the poleward motion of extratropical cyclones from a potential vorticity tendency analysis abstractthe poleward propagation of midlatitude storms is studied using a potential vorticity pv tendency analysis of cyclone tracking composites in an idealized zonally symmetric moist gcm a detailed pv budget reveals the important role of the upper level pv and diabatic heating associated with latent heat release during the growth stage the classic picture of baroclinic instability emerges with an upper level pv to the west of a low level pv associated with the cyclone this configuration not only promotes intensification but also a poleward tendency that results from the nonlinear advection of the low level anomaly by the upper level pv the separate contributions of the upper and lower level pv as well as the surface temperature anomaly are analyzed using a piecewise pv inversion which shows the importance of the upper level pv anomaly in advecting the cyclone poleward the pv analysis also emphasizes the crucial role played by latent heat release in the poleward motion of the cyclone the l

provenance of lower cretaceous wolong volcaniclastics in the tibetan tethyan himalaya implications for the final breakup of eastern gondwana abstract lower cretaceous volcanic lithic arenites widely distributed in the tethyan himalaya provide insights into the continental breakup of eastern gondwana in southern tibet they are represented by the wolong volcaniclastics the volcanic rocks that contributed clastic material to the lower parts of this unit were predominantly alkali basalts whereas rhyolitic dacitic volcanism becomes the predominant source of the upper strata geochemical analyses of basaltic grains and of detrital cr spinels from the wolong volcaniclastics demonstrate the alkaline character of the volcanism and suggest within plate tectonic setting for the volcanism zircon u pb ages confirm that this volcanism continued from 140 ma to 119 ma hf isotope data on these early cretaceous zircons indicate that their parental magmas were mantle derived but in the later stage of magmatic activity mantle derived magmas were mixed with partial melts derived from the continental crust the lower cretaceous volcaniclastics occur along a broad belt paralleling the northern margin of greater india the onset of volcaniclastic deposition in the himalayas appears to become progressively younger toward the west but it ended synchronously during the late albian 102 ma the low volume of volcanic rocks and their intra plate tectonic setting suggest that they are the result of decompressional melting along extensional deep seated fractures cross cutting the continental crust and reflect changes in regional intra plate tectonic stresses when greater india began to separate from the australia antarctica supercontinent

ultrahigh temperature metamorphism followed by two stage decompression of garnet orthopyroxene sillimanite granulites from ganguvarpatti madurai block southern india the mg al granulites from ganguvarpatti consist of orthopyroxene sillimanite garnet quartz as peak assemblage with a few porphyroblasts of cordierite and sapphirine these assemblages were strongly overprinted by late symplectites and coronas orthopyroxene inclusions in garnet and porphyroblast cores have the highest xmg 0 80 and al2o3 content 10 7 wt the estimated near peak metamorphic conditions 1 000 50 c and 11 kbar using garnet orthopyroxene geothermobarometry are consistent with those determined using a petrogenetic grid the proposed multi stage evolution process implies an initial decompression deduced from multi phase symplectites followed by cooling during biotite formation further late decompression is explained from the orthopyroxene rims on biotite this proposed p t path thus suggests a unique and complex evolution history for the uht granulites of southern india present results are comparable with similar adjacent terranes in the gondwana supercontinent but the lack of structural and geochronological data makes a link with any major metamorphic event uncertain

the integrated effect of condensation in numerical simulations of extratropical cyclogenesis abstract by combining traditional sensitivity studies with techniques that focus on the conservation and invertibility properties of ertel s potential vorticity pv we illustrate the effect of latent heating on the structure and evolution of three simulated extratropical cyclones the cases include one continental cyclone development 15 december 1987 which we examine extensively and two cyclones over the western atlantic ocean 6 january 1983 and 5 january 1985 of somewhat greater intensity which are diagnosed to assess the generality of our findings for the continental case each storm featured a weaker cyclonic low level circulation when latent heating was removed from the simulation but the magnitude of the effect varied greatly in all cases the difference in intensity was attributed to velocities associated with a positive condensation produced pv anomaly above the warm front the amplification of the surface thermal perturbations was not strongly altered in even the case most affected by

the link between rossby wave breakings and weather regime transitions abstractthe link between rossby wave breaking rwb and the four wintertime weather regimes over the north atlantic domain is studied in this paper using the 40 yr ecmwf re analysis era 40 data frequencies of occurrence of anticyclonic and cyclonic wave breaking awb and cwb respectively events are computed each weather regime has its own characteristic pattern of rwb frequencies cwb events are found to be most frequent for the greenland anticyclone weather regime whereas awb events occur more for the atlantic ridge and the zonal regimes time lagged composites show that the rwb events characterizing each weather regime occur more often during the formation of the regime rather than during its decay this suggests a reinforcement of the weather regime by rwb an exception is the blocking weather regime which is destroyed by an increase of cwb events south of greenland weather regime transitions are then studied using the low frequency streamfunction tendency budget two types of precursors for th

crustal evolution in south india constraints from nd isotopes nd isotope analyses from a range of lithologies including charnockites metasediments and granitoids that comprise the high grade terrain of south india define contrasting age provinces north of the palghat cauvery shear zone the karnataka craton and the granulite blocks of nilgiri and madras are characterized by model nd ages from 3 4 to 2 4 ga with significant crustal growth during the late archean south of the palghat cauvery shear zone a pan african granulite facies event resulted in sm nd fractionation as observed in several incipient charnockite localities model nd age calculations that allow for sm nd fractionation at 550 ma yield ages in the range of 2 9 to 1 3 ga this range compares closely with published model nd ages from the high grade terrain of sri lanka mid proterozoic crustal growth 1 1 ga observed in the vijayan complex of sri lanka may have provided source material for metasediments characterized by young model nd ages in southern peninsular india the palghat cauvery shear z

ultrahigh temperature metamorphism in madurai granulites southern india evidence from carbon isotope thermometry abstract ultrahigh temperature uht metamorphism in the madurai block of the southern indian granulite terrain has been verified using the calcite graphite isotope exchange thermometer carbon isotope thermometry has been applied to marbles from a locality near the reported occurrence of sapphirine granulites that have yielded temperature estimates of around 1000 c the 13c and 18o values of calcite are homogenous implying equilibration of the isotopes during metamorphism however the 13c values of single graphite crystals show variations in the order of 1 within a hand specimen detailed isotopic zonation studies indicate that graphite preserves either the time integrated crystal growth history or reequilibrium fractionation during its cooling history the graphite cores preserve higher 13c values than the rims the fractionation between calcite and graphite cores gives the highest metamorphic temperature of about 1060 c which matches the petrologically inferred temperature estimates in the high

subsidence history of the tethys himalaya abstract this article reconstructs the evolution of the passive northern margin of peninsular india facing the neotethys from the earliest rifting stages in the carboniferous to final collision with the active southern margin of asia in the early eocene classical techniques of basin analysis were applied to an extensive and coherent stratigraphic data base facies analysis biostratigraphic dating and palaeoenvironmental interpretation of an over 10 km thick sedimentary succession from eight main composite sections allowed us to draw accurate sedimentation and backstripped subsidence curves and to place quantitative constraints on the palaeotectonic scenario inferred from the sedimentary record in each of the investigated composite sections three major stratigraphic gaps are consistently recognised in the rift sequence the rift unconformity mississippian the carboniferous permian hiatus largely kasimovian to asselian and the break up unconformity mid sakmarian two or even all three gaps may merge into a single hiatus spanning up to 70 ma overall gaps are associated with rift shoulder uplift which after calculation of backstripped subsidence sums up to 600 m at least in three of the investigated sections thermal subsidence and low sedimentation rates are documented by the mid permian to middle triassic drift sequence deposited while the neotethys was expanding between northern gondwana and the detached peri gondwanan blocks a marked increase in accumulation rates is recorded in the carnian norian but calculations of uniform lithospheric stretching suggest that extension was minor and associated with tectonic processes affecting distant parts of gondwana the tethys himalayan margin was uplifted around the jurassic cretaceous boundary at the onset of a major volcanic episode finally uplift exceeding in magnitude all previous events is documented by the uppermost units of the stratigraphic column deposited during the earliest stages of collision between india and asia in the latest paleocene to early eocene

early cretaceous volcaniclastic and quartzose sandstones from north central nepal composition sedimentology and geotectonic significance early cretaceous sandstones and shales from the thakkhola region chukh and tangbe formations were deposited on the subsiding northern tethyan margin of gondwana current directions indicate a source area to the south whereas the berriasian chukh formation is dominated by quartz arenites volcaniclastic sandstones and minor conglomerates dominate the tangbe formation of valanginian to aptian age upsection the composition of the volcaniclastic components changes from mainly basaltic to dominantly dacitic rhyolitic magmatism was preceded and accompanied by strong uplift in the source area of the chukh and tangbe clastics resulting in the erosion of probably more than several hundred meters of pre cretaceous sedimentary metamorphic and plutonic rocks a geochemical whole rock analysis of basaltic pebble fragments shows their alkaline character and suggests a within plate geotectonic setting for the volcanic source this volcanotectonic event is probably related to rifting between australia and greater india where seafloor spreading began in late valanginian hauterivian times

quantifying the climatological relationship between extratropical cyclone intensity and atmospheric precursors 1 we introduce a novel technique in which linear regression analysis is applied to clusters of tracked cyclones to statistically assess the factors controlling cyclone development we illustrate this technique by evaluating the differences between cyclones forming in the west and east north atlantic herein termed west and east atlantic cyclones enhanced cyclone intensity 2 days after genesis is found to be associated with deeper upper level troughs upstream of the cyclone center at the genesis time in both west and east atlantic cyclones however whilst west atlantic cyclones are also enhanced by the presence of strong fronts east atlantic cyclones are not instead east atlantic cyclones exhibit an enhancement when diabatically generated midlevel potential vorticity is present with the enhancement being of approximately equal magnitude to that associated with the potential vorticity in the upper level trough this is consistent with the paradigm of latent heat release in the warm conveyor belt region playing an important role in the development of east atlantic cyclones

north atlantic blocking during january 1979 linear theory the second half of january 1979 was a time of persistent and large scale blocking in the north atlantic region in this study we examine the instability properties of the flow during this period and relate the growing modes to the development that occurs we have analysed the growth rates phase frequencies and structures of the ten fastest growing modes within a five level quasi geostrophic model incorporating spherical geometry on each day for the period between 10 and 30 january 1979 large scale equivalent barotropic dipole or multipole instability modes are prevalent in the north atlantic during the second half of january these modes are stationary or slowly propagating and grow rapidly with efolding times as short as 1 7 days in some cases we find that there is a close connection between these modes and the dynamical developments observed subsequently a few days later associated with the early stages of block formation there are large scale eastward propagating westward tilting onset of blocking wave train modes the onset of blocking modes also appear to be associated with rapid cyclogenesis off the east coast of north america the formation of the north atlantic blocking system and diffluent flow also produces corresponding changes in the storm tracks during the early parts of this period the fastest growing monopole cyciogenesis instability modes have regions of preferential development in the climatological storm tracks over the pacific atlantic and siberian regions subsequently however the atlantic cyclogenesis modes split into wave trains poleward and equatorward of the block in the developments during this period we also examine the roles of the adjoint eigenmodes and of optimal perturbations which produce the largest initial tendency of the l2 norm squared of the streamfunction

the relationship between a zonal index and blocking activity abstract the degree to which northern hemisphere blocking activity is controlled by variations in zonal mean conditions is investigated a set of northern hemisphere winter season 500 hpa analyzed fields is examined for blocks using an objective index defined solely from the eddy fields with this blocking index it is shown that in most regions enhanced blocking activity is associated with relatively strong zonally averaged winds around 30 n and weak winds around 50 60 n also the preferred zonal positions of blocks are related to the state of the zonal mean flow a similar analysis is carried out using data from a perpetual january gcm simulation and the same relationship between blocking activity and zonally averaged conditions is found to be valid to an even stronger degree for these data to investigate whether anomalous zonal mean flows are actually controlling the associated level of blocking activity two experiments with the gcm are performed in one experiment the zonal mean state of the gcm i

the tethys himalayan passive margin from late triassic to early cretaceous south tibet the mesozoic succession of south tibet both in lithologies and stratigraphic thicknesses compares much more closely with that of central nepal than has been reported in the literature facies distribution from relatively proximal environments in the south to more distal settings in the north reflects the paleogeography of the tethys himalaya passive margin representing the southern edge of neotethys as in central nepal and nw himalaya accumulation rates increased greatly in the latest triassic when very thick shelfal siliciclastics and locally volcaniclastics tarap formation were followed by coastal sandstones zhamure formation contrary to reports in the literature this latter unit reaches well into the liassic at least in proximal southern sectors the base of the overlying kioto group yielding rich faunal associations characterized by benthic foraminifers and lithiotis similar to those of western tethys carbonate platforms is dated as middle liassic most probably late pliensbachian the monotonous growth of carbonate ramps during the middle liassic to early dogger was interrupted by two siliciclastic episodes related to major paleogeographic changes in the toarcian middle part of the kioto group and in the bajocian bathonian laptal formation an early callovian flooding event ferruginous oolite formation widespread all along the tethys himalaya was locally followed by deposition of a markedly lenticular pelagic unit previously reported only from the thakkhola graben dangar formation the overlying spiti shale is reduced to only 20 m in southern sectors where it is not younger than the oxfordian whereas in northern sectors the unit is several tens of m thick and mainly ascribed to the tithonian volcaniclastic deposition wolong formation reported herein for the first time probably began as early as the kimmeridgian early tithonian and lasted until aptian times when it was replaced by sedimentation of relatively deep water marlstones this magmatic episode related to tectonic extension associated with the detachment of india from gondwanaland took place earlier in south tibet and progressively later in central nepal and northern india as in nepal volcanic products changed with time from predominantly basaltic composition to intermediate and bimodal character the early cretaceous sedimentary evolution of south tibet matches that of offshore nw australia

paleocene eocene foreland basin evolution in the himalaya of southern tibet and nepal implications for the age of initial india asia collision siliciclastic sedimentary rocks derived from the southern lhasa terrane sitting depositionally upon rocks of the northern indian passive continental margin provide an estimate of the age of initial contact between the continental parts of the indian and asian plates we report sedimentological sedimentary petrological and geochronological data from upper cretaceous paleocene strata in the sangdanlin section located along the southern flank of the indus yarlung suture zone in southern tibet this is probably the most proximal and therefore the oldest record of the india asia collision these strata were deposited by high density turbidity currents or concentrated density flows and suspension settling of pelagic biogenic debris in a deep marine setting an abrupt change from quartz arenitic to feldspatholithic sandstone compositions marks the transition from indian to asian sediment provenance the abrupt compositional change is accompanied by changes in u pb ages of detrital zircons diagnostic of a sediment provenance reversal from indian to asian sources the timing of the transition is bracketed between 60 ma and 58 5 0 6 ma by detrital zircon u pb ages and zircon u pb ages from a tuffaceous bed in the upper part of the section in the context of a palinspastically restored regional paleogeographic framework data from the sangdanlin section combined with previously published data from the northern tethyan himalaya and the frontal nepalese lesser himalaya and subhimalaya suggest that a flexural wave migrated 1300 km southward across what is now the himalayan thrust belt from paleocene time to the present

comparative diagnosis of blocking versus nonblocking planetary scale circulation changes during synoptic scale cyclogenesis abstract a 17 day period during november 1980 is investigated to obtain insight into differing large scale 500 mb circulation changes during three consecutive synoptic scale cyclone events each event is defined by at least one rapidly intensifying surface cyclone over eastern north america or the western atlantic ocean the first event is followed in time by the retrogression of a downstream split flow type of block at 500 mb the second event is characterized by the intensification of a large scale 500 mb trough into a blocking cyclonic vortex during the third event no blocking systems are established or intensified instead the blocking cyclonic vortex is ejected downstream quasi geostrophic model diagnosis reveals that during the first two blocking events the large scale waves are reinforced by relatively large and spatially and temporally persistent transports of potential vorticity associated with 500 mb synoptic scale waves linked with the surface cyclones in the third nonblocking event d

basaltic volcanism mantle plumes and the mechanics of rifting the parana flood basalt province of south america dynamic modeling of continental extension between south america and africa shows that the mechanics of rifting played an important role in determining the pattern of volcanism within the parana and etendeka flood basalt provinces on the brazilian and namibian margins the key feature of the model is the development of a horizontal pressure gradient in the lower crust during the early stages of extension which provided a mechanism for transporting magma generated beneath the incipient sea floor spreading axis into the parana province 100 200 km distant the horizontal pressure gradient developed as a consequence of the dynamic interaction of preexisting weaknesses in the middle crust and upper mantle during rifting the model accounts for the large quantity of basalt the asymmetric distribution of basalt on the conjugate margins and the northward migration of the eruptive center with time the rapidity of magma genesis is in agreement with models of decompression melting during rifting the model indicates that although elevated asthenosphere temperatures associated with the tristan plume account for the volume of melt generated the mechanics of rifting control the location and style of emplacement the model suggests that extension in the region began ca 150 155 ma and lasted about 25 m y

triassic to cenozoic evolution of the nw australian continental margin and the birth of the indian ocean preliminary results of odp legs 122 and 123 the northwest australian continental margin is a very old sediment starved ne gondwanan margin with the opportunity to study the early structural and depositional evolution during the triassic to jurassic rifting stages neo tethys the earliest cretaceous transition from rifting to drifting and the early tectonic volcanic and paleoceanographic history of the indian ocean ocean drilling program odp legs 122 and 123 drilled eight sites in the area of the exmouth plateau and the adjacent abyssal plains sites 759 761 and 764 studied the triassic to cenozoic evolution of wombat plateau a small sub plateau of the northern exmouth plateau sites 765 penetrated almost 1 km of cretaceous to cenozoic sediments of the nearby argo abyssal plain and 270 m of the oldest indian ocean crust sites 762 and 763 studied the southern central exmouth plateau whereas site 766 was drilled into intrusive volcanics with morb affinity under the adjacent gascoyne abyssal plain at the foot of the western escarpment of the plateau the major discoveries during the drilling of the two continental margin deep ocean basin transects led to a better understanding of the early rift history of this margin during late permian to late triassic times stretching block tectonic movements fluviodeltaic shallow water carbonate environments major rhaetian carbonate buildup early rift volcanism of the rift drift transition processes major blockfaulting during jurassic times with local uplift rift flank tilting and subaerial erosion forming a post rift unconformity of the age and paleoenvironment of the oldest part of the indian ocean possibly not earlier than late berriasian to early valanginian breakup 20 ma younger than expected of the juvenile ocean stage transgressive condensed early neocomian belemnite sands calcisphere chalks and bentonites on wombat plateau of the mature ocean stage post mid cretaceous eupelagic chalks of the geochemical nature and origin of old oceanic crust and the overlying sediments in a geochemical reference hole and of the mesosoic chrono bio magneto stratigraphy and the age and causes of major relative sea level fluctuations especially during late triassic and early cretaceous times

pre breakup continental extension in east gondwanaland and the early opening of the eastern indian ocean abstract extension of continental crust by up to 360 km on a north northeast azimuth in the great australian bight occurred prior to the middle cretaceous 96 ma onset of seafloor spreading between australia and antarctica this large amount of continental extension is constrained to the late jurassic 160 ma middle cretaceous interval about a pole estimated to lie about 40 southeastward of southeastern australia using bathymetric data combined with seismic and magnetic determinations of the continent ocean boundaries off australia india and antarctica we determine a revised fit of east gondwanaland prior to continental extension and at various stages thereafter in the first stage from 160 to 132 5 ma m11 india australia rotated from antarctica with continental crustal extension between australia and antarctica and largely transform motion between the coromandel coast margin of india and the kron prins olav kyst margin of antarctica in the second stage from 132 5 to 96 ma india rotated northwestward away from australia antarctica producing m10 and younger magnetic anomalies along the western margin of australia continental extension was greatest between australia and antarctica during this stage the newly determined 132 5 96 ma rotation between india and australia provides an improved fit between the orientation of observed m10 m0 magnetic anomalies and the southward decrease in spreading rate off the western australian margin together with bathymetry the new rotation parameters lead to identification of the abandoned 96 ma spreading ridge along the lost dutchmen and dirck hartog ridges the naturaliste fracture zone is found to lie nearly parallel to the early cretaceous transform direction between india and antarctica suggesting that slow seafloor spreading required between australia and antarctica to accommodate the continental extension further east occurred between naturaliste fracture zone and the m4 m0 anomalies adjacent to the naturaliste plateau the revised fit of india in east gondwanaland reduces the eastward extent of greater india to 95 e but does not change its extent as far north as the cape range fracture zone the new pole determined for the early cretaceous rotation between india and australia antarctica lies within 15 of the southern tip of india significantly closer than in previous determinations thereby reducing the amount of seafloor spreading generated between africa and antarctica by the india antarctica rotation and thus offering a possible solution to the perceived spreading rate problems between m11 and m0 in the somali mozambique and antarctic basins

the dynamical link between surface cyclones upper tropospheric rossby wave breaking and the life cycle of the scandinavian blocking 1 the scandinavian blocking sb is a well known quasi stationary state of the atmospheric flow and one of the four main weather regimes over the euro atlantic domain in winter the aim of our study is to analyze the link between surface cyclones upper tropospheric rossby wave breakings and the life cycle of sb using era 40 reanalysis the onset and decay of sb are studied by considering the preferential transitions from the zonal regime to sb and from sb to the greenland anticyclone regime during the sb onset atlantic cyclones have straight trajectories that extend toward the north of scandinavia these surface cyclones are associated with anticyclonic wave breakings in the upper troposphere over europe during the sb decay cyclones are much less present in the eastern part of the atlantic and most of them present curved trajectories in mid atlantic they are shown to be linked to cyclonic wave breakings to the south of greenland

quaternary extension in southern tibet field observations and tectonic implications we summarize evidence for quaternary and active faulting collected in the field during three sino french expeditions to southeastern tibet 1980 1982 detailed mapping of quaternary and active faults as well as microtectonic measurements indicate that normal faulting has been the dominant tectonic regime north of the himalayas in the last 2 0 5 m y the maximum horizontal principal stress in south tibet appears to be only the intermediate principal stress 2 1 being vertical south of the chord joining the eastern and western syntaxes of the himalayan arc extensional strains are principally localized within seven regularly spaced rift zones three of which have been studied in some detail the extension direction is determined to be n96 e 7 mainly from statistical averaging of strikes of newly formed normal faults throw rates on normal faults are evaluated for different time spans 2 0 5 m y 60 40 kyr and 10 2 kyr b p using structural and topographic reliefs as well as synglacial and postglacial vertical offsets the rate of quaternary extension is about 1 m y 1 along an 1100 km long ese traverse across south tibet this corresponds to a spreading rate of 1 0 6 cm yr this rate and the divergent horizontal projections of slip vectors of earthquakes along the himalayan front constrain the rate at which rigid india underthrusts southern tibet to be 2 1 cm yr although most of the normal faults appear to be independent of and nearly orthogonal to the e w mesozoic tertiary tectonic fabric the yadong gulu rift appears to be guided for over 130 km by the older oblique ne sw nyainqentanglha range and fault zones along it this reactivated zone is the most prominent left lateral strike slip fault system in se tibet excepting this zone and the vicinity of the se extremity of the karakorum fault quaternary strike slip faulting is rare in south tibet i e south of the chord between the syntaxes of the himalayan arc north of the chord the tectonic style is different there minor conjugate strike slip faulting is widespread and appears to control quaternary normal faulting which is more diffuse and subdued than in south tibet along the chord the presence of a major zone of active right lateral en echelon strike slip faults karakorum jiali fault zone probably reflects the greater facility of eastward extrusion in north central tibet in response to the northward push of india the eastern himalayan syntaxis may be an obstacle to such extrusion movements south of the chord

a multiscale analysis of the extreme weather events over western russia and northern pakistan during july 2010 abstractthis manuscript presents a detailed multiscale analysis using observations model analyses and ensemble forecasts of the extreme heat wave over russia and historic floods over pakistan during late july 2010 with an emphasis on the floods over northern pakistan the results show that recirculation of air and dynamically driven subsidence occurring with the intensification of the blocking anticyclone in late july 2010 were key factors for producing the exceptionally warm temperatures over western russia downstream energy dispersion from the blocking region led to trough deepening northwest of pakistan and ridge building over the tibetan plateau thereby providing the linkage between the russian heat wave and pakistan flood events on the large scale in agreement with previous studies the extratropical downstream energy dispersion and enhanced convective outflow on the large scale associated with the active phase of the madden julian oscillation facilitated the formation of an intense upper level

transient eddy forcing of blocking flows abstract the net forcing of blocking flows by transient eddies having synoptic time scales is examined within the framework of quasi geostrophic theory temporal filtering is used to distinguish the effects of transients having synoptic lime scales i e periods less than approximately seven days from those having longer time scales convergences of transient eddy transports of heat and vorticity during blocking conditions are computed from highpass filtered time series the eddy flux convergences for individual blocking events are then composited according to the locations of the blocks the quasi geostrophic potential vorticity equation relating geopotential tendency and the eddy flux convergences of heat and vorticity is solved for composite blocking conditions the diagnosis is performed for both observed blocks and blocks simulated by a general circulation model the net quasi geostrophic geopotential tendencies due to transports by the synoptic scale transient eddies exhibit a quadrature relations

early cretaceous strata of the nepal himalayas conjugate margins and rift volcanism during gondwanan breakup early cretaceous sandstones shales and marlstones chukh tangbe and muding formations at least 625 m thick crop out north of the main central thrust in central nepal they were strongly deformed during himalayan collision with telescoping of facies transitions as a result of crustal shortening the sediments show northerly palaeoflow and were deposited on the steadily subsiding northern tethyan margin of gondwana berriasian deltaic deposits pass upward into valanginian albian storm dominated shelf deposits and into latest albian pelagic slope carbonates an unconformity probably of valanginian age separates the chukh and tangbe formations locally and is overlain by volcanic conglomerates the gondwanan margin succession matches well with that observed on the formerly conjugate margin of nw australia which separated from greater india during the valanginian to hauterivian volcanic detritus where suitable for analysis shows within plate geochemical affinity and reflects gondwanan fragmentation abundant volcanic detritus in aptian strata may have been derived from extensions of the rajmahal traps of northeast india however volcanism was active near central nepal in the valanginian and volcanic detritus possibly far travelled reached the area during the berriasian early cretaceous strata1 successions and relative sea level changes show a first order relationship to tectonism associated with gondwanan break up

the role of high and low frequency dynamics in blocking formation time evolutions of prominent blocking flow configurations over the north pacific and europe are compared based upon composites for the 30 strongest events observed during 27 recent winter seasons fluctuations associated with synoptic scale migratory eddies have been filtered out before the compositing a quasi stationary wave train across the atlantic is evident during the blocking amplification over europe while no counterpart is found to the west of the amplifying blocking over the north pacific correlation between the tropopause level potential vorticity pv and meridional wind velocity associated with the amplifying blocking is found to be negative over europe in association with the anticyclonic evolution of the low pv center but it is almost zero over the north pacific feedback from the synoptic scale eddies as evaluated in the form of 250 mb geopotential height tendency due to the eddy vorticity flux convergence accounts for more than 75 of the observed amplification for the pacific blocking and less than 45 for the european blocking this difference is highlighted in two types of contour advection with surgery experiments in one of them pv contours observed four days before the peak blocking time were advected by composite time series of the low pass filtered observational wind and in the other experiment they were advected by the low pass filtered wind from which the transient eddy feedback evaluated as above had been removed at every time step hence the latter data should be dominated by low frequency dynamics for the european blocking both experiments can reproduce the anticyclonic evolution of low pv air within a blocking ridge as observed for the pacific blocking in contrast the observed intrusion of low pv air into the higher latitudes cannot be reproduced without the transient feedback furthermore in a barotropic model initialized with the composite 250 mb flow observed three days before the peak time a simulated blocking development over the north pacific is more sensitive to the insertion of the observed transient feedback than that over europe these results suggest that the incoming wave activity flux associated with a quasi stationary rossby wave train is of primary importance in the blocking formation over europe whereas the forcing by the synoptic scale transients is indispensable to that over the north pacific

synoptic behavior of baroclinic eddies during the blocking onset abstract synoptic behavior of individual baroclinic eddies in the course of their interactions with amplifying blocking anticyclones is examined based upon a 30 year record of the tropospheric circulation in the northern hemisphere winter high pass filtered as well as unfiltered fields of geopotential height and potential vorticity were composited relative to the onset of the five different types of blocking patterns before the compositing the entire sequence of the fields was slightly shifted in time and space in such a way that the strongest baroclinic eddy during the onset of each blocking event occupies a prescribed position in the upstream storm track when it reaches its maximum intensity since this shifting considerably reduces the cancellation between the individual high frequency migratory eddies this type of compositing can present a more synoptically oriented view of those interactions than conventional compositing in our composite results one or two pairs of cyclonic and anticyclonic

silica undersaturated sapphirine spinel and kornerupine granulite facies rocks ne strangways range central australia small pods of silica undersaturated al rich and mg rich granulite facies rocks containing sapphirine pleonastic spinel kornerupine cordierite orthopyroxene corundum sillimanite and gedrite are scattered throughout the ne strangways range central australia these are divided into four distinct rock types namely orthopyroxene rich aluminous granofels and metapelitic gneisses containing sapphirine spinel or kornerupine two granulite facies metamorphic events are recognized of which only the first m1 is considered in this paper peak metamorphic mineral parageneses indicate that the m1 thermal maximum occurred at approximately 900 950 c and 8 9 kbar all samples are characterized by profuse and diverse coronitic and symplectic reaction textures these are interpreted as evidence for the sequential crossing of the following reactions in the system fmas cordierite spinel corundum sapphirine sillimanite cordierite spinel orthopyroxene sapphirine sillimanite sapphirine spinel sillimanite orthopyroxene corundum sapphirine sillimanite cordierite orthopyroxene corundum phase stability relationships in fmas and mash indicate an anticlockwise p t path terminated by isobaric cooling such a path is exemplified by early low p mineral parageneses containing spinel corundum and gedrite and the occurrence of both prograde and retrograde corundum reaction textures preserve evidence for an increase in ah2o and ab2o3 with progressive isobaric cooling this hydrous retrogression resulted from crystallization of intimately associated m1 partial melt segregations there is no evidence for voluminous magmatic accretion giving rise to the high m1 thermal gradient the m1 p t path may be the result of either lithospheric thinning after both crustal thickening and burial of the supracrustal terrane or concomitant crustal thickening and mantle lithosphere thinning

alleviation of a systematic westerly bias in general circulation and numerical weather prediction models through an orographic gravity wave drag parametrization systematic westerly biases in the northern hemisphere wintertime flow of the meteorological office 15 layer operational model and 11 layer general circulation model are described evidence that the failure to parametrize subgrid scale orographic gravity wave drag may account for such biases is presented this evidence is taken from aircraft studies surface pressure drag measurements and studies of the zonally averaged momentum budget a parametrization scheme is described in which the surface stress is proportional to the near surface wind speed and static stability and to the variance of subgrid scale orography the stress is absorbed in the vertical by considering the influence of such gravity wave activity on static stability and vertical wind shear a richardson number dependent wave breaking formulation is devised and the vertical stress profile determined by a saturation hypothesis whereby the breaking waves are maintained at marginal stability it is shown that wave breaking preferentially occurs in the boundary layer and in the lower stratosphere results from a simple zonally symmetric model show how the adjustment to thermal wind balance with a wave drag in the stratosphere warms polar regions by adiabatic descent and decelerates the mean westerlies in the troposphere the influence of the parametrization scheme on integrations of the 11 layer model is described and found to be generally beneficial in a discussion of the reasons why this problem has only recently emerged it is suggested that the satisfactory northern hemisphere winter circulations of previous coarser general circulation models were due to a compensation implied by underestimating both the surface drag and the horizontal flux of momentum by explicitly resolved large scale eddies

planetary scale climatology of explosive cyclogenesis and blocking abstract a climatology of the relationship between explosive cyclogenesis and atmospheric blocking has been constructed from an investigation of sea level pressure and 500 mb height analyses over the northern hemisphere during seven winter seasons planetary scale 500 mb geostrophic u and v wind components and component anomalies u and v were calculated over each explosive cyclone center and compared to the times and locations of block onsets blocking episodes were defined by the persistence for at least 5 days of negative zonal index 500 mb height at 40 n less than that at 60 n spanning at least 18 75 of longitude thirty three percent 43 of the explosive cyclones that were not analyzed during blocking episodes over the atlantic pacific sector of the northern hemisphere and over which there were anomalously strong planetary scale southerly winds v 0 anomalously weak westerly winds u u 2 were followed in not more than 5 days and within 60 of longitude by the onset o

representation of the scandinavia greenland pattern and its relationship with the polar vortex in s2s forecast models the strength of the stratospheric polar vortex is a key contributor to subseasonal prediction during boreal winter anomalously weak polar vortex events can be induced by enhanced vertically propagating rossby waves from the troposphere driven by blocking and wave breaking here we analyse a tropospheric pattern the scandinavia greenland s g pattern associated with both processes the s g pattern is defined as the second empirical orthogonal function eof of mean sea level pressure in the northeast atlantic the first eof is a zonal pattern resembling the north atlantic oscillation we show that the s g pattern is associated with a transient amplification of planetary wavenumber2 and meridional eddy heat flux followed by the onset of a weakened polar vortex which persists for the next 2 months we then analyse 10 different models from the s2s database finding that while all models represent the structure of the s g pattern well some models have a zonal bias with more than the observed variability in their first eof and accordingly less in their second eof this bias is largest in models with the lowest resolution skill in predicting the s g pattern is not high beyond week 2 in any model in contrast to the zonal pattern we find that the relationship between the s g pattern and enhanced eddy heat flux and a weakened polar vortex is initially well represented but significantly decays with lead time in most s2s models our results motivate improved representation of the s g pattern and its stratospheric response at longer lead times for improved subseasonal prediction of the stratospheric polar vortex

the triassic of the thakkhola nepal i stratigraphy and paleoenvironment of a north east gondwanan rifted margin the mesozoic sediments of thakkhola central nepal were deposited on a broad eastern north gondwanan passive margin at mid latitudes 28 41 s facing the southern tethys ocean to the north the facies is strikingly similar over a distance of several thousand kilometres from ladakh in the west to tibet and to the paleogeographically adjacent north west australian margin exmouth plateau odp legs 122 123 and timor in the east late paleozoic rifting led to the opening of the neo tethys ocean in early triassic times an almost uninterrupted about 2 km thick sequence of syn rift sediments was deposited on a slowly subsiding shelf and slope from early triassic to late valanginian times when break up between gondwana north west australia and greater india formed the proto indian ocean

multicyclic history of the northern india continental margin northwestern himalaya 1 the geologic evolution of northern india is best recorded in the stratigraphic succession of the zanskar range northwestern himalaya which represents the most complete transect through this ancient continental margin sedimentary history began in the late proterozoic and recorded a late pan african orogenic event around the cambrian ordovician boundary when the gondwana supercontinent was eventually assembled the following long period of epicontinental deposition in shallow seas linked to palaeo tethys lasted until the early permian when a neo tethyan rift began to open between paleo india and the cimmerian microcontinents neo tethyan history can be subdivided into two sedimentary megasequences both recording a major tectonic and magmatic event in the lower part the first one began with breakup in the late permian and lasted until the end of the jurassic the second one started in the early cretaceous with the final detachment of india from gondwana and the opening of the indian ocean and ended with the india eurasia collision in the early eocene the two megasequences can be in turn subdivided into six transgressive regressive supersequences bounded by tectonically enhanced unconformities basal sandstone units of early permian late permian norian callovian early cretaceous and paleocene age are invariably associated with oolitic ironstones or reworked glauco phosphorites and mark the transgre sive part of each supersequence next condensed nodular carbonates or shales with pelagic fauna are typically overlain by thick shallowing upward marly units capped by regressive platformal carbonates the six tectono eustatic supercycles reflect successive rifting episodes which punctuated the progressive separation of india from the rest of gondwana and document the combination of plate microplate reorganizations and eustatic climatic and oceanographic changes in the tethyan domain after the onset of collision between india and asia close to the paleocene eocene boundary obduction of the remnants of the neo tethys ocean floor onto the indian margin began and the latter underwent multiphase deformation with fold thrust shortening followed by heating and extension after the main metamorphic event ophiolitic nappes were re thrusted and finally emplaced with their sedimentary sole on top of the passive margin succession

systematic model forecast error in rossby wave structure diabatic processes can alter rossby wave structure consequently errors arising from model processes propagate downstream however the chaotic spread of forecasts from initial condition uncertainty renders it difficult to trace back from root mean square forecast errors to model errors here diagnostics unaffected by phase errors are used enabling investigation of systematic errors in rossby waves in winter season forecasts from three operational centers tropopause sharpness adjacent to ridges decreases with forecast lead time it depends strongly on model resolution even though models are examined on a common grid rossby wave amplitude reduces with lead 5 days consistent with underrepresentation of diabatic modification and transport of air from the lower troposphere into upper tropospheric ridges and with too weak humidity gradients across the tropopause however amplitude also decreases when resolution is decreased further work is necessary to isolate the contribution from errors in the representation of diabatic processes

the key role of diabatic outflow in amplifying the midlatitude flow a representative case study of weather systems surrounding western north pacific extratropical transition abstractrecurving tropical cyclones tcs undergoing extratropical transition et may substantially modify the large scale midlatitude flow pattern this study highlights the role of diabatic outflow in midlatitude flow amplification within the context of a review of the physical and dynamical processes involved in et composite fields of 12 western north pacific et cases are used as initial and boundary conditions for high resolution numerical simulations of the north pacific north american sector with and without the tc present it is demonstrated that a three stage sequence of diabatic outflow associated with different weather systems is involved in triggering a highly amplified midlatitude flow pattern 1 preconditioning by a predecessor rain event pre 2 tc extratropical flow interaction and 3 downstream flow amplification by a downstream warm conveyor belt wcb an ensemble of perturbed simulations demonstrates the robustness of these stages beyond earlier studies investigating pres recurv

stratigraphy and sedimentary history of the nepal tethys himalaya passive margin abstract the sedimentary history of the nepal tethys himalaya began with deposition of thick carbonates in the cambro ordovician followed by a mixed siliciclastic carbonate epicontinental succession recording two major deepening events in the early silurian and late devonian fossiliferous carbonate ramp deposits in the tournaisian were disconformably followed by white quartzose sandstones and black mudrocks with locally intercalated diamictites derived from sedimentary rocks and deposited in asymmetric tectonic basins rift stage break up in the mid early permian locally associated with effusion of tholeiitic lava flows was followed by a transgressive sandy to shaly locally coal bearing or bioclastic unit capped by condensed pelagic carbonates in the middle to late permian juvenile ocean stage subsidence of the cooling stretched crust led close to bathyal water depths in the olenekian but then slowed down in the middle triassic to increase again sharply in the late triassic owing to renewed extensional tectonic activity and sediment loading during up and out building of the indian continental terrace deposition of tropical platform carbonates finally became widespread in the middle liassic mature passive margin stage the initial fragmentation of gondwana in the middle jurassic led to rejuvenation of the indian craton and deposition of quartzo feldspathic hybrid arenites capped by condensed oolitic ironstones deposited at warm subtropical latitudes in the late bathonian middle callovian next a discontinuous pelagic grey marly limestone unit was followed by the ammonoid rich offshore spiti shale in the late jurassic the final disintegration of gondwana began in the berriasian when quartzose siliciclastics derived again from the rejuvenated indian craton and partly from recycling of older clastic successions were followed by thick deltaic to shelf volcaniclastics documenting eruption of alkali basalts in the valanginian followed in the hauterivian to albian by more felsic differentiates such as the trachyandesites exposed in the lesser himalaya 120 km to the south a widespread drowning episode fostered by waning volcaniclastic supply during a global eustatic rise is documented by a major glauconitic horizon deposited at middle southern latitudes in the late albian overlain by scaglia like pelagic limestones in the latest albian the final part of sedimentary history during the rapid northward flight of india and its collision with eurasia is not documented anywhere in nepal due to later erosion of upper cretaceous to lower tertiary strata

precambrian tectonics and crustal evolution in south india about 3 4 ga ago voluminous calc alkaline magmas represented by the granitoid gneisses of southern india were emplaced into a now poorly preserved non continental crust unstable ensialic basins initiated at about 3 0 ga were filled with volcanic and sedimentary rocks up to about 2 6 ga this basement cover sequence was deformed at the close of the archaean first by northward accretion and thickening of several crustal slabs formerly separated by prisms of stable shelf sediments structures produced by this episode were refolded and dislocated by large n s strike slip shear belts to impart intense steep planar fabrics to large volumes of the crust fluids rich in co possibly derived from sedimentary material driven beneath the crustal slabs by the thickening mechanism purged the deep crust of h o to form granulites upward migration of hot h o rich fluids encouraged partial melting at intermediate crustal levels these late archaean tectonic and thermal events began soon after the close of basin f

multi model analysis of northern hemisphere winter blocking model biases and the role of resolution blocking of the tropospheric jet stream during northern hemisphere winter december january february is examined in a multi model ensemble of coupled atmosphere ocean general circulation models gcms obtained from the coupled model intercomparison project phase 5 cmip5 the cmip5 models exhibit large biases in blocking frequency and related biases in tropospheric jet latitude similar to earlier generations of gcms underestimated blocking at high latitudes especially over europe is common in general model biases decrease as model resolution increases increased blocking frequency at high latitudes in both the atlantic and pacific basins as well as more realistic variability of atlantic jet latitude are associated with increased vertical resolution in the mid troposphere to lowermost stratosphere finer horizontal resolution is associated with higher blocking frequency at all latitudes in the atlantic basin but appears to have no systematic impact on blocking near greenland or in the pacific basin results from the cmip5 analysis are corroborated by additional controlled experiments using selected gcms key pointscmip5 models have large blocking biases and associated jet biasesincreased spatial resolution is associated with reduced blocking and jet biasesvertical and horizontal resolution give blocking changes in different regions 2013 american geophysical union all rights reserved

p t grids for silica undersaturated granulites in the systems mas n 4 and fmas n 3 tools for the derivation of p t paths of metamorphism abstract considering the minerals cordierite cd sapphirine sa hypersthene hy garnet ga spinel sp sillimanite si and corundum co in the system feo mgo al2o3 sio2 fmas the stable invariant points are co ga cd and sa constraints imposed by experimental data for the system mas indicate that under low ph2o conditions the invariant points occur at high temperature 900 c and intermediate pressure 7 10 kbar this temperature is higher than that commonly advocated for granulite facies metamorphism in granulites fe mg exchange geothermometers may yield temperatures of 100 150 c below peak metamorphic conditions and evidence for peak temperatures is best preserved by relict high temperature assemblages and by al rich cores in orthopyroxene application of the fmas grid to some well documented granulite occurrences introduces important constraints on their p t histories rocks of different bulk compositions occurring in close proximity in the field may record distinct segments of their p t paths this applies particularly to rocks with evidence for reaction in the form of coronas symplectites and zoned minerals consideration of curved reaction boundaries and xms isopleths may explain apparently contradictory results for the stability of cordierite obtained from low temperature experiments and thermochemical calculations on the one hand and hightemperature experimental data on the other

chemical compositions and tectonic significance of chrome rich spinels in the tianba flysch southern tibet abstract turbiditic sandstones from the mid late cretaceous tianba flysch sequence are well exposed near tianba in the north nieru valley southern tibet and contain significant amounts of chrome rich spinels microprobe results show that the spinels have a well developed fe ti trend and have cr documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape mathrm cr mathrm al end document 0 4 0 65 mg documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs

precursors to blocking anomalies the tangent linear and inverse problems abstract the development of perturbations or errors is considered during periods of observed northern hemisphere blocking the evolution of initial onset of blocking mode perturbations is studied using a two level tangent linear model with time dependent basic states taken from observations in the first half of november 1979 during this period a blocking high formed in the gulf of alaska between 5 and 12 november followed by decay and the subsequent development of a block in the north atlantic initial baroclinic wave train perturbations with large amplitudes stretching from east asia into the central pacific propagate eastward as they grow and become equivalent barotropic large amplitude large scale perturbations form over the gulf of alaska as the observed block amplifies subsequently downstream development occurs with rapid amplification of the perturbation near the east coast of north america followed by the formation of large scale tripole anomalies in the blocking region over the north atlanti

upstream cyclone influence on the predictability of block onsets over the euro atlantic region abstractatmospheric blocking has been shown to be a phenomenon that models struggle to predict accurately particularly the onset of a blocked state following a more zonal flow this struggle is i

explosive cyclogenesis and large scale circulation changes implications for atmospheric blocking abstract large scale circulation changes attending explosive surface cyclogenesis are quantitatively examined in two cases selected from recent winter seasons both cases feature a rapidly deepening surface cyclone over the western atlantic ocean but changes in the 500 mb geopotential height field near the cyclone differ in each case one event during january 1977 is characterized by the retrogression of an anticyclonic vortex blocking high in the 500 mb height field downstream of the surface cyclone the second case in february 1978 is distinguished by the formation of a 500 mb cyclonic vortex cutoff low upstream of the surface cyclone but no downstream anticyclonic vortex is observed the retrogression of the january 1977 block over the atlantic ocean coincides with the migration of a 500 mb synoptic scale perturbation associated with the surface cyclone from a planetary scale trough over north america toward a planetary scale ridge over europe in the february 1978 case the blocking cyclo

the triassic of the thakkhola nepal ii paleolatitudes and comparison with other eastern tethyan margins of gondwana during the triassic the thakkhola region of the nepal himalaya was part of the broad continental shelf of gondwana facing a wide eastern tethys ocean this margin was continuous from arabia to northwest australia and spanned tropical and temperate latitudes a compilation of permian triassic and early jurassic paleomagnetic data from the reconstructed gondwana blocks indicates that the margin was progressively shifting northward into more tropical latitudes the thakkhola region was approximately 55 s during late permian 40 s during early triassic 30 s during middle triassic and 25 s during late triassic this paleolatitude change produced a general increase in the relative importance of carbonate deposition through the triassic on the himalaya and australian margins regional tectonics were important in governing local subsidence rates and influx of terrigenous clastics to these gondwana margins but eustatic sea level changes provide a regional and global correlation of major marine transgressions prograding margin deposits and shallowing upward successions a general mega cycle characterizes the triassic beginning with a major transgression at the base of the triassic followed by a general shallowing upward of facies during middle and late triassic and climaxing with a regression in the latest triassic