extratropical influence on itcz shifts in slab ocean simulations of global warming abstractrecent studies with climate models have demonstrated the power of extratropical forcing in causing the intertropical convergence zone itcz to shift northward or southward and paleoclimate data support the notion that there have been large shifts in the itcz over time it is shown that similar notions apply to slab ocean simulations of global warming nine slab ocean model simulations from different modeling centers show a wide range of itcz shifts in response to doubling carbon dioxide concentrations which are experienced in a rather zonally symmetric way in the tropics using an attribution strategy based on fundamental energetic constraints it is shown that responses of clouds and ice in the extratropics explain much of the range of itcz responses there are also some positive feedbacks within the tropics due to increasing water vapor content and high clouds in the new itcz location which amplify the changes driven from the extratropics this study shows the clear importance of simulating

can the southern hemisphere annular mode affect china winter monsoon 1 many previous studies suggested that the anomalous northern hemisphere annular mode nam and associated low boundary forcing e g snow cover greatly influence the china winter monsoon cwm variability on interannual to inter decadal timescales in this article it is found that the southern hemisphere annular mode sam also well correlates with the two observed cwm major modes which has not been revealed before note that the two cwm major modes are obtained by performing empirical orthogonal function eof analysis on winter surface air temperature at 160 gauge stations across china for the 1951 2006 period they explain around 70 of the total cwm variances thefirsteofmodeexhibitsahomogeneousspatialpatternwiththecorrespondingprincipal component displaying a significant inter decadal variation which reflects the warming trend in china during the past 56 years the second eof mode shows a meridional seesaw patternandisbasicallyassociatedwithsignificantinterannualvariations bothoftheleading modes are intimately associated with the simultaneous sam like hemispheric circulation anomalies moreover thesam likeanomaliessignalprecursoryconditionsforthefirstcwm mode in boreal autumn the relevant physical mechanisms by which anomalous autumn sam may affect the cwm are investigated with ncar community atmospheric model version 3 cam3 when sam is in a strong phase during boreal autumn the circumantarctic upper level jet stream displaces poleward and the corresponding surface wind speeds reduce in the region between 45s and 30s inducing a hemispheric scale warm sea surface temperature sst belt beneath such an anomalously warm sst belt persists through boreal winter and weakens the hadley cell the weakened hadley cell in boreal wintercorrespondstoanomaloussoutherliesprevailinginthelowertroposphereoverchina which favor a weak cwm the intimate linkage between the autumn sam and cwm may be instrumental for understanding interactions between the northern and southern hemisphere and can provide a way to predict the cwm variations

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

source requirements for the golden mile kalgoorlie significance to the metamorphic replacement model for archean gold deposits the golden mile at kalgoorlie represents a giant archean hydrothermal gold system localized by ductile shear zones and hosted mainly by a differentiated tholeiitic sill chlorite carbonate and pyrite alteration zones cover the whole mineralized area 1 km 3 km and calculations suggest that for the golden mile production around 1200 t au the amounts of components added to these alteration zones are 340 mt co2 20 mt k and 5 mt s if one adopts a metamorphic replacement model for gold mineralization in which all ore components derive from devolatilization of greenstones at amphibolite facies or above these data suggest that a source area involving a 5 km thick greenstone slab of area 8 km 8 km could produce the necessary co2 k s h2o and au this is considered a reasonable volume of greenstone belt and under such a model the minimum spacing of large gold deposits would be approximately 20 km along strike neither special au enriched source rocks nor unreasonably large volumes of greenstone b

geochemistry of komatiites from kambalda western australia i chalcophile element depletion a consequence of sulfide liquid separation from komatiitic magmas the type examples of archean volcanic peridotite associated ni sulfide deposits occur at or toward the base of the ultramafic lava pile at kambalda western australia spinilex textured komatiites considered to represent silicate liquids derived from the original magma are significantly depleted in chalcophile elements throughout the entire ultramafic sequence relative to unmineralized and poorly mineralized komatiites elsewhere and to a theoretically modeled sulfide undersaturated komatiite system this depletion is not attributed to postformational modification of the komatiites by sea floor alteration or metamorphism although very low sulfur contents in the same rocks probably result from such processes the depletion is best interpreted as the result of scavenging of metals by sulfide liquid in equilibrium with the silicate magma implying that all the silicate magma now represented by the ultramafic sequence equilibrated with sulfide liquids at the magmatic stage these results provide convincing evidence against formation of the sulfide ores by in situ sulfide separation from the thick komatiitic peridotitc host the magnitude of the depletion in the spinilex textured komatiite divisions of the peridotitc hosts is much less than that expected for such an origin but for the entire sequence it is greater than that expected from metal partitioning relations and mass balance calculations for the volume and composition of the ultramafic sequence and the volume of associated sulfides this suggests that a proportion of the sulfide liquid that formed from the ultramafic magma s was lost from the magmatic system prior to extrusion such loss is a natural consequence of models for ascent and eruption of sulfur rich komatiitic magmas that involve prior concentration of sulfides plus olivine in high level magma chambers or separation and segregation of sulfide liquid during ascent from the upper mantle

tropical cooling at the last glacial maximum and extratropical ocean ventilation1 1 the ncar csm is used to simulate the climate at last glacial maximum the csm simulates a tropical sst cooling of 2 1 c it is shown that about half of this tropical cooling is associated with the upper ocean circulation especially the ventilation of thermocline and intermediate waters from the mid high latitude south pacific

interhemispheric thermal gradient and tropical pacific climate 1 we explore the impact of interhemispheric thermal gradients forcing on the tropical pacific ocean atmosphere climate in an intermediate coupled model the equatorial zonal sea surface temperature sst gradient strengthens with an increased northward interhemispheric thermal gradient the increase arising from earlier onset and later retreat of the seasonal cold tongue and intensification during the peak cold season when the mean interhemispheric thermal gradient is reversed the central equatorial pacific sst annual cycle abruptly reverses in phase with its cold season in mar may rather than sep nov while startling this response is consistent with a prevailing hypothesis that ties the cold tongue sst annual cycle phase to the hemispheric mean asymmetry of the intertropical convergence zone el nino southern oscillation activity is also sensitive to the interhemispheric thermal gradient with peak activity occurring when the mean gradient is small reducing rapidly as the mean gradient increases in either direction

cross seasonal influence of the december february southern hemisphere annular mode on march may meridional circulation and precipitation abstractnew evidence suggests that interannual variability in zonal mean meridional circulation and precipitation can be partially attributed to the southern hemisphere annular mode sam the dominant mode of climate variability in the southern hemisphere sh extratropics a cross seasonal correlation exists between the december february djf sam and march may mam zonal mean meridional circulation and precipitation this correlation is not confined to the sh it also extends to the northern hemisphere nh subtropics when the preceding djf sam is positive counterclockwise and clockwise meridional cells accompanied by less and more precipitation occur alternately between the sh middle latitudes and nh subtropics in mam in particular less precipitation occurs in the sh middle latitudes the sh tropics and the nh subtropics but more precipitation occurs in the sh subtropics and the nh tropics a framework is built to explain the cross seasonal impact of sam related sst anomalies evidence indic

the relationship between the itcz and the southern hemispheric eddy driven jet 1 we study the effect of a thermal forcing confined to the midlatitudes of one hemisphere on the eddy driven jet in the opposite hemisphere we demonstrate the existence of an interhemispheric teleconnection whereby warming cooling the northern hemisphere causes both the intertropical convergence zone itcz and the southern hemispheric midlatitude jet to shift northward southward the interhemispheric teleconnection is effected by a change in the asymmetry of the hadley cells as the itcz shifts away from the equator the cross equatorial hadley cell intensifies fluxing more momentum toward the subtropics and sustaining a stronger subtropical jet changes in subtropical jet strength in turn alter the propagation of extratropical waves into the tropics affecting eddy momentum fluxes and the eddy driven westerlies the relevance of this mechanism is demonstrated in the context of future climate change simulations where shifts of the itcz are significantly related to shifts of the southern hemispheric eddy driven jet in austral winter the possible relevance of the proposed mechanism to paleoclimates is discussed particularly with regard to theories of ice age terminations

the structure and predictability of the high latitude mode in the csiro9 general circulation model abstract the csiro9 general circulation model shows a zonally symmetric mode of variability which closely resembles the high latitude mode hlm in middle and high latitudes of the southern hemisphere the leading eof of the zonal mean zonal wind between 30 and 68 s whose amplitude has been taken as an index of the hlm shows opposing variations centered near 40 and 60 s accounting for 43 of the daily variance analysis has concentrated on composites for periods when the index changed quickly between significant peaks of the opposite sign or persisted with a large amplitude for an extended period the momentum flux variations are small at the northern and southern boundaries and the principal variations are centered near 49 s between the maxima in the zonal wind the changes in angular momentum content are around 30 smaller in the southern band eddy heat fluxes are less coherent but help in maintaining the zonal wind anomalies against friction a simple model of the zonal wind index with stochastic

observations of large scale ocean atmosphere interaction in the southern hemisphere abstract the authors provide a detailed examination of observed ocean atmosphere interaction in the southern hemisphere sh focus is placed on the observed relationships between variability in sh extratropical sea surface temperature sst anomalies the southern annular mode sam and the el nino southern oscillation enso results are examined separately for the warm november april and cold may october seasons and for monthly and weekly time scales it is shown that the signatures of the sam and enso in the sh sst field vary as a function of season both in terms of their amplitudes and structures the role of surface turbulent and ekman heat fluxes in driving seasonal variations in the sam and enso related sst anomalies is investigated analyses of weekly data reveal that variability in the sam tends to precede anomalies in the sst field by 1 week and that the e folding time scale of the sam related sst field anomalies is at least 4 months the persistence of the sam related sst anomalies is

observed relationships between the el nino southern oscillation and the extratropical zonal mean circulation abstract there is increasing evidence indicating that the climate response to variations in the el nino southern oscillation enso includes not only thermally forced zonal wind anomalies in the subtropics but also eddy driven zonal wind anomalies that extend into the mid high latitudes of both hemispheres in this study new insights into the observed seasonally varying signature of enso in the extratropical zonal mean circulation are provided and the associated linkages with the dominant patterns of extratropical variability are examined the zonal mean extratropical atmospheric response to enso is characterized by two principal features an equivalent barotropic dipole in the southern hemisphere sh zonal mean zonal flow with centers of action located near 40 and 60 during austral summer and a weaker but analogous dipole in the northern hemisphere nh with centers of action located near 25 and 45 during early and late boreal winter both structures are accompanied by eddy momentum flux ano

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

the response of the itcz to extratropical thermal forcing idealized slab ocean experiments with a gcm using a comprehensive atmospheric gcm coupled to a slab mixed layer ocean experiments are performed to study the mechanism by which displacements of the intertropical convergence zone itcz are forced from the extratropics the northern extratropics are cooled and the southern extratropics are warmed by an imposed cross equatorial flux beneath the mixed layer forcing a southward shift in the itcz the itcz displacement can be understood in terms of the degree of compensation between the imposed oceanic flux and the resulting response in the atmospheric energy transport in the tropics the magnitude of the itcz displacement is very sensitive to a parameter in the convection scheme that limits the entrainment into convective plumes the change in the convection scheme affects the extratropical tropical interactions in the model primarily by modifying the cloud response the results raise the possibility that the response of tropical precipitation to extratropical thermal forcing important for a variety of problems in climate dynamics such as the response of the tropics to the northern hemisphere ice sheets during glacial maxima or to variations in the atlantic meridional overturning circulation may be strongly dependent on cloud feedback the model configuration described here is suggested as a useful benchmark helping to quantify extratropical tropical interactions in atmospheric models

wave driven zonal flow vacillation in the southern hemisphere the variability of the zonal mean flow in the southern hemisphere during the period 1985 94 is studied using european centre for medium range forecasts analyses the dominant mode of variability has approximately equivalent barotropic variations of opposite signs centered at 40 8 and 608s this structure is dominant in all seasons and has similar variance in all seasons the temporal variance of the amplitude of this mode is well modeled as gaussian red noise with a correlation e folding time of about 10 days zonal wind anomalies are maintained against frictional drag by variations in the zonal flow accelerations driven by transient eddies and associated mean meridional circulations the eddy structures suggest that equatorward propagation is favored when the jet is displaced poleward and zonal propagation is favored when the jet is displaced equatorward

indices of the southern hemisphere zonal wind abstract the time and spatial variation of the southern hemisphere 500 hpa zonal wind has been examined using spectral analysis bandpass filtering and empirical orthogonal function eof analysis applied to a 15 year sample of australian hemispheric analyses spectral analysis of the entire 15 year record of the 500 hpa zonal mean westerly wind shows significant peaks only on the seasonal and interannual time scales the mean segmented spectra for each season failed to show any additional significant peaks at higher frequencies or any significant differences between seasons the primary pattern of variation revealed by eof analysis shows similar behavior on synoptic to seasonal time scales with compensating departures occurring at intervals of 20 latitude the first eof has opposing peaks near 40 and 60 s and shows an equivalent barotropic pattern when correlated with individual grid point values at 500 hpa and mean sea level pressure correlations of the zonal pattern with regional anomalies reveal

the impact of enso on wave breaking and southern annular mode events abstract this study examines the relationship between intraseasonal southern annular mode sam events and the el nino southern oscillation enso using daily 40 yr ecmwf re analysis era 40 data the data coverage spans the years 1979 2002 for the austral spring and summer seasons the focus of this study is on the question of why positive sam events dominate during la nina and negative sam events during el nino a composite analysis is performed on the zonal mean zonal wind eliassen palm fluxes and two diagnostic variables the meridional potential vorticity gradient a zonal mean quantity that is used to estimate the likelihood of wave breaking and the wave breaking index wbi which is used to evaluate the strength of the wave breaking the results of this investigation suggest that the background zonal mean flow associated with la nina el nino is preconditioned for strong weak anticyclonic wave breaking on the equatorward side of the eddy driven jet the type of wave breaking that is found

on the role of extratropical air sea interaction in the persistence of the southern annular mode using the daily atmosphere and ocean reanalysis data this study highlights the role of extratropical air sea interaction in the variability of the southern annular mode sam our analysis shows that the sam induced meridional dipolar sea surface temperature sst anomalies through surface heat fluxes can maintain persistent lower tropospheric temperature anomalies which further results in anomalous eddy momentum forcing enhancing the persistence of the sam with the finite amplitude wave activity diagnosis we illustrate that response of the eddy momentum forcing to sst anomalies can be attributed to changes in both baroclinic processes as baroclinic eddy generation and barotropic processes as wave breaking thus resultant diffusive eddy mixing with the former confined at high latitudes and the latter strongest at midlatitudes spectral analysis further suggests that the above air sea interactions are important for bimonthly and longer time scale sam variations the dipolar sst pattern may be an indicator for predicting subseasonal and interseasonal variabilities of the sam

tropical extratropical teleconnections in boreal summer observed interannual variability abstractmaximum covariance analysis is performed on the fields of boreal summer tropical rainfall and northern hemisphere nh 200 hpa height for the 62 yr period of record of 1948 2009 the leading mode which appears preferentially in summers preceding the peak phases of the el nino southern oscillation enso cycle involves a circumglobal teleconnection cgt pattern in the nh extratropical 200 hpa height field observed in association with indian monsoon rainfall anomalies the second mode which tends to occur in summers following enso peak phases involves a western pacific north america wpna teleconnection pattern in the height field observed in association with western north pacific summer monsoon rainfall anomalies the cgt pattern is primarily a zonally oriented wave train along the westerly waveguide while the wpna pattern is a wave train emanating from the western pacific monsoon trough and following a great circle the cgt is accompanied by a pronounced tropical extratropical seesaw in t

central north china precipitation as reconstructed from the qing dynasty signal of the antarctic atmospheric oscillation 1 based on the long term central north china precipitation cncp time series reconstructed from the qing dynasty official document the relationship between cncp and the antarctic atmospheric oscillation aao in june july is examined the analysis yields a significant negative correlation of 0 22 the signal of aao in cncp is further studied through analyses of the atmospheric general circulation variability related to aao it follows that aao related variability of convergence and convection over the tropical western pacific can exert impact on the circulation condition and precipitation in north china actually the precipitation in the yangtze river valley as well through atmospheric teleconnection known as the east asia pacific or pacific japan teleconnection wave pattern there is also an aao connected wave train in the vorticity field at high troposphere over eurasia providing an anti cyclonic circulation in central north china favorable to the decline of precipitation in positive phase of aao

southern hemisphere origins for interannual variations of snow cover over the western tibetan plateau in boreal summer abstractthe climate response to the tibetan plateau tp snow cover tpsc has been receiving extensive concern however relatively few studies have been devoted to revealing the potential factors

fast teleconnections to the tropical atlantic sector from atlantic thermohaline adjustment 1 we examine the first decade of adjustment of the north atlantic climate following an abrupt freshening of the high north atlantic and resulting slowdown of the atlantic meridional overturning circulation amoc in a coupled model with reference to previously proposed teleconnection mechanisms after an initial ocean driven cooling at the subtropical subpolar gyre boundary subsequent equatorward progression is dominated by an atmosphere surface ocean mechanism driving evaporative cooling in the tropical north atlantic and resulting in an anomalous southward itcz displacement by year 2 the tropical cooling is countered by fast ocean baroclinic adjustment to the reduced overturning that increases the volume of tropical surface waters as well as ocean circulation changes to the increased northeasterly trades however it is the atmosphere surface ocean teleconnection that explains the hemispheric asymmetric nature of the tropical atlantic surface climate impact to amoc slowdown underlining its crucial importance in high to low latitude teleconnections

mechanisms of enso forcing of hemispherically symmetric precipitation variability summary the patterns of precipitation anomalies forced by the el nino southern oscillation during northern hemisphere winter and spring are remarkably hemispherically symmetric and in the mid latitudes have a prominent zonally symmetric component observations of global precipitation variability and the moisture budget within atmospheric reanalyses are examined to argue that the zonally symmetric component is caused by interactions between transient eddies and tropically forced changes in the subtropical jets during el nino events the jets strengthen in each hemisphere and shift equatorward changes in the subtropical jet influence the transient eddy momentum fluxes and the eddy driven mean meridional circulation during el nino events eddy driven ascent in the mid latitudes of each hemisphere is accompanied by low level convergence and brings increased precipitation this changes in the transient eddy and stationary eddy moisture fluxes almost exactly cancel each other and in sum do not contribute to the zonal mean precipitation anomalies propagation of anomalous stationary waves disrupts the zonal symmetry flow around the deeper aleutian low and the eastward extension of the pacific jet stream supply the moisture for increased precipitation over the eastern north pacific and the western seaboard of the united states while transient eddy moisture convergence supplies the moisture for increased precipitation over the southern united states in each case increased precipitation is fundamentally caused by anomalous ascent forced by anomalous heat and vorticity fluxes

coupled ocean atmosphere ice response to variations in the southern annular mode abstract the coupled ocean atmosphere ice response to variations in the southern annular mode sam is examined in the national center for atmospheric research ncar community coupled climate model version 2 the model shows considerable skill in capturing the predominantly zonally symmetric sam while regional deviations between model and observation sam winds go a long way in explaining the generally small differences between simulated and observed sam responses in the ocean and sea ice systems vacillations in the position and strength of the circumpolar winds and the ensuing variations in advection of heat and moisture result in a dynamic and thermodynamic forcing of the ocean and sea ice both meridional and zonal components of ocean circulation are modified through ekman transport which in turn leads to anomalous surface convergences and divergences that strongly affect the meridional overturning circulation and potentially the pathways of intermediate water ventilation a heat budget analysis de

variation of the north atlantic subtropical high western ridge and its implication to southeastern us summer precipitation variations of the north atlantic subtropical high nash western ridge and their implication to the southeastern united states se us summer precipitation were analyzed for the years 1948 2007 the results show that the movement of the nash western ridge regulates both moisture transport and vertical motion over the se us especially in the last three decades during which the ridge moved westward towards the american continent when the nash western ridge is located southwest sw of its mean climate position excessive summer precipitation is observed due to an enhanced moisture transport in contrast when the western ridge is located in the northwest nw a precipitation deficit prevails as downward motion dominates the region composite analysis indicates that sw ridging results mainly from the nash center s intensification whereas nw ridging is likely caused by stationary wave propagation from the eastern pacific us western coast in recent decades both the sw and nw ridge positions have been observed to increase in frequency our results suggest that the increase in the sw ridging consistently follows the nash s intensification associated with anthropogenic forcing as projected by coupled climate models however the increased frequency of nw ridging tends to follow the positive pacific decadal oscillation pdo index thus the enhanced variability in the se us summer precipitation in recent decades might be a combined result of anthropogenic forcing and internal variability of the climate system results suggest that as anthropogenic forcing continues to increase the se us will experience more frequent wet summers and an increase in the frequency of dry summers during positive pdo phases

annular modes in global daily surface pressure annular modes are patterns characterized by synchronous fluctuations in surface pressure of one sign over the polar caps and the opposite sign at lower latitudes the southern annular mode sam and northern annular mode nam also called the arctic oscillation patterns are the leading empirical orthogonal functions eofs of slowly varying hemispheric cold season sea level pressure anomalies deviations from climatology daily indices of the sam and nam are a measure of the similarity between surface pressure anomaly patterns and the annular modes here it is shown that the first two eof time series of daily global year round zonally averaged surface pressure are nearly identical to the sam and nam indices together they account for more than 57 of the daily variance of zonally averaged surface pressure the sam and nam patterns extend through the tropics well into the opposite hemispheres fluctuations of the sam and nam indices are accompanied by interhemispheric transfer of mass

influence of the tropics on the southern annular mode abstractperturbations in the southern annular mode sam are shown to be significantly correlated with sst anomalies in the central tropical pacific during austral winter and sst anomalies in the eastern tropical pacific during austral summer the sam signature in the pacific sector resembles a tropically forced rossby wave train the so called pacific south american pattern while the signature in the indian ocean sector is a zonally elongated meridional dipole thus the sam contains strong zonally asymmetric variability and tends to behave differently in the eastern and western hemispheres with internal dynamics prevailing in the indian ocean sector and the forced response to tropical sst anomalies exerting a strong influence in the pacific sector the tropically forced component of the sam in the pacific sector is related to a geographically fixed active rossby wave source to the east of australia within the core of the subtropical jet in addition to the well documented positive trend in summer the

the signature of the annular modes in the tropical troposphere the extratropical annular modes are coupled with a distinct pattern of climate anomalies that spans the circulation of the tropical troposphere the signature of the annular modes in the tropical troposphere exhibits a high degree of equatorial symmetry it is associated with upper tropospheric zonal wind anomalies centered about the equator midtropospheric temperature anomalies located 208n and 208s and opposing mean meridional circulation anomalies that span the subtropics of both hemispheres the linkages between the annular modes and the tropical circulation are only evident during the cold season months and are most robust in association with the northern hemisphere annular mode nam the coupling between the annular modes and the circulation of the tropical troposphere is consistent with forcing by waves originating at extratropical latitudes both annular modes are characterized by anomalies in the eddy momentum flux convergence at tropical latitudes that act to reinforce the changes in the tropical wind and temperature fields the most pronounced tropical anomalies lag indices of the annular modes by 2 weeks and are found over the eastern tropical pacific where climatological westerlies permit extratropical waves to propagate into the deep tropics the linkages between the nam and the tropical tropospheric circulation are

coupled ocean atmosphere feedback in the southern annular mode abstract previous studies have demonstrated that while the southern annular mode sam is an intrinsic feature of the atmosphere it projects strongly onto the ocean and sea ice properties and circulation this study investigates the extent of back interaction whereby these oceanic sam anomalies feed back to the atmosphere a comparison between atmosphere only and full coupled climate models demonstrates that air sea interactions in the coupled system act to increase the persistence of the sam in the atmosphere to identify the nature of feedback from the ocean to the atmosphere ensemble experiments are carried out in both atmosphere only and full coupled models whereby a continuous sam like sea surface temperature sst anomaly is imposed both coupled and uncoupled experiments show a direct thermal response that affects the lower tropospheric temperature and surface meridional winds an indirect upper troposphere wide response is also seen whose characteristics are sensitive to the coupling for the

boreal spring southern hemisphere annular mode indian ocean sea surface temperature and east asian summer monsoon 1 the relationships among the boreal spring southern hemisphere annular mode sam the indian ocean io sea surface temperature sst and east asian summer monsoon easm are examined statistically in this paper the variability of boreal spring sam is closely related to the io sst when the sam is in its strong positive phase in boreal spring with low pressure anomalies over the south pole and high pressure anomalies over middle latitudes sstover the subtropics and middle latitudes of the south indian ocean sio increases which persists into the summer following the positive sst anomalies over the subtropics and midlatitudes of the sio sst in the equatorial indian ocean and bay of bengal increases in summer moreover the variability of sst in the equatorial indian ocean and bay of bengal is closely related to easm when sst in the equatorial indian ocean and bay of bengal increases easm tends to be weak therefore the io sst may play an important role bridging boreal spring sam and easm the atmospheric circulations and surface heat exchanges contribute to the sst anomalies in the sio when the spring sam is in its strong positive phases the regional ferrel cell weakens and the anomalous upward motions at 20s 30s cause an increase of low cloud cover and downward longwave radiation flux the surface atmospheric circulations also transport more less warmer cooler air from middle latitudes north of 50s high latitudes south of 60s into 50s 60s and warm the air which reduces the temperature difference between the ocean and atmosphere and consequently reduces sensible heat flux from the ocean to atmosphere the increased downward longwave radiation and decreased sensible heat are responsible for the sst increase in the sio the atmospheric circulation and surface heat flux anomalies are of opposite signs following the strong negative phases of sam

on the speed of the eddy driven jet and the width of the hadley cell in the southern hemisphere a strong correlation between the speed of the eddy driven jet and the width of the hadley cell is found to exist in the southern hemisphere both in reanalysis data and in twenty first century integrations from the intergovernmental panel on climate change ipcc fifth assessment report multimodel archive analysis of the space time spectra of eddy momentum flux reveals that variations in eddy driven jet speed are related to changes in the mean phase speed of midlatitude eddies an increase in eddy phase speeds induces a poleward shift of the critical latitudes and a poleward expansion of the region of subtropical wave breaking the associated changes in eddy momentum flux convergence are balanced by anomalous meridional winds consistent with a wider hadley cell at the same time faster eddies are also associated with a strengthened polewardeddymomentumflux sustainingastronger westerlyjet in midlatitudes the proposedmechanismis consistent with the seasonal dependence of the interannual variability of the hadley cell width and appears to explain at least part of the projected twenty first century trends one of the most salient features of earth s general circulation is the presence of hadley cells hcs in the tropical belts of both hemispheres associated with their large scale motions are some of the main characteristics of tropical and subtropical climates the intertropical convergence zone in the rising branch and the subtropical dry zones in the descending branches e g hartmann 1994 studying the factors determining the meridional extent of these overturning circulations is therefore essential to understand the spatial distribution of tropical and subtropical climates and its changes the role of the hcs is particularly crucial in the context of climate change and the observed widening of the atmospheric circulation observations show a poleward shift of the eddy driven jets and an expansion of the hcs in recent decades particularly in the southern hemisphere hu and fu 2007 johanson and fu 2009 lu et al 2009 and the role of radiative forcings induced by greenhouse gases and stratospheric ozone has been shown to be crucial in this context polvani et al 2011b

geochemical and stable isotope studies of the no 4 lode kalgoorlie western australia the no 4 lode is a silicified pyritic shear zone with gold telluride mineralization which is located in the golden mile dolerite along the western limb of the kalgoorlie syncline wallrocks in this zone have undergone a series of metamorphic and metasomatic events this alteration is characterized by an increase in the ko nao ratio introduction of co and s and significant enrichment of au ag te and other ore forming constituents major and trace element and isotopic data are presented 40 chemical analyses ore mineralization is thought to have formed by reaction of chloritic host rocks with a moderately reduced near neutral hydrothermal fluid at t 250 or 50oc isotope and geochemical data suggest that these ore fluids were of metamorphic derivation and may have incorporated magmatic c s and possibly precious metals at deeper levels in the crust j e s

definition of antarctic oscillation index following walker s work about his thmous three oscillations published during the 1920 30s many papers were written about atmospheric oscillations a iburth atmospheric oscillation in the middle and high southern latitudes was lbund and nanted the grotarctic oscillation ao a refiers to a large scale alternation of atmospheric mass between the mid latitudes and high latitudes surthce pressure in order to understand the spatial structure of sea level pressure variation in detail empirical orthogonal fitnction analysis is applied an objective index of the antarctic oscillation index aoi is defined as the diffierence of zonal mean sea level pressure between 40os and 65os the aoi has the potential tbr clarifying climate regimes in the southern hemisphere similar to how the na and the npo has been used in the northern hemisphere were there other oscillation s besides nao npo and s especially in the southern hemisphere it had been supposed that there might be other atmospheric oscillation s in the high southern latitudes although as early as in the first quarter of this century walker 1928 had stated that just as in the north atlantic there is a pressure opposition between the azores and iceland there is an opposition between the high pressure belt across chile and the argentine on the one hand and the low pressure area of weddell sea and the bellingshausen sea on the other the scarcity of data in the southern hemisphere hindered the search tbr new oscillation s during the last two decades more comprehensive data over the southern hemisphere became available and more analyses were carried out see kidson 1975 rogers and van loon 1982 mo and l 7 ite 1985 2 4o 1986 connolley 1997 gong and wang 1998 a tburth atmospheric oscillation in the middle and high southern latitudes was tbund and nanted as the antarctic oscillation a wang 1992 gong and wang 1998 the term ao relrs to a large scale alternation of atmospheric mass between the mid latitude sur hce pressure

expansion of the hadley cell under global warming 1 a consistent weakening and poleward expansion of the hadley circulation is diagnosed in the climate change simulations of the ipcc ar4 project associated with this widening is a poleward expansion of the subtropical dry zone simple scaling analysis supports the notion that the poleward extent of the hadley cell is set by the location where the thermally driven jet first becomes baroclinically unstable the expansion of the hadley cell is caused by an increase in the subtropical static stability which pushes poleward the baroclinic instability zone and hence the outer boundary of the hadley cell

are the north atlantic oscillation and the northern annular mode distinguishable this study addresses the question of whether persistent events of the north atlantic oscillation nao and the northern annular mode nam teleconnection patterns are distinguishable from each other standard daily index time series are used to specify the amplitude of the nao and nam patterns the above question is examined with composites of sea level pressure and 300 and 40 hpa streamfunction along with tests of field significance a null hypothesis is specified that the nao and nam persistent events are indistinguishable this null hypothesis is evaluated by calculating the difference between time averaged nao and nam composites it is found that the null hypothesis cannot be rejected even at the 80 confidence level the wave breaking characteristics during the nam life cycle are also examined both the positive and negative nam phases yield the same wave breaking properties as those for the nao the results suggest that not only are the nao and nam persistent events indistinguishable but that the nao nam events are neither confined to the north atlantic nor are they annular

geochemistry of fluid inclusions from the mcintyre hollinger gold deposit timmins ontario canada type 1 h 2 o co 2 type 2 h 2 o co 2 type 3 ch 4 co 2 h 2 o and type 4 ch 4 fluid inclusions type 1 type 3 and some type 2 inclusions are primary or pseudosecondary in origin whereas type 4 and most type 2 inclusions are secondary the primary or pseudosecondary type 1 and 2 inclusions homogenized at temperatures of 220 degrees to 385 degrees c secondary type 2 inclusions homogenized at 160 degrees to 215 degrees c crushing tests confirm the presence of co 2 in samples with type 1 and 2 inclusions visually estimated x co2 values in type 1 inclusions range from 3 to 24 mole percent with bulk molar volumes of 19 to 28 cm 3 mole mineralizing fluids were at equilibrium with graphite at temperatures of 380 degrees to 480 degrees c and pressures of 1 to 3 kb calculated oxygen fugacities lie near the quartz fayalite magnetite buffer the mineralizing fluids differ compositionally from fluids in other types of ore deposits but resemble fluids derived from metamorphic rocks and deep level felsic intrusions modified journal abstract

southern annular modes simulated by a climate model patterns mechanisms and uses abstract both high latitude hlm and low latitude modes llm of variability of zonal wind in the southern hemisphere have been identified through an analysis of a simulation for 1871 2200 by the csiro mark 3 climate model the extent to which these might both be described as annular modes based on their statistical patterns physical mechanisms and usefulness in climate study is assessed the modes are determined as eof1 and eof2 of vertically integrated zonal and monthly mean zonal wind for 1871 1970 these match well those from ecmwf re analysis era data and also from the earlier mark 2 model the mode index time series relate to largely annular patterns of local wind and surface pressure anomalies with hlm giving the familiar southern annular mode sam and other simulated quantities while modes calculated from 90 sectors are only moderately correlated mostly in the polar region for hlm the link increases with time scale there is little such relationship for llm a momentum equation

influence of the southern annular mode on the sea ice ocean system 1 the global sea ice ocean model orca2 lim driven by the ncep ncar national centers for environmental prediction national center for atmospheric research reanalysis daily 2 m air temperatures and 10 m winds and by monthly climatologies for precipitation cloud cover and relative humidity is used to investigate the impact of the southern annular mode sam on the antarctic sea ice ocean system our results suggest that the response of the circumpolar southern ocean consists of an annular and a nonannular component for the sea ice cover the non annular component seems to be the most important the annular component strongly affects the overall patterns of the upper ocean circulation when the sam is in its positive phase a northward surface ekman drift a downwelling at about 45 degreess and an upwelling in the vicinity of the antarctic continent are simulated the non annular component has a significant impact at the regional scale especially in the weddell ross amundsen and bellingshausen seas in those regions the pressure pattern associated with the sam induces meridional winds which advect warmer air in the weddell sea and around the antarctic peninsula and colder air in the amundsen and ross seas this implies a dipole response of sea ice to the sam with on average a decrease in ice area in the weddell sea and around the antarctic peninsula and an increase in the ross and amundsen seas during years with a high sam index the long term trend in the observed sea ice area does not appear to be related to the trend in the sam index

the effect of excess co2 on the calculated calcite and aragonite saturation horizons in the northeast pacific using the tco2 results of chen 1982a obtained during a cruise in the northeast pacific ocean june july 1981 we have calculated preindustrial and 1981 calcite and aragonite saturation horizons for a transect along 150 w between alaska and hawaii uptake of excess co2 by the oceans over the past 130 years has resulted in a significant change in the carbonate chemistry of the northeast pacific ocean the results indicate an apparent reduction in the thickness of the supersaturated lenses and an upward translation of the 100 saturation level by as much as 150 meters for calcite and 70 meters for aragonite in the coldwater region north of the subarctic front

interhemispheric influence of indo pacific convection oscillation on southern hemisphere rainfall through southward propagation of rossby waves tropical indo western pacific convection anomalies influence atmospheric circulation impacting climate far beyond the tropics here we present observational and modelling evidence for an interhemispheric effect of the boreal summer june august indo pacific convection oscillation ipco which is characterized by a zonal seesaw pattern between the north indian ocean nio and the western north pacific wnp it is found that the ipco is significantly correlated with simultaneous rainfall over many parts of the southern hemisphere sh including western australia and western brazil these interhemispheric connections in rainfall remain significant when then el nino southern oscillation the indian ocean dipole and the sh annular mode related signals are excluded simultaneously which may help to improve the sh seasonal predictions the physical mechanism that underlies this interhemispheric connection is investigated using observations rossby wave diagnostics and a series of atmospheric model experiments results suggest that convective heating anomalies associated with the ipco excite two distinct southward propagating equivalent barotropic wave trains that propagate into the extratropics in the sh the south africa mid latitudes wave train excited by the heat sink over the nio and the maritime continent subtropical australia wave train excited by the heat source over the wnp we further demonstrate that upper tropospheric northerlies over tropical africa and the indian ocean are responsible for the southward propagation of stationary rossby waves across the easterlies these equivalent barotropic waves then modulate the moisture transport baroclinicity and mid latitude storminess and thus affect rainfall anomalies in the sh the new wave train patterns provide novel insight into the teleconnection pathways of convective heating over the tropical indian ocean and western pacific

mechanisms of hemispherically symmetric climate variability inspired by paleoclimate evidence that much past climate change has been symmetric about the equator the causes of hemispherically symmetric variability in the recent observational record are examined using the national centers for environmental prediction national center for atmospheric research reanalysis dataset and numerical models it was found that the dominant cause of hemispherically symmetric variability is the el nino southern oscillation during an el nino event the tropics warm at all longitudes and the subtropical jets in both hemi spheres strengthen on their equatorward flanks poleward of the tropical warming there are latitude belts of marked cooling extending from the surface to the tropopause in both hemispheres at all longitudes and in all seasons the midlatitude cooling is caused by changes in the eddy driven mean meridional circulation changes in the transient eddy momentum fluxes during an el nino event force upper tropospheric ascent in midlatitudes through a balance between the eddy fluxes and the coriolis torque the eddy driven ascent causes anomalous adiabatic cooling which is primarily balanced by anomalous diabatic heating using a quasigeostrophic spherical model forced by an imposed surface eddy disturbance of chosen wave number and frequency it is shown that the anomalous eddy momentum fluxes are caused by the impact that the changes in the tropically forced subtropical jets have on the propagation in the latitude height plane of transient eddies changes in zonal winds and associated changes in the meridional gradient of potential vorticity create an anomalous region of low meridional wavenumber in the midlatitudes that refracts waves away both poleward and equatorward tropical forcing of variability in the eddy driven mean meridional circulation is another way in addition to rossby wave teleconnections whereby the tropics can influence extratropical climate unlike teleconnections this mechanism causes climate variability that has strong zonally and hemispherically symmetric components and operates throughout the seasonal cycle

influence of the may southern annular mode on the south china sea summer monsoon the possible impact of the may southern hemisphere sh annular mode sam on the following south china sea scs summer monsoon scssm is examined a close inverse relationship between the two is revealed in the observations the simultaneous south pacific dipole spd a dipole like sea surface temperature anomaly pattern in the south pacific acts as the oceanic bridge to preserve the may sam signal and prolong it into june september observational evidence and numerical simulations both demonstrate that the spd communicates its large thermal inertia signal to the atmosphere regulating the southern pacific subtropical jet spsj variability over eastern australia corresponding to the adjustment of circulation associated with the spsj is a prominent tripolar cross pacific teleconnection pattern stretching from the sh middle high latitudes into the nh east asia coastal region referred to as the south north pacific snp teleconnection pattern wave ray tracing analysis manifests that the snp acts as the atmospheric bridge to propagate the related wave energy across the equator and into the maritime continent and scs monsoon region modulating the vertical motion and middle lower tropospheric flows and favoring the out of phase variation of the scssm therefore the coupled oceanic atmospheric bridge process and the related rossby wave energy transmission are possible mechanisms for the significant influence of the may sam on the variability of the following scssm therefore the may sam provides a fresh insight into the prediction of the scssm from the perspective of the sh high latitudes

southern ocean wind response to north atlantic cooling and the rise in atmospheric co2 modeling perspective and paleoceanographic implications 1 a recent study found enhanced upwelling rates in the southern ocean during the last glacial termination that coincided with the deglacial warming in antarctica and the rise in atmospheric co2 they hypothesized that the intensification of southern hemisphere midlatitude westerlies the presumed cause of the increased wind driven upwelling was triggered by an initial cooling within the glacial north atlantic whose influence was then communicated to the southern midlatitudes through an atmospheric teleconnection in this study we explore the viability of the above hypothesis using a modeling strategy focusing on the atmospheric teleconnection in simulations where north atlantic cooling was applied the model intertropical convergence zone shifted southward and westerlies and wind stress over southern ocean increased by as much as 25 while the perennial westerly anomalies occur over the entire southern ocean they are strongest over the south pacific during the austral winter when the wind stress anomalies were applied to an earth system model incorporating interactive marine biogeochemistry atmospheric co2 rises between 20 and 60 ppm depending on the biological response we thus confirm the viability of the proposed atmospheric teleconnection hypothesis the teleconnection appears to involves two distinct steps first the north atlantic cooling shifts the intertropical convergence zone southward weakening the southern branch of the hadley circulation and second how the altered hadley circulation in turn modifies the structure of midlatitude westerlies in the south pacific via the former s influence on the southern hemisphere subtropical jet this study underscores the control of the northern hemisphere has on southern midlatitude westerlies mediating by tropical circulation in contrast to past paleoclimate hypotheses that the magnitude and position of the southern midlatitude westerlies was controlled by global mean temperature our results do not preclude other potential mechanisms for affecting southern ocean ventilation in particular through oceanic pathways