microphysical characteristics of overshooting convection from polarimetric radar observations the authors present observations of the microphysical characteristics of deep convection that overshoots the altitude of the extratropical tropopause from analysis of the polarimetric radar variables of radar reflectivity factor at horizontal polarization zh differential reflectivity zdr and specific differential phase kdp identified overshooting convective storms are separated by their organization and intensity into three classifications organized convection discrete ordinary convection and discrete supercell convection composite analysisof identifiedstorms foreach classification reveals microphysical featuressimilar tothose found inpreviousstudiesofdeepconvection withdeepcolumnsofhighlypositivezdrandkdprepresentinglofting of liquid hydrometeors within the convective updraft and above the melting level in addition organized and discrete supercell classifications show distinct near zero zdr minima aligned horizontally with and at altitudes higher than the updraft column features likely indicative of the frequent presence of large hail in each case composites for organized convective systems show a similar zdr minimum throughout the portion of the convective core that is overshooting the tropopause corresponding to zh in the range of 15 30dbz and negative kdp observations in agreement with the scattering properties of small hail and or lump or conical graupel additional analyses of the evolution of overshooting storms reveals that the zdr minima indicative of hail in the middle and upper troposphere and graupel in the overshooting top are associated with the mature and decaying stages of overshooting respectively supporting their inferred contributions to the observed polarimetric fields

unexpected tunnelling volume losses in the westminster area london during construction of the running tunnels for the jubilee line extension london large variations in tunnelling volume loss were measured over about a 2 km distance between waterloo south of the thames and the area north of st james s park at the design stage a value of volume loss of 2 was adopted which was thought to be conservative in practice volume losses of greater than 3 were measured in westminster and in st james s park south of the lake north of the st james s park lake volume losses were less than 2 as expected reliable estimates of volume loss are required for the planning and approval of future tunnelling projects in london and so a detailed investigation was undertaken to establish the reasons for the observed differences two primary and interlinked causes for the large volume losses are identified first the method of tunnelling and construction control south of the lake up to 1 9 m of unsupported tunnel heading was often advanced ahead of the shield and as a result abo

composite vortex2 supercell environments from near storm soundings abstractthree dimensional composite analyses using 134 soundings from the second verification of the origins of rotation in tornadoes experiment vortex2 reveal the nature of near storm variability in the environments of supercell thunderstorms based upon the full analysis it appears that vertical wind shear increases as one approaches a supercell within the inflow sector providing favorable conditions for supercell maintenance and possibly tornado formation despite small amounts of low level cooling near the storm the seven analyzed tornadic supercells have a composite environment that is clearly more impressive in terms of widely used metrics than that of the five analyzed nontornadic supercells including more convective available potential energy cape more vertical wind shear higher boundary layer relative humidity and lower tropospheric horizontal vorticity that is more streamwise in the near storm inflow the widely used supercell composite parameter scp and significant tornado param

does wind shear cause hydrometeor size sorting abstractseveral recent studies have implicated vertical wind shear in producing steady state size sorting of a distribution of hydrometeors falling at their terminal velocity which varies as a function of hydrometeor diameter in particular this mechanism has been invoked to explain both the strength and storm relative orientation of the commonly observed differential reflectivity zdr arc in supercell thunderstorms however the actual role of the shear has not been fully clarified in this study a simple analytical model is used to show that the fundamental source of size sorting is the storm relative wind field itself and in particular its mean taken over the depth of the sorting layer wind shear is only strictly required for producing sustained size sorting in the special but common case of a precipitation source having a motion that lies on the hodograph such as with the environmental winds at the source level in supercells the precipitation source the rotating updraft does not necessari

tunnelling induced consolidation settlements in london clay changes in stresses and pore pressure induced by tunnel excavation in low permeability soil inevitably lead to further ground displacements following the construction this can be referred to as consolidation ground displacements which usually take many years to reach their long term steady state values depending on the permeability and compressibility of the soil as the number of case histories on both the magnitude and the extent of consolidation ground displacements is limited there is no empirical formulation available to predict the magnitude and extent of such displacements this paper describes a suite of finite element analyses carried out as a parametric study aiming to quantify rationally the extent and magnitude of consolidation settlement for both transient and steady state long term conditions the study focuses only on a tunnel constructed in open face mode in heavily overconsolidated london clay the model parameters considered are tunnel geometry soil anisotropic permeability volume

observations of polarimetric signatures in supercells by an x band mobile doppler radar abstractpolarimetric weather radars significantly enhance the capability to infer the properties of scatterers within a resolution volume previous studies have identified several consistently seen polarimetric signatures in supercells observed in the central united states nearly all of these studies used data collected by fixed site s and c band radars because there are few polarimetric mobile radars relatively little has been documented in high resolution polarimetric data from mobile radars compared to s and c bands there has been very limited examination of polarimetric signatures at x band the primary focus of this paper is on one signature that has not been documented previously and one that has had little documentation at x band the first signature seen in at least seven supercell datasets collected by a mobile x band polarimetric radar consists of a narrow band of locally reduced reflectivity factor zh and differential reflectivity typically near the location where the hook echo attac

a dual polarization radar based assessment of the 8 may 2003 oklahoma city area tornadic supercell abstract on 8 may 2003 a tornadic supercell tracked through portions of the oklahoma city oklahoma metropolitan area and produced violent damage along portions of its path this storm passed through the dense in situ radar network in central oklahoma and provided close range operational prototype polarimetric and terminal doppler weather radar observations of the storm as it made the transition into the tornadic phase the time evolving polarimetric features were scrutinized with regard to storm morphology particularly as related to the development of a rear flank downdraft pulse within the storm immediately preceding the long track tornado event two new polarimetric terms are introduced the zdr shield and kdp foot along with a discussion of the orientation of the zdr and kdp columns relative to midlevel rotation signatures storm downdraft and gust front characteristics are discussed relative to polarimetric fields and background environment characteristics highlighted for this event are a warm

polarimetric radar metrics related to tornado life cycles and intensity in supercell storms abstractpolarimetric radar signatures have been related to the typical evolution of supercell storms including through tornado life cycles now that polarimetric radar observations are available for a large sample of supercell storms time series of new radar metrics can be derived these metrics can be compared with phases of known tornado life cycles in an effort to develop new methods of anticipating tornadoes and to increase understanding of storm scale structural and microphysical changes through supercell and tornado life cycles in this paper radar metrics including measures of differential reflectivity zdr columns zdr arcs polarimetrically inferred hailfall regions and mean value of copolar correlation coefficient hv in the echo appendage are compared to the tornado life cycle and to storm maximum tornado intensity in a sample of 35 tornadic supercells it is shown that these radar metrics may change repeatedly and thus can be used to distinguish tornadic and nontornadic periods in single su

measurement and characterization of infrasound from a tornado producing storm a hail producing supercell on 11 may 2017 produced a small tornado near perkins oklahoma 35 97 97 04 at 2013 utc two infrasound microphones with a 59 m separation and a regional doppler radar station were located 18 7 and 70 km from the tornado respectively elevated infrasound levels were observed starting 7 min before the verified tornado infrasound data below 5 hz was contaminated with wind noise but in the 5 50 hz band the infrasound was independent of wind speed with a bearing angle that was consistent with the movement of the storm core that produced the tornado during the tornado a 75 db peak formed at 8 3 hz which was 18 db above pre tornado levels this fundamental frequency had overtones 18 29 36 and 44 hz that were linearly related to mode number analysis of a larger period of time associated with two infrasound bursts the tornado occurred during the first event shows that the spectral peaks from the tornado were present from 4 min before to 40 min after tornadogenesis this suggests that the same geophysical process es was active during this entire window

rapid scan polarimetric doppler radar observations of tornadogenesis and tornado dissipation in a tornadic supercell the el reno oklahoma storm of 24 may 2011 abstracton 24 may 2011 a mobile rapid scan x band polarimetric doppler radar raxpol collected data on a supercell as it produced two tornadoes near el reno oklahoma the first tornado rated an ef 3 was documented from intensification to decay and the genesis and intensification of a second tornado that was rated an ef 5 was subsequently also documented the objective of this study is to examine the spatiotemporal evolution of the rotation associated with the tornadoes i as the first tornado weakened to subtornadic intensity and ii as the second tornado formed and intensified it is found that weakening did not occur monotonically the transition from tornadic to subtornadic intensity over the depth of the radar volume 4 km occurred in less than 30 s but this behavior is contingent upon the threshold for doppler shear used to define the tornado similarly the onset of a tornadic strength doppler velocity couplet occurred within a 30 s period over all elevations additionally the evolutio

modelling of long term ground response to tunnelling under st james s park london following a tunnel excavation in low permeability soil it is commonly observed that the ground surface continues to settle and ground loading on the tunnel lining changes as the pore pressures in the ground approach a new equilibrium condition the monitored ground response following the tunnelling under st james s park london shows that the mechanism of subsurface deformation is composed of three different zones swelling consolidation and rigid body movement the swelling took place in a confined zone above the tunnel crown extending vertically to approximately 5 m above it on the sides of the tunnel the consolidation of the soil occurred in the zone primarily within the tunnel horizon from the shoulder to just beneath the invert and extending laterally to a large offset from the tunnel centreline above these swelling and consolidation zones the soil moved downward as a rigid body in this study soil fluid coupled three dimensional finite element analyses were performed to simulate the mechanism of long term ground response monitored at st james s park an advanced critical state soil model which can simulate the behaviour of london clay in both drained and undrained conditions was adopted for the analyses the analysis results are discussed and compared with the field monitoring data it is found that the observed mechanism of long term subsurface ground and tunnel lining response at st james s park can be simulated accurately only when stiffness anisotropy the variation of permeability between different units within the london clay and non uniform drainage conditions for the tunnel lining are considered this has important implications for future prediction of the long term behaviour of tunnels in clays

intrinsic and extrinsic controls of spatial and temporal variations in modern fluvial tufa sedimentation a thirteen year record from a semi arid environment sedimentological and hydrochemical parameters of the river piedra north east spain were monitored every six months from 1999 to 2012 at 24 sites at which tablets were installed all along the river the river water is of hco3 so4 ca type and is notably influenced by inputs from upstream karstic springs tufa deposition was first detected 8 km downstream of these springs and greatly increased from there primarily along the steeper stretch i e within the monasterio de piedra natural park then deposition decreased through the most downstream stretch with smaller ground water inputs the spatial evolution of the tufa thickness with parallel variations of pwp plummer wigley parkhurst rates was thus determined by the river water pco2 which was controlled by ground water inputs and by the river bed slope five fluvial subenvironments and seven sedimentary facies were characterized the water flow conditions are the primary factor responsible for the distinct deposition rates of facies mainly through co2 outgassing stromatolites and moss tufa and alga tufa had the highest rates whereas loose tufa formed in slow flowing water and tufa of spray areas had thinner deposition a six month pattern in the deposition rate was detected through thickness measurements that pattern was parallel to the seasonal pwp rates the increased deposition during warm periods spring and summer mean 5 08 mm compared with cool periods autumn and winter mean 2 77 mm is linked chiefly to temperature which controlled the seasonal changes in the physico chemical and biological processes this finding is supported by a principal components analysis seasonal variations of insolation and day duration also contributed to such a deposition pattern large discharge events which provoked erosion of tufa deposits and dilution of water caused the reversal of the seasonal deposition rate pattern stromatolites are likely to preserve the most complete sedimentary record although tufas are a potentially sensitive record of climate related parameters erosion is an intrinsic process that may overwhelm the effects of such parameters this issue should be considered in palaeoclimatic studies based on the tufa record particularly in semi arid conditions

micro erosion meter measurements of travertine deposition rates a case study from louie creek northwest queensland australia although originally designed to measure surface denudation the micro erosion meter mem can be adapted easily to measure deposition rates of chemical sediments such as travertines and speleothems at louie creek northwest queensland australia travertine deposition rates measured using the mem average 4 15 mm a 1 however this figure masks considerable rate variability both purely hydraulic and hydraulically related variables appear to be the major mechanisms controlling deposition rates the most rapid rates occur within relatively high energy hydraulic regimes impact and flow zones whilst deposition rates in pools separating individual travertine barrages standing water zones are relatively slow dsposition rate variations within spray and impact zones are related directly to discharge the highest rates in flow zones correlate with the incorporation into the travertine of in situ and allochthonous biogenic material such as caddis fly larvae green algal mats and phytoclasts which proliferate or are entrapped easily under such hydraulic conditions considerable spatial variability in deposition rates also prevails the highest rates for a given set of hydraulic conditions occur at two sites the upper everglades and the lower everglades the mem also measures net erosion of travertines at louie creek most of the travertine erosion occurs in the wet season and is confined primarily to standing water zones 1997 john wiley sons ltd

mobile x band polarimetric doppler radar observations of the 4 may 2007 greensburg kansas tornadic supercell abstracton 4 may 2007 a supercell produced an ef 5 tornado that severely damaged the town of greensburg kansas volumetric data were collected in the greensburg storm by the university of massachusetts x band mobile polarimetric doppler radar umass x pol for 70 min 10 tornadoes were detected this mobile doppler radar dataset is one of only a few documenting an ef 5 tornado and the supercell s transition from short track cyclic tornado production mode 1 to long track tornado production mode 2 using bootstrap confidence intervals it is determined that the mode 2 tornadoes moved in the same direction as the supercell vault in contrast the mode 1 tornadoes moved to the left with respect to the vault from polarimetric data collected in this storm the authors infer the presence of large oblate drops high zdr high hv in the forward flank and surrounding some of the tornadoes the authors speculate that the weak echo column wec in the greensburg tornado which extended above 10 km agl

the bowdle south dakota cyclic tornadic supercell of 22 may 2010 surface analysis of rear flank downdraft evolution and multiple internal surges abstractmobile mesonet sampling in the hook echo rear flank downdraft rfd region of a tornadic supercell near bowdle south dakota provided the opportunity to examine rfd thermodynamic and kinematic attributes and evolution focused analysis of the fifth low level mesocyclone cycle that produced two significant tornadoes including a violent tornado revealed four rfd internal surge rfdis events rfdiss appeared to influence tornado development intensity and demise by altering the thermodynamic and kinematic character of the rfd region bounding the pretornadic and tornadic circulations significant tornadoes developed and matured when the rfd modulated by internal surges was kinematically strong only weakly negatively buoyant and very potentially buoyant in contrast the demise of the bowdle tornado was concurrent with a much cooler rfdis that replaced more buoyant and far more potentially buoyant rfd air near the tornado this surge also likely contributed to a displacement of the tornado from

storm relative helicity revealed from polarimetric radar measurements the dual polarization radar variables are especially sensitive to the microphysical processes of melting and size sorting of precipitation particles in deep convective storms polarimetric measurements of such processes can provide information about the airflow in and around the storm that may be used to elucidate storm behavior and evolution size sorting mechanisms include differential sedimentation vertical transport strong rotation and wind shear in particular winds that veer with increasing height typical of supercell environments cause size sorting that is manifested as an enhancement of differential reflectivity zdr along the right or inflow edge of the forward flank downdraft precipitation echo which has been called the zdr arc signature in some cases this shear profile can be augmented by the storm inflow it is argued that the magnitude of this enhancement is related to the low level storm relative environmental helicity srh in the storm inflow to test this hypothesis a simple numerical model is constructed that calculates trajectories for raindrops based on their individual sizes which allows size sorting to occur the modeling results indicate a strong positive correlation between the maximum zdr in the arc signature and the low level srh regardless of the initial drop size distribution aloft additional observational evidence in support of the conceptual model is presented potential changes in the zdr arc signature as the supercell evolves and the low level mesocyclone occludes are described

a numerical study of the effect of groundwater movement on long term tunnel behaviour soft ground tunnelling beneath the water table induces pore water pressure changes and alters the hydraulic regime in the ground there are various factors that control the tunnel soil interaction behaviour during the equilibration period after tunnel construction through to the long term steady state through the presentation of results from coupled non linear finite element analyses this paper considers the differences in predicted ground and lining responses in the long term for different post tunnelling flow conditions a 4 m diameter circular tunnel constructed 20 m below ground level is adopted for the geometry with the soil conditions based on those found in london uk and seoul south korea the lining permeability is varied from fully permeable to impermeable and an approach to modelling finite lining permeability is presented and assessed for the permeable lining analyses two flow regimes are modelled one in which the water table is maintained at its original elevation and one in which the

method to evaluate the long term surface movements by tunneling in london clay abstractlong term ground movements occur after tunnel construction in clayey soils due to dissipation of excess pore pressure generated during construction and a new seepage state that depends on the drainage conditions of the tunnel a methodology was proposed in the past to evaluate the long term surface settlements for tunnels in london clay this paper extends the previous work by proposing a new method to estimate both consolidation induced vertical and horizontal displacements as well as consolidation induced peak horizontal strains in this method a new relative soil lining permeability index which was modified from the earlier work is proposed by assuming a radial seepage flow into a tunnel using this index along with tunnel geometry and soil properties a series of equations was derived to better facilitate the calculation of the long term ground displacements and strains compared to the normalized charts adopted in the previous evaluation method the applicability of the proposed method is

sensitivity of central oklahoma convection forecasts to upstream potential vorticity anomalies during two strongly forced cases during mpex abstractthe role of upstream subsynoptic forecast errors on forecasts of two different central oklahoma severe convection events 19 and 31 may 2013 characterized by strong synoptic forcing during the mesoscale predictability experiment mpex are evaluated by applying the ensemble based sensitivity technique to wrf ensemble forecasts with explicit convection during both cases the forecast of the timing and intensity of convection over central oklahoma is modulated by the southward extent of upstream midtropospheric potential vorticity anomalies that are moving through the base of a larger scale upstream trough but pass by central oklahoma prior to convective initiation in addition the convection forecasts are also sensitive to the position of lower tropospheric boundaries such that moving the boundaries in a manner that would lead to increased equivalent potential temperature over central oklahoma prior to convective initiation leads to more precipitation statistical pv inversion and correlation c

a preliminary polarimetric radar comparison of pretornadic and nontornadic supercell storms abstractsupercell thunderstorms produce a variety of hazards including tornadoes a supercell will often exist for some time prior to producing a tornado while other supercells never become torna

c and o stable isotope variability in recent freshwater carbonates river krka croatia three types of recent carbonate precipitates from the river krka croatia were analysed 1 bulk tufa from four main cascades in a 34 km long section of the river flow through the krka national park 2 a laminar stromatolite like incrustation formed in the tunnel of a hydroelectric power plant close to the lowest cascade and 3 recent precipitates collected on artificial substrates during winter spring and summer periods stable isotope compositions of carbon d 13 c and oxygen d 18 o in the carbonate and organic carbon d 13 corg were determined and compared with d 18 o of water and d 13 c of dissolved inorganic carbon dic the source of dic which provides c for tufa precipitation was determined from the slope of the line dic dic0 1 vs d 13 c dic dic dic0 sayles curry 1988 the d 13 c value of added dic was 13ae6 corresponding to the dissolution of co2 with d 13 c between 19ae5 and 23ae0 vienna pee dee belemnite vpdb the observed difference between the measured and calculated equilibrium temperature of precipitation of bulk tufa barriers indicates that the higher the water temperature the larger the error in the estimated temperature of precipitation this implies that the climatic signals may be valid only in tufas precipitated at lower and relatively stable temperatures the laminar crust comprising a continuous record of the last 40 years of precipitation shows a consistent trend of increasing d 13 c and decreasing d 18 o the lack of covariation between d 13 c and d 18 o indicates that precipitation of calcite was not kinetically controlled for either of the elements d 13 c and d 18 o of precipitates collected on different artificial substrates show that surface characteristics both of substrates and colonizing biota play an important role in c and o isotope fractionation during carbonate precipitation

low levelzdrsignatures in supercell forward flanks the role of size sorting and melting of hail abstractthe low levels of supercell forward flanks commonly exhibit distinct differential reflectivity zdr signatures including the low zdr hail signature and the high zdr arc the zdr arc has been previously associated with size sorting of raindrops in the presence of vertical wind shear here this model is extended to include size sorting of hail idealized simulations of a supercell storm observed by the norman oklahoma koun polarimetric radar on 1 june 2008 are performed using a multimoment bulk microphysics scheme in which size sorting is allowed or disallowed for hydrometeor species several velocity diameter relationships for the hail fall speed are considered as well as fixed or variable bulk densities that span the graupel to hail spectrum a t matrix based emulator is used to derive polarimetric fields from the hydrometeor state variables size sorting of hail is found to have a dominant impact on zdr and can result in a zdr arc from melting hail even when size sorting is disallowed in

a dual wavelength polarimetric analysis of the 16 may 2010 oklahoma city extreme hailstorm abstracta comparative analysis of a supercell hailstorm using simultaneous observations with s band and c band polarimetric radars supported by abundant ground truth reports is presented in this study the storm occurred on 16 may 2010 and produced a swath of extremely damaging hail across a large portion of the oklahoma city oklahoma metro area hail sizes over 10 cm in diameter and hail drifts upward of 1 5 m in height were reported both s band koun and c band university of oklahoma polarimetric radar for innovations in meteorology and engineering ou prime polarimetric radars in norman oklahoma sampled the storm at ranges less than 60 km so that high resolution dual wavelength polarimetric data were obtained at c band this analysis mostly presents raw z and zdr due to problems with differential phase resulting from an incorrect censoring threshold in the examined case while taking into account the possibility of attenuation in the interpretation of these data among the issues investigat

the arcadia oklahoma storm of 17 may 1981 analysis of a supercell during tornadogenesis abstract on 17 may 1981 an extensive dataset was collected for a supercell thunderstorm that produced an f2 tornado near arcadia in central oklahoma coordinated dual doppler scans of the storm by 10 cm research radars were collected at approximately 5 min intervals from 30 min before the tornado touched down until 15 min after the tornado had dissipated the arcadia storm was also well sampled by a 444 m tall instrumented tower the low level inflow updraft mesocyclone and rear precipitation core of the supercell all passed across the tower a comparison of the instrumented tower measurements with a dual doppler synthesis reveals that the latter qualitatively resolved the low level flow however the magnitudes of the low level horizontal winds and updraft speed were underestimated in addition the vertical shear of the horizontal wind in the lowest kilometer was unresolved in the doppler winds in the storm environment horizontal vorticity was strong 1 5 10 2 s 1 and approximately streamwise

rapid scan super resolution observations of a cyclic supercell with a dual polarization wsr 88d abstract in recent years there has been widespread interest in collecting and analyzing rapid updates of radar data in severe convective storms to this end conventional single polarization rapid scan radars and phased array radar systems have been employed in numerous studies however rapid updates of dual polarization radar data in storms are not widely available for this study a rapid scanning strategy is developed for the polarimetric prototype research weather surveillance radar 1988 doppler wsr 88d radar in norman oklahoma koun which emulates the future capabilities of a polarimetric multifunction phased array radar mpar with this strategy data are collected over an 80 sector with 0 5 azimuthal spacing and 250 m radial resolution super resolution with 12 elevation angles thus full volume scans over a limited area are collected every 71 73 s the scanning strategy was employed on a cyclic nontornadic supercell storm in western oklahoma on 1 june 2008 the evolution of the pola