compressive and tensile failure of inclined well bores and determination of in situ stress and rock strength in this paper we investigate the occurrence of compressive and tensile failures of arbitrarily inclined well bores under a wide variety of stress conditions the principal assumptions in this analysis are that the rock is isotropic and that it deforms elastically to the point of failure as has been shown by previous investigators for a given stress state and well bore orientation it is straightforward to predict the orientation of the failures around the well bore as well as whether failure is likely to occur depending on such parameters as rock strength and borehole fluid pressure however as the stress state is almost never known in situ we demonstrate how observations of compressive and tensile wall failures in inclined holes can be used to constrain in situ stress orientations and magnitudes if there are independent data on the magnitude of the least principal stress from either leak off or microfrac tests and on the formation pore pressure we further demonstrate how once the stress state is determined it is possible to assess both an upper bound on the effective in situ rock strength and the degree to which increasing the borehole fluid pressure or mud weight can reduce the likelihood of borehole failure through application of this methodology to an inclined well bore in an area of complex faulting in the gulf of mexico we illustrate how it is possible to utilize observations of borehole failures to determine the magnitude and orientation of the stress tensor in areas such as offshore sedimentary basins where drilling inclined well bores is quite common

stress perturbations associated with active faults penetrated by boreholes possible evidence for near complete stress drop and a new technique for stress magnitude measurement detailed studies of stress induced wellbore breakouts in wells drilled through active faults reveal stress field discontinuities that are apparently associated with recent fault movements these discontinuities are expressed as localized rotations in wellbore breakout orientation in the vicinity of the fault penetrated by the borehole this phenomenon is observed in a variety of tectonic environments and rock types utilizing cases where relatively complete knowledge of the horizontal principal stresses is available from in situ measurements we use three dimensional dislocation modeling to demonstrate that these discontinuities can be explained as the superposition of a reference stress state and a perturbation caused by movement on preexisting faults case studies from normal strike slip and reverse faulting stress states indicate that nearly complete stress drop is required to match the observed breakout orientation anomalies hydraulic fracturing data independently confirm the occurrence of near complete stress drop on some faults penetrated by drilling modeling of the observed interactions between breakouts and fractures can also be used to obtain information about the magnitude of in situ stress

sting jets in simulations of a real cyclone by two mesoscale models the existence of sting jets as a potential source of damaging surface winds during the passage of extratropical cyclones has recently been recognized however there are still very few published studies on the subject furthermore although it is known that other models are capable of reproducing sting jets in the published literature only one numerical model the met office unified model metum has been used to numerically analyze these phenomena this article aims to improve our understanding of the processes that contribute to the development of sting jets and show that model differences affect the evolution of modeled sting jets a sting jet event during the passage of a cyclone over the united kingdom on 26 february 2002 has been simulated using two mesoscale models namely the metum and the consortium for small scale modeling cosmo model to compare their performance given the known critical importance of vertical resolution in the simulation of sting jets the vertical resolution of both models has been enhanced with respect to their operational versions both simulations have been verified against surface measurements of maximum gusts satellite imagery and met office operational synoptic analyses as well as operational analyses from the ecmwf it is shown that both models are capable of reproducing sting jets with similar though not identical features through the comparison of the results from these two models the relevance of physical mechanisms such as evaporative cooling and the release of conditional symmetric instability in the generation and evolution of sting jets is also discussed

structure of a frontal cyclone a diagnostic study of a mid latitude cyclone has been carried out using routinely available numerical weather prediction model products and imagery the cyclone was intense but not exceptionally so and the results are believed to have some generality the detailed description of the cyclone structure just before it began to deepen rapidly integrates concepts from a number of researchers into a common framework a dominant feature of the cyclone close to its centre was the cloud head a region of cloud with a sharp convex outer edge which formed poleward of the main polar front cloud band the cloud head was caused by two flows that entered it from the east ascending and fanning out within it one flow the cold conveyor belt brought low wet bulb potential temperature w air back into the cloud head from low levels ahead of the warm front the other flow was due to high w air that peeled off from the base of the main warm sector airflow i e part of the warm conveyor belt and travelled in the boundary layer back towards the cyclone centre first undercutting dry air that had earlier descended from the upper troposphere called a dry intrusion and then ascending at the upper boundary of the cloud head above the cold conveyor belt the transverse circulation that gave the ascent within the cloud head also led to the cold front fracturing along its length into two separate sharp surface cold fronts with a more diffuse frontal region in between frontal fracture the two sharp surface cold fronts were associated with narrow cold frontal rainbands line convection one of the line convection segments forming the southern edge of the cloud head the overrunning of the dry intrusion in the region of the frontal fracture led to a structure known as a split front in which an upper level humidity front began to run ahead of the position of the surface cold front a feature of the cyclone at this intermediate stage in its evolution was that a large proportion of the precipitation was being generated by ascent of relatively cold air the cold conveyor belt in the cloud head as part of the thermally indirect circulation at the left exit of a developing secondary upper level jet

wind profiler observations of a sting jet some of the most damaging surface winds experienced in midlatitude cyclonic storms have been attributed to a phenomenon known as a sting jet previous studies have deduced how sting jets develop from their midtropospheric origin but there have been no direct observations of these wind features in the midtroposphere during windstorm jeanette on 27 october 2002 the tip of the storm s cloud head passed over a vhf wind profiler at aberystwyth wales allowing the structure of a sting jet to be measured with high spatial and temporal resolution these observations showed a multiple slantwise structure to the sting jet region with two tails of increased winds that persisted after the passing of the cloud head aloft simulations by the met office unified model um showed that the slantwise structure followed w surfaces and that the sting jet descended along surfaces as it passed over the uk accelerating and drying during its descent the horizontal and vertical scales of the observed structures are compatible with slantwise convection releasing conditional symmetric instability within the cloud head further observations of the sting jet were obtained by a uhf wind profiler at cardington in eastern england where the sting jet had merged with the cold conveyor belt circulating around the storm an unstable temperature profile in the lowest kilometre over cardington enabled damaging gusts of strong winds to be brought to the surface in convective plumes however this strong vertical mixing was not represented correctly in the um copyright 2009 royal meteorological society

constraining the full stress tensor from observations of drilling induced tensile fractures and leak off tests application to borehole stability and sand production on the norwegian margin abstract understanding the interaction between rock strength in situ stress and engineering practice allows one to minimize wellbore failures by designing optimally stable borehole trajectories and appropriate mud weights we utilize an interactive software system stress and failure of inclined boreholes sfib peska zoback 1996 to illustrate how observations of drilling induced compressive and tensile wellbore failures in vertical and inclined wellbores can be integrated with other routinely available information to yield an estimate of the full stress tensor we further illustrate how such information allows one to place bounds on in situ effective rock strength we consider a deviated well in the visund oil field on the flanks of the viking graben along the norwegian margin a good quality electrical imaging log revealed drilling induced tensile wall fractures in an orientation consistent with other observations of stress orientation in the region interpretation of these fractures indicates that the maximum horizontal stress is 72 6 5 mpa at an azimuth of 100 10 no breakouts were detectable in the well indicating that the uniaxial compressive rock strength is greater than approximately 19 mpa we demonstrate how we utilized this information to design an optimally stable wellbore trajectory to minimize sand production

the sting at the end of the tail damaging winds associated with extratropical cyclones strong surface winds often accompany the low level jets that occur along the cold fronts of extratropical cyclones but there is evidence that the strongest surface winds occur in a distinctly different part of a certain class of cyclone the most damaging extratropical cyclones go through an evolution that involves the formation of a bent back front and cloud head separated from the main polar front cloud band by a dry slot when the cyclone attains its minimum central pressure the trailing tip of the cloud head bounding the bent back front forms a hook which goes on to encircle a seclusion of warm air the most damaging winds occur near the tip of this hook the sting at the end of the tail observations of the great storm of october 1987 in south east england are re examined in some detail to study this phenomenon the cloud head is shown to have a banded structure consistent with the existence of multiple mesoscale slantwise circulations air within these circulations leaves the hooked tip of the cloud head and enters the dry slot much faster than the rate of travel of the cloud head tip implying rapid evaporation and diabatic cooling immediately upwind of the area of damaging surface winds the circumstantial evidence from the observational study leads one to hypothesize that the mesoscale circulations and the associated evaporative heat sinks may play an active role in strengthening the damaging winds regardless of how important this role may be the evolution of the cloud pattern seen in satellite imagery is a useful tool for nowcasting the occurrence and location of the worst winds copyright 2004 royal meteorological society

the role of mesoscale instabilities in the sting jet dynamics of windstorm tini sting jets sj occur as an additional region of low level strong winds in some shapiro keyser type extra tropical cyclones while sjs are widely accepted as being distinct from the warm and cold conveyor belts the mechanisms responsible for their occurrence are still not fully understood here we determine the relative importance of the release of mesoscale instabilities and synoptic scale cyclone dynamics so addressing an area of current debate numerical weather prediction simulations of a sj containing windstorm are analysed and lagrangian trajectories used to assess the evolution of and mesoscale atmospheric instabilities e g symmetric and inertial instabilities in the descending airstream the sj undergoes a two stage descent cooling via sublimation followed by a large acceleration accompanied by instability release combined tilting and stretching of vorticity play a major role in the local onset of instability on the airstream vorticity and frontogenesis fields have a narrow slantwise banded structure in the cloud head and around the sj the descending sj modifies the widespread frontolysis expected from the large scale dynamics alone in the frontal fracture region a coarser resolution simulation also generates strong winds in the frontal fracture region although these are significantly weaker than in the higher resolution simulation the sj airstream in the coarser resolution simulation undergoes a weaker descent without instability generation and descends in a widespread frontolytic region hence while the sj undergoes a process of destabilisation that enhances its descent and acceleration in the higher resolution simulation enhancing the strong winds already generated by the synoptic scale cyclone dynamics this destabilisation does not occur in the sj produced by a coarser resolution simulation resulting in weaker winds this analysis reveals the synergy between the paradigms of sj occurrence through the release of mesoscale instabilities and synoptic scale cyclone dynamics and demonstrates that the current debate may in part be a consequence of the model resolutions used by different studies

near surface strong winds in a marine extratropical cyclone acceleration of the winds and the importance of surface fluxes a rapidly developing extratropical cyclone named tini brought strong winds to ireland and the united kingdom on 12 february 2014 a mesoscale model simulation is used to analyze the development of the strong winds through the terms in the horizontal momentum equation the maximum of near surface wind speed equatorward of the cyclone was composed of two different airstreams that underwent different paths to acceleration first horizontally moving air in the cold conveyor belt was accelerated by the along flow pressure gradient force but was decelerated by friction second descending air accelerated into the eastern end of the maximum of near surface wind speed and was associated in part with a sting jet caused by the increasing along flow horizontal pressure gradient force at lower levels when this descending air entered the boundary layer it too was decelerated by surface friction surface fluxes of heat and moisture were necessary to destabilize and deepen the boundary layer allowing mixing of the strongest winds from the free troposphere down to the surface a simulation with the surface fluxes turned off during cyclogenesis showed a more stable boundary layer around the bent back front which inhibited the strongest winds from reaching the surface the descent of the sting jet air was associated with a maximum in quasigeostrophic omega which consisted of both synoptic scale and mesoscale descent the latter associated with frontolysis occurring at the end of the bent back front thus the near surface wind maximum was created by the synoptic scale and mesoscale dynamics whereas localized moist processes were negligible

stress orientation on the norwegian continental shelf derived from borehole failures observed in high resolution borehole imaging logs abstract knowledge of stress orientation is crucial for the understanding of many processes in the earth s crust such as tectonic development earthquake occurrence and fluid transport along faults in the case of the norwegian continental shelf which is a prolific area for hydrocarbon production this knowledge also plays an important role for engineering decisions with respect to wellbore stability and reservoir management therefore data on stress orientation have been collected extensively over the past few years in this region however nearly all data published for the norwegian continental shelf for depths less than 6 km are based on the evaluation of four arm caliper data a method with intrinsic limitations for greater depths stress orientation is derived from earthquake focal plane mechanisms this article presents stress orientation data derived from an extensive set of image logs throughout the norwegian continental shelf the analysis is based on the identification of compressive and tensile failures of the borehole wall in electrical and acoustic borehole imaging logs this method for the determination of the stress orientation is found to be highly reliable and capable of delivering detailed and accurate results and thus is far superior to the analysis of breakouts from four arm caliper logs the analysis of image logs shows that the stress orientation is consistent both regionally and with depth strong variations in stress orientation which are often interpreted from earlier analyses of four arm caliper data are not observed this may indicate that some of the earlier four arm caliper analyses may have been biased by the misinterpretation of drilling induced artefacts as stress induced breakouts stress induced failures of the borehole wall are observed in only about 40 of the wells analysed in this paper this does not support the conclusion that the horizontal stresses are isotropic it just indicates that the stress difference in combination with the borehole conditions downhole pressure and temperature was insufficient to induce these failures

stress induced borehole elongation a comparison between the four arm dipmeter and the borehole televiewer in the auburn geothermal well the nature and origin of borehole elongation recorded by the four arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in auburn new york a preferred orientation n10 w s10 e 10 and a less prominant e w orientation of borehole elongation was observed on two runs of the dipmeter comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures obtained from hydrofracturing tests and televiewer data show that the n10 w s10 e borehole elongations 1 are axisymmetric 2 are aligned with the minimum horizontal stress sh and 3 are not associated with natural fractures intersecting the well these elongations are interpreted as stress induced well bore breakouts the e w elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts this asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter this study demonstrates that the dipmeter can be used to determine the orientation of sh by mapping breakouts confirming the results of earlier less detailed studies and provides a firm basis for mapping regional stress patterns using existing dipmeter data

the effects of changing resolution on mesocale modelling of line convection and slantwise circulations in fastex iop16 data are presented from modelling a rapidly developing cyclone in intensive observation period 16 of the fronts and atlantic storm tracks experiment using the new non hydrostatic version of the met office unified model at a number of different horizontal and vertical resolutions the model produces a good representation of the system including multiple fronts with line convection cloud heads and slantwise cross frontal circulations similar to those seen in the observations results from the model with various grid lengths from 60 km nested down to 2 km with 45 vertical levels show that more realistic detail is produced as the grid length is reduced but that the large scale structures remain consistent by spectral analysis it is found that structures on scales shorter than approximately five grid lengths are attenuated the line convection at the fronts is aliased onto the grid length scale except in the 2 km model where evidence of a three dimensional structure starts to appear the 2 and 4 km models have also been run with enhanced vertical resolutions it is concluded that whilst a 24 km 45 level model is sufficient to represent the overall frontal structure a model with resolution at least 2 km in the horizontal and 90 vertical levels is required to represent small scale multiple slantwise circulations similar to those observed in the dropsonde data crown copyright 2003

the sting at the end of the tail model diagnostics of fine scale three dimensional structure of the cloud head this is the second in a series of papers on the sting at the end of the tail a mesoscale region of potentially damaging surface winds that can occur close to the evaporating tip of a cloud head wrapped around the bent back front of an extratropical cyclone in the first paper the sting phenomenon was identified from a purely observational study of the great storm of october 1987 in the present paper an observationally validated forecast run from a high resolution numerical weather prediction model is used to examine the evolving three dimensional structure of the sting phenomenon it is shown that the damaging surface winds in the october 1987 storm were due to a well defined mesoscale sting jet sj identifiable as a coherent ensemble of trajectories originating in cloudy air at about 650 hpa there is evidence of multiple mesoscale slantwise circulations and the sj appears to form within the descending part of these circulations air within the sj descends to the 900 hpa level over a period of about 4 h during which time it accelerates from less than 20 to above 45 m s 1 with extremes greater than 50 m s 1 although the wet bulb potential temperature of air in the sj remains constant during its descent to 900 hpa evaporation leads to a reduction of up to 5 k or more in dry bulb potential temperature in some parts of the jet the sj is situated behind the primary cold front and is distinct from the associated warm conveyor belt low level jet it is also distinct from the cold conveyor belt low level jet which remains below and behind it as the sj skirts the bent back front crown copyright 2005

a new boundary layer mixing scheme part i scheme description and single column model tests a new boundary layer turbulent mixing scheme has been developed for use in the ukmo weather forecasting and climate prediction models this includes a representation of nonlocal mixing driven by both surface fluxes and cloud top processes in unstable layers either coupled to or decoupled from the surface and an explicit entrainment parameterization the scheme is formulated in moist conserved variables so that it can treat both dry and cloudy layers details of the scheme and examples of its performance in single column model tests are presented

seismicity and seismotectonics of norway and nearby continental shelf areas the earthquake activity of norway and nearby offshore areas is low to intermediate with few events above magnitude 5 recent significant improvements in instrumental coverage in parallel with a better utilization of older including historical data have shown that the seismicity in the south is predominantly confined to the coastal areas and to the viking graben while from the northern north sea to svalbard the earthquakes in a broad sense follow the continental margin fifty one focal mechanism solutions from these areas about half of them new reveal stress directions that clearly indicate a connection to the plate tectonic ridge push force at least for the areas at a minimum distance from the continental margin along the margin stress directions also indicate a possible connection to postglacial uplift as well as to lithospheric loading effects a dominance of normal faulting on the landward side and reverse faulting on the oceanic side agrees with this interpretation on a regional level the seismicity in these areas correlate quite well with geologic features such as grabens fault zones fault complexes fracture zones and the margin itself indicating that these structures act in a general sense as weakness zones in the presence of a regionally more stable stress field in the northern north sea however an area with quite anomalous stress orientations with strike slip faulting is found in a region transitional between normal and reverse faulting most of the earthquake foci are confined to the presumably brittle parts of the crust but many events are also located quite close to and on both sides of the moho discontinuity

in situ stress from breakouts in the danish sector of the north sea abstract borehole breakouts from 26 wells situated in the danish central graben and one well situated in the northwestern section of the ringkobing fyn high have been studied the data provide information on the orientation of the contemporary principal horizontal stresses down to depths of 4 7 km statistics were used to obtain a mean azimuth of breakouts for each well and each individual breakout was weighted by its length data quality of breakouts is assigned according to the world stress map quality ranking scheme the breakout data reveal that s h orientations in the danish central graben are extremely scattered no regional trend in mean s h orientation can be identified as a result of the large standard deviation 77 similar scatterings of s h orientations have been reported from adjacent regions of the north sea the results indicate that the state of stress in the sedimentary cover of the danish central graben is influenced by a local stress generating mechanism rather than platewide stress transmissions mechanisms three units with different states of stress have been identified and found to correspond somewhat with the lithostratigraphic divisions of the post chalk group chalk group and pre chalk group

origin of strong winds in an explosive mediterranean extratropical cyclone abstractduring 2 3 december 2012 the black sea and east coast of romania were affected by a rapidly deepening mediterranean cyclone the cyclone developed a bent back front along which short lived

conditional symmetric instability in sting jet storms sting jets are transient mesoscale jets of air that descend from the tip of the cloud head towards the top of the boundary layer in severe extratropical cyclones and can lead to damaging surface wind gusts this recently identified jet is distinct from the well documented jets associated with the cold and warm conveyor belts one mechanism proposed for their development is the release of conditional symmetric instability csi here the spatial distribution and temporal evolution of several csi diagnostics in four severe storms are analysed a sting jet has been identified in three of these storms for comparison we also analysed one storm that did not have a sting jet even though it had many of the apparent features of sting jet storms the sting jet storms are distinct from the non sting jet storms by having much greater and more extensive conditional instability ci and csi csi is released by ascending air parcels in the cloud head in two of the sting jet storms and by descending air parcels in the other sting jet storm by contrast only weak ci to ascending air parcels is present at the cloud head tip in the non sting jet storm csi released by descending air parcels as diagnosed by decaying downdraught slantwise convective available potential energy dscape is collocated with the sting jets in all three sting jet storms and has a localised maximum in two of them consistent evolutions of saturated moist potential vorticity are found we conclude that csi release has a role in the generation of the sting jet that the sting jet may be driven by the release of instability to both ascending and descending parcels and that dscape could be used as a discriminating diagnostic for the sting jet based on these four case studies copyright 2011 royal meteorological society and british crown copyright the met office

attribution of strong winds to a cold conveyor belt and sting jet a high resolution version of the wrf weather research and forecasting model has been used to study the fine structure of a cloud head and its associated cold conveyor belt jet cj and sting jet sj in an intense extratropical cyclone that produced damaging surface winds in northern ireland and central scotland on 3 january 2012 the model was run with many different initialisation times and physical parametrisations and a run was selected that verified well against a variety of observations new methods have been devised to visualise the 3d structure of the cj and sj and to attribute strong surface winds to one or other of them and the validity of regarding the sj as a semi lagrangian feature has been assessed the model suggests that whereas the cj remained mainly below the 850hpa level as it circulated around the bent back front the sj consisted of a stream or streams of air within the bent back frontal zone that first ascended from close to the surface into the middle and upper level parts of the cloud head before descending from evaporating cloud filaments at the tip of the cloud head and reaching the top of the boundary layer slightly ahead of the cj the simulations did not support the idea that either the evaporation or conditional symmetric instability csi played a major role in the development of these jets the strong gusts up to 47ms 1 w hich were recorded on the north coast of ireland appear to have been due mainly to the cj which by then was undercutting the sj the sj was responsible for stronger surface winds than the cj several hours earlier during the initial stage of frontal fracture but only for a limited period

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

dynamics of sting jet storm egon over continental europe impact of surface properties and model resolution intense shapiro keyser cyclones are often accompanied by a sting jet sj an air stream that descends from the cloud head into the frontal fracture region and can cause extreme surface gusts previous case studies have concentrated on the north atlantic and the british isles here we present the first ever detailed analysis of an sj over continental europe and investigate the influence of topography on its dynamical evolution based on observations and high resolution simulations using the icosahedral nonhydrostatic model icon windstorm egon intensified over the english channel and then tracked from northern france to poland on 12 13 january 2017 causing gusts of almost 150 km h 1 and important damage icon reproduces the storm dynamics although it delays the explosive deepening shifts the track southward over belgium and germany and underestimates gusts over land storm characteristics show weak sensitivity to varying grid spacing between 1 6 and 6 5 km while switching off the convection parametrization at 3 3 km grid spacing improves correlations with surface observations but deteriorates the mean error trajectories reveal typical sj characteristics such as mid level descent strong acceleration and conditional symmetric and other mesoscale instabilities while evaporative cooling is stronger than in previous cases from the literature preventing drying during descent the sj identification and the occurrence of mesoscale instabilities depend considerably on model resolution convective parametrization output frequency and employed thresholds for trajectory selection sensitivity experiments with modified surface characteristics show that the combined effects of warm air blocking by the alps higher roughness over land and reduced surface fluxes cause egon to fill more quickly and to move on a faster more northern track across germany while the sj response is complex showing some compensating effects surface gusts strongly increase when roughness is reduced these results suggest that weather forecasters in continental europe should be more aware of the potential risks associated with sjs

stacked slantwise convective circulations it is well known that classical ana cold fronts tend to be characterized by mesoscale circulations in which upright line convection feeds a layer of concentrated rearward slantwise ascent occasionally however as in the case study presented in this paper two and sometimes more of these mesoscale circulations coexist within the same cold frontal zone the two slantwise circulations described were observed to be stacked one above the other with a vertical wavelength of less than 2 km although it is often suspected that the circulations at ana cold fronts are enhanced by mesoscale processes such as conditional symmetric instability csi or m adjustment it is notoriously difficult to discriminate between these circulations and the larger scale transverse circulation within which they are embedded the occurrence in this study of multiple circulations with small vertical scale helps to distinguish them from the large scale circulation and this has motivated the detailed examination of this case mesoscale circulations of the kind described are difficult to detect numerical weather prediction nwp models even high resolution models do not usually represent them and conventional observations do not show them clearly this study takes advantage of observations from a high resolution microwave doppler radar plus a high resolution analysis of ultra high frequency wind profiler radar data analysed in the context of output from an operational mesoscale nwp model the study defines the mesoscale structure of the event sufficiently carefully to provide a basis for future idealized modelling studies to investigate the possible roles of csi and m adjustment both of which appear to play a part in the maintenance of the circulations

contemporary stress field distortion in the polish part of the western outer carpathians and their basement abstract the western carpathians seem to be the crucial place to understand the nature of the regional turn of the present day maximum horizontal stress shmax direction from the northwest which is characteristic for the west european stress province towards the north specific for the western edge of the east european platform shmax orientations have been investigated in fourteen deep wells located in the western part of the polish outer carpathians by borehole breakout analyses from six arm dipmeter data this tool proved to be useful to determine breakout orientation and to discriminate stress induced breakouts from mechanical failures of the borehole wall the analysed dipmeter data come from wells most of them deeper than 3000 m which penetrate cretaceous tertiary sequences of the carpathian flysch nappes 4 wells the palaeozoic tertiary autochthonous sedimentary cover of the upper silesian and the malopolska massifs 13 wells and their precambrian metamorphic basement 4 wells in the investigated part of the upper silesian massif shmax for separate depth sections shows a general counterclockwise rotation with increasing depth for the carpathian nappes breakout data of moderate quality indicate nne oriented shmax while for the autochthonous basement sequence good quality data point to a nnw mean direction of shmax in the deepest well sections which penetrate the crystalline basement of the upper silesian massif the tendency to further stress rotation towards the northwest was observed the range of the angular shmax rotation with depth for the utmost structural levels exceeds 60 in the central part and decreases to 40 for the eastern edge of the upper silesian massif no stress rotation is evident in the westernmost part of this massif numerous second and third order stress deviations give evidence for recent fault reactivation and rotational stresses in horizontal planes for the autochthonous sedimentary cover of the malopolska massif n to nne oriented compression was determined hitherto acquired data suggest insignificant stress rotation from the north in unfolded sequences of the miocene molasse beneath the nappes to the north northeast in deeper palaeozoic mesozoic complexes in one well ne trending shmax was determined in folded miocene molasse beneath the main decollement surface this stress orientation is similar to stress directions in the nappes covering the upper silesian massif shmax directions in the autochthonous complex beneath the nappes of the western outer carpathians generally are subperpendicular to the overall trend of the orogen creating a fan like pattern of stress trajectories nne oriented compression within the nappes covering the upper silesian massive within the autochthonous complex of the malopolska massif and in the carpathian foreland probably is exerted by the carpatho pannonian plate advancing towards the north northeast relative to the european plate active movement occurs along the mur muerz ilina fault zone on the western boundary of this plate and probably along the eastern carpathians suture on its eastern margin nw directed compression in the basement of the upper silesian massif is in agreement with shmax orientation within the bohemian massif and the west european stress province thus plate forces are thought to contribute to its origin

distinguishing the cold conveyor belt and sting jet airstreams in an intense extratropical cyclone abstractstrong winds equatorward and rearward of a cyclone core have often been associated with two phenomena the cold conveyor belt ccb jet and sting jets here detailed observations of the mesoscale structure in this region of an intense cyclone are analyzed the in situ and dropsonde observations were obtained during two research flights through the cyclone during the diabatic influences on mesoscale structures in extratropical storms diamet field campaign a numerical weather prediction model is used to link the strong wind regions with three types of airstreams or coherent ensembles of trajectories two types are identified with the ccb hooking around the cyclone center while the third is identified with a sting jet descending from the cloud head to the west of the cyclone chemical tracer observations show for the first time that the ccb and sting jet airstreams are distinct air masses even when the associated low level wind maxima are not spatially distinct in the model the ccb experie

well bore breakouts and in situ stress the detailed cross sectional shape of stress induced well bore breakouts has been studied using specially processed ultrasonic borehole televiewer data we show breakout shapes for a variety of rock types and introduce a simple elastic failure model which explains many features of the observations both the observations and calculations indicate that the breakouts define relatively broad and flat curvilinear surfaces which enlarge the borehole in the direction of minimum horizontal compression this work supports the hypothesis that breakouts result from shear failure of the rock where the compressive stress concentration around the well bore is greatest and that breakouts can be used to determine the orientation of the horizontal principal stresses in situ

effect of borehole deviation on breakout orientations well bore breakouts are zones of spalling and fracture that form on opposite sides of a well bore and tend to change the cross sectional shape of the borehole from circular to roughly elliptical in vertical holes drilled in areas where one principal stress sv is vertical breakouts tend to form at opposite ends of the borehole diameter parallel to the least compressive horizontal principal stress direction sh this paper uses an analytical elastic solution for stress at the wall of a borehole to analyze the rotation of breakout orientations away from the direction of sh as the borehole deviates from the direction of the vertical principal stress the calculated orientations of breakouts in deviated boreholes depend on the type of faulting regime in which the well was drilled i e normal strike slip or thrust on the deviation angle o of the borehole axis from vertical on the angle between the horizontal projection of the borehole axis and the direction of sh and on the relative magnitudes of the three principal stresses sh sh the greatest compressive horizontal stress and sv in the strike slip faulting regime regardless of the values of sv sh and sh a borehole must deviate at least 35 from vertical before the horizontal projection of the breakout orientation differs by more than 10 from sh in the normal and thrust faulting regimes however the borehole deviation angle ocrit required to rotate projected breakout orientations by 10 from sh approaches zero as the value of sh approaches that of sh in the thrust faulting regime only about 3 of all combinations of sv sh and sh will produce ocrit values less than 10 while about 12 of all such combinations will yield ocrit 10 in the normal faulting regime about 12 and 33 of such combinations will yield ocrit 20 in the thrust and normal faulting regimes respectively careful study of changes in breakout orientation as a function of borehole deviation may improve the resolution of inferred stress directions when studying breakouts in deviated boreholes in these two faulting regimes

sting jets in extratropical cyclones a review this paper reviews the current state of knowledge of sting jets in extratropical cyclones sting jets were formally identified in 2004 by the pioneering work of keith browning reviewing this and subsequent studies we define the sting jet as a coherent air flow that descends from mid levels inside the cloud head into the frontal fracture region of a shapiro keyser cyclone over a period of a few hours leading to a distinct region of near surface stronger winds it therefore lies above the cold conveyor belt during some stage its life but at least in some cases descends to reach the top of boundary layer ahead of the cold conveyor belt it is not attributed to a specific mechanism in this definition we conclude that it is likely that a continuum of sting jet descent and speed up mechanisms exists at one extreme is balanced descent partly associated with frontolysis in the frontal fracture region more horizontally small scale and stronger frontolytic descent may occur associated with weak stability to slantwise convective downdraughts instability to slantwise convective downdraughts may occur in some systems leading to multiple slantwise convective downdraughts associated with the release of conditional symmetric instability and even possibly symmetric instability the global climatology of sting jets and the interaction between the atmospheric boundary layer and sting jets are revealed as specific areas where more research is needed finally we describe eight myths and misunderstandings that exist in the current literature with the aim of guiding future research into the sting jet phenomenon

regional patterns of tectonic stress in europe nearly 1500 stress orientation determinations are now available for europe the data come from earthquake focal mechanisms overcoring measurements well bore breakouts hydraulic fracturing measurements and young fault slip studies and sample the stress field from the surface to seismogenic depths three distinct regional patterns of maximum compressive horizontal stress shmax orientation can be defined from these data a consistent nw to nnw shmax stress orientation in western europe a wnw ese shmax orientation in scandinavia similar to western europe but with a larger variability of shmax orientations and a consistent e w shmax orientation and n s extension in the aegean sea and western anatolia the different stress fields can be attributed to plate driving forces acting on the boundaries of the eurasian plate locally modified by lithospheric properties in different regions on average the orientation of maximum stress in western europe is subparallel to the direction of relative plate motion between africa and europe and is rotated 17 clockwise from the direction of absolute plate motion the uniformly oriented stress field in western europe coincides with thin to medium lithospheric thickness approximately 50 90 km and high heat flow values 80 m w m2 in western europe a predominance of strike slip focal mechanisms implies that the intermediate principal stress is vertical the more irregular horizontal stress orientations in scandinavia coincide with thick continental lithosphere 110 170 km and low heat flow 50 m w m2 the cold thick lithosphere in this region may result in lower mean stresses associated with far field tectonic forces and allow the stress field to be more easily perturbed by local effects such as deglaciation flexure and topography the stress field of the aegean sea and western anatolia is consistent with n s extension in a back arc setting behind the hellenic trench subduction zone the stress field is influenced in places by regional geologic structures e g in the western alps where shmax directions show a slight tendency toward a radial stress pattern not all major geologic structures however appear to affect the shmax orientation e g in the vicinity of the rhine rift system horizontal stress orientations are continuous

drilling induced tensile wall fractures implications for determination of in situ stress orientation and magnitude abstract detailed investigation of failure of the borehole wall in two scientific drilling projects the german ktb kontinentales tiefbohrprogramm der bundesrepublik deutschland and the european geothermal research project at soultz sous forets france has lead to new insight in the phenomena of tensile fractures induced in the wellbore wall during drilling comparison of the orientation of the fractures with the orientation of the horizontal principal stress known from breakout and hydraulic fracturing analysis demonstrates that these fractures are reliable indicators of the orientation of the maximum horizontal principal stress s h a model for the initiation of the fractures is presented which points out the important influences of a the tectonic stress state b increased mud pressures during drilling operation and c thermal stresses induced by circulation of relatively cold drilling mud analysis of drilling induced fractures in the gpk1 borehole at soultz sous forets where the magnitude of s h is known from hydraulic fracturing experiments demonstrates the validity of this model for the initiation of the fractures further a new method is proposed to estimate the magnitude of s h from the occurrence of drilling induced fractures and knowledge of thermally induced stress and pumping pressure during drilling the method is successfully applied to both ktb boreholes an independent method to estimate the magnitude of s h based on the analytical calculation of the stress intensity factor for drilling induced fractures taking into consideration both increased mud pressure and thermal stress is also presented application of this method confirms the results derived with the analysis described above additionally the evaluation of the orientation of the fractures with respect to the wellbore axis indicates that over major depth sections of the investigated wells the vertical stress is a principal stress