a polar low embedded in a blocking high over the pacific arctic a polar low pl is a short lived phenomenon involving strong winds that occurs over polar oceans in october 2009 the r v mirai encountered a pl with a 600 km wide comma shaped cloud that developed over the chukchi sea a shipboard doppler radar and radiosondes were used to understand the fine structure of this pl analyses of low level winds and the thermodynamic structure indicated that the development of the pl was decoupled from sea surface thermal forcing the pl was likely triggered by an intrusion of a potential vorticity pv anomaly at the tropopause a southerly warm advection associated with a blocking high over alaska resulted in rapid development of the pl in front of the cold dome induced by the upper level pv anomaly the westerly winds after passage of the pl seemed to modify the upper ocean structure dramatically

present day crustal deformation characteristics of the southeastern tibetan plateau and surrounding areas by using gps analysis abstract the southeastern tibetan plateau and surrounding areas comprise a typical tectonic belt in mainland china characterized by a complex geological background and intense tectonic activity we study present day crustal deformation characteristics of this region based on gps data for the periods 1999 2007 and 2009 2011 we first analyze the variations in crustal motion and strain rate and then discuss the 3d crustal motion and local sub block activities as well as the correlation between the intensity of crustal activity and the strain rate distribution finally we explain the present day geodynamic characteristics of the region our results indicate that the entire region shows overall clockwise motion with respect to the stable eurasian plate the tectonic boundary belts between this region and the south china block display significant compressional strain accompanied by associated extensional strain relatively high maximum shear strain and the transition zones of the significant plane strain gradients are also mainly concentrated along the ganzi yushu xianshuihe anninghe zemuhe xiaojiang lijiang xiaojinhe and red river faults as well as the western and southern yunnan province 3d crustal velocities further reflect significant differences in tectonic activity between different structural belts we conclude that the regions showing higher shear strain and the transition zones of the significant plane strain gradients correspond to the areas with frequent earthquakes according to the crustal deformation and strain characteristics we infer that the present day geodynamic setting of the region is related to the ongoing india eurasia collision and the associated resistance of the stable alashan ordos and south china blocks resulting in the extrusion of the southeastern tibetan plateau crustal material with an overall clockwise flow around the eastern himalayas and significant compressional strain along the tectonic boundary belts furthermore notable compressional strain and enhanced sub block motions occurred around the longmenshan fault area following the wenchuan earthquake

frontogenesis and the development of secondary wave cyclones in fastex two major mechanisms of frontogenesis deformation and shear are important in frontal wave cyclone development horizontal deformation can suppress the nonlinear wave development using an analytic model bishop and thorpe have shown that large strain rates inhibit any wave slope amplification for real cases this ambient strain can be measured using the vorticity divergence attribution method developed by bishop this technique permits us to confirm the crucial role of such strain on the evolution of cases of wave development during the fronts and atlantic storm track experiment fastex horizontal shear in the presence of an along front thermal gradient is also an important mechanism of frontogenesis using an eady model joly and thorpe have shown that in cases of large along front thermal gradient frontal waves have growth rates smaller than the front itself and thus would not develop the domain independent attribution method developed by bishop is here extended to a geopotential field partition this leads via a nonlinear balance condition to the estimation of the ambient along front potential temperature gradient the role of such an along front potential temperature gradient is discussed as well as the relative contributions of the two frontogenesis mechanisms for the fastex cases

objective classification of extratropical cyclogenesis extratropical cyclones experience vastly different genesis conditions at the first point of their tracks a novel method is introduced to characterize this variability and classify genesis events by computing 30 diagnostic variables that describe the synoptic scale environment of 16029 genesis events in the northern hemisphere extratropics using era interim reanalyses from 2000 2011 these variables are referred to as precursors and include parameters characterizing upper level forcing low level baroclinicity thermodynamic stability surface fluxes and moist processes the genesis events spread over a large portion of the 30 dimensional precursor phase space and no obvious clusters occur which highlights the high variability of cyclogenesis processes and indicates that they form in a continuum rather than a few distinct categories a projection of the genesis events to the first two principle components pc of the precursor phase space allows reducing the dimensionality and introducing a meaningful segmentation of the genesis events in five classes the first two pcs are characterized by upper level forcing e g the amplitude of the upper level potential vorticity pv anomaly and low tropospheric diabatic processes e g precipitation and diabatically produced low level pv respectively the first of the five identified classes constitutes the center of the pc1 pc2 phase space and represents average conditions composites reveal that the four classes of events characterized by large positive or negative scores of pc1 and pc2 occur in distinct and strongly differing flow regimes characterized by the strength of the upper level forcing the structure of the upper level jet and the amplitude of low level moist processes and baroclinicity the four classes also have clearly differing geographical distributions many well known cyclogenesis events fall within classes characterized by strong low level moist processes with or without strong upper level forcing also discussed are the robustness of the method and the linkage to classical concepts of cyclone classifications

experimental study and active tectonics on the zhangjiakou penglai fault zone across north china abstract the zhangjiakou penglai fault zone zpfz as a large scale wnw trending active fault zone with frequent seismic activity is an area prone to moderate to intense earthquakes across north china a detailed analysis of the zpfz has been carried out based on earthquake activity deep structural response dynamic mechanism and physical simulation by conducting an en echelon fault model experiment the results show that the zpfz is a lithospheric active fault zone that has controlled some small en echelon quaternary pull apart basins and has triggered many earthquakes as seismogenic structures the earthquake location and intensity distribution by the experimental simulation fit well with those of actual earthquakes the earthquake distribution is controlled obviously by the en echelon structural properties the intensity of seismic activity is strong in the middle and weak at the western and eastern ends of the fault zone migrating from the southeast to the northwest along the entire fault zone this wnw trending fault zone in north china is closely related to the surrounding plate activities the zpfz is not only dominated by the collision of the indian plate to the eurasian plate but is also influenced by the subduction of the pacific plate it depends on the comprehensive reflection of two geodynamic settings from the western collision of the indian to the eurasian plates and the eastern subduction of the pacific ocean plate to the eurasian plate

lithosphere structure and thickness beneath the north china craton from joint inversion of ambient noise and surface wave tomography 1 we imaged detailed 3 d crustal and uppermost mantle seismic structures in the north china craton from inversion of rayleigh wave phase velocity at periods of 6 to 143 s the phase velocities were obtained from a combination of ambient noise and teleseismic surface wave tomography and then the phase velocities were inverted to s wave velocities the results show that both the huabei basin and ordos block have markedly rapid variations in both crustal velocities and the moho depth huabei basin has a thin 31 34 km crust with low velocities while ordos block has a thick 40 km crust with high velocities we also estimated the lithospheric thickness from the inverted s wave velocities using a simple s wave velocity temperature relationship huabei basin was imaged as a low s wave velocity anomaly in the uppermost mantle with very thin lithosphere 65 km while ordos block was revealed as a high s wave velocity anomaly with rather thick lithosphere 120 km these results indicated that huabei basin and ordos block have different thermal and or chemical properties and had experienced different mantle processes and evolution histories since the cenozoic furthermore slow s wave velocities and very thin lithosphere 65 km were also found beneath hetao and weihe rifts bounding ordos block at north and south respectively however shanxi rift the boundary between huabei basin and ordos block had a much thicker and higher velocity lithosphere than hetao and weihe rifts

case studies of high wind events in barrow alaska climatological context and development processes the beaufort chukchi cyclones of october 1963 and august 2000 produced the highest winds ever recorded in barrow alaska in both cases winds of 25 m s21 were observed with gusts unofficially reported at 33 m s 21 the october 1963 storm caused significant flooding contaminated drinking water and interrupted power supplies the august 2000 storm caused the wreck of a 6 million dredge and removed roofs from 40 buildings both storms were unusual in that they tracked eastward from the east siberian sea into the chukchi and beaufort seas rather than following a more typical northward track into the arctic ocean this paper addresses through modeling and analysis the development processes of these two storms the october 1963 system was a long lived warm core zonally elongated cyclone that traversed around the arctic basin through the canadian archipelago the august 2000 system was an open wave cyclone that dissipated rapidly into a weak cold core eddy in the alaskan sector of the beaufort sea approximating the contributions to development using terms in a quasigeostrophic omega equation it was found that both storms were characterized by the increasing importance of the convergence of the q vector representing differential vorticity advection and thermal advection in the midtroposphere at the expense of forcing by the turbulent fluxes of heat moisture and momentum in the boundary layer however the influence of surface turbulent fluxes in the early stages of development was important particularly for the august 2000 cyclone which passed over an extensive coastal lead in the east siberian sea this study concludes that the observed retreat in western arctic ice cover is unlikely to be an important contributor to increasing cyclonic activity in the region but that ice retreat north of eurasia could have an impact

contemporary crustal deformation around the southeast borderland of the tibetan plateau 1 we derive a detailed horizontal velocity field for the southeast borderland of the tibetan plateau using gps data collected from the crustal motion observation network of china between 1998 and 2004 our results reveal a complex deformation field that indicates that the crust is fragmented into tectonic blocks of various sizes separated by strike slip and transtensional faults most notably the regional deformation includes 10 11 mm yr left slip across the xianshuihe fault 7 mm yr left slip across the anninghe zemuhe xiaojiang fault zone 2 mm yr right slip across a shear zone trending northwest near the southern segment of the lancang river fault and 3 mm yr left slip across the lijiang fault deformation along the southern segment of the red river fault appears not significant at present time the region south and west of the xianshuihexiaojiang fault system whose eastward motion is resisted by the stable south china block to the east turns from eastward to southward motion with respect to south china resulting in clockwise rotation of its internal subblocks active deformation is detected across two previously unknown deformation zones one is located 150 km northwest of and in parallel with the longmenshan fault with 4 6 mm yr right slip and another is continued south southwestward from the xiaojiang fault abutting the red river fault with 7 mm yr left slip while both of these zones are seismically active the exact locations of faults responsible for such deformation are yet to be mapped by field geology comparing our gps results with predictions of various models proposed for tibetan plateau deformation we find that the relatively small sizes of the inferred microblocks and their rotation pattern lend support to a model with a mechanically weak lower crust experiencing distributed deformation underlying a stronger highly fragmented upper crust

quantifying the climatological relationship between extratropical cyclone intensity and atmospheric precursors 1 we introduce a novel technique in which linear regression analysis is applied to clusters of tracked cyclones to statistically assess the factors controlling cyclone development we illustrate this technique by evaluating the differences between cyclones forming in the west and east north atlantic herein termed west and east atlantic cyclones enhanced cyclone intensity 2 days after genesis is found to be associated with deeper upper level troughs upstream of the cyclone center at the genesis time in both west and east atlantic cyclones however whilst west atlantic cyclones are also enhanced by the presence of strong fronts east atlantic cyclones are not instead east atlantic cyclones exhibit an enhancement when diabatically generated midlevel potential vorticity is present with the enhancement being of approximately equal magnitude to that associated with the potential vorticity in the upper level trough this is consistent with the paradigm of latent heat release in the warm conveyor belt region playing an important role in the development of east atlantic cyclones

the spatial distribution and evolution characteristics of north atlantic cyclones a climatology of extratropical cyclones is produced using an objective method of identifying cyclones based on gradients of 1 km height wet bulb potential temperature cyclone track and genesis density statistics are analyzed and this method is found to compare well with other cyclone identification methods the north atlantic storm track is reproduced along with the major regions of genesis cyclones are grouped according to their genesis location and the corresponding lysis regions are identified most of the cyclones that cross western europe originate in the east atlantic where the baroclinicity and the sea surface temperature gradients are weak compared to the west atlantic east atlantic cyclones also have higher 1 km height relative vorticity and lower mean sea level pressure at their genesis point than west atlantic cyclones this is consistent with the hypothesis that they are secondary cyclones developing on the trailing fronts of preexisting parent cyclones the evolution characteristics of composite west and east atlantic cyclones have been compared the ratio of their upper to lower level forcing indicates that type b cyclones are predominant in both the west and east atlantic with strong upper and lower level features among the remaining cyclones there is a higher proportion of type c cyclones in the east atlantic whereas types a and c are equally frequent in the west atlantic

crustal and upper mantle structure of the southeastern tibetan plateau from joint analysis of surface wave dispersion and receiver functions abstract researches on the southeastern tibetan plateau provide important insights into the tectonic evolution of the tibetan plateau in this study we have constructed a high resolution 3d shear wave velocity model through joint inversion of receiver functions and surface wave dispersion data the crustal thickness and poisson s ratio models are first determined by h k stacking of receiver functions the crustal thickness changes from 30 km in the south to 62 km in the north presenting strong lateral variations the fundamental mode of rayleigh wave dispersion data spanning periods from 8 to 65 s were then jointly used to constraint the absolute shear wave velocity the shear wave velocity structure shows lateral variations there are low velocity zones distributed in the crust and upper mantle two continuously distributed low velocity zones are clearly presented in the middle to lower crust which extend from north toward southeast and southwest respectively joining together in southern yunnan in this study we deduced the migration model of soft materials in middle to lower crust in southeastern tibetan plateau which explains that the resistance from sichuan basin separates the flowing materials from tibetan plateau into southeast and northwest branches they flow along the west margin of sichuan basin and then extrude out from northeastern and southeastern tibetan plateau respectively the southeast branch is blocked and cannot flow in the entire crust it is limited in a certain range of depths and channels the two low velocity zones in this study possibly present two flow channels of the middle to lower crustal materials extruded from the tibetan plateau

a multidisciplinary approach to seismic hazard in southern california abstract a serious obstacle facing seismic hazard assessment in southern california has been the characterization of earthquake potential in areas far from known major faults where historical seismicity and paleoseismic data are sparse this article attempts to fill the voids in earthquake statistics by generating master model maps of seismic hazard that blend information from geology paleoseismology space geodesy observational seismology and synthetic seismicity the current model suggests that about 40 of the seismic moment release in southern california could occur in widely scattered areas away from the principal faults as a result over a 30 yr period nearly all of the region from the pacific ocean to 50 km east of the san andreas fault has a greater than 50 50 chance of experiencing moderate shaking of 0 1 g or greater and about a 1 in 20 chance of suffering levels exceeding 0 3 g for most of the residents of southern california thelion9s share of hazard from moderate earthquake shaking over a 30 yr period derives from smaller closer more frequent earthquakes in the magnitude range 5 m 7 rather than from large san andreas ruptures whatever their likelihood

dynamical characterization of the fastex cyclogenesis cases summary a series of diagnostics based on the automatic tracking of cyclones is applied to the 25 life cycles captured during the fastex field experiment the tracking enables a setting of the various cases into a common frame of reference that moves with the system time filtering is used to further separate the events into a basic state and perturbations information is obtained on environmental properties such as strain or baroclinicity combining these diagnostics it is shown that instability mechanisms based on the existence of potential vorticity strips or the control of these instabilities by deformation may be involved in the initial genesis of a number of cases but do not seem to characterize specific types nor to determine a systematic behaviour on the other hand it is shown that rapid deepening phases leading eastern atlantic systems to their maximum amplitude happens suddenly and at the same time as crossing the jet stream even in the absence of a clear additional upper level feature for cold air systems development means meeting a diffluent zone this is unlike the american east coast systems that are associated with an exit entrance complex another remarkable feature is the generation of a frontal waveas a re sult of the parent vorticity maximum being apparently stretched and split this has occurred in 25 of cases a number of other properties of the fastex cases are shown such as several occurrences of large

arctic cyclogenesis at the marginal ice zone a contributory mechanism for the temperature amplification 1 rapid sea ice retreat over the arctic ocean has a leading role in arctic amplification the sea ice extent dramatically recovers during every freezing season so despite the recent summer sea ice retreat there must be extraordinary heat exchange between the lower atmosphere and upper ocean however the underlying mechanisms for this remain uncertain here we show that autumn frontal cyclogenesis is a crucial event in the arctic air sea coupled system our shipboard doppler radar and intensive radiosonde observations at the marginal ice zone detected an explosive frontal cyclogenesis with coupling between upper and lower tropospheric vortices the thermal contrast between ocean and ice surfaces is likely favorable to cyclogenesis with an identical life cycle to that at mid latitudes this suggests a northward shift of meridional heat transport the 1 5 k temperature decrease in the upper ocean after the cold front has passed reveals that a large amount of heat is transported into the atmosphere this is an invaluable example of the fact that sea ice retreat contributes to polar amplification of surface air temperature increase

detailed crustal structure of the north china and its implication for seismicity abstract since the mesozoic cenozoic era the north china craton has experienced an important tectonic transition and it has given rise to complicated crustal structure and strong earthquake activity based on the large scale surface gravity data we studied the detailed crustal structure and seismogenic mechanism of the north china the results indicate that the north china presents typical characteristics of adjoining depression and uplift alternating basins and hills inhomogeneous density and also great differences in crustal structure and moho topography the upper and middle crustal structures are dominated by the nne striking tectonic units with many faults cut down to the middle crust the lower crust is characterized by the folding structure with high and low density placed alternately from west to east presenting lateral heterogeneous feature adjusted by the gravity isostasy moho topography of the north china fluctuates greatly compared with the north china basin crustal thickness in the western taihang northern yanshan and luzhong areas are much thicker while those densities are lower than the north china basin the dominating tectonic direction of the moho topography strikes ne to nne and undulates alternately from west to east the epicenters are mostly concentrated in the upper and middle crust especially the transitional areas between the high and low gravity anomalies the tancheng earthquake in 1668 sanhe earthquake in 1673 tangshan earthquake in 1976 and all other seismic tectonic zones of the north china are all distributed in area where magma moves strongly beneath the crust which is considered to be related to the movement of the high density unstable and heat flows along the deep passage from the uppermost and asthenosphere due to the subduction of the pacific slab towards the eurasian plate

a classification of fastex cyclones using a height attributable quasi geostrophic vertical motion diagnostic a systematic and objective procedure is developed for applying the simple cyclone classification scheme of petterssen and smebye this method uses a height attributable solution of the quasi geostrophic equation to identify and quantify the relative importance of upper and lower tropospheric forcing and also the time trend in the horizontal spacing of the forcing at these two levels by applying this classification method to a sample of cyclogenesis events during their maximum intensification stage from the fronts and atlantic storm track experiment field experiment the type a and type b scheme of petterssen and smebye is reproduced and extended to include a type c type c consists of upper level dominated cyclones that form at high latitudes and in their initial stages resemble comma cloud type polar lows detailed examples of each of the three types are presented some cyclones can undergo more than one period of development and it is found that each development period can be classified as a different cyclogenesis category a or b these cyclones are classified as hybrid type a b there is some evidence that cyclone forecast accuracy depends on cyclone type thereby suggesting the potential for this method to be used to assign confidence levels for forecasts of cyclogenesis produced by numerical weather prediction models type b cyclones appear more difficult to predict because their development depends initially on the interaction between significant features in the upper and lower troposphere copyright 2002 royal meteorological society t d hewson s contribution is crown copyright

fastex iop 18 a very deep tropopause fold i synoptic description and modelling the life cycle of a very deep tropopause fold 820 hpa is documented with aircraft and ship observations during the intensive observing period 18 of the fronts and atlantic storm track experiment fastex the initial setting involves a coherent tropopause disturbance and an associated arctic tropopause fold the confluence episode that results from the phasing up of the tropopause disturbance and a southern ridge ends in the formation of an intense jet streak the dynamics of which are associated with the development of a polar tropopause fold a diagnostic analysis suggests that the final dramatic stratospheric intrusion is the consequence of the vertical superposition of the arctic and polar tropopause folds the mesoscale non hydrostatic meso nh model is used to discuss this hypothesis mixing of the passive stratospheric tracer within the marine boundary layer is investigated with sensitivity tests which unplug in turn the model physical parametrizations finally upper level forcings associated with the development of the tropopause fold are investigated in detail in a companion paper

the impact of typhoon jangmi 2008 on the midlatitude flow part ii downstream evolution extratropical transition et of a tropical cyclone tc can modify the midlatitude flow and thus have implications for the weather and predictability in downstream regions such as north america or europe albeit recurving and undergoing et the downstream impact of typhoon jangmi in september 2008 during the thorpex pacific asian regional campaign t parc was weak in this study we explore the physical processes inhibiting the reintensification of jangmi and governing the forecast uncertainty during et the focus is on the relative contribution of the tc and the midlatitude flow quasi geostrophic diagnostics reveal that jangmi is located south of and in phase with a midlatitude trough jangmi does not couple with the region favourable for reintensification ahead of the trough and subsequently decays instead a weak frontal wave like cyclone develops the role of the phasing of typhoon jangmi and the midlatitude rossby wave pattern is tested in sensitivity experiments with the cosmo model in which jangmi has been relocated the simulations reveal two contrasting groups of scenarios the first group reflects the weak actual et and subsequent decay accompanied by a broad ridge over the pacific the second group is characterized by a strong et with extratropical reintensification the triggering of a pronounced rossby wave train and downstream cyclogenesis the displacement of jangmi s initial position in the two contrasting groups is less than 1 25 130 km in the frame moving with the environmental background flow a critical bifurcation point for the track of jangmi exists the relative position to this bifurcation point determines whether jangmi decays or reintensifies and triggers a rossby wave train a simple discrimination parameter is derived that allows for classifying the scenarios the observed behaviour gives a simple explanation for the reduced predictability of the track and of the midlatitude flow in downstream regions during et

evolution of the late cenozoic tectonic stress regime in the shanxi rift central north china plate inferred from new fault kinematic analysis abstract the shanxi rift an intracontinental belt along the eastern margin of the ordos block north china plate has undergone multi stage extensional deformation during the late cenozoic in this study new fault kinematic analysis of boundary faults in the shanxi rift constrained by geochronological data defines a three stage tectonic stress regime since the late miocene providing new structural evidence for deciphering the northeastward growth of the tibetan plateau the earliest stage involved a transtensional stress regime of nw se extension and ne sw compression in the late miocene early pleistocene ca 10 1 8 ma and characterized by mean principal stress axes of 1 at 344 7 87 2 2 at 217 6 01 1 and 3 at 128 1 01 0 the early transtensional stress regime was responsible for the opening of the shanxi rift and was very likely associated with intensive right lateral pull apart activity in the eastern ordos block due to the northeastward growth of the tibetan plateau during the second stage the stress regime changed to less intense ne sw extension with mean stress orientations of 323 3 85 2 for 1 127 5 02 9 for 2 and 214 9 02 6 for 3 in the early late pleistocene ca 1 8 0 11 ma this stage is marked by a distinct shift from fluvio lacustrine to fluvio piedmont sedimentary facies at the end of the early pleistocene and the widespread eruption of basalt in the datong basin north of the shanxi rift this short lived extension appears to be the result of relaxation in the midst of crustal shortening during growth of the tibetan plateau the third stage was transtensional characterized by nnw sse extension and wnw ese compression 1 at 060 88 9 2 at 074 9 03 9 and 3 at 164 00 since the late pleistocene ca 0 11 ma causing dextral shear deformation in the shanxi rift and the disappearance of its paleo lake this stage resulted from regional ene wsw shortening due to northeastward growth of the tibetan plateau

self potential signals associated with variations of the hydraulic head during an infiltration experiment 1 a field experiment was performed to monitor the variations of the hydraulic head in the vicinity of a ditch during a water infiltration experiment and using the self potential method the coupling between electric and hydraulic flows is electrokinetic in nature the electrical signals are measured at the ground surface with a set of ten non polarisable petiau pb pbcl2 electrodes over a section perpendicular to the ditch the electrical potential is linearly related to the depth of the water table which is here quite shallow between 1 to 2 m a rough estimate of the electrokinetic coupling coefficient obtained in the field is 10 mv per meter of hydraulic head 1000 mv mpa 1 of pore fluid pressure the order of magnitude of this estimate agrees with a laboratory experiment performed with a soil sample from the test site the good correlation found between electrical potential and hydraulic head variations opens the door to direct tomography of hydraulic head fluctuations with many innovative applications in hydrogeology especially because the potential depth to which this method could be applicable is high several hundred meters

a thin viscous sheet model for continental deformation summary for the purposes of describing its large scale and long term deformation the continental lithosphere is regarded as a continuum obeying a newtonian or a power law rheology the flow of a thin sheet of power law material overlying an inviscid substrate is studied under the assumption that vertical gradients of the horizontal velocity are negligible a numerical model is used to investigate the deformation of such a sheet under conditions approximating those of continent continent collision the material flows in response to forces applied to its boundaries for example the indenting of one continent by another and to forces in its interior arising from gradients in crustal thickness the horizontal divergence of the flow produces changes in the crustal thickness and hence a time dependent form to the flow itself for a given set of boundary conditions the flow depends on the stress exponent in the power law rheology n and on the argand number which is a measure of the ratio between the stress arising from crustal thickness contrasts and the stress required to deform the material at the ambient strain rates when the effective viscosity of the medium is very high ar o crustal thickness variations do not influence the flow if the material is newtonian n l the deformation associated with an influx of material approximating an indenter is of much greater lateral dimension than the width of the indenter whereas when material has a power law rheology n 3 5 are used the deformation is confined to a region of lateral extent comparable to that of the indenter as ar increases the forces arising from crustal thickness contrasts exert more influence on the flow and the maximum crustal thickness that can be sustained by a given influx of material is related by a simple expression to the effective viscosity of the medium at the ambient strain rates in the limit of a very weak medium ar 10 the lithosphere is unable to sustain appreciable crustal elevation contrasts the results of these numerical experiments show that systems in which the effective viscosities are such that the maximum deviatoric stresses are between 1 kbar

the volcano electric effect 1 the formation of a magmatic intrusion at depth is responsible for the formation of various thermohydromechanical thm disturbances including the upsurge of shock waves and diffusion of pressure fronts in the volcanic system we couple electromagnetic theory maxwell equations and thermoporoelasticity biot equations to look at the ground surface electrical signature of these thm disturbances the nature of this coupling is electrokinetic i e associated with water flow relative to the mineral framework and the drag of the excess of charge located in the vicinity of the pore water mineral interface the groundwater flow disturbance being related here to the thm disturbances in drained conditions a new set of laboratory data shows that the electrokinetic coupling is very substantial in fractured basaltic and volcaniclastic materials and in scoria with several hundreds of millivolts of electrical potential gradient produced per megapascal of pore fluid pressure variations our theoretical analysis predicts the diffusion of electromagnetic disturbances and quasi static electrical signals these signals can be used as precursors of a volcanic eruption indeed electromagnetic phenomena recorded at the ground surface of a volcanic system once properly filtered to remove external contributions provide a direct and quasi instantaneous insight into the thm disturbances occurring in the heart of the volcanic structure prior and during a volcanic event tomography of the quasi static electrical field is discussed and applied to self potential profiles performed at the piton de la fournaise volcano during the preparation phase of the march 1998 eruption

the extratropical transition of hurricane irene 1999 a potential vorticity perspective extratropical transition et of tropical cyclones is common in all ocean basins where tropical cyclones recurve polewards after the tropical cyclone experiences et a rapid deepening can take place resulting in the development of a very large and deep extratropical cyclone the et of hurricane irene 1999 was an example of such an explosive et irene formed in the caribbean and experienced et as it moved poleward resulting in a low pressure system which deepened 39 hpa in 24 hours according to the met office analyses the extent to which the hurricane was responsible for the explosive extratropical development has been determined by performing met office unified model forecasts from initial states with and without the hurricane the circulation and temperature anomalies associated with the hurricane were removed from the initial state using potential vorticity inversion the moisture anomaly co located with the hurricane core was also removed the results show that an extratropical cyclogenesis event takes place regardless of the presence of the hurricane in the initial conditions however the hurricane makes a significant difference to the track and central mean sea level pressure evolution of the resulting extratropical cyclone when irene was present the track of the extratropical cyclone was more zonal and the cyclone deepening rate was twice as fast as when irene was not present these effects appear to be particularly associated with a negative potential vorticity anomaly and enhanced divergent flow in the region of the upper level outflow of the transforming hurricane rather than with the hurricane vortex results also show that the presence of the hurricane resulted in a significant downstream surface low development in the eastern atlantic copyright 2004 royal meteorological society

mechanism of crustal deformation in the sichuan yunnan region southeastern tibetan plateau insights from numerical modeling abstract the characteristics of crustal deformation and its dynamical mechanisms in the sichuan yunnan region are of interest to many researchers because they can help explain the deformation pattern of the eastern tibetan plateau in this paper we employ a precise three dimensional viscoelastic finite element model to simulate the crustal deformation in the sichuan yunnan region southeastern tibetan plateau we investigate the influence of lower crustal flow and rheological variations by comparing the modeled results with gps observations the results demonstrate that lower crustal flow plays an important role in crustal deformation in the sichuan yunnan region the best fitting is achieved when the flow velocity of the lower crust is approximately 10 11 mm a faster than that of the upper crust additionally crustal rheological properties affect regional crustal deformation when the viscosity of the middle and lower crust in the south china block reaches 1022 and 1023 pa s respectively the modeled results match observations well especially for the magnitude of crustal motion within the south china block finally our dynamic model shows that the maximum principal stress field of the sichuan yunnan region exhibits clear zoning gradually shifting from an approximately east west orientation in the northern bayan har block to southeast in the south china block southwest in the western yunnan block and a radially divergent distribution in the middle yunnan and southern yunnan blocks

on a threefold classification of extratropical cyclogenesis a recently proposed extension to the twofold extratropical cyclogenesis classification scheme of petterssen and smebye is discussed a third class of extratropical cyclone type c is described in which initial development is controlled by a pre existing upper level potential vorticity pv anomaly in its early stages such a system is indistinguishable from the classical type b cyclone of the petterssen and smebye scheme however subsequent development cannot be understood in terms of a co operative interaction of the upper level feature with a low level baroclinic zone rather the cyclogenetic dynamics of type c systems are dominated by the action of strong midlevel latent heating such heating can generate important anomalies of pv that act to suppress the formation of a low level thermal anomaly and that interact destructively with the pre existing upper level feature candidate type c events are identified using recently developed height attributable quasi geostrophic vertical motion diagnostics the application of one such diagnostic to a climatology of instantaneous cyclonic features suggests that type c events may occur with reasonable frequency the generic behaviour of system types in the proposed threefold classification scheme is compared with the actual dynamics of some cyclones from the fronts and atlantic storm track experiment fastex the analysis is based on piecewise pv inversions and numerical simulations this approach is able to provide a good description of a case of standard type b development consistent with the qualitative description of petterssen and smebye and with the quasi geostrophic diagnostics within the same framework two systems are discussed whose behaviours do not fit the simple a b classification but are consistent with the proposed type c mechanism copyright 2003 royal meteorological society

horizontal potential vorticity dipoles on the convective storm scale the structure and dynamics of potential vorticity pv anomalies generated by convective storms is investigated both theoretically and in a numerical model case study linear theory suggests that if the storm induced heating is on a sufficiently small scale relative to the rossby radius of deformation and the environment contains moderate vertical wind shear of order 1 m s 1 km 1 then the dominant mode of a diabatically generated pv anomaly is a horizontally oriented dipole the horizontal dipoles are typically of 10 pvu compared with the 1 pvu vertical dipoles that have been studied extensively throughout the literature furthermore the horizontal pv dipoles are realized almost entirely as relative vorticity anomalies on a time scale of the order of tens of minutes after the heating has been turned on the analysis of horizontal pv dipoles offers a new perspective on the vorticity dynamics of individual convective cells implying that moist processes play a role in the maintenance of vertical vorticity in the convective storm environment copyright 2009 royal meteorological society

syn collisional transform faulting of the tan lu fault zone east china origin of the continental scale tan lu fault zone tlfz east china remains controversial about 550 km sinistral offset of the dabie orogenic belt dob and sulu orogenic belt sob is shown along the ne nne striking tlfz syn collisional sinistral ductile shear belts in the tlfz have been identified thirteen phengite bulk separates from the mylonites were dated by the 40ar 39ar method they gave cooling ages of the 198 181 ma for the shear belts along the eastern margin of the dob and 221 210 ma from the western margin of the sob distribution of the foreland basin deposits suggests that sinistral offset of the dob and sob by the tlfz took place prior to deposition of the upper triassic strata the marginal structures around the dob and sob support syn collisional faulting and indicate anticlockwise rotation of the dob during the displacement the folding and thrust faulting related to crustal subduction coeval with the tan lu faulting is older than the foreland basin deposition related to the orogenic exhumation several lines of evidence demonstrate that the tlfz was developed as a syn collisional transform fault during latest middle to earliest late triassic time when the dob and sob experienced crustal subduction of the south china block scb eastward increase of the crustal subduction rates is believed to be responsible for the sinistral transform faulting

life cycle study of a diabatic rossby wave as a precursor to rapid cyclogenesis in the north atlantic dynamics and forecast performance abstractthe life cycle of a north atlantic cyclone in december 2005 that included a rapid propagation phase as a diabatic rossby wave drw is investigated by means of operational analyses and deterministic forecasts from the ecmwf a quasigeostrophic omega diagnostic has been applied to assess the impact of upper level forcing during the genesis propagation and intensification phase respectively the system was generated in the gulf of mexico as a mesoscale convective vortex mcv influenced by vertical motion forcing from a nearby upper level trough the drw propagation phase was characterized by a shallow low level diabatically produced potential vorticity pv anomaly that rapidly propagated along the southern border of an intense baroclinic zone no significant upper level forcing could be identified during this phase of the development eventually explosive intensification occurred as the region of vertical motion forced by an approaching upper level trough reached the position of the drw the

lithospheric rheology and moho upheaval control the generation mechanism of the intraplate earthquakes in the north china basin abstract many devastating intraplate earthquakes such as the 1966 xingtai earthquake ms 7 2 and the 1976 tangshan earthquake ms 7 8 occurred in the north china basin ncb this study aims to investigate the generation mechanism of the large intraplate earthquakes in the ncb and the spatial distribution of earthquake activity through numerical experiments in order to simulate the interseismic stress accumulation process in the ncb we set up several 3d finite element models based on different lithospheric rheological structure and apply boundary conditions of horizontal compression we find that stress concentration with high rate in the regions where moho upheaves is responsible for the large earthquakes in the ncb during the interseismic period large stress rate is located nearly around the bottom of the brittle upper crust where stress accumulates fast to reach fault strength and active the main shocks aftershocks in the seismogenic layers could be triggered by the main shocks two factors are critical to the crustal stress accumulation process 1 the first is moho upheaval in the seismic zones 2 the second is viscosity contrast among the crustal layers our results support the lithospheric rheological structure in the ncb as following the brittle upper crust brittle ductile transition in the middle crust the ductile lower crust and the ductile lithospheric upper mantle

the role of shearwise and transverse quasigeostrophic vertical motions in the midlatitude cyclone life cycle abstract the total quasigeostrophic qg vertical motion field is partitioned into transverse and shearwise couplets oriented parallel to and along the geostrophic vertical shear respectively the physical role played by each of these components of vertical motion in the midlatitude cyclone life cycle is then illustrated by examination of the life cycles of two recently observed cyclones the analysis suggests that the origin and subsequent intensification of the lower tropospheric cyclone responds predominantly to column stretching associated with the updraft portion of the shearwise qg vertical motion which displays a single dominant middle tropospheric couplet at all stages of the cyclone life cycle the transverse qg omega associated with the cyclones frontal zones appears only after those frontal zones have been established the absence of transverse ascent maxima and associated column stretching in the vicinity of the surface cyclone center suggests that the transverse plays little role i

secondary frontal waves in the north atlantic region a dynamical perspective of current ideas the current understanding of the dynamics of secondary cyclogenesis on frontal systems in the north atlantic region is reviewed these secondary cyclones are often poorly forecast and in extreme cases can have damaging consequences but because of their small scales and potential for rapid growth detailed observations and analyses are limited in this paper recent work is described and compared it is argued that on the synoptic scale the development of primary baroclinic waves is well understood but on the subscales of these systems where the secondaries develop there is a wider variety of mechanisms which may cause or modify cyclone growth this variety may be reflected in a wider range of resulting systems various dynamical models have been postulated secondary frontal waves are seen as the instability of a low level potential vorticity strip or warm band at a front with possible finite amplitude triggering by upper level features latent heating is thought to provide a suitable unstable potential vorticity strip but the degree to which the latent heating contributes to the instability itself is a matter of dissent secondary systems are often shallow so boundary layer processes are important but the influence of these is not well understood laboratory experiments have suggested that the boundary layer will act to suppress instability in general frontogenetic strain flow while acting to intensify the basic state front suppresses wave development in contrast recent work suggests that a frontolytic strain flow may be important in enhancing the development of one class of waves the fastex experiment an international field study of north atlantic secondary cyclogensis has recently attempted to observe these systems in detail it is hoped that the data which have been obtained will help to resolve some of the outstanding issues in this field

explosive cyclogenesis over the eastern united states abstract cases of explosive cyclogenesis bombs were identified over the central and eastern united states and were compared with nonexplosive cyclone development in the same region the tendency equations for vorticity and geopotential thickness and a modified divergence equation were used to find signatures of distinction between these two types of cyclogenesis whose recognition might improve forecasting skills bombs tend to show a marked decrease of vorticity with height during their incipient and explosive stages whereas regular cyclones reveal only weak vertical vorticity gradients in the troposphere the low tropospheric spin up in bombs precedes significantly that in the upper troposphere preexisting low tropospheric vorticity maxima are associated with low level jet streaks whereas regular cyclones possess an ill defined level of nondivergence i e a broad region between 800 and 400 mb of divergence values close to zero incipient bombs have a well marked zero divergence level near 50

secondary cyclogenesis the initiation phase of a frontal wave observed over the eastern atlantic the initiation phase of a secondary frontal wave in the wake of a primary cyclogenesis event over the atlantic is documented north of the trailing surface cold front and south west of the primary cyclone an intense upper level jet generates a direct and transverse ageostrophic circulation in its entrance region evidence is shown for two conflicting roles of this circulation first stabilization of the front through frontogenetic cross frontal low level convergence and second an increase of the potential for instability of the front through diabatic e g latent heat release potential vorticity pv redistribution in the upward branch of the circulation following saturation of the primary cyclogenesis and the associated along front north eastwards shift of the upper level jet the low level branch of the ageostrophic circulation behaves like a zipper closing on the front while in the upward branch an anomalous strip of pv builds along the cold front isentropic pv maps show that parcles of stratospheric origin embedded in the downward branch of the ageostrophic circulation a tropopause fold may have ended in the vicinity of the strip of anomalous low level pv perhaps contributing to an increase in the potential for instability of the surface front using the domain independent attribution method of bishop it is shown that the frontal wave forms on a part of the cold front where first the along front stretching rate due to the environmental flow decays below the critical threshold value 0 6 10 5 s 1 prescribed by theoretical studies and second the across front frontogenetic component due to the ageostrophic circulation decays this is consistent with semi geostrophic theory where the cross frontal convergence and the stretching deformation are linked through the sawyer eliassen equation results add to other recent observational findings that the potential for instability the evolving environmental flow and the induced ageostrophic convergence each have a crucial role in differentiating between frontal waves that will grow and those that will be suppressed

present crustal deformation and stress strain fields of north china revealed from gps observations and finite element modelling abstract north china is located on the n s seismic belt of mainland china and is characterized by dense faults and intense seismicity we analyzed the current regional crustal deformation using gps observations from 1999 to 2007 and 2011 2017 we then established a dynamic finite element model based on the geological structure geophysical parameters and gps velocity constraints to analyze the strain stress features finally we discuss the rationality of the simulation results the variations in crustal activity which may have been caused by the post earthquake impact of the 2011 mw 9 0 tohoku and 2008 mw 7 9 wenchuan earthquakes and the geodynamics of north china most parts of north china exhibited extensional stress in an approximately nw se direction during 2011 2017 in the two study periods the maximum shear strain rates predominantly occurred in western north china the central and eastern parts had relatively smaller values in 2011 2017 these characteristics indicate that the post earthquake impact of the tohoku earthquake significantly influenced most parts central and eastern of north china whereas the wenchuan earthquake mainly affected the western part our work quantitatively described the variations in current crustal movement velocities stress strain fields and fault activity rates in north china these characteristics indicate that the unique tectonic environment intense crustal activity and earthquake prone nature of north china require continuous research attention the results obtained in this study not only portray the current tectonic activity deformations but also reveal recent geodynamic processes in north china

a new method to objectively classify extratropical cyclones for climate studies testing in the southwest pacific region abstract extratropical cyclones can vary widely in their configuration during cyclogenesis development mechanisms spatial and temporal characteristics and impacts an automated method to classify extratropical cyclones identified in era interim data from 1979 to 2010 in the australia and new zealand region has been developed the technique uses k means clustering on two upper tropospheric flow fields at the time of cyclogenesis and identifies four distinct clusters composites of these clusters are investigated along with their life cycles and their spatial and temporal variability the four clusters are similar to a previous manual classification cluster 1 develops in the equatorward entrance region of the subtropical jet clusters 2 and 4 develop in the poleward exit region of the subtropical jet but with different relative positions of the upper level trough and jet streak and cluster 3 resembles secondary cyclogenesis on a preexisting front far poleward of the subtropical jet the clusters have

a 10 yr climatology of diabatic rossby waves in the northern hemisphere abstractdiabatic rossby waves drws are low tropospheric positive potential vorticity pv anomalies in moist and sufficiently baroclinic regions they regenerate continuously by moist diabatic processes and potentially develop into explosively intensifying cyclones in this study a specific drw tracking algorithm is developed and applied to operational ecmwf analyses to compile a first climatology of drws in the northern hemisphere for the years 2001 10 drws are more frequent over the north pacific than over the north atlantic with on average 81 and 43 systems per year respectively less than 15 of these systems intensify explosively on average 12 per year over the pacific and 5 over the atlantic drws are most frequent in summer but most of the explosively intensifying drws occur in autumn and winter drws are generated typically between 30 50 n over the eastern parts of the continents and the western central parts of the oceans they propagate fairly zonally along the midlatitude baroclinic zone

the role of secondary cyclones and cyclone families for the north atlantic storm track and clustering over western europe secondary cyclones are those that form in association with a pre existing primary cyclone typically along a trailing cold front in previously studied cases they have been shown to cause extreme damage across europe particularly when multiple cyclones track over the same location in rapid succession known as cyclone clustering to determine the dynamical relationship between primary and secondary cyclones over the north atlantic a frontal identification algorithm is partnered with a cyclone identification method to objectively identify secondary cyclones in 35 extended winter periods using reanalysis data cyclones are grouped into cyclone families consisting of a single primary cyclone and one or more secondary cyclones this paper aims to quantify the differences between secondary and primary cyclones over the north atlantic and how cyclone families contribute to episodes of cyclone clustering across western europe secondary cyclones are shown to occur most frequently in the central and eastern north atlantic whereas primary cyclones are commonly found over the western north atlantic cyclone families have their strongest presence over the north atlantic ocean and contribute more than 50 of cyclones over the main north atlantic storm track a final category solo cyclones which are not associated with cyclogenesis on any connected fronts are most commonly identified over continental regions as well as the mediterranean sea primary cyclones are associated with the development of an environment that is favourable for secondary cyclone growth enhanced rossby wave breaking following primary cyclone development leads to an increase in the upper level jet speed and a decrease in low level stability secondary cyclogenesis commonly occurs in this region of anomalously low stability close to the european continent during periods of cyclone clustering secondary cyclones are responsible for approximately 50 of the total number of cyclones the increase in jet speed and decrease in static stability initiated by the primary cyclones acts to concentrate the genesis region of secondary cyclones and direct the cyclones that form along a similar track while there is an increase in the secondary cyclogenesis rate near western europe during periods of european clustering the basin wide secondary cyclogenesis rate decreases during these periods thus the large scale environment redistributes secondary cyclones during periods of clustering rather than increasing the total number of secondary cyclones

the climatology of synoptic scale ascent over western north america a perspective on storm tracks abstractthe position and variability of storm tracks across western north america are examined during the october april cool seasons spanning 1989 2010 the location and intensity of storms are represented by strong synoptic scale ascent which is diagnosed by the alternative balance omega equation applied to ecmwf re analysis interim data this dynamically filtered method removes poorly resolved updrafts arising from subsynoptic scale phenomena such as convection and mountain waves the resulting vertical motions are illustrated for the case of a strong storm traversing the western united states summary statistics of synoptic scale ascent are compiled over months seasons and the entire 21 yr period locations exhibiting high mean values of ascent are deemed to represent storm tracks the climatological mean storm track exhibits a sinusoidal shape across the eastern pacific and western north america the composite evolution of strong storms moving along specific segments of the storm track show regional

constitutive equations for ionic transport in porous shales 1 the constitutive coupled equations describing ionic transport in a porous shale are obtained at the scale of a representative elementary volume by volume averaging the local nernst planck and stokes equations the final relationships check the onsager reciprocity to the first order of perturbation of the state variables with respect to the thermostatic state this state is characterized by a modified version of the donnan equilibrium model which accounts for the partition of the counterions between the stern and diffuse gouy chapman layers after upscaling the local equations the material properties entering the macroscopic constitutive equations are explicitly related to the porosity of the shale its cation exchange capacity and some textural properties such as the electrical cementation exponent entering archie s law this new model is then applied to predict the salt filtering and electrodiffusion efficiencies of a shale layer

the key role of diabatic outflow in amplifying the midlatitude flow a representative case study of weather systems surrounding western north pacific extratropical transition abstractrecurving tropical cyclones tcs undergoing extratropical transition et may substantially modify the large scale midlatitude flow pattern this study highlights the role of diabatic outflow in midlatitude flow amplification within the context of a review of the physical and dynamical processes involved in et composite fields of 12 western north pacific et cases are used as initial and boundary conditions for high resolution numerical simulations of the north pacific north american sector with and without the tc present it is demonstrated that a three stage sequence of diabatic outflow associated with different weather systems is involved in triggering a highly amplified midlatitude flow pattern 1 preconditioning by a predecessor rain event pre 2 tc extratropical flow interaction and 3 downstream flow amplification by a downstream warm conveyor belt wcb an ensemble of perturbed simulations demonstrates the robustness of these stages beyond earlier studies investigating pres recurv

mechanism of the spatial distribution and migration of the strong earthquakes in china inferred from numerical simulation abstract strong earthquakes that occurred in the chinese continent are usually characterized by grouped activity long distance jumping migration and different main activity areas formed in different times in the present study a three dimensional 3 d finite element model was set up for the chinese continent involving surface topography major active fault zones and initial stress field to study the mechanism of the long distance jumping migration of main active areas for the strong earthquakes that occurred in the chinese continent a number of numerical simulation experiments have been made by introducing the birth and death of element groups under different boundary loading configurations our results show that 1 in an environment where always exists an initial stress field in the earth s crust the areas where strong earthquakes have occurred taken as a killed element in the model have no longer abilities to concentrate the stress largely enough and can cause the stress adjustment by an order of mpa in a large area which may be one of the main factors affecting the long distance jumping migration of the follow up strong earthquakes and 2 it is hard to accurately predict where the follow up strong earthquakes will occur because it could be affected by many factors such as the loading manner geological structure active fault zones initial stress field or stress field adjustment induced by strong earthquakes but in an active period of earthquakes the major activity area migration of strong earthquakes may be affected largely by the boundary loading configurations these results suggest that it is helpful to predict a trend of the strong earthquake migration by investigating various kinds of boundary loading manners and the relationship between stress field adjustment induced by strong earthquakes and the regions where the strong earthquakes occurred

the hydroelectric problem of porous rocks inversion of the position of the water table from self potential data summary the self potential sp method is a fast and cheap reconnaissance tool sensitive to ground water flow in unconfined aquifers a model based on the use of green s functions for the coupled hydroelectric problem yields an integral equation relating the sp field to the distribution of the piezometric head describing the phreatic surface and to the electrical resistivity contrast through this phreatic surface we apply this model to sp data measured on the south flank of the piton de la fournaise volcano a large shield volcano located on reunion island indian ocean the phreatic surface inverted with the help of the simplex algorithm from the sp data agrees well with the available information in this area one borehole and electromagnetic em data this interpretation scheme which we call electrography has many applications to the crucial problem of water supply in volcanic areas where drilling is expensive

metamorphic core complexes vs synkinematic plutons in continental extension setting insights from key structures shandong province eastern china abstract continental extension is an important geodynamical process mostly diagnostic of a peculiar behaviour of the crust accommodated by geological structures that highlight these specific conditions in the crust though a metamorphic core complex mcc reveals a much stronger crustal extension than a synkinematic pluton the nature of those two structures implies different implications in terms of crustal extension mechanisms and geodynamic significations in eastern asia a major continental extensional event occurred during mesozoic and early cenozoic times the resulting various extensional events described in previous studies consist in large intracontinental basins important volcanism emplacement of plutons in the upper crust and exhumation of mccs an efficient description of mccs and plutons in eastern asia is essential to discriminate important differences of those two structures in terms of strain amount undergone by continental crust and geodynamic significations in that way an integrated structural and geophysical study has been realized to precisely discriminate the structure in the jiaodong peninsula shandong province eastern china previously regarded as simple sheared plutons a succession of three main stages have been identified all pertaining to a nw se extensional setting 1 the exhumation of the late jurassic early cretaceous linglong mcc below the se dipping linglong detachment fault 2 the emplacement of the guojialing syntectonic pluton below the n dipping extensional guojialing intracrustal shear zone 130 124 ma and 3 a penetrative brittle normal faulting associated with gold mineralizations 120 ma as a result the maximum amount of extension in jiaodong peninsula characterized by partially melted lower to middle crust upward into the linglong mcc should be revised to late jurassic early cretaceous period

tropopause undulations and the development of extratropical cyclones part i overview and observations from a cyclone event abstract the hypothesis that the development of extratropical cyclones is influenced by the evolution of tropopause undulations is described and examined these undulations exhibit large temperature and potential vorticity anomalies and are often observed prior to and during surface cyclogenesis typically an undulation has a half wavelength of approximately 2000 km and a vertical amplitude of over 200 mb warm and cold temperature anomalies which lie respectively over the low and under the high portions of the undulation are often embedded within strong upper level flow so that large temperature advections are found upstream and over developing cyclones a case analysis of a cyclone event indicates that the distributions of tropospheric height change and vorticity change can be strongly sensitive to the undulation related temperature changes in the lower stratosphere especially near 200 mb

layer wise attribution of vertical motion and the influence of potential vorticity anomalies on synoptic development a methodology is presented for attributing vertical motion to potential vorticity pv in a explicit manner using the quasi geostrophic omega equation the methodology is then used to determine the contribution individual pv anomalies make to the synoptic development it is shown how the total vertical motion may be decomposed into self generating and interaction terms the former correspond to vertical motion that arises from one pv region alone whilst each of the interaction terms represent vertical motion due to the interaction of two different regions of pv the method is applied to a number of cyclones studied in the fronts and atlantic storm tracks experiment in order to determine the dynamical role of individual pv regions in cyclogenesis for purposes of comparison cyclones were chosen to be representative of the types a b and c of an extended petterssen smebye scheme devised by deveson browning and hewson in terms of our new pv method the type a and b cyclones exhibit only subtle differences with the upper level layer of pv playing a larger role in the case of the type b cyclone a much larger difference is apparent between the type a and b cyclones on the one hand and the type c cyclone on the other in the type c cyclone the upper level pv self generating term plays an important role whereas in the type a and b cases the influence of the upper level pv is largely restricted to the interaction terms in all of the cases the vertical motion attributable to the interaction between the low level pv and boundary thermal gradient was found to be large hence from the viewpoint of instantaneous attribution we conclude that the low level pv is always important copyright 2003 royal meteorological society

migration trend of strong earthquakes in north china from numerical simulations abstract lu et al 2011 established a finite element model around the entire chinese continent to simulate the distant migration of strong earthquakes by killing the elements in this study a new finite element model of north china has been established in the existing chinese continental model using the gps observations and the finite element sub model technique through taking into account geological structure active faults surface topography moho discontinuity and 3 d velocity structure of the crust and upper mantle in the region furthermore the stress field adjustment was realized by reducing the element stiffness rather than by killing the elements we calculated the displacement of the chinese continent model and took the displacement located at the boundary of north china as the boundary loadings then computed the initial stress field by considering the gravity effect the migration of the strong earthquake regions was simulated by performing a number of tests with various kinds of short term boundary loadings locations of strong earthquakes were determined with the highest g the risk factor of the fault value and adjustment of the stress field our results showed that high stress disturbance regions could be possible regions of future strong earthquakes and that the initial stress field in north china can be well estimated if an optimal boundary loading configuration is chosen in the chinese continental model these results suggest that the strong earthquake forecast in north china may strongly depend on the stress field and strong earthquake activities in a much wider area such as the chinese continent

tropopause undulations and the development of extratropical cyclones part ii diagnostic analysis and conceptual model abstract a case study of a developing cyclone is used to show that the three dimensional distribution of height change during development can be strongly sensitive to temperature changes which occur in the lower stratosphere in association with an evolving tropopause undulation quantitative analysis of the storm with a geopotential height tendency equation indicates that a synergistic process developed between the stratosphere and troposphere whereby the vertical motion pattern maintained and intensified the upper level temperature anomalies while the subsequent upper level temperature advection led to an enhanced vertical circulation using the results of this diagnostic study a conceptual model is constructed the conceptual model is based on the hydrostatic and wind field adjustments that occur as tropopause undulations propagate over favored regions of tropospheric warm advection and less stable air

crust mantle structure difference across the gravity gradient zone in north china craton seismic image of the thinned continental crust the archean north china craton ncc has been tectonically modified and lost its thick lithospheric keel during the mesozoic and cenozoic the processes and mechanisms of the lithospheric modification and its appearance in and the relation between different subregions of the ncc are still poorly understood seismic data from 45 stations along a 470 km long profile cross the bohai bay basin bbb and the taihangshan mountain range tmr in the ncc were employed to construct a coherent structural image of the crust and uppermost mantle an integrated receiver function imaging technique combining the common conversion point stacking approach with waveform inversion and forward modeling was proposed to extract the structural information beneath the study region modeling of bouguer gravity anomalies was also applied to constrain the density distribution the imaging result reveals distinct structural features between the mountain range and the basin area and presents a picture of uneven crust thinning within the study region in the east bbb the crust is significantly thinned due mainly to the reduction in the thickness of the lower crust including the crust mantle transition zone by up to 12 km the west tmr in contrast is characterized by a relatively thick lower crust of 20 km the teleseismic waveform data and the gravity observation suggest a thicker crust and a buoyant mantle lithosphere beneath the tmr compared with the bbb the contrasting crustal structural features appear coupled with the lithospheric processes and possibly reflect that different tectonic mechanisms and deformation regimes dominated the evolution of the two regions the north south gravity lineament lying between the tmr and bbb might represent a deep intra continental boundary separating the ncc into topographically and tectonically different regions

rossby wave initiation by recurving tropical cyclones in the western north pacific abstractthe interaction of recurving tropical cyclones tcs with midlatitude rossby waves during extratropical transition et can significantly alter the midlatitude flow configuration this study provides a climatological investigation of rossby wave initiation rwi by transitioning tcs in the specific configuration of an initially zonal midlatitude waveguide and elucidates physical processes governing ab initio flow amplification during et recurving tcs interacting with a zonally oriented waveguide in the western north pacific wnp basin from 1979 to 2013 are categorized into cases initiating rossby waves tc rwi or not tc norwi interactions with a zonally oriented waveguide occurred for 22 7 of the recurving tcs and one third of these resulted in tc rwi in the presence of a tc the probability of rwi on a zonally oriented waveguide is 3 times larger than in situations without a tc the occurrence of tc rwi exhibits a seasonality and is relatively more common during boreal summer than in aut

a polar low named vera the use of potential vorticity diagnostics to assess its development 20 november 2008 the norwegian meteorological institute issued an extreme weather warning for trondelag county a storm was expected in the afternoon the storm a polar low pl was named vera vera was the second of two polar lows that developed along a wedge of warm air at the rear of a synoptic scale low that moved northeastwards into northern norway the dynamical development may be explained by classic dynamical theory low level warm air seclusion and shallow secondary circulation in a frontal zone that couples to transient upper level disturbances the study focuses on the potential vorticity pv perspective of the pl development and we have modified the initial pv field to study the effect of each individual pv perturbation two pv and two low level temperature anomalies have been chosen the pv anomalies retained their structure during the development while the temperature anomalies became less coherent and difficult to define by the end of the cyclogenesis period by modifying the initial conditions in the upper troposphere over greenland it is shown that in this case the upper pv anomaly had the strongest effect on the development and that this effect remained strong throughout the cyclogenesis until the polar low made landfall the effect from the low level pv anomaly became large after onset of cyclogenesis reflecting the positive feedback although its impact on the development remained smaller than that of the upper pv anomaly it is also shown that the topography of greenland was important in determining the correct position of this polar low development copyright 2011 royal meteorological society

a satellite derived classification scheme for rapid maritime cyclogenesis abstract guided by the conjecture that there exist characteristic synoptic scale flow patterns conducive to extratropical cyclogenesis a satellite based classification scheme is proposed to differentiate between various types of rapid maritime cyclogenesis in the western north atlantic region the scheme is derived from signatures in visible and infrared satellite imagery observed prior to and during rapid deepening consideration of the western north atlantic region is motivated by the presence of a relatively dense upstream observational network and by the absence of the direct influence of orography in a maritime environment the focus on rapid development is predicated upon the assumption that the cloud signatures will be more clearly defined than in cases of slower ordinary development examination of satellite imagery for an ensemble of 50 cyclogenesis events that occurred during the 1970s and 1980s 46 of which satisfied the experiment on rapidly intensifying cyclones over the atlantic criterio

geodetic strain rate and earthquake size new clues for seismic hazard studies abstract earthquakes deliver in few seconds the elastic energy accumulated in hundreds of years where and when will be the next earthquake remains a difficult task due to the chaotic behaviour of seismicity and the present lack of available tools to measure the threshold of the crustal strength however the analysis of the background strain rate in italy and the comparison with seismicity shows that larger earthquakes occur with higher probability in areas of lower strain rate we present a statistical study in which a relationship linking the earthquake size magnitude and the total strain rate sr is found we combine the information provided by the gutenberg richter law gr of earthquake occurrence and the probability density distribution of sr in the italian area following a bayesian approach we found a simple family of exponential decrease curves describing the probability that an event of a given size occurs within a given class of sr this approach relies on the evidence that elastic energy accumulates in those areas where faults are locked and the sr is lower therefore in tectonically active areas sr lows are more prone to release larger amount of energy with respect to adjacent zones characterised by higher strain rates the sr map of italy compared with 5 years seismicity supports this result and may become a powerful tool for identifying the areas more prone to the next earthquakes

structure of the mantle transition zone beneath the north china craton abstract detailed information on deep structural features can improve current understanding of lithospheric thinning and destruction of the north china craton in this study we analyzed receiver functions rfs from teleseismic p waveforms recorded by 246 seismic stations beneath the north china craton ncc to determine the topography of the mantle transition zone mtz the results reveal specific features in the 410 and 660 km discontinuities and outlined mtz thickness beneath the study area the mtz structure shows two anomalously thickened regions beneath the ncc up to 30 40 km thicker than the global average which are mainly concentrated in the eastern and western sections of the eastern ncc encc the thickened regions are discontinuous and separated by a distance of about 400 km double 660 km discontinuities also appear in the southeastern encc combining these results with previous findings we propose a model in which mtz thickening is caused by discrete remnants of the subducted western pacific slab discontinuities resulting from the stagnant slabs may retain evidence of changes in the rate of pacific plate subduction as well as the phase transition of the subducted slabs within the mtz

diminutive frontal waves a link between fronts and cyclones abstract a number of recent publications have dealt with cyclone identification and tracking following on this paper extends the typical cyclone life cycle back in time to embrace a new feature called a diminutive frontal wave one aim is to improve predictability by extending tracks this is particularly important for small cyclonic windstorms which can often be missed in postprocessed output from operational ensemble and climate runs the recognition of diminutive waves requires a new front relative low level vorticity partition the parts are labeled frontal vorticity and disturbance vorticity and are computed respectively from front parallel and cross front low level wind components a diminutive frontal wave then lies wherever there is a local along front maximum in the disturbance vorticity computations require local coordinates these are conveniently provided at all grid points by objective front diagnostics analysis of cyclone type transitions over the north atlantic in opera

streaming potential in volcanic rocks from mount pelee streaming potential and electric conductivity have been measured in a laboratory on 11 consolidated samples coming from five deposits of the different evolutionary stages of mount pelde volcano the streaming potential coupling coefficient ranges from 35 to 4905 mv mpa 1 and increases with increasing permeability this increase is mainly due to the dependency of rock effective conductivity with permeability the permeability of the samples varies from 0 146x10 12 to 34x10 12 m 2 the zeta potential at ph 7 and water conductivity of 2 1x10 4 s m l is relatively small for the majority of the samples it ranges from 4 to 19 rev according to water conductivity analysis on mount pel e streaming potential coupling coetficients of 25 to 406 mv mpa 1 can be expected for this volcano

classifying dynamical forcing mechanisms using a climatology of extratropical cyclones summary a climatology of almost 700 extratropical cyclones is compiled by applying an automated feature tracking algorithm to a database of objectively identified cyclonic features cyclones are classified according to the relative contributions to the midlevel vertical motion of the forcing from upper and lower levels averaged over the cyclone intensification period average u lratio and also by the horizontal separation between their upper level trough and low level cyclone tilt the frequency distribution of the average u lratio of the cyclones contains two significant peaks and a long tail at high u lratio although discrete categories of cyclones have not been identified the cyclones comprising the peaks and tail have characteristics that have been shown to be consistent with the type a b and c cyclones of the threefold classification scheme using the thresholds in average u lratio determined from the frequency distribution type a b and c cyclones account for 30 38 and 32 of the total number of cyclones respectively cyclones with small average u l ratio are more likely to be developing cyclones attain a relative vorticity 1 2 10 4 s 1 whereas cyclones with large average u lratio are more likely to be non developing cyclones 60 of type a cyclones develop whereas 31 of type c cyclones develop type a cyclogenesis dominates in the development region east of the rockies and over the gulf stream type b cyclogenesis dominates in the region off the east coast of the usa and type c cyclogenesis is more common over the oceans in regions of weaker low level baroclinicity

a climatological assessment of intense extratropical cyclones from the potential vorticity perspective extratropical cyclones etcs are known to intensify due to three vertically interacting positive potential vorticity perturbations that are associated with potential temperature anomalies close to

post 1906 stress recovery of the san andreas fault system calculated from three dimensional finite element analysis 1 the m 7 8 1906 san francisco earthquake cast a stress shadow across the san andreas fault system inhibiting other large earthquakes for at least 75 years the duration of the stress shadow is a key question in san francisco bay area seismic hazard assessment this study presents a three dimensional 3 d finite element simulation of post 1906 stress recovery the model reproduces observed geologic slip rates on major strike slip faults and produces surface velocity vectors comparable to geodetic measurements fault stressing rates calculated with the finite element model are evaluated against numbers calculated using deep dislocation slip in the finite element model tectonic stressing is distributed throughout the crust and upper mantle whereas tectonic stressing calculated with dislocations is focused mostly on faults in addition the finite element model incorporates postseismic effects such as deep afterslip and viscoelastic relaxation in the upper mantle more distributed stressing and postseismic effects in the finite element model lead to lower calculated tectonic stressing rates and longer stress shadow durations 17 74 years compared with 7 54 years all models considered indicate that the 1906 stress shadow was completely erased by tectonic loading no later than 1980 however the stress shadow still affects present day earthquake probability use of stressing rate parameters calculated with the finite element model yields a 7 12 reduction in 30 year probability caused by the 1906 stress shadow as compared with calculations not incorporating interactions the aggregate interaction based probability on selected segments not including the ruptured san andreas fault is 53 70 versus the noninteraction range of 65 77

a pv perspective on the vertical structure of mature midlatitude cyclones in the northern hemisphere development of extratropical cyclones can be seen as an interplay of three positive potential vorticity anomalies an upper level stratospheric intrusion low tropospheric diabatically produced potential vorticity pv and a warm anomaly at the surface acting as a surrogate pv anomaly this study based on the interim ecmwf re analysis era interim dataset quantifies the amplitude of the pv anomalies of mature extratropical cyclones in different regions in the northern hemisphere on a climatological basis a tracking algorithm is applied to sea level pressure slp fields to identify cyclone tracks surface potential temperatureanomalies duandverticalprofilesofpvanomalies dpvarecalculatedatthetimeofthecyclones minimumslpinaverticalcylinderaroundthesurfacecyclonecenter tocomparethecyclones characteristics they are grouped according to their location and intensity composite dpv profiles are calculated for each region and intensity class at the time of minimum slp and during the cyclone intensification phase in the maturestage allthree anomaliesare on averagelargerfor intense thanforweak wintercyclones e g 0 6 versus 0 2 potential vorticity units pvu 1 pvu 510 26 kk g 21 m 2 s 21 at lower levels and 1 5 versus 0 5 pvu at upper levels the regional variability of the cyclones vertical structure and the profile evolution is prominent cyclones in some regionsare moresensitiveto the amplitude ofa particularanomalythanin other regions values of du and low level dpv are on average larger in the western parts of the oceans than in the eastern parts results for summer are qualitatively similar except for distinctively weaker surface du values