monsoon gyres of the northwest pacific influences of enso the mjo and the pacific japan pattern abstractan objective definition of monsoon gyres in the northwest pacific was developed in order to construct a gyre climatology over a 31 yr period 53 gyres were identified with a median formation location at 16 5 n 135 e more than 80 formed during july september more than half of gyres developed during el nino periods at a median location 1200 km farther to the east southeast than during la nina cyclonic winds at 850 hpa extended across a diameter of more than 4000 km with maximum tangential wind near the 1000 km radius a precipitation maximum extended westward for several thousand kilometers south of the gyre typhoons were most common north and east of the gyre centers more than 70 of gyres developed during large amplitude mjo events with a strong preference for real time multivariate mjo rmm phases 5 7 in boreal summer these phases contain circulation and convective anomalies that coincide most closely with those of the climatological monsoon trough gyres are most likely to form when

development of a one month long westward propagating subtropical low in boreal summer abstracta strong mjo event produced an upper tropospheric jet streak in northeast asia and repeated wave breaking in the jet exit region along 150 e during july 1988 a midlatitude low moved equatorward and intensified in the presence of bandpass filtered 15 100 day q vector forcing for upward motion associated with the wave breaking this forced ascent helped to moisten the atmosphere enough to increase the column water vapor to above 55 mm this value was sufficiently large to support a self sustaining low even after the upper forcing weakened the horizontal scale of the q vector forcing was about 1500 km consistent with the scale of most favorable convective response to quasigeostrophic forcing in the subtropics described by nie and sobel the low lasted one month as it moved southwestward then westward while remaining north of 20 n maximum precipitation along the track of the low exceeded 700 mm with an anomaly more than 400 mm a climatology of long lasting lows was carried out for the monsoo

large scale patterns associated with tropical cyclogenesis in the western pacific abstract five characteristic low level large scale dynamical patterns associated with tropical cyclogenesis in the western north pacific basin are examined along with their capacity to generate the type of mesoscale convective systems that precede genesis an 8 yr analysis set for the region is used to identify and create composites for the five characteristic patterns of monsoon shear line monsoon confluence region monsoon gyre easterly waves and rossby energy dispersion this brings out the common processes that contribute to tropical cyclogenesis within that pattern which are described in detail a 3 yr set of satellite data is then used to analyze the mesoscale convective system activity for all cases of genesis in that period and to stratify based on the above large scale patterns it is found that mesoscale convective systems develop in all cases of genesis except one seventy percent of cases developed mesoscale convective systems at more than one time during the genesis period and 44 of

origin and metamorphic history of an early cretaceous polybaric granulite terrain fiordland southwest new zealand regionally extensive two pyroxene granulites in fiordland southwest new zealand are products of metamorphism of a suite of anhydrous magmas which crystallized two pyroxenes the granulite protolith igneous charnockitic rock synkinematically intruded metasediment and other orthogneiss in an early cretaceous subduction related magmatic arc and during cooling experienced deformation induced recrystallization to form granoblastic gneiss the granulites occur side by side with coeval rocks of amphibolite facies mineral zoning and textural relationships in both granulites and amphibolite facies rocks provide evidence of two distinct periods of crystallization 1 an early high temperature comparatively low pressure event accompanying magmatic intrusion andalusite sillimanite facies series recorded locally in the country rock followed by 2 high pressure metamorphism under conditions of 650 700 c at 12 13 kbar garnet granulite locally overprinted earlier formed two pyroxene granulite during the latter event the pressure increase 6 kbar between the two events is attributed to crustal thickening by overthrusting and is equivalent to unloading of a 20 km thick slab over rocks already buried at mid crustal depths both events occurred over a 20 m y interval between the time of magmatic emplacement of the granulite protolith and uplift controlled final cooling of the terrain the phanerozoic granulites in fiordland share some petrologic similarities with precambrian granulite terrains suggesting that at least some aspects of the former may serve as a useful model for development of the latter

the kinematic structure of hurricane gloria 1985 determined from nested analyses of dropwindsonde and doppler radar data abstract a set of three dimensional filtered multiply nested objective analyses has been completed for the wind field of hurricane gloria for 0000 utc 25 september 1985 at this time gloria was one of the most intense hurricanes ever observed in the atlantic basin with a minimum sea level pressure of 919 mb the nested analyses based on observations from airborne doppler radar and omega dropwindsondes simultaneously describe eyewall and synoptic scale features and are the most comprehensive analyses of a single hurricane constructed to date the analyses have been used to document the multiscale kinematic structure of gloria and to investigate the relationship between the kinematic fields and the motion of the vortex the analyses indicate that the vortex was unusually barotropic the radius of maximum wind rmw was nearly vertical below 500 mb with a slight inward slope with height between 750 and 550 mb the strongest azimuthal mean tangential winds were found well above the boundary layer near

sensitivity of tropical cyclone track to the vertical structure of a nearby monsoon gyre abstractthe impact of different vertical structures of a nearby monsoon gyre mg on a tropical cyclone tc track is investigated using idealized numerical simulations in the experiment with a relatively deeper mg the tc experiences a sharp northward turn at a critical point when its zonal westward moving speed slows down to zero at the same time the total vorticity tendency for the tc wavenumber 1 component nearly vanishes as the vorticity advection by the mg cancels the vorticity advection by the tc at this point the tc motion is dominated by the beta effect as in a no mean flow environment and takes a sharp northward turn in contrast the tc does not exhibit a sharp northward turn with a shallower mg nearby in the case with a deeper mg a greater relative vorticity gradient of the mg promotes a quicker attraction between the tc and mg through the vorticity segregation process in addition a larger outer size of the tc also favors a faster westward propagation from its initial position thus

evolution of depleted mantle the lead perspective abstract isotopic data have established that compared to estimated bulk earth abundances the sources of oceanic basaltic lavas have been depleted in large ion lithophile elements for at least several billions of years various data on the tertiary mesozoic gorgona komatiite and cretaceous oka carbonatite show that those rocks also sample depleted mantle sources this information is used by analogy to compare pb isotopic data from 2 6 billion year old komatiite and carbonatite from the suomussalmi belt of eastern finland and munro township ontario that are with associated granitic rocks and ores that should contain marked crustal components within experimental error no differences are detected in the isotopic composition of initial pb in either of the rock suites these observations agree closely with sr and nd data from other laboratories showing that depleted mantle could not have originated in those areas more than a few tenths of billions of years before the rocks were emplaced on a world wide basis the pb isotope data are consistent with production of depleted mantle by continuous differentiation processes acting over approximately the past 3 billion years the data show that pb evolution is more complex than the simpler models derived from the rb sr and sm nd systems the nature of the complexity is still poorly understood

a deep crustal shear zone exposed in western fiordland new zealand an approximately 180 km long deep crustal shear zone in western fiordland new zealand has been shown to have formed during continental extension between 116 and 100 ma the western fiordland shear zone forms a major tectonic boundary between two sets of gneisses with unrelated deformation histories a detailed study of the northern part of the shear zone has revealed that the shear zone formed at depths of 40 km approximately 12 kbar and 680 c and was originally very gently dipping or subhorizontal prior to subsequent upright folding the current thickness postfolding of the shear zone is 3 4 km abundant asymmetric structures in the shear zone indicate noncoaxial deformation and a top to the ne sense of shear unlike ductile shear zones in metamorphic core complexes from elsewhere in the world there is no evidence that decompression of the shear zone rocks or foot wall rocks occurred during the active life of the shear zone suggesting that displacement along the shear zone by noncoaxial deformation must have been largely horizontal this shear zone provides important evidence for the nature of deep crustal deformation occurring during continental extension

evidence of early cretaceous collisional style orogenesis in northern fiordland new zealand and its effects on the evolution of the lower crust structural metamorphic and kinematic data from a well exposed section of lower crustal rocks in northern fiordland new zealand reveal a history of intense contractional deformation and high p metamorphism at the roots of a convergent orogen high p 14 kbars granulite facies garnet clinopyroxene bearing reaction zones occur adjacent to anorthositic veins within gabbroic and dioritic gneiss these veins and reaction zones were variably deformed by two phases of high p granulite facies deformation quantitative kinematic analyses conducted using systems of rotated veins and reaction zones indicate that the first phase produced steeply dipping shear zones within a sinistral pure shear dominated flow regime wk 0 69 this deformation occurred at conditions of p 14 0 1 3 kbars and t 676 34 c and resulted in subhorizontal arc parallel ne sw stretching and up to 60 subhorizontal shortening in high strain zones of the lower crust at depths 45 km the second phase of deformation occurred at p 14 1 1 2 kbars and t 674 36 c and produced vertically stacked gently dipping ductile thrust faults that accommodated arc normal nw directed displacement these features reflect major tectonic thickening of the crust oblique convergence and high p metamorphism during the collision of the roots of a convergent orogen represented by plutons of the median tectonic zone in eastern fiordland with the paleo pacific margin of gondwana represented by western fiordland distinctive kinematic styles suggest that this collision resulted in a partitioning of the arc parallel ne sw and arc normal nw se components of oblique convergence onto sinistral strike slip and ductile thrust faults respectively at lower crustal levels

generation of trondhjemite from partial melting of dacite under granulite facies conditions an example from the new jersey highlands usa abstract new field and geochemical data place the losee metamorphic suite a tonalite trondhjemite complex of northern new jersey into the context of a major proterozoic continental are represented by a discontinuous belt of northern appalachian metadacite samples of losee rock range from extremely leucocratic trondhjemite locally associated with amphibolite to banded biotite hornblende pyroxene and garnet bearing tonalites the major element and ree composition of the tonalite closely resembles dacite from continental are settings and model melts extracted from an eclogite residue by partial melting at 15 kbar the ree composition of most losee trondhjemite is enriched in ree particularly hree compared with losee tonalite and is interpreted as the product of local anatectic melting of losee tonalite metadacite that occurred in a granulite facies environment during the grenville orogeny

ion microprobe dating of paleozoic granitoids devonian magmatism in new zealand and correlations with australia and antarctica abstract precise ion microprobe u pb zircon ages have been obtained from a representative set of paleozoic igneous rocks from the western province of the south island new zealand granitoid rocks forming the karamea batholith and related plutons in the buller terrane all yield crystallisation ages that are indistinguishable within a 5 ma uncertainty at 375 ma middle late devonian previous workers have suggested that the batholith was emplaced over a long time interval and comprises rocks ranging in age from 370 to 310 ma with the bulk in the early carboniferous granitoid rocks with carboniferous ages 330 ma do occur further to the west and younger cretaceous granitoids occur within the karamea batholith but these are not volumetrically significant a sample from the ultramafic mafic riwaka complex in the adjacent takaka terrane gave a crystallisation age of 376 9 5 6 ma 2 indicating emplacement coeval with the karamea batholith the paleozoic granitoids contain a large amount of inherited zircon with distinct 390 500 600 and 1000 ma components the 390 ma age corresponds to widespread plutonism in the lachlan fold belt in se australia the 500 600 ma ross delamerian age and 1000 ma grenville age age components have also been observed in granitoids from the lachlan fold belt and in ordovician metasedimentary rocks from se australia and new zealand the inherited zircons in the karamea batholith could be derived from continental basement at depth from the incorporation of upper crustal material in the granitoid magmas or both the devonian granitoids in new zealand can now be correlated with rocks of similar age in northern victoria land admiralty intrusives and marie byrd land ford granodiorite in west antarctica in ne tasmania and in the central part of the lachlan fold belt in se australia on a reconstruction of the sw pacific margin of gondwana prior to later break up it is possible to trace out a semi continuous magmatic belt in excess of 2000 km in length

structure and kinematics of oblique continental convergence in northern fiordland new zealand abstract southeast of the alpine fault in fiordland new zealand late tertiary faults envelope exposures of early cretaceous high p 12 16 kbar granulite facies orthogneisses these exposures allowed us to examine how pre cenozoic structures influenced variations in the degree and style of kinematic partitioning within a zone of oblique continental convergence fault slip data and kinematic modelling show that oblique slip and reverse displacements preferentially were partitioned east of the alpine fault onto curved ne striking surfaces and moderately dipping 30 52 n and nw striking surfaces respectively approximately 3 0 5 5 km of exhumation and 6 5 7 0 km of oblique dextral displacement occurred on faults that display palm tree style geometries and subhorizontal detachments in profile this heterogeneous style contrasts with the near horizontal slip on subvertical surfaces that define the alpine fault north of milford sound the principal axes of instantaneous strain we determined using faults are compatible with principal stress axes derived from earthquakes our data indicate that mechanical anisotropies created by inherited structures controlled the locations and highly variable geometries of faulting since 7 9 ma the effects of these pre existing structures and a focusing of contractional deformation along the northeast margin of fiordland resulted in an unusually high degree of strike slip partitioning across the southernmost onshore segment of the alpine fault

stresses and strains in a twisted subduction zone fiordland new zealand summary in the fiordland region of the south island of new zealand the subducted australian plate steepens from south to north becoming near vertical below 75 km depth between doubtful and milford sounds this steepening is accompanied by a sharp change in strike of the subduction zone of about 17 here we investigate stress and strain in this twisted subduction zone using earthquakes recorded during a three month deployment of 24 portable digital seismographs we determine focal mechanisms of 115 earthquakes of ml 2 5 4 5 using both first motion polarity data and amplitudes of seismogram envelopes we also invert for the stress tensor orientation for regions within both the subducted and overlying plates using a method which invokes the coulomb failure criterion and considers all p wave first motions together regardless of whether or not they are sufficient to define single event focal mechanisms focal mechanisms and stress inversions for earthquakes in the overlying plate indicate normal faulting shallower than 16 km and thrust faulting at greater depths this stress and strain regime is related to the 17 change in strike of the subduction zone which leads to an arching up of the subducted plate at the bend such arching is consistent with the exposure of lower crustal granulite facies rocks near the bend earthquakes in the subducted plate show predominantly normal faulting relative to the plate arrival time inversions for 3 d seismic velocity structure indicate that a zone of high vp 8 5 km s 1 in the uppermost mantle of the overlying plate abuts the vertical portion of the subduction zone stresses and strains in the subducted plate are consistent with a model in which the sharp change in strike of the subduction zone is a consequence of the obliquely converging subducted plate having to bend around this zone the steep dip of the subducted plate to the north appears to be a natural consequence of the minimization of membrane stress in the plate arising from the sharp bend along strike this mechanism for steepening the plate is quite different to that of trench retreat usually used to explain steep subduction

observational analysis of sudden tropical cyclone track changes in the vicinity of the east china sea abstractan observational analysis of observed sudden typhoon track changes is conducted with a focus on the underlying mechanism and the possible role of slowly varying low frequency flows four typhoons that took a generally northwestward track prior to sharply turning northeastward in the vicinity of the east china sea are investigated it is found that the sudden track changes occurred near the center of the madden julian oscillation mjo scale cyclonic circulation or at the bifurcation point of the steering flows at 700 hpa and they were all associated with a well developed quasi biweekly oscillation qbw scale gyre calculation of vorticity advection suggests that the peripheral ridging resulting from the interaction between the typhoons and the flows on the mjo and qbw scales can compress the typhoon circulation leading to an area of high winds to the east or south of the typhoon center the enhanced synoptic scale winds shifted the typhoons northward and placed them in a northeastward orbit unde

ftir microspectroscopy of ediacaran phosphatized microfossils from the doushantuo formation weng an south china abstract phosphatized microfossils from ca 580 ma from the doushantuo formation in the weng an region of south china were analyzed by fourier transform infrared ftir microspectroscopy for their chemical characterization two morpho types of phosphatized embryo like fossils megasphaera and megaclonophycus were analyzed together with algal fossils transmission ir spectra of the microfossils have absorption bands of around 2960 cm 1 and 2925 cm 1 indicating the presence of aliphatic hydrocarbon anti symmetric aliphatic ch 3 and aliphatic ch 2 and have an additional band of around 1595 cm 1 probably derived from aromatic moieties aromatic c c in addition ir microscopic mapping shows that aliphatic hydrocarbon and aromatics are distributed inside the embryo like fossils the embryo like fossils appear to show three types of ch 3 ch 2 peak height ratios r 3 2 and aromatic c c ch 2 peak height ratios r c c 2 values 1 high r 3 2 low r c c 2 type r 3 2 0 2 1 0 and r c c 2 0 2 2 low r 3 2 medium r c c 2 type r 3 2 0 2 0 6 and r c c 2 1 4 and 3 low r 3 2 high r c c 2 type r 3 2 0 2 0 6 and r c c 2 1 8 all three types are contained in both megasphaera and megaclonophycus raman spectra for the carbonaceous matter within the rock sample show a similar degree of thermal alteration indicating that the organics were embedded in situ prior to thermal maturation the ir spectroscopic differences might reflect differences in original organic compositions of microorganisms and or immediate post mortem alteration this suggests that the origins of phosphatized embryo like fossils are more diverse than was previously recognized on the basis of their morphology a comparison of r 3 2 and r c c 2 values in the embryo like fossils with those of the algal fossils and the extant microorganisms indicates the possible interpretation that some of the embryo like fossils belong to animal embryo others are algae but none of them originate from bacteria

cocorp and the continental crust this is a speculative paper on the continental crust a major frontier of modern earth science seismic reflection profiling data from the cocorp project coupled with other kinds of geophysical and geological observations suggest some fresh perspectives on the crust for example there is evidence for great differences within the basement at a single site and from one cocorp site to another a simple layered model is surely not an adequate representation of the crust in most areas there is however the puzzling and rather common occurrence of limited zones of parallel though not always flat layered features at various depths in certain parts of the crust are the corresponding rocks metasedimentary or igneous or both there are transparent zones from which little or no coherent reflected seismic energy is detected are the corresponding rocks intrusions or highly deformed metasediments can degree of deformation suggest whether rocks were deformed in the hanging wall or footwall of a thrust there is evidence for large scale thrusting and related features that emphasizes the great importance of the wilson cycle to continental tectonics and that raises the possibility that water and rocks of sedimentary origin are trapped deep in the crust by the thrusting process and remain there for long periods with a variety of possible rheological and petrological consequences in some places the modern moho and adjacent rocks may correspond to parts of former oceanic or continental margin sections that have been emplaced at depth as a result of thrusting the widely held concept of the moho as a consistent boundary that is everywhere similar and that always separates the same kinds of rocks may be a major barrier to further progress in understanding the continental crust

granulite formation during continental extension in fiordland new zealand the formation of the high pressure high temperature rocks known as granulites has traditionally been attributed to metamorphism in the deeper parts of continental collision zones and magmatic arcs1 3 more recently greater consideration has been given to the possibility of granulite formation during continental rifting4 6 and in particular4 to whether granulites are forming today beneath the north american basin and range province here we report thermobarometric data and single zircon u pb ages for an analogous but much more deeply exhumed extensional terrain in fiord land new zealand7 8 where early cretaceous granulites underwent renewed granulite facies metamorphism at significantly shallower crustal levels following the extensional collapse of magmatically thickened continental crust our data show that granulite facies metamorphism can take place during continental extension and demonstrate that in western new zealand it was accompanied at higher structural levels by the emplacement of one or more metamorphic core complexes7 9 in keeping with the model postulated4 for the basin and range province

diagnosis of the mjo modulation of tropical cyclogenesis using an empirical index the modulation of tropical cyclone activity by the madden julian oscillation mjo is explored using an empirical genesis potential gp index composite anomalies of the genesis index associated with the different mjo phases are consistent with the composite anomalies in tc genesis frequency that occur in the same phases indicating that the index captures the changes in the environment that are at least in part responsible for the genesis frequency changes of the four environmental variables that enter the genesis potential index the midlevel relative humidity makes the largest contribution to the mjo composite gp anomalies the second largest contribution comes from the low level absolute vorticity and only very minor contributions come from the vertical wind shear and potential intensity when basin integrated mjo composite anomalies of the gp index are regressed against basin integrated composite anomalies of tc genesis frequency the results differ quantitatively from those obtained from the analogous calculation performed on the annual climatologies in the two quantities the gp index captures the mjo modulation of tc genesis to a lesser degree than the climatological annual cycle of genesis to which it was originally tuned this may be due to weaknesses of the reanalysis or indicative of the importance of precursor disturbances not well captured in the gp index computed from weekly data to the intraseasonal tc genesis frequency fluctuations

shrimp monazite and zircon geochronology of high grade metamorphism in new zealand ion microprobe dating of zircon and monazite from high grade gneisses has been used to 1 determine the timing of metamorphism in the western province of new zealand and 2 constrain the age of the protoliths from which the metamorphic rocks were derived the western province comprises westland where mainly upper crustal rocks are exposed and fiordland where middle to lower crustal levels crop out in westland the oldest recognisable metamorphic event occurred at 360 370 ma penecontemporane ously with intrusion of the mid palaeozoic karamea batholith c 375 ma metamorphism took place under low pressure high temperature conditions resulting in upper amphibolite sillimanite grade meta morphism of lower palaeozoic pelites greenland group orthogneisses of younger cretaceous age formed during emplacement of the rahu suite granite intrusives c 110 ma and were derived from protoliths including cretaceous separation point suite and devonian karamea suite granites in fiordland high grade paragneisses with greenland group zircon age patterns were metamorphosed m1 to sillimanite grade at 360 ma concomitant with crustal thickening and further granite emplace ment m1 mineral assemblages were overprinted by higher pressure kyanite grade metamorphism m2 at 330 ma it remains unclear whether the m2 event in fiordland was primarily due to tectonic burial as suggested by regional recumbent isoclinal folding or whether it was due to magmatic loading in keeping with the significant volumes of granite magma intruded at higher structural levels in the formerly contiguous westland region metamorphism in fiordland accompanied and outlasted emplacement of the western fiordland orthogneiss wfo at 110 125 ma the wfo equilibrated under granulite facies conditions whereas cover rocks underwent more limited recrystallization except for high strain shear zones where conditions of lower to middle amphibolite facies were met the juxtaposition of palaeozoic kyanite grade rocks against cretaceous wfo granulites resulted from late mesozoic extensional defor mation and development of metamorphic core complexes in the western province

structure and dynamics of the summertime pacific japan teleconnection pattern convective activity over the tropical western pacific is known to influence the extratropical circulation over east asia in the boreal summer in the form of teleconnection called the pacific japan pj pattern but its structure and dynamics have not yet been studied in depth in this study a composite analysis is performed for 32 monthly events of enhanced convection observed to the east of the philippines the composited monthly mean vorticity anomalies associated with the pj pattern are elongated zonally with a distinct poleward tilt with height this structure differs fundamentally from a combination of the first baroclinic mode in the tropics and the barotropic structure in midlatitudes as has widely been accepted as a conceptual model of the pj pattern a wave activity flux points polewards only in the lower troposphere indicating that rossby wave teleconnection occurs primarily through a low level south westerly jet those tilted anomalies over the western pacific can effectively gain kinetic energy in the exits of the mean jet streams in the upper and lower troposphere and available potential energy ape in the presence of the vertically sheared jets the enhanced convection can generate ape effectively and the associated low level anomalous circulation acts to increase moisture supply into the convective region while enhancing evaporation from the pre warmed ocean surface it is thus hypothesized that the pj pattern may be regarded as a dynamical mode that can be effectively excited in the zonally asymmetric baroclinic mean flow associated with the asian summer monsoon with an efficient self sustaining mechanism through moist processes copyright 2006 royal meteorological society

the interplay and effects of deformation and crystallized melt on the rheology of the lower continental crust fiordland new zealand abstract microstructural electron backscatter diffraction ebsd and misorientation analyses of a migmatitic granulite facies orthogneiss from the exhumed lower crust of a cretaceous continental arc in fiordland new zealand show how deformation was accommodated during and after episodes of melt infiltration and high grade metamorphism microstructures in garnet omphacite plagioclase and k feldspar suggest that an early stage of deformation was achieved by dislocation creep of omphacite and plagioclase with subsequent deformation becoming partitioned into plagioclase continued deformation after melt infiltration resulted in strain localization in the leucosome of the migmatite where a change of plagioclase deformation mechanism promoted the onset of grain boundary sliding most likely accommodated by diffusion creep in fine recrystallized plagioclase grains our results suggest three distinctive transitions in the rheology of the lower crust of this continental arc where initial weakening was primarily achieved by deformation of both omphacite and plagioclase subsequent strain localization in plagioclase of the leucosome indicates that the zones of former melt are weaker than the restite and that changes in deformation mechanisms within plagioclase and an evolution of its strength primarily control the rheology of the lower crust during and after episodes of melting and magma addition

tropical cyclogenesis within an equatorial rossby wave packet a packet of equatorial rossby er waves that lasted 2 5 months is identified in the lower troposphere of the northwest pacific waves within the packet had a period of 22 days a wavelength of 3600 km a westward phase speed of 1 9 m s 1 and a near zero group speed the wave properties followed the er wave dispersion relation with an equivalent depth near 25 m the packet was associated with the development of at least 8 of the 13 tropical cyclones that formed during the period a composite was constructed around the genesis locations tropical cyclones formed east of the center of the composite er wave low in a region of strong convection and a separate 850 hpa vorticity maximum the background flow during the life of the packet was characterized by 850 hpa zonal wind convergence and easterly vertical wind shear wave amplitude peaked at the west end of the convergent region suggesting that wave accumulation played a significant role in the growth of the packet the presence of easterly vertical wind shear provided an environment that trapped energy in the lower troposphere each of these processes increases wave amplitude and thus the likelihood of tropical cyclone formation within the waves the initial low pressure region within the wave packet met lander s definition of a monsoon gyre it developed to the west of persistent localized convection that followed the penetration of an uppertropospheric trough into the subtropics it is argued that the monsoon gyre represented the initial er wave low within the packet

western fiordland orthogneiss early cretaceous arc magmatism and granulite facies metamorphism new zealand u pb isotopic analyses of zircons from a distinctive suite of previously undated granulite facies metaplutonic rocks here termed the western fiordland orthogneiss wfo in fiordland southwest new zealand indicate synkinematic magmatic emplacement between 120 and 130 ma ago these rocks were previously interpreted as possibly being of precambrian age initial pb and sr ratios are consistent with arc subduction related magmagenesis with little or no involvement of ancient continental crust subsequent high pressure 12 kb metamorphism of the wfo may reflect a major collision event involving crustal thickening by overthrusting of a 15 km thick sequence metamorphism ceased 116 ma ago based on206pb 238u ages of zircon from a retrogressed granulite u pb isotopic analysis of apatite along with previously published rb sr mineral ages indicate that final uplift and cooling to 300 400 c was largely completed by 90 ma the average uplift rate during this period is inferred to have been in excess of 1 mm yr unmetamorphosed gabbronorites of the darran complex in eastern fiordland inferred by some investigators to be the granulite protolith yield concordant u pb zircon ages of 137 1 ma u pb ages of apatite and previously published k ar mineral ages indicate that these rocks experienced a rapid and simple cooling history lasting only a few million years the high grade wfo and unmetamorphosed darran complex are now separated by a profound structural break however the ages and similarities in initial pb and sr isotopic ratios suggest that both suites are products of the same early cretaceous cycle of subduction related magmatism the timing of early cretaceous magmatism and metamorphism collision and resultant crustal thickening and subsequent great uplift and erosion in fiordland has important implications for terrane accretion and the evolution of relative plate motions along the new zealand segment of the gondwana margin

early cretaceous age of orthogneiss from the charleston metamorphic group new zealand discordant u pb zircon isotopic data from amphibolite facies orthogneisses of the charleston metamorphic group western south island new zealand define a lower intercept age of 114 18 m y that is interpreted as the crystallization age of the orthogneiss magmas the upper intercept age of 1026 97 m y reflects inherited components of precambrian zircon derived from the source region of the magmas the age and whole rock chemical characteristics indicate that the orthogneisses are part of the same phase of early cretaceous magmatic activity that produced voluminous arc related calc alkaline plutonic rocks throughout western south island previously published k ar and rb sr mineral ages indicate uplift and cooling of the charleston metamorphic group to less than 400 c by 110 90 m y this uplift occurred as a consequence of low angle normal faulting related to the late cretaceous breakup of gondwana and suggests that regional continental lithospheric extension was an important aspect of the cretaceous tectonic evolution of the region

continental crust under compression a seismic refraction study of south island geophysical transect i south island new zealand 1 the 1996 south island geophysical transect sight active source seismic survey was designed to show the style of lithospheric thickening due to late cenozoic oblique convergence across the australian pacific plate boundary in new zealand as part of this study two seismic refraction lines were shot across central south island and offshore extensions of the continental crust in the tasman sea and pacific ocean we present the data and a 603 km long seismic velocity profile of the crust and uppermost mantle along one of these seismic transects a tomographic inversion of 62 563 travel times from crustal and upper mantle refractions and wide angle reflections resulted in a model with a two layer crust upper crustal velocities were between 5 9 and 6 3 km s and lower crustal velocities were between 6 5 and 7 0 km s continental compression has locally reduced the seismic velocities in the pacific plate crust by 0 2 0 3 km s a possible effect of high strain and fluids in the crust the thickening of the crust from 28 km at the east coast of south island to 37 km beneath the southern alps can account for about 25 of the 80 110 km shortening of pacific plate crust while the rest must be accounted for by rapid erosion of mesozoic sedimentary rocks on the west side of the orogen in our model the lower crust forms a continuous 2 6 km thick layer beneath central south island the asymmetric topography of the southern alps is reflected in the crustal root which has a steeper flank at the west coast this observation is consistent with westward underthrusting of pacific lower lithosphere beneath south island that has been suggested in earlier studies

interactions between typhoon megi 2010 and a low frequency monsoon gyre abstractthe arw model is used to investigate the sharp northward turn of super typhoon megi 2010 after it moved westward and crossed the philippines the ncep analyzed fields during this period are separated into a slowly varying background flow component a 10 60 day low frequency component representing the monsoon gyre and a 10 day high pass filtered component representing megi and other synoptic scale motion it appears that the low frequency 10 60 day monsoon gyre interacted with megi and affected its track to investigate the effect of the low frequency mode on megi numerical experiments were designed in the control experiment the total fields of the analysis are retained in the initial and boundary conditions and the model is able to simulate megi s sharp northward turn in the second experiment the 10 60 day monsoon gyre mode is removed from the initial and lateral boundary fields and megi moves westward and slightly northwestward without turning north tracks of the relative positions b

lead isotopic compositions of south sandwich island volcanic rocks and their bearing on magmagenesis in intra oceanic island arcs pb isotope ratios have been measured in 12 volcanic rocks from the south sandwich islands the ranges are 206pb204pb 18 51 18 66 207pb204pb 15 55 15 64 208pb204pb 38 42 38 64 in 207pb204pb 206pb204pb and 208pb204pb 206pb204pb correlation diagrams the south sandwich data plot distinctly above the fields for ocean ridge basalts and yield trends showing apparent mixing with a sedimentary end member similar to south atlantic pelagic sediments as reported by chow and patterson 1962 and this study armstrong and cooper 1971 have likewise shown that volcanics from the lesser antilles show mixing trends with north atlantic sediments in pb isotope correlation diagrams the north atlantic sediments have distinctly higher 206pb204pb and 208pb204pb ratios compared to the south atlantic sediments the parallel relationships between sediments and volcanic island arc rocks of the north and south atlantic provide strong evidence for a component of pb from subducted sediments in the lavas of the west atlantic basin in contrast to these data lavas from the mariana arc in the western pacific show little or no component of pb from pelagic sediments the reason for the different behaviors in the two settings is speculative

sources and evolution of arc magmas inferred from coupled o and hf isotope systematics of plutonic zircons from the cretaceous separation point suite new zealand abstract coupled o and hf isotopic compositions of zircons from early cretaceous 113 124 ma granitoids of the separation point suite sps new zealand obtained by cathodoluminescence imaging guided micro beam methods sims la icpms are used as a record of evolving magma compositions in a prominent mesozoic arc system eight representative sps samples from individual plutons in the nelson and fiordland regions yield magmatic zircons with initial hf isotope ratios expressed in e hf ranging from 4 to 11 nelson and 5 to 12 fiordland respectively initial hf isotope ratios of zircons are extremely heterogeneous within individual samples with the vast majority of values distinctly less radiogenic than depleted mantle at 120 ma e hf 16 o isotope ratios are likewise variable with 18 o zircon smow values of 2 8 nelson and 0 7 fiordland the within rock variability in both zircon hf and o isotope ratios is testimony to open system processes that operated during magma evolution and zircon crystallisation average 18 o zircon for cores and rims allow constraints to be placed on the o isotopic composition of magmas from which zircon precipitated 18 o magma 4 8 elevated 18 o magma 6 5 require involvement of 18 o enriched supracrustal material weathered continental crust or low t seawater hydrothermally altered oceanic crust while 18 o magma 18 o depleted crustal component whole rock sr isotope nb ta and nd pb systematics are inconsistent with 18 o depleted slab melts 18 o 0 6 as a source component for sps magmas instead low 18 o values suggest incorporation of high t meteoric hydrothermally altered country rocks similar to those of the largs terrane presently exposed in northern fiordland in diagrams of sio 2 versus inferred 18 o magma the most primitive sps samples from the nelson and fiordland regions plot close to the expected composition for primitive arc magmas more evolved granitoids however show strongly divergent trends of o isotope composition as a function of sio 2 suggestive of assimilation coupled to fractional crystallisation afc in contrasting crustal environments emplacement level contamination by local crust is supported by age distributions of inherited zircons which indicate a predominance of palaeozoic and mesozoic zircons in nelson and fiordland granitoids respectively

the effects of vertical wind shear on the distribution of convection in tropical cyclones abstract the influence of vertical wind shear on the azimuthal distribution of cloud to ground lightning in tropical cyclones was examined using flash locations from the national lightning detection network the study covers 35 atlantic basin tropical cyclones from 1985 99 while they were over land and within 400 km of the coast over water a strong correlation was found between the azimuthal distribution of flashes and the direction of the vertical wind shear in the environment when the magnitude of the vertical shear exceeded 5 m s 1 more than 90 of flashes occurred downshear in both the storm core defined as the inner 100 km and the outer band region r 100 300 km a slight preference for downshear left occurred in the storm core and a strong preference for downshear right in the outer rainbands the results were valid both over land and water and for depression storm and hurricane stages it is argued that in convectively active tropical cyclones deep divergent circulations oppose the ver

tropical cyclone activity in the northwest pacific in relation to the el nino southern oscillation phenomenon abstract the interannual variations in tropical cyclone activity in the northwest pacific nwpac and their relationships with the el nino southern oscillation enso phenomenon were studied using the method of spectral analyses time series of a southern oscillation index soi defined as the sea level pressure difference between easter island and darwin and tropical cyclone activity in the entire nwpac ocean basin as well as in different regions of the nwpac were analyzed two spectral peaks are apparent in all these time series one corresponds to the generally accepted southern oscillation with a period of 3 to 3 5 years and another at the quasi biennial oscillation qbo frequency cross spectral analyses between the soi and tropical cyclone activity show significant coherence in these two spectral peaks the dominant peak is at the southern oscillation frequency with the soi leading typhoon activity by almost a year at the qbo frequency the two series are almost in phase cyclone activity in t

a global climatology of monsoon low pressure systems the first global climatology of monsoon low pressure systems is presented here based on the era interim reanalysis low pressure systems are classified into three intensity categories and particular focus is given to systems in the category corresponding to a traditional definition of monsoon depressions vortex tracks are identified using an automated algorithm applied to the distributions of 850 hpa relative vorticity sea level pressure and surface wind speed for 1979 2012 roughly two to three times as many monsoon low pressure systems form in the northern hemisphere as in the southern hemisphere during local summer the frequency of genesis typically peaks in local summer but low pressure systems form throughout the year in every monsoon region interannual variability is weak with standard deviations of summer counts typically being below 10 of the long term summer mean regional composites reveal that monsoon depressions in india the western pacific and northern australia share a common structure consisting of a warm over cold core and a top heavy column of potential vorticity that extends from the surface to the upper troposphere a separate class of monsoon low pressure systems develops over dry regions of west africa and western australia with a shallow composite structure having a warm core in the lower troposphere and cyclonic potential vorticity confined to a thin near surface layer low pressure systems in nearly all monsoon regions are estimated to account for a large fraction from about 40 to more than 80 of summer precipitation on the poleward edge of the climatological mean precipitation maxima

cluster analysis of typhoon tracks part ii large scale circulation and enso abstract a new probabilistic clustering method based on a regression mixture model is used to describe tropical cyclone tc propagation in the western north pacific wnp seven clusters were obtained and described in part i of this two part study in part ii the present paper the large scale patterns of atmospheric circulation and sea surface temperature associated with each of the clusters are investigated as well as associations with the phase of the el nino southern oscillation enso composite wind field maps over the wnp provide a physically consistent picture of each tc type and of its seasonality anomalous vorticity and outgoing longwave radiation indicate changes in the monsoon trough associated with different types of tc genesis and trajectory the steering winds at 500 hpa are more zonal in the straight moving clusters with larger meridional components in the recurving ones higher values of vertical wind shear in the midlatitudes also accompany the straight moving tracks compared to

sm nd and rb sr isotopic and geochemical systematics in phanerozoic granulites from fiordland southwest new zealand sm nd and rb sr isotopic analyses are reported for granulite facies orthogneisses from fiordland southwest new zealand whole rock samples define a rb sr isochron age of 120 15 ma and an initial 87sr 86sr ratio of 0 70391 4 nd values at 120 ma show a relatively wide range of from 0 4 to 2 7 indicating decoupling of sr nd isotope systems associated ultramafic rocks have initial 87sr 86sr ratios of from 0 70380 to 0 70430 and nd values of from 0 1 to 3 0 the different initial ratios suggest that the various intrusions although contemporaneous were not derived through fractionation of a single parent magma a metasedimentary enclave incorporated during emplacement of the granulitic rocks preserves a proterozoic isotopic signature with a measured nd 0 value of 10 2 87sr 86sr ratio of 0 73679 and a tnd provenance age of 1490 ma the rb sr whole rock age of the granulites is the same as obtained from recent u pb zircon dating mattinson et al 1986 and is interpreted as the time of magmatic emplacement and essentially contemporaneous granulite facies metamorphism rb sr and sm nd analyses of mineral systems indicate that the terrain had cooled below 300 c by 100 ma providing further evidence that high grade metamorphism was of exceptionally short duration

a subtropical cyclonic gyre associated with interactions of the mjo and the midlatitude jet abstractthis paper describes a large cyclonic gyre that lasted several days in the northwest pacific during july 1988 cyclonic winds at 850 hpa extended beyond the 2000 km radius with a radius of maximum winds of 700 800 km the gyre exhibited clear skies within and north of its center active convection extended 4000 km in longitude to its south the madden julian oscillation mjo was in its active phase in the indian ocean prior to gyre formation consistent with earlier studies diabatic heating in the mjo was associated with an anomalous upper tropospheric westerly jet over the northeast asian coast and a jet exit region over the northwest pacific repeated equatorward wave breaking events developed downwind of the jet exit region one such event left behind a region of lower tropospheric cyclonic vorticity and convection in the subtropics that played a key role in the gyre formation a second wave breaking event produced strong subsidence north of the mature gyre that contributed to its convective a

monsoonal interactions leading to sudden tropical cyclone track changes abstract sudden poleward track changes of tropical cyclones embedded in monsoon gyres in the western north pacific are documented during these track changes which are generally not well forecast the cyclones are often accompanied by a separate comma shaped area of gale force winds and deep convection along the eastern periphery this monsoon surge is distinct from the tropical cyclone synoptic analyses often reveal a building anticyclone to the east or southeast of the monsoon gyre the hypothesis that the sudden track change is initiated by a binary interaction of the tropical cyclone and monsoon gyre is tested with a nondivergent barotropic model tropical cyclone scale vortices with initial positions within the eastern semicircle of a larger monsoon gyre scale vortex initially coalesce with the monsoon gyre and then exhibit sudden poleward track changes that are similar to the observations during the coalescence phase the large and relatively weak monsoon gyre undergoes a induced dispersion in

contrasting18o enrichment and origins of high himalayan and transhimalayan intrusives abstract twelve analysed leucogranites of the high himalaya in bhutan chung la monlakarchung and garhwal badrinath are among the most 18 o enriched granites known 11 5 12 4 18 o smow with two exceptions and separate minerals show good isotopic concordance the data strongly support an origin of the granites by anatexis of continental basement such as the indian crystalline basement sheet or slab undercut by the main central thrust of which five samples were analysed in contrast the pre collision transhimalayan gangdese batholiths to the north of the indus tsangpo suture as exemplified by the ladakh intrusives show an initially oceanic trend of 18 o vs sio 2 that becomes gradually somewhat enriched with respect to hachijo jima while not completely outside the range of enrichment that seems possible by fractional crystallisation this could tie in with the 87 sr inhomogeneities reported by honegger et al 9 which may be due to assimilation of variably radiogenic eurasian continental basement for both the leucogranites and ladakh intrusives the 18 o levels and the concordance between minerals rule out significant cumulative water rock ratios in syn or post magmatic interaction with subsurface waters

development of synoptic scale disturbances over the summertime tropical northwest pacific abstract this study addresses the origin of the synoptic scale disturbances that occur in the tropical western north pacific ocean wp region in northern hemisphere summer these have been called easterly waves and tropical depression type td disturbances this analysis uses the national center for environmental prediction national center for atmospheric research reanalysis dataset by performing a regression analysis on several terms in the vorticity equation at 850 hpa it is shown that the td disturbances propagate approximately as barotropic rossby waves at 850 hpa given this ray tracing calculations and the wave activity diagnostic introduced by plumb are used to show that wave accumulation is a promising candidate for the initial development mechanism of the td disturbances the expected local growth rate from this mechanism is simply the convergence of the group velocity which reaches values corresponding to a growth timescale of 3 days this convergence is dominated by but somewhat lar

multigenetic gravity couple across a modern convergent margin inheritance from cretaceous asymmetric extension summary profiles of the pronounced gravity couple associated with the puysegur margin in new zealand suggest that the crust of the fiordland block which occupies the leading edge of the overriding pacific plate thins rapidly trenchwards and is domed upwards the crust beneath parts of central western fiordland appears to be anomalously thin 10 km and causes a major 180 mgal positive anomaly in the forearc region the density contrast caused by subduction of the australia plate to upper mantle depths contributes little to this positive bouguer anomaly the radical crustal thinning cannot have originated chiefly by differential uplift coupled with erosion in response to late cenozoic convergence as proposed earlier by others the amount of crustal thinning required is not consistent with the limited volume of sediment in surrounding basins moreover the timing of thinning is chiefly cretaceous not late cenozoic an alternative hypothesis of tectonic denudation is invoked that attributes the crustal structure of fiordland to cretaceous early tertiary asymmetric continental extension and consequent crustal thinning because the present crustal structure retains inherited geometry from cretaceous tectonism the observed positive gravity anomaly over fiordland is not due solely to the modern plate convergence but reflects the earlier extension and hence the gravity couple is multigenetic

mantle plume heads and the initiation of plate tectonic reorganizations we present results of numerical simulations which examine the plausibility of a reorganization of plate motions brought about by the interaction of a hot low viscosity plume head with the underside of a tectonic plate a numerical model of highly viscous fluid flow driven by thermal buoyancy is employed to examine the interaction of mantle plumes with surface plates in a two dimensional cartesian geometry plate like boundary conditions applied to the upper surface consist of a large active plate with fixed speed plus a smaller passive plate whose speed and direction of motion are permitted to react to tractions induced by the underlying mantle flow driven by the active plate the passive plate is also subject to applied end loads intended to simulate incipient subduction the mantle plume is initiated with a hot patch on the lower boundary and viscosity varies with temperature following an arrhenius rheology the calculations performed with fixed aspect ratio 4 1 and fixed rayleigh number ra 106 where ra refers to the strength of the starting plume were found to depend on three parameters the strength of the viscosity variation the size of the applied end load and the speed of the active plate these calculations indicate that plate motions can be sharply influenced by the lubricating effects of mantle plume heads even to the point of causing a reversal in the direction of plate motion

what percentage of western north pacific tropical cyclones form within the monsoon trough abstractit is frequently stated that 70 80 of western north pacific tropical cyclones form within the monsoon trough but without an objective definition of the term several definitions are tested here when the monsoon trough mt is defined as the contiguous region where long term 1988 2010 mean july november 850 hpa relative vorticity is positive 73 of all july november tropical cyclones form within the mt this percentage varies interannually however from as low as 50 to nearly 100 the percentage correlates with the nino 3 4 index with more storms forming within the mt during warm periods when the mt is defined instead using long term monthly mean 850 more than 80 of tropical cyclones form within the mt in all months except july and august when more than 30 of storms form poleward of the mt it is hypothesized that the known peak in the frequency of upper tropospheric midlatitude wave breaking in july and august is responsible it is argued that any long term mean provides a suita

the role of tropical waves in tropical cyclogenesis abstract this paper analyzes relationships between tropical wave activity and tropical cyclogenesis in all of the earth s major tropical cyclone basins twenty nine years of outgoing longwave radiation data and global reanalysis winds are filtered and analyzed to determine statistical relationships between wave activity in each basin and the corresponding cyclogenesis composite analyses relative to the storm genesis locations show the structures of the waves and their preferred phase relationships with genesis five wave types are examined in this study including mixed rossby gravity waves tropical depression type or easterly waves equatorial rossby waves kelvin waves and the madden julian oscillation the latter is not one of the classical tropical wave types but is a wavelike phenomenon known to have a strong impact on tropical cyclogenesis tropical cyclone formation is strongly related to enhanced activity in all of the wave filter bands except for the kelvin band in each basin the structure o