north pacific ocean as inferred by topex poseidon sea surface height ssh data the low frequency signal of the kuroshio extension over the last decade was characterized by a modulation in its zonal mean flow intensity the mean kuroshio extension jet weakened progressively from 1993 to 1996 and this trend reversed after 1997 the ability to simulate the major trends in the observed ssh signals with linear vorticity dynamics leads the authors to conclude that the modulation in the zonal mean jet was remotely forced by wind stress curl anomalies in the eastern north pacific ocean related to the pacific decadal oscillations pdos to be specific the weakening strengthening trend in 1993 96 1997 2001 was caused by westward expansions of negative positive ssh anomalies south of the kuroshio extension and positive negative ssh anomalies north of the kuroshio extension emerg

evidence for sst forced anomalous winds revealed from simultaneous radiosonde launches from three ships across the kuroshio extension front abstractsimultaneous launches of radiosondes were conducted from three research vessels aligned meridionally across a sea surface temperature sst front on the flank of the kuroshio extension the soundings carried out every 2 h over 5 days in early july 2012 provided a unique opportunity in capturing unambiguous data on anomalous easterly winds derived from a pronounced meridional sst gradient the data indicate that a meridional contrast in surface heat fluxes from the underlying ocean enhanced the air temperature anomaly across the sst front which was observed from the surface up to 300 m altitude correspondingly high and low pressure anomalies that reached 800 m altitude formed on the north and south sides of the sst front respectively these temperature and pressure anomalies were maintained even during the passage of synoptic scale disturbances although the free tropospheric winds are overall westerly winds below the 1000 m level were easterly due to geostrophic anomalies driven by the northw

aspherical earth structure from fundamental spheroidal mode data free oscillation data reveal heterogeneity in the earth s mantle whose geographical pattern is dominated by spherical harmonics of angular degree two and correlates well with the hydrostatically referenced geoid the heterogeneity can be modelled as localized in the transition zone 420 670 km depth and may be related to a large scale component of mantle convection

the state of stress in subducting slabs as revealed by earthquakes analysed by moment tensor inversion abstract we have used a data set of earthquakes whose mechanisms have been studied here or elsewhere by moment tensor inversion to confirm some earlier ideas concerning the state of stress in subducting slabs the moment tensor method offers the advantages of speed and objectivity over earlier methods usually based exclusively on first motion data deep earthquakes below 300 400 km tend to have compression axes aligned with the dip of the subducting slab the behavior of intermediate earthquakes from 70 to 300 km is less clear there is some evidence for down dip tension but the alignment is not as obvious as it is in the case of the compression axes of deep events tonga shows a tendency toward down dip compression at intermediate depths but other deep extending slabs as well as shallow extending slabs slabs with maximum depths shallower than 300 km seem to be closer to down dip tension

extremal bounds on the seismic velocities in the earth s mantle summary based on global travel time constraints of the function p lee johnson the confidence region for the lower mantle p and s velocity profiles have been determined an exact method bessonova et al is used to compute the extremal bounds on velocity bounds on the lower mantle p velocity have an average resolution of 70 km in the depth range of 800 2900 km the average bound width is 0 14 km s 1 at the 97 per cent confidence level bounds on the lower mantle s velocity have an average resolution of 85 km in the depth range 850 2900 km and an average width of 0 13 km s 1 these results indicate that significant differences exist among the published velocity models and that the bounds can be used to discriminate among them the confidence regions are computed with an assumed upper mantle velocity model and are therefore subject to small baseline adjustments in velocity the introduction of approximate bounds on the upper mantle p increases the lower mantle bound width by 30 per cent for the p velocity in this case one obtains constraints on the absolute velocity function

frequency dependence of q in the mantle underlying the shield areas of eurasia part iii the q model summary a large set of teleseismic body wave data covering a broad range in frequency was analysed to determine the frequency arid depth dependence of q for p and s waves under the northern shield areas of eurasia based on numerous f estimates for p and s waves covering the seismic band between 0 02 and 8 hz a q model of the eurasian shield was constructed the data require a model in which q increases with frequency and which is characterized by q values in the upper mantle that are generally higher than those of global average models the model with the best fit includes a minimum in q between about 100 and 200 km depth and high q values on the order of thousands throughout most of the deeper mantle these results are generally consistent with proposed models of attenuation as a thermally activated process which is influenced by the temperature and pressure in the earth preliminary results suggest that t under tectonic regions is higher than t under shield regions for all frequencies over the 0 02 to 8 hz frequency range suggesting that q varies regionally as well as with frequency and depth

velocity structure in the izu bonin seismic zone and the depth of the olivine spinel phase transition in the slab in this study a method is presented for determining the in situ elastic wave velocities of slabs simultaneously with the relative relocations of earthquakes the method is an extended arrival time difference atd scheme that incorporates a realistic model several assumptions are made about the characteristics of ray paths in and around the slab in order to take advantage of the realism of the model without completely sacrificing the simplicity inherent in the atd technique the errors introduced by these approximate rays are estimated by comparing them with more exact rays calculated with a three dimensional ray tracing routine in general the comparisons suggest that these errors are usually much less than 0 1 s the inverse method is tested on the same set of hypothetical data the results of these tests show that the parameters that influence the arrival time differences the most are the amplitude of the slowness anomaly within the slab and the azimuths and takeoff angles for rays leaving the master event the arrival time differences are relatively insensitive to the other parameters describing the slab strike dip half width and the position of the master event which implies that the scheme is fairly insensitive to the particular choice of analytic function to describe the slowness variation within the slab convergence of the inverse routine is rapid in the tests usually less than five iterations are required before a stable solution is reached it appears that coupling between solutions for slab parameters and ray directions is insignificant unlike the standard atd approach solutions for hypocenters and velocities are not directly coupled in this scheme although well located events are required to insure that the hypocenters are not unduly biased by variations in structure once the velocity structure of the slab is determined that information can be used routinely by this scheme to relocate less well recorded events this method was applied to arrival time data from earthquakes located between 200 and 600 km depth in the izu bonin subduction zone structure in the 200 300 km depth range could not be resolved and results in the 500 600 km depth range proved to be too sensitive to noise data from events between 27 n and 31 n show that p wave velocities within the slab from 400 to 500 km depth are 4 6 higher than those of the ambient mantle between 300 and 400 km depth the slab structure varies regionally north of about 32 5 n the p wave velocity within the slab is 3 4 higher than ambient from 180 to 375 km depth in contrast the velocities south of 32 5 n increase from 6 7 higher than ambient in the 375 410 km depth range to 8 10 higher in the 325 375 km depth range and appear to be 9 higher than ambient in the 270 325 km depth range the determination of the high velocities in this region between 325 and 375 km depth proved to be independent of the selection of data and of the choice of starting model above 325 km depth however the velocity determinations are somewhat dependent on the choice of starting model as a result of this dependence no upper bound on the depth of the high velocities could be resolved a plausible explanation for the exceptionally high p wave velocities within the slab south of 32 5 n is that the olivine spinel phase change boundary is elevated in this part of the slab while north of 32 5 n it is not significantly elevated it is not known if the phase change is elevated south of 31 n but the velocities between 400 and 500 km depth in this region imply that it is not depressed the high velocity zone south of 32 5 n lies in an area that marks the beginning of a seismic gap increasing in breadth to the south between deep and shallow seismicity the dip of the slab also becomes gradually steeper to the south of this region in contrast the lower velocities north of 32 5 n occur in a region where the seismicity is fairly continuous and is aligned along a shallow dipping plane if the seismic gap south of 32 5 n represents a region of high velocity then the increasingly vertical dip of the slab in the south could be due to a substantial gravitational force provided by the excess mass extending above the ambient olivine spinel phase boundary the decreasing width of the gap to the north suggests that the evolution of the izu bonin seismic zone has been governed by a propagating instability from the south

a simple model of the 1982 83 californian el nino steric height steric height anomaly sea level and sea level anomaly show that the 1940 41 and the 1982 83 californian el nino events were resonant responses of the california current to the expansion and intensification of the aleutian low and decrease in strength of the north pacific high in both cases the subsurface anomalies were dynamically produced by onshore transport of subarctic water and a downward tilt of the inshore thermocline sea surface temperature anomalies however resulted from thermodynamic as well as dynamic processes most previous californian el nino or anti el nino events probably were resonant or anti resonant responses of the seasonal cycle of the california current to anomalous large scale atmospheric forcing

double seismic zones kinematics the kinematics of a double seismic zone of subducting lithosphere at an intermediate depth is studied a simple geometrical argument shows that the strain rate due to unbending of subducting lithosphere can be as large as 10 15 s 1 and large enough to account for the seismic strain rate in this depth range the geometrical unbending of subducting lithosphere in the mantle and the presence of a double seismic zone there can be therefore considered essentially equivalent phenomenon we model a double seismic zone required from this unbending in order to investigate what constraint the presence of a double seismic zone can place on the properties of the descending lithosphere the thickness of a double seismic zone is controlled by the thermal structure and the rheological properties of the subducting slab a preliminary result for the double seismic zone beneath tohoku japan indicates a possibility that the currently available flow law of dry olivine does not properly describe the double seismic zone or at least presents some inconsistency in our knowledge of the mechanical properties e g thermal structure rheology of oceanic lithospheres

geometric effects of global lateral heterogeneity on long period surface wave propagation long period rayleigh waves from iranian earthquakes have large amplitude asymmetries between minor arc and major arc arrivals e g r 2 and r 3 at digital stations in the azimuth range n20 w to n60 e these asymmetries are as large as a factor of 2 at a period of 256 s and persist to periods greater than 300 s in some cases the entire rayleigh wave group arrival spanning periods from 100 to 300 s is either uniformly enhanced in amplitude or diminished to such a degree that the group arrival appears to be missing the amplitude anomalies are generally not accompanied by significant phase anomalies the irregular azimuthal distribution of the amplitude asymmetries and their occurrence for events with different focal mechanisms and epicentral separations of several hundred kilometers preclude an explanation of these observations by source complexity events in the mediterranean and nepal do not produce similar amplitude asymmetries at the same stations the anomalies are thus most likely due to focusing and defocusing propagation effects as a preliminary investigation of the effects of lateral heterogeneity of upper mantle velocity structure on long period surface wave amplitudes surface wave ray tracing calculations are performed using recently proposed global phase velocity distributions dramatic deviations from great circle paths are predicted for long propagation paths e g r 3 the particular spatial distribution of lateral velocity gradients around a given source location determines whether substantial amplitude asymmetries will be observed between minor arc and major arc arrivals and whether these will persist for sequential great circle orbits the 200 s period amplitude asymmetry observed at kip for the iranian source region r 2 4 r 3 is well predicted by the ray tracing results the absence of this anomaly for the other source regions is also predicted other observed anomalies are not all well predicted but it is clear that geometric effects can contribute significantly to the observed variations of rayleigh and love wave amplitudes this is the probable explanation for the instability of q estimates made from surface waves other source regions producing large surface wave amplitude anomalies include japan and southeastern alaska

covariations of sea surface temperature and wind over the kuroshio and its extension evidence for ocean to atmosphere feedback abstract satellite microwave measurements are analyzed revealing robust covariability in sea surface temperature sst and wind speed over the kuroshio extension ke east of japan ocean hydrodynamic instabilities cause the ke to meander and result in large sst variations increased reduced wind speeds are found to be associated with warm cold sst anomalies this positive sst wind correlation in ke is confirmed by in situ buoy measurements and is consistent with a vertical shear adjustment mechanism namely an increase in sst reduces the static stability of the near surface atmosphere intensifying the vertical turbulence mixing and bringing fast moving air from aloft to the sea surface south of japan the kuroshio is known to vary between nearshore and offshore paths these paths are very persistent and can last for months to years as the kuroshio shifts its path coherent wind changes are detected from satellite data in particular winds are high south of tokyo when the kuroshio takes the near

geoid anomalies in a dynamic earth in order to obtain a dynamically consistent relationship between the geoid and the earth s response to internal buoyancy forces we have calculated potential and surface deformation love numbers for internal loading these quantities depend on the depth and harmonic degree of loading they can be integrated as green functions to obtain the dynamic response due to an arbitrary distribution of internal density contrasts spherically symmetric self gravitating flow models are constructed for a variety of radial newtonian viscosity variations and flow configurations including both whole mantle and layered convection we demonstrate that boundary deformation due to internal loading reaches its equilibrium value on the same time scale as postglacial rebound much less than the time scale for significant change in the convective flow pattern by calculating relaxation times for a series of spherically symmetric viscous earth models for uniform mantle viscosity the geoid signature due to boundary deformations is larger than that due to internal loads resulting in net negative geoid anomalies for positive density contrasts geoid anomalies from intermediate wavelength density contrasts are amplified by up to an order of magnitude geoid anomalies are primarily the result of density contrasts in the interior of convecting layers density contrasts near layer boundaries are almost completely compensated layered mantle convection results in smaller geoid anomalies than mantle wide flow for a given density contrast viscosity stratification leads to more complicated spectral signatures because of the sensitivity of the dynamic response functions to model parameters forward models for the geoid can be used to combine several sources of geophysical data e g subducted slab locations seismic velocity anomalies surface topography to constrain better the structure and viscosity of the mantle

decadal variability in the kuroshio oyashio extension simulated in an eddy resolving ogcm abstract through analysis of a hindcast integration of an eddy resolving quasi global ocean general circulation model decadal variability in the kuroshio oyashio extension region is investigated with particular emphasis on that of the subarctic oyashio and the kuroshio extension ke fronts the ke front is deep and is accompanied by a sharp sea surface height ssh gradient with modest sea surface temperature sst gradient in contrast the subarctic front is shallow and is recognized as a zone of tight gradient in sst but not ssh as a decadal scale change from a warm period around 1970 to a cool period in the mid 1980s those fronts in the model migrate southward as observed and the associated pronounced cooling is confined mainly to those frontal zones reflecting the distinctive vertical structure of the fronts the mixed layer cooling is the strongest along the subarctic front whereas the subsurface cooling and the associated salinity changes are most pronounced along the ke front concomitan

north pacific cloud feedbacks inferred from synoptic scale dynamic and thermodynamic relationships abstract daily satellite cloud observations and reanalysis dynamical parameters are analyzed to determine how midtropospheric vertical velocity and advection over the sea surface temperature gradient control midlatitude north pacific cloud properties optically thick clouds with high tops are generated by synoptic ascent but two different cloud regimes occur under synoptic descent when vertical motion is downward during summer extensive stratocumulus cloudiness is associated with near surface northerly wind while frequent cloudless pixels occur with southerly wind examination of ship reported cloud types indicates that midlatitude stratocumulus breaks up as the boundary layer decouples when it is advected equatorward over warmer water cumulus is prevalent under conditions of synoptic descent and cold advection during winter poleward advection of subtropical air over colder water causes stratification of the near surface layer that inhibits upward mixing of moisture and suppresses cloudiness until a

aspherical structure of the core mantle boundary from pkp travel times maps of aspherical structure in the vicinity of the core mantle boundary have been constructed from a tomographic analysis of p df and p ab travel times in the distance range 150 180 these maps reveal long wavelength features not previously detected by mantle tomography the peak to peak amplitude of these features is on the order of 1 s in vertical travel time too large to be explained by conventional thermal boundary layer models or dynamically supported topography on the core mantle boundary we hypothesize the existence of one or more chemical boundary layers whose large scale accumulations on the surface of the core may in some ways be analogous to continents at the earth s surface

atmospheric response to zonal variations in midlatitude sst transient and stationary eddies and their feedback midwinter storm track response to zonal variations in midlatitude sea surface temperatures ssts has been investigated using an atmospheric general circulation model under aquaplanet and perpetual january conditions zonal wavenumber 1 sst variations with a meridionally confined structure are placed at various latitudes having these sst variations centered at 308n leads to a zonally localized storm track while the storm track becomes nearly zonally uniform when the same sst forcing is moved farther north at 408 and 508n large small baroclinic energy conversion north of the warm cold sst anomaly near the axis of the storm track near 408n is responsible for the large small storm growth the equatorward transfer of eddy kinetic energy by the ageostrophic motion and the mechanical damping are important to diminish the storm track activity in the zonal direction significant stationary eddies form in the upper troposphere with a ridge trough northeast of the warm cold sst anomaly at 308n heat and vorticity budget analyses indicate that zonally localized condensational heating in the storm track is the major cause for these stationary eddies which in turn exert a positive feedback to maintain the localized storm track by strengthening the vertical shear near the surface these results indicate an active role of synoptic eddies in inducing deep tropospheric scale response to midlatitude sst variations finally the application of the model results to the real atmosphere is discussed

diffracted sp generated under the australian shield diffracted sp is found to be generated under the australian shield by deep seated tonga honshu and bonin events this seismic phase is set up at the moho as a p head wave by a critically incident upgoing sv wave at an epicentral distance of around 50 the simple source time history inferred from p or sh particle motion and the absence of source structure effects on sv waveforms from a deep source suggest a diffracted sp wave for the explanation of distorted sv waves recorded at the mundaring station the polarity of this phase arriving immediately after direct sv indicates a p type of wave excluding the possibility of other type of s waves like scs using a wkbj spectral method for sv wave propagation synthetic seismograms for the direct sv and diffracted sp are computed with some modification of the p velocity model by mathur and the s velocity model presented by goncz and cleary for the australian shield synthetics produce the distinctive interference between direct sv and diffracted sp seen in the data the arrival time difference between direct s and diffracted sp is sensitive to the p velocity of the upper mantle results of the analysis reveal higher p velocities in the upper mantle along the east west path than along the north south path from mundaring station the analysis of teleseismic sv waveforms and the diffracted sp phase is a new and useful technique for determining regional variations in upper mantle p velocity structure

atmospheric pressure response to mesoscale sea surface temperature variations in the kuroshio extension region in situ evidence several research cruises were conducted across the kuroshio extension front to examine the low level atmospheric responses to mesoscale variations in sea surface temperature sst surface meteorological observations including sea level pressure slp and sst were collected at two moored buoys that were located on either side of the kuroshio extension and from a research vessel as it moved between the two buoys during the various cruises spatial perturbations in slp along the ship transects calculated by subtracting moored buoy slp from that of the moving ship tend to be positive negative where sst is lower higher on spatial scales of about 100 km and the magnitude of these slp perturbations near the sst front can exceed 1 0 hpa radiosonde data also show that the atmospheric boundary layer thins thickens over lower higher sst although the contribution of across track component in the wind cannot be calculated the along track component of divergence suggests low level convergence over higher sst the thermally induced pressure gradient is important in the momentum budget suggesting that sea breeze like local circulations formed over the sst fronts indeed the pressure adjustment mechanism can sometimes dominate even on a scale of 100 km although it is not always observed the time scale in which the boundary layer thickness adjusted to sst is estimated to be 1 day or less

observations of body wave multipathing from broadband seismograms evidence for lower mantle slab penetration beneath the sea of okhotsk we present observations of anomalously broad and complex sh waveforms from two deep focus earthquakes in the southern kurils to digital world wide standard seismograph network and regional seismic test network stations in north america by making use of broadband three component seismograms and relying on a variety of phases one can limit the class of possible explanations for these phases in particular it is shown that the anomalous arrivals are not due to source complexity near receiver structure a triplication from a lower mantle velocity gradient a low q zone in the mid lower mantle or shear wave splitting we show that these arrivals correspond to relatively fast paths and have enhanced amplitudes indicating that they are most probably caused by multipathing due to interaction with a high velocity lower mantle feature below the source region we examine the hypothesis that this feature may be a lower mantle extension of the kuril slab ray tracing experiments show that multipathing is indeed expected along the azimuths corresponding to the north american stations used in this study for a realistic slab model observations of reversed polarity arrivals are consistent with such an explanation where it appears that two rays comprising the arrival emerge from different points on the focal sphere one test of this explanation is that slab induced multipathing should not be seen along back of slab oceanic azimuths examinations of seven events for which the stations are in this azimuth range do not exhibit the same broadening and complexity of the sh waveforms identification of slab induced multipathing associated with deep focus events has two important consequences first it appears to require slab penetration beyond the 650 km discontinuity at least 300 400 km into the lower mantle under the sea of okhotsk second these phases may act as a contaminant when attempting to study other seismic phenomena such as discontinuities low q zones near receiver structure or source complexity

the depths of the deepest deep earthquakes the maximum depth of seismic activity is a fundamental observation providing a constraint on models of mantle dynamics although most recent investigations of mantle seismicity and dynamics state that seismicity extends to about 700 km focal depths of 720 km have been reported for large earthquakes as well as depths greater than 800 km for small events we have examined focal depths of events in several catalogs and conclude that 1 the deepest reliable focal depths are at about 670 680 km and events with focal depths beneath 600 km occur in several widely separated geographic regions 2 observations supporting focal depths exceeding 680 km are usually few poor or inconsistent 3 the reduction of seismic activity beneath about 650 km is quite abrupt however we cannot determine whether activity stops completely at 670 680 km or the maximum size of events decreases gradually beneath 650 km with magnitudes of 6 5 7 0 occasionally occurring at 650 km magnitudes of 5 5 6 0 at 680 km 4 0 4 5 at 695 km etc several models can explain the absence of seismic activity in the lower mantle two models are consistent with the abrupt termination of activity at about 650 680 km in widely separated areas a barrier which resists penetration by the subducting lithosphere or a phase transition which modifies the properties of the subducted material as it goes into the lower mantle

influence of kuroshio sst front in the east china sea on the climatological evolution of meiyu rainband the influence of kuroshio sea surface temperature sst front in the east china sea ecs on the temporal evolution of climatological meiyu rainband was investigated using a suite of high resolution satellite observations and a reanalysis dataset from 2000 to 2011 during the northward seasonal march of meiyu rainband from the warmer flank of the sst front to the colder flank the climatological rainband strength weakened substantially despite large scale environment became more conducive to intensify precipitation a sharp reduction in occurrence frequency of precipitation with relatively shallower depth and smaller intensity was responsible for the weakening of meiyu rainband during the northward migration of meiyu rainband individual precipitation events became deeper and more intensive and the contribution of convective precipitation to the rainband was enhanced associated with the seasonal northward extension of high convective instability region over the ecs the characteristics of meiyu rainband evolution were generally supported by cloud observations when meiyu rainband was located on the warmer flank of the sst front local enhanced mean surface wind convergence and variance of convergence at synoptic timescale by the warm sst of the kuroshio favored strong surface convergence that may trigger precipitation a detailed moisture budget analysis revealed that the major part of moisture for meiyu precipitation was supplied by low level wind convergence with much smaller contribution from moisture advection the variation of climatological precipitation associated with meiyu northward migration depended on sst modulation of both surface evaporation and low level moisture convergence over the ecs

uppermantle anisotropy and the oceanic lithosphere rayleigh wave and love wave dispersion data for oceanic paths cannot be satisfied by an isotropic uppermantle and it is incorrect to invert these two datasets independently for separate isotropic structures available phase and group velocity data are inverted for oceanic structure as a function of age taking into account anelastic dispersion sphericity and anisotropy the resulting models are quite different from previous results which ignore the above effects and the extra parameters involved in proper anisotropic inversion the models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age and an anisotropic low velocity zone with an age dependent anisotropy the lid or seismic lithosphere reaches a maximum thickness of 50 km which is about one half the thickness obtained in previous isotropic or pseudo isotropic inversions the seismic lithosphere therefore may be comparable in thickness to the elastic or flexural lithosphere raising the possibility that both are controlled by effects other than temperature stress and time such as mineralogy crystal orientation or partial melting the velocities in the low velocity zone are higher than inferred by previous surface wave studies

interdecadal variability of the early summer surface heat flux in the kuroshio region and its impact on the baiu frontal activity 1 in the kuroshio region kr the early summer surface heat flux shf exhibits a rapid increase around 1990 as a climate shift which is rooted in the oceanic interdecadal variability in the north pacific the sea surface temperature sst in the kr where sst is largely controlled by subsurface ocean circulations is positively correlated with the local upward shf the positive shf anomalies in the 1990s reinforced the baiu frontal activity with an atmospheric large scale meridional dipole in the western north pacific as such the oceanic interdecadal variability has an impact on the atmospheric circulation through coherent sst and shf variations even in early summer in the kr

deep seismicity and modes of deformation in tonga subduction zone the geometry of deep 400 km earthquakes in the subducting western edge of the pacific plate when related to the local distribution of seismic activity reveals a complex pattern of planes of shear failure enabling the modes of deformation by which the descending plate shortens and thickens to be identified the deepest part of the slab is displaced laterally suggesting that it fails to penetrate the discontinuity at 670 km

western boundary currents and frontal air sea interaction gulf stream and kuroshio extension abstract in the northern hemisphere midlatitude western boundary current wbc systems there is a complex interaction between dynamics and thermodynamics and between atmosphere and ocean their potential contribution to the climate system motivated major parallel field programs in both the north pacific kuroshio extension system study kess and the north atlantic climate variability and predictability clivar mode water dynamics experiment climode and preliminary observations and analyses from these programs highlight that complexity the gulf stream gs in the north atlantic and the kuroshio extension ke in the north pacific have broad similarities as subtropical gyre wbcs but they also have significant differences which affect the regional air sea exchange processes and their larger scale interactions the 15 yr satellite altimeter data record which provides a rich source of information is combined here with the longer historical record from in situ data to describe and compare the curr

decadal variability of the kuroshio extension observations and an eddy resolving model hindcast abstract low frequency variability of the kuroshio extension ke is studied using observations and a multidecadal 1950 2003 hindcast by a high resolution 0 1 eddy resolving global ocean general circulation model for the earth simulator ofes in both the ofes hindcast and satellite altimeter observations low frequency sea surface height ssh variability in the north pacific is high near the ke front an empirical orthogonal function eof analysis indicates that much of the ssh variability in the western north pacific east of japan is explained by two modes with meridional structures tightly trapped along the ke front the first mode represents a southward shift and to a lesser degree an acceleration of the ke jet associated with the 1976 77 shift in basin scale winds the second mode reflects quasi decadal variations in the intensity of the ke jet both the spatial structure and time series of these modes derived from the hindcast are in close agreement with observations a linear rossby wave

ocean tidal cooling effect on summer sea fog over the okhotsk sea 1 ocean tide is a periodic phenomenon of the rise and fall of the sea level that depends on the bathymetry and positions of the moon and sun relative to the earth in the okhotsk sea the ocean tide causes strong vertical mixing in the upper ocean generating rich structures in summer sst with extraordinarily cold patches on kashevarov bank along the kuril islands northeast of the terpeniya peninsula and inside shelikhov bay the present study analyzes and synthesizes a suite of ship board and satellite observations and numerical simulations to investigate the ocean tidal cooling effect on summer sea fog over the okhotsk sea over the tide induced cold patches atmospheric stability increases and surface wind weakens markedly possibly through suppressed atmospheric vertical mixing our analysis of ship board observations reveals frequent sea fog occurrence over the cold patches with a maximum exceeding 70 along the kuril islands in july august numerical simulations with the weather research and forecasting wrf model support that the cold patches cool air temperature decelerate surface wind and form a strong surface inversion layer up to 0 5 km high creating favorable conditions for sea fog occurrence the wrf simulation without the tidal cooling effect reduces sea fog occurrence by more than 20 over cold patches illustrating the importance of sst products for climate models

a worldwide comparison of predicted s wave delays from a three dimensional upper mantle model with p wave station corrections abstract this paper is a comparison on a worldwide scale between p station corrections deduced from isc residuals dziewonski and anderson and synthetic s station corrections computed using a three dimensional upper mantle model obtained from mantle wave data woodhouse and dziewonski the upper mantle s velocity model is described by a spherical harmonic expansion up to degree 8 the p station corrections are smoothed using a similar expansion in order that the two data sets can be compared correlations between p station corrections t p and synthetic s station corrections t s relevant to various depths of integration indicate that a station correction contains information about structures down to at least 670 km for this depth of integration the correlation coefficient of the two data sets is 0 59 the slope a of the relation t s a t p b obtained for the worldwide distribution of stations is in good agreement with results of previous regional studies using direct readings of p and s arrival times a 3 61 0 13 an analysis of regional variations of the relation t s a t p b is carried out on the basis of two published global tectonic patterns okal jodan results for oceanic regions are not reliable due to the lack of data on continental areas a significant difference appears between mountains a 2 7 0 3 and shields a 4 5 0 4 for okal s pattern a 5 7 1 5 for jordan s pattern the largest a value for shields rules out an explanation by partial melting as proposed in previous studies thermal heterogeneities lead to low a values undulations of the lithosphere asthenosphere boundary appear to be the most feasible explanation of the high slope beneath shields they are also able to explain the range of variation of the station corrections the lowest values of the station corrections correspond to a total vanishing of the low velocity zone beneath the oldest shields for mountains the mean values of the station corrections as well as the low a value can be accounted for by a slight increase of poisson s ratio together with a significant density increase

an anomalous low velocity region above the deep earthquakes in the japan subduction zone p wave travel time residuals for local intermediate and deep focus earthquakes are studied to infer a velocity model of the asthenosphere beneath the southern okhotsk sea and the western japan sea tectonically both regions belong to plate subduction zones large positive travel time anomalies are observed at stations above the deepest earthquakes consideration of source path and receiver effects leads to a conclusion that within the asthenosphere there is a lower velocity region below about 300 km depth with velocities about 5 10 below the jeffreys bullen velocity model

the dynamical and thermal structure of deep mantle plumes abstract if the interpretation of the d layer at the base of the mantle as a thermal boundary layer with a temperature increment in the order of 800 k is correct then the formation of deep mantle plumes to vent material from it appears inevitable we demonstrate quantitatively that the strong temperature dependence of viscosity guides the upward flow into long lived chimneys that are 20 km in diameter near the base of the mantle and decrease in width with progressive upward softening and partial melting of plume material the speed of flow up the axis of the plume is correspondingly fast 1 6 m y 1 at the base and 4 8 m y 1 at 670 km depth thermal diffusive spreading of a heated plume is compensated by a slow horizontal convergence of mantle material toward the chimney in response to the lower pressure there this convergence which contributes only a small increment to the flux of material up the plume also serves to throttle the flow in the chimney the global plume mass flux necessary to transport 1 6 10 12 w of core heat upward through the mantle is 1 8 10 6 kg s 1 at its base plume material is probably still significantly below its solidus or eutectic temperature but substantial partial melting is very likely as it rises we speculate that a small fraction of this fluid component eventually emerges at the surface in hot spots with the fate of the remainder being unknown the behaviour and properties of d and of plumes are closely coupled not only are plumes a necessary consequence of a thermal boundary layer but their existence is impossible without that layer

observations of shear coupled p waves teleseismic sv waves couple to p waves in the lithosphere in several ways p waves converted from discontinuities in the lithosphere precede the main sv arrival as small amplitude sp precursors large amplitude p waves follow the main sv arrival after conversion by reflection at the free surface and post critical reflection from a discontinuity in the lithosphere spdiff denotes a converted p wave diffracted along the underside of the crust when a teleseismic sv wave strikes it from below near the critical angle of incidence we observed several of these shear coupled p waves on seismograms of deep earthquakes recorded at broadband seismic stations rstn in north america for these paths large amplitudes relative to sv characterize the lithospheric multiple near 50 with amplitudes decreasing rapidly beyond 60 calculation of synthetic seismograms indicate that a post critical reflection from a discontinuity at 70 80 km depth where compressional velocity increases abruptly to about 8 5 km s produce the largest amplitude p arrival the observations of these shear coupled p waves presents a previously untapped source of information about the fine structure of the upper mantle

summertime evolution of decadal sea surface temperature anomalies in the midlatitude north pacific abstract to clarify the summertime evolution of decadal sea surface temperature sst anomalies and related physical processes in the midlatitudes of the north pacific numerical solutions of a three dimensional bulk mixed layer model are analyzed focusing on the contribution of the net shortwave radiative forcing at the sea surface a quantitative heat budget analysis for the ocean mixed layer relating to late 1980s decadal sst change reveals that the decadal sst anomalies decay from late spring to early summer over the entire midlatitudes of the north pacific this quasi seasonal decay of the decadal sst anomalies is controlled by an anomalous local thermal damping i e anomalous surface heat fluxes from midsummer to early autumn the anomalous net shortwave radiation flux associated with a meridional shift of the storm track acts to induce strong seasonal damping of the decadal sst anomaly in the northern kuroshio oyashio extension region in contrast in the north of the subtropical frontal region

large scale dynamics of the meiyu baiu rainband environmental forcing by the westerly jet abstract meiyu baiu is the major rainy season from central china to japan brought by a zonally elongated rainband from june to mid july large scale characteristics and environmental forcing of this important phenomenon are investigated based on a reanalysis dataset the meiyu baiu rainband is accompanied by a trough of sea level pressure horizontal shears and sharp moisture gradients near the surface a westerly jet tilted northward with height and large northeastward moisture transport from the south the analysis here reveals the westerly jet as an important culprit for meiyu baiu along the rainband mean ascending motion corresponds well with a band of warm horizontal temperature advection in the midtroposphere throughout summer this adiabatic induction of upward motion originates from the advection of warm air by the westerlies from the eastern flank of the tibetan plateau the ascending motion both induces convection and is enhanced by the resultant condensational heating the westerly jet anch

structure of the earth mantle and core the deep interior structure of the earth has been extensively analyzed using a wide variety of seismic phases and techniques during the last four years most studies have emphasized quantitative three dimensional mapping of the lateral velocity heterogeneity of the mantle and core these aspherical velocity variations are believed to be direct manifestations of thermal and compositional heterogeneity associated with convective processes a first generation of global models for the lateral velocity variations in the deep earth has been produced providing tantalizing images of large scale structures suggestive of a non steady state thermal convection system the upper 400 km of the mantle has the strongest lateral velocity variations of up to 10 for shear velocity surface wave analyses that do not require a priori regionalizations have demonstrated that there is a strong association between surface tectonic provinces and the uppermost mantle velocity variations thus the thermal and convective state of the upper 200 km of the mantle can be reliably interpreted in the context of plate tectonics the upper mantle models support the contention that continents have deep roots with differences in velocity structure from oceanic and active tectonic regions extending as deep as 400 km very long wavelength lateral velocity variations of a few percent have been detected in the transition zone at depths from 400 to 670 km as well as throughout the lower mantle these deep seated variations have little correspondence to surface tectonics and efforts to interpret their nature are just beginning the lowermost 200 km of the mantle d region has lateral velocity fluctuations comparable to those in the upper mantle and evidence has been presented for the presence of a sizable velocity discontinuity at the top of the d layer a combined thermal and compositional boundary layer roughly mirroring the lithosphere is a likely explanation for this anomalous zone the core mantle boundary appears to have significant 10 km long wavelength topography presumably sustained by dynamic stresses from deep mantle convection the inner core may have strong lateral heterogeneity or axially symmetric anisotropy suggesting a complex thermal and compositional state significant progress has been made in characterizing the frequency dependence of anelastic attenuation in the mantle in the short period body wave band models for teleseismic p wave attenuation operators have converged with t values of 0 7 1 0 s appropriate at 1 hz and t values of 0 4 0 6 s appropriate at 4 hz regional variations of attenuation are slowly being mapped out as well

atmospheric manifestation of tropical instability wave observed by quikscat and tropical rain measuring mission observations from two new spaceborne microwave instruments in 1999 clearly reveal the atmospheric manifestation of tropical instability waves north of the pacific equatorial cold tongue a unique zonal temporal band pass filter enables the isolation of the propagating signals and the determination of their phase differences the phase differences between the propagation of wind and sea surface temperature sst signals observed from space and the vertical wind profiles measured from a research ship are consistent with the hypothesis that the coupling between wind and sst is caused by buoyancy instability and mixing which reduces the wind shear in the atmospheric boundary layer the coupling causes higher evaporative cooling over the warm phase and infers a negative thermal feedback

early syn rift evolution in the west cameros basin upper jurassic nw iberian range spain and pedogenetic calcretes in early syn rift alluvial systems upper jurassic west cameros basin northern spain discussion the brezales formation originally defined as the senora de brezales formation platt 1986 1990 see also martin closas and alonso millan 1998 clemente vidal 2010 comprises a syn rift alluvial fan succession displaying strong lateral and vertical facies changes sacristan horcajada et al 2015 primarily relate these variations to drainage area and basin scale tectonics they suggest that source area lithology can be considered as a constant factor in this regard it is not clear why sacristan horcajada et al fail to discuss the work of platt 1995 which showed how sedimentation and clastic supply was strongly controlled by subcrop geology as well as kilometer and outcrop scale faulting deposition across the area recorded progressive erosion and unroofing of the underlying succession and varying subcrop beneath the complex cimmerian unconformity in the south of the basin a progradational coarsening upwards facies trend noted by sacristan horcajada 2015 reflects local reworking of upper oxfordian sandstones at the unconformity leading to the deposition of red bed sandstones in the basal section of the brezales formation only later did erosion of deeper lying marine jurassic limestones result in the deposition of conglomerates an example occurs at espejon where the brezales formation is not absent as suggested by sacristan horcajada et al 2015 but features a basal

multiple scs travel times and attenuation beneath mexico and central america multiple scs phases recorded for the june 19 1982 e1 salvador earthquake m s 7 0 are analyzed to determine whole mantle attenuation and upper mantle travel time anomalies beneath mexico central america and northern south america recordings from the ultra long period seismographs at pasadena and berkeley and the sro station anmo provide eight scs n arrivals with 15 bouncepoints concentrated within mexico the whole mantle qscs for these paths is estimated as 145 n 27 in the frequency range 8 to 40 mhz and the average scsn scs n jb residual atsc s at a period of 50 sec is 5 sec eight scs n phases of similar periods recorded at gdsn stations in south america yield a qscs estimate of 232 n 89 and atsc s 3 9 sec for paths beneath central america and cs 93 n 17 and atsc s 0 3 sec for paths beneath northern south america these results indicate that the variations in travel times and attenuation beneath continental regions are as pronounced as differences reported between old oceanic and stable shield regimes

oceanic influence on the baiu frontal zone in the east china sea a high resolution transect of atmospheric soundings across the kuroshio current in the east china sea was conducted onboard a ship in june 2012 with the objective of analyzing the influence of the complex sea surface temperature sst distribution on the baiu frontal zone bfz expendable bathythermograph castings and continuous surface meteorological observations were also examined two distinct mesoscale atmospheric fronts characterized by changes of wind direction in the lower troposphere and surface air temperature were found in the bfz one northern atmospheric front was observed around the sst front in relation to a warm water tongue extending from the kuroshio a high sst region around the northern atmospheric front enhances unstable near surface stratification and intensifies turbulent heat flux they help modify the marine atmospheric boundary layer in the bfz the other southern atmospheric front was at the southern end of the bfz intense evaporation over the kuroshio and moisture transport by southerly winds were important in forming the conditionally unstable air masses in the lower troposphere of the bfz

atmospheric boundary layer structure and turbulence during sea fog on the southern china coast abstractsmall scale turbulence has an essential role in sea fog formation and evolution but is not completely understood this study analyzes measurements of the small scale turbulence together with the boundary layer structure and the synoptic and mesoscale conditions over the life cycle of a cold advection fog event and a warm advection fog event both off the coast of southern china the measurement data come from two sites one on the coast and one at sea these findings include the following 1 for cold advection fog the top can extend above the inversion base but formation of an overlaying cloud causes the fog to dissipate 2 for warm advection fog two layers of low cloud can merge to form deep fog with the depth exceeding 1000 m when strong advection of warm moist air produces active thermal turbulence mixing above the thermal turbulence interface 3 turbulence near the sea surface is mainly thermally driven for cold advection fog but mechanically driven for warm advection fog 4 the mo

the backus gilbert approach to the three dimensional structure in the upper mantle i lateral variation of surface wave phase velocity with its error and resolution summary the backus gilbert method is applied to obtain the phase velocity variations on a sphere from the measured phase velocity narrow peak kernels with radii of about 2000 km are obtained for almost everywhere on the sphere the phase velocity results are thus interpreted as an average within such regions the most trouble comes from the antipodal peak in the resolution kernel this is evaluated as contamination and is incorporated in the error estimation the total error which is a root mean square of contamination from the antipodal peak and statistical error estimated from the data covariance matrix is about 1 per cent of the phase velocity in the average earth model which is the preliminary reference earth model prem however there is about a factor of 2 variation of errors on the sphere maximum variations of phase velocity are about 3 4 per cent of the phase velocity in the average earth model and thus there still remain anomalies which exceed estimated errors the estimated errors correspond to one standard deviation under the assumptions of uncorrelated gaussian distribution for high confidence interval they show that statistically significant anomalies are scarce for the current data set generally love wave phase velocity maps show more resolved features than rayleigh wave maps and we can see in high confidence maps fast velocities in old oceans and old continents and slow velocities in tectonically active regions like the east pacific rise and various back arc regions

magnitude bias in the great basin and its implications for explosion magnitude versus yield estimates comparison of teleseismic p wave delays in the vicinity of the central nevada test site in hot creek valley nevada with p delay data over a wider region in the great basin shows that upper mantle speeds under hot creek valley stations are higher than the average for the great basin as a whole but lower than those beneath pahute mesa these observations indicate that the caldera complex in hot creek valley may have a high speed root similar to that proposed to exist beneath the silent canyon caldera at pahute mesa however the hot creek valley anomaly is not as strong as the pahute mesa anomaly these high speed upper mantle structures cause defocusing for outgoing rays resulting in a shadow zone at the distance range corresponding to many european stations the shadow zone caused by the pahute mesa structure is much more pronounced and consequently magnitudes of pahute mesa explosions can be underestimated relative to the magnitude of hot creek valley explosions of similar yield when magnitude versus yield relationships developed using pahute mesa data are applied to other areas such as hot creek valley they can result in a biased estimate of yield

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 review of crust and upper mantle structure studies of the snake river plain yellowstone volcanic system a major lithospheric anomaly in the western u s a abstract the snake river plain yellowstone volcanic system is one of the largest basaltic volcanic field in the world here there is clear evidence for northeasterly progression of rhyolitic volcanism with its present position in yellowstone many theories have been advanced for the origin of the snake river plain yellowstone system yellowstone and eastern snake river plain have been studied intensively using various geophysical techniques some sparse geophysical data are available for the western snake river plain as well teleseismic data show the presence of a large anomalous body with low p and s wave velocities in the crust and upper mantle under the yellowstone caldera a similar body in which compressional wave velocity is lower than in the surrounding rock is present under the eastern snake river plain no data on upper mantle anomalies are available for the western snake river plain detailed seismic refraction data for the eastern snake river plain show strong lateral heterogeneities and suggest thinning of the granitic crust from below by mafic intrusion available data for the western snake river plain also show similar thinning of the upper crust and its replacement by mafic material the seismic refraction results in yellowstone show no evidence of the low velocity anomalies in the lower crust suggested by teleseismic p delay data and interpreted as due to extensive partial melting however the seismic refraction models indicate lower than normal velocities and strong lateral inhomogeneities in the upper crust particularly obvious in the refraction data are two regions of very low seismic velocities near the mallard eake and sour creek resurgent domes in the yellowstone caldera the low velocity body near the sour creek resurgent dome is intepreted as partially molten rock together with other geophysical and thermal data the seismic results indicate that a sub lithospheric thermal anomaly is responsible for the time progressive volcanism along the eastern snake river plain however the exact mechanism responsible for the volcanism and details of magma storage and migration are not yet fully understood

downdip tensional earthquakes beneath the tonga arc a double seismic zone characteristics of seismicity at intermediate depth beneath the tonga arc are studied special attention is paid to newly identified downdip tensional events because the dominance of downdip compression has been known in this area we reexamine the relatively shallow 70 km downdip tensional events reported in the harvard centroid moment tensor solutions by modeling bodywave waveforms of world wide standard seismograph network seismograms and conclude that they are in fact intraplate downdip tensional events furthermore these downdip tensional events are consistently located below and seaward of downdip compressional events and appear to constitute a double seismic zone the result of a relative relocation technique applied to these earthquakes also supports this observation which was originally based on routinely determined epicenters the subducting slab beneath the tonga arc has been considered as a prototype of a compressionally loaded slab the existence of a double seismic zone in tonga therefore would suggest that double seismic zones located at intermediate depth in subducting slabs are more common than previously thought

upper mantle anisotropy a preliminary model seismic anisotropy in the upper mantle can be explained by crystallographic mineral alignment achieved through dislocation motion the physical mechanism of mineral alignment requires upper mantle shear flow which reorients and aligns minerals by dislocation glide and climb governed by the dominant glide system of each mineral the dominant glide systems are assumed to be 100 0l0 for olivine and 001 100 for the pyroxenes these yield a predominantly orthorhombic fabric with the olivine 100 and the pyroxene 001 axes aligned in the upper mantle flow direction and the olivine 010 and the pyroxene 100 axes aligned normal to the upper mantle flow plane these glide systems have a threshold temperature of enhanced mobility of 1100 1200 k which yields a solid state thermally defined lithosphere asthenosphere boundary in an olivine pyroxene mantle consistent with recent seismic determinations of the thickness of the lithosphere mantle anisotropy due to mineral alignment is then actively maintained below this boundary asthenosphere and mesosphere and is a fossil state above this boundary lithosphere we use the dominant glide systems to establish the crystallographic orientation of olivine and pyroxene in calculating the maximum seismic anisotropy of two petrologic models pyrolite and piclogite for the upper mantle by an extrapolation of single crystal anisotropic mineral elastic properties to a depth of 400 km the real earth seismic anisotropy will be bound by the limits of maximum anisotropy from perfect mineral alignment and minimum anisotropy isotropy from random mineral alignment the seismic anisotropy of the upper 220 km is best represented by the pyrolite model which reduces to quasi hexagonal symmetry with the unique axis in the direction of mantle flow the lehmann discontinuity is conjectured to be due to a change in composition from pyrolite to piclogite and therefore may represent a change in anisotropy the piclogite model has orthorhombic symmetry distinctly different from that of the pyrolite the piclogite anisotropy model can appear quasi isotropic when measured by transverse isotropy parameterization if the mantle flow is mainly horizontal with a horizontal shear plane that is the shear flow gradient duh dr dominates

a seismic q profile for the lower mantle from short period p waves a few studies of the quality factor q the ratio of peak to dissipated energies of seismic waves in the earth s mantle have used a limited data set of spectral ratios for body waves1 3 most estimates of q have come from the analysis of surface waves and free oscillations but use of such data to estimate q in the deep mantle suffers from a significant lack of resolution to improve this resolution in the lower mantle we have compiled a large data base of digital short period p wave recordings from underground nuclear explosions we have analysed p and pp waves to develop a set of t seismic travel time divided by effective path q station corrections corresponding to the upper mantle beneath each station and a t distance profile the t distance profile is inverted to determine a q depth profile for the lower mantle a thermal activation model used to interpret the q depth profile and to estimate a lower mantle geotherm enables a thermal boundary layer to be identified in the lowermost 200 km of the mantle this boundary layer is large enough to be indicative of mantle convection driven by heat flow from the earth s core

distribution and modification of north pacific intermediate water in the kuroshio oyashio interfrontal zone abstract a multiship ctd survey was conducted in the kuroshio oyash interfrontal zone in the area of 30 41 n 140 e 180 from may to june 1992 to examine the distribution modification process and formation site of north pacific intermediate water npiw low salinity oyashio water and high salinity kuroshio water merge along the kuroshio extension just off the east coast of japan and together flow eastward eastward geostrophic transport and salinity across the kuroshio strong current indicate that the mixture of the kuroshio and oyashia waters along the kuroshio extension can produce new npiw transport estimate suggests that the new npiw bifurcates into the interfrontal zone and into the recirculation of the subtropical gyre a salinity minimum structure can he also created due to the isopycnal mixing along the kuroshio extension between the oyashio and kuroshio waters which have different salinity and vertical velocity structures the low salinity oyashio water seen along the oyashio branches and t

the influence of sea surface temperature gradients on stratiform cloudiness along the equatorial front in the pacific ocean abstract satellite observations of visible cloudiness and sea surface temperature sst are used to test the hypothesis that the configuration of cool low level winds blowing across a sharp sst front in the equatorial eastern pacific gives rise to stratiform clouds on the warm downstream side of the front the results show that there is a maximum in low clouds over the equatorial front during the cold season of 1988 when the front and cross isotherm winds were strong the low cloud maximum was reduced in the warm el nino year of 1987 consistent with the weakening of the front instability waves along the equatorial front were pronounced during the summer and autumn of 1988 the results show a strong association between visible cloud and the sst waves with enhanced reduced cloudiness in the warm troughs cold crests of the waves

shear wave polarization anisotropy in the upper mantle beneath honshu japan shear wave polarization anisotropy in the wedge portion of the upper mantle between a subducting plate and the earth s surface is investigated using three component seismograms of intermediate depth and deep earthquakes recorded at 14 local stations in honshu japan eighty nine high quality seismograms were selected from a period of 3 years the data used in this study are restricted such that incidence angles are smaller than the critical angle of 30 to the earth s surface in order to avoid phase shifts in the shear wave train to find directions of the maximum and minimum velocities in split shear waves where shear waves are resolved into two phases with the maximum time separation each set of the two horizontal component seismograms is rotated in the horizontal plane the split shear waves thus obtained are again recombined after the correction of anisotropy and the anisotropy corrected particle motion is compared with the focal mechanism for a cross check of the observed anisotropy directions of the maximum axes are plotted on azimuthincidence angle stereograms at each station the stereograms and the cross sections of seismic ray paths show that 1 the anisotropic material is distributed at intermediate location between earthquake sources and receiving stations and 2 the anisotropic region is separated into two parts one in the north of the present study area with the polarization of the maximum velocity shear wave trending 0 to 30 from the north north anisotropy and the other in the south with it trending 90 to 120 south anisotropy the maximum time delays between the two shear waves along a vertical seismic ray is about l s for both the anisotropic regions the horizontal extent of the anisotropic area in the north is 50 km at depths of 50 to 150 km perhaps prevalent in west honshu however the depth of anisotropic material is not well constrained because of insufficient coverage of seismic ray paths and angles if we assume the vertical extent of the anisotropic material to be 100 km the maximum velocity contrast would be 4 if we adopt a crack alignment model for the observed anisotropy cracks are inferred to be distributed vertically trending 0 to 30 in the north and 90 to 120 in the south if we assume an olivine alignment model olivine crystals are inferred to be aligned in the north with the a axis of the slip direction trending 0 to 30 and the slip plane normal to the b axis being vertical and in the south anisotropy with the axis trending 90 to 120 and the slip plane being horizontal

observations of marine atmospheric boundary layer transitions across the summer kuroshio extension abstract the baiu and kuroshio extension ke fronts both zonally oriented and nearly collocated east of japan are the dominant summertime features of the atmosphere and ocean respectively over the midlatitude northwest pacific an atmospheric sounding campaign was conducted on board the r v roger revelle during the 2005 summer transects of soundings across the ke front are analyzed to study its effects on the atmosphere along with continuous surface meteorological and ceilometer cloud base observations while the ke front remained nearly stationary during the cruise the baiu front displayed large meridional displacements that changed wind direction across the ke front the presence of sharp sea surface temperature sst gradients anchored by the ke enhanced the thermal and moisture advection causing substantial changes in the marine atmospheric boundary layer mabl structure when the baiu front was displaced north of the ke front southwesterly winds advected warm humid air from the subtropics

evidence of a lower mantle shear velocity discontinuity in s and ss phases teleseismic recordings of direct s and ss body wave phases and their core reflected counterparts scs and sscs from intermediate and deep focus earthquakes are used to analyze the lowermost mantle shear velocity structure beneath alaska a model with a 2 75 shear velocity increase 280 km above the core mantle boundary accurately matches waveform complexi ties in both the s and ss wavetrains variations in source depth produce systematic shifts in the timing of the triplication arrivals between the s and ss travel time branches that are readily ob served in long period wwssn tangential component recordings the systematic range and depth dependence of the observed shifts are well predicted by the discontinuity model and preclude explanations of the waveform complexity as resulting from multi ple ruptures at the source receiver reverberations or near source scattering from slab structure accurate models of the seismic velocity structure in the lower most 200 km of the mantle d region are essential for calcula tions of the thermal history and dynamics of the core and mantle several recent investigations of seismic body waves have indi cated the presence of velocity stratification above the core mantle boundary lay and helmberger 1983 wright et al 1985 while models of long wavelength lateral velocity variations in the lower mantle indicate strong heterogeneities in the d region dziewon ski 1984 clayton and comer 1983 current thermal models indicate a large temperature contrast of about 1000 o between the core and mantle requiring a thermal boundary layer at the base of the mantle jeanloz and richter 1979 loper 1984 this is consistent with the general decrease in velocity gradients observed in the lowermost mantle doornbos 1983 doornbos et al 1986 the combined effects of stratification lateral hetero geneity and decreased velocity gradients complicate interpreta tion of seismic data sampling the d region it is particularly important to resolve whether velocity discontinuities are actually present within d since compositional stratification would strongly affect the thermal boundary layer dynamics as well as the interpretation of the lateral velocity variations this paper presents an analysis of a combination of seismic body waves that is particularly sensitive to the presence of a velocity discontinuity in d lay and helmberger 1983 found evidence for a 2 75 shear velocity discontinuity about 280 km above the core in s waves from intermediate and deep focus earthquakes the long period tangential component seismograms they analyzed show wave form complexities in the distance range 75 o to 95 o that were attributed to a triplication produced by an abrupt velocity in crease this interpretation was criticized by schlittenhardt et al 1985 who argue that such a discontinuity is incompatible with

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

a direct measurement of the distance between a hypocenter in a benioff wadati zone and the slab asthenosphere contact we made a direct measurement of the distance from a hypocenter in the benioff wadati zone to the boundary between the downgoing slab and overlying asthenosphere this was accomplished by identifying a low amplitude p wave reflection off the slab asthenosphere contact which arrives at teleseismic stations several seconds after the initial p arrival the measured delay time after p of the reflected phase shows a consistent azimuthal variation thus eliminating possible source or receiver effects the relative amplitude polarity and delay time of this observed phase are consistent with a model in which the distance between hypocenter and slab asthenosphere contact at this depth is about 38 5 km the event studied was an intermediate depth 181 km earthquake in the southern kuriles which occurred in the lower layer of a double seismic zone our measured distance when compared to the distance between the two seismic zones indicates that the upper layer of seismicity is within 15 km of the slab asthenosphere contact appendix is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington u c 20009 document jb1 010 1 00 payment must accompany order

the dynamical structures of d and deep plumes in a non newtonian mantle the dynamical structures of the d layer and deep mantle plumes have been determined for a mantle with a power law creep rheology generalising recent newtonian analyses the lateral scales of d and plumes are determined by a balance between thermal diffusive thickening and lateral inflow the non newtonian effect of concentrating shear in regions of high stress acts to thicken the region of rapid flow in both d and plumes this effect is nearly counterbalanced by the increased lateral inflow in the non newtonian case resulting in a modest broadening of the lateral scales of the regions of rapid flow these changes are structurally unimportant and the essential physics of core cooling via convective flow in a thin d layer and narrow plumes is remarkably independent of mantle rheology

aspherical heterogeneity of the mantle from phase velocities of mantle waves long period surface waves are used to map the lateral heterogeneity of the upper 100 600 km of the mantle there is good correlation of velocity with surface tectonics and heat flow convergence regions are generally slow for love waves and fast for rayleigh waves back arc basins have slower than average shallow mantle some island arcs show evidence of fast material at greater depth deep seated slow anomalies underlie the red sea afar region of north east africa western north american northern east pacific rise indian ocean triple junction and the tasman sea campbell plateau regions the fastest regions are in the north central australia new guinea and the south atlantic