a wave cisk model of squall lines abstract the wave cisk model of raymond incorporating lag effects in the updraft and downdraft is implemented as an initial value problem in physical space examples of both midlatitude and tropical squall lines are successfully simulated diagnosis of the model shows that condensational heating in the updraft is the primary driving mechanism of a mature squall line with evaporative cooling and convective momentum transfer playing subsidiary roles however an instability involving the displacement of boundary layer air by downdrafts apparently plays an important role in squall line initiation a weakness of the model is its inability to predict the direction of squall line propagation relative to the low level wind shear this is traced to the insensitivity of the convective parameterization to midlevel entrainment however unlike strict two dimensional squall lint models the parameterization allows cross stream mass transfer to occur in the context of overall slab symmetry such transfer is dynamical

gravel topped offshore bar sequences in the lower carboniferous of southern ireland within the kinsale formation lower carboniferous of southern ireland are pebbly sandstones and conglomerates contained in what is known locally as the garryvoe conglomerate facies in this facies there are three main groups of lithologies a heterolithic mudrocks and sandstones characterized by a wide variety of wave produced structures b sandstones dominated by swaley cross stratification scs parallel lamination and rare hummocky cross stratification hcs and c pebbly sandstones and conglomerates occurring as discrete beds or as gravel clasts dispersed through scs sets successions of the facies comprise units of heterolithic mudrock and rippled sandstone alternating repeatedly with coarsening upward units of scs pebbly sandstone capped by top surface granule and pebble lags the garryvoe conglomerate facies accumulated in a system of offshore bars on a muddy shallow marine shelf that was dominated by waves and currents generated by storms sands and gravels were bypassed from a contemporaneous northerly coastal zone to the shelf where they were moulded by the storm generated flow into low broad sand ridges offshore bars the elongate bars were spaced kilometres apart oriented obliquely to the coast and separated by muddy interbar troughs their surfaces were largely covered by hummocky and swaley forms long term gradual seaward migration of the offshore bars concentrated gravels on landward flanks from the dispersed pebbly sands that were on the crests and seaward flanks exceptionally intense storms could form laterally extensive winnowed gravel lags above thinned bar sequences such storms could also flush gravel bearing turbidity currents into muddy interbar trough areas

mesoproterozoic carbonate systems in the borden basin nunavut existing stratigraphic nomenclature lithologic descriptions and geological interpretations for an economically important mesoproterozoic dolostone in the milne inlet graben borden basin nunavut do not adequately portray its unusual facies or their spatio temporal configuration four new stratigraphic units are introduced to replace this dolostone formerly known as the society cliffs formation in the southeastern half of the graben the iqqittuq formation represents a distally steepened ramp that grades northwestward into deep water mudstone that is indistinguishable from that of the underlying arctic bay formation the overlying angmaat formation represents a rimmed restricted peritidal platform that grades northwestward across a tepee cortoid shoal barrier into the unusual deep water dolo laminite of the nanisivik formation deep water carbonate mounds up to hundreds of metres thick and kilometres in areal dimensions belong to the ikpiarjuk formation these mounds are geometrically equivalent

sediment transport in the new york bight north american atlantic shelf vincent c e swift d j p and hillard b 1981 sediment transport in the new york bight north american atlantic shelf mar geol 42 369 398 aanderaa current meter data collected during the course of noaa s new york bight project are sufficiently extensive in time 135000 observation hours and space 41 stations to permit an estimate of the sediment transport in this area the analysis is based on mean flow observations the role of wave oscillatory currents in resuspending sediment is considered but not explicitly included in the sediment transport calculations an estimate of the potential sediment transport rate qb at each station for three different threshold velocities uth 12 16 and 20 cm s 1 were made using a bagnoldtype transport equation qb const uc uth 3 for uc uth qb 0 for uc uth where uc is the mean current speed comparison was made between the results from this simple equation and other bedload and suspended load transport rates which include wave data for a limited subset of the bight data this comparison indicates that the bagnold results are reasonable for the along isobath transport estimates but are not reliable for the cross isobath transport in the cross isobath direction waves appear to play a dominant role in determining the transport rate the comparison also indicates that the bagnold approach tends to overestimate transport in deep water in shallow water resuspension of sand and rotor pumping of current meters both may become important and sediment transport calculations may not be accurate fine sediment suspended transport is approximately double the potential bedload transport for fine sand 0 02 cm but does not dominate the total transport as is believed to occur on the washington shelf smith and hopkins 1972 the data show that the new york bight is a storm dominated shelf with the general southwestward drift of water 6 cm s 1 modulated by more intense storm induced flows the transport calculations indicate that the bulk of sediment transport occurs during the winter months when wind stress is at a maximum and the water column is well mixed two major transport provinces are present a the hudson shelf valley and b the rest of the shelf the shelf valley acts as a sink and a barrier to the continuity of the mainly southwestward transport of sediment 104 g cm 1 yr 1 along the shelf within the valley the potential transport of material is of the order of l05 g cm 1 yr 1 along the valley axis progressive vector transport paths for fine sediment indicate that removal of sediment out of the ends of the valley can occur rapidly however consider ation of the finesediment budget for the whole hudson shelf valley and of the attenua tion of wave activity with depth show that these results are not inconsistent with the presence of high mud concentrations in the valley up valley sediment rates predominate during the period for which data are available

morphology and processes associated with the accumulation of the fine grained sediment deposit on the southern new england shelf abstract a 13 000 km2 area of the southern new england continental shelf which is covered by anomalously fine grained sediment has been surveyed by means of high resolution seismic reflection and side scan sonar techniques to map its morphology and structure and a near bottom instrument system contributed to understanding present activity of the deposit seismic reflection profiles show that the fine grained deposit which is as much as 13 m thick has accumulated during the last transgression because it rests on a reflector that is geomorphically similar to and continuous with the holocene transgressive sand sheet still exposed on the shelf to the west the ridge and swale topography comprising the sand sheet on the shelf off new jersey and long island are relict in origin as the e same features are found buried under the fine sediment deposit southwestward migrating megaripples observed on the sonographs in the eastern part of the deposit are evidence that sediment is still actively accumulating in this area in the western part of the deposit where surface sediment is composed of silt plus clay evidence of present sediment mobility consists of changes in the near bottom suspended matter concentrations primarily associated with storms nantucket shoals and georges bank are thought to be the sources for the fine textured sediment storms and strong tidal currents in these shoal areas may still erode available fine grained material which then is transported westward by the mean drift to the southern new england shelf where a comparatively tranquil environmen permits deposition of the fine material

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

the evolution of a thick shallow marine succession the south munster basin ireland the relatively fine grained late devonian to early carboniferous cork beds succession of the south munster basin includes continuous sections of paralic facies that are over 1000 m thick and individual sandstone units over 300 m thick however the succession does not reflect prolonged phases when facies belts were stationary but rather multiple stacking of small scale high frequency sequences each associated with pronounced migration of shorelines what seems to have been unusual about the south munster basin succession was that the geographical positioning of these high frequency sequences was fixed this resulted from an unusual combination of tectonics shelf hydrodynamics sedimentation rates and the textural maturity of the sediment within the basin of these tectonics was probably most critical particularly the juxtaposition of rapid subsidence in basinal areas and a basin margin zone to the north that was sufficiently up standing to pin the maximum extent of transgression during repeated highstands of sea level yet not so upstanding as to have diverted the major regional drainage system the embayed palaeogeography of the area may also have been influential

a chronology of foreland deformation ultra violet laser 40ar 39ar dating of syn late orogenic intrusions from the variscides of southwest ireland abstract the upper palaeozoic sedimentary rocks of the munster and south munster basins southern ireland lie within the rhenohercynian zone of the european variscan orogeny this foreland region accommodated shortening during the asturian phase of variscan deformation at the end of the carboniferous by the development of kilometre scale and lower order folding high angle reverse faulting and regional fabric development at the southwestern extremity of the belt lies the black ball white ball heads area of the beara peninsula where high level igneous intrusions locally exhibit a close relationship with both the ductile and late brittle phases of variscan deformation 40 ar 39 ar ultra violet laser analysis of phlogopite crystals from these intrusions principally trachytic dykes has yielded ages that when combined with structural field relationships help to constrain the timing of variscan deformation in southern ireland these ages include 314 44 1 00 ma for a penetratively deformed lamprophric pipe on black ball head 301 98 1 47 298 08 0 61 ma for dyke material associated with later stage brittle deformation and a date of 296 88 0 60 ma for an undeformed post orogenic dyke on white ball head

mesoscale gravity waves and their environment in the central united states during storm fest abstract in an effort to better understand mesoscale gravity waves in winter storms in the central united states their frequency of occurrence wave characteristics the general conditions under which they occur and their effects upon the weather mesoscale surface and rawinsonde data as well as radar and satellite imagery collected during the storm scale operational and research meteorology fronts and experimental system test are analyzed in addition factors affecting the ability of objective surface map analysis to properly represent the waves are investigated thirteen coherent pressure pulse events with amplitudes of 0 2 4 0 mb and periods of 1 6 h were identified in the surface pressure data during the 6 weeks of the project involving 34 of the total hours investigated a variety of wave types occurred including wavelets wave trains and singular waves the three largest amplitude events were analyzed in detail using autospectral analysis and a barnes time to space conversion objective analysis

a mesoscale gravity wave event observed during ccope iii wave environment and probable source mechanisms abstract synoptic and special mesoscale observations taken during the cooperative convective precipitation experiment ccope are used to describe the multiscale environment of a gravity wave event understand the wave environment interactions that led to the development of severe thunderstorms and asses possible wave generation mechanisms the storms formed sequentially as a packet of gravity waves propagated across a stationary thunderstorm outflow boundary convection developed most rapidly in that part of the mesonetwork in which existed the combination of relatively high parcel buoyant energy weak restraining inversion strong storm downdraft potential and substantial vertical wind shear associated with a mesoscale jet streak synoptic scale analysis reveals that the waves were excited north of a stationary front and within the right exit region of the jet streak as it approached a stationary ridge in the 300 mb height field strong indications of unbalanced flow were diagnosed within the gravit

sub greenschist facies metamorphism from the variscides of sw ireland an early syn extensional peak thermal event illite crystallinity studies on metaclastics from the variscides of sw ireland range in value from 0 18 to 0 25 2 indicating a metamorphic grade in the upper anchizone lower epizone c 275 325 c chlorite geothermometry yields a similar metamorphic temperature range 280 315 c combining these data with known overburden estimates for the area c 5km implies late palaeozoic geothermal gradients in excess of 60 ckm 1 fluid inclusion studies on quartz veins in these metaclastics reveal two vein types characterized by fluid densities of 0 7 0 93 g cm 3 group 1 and 0 9 1 0gcm 3 group 2 respectively this variation in fluid density is thought to be dominantly controlled by temperature with group 1 veins linked to late palaeozoic extension and high geothermal gradients and group 2 veins associated with subsequent variscan deformation and lower temperature conditions

thrust surface geometry implications for thrust belt evolution and section balancing techniques abstract the application of modern concepts of thrust tectonics to orogenic belts has yielded many detailed restorable sections thrusts generally restore with a staircase geometry onto the undeformed stratigraphic template since the work of rich 1934 it has been generally assumed that thrusts have propagated with a staircase trajectory and that hangingwall structures result from the movement of the thrust sheet up footwall ramps however thrusts often cut through previously folded strata with a smooth trajectory smooth trajectory thrusts can be identified from footwall geometry and strain state once a smooth trajectory thrust has been identified it is insufficient to produce a balanced deformed section and its restored counterpart sequential balanced sections must be constructed reversing the deformation history the restoration of thrusts to a staircase trajectory has no mechanical significance as the thrust is merely acting as a marker if restored back beyond the time at which it propagated thrust ramps are not necessarily actual steps in the thrust surface they are often just zones where the thrust cuts through bedding in a smoothly curving trajectory ductile deformation in thrust belts can reduce bed length at depth thus removing the need for structures which are necessary to preserve constant bed lengths ductile deformation in the internal zones of orogenic belts renders the construction of balanced sections in these zones highly problematical

baroclinic instability in an environment of small stability to slantwise moist convection part i two dimensional models abstract in the semigeostrophic system the growth rate of baroclinic waves varies with the inverse square root of the potential vorticity which acts as the effective static stability recent observations in the ascent regions of middle latitude cyclones show that the effective potential vorticity for saturated air is very near zero in this paper we examine the structure and rate of growth of baroclinic cyclones when the effective potential vorticity is small for upward saturated displacements but large in regions of descent analytic solutions for two dimensional disturbances in a two layer semigeostrophic model and numerical simulations using a multilevel semigeostrophic model show that when the effective potential vorticity is small in regions of upward motion growth rates are modestly increased and the region of ascent intensifies and collapses onto a thin ascending sheet in the limit of zero moist potential vorticity the fastest growing wave has a finite growth rate which is about 2 5 times the

post acadian sediment recycling in the devonian old red sandstone of southern ireland abstract the upper devonian munster basin of southern ireland has traditionally been viewed as a post orogenic molasse deposit that was sourced from the caledonides of central ireland and subsequently deformed by the end carboniferous variscan orogenic event the basin fill is composed of super mature quartz arenite sandstone that clearly represents a second cycle of deposition the source of this detritus is now recognized as lower devonian dingle basin red bed sequences to the north this genetic link is based on the degree of similarity in the detrital mica chemistry in both of these units micas plot in identical fields and define the same trends in addition the two sequences show increased textural and chemical maturity up sequence and define indistinguishable 40 ar 39 ar age ranges for the detrital mica grains partial resetting of the ar ages can be attributed to elevated heat flow in the region caused by munster basin extension and subsequent variscan deformation the combined evidence from southwest ireland therefore points to a caledonian or possibly taconian primary source area that initially shed detritus into the lower devonian dingle basin which was subsequently recycled into the upper devonian munster basin following mid devonian acadian basin inversion

offshore bedrock geology of eclipse sound and pond inlet connecting the structure and stratigraphy of bylot and northern baffin islands understanding the mesoproterozoic and younger structural history of the eclipse sound pond inlet area is essential for the interpretation of its archean to paleoproterozoic geological history and c

the dependence of numerically simulated convective storms on vertical wind shear and buoyancy abstract the effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three dimensional numerical cloud model by varying the magnitude of buoyant energy and one directional vertical shear over a wide range of environmental conditions associated with severe storms the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature these include short lived single cells certain types of multicells and rotating supercells the relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and in particular suggests optimal conditions for the development of supercell type storms applications of this parameter to well documented severe storm cases agree favorably with the model results suggesting both the value of the model in studying these modes of convection as well as the value of this representation i

anatomy of a cyclically packaged mesoproterozoic carbonate ramp in northern canada abstract carbonates in the upper member of the mesoproterozoic victor bay formation are dominated by lime mud and packaged in cycles of 20 50 m these thicknesses exceed those of classic shallowing upward cycles by almost a factor of 10 stratigraphic and sedimentological evidence suggests high amplitude high frequency glacio eustatic cyclicity and thus a cool global climate ca 1 2 ga the victor bay ramp is one of several late proterozoic carbonate platforms where the proportions of lime mud carbonate grains and microbialites are more typical of younger phanerozoic successions which followed the global waning of stromatolites facies distribution in the study area is compatible with deposition on a low energy microtidal distally steepened ramp outer ramp facies are hemipelagic lime mudstone shale carbonaceous rhythmite and debrites mid ramp facies are molar tooth limestone tempestite with microspar intraclast lags in a marine environment where stromatolitic and oolitic facies were otherwise rare large stromatolitic reefs developed at the mid ramp coeval with inner ramp facies of microspar grainstone intertidal dolomitic microbial laminite and supratidal evaporitic red shale deep subtidal outer ramp cycles occur in the southwestern part of the study area black dolomitic shale at the base is overlain by ribbon nodular and carbonaceous carbonate facies all of which exhibit signs of synsedimentary disruption cycles in the northeast are shallow subtidal and peritidal in character shallow subtidal cycles consist of basal deep water facies and an upper layer of subtidal molar tooth limestone tempestite interbedded with microspar calcarenite facies peritidal cycles are identical to shallow subtidal cycles except that they contain a cap of dolomitic tidal flat microbial laminite and rarely of red shale sabkha facies or of sandy polymictic conglomerate a transect along the wall of a valley extending 8 5 km perpendicular to depositional strike reveals progradation of inner ramp tidal flats over outer and mid ramp facies during shoaling the maximum basinward progradation of peritidal facies coincides with a zone of slope failure that may have promoted the development of the stromatolitic reefs the sea level history of the victor bay formation is represented by three hectometre scale sequences an initial flooding event resulted in deposition of the lower victor bay shale member upper member carbonate cycles were then deposited during highstand mid ramp slumping was followed by late highstand reef development the second sequence began with development of an inner ramp lowstand unconformity and a thick mid ramp lowstand wedge a second transgression promoted a more modest phase of reef development at the mid ramp and shallow water deposition continued inboard a third and final transgressive episode eventually led to flooding of the backstepping ramp overall consistent cycle thickness and absence of truncated cycles as well as the high rate and amount of creation of accommodation space suggest that the periodicity and amplitude of sea level fluctuation were relatively uniform and point to a eustatic rather than tectonic mechanism of relative sea level change high amplitude high frequency eustatic sea level change is characteristic of icehouse worlds in which short term large scale sea level fluctuations accompany rapidly changing ice volumes affected by milankovitch orbital forcing packaging of cyclic upper victor bay carbonates therefore supports the hypothesis of a late mesoproterozoic glacial period as proposed by previous workers

seafloor features delineate late wisconsinan ice stream configurations in eastern parry channel canadian arctic archipelago abstract multibeam imagery and 3 5 khz sub bottom profiles acquired from ccgs amundsen between 2003 and 2013 by arcticnet and the ocean mapping group at the university of new brunswick provide information on seafloor features geology bathymetry and morphology in eastern parry channel and the adjoining large channels in the canadian arctic archipelago together these include peel sound barrow strait lancaster sound wellington channel prince regent inlet admiralty inlet and navy board inlet those data are in part complemented by high resolution single channel seismic reflection profiles acquired by the geological survey of canada in the 1970s and 1980s and by sediment cores that provide chronological and depositional information the occurrence and pattern of streamlined mega scale ridge and groove lineations msgls indicate that these waterways were occupied by glacial ice streams in the past chronological information from marine and adjoining terrestrial areas suggests a long history of glacial events ranging in time from early pleistocene to late wisconsinan seafloor morphology and msgl trends together with terrestrial ice flow patterns indicate that ice streams flowed into barrow strait from peel sound and wellington channel and ice streams in prince regent admiralty and navy board inlets flowed northward into and eastward along lancaster sound recession of the ice stream westward along parry channel occurred 16 cal ka bp to 10 8 cal ka bp thick ice contact sediments deposited by a late ice advance from prince regent inlet constitute the seabed across a large area of western lancaster sound timing for that late ice advance appears to be bracketed between the 11 5 cal ka bp lift off of the eastern parry ice stream north of prince leopold island and the 10 0 cal ka bp deglaciation of prince regent inlet seafloor morphology and lineation trends suggest that ice delivered by the ice stream in peel sound was the westernmost tributary to the ice stream occupying lancaster sound during the late wisconsinan glaciation bathymetric data and msgls indicate that the ice stream emanating from m clintock channel flowed westward

tectono sedimentary ripples in devonian shallow marine siliciclastic sediments southern ireland abstract tectonically altered sedimentary ripples occur commonly in the marine devonian old head sandstone formation of southern ireland these tectono sedimentary ripples are dominantly wave produced and have sharp v shaped troughs where spaced pressure solution cleavage surfaces are located at a high angle to bedding the ripples control the spacing of cleavage and influence cleavage orientation the profile shape of the ripple is a function of stress refraction and concentration within the stiff sandstone layers of a multilayer sequence ripple symmetry is affected by tectonic deformation which plays an important role in the development of tectono sedimentary ripples tectonically flattened wave produced ripples occur where cleavage is oriented parallel to bedding due to an anomalous deformation in the old head sandstone formation at galley head selected ripple profiles have been undeformed by computer simulation to reconstruct ancient wave conditions this use of tectono sedimentary ripples for this purpose has its limitations and a number of guidelines are given for application of this technique elsewhere

structural evolution of the irish variscides the effects of the variscan orogeny on the upper palaeozoic succession are recognizable throughout central and southern ireland the deformation can be zoned using structural styles and trends which illustrate a northward decrease in deformation intensity coupled with increasing control by pre variscan structures in the basement the most intense deformation occurs to the south of the dingle dungarvan line where shortening approaches 50 as a result of layer parallel shortening followed by buckling and finally thrusting the deformation is considered to have developed above a shallow dipping sole thrust which has been located offshore by the swat seismic reflection profiles cross faults which are common throughout the orogen resulted from n s shear couples this is consistent with their origin as accommodation structures due to differential shortening along strike the original shape of the munster basin has exerted a control on the distribution and overall facing of the major structures the sole thrust extends to the north of the dingle dungarvan line and the structural zonation of the orogen is due to variations in the stratigraphic level of this thrust the leinster massif is considered to be essentially autochthonous slip on the sole thrust decays towards the massif which acted as a rigid passive block and was partially responsible for the arcuate trend of the orogen

a study of mesoscale convective bands behind cold fronts part i mesoscale organization this paper reports observations made over the north atlantic of a system of convective cloud bands found within the cold air behind an occluded front the observations were made from an instrumented aircraft which additionally released a pattern of dropsondes measuring temperature relative humidity and wind as functions of pressure these data are analysed to establish some of the mesoscale cloud scale and microphysical properties of the system here in part i the mesoscale structure is described and compared with the predictions of various theoretical models the convective cloud structure emerges as a consequence of the mesoscale organization but appears to play only a minor role in its creation and maintenance one of the theoretical models considered conditional symmetric instability provides a piausible explanation of the mesoscale observations

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones part xv a numerical modeling study of frontogenesis and cold frontal rainbands abstract a two dimensional hydrostatic primitive equation model is used to investigate the dynamics of frontogenesis in a moist atmosphere the development of a cold front is simulated through shear deformation associated with the non linear evolution of an eady wave simulations are performed with 5 10 40 and 80 km horizontal resolutions and 14 levels in the vertical four in the boundary layer compared to the dry case the inclusion of moisture in the model produces a stronger low level jet ahead of the front and a stronger upper level jet moisture also produces a stronger ageostrophic circulation across the front and a more concentrated updraft just ahead of the surface front the updraft develops a banded structure above and behind the surface front with a wavelength of about 70 km bands form near the back edge of the cloud shield and move toward the surface front with a relative velocity of 1 m s 1 these characteristics agree with observations of wide cold frontal rainbands the banded str

observational evidence for asymmetric inertial instability abstract we present a detailed analysis of a mesoscale circulation phenomenon that appeared on satellite images as a group of propagating cloud wavelets these wavelets developed on the anticyclonic side of a strong upper level subtropical jet in a region of negative potential vorticity p during their lifetime the wavelets were located over the north american synoptic sounding network the meteorological conditions surrounding their occurrence are examined we investigate the various physical mechanisms that may have been responsible for generating the observed cloud wavelets in consideration of the time scale of the wavelets and their proximity to the region where p 0 inertial instability appears to be the most likely dynamical mechanism for explaining their existence using hourly satellite images we determined that the wavelets propagated downstream at a phase speed 25 m s 1 slower than the maximum wind speed of the jet with life cycles of 4 5 h horizontal wavelengths of 400 km and periods

the relevance of conditional symmetric instability to the prediction of mesoscale frontal rainbands this paper examines the theory of conditional symmetric instability bennetts and hoskins 1979 and considers its relevance to meso scale frontal rainbands the theoretical growth rate of the instability is evaluated from synoptic scale data obtained from a numerical forecast model and compared with observations of the horizontal structure of rainfall observed by radar one case study is presented in detail and a further 44 cases summarized rainbands were observed on 80 of the occasions on which they were predicted

evidence for reversal of basin polarity during carbonate ramp development in the mesoproterozoic borden basin baffin island distribution of facies in the lower half of the bylot supergroup suggests overall westward deepening of the mesoproterozoic borden basin in marked contrast the upper half of the succession records a reversal in the overall bathymetric trend such that the eastern portion underwent relative deepening as the west experienced relative shallowing strata deposited during this reversal belong to the victor bay formation a ramp composed predominantly of limestone karsting of carbonate strata and development of an angular unconformity in the west contrast with back stepping and drowning of the ramp in the east followed by mantling by deep water limestone carbonaceous carbonate and turbidites increased accommodation space during this time via both tectonic subsidence and eustatic sea level rise led to a profusion of stromatolite pinnacle reefs and large biostromes the reversal of basin polarity is best reconciled with development of a distal foreland basin superimposed on the borden aulacogen crustal rethickening and uplift occurred along reactivated basement faults during an eastward directed compressional event and could be related to thrusting of similar age and vergence in the coppermine river group of northwestern canada

transgressive facies in the south munster basin ireland this paper describes the sedimentation style associated with the basal carboniferous transgression in southern ireland and the influence which this event had on the palaeogeography of the region the transgression as marked by the base of the carboniferous succession is shown to represent one of several genetically related transgressive pulses which commenced during the late devonian at this time an east west trending graben the south munster basin developed in southern ireland this was initially a non marine depositional site in which sediment was derived from the north and west subsidence and eustatic sea level rise resulted in a marine transgression which proceeded in a rhythmic style resulting in a number of transgressive stillstand pulses the first transgressive pulse t1 advanced in a westerly direction along the basin axis resulting in the development of an epicontinental like sea the shoreline remained essentially static along the northern basin margin initially until a second transgressive pulse t2 resulted in expansion of the marine area the latter proceeded by gradual northward erosive advance of a barred coastal area as far as the northern basin margin where the stability of the bounding platform halted its progress erosion of the barrier shoreface was insufficient to destroy all the backbarrier lagoonal deposits which are preserved as a thin transgressive diachronous unit which grades northwards to a coastal alluvial plain immediately preceding the basal carboniferous transgression t3 a shallow wave dominated storm influenced shelf sea occupied the basinal area two sublittoral sand bar complexes developed on the shelf under the influence of shore parallel current regimes apparently derived from source areas located on either side of the epicontinental sea the basal carboniferous transgression took place in two pulses the first t3a resulted in a rapid reduction in sand supply to the shelf and deposition of clay the barrier shoreline responded by erosively retreating across the lagoon leaving a transgressive lag in its wake its northwards advance was however limited due to the relative stability of the northern platform sand supply to the shelf was completely terminated in the second pulse t3b and the barrier rapidly migrated erosively across the northern platform for a considerable distance such that the coastal plain is overlain by a thin transgressive lag this transgressive phase was immediately followed by shoreline stillstand and progressive shallowing of the shelf an open sandy shelf developed on which offshore sand bars accumulated under a storm and wave dominated regime clay deposition continued in the deeper part of the basinal area but was eventually terminated as the shelf sands prograded centripetally into the basin the main factor that controlled the style of the overall transgression was an interplay between eustatic sea level rise and basin subsidence the rate of relative sea level rise together with the effect of differential subsidence and fluvial input from the north appear to have diminished with time the rate at which successive transgressive pulses advanced northwards shows an overall progressive increase

the numerical simulation of an unbalanced jetlet and its role in the palm sunday 1994 tornado outbreak in alabama and georgia abstract meso beta scale numerical model simulations and observational data are synthesized in an effort to develop a multistage paradigm for use in forecasting tornadic convection in the southeastern united states the case study to be utilized as an example of the multistage sequence of events is the palm sunday 1994 outbreak which culminates with the development of an unbalanced mesoscale jet streak or jetlet that focuses a given region for significant values of low level vertical wind shear low level confluence and vertical vorticity midtropospheric cooling and storm relative helicity the five stage paradigm includes 1 the existence of a jet exit region accompanying a deep balanced thermally indirect circulation south of the outbreak and a return branch ageostrophic low level southerly jet both typically accompanying the subtropical jet stream and the leading edge of hot continental air 2 the existence of a jet entrance region accompanying a deep balanced thermally direct circulation north of

band formation in a new england winter storm abstract this case study addresses mechanisms of band formation in a new england winter storm the structure of the bands and their environment are documented with synoptic observations radar data and analyses of instrumented aircraft flights through the bands we postulate that processes on three scales are responsible for the bands observed that the bands are probably a manifestation of mesoscale symmetric instability and that potential energy for the instability is generated by synoptic scale differential lapse rate advection and converted to kinetic energy by symmetric overturning frontogenetical forcing results in an intermediate or subsynoptic scale region of ascent which brings the atmosphere to saturation and initiates the release of potential energy

numerical simulation of the large amplitude mesoscale gravity wave event of 15 december 1987 in the central united states abstract an observational study employing spectral methods is first made to establish a background for a modeling effort of the mesoscale gravity wave event of 15 december 1987 the waves are found to have wavelengths of 100 160 km phase speeds of approximately 30 m s 1 and lifetimes of over 6 h conditions for their maintenance are evaluated indicating the presence of a wave duct and a supportive role for wave cisk convection shearing instability and geostrophic adjustment are all implicated as possible source mechanisms for the observed waves the case is then simulated with the pennsylvania state university national center for atmospheric research mm4 mesoscale forecast model with the following primary objectives i to test the model s ability to simulate a mesoscale gravity wave event ii to examine in detail the environments of mesoscale gravity wave development and iii to investigate the mechanisms of mesoscale gravity wave generation and maintenance the full physics control experim

a study of a mesoscale solitary wave in the atmosphere originating near a region of deep convection abstract an analysis of a mesoscale wave which occurred over the eastern united states on 6 march 1969 is presented its origin is attributed to the perturbation of a midtropospheric inversion by a squall line after the wave formed it propagated in the direction of the mid and upper level tropospheric flow and expanded as an arc with the center located near the region of convective activity the wave travelled from western tennessee and kentucky over a distance of more than 1000 kilometers to nova scotia with a mean speed of 55 m s 1 the event was quite obvious on surface barographs throughout this region pressure traces showed an obvious v shaped pressure drop of 3 to 6 mb over much of the wave path the wave persisted for about 9 hours with little change in character the synoptic situation is analysed and compared with similar atmospheric conditions in other studies the generation mechanism of an internal gravity wave of depression is investigated by a simple model it is found that wave of depre

the lagrangian parcel dynamics of moist symmetric instability abstract a simple model describing the slantwise ascent of a two dimensional horizontal air tube subject to moist symmetric instability is developed under the assumptions that the froude number is small and that mixing is absent it is shown that in general the horizontal velocities attained by the tube are comparable to those of the mean flow and that vertical velocities of up to a few meters per second are possible the tube ascends slantwise in such a way that its buoyancy remains nearly zero unless the environment is my very nearly moist adiabatic in which case ascent at an angle of 45 to the vertical is preferred results of the analysis support the contentions of bennetts and hoskins and emanual that moist symmetric instability is the cause of some mesoscale rainbands in a companion paper it is demonstrated that the stability of the moist baroclinic atmosphere to two dimensional slantwise displacements of arbitrary magnitude can be approximately assessed by reversibly lifting parcel along sur

dynamical forcing and mesoscale organization of precipitation bands in a midwest winter cyclonic storm abstract a winter snowstorm developed on 10 11 february 1988 over the midwestern united states and produced several inches of snowfall locally over east central illinois analysis of the mesoscale organization of the storm revealed the presence of complex banded structure throughout its 17 h evolution three distinct types of mesoscale precipitation bands were identified during the course of the storm using a 10 cm doppler radar as part of the university of illinois winter precipitation program the bands had different orientations directions of movement relationships to synoptic scale frontal zones and mechanisms for development the mesoscale organization of this storm system is reviewed mesoscale synoptic scale and doppler analyses of the storm structure are presented the role of boundary layer convergence conditional symmetric instability and frontogenetical forcing in the formation and maintenance of the different mesoscale precipitation bands is discussed

the interactions of gravity waves with mesocyclones preliminary observations and theory abstract apparent interactions between ducted gravity waves and preexisting mesocyclones are investigated preliminary analyses of weather surveillance radar 1988 doppler wsr 88d observations from several cases reveal that the intersection of fine lines whose propagation speed is consistent with that of gravity waves and existing mesocyclones leads to an increase in the rotational velocity of the mesocyclone utilizing simplified ducted wave kinematics and the vorticity equation changes in vorticity associated with convergence divergence and perturbation wind shear within the gravity wave are examined convergence ahead of wave ridges may be significant causing mesocyclone intensification through vorticity stretching it will also be shown that a wave may significantly change the vertical wind shear and streamwise vorticity in storm inflow a simple one dimensional model is presented which shows that vorticity decreases temporarily ahead of the wave ridge then increases rapidly behind the ridge as

displacement distance methods in the analysis of fold thrust structures and linked fault systems a new method for analysing the internal strain in thrust sheets is described the displacement distance diagram can be used to quantify the relative shortening or relative stretch between the hangingwall and footwall beds of a thrust and is a useful way of analysing commonly occurring fold thrust structures the stretch is a function of the relative rates of thrust propagation and thrust slip the cumulative displacement distance diagram described here can be used to calculate the absolute shortening or extension when this is accommodated above a single decollement in a linked fault system this method offers a useful way of analysing duplex structures and large scale foreland thrust zones as well as extensional fault systems and can be used as an alternative to or in conjunction with balanced cross sections both methods can be used to quantify the variation in shortening above a single detachment zone this variation may be mechanically significant reflecting lithological control on thrust or normal fault growth

surface mesoscale processes during the 1994 palm sunday tornado outbreak the tornadic storms that developed in the 27 march 1994 palm sunday outbreak were confined to a narrow zone extending from central and northern alabama to western north carolina analysis of surface observations and soundings is used to examine the mesoscale environment of the region starting 14 h prior to storm development the evolution of a shallow front that formed the northern boundary of the outbreak region is tied to several diabatic processes including evaporation of precipitation and differential solar heating the resulting front was found to both limit severe convection and focus supercell development later in the day during the night before the outbreak as copious widespread precipitation fell into dry air evaporation maintained a cold air pool north of the front by contrast moderate southerly flow provided warm moist conditions to the south precipitation enhanced cold air damming along the eastern slopes of the appalachians also may have provided a source of cold air for subsequent frontogenesis over areas farther west during the daylight hours differential solar heating across the front further enhanced frontogenesis intensification of convection just prior to the first tornadoes was found to be associated with areas of breaks in the overcast near and upstream of tornadogenesis similarly cells that intensified were moving over a surface that had been thoroughly moistened by previous rainfall supercells that intersected and moved along the frontal boundary maintained their tornadic strength for many hours whereas storms that crossed the boundary disintegrated blockage of inflow by upstream storm cells may also have contributed to the rapid reduction of intensity of one of the tornadic cells

late pliocene early pleistocene athalassa formation north central cyprus carbonate sand bodies in a shallow seaway between two emerging landmasses the late pliocene early pleistocene athalassa formation accumulated within the neogene mesaoria basin of northern cyprus bordered by two subdued but rising landmasses the kyrenia range to the north and the troodos ophiolitic massif to the south in the eastern part of the basin the formation is dominated by cross stratified bioclastic rich sandstones interpreted as shallow marine carbonate sand bodies the sediments are described in terms of six calcarenite facies and subfacies and one sandstone fades palaeocurrent analysis indicates that the carbonate sand bodies formed near the southern margin of the kyrenia landmass and then migrated southwards across a shallow marine platform the driving force is believed to have been storms generated by strong winds such winds during the late pliocene early quaternary were probably stronger than today in this area other factors influencing deposition of the formation include minor tectonic instability and probable eustatic sea level changes study of the athalassa formation thus provides insights into late pliocene pleistocene palaeoenvironments in the easternmost mediterranean

alluvial sedimentation patterns in the munster basin ireland post caledonian southern ireland witnessed the development of a ne sw orientated half graben known as the munster basin more than 7 km of non marine sediments accumulated in the basin during the late middle and late devonian marine conditions became established in the southern part of the basin at the end of the devonian in this paper a model for the evolving style of sedimentation in the basin and its periphery is constructed with the aim of identifying the major factors which controlled sedimentation patterns and the architecture of the basin fill the depositional history of the basin is considered in terms of four successive episodes during episode i gravelly alluvial fans flanked upland areas around the northeastern and northern basin perimeter these graded southwestwards to a floodplain dominated by sheet floods in the western part of the basin the first of three major fluvial influxes into the basin commenced during episode ii the first influx developed into a large sandy braided complex the sediment was derived from a distant source area located to the north and west of the basin and was transported diagonally across the basin towards the southeast episode iii witnessed a second influx which drained into the basin from the northeast and north river channels were of low sinuosity and graded distally to an ephemeral playa lake episode iv was marked by a third fluvial influx from the west and northwest this was confined to the southern half of the basin and drainage was directed towards the east the fluvial distributaries were flanked by permanently flooded overbank areas this influx coincided with the first marine transgression which advanced westwards the end of episode iv coincided with the beginning of the carboniferous and was marked by a major marine transgression sediment input to the basin was influenced by stable areas occupied by granitic plutons on either side of the basin and a southward downthrowing fault along its northern margin the drainage direction was principally controlled by e w trending within basin faults and an e w trending stable area located to the south the basin was fundamentally of the axial transport type the main drainage having been directed towards the east though there was also a strong lateral influx from the north northwest and northeast stable areas around the basin periphery resulted in either no sediment preservation or sequences of multistorey channel deposits while thick sequences dominated by fine grained floodplain or overbank deposits characterized areas of higher subsidence rate within the basin movement on the northern basin margin fault was probably the major cause of the first fluvial influx while regional subsidence of the basin and its northern periphery resulted in the second influx the third influx was a response to local subsidence in the southern part of the munster basin this also contributed to the simultaneous westward marine transgression in this area towards the end of the devonian source area denudation and retreat in association with a sea level rise were ultimately responsible for terminating the alluvial regime in the munster basin

mesoscale dynamics in the palm sunday tornado outbreak abstract radar and satellite imagery suggest that strong mesoscale forcing occurred in the palm sunday tornado outbreak on 27 march 1994 parallel lines of severe thunderstorms within each of three mesoscale convective systems developed just ahead of a cold front in mississippi and alabama on this date analyses of routine meteorological observations barograph data and forecasts from the eta and ngm models and a mesoscale research model mass are used to examine the relative roles of large scale dynamics and mesoscale processes in triggering and organizing the mesoscale convection quasigeostrophic forcing was absent in the outbreak region likewise a thermally direct circulation system transverse to the upper level jet that was present to the northwest of the outbreak region was decoupled from the strong low level ascent occurring in northern alabama and mississippi at the time of the outbreak strong ageostrophic frontogenesis in the presence of conditional symmetric instability csi was the chief

a mesoscale gravity wave event observed during ccope part ii interactions between mesoscale convective systems and the antecedent waves abstract this paper presents the results of a very detailed investigation into the effects of preexisting gravity waves upon convective systems as well as the feedback effects of convection of varying intensity upon the waves the analysis is based on the synthesis of synoptic surface and barograph data with high resolution surface mesonetwork radar and satellite data collected during a gravity wave event described by koch and golus in part i of this series of papers use is also made of the synoptic barograph data and satellite imagery to trace the waves beyond the mesonetwork and thus determine their apparent source region just upstream of the mesonetwork it is shown that two of the gravity waves modulated convection within a weak squall line as they propagated across the line the other six waves remained closely linked with convective systems that they appeared to trigger however it is shown that the waves were not excited by convection furthermore the waves retained their signatures in the su

the sedimentology stratigraphy and preservation of intertidal deposits in the minas basin system bay of fundy abstract intertidal sediments of the minas basin a macrotidal estuary at the head of the bay of fundy can be subdivided into six major facies tidal marsh beach mudflat sandflat channel lag and sandbar each is characterized by its grain size distributions sedimentary structures and biological communities these sedimentary facies occur in three types of high to low tide zonation depending on the local sediment source and wave and current energy the holocene stratigraphy presently preserved in the upper intertidal zone of minas basin consists of a relatively thin on the average less than 1 2 m wedge of sediment overlying bedrock only in a few sheltered locations where deposits accumulate to several meters is the marine transgressive stratigraphy well represented the hypothetical progradational or marine regressive stratigraphy of upper intertidal sediments would probably resemble from top to bottom the high to low tide sequence of facies occurring today on sheltered tidal flats lebensspuren would provide the most reliable representation of the ecology of intertidal sediments in minas basin they are useful in delineating communities as well as being sensitive indicators of sediment deposition microfauna are too easily transported or reworked field data from relict intertidal deposits dated 2300 3400 yr b p indicate calcareous organism hard parts would probably provide a biased fossilized record indirect evidence is discussed which suggest in situ dissolution of shells in certain intertidal sediments

a new frontier province offshore northwest greenland structure basin development and petroleum potential of the melville bay area in the melville bay area offshore northwest greenland very large structures and sedimentary basins which were predicted many years ago on the basis of magnetic and gravity data have been confirmed by a recent reconnaissance seismic survey with implications that are encouraging for petroleum exploration in the area the melville bay area flanks a small ocean basin in baffin bay that is thought to have formed by oblique sea floor spreading in the eocene there are two major coast parallel basins in the area the inner basin the melville bay graben is essentially a half graben with a maximum thickness of sediments exceeding 13 km a complex fault controlled ridge system separates this basin from the outer kivioq basin in which up to 7 km of sediments have accumulated by analogy with onshore geology in the surrounding areas and well data from the continental shelves off southern west greenland and labrador to the south it is expected that the first phase of rifting and sedimentation took place in the early middle cretaceous while a second phase of rifting took place in the latest cretaceous and early paleocene later compression and inversion affected the northern part of the area leading to the formation of large anticlinal structures copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received january 30 1996 revised manuscript received september 9 1996 final acceptance january 21 1997 2geoarctic consulting ltd 1620 9th street nw calgary alberta t2m 3l4 canada 3nunaoil a s pilestraede 52 dk 1112 copenhagen denmark 4geological survey of denmark and greenland thoravej 8 dk 2400 copenhagen denmark we wish to acknowledge the companies partaking in the kanumas project bp exxon japan national oil company shell statoil and texaco for allowing us the opportunity to publish this paper our thanks also to rene forsberg and simon ekholm national survey and cadastre for processing the gravity data for the paper and to alan menelly consultant for discussions on the structural development of the area airborne gravity data were made available courtesy of john brozena of the u s naval research laboratory

mesoscale structure in the megalopolitan snowstorm of 11 12 february 1983 part i frontogenetical forcing and symmetric instability abstract a cyclone moving northeastward off the coast of the northeastern united states on 11 12 february 1983 was accompanied by a band of heavy snow across all the major cities of this region from washington to boston frontegenetical forcing and symmetric instability are discussed as possible explanations of the intense precipitation rawinsonde data were analyzed to investigate the roles of these effects in this case we found that intense ascent was part of a thermally direct transverse circulation to be expected in response to frontogenetical forcing when the symmetric stability in the warmer air is small symmetric instability per se in the saturated major cloud mass may have been responsible for pulselike oscillations in its top these were men in satellite imagery elongated in the direction of the tropospheric thermal wind

a mesoscale gravity wave event observed during ccope i multiscale statistical analysis of wave characteristics abstract this paper is the first in a series of three papers concerning a gravity wave event that occurred over the north central united states on 11 12 july 1981 the event is analyzed with superb detail resulting from the availability of digitized radar surface mesonetwork and other special data from the cooperative convective precipitation experiment ccope in montana the subject matter of this paper consists of 1 a statistical determination of the wave characteristics 2 a demonstration that the observed phenomena display a nature consistent with that of gravity waves and 3 a discussion of the principles and limitations of statistical methods for detecting and tracking mesoscale gravity waves two distinct wave episodes of 8 h duration within a longer 33 h period of wave activity are studied in detail both episodes contain strongly coherent bimodal wave activity the primary secondary wave mode isolated from autospectral and perturbation map analyses displays mean periods of 2 5 0 9 h

the structure of mountain fronts commonly the part of a mountain front which is visible at the surface consists of foreland dipping thrust belt rocks elevated above their regional structural position and overlain more or less conformably by molasse several explanations for their geometry are possible 1 major detachments exist within or beneath the molasse resulting in transport of the foreland basin examples of this geometry come from the swiss molasse plain the southern pyrenees and the mackenzie mountains of canada 2 displacement is lost on major backthrusts beneath the frontal monocline examples cited here are the rockies of alberta the sulaiman ranges of pakistan the mackenzies and the andes in peru 3 thrust sheets travelled over an old land surface and syntectonic molasse contemporaneously offlaps the topographic high of the thrust front this phenomenon occurs along the alpine thrust front in haute provence 4 the frontal fold represents deformation above a large scale thrust tip no unequivocal example of tip line strain at this scale has been recorded although this type of deformation may occur in the brooks range of alaska in many areas mountain fronts show a combination of these idealized geometries

the middle devonian shoreline in north devon england the hollowbrook formation is an early middle devonian regressive succession of sandstones and heterolithic facies marking a passage from shallow marine shelf muds through a sandy shoreface to continental ephemeral stream sheet sands ten facies are recognized arranged in two sequence types the shelf sequence consists of alternations of bioturbated muddy sandstone fair weather sediment and shelly concentrates or parallel laminated fine sandstone storm deposits the nearshore and foreshore sequences coarsen upwards and pass from bioturbated muddy sandstone shelf to lenticular beds inner shelf then either wavy and flaser beds fair weather lower shoreface or hummocky beds and multistorey parallel laminated sands with bioturbated tops lower shoreface storm shoals upper shoreface wave ripple cross laminated sandstones follow then parallel and planar cross laminated sandstones foreshore and parallel laminated lithic sandstone continental sheet flood the lower parts of the shoreface sequence and inner shelf are burrowed by skolithos arenicolites and chondrites the sequence differs from the high energy 9oregon coast9 shore in the absence of a megarippled facies and presence of much bioturbation but closely matches the sequence found in modern low energy wave influenced sandy shores such as sapelo island georgia

wavelet analysis and the governing dynamics of a large amplitude mesoscale gravity wave event along the east coast of the united states detailed diagnostic analyses are performed upon a mesoscale numerical simulation of a well observed gravity wave event that occurred on 4 january 1994 along the east coast of the united states the value of using wavelet analysis to investigate the evolving gravity wave structure and of using potential vorticity pv inversion to study the nature of the flow imbalance in the wave generation region is demonstrated the cross stream lagrangian rossby number the residual in the nonlinear balance equation and the unbalanced geopotential height field obtained from pv inversion are each evaluated for their usefulness in diagnosing the flow imbalance all of these fields showed clear evidence of strong imbalance associated with a middle to upper tropospheric jet streak and tropopause fold upstream of the large amplitude gravity wave several hours before the wave became apparent at the surface analysis indicates that a train of gravity waves was continuously generated by geostrophic adjustment in the exit region of the unbalanced upper level jet streak as it approached the inflection axis in the height field immediately downstream of the maximum imbalance associated with the tropopause fold a split front in the middle troposphere characterized by the advance of the dry conveyor belt above the warm front was overtaken by one of these propagating waves during this merger process a resonant interaction resulted which promoted the rapid amplification and scale contraction of both the incipient wave nonlinear wave development and the split front frontogenesis the gravity wave and front aloft became inseparable following this merger the situation became even more complex within a few hours as the vertical motion enhanced by this front wave interaction acted upon a saturated potentially unstable layer to produce elevated moist convection an analysis of the temporal changes in the vertical profile of wave energy flux suggests that moist convective downdraughts efficiently transported the wave energy from the midlevels downward beneath the warm front surface where the wave became ducted however pure ducting was not sufficient for maintaining and amplifying the waves rather wave cisk conditional instability of the second kind was crucial this complex sequence of nonlinear interactions produced a long lived large amplitude gravity wave that created hazardous winter weather and disrupted society over a broad and highly populated area although gravity waves with similar appearance to this large amplitude wave of depression occasionally have been seen in other strong cyclogenesis cases involving a jet streak ahead of the upper level trough axis it is unknown whether other such events share this same sequence of interactions

a case study of gravity waves convective storms interaction 9 may 1979 abstract an analysis is presented of a series of severe storms which occurred in the north central united states on 9 may 1979 and whose spatial distribution and movement correlate well with observed gravity waves two gravity wave trains of 2 1 3 mb amplitude 2 5 3 3 h period and 240 265 km horizontal wavelength were isolated through power spectra analysis and cross correlation techniques applied to national weather service barograph traces the wave trains propagated in the 200 direction which coincided with the jet axis with a phase velocity of 20 30 m s 1c and within a 300 km wide band the storms were identified on enhanced infrared goes satellite pictures with the help of radar summaries these convective systems initially developed in nebraska and propagated north northeast at 25 m s 1 revealing wave like characteristics with a separation of 300 400 km the convective systems were closely linked to the observed wave trains with cell intensity height and associated rainfall maximized at the wa

evolution of the barrier islands of southern long island new york three lines of evidence based on data from more than 400 boreholes and vibrocores have been used to reconstruct the evolution of the barrier islands during the holocene transgression in southern long island new york 1 the holocene transgressive stratigraphic sequence behind the present barriers 2 the stratigraphic patterns of the inner shelf and 3 the morphology of the now buried late pleistocene coastal features the extensive preservation of backbarrier sediments radiocarbon dated between 7000 and 8000 yr bp on the inner shelf of southern long island suggests that the barriers have not retreated by continuous shoreface erosion alone but have also undergone discontinuous retreat by in place drowning of barriers and stepwise retreat of the surf zone such stepwise retreat of the surf zone has prevented the backbarrier sediments from being reworked based on the presence of submerged barrier sand bodies in seismic records it is inferred that about 9000 years ago when the sea stood about 24 m below the present sea level a chain of barriers developed on the present shelf about 7 km offshore of the present barriers with continued sea level rise the 24 m barrier built upward until the sea reached about 15 m msl just prior to 7000 yr bp the barriers were then submerged by the rapidly rising sea and the surf zone shifted rapidly landward to a position about 2 km from the present shoreline the surf zone overstepped to the landward margin of the old lagoon which had become fixed at the steep seaward face of mid wisconsinan or sangamonian coastal barriers during the past 5000 or 6000 years the shoreface has retreated continuously by about 2 km evidence from southern long island and elsewhere in regions of coastal submergence indicates that rapid sea level rise and low sand supply seem to favour the stepwise retreat of barriers whereas slow rates of submergence and a greater supply of sand generally favour continuous shoreface retreat stationary upbuilding or seaward progradation of barriers may occur when supply of sand is great and or submergence is slowed or reversed morphologic highs on the pretransgression surface such as old barrier ridges tend to fix the migrating barrier shoreline during either continuous retreat or stepwise retreat of barriers

a mid frasnian marine incursion into the southern part of the munster basin evidence from the foilcoagh bay beds sherkin formation sw county cork ireland

origin evolution and finescale structure of the st valentine s day mesoscale gravity wave observed during storm fest part iii gravity wave genesis and the role of evaporation abstract on 14 february 1992 a long lived moderate amplitude mesoscale gravity wave formed in kansas during the storm scale operational and research meteorology fronts experiment systems test storm fest wave formation was evident in correlated surface pressure and wind fields the wave of depression accompanied by a weak rainband tracked across the state a wealth of data was collected on the mature wave as it passed over the storm fest dual doppler domain however the mechanism of genesis remained difficult to ascertain since wave formation occurred in a region of less comprehensive observations the genesis of the storm fest gravity wave is successfully simulated using the fifth generation pennsylvania state university national center for atmospheric research penn state ncar mesoscale model mm5 which was run at 6 km grid spacing in the innermost domain the lee cyclone movement dry airmass development and gravity wave formation over kansas were successfully captured by the model results

frontogenesis in the presence of small stability to slantwise convection abstract it is often observed that despite the existence of near neutrality to slantwise convection rainbands and snowbands can persist for long periods with narrow intense updrafts producing large quantities of precipitation in many cases this is probably due to the presence of active frontogenesis which as shown here maintains such structures in order to investigate this process we use two dimensional semigeostrophic theory to solve the deformation forced frontogenesis problem for a circumstance in which the stability to moist slantwise convection is small but positive in this case numerical simulation is necessary to determine the evolution of the front several previous studies have described the role of diabatic forcing in modifying the cross frontal circulation by use of the sawyer eliassen equation in particular analytic solutions of that equation for the case of small moist symmetric stability show that a narrow updraft should occur ahead of the maximum geostrophic frontogenesis numeri

a sedimentological evaluation of the devonian carboniferous boundary stratotype in southern ireland abstract the stratotype section for the base of the british dinantian devonian carboniferous boundary is currently located at the interface of two marine formations at the old head of kinsale this corresponds with the boundary of the ln and vi miospore subzone floral assemblages the succession immediately below the interface records an upward change from inner shelf into transgressive backbarrier sediments due to the initiation and progressive influence of a storm dominated migrating microtidal barrier complex the formation junction is considered to reflect a non sequence arising from subsequent erosive shoreface retreat and destruction of the barrier superstructure which was followed by apparently sudden deepening and the deposition of pro delta facies comparisons with other sections at this stratigraphical level in southern ireland indicates that barrier construction with landward migration into backbarrier bays occurred during a destructive phase of deltaic development in latest devonian times a rapid transgression associated with a cessation of sand supply then took place resulting in variable reworking of the underlying sequences and discontinuous shoreline retreat this was followed by the deposition of storm influenced calcareous shelf and inshore bay sediments over laterally diverse delta platform successions with continued deepening a pro delta environment was established over the area in the earliest carboniferous vi miospore subzone which thus records the relatively unusual preservation of barrier and backbarrier sequences in a regionally transgressive situation

an observation of banded convective development in the presence of weak symmetric stability abstract satellite imagery dramatically portrays a mesoscale organization of deep convection over the south central united states on 5 june 1986 free convection was expected over the region the rapid development and organization of the convection simultaneously across a broad area suggests the presence of a mesoscale instability analysis of satellite and conventional data suggests that a layer of weak symmetric stability modified the atmosphere s response to free convective instability contributing to the highly organized banded structure observed

a case study of an unusually intense atmospheric gravity wave abstract a remarkable long lived large amplitude gravity wave in the carolinas and virginia on 27 february 1984 is investigated by means of a subsynoptic scale case study the wave was characterized by a minor wave of elevation followed by a sharp wave of depression with a period of 2 3 h a horizontal wavelength of 100 150 km and surface pressure perturbation amplitudes of 3 14 mb the wave propagated toward the east southeast at 1 5 m s 1 accelerating to more than 20 m s 1 after it crossed the atlantic coast wave passage was accompanied by gusty surface easterly winds reaching 30 m s 1 and an abrupt termination of precipitation with the rapid surface pressure fall the synoptic criteria identified by uccellini and koch as common to many cases of large amplitude gravity waves were present in this case gravity waves were first detected across western tennessee and northern mississippi in a wake depression region to the rear of an advancing squall line an amplifying wave emerged out of the wave packet

jetlet formation from diabatic forcing with applications to the 1994 palm sunday tornado outbreak abstract the three dimensional responses of simple stably stratified barotropic and baroclinic flows to prescribed diabatic forcing are investigated using a dry hydrostatic primitive equation numerical model the north carolina state university geophysical fluid dynamics model a time dependent diabatic forcing is utilized to isolate the effects of latent heat release in a midlatitude convective system examination of the mass momentum adjustments to the diabatic forcing is performed with a focus on the development of an isolated midlevel wind maximum the results of both cases suggest the formation of a midlevel wind maximum in the form of a perturbation meso scale cyclone which later propagates downstream as the heating is decreased the scale of the perturbation cyclone remains at a sub rossby radius of deformation length scale therefore the mass perturbations adjust to the wind perturbations as the mesocyclone propagates downstream transverse vertical circulations which favor ascent on the r

formation and evolution of frontal rainbands and geostrophic potential vorticity anomalies abstract a viscous semigeostrophic model is developed and used to study the formation and evolution of frontal rainbands in association with the dry and moist geostrophic potential vorticity gpv anomalies the numerical results show that when moist gpv mgpv becomes negative in the saturated region but the flow is still stable to viscous symmetric perturbations banded substructures can be generated internally by a positive feedback between the moist circulation bands and geostrophic forcing anomalies in association with the generation of mesoscale gpv anomalies in addition to the previous diagnostic results for idealized forcings the new aspect here is that the large scale moist ascent evolves into much finer multiple moist bands as soon as the positive feedback begins to generate banded substructures in the forcing and gpv fields when mgpv is positive multiple rainbands can only be generated externally by preexisting gpv or mgpv anomalies these rainbands can be self maintained by a weak feedba

gravity wave induced perturbations in marine stratocumulus we discuss the role of atmospheric gravity waves in modulating cloud radiative and dynamical properties over the southeast pacific satellite imagery and satellite retrieved cloud properties during october 2008 illustrate three distinct episodes of horizontal propagation of gravity wave trains across the large scale stratocumulus sc cloud deck capping the local marine boundary layer in one period 79 october 2008 the waves modulated cloud top height by up to 400 m peak to trough propagating perpendicular to the synoptic boundary layer flow with phase speed 15 3 m s1 period approximate to 1 h and horizontal wavelength 55 km the gravity waves were observed to be non dispersive these waves were first evident in the cloud deck near 30 degrees s 85 degrees w during a 24 h period beginning at midday on 7 october 2008 and propagated northeastward toward the peruvian coast for the following 48 h during this time they induced both reversible and non reversible changes in cloud radiative and cloud dynamic properties such that areas of clear sky developed in the troughs of passing wave fronts these pockets of open cells persisted long after the passage of the gravity waves advecting northwestward with the background wind using the analysis fields of the european centre for medium range weather forecasts in conjunction with infrared and microwave satellite imagery we show that these gravity waves emerged from a disturbed subtropical jet stream the radiant of the waves was coincident in all cases with centres of large negative residuals in nonlinear balance suggesting that geostrophic readjustment of sharply divergent flows associated with the disturbed jet provided a source for the wave energy conversely gravity waves were not observed in more quiescent jet conditions this case study highlights the important and irreversible effects that gravity waves propagating in the troposphere can have on cloud radiative properties and hence surface radiation budgets over a very wide area it also highlights the importance of synoptic influence on sc covered marine boundary layers copyright c 2012 royal meteorological society

the synoptic setting and possible energy sources for mesoscale wave disturbances abstract thirteen case studies of mesoscale wave disturbances characterized by either a singular wave of depression or wave packets with periods of 1 4 h horizontal wavelengths of 50 500 km and surface pressure perturbation amplitudes of 0 2 7 0 mb are reviewed to isolate common synoptic features for these cases and to shed light on possible energy sources for the waves a strong thermal inversion in the lower troposphere north of a frontal boundary and a jet streak propagating toward a ridge axis in the upper troposphere are commonly observed in all the cases in general the area of wave activity is bounded by the jet axis to the west or northwest a surface front to the southeast an inflection axis between the trough and ridge axes to the southwest and the ridge axis to the northeast the conditions specified by lindzen and tung as being necessary to form a wave duct which include the existence of the lower tropospheric inversion seem to be met in many of these cases this suggests that a du

a review of the structure and dynamics of upper level frontal zones abstract this article presents a review of upper level fronts with the intent of synthesizing observational and modeling studies into a conceptual and dynamical description of these fronts and their evolution relative to the life cycle of midlatitude baroclinic waves the discussion begins by tracing present day concepts concerning the structure of upper level frontal systems which are based on composite analyses of radiosonde and aircraft data from their origins in the pioneering analyses of upper air data in the 1930s perspectives from scales both smaller and larger than upper level frontal systems are provided respectively by considering the effects of turbulent processes on frontal structure and dynamics and by relating variations in frontal structure to the evolution of the baroclinic waves that provide the dynamical environment for upper level frontogenesis the dynamics of upper level fronts are shown to comprise the interactions between the primary geostrophic and secondary ageostrophic cir