uncertainties in the relative positions of the australia antarctica lord howe and pacific plates since the late cretaceous we determined parameters that describe finite rotations and their uncertainty regions for relative plate motion at the spreading centers between the pacific and antarctica plates between australia and antarctica and between the lord howe rise and australia we combined these to yield a range of possible finite rotations describing the relative positions of the pacific australia antarctica and lord howe plates since the late cretaceous if the pacific australia plate boundary has had its present trend since anomaly 18 time reconstructions show 330 110 km of motion of the pacific plate relative to the lord howe rise since anomaly 5 time 9 8 m y 420 110 km since anomaly 6 time 19 5 m y 770 330 km since anomaly 13 time 35 6 m y and 820 260 km since anomaly 18 time 43 0 m y we examined two cases for times prior to anomaly 18 assuming a late cretaceous age of australia antarctica separation if a plate boundary existed between the lord howe rise and pacific plates since the late cretaceous with no plate boundary in antarctica reconstructions with the lord howe rise fixed predict 610 200 km of westward motion of the pacific plate between the times of anomalies 31 and 22 followed by 260 100 km of northward motion between the times of anomalies 22 and 18 if the lord howe rise was fixed to the pacific plate until the eocene but a plate boundary existed between east and west antarctica reconstructions show very little motion across this boundary between the times of anomalies 31 and 22 followed by convergence between the times of anomalies 22 and 18 this second case also brings 70 80 m y paleomagnetic poles from the pacific and east antarctica plates into better agreement than the first case but large uncertainties in the reconstructions do not allow the first case to be conclusively eliminated

the upper level circulation anomaly over central asia and its relationship to the asian monsoon and mid latitude wave train in early summer a large intraseasonal variation in geopotential height over the central asia region where the asian subtropical jet is located occurs between may and june and the most dominant variation has a wave like distribution this variation in geopotential height influences precipitation across south and southeast asia in this paper we use composite analysis to determine the causes of this intraseasonal variation over central asia the wave train propagates from the northern atlantic ocean to central asia over a period of a week and generates an anomaly in geopotential height over the region the tropical disturbance which is similar to the madden julian oscillation appears a few days before the maximum of the anticyclonic anomaly over central asia and is accompanied by active convection over the indian ocean and suppressed convection over central america results of numerical experiments using a linear baroclinic model show that the active convection over the northern indian ocean causes the anticyclonic anomaly over central asia the wave train that extends from the northern atlantic ocean to central asia is generated by negative thermal forcing over central america and the phase distribution of this wave train is similar to that observed in the composite analysis central asia is the region where the effects of the tropics and middle latitudes overlap and it is an important connection point between the asian monsoon and middle latitudes

roles of synoptic to quasi biweekly disturbances in generating the summer 2003 heavy rainfall in east china abstractduring the mei yu season of the summer of 2003 the yangtze and huai river basin yhrb encountered anomalously heavy rainfall and the northern yhrb nyhrb suffered a severe flood because of five continuous extreme rainfall events a spectral analysis of daily rainfall data over yhrb reveals two dominant frequency modes one peak on day 14 and the other on day 4 i e the quasi biweekly and synoptic scale mode respectively results indicate that the two scales of disturbances contributed southwesterly and northeasterly anomalies respectively to the mei yu frontal convergence over the southern yhrb syhrb at the peak wet phase an analysis of bandpass filtered circulations shows that the lower and upper regions of the troposphere were fully coupled at the quasi biweekly scale and a lower level cyclonic anomaly over syhrb was phase locked with an anticyclonic anomaly over the philippines at the synoptic scale the strong northeasterly components of an anticyclonic anomaly with a deep cold

orographic effects of the tibetan plateau on the east asian summer monsoon an energetic perspective this paper investigates the dynamical processes through which the tibetan plateau tp influences the east asian summer monsoon easm within the framework of the moist static energy mse budget using both observations and atmospheric general circulation model agcm simulations the focus is on the most prominent feature of the easm the so called meiyu baiu mb which is characterized by a well defined southwest northeast elongated quasi stationary rainfall band spanning from eastern china to japan and into the northwestern pacific ocean between mid june and mid july observational analyses of the mse budget of the mb front indicate that horizontal advection of moist enthalpy and primarily of dry enthalpy sustains the front in a region of otherwise negative net energy input into the atmospheric column a decomposition of the horizontal dry enthalpy advection into mean transient and stationary eddy fluxes identifies the longitudinal thermal gradient due to zonal asymmetries and the meridional stationary eddy velocity as the most influential factors determining the pattern of horizontal moist enthalpy advection numerical simulations in which the tp is either retained or removed show that the tp influences the stationary enthalpy flux and hence the mb front primarily by changing the meridional stationary eddy velocity with reinforced southerly wind over the mb region and northerly wind to its north changes in the longitudinal thermal gradient are mainly confined to the near downstream of the tp with the resulting changes in zonal warm air advection having a lesser impact on the rainfall in the extended mb region

correlations between the classic parana and cape karoo sequences of south america and southern africa and their basin infills flanking the gondwanides du toit revisited

paleozoic plate dynamics current plate motions can be accounted for by a balance of active forces slab pull ridge push and for continental plates trench suction with drag beneath the plate as a resistive force if we assume that the same forces have acted through time we can reconstruct plate motions from the geometry of past plate boundaries paleozoic reconstructions are made with paleomagnetic tectonic climatic and biogeographic data as no ocean floor remains paleomap reconstructions are used to estimate past plate speeds and to test simple dynami cal models in order to determine which ranges of forces best accounts for the observations over the last 600 m y plate speeds averaged over 40 to 100 m y intervals show considerable variation gondwana s speed oscillates from 20 to 60 km m y over a long timescale 200 400 m y with considerable noise superposed over the paleozoic era motions for large continental regions average 28 krn m y force balance models based on present day observations suggest that continental regions without a large attached slab would move 30 mrn yr the opening and closing of the ocean between laurentia and gondwana 560 400 ma is used to test dynamical models and the parameter values assumed in the late precambrian laurentia rifted away from gondwana in the earliest cambrian it was near 40os by late cambrian and ordovician it had moved to the equator during the silurian and devonian laurentia reversed direction and later collided with gondwana at 40os in a model of the forces acting on the plates slab pull ridge push and trench suction are assumed to balance plate drag only certain ranges of ridge push and trench parameters can model both the opening and subsequent closing of the ocean the dynamic models with parameter values inferred from present rates bracket the rates required by the reconstructions

reference frames for plate tectonics and uncertainties abstract paleomagnetic hotspot and mean lithosphere frameworks are compared for the cenozoic era errors in the relative motions of plate pairs accumulate to give uncertainties in reference frames uncertainties in the poles of the mean lithosphere framework are estimated to be less than 1 and for the hotspot framework 1 1 assuming a 50 km error in location of individual hotspots the a 95 s for paleomagnetic data range from 1 to 5 with these uncertainties the differences between the paleomagnetic and mean lithosphere coordinate systems are not found to be statistically significant and the hotspot frame barely differs from the mean lithosphere frame during the early tertiary on the other hand the hotspot and paleomagnetic axes diverge in opposing directions in the mean lithosphere framework and can be distinguished this difference can be attributed to the pacific hotspots having more than 10 motion relative to the mean lithosphere whereas the african set of hotspots does not statistically differ from the mean lithosphere frame one possible explanation is a shift of the pacific hotspots relative to those in the atlantic

the role of subduction induced subsidence in the evolution of the karoo basin abstract the stratigraphic record indicates that during the late carboniferous to early triassic south africa experienced an episode of large scale subsidence that resulted in the development of the karoo basin the southern margin of the region was contemporaneously dominated by an episode of compressional tectonics and there is evidence for subduction of the paleo pacific plate beneath the karoo basin we propose that the long wavelength component of the basin subsidence resulted from the deflection of the lithosphere due to mantle flow coupled to the adjacent subduction this was followed by a recovery phase during which the entire region was uplifted on cessation of subduction and subsequent loss of dynamic support for subsidence contributing to the present day high elevation topography of south africa numerical models of mantle convection are presented and show that a shallow dipping slab is able to reconcile the observed long wavelength subsidence of the basin a significant component of the n

intraseasonal teleconnection between north american and western north pacific monsoons with 20 day time scale abstract based on a recently released high resolution reanalysis dataset for the north american region the intraseasonal variability isv with a time scale of about 20 days of the north american monsoon nam is examined the rainfall signals associated with this phenomenon first emerge near the gulf of mexico and eastern pacific at about 20 n they subsequently migrate to the southwestern united states along the slope of the sierra madre occidental the rainfall quickly dissipates upon arrival at the desert region of arizona and new mexico aznm the enhanced rainfall over aznm is accompanied by strong southeasterly low level flow along the gulf of california this pattern bears strong resemblance to the circulation related to gulf surge events as documented by many studies the southeasterly flow is associated with an anomalous low vortex over the subtropical eastern pacific ocean off california and a midlatitude anticyclone over the central united states in the lower troposphere this flow pat

evidence for relative motions between the indian and australian plates during the last 20 m y from plate tectonic reconstructions implications for the deformation of the indo australian plate we use plate tectonic reconstructions to establish whether motions between india and australia occurred since chron 18 43 ma we test the africa antarctica australia india plate circuit closure at chrons 5 10 ma 6 21 ma and 13 36 ma using a compilation of magnetic anomalies and fracture zone traces from the southeast southwest central indian and the carlsberg ridges additional reconstructions at chrons 23 55 ma and 26 61 ma are used to estimate the overall motion between india and australia relative motions between the indian and australian plates are estimated using the plate circuit india africa australia a new statistical approach based on spherical regression analyses is used to assess the uncertainty of the best fitting finite rotations from the uncertainties in the data the uncertainty in a rotation is described by a covariance matrix directly related to the geometry of the reconstructed plate boundary to the distribution and estimated errors of the data points along it our parameterization of the rotations allows for simple combination of the rotation uncertainties along a plate circuit path results for chron 5 are remarkably consistent with present day kinematics in the indian ocean except that the arabian and indian plates are found to be separate plates comparisons of the motions between the indian and african plates across the carlsberg ridge with that between the australian and african plates across the central indian ridge evidence a significant counterclockwise rotation of the australian plate relative to the indian plate about a pole located in the central indian basin the determinations are consistent for chrons 26 13 6 and 5 determination at chron 23 is different but questionable due to the small number of available data we propose two alternative solutions that both predict convergence within the wharton and central indian basins and extension in the vicinity of the chagos laccadive ridge the first solution assumes that all the deformation in the equatorial indian ocean started 7 ma ago as found by ocean drilling program leg 116 hence all the determinations at different times represent the total motion between india and australia the averaged india australia euler vector chrons 5 6 13 and 26 11 1 s 78 0 3 54 lies within the central indian basin and yields a n s contraction of 46 52 km at 85 and 80 63 km at 90 however the difference of the india australia euler vectors at chrons 5 and 6 suggests that the india australia convergence started between 10 and 21 ma following the continent continent collision of india with asia in the early miocene the second averaged solution chrons 6 13 and 26 5 2 s 74 3 e 5 93 predicts a total n s contraction of 123 73 km at 85 e and 178 91 km at 90 e both models are compatible with the deformation pattern observed in the equatorial indian ocean

multiscale stratigraphic analysis of a structurally confined submarine fan carboniferous ross sandstone ireland discussion in promoting the ross formation carboniferous shannon basin 2 as an excellent outcrop analog for gulf of mexico oil rich pliocene pleistocene salt withdrawal minibasins pyles 2008 reaffirmed the popular deep sea turbidite model for the ross formation collinson et al 1991 chapin et al 1994 elliott 2000 martinsen et al 2000 lien et al 2003 without mentioning a detailed published reinterpretation of the ross formation as lacustrine river fed turbidites hyperpycnites and wave modified turbidites higgs 2004 oil field development in technologically challenging deep water settings can have costly economic consequences if based on predictions emanating from inappropriate outcrop analogs such consequences include in order of increasing costliness 1 selection of nonoptimum perforation intervals causing lower production flow rates and lower ultimate recovery 2 nonoptimum placement spacing and number of development wells with the same effects and 3 inaccurate predictions of reserves volume and production rates leading to unwarranted declaration of field economic viability hence major expenditures such as platforms development drilling programs and pipelines or nonviability higgs 2004 for an outcrop to be considered analogous to any given subsurface example the two facies associations should be essentially indistinguishable insofar as this can be judged from the existing core control in other words the interpreted depositional processes should be the same resulting in near identical sand body reservoir architecture given the passive margin context and present deep water below storm wavebase slope setting of the gulf of mexico minibasins e g pyles 2008 a similar deep marine setting can be inferred for the pliocene pleistocene in contrast the ross formation may be neither marine nor of deep water origin sedimentological evidence summarized below suggests 1 lowered salinity amenable to much greater frequency and duration of hyperpycnal flows than in

distinct quasi biweekly features of the subtropical east asian monsoon during early and late summers using global precipitation climatology project daily rainfall and era interim reanalysis data we investigate the distinct characteristic of quasi biweekly variation qbv 12 20 days over east asia ea during early june 10 july 20 and late july 21 august 31 summer the qbv maximum variance is found over the core region of ea 30 40 n 110 130 e which includes eastern china lower reaches of the yellow huaihe and yangtze rivers and the korean peninsula at both its peak wet and dry phases qbv over the core region has a baroclinic structure but with different spatial distributions different lower level prevalent wind anomalies and different upper level major circulation anomalies in the two subseasons meanwhile the two subseasons have different propagating tracks prior to reaching the peak phase and different precursors associated with the local genesis of qbv furthermore during the transition from the peak dry to peak wet phase of qbv the major monsoon circulations have different behaviors that tropical monsoon trough extends eastward in early summer but retreats westward in late summer and the south asia high sah and western north pacific wnp subtropical high move toward away from each other in early late summer the abrupt change of mean state in mid to late july which includes the northward migration of westerly jet sah and wnp and the weakening and broken of westerly jet is considered the root cause of the change in behavior of qbv finally we indicate that the tropical monsoon trough and midlatitude westerly jet are possible sources of qbv over subtropical ea in both subseasons and provide useful guidance for 2 3 week predictions over ea

influence of the tectosphere upon plate motion this paper tests two hypotheses for the influence of thick lithosphere the tectosphere upon plate motion the first is that the tectosphere reaches down into high viscosity regions of the asthenosphere effectively slowing the motion of continental plates the second is that the tectosphere reaches down below the slow moving convective boundary layer into regions of rapid mantle convection and effectively speeds or slows the motion of continental plates our data imply that the tectosphere speeds plate motion rather than impedes plate motion and are thus most consistent with the second hypothesis

impact of the quasi biweekly oscillation over the western north pacific on east asian subtropical monsoon during early summer 1 the impact of quasi biweekly oscillation qbwo over the western north pacific on east asian summer monsoon easm is investigated the life cycle of qbwo is divided into eight phases defined by the two leading principal components pc1 and pc2 of an empirical orthogonal function analysis subtropical rainfall shows significant changes with a northwestward propagation of convection from equatorial regions to the south china sea scs the most significant variations occur in qbwo phases 3 and 4 enhanced convection over scs and phases 7 and 8 reduced convection over scs the east asia mei yu significantly decreases in qbwo phases 3 and 4 but increases in phases 7 and 8 the qbwo influences easm through modulating the subtropical monsoon flow and extratropical circulation the response of lower tropospheric atmosphere to qbwo shows a northwestward propagation and a downstream wave train that extends northward into the western north pacific modulating the scs monsoon trough and the easm flow associated with moisture transportation the mid tropospheric extratropical circulation and the western pacific subtropical high also show obvious changes accompanying qbwo evolution resulting in circulation patterns associated with cold air activity moreover changes with qbwo are found in the upper tropospheric east asian westerly jet stream and the south asian high and these changes contribute to upper level divergence over subtropical east asia

the permo carboniferous dwyka formation of southern africa deposition by a predominantly subpolar marine ice sheet abstract the 800 m thick glacigene dwyka formation was deposited along the northern margin of the permo carboniferous dwyka basin which covered an area of approximately 2 10 6 km 2 in southwestern gondwana the palaeogeographic setting geochemical data of the mudrocks and diamictites and the palaeontology indicate marine conditions during sedimentation ice lobes from spreading centres in the north east and south coalesced in the basin to form an extensive ice cover from the westphalian to the late sakmarian lodgement rain out and subaqueous debris flow diamictons subaqueous and subglacial melt water sands suspended mud and turbidity current sands and silts accumulated in the dwyka basin sedimentation started on the continental shelf during a grounded ice sheet stage predominantly lodgement processes then a floating ice stage predominantly debris rain out and finally an ice sheet disintegration stage debris rain out sand fall out and suspension settling of mud the palaeogeographic setting presence of marine conditions in the basin and the scale of glaciation indicate deposition from a predominantly mid latitudinal marine ice sheet the overall characteristics of the glacial sequence are neither typical of a polar nor a temperate setting and for such ancient glaciations a subpolar setting with the presence of unstable ice shelves is suggested

plate reconstruction uncertainties using empirical probability density functions we present a method of determining plate reconstruction uncertainties using empirical probability density functions pdfs we convert estimated positioning errors of fracture zone and magnetic anomaly crossings into data pdfs which describe the uncertainty in the location of each fracture zone or magnetic anomaly crossing an empirical pdf is formed for the rotation between a single plate pair based on the ability to align the rotated data along a series of ridge and transform segments monte carlo techniques are then used to sample the pdfs for rotations between single plate pairs to form a pdf for a sequence of rotations this is accomplished with a frequency of occurrence approach for a gridded representation of possible combined rotations we also develop pdfs for the reconstructed positions of points on the rotated plates from the pdf for the rotation confidence regions for any of the pdfs are formed by contouring the cumulative probabilities of grid points within the pdf we provide comparisons with other previously published studies for the anomaly 13 single plate pair reconstruction between the pacific and antarctic plates as well as for the anomaly 6 19 8 ma combined reconstruction between the pacific and north american plates results for the anomaly 13 reconstruction are generally consistent with previous studies but smaller confidence regions are attributed to the more robust nature of the empirical pdf approach that we have used the 95 confidence region for the anomaly 6 reconstruction is less than half that of the worst case scenario the benefit of our monte carlo technique is that it adequately samples the pdfs for all of the rotations thus accurately including the effects of coupling uncertainties between pole location and amount of rotation

a method for bounding uncertainties in combined plate reconstructions we present a method for calculating uncertainties in plate reconstructions that does not describe the uncertainty in terms of uncertainties in pole positions and rotation angles if a fit of magnetic anomalies of the same age and fracture zones that were active as transform faults at that time can be found such a reconstruction can be perturbed and degraded by small rotations about each of three orthogonal axes partial uncertainty poles if the uncertainty in the reconstruction is a consequence of independent small but acceptable rotations about these axes then the uncertainties in reconstructed points will be elliptical in shape the dimensions and orientation of such ellipses will depend upon the magnitudes of the perturbing rotations and upon the relative geometry of the partial uncertainty poles and the points in question in a sequence of rotations each rotation will contribute an elliptical region of uncertainty for each reconstructed point and these ellipses can be combined as independent statistical quantities to obtain a confidence ellipse for the sequence of rotations as a test we calculated uncertainties for three points on the pacific plate with respect to north america at the time of anomaly 6 20 ma the computed uncertainties are similar in shape to those that we previously obtained for a sequence of marginally acceptable rotations but the major axes of the ellipses presented here are about 25 shorter

the fan that never was discussion of upper carboniferous fine grained turbiditic sandstone from southwest england a model for growth in an ancient delta fed subsea fan discussion and reply

blocking highs over asia and monsoon droughts over india severe summer droughts of the indian subcontinent have been found to accompany prolonged breaks in the south west monsoon data from the years of severe drought suggest that the associated breaks were due to upper tropospheric blocking ridges over east asia we present here a model for the evolution of two such blocking ridges the east asia eabr and the west asia wabr apparently an intense wabr the initiator of the monsoon break precedes the formation of the eabr this cycle could be a way of predicting years of intense drought or monsoon activity

teleconnections associated with northern hemisphere summer monsoon intraseasonal oscillation the boreal summer intraseasonal oscillation bsiso has strong convective activity centers in indian i western north pacific wnp and north american na summer monsoon sm regions the present study attempts to reveal bsiso teleconnection patterns associated with these dominant intraseasonal variability centers during the active phase of ism a zonally elongated band of enhanced convection extends from india via the bay of bengal and philippine sea to tropical central pacific with suppressed convection over the eastern pacific near mexico the corresponding extratropical circulation anomalies occur along the waveguides generated by the north african asian jet and north atlantic north european jet when the tropical convection strengthens over the wnpsm sector a distinct great circle like rossby wave train emanates from the wnp to the western coast of united states us with an eastward shift of enhanced meridional circulation in the active phase of nasm large anticyclonic anomalies anchor over the western coast of us and eastern canada and the global teleconnection pattern is similar to that during a break phase of the ism examination of the evolution of the bsiso teleconnection reveals quasi stationary patterns with preferred centers of teleconnection located at europe russia central asia east asia western us and eastern us and canada respectively most centers are embedded in the waveguide along the westerly jet stream but the centers at europe and russia occur to the north of the jet induced waveguide eastward propagation of the iso teleconnection is evident over the pacific north america sector the rainfall anomalies over the elongated band near the monsoon domain over the indo western pacific sector have an opposite tendency with that over the central and southern china mexico and southern us providing a source of intraseasonal predictability to extratropical regions the bsiso teleconnection along and to the north of the subtropical jet provides a good indication of the surface sir temperature anomalies in the nh extratropics

quasi biweekly impact of the atmospheric heat source over the tibetan plateau on summer rainfall in eastern china we investigated the intraseasonal relationship between the atmospheric heat source over tibetan plateau tp and summer rainfall in eastern china a quasi biweekly oscillation qbwo is the common dominant periodicity over both the tp and eastern china crucially the tp heat source qbwo leads rainfall qbwo over its downstream region by 2 8 days the qbwo over the tp shows a significant eastward propagation phase composite further identified the specific propagation pathway tp qbwo first propagates eastward to central china southward to southern china and then northeastward to the lower reaches of the yangtze river with a zigzag propagating pathway mechanistically the eastward propagation of the upper level divergence caused by the movement of the 200 hpa jet core and south asian high contributes to the eastward propagation of the rainfall qbwo simultaneously the eastward westward shift in the western north pacific subtropical high causes deepening flattening of the monsoon trough and the occurrence of an anomalous cyclone anticyclone over the western north pacific an anomalous anticyclonic cyclonic circulation around the tp appears with the wet to dry dry to wet phase transition of the tp qbwo together they play a crucial part in the southward northeastward movement of the qbwo further dynamic analysis indicates that the horizontal moisture advection acts on the whole eastward propagating process of the qbwo whereas the horizontal vorticity advection is only significant when qbwo is over the tp this study shows that the fluctuations in tp heat source are important indicators in extended forecasts of summer rainfall in eastern china

the origin and dispersion characteristics of the observed tropical summertime synoptic scale waves over the western pacific abstract the origin initiation and dispersion behavior of the observed summertime synoptic scale disturbances in the tropical western pacific are studied these westward propagating disturbances have the strongest growth rate over the region of 130 160 e off the equator the three dimensional wave activity flux associated with a wave packet in the vicinity of this region is computed in general wave activity is directed westward there is accumulation of activity flux which gives rise to the amplification of waves in the low levels such accumulation can be attributed to the convergence of both the mean flow and the intrinsic group velocity diabatic forcing also contributes to the growth of disturbances and is most important in the 500 600 hpa layer along the east west oriented storm tracks of the synoptic scale disturbances there are two different dynamical regimes west of 150 e enhanced convection is associated with increased specific humidity at the top of the planetary boundary layer an

the fan that never was upper carboniferous fine grained turbiditic sandstones from southwest england a model for growth in an ancient delta fed subsea fan discussion

geochemical evidence for lacustrine microbial blooms in the vast permian main karoo parana falkland islands and huab basins of southwestern gondwana early permian black pyritic shale units i e the whitehill irati and huab formations and black rock member in southwestern gondwana basins have elevated 13c values of total organic carbon up to 17 pdb hydrogen indices between 300 and 1000 mg co2 g c and oxygen indices 30 mg co2 g c these data suggest a manifestation of a microbial bloom event values for 13c between 26 and 22 pdb hydrogen 100 mg co2 g c and oxygen indices of total organic carbon above and below these rock units are typical for palaeozoic terrestrial type iii organic matter carbon 13 isotope stratigraphy concur with palaeontological evidence that these formations are stratigraphical equivalents and therefore that the microbial blooms covered a vast area 5 million km2 possibly earth s most expansive microbial bloom the palaeoenvironment of the rock units preceding and including the black shales was most likely lacustrine with fresh to brackish water as shown by stable isotope c o and s evidence from organic matter carbonates and pyrite the implication is that a broad tectonic belt which formed as a result of compressional tectonics during the late carboniferous to early permian from the palaeo west must have been sufficiently well developed to cut off any contact with seawater earlier than predicted late permian from previous stratigraphic and sedimentological studies stable isotope data supported by mineralogical evidence indicate that conditions particularly in the upper portions of the lacustrine oil shales were brackish and locally may have been evaporitic we envisage that the microbial blooms possibly botryococcus peaked in the upper half of the black shale units conditions rapidly became unfavourable for microbial blooms across the entire basin in the overlying formations manifested by a change from oil shales type i organic matter to organic poor type iii shales this may possibly have been a consequence of tectonic activity and interrelated causes stable isotope data of carbonates in the overlying sediments indicate that in the palaeo north the basin became evaporitic drying up and in the palaeo southern part of the basin high latitude altitude water flooded the basin and so brought to a close the microbial blooms

an observational study of the south china sea monsoon during the 1979 summer onset and life cycle abstract the onset and life cycle of the 1979 south china sea summer monsoon were examined in the context of the 30 60 and 12 24 day monsoon modes the former intraseasonal mode formed the northward migrating monsoon trough ridge while the latter intraseasonal mode propagated westward in the south china sea the monsoon in this region exhibited three cycles over the summer may august with the onset taking place about one cycle ahead of the onset of the indian and japanese monsoons climatologically a summer trough line radiated out from the indian monsoon trough region across indochina to the northern south china sea the monsoon onset occurred when the 30 60 day monsoon trough and the 12 24 day low center arrived simultaneously at the northern south china sea close to the climatological summer trough line in the middle of may the breaks occurred when the 30 60 day monsoon ridge lines and the 12 24 day high center met near 15 20 n in the northern south china sea the south china sea monsoon wa

characteristics and mechanisms of the subseasonal eastward extension of the south asian high abstractthis study investigates the features of eastward extension of the south asian high sah and its connection with diabatic heating and rainfall over eastern asia on subseasonal time scales the causes of sah s eastward extension are examined by potential vorticity pv diagnosis with emphasis on the joint role of diabatic heating feedback and midlatitude wave train the sah s eastward extension features eastward propagation of a wave train across eurasia among the wave train the migration of weak high from the western flank of the tibetan plateau tp to the east of tp contributes to the sah s eastward extension at the early stage when the sah approaches its easternmost position a strong negative pv positive geopotential height center prevails to the east of the tp at 200 hpa the associated anomalies in diabatic heating and rainfall include the anomalous heating and above normal rainfall over the south china sea scs and subtropical western pacific occurring 12 days before the sah s eastern

errors in plate rotations as described by covariance matrices and their combination in reconstructions we use covariance matrices to describe the errors in plate rotations and to combine the contrbutions of individual plate pairs for plate reconstructions first for the rotation of a pair of plates the covariance matrix which describes the errors in the rotation is defined then we show how individual covariance matrices can be combined in a circuit of successive plate rotations to assess the errors in a plate reconstruction using the covariance matrix for accumulated errors from a sequence of rotations we can determine the uncertainties in the position of selected points on one plate in the plate circuit to another that is assumed to be fixed as an example the position of the pacific plate relative to north america is reconstructed at chron 6 20 ma this choice is made to allow a direct comparison with published error assessments using the accumulated covariance matrix we find similar uncertainties in the positions of their selected points on the pacific plate as a further test this reconstruction is repeated using seafloor spreading data that directly relate antarctica to africa bypassing the link of india this eliminates the largest source of error in the plate circuit that due to the short ridge segment between africa and india this revised shortened circuit results in generally smaller errors in the positions of points on the pacific plate the covariance matrices of the two alternative circuits are used to construct the optimal estimate and its associated error the optimal estimate and its error region intersect the two alternative reconstructions and their error regions

variations in amount and direction of seafloor spreading along the northeast atlantic ocean and resulting deformation of the continental margin of northwest europe the ne atlantic ocean opened progressively between greenland and nw europe during the cenozoic seafloor spreading occurred along three ridge systems the reykjanes ridge south of iceland the mohns ridge north of the jan mayen fracture zone jmfz and the aegir and kolbeinsey ridges between iceland and the jmfz at the same time compressional structures developed along the continental margin of nw europe we investigate how these compressional structures may have resulted from variations in the amount and direction of seafloor spreading along the ridge system assuming that greenland is rigid and stationary we have used a least squares method of palinspastic restoration to calculate differences in direction and rate of spreading along the reykjanes kolbeinsey aegir and mohns ridges the restoration generates relative rotations and displacements between the oceanic segments and predicts two main periods of left lateral strike slip along the main oceanic fracture zones 1 early eocene to late oligocene along the faeroe fracture zone and 2 late eocene to early oligocene and during the miocene along the jmfz such left lateral motion and relative rotation between the oceanic segments are compatible with the development of inversion structures on the faeroe rockall plateau and norwegian margin at those times and probably with the initiation of the fugloy ridge in the faeroe shetland basin during the eocene and oligocene the iceland mantle plume appears to have been in a position to generate differential seafloor spreading along the ne atlantic and resulting deformation of the european margin

quasi biweekly oscillation over the tibetan plateau and its link with the asian summer monsoon abstract intraseasonal variation isv is especially prominent and unique in the asian summer monsoon region in this work the dominant isv mode over the tibetan plateau tp in the summer monsoon season june august together with its structure and evolution is identified using station observations global precipitation climatology project precipitation data and era interim during 1979 2011 results indicate that quasi biweekly oscillation qbwo is the dominant mode of isv over the tp and is significant in terms of the circulation precipitation and diabatic heating fields in particular the qbwo is closely related to the onset and active break phases of the tp summer monsoon in most cases the qbwo originates from the equatorial western pacific and first propagates northwestward to the bay of bengal and northern india then northward to the southeastern tp and finally eastward to the east asian area showing a clockwise propagation pathway two main mechanisms are responsible for the northward

hotspot tracks and the early rifting of the atlantic abstract many hotspot tracks appear to become the locus of later rifting as though the heat of the hotspot weakens the lithosphere and tens of millions of years later the continents are split along these weakened lines examples are the west coast of greenland east coast of labrador madeira hotspot the south coast of mexico north coast of honduras guyana hotspot and the south coast of west africa north coast of brazil st helena hotspot a modern day analog of a possible future rift is the snake river plain where the north american continent is being pre weakened by the yellowstone hotspot track this conclusion is based on reconstructions of the motions of the continents over hotspots for the past 200 million years the relative motions of the plates are determined from magnetic anomaly isochrons in the oceans and the motion of one plate is chosen ad hoc to best fit the motions of the plates over the hotspots however once the motion of this one plate is chosen the motions of all the other plates are prescribed by the relative motion constraints in addition to the correlation between the predicted tracks and sites of later continental breakup exposed continental shields correlate with the tracks their exposure may be the result of hotspot induced uplift which has led to erosion of their former platform sediment cover

jackfork group southeastern oklahoma new gas play in the ouachita overthrust recent discovery of natural gas in sandstones of the jackfork group of southeastern oklahoma has led to revised interpretations of hydrocarbon potential in the ouachita thrust province of eastern oklahoma jackfork reservoirs consist of fine to very fine grained submarine fan lobe sandstones with low matrix permeability and porosity production is dependent upon natural fractures enhanced in most cases by artificial stimulation individual wells have produced at rates of 1 3 5 7 mcf footnote per day and possess estimated reserves in the range of 2 0 7 6 gcf footnote hyperbolic decline suggests gas contribution from the matrix possibly due to the presence of microfractures drilling has concentrated on two subsidiary thrust blocks in the hanging wall of the ti alley thrust southern latimer county however recent outcrop petrographic and sedimentological analyses have shown that traditional depositional models of the jackfork are overly limited and that potential jackfork reservoirs exist across a broad area to the south of the current play such analyses have revealed the existence of thick medium coarse grained channel sequences at a number of localities in the lynn mountain syncline similar sequences may also exist well to the south in the boktukola syncline where thick sand intervals have been identified petrographic study of samples from the lynn mountain syncline suggests that channel sequences may have significantly higher reservoir quality than is found in productive jackfork sandstones to the north traditional assumptions pos ulating low regional hydrocarbon potential for the jackfork therefore stand in need of revision

global plate motions relative to the hot spots 64 to 56 ma we examined the early tertiary global plate velocities with respect to the hot spots and compared these velocities both to those at present and to early tertiary velocities inferred by assuming that no net torque is exerted on the lithosphere as a whole in our reconstruction the velocities of the pacific and african plates were inferred directly from their hot spot tracks and the velocities of other plates with respect to the hot spots were calculated from the motion of the pacific or african plate and by relative motions estimated from seafloor spreading data the relative motion between assumed separate north pacific and south pacific chatham rise plates was estimated by assuming the hot spots in the atlantic ocean basin have been fixed with respect to those in the pacific ocean basin thereby avoiding the use of a poorly defined relative motion circuit we found that the characteristics of early tertiary plate motions with respect to the hot spots resemble those at present the root mean square velocity of every major continental plate with respect to the hot spots during the early tertiary exceeds its present velocity but with the exception of the indian plate is less than the root mean square velocity of every early tertiary oceanic plate equatorial lithosphere moved faster than polar lithosphere during the early tertiary but the difference is less than at present over the interval 64 to 56 ma the no net torque absolute velocities differ from the assumed fixed hot spot velocities by only 0 04 ma which is insignificant thus two dissimilar approaches fixed hot spots and no net torque of the lithosphere when applied to identical early tertiary relative plate velocities yield similar absolute plate velocities we attribute the differences between these two reference frames found in prior investigations to relative plate velocities different than we assume here

role of the tibetan plateau thermal forcing in the summer climate patterns over subtropical asia the mechanism of the tibetan plateau tp thermal forcing in influencing the summer climate patterns over subtropical asia is investigated by means of ncep ncar reanalysis diagnosis results show that since the tp is a huge elevated heating source with the strongest heating in the surface layers in summer the thermal adaptation results in a shallow cyclonic circulation near the surface and a deep anticyclonic circulation above it according to the steady barotropic vorticity equation for large scales airflow must converge in the lower layers and diverge in the higher layers over the eastern side of the tp however the western side of the tp is characterized by a reversed structure i e divergence in lower layers but convergence in higher layers hence pumping and sucking processes bring in upward and downward movement over the east and west sides of the tp respectively such a circulation is embedded in the large scale circulation that is forced by the eurasian continental heating because the tp together with iran plateau are located at the central and eastern parts of the continent and because the orography induced circulation is in phase with the continental scale circulation the role of the tp thermal forcing is to intensify the east asian monsoon to its east and the dry and hot desert climate in mid asia to its west the summertime thermal forcing of the rockies and andes can generate similar circulations along the two subtopics as the tp does since they are located near the western coasts but the lower troposphere poleward flow that is induced by orographic thermal forcing does not coincide with the poleward flows over the eastern coastal region that is induced by continental heating and the monsoon rainfall in north and south america is not as strong as in east asia however the equatorward flow and the associated subsidence induced by the two mountain ranges along the western coasts of both north and south america are in phase with those induced by continental heating these contribute to the formation of the stable low stratus clouds and strong long wave radiative cooling over the eastern subtropical pacific regions just off the western coast of the continent

pacific plate reconstructions and uncertainties abstract the pacific plate is positioned into the hotspot reference frame first directly relative to the pacific hotspots and then indirectly relative to the african hotspots by using seafloor spreading data the reconstructions are repeated for 10 15 37 48 and 61 ma the errors associated with each link for both approaches are expressed by covariance matrices which can be combined to yield the overall error in the case of the relative plate motion circuit assuming the hotspots are fixed and that the reconstructions record the true relative positions of the plates the reconstructions should be equivalent within their uncertainties in fact however there is agreement within the uncertainties only for 10 ma with the misfit increasing with age for the earlier reconstructions these misfits can he accounted for by three alternative explanations large hotspot location uncertainties a shift in time of the pacific group of hotspots relative to the african group or an additional plate boundary in the relative plate motion circuit which we assume to be in antarctica by examining each of these possibilities in turn we conclude that the uncertainties in individual hotspot locations required to bring the reconstructions into agreement are unreasonably large and that the data available at present do not allow us to distinguish which of the remaining two possibilities may be the primary source of reconstruction errors

the bude formation lower westphalian sw england siliciclastic shelf sedimentation in a large equatorial lake the 1300 m thick turbiditic bude formation was deposited in a lake lake bude but disagreement persists over whether the environment was a deltaic or deep water fan the tectonic setting of the lake was the northern flank of a northerly advancing variscan foreland basin close to the westphalian palaeo equator palaeocurrents indicate sediment sourcing from all quadrants except the south there is a dm m scale cyclicity whereby sandstone bodies comprising amalgamated event beds alternate with mudstone intervals containing non amalgamated event beds the ideal cycle is a symmetrical coarsening up fining up cycle consisting of three facies i 2 and 3 arranged in 12321 order facies 3 in the middle of the cycle is an amalgamated sandstone body up to 10 m thick which interfingers laterally with thin cm mudstone layers the sandstone body comprises amalgamated beds of very fine sandstone which are largely massive and up to 0 4 m thick channels are absent except for scours up to 0 2 m deep which truncate the interfingering mudstone layers sandstone bodies are inferred to be tongue shaped in three dimensions facies 1 and 2 completing the 12321 cycle are respectively dark grey fine and light grey coarse varved mudstone containing thin 0 4 m sandstone event beds fossils and burrows indicate that facies 1 and 2 were deposited respectively in brackish rarely marine and fresh water hence the ideal cycle 12321 reflects an upward decrease then increase in salinity brackish fresh brackish this is attributed to the lake sill being periodically overtopped by the sea due to glacio euitatic sea level oscillations the resulting oscillations in lake depth produced the coarsening up fining up regressivetransgressive cyclicity the central sandstone body representing the regressive maximum event beds are interpreted as river fed turbidites deposited during catastrophic storm floods combinedflow ripples and other wave influenced structures occur in event beds throughout the ideal cycle suggesting deposition of the entire bude formation above storm wave base the proposed environment is a shelf of continental shelf dimensions but lacustrine instead of marine sandstone bodies are interpreted to be river connected tongues or lobes the absence of cycles containing nearshore or emergent facies is attributed to i the lake sill preventing the water level from falling below sill level thereby insulating the lake floor from eustatically forced emergence and ii relatively distal deposition beyond the reach of shoreline progradations the lack of palaeoflow from the south is attributed to a now eroded deep water trough lying to the south in front of the northerly advancing orogen some facies 2 laminated mudstone beds grade laterally into massive and or contorted beds interpreted as in situ seismites facies 4 consistent with an active foreland basin setting development of seismites was possibly facilitated by gas bubbles and or weak cohesion in the fresh water bottom mud the late quaternary black sea with its broad northwestern shelf is probably a good physiographical analogue of lake bude and was likewise fresh at times

active break cycles diagnosis of the intraseasonal variability of the asian summer monsoon in this study various diagnostics have been applied to daily observed outgoing longwave radiation olr and ecmwf reanalysis era products to provide a comprehensive description of the active break cycles associated with the asian summer monsoon and to address the differing behaviour of the two dominant time scales of intraseasonal variability 10 20 days and 30 60 days composite analysis of olr based on filtered daily all india rainfall air for the 40 day 30 60 days intraseasonal mode indicates that during active phases convection is significantly enhanced over the indian continent extending over the bay of bengal maritime continent and equatorial west pacific while convection is suppressed over the equatorial indian ocean and northwest tropical pacific resulting in a quadrapole structure over the asian monsoon domain in response to this heating pattern the large scale hadley lateral and the two east west transverse tropical circulations are enhanced there is also a significant impact on the extra tropical circulation through excitation and propagation of rossby waves in contrast the 15 day mode is more regional to the monsoon domain and has a prominent east west orientation in convection only the local hadley circulation over the monsoon region is modulated by this mode the evolution of these two modes as revealed by pop principal oscillation pattern analysis shows that the 40 day mode originates over the equatorial indian ocean once formed it has poleward propagation on either side of the equator and eastward propagation into the equatorial west pacific from the equatorial west pacific northward propagation over the west pacific and westward propagation into the indian longitudes are prominent the propagative features are complex and interactive and are responsible for the quadrapole structure in convection seen from the composites the interannual variability assessed from the pop coefficient time series indicates that the 40 day mode is strong during the onset phase of the monsoon in all the years but systematic propagation over the entire season depends crucially on the activity of the oceanic tcz tropical convergence zone the pop analysis of the 15 day mode indicates that this event originates over the equatorial west pacific associated with westward propagating rossby waves amplifies over the northwest tropical pacific and modulates both the continental and oceanic tczs over indian longitudes simultaneously this mode is pronounced during the established phase of the monsoon due to the complexity in the propagational features of both the intraseasonal modes it is concluded that understanding the subseasonal variability of one regional component of the asian summer monsoon asm requires understanding the entire asm system

impact of indian summer monsoon on the south asian high and its influence on summer rainfall over china by using the monthly era 40 reanalysis data and observed rainfall data we investigated the effect of the indian summer monsoon ism on the south asian high sah at 200 hpa and the role played by the sah in summer rainfall variation over china it is found that in the interannual timescale the east west shift is a prominent feature of the sah with its center either over the iranian plateau or over the tibetan plateau when the ism is stronger weaker than normal the sah shifts westward eastward to the iranian plateau tibetan plateau the east west position of sah has close relation to the summer rainfall over china a westward eastward location of sah corresponds to less more rainfall in the yangtze huai river valley and more less rainfall in north china and south china a possible physical process that the ism affects the summer rainfall over china via the sah is proposed a stronger weaker ism associated with more less rainfall over india corresponds to more less condensation heat release and anomalous heating cooling in the upper troposphere over the northern indian peninsula the anomalous heating cooling stimulates positive negative height anomalies to its northwest and negative positive height anomalies to its northeast in the upper troposphere causing a westward eastward shift of the sah with its center over the iranian plateau tibetan plateau as a result an anomalous cyclone anticyclone is formed over the eastern tibetan plateau and eastern china in the upper troposphere the anomalous vertical motions in association with the circulation anomalies are responsible for the rainfall anomalies over china our present study reveals that the sah may play an important role in the effect of ism on the east asian summer monsoon

zonal oscillation of western pacific subtropical high and subseasonal sst variations during yangtze persistent heavy rainfall events abstractthis study examines the relationship between the zonal oscillation of the western pacific subtropical high wpsh and underneath sea surface temperature sst variation on a subseasonal time scale associated with the persistent heavy rainfall phr events over the middle and lower reaches of the yangtze river valley mlyrv in china a total of 76 phr events and 45 break events in the summers of 1979 2011 are first identified over the mlyrv and divided into early and late summer groups during the phr events over the mlyrv for both groups the wpsh stretches more westward accompanied by the positive anomalies of the 500 hpa geopotential height field over east asia and its coastal region south of 30 n and the subseasonal warmer ssts beneath the wpsh western edge the time lagged composites suggest that the wpsh western edge exhibits westward then eastward migration on a subseasonal time scale for the phr events the zonal changes of the wpsh and anomalous circulation and sst anomaly ssta signal

intraseasonal variability of the south china sea summer monsoon the objective of this study is to explore based on the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data the intraseasonal variability of the south china sea scs summer monsoon sm in terms of its structure and propagation as well as interannual variations a possible mechanism that is responsible for the origin of the 10 20 day oscillation of the scs sm is also proposed the 30 60 day hereafter the 3 6 mode and 10 20 day hereafter the 1 2 mode oscillations are found to be the two intraseasonal modes that control the behavior of the scssm activities for most of the years both the 3 6 and 1 2 modes are distinct but may not always exist simultaneously in a particular year and their contributions to the overall variations differ among different years thus the interannual variability in the intraseasonal oscillation activity of the scs sm may be categorized as follows the 3 6 category in which the 3 6 mode is more significant in terms of the percentage of variance explained than the 1 2 mode the 1 2 category in which the 1 2 mode is dominant and the dual category in which both the 3 6 and 1 2 modes are pronounced composite analyses of the 3 6 category cases indicate that the 30 60 day oscillation of the scs sm exhibits a trough ridge seesaw in which the monsoon trough and subtropical ridge exist alternatively over the scs with anomalous cyclones anticyclones along with enhanced suppressed convection migrating northward from the equator to the midlatitudes the northward migrating 3 6 mode monsoon trough ridge in the lower troposphere is coupled with the eastward propagating 3 6 mode divergence convergence in the upper troposphere it is also found that for the years in the dual category the scs sm activities are basically controlled by the 3 6 mode but modified by the 1 2 mode composite results of the 1 2 mode category cases show that the 10 20 day oscillation is manifest as an anticyclone cyclone system over the western tropical pacific propagating northwestward into the scs a close coupling also exists between the upper level convergence divergence and the low level anticyclone cyclone it is found that the 1 2 mode of the scs sm mainly originates from the equatorial central pacific although a disturbance from the northeast of the scs also contributes to this mode the flow patterns from an inactive to an active period resemble those associated with a mixed rossby gravity wave observed in previous studies

paleomagnetic tests of pacific plate reconstructions and implications for motion between hotspots the plate motion circuit through the south pacific and antarctica is shown to fail paleomagnetic tests of consistency these failures imply that reconstructions of pacific basin plates relative to surrounding plates inferred from this circuit are systematically in error and that estimates of motion between hotspots inferred from this circuit are probably too large therefore the motions between hotspots remain poorly known and may be much smaller than previously estimated

global extratropical response to diabatic heating variability of the asian summer monsoon abstract global teleconnections associated with the asian summer monsoon convective activities are investigated based on monthly data of 29 northern hemisphere summers defined as june september jjas two distinct teleconnection patterns are identified that are associated respectively with variabilities of the indian summer monsoon and the western north pacific summer monsoon the indian summer monsoon convective activity is associated with a global pattern that has a far reaching connection in both hemispheres whereas the western north pacific summer monsoon convective activity is connected to a southern hemisphere wave train that influences the high latitude south pacific and south america a global primitive equation model is utilized to assess the cause of the global circulation anomalies the model responses to anomalous heatings of both monsoon systems match the general features of the observed circulation anomalies well and they are mainly controlled by linear processes the response patterns ar

the effects of midlatitude waves over and around the tibetan plateau on submonthly variability of the east asian summer monsoon abstract convective variability at submonthly time scales 7 25 days over the yangtze and huaihe river basins yhrbs and associated large scale atmospheric circulation during the mei yu season were examined using interpolated outgoing longwave radiation olr and ncep ncar reanalysis data for 12 yr having active submonthly convective fluctuation over the yhrbs within the period 1979 2004 correlations between convection anomalies over the yhrbs and upper level streamfunction anomalies at every grid point show two contrasting patterns one pattern exhibits high correlations along the northern to eastern peripheries of the tibetan plateau defined as the net pattern whereas the other has high correlations across the tibetan plateau defined as the at pattern composite analysis of the net pattern shows slow southward migration of convection anomalies from the northeastern periphery of the tibetan plateau to southern china in relation to southward migration of the mei yu front caused by simultaneous am

influence of the anticyclonic anomaly in the subtropical jet over the western tibetan plateau on the intraseasonal variability of the summer asian monsoon in early summer abstractthe upper level troposphere over the western tibetan plateau where the subtropical jet is located in summer is a region of marked intraseasonal variability in geopotential height gph this study investigates the influence of an anomaly in this region on the summer asian monsoon to this end the gph index is defined as the daily geopotential height anomaly at 200 hpa over the region based on 40 yr european centre for medium range weather forecasts re analysis era 40 data composites with respect to strongly positive values of the gph index are analyzed the results indicate that the temporary anomaly in the subtropical jet influences the monsoon over south asia southeast asia and probably also over east asia because of two main processes the eastward propagation of quasi stationary rossby wave anomalies at upper and lower levels along the subtropical jet and a belt of strong westerlies at 15 n arabian sea bay of bengal the philippines the two mechanisms that underlie the lower level ro

plates and their motions the last reviews which covered research in plate motions were those of herron and pitman 1975 on marine magnetic anomalies and dewey 1975 on plate tectonics both reporting on research for the period 1971 1974 in the last 12 years there has been considerable refinement of relative motion models as well as further development of global models also major effort has gone into defining reference frames for the study of plate motions and discriminating between them more recently the role of errors in individual plate rotations and the associated uncertainties in reconstructions have received attention in this report i concentrate on work published in the last 4 years 1983 1986 citing a minimum of publications from previous years however some papers in press for early 1987 have been included this report first reviews work on relative plate motions for the present and past and reconstructions and then models for these motions global ones for driving forces and local ones determining subduction history and back arc spreading the problem of reference frames both hotspot and paleomagnetic is discussed next i end with a review of work on the errors in plate motions

eddy shedding from the upper tropospheric asian monsoon anticyclone abstract the authors investigate the transient behavior of the asian monsoon anticyclone in the summertime upper troposphere for the four northern summers 1987 90 the evolution of potential vorticity near the tropopause shows the development of westward migrating anticyclones breaking off from the main anticyclone a few times each summer these disturbances are relatively shallow being confined to the upper troposphere

the subduction of the farallon plate beneath north america as derived from relative plate motions high rates of subduction and near normal convergence of the farallon plate correlate with the duration of the laramide orogeny in the western cordillera the motion of the farallon plate relative to north america is reconstructed back to the late mesozoic using relative plate motion data this reconstruction involves the use of a plate circuit in which each plate is linked to another with seafloor spreading information in order to relate converging plates two models for relative motions are considered the preferred model predicts an increase in the subduction rate of the farallon plate exceeding 150 mm yr with a direction almost due east and perpendicular to the continental margin the duration of this nonoblique normal high rate subduction correlates well with the duration of the laramide orogeny this correlation must be regarded as only suggestive the probable errors when combined and propagated through the relative motion circuit may be of the order of the effect observed however it is encouraging that these reconstructed farallon north american relative motions are similar to the published predictions of others using the alternative more direct approach of hot spot reconstructions

eocene to recent development of the south west indian ridge a consequence of the evolution of the indian ocean triple junction summary the south west indian ridge the contact between the african and antarctic plates lies between the bouvet triple junction in the south atlantic and the indian ocean triple junction about 2100 km east of madagascar from the vicinity of prince edward island at 40 e it trends north easterly and it is segmented by a suite of deep north south gashes terminating on the north east with two spectacular meridional fracture zones the atlantis ii and the melville at 57 30 e and 60 30 e respectively from there northeast to the indian ocean triple junction at 25 30 s 70 00 e the ridge trends n75 e it is characterized by a triangle of rough topography with the triple junction at the eastern apex from all available data an instantaneous pole of relative motion for africa antarctica was computed it lies at 8 4 n 42 4 w with a rate of 0 15 myr 1 since the marked change in the direction and rate of spreading in the madagascar crozet and central indian basins that occurred in the eocene 44 ma anomaly 19 the poles of relative motion for the african indian and antarctic plates have changed very little we fixed the africa antarctica and africa india poles and computed that for india antarctica we justified this pole by comparisons of predicted isochrons with observed magnetic lineations and determined the tectonic history of the triple junction since the eocene 44 ma anomaly 19 this junction has moved as rapidly east wards with respect to africa as antarctica has moved south the resultant geometry and slow spreading account for the triangle of rough topography produced by the south west indian ridge east of the melville fracture zone the triple junction evolved as a stable ridge ridge ridge type with the south east indian ridge remaining approximately constant in length it was not resolved whether this constancy in length is maintained by frequent ridge jumps or by oblique spreading on the south west and central indian ridges near the triple junction

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

anticorrelated intensity change of the quasi biweekly and 30 50 day oscillations over the south china sea 1 over the south china sea the year to year variations in the intensity of the quasi biweekly qbw and 30 50 day oscillations during june july are anti correlated an explanation is offered for the out of phase relationship we found during strong qbw years the june july mean convection and easterly vertical shear are enhanced over the equatorial western central pacific with corresponding low level cyclonic meridional shear to the northwest these conditions concurring with the equatorial eastern pacific warming are favorable for emanation of moist rossby waves from the equatorial western pacific on the other hand the 30 50 day becomes active when the mean convection is enhanced over the eastern indian ocean and maritime continent where this mode stems from and develops which often corresponds to cold western io one of these two large scale settings often occurs in the absence of the other so that when one mode is strong during june july the other mode tends to be weak

plate driving forces over the cenozoic era plate reconstructions are used to estimate plate torques for the cenozoic era assuming a dynamical balance between active torques slab pull and ridge push and plate drag as the passive torque in a published one dimensional model for the motion of an oceanic plate the plate drag balances slab pull and ridge push expressing each of these forces in terms of age and sub duction rate and using values at 15 trenches coefficients are found which give a least squares fit here we have retained a common age factor which gives a greater weight to older more rapidly moving plates and the contribution due to ridge push is larger than that found in the previous study but still much smaller than the slab pull force this one dimensional force model is generalized to two dimensional plates moving over the earth s surface and we obtain a torque balance equation in which slab pull and ridge push torques are proportional to boundary chord vectors with the weights depending on powers of subduction velocity at the middle of the chords for each plate we find the unique angular velocity which satisfies the torque balance requirement and this balance torque is compared with the plate drag torque obtained from the plate s geometry and reconstructed angular velocity comparison of the torques is made for two published models for present day plate motions as well as six published reconstructions for time intervals spanning the cenozoic for the present the mismatch between the balanced torque and drag torque is about the same as the difference between the two alternative published models torques are fairly stable throughout the cenozoic with the misfit increasing systematically for earlier reconstructions

20 50 day oscillation of summer yangtze rainfall in response to intraseasonal variations in the subtropical high over the western north pacific and south china sea the spatio temporal variability in summer rainfall within eastern china is identified based on empirical orthogonal function eof analysis of daily rain gauge precipitation data for the period 1979 2003 spatial coherence of rainfall is found in the yangtze basin and a wavelet transform is applied to the corresponding principal component to capture the intraseasonal oscillation iso of yangtze rainfall the ensemble mean wavelet spectrum representing statistically significant intraseasonal variability shows a predominant oscillation in summer yangtze rainfall with a period of 20 50 days a 10 20 day oscillation is pronounced during june and july this finding suggests that the 20 50 day oscillation is a major agent in regulating summer yangtze rainfall composite analyses reveal that the 20 50 day oscillation of summer yangtze rainfall arises in response to intraseasonal variations in the western north pacific subtropical high wnpsh which in turn is modulated by a rossby wave like coupled circulation convection system that propagates northward and northwestward from the equatorial western pacific when an anomalous cyclone associated with this rossby wave like system reaches the south china sea scs and philippine sea the wnpsh retreats northeastward due to a reduction in local pressure under these conditions strong monsoonal southwesterlies blow mainly toward the scs philippine sea while dry conditions form in the yangtze basin with a pronounced divergent flow pattern in contrast the movement of an anomalous anticyclone over the scs philippine sea results in the southwestward extension of the wnpsh consequently the tropical monsoonal southwesterlies veer to the northeast over the scs and then converge toward the yangtze basin producing wet conditions therefore the 20 50 day oscillation of yangtze rainfall is also manifest as a seesaw pattern in convective anomalies between the yangtze basin and the scs philippine sea a considerable zonal shift in the wnpsh is associated with extreme dry wet episodes in the yangtze basin with an abrupt eastward westward shift in the wnpsh generally leading the extreme negative positive yangtze rainfall anomaly by a 3 8 period of the 20 50 day oscillation this finding may have implications for improving extended range weather forecasting in the yangtze basin

subseasonal intensity variation of the south asian high in relationship to diabatic heating observation and cmip5 models this study investigates the subseasonal intensity variation of south asian high sah and the dynamic linkage with precipitation induced diabatic heating during the summer of 1979 2005 based on the observation and 18 models from the coupled model intercomparison project cmip5 the sah s intensity variation with a period of approximately 10 36 days is identified both in the observation and 18 models by performing an empirical orthogonal function eof analysis on the standardized subseasonal anomalies in geopotential height at 100 hpa over the sah s main body region with the observed strengthening of the sah an enhanced rainfall belt between 70 120 e migrates northward from the equatorial region the northward propagating rainfall belt occupies almost the whole indian subcontinent indochina peninsula and subtropical east asian regions between 20 40 n when the sah reaches the strongest the relative vorticity diagnosis reveals the dynamical linkage between the subseasonal sah s intensity variation and the precipitation anomalies over the asian monsoon region 1 the observed northward propagating rainfall band forms a horizontal gradient of diabatic heating favoring an enhancement of the sah over its southern part 2 when the rainfall band approaches the regions of south and east asia between 20 40 n the increased vertical gradient of diabatic heating in the upper level contributes significantly to the intensification of the sah 3 the horizontal advection process favors the westward expansion of the sah the observation to model comparisons indicate that the model s capacity to reproduce the sah s intensity variation is highly associated with simulations of the anomalous rainfall band and its northward propagation a realistic reproduction of precipitation anomalies is fundamental to simulating the dynamical processes related to diabatic heating and thus the simulation of the sah s subseasonal intensity variation

uncertainties and implications of the late cretaceous and tertiary position of north america relative to the farallon kula and pacific plates we present updated global plate reconstructions and calculated uncertainties of the pacific kula and farallon vancouver plates relative to north america for selected times since 68 ma improved magnetic data from the indian ocean decrease the uncertainties in the global plate circuit approach these uncertainties are now considerably smaller than those inherent in equivalent reconstructions based on the assumption of fixed hotspots major differences between these results and those of others are due to our use of more detailed africa north america reconstructions separate vancouver and farallon plate reconstructions and the assumption of a rigid antarctica plate during cenozoic time the uncertainties in the relative positions of the pacific and north america plates since the time of anomaly 7 26 ma range up to 100 km in position or from 1 to 3 m y in time if the mendocino triple junction initiated at about 28 5 ma its position would have been at 31 3 n 130 km relative to fixed north america unacceptable overlap of oceanic crust of the pacific plate with continental crust of western north america in the anomaly 10 30 ma reconstruction is a minimum of 340 200 km along an azimuth of n60 e and may be accounted for by basin and range extension pacific north america displacement in the past 20 ma is found to be considerably less than that calculated by fixed hotspot reconstructions farallon vancouver north america convergence velocity decreased greatly between the times of anomalies 24 and 21 56 to 50 ma prior to the 43 ma age of the hawaiian emperor bend and the often quoted 40 ma end of the laramide orogeny a change in direction of farallon north america convergence occurred sometime between 50 and 42 ma and also may not correlate with the time of the hawaiian emperor bend the lack of data from subducted parts of the farallon and kula plates permits many possibilities regarding the position of the kula farallon ridge the age of subducted crust or the position of oceanic plateaus during the laramide orogeny leaving open the question of the relationship between plate tectonic scenarios and tectonic style during laramide time displacements of points on the various oceanic plates along the west coast of an arbitrarily fixed north america during the interval between anomalies 30 31 and 18 68 to 42 ma are found to be pacific plate 1700 200 km northward farallon plate 3200 400 km northeastward vancouver plate 3000 400 km northeastward kula plate if attached to the pacific plate after a24 time 2500 400 km northward

genesis of the south asian high and its impact on the asian summer monsoon onset abstractthe formation of the south asian high sah in spring and its impacts on the asian summer monsoon onset are studied using daily 40 yr ecmwf re analysis era 40 data together with a climate mean composite technique and potential vorticity diabatic heating pv q analysis results demonstrate that about 2 weeks before the asian summer monsoon onset a burst of convection over the southern philippines produces a negative vorticity source to its north the sah in the upper troposphere over the south china sea is then generated as an atmospheric response to this negative vorticity forcing with the streamline field manifesting a gill type pattern afterward the persistent rainfall over the northern indochinese peninsula causes the sah to move westward toward the peninsula consequently a trumpet shaped flow field is formed to its southwest resulting in divergence pumping and atmospheric ascent just over the southeastern bay of bengal bob near the surface as a surface anticyclone is formed over t

how are heat waves over yangtze river valley associated with atmospheric quasi biweekly oscillation over yangtze river valley yrv where heat wave hw events most frequently occur in china during 1979 2014 30 out of 57 hw events nearly 55 in july and august is found to be related with the dry phases of atmospheric quasi biweekly oscillation qbwo when a significant low level anticyclonic anomaly laa associated with qbwo appears over yrv temperature rises sharply according to the adiabatic heating caused by subsidence and the enhanced downward solar radiation due to decreased clouds the laa with subsidence over yrv is primarily generated by quasi biweekly atmospheric waves which are classified to three types through case by case categorization named as mid latitude wavetrain wnp western north pacific wavetrain and double wavetrains respectively the mid latitude wavetrain qbwo causes the laa through subsidence induced by upper level cyclonic vorticity which is associated with an eastward southeastward migrating wave train from eastern europe to wnp in the upper troposphere the wnp wavetrain qbwo forms laa through a northwestward migrating lower tropospheric wave train emanating from tropical wnp to southeastern china the double wavetrains qbwo triggers laa through both the low level shear anticyclonic vorticity provided by a low level northwestward westward propagating wave train from tropical wnp to south china sea and the upper level positive vorticity associated with an eastward southeastward migrating wave train from eastern europe to southeastern china in the upper troposphere in all cases south asian high extends eastward and wnp subtropical high extends westward during hw events tracing these distinct precursory circulation anomalies may facilitate better understanding and short medium range forecast of hw

permian passive margin submarine fan complex karoo basin south africa possible model to gulf of mexico abstract the tectonic development of the southwestern part of the intracratonic karoo basin was related to a subduction zone and an orogenic fold belt however the entire lower permian ecca group basin fill succession exhibits the depositional characteristics of a passive margin setting the subbasins that developed during subsidence accumulated large submarine fan complexes that were succeeded by a river dominated deltaic system the subbasin fill in the west southwestern area tanqua karoo is approximately 250 m thick and is comprised of six arenaceous submarine fan systems separated by basinal shales the uppermost fan system is overlain by prodelta shales and siltstones followed by delta front and delta plain sediments the fan complex displays middle and outer fan deposits over an area of about 650 km2 the individual fans vary in maximum thickness from 24 to over 60 m the cyclicity of the fan deposition is believed to have been controlled by fluctuations in relative sea level with an average periodicity of about 100 000 years paleocurrent directions vary between the six units reflecting changes in deltaic point source locations between sse and wsw the sixth fan system is located to the south downlaps onto the last of the five sequences and may represent a slope fan with major slumps and channels the strata are not affected by folding or vegetation permitting three dimensional viewing of channel fills and levee overbank relationships lateral migration of channels and the transition from channelized to non channelized lobe and sheet deposits the sediments of the different subenvironments seem to have their own typical sedimentary structures which makes it possible to start defining the placing of thin bedded turbidites and their potential relationships to channel fill deposits the gentle tectonic development of the southwestern karoo basin as is reflected in the distribution of the lower shale formations low sand shale ratio and overall fine grain size throughout the entire submarine fan deltaic mega sequence reflects a passive margin setting these well exposed outcrops contain many sedimentary characteristics that can be related to those of the mississippi delta and fan therefore this area can provide important elements that will be useful for the development of models of deep water sands in the northern margin of the gulf of mexico

tectonic history of the juan de fuca ridge over the last 40 million years interpretation of a new compilation of magnetic anomaly data for north of the mendocino fracture zone and younger than chron 15 39 ma indicates a transition from a pattern of stable transform faults to a pattern of persistent ridge propagation reorganizations of the propagation pattern occurred at 30 ma in response to a counterclockwise change in direction of relative motion and at 19 ma in response to a clock wise change in addition there are significant changes in the gradient of the spreading rate apparently without major changes in motion direction at 27 and 24 ma the change at 30 ma is apparently the result of the separation of the juan de fuca plate from the rest of the farallon plate along the pioneer fracture zone the pattern of absolute motion after 30 ma does not generally support menard s pivoting subduction model and suggests that juan de fuca plate motion is being significantly affected by forces transmitted across the mendocino transform fault

some geometrical aspects of uncertainties in combined plate reconstructions the uncertainties in both the position of a pole of rotation and the rotation angle describing a plate reconstruction depend not only on the number and quality of data used but also on two geometrical factors the length of plate boundary represented by the data and the distance from the best fit pole to the center of the data region we describe a simple geometrical method that can be used to calculate minimum uncertainties in reconstructions based on positions of magnetic anomalies and fracture zones with finite uncertainties uncertainties in pole positions and angles corresponding to 10 km uncertainty in individual data points can when combined yield uncertainties in reconstructed positions greatly in excess of 10 km per rotation for example an uncertainty of 10 km in anomaly 6 reconstructions in the south pacific southeast indian northwest indian and north atlantic oceans would result in uncertainty of up to 190 km in the reconstructed position of the pacific plate with respect to north america at 19 8 m y b p existing data show that the realistic uncertainties for this case are twice as large as the calculated minimum uncertainties

wave modified turbidites combined flow shoreline and shelf deposits cambrian antarctica sandstone tempestite beds in the starshot formation cen tral transantarctic mountains were deposited in a range of shoreline to shelf environments detailed sedimentological analysis indicates that these beds were largely deposited by wave modified turbidity currents these currents are types of combined flows in which storm generated waves overprint flows driven by excess weight forces the interpreta tion of the tempestites of the starshot formation as wave dominated turbidites rests on multiple criteria first the beds are generally well graded and contain bouma like sequences like many turbidites the soles display abundant well developed flutes they also contain thick divisions of climbing ripple lamination the lamination however is dominated by convex up and sigmoidal foresets which are geometries identical to those produced experimentally in current dominated com bined flows in clear water finally paleocurrent data support a tur bidity current component of flow asymmetric folds in abundant con volute bedding reflect liquefaction and gravity driven movement and hence their orientations indicate the downslope direction at the time of deposition the vergence direction of these folds parallels paleocur rent readings of flute marks combined flow ripples and a number of other current generated features in the starshot event beds indicating that the flows were driven down slope by gravity the wave component of flow in these beds is indicated by the presence of small to large scale hummocky cross stratification and rare small two dimensional ripples wave modified turbidity currents differ from deep sea turbidity cur rents in that they may not be autosuspending and some proportion of the turbulence that maintains these flows comes from storm waves such currents are formed in modern shoreline environments by a com bination of storm waves and downwelling sediment laden currents they may also be formed as a result of oceanic floods events in which intense sediment laden fluvial discharge creates a hyperpycnal flow event beds in the starshot formation may have formed from such a mechanism oceanic floods are formed in rivers of small to medium size in areas of high relief commonly on active margins the starshot formation and the coeval douglas conglomerate are clastic units that formed in response to uplift associated with active tectonism sedi mentological and stratigraphic data suggest that coarse alluvial fans formed directly adjacent to a marine basin the geomorphic conditions were therefore likely conducive to rapid fluvial discharge events asso ciated with storms the abundance of current dominated combined flow ripples at the tops of many starshot beds indicates that excess weight forces were dominant throughout deposition of many of these beds

northern hemisphere summer monsoon singularities and climatological intraseasonal oscillation abstract using climatological pentad mean outgoing longwave radiation olr and european centre for medium range weather forecasts analysis winds the authors show that the northern hemisphere summer monsoon displays statistically significant climatological intraseasonal oscillations cisos the extreme phases of ciso characterize monsoon singularities monsoon events that occur on a fixed pentad with usual regularity whereas the transitional phases of ciso represent the largest year to year monsoon variations the ciso results from a phase locking of transient intraseasonal oscillation to annual cycle it exhibits a dynamically coherent structure between enhanced convection and low level convergent upper level divergent cyclonic anticyclonic circulation its phase propagates primarily northward from the equator to the northern philippines during early summer may july and westward along 15 n from 170 e to the bay of bengal during august and september the propagation of ciso links monsoon singular

characterizing two types of transient intraseasonal oscillations in the eastern tibetan plateau summer rainfall during summer the intraseasonal disturbances over the eastern tibetan plateau etp can initiate development of severe weather system downstream previous studies yielded inconsistent results on the intraseasonal variability isv of summer rainfall in terms of periodicity genesis process and propagation pathway over the ept based on small samples in this study we detected two dominant peaks of transient isv centered on quasi biweekly 12 24 days qbw and quasi 9 8 11 days using daily rainfall data over the etp during the period of 1992 2012 composite analysis revealed that the two isvs were predominantly associated with the non stationary wave trains which traveled along different pathways for the qbw its mid latitude wave train featured a upper level southeastward migration originating in northern europe and traveling via the east european plain the ural mountains lake balkhash lake baikal the mongolian plateau and then continued southward to the etp and south asia and its tropical wave train was characterized with a northwestward northward migration in low level starting from the philippine sea ps south china sea scs region moving over northern bay of bengal scs region and arriving over the southern fridge of tp and southern china in contrast for quasi 9 day the most significant mid latitudes variability featured an eastward propagating upper level wave train originating from western europe passing across the mediterranean the black and caspian seas arriving over the tp and moving towards east asia and the most evident tropical variability exhibited a clear northwestward westward migration of a low level wave train originating from ps passing over taiwan and subsequently moving towards southeastern china their different spatiotemporal features of associated wave trains caused their distinct linkages with eastern china rainfall anomalies a meridional pattern with a giant ural mountain ridge was the most remarkable precursory signals in upstream region before the qbw wet phase occurrence which was different from the quasi 9 day the major processes generating the local wet spells for the two modes were commonly linked to the preceding boundary warming the upper level negative vorticity and low level prevalent winds which triggered the ascending anomaly and lower tropospheric pre moistening we also discussed the co variation of the wave trains between mid latitudes and low latitudes the distinct evolution related with the two isvs over the etp described here may provide a useful guidance for 2 3 weeks extended range forecasts over the etp and its downstream regions

delaware mountain group west texas and southeastern new mexico a case of refound opportunity part 1 brushy canyon exploration in permian guadalupian deep water sandstones of the delaware mountain group west texas and southeast new mexico represents a success story of the 1990s derived from reevaluation of reservoirs previously deemed uneconomical recent discoveries have concentrated on the brushy canyon in new mexico and to a lesser extent the cherry canyon in texas brushy canyon reservoirs in particular previously were overlooked due to indications of poor reservoir quality from log and well test data however oil shows observed on mud logs across the northern delaware basin led to new completion efforts in the late 1980s and 1990s using gel sand fracture stimulations productive reservoirs are very fine to fine grained arkosic to subarkosic sandstones with porosities of 12 25 and permeabilities typically of 1 5 md better reservoir quality is concentrated in massive channel sandstones variably interpreted as deposited by turbidity or saline density currents significant clay content lamination and close interbedding between oil and water bearing units make log analysis and reserve estimates problematic as a result the mud log remains the cheapest most practical indicator of pay reservoir sandstones can be divided into a series of major productive trends related to proximal slope and more distal basin floor depositional settings well productivity is variable within each trend but primary recovery rarely exceeds 10 options for enhanced recovery include pressure maintenance waterflooding and carbon dioxide flooding early indications suggest that carbon dioxide flooding may be most appropriate in these low permeability clay bearing reservoirs

comments on sequence stratigraphy of an argillaceous deepwater basin plain succession vischkuil formation permian karoo basin south africa from van der merwe flint and hodgson marine and petroleum geology 2010 27 321 333

mechanism of the northward propagating intraseasonal oscillation insights from a zonally symmetric model abstract the propagation and initiation mechanisms of the boreal summer intraseasonal oscillation bsiso in the south asian summer monsoon are examined with a zonally symmetric atmospheric model in the axially symmetric model the effects of zonally propagating atmospheric waves are intentionally excluded the model specifies mean flows and depicts the lowest baroclinic mode and a barotropic mode in the free troposphere the two vertical modes are coupled by the time mean vertical wind shear the model atmosphere produces a 15 20 day oscillation which is characterized by northward propagation of convection from south of the equator to the indian monsoon trough region and a reinitiation of convection in the region between 10 s and the equator the northward propagation in the model is produced by the free troposphere barotropic divergence which leads convection by about a quarter of a cycle the vertical advection of summer mean easterly vertical wind shear by perturbation vertical motion inside the con

seasonal evolution of the upper tropospheric westerly jet core over east asia the location change of the westerly jet core at upper troposphere in june and july is investigated by using the ncep ncar reanalysis data the results show that the location of the westerly jet core changes rapidly from 140 e to 90 e during 35th 39th pentads which corresponds to the plum rain period over east asia the location change of the jet core is actually the relative intensity change of the different westerly jet centers the meridional temperature contrast in the troposphere is associated with the rapid location change of the jet core the diabatic heating changes are the primary factor determining the seasonal evolution of the westerly jet core over east asia

the uncertainties of finite rotations in plate tectonics incomplete knowledge of the pattern of magnetic lineations and fossil transform faults represented by sea floor spreading data on two plates generated by the same spreading center leads to uncertainties in a reconstruction of the past relative configuration of the plates a reconstruction may be represented by the finite rotation that describes one configuration relative to another in this paper a method of reconstruction is provided that reflects the uncertainties in the data the method minimizes a weighted least squares measure of fit as a function of the rotation parameters for a given rotation the measure of fit represents the sum of squares of the weighted distances of fixed and rotated data points representing corresponding former plate margin segments from a common plate margin the common margin is estimated from the locations of both fixed and rotated data points the estimated margin consists of a set of great circle arcs it is shown how the method of reconstruction may be utilized to obtain an uncertainty region for the pole and angle of rotation that characterize the finite rotation these techniques are then used to study the uncertainties of reconstructions in the south pacific for the times of anomalies 13 and 18 the best fit reconstructions and the uncertainty region for the anomaly 18 pole are in good agreement with previous work however the uncertainties in the anomaly 13 pole were substantially underestimated by previous investigators

intraseasonal teleconnection between the summer eurasian wave train and the indian monsoon this study investigated the most recurrent coupled pattern of intraseasonal variability between midlatitude circulation and the indian summer monsoon ism the leading singular vector decomposition svd pattern reveals a significant coupled intraseasonal variation between a rossby wave train across the eurasian continent and the summer monsoon convection in northwestern india and pakistan hereafter referred to as nism the wave train associated with an active phase of nism rainfall displays two high pressure anomalies one located over central asia and the other over northeastern asia they are accompanied by increased rainfall over the western siberia plain and northern china and decreased rainfall over the eastern mediterranean sea and southern japan the circulation of the wave train shows a barotropic structure everywhere except the anomalous central asian high located to the northwest of india where a heat induced baroclinic circulation structure dominates the time lagged svd analysis shows that the midlatitude wave train originates from the northeastern atlantic and traverses europe to central asia the wave train enhances the upper level high pressure and reinforces the convection over the nism region meanwhile it propagates farther toward east asia along the waveguide provided by the westerly jet after an outbreak of nism convection the anomalous central asian high retreats westward composite analysis suggests a coupling between the central asian high and the convective fluctuation in the nism the significance of the midlatitude ism interaction is also revealed by the close resemblance between the individual empirical orthogonal functions and the coupled svd modes of the midlatitude circulation and the ism it is hypothesized that the eastward and southward propagation of the wave train originating from the northeastern atlantic contributes to the intraseasonal variability in the nism by changing the intensity of the monsoonal easterly vertical shear and its associated moist dynamic instability on the other hand the rainfall variations over the nism reinforce the variations of the central asian high through the monsoon desert mechanism thus reenergizing the downstream propagation of the wave train the coupling between the eurasian wave train and nism may be instrumental for understanding their interaction and can provide a way to predict the intraseasonal variations of the indian summer monsoon and east asian summer monsoon

pole of rotation analysis of present day juan de fuca plate motion convergence rates between the juan de fuca and north america plates are calculated by means of their relative present day pole of rotation subduction rates as measured normal to the strike of the washington oregon trench are predicted to range from about 40 mm yr under washington to 20 mm yr under oregon an integral part of this analysis is the formulation of a numerical inversion scheme which calculates both the pole of rotation between two plates and the associated errors this method is used to determine the euler pole for pacific juan de fuca this pole can then be vectorially added to previously published poles for north america pacific and hot spot pacific to obtain north america juan de fuca and hot spot juan de fuca respectively the errors associated with these resultant poles are also determined by propagating the errors of the two summed angular velocity vectors with the assumption that hot spots are fixed with respect to a mantle reference frame if is computed that the average absolute velocity of the juan de fuca plate is approximately 15 mm yr thereby making it the slowest moving of the oceanic plates

biweekly and 21 30 day variations of the subtropical summer monsoon rainfall over the lower reach of the yangtze river basin abstract the lower reach of the yangtze river basin lyrb is located at the central region of the mei yu and baiu front which represents the subtropical east asian ea summer monsoon based on the newly released daily rainfall data two dominant intraseasonal variation isv modes are identified over the lyrb during boreal summer may august with spectral peaks occurring on day 15 the biweekly mode and day 24 the 21 30 day mode these two modes have comparable intensities and together they account for above about 57 of the total intraseasonal variance both isv modes exhibit baroclinic structures over the lyrb at their extreme phases however the genesis and evolutions associated with the two modes are different considering the genesis of their extreme wet phases over the lyrb the biweekly mode is initiated by a midlatitude jet stream vorticity anomaly moving southeastward while the 21 30 day mode is primarily associated with a low level westward propagation of an anticyclonic anomaly from

comment on a paper by zou et al 2017 entitled an integrated chemo and sequence stratigraphic framework of the early pennsylvanian deepwater outcrops near kirby arkansas usa and its implications on remnant basin tectonics