rocket triggered lightning propagation paths relative to preceding natural lightning activity and inferred cloud charge lightning mapping array lma data are used to compare the propagation paths of seven rocket triggered lightning flashes to the inferred charge structure of the thunderstorms in which they were triggered this is the first lma study of florida thunderstorm charge structure three sequentially within 16 min triggered lightning flashes whose initial stages were the subject of hill et al 2013 are reexamined by comparing the complete flashes to the preceding natural lightning to demonstrate that the three rocket triggered flashes propagated through an inferred negative charge region that decreased from about 6 8 to about 4 4 km altitude as the thunderstorm dissipated two other flashes were also sequentially triggered within 9 min in a thunderstorm that contained a convectively intense region ahead of a stratiform region with similar observed results finally two unique cases of triggered lightning flashes are presented in the first case the in cloud portion of the triggered lightning flash after ascending to and turning horizontal at 5 3 km altitude just above the 0 c level was observed to very clearly resemble the geometry of the in cloud portion of the preceding natural lightning discharges in the second case a flash was triggered relatively early in the storm s lifecycle that did not turn horizontal near the 0 c level as is usually the case for triggered lightning in dissipating storms but ascended to nearly 7 5 km altitude before exhibiting extensive horizontal branching

accuracy of the lightning mapping array 1 the location accuracy of the new mexico tech lightning mapping array lma has been investigated experimentally using sounding balloon measurements airplane tracks and observations of distant storms we have also developed simple geometric models for estimating the location uncertainty of sources both over and outside the network the model results are found to be a good estimator of the observed errors and also agree with covariance estimates of the location uncertainties obtained from the least squares solution technique sources over the network are located with an uncertainty of 6 12 m rms in the horizontal and 20 30 m rms in the vertical this corresponds well with the uncertainties of the arrival time measurements determined from the distribution of chi square values to be 40 50 ns rms outside the network the location uncertainties increase with distance the geometric model shows that the range and altitude errors increase as the range squared r2 while the azimuthal error increases linearly with r for the 13 station 70 km diameter network deployed during steps the range and height errors of distant sources were comparable to each other while the azimuthal errors were much smaller the difference in the range and azimuth errors causes distant storms to be elongated radially in plan views of the observations the overall results are shown to agree well with hyperbolic formulations of time of arrival measurements e g proctor 1971 two appendices describe 1 the basic operation of the lma and the detailed manner in which its measurements are processed and 2 the effect of systematic errors on lightning observations the latter provides an alternative explanation for the systematic height errors found by boccippio et al 2001 in distant storm data from the lightning detection and ranging system at kennedy space center

laboratory and seismological observations of lower mantle isotropy we have carried out seismological and mineral physics investigations to identify the extent and origin of elastic anisotropy in the lower mantle based on observations of shear wave splitting we conclude that the lower mantle is effectively isotropic this result is surprising since the lower mantle is composed of elastically anisotropic minerals silicate perovskite mgo sio 2 that have been extensively strained by geologic processes to reconcile the seismic observations we have measured texture development during deformation and high temperature recrystallization of mantle silicates we show that these experiments provide a direct explanation for the shear wave splitting measurements the lower mantle appears isotropic because silicate perovskite maintains an isotropic texture during deformation and recrystallization

correlated lightning mapping array and radar observations of the initial stages of three sequentially triggered florida lightning discharges 1 correlated lightning mapping array and vertical scan radar images are presented for three rocket and wire triggered lightning flashes that occurred sequentially within 17 min in the presence of a decaying multicellular convective storm system over north central florida the initial stage is of each flash propagated generally vertically to the altitude of the 0 c melting level about 5 km and then subsequently propagated for many kilometers horizontally along the melting level contour radar images suggest that the propagation paths of the is channels below and above the melting level were heavily influenced by precipitation gradients flash uf 11 24 exhibited a 12 6 km unbranched is channel the longest unbranched channel observed in the study by a factor of three during flash uf 11 25 119 ms following the cessation of the measured is current at ground and prior to the first return stroke a natural cloud to ground discharge perhaps induced by the is initiated between 2 5 and 4 km altitude and struck ground 5 to 7 km from the launching facility the is of flash uf 11 26 propagated upward through a descending precipitation packet and apparently induced a naturally appearing bi level intracloud discharge via an upward negative leader that initiated within the is breakdown region 3 5 km from the launching facility the upward negative leader propagated from 5 6 to 9 3 km altitude in a time of 11 ms the electrical current measured at ground during the is of flash uf 11 26 exhibited a 57 ms polarity reversal transferring 19 c of positive charge to ground

an anomalous triggered lightning flash in florida 1 an anomalous rocket and wire triggered lightning flash a flash whose leaders do not follow the triggering wire remnants to ground is characterized via high speed video images at 10 and 300 kilo frames per second still camera images 66 72 mhz source locations from a lightning mapping array channel base current and electric field and electric field derivative de dt measurements this is the first anomalous flash of about 410 classically triggered flashes in north central florida the flash began with an upward positively charged leader upl initiating from the tip of the upward moving triggering wire about 280 m above ground level all but the bottom 17 m of wire exploded became luminous 37 6 ms after upl initiation a stepped leader initiated likely from the top of the wire remnants 282 m above ground level about 1 3 ms after the wire explosion and propagated downward for 2 1 ms attaching to the top of a grounded utility pole 117 m southwest of the launching facility the line charge density on the stepped leader is estimated to be of the order of 10 3 c m 1 contrary to previously reported anomalous flashes in france and new mexico roughly 16 and 31 respectively of their triggered flashes in our event there was not a tens of milliseconds current zero period preceding the stepped leader there was no observed downward dart leader in the upl channel prior to the stepped leader to ground and there was a failed attempt to reestablish current in the exploded wire channel between the upl and ground

carbon dioxide injection and associated hydraulic fracturing of reservoir formations the storage potential of subsurface geological systems makes them viable candidates for long term disposal of significant quantities of co2 the geo mechanical responses of these systems as a result of injection processes as well as the protracted storage of co2 are aspects that require sufficient understanding a hypothetical model has been developed that conceptualises a typical well reservoir system comprising an injection well where the fluid co2 is introduced and a production abandoned well sited at a distant location this was accomplished by adopting a numerical methodology discrete element method specifically designed to investigate the geo mechanical phenomena whereby the various processes are monitored at the inter particle scale fracturing events were simulated in addition the influence of certain operating variables such as injection flow rate and fluid pressure was studied with particular interest in the nature of occurring fractures and trend of propagation the pattern and magnitude of pressure build up at the well vicinity pressure distribution between well regions and pore velocity distribution between well regions modelling results generally show an initiation of fracturing caused by tensile failure of the rock material at the region of fluid injection however fracturing caused by shear failure becomes more dominant at the later stage of injection furthermore isolated fracturing events were observed to occur at the production abandoned wells that were not propagated from the injection point this highlights the potential of co2 introduced through an injection well which could be used to enhance oil gas recovery at a distant production well the rate and magnitude of fracture development are directly influenced by the fluid injection rate likewise the magnitude of pressure build up is greatly affected by the fluid injection rate and the distance from the point of injection the dem modelling technique illustrated provides an effective procedure that allows for more specific investigations of geo mechanical mechanisms occurring at subsurface systems the application of this methodology to the injection and storage of co2 facilitates the understanding of the fracturing phenomenon as well as the various factors governing the process

a gps based three dimensional lightning mapping system initial observations in central new mexico a gps based system has been developed that accurately locates the sources of vhf radiation from lightning discharges in three spatial dimensions and time the observations are found to reflect the basic charge structure of electrified storms observations have also been obtained of a distinct type of energetic discharge referred to as positive bipolar breakdown recently identified as the source of trans ionospheric pulse pairs tipps observed by satellites from space the bipolar breakdown has been confirmed to occur between the main negative and upper positive charge regions of a storm and found to be the initial event of otherwise normal intracloud discharges the latter is contrary to previous findings that the breakdown appeared to be temporally isolated from other lightning in a storm peak vhf radiation from the energetic discharges is observed to be typically 30 db stronger than that from other lightning processes and to correspond to source power in excess of 100 kw over a 6 mhz bandwidth centered at 63 mhz

three dimensional imaging of upward positive leaders in triggered lightning using vhf broadband digital interferometers 1 upward positive leaders upls in two artificially initiated lightning flashes were imaged in three dimensions using vhf broadband digital interferometers and a high speed video camera with time synchronized channel base current measurements locatable vhf sources of the two upls began at 1 1 km and 1 5 km a few milliseconds after the upl inception and ascended to 2 4 km and 3 7 km respectively with average 3 d speeds on the order of 106 ms 1 the initial stage currents for both flashes were unusually large and had peak values of 6 ka and 18 ka vhf sources associated with positive leader propagation were located when the average current was higher than 3 ka and had significant pulse activity the source altitudes and channel base currents suggest that there might have been a region of significant negative charge at altitudes from 2 to 4 km which is below the freezing level of typical thunderstorms in florida

the 2010 eruption of eyjafjallajokull lightning and plume charge structure six lightning mapping array lma stations were deployed in april 2010 around eyjafjallajokull volcano in southern iceland single station lma observations were made during the first explosive period 14 18 april and three dimensional lma observations were made during the second explosive period 5 22 may the single station observations revealed that continuous rf electrical activity caused by high rates of small vent discharges occurred during the first explosive period but not the second indicating that the strength of vent charging varied between the first and second explosive periods during the second explosive period very little lightning was detected between 5 and 10 may while moderate rates of lightning were detected between 11 and 21 may signaling that another change occurred on 11 may that affected plume electrification the data do not make clear if it was changing eruptive activity or changing meteorological activity that resulted in the sudden onset of lightning the plume charge structure during the second explosive period was inferred from the three dimensional lightning data showing that the dominant charge structure varied between a positive monopole and a negative over positive dipole the predominance of a low altitude region of positive charge and the observation that electrical activity was concentrated near the vent indicate that net positive vent charging was dominating the electrification

hydraulic fracturing experiment at the university of regina campus a hydraulic fracturing stress determination was carried out during may and june 1979 in a water well intended for the geothermal feasibility project on the campus of the university of regina sas

plate motions in the north pacific the 43 ma nonevent the hawaiian emperor seamount chain in the north pacific ocean is commonly considered to have been produced by motion of the pacific plate over a hotspot if the hotspot is assumed to have remained fixed in a mantle frame of reference the 60 change in trend between the hawaiian and emperor portions of the chain results from a change in motion direction of the pacific plate relative to the mantle at 43 ma during middle eocene time such a large and abrupt direction change should result in significant plate reorganizations and tectonic events in the pacific and surrounding plates but no evidence for these events can be found in addition in this paper it is shown that there were no changes in relative plate motions between pacific area plates that can be associated with the hawaiian emperor bend this is done by calculating motion of the pacific farallon and kula plates relative to asia and north america using the plate circuit farallon pacific antarctica africa north america asia with no major regional tectonic event at the time of the bend it is suggested that there was no plate reorganization at 43 ma and that the emperor portion of the seamount chain was formed by a nonstationary hotspot

radio interferometric observations of cloud to ground lightning phenomena in florida radio frequency observations of cloud to ground lightning in florida have been analyzed to document a number of features of the lightning the observations have been made using an interferometer system which determined the direction to the lightning radiation as a function of time during close lightning discharges observations are presented for about 50 radiating events during five multiple stroke normal polarity flashes to ground the results confirm and extend results of a similar study of new mexico lightning by rhodes et al 1994 dart leaders in cloud k events and attempted leaders are found to be the same phenomena namely a negative polarity streamer that propagates horizontally and or vertically to ground at estimated speeds of about 10 7 ms 1 down to 10 6 ms 1 the step or impulsive fast electric field change produced by some k events is found to be caused by positive breakdown back at the starting point of the negative streamer after the streamer has progressed over some or all of its distance this breakdown appears to initiate a forward stroke along the streamer channel which can renew the breakdown at the front end of the channel k breakdown which happens to occur during a continuing current discharge to ground produces an m event channel brightening when it connects with the conducting channel to ground the step fast field change of the m events is found to be produced at the time of connection inside the cloud no fast field change is detected when this breakdown reaches ground that would be associated with a return stroke m events can also be initiated by fast 10 7 ms 1 positive streamers which often propagate away from the leader source region within a few milliseconds of the arrival of a return stroke back in the source region these streamers often generate an even faster negative recoil event back along their extent which propagates down the channel to ground as the m event in all cases the current increase or channel brightening produced by k and m events is predicted to occur in a forward direction that is toward or down the channel to ground in the same direction as the initiating negative streamer positive breakdown is detected only immediately following return strokes or during some k streamers in both cases the electric stresses are expected to be very large suggesting that positive breakdown which produces a conducting channel is difficult to initiate results for one flash suggest that negative charge was left at low altitude by the initial stroke to ground this forced the subsequent leaders to develop a new path to ground first as series of attempted leaders and then as a dart stepped leader

interpretation of sks waves using samples from the subcontinental lithosphere abstract the seismic properties of five south african kimberlite nodules have been calculated from petrofabric measurements these garnet lherzolite and harzburgite composition nodules 56 80 olivine are known from previous studies to have originated at depths of 120 170 km in the subcontinental lithosphere their in situ seismic properties have been calculated by extrapolating the elastic constants to the appropriate temperature 900 1050 c and pressure 3 0 3 5 gpa conditions the average of the five samples has a maximum s wave anisotropy v s of 3 7 which is sufficiently high to explain previously reported teleseismic sks delay times t in continental shield areas of up to 1 7 s the biggest delay time is observed when the foliation is vertical the lineation horizontal and the fastest s wave polarized parallel to the lineation i e an orientation for transcurrent motion delay times of over 1 s can only be generated by this orientation a strong mantle crust mechanical coupling is suggested for such situations the potential use of seismic anisotropy as an indicator of strain in the lithosphere has been investigated using experimental and simulated fabric data for olivine the most abundant phase 70 in the upper mantle the v p and v s seismic anisotropy increases with fabric strength and finite strain recrystallization tends to reduce fabric strength and seismic anisotropy resulting in saturation values for experimental and simulated fabrics which correspond to approximately 50 60 strain or 8 9 v s for pure olivine aggregates a survey of 25 naturally deformed peridotites of oceanic origin suggests an average maximum s wave anisotropy for the olivine component of 9 or about 8 for a lherzolite or harzburgite rock composition when the orthopyroxene component is taken into account the ophiolite samples are twice as anisotropic as the kimberlite nodules if an average anisotropy value is representative of the lithosphere then the sks delay times represent variations in anisotropic layer thickness for delay times over 1 s as the orientation is constrained to be foliation vertical and lineation horizontal the magnitude of s wave anisotropy is less sensitive than v p to variations in olivine volume fraction in range 50 100 and to deformation or fabric intensity further suggesting that s wave anisotropy is particularly apt for the determination of the anisotropic lithosphere thickness for smaller delay times there is some trade off between structural orientation and thickness

high speed video observation of stepwise propagation of a natural upward positive leader using a high speed video camera operated at 150 000 frames per second we have documented the upward propagation of an initial positive leader from a 325 m meteorological tower in beijing the stepwise development of the upward positive leader was clearly revealed during its self sustained propagation toward the cloud base providing the first optical evidence for the stepping processes of a positive leader the leader developed with definitive intermittent pauses and re establishment with abrupt jump of the leader top obvious brush like corona zone emitting outward from the leader top was identified in the frame of stepping and the luminosity waves propagated downward along the already formed channel from the leader top immediately following the stepping indicating that a current wave was generated at the leader top and subsequently traveled down the channel the channel luminosity decreased during the leader pause stage with the corona zone dimmed correspondingly the positive leader experienced an average interstep interval of 61 7 s ranging between 30 s and 120 s and an average 2 d speed of 8 1 104 m s the transient speed of the step jump was estimated to be larger than 7 3 105 m s with an average step length of 4 9 m the need of sufficient positive charge accumulation at the leader top could be the main cause for the stepping characteristics

vhf lightning mapping observations of a triggered lightning flash 1 on 3 august 2010 an extensive lightning flash was triggered over langmuir laboratory in new mexico the upward positive leader propagated into the storm s midlevel negative charge region extending over a horizontal area of 13 13 km and 7 5 km altitude the storm had a normal polarity tripolar charge structure with upper positive charge over midlevel negative charge lightning mapping array lma observations were used to estimate positive leader velocities along various branches which were in the range of 1 3 104 m s 1 slower than in other studies the upward positive leader initiated at 3 4 km altitude but was mapped only above 4 0 km altitude after the onset of retrograde negative breakdown indicating a change in leader propagation and vhf emissions the observations suggest that both positive and negative breakdown produce vhf emissions that can be located by time of arrival systems and that not all vhf emissions occurring along positive leader channels are associated with retrograde negative breakdown

a 3 d kinematic model of fabric development in polycrystalline aggregates comparisons with experimental and natural examples abstract a 3 d generalization of the approach previously developed by etchecopar for the simulation of fabrics in polycrystalline aggregates is presented the model is based on a geometric minimization of gaps overlaps and boundary displacements between deformed neighbouring cells each cell may deform using a small number

anisotropy of the asthenosphere the higher mode data of the pacific revisited surface wave data previously used by the authors to constrain upper mantle anisotropy in the pacific ocean are re examined after an error was found in the calculations of the love wave phase velocities sub lithospheric anisotropy is still required by the corrected data but it extends to shallower depth than we originally proposed using different parameterizations of the upper mantle we present strong evidence that the bottom of the anisotropic layer has been reached around 250 km in the pacific beneath north america no revision of our data is required and anisotropy could extend to around 400 km depth our results are in agreement with an upper mantle anisotropy due to preferred orientation of olivine crystals in an overall horizontal shear strain parallel to the present day plate motion we suggest that this preferred orientation of the crystals mainly occurs within the upper mantle low velocity layer

microscopic modelling of the hydraulic fracturing process a microscopic perspective is introduced in this study which offers a detailed insight at the inter particle level to the geo mechanical responses caused by fluid injection and the resulting pressure build up this was achieved by employing the discrete element method dem to model the pressure development and the subsequent fracturing and or cavity propagation this technique represents the formation material as an assembly of discrete particles linked to each other through contacts numerical experiments were carried out on two sample materials for the first instance tests were carried out on a bulk material representative of a generic intact rock with the breakage of inter particle bonds indicating the formation of cracks the second series of tests was carried out on granular type materials such as sand where particle separation signified cavity initiation and separation it was observed from the dem modelling results that the intact rock material showed a predominance of mode ii fracturing at high fluid velocities however when the fluid velocity is reduced considerably the fracturing behaviour tended towards more of mode i also records of the pressure development were taken from the numerical results and were used to monitor the fracturing events the outcome of this study highlights important aspects of the hydraulic fracturing process especially at the particle particle scale and thus provides a strong basis for more exhaustive studies involving larger scale reservoir modelling and more complex fracturing scenarios

evolving complex electrical structures of the steps 25 june 2000 multicell storm abstract data from a three dimensional lightning mapping array lma and from two soundings by balloon borne electric field meters efms were used to analyze the electrical structures of a multicell storm observed on 25 june 2000 during the severe thunderstorm electrification and precipitation study steps this storm had a complex multicell structure with four sections each of whose electrical structure differed from that of the others during all or part of the analyzed period the number of vertically stacked charge regions in any given section of the storm ranged from two to six the most complex charge and lightning structures occurred in regions with the highest reflectivity values and the deepest reflectivity cores intracloud flashes tended to concentrate in areas with large radar reflectivity values though some propagated across more than one core of high reflectivity or into the low reflectivity anvil intracloud lightning flash rates decreased as the vertical extent and maximum value of ref

lateral flow of hot plume material ponded at sublithospheric depths local buoyancy forces drive the flow of ponded plume material along the base of the lithosphere this processes complicates the geological effects of plumes beyond those of simple passage of plates over point heat sources variations in the depth to the base of the lithosphere significantly affect lateral flow the flow rate is modified to a moderate extent by locally thin lithosphere beneath midplate hotspots such as hawaii the effect is relevant when numerical models are rescaled to better fit the observed uplift and the observed distance from the hotspot to the nose of the swell variations in the depth to the base of the lithosphere have a much stronger effect on flow near ridge axes effectively forming an upside down drainage pattern plume material flows upslope toward ridge axes from off axis plumes and along ridge axes from on axis plumes at sufficiently low spreading rates thinner lithosphere exists above plume material than above normal asthenosphere the edges of normal lithosphere adjacent to plume material act to some extent as levees which limit the lateral spreading of plume material pressure release melt is associated with the upslope flow of plume material it is expected to cause volcanism away from the plume and to sometimes supply melt depleted plume material to ridge axes that are upslope from the region of voluminous melting

forward modeling of the development of seismic anisotropy in the upper mantle development of seismic anisotropy in response to upper mantle flow is approached through an integrated numerical model this model allows to predict the splitting parameters for a shear wave propagating across an upper mantle which deformed in response to a given geodynamic process it consists of 1 thermo mechanical modeling of the finite strain field 2 modeling olivine lattice preferred orientation lpo generated by this strain field 3 calculation of the 3 d elastic properties associated with this lpo and 4 estimation of the shear wave splitting parameters the time lag between the fast and slow split shear wave arrivals dt and the polarization azimuth of the fast wave modeled olivine lpo are constrained relative to lpo measured in naturally and experimentally deformed peridotites comparison of predicted shear wave splitting parameters with seismological data allows us to quantify the possible contribution of the modeled upper mantle flow to the measured splitting values and hence to constrain the interpretation of shear wave splitting data in terms of upper mantle flow we use this forward model to investigate the seismic anisotropy generated in ocean basins by a velocity gradient between the plate and the deep mantle fast shear wave polarizations calculated assuming a constant plate motion are in good agreement with both the sks polarization and the fast propagation direction for p and rayleigh waves observed in the pacific and indian oceans suggesting that away from mid ocean ridges seismic anisotropy in oceanic basins primarily results from asthenospheric deformation by resistive drag beneath the plate delay times are however overestimated this may be ascribed to a stronger strain localization in nature or to partial erosion of the anisotropic layer by hotspots indeed hotspot activity may explain the short length scale variations of dt in the southern pacific finally twolayer models that simulate a change in pacific plate motion as suggested by the bend in the hawaii emperor chain fail to reproduce the observed shear wave splitting this is consistent with previous suggestions that the emperor chain track may not faithfully record the pacific plate absolute motion before 43 ma 1998 elsevier science b v all rights reserved

the role of recrystallization in the preferred orientation of olivine abstract the effects of recrystallization on the preferred orientation in olivine have been studied the recrystallization mechanisms studied include grain growth the deformation induced grain boundary migration digbm and subgrain rotation sgr grain boundary migration is involved in the first two but not in sgr significant preferred orientation was found only in the latter two where dislocations are involved the combined microstructural and fabric preferred orientation observations indicate that the grain boundary migration produces strong preferred orientation when the driving force is the dislocation energy but not when the grain boundary energy is the driving force the nature of preferred orientation due to dislocation related recrystallization digbm or sgr was found to depend on the mechanism of recrystallization the digbm produces preferred orientation in which the low dislocation density grains with unfavourable orientation for easy slip dominate thereby significantly altering the preferred orientation formed by dislocation glide in contrast sgr does not essentially alter the deformation fabric and therefore the fabric associated with sgr recrystallization is related to the geometry of flow the present results demonstrate that the existence of seismic anisotropy in the upper mantle is strong evidence for the dislocation mechanism s of deformation and suggest that care must be exercised in applying the results of laboratory fabric studies made for a particular mechanism of recrystallization to the earth s interior where the dominant mechanism s of dynamic recrystallization can be different

seismic anisotropy in ocean basins resistive drag of the sublithospheric mantle we use finite element models to evaluate the effect of asthenospheric strain associated with the motion of an oceanic plate over a presumed stationary mantle on shear wave splitting observations modeled velocity profiles display a clear strain localization within a horizontal shear zone several tens of kilometers wide developed between an almost rigid mechanical lithosphere and a mildly deformed upper mantle for young oceanic lithosphere cooling results in migration of the maximum shear strain rate towards deeper levels and progressive widening of the shear zone shear strain accumulates with plate displacement the deformed layer thickness depends on plate age and velocity seismic anisotropy depends on the preferred orientations of olivine developed and thus on the strain field for a ray propagating vertically e g sks the fast wave will be polarized parallel to the flow direction i e the apm the delay time will depend on the thickness of the sheared layer and on its intrinsic anisotropy it will therefore increase away from the ridge at a progressively decreasing rate and depend on the absolute plate velocity the estimated anisotropies agree with seismic anisotropy measurements in old domains of ocean basins suggesting that away from mid ocean ridges this simple model may provide a first approximation of the mechanism responsible for the observed seismic anisotropy