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

historical development of the gravity method in exploration the gravity method was the first geophysical technique to be used in oil and gas exploration despite being eclipsed by seismology it has continued to be an important and sometimes crucial constraint in a number of exploration areas in oil exploration the gravity method is particularly applicable in salt provinces overthrust and foothills belts underexplored basins and targets of interest that underlie high velocity zones the gravity method is used frequently in mining applications to map subsurface geology and to directly calculate ore reserves for some massive sulfide orebodies there is also a modest increase in the use of gravity techniques in specialized investigations for shallow targets gravimeters have undergone continuous improvement during the past 25 years particularly in their ability to function in a dynamic environment this and the advent of

the role of tropical atlantic sst anomalies in modulating western north pacific tropical cyclone genesis the connection between north tropical atlantic nta sea surface temperature sst anomalies and tropical cyclone tc genesis over the western north pacific wnp and associated physical mechanisms are investigated in this study we demonstrate a remarkable negative correlation of wnp tc genesis frequency with the preceding boreal spring nta sst anomalies our analysis suggests that major factors for tc genesis including distributions of large scale vorticity and midtropospheric humidity are rendered unfavorable by remote teleconnections while barotropic energy conversion from the large scale flow is suppressed as shown in recent studies the remote teleconnection from the atlantic is sustained and enhanced throughout the typhoon season through local air sea interactions these results suggest that boreal spring nta sst anomaly could be a new predictor for the seasonal wnp tc activity

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

decomposition of surface drifter observations in the atlantic ocean 1 surface drifter observations are decomposed into mean seasonal annual and semiannual and eddy components via gauss markov estimation this approach helps separate seasonal fluctuations and mean values in the observationally sparse tropical and south atlantic where monthly mean values cannot be calculated at the spatial scale of the major currents in some regions large differences are found between these means and those obtained by simple binned averaging the differences are attributed to inhomogeneous sampling of seasonal variability and to the inherent bias of lagrangian observations towards periods of low velocity the analysis reveals strong seasonal variations of some surface currents including a significant late spring reversal of the western north equatorial counter current

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

warming in the agulhas current system since the 1980 s 1 since the 1980 s the sea surface temperature of the agulhas current system has increased significantly the warming is due to an augmentation of its transport in response to an increase in wind stress curl in the south indian ocean at relevant latitudes this causes an increase in the fluxes of salt and heat into the atlantic ocean and in the transfer of energy from the ocean to the atmosphere therefore the changes we are witnessing in the region could have far reaching consequences on top of the regional impacts on ecosystem and climate the increase in wind stress curl is consistent with a poleward shift of westerly wind in the southern hemisphere reported by others

atlantic meridional overturning circulation and the southern hemisphere supergyre 1 the ocean s role in climate manifests itself through its high heat capacity its own rich internal dynamics and its ability to transport vast quantities of heat and freshwater of particular interest is the global ocean circulation associated with the atlantic meridional overturning amoc because observations are sparse the detailed global structure of the amoc remains poorly understood particularly the pathways along which water returns to the atlantic to compensate the export of north atlantic deep water nadw here we provide the first quantitative 3 dimensional global view of the amoc using a lagrangian reconstruction which integrates hundred of thousands water particle trajectories in an ocean model the resulting pattern elucidates the role of the wind in structuring the pathways of the amoc in particular the lagrangian analysis reveals a strong link with the three subtropical gyres of the southern hemisphere sh which merge into a supergyre spanning the three ocean basins the coupling between the upper ocean wind driven circulation and the overturning in the model suggests that changes in the sh winds can alter the pathways of the amoc and therefore the water properties and the associated heat and freshwater transports

advective time scales of agulhas leakage to the north atlantic in surface drifter observations and the 3d ofes model abstractthe advective transit time of temperature salinity anomalies from the agulhas region to the regions of deep convection in the north atlantic ocean is an important time scale in climate because it has been linked to variability in the atlantic meridional overturning circulation studying this transit time scale is difficult because most observational and high resolution model data are too short for assessment of the global circulation on decadal to centennial time scales here results are presented from a technique to obtain thousands of supertrajectories of any required length using a monte carlo simulation these supertrajectories allow analysis of the circulation patterns and time scales based on lagrangian data in this case observational surface drifter trajectories from the global drifter program and lagrangian data from the high resolution ogcm for the earth simulator ofes the observational supertrajectories can only be used to study the two dimensional 2d surface flow whereas th

the eastern tibetan plateau geothermal belt western china geology geophysics genesis and hydrothermal system abstract the eastern tibetan plateau geothermal belt etgb which is located in 98 102 e 28 32 n belongs to the eastern part of the mediterranean himalayan geothermal belt recently about 248 natural hot springs have been found in the etgb 60 of these springs have temperatures of 40 c and 11 springs have temperature above the local water boiling point using the helium isotopic data gravity magnetic and seismic data we analyzed the thermal structure and the relationship between hydrothermal activity and geothermal dynamics of the etgb results show that 1 the 248 springs can be divided into three geothermal fields kangding luhuo geothermal field kgf litang ganzi geothermal field lgf and batang xiangcheng geothermal field bgf the bgf and lgf have hot crust and warm mantle and are characterized by the higher heat flux 66 26 mw m2 and higher ratios of crust derived heat flux to total flux 47 46 60 62 the kgf has cool crust and hot mantle and is characterized by the higher heat flux and lower qc qm 2 there is a relatively 4 6 m higher gravimetric geoid anomaly dome which is corresponding with the etgb and in hydrothermal activity areas of the bgf and lgf there is a northwest southeast trending tensile stress area and the upper middle crust uplift area 3 an abnormal layer exists in the middle lower crust at a depth of 13 30 km beneath the etgb and this layer is 8 10 km thick and is characterized by lower velocity vp 2 5 high conductivity 10 m and high temperature 850 1000 c finally based on the heat source and geological and geophysical background we propose kangding type and batang type hydrothermal system models in the etgb

what caused the significant increase in atlantic ocean heat content since the mid 20th century as the upper layer of the world ocean warms gradually during the 20th century the inter ocean heat transport from the indian to atlantic basin should be enhanced and the atlantic ocean should therefore gain extra heat due to the increased upper ocean temperature of the inflow via the agulhas leakage consistent with this hypothesis instrumental records indicate that the atlantic ocean has warmed substantially more than any other ocean basin since the mid 20th century a surface forced global ocean ice coupled model is used to test this hypothesis and to find that the observed warming trend of the atlantic ocean since the 1950s is largely due to an increase in the inter ocean heat transport from the indian ocean further analysis reveals that the increased inter ocean heat transport is not only caused by the increased upper ocean temperature of the inflow but also and more strongly by the increased agulhas current leakage which is augmented by the strengthening of the wind stress curl over the south atlantic and indian subtropical gyre

three dimensional crustal structure in central taiwan from gravity inversion with a parallel genetic algorithm the genetic algorithm method is combined with the finite element method for the first time as an alternative method to invert gravity anomaly data for reconstructing the 3d density structure in the subsurface the method provides a global search in the model space for all acceptable models the computational efficiency is significantly improved by storing the coefficient matrix and using it in all forward calculations then by dividing the region of interest into many subregions and applying parallel processing to the subregions central taiwan a geologically complex region is used as an example to demonstrate the utility of the method a crustal block 120 150 km 2 in area and 34 km in thickness is represented by a finiteelement model of 76 500 cubic elements each 2 2 2 km 3 in size an initial density model is reconstructed from the regional 3d tomographic seismic velocity using an empirical relation between velocity and density the difference between the calculated and the observed gravity anomaly i e the residual anomaly shows an elongated minimum of large magnitude that extends along the axis of the taiwan mountain belt among the interpretive models tested the best model shows a crustal root extending to depths of 50 to 60 km beneath the axis of the western central and eastern central ranges with a density contrast of 400 or 500 kg m 3 across the moho both predictions appear to be supported by independent seismological and laboratory evidence

exploring typhoon variability over the mid to late holocene evidence of extreme coastal flooding from kamikoshiki japan sediment cores from two coastal lakes located on the island of kamikoshiki in southwestern japan lake namakoike and lake kaiike provide evidence for the response of a backbarrier beach system to episodic coastal inundation over the last 6400 years sub bottom seismic surveys exhibit acoustically laminated parallel to subparallel seismic reflectors intermittently truncated by erosional unconformities sediment cores collected from targeted depocenters in both lakes contain finely laminated organic mud interbedded with coarse grained units with depths of coarse deposits concurrent with prominent seismic reflectors the timing of the youngest deposit at kamikoshiki correlates to the most recently documented breach in the barrier during a typhoon in 1951 ad assuming that this modern deposit provides an analog for identifying past events paleo typhoons may be reconstructed from layers exhibiting an increase in grain size a break in fine scale stratigraphy and elevated sr concentrations

modelling of ground deformation and gravity fields using finite element method an application to etna volcano summary elastic finite element models are applied to investigate the effects of topography and medium heterogeneities on the surface deformation and the gravity field produced by volcanic pressure sources changes in the gravity field cannot be interpreted only in terms of gain of mass disregarding the ground deformation of the rocks surrounding the source contributions to gravity changes depend also on surface and subsurface mass redistribution driven by dilation of the volcanic source both ground deformation and gravity changes were firstly evaluated by solving a coupled axisymmetric problem to estimate the effects of topography and medium heterogeneities numerical results show significant discrepancies in the ground deformation and gravity field compared to those predicted by analytical solutions which disregard topography elastic heterogeneities and density subsurface structures with this in mind we reviewed the expected gravity changes accompanying the 1993 1997 inflation phase on mt etna by setting up a fully 3 d finite element model in which we used the real topography to include the geometry and seismic tomography to infer the crustal heterogeneities the inflation phase was clearly detected by different geodetic techniques edm gps sar and levelling data that showed a uniform expansion of the overall volcano edifice when the gravity data are integrated with ground deformation data and a coupled fem modelling was solved a mass intrusion could have occurred at depth to justify both ground deformation and gravity observations

interannual variation in the tropical cyclone formation over the western north pacific abstract the interannual variation in tropical cyclone genesis frequency over the western north pacific was examined for the active tropical cyclone including summer and fall during 1979 94 an emphasis was put on the possible effect of the interannual variation of atmospheric circulation and monsoon trough on tropical cyclone occurrence the major findings of this study are the following a distinct increase decrease of tropical cyclone genesis frequency occurs north of the climatological location of the monsoon trough in the philippine sea during summers june august with anomalous cold warm sea surface temperature sst over the nino3 region the interannual variation of tropical cyclone genesis in this region results from the appearance of an anomalous cyclonic anticyclonic cell situated in a summer teleconnection wave train emanating from the western tropical pacific and progressing along the rim of the north pacific in addition to the north south interannual variation there is also a long

anthropogenic impact on agulhas leakage recent work suggests that changes of the southern hemisphere sh winds led to an increase in agulhas leakage and a corresponding salinification of the atlantic climate model projections for the 21st century predict a progressive southward migration and intensification of the sh westerlies the potential effects on the ocean circulation of such an anthropogenic trend in wind stress are studied here with a high resolution ocean model forced by a step function change in sh wind stress that involves a 7 increase in westerlies strength and a 2 shift in the zero wind stress curl the model simulation suggests a rapid dynamic adjustment of agulhas leakage by 4 5 sv about a third of its original value after a few years the change in leakage is reflected in a concomitant change in the transport of the south atlantic subtropical gyre but leads only to a small increase in the atlantic meridional overturning circulation amoc of o 1 sv after three decades a main effect of the increasing inflow of indian ocean waters with potential long term ramifications for the amoc is the salinification and densification of upper thermocline waters in the south atlantic which extends into the north atlantic within the first three decades

3 d constrained inversion of gravimetric data to map the tectonic terranes of southeastern laurentia using simulated annealing abstract inversion of gravity anomaly data can be an effective tool in reconstructing the geologic history of a region by segregating tectonic terranes with different physical properties recent advances in computational capabilities coupled with lithospheric scale seismic experiments provide the opportunity to conduct 3d regional scale constrained inversions of gravity data using global optimization algorithms here a method for inverting gravity anomaly data by combining a finite element method based forward calculation with a simulated annealing algorithm is introduced the method is applied to the southeastern laurentia region which is comprised of an amalgamation of crustal blocks spanning a tectonic history of over 1 5 ga the method better defines the gross crustal density distribution of the region and proves to be efficient in spatially discriminating between the different tectonic terranes the tectonic terranes fall within four distinct groups based on the average crustal density each of which seem to have undergone a distinct geologic history

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

salt exchange in the indian atlantic ocean gateway since the last glacial maximum a compensating effect between agulhas current changes and salinity variations the import of relatively salty water masses from the indian ocean to the atlantic is considered to be important for the operational mode of the atlantic meridional overturning circulation amoc however the occurrence and the origin of changes in this import behavior on millennial and glacial interglacial timescales remains equivocal here we reconstruct multiproxy paleosalinity changes in the agulhas current since the last glacial maximum and compare the salinity pattern with records from the indian atlantic ocean gateway i aog and model simulations using a fully coupled atmosphere ocean general circulation model the reconstructed paleosalinity pattern in the agulhas current displays coherent variability with changes recorded in the wider i aog region over the last glacial termination we infer that salinities simultaneously increased in both areas consistent with a quasi interhemispheric salt seesaw response analogous to the thermal bipolar seesaw in response to a reduced cross hemispheric heat and salt exchange during times of weakened amoc interestingly these hydrographic shifts can also be recognized in the wider southern hemisphere which indicates that salinity anomalies are not purely restricted to the agulhas current system itself more saline upstream agulhas waters were propagated to the i aog during heinrich stadial 1 hs1 however the salt flux into the south atlantic might have been reduced due to a decreased volume transport through the i aog during the amoc slowdown associated with hs1 hence our combined data model interpretation suggests that intervals with higher salinity in the agulhas current source region are not necessarily an indicator for an increased salt import via the i aog into the south atlantic

latitudinal dependence of atlantic meridional overturning circulation amoc variations 1 amoc variations are often thought to propagate with the kelvin wave speed resulting in a short time lead between high and low latitudes amoc variations however as shown in this paper using a coupled climate model gfdl cm2 1 with the existence of interior pathways of north atlantic deep water nadw from flemish cap to cape hatteras as that observed recently amoc variations estimated in density space propagate with the advection speed in this region resulting in a much longer time lead several years between subpolar and subtropical amoc variations and providing a more useful predictability the results suggest that amoc variations have significant meridional coherence in density space and monitoring amoc variations in density space at higher latitudes might reveal a stronger signal with a several year time lead

observed and modeled global ocean turbulence regimes as deduced from surface trajectory data a large scale tool for systematic analyses of the dispersal and turbulent properties of ocean currents and the subsequent separation of dynamical regimes according to the prevailing trajectories taxonomy in a certain area was proposed by rupolo in the present study this methodology has been extended to the analysis of model trajectories obtained by analytical computations of the particle advection equation using the lagrangian open source software package tracing the water masses of the north atlantic and the mediterranean tracmass and intercomparisons have been made between the surface velocity fields from three different configurations of the global nucleus for european modelling of the ocean nemo ocean sea ice general circulation model lagrangian time scales of the observed and synthetic trajectory datasets have been calculated by means of inverse lagrangian stochastic modeling and the influence of the model field spatial and temporal resolution on the analyses has been investigated in global scale ocean modeling compromises are frequently made in terms of grid resolution and time averaging of the output fields because high resolution data require considerable amounts of storage space here the implications of such approximations on the modeled velocity fields and consequently on the particle dispersion have been assessed through validation against observed drifter tracks this study aims moreover to shed some light on the relatively unknown turbulent properties of near surface ocean dynamics and their representation in numerical models globally and in a number of key regions these results could be of interest for other studies within the field of turbulent eddy diffusion parameterization in ocean models or ocean circulation studies involving long term coarse grid model experiments

taiwan orogeny thin skinned or lithospheric collision abstract the taiwan orogeny is young and presently very active it provides an excellent environment for studying ongoing orogenic processes especially since the region is monitored intensively with dense seismological and geodetic networks and new studies aiming at deciphering shallow and deep structures in and around taiwan have been recently conducted or are being planned the available data can be used continually to test critically hypotheses of the taiwan orogeny hypotheses dealing with the mechanics of mountain building are basic to the understanding of taiwan orogeny and are particularly amenable to testing the widely cited thin skinned tectonics hypothesis was formulated to explain mainly the geologic and relatively shallow

salinity changes along the upper limb of the atlantic thermohaline circulation lagrangian analyses of a global ocean circulation model quantify the salinity changes experienced by the warm limb of the thermohaline circulation during the northward flow to the atlantic deep convection regions 6 sv out of the estimated 10 sv transfer from 45 s to 47 n flow through regions of prevailing surface evaporation the southern and northern formation regions of salinity maximum water and the gulf of cadiz mediterranean sea domain the remaining transport gains salinity through mixing with adjacent waters as much as 6 sv flow through the low salinity surface mixed layer at the latitudes of the itcz whose effect annihilates that of the southern region of salinity maximum water most of the salinity increase corresponds to the transformation of south to north atlantic central water with strong diapycnal transfers for the water that intersects the high and low salinity regions and nearly isopycnal modifications for the water that avoids these regions

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

the relationship between the southern oscillation index and tropical cyclone tracks in the eastern north pacific points of origin and downgradation of tropical cyclones in the eastern north pacific enp east of 160 w are related to the southern oscillation index soi during the hurricane season all enp tropical storms and hurricanes from 1966 through 1997 were grouped into three soi based categories those occurring during strong el nino events mean soi 0 6 or near zero periods 0 6 mean soi 0 6 during el nino storm seasons enp tropical cyclones originated approximately 5 7 617 km west and downgraded 7 5 780 km west of the long term mean longitudes for the positive soi group near zero group storms also followed more northerly tracks than the negative soi group storms however no significant differences in storm track are evident between the positive soi and near zero groups and the track length is not significantly different for any storm group

hybrid optimization for lithologic inversion and time lapse monitoring using a binary formulation we have developed a hybrid optimization algorithm for binary inversion of geophysical data associated with lithologic inversion and time lapse monitoring the binary condition is designed to invert geophysical data for well defined physical properties within discrete lithologic units such as a salt body within a sedimentary host or temporal changes in physical property associated with dynamic processes such as the density and conductivity change in an oil and gas reservoir or groundwater aquifer the solution of such inverse problems with discrete model values requires specialized optimization algorithms to meet this need we develop a hybrid optimization algorithm by combining a genetic algorithm with quenched simulated annealing the former allows for easy incorporation of prior geologic information and rapid buildup of large scale model features whereas the latter guides genetic algorithm to faster evolution by rapidly adjusting the finer model features in examining the performance of the hybrid

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

southern ocean origin for the resumption of atlantic thermohaline circulation during deglaciation during the two most recent deglaciations the southern hemisphere warmed before greenland at the same time the northern atlantic ocean was exposed to meltwater discharge which is generally assumed to reduce the formation of north atlantic deep water yet during deglaciation the atlantic thermohaline circulation became more vigorous in the transition from a weak glacial to a strong interglacial mode here we use a three dimensional ocean circulation model to investigate the impact of southern ocean warming and the associated sea ice retreat on the atlantic thermohaline circulation we find that a gradual warming in the southern ocean during deglaciation induces an abrupt resumption of the interglacial mode of the thermohaline circulation triggered by increased mass transport into the atlantic ocean via the warm indian ocean and cold pacific ocean water route this effect prevails over the influence of meltwater discharge which would oppose a strengthening of the thermohaline circulation a southern ocean trigger for the transition into an interglacial mode of circulation provides a consistent picture of southern and northern hemispheric climate change at times of deglaciation in agreement with the available proxy records

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

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

combining altimeter and subsurface float data to estimate the time averaged circulation in the upper ocean 1 a new technique is presented for estimating time averaged upper ocean geostrophic velocity from a combination of altimeter data and subsurface float data the technique makes uses of the strong relationship between sea surface height anomaly and anomalous velocity at depth to reduce mesoscale eddy variability in subsurface float displacements the technique is demonstrated on a region in the north atlantic that was well sampled by argo floats the 2004 through 2006 time averaged density field was estimated from the surface to 2000 db by combining altimeter and hydrographic data from the floats in addition a reference velocity field was estimated at 1000 db based on a combination of altimeter data and subsurface float displacements the reference velocity field was combined with geostrophic shear based on the density field to produce a three dimensional estimate of geostrophic velocity from the surface to 2000 db the gulf stream transport in the upper 2000 db is estimated to be 76 sv at 73 w in addition an estimate of the 3 year average dynamic height at the surface was computed by combining the 1000 db reference dynamic height and the time averaged density field

eddy diffusivity estimates from lagrangian trajectories simulated with ocean models and surface drifter data a case study for the greater agulhas system the lagrangian analysis of sets of particles advected with the flow fields of ocean models is used to study connectivity that is exchange pathways time scales and volume transports between distinct oceanic regions one important factor influencing the dispersion of fluid particles and hence connectivity is the lagrangian eddy diffusivity which quantifies the influence of turbulent processes on the rate of particle dispersal because of spatial and temporal discretization turbulence is not fully resolved in modeled velocities and the concept of eddy diffusivity is used to parameterize the impact of unresolved processes however the relations between observation and model based lagrangian eddy diffusivity estimates as well as eddy parameterizations are not clear this study presents an analysis of the spatially variable near surface lateral eddy diffusivity estimates obtained from lagrangian trajectories simulated with 5 day mean velocities from an eddy resolving ocean model inalt01 for the agulhas system inalt01 features diffusive regimes for dynamically different regions some of which exhibit strong suppression of eddy mixing by mean flow and it is consistent with the pattern and magnitude of drifter based eddy diffusivity estimates using monthly mean velocities decreases the estimated diffusivities less than eddy kinetic energy supporting the idea that large and persistent eddy features dominate eddy diffusivities for a noneddying ocean model orca05 lagrangian eddy diffusivities are greatly reduced particularly when the gent and mcwilliams parameterization of mesoscale eddies is employed

attribution of decadal variability in tropical cyclone passage frequency over the western north pacific a new approach emphasizing the genesis location of cyclones abstractvariability in tropical cyclone tc activity is a matter of direct concern for affected populations on interannual and longer time scales variability in tc passage frequency can be associated with total tc frequency over the concerned ocean basin basinwide frequency bf the spatial distribution of tc genesis in the basin genesis distribution gd and the preferable track pt that can be considered as a function of genesis locations to facilitate investigation of mechanisms responsible for the variability the authors propose an approach of decomposing anomalies in the passage frequency into contributions of variability in bf gd and pt which is named the integration of statistics on tc activity by genesis location istagl analysis application of this approach to tc best track data in the western north pacific wnp basin reveals that overall distribution of the passage frequency trends over the 1961 2010 period is mainly due to the pt trends on decadal time scales passage frequen

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

the abrupt shift of typhoon activity in the vicinity of taiwan and its association with western north pacific east asian climate change bayesian analysis is applied to detect changepoints in the time series of seasonal typhoon counts in the vicinity of taiwan an abrupt shift in the typhoon count series occurs in 2000 on average 3 3 typhoons per year have been noted before 2000 1970 99 with the rate increasing to 5 7 typhoons per year since 2000 2000 06 this abrupt change is consistent with a northward shift of the typhoon track over the western north pacific east asian region and an increase of typhoon frequency over the taiwan east china sea region the northward shift of the typhoon track tends to be associated with typhoon enhancing environmental conditions over the western north pacific namely the weakening of the western north pacific subtropical high the strengthening of the asian summer monsoon trough and the enhanced positive vorticity anomalies in the lower troposphere based on observational analysis and model simulations warm sea surface temperature anomalies over the equatorial western and central pacific appear to be a major factor contributing to a northward shifted typhoon track

contractional transcurrent rotational and extensional tectonics examples from northern taiwan abstract contraction transcurrent faulting block rotation and even extension are four essential tectonic mechanisms involved in the progressive deformation of arcuate collision belts the neotectonic evolution of the taiwan mountain belt is mainly controlled by the oblique convergence between the eurasian plate and the philippine sea plate as well as the corner shape of the plate boundary based on field observations and tectonic analysis and taking geophysical data and experimental modelling into account we interpret the curved belt of northern taiwan in terms of contractional deformation with compression thrust sheet stacking folding and transcurrent faulting combined with increasing block rotation bookshelf type strike slip faulting and extension as a consequence the formation of the extensional taipei basin the division of conjugate strike slip faulted domains and the variable nature and distribution of paleostresses should not be interpreted in terms of distinct plio quaternary episodes but should reflect a single albeit complicated regional pattern of deformation our study demonstrates that in taiwan contractional extensional and transcurrent tectonics as well as rotations combine together and interact within a single complex framework the crescent shaped mountain belt develops in response to oblique indentation by an asymmetric wedge indenter the distribution nature and relative importance of these deformation modes are a function of the shape of the indenter and the average direction of convergence

advective timescales and pathways of agulhas leakage current research indicates an increase in agulhas leakage for the past and coming decades this change potentially alters the strength of the atlantic meridional overturning circulation in particular through advection of positive density anomalies into the north atlantic to explore the fate of agulhas leakage results from a lagrangian analysis were evaluated with virtual floats advected within an eddy permitting ocean model orca025 a considerable fraction of agulhas leakage reached the subtropical north atlantic of a mean agulhas leakage transport of 15 3 sv entering the south atlantic 9 7 7 7 and 6 1 sv crossed sections at 6 degrees s 6 degrees n and 26 degrees n respectively the most probable transit time of leakage to reach the respective latitudes is one to two decades we suggest that changes in agulhas leakage could manifest in the gulf stream regime most probably within two decades these results were supported by an eddy resolving implementation of the ocean model inalt01

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

global teleconnections of meridional overturning circulation anomalies there is a wide range of evidence from both models and palaeoclimatic data that indicates the possibility of abrupt changes in the oceanic meridional overturning circulation moc however much of our dynamical understanding of the moc comes from steady state models that rely upon the assumption of thermodynamic equilibrium and are therefore only valid on millennial time scales here a dynamical model for the global teleconnections of moc anomalies on annual to multidecadal time scales is developed it is based on a linear theory for the propagation of zonally integrated meridional transport anomalies in a reduced gravity ocean and allows for multiple ocean basins connected by a circumpolar channel to the south the theory demonstrates that the equator acts as a low pass filter to moc anomalies as a consequence moc anomalies on decadal and shorter time scales are confined to the hemispheric basin in which they are generated and have little impact on the remainder of the global ocean the linear theory is compared with the results of a global nonlinear numerical integration which it reproduces to a good approximation

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

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

from space to lithosphere inversion of the goce gravity gradients supply to the earth s interior study the emergence of high resolution satellite measurements of the gravitational field goce mission offers promising perspectives for the study of the earth s interior these new data call for the development of innovant analysis and interpretation methods here we combine a forward prism computation with a bayesian resolution approach to invert for these gravity gradient data configuration we apply and test our new method on satellite data configuration i e 225 km height with a global and homogeneous geographic distribution we first quantify the resolution of our method according to both data and parameteriza tion characteristics it appears that for reasonable density contrast values 0 1 g cm 3 crustal structures have to be wider than 28 km to be detectable in the goce signal deeper bodies are distinguishable for greater size 35 km size at 50 km depth 80 km at 300 km depth we invert the six tensor components among which five are independent by carefully testing each of them and their different combinations we enlighten a trade off between the recovery of data and the sensitivity to inversion parameters we particularly discussed this characteristic in terms of geometry of the synthetic model tested 2 plasman et al structures orientation 3 d geometry etc in terms of rms value each component is always better explained if inverted solely but the result is strongly affected by the inversion parameterization smoothing variances etc on the contrary the simultaneous inversion of several components displays a significant improvement for the global ten sor recovery more dependent on data than on density variance or on smoothness control comparing gravity and gradient inversions we highlight the superiority of the gg data to better reproduce the structures especially in terms of vertical location we succesfully test our method on a realistic case of a complex subduction case for both gradient and gravity data while the imaging of small crustal structures requires terrestrial gravity dataset the longest wavelength of the slab is well recovered with both data sets the precision and homogeneous coverage of goce data however counterbalance the heterogeneous and often quite nonexistance coverage of terrestrial gravity data this is particularly true in large areas which requires a coherent assemblage of heterogeneous data sets or in high relief vegetally covered and offshore zones

modulation of western north pacific tropical cyclone activity by the atlantic meridional mode this study examines the year to year modulation of the western north pacific wnp tropical cyclones tc activity by the atlantic meridional mode amm using both observations and the geophysical fluid dynamics laboratory forecast oriented low ocean resolution version of cm2 5 flor global coupled model 1 the positive negative amm phase suppresses enhances wnp tc activity in observations the anomalous occurrence of wnp tcs results mainly from changes in tc genesis in the southeastern part of the wnp 2 the observed responses of wnp tc activity to the amm are connected to the anomalous zonal vertical wind shear zvws caused by amm induced changes to the walker circulation during the positive amm phase the warming in the north atlantic induces strong descending flow in the tropical eastern and central pacific which intensifies the walker cell in the wnp the intensified walker cell is responsible for the suppressed enhanced tc genesis in the eastern western part of the wnp by strengthening weakening zvws 3 the observed wnptc amm linkage is examined by the long term control and idealized perturbations experiment with flor fa a suite of sensitivity experiments strongly corroborate the observed wnptc amm linkage and underlying physical mechanisms

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

plate collision and paleostress trajectories in a fold thrust belt the foothills of taiwan abstract field analyses of compressional faulting and folding in the foothills of western taiwan enable us to reconstruct paleostress trajectories over a large area and to establish the relative chronology of tectonic events two main compressional events have contributed to the present structure of the fold thrust belt stratigraphic data show that these events are plio pliocene in age older normal faulting indicates nnw sse extension across the chinesse passive continental margin during the neogene the two main compressional events of the taiwan collision correspond to similar fan shaped distributions of maximum compressive stress trajectories with a counterclockwise shift of 30 50 between the two events using the relationship between recent stress trajectories and the direction of recent plate motion as a guide we reconstruct the direction of plate convergence for the older event we suspect that the relative motion philippine sea plate eurasia has rotated counterclockwise of at least 35 45 in taiwan during collision this conclusion is in agreement with independent plate tectonic reconstructions several problems provide objectives to further tectonic and paleomagnetic studies including the duration and diachronism of compressional events as well as possible clockwise rotation of northernmost taiwan

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

3d gravity inversion through an adaptive learning procedure we have developed a gravity inversion method to estimate a 3d density contrast distribution producing strongly interfering gravity anomalies the interpretation model consists of a grid of 3d vertical juxtaposed prisms in the horizontal and vertical directions iteratively our approach estimates the 3d density contrast distribution that fits the observed anomaly within the measurement errors and favors compact gravity sources closest to prespecified geometric elements such as axes and points this method retrieves the geometry of multiple gravity sources whose density contrasts positive and negative values are prescribed by the interpreter through the geometric element at the first iteration we set an initial interpretation model and specify the first guess geometric elements and their target density contrasts each geometric element operates as the first guess skeletal outline of the entire homogeneous gravity source or any of its homogeneous parts to be reconstructed from the second iteration on our method automatically redefines a new set of geometric elements the associated target density contrasts and a new interpretation model whose number of prisms increases with the iteration the iteration stops when the geometries of the estimated sources are invariant along successive iterations tests on synthetic data from geometrically complex bodies and on field data collected over a mafic ultramafic body and a volcanogenic sedimentary sequence located in the tocantins province brazil confirmed the potential of our method in producing a sharp image of multiple and adjacent bodies

moho depth variations in the taiwan orogen from joint inversion of seismic arrival time and bouguer gravity data abstract the joint inversion of different geophysical datasets is an effective means to reduce the non uniqueness and improve the reliability of geophysical inversion in this study seismic arrival time and bouguer gravity datasets are jointly inverted to obtain an image of 3 d velocity structures in the taiwan orogen the model obtained from joint inversion fits the arrival time observations at least as well as when inverted individually and the gravity observations are much better fit when included in the inversion implying a reduction in ambiguity by simultaneously modeling the disparate datasets moho depth variations estimated by the 3 d p wave velocity model suggest a maximum moho depth of 56 km located beneath the backbone central range and the trend of the moho is largely consistent with the topography of the central range with eastward asymmetric crustal thickening the root beneath the central range appears to be smaller in lateral extent than previously imaged and the velocity gradients into the uppermost mantle are significantly higher the lack of evidence for a significant amount of eurasian crust in the mantle supports geodynamical models of accreted rather than consumed continental crust in a collisional environment

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

tomographic imaging of lithospheric structures under taiwan abstract tomographic images of the crustal and mantle velocity structures under taiwan are obtained by simultaneous inversion of local earthquake p wave arrival times for hypocenters and p wave velocity structures in northern taiwan a high velocity zone coinciding with the wadati benioff zone can readily be identified as the subducted philippine sea plate the imaged zone dips toward the north at an angle of 40 from a depth range of 20 55 to 100 130 km an upper mantle low velocity wedge ranging from 40 to 80 km in depth exists above the subducted slab above this wedge is the ilan plain of northern taiwan which lies at the west end of the okinawa trough a well recognized back arc basin the crustal velocities under the plain are also relatively low the well defined high velocity zone and the low velocity wedge provide some constraints on the thermal structures of the subduction system under northern taiwan in tomographic images across the central section of taiwan thickening of the crust and up arching of the lower crustal materials under the central range are commonly observed the crust under the western foothills region is clearly thinner and the near surface low velocity layers are well developed the structures under the central range show that although the taiwan orogeny is quite young a root deeper in the north and shallowing to the south has formed the results of our tomography show that a significant portion of the lithosphere is involved in the taiwan orogeny