mesoscale convective systems in weakly forced large scale environments part ii generation of a mesoscale initial condition abstract a series of five mesoscale convective systems mcss developed within a weakly forced large scale environment on 11 and 12 may 1982 two of these systems had a large component of motion against the midtroposphoric flow and propagated in a direction nearly opposite to that of the traveling upper level disturbances this description of the evolution of convection is very different from traditional ones in which convection develops and moves more or less in phase with traveling upper level disturbances observations indicate that the initiation and evolution of convection are tied to mesoscale features that are not well observed by the conventional observing network making the structure of the model initial condition a potentially crucial factor in the success or failure of any subsequent numerical simulation it is found that the initial conditions created using the conventional initialization procedure of the pennsylvania state university national center for atmospheric research mesoscale model d

sensitivity of a heavy rain producing western mediterranean cyclone to embedded potential vorticity anomalies the development and track of a surface cyclone that produced heavy precipitation in the western mediterranean region on 28 29 september 1994 is numerically simulated using a mesoscale model diagnostic calculations reveal that surface pressure falls and upward motion occur in response to a well defined pattern of upward quasi geostrophic forcing at all tropospheric levels in addition convective instability and low tropospheric water vapour flux convergence are significant over the western mediterranean and therefore the environment is highly supportive for convection development the appreciable dynamical forcing at upper levels appears to be associated with two positive potential vorticity pv anomalies that are embedded within the large scale trough and rotate about each other motivated by the fact that the small scale features of the pv field are more prone to analysis or forecast error than the large scale components a sensitivity study is conducted in order to analyse the dependence of the mesoscale forecast on the initial intensity and position of the two embedded pv centres this is accomplished by first applying a piecewise pv inversion technique which allows the balanced flow associated with each pv centre to be calculated and then the inverted mass and wind fields are used to modify the model initial conditions eight simulations are run after doubling or removing one or both anomalies sensitivity to intensity and eight other simulations after displacing the anomalies towards or away from the iberian peninsula sensitivity to position the results exhibit a clear dependence of the track and shape of the surface cyclone and its associated pattern of low tropospheric warm air advection on the characteristics of the pv anomalies therefore spatial details of the mesoscale forecast are shown to be highly sensitive to the precise structure of the upper level dynamic forcing nevertheless for the full set of arbitrarily defined initial conditions one or several low pressure systems develop in the western mediterranean area and heavy precipitation always occurs on the other hand there is an overall tendency of the simulations to favour cyclone development leeward of the atlas mountain range and local rainfall enhancements over the exposed mountains of eastern spain the relative roles of the orography and sea surface latent heat flux versus the action of the upper level pv centres are examined by means of additional simulations

conditions of formation and diagenetic evolution of upper proterozoic phosphate nodules from southern sweden evidence from petrology mineral chemistry and isotopes abstract dark gray to black cryptocrystalline francolite occurs as nodules 2 8 cm in diameter which are embedded in organic matter rich mudstones of the visingso group upper proterozoic southern sweden the 13cpdb values 18 4 to 0 98 of structural co2 complemented by studies of the petrographic character and strontium isotopic composition of francolite indicate precipitation in the suboxic and sulfate reduction zones francolite is intergrown with berthierine that has formed in the suboxic fe reduction zone calcite enriched in mn and to a lesser extent fe occurs as fracture and void fillings and as replacement of francolite mn and mg rich calcian siderites have precipitated as pseudomorphs after bacteria in the zone of microbial methanogenesis the carbon 13 c pdb 0 75 to 7 04 and oxygen 18 o pdb 14 21 to 10 58 isotopes of calcite suggest derivation of carbonate ions from microbial methanogenesis and from thermal decarboxylation of organic matter at temperatures of 60 to 80 c some of the void and fracture filling calcites 13 c 20 8 to 18 63 18 o 5 46 to 5 21 have however precipitated at lower temperatures 25 30 c in the sulfate reduction zone

non stoichiometry of interlayer cations in micas from low to middle grade metamorphic rocks in the ryoke and the sanbagawa belts japan micas in 17 pelitic k feldspar free and 8 psammitic k feldspar bearing rocks from the wazuka and the asemi gawa areas in the ryoke and the sanbagawa metamorphic terrains respectively were analyzed on an electron probe microanalyzer the deficiency of alkali cations in the low to middle grade metamorphic micas is ascribed to the illite substitution kxii aliv xii vacancy siiv

numerical simulations of low cape flows over a mountain ridge abstract in a recent study the authors performed numerical simulations of conditionally unstable flows past a mesoscale mountain ridge in order to investigate the statistically stationary features of the solution precipitation characteristics for intermediate to high values of convective available potential energy cape that study proposed a functional dependence of the rain rate on three parameters related respectively to the triggering and the orographic forcing of convection and to the ratio of the advective to convective time scales the present study extends that analysis to cover larger regions of the parameter space including experiments corresponding to a wider range of cape it is found here that the low cape moderate wind experiments do not fit the functional dependence for rain rate amount and location proposed in the authors previous study the analysis of the present solutions suggests that two additional nondimensional parameters should be taken into account

a numerical study of three catastrophic precipitating events over southern france i numerical framework and synoptic ingredients this study examines the simulation of three torrential rain events observed on 13 14 october 1995 the cevennes case 12 13 november 1999 the aude case and 8 9 september 2002 the gard case over the southeastern part of france using the meso nh non hydrostatic mesoscale numerical model these cases were associated with extreme heavy precipitation events hpes with significant precipitation amounts exceeding 500 mm in less than 24 hours several sets of numerical experiments were performed with 10 km and 2 5 km horizontal resolutions in part i of this study special attention is paid to the experimental design for obtaining realistic simulations of hpes with the meso nh model as well as the evolution of the synoptic patterns in which the rainfall events are embedded the best 2 5 km numerical simulations show the ability of the meso nh model to reproduce significant quasi stationary rainfall events moreover the model fairly reproduces the low level mesoscale environments associated with the three hpes the hpes formed in a slow evolving synoptic environment favourable for the development of convective systems diffluent upper level southerly flow pv anomalies etc at lower levels a southerly to easterly moderate to intense flow provided conditionally unstable and moist air as it moved over the relatively warm mediterranean sea typical for this time of the year late summer and autumn the two extreme cases gard and aude differ from the more classical event cevennes in terms of larger low level moisture fluxes weaker values of conditional convective instability as in the aude case is counterbalanced by a stronger warm and moist low level jet the mesoscale triggering and or sustaining ingredients for deep convection and the physical mechanisms leading to the stationarity of these rainfall events are presented and discussed in a companion paper

tem and xrd determination of crystallite size and lattice strain as a function of illite crystallinity in pelitic rocks average crystallite size and mean square strain of illite in rock specimens and clay separates were measured independently in tem images and by single line fourier voigt method profile analysis of the c 1 nm peak of xrd patterns for a prograde sequence of pelitic rocks illite crystallinity indices 0 17 0 58 d2h from the gaspepeninsula quebec the tem determined crystallite sizes in clay separates approxi mate those determined by fourier profile analyses and those calculated from illite crystallinity indices by the scherrer equation with the exception of the diagenetic sample the crystallite sizes and mean square strains of illite in rock samples exhibit a trend similar to that determined by profile analyses but the average crystallite sizes are up to five times larger than those measured for clay separates tem images show that all rock samples have a wide range of crystallite sizes and the proportions of larger crystallites increase with metamorphic grade the diagenetic illite is defect rich fine grained mean thickness by volume c 70 nm 1m d material anchizonal illite tends to occur as separate aggregates of small 1m d and larger 2m 1 crystals c 200 nm comprising arrays of subparallel coalescing packets the epizone sample has thick c 400 nm defect free crystals of muscovite occurring in stacks of parallel layers or subhedral crystals intergrown with large angle boundaries cleaved crystals that are free of intracrystalline layer terminations are dominant in clay separates of all samples having ranges of smaller sizes with volume average thicknesses of c 43 43 and 81 nm c 14 28 67 nm by the voigt method respectively for the three zones the results suggest that illite crystallinity indices do not provide a direct measure of a single microstruc tural state of illite in rocks although they yield consistent limits for average crystallite sizes for the anchizone 23 48 nm here therefore they serve as a general parameter of the degree of recrystallization on a relative basis in part because the contributions of all peak broadening variables mixed layering size and strain decrease regularly with prograde regional metamorphism of pelites the microstructural changes caused by rock disaggregation are probably a function of those variables as well the data collectively demonstrate a trend from metastable defect rich small crystals towards a stable assemblage of larger defect free crystals through dissolution of strained crystals and neocrystallization consistent with the ostwald step rule

dancing sprites detailed analysis of two case studies on 29 30 october 2013 a low light video camera installed at pic du midi 2877 m recorded transient luminous events above a very active storm over the mediterranean sea the minimum cloud top temperature reached 73 c while its cloud to ground cg flash rate exceeded 30 fl min 1 some sprite events have long duration and resemble to dancing sprites we analyze in detail the temporal evolution and estimated location of two series of sprite sequences as well as the cloud structure the lightning activity the electric field radiated in a broad range of low frequencies and the current moment waveform of the lightning strokes i in each series successive sprite sequences reflect time and location of corresponding positive lightning strokes across the stratiform region ii the longer time delayed 20 ms sprite elements correspond to the lower impulsive charge moment changes icmc of the parent strokes 200 c km and they are shifted few tens of kilometers from their sp cg stroke however both short and long time delayed sprite elements also occur after strokes that produce a large icmc and that are followed by a continuing current iii the long time delayed sprite elements during the continuing current correspond to surges in the current moment waveform they occur sometimes at an altitude apparently lower than the previous short time delayed sprite elements possibly because of changes in the local conductivity iv the largest and brightest sprite elements produce significant current signatures visible when their delay is not too short 3 5 ms

sensitivities of a flash flood event over catalonia a numerical analysis abstract on 9 and 10 june 2000 the northeastern part of the iberian peninsula was affected by heavy rains that produced severe floods over densely populated areas the zones most affected were the provinces of tarragona and barcelona located in the region of catalonia five people were killed 500 were evacuated and the property losses were estimated to exceed 65 million euros the episode was characterized by the entrance of an atlantic low level cold front and an upper level trough that contributed to the generation of a mesoscale cyclone in the mediterranean sea east of mainland spain the circulation associated with this mesoscale cyclone advected warm and moist air toward catalonia from the mediterranean sea the convergence zone between the easterly flow and the atlantic front as well as the complex orography of the region are shown to be involved in the triggering and organization of the convective systems radar shows the development of two long lived mesoscale convective systems that merged

zircon titanite and apatite u th he ages and age eu correlations from the fennoscandian shield southern sweden craton cores far from plate boundaries have traditionally been viewed as stable features that experience minimal vertical motion over 100 1000 ma time scales here we show that the fennoscandian shield in southeastern sweden experienced several episodes of burial and exhumation from 1800 ma to the present apatite titanite and zircon u th he ages from surface samples and drill cores constrain the long term low temperature history of the laxemar region single grain titanite and zircon u th he ages are negatively correlated 104 838 ma for zircon 160 945 ma for titanite with effective uranium eu u 0 235 th a measurement proportional to radiation damage apatite ages are 102 258 ma and are positively correlated with eu these correlations are interpreted with damage diffusivity models and the modeled zircon he age eu correlations constrain multiple episodes of heating and cooling from 1800 ma to the present which we interpret in the context of foreland basin systems related to the neoproterozoic sveconorwegian and paleozoic caledonian orogens inverse time temperature models constrain an average burial temperature of 217 c during the sveconorwegian achieved between 944 ma and 851 ma and 154 c during the caledonian achieved between 366 ma and 224 ma subsequent cooling to near surface temperatures in both cases could be related to long term exhumation caused by either post orogenic collapse or mantle dynamics related to the final assembly of rodinia and pangea our titanite he age eu correlations cannot currently be interpreted in the same fashion however this study represents one of the first examples of a damage diffusivity relationship in this system which deserves further research attention

numerical simulation of the meso β scale structure and evolution of the 1977 johnstown flood part i model description and verification abstract the pennsylvania state university ncar mesoscale model originally developed by anthes and warner is modified to simulate the meso scale structure and evolution of convectively driven weather systems the modifications include i two way interactive nested grid procedures ii the fritsch chappell convective parameterization scheme and iii the blackadar boundary layer package an 18 h simulation of the johnstown flood of july 1977 is conducted compared to the documentation of hoxit et al and bosart and sanders the simulation reproduced many of the different aspect of the mesoscale convective complex and squall line that were responsible for the heavy rain over western pennsylvania in particular the model predicts the size propagation rate and orientation of the mesoscale convective components that were observed in the mid atlantic states the simulated evolution of the planetary boundary layer cool outflow boundaries and surface pressure perturbations such as meso scale lows h

evidence for the role of the lid and underunning in an outbreak of tornadic thunderstorms abstract on the last day of may 1985 a series of tornadic thunderstorms devastated pans of ohio pennsylvania new york and ontario canada analysis of this outbreak reveals that a lid which moved from the southwestern united states the previous day played a major role in enabling the latent instability to achieve large values severe convection began along the edge of the lid underrunning in a region experiencing baroclinically forced ascent associated with a migrating jet streak this paper discusses the role of the lid in the development of the latent instability the relationship between underrunning and the migrating jet streak and the effects of terrain on the evolution of latent instability and on the formation of the lid finally we present a climatological study of the lid in order to show why the convection was so severe yet so unusual in this part of the country

a long lived mesoscale convective complex part i the mountain generated component abstract using data collected during colorado state university s south park area cumulus experiment in 1977 a sequence of multi scale convective events leading to the formation of a mesoscale convective complex is described in the first phase surface based cool advection in the elevated mountain basin delayed the full transition of the morning boundary layer into a deep mixed layer until well after convective instability was reached over the adjacent ridges the second phase was earmarked by the formation of convective precipitation echoes at hot spots over the high mountain terrain two groups of cells then propagated eastward across the mountain basin forming a line of discrete cells which moved across the foothills toward the high plains the cells further intensified at the foothills high plains interface and formed a still larger north south line of thunderstorms in the third phase this north south line of thunderstorms evolved into an expanding meso scale convective cluster as it contin

mesoscale air motions associated with a tropical squall line abstract composites of radar and wind observations in a coordinate system attached to a moving tropical squall line confirm that such a squall system is composed of two separate circulation features a convective squall line region and a stratiform anvil region the squall line region is characterized by mesoscale boundary layer convergence which feeds deep convective updrafts and mid to upper level divergence associated with outflow from the cells the anvil region is characterized by mid level convergence which feeds both a mesoscale downdraft below the anvil and a mesoscale updraft within the anvil cloud before this study the mesoscale updraft in the anvil cloud of the tropical squall system had been somewhat speculative and both the anvil updraft and downdraft had been inferred only qualitatively the occurrence of the anvil updraft is now proven and quantitative profiles of the mesoscale anvil updraft and downdraft have been obtained

development of slaty cleavage and degree of very low grade metamorphism a review illite crystallinity ic and other indicators of the grade of very low grade metamorphism associated with the appearance of various stages of slaty cleavage in phyllosilicate rich rocks have been compiled from a wide variety of terranes ic values have been converted to a kubler equivalent standard scale but the diverse characterizations of the cleavage fabrics in published descriptions do not always allow an unequivocal identification of equivalent stages of cleavage development nevertheless there exists a distinct relationship between grade and the appearance of various stages of cleavage development 1 indications of incipient slaty cleavage such as s0 s1 pencil structure appearance of primary s1 crenulation cleavage and of closely spaced cleavage without parallel fabric in the microlithons is associated with a wide range of mostly medium and high grade diagenetic ic values 2 the appearance of smooth cleavage with a strong parallel fabric in the microlithons and or quartz mica beards and the chlorite mica stacks shortened at a high angle to 001 and of irregular cleavage in sandy beds is associated with a much narrower range of predominantly low and medium grade anchimetamorphic grades rarely high grade diagenetic the first appearance of these stages of cleavage development with higher grades can often be related to post kinematic magmatic heating polymetamorphism pre cleavage metamorphism or static recrystallization without cleavage formation for example in low strain zones there exists a relationship between finite strain fabric and metamorphic grade in mudstones and slates in coarser clastic rocks the same finite strain fabric relationship occurs at appreciably higher grades a relationship between finite strain in carbonate rocks and ic in the nearby rocks has been reported from the helvetic zone of the swiss alps the earlier stages of cleavage formation are associated with little improvement in ic the narrow range of ic associated with smooth cleavage is concluded to represent recrystallization and grain growth concurrent with cleavage formation

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

structural evolution of a nappe complex southern vanoise massif french penninic alps abstract the arpont parrachee region in the southern vanoise massif comprises a stack of minor fold and thrust nappes that were emplaced during subduction and closure of the piemont ocean basin in late cretaceous to eocene time the stack includes the arpont nappe composed mainly of pre permian schist metamorphosed to blueschist facies early in the alpine history and several sheets of permian to eocene metasedimentary rocks nappe formation recumbent folding and associated ductile deformation postdated the high pressure metamorphic peak and probably involved translation to the northwest the rocks were then refolded by large and small scale folds trending roughly e w these deformational events were accompanied by a decrease in metamorphic pressure indicating uplift they were followed by regional greenschist facies metamorphism which caused breakdown of high pressure parageneses annealing of microstructures and widespread growth of albite porphyroblasts the entire nappe pile was then refolded by large and small scale folds overturned towards the southeast reorientation of small scale structures with increasing strain by this event indicates a large component of ese directed shear which culminated in the formation of anastomosing ductile shear zones

mesoscale convective complexes and persistent elongated convective systems over the united states during 1992 and 1993 abstract large long lived convective systems over the united states in 1992 and 1993 have been classified according to physical characteristics observed in satellite imagery as quasi circular mesoscale convective complex mcc or elongated persistent elongated convective system pecs and cataloged the catalog includes the time of initiation maximum extent termination duration area of the 52 c cloud shield at the time of maximum extent significant weather associated with each occurrence and tracks of the 52 c cloud shield centroid both mcc and pecs favored nocturnal development and on average lasted about 12 h in both 1992 and 1993 pecs produced 52 c cloud shield areas of greater extent and occurred more frequently compared with mccs the mean position of initiation for pecs in 1992 and 1993 followed a seasonal shift similar to the climatological seasonal shift for mcc occurrences but was displaced eastward of the mean position of mcc initiation in 1992 and 1993 the spatial distribution

the spatial and temporal variability of convective storms over the northeast united states during the warm season abstract a spatial and temporal climatology of convective storms over the northeast united states during the warm season april september is presented using composite national operational weather radar nowrad data at 2 km grid spacing from 1996 to 2007 as well as cloud to ground lightning from the national lightning data network nldn on a 10 km grid from 2001 to 2007 there are preferred regions for convective storms within new york s hudson river valley western and southeastern pennsylvania central new jersey and across the delmarva peninsula a favored initiation area during the early afternoon is the immediate lee of the appalachians with a tendency for these convective systems to move eastward to the coast by late evening there is a sharp gradient in convective frequency within 20 km of the coast on average as a result of the relatively stable marine boundary layer but as the sea surface warms by midsummer this convective activity increases near the coast with a nocturnal 0600 1200 utc c

the relationship of surface pressure features to the precipitation and airflow structure of an intense midlatitude squall line abstract observations from the oklahoma kansas preliminary regional experiment for storm central ok pre storm have been used to document the surface pressure features accompanying an intense midlatitude squall line with trailing stratiform precipitation three well known features are observed a pre squall mesolow a squall mesohigh and a wake low particular attention is given to the wake low its life cycle and association with the trailing stratiform portion of the squall line during the formative stage the pressure field to the rear of the squall line mesohigh is relatively flat with only weak stratiform precipitation present as the squall line enters the developing to mature stages a pronounced wake low appears at the back edge of the surface stratiform precipitation area the squall line at this time is characterized by a strong rear inflow jet descending from the upper troposphere as far as 500 km behind the leading convective line to the lower troposphere just behind the line the trailin

on assessing local conditional symmetric instability from atmospheric soundings abstract the standard parcel method of assessing the susceptibility of the atmosphere to moist convection using tephigrams is extended to account for the centrifugal as well as the gravitational potential energy of the displaced air parcel this leads to a measure of the stability of the moist baroclinic atmosphere to finite slantwise reversible displacements of a two dimensional air parcel such a measure differs from previously derived measures of conditional symmetric instability which have considered only infinitesimal displacements in saturated atmospheres it is demonstrated that the combined gravitational and centrifugal potential of a two dimensional air parcel or tube can be assessed by displacing the tube slantwise along a surface of constant angular momentum and that this combined potential energy can be estimated using a single atmospheric sounding several examples of the application of this technique are presented in the context of a case study of apparent slantwise convection the result

diurnal boundary layer development over sloping terrain abstract a one dimensional prognostic model of the atmospheric boundary layer coupled to a surface energy budget is described which utilizes a profile formulation non local for exchange coefficients in the daytime convective boundary layer and an exchange coefficient scheme based on local richardson number for the stable nocturnal boundary layer this combined local and non local model is used to simulate the full diurnal cycle of the boundary layer behavior of days 33 34 of the wangara experiment results of the simulation indicate that these simplified exchange coefficient schemes simulate the mean features of the boundary layer as well as the more complex and computationally expensive higher order closure models this diurnal boundary layer formulation is incorporated into a two dimensional mesoscale model employing a terrain following coordinate system to examine boundary layer behavior over sloping terrain similar to that of the great plains of the united states particular emphasis is placed on th

warm core vortex amplification over land abstract a convectively generated mesoscale vortex that was instrumental in initiating and organizing five successive mesoscale convective systems over a period of three days is documented two of these convective systems were especially intense and resulted in widespread heavy rain with localized flooding based upon radar and satellite data the detectable size of the vortex became much larger following the strong convective developments nearly tripling its initial diameter over its three day life cycle during nighttime when convection typically intensified within the vortex movement of the system tended to slow following dissipation of the convection in the morning the daytime movement accelerated cross sections of potential vorticity taken through the vortex center clearly show a maximum at midlevels and a well defined minimum directly above the vortex and the potential vorticity maximum were essentially colocated and the system was nearly axisymmetric in the vertical over the three day life

processes controlling the structure and longevity of two quasi linear convective systems crossing the southern new england coast abstractthis paper explores the structural evolution and physical processes that explain the modification of two quasi linear convective systems qlcss that encountered the densely populated new york city atlantic coastal region one qlcs on 31 may 2002 traversed the atlantic coastal boundary with little change in its intensity producing widespread severe wind damage across new york city and long island during this event warm air advection at 925 hpa helped destabilize the layer above this level over the coastal zone while the marine boundary layer deepened below this level the 0 3 km line perpendicular vertical wind shear was relatively strong which supported ascent along the leading edge of the diabatically generated cold pool the surface based convective system became slightly elevated as it moved over the marine waters in contrast the 23 july 2002 qlcs decayed upon encountering the atlantic coastline despite its coincidence with a surface cold front the most unstable cape values during thi

structural history of high pressure metamorphic rocks in the southern vanoise massif french alps and their relation to alpine tectonic events abstract a nappe of amphibolite facies metamorphic rocks of pre permian age in the southern vanoise massif the arpont schist has been affected by an alpine hp lt metamorphism the first mesoscopically recognizable deformation d 1 post dated the high pressure peak jadeitic pyroxene quartz glaucophane lawsonite and was associated with glaucophane epidote d 1 produced a flat lying schistosity and a nw trending glaucophane lineation and was probably associated with nappe displacement involving nw directed subhorizontal shear d 2 formed small scale folds and a foliation associated with chlorite albite the changing parageneses during the period pre d 1 to d 1 to d 2 suggest decreasing pressure so that the deformation appears to have been related to the uplift history rather than to the process of tectonic burial d 2 was followed by a static metamorphism green biotite chlorite albite possibly of lepontine age se directed backthrusting and folding d 3 and later differential uplift along steep faults took place under low grade conditions

fold interference pattern at the top of basement domes and apparent vertical extrusion of hp rocks ambin and south vanoise massifs western alps the ambin and south vanoise brianconnais basement domes located within the hp metamorphic zone were chosen for a reappraisal of the early tectonic evolution of the internal alps in their western segment finite strain analyses have shown that hp rocks were exhumed in two main successive stages more or less expressed according to their structural position in the massifs a partitioning of deformation from core to rim of the domes is thus evidenced the d1 stage was roughly coeval with the observed peak metamorphic conditions and corresponds in the core of the ambin dome to a non coaxial regime with dominant horizontal shortening and n to nw movement direction the d2 stage well expressed in the upper part of the domes took place under low blueschist facies conditions and culminated under greenschist facies conditions it developed a retrogressive foliation and pervasive e verging shear zones at all scales that locally define major 2 tectonic contacts the d2 shearing is responsible for the development of spectacular f1 f2 fold interference structures recognised in the western part of the south vanoise dome in this area we interpret the steeply dipping hp fabric s1 defining the axial planes of the first generation of now upright folds f1 as linked to an early flat lying nappe edifice 1 subsequently steepened by the d2 shearing geometry and kinematic characteristics for the early d1 nappe forming event are strongly consistent with most evolutionary models assuming that oceanic to european and apulian crust derived nappes were initially exhumed during n to nw verging overthrusting events synthetic to the subduction they tend also to suggest that the penninic hp units may have suffered an early exhumation by low angle thrusting rather than by vertical extrusion

scale invariant sheath folds in salt sediments and shear zones abstract sheath folds are developed in a broad spectrum of geological environments in which material flow occurs including gravity driven surficial deformation in ignimbrites unconsolidated sediments and salt together with deeper level ductile shear zones in metamorphic rocks this study represents the first geometric comparison of sheath folds in these different settings across a wide range of scales elliptical closures defining eye folds represent y z cross sections through highly curvilinear sheath folds our analysis of the published literature coupled with field observations reveals remarkably similar ellipticities r yz for sheath folds in metamorphic shear zones r yz 4 23 salt r yz 4 29 sediment slumps r yz 4 34 glaciotectonites r yz 4 48 and ignimbrites r yz 4 34 nested eye folds across this range of materials n 1800 reveal distinct and consistent differences in ellipticity from the outer r yz to the inner most r y z elliptical rings of individual sheath folds the variation in ratios from outer to inner rings r r yz r y z in gravity driven surficial flows typically displays a relative increase in ellipticity to define cats eye folds r r yz that are remarkably constant r 2 0 99 across 9 orders of magnitude sheath y axes range from 0 1 mm to 75 km our findings lead us to conclude that the geometric properties of sheath folds are scale invariant and primarily controlled by the type and amount of strain with r also reflecting the rheological significance of layering associated with original buckle fold mechanisms the scaling pattern of sheath folds reflects the length scales of the precursor buckle folds and width of deformation zones across a broad range of materials and environments with continued deformation the layering marking the original folds may become increasingly passive to define sheath folds these empirical relationships suggest sheath folding is a fundamental mode of viscous response across a broad spectrum of materials strain rates and scales encompassing a variety of deformation settings

the interaction of simulated squall lines with idealized mountain ridges abstract numerical simulations of squall lines traversing sinusoidal mountain ridges are performed using the advanced regional prediction system cloud resolving model precipitation and updraft strength are enhanced through orographic ascent as a squall line approaches a ridge the simulated squall line then weakens as it descends the ridge because some of the cold pool is blocked by the terrain resulting in less lift along the gust front and weaker convective cells the flow within the cold pool accelerates slightly and the depth of the cold air decreases owing to upstream blocking transitioning the flow in the cold pool head from subcritical to supercritical then back to subcritical at the bottom of the ridge a hydraulic jump forms when the flow transitions the second time enabling the development of a new convective line downwind of the mountain these new updrafts grow and eventually replace the older updrafts that weakened during descent this process results in the discrete propagation of a squ

triple doppler analysis of a discretely propagating long lived high plains squall line abstract a nonsevere squall line that developed on 21 june 1993 along the northern foothills of the colorado rocky mountains is analyzed using a series of triple doppler analyses this squall line developed in a relatively dry environment characterized by weak low level but strong upper level vertical shear of the horizontal winds the drier thermodynamic profile as characterized by a higher lifting condensation level and weak low level shear resulted in convection forming not along but rather 7 10 km behind the leading edge of the shallow cold pool the strong upper level shear established a predominantly leading anvil this led to a suppression zone immediately ahead of the leading line which in turn resulted in a discrete mode of propagation of the squall line three different cycles were observed each cycle had a distinct line of convective cells that initiate intensify and then decay in each case the new cells developed 20 40 km out ahead of the decaying line of the previous cycle many studi

a climatology of the structure evolution and propagation of midlatitude cyclones in the southeast united states abstractthe seasonal and interannual variability of the structure evolution and propagation of midlatitude cyclones in the southeast united states are studied using a composite analysis in the upper levels the composites show that the axis of the wintertime upper level trough remains north south oriented and propagates eastward along 40 n while the summertime upper level trough has a much slower propagation at a farther north latitude and an axis that is tilted in the northeast southwest direction upper level circulation changes are consistent with a shift from wintertime cyclonic behavior to summertime anticyclonic behavior midlatitude cyclones significant changes in the low level structure and precipitation patterns of midlatitude cyclones ensue from these upper level changes while the winter composite is characterized by eastward propagating midlatitude cyclones that extend deep into the subtropics the summer composite is characterized by semistationary midlatitude troughs that only briefl

coupled modes of large scale climatic variables and regional precipitation in the western mediterranean in autumn the variability of autumn precipitation in the western mediterranean and its relationship to the large scale atmospheric variability during the period 1948 to 1989 is assessed a singular value decomposition analysis is used to establish modes of coupled variability between regional precipitation and geopotential height z300 zonal u wind and meridional v wind wind components at the 300 hpa level the z300 precipitation coupling which accounts for 52 of the total squared covariance is strong during the autumn the first z300 coupled mode in its positive phase is characterised by a dipole structure with negative anomalies over scandinavia and positive anomalies over the iberian peninsula in the z300 and negative precipitation anomalies in the western mediterranean in its negative phase a coupled pattern is found showing a high over low block and positive precipitation anomalies over the mediterranean area the coupling depicted by the second mode is weaker than that found in the first mode the second coupled mode 21 of the total squared covariance is characterised by negative anomalies in the eastern north atlantic and positive ones over north africa and the central mediterranean in the z300 and negative anomalies in the regional precipitation consistent with the results of the two first modes mentioned the coupled patterns of either u wind precipitation or v wind precipitation are found to be coherent with those for z300 precipitation composite maps were obtained to give a representation of the average circulation associated with coherent precipitation variability in the western mediterranean the regional impacts of both modes are investigated and the large scale dynamic patterns presented are important modes of variability taking into account data for the whole of the twentieth century results show that the first singular mode is responsible for the decadal trends and long term changes in precipitation the late 1970s and 1980s is shown as the drier period and the late 1950s and early 1960s as the wettest years of the century

pyrite chlorite and pyrite biotite relations in sandstones abstract authigenic euhedral pyrite in feldspathic sandstones of the visingso group upper proterozoic southern sweden is observed to be closely associated with authigenic fine crystalline interstitial chlorite and or sand sized chlorite or biotite microprobe analyses revealed that chlorites which are accompanied by relatively large amounts 3 vol of pyrite are characterized by a lower fe fe mg ratio than chlorites with lesser amounts 0 5 vol of associated pyrite the lower fe fe mg ratio of the former chlorites might have resulted from subsequent substitution of fe 2 by mg 2 in an initially fe rich chlorite the released fe 2 would then react with sulfide ions in an anoxic sulfidic environment to form pyrite another alternative is that the chlorites with lower fe fe mg ratio were crystallized from solutions characterized by a higher activity of mg 2 than chlorites with higher fe fe mg ratio iron from the biotite grains became available due to diagenetic illitization kaolinization and or chloritization

on the significance of aragonite occurrences in the western alps aragonite occurrences from two areas of the western alps are described it is shown that aragonite has been formed under blueschist metamorphic conditions in the western vanoise while it has been precipitated under sub surface conditions in the queyras region an uplift p t path of the aragonite bearing rocks of the western vanoise is constructed using two independent methods 1 temperature estimates using the sr content of aragonite in the successive veins and 2 the kinetics of the aragonitecalcite solid state transition the uplift p t path has an unusual shape with an important temperature decrease 100 to 150 c for a pressure decrease of 0 2 gpa following blueschists metamorphism p 0 7 gpa t 300 c thermal models show that this unusual p t path of the western vanoise can be explained if one maintains a low temperature between 125 and 175 c at the base of the tectonic unit containing the aragonite bearing rocks during part of its burial history followed by the whole of its exhumation a tectonic scenario is proposed to account for the observed and modelled p t path

formation of mesoscale lines of pirecipitation severe squall lines in oklahoma during the spring abstract four distinct kinds of severe mesoscale convective line development are identified in oklahoma during the spring based on the analysis of an 11 year period of reflectivity data from the national severe storms laboratory s 10 cm radar in norman oklahoma the primary classes of fine formation are broken line back building broken areal and embedded areal each is described in detail along with illustrative examples comparisons are made with other observations and with numerical model simulations the former two classes of line formation have been previously documented while the latter two have not only the broken areal squall line has been realistically simulated numerically the environment for each of the types of line development was determined from data from the standard national weather service surface and upper air networks and from special rawinsonde launches it was found that broken line formation tends to occur along cold fronts in a multicell environment while back building occur

mesoscale convective systems in weakly forced large scale environments part iii numerical simulations and implications for operational forecasting abstract during a 24 h period beginning 1200 utc 11 may 1982 a series of mesoscale convective systems developed within a weakly forced large scale environment two of these systems had a large component of motion against the midtropospheric flow and propagated in a direction nearly opposite to that of the travelling upper level disturbances this evolution of convection is very different from traditional ones in which convection develops and moves more or less in phase with traveling upper level disturbances it presents a tremendous challenge for three dimensional numerical models since the initiation and evolution of convection are tied to mesoscale features that are not well observed by the conventional upper air network and may not be well approximated in the model parameterization schemes mesoscale model simulations are conducted to evaluate the ability of the model to reproduce this complex event and to examine the model sensitivities to differences in the convective trigger function and model i

the new york bight jet climatology and dynamical evolution abstract this paper describes the southerly new york bight nyb jet 11 17 m s 1 that develops primarily during the warm season just above the surface offshore east of the northern new jersey coast and south of long island the nyb observations from two offshore buoys are used to develop a 9 yr climatology of 134 jet events from 1997 to 2006 there is a seasonal maximum 2 5 events per month during june and july with a skew toward the spring months the wind directions for the jet trace out a nearly elliptical orbit for the 24 h period around the time of jet maximum at 2300 utc 1900 eastern daylight time edt on average composites reveal that the nyb jet occurs on days with southwesterly synoptic flow and the jet is part of a larger scale 200 300 km wind enhancement offshore of the mid atlantic and northeast u s coasts during the early evening hours high resolution observations surface mesonet aircraft soundings and a terminal doppler weather radar and weather research and forecastin

organizational modes of midlatitude mesoscale convective systems this paper discusses common modes of mesoscale convective organization using 2 km national composite reflectivity data the authors investigated linear mesoscale convective systems mcss that occurred in the central united states during may 1996 and may 1997 based upon the radar observed characteristics of 88 linear mcss the authors propose a new taxonomy comprising convective lines with trailing ts leading ls and parallel ps stratiform precipitation while the ts archetype was found to be the dominant mode of linear mcs organization the ls and ps archetypes composed nearly 40 of the studied population in this paper the authors document the characteristics of each linear mcs class and use operational surface and upper air data to describe their different environments in particular wind profiler data reveal that the stratiform precipitation arrangement associated with each class was roughly consistent with the advection of hydrometeors implied by the mean middle and upper tropospheric storm relative winds which were significantly different among the three mcs modes case study examples are presented for both the ls and ps classes which have received relatively little attention to this point as well the authors give a general overview of the synoptic scale meteorology accompanying linear mcss in this study which was generally similar to that observed by previous investigators

sem study of authigenic rutile anatase and brookite in proterozoic sandstones from sweden abstract scanning electron microscopic examinations revealed interstitial rutile anatase and brookite to be common in upper proterozoic sandstones of the visingso group in southern sweden anatase is observed as either single discrete crystals or as numerous crystals filling and lining pore space rutile and brookite occur predominantly as clusters of crystals within interstitial cements on detrital grains e g feldspar and quartz or as overgrowths on detrital and authigenic titanium oxides these titanium oxides have been formed diagenetically from percolating pore solutions rich in titanium ions the source of titanium ions is suggested to be mainly detrital fe ti oxides sphene and biotite grains

characterizing thunderstorm gust fronts near complex terrain abstractfire safety aviation wind energy and structural engineering operations are impacted by thunderstorm outflow boundaries or gust fronts gfs particularly when they occur in mountainous te

diagenetic alteration of detrital biotite in proterozoic sedimentary rocks from sweden abstract the alteration of detrital biotites has been studied in two clastic proterozoic sedimentary sequences from southern and central sweden namely the visingso group and the dala sandstone respectively the results showed that the biotites are altered through replacement by clay minerals illite chlorite and less commonly kaolinite biotite may either be replaced pseudomorphically one biotite crystal by one clay mineral crystal or by fine crystalline clay minerals which merge into the interstitial clay matrix in reddish rocks biotite may be associated with pigmentary hematite and in greenish rocks with pyrite the variation in the two textural habits of biotite alteration i e pseudomorphic or fine crystalline is related to physico chemical properties of pore solution and nature of biotite particles

application of theory to simulations of observed cases of orographically forced convective rainfall abstractin two recent papers the authors reported on numerical simulations of conditionally unstable flows past an idealized mesoscale mountain ridge these idealized simulations which were performed with a three dimensional explicitly cloud resolving model allowed the investigation of simulated precipitation characteristics as a function of the prescribed environment the numerical solutions were carried out for a uniform wind flowing past a bell shaped ridge and using an idealized unstable sounding with prescribed values of the relevant parameters in the present work the application of these theoretical results to observed cases of orographically forced convective rainfall including the big thompson flood 1976 colorado the oahu flood 1974 hawaii and the gard flood 2002 france is reported specifically numerical simulations have been carried out using observed and idealized soundings relevant to these cases but with idealized topography it is found that using the observed soundings but

rainfall occurrence in the u s warm season the diurnal cycle the diurnal occurrence of warm season rainfall over the u s mainland is examined particularly in light of forcings at multiple scales the analysis is based on a radar dataset of 12 seasons duration covering the u s mainland from the continental divide eastward the dataset resolves 2 km features at 15 min intervals thus providing a detailed view of both large and regional scale diurnal patterns as well as the statistics of events underlying these patterns the results confirm recent findings with respect to the role of propagating rainfall systems and the high frequency at which these are excited by sensible heating over elevated terrain between the rockies and the appalachians 60 of midsummer rainfall occurs in this manner most rainfall in the central united states is nocturnal and may be attributed to the following three main forcings 1 the passage of eastward propagating rainfall systems with origins near the continental divide at 105 w 2 a nocturnal reversal of the mountain plains solenoid which is associated with widespread ascent over the plains and 3 the transport of energetic air and moisture convergence by the great plains low level jet other features of interest include effects of the appalachians semidiurnal signals of regional significance and the impact of breezes along the gulf of mexico a modest effort was put forth to discern signals associated with el nino and the southern oscillation while tendencies in precipitation patterns are observed the record is too short to draw conclusions of general significance

structures and fabrics in a crustal scale shear zone betic cordillera se spain abstract a broad zone of dominantly ductile high strain deformation lies beneath the aguilon nappe in the sierra alhamilla southern spain it forms part of a crustal scale movement zone traceable through much of the betic cordillera which separates the higher betic nappes from the underlying nevado filabride complex the zone is characterized in outcrop by a distinctive platy foliation and a strong nne trending stretching lineation microstructural characteristics include quartz ribbons mica fish augen of feldspar and other minerals in a matrix of dynamically recrystallized quartz and extensional crenulation cleavages narrow bands of ultramylonite and cataclasite occur within and on the margins of the movement zone deformation occurred under lower greenschist facies conditions and was accompanied by retrogression of earlier higher grade mineral assemblages structures in the movement zone developed in a temporal sequence beginning with isoclinal folding and transposition of older foliations this was followed by the formation of extensional crenulation cleavages and the progressive localization of strain into the ultramylonite bands mylonitic foliation in these bands is deformed by syn mylonite folds restricted to the bands all these structures were then deformed by s to se vergent small scale folds restricted to the movement zone as a whole cataclasis associated with alteration is localized along the ultramylonite bands and indicates a transition to late stage brittle deformation the lower boundary of the movement zone is gradational strain decreases recrystallized grainsize and the degree of recrystallization of quartz increases and pressure solution becomes the dominant deformation mechanism in mica schist asymmetric quartz fabrics in the movement zone indicate a nne sense of shear but variations in the degree of asymmetry suggest that flow was partitioned with the ultramylonite bands taking up much of the shear strain and the intervening rocks deforming more slowly and with a lower degree of non coaxiality diffuse fabrics in the fine grained ultramylonite bands may indicate a switch to a grainsize sensitive deformation mechanism and an overall downward increase in the opening angle of crossed girdle fabrics may reflect increased water activity at depth

mesoscale numerical study of two cases of long lived quasi stationary convective systems over eastern spain a set of mesoscale numerical simulations using the pennsylvania state university national center for atmospheric research model is used to investigate two cases of extreme precipitation over eastern spain both cases 3 4 november 1987 and 20 october 1982 were characterized by quasi stationary mesoscale convective systems that developed over the valencia region and lasted more than 30 and 12 h respectively rainfall totals in 24 h exceeded 800 mm on 3 4 november and 400 mm on 20 october at some localities of that region the first event occurred within a weak and very stagnant synoptic pattern under a persistent easterly northeasterly low level jet stream impinging on the valencian orography in contrast the second case involved a westwardmoving surface low driven by an upper level jet streak which evolved along the northern edge of an upperlevel cutoff low over north africa in both cases the mesoscale model forecast spatial details of the precipitation field reasonably accurately as well as capturing its long duration but underestimated the storm total precipitation model output fields suggest that the development of a surface mesolow by latent heat release as well as lee cyclogenesis induced by the atlas mountains could have played an important role in both events by providing low level convergence and enhanced upslope winds thus a factor separation technique is used to explore this issue for the event of 3 4 november 1987 latent heat is decisive for explaining the precipitation maximum over central valencia and the atlas orography induces rainfall enhancement over the same zone for the event of 20 october 1982 the latent heat release is again shown to be important whereas the atlas mountains orography factor appears to inhibit rainfall this is the first time that it has been documented that the atlas induced modulation of the surface pressure field is not a positive factor for heavy precipitations over eastern spain this exceptional case may be due to a negative interaction between the atlas mountains and the upper level dynamics and frontal forcing for this event

the structure and tectonic evolution of the aguilon fold nappe sierra alhamilla betic cordilleras se spain abstract detailed structural work in the sierra alhamilla se spain shows that the aguilon nappe comprising triassic and older metasedimentary rocks is a fold nappe the most prominent set of small scale folds changes from dominantly n vergent in the upper right way up limb to s vergent in the greatly thinned lower limb the nappe closes to the north and must have been emplaced in this direction nappe formation was accompanied by small scale folding and extensive solution transfer producing a pronounced differentiated crenulation cleavage these structures overprint an earlier set of folds and cleavage and are overprinted in turn by late n vergent structures the lower limb of the nappe was thinned and disrupted during continued nappe transport pre triassic schist in the core of the nappe was affected by medium grade metamorphism of probable post triassic age the contact with low grade permo triassic sediments above and below the schist coincides with a distinct change in metamorphic grade this contact may be a post metamorphic extensional fault that is now folded around the nappe which suggests that nappe formation was preceded by extensional faulting this is consistent with gravity spreading as the driving process for nappe emplacement

tectonic sequence diagrams and the structural evolution of schists and gneisses in multiply deformed terranes the current practice of numbering deformation phases d 1 d n in a multiple deformed terrane obscures the link between data and inference and can lead to erroneous interpretations routine production of tectonic sequence diagrams tsds allows a method whereby all deformation and metamorphic mineral growth events their overprinting and duration based on relative timing are systematically recorded different hypotheses as to correlation of tsds across a region can then be assessed objectively including correlation of characteristic sequences that can often be recognized in tsds from single outcrops tsds ensure that absolute dating is applied to specific events within a sequence eliminating the practice where a date is imprecisely correlated tsds also place a focus on the independent character of events here confirmed by absolute dating here we demonstrate how tsds show that many fold nappes are recumbent folds transected by later unrelated ductile shear zones tsds also show that p t t paths and exhumation rates must include starting and stopping of events periods of quiescence and changes in tectonic mode from shortening to extension tsds allow objective analysis of the complexity present in many metamorphic tectonites but which is obscured by conventional methodology

the influence of strain lithology and stratigraphical depth on white mica illite crystallinity in mudrocks from the vicinity of the corris slate belt wales implications for the timing of metamorphism in the welsh basin low and very low grade metamorphism in a mudrock dominated succession ranging from upper cambrian to wenlock is characterized by the white mica illite crystallinity technique kubler indices indicate that grade ranges from late diagenetic to low epizonal the prograde reaction most easily observed by xrd study is the progressive ordering of k na micas diagnostic 2m 1 polytypic reflections become recognizable at 0 4 2 and strengthen as grade advances grade generally correlates with thickness of overburden in the 9 km thick succession however strain exercises additionally a profound influence on grade and the distribution of strain was related to decollement resulting from inhomogeneities and ductility contrasts within the succession strain energy is seen as an additional and important variable in the development of white mica crystallinity in slates the distribution of metamorphic grade implies that the lower palaeozoic succession was augmented by several kilometres of lower devonian old red sandstone strata at the metamorphic culmination the culmination was syntectonic and represents an acadian rather than an early diastathermal event subsequent dextral movement on the bala fault displaced the regional isocryst pattern by c 4 km retrogressive smectite appears to be localized to the vicinity of the bala fault and is probably of variscan age

diurnal evolution and distribution of warm season convective storms in different prevailing wind regimes over contiguous north china the diurnal evolution and distribution of warm season convective storms in different prevailing wind regimes at the 925 hpa and 500 hpa levels over contiguous north china have been studied using a climatology based on radar reflectivity mosaics soundings and reanalysis data from 15 may to 15 september in 2008 2011 in the wind regimes at the 925 hpa level the frequency of occurrence of convection is highest for south southwesterly flows followed by that for south southeasterly flows the low level southerly warm and moist flow over the foothills and plains favors initiation and intensification of convection resulting from topographic forcing among the wind regimes at the 500 hpa level the frequency of occurrence of convection shows a pronounced maximum for west southwesterly flows and most of these storms initiate and develop over the foothills and plains convection in the wind regime shows the morphology and slowly east southeastward moving characteristics of well organized longer lived systems with environmental conditions conducive to vertical wind shear and instability at the 500 hpa level the high frequency of occurrence of convection for west southwesterly flows is followed by that for west northwesterly flows under west northwesterly flows convective storms initiated over mountains located to the northwest in the early afternoon move rapidly to the plains in the southeast of the study region these storms show the primary formation characteristics of shorter lived convection and intensify noticeably as they move from the mountains to the foothills and plains

on the severe convective storm of 29 october 2013 in the balearic islands observational and numerical study on 29 october 2013 a severe squall line developed to the west of the balearic islands spain ahead of an advancing cold front and then crossed the archipelago we first provide an observational characterization of the event based on surface reports remote sensing products radiosoundings and synoptic information we also achieve by means of numerical experiments new insights into the kinematic and thermodynamic factors that governed the genesis and evolution of the linear convective system radar and satellite images confirm the fast movement and linear shape of the system with an indication of a possible transition into a bow echo structure during its later stages the synoptic setting at mid upper tropospheric levels was dominated by a cold trough extended over western europe associated with a jet stream located downstream convection evolved under the right entrance region of the jet and initiated under the crucial influence of a surface low that developed over the mediterranean sea ahead of the cold front the low not only cooperated with the upper level dynamical forcing to erode a capping inversion initially present over the balearics and moisten the atmospheric column above but also shaped and enhanced a convergence line along which the first convective cells grew and self aggregated this scenario is confirmed by numerical simulations of the case which also emphasize the important role of regional topography in the production of the aforementioned maritime convergence through the mesoscale modulation of the low level flow additional simulations show that i the destabilization of the low level air mass necessary for triggering and feeding an organized convective system on 29 october 2013 was attributable to prior evaporation from the mediterranean and ii sea surface temperatures appear to be critical for a successful fine grid numerical forecast of the mode degree of severity timing and track of the convective precipitation system

the spatial and temporal distribution of organized convective structures over the northeast and their ambient conditions abstract organized convective structures over the northeastern united states were classified for two warm seasons may august using 2 km composite radar i e the national operational weather radar nowrad data nine structures were identified three types of cellular convection clusters of cells isolated cells and broken lines five types of linear convection lines with no stratiform precipitation lines with trailing stratiform precipitation lines with parallel stratiform precipitation lines with leading stratiform precipitation and bow echoes and one nonlinear system the occurrence of all structures decreases from the western appalachian slopes eastward to the atlantic coast isolated cellular convection forms primarily during the morning to late afternoon 1200 2100 utc mainly over the high terrain clusters of cells form primarily over the appalachians and the atlantic coastal plain during the daytime 1200 0000 utc linear convection is favored from midafternoon to early evening 18

a numerical study of three catastrophic precipitating events over southern france ii mesoscale triggering and stationarity factors in the western mediterranean basin large amounts of precipitation can accumulate in less than a day when a mesoscale convective system mcs stays over the same area for several hours heavy precipitating events hpes in this region especially southern france are not only characterized by significant precipitation rates typically more than 200 mm in less than 24 or 48 hours but also by quasi stationary behaviour the aim of this present study is to use realistic simulations of past events to analyze and better understand the physical mechanisms which lead to the stationarity of hpes over southern france using a high resolution 2 5 km non hydrostatic mesoscale atmospheric model we focused on three hpes 13 14 october 1995 the cevennes case 12 13 november 1999 the aude case and 8 9 september 2002 the gard case the experimental design for simulating realistic structures and evolutions of the hpes with the meso nh model has been presented in a companion paper in that study the evolution of the synoptic patterns in which the hpes occurred were analysed in this paper the importance of mesoscale ingredients such as the moist and conditionally unstable low level jet llj is examined in terms of their ability to focus the deep convection over the same area for several hours the cevennes case is typical of a so called cevenole event in france for which orographic forcing is the primary mechanism which acts to continuously generate convective cells upwind of the massif central the unusual location of the gard event is explained by a cold pool induced by the evaporation of precipitation which acts as a relief like feature to force the conditionally unstable and moist llj to rise this constitutes a quasi stationary forcing as the cold pool is blocked in the rhone valley for the third case diabatic cooling and the massif central act to enhance the precipitation but have almost no impact on the location of the anchoring point of the precipitating system

convective episodes in the east central united states nine years of composited radar data are investigated to assess the presence of organized convective episodes in the east central united states in the eastern united states the afternoon maximum in thunderstorms is ubiquitous over land however after removing this principal diurnal peak from the radar data the presence and motion of organized convective systems becomes apparent in both temporally averaged fields and in the statistics of convective episodes identified by an objective algorithm convective echoes are diurnally maximized over the appalachian chain and are repeatedly observed to move toward the east partly as a result of this the daily maximum in storms is delayed over the piedmont and coastal plain relative to the appalachian mountains and the atlantic coast during the 9 yr studied the objective algorithm identified 2128 total convective episodes 236 yr 1 with several recurring behaviors many systems developed over the elevated terrain during the afternoon and moved eastward often to the coastline and even offshore in addition numerous systems formed to the west of the appalachian mountains and moved into and across the eastern u s study domain in particular many nocturnal convective systems from the central united states entered the western side of the study domain frequently arriving at the eastern mountains around the next day s afternoon maximum in storm frequency a fraction of such well timed systems succeeded in crossing the appalachians and continuing across the piedmont and coastal plain convective episodes were most frequent during the high instability low shear months of summer which dominate the year round statistics even so an important result is that the episodes still occurred almost exclusively in above average vertical wind shear despite the overall dominance of the diurnal cycle the data show that adequate shear in the region frequently leads to long lived convective episodes with mesoscale organization

diagenetic chloritization of feldspars in sandstones abstract detrital microcline and albite are commonly replaced diagenetically by chlorite in sandstones of the visingso group upper proterozoic southern sweden authigenic quartz and in some cases albite and illite are associated with the chlorite the sem examinations suggest that chloritization of feldspar has usually been preceded by dissolution of the replaced feldspar grain fe 2 and mg2 which are needed for the chloritization have partly been derived from the detrital fe mg silicates mainly biotite fe oxide pigment and fe ti oxide grains whereas si4 and al3 are supplied mostly by the altered feldspars the k released from microcline and na from albite were mostly incorporated in authigenic illite and albite respectively

ductile shear deformation of quartzite in an alpine crustal thrust ambin massif abstract in this paper we show that fabric analysis gives good results when the sampling is done in an homogeneous material in a well known tectonic environment a quartzitic layer situated in the autochtonous basement of the ambin massif below the nappe des schistes lustres french italian alps has been choosen because the first ductile deformation phase is clearly defined by the microstructures and because the metamorphic history is well known the quartz c axis diagrams are characterized by two asymmetric crossed girdles and the one containing the maxima is inclined westwards we propose that these fabrics result from plastic deformation of the quartzite occurring with the basal plane as a dominant gliding plane the fabrics define a shear sense towards the west the angle between the basal planes and the foliation which varies from 15 to 40 is at least qualitatively related to the macroscopic strain our study confirms the existence of a regional large crustal thrust which has occurred during the obduction of oceanic material schistes lustres on the european continent

sequence and style of major post nappe structures simplon pennine alps abstract in the upper pennine nappe complex of the simplon pennine alps switzerland and italy at least three phases of major post nappe folding in places associated with thrusting can be distinguished these are superimposed on an earlier formed partly chaotic complex of tectonic units including the bernhard and monte rosa continental flakes and the zermatt saas and antrona ophiolite complexes the earliest post nappe folds were essentially isoclinal throughout the whole region and were accompanied by a strong schistosity which is the main foliation in most areas later two successive phases of back folding led to the present overall structure both phases typically show rapid variations in style from open folds lacking axial planar schistosity to very tight structures with complete foliation transposition this has been demonstrated by systematically mapping the major axial traces over the whole region successively removing the major structures in reverse order shows that the ophiolite complexes were originally part of a continuous unit marking an important suture between the bernhard and monte rosa nappes

wave disturbances and their role in the maintenance structure and evolution of a mesoscale convection system abstractthis study investigates a nocturnal mesoscale convective system mcs observed during the plains elevated convection at night pecan field campaign a series of wavelike features were obse

the impact of spatial variations of low level stability on the life cycle of a simulated supercell storm abstract this study reports on the dynamical evolution of simulated long lived right moving supercell storms in a high cape strongly sheared mesoscale environment which initiate in a weakly capped region and subsequently move into a cold boundary layer bl and inversion region before dissipating the storm simulations realistically approximate the main morphological features and evolution of the 22 may 1981 binger oklahoma supercell storm by employing time varying inflow lateral boundary conditions for the storm relative moving grid which in turn are prescribed from a parent fixed steady state mesoscale analysis to approximate the observed inversion region to the east of the dryline on that day a series of full life cycle storm simulations have been performed in which the magnitude of boundary layer coldness and the convective inhibition are varied to examine the ability of the storm to regenerate and sustain its main updraft as it moves into environments with increasing convective stability the

from passive margin to continental collision a tectonic scenario for the western alps general transverse section just south of the pelvoux massif european margin of tethys an ancient atlantic type margin it was subject to extension from triassic to the beginning of late cretaceous times and to collision thereafter as the result of convergence of the eurasian and african continents paleogeographic evolution is outlined a new alpine tectogenetic reconstruction is proposed an attempt is made to establish how the previous extensional structures influenced the later tectonic evolution modified journal abstract

a numerical model study of an intense cutoff low pressure system over south africa abstract investigations of extreme rainfall events in the southern african region are limited by the paucity of the observational network furthermore the lack of full radar coverage for south africa makes quantitative precipitation estimation difficult therefore numerical modeling represents the most effective method for improving the understanding of the mechanisms that contribute to extreme rainfall events in this region with the caveat that accurate validation of model simulations is hampered by the limited observations in the region this paper describes an intense cutoff low event over south africa that led to record rainfall and flash flooding along the south coast of the country and adjoining hinterland analyses from the global forecast system model showed that the cutoff aloft was accompanied by a strong low level jet llj impinging onto the south coast where rainfall was heaviest and that lapse rates were steep in the lower troposphere simulations of the event were carried out using a num

initiation and development of a mesoscale convective system in the ebro river valley and related heavy precipitation over northeastern spain during hymex iop 15a during intensive observation period 15a 20 october 2012 of the first special observation period of the hydrological cycle in the mediterranean experiment north eastern spain experienced heavy precipitation 130 mm in 24 h associated with a retrograde regeneration mesoscale convective system mcs developing in the exit region of the ebro river valley erv the life cycle of the mcs that brought intense hourly rainfall 34 mm from the foothill of iberian plateau to the central pyrenees as well as the detailed structure of moist marine flow upstream were analysed using a combination of ground based airborne and space borne observations as well as model analyses over the balearic sea the south westerlies along the north eastern flank of a surface low converged with south easterlies from north africa creating a near surface moisture tongue in the region of the balearic islands and a southeast northwest oriented convergence line within a cloud cluster advecting from northern africa airborne lidar measurements acquired upstream of the erv evidenced water vapour mixing ratios in excess of 15 g kg 1 in the marine atmospheric boundary layer in the mid level 700 hpa the presence of an elevated moisture plume from tropical africa contributed for about one third to the large moisture content present over the western mediterranean sea in this moist environment the mcs was initiated over the orography of the north eastern tip of the iberian plateau due to the combined influence of the approaching convergence line ahead of the surface low and the convergence resulting from weak north westerlies channeled in the erv and the easterlies impinging on the coastal range after the initiation phase the mcs further developed over the foothill of iberian plateau and moved into the erv and along the southern flank of the pyrenees thanks to the penetration of the warm and moist maritime south easterly flow through the narrow gap between the north eastern part of the iberian plateau and the catalan coastal range

the potential role of atmospheric bores and gravity waves in the initiation and maintenance of nocturnal convection over the southern great plains abstractthis investigation explores the relationship among bores gravity waves and convection within the nocturnal environment through the utilization of measurements taken during the internation

quartz and fe dolomite cements record shifts in formation water chemistry and hydrocarbon migration in devonian shoreface sandstones ghadamis basin libya cementation by quartz overgrowths and subsequently by carbonates is a very common global paragenetic phenomenon in sandstones of many basins that is poorly constrained in the literature integrated

the structure evolution and dynamics of a nocturnal convective system simulated using the wrf arw model abstractprevious studies have documented a nocturnal maximum in thunderstorm frequency during the summer across the central united states forecast skill for these systems remains relatively low and the explanation for this nocturnal maximum is still an area of active debate this study utilized the wrf arw model to simulate a nocturnal mesoscale convective system that occurred over the southern great plains on 3 4 june 2013 a low level jet transported a narrow corridor of air above the nocturnal boundary layer with convective instability that exceeded what was observed in the daytime boundary layer the storm was elevated and associated with bores that assisted in the maintenance of the system three dimensional variations in the system s structure were found along the cold pool which were examined using convective system dynamics and wave theory shallow lifting occurred on the southern flank of the storm conversely the southeastern flank had deep lifting with favorable integrated vertical shear ov

sr and nd isotopic evidence for punctuated clay diagenesis texas gulf coast we report rb sr sm nd and mineralogical data for leached whole rock 1200 m independent of the duration of burial the exchangeable sr in the clay has remained an open system and has undergone isotopic exchange since that time minimum fluid rock ratios of 0 2 to 2 are modeled from sr isotopic data consistent with rock dominated open system diagenesis leachates and residues of the 0 1 zm fraction below the smectite illite transition appear to have achieved nd isotopic equilibrium during clay diagenesis and show no signs of subsequent exchange the clay residues have low 147sm 144nd 0 085 indicating that authigenic illite has a lower sm nd ratio than its bulk rock protolith conversely the coexisting exchangeable ree inventory has elevated sm nd as reflected by leachate 14vsm 144nd as high as 0 188 this sm nd fractionation in conjunction with the preserved isotopic equilibrium may be useful for dating diagenesis and associated fluid rock interaction in older rocks

numerical study of an observed orogenic mesoscale convective system part 1 simulated genesis and comparison with observations abstract the interaction of topographically induced thermally and mechanically driven diurnal flow regimes in the lee of the rockies is shown to lead to the growth of a mesoscale convective system mcs an organic mcs observed during the 1977 combined south park area cumulus experiment and high plains experiment is numerically simulated with a two dimensional nonhydrostatic cloud model covering spatial scales of 1000 km in this numerical investigation meso meso and meso scales of motion are represented simultaneously as a result interesting features of cloud mesoscale interaction are predicted that cannot be represented in cloud parameterization frameworks based on the results of this simulation a six stage conceptual model of orogenic development is given

the generation of a mesoscale convective system from mountain convection a mesoscale convective system mcs that formed just to the east of denver is investigated with a nonhydrostatic numerical model to determine which processes were important in its initiation the mcs developed from outflow from previous convective activity in the rocky mountains to the west model results indicate that this outflow was necessary for the development of the mcs even though a convergence line was already present in the area where the mcs developed a simulation with a 3 km grid spacing more fully resolves the convective activity in the mountains but the development of the mcs can be simulated with a 6 67 km grid cloud effects on solar radiation and ice sedimentation both influence the strength of the outflow from the mountain convection but only the ice sedimentation makes a significant impact on the development of the mcs after its initiation the frequent convective activity in the rocky mountains during the warm season provides outflow that would make mcs generation favorable in this region thus there is a close connection between mountain convective activity and mcs generation the implications of such a connection are discussed and possible directions of future research are indicated

coherent regeneration and the role of water vapor and shear in a long lived convective episode abstract in a recent radar based climatological study of warm season precipitation over the continental united states carbone et al found a high frequency of long lived coherent rainfall episodes many of the events were of longer duration than normally associated with mesoscale convective complexes and exhibited phase speeds 10 m s 1 in excess of the phase speed associated with synoptic systems the observations led to the speculation that cold pool dynamics and wavelike propagation mechanisms were responsible for the longevity of the systems one of the long lived episodes included in the statistics of the carbone et al study is described here occurring on 14 15 july 1998 the system lasted 50 h and traveled over 2800 km at its peak intensity the system was a bow echo producing damaging wind large hail and local flash flooding an interesting aspect of the event was an abrupt 90 turn in the storm s orientation and propagation vector midway through its life the environmental factors that led t

tubular folds and sheath folds definitions and conceptual models for their development with examples from the grapesvare area northern sweden abstract two parameters are used in the classification of highly non cylindrical folds the hinge line angle and the ratio of the length of the cone axis to that of the long axis of the cross section of the structure at the position where the hinge angle was measured if in a non cylindrical fold a cross section can be selected so that the hinge angle w measured where the cross section cuts the cone is less than 90 and the length of the cone axis x is more than a quarter of the length of the long axis y of the cross section the fold is a sheath fold a tight sheath fold with w x y 1 can be termed a tubular fold a tubular fold is thus an extreme type of sheath fold while sheath folds with w 20 but x y 0 25 but tubular folds from the grapesvare area comply to the definition given above and they occur in a structural setting that is consistent with the models described

the detection and significance of diurnal pressure and potential vorticity anomalies east of the rockies abstract harmonic analysis of pressure temperature and precipitation data from 1000 automated surface observing system asos stations reveals a mix of stationary and east west moving disturbances east of the rockies optimization of the pressure data using a temperature based tide assumption separates a strong sun following continentally enhanced tide from a smaller eastward propagating wave epw the latter signal moves at a similar speed to the previously discovered eastward moving precipitation systems analysis of asos summer precipitation data confirms eastward propagation but east of 90 w it shows nonpropagating diurnal convection at a fixed local time i e 1800 lst analysis of winter days still finds the epw suggesting that it is the cause and not the result of the propagating precipitation a possible mechanism for the epw is developed from the linear bousinesq equations with heating and wind shear solutions show eastward moving diurnal pulses of potential vorticity pv generated by

initiation of precipitation episodes relative to elevated terrain abstract the western and central united states experience a pronounced diurnal cycle in rainfall during the warm season over the higher terrain west of 105 w most precipitation occurs in the afternoon whereas the central united states experiences more nocturnal events this coherent phase transition between the rocky mountains and the u s great plains is well defined for all warm seasons between 1996 and 2003 provided that the rainfall observations are remapped relative to the elevated terrain in the western united states prior to north south averaging due to the westward shift of the continental divide north of 42 n and its intersection with the warm season storm track for 2002 the diurnal coherence greatly improves after remapping the 2002 rainfall observations this speaks to the long range influence of orography on precipitation frequency and suggests that the primary east west corridor of precipitation for an individual warm season intersects the cordillera over a fairly narrow latitude range

mesoscale convective systems in weakly forced large scale environments part i observations abstract during a 24 h period beginning 1200 utc 11 may 1982 a series of five mesoscale convective systems mcss developed within a weakly forced large scale environment analyses indicate that the large scale flow created a broad region of potential buoyant energy but owing to a restraining inversion and weak large scale upward motion convection was initiated only where lifting associated with mesoscale features was able to eliminate the inversion the series of mcss developed sequentially and moved eastward across the moist axis two of these systems had a large component of motion against the mean tropospheric flow and propagated in a direction nearly opposite to that of the traveling upper level disturbances each system produced an outflow of cold downdraft air that spread progressively farther south than that from the preceding system this description of the development and evolution of convection is very different from traditional ones wherein convection develops and moves more or less in pha

large scale wind and precipitation extremes in the mediterranean a climatological analysis for 1979 2012 a new method for identifying high impact large scale wind and precipitation events in the extended mediterranean region is outlined and applied to the european centre for medium range weather forecasts ecmwf reanalysis dataset era interim for the years 1979 2012 the method highlights large scale 10 m gust and precipitation events that classify as extreme if integrated over a spatial scale of 1000 km and a temporal scale of 3 days the method detects successfully high impact events and reveals clear seasonal differences among the subregions of the mediterranean western mediterranean precipitation extremes are more intense and occur mainly in autumn while eastern mediterranean events occur in winter composite dynamical analyses of large scale wind and precipitation extremes and a combination of them highlight coherent dynamical flow structures associated with the extremes in the different subregions of the mediterranean precipitation events are preceded by an upper level trough and strong jet on its western flank followed by cyclogenesis mainly in the western mediterranean and or a merging of the polar with the subtropical jet over northeastern africa in the eastern mediterranean strong surface wind extremes develop around cyclones that intensify south of a deep parent cyclone near the exit of a strong anticyclonically curved jet propagate eastwards and create a cold and dry northerly wind anomaly at the surface furthermore combined large scale wind and precipitation extremes often occur simultaneously near cyclones either north atlantic cyclones which project the wind and precipitation into the western mediterranean or mediterranean cyclones the latter produce wind extremes over a localized area which often overlaps entirely with the region that receives extreme precipitation

impact of environmental variations on simulated squall lines interacting with terrain abstractthe complex evolution of convective systems crossing or attempting to cross mountainous terrain represents a substantial forecasting challenge this study examines the processes associated with environments of crossing squall lines which were able to redevelop strong convection in the lee of a mountain barrier and noncrossing squall lines which were not able to redevelop strong convection downstream of the barrier in particular numerical simulations of mature convective systems crossing idealized terrain roughly approximating the appalachian mountains were used to test the first order impact of variations in the vertical wind profile upon system maintenance by itself the wind profile showed no ability to uniquely discriminate between simulated crossing and noncrossing squall lines each test revealed a similar pattern of orographic enhancement suppression and lee reinvigoration in which a hydraulic jump deepened the system s cold pool and renewed the low level lifting increasing th

a radar based climatology of mesoscale convective systems in the united states abstractthis research applies an automated mesoscale convective system mcs segmentation classification and tracking approach to composite radar reflectivity mosaic images that cover the contigu