the influence of wind direction upon flow along the west coast of britain and in the north channel of the irish sea abstract this paper briefly describes the development of a three dimensional nonlinear hydrodynamic model of the sea region off the west coast of scotland the north channel and the irish sea the model uses a sigma coordinate in the vertical and subgrid scale mixing of momentum is parameterized by a vertical eddy viscosity computed using a turbulence energy submodel numerical calculations illustrate the importance of wind direction and topography in determining flow pathways along the west coast of scotland through the north channel and within the irish sea the role of a northward flow into the irish sea through st george s channel arising from wind events over the celtic sea in controlling the flow in the north channel and deep regions of the irish sea is also considered the series of calculations presented here helps to explain the spatial and temporal variability of the observed flows from both direct measurements and tracer studies found off the west cost of scotland and in the north chan

formation of an a ā lava delta insights from time lapse multibeam bathymetry and direct observations during the stromboli 2007 eruption five consecutive multibeam bathymetries collected before during and after the 2007 stromboli eruption combined with visual inspections allowed us to document the morphological evolution of an a lava fed delta and to reconstruct the main processes acting during its submarine emplacement the 2007 stromboli delta extended down to 600 m water depth and covered an area of 420 103 m2 with a maximum thickness of 65 m and a total estimated volume of 7 106 m3 i e three times larger than its subaerial counterpart the lava delta grew mainly through the emplacement of discrete lobes about 50 150 m in size lobes were fed from point sources along the paleoshoreline and their subaqueous pathways seem to be mainly controlled by the submarine morphology with flows mostly filling in depressions left by previous lobes the main controlling factors on the lobe morphology and thickness are the effusion rates and the pre eruption morphology i e the geometry and gradients of the basal surface data also shows that sudden slope failure of portions of the submarine delta may occur simultaneously with accretion implying that a significant part of the delta material can be transported to greater depths by submarine gravity flows the present study is relevant for future monitoring and hazard assessment during the growth of active lava fed deltas as well as for a better interpretation of ancient volcaniclastic successions inland

a vertically averaged circulation model using boundary fitted coordinates abstract a two dimensional vertically averaged circulation model using boundary fitted coordinates has been developed for predicting sea level and currants in estuarine and shelf waters the basic idea of the approach is to use a set of coupled quasi linear elliptic transformation equations to map the physical domain to a corresponding transformed plane such that all boundaries are coincident with coordinate lines and the transformed mesh is rectangular the hydrodynamic equations are then solved by a multi operation finite difference technique in the rectangular mesh transformed grid comparisons of the circulation model predictions for tidally forced flows in a wedge section with both flat and quadratic bottom topography and in a flat channel with exponential variation in width were in excellent agreement with corresponding analytic solutions simulation of steady state wind induced setup in a closed basin formed using elliptic cylindrical coordinates also was in excellent agreement with the analytic

characteristics of gravity waves generated by surface topography on venus comparison with the vega balloon results abstract data from the 1985 vega venus balloon mission indicate that the mountainous region known as aphrodite influences atmospheric motions at balloon float altitudes near 54 km an altitude located within the middle cloud region it is shown that stationary gravity waves generated by surface topography and doppler shifted by a wind blowing over the terrain can propagate upward to the middle cloud layers under the right circumstances waves are amplified considerably in excess of their amplification due to the decrease of density with altitude the additional amplification is due to resonance that results from variations of static stability and mean zonal wind with altitude computed atmospheric propagation characteristics combined with terrain slopes in aphrodite estimated from pioneer venus radar altimeter data can be sufficient to produce wind amplitudes at 54 km comparable to those observed by the vega 2 balloon as it overflew aphrodite the dominant waves have horizontal wavelengths of the ord

modeling the effect of wave current interaction on the three dimensional wind driven circulation of the eastern irish sea abstract a high resolution 0 5 north south by 1 0 west east three dimensional hydrodynamic model of the eastern irish sea is used to examine the influence of enhanced bed friction due to wind wave effects upon the three dimensional wind induced circulation of the eastern irish sea the model uses a mixed finite difference modal approach in which a standard finite difference grid is employed in the horizontal with the galerkin method with an expansion of functions modes in the vertical giving a continuous current profile from sea surface to seabed vertical eddy viscosity within the model is a function of the flow field the model is used to examine the wind induced response of the area to spatially uniform and constant in time northerly and westerly wind stresses of 1 n m 2 the effect upon bed stresses and hence the three dimensional circulation of the region of enhanced bed turbulence due to wind wave effects is also considered using idealized wave fields changes in bed stress particularl

the influence of eddy viscosity parameterization and turbulence energy closure scheme upon the coupling of tidal and wind induced currents a three dimensional model of the irish sea and the shelf and shelf edge region off the west coast of scotland is used to examine the interaction of wind induced surface currents and m 2 tidal currents which can lead to an increased near surface m 4 tidal current in the region calculations are performed using uniform southerly and westerly wind stresses with vertical eddy viscosity computed using either a simple flow dependent form of viscosity or one related to the flow and surface wind stress or derived using a two equation turbulence model resulting m 4 tidal distributions computed with the various viscosity formulations are compared with each other the spatial distribution the m 4 tidal current in the case of the flow dependent viscosity shows a significant enhancement of the surface m 4 tide due to non linear coupling between the surface shear and the tidally dependent viscosity in deep water this is the dominant mechanism giving rise to an enhancement in near surface m 4 current in shallow water however where other non linear processes are important in generating the m 4 tide namely changes in water depth and friction these are significant as well as the non linear surface shear effect in changing the m 4 tidal distribution however when an eddy viscosity formulation depending upon flow and surface wind stress is used the non linear coupling mechanism producing an enhanced m 4 tidal surface current is reduced and no increase in m 4 surface current occurs calculations with the two equation turbulence model do not produce an increase in the near surface m 4 tide as the near surface viscosity in this model is determined principally by the wind stress rather than the tidal current some conclusions concerned with developing a simple eddy viscosity model having similar characteristics to the turbulence energy model and experimental data sets for validation are considered at the end of the paper

characterization of mesoscale gravity waves in the upper and lower clouds of venus from vex virtis images 1 images obtained from the visible and infrared thermal imaging spectrometer virtis m instrument onboard venus express present visible trains of alternating bands of cloud brightness in two different layers at the upper cloud tops 66 km altitude observed in the dayside hemisphere using reflected ultraviolet light 380 nm and in the lower cloud 47 km altitude observed in the nightside hemisphere using thermal radiation 1 74 m the waves are nearly zonal with the bands perpendicular to latitude circles have wavelengths of 60 150 km propagate westward with low phase velocities relative to the zonal flow and are confined in wave packets of 400 to 1800 km in length the waves in the lower cloud observed in the infrared are widely distributed around the planet and their appearance varies widely throughout the virtis data set the locations of both types of waves seem not correlated with latitude local times surface topography or the structure of the wind in both cases the characteristics of the waves correspond to gravity waves propagating in confined stable layers of the atmosphere we examine the properties of these waves in terms of a linear model and perform a simple analysis to discuss the vertical stability of the atmosphere within venus clouds

south polar features on venus similar to those near the north pole venus has no seasons slow rotation and a very massive atmosphere which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets infrared observations by previous missions to venus revealed a bright dipole feature surrounded by a cold collar at its north pole the polar dipole is a double eye feature at the centre of a vast vortex that rotates around the pole and is possibly associated with rapid downwelling the polar cold collar is a wide shallow river of cold air that circulates around the polar vortex one outstanding question has been whether the global circulation was symmetric such that a dipole feature existed at the south pole here we report observations of venus south polar region where we have seen clouds with morphology much like those around the north pole but rotating somewhat faster than the northern dipole the vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper the spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition

the late holocene gargano subaqueous delta adriatic shelf sediment pathways and supply fluctuations the gargano subaqueous delta formed on the eastern and southeastern sides of the gargano promontory in the western adriatic this subaqueous deposit represents the southernmost portion of the late holocene highstand systems tract hst growing along the western side of the adriatic as an extensive wedge of deltaic and shallow marine mud the late holocene hst rests above a regional downlap surface that marks the time of maximum landward shift of the shoreline attained around 5 5 cal kyr bp at the end of the late pleistocene holocene sea level rise high resolution seismic stratigraphic and tephra correlation indicate the presence of a thin basal unit recording condensed deposition between 5 5 and 3 7 cal kyr bp over much of the basin above this unit sediment accumulation rates increased to high values as much as 1 5 cm yr 1 reflecting the stabilisation of relative sea level and the forcing from high frequency climatic or anthropogenic changes affecting river dynamics the late holocene mud wedge of which the gargano subaqueous delta is a significant component reaches up to 35 m in thickness and has a volume of ca 180 km3 the shore parallel thickness distribution of the mud wedge reflects the dominant oceanographic regime of the basin and the asymmetric location of the mostly western sediment sources with a combined modern delivery of 51 7 106 t yr 1 of mean suspended load in sections perpendicular to the coast the late holocene mud wedge appears composed of forestepping clinoforms with gently dipping foresets typically 0 5 the gargano subaqueous delta is characterised by a submarine topset in water depths shallower than 25 28 m and accounts for about 1 7th of the total volume of the late holocene mud wedge despite the absence of direct river supply to the gargano area in the area of maximum interaction between shore parallel currents and basin morphology progradation occurs onto a flat and barren bedrock outcrop in about 50 80 m water depth the rapid transition from a thickness of 30 m of late holocene mud to nil is a good indication of the role of southward flowing bottom hugging shelf currents in causing the redistribution of sediment along the adriatic inner shelf additional evidence of this regime comes from 1 the most recent sigmoid defined at seismic stratigraphic scale deposited since the onset of the little ice age showing a shore parallel thickness distribution and a main depocentre to the southeast of the gargano promontory 2 the maximum values of sediment accumulation rates over the last century documented by 210pb measurements defining a narrow shore parallel belt immediately seaward of the depocentre of the most recent sigmoid the gargano subaqueous delta grows from the outbuilding of progressively younger progradational sigmoids that tend to parallel the previous ones the gargano subaqueous delta differs from other documented late holocene subaqueous deltas because its growth reflects 1 sediment transport dominated by bottom currents sub parallel to the strike of the composing clinoforms 2 a complex supply regime including the po delta 350 km to the north and several coalescing apennine rivers acting as line source 3 several alternating intervals of enhanced outbuilding and condensed deposition and 4 an in phase growth of the most recent sigmoid with the major progradation of the po delta during the little ice age

images from galileo of the venus cloud deck images of venus taken at 418 violet and 986 near infrared nir nanometers show that the morphology and motions of large scale features change with depth in the cloud deck poleward meridional velocities seen in both spectral regions are much reduced in the nir in the south polar region the markings in the two wavelength bands are strongly anticorrelated the images follow the changing state of the upper cloud layer downwind of the subsolar point and the zonal flow field shows a longitudinal periodicity that may be coupled to the formation of large scale planetary waves no optical lightning was detected

a three dimensional baroclinic model of the irish sea formation of the thermal fronts and associated circulation a high resolution three dimensional baroclinic shelf sea model is developed and applied to the determination of the various processes influencing the generation and position of thermal fronts and the associated circulation in the irish sea the model has a horizontal grid resolution of approximately 3 6 km by 3 0 km and can resolve the thermal fronts in the region in particular in the western irish sea although the grid is not sufficiently fine to resolve small scale features along these fronts produced by baroclinic instabilities using meteorological forcing from dublin airport located close to the center of the region and tidal forcing a series of numerical experiments were performed to examine the processes influencing the location and dynamics of thermal fronts and associated circulation in the irish sea the results show a reasonable qualitative agreement with observations of the thermal stratification and the associated circulation in the western irish sea the ability of the model to reproduce the main features of the frontal structures in the region having been established it is used to examine the interannual variability of the density flow field calculations using meteorological forcing from different years show that the western irish sea fronts and the associated cyclonic circulation are persistent features although exact details of the fronts and their times of formation and breakdown show a large interannual variability model results also reveal a patch of thermal stratification in the northern part of the eastern irish sea with northward thermal density driven currents in this region

human influence and the changing geomorphology of mediterranean deltas and coasts over the last 6000 years from progradation to destruction phase the present geomorphology of the mediterranean s coasts is largely a product of an intricate long term relationship between nature and human societies a cradle of ancient civilisations the mediterranean has seen its shores occupied by humans since prehistory and is therefore a particularly pertinent unit of analysis the morphotectonic context and other forcing agents e g climate shaped out a highly diversified coastal morphology and generated a sediment supply regime potentially favourable to the formation of numerous open coast deltas and bay head deltas in infilled rias as sea level stabilised during the mid holocene this supply of riverine sediment has also been the key agent in mediating human occupation of the mediterranean s clastic coasts expressions of this relationship have been extensively archived in clastic coastal deposits including base level deltaic and estuarine sedimentary sinks which comprise records to explore the interactions between geosystems and the human environment the stratigraphic sequences in these coastal sedimentary archives comprise in many places a clearly identified anthropogenic signature notably in ancient harbours some of which underwent extremely rapid silting up due to massive sediment sourcing generated by new agricultural practices from the neolithic onwards increasing human influence especially over the last 3000 years has been in turn an important driver of changes in sediment supply strongly modulating deltaic development pulses of sediment supply from catchments rendered vulnerable by human perturbations during the roman period resulted in a new cycle of inception of many other deltas and in rapid delta growth e g the ebro the po the arno and the ombrone another progradation dynamic during the little ice age at a time of strong rural population growth river discharge increases technological developments and urbanisation further consolidated delta growth understanding the life cycle of these deltas since their initial formation is in turn key to unravelling the relative role of natural and anthropogenic forcing agents rapid climate changes are deemed to have contributed through both the stripping of landscapes rendered fragile by human activities and active fluvial sediment transport to the coast but disentangling climate change effects from human impacts in the mediterranean remains a challenge the patterns of subsequent deltaic growth and delta morphodynamics reflect adaptations to pulsed sediment supply river discharge variations the microtidal fetch limited context of the mediterranean and direct engineering interventions the progradation dynamic of the roman period and little ice age contrasts markedly with the situation of common coastal destabilisation over the last two centuries particularly well documented for the last 50 years this period has been characterised by reduced sediment flux to base level geosystems due to catchment reforestation retenion within reservoirs fluvial regulation and dredging resulting in the erosion of deltas and barrier lagoon and beach dune systems large stretches of shoreline and narrow coastal plains have been massively engineered for coastal defence and protection against erosion but also for the construction of marinas leisure harbours and artificial beaches resulting in the emergence of veritable artificial seafronts these interventions have collectively and progressively raised societies to a pervasive and overarching position in the geomorphic stability instability of the mediterranean s coasts a situation that will be exacerbated by pressures from sea level rise paving the way for rampant coastal erosion and delta destruction

mapping turbidity patterns in the po river prodelta using multi temporal landsat 8 imagery abstract thirty meters resolution turbidity maps derived from landsat 8 l8 images were used to investigate spatial and temporal variations of suspended matter patterns and distribution in the area of po river prodelta italy in the period from april 2013 to october 2015 the main focus of the work was the study of small and sub mesoscale structures linking them to the main forcings that control the fate of suspended sediments in the northern adriatic sea a number of hydrologic and meteorological events of different extent and duration was captured by l8 data quantifying how river discharge and meteo marine conditions modulate the distribution of turbidity on and off shore at sub mesoscale peculiar patterns and smaller structures as multiple plumes and sand bars were identified thanks to the unprecedented spatial and radiometric resolution of l8 sensor the use of these satellite derived products provides interesting information particularly on turbidity distribution among the different delta distributaries in specific fluvial regimes that fills the knowledge gap of traditional studies based only on in situ data a novel approach using satellite data within model implementation is then suggested

the influence of wind effects upon internal tides in shelf edge regions the interaction of the internal tide with wind induced currents in the shelf edge region off the west coast of scotland is studied using a baroclinic shelf edge model the model is used in cross shelf form with a horizontal finite difference grid of the order of 0 6 km and 50 sigma levels in the vertical to study the modification of the internal tide produced by upwelling and downwelling winds horizontal mixing in the model is parameterized using either the laplacian form of the horizontal diffusion or the biharmonic form and the sensitivity of the solution to both forms is examined coefficients for the vertical diffusion of momentum and density are determined using either an algebraic expression involving the richardson number or from a two equation turbulence energy submodel calculations show that in the case of an upwelling favorable wind the density gradient in the near bed region is increased leading to a slight modification compared to the tide only solution of the internal tide at the fundamental frequency with significant increases in amplitude of the higher harmonics due to the increase in the nonlinear terms produced by the increase in the density gradient with a downwelling favorable wind the amplitude of the current and internal displacement of the internal tide at the fundamental frequency are significantly reduced due to the change in the density field in the region of internal tidal production this also leads to a reduction in the amplitude of the higher tidal harmonics by using a fine grid in the horizontal the coefficients in the horizontal diffusion terms were set at a minimum and no significant difference in solutions computed with the laplacian or biharmonic diffusion terms was found similarly there are no differences in the major features of the flow field computed with the various parameterizations of the vertical diffusion although there are some differences in the magnitude of the diffusion coefficients

eddy viscosity and tidal cycles in a shallow sea abstract the very pronounced spring neap tidal cycle in the south australian gulfs leads to an unusually large variation in the magnitude of the tidal currents measurements of the currents in these gulfs show that the non tidal circulation depends on the strength of the tidal currents and hence on the spring neap cycle a simple model is produced in which the vertical eddy viscosity is a function of both wind strength and tidal currents results from the model agree with the observations and suggest a means whereby variations in tidal mixing may be accounted for in hydrodynamic modelling of the circulation in shallow seas

a three dimensional model of diurnal and semidiurnal tides on the european shelf a three dimensional hydrodynamic model of the continental shelf is used to examine the sensitivity of computed diurnal k1 and o1 and semidiurnal m2 s2 and n2 tidal elevations and currents to changes in eddy viscosity profile friction coefficient and water depth the influence of the tide generating potential is also considered the model uses a standard finite difference grid in the horizontal with a functional approach in the vertical thereby giving a continuous tidal current profile from sea surface to seabed the magnitude of the vertical eddy viscosity depends upon the flow field comparisons are made between model computed profiles and harmonic analyses of 278 current time series at a range of locations in varying water depths with particular emphasis on locations where there are current measurements at a number of points in the vertical a detailed examination of these comparisons shows that frictional effects in the near bed region are particularly important in determining near bed shear and that an accurate specification of water depth is critical for tidal current magnitude the spatial distribution of computed current ellipses shows that the semidiurnal currents are strongest in shallow water with the diurnal currents exhibiting an intensification in the shelf edge region the inclusion of the equilibrium tide is particularly important for the correct determination of the magnitude of the k1 tidal current as well as k1 elevations in the north sea the detailed comparisons show that the magnitude of the tidal currents is correctly determined to within 5 cm s 1 at 220 locations with the model accurately to within 2 cm s 1 reproducing the vertical variation the most sensitive test of a three dimensional model of the tidal current at most locations

morphological changes and sedimentary processes induced by the december 2003 flood event at the present mouth of the grand rhone river southern france the study which is based on repetitive bathymetric surveys assesses changes and effects of one of the most important floods recorded in the rhone delta area bottom morphology and sediment distribution in the rhone outlet after the december 2003 flood are discussed by comparison between digital terrain maps dtms of november 2003 and january 2004 the post flood morphology shows that the whole of the system is active mainly in the east the channel of the rhone has been hollowed out on the left bank by more than 5 m the eastern coast of the mouth has retreated 400 m the mouth bar has prograded 200 m and the slope of the delta front has increased by 0 19 the overlay of pre and post flood dtms makes it possible to estimate the total volume deposited in the 0 to 20 m zone as 7 8 10 the acquisition of bathymetric measurements immediately before and after a major flood allows more than a simple morphological description in addition an analysis of the solid load transfer processes towards the prodelta is achievable three mechanisms are highlighted most of the material eroded in the channel and supplied to the delta front corresponds to fine sediment that drape homogeneously over the pre flood morphology of the delta front the transit of the coarsest sediment primarily sand is slowed down in the channel of the rhone this sediment builds up in relatively small areas leading to the formation of gullies on the prodelta slope the gullies have fixed positions and disappear gradually towards the west following the progressive migration of the active band towards the east these old features are not reactivated by floods occurring after their formation during the flood only a small volume of coarse sediment bypasses through the gullies and the fine deposits are remobilised rapidly or compacted flood input concerns essentially the delta front which traps 90 of the fluvial solid discharge between 0 and 20 m depth the coarse prodelta supply is then due mainly to mass movements of unconsolidated material deposited beforehand on the top of the delta front consequently the main nourishment of the prodelta does not occur directly during and or immediately after a flood event but is delayed by sediment being temporarily trapped on the delta front

recent morphological changes of the yellow river huanghe submerged delta causes and environmental implications abstract the yellow river huanghe submerged delta yrsd has been under the threat of erosion and retreat during the anthropocene due to dramatic climatic and anthropogenic changes in the yellow river basin the analysis of field data shows that over the period of 1977 2005 the changes in climate decrease in precipitation and increase in air temperature and human interventions increase in water diversion projects throughout the watershed have resulted in the sharp reductions of river flow and sediment discharges into the bohai sea consequently over the decadal timescale morphological evolution of the yrsd has gone through three stages i e rapid accumulation 5 77 10 8 m 3 year in 1977 1985 moderate accumulation 3 80 10 8 m 3 year in 1986 1995 and slow accumulation 0 91 10 8 m 3 year in 1996 2005 climatic change within the catchment characterized by the rapid increase of air temperature contributed significantly to the transitions from the rapid accumulation to the moderate accumulation and to the subsequent slow accumulation the decadal morphological changes of the yrsd also show peculiar deposition erosion characteristics over the medium timescale under river input reduction within the three decades the patterns of the main sedimentary body exhibit irregular ellipses with the long axis parallel to the 5 or 10 m isobaths and short axis perpendicular to the isobaths the depocentres of the yrsd are located between the 10 and 15 m isobaths close to the respective river mouths with a high vertical accretion rate of 1 20 m year the time series data of annual volumetric change of the yrsd and river sediment load from 1977 to 2005 further demonstrate significant linear positive relationships between deltaic geomorphic change and fluvial input over shorter timescales annual and 3 year the critical sediment discharges for maintaining the deposition erosion equilibrium state of the yrsd over the annual and 3 year timescales are found to be 1 79 10 8 t year and 1 29 10 8 t year respectively the analysis from the latest hydrological data 2006 2015 suggests that over the decadal timescale the evolution state of the yrsd currently has transitioned from constructive to destructive due to the weakened fluvial input moreover there exists a close quantitative link between the progradation of the yellow river subaerial delta yrad and the yrsd over the five year timescale indicating that every 1 10 8 m 3 year increase of the yrsd s yearly volumetric change will result in a 3 28 km 2 year increase of the yrad s yearly land accretion area and the yrad will reach the extension retreat balance state when yearly morphological change of the yrsd is at 0 73 10 8 m 3 year

a high resolution three dimensional model of the m2 m4m6 s2 n2 k1and o1tides in the eastern irish sea abstract the spatial distribution of the m 2 s 2 n 2 m 4 m 6 k 1 and o 1 tidal elevations and currents in the eastern irish sea is examined using a high resolution three dimensional model of the region the model uses a functional representation of the current in the vertical and can resolve the near bed high shear bottom boundary layer comparison of computed and observed tidal elevations and currents shows that the grid is sufficiently fine of order 1 km and the near bed region sufficiently well resolved to enable tidal elevations and currents particularly near bed currents to be accurately reproduced in order to accurately reproduce the near bed currents its is essential to reduce eddy viscosity close to the bed and enhance the bottom friction coefficient above that used in two dimensional models calculations of the m 2 m 4 and m 6 tidal currents with and without the other tidal constituents show that it is essential to include the other constituents if tidal elevations and currents are to be determined with a high level of accuracy with the m 6 tide being significantly influenced by the presence of the other constituents the presence of other tidal constituents not only increases bottom friction in an analogous manner to a two dimensional model but because the model involves a flow dependent viscosity they increase its magnitude which affects current structure the calculation of parameters such as the maximum bed stress which is important in sediment transport can be severely underestimated if the other tidal constituents are not included

jupiter cloud composition stratification convection and wave motion a view from new horizons several observations of jupiter s atmosphere made by instruments on the new horizons spacecraft have implications for the stability and dynamics of jupiter s weather layer mesoscale waves first seen by voyager have been observed at a spatial resolution of 11 to 45 kilometers these waves have a 300 kilometer wavelength and phase velocities greater than the local zonal flow by 100 meters per second much higher than predicted by models additionally infrared spectral measurements over five successive jupiter rotations at spatial resolutions of 200 to 140 kilometers have shown the development of transient ammonia ice clouds lifetimes of 40 hours or less in regions of strong atmospheric upwelling both of these phenomena serve as probes of atmospheric dynamics below the visible cloud tops

evaluation of seabed mapping methods for fine scale classification of extremely shallow benthic habitats application to the venice lagoon italy abstract recent technological developments of multibeam echosounder systems mbes allow mapping of benthic habitats with unprecedented detail mbes can now be employed in extremely shallow waters challenging data acquisition as these instruments were often designed for deeper waters and data interpretation honed on datasets with resolution sometimes orders of magnitude lower with extremely high resolution bathymetry and co located backscatter data it is now possible to map the spatial distribution of fine scale benthic habitats even identifying the acoustic signatures of single sponges in this context it is necessary to understand which of the commonly used segmentation methods is best suited to account for such level of detail at the same time new sampling protocols for precisely geo referenced ground truth data need to be developed to validate the benthic environmental classification this study focuses on a dataset collected in a shallow 2 10 m deep tidal channel of the lagoon of venice italy using 0 05 m and 0 2 m raster grids we compared a range of classifications both pixel based and object based approaches including manual maximum likelihood classifier jenks optimization clustering textural analysis and object based image analysis through a comprehensive and accurately geo referenced ground truth dataset we were able to identify five different classes of the substrate composition including sponges mixed submerged aquatic vegetation mixed detritic bottom fine and coarse and unconsolidated bare sediment we computed estimates of accuracy namely overall user producer accuracies and the kappa statistic by cross tabulating predicted and reference instances overall pixel based segmentations produced the highest accuracies and the accuracy assessment is strongly dependent on the number of classes chosen for the thematic output tidal channels in the venice lagoon are extremely important in terms of habitats and sediment distribution particularly within the context of the new tidal barrier being built however they had remained largely unexplored until now because of the surveying challenges the application of this remote sensing approach combined with targeted sampling opens a new perspective in the monitoring of benthic habitats in view of a knowledge based management of natural resources in shallow coastal areas

the m2 tide and its residual on the outer banks of the gulf of maine abstract tidal computations are reported for the gulf of maine with emphasis on its seaward banks georges bank browns bank nantucket shoals and the nearshore region off cape sable the model is 3d and nonlinear with quadratic vertical viscosity stratification is ignored the objective is to establish a theoretical baseline for tidal and residual currents on detailed topography against which seasonal changes may be examined two triangular meshes are used the base case corresponds to earlier studies with roughly 6 km resolution on the banks a more refined and extended mesh provides resolution at 2 3 km in critical areas and has boundaries farther removed from the banks both meshes provide very good fits with observed m2 elevations comparison of computed and observed m2 current profiles at 76 sites reveals general agreement that improves with resolution for the refined mesh and the 48 sites with records exceeding 60 days average deviations for m2 ellipse parameters are 6 1 4 7 cm s 1 for the

drowning of the mississippi delta due to insufficient sediment supply and global sea level rise global sea level rise reduced sediment supply and subsidence threaten the stability of the mississippi delta calculations of riverine sediment load and storage indicate that 10 000 13 500 km2 of the delta could be submerged by ad 2100

modeling the nonlinear effect of wind on rectilinear tidal flow 1 observations of near bed alongshore flow in 4 10 m depth at terschelling netherlands show that strong alongshore winds 15 20 m s in the flood direction reduce the tide current range and alter the tidal flow curve by bringing maximum flood flow forward in time and delaying maximum ebb flow these nonlinear effects which are more pronounced in shallower water are reproduced well by a single point model in the vertical driven by large scale o km sea surface gradients and wind stress using a quadratic bottom stress formulation and a time dependent eddy viscosity derived from a k e turbulence closure model subsequent idealized model simulations using a terschelling based m2 sea surface gradient and wind speeds between 0 and 20 m s show that the wind induced modifications of the tidal flow are consistent with the interaction of the wind induced flow with the tidal flow through the quadratic bed stress the wind driven flow enhances friction during the flood phase more than it reduces friction during the ebb flow thereby increasing friction over a tidal cycle and as a consequence reducing the tide current range the predicted increase in asymmetry of bed friction during flood and ebb flow with increasing wind speed also increases decreases the m4 m6 amplitude consistent with the observations the m4 m2 amplitude ratio is predicted to be largest when the flow has just become unidirectional that is when the wind driven flow equals the tidal current

the wind induced circulation and the interaction of wind forced and tidally driven currents on the european shelf abstract a three dimensional hydrodynamic model of the continental shelf is used to examine the wind induced flow on the shelf produced by uniform northerly and westerly wind stresses the model has a functional approach in the vertical and a finite difference grid in the horizontal a flow dependent eddy viscosity is used to parameterize vertical mixing of momentum initial calculations of the wind driven flow in the absence of tides are used to examine the spatial variability of the currents in response to uniform northerly and westerly winds and the time taken to reach a steady state results of subsequent calculations including tidal turbulence show that the wind induced flow is modified by the non linear interaction between tidal and wind driven currents arising from the flow dependent eddy viscosity term and bottom friction effects the spatial variability of wind induced currents on the shelf is related to topographic features and used to explain some of the variability found in the flow fields on the shelf that have been deduced from measurements a comparison of tidal current ellipses at the fundamental frequency and higher harmonic derived from a harmonic analysis of tidal and wind driven flows shows that the surface current ellipses particularly those of the higher harmonic are modified by the presence of the wind driven flow the processes giving rise to this modification are the time variability of the eddy viscosity and the near surface shear produced by the wind stress

a three dimensional model of the m4 tide in the irish sea the importance of open boundary conditions and influence of wind a fully nonlinear three dimensional hydrodynamic model of the irish sea is used to examine the processes determining the spatial variability of the m4 tide in the irish sea the model is based upon a mixed spectral finite difference approach with an expansion of functions in the vertical yielding a continuous current profile and a finite difference grid in the horizontal the model has a sufficiently fine grid to enable the nonlinear advective terms to be resolved in their finite difference form and the spatial variability of the m4 tide to be represented computed m4 elevations and currents determined using a radiation open boundary condition with both m2 mid m4 elevation and current input and a flow dependent viscosity are found to be in satisfactory agreement with observations considering the limited grid resolution of the model and the level of noise in the m4 tide as a percentage of the signal is much higher than for m2 this agreement is good enough to establish the credibility of using the model to examine the processes influencing the m4 tide which are discussed in detail the importance of an m4 current input to the radiation condition and the difficulty of using an elevation specified open boundary condition to reproduce the m4 tide in this region are considered in some detail the nonlinear advective terms are shown to have a limited local influence namely around headlands in generating the m4 tide the influence of wind effects upon m4 tidal currents particularly through the nonlinear term associated with a time dependent eddy viscosity is examined and shown to produce a significant increase in the m4 near surface tidal current and a modification of the current profile in essence the change of the m4 tidal current by meteorological effects will give rise to noise in any observed m4 current due to the random nature of the wind fields

new insights on the subsidence of lipari island aeolian islands southern italy from the submerged roman age pier at marina lunga abstract lipari island belongs to the aeolian archipelago located in the southern tyrrhenian sea italy which is one of the most active volcanic areas of the mediterranean basin although this region has been settled since prehistory only during roman times were coastal installations built in these islands in this study we present and discuss data on the relative sea level change estimated from a submerged pier of roman age dated 2100 100 bp this structure about 140 60 m is located along the coast of marina lunga corresponding to the present location of the main harbor of lipari island this pier which was accidentally discovered in 2008 during preliminary excavations for the construction of a new pier is a valuable indicator of relative sea level changes and vertical land movements its top surface is presently located at 9 1 0 05 m while the foundations at the outer end of the pier are at 11 6 0 05 m above a shoreline placed at 13 0 0 05 m we studied this site through direct archaeological investigations and ultra high resolution multibeam bathymetry the current submergence of this pier can be explained by the cumulative effect of the relative sea level changes caused by the regional glacio hydro isostatic signal active since the end of the last glacial maximum and the local volcano tectonic land subsidence from our investigations a relative sea level change at 12 3 0 7 m with a subsidence rate at 5 79 0 01 mm y 1 and an average value of volcano tectonic contribution at 5 17 0 01 m y 1 for the last 2100 100 years bp is estimated from comparison against the latest predicted sea level model for the southern tyrrhenian sea these rates of relative sea level change led to the disuse of the harbor after around the fourth century ad in agreement with archaeological interpretations our results provide new insights on the recent evolution of this active volcanic area

distributary channels and their impact on sediment dispersal a global analysis of world deltas with details from a natural and an anthropogenic influenced delta demonstrates how distributary channels control the flux of sediment into the coastal ocean the study addresses the range in the number of distributary channels across world deltas using remote sensing techniques a power law relationship is found between the number of distributary channels and the length of river and separately the delta gradient these relationships hold for all types of deltas whether controlled or strongly influenced by waves river discharge tides or ice permafrost or sea ice nature controlled deltas such as the klinaklini delta have distributary channels that act as overflow conduits that become active during flooding events anthropogenic controlled deltas like the po delta have distributary channels that are controlled for flood mitigation or low flow maintenance anthropogenic influences greatly impact the natural rate of delta progradation through changes in sediment supply controlling the position of distributary channels and impacting subsidence from gas and groundwater extraction even with flood controls the po delta traps 16 of the sediment load in its channels that are becoming super elevated at rates of 4 to 10 cm yr with respect to the delta plain a new model is formulated and shown to predict accurately the sediment flux through each channel along with their hydraulic properties deltas with high numbers of distributary channels produce hypopycnal plumes with reduced transport capacity as a result sediment diffuses out of the multi channel deltas as a buoyantly driven plume rather than as a momentum driven jet

ground based near infrared imaging observations of venus during the galileo encounter near infrared images of venus obtained from a global network of ground based observatories during january and february 1990 document the morphology and motions of the night side near infrared markings before during and after the galileo venus encounter a dark cloud extended halfway around the planet at low latitudes 40 and persisted throughout the observing program it had a rotation period of 5 5 0 15 days the remainder of this latitude band was characterized by small scale 400 to 1000 kilometers dark and bright markings with rotation periods of 7 4 1 days the different rotation periods for the large dark cloud and the smaller markings suggests that they are produced at different altitudes mid latitudes 40 to 60 were usually occupied by bright east west bands the highest observable latitudes 60 to 70 were always dark and featureless indicating greater cloud opacity maps of the water vapor distribution show no evidence for large horizontal gradients in the lower atmosphere of venus

modelling the response of the north channel of the irish sea to idealized time varying winds and boundary forcing abstract a three dimensional high resolution horizontal grid of order 1 km model of the north channel of the irish sea is used to examine the response of the region to wind and open boundary forcing at a number of periods calculations show that with wind forcing at the inertial period currents are produced through the water column although with longer and shorter period forcing the depth of penetration of the wind s momentum is confined to a near surface layer in the case of short period forcing the wind stress and elevation gradient terms are balanced by the acceleration term whereas at longer periods the acceleration term is small and the balance is between rotational and elevation gradient terms and the wind stress the direction of the wind stress which produces a maximum out flowing current in the centre of the north channel depends upon the period of the forcing and the depth below the surface of the out flowing current although calculations show that to first order the motion in the centre of the channel can be described by linear dynamics coupling between the time varying eddy viscosity and wind shear in the surface layer modifies the m 2 tidal current in the surface region in the case of flow produced by open boundary forcing the current is in essence aligned with the orientation of the channel and above the near bed region is dominated by currents at the period of the boundary forcing close to the bed higher frequency harmonics are generated although there is no evidence at any depth of the m 2 harmonic found in the wind driven flow case

hydrodynamic and geomorphic controls on mouth bar evolution 1 while river deltas are one of the major repositories for sediments and carbon on earth there exists a paucity of field data on the formation of distributary mouth bars one of their key features here we present results from an experiment that tested a model of mouth bar development using hydroacoustic optical sedimentary and geochemical tools on a mouth bar in a crevasse splay near the mouth of the mississippi river our results validate an existing model for mouth bar development which we extend to explain mouth bar stratigraphy we propose that changes across a hydrological cycle are important for mouth bar development resulting in a stratigraphy that has alternating fine and coarse grain sediments results also indicate that sand is carried up to 6 km from the main stem of the mississippi river despite repeated channel bifurcations which has important implications for our interpretation of the rock record understanding of coastal sedimentary systems and the restoration of large deltas

three dimensional modal model of wind induced flow in a sea region abstract the solution of the linear three dimensional hydrodynamic equations describing wind induced flow in a sea region is developed using the galerkin method through the vertical a basis set of b splines is shown to have some computational advantages over a set of eigenfunctions vertical modes however a basis set of modes leads to a system of essentially uncoupled equations and current profiles can be interpreted in terms of vertical modes the influence of wind induced surface turbulence and turbulence at depth due to tidal motion upon current profiles in both deep 260 m and shallow 35 m sea regions is examined the variation in the angle between surface current and surface wind for different viscosity profiles and the effect of bottom friction upon it is considered the magnitude and direction of the surface current is significantly influenced by surface eddy viscosity however viscosity at depth due to tidal motion also has an important effect upon the surface current the time evolution of current structure following the sudden onset of a wind is examined using the modal model calculations show that the rate of damping of the internal modes is inversely proportional to the square of the depth consequently wind induced current structure takes longer to reach a steady state in a deep sea region than a shallow area the influence of sea surface elevation gradients in determining the direction of surface current is also considered

shallow gas and flood deposition on the po delta abstract sediment cores acquired on the po delta northwestern adriatic sea in water depths of 10 to 25 m yielded anomalous concentrations of methane up to 41 300 ppm of the 19 unique sites analyzed 5 sites 9 cores had more than 90 ppm of ch 4 and of those 3 sites 4 cores had more than 13 800 ppm methane compositional and isotopic analyses of the gas support a bacterial origin anomalous methane concentrations were found in kasten gravity and box cores where more than one core type was acquired at a single location all cores contained anomalous methane despite the regional high productivity in the adriatic all of the highest gas concentrations were found in the region associated with the thickest accumulation of recent flood deposits off the most active channel of the po delta po di pila cores acquired in this region contain primary sedimentary structures that indicate rapid burial of thick 10 cm flood deposits and a relative lack of bioturbation down to the base of the flood layer we propose that in the po delta flood deposits deliver significant amounts of terrigenous organic matter that can be rapidly buried on the prodelta effectively removing this organic matter from aerobic oxidation and biological uptake and leading to the potential for methanogenesis with burial in areas unaffected by this high flux of organic matter and rapid thick flood deposition or in between flood events our data indicate that the conditions for methanogenesis and gas accumulation have not been met we suggest that in these areas the physical and biological reworking of the surficial sediment between flood events may effectively oxidize and mineralize organic matter derived from both marine and terrestrial sources and limit bacterial methanogenesis in the subsurface

short term evolution of po della pila delta lobe from time lapse high resolution multibeam bathymetry 2013 2016 abstract over the last few years 2013 2016 repeated high resolution multibeam surveys were carried out at the recent most delta lobe of the po river in correspondence to po della pila the collected multibeam bathymetry together with backscatter data seabed samples and high resolution seismic profiles provided insights on the short term morphological and sedimentological evolution of this extremely dynamic submarine portion of the delta a high variety of geomorphological features and depositional bodies were observed from the mouth bar to the prodelta slope such as for example the alongshore and transverse bars formed under the effect of marine currents gravitational instability phenomena and collapse depressions driven by fluid expulsion concurrently the analysis of the seabed reflectivity and sediment samples allowed the identification of two main dominant types of seafloor sediment corresponding to sandy and muddy seabed and the mapping of their variable distribution in the study area the comparison of time lapsed high resolution dems showed that the main changes occurred on the northern side of the prodelta slope where a new lobe shaped fine sediment deposit built up to 4 5 m adding roughly a volume of 1 16 mm3 of new sediments at the same time in the prodelta slope transverse depositional bars showed a clear migration toward the south of the system and local subsidence phenomena up to 1 5 m between 7 and 10 m water depth are observed

morphology and dynamics of the upper cloud layer of venus esa s venus express probe has been in orbit since april 2006 eight research papers in this issue present new results from the mission covering the atmosphere polar features interactions with the solar wind and the controversial matter of venusian lightning hakan svedham et al open the section with a review of the similarities and mostly differences between venus and its twin the earth andrew ingersoll considers the latest results and also how the project teams plan to make the most of the probe s remaining six years of life venus is completely covered by a thick cloud layer with the cloud tops in fast retrograde rotation global and small scale properties of these clouds and their temporal and latitudinal variations are investigated and the wind velocities are derived the southern polar region is highly variable and can change dramatically on time scales as short as one day perhaps arising from the injection of so2 into the mesosphere venus is completely covered by a thick cloud layer of which the upper part is composed of sulphuric acid and some unknown aerosols1 the cloud tops are in fast retrograde rotation super rotation but the factors responsible for this super rotation are unknown2 here we report observations of venus with the venus monitoring camera3 on board the venus express spacecraft we investigate both global and small scale properties of the clouds their temporal and latitudinal variations and derive wind velocities the southern polar region is highly variable and can change dramatically on timescales as short as one day perhaps arising from the injection of so2 into the mesosphere the convective cells in the vicinity of the subsolar point are much smaller than previously inferred4 5 6 which we interpret as indicating that they are confined to the upper cloud layer contrary to previous conclusions7 8 but consistent with more recent study9

po river plume on the adriatic continental shelf dispersion and sedimentation of dissolved and suspended matter during different river discharge rates abstract suspended matter and dissolved nutrients were studied in the prodelta of the po river northern adriatic sea immediately after one of the greatest floods of the last century which occurred in october 2000 and in four successive seasonal conditions hydrology total suspended matter tsm particulate organic carbon poc and particulate nitrogen pn content organic carbon stable isotopes 13 c poc particle grain size spectra phytoplankton and dissolved inorganic nutrients i e nitrate nitrite ammonium phosphate and silicate were measured in different discharge conditions to describe processes occurring in the po river delta the main effect of high river discharge was a large volume of low salinity water at the surface that extended over the entire study area the concentration of most sampled variables decreased along a dilution gradient from the po river distributaries mouths to the offshore for tsm at the surface riverine input and dilution were the main factors affecting its distribution at the bottom however increased tsm in the nearshore was due to rapid sinking of suspended matter at the river mouth while resuspension and advection dominated the transport of near bottom sediments offshore at 15 20 m depth in the offshore where resuspension was active an increase in ammonium and decrease in oxygen supported the presence of regeneration processes occurring at the bottom during the october 2000 flood event high nutrient concentrations promoted new production triggering an algal bloom in the southern region of the study area the origin of particulate organic carbon in the river delta was then estimated from a mixing model based on 13 c poc values and carbon nitrogen c n molar ratios and as the contribution of three distinct sources of organic carbon were determined i e marine riverine and terrestrial the riverine end member accounted for 50 of the surface poc and generally decreased towards the offshore the terrestrial carbon contribution was generally the least abundant 20 28 at the surface and at depth respectively and exhibited peak values 30 40 during the october 2000 flood last the marine contribution was the most abundant at the bottom 40 and generally increased offshore during the october 2000 flood the fluvial contribution of particulate organic carbon that is the terrestrial and riverine fractions represented approximately 80 of the total particulate organic carbon in the po river delta

evaluation of image based multibeam sonar backscatter classification for benthic habitat discrimination and mapping at stanton banks uk in recent years efforts have increased to develop quantitative computer directed methods for segmentation of multibeam mbes backscatter data this study utilises mbes backscatter data acquired at stanton banks uk and subsequently processed through the qtc multiview software environment in a bid to evaluate the program s ability to perform unsupervised classification statistical comparison with ground truth data grab stills and video enabled cross validation of acoustic segmentation and biological assemblages observed at the site 132 unspecified variables were extracted from user specified rectangular patches of the backscatter image reduced to three vectors by pca then clustered and classified by the software multivariate analyses of ground truth data were conducted on 75 stills images and 51 grab samples video footage coincident with the stills was divided into 30 s segments and coded by dominant substrate and species cross tabulation determined the interrelationship between software classifications multivariate analysis of the biological assemblages and coded video segments multiview optimally identified 19 classes using the automated clustering engine these were revised to 6 habitats a posteriori using combined analysis of ground truth data and multiview data products these habitats broadly correspond to major physiographic provinces within the region multivariate statistical analysis reveals low levels of assemblage similarity 35 for samples occurring within multiview classes irrespective of the mode of acquisition coded video data is more spatially appropriate than the other methods of ground truthing investigated although it is less well suited to the extraction of truly quantitative data multivariate analysis indicates assemblages within physiographically distinct multiview classes have a low degree of biological similarity supporting the notion that abiotic proxies may be contraindicative of benthic assemblage variations qtc multiview performs well as a mechanism for computer assisted segmentation of mbes backscatter imagery into acoustic provinces however a degree of caution is required prior to ascribing ecological significance to these classifications c 2008 elsevier ltd all rights reserved

flooding scenarios due to land subsidence and sea level rise a case study for lipari island italy archaeological and instrumental data indicate that the southern sector of the volcanic island of lipari has been subsiding for the last 2100 years due to isostatic and tectonic factors at variable rates of up to 11 mm yr based on this data a detailed marine flooding scenario for 2100 a d is provided for the bay of marina lunga in the eastern part of the island from i an ultra high resolution digital terrain and marine model dtmm generated from multibeam bathymetry mb and unmanned aerial vehicles uav ii the rate of land subsidence from gps data and iii the regional sea level projections of the international panel on climate change ipcc when land subsidence is considered the upper bound of sea level rise is estimated at 1 36 m and 1 60 m for rcp4 5 and rcp8 5 climate change scenarios respectively here we show the expected impact of marine flooding at lipari for the next 85 years and discuss the hazard implications for the population living along the shore this article is protected by copyright all rights reserved

the adriatic sea general circulation part ii baroclinic circulation structure abstract in the second part of the paper dedicated to the adriatic sea general circulation the horizontal structure of the hydrographic parameters and dissolved oxygen fields is described on a seasonal timescale maps of temperature and salinity climatological fields reveal the enhanced seasonal variability of the adriatic sea which at the surface is associated with the major dilution effects of river runoff the density and derived dynamic height fields show for the first time the baroclinic geostrophic structure of the general circulation winter is dominated by compensation effects between temperature and salinity fronts along the western coastline the resulting baroclinic circulation is weak and suggests the presence of barotropic current components not accessible by the dataset spring and summer seasons have the smallest spatial scales in the temperature and salinity fields and stronger subbasin scale gyres and current systems which have been classified in a schematic representation of the circu