seafloor undulation pattern on the adriatic shelf and comparison to deep water sediment waves abstract on the adriatic shelf a large field of seafloor and subsurface undulations typically 300 m wide 2 5 m high and several km long parallel to the bathymetric contour affects the progradational clinoforms of the late holocene prodelta wedge above a regional downlap surface that shows evidence of deformation and fluid escape the undulations are associated with mud reliefs that occur farther seaward in elongated swarms perpendicular to the regional slope and to the crests of the undulations a quantitative measurement of key morphobathymetric parameters such as wavelength height asymmetry and wave form indexes was performed on 13 selected seismic reflection profiles perpendicular to the undulations these measurements are determined with respect to water depth or downslope distance from the shallowest undulation the results highlight substantial differences from deep water sediment waves these differences include 1 most undulations show a staircase morphology with sub horizontal upslope limbs of 100 300 m delimited seaward by sharp edges and steep downslope limbs 2 landward or upslope dipping limbs do not develop 3 there is no consistent downslope decrease in wavelength or amplitude as opposed to most cases of sediment waves related to overflowing turbidity currents 4 there is a consistent downslope loss in crest continuity approaching areas where mud reliefs and sediment deformation are evident at the seafloor 5 many of the undulations show differences in angle of climb and in some cases a single undulation at the seafloor results from the burial and merger of more undulations in the underlying section these differences compared to bottom current or turbidity current sediment waves are augmented by the observation that the adriatic shallow water undulations are also typically associated with gas charged sediment fluid escape sediment deformation and localised failure planes it is therefore suggested that seafloor undulations evolved in response to sediment deformation and were successively amplified by differential deposition from bottom currents crossing an irregular seafloor in general we feel that case by case solutions should be found to explain the origin and evolution of seafloor wavy features based on the geologic stratigraphic setting the recognition of possible weak layers and the co existence of a variety of other deformation geometries that may occur within or adjacent to the field of wavy features the adriatic example can reinforce recent suggestions that besides purely depositional bedforms there exist also wave like deformation structures and multi process sediment waves faugeres et al 2002 multi process generated sediment waves on the landes plateau bay of biscay north atlantic marine geology 182 279 302

the two dimensional dynamics of west african squall lines the two dimensional dynamics of multicell and unicell squall lines are examined using a numerical model both types feature a convective jump updraught with extensive deep rearward extending anvils the multicell case contains travelling convection cells and is unsteady but persistent whereas the unicell case is quasi steady in the multicell case an extensive density current is produced by the evaporation and drag of rain falling from a succession of convection cells which travel rearwards relative to the density current head the circulation within the density current is complex and consists of three mutually interactive branches a rotor a cold downdraught and a subsidence region in the unicell case a density current is not produced and the updraught is forced by a propagating wave of elevation generated as an interaction between the updraught water loading and evaporation in a very localized area the squall line structure is compared with other models and it is shown that certain propagating two dimensional tropical and mid latitude squall lines are dynamically similar their detailed structure being controlled by the inflow wind profile the multicell case is compared with a quasi two dimensional west african squall line which occurred on 22 june 1981 during the convection profonde tropicale copt 81 experiment performed in the northern part of the ivory coast good agreement is found between the model and the observations and hence the dynamics of the observed squall line is quantified the unicell case in which a density current and conventional downdraughts are absent has yet to be identified in atmospheric observations

electrically conductive crust in southern tibet from indepth magnetotelluric surveying the crust north of the himalaya is generally electrically conductive below depths of 10 to 20 km this conductive zone approaches the surface beneath the kangmar dome dipping north and extends beneath the zangbo suture a profile crossing the northern yadong gulu rift shows that the high conductivity region extends outside the rift and its top within the rift coincides with a bright spot horizon imaged on the indepth cmp common midpoint profiles the high conductivity of the middle crust is atypical of stable continental regions and suggests that there is a regionally interconnected fluid phase in the crust of the region

electromagnetic study of the active continental margin in northern chile magnetotelluric and geomagnetic deep sounding measurements were carried out in the magmatic arc and forearc regions of northern chile between 19 5 and 22 s to study the electrical conductivity structures of this active continental margin the instruments used covered a very broad period range from 10 4 s to approx 2 104 s and thus enabled a resolution of deep as well as shallow structures in this paper we focus on the interpretation of data from an east west profile crossing chile from the pacific coast to the western cordillera at 20 5 s a decomposition of the impedance tensors using the groom bailey decomposition scheme shows that a two dimensional interpretation is possible the resulting regional strike direction is n9 w two dimensional models were calculated in this coordinate frame and include the significant bathymetry of the trench as well as the topography of the andes the final model shows a generally high resistivity in the forearc and a very good conductor below the precordillera unlike earlier models from areas further south a good conductor is not observed below the magmatic arc itself this correlates with the so called pica gap in the volcanic chain and a higher age of volcanic activity compared with adjacent areas

the influence of dunes on mixing in a migrating salt wedge fraser river estuary canada dune bedforms and salt wedge intrusions are common features in many estuaries with sand beds and yet little is known about the interactions between the two flow visualization with an echosounder and velocity measurements with an acoustic doppler current profiler over areas of flat bed and sand dunes in the highly stratified fraser river estuary canada were used to examine the effect of dunes on interfacial mixing as the salt wedge migrates upstream over the flat bed mixing is restricted to the lower portion of the water column however as the salt wedge migrates into the dune field from the flat bed there is a dramatic change in the flow and large internal in phase waves develop over each of the larger dunes with water from the salt wedge reaching the surface of the estuary the friction richardson number shows that bed friction is more important in interfacial mixing over the dunes than over the flat bed and a plot of internal froude number versus obstacle dune height shows that the salt wedge flow over the dunes is mainly supercritical such bedforms can be expected to cause similar effects in interfacial mixing in other estuaries and sediment laden density currents and may thus be influential in fluid mixing and sediment transport copyright 2010 john wiley sons ltd

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

an ensemble of convective systems on 11 february 1993 during toga coare morphology rainfall characteristics and anvil cloud interactions abstract an active day during the coupled ocean atmosphere response experiment coare intensive observation period iop is examined in which nine convective systems evolved and moved eastward across the region of shipboard radar coverage in the intensive flux array ifa within westerly wind burst conditions the detailed genesis morphology and interactions between these cloud systems are documented from a radar and satellite perspective one of these systems was a large and complex elliptical cluster among the largest observed during the tropical ocean global atmosphere coare multiple parallel deep convective lines spaced 20 30 km apart and embedded within this system were initially oriented from north northwest to south southeast oblique to the storm motion furthermore the lines underwent counterclockwise realignment as the system moved eastward the influence of strong lower tropospheric directional and speed shear on these convective system properties is examined in the context of a dynamic

radar characteristics of continental coastal and maritime convection observed during amma namma ground based radar observations at three distinct geographical locations in west africa along a common latitudinal band niamey niger continental kawsara senegal coastal and praia republic of cape verde maritime are analyzed to determine convective system characteristics in each domain during a 29 day period in 2006 ancillary datasets provided by the african monsoon multidisciplinary analyses amma and nasa amma namma field campaigns are also used to place the radar observations in context results show that the total precipitation is dominated by propagating mesoscale convective systems convective characteristics vary according to environmental properties such as vertical shear cape and the degree of synoptic forcing data are bifurcated based on the presence or absence of african easterly waves in general african easterly waves appear to enhance mesoscale convective system strength characteristics e g total precipitation and vertical reflectivity profiles at the inland and maritime sites the wave regime also resulted in an increased population of the largest observed mesoscale convective systems observed near the coast which led to an increase in stratiform precipitation despite this increase differentiation of convective strength characteristics was less obvious between wave and no wave regimes at the coast owing to the propagating nature of these advecting mesoscale convective systems interaction with the regional thermodynamic and dynamic environment appears to result in more variability than enhancements due to the wave regime independent of location copyright c 2011

numerical models on the influence of partial melt on elastic anelastic and electrical properties of rocks part ii electrical conductivity abstract partial melting influences both the elastic and electrical properties of mantle rocks significantly but in a different manner a set of theoretical models of the electrical conductivity of partially molten rocks is developed for different geometries of the melt distribution the models correspond to a similar set on elasticity and anelasticity presented in a preceding paper part i both model sets allow combined interpretations of seismic and geoelectric observations from anomalous hot mantle regions by a systematic variation of the melt geometry the following melt geometries are assumed in the conductivity models melt films tubes isolated ellipsoidal inclusions films and ellipsoidal inclusions with a variable degree of interconnection distributed geometries and superpositions of spheres with films and with tubes unexplored conduction mechanisms near the melting temperature film thicknesses of molecular sizes or effects of volatiles are not considered resistor network theory is utilized to account for a variable degree of interconnection and distributed geometries thereby a new possible interpretation of archie s law is found in terms of varying interconnection furthermore it is found that a reduced degree of interconnection may have an important influence on the conductivity at melt fractions characteristic for a weak to moderate decrease in seismic velocity the model results are compiled together with the elastic models of part i in a set of diagrams which may be applied systematically to observed electrical and seismic data to find constraints on the state of melting

the 11 august 2006 squall line system as observed from mit doppler radar during the amma sop on the evening of 9 august 2006 a mesoscale convective system mcs having a north south oriented squall line organization formed over the border between chad and nigeria it propagated westward intensified over nigeria on 10 august and reached niamey niger at 0320 utc on 11 august its passage over niamey was accompanied by dust lifting and was well tracked by the massachusetts institute of technology mit doppler radar the three dimensional structure of the airflow and precipitation pattern is investigated from regular radar volume scans performed every ten minutes between 0200 and 0321 utc the 3d wind components are deduced from the multiple doppler synthesis and continuity adjustment technique muscat applied to a set of three volume scans obtained over a time period of one hour which are equivalent to a three radar observation of the squall line when considering a reference frame moving with the system and the hypothesis of a stationary field results of the wind synthesis reveal several features commonly observed in tropical squall lines such as the deep convective cells in front of the system fed by the monsoon air and extending up to 15 km altitude and the well marked stratiform rain region at the rear associated with mesoscale vertical motions forward and trailing anvils are clearly identified as resulting from the outflow of air reaching the tropopause and transported to this level by the sloping convective updraughts occurring in a sheared environment in the northern part a deeper and stronger front to rear flow at mid levels is found to contribute to the rearward deflection of the leading line and to promote a broader over 300 km stratiform cloud region eddy vertical transports of the cross line momentum mainly accounts for the mid level flow acceleration due to a momentum redistribution from low to higher levels the height distribution of hydrometeors and their associated production terms derived from a one dimensional microphysical retrieval model indicate the distinct roles of the convective and stratiform regions in the formation of graupel and rain and the respective contributions of cold riming and warm coalescence melting processes cooling from melting and heating cooling from condensation evaporation processes yield a net decrease and increase of the potential temperature at low and mid to upper levels respectively with respect to an environmental thermodynamic profile taken three hours ahead of the analysis finally the upper level rearward flow could convey the non negligible proportion of ice particles farther from the leading deep convection to the trailing stratiform region thereby favouring the extent of this region

new high resolution acoustic data from the braided system of the orinoco deep sea fan abstract the interpretation of approximately 100 km of em12 multibeam bathymetry and backscatter data together with high resolution topas profiles obtained during a transit over the orinoco deep sea fan near the barbados accretionary prism shows that the braided drainage pattern seen on gloria images by belderson et al 1984 corresponds to wide 10 km low relief

the oceanic mesoscale convective system and associated mesovortex observed 12 december 1992 during toga coare this study documents the precipitation and kinematic structure of a mature mature to decaying westward propagating near equatorial oceanic mesoscale convective system mcs observed by airborne doppler radars during toga coare the tropical ocean global atmosphere coupled ocean atmosphere response experiment this system occurred on 12 december 1992 during the convectively active phase of an intraseasonal oscillation and was followed at its dissipating stage by a redevelopment of convection that led to the mcs observed on 13 december 1992 these two successive mcss were associated with a two day atmospheric disturbance radar deduced airflows at two time periods reveal many similarities with other tropical oceanic cloud clusters in particular a marked rear inflow jet associated with a midlevel cyclonic mesovortex was observed within the rear of the stratiform region the mesovortex was better defined both in size and depth during the mature to decaying stage and was located more inside the system within a region of convergence due to the westward propagation of the rear inflow countergradient transports of momentum normal to the mean orientation of the system at midlevels and downgradient transports at lower and higher levels helped to intensify this rear inflow these transports were mostly accomplished by eddy structures cyclonic vorticity was concentrated at the rear of the mcs and peaked at the centre of the observed closed wind circulation as previously observed stretching of the pre existing vertical vorticity was the dominant dynamical mechanism which helped to amplify the mesovortex at mid to upper levels while tilting of the horizontal vorticity into the vertical was a lesser mechanism and had an opposite effect in most respects advective processes were negatively correlated with the stretching and tilting mechanisms but not sufficiently to be balanced the resulting tendency was an increase of cyclonic vorticity at low to mid levels and a net decrease above

large scale sediment waves and scours on the modern seafloor and their implications for the prevalence of supercritical flows large scale 20 m to 7 km wavelength bedforms are common on the seafloor yet there is a lack of consensus on how they form and thus what to call them we conducted statistical analysis on a dataset of 82 seafloor bedforms that span a range of water depths and environments the data form three distinct groups 1 small scale 20 300 m wavelength sediment waves with mixed relief made of medium sand to cobble sized sediment that form in confined settings which we call small sediment waves 2 large scale 300 7000 m wavelength sediment waves with mixed relief made of fine grained sediment that form in relatively unconfined settings which we call large sediment waves and 3 large scale fully enclosed depressions in the seafloor which we call scours there is a statistically significant data gap in the size of bedforms between small sediment waves and large sediment waves that does not appear to be a sampling artefact this data gap probably results from the environments in which sediment waves form being either confined e g channel or canyon or unconfined e g open slope bedform migration direction is available for 36 of the data and includes small and large scale sediment waves of these examples all are shown to migrate up current up current migration is indicative of supercritical flow thus this data suggests that supercritical flows operate in a wide range of environments and can generate both small and large sediment waves therefore we suggest that small and large sediment waves form by similar processes despite the gap in bedform wavelength and sediment size the migration direction for scours remains unknown scours may form from similar processes to small and large sediment waves or alternatively they may be a completely separate bedform type that form when erosive flows exploit pre existing defects in the seafloor this novel statistical analysis of a global database shows that up current migrating bedforms associated with supercritical flow are unusually widespread and are recognised at two distinct scales

quaternary sedimentation and origin of the orinoco sediment wave field on the demerara continental rise ne margin of south america abstract new core data from a sediment wave field on the demerara outer ridge show that the waves are mainly built from turbidity currents that flow northwards down the demerara margin the contour currents circulating parallel and obliquely to the margin are apparently not as important to wave formation as previously proposed detailed analysis of the sedimentary facies of cores taken on the crest and flank of a sediment wave indicates that fine grained turbiditic deposits are dominant hemipelagic pelagic deposits are interbedded with the turbidites sediment redistribution by contour currents was only evidenced by the presence of peculiar clay mineral assemblages and microfaunal associations as well as some sedimentary structures such as truncations and cross bedding the turbiditic processes were active during the last glacial in contrast the holocene is characterised by pelagic sedimentation a combination of seismic and core data suggests that the sediment waves result from predominantly turbiditic depositional processes interacting with minor contour currents and synsedimentary deformation processes

upper slope to shelf edge delta architecture miocene cruse formation orinoco shelf margin trinidad trinidad is an uplifted segment of the neogene orinoco shelf created largely by the paleo orinoco river and delta the atlantic facing shelf margin sediment prism has an internal clinoform architecture with both sandy marine and nonmarine topsets and muddy deepwater slope deposits that contain turbidite channels and collapsed shelf edge blocks the shelf prism is 10 km thick and 200 km wide at present built from late miocene to present the shelf margin had an irregularly rising trajectory towards the atlantic with very thick topset aggradation and rapid progradation of the fronting deepwater slope the 18 33 km my progradation rate for the shelf margin with exceptionally high shelf subsidence rates up to 1000 m my documents a high sediment supply despite very high shelf subsidence and strongly suggests prominent sand bypass from shelf into deepwater areas for much of the neogene interval the early proximal onshore south trinidad part of this sediment prism the late miocene and early pliocene cruse formation irregularly outcrops for tens of kilometers along southern trinidad in a disrupted but near downdip shelf to basin direction from west to east this distribution allows the late miocene shelf break position in the paleo columbus channel to be identified in the outcrops separating a western shelf and shelf edge delta segment from an eastern highly deformed segment with very large house size blocks of shallow water facies collapsed from the shelf edge that are disoriented and embedded in deformed slope mudstones these eastward distorted outcrops are interpreted as within the headward reaches of a columbus canyon system otherwise known from seismic interpretation offshore in the columbus channel in this eastward outcrop area below the shelf edge the facies are mainly large shelf edge collapse mass transport blocks as well as in situ turbidite filled slope channels thin bedded turbidites debrites and abundant slope mudstones most of the sandstone blocks and associated chaotic beds contain highly deformed parallel laminated and hummocky cross strata betraying their former shelf location landward of the identified shelf edge location there are stacked parasequences each 3 15 m thick of undeformed upward coarsening shelf edge delta deposits in places sharply truncating erosional truncation the slope mudstones and mass transport deposits the significant downcutting of most of the topset orinoco channels their position so close to the shelf edge as well as the generally erosional contact between base of topsets and underlying slope mudstones suggests that the topset deltas were forced regressive probably driven across the shelf by falling relative sea level despite high subsidence rates at this time the outcropping facies architectures both vertically and laterally from shelf to deepwater slope generate a hypothesis that the early paleo orinoco shelf margin grew by an alternation of upward and basinward growing clinoforms particularly marked is the earliest pliocene period of marked forced regression of the orinoco delta possibly when short periods of icehouse eustatic sea level fall outpaced subsidence rate this lesson from the outcrop area is used to further understand the flat rise flat rise shelf edge trajectory pattern that persisted throughout the neogene margin development as seen on seismic lines across the columbus basin

test of a convective wake parameterization in the single column version of ccm3 abstract a convective wake parameterization incorporated into the single column scm version of the ncar community climate model ccm3 is tested using observational data from 12 squall line cases to determine whether it can successfully reproduce convectively driven wakes in a global climate model the key spatial thermodynamic and kinematic properties of the modeled versus the observed wakes are examined as these features determine the effects of the wakes on surface fluxes and the initiation of convection effects that should be simulated correctly in general circulation models if deep convection and the resulting earth atmosphere energy exchanges are to be adequately represented results from these simulations indicate that while the scm convective wake scheme combination generally produced long lasting squall wake systems the wakes were often too shallow too warm and too moist these differences occurred despite the ability of ccm3 s standard cumulus parameterization to provide the wake scheme

upscale effects of deep convection during the north american monsoon abstractthe ability of deep monsoon convection to influence the larger scale circulation over north america is investigated for a 6 day long case study during the 2006 north american monsoon results from rossby wave ray tracing and numerical simulations using the advanced research weather research and forecasting model indicate that north american monsoon convection provides a source region for stationary rossby waves two wave trains are seen in the numerical model simulations with behaviors that agree well with expectations from theory and ray tracing the shorter and faster moving wave train moves eastward from the source region in mexico and reaches the western atlantic within 4 days the longer and slower moving wave train travels northeastward and reaches the coastal new england region within 6 days an upstream tail of anticyclonic vorticity extends westward from the source region into the central pacific ocean the monsoon convection appears to help cut off the low level anticyclonic flow by deve

bedforms on the submarine flanks of insular volcanoes new insights gained from high resolution seafloor surveys a comparative analysis of bedform fields along the submarine flanks of insular volcanoes characterized by different morpho structural settings volcanic and meteo marine regimes vanuatu kermadec bismark madeira and aeolian archipelagos is presented here to provide insights on the size distribution morpho dynamic and genesis of such bedforms two main types of bedforms are recognized according to their size location and preconditioning triggering processes small scale bedforms have wavelengths of tens to hundreds of metres and wave heights of metres because of their small size they are typically not recognizable at water depths greater than 400 m from vessel mounted bathymetric surveys however few examples of small scale bedforms are reported from upper volcanic flanks where steep gradients commonly hinder their formation their recognition is mostly limited to the thalweg of shallow and flat bottomed channels that carve the insular shelf on slope gradients 15 small scale bedforms are mostly related to erosional depositional processes due to sedimentary gravity flows that are often the result of a cascading effect between volcanic and non volcanic processes for example flood discharges and retrogressive landslides large scale bedforms occur at all water depths having wavelengths of hundreds thousands of metres and wave heights up to few hundreds of metres the origin of large bedforms is more difficult to ascertain especially if only bathymetric data are available some diagnostic criteria are presented to distinguish between bedforms associated with landslide deposits and those associated with density currents in this latter case relevant sediment sources and slope gradients 8 are key factors for bedform development erosional depositional bedforms are typically related to eruption fed density flows formed during large caldera collapses or to large turbidity flows bedforms generated by turbidity flows are often observed in the lower volcanic flanks where an abrupt decrease of gradients is present often matching a change from confined to unconfined settings in summary this study provides insights to interpret bedforms in modern and ancient marine volcaniclastic settings elsewhere

turbidity current sediment waves on the submarine slopes of the western canary islands two sediment wave fields have been identified on the flanks of the western canary islands of la palma and el hierro using a high quality 2 d and 3 d dataset that includes geosea and tobi imagery 3 5 khz profiles and short sediment cores the la palma sediment wave field covers some 20 000 km2 of the continental slope and rise and consists of sediment waves with wave heights of up to 70 m and wavelengths of up to 2 4 km the wave crestlines have a complex morphology with common bifurcation and a clear sinuosity waves have migrated upslope through time cores recovered from the wave field contain volcaniclastic turbidites interbedded with pelagic hemipelagic layers the wave field is interpreted as having formed beneath unconfined turbidity currents a simple previously published two layer model is applied to the waves revealing that they formed beneath turbidity currents flowing at 10 100 cm s 1 with a flow thickness of 60 400 m and a sediment concentration of 26 427 mg l the el julan sediment wave field lies within a turbidity current channel on the southwest flank of el hierro the sediment waves display wave heights of about 6 m and wavelengths of up to 1 2 km the waves are migrating upslope and migration is most rapid in the centre of the channel where the flow velocity is highest this wave field has been formed by channelised turbidity currents originating on the flanks of el hierro

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

deepwater sedimentation and cenozoic deformation in the southern new caledonia trough northern zealandia sw pacific abstract the new caledonia trough nct is a 2000 3000 m deep bathymetric feature that extends 2500 km from taranaki new zealand to the western margin of new caledonia northern zealandia sw pacific the underlying sedimentary basin originates from cretaceous extension but underwent a significant eocene tectonic event that shaped its present physiography we present an analysis of the basin based on multibeam data seismic profiles and rock samples collected on the tan1312 and tan1409 expeditions onboard r v tangaroa combined with legacy data we focus on the southern part of the basin where new data reveal a link between compressive deformation of paleocene strata and their potential reworking into the basin on the western basin side upper cretaceous to paleocene strata were deformed by local reverse faults and folds that created a sub circular bathymetric ridge and seabed exposure this folded unit seismic unit 2 is sharply overlain by a restricted interval imaged as chaotic high amplitude reflections that are interpreted as syntectonic mass transport deposits due to slope oversteepening seismic unit 1b this unit is stratigraphically below the main basin onlap surface and seismic mapping revealed that it rapidly thins away from the mouth of a present day submarine canyon imaged on the western slope of the basin and that is diverted by exposures of unit 2 deformed strata deformed and syntectonic intervals are in turn overlain by a flat lying unit seismic unit 1a we interpret as reflecting a passive basin fill our new data provide insight into an extensive deep water basin that is remote from terrigenous sediment sources and new constraints on its cenozoic tectonic history stratigraphic ages are constrained by seismic ties to taranaki basin petroleum wells and biostratigraphic dating of dredged samples this specific site has particular significance for understanding tectonic events in the southwest pacific indeed our observations show that deformation is younger than the paleocene and is envisaged to be a local expression of a widespread cenozoic compressive event called tecta tectonic event of the cenozoic in the tasman area which affected the region after the mesozoic rifting on a regional perspective this study provides new insights on the evolution of the submerged zealandia continent and associated geodynamic processes such as gondwana break up and initiation of the tonga kermadec subduction

mechanisms for the generation of mesoscale vorticity features in tropical cyclone rainbands a high resolution tropical cyclone model with explicit cloud microphysics has been used to investigate the dynamics and energetics of tropical cyclone rainbands analysis of the vorticity interactions that occur within the simulated rainbands demonstrates that couplets of cyclonic anticyclonic mesovortices can be produced in outer bands the primary source of this vorticity is the upward tilting of system generated horizontal vorticity by diabatic heating gradients the vertical heating gradient in the stratiform cloud also creates a potential vorticity pv dipole that accelerates the tangential flow and develops a midlevel jet the strength of the jet is enhanced by the vortex pair that is oriented radially across the rainband the fourier decomposition of the absolute vorticity field shows two counterpropagating vortex rossby waves associated with the rainband the wave located on the inner side of the band transports energy toward the vortex center the outer wave is made up of high wavenumbers and uses the vorticity gradients generated by the rainband the results support the hypothesis that the heating profile in the stratiform regions of rainbands generates cyclonic pv across the freezing level which develops a midlevel jet this mechanism creates a vorticity gradient that enables the propagation of vortex rossby waves that could allow the rainbands to interact with the mean flow and potentially influence the evolution of the storm by contributing to the symmetric component of vorticity and the development of secondary eyewalls

electrical properties of granite with implications for the lower crust the electrical properties of granite appear to be dominantly controlled by the amount of free water in the granite and by temperature minor contributions to the electrical properties are provided by hydrostatic and lithostatic pressure structurally bound water oxygen fugacity and other parameters the effect of sulfur fugacity may be important but is experimentally unconfirmed in addition to changing the magnitude of electrical properties the amount and chemistry of water in granite significantly changes the temperature dependence of the electrical properties with increasing temperature changes in water content retain large but lessened effects on electrical properties near room temperature a monolayer of water will decrease the electrical resistivity by an order of magnitude several weight percent water may decrease the electrical resistivity by as much as 9 orders of magnitude and decrease the thermal activation energy by a factor of 5 at elevated temperatures just below granitic melting a few weight percent water may still decrease the resistivity by as much as 3 orders of magnitude and the activation energy by a factor of 2 above the melting temperature 650 to 1100 c depending upon water pressure a few weight percent water will decrease the resistivity by less than an order of magnitude and will barely change the activation energy remarkably the few weight percent water must be present as free water experiments with hydrated hornblende schist with structural water indicate an electrical resistivity very similar to that for dry granite the implications of these results together with the findings of deep magnetic sounding and magnetotelluric surveys suggest much more free water than is commonly associated with the lower crust and possibly into the upper mantle

3d seismic analysis of the west shetland drift system implications for late neogene palaeoceanography of the ne atlantic abstract detailed seismic stratigraphic analysis of the west shetland drift located on the shetland margin of the faeroe shetland channel has been undertaken using commercial 3d seismic data emphasis was placed on the interpretation of a significant plastered contourite drift body the west shetland drift slope section with the aim of reconstructing the palaeoceanographic regime of the west shetland slope during the past 5 ma although limited in areal extent the west shetland drift slope section provides a key record of the depositional environment and bottom current activity on the west shetland slope during the late neogene the drift body was divided into three seismic stratigraphic units and depositional processes responsible for each unit were interpreted resulting in proposal of an evolutionary model in which a mixed downslope alongslope depositional system was succeeded by alongslope current derived contourite drift deposition during the early pliocene to mid pleistocene during this time sw flowing alongslope currents impinged upon the west shetland slope between the basin floor and a mid to upper slope position the final stage of deposition consisted of slope wedge progradation associated with mid to late pleistocene glaciation contourite deposition on the west shetland slope was punctuated by periods of glaciation activity during which alongslope current activity appears to have been disrupted suggesting a link between alongslope current activity and glaciation detailed mapping of key smaller scale features including a spectacular bottom current sediment wave field and iceberg ploughmarks both of which were identified for the first time during this study was instrumental in constraining the palaeocurrent regime and would not have been possible without the high spatial resolution of the 3d seismic data this study therefore highlights the efficacy of 3d seismic data as a tool for large scale spatial and temporal analysis of contourite drifts palaeoceanographic research

a model for the growth of mudwaves in the presence of time varying currents abstract mudwaves are produced in a model when a periodic current produces lee waves that alter the deposition erosion rates of sediment at the bottom of an ocean a technique analogous to using a lagrangian representation for calculating the velocity perturbations associated with these lee waves is determined and then applied to a situation typical of one observed in the argentine basin the fact that the imposed current is variable results in the perturbation velocities also being time dependent with two major time scales one of these time scales is the period of the variable current which is taken to be on the order of weeks this is consistent with the dominant periods indicated in the data the other time scale is on the order of a day or two and is associated with the time required for the time dependent part of the imposed current total current minus its time averaged part to cross a ridge waves on this time scale are excited when the imposed current passes through a value that changes the character of the lee waves from vertically propagating to bottom trapped or vice versa the long term erosion deposition and mudwave growth rates are insensitive to the details of these shorter time scale variations

baroclinicity influences on storm divergence and stratiform rain subtropical upper level disturbances abstract divergence structures associated with the spectrum of precipitating systems in the subtropics and midlatitudes are not well documented a mesoscale model is used to quantify the relative importance different baroclinic environments have on divergence profiles for storms primarily caused by upper level disturbances in southeastern texas a subtropical region the divergence profiles simulated for a subset of the modeled storms are consistent with those calculated from an s band doppler radar realistic convective and stratiform divergence signals are also generated when applying a two dimensional convective stratiform separation algorithm to reflectivities derived from the mesoscale model although the model appears to underestimate stratiform rain area divergence profiles from the modeled precipitating systems vary in magnitude and structure across the wide range of baroclinicities common in southeastern texas barotropic storms more characteristic of the tropics generate the most elevated diver

numerical study of a sahelian synoptic weather system initiation and mature stages of convection and its interactions with the large scale dynamics summary a 24 h multi scale simulation of the life cycle of a sahelian squall line is presented the initial and coupling e elds have been taken from the european centre for medium range weather forecasts re analysis era 15 after humidity corrections to avoid spurious absolute and conditional convective instabilities comparisons of modelsynthetic and meteosat infra red radiances indicate that the simulated scenario of convection development and structure are realistic though differences are found concerning the size of the squall line with a delay of 2 3 h the simulated arc shaped structure and surface signature e t well with radar and ground station observations respectively the mature stage of the simulated squall line presents a cross line structure similar to conceptual models an intense rear to front e ow is generated below the trailing stratiform part an acceleration of the african easterly jet aej is simulated behind the system occurring across its full width this leads to the generation of a dipole of counter rotating vortices the resulting potential vorticity signature leads to local reinforcement of the barotropic instability on the north e ank of the aej this simulation is used to analyse the impact of the convection at synoptic scales and to compare it with era 15 it suggests that the convection contributes to reinforce the monsoon at least up to 500 km the monsoon ine ow moves eastward and westward with time scales shorter and longer than 24 h respectively the tropical easterly jet intensie es to the south west of the convection area up to 700 km away the aej is strongly intensie ed ahead of the trough where active convection occurs organized convection developing in the vicinity of the aej core induces weakening of the aej ahead of the squall line and strengthening behind it a common result in the simulation and in era 15 is that the aej core moves westward faster due to the convective activity

the role of environmental shear and thermodynamic conditions in determining the structure and evolution of mesoscale convective systems during toga coare abstract a collection of case studies is used to elucidate the influence of environmental soundings on the structure and evolution of the convection in the mesoscale convective systems sampled by the turboprop aircraft in the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare the soundings were constructed primarily from aircraft data below 5 6 km and primarily from radiosonde data at higher altitudes the well documented role of the vertical shear of the horizontal wind in determining the mesoscale structure of tropical convection is confirmed and extended as noted by earlier investigators nearly all convective bands occurring in environments with appreciable shear below a low level wind maximum are oriented nearly normal to the shear beneath the wind maximum and propagate in the direction of the low level shear at a speed close to the wind maximum when there is appreciable shear at middle levels 800 400 mb convective bands form parallel to the shear with

a real time automated convective and stratiform precipitation segregation algorithm in native radar coordinates a new convective stratiform c s precipitation segregation algorithm was developed for applications with single radar volume scan data and in its native spherical coordinates the new algorithm consists of two parts the first is to find convective rainfall cores based on physical characteristics of different rainfall types and the second is to delineate the full convective area through seeded region growing the new scheme takes into account radar sampling characteristics and a variety of precipitation scenarios where the c s delineation was relatively challenging the new c s delineation scheme has two impacts on radar quantitative precipitation estimation qpe i correctly separate convective and stratiform regions such that appropriate ze r relationships can be applied ii correctly define the stratiform area such that a vertical profile of reflectivity vpr correction can be applied the vpr correction is very important to reduce overestimation errors in radar qpes associated with bright band the new algorithm was tested on many events and showed improved performance over previous schemes especially when handling strong bright band and melting graupels in stratiform precipitation the new scheme was also tested in radar quantitative precipitation estimation qpe and it consistently reduced the root mean square error and mean absolute bias in the radar qpe when compared with gauges

turbidity current sediment waves on irregular slopes observations from the orinoco sediment wave field abstract the orinoco sediment wave field covers an area of at least 29 000 km2 on the southern margin of the orinoco valley at a water depth of 4400 4825 m wave dimensions are highly variable across the wave field with wavelengths of 110 2600 m and wave heights of 1 15 m slope gradients are also very variable with values of 0 14 0 48 overall the sedimentary sequence on the upslope wave flanks is about 40 thicker than that on the downslope flanks leading to upslope wave migration in the manner of antidunes in addition reflectors on the upslope flanks generally display higher reflectivity than those on the downslope flanks suggesting that a higher proportion of coarser sediment occurs on the upslope flank an unconfined turbidity current origin is proposed for the orinoco sediment waves based upon detailed analysis of regional stratigraphic seismic facies and sediment wave distribution morphology and dimensions sediment waves are not related to flows passing along or spilling out of the orinoco valley or to bottom currents flowing parallel to the slope turbidity currents responsible for wave generation are interpreted as originating from slope failures on the adjacent venezuela guyana and suriname continental margins simple numerical modelling has enabled turbidity current flow characteristics across the orinoco sediment waves to be estimated internal froude number 0 7 1 1 flow thickness 24 645 m and flow velocity 31 82 cm s 1 a key finding of this study is that there appears to be a close relationship between the changes in slope gradient and those in wave dimensions across the wave field the irregular gradient of the present day wave field is partly a reflection of the irregular bounding surface of the sediment waves which is represented by mass flow deposits and associated mud diapirs the changes in slope gradient along this lower boundary lead to variations in the flow thickness and flow velocity of passing turbidity currents which in turn control the wave dimensions generally on lower gradients beyond minor breaks of slope flow thickness increases and flow velocity decreases leading to an increase in wavelength and a decrease in height

a braided distributary system on the orinoco deep sea fan abstract a long range side scan sonar gloria survey has been made of part of the orinoco deep sea fan that abuts against the deformation front of the barbados outer ridge i e in a pre orogenic setting immediately east of the deformation front sinuous channels up to 65 m deep and 3 km wide extend downslope and become very shallow a few metres or less deep and branch into a pattern that resembles stream braiding near the foot of the slope here there is a possible suprafan lobe and an almost flat perched sediment pond dammed by a buried basement ridge in this locality many of the acoustic contrasts on the sonographs are primarily due to differences in sediment type and small scale roughness rather than to variations in slope angle possible debris flows aligned along some of the braided channels have been identified from high resolution profiles this braided system of shallow channels then converges into a single channel that overtops the dam because of their braided nature the internal structure of the resulting deposits is likely to be complex these deposits should eventually be incorporated into the barbados ridge complex in contrast to this pre orogenic setting gloria sonographs also suggest that some orinoco sediment moves down along synclinical axes of folds on the barbados ridge complex i e in a syn orogenic setting

genesis of typhoon chanchu 2006 from a westerly wind burst associated with the mjo part ii roles of deep convection in tropical transition abstractin this study the life cycles of a series of four major mesoscale convective systems mcss during genesis and their roles in transforming a vertically tilted vortex associated with a westerly wind burst hereafter the wwb vortex into typhoon chanchu 2006 are examined using 11 day cloud resolving simulations presented in part i it is found that the tilted wwb vortex at early stages is characterized by an elevated cold core layer about 200 hpa thick below and a weak warm column above with large vertical wind shear across the layer which extends over a horizontal distance of about 450 km between the vortex s 400 and 900 hpa centers during the final two days of the genesis process the upper level warm column increases in depth and intensity as a result of the absorption of convectively generated vortices cgvs including a mesoscale convective vortex mcv causing more rapid amplification of cyclonic vorticity in the middle than the lower troposphere the commencement of sustained intens

middle miocene mound shaped sediment packages on the slope of the xisha carbonate platforms south china sea combined result of gravity flow and bottom current deep water mound shaped sediment packages on the northern slope of the xisha carbonate platforms in the northern south china sea were analyzed by integrating high resolution multi channel seismic and drilling data the mounds are distributed in the beijiao depression of the qiongdongnan basin within the t41 t40 seismic horizons which correspond to the middle miocene mound shaped reflections were identified both in the ne sw and nw se oriented seismic profiles the mound shapes are most prominent in the center of the nw se oriented seismic profiles and the undulating tops flatten out towards the nw and se similar reflections are mostly asymmetric with steeper eastern flanks in the ne sw oriented seismic profiles and they are mostly round in shape the wave impedance from the inversion calculation is 6 8 x 10 6 kg m 2 s it is much lower than that of the reef reservoir in the lh11 1 reef oilfield paleogeographic analysis shows that the xisha uplift was dominated by tropical shallow carbonate platforms while the beijiao depression became a bathyal environment in the middle miocene drilling data confirmed that the mound shaped sediment packages are mainly composed of calcareous mudstone therefore we infer that the mound shaped sediment packages could be reef complexes or they were presumably built by combined gravity flow and bottom current c 2015 elsevier ltd all rights reserved

the tributary valley systems of the almeria canyon alboran sea sw mediterranean sedimentary architecture three tributary valley systems of the almeria canyon dalias andarax and gata located on the almeria margin alboran sea sw mediterranean were studied using high resolution techniques including swath bathymetry and topas seismic reflection profiles a detailed morphological and seismic stratigraphy study shows that the tributary valley systems tvs are formed by two types of valleys gullies and leveed channels dalias tvs is the best developed system covering an area of more than 300 km 2 from the shelf edge off cabo de dalias to the almeria canyon 100 1500 m depth andarax tvs covers about 65 km 2 from the shelf off the andarax river mouth to the westernmost branch of the almeria canyon 40 300 m depth gata tvs covers more than 100 km 2 from the shelf edge off cabo de gata to the almeria canyon 200 650 m depth tributary valley systems can be divided into two models based on the detailed morpho seismic study the sea level controlled model and the sediment supply controlled model the sea level controlled model includes the dalias and gata tvs this model is mainly governed by sea level fluctuations and the valleys grow as a result of the activity of turbidity currents and hemipelagic sedimentation displaying a retrogressive upslope pattern the valleys development would have been favoured by glacio eustatic oscillations during the late quaternary a tentative chronostratigraphic correlation has been made relating the evolution of dalias and gata tvs with the marine isotopic stages and sea level curves tectonics and margin physiography play a secondary role in the development of this type of valley the sediment supply controlled model is applicable to the andarax tvs the growth of the valleys is controlled by the ephemeral sediment discharges from the andarax river the valleys are small scale gullies located on the shelf and slope which would grow as a result of the turbidity currents which channel the fluvial sediment supplied in form of hyperpycnal currents this model would have been developed during the last highstand of sea level once the coast line reached its present situation d 2005 elsevier b v all rights reserved

electrical conductivity of molten basalt and andesite to 25 kilobars pressure geophysical significance and implications for charge transport and melt structure electrical conductivities of molten hawaiian tholeiite and crater lake andesite were measured between 1200 c and 1400 c at atmospheric pressure and at pressures up to 17and 25 kbar respectively isobaric plots of log versus 1 t is electrical conductivity are linear with the exception of the zero pressure tholeiite melt data conductivities decrease with increasing pressure in both melts with the andesitic melt exhibiting a greater pressure dependence between 5 and 10 kbar abrupt decreases in the slopes of isothermal log versus p plots i e decreases in activation volume are observed for both rock melts this discontinuity probably reflects changes in melt structure as opposed to changes in conduction mechanism in each pressure range the data for each rock melt can be described reasonably well by an equation of the form 0 exp ea p v kt where 0 is a preexponential constant ea is the activation energy and v is the activation volume a qualitative model involving depolymerization of the melt with increased pressure leading to increased efficiency of packing can explain the observed discontinuity in activation volume as well as the observed pressure dependences of other melt physical properties such as viscosity and density conductivity versus melt fraction curves for partially molten peridotite are reevaluated using high pressure tholeiitic melt conductivities and crystalline conductivity values recently determined by other workers minimum melt fraction estimates of 5 10 are required to explain upper mantle regions of anomalously high electrical conductivity in terms of a partial melting hypothesis

mesoscale convection and bimodal cyclogenesis over the bay of bengal abstractmesoscale convective systems mcss are an essential component of cyclogenesis and their structure and characteristics determine the intensity and severity of associated cyclones case studies were performed by simulating tropical cyclones that formed during the pre and postmonsoon periods in 2007 and 2010 over the bay of bengal bob the pre post monsoon environment was characterized by the coupling of northwesterly southwesterly wind to the early advance southwesterly northeasterly monsoonal wind in the bob the surges of low level warm southwesterlies with clockwise rotating vertical shear in the premonsoon period and moderately cool northeasterlies with anticlockwise rotating vertical shear in the postmonsoon period transported moisture and triggered mcss within preexisting disturbances near the monsoon trough over the bob mature mcss associated with bimodal cyclone formations were quasi linear and they featured leading edge deep convection and a trailing stratiform precipitation r

incorporating diagnosed intercept parameters and the graupel category within the arps cloud analysis system for the initialization of double moment microphysics testing with a squall line over south china abstractin this study a new set of reflectivity equations are introduced into the advanced regional prediction system arps cloud analysis system this set of equations incorporates double moment microphysics information in the analysis by adopting a set of diagnostic relationships between the intercept parameters and the corresponding mass mixing ratios a reflectivity and temperature based graupel classification scheme is also implemented according to a hydrometeor identification hid diagram a squall line that occurred on 23 april 2007 over southern china containing a pronounced trailing stratiform precipitation region is used as a test case to evaluate the impacts of the enhanced cloud analysis scheme the results show that using the enhanced cloud analysis scheme is able to better capture the characteristics of the squall line in the forecast the predicted squall line exhibits a wider stratiform region and a more clearly defined transition zone between the leading convection and the trailing str

warm core formation in tropical storm humberto 2001 at 0600 utc 22 september 2001 humberto was a tropical depression with a minimum central pressure of 1010 hpa twelve hours later when the first global positioning system dropwindsondes gps sondes were jettisoned humberto s minimum central pressure was 1000 hpa and it had attained tropical storm strength thirty gps sondes radar from the wp 3d and in situ aircraft measurements are utilized to observe thermodynamic structures in humberto and their relationship to stratiform and convective elements during the early stage of the formation of an eye the analysis of tropical storm humberto offers a new view of the pre wind induced surface heat exchange pre wishe stageoftropicalcycloneevolution humbertocontainedamesoscaleconvectivevortex mcv similar to observations of other developing tropical systems the mcv advects the exhaust from deep convection in the form of an anvil cyclonically over the low level circulation center on the trailing edge of the anvilanareaofmesoscaledescentinducesdryadiabaticwarmingin thelowertroposphere thenascentwarm core at low levels causes the initial drop in pressure at the surface and acts to cap the boundary layer bl as bl air flows into the nascent eye the energy content increases until the energy is released from under the cap on the down shear side of the warm core in the form of vigorous cumulonimbi which become the nascent eyewall this series of events show one possible path in which a mesoscale convective system may evolve into a warm cored structure and intensify into a hurricane

channel related sediment waves on the eastern slope offshore dongsha islands northern south china sea abstract the characteristics and origin of the sediment waves on the eastern slope offshore dongsha islands northern south china sea scs were analyzed by integrating high resolution multibeam bathymetric seismic and piston core data four sediment wave fields were identified which are the west dongsha channel wdsw west taiwan channel wtsw south taiwan channel stsw and west penghu channel wpsw sediment wave fields respectively they are distributed on the right levees looking downstream and adjacent overbank areas of related channels wdsw wtsw and stsw or developed outside the channel mouths wpsw each sediment wave field consists of several to tens of rows of sediment waves these sediment waves are up to 2 8 7 2 km in wavelength and 30 60 m in wave height with wave crests orthogonal to or oblique to the orientation of the channels the sediment waves gradually decrease in dimension both in downslope direction and with the distance increasing away from the channel most sediment waves are asymmetric in cross sections with a thicker upslope flank and a thinner downslope flank and therefore migrate upslope piston cores suggest that sandy turbidites developed with normal size grading dominate the channels while massive muds with thin sandy or silty turbidite interbeds prevail in the inter channel regions on which the sediment waves situated the sediment waves on the channel levees and related overbank areas wdsw wtsw and stwd were presumably built by the turbidity currents overspilled from the channels while those in wpsw located outside the mouth of the west penghu channel are suggested generated by unconfined sheet like turbidity currents outside the channel mouth

airflow within major alpine river valleys under heavy rainfall summary this study documents the aire ow within major alpine river valleys in the presence of precipitation the analysis seeks a conceptual understanding of the effect of rain on the valley e ow ground based and airborne doppler radar and surface data from the mesoscale alpine programme show that during persistent rainy periods the subsidence caused by melting and evaporation of precipitation particles contributes to the formation of a down valley e ow this down valley eow opposes moist southerly e ow aloft which is lifted over the topographic barrier and in which precipitation particles are formed

vertical variability of cloud hydrometeors in the stratiform region of mesoscale convective systems and bow echoes abstract during the bow echo and mesoscale convective vortex experiment the noaa p 3 research aircraft executed 17 spiral descents to the rear of convective lines to document the vertical variability of hydrometeors above within and below the stratiform melting layer ten spirals were behind lines that exhibited bowing at some stage in their evolution although quick descents on some spirals forced sampling of different particle zones clear trends with respect to temperature were seen for 16 spirals the ambient relative humidity with respect to ice was in the range of 100 4 at temperatures between 10 c and the melting layer but exhibited steady decreases below the melting layer to an average relative humidity with respect to water of 77 15 at 9 c in contrast one spiral conducted on 29 june 2003 directly behind a developing bow echo had a relative humidity with respect to ice averaging 85 at heights above the 0 c level and relative humidity with respect to ice further decreased below the

microphysics in an oceanic mesoscale convective system during the taiwan area mesoscale experiment the microphysical processes in both the melting layer and the warm rain region of an oceanic mesoscale convective system observed during the taiwan area mesoscale experiment tamex are studied using airborne observations two flight cases are used one flown in the transitional region and the other in the stratiform region in the melting layer the particle number density decreases by an order of magnitude from the top to the bottom of the layer this is caused by the sharp increase of particle fall speed as snowflakes melt into rain the ice water content is higher in the transitional region thus cooling the environment more efficiently during melting in the warm rain region the microphysical process is dominated by coalescence process large raindrops are generated and the corresponding median diameter of all raindrops increases by a factor of 2 to 3 from the bottom of the melting layer to the ground level the breakup process is more efficient in the transitional region

the radiative budgets of a tropical mesoscale convective system during the emex step amex experiment 1 observations this paper is the first of a series of two that aim to describe the spatial and temporal variation of the radiative heating associated with tropical mesoscale convective systems mcss this paper describes the analysis of data collected in and around a tropical cloud cluster system studied as part of the equatorial mesoscale experiment emex the data analysis indicates that the cluster originated off the northern coast of australia along the midlevel monsoon trough and lasted approximately 12 hours the system moved with a velocity of about 12 m s toward the northeast and the low level surface northwesterly flow at the vicinity of the premonsoon trough area seems continuously to feed the emex 9 cloud cluster with energetic warm moist equatorial air data obtained from aircraft penetrations show features similar to tropical mcss reported elsewhere such as an area of strong to moderate convection surrounded by a broad region of stratiform precipitation radar echo bright band in the stratiform region onion type sounding behind the convective region the vertical structures of the emex 9 cloud cluster also contain two types of imbedded convection an upright vertical structure and a pronounced rearward slope approximately 17 having a vertical extent of 14 5 km and above and a horizontal scale of about 40 km the cloud base and cloud top altitude in the stratiform region are estimated to be of the order of 4 8 km and 15 to 16 km respectively the composite aircraft shortwave radiation data from the stratiform region show a significant attenuation of shortwave flux through the cloud the estimated transmission is 14 at cloud base the upward and downward solar flux profiles are almost parallel to each other in the atmosphere inside and below the cloud base suggesting very little solar heating in these regions the upward and downward infrared radiation fluxes measured in the tropical mcs also show little infrared heating above and below the cloud cluster

generation and propagation of african squall lines a study of squall lines affecting minna nigeria during 1974 1976 emphasizes two particular aspects of their dynamics that a strong jet around 650 mb is essential for their development and that the forward edge of the squall line moves slightly faster than the maximum jet speed a linear model of the squall line as a superposition of normal modes of an unstably stratified sheared flow sheds light on these observations if the flow profile has a mid level maximum constructive interference of normal modes gives rise to an expanding circle of convection with an arc front moving slightly faster than the maximum mean flow speed followed by individual cells if however shear is unidirectional there is no arc front and a line of cells is formed moving at the middle level mean flow speed these two cases are suggested as models for tropical and mid latitude squall lines respectively while a further case provides a possible model for storm splitting

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

records of continental slope sediment flow morphodynamic responses to gradient and active faulting from integrated auv and rov data offshore palos verdes southern california borderland abstract variations in seabed gradient are widely acknowledged to influence deep water deposition but are often difficult to measure in sufficient detail from both modern and ancient examples on the continental slope offshore los angeles california autonomous underwater vehicle remotely operated vehicle and shipboard methods were used to collect a dense grid of high resolution multibeam bathymetry chirp sub bottom profiles and targeted sediment core samples that demonstrate the influence of seafloor gradient on sediment accumulation depositional environment grain size of deposits and seafloor morphology in this setting restraining and releasing bends along the active right lateral palos verdes fault create and maintain variations in seafloor gradient holocene down slope flows appear to have been generated by slope failure primarily on the uppermost slope 100 200 m water depth turbidity currents created a low relief

improving simulations of convective systems from trmm lba easterly and westerly regimes abstract the 3d goddard cumulus ensemble model is used to simulate two convective events observed during the tropical rainfall measuring mission large scale biosphere atmosphere trmm lba experiment in brazil these two events epitomized the type of convective systems that formed in two distinctly different environments observed during trmm lba the 26 january 1999 squall line formed within a sheared low level easterly wind flow on 23 february 1999 convection developed in weak low level westerly flow resulting in weakly organized less intense convection initial simulations captured the basic organization and intensity of each event however improvements to the model resolution and microphysics produced better simulations as compared to observations more realistic diurnal convective growth was achieved by lowering the horizontal grid spacing from 1000 to 250 m this produced a gradual transition from shallow to deep convection that occurred over a span of hours as opposed to an abrupt appearance of

experiments on oscillatory flow and combined flow bed forms implications for interpreting parts of the shallow marine sedimentary record abstract analog laboratory experiments were conducted to investigate subaqueous bed forms generated under storm like oscillatory and combined flow experiments were carried out in a large wave tunnel and used a range of sand sizes fine and very fine wave periods 10 5 and 8 s oscillatory velocities 0 to 125 cm s and unidirectional velocities 0 to 25 cm s at low unidirectional velocities 10 cm s addition of an increasing collinear oscillatory flow caused the bed to evolve from small scale wavelength 100 cm symmetric orbital ripples to plane bed at higher unidirectional velocities 10 cm s a similar trend was noted but ripples were more asymmetric three phase diagrams are presented to summarize the observed relationships of bed configurations to flow conditions these diagrams are intended to assist in the interpretation of shallow marine sedimentary environments where oscillatory and combined flow are thought to be omnipresent distinctive features of small scale asymmetric combined flow ripples generated are a 3d planform round crest and convex up sigmoidal profile with local pronounced scour at the toe of the stoss side giving the ripple profile a boxy appearance similarly large scale asymmetric combined flow ripples had broad and round crests convex up stoss sides and compressed profiles due to scouring at the toe of the stoss side hummocky bed forms were generated under moderate to high oscillatory velocities and low unidirectional velocities hummocks were not observed as a distinct bed state but rather appeared to mark transitions in bed form scale and symmetry hummocks were more prevalent at longer oscillatory periods and in finer grained sediment stratification produced by synthetically aggrading hummocky bed profiles closely resembles hummocky cross stratification with the introduction of only a small unidirectional flow component hummocks evolve into downstream migrating large scale asymmetric ripples and the resultant cross stratification becomes similar to that produced by unidirectional flow dunes accordingly these experiments suggest that much of the hummocky cross stratification observed in the stratigraphic record is produced by storm generated long period oscillatory dominant combined flows inasmuch as long period high energy waves require deep wide basins to form hummocky cross stratification may therefore serve as a useful indicator of deposition in unrestricted open water conditions

sediment waves in a modern high energy glacilacustrine environment a 4 7 km2 field of sediment waves occurs in front of the slims river delta in kluane lake the largest lake in the yukon territory slims river heads in the kaskawulsh glacier part of the st elias ice field and discharges up to 400 m3 s 1 of water with suspended sediment concentrations of up to 7 g l 1 the 19 km long sandur of slims river was created in the past 400 years since kaskawulsh glacier advanced and dammed the lake and the sandur has advanced into kluane lake at an average rate of 48 m a 1 however this rate is decreasing as flow is diverted from slims river because of the retreat of the kaskawulsh glacier the sandur and a road constructed on the delta remove coarse grained sediment so the river delivers dominantly mud to the lake inflow during summer generates quasi continuous turbidity currents with velocities up to 0 6 m s 1 the front of the delta consists of a plane surface sloping lakeward at 0 0188 1 08 a field of sediment waves averaging 130 m in length and 2 3 m in amplitude has developed on this surface slopes on the waves vary from 0 067 3 83 i e sloping in the opposite direction to the regional slope to 0 135 7 69 the internal structure of the sediment waves as documented by seismic profiling shows that sedimentation on the stoss portion of the wave averages 2 7 times that on the lee portion rates of sediment accumulation in the wave field are about 0 3 m a 1 so these lacustrine waves have formed in a much shorter period of time less than 200 years and are advancing upslope towards the delta much more quickly 1 to 2 m a 1 than typical marine sediment waves these waves formed on the flat surface of the lake floor apparently in the absence of pre existing forms and they are altered and destroyed as the wave field advances and the characteristics of the turbidity currents change

radar reflectivity as a proxy for convective mass transport 1 more observations of vertical mass transport in deep convection are needed to improve dynamical understanding of detrainment processes and for verification of transport models a methodology for using radar reflectivity as a direct observation of vertical transport of mass from the boundary layer to the upper troposphere and lower stratosphere is investigated and the level of maximum detrainment lmd is proposed the case investigated is the 26 january 1999 squall line from the tropical rainfall measuring mission large scale biosphere atmosphere field campaign echo top heights and dual doppler derived divergence profiles are used to define the mass detrainment range over 10 of anvil echo tops occurred above the sounding derived level of neutral buoyancy of 15 4 km during the mature stage of the storm and convective tops reached above 18 km anvil ice water content with a simple correction for ice fall speed is found to be a good proxy for both the lmd which for the storm analyzed is 11 25 km and for the detrainment range of 6 to 17 km more cases need to be analyzed to confirm the strength of this methodology but the case study presented shows a strong correlation between anvil properties determined from radar reflectivity and the mass detrainment profile thus radar reflectivity can be used as an indicator of the lmd to test model convective and transport parameterizations

observed structure of mesoscale convective systems and implications for large scale heating mesoscale convective cloud systems that produce large amounts of rain in mid latitudes and most of the rain in the tropics consist of a combination of convective and stratiform cloud the convective regions contain numerous deep cells that are often but not always arranged in lines the stratiform region is an outgrowth of the convective ensemble it lies adjacent to the convective region and is seeded by ice particles detrained from convective towers sometimes it lies to the rear of a propagating convective line while on other occasions it surrounds the convection the heating of the large scale environment by a mesoscale convective system is affected by both the convective and stratiform regions although processes such as melting and radiation are important the net heating by a system is dominated by condensation and evaporation associated with vertical air motions this paper reviews recent observational evidence regarding the mean vertical motion profiles in the convective and stratiform regions of mesoscale convective systems and the implications of these mean motions for the vertical distribution of heating of the large scale environment in both the convective and the stratiform regions vertical motions have been determined by various techniques including composites of rawinsonde and aircraft wind data single and dual doppler precipitation radar analyses and wind profiler observations in stratiform regions these data consistently show mean vertical velocity that is upward in the upper troposphere and downward in the lower troposphere the level separating upward from downward motion is located from 0 to 2 km above the 0 c level depending on location within the stratiform region diagnostic calculations show that these vertical motion profiles imply heating of the upper troposphere and cooling of lower levels by stratiform region processes data on vertical motions in the convective regions are less consistent from case to case these data sometimes indicate that the mean vertical velocity in convective regions is maximum in the lower troposphere in other cases the data indicate a maximum in the high troposphere diagnostic calculations show that heating profiles diagnosed from these two types of profile are quite different the first having a maximum of heating in the lower troposphere while the second has a maximum in the middle troposphere although it is difficult to determine whether or not the differences in estimates arise from different types of observations analysis methods or sampling strategies it seems likely that they stem from differences in the large scale environment of the different mesoscale systems the ubiquitous occurrence of stratiform regions in mesoscale convective systems and hurricanes together with their consistent heating profiles which systematically concentrate heating in upper levels while cooling lower levels are a major consideration in evaluating the interaction of mesoscale systems with the large scale environment however the consistency of the stratiform profiles from case to case indicates that the variability of net convective plus stratiform heating profiles from case to case lies primarily in the variation of the convective region profiles from one case to another it is suggested that future work should focus on the convective region vertical profiles of vertical motion and heating and on the large scale environmental factors that may control the variation of these profiles from case to case

searchlight precipitation advection tracking using multiplatform low earth orbiting satellite data this paper presents a new algorithm searchlight capable of tracking precipitation advection through the complex spatiotemporal sampling pattern of multiplatform low earth orbiting leo passive and active microwave satellite data sets the algorithm is based on the concept of shining a searchlight forward in time along proposed advection velocity vectors from a given leo overpass the searchlight beam links precipitation patterns in the current satellite overpass to corresponding patterns in multiple future overpasses a global optimization determines an advection model by maximizing mutual information between linked precipitation measurements the algorithm has been validated against surface radar over a region covering the central and eastern u s

near surface density currents observed in the southeast pacific stratocumulus topped marine boundary layer abstractdensity currents i e cold pools or outflows beneath marine stratocumulus clouds are characterized using 30 days of ship based observations obtained during the 2008 variability of american monsoon systems vamos ocean cloud atmosphere land study regional experiment vocals rex in the southeast pacific an air density increase criterion applied to the improved meteorological imet sensor data identified 71 density current front core peak density and tail dissipating zones the similarity in speeds of the mean density current propagation speed 1 8 m s 1 and the mean cloud level advection relative to the surface layer wind 1 9 m s 1 allowed drizzle cells to deposit elongated density currents in their wakes scanning doppler lidar captured prefrontal updrafts with a mean intensity of 0 91 m s 1 and an average vertical extent of 800 m updrafts were often surmounted by low lying shelf clouds not connected to the overlying stratocumulus cloud the observed density currents were 5 10 time

development of an intense warm core mesoscale vortex associated with the 8 may 2009 super derecho convective event abstractin this study the dynamical processes contributing to warm core meso scale vortex formation associated with the 8 may 2009 super derecho are examined utilizing two complementary quasi lagrangian approaches a circulation budget and backward trajectory analyses applied to a fortuitous numerical simulation of the event warm core meso scale vortex formation occurs in a deeply moist potentially stable environment that is conducive to the development of near surface rotation and is somewhat atypical compared to known derecho supporting environments air parcels in the vicinity of the developing vortex primarily originate near the surface in the streamwise vorticity rich environment associated with the vertical wind shear of the low level jet immediately to the east of the eastward moving system cyclonic vertical vorticity is generated along inflowing air parcels primarily by the ascent induced tilting of streamwise vorticity and amplified primarily by ascent induced vortex tube stretching de

convection permitting simulations of the environment supporting widespread turbulence within the upper level outflow of a mesoscale convective system abstract widespread moderate turbulence was recorded on three specially equipped commercial airline flights over northern kansas near the northern edge of the extensive cirrus anvil of a nocturnal mesoscale convective system mcs on 17 june 2005 a noteworthy aspect of the turbulence was its location several hundred kilometers from the active deep convection i e large reflectivity regions of the mcs herein the mcs life cycle and the turbulence environment in its upper level outflow are studied using rapid update cycle ruc analyses and cloud permitting simulations with the weather research and forecast model wrf it is demonstrated that strong vertical shear beneath the mcs outflow jet is critical to providing an environment that could support dynamic e g shearing type instabilities conducive to turbulence comparison of a control simulation to one in which the temperature tendency due to latent heating was eliminated indicates that strong vertical shear and corresponding reductions in the l

morphological evolution of a well constrained subaerial subaqueous source to sink system wabush lake since 1964 the iron ore company of canada has deposited iron tailings resulting from mining operations into wabush lake western labrador canada this activity has resulted in a continuous hyperpycnal flow flowing over the lake floor bathymetric surveys were carried out between 1999 and 2008 as part of the overall environmental iron ore company of canada plans to maintain safe disposal strategies of tailings into the lake here this dataset is used to study the evolution of different channels present in wabush lake and their link with knickpoints found at the head of most of these channels the channels show notable evolution from one survey to the next some knickpoints and channels may be followed throughout more than one survey the evolution of these knickpoints is the process responsible for the creation of erosional channels the context in which they appear as well as the evolution of some of the subaqueous channels is analysed cyclic steps and sediment waves are also found in the lake these rhythmic bedforms also created by the passage of turbidity currents are analysed sediment waves found in wabush lake show values for both wavelength and wave height that are approximately one order of magnitude smaller than most of those found in the marine environment

mesoscale convective systems 1 mesoscale convective systems mcss have regions of both convective and stratiform precipitation and they develop mesoscale circulations as they mature the upward motion takes the form of a deep layer ascent drawn into the mcs in response to the latent heating and cooling in the convective region the ascending layer overturns as it rises but overall retains a coherent layer structure a middle level layer of inflow enters the stratiform region of the mcs from a direction determined by the large scale flow and descends in response to diabatic cooling at middle to low levels a middle level mesoscale convective vortex mcv develops in the stratiform region prolongs the mcs and may contribute to tropical cyclone development the propagation of an mcs may have a discrete component but may further be influenced by waves and disturbances generated both in response to the mcs and external to the mcs waves of a larger scale may affect the propagation velocity by phase locking with the mcs in a cooperative mode the horizontal scale of an mcs may be limited either by a balance between the formation rate of convective precipitation and dissipation of stratiform precipitation or by the rossby radius of the mcv the vertical redistribution of momentum by an mcs depends on the size of the stratiform region while the net vertical profile of heating of the large scale environment depends on the amount of stratiform rain regional variability of the stratiform rain from mcss affects the large scale circulation s response to mcs heating

effects of under resolved convective dynamics on the evolution of a squall line abstractsimulations of a squall line observed on 20 may 2011 during the midlatitude continental convective clouds experiment mc3e using 750 and 250 m horizontal grid spacing are performed the h

observations of the structure and evolution of hurricane edouard 2014 during intensity change part ii kinematic structure and the distribution of deep convection abstractthe structural evolution of the inner core and near environment throughout the life cycle of hurricane edouard 2014 is examined using a synthesis of airborne and satellite measurements this study specifically focuses on differences in the distribution of deep convection during two periods when edouard intensified toward hurricane status and when edouard peaked in intensity and began to weaken while both periods saw precipitation maximized in the downshear left and upshear left quadrants deep convection was only seen from the aircraft during the intensifying period deep convection was located farther inside the radius of maximum winds rmw during the intensifying period than the weakening period this convection is traced to strong updrafts inside the rmw in the downshear right quadrant tied to strong low level convergence and high convective available potential energy cape as the storm remained over warm water in a moist environment strong updrafts persisted upshear left and were collo

simulation and interpretation of the genesis of tropical storm gert 2005 as part of the nasa tropical cloud systems and processes experiment abstract several hypotheses have been put forward for the mechanisms of generation of surface circulation associated with tropical cyclones this paper examines high resolution simulations of tropical storm gert 2005 which formed in the gulf of mexico during nasa s tropical cloud systems and processes experiment to investigate the development of low level circulation and its relationship to the precipitation evolution two simulations are examined one that better matches available observations but underpredicts the storm s minimum sea level pressure and a second one that somewhat overintensifies the storm but provides a set of simulations that encapsulates the overall genesis and development characteristics of the observed storm the roles of convective and stratiform precipitation processes within the mesoscale precipitation systems that formed gert are discussed during 21 25 july two episodes of convective system development occurred in each precipitation system evolution was characterized by i

the influence of partial melting on the electrical behavior of crustal rocks laboratory examinations model calculations and geological interpretations abstract the complex electrical impedance of a granulite has been determined over the frequency range 10 1 to 105 hz at temperatures between 600 and 1200 c at normal pressure and different oxygen fugacities in the stability field of magnetite the impedance spectroscopic is measurements are compared with the results of melting experiments performed under the same experimental conditions and with the same rock sample as the is measurements a strong increase in the electrical conductivity of about one and a half orders of magnitude is observed during partial melting this increase is explained by the formation of an interconnected network of melt the wetting of the grain surfaces starts slightly above the solidus however complete interconnection of the network is detected at higher temperatures 1070 c and hence higher melt fractions 10 vol this is explained by deviations from the equilibrium fabric of the partially molten sample with a modified brick layer model mblm the electrical conductivity is calculated as a function of the observed melt portion this model is valid if the melt forms a complete interconnected network at the grain boundaries the electrical conductivity at different temperatures was modeled using the results of the melting experiments and the mblm melt 10 s m with ea melt 1 ev solid 0 01 s m with ea solid 1 4 ev the results of the laboratory examinations were applied to different crustal regions where partially molten rocks are assumed to exist the same mblm is used to estimate the melt fraction that is necessary to explain the high conducting zones hczs observed in the crust beneath the andean orogen the pyrenees and the tibetan plateau at least 14 4 and 4 vol of interconnected melt are necessary to produce the observed conductivity respectively the actual amount of melt should be higher due to perturbation problems and melt trapped in pockets

the effect of feldspar on quartz h 2 o co 2 dihedral angles at 4 kbar with consequences for the behaviour of aqueous fluids in migmatites an investigation was made of the effect of trace amounts of feldspar na and or k on dihedral angles in the quartz h2o co2 system at 4 kbar and 450 1050 c quartz quartz h2o dihedral angles in feldspar bearing quartz aggregates are observed to be the same as those in pure quartz aggregates at temperatures below 500 c above this temperature they decrease with increasing temperature until the solidus the final angle at the inception of melting is about 65 for microcline quartz h2o and microcline albite quartz h2o and much less than 60 the critical value for formation of grain edge fluid channels in an isotropic system for the albite quartz h2o system co2 was observed to produce a constant quartz quartz fluid dihedral angle of 97 in feldspar bearing quartz aggregates at all temperatures studied also examined were the dihedral angles for the two co existing supersolidus fluids in quartz aggregates in all systems the quartz volatile fluid angle is greater than 60 whereas the quartz melt angle is lower than 60 both supersolidus angles decrease with increasing temperature the transition from nonconnected to connected porosity with increasing temperature observed in the quartz albite h2o system some tens of degrees below the solidus termed a permeability transition if a common feature of rocks near their melting points will play an important role in controlling the permeability of high grade rocks to aqueous fluids

seismic gravity and petrological evidence for partial melt beneath the thickened central andean crust 21 23 s on the basis of seismic refraction investigations and gravimetric data we have modelled the crustal structure of the southern central andes 21 23 s a pronounced variation in crustal parameters is seen in n s and w e crossing seismic profiles over the entire andean orogene characterized by a crustal thickness of up to 70 km under the magmatic arc and backarc strongly reduced seismic velocities and a bouguer minimum of 450 mgal anomalously low velocities of 5 9 6 0 km s in the deeper crust of the western cordillera and altiplano regions lead to an over compensation of the bouguer minima resulting in values of crustal densities higher than estimates based purely on seismic velocity measurements in an attempt to reconcile these differences the behavior of crystalline rocks based on published laboratory data was studied under varying pressure and temperature conditions up to the range of partial melting if the temperature is increased above the melting point a rapid decrease in seismic velocity is accompanied by a slow decrease in density for the central andes a good fit of the observed and calculated bouguer anomalies is obtained if the densities of the rocks from the low velocity zone lvz beneath the western cordillera and the altiplano are varied model calculations lead to a velocity density relation for partial molten rocks that allows the melt proportions of rocks to be estimated model calculations indicate that 15 20 vol of basaltic to andesitic melt at depth is necessary to explain the lvz and bouguer anomaly beneath the arc and parts of the backarc high heat flow values 100 mw m2 support the idea that large areas of the deeper andean crust are strongly weakened by the presence of partially molten rocks resulting in reduced seismic velocities with the western cordillera the active volcanic arc of the andean mountain range acting as a ductile buffer between the two more rigid crustal blocks of the forearc and backarc regions

late quaternary multi genetic processes and products on the northern gulf of cadiz upper continental slope sw iberian peninsula abstract on continental margins the upper slope to shelf break environment forms a critical region where sediment supply hydrographic activity and gravitational processes determine how and when sediments are partitioned between the shallow and deep marine realm on the sw iberian margin relatively few studies have addressed the dynamics of this region although it holds key information regarding the link between the sedimentary evolution of the continental shelf and the contourite depositional system on the middle slope this work therefore presents a high resolution analysis of the morphological and stratigraphic expressions of late quaternary dominantly last glacial and present day interglacial sedimentary processes on the upper slope and shelf margin sector between 7 and 7 30 w the integration of seismic bathymetric and hydrographic data reveals the presence of alongslope processes and products a bottom current related plastered drift moat erosional surface and terrace an internal wave tide controlled sediment wave field downslope gravitational processes and products an upper slope shelf margin valley system slumps debrites gullies neotectonic elements diapirs and fluid flow features pockmarks bright spots the spatial distribution of these features indicates that the study area becomes increasingly alongslope dominated towards the w and oppositely more downslope dominated towards the e because sediment supply to the latter area is enhanced under the dominant eastward dispersal of fluvially supplied sediments on the shelf in addition glacial interglacial variations in the amount of sediments supplied to the shelf edge and the intensity of oceanographic processes in the study area also generate a distinct temporal variability with glacial and interglacial intervals respectively recording principally downslope and alongslope controlled morphological elements finally regardless of these overall spatial and temporal patterns diapirism and fluid flow are inferred to locally destabilize sediments and induce small scale mass wasting in the study area these findings are not only relevant to the northern gulf of cadiz but also to the general understanding of sedimentary dynamics and controls in mixed downslope and alongslope controlled upper slope to shelf margin settings worldwide

kinematic characteristics of air flowing into and out of precipitating convection over the west pacific warm pool an airborne doppler radar survey air flowing into and out of 25 cloud systems over the west pacific warm pool was sampled by doppler radars on board two noaa wp 3d aircraft and the ncar electra aircraft during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare in convective cells updraught inflows and downdraught outflows tended to be positioned adjacent to each other at sharp updraught downdraught interfaces sloping at various angles and directions the updraught inflows were sometimes shallow and sometimes deep often extending well above the boundary layer downdraught outflow magnitudes were usually stronger than updraught inflows and the horizontal directions of the inflow and outflow were frequently offset from each other at angles of 90 in stratiform precipitation regions the dominant airflow features were descending mid level inflows located at the bases of anvils and often extending into the interior of the precipitation system these stratiform inflows originated at levels between 5 and 10 km and descended to about 3 km a few extended down to the surface stratiform inflows were typically strong and sandwiched between weaker stratiform outflows at upper and lower altitudes the stratiform region inflow and outflow directions were frequently offset by 90 in the horizontal the mid level inflow currents entered the stratiform regions horizontally from a direction similar to that of the large scale ambient wind the mid level stratiform inflow tended to occur in the same vertical plane as the convective downdraught outflow although the mid level stratiform inflow appeared to be slowed by horizontal pressure gradients before connecting with the convective downdraught outflow in other respects the mesoscale systems differed from a simplified two dimensional model of airflow the systems moved primarily by discrete propagation and updraughts and downdraughts tended to have orthogonal horizontal relative airflow

life cycle variations of mesoscale convective systems over the americas abstract using goes 7 isccp b3 satellite data for 1987 88 the authors studied the evolution of the morphological and radiative properties of clouds over the life cycles of deep convective systems cs over the americas at both tropical and middle latitudes a deep convective cloud system is identified by adjacent satellite image pixels with infrared brightness temperatures tir 245 k 28 c that at some time contain embedded convective clusters that are defined by pixel values of tir 218 k 55 c the first part of the analysis computes parameters for each convective system that describe the system areal size number of convective clusters fractional convective area average and maximum size of the convective clusters shape eccentricity and orientation mean tir variance of tir tir gradient and the mean variance and gradient of collocated visible reflectances when available the second part of the analysis searches a 5 5 region centered on each convective system but in the subsequent

conditions for the ignition of catastrophically erosive turbidity currents abstract the basic impediment to a clear understanding of eroding and depositing turbidity currents has been the lack of a proper formulation of bed sediment entrainment this problem is addressed herein a detailed analysis indicates that the bagnold criterion is necessary but insufficient for self sustaining turbidity currents the analysis reveals two possible equilibrium states a relatively low velocity ignitive state and a high velocity dense catastrophic state a stability analysis indicates that the ignitive state is unstable flows below it invariably die out and flows above it ignite i e accelerate and entrain sediment to the catastrophic state which is stable the ignitive state thus defines the criterion for a self sustaining turbidity current estimates of the catastrophic state suggest that it is highly erosive and competent to scour out submarine canyons

thermodynamic properties of mesoscale convective systems observed during bamex dropsonde observations from the bow echo and mesoscale convective vortex experiment bamex are used to document the spatiotemporal variability of temperature moisture and wind within mesoscale convective systems mcss onion type sounding structures are found throughout the stratiform region of mcss but the temperature and moisture variability is large composite soundings were constructed and statistics of thermodynamic variability were generated within each subregion of the mcs the calculated air vertical velocity helped identify subsaturated downdrafts it was found that lapse rates within the cold pool varied markedly throughout the mcs layered wet bulb potential temperature profiles seem to indicate that air within the lowest several kilometers comes from a variety of source regions it was also found that lapse rate transitions across the 0 c level were more common than isothermal melting layers the authors discuss the implications these findings have and how they can be used to validate future high resolution numerical simulations of mcss

modeled and observed variations in storm divergence and stratiform rain production in southeastern texas abstractstorm divergence profiles observed by an s band doppler radar are compared to ensemble simulations of 10 disparate precipitating systems occurring in warm season weakly baroclinic and strongly baroclinic environments in southeastern texas eight triply nested mesoscale model simulations are conducted for each case using single and double moment microphysics with four convective treatments i e two convective parameterizations and explicit versus parameterized convection at 9 km observed and simulated radar reflectivities are objectively separated into convective stratiform and nonprecipitating anvil columns and comparisons are made between ensemble mean echo coverages and levels of nondivergence lnds in both the model and observations storms occurring in less baroclinic environments have more convective rain area less stratiform rain area and more elevated divergence profiles the model ensemble and observations agree best for well organized leading line trailing stratiform systems

genesis of typhoon nari 2001 from a mesoscale convective system 1 in this study the origin and genesis of typhoon nari 2001 as well as its erratic looping track are examined using large scale analysis satellite observations and a 4 day nested cloud resolving simulation with the finest grid size of 1 33 km observational analysis reveals that nari could be traced 5 days back to a diurnally varying mesoscale convective system with growing cyclonic vorticity and relative humidity in the lower troposphere and that it evolved from a mesoscale convective vortex mcv as moving over a warm ocean under the influence of a subtropical high a weak westerly baroclinic disturbance an approaching and departing typhoon danas to the east and the kuroshio current results show that the model reproduces the genesis final intensity looping track and the general convective activity of nari during the 4 day period it also captures two deep subvortices at the eye eyewall interface that are similar to those previously observed a few spiral rainbands and a midget storm size associated with nari s relatively dry and stable environment we find that 1 continuous convective overturning within the mcv stretches the low level vorticity and moistens a deep mesoscale column that are both favorable for genesis 2 nari s genesis does not occur until after the passage of the baroclinic disturbance 3 convective asymmetry induces a smaller sized vortex circulation from the preexisting mcv 4 the vortex vortex interaction with danas leads to nari s looping track and temporal weakening and 5 midlevel convergence associated with the subtropical high and danas accounts for the generation of a nearly upright eyewall

quaternary sandy deposits and canyons on the venezuelan margin and south barbados accretionary prism abstract the geomorphological and tectonic setting distribution and origin of late quaternary sandy deposits on the southern termination of the barbados accretionary prism and the adjacent abyssal plain have been investigated using seabeam and 3 5 khz echosounding data and lithological and mineralogical analyses of 28 kullenberg cores quaternary sands on this prism are deposited in piggyback basins they are transported along three major canyons the morphology and trend of which are highly variable and which are tectonically controlled the narrow and relatively shallow canyon sections are in some ways like the major distributary channels of deep sea fans but they are true canyons in terms of the sedimentary processes taking place namely active erosion associated with the continuous uplift of tectonic structures and deposition of only slightly elevated sediment levees the sand is partly trapped on basin floors as flat sediment sheets composed of thinly and thickly bedded fine grained sandy turbidites high deposition rates occurred during the last period of low sea levels the sands originated from the orinoco trinidad shelf as inferred from geographical considerations and clay and heavy mineral provenance data predominently kaolinite illite hornblende and epidote sands of the abyssal plain settled on a deep sea fan system that trends north south parallel to the toe of the prism most of the sediments are introduced at the southern end of the system where they are delivered by the three major canyons which merge on the fan in a northward braided channel system this material consists of sandy turbidites that originated from the orinoco trinidad margin the grain size of the sands is similar to or coarser than the grain size of the prism sands sand components are identical and preclude supply from the amazon river the sedimentation rate during periods of low sea level seems to be lower a significant percentage of smectite in the clay fraction suggests that a minor part of the material may be derived from the demerara margin located closer to the main smectite source i e the amazon delta these results emphasize the difference between the sand distribution on active and passive margins

initiation and evolution of turbidity current sediment waves in the magdalena turbidite system this study describes an extensive sediment wave field in the magdalena turbidite system caribbean sea colombia which occupies an area of at least 15000 km2 on the continental slope 3330 3800 m the waves display wavelengths up to 1 9 km wave heights up to 18 m and crestlines that are aligned roughly parallel to the regional bathymetric contours preferential deposition on the upslope wave flank has led to upslope migration in the manner of antidunes the magdalena sediment waves are interpreted as forming beneath unconfined turbidity currents which may result from the downslope evolution of slumps and mass flows the unconfined turbidity currents are derived from several point sources along the continental slope and spread laterally as they flow downslope this has led to the formation of a laterally extensive sediment wave field simple numerical modelling estimates that the turbidity currents responsible for wave generation were near or super critical with flow thickness and velocity estimated at 40 160 m and 36 82 cm s 1 respectively however later phases of wave growth were not dependent on specific flow conditions the most important aspect of this study is that the entire sediment wave unit from the basal boundary to the present day seafloor has been investigated using ultra high resolution seismic profiles the sediment wave unit rests upon an irregular discontinuity that marks a recent change in the sedimentary regime of the magdalena turbidite system from channelised to unchannelised gravity flows above this boundary the sediment waves display a growth pattern characterised by an increase in wave dimensions in addition the wave dimensions appear to become more regular through time however breaks of slope in the lower bounding surface of the wave field have produced variations in wave morphology that are still visible at the present day seafloor this indicates that there is a close relationship between variations in slope angle and turbidity current flow characteristics which in turn leads to variations in wave morphology

evolution of pliocene to recent abyssal sediment waves on bounty channel levees new zealand abstract levees bordering bounty channel 900 km east of new zealand accommodate a 400 m thick sequence maximum of sediment waves that have formed since pliocene times these bedforms with amplitudes of 2 17 m and wavelengths of 0 6 6 km occur in 4100 4900 m of water and were formed by turbidity currents as indicated by their restriction to levee backslopes the frequent occurrence of turbidites in cores and the preferential but not exclusive development of waves on the left bank levee in accord with the southern hemisphere coriolis deflection the wave field was instigated in the late pliocene when glacially lowered sea level allowed rivers draining the southern alps of south island to discharge directly into bounty channel and its attendant canyons the field grew vertically through the coalescence of small waves into larger bedforms that continually migrated across and up levee backslopes at an average rate of 5 6m 100 yrs wave growth decreased into the late pleistocene probably in response to progressive containment of turbidity currents as the relief of bounty channel increased to 200 m or more the glacial periods of wave growth were interrupted by interglacial interludes of quiescence when the field was draped mainly by pelagic calcareous ooze

sediment waves with a biogenic twist in pleistocene cool water carbonates great australian bight abstract sediment waves composed of fine grained carbonate ooze with in place bryozoans are a characteristic element of the pleistocene of the great australian bight gab the low amplitude and strongly elongate sediment waves are up to 10 km long 1 km wide 40 m high and oriented sub parallel to contours immediately off the shelf slope break they are asymmetrical showing up slope migration and mainly occur in trains the sediment waves were drilled during odp leg 182 in 1998 and were interpreted as biogenic reef mounds new high quality seismic and multibeam bathymetry data were acquired on the galathea 3 expedition in 2006 allowing description of the morphology and internal architecture of the sediment waves in unprecedented detail leading to an alternative interpretation of their formation most sediment waves were initiated by preferential deposition on the landward side of irregular erosion surfaces sediment wave accretion took place under the influence of density driven currents which decelerated up the landward dipping flanks and accelerated down the seaward dipping flanks of the sediment waves the currents are interpreted as dense water cascades formed by summer evaporation and strong winter cooling by analogy with oceanographic processes in the present day gab the lithological composition varied with climate and sea level but sediment wave formation did not sediment waves formed and accreted during both glacials and interglacials in contrast to the previous interpretations which involved growth in glacial periods only bryozoans influenced the depositional environment by adding sediment trapping fine grained particles and stabilizing the muddy sea floor this caused the sediment waves to gain a more prominent sea floor relief than most muddy siliciclastic sediment waves formed by similar depositional processes the interpretation of the sediment waves as purely biogenic build ups is rejected and the sediment waves are most appropriately described as biogenically influenced sediment waves