paleomagnetism of some lithological units from the lower paleozoic of the vendee france a discussion a recent publication in this journal seguin 1983 describing paleomagnetic results for lower paleozoic formations from the vendee region has obligated us to communicate some facts and details about this study followed by some general comments as noted by seguin at the end of his paper p 277 we ourselves collected the studied samples and we have had the opportunity to discuss with him in writing on several occasions the results and the methods employed even though he states that the opinions and ideas presented in this paper are the sole responsibility of the writer we consider it our duty to inform the readers of this journal and those who wish to use the results of our reservations about this paper for which we declined to accept co authorship offered to us by the senior author we will restrict our comments to the most essential issues our involvement in the sampling and field aspects of this study enables us to comment in detail on 1 the number of samples collected 2 the structural corrections and 3 seguin s use of the structural data lastly we will comment on seguin s discussion and interpretation of the obtained results table 1 of seguin 1983 pp 262 263 indicates a very sizeable number of samples n in reality the number of samples collected by us was very limited 9 and was designed primarily to give initial indications of the paleomagnetic suitability sites 1 2 and 3 represent three handsamples 2 to 3 dm3 taken at the same quarry each of the sites 4 5 7 8 9 and 10 corresponds actually to one single handsample it is deceptive therefore to describe these handsamples as sites creating the false impression that a representative collection was made for the formations of the chantonnay synclinorium our second and much more serious point concerns the structural data in the form of strikes and dips and their use to correct the in situ declination and inclination values d and z to those with respect to bedding de and z the handsamples 4 7 10 and 11 that we collected were oriented with respect to bedding

a general rule for synoptic eddy feedback onto low frequency flow in this study scale interaction between synoptic eddies and low frequency flow is investigated it is demonstrated here that there is a general rule the left hand rule that describes synoptic eddy feedback onto low frequency flow the rule is that low frequency anomalies systematically stir and deform the transient eddies in such a way that the irrotational eddy vorticity fluxes are directed preferentially about 90 toward the left hand side of the low frequency flow thus this eddy feedback plays a positive role in maintaining and prolonging low frequency flow under the stormy atmosphere similarly we show that the irrotational eddy temperature and moisture fluxes are also directed preferentially about 90 toward the left hand side of the low frequency flow in the northern hemisphere the eddy temperature fluxes and their vertical structure play a positive role in reinforcing the low frequency flow in the low levels the moisture fluxes play a role in enhancing low frequency flow by providing eddy induced moisture convergence and divergence

interdecadal change in the north atlantic storm track during boreal summer around the mid 2000s role of the atmospheric internal processes the first eof mode eof1 of summer storm track activity over the north atlantic is characterized by a dipole structure with negative storm track anomalies over the south coast of greenland extending northeast across iceland to the norwegian sea and positive anomalies over coastal western europe this study shows that a significant interdecadal change in the north atlantic storm track during boreal summer occurred around the mid 2000s after the mid 2000s the eof1 occurs more frequently at its positive phase which is associated with an interdecadal increase in the geopotential height anomalies around greenland on the intra seasonal timescale the anticyclonic anomalies around greenland are crucial for the occurrence of positive eof1 events via triggering eastward propagating rossby waves therefore the interdecadal increase in the geopotential height anomalies around greenland tends to facilitate the occurrence of the positive eof1 event and is therefore a key driver of the interdecadal change in the summer storm track activity over the north atlantic further analysis indicates that the development of anticyclonic anomalies around greenland is maintained by the self interaction among the low and high frequency transients themselves moreover the anomalous synoptic eddy activities associated with the change in storm tracks can in turn amplify and maintain the rossby waves triggered by the anticyclonic anomalies around greenland in the synoptic scale eddy feedback process

the link between the north pacific climate variability and the north atlantic oscillation via downstream propagation of synoptic waves abstractthe north atlantic oscillation nao response to the northeast pacific climate variability is examined using the era 40 dataset the main objective is to validate a mechanism involving downstream wave propagation processes proposed in a recent idealized companion study a low frequency planetary scale ridge trough anomaly located in the eastern pacific north american sector induces more equatorward poleward propagation of synoptic scale wave packets on its downstream side which favors the occurrence of anticyclonic cyclonic wave breakings in the atlantic sector and the positive negative nao phase the mechanism first provides an interpretation of the canonical impact of the el nino southern oscillation on the nao in late winter the wintertime relationship between the pacific north american oscillation pna and the nao is also investigated for out of phase fluctuations between the pna and nao indices i e the most recurrent situation in late winter the eastern pacific pna ridge trou

the british baikal corridor a teleconnection pattern along the summertime polar front jet over eurasia abstractthe british baikal corridor bbc pattern a new teleconnection along the summertime upper tropospheric polar front jet pfj is investigated based on observational and reanalysis datasets

an idealized nonlinear model of the northern hemisphere winter storm tracks abstract in this paper a nonlinear dry model forced by fixed radiative forcing alone has been constructed to simulate the northern hemisphere winter storm tracks a procedure has been devised to iterate the radiative equilibrium temperature profile such that at the end of the iterations the model climate closely resembles the desired target climate this iterative approach is applied to simulate the climatological storm tracks in january it is found that when the three dimensional temperature distribution in the model resembles the observed distribution the model storm tracks are much too weak it is hypothesized that this is due to the fact that eddy development is suppressed in a dry atmosphere owing to the lack of latent heat release in the ascending warm air to obtain storm tracks with realistic amplitudes the static stability of the target climate is reduced to simulate the enhancement in baroclinic energy conversion due to latent heat release with this modification the storm tracks in the

development and maintenance mechanism for the semiannual oscillation of the north pacific upper level circulation abstractthe north south semiannual oscillation sao of the north pacific jet stream part of the atmospheric sao in the northern hemisphere can be well depicted by the semiannual component of the monthly mean eddy streamfunction expressed by the semiannual eddy streamfunction budget the dynamic processes develop and maintain the sao including the adjustment between vorticity advection and convergence of vorticity flux of the monthly mean mode and the convergence of transient vorticity flux an empirical orthogonal function analysis of these dynamic processes shows an east west elongated cyclonic anticyclonic cell of the semiannual eddy streamfunction anomaly which appears in january and july october and april south of the siberia alaska landmass the maximum minimum adjustment processes by the monthly mean mode and the maximum minimum feedback impact of transient activity on the sao occur in december and june september and march a month ahead of the maximum minimum north south sao of th

geodynamic model for the palaeozoic crustal consolidation of western and central europe abstract the crystalline basement of western and central europe consists of a mosaic of crustal elements which were consolidated during pre grenvillian the grenvillian dalslandian morarian cadomian caledonian and hercynian orogenic cycles contemporaneous with the caledonian suturing of the precambrian laurentia greenland and fennosarmatian shields a number of gondwana derived cadomian micro cratons were accreted to the southern margin of laurasia following the late caledonian paroxysm the devonian and early carboniferous evolution of europe was dominated by continued northward subduction of the proto tethys plate at an arc trench system parallelling the southern margin of laurasia the accretion of additional gondwana derived continental fragments back arc rifting and a sinistral translation of major proportions between the laurentia greenland and the fennosarmatian sub plates the acadian and bretonian orogenies were of the pacific type the visean collision of gondwana with laurasia marked the onset of the himalayan type variscan orogeny during which collision related compressive stresses overpowered the devonian early carboniferous back arc rift systems and caused the development reactivation of a subduction zones the central armorican and saxothuringian successor basins became folded and destroyed during the latest visean whilst the variscan foredeep became scooped out in part by nappes involving the basement during the late westphalian major crustal shortening during the variscan diastrophism was accompanied by the anatectic remobilisation of subducted crustal and upper mantle material and a widespread syn and late orogenic magmatism the latest carboniferous early permian reorientation of the convergence direction between gondwana and laurasia induced the development of a complex wrench fault system transecting the variscan fold belt and an extensive post orogenic volcanism the hypotheses summarised here require confirmation by further palaeomagnetic and radiometric data and faunal analyses

circumglobal teleconnections the jet stream waveguide and the north atlantic oscillation abstract monthly and seasonally averaged upper tropospheric northern hemisphere winter fields are examined to determine whether the waveguiding effect of the time averaged tropospheric jets on low frequency disturbances that is predicted by theory does affect the behavior of these disturbances it is found that indeed disturbances in the vicinity of the mean jets particularly the jet that stretches across south asia are fundamentally different from those that reside in regions where the mean winds have weaker meridional gradients like the mid pacific patterns of variability in the jets tend to be smaller scale and to consist of zonally oriented chains of anomalies while variability in the mid pacific is composed of patterns with distinct meridional orientation because they are meridionally trapped and zonally elongated patterns associated with the jet stream waveguide connect activity at points that are much farther apart than do patterns in other regions of the globe within the south asian waveg

adjustment of the atmospheric circulation to tropical pacific sst anomalies variability of transient eddy propagation in the pacific north america sector nas a pattern that is shifted southward northward compared with climatology paths of coherent phase propagation of transient eddies and of the propagation of wave packets are analyzed a coherent path of propagation across the pacific towards north america is identified that is more zonal during el niwinters and during la nihas a dominant path heading northeastward to the pacific northwest a second path heading southeastward from the central pacific to the tropical east pacific is more accentuated during la ni nas than el ni nos these changes in wave propagation are reproduced in an ensemble of seasonal integrations of a general circulation model forced by a tropical pacific sea surface temperature pattern confirming that the changes are forced by changes in the mean atmospheric state arising from changes in tropical sea surface temperature a simplified model with a specified basic state is used to model the storm tracks for el ni no and la ni na winters the results suggest that the changes in transient eddy propagation and the eddy statistics can be understood in terms of the refraction of transient eddies within different basic states copyright c 2010 royal meteorological society

a simple kinematic source of skewness in atmospheric flow fields abstractgeopotential height fields exhibit a well known pattern of skewness with distributions that are positively skewed on the poleward side of the midlatitude jets storm tracks and negatively skewed on the equatorward side this pattern has often been interpreted as a signature of nonlinear dynamical features such as blocking highs and cutoff lows and there is renewed interest in the higher moments of flow variables as indicators of the nature of the underlying dynamics however this paper suggests that skewness can arise as a simple kinematic consequence of the presence of jet streams and so may not be a reliable indicator of nonlinear dynamical behavior in support of this reanalysis data are analyzed to demonstrate a close link between the jet streams and the skewness patterns further evidence is provided by a simple stochastic kinematic model of a jet stream as a gaussian wind profile the parameters of this model are fitted to data from the reanalysis and also from an aquaplanet general circ

upper tropospheric potential vorticity fluctuations and the dynamical relevance of the time mean analysis of frequency distribution functions of potential vorticity pv on middleworld isentropic surfaces that intersect the tropopause reveals that dynamics on these surfaces are dominated by the tropopause separating subtropical and polar pv pools with definitive characteristic values the dominance of the tropopause on these surfaces suggests that the subseasonal transient variance should be a function solely of the time mean pv exploiting this relation it is shown that knowledge of the annual mean pv distribution allows quite skillful deduction of interannual anomalies in transient variance this analysis is extended to the dynamic tropopause where it is shown that polar and subtropical jets clearly emerge in fields of the most frequent tropopause potential temperature implications of these results on the current understanding of how patterns of interannual variance arise are discussed

a comparison of climatological subseasonal variations in the wintertime storm track activity between the north pacific and atlantic local energetics and moisture effect distinct differences of the storm track jet relationship over the north pacific and north atlantic are investigated in terms of barotropic and baroclinic energetics using ncep 2 reanalysis data for the period of 1979 2008 from fall to midwinter the pacific storm track pst activity weakens following the southward shift of the pacific jet whereas the atlantic storm track ast activity remains steady in position and intensifies regardless of the slight southward shift of the atlantic jet this study is devoted to seeking for the factors that can contribute to this conspicuous difference between the two storm tracks on climatological subseasonal variation by analyzing eddy properties and local energetics different eddy properties over the two oceans lead to different contribution of barotropic energy conversion to the initiation of storm tracks in the north atlantic meridionally elongated eddies gain kinetic energy efficiently from stretching deformation of the mean flow in the jet entrance on the other hand the term associated with shearing deformation is important for the initiation of pst analysis of baroclinic energetics reveals that the intensification of the ast activity in midwinter is mainly attributed to coincidence between location of maximum poleward and upward eddy heat fluxes and that of the largest meridional temperature gradient over slight upstream of the ast the relatively large amount of precipitable water and meridional eddy moisture flux along baroclinic energy conversion axis likely provides a more favorable environment for baroclinic eddy growth over the north atlantic than over the north pacific in the meantime the midwinter minimum of the pst activity is attributable to the southward shift of the pacific jet stream that leads to discrepancy between core region of poleward and upward heat fluxes and that of meridional thermal gradient weakening of eddy mean flow interaction due to eddy shape and reduction of moist effect are also responsible for the weakening of storm track activities in midwinter when the strongest baroclinicity exists over the north pacific

late paleozoic remagnetization of the trenton limestone samples of the middle ordovician trenton limestone were collected from 8 sites in quebec ontario and new york state for paleomagnetic study stepwise thermal demagnetization reveals a very well defined characteristic magnetization that has a corresponding paleomagnetic pole at 53 0 n 126 9 e k 97 7 a 95 2 7 this pole is not at all close to other ordovician poles from cratonic north america but is near late carboniferous and early permian ones indicating that the trenton was remagnetized in the late paleozoic an earlier paleomagnetic investigation of the trenton gave a pole that did not appear to be late paleozoic in age however we demonstrate that this earlier study failed to isolate the ancient characteristic magnetization rock magnetic experiments and analyses of magnetic extracts show that the carrier of magnetization is fe3o4 that does not contain ti or other elements in solid solution that would indicate a detrital source the magnetite and its associated remanence appear to have a diagenetic origin

atmosphere ocean thermal coupling in the north atlantic a positive feedback in this article it is examined whether a positive atmosphere ocean feedback is found over the north atlantic through a series of general circulation model gcm experiments a 60 year integration of an atmospheric gcm agcm coupled with a 50 m deep motionless ocean was conducted the coupled run was compared with two uncoupled runs one with prescribed mid latitude climato logical sea surface temperatures ssts and the other with daily ssts derived from the coupled experiment the uncoupled atmosphere forces the slab ocean to obtain sst responses in these runs consistent with previous studies the coupled atmosphere ocean fields show interannual variances larger than those in the uncoupled runs due to reduction in the local thermal damping patterns of maximum atmosphere ocean covariability show the north atlantic oscillation nao and tripole sst anomalies both in the coupled and uncoupled fields indicating a dominant role of the atmosphere in generating the sst anomalies on the other hand analyses of the temporal variability in the three runs suggest an active role of sst anomalies in determining the polarity of the air sea coupled variability longer than the interannual time scale a combined analysis of forcing sst upper air height and the response sst anomalies in the uncoupled run identified that a patch of positive sst anomalies in the mid latitude band around 40 n effectively excite the positive phase of the nao which in turn reinforces the tripole sst anomalies this relationship was further confirmed by a nine member ensemble agcm experiment forced by the relevant sst anomalies since the forcing and response sst anomaly patterns bear some resemblance these results manifest positive feedback at work in the coupled atmosphere ocean patterns the processes responsible for this positive feedback were elaborated by a series of linear model experiments the local thermal adjustment of the atmosphere to the sst anomalies results in increased precipitation over the gulf stream region associated diabatic heating applied to a linear baroclinic model yields a positive height response to the east which highly influences the southern part of the nao this stationary response in turn induces a northward deflection in the storm track activity leading to an eddy vorticity feedback that tends to force the positive phase of the nao

the role of stationary eddies in shaping midlatitude storm tracks transient and stationary eddies shape the extratropical climate through their transport of heat moisture and momentum in the zonal mean the transports by transient eddies dominate over those by stationary eddies but this is not necessarily the case locally in particular in storm track entrance and exit regions during winter stationary eddies and their interactions with the mean flow dominate the atmospheric energy transport here it is shown that stationary eddies can shape storm tracks and control where they terminate by modifying local baroclinicity simulations with an idealized aquaplanet gcm show that zonally localized surface heating alone e g ocean heat flux convergence gives rise to storm tracks which have a well defined length scale that is similar to that of earth s storm tracks the storm tracks terminate downstream of the surface heating even in the absence of continents at a distance controlled by the stationary rossby wavelength scale stationary eddies play a dual role within about half a rossby wavelength downstream of the heating region stationary eddy energy fluxes increase the baroclinicity and therefore contribute to energizing the storm track farther downstream enhanced poleward and upward energy transport by stationary eddies reduces the baroclinicity by reducing the meridional temperature gradients and enhancing the static stability transports both of sensible and latent heat water vapor play important roles in determining where storm tracks terminate

paleomagnetism and the evolution of pangea we present new apparent polar wandering apw paths for the latest carboniferous to middle jurassic of europe northern asia north america and gondwana the paths have been constructed by ordering the paleopoles into a time sequence and calculating running averages globally this statistical analysis cannot be carried back before the latest carboniferous because the paleomagnetic record becomes inadequate the polar paths have all been rotated along with the land masses from which they have been observed into the classical configuration of wegener pangea a as quantified by later workers the mean paleopoles agree in the early jurassic but disagree in the latest carboniferous permian and early triassic this result is insensitive to reasonable choices made regarding the arrangement of the continents within gondwana it is true either for results from gondwana as a whole or from africa and south america alone this disagreement in apw paths suggests but does not prove that pangea a lasted for only a short interval of time in the early to middle jurassic 190 170 m y and perhaps the latest triassic 200 m y alternatively we may say either that the paleomagnetic record is biassed by sampling inadequacies or by systematically incorrect age assignments or that the earth s field has been non dipolar we regard these explanations as less likely although they cannot be discounted the polar paths can be reconciled by rotating gondwana anticlockwise by about 35 relative to laurasia placing africa beneath europe and south america beneath eastern north america this configuration is called pangea b pangea b could be a valid reconstruction for the latest carboniferous and early permian approximately 290 260 m y pangea b provides a statistically satisfactory resolution of the paleomagnetic problem it also provides a symmetrical arrangement of the continents bordering the appalachian hercynian fold belt for the late paleozoic which pangea a does not it provides a satisfactory framework for the early evolution of the gulf of mexico and it provides an explanation of the absence of geological evidence for a tethys ocean in the paleozoic the transition between b and a cannot be accurately reconstructed from the paleomagnetic data because the resolution of the record is as yet inadequate but it presumably occurred by a 3500 km minimum dextral megashear between laurasia and gondwana during the late permian and triassic approximately 250 200 m y without the formation of ocean between them and was accompanied by lesser motions between north america and europe the sense of megashear is the same as that invoked by arthaud and matte 1977 on geological grounds but the magnitude and timing are different our interpretation favors the idea that continental drift is a continuous process not confined to jurassic and later times but extending backwards into the triassic and permian we suggest that pangea was not an immobile configuration as envisaged by wegener and most subsequent workers but that it evolved more or less continuously

eddy zonal flow interactions and the persistence of the zonal index abstract an idealized atmospheric general circulation model is used to investigate the factors controlling the time scale of intraseasonal 10 100 day variability of the extratropical atmosphere persistence on these time scales is found in patterns of variability that characterize meridional vacillations of the extratropical jet depending on the degree of asymmetry in the model forcing patterns take on similar properties to the zonal index annular modes and north atlantic oscillation it is found that the time scale of jet meandering is distinct from the obvious internal model time scales suggesting that interaction between synoptic eddies and the large scale flow establish a separate intraseasonal time scale a mechanism is presented by which eddy heat and momentum transport couple to retard motion of the jet slowing its meridional variation and thereby extending the persistence of zonal index and annular mode anomalies the feedback is strong and quite sensitive to model parameters when the mod

decadal covariability of the northern wintertime land surface temperature and atmospheric circulation abstractthe decadal covariability of northern wintertime land surface temperature and 500 hpa geopotential anomalies is examined using the national centers for environmental prediction national center for atmospheric research and the twentieth century reanalyses over the twentieth century and a 996 yr preindustrial climate simulation from the canadian earth system model based on the reanalysis data the covariability is dominated by two leading maximum covariance analysis mca modes mca1 is characterized by temperature anomalies over most of canada the eastern united states mexico and eurasian mid to high latitudes accompanied by anomalies of opposite sign elsewhere over northern landmasses mca2 features temperature anomalies over most of north america eurasia and greenland with opposite anomalies elsewhere in the upper troposphere the synoptic vorticity fluxes reinforce the anomalous circulation while in the lower troposphere advection by the anomalous mean flow offsets the eddy forcing and

the building blocks of northern hemisphere wintertime stationary waves abstractan intermediate complexity moist general circulation model is used to investigate the forcing of stationary waves in the northern hemisphere boreal winter by land sea contrast horizontal h

reconstructing sea level pressure variability via a feature tracking approach abstractthe aim of this paper is to quantify the contribution of synoptic transients to the full spectrum of space time variability of sea level pressure slp in middle latitudes in previous work by the authors it was shown that tracking cyclones and anticyclones in an idealized atmospheric model allows one to reconstruct a surprisingly large fraction of the model s variability including not only synoptic components but also its large scale low frequency component motivated by this result the authors performed tracking of cyclones and anticyclones and estimated cyclone and anticyclone size and geometry characteristics in the observed slp field using the 1948 2008 ncep ncar reanalysis dataset the reconstructed synoptic field was then produced via superimposing radially symmetrized eddies moving along their actual observed trajectories it was found that similar to earlier results for an idealized model the synoptic reconstruction so obtained accounts for a major fraction of the full observed slp v

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

tropical axisymmetric mode of variability in the atmospheric circulation dynamics as a neutral mode abstract there is an observational evidence that the variability in the global upper tropospheric flow fields on a monthly basis is dominated by a zonally uniform pattern symmetric about the equator this fluctuation is characterized by the zonal mean zonal wind anomaly having the same sign within the tropics and thus has been related to changes in the global atmospheric angular momentum in this paper the mechanism of this variability referred to as the tropical axisymmetric mode tam was investigated using the ncep ncar reanalysis an atmospheric general circulation model agcm and a linear baroclinic model an index of the tam defined by the leading principal component of the observed 300 hpa streamfunction anomalies shows quite significant correlation with the nino 3 sst anomalies consistent with a well known coherence between the angular momentum and el nino while this suggests that tam can be forced effectively by el nino events data analyses and an agcm experiment with climatological ss

intraseasonal variations of the british baikal corridor pattern abstractthe british baikal corridor bbc pattern is the dominant waveguide mode trapped along the summertime polar front jet over northern eurasia it consists of four geographically fixed centers

identifying rossby wave trains and quantifying their properties a novel method is introduced to automatically identify upper level rossby wave trains and to objectively diagnose their properties based on the envelope of the upper tropospheric meridional wind represented in a hovmoller diagram the algorithm identifies individual rossby wave trains as objects these depend to some extent on user defined parameters the utility of the method is demonstrated in two areas of application first the skill of a particular numerical weather prediction model is analysed for a specific case of a long lived rossby wave train for this purpose a novel diagnostic is designed based on a hovmoller diagram of the rossby wave train objects that contains forecast data with the same lead time throughout the diagram automatically calculated properties of the different forecast rossby wave trains are compared second the climatological behaviour of rossby wave train objects is investigated in long time series from reanalysis data there are preferred regions for the generation and the decay of rossby wave trains and these regions show significant differences for rossby wave trains of different minimum lifetimes in addition there are substantial differences between the seasons

the transient atmospheric response to midlatitude sst anomalies abstract to study the transient atmospheric response to midlatitude sst anomalies a three layer quasigeostrophic qg model coupled to a slab oceanic mixed layer in the north atlantic is used as diagnosed from a coupled run in perpetual winter conditions the first two modes of sst variability are linked to the model north atlantic oscillation nao and eastern atlantic pattern eap respectively the dominant atmospheric modes in the atlantic sector the two sst anomaly patterns are then prescribed as fixed anomalous boundary conditions for the model atmosphere and its transient responses are established from a large ensemble of simulations in both cases the tendency of the air sea heat fluxes to damp the sst anomalies results in an anomalous diabatic heating of the atmosphere that in turn forces a baroclinic response as predicted by linear theory this initial response rapidly modifies the transient eddy activity and thus the convergence of eddy momentum and heat fluxes the latter transforms t

anatomy of synoptic eddy nao interaction through eddy structure decomposition abstracta method of eddy structure decomposition is proposed to detect how low frequency flow associated with the north atlantic oscillation nao organizes systematically synoptic eddy se activity to generate in phase and upstream feedbacks in this method a statistical eddy streamfunction ses field defined by the three point covariance of synoptic scale streamfunction is introduced to characterize spatiotemporal se flow structures the ses field is decomposed into basic and anomalous parts to represent the climatological se flow structure and its departure these two parts are used to calculate the basic and anomalous eddy velocity eddy vorticity and thus eddy vorticity flux fields in order to elucidate those two se feedbacks onto the nao this method is validated by the fact that the observed anomalous eddy vorticity flux field can be reproduced well by two linear terms the basic eddy velocity field multiplied by anomalous eddy vorticity field and the anomalous eddy velocity field multiplied

relation between annular modes and the mean state southern hemisphere summer abstract the annular modes emerge as the leading mode of extratropical month to month climate variability in both hemispheres here the influence of the background state on the structure and dynamics of the southern hemisphere annular mode sam during the austral summer when the climatology is characterized by a single well defined eddy driven jet is studied subsets of the climatology are constructed for early and late summer and for contrasting polarities of the enso cycle the analysis is based both on observations and on perpetual state gcm experiments the main differences between the subsets involve variations of the latitude of the mean jet it is found that in all the cases the sam is characterized by latitudinal shifts of the jet about its mean position reinforced by a positive momentum flux feedback from baroclinic waves this result is consistent with previous studies of the dynamics of the zonally averaged circulation but is found here to hold over all longitudes and for different positi

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

kinematics of eddy mean flow interaction in an idealized atmospheric model abstractthe authors analyze atmospheric variability simulated in a two layer baroclinic channel quasigeostrophic model by combining eulerian and feature tracking analysis approaches the leading mode of the model s low frequency variability lfv is associated with the irregular shifts of the zonal mean jet to the north and south of its climatological position accompanied by simultaneous intensification of the jet while the deviations from the zonal mean fields are dominated by propagating anomalies with wavenumbers 3 5 the model s variability is shown to stem from the life cycles of cyclones and anticyclones in particular synthetic streamfunction fields constructed by launching idealized composite mean eddies along the actual full model simulated cyclone anticyclone tracks reproduce nearly perfectly not only the dominant propagating waves but also the jet shifting lfv the composite eddy tracks conditioned on the phase of the jet shifting variability migrate north or south along with the zonal mea

barotropic effects on atmospheric storm tracks the effect of barotropic dynamics on atmospheric midlatitude storm tracks is investigated for the northern hemisphere winter season using both observed data analyses and linear barotropic model experiments it is shown that when the model flow is initialized with a realistic wave packet barotropic processes alone can produce key features of the observed storm track structure the author attributes this result both to the barotropic waveguide effect and to the fact that the geographical locations of barotropic growth coincide reasonably well with the baroclinic growth of the atmospheric storm track eddies this study also shows that barotropic dynamics are more relevant for storm tracks in lower latitudes than for those in higher latitudes consistent with the fact that the lower latitude storm tracks are more closely associated with the subtropical jet rather than with the polar front jet that is driven by baroclinic eddies

dynamics of synoptic eddy and low frequency flow interaction part ii a theory for low frequency modes abstract amidst stormy atmospheric circulation there are prominent recurrent patterns of variability in the planetary circulation such as the antarctic oscillation aao arctic oscillation ao or north atlantic oscillation nao and the pacific north america pna pattern the role of the synoptic eddy and low frequency flow self feedback in the formation of these dominant low frequency modes is investigated in this paper using the linear barotropic model with the self feedback proposed in part i it is found that the ao like and aao like leading singular modes of the linear dynamical system emerge from the stormy background flow as the result of a positive self feedback this self feedback also prefers a pna like singular vector as well among other modes under the climatological conditions of northern winters a model with idealized conditions of basic mean flow and activity of synoptic eddy flow and a prototype model are also used to illustrate that there is a natural scale selection for the aao

left hand rule for synoptic eddy feedback on low frequency flow 1 in this study scale interaction between synoptic eddies and low frequency flow is investigated the synoptic eddy feedback is a key process in sustaining the low frequency flow we show clear evidence using ncep reanalysis data that there is a general underlying rule the left hand rule governing the synoptic eddy feedback onto low frequency flow this rule states that eddy vorticity fluxes are directed preferentially about 90 degrees toward their left hand side so that they converge into cyclonic flow and diverge from anticyclonic flow therefore the eddy vorticity flux plays a positive role in reinforcing low frequency flow citation kug j s and f f jin 2009 left hand rule for synoptic eddy feedback on low frequency flow geophys res lett 36 l05709 doi 10 1029 2008gl036435

variability of the southern hemisphere winter split flow a case of two way reinforcement between mean flow and eddy anomalies abstract a new split jet index is defined in this study and composites based on this index show that the split flow regime is characterized by a cold warm cold tripolar temperature anomaly in the south pacific that extends equatorward from the southern hemisphere sh high latitudes while nonsplit flow occurs when the phase of the tripolar temperature anomaly is reversed analyses of the heat budget reveal that the temperature anomalies associated with the split nonsplit flow are mainly forced by mean flow advection instead of local diabatic heating or convergence of eddy heat fluxes localized eliassen palm e p flux diagnostics suggest that the zonal wind anomalies are maintained by the eddy vorticity flux anomalies these diagnostic results are confirmed by numerical experiments conducted using a stationary wave model forced by observed eddy forcings and diabatic heating anomalies the model results show that the effects of the vorticity flux dominates over those of the heat flux which tend to damp

dynamics of synoptic eddy and low frequency flow interaction part i a linear closure abstract the interaction between synoptic eddy and low frequency flow self has been recognized for decades to play an important role in the dynamics of the low frequency variability of the atmospheric circulation in this three part study a linear framework with a stochastic basic flow capturing both the climatological mean flow and climatological measures of the synoptic eddy flow is proposed based on this linear framework a set of linear dynamic equations is derived for the ensemble mean eddy forcing that is generated by anomalous time mean flows by assuming that such dynamically determined eddy forcing anomalies approximately represent the time mean anomalies of the synoptic eddy forcing and by using a quasi equilibrium approximation an analytical nonlocal dynamical closure is obtained for the two way self feedback this linear closure directly relating time mean anomalies of the synoptic eddy forcing to the anomalous time mean flow becomes an internal part of a new linear dynamic system for an

diabatic and orographic forcing of northern winter stationary waves and storm tracks abstract in this study a dry global circulation model is used to examine the contributions made by orographic and diabatic forcings in shaping the zonal asymmetries in the earth s northern hemisphere nh winter climate by design the model mean flow is forced to bear a close resemblance to the observed zonal mean and stationary waves the model also provides a decent simulation of the storm tracks in particular the maxima over the pacific and atlantic and minima over asia and north america are fairly well simulated the model also successfully simulates the observation that the atlantic storm track is stronger than the pacific storm track despite stronger baroclinicity over the pacific sensitivity experiments are performed by imposing and removing various parts of the total forcings in terms of the nh winter stationary waves in the upper troposphere results of this study are largely consistent with previous studies diabatic forcings explain most of the modeled stationary waves with orographic

present weathering rates in a humid tropical watershed nsimi south cameroon the study of biogeochemical and hydrological cycles in small experimental watersheds on silicate rocks common for the temperate zone has not yet been widely applied to the tropics especially humid areas this paper presents an updated database for a six year period for the small experimental watershed of the mengong brook in the humid tropics nsimi south cameroon this watershed is developed on precambrian granitoids north congo shield and consists of two convexo concave lateritic hills surrounding a large flat swamp covered by hydromorphic soils rich in upward organic matter mineralogical and geochemical investigations were carried out in the protolith the saprolite the hillside lateritic soils and the swamp hydromorphic soils biomass chemical analyses were done for the representative species of the swamp vegetation the groundwater was analysed from the parent rock saprolite weathering front to the upper fringe in the hillside and swamp system the chemistry of the wet atmospheric and throughfall deposits and the mengong waters was monitored in the nsimi watershed the carbon transfer occurs primarily in an organic form and essentially as colloids produced by the slow biodegradation of the swamp organic matter these organic colloids contribute significantly to the mobilization and transfer of fe al zr ti and th in the uppermost first meter of the swamp regolith when the organic colloid content is low i e in the hillside groundwater th and zr concentrations are extremely low 3 pmol l icp ms detection limits strongly insoluble secondary thorianite tho 2 and primary zircon zrsio 4 crystals control their mobilization respectively this finding thus justifies the potential use of both these elements as inert elements for isoelement mass balance calculations pertaining to the hillside regolith chloride can not be used as a conservative tracer of hydrological processes and chemical weathering in this watershed biogenic recycling significantly influences the low cl input fluxes sodium is a good tracer of chemical weathering in the watershed the sodium solute flux corrected from cyclic salt input was used to assess the chemical weathering rate even though low 2 8 mm kyr the chemical weathering rate predominates over the mechanical weathering rate 1 9 mm kyr compared to the rio icacos watershed the most studied tropical site the chemical weathering fluxes of silica and sodium in the mengong are 16 and 40 times lower respectively this is not only related to the protective role of the regolith thick in both cases but also to differences in the hydrological functioning this is to be taken into account in the calculations of the carbon cycle balance for large surfaces like that of the tropical forest ecosystems on a stable shield at the global level

el nino la nina and the nonlinearity of their teleconnections the paradigm of an atmospheric system varying linearly with respect to extreme phases of the el nino southern oscillation is questioned it is argued that the global response to tropical pacific sea surface temperature forcing will be inherently nonlinear a physical basis for this intrinsic nonlinearity is the thermodynamic control on deep convection climate statistics for warm and cold events of the tropical pacific are analyzed separately for the northern winter periods during 1950 96 composite analysis of 500 mb heights reveal planetary scale teleconnection patterns as noted in earlier studies a new result is the evidence for an appreciable 358 longitude phase shift between the warm and cold event circulation composites and the two wave trains appear to have different tropical origins a large nonlinear component in north american surface climate anomalies is also found which is consistent with such a phase shift in teleconnections in the tropics rainfall anomalies also show evidence of nonlinear behavior the maximum rain anomalies along the equator are located east of the date line during warm events but west of the date line during cold events the interpretation of this behavior is complicated however by the fact that composite warm event sst anomalies are not the exact inverse of their cold event counterparts idealized atmospheric general circulation model agcm experiments are performed in order to test the question of whether the observed nonlinearity is an intrinsic property of the atmospheric system the model is forced with a composite sst anomaly that undergoes a realistic seasonally varying enso life cycle as described by e rasmusson and t carpenter both positive and negative phases of the sst anomaly are used and a 40 member ensemble of warm and cold event model simulations is conducted a nonlinear climate response in the agcm is found that closely resembles the observed composites including a shift in the equatorial positions of the maxmium rain responses and a phase shift of teleconnection patterns in the upper troposphere barotropic model experiments indicate that the inherent nonlinearity in the tropical rain response may itself be responsible for the phase shift in the extratropical teleconnection patterns

palaeomagnetism of some lithological units from the lower palaeozoic of the vendee france abstract results of the first palaeomagnetic study carried out in the west vendean region at the southern edge of the armorican massif are presented the lithological units sampled range from middle to upper cambrian and silurian after alternating field demagnetization and thermal cleaning la lombardiere basaltic rocks of silurian age yielded only one residual component of magnetization d 214 i 11 after tilt correction the corresponding palaeopole is located at 28 s 321 e la meilleraie sandstone and quartzite of lower ordovician age which are equivalent to the armorican sandstone also contain one single residual component of magnetization d 244 i 5 after demagnetization and tilt correction the corresponding palaeopole is 15 s 293 e finally quartzites and rhyolites of middle to upper cambrian age are characterized by two and possibly three components of magnetization the mean direction of the main residual component after demagnetization and tilt correction is d 319 i 9 the corresponding palaeopole position is 40 n 222 e the apparent path wander of the poles obtained in the vendee is compared with the one of stable europe western and gondwana a convergence of the poles from the vendee and stable europe is observed from the beginning of ordovician time and a reasonable similarity at silurian time this study partly fills the gap of palaeomagnetic data for the period upper cambrian silurian for the armorican plate as early as upper cambrian the vendee was an integral part if the armorican plate the plate tectonics scenario proposed in this paper is the following accelerated separation of the armorican block from gondwana at middle upper cambrian time motion of the armorican block towards stable europe at ordovician time and proximity of armorican plate to the northwest european craton at silurian time if this scenario is right the nature of the hercynian orogen is more likely the result of a collision the armorican plate acting as a buffer zone palaeomagnetic studies of the vendean bocage rock sequence are considered important for future work

effect of latitudinal variations in low level baroclinicity on eddy life cycles and upper tropospheric wave breaking processes abstract an analysis of the potential vorticity gradient and the refractive index in quasigeostrophic qg flows on the sphere reveals that the absolute vorticity and the stretching parts have two contradictory effects on the horizontal shape of the baroclinic waves when the full variations of the coriolis parameter are taken into account in each term the absolute vorticity effect favors the anticyclonic southwest northeast tilt and anticyclonic wave breaking awb and is stronger in the upper troposphere in contrast the stretching effect promotes the cyclonic northwest southeast tilt and cyclonic wave breaking cwb and is more efficient at lower levels a positive eddy feedback acting on the latitudinal variations of the zonal winds is deduced because the absolute vorticity and the stretching effects are respectively more and less efficient with increasing latitude a more northward southward jet renders awb more less probable and cwb less more probable the jet is pushed or maintained mor

late ordovician glaciomarine deposits orea shale in the sierra de albarracin spain abstract a description and interpretation is given of marine fragment bearing arenaceous shales occuring near the ordovician silurian boundary in northeast spain these deposits known as the orea shales have been reported before as non glacial or questionably glaciomarine sedimentary features and scanning electron microscopical examination of quartz grains however reveal that much of the debris has been supplied by ice rafting paratillite close similarity between these spanish deposits and coeval normandian paratillites supports the theory that the iberian peninsula and northwest france belonged to one depositional realm probably forming a microcontinent armorica separated from the glaciated gondwanaland

interannual variability in north atlantic weather data analysis and a quasigeostrophic model abstractthis paper addresses the effect of interannual variability in jet stream orientation on weather systems over the north atlantic basin nab the observational analysis relies on 65 yr of ncep ncar reanalysis 1948 2012 the total daily kinetic energy of the geostrophic wind gtke is taken as a measure of storm activity over the north atlantic the nab is partitioned into four rectangular regions and the winter average of gtke is calculated for each quadrant the spatial gtke average over all four quadrants shows striking year to year variability and is strongly correlated with the north atlantic oscillation nao the gtke strength in the northeast quadrant is closely related to the diffluence angle of the jet stream in the northwest quadrant to gain insight into the relationship between the diffluence angle and its downstream impact a quasigeostrophic baroclinic model is used the results show that an initially zonal jet persists at its initial latitude over 30 days or longer while a tilted

organization of storm track anomalies by recurring low frequency circulation anomalies abstract from previous studies it is known that anomalous momentum fluxes by bandpass eddies are important in maintaining long lasting tropospheric flow anomalies evidence is presented that suggests that these anomalous fluxes do not occur at random but happen because the structure of storm track activity is modified by the presence of prominent low frequency large scale circulation anomalies this behavior is noted in an extended integration of a perpetual january simulation with a general circulation model gcm because nonlinear feedbacks between low and high frequency variability make it difficult to establish causal relationships between these two ranges of variability a model is constructed that approximates the storm track activity that would be expected to accompany a given low frequency without including the feedback of the high frequencies onto the low frequency state this model is based on the linearized primitive equations and uses a series of short integrations from random initial condi