the paleoproterozoic magmatic metamorphic events and cover sediments of the tiekelik belt and their tectonic implications for the southern margin of the tarim craton northwestern china abstract the tiekelik belt in the southwestern part of the tarim craton nw china consists of archean paleoproterozoic orthogneisses and granitoids and younger sedimentary successions u pb dating of paleoproterozoic rocks in the tiekelik belt has provided new information on the southwestern margin of the tarim craton two orthogneisses from the heluositan complex yielded crystallization ages in the interval 2310 2260 ma and metamorphic ages of 2040 2007 ma and 1830 ma respectively two syenogranites from the buweituwei pluton yielded crystallization ages of 1900 and 1795 ma detrital zircon analyses from sedimentary rocks nonconformably overlying the buweituwei and akazi plutons indicate maximum depositional ages between 1950 ma and 1780 ma major detrital inputs are from the basement in the region and form prominent peaks at 1900 1800 ma and 2300 2200 ma our new data combined with previous results allow us to summarize the archean paleoproterozoic tectonic evolution of the tiekelik belt as follows 1 emplacement of archean aged ttg magmas during the 3 14 2 76 ga interval 2 a series of 2 41 2 26 ga magmatic events that represent an important period of crustal reworking within the tarim craton 3 2 03 1 80 ga magmatic and metamorphic events that include the emplacement of a 1 9 ga mafic dyke suite into the heluositan complex along with several episodes of intraplate magmatism the late magmatic events are coeval with metamorphism and may support an orogenic extensional model for the tiekelik belt during the 1 9 1 8 ga interval 4 post 1 8 ga subsidence and formation of a changcheng sequence in the tiekelik belt the paleoproterozoic ages of major tectonothermal events within the tiekelik north altyn dunhuang block and alashan block are almost identical and it is argued that they were connected at that time as north china and tarim were part of the larger columbia supercontinent

zircons from the tarim basement provide insights into its positions in columbia and rodinia supercontinents abstract the positions of the tarim craton in two precambrian supercontinents columbia and rodinia still remain unknown or controversial as the craton is largely covered by desert in the central part and only sparse precambrian basement rocks are scattered at its margins in this contribution we attempt to use new in situ zircon u pb ages and hf isotopic data combined with comprehensive compiled data from precambrian basement rocks at its margins to provide new insights into positions in two precambrian supercontinents detrital zircon profiles of northern tarim and southern siberia are characterized by a peak at 2 0 1 8 ga and the lack of 1 7 1 1 ga zircons moreover both the 2 0 1 8 ga detrital zircons show remarkable similarities dominated by mostly negative ehf t values ranging from 15 to 0 in addition 2 0 1 8 ga collisional granitic rocks are exposed in two terranes these suggest that northern tarim likely collided with southern siberia at 2 0 1 8 ga during the assembly of columbia in southern tarim neoproterozoic magmatic rocks were closely related with the evolution of rodinia the 0 9 ga ma gneissic granites in altyn tagh area were formed in collisional settings due to the collision between southern tarim and northern india during the assembly of rodinia which is supported by distinctly comparable zircon age spectra and hf isotopes from neoproterozoic strata in two terrenes this model considers the tarim craton as a single block in the period from columbia to rodinia which can explain different tectonomagamtic events in northern and southern tarim

suppression of eddy diffusivity across jets in the southern ocean abstract geostrophic eddies control the meridional mixing of heat carbon and other climatically important tracers in the southern ocean the rate of eddy mixing is typically quantified through an eddy diffusivity there is an ongoing debate as to whether eddy mixing in enhanced in the core of the antarctic circumpolar current or on its flanks a simple expression is derived that predicts the rate of eddy mixing that is the eddy diffusivity as a function of eddy and mean current statistics this novel expression predicts suppression of the cross jet eddy diffusivity in the core of the antarctic circumpolar current despite enhanced values of eddy kinetic energy the expression is qualitatively and quantitatively validated by independent estimates of eddy mixing from altimetry observations this work suggests that the meridional eddy diffusivity across the antarctic circumpolar current is weaker than presently assumed because of the suppression of eddy mixing by the strong zonal current

rossby wave propagation into the northern hemisphere stratosphere the role of zonal phase speed sudden stratospheric warming ssw events are to a dominant part induced by upward propagating planetary waves while theory predicts that the zonal phase speed of a tropospheric wave forcing a ects wave propagation into the stratosphere its relevance for ssw events has so far not been considered this study shows in a linear wave diagnostic and in reanalysis data that phase speeds tend eastward as waves propagate upward indicating that the stratosphere preselects eastward phase speeds for propagation especially for zonal wave number 2 this also a ects ssw events split ssw events tend to be preceded by anomalously eastward zonal phase speeds zonal phase speed may indeed explain part of the increased wave ux observed during the preconditioning of ssw events as for example for the record 2009 ssw event

final amalgamation of the tianshan and junggar orogenic collage in the southwestern central asian orogenic belt constraints on the closure of the paleo asian ocean abstract the tianshan and junggar orogenic collage occupies the southwestern part of the central asian orogenic belt and was assembled by collision accretion of several continental blocks and island arcs during late paleozoic early mesozoic time following the consumption of the junggar and south tianshan oceanic basins in the western segment of the paleo asian ocean considerable and continuing controversy has surrounded when where and how this orogenic collage was eventually amalgamated which plays a crucial role in understanding the formation of the central asian orogenic belt this review synthesizes the most recent data and geologic evidence that place critical constraints on the closure history of the oceanic domains a comprehensive data compilation indicates that the formation of ophiolites along major sutures in the tianshan and junggar region lasted to the early carboniferous for the kalamaili suture zone to the mid carboniferous for the west junggar region and the north tianshan suture zone and to the late carboniferous for the south tianshan suture zone ca 325 310 ma ultra high pressure metamorphism along the western part of the south tianshan suture occurred nearly synchronously with the collision between the tarim craton and the central tianshan yili block the oceanic closure and collision events were sequentially followed by widespread and intensive a type granitic and bimodal magmatism which commenced in the mid carboniferous along the kalamaili belt and in the latest carboniferous to earliest permian in other regions contemporaneously large scale strike slip shearing took place along major faults subparallel to main sutures with a dominant dextral sense and deformation time since the carboniferous permian transition available data and geological evidence support an eastward propagating scissor like closure of the western segment of the paleo asian ocean along the south tianshan and north tianshan suture zones over a period from the mid to end carboniferous with the south tianshan belt representing the final suturing site in the early permian the tarim mantle plume likely merely affected the southwestern part of the assembled tarim and tianshan region as indicated by regional discrepancy in type and geochemistry of early permian a type granitoids the amalgamation of the tianshan and junggar orogenic collage was associated with the tectonic bending of the kazakhstan orocline leaving a piece of trapped oceanic crust in its middle part beneath the present junggar basin

climatology of upper tropospheric lower stratospheric utls jets and tropopauses in merra abstracta global climatology 1979 2012 from the modern era retrospective analysis for research and applications merra shows distributions and seasonal evolution of upper tropospheric jets and their relationships to the stratospheric subvortex and multiple tropopauses the overall climatological patterns of upper tropospheric jets confirm those seen in previous studies indicating accurate representation of jet stream dynamics in merra the analysis shows a northern hemisphere nh upper tropospheric jet stretching nearly zonally from the mid atlantic across africa and asia in winter spring this jet splits over the eastern pacific merges again over eastern north america and then shifts poleward over the north atlantic the jets associated with tropical circulations are also captured with upper tropospheric westerlies demarking cyclonic flow downstream from the australian and asian monsoon anticyclones and associated easterly jets multiple tropopauses associated with the thermal tropopause break

miocene volcanism in the lhasa block tibet spatial trends and geodynamic implications miocene ultrapotassic up shoshonitic p and calc alkaline ca volcanism is recognized widely over the tibetan plateau this volcanism occurred after the end of india s oceanic lithosphere subduction beneath the plateau ambiguities about the distribution and significance of this volcanism arise in part from a paucity of geochronologic and geochemical data we have sampled two volcanic fields in the lhasa block 1 the eastern edge of the zabuye salt lake central part of the block 2 the southwestern edge of the yangbajin graben major and trace elements display high k2o 6 06 6 54 over a wide range of sio2 75 03 55 30 na2o 1 32 3 30 and lree hree enrichment with a significant rare earth element fractionation 266 la yb n 6 42 as well as negative nb ta and ti anomalies these features indicate that our samples are chemically identical to the post collision miocene up to p volcanic rocks already identified all over the tibetan plateau and the southern plateau specifically but distinct from the ca rocks found in the lhasa block the miocene volcanics found in the lhasa block present greater chemical variation than the rest of the tibetan plateau 40 ar 39 ar ages on both sanidine and biotite gave ages ranging from 16 16 g 0 12 ma to 16 01 g 0 12 ma and 10 60 g 0 14 ma to 10 88 g 0 17 ma 2 c excluding systematic errors relative to fish canyon sanidine at 28 02 ma for zabuye salt lake and yangying geothermal field volcanics respectively these results are consistent with the range of previously published ages from this part of the tibetan plateau the presence of n s trending dikes and the location of the volcanic fields suggest that local e w extension in the lhasa block was coeval we propose that the synchronous up p and ca volcanism in the lhasa block between 23 and 8 ma is the result of progressively deepening northward subduction of indian continental lithosphere producing asthenospheric upwelling convective thinning delamination of lithospheric mantle fueled by the hot asthenosphere induced partial melting of an enriched sub continental mantle lithosphere as well as eclogitic lower crust this mechanism could also explain the local e w extension observed in the same period 18 10 ma we also propose that lateral migration of the deepening indian continental lithosphere mantle slab could explain the observed younger volcanism in the eastern part of the lhasa terrane

an early paleoproterozoic high k intrusive complex in southwestern tarim block nw china age geochemistry and tectonic implications abstract systematic geochronologic geochemical and nd isotopic analyses were carried out for an early paleoproterozoic high k intrusive complex exposed in southwestern tarim nw china the results provide a better understanding of the paleoproterozoic tectonic evolution of the tarim block zircon u pb age dating indicates two paleoproterozoic magmatic episodes occurring at ca 2 41 ga and ca 2 34 ga respectively which were followed by a ca 1 9 ga metamorphic event the 2 41 ga granodiorite adamellite suite shares characteristics of late to post orogenic metaluminous a type granites in its high alkalinity na2o k2o 7 6 9 3 total ree 410 788 ppm zr 370 660 ppm and y 21 7 58 4 ppm contents end t values for the suite range from 3 22 to 4 71 and accordingly the nd modal ages t2dm vary between 3 05 ga and 3 17 ga based on geochemical data the 2 34 ga suite can be subdivided into two sub suites namely a type and s type however both types have comparable nd isotope compositions end t 0 41 to 2 08 and similar narrow t2dm ranges 2 76 2 91 ga geochemical and nd isotopic data for the high k intrusive complex in conjunction with the regional geological setting suggest that both the 2 41 ga suite and the 2 34 ga a type sub suite might have been produced by partial melting of the archean mafic crust in a continental rift environment the s type sub suite is thought to have formed by partial melting of felsic pelites and or metagreywackes recycled from archean crust ttg gabbro enclaves with positive end t value 2 15 have been found to be intermingling within the 2 34 ga suite ca 2 34 2 36 ga gabbroic dykes and adamellites have previously been documented in eastern tarim these observations indicate that the high k intrusions may reflect the emergence of depleted mantle upwelling beneath the tarim block at that time we suggest a three stages model for the precambrian crustal evolution in the tarim block 1 the formation of proto crust ttg by ca 2 5 ga 2 episodes of felsic magmatism possibly occurring in continental rift environments at ca 2 41 ga and ca 2 34 2 36 ga and 3 ca 1 9 ga metamorphism that may represent the solidification of the precambrian basement of the tarim block

tectonics of western tibet between the tarim and the indus a tarim to indus traverse provides insight into the tectonics of western tibet the kunlun was the site of a mid paleozoic collision at least three phases of post paleozoic accretion have thickened the blanket of sediments that covers western tibet sizeable parts of western qiangtang have remained stable however since the mid mesozoic since the neogene deformation and volcanism have been localized near the edges of the plateau strike slip motion along the karakorum and altyn tagh faults has been coeval with overthrusting in the himalayas and kunlun such slip partitioning and the volcanism appear to result simply from northward subduction of india and southward subduction of the tarim as tibet is extruded eastwards by india s penetration into asia

does the holton tan mechanism explain how the quasi biennial oscillation modulates the arctic polar vortex idealized experiments with the whole atmosphere community climate model waccm are used to explore the mechanism s whereby the stratospheric quasi biennial oscillation qbo modulates the northernhemispherewintertimestratosphericpolarvortex overall theeffectofthecriticallineemphasized in the holton tan mechanism is less important than the effect of the mean meridional circulation associated with qbo winds for the polar response to the qbo more specifically the introduction of easterly winds at the equator near 50 hpa 1 causes enhanced synoptic scale eliassen palm flux epf convergence in the subtropics from 150 to 50 hpa which leads to the subtropical critical line moving poleward in the lower stratosphere and2 createsabarriertoplanetarywavepropagationfromsubpolarlatitudestomidlatitudesin the middle andupper stratosphere e g less equatorwardepf near 508n whichleads to enhancedplanetary wave convergence in the polar vortex region these two effects are mechanistically distinct while the former is relatedtothesubtropicalcriticalline thelatterisduetothemeanmeridionalcirculationofthe qbo allof these effects are consistent with linear theory although the evolution of the entire wind distribution is only quasi linear because induced zonal wind changes cause the wave driving to shift and thereby positively feed back on the zonal wind changes finally downward propagation of the qbo in the equatorial stratosphere upper stratospheric equatorial zonal wind and changes in the tropospheric circulation appear to be less important than lower stratospheric easterlies for the polar stratospheric response overall an easterly qbo wind anomaly in the lower stratosphere leads to a weakened stratospheric polar vortex in agreement with previous studies although not because of changes in the subtropical critical line

zonal jet structure and the leading mode of variability an observational analysis of the northern hemisphere circulation during winter reveals that the leading mode of variability depends on longitude in particular the first eof of the zonal mean circulation differs over the atlantic and pacific sectors these results provide motivation for a series of model runs where a simple gcm is used to investigate the effects of the zonal jet structure on the leading mode of variability in the northern hemisphere model results indicate that the leading mode of variability depends on the distance between the eddy driven and subtropical jets when the jets are well separated the leading mode of variability describes latitudinal shifting of the eddy driven jet however when the two jets are nearly collocated pulsing of the combined jet dominates the variability this change coincides with a weakening of the positive feedback between the eddies and zonal flow anomalies these results provide a possible explanation for the reduced amplitude of the northern annular mode in the pacific sector relative to that in the atlantic sector during northern hemisphere winter

tarim and north china cratons linked to northern gondwana through switching accretionary tectonics and collisional orogenesis accretionary and collisional orogenesis in the tarim and north china cratons during paleozoic time can be correlated with events associated with the assembly and subsequent incipient dispersal of gondwana zircon u pb and hf isotopic data from the northern margins of the two cratons and neighbors have revealed comparable ehf t time patterns zircons with magmatic ages of 500 400 ma display a large spread and decreasing ehf t values with time whereas 400 310 ma zircons have dominantly positive ehf t values and an overall increasing trend the marked shift of the zircon hf array at ca 400 ma was most likely related to a major tectonic switch from advancing to retreating accretionary orogenesis corresponding to the development of regional extension the commencement of subduction at 500 ma and establishment of an advancing accretionary orogen along the preexisting passive margin was synchronous with early paleozoic continental collisional events along the southern margins of the two cratons the temporal agreement of these events and their accordance with collision and or accretion events during gondwana assembly suggest that the tarim and north china cratons likely collided with the northern australia margin of east gondwana at ca 500 ma they subsequently dispersed from gondwana in the early devonian coinciding with switching accretionary tectonics along the northern margins of the two cratons that were possibly induced by the slab rollback of the subducting paleo asian ocean plate

the relationship between the itcz and the southern hemispheric eddy driven jet 1 we study the effect of a thermal forcing confined to the midlatitudes of one hemisphere on the eddy driven jet in the opposite hemisphere we demonstrate the existence of an interhemispheric teleconnection whereby warming cooling the northern hemisphere causes both the intertropical convergence zone itcz and the southern hemispheric midlatitude jet to shift northward southward the interhemispheric teleconnection is effected by a change in the asymmetry of the hadley cells as the itcz shifts away from the equator the cross equatorial hadley cell intensifies fluxing more momentum toward the subtropics and sustaining a stronger subtropical jet changes in subtropical jet strength in turn alter the propagation of extratropical waves into the tropics affecting eddy momentum fluxes and the eddy driven westerlies the relevance of this mechanism is demonstrated in the context of future climate change simulations where shifts of the itcz are significantly related to shifts of the southern hemispheric eddy driven jet in austral winter the possible relevance of the proposed mechanism to paleoclimates is discussed particularly with regard to theories of ice age terminations

divergent double subduction tectonic and petrologic consequences divergent double subduction involving removal of an oceanic basin from both sides and collision has distinct fingerprints of magmatism and significant implications for the tectono magmatic evolution of orogenic belts the complete evolution of a divergent double subduction system involves four stages 1 initial interaction between the two divergent subduction zones on both sides of a single oceanic plate 2 closure of the oceanic basin when the two overriding plates meet followed by 3 detachment of the oceanic lithosphere from the overlying crust and sedimentary sections 4 sinking and disappearance of the oceanic slab into the mantle detachment of the oceanic slab leads to intense decompressional melting of mantle and triggers melting of accretionary wedge strata and lower crust resulting in large scale magmatic and volcanic activity the main consequences of a divergent double subduction system are that it produces opposed thrust systems extensive long lived granitoid magmatism with mantle isotopic signature and volcanism that evolves toward bimodalism this model can be applied to the western half of the paleozoic lachlan fold belt southeastern australia to explain the wide scale silurian to early carboniferous granitoid magmatism its spatial and temporal relationships and late bimodal magmatism closure of the oceanic basin is thought to have occurred during the early to middle devonian detachment of the oceanic slab led to felsic to intermediate composition magmatism bimodal volcanism involving local basaltic flows is a reflection of subsequent sinking of the slab

tectonic evolution of the ne section of the pamir plateau new evidence from field observations and zircon u pb geochronology abstract the pamir plateau at the western end of the india asia collision zone underwent long term terrane drifting accretion and collision between early paleozoic and mesozoic however the detailed evolution of this plateau in particular the timing of the proto and palaeo tethys ocean subduction and closure remains enigmatic here we report new field observations and zircon u pb ages and hf isotopic compositions of the representative rocks from the so called precambrian basement in the northeastern pamir i e the bulunkuole group the rock associations of the bulunkuole group indicate volcano sedimentary sequences with arc affinities geochronological data demonstrate that the deposition age of the bulunkuole group in the ne section of the pamir was middle to late cambrian 530 508 ma rather than paleoproterozoic the deposition age became progressively younger from south to north the amphibolite to granulite facies metamorphism of the bulunkuole group took place at ca 200 180 ma unlike the scenario in the southern kunlun terrane skt in the eastern section of the west kunlun orogenic belt wkob early paleozoic metamorphism ca 440 ma was absent in this area two phases of magmatic intrusions composed of granites and minor gabbros with arc geochemical signatures emplaced at 510 480 ma and 240 200 ma the amphibolite meta mafic sheet 519 ma and the meta rhyolite 508 ma have zircon ehf t values of 1 6 to 5 9 and 1 5 to 1 4 respectively the 511 ma gneissic granite sheet and the 486 ma gabbro have zircon ehf t values of 0 1 to 2 4 and 1 3 to 3 6 respectively zircon ehf t of the 245 ma augen gneissic granite sheet varies from 2 2 to 2 0 whereas the metamorphic zircons from the amphibolite 193 ma and high pressure mafic granulite sample 187 ma have negative ehf t values of 5 3 to 2 and 15 to 12 respectively in line with rock association and the deposition age of the bulunkuole group and the saitula group in the eastern section of wkob we propose that both of them were accretionary wedge between the tarim and tianshuihai terrane formed during the proto tethys ocean south southwestward subduction present orientation the timing of deposition and metamorphism documents two distinct phases of arc magmatism and sedimentary basin evolution this indicates that the proto tethys ocean closed at ca 440 ma in the eastern section of wkob whereas in the western section a remnant of the proto tethys ocean between the tarim and the ne pamir did not close till late triassic this remnant ocean was filled by the ordovician triassic sequences the accretion between ne pamir and the central pamir was completed by ca 180 ma as demonstrated by the metamorphic zircon u pb age of the high pressure mafic granulite in the ne pamir

tropospheric rossby wave breaking and the nao nam objective analysis of several hundred thousand anticyclonic and cyclonic breaking rossby waves is performed for the northern hemisphere nh winters of 1958 2006 a winter climatology of both anticyclonic and cyclonic rossby wave breaking rwb frequency and size zonal extent is presented for the 350 k isentropic surface over the nh and the spatial distribution of rwb is shown to agree with theoretical ideas of rwb in shear flow composites of the two types of rwb reveal their characteristic sea level pressure anomalies upper and lower tropospheric velocity fields and forcing of the upper tropospheric zonal flow it is shown how these signatures project onto the centers of action and force the velocity patterns associated with the north atlantic oscillation nao and northern hemisphere annular mode nam previous studies have presented evidence that anticyclonic cyclonic breaking leads to the positive negative polarity of the nao and this relationship is confirmed for rwb over the midlatitudes centered near 50 n however an opposite and statistically significant relationship in which cyclonic rwb forces the positive nao and anticyclonic rwb forces the negative nao is shown over regions 20 to the north and south centered at 70 and 30 n respectively on a winter mean basis the frequency of rwb over objectively defined regions covering 12 of the area of the nh accounts for 95 of the nao index and 92 of the nam index a 6 hourly analysis of all the winters indicates that rwb over the objectively defined regions affects the nao nam without a time lag details of the objective wave breaking analysis method are provided in the appendix

high sr y and la yb ratios the meaning of the adakitic signature abstract the name of adakite is used to describe a far too large group of rocks whose sole common feature is high sr y and la yb ratios however such a signature can be achieved via different processes melting of a high sr y and la yb source deep melting with abundant residual garnet fractional crystallization or afc or interactions of felsic melts with the mantle causing selective enrichment in lree and sr over hree a database of the compositions of adakitic rocks including high silica and low silica adakites martin h smithies r h rapp r p moyen j f champion d c 2005 an overview of adakite tonalite trondhjemite granodiorite ttg and sanukitoid relationships and some implications for crustal evolution lithos 79 1 2 1 24 continental adakites and archaean adakites was assembled geochemical modeling of the potential processes is used to interpret it and reveals that 1 the classical model of slab melting provides the best explanation for the genesis of high silica adakites 2 low silica adakites are explained by garnet present melting of an adakite metasomatized mantle i e at depths greater than 2 5 gpa 3 continental adakites is a term encompassing a huge range of rocks with a corresponding diversity of petrogenetic processes and most of them are different from both low and high silica adakites 4 archaean adakites show a bimodal composition range with some very high sr y examples similar to part of the ttg suite reflecting deep melting 2 0 gpa of a basaltic source with a relatively high sr y while lower sr y rocks formed by shallower 1 0 gpa melting of similar sources comparison with the archaean ttg suite highlights the heterogeneity of the ttgs whose composition spreads the whole combined range of hsa and archaean adakites pointing to a diversity of sources and processes contributing to the ttg suite

jiangnan orogen in south china developing from divergent double subduction abstract the jiangnan orogen is considered as a continent continent collisional belt resulting from the closure of a meso neoproterozoic ocean separating the southeastern margin of the yangtze block from the northwestern margin of the cathaysia block recent data indicate the existence of early neoproterozoic 1000 825 ma volcanic arc assemblages on both sides of the orogen suggesting that the ocean lithosphere between the yangtze and cathaysia blocks must have undergone divergent double sided subduction during the period of 1000 825 ma the divergent double subduction eventually resulted in the closure of the ocean basin at 825 ma leading to the soft collision of the yangtze and cathaysia blocks to form the jiangnan orogen without involvement of continental deep subduction high grade metamorphism of continental crust and uplift exhumation of high grade metamorphic rocks shortly after the collision the initial detachment of the ocean lithosphere from the overlying crust and sedimentary sections induced underplating of mantle magmas triggering partial melting of accretionary wedge strata to form some peraluminous s type granites in the period 825 815 ma finally the sinking of the oceanic slab pulled down the overlying strata to form some basins in which the banxi group and its equivalent strata including bimodal volcanic rocks were formed in the period 815 750 ma

the tropospheric response to tropical and subtropical zonally asymmetric torques analytical and idealized numerical model results abstractthe tropospheric response to prescribed tropical and subtropical zonally asymmetric torques which can be considered as idealizations of vertical momentum transfers by orographic gravity waves or convection is investigated the linear analytical gill model response to westward upper tropospheric torques is compared to the response to a midtropospheric heating which is a familiar point of reference the response to an equatorial torque projects onto a kelvin wave response to the east that is of opposite sign to the response to the east of the heating at upper levels in contrast the torque and heating both produce rossby gyres of the same sign to the west of the forcing and the zonal mean streamfunction responses are identical when the forcings are shifted into the northern hemisphere the streamfunction responses have opposite signs there is upwelling in the southern northern hemisphere in response to the torque heating the nonlinear response to westward torques was explored in idealized

eddy zonal flow interactions and the persistence of the zonal index abstract an idealized atmospheric general circulation model is used to investigate the factors controlling the time scale of intraseasonal 10 100 day variability of the extratropical atmosphere persistence on these time scales is found in patterns of variability that characterize meridional vacillations of the extratropical jet depending on the degree of asymmetry in the model forcing patterns take on similar properties to the zonal index annular modes and north atlantic oscillation it is found that the time scale of jet meandering is distinct from the obvious internal model time scales suggesting that interaction between synoptic eddies and the large scale flow establish a separate intraseasonal time scale a mechanism is presented by which eddy heat and momentum transport couple to retard motion of the jet slowing its meridional variation and thereby extending the persistence of zonal index and annular mode anomalies the feedback is strong and quite sensitive to model parameters when the mod

north atlantic extratropical rossby wave breaking during the warm season wave life cycle and role of diabatic heating abstractthis study investigates the life cycle of anticyclonic rossby wave breaking during the extended warm season july october over the north atlantic basin it was found that upper tropospheric breaking waves are coupled with lower level perturbations and can be traced back to a wave train that extends from the north pacific the overturning of potential vorticity pv contours during wave breaking is associated with the rapid development of an upper level ridge which occurs along the east coast of north america and over a warm and moist airstream the ridge development is investigated using the pv budget analysis and trajectory analysis the pv budget analysis suggests that the horizontal advection of pv by the perturbed flow dictates the movement and the later decay of the ridge the ridge amplification opposed by the horizontal advection of pv is driven by the vertical advection and the diabatic production of pv both of which are connected to diabatic heating the vital role of diabatic heatin

phase speed spectra and the recent poleward shift of southern hemisphere surface westerlies 1 the poleward shift of the southern hemisphere surface westerlies in recent decades is examined in reanalysis data and in the output of coupled atmosphere ocean and uncoupled atmospheric models the space time spectra of the eddy momentum fluxes in the upper troposphere reveal a trend that marks an increase in the eastward phase speed of the tropospheric eddies accompanied by a poleward displacement of the region of wave breaking in the subtropics a dynamical mechanism is suggested that may help explain the connections among the lower stratospheric wind anomalies the increased eastward propagation of tropospheric eddies and the poleward shift of the tropospheric circulation

age and origin of high ba sr appinite granites at the northwestern margin of the tibet plateau implications for early paleozoic tectonic evolution of the western kunlun orogenic belt abstract the buya appinite granite is a typical high ba sr granite emplaced at the northern west kunlun orogenic belt along the northwestern margin of the tibetan plateau the granite is dated at ca 430 ma using the shrimp u pb zircon method it consists of alkaline feldspar granites with coeval appinite enclaves the granite possesses high sio2 69 77 72 69 k2o 4 44 5 10 and total alkalinity k2o na2o 8 80 9 92 sr 655 1100 ppm ba 1036 1433 ppm and lree and low hree and hfse contents and insignificant negative eu anomalies consequently the samples have very high sr y 74 141 and la yb n 37 96 ratios on the other hand they have low mgo or mg cr and ni contents and low radiogenic nd isotopes nd t 8 4 to 10 4 the high ba sr and other geochemical signatures of the granite also appear in the appinite enclaves except that the appinite enclaves have relatively higher abundances in these elements and higher nd t values 5 7 to 6 7 elemental and isotope compositions suggest that the appinites were derived from partial melting of an enriched lithospheric mantle source probably induced by upwelling of the asthenosphere due to the delamination of a subducted slab the granite was likely derived from partial melting of the mafic lower crust with residual garnet associated with involvement of minor lile enriched appinitic magma followed by crystal fractionation of hornblende biotite apatite and allanite in combination with previous investigations on the evolution of the western kunlun we suggest that the buya high ba sr plutons represent the end of an early paleozoic crust thickening event after a terrane accretion on southern tarim craton and the beginning of a post orogenic collapse phase in the paleozoic west kunlun orogenic belt

decomposition of atmospheric disturbances into standing and traveling components with application to northern hemisphere planetary waves and stratosphere troposphere coupling abstractthis study updates a body of literature that aims to separate atmospheric disturbances into standing and traveling zonal wave components classical wavenumber frequency analysis decomposes longitude and time dependent signals into contributions from distinct spatial and temporal scales here an additional decomposition of the spectrum into standing and traveling components is described previous methods decompose the power spectrum into standing and traveling parts with no explicit allowance for covariance between the two this study provides a simple method to calculate the variance of each of these components and the covariance between them it is shown that this covariance is typically a significant portion of the variance of the total signal the approach also preserves phase information and allows for the reconstruction of the real space standing and traveling components the technique is applied to reanalysis wintertime geopotential height anomalies in the northern hemisphere in order to in

afro eurasian intermediate frequency teleconnection and modulation by enso abstractthe afro eurasian intermediate frequency atmospheric teleconnection conveys meteorological signals zonally leads to various atmospheric variations and causes extreme events along its path

baroclinic anomalies associated with the southern hemisphere annular mode roles of synoptic and low frequency eddies 1 using the era 40 reanalysis data we study the different roles of synoptic and low frequency eddies in sustaining the latitudinal shift of the low level baroclinicity associated with the southern hemisphere annular mode the eddy effect is assessed through the direct eddy thermal forcing via eddy heat flux and the indirect forcing via eddy driven mean meridional circulation mmc we find that in addition to the synoptic eddy induced mmc suggested by robinson 2006 the direct eddy thermal forcing by low frequency eddies is significant in driving the baroclinic anomalies these two processes together prevail over the direct baroclinicity deduction by synoptic eddies the different effects of synoptic and low frequency eddies might be attributed to the distinct latitudinal distributions of their low level eddy heat flux relative to the midlatitude jet the different roles of the mmc induced by synoptic eddy momentum and heat flux are also emphasized with the former leading the baroclinic anomalies and the latter acting to extend the baroclinic anomalies

tropical mixing barriers in the lower stratosphere in the geophysical fluid dynamics laboratory skyhi model large scale isentropic mixing in the tropical lower stratosphere is investigated by computing lagrangian trajectories using winds from the geophysical fluid dynamics laboratory skyhi general circulation model the use of model simulated winds avoids some problems with analyzed winds in the tropics during the solstitial seasons a weak mixing zone is present in the tropics in the model simulations the weak mixing zone is relatively isolated from the midlatitude surf zones in the northern and southern hemispheres by two mixing barriers a strong one on the summer hemisphere side and a weak one on the winter side the mixing barriers vary seasonally in response to seasonal variations of the tropical zonal mean zonal flow and wave spectrum the roles of the zonal mean flow and of different parts of the wave spectrum in meridional transport are tested using filter techniques effective meridional diffusion coefficients are calculated by using filtered and antifiltered winds i e winds with selected spatial scales either attenuated or amplified the results suggest that mixing in the tropical easterlies occurs near the critical layers for the large scale zonal wavenumber 10 westward moving waves which is where the waves would be expected to break wave spectrum analysis indicates that during the solstitial seasons there is a zone in the tropics exactly matching the weak mixing zone where there is relatively little power in westward moving waves the tropical mixing barriers are a result of the relative lack of such waves

phase speed cross spectra of eddy heat fluxes in the eastern pacific this study investigates the observed spectral character of eddy heat fluxes near the ocean surface focusing on the distribution in wavenumber and phase speed space eddy heat fluxes in the eastern pacific are calculated from concurrent satellite sea surface height and sea surface temperature data a high resolution coupledclimatemodelis alsoanalyzedin ordertoverifythephysicalmechanismsinvolvedandtovalidatethe model against observations wavenumber frequency and phase speed power spectra and cross spectra are constructed and presented as a function of latitude these spectra reveal the dominance of coherent mesoscale eddies in both the length scale and phase speed of eddy heat fluxes the breadths of the spectra are characterized via spectral moments these moments show that the eddy fluxes are relatively concentrated around the dominant wavenumber and phase speed good agreement is found between the model and the observed spectra the integrated heat transport and corresponding eddy diffusivity are shown to compare well with previous studies but the results give a deeper insight into what determines the heat flux implications for eddy parameterization are discussed

on the sporadic nature of meridional heat transport by transient eddies the present study analyses meridional atmospheric heat transport due to transient eddies in the european centre for medium range weather forecasts era interim reanalysis daily 0 7 latitude and longitude resolution data at the 850 mb pressure level are used probability density functions pdfs of meridional transient eddy heat transport display a near zero most likely value and a very large skewness which highlights the dominant role played by extreme events when considering zonal sections in both the northern and southern hemispheres events in the top five percentiles typically contribute to over half of the net poleward transport as a result of this sensitivity to extremes a large fraction of the heat transport by transient eddies at a given location and season is realised through randomly spaced bursts a few per season rather than through a continuum of events the predominance of extreme events can be explained by the favourable phase relationship between meridional velocity and moist static energy temporal anomalies this and the spatiotemporal characteristics of the events are compatible with eady type growing systems copyright 2012 royal meteorological society

phase speed spectra of transient eddy fluxes and critical layer absorption abstract tropospheric zonal mean eddy fluxes of heat and momentum and the divergence of the eliassen palm flux are decomposed into contributions from different zonal phase speeds data analyzed are ecmwf operational global analyses covering 1980 87 eastward moving medium scale waves zonal waves 4 7 dominate the spectra of lower tropospheric heat fluxes in both hemispheres and all seasons upper tropospheric wave flux spectra are similar to the low level spectra in midlatitudes but shift to slower zonal phase speeds as low latitudes are approached the cause of this shift is the selective absorption of faster moving components in midlatitudes as the waves propagate meridionally latitude phase speed distributions of eddy fluxes are constructed and compared to the zonal mean wind structure these results demonstrate that upper tropospheric eddies break and decelerate the zonal mean flow approximately 10 20 in latitude away from their critical line where phase speed equals zonal wind speed compari

investigation of double tropopause spatial and temporal global variability utilizing high resolution dynamics limb sounder temperature observations 1 this study examines the seasonal variation of the double tropopause dt using data from the high resolution dynamics limb sounder the combination of high data density and high vertical resolution available with this satellite instrument allows for the detailed analysis of fine scale structures such as the dt the spatial distribution of dt frequency is examined for all seasons from 2005 to 2007 global analysis of this distribution reveals that dts have a strong tendency to follow the zonal wind pattern and are present all year over the andes moreover during northern hemisphere winter spring there is a 15 decrease in the dt frequency over the eastern pacific and western atlantic two regions of wave breaking produced from a weakening of the zonal flow significant dt thickness values are also present over these regions but are found to extend further poleward than the corresponding frequency pattern a time series of dt frequencies is analyzed and shows an increase in daily frequencies during 2006 that highlights the interannual variability of this thermal structure for the first time dt duration is investigated in the extratropics utilizing a hovmoller diagram of dt frequency this representation highlights two preferred regions of formation the pacific and atlantic the slope of the feature gives it a speed of 18 m s in the northern hemisphere and a slightly faster speed for the southern hemisphere these speeds and the corresponding structures highlight a potential connection between upper tropospheric waves and dts

growth and evolution of precambrian continental crust in the southwestern tarim terrane new evidence from the ca 1 4 ga a type granites and paleoproterozoic intrusive complex abstract the precambrian tectonic evolution and growth of continental crust in the southwestern tarim craton in nw china remain enigmatic in this contribution we report petrography zircon u pb ages geochemistry and nd hf o isotope data on the ca 1 4 ga granitic pluton in southwestern tarim terrane we also present zircon u pb ages and hf isotope data on the paleoproterozoic intrusive complex from this area and use the combined data to evaluate precambrian tectonic evolution of the region in relation to the columbia supercontinent the ca 1 4 ga azibailedi pluton is mainly composed of biotite monzogranite with contents sio2 72 8 75 1 wt the major element chemistry of the pluton reveals alkali calcic and ferroan affinities and metaluminous to peraluminous feature with a cnk ranging from 0 86 to 1 15 the granite shows high total ree contents with variable enrichment in lree la yb n 8 5 12 2 both ree and other incompatible elements features define a type affinities the initial epsilon nd values vary from 3 5 to 2 2 and zircon hf t and 18o values range from 4 1 to 6 1 and 7 1 to 8 6 integrating geological geochemical and nd hf o isotope data we suggest that the azibailedi a type granites were derived from pre existing early paleoproterozoic mafic lower crust with involvement of variable amount of paleoproterozoic juvenile crust possibly trigged by basaltic magma upwelling during the breakup of the columbia supercontinent u pb geochronology and hf isotopic analyses of zircons from the paleoproterozoic heluositan intrusive complex show crustal growth episodes during 2 2 4 2 ga with peaks at 2 3 2 5 ga 3 3 ga and 3 6 3 8 ga distinct from the other precambrian terranes of the tarim craton a comprehensive synthesis of the records of assembly and breakup of columbia supercontinent from different precambrian terranes in the tarim craton show significant differences the temporal distinction in tectonothermal events and the marked difference in the continental crust growth processes suggest that the early precambrian basement of the tarim craton was possibly composed of discrete terranes which were fragmented from different ancient cratonic nuclei

formation and adjustment of typhoon impacted reef islands interpreted from remote imagery nadikdik atoll marshall islands abstract in 1905 a devastating typhoon hit nadikdik atoll 5 54 n and 172 09 e in the southern marshall islands evidence suggests that large sections of reef islands on nadikdik were overwashed and destroyed comparison of aerial photographs taken in 1945 and modern satellite imagery provides a unique record of the geomorphic adjustment of islands after the typhoon between 1945 and 2010 the vegetated area of islands on nadikdik grew from 0 74 to 0 90 km2 observed changes to nadikdik reef islands manifested through a range of styles and were largely accretionary of note the formation of a new island was tracked from an embryonic deposit to a fully vegetated and stable island over a 61 year period similarly a number of previously discrete islands have agglomerated and formed a single larger island these changes were rapid and indicate that reef island formation can occur quickly evidence suggests that despite the typhoon occurring over a century ago the geomorphic adjustment of islands is still on going

sensitivity of the latitude of the surface westerlies to surface friction the sensitivity to surface friction of the latitude of the surface westerlies and the associated eddy driven midlatitude jet is studied in an idealized dry gcm the westerlies move poleward as the friction is reduced in strength an increase in the eastward phase speed of midlatitude eddies is implicated as playing a central role in this shift this shift in latitude is mainly determined by changes in the friction on the zonal mean flow rather than the friction on the eddies if the friction on the zonal mean is reduced instantaneously the response reveals two distinctive adjustment time scales in the fast adjustment over the first 10 20 days there is an increase in the barotropic component of zonal winds and a substantial decrease in the eddy kinetic energy the shift in the surface westerlies and jet latitude occurs in a slower adjustment the space time eddy momentum flux spectra suggest that the key to the shift is a poleward movement in the subtropical critical latitude associated with the faster eastward phase speeds in the dominant midlatitude eddies the view is supported by simulating the upper tropospheric dynamics in a stochastically stirred nonlinear shallow water model

rossby wave propagation into the tropics in two gfdl general circulation models during the northern winter the eastern pacific is characterized by upper level westerly flow extending from the equator into the midlatitudes of both hemispheres theoretical and simple modeling studies suggest that such a region should favor the penetration of rossby waves into the tropics from higher latitudes observational results by kiladis and weickmann using 200 mb data indicate that rossby waves do indeed propagate freely into the tropical eastern pacific during the northern winter from the asian jet exit region they also confirmed that cross equatorial dispersion of energy from the northern into the southern hemisphere occurs frequently the present study examines these interactions in climatological runs of two gfdl gcms the northern wintertime mean states of these models are characterized by a rather realistically simulated upper level westerly regime in the tropical pacific despite the relative weakness of the asian jet and wave activity with respect to observations propagation of rossby waves into the tropics is present in both models and these waves are strongly positively tilted as seen in the observations a momentum budget of the zonal wind and e vector diagnostics over the tropical pacific indicate that these transients are an important component of the momentum balance of the equatorial westerlies in both the observations and in the models

on the role of planetary scale waves in the abrupt seasonal transition of the northern hemisphere general circulation the role of planetary scale waves in the abrupt seasonal transition of the northern hemisphere nh general circulation is studied in reanalysis data the winter to summer transition involves the growth of planetary scale wave latent heat and momentum transports in the region of monsoons and anticyclones that dominate over the zonal mean transport beginning in midspring the wave dominated regime coincides with an abrupt northward expansion of the cross equatorial circulation and reversal of the trade winds in the upper troposphere the transition coincides with the growth of cross equatorial planetary scale wave momentum transport and a poleward shift of subplanetary scale wave transport and jet stream the dynamics of the seasonal transition are captured by idealized aquaplanet model simulations with a prescribed subtropical planetary scale wave sea surface temperature sst perturbation the sst perturbation generates subtropical planetary scale wave streamfunction variance and transport in the lower and uppertroposphereconsistentwithquasigeostrophictheory beyondathresholdsst atransitionofthezonalmean circulation occurs which coincides with a localized reversal of absolute vorticity in the nh tropical upper troposphere the transition is abrupt in the lower troposphere because of the quadratic dependence of the wave transport on the sst perturbation and involves seasonal time scale feedbacks between the wave and zonal meanflow in theupper troposphere including cross equatorial wave propagation thezonal mean vertical and meridional flows associated with the circulation response are in balance with the planetary scale wave momentumand latentheat meridionalflux divergences the resultshighlightthe leading order roleofmonsoon anticyclone transport in the seasonal transition including its impact on the meridional extent of the hadley and ferrel cells they can also be used to explain why the transition is less abrupt in the southern hemisphere

overtransmission of rossby waves at a lower layer critical latitude in the two layer model abstractrossby waves propagating from the midlatitudes toward the tropics are typically absorbed by critical latitudes cls in the upper troposphere however these waves typically encounter cls

assembly of the lhasa and qiangtang terranes in central tibet by divergent double subduction abstract integration of lithostratigraphic magmatic and metamorphic data from the lhasa qiangtang collision zone in central tibet including the bangong suture zone and adjacent regions of the lhasa and qiangtang terranes indicates assembly through divergent double sided subduction this collision zone is characterized by the absence of early cretaceous high grade metamorphic rocks and the presence of extensive magmatism with enhanced mantle contributions at ca 120 110 ma two jurassic cretaceous magmatic arcs are identified from the caima duobuza rongma kangqiong amdo magmatic belt in the western qiangtang terrane and from the along tso yanhu daguo baingoin daru tso magmatic belt in the northern lhasa terrane these two magmatic arcs reflect northward and southward subduction of the bangong ocean lithosphere respectively available multidisciplinary data reconcile that the bangong ocean may have closed during the late jurassic early cretaceous most likely ca 140 130 ma through arc arc soft collision rather than continent continent hard collision subduction zone retreat associated with convergence beneath the lhasa terrane may have driven its rifting and separation from the northern margin of gondwana leading to its accretion within asia

proto tethys oceanic slab break off insights from early paleozoic magmatic diversity in the west kunlun orogen nw tibetan plateau abstract continental collision and subsequent slab break off can induce granitoid magmatism of variable compositions and ages we present new geochronological and geochemical data from granitoids in the eastern part of the west kunlun orogen situated along the northwestern margin of the tibetan plateau our data reveal a distinct late ordovician middle silurian 450 428 ma magmatic flare up event after closure of the proto tethys ocean proto kunlun ocean and following continental collision some high sr y granitoids show variable whole rock 87sr 86sr i end t 206pb 204pb t and zircon ehf t values indicating that these rocks were derived from heterogeneous sources comprising both juvenile and older material from the lower crust under amphibolite facies conditions we identify a linear spatial distribution of small scale and short lived magmatism and magmatic diversity a s i type along the suture zone and suggest that this late ordovician middle silurian magmatism in the west kunlun orogen was associated with slab break off of the proto tethys oceanic plate the results improve our understanding of the closure of the proto tethys ocean crustal growth and the final formation of gondwana in the nw tibetan plateau region

on the speed of the eddy driven jet and the width of the hadley cell in the southern hemisphere a strong correlation between the speed of the eddy driven jet and the width of the hadley cell is found to exist in the southern hemisphere both in reanalysis data and in twenty first century integrations from the intergovernmental panel on climate change ipcc fifth assessment report multimodel archive analysis of the space time spectra of eddy momentum flux reveals that variations in eddy driven jet speed are related to changes in the mean phase speed of midlatitude eddies an increase in eddy phase speeds induces a poleward shift of the critical latitudes and a poleward expansion of the region of subtropical wave breaking the associated changes in eddy momentum flux convergence are balanced by anomalous meridional winds consistent with a wider hadley cell at the same time faster eddies are also associated with a strengthened polewardeddymomentumflux sustainingastronger westerlyjet in midlatitudes the proposedmechanismis consistent with the seasonal dependence of the interannual variability of the hadley cell width and appears to explain at least part of the projected twenty first century trends one of the most salient features of earth s general circulation is the presence of hadley cells hcs in the tropical belts of both hemispheres associated with their large scale motions are some of the main characteristics of tropical and subtropical climates the intertropical convergence zone in the rising branch and the subtropical dry zones in the descending branches e g hartmann 1994 studying the factors determining the meridional extent of these overturning circulations is therefore essential to understand the spatial distribution of tropical and subtropical climates and its changes the role of the hcs is particularly crucial in the context of climate change and the observed widening of the atmospheric circulation observations show a poleward shift of the eddy driven jets and an expansion of the hcs in recent decades particularly in the southern hemisphere hu and fu 2007 johanson and fu 2009 lu et al 2009 and the role of radiative forcings induced by greenhouse gases and stratospheric ozone has been shown to be crucial in this context polvani et al 2011b

wave mean flow interactions and the maintenance of superrotation in a terrestrial atmosphere abstractthe interplay between mean meridional circulation and transient eddies through wave mean flow interaction processes defines the general behavior of any planetary atmospheric circulation under a higher rossby number regime equatorward momentum transports provided by large scale disturbances generate a strong zonal flow at the equatorial region at intermediate rossby numbers equatorial kelvin waves play a leading role in maintaining a superrotating jet over the equator however at high rossby numbers the kelvin wave only provides equatorward momentum fluxes during spinup and the wave mean flow process that maintains this strongly superrotating state has yet to be identified this study presents a comprehensive analysis of the tridimensional structure and life cycle of atmospheric waves and their interaction with the mean flow which maintains the strong long lived superrotating state in a higher rossby number regime atmosphere the results show that the mean zonal superrotating circulation i

the tethyan himalayan detrital record shows that india asia terminal collision occurred by 54 ma in the western himalaya the himalayan orogen is a type example of continent continent collision knowledge of the timing of india asia collision is critical to the calculation of the amount of convergence that must have been accommodated and thus to models of crustal deformation sedimentary rocks on the indian plate near the suture zone can be used to constrain the time of collision by determining first evidence of asian derived material deposited on the indian plate however in the himalaya for this approach to be applied successfully it is necessary to be able to distinguish between asian detritus and detritus from oceanic island arcs that may have collided with india prior to india asia collision zircons from the indian plate asian plate and kohistan ladakh island arc can be distinguished based on their u pb ages combined with hf signatures we undertook a provenance study of the youngest detrital sedimentary rocks of the tethyan himalaya of the indian plate in the western himalaya we show that zircons of asian affinity were deposited on the indian plate at 54 ma we thus constrain terminal india asia collision when both sutures north and south of the kohistan ladakh island arc were closed to have occurred in the western himalaya by 54 ma

carboniferous triassic subduction and accretion in the western kunlun china implications for the collisional and accretionary tectonics of the northern tibetan plateau a newly defined 250 km by 500 km carboniferous triassic subduction accretion complex the mazar accretionary prism in the western kunlun comprises two subduction complexes and a forearc basin succession 1 the bazar dara subduction complex contains imbricated blocks of sandstone arenite limestone and metavolcanic rocks in a matrix of weakly metamorphosed triassic deep sea turbidites the metavolcanic rocks include basalt diabase spilite and andesitic porphyry trace element geochemistry shows that pillow and amygdaloidal basalts are oceanic island tholeiites this zone has ordovician to permian fossils and is situated on the older more highly deformed and metamorphosed side of the prism adjacent to the sailiyak magmatic arc 2 the heweitan subduction complex is composed of blocks of limestone turbidite and radiolarite in a slate phyllite matrix intercalated with calc alkalic volcanic rocks this complex has permian to triassic fossils and is situated on the younger less deformed and metamorphosed side of the prism adjacent to the suture zone 3 the qitai forearc basins are infilled with turbidites late triassic intercalated with carbonates these rocks overlie the accretionary prism the accretion related structure is dominated by large scale northeast dipping thrusts and subvertical cleavage stitched by 215 190 ma granites there is an overall decrease in metamorphic grade and deformation intensity from the arc to the suture zone across the bazar dara and heweitan subduction complexes the mazar accretionary prism formed by subduction accretion processes during closure of the paleotethyan ocean and the final docking of the gondwanan karakoram qiangtang block to the cathaysian eurasian kunlun block

the early development of the 2015 16 quasi biennial oscillation disruption abstractan unprecedented disruption of the quasi biennial oscillation qbo started to develop from late 2015 the early development of this event is analyzed using the space time spectra of eddies

abrupt transition to strong superrotation driven by equatorial wave resonance in an idealized gcm persistent superrotation is seen in the atmospheres of other terrestrial bodies venus titan but not in that of present earth which is distinguished by equatorial easterlies nevertheless superrotation has appeared in numerical simulations of earth s atmosphere from two layer models to multilevel comprehensive gcms simulations of warm climates that generate enhanced tropical convective variability seem particularly prone to superrotation which has led to hypotheses that the warmer atmospheres of the early pliocene and eocene may have been superrotating and that the phenomenon may be relevant to future climate projections this paper considers a positive feedback leading to superrotation based on an equatorial wave resonance that occurs in a westerly backgroundflow the authors present simulations with an idealized multilevel gcm forced with a zonally varying equatorial heating which show abrupt transitions to strongly superrotating states linearshallowwatertheoryisusedtoshow thatthesetransitions occur asthesuperrotating jetvelocity approaches the phase speed of free equatorial rossby wave modes leading to a resonant amplification of the response to eddy heating and its associated equatorward momentum flux the resonance and transition are most prominent in simulations where the meridional temperature gradient has been reduced and hysteresis behavior is seen when the gradient is eliminated completely no evidence is found in these simulations for the midlatitude wave feedback believed to drive abrupt transitions in two layer models and there is only a minor role for the axisymmetric feedback based on vertical advection by the hadley circulation

tectonic environment of the devonian gramscatho basin south cornwall framework mode and geochemical evidence from turbiditic sandstones the portscatho formation within the allochthonous unit of the middle and upper devonian gramscatho group is a thick sequence of deep water sandstones and interbedded slates deposited by southerly derived turbidity currents into the gramscatho basin of south cornwall throughout an approximately 3 5 km thick sequence the portscatho formation is petrographically and chemically coherent except that the upper section shows a higher proportion of metamorphic clasts high but variable cr and low uniform zr abundances complementary framework mode and bulk geochemistry indicate that the sandstones were derived from a dissected continental magmatic arc of predominantly acidic composition similar to average upper continental crust but with an admixture of minor intermediate basic material flysch deposition took place in a fore arc setting the presence of an arc to the south of cornwall during the devonian implies that there was subduction at the margin of the gramscatho basin whose ultimate closure was accommodated by the northward stacking of flysch ophiolite nappes

differentiating advancing and retreating subduction zones through regional zircon hf isotope mapping a case study from the eastern tianshan nw china abstract advancing and retreating subduction zones at convergent margins primary sites of continental crust growth and loss are the cornerstones of tectonic evolution of accretionary orogens yet distinguishing the tectonic mode advancing retreating or switching of subduction zones in fossil orogens is not always straightforward due to the scarcity of strong evidence as an alternative approach we utilized zircon hf isotope mapping of arc magmatism previously published data from different tectonic units in the eastern tianshan and the northern tarim revealing that a an early paleozoic ca 450 ma southward subduction of the junggar oceanic plate subduction zone advance resulted in compression and crustal thickening in the northern tarim upper plate as evidenced by increasingly more enriched zircon hf isotopic compositions and b a slab rollback retreat of the junggar oceanic plate probably since ca 450 440 ma tectonic switching from subduction zone advance to retreat as manifested by progressive increases in zircon ehf t values induced crustal extension and opening of the south tianshan back arc basin in the northern tarim separating the central tianshan continental arc as a micro continent sliver this case study highlights the great potential of regional zircon hf isotope mapping besides traditional investigations in helping reveal the enigmatic tectonic mode of subduction zones in ancient orogens

atmospheric circulation and its effect on arctic sea ice in ccsm3 simulations at medium and high resolution the simulation of arctic sea ice and surface winds changes significantly when community climate system model version 3 ccsm3 resolution is increased from t42 2 8 to t85 1 4 at t42 resolution arctic sea ice is too thick off the siberian coast and too thin along the canadian coast both of these biases are reduced at t85 resolution the most prominent surface wind difference is the erroneous north polar summer anticyclone present at t42 but absent at t85 an offline sea ice model is used to study the effect of the surface winds on sea ice thickness in this model the surface wind stress is prescribed alternately from reanalysis and the t42 and t85 simulations in the offline model ccsm3 surface wind biases have a dramatic effect on sea ice distribution with reanalysis surface winds annual mean ice thickness is greatest along the canadian coast but with ccsm3 winds thickness is greater on the siberian side a significant difference between the two ccsm3 forced offline simulations is the thickness of the ice along the canadian archipelago where the t85 winds produce thicker ice than their t42 counterparts seasonal forcing experiments with ccsm3 winds during spring and summer and reanalysis winds in fall and winter relate the canadian thickness difference to spring and summer surface wind differences these experiments also show that the ice buildup on the siberian coast at both resolutions is related to the fall and winter surface winds the arctic atmospheric circulation is examined further through comparisons of the winter sea level pressure slp and eddy geopotential height at both resolutions the simulated beaufort high is quite weak weaker at higher resolution eddy heights show that the wintertime beaufort high in reanalysis has a barotropic vertical structure in contrast high ccsm3 slp in arctic winter is found in association with cold lower tropospheric temperatures and a baroclinic vertical structure in reanalysis the summertime arctic surface circulation is dominated by a polar cyclone which is accompanied by surface inflow and a deep ferrel cell north of the traditional polar cell the arctic ferrel cell is accompanied by a northward flux of zonal momentum and a polar lobe of the zonal mean jet these features do not appear in the ccsm3 simulations at either resolution

timing of the final closure of the proto tethys ocean constraints from provenance of early paleozoic sedimentary rocks in west kunlun nw china abstract collision can be subdivided into soft and hard types with the soft collision occurring after double sided oceanic subduction and the hard collision after single sided oceanic subduction although two types of collision involve different geodynamics and generate distinct petrological assemblages whether they can preserve distinct records of detrital zircons remains unclear this study confirms soft collision between the north western kunlun terrane nkt and the south western kunlun terrane skt after the closure of the proto tethys ocean we further compare detrital zircon hf isotope compositions of the soft collision with those of the hard collision related to the amalgamation of rodinia in southern tarim our results show that the nkt is characterized by dominant ca 800 ma zircons whereas the skt is featured by ca 244 ma ca 440 ma and ca 620 ma zircons as such sample 17wp53 deposited at 431 ma in the nkt displays a dominant peak at ca 500 ma indicating minor material exchange between the nkt and the skt at ca 431 ma given the 420 405 ma north kudi granites displaying geochemical features of within plate granites formed at a post orogenic stage we infer that the final closure of the proto tethys ocean occurred at 431 420 ma along western kunlun moreover zircon ehf t data indicate that the soft collision between the nkt and the skt during the amalgamation of gondwana produced ca 40 of juvenile crustal materials whereas the hard collision related to the formation of rodinia generated ca 12 of juvenile crustal materials more juvenile materials generated in the soft collision may be attributed to complete detachment and sinking of a oceanic slab

a climatology of rossby wave breaking on the southern hemisphere tropopause abstracta 30 yr climatology of rossby wave breaking rwb on the southern hemisphere sh tropopause is formed using 30 yr of reanalyses composite analysis of potential vorticity and meridional fluxes of wave activity show that rwb in the sh can be divided into two broad categories anticyclonic and cyclonic events while there is only weak asymmetry in the meridional direction and most events cannot be classified as equatorward or poleward in terms of the potential vorticity structure the position and structure of the fluxes associated with equatorward breaking differs from those of poleward breaking anticyclonic breaking is more common than cyclonic breaking except on the lower isentrope examined 320 k there are marked differences in the seasonal variations of rwb on the two surfaces with a winter minimum for rwb around 350 k but a summer minimum for rwb around 330 k these seasonal variations are due to changes in the location of the tropospheric jets and dynamical tropopause during winter the

petrogenesis of early cambrian granitoids in the western kunlun orogenic belt northwest tibet insight into early stage subduction of the proto tethys ocean

an island arc origin of plagiogranites at oytag western kunlun orogen northwest china shrimp zircon u pb chronology elemental and sr nd hf isotopic geochemistry and paleozoic tectonic implications abstract this paper presents detailed shrimp zircon u pb chronology major and trace element and sr nd hf isotope geochemistry of three intrusive plagiogranite bodies formed in an island arc setting within the oytag ophiolite suite of the oytag kuda suture zone shrimp zircon u pb dating of two of these intrusions shows that they were emplaced into the oytag volcanic rocks at 337 5 4 1 ma and 327 7 4 9 ma and that the younger intrusion contains inherited zircons ranging from 435 3 to 480 8 ma both intrusions are composed of low al trondhjemite and tonalite the rocks have low k 2 o and sr and high y contents with low sr y ratios they have relatively low rare earth element ree concentrations and are depleted in light ree lree and relatively enriched in heavy ree hree with marked negative eu anomalies in the chondrite normalized ree patterns they have initial 87 sr 86 sr ratios of 0 7048 to 0 7068 and e nd t values of 6 2 to 7 6 which are lower than those of typical morb in situ hf isotopic compositions of zircons with early carboniferous age from both intrusions are characterized by positive initial e hf values ranging from 12 5 to 19 5 similar to typical morb the inherited ordovician zircons in the younger intrusion have initial e hf values of 1 9 to 3 1 similar to zircons from ordovician granitoids in the region detailed elemental and isotopic data suggest that the oytag plagiogranites were formed in an oceanic island arc setting by differentiation of arc tholeiitic magmas that formed in response to the intra oceanic subduction the inherited zircons are interpreted as the xenocrysts captured from the incipient oceanic crust that contains relicts of discrete fragments of continental crust with ordovician zircons through which the plagiogranite was emplaced the oytag ophiolite suite might be the remnants of an ancient island arc the basement of which was the incipient oceanic crust the oytag kuda suture zone is suggested to be a multiple suture zone that represents the remnants of both the proto tethyan and paleo tethyan oceans the western kunlun orogen was therefore not a long lived active continental margin during the early and late paleozoic times it most likely underwent at least two orogenic cycles and thus might represent a multiple orogenic belt

the equilibration of short baroclinic waves abstract the life cycles of short baroclinic waves are investigated with the intention of completing a simple classification of nonlinear equilibration scenarios short waves become important in moist environments as latent heating reduces the scale of maximum baroclinic instability long wave life cycles wavenumber 6 were previously found to depend on details of the low level momentum fluxes established during the earliest stages of development these fluxes also serve as a focal point for the present study for a realistic zonally symmetric jet on the sphere the normal mode life cycle of a short wave wavenumber 8 under both dry and moist conditions is described latent heating intensifies the low pressure system and frontal zones but does not alter the broader details of the life cycle the normal modes have predominantly equatorward momentum fluxes in contrast to the mainly poleward momentum fluxes of long waves the short waves are more meridionally confined the equatorward momentum fluxes dir

the role of rossby wave breaking in shaping the equilibrium atmospheric circulation response to north atlantic boundary forcing abstract the role of rossby wave breaking rwb is explored in the transient response of an atmospheric general circulation model to boundary forcing by sea ice anomalies related to the north atlantic oscillation nao when the ncar community climate model version 3 was forced by an exaggerated sea ice extent anomaly corresponding to one arising from a positive nao a localized baroclinic response developed and evolved into a larger scale equivalent barotropic pattern resembling the negative polarity of the nao the initial baroclinic response shifted the phase speeds of the dominant eddies away from a critical value equal to the background zonal flow speed resulting in significant changes in the spatial distribution of rwb the forcing of the background zonal flow by the changes in rwb accounts for 88 of the temporal pattern of the response and 80 of the spatial pattern of the zonally averaged response although results here focus on one experiment this rwb critical line mechanism appears to be