observations and geologic significance of marine snow in a shallow water partially enclosed marine embayment because of their fragile nature marine snow sized aggregates aggregates 0 5 mm in longest dimension have been generally overlooked in shallow water environments we report in situ observations and measurements in cape lookout bight north carolina that indicate that marine snow is probably always present and usually abundant underwater photographs show that over a period of hours marine snow varies in size from 8 to 71 10 5 ml and in abundance from 291 to 489 l 1 but that such variations in size and abundance are not obviously related to tide total suspended sediment concentration or current speeds in the 10 to 20 cm s 1 range photographs and concurrent transmissometer records suggest that variations in size shape and abundance of marine snow may be sufficiently great that particulates do not remain optically constant and thus affect beam transmission irrespective of total suspended sediment concentration levels marine snow is significant geologically in that it has high settling rates 50 to 200 m per day and may be the package in which much of the vertical mass flux occurs if so it offers an explanation for the high accumulation rates observed in coastal and estuarine fluid mud deposits

the source of alluvium in large rivers of the lower coastal plain of north carolina summary despite high erosion rates in the north carolina piedmont and extensive sediment delivery to coastal plain reaches of piedmont draining streams sediment budget studies and estuarine sedimentology suggest that relatively little piedmont derived sediment reaches the lower coastal plain dominant sources of alluvium in the lower coastal plain reaches of piedmont draining rivers were inferred from alluvial floodplain soils piedmont derived alluvial soils are characterized by mixed mineralogy and presence of mica flakes alluvial soils derived from erosion of coastal plain uplands are characterized by siliceous mineralogy and an absence of mica flakes the coastal alluvial soils which occur in fluvial estuarine transition zones being drowned by rising sea level are organic or buried organic soils the distribution of these soils along the tar and neuse rivers in the lower coastal plain shows almost complete domination of fluvial estuarine transition zones by soils of the coastal group and by soils of the coastal plain and coastal groups for 40 km or more inland of the upper estuaries no soils of the piedmont group were found in fluvial estuarine transition zones or lowermost fluvial reaches this suggests that the piedmont is a relatively insignificant source of alluvium in the lower reaches of the rivers the absence of piedmont sediment in the lower coastal plain is attributed to extensive sediment storage upstream dilution by coastal plain sediments and coastal plain erosion rates which may be higher than was previously believed

storm impacts on hydrodynamics and suspended sediment fluxes in a microtidal back barrier estuary abstract recent major storms have piqued interest in understanding the responses of estuarine hydrodynamics and sediment transport to these events to that end flow velocity wave characteristics and suspended sediment concentration ssc were measured for 11 months at eight locations in chincoteague bay md va usa a shallow back barrier estuary daily breezes and episodic storms generated sediment resuspending waves and modified the flow velocity at all sites which occupied channel shoal and sheltered bay environments with different bed sediment characteristics despite comparable ssc during calm periods ssc at the channel locations was considerably greater than at the shoal sites during windy periods because of relatively more erodible bed sediment in the channels sediment fluxes were strongly wind modulated within the bay s main channel depth integrated unit width sediment flux increased nonlinearly with increasing wind speed when averaged over all sites about 35 of the flux occurred during windy periods wind speed greater than 6 m s 1 which represented just 15 of the deployment time at channel sites the net water and sediment fluxes were opposite to the direction of the wind forcing while at shoal sites the fluxes generally were aligned with the wind implying complex channel shoal dynamics yearly sediment fluxes exceed previous estimates of sediment delivery to the entirety of chincoteague bay these observations illustrate the dynamic sedimentary processes occurring within microtidal back barrier lagoons and highlight the importance of storm events in the hydrodynamics and overall sediment budgets of these systems

rapid filamentation zones in intense tropical cyclones intense tropical cyclones often possess relatively little convection around their cores in radar composites this surrounding region is usually echo free or contains light stratiform precipitation while subsidence is typically quite pronounced in this region it is not the only mechanism suppressing convection another possible mechanism leading to weak echo moats is presented in this paper the basic idea is that the strain dominated flow surrounding an intense vortex core creates an unfavorable environment for sustained deep moist convection strain dominated regions of a tropical cyclone can be distinguished from rotationdominated regions by the sign of s 2 s 2 2 where s1 ux y and s2 x uy are the rates of strain and x uy is the relative vorticity within the radius of maximum tangential wind the flow tends to be rotation dominated 2 s 2 s 2 so that coherent structures such as mesovortices can survive for long periods of time outside the radius of maximum tangential wind the flow tends to be strain dominated s 2 s 2 2 resulting in filaments of anomalous vorticity in the regions of strain dominated flow the filamentation time is defined as fil 2 s 2 s 2 2 1 2 in a tropical cyclone an approximately 30 kmwide annular region can exist just outside the radius of maximum tangential wind where fil is less than 30 min and even as small as 5 min this region is defined as the rapid filamentation zone since the time scale for deep moist convective overturning is approximately 30 min deep convection can be significantly distorted and even suppressed in the rapid filamentation zone a nondivergent barotropic model illustrates the effects of rapid filamentation zones in category 1 5 hurricanes and demonstrates the evolution of such zones during binary vortex interaction and mesovortex formation from a thin annular ring of enhanced vorticity

petrological statistical approach to interpret recent and subrecent lagoon subfacies idku nile delta of egypt abstract an approach combining petrology and statistics cluster analysis is developed to better distinguish a series of subfacies in surficial and short core samples from idku lagoon in the northwestern nile delta egypt the method integrates lithology physical and biogenic structures grain size and composition of the sand size fraction seven lithofacies eight grain size types and six clusters reveal comparable geographic distributions that are a direct response to geomorphic setting and depositional processes both of which have been modified by man although positioned in an arid setting and affected by anthropogenic factors land reclamation pollutants regional subfacies distribution patterns in idku lagoon are largely a function of the spatial configuration of freshwater dominated to brackish to higher salinity dominated near inlet zones typical of lagoons receiving significant freshwater input within idku a northern depositional province near the inlet and along the coastal sand barrier is defined by associations of terrigenous and coarse grained sediment types a southern province bounded by lagoon margins and marshes is characterized by finer grained sediment types with a high biogenic content recording lower energy levels the petrological statistical approach is used to identify and interpret lagoon subfacies in older to 6000 years b p core sections in idku region and in former abu qir lagoon additionally cluster analysis serves to determine specific lagoon subfacies from hand samples alone whether from surface grabs or cores this is based on a comparison of lithofacies and clusters determined for surficial and short core samples in the idku region to test the method a separate cluster analysis also using surficial and short core samples was used to define manzala lagoon subfacies in the northeastern nile delta results are generally comparable to those obtained in the idku study and show a close relation among manzala lagoon subfacies geomorphic configuration and depositional processes the petrological statistical method could be applied to other regions and also to the geological record

objective convective updraft identification and tracking part 1 structure and thermodynamics of convection in the rainband regions of two hurricane simulations to better understand the life cycles of convective elements in numerical model simulations a convective updraft tracking algorithm dubbed the statistical and programmable objective updraft tracker spout is developed spout identifies updraft cores in horizontal slices through a given model data set links these cores in three dimensions to form vertically coherent updrafts and then tracks updrafts in time via estimates of the mean local advection spout is evaluated in idealized hurricane simulations from both the regional atmospheric modeling system rams and weather research and forecasting wrf in both simulations spout indicates most updrafts live less than 60 min but some can persist for over 2 h updrafts are typically manifested as shallow cumulus cumulus congestus and deep cumulonimbus overall there is reasonable agreement between the vigor of convection and the amount of localized conditional convective instability also the majority of updrafts attain a tilted structure that is in accordance with the localized vertical wind shear nonetheless there are striking differences between models with the higher resolution wrf simulation producing around twice as many updrafts as rams moreover the wrf updrafts are significantly weaker this paper highlights the utility of spout for studying convective life cycles in high resolution numerical simulations and provides some basic features of convection in two hurricane simulations

drill hole design for dilational ore shoot targets in fault fill veins ore along fault fill veins typically has an uneven distribution with semilinear high grade ore shoots separated by lower grade zones or barren fault segments therefore a successful drill campaign must be optimally designed for intersection of ore shoots and not the intervening zones however the typical drill hole design for fault fill veins which targets the vein directly downdip from the highest grade outcrops will miss most ore shoots that rake less than 80 to 90 in the structure dilational ore shoots form along pre or synmineralization faults in localized elongated structural openings perpendicular to the slip vector the rake of such ore shoots in fault fill veins can be predicted using models of stress controlled fault fracture kinematics equations are presented that use fault kinematic data to design drill holes for optimal success in targeting such ore shoots the equations calculate the universal transverse mercator utm coordinates of the drill target given fault fill vein orientation slip vector rake usually determined from slickenlines vertical depth to intersect the ore shoot and the utm coordinates of geochemically anomalous outcrops along the fault vein although the method assumes that fault kinematics control ore shoot orientation and is not applicable to all fault vein ore shoots such as those formed at intersections of faults or shear zones with permeable beds other faults or dikes the method increases the probability of success for drill testing ore shoots through optimal drill hole design

the multiple vortex nature of tropical cyclogenesis abstract this study explores the extent to which potential vorticity pv generation and superposition were relevant on a variety of scales during the genesis of tropical storm allison allison formed close to shore and the combination of continuous doppler radar satellite aircraft and surface observations allows for the examination of tropical cyclogenesis in great detail preceding allison s genesis pv superposition on the large scale created an environment where decreased vertical shear and increased instability surface fluxes and low level cyclonic vorticity coexisted this presented a favorable environment for meso scale pv production by widespread convection and led to the formation of surface based meso scale vortices termed convective burst vortices cbvs the cbvs seemed to form in association with intense bursts of convection and rotated around each other within the meso circulation field one cbv eventually superposed with a mesoscale convective vortex mcv resulting in a mor

a unified view of tropical cyclogenesis and intensification idealized high resolution numerical simulations of tropical cyclogenesis are presented in a model that represents deep convection by a warm rain process only starting with an initially weak cloud free axisymmetric warm cored vortex maximum wind speed 5 m s 1 at a radius of 100 km rapid vortex intensification begins after a gestation period on the order of 2 days from a three dimensional perspective the genesis process is similar to that in the rotating convection paradigm for vortex intensification starting with a much stronger initial vortex vmax 15 m s 1 the patterns of deep convection and convectively amplified cyclonic relative vorticity are far from axisymmetric during the genesis period moreover the organization of the cyclonic relative vorticity into a monopole structure occurs at relatively low wind speeds before the maximum local wind speed has increased appreciably barotropic processes are shown to play an important role in helping to consolidate a single signed vorticity monopole within a few hours near the intensification begin time the rotating convection paradigm appears adequate to explain the basic genesis process within the weak initial vortex providing strong support for a hypothesis of montgomery and smith that the genesis process is not fundamentally different from that of vortex intensification in particular genesis does not require a trigger and does not depend on the prior existence of a mid level vortex

archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec part i geologic relations and formation of the vein system the sigma deposit consists of an archean gold bearing vein system in metavolcanic rocks intruded by an irregular body of porphyritic diorite both affected by regional deformation and in turn cut by younger undeformed feldspar porphyry dikes the veins cut all rock types and are composed chiefly of quartz and tourmaline with minor amounts of carbonates pyrite chlorite scheelite and free gold they were emplaced during or after a greenschist facies metamorphism postdating the intrusion of feldspar porphyry dikes the veins were not significantly affected by any subsequent metamorphism or tectonism two principal types of veins occur in the mine subvertical veins and subhorizontal veins they are contemporaneous and cogenetic subvertical veins occur within steeply dipping east west trending ductile shear zones along which reverse subvertical displacements have taken place the veins occupy openings created by overriding of undulations and irregularities of foliation and slip planes during progressive shearing movements within the shears subhorizontal veins occupy extensional fractures which developed between ductile shear zones preferentially in the more competent host rocks these veins were formed by one or several episodes of open space filling geologic relations indicate that the mineralized veins were emplaced progressively in a dynamic tectonic environment during and shortly after the formation of ductile shear zones a structural analysis has shown that the ductile shear zones and the two vein types can be related to a single strain ellipsoid of the following orientation the z axis trending north south and horizontal the y axis plunging 10 degrees west and the x axis plunging 80 degrees east the deformation responsible for the generation of ductile shear zones and emplacement of the veins is ascribed to a late north south trending compression postdating regional deformation

sedimentation in the albemarle pamlico lagoonal system synthesis and hypotheses abstract relative to its size and in terms of its sedimentary processes the albemarle pamlico lagoonal system is one of the least studied coastal lagoons in the united states a synthesis of the current knowledge about sedimentation in the albemarle pamlico system is presented based on archived data published over the last 30 years and new unpublished data collected over the past two years the literature reflects considerable past research effort on sediment grain size and mineralogy but very little on sediment dynamics or flux of suspended particulate material the physiographic complexity of the system which includes barrier islands a deep central basin four river systems and extensive fringing embayments does not appear to be reflected in the form of sedimentologic complexity in general the surficial cover of sediments ranges from medium sands in the inlets and on the shoals of the outer banks to fine silts and organic rich clays in the central basin and embayed river mouths and channels the transition zones from sands to muds are typically sharp and are usually related to bathymetry it is concluded that 1 parts of the albemarle pamlico lagoonal system may have high sedimentation rates relative to rates of sediment input and that rapid vertical flux by large aggregates offers an explanation for the fluid mud deposits that would otherwise be absent 2 fine grained sediments that escape the estuarine sediment trap are confined to pamlico sound by the outer banks barrier islands and are simply recycled until finally coming to rest in the deep basin 3 short term advective processes are secondary to longer term processes such as sea level rise and barrier island migration in the net advection of albemarle pamlico sediments and 4 at the present rate of terrigenous sediment input and relative sea level rise the albemarle pamlico lagoonal system will never reach a sediment filled state

multistage evolution of the calera epithermal ag au vein system orcopampa district southern peru first results in the orcopampa district southern peru the calera vein and its splits comprise a complex multistage epithermal fissure vein system of early miocene age hosted by slightly older silicic and intermediate volcanic rocks the several veins of the district are hosted by normal faults that strike n 45 degrees e to east west the calera vein system is the largest and economically most important yet discovered in the district produced ore and reserves contain over 40 million ounces of silver and 0 4 million ounces of gold five paragenetic stages as well as multiple episodes of fracturing faulting and hydrothermal brecciation are recognized the early stage is defined by quartz or adularia or sericite or pyrite altered wall rock and by mineralogically similar veinlets altered wall rock rich in adularia borders the vein at depth and yields laterally to sericite rich rock within a few meters of the vein whereas altered wall rock with abundant sericite borders the vein in upper levels early stage material is cut and brecciated by several substages of the mn stage which are characterized by abundant rhodonite and rhodochrosite containing bands composed largely of sphalerite and other sulfide minerals or tetrahedrite rich ores contain 10 2 to 10 3 ppm te mainly in hessite ag 2 te the mn stage is followed by two quartz rich substages the second substage contains tetrahedrite this quartz stage is in turn succeeded by the bonanza stage which contains native gold miargyrite pyrargyrite and several other silver sulfosalts and precious and base metal tellurides in quartz gangue this stage contains about 50 percent of the precious metal values of the calera system late quartz and sphalerite galena veins with barite marcasite and stibnite and hydrothermal breccia dikes of the late stage are volumetrically minor ore shoots typically occur in zones of intense fracturing indicated by abundant stockwork veins and vein splits based on the form and zoning of the west plunging main ore shoot ore forming fluids appear to have moved diagonally upward several superimposed stages have different distributions within the main ore shoot the mn stage is better developed at depth and the quartz stage is dominant in upper levels the au rich ores of the bonanza stage are found preferentially in a zone of intersection of vein splits that appears to have controlled fluid flow mineralization throughout the district is very similar the bonanza stage however has been identified only in the calera vein the paragenetic sequence has resulted from a series of progressively evolving hydrothermal fluids initial abundant rhodonite is replaced by rhodochrosite and eventually by quartz as the dominant gangue mineral the base metal sulfide and tetrahedrite bands must have formed from compositionally very different hydrothermal fluids the bonanza stage also represents a distinct fluid with much lower ag au relatively high a te a s and low manganese content the close spatial and temporal association with dacite dikes and flows the relatively high te content of the ores and the high a te a s ratios implied by some of the phase assemblages suggest the involvement of deep seated hydrothermal fluids

the role of vortical hot towers in the formation of tropical cyclone diana 1984 abstract a high resolution 3 km horizontal grid spacing near cloud resolving numerical simulation of the formation of hurricane diana 1984 is used to examine the contribution of deep convective processes to tropical cyclone formation this study is focused on the 3 km horizontal grid spacing simulation because this simulation was previously found to furnish an accurate forecast of the later stages of the observed storm life cycle the numerical simulation reveals the presence of vortical hot towers or cores of deep cumulonimbus convection possessing strong vertical vorticity that arise from buoyancy induced stretching of local absolute vertical vorticity in a vorticity rich prehurricane environment at near cloud resolving scales these vortical hot towers are the preferred mode of convection they are demonstrated to be the most important influence to the formation of the tropical storm via a two stage evolutionary process i preconditioning of the local environment via diabatic production of mul

role of cumulus congestus in tropical cyclone formation in a high resolution numerical model simulation abstractthe role of cumulus congestus shallow and congestus convection in tropical cyclone tc formation is examined in a high resolution simulation of tropical cyclone fay 2008 it is found that cumulus congestus plays a dominant role in moistening the lower to middle troposphere and spinning up the near surface circulation prior to genesis while deep convection plays a key role in moistening the upper troposphere and intensifying the cyclonic circulation over a deep layer the transition from the tropical wave stage to the tc stage is marked by a substantial increase in net condensation and potential vorticity generation by deep convection in the inner wave pouch region this study suggests that tc formation can be regarded as a two stage process the first stage is a gradual process of moisture preconditioning and low level spinup in which cumulus congestus plays a dominant role the second stage commences with the rapid development of deep convection in the inner pouch region after the air colum

tropical cyclone convection the effects of ambient vertical vorticity we present idealized numerical model experiments to isolate and quantify the influence of ambient vertical vorticity on the dynamics of deep convection such as that in the inner core region of a tropical depression the vertical vorticity is represented either by a uniform horizontal shear a uniform solid body rotation or a combination of both we show that the growing convective cells amplify locally the ambient rotation at low levels by more than an order of magnitude and that this vorticity which is produced by the stretching of existing ambient vorticity persists long after the initial updraught has decayed significant amplification of vorticity occurs even for a background rotation rate typical of the undisturbed tropical atmosphere and even for clouds of only moderate vertical extent this finding has important implications for tropical cyclogenesis and provides a basis for a unified theory of tropical cyclogenesis and tropical cyclone intensification the presence of ambient vertical vorticityreduces the updraught strength slightly more when the vorticity is associated with horizontal shear than when it is associated with solid body rotation on account of enhanced entrainment the reduction of the updraught strength can be attributed to the reduction of the lateral inflow by the centrifugal and coriolis forces despite the significant amplification of vorticity the sum of the centrifugal and coriolis forces is mostly small compared with the lateral pressure gradient thus at the level of background rotation studied the rossby elasticity effects in the updraught postulated by montgomery et al are not large but may be important for higher levels of background rotation the simulations ignore several processes that are likely to be important in reality such as ambient vertical shear and surface friction but they provide important benchmark calculations for interpreting the additional complexity arising from the inclusion of these effects copyright c 2011 royal meteorological society

simulating the evolution of coastal morphology and stratigraphy with a new morphological behaviour model geombest abstract a new morphological behaviour model is used to simulate evolution of coastal morphology associated with cross shore translations of the shoreface barrier and estuary the model encapsulates qualitative principles drawn from established geological concepts that are parameterized to provide quantitative predictions of morphological change on geological time scales order 10 3 years as well as shorter time scales applicable for long term coastal management order 10 1 to 10 2 years changes in sea level and sediment volume within the shoreface barrier and estuary drive the model behaviour further parameters defining substrate erodibility sediment composition and time dependent shoreface response constrain the evolution of the shoreface towards an equilibrium profile results from numerical experiments are presented for the low gradient autochthonous setting of north carolina and the steep allochthonous setting of the washington shelf simulations in the currituck region of north carolina examined the influence of sediment supply substrate composition and substrate erodibility on barrier transgression results demonstrate that the presence of a lithified substrate reduces the rate of barrier transgression compared to scenarios where an erodible sand rich substrate exists simulations of the washington coast 20 km north of the columbia river confirmed that the model can reproduce complex stratigraphy involving regressive and transgressive phases of coastal evolution results suggest that the first major addition of sediment to the shelf occurred around 12 900 years ago and resulted from the rapid addition of sediment volume from the columbia river attributed to the missoula floods this was followed by a period where little or no sediment was added 12 400 9100 bp and a third period when most sediment was added to the shelf 9100 bp to present from the columbia river comparing results from each setting demonstrates an indirect control that substrate slope has on shoreface transgression rates shoreface transgression is shown to be sensitive to the rate of estuarine sedimentation with the sensitivity increasing as substrate slope decreases

the influence of dikes on auriferous shear zone development within granitoid intrusions the bourlamaque pluton val d or district abitibi greenstone belt shear zone related gold quartz veins in granitoid intrusions are commonly intimately associated with mafic dikes which may have a profound influence on the localization orientation and kinematics of auriferous shear zones the bourlamaque pluton of the val d or district contains several economic auriferous shear zones most of which follow and overprint diorite dikes mineralization in all deposits consists of quartz tourmaline pyrite veins in reverse oblique orientation with a significant range of strike dip and slip direction the geometry and kinematics of shear zone and vein array within the pluton is more complex than the simple conjugate pattern predicted for a deforming homogeneous intrusion the stress tensor determined from the auriferous shear zones within the pluton indicates the same northerly directed compression recorded by similar shear zones outside the pluton this indicates that the complex shear zone and vein pattern within the pluton reflects the influence of diorite dikes which

structural localization and origin of compartmentalized fluid flow comstock lode virginia city nevada bonanza grade orebodies in epithermal style mineral deposits characteristically occur as discrete zones within spatially more extensive fault and or fracture systems empirically the segregation of such systems into compartments of higher and lower permeability appears to be a key process necessary for high grade ore formation and most commonly it is such concentrations of metals that make an epithermal vein district world class in the world class silver and gold producing comstock mining district nevada several lines of evidence lead to the conclusion that the comstock lode is localized in an extensional stepover between right lateral fault zones this evidence includes fault geometries kinematic indicators of slip the hydraulic connectivity of faults as demonstrated by veins and dikes along faults and the opening of a normal fault bounded asymmetric basin between two parallel and overlapping northwest striking lateral to lateral oblique slip fault zones during basin opening thick generally subeconomic banded quartz adularia veins were deposited in the normal fault zone the comstock fault and along one of the bounding lateral fault zones the silver city fault as deformation continued the intrusion of dikes and small plugs into the hanging wall of the comstock fault zone may have impeded the ability of the stepover to accommodate displacement on the bounding strike slip faults through extension within the stepover a transient period of transpressional deformation of the comstock fault zone ensued and the early stage veins were deformed through boudinaging and hydraulic fragmentation fault motion inversion and high and low angle axial rotations of segments of the fault planes and some fault bounded wedges this deformation led to the formation of spatially restricted compartments of high vertical permeability and hydraulic connectivity and low lateral hydraulic connectivity bonanza orebodies were formed in the compartmentalized zones of high permeability and hydraulic connectivity as heat flow and related hydrothermal activity waned along the comstock fault zone extension was reactivated in the stepover along the occidental zone of normal faults east of the comstock fault zone volcanic and related intrusive activity in this part of the stepover led to a new episode of hydrothermal activity and formation of the occidental lodes

role of large particles in the transport of elements and organic compounds through the oceanic water column abstract during the past decade data from a variety of sources have been obtained which show conclusively that the relatively rare large particles sinking through the water column are responsible for the majority of the downward vertical mass flux in the sea this finding has important implications for understanding the transfer distribution and fate of elements and organic compounds in marine waters the large 100 m detrital particles responsible for vertical flux are primarily biogenic and range in size and composition from small discrete fecal pellets and plankton hard parts to large amorphous aggregates or snow which contain both organic and inorganic constituents depending on size shape and density these particles sink at rates ranging from 1000 m day 1 several methods have been developed for sampling these particles of which in situ sediment trapping has probably furnished the most comprehensive qualitative and quantitative information on the role large particles play in material transport flux studies have highlighted the importance of marine heterotrophs in packaging fine suspended particulate matter into large rapidly sinking particles which accelerate the movement of incorporated materials to depth large particle production via biological packaging is not restricted to the euphotic zone but can occur at all depths and information is now accruing on rates of production of large particles in the water column chemical analyses of sedimenting particles collected in sediment traps and those sampled by other means have allowed quantifying vertical fluxes and residence times of elements radionuclides and organic compounds natural and anthropogenic in various oceanic regimes pertinent studies dealing with the above aspects are reviewed and several areas for future research are suggested

sheared deep vortical convection in pre depression hagupit during tcs08 1 airborne doppler radar observations from the recent tropical cyclone structure 2008 field campaign in the western north pacific reveal the presence of deep buoyant and vortical convective features within a vertically sheared westward moving pre depression disturbance that later developed into typhoon hagupit on two consecutive days the observations document tilted vertically coherent precipitation vorticity and updraft structures in response to the complex shearing flows impinging on and occurring within the disturbance near 18 north latitude the observations and analyses herein suggest that the low level circulation of the pre depression disturbance was enhanced by the coupling of the low level vorticity and convergence in these deep convective structures on the meso gamma scale consistent with recent idealized studies using cloud representing numerical weather prediction models further examination of these new observations is needed to quantify the relative role of these vortical convection features in the tropical cyclone spin up process

distribution of modern salt marsh foraminifera in the albemarle pamlico estuarine system of north carolina usa implications for sea level research abstract we described the distributions of foraminifera from ten physiographically distinct salt marshes in the albemarle pamlico estuarine system north carolina using 193 surface samples we defined elevation dependent ecological zones at individual sites using cluster analysis and detrended correspondence analysis additionally seven principal biozones of salt marsh foraminifera were identified that have distinctive spatial distributions reflecting a pattern of salinity regimes caused by the current configuration of barrier island inlets high salinity sites along the southern outer banks are associated with sub tidal calcareous assemblages low marshes dominated by miliammina fusca and high marsh environments defined by haplophragmoides wilberti trochammina inflata and arenoparrella mexicana in contrast lower salinity marshes have ammobaculites spp in sub tidal settings miliammina fusca dominated low marshes and high marsh settings characterized by jadammina macrescens spatial variation of foraminiferal populations and the potential for biozones to migrate in response to changing inlet configuration and salinity suggests that datasets of modern salt marsh foraminifera from multiple environments would be appropriate for reconstructing holocene relative sea level in north carolina

structurally controlled fluid flow high grade silver ore shoots at martha epithermal mine deseado massif argentina abstract the role of structurally controlled fluid flow during epithermal ore shoot formation is addressed through a structural study of the high grade martha mine epithermal deposit deseado massif patagonia argentina martha is a silver rich deposit characterised by a complex mineralogy dominated by ag as sb sulphosalts and cu pb zn sulphides mineralised veins can be subdivided into two groups master structures that trend approximately nw se and second order structures that trend e w and coalesce into the master structures the martha vein system is interpreted as a hard linked step over zone between two nw se trending fault segments furthermore the geometry of ore shoots at martha mine suggests a first order structural control on their location and orientation at the deposit scale mineralisation is concentrated in the step over zone mineralisation and presumably hydrothermal fluid flow was concentrated at the intersection between the two main vein groups finally at the scale of single veins jogs and subordinate step overs were important channels for hydrothermal fluids and the formation of high grade ore shoots

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

tropical cyclone convection the effects of a vortex boundary layer wind profile on deep convection we describe idealized numerical model experiments to study the effects of a vortex boundary layer wind profile on the generation of vertical vorticity in tropical deep convection situations are considered in which there is either no vertical shear above the boundary layer or negative vertical shear appropriate to a warm cored vortex deep convection growing in these environments develops dipole structures of vertical vorticity in which the cyclonic gyre is favoured and persists longer than the anticyclonic one the orientation of the dipole at a particular height is determined partly by that of the ambient horizontal vortex lines which rotate with height and also by the vertical advection of vertical vorticity from below an increase in the magnitude of boundary layer shear enhances the distortion of the initial thermal weakening its subsequent ascent rate this effect is detrimental to vertical vorticity production by stretching but because the increase in shear implies an increase in the magnitude of horizontal vorticity that can be tilted its net effect on the vertical vorticity production by tilting cannot be foreseen in the calculations described the effect of the increased horizontal vorticity dominates so that updraughts rising in stronger vertical shear have larger vertical vorticity maxima despite smaller vertical velocity maxima with negative vertical shear above the boundary layer the vorticity dipole reverses in sign with height as in a recent study of the effects of unidirectional shear the results provide a basis for appraising a recently proposed conceptual model for the inward contraction of eyewall convection in tropical cyclones as well as a starting point for developing an improved understanding of the formation of a vorticity monopole during tropical cyclogenesis

fluvial sediment delivery to a coastal plain estuary in the atlantic drainage of the united states abstract drastic changes in sediment production in drainage basins can have significant impacts on sediment yield to estuaries however significant but less spectacular changes in fluvial sediment regimes have not greatly influenced sediment output of some rivers in the united states atlantic drainage the limited influence of moderate or incremental changes in fluvial sediment systems on estuarine sediment delivery may be attributable to the large proportion of eroded sediment which is stored within the basins and the transport limited nature of long term sediment yields a sediment budget for the pee dee river basin and waccamaw river winyah bay estuary of the carolinas shows that only a small proportion of gross eroded sediment within the basin about 4 reaches the estuary on an average annual basis because the system appears to be transport limited it is estimated that an 88 reduction in the quantity of eroded sediment reaching streams would be necessary to produce significant change in sediment yield to the estuary any increase in sediment production would not be reflected at all in the estuary unless it was accompanied by a corresponding increase in fluvial sediment conveyance capacity estuarine sedimentary records thus may not reflect some significant changes in fluvial sediment systems

numerical study on the extremely rapid intensification of an intense tropical cyclone typhoon ida 1958 abstractextremely rapid intensification eri of typhoon ida 1958 was examined with a 2 km mesh nonhydrostatic model initiated at three different times ida was an extremely intense tropical cyclone with a minimum central pressure of 877 hpa the maximum central pressure drop in 24 h exceeded 90 hpa eri was successfully simulated in two of the three experiments a factor crucial to simulating eri was a combination of shallow to moderate convection and tall upright convective bursts cbs under a strong environmental vertical wind shear 10 m s 1 shallow to moderate convection on the downshear side that occurred around the intense near surface inflow moistened the inner core area meanwhile dry subsiding flows on the upshear side helped intensification of midlevel 8 km inertial stability first a midlevel warm core appeared below 10 km in the shallow to moderate convection areas being followed by the development of the upper level warm core associated with tall convection when tall upright

a numerical study of outer rainband formation in a sheared tropical cyclone abstractthe dynamical process of outer rainband formation in a sheared tropical cyclone tc is examined in this study using the fully compressible nonhydrostatic tc model after the easterly vertical wind shear of 10 m s 1 was imposed upon an intensifying strong tc an outer rainband characterized by a wavenumber 1 structure formed as a typical principal rainband downshear further analysis indicates that the outer rainband formation was closely connected to the activity of the inner rainband previously formed downshear moving radially outward the inner rainband tended to be filamented owing to the strong radial gradient of angular velocity as the inner rainband approached the outer boundary of the inner core convection in its middle and upwind segments reinvigorated and nascent convective cells formed upwind of the rainband caused mainly by the decreased filamentation and stabilization subsequently the rainband reorganized into a typical outer rainband three different scenarios are found to be

the formation of moist vortices and tropical cyclones in idealized simulations abstractthe upscale aggregation of convection is used to understand the emergence of rotating coherent midtropospheric structures and the subsequent process of tropical cyclone formation the cloud model version 1 cm1 is integrated on an f plane with uniform sea surface temperature sst and prescribed uniform background flow deep convection is maintained by surface fluxes from an ocean with uniform surface temperature convection begins to organize simultaneously into moist and dry midtropospheric patches after 10 days after 20 days the patches begin to rotate on relatively small scales moist cyclonic vortices merge eventually forming a single dominant vortex that subsequently forms a tropical cyclone on a realistic time scale of about 5 days radiation that interacts with clouds and water vapor aids in forming coherent rotating structures using the path to genesis provided by the aggregated solution the relationship between thermodynamic changes within the vortex and changes in the character

convective contribution to the genesis of hurricane ophelia 2005 abstract the convection occurring in the tropical depression that became hurricane ophelia 2005 was investigated just prior to tropical storm formation doppler radar showed a deep wide intense convective cell of a type that has been previously thought to occur in intensifying tropical depressions but has not heretofore been documented in detail the updraft of the cell was 10 km wide 17 km deep had updrafts of 10 20 m s 1 throughout its mid to upper levels and contained a cyclonic vorticity maximum the massive convective updraft was maintained by strong positive buoyancy which was maximum at about the 10 km level probably aided by latent heat of freezing evaporative cooling and precipitation drag occurred in the rain shower of the cell but were insufficient to produce a strong downdraft or gust front outflow to force the updraft the convective updraft was fed by a layer of strong inflow that was several kilometers deep wind induced turbulence just above the ocean surface enriched the equi

structural controls on jurassic gold mineralization and cretaceous tertiary exhumation in the foreland of the southern patagonian andes new constraints from la paloma area deseado massif argentina abstract fluid rock interaction occurring within high permeability conduits represented by fault fracture meshes is well known to control the development of hydrothermal ore deposits in this study we document the fundamental role of four sets of precursor joints reactivated as dilational faults displaying variable normal dip slip and strike slip components of motion in the formation of epithermal au ag deposits of economic interest paleostress analysis unravels how all the resulting four sets of hybrid extension shear fractures are kinematically compatible with an extensional stress field characterized by multiple permutations between the 3 and the 2 axes such permutations are interpreted to be associated with dominantly normal fault reactivation of suitably oriented early joint sets as a result of continued regional extension and by orthogonal stretching produced by differential downthrow of the hanging wall blocks of laterally terminating jurassic normal faults later fault reactivation appears to be associated with far field propagation of andean stresses marked by superposed strike slip and reverse fault slip components recording roughly e w horizontal compression this late fault reactivation could be related with a late early cretaceous shortening event known to have affected the studied sector of the deseado massif the subsequent tectonic evolution of the study area occurred within the general framework of a slow cretaceous to tertiary exhumation recorded by apatite fission track cooling ages our new thermochronometric results recording steady state cooling at a rate of c 1 c ma during the last 90 ma shed new light onto the post jurassic geodynamic evolution of the foreland of the southern patagonian andes

downstream trends in discharge slope and stream power in a lower coastal plain river conceptual models of river estuary interaction are typically based on a notion of systematic downstream change in the intensity of fluvial processes low slopes backwater effects and effects of antecedent topography and landforms may complicate downstream tends in water and sediment flux in coastal plain rivers an analysis of the lower trinity river texas shows no consistent downstream pattern of increases or decreases in the discharge stream power or water surface slope flows may decrease downstream due to coastal backwater effects in the lowermost reaches and due to diversion of flow into valley bottom depressions during high flows in both the fluvial and fluvial estuarine transition reaches in general however stream power and slope decrease in the lower reaches consistent with earlier findings of limited fluvial sediment delivery to the coastal zone some tributaries may become distributaries at high but sub bankfull flows as backwater effects reverse flows into depressions associated with paleomeanders the paleomeanders and possibly the locations of these reversible channels are related to antecedent topography associated with aggradation degradation cycles over the past 100 ka low gradient coastal plain rivers may not function as simple conduits from land to sea further the transition from fluvial to coastal dominance may be variable along the river with the variability controlled not just by the relative magnitude of river and tidal or backwater forcing but also by valley topography controlled in part by antecedent landforms

ore deposits at the fresnillo mine zacatecas mexico the fresnillo mine ore deposits consist of replacement chimney and manto bodies disseminated sulfide bodies and vein deposits hosted mainly in cretaceous marine sedimentary and volcanic rocks the base metal silver deposits are zoned to the southeast away from a small quartz monzonite stock with increasing silver content and decreasing base metal values with distance from the stock wall rocks adjacent to the stock exhibit silicification and calc silicate alteration that has been partially replaced by the sulfide minerals vein wall rocks exhibit potassic phyllic argillic and propylitic alteration with increasing distance from the veins chimney and manto bodies contain pyrite pyrrhotite sphalerite chalcopyrite galena tetrahedrite marcasite arsenopyrite and silver minerals chimney and manto bodies predate or are contemporaneous with base metal veins containing a similar mineralogy younger silver rich veins consist primarily of pyrargyrite with lesser acanthite proustite miargyrite polybasite tetrahedrite galena sphalerite and chalcopyrite individual veins exhibit increasing silver and decreasing base metal concentrations with increasing elevation fluid inclusions in quartz calcite and sphalerite contain two phases water and water vapor and are dilute 0 12 equiv wt nacl solutions filling temperatures and salinities vary sharply between growth zones in ore and gangue minerals with distinct salinity increases in sphalerite filling temperatures in chimney manto and deep vein quartz and calcite range between 240 degrees and 350 degrees c while shallow and distal quartz calcite and sphalerite from veins yield temperatures between 140 degrees and 275 degrees c sphalerite geobarometry of samples from the cueva santa manto yielded a total pressure of 730 bars pressure correction for the fluid inclusion filling temperatures from samples in chimney and manto deposits is 70 degrees c silverrich veins formed from fluids that were boiling indicating a depth of formation of 350 m below the paleosurface sulfur isotope analyses of galena and sphalerite from chimney manto and vein deposits exhibit overlapping ranges of values with galena depleted in 34 s with respect to sphalerite galena delta 34 s values from all deposit types at fresnillo vary between 4 1 and 8 0 per mil while sphalerite ranges between 2 0 and 5 0 per mil the calculated delta 34 s sub sigma s utilizing fluid inclusion filling temperatures is 3 0 or 0 4 per mil such a composition may have been derived from a slight shift in ore fluid ph as indicated by the wall rock alteration assemblages or by increased log f sub o 2 as indicated by minor hematite and amethystinc quartz from an original delta 34 s sub sigma s of 0 per mil galena lead isotope data indicate that mantos and veins formed from the same deep crustal source the fluctuating temperature and salinity values from growth zones in ore and gangue minerals deep crustal source of the lead and magmatic origin of the sulfur argue for a mineralizing system that derived its fluids from magmatic and meteoric sources the magmatic fluids associated with the quartz monzonite stock spread upward and outward along major regional faults and bedding planes of the sedimentary rocks mixing and cooling with meteoric fluids the ore and gangue minerals may have been precipitated due to mixing of these two fluids boiling of ore fluids may have caused ore mineral precipitation in the silver rich veins as suggested by sharp vertical increase in silver concentrations at the 350 m below the present surface level

modeling hydrodynamics of large lagoons insights from the albemarle pamlico estuarine system abstract large estuaries are influenced by winds over adjacent coastal ocean and land areas causing significant spatial variations in water levels currents and surface waves in this study we apply a numerical model to simulate hydrodynamics and waves in the albemarle pamlico estuarine system a large and shallow back barrier basin in eastern north carolina over a one month study period september 2008 with observations from several storm wind events of differing time scales and directions model performance is evaluated for a spatially varying wind field from the north american regional reanalysis narr dataset in comparison to spatially uniform forcing from wind observations at offshore coastal and land based sites across the region a spatially uniform wind field from offshore winds observations results in statistically better hydrodynamic simulations of water levels r 0 88 in the estuaries than narr r 0 48 after comparison with measurements and indicates the importance of strong marine winds over most of the estuary surface area the influence of a prominent bathymetric feature on hydrodynamics in pamlico sound is also investigated by numerically removing a 30 km long and 2 3 m deep shoal from the model grid and replacing it with an idealized depth of 6 m the removal of the shoal increases water level setup by 14 at the estuarine shoreline decreases current magnitudes by up to 40 in the shoal region and increases significant wave heights locally by up to 25 in the sound indicating the importance of this relict geomorphic feature as a major control on the hydrodynamic response of the system during wind events the results suggest that increasing the water depth over the shoal can lead to higher storm surges and wave heights with the possibility of increased inundation and erosion of the back barrier and mainland coastal regions the complex bathymetry and marine wind influence are critical input conditions for modeling large and shallow lagoonal estuaries like the albemarle pamlico estuarine system

complexities in barrier island response to sea level rise insights from numerical model experiments north carolina outer banks using a morphological behavior model to conduct sensitivity experiments weinvestigate the sea level rise response of a complex coastal environment to changes ina variety of factors experiments reveal that substrate composition followed in rankorder by substrate slope sea level rise rate and sediment supply rate are the mostimportant factors in determining barrier island response to sea level rise we find thatgeomorphic threshold crossing defined as a change in state e g from landward migratingto drowning that is irreversible over decadal to millennial time scales is most likely tooccur in muddy coastal systems where the combination of substrate composition depth dependent limitations on shoreface response rates and substrate erodibility mayprevent sand from being liberated rapidly enough or in sufficient quantity to maintain asubaerial barrier analyses indicate that factors affecting sediment availability such aslow substrate sand proportions and high sediment loss rates cause a barrier to migratelandward along a trajectory having a lower slope than average barrier island slope therebydefining an effective barrier island slope other factors being equal such barrierswill tend to be smaller and associated with a more deeply incised shoreface therebyrequiring less migration per sea level rise increment to liberate sufficient sand to maintainsubaerial exposure than larger less incised barriers as a result the evolution of larger lessincised barriers is more likely to be limited by shoreface erosion rates or substrateerodibility making them more prone to disintegration related to increasing sea level riserates than smaller more incised barriers thus the small deeply incised north carolinabarriers are likely to persist in the near term although their long term fate is less certainbecause of the low substrate slopes that will soon be encountered in aggregate results point to the importance of system history e g previous slopes sediment budgets etc in determining migration trajectories and therefore how a barrier island will respondto sea level rise although simple analytical calculations may predict barrier responsein simplified coastal environments e g constant slope constant sea level rise rate etc our model experiments demonstrate that morphological behavior modeling is necessary toprovide critical insights regarding changes that may occur in environments havingcomplex geometries especially when multiple parameters change simultaneously

a vortical hot tower route to tropical cyclogenesis abstract a nonhydrostatic cloud model is used to examine the thermomechanics of tropical cyclogenesis under realistic meteorological conditions observations motivate the focus on the problem of how a midtropospheric cyclonic vortex a frequent by product of mesoscale convective systems during summertime conditions over tropical oceans may be transformed into a surface concentrated warm core tropical depression as a first step the vortex transformation is studied in the absence of vertical wind shear or zonal flow within the cyclonic vorticity rich environment of the mesoscale convective vortex mcv embryo the simulations demonstrate that small scale cumulonimbus towers possessing intense cyclonic vorticity in their cores vortical hot towers vhts emerge as the preferred coherent structures the vhts acquire their vertical vorticity through a combination of tilting of mcv horizontal vorticity and stretching of mcv and vht generated vertical vorticity horizontally localized and exhibiting conve

natural and anthropogenic induced changes in a tidal inlet morphological evolution of oregon inlet abstract natural processes driving the dynamics of tidal inlets have been studied in length however as human influence in the coastal environment persists there is a need to comprehend how both natural and human induced processes drive different aspects of tidal inlet morphological evolution an effort to understand the combined effects of natural and anthropogenic induced processes in a tidal inlet is pursued by studying oregon inlet considered one of the most dynamic inlets in the outer banks of north carolina usa the temporal and spatial scales of the anthropogenic processes driving the morphological evolution of this tidal inlet are studied by means of remotely sensed data and in situ observations gathered from 2005 until 2015 effects of natural process that cannot be gathered from observations are studied via a morphological model based on delft3d evolutional trends include the cyclical response of the main channel of the inlet to dredging a 13 northward rotation of the main channel and frequent sediment transport reversal in the southern shoulder simulations indicate a net sediment transport rate into the inlet of 205 000 m3 yr tidal currents are responsible for 55 of such transport while waves account for the remaining 45 after a 2 year non dredging modeling scenario sediments from the subaqueous spit form a detached shoal in the north side of the flood delta and the main channel remains open branching into two dominant channels observations and model results indicate that oregon inlet has been in a state of stable equilibrium in the past decade natural and human induced processes contribute to such equilibrium this study exemplifies the decadal behavior of a tidal inlet influenced by natural processes infrastructure and dredging

geologic evolution of the caylloma epithermal vein district southern peru the silver and base metal rich caylloma epithermal district in the tertiary volcanic belt of southern peru has been worked intermittently since the incaic period and has produced over 100 million ounces moz of ag intermediate sulfidation mineralization is present in veins hosted by miocene andesitic volcanic and volcaniclastic rocks with minor ore in underlying folded jurassic sedimentary basement new 40 ar 39 ar dates give a host rock age of 20 30 0 11 ma andesitic volcanic matrix a hydrothermal alteration age of 18 35 0 17 ma adularia in vein wall rock and postmineralization ages of 11 8 0 8 and 12 25 0 07 ma sanidine and biotite from a rhyolite dome gangue minerals include quartz calcite rhodonite rhodochrosite pyrite and minor adularia illite barite and helvite ore minerals include sphalerite galena chalcopyrite and tetrahedrite hydrothermal alteration is pervasive in lava flows but weak and localized near veins in volcaniclastic rocks hydrothermal alteration types include silicification quartz adularia and quartz illite and propylitization chlorite calcite illite banded veins show four stages of mineral precipitation 1 early sugary quartz chalcedony pyrite 2 manganese minerals 3 quartz sulfides and 4 late calcite quartz cyclic bands in the manganese stage early sulfides coarse to medium grained quartz late rhodonite calcite chalcedony are a few millimeters to 5 cm thick and form ore bands up to 1 m thick veins occupy dextral normal faults 020 050 45 70 se and extension fractures 060 090 70 90 se and are 1 to 25 m wide and as much as several kilometers long the veins display complex and multi episodic filling with textures characteristic of open space precipitation such as crustiform banding symmetric banding vugs breccias and cockade and comb textures we present a structural model in which the principal veins formed in subparallel northeast striking dextral normal faults and related extension fractures within a northwest striking structural corridor bounded by sinistral regional faults second and third order veins formed by bookshelf sliding related to movement on higher order dominantly strike slip faults slickenlines have low rakes 20 50 sw and fault kinematic analysis suggests the extension axis was oriented 4 330 and the shortening axis 55 234 in agreement with the strain field commonly proposed for the early middle miocene of southern peru ore grade is discontinuous with high grade ore zones having strike lengths of tens to hundreds of meters and extending about 300 m downdip ore shoots in fault hosted veins are narrow subvertical zones a few tens of meters wide measured in the plane of the vein separated by lower grade ore zones ore shoots in extension fractures are shorter downdip and horizontally more continuous some ore shoots occur as half cymoids that form along the main vein only in the hanging wall of synmineral transverse faults mineral composition and metal content are zoned horizontally and vertically silver base metals and calcite and manganese minerals increase to the northeast and downward and sulfide content increases gradually with depth shallower levels of the hydrothermal system are exposed to the west and southwest in the district evidence from sulfur isotopes and high salinity fluid inclusions is consistent with a model in which magmatic fluids played a role in the hydrothermal system introduced through channels of enhanced structural permeability the cyclic nature of mineral precipitation with abrupt changes in mineralogy textures and fluid composition leads us to postulate that cyclic injections of magma derived hydrothermal fluids occurred economic mineralization is estimated to have formed at a depth of about 650 m below the paleowater table with a temperature of formation of 270 c

shoreline erosion and decadal sediment accumulation in the tar pamlico estuary north carolina usa a source to sink analysis abstract estuaries contain vital habitats and it is important to understand how these areas respond to human activities and natural processes such as sea level rise and wave attack as estuarine shorelines erode or become modified with hard structures there is potential for significantly altering the availability of sediment and the filling of coastal systems this study used a source to sink approach and quantified rates of shoreline erosion in the tar pamlico sub estuary a tributary of the larger albemarle pamlico estuarine system apes the average shoreline change rate scr determined using an end point method was 0 5 0 9 m yr 1 for the tar pamlico incorporating bulk density estimates this contributes 0 6 105 tons of fine sediment to the system annually or after accounting for fluvial input about 40 of the total sediment supply to the sub estuary the role of the tar pamlico as a sink for these sediments was addressed using the radionuclide tracers 210pb and 137cs radionuclide activities and sediment accumulation rates identified several depositional regions in particular in the middle of the estuary linear sediment accumulation rates ranged from 0 10 0 02 to 0 38 0 02 g cm 2 yr 1 and total storage of fine sediment in the system was 1 6 105 t yr 1 it was not possible to confidently discern a change in the rate of shoreline erosion or seabed accumulation a preliminary budget for fine sediments grain size

hurricane boundary layer theory in the light of the plethora of definitions for the hurricane boundary layer we advocate a dynamical definition based on the distribution of agradient flow we seek also to clarify the fundamental role of the boundary layer in the hurricane intensification process in particular we contrast the differences between unsteady boundary layers that are able to facilitate the spin up of the vortex above and steady boundary layers that cannot if slaved to the time dependent vortex aloft the latter can spin up the interior vortex only indirectly by changing its thermodynamic properties through vertical advection of these from below and adjustment to thermal wind balance these differences are highlighted by an analytical demonstration that the application of a zero vertical gradient condition on velocity above a steady boundary layer does not provide a direct means of allowing the boundary layer to determine the flow in the interior vortex this result assumes that frictional forces are negligible at this boundary finally echoing a few previous insights we question the applicability of conventional boundary layer theory at radii of strong ascent into the eyewall where the flow is akin to that of separation in aerodynamic boundary layers copyright c 2010 royal meteorological society

mesoscale observations of the genesis of hurricane dolly 1996 abstract recent numerical studies of tropical cyclone genesis suggest a new paradigm for how the surface vortex is established based on a highly nonaxisymmetric mechanism involving the interaction of low level cyclonic circulations generated by deep cumulonimbus convection a reexamination of mesoscale observations during the genesis of hurricane guillermo 1991 confirms the presence of multiple cyclonic circulations more recently airborne doppler radar wind observations during the genesis of atlantic hurricane dolly 1996 also reveal multiple lower to middle tropospheric mesoscale cyclonic circulations during sequential 15 20 min compositing periods a particularly well organized but initially weak mean tangential wind of 7 m s 1 low level cyclonic vortex embedded within the pre dolly tropical disturbance is observed coincident with deep vertically penetrating cumulonimbus convection the earliest observations of this vortex show the peak circulation near 2 km height with a mean diameter of 30 4

controls on the stratigraphic framework and paleoenvironmental change within a holocene estuarine system pamlico sound north carolina usa abstract this study examines the holocene stratigraphic record and paleoenvironmental evolution of a large estuarine system at high temporal and spatial resolution in the context of changing climate sea level and hydrodynamics new data are used to examine two time periods of increased marine influence within pamlico sound in northeastern north carolina interpreted to be the result of extensive barrier island segmentation synchronous with periods of rapid climate change during the late holocene the study reveals the controls on the stratigraphic development and the highly dynamic character of the coastal system in response to climate and sea level change as it interacts with paleotopography these findings can be used to inform projections of future environmental changes estuarine waters occupied paleovalleys in the pamlico sound region as early as ca 7500 cal bp and pleistocene interfluves separated the paleovalleys from the atlantic ocean until ca 5500 cal bp when they were flooded by rising sealevel forming the broad shallow pamlico sound initial barrier islands and shoals likely formed sometime between 5500 and 5000 cal bp providing the geomorphic setting for continued estuarine conditions behind the barriers at ca 4000 cal bp an increase in marine influence and sand content is detected in multiple cores and is correlated to seismic data within the pamlico sound basin this change is interpreted to be the result of increased segmentation of barrier islands thus a greater number of inlets or wider inlets which is consistent with a rapid transgression seen in other areas of the u s east coast the segmentation may have been partially facilitated by a rapid increase in lagoonal area and tidal prism by overtopping of interfluves greater barrier island continuity is evident from 3500 to 1200 cal bp as indicated by muddy deposits with low brackish estuarine foraminiferal assemblages at ca 1200 cal bp seismic sedimentological and micropaleontological data suggest an increase in wave and current energy and marine influence throughout southeastern pamlico sound these changes are interpreted to represent extensive segmentation of the barrier islands during the medieval climate anomaly mca since ca 500 cal bp the pamlico sound system has returned to a more restricted state as inlets have closed currently only three major inlets segment the outer banks the barrier island system fronting pamlico sound but warming climate and increasing rates of sea level rise suggest that another episode of barrier island segmentation began about a half century ago and appears that it may extend into the near future

controls on late quaternary incised valley dimension along passive margins evaluated using empirical data incised valleys are canyon like features that initially form near the highstand shoreline and evolve over geological time as rivers erode into coastal plains and continental shelves to maintain equilibrium gradient profiles in response to sea level fall most of these valleys flood during sea level rise to form estuaries incised valley morphology strongly controls the rate of creation of sediment accommodation valley fill facies architecture and the preservation potential of coastal lithosomes on continental shelves and affects coastal physical processes nonetheless little is known about what dictates incised valley size and shape and whether these metrics can be used to explain principal formation processes the main control on alluvial channel morphology over human time scales is discharge this is based on numerous empirical studies and is well constrained because all variables are easily measured at this short time scale knowledge of long term river evolution over a complete glacio eustatic cycle on the contrary remains largely conceptual experimental and based on individual systems because variables that are thought to drive morphological change are not easily quantified in spite of this difficulty existing models of incised valley formation at the coast suggest that valley evolution is driven largely by downstream forcing mechanisms highlighting sea level and shelf gradient morphology as the dominant controls on valley incision although valleys are cut by rivers whose channels are a direct reflection of discharge little empirical data exist in coastal areas to address the degree to which valley evolution is governed by upstream controls the late quaternary is the best time period to examine because it provides the most complete sedimentary record and many variables including sea level tectonics substrate lithology and drainage network characteristics are accurately constrained here 38 late quaternary valleys along the coast of two different passive continental margins are compared which suggests that valley shape and size are governed primarily by upstream intrinsic controls such as discharge valley width depth and cross sectional area are found to be predictable at the highstand shoreline and are scaled with the size of their drainage basin which has important implications for estimating sediment discharge to continental shelves and deep water environments during periods of low sea level

a numerical study of deep convection in tropical cyclones idealized numerical model simulations are used to investigate the generation and evolution of vertical vorticity by deep convection in a warm cored vortex of near tropical storm strength deep convective updraughts are initiated by thermal perturbations located at different radii from the vortex axis it is found that as the location of the thermal perturbation is moved away from the axis of rotation the updraught that results becomes stronger the cyclonic vorticity anomaly generated by the updraught becomes weaker the structure of the vorticity anomaly changes markedly and the depth of the anomaly increases for an updraught along or near the vortex axis the vorticity anomaly has the structure of a monopole and little or no anticyclonic vorticity is generated in the core vorticity dipoles are generated in updraughts near or beyond the radius of maximum tangential wind speed and this structure reverses in sign with height in all cases the vorticity anomalies persist long after the initial updraught has decayed implications of the results for understanding the vorticity consolidation during tropical cyclogenesis are discussed the effects of eddy momentum fluxes associated with a single updraught on the tangential mean velocity tendency are investigated and a conceptual framework for the interpretation of these eddy fluxes is given the simulations are used to appraise long standing ideas suggesting that latent heat release in deep convection occurring in the high inertial stability region of a vortex core is more efficient than deep convection outside the core in producing temperature rise in the updraught

simulations of shallow supercell storms in landfalling hurricane environments abstract numerical simulations of the convective storms that form in tornado producing landfalling hurricanes show that shallow supercells are possible even though buoyancy is limited because ambient lapse rates are close to moist adiabatic updrafts generally reach peak intensity at low levels often around 2 km above the surface by comparison a simulated midlatitude supercell typical of the great plains of the united states exhibits a pronounced increase in storm size both horizontally and vertically at low levels however the hurricane spawned storms may contain updrafts that rival or exceed in intensity those of great plains supercells at similar levels simulations made using a tornado proximity sounding from the remnants of hurricane danny in 1985 produce a small but intense supercell a finding consistent with the available observational evidence although the amplitude of parcel buoyancy is often small in hurricane environments its concentration in the strongly sheared lower troposphere pro

book review the techniques of modern structural geology volume 2 folds and fractures john g ramsay and martin i huber academic press london 1987 xi 309 398 pp price stg17 50 us 34 50 paperback

tropical convection the effects of ambient vertical and horizontal vorticity we present a series of idealized numerical model experiments to investigate aspects of deep convection in tropical depressions including the effects of boundary layer wind structure on storm structure especially on vertical vorticity production and updraught splitting and the combined effects of horizontal and vertical shear on vertical vorticity production with and without background rotation in warm cored disturbances such as tropical depressions the vertical shear and horizontal vorticity change sign at some level near the top of the boundary layer so that unlike in the typical middle latitude supercell storm the tilting of horizontal vorticity by a convective updraught leads not only to dipole patterns of vertical vorticity but to a reversal also in sign of the updraught rotation with height this finding has implications for understanding the merger of convectively induced vorticity anomalies during vortex evolution ambient cyclonic horizontal shear and or cyclonic vertical vorticity favour amplification of the cyclonically rotating gyre of the dipole consistent with an earlier study storm splitting occurs in environments with pure horizontal shear as well as pure vertical shear but the morphology of splitting is different in both situations splitting is found to require a relatively unstable sounding and relatively strong wind shear

delivery of upper basin sediment to the lower neuse river north carolina u s a extensive storage of upper basin piedmont sediment and apparent low sediment supply to streams in lower basin coastal plain areas generates questions as to the source of alluvium in lower reaches of rivers of the u s atlantic drainage this was investigated on the neuse river north carolina using a mineralogical indicator of sediment source areas the utility of mica flakes for discriminating between piedmont and non piedmont sources of sediment in the lower coastal plain reaches of the neuse was established on the basis of an examination of the u s national soils database and of 26 soil surveys of the north carolina coastal plain from the neuse river estuary to 48 km upstream there are no mica flakes in floodplain soils or in river bank and channel shelf sediments mica flakes become more common upstream this suggests that a very small proportion of the sediment eroded in the piedmont portion of the watershed is delivered to the river mouth the small amounts which presumably do reach the lower coastal plain are so diluted by coastal plain derived alluvium that no piedmont origin can be discerned this demonstrates a dominantly coastal plain source and underscores the importance of storage and discontinuous transport in fluvial sediment systems more importantly results suggest that upper and lower basin sediment dynamics are not only non linearly related but may be virtually decoupled

characteristics of convective processes and vertical vorticity from the tropical wave to tropical cyclone stage in a high resolution numerical model simulation of tropical cyclone fay 2008 abstractthe statistics of convective processes and vertical vorticity from the tropical wave to tropical cyclone stage are examined in a high resolution simulation of tropical cyclone fay 2008 the intensity of vertical velocity follows approximately the truncated lognormal distribution in the model simulation which is consistent with previous observational studies the upward motion at the pregenesis stage is weaker compared to mature hurricanes or midlatitude thunderstorms the relatively strong upward velocities occupying a small areal fraction make a substantial contribution to the upward mass and moisture fluxes and condensation it is also found that upward motion and downward motion both intensify with time but the former is stronger than the latter and the mean vertical motion and the mean vertical mass flux thus increase with time by contrast the maximum anticyclonic vorticity is comparable to the maximum cyclonic vorticity in magnitude both cyclonic vorticity and anticyclonic vorticity in

inner core vacillation cycles during the intensification of hurricane katrina a simulation of hurricane katrina 2005 using the australian bureau of meteorology s operational model for tropical cyclone prediction tclaps shows that the simulated vortex vacillates between almost symmetric and highly asymmetric phases during the symmetric phase the eyewall comprises elongated convective bands and both the low level potential vorticity pv and pseudo equivalent potential temperature e fields exhibit a ring structure with the maximum at some radius from the vortex centre during this phase the mean flow intensifies comparatively rapidly as the maximum acceleration of the mean tangential wind occurs near the radius of maximum mean tangential wind rmw in contrast during the asymmetric phase the eyewall is more polygonal with vortical hot towers vhts located at the vertices the low level pv and e fields have monopole structures with the maximum at the centre the intensification rate is lower than during the symmetric phase because the mean tangential wind accelerates most rapidly well within the rmw the symmetric to asymmetric transition is accompanied by the development of vhts within the eyewall the vhts are shown to be initiated by barotropic convective instability associat ed with the ring like structure of pv in the eyewall where the convective instability is large during the reverse asymmetric tosymmetric transition the vhts weaken as the local vertical wind shear increases and the convective available potential energ yi s consumed by convection the weakened vhts move outwards similar to vortex rossby waves and are stretched by the angular shear of the mean vortex simultaneously the rapid filamentation zone outside the rmw weakens becoming more favourable for the development of convection the next symmetric phase emerges as the convection reorganizes into a more symmetric eyewall it is proposed that vacillation cycles occur in young tropical cyclones and are distinct from the eyewall replacement cycles that tend to occur in strong and mature tropical cyclones copyright c 2011 royal meteorological society

tropical cyclogenesis and vertical shear in a moist boussinesq model tropical cyclogenesis is studied in the context of idealized three dimensional boussinesq dynamics with perhaps the simplest possible model for bulk cloud physics with low altitude input of water vapour on realistic length and time scales numerical simulations capture the formation of vortical hot towers from measurements of water vapour vertical velocity vertical vorticity and rain it is demonstrated that the structure strength and lifetime of the hot towers are similar to results from models including more detailed cloud microphysics the effects of low altitude vertical shear are investigated by varying the initial zonal velocity profile in the presence of weak low level vertical shear the hot towers retain the low altitude monopole cyclonic structure characteristic of the zero shear case starting from zero velocity some initial velocity profiles with small vertical shear can have the effect of increasing cyclonic predominance of individual hot towers in a statistical sense as measured by the skewness of vertical vorticity convergence of horizontal winds in the atmospheric boundary layer is mimicked by increasing the frequency of the moisture forcing in a horizontal subdomain when the moisture forcing is turned off and again for zero shear or weak low level shear merger of cyclonic activity results in the formation of a larger scale cyclonic vortex an effect of the shear is to limit the vertical extent of the resulting emergent moist vortex for stronger low altitude vertical shear the individual hot towers have a low altitude vorticity dipole rather than a cyclonic monopole the dipoles are not conducive to the formation of larger scale vortices and thus sufficiently strong low level shear prevents the vortical hot tower route to cyclogenesis the results indicate that the simplest condensation and evaporation schemes are useful for exploratory numerical simulations aimed at better understanding of competing effects such as low level moisture and vertical shear

precipitation and evolution sensitivity in simulated deep convective storms comparisons between liquid only and simple ice and liquid phase microphysics abstract weisman and klemp suggested that their liquid only deep convective storm experiments should be repeated with a liquid ice microphysics scheme to determine if the solutions are qualitatively the same using a three dimensional nonhydrostatic cloud model such results are compared between three microphysics schemes the kessler liquid only scheme used by weisman and klemp a lin farley orville like scheme with liquid and ice parameterization li and the same lin farley orville like microphysics scheme but with only liquid processes turned on lr convection is simulated using a single thermodynamic profile and a variety of shear profiles the shear profiles are represented by five idealized half circle wind hodographs with arc lengths us of 20 25 30 40 and 50 m s 1 the precipitation cold pool characteristics and storm evolution produced by the different schemes are compared the kessler scheme produces similar accumulated precipitation over 2 h compared to lr for all shear regimes