linearized inversion of seismic reflection data this is the first of a series of papers giving the solution of the inverse problem in seismic exploration the acoustic approximation is used together with the assumption that the velocity field has the form the forward problem is then linearized thus neglecting multiple reflected waves and the inverse problem of estimating is set up its rigorous solution can be obtained using an iterative algorithm each step consisting of a classical kirchhoff migration hyperbola summation plus a classical forward modeling step circle summation

soil surface water content estimation by full waveform gpr signal inversion in the presence of thin layers we analyzed the effect of shallow thin layers on the estimation of soil surface water content using full waveform inversion of off ground ground penetrating radar gpr data strong dielectric contrasts are expected to occur under fast wetting or drying weather conditions thereby leading to constructive and destructive interferences with respect to surface reflection first synthetic gpr data were generated and subsequently inverted considering different thin layer model configurations the resulting inversion errors when neglecting the thin layer were quantified and then the possibility to reconstruct these layers was investigated second laboratory experiments reproducing some of the numerical experiment configurations were conducted to assess the stability of the inverse solution with respect to actual measurement and modeling errors results showed that neglecting shallow thin layers may lead to significant errors on the estimation of soil surface water content 0 03 m3 m3 depending on the contrast accounting for these layers in the inversion process strongly improved the results although some optimization issues were encountered in the laboratory the proposed full waveform method permitted to reconstruct thin layers with a high resolution up to 2 cm and to retrieve the soil surface water content with an rmse less than 0 02 m3 m3 owing to the full waveform inverse modeling these results suggest that the proposed gpr approach is promising for field scale mapping of soil surface water content of nondispersive soils with low electrical conductivity and for instances when soil layering is encountered

observations of dual slantwise circulations above a cool undercurrent in a mesoscale convective system a series of mesoscale convective systems mcss was observed in the uk during one of the intensive observation periods iop 3 in the convective storm initiation project csip a detailed case study of one of the mcss involving some novel interpretation of single doppler radar data reveals the evolution of stacked slantwise circulations associated with elevated upright convection a feature of this occasion was the existence near the surface of a strong undercurrent of cool air flowing against the direction of travel of the storm the air feeding both the upright and slantwise ascent originated not from near the surface but rather from layers between 1 and 3 km the upright convection was intense at first and was accompanied by a region of dry subsidence surrounding it together with the alternating layers of slantwise ascent and descent within the storm s precipitation area when the elevated upright convection weakened vigorous slantwise motions continued for some time but their slope decreased from the initial 1 in 4 to 1 in 9 the lowermost layer of slantwise descent corresponded to a moderately intense rear inflow jet the rear inflow jet did not penetrate the cool undercurrent and reach the surface instead beneath where it impacted the warm air capping the undercurrent the undercurrent took on the structure of a gravity wave without stagnation the raised head of the undercurrent lifted overlying air of high wet bulb potential temperature sufficiently to overcome the convective inhibition copyright c 2010 royal meteorological society

observations of elevated convection initiation leading to a surface based squall line during 13 june ihop_2002 abstract the evolution of a mesoscale convective system mcs observed during the international h2o project that took place on the great plains of the united states is described the mcs formed at night in a frontal zone with four initiation episodes occurring between approximately 0000 and 0400 local time radar radiosonde and surface data together show that at least three of the initiation episodes were elevated occurring from moist conditionally unstable layers located above the boundary layer which had been stabilized by previous mcss initiation occurred in northwest southeast oriented lines where a southerly nocturnal low level jet terminated generating elevated convergence one initiation episode was observed using the s band dual polarization doppler radar s pol and occurred at the intersection of this convergence zone with a propagating wave calculations of the scorer parameter were consistent with wave trapping downdrafts from the developing convection generated both waves and bores w

secondary initiation of multiple bands of cumulonimbus over southern britain ii dynamics of secondary initiation summary the convective storm initiation project csip pilot field programme took place in the summer of 2004 in southern england during this field campaign a case of a cold pool outflow initiating an arc of convection downwind of the generating storm the primary storm was observed three further arcs were initiated further downwind of this first arc these arcs all later gave significant rainfall over south east england results from the modelling studies described in this paper show that gravity waves generated by the primary storm may have been responsible for initiating the further three arcs of convective showers that were observed the modelled primary storm generates waves with a range of vertical wavelengths these are separated by dispersion with the higher order modes with the largest vertical wavelengths travelling fastest approximately 30 m s 1 the fastest two modes suppressed convection and later modes increased boundary layer depth and so initiated convection the multiple peaks from non hydrostatic effects in the third mode may have been responsible for the two main arcs observed and the fourth mode may have been responsible for the third arc the amplitude of the modelled waves at low levels was much larger downwind of the primary storm than upwind and only initiated convection there which agrees with the observations of the arcs forming downwind of the primary storm this asymmetry appears to be caused by the moving wave source and asymmetric wave trapping finally we discuss the implications for numerical weather prediction nwp reducing the resolution of the model and varying the magnitude of the wind speed used shows that a non hydrostatic high resolution 1k m nwp model should be able to capture such wave processes if the generating storm is forecast or analysed correctly

a comparison of stratosphere troposphere transport in convection permitting and convection parameterizing simulations of three mesoscale convective systems 1 the transport of stratospheric air into the troposphere within deep convection was investigated using the met office unified model version 6 1 three cases were simulated in which convective systems formed over the uk in the summer of 2005 for each of these three cases simulations were performed on a grid having 4 km horizontal grid spacing in which the convection was parameterized and on a grid having 1 km horizontal grid spacing which permitted explicit representation of the largest energy containing scales of deep convection cross tropopause transport was diagnosed using passive tracers that were initialized above the dynamically defined tropopause 2 potential vorticity unit surface with a mixing ratio of 1 although the synoptic scale environment and triggering mechanisms varied between the cases the total simulated transport was similar in all three cases the total stratosphere to troposphere transport over the lifetime of the convective systems ranged from 25 to 100 kg m2 across the simulated convective systems and resolutions which corresponds to 5 20 of the total mass located within a stratospheric column extending 2 km above the tropopause in all simulations the transport into the lower troposphere defined as below 3 5 km elevation accounted for 1 of the total transport across the tropopause in the 4 km runs most of the transport was due to parameterized convection whereas in the 1 km runs the transport was due to explicitly resolved convection the largest difference between the simulations with different resolutions occurred in the one case of midlevel convection considered in which the total transport in the 1 km grid spacing simulation with explicit convection was 4 times that in the 4 km grid spacing simulation with parameterized convection although the total cross tropopause transport was similar stratospheric tracer was deposited more deeply to near surface elevations in the convection parameterizing simulations than in convection permitting simulations

durability of carbonate rock as building stone with comments on its preservation carbonate rocks have been extensively used as building stones because of their availability workability and attractiveness unfortunately however some stones suffer from chemical attack or freeze thaw activity the environmental affects especially those due to pollution of the atmosphere are discussed in terms of weathering processes salt crystallization and acid deposition a review of some recent research in relation to deterioration of stone in urban environments is given and carbonate rocks are classified in relation to position within a building geographical location and degree of pollution some comments on stone preservation are provided especially in terms of the properties a preservative should possess

variable cirrus shading during csip iop 5 ii effects on the convective boundary layer a combination of radiosonde wind profiler and aircraft observations together with large eddy modelling show that shading from orphaned cirrus anvils had significant effects on the boundary layer during csip iop 5 the control of boundary layer development by the cirrus shading and the subsidence induced by the cirrus cover led to a boundary layer that at an aircraft altitude of around 500 m was less turbulent 0 8 g kg 1 drier and 0 3 k warmer under thick cirrus than in clear skies in addition at the top of the boundary layer turbulence persisted for some time after the onset of cirrus shading allowing continued entrainment and so stabilization of the previously well mixed boundary layer these effects which would have inhibited convective initiation under the cirrus are consistent with the results of the first part of this study marsham et al 2007 power spectra show that while vertical velocities were dominated by variations on the scale of the boundary layer depth for water vapour mixing ratios and potential temperatures mesoscale variations were comparable or dominant in some cases a spectral gap is observed between these two scales of contributions radiosonde data and modelling show that in addition to the variations in the boundary layer caused by the variable cirrus cover pre existing variations in lid strength and boundary layer moisture were also significant on this day these water vapour variations are also detectable in retrievals of total column water vapour from global positioning systern data copyright c 2007 royal meteorological society

variable cirrus shading during csip iop 5 i effects on the initiation of convection observations from the convective storm initiation project csip show that on 29 june 2005 intensive observation period 5 cirrus patches left over from previous thunderstorms reduced surface sensible and latent heat fluxes in the csip area large eddy model lem simulations using moving positive surface flux anomalies show that we expect the observed moving gaps in the cirrus cover to significantly aid convective initiation in these simulations the timing of the ci is largely determined by the amount of heat added to the boundary layer but weak convergence at the rear edge of the moving anomalies is also significant meteosat and rain radar data are combined to determine the position of convective initiation for all 25 trackable showers in the csip area the results are consistent with the lem simulations with showers initiating at the rear edge of gaps at the leading edge of the anvil or in clear skies in all but one of the cases the initiation occurs in relatively clear skies in all but two of the cases with the exceptions probably linked to orographic effects for numerical weather prediction the case highlights the importance of predicting and assimilating cloud cover the results show that in the absence of stronger forcings weak forcings such as from the observed cirrus shading can determine the precise location and timing of convective initiation in such cases since the effects of shading by cirrus anvils from previous convective storms are relatively unpredictable this is expected to limit the predictability of the convective initiation copyright 2007 royal meteorological society

preliminary observations on the impact of complex stress histories on sandstone response to salt weathering laboratory simulations of process combinations historic sandstone structures carry an inheritance or a memory of past stresses that the stone has undergone since its placement in a facade this inheritance which conditions present day performance may be made up of long term exposure to a combination of low magnitude background environmental factors for example salt weathering temperature and moisture cycling and superimposed upon these less frequent but potentially high magnitude events or exceptional factors for example lime rendering severe frost events fire the impact of complex histories on the decay pathways of historic sandstone is not clearly understood but this paper seeks to improve that understanding through the use of a laboratory process combination study blocks of quartz sandstone peakmoor from nw england were divided into subsets that experienced different histories lime rendering and removal fire and freeze thaw cycles in isolation and combination that reflected the event timeline of a real medieval sandstone monument in ne ireland bonamargy friary mccabe et al 2006b these subsets were then subject to salt weathering cycles using a 10 salt solution of nacl and mgso4 that represents the every day stress environment of for example sandstone structures in coastal or polluted urban location block response to salt weathering was monitored by collecting drying and weighing the debris that was released as blocks were immersed in the salt solution at the beginning of each cycle the results illustrate the complexity of the stone decay system showing that seemingly small variations in stress history can produce divergent response to salt weathering cycles applied to real world historic sandstone structures this concept may help to explain the spatial and temporal variability of sandstone response to background environmental factors on a single facade and encourage conservators to include the role of stress inheritance when selecting and implementing conservation strategies

inscription legibility method for estimating rock weathering rates abstract relative legibility of dated inscription is closely associated with measured surface recessions for 3895 vermont marble tombstones and the resulting ordinal to ratio transfer function allows weathering rates to be computed for many exposed rock surfaces that cannot be measured by more accurate methods case studies demonstrate applications of the technique 1 surfaces of horizontal ground level marble plaques have dissolved at steady rates of 1 3 mm 100 yr in providence ri and 1 1 mm 100 yr in richmond va despite reports of increasing acid rain 2 vertical faces of century old marble tombstones in upper midwestern united states small towns have receded 10 times faster 1 4 mm 100 yr than have stones in less polluted environments 3 vertical faces of limestone monuments have receded at half the rate 0 5 mm 100 yr of vermont marble tombstones 0 9 mm 100 yr in louisville ky 4 aspect differences have not affected recession rates of marble pillar surfaces near philadelphia pa 5 aspect is important to sandstone granular weathering rates at inscription rock nm where north facing cliffs recede 3 times faster 0 9 mm 100 yr than do southeast facing cliffs 6 horizontal pre weathered quartizite surfaces at a scenic overlook in maryland recede at 0 6 mm 100 yr

weathering of sandstone lotus petals at the angkor site a 1 000 year stone durability trial this article is based on field investigations carried out at ta keo and banteay srei temples angkor cambodia which have similar environmental histories and display the same recurrent decorative pattern lotus petal in three different sandstone lithotypes based on two original scales of mechanical and chemical weathering the degree of deterioration of c 2000 sandstone petals was visually assessed resulting in the proposal of a durability scale an explanatory scheme was provided based on laboratory analyses of stone materials icp aes xrd sem eds polarizing microscopy and mercury injection the key drivers of sandstone durability are both mineralogical and petrophysical the remarkable preservation of the pink sandstone is due to the quartzose nature of its clasts the non swelling clay content of its abundant matrix kaolinite and its porosity structure large connected pores and probable non connected porosity the overall good preservation of the green sandstone is due to its extremely low porosity and specific surface area associated with its strong cementation the severe deterioration of the grey sandstone is due to its laminated structure oriented biotites the susceptibility to hygric swelling and solution of its binding agents chlorite smectite and calcite and its porosity structure which evolves during a two stage weathering sequence the first stage is characterized by a bimodal porosity due to the partial clogging of macropores by swelling clays and the second stage by a substantial increase in porosity and the penetration of salts barite and anhydrite conversely oxidation phenomena associated with weathering can lead to a drastic reduction of porosity

convergence zones and their impact on the initiation of a mesoscale convective system in west africa during the african monsoon multidisciplinary analysis amma campaign in 2006 extended surface and boundary layer measurements were performed to study the influence of soil moisture patterns on the generation of thermally forced circulations and triggering of deep convection however not all processes involved in the triggering of a mesoscale convective system mcs could be identified in previous studies therefore cosmo consortium for small scale modeling simulations were carried out investigating possible trigger mechanisms on 31 july 2006 an mcs was initiated and on 1 august soil moisture inhomogeneities resulted in a thermally forced circulation with an associated convergence zone but no deep convection was triggered it was found that the mcs on 31 july was influenced by a cyclonic vortex and favoured by the superposition of two convergence zones of different origins initiation of the mcs occurred in the simulation when moist monsoon air was transported to the north associated with a cold pool ahead of another mcs and reached the convergence zone on 1 august the simulation reproduced the thermally forced circulation caused by the soil moisture pattern which had been produced by the precipitation of the mcs however due to low humidity in the boundary layer and low convective available potential energy the lifting along the convergence zone did not trigger deep convection copyright 2011 royal meteorological society

two dimensional full wavefield inversion of wide aperture marine seismic streamer data summary a 2 d full wavefield inversion method is presented for the processing of wide aperture data the diversity of information contained within such datasets may be handled in a complete manner by first matching the traveltimes of the main events and then progressing to waveform fitting of the data through explicit full wavefield modelling our wavefield inversion scheme is based upon a finite difference solution of the 2 d elastic wave equation in the time distance domain the strength of adopting such an approach is the ability to generate all possible wave types within a given 2 d model multiples converted waves etc and thus to simulate and accurately model complex seismic wavefields the aim of the inversion is to find the 2 d p wave velocity model that minimizes the least squared difference between the observed and synthetic data across the full range of offsets following extensive testing on synthetic data the wavefield inversion scheme has been applied to wide aperture real marine seismic streamer datasets we present results from the synthetic testing and the wavefield inversion of wide aperture real data out to 12 km offset that was recorded on a single streamer even though current computational restrictions allow only a small subsection of the data to be analysed these examples demonstrate the potential value of wide aperture 2 d full wavefield inversion

multi sensor observations of a wave beneath an impacting rear inflow jet in an elevated mesoscale convective system observations of a wave generated below and propagating with an elevated mesoscale convective system mcs are presented the mcs and the wave tracked directly across the 90 km extent of the observational network deployed for the convective storm initiation project csip and maintained a coherent structure and velocity during this 1 5 hour period the rear inflow jet of the mcs was observed to impact upon but not penetrate the stable undercurrent that was located beneath the mcs apparently constricting the depth of the undercurrent which did not participate in the main convective updraught the wave crest was located approximately 15 km ahead of this constriction the overall wave led to between 200 and 1000 m of ascent and approximately 1500 m of descent however undulations were superimposed on the overall wave with a wavelength of approximately 7 km and a crest totrough amplitude of approximately 1000 m these undulations were associated with double maxima in surface pressure and the elevation of the observed low level wind anomaly where low level winds were backed by more than 90 t hese winds were never at rest relative to the system and the wave was therefore a gravity wave without stagnation the hydrostatic effect expected from the observed lifting in the wave was broadly consistent with the observed surface pressure perturbation of 2 hpa no cold pool outflow was ever observed instead the observed surface cooling of approximately 4 c was shown to be consistent with reduced solar insolation the generation of the observed wave structure and its implications for the maintenance of the mcs and numerical modelling of the system are discussed copyright c

joint acoustic full waveform inversion of crosshole seismic and ground penetrating radar data in the frequency domain abstractintegrating crosshole ground penetrating radar gpr with seismic methods is an efficient way to reduce the uncertainty and ambiguity of data interpretation in shallow geophysical investigations we have developed a new approach for joint full waveform inversion fwi of crosshole seismic and gpr data in the frequency domain to improve the inversion results of both fwi methods in a joint objective function three geophysical parameters p wave velocity permittivity and conductivity are effectively connected by three weighted cross gradient terms that enforce the structural similarity between parameter models simulation of acoustic seismic and scalar electromagnetic problems is implemented using 2d finite difference frequency domain methods and the inverse problems of seismic fwi and gpr fwi are solved using a matrix free truncated newton algorithm the joint inversion procedure is performed in several hierarchical frequencies and the three parameter models are sequentially inverted at each

secondary initiation of multiple bands of cumulonimbus over southern britain i an observational case study summary special observing facilities have been assembled in southern england as part of the convective storm initiation project csip to study the mesoscale and convective scale processes that determine precisely where warm season convective showers will break out this paper reports the results of a case study during the pilot field campaign of csip in july 2004 one purpose of the pilot project was to demonstrate the value of various observational facilities and to evaluate the usefulness of a variety of analysis and synthesis techniques amongst other things the case study demonstrates the utility of high resolution imagery from the meteosat second generation satellite for tracking the early stages of the convective clouds and of a new clear air scanning radar at chilbolton for mapping both the top of the boundary layer and the initialgrowth of the convective cells that penetrate it the particular event studied involved the triggering of convection that developed into three parallel arcs of showers and thunderstorms the first arc was triggered along the leading edge of the outflow density current from an earlier cluster of showers but the convection in the second and third arcs was triggered by a different mechanism the paper describes in detail the way in which this convection broke through the stable layer or lid at the top of a boundary layer of variable depth the strength of the lid decreased and the depth of the boundary layer increased with timeas a result of diurnal heating but the precise locations where convection finally broke through were determined by the spatial variability in boundary layer depth the analysis suggests that a wave like modulation of the boundary layer depth of amplitude 150 m perhaps due to a gravity wave disturbance from the earlier cluster of showers had a greater influence on where the convection was triggered than the modest hills typically 200 m high in southern england

sandstone weathering a century of research and innovation abstract a review of sandstone weathering research particularly in the past 100 years reveals a trajectory of enquiry from early description and classification of features to development of process based explanations to decreasing scales of investigation and a disparity between understanding of process es and explanations of the genesis of sandstone weathering features developments in expositions on mesoscale weathering features on sandstone surfaces are discussed demonstrating a range of approaches to weathering phenomena field based and laboratory based that must be linked to provide an explanation of observed features on a landform scale throughout the twentieth century a thematic chronology highlights certain trends in research description of forms often in arid and semi arid environments single process form models an emphasis on experimentation difficulties in measuring weathering rates and a persistent emphasis on physical causes of breakdown a new research agenda is promoted in which biodeterioration and chemical processes gain parity a holistic approach based on conceptual modeling of weathering systems gains prominence and scale issues are addressed more rigorously

sandstone weathering in tropical climate results of low destructive investigations at the temple of angkor wat cambodia abstract investigations at the temple of angkor wat aimed at the explanation of the major weathering processes of building sandstone as well as at the role of both intrinsic factors i e sandstone petrography and properties and extrinsic factors i e climatic and environmental influences since material sampling at the temple was limited to a few boreholes because of the high artistic rank of the building non destructive and low destructive in situ investigation methods like ultrasonic wave and drilling resistance measurements had to be applied to obtain information about the material properties of sandstone and their changes due to weathering moreover hydric swelling behaviour of the sandstone was determined on undecorated pieces of fallen blocks from the walls additional random test stable isotopic investigations of environmental influences and salts and thorough investigations of the spatial distribution of salts in the ashlars at two selected places with typical weathering patterns completed the set of data the results demonstrate that the weathering process is mainly triggered by rain dry cycles salt load found in the stone is composed of gypsum and nitrate compounds sulphur stable isotope investigations of potential sources of gypsum lead to the conclusion that soluble components of bat droppings are the major source of salts influences of environmental factors like sulphate in rainwater or so2 from the air on salt formation are unlikely gypsum may reinforce the surface deterioration due to high swelling shrinking movements of the sandstone 1 mm m during intensive wetting drying cycles

role of clay minerals in the physicomechanical deterioration of sandstone 1 extensive weathering suffered by sandstone in natural outcrops as well as in historical buildings could be attributed among other mechanisms to the action of wetting and drying cycles we have recently shown how to quantify the stresses generated during such cycles to determine whether damage can take place this procedure is further developed in this paper and applied to the tarifa sandstone a sandstone with a 7 wt content of clay minerals and used in the main facade of the church of san mateo in tarifa cadiz spain for which the relevant material properties are measured it is shown that tensile stresses during drying can cause cracking of thin elements and that shear forces can cause buckling of wetted surfaces more generally eventually resulting in scaling and or contour scaling these predictions are supported by visual observations on the monument showing degradation patterns characteristic of those types of damage similar weathering forms have been observed in natural sandstone landscapes application of swelling inhibitors e g cationic surfactants that selectively adsorb on the clay basal planes results in a substantial swelling reduction this confirms that the swelling clays typically present in sandstone are pivotal for its weathering and indicates that swelling inhibitors are a potentially valuable treatment to prevent or minimize damage to stone the circumstances that would lead to weathering are discussed in relation to sandstone material properties in the wet and dry state clay bearing stones are shown to exhibit softening during wetting as well as viscoelastic stress relaxation which is expected to limit the extent of damage these results may aid in the better understanding of sandstone weathering both in nature and in urban environment and may help develop conservation methods to mitigate wetting drying damage in ornamental sandstone or to prevent pore plugging in reservoir sandstones

what is the mechanism for the modification of convective cloud distributions by land surface induced flows abstract the aim of this study is to determine the mechanism that modulates the initiation of convection within convergence zones caused by land surface induced mesoscale flows an idealized modeling approach linked quantitatively to observations of vegetation breezes over tropical benin was used a large eddy model was used with a prescribed land surface describing heterogeneities between crop and forest over which vegetation breezes have been observed the total surface fluxes were constant but the bowen ratio varied with vegetation type the heterogeneous land surface created temperature differences consistent with observations which in turn forced mesoscale winds and convection at the convergence zones over the crop boundaries at these convergence zones optimum conditions for the initiation of convection were found in the afternoon the equivalent potential temperature was higher in the convergence zones than over anywhere else in the domain due to reduced entrainment and the mesoscale convergence

applications of multiscale waveform inversion to marine data using a flooding technique and dynamic early arrival windows a recently developed time domain multiscale waveform tomography mwt method is applied to synthetic and field marine data although the mwt method was already applied to synthetic data the synthetic data application leads to a development of a hybrid method between waveform tomography and the salt flooding technique commonly use in subsalt imaging this hybrid method can overcome a convergence problem encountered by inversion with a traveltime velocity tomogram and successfully provides an accurate and highly resolved velocity tomogram for the 2d seg eage salt model in the application of mwt to the field data the inversion process is carried out using a multiscale method with a dynamic early arrival muting window to mitigate the local minima problem of waveform tomography and elastic effects with the modified mwt method reasonably accurate results as verified by comparison of migration images and common image gathers were obtained the hybrid method with the salt flooding technique is not used in this field data example because there is no salt in the subsurface according to our interpretation however we believe it is applicable to field data applications