downward control of the mean meridional circulation and temperature distribution of the polar winter stratosphere abstract according to the downward control principle the extratropical mean vertical velocity on a given pressure level is approximately proportional to the meridional gradient of the vertically integrated zonal force per unit mass exerted by waves above that level in this paper a simple numerical model that includes parameterizations of both planetary and gravity wave breaking is used to explore the influence of gravity wave breaking in the mesosphere on the mean meridional circulation and temperature distribution at lower levels in the polar winter stratosphere the results of these calculations suggest that gravity wave drag in the mesosphere can affect the state of the polar winter stratosphere down to altitudes below 30 km the effect is most important when planetary wave driving is relatively weak that is during southern winter and in early northern winter in southern winter downwelling weakens by a factor of 2 near the stratopause and by 20 at 30 km when gravity wave drag is not included

a data study of the influence of the equatorial upper stratosphere on northern hemisphere stratospheric sudden warmings equatorial winds in the stratosphere are known to influence the frequency of stratospheric midwinter sudden warmings sudden warmings in turn influence the earth s climate both through their direct influence on polar temperatures and through the temperature dependence of ozone depletion in the lower stratosphere the conventional holton tan explanation for the equatorial influence on sudden warmings is in terms of the equatorial winds in the lower stratosphere 20 30 km acting as a waveguide for midlatitude planetary wave propagation this study employs stratospheric temperature analyses and equatorial rocketsonde wind data extending to 58 km to diagnose the relationship between the northern hemisphere polar temperatures and equatorial zonal winds at all height levels in the stratosphere in addition to the recognized holton tan relationship linking the polar temperatures to the quasi biennial oscillation in equatorial winds in the lower stratosphere a strong correlation of polar temperatures with equatorial winds in the upper stratosphere is found we suggest that this may be associated with the strength and vertical extent of the westerly phase of the semi annual oscillation in the upper stratosphere although the observations alone cannot provide a conclusive causal relationship the main diagnostic tools employed are correlation studies and composite analysis the results underline the need for continued high quality equatorial wind measurements at all stratospheric levels

experiments on tropical stratospheric mean wind variations in a spectral general circulation model abstract a 30 level version of the rhomboidal 15 gfdl spectral climate model was constructed with roughly 2 km vertical resolution in common with other comprehensive general circulation models this model fails to produce a realistic quasi biennial oscillation qbo in the tropical stratosphere a number of simulations were conducted in which the zonal mean winds and temperatures in the equatorial lower and middle stratosphere were instantaneously perturbed and the model was integrated while the mean state relaxed toward its equilibrium the time scale for the mean wind relaxation varied from somewhat over one month at 40 km to a few months in the lower stratosphere this is similar to the time scales of observed qbo wind reversals the wind relaxations in the model also displayed the downward phase propagation characteristic of qbo wind reversals and mean wind anomalies of opposite sign to the imposed perturbation appear at higher levels in the gcm however the downward propagation is clear only abov

effects of an imposed quasi biennial oscillation in a comprehensive troposphere stratosphere mesosphere general circulation model a 48 yr integration was performed using the geophysical fluid dynamics laboratory skyhi troposphere stratosphere mesosphere gcm with an imposed zonal momentum forcing designed to produce a quasi biennial oscillation qbo in the tropical stratosphere in response to this forcing the model generates a qbo in the tropical circulation that includes some very realistic features notably the asymmetry between the strength of the descending easterly and westerly shear zones and the tendency for the initial westerly accelerations to appear quite narrowly confined to the equator the extratropical circulation in the northern hemisphere nh winter stratosphere is affected by the tropical qbo in a manner similar to that observed in particular the polar vortex is generally weaker in winters in which there are easterlies in the tropical middle stratosphere roughly twothirds of the largest midwinter polar warmings occur when the equatorial 30 mb winds are easterly again in rough agreement with observations despite this effect however the total interannual variance in the zonalmean extratropical circulation in the model apparently is slightly decreased by the inclusion of the tropical qbo the observed qbo dependence of the winter mean stratospheric extratropical stationary wave patterns is also quite well reproduced in the model the qbo was also found to have a profound influence on stratospheric stationary waves at low latitudes near and above 10 mb the nh stationary waves were found to penetrate across the equator during the westerly qbo phase but to be restricted to latitudes poleward of 108n during the easterly phase this means that the equatorial qbo in prevailing wind near and above 10 mb has a significant zonally asymmetric component if this is also true in the real atmosphere there are important implications for the adequacy of the current observational rawindsonde network near the equator analysis of the zonal mean zonal momentum budget in the tropical stratosphere reveals that the resolved waves in the model are strong enough to force the realized accelerations through much of the qbo cycle the exception appears to be the easterly acceleration phase below about 20 mb the implications of this for the generation of a self consistent qbo by gcms will be considered the effects of the imposed qbo on the troposphere were found to be very modest there does appear to be a statistically significant weakening by 1ms 21 of the high latitude winter vortex in the middle and upper troposphere given the very high predictability of the stratospheric qbo itself this effect could possibly be used to enhance the skill of seasonal weather forecasts no significant qbo influence was found in the model precipitation field

microgranular enclaves as evidence of rapid cooling in granitoid rocks the case of the los pedroches granodiorite iberian massif spain microgranular enclaves from the los pedroches granodiorite lpg los pedroches batholith iberian massif spain have sr nd isotopic and mineral chemical compositions close to those of their host this similarity is not related to restite unmixing as indicated by the igneous textures of the enclaves a number of other geological and geochemical lines of evidence including the high ree and hfse contents of the microgranular enclaves relative to the host granitoid strongly suggest that this similarity cannot be explained by magma mixing alternatively a crystallization process by rapid cooling within the host granitoid magma could explain the geochemical and textural characteristics of the microgranular enclaves including shape grain size mineralogy texture chemistry and sr nd isotopic composition such a crystallization occurred at the walls of the magma conduits through which the granitic magmas were emplaced in the upper crust this process should be considered as an alternative hypothesis to magma mixing for the generation of some microgranular enclaves especially where no direct evidence exists for the presence of basic magmas coeval with granitoids and where there is a lack of isotopic contrast between hosts and enclaves as the process is favoured by feeder dyke related emplacement we suggest that abundance of microgranular enclaves can be related to the mechanism of emplacement of granitoid bodies

cross equatorially radiating stratospheric rossby waves upper atmosphere research satellite observations of constituent distributions in the middle stratosphere show that extratropical rossby waves from the winter hemisphere can at certain times radiate across the equator and reach the summer subtropics before they break and are absorbed conditions are most favorable for rossby waves to radiate into the tropics when the westerlies of the winter hemisphere extend to low latitudes as usually occurs during november and december in the northern hemisphere cross equatorial radiation of quasi stationary rossby waves requires westerly equatorial winds as occurred in the middle stratosphere in late 1992 constituent distribution maps show numerous episodes of rossby wave radiation across the equator during this early winter period but not after early january 1993 wave breaking in both the winter and summer subtropics above 22 mb causes constituent exchange between the tropics and extratropics including deep tropical in mixing

atlantic seasonal hurricane frequency part i el nino and 30 mb quasi biennial oscillation influences abstract this is the first of two papers on atlantic seasonal hurricane frequency in this paper seasonal hurricane frequency as related to e1 nino events during 1900 82 and to the equatorial quasi biennial oscillation qbo of stratospheric zonal wind from 1950 to 1982 is discussed it is shown that a substantial negative correlation is typically present between the seasonal number of hurricanes hurricane days and tropical storms and moderate or strong 15 cases el nin off the south american west coast a similar negative anomaly in hurricane activity occurs when equatorial winds at 30 mb are from an easterly direction and or are becoming more easterly with time during the hurricane season this association of atlantic hurricane activity with el nino can also be made with the southern oscillation index by contrast seasonal hurricane frequency is slightly above normal in non el nino years and substantially above normal when equatorial stratospheric winds blow from a westerly direction and or are bec

quasi biennial oscillation of short period planetary waves and polar night jet in winter antarctica observed in saber and merra 2 and mechanism study with a quasi geostrophic model

the influence of the quasi biennial oscillation on the troposphere in winter in a hierarchy of models part i simplified dry gcms abstracta dry primitive equation model is used to explain how the quasi biennial oscillation qbo of the tropical stratosphere can influence the troposphere even in the absence of tropical convection anomalies and a variable stratospheric polar vortex qbo momentum anomalies induce a meridional circulation to maintain thermal wind balance this circulation includes zonal wind anomalies that extend from the equatorial stratosphere into the subtropical troposphere in the presence of extratropical eddies the zonal wind anomalies are intensified and extend downward to the surface the tropospheric response differs qualitatively between integrations in which the subtropical jet is strong and integrations in which the subtropical jet is weak while fluctuation dissipation theory provides a guide to predicting the response in some cases significant nonlinearity in others particularly those designed to model the midwinter subtropical jet of the north pacific prevents its universal application when the ext

interannual variations of global total ozone revealed from nimbus 4 buv and ground based observations an objective analysis is made by the hybrid use of nimbus 4 buv and ground based network data to investigate interannual variations in global distributions of total ozone much improvement in spatial resolution and reliability of the analysis is attained from the deduced time changes in 7 years april 1970 to may 1977 the quasi biennial and 4 year oscillations qbo and fyo are separated by numerical filtering characteristic features of these oscillations are investigated by examining time changes of global patterns as well as some spatial mean values the qbo in total ozone is characterized by large variabilities in time and space typical features are as follows in the tropics positive deviations nearly coincide with the westerly phase of equatorial zonal wind at 50 mbar zonally uniform phase changes exhibiting cross equatorial northward propagation are observed phase propagation is continuous to northern mid latitudes where the ozone distributions are accompanied by zonal wave number 3 4 disturbances in northern high latitudes deviations superposed by wave number 1 distribution are found often opposite to mid latitudes in the southern hemisphere the phase is reversed around 15 s and nearly out of phase relation to northern mid latitudes is observed wave number 1 is the dominant wave component through out the southern hemisphere the fyo in total ozone is suggested as a global phenomenon this oscillation is characterized as follows a roughly symmetric distribution with respect to the equator is observed with the out of phase relation between tropics and extratropics there also appears a phase propagation starting from southern high and mid latitudes and reaching northern high latitudes zonally uniform phase changes with wave number 3 disturbances are seen in the northern mid latitudes in the equatorial region and southern hemisphere systematic phase precedings in the western hemisphere are observed for both qbo and fyo planetary scale total ozone waves of zonal wave number 1 in the winter hemisphere are seen to penetrate into the summer hemisphere

geochemistry of enclaves and host granites from the nelas area central portugal abstract tonalitic granodioritic and monzogranitic enclaves occur in the hercynian peraluminous porphyritic biotite granite and biotite muscovite granite from the nelas region some variation diagrams show linear trends but others show dispersion the enclaves generally have closely similar isotopic signatures to those of the host granites they contain xenocrystic plagioclase with the same composition as phenocrysts of the host granite and have biotite as the sole ferromagnesian phase with a composition typically similar to that of the host granite however some cores of enclaves have biotite slightly chemically distinct from that of rims the modelling of major and trace elements of granodioritic enclaves and hybrid host granite indicate that they result from simple mingling mixing between a tonalitic magma and the host granite magma microgranular enclaves are thus interpreted to be globules of a more mafic magma probably from an enriched mantle source partial equilibration has been achieved between these enclaves and the host granite

assembly of a dike fed magma chamber the jackass lakes pluton central sierra nevada california the mechanisms of ascent assembly and emplacement of granitic magma in the crust are critical to understanding the dynamics of continental margin growth yet these mechanisms remain controversial and poorly understood detailed study of structural and petrologic fabrics in the middle cretaceous jackass lakes pluton wall rock system central sierra nevada california coupled with u pb geochronology indicates that the pluton formed via sheet like assembly of a dike fed magma chamber final emplacement of the pluton was facilitated by multiple brittle and ductile mechanisms that were active at different times and places within the system this supports hybrid viscoelastic emplacement models as realistic alternatives to end member models i e dike versus diapir fracture propagation which initiated 40 of the space required for emplacement may have been facilitated by a small component of arc parallel dextral shear that produced north northwest striking tension gashes a combination of ductile wall rock shortening during lateral expansion of sheets and return flow of elongate strongly deformed wall rock septa produced an additional 25 of the space required other mechanisms including coeval formation of the overlying minarets caldera and stoping in the subvolcanic part of the magma chamber must account for the remaining 35 space implying that vertical transfer of material is an important emplacement mechanism at shallow crustal levels

evidence of magma mixing identified in the early eocene caina pluton from the gangdese batholith southern tibet abstract abundant mafic enclaves are enclosed within the quxu batholith in the eastern gangdese magmatic belt southern tibet this study focuses on the petrogenesis and affinity of these mafic enclaves with their host diorite granodiorite as well as their mechanism of formation and tectonic setting zircon u pb geochronological and hf isotopic results demonstrate that the mafic enclaves and their hosts were emplaced at 50 ma with similar positive zircon ehf t values of 9 12 al in hornblende geobarometry suggests that the mafic enclaves and their hosts intruded at depths of 11 13 km the geochronological and geochemical data point to a magma mixing process resulting in the formation of the host rocks and mafic enclaves our conclusion is further supported by mesoscopic field and microscopic thin section observations consistent with magma mixing we argue that the emplacement of these rocks within the eastern gangdese belt was triggered by slab rollback of the subducted neotethyan oceanic lithosphere during the early phases of the indo asian collision

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

rossby wave propagation into the tropical stratosphere observed by the high resolution doppler imager stratospheric wind observations by the high resolution doppler imager on the upper atmosphere research satellite show that quasi stationary rossby waves propagate into the tropics rossby wave breaking and dissipation causes meridional transport and direct deposition of momentum and has a significant influence on the evolution of the mean tropical winds in the upper stratosphere deeper penetration into the tropics occurs when the quasi biennial oscillation is in its westerly phase above 30 km during northern winter subtropical momentum deposition by rossby waves occurs only in late november through december while during southern winter this occurs primarily in august and september

distribution of major stratospheric warmings in relation to the quasi biennial oscillation data from 1953 to the present indicate that major warmings in the northern hemisphere winter have not occurred when the equatorial monthly mean zonal winds are deep westerly i e westerly over more than about 5 8 of the 10 85 mb layer sixteen winters have had a major warming in the last 35 years six january february periods had deep equatorial westerlies but did not experience a major warming major warmings do not require deep equatorial easterlies nor is the occurrence of a major warming significantly correlated with the sign of the zonal mean wind at any particular level between 10 and 50 mb although as noted by previous investigators more than half of the observed major warmings have occurred when the equatorial flow is easterly at a given level between 10 and 50 mb we suggest that a more relevant qbo statistic may be found in the depth of qbo wind regimes the previously proposed connection between the equatorial quasi biennial oscillation and the major warmings of the northern hemisphere winter is supported by these observations

geological characteristics and genesis of the jurassic no i porphyry cu au deposit in the xiongcun district gangdese porphyry copper belt tibet abstract the xiongcun district located in the western segment of the gangdese porphyry copper belt gpcb hosts the only known jurassic mineralization in the gpcb tibet prc the no i deposit in the xiongcun district is related to the middle jurassic quartz diorite porphyry 167 161 ma and the mineralization was formed at ca 161 5 2 7 ma ore bearing middle jurassic quartz diorite porphyry emplaced into the early jurassic volcano sedimentary rock sequences of the xiongcun formation veinlets and disseminated mineralization developed within the middle jurassic quartz diorite porphyry and the surrounding metamorphosed tuff hosting a measured and indicated resource of 1 04 mt copper 143 31 t gold and 900 43 t silver with an average grade of 0 48 copper 0 66 g t gold and 4 19 g t silver the mineralization can be assigned to four stages including three main stages of hypogene mineralization and one epigenetic stage the main alteration associated with mineralization is potassic seven mineralization related hydrothermal veins have been recognized including quartz sulfide biotite sulfide magnetite sulfide quartz molybdenite sulfide chalcopyrite pyrite pyrrhotite pyrite and polymetallic veins the s and pb isotopic compositions of the ore sulfides and the re contents of the molybdenite suggest a mantle source for the ore forming materials with minor contamination from the subducted sediments hydrogen and oxygen isotope compositions of quartz in the ores suggest that both magmatic and meteoric waters were involved in the ore forming process the ore bearing porphyry 167 161 ma and ore forming 161 5 2 7 ma ages of the no i deposit correspond to the time of northward subduction of neo tethys oceanic slab the geochemical data of the ore bearing porphyry indicate that the no i deposit formed in an intra oceanic island arc setting and the ore bearing porphyry originated from the partial melting of mantle with limited contribution of subducted sediments the genesis of the ore bearing porphyry and no i deposit is interpreted as being related to northward intra oceanic subduction of neo tethys oceanic slab in the middle jurassic time 167 161 ma

longitudinal variation of the stratospheric quasi biennial oscillation the longitudinal dependence of interannual variations of tropical stratospheric wind is examined in a detailed general circulation model simulation and in the limited observations available a version of the skyhi model is run with an imposed zonally symmetric zonal momentum source that forces the zonal mean zonal wind evolution in the tropical stratosphere to be close to an estimate of the observed zonal wind based on radiosonde observations at singapore during the period 1978 99 this amounts to a kind of simple assimilation model in which only the zonal mean wind field in the tropical stratosphere is assimilated and other quantities are allowed to vary freely a total of five experiments were run one covering the full 1978 99 period and four for 1989 99 the results at and above about 30 hpa are fairly simple to characterize when the zonal mean wind near the equator at a particular level is easterly the monthly mean wind has only very small zonal contrasts when mean westerlies are present near the equator significant zonal asymmetries occur at low latitudes most notably easterly anomalies over south america and westerly anomalies in the eastern pacific region these anomalies generally display a continuous meridional phase propagation with the extratropical quasi stationary eddy field in the winter hemisphere the net result is a significantly weaker peak to peak amplitude of the quasi biennial oscillation qbo in zonal wind over the south american sector than over the rest of the equatorial band the zonal contrast in qbo amplitude near 10 hpa exceeds 10 in the lower stratosphere the zonal asymmetries in the prevailing wind are fairly small asymmetries seem to reflect the upward extension of the tropospheric walker circulation and are less strongly modulated by the quasi biennial oscillation in zonal mean circulation the model results were checked against limited station observations at nairobi 1 38s 36 78e singapore 1 48n 103 98e rochambeau 4 88n 52 48w and bogota 4 78n 74 18w overall reasonable agreement was found between the monthly mean zonal winds in the model simulation and these station data the low latitude wind field in monthly mean ncep gridded analyses was also examined these analyses have some obviously unrealistic features in the tropical stratosphere but some of the behavior seen in the skyhi model simulations can be identified as well in the ncep analyses

four magmatic fabrics in the tuolumne batholith central sierra nevada california usa implications for interpreting fabric patterns in plutons and evolution of magma chambers in the upper crust for the first time four distinct magmatic fabrics are documented in a composite plutonic body the tuolumne batholith central sierra nevada california usa one type of fabric was formed by strain caused by highly localized magma flow type 1 whereas the other three chamber wide fabrics recorded strain increments during boundary processes along batholith margins type 2 superimposed by increments of heterogeneous regional tectonic strain types 3 and 4 our present work indicates that in contrast to studies that consider magmatic fabrics to be simple structures formed by a single process magmatic lineations and foliations in plutons may reflect accumulated finite strain and form as composite structures recording multiple strain increments in relatively static actively deforming and rheologically complex crystal mushes at lower melt percentages we demonstrate that multiple magmatic fabrics in a single batholith may record remarkably different processes and thus preserve a temporal record of strain in the batholith from strain during internal chamber processes to postem placement regional tectonic strain however it may be commonly very problematic to infer the exact nature of flow or even fabric forming process from the preserved rock record our study also exemplifies how examination of magmatic fabric patterns in plutons complemented with geochronology may provide crucial constraints on the interplay among successive magma emplacement fabric preservation temporal evolution of strain fields in a crystallizing magma chamber and the development of crystal mush zones

constraints on the collision and the pre collision tectonic configuration between india and asia from detrital geochronology thermochronology and geochemistry studies in the lower indus basin pakistan abstract knowledge of the timing of india asia collision is a fundamental prerequisite for understanding the evolution of the himalayan tibetan orogen and its role in global climate oceanic chemistry and ecological evolution despite much active research the basic pre collision tectonic configuration and the timing of terminal india asia suturing remain debated for example debates regarding when and how the intervening kohistan ladakh arc was sutured with india and asia still remain elusive some models propose the arc collided with asia at about 100 ma with india asia collision at ca 55 ma whilst a newer model proposed the arc s collision with india at 50 ma and subsequently with asia at 40 ma another example is the recent proposition that an oceanic greater india basin separated the tethyan himalaya microcontinent from the remaining indian plate until 20 25 ma with the consumption of this oceanic basin marking the final collision at this time these controversies relate to whether the commonly documented 50 ma contact represents the terminal india asia suturing or the amalgamation between various arcs or microcontinents with india or asia here we present an integrated provenance study of geochronology thermochronology and geochemistry on the late cretaceous pleistocene sediments from the lower indus basin on the indian plate the detrital zircon u pb and fission track data show a reversal in sediment source from a pure indian signature to increasing inputs from the suture zone and the asian plate between the middle paleocene and early oligocene the nd and sr isotopes narrow down this change to 50 ma by revealing input of asian detritus and the establishment of a nd sr isotopic pattern similar to the present day indus fan by 50 ma with no significant variations up section contrary to what might be expected if later major collisions had occurred our isotopic data indicate that greater india was occupied by a fluvial deltaic system analogous to the present day indus and named as the paleo indus which has been transporting asian detritus southward across the suture zone and kohistan ladakh arc since 50 ma suggesting no other ocean basins intervened between india and asia after this time in this region our data require that in the west the india asia collision were accomplished by 50 ma

climatology of the equatorial lower stratosphere abstract twenty years of radiosonde data have been analyzed in an attempt to develop a latitudinal structure climatology of winds temperature and geopotential at 30 and 50 mb in the equatorial stratosphere the fine latitudinal resolution provided by the wmo station network reveals several interesting features in the latitudinal structure of the annual and quasi biennial cycles which dominate this region for example the westerly and easterly acceleration phases of the quasi biennial oscillation are markedly different westerly accelerations appear first at the equator spreading outward with time to higher latitude and an more intense on average than the easterly accelerations the easterly accelerations are more uniform in latitude but leer uniform in time sometimes occurring in two stages the quasi biennial wind and temperature oscillations are symmetric about the equator while the annual harmonic in zonal wind is antisymmetric about the equator but is not proportional to the coriolis paramete

the influences of zonal flow on wave breaking and tropical extratropical interaction in the lower stratosphere abstract the influences of the zonal mean flow on rossby wave breaking and tropical extratropical interaction in the lower stratosphere are investigated using a high resolution barotropic model it is found that the zonal mean wind in the subtropics of the winter hemisphere denoted as 30 is pivotal to the location and intensity of rossby wave breaking when 30 is positive and relatively large significant wave breaking occurs in two regions one in the midlatitudes of the winter hemisphere and the other in the tropics when 30 is small or negative on the other hand wave breaking occurs primarily in the middle to high latitudes of the winter hemisphere it is also found that when 30 is large wave breaking is sensitive to the phase of the equatorial quasi biennial oscillation qbo in that if the qbo is westerly significant wave breaking takes place in the midlatitudes of the winter hemisphere and the subtropics of the summer hemisphere and no wave breaking occurs in the equatorial region and

dynamical response in the northern hemisphere midlatitude and high latitude winter to the qbo simulated by ccsr nies ccm 1 an analysis of the relationship between zonal wind in the equatorial stratosphere and zonal wind temperature and eliassen and palm e p flux in the northern hemisphere extratropical winter was performed using the ccsr nies chemistry climate model ccm and the japanese 25 year reanalysis jra 25 data the tropical zonal wind of the ccm was forced by observations including the observational equatorial quasi biennial oscillation qbo the influence of the qbo on the northern hemisphere winter was estimated by a composite analysis with statistical significance the analyses suggest that the difference in latitude of the critical line zero value line of zonal wind in the low latitudes around 10 hpa as well as 50 hpa between the easterly and westerly phases is related to the wave propagation and circulation over the whole depth of the stratosphere the circulation anomaly is further related to the temperature anomaly at the northern hemisphere midlatitudes and the zonal wind anomaly at the high latitudes these results suggest a mechanism through which 10 hpa qbo could influence the polar vortex while the mechanism of 50 hpa qbo influence is unclear but the possibility is not ruled out

nonlinear relation of the arctic oscillation with the quasi biennial oscillation a nonlinear principal component analysis nlpca is applied to a set of monthly mean time series from january 1956 to december 2007 consisting of the arctic oscillation ao index derived from 1 000 hpa geopotential height anomalies poleward of 20 n latitude and the zonal winds observed at seven pressure levels between 10 and 70 hpa in the equatorial stratosphere to investigate the relation of the ao with the quasi biennial oscillation qbo the nlpca is conducted using a new compact neural network model the nlpca modeling of the dataset of the ao index and qbo winds offers a clear picture of the relation between the two oscillations in particular the phase of covariation of the oscillations defined by the two nonlinear principal components of the dataset progresses with a predominant 28 4 month periodicity this predominant cycle is modulated by an 11 year cycle the variation of the ao index with the qbo phase also shows that the average ao index is positive when the westerly qbo phase descends past 30 hpa and conversely the average ao index is negative when the easterly qbo phase descends past 30 hpa this relationship is evident during the boreal cold season from november to april but non existent during the boreal warm season from may to october

connections between the stratospheric quasi biennial oscillation and tropospheric circulation over asia in northern autumn 1 we investigate the variations in tropospheric circulation over asia associated with the stratospheric quasi biennial oscillation qbo during northern hemisphere nh autumn september november using the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis and ncep department of energy doe reanalysis ii data sets for a 25 year period 1980 2004 the anomaly fields in this study are expressed as the easterly years minus the westerly years of the qbo the zonal wind distribution at 200 hpa indicates easterly anomalies at low latitudes from india through taiwan statistically significant westerly anomalies at midlatitudes including the tibetan plateau to northern china and significant easterly anomalies in the high latitude eurasia north of 50 n a momentum balance analysis indicates that these anomalies over asia are attributable to atmospheric waves and residual mean meridional flow significant northward and descending anomalies are observed in the lower stratosphere over asia with detectable signals in the troposphere around tibet the adiabatic heating due to descending motions in the region centering on india and bangladesh is consistent with the distribution of rainfall anomalies the formation of zonal wind anomalies over south asia seems to be associated with not only wave activities but also adiabatic heating and thermal advection we suggest that the qbo may be linked to tropospheric circulation over asia through wave activities and convective activities in autumn and the wave activities in the low latitudes associated with the qbo seem to be connected with the rainfall distribution over the asian monsoon region

model studies of the interannual variability of the northern hemisphere stratospheric winter circulation the role of the quasi biennial oscillation a series of experiments are described that examine the sensitivity of the northern hemisphere winter evolution to the equatorial quasi biennial oscillation qbo the prime tool for the experiments is a stratosphere mesosphere model the model is integrated over many years with the modelled equatorial winds relaxed towards observed values in order to simulate a realistic qbo in experiment a the equatorial winds are relaxed towards singapore radiosonde observations in the height region 16 32 km in contrast to previous modelling studies the holton tan relationship warm cold winters associated with easterly westerly qbo winds in the lower stratosphere is absent however in a second experiment run b in which the equatorial winds are relaxed towards rocketsonde data over the extended height range 16 58 km a realistic holton tan relationship is reproduced a series of further studies are described that explore in more detail the sensitivity to various equatorial height regions and to the bottom boundary forcing the experiments suggest that the evolution of the northern hemisphere winter circulation is sensitive to equatorial winds throughout the whole depth of the stratosphere and not just to the lower stratospheric wind direction as previously assumed

modeling the quasi biennial oscillation s influence on isentropic tracer transport in the subtropics tracer transport in the lower stratosphere is investigated using an off line semi lagrangian transport model and winds from a mechanistic three dimensional middle atmosphere model interpolated to the 650 k isentropic surface over a winter season by comparing two simulations the effect of the quasi biennial oscillation s qbo s easterly or westerly wind phases on low latitude transport is examined especially regarding the formation of an apparent subtropical transport barrier at the equatorward edge of the surf zone the tracer field is diffused less than potential vorticity pv and shows sharper gradients and finer structures developing over the winter in both qbo phases the winter extratropical surf zone is bounded by large tracer gradients equatorward of about 15 latitude the inability of quasi stationary rossby waves to propagate into qbo easterlies leads to a much sharper edge forming between the rapidly stirred extratropical surf zone and the relatively unstirred tropics during the easterly qbo phase than occurs during the westerly qbo phase in the westerly phase some rossby wave activity can propagate across the equatorial westerlies and break on reaching the summer hemisphere easterly winds causing mixing there simulations using a tracer initially confined to the tropics show that more tropical air is mixed out to the winter extratropics by rossby wave stirring when the qbo phase is easterly despite the sharper band of stronger tracer or pv gradient which separates the tropics and the winter extratropics in this phase while air was mixed out of the tropics in both qbo phase simulations neither qbo phase simulation showed extratropical air being irreversibly mixed into the tropics these results are related to observations of the tropical reservoir of stratospheric aerosols especially the dynamics and transport of its winter hemisphere boundary

sensitivity of the boreal winter circulation in the middle atmosphere to the quasi biennial oscillation in maecham5 simulations the polar vortex in the northern hemisphere exhibits high intraseasonal and interannual variability which to some degree may be controlled by the quasi biennial oscillation qbo in the tropical stratosphere here we analyze the qbo signal in the northern hemisphere polar vortex in a model simulation using the general circulation model maecham5 middle atmosphere european center hamburg model which simulates the qbo as an internal mode of variability composites have been computed for the westerly and easterly qbo phases from early winter to late winter november december december january and january february of a 50 year experiment containing 20 complete qbo cycles this method identifies tropical and midlatitude patterns in wind and temperature that are related to the secondary meridional circulation of the qbo extending towards the winter pole in the tropics significant qbo signature is observed in the mesosphere up to 0 05 hpa only in early winter and mainly in the easterly qbo phase forced by the parameterized gravity waves mean flow interaction at high latitudes maecham5 shows a significantly warmer colder polar stratosphere in the easterly westerly qbo phase at 30 hpa accompanied by a weaker stronger polar vortex in the late winter months from december to february december to january in the easterly westerly phase of the qbo in early winter there is no significant change in temperature and zonal mean zonal wind in the polar stratosphere the analysis of ep fluxes shows a different behavior between qbo phases with changes in the waveguide wave propagation occurs upwards and polewards in the easterly qbo phase at 30 hpa while waves are refracted equatorward in the westerly phase no relationship has been found between the tropical qbo and the final warming at the end of the boreal winter

forcing mechanism of the seasonally asymmetric quasi biennial oscillation secondary circulation in era 40 and maecham5 1 the seasonality of the quasi biennial oscillation qbo and its secondary circulation is analyzed in the european reanalysis era 40 and middle atmosphere european centre hamburg model maecham5 general circulation model data sets through the multitaper method singular value decomposition mtm svd in agreement with previous studies the results reveal a strong seasonal dependence of the qbo secondary circulation this is characterized by a two cell structure symmetric about the equator during autumn and spring however anomalies strongly weaken in the summer hemisphere and strengthen in the winter hemisphere leading to an asymmetric qbo secondary circulation characterized by a single cell structure displaced into the winter hemisphere during the solstices in era 40 this asymmetry is more pronounced during the northern than during the southern winter these results provide the first observation of the qbo secondary circulation asymmetries in the era 40 reanalysis data set across the full stratosphere and the lower mesosphere up to 0 1 hpa the mtm svd reconstruction of the seasonal qbo signals in the residual circulation and the qbo signals in eliassen palm ep flux divergences suggest a particular mechanism for the seasonal asymmetries of the qbo secondary circulation and its extension across the midlatitudes the analysis shows that the qbo modulates the ep flux in the winter hemispheric surf zone poleward of the qbo jets the zonal wind forcing by ep flux divergence is transformed by the coriolis effect into a meridional wind signal the seasonality in the stratospheric ep flux and the hemispheric differences in planetary wave forcing cause the observed seasonality in the qbo secondary circulation and its hemispheric differences

coupling of the quasi biennial oscillation and the extratropical circulation in the stratosphere through planetary wave transport abstract a significant fraction of the interannual variability of the wintertime stratosphere in the northern hemisphere is related to the quasi biennial oscillation qbo in tropical winds disturbed conditions of the polar night vortex are favored in years when the winds over the equator are easterly more quiescent conditions prevail at high latitudes when the phase of the tropical qbo is westerly the effects of tropical winds on the extratropical circulation are studied in the equivalent barotropic framework on the sphere calculations are performed with the tropical flow representative of easterly and westerly phases of the qbo with planetary wave forcing representative of conditions in the lower stratosphere the wintertime polar vortex is highly disturbed during the easterly phase of the qbo the evolution taking the form of a canadian warming in contrast more quiescent conditions prevail with the same forcing but with tropical winds representative of the westerly phase of the qbo the vortex

on the subtropical edge of the stratospheric surf zone abstract the formation of a subtropical transport barrier in the wintertime stratosphere is investigated in the context of a high resolution shallow water model in which rossby waves are topographically forced on a zonally symmetric basic state two sets of experiments are performed in the first adiabatic set no dissipation or forcing of the mean state is imposed in the second set the layer thickness is relaxed to an equilibrium state taken to be representative of middle stratospheric radiative equilibrium temperatures it is found that in the adiabatic case only a very weak subtropical barrier forms for forcing amplitudes that generate realistically steep potential vorticity gradients at the edge of the polar vortex the vigorous wave breaking in the surf zone generates secondary waves that spread and in turn break well into the summer hemisphere in contrast the inclusion of relaxation to a realistic thermal equilibrium leads to the formation of a subtropical region of steep pv gradients the

modeling the quasi biennial oscillation s effect on the winter stratospheric circulation abstract the influence of the equatorial quasi biennial oscillation qbo on the winter middle atmosphere is modeled with a mechanistic global primitive equation model the model s polar vortex evolution is sensitive to the lower stratosphere s tropical winds with the polar vortex becoming more less disturbed as the lower stratospheric winds are more easterly westerly this agrees with the observed relationship between wintertime polar circulation strength and the phase of the qbo in the lower stratosphere in these experiments it is the extratropical planetary rossby waves that provide the tropical extratropical coupling mechanism more easterly tropical winds in the lower stratosphere act to confine the extratropical rossby waves farther north and closer to the vortex at the qbo altitudes weakening the vortex relative to the case of westerly qbo phase while the qbo winds occur in the lower stratosphere the anomaly in the polar vortex strength is strongest at higher levels