the poleward motion of extratropical cyclones from a potential vorticity tendency analysis abstractthe poleward propagation of midlatitude storms is studied using a potential vorticity pv tendency analysis of cyclone tracking composites in an idealized zonally symmetric moist gcm a detailed pv budget reveals the important role of the upper level pv and diabatic heating associated with latent heat release during the growth stage the classic picture of baroclinic instability emerges with an upper level pv to the west of a low level pv associated with the cyclone this configuration not only promotes intensification but also a poleward tendency that results from the nonlinear advection of the low level anomaly by the upper level pv the separate contributions of the upper and lower level pv as well as the surface temperature anomaly are analyzed using a piecewise pv inversion which shows the importance of the upper level pv anomaly in advecting the cyclone poleward the pv analysis also emphasizes the crucial role played by latent heat release in the poleward motion of the cyclone the l

mesoscale aspects of a dry intrusion within a vigorous cyclone the results of a diagnostic study using radar and satellite imagery together with surface reports and output from regional and mesoscale models are presented for an occasion of a rapidly deepening cyclone that crossed the british isles the study shows how air descended from near tropopause level in the form of mesoscale dry intrusions which appeared to overrun parts of the warm conveyor belt ahead of a surface cold front one of the dry intrusions is analysed in detail because it is thought to have led to the large changes that were observed in the character of the wide frontal rain band in some places the precipitation was entirely suppressed whilst in other places the precipitation became convective with a tornadic squall line developing although the effect of the dry intrusion was seen most clearly in the precipitation distribution as determined by radar the approach of the dry intrusion was also clearly detected in the satellite water vapour imagery and foreshadowed in the model forecasts the mesoscale model despite some limitations reproduced many of the observed mesoscale features it also provided insight into the detailed behaviour of the dry intrusion associated with the tornadic squall line it showed that the dry intrusion was characterized by a mesoscale filament of high potential vorticity pv which was extruded from the lower part of a large region of high pv near a low tropopause the extruded pv anomaly plunged to within a kilometre of the surface where it overran part of the warm conveyor belt the dry intrusion was also characterized by relatively low wet bulb potential temperature w and it led to potential instability where it overran the warm air the warm conveyor belt itself was characterized not only by a high w but also by a separate strip of high pv generated locally mainly by condensation the quality of the mesoscale model simulation gives grounds for optimism that such models are capable in principle of predicting severe mesoscale weather events when as in this case they are orchestrated by resolved larger scale dynamics

the combined effects of gulf stream induced baroclinicity and upper level vorticity on u s east coast extratropical cyclogenesis abstract the atlantic surface cyclone intensification index ascii is a forecast index that quantifies the strength of low level baroclinicity in the coastal region of the carolinas it is based on the gradient between the coldest 24 h average air temperature at cape hatteras and wilmington north carolina and the temperature at the western boundary of the gulf stream the resulting prestorm baroclinic index psbi is used to forecast the probability that a cyclone in the domain will exhibit rapid cyclogenesis the initial ascii study covered the years 1982 90 this dataset was recently expanded to cover the years 1991 2002 which doubled the number of cyclone events in the sample these additional data provide similar position and slope of the linear regression fits to the previous values and explain as much as 30 of the variance in cyclone deepening rate despite operational value the neglect of upper tropospheric forcing as a predictor in the original ascii formulation precludes explanation of a l

storm track dynamics this paper reviews the current state of observational theoretical and modeling knowledge of the midlatitude storm tracks of the northern hemisphere cool season observed storm track structures and variations form the first part of the review the climatological storm track structure is described and the seasonal interannual and interdecadal storm track variations are discussed in particular the observation that the pacific storm track exhibits a marked minimum during midwinter when the background baroclinicity is strongest and a new finding that storm tracks exhibit notable variations in their intensity on decadal timescales are highlighted as challenges that any comprehensive storm track theory or model has to be able to address physical processes important to storm track dynamics make up the second part of the review the roles played by baroclinic processes linear instability downstream development barotropic modulation and diabatic heating are discussed understanding of these processes forms the core of our current theoretical knowledge of storm track dynamics and provides a context within which both observational and modeling results can be interpreted the eddy energy budget is presented to show that all of these processes are important in the maintenance of the storm tracks the final part of the review deals with the ability to model storm tracks the success as well as remaining problems in idealized storm track modeling which is based on a linearized dynamical system are discussed perhaps on a more pragmatic side it is pointed out that while the current generation of atmospheric general circulation models faithfully reproduce the climatological storm track structure and to a certain extent the seasonal and enso related interannual variations of storm tracks in depth comparisons between observed and modeled storm track variations are still lacking

comments on the evolution and dynamical role of reduced upper tropospheric potential vorticity in intensive observing period one of fastex abstract the existence and production of reduced upper tropospheric potential vorticity rupv by heating is considered an objective technique is used that identifies anomalies of pv arising from a particular physical process here latent heat release the evolution of two rupv anomalies and a related diabatically increased lower tropospheric pv ilpv anomaly occurring during intensive observing period one of the cyclones from the fronts and atlantic storm track experiment fastex is examined using model analyses sounding data and trajectory calculations three distinct airflows are identified emanating from the ilpv anomaly each with a different evolution results show that rupv anomalies exist in the atmosphere and in a weaker form in numerical models the dynamical role of rupv anomalies is examined using a nonlinear balance pv inversion and reruns of the u k meteorological office limited area model this shows that instantaneously the flow and temperature perturbations associated with rupv an

simulations of the potential vorticity structure and budget of fronts 87 iop8 dropsonde observations in the cold fronts sampled during the joint british french fronts 87 experiment along the west coast of europe have shown that the dry and moist potential vorticity fields q d and q e respectively have significant anomalies on the mesoscale the processes associated with these anomalies during a 12 h period encompassing the observation time have been examined by simulating the q d and q e structures observed near the cold front of iop8 using the meteo france mesoscale peridot model and by developing and using an eulerian potential vorticity budget module high resolution dropsonde rawinsonde and doppler radar observations are used as verification of the simulated potential vorticity structures initial and boundary conditions are obtained from three different analysis systems the simulated potential vorticity structures are sensitive to the initial conditions because the analyses over the data sparse atlantic ocean vary significantly from one analysis system to another of the seven persistent mesoscale potential vorticity features identified in the observations five were simulated reasonably well using at least one of the initial analyses and examined with the potential vorticity budget the low level pre frontal positive q d anomaly along the length of the cold front is maintained through a balance between lagrangian source sink terms dominated by differential diabatic heating and vertical advection within the main frontal updraught this balance maintains the q d anomaly in a region of near zero q d tendency between areas of q d generation near the surface and q d destruction in the middle troposphere a mid tropospheric region of negative q e directly behind the surface cold front appears to be produced by a weak but persistent generation by the solenoid term in the region of strong humidity gradients along the back edge of the mid tropospheric cloud shield this position and the model evolution suggest that the solenoid created region of negative q e can lead to enhanced mid tropospheric updraughts through conditional symmetric instability or a combination of conditional symmetric instability and large scale forcing the magnitudes of regions of negative q d and q e on the anticyclonic side of the upper level jet decrease throughout the simulation due to horizontal momentum diffusion while a post frontal low level negative q e region is generated principally by temperature and moisture diffusion

style of atlassic tectonic deformation and geodynamic evolution of the southern tethyan margin tunisia the structure of the southern atlas fold and thrust belt of tunisia was investigated using new geologic mapping seismic reflection data together with the construction of a balanced cross section the structural architecture of the tunisian foreland consists in a mixed tectonic style with deep seated basement faults shallower decollements within sedimentary cover and salt diapirism the restoration of the cross section shows a surface shortening of 8 1 km similar to 7 3 sequential restoration of the balanced cross section has been permitted to decipher the structure and evolution of the southern tethyan margin of tunisia structural geometry and orientation of the pre existing permian to cretaceous extensional structures controlled subsequent contractional deformation within the sedimentary cover during the shortening this inherited tectonic framework controlled the development of ene trending thrust related anticlines such as the orbata and chemsi structures nw trending lateral ramp such as the gafsa and fejej faults and diapir structures as the beidha anticline the inversion of the margin can be correlated with the onset of the convergence between africa and eurasia the first phase of the orbata thrusting growth might occur in late cretaceous continuous inversion of the margin occurred during the eocene and mainly during the late miocene to present day this study underlines the predominant role of inherited basement structures acquired during the evolution of the southern tethyan margin and their influence on the geometry of the atlassic thrust belt this structural analysis provides new perspectives for future hydrocarbon exploration in this poorly explored region c 2015 elsevier ltd all rights reserved

a characteristic life cycle of upper tropospheric cyclogenetic precursors during the experiment on rapidly intensifying cyclones over the atlantic erica abstract this paper documents a characteristic life cycle of upper tropospheric precursors to surface cyclogenesis observed during the field phase of the experiment on rapidly intensifying cyclones over the atlantic erica december 1988 february 1989 this life cycle begins with the development of an elongated region of lower dynamic tropopause that forms in association with an intensifying midtropospheric jet front over central north america the elongated disturbance subsequently compacts into a more circular configuration prior to crossing the east coast of north america and frequently is associated with rapid surface cyclogenesis offshore a representative example of the life cycle outlined above is documented through a detailed case study of the upper precursor associated with the second erica intensive observation period iop 2 cyclone emphasis is placed upon i description of the tropopause structure and evolution during the upper precursor life cycle ii diagnosis of mechanisms leading to t

comparative analysis of laboratory and field tracer tests for investigating preferential flow and transport in mining waste rock abstract a comparison of different tracer tests conducted in mining waste rock from the aitik site in northern sweden is made by use of temporal moment analysis and advection dispersion modelling of experimental breakthrough curves the tracer tests were carried out in both laboratory columns and field lysimeters and the experimental conditions included both saturated and unsaturated flow ranging from being close to steady state to being highly transient the objectives were to investigate the possible occurrence of preferential flow and the transport behaviour of two tracers bromide and uranine under geochemical conditions prevailing in mining waste rock no indications of significant preferential flow were found in the laboratory columns in the field there were indications of water flowing preferentially in about 55 70 of the total water content in relatively old waste rock the tracers bromide and uranine behave differently with uranine being both retained and delayed relative to bromide these effects on uranine are most probably due to low ph conditions in parts of or along the entire length of the tracer pathway in the mining waste rock suggesting that uranine may be useful as an indicator of limited acidic zones within a larger transport domain in mining waste rock acidic zones are associated with higher pollutant generation 1997 elsevier science b v all rights reserved

liquid release tests in unsaturated fractured welded tuffs i field investigations wetting front movement flow field evolution and drainage of fracture flow paths were evaluated within the topopah spring welded tuff at yucca mountain nevada equipment and techniques were developed for in situ quantification of formation intake rates flow velocities seepage rates and volumes of fracture flow paths localized injections of liquid into a low permeability zone lpz and a high permeability zone hpz along a borehole were detected in two boreholes below the point of injection for the lpz tests water did not seep into an excavated slot that defined the lower boundary of the test bed and the liquid intake rate under constant head conditions was observed to steadily decrease by two orders of magnitude in the hpz liquid intake rates under constant head conditions were significantly higher and did not exhibit a strong systematic decline hpz tests were also conducted under a range of constant flow conditions slot seepage rates showed intermittent responses and the percentage of injected water recovered in the slot increased as each test progressed a maximum of 80 of the injected water was recovered during high rate injection tests the flow path volumes were found to increase during the course of each hpz test the data collected during these field tests has provided useful information for developing an understanding of liquid flow in unsaturated fractured welded tuff it has also provided a basis for quantitative comparisons with numerical simulations of liquid release experiments as demonstrated in a companion paper j hydrol 256 2002

surface flux regulation of the coupling between cumulus convection and baroclinic waves abstract the authors examine the role of convection in the dynamics of eddy life cycles through numerical experiments using initial states that are baroclinically and conditionally unstable in midlatitudes the location of wave induced convection and its influence on the growing wave depends on how strongly the wave is coupled to the lower boundary through surface fluxes for all three convective schemes used here emanuel modified grell modified kuo convective destabilization is favored in the wave s warm sector when there are no surface fluxes included in the simulation and in the cold sector when there are convection is also shallower when it occurs in the cold sector though still precipitating for simulations using emanuel convection the relatively shallow convection plays a central role in a water cycle wherein 1 evaporation gives moisture to the cold sector s boundary layer 2 convection pumps some of the moisture into the lower troposphere above the boundary layer 3 the large scale circ

recent spatial and temporal changes in the stress regime along the southern tunisian atlas front and the gulf of gabes new insights from fault kinematics analysis and seismic profiles tectonic deformations in the southern atlassic front of tunisia saft and the gulf of gabes result from the nubia eurasia convergence this study based on the inversion of geologically determined fault slip vectors presents evidences for spatial and temporal changes in the stress state fault kinematics analyses reveal a temporal change in states of stress during the late cenozoic a paleostress miocene pliocene state is characterized by a regional compressional tectonic regime with a mean n134 09 e trending horizontal maximum stress axis 1 a modern quaternary to present day state of stress also corresponds to compressional tectonic regime with a regionally mean n05 10 e trending horizontal 1 the saft corresponds to two distinct domains a far foreland atlassic front related to contractional deformation associated with southward propagate thrusting and eastward the gulf of gabes characterized by normal component nw to wnw trending faults at the crustal margin scale probably related with a transtensional tectonic regime we propose that the spatial and temporal changes in the stress during the miocene pliocene and quaternary may result from the geodynamic evolution of the tunisian atlas in relation to the rotation of corsica sardinia blocks and the separation of the sicilian continental lithosphere from the ionian oceanic lithosphere these temporal and spatial stress changes along the saft and the gulf of gabes are probably the engine behind the moderate seismicity leading at the same time to a reactivation of the inherited major structures created during the evolution of the southern tethyan margin

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

an application of potential vorticity inversion to improving the numerical prediction of the march 1993 superstorm in this study a methodology is proposed to improve the model initial conditions based on available surface temperature observations from ships buoys and drifters it is tested with the numerical prediction of the 12 14 march 1993 superstorm that is initialized at its incipient stage over the gulf of mexico in this methodology the authors make use of the piecewise potential vorticity pv inversion technique and treat the temperature errors at the lowest level as a surrogate pv anomaly after inverting the wind and mass perturbations from the surface thermal anomaly and its pertinent interior pv anomaly a three dimensional dynamically consistent set of errors are obtained and added to the model initial conditions to improve the representation of the lower troposphere over the data sparse ocean it is found that the numerical model prediction initialized with the modified initial conditions exhibits significant improvements in the early rapid deepening and the track of the superstorm over ocean the development of a prefrontal squall line and the central sea level pressure traces during the life cycle of the cyclone as verified against observations these results show that the methodology proposed is promising in improving the representation of lower tropospheric meteorological variables in the model initial conditions based on available surface observations over data sparse regions

dynamical aspects of the life cycle of the winter storm lothar 24 26 december 1999 dynamical aspects of the life cycle of the winter storm lothar 24 26 december 1999 are investigated with the aid of the european centre for medium range weather forecasts analysis data and mesoscale model simulations neither of these datasets capture the full amplitude of the observed extreme pressure fall and surface wind speeds but they do help identify a range of key dynamical and physical features that characterize the development of this unusual event the analysis and interpretation is primarily based upon the evolution of the lower and upper level potential vorticity pv field complemented by three dimensional trajectory calculations lothar originated in the western atlantic and travelled as a shallow low level cyclone of moderate intensity towards europe this translation took place below and slightly to the south of a very intense upper level jet and was accompanied by continuous and intense condensational heating that sustained a pronounced positive low level pv anomaly not unlike the concept of a diabatic rossby wave no significant pv anomalies were evident at the tropopause level during this early phase of the life cycle the surface cyclone intensified rapidly when the shallow cyclone approached the jet stream axis the circulation induced by the diabatically produced low tropospheric pv anomaly on steeply sloping isentropic surfaces that transect the intense upper level jet contributed significantly to the rapid formation of a narrow and deep tropopause fold this stratospheric pv anomaly virtually merged with the diabatically produced ephemeral pv feature to form a vertically aligned tower of positive pv at the time of maximum storm intensity a sensitivity study with a dry adiabatic hindcast simulation shows no pv tower configuration and only a very weak surface development and confirms the primary importance of the cloud diabatic heating for the tropopause fold formation and the rapid bottom up intensification of lothar a comparison of the anomalously high atlantic sea surface temperatures in december 1999 with the water vapour source regions for the latent heat release that accompanied the rapid intensification phase of lothar shows a close relationship this is of importance when discussing the possible implications of climate variability and change on the development of north atlantic winter storms copyright 2002 royal meteorological society

analysis of the slope of isentropic surfaces and its tendencies over the north atlantic the maintenance of baroclinicity along mid and high latitude storm tracks is a matter of ongoing debate using an isentropic framework a novel diagnostic based on the tendency equation for the slope of isentropic surfaces a measure of the potential for baroclinic development is presented the tendency comprises contributions from dynamic processes latent heat release radiation and subgrid scale turbulence which incorporates the effect of sensible heat fluxes a climatology of these tendencies over the north atlantic is compiled for the winters of 2009 and 2010 it is found that adiabatic tilting flattens the isentropic surfaces reflecting the action of growing baroclinic cyclones this tendency is balanced climatologically by the generation of slope by diabatic processes in the lower troposphere the most intense diabatic increase of slope is found along the oceanic frontal zone associated with the gulf stream and at higher latitudes in the labrador sea the nordic seas and the barents sea latent heat release and sensible heat fluxes both contribute substantially in these regions a quantitative analysis of cold air outbreaks emphasizes their important role in restoring the slope in the lower troposphere over the gulf stream region and off the sea ice edge at high latitudes in the upper troposphere latent heat release due to cloud microphysical processes is the dominant mechanism maintaining the slope

effect of unsaturated flow modes on partitioning dynamics of gravity driven flow at a simple fracture intersection laboratory study and three dimensional smoothed particle hydrodynamics simulations in this work we study gravity driven flow of water in the presence of air on a synthetic surface intersected by a horizontal fracture and investigate the importance of droplet and rivulet flow modes on the partitioning behavior at the fracture intersection we present laboratory experiments three dimensional smoothed particle hydrodynamics sph simulations using a heavily parallelized code and a theoretical analysis the flow rate dependent mode switching from droplets to rivulets is observed in experiments and reproduced by the sph model and the transition ranges agree in sph simulations and laboratory experiments we show that flow modes heavily influence the bypass behavior of water flowing along a fracture junction flows favoring the formation of droplets exhibit a much stronger bypass capacity compared to rivulet flows where nearly the whole fluid mass is initially stored within the horizontal fracture the effect of fluid buffering within the horizontal fracture is presented in terms of dimensionless fracture inflow so that characteristic scaling regimes can be recovered for both cases rivulets and droplets the flow within the horizontal fracture transitions into a washburn regime until a critical threshold is reached and the bypass efficiency increases for rivulet flows the initial filling of the horizontal fracture is described by classical plug flow meanwhile for droplet flows a size dependent partitioning behavior is observed and the filling of the fracture takes longer for the case of rivulet flow we provide an analytical solution that demonstrates the existence of classical washburn flow within the horizontal fracture

a lagrangian based analysis of extratropical cyclones ii a detailed case study a detailed case study analysis is undertaken of the occurrence of significant coherent ensembles of trajectories cets that accompany atlantic cyclogenesis the approach is based upon the lagrangian based analysis scheme introduced in part i the analysis reveals the existence of several distinct moist ascending and dry descending cets two types of moist ascending cets associated with strong condensational processes ascend from the boundary layer of the warm sector either in the close vicinity of the cyclone centre or in the trailing cold frontal region the latter is the main contributor to the precipitation along the cold front during the early phase of the development another type of moist cets distinguished by maximum water vapour flux travels at low levels through the warm sector and ascends to mid tropospheric levels in the warm frontal region where it produces strong precipitation around the time of maximum storm intensity cets with an upper level origin are linked to the classical dry intrusion different cets correspond to strong descent of upper level tropospheric air that penetrated to the lower troposphere the movement of stratospheric air toward the centre of the maturing cyclone and an event of stratosphere to troposphere exchange upstream of the upper level trough two different visualizations of time sequences of the moist ascending cets indicate that they represent well defined flexible tubes or airstreams that exist over a time period comparable with the duration of the main cyclone intensification they provide a translating flexible but coherent river bed for the quasi continuous ascent of moist boundary layer air to the upper troposphere these tubes are akin to the concept of warm conveyor belts and the present analysis method objectively diagnoses their geometrical and physical characteristics and potential vorticity pattern some consideration is also given to the relationship of cets and tropospheric rivers and to possible shortcomings of the approach

active oblique ramp faulting in the southern tunisian atlas abstract the gafsa fault is the longest and most active structure of the fold and thrust belt achieving southeastward propagation of the atlas belt of eastern north africa onto the saharan platform the gafsa fault is a 75 km long dextral oblique basement fault ramp that poses a sizable challenge in earthquake hazard assessment because the post paleozoic sedimentary cover is decoupled from its basement above the basement fault in this study we combine seismic lines interpretation tectonic geomorphology and paleoseismological investigations to assess the level of seismic hazard of this fault and evaluate its role in the geodynamic framework of the central mediterranean we show that despite a moderate instrumental and historical seismicity the fault has produced m 6 earthquakes with a return period of ca 500 5000 years during the late quaternary the latest large event having produced a surface rupture on the fault occurred around 8000 yr bp suggesting an m 6 earthquake is overdue on the fault the fault has a minimum reverse component of slip rate of 0 21 0 34 mm yr over the past 50 ka the occurrence of m 7 paleoearthquakes on the fault may be suspected but not established such very strong earthquakes would require transient coseismic linkage of the buried basement fault with the overlying listric fault ramping off the decollement layer the level of seismic hazard may be underestimated on the gafsa fault indeed given the geometry of the basement cover fault system a number of earthquakes generated in the basement would have led to coseismic surface folding instead of to surface rupture the gafsa fault is a major structure accommodating eastward extrusion spreading of the atlas belt onto the saharan and pelagian plateforms above the retreating ionian lithospheric slab

yucca mountain earth science issues at a geologic repository for high level nuclear waste abstract the nation has over 40 000 metric tonnes mt of nuclear waste destined for disposal in a geologic repository at yucca mountain in this review we highlight some of the important geoscience issues associated with the project and place them in the context of the process by which a final decision on yucca mountain will be made the issues include understanding how water could infiltrate the repository corrode the canisters dissolve the waste and transport it to the biosphere during a 10 000 year compliance period in a region the basin and range province that is known for seismic and volcanic activity although the site is considered to be dry a considerable amount of water is present as pore waters and as structural water in zeolites the geochemical environment is oxidizing and the present repository design will maintain temperatures at greater than 100 c for thousands of years geoscientists in this project are challenged to make unprecedented predictions about coupled thermal hydrol

approximate boundaries between different flow regimes in fractured rocks recent studies have shown how water films at near zero matric potentials on fracture surfaces could permit fast flow in unsaturated fractures the present work is aimed at delineating the ranges of conditions necessary to permit film flow the approximate matric potential needed to permit thickening of water films on fracture surfaces was estimated through correlating air entry matric potentials and permeabilities for a wide range of porous media an upper matric potential limit associated with saturating the fracture was related to the fracture aperture these two limits one dependent on matrix permeability and the other on fracture aperture delineate the matric potential range within which thick water films develop on fracture surfaces rocks with matrix permeabilities less than 10 14 m2 and fractures with apertures greater than 30 m permit some matric potential range over which thick water films can form highly transmissive films can develop on fracture surfaces only under near zero matric and pressure potentials

gravity constraints on the structure of the northern margin of tunisia implications on the nature of the northern african plate boundary summary bouguer gravity data were analysed to determine the general crustal and upper mantle structure in northern tunisia residual gravity anomalies were determined by removing the gravitational effect of crustal thickness variations imaged by regional seismic experiments residual gravity anomalies contain short wavelength anomalies superimposed on a long wavelength component that decreases in amplitude northward towards the tunisian coastline an edge enhancement analysis e g enhanced analytic signals of the short wavelength anomalies suggests a previously unknown east west trending gravity anomaly south of 37 n with source depths of between 3 and 7 km modelling of residual and bouguer gravity anomalies indicate that there are two possible solutions for the residual gravity decrease in northern tunisia 1 thickening of cenozoic and mesozoic sediments north of a strike slip fault or 2 a crustal and uppermantle low density zone interpreted as being crustal material of the remnant subducted african plate the latter result is favoured based on seismic tomographic images of the mediterranean region which implies that subducting material exists under the african coast geological interpretations suggesting that the tell atlas may be a thrust wedge accreted by underplating of the african continental crust and seismic refraction models indicating a thinning of sediments in northern tunisia the east west trending gravity anomalies south of 37 n correspond to an important structural feature that may be related to either a structural boundary e g a transform fault or subduction beneath the african plate

the microphysical building blocks of low level potential vorticity anomalies in an idealized extratropical cyclone abstractdiabatically generated low level potential vorticity pv anomalies in extratropical cyclones enhance near surface winds and influence the cyclone s development positive and negative pv anomalies in the warm frontal region of an extratropical cyclone simulated with an idealized moist baroclinic channel model are investigated to identify the microphysical processes that produce them using a novel method based on backward trajectories from the pv anomalies the contribution of different microphysical processes to the formation of the anomalies is quantified it is found that for each anomaly typically one specific microphysical process takes the leading role in its diabatic generation a large but rather weak low and midlevel positive anomaly is produced by depositional growth of ice and snow two smaller but stronger positive anomalies at lower levels are generated mainly by in cloud condensational heating at the warm front and below cloud rain evaporation and snow melting 200 km farther nor

rossby wave packets on the midlatitude waveguide a review abstractrossby wave packets rwps are rossby waves for which the amplitude has a local maximum and decays to smaller values at larger distances this review focuses on upper tropospheric transient rwps along the midlatitude jet stream their central characteristic is the propagation in the zonal direction as well as the transfer of wave energy from one individual trough or ridge to its downstream neighbor a process called downstream development these rwps sometimes act as long range precursors to extreme weather and presumably have an influence on the predictability of midlatitude weather systems the paper reviews research progress in this area with an emphasis on developments during the last 15 years the current state of knowledge is summarized including a discussion of the rwp life cycle as well as rossby waveguides recent progress in the dynamical understanding of rwps has been based in part on the development of diagnostic methods these methods include algorithms to identify and track rwps

the integral role of a diabatic rossby vortex in a heavy snowfall event abstract on 24 25 february 2005 a significant east coast cyclone deposited from 4 to nearly 12 in 10 30 cm of snow on parts of the northeastern united states the heaviest snowfall and most rapid deepening of the cyclone coincided with the favorable positioning of an upper level short wave trough immediately upstream of a preexisting surface cyclone the surface cyclone in question formed approximately 15 h before the heaviest snowfall along a coastal front in a region of frontogenesis and heavy precipitation the incipient surface cyclone subsequently intensified as it moved to the northeast consistently generating the strongest convection to the east northeast of the low level circulation center the use of potential vorticity pv inversion techniques and a suite of mesoscale model simulations illustrates that the early intensification of the incipient surface cyclone was primarily driven by diabatic effects and was not critically dependent on the upper level wave these facts taken in conjunct

convergent flow observed in a laboratory scale unsaturated fracture system 1 an experiment was designed to observe water flow in a simple analogue fractured rock network the fracture network was modeled by the gaps between an array of limestone blocks whose permutations generated different realizations of the network three out of five of these realizations displayed flow convergence in contrast to that predicted by porous continuum models such convergence occurs because fracture intersections act as capillary barriers that integrate or focus flow within the network

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

seismotectonics of the lower cheliff basin structural background of the el asnam algeria earthquake the 1980 el asnam earthquake should be understood within its tectonic environment a seismotectonic map of the lower cheliff basin scale 1 500 000 has been synthesized from known geologic tectonic and seismological work on the region and from satellite photos the data set was integrated by a computer in order to handle different scales and projections several important tectonic features divide the region into 5 domains active faults and recent folds are consistent with a nnw sse direction of compression the cheliff basin is limited to the south by the relizane fault the basin is also crossed by three broken folds the eastern one being the one associated with the el asnam fault historical and instrumental seisinicity seems to be located at both ends of relizane fault it is suggested that the sites corresponding to folds and reverse faulting crossing the basin are relevant to seismic risk a simple tectonic model is proposed

the linkage between the warm and the cold conveyor belts in an idealized extratropical cyclone abstractthis study continues the investigation of airstreams in idealized moist baroclinic waves and addresses the formation of the cold conveyor belt ccb its linkage to the warm conveyor belt wcb and their impact on the development of a midlatitude cyclone the ccb is identified as a coherent bundle of trajectories characterized by weak ascent and a strong increase of potential vorticity pv along the flow in contrast to the wcb defined as the trajectories with maximum ascent the authors illuminate the role of the two conveyor belts in the formation of two strong pv anomalies that form in the upper wcb negative pv anomaly and lower troposphere ccb positive pv anomaly respectively and thereby establish a link between these airstreams and relevant aspects of the dynamics of extratropical cyclones the ccb moves close to the surface along the colder side of the bent back front and experiences a pv increase as it passes below a region of maximum latent heat release at midtropospheric level

urban geological mapping geotechnical data analysis for rational development planning urban geology provides information on urban geologic environments as a scientific basis for planners and engineers for rational land use planning and urban development such mapping can be classified in terms of purpose content and scale in this study procedure for preparation of engineering geological mapping in tunis city tunisia is given as a case study the main restricting factors for urban development such as lithology topography slope seismotectonic water table depth flooding susceptibility and seismic induced effects were considered in the preparation of maps all these information layers were manipulated using the geographic information system gis and they were then combined to produce uniform engineering geological maps results are illustrated as a suitability map for construction in the study area consequently the study area was categorized into four different zones as 1 a high region with potential risk of superficial perturbation 2 a low and flat zone with flooding risk 3 a low zone with flooding and probability of sliding risk 4 a region with mud levels and settlement risk

liquid phase structure within an unsaturated fracture network beneath a surface infiltration event field experiment 1 we conducted a simple field experiment to elucidate structure i e geometry of the liquid phase water resulting from ponded infiltration into a pervasive fracture network that dissected a nearly impermeable rock matrix over a 46 min period dyed water was infiltrated from a surface pond while electrical resistance tomography ert was employed to monitor the rapid invasion of the initially dry fracture network and subsequent drainage we then excavated the rock mass to a depth of 5 m mapping the fracture network and extent of dye staining over a series of horizontal pavements located directly beneath the pond near the infiltration surface flow was dominated by viscous forces and the fracture network was fully stained with increasing depth flow transitioned to unsaturated conditions and the phase structure became complicated exhibiting evidence of fragmentation preferential flow fingers irregular wetting patterns and varied behavior at fracture intersections ert images demonstrate that water spanned the instrumented network rapidly on ponding and also rapidly drained after ponding was terminated estimates suggest that our excavation captured from 15 to 1 or less of the rock volume interrogated by our infiltration slug and thus the penetration depth from our short ponding event could have been quite large

seepage into an underground opening constructed in unsaturated fractured rock under evaporative conditions 1 liquid release tests performed in boreholes above an underground opening constructed in unsaturated fractured rock are used in this study to evaluate seepage into a waste emplacement drift evidence for the existence of a capillary barrier at the ceiling of the drift is presented based on field observations including spreading of the wetting front across the ceiling and water movement up fractures exposed in the ceiling before seepage begins the capillary barrier mechanism has the potential to divert water around the opening resulting in no seepage when the percolation flux is at or below the seepage threshold flux liquid release tests are used to demonstrate that a seepage threshold exists and to measure the magnitude of the seepage threshold flux for three test zones that seeped the seepage data are interpreted using analytical techniques to estimate the test specific strength of the rock capillary forces 1 that prevent water from seeping into the drift evaporation increases the seepage threshold flux making it more difficult for water to seep into the drift and producing artificially inflated 1 values with adjustments for evaporation the minimum test specific threshold is 1600 mm yr with a corresponding 1 value of 0 027 m

infiltration flux distributions in unsaturated rock deposits and their potential implications for fractured rock formations 1 although water infiltration through unconsolidated rocks and fractured rock formations control flow and transport to groundwater spatial distributions of flow paths are poorly understood infiltration experiments conducted on packs of rocks showed that a well constrained distribution of fluxes develops despite differences in rock type angular diabase and sandstone and subangular serpentinite rock size 30 to 200 mm and packing up to 42 rock layers fluxes stabilize into a geometric exponential distribution that keeps about half of the system depleted of flow retains a small fraction of high flow regions and has a characteristic scale determined by the rock size modification of a statistical mechanical model shows that gravity directed random flow paths evolve to the observed flux distribution and that it represents the most probable distribution key similarities between infiltration in rock deposits and fractured rock formations indicate that the geometric flow distribution may also apply in the latter systems

tropopause folds and cross tropopause exchange a global investigation based upon ecmwf analyses for the time period march 2000 to february 2001 1 a new methodology is proposed to identify folds of the dynamical tropopause taken as the 2 potential vorticity pv units pvu isosurface from global analysis data sets from the european centre for medium range weather forecasts ecmwf it consists of a three dimensional subdivision of the atmosphere into stratospheric and tropospheric parts and a subsequent examination of multiple tropopause crossings in vertical profiles of the analyses the method is applied to a 1 year period starting in march 2000 seasonal mean fold frequency distributions show that folds occur preferentially in the subtropics with maximum frequencies of about 30 pronounced maxima are located in the subtropical bands that extend from 20 e to 120 e on both hemispheres during summer generally subtropical folds are comparatively shallow deep folds occur most frequently in midlatitudes during winter over eastern north america and the western north atlantic with maximum frequencies of about 1 detailed investigation of the relationship between individual folds and cross tropopause exchange events reveals that on the average individual folds in the extratropics are associated with larger exchange mass fluxes compared to the subtropics however due to the much higher frequency of subtropical folds the percentage of exchange events that are associated with tropopause folds is larger near 20 40 latitude 50 70 than further poleward 20 30 during winter and 10 20 during summer this indicates that tropopause folds are the key feature for cross tropopause exchange in the subtropics whereas in the extratropics other tropopause structures are at least of equal importance

role of salient potential vorticity elements in an event of frontal wave cyclogenesis extratropical cyclogenesis is usually accompanied by both an upper level trough and a surface front with its cloud diabatic accoutrements in the present study these distinctive structures are interpreted as salient elements of the atmosphere s potential vorticity pv distribution and their role examined for one particular event of frontal wave cyclogenesis the strategy adopted is a form of diagnosis by pv dismemberment it entails adopting a successful forecast with a limited area model as a surrogate for the actual event and then performing a sequence of simulations with modified initial conditions that correspond in each case to the removal of one or more of the salient pv elements this approach provides an assessment of the relative significance of the individual elements permits an insightful comparison of various extant theories of cyclogenesis and pinpoints the particular pv elements influencing the event s predictability it is shown that the replication of the simulated cyclone requires an adequate representation both of specific fine scale pv features at tropopause levels and of the diabatically maintained low level pre frontal pv band thus a tenable theory of cyclogenesis that incorporates this not atypical event should both recognize and help clarify the dependence of cyclogenesis upon the relative locations movement scales and structures of the aforementioned salient pv elements

a model aided study of the origin and evolution of the anomalously high potential vorticity in the inner region of a rapidly deepening marine cyclone abstract high spatial and temporal resolution fields generated by a mesoscale prediction model are used to study a case of rapid marine cyclogenesis 26 mb in 12 h within the context of potential vorticity pv thinking the case which occurred on 23 february 1987 near the east coast of the united states was well simulated by the model as was verified by ship reports and satellite imagery three components of the cyclone were investigated 1 a surface thermal anomaly or surrogate pv anomaly 2 a low level diabatically produced pv anomaly in and near the frontal cloud band and 3 a dry pv anomaly of upper tropospheric and lower stratosphoric origin trajectory tracing revealed that the surface thermal anomaly was caused primarily by northward transport of warm air into the central region of the low although surface sensible heat flux also contributed to the warm anomaly a sensitivity experiment run with the flux withheld showed that it had little impact on the depth of the storm furthermore

reexamining the cold conveyor belt abstract despite the popularity of the conveyor belt model for portraying the airflow through midlatitude cyclones questions arise as to the path of the cold conveyor belt the lower tropospheric airflow poleward of and underneath the warm front some studies beginning with carlson s analysis of the eastern u s cyclone of 5 december 1977 depict the cold conveyor belt moving westward reaching the northwest quadrant of the storm turning abruptly anticyclonically rising to jet level and departing the cyclone downstream hereafter the anticyclonic path other studies depict the cold conveyor belt reaching the northwest quadrant turning cyclonically around the low center and remaining in the lower troposphere the cyclonic path to clarify the path of the cold conveyor belt the present study reexamines carlson s analysis of the cold conveyor belt using an observational and mesoscale numerical modeling study of the 5 december 1977 cyclone this reexamination raises several previously unappreciated

interaction of potential vorticity anomalies in extratropical cyclogenesis part i static piecewise inversion the relative importance of various potential vorticity pv perturbations and their mutual interactions associated with the superstorm of 12 14 march 1993 are investigated by applying a piecewise pv inversion diagnostic system to a 36 h simulation of the storm it is shown that the contributions from all pv anomalies to the surface development increase with time although their relative significance varies during the rapid deepening stage in general the upper level dry pv anomalies contribute the most to the rapid deepening of the storm followed in order by the lower level thermal anomaly and latent heat release comparing the pv anomalies and their inverted circulations reveals that there exists a favorable phase tilt between the upper and lower level anomalies that allows lower and upper level mutual interactions in which the circulations associated with the upper level pv anomalies enhance the lower level anomalies and vice versa in addition to the vertical interactions lateral interactions are also present among the upper level pv anomalies and the background flow it is also found that the background flow advection dominates the vortex vortex and vortex background flow interactions in the deepening of the storm the vortex vortex interactions of the two upper level positive pv anomalies cause the negative tilt of the main upper level trough during the rapid deepening period

potential vorticity anomalies of the lowermost stratosphere a 10 yr winter climatology abstract inspection of the potential vorticity pv distribution on isentropic surfaces in the lowermost stratosphere reveals the ubiquitous presence of numerous subsynoptic positive pv anomalies to examine the space time characteristics of these anomalies a combined identification and tracking tool is developed that can catalog each individual anomaly s effective amplitude location overall spatial structure and movement from genesis to lysis a 10 yr winter climatology of such anomalies in the northern hemisphere is derived for the period 1991 2001 based upon the 40 yr european centre for medium range weather forecasts ecmwf re analysis era 40 the climatology indicates that the anomalies are frequently evident above high topography and in a quasi annular band at about 70 n are long lived days to weeks and that their effective amplitude is typically 2 pv units pvu higher than that of the ambient environment in addition the derived climatologies and associated composites pose questions

role of moist processes in the tracks of idealized midlatitude surface cyclones abstractthe effects of moist processes on the tracks of midlatitude surface cyclones are studied by performing idealized mesoscale simulations in each simulation a finite amplitude surface cyclone is initialized on the warm air side of a zonal baroclinic jet for some simulations an upper level cyclonic anomaly upstream of the surface cyclone is also added initially sensitivities to the upper level perturbation and moist processes are analyzed by both performing a relative vorticity budget analysis and adopting a potential vorticity pv perspective whatever the simulation there is a systematic crossing of the zonal jet by the surface cyclone occurring after roughly 30 h a pv inversion tool shows that it is the nonlinear advection of the surface cyclone by the upper level pv dipole which explains the cross jet motion of the surface cyclone the simulation with an initial upper level cyclonic anomaly creates a stronger surface cyclone and a more intense upper level pv dipole than the simulation with

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