the role of magma mixing in triggering the current eruption at the soufriere hills volcano montserrat west indies the andesite lava currently erupting at the soufriere hills volcano montserrat contains ubiquitous mafic inclusions which show evidence of having been molten when incorporated into the andesite the andesite phenocrysts have a range of textures and zonation patterns which suggest that non uniform reheating of the magma occurred shortly before the current eruption reheating resulted in remobilisation of the resident magma and may have induced eruption

calcium carbonate nodules in soils 13o 16o and 13c 12c ratios and 14c contents abstract 18 o values 13 c values and 14 c ages were determined in ten caco 3 nodule populations collected from soil and paleosols in the israeli coastal plain the selected soils were carbonate free when formed and the nodules in them represent either reprecipitation of carbonate illuviated from overlying horizons descending mode or precipitated from a raised brackish water table ascending mode the 14 c ages represent the times of migration illuviation or eustatic movement both climate related and the stable isotopic conditions reflect the environmental conditions at such times the 13 c values of most populations were found to have a wide range and cannot be used to reconstruct former climates this wide range is attributed to microvariations of pco 2 in the soil because the 18 o ranges in the same samples are usually comparable to analytical uncertainties and because the 18 o mean values follow an age correlated pattern they permit us to place the soils in one of three categories in two cases where nodules were soft both turned out to be young 1000 years and to have wide ranges in 18 o values the latter are apparently due to continual re equilibration with new soil solutions in three cases of the descending mode of nodule formation 12 000 14 000 year old hard nodules had very narrow 18 o whose means reflect the rainfall value at that time the period between 12 000 14 000 years b p is independently known to be one of higher precipitation evaporation ratio and of more intensive soil formation these ascending mode populations of hard nodules had narrow ranges in 18 o reflecting a mixture of sea water and rainfall and all turned out to be 3 000 4 000 years old at this period the sea reached its highest elevation resulting in raising the nearcoast water table

palaeomagnetic estimates of crustal shortening in the himalayan thrusts and zangbo suture this article reports new palaeomagnetic results from precisely dated late palaeocene limestones from the former northern margin of the indian subcontinent now in tibet between the major himalayan thrusts and the india tibet suture zone convergence in the suture and intracontinental thrusting can be estimated separately and are respectively found to be of the order of 550 km 650 km and 400 km 400 km comparison with kinematic models derived from magnetic anomalies constrains the age of the collision at about 50 myr

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

volcanology messy magma mixtures andesite magmas were once thought to be simple melts derived from a subducting oceanic slab or the mantle analysis of lavas at mount hood shows that instead andesites are a complex mixture of magmas formed in the continental crust just before eruption

an isotopic study of paleosol carbonates from olduvai gorge the isotopic composition of paleosol carbonates from olduvai gorge can be used to give estimates of the paleoclimatic history of east africa during the plio pleistocene oxygen isotopes are indicative of major changes in the isotopic composition of meteoric water while carbon isotopes are indicative of major changes in the fraction of biomass using the hatch slack c4 photosynthetic pathway three major periods of climatic change in this terrestrial setting occurred at about 1 67 1 3 and 0 6 myr these involved major changes in flora as well as major changes in the isotopic composition of meteoric water overall the climate has become warmer and more arid over the past 2 2 myr

northwestward decline of magnetic susceptibility for the red clay deposit in the chinese loess plateau 1 the loess paleosol red clay sequence in the chinese loess plateau has attracted attention for its potential in recording late cenozoic climatic changes over northern china although the details of the climatic implications of the proxies for example magnetic susceptibility and the reconstructed summer monsoon changes remain unclear here we report on a new section from baishui in gansu province and compare it with the lingtai and jingchuan sections by correlating the magnetic susceptibility from these sections we show that there is a clear systematic decrease of the magnetic susceptibility in the red clay deposits from the southeast lingtai section to the northwest baishui section this result suggests that the climatic parameters probably precipitation had a decreasing northwestward gradient during the red clay deposition this climatic pattern is similar to the present condition implying that the influence of the east asian summer monsoon on the chinese loess plateau has persisted from at least 6 ma

a biostratigraphic zonation of the middle and upper siwaliks of the potwar plateau of northern pakistan abstract two biostratigraphic reference sections are designated for the middle and upper siwalik formations of northern pakistan the stratigraphic ranges of 41 mammalian taxa are established in the reference sections and the two sections are correlated to each other and to the standard magnetic polarity time scale by the magnetic polarity stratigraphy the resulting stratigraphic and magnetostratigraphic framework is used to define four contiguous biostratigraphic interval zones the proposed interval zones are bounded by five important faunal events which are identified in the reference sections the four proposed interval zones and the approximate ages in the reference sections of their lower and upper boundaries are 1 the hipparion s l interval zone 7 4 9 5 m y b p 2 the selenoportax lydekkeri interval zone 5 3 7 4 m y b p 3 the hexaprotodon sivalensis interval zone 5 3 2 9 m y b p and 4 the elephas planifrons interval zone 2 9 1 5 m y b p the paleomagnetic and biostratigraphic evidence indicates that the tatrot beds from which pilgrim developed his tatrot faunal zone are between 2 5 and 3 4 m y b p with a preferred maximum age of 2 9 m y b p the biostratigraphic evidence indicates the sethi nagri locality y311 the primary source of pilgrim s nagri faunal zone is in the hipparion s l interval zone the paleomagnetic evidence suggests an approximate age of 9 m y b p a major faunal event at 9 5 m y b p introduced equids suids and large giraffes from eurasia into the indain subcontinent a second more diffuse faunal event between 5 3 and 2 9 m y b p introduced several african taxa as well as equus and cervids from eurasia

a multifaceted climatology of atmospheric blocking and its recent linear trend abstract a dynamically based climatology is derived for northern hemisphere atmospheric blocking events blocks are viewed as large amplitude long lasting and negative potential vorticity pv anomalies located beneath the dynamical tropopause the derived climatology based on the 40 yr european centre for medium range weather forecasts ecmwf re analysis era 40 provides a concise coherent and illuminating description of the main physical characteristics of blocks and the accompanying linear trends the latitude longitude distribution of blocking frequency captures the standard bimodal geographical distribution with major peaks over the north atlantic and eastern north pacific in all four seasons the accompanying pattern for the age distribution the genesis lysis regions and the track of blocks reveals that 1 younger blocks 1 4 days are more prevalent at lower latitudes whereas significantly older blocks up to 12 days are located at higher latitudes 2 genesis is confined predominantly t

δ13c of organic carbon in the bengal fan source evolution and transport of c3 and c4 plant carbon to marine sediments carbon isotopic measurements on organic carbon oc in sediment cores from the bengal fan odp leg 116 show a dramatic 10 increase beginning ca 7 ma ago and a rapid decrease after 0 9 ma these shifts reflect changes in the mixing ratio of terrigenous carbon derived from c3 and c4 plants the rapid increase in 13c of bengal fan oc at 7 ma shows that late miocene expansion of c4 plants already documented in the siwaliks was widespread over all the himalayan foreland after 7 ma relations of 13c with sedimentological parameters show that c4 plants dominate in the foreland whereas c3 plants remain abundant in the mountain range variations in the source of the sediments and of the oc appear to be sensitive to climate hydrologic conditions in the basin major changes in the isotopic composition of the carbon flux in one of the worlds largest river systems modify the isotopic budgets of both marine dissolved carbon and the sedimentary carbon mass

blocking over the south pacific and rossby wave propagation abstract atmospheric blocking events over the south pacific are investigated using a 39 yr record of 500 hpa height fields from the ncep ncar reanalysis dataset the analysis extends earlier work using a 16 yr record and confirms that the occurrence of blocking over the southeast pacific is strongly modulated by the enso cycle during austral spring and summer comparison of results at 500 hpa with the 300 hpa meridional wind component showed that blocking events are associated with large scale wave trains lying across the south pacific from the region of australia to southern south america similar wave trains are evident in both hemispheres in singular value decomposition analyses between 300 hpa meridional wind components and tropical pacific outgoing longwave radiation olr anomalies the hypothesis that the divergence associated with tropical olr anomalies forces an extratropical wave response that results in enhanced blocking over the southeast pacific was tested using a linearized barotropic vorti

the south pacific convergence zone spcz a review abstract the circulation features associated with the south pacific convergence zone spcz and its accompanying cloud band are reviewed and discussed the paper focuses on the following topics location structure and characteristics of the spcz theories and observations concerning its existence the significance and scope of the spcz in global scale circulation patterns quasi periodic changes in its location and strength and synoptic scale features within its regional influence e g cyclones subtropical jets it concludes with some challenging problems for the future

pakistan mammal tooth stable isotopes show paleoclimatic and paleoenvironmental changes since the early oligocene abstract this research presents an isotopic study of three large mammal groups elephantoid proboscideans hyracodontid and rhinocerotid rhinocerotoids equids of the hipparion group from the bugti hills sequence eastern balochistan pakistan combined with published data from the miocene siwalik group northern central pakistan these two exceptional fossil records from pakistan provide an unambiguous source of biotic information from the early oligocene up to the late miocene the 13 c c and 18 o c results from the same herbivore groups show several significant variations in environmental and climatic conditions throughout the 30 to 7 5 myr period in this region first from 30 to 22 myr the environment is characterized by a relatively dry but dense forest existing under a temperate to subtropical climate with a more closed tropical environment at 23 myr oligocene 18 o of the terrestrial herbivore teeth agrees with the marine foraminifera 18 o and mg ca trends suggesting that the pakistan region was affected by global climate rather than regional conditions after 22 myr the 18 o c mammal enamel results show a long term decreasing trend until 15 myr toward a wetter environment with the appearance of tropical forests in response to the probable onset of the asian monsoon this is a period of high tectonic activity with the india asia collision leading to uplift of the tibetan plateau and shrinkage of the epicontinental paratethys sea this activity modified the land sea distribution and the thermal contrast between ocean and continent the driving force of the monsoon climate the middle miocene environment in pakistan experienced moist conditions under an intense monsoon system with relatively closed rainforest after 12 myr the 18 o c enamel values record a positive shift until 9 3 myr toward a drier environment with an increase of seasonality as suggested by higher 18 o c variability after 9 3 myr these late miocene drier climatic conditions and the asian monsoon intensification could potentially favour the c 4 photosynthetic pathway and hence the development of grassland to the detriment of subtropical forests resulting in the higher enamel 13 c values recorded after 9 3 myr

the impact of neogene grassland expansion and aridification on the isotopic composition of continental precipitation the late cenozoic was a time of global cooling increased aridity and expansion of grasslands in the last two decades numerous records of oxygen isotopes have been collected to assess plant ecological changes understand terrestrial paleoclimate and to determine the surface history of mountain belts the 18o values of these records in general increase from the mid miocene to the recent we suggest that these records record an increase in aridity and expansion of grasslands in midlatitude continental regions we use a nondimensional isotopic vapor transport model coupled with a soil water isotope model to evaluate the role of vapor recycling and transpiration by different plant functional types this analysis shows that increased vapor recycling associated with grassland expansion along with biomechanistic changes in transpiration by grasses themselves conspires to lower the horizontal gradient in the 18o of atmospheric vapor as an air mass moves into continental interiors the resulting signal at a given inland site is an increase in 18o of precipitation with the expansion of grasslands and increasing aridity matching the general observed trend in terrestrial cenozoic 18o records there are limits to the isotopic effect that are induced by vapor recycling which we refer to here as a hydrostat in the modern climate this hydrostatic limit occurs at approximately the boundary between forest and grassland ecosystems

ages and paleoenvironment of miocene mammalian faunas from thailand abstract the geological survey of continental basins in northern thailand has led to the discovery and the study of several mammalian assemblages in that area all localities from northern thailand occur in a time span ranging from about 16 to 14 ma in addition a diachronism is apparent among the different localities and is indicated by the different stages of evolution in the tooth morphology of rodents ruminants rhinos and mastodonts mae long li basin would be the oldest locality about 16 ma followed by had pu dai lampang basin and then huai siew and ban san klang both in pong basin ban na sai li basin and mae teep would be contemporaneous with ban san klang and mae moh is thought to be the youngest locality in order to study the paleoenvironment of the thai neogene faunas we have used the cenogram method in which structure reflects the general environment of a faunal community we also compared the faunal communities from thailand with those from the pakistan siwaliks and from china in the latter areas the microfauna is well represented and the large mammals are numerous thus suggesting a wet environment with a likely monsoonal climate the middle miocene paleoenvironment in south asia seems to have been quite open and small areas of forests were probably intermixed with grassland the cenogram structure completely excludes an environment dominated by primary forest or by steppe

the siwaliks of pakistan time and faunas in a miocene terrestrial setting magnetostratigraphy provides unparalleled chronologic precision for long terrestrial sedimentary records the siwaliks of the potwar plateau northern pakistan present perhaps the best example of a sequence of well dated faunal horizons spanning most of the neogene in a single terrestrial biogeographic province temporal control on fossil localities tied to multiple paleomagnetic sections is ca 0 1 m y less given special conditions of short magnetozone duration or superpositional relationships new correlations are presented for two long sections in the lower siwaliks showing the power and the limitations of mag netostratigraphic correlation within the siwalik depositional setting correlation of potwar fossil localities to those of an east african section also dated paleomagnetically are established with fossil localities from those two biogeographic provinces shown to be coeval on a scale of 10 5 yr the composite biostratigraphy rendered by the thick well exposed well dated potwar siwalik

magnetostratigraphy of the middle miocene continental sedimentary sequences of the mae moh basin in northern thailand evidence for counterclockwise block rotation abstract a magnetostratigraphic study has been performed on the mae moh basin well known for its lignite mining in the lampang province paleomagnetic samples were collected from 66 stratigraphic levels rock magnetic investigations indicate the presence of low coercivity minerals specimens subjected to progressive thermal or alternating field demagnetization procedures show that nearly all of them exhibit a low temperature magnetization component and a high temperature characteristic component chrm with either positive or negative virtual geomagnetic pole latitudes and opposite polarity considered as the characteristic miocene magnetization the overall mean paleomagnetic direction incl 22 2 decl 358 3 15 95 4 documents a counterclockwise vertical axis rotation of about 13 1 32 with respect to the expected miocene direction derived from the eurasian polar wander curve incl 42 decl 11 our paleomagnetic results are not consistent with the previously reported paleomagnetic data the rotation observed in the mae moh basin can be the response to local tectonics a section sampled for magnetostratigraphy reveals a polarity sequence of nine magnetozones that can reliably be correlated to the geomagnetic polarity time scale according to biochronological constraints the magnetostratigraphic results from the mammal bearing succession correlate with chron c5abn c5an2n between 13 5 and 12 1 ma according to the mean sedimentation rate of about 17 5 cm ka ages of 12 5 and 12 8 ma are proposed for the fossiliferous levels j5 and k1 k2 lignite zones were the mammal remains were found

characteristics of atmospheric circulation over east asia associated with summer blocking the boreal summer blocking regions were defined using the reanalysis data over the three decades of 1981 2010 and the influence of the blocking on atmospheric circulation in east asia was examined the summer blocking occurred mostly in north europe ural region sea of okhotsk ok and northeastern pacific the summer blocking was the major mode in these four regions according to principal component analysis using 500 hpa geopotential heights among the four blocking regions ok blocking frequencies ok bfs showed negative and positive correlations with summer temperature and precipitation of northeast asia centered around the east sea sea of japan respectively in particular the ok bf had a statistically significant correlation coefficient of 0 54 with summer temperatures in the korean peninsula this indicates that the summer temperature and precipitation in this region were closely related to the ok blocking according to the composite analysis for the years of higher than average bf positive bf years the ok high became stronger and expanded while the north pacific high was weakened over the korean peninsula and japan and an anomalously deep trough was developed in the upper layer 200 hpa as the cool ok high expanded the temperature decreased over northeast asia centered around the east sea sea of japan and the lower level 850 hpa air converged cyclonically resulting in the increased precipitation which induced the divergence in the upper layer and thereby strengthened the jet stream thus the boreal summer ok blocking systematically influencing the area as the most dominant mode

a 16 ma record of paleodiet using carbon and oxygen isotopes in fossil teeth from pakistan abstract the siwalik sequence of northern pakistan contains a 16 ma record of paleosol carbonate and fossil teeth from which a record of paleovegetation can potentially be reconstructed and compared the carbon isotopic composition of paleosol carbonate and organic matter from siwalik strata reflects a major paleoecological change on the floodplains of major rivers beginning7 3 ma ago by 6 ma c 3 dominated plant communities probably composed of mostly trees and shrubs were displaced by nearly continuous c 4 grassland we find that the carbon isotopic ratios in herbivore tooth enamel reflect this dramatic ecologic shift carbonate in enamel older than 7 ma averages 11 in 13 c pdb consistent with a largely c 3 diet enamel from the plio pieistocene averages 1 9 in 13 c similar to the value displayed by modern c 4 grazers analysis of post burial carbonate cements and the concordance with isotopic evidence from paleosols argues strongly against major isotopic alteration of the enamel while coexisting bone may have been altered early in burial this study confirms that enamel apatite is useful for paleodietary reconstruction much further back in the geologic record than was previously thought

neogene mammalian faunal change in southern asia correlations with climatic tectonic and eustatic events the fluvial neogene siwalik formations of northern pakistan span long time intervals with only minor hiatuses and being highly fossiliferous are uniquely suited for studies of change in mammalian faunas magnetostratigraphic correlations of a critical stratigraphic section give dates for 45 middle and late miocene biostratigraphic events these mark either first appearances or extinctions in the mammal fauna and show that in the siwaliks there were major fauna turnovers at between 20 and 16 ma and at 9 5 and 7 4 ma two minor faunal events are dated at 13 2 and about 12 ma many species making their first appearance were immigrants from europe or africa and indicate when connections to those regions existed immigration and extinction were the dominant modes of faunal change in situ evolution was much less important the siwalik biostratigraphic record correlates closely to climatic oceanographic and tectonic events which probably controlled immigration into southern asia abiotic events were therefore important factors affecting evolution of the mammal communities

experimental simulation of magma mixing at high pressure abstract magma mixing features are observed in many plutonic and volcanic environments they result from the juxtaposition of two chemically contrasted magmas usually not only during the replenishment of a magmatic reservoir but also syn eruptively within the conduit despite its ubiquity only a few experimental studies have explored mixing between magmas existing data have been mostly acquired at atmospheric pressure and high shear rates 10 1 s 1 which differ from those accompanying magma mixing in reservoirs to fill this gap we performed high pressure mixing experiments at strain rates ranging from 4 10 4 to 1 10 3 s 1 layers of a synthetic crystal free haplotonalite and a natural partially molten basalt were juxtaposed in a paterson apparatus at 300 mpa and deformed between 900 and 1200 c the experiments shed light on the first stages of magma mixing and illustrate the role and behaviour of crystals either pre existing or newly grown experiments evidence a rheological threshold for mafic material disruption which sets in abruptly as its melt fraction exceeds 50 which in the experiments occurs in the narrow temperature interval 1160 1170 c below this threshold plagioclase crystals in the mafic magma form a rigid touching network and all the deformations are accommodated by the less viscous felsic layer above it the crystal network collapses allowing typical mingling mixing features to appear altogether such as enclaves melt filaments and single xenocrysts isolated into the felsic end member coexisting with newly grown phases plagioclase and pyroxene whose compositions spread out over considerable ranges the pre existing fabric of the mafic magma is only slightly affected by deformation altogether providing few clues on either the regime or geometry of applied deformation during the magmatic stage

the 14c dates and 13c 12c ratios of soil organic matter as a means of studying the past vegetation in intertropical regions examples from colombia south america abstract the 14 c ages and 13 c 12 c values were obtained on soil organic matter of various soils sampled in the guasca valley adjacent to the high plain of the sabana de bogota in the colombian cordillera oriental a soil distribution is observed as a function of climatic and altitudinal changes in the lowest parts of the valley planosols are found from the bottom of the valley to 2700 2800 m at altitudes up to 2900 m brunizems and ferrisols occur above 3000 m andic soils are almost everywhere present in more humid mountain zones at present the landscape is widely open without any natural forest nevertheless it was proved by pollen analytical data that at altitudes up to 3000 m the andean forest replaced a paramo formation 13 000 yr ago to conciliate the facts with the known evolution of the vegetal population a first hypothesis consists of admitting that open landscapes were due to a recent anthropogenic destruction of the forest the forest degradation hypothesis was tested by determination of the 13 c 12 c ratio because the trees have a 13 c of 25 to 28 influence of plants with c 3 photosynthesis pathway whereas herbs characteristic of open vegetation such as tropical grasses may have a 13 c of 23 to 16 due to a c 4 photosynthetic cycle the organic matter dated at 13 000 30 000 yr has 13 c close to 25 in the andic soil zone this indicates that at elevations of around 3000 m a cold paramo vegetation was probable for organic matter dated at 12 000 6000 yr 13 c shows a variation from 23 to 21 that does not indicate forest conditions it is uncertain that a forest stage occurred in the past for the planosols brunizem and ferrisol organic matter dated at 13 000 20 000 yr has a 13 c 23 compatible with the paramo vegetational phase occurring at that time for organic matter dated at 9500 yr and less 13 c varies from 20 to 17 these values do not confirm the evidence of forest conditions but rather the existence of open vegetation typified by a mixture of c 3 plants shrubs and rare trees and tropical graminaea thus the 13 c values prove that the valley has known drier and warmer influences that prevented the forest from developing during the holocene to explain the origin of the open landscapes of the valley the hypothesis of recent human deforestation must be discarded moreover the valley appears as a persistent dry enclave in the oriental cordillera

magma mixing in granitic rocks of the central sierra nevada california abstract the el capitan alaskite exposed in the north american wall yosemite national park was intruded by two sets of mafic dikes that interacted thermally and chemically with the host alaskite comparisons of petrographic and compositional data for these dikes and alaskite with published data for sierra nevada plutons lead us to suggest that mafic magmas were important in the generation of the sierra nevada batholith specifically we conclude that 1 intrusion of mafic magmas in the lower crust caused partial melting and generation of alaskite rhyolitic magmas 2 interaction between the mafic and felsic magmas lead to the observed linear variation diagrams for major elements 3 most mafic inclusions in sierra nevada plutons represent chilled pillows of mafic magmas related by fractional crystallization and granitoid assimilation that dissolve into their felsic host and contaminate it to intermediate granodioritic compositions 4 vesiculation of hydrous mafic magma upon chilling may allow buoyant mafic inclusions and their disaggregation products to collect beneath a pluton s domed ceiling causing the zoning mafic margins to felsic core that these plutons exhibit

characteristics of southern hemisphere blocking as determined from a time series of observational data a time series of 500 mb geopotential heights has been used to assess characteristics of southern hemisphere blocking a zonal index similar to the index used in an analogous study of northern hemisphere blocking has been used characteristics of blocking situations have been computed with a simple algorithm which has been programmed and are presented as statistics we found one preferred region for blocking action the australian new zealand region two other regions where blocks occur are the atlantic east of south america and the indian ocean south east of south africa the number of days with blocked flow is considerably less over the atlantic and the indian ocean than in the australian new zealand region the annual variation shows two maxima one peak value of 19 in april and one extended maximum of c 20 during june august in the australian new zealand region there is no clear indication of a seasonal variation in the atlantic and the indian ocean region investigation of individual blocking episodes reveals that the majority of the blocks have a mean eastward velocity although the longer they last the more of them are westward moving longlasting episodes are almost exclusively found in the australian region

an extratropical air sea interaction over the north pacific in association with a preceding el nino episode in early summer abstract using data for the month of june from 1951 through 2000 this study examined the air sea interactions over the north pacific after el nino matured during the preceding fall season the principal findings of this work are the following 1 a coherent region near the international date line idl in the extratropical north pacific revealed an area of significant negative correlations sncs between the preceding november sea surface temperature sst in the nino 3 region and the june sst in the north pacific also two indexes of the june okhotsk high show a significant positive correlation with the november sst in the nino 3 region during the 1963 2000 period 2 the strong southeastward wave flux from the upstream area of the okhotsk sea over much of the north pacific in the midlatitudes is associated with a strong preceding el nino event the development of the okhotsk high and a negative 500 hpa geopotential height sst anomaly around the coherent region the stationary wave propagation plays a

signs of magma ascent in lp and vlp seismic events and link to degassing an example from the 2010 explosive eruption at merapi volcano indonesia the link between seismicity and degassing is investigated during the vei 4 eruptions of merapi volcano indonesia in october and in early november 2010 seismicity comprised a large number and variety of earthquakes including volcano tectonic events a sustained period of long period seismicity lps i e long period events lp very long period events vlp and tremor lps seismicity is ascribed to the excitation of fluid filled cavity resonance and inertial displacement of fluids and magma we investigate here lps that occurred between 17 october and 4 november 2010 to obtain insights into the volcano eruption processes which preceded the paroxysmal phase of the eruption on 4 5 november we proceed to the moment tensor inversion of a well recorded large vlp event during the intrusion phase on 17 october 2010 i e before the first explosion on 26 october by using two simplified models crack and pipe we find a shallow source for this vlp event at about 1 km to the south of the summit and less than 1 km below the surface we analyze more than 90 lp events that occurred during the multi phase eruption 29 october 4 november we show that most of them have a dominant frequency in the range 0 2 4 hz we could locate 48 of those lp events at least 3 clusters of lp events occurred successively we interpret these observations as generated by different fluid filled containers in the summit area that were excited while magma rose we also observe significant variations of the complex frequency during the course of the eruption we discuss these changes in terms of a variable ratio of fluid to solid densities and or by possible conduit geometry change and or permeability of the conduit or the edifice and or by resonance of different fluid containers during the release of more than 0 4 tg of so2 and large but unknown masses of other volcanic gases finally we also discuss how the major explosions of the eruption were possibly triggered by passing waves resulting from regional tectonic earthquakes on 3 and 4 november

an analysis of a relatively rare case of continental blocking planetary and synoptic scale analyses of a relatively rare continental blocking event that occurred over north america during the spring of 1980 are undertaken to determine whether or not this event was different from its counterparts which occur over oceanic regions the planetary scale analysis demonstrates that during the spring season a ridge was located further inland over the north american continent and amplified with respect to climatology the position of this ridge may have been linked to a broad region of colder than normal sea surface temperatures found over the north central pacific during the spring season and much of the previous winter simple sutcliffe type and thermodynamic analyses of the accompanying lower tropospheric warm anomaly associated with the ridging show that lower tropospheric temperature advection and subsidence associated with anticyclonic vorticity advection by the time mean thermal wind produced much of the anomalous warmth a simple synoptic scale analysis was performed using both the zwack okossi zo equation and potential vorticity pv thinking approaches these complementary analyses demonstrated that synoptic scale cyclones were instrumental in the formation and maintenance and or intensification of this blocking event the pv analysis demonstrated that low pv air was swept polewards and then was advected over the blocking region sustaining the broad region of low potential vorticity associated with the block over north america the zo analysis showed that the advection of anticyclonic vorticity was the most important mechanism forcing geopotential height rises at 500 hpa over the block centre the region of low pv and zo height rises could be associated with the anticyclonic shear side of an upstream jet maximum typically found in association with developing and or intensifying blocking events thus negative pv advection correlated significantly with calculated zo height rises finally it is suggested that a favourable phase relationship between the upstream cyclones and the large scale ridge is necessary for block development or intensification

a climatology of anticyclones and blocking for the southern hemisphere abstract an automated procedure for locating and tracking high pressure centers is applied to 10 years of twice daily ecmwf analyses during 1980 89 to survey the behavior of anticyclones in the southern hemisphere anticyclones are concentrated in the 25 45 s band with preferred regions consistent with previous studies except in the new zealand nz south pacific sector where a double occurrence maximum noted in earlier studies was only weakly evident marked interannual variability was found in this region with the poleward branch of maximum occurrence south of 50 s present in only 3 out of 10 years mean central pressure maximized about 10 south of the time averaged ridge with highest values in winter anticyclones poleward of 50 s involve an anomalous breakdown of the westerlies with mean central pressures there 20 30 hpa higher than climatology highs tend to form and intensify in western regions of ocean basins and weaken and dissipate in the east of these oceans regions southeast of australi

magnetic polarity stratigraphy and ages of siwalik group rocks of the potwar plateau pakistan abstract six magnetic polarity sections have been established over the potwar plateau region of pakistan including the major stratotypes of the siwalik group in all six sections the dominant feature of the magnetic polarity stratigraphy is a long normal polarity zone which is contained within the nagri formation this conspicuous normal polarity zone has been radiometrically dated at 9 5 0 6 m y which identifies it as magnetic chron 9 radiometric dates from the upper siwalik formation have also been used to identify the chron 2 3 boundary in two of the sections the magnetic polarity stratigraphy of three of the sections has been correlated securely with the accepted magnetic polarity time scale so that the ages of the local stratigraphy are indexed accordingly based exclusively on data from stratotype sections the chinji nagri and dhok pathan formations have nominal age ranges of 10 1 13 1 7 9 10 1 and 5 1 7 9 m y age fluctuations on the order of 105 years may be anticipated for these formational boundaries within radius of some 20 km of the designated stratotype mean sediment accumulation rates during the chinji nagri and dhok pathan interval range from 13 to 52 cm 103 yr essentially linear sediment accumulations are locally maintained over time intervals of several million years the chinji nagri lithofacies boundary marks a transition from slow to faster sediment accumulation over much of the potwar plateau indicating a fundamental sedimentary tectonic change at this time

late oligocene recent stress evolution in rift basins of northern and central thailand implications for escape tectonics abstract the tertiary rift basins of thailand are known through sub surface seismic and borehole data collected for hydrocarbon and coal exploration outcrops in open cast coal mines and a few natural outcrops these data provide mixed perspectives on how the basins evolved some providing data on ages and structural geometries others palaeostress data in general the region evolved under approximately e w extension although the extension direction probably changed periodically within basins extension was episodically interrupted by inversion events associated with sub horizontal nw se to ne sw 1 direction there is no evidence to suggest that the string of rift basins running from n thailand and laos into the gulf of thailand evolved in a similar way on the contrary the evolution of each basin seems different although certain regional trends along the rift system are apparent as follows 1 oligocene lower miocene extension is widespread in the region 2 in central and northern thailand middle miocene extension is also important and extension persisted into the upper miocene pliocene 3 in the extreme south of the area w natuna basin penyu basin malay basin extension ceased in the earliest miocene 4 in the northern gulf of thailand extension ceased in the middle miocene 5 thermal subsidence is greatest up to 4 km in the south malay pattani w natuna and penyu basins and least in northern thailand a few tens to hundreds of metres 6 inversion in the southern gulf of thailand was intense and occurred during the lower and middle miocene in the northern gulf of thailand inversion is very mild and occurred during the lower and middle miocene onshore inversion is patchy during the miocene but is strongest in the northwestern rift basins particularly the li basin the most widespread inversion event that affects the north occurred during the plio pleistocene it might be associated with the change from left to right lateral motion on the red river fault the relationship between strike slip faults and rift basins in terms of timing of extensional and inversion events and palaeostress orientation and evolution is more complex than can be explained by simple escape tectonic models

timing of volcanism in the sierra nevada of california evidence for pliocene delamination of the batholithic root recent seismic experiments across the southern sierra nevada california show that the range lacks a thick crustal root xenolith studies indicate that delamination and loss of much of the lower crust may have occurred between 10 and 3 ma we estimate that delamination occurred ca 3 5 ma on the basis of a sudden pulse of mafic potassic magmatism within and just east of the sierra nevada from 4 to 3 ma this pulse interrupted the low level of volcanism that had prevailed regionally since 13 ma delamination could have promoted magmatism via decompression melting heating of the shallow lithosphere by upwelling asthenosphere and foundering of crustal rocks into the mantle and could have provided dynamic support to the range foundering of the lower crust may have occurred spontaneously owing to negative buoyancy or may have been triggered by extension between the sierra nevada and death valley

traveling waves and regional transitions in blocking activity in the northern hemisphere abstract in preference to the use of persistent height anomalies for determining the presence of blocking new criteria were developed which take the observed flow conditions into account these criteria were applied daily at 500 mb using filtered northern hemisphere height maps retaining zonal waves 0 5 beginning in july 1981 blocking statistics for the 3 yr period through june 1984 are in remarkably close agreement with the results from longer period published data sets involving the use of a split jet flow as a principal criterion thus this data set albeit short is deemed appropriate for investigating the long wave properties of blocks during july 1981 june 1984 47 blocks were observed the long wave composition of blocks lasting at least 10 days 24 cases is examined in detail contrary to austin s 1980 hypothesis that blocking should arise from the constructive interference of stationary long waves with enhanced amplitude but normal phase it is found that traveling waves predominantly re

formation of a rain shadow o and h stable isotope records in authigenic clays from the siwalik group in eastern bhutan we measure the oxygen and hydrogen stable isotope composition of authigenic clays from himalayan foreland sediments siwalik group and from present day small stream waters in eastern bhutan to explore the impact of uplift of the shillong plateau on rain shadow formation over the himalayan foothills stable isotope data from authigenic clay minerals 2 m suggest the presence of three paleoclimatic periods during deposition of the siwalik group between 7 and 1 ma the mean 18o value in paleometeoric waters which were in equilibrium with clay minerals is 2 5 lower than in modern meteoric and stream waters at the elevation of the foreland basin we discuss the factors that could have changed the isotopic composition of water over time and we conclude that a the most likely and significant cause for the increase in meteoric water 18o values over time is the amount effect specifically a decrease in mean annual precipitation b the change in mean annual precipitation over the foreland basin and foothills of the himalaya is the result of orographic effect caused by the shillong plateau s uplift the critical elevation of the shillong plateau required to induce significant orographic precipitation was attained after 1 2 ma c by applying scale analysis we estimate that the mean annual precipitation over the foreland basin of the eastern bhutan himalayas has decreased by a factor of 1 7 2 5 over the last 1 3 million years 2018 american geophysical union all rights reserved

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

chaungtha a new middle miocene mammal locality from the irrawaddy formation myanmar abstract we describe here a mammalian assemblage originating from the locality of chaungtha irrawaddy formation myanmar it represents one of the rare descriptions of a precisely located in space vertical section and time fossil mammal fauna from the irrawaddy formation classically the fossil record of irrawaddy formation is essentially known from isolated fossils of imprecise or unknown provenance especially concerning the stratigraphic position of the fossils along several hundred meter thick sections the chaungtha faunal association consists of the rhino brachypotherium fatehjangense the pig conohyus thailandicus the ruminants cf siamotragulus sanyathanai cf siamotragulus sp and a gomphotheriid proboscidean this assemblage indicates that the locality is miocene in age and not late eocene as previously claimed and roughly contemporaneous with the chinji formation of india pakistan ca 14 11 ma and with the mae moh group of northern thailand the chaungtha fauna even if it displays regional characteristics shows a strong resemblance to those of the middle miocene of india pakistan and of thailand and reinforces the idea that south east asia and pakistan were part of the same biogeographical province during the middle miocene

blocking in the southern hemisphere abstract the focus of this paper is on the frequency and spatial distributions of blocking and persistent anomalies of geopotential height over the southern hemisphere the analysis is based upon daily height fields at 1000 and 500 mb for both summer and winter histogram frequency distributions of height anomalies and maps of the skewness and kurtosis have been computed blocking events are objectively defined by requiring a large positive anomaly to exist for 5 days or more composite flow and anomaly fields for several cases are presented and examined in detail the geographical distribution of the frequency of lame amplitude 150 gpm anomalies at 500 mb that persist for only 1 3 days is very similar to that of the high frequency band 2 8 day period variances that identity the storm tracks in the southern hemisphere the primary location for blocking in the southern hemisphere is in the new zealand sector and blocking occurs through a local enhancement of the climatological split in the mean westerli

tectonics or climate what drove the miocene global expansion of c4 grasslands investigations into the most plausible causes which triggered the late miocene global expansion of c4 grasslands have reached no consensus and are still being debated the global decline in co2 levels in the late miocene has been thought to be the most common driver although c4 grassland expansion was largely confined to the late miocene their first appearance varied significantly in different parts of the old and new world and therefore emphasizes role of local and or regional factors may or may not be in combination with one or more global factors the dynamic himalayan orogen constitutes a significant global tectonic event that is believed to have affected global climate hence a study of the himalayan foreland basin sediments could help in gleaning out possible causes behind this major paleoecologic event which could perhaps be directly or indirectly related stable carbon isotope analyses of a total of 141 pedogenic carbonates in the mio pleistocene siwalik paleosols of the ramnagar sub basin are coherent providing a better insight into paleovegetational changes across the sub basin on temporal and spatial scales furthermore paleovegetational history during oligocene is reconstructed from dagshai paleosols exposed in the subathu sub basin the isotopic results show dominance of c3 vegetation pre 7 ma and dominance of c4 vegetation post 5 ma percentage abundance of c4 vegetation was less than 20 pre 7 ma but increased to more than 40 post 5 ma reaching up to 100 in the youngest analyzed sediments there is exclusive dominance of c3 vegetation during oligocene these results conform to the pattern of change in vegetation documented in other parts of the himalayan belt the global expansion of c4 grasslands largely during late miocene have long been linked with then climate changes particularly brought by declining atmospheric co2 level large scale fires intensification of monsoon seasonality and aridity as demonstrated by various researchers these major hypotheses explaining expansion of c4 grasslands during late miocene are not very convincing due to significant shortcomings associated with them for example expansion of c4 grasslands in non monsoonal regions put serious constraints on the monsoonal intensification hypothesis likewise aridity as being the primary driver of c4 grassland expansion seems hard to support since there is no substantial evidence that could suggest global onset of arid conditions at about same geologic time and some most arid periods like the triassic show no evidence of c4 plants we suggest that the initial lowering of co2 below 450 ppmv created an environment for the beginning of c4 vegetation but the persistence of this threshold value for a considerable time during late miocene appears to be the probable cause of the late miocene global expansion of c4 grasslands irrespective of their time of first appearance it has been deduced through the correlation of himalayan tectonic events with atmospheric co2 levels and paleovegetational changes since upper miocene times that it was indeed the late miocene continuous intense tectonic instability of the himalayas that significantly decreased atmospheric co2 levels and which perhaps played a key role in changing the nature of photosynthetic pathways

how old is the asian monsoon system palaeobotanical records from china the recent discovery of monsoon records in early miocene raised a question of the time when the east asian monsoon system initiated a distinguishing feature of the modern monsoon system is its geographic distribution which disturbs the zonal pattern indigenous to the planetary climate system and the appearance of the monsoonal climate pattern in the geological records should signify the onset of the monsoon system here we present the results of a compilation of palaeobotanical and lithological data from 125 sites over china that has revealed two completely different patterns of climate zones the palaeogene pattern with a broad belt of aridity stretched across china from west to east and the neogene pattern with the arid zone restricted to northwest of china which has persisted until today the reorganization of the climate system around the oligocene miocene boundary provides evidence for the establishment of the modern east asian monsoon since then the neogene has witnessed significant variations of the monsoon system including enhancement of aridity and monsoon intensity at about 15 13 my around 8 my and 3 my the new data do not support the onset of the asian monsoon system around 8 my rather the new data led to a hypothesis that the transition to the monsoon climate system in east asia occurred in the latest oligocene

a complete magnetic polarity stratigraphy of the miocene continental deposits of mae moh basin northern thailand and a reassessment of the age of hominoid bearing localities in northern thailand northern thailand comprises more than 40 tertiary intermontane basins these basins tectonically interpreted as grabens or half grabens have yielded hominoid fossils and rich neogene mammal faunas relative ages provided by biochronological studies are controversial and neither absolute ages nor correlations with marine deposits are available a precise temporal framework provided by magnetic polarity stratigraphy is therefore crucial to understand the evolution of these southeast asian mammalian faunas to estimate the timing and duration of basin formation and finally to allow correlations with other neogene hominoid localities of the old world a complete magnetostratigraphic study which significantly extends previous paleomagnetic investigations has been conducted in the miocene sequence of mae moh basin lampang province northern thailand based on the biostratigraphic constraints the 15 polarity zones recognized from the composite section have been correlated with chrons c5acr c5r 3r between 14 1 and 12 0 ma the present study provides a high resolution magnetostratigraphic reference for the continental middle miocene of all southeast asia by correlation with the miocene sequence of the nearby basin of chiang muan the large bodied hominoid khoratpithecus chiangmuanensis bearing levels can be precisely dated between 12 4 and 12 2 ma

a review of fossil rhinoceroses from the neogene of myanmar with description of new specimens from the irrawaddy sediments abstract four genera and one indeterminate genus total eight species of fossil rhinoceroses mammalia perissodactyla rhinocerotidae are recognized from the neogene of central myanmar in the early miocene most area of central myanmar were under the shallow marine condition and no rhinocerotid remain has been documented yet during the middle to late miocene the rhinocerotid remains are commonly found and are represented by diceratherium naricum brachypotherium perimense brachypotherium fatehjangense and an indeterminate rhinocerotid in the latest miocene these archaic rhinoceroses became extinct in the late neogene the extant genera rhinoceros late miocene to pleistocene and dicerorhinus plio pleistocene first appeared in myanmar they appear to have dispersed to the island southeast asia from the continental asia during the early pleistocene to middle pleistocene when the eustatic sea level became low remarkably

the anomalous structures of atmospheric and oceanic variables associated with the frequency of north pacific winter blocking 1 from empirical orthogonal function eof analysis of the atmospheric and oceanic variables over the north pacific during the northern hemispheric winter 1960 2009 we were able to determine that the second mode of the eof is related to north pacific winter blocking our composite analysis reveals that the structures of the variables during winters with contrasting frequencies of blocking events are systematically different and show quite opposite pattern in the north pacific during winters with frequent blocking occurrence a north south dipole pattern of geopotential height anomaly is formed and the associated westerly winds are weakened strengthen north south of 35 n these factors bring variations of ocean advection and ocean surface heat flux resulting in a dipole pattern of sea surface temperature sst with a warm anomaly north of 35 n and a cold anomaly to the south the effect of sst on blocking is examined using an atmospheric general circulation model agcm experiment in the experiment the sst anomaly related to blocking is applied as a boundary forcing of the agcm to investigate the effect of sst on the formation of blocking from the experiment we also concluded that the winter blocking is not induced by north pacific sst forcing although consistent linkage between oceanic and atmospheric variables is evident

blocking systems over an aqua planet 1 it is well established that forced planetary waves are critically important for blocking formation to test whether blocking can be generated and maintained in the absence of topographic forcing we carry out aqua planet simulations using ncar cam2 results show that blockings occur frequently under the aqua planet conditions which have no forcing such as land sea contrast orography and stationary remote tropical forcing features of simulated blockings well resemble that in the real atmosphere showing typical like patterns persistence and quasi stationary behavior with occasionally westward shifting it is found that the onset and maintenance of simulated blockings are due to interaction between quasi stationary free rossby waves and baroclinic eddies for 10 year simulations the blocking frequency is slightly higher than that in the northern hemisphere nh in the real atmosphere these suggest that blocking is a natural consequence of rotating and baroclinic atmospheres while locally topographic forcing and remote tropical forcing are not necessary conditions

the climatology of blocking anticyclones for the northern and southern hemispheres block intensity as a diagnostic abstract a 30 yr climatology of blocking events was compiled by stratifying the data into seasonal and three regional categories for both the northern and southern hemispheres using the ncep ncar reanalyses several characteristics of blocking anticyclones were included in the study and these were frequency of occurrence preferred formation regions duration blocking days and intensity the block intensity bi calculation was modified successfully from a previous study in order to automate the procedure for use with large datasets and it is applied for the first time to derive a long term observational record of this quantity this modification also makes bi suitable for use as a diagnostic tool blocking events in the northern southern hemisphere were the most persistent and strongest during the cold season and over the atlantic pacific region as found using bi to measure intensity the characteristics of blocking events derived in this study were compared to previous long term climatological s

the wintertime southern hemisphere split jet structure variability and evolution a persistent feature of the southern hemisphere upper level time mean flow is the presence of a split jet across the south pacific east of australia during the austral winter the split jet is composed of the subtropical jet stj on its equatorward branch and the polar front jet pfj on its poleward branch the ncep ncar reanalysis is used to investigate the structure and evolution of the split jet results show that the presence absence of the pfj determines the degree of split flow given that the stj is a quasi steady feature a splitflow index sfi is developed to quantify the variability of the split jet in which negative values represent strong split flow and positive values nonsplit flow correlations with teleconnection indices are investigated with the sfi positively correlated to the southern oscillation index and negatively correlated to the antarctic oscillation the sfi is used to construct composites of heights temperature and wind for split flow and non split flow days the composites reveal that relatively cold conditions occur in the south pacific in association with nonsplit flow regimes and split flow regimes occur when relatively warm conditions prevail in the latter situation cold air bottled up over antarctica helps to augment the background tropospheric thickness gradient between antarctica and the lower latitudes with a resulting increase in the thermal wind and the pfj it is surmised that frequent cold surges out of antarctica moving into the south pacific are associated with non split flow regimes in this context the variability of the split jet responds to large scale baroclinic processes and is further modulated by synoptic scale disturbances

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

preferential eruption of andesitic magmas through recharge filtering at subduction zones andesite lavas erupt in greater abundance than the individual magmas that mix to produce them textural and geochemical analyses of andesites from mount hood oregon reveal that injection and mixing of iron and magnesium rich magma in the magma chamber can initiate the volcanic eruption andesitic volcanic rocks are common in subduction zones and are argued to play an important role in the formation and evolution of the continental crust at convergent margins1 2 3 4 andesite formation is dominated by mixing between iron and magnesium rich mafic magmas and silica rich felsic magmas1 2 4 the abundance of andesites in many subduction zones suggests they erupt in preference to the magmas that mix to produce them4 however the reasons for this remain unclear here we use textural and geochemical analyses of andesites from mount hood oregon to show that eruptions are closely linked with episodes of mafic recharge the intrusion of mafic magma into a shallow felsic magma reservoir the felsic and mafic magmas involved rarely erupt by themselves probably because the former are too viscous and the latter too dense mafic recharge overcomes these barriers to eruption and as it also promotes efficient mixing results in preferential eruption of mixed andesitic magmas the abundance of andesites therefore relates to local crustal conditions and the ability of magmas to erupt we suggest that volcanoes such as mount hood that erupt homogeneous andesitic compositions through time are those that are the most reliant on mafic recharge to initiate eruptions

activation of the nyainqentanghla shear zone implications for uplift of the southern tibetan plateau neogene extension of the tibetan plateau is manifested as a series of north south trending graben the most prominent of which is the yadong gulu rift the nyainqen tanghla shan a ne sw trending mountain range 100 km nw of lhasa bounds the western margin of the yangbajian graben the central segment of the yadong gulu rift the eastern edge of the nyainqentanghla massif is marked by a low angle 25 o detachment fault shear zone of amphibolite grade mylonites the noar 3 ar thermal history results from samples collected along two deeply incised valleys within the massif reveal that a rapid cooling event propagated from 8 ma in the core of the range to 4 ma within the high strain zone at the eastern boundary assuming that faulting initiated at high angle 60o thermal histories were fit to a numerical simulation of slip on a normal fault to yield estimates of both the age of fault initiation and the slip rate history the form of the isotopically derived thermal histories are similar to general form predicted by the thermal model and suggests that significant movement began at 8 1 ma in the southern valley goring la and proceeded at an average slip rate of 3 mm yr between 8 and 3 ma a more complex history is required to fit the data from the northern valley balum chun but the timing of initiation and average slip rate are similar to the goring la result numerical simulations in which the fault angle is varied indicate that the isotopically derived temperature histories are inconsistent with slip occurring at low angle 40o because the extension direction of the yangbajian graben is representative of most rifts on the southern tibetan plateau our data suggest that crustal thickness and elevation reached close to their present values by 8 1 ma a carbon isotopic shift in pedogenic carbonates from the siwalik formation at about 7 5 ma appears to reflect intensification of the asian monsoon and by inference that the plateau had attained an important threshold elevation by that time formation of a diffuse plate boundary in the indian oceanic lithosphere beginning at 7 5 8 0 ma is also consistent with this history we suggest that the plateau had attained a threshold area and elevation by 8 1 ma sufficient to trigger these three independent manifestations

mio pleistocene zanda basin biostratigraphy and geochronology pre ice age fauna and mammalian evolution in western himalaya article i nfo the pliocene 5 3 2 6 ma of tibet witnessed the drying of the northern tibetan plateau and the approach to the pleistocene ice age within the background of intensifying indian and east asian monsoons yet little is known about pliocene mammals living on the high tibetan plateau despite the fact that fossil mammals elsewhere consti tute an important knowledge base for terrestrial environments the late miocene to pleistocene zanda basin at the northern foothills of the himalayas affords a welcome opportunity to evaluate the biological response to environ mental change at high elevations abundant well preserved fossil mammals and fish from an 800 m continuous section of fine to coarse grained sediments thus open a rare window into a past biological world for example the discovery of an ancestral wooly rhino from zanda basin that was the precursor of its late pleistocene megafaunal descendants leads to our out of tibet hypothesis suggesting that the high tibetan plateau was a pliocene cradle for ice age cold adaptations in this paper we document in detail the mammalian biostratigraphy chronology and paleozoogeography based on zanda basin fossil mammals our high resolution biostratigraphy and biochronology offer for the first time independent constraints that both support and modify recent magnetostratigraphic correlations using charac teristic pliocene and pleistocene mammals particularly the small mammal assemblages in the lower part of the section and monodactylid equus from the upper section we propose a correlation to c1n to c3an 1r with an age range of 400 ka to 6 4 ma within the 800 m zanda section the lower 0 150 m is of latest miocene age spanning 6 4 5 3 ma sparsely fos siliferous the lower section has produced five taxa so far ochotona panthera qurliqnoria palaeotragus a nd hipparion all are consistent with a late miocene age the middle 150 620 m section spans the entire pliocene this section is by far the most fossiliferous including such typical pliocene small mammals as prosiphneus mimomys apodemus a ndtrischizolagus as well as large mammals such as coelodonta thibetana hipparion zandaense chasmaporthetes nyctereutes meles antilospira and others in the upper 620 800 m section the fos sils are rare but do include characteristic pleistocene taxa such as equus zoogeographically zanda basin mammals are a mixture from two major sources taxa such as mimomys prosiphneus trischizolagus chasmaporthetes nyctereutes meles a ndxenocyon are commonly found in north china or east asia in contrast several forms such as unique species of pikas ochotona squirrels aepyosciurus and ancestral tibetan antelope qurliqnoria seem to belong to an indigenous tibetan fauna evolved within the plateau a lack of shared taxa with the oriental realm suggests a formidable barrierby the himalayas despite a short distance 100 km between zanda basin and the indian subcontinent

experimental mixing of hydrous magmas deformation experiments involving hydrous magmas of different compositions basalt and haplotonalite have been performed in a paterson press at 300 mpa in the temperature range 600 c 1020 c with water saturated melts during 2 4 h prior to deformation the two end member magmas were annealed at either 950 c or 1000 c yielding magmas with crystal contents in the range 31 53 wt and 2 sets of viscosity contrasts under the experimental conditions investigated i e moderate shear rates 950 c in the temperature range 950 985 c a few mixing and mingling textures occur though both end members essentially retain their physical integrity it is only at or above 1000 c that a dramatic jump in mingling efficiency happens corresponding to a crystal fraction of 45 vol textures include entrainment of mafic crystals into the felsic magma mafic felsic banding enclave formation and diffusion induced interface the latter only over limited distances 300 m due to the short run durations in the most strained parcels of interacting magmas complex mixing mingling textures were produced similar to those observed in volcanic and plutonic rocks in arc settings the experiments show that mixing between hydrous felsic and mafic magmas takes place at around 1000 c a temperature which is almost 200 c lower than mixing under dry conditions magma mixing is commonly invoked as a trigger for volcanic eruptions our experiments suggest that such eruptions can be driven by small 15 c temperature fluctuation in the reservoir our results also suggest that slow replenishment of a felsic reservoir by mafic inputs will likely result in stratification between end members rather than in a homogeneous mixture

paleomagnetic chronology fluvial processes and tectonic implications of the siwalik deposits near chinji village pakistan a 2800 m section of siwalik strata containing the stratotypes for both the chinji and nagri formations has been dated by magnetic polarity stratigraphy and the observed polarity zonation has securely been correlated with the chron 17 7 segment of the time scale the base of the section is the base of the kamlial formation which occurs near the top of chron 17 18 3 m y the kamlial chinji formation boundary occurs in the middle of chron 15 14 3 m y the chinji nagri boundary near the bottom of chron 10 10 8 m y and the nagri dhok pathan boundary at the chron 8 9 boundary 8 5 m y the siwalik deposits near chinji village consist of four distinct classes of fluvial cycles each with a characteristic periodicity a first order of 10 7 years a second order of 10 6 years a third order of 10 4 10 5 years and a fourth order of 10 0 10 4 years the river system responsible for siwalik sedimentation flowed from west to east and had properties much like the modern ganges river syste

effect of orogeny plate motion and land sea distribution on eurasian climate change over the past 30 million years the eurasian climates of today 10 million and 3o million years ago are simulated using an atmospheric general circulation model that incorporates realistic continental geography and epicontinental sea distributions the resulting climates compare well with various palaeoclimate records the retreat of the paratethys an epicontinental sea shifts the central asian climate from temperate to continental conditions and plays as important a role as uplift of the himalayan tibetan plateau in driving the asian monsoon changes

persistent positive anomalies in the southern hemisphere circulation abstract long time series of reanalyses from ncep ncar and from ecmwf are used to investigate the occurrence of persistent positive anomalies ppas in the 500 hpa geopotential height field over the southern hemisphere extratropics during 1958 2001 defining persistent anomalies as those of at least 100 m in magnitude lasting for at least 5 days it is found that the region of most frequent occurrence is over the south pacific a cluster analysis of monthly ppa counts shows two distinct patterns one a zonal wavenumber 1 zw1 pattern centered over the southeast pacific near 60 s and the other a zonal wavenumber 3 zw3 pattern with centers near new zealand and over the southern atlantic and indian oceans results were insensitive to the choice of dataset and to the removal of a linear trend from the daily height fields the southeast pacific ppa region is strongly modulated by enso while the zw3 pattern appears only weakly related to enso variability a strong upward trend is apparent in occurrence o

a climatology of the northern hemisphere winter anticyclones 1 a climatology of the northern hemisphere winter anticyclonic activity is presented based on the european centre for medium range weather forecasts reanalysis data set for the 1957 2002 period era 40 and a system centered method of tracking diagnostics the method tracks the anticyclonic systems and monitors their evolution along their paths thus allowing documentation of aspects that have been previously overlooked due to the common perception of anticyclones as semi stationary relatively uniform slowly evolving structures the anticyclonic signal is examined in a wide range of meteorological fields and at multiple levels over the continental masses over the subtropical ocean basins and over the sectors where blocking highs tend to develop structural features thermal and vorticity properties and mobility characteristics of the corresponding anticyclones are highlighted over continental regions an association with low level pools of cold air is found to be prevalent for the eurasian anticyclones but less so for the north american anticyclones in the subtropical zone the anticyclonic signal in the regions affected by the winter monsoon including southeastern asia and the western pacific features prominently in the upper levels in the eastern sectors of the subtropical ocean basins the anticyclonic signal is less deep intense anticyclonic development at low levels is also identified over the western sectors of the subtropical continents where it appears associated to the effect of orography and of low level cooling the dominant type of anticyclone observed in the regions of blocking is characterized by 5 6 days timescales and considerable eastward mobility

isotopic reconstructions of habitat change surrounding the extinction of sivapithecus a miocene hominoid in the siwalik group of pakistan abstract this research presents an isotopic study of a wide range of mammalian taxa from the miocene siwalik group of pakistan with a focus on two time intervals 9 3 9 2 ma when the hominoid sivapithecus was present and 8 1 8 0 ma shortly after sivapithecus became extinct the purpose of this investigation is to reconstruct the vegetation mosaic at both time levels in order to determine what sivapithecus habitat was like and what changes in habitat and climate may have taken place by the time sivapithecus went extinct both carbon and oxygen stable isotopes were sampled from inorganic carbonate in tooth enamel results indicate a vegetation mosaic of both closed and open habitat at both time intervals but a decrease in forest accompanied by an increase in open habitat including c 4 grasses during the younger interval individuals from many species cluster with each other with respect to both carbon and oxygen isotope values indicating a spectrum of feeding adaptations exploiting different parts of the habitat isotopic values for sivapithecus suggest that it fed in the forest upper canopy taxa feeding in the most closed wet habitat become extinct by 8 1 ma furthermore higher 18 o values over time suggest a change in climate with a reduction in annual rainfall perhaps accompanied by changes in precipitation sources or rainfall regime as well these results suggest that forests became fragmented over time while still present in the younger level much of the forest was replaced by open habitat including patches of c 4 grass forest loss and fragmentation is a likely cause of the extinction of sivapithecus

magnetostratigraphy of the miocene chiang muan formation northern thailand implication for revised chronology of the earliest miocene hominoid in southeast asia abstract a paleomagnetic study has been conducted on the miocene chiang muan formation in northern thailand in order to provide a chronology for the earliest large bodied miocene hominoid in southeast asia the chiang muan formation is mainly composed of clay silt and sand beds indicating lacustrine and fluvial environments paleomagnetic samples were collected from 124 horizons along an approximately 150 m thick section from the chiang muan formation at the opencast chiang muan mine rock magnetic experiments and stepwise thermal demagnetizations revealed that the main carrier of the magnetization of the sediments is magnetite and the samples have stable magnetization exceptionally stable magnetization is also carried by hematite which is represented by red colored sediments characteristic remanent magnetization chrm directions calculated by the principal component analysis revealed normal or reversed polarities of magnetization which allow the application of the reversal test of mcfadden and mcelhinny mcfadden p l mcelhinny m w 1990 classification of the reverse test in paleomagnetism geophys int 103 725 729 the mean paleomagnetic directions of the normal and reversed polarities passed the reversal test with a classification c indicating that the chiang muan formation preserved the primary magnetization in total five normal and four reversed polarity zones are recognized from the studied section based on paleontological age constraints this magnetostratigraphic column of the chiang muan formation correlates best with chron c5aan c5n of the geomagnetic polarity time scale gpts from the geological time scale gts2004 developed by gradstein et al gradstein f ogg j smith a eds 2004 a geological time scale 2004 cambridge univ press cambridge uk p 589 this correlation revealed that sedimentation of the chiang muan formation began approximately at 13 ma and continued until 9 8 ma with a mean sedimentation rate of approximately 4 2 cm ky the age of the earliest southeast asian hominoid is between 12 4 and 13 0 ma

the planetary and synoptic scale interactions in a southeast pacific blocking episode using pv diagnostics abstract the synoptic and planetary scale forcing in two blocking anticyclones occurring over the southeast pacific ocean was examined using potential vorticity diagnostics while many studies have examined the dynamic and thermodynamic forcing associated with blocking events in the northern hemisphere nh very few studies have examined blocking in the southern hemisphere sh climatological analysis suggests sh blocking events in the pacific region have similar characteristics to their nh counterparts however the occurrence of blocking is rare elsewhere in the sh and these events are relatively short lived some studies of nh blocking dynamics have also shown that the extent to which the planetary and synoptic scale and planetary synoptic scale interaction forcing that contribute to the genesis and maintenance of pacific and atlantic region events can be different thus a study of the relevant atmospheric dynamics associated with blocking events in the sh was carried out in order to determine wh

severe heat waves in southern australia synoptic climatology and large scale connections this paper brings a new perspective on the large scale dynamics of severe heat wave hw events that commonly affect southern australia through an automatic tracking scheme the cyclones and anticyclones associated with hws affecting melbourne adelaide and perth are tracked at both the surface and upper levels producing for the first time a synoptic climatology that reveals the broader connections associated with these extreme phenomena the results show that a couplet or pressure dipole formed by transient cyclones and anticyclones can reinforce the hw similarly to what is observed in cold surges cs with an obvious opposite polarity our results show that there is a large degree of mobility in the synoptic signature associated with the passage of the upper level ridges before they reach australia and the blocking is established with hw associated surface anticyclones often initiating over the west indian ocean and decaying in the eastern pacific in contrast to this result the 500 hpa anticyclone tracks show a very small degree of mobility responding to the dominance of the upper level blocking ridge an important feature of hws is that most of the cyclones are formed inland in association with heat troughs while in cs the cyclones are typically maritime often explosive associated with a strong cold front hence the influence of the cyclone is indirect contributing to reinforce the blocking ridge through hot and dry advection on the ridge s western flank additional insights are drawn for the record adelaide case of march 2008 with fifteen consecutive days above 35 c breaking the previous record by 7 days sea surface temperatures suggest a significant air sea interaction mechanism with a broad increase in the meridional temperature gradient over the indian ocean amplifying the upstream rossby waves that can trigger hw events a robust cooling of the waters close to the australian coast also contributes to the maintenance of the blocking highs locally which is a fundamental ingredient to sustain the hws

a diagnosis of two blocking events that occurred simultaneously in the midlatitude northern hemisphere using the goddard laboratory for atmospheres goddard earth observing system 1 analyses the horizontal distribution of atmospheric forcing processes involved in the growth maintenance and decay of two northern hemisphere midlatitude blocking anticyclones that occurred simultaneously were examined with the goal of determining whether there was a dynamic connection between the two cases the complete form of the zwack okossi equation which is a generalization of the petterssen sutcliffe development equation was used as the primary diagnostic tool the basic analyses were partitioned into their planetary scale and synoptic scale components noninteraction 500 hpa height tendencies as well as scale interaction 500 hpa height tendencies based on the results of this diagnosis there was no dynamic connection between these blocking anticyclones this result agrees with findings of other studies based on a statistical analysis of simultaneous blocking these results also imply that blocking may be a local phenomenon the diagnostic results from these blocking events were in many respects similar to those of previous studies however some key differences were found for example it was found here that for both mode 2 blocking events temperature advection was an important mechanism in block formation earlier results showed vorticity advection as the primary atmospheric forcing process in block formation for a mode 1 block also the scalepartitioned results show that upstream cyclones contributed to block formation and intensification in these events directly through the synoptic scale component often with the support of the interaction component of the total forcing earlier scale partitioned results showed that the interaction component of the total forcing was most important in the formation of a mode 1 block

bidimensional diagnostics variability and trends of northern hemisphere blocking abstractin this paper northern hemisphere winter blocking is analyzed through the introduction of a set of new bidimensional diagnostics based on geopotential height that provide information about the occurrence the duration the intensity and the wave breaking associated with the blocking this analysis is performed with different reanalysis datasets in order to evaluate the sensitivity of the index and the diagnostics adopted in this way the authors are able to define a new category of blocking placed at low latitudes that is similar to midlatitude blocking in terms of the introduced diagnostics but is unable to divert or block the flow furthermore over the euro atlantic sector it is shown that it is possible to phenomenologically distinguish between high latitude blocking occurring over greenland north of the jet stream and dominated by cyclonic wave breaking and the traditional midlatitude blocking localized over europe and driven by anticyclonic wave breaking these latter events are uniform

austral summer foehn winds over the mcmurdo dry valleys of antarctica from polar wrf foehn winds are a prominent feature of the mcmurdo dry valleys mdvs climate and are responsible for periods of strong winds and warming the foehn mechanism determined from a case study presented in earlier work is shown here to be robust for a set of the mdvs summer foehn events over the 1994 2009 period using output from the polar weather research and forecasting model polar wrf gap flow south of the mdvs is evidenced by the positive relationship between the pressure gradient and near surface wind speed along the gap subsequently mountain waves are generated and result in adiabatic warming and the downward transport of warm air into the mdvs and differences in mountain wave characteristics depend on the ambient wind direction and the degree of flow nonlinearity pressure driven channelling then brings warm foehn air downvalley although a large range of synoptic scale circulation patterns can drive foehn events the warmest foehn events are typically associated with blocking highs over the australian sector of the southern ocean leading to warm air advection over continental antarctica the episodic nature of foehn events and the tenuous connections between such events and interannual modes of climate variability suggests that intraseasonal variability may be more important for determining their frequency and magnitude the extraordinarily warm austral summer of 2001 2002 across antarctica shows that advection of warm maritime air into the continental interior and strong flow aloft result in warm foehn conditions and significant melt for the mdvs

drivers of decadal variability in the tasman sea in this study we compare optimally interpolated monthly time series tasman sea xbt data and a comprehensive set of ocean data assimilation models forced by atmospheric reanalysis to investigate the stability of the tasman sea thermocline and the transport variability of the east australian current eac the tasman front and eac extension we find that anomalously weaker eac transport at 25 s corresponds to an anomalously weaker tasman front and anomalously stronger eac extension we further show that post about 1980 and relative to the previous 30 years the anomalously weaker eac transport at 25 s is associated with large scale changes in the tasman sea specifically stronger stratification above the thermocline larger thermocline temperature gradients and enhanced energy conversion significant correlations are found between the maria island station sea surface temperature sst variability and stratification thermocline temperature gradient and baroclinic energy conversion suggesting that nonlinear dynamical responses to variability in the basin scale wind stress curl are important drivers of decadal variability in the tasman sea we further show that the stability of the eac is linked via the south caledonian jet to the stability of the pan basin subtropical south pacific ocean storm track

effects of changing environments on siwalik rodent faunas of northern pakistan abstract fossil assemblages from the siwalik group collected over the past six years reveal the development of the modern rodent fauna of the potwar plateau pakistan the history of the potwar rodent fauna proceeds through four stages 1 extinction of archaic elements by 9 ma 2 faunal turnover around 7 ma by phyletic evolution immigration and local extinction 3 attainment of modern grade at about the pliocene pleistocene boundary and 4 increase in abundance of desert forms and agricultural pests probably associated with man and overgrazing

an isotopic study of a fluvial lacustrine sequence the plio pleistocene koobi fora sequence east africa stable isotopic analyses of plio pleistocene and modern sediments in the fluvial lacustrine system occupying the turkana basin east africa provide constraints on the paleoenvironmental and diagenetic histories of the pliocene through the recent sediments in the basin the 13c values for carbonates in lacustrine sediments range from 15 to 22 relative to pdb depending on the varying proportions of co2 from the atmospheric reservoir and from various metabolic sources the 18o values of carbonates in lacustrine sediments indicate that the isotopic composition of paleolake water varied by over 10 from the pliocene to the present the 13c values for pedogenic carbonates record paleoccologic variations and suggest that c4 plants did not become well established in the preserved depositional parts of the basin until about 1 8 myr ago the 18o values pedogenic carbonates suggest a range of over 10 for the isotopic composition of soil water during this interval they also suggest a period of major climatic instability from about 3 4 to 3 1 myr and at about 1 8 myr together the 13c and 18o values of pedogenic carbonates indicate that the present conditions are as arid and hot as any that had prevailed during deposition of these plio pleistocene sediments

the role of amundsen bellingshausen sea anticyclonic circulation in forcing marine air intrusions into west antarctica persistent positive 500 hpa geopotential height anomalies from the ecmwf era interim reanalysis are used to quantify amundsen bellingshausen sea abs anticyclonic event occurrences associated with precipitation in west antarctica wa we demonstrate that multi day minimum 3 day duration anticyclones play a key role in the abs by dynamically inducing meridional transport which is associated with heat and moisture advection into wa this affects surface climate variability and trends precipitation rates and thus wa ice sheet surface mass balance we show that the snow accumulation record from the roosevelt island climate evolution rice ice core reflects interannual variability of blocking and geopotential height conditions in the abs ross sea region furthermore our analysis shows that larger precipitation events are related to enhanced anticyclonic circulation and meridional winds which cause pronounced dipole patterns in air temperature anomalies and sea ice concentrations between the eastern ross sea and the bellingshausen sea weddell sea as well as between the eastern and western ross sea

a unified three dimensional instability theory of the onset of blocking and cyclogenesis abstract the instability characteristics of three dimensional flow typical of the northern hemisphere average winter troposphere are examined in a two layer spherical quasigeostrophic model the properties of the four fastest growing small amplitude disturbances that develop on the basic state have been analyzed for three cases case 1 2a and 3 having increasingly larger static stability parameters for case 1 the fastest growing disturbance mode which is propagating eastward rather rapidly has a monopole cyclogenesis structure with maximum amplitudes slightly downstream of the jetstream maxima in the pacific ocean and off the cast coast of north america comparisons of streamfunctions squared and momentum and heat fluxes with bandpass filtered observations for transient eddies which pick out the developing storms are quite reasonable considering that a two layer model is used and the contributions from individual linear modes are considered for case 2a the fastest growing mode has large scale hi

the interactions between a midlatitude blocking anticyclone and synoptic scale cyclones that occurred during the summer season abstract using the goddard laboratory for atmospheres goddard earth observing system 5 yr analyses and the zwack okossi equation as the diagnostic tool the horizontal distribution of the dynamic and thermodynamic forcing processes contributing to the maintenance of a northern hemisphere midlatitude blocking anticyclone that occurred during the summer season were examined during the development of this blocking anticyclone vorticity advection supported by temperature advection forced 500 hpa height rises at the block center vorticity advection and vorticity tilting were also consistent contributors to height rises during the entire life cycle boundary layer friction vertical advection of vorticity and ageostrophic vorticity tendencies during decay consistently opposed block development additionally an analysis of this blocking event also showed that upstream precursor surface cyclones were not only important in block development but in block maintenance as well in partitioning the basic data

a new look for the southern hemisphere jet stream a new jet stream description defined as the geostrophic streamline of maximum average velocity is proposed an objective algorithm for detecting and tracking the jet has been developed tested and applied to the ncep ncar 200 hpa geopotential height in the southern hemisphere for the period 1958 2002 the results show the variability of the double character of the southern hemisphere jet with a marked seasonality during the warm season a single jet can be found around 40 s while autumn and winter are characterized by a clear double jet structure with a strong and dominant subtropical jet located around 30 s and a polar front jet progressively displaced toward southern latitudes and reaching 60 s by the end of the cold season in general a trend toward slower subtropical jets and stronger polar front jets has been detected during the study period the southern annular mode appears as a main modulator of the latitude and strength of the polar front jet influencing to a minor extent its subtropical counterpart the enso cycle strongly modifies the latitude and specially the strength of the subtropical jet affecting its preferred wavenumber as well nevertheless the effect of this oscillation seems fairly restricted in the pacific thus limiting the ability of this jet to drive the el nino teleconnections along the southern hemisphere the consistency of the results when compared with previous jet climatologies suggests that the new approach is a reliable jet tracking method thus providing a new tool to analyze climatic variability at hemispheric scales

a diagnosis of a long lasting blocking event over the southeast pacific ocean abstract a long lasting blocking event occurred over the southeast pacific ocean near the west coast of south america from 29 july through 14 august 1986 this blocking happened in a recently found new region of blocking in the southeast pacific during the blocking event the transient eddies were forced to move to the north and south of the blocking this caused precipitation over south america to increase to the north of the blocking high and diminish over southern south america the blocking event is analyzed in detail and its impact on the winter general circulation is discussed change in amplitude of several wavenumbers and the zonal wind zero wavenumber suggest that the blocking event is essentially a local phenomenon since transient eddies are prevented from moving through the blocking high the variance of meridional wind is small however the variance of geopotential height is maximized because of the persistence of the block this signature of the blocking on the general circulation is simil

teleconnection between the north indian ocean high swell events and meteorological conditions over the southern indian ocean the link between north indian ocean nio high swell events and the meteorological conditions over the southern indian ocean sio is explored in this article using a combination of in situ measurements and model simulations for the year 2005 high waves without any sign in the local winds sometimes cause severe flooding events along the south west coast of india locally known as the kallakkadal events and cause major societal problems along the coasts in situ observations report ten high swell events in nio during 2005 our study confirm that these events are caused by the swells propagating from south of 30 s in all cases 3 5 days prior to the high swell events in nio we observed a severe low pressure system called the cut off low col in the southern ocean these cols are quasi stationary in nature providing strong 25 ms 1 and long duration 3 days surface winds over a large fetch essential conditions for the generation of long period swells the intense equator ward winds associated with cols in the sio trigger the generation of high waves which propagate to nio as swells furthermore these swells cause high wave activity and sometimes kallakkadal events along the nio coastal regions depending on the local topography angle of incidence and tidal conditions our study shows that such natural hazards along the nio coasts can be forecasted at least 2 days in advance if the meteorological conditions of the sio are properly monitored this article is protected by copyright all rights reserved

a midlatitude climatology and interannual variability of 200 and 500 hpa cut off lows abstracta climatology of midlatitude 200 and 500 hpa cut off low systems in the northern and southern hemispheres is constructed from the ncep ncar reanalysis by detecting and tracking under one

contrasting relationship between wintertime blocking highs over europe siberia and temperature anomalies in the yangtze river basin abstractbased on the japanese 55 year reanalysis dataset this study identifies 92 europe siberia blocking high events esbs over the 60 winters november to march from 1958 1959 to 2017 2018 ac

synoptic climatology of 500 mb circulation changes during explosive cyclogenesis abstract changes in the 500 mb circulation are examined near and during each of 141 explosive surface cyclogenesis cases during the period 1 september 1980 through 31 may 1987 june through august excluded over the western half of the northern hemisphere two types of circulation changes evident in the geopotential height fields are investigated 1 amplification of 500 mb troughs and or ridges in which the explosively deepening cyclones bombs are imbedded and 2 formation of 500 mb cyclones closed lows or anticyclones closed highs near the bombs by either stratification most bombs in the sample are found not to be associated with nearby 500 mb circulation changes on the time scale of the explosive deepening relatively weak bombs are more likely to be associated with identifiable circulation changes than those which are moderate or strong antecedent conditions for the bomb related circulation changes are examined for example bombs associated with 500 mb trough ridge amplifications are conne

a time framework based on magnetostratigraphy for the siwalik sediments of the khaur area northern pakistan the magnetostratigraphy of eleven new sections in the khaur area of northern pakistan is presented all specimens have been subjected to thermal demagnetization the sections taken in adjacent ravines incising the siwalik formations nearly penpendicular to strike form a temporal framework in which to interpret the biological and lithological information a composite section is constructed from several long sections and is correlated to the magnetic polarity time scale chron 6 to chron 15 providing absolute age information for the biostratigraphic zonations of barry et al 1982 detailed sections along the strike of major stratigraphic marker beds document an isochronous horizon and form the basis for paleoenvironmental reconstructions the preservation of a polarity transition in fluvial sediments suggests continuity of sedimentation on a time scale of 103 104 years

paleontological view of the ages of the deccan traps the cretaceous tertiary boundary and the india asia collision volcanism in the deccan traps of india occurred over at most three magnetic chrons centered on a main reversed chron paleontological data indicate that this reversed chron must coincide with 29r which contains the cretaceous tertiary k t boundary recent 40 ar 39 ar data may therefore provide one of the best estimates of the absolute age of the k t boundary 65 7 2 0 ma moreover the eurasian character of k t boundary terrestrial faunas in india suggests that this was also close to the time of india asia collision this is significantly earlier than generally recognized and implies about 4000 km of continental shortening in the collision zone probably absorbed jointly by crustal thickening and strike slip extrusion

growth of planetary crusts the planets and satellites of the solar system show much diversity but most have formed crusts which differ substantially from their bulk compositions three principal types of crust may be broadly distinguished primary formed after accretional heating e g lunar highlands secondary formed following partial melting in planetary mantles e g lunar maria terrestrial oceanic crust and tertiary formed by processing of secondary crusts of which the continental crust of the earth is the only identifiable example crustal growth before 3800 m y was complicated by the heavy planetesimal bombardment active erosion on the earth is likely to have destroyed the brecciated rubble resulting from over 200 mare orientale scale events in this period the mercurian crust is probably primary perhaps analogous to the lunar highlands in contrast the observable martian and venusian crusts are secondary dominated by basaltic volcanism the icy crusts of the satellites of the outer planets are mixtures of both primary and secondary crusts with complex histories ganymede is of special interest in displaying a secondary grooved terrain water ice crust which has split an older more heavily cratered possibly primary crust slight expansion has resulted probably from polymorphic transitions from high density ice viii to low density ice i the primary lunar crust 12 of lunar volume grew in 108 years secondary crusts derived by partial melting of mantles grow at a much slower rate total production of terrestrial oceanic crust over 4000 m y is only 2 of planetary volume whereas terrestrial continental crustal growth is even slower producing over the same period a volume only about 0 33 that of the earth crustal growth on the other planets appears to be an irreversible process without evidence of recycling no evidence for massive planetary expansion as required by expanding earth hypotheses is apparent on the other planets or satellites of the solar system

evolution and variability of the asian monsoon system state of the art and outstanding issues the asian monsoon is comprised of the indian and east asian subsystems these two components are linked to one another in varying degrees by regions of strong sensible heating indo asian landmass and strong latent heat export the western pacific warm pool and the southern subtropical indian ocean variability within the indian and east asian subsystems interactions among them and the extent to which they interact with other climate phenomena e g enso are current topics of modern and paleoclimate research this work provides an overview of past and current paleomonsoon research on tectonic to interannual time scales with a primary focus on marine sediment records while past and current work has contributed greatly to our understanding of paleomonsoon variability at all time scales additional efforts are required to make further progress in two critical areas 1 additional efforts are needed in terms of proxy development and evaluation requiring concerted efforts at long term sediment trap deployments in key monsoon influenced regions as well as development of adequate and widely available core top databases these are necessary to assess the impact of modern oceanographic and seafloor processes on potential monsoon proxies 2 additional effort is also needed in acquiring a sufficient geographic distribution of downcore records to assess linkages among the subsystems and their role in the context of extratropical climate change these records should have high sedimentation rates including varved sections this requires substantial survey support to identify the most appropriate coring and drilling targets c 2004 elsevier ltd all rights reserved