stationary rossby wave propagation in a baroclinic atmosphere observational studies of teleconnections in both soisticial seasons have suggested various patterns of behaviour linked mainly to westerly jets and equatorial westerlies these have been interpreted using barotropic rossby wave theory and simulated using stationary forcing in barotropic models linearized about 300 hpa flows in this paper the relevant propagation behaviour is investigated using a baroclinic model with three dimensional climatological basic states time integrations are performed using localized thermal forcing as a wavemaker the propagation results are qualitatively very similar to those obtained with the barotropic model though there are quantitative differences the westerly jets still act as strong waveguides the shorter wavelengths and smaller wave activity speeds found with the baroclinic model are generally in better agreement with observation propagation into and from the upper tropospheric equatorial westerlies in the east pacific propagation across north america and propagation from europe across the arabian gulf are all found the extent to which upper tropospheric westerlies reach towards the equator influences the propagation into those regions barotropic models can only represent such behaviour if the basic state reflects the near equatorial upper tropospheric zonal wind structure

geomagnetic field intensity between 70 000 and 130 000 years b p from a volcanic sequence on la reunion indian ocean abstract a detailed paleointensity study was made of a sequence of 70 successive lava flows of the piton des neiges volcano on the island of la reunion indian ocean radiometric dating brackets the age of this sequence between 130 3 ka and 72 3 ka rock magnetic investigations show that titanomagnetites in the pseudo single domain range are the main magnetic carrier of the natural remanent magnetisation nrm over 350 samples were used for paleointensity determinations carried out with the thellier method in vacuum or in an argon atmosphere of these 89 samples yielded reliable results with within flow scatter often lower than 20 these results indicate that the geomagnetic field intensity has varied at la reunion between 13 and 65 t during the period of time explored the average value 42 t is higher than the present field at la reunion 35 t the results from the upper part of the section are consistent with previous results obtained for the 82 98 ka period also at la reunion 1 and document a broad low around 95 ka not associated with large directional changes on a larger geographic scale the paleointensity values from la reunion are significantly higher than those obtained from mount etna 2 precise comparison is however difficult because of the lack of detail in the etna results in the lower part of the section a marked intensity low coinciding with significant deviation from the dipole field direction is observed at 115 ka and could correspond to the end of the blake event

tectonometamorphic evolution of the himalayan metamorphic core between the annapurna and dhaulagiri central nepal the metamorphic core of the himalaya in the kali gandaki valley of central nepal corresponds to a 5 km thick sequence of upper amphibolite facies metasedimentary rocks this greater himalayan sequence ghs thrusts over the greenschist to lower amphibolite facies lesser himalayan sequence lhs along the lower miocene main central thrust mct and it is separated from the overlying low grade tethyan zone tz by the annapurna detachment structural petrographic geothermobaro metric and thermochronological data demonstrate that two major tectonometamorphic events charac terize the evolution of the ghs the first eohimalayan episode included prograde kyanite grade metamorphism during which the ghs was buried at depths greater than c 35 km a nappe structure in the lowermost tz suggests that the eohimalayan phase was associated with underthrusting of the ghs below the tz a c 37 ma 40ar 39ar hornblende date indicates a late eocene age for this phase the second neohimalayan event corresponded to a retrograde phase of kyanite grade recrystallization related to thrust emplacement of the ghs on the lhs prograde mineral assemblages in the mct zone equilibrated at average t 880 k 610 c and p 940 mpa 35 km probably close to peak of meta morphic conditions slightly higher in the ghs final equilibration of retrograde assemblages occurred at average t 810 k 540 c and p 650 mpa 24 km indicating re equilibration during exhumation controlled by thrusting along the mct and extension along the annapurna detachment these results suggest an earlier equilibration in the mct zone compared with higher levels as a consequence of a higher cooling rate in the basal part of the ghs during its thrusting on the colder lhs the annapurna detachment is considered to be a neohimalayan synmetamorphic structure representing extensional reactivation of the eohimalayan thrust along which the ghs initially underthrust the tz within the upper ghs a metamorphic discontinuity across a mylonitic shear zone testifies to significant late to post metamorphic out of sequence thrusting the entire ghs cooled homogeneously below 600 700 k 330 430 c between 15 and 13 ma middle miocene suggesting a rapid tectonic exhumation by movement on late extensional structures at higher structural levels

calculated mineral equilibria in the pelite system kfmash k 2 o feo mgo al 2 o 3 sio 2 h 2 o

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

relative changes of the geomagnetic field intensity during the last 280 kyear from piston cores in the acores area abstract relative changes in geomagnetic field intensity over the last 280 kyears have been recovered from the study of three marine cores from the acores area one core was precisely dated by oxygen isotope study and the other two records were linked to it using light reflectance analysis which allowed precise correlation rock magnetic analysis shows that the main magnetic mineral is magnetite with a very homogeneous grain size distribution in the pseudo single domain range for the three cores changes in the amount of magnetite do not exceed a factor of 10 therefore these cores appear to be suitable for relative palaeointensity determinations two mineral magnetic components with periodicities of 23 and 18 kyears are present in the records of bulk magnetic parameters and natural remanent magnetisation nrm but the power at these frequencies is not significant at the 95 level for the normalised remanence records for each core normalisation of the nrm using different normalising parameters yields virtually identical results using saturation isothermal remanent magnetisation sirm as the normalising parameter the results of the three cores were then combined into a stacked curve squared coherence analysis between this stacked curve and bulk mineral magnetic parameters reveals that the 18 kyear component is still present in the record but that the power spectrum is barely above noise level at this frequency some of the features of this north atlantic record are consistent with the main characteristics already documented in other sedimentary or volcanic records for instance distinct periods of low intensity are observed around 40 120 and 190 kyears and periods of high intensity at 50 and 80 kyears because of the uniformity of the mineral magnetic characteristics of the three cores we suggest that this record may be a suitable palaeointensity reference curve for the central north atlantic ocean region

structural and metamorphic control on the exhumation of high p granulites the carvalhos klippe example from the oriental andrelândia nappe system southern portion of the brasilia orogen brazil abstract high pressure granulites are formed within the lowermost continental crust if exhumation is driven only by erosion these granulites will remain at their site of formation indefinitely their exposure then requires a complex process in this study the andrel ndia nappe system is used to investigate the formation and exhumation of high pressure granulites related to subduction collision extrusion processes this nappe system is part of the southern portion of the neoproterozoic brasilia orogen in brazil which comprises a pile of syn metamorphic rootless nappes in which high pressure granulites are an important constituent the andrel ndia nappe system is thrusted by a magmatic arc allochthon and it overrides the allochthonous passive margin that is represented by rocks of the carrancas nappe system metamorphism within the andrel ndia nappe system presents an inverted pattern that varies from top to bottom and from granulite to amphibolite facies conditions under a high pressure regime the carvalhos klippe is part of the uppermost nappe and is located 60 km ahead of its original allochthon this klippe is composed of rutile kyanite garnet k feldspar granulites and it displays ternary feldspars and associated mafic granulites that in turn contain garnet clinopyroxene plagioclase quartz as a peak mineral assemblage both granulite types crystallized at a higher pressure than the rocks within the orthopyroxene stability field the kyanite bearing granulites show a clockwise p t path which is inferred from reaction textures and thermobarometry peak conditions were attained at 825 c and 12 kbar at 617 7 1 3 ma which is determined by an id tims analysis of monazite the convergent kinematic flow of the klippe was directed eastward then northeastward and finally changed northward to northeastward which is contemporaneous with extension and thinning under high temperature conditions melt filled dilation shear zones were observed and the melt worked as a lubricant within the shear zones facilitating granulite exhumation extrusion

normalised natural remanent magnetisation intensity during the last 240 000 years in piston cores from the central north atlantic ocean geomagnetic field intensity or environmental signal we have examined in detail the stratigraphic variations in magnetic parameters of four cores from the north atlantic ocean in areas where the depositional environment has varied with climatic changes our objective is to assess whether normalisation of the natural remanent magnetisation nrm intensity can cancel the effect of climatically induced variations in magnetic mineral content and grain size and whether a reliable record of relative changes in geomagnetic field intensity can be obtained after selecting the core sections which meet published criteria for paleointensity normalisation we have attempted to obtain a record of the geomagnetic field intensity variations over the past 240 kyear using both arm and irm as normalising factors for the nrm the two methods yield overall similar results except for the interval 20 30 kyear where irm normalisation yields a record more consistent with previous sedimentary and volcanic results than does the more frequently employed arm normalisation the final intensity record docmments a picture of the dipole field moment which presents large similarities with profiles obtained from sediments deposited in different environmental conditions in various regions around the world we observe a major low at about 42 kyear which could correspond to the laschamp event a broad low in the interval 90 130 kyear possibly connected to the blake event and another low at about 190 kyear which could reflect the biwa i event the processes of acquisition of depositional and postdepositional remanent magnetisation and the physics of the normalising methods are still insufficiently understood however these results obtained from a region characterised by complex environmental dynamics confirm the potential of sedimentary deep sea cores for relative paleointensity determinations

terrane accretion and upward extrusion of high pressure granulites in the neoproterozoic nappes of southeast brazil petrologic and structural constraints the high grade crystalline nappes exposed southeast of the sao francisco craton comprise two distinct units of mainly granulite facies rocks that represent a composite section of neoproterozoic deep continental crust the socorro guaxupe nappe above derived from an arc terrane and the tres pontas varginha nappe below metamorphism in the tres pontas varginha nappe is characterized by the exceptional preservation of kyanite granulites 700 750 c 15 kbar and followed by limited retrogression maximum temperatures around 900 950 c were reached toward the base of the overlying socorro guaxupe nappe during the intrusion of charnockitic mangeritic magmas lower pressure metamorphism accompanied by anatexis prevailed at shallower crustal levels our petrological results document an inverted thermal structure with isobaric heating of the top of the high pressure granulite nappe both granulite nappes were transported more than 200 km eastward above lower nappes involving reworked basement and passive margin units both metamorphosed to high pressure but lower temperature conditions significant thinning and cooling of the two granulite nappes may have occurred before their emplacement onto the lower nappes the proposed geodynamic scenario considers that continental subduction took place westward underneath neoproterozoic oceanic lithosphere the two granulite units crystallised at 45 km depths under distinct paleogeotherms within this subduction zone around 630 ma the kyanite granulites were rapidely exhumed through the mechanism of low angle forced extrusion whereas syncollisional collapse affected the soft anatectic middle crust of the overlying arc terrane the final emplacement of the thinned nappe pile onto the cold sao francisco craton and its platform cover with at most anchizonal to greenschist facies metamorphism occurred around 600 ma

deep subduction and rapid exhumation role of crustal strength and strain weakening in continental subduction and ultrahigh pressure rock exhumation 1 the exhumation of crustal ultra high pressure uhp material depends on temporal and spatial variations in its detachment within the subduction channel this dependence is investigated using numerical models with variable initial crustal strengths representing a range of initial crustal compositions and parameterized strain weakening representing a range of processes that reduce effective crustal viscosity during deformation competition between down channel shear traction favoring subduction and up channel buoyancy favoring exhumation is expressed as the exhumation number e which can vary with time and position along the channel exhumed lower strength crust which resists subduction owing to weak down channel traction records peak conditions 38 kbar given sufficient strain weakening exhumation proceeds at 60 km ma 1 indicating that buoyancy e 1 drives exhumation in these models in all models exhuming uhp material forms a deforming ductile plume with a range of possible structural relationships predicted between exhumed uhp and hp materials

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

the grenville orogen explained applications and limitations of integrating numerical models with geological and geophysical data numerical models offer powerful insights into tectonic processes especially when their validity can be tested against geological and geophysical observations from natural orogenic belts here we explain some of the criteria for success in integrating orogenic models with data using examples from the grenville orogen model designs must be simplified by comparison with nature to illuminate the first order processes that control orogenic evolution which limits the extent to which model results can reproduce geological observations for the western grenville orogen observed variations in geological properties are represented by lower crustal blocks with strength decreasing from the exterior to the interior of the model go series models with this design reproduce the first order crustal architecture of the georgian bay and montreal val d or lithoprobe transects both constant convergence and stop convergence models produce similar geometries but only stop convergence models produce normal sense shear

tropospheric precursors of anomalous northern hemisphere stratospheric polar vortices regional extratropical tropospheric variability in the north pacific and eastern europe is well correlated with variability in the northern hemisphere wintertime stratospheric polar vortex in both the ecmwf reanalysis record and in the whole atmosphere community climate model to explain this correlation the link between stratospheric vertical eliassen palm flux variability and tropospheric variability is analyzed simple reasoning shows that variability in the north pacific and eastern europe can deepen or flatten the wintertime tropospheric stationary waves and in particular its wavenumber 1 and 2 components thus providing a physical explanation for the correlation between these regions and vortex weakening these two pathways begin to weaken the upper stratospheric vortex nearly immediately with a peak influence apparent after a lag of some 20 days the influence then appears to propagate downward in time as expected from wave mean flow interaction theory these patterns are influenced by enso and october eurasian snow cover perturbations in the vortex induced by the two regions add linearly these two patterns and the quasi biennial oscillation qbo are linearly related to 40 of polar vortex variability during winter in the reanalysis record

synconvergent ductile flow in variable strength continental crust numerical models with application to the western grenville orogen 1 we present results from numerical models for a convergent orogen with laterally variable lower crustal strength representing a simplified orogenic system in which a strong craton flanked by progressively weaker terranes collides with another continent with progressive convergence crustal thickening and thermal relaxation lower crust becomes decoupled from upper and middle crust forming a ductile orogenic infrastructure beneath a stronger superstructure collision with strong external crust results in uplift and expulsion of ductile nappes from the orogenic core creating allochthonous terranes overlying a lower crustal indentor the extent of transport and exhumation of lower crustal nappes over the indentor reflects the amount of convergence and the erosion rate the western grenville orogen displays across strike variations in age tectonic history and protolith association suggesting a systematic variation in precollision crustal strength the laurentian craton margin and accreted terranes were variably reworked at synorogenic depths of 25 35 km during the ottawan orogeny deformation propagated from younger monocyclic rocks in the southeast into older polycyclic rocks flanking the craton on the northwest a comparison between numerical model results and crustal scale cross sections from the georgian bay and montreal val d or transects shows close correspondence between crustal structure and model geometry this indicates that the models produce geologically realistic results and provides a context for interpreting the tectonic evolution of the western grenville orogen contrasts between the results of homogeneous channel flow models and the present ductile nappe models suggest that the effects of different styles of ductile flow can be distinguished in the geologic record

the time averaged geomagnetic field as recorded by lava flows over the past 5 myr summary a recently compiled lava flow data base spanning the last 5 million years is used to investigate properties of the time averaged geomagnetic field more than 90 per cent of the power in the palaeofield can be accounted for by a geocentric axial dipole however there are significant second order structures in the field declination and inclination anomalies for the new data base indicate that the main second order signal is the far sided effect and there is also evidence for non zonal structure vgp virtual geomagnetic pole latitude distributions indicate that over the last 5 million years normal and reverse polarity morphologies are different and that any changes in the normal polarity field morphology are undetectable given the present data distribution regularized non linear inversions of the palaeomagnetic directions support all these observations we test the hypothesis that zonal models for the time averaged field are adequate to describe the data and find that they are not non zonal models are needed to fit the data to within the required tolerance level normal and reverse polarity field models obtained are significantly different field models obtained for the brunhes epoch data alone are much smoother than those obtained from combining all the normal polarity data simulations indicate that these differences can be explained by the less extensive data distribution for the brunhes epoch the field model for all of the normal polarity data ln1 contains features observed in the historical field maps although the details differ ln1 suggests that although the two northern hemisphere flux lobes observed in the historical field are stationary to a first order approximation they do show changes in position and amplitude a third less pronounced flux lobe is observed in ln1 over central europe the lack of structure in the southern hemisphere is due in part to the paucity of data jackknife estimates of the field models for different subsets of the data suggest that a few sites contribute significant structure to the final field models more conservative estimates of the time averaged field morphology are obtained by removing these sites

decadal change of the spring snow depth over the tibetan plateau the associated circulation and influence on the east asian summer monsoon abstract the decadal change in the spring snow depth over the tibetan plateau and impact on the east asian summer monsoon are investigated using station observations of snow depth data and the ncep ncar reanalysis for 1962 93 during spring march april both the domain averaged snow depth index sdi and the first principal component of the empirical orthogonal function eof analysis exhibit a sharp increase in snow depth after the late 1970s which is accompanied by excessive precipitation and land surface cooling the correlation between sdi and precipitation shows a coherent remote teleconnection from the tibetan plateau northern india to western asia it is found that the increased snow depth over the plateau after the mid 1970s is concurrent with a deeper india burma trough an intensified subtropical westerly jet as well as enhanced ascending motion over the tibetan plateau additional factors for the excessive snowfall include more moisture supply associated with the intensification of the south

relation between eurasian snow cover snow depth and the indian summer monsoon an observational study abstract satellite derived snow cover data for 22 yr and snow depth data for 9 yr over eurasia have been analyzed to reexamine the possible relation of snow with the indian summer monsoon in contrast to the previous studies that use snow cover averaged over all of eurasia as a single number the frequency of occurrence of snow at each grid point over eurasia is correlated with the indian summer monsoon rainfall thus specific geographical regions over eurasia that are responsible for the well known inverse relationship between eurasian snow cover and indian monsoon rainfall are delineated it is found somewhat surprisingly that western eurasia is the only geographical region for which a significant inverse correlation exists between winter snow cover and subsequent summer monsoon rainfall however composites for high and low snow cover over eurasia show spatially homogeneous large scale patterns of snow cover and surface temperature anomalies winters of high and low snow cover for eurasia are found t

pseudo and real inverted metamorphism caused by the superposition and extrusion of a stack of nappes a case study of the southern brasilia orogen brazil the southern brasilia orogen is a neoproterozoic belt that occurs along the southernmost border of the sao francisco craton where the andrel ndia nappe system represents the subducted sedimentary domain and is divided into three allochthonous groups of which the ages and p t conditions of metamorphism are studied here the basal unit the andrel ndia nappe exhibits an inverted metamorphic pattern the base of the structure composed of staurolite garnet biotite kyanite quartz and muscovite marks the metamorphic peak whereas at the top the association of the metamorphic peak does not contain staurolite the liberdade nappe the middle unit presents a normal metamorphic pattern its base close to the andrel ndia nappe shows paragneiss with evidence of in situ partial melting and towards the top coarse grained staurolite schist is found the staurolite out and melt in isograds are coincident and parallel to the main foliation thus the shear zone that limits the nappes is syn metamorphic reheating the underlying andrel ndia nappe and influencing the establishment of metamorphic inversion this suggestion is supported by the monazite chemical ages which indicates that the andrel ndia nappe metamorphic peak 586 15 ma is younger than that of the liberdade nappe 622 3 7 6 ma the upper unit the serra da natureza klippe bears a typical high pressure granulite mineral assemblage that is composed of kyanite garnet k feldspar rutile and leucosome as well as a metamorphic peak at 604 5 6 1 ma this tectonic assembly with inverted and non inverted metamorphic patterns and generation of klippen structures is consistent with exhumation models and a strong indentor located in the lower continental crust

changes of the geomagnetic field vector obtained from lava sequences on the island of vulcano aeolian islands sicily abstract a combined geochronologic k ar and palaeomagnetic study has been conducted on five volcanic sections 70 flows on the island of vulcano the sections span the interval from 15 2 to 135 4 ka with large hiatuses rock magnetic investigations indicate that the natural remanent magnetisation nrm is carried by titanomagnetites in the four oldest sections with a contribution from high coercivity magnetic minerals in the youngest section palaeomagnetic directions obtained by thermal demagnetisation document a large magnetic excursion at around 110 ka with virtual geomagnetic poles vgps that lie over eastern siberia these directions may represent a volcanic record of the termination of the blake event only about 15 of the samples from 19 flows proved suitable for palaeointensity thellier and thellier determinations these measurements indicate that the geomagnetic field has varied at vulcano between 16 and 53 t in the explored time interval when combined with previous results obtained at mt etna for the period from 140 to 60 ka tric et al 1994 phys earth planet inter 85 113 129 these results document a broad low at around 115 ka the palaeointensity values from vulcano and etna are consistent with global values suggesting the presence of a dominant dipole field contribution these values on the other hand are significantly smaller than those recently obtained from la reunion in the southern hemisphere this suggests that large long lived non dipolar components of the geomagnetic field may be present at la reunion in the interval from 130 to 90 ka these observations are consistent with the fact that the vgp angular dispersion calculated from non excursional data is significantly smaller at vulcano than at la reunion

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

propagation of the arctic oscillation from the stratosphere to the troposphere geopotential anomalies ranging from the earth s surface to the middle stratosphere in the northern hemisphere are dominated by a mode of variability known as the arctic oscillation ao the ao is represented herein by the leading mode the first empirical orthogonal function of low frequency variability of wintertime geopotential between 1000 and 10 hpa in the middle stratosphere the signature of the ao is a nearly zonally symmetric pattern representing a strong or weak polar vortex at 1000 hpa the ao is similar to the north atlantic oscillation but with more zonal symmetry especially at high latitudes in zonal mean zonal wind the ao is seen as a north south dipole centered on 40 45 n in zonal mean temperature it is seen as a deep warm or cold polar anomaly from the upper troposphere to 10 hpa the association of the ao pattern in the troposphere with modulation of the strength of the stratospheric polar vortex provides perhaps the best measure of coupling between the stratosphere and the troposphere by examining separately time series of ao signatures at tropospheric and stratospheric levels it is shown that ao anomalies typically appear first in the stratosphere and propagate downward the midwinter correlation between the 90 day low pass filtered 10 hpa anomaly and the 1000 hpa anomaly exceeds 0 65 when the surface anomaly time series is lagged by about three weeks the tropospheric signature of the ao anomaly is characterized by substantial changes to the storm tracks and strength of the midtropospheric flow especially over the north atlantic and europe the implications of large stratospheric anomalies as precursors to changes in tropospheric weather patterns are discussed

how stationary is the relationship between siberian snow and arctic oscillation over the 20th century 1 both observational and numerical studies suggest that fall snow cover extent over eurasia is linked to subsequent winter variations in the predominant northern hemisphere teleconnection pattern known as the arctic oscillation ao the present study uses the recent 20th century reanalysis to explore the snow ao relationship over the entire 20th century for the first time 20th century reanalysis is first shown to have a consistently realistic simulation of the onset of the eurasian snow cover compared to a large number of in situ observations it is then used to explore the snow ao relationship over both the satellite and presatellite periods results show that this teleconnection is not stationary and did not emerge until the 1970s the possible modulation of the teleconnection by the quasi biennal oscillation is then discussed because it could have favored the influence of snow anomalies on the arctic oscillation in recent decades these results have important implications for seasonal forecasting and suggest in particular that statistical predictions of the wintertime ao should not be based on snow predictors alone

crustal flow modes in large hot orogens abstract crustal scale channel flow numerical models support recent interpretations of himalayan tibetan tectonics proposing that gravitationally driven channel flows of low viscosity melt weakened middle crust can explain both outward growth of the tibetan plateau and ductile extrusion of the greater himalayan sequence we broaden the numerical model investigation to explore three flow modes homogeneous channel flow involving laterally homogeneous crust heterogeneous channel flow involving laterally heterogeneous lower crust that is expelled and incorporated into the mid crustal channel flow and the hot fold nappes style of flow in which mid lower crust is forcibly expelled outward over a lower crustal indentor to create fold nappes that are inserted into the mid crust the three flow modes are members of a continuum in which the homogeneous mode is driven by gravitational forces but requires very weak channel material the hot fold nappe mode is driven tectonically by for example collision with a strong crustal indentor and can occur in crust that is subcritical for homogeneous flows the heterogeneous mode combines tectonic and gravitationally driven flows preliminary results also demonstrate the existence and behaviour of mid crustal channels during advancing and retreating dynamical mantle lithosphere subduction an orogen temperature magnitude t m diagram is proposed and the positions of orogens in t m space that may exhibit the flow modes are described together with the characteristic positions of a range of other orogen types

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

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

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

thermal model for the zanskar himalaya abstract crustal thickening along the northern margin of the indian plate following the 50 ma collision along the indus suture zone in ladakh caused widespread high temperature medium pressure barrovian facies series metamorphism and anatexis in the zanskar himalaya metamorphic isograds are inverted and structurally telescoped along the main central thrust mct zone at the base of the high himalayan slab along the zanskar valley at the top of the slab isograds are the right way up and are also telescoped along northeast dipping normal faults of the zanskar shear zone zsz which are related to culmination collapse behind the miocene himalayan thrust front between the mct and the zsz a metamorphic anatectic core within sillimanite grade rocks contains abundant leucogranite granite crustal melts of probable himalayan age a thermal model based on a crustal scale cross section across the zanskar himalaya suggests that m1 isograds developed during early himalayan barrovian metamorphism were overprinted during high grade mct related anatexis and folded around a large scale recumbent fold developed in the hanging wall of the mct

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

high precision geothermobarometry across the high himalayan metamorphic sequence langtang valley nepal one of the long recognized features of himalayan geology is the apparent inversion of metamorphic sequences as evidenced in both metamorphic parageneses and thermobarometric data with the aid of an extended thermobarometric dataset from the langtang valley section of the higher himalayan crystallines it can be demonstrated that the relatively large uncertainties associated with traditional thermobarometric techniques severely limit the tectonic interpretation of metamorphic gradients across the himalayas we apply the recently developed dpt approach which significantly improves the precision to which pressure and temperature diverences between samples may be calculated high precision thermo barometric data reveal an isothermal rather than inverted temperature array at langtang while the pressure data suggest significant structural complexity with the higher himalayan crystallines in the langtang section comprising two distinct possibly duplicated sequences each having experienced con siderable structural attenuation following metamorphism

on the three dimensional propagation of stationary waves abstract a locally applicable nonzonally averaged conservation relation is derived for quasi geostrophic stationary waves on a zonal flow a generalization of the eliassen palm relation the flux which appears in this relation constitutes it is argued a useful diagnostic of the three dimensional propagation of stationary wave activity this is illustrated by application to a simple theoretical model of a forced rossby wave train and to a northern hemisphere winter climatology results of the latter procedure suggest that the major forcing of the stationary wave field derives from the orographic effects of the tibetan plateau and from nonorographic effects diabatic heating and or interaction with transient eddies in the western north atlantic and north pacific oceans and siberia no evidence is found in the data for wave trains of tropical origin forcing by the orographic effects of the rocky mountains seems to be of secondary importance

diffusion controlled biotite breakdown reaction textures at the solid liquid transition in the continental crust two phase quartz intergrowths with garnet cordierite and tourmaline occur commonly in prograde high temperature migmatites granulites as well as in the last crystallization stages of biotite granites structural microtextural and mineralogical data show that they result from the breakdown of biotite in the presence of a melt phase associated with incongruent dissolution of feldspars into the melt and silica release giving quartz in silica saturated rocks biotite breakdown and growth of al rich ferromagnesian minerals occurring at the solid liquid transition in the crust early melting or final crystallization is kinetically controlled by fe and mg mass transport the network forming cations si and al being locally compensated for by feldspar dissolution crystallization this process leads to significant changes with respect to equilibrium dehydration melting reactions wherein quartz is a reactant and k feldspar a reaction product therefore quartz inclusions commonly occurring in garnets from granulite facies metapelites and metagraywackes are not simply grains passively included during garnet growth they may also correspond to newly crystallized phases resorption of feldspar may lead to more alkaline melt and to crystalline residue richer in al than expected under equilibrium conditions hence excess alumina in granulite facies rocks is not necessarily related to initial alumina rich whole rock compositions as currently considered but may be due at least partly to kinetics of melting

crustal channel flows 2 numerical models with implications for metamorphism in the himalayan tibetan orogen 1 results from a thermal mechanical model ht1 that includes midcrustal channel flow are compatible with many features of the himalayan tibetan system radioactive self heating and rheological weakening of thickened model orogenic crust lead to the formation of a hot low viscosity midcrustal channel and a broad plateau channel material corresponding to the greater himalayan sequence ghs flows outward from beneath the plateau in response to topographically induced differential pressure at the plateau flank it is exhumed by focused surface denudation and juxtaposed with cooler newly accreted material corresponding to the lesser himalayan sequence lhs the model channel is bounded by coeval thrust and normal sense ductile shear zones interpreted to represent the main central thrust mct zone and south tibetan detachment system respectively inverted metamorphism associated with the model mct zone results from distributed ductile shear along the mct and extrusion of the hot channel a variety of model p t t path styles resembling those observed in the ghs and lhs are produced for points traveling through contrasting tectonic regimes that coexist in different parts of the model predicted times of peak metamorphism cooling and erosion of metamorphic facies are generally compatible with observations although model ghs cooling ages are too young the times of m1 and m2 metamorphic events observed in the ghs correspond to model times of maximum burial and maximum heating respectively the results highlight the need to integrate tectonics and metamorphism in continental collision models and demonstrate the importance of lateral transport of both heat and material in large hot orogens

a petrogenetic grid for pelitic schists in the system sio 2 al 2 o 3 feo mgo k 2 o h 2 o a quantitative petrogenetic grid for pelitic schists in the system kfmash that includes the phases garnet chlorite biotite chloritoid cordierite staurolite talc kyanite andalusite sillimanite and pyrophyllite with quartz h2o and muscovite or k feldspar in excess is presented the grid is based on thermodynamic data of berman et al 1985 and berman 1988 for endmember kfash and kmash equilibria and natural fe mg partitioning for the kfmash system calculation of p t slopes and the change in fe fe mg along reactions in the kfmash system were made using the gibbs method in addition the effect on the grid of mno and cao is evaluated quantitatively the resulting grid is consistent with typical buchan and barrovian parageneses at medium to high grades at low grades the grid predicts an extensive stability field for the paragenesis chloritoid biotite which arises because of the unusual facing of the reaction chloritoid biotite quartz h2o garnet chlorite muscovite which proceeds to the right with increasing t in the kfmash system however the reaction proceeds to the left with increasing t in the mnkfash system so the assemblage chloritoid biotite is restricted to bulk compositions with high fe fe mg mn typical metapelites will therefore contain garnet chlorite at low grades rather than chloritoid biotite

eurasian snow cover variability and northern hemisphere climate predictability we present observational evidence demonstrating dynamic interactions and feedbacks between multi seasonal snow cover and winter time circulation anomalies over mid high latitudes the cooling effect of snow cover is associated with a strengthened and more expansive siberian high with more frequent topographically constrained intrusions west and north early season snow cover variability leads to altered general circulation patterns consistent with the dominant mode of winter variability observed in the northern hemisphere troposphere the implications of the surface atmosphere coupling for seasonal to interannual predictability are also discussed

links between tropical convection and variations of the extratropical circulation during toga coare abstract data from the intensive observation period of the tropical ocean global atmosphere coupled ocean atmosphere response experiment november 1992 february 1993 have been used to investigate the links between intraseasonal variations in tropical convection and those in forcing of upper tropospheric rossby waves in the extratropics the primary databases are geostationary meteorological satellite imagery and tropical wind analyses from the bureau of meteorology australia a number of 5 day periods showing convection in different locations were chosen for each period mean fields of divergence cloud top temperature and upper tropospheric rossby wave source are presented vorticity budgets are used to demonstrate the processes responsible for the rossby wave source patterns the approach follows earlier studies of links between interannual variations of tropical convection associated with the southern oscillation and variations of the extratropical circulation it is shown that the regions of tropi

geomagnetic field intensity over the last 42 000 years from core soh 4 big island hawaii a record of the absolute geomagnetic field intensity spanning the last 42 kyr has been obtained from 100 lava flows 187 successful thellier experiments recovered in the top 468 m of core from the soh 4 well on the island of hawaii assuming a linear extrusion rate between the present and the 42 kyr date obtained with a refined k ar technique this corresponds to an average of one flow every 420 years rock magnetic analysis identifies low ti content and high ti content magnetites in 75 and 25 of the samples respectively as the main carriers of magnetization the low ti magnetites are very stable while some transformations occur upon heating in the other samples but both groups allow reliable paleointensity determinations the directional record documents inclinations consistent with a geocentric dipole field for the last 16 kyr and between 38 and 42 kyr between 16 and 38 kyr shallower and in some cases negative inclinations were observed because of the high extrusion rate and the exceptional percentage of reliable intensity determinations the record of the geomagnetic field intensity over the last 42 kyr has a resolution comparable to the best sedimentary records the geomagnetic field intensity at hawaii appears to have varied between 18 and 79 t and is characterized by large fluctuation with peak to peak amplitudes of 20 25 t the observed values are quite consistent with other values obtained from hawaii for the last 31 kyr mankinen and champion 1993a b tanaka and kono 1991 coe et al 1978 the mean intensity over the explored time interval 45 t is slightly higher than the present value of the geomagnetic field in hawaii

the origin of himalayan anatexis and inverted metamorphism models and constraints abstract the key to comprehending the tectonic evolution of the himalaya is to understand the relationships between large scale faulting anatexis and inverted metamorphism the great number and variety of mechanisms that have been proposed to explain some or all of these features reflects the fact that fundamental constraints on such models have been slow in coming recent developments most notably in geophysical imaging and geochronology have been key to coalescing the results of varied himalayan investigations into constraints with which to test proposed evolutionary models these models fall into four general types 1 the inverted metamorphic sequences within the footwall of the himalayan thrust and adjacent hanging wall anatexis are spatially and temporally related by thrusting 2 thrusting results from anatexis 3 anatexis results from normal faulting and 4 apparent inverted metamorphism in the footwall of the himalayan thrust is produced by underplating of right way up metamorphic sequences we review a number of models and find that many are inconsistent with available constraints most notably the recognition that the exposed crustal melts and inverted metamorphic sequences not temporally related the generalization that appears to best explain the observed distribution of crustal melts and inverted metamorphic sequences is that due to specific petrological and tectonic controls episodic magmatism and out of sequence thrusting developed during continuous convergence juxtaposing allochthonous igneous and metamorphic rocks this coincidental juxtaposition has proven to be something of a red herring unduly influencing attention toward finding a causal relationship between anatexis and inverted metamorphism

concurrent variation between the east asian subtropical jet and polar front jet during persistent snowstorm period in 2008 winter over southern china 1 the concurrent variation features between the east asian subtropical jet and polar front jet were investigated during persistent snowstorm period in 2007 2008 winter over southern china the east asian subtropical jet was divided into two parts 1 the plateau jet located along the southern side of the tibetan plateau and 2 the ocean jet situated at the southeastern japan island the concurrent intensity variation among the polar front jet plateau jet and ocean jet and the associated atmospheric anomalous signals were examined a possible mechanism for concurrent variation among the three jets was also investigated from a perspective of synoptic scale transient eddy activities stea the enhanced plateau jet was simultaneously correlated with the weakened polar front jet while the variation of the ocean jet lagged the variation of the plateau jet polar front jet about 5 days the concurrent variation between the plateau jet and the polar front jet acted as an important bridge that linked the snowstorm to the atmospheric anomalous signals associated with the cold and warm air activities due to the opposite trends of stea variation over the southern and northern sides of the tibetan plateau the plateau jet and the polar front jet exhibited a significant concurrent variation feature the stea anomalies over the plateau jet and polar front jet regions propagated downstream to the east asian coast as a wave train along the southern and northern sides of the tibetan plateau respectively resulting in a 5 day lag variation relationship between the ocean jet and the plateau jet polar front jet

the effect of boreal late autumn snow cover over western and central china on the northern hemisphere wintertime blocking frequency abstractthe impact of snow cover in western and central china during late autumn on wintertime blocking occurrence is investigated using reanalysis data the study results show that wintertime atmospheric circulations affected by late autumn snow cover anomalies form favorable conditions for increased blocking frequency bf especially in the north pacific and north atlantic evidence is also presented that the stratosphere troposphere interactions are the key mechanism of the lag response of wintertime north pacific and north atlantic bfs to the late autumn snow cover that is positive anomalous snow cover can induce a dipole anomaly in the geopotential height field over the lower stratosphere due to the decrease of the 300 1000 hpa thickness and the concurrent variation between the east asian plateau jet and the polar front jet the associated positive geopotential height anomalies are located over northwestern eurasia meanwhile western and central china features remarkably negative geopotential he

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

high pressure granulites formation recovery of peak conditions and implications for tectonics high pressure granulites are characterised by the key associations garnet clinopyroxene plagioclase quartz in basic rocks and kyanite k feldspar metapelites and felsic rocks and are typically orthopyroxene free in both basic and felsic bulk compositions in regional metamorphic areas two essential varieties exist a high to ultrahigh temperature group and a group representing overprinted eclogites the high to ultrahigh temperature type formerly contained high temperature ternary feldspar now mesoperthite coexisting with kyanite is associated with garnet peridotites and formed at conditions above 900 c and 1 5 gpa clinopyroxene in subordinate basic rocks is al rich and textural evidence points to a high pressure high temperature melting history the second variety contains symplectite like or poikilitic clinopyroxene plagioclase intergrowths indicating former plagioclase free i e eclogite facies assemblages this type of rock formed at conditions straddling the high pressure amphibolite high pressure granulite field at around 700 850 c 1 0 1 4 gpa importantly in the majority of high pressure granulites orthopyroxene is secondary and is a product of reactions at pressures lower than the peak recorded pressure in contrast to low and medium pressure granulites which form at conditions attainable in the mid to lower levels of normal continental crust high pressure granulites of nonxenolith origin mostly represent rocks formed as a result of short lived tectonic events that led to crustal thickening or subduction of the crust into the mantle short times at high temperature conditions are reflected in the preservation of prograde zoning in garnet and pyroxene high pressure granulites of both regional types although rare are known from both old and young metamorphic terranes e g c 45 ma namche barwa e himalaya 400 340 ma european variscides 1 8 ga hengshan china 1 9 ga snowbird saskatchewan and 2 5 ga jianping china this spread of ages supports proposals suggesting that thermal and tectonic processes in the lithosphere have not changed significantly since at least the end of the archean

neoproterozoic high pressure metamorphism and tectonic constraint from the nappe system south of the sao francisco craton southeast brazil abstract the neoproterozoic giant nappe system exposed south of the sao francisco craton underwent a minimum of 150 km of near horizontal northeastward displacement this nappe system comprises an uppermost unit derived from a plutonic magmatic arc terrane with high pressure high temperature intermediate to mafic granulites at its base socorro guaxupe nappe underlain in sequence by a high pressure kyanite granulite nappe an amphibolite facies metapelite nappe and finally by a quartzite nappe which forms the lowest part of the pile and rests on a parautochthonous unit related to the passive margin of the craton the kyanite granulites crystallized ca 13 kbar 750 c and have only at their top sillimanite related to t increase overprinting t 890 c a consequence of downward heat advection from the overlying socorro guaxupe granulites equilibrated at 900 c pressures of 13 14 kbar are documented in the underlying metapelite nappe with temperatures of 640 670 c in which lenses of eclogite indicate p max of ca 17 5 kbar phyllites of the parautochthonous unit are directly overlain by hp granulites in the north and record p 7 kbar and t 500 c the distribution of metamorphic facies is reminiscent of inverted metamorphism with eclogites from subduction related metamorphism and kyanite granulites from early extrusion of subducted continental crust the metamorphic conditions of the parautochthon may represent a stage achieved during late metamorphic thinning of the nappe pile the overall picture suggests that high pressure units recrystallized in a subduction zone located to the wsw the frontal thrusts of the nappe system show a late north northeastward transported thin skinned pattern

seasonal variations of the synoptic scale transient eddy activity and polar front jet over east asia abstract seasonal variations of the synoptic scale transient eddy activity stea and the jet streams over east asia are examined through analysis of the 40 yr european centre for medium range weather forecasts ecmwf re analysis era 40 data extracted from the 6 hourly upper level wind fields the distribution of the jet core numbers exhibits a distinct geographical border for the east asian subtropical jet easj and the east asian polar front jet eapj at the latitudes of the northern tibetan plateau tp in the cool seasons two branches of the stea and low level baroclinicity exist over the east asian landmass accompanied by the two jet state of the easj and eapj in the warm seasons a single jet pattern of the easj along the north flank of the tp is accompanied by the weakened stea over the mid to high latitudes of east asia further analysis shows two distinct features of the seasonal variations of the stea over east asia compared with that over the north pacific first during the transit

deformation conditions and quartz c axis fabric development along nappe boundaries the andrelândia nappe system southern brasilia orogen brazil abstract the liberdade and andrel ndia nappes se brazil record the western gondwana amalgamation in the southern brasilia orogen during the ediacaran the liberdade shear zone acted as the boundary between these two overlapping nappes quartz c axis fabrics and strain data from quartzite samples and petrological data from hosting metapelite rocks were analyzed to investigate the tectonic processes involved in nappe development further constraints were achieved by conducting petrological modeling and geothermobarometry using p t isochemical phase diagram approaches quartz axis plots show consistency with different kinematic criteria verified in the field in meso and macroscale the fabrics are associated to both coaxial deformation and non coaxial deformation quartz microstructures metamorphic assemblages and c axis concentrations primarily around y and x structural directions suggest that deformation was accommodated by grain boundary migration recrystallization under temperature above 500 c disregarding pressure effects the opening angles of quartz c axis fabrics suggest temperatures between 480 and 640 c muscovite quartzite and 650 720 c sillimanite quartzite considering pressure data the opening angles indicate conditions of 550 650 c and 7 10 kbar muscovite quartzite and 600 730 c and 4 7 kbar sillimanite quartzite reflecting primarily distinct baric regimes sillimanite bearing samples estimatives are supported by ubiquitous presence of chessboard subgrain patterns in quartz and by modeled isochemical phase diagrams that constrain conditions of 660 730 c and 6 7 kbar for garnet sillimanite biotite schist samples altogether these results indicate progressive tectonic evolution linked to oblique convergence between tectonic units represented by the andrel ndia and liberdade nappes and the paleoproterozoic basement besides recording distinct thermal and baric regimes the nappes also present different structural styles suggesting that pressure and temperature are important boundary conditions for the nappe structural style

33 000 yr k ar dating of the volcano tectonic horst of the isle of ischia gulf of naples the gulf of naples corresponds to a tectonic sink connected with recent volcanic activity in the south campanian area phlegrean fields ischia and vesuvius at its extreme northwest the isle of ischia was early recognized as a volcano tectonic horst by rittmann1 previous data2 concluded that its uplift ended around 300 000 yr and that the green tuff formation of which it is predominantly composed had an age of some 700 000 yr but tectonic and morphological studies together with original tephrostratigraphical observations on the slope of the horst led us to do some new k ar datings these revealed that the 780 m uplift of the horst from the sea level is younger than 33 000 yr the green tuff which was considered to be the oldest volcanic unit in the island is now dated at 56 000 yr its eruption following the dismantlement of a first volcanic complex now dated as not older than 130 000 yr

the blake magnetic polarity episode in cores from the mediterranean sea abstract palaeomagnetic and oxygen isotope studies on samples taken from five cores in the mediterranean area are described directions of the stable remanent magnetisation show the presence of an anomalous reversed zone during the transition between the oxygen isotope substages 5e and 5d this position corresponds to the age of about 117 kyr b p and thus to the blake polarity episode the duration of this episode is estimated to be about 6000 years the study of the anisotropy of the magnetic susceptibility shows no indication of sedimentological disturbances in recorded sections the blake episode therefore represents a stratigraphic marker which may be used to link the continental and marine palaeoclimatic and sedimentary records

the role of linear interference in northern annular mode variability associated with eurasian snow cover extent one of the outstanding questions regarding the observed relationship between october eurasian snow cover anomalies and the boreal winter northern annular mode nam is what causes the multiple week lag between positive eurasian snow cover anomalies in october and the associated peak in rossby wave activity flux from the troposphere tothe stratospherein december thisstudy exploresthe following hypothesis about thislag in order toachieve amplificationofthe waveactivity the vertically propagatingrossbywave train associated with the snow cover anomaly must reinforce the climatological stationary wave which corresponds to constructive linear interference between the anomalous wave and the climatological wave it is shown that the lag in peak waveactivityflux arisesbecause the rossby wave train associatedwiththe snowcover isin quadrature orout of phasewiththeclimatologicalstationarywavefromoctobertomid november beginninginmid novemberthe associated wave anomaly migrates into a position that is in phase with the climatological wave leading to constructive interference and anomalously positive upward wave activity fluxes until mid january climate models from the coupled model intercomparison project 3 cmip3 do not capture this behavior this linear interferenceeffectisnot onlyassociatedwith stratospheric variabilityrelatedtoeurasiansnowcoveranomalies but is a general feature of northern hemisphere troposphere stratosphere interactions and in particular dominated the negative nam events of the fall winter of 2009 10

titanite petrochronology of the southern brasilia orogen basement effects of retrograde net transfer reactions on titanite trace element compositions abstract combining u pb geochronology and trace element characteristics of accessory minerals more reactive during metamorphism and deformation than zircon such as titanite catisio5 is a powerful tool for elucidating pressure temperature time p t t evolution of orogenic basement complexes this study reports in situ titanite u pb and trace element data from upper amphibolite facies metatexitic orthogneisses of the pouso alegre complex in the basement of the neoproterozoic southern brasilia orogen se brazil the titanite data is combined with thermodynamic modeling major phase compositions and u pb zircon dating and used to constrain the p t t path of the complex during the neoproterozoic orogenesis the investigated garnet amphibole gneisses record peak metamorphic conditions of 750 775 c and 10 5 12 5 kbar associated with partial melting and dated at ca 630 620 ma based on u pb analyses of hree y depleted titanite cores inferred to have crystallized in the presence of garnet near the peak p t conditions extensive melt crystallization at ca 616 ma is constrained by u pb dating of leucosome zircons the exhumation of the complex and re equilibration to ca 550 625 c at 6 9 kbar led to widespread generation of biotite epidote clinozoisite partially replacing amphibole garnet along the main foliation trace element signatures of these retrograde net transfer reactions are recorded in the titanite rims which are hree y enriched strontium depleted and were dated at 605 7 6 2 ma the average zirconium contents of the titanite rims are higher than cores suggesting disequilibrium partitioning of zirconium into titanite during the retrograde path resulting in overestimated zr in titanite temperatures for the rims the exhumation of the complex was concomitant with the intrusion of folded and recrystallized leucogranite dykes dated at 607 0 5 7 ma attesting the persistence of deformation after their intrusion assuming that the pouso alegre complex is part of the sao francisco paleocontinent reworked during the brasilia orogeny the data constrain the minimum age for the collision between the sao francisco paleocontinent and the paranapanema block at ca 620 630 ma and agree with the idea of long lived metamorphism and deformation in the southern brasilia orogen