morphology and environment of cold water coral carbonate mounds on the nw european margin cold water coral carbonate mounds owing their presence mainly to the framework building coral lophelia pertusa and the activity of associated organisms are common along the european margin with their spatial distribution allowing them to be divided into a number of mound provinces variation in mound attributes are explored via a series of case studies on mound provinces that have been the most intensely investigated belgica hovland pelagia logachev and norwegian mounds morphological variation between mound provinces is discussed under the premise that mound morphology is an expression of the environmental conditions under which mounds are initiated and grow cold water coral carbonate mounds can be divided into those exhibiting inherited morphologies where mound morphology reflects the morphology of the colonised features and developed morphology where the mounds assume their own gross morphology mainly reflecting dominant hydrodynamic controls finer scale surface morphological features mainly reflecting biological growth forms are also discussed

basement controlled multiple slope collapses rockall bank slide complex ne atlantic abstract the eastern flank of the rockall bank is dominated by the scarps of a large slide complex with unusual low aspect ratio 120 km wide and 150 km long with the use of an extensive 2d seismic dataset re processed high resolution multibeam bathymetry a tobi mosaic and one piston core we demonstrate that the headwall of the rockall bank slide complex previously referred to as the rockall bank mass flow may have occurred as a multiphase slope collapse in at least three episodes of instability since 16 ka bp with each of the events generating a slide with a more typical elongate morphology reconstructions of the pre slide seafloor suggest a volume of collapsed sediments in the range265 765 km3 seismic facies investigation indicates that the slope and failed sediments comprise almost exclusively contourites that are prone to failure due to their well sorted character and high water content a systematic examination of the slope morphology seismic facies and sub seafloor structures demonstrates a direct relationship between the rbsc seafloor scarps and the basement morphology focused fluid flow along basement bounding faults and or differential compaction across the scarps are considered to have had an important role in slope failure this study highlights the importance of deeply buried structures in the stability of slopes it also shows how detailed examination of high resolution data across large areas of slope instability can reveal smaller scale multiple events we believe that where contour swept slopes are steep the resulting intensification of near bottom velocities prevents healing slope processes and as a result steep slope gradients remain steep and thus unstable

cold water coral mounds in an erosive environmental setting tobi side scan sonar data and rov video footage from the northwest porcupine bank ne atlantic abstract cold water coral mounds are common features in certain regions along the atlantic margin they occur in mound provinces in various settings characterised by specific environmental conditions that steer and influence coral mound initiation growth and demise e g bottom current intensity sediment input and food supply in order to add detail to the diversity of environmental conditions described in relation to these structures this study investigates mounds in a generally erosive setting on the northwest porcupine bank ne atlantic in contrast to previous studies in less hydrodynamically active settings tobi towed ocean bottom instrument side scan sonar data revealed abundant erosive features in the study area they occur in the form of erosional scarps erosional pits and locally scoured seabed furthermore two large several hundred metres high and 101 small tens of metres high cold water coral mounds were identified on the tobi images most of the mounds are located on top of erosional scarps pointing to the cold water corals preference for areas with enhanced current intensities within the study area a general trend of northward decreasing mound heights and increasing abundance of erosive features can be observed high resolution rov remotely operated vehicle video observations at four sites within the tobi coverage illustrate that only the southernmost mound shows signs of active mound growth while the other mounds represent relict structures with limited coral cover opportunistically taking advantage of available hard substrate in the form of consolidated lithified sediments the distribution of erosion features seabed features and seabed facies on the northwest porcupine bank indicates an environmental window in which the interplay of coral growth sediment input and sediment preservation leads to the formation of mound sediments and therefore mound growth whereas too weak bottom currents do not support thriving coral thickets too strong bottom currents hamper any deposition and thus mound growth as this environmental window varies over time mound sizes on the porcupine bank and probably also in other mound settings most likely reflect the duration in time of such an environmental window of optimal growth conditions around a given mound rather than an indication of the overall age of the mound

role of topography in forcing low level jets in the central united states during the 1993 flood altered terrain simulations regional model sensitivity simulations in which the height of elevated terrain was reduced to explore simulated changes in features of the low level jet llj are presented such an approach has not been reported and it provides complementary insight to the previous llj studies the simulations were carried out for a 45 day period during the 1993 summer flood in the central united states when strong lljs were frequent the simulations illustrate directly the significance of topographical blocking leeside cyclogenesis and terrain thermal effects exerted by the rocky mountains in support of llj formation in particular it is shown that in the absence of topography the ridging from the bermuda high extended considerably westward with weaker southerly flow over the high plains thus diminishing the potential for llj development the slope induced nocturnal horizontal thermal gradient was indicated to have a significant role in the formation of the llj

the late spring maximum of rainfall over the u s central plains and the role of the low level jet abstract the seasonal rainfall over the u s central plains features a late spring maximum a spring fall annual mode revealed from the empirical orthogonal function analysis on rainfall delineates a maximum center over the central plains that coincides with the large late spring rainfall this paper examines the large scale dynamical and hydrological processes in forming the rainfall center the ncep department of energy doe reanalysis 2 data reveal that the baroclinic structure of the continental scale circulation during late spring may and june induces a vertically out of phase divergent circulation forming strong convergence of water vapor flux over the central plains such circulation features generate concentrated convective activity in this region the upper level anticyclone development with the north american monsoon in july replaces the late spring baroclinic structure and in turn reduces the convective activity the great plains low level jet llj plays a role in the downscaling process

late mesozoic gravity sliding and oxfordian hydrocarbon reservoir potential of the northern yucatan margin abstract the stratigraphy and structural evolution of the western florida margin is much better understood than its northern yucatan conjugate because previous hydrocarbon exploration has been more extensive on the florida margin in the deep water northeastern gom the post salt section records late jurassic cretaceous gravity sliding of rafted blocks along a basinward dipping layer of callovian salt this study uses approximately 31 000 line km of 2d seismic data to describe a coeval area of widespread gravity sliding along the less studied northern yucatan margin we define three structural domains based on their distinctive salt structures and associated deformation 1 a region in the northeastern study area consists of relatively undeformed late jurassic cretaceous section underlain by 0 300 m thick salt 2 areas in the central and southwestern study area contain late mesozoic gravity slides defined by 300 600 m thick salt rollers and normal faults rooted onto a 1 4 basinward dipping salt detachment and 3 the distal margin of the western and central study area exhibits large salt diapirs up to 6 km tall that deform quaternary stratigraphic units in the central yucatan study area containing late mesozoic gravity slides a stratigraphic unit equivalent to the productive oxfordian norphlet sandstone of the deep water northeastern gom is identified based on its similar seismic character reconstructing the extent of this norphlet equivalent unit along the yucatan margin to its location during oxfordian deposition places it adjacent to an extensive area of norphlet sandstone mapped in the deep water northeastern gom by previous authors our reconstruction suggests a 48 000 km2 fairway of potential aeolian late jurassic reservoirs on the yucatan and campeche margins that includes productive reservoirs in the southeastern bay of campeche which previous authors correlated with the norphlet formation

the response of simulated nocturnal convective systems to a developing low level jet some recent numerical experiments have examined the dynamics of initially surface based squall lines that encounter an increasingly stable boundary layer akin to what occurs with the onset of nocturnal cooling the present study builds on that work by investigating the added effect of a developing nocturnal low level jet llj on the convective scale dynamics of a simulated squall line the characteristics of the simulated llj atop a simulated stable boundary layer are based on past climatological studies of the llj in the central united states a variety of jet orientations are tested and sensitivities to jet height and the presence of lowlevel cooling are explored the primary impacts of adding the llj are that it alters the wind shear in the layers just above and below the jet and that it alters the magnitude of the storm relative inflow in the jet layer the changes to wind shear have an attendant impact on low level lifting in keeping with current theories for gust front lifting in squall lines the changes to the system relative inflow in turn impact total upward mass flux and precipitation output both are sensitive to the squall line relative orientation of the llj the variations in updraft intensity and system relative inflow are modulated by the progression of the lowlevel cooling which mimics the development of a nocturnal boundary layer while the system remains surfacebased the below jet shear has the largest impact on lifting whereas the above jet shear begins to play a larger role as the system becomes elevated similarly as the system becomes elevated larger changes to systemrelative inflow are observed because of the layer of potentially buoyant inflowing parcels becoming confined to the layer of the llj

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

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

numerical study of nocturnal low level jets over gently sloping terrain abstractnocturnal low level jets lljs over gently sloping terrain typical of the u s great plains are investigated by means of direct numerical simulation such lljs develop in a tilted atmospheric boundary layer as a result of inertia gravity oscillations initiated by a change of the surface thermal forcing during the evening transition external parameters are the free atmospheric geostrophic wind ambient atmospheric stratification surface buoyancy forcing and slope angle the governing momentum and buoyancy balance equations are written in slope following coordinates and solved numerically in the boussinesq approximation the surface forcing is prescribed in a form of surface buoyancy or buoyancy flux both of which are slope uniform but change in time lljs over slopes are contrasted with lljs over flat terrain slope induced effects essentially modify the entire structure of nocturnal lljs the shape of the llj wind profile over a slope is characterized by a sharper and larger magnitude maximum

alboran basin southern spain part ii neogene tectonic implications for the orogenic float model we infer that the alboran basin the first western mediterranean basin found after crossing gibraltar is an orogenic float underlained by a de collement system a multi layered ductile shear extending from 10km to between 30 and 40km below sea level this float was formed as consequence of the collision of the african eurasian plates in the oligocene late miocene synchronous with this compression the float experienced basin wide crustal thinning and subsidence about 25 m year ago by subcrustal processes since latest miocene the float has undergone compression due to the continuous convergence of eurasia and africa the faults created as a result of this compression are dominated by a conjugate system of northeast trending left lateral and northwest right lateral strike slip faults this deformation is taking place under a simple shear mechanism associated with the northwest and northeast lateral faults are zones of compression trending west and east of north extending from the base of the basin s north upper slope to the alboran ridge the initial morphology of the alboran ridge on the southern side of the alboran basin was due to the construction of a volcanic edifice at the northeast end of the ridge and igneous activity along northeast trending fractures southwest of the edifice at the northeast end of the alboran ridge motion along a right lateral fault cutting across the ridge led to sediment collapse and the creation of a prominent embayment on the ridge s northwest flank deformation is more subdued in the western than in the eastern part of the alboran basin a tectonic style due either to differences in sediment rheology or that the accommodation of the convergence of africa and iberia is more diffused and attenuated in the west than in the east

variability of cold water coral mounds in a high sediment input and tidal current regime straits of florida cold water coral mound morphology and development are thought to be controlled primarily by current regime this study however reveals a general lack of correlation between prevailing bottom current direction and mound morphology i e footprint shape and orientation as well as current strength and mound size i e footprint area and height these findings are based on quantitative analyses of a high resolution geophysical dataset collected with an autonomous underwater vehicle from three cold water coral mound sites at the toe of slope of great bahama bank the three sites 80 km2 total have an average of 14 mounds km 2 indicating that the great bahama bank slope is a major coral mound region at all three sites living coral colonies are observed on the surface of the mounds documenting active mound growth morphometric analysis shows that mounds at these sites vary significantly in height 1 to 83 m area 81 to 6 00 000 m2 shape mound aspect ratio 0 1 to 1 and orientation mound longest axis 0 to 180 the autonomous underwater vehicle measured bottom current data depict a north south flowing current that reverses approximately every six hours the tidal nature of this current and its intermittent deviations during reversals are interpreted to contribute to the observed mound complexity an additional factor contributing to the variability in mound morphometrics is the sediment deposition rate that varies among and within sites at most locations sedimentation rate lags slightly behind mound growth rate causing mounds to develop into large structures where sedimentation rates are higher than mound growth rates sediment partially or completely buries mounds the spatial distribution and alignment of mounds can also be related to gravity mass deposits as indicated by geomorphological features for example slope failure and linear topographic highs in the three dimensional bathymetry in summary variability in sedimentation rates current regime and underlying topography produce extraordinarily high variability in the distribution development and morphology of coral mounds on the great bahama bank slope

gas hydrate crystals may help build reefs during a recent cruise in the porcupine basin off southwest ireland we discovered two extensive and hitherto largely unsuspected deep water reef provinces including a giant cluster of hundreds of buried mounds the ring shapes of many reefs suggest that they are caused by an axial fluid expulsion at the sea bed a transient flow well confined in space and time we are exploring various hypotheses but a stimulating avenue for research is opened by a glacially controlled growth pulse and subsequent decay of a shallow layer of gas hydrates as a methane buffer and probably indirectly as a ground for overlying biological communities

remote sensing of geomorphology and facies patterns on a modern carbonate ramp arabian gulf dubai u a e abstract the occurrence of power law relationships in the spatial distribution of sedimentary lithotopes has been identified in both modern and ancient carbonate depositional bodies in this study facies patterns and their spatial relationships are investigated quantitatively in an arabian gulf shallow subtidal carbonate ramp setting using a synergy of ikonos satellite imagery and vessel based acoustic bathymetry survey three dimensional reconstruction of the facies distribution on the seabed enabled quantification of relationships between eight dominant facies classes and the association of particular lithotopes to water depth fractal behavior was investigated using a combination of boundary and patch based metrics and the spatial distribution of early diagenetically cemented hardgrounds and unconsolidated carbonate sand were shown to display strong fractal properties in contrast we show that landscape scale processes can be treated as essentially deterministic and facies neighborhood patterns are strongly probabilistic identifying that the heterogeneity of shallow subtidal carbonate facies scales with a power law within certain thresholds has the potential to serve as a tool in environmental reconstruction in the ancient where information on the lateral persistence of facies units is difficult to obtain the findings are relevant to the interpretation of stratigraphic sequences and paleo depth analysis

crustal thinning mantle exhumation and serpentinization in the porcupine basin offshore ireland evidence from wide angle seismic data new wide angle seismic data were gathered along a 230 km long profile that runs east west across a deep structural feature in the porcupine basin offshore ireland known as the porcupine arch ocean bottom seismometers were deployed at 3 4 km intervals and seismic sources fired every 120 m along it prominent primary and secondary arrivals indicate that the continental crust is extremely thin locally less than 2 km across the basin centre the sedimentary succession is up to 12 km thick and comprises three distinctive seismic layers the two uppermost layers are interpreted as mostly a post rift succession of cretaceous and cenozoic strata the lowest layer thins rapidly towards the basin centre and is interpreted as a succession of predominantly jurassic synrift sediments a strong asymmetry in both the geometry of the crust and the sedimentary layers is probably related to a simple shear mode of extension and the subsidence that it induced crustal thinning is far greater than in the adjacent rockall basin and local exhumation of continental mantle lithosphere may have occurred in parts of the porcupine basin low p n velocities beneath the porcupine arch are compatible with larger amounts of mantle serpentinization than in the rockall basin

climatology of the simulated great plains low level jet and its contribution to the continental moisture budget of the united states abstract the great plains region of the united states is characterized by some of the most frequent and regular occurrences of a nocturnal low level jet llj while the llj is generally confined to the lowest kilometer of the atmosphere it may cover a substantial region of the great plains and typically reaches maximum amplitudes of more than 20 m s 1 a two month springtime simulation with the goddard earth observing system geos 1 atmospheric general circulation model agcm has produced a great plains llj with a vertical and temporal structure directionality and climatological distribution that compare favorably with observations the diurnal cycle of the low level flow is dramatic and coherent over a subcontinental area that includes much of the western united states and northern mexico this cycle can be interpreted as the nightly intrusion of the anticyclonic subtropical gyre associated with the bermuda high into the north american continent as surface friction decreases the agcm also sim

structure and evolution of numerically simulated squall lines abstract using a three dimensional numerical cloud model we investigate the effects of vertical wind shear on squall line structure and evolution over a wide range of shear magnitudes depths and orientations relative to the line we find that the simulated squall lines are most sensitive to the magnitude of the component of shear perpendicular to the line and that we may reproduce much of the range of observed structures by varying this single parameter for weak shear a line of initially upright to downshear tilted short lived cells quickly tilts upshear producing a wide band of weaker cells extending behind the surface outflow boundary for moderate to strong shear the circulation remains upright to downshear tilted for longer periods of time with vigorous short lived cells confined to a relatively narrow band along the system s leading edge at later times however these systems may also weaken as the circulation tilts upshear for strong deep shears oriented obliquely to the line the squal

an observational study of warm season southern appalachian lee troughs part ii thunderstorm genesis zones abstract the thunderstorm genesis regions during warm seasons lee trough episodes in the southern appalachians are examined in this study a composite of cloud to ground lightning data during 1985 lee trough cases indicates that the time of maximum activity is the late afternoon a stratification of cases by the strength of the large scale forcing indicated that both the strength and location of afternoon convection depended on synoptic and subsynoptic scale process days with strong or moderate cyclonic forcing produced the most lightning but the strong forcing days produced convection primarily in the coastal plain while moderate forcing days spread convection from the mountains to the coast conversely days with relatively little cyclonic forcing were dominated by mountain convection nocturnal convection tended to weaken in general except when storms passed over chespeake bay or approached the coast of the carolinas examples from individual cases used in the composite are used to demonstrate the

alboran basin southern spain part i geomorphology abstract bathymetric 3d relief and shaded relief maps created from multibeam echo sounding data image the morphology of the alboran basin a structural low along the east west trending eurasian african plates boundary topographic features in the basin are the consequence of volcanism associated with miocene rifting rift and post rift sedimentation and recent faulting resulting from the convergence of the african eurasian plates pleistiocene glacially induced regressions transgressions when the sea level dropped to about 150 m below its present level gas seeps and bottom currents recent faulting and the pleistocene transgressions regressions led to mass wasting formation of turbidity currents and canyon erosion on the basin s slopes recent fault traces at the base of the northern basin slope have also served as passageways for thermogenic methane the oxidation of which by bacteria led to the formation of carbonate mounds along the fault intercepts on the sea floor expulsion of thermogenic or biogenic gas has led to the formation of pockmarks erosion by bottom currents has resulted in the formation of moats around seamounts and erosion of the seafloor of the alboran ridge and kept the southern edge of the 36 10 n high sediment free

the evolution of the porcupine and rockall basins offshore ireland the geological template for carbonate mound development the margins of the deep water sedimentary basins west of ireland contain a number of large clusters provinces of spectacular carbonate mounds and build ups these basins have a complex development history involving the interplay of rift tectonics thermal subsidence igneous activity and oceanographic variations the porcupine and rockall basins both rest upon thin continental crust the consequence of major rift episodes in permo triassic late jurassic and early cretaceous times phases of volcanism occurred in the early cretaceous and especially in the early cenozoic fluid flow within the basins is likely to have been controlled by the overall basin geometry and by the distribution and linkage of permeable strata with fault systems stratal surfaces and unconformities a number of regional unconformities controlled by both basin tectonic and regional oceanographic effects can be mapped and correlated throughout the porcupine and rockall basins the youngest of these unconformities c10 early pliocene can be traced throughout much of the nw european atlantic margin it forms the horizon on which virtually all the carbonate mounds in the basins develop suggesting a geologically instantaneous mound nucleation and growth event although the control on their development is uncertain the mound clusters show a spatial association with lithified strata buried contourite and deltaic deposits slope failure features and with the basin margins analysis of these relationships points to a combination of geological and oceanographic processes controlling mound initiation and growth

sediment source regions and paleotransport of the upper jurassic norphlet formation eastern gulf of mexico the upper jurassic norphlet formation is an eolian sandstone and important hydrocarbon reservoir that overlies the louann salt in the gulf of mexico gom because the sand was concentrated into dunes formed by late jurassic winds determining the source areas and paleotransport direction of the sand can improve predictions of the distribution of the dune facies around the gom paleo wind blown sediment transport into the proto gom was controlled by wind direction and magnitude and the extant topography of the basin and adjacent uplands analysis of the norphlet formation in the eastern gom shows that wadis and alluvial fans controlled by the location of highs were the primary route for introducing sediment of varied provenance into the eolian erg eolian transport directions interpreted from dip log analyses are south directed in southern alabama and west to northwest directed in western florida interpretations of regional two dimensional prestack depth migrated seismic data show that erosional incision of the middle ground arch occurred prior to and during the time of norphlet deposition this as well as preexisting lows in the basement topography may have facilitated basinward sand transport of sediment that fed the norphlet formation erg preserved in the deep water subsurface eastern gom

an observational study of the northern hemisphere extratropical summertime general circulation abstract the three dimensional structure of the extratropical northern hemisphere summertime general circulation is documented by making use of twice daily operational analyses at nine pressure levels 1000 100 mb for 12 summers 1966 77 two distinct regimes of standing waves quite unlike the wintertime standing waves appear a subtropical regime which is clearly a monsoonal response to thermal forcing and a higher latitude regime in which the standing waves are of smaller scale and much weaker than in winter and tend to be equivalent barotropic in structure with almost no vertical tilt in the mid and upper troposphere while the transient eddies shift poleward from their wintertime location and are weaker in summer their properties and relation to the mean flow are much the same as blackmon et al 1977 lau 1978 1979a b and lau and wallace 1979 found for the winter in both seasons the regions of strongest transient activity generally coincide with the regions where the height scale of the m

a model for the development of a carbonate mound population in the rockall trough based on deep towed sidescan sonar data a large carbonate mound population is identified on deep towed tobi towed ocean bottom instrument sidescan data along the eastern margin of the rockall trough west of ireland individual mounds are circular to elliptical in plan view varying from 50 to 850 m in width and up to about 200 m in height strong ne flowing contour currents at 800 m water depth are inferred from large scale sedimentary bedforms smaller mound arrays are spatially associated with slope parallel escarpments produced by mass wastage while around the largest mounds the sharp escarpments may have been smoothed by the vigorous contour currents current streamlining effects control the shape of the mounds which become more elliptical as their size increases thereby minimising the hydraulic drag force the frequency distribution of mound size follows a general power law which is determined by the growth rate of the framework building coral species and the rate at which they colonised the substrate initially bottom currents support mound growth until the mounds become so large that hydraulic drag forces retard their growth a model for the evolution of the population predicts that increased hydraulic drag forces on the larger mounds cause a sharp decrease in their number in agreement with the observations the model also allows an age structure for the population to be determined and correlations between the growth of the mound population and palaeoclimatic variations in the ne atlantic to be attempted

the west melilla cold water coral mounds eastern alboran sea morphological characterization and environmental context a new mound field the west melilla mounds interpreted as being cold water coral mounds has been recently unveiled along the upper slope of the mediterranean moroccan continental margin a few kilometers west of the cape tres forcas this study is based on the integration of high resolution geophysical data swath bathymetry parametric sub bottom profiler ctd casts acoustic doppler current profiler adcp rov video and seafloor sampling acquired during the topomed gassis 2011 and melcor 2012 cruises up to 103 mounds organized in two main clusters have been recognized in a depth range of 299 590 m displaying a high density of 5 mounds km2 mounds 1 48 m high above the surrounding seafloor and on average 260 m wide are actually buried by a 1 12 m thick fine grained sediment blanket seismic data suggest that the west melilla mounds grew throughout the early pleistocene holocene settling on erosive unconformities and mass movement deposits during the last glacial interglacial transition the west melilla mounds may have suffered a drastic change of the local sedimentary regime during the late holocene and unable to stand increasing depositional rates were progressively buried at the present day temperature and salinity values on the west melilla mounds suggest a plausible oceanographic setting suitable for live cwcs nonetheless more data is required to groundtruth the west melilla mounds and better constrain the interplay of sedimentary and oceanographic factors during the evolution of the west melilla mounds

fault associated seabed mounds carbonate knolls off western ireland and north west australia abstract groups of seabed mounds suspected to be modern carbonate knolls or bioherms have been located on reflection seismic data in the porcupine basin off western ireland and in the vulcan sub basin off north west australia the size of these mounds is impressive often being over 1 km across and over 100 m high in the porcupine basin they occur in water depths of 650 1000 m whereas in the vulcan sub basin they occur in water depths of 200 350 m shallow seabed coring in the porcupine basin has provided data on the age lithological composition and hydrocarbon concentrations in the upper 3 m layer of sediment both on and off the mounds in both basins the mounds occur close to faults which may provide conduits for upward migrating hydrocarbons the seepage of hydrocarbons is suspected to have caused local eutrophication or fertilization by providing nutrients to bacteria which in turn are part of the food chain for higher organisms the dominant organism in the porcupine basin examples appears to be the deep water coral lophelia sp whereas in the vulcan sub basin the mounds appear to be halimeda dominated

a satellite based climatology of central and southeastern u s mesoscale convective systems abstracta satellite based climatology is presented of 9607 mesoscale convective systems mcss that occurred over the central and southeastern united states from 1996 2017 this climatology is cons

pleistocene geochemical stratigraphy of the borehole 1317e iodp expedition 307 in porcupine seabight sw of ireland applications to palaeoceanography and palaeoclimate of the coral mound development stable isotopes and element compositions of the fine grained matrix were measured for iodp expedition 307 hole u1317e drilled from the summit of challenger mound in porcupine seabight northeast atlantic to explore the palaeoceanographic and palaeoclimatic background to development of the deep water coral mound the 155 m long mound section was divided into two units by an unconformity at 23 6 mbsf unit m1 2 6 1 7 ma and unit m2 1 0 0 5 ma results from 519 specimens show a difference in 13c value between unit m1 0 6 to 5 0 and unit m2 1 0 to 1 0 but such a distinct difference was not seen in 18o values 1 0 2 5 caco3 content 40 60 wt sr ca ratio 2 0 8 0 mmol mol 1 and mg ca ratio 10 0 20 0 mmol mol 1 through the mound positive 18o and negative 13c shifts at the mound base are consistent with the oceanographic changes in the northeast atlantic at the beginning of the quaternary the positive 13c regression in unit m2 suggests a linkage to the mid pleistocene intensified glaciation in the northern hemisphere warm mediterranean upper core water of mediterranean outflow water eastern north atlantic water and cold labrador sea water of north atlantic deep water are key oceanographic features that cause spikes and shifts in stable isotope and element composition however the stable isotope values of the sediment matrix could not primarily record the glacial interglacial eustatic temperature change but indirectly indicate current regimes of the intermediate oceanic layer where the coral mound grew similarly elemental ratios and caco3 content may not represent the productivity and temperature of surface sea water respectively but superpose the fractions from both surface and bottom water it is concluded that palaeoceanographic change coupled to the pleistocene glacial interglacial cycles is a key control on the geochemical stratigraphy of the matrix sediments of the carbonate mound developed in porcupine seabight copyright 2011 john wiley sons ltd

the enya mounds a lost mound drift competition the genesis and evolution of cold water coral banks along the northeastern atlantic margin is known to be influenced by several factors among which the palaeotopography and nature of the coral settling surface the presence of bottom currents and sediment supply in this paper a case study is presented of the enya mound cluster located in the southernmost tip of the belgica mound province west of ireland below this mound cluster seismic stratigraphy revealed a yet unmapped local unconformity rd1b being part of a composite erosion event rd1 as such from the late miocene to late pliocene at least two erosional events have incised the margin ending with the final rd1a moundbase unconformity acting as a base for the enya mounds during the quaternary the mounds became outgrown and were covered by a mounded contourite drift in addition they are closely associated with a cluster of seabed pockmarks the bottom current regime which became active since the middle pleistocene has certainly influenced the fate of this mound cluster the occurrence of the pockmarks seems to be related to relatively recent fluid migration processes however leaving an open question if any previous seepage phases were involved in the growth or initiation of the coral banks

multiscale analysis of a mature mesoscale convective complex abstract a multiscale analysis reveals diverse atmospheric structure and processes within a mesoscale convective complex mcc observed during the oklahoma kansas preliminary regional experiment for storm central pre storm experiment this midlatitude system was the second in a series of four mccs that developed and traveled along a quasi stationary frontal zone over the central united states on 3 4 june 1985 objectively analyzed mesoscale upper air soundings encompassing the mcc are interpreted in tandem with more detailed dual doppler radar measurements that disclose the storm s internal airflow and precipitation structure the mature mcc is found to include a variety of local environments and associated weather ranging from tornadic thunderstorms to more linear convective bands and widespread chilling rains a corresponding spectrum of mesoscale ver6cw motion profiles is documented these findings are related to previous composite based portrayals of mccs as well as detailed case studies of simple

carbonate mound development at the sw rockall trough margin based on high resolution tobi and seismic recording abstract in 2002 high resolution sidescan sonar images of a mound area at the sw rockall trough margin were recorded with the tobi deep towed sidescan sonar processed tobi images with a pixel resolution of 6 m provide a unique overview of the carbonate mound distribution and related sedimentary features around the mounds three morphologically distinct areas can be recognised on the tobi mosaic in area i between 500 and 600 m water depth upslope of the mounds giant sediment waves are found with wavelengths up to 500 m with wave crests of more than 10 km long and with an amplitude of up to 30 m reflected with a high backscatter on the tobi image area ii between 600 and 1000 m water depth along the upper margin flank is characterised by clustered and isolated carbonate mounds forming elongated ridges with an orientation perpendicular to the slope sedimentary structures such as flow ridges sediment waves local scouring at the foot of some mounds and draping of sediment around mounds indicate the influence of strong near bed currents oriented in two main current directions parallel to the margin as well as in a similar direction as the mound clusters the mound clusters are several kilometres long can be over 380 m high and are dissected by downslope directed channels on the tobi image the mounds appear as regions of high backscatter caused by the presence of cold water coral colonies on the sediment and by distinct shadows all mounds have their tops at a specific depth level 500 600 m water depth area iii between 900 and 1200 m water depth below the mounds is characterised by disturbed sediments with distinct slump scars and flow ridges 2d high resolution seismic profiling perpendicular and parallel to the slope across the mounds does in general not reveal strong internal reflectors within the mounds in contrast three strong reflectors can be observed in the sedimentary sequence underneath the mounds the upper reflector c10 of early pliocene age is an erosional unconformity above which most of the mounds and sediment waves seem to have developed the second erosional unconformity c20 of middle miocene age is formed by an apparent irregular surface that locally is dissected by some small faults reflectors c10 and c20 have been found in two different mound clusters in the mound area indicating that mound development possibly started after formation of reflector c20 the third reflector forms the acoustic basement which is locally dissected by some small faults that are located below the mounds at least two stages of mound formation are recognised on the seismic profiles

subseasonal variations in warm season moisture transport and precipitation over the central and eastern united states abstract subseasonal variations in warm season may august precipitation over the central and eastern united states are shown to be strongly linked to variations in the moisture entering the continent from the gulf of mexico within a longitudinally confined channel referred to here as the texas corridor or tc these variations reflect the development of low level southerly wind maxima or jets on a number of different timescales in association with distinct subcontinental and larger scale phenomena on the diurnal timescale the tc moisture flux variations are tied to the development of the great plains low level jet the composite nighttime anomalies are characterized by a strong southerly moisture flux covering northeast mexico and the southern great plains and enhanced boundary layer convergence and precipitation over much of the upper great plains the strongest jets tend to be associated with an anomalous surface low over the great plains reflecting a predilection for periods when midlatitude

climatology of summer midtropospheric perturbations in the u s northern plains part i influence on northwest flow severe weather outbreaks northwest flow severe weather outbreaks nwf outbreaks describe a type of summer convective storm that occurs in areas of mid level nwf in the central united states convective storms associated with nwf outbreaks often travel a long distance systematically along a northwest southeast oriented track across the northern plains previous studies have observed that these migrating convective storms are frequently coupled with subsynoptic scale midtropospheric perturbations mps initiated over the rocky mountains this study traces mps for the decade of 1997 2006 using the north american regional reanalysis to examine their climatology and possible influence on nwf outbreaks mps are characterized by a well organized divergent circulation with persistent ascending motion at the leading edge promoting convection the divergent circulation is further enhanced by low level convergence along the northern terminus of the great plains low level jet the downstream propagation of mps assists in forming the progressive feature of the associated convective storms mps have a maximum frequency in july consistent with nwf outbreaks in july and august the fully developed north american anticyclone produces prevailing nwf over the northern plains where up to 60 of rainfall and storm reports are linked to mps the movement timing and rainfall distribution of mps remarkably resemble those of nwf outbreaks when encountering strong low level jets ascending motion and convergence of water vapor flux associated with mps intensify considerably and precipitation is greatly enhanced it is likely that nwf outbreaks are generated whenever mps occur in association with strong low level jets

cold water coral mounds evidence for early holocene climate change and slope failure 1 cold water coral mounds occur in discrete clustered populations over a broad region from the glaciated norwegian continental margins to the non glaciated margins of iberia and northwest africa here we report on an interesting correlation between the holocene growth of a mound population west of ireland and early holocene paleoclimatic variations in the north atlantic region notably the well documented 8 200 yr cold event an age structure for the population is calculated from growth rate estimates for the coral framework constructor lophelia pertusa and a previously formulated population growth model the model growth curve for the holocene period fits the observed data well except for a significant deflection in the data trend at about 8 500 calendar years ago this corresponds to the time that the glacial lakes agassiz and ojibway which were once dammed by a remnant of the laurentide ice sheet drained catastrophically into the labrador sea and triggered the 8 200 yr event this cold period may also have played a role in triggering major submarine landslides such as the storegga slide

the spatial distributions of faults and deep sea carbonate mounds in the porcupine basin offshore ireland localised populations of deep water carbonate mounds occur throughout the ne atlantic margin of ireland the uk and norway but the mechanisms responsible for their nucleation and growth are not well known based in part on the interpretation of seismic data from the porcupine basin offshore ireland it has been proposed previously that deeply rooted faults are present immediately beneath mounds and act as conduits for the vertical migration of mound feeding hydrocarbons several discrete carbonate mound populations or provinces are present in the porcupine basin above a number of distinct fault systems at different levels in the stratigraphy however detailed mapping of the distributions of both mounds and faults for two of these provinces in the northern part of the basin using 3d and 2d seismic data demonstrates that there is a poor spatial relationship between the two furthermore virtually all the reflector offsets directly beneath the mounds which have previously been interpreted as faults can be attributed to seismic artefacts such as velocity pull ups and diffraction cones therefore our findings strongly suggest that seismically mappable faults do not play a pivotal role as conductive fractures in the evolution of the mounds however mounds located towards the nw margin of the porcupine basin are underlain by a shallow intensely faulted slide package which provides one potential association between faults and mounds

maintenance of summer monsoon circulations a planetary scale perspective abstract the monsoon circulation which is generally considered to be driven by the landmass ocean thermal contrast like a gigantic land sea breeze circulation exhibits a phase reversal in its vertical structure a monsoon high aloft over a continental thermal low is juxtaposed with a midoceanic trough underlaid by an oceanic anticyclone this classic monsoon circulation model is well matched by the monsoon circulation depicted with the observational data prior to the first global atmospheric research program garp global experiment fgge however synthesizing findings of the global circulation portrayed with the post fgge data it was found that some basic features of major monsoon circulations in asia north america south america and australia differ from those of the classic monsoon circulation model therefore a revision of the classic monsoon theory is suggested with four different wave regimes selected to fit the horizontal dimensions of these monsoon circulations basic features common to

a high plains squall line associated with severe surface winds abstract the characteristics of a severe squall line are examined using data acquired from the 1981 cooperative convective precipitation experiment ccope the case is unusual in that the squall line was decoupled from an immediate surface based inflow source due to a meso scale 20 200 km outflow pool produced by a separate mesoscale convective system both systems participated in the development of a mesoscale convective complex which subsequently produced sustained severe surface winds throughout its entire life cycle despite the absolutely stable presquall atmospheric boundary layer the squall line produced radar reflectivity values of 70 dbz and storm induced outflow of 30 m s 1 aircraft soundings in the presquall environment suggest the storm was sustained by an elevated layer of high valued c air overriding the cold dome produced by the developing mcc the strongest surface winds were located upshear from the convective line and consisted of a northerly alongline component because the

a shallow water model of the diurnal dryline this study explores the diurnal variation in the movement and structure of the dryline using a one dimensional shallow water model the model is adapted to test some common theories of dryline motion including the diurnal variation in surface friction static stability inversion erosion and momentum mixing aloft these mechanisms of diurnal variation are first studied individually and then in unison a diurnal variation in the surface friction produces a model dryline that moves westward during the day in disagreement with observations and has a southerly wind maximum near midnight a diurnal variation in the static stability produces a model dryline that steepens in slope and moves eastward during the day and then surges westward at night with a southerly wind maximum 6 to 9 h after the minimum stability inversion erosion during the day produces a nearly vertical model dry front that moves eastward during the day with surface southwesterlies at sunset the model dryline surges westward with a southerly wind maximum before midnight a diurnal variation of the momentum mixing aloft has no significant effect on the model dryline results show that the combined case with a diurnal variation of surface friction inversion erosion and static stability with terrain most accurately describes the observed dryline system the westward surge depicted in the model is compared to the flow evolution of the corresponding dam break problem for a rotating fluid

atmospheric responses to north atlantic sst anomalies in idealized experiments part i northern hemispheric circulation abstractidealized model experiments using the ncar cesm1 0 5 under equinox conditions are designed and performed to address two fundamental questions about the effects of the sea surface temperature sst variation associated with the atlantic multidecadal oscillation amo on circulation and precipitation in north america and europe 1 is the observed relationship between the amo sst and the warm season precipitation in north america a statistical coincidence and 2 why is the response of negative precipitation anomaly to warm sst in the amo fairly uniform across most of north america whereas the positive precipitation anomaly in the cold sst rather spotty model experiments are done with either a warm or cold sst anomaly in an aquaplanet a planet with idealized continents and a planet with both idealized continents and orography major results show that the atmospheric response to warm sst anomaly in the north atlantic is fairly similar among the three sets of experiments in the lower troposphere

structure and development of giant carbonate mounds at the sw and se rockall trough margins ne atlantic ocean abstract high resolution seismic reflection profiling carried out in 1997 1999 showed that giant carbonate mounds occur between 500 and 1200 m water depth along both the se and sw margins of rockall trough the mounds rise 5 300 m above the surrounding seafloor and have diameters at their bases of up to 5 km buried mounds at relatively shallow depths below the seafloor are also found both individual and complex clusters of mounds can be recognized smaller and individual sometimes buried mounds are found at the upper slope on the sw rockall trough margin higher steeper and individual mounds are found deeper downslope 900 1100 m at the middle slope the mounds merge into a complex structure and form complex clusters with a very irregular upper surface and an apparent lack of internal reflectors 600 1000 m depth initial results of high resolution 3d seismic profiling at 30 m line spacing in august 2000 in two boxes of 750 m 14 5 km covering a small central part of the sw rockall trough mound area indicate two stages of mound development here the latest probably of pliocene holocene age this age based on the presence of a regionally recognizable unconformity below the mounds is also assumed for the mounds of the se rockall trough porcupine bank margin

shelf to slope sedimentation processes and the impact of plio pleistocene glaciations in the northeast atlantic west of ireland abstract the eastern margin of the rockall trough between 54 30 and 56 30 n straddles the southern limit of the glaciated north atlantic margin a complex system of canyons channels and slope failure features on the steep margins of the trough is resolved on the trim tobi rockall irish margins project deep towed sidescan survey the canyons consist of a complex headwall gullied region produced by multiple slope failure events and interconnect to form a cauliform pattern in plan view individual gullies are u shaped in cross section in the upper parts of the margin and are connected downslope to single deeply incised v shaped channels these channels feed extensive aprons of sediment on the lower slope supplied by failure of the headwall regions and sediment transport along the shelf into the canyon headwalls the change in the canyon morphology systems reflects a more abundant supply of glaciomarine sedimentary debris from pleistocene ice sheets whose southerly limit lay along this part of the eastern rockall margin a good correlation between acoustic sidescan backscatter and more deeply penetrating 3 5 khz profiler data suggests that sediment transport pathways were stable through time slope failure escarpments occur in association with the canyon systems along the upper part of the slope canyons are absent in the north of the area where the slope gradient is lowest this is interpreted as the result of progradation of sheet like flows of glaciomarine debris across the southern part of the donegal fan a poor correlation between acoustic backscatter and sub bottom profile data indicates that sediment transport pathways varied through time in the region evidence for strong northeast flowing bottom currents is present along the upper slope and shelf these currents transport and sort sediments along the entire eastern margin of the rockall trough from the south of the porcupine bank to the hebrides terrace seamount

basin architecture salt tectonics and upper jurassic structural styles desoto canyon salt basin northeastern gulf of mexico despite awareness of the importance of continental extension during rifting there are few quantitative studies that show the influence of crustal extension on basin architecture the distribution of salt and late jurassic sedimentation in the desoto canyon salt basin northeastern gulf of mexico application of simplified isostatic principles using a lithospheric buoyancy model allow quantification of total tectonic subsidence crust thickness crustal extension and crust type interpretation of over 4800 km of migrated multifold seismic reflection profiles and well data integrated with computed isostatic relations provide the basis to characterize middle jurassic callovian age salt halokinetic processes and to describe the structural development of overlying upper jurassic strata an average crustal thickness of 25 km and crustal extension s values between 1 4 and 1 8 suggest the sedimentary succession is underlain by moderately stretched and attenuated continental crust the widespread distribution and geometry of dipping subsalt reflectors particularly in the shelfal areas provide evidence for a late triassic early jurassic phase of rifting prior to deposition of middle jurassic salt the distribution of autochthonous salt and the overlying upper jurassic sediments reflect the presalt structural imprint and suggest that the basic architecture of the basin was established by the middle jurassic following significant attenuation of the crust although deposition occurred in a slowly subsiding stable marginal setting salt movement and associated growth faulting are the most significant tectonic elements affecting the stratigraphic and structural development of the overlying strata faults related to growth of salt structures root at the base of salt in what appears to be a common detachment or decollement for salt movement the original distribution of salt is widespread and sheetlike with an estimated minimum thickness of 760 m progressive basinward subsidence of the margin and differential sediment loading by the overburden are the primary mechanisms initiating mobilization of salt and subsequent deformation of sediments during the late jurassic and from the late cretaceous through the early cenozoic

the unusual early morning tornado in ciudad acuna coahuila mexico on 25 may 2015 abstractthis study analyzes the synoptic and mesoscale conditions present during initiation and intensification of the supercell thunderstorm that produced a tornado in ciudad acuna a community located in the state of coahuila mexico 10 km southwest of the u s border early morning convective activity first detected by radar at 0628 utc 25 may 2015 developed into an intense and well defined supercell thunderstorm that produced a tornado between approximately 1045 and 1130 utc hourly analyses from the rapid refresh model indicated an upslope component to surface flow in the region of convection initiation over the serranias del burro sdb along the storm s trajectory dewpoint temperatures increased from 15 to 22 c convective available potential energy increased from 1500 to near 4000 j kg 1 and convective inhibition changed from 150 j kg 1 at the time of convection initiation to near zero in ciudad acuna simulations from the weather research and forecasting model confirmed the sensitivity o

investigations of the bottom current sculpted margin of hatton bank ne atlantic the northwest hatton bank margin is an ideal locality to demonstrate the interaction between bottom currents and slope configuration in controlling the distribution and morphology of bottom current deposits the slope area investigated is isolated from any major terrigenous sediment supply and at present is influenced by the deep northern boundary current dnbc swath bathymetry and high resolution acoustic data allow us to evaluate both local and regional controls on slope sedimentation and the possible mechanisms for bottom current velocity variability across a slope setting within the nw european continental margin the slope exhibits sculpting by bottom currents that flow in a predominantly southwest to northeast direction and is only locally modified by slope failures positive relief features such as the endymion spur play an important role in constraining and accelerating bottom current flow and consequently in redistributing sediment along the margin we demonstrate that the size morphology and distribution of bottom current deposits along the slope vary as a function of the interaction between bottom currents regional slope orientation and local seafloor topography

radar observations of the diurnally forced offshore convective lines along the southeastern coast of taiwan this study documents offshore convective lines along the southeastern coast of taiwan a frequent but poorly understood mesoscale phenomenon that influences coastal weather during the taiwan mei yu season doppler radar and surface observations were gathered from a specially chosen period 11 15 may 1998 when the offshore convective lines were active off the southeastern coast of taiwan these observations were used to show the basic character structure and possible formative processes of offshore convective lines the synoptic environment accompanying these events was found to be relatively undisturbed and featured uniformly prevailing southerly south southeasterly winds in the boundary layer with southwesterlies westerlies aloft examination of radar data during the study period indicates that the lines generally occurred 10 30 km offshore and were characterized by an elongated narrow zone 5 10 km wide of heavy precipitation the lines were oriented roughly parallel to the coastline and generally did not move significantly the intensity of the radar reflectivity associated with the lines exhibited a marked diurnal variation and was closely related to the coastal offshore flow developing at night detailed analyses of an event on 14 15 may 1998 further show the important physical link between the offshore flow and the development of the line the offshore line was found to be located near and immediately ahead of the seaward extent of the offshore flow particularly a very narrow zone 2 km of low level heavy precipitation 40 45 dbz coincided with regions of strong updrafts and convergence where the prevailing southerly onshore flow encountered the cool offshore flow nearshore this offshore flow induced convergence given a stable thermodynamic condition in the lowest 1 km in the inflow region was a crucial low level forcing that provided lifting to trigger moist deep convection in this case the line s precipitation tilt eastward was confined primarily to the warmer inflow side rather than feeding the offshore flow to the west of the line no consistent upshear tilt of updrafts throughout the storm layer was observed which is consistent with the presence of a strong westerly shear in the line s environment both of these observations explain a relatively strong weak modification of low level onshore offshore flow by precipitation additionally a combination of surface and doppler radar observations indicates that the leading edge of the offshore flow moved seaward very slowly at 0 7 m s 1 and possessed a frontal character with notable discontinuities in near surface wind and temperature instead of pressure and dewpoint temperature

the magellan mound province in the porcupine basin the magellan mound province is one of the three known provinces of carbonate mounds or cold water coral banks in the porcupine seabight west of ireland it has been studied in detail using a large and varied data set 2d and 3d seismic data sidescan sonar imagery and video data collected during rov deployment have been used to describe the mounds in terms of origin growth processes and burial the aim of this paper is to present the magellan mounds and their setting in an integrated holistic way

separate tree ring reconstructions of spring and summer moisture in the northern and southern great plains the two most severe droughts to impact the great plains in the twentieth century the 1930s dust bowl and 1950s drought were the result of multiyear moisture deficits during the spring and especially the summer season tree ring reconstructions of the palmer drought severity index indicate similar droughts in magnitude have occurred in previous centuries but these reconstructions do not capture the potential distinct seasonal drought characteristics like those of the 1930s and 1950s separate tree ring reconstructions of the spring and summer z index based on earlywood latewood and adjusted latewood width chronologies have been developed for two regions in the northern and southern great plains of the us the reconstructions extend from 1651 to 1990 and 1698 1990 respectively with instrumental data added from 1991 to 2017 the four reconstructions explain from 39 to 56 of the variance during the 1945 1990 calibration interval and are significantly correlated with independent moisture balance observations during the 1900 1944 validation period the reconstructions reproduce similar seasonal sea surface temperature and 500 mb geopotential height spatial correlation patterns detected with the instrumental data the 1930s is estimated to have been the most extreme decadal summer drought to impact the two regions concurrently in the last few centuries on average spring moisture deficits were more severe during the multidecadal droughts of the mid to late nineteenth century but the timing of drought onset and termination differed between the study regions in the recent two decades the spring moisture balances for the two study regions have largely been opposite and this has been one of the most extreme periods of anti phasing in the last few centuries seasonal moisture reversals are not randomly distributed in time based on the reconstructed estimates and are related to sea surface temperature anomalies in the tropical pacific and to mid tropospheric circulation changes over the north pacific north american sector during may and june

the synoptic scale environment associated with the low level jet of the great plains abstract the synoptic scale conditions of the upper and lower tropospheric circulation and water vapor transport during the occurrence of the low level jet llj over the great plains were analyzed in terms of composite stream and potential functions for 64 cases over a period of 11 springs 1979 89 the llj formation takes place when a developing baroclinic wave with an upper level jet appears east of the rocky mountains the divergent circulation associated with this baroclinic wave exhibits the coupling of the upper tropospheric divergence with the lower level convergence ahead of this wave as predicted by the classic baroclinic wave theory the precipitation generated by severe storms over the surface low northeast of the llj is maintained by the water vapor converged by the lower tropospheric convergence

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

a record of fluctuating bottom currents on the slopes west of the porcupine bank offshore ireland implications for late quaternary climate forcing abstract both local and regional controls on slope sedimentation west of porcupine bank are assessed using an array of 25 gravity cores integrated with shallow seismic tobi side scan and high resolution bathymetry data the cores were retrieved from an area of smooth distally steepened slope between 52 and 53 n in water depths of 950 to 2750 m the slope here is unmodified by gravity failures and is swept by bottom currents that flow from s to n along the margin the cores reveal a coherent shallow stratigraphy that can be traced along and between transects at upper mid and lower slope levels ams 14 c dating oxygen isotopes and carbonate profiles suggest the cored record could extend as far back as 500 ka in the longest cores with most cores providing details of the slope response to the last interglacial last glacial and holocene forcing the facies indicate deposition was dominated by a combination of bottom currents ice rafting and hemipelagic settling with carbonate prone deposits during interglacials and siliciclastic deposits during glacials inferred contourites imply that strong currents operated during interglacials with weaker current reworking during glacial conditions a pair of erosion surfaces record significant mid and upper slope scouring during marine isotope stage mis 3 and in the early holocene the lateral facies distribution implies stronger currents at shallower levels on the slope although there is evidence that the core of the current migrated up and down the slope and that sand might locally have spilt down slope the bathymetry influenced both the wider geometry of the condensed contourite sheet and the local thickness and facies variation across the slope a significant result of the study is the identification of a pair of thin sand mud contourite couplets that record enhanced bottom current reworking corresponding to periods of interstadial warming during mis 3 the couplets can be correlated to the terrestrial records onshore ireland and imply that the ne atlantic margin oceanographic and onshore climate records are strongly coupled at interstadial level

synergism between the low level jet and organized convection at its exit region abstract previous studies suggest that the enhanced meridional extent of some south american low level jet events known as chaco jets is a consequence of a positive feedback between the low level wind and strong convection that is usually observed at their exit region to assess how this interaction takes place a chaco low level jet event observed between 18 and 19 december 2002 i e during the south america low level jet experiment and the associated mesoscale convective system that evolved at its exit region have been selected to perform numerical experiments where diabatic heating effects associated with phase changes can be quantified this case study has also been used to analyze the diurnal oscillations related to planetary boundary layer pbl mechanisms in order to describe whether the observed evolution of the low level wind can be explained either by pbl related forcing or by the interaction with convection the sensitivity experiments confirm that there is a positive feedback at low level

geologic framework of norphlet and pre norphlet strata of the onshore and offshore eastern gulf of mexico area abstract hydrocarbon accumulations have been discovered in the jurassic norphlet formation in the onshore and offshore eastern gulf of mexico area an understanding of the regional geologic framework of the norphlet and pre norphlet stratigraphic succession in the study area is crucial to successful exploration for and development of norphlet hydrocarbon reservoirs in the eastern gulf region these strata include jurassic sedimentary rocks and pre jurassic sedimentary and crystalline rocks of these strata only the norphlet formation has produced economic quantities of hydrocarbons from reservoirs which include eolian dune interdune wadi and marine sandstones however the pre norphlet geology and paleotopography of the area controlled to a large degree norphlet depositional patterns and subsequent structural development especially important were the locations of pre jurassic paleohighs and the distribution and thickness patterns of the underlying jurassic louann salt norphlet hydrocarbon traps are generally associated with structures that have resulted from halokinesis of the louann traps include salt anticlines faulted salt anticlines and extensional faults associated with salt movement in addition to these salt related structural traps traps resulting from pre salt basement paleotopography may exist in the study area these traps might include norphlet structural highs associated with preexisting basement highs and norphlet stratigraphic terminations along the flanks of basement highs where norphlet reservoir facies are present the key factor controlling hydrocarbon accumulation potential is structural setting in the mississippi alabama florida mafla region that is underlain by the norphlet formation four structural settings have been identified types a and b structural settings are characterized by norphlet sediments overlying basement or thin salt no norphlet fields have been established in these settings types c and d structural settings are characterized by structures related to movement of thick louann salt all norphlet fields established in the mafla region occur in these settings four geographic regions have been defined in the study area for the purpose of characterizing norphlet petroleum potential region 1 has excellent potential for future norphlet discoveries region 2 has low to moderate potential and regions 3 and 4 have very little to no potential

mechanisms supporting long lived episodes of propagating nocturnal convection within a 7 day wrf model simulation abstract a large domain explicit convection simulation is used to investigate the life cycle of nocturnal convection for a one week period of successive zonally propagating heavy precipitation episodes occurring over the central united states similar to climatological studies of phase coherent warm season convection the longest lived precipitation episodes initiate during the late afternoon over the western great plains 105 100 w reach their greatest intensity at night over the central great plains 100 95 w and typically weaken around or slightly after sunrise over the midwest 95 85 w the longest lived episodes exhibit average zonal phase speeds of 20 m s 1 consistent with radar observations during the period composite analysis of the life cycle of five long lived nocturnal precipitation episodes indicates that convection both develops and then propagates eastward along an east west oriented lower tropospheric frontal zone an elevated 2 km deep layer of high e air helps sustain convect

climatology of summer midtropospheric perturbations in the us northern plains part ii large scale effects of the rocky mountains on genesis propagating convective storms across the us northern plains are often coupled with preexisting midtropospheric perturbations mps initiated over the rocky mountains a companion study part i notes that such mps occur most commonly at 12 utc early morning and 00 utc late afternoon using a regional reanalysis and a general circulation model gcm this study investigates how such a bimodal distribution of the mp frequency is formed the results point to two possible mechanisms working together while each has a different timing in terms of maximum effect the diurnal evolutions between the midtropospheric flows over the rockies and over the great plains are nearly out of phase due to inertial oscillation during the nighttime the westerly flows at 700 500 mb over the rockies intensify while flows at the same level over the great plains turn easterly these two flows converge over the eastern rockies and induce cyclonic vorticity through vortex stretching after sunrise the convergence dissipates and the cyclonic vorticity is redistributed by horizontal vorticity advection moving it downstream this process creates a climatological zonally propagating vorticity signal which in turn facilitates the early morning mp genesis at 12 utc the analysis also reveals marked dynamic instability conducive to subsynoptic scale disturbances in the midtroposphere over the rockies strong meridional temperature gradients appear over the north facing slopes of the rockies due to terrain heating to the south and the presence of cooler air to the north this feature along with persistent vertical shear creates a charney stern type of instability i e sign changes of the meridional potential vorticity gradient meanwhile the development of terrain boundary layer reduces the rossby deformation radius which subsequently enhances the likelihood for baroclinic short waves such effects are most pronounced in the late afternoon and therefore are supportive to the mp genesis around 00 utc examination of gcm experiments with and without orography further supports the critical role of the rocky mountains and its associated boundary layer impacts on the formation of mps

grounding pleistocene icebergs shape recent deep water coral reefs the widespread view that scleractinian corals in cold and deep waters of high latitudes are slow growing organisms that do not form reefs is challenged by the discovery of a huge coral reef over 13 km in length 10 to 35 m in height and up to 300 m in width formed by the coral lophelia pertusa in water depths of 270 to 310 m at 64 n on the sula ridge mid norwegian shelf cruises in 1994 1995 and manned submersible operations in may 1997 provide data and observations from which the structure and development of the sula ridge coral reef have been determined the fennoscandian icesheet retreated from the mid norwegian shelf prior to 12 000 years before present and modern oceanographic conditions were established at 8000 years before present coral growth since that time has resulted in a large deep water shelf reef for which recent stable isotopic studies have demonstrated high growth rates for these azooxanthellate cold water corals information on the geometry of deep water coral reefs and their environmental controls is still fragmentary controversial and raises issues of conservation in this area of active fishing and oil exploration this paper reports on the discovery of what is probably one of the largest deep water coral reefs existing in the northeast atlantic and indicates that its siting is due to post glacial structures iceberg plough marks events the second storegga slide and local conditions on the seafloor surprisingly reef accumulation rates on the sula ridge are comparable with those measured on tropical coral reefs

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

insights into the mode of the south georgia rift extension in eastern georgia usa abstract the south georgia rift sgr lies oblique to the east coast margin of north america and across the alleghenian suture between laurentia and africa in southern georgia regionally the sgr can be divided into a southwest compartment and a northeast compartment across the jacksonville structure that is located in the vicinity of that suture analytical and numerical models are used to characterize the mode of rifting in the northeast compartment borehole cocorp seismic and regional geophysical information from the compartment that were used previously to infer the geometry of the basin are reassessed with the use of those models to analyze the lithospheric conditions influencing triassic extension this approach led to the interpretation of core complex mode extension and to the proposal of a model of progressive rifting the model shows how the riddleville and main sgr basins are associated and how changes in structural style of those two basins resulted from changing lithospheric conditions during extension the core complex model also indicated that extension was influenced by distributed deformation of a younger warmer and less stable lithosphere adjacent to the permian suture whereas extension in other east coast rifts that lie subparallel to structural fabric was probably localized by preexisting zones of weakness

structural framework and fault analysis in the east central gulf of mexico shelf implications for offshore co2 storage abstract a vast co2 storage resource exists offshore in cretaceous through neogene sandstone in the desoto canyon salt basin in the east central gulf of mexico continental shelf understanding the structural styles the likelihood of reactivation and seal properties of the faults in this area is essential for selecting safe carbon storage sites and minimizing the risk of injected co2 migrating beyond the confines of the storage complex the desoto canyon salt basin has variable structural styles in the basin with different insights for co2 storage the mobile viosca knoll shelf contains stable shelf and a large four way structural closure where provide favorable storage opportunities the destin dome region contains three groups of peripheral faults of the destin fault system faults that strike along shmax dip at 60 and steeply dipping faults are predicted to have elevated risk of slip and dilation the w e striking fault group has an overall higher slip and dilation tendency than the other two groups under the same injection conditions fault seal analysis shows that elevated risk along faults occurs at sandstone sandstone juxtaposition zones and zones with high fault throw and low sgr values storage plans should avoid the faults with elevated risk to ensure that the injectate will not flow into or pressurize the fault zones ideal injection sites within the destin fault system in the destin dome region are in hanging wall rollovers that contain low fault throw and shale sandstone juxtapositions future research should focus on geomechanical pressure and flow simulation of the potential reservoirs and associated seals in the area of the peripheral faults