synchronous uplift of the lower crust of the ivrea zone and of southern calabria and its possible consequences for the hercynian orogeny in southern europe abstract along the border of the adriatic microplate pre alpine granulite facies rocks from the deepest crust are outcropping at only two places in the ivrea zone of the southern alps and in southern calabria in these two areas the main features of the present crustal structures i e overlapping of large continental crustal and upper mantle segments are interpreted as resulting from their hercynian geodynamic evolutions the tilted nearly complete crustal sections in both areas display very similar lithological sequences and experienced a common geological evolution as deduced from petrological and radiometric dates at the end of hercynian time 295 m y the ivrea body and the lower crustal rocks of southern calabria were contemporaneously sheared off from the upper mantle and uplifted into intermediate crustal levels where they slowly cooled during mesozoic time the tectonic uplift was accompanied by granitoid plutonism and andesitic to rhyolitic volcanism which continued after the hercynian uplift considering the presently similar crustal structures and the upper carboniferous and permian geological evolutions along the whole adriatic plate boundary the ivrea zone and southern calabria are used to resolve the pre alpine history of the boundary zone between the adriatic and the central european block the uplift of the lower crustal upper mantle flakes of the adriatic block was due to flat overthrusting of these flakes on the continental crust of central europe the material of the central european crust underthrust subducted thereby melted during the re equilibration of the geotherms which had been disturbed by the subduction process this led to an extensive calc alkaline plutonism and volcanism of crustal origin along the adria boundary in this boundary region the overlying uppermost crustal levels schiefergebirgsstockwerk were synchronously folded asturian phase in response to the overlapping of the deeper crustal levels subsequently to the orogeny the mountain chain was eroded and molasse basins developed on the overthrust adriatic crustal segment during the lower permian in this model the granulite facies flakes of the ivrea zone and of southern calabria are interpreted as pre hercynian lower crustal segments which were thrust into the middle crust during the hercynian orogeny thus giving rise to wave velocity inversions in the crust further it is proposed that similar geodynamic processes have played a role in the genesis of the conrad discontinuity which is present in many parts of the hercynian fold belt but only in the ivrea zone and in southern calabria the crustal discontinuities formed in hercynian time were uplifted to the surface as a result of alpine reactivation of the adriatic boundary zone and due to their special positions in the bends of the alpine apennine maghrebide mountain system according to the present knowledge of the carboniferous paleogeography and of the orogenic evolution on both sides of the adria sufure zone this fault zone was located within the european continent its role during the hercynian orogeny is discussed envisaging two possibilities an a subduction zone or a subfluence zone in the sense of behr and weber

energetics of winter troughs entering south america abstract the energetics and behavior of midtropospheric troughs over the southern hemisphere and their relationship with south america surface cyclogenesis were studied during the winters of 1999 2003 all surface cyclogenesis situations over uruguay and adjacent areas associated with 500 hpa troughs were analyzed the atmospheric circulation associated with type b and type c cyclones form the basis for two composites composite b with 25 cases and composite c with 13 cases the results showed that the midtropospheric troughs were more intense in composite c than in composite b before the surface cyclogenesis and that the opposite occurred during the surface cyclogenesis the baroclinic conversion was dominant in both composites in composite b the ageostrophic flux convergence afc contributed positively to the intensification of the surface cyclone since it imported energy into the area before the cyclogenesis started but in composite c the afc served as a sink because it exported energy based

wave packets and life cycles of troughs in the upper troposphere examples from the southern hemisphere summer season of 1984 85 abstract in this paper reanalysis data for the southern hemisphere summer season of 1984 85 produced by the european centre for medium range weather forecasts have been analyzed to examine wave packets and life cycles of baroclinic waves a semiobjective algorithm has been devised to track wave packets it is found that the perturbations in the upper troposphere are dominated by wave packets some of these wave packets can be tracked for several weeks during which they can make up to two trips around the latitude circle the energy life cycles of waves that make up several of these wave packets were analyzed and apart from the incipient waves that started the wave packets most of the subsequent wave development was found to be dominated by convergence and divergence of energy fluxes rather than due to baroclinic or barotropic conversions demonstrating that these wave packets are indeed coherent entities that propagate due to downstream development or dispersion the energy life cycle of the most

the 4 day wave in the antarctic mesosphere a zonal wave number one eastward propagating planetary wave observed in the high latitude winter stratosphere with a period near 4 days has been studied by a number of previous authors radar observations coupled with stratospheric analyses are here used to demonstrate that this wave known as the 4 day wave extends into the antarctic upper mesosphere previous workers have asserted that the wave is a manifestation of the observation of warm pools rotating in the polar vortex and that the pool seems to behave in a quasi nondispersive manner the observation of the 4 day wave in the upper mesosophere presented here appears to validate previous claims that the warm pools are being maintained by wavelike dynamics rather than simple advection

storm track dynamics this paper reviews the current state of observational theoretical and modeling knowledge of the midlatitude storm tracks of the northern hemisphere cool season observed storm track structures and variations form the first part of the review the climatological storm track structure is described and the seasonal interannual and interdecadal storm track variations are discussed in particular the observation that the pacific storm track exhibits a marked minimum during midwinter when the background baroclinicity is strongest and a new finding that storm tracks exhibit notable variations in their intensity on decadal timescales are highlighted as challenges that any comprehensive storm track theory or model has to be able to address physical processes important to storm track dynamics make up the second part of the review the roles played by baroclinic processes linear instability downstream development barotropic modulation and diabatic heating are discussed understanding of these processes forms the core of our current theoretical knowledge of storm track dynamics and provides a context within which both observational and modeling results can be interpreted the eddy energy budget is presented to show that all of these processes are important in the maintenance of the storm tracks the final part of the review deals with the ability to model storm tracks the success as well as remaining problems in idealized storm track modeling which is based on a linearized dynamical system are discussed perhaps on a more pragmatic side it is pointed out that while the current generation of atmospheric general circulation models faithfully reproduce the climatological storm track structure and to a certain extent the seasonal and enso related interannual variations of storm tracks in depth comparisons between observed and modeled storm track variations are still lacking

trapped waves in the edge region of stratospheric polar vortices 1 a global distribution and seasonal variability of short period 2 days disturbances in the lower and middle stratosphere are investigated using 6 hourly european centre for medium range weather forecasts reanalysis data over 15 years 1979 1993 two dimensional spectral analysis and a recently developed lagrangian mean diagnostic are used for the analysis it is shown that the short period disturbances are most active around the polar night jet in each winter hemisphere they have a wavelike structure in the longitudinal direction with typical zonal wavelengths of 1 700 2 000 km i e zonal wave number 10 12 and a latitudinally evanescent structure with a half width of about 1 500 km suggesting that they are waves trapped in the edge region of the polar vortex where the latitudinal gradient of isentropic potential vorticity is maximized the trapped waves have a nearly barotropic structure over a depth greater than 10 km because the polar vortex in the northern hemisphere is much deformed and not symmetric around the pole dynamical characteristics of the trapped waves in the southern hemisphere alone are investigated by applying a lag correlation analysis to the reanalysis data the characteristics of trapped waves are fairly dependent on the state of the polar vortex such as zonal wind speed and its vertical shear they have a significant westward intrinsic phase velocity from june through october when the polar vortex is most stable this indicates that the trapped waves during this period have their own dynamics contrary to the filaments being passively advected by the large scale flow

marginal stability and predator prey behaviour within storm tracks a predator prey relationship between storm track intensity and growth rate is revealed in reanalysis data of the north atlantic and north pacific as well as in an idealized global circulation model with a zonally asymmetric heating dipole averaging in the phase space of these two quantities reveals that both quantities oscillate on approximately monthly time scales these oscillations occur due to quasi periodic bursts in storm track activity that reduce excess baroclinicity and bring the flow back towards a state that is marginally stable to those bursts many detailed properties of these oscillations are reproduced well by a two dimensional dynamical system especially in respect of the north atlantic storm track which is more zonally constrained than that in the north pacific it is predicted and observed that on average stronger storm events occur less frequently but grow on a shorter time scale the results suggest that nonlinearly oscillating behaviour around a state of baroclinic neutrality is a general feature of localized storm tracks and they offer a new perspective on the study of baroclinic instability

the role of wave packets in wave mean flow interactions during southern hemisphere summer abstract in this study reanalysis data produced by the european centre for medium range weather forecasts for 14 southern hemisphere sh summer seasons have been analyzed all cases of hemispheric transient eddy kinetic energy teke maxima have been identified and the evolution of the local energetics and planetary scale flow anomalies accompanying these teke growth decay episodes are composited the longitude time evolution of the composite energetics shows the clear signature of a wave packet propagating eastward at a group velocity of about 27 longitude per day and undergoing a life cycle of growth and decay with the energetics within a volume close to the wave packet center dominating the hemispheric mean energetics when individual cases are examined 52 are found to resemble the composite and have the energetics life cycle dominated by the evolution of a single wave packet and an additional 21 are found to be dominated by the evolution of two wave packets having similar amplitudes only the

a 6 5 day westward propagating planetary wave origin and characteristics a large 10 30 m s 1 6 7 day period westward propagating planetary wave was seen in both ground radar and satellite data within the 80 100 km height regime during august and september 1993 previous analyses of these data argue that it was most likely a manifestation of the 1 2 rossby planetary wave commonly referred to as the 5 day wave perhaps shifted to longer periods by interaction with the mean zonal winds in this study the global scale wave model gswm hagan et al 1993 is used to analyze the characteristics of this westward propagating wave we propose that the observed wave is not a doppler shifted 5 day wave but rather an unstable mode drawing energy from unstable regions in the upper mesosphere whose realization is global in scale the concept of atmospheric instability is used to determine a likely source region and the model is used determine the characteristic period growth rate and perturbation fields of the instability driven wave

covariation of finite amplitude wave activity and the zonal mean flow in the midlatitude troposphere part ii eddy forcing spectra and the periodic behavior in the southern hemisphere summer abstractpreviously in part i of this study the authors used latitude by latitude budgets of the vertically integrated finite amplitude wave activity fawa to describe the covariation of the zonal mean state and eddy amplitude in the austral summer within 40 55 s fawa exhibits a marked 20 30 day periodicity driven mainly by the low level meridional eddy heat flux consistent with the recently identified baroclinic annular mode bam the present article examines the spectra of eddy heat flux that produce the periodic behavior in the southern hemisphere storm track analysis of the era interim product reveals that the 20 30 day periodicity in raw fawa and eddy heat flux is particularly robust during the warm season a dry gcm is shown to reproduce qualitatively bam like eddy heat flux spectra if the zonal mean state resembles that of the austral summer and if the surface thermal damping is sufficiently strong the observed eddy heat flux cospectra in summer contain a few dominant frequencies for each o

new geochronological information by rb sr and u pb investigations from the pre alpine basement of grande kabylie algeria this study presents the first geochronological results apart from previously obtained mica ages from metamorphic basement complex occurring within the internal zone of the alpine chain of algeria the rb sr whole rock and u pb zircon data reveal the existence of an episode of anatectic magmatism around 510 ma ago that corresponds to late pan african orogenic events a deep crustal fault is thought to represent a major phase of shearing associated with hercynian blastomylonitic metamorphism and the production of granitic remelts at 271 12 ma reworking of an ancient basement is demonstrated by the presence of inherited radiogenic lead in zircons from lower palaeozoic orthogneisses and metarhyolites upper intercepts on concordia plots yield ages of 1950 100 and 1321 30 ma respectively apart from the dating results which may provide new insight into the geological history of the region this study also provides general implications for the interpretation of geochronological data in metamorphic and

barotropic and baroclinic annular variability in the southern hemisphere abstractthe leading patterns of large scale climate variability in the southern hemisphere are examined in the context of extratropical kinetic energy it is argued that variability in the southern hemisphere extratropical flow can be viewed in the context of two distinct and largely independent structures both of which exhibit a high degree of annularity 1 a barotropic structure that dominates the variance in the zonal mean kinetic energy and 2 a baroclinic structure that dominates the variance in the eddy kinetic energy the former structure corresponds to the southern annular mode sam and has been extensively examined in the literature the latter structure emerges as the leading principal component time series of eddy kinetic energy and has received seemingly little attention in previous work the two structures play very different roles in cycling energy through the extratropical troposphere the sam is associated primarily with variability in the meridional propagation of wave activity has a s

rossby wave packets on the midlatitude waveguide a review abstractrossby wave packets rwps are rossby waves for which the amplitude has a local maximum and decays to smaller values at larger distances this review focuses on upper tropospheric transient rwps along the midlatitude jet stream their central characteristic is the propagation in the zonal direction as well as the transfer of wave energy from one individual trough or ridge to its downstream neighbor a process called downstream development these rwps sometimes act as long range precursors to extreme weather and presumably have an influence on the predictability of midlatitude weather systems the paper reviews research progress in this area with an emphasis on developments during the last 15 years the current state of knowledge is summarized including a discussion of the rwp life cycle as well as rossby waveguides recent progress in the dynamical understanding of rwps has been based in part on the development of diagnostic methods these methods include algorithms to identify and track rwps

eocene simple shear and plio quaternary pure shear folding in the central eastern algerian atlas tertiary folds of the central and eastern part of the algerian atlas were studied in order to assess their kinematics and regimes of deformation folds developed following two main phases of deformation during the eocene and the pliocene the ne sw trending eocene folds show a clockwise rotation of fold axis with depth noncylindrical geometry and a right stepping en echelon configuration early secondary structures inside each fold are also rotated clockwise with respect to the younger folds these data are in agreement with progressive simple shear deformation pliocene folds strike e w and display a cylindrical geometry associated plio quaternary brittle structures show no rotational path these observations are compatible with pure shear style of deformation these results in combination with focal mechanism solutions have important implications for the understanding of the kinematic evolution of the western segment of the african european plate boundary for algeria they imply that transcurrent motion during the paleogene was followed by coaxial shortening with a nnw direction during neogene quaternary times comparison with published data for morocco and tunisia suggests that this transcurrent regime developed from west to east continuing from the middle jurassic through to the miocene

the significance of the pdaeomagnetism of jurassic cretaceous rocks from south america predrift movements hairpins and magnetostratigraphy summary in this paper we show that 1 the positions of the cretaceous palaeomagnetic poles pp for south america and africa exhibit elongated distributions that are due to rapid movement of these continents from the south pole 2 the positions of the middle late jurassic virtual geomagnetic poles for south america exhibit an elongated distribution along the meridians 20 200 e it is suggested that this is due to a rapid shift of south america in middle late jurassic time 3 the late early early late cretaceous sections of the apparent polar wandering paths for south america and africa are consistent with south atlantic seafloor spreading data on the basis of the comparison of the reliable late palaeozoic late cretaceous pps for south america and africa taking into account the restrictions established by geological palaeontological and seafloor spreading data it is suggested that minor movements could have occurred within western gondwana in middle late jurassic time along a narrow zone which later became the south atlantic divergent boundary four hairpins are defined in the late palaeozoic late cretaceous section of the apparent polar wandering path for south america the two youngest of these can be correlated with the origin of the south atlantic ocean basin and the onset of the andean orogeny respectively the magnetostratigraphy for the serra geral lava flow sequence suggests that some of these flows were poured out rapidly without significant interruption

paleozoic evolution of the armorica plate on the basis of paleomagnetic data new paleomagnetic data support the contention that armorica and gondwana formed a coherent block until ordovician time however by early devonian time armorica collided with the north american northern european assembly to form the old red continent and the collision itself was responsible for the acadian orogeny not for the earlier taconic orogeny as postulated previously the carboniferous collision of gondwana with the old red continent subsequently formed pangaea and produced the appalachian hercynian orogeny

an observational study of medium scale wave dynamics in the southern hemisphere summer part i wave structure and energetics abstract medium scale waves zonal wavenumbers 4 7 frequently dominate southern hemisphere sh summer midlatitude circulation patterns this work is an observational study that focuses on their temporal and spatial characteristics along with detailing the forcing mechanisms responsible for their formation medium scale wave characteristics for three sh summers 1978 79 through 1980 81 are discussed it is shown that the time mean medium scale wave structure is consistent with the basic state linear wave propagation characteristics the energetics of the medium scale waves are studied using the transformed eulerian mean formalism of plumb it is found that wave zonal mean exchange is a valid concept for describing the sh summer atmospheric circulation and that the flow vacillates between periods of highly perturbed and zonally symmetric states with a time wale on the order of 10 20 days these vacillations result from nonlinear baroclinic instabilities and the medium scale waves exhibit well defined

early carboniferous basins of the atlas meseta domain morocco sedimentary model and geodynamic evolution in the atlas meseta basins of morocco early carboniferous clastics comprise wave dominated shelf sediments turbidites and mass flow deposits crustal extension controlled the formation of troughs continental uplift and general marine subsidence sedimentation passed from turbidites into storm deposits the moroccan meseta formed a complex marine basin composed of deep troughs shallow shelves and islands the late visean marine transgression advanced from the north and reached as far south in the high atlas domain as the tizi n test fault zone the variscan compressive phase ended the early carboniferous sedimentation

vertical structure physical properties and energy exchange of the east asian trough in boreal winter the relation between the intensity of the east asian trough and the strength of the east asian winter monsoon is documented a prominent dipole of the available potential energy of the zonal mean flow can be observed over the midlatitudes and polar regions and is related to temperature anomalies variation in the intensity of the east asian trough is caused by variation in the energy conversion from the available potential energy of the zonal mean flow to the east asian trough the in phase relation between the intensities of the east asian jet and east asian trough is illustrated by the relation between the potential energy and kinetic energy of stationary eddies the dipole of height anomalies over the midlatitude and polar regions develops in late autumn and decays in early spring we investigate the effect of both stationary and transient eddy forcing on the evolution of the dipole the combined forcing of the two types of eddy makes an important contribution to the development maintenance and decay of the dipole

application of wavelet transform to meteosat derived cold cloud index data over south america abstract cold cloud index cci data derived from meteosat infrared imagery are used to detect periodicities in convective activity in south america the generally used fourier transform ft cannot provide time localized information but gives information on the average periodicity of oscillations over the entire time domain as many events in the atmosphere are intermittent wavelet transform wt is used to identify periodic events in cci data first the morlet wt is applied to different combinations of time series data of known periodicities to demonstrate the advantage of wt over ft later it is applied to cci data over four 9 square areas between the latitudes 4 5 n and 31 5 s and longitudes 54 45 w near the equator periodic convective activities are observed to be more prominent in the boreal summer than in the austral summer between the latitudes 4 5 and 22 5 s 1 2 3 approximately 5 and 8 10 day oscillations are seen in the austral summer and seldom is any convective activity seen in

rossby wave propagation into the tropics in two gfdl general circulation models during the northern winter the eastern pacific is characterized by upper level westerly flow extending from the equator into the midlatitudes of both hemispheres theoretical and simple modeling studies suggest that such a region should favor the penetration of rossby waves into the tropics from higher latitudes observational results by kiladis and weickmann using 200 mb data indicate that rossby waves do indeed propagate freely into the tropical eastern pacific during the northern winter from the asian jet exit region they also confirmed that cross equatorial dispersion of energy from the northern into the southern hemisphere occurs frequently the present study examines these interactions in climatological runs of two gfdl gcms the northern wintertime mean states of these models are characterized by a rather realistically simulated upper level westerly regime in the tropical pacific despite the relative weakness of the asian jet and wave activity with respect to observations propagation of rossby waves into the tropics is present in both models and these waves are strongly positively tilted as seen in the observations a momentum budget of the zonal wind and e vector diagnostics over the tropical pacific indicate that these transients are an important component of the momentum balance of the equatorial westerlies in both the observations and in the models

intraseasonal variations in the southern hemisphere circulation abstract intraseasonal variations in the southern hemisphere atmospheric circulation have been examined through the application of a 10 50 day bandpass filter to daily ecmwf analyses for 1980 88 variations on this time scale contribute more than 40 of the daily variance in 500 hpa geopotential over much of the middle and high latitudes of the southern hemisphere eof analysis of the unnormalized variance for all seasons shows that 49 of this variance can be explained by zonal wave trains centered on the south pacific and southern atlantic indian oceans a high latitude mode of global extent and a wavenumber 3 pattern at midlatitudes these modes are essentially equivalent barotropic but slope westward with height so that the patterns at 100 hpa typically lag those at 1000 hpa by around 1o longitude there appears to be little interaction with the low latitude circulation all of the leading modes propagate eastward but the most consistent movement is shown by the south pacific wave train represented

pre mesozoic paleomagnetism and plate tectonics although the arguments perhaps did not convince everyone at the time the paleomagnetic polar wander paths for europe and north america plotted by runcom 1956 certainly convinced me as a young graduate student that continental drift as we called it in those pre plate tectonic days deserved serious attention then throughout the 1960s the geoscience world seemed busy documenting and refining the models of seafloor spreading and plate tectonics that governed the opening of today s oceans as the number of publications espousing plate tectonics seemed to grow exponentially an often tacit assumption was that the continental breakup was a unique event and that pangea was a quasi primordial continental configuration ahead of his time however j tuzo wilson 1966 queried in a now classical paper did the atlantic close and then re open the 1973 penrose conference in vail colorado on pre mesozoic plate tectonics dewey spall 1975 showed that by then many earth scientists were preoccupied with proving that the tacit assumption was wrong and that wilson was right but compared to mesozoic and later plate tectonics the task of quantifying pre mesozoic continental movements is much more difficult since there are no seafloor magnetic anomalies to work with and much of the potential evidence e g ophiolites diagnostic supracrustal sequences high pressure low temperature metamorphic rocks has been destroyed by that ultimate plate tectonic process the continent continent collision and by sub sequent uplift and erosion nevertheless a multitude of observations facts interpretations reinterpretations proposals and hypotheses can now be found in the literature for virtually any pre mesozoic period and any geographic

transport of passive tracers in baroclinic wave life cycles abstract the transport of passive tracers in idealized baroclinic wave life cycles is studied using output from the national center for atmospheric research community climate model ccm2 two life cycles lcn and lcs are simulated starting with baroclinically unstable initial conditions similar to those used by thorncroft et al in their study of two life cycle paradigms the two life cycles lcn and lcs have different initial horizontal wind shear structures that result in distinctive nonlinear development in terms of potential vorticity potential temperature pv theta diagnostics the lcn case is characterized by thinning troughs that are advected anticyclonically and equatorward while the lcs case has broadening troughs that wrap up cyclonically and poleward four idealized passive tracers are included in the model to be advected by the semi lagrangian transport scheme of the ccm2 and their evolutions are investigated throughout the life cycles tracer budgets are analyzed in terms of the transfo

the variscan belt in central europe main structures geodynamic implications open questions abstract the variscan belt of europe originated from the confrontation of northern europe and gondwana with intervening pre variscan blocks cadomian and older armorica tepla barrandean moravo silesian though a strike slip component cannot be excluded geological evidence suggests a subduction collision process newly discovered features include basaltic rocks with morb affinities high pressure metamorphic rocks trench deposits and large scale allochthonism which also affects the pre variscan basement and has often led to an inversion of the metamorphic isogrades large scale thrusting is evident at all crustal levels and is also observable by geophysical methods the structure of the variscan crust is best described as horizontal tectonic layering late ordovician through carboniferous convergence closed one rhenohercynian and one saxo thuringian basin to the north and at least one mediterranean basin to the south of the pre variscan blocks subduction occurred from the north as well as from the south down under the dorsal core region the exact timing and the driving mechanism of this bilateral activity remains a problem likewise uncertain are the exact limination of the pre variscan blocks and the existence and width of oceanic areas in the saxothuringian zone and in the south facing part of the moldanubian zone there is good evidence of early palaeozoic rifting and of late ordovician through carboniferous plate convergence palaeomagnetic and palaeoclimatic constraints however suggest only a limited extent of oceanic basins in these areas while they appear to allow a wider ocean at the rhenohercynian saxothuringian boundary which is relatively unobtrusive from the geological point of view research during the past decade has produced a wealth of information on the variscan fold belt in europe the resulting geodynamic models however are extremely diverging evidently it is not the time yet for definitive statements the present paper intends to review the state of knowledge to deduce such basic items of a geodynamic model as appear reasonably well documented and to point out the most urgent open questions stress will be laid on central europe which offers a complete cross section through the northern flank of the variscan belt and where we have carried out most of our studies during the last years

southern margin of the variscan belt the north western gondwana mobile zone eastern morocco and northern algeria stratigraphic and structural correlations between the palaeozoic massifs of eastern morocco and northern algeria allow three tectonic domains to be distinguished 1 the cratonic zone i e the west african platform which remained outside the variscan chain and its peripherical margin moroccan anti atlas and algerian ougarta 2 a wsw ene trending zone over 1500 km from marrakech to kabylia and calabria in their assumed palaeozoic location this zone was characterized during the late palaeozoic by a continuous instability indicated by the development of successive turbiditic basins and a major orogeny at the devonian carboniferous boundary and 3 central and western morocco which corresponds to the external zones of the european hercynides

global characteristics of medium scale tropopausal waves observed in ecmwf operational data global characteristics and seasonal variation of medium scale zonal wavelengths of 2000 3000 km waves observed around the midlatitude tropopause are examined using 6 hourly european centre for medium range weather forecasts operational data over four years 1990 93 covering both hemispheres medium scale waves and synoptic scale waves are extracted using time filters and their characteristics are compared hovmoller diagrams indicate the existence of medium scale waves in the southern hemisphere as well as in the northern hemisphere the zonal wavelengths of medium scale waves are slightly larger in the southern hemisphere than in the northern hemisphere medium scale waves are mostly active in three regions the north atlantic in winter dec jan feb the north pacific in spring mar apr may mam and the south indian ocean in autumn mam these regions are roughly corresponding to and slightly downstream of storm tracks where synoptic waves are dominant significant differences in seasonal variation of the intensity between the two kinds of waves are also found the maximum of wave amplitudes is seen around the tropopause at latitudes slightly higher than the jet stream axis where the meridional gradient of the quasigeostrophic potential vorticity qpv is maximized the positive large qpv gradient is attributed to the atmospheric structure around the midlatitude tropopause that is located in vertical westerly shear of the jet stream this fact suggests that the medium scale waves are waves trapped around the midlatitude tropopause

new39ar 40ar ages of hercynian and alpine thermotectonic events in grande kabylie algeria abstract the grande kabylie massif is situated within the internal zone of the alpine chain of northern algeria new 39 ar 40 ar ages which have been obtained from several key areas within the massif are compared with previous u pb and rb sr data the distinct isotopic signatures obtained lead to the recognition of several units with different tectonometamorphic histories that were intimately imbricated during the alpine orogeny in the north three structurally bound zones occur that form a core complex which is tectonically overlain by a nappe of low grade and non metamorphosed rocks from north to south the core complex is composed of 1 1 the naciria massif composed of high temperature paragneisses intruded by peraluminous granites measurements on biotites and feldspars from these series indicate that high temperature post kinematic recrystallization of these minerals occurred ca 80 ma ago before a low temperature event that produced some argon loss at ca 27 ma ago 2 2 structurally underlying the naciria zone is the sidi ali bou nab massif which consists of biotite bearing micaschists intruded by a heterogeneously mylonitized hercynian granite biotites and muscovites yield convergent 39 ar 40 ar and rb sr ages at 25 ma for this mylonitization synchronous with southeasterly overthrusting 3 3 further south orthogneisses anatectic paragneisses marbles and minor kinzigites form a second high temperature gneissic complex as for the naciria massif 39 ar 40 ar data on biotites and muscovites indicate that isotopic closure occurred 80 ma ago above the core complex is a thick series of epizonal phyllites that are unconformably overlain by unmetamorphosed permo triassic red beds of the dorsale calcaire low grade metamorphism in the phyllitic series is dated at 295 315 ma and thus reflects the influence of hercynian metamorphism from these results we consider the phyllitic series and its dorsale calcaire cover to be allochthonous units thrust upon a high temperature metamorphic basement during the early miocene

structural evidence and rbsr 39 40ar mica ages relationships for the existence of an hercynian deep crustal shear zone in grande kabylie algeria and its alpine reworking abstract in this paper the hercynian age of the deep crustal shear zone of grande kabylie is determined alpine and hercynian events in the crystallophyllian basement of northeast algeria are separated from field relations and geochronological data obtained with two radiometric systems evidence is presented to show that the blastomylonitic shear belt cutting the crystalline basement of grande kabylie is hercynian in age and that the medium to high grade metamorphism of algiers massif must be older than 243 5 ma the sidi ali bou nab sabn granite dated at 271 12 ma is seen to contain enclaves of mylonitic rocks and is itself affected by a second phase of shearing that appears to be synchronous with emplacement the latest phase of shearing has influenced the granite whole rock systems by increasing their rb sr ratios whilst preserving the alignment of points around a reference isochron of 271 12 m a the influence of eo alpine events is restricted to the opening of k ar muscovite and rb sr biotite systems ages scattered between 25 and 90 ma whereas rb sr muscovite ages show little or no evidence for rejuvenation with ages around 250 ma the rb sr mineral dates presented here along with previously published 39 40 ar step heating age data can be interpreted in the light of structural and metamorphic evidence which shows that pre sabn shearing occurred at temperatures around 650 c and that syn sabn metamorphism and deformation occurred at a temperature between 500 and 550 c it would appear that post hercynian thermal events in the grande kabylie shear zone were no more intense than 300 500 c

two types of baroclinic life cycles during the southern hemisphere summer abstract baroclinic eddy life cycles of the southern hemisphere sh summer are investigated with ncep ncar reanalysis data a composite analysis is performed for the years 1980 through 2004 individual life cycles are identified by local maxima in synoptic scale eddy energy two types of baroclinic life cycles are examined each defined by the strength of the barotropic energy conversion 2 days prior to the maximum baroclinic growth for one life cycle the barotropic conversion is anomalously weak before the maximum baroclinic growth for the other the barotropic conversion is anomalously strong these two life cycles are referred to as the weak barotropic wb and strong barotropic sb life cycles the analyses for the wb life cycle find that a poleward anomalous wave activity flux is observed within the sh tropics and subtropics just before the initial growth of the synoptic scale eddies in contrast the sb life cycle exhibits an equatorward anomalous wave activity flux prior to the initial wave de