the leka opholite complex central norwegian caledonides field characteristics and geotectonic significance the leka ophiolite complex loc of lower ordovician age u pb zircon age of 497 2 ma contains the following components 1 a lower strongly deformed harzburgite unit representing the depleted upper mantle this unit becomes progressively richer in dunite towards 2 a sequence of ultramafic cumulates unconformably overlying the harzburgite tectonite the crystallization sequence in the ultramafic cumulates is olivine chromite clinopyroxene orthopyroxene in the south western part of the ultramafic cumulate sequence layers of metagabbro appear interlayered with banded dunite wehrlite the above mentioned rock sequences may be in tectonic contact with 3 layered metagabbros which give way upwards to laminated and vari textured metagabbro within the laminated vari textured metagabbro is the first appearance of 4 metabasalt dykes which increase upwards in abundance from scattered single dykes to a 100 sheeted dyke swarm associated with the vari textured metagabbro and metabasalt dykes are minor acid intrusions within the upper part of the dyke swarm is the first appearance of 5 pillow lavas which are associated with thick volcaniclastic metasediments at apparently higher stratigraphic levels geochemically the metabasalt dykes and associated pillow lavas range from predominant island arc tholeiite iat to morb character and typical metaboninites are also present this range of geochemical composition as well as the crystallization sequence of the cumulates strongly suggests that the first stages in the formation of the loc was by spreading above a subduction zone the pillow lavas associated with volcaniclastic rocks are of morb or wpb type and these probably represent the later spreading stages of the loc in a back arc basin but at sufficient distance to be unaffected by the geochemical fingerprints of the subduction process

impact of high potential vorticity intrusions into the tropical upper troposphere in south atlantic on precipitation over northeast brazil 1 interannual variations of high potential vorticity intrusions at 10 s in the upper troposphere during ndjfm are shown to be negatively correlated with rainfall over northern northeast brazil neb that is higher intrusions associated with stronger equatorial westerlies may provoke droughts higher intrusions lead to the formation of an anomalous cyclonic vortex over neb which causes convergence in the upper troposphere and sinking motion at lower levels the number of intrusions in ndjfm has highest correlation significant at 99 confidence level with the rainfall of the principal rainy season in fmam

eclogites and eclogites in the western gneiss region norwegian caledonides the western gneiss region wgr marks the outcrop of a composite terrane consisting of variably re worked proterozoic basement and parautochthonous or autochthonous cover units the wgr exhibits a gross structural petrographic and thermobarometric zonation from southeast to northwest reflecting an increasing intensity of scandian late palaeozoic

observations of rossby waves linked to convection over the eastern tropical pacific rossby wave activity propagating into the eastern tropical pacific from the midlatitudes during northern winter is examined in some detail these waves are associated with the intrusion of high potential vorticity air into low latitudes and they modulate cloudiness stability and vertical motion in the vicinity of the itcz in the upper troposphere and lower stratosphere the horizontal phase and group propagation of the wave activity are qualitatively like those of a nondivergent barotropic rossby wave as the waves move equatorward they become more shallow and propagate upward into the stratosphere the horizontal and vertical propagation is consistent with the tilts of the waves the large scale three dimensional background flow and with the signatures of momentum and heat fluxes associated with the wave activity in the lower troposphere paired cyclonic anomalies on either side of the equator accompany the upper level wave activity to the west of the itcz cloudiness signal these waves amplify following the peak in the itcz cloudiness and propagate westward along the equator this suggests that the upper level wave activity and possibly the associated convective heating can trigger the excitation of the equatorially trapped rossby modes the transient wave activity appears to be a crucial component of the momentum balance of the eastern tropical pacific circulation there is substantial interannual variability in the wave activity consistent with observed changes in the large scale basic state associated with the southern oscillation

a geothermobarometric investigation of garnet peridotites in the western gneiss region of norway in the western gneiss region of norway are found numerous peridotite lenses which have been extensively recrystallized under amphibolite fades conditions during the caledonian orogeny however evidence for an earlier caledonian high pressure metamorphism has been recorded by abundant eclogite and granulite relicts within gneiss and by the presence of at least ten garnet perioditite bodies preserved within chlorite peridotites two garnet bearing ultramafic assemblages have been recognized olivine orthopyroxene clinopyroxene garnet and olivine ortho pyroxene pargasitic amphibole garnet

geologic thermobarometry of retrograded metamorphic rocks an indication of the uplift trajectory of a portion of the northern scandinavian caledonides kyanite grade pelitic schists from the efjord area 68 15 n 16 45 e northern norway show abundant textural evidence of retrograde reequilibration during late orogenic uplift and cooling of this part of the scandinavian caledonides graphical analysis of mineral compositions in seven samples that show a range of retrograde textures indicates that they reached final chemical equilibrium under nonuniform pressure temperature conditions three element partitioning geothermometers and geobarometers yield consistent pt estimates in individual samples which together define a trend in pt space the sample showing the fewest signs of retrogression yields the highest pressure and temperature estimates whereas samples exhibiting abundant reequilibration textures give lower pt estimates we suggest that the trend indicated by these samples reflects a portion of the pt trajectory assumed by the efjord area during uplift thus the judicious use of element partitioning geothermometers and geobarometers on samples showing signs of retrograde metamorphism may yield important new information concerning the late tectonic evolution of metamorphic terrains

estimation of deformation temperatures flow stresses and strain rates from an intra continental shear zone the main boundary thrust nw himalaya uttarakhand india abstract this work generates thermal and tectonic data from the mylonitized rocks of the main boundary thrust mbt south and north to this major thrust the siwalik range and the lesser himalaya respectively have been receiving a renewed interest amongst the petroleum geoscientists understanding temperature flow stress and strain rates related to a major thrust is crucial in thermal mechanical modelling of the terrains adjacent to it strongly sheared proterozoic chandpur phyllites and abundant syntectonic quartz veins occur along the mbt zone one of the major foreland verging thrusts in the himalayan orogen near the sahenshahi temple at dehradun uttarakhand state india microstructure analyses show intense ductile top to s shear in terms of s c fabric and xrd analyses indicate presence of clays e g illite and clinochlore these clays not only bear the signatures of the intense fluid activity but also enhance the fault movement by reducing the mechanical strength of the fault zone rocks thermometry based on qualitative quartz grain boundary mobility 300 550 c and quantitative laser raman spectroscopy for carbonaceous materials 340 370 c reveal the maximum estimates of the deformation temperature and metamorphic temperature respectively the higher temperature microstructures can be found in lower temperature domains under the presence of fluids hence the quartz thermometry estimates a broader temperature range than the raman thermometry previous works report that the phyllites present at the base of a thrust sheet experiences deformation at

effect of the hadley circulation on the reflection of planetary waves in three dimensional tropospheric flows the nonlinear behavior of quasi stationary planetary waves excited by midlatitude orographic forcing is considered in a three dimensional primitive equation model that includes a representation of the hadley cir culation the hadley circulation is forced by newtonian cooling to a zonally symmetric reference temperature and vertical diffusion on the zonally symmetric component of the flow to quantify the effect of the hadley circulation on wave propagation breaking and nonlinear reflection an initial state with no meridional flow but with the same zonal flow as the hadley state is also considered in order to allow the propagation of large scale waves over extended periods rayleigh friction is applied at low levels to delay the onset of baroclinic instability as in the absence of a hadley circulation the waves in the hadley state propagate toward low latitudes where the background flow is weak and the waves are therefore likely to break potential vorticity fields on isentropic surfaces are used to diagnose wave breaking nonlinear pseudomomentum conservation relations are used to quantify the absorption reflection behavior of the wave breaking region in the presence of a hadley circulation representative of winter conditions the nonlinear reflection requires more forcing to get established but a reflected wave train is still present in the numerical simulations both for a longitudinally symmetric forcing and for the more realistic case of an isolated forcing the effect of the thermal damping on the waves is more severe in the current three dimensional simulations than in the shallow water case considered in an earlier study both the directly forced wave train and the reflected wave train are quite barotropic in character however in the shallow water case one is essentially assuming an infinite vertical scale

stationary wave reflection as a mechanism for zonalizing the atlantic winter jet at the lgm abstractcurrent estimates of the height of the laurentide ice sheet lis at the last glacial maximum lgm range from around 3000 to 4500 m modeling studies of the lgm using low end estimates of the lis height show a relatively weak and northeastward tilted winter jet in the north atlantic similar to the modern jet while simulations with high end lis elevations show a much more intense and zonally oriented jet here an explanation for this response of the atlantic circulation is sought using a sequence of lgm simulations spanning a broad range of lis elevations it is found that increasing lis height favors planetary wave breaking and nonlinear reflection in the subtropical north atlantic for high lis elevations planetary wave reflection becomes sufficiently prevalent that a poleward directed flux of wave activity appears in the climatology over the midlatitude north atlantic this entails a zonalization of the stationary wave phase lines and thus of the midlatitude jet

biostratigraphic and detrital zircon age constraints on the basement of the himalayan foreland basin implications for a proterozoic link to the lesser himalaya and cratonic india the himalayan foreland basin in the ganga valley is key to assessing the pre collision relationship between cratonic india and the himalaya the world s largest mountain chain the subsurface ganga supergroup representing the sedimentary basement of the ganga valley has been interpreted as a northern extension of the proterozoic vindhyan supergroup in cratonic india this interpretation is contentious because the depositional age of the ganga supergroup is not resolved whereas the lower ganga supergroup is widely regarded as proterozoic the upper ganga supergroup has been variously inferred to include neoproterozoic lower palaeozoic or cretaceous strata here we integrate biostratigraphic and detrital zircon data from drill cores to show that the entire ganga supergroup is likely proterozoic and can be correlated with proterozoic successions on the northern indian craton and in the lesser himalaya this helps redefine the first order stratigraphic architecture and indicates broad depositional continuity along the northern indian margin during the proterozoic this article is protected by copyright all rights reserved

chemical and dynamical discontinuity at the extratropical tropopause based on start08 and waccm analyses 1 using isentropic trace gas gradients of o3 and co the discontinuity in the chemical composition of the upper troposphere ut and lower stratosphere ls is examined on middle world isentropes from 300 to 380 k the analysis is a follow up study of the dynamical discontinuity as represented by the potential vorticity pv gradient based tropopause which is based on the product of isentropic pv gradients and wind speed overall there is fairly good consistency between the chemical discontinuity in trace gas distributions and the pv gradient based tropopause trace gas gradients at the pv gradient based tropopause are stronger in winter than in summer revealing the seasonal cycle of the tropopause transport barrier the analysis of the trace gas gradients also identifies atmospheric transport pathways in the upper troposphere lower stratosphere utls several regions where trace gas gradients are found to be decoupled from the dynamical field indicate preferred transport pathways between the ut and ls in particular anomalous co and o3 gradients above eastern africa eastern asia and the west pacific are likely related to convective transport and anomalous o3 gradients over the north atlantic and north pacific are related to isentropic transport connected to frequent wave breaking the results indicate that the pv gradient based tropopause definition provides a good identification of the dynamical and chemical discontinuity and is therefore effective in locating the physical boundary in the utls

intrusions into the tropical upper troposphere three dimensional structure and accompanying ozone and olr distributions abstract the evolution and structure of stratospheric intrusions into the upper troposphere ut over the northern tropical pacific is examined in terms of both potential vorticity pv and ozone o3 analysis of 20 years of ncep ncar reanalysis pv shows that the intrusion events have remarkably similar evolution and structure at 350 k with all events producing narrow tongues of high pv that have an almost north south orientation and last around 3 days nearly all events extend up into the lower stratosphere but only for a small percentage is there deep downward penetration the intrusions explain a large amount of the observed variability in upper tropospheric o3 above hilo hawaii with large values occurring when a tongue of high pv passes over hilo and low values when hilo is just upstream of a high pv tongue there is also an increase in total column ozone within the pv tongues but for most intrusions the increase is relatively small the relationship between deep convection as diagnosed by sate

cross equatorial response to middle latitude forcing in a zonally varying basic state abstract a nonlinear model based on the shallow water equations is used to study cross equatorial propagation of forced waves in the presence of a longitudinally varying time mean basic state zonal wind field it is found that global scale planetary waves are unable to propagate past a critical latitude where the mean zonal wind speed vanishes however if the longitudinally asymmetric basic state includes a duet in which the zonal winds are westerly waves of zonal scale less than the zonal scale of the westerly duct may propagate from one hemisphere to the other even though the zonally symmetric mean zonal wind remains easterly in the equatorial region the amplitude of the response in one hemisphere to forcing in the opposite hemisphere increases strongly with the magnitude of the westerlies in the equatorial duct the existence and annual variations of a westerly duct region in the upper troposphere in the eastern pacific appear to account for some features of the low frequency variability in the no

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

gas potential of proterozoic and phanerozoic shales from the nw himalaya india inferences from pyrolysis abstract organic richness and kerogen properties of sixty seven shales obtained from the outcrops and underground mines of jammu kashmir and ladakh regions of northwest himalaya india have been studied to evaluate their gas generation potential using rock eval pyrolysis ranging in age from the proterozoic to tertiary organic matter content and characteristics of the carbonaceous and coaly shales vary widely indicating that sedimentary and burial history significantly affected the preservation and maturation of organic components in rocks the total organic carbon toc content ranges from 0 01 to 1 2 in the permian jurassic and paleozoic tertiary shales of ladakh to as high as 32 5 in the eocene shales coaly shales from jammu the thermo labile hydrocarbons s1 and those from cracking of kerogen s2 released from the pyrolysis of eocene subathu shales are observed to be high from 0 1 to 2 6 and from 0 5 to 15 5 mg hc g rock respectively rock eval thermal maturity parameters indicated by tmax temperature at highest yield of s2 490 c and calculated vitrinite reflectance 1 5 to 3 7 ro suggest a post mature dry gas stage for the hydrocarbon generation based on hydrogen index hi and tmax correlations organic matter in the subathu shales is characterized by a late metagenetic gas prone type iii kerogen and a fair to excellent gas potential is exhibited by these shales the interbedded shale units in the proterozoic sirban limestone formation occurring as an isolated inlier in jammu show toc values from 0 1 to 1 4 with quite low s1 s2 and hi values thermal maturity of shales within the stromatolitic sirban succession indicates a post mature and or already spent hydrocarbon stage the plio pleistocene carbonaceous clays lignites and mudstones from the lower karewa group of kashmir basin are organically rich with toc content ranging from 5 86 to 29 4 a thermally immature type ii type iii kerogen is indicated by the hi 109 to 278 mg hc g toc and tmax 399 to 427 c plots of the karewa samples the exposed lower triassic black shales from the permian triassic boundary sections in kashmir are comparatively lean in organic matter with toc values ranging from 0 18 to 0 93 whereas the permian jurassic and paleozoic tertiary shales from ladakh have a toc content ranging from 0 01 to 1 22 the pyrolyzable organic carbon is

carbon isotopic profile across the bilara group rocks of trans aravalli marwar supergroup in western india implications for neoproterozoic cambrian transition abstract the rocks of marwar supergroup in the trans aravalli sector in western india are presumed to span the time interval between neoproterozoic and early cambrian this predominantly unfossiliferous marine sedimentary sequence is characterized by a lower arenaceous facies jodhpur group middle carbonate facies bilara group and upper argillaceous arenaceous facies nagaur group rocks the sedimentation has been essentially in a shallow basin described either as the fore land slope of the rising aravalli mountains or a sag basin which developed and evolved due to subsidence of the updomed crust during neoproterozoic malani magmatism that failed to open rifts the carbon isotopic profile for the bilara group carbonate rocks in the lower part shows marked oscillations and broadly negative 13 c character with negative anomalies as low as pdb observed near the base of dhanapa formation lower unit and pdb in the overlying gotan formation middle unit the upper part of the profile shows a gradual positive shift the carbon isotopic signatures of the bilara group rocks can be correlated with the end neoproterozoic early cambrian vendian tommotian carbon isotopic evolution curve extremely low 13 c values indicate the glaciation related cold climatic postulates of the end neoproterozoic followed by the warmer climatic conditions as indicated by the positive shift the carbon isotopic data for gotan formation carbonates at variance with the globally observed 13 c trends for early tertiary do not support the recently proposed tertiary age for the bilara group

connections between potential vorticity intrusions and convection in the eastern tropical pacific abstract the connections between intrusions of stratospheric air into the upper troposphere and deep convection in the tropical eastern pacific are examined using a combination of data analysis potential vorticity pv inversion and numerical simulations analysis of ncep ncar reanalyses and satellite measurements of outgoing longwave radiation during intrusion events shows increased cloudiness lower static stability upward motion and a buildup of convective available potential energy cape at the leading edge of the intruding tongue of high pv potential inversion inversion calculations show that the upper level pv makes the dominant contribution to the changes in the quantities that characterize convection this supports the hypothesis that upper level pv anomalies initiate and support convection by destabilizing the lower troposphere and causing upward motion ahead on the pv tongue the dominant role of the upper level pv is confirmed by simulations using the fifth generation pennsylvania state u

lithosphere crust and basement ridges across ganga and indus basins and seismicity along the himalayan front india and western fold belt pakistan abstract spectral analysis of the digital data of the bouguer anomaly of north india including ganga basin suggest a four layer model with approximate depths of 140 38 16 and 7 km they apparently represent lithosphere asthenosphere boundary lab moho lower crust and maximum depth to the basement in foredeeps respectively the airy s root model of moho from the topographic data and modeling of bouguer anomaly constrained from the available seismic information suggest changes in the lithospheric and crustal thicknesses from 126 134 and 32 35 km under the central ganga basin to 132 and 38 km towards the south and 163 and 40 km towards the north respectively it has clearly brought out the lithospheric flexure and related crustal bulge under the ganga basin due to the himalaya airy s root model and modeling along a profile se nw across the indus basin and the western fold belt wfb sibi syntaxis pakistan also suggest similar crustal bulge related to lithospheric flexure due to the wfb with crustal thickness of 33 km in the central part and 38 and 56 km towards the se and the nw respectively it has also shown the high density lower crust and bela ophiolite along the chamman fault the two flexures interact along the western syntaxis and hazara seismic zone where several large great earthquakes including 2005 kashmir earthquake was reported the residual bouguer anomaly maps of the indus and the ganga basins have delineated several basement ridges whose interaction with the himalaya and the wfb respectively have caused seismic activity including some large great earthquakes some significant ridges across the indus basin are i delhi lahore sargodha ii jaisalmer sibi syntaxis which is highly seismogenic and iii kachchh karachi arc kirthar thrust leading to sibi syntaxis most of the basement ridges of the ganga basin are oriented ne sw that are as follows i jaisalmer ganganagar and jodhpur chandigarh ridges across the ganga basin intersect himalaya in the kangra reentrant where the great kangra earthquake of 1905 was located ii the aravalli delhi mobile belt admb and its margin faults extend to the western himalayan front via delhi where it interacts with the delhi lahore ridge and further north with the himalayan front causing seismic activity iii the shahjahanpur and faizabad ridges strike the himalayan front in central nepal that do not show any enhanced seismicity which may be due to their being parts of the bundelkhand craton as simple basement highs iv the west and the east patna faults are parts of transcontinental lineaments such as narmada son lineament v the munghyr saharsa ridge is fault controlled and interacts with the himalayan front in the eastern nepal where bihar nepal earthquakes of 1934 has been reported some of these faults lineaments of the indian continent find reflection in seismogenic lineaments of himalaya like everest arun kanchenjunga lineaments a set of nw se oriented gravity highs along the himalayan front and the ganga and the indus basins represents the folding of the basement due to compression as anticlines caused by collision of the indian and the asian plates this study has also delineated several depressions like saharanpur patna and purnia depressions

oxygen and carbon isotope compositions of carbonates in a prominent lithologically mixed unit in the central south norwegian caledonides a prominent pre scandian lithologically mixed unit in the central south norwegian caledonides contains more than 100 partly carbonated and hydrated metaperidotite bodies and locally fossiliferous detrital serpentinites the lateral consistency of this mixed unit was not fully appreciated in the past therefore parts of the mixed unit along strike were interpreted to belong to several different tectonostratigraphic levels here we present new carbonate stable isotope data that suggest that the carbonates of the mixed unit between bergen and otta re equilibrated at unit wide similar peak metamorphic conditions the isotope compositions are characteristic for this unit and indicate that it represented one single tectonic unit during the scandian orogeny the carbonates in the melange are characterized by a narrow range of 18o smow values between 11 and 15 5 and three groups of 13c pdb values i 1 6 to 0 3 ii 1 8 to 3 9 and iii 6 to 8 6 carbonates of group iii probably were affected by decarbonation or by a fluid containing organic carbon whereas carbonates of group i and ii overlap with 13c values typical for ediacaran silurian marine carbonates and may have retained their initial 13c imprint we suggest that the 18o values re equilibrated with unit wide released metamorphic fluids during scandian metamorphism an outcrop scale homogenisation of the 13c values reflects the local carbon isotope signature of the released metamorphic fluids that circulated channelized through the melange unit

mantle fragments in the scandinavian caledonides abstract mantle fragments of ultramafic composition are widespread in the scandinavian caledonides sc lenses and boudins of alpine type peridotites in the scandinavian caledonides represent parts of dismembered ophiolite sequences and fragments of sub continental upper mantle metaperidotites of nappes in internal positions are generally isofacial with the metamorphic envelope usually caledonian metasediments but in places also precambrian metagranitoids forming the basement cores of the nappes caledonian metamorphism strongly modified the texture and mineralogy of the peridotites and resulted in a systematic metamorphic pattern which is consistent with the pattern observed in the envelope metaperidotites of the external massifs display at least a two stage metamorphic history an early caledonian high pressure high temperature phase related to early crustal stacking and a late caledonian regional metamorphic overprint which produced a regular barrovian type metamorphic pattern of in situ metamorphism metaperidotites from nappes in intermediate positions iapetus ocean ophiolites and ultramafic rocks from island arc environments show strongly diverging histories metaperidotites from internal ophiolites oceanic ophiolites koli lack any evidence of subduction metamorphism are serpentinized to various degrees show abundant primary mantle relic mineralogies and the caledonian metamorphic overprint is low metaperidotites from external island arc ophiolites and other associations seve often show relic high pressure metamorphism related to the finnmarkian phase of the caledonian orogeny the seve metaperidotites are occasionally associated with eclogites and show a weak overprint of late caledonian regional metamorphism alpine type peridotites are absent in the foreland of the baltic shield and in the innermost nappes lofoten the metamorphic characteristics and evolution recorded by the metaperidotites in the scandinavian caledonides allow a general reconstruction of the dynamics of collision belt formation

organic geochemistry of the vindhyan sediments implications for hydrocarbons abstract the organic geochemical methods of hydrocarbon prospecting involve the characterization of sedimentary organic matter in terms of its abundance source and thermal maturity which are essential prerequisites for a hydrocarbon source rock in the present study evaluation of organic matter in the outcrop shale samples from the semri and kaimur groups of vindhyan basin was carried out using rock eval pyrolysis also the adsorbed low molecular weight hydrocarbons methane ethane propane and butane were investigated in the near surface soils to infer the generation of hydrocarbons in the vindhyan basin the total organic carbon toc content in shales ranges between 0 04 and 1 43 the s1 thermally liberated free hydrocarbons values range between 0 01 0 09 mghc grock milligram hydrocarbon per gram of rock sample whereas the s2 hydrocarbons from cracking of kerogen show the values between 0 01 and 0 14 mghc grock based on the tmax temperature at highest yield of s2 and the hydrogen index hi correlations the organic matter is characterized by type iii kerogen the adsorbed soil gas ch4 c1 c2h6 c2 c3h8 c3 and nc4h10 nc4 concentrations measured in the soil samples from the eastern part of vindhyan basin son valley vary from 0 to 186 ppb 0 to 4 ppb 0 to 5 ppb and 0 to 1 ppb respectively the stable carbon isotope values for the desorbed methane 13c1 and ethane 13c2 range between 45 7 to 25 2 and 35 3 to 20 19 vpdb respectively suggesting a thermogenic source for these hydrocarbons high concentrations of thermogenic hydrocarbons are characteristic of areas around sagar narsinghpur katni and satna in the son valley the light hydrocarbon concentrations c1 c4 in near surface soils of the western vindhyan basin around chambal valley have been reported to vary between 1 2547 ppb 1 558 ppb 1 181 ppb 1 37 ppb and 1 32 ppb respectively with high concentrations around baran jhalawar bhanpur garot regions kumar et al 2006 the light gaseous hydrocarbon anomalies are coincident with the wrench faults kota dholpur ratlam shivpuri kannod damoh son banspur rewa wrench in the vindhyan basin which may provide conducive pathways for the migration of the hydrocarbons towards the near surface soils

thermobarometric profile through the caledonian nappe stack of western ofoten north norway p t estimates from pelite thermobarometry along a transect through the caledonian nappe stack in ofoten north norway 68 30 n plot as a trend in p t space ranging from 443 c 6 9 kb to 688 c 10 6 kb the p t range for each nappe overlaps the others except for those from the lowest unit narvik group which has significantly higher values within the p t ranges for each nappe the position on the trend of a given sample is independent of its tectonic position results support our earlier conclusion based on structural and petrographic grounds that the regional metamorphic peak was reached during or after stacking of the nappes in the siluro devonian scandian orogeny

late eocene sea retreat from the tarim basin west china and concomitant asian paleoenvironmental change the paleogene sediments of the southwest tarim basin along the west kunlun shan in western china include the remnants of the easternmost extent of a large epicontinental sea this shallow sea once extended across the eurasian continent before it retreated westward and eventually separated as the paratethys sea climate modeling results suggest that this sea retreat is an equally important forcing mechanism as the tibetan plateau uplift in the aridification of the asian continental interior and the intensification of the asian monsoon system the age and paleogeography of the retreat are poorly constrained hindering the understanding of its cause and paleoenvironmental impacts this study reports litho and biostratigraphic results from two sections recording the last major regression out of the tarim basin that is expressed by a regional transition from marine clastics and limestones to continental red beds rich micro and macrofossil assemblages including benthic foraminifera ostracods bivalves calcareous nannofossils and organic walled dinoflagellate cysts dinocysts indicate a shallow proximal and marine environment strong similarity to assemblages known from central asia and europe confirms that surface ocean connections extended across eurasia from the tarim basin to the western tethys during the latest eocene moreover the recovered fossil associations date the last marine sediments as earliest priabonian in age 37 ma overlap between dinoflagellate mps interval zone and calcareous nannofossil zone cp 14 the retreat of the sea from the tarim basin is time equivalent with the sea level lowstand at the bartonian priabonian boundary but pre dates both the oligocene miocene regional uplift of the pamir mountains and kunlun shan and the major eustatic sea level falls of the eocene oligocene transition 34 ma and mid oligocene 30 ma which are usually held responsible for the sea retreat furthermore a concomitant and significant aridification step occurs at 36 6 ma top of chron c17n 1n as recorded by regional sedimentary records of the xining basin along the northeastern tibetan plateau suggesting that the tarim sea served as a significant moisture contributor for the asian interior

the effect of model bias on the equatorward propagation of extratropical waves the effect of model bias on the equatorward propagation of extratropical waves in a gcm simulation is assessed within the context of simple wave guiding principles the modes representing these waves are identified through the use of empirical orthogonal function analysis performed on the 200 mb zonal wind filtered to retain variations between 6 and 30 days the temporal evolution and vertical structure of these modes are examined through the use of time lagged composite analysis the differences between observed and simulated wave propagation is examined in relationship to the theoretical wave guiding properties associated with the observed and simulated time mean flow the utility of simple wave guiding theory for describing the observed and modeled wave propagation is assessed the model bias in the time mean flow is closely associated with the differences in the propagation of the transient waves the excessively strong wave guiding properties associated with the simulated pacific jet appear to inhibit the proper meridional propagation of wave energy into the tropical central and eastern pacific in the simulation waves that do propagate into the tropical pacific either dissipate or are reflected near the equator while in the observations wave energy propagates into the southern hemisphere on the other hand the wave guiding by the subtropical and midlatitude jets over the atlantic is weaker in the simulation than in the observations in this region wave energy propagates primarily into the tropics in the simulation while some of the observed wave energy is reflected toward the east and northeast over the atlantic and northern africa the locations of the theoretical critical lines and wave guides of the time mean flow although based on many simplifying assumptions are remarkably consistent with the propagation characteristics of these waves

the p t evolution of the middle koli nappe complex scandinavian caledonides 68 n and its tectonic implications near 68 n the scandinavian caledonides are composed of 3 tectonic domains each of which has a different tectonostratigraphy the lower 2 domains can be related stratigraphically to scandinavia prior to caledonian deformation whereas the highest domain the middle koli nappe complex mknc represents a fore arc accretionary complex that was accreted to scandinavia during caledonian deformation subsequent to accretion the flyschoid sediments that dominate the mknc were metamorphosed to the amphibolite facies in the area covered by this study the mknc is composed of two nappes a lower langvatn nappe and an upper marko nappe each of which has a unique early metamorphic history pelitic mineral assemblages in the marko nappe constrain the peak p t to be 625 7 0 kbars whereas ultramafic mineral assemblages in the lower langvatn nappe constrain its peak temperature to be 580 c p t estimates from garnet biotite and garnet plagioclase geothermobarometry for both nappes overlap ranging from 528 c and 6 6 kbars to 620 c and 8 8 kbars with an average of 567 32 c and 8 0 0 9 kbar

formation of sapphirine during retrogression of a basic high pressure granulite roan western gneiss region norway sapphirine bearing rocks occur in the northern part of the western gneiss region vestranden central norway the sapphirine bearing rocks are characterized by a high mgo mgo feo ratio high al2o3 mgo and cao and low sio2 contents these rocks form layers within larger complexes which originated as layered magmatic rocks high pt metamorphism produced a cpx ky gt assemblage the p and t estimates are p 14 5 2 kbar and t 870 50 c during retrogression the high p granulite assemblage broke down to form an intermediate p granulite mineralogy comprising orthopyroxene spinel anorthite andesine sapphirine and corundum textural relationships suggest that sapphirine formed by the reaction spinel kyanite sapphirine corundum and probably also by a reaction between corundum spinel and orthopyroxene all reactions took place within the stability field of kyanite textural and micro chemical relationships indicate equilibrium conditions during the peak metamorphism whereas pronounced disequilibrium characterizes the mineral associations formed during the early retrogression at low ph2o the investigation shows that parts of the northern segment of the western gneiss region underwent a metamorphic evolution similar to the caledonian one recorded from eclogite granulite terrains further south

a tectonic model for the metamorphic evolution of the basal gneiss complex western south norway a review of currently available information relevant to the basal gneiss complex bgc of western south norway combined with the authors own observations leads to the following conclusions 1 most of the bgc consists of proterozoic crystalline rocks and probably subordinate lower palaeozoic cover 2 the last major deformation of these rocks was during the caledonian orogeny and involved large scale thrusting recumbent folding and doming the structural development of the bgc is closely tied in with that of the caledonian allochthon 3 the whole eclogite bearing part of the bgc has suffered a high pressure metamorphism with conditions of between 550 c 12 5 kbar sunnfjord and about 750 c 20 kbar more og romsdal at the metamorphic climax 4 this metamorphism was of caledonian age probably rather early in the caledonian tectonic history of the bgc and is considered to have been a rather transient event by setting these conclusions in a framework provided by geophysical evidence for the deep structure of the crust in southern norway we have constructed a geotectonic model to explain the recorded metamorphic history of the bgc it is suggested that considerable crustal thickening was caused by imbrication of the baltic plate margin during continental collision with the greenland plate this resulted in high pressure metamorphism in the resulting nappe stack progradation of the suture caused underthrusting of the baltic foreland below the eclogite bearing terrain causing it to emerge at the earth s surface aided by tectonic stripping and erosion application of isostacy equations to the model shows that eclogites can be formed by in situ metamorphism in crustal rocks and reappear at the land surface above a normal thickness of crust in a single orogenic episode of approximately 65 70 ma duration

nonlinear barotropic response to a localized topographic forcing formation of a tropical surf zone and its effect on interhemispheric propagation abstract the nonlinear response of a barotropic nondivergent spherical flow representative of the upper troposphere but without a tropical hadley cell to localized extratropical topographic forcing is examined using high resolution contour surgery calculations the response is shown to vary greatly with forcing amplitude and can be significantly different from the linear response at large amplitude rossby wave breaking occurs in the tropics irrespective of the direction of the equatorial winds and leads to small scale stirring and the formation of a tropical surf zone which inhibits the meridional propagation of the disturbance

convective destabilization by a tropopause fold diagnosed using potential vorticity inversion there is observational evidence to suggest that at the time tropopause folds in extra tropical cyclones are descending into the mid troposphere there is frequently a destablization of the lower troposphere to moist convection here we consider the dynamical reasons for such a linkage using so called potential vorticity pv attribution concepts in particular pv inversion is used to find the wind shear attributable to the tropopause fold itself then this shear is used to quantify the tendency to generate regions of potential instability for an observed case of a modest tropopause fold it is found that the pv anomaly contained in the tropopause fold contributed substantially to the instantaneous convective destabilization in the sense of increasing the potential instability indeed at some locations it overcame a tendency to stabilize by the atmosphere without the fold on the other hand only a fraction of the region with increased potential instability experienced sufficient large scale ascent to lead to convection and it remains to be seen whether folds in general make a significant contribution to the generation of potential instability that can actually be realized the importance of tropopause folds or indeed of tropopause depressions in general in the context of convection is that their small horizontal scale has the potential to focus and amplify any convective destabilization locally this may account for the localization of outbreaks of severe convective weather which it is important to forecast accurately currently numerical weather prediction models often do not handle these small scales very accurately

planetary scale tropopause folds in the southern subtropics daily measurements of tropospheric ozone at la reunion island 55 e 21 s in july 1998 show that ozone layers are quasi permanent in the troposphere between 6 and 10 km with values reaching 80 to 100 ppbv meridional cross sections of potential vorticity reveal that these layers are related to tropopause folds beneath the subtropical jet folding is persistent and extends over a considerable longitude range from mid atlantic to mid pacific we suggest that this structure is due to the convergent flow associated to the descent branch of the hadley circulation during austral winter

deformation of the baltic continental crust during caledonide intracontinental subduction views from seismic reflection data deep seismic profiling in norway and sweden provides documentation of the amount and style of deformation of the baltic crust in response to caledonian intracontinental subduction the seismic data demonstrate that the preserved caledonide allochthon in central scandinavia is 15 to 20 km thick considerably greater than the 2 to 5 km predicted from surface geologic data much of the thickness of allochthonous rocks results from imbrication of the baltic basement within a thin skinned style thrust complex seismic data across the skardora antiform one of the basement windows in the central caledonides indicate that the window represents an antiformal stack of thrust sheets involving basement and cover rocks these data suggest that many of the basement windows in the scandinavian caledonides may result from similar thrust culminations and that the basement windows do not expose autochthonous baltic basement documentation of the response of the baltic crust during intracontinental subduction provides new constraints on reconstructions of the scandinavian caledonides and insights into the style of deformation occurring in other collisional orogens

seismic reflection coefficients from mantle fault zones summary several bright reflections from structures within the mantle can be seen on birps deep seismic reflection profiles we have calculated apparent reflection coefficients for the brightest of these events and obtain values around 0 1 it is not possible to produce such large reflections by either compositional layering or seismic anisotropy if olivine and pyroxene are the only significant minerals in the mantle these large reflections can be produced by a mafic layer or a partially hydrated layer within normal peridotite the brightest reflections seem to be best explained as major faults or shear zones within the mantle

an overview of pre devonian petroleum systems unique characteristics and elevated risks abstract the radiation of land plants at the onset of the devonian resulted in a change in the character of available biomass which in turn introduced changes to the nature of petroleum systems this study examines the nature of pre devonian petroleum systems prior to this significant evolutionary event conventional hydrocarbon resources have been associated with pre devonian petroleum systems across the globe including the neoproterozoic infracambrian huqf supergroup of the oman basin the riphean vendian sequences of east siberia the cambrian of the murzuq basin the ordovician of the tarim basin and the silurian qusaiba of saudi arabia although individual accumulations can be quite significant e g hassi messaoud has ultimate recoverable reserves of 10 billion barrels the relative importance of pre devonian derived oils is thought to be limited compared to the global conventional resource base with growing interest in unconventional resources the relative importance of these systems is expected to increase as resource plays such as the ordovician utica shale of the appalachian basin the cambrian of china and possibly the silurian of central and eastern europe develop the advanced ages of these systems result in some unique properties and amplify risks that exist in younger petroleum systems differences in the nature of the biomass contributing to pre devonian source rocks may give rise to oils that display unique geochemical characteristics for example there are some precambrian oils where c 29 steranes dominate even though land plants were absent there are also ordovician source rocks dominated by gloeocapsamorpha prisca a primitive prokaryote which yield oils containing limited amounts of c 20 components and nearly lack pristane and phytane the potential for unconventional reservoirs in pre devonian systems may also be highly dependent upon the age of the system as biological evolution influences the availability and nature of biogenic silica an important factor controlling brittleness and fracability literature has shown that biogenic silica from different sources displays varying degrees of resistance to diagenesis which allows the formation of a silica network and influences brittleness for example radiolaria present during the cambrian are more resistant to diagenesis than diatoms which did not evolve until the jurassic risks associated with preservation of hydrocarbons are also amplified in pre devonian petroleum systems many such systems have been exposed to significant thermal stresses resulting in the cracking of oil and wet gas others have had complex tectonic histories potentially resulting in the breaching of seals or changes in pvt conditions that can result in gas loss gas loss may also occur through diffusion from these older reservoirs as a result of long residence times

on the effects of the hadley circulation and westerly equatorial flow on planetary wave reflection the nonlinear behaviour of quasi stationary planetary waves that are excited by mid latitude orographic forcing is considered in a global shallow water model taken to represent the upper troposphere the waves propagate toward low latitudes where the background flow is normally weak and the waves are therefore likely to break nonlinear pseudomomentum conservation relations are used to quantify the absorption reflection behaviour of the wave breaking region two different flow scenarios are represented i initial states without a representation of the hadley circulation but where the axisymmetric equatorial background flow changes from being weak and easterly to moderate westerly ii initial states that include a representation of the hadley circulation and that have weak equatorial easterlies based on linear arguments both i and ii are expected to influence the progression of the wave train the nonlinear behaviour in the presence of low latitude westerly background flows is different from linear predictions for large amplitude forcing wave breaking takes place even though there is no zero wind line in the initial state and the cross equatorial wave propagation that took place for small amplitude forcing is stopped before it can reach the equator nonlinear reflection is found to take place back into the hemisphere of origin but not across to the other hemisphere in the presence of a hadley circulation representative of winter conditions the nonlinear reflection takes longer to get established i e it requires more forcing but a reflected wave train is still present in the numerical simulations both for a longitudinally symmetric forcing and for the more realistic case of an isolated forcing a summer hadley circulation allows wave activity to get to the winter hemisphere as the forcing is increased wave breaking occurs and eventually nonlinear reflection

metamorphism in basement rocks and the implications for the tectonic evolution nasafjall window scandinavian caledonides the rocks of the nasafjall window comprise proterozoic granitoids with a metasedimentary cover of late precambrian to ordovician age the mierkenis group the metamorphic grade in the window varies from greenschist facies in the eastern part of the window to amphibolite facies in the western part the metamorphic maximum is syn to post kinematic in relation to the formation of the thrust related pervasive foliation this suggests a rapid basement heating in response to the late silurian to early devonian nappe emplacement the caledonian metamorphism terminated in middle devonian times and the retrograde phase was characterized by decompression this implies that the later stage of the thrusting was not associated with an increase in thickness of the nappe pile above the rocks of the nasafjall window

longitudinal variation of the stratospheric quasi biennial oscillation the longitudinal dependence of interannual variations of tropical stratospheric wind is examined in a detailed general circulation model simulation and in the limited observations available a version of the skyhi model is run with an imposed zonally symmetric zonal momentum source that forces the zonal mean zonal wind evolution in the tropical stratosphere to be close to an estimate of the observed zonal wind based on radiosonde observations at singapore during the period 1978 99 this amounts to a kind of simple assimilation model in which only the zonal mean wind field in the tropical stratosphere is assimilated and other quantities are allowed to vary freely a total of five experiments were run one covering the full 1978 99 period and four for 1989 99 the results at and above about 30 hpa are fairly simple to characterize when the zonal mean wind near the equator at a particular level is easterly the monthly mean wind has only very small zonal contrasts when mean westerlies are present near the equator significant zonal asymmetries occur at low latitudes most notably easterly anomalies over south america and westerly anomalies in the eastern pacific region these anomalies generally display a continuous meridional phase propagation with the extratropical quasi stationary eddy field in the winter hemisphere the net result is a significantly weaker peak to peak amplitude of the quasi biennial oscillation qbo in zonal wind over the south american sector than over the rest of the equatorial band the zonal contrast in qbo amplitude near 10 hpa exceeds 10 in the lower stratosphere the zonal asymmetries in the prevailing wind are fairly small asymmetries seem to reflect the upward extension of the tropospheric walker circulation and are less strongly modulated by the quasi biennial oscillation in zonal mean circulation the model results were checked against limited station observations at nairobi 1 38s 36 78e singapore 1 48n 103 98e rochambeau 4 88n 52 48w and bogota 4 78n 74 18w overall reasonable agreement was found between the monthly mean zonal winds in the model simulation and these station data the low latitude wind field in monthly mean ncep gridded analyses was also examined these analyses have some obviously unrealistic features in the tropical stratosphere but some of the behavior seen in the skyhi model simulations can be identified as well in the ncep analyses

climatology of intrusions into the tropical upper troposphere regions of upper tropospheric equatorial westerly winds observed over the pacific and atlantic oceans during northern fall to spring are important for extratropical tropical interactions this paper focuses on one feature of these westerly ducts that has received relatively little attention to date the occurrence of rossby wave breaking events that transport tongues of extratropical air deep into the tropics mix tropical and subtropical air and can affect deep convection a climatology of these intrusion events formed from 20 years of meteorological analyses shows a strong dependence on the basic state flow notably intrusion events are found to occur almost exclusively within westerly ducts with more events in the presence of stronger equatorial westerlies it is also found that there is strong interannual variability in the frequency of pacific events with fewer events during the warm phases of enso consistent with the changes in the basic flow since these intrusion events laterally mix trace constituents and have been linked to tropical convection their spatial and temporal variability may cause related variability in the distribution of trace constituents and tropical convection

u pb ages of ophiolites and arc related plutons of the norwegian caledonides implications for the development of iapetus u pb zircon ages are reported for four ophiolites and three crosscutting arc related plutons from the norwegian caledonides plagiogranite differentiated from gabbro of the karmoy ophiolite is dated at 493 7 4 ma whereas arc related trondhjemite cutting this ophiolite crystallized at 485 2 ma a crosscutting clinopyroxene phyric gabbro intrusion is dated at 470 9 5 ma by near concordant magmatic titanite sphene and discordant u rich 2903 6677 ppm zircon lower intercepts of 247 68 and 191 70 ma defined by the plagiogranite and clinopyroxene phyric gabbro best fit lines may reflect a real low t alteration rift related event

kinematic evolution of the lower plate during intracontinental subduction an example from the scandinavian caledonides geophysical data combined with pressure temperature time data form the basis for a reconstruction of the kinematic evolution of the scandinavian caledonides collisional orogenic belt the reconstruction suggests that the early stages of collision between baltica and laurentia involved intracontinental subduction of a minimum of 150 km of baltic continental crust to a depth of at least 100 km the subduction juxtaposed strong laurentian upper mantle rocks in the upper plate against weak baltic crustal rocks in the lower plate continued plate convergence coupled with the buoyancy of the baltic rocks resulted in thrust imbrication of a substantial portion of the lower plate and extrusion of the crustal rocks from the subduction zone thrusting also resulted in incorporation of fragments of the laurentian upper mantle into the baltic crust the reconstruction also suggests that direct interaction between the laurentian and baltic crustal rocks and the time of greatest crustal thickness in the orogen occurred after extrusion of the baltic crust from the subduction zone one implication of this suggestion is that the eclogite coesite assemblage presently exposed at the surface in the hinterland of the caledonides probably formed early in the collision sequence during subduction rather than during the time of greatest crustal thickness the reconstruction also suggests that exposure of the high pressure mineral assemblage was a two phase process involving extrusion from the subduction zone by thrusting during convergence and unroofing by a combination of extension on low angle normal faults and erosion the kinematic model derived for the scandinavian caledonides provides a possible scenario for the evolution of other collisional orogenic belts containing very high pressure mineral assemblages formed in situ in continental rocks and associated ultamafic rocks of mantle origin

water vapor isotopic composition of a stratospheric air intrusion measurements from the chajnantor plateau chile measurements of water vapor isotopic composition in stratospheric air intrusions can be used to constrain the dilution of the intrusion as it mixes into the middle troposphere the intrusion studied here occurred on 17 and 18 august 2012 with measurements obtained at an altitude of 5 km in the chilean andes at the atacama large millimeter array astronomical observatory on the chajnantor plateau surface ozone concentrations rose 16 ppb in 6 h and were associated with a potential vorticity intrusion on the 330 k isentropic surface a simulated stratospheric ozone tracer reaching chajnantor also supports the interpretation of a stratospheric intrusion beginning around 18 00 utc on 17 august the mixing ratio dropped from 3000 ppmv to 430 ppmv as the water vapor d values dropped from 153 to 438 over 13 h while the 18o values dropped from 20 to 63 the average mixing ratio d and 18o values during august 2012 were measured to be 1500 ppmv 250 and 34 respectively the minimum water vapor concentration during the intrusion was in the driest 5 of measurements made during that month while the minimum d and 18o values were within the lowest 0 5 of measurements made during that month simple two component models of mixing between stratospheric or upper tropospheric air with boundary layer air fail to reproduce observations but a three component mixing model in which the stratospheric intrusion mixes with an upper tropospheric background air mass as it mixes with boundary layer air on chajnantor matches the observations

shear deformation and eclogite formation within granulite facies anorthosites of the bergen arcs western norway the anorthosites of the bergen arcs contain two distinct metamorphic mineral assemblages which are stable under different p t conditions a granulite facies assemblage which equilibrated at t 800 900 c p 10 kbar is defined by the minerals plagioclase al rich diopside cpx i garnet gnt i scapolite orthopyroxene dark brown hornblende this assemblage is linked by corona structures to a primary magmatic mineralogy where coexistence of olivine and plagioclase limits the maximum crystallization pressure of the anorthosites to 8 kbar at 1200 c the anorthosites are transected by a series of fine grained shear zones in which the granulite facies assemblage is replaced by an eclogite mineralogy defined by omphacite cpx ii jd40 50 garnet kyanite epidote clinozoisite phengite quartz amphibole with plagioclase sometimes remaining in the marginal parts mineral compositions indicate equilibration conditions for the eclogite paragenesis of t 700 800 c p 16 19 kbar a series of textural and mineralogical changes which can be observed as the strain increases into the shear zones demonstrates that the eclogite mineralogy is formed at the expense of the granulite facies minerals during the early stages of shear zone development the eclogite mineralogy defines a strong mylonitic fabric which again is truncated by centimetres thick secondary shear zones containing clasts of both granulite and eclogite minerals these latter fine grained ultramylonites may be connected to uplift of this deep seated complex the eclogite shear zones are highly oblique to the granulite structures indicating that the eclogite shear zones formed under a new stress regime rb sr dating shows that the granulite facies assemblage formed in sveconorwegian time or earlier while minerals from shear zones define ages around 400 ma indicating a caledonian formation of the eclogites this work demonstrates the critical role of deformation in triggering metamorphic reactions whether the shear stress also was important in stabilizing the eclogite assemblages is not clear from the available data

the link between cut off lows and rossby wave breaking in the southern hemisphere the climatological link between cut off low col pressure systems that occur from 20 to 50 s and rossby wave breaking rwb in the southern hemisphere sh is examined for 1979 2008 it is shown that cols are associated with either rwb events 89 or with potential vorticity pv intrusions where there is north south advection of high pv air 11 in the vast majority of cols the rwb events occur upstream on or before the day of the col formation the evolution of the pv geopotential heights static stability absolute vorticity and temperature advection fields during the cols are consistent with the formation of high pv anomalies that induce cyclonic circulations as predicted by theory rwb plays a key role in producing the split flow associated with cols in the sh which in turn produces absolute vorticity anomalies by shear curvature vorticity conversion and creates static stability anomalies the cols associated with rwb at 330 k are deeper and more persistent than those associated with 350 k rwb and surface processes differ depending on the isentropic surface on which the associated rwb occurs the seasonality of the rwb and cols are similar and is linked to the seasonal march of the westerly jets copyright 2010 royal meteorological society

tropical upper tropospheric potential vorticity intrusions during sudden stratospheric warmings abstractthe intrusion of lower stratospheric extratropical potential vorticity into the tropical upper troposphere in the weeks surrounding the occurrence of sudden stratospheric warmings ssws is examined the analysis reveals that ssw related pv intrusions are significantly stronger penetrate more deeply into the tropics and exhibit distinct geographic distributions compared to their climatological counterparts while climatological upper tropospheric and lower stratospheric utls pv intrusions are generally attributed to synoptic scale rossby wave breaking it is found that ssw related pv intrusions are governed by planetary scale wave disturbances that deform the extratropical meridional pv gradient maximum equatorward as these deformations unfold planetary scale wave breaking along the edge of the polar vortex extends deeply into the subtropical and tropical utls in addition the material pv deformations also reorganize the geographic structure of the utls waveguide which alters where synopti

c o sr and pb isotope systematics of carbonate sequences of the vindhyan supergroup india age diagenesis correlations and implications for global events abstract the vindhyan supergroup of central india records a substantial portion of proterozoic time and contains some of the most disputed precambrian cambrian fossil discoveries despite the significance of these fossil finds many issues including reliable geochronology remained unresolved similarly the geochemical aspects of the sedimentary sequences and their implications to the evolution of proterozoic oceans have been studied only at a reconnaissance level here we report the results of the pb pb dating for the rohtasgarh limestone from the lower vindhyan supergroup giving an age of 1601 130 ma an estimate that is in accord with the recent u pb zircon dating of the lower vindhyan supergroup by rasmussen et al geology 30 2002 103 and ray et al geology 30 2002 131 sr isotope stratigraphy of carbonates from the upper vindhyan supergroup suggests a mid neoproterozoic 750 650 ma age for these formations this in turn argues for a long hiatus between the deposition of the lower and upper vindhyan supergroups our results conflict with the reports of cambrian age small shelly fossils and ediacaran fossils from the upper vindhyan rocks at the same time they suggest that the alleged trace fossils in the lower vindhyan rocks must be of paleoproterozoic age the most common 18 o values for calcitic components from limestone formations of the supergroup range from 10 to 7 similar to paleo neoproterozoic carbonates worldwide the modes of 13 c in the lower and upper vindhyan supergroups are 0 2 and 3 2 respectively again consistent with the worldwide dataset the secular patterns of carbon isotope trends do not support the earlier assumptions that the carbonate sequences at the southern margin correlate with those at the western or northern margins of the vindhyan basin c and sr isotope data provide new calibration points for the seawater evolutionary curves particularly for the paleoproterozoic for strontium isotopes the data from the lower vindhyan supergroup suggest that seawater departed probably less rapidly from mantle values than was previously believed

the 1985 86 intraseasonal oscillation and the role of the extratropics abstract an intraseasonal oscillation that occurred in the 1985 86 northern winter is documented in this study the tropical convection of this event is dominated by the mixture of a standing oscillation over the maritime continent and an eastward moving feature from the indian ocean into the central pacific the time evolution of the upper tropospheric circulation patterns instead of propagating eastward along the equator as suggested in the existing composites of the intraseasonal oscillation is characterized by a series of wave patterns in the northern hemisphere and does not complete the cycle around the globe the familiar moist kelvin wave explanation for the intraseasonal oscillation receives little support from diagnosis of this event using zonal wind height field streamfunction and potential vorticity only in the lower troposphere near the date line is the convincing evidence for its existence found a scenario for the intraseasonal oscillation which is suggested by the analysis includes

interactions between enso transient circulation and tropical convection over the pacific abstract the interannual variability of transient waves and convection over the central and eastern pacific is examined using 30 northern winters of ncep ncar reanalyses 1968 69 1997 98 and satellite outgoing longwave radiation data starting in 1974 there is a clear signal associated with the el nino southern oscillation such that differences in the seasonal mean basic state lead to statistically significant changes in the behavior of the transients and convection with periods less than 30 days which then feed back onto the basic state during a warm event el nino phase the northern hemisphere subtropical jet is strengthened over the central pacific the region of upper tropospheric mean easterlies over the tropical western pacific expands eastward past the date line and the upper tropospheric mean westerly duct over the tropical eastern pacific is weakened the transients tend to propagate along the almost continuous waveguide of the subtropical jet equatorward propagation into the westerly

invigoration and capping of a convective rainband ahead of a potential vorticity anomaly abstractdeep convection frequently occurs on the eastern side of upper level troughs or potential vorticity pv anomalies this is consistent with uplift ahead of a cyclonic pv anomaly and consequent reduction in static stability and increase of convective available potential energy cape nevertheless the causal link between upper level pv and deep convection has not been proven and given that lift moisture and instability must all be present for deep convection to occur it is not clear that upper level forcing is sufficient in this paper a convective rainband that intensified ahead of a cyclonic pv anomaly in an environment with little cape 10 j kg 1 is examined to determine the factors responsible for its intensification the key feature was a low level convergence line arising from the remnants of an occluded front embedded in the low level cyclonic flow the rainband s intensity and morphology was influenced by the remnants of a tropopause fold that capped convection at midlevels in the

interaction of extratropical rossby waves with westerly quasi biennial oscillation winds the role of laterally radiating stratospheric rossby waves from the winter hemisphere in the momentum balance of the quasi biennial oscillation qbo remains an unresolved issue observations of extratropical rossby waves penetrating close to the equator suggest that rossby wave absorption in the tropics must occur at least occasionally this paper presents numerical simulations using a global shallow water model to examine the pattern of wave absorption at low latitude during the westerly wind phase of the qbo earlier results indicating that extratropical rossby waves radiating to the equator do not break there when the qbo phase is westerly are reproduced it is shown that the westerly qbo jet can persist undiminished at its core over seasonal length integrations because the laterally radiating rossby waves are absorbed along the qbo jet s flanks where easterly acceleration occurs the net effect of the rossby waves on the westerly qbo jet is a reduction in the width of its meridional profile but not its core strength this behavior is interpreted by considering the filtering of equatorward radiating rossby waves by critical layer absorption a process that depends on the background zonal mean wind and the waves phase speed and amplitude the simulations also show that adequate horizontal resolution is needed to capture the suppression of wave breaking at the qbo jet core and persistence of the jet core strength over seasonal timescales the implications of this result for simulations of the qbo in general circulation models are considered

identification and era 15 climatology of potential vorticity streamers and cutoffs near the extratropical tropopause abstract a novel approach is introduced to identify potential vorticity pv streamers and cutoffs as indicators of rossby wave breaking near the extratropical tropopause and to compile climatologies of these features on different isentropic surfaces the method is based on a contour searching algorithm that identifies the dynamical tropopause 2 potential vorticity units pvu pvu 1 10 6 k kg 1 m2 s 1 isoline on isentropic surfaces the contour is then analyzed to search for cutoffs and filament like streamers whereas the identification of cutoffs is unambiguous the one for streamers requires the specification of two parameters that determine the width and length of the contour feature to be classified as a streamer this technique has been applied to the pv distribution in the northern hemisphere on isentropes from 295 to 360 k during the time period from 1979 to 1993 using the 15 yr european centre for medium range weather forecasts ecmwf re analysis era 15 the climatology reveals a pronou

polyorogenic 40 ar 39 ar mineral age record in the seve and koli nappes of the gaddede area northwestern jamtland central scandinavian caledonides in the scandinavian caledonides eugeoclinal terranes represented in the koli nappes were thrust 500 km onto the baltoscandian platform during the early to middle paleozoic immediately underlying thrust sheets of the seve nappe complex are suspected to have been derived from the outer margin of continent baltica contrasting tectonothermal histories are recorded in seve and koli nappes exposed in the gad dede area northern jamtland county sweden eclogite bearing seve rocks underwent an initial amphibolite grade regional metamorphism smi with different structural units experiencing contrasting high to intermediate pressure conditions subsequent ductile imbrication sm2 of high and intermediate pressure structural units occurred prior to 460 470 ma cooling through temperatures required for intracrystalline retention of argon in hornblende a later thermal overprint sm3 everywhere rejuvenated seve biotite and muscovite and locally hornblende argon systems at 430 pm 5 ma 40 ar 39 ar plate

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

dry intrusions lagrangian climatology and dynamical impact on the planetary boundary layer abstractdry air intrusions dis are dry deeply descending airstreams from the upper troposphere toward the planetary boundary layer pbl the significance of dis spans a variety of aspects including the interaction with convection extratropical cyclones and fronts the pbl and extreme surface weather here a lagrangian definition for di trajectories is used and applied to ecmwf interim reanalysis era interim data based on the criterion of a minimum descent of 400 hpa during 48 h a first global lagrangian climatology of di trajectories is compiled for the years 1979 2014 allowing quantitative understanding of the occurrence and variability of dis as well as the dynamical and thermodynamical interactions that determine their impact dis occur mainly in winter while traveling equatorward from 40 50 latitude dis typically reach the lower troposphere with maximum frequencies of 10 in winter in the storm track regions as well as over the mediterranean sea arabian sea and eastern north pa

local mixing events in the upper troposphere and lower stratosphere part ii seasonal and interannual variability the lyapunov diffusivity is used to investigate local isentropic mixing events in the upper troposphere lower stratosphere utls region the diagnostic highlights the seasonal cycle of the longitudinally varying mixing properties in particular those associated with the monsoon circulations and the westerly ducts in the subtropics the results are broadly consistent with studies of rossby wave breaking frequencies the mixing structure is shown to be modulated by modes of atmospheric variability el nino southern oscillation enso is found to strongly influence the mixing structure throughout the tropics and subtropics the sub tropical jet is associated with longitudinal bands of mixing minima isentropic mixing barriers separated by synoptic scale regions of strong mixing activity the greatest enso modulation in december february is confined to the pacific sector where the barriers associated with the subtropical jets extend farther into the eastern pacific and in the western pacific a barrier is found at the equator during the positive phase during june august the influence is seen to extend beyond the pacific region with the barrier at the subtropical jet in the southern hemisphere increasing in strength at all longitudes and with an increase in strength and isolation of monsoon related mixing over asia and north america the local influence of the north atlantic oscillation in wintertime is investigated during the positive phase a double barrier structure is associated with the subtropical jet the northern branch crosses the atlantic toward scandinavia and the southern branch tends toward north africa the antarctic oscillation is shown to influence whether the subvortex region is isolated from midlatitudes

the legacy of crystal plastic deformation in olivine high diffusivity pathways during serpentinization crystal plastic olivine deformation to produce subgrain boundaries composed of edge dislocations is an inevitable consequence of asthenospheric mantle flow although crystal plastic deformation and serpentinization are spatio temporally decoupled we identified compositional readjustments expressed on the micrometric level as a striped fe enriched bar x text fe 0 24 0 02 zones 0 12 0 02 bulk or fe depleted bar x text fe 0 10 0 01 zones 0 13 0 01 bulk zoning in partly serpentinized olivine grains from two upper mantle sections in norway focused ion beam sample preparation combined with transmission electron microscopy tem and aberration corrected scanning tem enabling atomic level resolved electron energy loss spectroscopic line profiling reveals that every zone is immediately associated with a subgrain boundary we infer that the zonings are a result of the environmental fe2 mg 1 exchange potential during antigorite serpentinization of olivine and the drive toward element exchange equilibrium this is facilitated by enhanced solid state diffusion along subgrain boundaries in a system which otherwise re equilibrates via dissolution reprecipitation fe enrichment or depletion is controlled by the silica activity imposed on the system by the local olivine orthopyroxene mass ratio temperature and the effect of magnetite stability the fe mg exchange coefficients k text d text atg text ol between both types of zoning and antigorite display coalescence toward exchange equilibrium with both types of zoning mn is enriched and ni depleted compared with the unaffected bulk composition nanometer sized heterogeneously distributed antigorite precipitates along olivine subgrain boundaries suggest that water was able to ingress along them crystallographic orientation relationships gained via electron backscatter diffraction between olivine grain domains and different serpentine vein generations support the hypothesis that serpentinization was initiated along olivine subgrain boundaries

classification of atmospheric river events on the u s west coast using a trajectory model author s ryoo jm waliser de waugh dw wong s fetzer ej fung i abstract 2015 american geophysical union all rights reserved we investigate transport pathways of water vapor associated with landfalling atmospheric river ar events that result in precipitation along the west coast of the u s for winters of 1997 2010 the water vapor transport pathways are determined by computing back trajectories with a trajectory model using the modern era retrospective analysis for research and applications reanalysis data set the majority of ar events 86 over the west coast of the u s are grouped into three trajectory types and two of them are closely associated with the ar events we designate the first type as ascending near landfall and of tropical origin at the second type as ascending near landfall and of extratropical origin ae and the third type as descending or parallel near landfall and of extratropical origin de which is accompanied but not directly associated with the ar events the magnitude and spatial distribution of precipitation of a given ar event are found to be strongly determined by the type of trajectories in general ar events composed of both at and ae trajectories have more frequent precipitation over a broad region of the western u s and ar events composed of both at and de trajectories have intense precipitation over the southwestern u s due to at trajectories ar events of at only trajectories have intense precipitation especially over the northwestern u s but are less frequent compared to those of at ae trajectories in addition different patterns of trajectory types among ar events are closely linked to upper level potential vorticity pv anomalies 66 of ar events are associated with anticyclonic rossby wave breaking events

long wavelength gravity anomalies over india crustal and lithospheric structures and its flexure abstract long wavelength gravity anomalies over india were obtained from terrestrial gravity data through two independent methods i wavelength filtering and ii removing crustal effects the gravity fields due to the lithospheric mantle obtained from two methods were quite comparable the long wavelength gravity anomalies were interpreted in terms of variations in the depth of the lithosphere asthenosphere boundary lab and the moho with appropriate densities that are constrained from seismic results at certain points modeling of the long wavelength gravity anomaly along a n s profile 77 e suggest that the thickness of the lithosphere for a density contrast of 0 05 g cm3 with the asthenosphere is maximum of 190 km along the himalayan front that reduces to 155 km under the southern part of the ganga and the vindhyan basins increasing to 175 km south of the satpura mobile belt reducing to 155 140 km under the eastern dharwar craton edc and from there consistently decreasing south wards to 120 km under the southernmost part of india known as southern granulite terrain sgt the crustal model clearly shows three distinct terrains of different bulk densities and thicknesses north of the smb under the ganga and the vindhyan basins and south of it the eastern dharwar craton edc and the southern granulite terrain sgt of bulk densities 2 87 2 90 and 2 96 g cm3 respectively it is confirmed from the exposed rock types as the sgt is composed of high bulk density lower crustal rocks and mafic ultramafic intrusives while the edc represent typical granite gneisses rocks and the basement under the vindhyan and ganga basins towards the north are composed of bundelkhand granite massif of the lower density the crustal thickness along this profile varies from 37 38 km under the edc increasing to 40 45 km under the sgt and 40 42 km under the northern part of the ganga basin with a bulge up to 36 km under its southern part reduced lithospheric and crustal thicknesses under the vindhyan and the ganga basins are attributed to the lithospheric flexure of the indian plate due to himalaya crustal bulge due to lithospheric flexure is well reflected in isostatic moho based on flexural model of average effective elastic thickness of 40 km lithospheric flexure causes high heat flow that is aided by large crustal scale fault system of mobile belts and their extensions northwards in this section which may be responsible for lower crustal bulk density in the northern part a low density and high thermal regime in north india north of the smb compared to south india however does not conform to the high s wave velocity in the northern part and thus it is attributed to changes in composition between the northern and the southern parts indicating a reworked lithosphere some of the long wavelength gravity anomalies along the east and the west coasts of india are attributed to the intrusives that caused the breakup of india from antarctica and africa madagascar and seychelles along the east and the west coasts of india respectively

extratropical forcing of tropical pacific convection during northern winter abstract statistical evidence is presented to support the notion that tropical convection in the eastern pacific and atlantic intertropical convergence zone itcz during northern winter can be forced by disturbances originating in the extratropics the synoptic scale transients in these regions are characterized at upper levels by strong positive tilts in the horizontal and appear to induce vertical motions ahead of troughs as in midlatitude baroclinic systems two case studies of such interactions are examined one for the eastern north pacific itcz and another somewhat different type of interaction for the south pacific convergence zone spcz over the western south pacific both cases are associated with upper level troughs strong cold advection deep into the tropics and the formation of a frontal boundary at low levels the itcz case is characterized by the advection of anomalously high isentropic potential vorticity air southward a strong poleward flux of heat and westerly momentum and the devel

observations of 2 4 day inertia gravity waves from the equatorial troposphere to the f region during the sudden stratospheric warming event of 2009 1 we have observed strong 2 4 day wave activity in the f region peak critical frequency fof2 at 7 5 n obtained from gps radio occultation measurements of the constellation observing system for meteorology ionosphere and climate cosmic satellites and the horizontal component of geomagnetic field variations over tirunelveli 8 7 n 77 8 e 1 75 n dip angle during the sudden stratospheric warming ssw event of 2009 a similar wave is observed strongly in the meridional winds observed by the mf radar at tirunelveli the meridional winds at 9 n and the equator obtained from era interim which is the latest global atmospheric reanalysis produced by the european centre for medium range weather forecasts shows clearly the 2 4 day wave propagating eastward with zonal wave number 6 over the central and eastern pacific both before and during the ssw event and over the indian sector during the ssw event only the potential vorticity pv intrusion at 200 hpa to lower latitudes is near the central pacific before the onset of the ssw event however during the ssw event the pv intrusion is observed more strongly near the indian sector in addition to the weaker intrusion near the central pacific it clearly indicates the rossby wave propagation to equatorial latitudes in the form of pv intrusion and it selectively enhances the periodicities generated owing to equatorial convective heating these waves could propagate to upper heights and cause variations in the mesosphere thermosphere ionosphere system

chemical discontinuity at the extratropical tropopause and isentropic stratosphere troposphere exchange pathways diagnosed using aura mls data 1 the chemical discontinuity at the extratropical tropopause extp and stratosphere troposphere exchange ste pathways are investigated using the long lived chemical species carbon monoxide co and ozone o3 measured by the aura microwave limb sounder mls a relative coordinate tropopause latitude tplat is developed based on potential vorticity pv from the goddard earth observing system version 5 geos 5 data assimilation system tplat is defined as the shortest geographic distance along an isentropic surface from the extratropical tropopause extp to an observation location our results show that this coordinate highlights the sharp chemical discontinuities at the extp more clearly than the widely used equivalent latitude coordinate geographical distributions of ste pathways and barriers are investigated based on meridional gradients in o3 abundances in the new tplat coordinate in conjunction with analysis of rossby wave breaking between 330 k and 360 k in northern hemispheric nh winter dec jan feb nh ste pathways are seen mainly above the northeast pacific in nh summer jun jul aug the nh pathway covers all longitudes at 330 k however it is mainly located above asia at 340 k and above the atlantic and the north pacific at 350 k and 360 k in the southern hemisphere sh there is a weaker ste region above the eastern indian ocean and the southwestern pacific at and above 350 k in sh winter and a stronger ste region over the southeastern pacific at these levels during sh summer in addition this study shows nh pv gradients are slightly stronger near the extp in summer than in winter even though the subtropical jet is weaker and rossby wave breaking is stronger in summer than in winter

coesite in the straumen kyanite eclogite pod norway the occurrence of coesite in the straumen kyaniteeclogite pod in the western gneiss region wgr norway is described although the microtextures of coesite and of its partial or complete transformation into quartz are similar to those described at the first coesite occurrence in norway the grytting dolomite eclogite pod there are some significant differences at this second locality these include the host mineral of the sio2 inclusions being garnet instead of clinopyroxene and also occasionally kyanite an initial coesite eclogite sub facies paragenesis was followed by a quartz eclogite sub facies paragenesis which in addition to rutile and dolomite or calcite contains the highest number 7 of silicate phases known in any norwegian eclogite garnet clinopyroxene kyanite quartz phengite zoisite and clinoamphibole this second occurrence of definite coesite i consolidates the very high pressury estimates about 30 kbar minimum previously deduced for certain eclogite pods occurring in the wgr and ii justifies the recognition of the norwegian coesite eclogite province constituted of a nappe terrane of about 30 kbar parageneses now residing in the wgr

horizontal and vertical structure of cross equatorial wave propagation abstract observational evidence of interhemispheric wave propagation through the equatorial upper tropospheric mean westerlies in the eastern pacific ocean is found in nine years 1980 81 to 1988 89 of european centre for medium range weather forecasts analyses during boreal winter using time mean standard deviation and one point correlation fields of potential vorticity on isentropic surfaces ipv it is found that waves associated with local fluctuations with periods between 6 and 30 days propagate from the northern hemisphere extratropics cross the equator and continue into the southern hemisphere extratropics this result is in agreement with hypotheses that claim regions of time mean westerlies in the tropics act as ducts allowing extratropical rossby waves to propagate into and through the tropics horizontal structure of the waves appears to change little during the course of the interhemispheric propagation however in the lower troposphere where the mean zonal wind is easterly the lowe

synoptic scale rossby waves and the geographic distribution of lateral transport routes between the tropics and the extratropics in the lower stratosphere atmospheric transport between the tropics and the extratropics in the lowest part of the stratosphere during northern hemisphere winter is investigated the role of synoptic scale disturbances that propagate laterally into the tropics is examined using the middle atmosphere version of the national center for atmospheric research community climate model version 3 general circulation model in the lower stratosphere synoptic scale rossby waves propagate vigorously from the northern i e winter extratropics through two westerly ducts where the westerly zonal mean winds near the equator are favorable to rossby wave propagation the waves break in the westerly ducts and modify the mean potential vorticity pv structure to connect subtropical and equatorial regions of sharp pv gradients frequent wave breaking and the wave induced pv structure create distinct routes where transport occurs vigorously between the tropics and the northern extratropics interhemispheric transport also occurs through regions associated with the westerly ducts in the southern summer hemisphere lower stratosphere synoptic scale disturbances propagate mainly as tongues of pv elongated from extratropical disturbances the transport between the tropics and the southern extratropics has a strong geographic preference but is dominated by the monsoon circulation as was shown for the upper troposphere by chen 1995 pv tongues and other transient anomalies are of secondary importance

40 ar 39 ar mineral age record of early caledonian tectonothermal activity in the baltoscandian miogeocline central scandinavia in central portions of the scandinavian caledonides greenschist facies volcanosedimentary successions within the koeli nappe complex have been thrust several hundred kilometers eastward onto the baltoscandian platform these were derived from eugeoclinal terranes situated outboard west of the baltica continent during the early paleozoic the koeli nappe complex is tectonically underlain by higher grade units within the seve nappe complex these are composed of amphibolite and granulite facies rocks and locally contain eclogites the seve nappes tectonically separate koeli units from structurally lower allochthons derived from more inboard environments along the baltoscandian miogeocline previous mineral isotopic age determinations from seve and koeli units have been in the 430 to 390 ma range and have been interpreted to presumably date cooling following scandian middle silurian to early devonian metamorphism however incremental release sup 40 ar sup 39 ar dates recorded by minerals within some of the koeli and seve nappes exposed in jaemtland sweden taennforsen and are districts provide evidence of earlier tectonothermal activity hornblendes from the seve and koeli nappe complexes display variably discordant age spectra as a result of low temperature experimental evolution of loosely bound extraneous argon components however in most analyses plateau ages of 510 to 475 ma koeli and 465 to 455more ma seve are defined in contrast muscovite and biotite from all tectonic units record scandian cooling ages between 245 and 410 ma the older events recorded by hornblende within these seve and koeli units are evidence of early caledonian tectonothermal activity and subsequent diachronous cooling during the early middle ordovician less

attribution and its application to mesoscale structure associated with tropopause folds it is important in meteorology to be able to establish a link between various features this link in its strongest form would be referred to as cause and effect but this is extremely difficult to establish for atmospheric flows a weaker but nonetheless powerful link is attribution which attempts to provide a way to associate various fundamental features such as potential vorticity anomalies to weather events involving regions of ascent attribution is not new and it is implicit in the way that atmospheric evolution is usually described in this paper an attempt is made to define more precisely what are the steps and assumptions being made in such a method these ideas become more concrete by applying them to a simple model of a two dimensional front at which there is a tropopause fold the aim is to find the vertical motion attributable to the descended tropopause fold in an extra tropical cyclone this is the first step in a longer programme of research designed to provide a test of the hypothesis that such a descended tropopause can trigger mesoscale phenomena such as convection and cyclones

wave breaking and mixing at the subtropical tropopause abstract this paper discusses rossby wave breaking on the isentropic surfaces that intersect the subtropical tropopause using winds and isentropic potential vorticity from high resolution meteorological analysis the focus is both on particular aspects of individual wave breaking events as well as on more general aspects such as the spatial and temporal distribution of the mixing associated with these events the direction and intensity of wave breaking is shown to exhibit the same dependence on stagnation points in the wind field as that seen in previous highly idealized numerical model studies wave breaking that results in stratospheric intrusions into the troposphere can be categorized as weak or strong depending on the development of filaments or larger coherent vortices or cutoff lows the events presented show a deep vertical structure that approximately spans the region between the 330 k and 370 k isentropic surfaces where the tropopause is steeply sloping through the subtropical jets this i