suppression of eddy diffusivity across jets in the southern ocean abstract geostrophic eddies control the meridional mixing of heat carbon and other climatically important tracers in the southern ocean the rate of eddy mixing is typically quantified through an eddy diffusivity there is an ongoing debate as to whether eddy mixing in enhanced in the core of the antarctic circumpolar current or on its flanks a simple expression is derived that predicts the rate of eddy mixing that is the eddy diffusivity as a function of eddy and mean current statistics this novel expression predicts suppression of the cross jet eddy diffusivity in the core of the antarctic circumpolar current despite enhanced values of eddy kinetic energy the expression is qualitatively and quantitatively validated by independent estimates of eddy mixing from altimetry observations this work suggests that the meridional eddy diffusivity across the antarctic circumpolar current is weaker than presently assumed because of the suppression of eddy mixing by the strong zonal current

eddy zonal flow feedback in the southern hemisphere abstract the variability of the zonal mean zonal wind in the southern hemisphere is studied using eof analysis and momentum budget diagnostics of ncep reanalysis data 1978 97 the leading eof of the zonal mean zonal wind is well separated from the remaining eofs and represents the north south movement of the midlatitude jet analysis of the momentum budget shows that a positive feedback between the zonal mean wind anomalies and the eddy momentum fluxes accounts for the unusual persistence of eof1 and plays an important role in the selection of the leading eof of midlatitude variability further analysis also shows a propagating feedback common to both eof1 and eof2 which is responsible for the poleward drift of wind anomalies with time the observations support the following feedback mechanism anomalous baroclinic wave activity is generated at the latitude of anomalous temperature gradient that by thermal wind coincides with the latitude of the anomalous zonal jet the net propagation of baroclinic

midlatitude atmospheric transient eddy feedbacks influenced enso associated wintertime pacific teleconnection patterns in two pdo phases the el nino southern oscillation enso associated wintertime atmospheric teleconnection patterns in two pacific decadal oscillation pdo phases are investigated using era 20c reanalysis data for 1950 2010 a strengthened enso associated pacific north american pna teleconnection pattern presents in pdo positive phase while a west pacific wp pattern over northwestern pacific and a squeezed pna pattern coexist when enso occurs in pdo negative phase the dynamical role of atmospheric transient eddy feedbacks to the teleconnection patterns are highlighted in the present study when enso occurs in pdo positive phase the uniform strengthened westerly jet anomalies downstream of the climatological main body of jet accompany with energetic transient eddy anomalies over northeastern pacific the transient eddy feedbacks largely enhance and favor the strengthened pna pattern when enso occurs in pdo negative phase the strengthened westerly jet anomalies appear to separate into two parts one locating north of the climatological main body of jet and the other at the downstream the accompanied transient eddy anomalies also split into two parts under such conditions the transient eddy feedbacks are limited over northeastern pacific and favor a weak pna pattern however the transient eddy anomalies over northwestern pacific strengthen and the feedbacks also strengthen and largely contribute to the wp pattern moreover the transient eddy anomalies over northwestern pacific seem to be anchored along the anomalously poleward strengthened oceanic subarctic frontal zone safz in pdo negative phase the enhanced atmospheric baroclinicity anomalies coupled with the strengthened safz energize atmospheric transient eddy anomalies and work as the potential maintenance in shaping the wp pattern

causes of reduced north atlantic storm activity in a cam3 simulation of the last glacial maximum abstract the aim of this paper is to determine how an atmosphere with enhanced mean state baroclinity can support weaker baroclinic wave activity than an atmosphere with weak mean state baroclinity as a case study a last glacial maximum lgm model simulation previously documented to have reduced baroclinic storm activity relative to the modern day climate simulated by the same model despite having an enhanced midlatitude temperature gradient is considered several candidate mechanisms are evaluated to explain this apparent paradox a linear stability analysis is first performed on the jet in the modern day and the lgm simulation the latter has relatively strong barotropic velocity shear it was found that the lgm mean state is more unstable to baroclinic disturbances than the modern day mean state although the three dimensional jet structure does stabilize the lgm jet relative to the eady growth rate next feature tracking was used to assess the storm track seeding and temporal growth of distur

interannual and decadal modulations recently observed in the pacific storm track activity and east asian winter monsoon abstract interannual variability of the north pacific storm track observed over 17 recent winters is documented the local storm track activity is measured by a meridional flux of sensible heat associated with the lower tropospheric subweekly fluctuations the interannual variability in the heat flux over the northwestern nw pacific is found to be strongest in midwinter the first empirical orthogonal function of the interannual variability in midwinter captures the decadal tendency toward the enhanced storm track activity in midwinter over the nw pacific in association with the decadal weakening of the east asian winter monsoon siberian high and the aleutian low that occurred in the late 1980s the most marked signature of this enhancement is that the midwinter minimum in the storm track activity which had been apparent in the early to mid 1980s almost disappeared afterward as opposed to linear theory of baroclinic instability the enhanced activity occurred despite the weakening of the pacific j

geographic vectors of human mobility in the andes 34 36 s comparative analysis of minor obsidian sources abstract we have carried out long term comparative in a wide latitudinal range of the andes 29 37 south encompassing selected areas that differ in ecology and biogeography this latitudinal span shows diversity in subsistence modes across time and space ranging from andean agro pastoralists in the north to patagonian hunter gatherers in the south as part of this research a program of geochemical and archaeological characterization of obsidian sources and distributions is being developed attempting to assess connections between different biogeographical contexts this work has allowed recognizing five andean sources with different geological and topographical properties stemming from this macro regional endeavor in this paper we present a comparative analysis of the human use of two sources that based on the intensity of human use on a macro regional scale can be interpreted as minor sources this study is framed on gis least cost models for human circulation across rugged landscapes allowing access to the sources we assess temporal and spatial patterns of human occupation of high altitude andean deserts and neighboring areas comparing two of obsidian sources laguna del diamante 34 s and cerro huenul 36 s the results indicate the existence of asymmetric distributions particularly in the case of laguna del diamante this evidence is used to assess the existence of dominant geographic vectors of human access and use of the andean highlands on this basis we explore the analytical potential of minor sources for the study of human biogeography and organization of technology

variations of northern hemisphere storm track and extratropical cyclone activity associated with the madden julian oscillation abstractthis study investigates the intraseasonal variations of the northern hemispheric storm track associated with the madden julian oscillation mjo during the extended boreal winter november april using 36 yr 1979 2014 of reanalysis data from era interim two methods have been used to diagnose storm track variations in the first method the storm track is quantified by the temporal filtered variance of 250 hpa meridional wind vv250 or mean sea level pressure pp the intraseasonal anomalies of vv250 composited for eight mjo phases are characterized by a zonal band of strong positive or negative anomalies meandering from the pacific all the way across north america and the atlantic into northern europe with weaker anomalies of opposite sign at one or both flanks the results based on pp are consistent with those based on vv250 except for larger zonal variations which may be induced by surface topography in the second method an objective cyclone tracking scheme has been used to track the

the lami pyroclastic succession lipari aeolian islands a clue for unravelling the eruptive dynamics of the monte pilato rhyolitic pumice cone abstract the lami succession piled up during the explosive activity of the monte pilato on lipari island central aeolian arc italy it comprises a repetitive alternation of fall and pyroclastic density current beds which define 13 units separated by fine ash beds despite the homogeneous rhyolitic composition the juveniles fragments show strong textural heterogeneities from highly vesicular pumice to dense black obsidians the pumice types are termed i tube which shows elongated tubular vesicles ii frothy highly vesicular with large sub rounded vesicles and iii agglomerated and welded two types of obsidian pyroclasts are recognized i aphyric black obsidian and ii grey obsidian showing spherulitic texture all these pyroclastic types occur throughout the stratigraphic succession and mixed in the same bed they account for changing physical conditions along the conduit which is hypothesised to be filled by a melt plug during the eruption of 12 out of 13 units the strong textural heterogeneities of the juvenile fragments testify for the existence of differential shear rates which can be explained though two shear mechanism i simple shear producing horizontal zonation of texture in the conduit with black obsidians along the conduit walls passing to tube and frothy pumice to the centre and ii pure shear producing a vertical zonation in the conduit with black obsidians at the top overlying frothy pumice agglomerated and welded pumice of unit 13 is thought to represent the portion of magma heated by a batch of hotter melt that entered the magma chamber and triggered the eruption the deposits of unit 13 represent a unique case of spatter accretion due to accumulation of hot low viscous rhyolitic pumice fragments emplaced from pyroclastic fountaining

provenance study on prehistoric obsidian objects found in romania eastern carpathian basin and its neighbouring regions using prompt gamma activation analysis abstract macroscopic characteristics such as hardness relatively easy workability transparency translucency and shiny black colour of the carpathian 1 c1 type obsidian which is one significant variety of the carpathian obsidians made it highly valuable in the prehistoric times it was transported several hundreds of kilometres away from the geological source becoming wide spread in the eastern part of the carpathian basin as well seventy two pieces of prehistoric neolithic to bronze age obsidian artefacts tools arrow heads chips and fragments found in different parts of romania transylvania banat and muntenia have been investigated by non destructive prompt gamma activation analyses the aim of the study was to determine the provenance of their raw materials the geochemical composition of the artefacts showed high similarity with that of the obsidian samples collected at outcrops from the slovakian side of the tokaj mountains based on characteristic major and trace element concentrations most of the studied romanian obsidian artefacts are characterized as c1 type obsidians however some archaeological pieces from banat and muntenia have been identified as carpathian 2 c2 tolcsva erd benye and mad type based on the pgaa results any other provenance such as lipari melos sardinia yali antiparos or armenia can be excluded with high significance our results suggest that in parallel with the predominance of the c1 type obsidian raw material in the transylvanian basin simultaneous use of c2 type obsidian raw material can be shown outside transylvania in banat and muntenia and especially during the neolithic this can imply different connections and raw material supply routes from the tokaj mountains to transylvania and to the southern regions during the neolithic and the copper age

chemical characterization of obsidians from different mediterranean sources by non destructive sem eds analytical method the aim of our research is to check the sem eds non destructive analytical method for discriminating and locating the possible sources of obsidian artefacts moreover in order to obtain a significant discrimination of mediterranean obsidians we analysed samples collected from outcrops of the major sources monte arci sardinia and palmarola lipari pantelleria gyali and melos islands all samples were analysed by both xrf whole rock and sem eds glass and microliths microphenocrysts the xrf analysis reveals that major elements discriminate obsidian the discrimination using major elements is very useful because the amount of trace elements is lower than the detection limit of a si li ed detector the major elements particularly sio2 al2o3 cao na2o and k2o of obsidian glass discriminate the six main mediterranean sources our work demonstrates therefore the possibility of discriminating different provenance of obsidian artefacts using sem eds by means of a relatively rapid effective and above all non destructive method

on the likelihood of tropical extratropical cloud bands in the south indian convergence zone during enso events abstractthe southern hemisphere subtropical convergence zones are important regions of rainfall in the subtropics the south indian ocean convergence zone sicz has the strongest seasonality and exhibits substantial interannual variability in strength and position during austral summer on synoptic time scales the sicz is a preferred region for the formation of tropical extratropical te cloud bands with local maxima over the southern african mainland and madagascar this study investigates how the seasonality in satellite observed cloud band frequency emerges from the interplay between the asynchronous seasonal cycles in convective instability and upper level flow as represented by reanalysis data these atmospheric mean states are diagnosed with a gross convective instability metric and a method to distinguish between subtropical and eddy driven jet axes month by month analysis of these diagnostics elucidates how mean state perturbations during enso events modify cloud band likelihood typically 1

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

mechanisms controlling the downstream poleward deflection of midlatitude storm tracks abstractthe atlantic and pacific storm tracks in the northern hemisphere are characterized by a downstream poleward deflection which has important consequences for the distribution of heat wind and precipitation in the midlatitudes in this study the spatial structure of the storm tracks is examined by tracking transient cyclones in an idealized gcm with a localized ocean heat flux the localized atmospheric response is decomposed in terms of a time and zonal mean background flow a stationary wave and a transient eddy field the lagrangian tracks are used to construct cyclone composites and perform a spatially varying pv budget three distinct mechanisms that contribute to the poleward tilt emerge transient nonlinear advection latent heat release and stationary advection the downstream evolution of the pv composites shows the different role played by the stationary wave in each region in the region where the tilt is maximized all three mechanisms contribute to the poleward propagation of the

on the zonal structure of the north atlantic oscillation and annular modes abstract the zonal structure and dynamics of the dipolar patterns of intraseasonal variability in the extratropical atmosphere namely the north atlantic oscillation nao and the so called annular modes of variability are investigated in an idealized general circulation model particular attention is focused on the relationships linking the zonal structure of the stationary waves synoptic variability i e the storm tracks and the zonal structure of the patterns of intraseasonal variability large scale topography and diabatic anomalies are introduced to modify and concentrate the synoptic variability establishing a recipe for a localized storm track comparison of the large scale forcing synoptic variability and patterns of intraseasonal variability suggests a nonlinear relationship between the large scale forcing and the variability it is found that localized nao like patterns arise from the confluence of topographic and diabatic forcing and that the patterns are more localized than one would e

moving obsidian the case of antofagasta de la sierra basin southern argentinean puna during the late middle and late holocene abstract this paper presents the results of an xrf analysis on the provenience of 118 obsidian artifacts from archaeological sites of the antofagasta de la sierra basin catamarca province argentina dating to the late middle and late holocene c 4500 1100 bp the time span considered encompasses a local process of gradual transformation from hunter gatherer early agro pastoral groups to consolidated agro pastoral societies for this study non destructive elemental analysis of obsidian artifacts was conducted using two different x ray fluorescence spectrometers ed xrf this information was then supplemented by previous provenience results undertaken on 59 obsidian archaeological artifacts from the same area a comparative synthesis of chemical and macroscopic characterization of five obsidian sources located in southern argentinean puna is also presented the provenance of archaeological materials was assigned by comparison with twelve presently known argentine sources on this basis late middle and late holocene obsidian regional movement patterns differential distribution and use of this raw material are discussed furthermore this obsidian research lends support to the existence of exchange networks based on the use of different extra regional obsidian sources located in the northern argentinean puna

significance of a midlatitude sst frontal zone in the formation of a storm track and an eddy driven westerly jet abstract in a set of idealized aquaplanet experiments with an atmospheric general circulation model to which zonally uniform sea surface temperature sst is prescribed globally as the lower boundary condition an assessment is made of the potential influence of the frontal sst gradient upon the formation of a storm track and an eddy driven midlatitude polar front jet pfj and on its robustness against changes in the intensity of a subtropical jet stj in experiments with the frontal midlatitude sst gradient as that observed in the southwestern indian ocean transient eddy activity in each of the winter and summer hemispheres is organized into a deep storm track along the sst front with an enhanced low level baroclinic growth of eddies in the winter hemisphere another storm track forms just below the intense stj core but it is confined to the upper troposphere with no significant baroclinic eddy growth underneath the near surface westerlies are strongest near the midlatitude sst front as observe

the basic ingredients of the north atlantic storm track part ii sea surface temperatures abstractthe impact of north atlantic sst patterns on the storm track is investigated using a hierarchy of gcm simulations using idealized aquaplanet and semirealistic boundary conditions in the atmospheric component hadam3 of the third climate configuration of the met office unified model hadcm3 this framework enables the mechanisms determining the tropospheric response to north atlantic sst patterns to be examined both in isolation and in combination with continental scale landmasses and orography in isolation a gulf stream sst pattern acts to strengthen the downstream storm track while a north atlantic drift sst pattern weakens it these changes are consistent with changes in the extratropical sst gradient and near surface baroclinicity and each storm track response is associated with a consistent change in the tropospheric jet structure locally enhanced near surface horizontal wind convergence is found over the warm side of strengthened sst gradients associated with ascending air and i

obsidian provenance determination by back scattered electron imaging obsidian glass is a significant component of the lithic artefact assemblage of primitive cultures the ability to characterize and correlate artefacts with specific sources provides significant information about prehistoric patterns of procurement and exchange1 because visual and light optical microscopic methods have proved ineffective in characterizing obsidian chemical methods such as x ray fluorescence2 xrf and instrumental neutron activation analysis3 inaa are usually used to try to determine provenance here we show that electron microscopy specifically back scattered electron bse imaging may be used to characterize obsidian petrographically the variety and number of bse observable features are generally sufficient to petrographically fingerprint individual obsidian sources sources are also sufficiently homogeneous so that bse characterization can determine provenance for individual artefacts of archaeological obsidian

obsidian use and mobility during the early and middle holocene in the salt puna nw argentina abstract we discuss the use of obsidian as a tool to understand the mobility range of hunter gatherers living in a high elevation desert in the salt puna specifically in the area of antofagasta de la sierra catamarca between ca 9000 and 6000 bp xrf analyses of a vertical sample of obsidian artifacts pertaining to early and middle holocene contexts from three archaeological sites show the use of various sources within a range of 40 95 km respectively from the study area our analyses suggest that mobility patterns during the early colonization phase early holocene of this high elevation region included two sources located in the eastern and northwestern areas of the salt puna and reveal a process of landscape learning by contrast during the phase of effective occupation middle holocene a period coinciding with climatic fluctuations and decreasing rainfall a greater number of obsidian sources were used suggesting increased knowledge of the landscape as well as a pattern of territorial range shifting

mechanisms determining the winter atmospheric response to the atlantic overturning circulation abstractin climate models an intensification of the atlantic meridional overturning circulation amoc precedes a warming in the north atlantic subpolar basin by a few years in the ipsl cm5a lr model this warming may explain the atmospheric response to the amoc observed in winter which resembles a negative phase of the north atlantic oscillation nao to firmly establish the causality links between the ocean and the atmosphere and illustrate the underlying mechanisms in this model ensembles of atmosphere only simulations are conducted prescribing the sst and sea ice anomalies that follow an amoc intensification in late winter the north atlantic sst and sea ice anomalies drive atmospheric circulation anomalies similar to those found in the coupled model simulations only driven by the sst anomalies related to the amoc show that the largest oceanic influence is due to the warm subpolar sst anomaly which enhances the oceanic heat release and decreases the lower tropospheric baroclinicity in the reg

a consistent poleward shift of the storm tracks in simulations of 21st century climate 1 a consistent poleward and upward shift and intensification of the storm tracks is found in an ensemble of 21st century climate simulations performed by 15 coupled climate models the shift of the storm tracks is accompanied by a poleward shift and upward expansion of the midlatitude baroclinic regions associated with enhanced warming in the tropical upper troposphere and increased tropopause height the poleward shift in baroclinicity is augmented in the southern hemisphere and partially offset in the northern hemisphere by changes in the surface meridional temperature gradient the poleward shift of the storm tracks also tends to be accompanied by poleward shifts in surface wind stress and precipitation and a shift towards the high index state of the annular modes these results highlight the integral role that the storm tracks play in the climate system and the importance of understanding how and why they will change in the future

the dynamic history of the trans mexican volcanic belt and the mexico subduction zone abstract the trans mexican volcanic belt tmvb is a 1000 km long neogene continental arc showing a large variation in composition and volcanic style and an intra arc extensional tectonics it overlies the rivera and cocos slabs which display marked changes in geometry geophysical studies indicate that lithospheric mantle is very thin or absent beneath the forearc and arc the fluids from the slab are released in a 40 to 100 km wide belt beneath the frontal part of the arc and the lower crust beneath the arc is partially molten east of 101 w the tmvb is built on a precambrian to paleozoic crust with thickness of 50 55 km west of 101 w the tmvb is underlain by jurassic to cenozoic marine and continental arcs with a 35 40 km thick crust the evolution of the tmvb occurred in four stages 1 from 20 to 10 ma the initial andesitic arc moved inland showing progressively drier melting and eventually slab melting suggesting flattening of the subducted slab 2 since 11 ma a pulse of mafic volcanism migrated from west to east reaching the gulf of mexico by 7 ma this mafic lavas marks the lateral propagation of a slab tear triggered by cessation of subduction beneath baja california 3 thereafter the volcanic front started moving trenchward with a marked phase of silicic volcanism between 7 5 and 3 ma local emplacement of small volume intraplate like basalts since 5 ma and development of extensional faulting these features are related to slab rollback enhancing asthenophere flux into the mantle wedge and promoting partial melting of the crust 4 the modern arc consists of a frontal belt dominated by flux and slab melting and a rear belt characterized by more differentiated rocks or by mafic lavas with little or no evidence of subduction fluids but higher asthenosphere fingerprint

configuration of a southern ocean storm track abstractdiagnostics of ocean variability that reflect and influence local transport properties of heat and chemical species vary by an order of magnitude along the southern ocean s antarctic circumpolar current acc topographic hotspots are important regions of localized transport anomalies this study uses a primitive equation channel model to investigate the structure of eddy kinetic energy eke one measure of variability in an oceanic regime a storm track approach emphasizes the importance of stationary eddies which result from flow interactions with topography on setting eke distributions the influence of these interactions extends far downstream of the topography and impacts eke patterns through localized convergence and divergence of heat unlike for zonal averages local contributions to the stationary fluxes from terms that integrate to zero in a zonal average are important the simulations show a strong sensitivity of the zonal structure as well as the distribution and amplitude of sta

empirical relationships between summertime oceanic heat anomalies in the nordic seas and large scale atmospheric circulation in the following winter a lagged regression analysis between an index of observed summertime atlantic water temperature awt variability at the entrance to the barents sea in the period 1982 2005 and year round atmospheric ncep ncar reanalysis data is used to show that subsurface oceanic heat anomalies in high latitudes are significant precursors of wintertime atmospheric variability in middle latitudes in particular positive awt anomalies precede predominantly westerly wind anomalies in high latitudes and easterly wind anomalies in middle latitudes the mid latitude wind anomalies while being generally equivalent barotropic in the upper troposphere have a strong low level baroclinic contribution over eurasia the near surface easterly wind anomalies in this area are locally deflected southward maintaining cold spots near orography the summertime oceanic anomalies explain about 40 of the variance in the surface air temperature averaged over eurasia from 35 to 45 n and about 50 of the variance in surface winds over the far east asia in the following winter we suggest that the remote connections arise from reorganization of the mid latitude storm tracks the awt anomalies explain about 60 of the variance in the upper tropospheric storm track activity averaged over the pacific and eurasia from 35 to 55 n and in the lower tropospheric poleward synoptic eddy heat flux over western eurasia finally we show that the awt associated wintertime atmospheric anomalies appear in quadrature with the concurrent anomalies associated with the north atlantic oscillation these findings suggest that oceanic heat anomalies in high latitudes may be a useful predictor of atmospheric variability

chemical differentiation of obsidian within the glass buttes complex oregon two hundred twenty five source samples from the multi component obsidian source at glass buttes oregon were characterized by neutron activation analysis to determine the number of chemical groups present seven geochemical groups were found within the glass buttes complex an abbreviated neutron activation analysis procedure previously used to differentiate between obsidian sources in mesoamerica was also successful in separating obsidian from different outcrops at glass buttes thirty one artifacts from the robins spring site on glass buttes were also analysed the abbreviated naa procedure was also successful at assigning the artifacts to the different subsources at glass buttes

eddy activity sensitivity to changes in the vertical structure of baroclinicity abstractthe relation between the mean meridional temperature gradient and eddy fluxes has been addressed by several eddy flux closure theories however these theories give little information on the dependence of eddy fluxes on the vertical structure of the temperature gradient the response of eddies to changes in the vertical structure of the temperature gradient is especially interesting since global circulation models suggest that as a result of greenhouse warming the lower tropospheric temperature gradient will decrease whereas the upper tropospheric temperature gradient will increase the effects of the vertical structure of baroclinicity on atmospheric circulation particularly on the eddy activity are investigated an idealized global circulation model with a modified newtonian relaxation scheme is used the scheme allows the authors to obtain a heating profile that produces a predetermined mean temperature profile and to study the response of eddy activity to changes in the vertical structure o

northern hemisphere winter atmospheric transient eddy heat fluxes and the gulf stream and kuroshio oyashio extension variability abstractspatial and temporal covariability between the atmospheric transient eddy heat fluxes i e t and q in the northern hemisphere winter january march and the paths of the gulf stream gs kuroshio extension ke and oyashio extension oe are examined based on an atmospheric reanalyses and ocean observations for 1979 2009 for the climatological winter mean the northward heat fluxes by the synoptic 2 8 days transient eddies exhibit canonical storm tracks with their maxima collocated with the gs and ke oe the intraseasonal 8 days 3 months counterpart while having overall similar amplitude shows a spatial pattern with more localized maxima near the major orography and blocking regions lateral heat flux divergence by transient eddies as the sum of the two frequency bands exhibits very close coupling with the exact locations of the ocean fronts linear regression is used to examine the lead lag relationship between interannual changes in the northward heat fluxes by the transient

a role for barotropic eddy mean flow feedbacks in the zonal wind response to sea ice loss and arctic amplification abstractprevious studies have suggested that in the zonal mean the climatological northern hemisphere wintertime eddy driven jet streams will weaken and shift equatorward in response to arctic am

an observational study of fronts and frontal mergers over the continental united states abstract the stormscale operational and research meteorology fronts experiment systems tests storm fest field program was carried out over the central united states to investigate the structure and dynamics of fronts and their attendant precipitation systems adjacent to complex topography and to evaluate new observing networks and analysis techniques for mesoscale research and weather forecasting this study presents the analysis of data taken between 8 and 10 march 1992 which was the most active period of storm fest this three day observing period was characterized by the passage of an extratropical cyclone and related fronts the synoptic scale conditions related to the cyclone and frontal evolutions are described multiple frontal zones i e pacific and arctic cold fronts quasi stationary polar front dryline maritime warm front and associated regions of precipitation are documented and their origins and interactions are explored these features both well defined and subtle were observed wi

the southern tyrrhenian subduction zone deep geometry magmatism and plio pleistocene evolution abstract we report on a high resolution vp vp vs and qp model of the southern tyrrhenian subduction zone obtained by the inversion of p and s wave arrival times and t values from intraslab seismicity the arcuate shape of the southern apennines calabrian arc sicilian maghrebides is perfectly mirrored by two rather continuous low and high vp bands lying beneath the belt system at ca 25 and 100 km respectively between 100 and 300 km two independent high vp slabs lie beneath the neapolitan region and the southern tyrrhenian sea separated by unperturbed mantle we suggest that the ca 150 km wide slab window beneath the southern apennines opened after a tear occurring within a composite subduction system formed by the apulian continental lithosphere and the ionian oceanic slab the abrupt slab rupture induced ultrafast southeastward retreat of the ionian slab and the 19 cm yr spreading of the back arc oceanic marsili basin between ca 2 1 and 1 6 ma ago the 25 km low vp zone beneath the arc denotes continental upper crustal rocks below the chain its striking continuity requires a unique orogenic wedge at 25 km depth below the southern apennines the calabrian arc and the sicilian maghrebides the alternative explanation would imply the ubiquitous occurrence of autochthonous lower plate rocks at 25 km depth i e a puzzling autochthonous continental calabria the ionian slab beneath calabria shows high vp high qp and low vp vs anomalies typical of old oceanic lithosphere intermediate depth seismicity is concentrated within its thin oceanic crust suggesting the occurrence of vigorous metamorphism the slab dehydration promotes the melting of the overlying mantle as testified by high vp vs and low qp anomalies between the slab and the aeolian magmatic arc

prefrontal wind shift lines in the plains of the united states abstract in the central united states cold fronts are sometimes preceded by a surface wind shift by several hours these wind shifts are examined to determine their origins and characteristics a climatology and a case study of an autumn prefrontal wind shift are presented data collected by the recently implemented oklahoma mesonet and a network of wind profilers permit finescale analyses of the autumn prefrontal wind shift it is found that prefrontal wind shifts are associated with both lee troughs and drylines the climatology reveals that in the central united states fronts are most frequently up to 60 of them preceded by wind shifts just east of the rockies where lee troughs and drylines originate this paper focuses on a case study of a prefrontal wind shift associated with a lee trough that forms when a front approaches the lee trough the prefrontal wind shift associated with the lee trough forms in the lee of the mountains but propagates away from the mountains when downslope flow decreas

secondary cyclogenesis along an occluded front leading to damaging wind gusts windstorm kyrill january 2007 abstractwindstorm kyrill affected large parts of europe in january 2007 and caused widespread havoc and loss of life in this study the formation of a secondary cyclone kyrill ii along the occluded front of the mature cyclone kyrill and the occurrence of severe wind gusts as kyrill ii passed over germany are investigated with the help of high resolution regional climate model simulations kyrill underwent an explosive cyclogenesis south of greenland as the storm crossed poleward of an intense upper level jet stream later in its life cycle secondary cyclogenesis occurred just west of the british isles the formation of kyrill ii along the occluded front was associated i with frontolytic strain and ii with strong diabatic heating in combination with a developing upper level shortwave trough sensitivity studies with reduced latent heat release feature a similar development but a weaker secondary cyclone revealing the importance of diabatic processes during the formation of kyrill ii kyrill ii moved

midwinter suppression of baroclinic wave activity in the pacific abstract seasonal variations in baroclinic wave activity and jet stream structure in the northern hemisphere are investigated based upon over 20 years of daily data baroclinic wave activity at each grid point is represented for each day by an envelope function the lowpass filtered time series of the squared highpass filtered geopotential height baroclinic wave activity over the atlantic exhibits a single maximum in january whereas in the pacific it exhibits peaks in late autumn and in early spring and a significant weakening in midwinter which is more evident at the tropopause level than near the surface this suppression occurs despite the fact that the low level baroclinity and the intensity of the jet stream are strongest in midwinter based on the analysis of 31 day running mean fields for individual winters it is shown that over both the oceans baroclinic wave activity is positively correlated with the strength of the upper tropospheric jet for wind speeds up to 45 m s 1 when the strength of t

baroclinic adjustment and dissipative control of storm tracks abstractthe steady state response of a midlatitude storm track to large scale extratropical thermal forcing and eddy friction is investigated in a dry general circulation model with a zonally symme

the identification of archaeological obsidian sources on kamchatka peninsula russian far east using geochemical and geological data current progress abstract the current state of the art of provenance studies for archaeological obsidian on kamchatka peninsula is presented prehistoric people widely used obsidian as a raw material for making tools and acquired it from several primary sources the exact position of seven sources allowed us to understand the general features of obsidian geochemistry and tectonic position of obsidian bearing volcanic formations this also made it possible to suggest the localization of seven still unknown sources for archaeological obsidian on kamchatka verification of our preliminary conclusions can be made by fieldwork in selected areas

pliocene quaternary volcanism and faulting at the intersection of the gulf of california and the mexican volcanic belt the junction of the western mexican volcanic belt and the gulf of california represents a superposition of subduction and continental rifting tectonic regimes in the late cenozoic subduction of the oceanic rivera plate has caused late cenozoic uplift of western mexico forming the jalisco block this paper addresses three questions where is the northern boundary of the jalisco block how is the continental fracture system related to that offshore and what is the spatial distribution and composition of subduction related lavas 40 ar 39 ar dates on cretaceous to paleogene silicic ash flows show that the northern boundary of the jalisco block may be defined by the abrupt change in basement age from cretaceous to miocene 40 ar 39 ar and k ar dates on faulted lavas from the nayarit region indicate that extension at the edge of the jalisco block has occurred since ca 4 2 ma the least principal stress 3 direction associated with these faults has had two different orientations from 4 2 ma to the present several pliocene to holocene 4 20 1 05 and 0 65 ma lava flows and aligned cinder cones have a n45 w associated least principal stress direction whereas three pliocene 3 36 3 38 and 3 11 ma lava flows are cut by faults indicating a north to north northeast least principal stress direction the two different stress directions may arise either from structural features in the basement of the arc or from changes in offshore plate boundaries e g 2 5 ma when the rivera and mathematicians plates were locked together whole rock major and trace element analyses of lavas from the coastal nayarit region reveal three different lava types an alkali basalt series basaltic andesite and andesite the alkali basalts show feo and tio 2 enrichment and have low ba zr and ba la ratios consistent with derivation from an oceanic island type mantle the basaltic andesites and andesites are both alkaline and calc alkaline contain hydrous phenocrysts and have high sr zr and la nb ratios consistent with a subduction related source among these lavas there is a correlation between sr zr oxygen fugacity and h 2 o contents suggesting that an oxidized hydrous fluid is involved in the genesis of the subduction related lavas the distribution of subduction related volcanic centers in the coastal nayarit region and areas southeast within the jalisco block defines front that parallels the middle america trench and is consistent with a 45 dip on the subducted rivera plate

orographic control of storm zones on mars low pressure cyclones and their accompanying frontal systems in the middle latitudes of the earth s troposphere develop travel eastwards and decay preferentially within latitudinally and longitudinally confined geographical regions known as storm zones1 these zones can be readily identified in the circulation statistics of terrestrial weather systems2 mars like the earth is a rapidly rotating solid planet and has a seasonally varying shallow atmosphere large scale orography and in a broadly defined context continental structures3 although there are also important differences between the two planets travelling weather systems do exist on mars3 this raises the question of whether storm zones also occur there and if so by what mechanisms here we report the results of numerical simulations of global atmospheric circulation patterns on mars we find that storm zones can exist during the northern winter and that continental scale orography rather than surface thermal contrasts is the main factor determining the development of these zones storm zones on mars should play an important role in the martian climate cycle4 5 by influencing the transport of for example heat momentum water vapour and atmospheric dust3 6 8 towards the poles

episodic back arc extension during restricted mantle convection in the central mediterranean abstract in the central mediterranean during the last 80 myr africa has been slowly converging toward eurasia with an average relative velocity of less than 1 cm yr 1 for 50 myr this slow convergence led to the build up of the alpine orogenic belt and to the initiation of consumption of the former tethys ocean in the last 30 myr however the whole central western mediterranean has been swept by rapid episodes of trench migration up to 6 cm yr 1 and back arc opening which consumed the whole former tethys ocean we combine plate tectonic history geological timing and laboratory modelling to reconstruct the subduction history and the evolution of the central mediterranean over the last 80 myr we find that the dynamic evolution of the subducting oceanic lithosphere can reconcile the rapid episodic back arc migration with the slow african convergence but only if the subduction process is restricted to the upper mantle

late pleistocene to precolumbian behind the arc mafic volcanism in the eastern mexican volcanic belt implications for future hazards an area of widespread alkaline to subalkaline volcanism lies at the northern end of the cofre de perote citlaltepetl pico de orizaba volcanic chain in the eastern mexican volcanic belt mvb two principal areas were active about a dozen latest pleistocene to precolumbian vents form the 11 km wide e w trending cofre de perote vent cluster cpvc at 2300 2800 m elevation on the flank of the largely pleistocene cofre de perote shield volcano and produced an extensive lava field that covers s 100 km 2 more widely dispersed vents form the naolinco volcanic field nvf in the sierra de chiconquiaco north of the city of jalapa xalapa three generations of flows are delineated by cone and lava flow morphology degree of vegetation and cultivation and radiocarbon dating the flows lie in the behind the arc portion of the northeastern part of the mvb and show major and trace element chemical patterns transitional between intraplate and subduction zone environments flows of the oldest group originated from la joya cinder cone radiocarbon ages v42 000 yr bp at the eastern end of the cpvc this cone fed an olivine basaltic flow field of v20 km 2 that extends about 14 km southeast to underlie the heavily populated northern outskirts of jalapa the capital city of the state of veracruz the central cone group ccg of intermediate age consists of four morphologically youthful cinder cones and associated vents that were the source of a lava fields 27 km 2 of late pleistocene or holocene age the youngest group includes the westernmost flow from cerro colorado and a lava flow v2980 bp from the rincon de chapultepec scoria cone of the nvf the latest eruption from the compound el volcancillo scoria cone occurred about 870 radiocarbon years ago and produced two chemically and rheologically diverse lava flows that are among the youngest precolumbian flows in mexico and resemble paired aa pahoehoe flows from mauna loa volcano the el volcancillo eruption initially produced the high effusion rate short duration toxtlacuaya alkaline aa lava flow from the southeastern crater this 12 km long hawaiite average 50 5 sio2 flow was followed by extrusion of the calc alkaline r o naolinco lava flow from the northwestern crater this large volume v1 3 km 3 tube fed basaltic pahoehoe flow average sio2 49 traveled 50 km inferred effusion rates suggest emplacement over a decade long period flows of all three age groups are transected by highway 140 and the railway that form major transportation arteries between jalapa and puebla this area has not previously been considered to be at volcanic risk but volcanism here has continued into precolumbian time future eruptions of similar magnitude and location to those documented here could pose significant hazards to transportation corridors and to densely populated areas in and to the north of jalapa slight

sensitivity of the latitude of the surface westerlies to surface friction the sensitivity to surface friction of the latitude of the surface westerlies and the associated eddy driven midlatitude jet is studied in an idealized dry gcm the westerlies move poleward as the friction is reduced in strength an increase in the eastward phase speed of midlatitude eddies is implicated as playing a central role in this shift this shift in latitude is mainly determined by changes in the friction on the zonal mean flow rather than the friction on the eddies if the friction on the zonal mean is reduced instantaneously the response reveals two distinctive adjustment time scales in the fast adjustment over the first 10 20 days there is an increase in the barotropic component of zonal winds and a substantial decrease in the eddy kinetic energy the shift in the surface westerlies and jet latitude occurs in a slower adjustment the space time eddy momentum flux spectra suggest that the key to the shift is a poleward movement in the subtropical critical latitude associated with the faster eastward phase speeds in the dominant midlatitude eddies the view is supported by simulating the upper tropospheric dynamics in a stochastically stirred nonlinear shallow water model

the effect of the madden julian oscillation on the north atlantic oscillation using idealized numerical experiments abstractthe aim of the paper is to investigate the influence of the madden julian oscillation mjo on the north atlantic oscillation nao using a quasigeostrophic model on the sphere a simplifie

sensitivity of the position and variability of the eddy driven jet to different sst profiles in an aquaplanet general circulation model abstractthe response of the storm track and eddy driven jet to various steady sea surface temperature sst forcings is analyzed using the aquaplanet configuration of the atmospheric general circulation model action de recherche petite echelle grande echelle climat arpege climat the sst profiles are zonally homogeneous and piecewise linear functions of the latitude it allows for modifying the tropical component that controls the intensity of the subtropical jet without changing the midlatitude sst front and vice versa sensitivities to the position width and intensity of the midlatitude sst front as well as to the tropical ssts are investigated the baroclinicity and the storm track eddy activity both intensify for a stronger a wider or a more equatorward sst front the eddy driven jet always lies on the poleward side of the sst front and its relative distance to the front is interpreted in terms of upper tropospheric rossby wave breakings a focus is then made on the eddy driven jet variability t

effect of upper and lower level baroclinicity on the persistence of the leading mode of midlatitude jet variability abstractthe sensitivity of the variability of an eddy driven jet to the upper and lower level baroclinicity of the mean state is analyzed using a three level quasigeostrophic model on the sphere

decadal windstorm activity in the north atlantic european sector and its relationship to the meridional overturning circulation in an ensemble of simulations with a coupled climate model the relationship between decadal variations in the north atlantic meridional overturning circulation moc and north atlantic western european windstorm activity during the extended winter season is studied according to an ensemble of three 240 year long simulations performed with the echam5 mpiom model periods of high decadal windstorm activity frequently occur in the years following a phase of weak moc i e when the moc starts to recover these periods are characterised by a distinctive pattern in the mixed layer ocean heat content ohc a positive anomaly is located in the region 45 n 52 n 35 w 16 w west of france negative anomalies are located to the north and south the signal can be detected both in the heat content of the oceanic mixed layer and in the sea surface temperatures its structure is consistent with anomalously enhanced baroclinic instability in the region with the strong negative ohc gradient 30 w 10 w 45 n 60 n which eventually produces a higher probability of windstorms

green grey and black a comparative study of sierra de las navajas mexico and lipari italy obsidians abstract sierra de las navajas state of hidalgo mexico and lipari aeolian islands italy were among the most important sources for obsidian trade in mesoamerica and in the mediterranean during the stone age in this paper obsidians from these two localities were compared in terms of their aspect chemical composition microcrystallinity and microvesiculation in sierra de las navajas the typical deep green obsidian with a golden hue has been analyzed together with a less common dark grey porphyritic variety lipari obsidian is commonly black but a light grey variety also occurs obsidian of both varieties was analyzed for this paper microvesicularity was investigated through scanning electron microscope sem observation microporosimetry and for sierra de las navajas green obsidian through a preliminary x ray computed microtomographic study crystallinity and micro or nano crystallinity were investigated through x ray powder diffraction and eds energy dispersion system microanalyses finally the chemical composition in terms of major and trace elements including rare earth elements was determined using x ray fluorescence xrf and inductively coupled plasma mass spectrometry icp ms the comparison of samples of different colors suggests that the characteristic green color of sierra de las navajas obsidians could be related to their relatively high iron content and to the occurrence of many elongated and iso oriented vesicles which may also be responsible for the obsidian s golden hue low iron and an absence of vesicles give lipari obsidian its normal black color the light grey obsidian from lipari probably owes its color and imperfect conchoidal fracture to numerous bubbles of less than 1 m in size and to nano crystallinity sierra de las navajas obsidians show a significant chemical variability in terms of trace elements that can be explained by common evolutionary processes in the magma chamber however this variability is also internal to a single volcanic complex and this makes the trace element contents unsuitable to differentiating between the different sub sources of the same area on lipari our data do not allow us to distinguish between the two sub sources of vallone del gabellotto and canneto dentro on the basis of major and trace elements on the whole our study suggests that caution should be used for both lipari and sierra de las navajas when identifying obsidian sub sources on the basis of trace element contents

tephrostratigraphy chronology and climatic events of the mediterranean basin during the holocene an overview the identification and characterisation of high frequency climatic changes during the holocene requires natural archives with precise and accurate chronological control which is usually difficult to achieve using only 14c chronologies the presence of time spaced tephra beds in quaternary mediterranean successions represents an additional independent tool for dating and correlating different sedimentary archives these tephra layers are potentially useful for resolving long standing issues in paleoclimatology and can help towards correlating terrestrial and marine paleoclimate archives known major tephras of regional extent derive from central and southern italy the hellenic arc and from anatolia a striking feature of major holocene tephra deposition events in the mediterranean is that they are clustered rather than randomly distributed in time several tephra layers occurred at the time of the s1 sapropel formation between c 8 4 and 9 0 ka bp mercato gabellotto fiumebianco e1 cappadocia and ot

the structure and evolution of a continental winter cyclone part i frontal structure and the occlusion process the frontal structure and occlusion process in a cyclone of moderate intensity that affected the central united states in january 1995 is examined the deep warm frontal zone associated with this cyclone had a lateral extension to the southwest of the sea level pressure minimum that although characterized by cold air advection near the surface had many of the characteristics of a warm front aloft in fact this feature had a structure similar to the so called bent back fronts previously documented only in association with explosively deepening maritime cyclones the development of a warm occluded structure was investigated with the aid of a numerical simulation of the event performed using the university of wisconsin nonhydrostatic modeling system the development of the warm occluded structure was asynchronous in the vertical occurring first at midtropospheric levels and later near the surface in contrast to the classical occlusion process near the surface the warm occluded front was formed as the warm front was overtaken by the frontogenetically inactive portion of the historical coldfrontal zone at midtropospheric levels the warm occluded structure formed as a result of the cold frontal zone approaching and subsequently ascending the warm frontal zone in accord with a component of the classical occlusion mechanism the observed asynchronous evolution of the occluded structure is proposed to result from the vertical variation in vortex strength associated with the upper level potential vorticity pv anomaly that controls the cyclogenesis it is suggested that the occlusion process begins aloft where the associated vortex strength is greatest and gradually penetrates downward toward the surface during the cyclone life cycle additionally a characteristic treble clef shape to the upper level pv anomaly is shown to be a sufficient condition for asserting the presence of a warm occluded structure in the underlying troposphere

residual topography lithospheric structure and sunken slabs in the central mediterranean abstract the central mediterranean comprises subduction collision and backarc extension all in a relatively small area in this paper we analyze the topography of this region examining the influence of subducting slabs on overriding plates we take the observed surface elevation remove the contribution of the crust to it and use the residual topography to identify regions that are unusually low unusually high or normal then we calculate lithospheric thickness where local isostasy applies the results provide information about the structure of the lithosphere in this complex region and about the vertical tectonics in particular we found a difference between the south tyrrhenian subduction zone and the apennines consistent with the processes of slab rollback and slab break off respectively in the south tyrrhenian the edge of the oceanic plate is strongly pulled down whereas the edge of the overriding plate the calabrian peninsula is uplifted this opposite trend indicates weak plate coupling that is the subducting slab which is rapidly rolling back hangs almost entirely on the oceanic plate and the overriding plate is free in contrast in the apennines high residual topography and uplifting are detected on both sides of the mountain belt consistent with complete break off of the subducted lithosphere

provenance of obsidian artifacts from the natural protected area laguna del diamante mendoza province argentina and upper maipo valley chile by la icp ms method abstract by means of inductively coupled plasma mass spectrometry associated with laser ablation la icp ms we analyzed several obsidian artifacts from the natural protected area laguna del diamante mendoza argentina and upper maipo valley chile this analytical method almost non destructive is a powerful tool for the determination of trace elements and is very useful in characterizing and determining the provenance of obsidian fragments of archeological interest although care must be taken to avoid or account for heterogeneities within obsidian such as microcrysts in the macro region of study two types of sources can be differentiated on the basis of their primary location high altitude sources emplaced in the andes range 2500 m a s l including laguna del diamante laguna del maule and las cargas sources and low altitude 1500 m a s l extra andean sources situated on the eastern plains cerro huenul and el peceno in addition while the primary location of arroyo paramillos source is currently unknown we consider it as a sub source of laguna del diamante since its wide archaeological distribution has a main core within laguna del diamante area and in the upper maipo river basin considering this pattern the assignation of provenances presented here improves the basis for assessing the use of high andean environments from both sides of the mountain range in addition we will also improve the geochemical discrimination between the two sources arroyo paramillos and las cargas that based on only previous xrf analysis are chemically overlapping leading to an incorrect interpretation of their pattern of archaeological distribution the better characterization of the obsidian sources of the laguna del diamante and neighboring regions allows discussions of mobility exchange and human use of this lithic resource in the highland of central western argentina central chile

the present day simulation and twenty first century projection of the climatology of extratropical transition in the north atlantic abstractthis study explores the simulations and twenty first century projections of extratropical transition et of tropical cyclones tcs in the north atlantic with a newly developed global climate model the forecast oriented low ocean resolution flor version of the geophysical fluid dynamics laboratory gfdl coupled model version 2 5 cm2 5 flor exhibits good skill in simulating present day et properties e g cyclone phase space parameters a version of flor in which sea surface temperature sst biases are artificially corrected through flux adjustment flor fa shows much improved simulation of et activity e g annual et number this result is largely attributable to better simulation of basinwide tc activity which is strongly dependent on larger scale climate simulation flor fa is also used to explore changes of et activity in the twenty first century under the representative concentration pathway rcp 4 5 scenario a contrasting pattern is found in which regional tc density increas

stratospheric impact on tropospheric winds deduced from potential vorticity inversion in relation to the arctic oscillation the zonal mean state of the atmosphere in the northern hemisphere in winter is determined by the temperature at the earth s surface and by two potential vorticity pv anomalies defined as that part of the pv field that induces a wind field centred over the north pole one in the upper troposphere lower stratosphere utls extending to the subtropics and the other over the polar cap in the lower to middle stratosphere isentropic pv inversion demonstrates that the utls pv anomaly induces the main part of the zonal mean wind in the troposphere including the subtropical jet stream while the stratospheric pv anomaly induces the polar night stratospheric jet the stratospheric pv anomaly has a greater amplitude and extends further downwards if the arctic oscillation ao index is positive also the utls pv anomaly has a slightly larger amplitude if the ao index is positive but the meridional pv gradient in the subtropics that is associated with this anomaly is greatest when the ao index is negative resulting in a stronger subtropical jet when the ao index is negative pv inversion translates the utls pv anomaly into a wind anomaly and a static stability anomaly the resulting differences in the vertical wind shear and in the brunt vaisala frequency between the two ao phases show a larger baroclinicity in the extratropics when the ao index is positive this explains why more extratropical cyclones are observed when the ao index is positive copyright 2010 royal meteorological society

numerical experiments of the storm track sensitivity to oceanic frontal strength within the kuroshio oyashio extensions the sensitivity of the north pacific storm track to midlatitude oceanic frontal strength within the kuroshio oyashio extensions is investigated by applying artificially changed meridional sea surface temperature sst gradients in the weather research forecasting model version 3 4 the result of sensitivity experiments further confirms the close relationship between the storm track activity and meridional sst gradient i e the storm track activity can be intensified as a response to increases in the oceanic frontal strength in order to better understand the mechanism for the storm track intensification due to increased sst gradient velocity temperature correlation and local energetics are analyzed the result indicates that the enhancement of the meridional sst gradient leads to amplitude magnification of eddy meridional velocity and temperature and their phase consistency suggesting that synoptic scale eddies tend to approach the optimum structure for the baroclinic energy conversion which is mainly responsible for the sst front induced enhancement of storm track activity in order to estimate the impact of the oceanic front on the maintenance of the near surface baroclinicity further investigation is made by the composite analysis with the increase in oceanic frontal strength the near surface baroclinicity experiences a slow but strong restoration the increase in the meridional sst gradient results in the intensification in the cross frontal differential sensible heat flux which can more effectively offset the relaxing effect of the transient eddy poleward heat transport

temporal evolution of a three component system the island of lipari aeolian arc southern italy the volcanic products from lipari define an evolutionary trend with a high gradient of k enrichment similar to the calc alkaline to potassic volcanism of other islands in the aeolian arc stratigraphic reconstruction of the island based on field and geochronological data indicate that the volcanic activity can be subdivided in two stages the first stage from 223 to 42 ka consists of six eruptive cycles and is characterized by basalts and basalt andesites showing progressive increase in both sio2 and k2o contents with time the second stage consists of four cycles erupted since 42 ka and is marked by an apparent rejuvenation of the geochemical system with the appearance of the first rhyolitic products fractional crystallization assimilation and mixing models suggest that the geochemistry of lipari volcanism evolved with time by a complex interplay between two mantle derived components one sub alkaline and the other alkaline in addition to crustal melts and or crustally derived materials a petrogenetic model in which fractional crystallization was subordinate to mixing best fits the geochemical data and petrographic observations of macro and microscopic features melts from the crustal and mantle end members are almost always present in the system but the relative proportions appear to vary with time the sub alkaline mantle component source of tyrrhenian tholeiites is an important contributor to the early evolution of the volcanism in lipari input from the alkaline mantle component source of the roman comagmatic province increases with time and the crustal component becomes dominant in the later activity the preferred petrogenetic model for the temporal evolution of the volcanic system in lipari involves melting initially caused by an increase in the thermal input related to the opening of the tyrrhenian sea and or to subduction processes the quick rise of the isotherms and almost contemporaneous melting of source materials with different compositions favored complex mixing during ascent of the melts

response of baroclinic life cycles to barotropic shear abstract cyclonic barotropic shear of incrementally increasing magnitude is imposed on an idealized midlatitude jet and the life cycles of baroclinically unstable wavenumber 6 perturbations growing on these jets are studied when the barotropic shear parameter passes a critical value the life cycle makes an abrupt transition from anticyclonic to cyclonic behavior the abrupt transition in behavior is most evident in the barotropic decay of eddy kinetic energy in the structure of the eddies as seen in potential vorticity maps and in the nature of the zonal flow accelerations produced during the life cycle it is suggested that the abrupt transition can be interpreted as arising from a positive feedback between eddy propagation and eddy induced zonal flow accelerations dependences on the zonal scale of the eddy are also investigated wavenumber 8 exhibits cyclonic behavior while wavenumber 4 exhibits anticyclonic behavior for all values of cyclonic shear considered this dependence on zonal scale is c

modeled climate state and dynamic responses to anomalous north american snow cover abstract the radiative and thermal properties of widespread snow cover anomalies have the potential to modulate local and remote climate over monthly to seasonal time scales in this study physical and dynamical links between anomalous north american snow conditions and northern hemisphere climate are examined a pair of 40 member ensemble agcm experiments is run with prescribed high and low snow forcings over north america during the course of an entire year ey the difference between the two ensemble averages reflects the climatic response to sustained ey snow forcing local surface responses over the snow forcing occur in all seasons and a significant remote surface temperature response occurs over eurasia during spring a hemispheric scale transient eddy response to ey forcing also occurs which propagates downstream from the forcing region to eurasia and then reaches a maximum in extent and amplitude in spring the evolution of this transient eddy response is indicative of considerable downstr

the gulf stream influence on wintertime north atlantic jet variability in this paper we investigate the influence of the gulf stream sst front on the north atlantic eddy driven jet and its variability by analysing the ncep cfsr dataset and a pair of agcm simulations forced with realistic and smoothed gulf stream sst boundary conditions the gulf stream sst front acts to generate stronger meridional eddy heat flux in the lower troposphere and an eddy driven jet over the eastern north atlantic that is located further polewards compared to the simulation with smoothed sst the strong gulf stream sst gradient is found to be crucial in more accurately capturing the trimodal distribution of the eddy driven jet latitude with the more poleward climatological jet being the result of the jet occupying the northern jet position more frequently in the simulation forced with observed ssts the more frequent occurence of the northern jet location is associated with periods of high eddy heat flux over the gulf stream region composite analysis of high eddy heat flux events reveals that the significantly higher heat flux is followed by larger and more persistient poleward jet excursions in the simulations with realistic ssts compared to the simulation with smoothed ssts with upper tropospheric eddy momentum fluxes acting to maintain the more poleward eddy driven jet periods of high eddy heat flux over the gulf stream region are also shown to be associated with increased blocking frequency over europe which are clearly distinct from periods with a northern jet position

the winter concurrent meridional shift of the east asian jet streams and the associated thermal conditions abstractin this study the concurrent meridional shift of the east asian polar front jet eapj and the east asian subtropical jet easj and the associated thermal conditions have been investigate

atmospheric responses and feedback to the meridional ocean heat transport in the north pacific abstractatmospheric responses and feedback to meridional ocean heat transport oht have been investigated using a global climate model that is interactively connected with a high resolution regional ocean model embedded in the western north pacific compared with a global climate model without the regional model the net heat supply into the kuroshio oyashio extension koe region is increased as a result of the increase of the mean northward ocean heat transport oht by the western boundary currents and mesoscale eddies resultant sea surface temperature sst rise sharpens the meridional sst gradient and reinforces the cross frontal difference of the surface heat flux and thereby enhances lower tropospheric baroclinicity these changes cause northward deflection and strengthening of the wintertime storm track over the north pacific which leads to the pacific north american pna like pattern anticyclonic response of the mean westerly jet the increase of the eddy northward atmospheric heat flux ahf

on the provenance of prehistoric obsidian artifacts in south korea abstract using a series of geochemical data from obsidian samples taken from unmodified rocks and prehistoric sites we investigated the provenance of some obsidian artifacts found in south korea by using la icp ms and shrimp methods we analyzed rare earth elements rees and lead pb isotopic ratios of obsidian samples from the north korean side of the baekdusan mountain nk and artifacts from a neolithic site in gadeokdo southeast coast of south korea bg published accounts on the elemental correlation of previously analyzed samples were re examined in consideration of their geological compatibility it appears that the prehistoric artifacts from the middle to northern part of south korea have a genetic relationship with obsidians from the baekdusan area whereas those of the southern part are related to kyushu japan ree patterns of the bg and the nk samples demonstrate a prominent contrast between them suggesting their different provenances presumably the bg obsidians are related to the volcanic rocks of kyushu given that pb isotopic ratios are indicative of the relative contribution of crust versus mantle component to the volcanic magma they indicate the addition of a crustal component to the volcanic magma for the baekdusan volcanic rocks and the nk obsidians the kyushu volcanics and the bg obsidians have a relative affinity to the mantle component the geochemical approach adopted in the current research may be regarded as an accurate and effective means to discriminate and isolate obsidian sources helpful for provenance and other archaeological study of obsidian artifacts

influence of the east asian winter monsoon on the storm track activity over the north pacific 1 we investigate the relationship between the east asian winter monsoon eawm and synoptic eddy activity over the north pacific ocean it is well known that the subtropical pacific jet becomes stronger during strong monsoon periods than during weak monsoons the storm track is generally expected to be active when the eawm is strong owing to the enhanced subtropical jet contrary to this expectation synoptic eddy activity is significantly reduced in strong eawm years and conversely significantly increased during weak years in addition we found that eawm induced lower level cooling brings about the reverse relationship a stronger jet but with weaker storm activities it is suggested that the local baroclinicity induced by the eawm modulates the variation of both the jet and north pacific storm track simultaneously in the interannual time scale because major lower level cooling is located in the western parts of both the subtropical jet and the storm track in longitudes and between the two central axes in latitudes it induces the opposite sign of anomalous local baroclinicity at the two active regions and causes this reverse relationship the wave seeding from east asia to the north pacific storm track is weakened owing to the anomalous lower level cooling in the northwestern pacific which also results in reduction of eddy generation and storm track activities

structure and evolution of winter cyclones in the central united states and their effects on the distribution of precipitation part v thermodynamic and dual doppler radar analysis of a squall line associated with a cold front aloft abstract on 8 9 march 1992 a long lived squall line traversed the state of kansas producing hail and damaging winds it was shown previously that this squall line was part of a synoptic scale rainband 2000 km in length that was associated with a cold front aloft cfa the present study is concerned with the detailed mesoscale structure of this squall line and its relationship to the cfa examination of synoptic scale cross sections based on rawinsonde ascents and a mesoscale cross section of winds derived from dual doppler radar measurements shows that the squall line was exactly coincident with the nose of the cfa the dual doppler analysis also shows that the inflow of air to the squall line was elevated drawing in air from the potentially unstable layer within the weak warm frontal like feature that was being occluded by the cfa the stability analysis of the air in the pre squall line environment shows that when the cfa overtook the surface position of the drytrough the thermal and moisture s

the interaction between moist diabatic processes and the atmospheric circulation in african easterly wave propagation an objective tracking algorithm is used to characterise the three dimensional structure of african easterly waves aews in era interim reanalysis and a met office unified model um simulation a special focus is dedicated to the coupling of dynamical aspects of the wave and moist convection the relation between baroclinic features of the wave and latent heating is explored latent heating at and slightly ahead of the wave trough is found to reinforce and sustain the anomalous wave circulation through potential vorticity pv generation and vortex stretching the coupling of moist processes and the circulation takes place mainly through moisture convergence at lower mid tropospheric levels between 850 hpa and 500 hpa these findings are confirmed and examined in more detail in a case study of a strong aew based on high resolution um simulations pv tracers are used to investigate how different moist diabatic processes invigorate the wave again moisture anomalies are found to be the main contributors to generating small scale convergence centres and updrafts ahead of the trough at mid tropospheric levels although buoyancy effects are ultimately responsible for the convective uplift the results suggest that mesoscale circulations associated with the aew dynamics are crucial in creating the small scale moist static instabilities and vortices which are essential for the aew maintenance boundary layer mixing and advection from the northern sahel may create pockets of high pv air around the trough in some instances but this mechanism of wave sustainment needs further investigation

on the existence of storm tracks abstract given that middle latitude weather systems transport heat in a manner such as to weaken the baroclinicity that is thought to be crucial to their growth it is perhaps surprising that concentrated regions of such eddy activity i e storm tracks are found in the northern hemisphere winter the existence and possible self maintenance of storm tracks is investigated using a linear stationary wave model with storm track region forcings taken from data averaged over a number of winters it is found that the direct thermal effect of the eddies does indeed act against the existence of the storm track their vorticity fluxes lead to some reduction of this effect it is argued that the mean diabatic heating in the storm track region is an indirect eddy effect this heating is found to maintain the mean maximum in baroclinicity in the region further the mean low level flow induced by the eddy effects is such as to enhance the warm western oceanic boundary currents that are crucial to the existence of t

an introduction to the application of x ray microtomography to the three dimensional study of igneous rocks imaging rocks in three dimensions through x ray microtomography enables routine visualization of structures in samples which can be spatially resolved down to the sub micron scale although x ray tomography has been applied in biomedical research and clinical settings for decades it has only recently been applied to studies of rocks and few geoscientists realize its value and potential this contribution provides an introduction to the principles and techniques of x ray microtomography to the study of igneous rock textures as well as reviewing the current state of the art we hope that this short review will encourage more geoscientists to apply x ray microtomography in their research and that this will lead to new insights into the processes that occur in magmatic as well as other geological systems

the role of the central asian mountains on the midwinter suppression of north pacific storminess abstractthe role of the central asian mountains on north pacific storminess is examined using an atmospheric general circulation model by varying the height and the areas of the mountains a series of model integrations show that the presence of the central asian mountains suppresses the north pacific storminess by 20 30 during boreal winter their impact on storminess is found to be small during other seasons the mountains amplify stationary waves and effectively weaken the high frequency transient eddy kinetic energy in boreal winter two main causes of the reduced storminess are diagnosed first the decrease in storminess appears to be associated with a weakening of downstream eddy development the mountains disorganize the zonal coherency of wave packets and refract them more equatorward as the zonal traveling distance of wave packets gets substantially shorter downstream eddy development gets weaker second the central asian mountains suppress the global baroclinic energy conversion the decre

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

a novel approach in the mineralogy of carpathian mahogany obsidian using complementary methods abstract carpathian obsidians can have various macroscopic features they are typically black or grey and their transparency ranges from clear to opaque the tolcsva source very rarely can yield brown or red mahogany type obsidian archaeological as well as geological pieces of mahogany obsidian were previously identified and characterised using prompt gamma activation analysis pgaa in 2007 the exact location of the red variant s outcrop was identified on the szokolya hill tolcsva the aim of this study was to better understand the possible reasons for the colouring of red obsidian a novel approach was applied using multiple methods for the analysis of the samples for comparison other carpathian type namely black obsidian from tolcsva and red obsidian from bogazkoy anatolia were also studied besides the pgaa measurements of the bulk elemental composition mossbauer spectroscopy and transmission electron microscopy tem were used to study the samples in order to identify the presence of ferrous or ferric iron with the help of small angle neutron scattering sans the bulk nanostructures of the samples have been investigated and their surface or volume fractal dimensions have been determined black obsidians showed isotropy while mahogany samples displayed a considerable anisotropy in the bulk pore orientation according to our results a large amount of the iron is dominantly located in different phases in the case of mahogany and black obsidians based on the summarised results the differences between the red and black variants can be also explained by the different oxidation states of the fe ions which may explain the colour difference

glass geochemistry of pyroclastic deposits from the aeolian islands in the last 50 ka a proximal database for tephrochronology abstract volcanic ash 1000 analyses provides a basis for proximal distal and distal distal tephra correlations tephra deposits from the different aeolian islands are geochemically diverse with some individual eruptions showing diagnostic geochemical heterogeneity recognised both stratigraphically and or spatially major element glass analyses reveal that vulcano 0 21 ka and stromboli 4 13 ka have erupted potassic shoshonitic and k series tephra with broadly overlapping compositions but data presented here demonstrates that their eruptive products can be distinguished using either tio2 contents or their hfse th ratios whilst individual volcanic sources often produce successive tephra deposits with near identical major and minor element compositions through time i e lipari vulcano trace element glass data can help to decipher successive eruptions changes in lree and th concentrations of volcanic glasses erupted spanning approximately the last 50 ka greatly enhance the potential to discriminate successive eruptive units on lipari the new proximal glass database has been used to verify new ionian sea core m25 4 12 and existing distal occurrences of aeolian island derived tephra enabling the reassessments of past ash dispersals finally proximal and distal data have been used to establish an integrated proximal distal eruptive event stratigraphy for the aeolian islands

structure and evolution of winter cyclones in the central united states and their effects on the distribution of precipitation part iv the evolution of a drytrough on 8 9 march 1992 abstract the structure and evolution of a drytrough i e a surface pressure trough that has characteristics of both a lee trough and a dryline from the southern great plains to the lower mississippi valley are described using both observational data and outputs from a mesoscale model an elevated zone of cold air advection associated with a cold front aloft interacted with the drytrough over the southern great plains to form a structure similar to a warm occlusion this type of structure figures importantly in a new conceptual model that has been proposed for cyclones in the central united states

suppression of baroclinic instability in horizontally sheared flows abstract baroclinic instability in the presence of a meridionally sheared barotropic component to the basic flow is studied using a two level model the inclusion of a linear shear results in merldionally confined normal modes with growth rates much reduced compared to the unsheared case similar results hold for more complicated situations such as a baroclinic jet with barotropic shear the results are applied to life cycle calculations in which it is shown that the nonlinear decay phase of a baroclinic disturbance sets up barotropic shears whichtend to suppress further baroclinic developments an example of the southern hemisphere winter mean flow is found to be strongly stabilized by virtue of a strong sheared barotropic part of the zonal flow