the dynamics of the extratropical response to madden julian oscillation convection the rossby wave source rws and the corresponding extratropical wave response to tropical convection associated with different phases of the madden julian oscillation mjo is investigated with the dynamical core of a climate model the initial flow is specified to correspond to the boreal winter climatological flow and an imposed tropical heating that is derived from the observed precipitation for all eight mjo phases one key question addressed here is why does the extratropical rossby wave train depart the subtropics at a longitude well to the east of the rws for all eight mjo phases it is found that the extratropical response over the north pacific and north america is almost entirely due to the mjo convection over the western tropical pacific the rws is excited within the first 24 h after the model heating is turned on for mjo phases 1 3 and 8 the rws leads to the development of a cyclonic anomaly over southeast asia via advection of the climatological absolute vorticity by the anomalous divergent wind in the subtropics and by horizontal convergence in the tropics mjo phases 4 7 show opposite features the resulting anomaly is then advected eastward by the climatological zonal wind toward the central pacific after which dispersion into the extratropics and the excitation of a pacific north american teleconnection pattern takes place

which mjo events affect north american temperatures abstracttropical convection from the madden julian oscillation mjo excites and amplifies extratropical rossby waves around the globe this forcing is reflected in teleconnection patterns like the pacific north american pna pattern and it can ultimately result in temperature anomalies over north america previous studies have not explored whether the extratropical response might vary from one mjo event to another this study proposes a new index the multivariate pna mvp to identify variations in the extratropical waveguide over the north pacific and north america that might affect the response to the mjo the mvp is the first combined eof of 20 100 day olr 850 hpa streamfunction and 200 hpa streamfunction over the north pacific and north america the north american temperature patterns that follow each phase of the mjo change with the sign of the mvp for example real time multivariate mjo rmm phase 5 usually leads to warm anomalies over eastern north america this relationship was only found

improvements to regional explosion identification using attenuation models of the lithosphere 1 regional p s amplitudes have been recognized as an effective discriminant between earthquakes and explosions while closely spaced events generally discriminate easily the application of this technique to broad regions has been hampered by large variations in the amplitude of phases due to the attenuation of the crust and upper mantle making use of a recent p wave and s wave attenuation model of the lithosphere we have found that correcting the events using our amplitude methodology significantly reduces the scattering in the earthquake population we demonstrate an application of this technique to station nil using broad area earthquakes and the 1998 indian nuclear explosion using the pn lg discriminant in the 1 2 hz passband we find that the explosion which is lost in the scatter of the earthquakes in the uncorrected discriminant clearly separates by correcting for attenuation structure we see a similar reduction in scatter and separation for the pn sn and pg lg discriminants

frequency dependent lg q within the continental united states frequency dependent crustal attenuation 1 q is determined for seven distinct physiographic tectonic regions of the continental united states using high quality lg waveforms recorded on broadband stations in the frequency band 0 5 to 16 hz lg attenuation is determined from time domain amplitude measurements in one octave frequency bands centered on the frequencies 0 75 1 0 3 0 6 0 and 12 0 hz modeling errors are determined using a delete j jackknife resampling technique the frequency dependent quality factor is modeled in the form of q q 0 f regions were initially selected based on tectonic provinces but were eventually limited and adjusted to maximize ray path coverage in each area earthquake data was recorded on several different networks and constrained to events occurring within the crust m b 3 5 in size a singular value decomposition inversion technique was applied to the data to simultaneously solve for source and receiver terms along with q for each region at specific frequencies the lowest crustal q was observed in northern and southern california where q is described by the functions q 152 37 f 0 72 0 16 and q 105 26 f 0 67 0 16 respectively the basin and range province pacific northwest and rocky mountain states also display lower q and a strong frequency dependence characterized by the functions q 200 40 f 0 68 0 12 q 152 49 f 0 76 0 18 and q 166 37 f 0 61 0 14 respectively in contrast in the central and northeast united states q functions are q 640 225 f 0 344 0 22 and q 650 143 f 0 36 0 14 respectively show a high crustal q and a weaker frequency dependence these results improve upon previous lg modeling by subdividing the united states into smaller distinct tectonic regions and using significantly more data that provide improved constraints on frequency dependent attenuation and errors a detailed attenuation map of the continental united states can provide significant input into hazard map mitigation both scattering and intrinsic attenuation mechanisms are likely to play a comparable role in the frequency range considered in the study

mechanisms for a pna like teleconnection pattern in response to the mjo abstractkinematic mechanisms of the pacific north america pna like teleconnection pattern induced by the madden julian oscillation mjo is examined using an atmospheric general circulation model gcm and a barotropic rossby wave theory observation shows that a negative pna like teleconnection pattern emerges in response to mjo phase 2 forcing with enhanced suppressed convection located over the indian western pacific ocean the gcm simulations show that both forcing anomalies contribute to creating the pna like pattern indian ocean forcing induces two major rossby wave source rws regions a negative region around southern asia and a positive region over the western north pacific wnp the negative rws to the north of the enhanced convection in the indian ocean arises from southerly mjo induced divergent wind crossing the asian jet unexpectedly another significant rws region develops over the wnp owing to refracted northerly divergent wind a ray tracing method demonstrates three different w

the malaguide los reales nappe an example of crustal thinning related to the emplacement of the ronda peridotites betic cordillera abstract the malaga region in southern spain represents a cross section through the continental crust and subcontinental mantle of the westernmost portion of the internal zone of the betic cordillera recent petrological and structural studies carried out in this region show a link between the malaguide complex and the underlying los reales nappe where the ronda peridotites were incorporated as allochthonous slabs the ronda peridotites are covered by the metamorphic sequence of the los reales nappe which consists of acidic granulites migmatites and schists the tectonometamorphic evolution of these granulite facies rocks involves a first high temperature 800 c high pressure 10 kbar metamorphism replaced by high temperature 750 c low pressure 3 5 kbar conditions this strong thermal event which is also recognized in biotite bearing schists of the los reales nappe and even in the overlying malaguide complex developed during an extensional deformation related to the diapiric stage of the ronda peridotite emplacement stretching lineations from the mylonites related to this extensional event are n 110 e in orientation and kinematic criteria show that low grade metamorphic rocks malaguide complex move down on to higher grade ones los reales nappe from west to east consequently we interpret that the malaguide complex and los reales nappe form a single domain of continental crust which was thinned during the emplacement of the ronda peridotites stretching lineations are subparallel to the trend of the betic cordillera and can be integrated in a model of lithospheric transcurrent thinning

a moist linear baroclinic model coupled dynamical convective response to el nino a newly developed linear baroclinic model lbm and its application to the tropical enso teleconnection is described the model based on primitive equations linearized about the observed zonally varying basic state in northern winter involves linear schemes for the cumulus convection and surface sensible and latent heat fluxes referred to as the moist lbm this enables us to solve a steady state response of the coupled dynamical convective system to a given sst anomaly which is fairly different from the conventional dry lbm linear representation of the convection is acceptable for a realistic range of sst anomalies reproducing well the rossby wave train computed in the conventional lbm forced by a tropical heating the moist lbm is used to examine the formation mechanisms of an anomalous low level anticyclone near

atmosphere ocean thermal coupling in the north atlantic a positive feedback in this article it is examined whether a positive atmosphere ocean feedback is found over the north atlantic through a series of general circulation model gcm experiments a 60 year integration of an atmospheric gcm agcm coupled with a 50 m deep motionless ocean was conducted the coupled run was compared with two uncoupled runs one with prescribed mid latitude climato logical sea surface temperatures ssts and the other with daily ssts derived from the coupled experiment the uncoupled atmosphere forces the slab ocean to obtain sst responses in these runs consistent with previous studies the coupled atmosphere ocean fields show interannual variances larger than those in the uncoupled runs due to reduction in the local thermal damping patterns of maximum atmosphere ocean covariability show the north atlantic oscillation nao and tripole sst anomalies both in the coupled and uncoupled fields indicating a dominant role of the atmosphere in generating the sst anomalies on the other hand analyses of the temporal variability in the three runs suggest an active role of sst anomalies in determining the polarity of the air sea coupled variability longer than the interannual time scale a combined analysis of forcing sst upper air height and the response sst anomalies in the uncoupled run identified that a patch of positive sst anomalies in the mid latitude band around 40 n effectively excite the positive phase of the nao which in turn reinforces the tripole sst anomalies this relationship was further confirmed by a nine member ensemble agcm experiment forced by the relevant sst anomalies since the forcing and response sst anomaly patterns bear some resemblance these results manifest positive feedback at work in the coupled atmosphere ocean patterns the processes responsible for this positive feedback were elaborated by a series of linear model experiments the local thermal adjustment of the atmosphere to the sst anomalies results in increased precipitation over the gulf stream region associated diabatic heating applied to a linear baroclinic model yields a positive height response to the east which highly influences the southern part of the nao this stationary response in turn induces a northward deflection in the storm track activity leading to an eddy vorticity feedback that tends to force the positive phase of the nao

fluid circulation related to deformation in the zabargad gneisses red sea rift abstract a fluid inclusion study in relation to textures has been performed on pan african granulite facies gneisses from zabargad island red sea rift egypt the gneiss samples were collected at a maximum distance of 60 m above the contact with mantle peridotites with which they are co structured by a high t plastic deformation during an isothermal decompression starting from conditions estimated at 35 km depth and 850 c base of the pan african crust a first metasomatism of the crustal section during decompression is represented by co2 fluid inclusions trapped at minimum conditions of 15 km depth and 800 c the co2 fluid inclusion planes are controlled in orientation by the high t plastic flow structures but have been subsequently deformed during medium t plastic deformation in quartz the second metasomatism is represented by solid rich aqueous fluid inclusions which were trapped at minimum p t conditions of 3 7 km depth and 450 c corresponding to a very high thermal gradient they trace the introduction either of seawater or of fluids resulting from leaching of the middle miocene evaporites within the gneisses during their residence at a shallow depth below the seafloor two models are proposed in the literature in order to reconstruct the geodynamic history of zabargad island one brueckner h k elhaddad m a hamelin b hemming s kroner a reisberg l seyler m 1995 a pan african origin and uplift for the gneisses and peridotites of zabargad island red sea a nd sr pb and os isotope study j geophys res 100 22283 22297 suggests that most of the decompression p t path is pan african in age and only the aqueous metasomatism is related to the rifting history of the red sea the second nicolas a boudier f montigny r 1987 structure of zabargad island and early rifting of the red sea j geophys res 92 461 474 boudier f nicolas a ji s kienast j r mevel c 1988 the gneiss of zabargad island deep crust of a rift tectonophysics 150 209 227 supposes the existence of an asthenospheric diapir intrusive through the deep pan african crust leading to a continuous deformation event during early rifting of the red sea although it is impossible to date trapping of fluid inclusions and to know with certainty the origin of the fluids our preference is for the second model but slightly modified the high t decompression path traced by co2 fluid inclusions relayed by solid rich aqueous inclusions traces a continuous process of crustal thinning such a continuous path would assign to a single event the thinning and uplift of the deep crust and uppermost lithosphere to shallow basin bottom during the red sea early rifting in such an interpretative model the northern and central peridotite bodies are representative of the uppermost continental lithosphere and only the southern body could belong to an ascending asthenospheric diapir centred on the southeast of zabargad island

role of moist energy advection in formulating anomalous walker circulation associated with el nino 1 the role of meridional moist energy advection in formulating anomalous walker circulation during el nino events is investigated using observational data and linearized gcm during the el nino mature phase the warm pool is extended to the central pacific so that the magnitudes of equatorial sst become uniform over the western central pacific in contrast to the uniform sst distribution over the western central pacific the maximum of equatorial convective activities are zonally displaced from the western to the central pacific that is in line with the fact that the strong anomalous descending motions are located over the western pacific without local negative sst anomalies it is demonstrated here that suppressed convection over the western pacific is associated with cold dry moist energy advection due to low level equatorward winds the meridional cold dry moist energy advection leads the vertical warm wet moist energy advection and adiabatic warming processes descending motion to balance the moist energy budget it is shown that this meridional wind is a part of a cyclonic rossby wave in response to the anomalous convection induced by el nino sst this mechanism suggested here is validated by using a linearized gcm the model results show the downward branch of the anomalous walker circulation over the western pacific is significantly reduced when the moist energy advection is not allowed

attenuation of lg in the western us using the usarray 1 the unprecedented breadth and density of the usarray allows us to resolve lateral variations of 1 hz lg attenuation to 0 5 degrees over much of the western united states we collected over 31 000 lg amplitudes from 547 events and 408 stations of the initial usarray footprint two dimensional tomographic inversion yielded q ranging from 60 to 550 with a variance reduction of 47 relative to the best fit constant q model q 155 q is low over most of the region with lowest values associated with recent volcanic activity and active shear zones high q is found in older stable crust notably the colorado and columbia plateaus while smaller islands of high q are associated with batholiths including the sierra nevada peninsular and bitterroot ranges the western mojave and okanogan highlands as well as other areas of competent crust such as the harcuvar range and two topographically bounded blocks in the basin and range

mjo initiation in the real time multivariate mjo index abstractmadden julian oscillation mjo initiation in the real time multivariate mjo rmm index is explored through an analysis of observed case studies and composite events specific examples illustrate that both the dates of mjo initiation and the existence of the mjo itself can vary substantially among several well known mjo indices depending on whether the focus is on convection or circulation composites of primary mjo initiation events in which the rmm index rapidly increases in amplitude from a non mjo state to an mjo state are presented and are supplemented by two case studies from the 1985 86 winter season results illustrate that for primary mjo initiation events in the indian ocean rmm phase 1 slowly eastward propagating 850 hpa 200 hpa easterly westerly anomalies over the indian ocean precede the amplification of the rmm index by at least 10 days while suppressed convection over the western pacific ocean precedes the amplification by 5 days these local eastern hemispheric prede

dominant patterns of winter time intraseasonal surface air temperature over the conus in response to mjo convections the dominant patterns of the intraseasonal surface air temperature sat over the contiguous united states conus during wintertime december march are investigated in the period of 1979 2014 in the present study the first two leading modes revealed by the empirical orthogonal function eof analysis sufficiently represent the patterns by explaining nearly 80 of the total variance the eof1 mode has a monopole pattern with large loadings in the central north conus while the eof2 has a dipole pattern with loadings of opposing signs in the northwestern and southeastern conus the monopole pattern of the eof1 has a significant lead lag correlation with the eof2 dipole pattern these dominant patterns are traced back to the convective anomalies of the madden julian oscillation mjo which has eight phases characterized by the revised real time multivariate mjo index the connections are established dynamically by rossby wave trains propagating from the mjo convections to north america specifically the monopole warming eof1 is well developed by lagging about two pentads from enhanced mjo convections during phase 4 over the maritime continent as the wave sources the dipole pattern eof2 of warm west cool east starts to develop during mjo phase 7 with enhanced convections over the western pacific and reaches a maximum about two pentads later such dynamic lead lag relationships on intraseasonal time scales are revealed by both diagnostic analysis and numerical experiments using a linear baroclinic model which are potentially useful for predicting intraseasonal variations in sat over the conus

a case for the use of 3d attenuation models in ground motion and seismic hazard assessment abstract attenuation relationships that are used to characterize estimated ground motion often ignore details of the earth s highly variable 3d velocity and attenuation structure increasingly available attenuation models can be used to refine the expected ground motions first some tests are performed to look at the effect of the variability in several parameters such as crustal attenuation upper mantle attenuation and crustal thickness a concrete example is then provided using the results of a recent crust and upper mantle attenuation model of the middle east variations in 1 hz spectral accelerations of 30 40 are found simply from the same event recorded in different directions because overall regional variability is expected to be even higher this effect seems significant enough to be accounted for in strong ground motion estimates and seismic hazard assessment this has the potential to account for some of the smaller scale amplitude variations not considered using broadly applied 1d attenuation relationships

interannual variability of the spring atmospheric heat source over the tibetan plateau forced by the north atlantic ssta data analysis indicates that the interannual variability of the spring atmospheric heat source over the tibetan plateau tp depends largely on the intensity of the overlying subtropical westerly jet wj which is closely related to the early spring february march april sea surface temperature anomaly ssta tripole pattern over the north atlantic i e the ssta tripole pattern with a warm core to the southeast of newfoundland and two cold cores to the south of iceland and southeast of bermuda respectively such an ssta pattern can be regarded as a response to the atmospheric forcing of the preceding january february march north atlantic oscillation numerical experiment results from both linear baroclinic model with an idealized diabatic heating profile and an atmospheric general circulation model with prescribed ssta forcing demonstrate that the warm core alone of the tripole pattern can stimulate a steady downstream rossby wave train which further intensifies the spring wj over the tp as a result a positive anomaly of surface sensible heating occurs over most parts of the tp whereas the precipitation and corresponding latent heating is characterized by a seesaw pattern with a positive negative anomaly over the northern southern tp meanwhile the air column radiation cooling effect is enhanced to a certain degree over the plateau further analysis suggests that the early spring ssta over the north atlantic may exert a seasonal lagged impact upon the east asian summer monsoon by modulating the thermal forcing over the tp

zabargad peridotite evidence for multistage metasomatism during red sea rifting new analyses of rare earth elements rees and abundances of k rb sr ba th u ta and hf in peridotites from zabargad island red sea indicate that light ree enriched amphibole peridotites in the northern and central bodies have undergone a complex multistage metasomatic history during red sea rifting the metasomatism is partly attributed to the passage of alkalic basalts through the mantle lithosphere which possibly occurred during the early continental rift history of the red sea the metasomatism also results from the interaction of the uppermost lithosphere with hydrous crustal fluids released from thinning continental crust the last metasomatic event is associated with the development of an oceanic hydrothermal system in the red sea after the continental breakup the available data also suggest that the zabargad peridotites represent pieces of pan african lithospheric mantle the northern and central bodies pierced by asthenospheric material the southern body

an early miocene age for a high temperature event in gneisses from zabargad island red sea egypt mantle diapirism in the last decade much attention has been focused on the tectonothermal and geochemical evolution of rocks outcropping on zabargad island red sea egypt this island though of limited size 4 km has an almost unique geodynamic setting 50 kmwest of the red sea axis and reveals a close association of mafic ultramafic rocks with a metamorphic gneiss complex understanding the geodynamic evolution of the island was expected to elucidate the processes operating in a young rift setting environment and crust mantle interface tectonics since the first work of bonatti et al 1981 however genetic models have been limited by the the scant data on the timing of juxtaposition between the peridotites and the gneisses as well as the nature of the mafic ultramafic rocks one interpretation considers the peridotites as an asthenospheric mantle diapir intruding a pan african continental crust during the early stages of the red sea opening e g nicolas et al 1987 the fewattempts todate the time of intrusion of the peridotites are consistent with this view nicolas et al 1985 for example inferred a k ar age of 23 7 myr for amphiboles extracted fromanamphibolite this value concurs with the more precise ar ar age 18 7 1 3 myr given by hornblende extracted from a pegmatoidal pocket of a coarse grained hornblendite in harzburgite trieloff et al 1997 both ages are identical within errors of a 18 4 1 0myr zircon age obtained by oberli et al 1987 although there is a good agreement between the three methods oberli s zircon value has been presented only in an abstract thus making it difficult to properly evaluate k ar and ar ar ages have also been questioned for decoupling of parent and daughter nuclides villa 1990 or for their meaning in terms of a geological event uplift hydrothermalism or emplacement age due to their known susceptibility to low grade events an alternative interpretation considers the peridotites and the gneisses to be panafrican brueckner et al 1988 1995 and that juxtaposition of both rock types occurred shortly after differentiation from a common depleted mantle source 700 ma this is apparently supported by the so called slap errorchron resulting from alignment of whole rock peridotite samples and cpx separates in the sm nd isochron diagram brueckner et al 1988 this model however has been challenged in two recent papers on the grounds of fluid inclusion boullier et al 1997 and noble gases and argon chronological studies trieloff et al 1997 in both models gneisses are seen to represent remnants of the pan african continental deep crust left behind during opening of the red sea rift pan african ages for the metamorphic gneiss complex are well established by sm nd and rb srmineral isochrons lancelot and bosch 1991 brueckner et al 1995 as well as by a zircon pb pb evaporation date brueckner et al 1995 from a felsic gneiss located a few hundred metres from the contact zone between the central peridotite body and the gneisses these ages however provide no constraints on the timing of juxtaposition of gneisses and peridotites in order to solve this fundamental problem and because of the known resistance to alteration of the mineral zircon we focused on the u pb dating of single zircon grains extracted from a felsic gneiss located at the contact zone with the central peridotite body

unraveling the teleconnection mechanisms that induce wintertime temperature anomalies over the northern hemisphere continents in response to the mjo abstractsignificant extratropical surface air temperature variations arise as a result of teleconnections induced by the madden julian oscillation mjo the authors elucidate the detailed physical processes responsible for the development of temperature anomalies over northern hemisphere continents in response to mjo induced heating using an intraseasonal perturbation thermodynamic equation and a wave activity tracing technique a quantitative assessment demonstrates that surface air temperature variations are due to dynamical processes associated with a meridionally propagating rossby wave train over east asia a local hadley circulation causes adiabatic subsidence following mjo phase 3 to be a main driver for the warming meanwhile for north america and eastern europe horizontal temperature advection by northerlies or southerlies is the key process for warming or cooling a ray tracing analysis illustrates that rossby waves with zonal wavenumbers 2 and 3 influence the surface warming over north amer

the global atmospheric circulation response to tropical diabatic heating associated with the madden julian oscillation during northern winter abstractthe detailed dynamical mechanisms of the upper tropospheric circulation response to the madden julian oscillation mjo convection are examined by integrating a primitive equation model a series of initial value calculations with the climatological boreal winter background flow forced by the mjo like thermal forcing successfully capture the key aspects of the observed circulation response to the mjo convection this suggests that a large fraction of mjo related circulation anomalies are direct responses to tropical heating in both the tropics and extratropics and can be largely explained by linear dynamics it is found that mjo like dipole heatings not only intensify tropical upper tropospheric anomalies but also weaken them at certain regions because of the interaction between equatorial kelvin and rossby waves the rossby wave train primarily excited by horizontal divergence of upper level perturbation flow propagates northeastward and then heads back to the equator in this way rossby wave act

the influence of the madden julian oscillation on canadian wintertime surface air temperature abstract using the homogenized canadian historical daily surface air temperature sat for 210 relatively evenly distributed stations across canada the lagged composites and probability of the above and below normal sat in canada for different phases of the madden julian oscillation mjo in the winter season are analyzed significant positive sat anomalies and high probability of above normal events in the central and eastern canada are found 5 15 days following mjo phase 3 which corresponds to an enhanced precipitation over the indian ocean and maritime continent and a reduced convective activity near the tropical central pacific on the other hand a positive sat anomaly appears over a large part of northern and northeastern canada about 5 15 days after the mjo is detected in phase 7 an analysis of the evolution of the 500 hpa geopotential height and sea level pressure anomalies indicates that the canadian sat anomaly is a result of a rossby wave train associated with the tropical convection anomal

on the three dimensional propagation of stationary waves abstract a locally applicable nonzonally averaged conservation relation is derived for quasi geostrophic stationary waves on a zonal flow a generalization of the eliassen palm relation the flux which appears in this relation constitutes it is argued a useful diagnostic of the three dimensional propagation of stationary wave activity this is illustrated by application to a simple theoretical model of a forced rossby wave train and to a northern hemisphere winter climatology results of the latter procedure suggest that the major forcing of the stationary wave field derives from the orographic effects of the tibetan plateau and from nonorographic effects diabatic heating and or interaction with transient eddies in the western north atlantic and north pacific oceans and siberia no evidence is found in the data for wave trains of tropical origin forcing by the orographic effects of the rocky mountains seems to be of secondary importance

the global response to tropical heating in the madden julian oscillation during the northern winter a life cycle of the madden julian oscillation mjo was constructed based on 21 years of outgoing long wave radiation data regression maps of ncep ncar reanalysis data for the northern winter show statistically significant upper tropospheric equatorial wave patterns linked to the tropical convection anomalies and extratropical wave patterns over the north pacific north america the atlantic the southern ocean and south america to assess the cause of the circulation anomalies a global primitive equation model was initialized with the observed three dimensional 3d winter climatological mean flow and forced with a time dependent heat source derived from the observed mjo anomalies a model mjo cycle was constructed from the global response to the heating and both the tropical and extratropical circulation anomalies generally matched the observations well the equatorial wave patterns are established in a few days while it takes approximately two weeks for the extratropical patterns to appear the model response is robust and insensitive to realistic changes in damping and basic state the model tropical anomalies are consistent with a forced equatorial rossby kelvin wave response to the tropical mjo heating although it is shifted westward by approximately 20 longitude relative to observations this may be due to a lack of damping processes cumulus friction in the regions of convective heating once this shift is accounted for the extratropical response is consistent with theories of rossby wave forcing and dispersion on the climatological flow and the pattern correlation between the observed and modelled extratropical flow is up to 0 85 the observed tropical and extratropical wave patterns account for a significant fraction of the intraseasonal circulation variance and this reproducibility as a response to tropical mjo convection has implications for global medium range weather prediction copyright 2004 royal meteorological society

time variation of 500 mb height fluctuations with long intermediate and short time scales as deduced from lag correlation statistics abstract the time variation of northern hemisphere wintertime 500 mb height fluctuations with short intermediate and long time scales is investigated using lag correlation patterns derived from time filtered data fluctuations with short 2 5 6 day periods time scales propagate eastward at a rate consistent with the notion of a steering level around 700 mb which supports an interpretation in terms of baroclinic waves the mobile teleconnection patterns associated with the intermediate 10 30 day periods time scales exhibit a pattern of time variation suggestive a rossby wave dispersion with a predominance of southward dispersion from middle latitudes into the tropics the geographically fixed teleconnection patterns characteristic of the longer time scales do not show a well defined pattern of time variation but their horizontal structure resembles that of the fastest growing normal mode associated with barotropic instability of the climatological mean wintertime flow

deep and high temperature hydrothermal circulation in the oman ophiolite petrological and isotopic evidence a systematic search for evidence of high temperature hydrous alteration within the gabbros of the samail ophiolite oman shows that most of the gabbros have been affected by successive stages of alteration starting above 975 c and ending below 500 c sr and o isotopic analyses provide constraints on the nature and origin of the fluids associated with these alteration events massive gabbros dykes and veins and their associated minerals depart from mid ocean ridge basalt morb source magma signatures 87sr 86sr 0 7032 and depleted 18o 10 a second group of samples including massive gabbros and high temperature dykes and veins is characterized by lower water rock ratios in the range of 3 5 these samples display a high temperature hydrothermal alteration related to seawater ingression the main fluid channels may be sub millimetre sized microcracks with a dominantly vertical attitude which constitute the recharge hydrothermal system whereas the dykes and veins represent the discharge part this model requires that these dykes have been generated by hydration of the crystallizing gabbros via seawater penetration near the internal wall of the magma chamber

regional variation of lg coda q in the continental united states and its relation to crustal structure and evolution records from broadband digital stations have allowed us to map regional variations of lg coda q across almost the entire united states using a stacked ratio method we obtained estimates of q 0 lg coda q at 1 hz and its frequency dependence for 218 event station pairs those sets of estimates were inverted using a back projection method to obtain tomographic images showing regional variations of q 0 and q 0 is lowest 250 300 in the california coastal regions and the western part of the basin and range province and highest 650 750 in the northern appalachians and a portion of the central lowlands intermediate values occur in the colorado plateau 300 500 the columbia plateau 300 400 the rocky mountains 450 550 the great plains 500 650 the gulf coastal plain and the southern portion of atlantic coastal plain 400 500 and the portions of the central lowlands surrounding the high q region 500 550 the pattern of q 0 variations suggests that the united states can be divided into two large q provinces one province spans the area from the rocky mountains to the atlantic coast is tectonically stable and exhibits relatively high q 0 the other extends westward from the approximate western margin of the rocky mountains to the pacific coast is tectonically active and exhibits low q 0 the transition from high to low lg coda q in the western united states lies further to the west than does an upper mantle transition for q and electrical resistivity found in earlier studies the difference in q 0 between the western and eastern united states can be attributed to a greater amount of interstitial crustal fluids in the west regions of moderately reduced q within the stable platform often occur where there are accumulations of mesozoic and younger sediments reduced q 0 in the southeastern united states may not be due to anelasticity but may rather be explained by a gradational velocity increase at the crust mantle boundary that causes shear energy to leak into the mantle

the influence of critical moho reflections on strong ground motions recorded in san francisco and oakland during the 1989 loma prieta earthquake the amplitudes of strong ground motions from the loma prieta earthquake recorded in the san francisco and oakland areas exceeded the levels predicted by standard empirical attenuation relations preliminary analysis of accelerograms having known trigger times strongly suggests that the elevation of ground motion amplitudes in the distance range of approximately 40 to 100 km was due to critical reflections from the base of the crust these reflections which are identified on the basis of their arrival times and phase velocity and by comparison with simulated accelerograms were large and occurred at relatively close range because of the deep focal depth of the earthquake and the strong velocity gradient at the base of the crust these motions were further amplified presumably by impedance contrast effects at soft soil sites in san francisco and oakland the effect of the critical reflections in amplifying peak accelerations of the loma prieta earthquake in the san francisco and oakland regions was as large as the effect of soft soil site conditions focal depth has an important influence on strong motion attenuation at distances beyond about 40 km and empirical attenuation relations derived from shallow crustal earthquakes may underpredict the ground motions of deeper crustal events in this distance range further analyses using an expanded data base that includes recordings of aftershocks are required to rigorously test the proposed explanation of the ground motions recorded in san francisco and oakland and the conclusions drawn from that explanation

a pan african origin and uplift for the gneisses and peridotites of zabargad island red sea a nd sr pb and os isotope study a sr nd pb and os isotopic study of peridotites and granulite facies gneisses from zabargad island in the red sea suggests that the tectonothermal petrogenetic and geochemical evolution of these rocks occurred largely during the pan african orogeny rather than the recent opening of the red sea sm nd model ages and whole rock errorchrons indicate that spinel iherzolites and gneisses differentiated from a common depleted mantle source about 700 ma the iherzolites were mylonitized metasomatized and amphibolitized during a structural event that juxtaposed the peridotites with the gneiss complex and uplifted the gneiss peridotite complex to relatively shallow crustal levels most radiometric dating schemes suggest a pan african age for this event the gneisses generally have lower 143nd 144nd 87sr 86sr 208pb 204pb 207pb 204pb and 206pb 204pb ratios than the peridotites they extend linear trends defined by the spinel and amphibole peridotites on sr nd sm nd and pb pb diagrams suggesting the gneisses were either the source or buffering medium for the pan african metasomatism only one post pan african event had a significant effect on the geochemistry of the gneiss peridotite complex shallow level metasomatism by ultrahot 750 900 c hypersaline solutions with high 87sr 86sr 0 710 ratio led to the development of gem quality olivine crystals as well as low pressure mineral assemblages in the peridotites gneisses and younger rocks plagioclase rich assemblages with apparent igneous textures troctolites that are most common in the southern peridotite body may have formed by interaction of these fluids with peridotite i e are pseudo troctolites metasomatism changed the 87sr 86sr sm nd and re os ratios of the plagioclase peridotites making them unsuitable representatives of the pan african mantle