successive aeolian saltation studies of idealized collisions as observed by bagnold and experimentally reconfirmed by other workers the impact angles of saltating grains are remarkably constant over a wide range of conditions lying between 10 and 16 it can be shown that successive saltation contains a mechanism which very effectively confines impact angles to that range this control mechanism is most effective at windspeeds less than about 15 30 m s 1 depending on grain diameter and mass the control mechanism is evaluated from model calculations of grain populations saltating over a level bed consisting of a layer of loose grains the grains are assumed to be spherical and uniform in size and mass also rigid and perfectly elastic the model also describes distributions of maximum height of grain paths and of lift off angles compared to other processes involved in aeolian saltation successive saltation is the only process with a high probability of transferring energy from horizontal into vertical grain movement this fact together with the calculations presented strongly suggests that successive saltation plays a major role in saltation in air successive saltation of uniform grains is theoretically impossible if the ground over which saltation occurs is tilted by about 15 against wind direction values of tilt angles in this range are observed in nature as stoss side angles of dunes and ripples leading to the concept that stoss sides are tilted up by deposition until successive saltation is subdued

quantifying upper ocean turbulence driven by surface waves 1 nearly all operational ocean models use air sea fluxes and the ocean shear and stratification to estimate upper ocean boundary layer mixing rates this approach implicitly parameterizes surface wave effects in terms of these inputs here we test this assumption using parallel experiments in a lake with small waves and in the open ocean with much bigger waves under the same wind stress and adjusting for buoyancy flux we find the mixed layer average turbulent vertical kinetic energy in the open ocean typically twice that in the lake the increase is consistent with models of langmuir turbulence in which the wave stokes drift and not wave breaking is the dominant mechanism by which waves energize turbulence in the mixed layer applying these same theories globally we find enhanced mixing and deeper mixed layers resulting from the inclusion of langmuir turbulence in the boundary layer parameterization especially in the southern ocean

computation of wind wave spectra in coastal waters with swan on unstructured grids abstract an unstructured grid procedure for swan is presented it is a vertex based fully implicit finite difference method which can accommodate unstructured meshes with a high variability in geographic resolution suitable for representing complicated bottom topography in shallow areas and irregular shoreline the numerical solution is found by means of a point to point multi directional gauss seidel iteration method requiring a number of sweeps through the grid the approach is stable for any time step while permitting local mesh refinements in areas of interest a number of applications are shown to verify the correctness and numerical accuracy of the unstructured version of swan

investigating the eddy diffusivity concept in the coastal ocean abstractthis paper aims to test the validity utility and limitations of the lateral eddy diffusivity concept in a coastal environment through analyzing data from coupled drifter and dye releases within the footprint of a high resolution 800 m high frequency radar south of martha s vineyard massachusetts specifically this study investigates how well a combination of radar based velocities and drifter derived diffusivities can reproduce observed dye spreading over an 8 h time interval a drifter based estimate of an anisotropic diffusivity tensor is used to parameterize small scale motions that are unresolved and underresolved by the radar system this leads to a significant improvement in the ability of the radar to reproduce the observed dye spreading

a high resolution coupled riverine flow tide wind wind wave and storm surge model for southern louisiana and mississippi part ii synoptic description and analysis of hurricanes katrina and rita abstract hurricanes katrina and rita were powerful storms that impacted southern louisiana and mississippi during the 2005 hurricane season in part i the authors describe and validate a high resolution coupled riverine flow tide wind wave and storm surge model for this region herein the model is used to examine the evolution of these hurricanes in more detail synoptic histories show how storm tracks winds and waves interacted with the topography the protruding mississippi river delta east west shorelines manmade structures and low lying marshes to develop and propagate storm surge perturbations of the model in which the waves are not included show the proportional importance of the wave radiation stress gradient induced setup

the impact process in aeolian saltation two dimensional simulations a critical event in the trajectory of a sand grain saltating in air is its interaction with the surface we examine the phenomenon of grain bed impacts in two dimensions using a combination of dynamical computer simulations analytical models and physical reasoning the results indicate that the grain bed collisions can be treated as two body collisions with the bed particle assuming an effective mass greater than its true mass also the presence of geometrical surface irregularities has a strong bearing on the interaction between saltating and surface grain populations as well as on the formation of small scale bedforms

eolian ripples as examples of self organization in geomorphological systems abstract ripples arise spontaneoulsy from sandy beds subjected to winds sufficient to cause the saltation of surficial grains while the initially fastest growing wavelengths are 4 6 times the mean hop length of grains impelled downwind by long trajectory high energy saltating grains the ripple wavelengths developed over long periods can be several times this numerical simulations based upon techniques pioneered by p k haff and coworkers reveal that a complex process of ripple coalescence is responsible for this evolution of the ripple field small fast moving ripples catch up with and are absorbed by larger slower forms each such merger resulting in a growth of the mean wavelength and a decline in the relative dispersion of the wavelengths an heuristic argument is presented which accounts for the fast initial growth and subsequent slowing of growth of the mean wavelength as the ripple field evolves ripple cross sectional shape appears to be controlled in large part by a distrianment function which represents the declining likelihood of a grain stopping on a surface as it slopes more steeply downwind that the resulting asymptotic wavelength in the simulations depends strongly upon impact angle supports sharp s 1963 suggestion that the length of the shadow zone plays an important role in controlling the final ripple wavelength

cross shelf thermal variability in southern lake michigan during the stratified periods 1 results from a field experiment in southern lake michigan are used to quantify the cross shelf nearshore variability in great lakes temperatures during the stratified season the experiment was conducted along the indiana coast of southern lake michigan with temperature and velocity moorings arranged in a cross shelf transect that extended to approximately 20 km from shore 40 m depth the field site is noteworthy because of its location at the end of a major axis of an elliptical great lake the relatively mild bathymetric slope and local shoreline orientation that is perpendicular relative to the dominant summer winds measurements demonstrate that the location of the thermocline bottom intersection is highly variable causing a wide zone of extreme thermal variability in the nearshore region with time scales of variability ranging from hours to months near inertial internal poincare waves are shown to cause large thermocline excursions but primarily only during periods of elevated activity several full upwelling events were observed but in general they were brief lasting only 1 2 days and had very limited spatial extent 2 5 km or less nonetheless the offshore extent of the upwelling front was shown to be reasonably estimated with a simple estimate of the cross shelf transport caused by alongshore wind events a persistent feature that determined the zone of elevated thermal variability the thermocline shelf intersection point was the strongly tilted thermocline which resulted in the thermocline being located very close to shore no evidence was found to support the hypothesis that internal kelvin waves affect thermal variability at the study location

significance of interdune deposits and bounding surfaces in aeolian dune sands bounding surfaces and interdune deposits provide keys for detailed interpretations of the development shape type wavelength and angle of climb of aeolian bedforms as well as overall sand sea conditions current alternate interpretations of bounding surfaces require very different but testable models for sand sea deposition two perpendicular traverses of jurassic entrada sandstone utah reveal relations among cross strata first order bounding surfaces and horizontal strata these field relations seem explicable only as the deposits of downwind migrating climbing enclosed interdune basins horizontal strata and dune bodies consisting of superimposed smaller crescentic dunes cross stratified deposits a 1 7 km traverse parallel to the palaeowind direction provides a time transgressive view showing continuous cosets of cross strata first order bounding surfaces and interdune deposits climbing downwind at an angle of a few tenths of a degree changes occur in the angle of climb cross strata structure and interdune deposits these reflect changes in depositional conditions through time a 1 5 km traverse perpendicular to the palaeowind direction provides a view at an instant in geological time showing first order bounding surfaces and interdune deposits forming flat laterally discontinuous lenticular bodies the distribution of interdune sedimentary structures in this traverse is very similar to that of some modern interdune basins such as those on padre island texas hierarchies of bounding surfaces in an aeolian deposit reflect the bedform development on an erg the presence of three orders of bounding surfaces indicates dune bodies consisting of smaller super imposed dunes the geometry of first order bounding surfaces is a reflection of the shape of the inter dune basins second order bounding surfaces originate by the migration of the superimposed dunes over the larger dune body and reflect individual dune shape and type third order bounding surfaces are reactivation surfaces showing stages in the advance of individual dunes the presence of only two orders of bounding surfaces indicates simple dunes modern and entrada interdune deposits show a wide variety of sediment types and structures reflecting deposition under wet damp and dry conditions interdune deposits are probably the best indicators of overall erg conditions and commonly show complex vertical sequences reflecting changes in specific depositional conditions

on the dependence of sea surface roughness on wave development abstract the aerodynamic roughness of the sea surface z0 is investigated using data from lake ontario from the north sea near the dutch coast and from an exposed site in the atlantic ocean off the coast of nova scotia scaling z0 by rms wave height gives consistent results for all three datasets except where wave heights in the atlantic ocean are dominated by swell the normalized roughness depends strongly on wave age younger waves traveling slower than the wind are rougher than mature waves alternatively the roughness may be normalized using the friction velocity u of the wind stress again young waves are rougher than mature waves this contradicts some recent deductions in the literature but the contradiction arises from attempts to describe z0 in laboratory tanks and in the field with a single simple parameterization here it is demonstrated that laboratory waves are inappropriate for direct comparison with field data being much smoother than their field equivalents in the open ocea

the role of wave current interaction in lake erie s seasonal and episodic dynamics although the significance of surface gravity waves has been consistently emphasized in previous limnetic studies the roles of wave current interactions in lake dynamics are not sufficiently understood due to the lack of high resolution wave information with a two way coupled hydrodynamic and wave model system this study investigated how the lake erie dynamics are impacted by the wave induced surface and radiation stresses on the seasonal mean and episodic scales the results showed that the surface radiation stress was the same as or an order of magnitude larger than the wave induced surface stress in the nearshore area 5 km offshore while the latter prevailed in the offshore areas by enhancing air lake momentum and heat transfers the wave enhanced surface stress improved the model s skill in simulating hydrodynamics in the central and eastern basins and it was of greater importance at least an order of magnitude larger in modifying surges offshore currents and thermal structures compared to those of the radiation stress nevertheless the radiation stress played key roles in wave induced nearshore currents especially in the shallow western basin their significances reached o 0 01 to 0 1 m s on the seasonal and episodic scales respectively and could have similar importance in other shallow water environments

modeling waves and wind stress 1 a model for wave and wind stress prediction is constructed the source functions that drive the space time evolution of the energy spectra are developed in form based on theory and laboratory and field experiments the calibration factors proportionality constants of the source functions are determined from a comparison of modeled and observed significant height and mean period the observations are for the month of january 2005 and are derived from an array of laser range finders mounted on a bridge between two platforms in the ekofisk oil field in the north sea the model calculates the form stress on the waves and adds it vectorially to the sheltering modified skin stress the resulting drag coefficient versus wind speed is shown to have the observed structure low in light winds increasing in moderate winds and increasing more slowly in very strong winds modeled spectral shapes in the four quadrants of hurricane bonnie 1998 match the scanning radar altimeter measurements modeled spectral properties in hurricane ike 2008 are compared against ndbc buoy estimates with good results drag coefficients in the mixed seas produced by hurricanes show dependence on wave age of the wind sea swell propagation direction and water depth the need for wave and stress modeling for atmosphere ocean coupling is emphasized the new wave model has all the necessary attributes to be the basis for such a coupler

complex mean circulation over the inner shelf south of martha s vineyard revealed by observations and a high resolution model 1 inner shelf circulation is governed by the interaction between tides baroclinic forcing winds waves and frictional losses the mean circulation ultimately governs exchange between the coast and ocean in some cases oscillatory tidal currents interact with bathymetric features to generate a tidally rectified flow recent observational and modeling efforts in an overlapping domain centered on the martha s vineyard coastal observatory mvco provided an opportunity to investigate the spatial and temporal complexity of circulation on the inner shelf adcp and surface radar observations revealed a mean circulation pattern that was highly variable in the alongshore and cross shore directions nested modeling incrementally improved representation of the mean circulation as grid resolution increased and indicated tidal rectification as the generation mechanism of a counter clockwise gyre near the mvco the loss of model skill with decreasing resolution is attributed to insufficient representation of the bathymetric gradients h h which is important for representing nonlinear interactions between currents and bathymetry the modeled momentum balance was characterized by large spatial variability of the pressure gradient and horizontal advection terms over short distances suggesting that observed inner shelf momentum balances may be confounded given the available observational and modeling data this work defines the spatially variable mean circulation and its formation mechanism tidal rectification and illustrates the importance of model resolution for resolving circulation and constituent exchange near the coast the results of this study have implications for future observational and modeling studies near the mvco and other inner shelf locations with alongshore bathymetric variability

particle dislodgement from a flat sand bed by wind the rate with respect to area and time at which grains are dislodged from a sand bed for given wind conditions is an important factor in determining the grain transport rate and the intensity of grain activity in each of the transport modes the literature of the subject contains little direct information about particle dislodgement the paper describes a series of experiments in which dyed sand grains spread on the surface of quartz dune sand in a wind tunnel were photographed at five second intervals while the sand was exposed to wind the data on rate of loss of coloured grains was used for two of three chosen size fractions to deduce the dislodgement rate for each size fraction the variation of this dislodgement rate with shear velocity is shown graphically for values of u between 24 cm s 1 and 50 cm s 1 because of the artificial method of distribution of the coloured sand grains the results should be applied with caution to natural conditions the interpretation of the observations of dyed grain loss involved the numerical simulation of the process which comprises removal of coloured grains slightly offset by replenishment as upwind coloured grains settle briefly in the observed zone an estimation of grain excursion length has to be incorporated in the simulation this estimation was made by trial but general corroboration was found from earlier work comparisons are made between dislodgement rates obtained thus and rates estimated by anderson 1986 and by jensen and sorensen 1986 reasonable agreement with the latter is found in the u range 30 cm s 1

modeling overfalls using vertically averaged and moment equations a new set of vertically averaged and moment equations which assumes a linear longitudinal velocity distribution and quadratic vertical velocity and pressure distributions is used for modeling flow in the vicinity of horizontal rectangular free overfall with smooth and rough beds and sharp crested weirs with sloping upstream faces these equations are modeled using a hybrid petrov galerkin and bubnov galerkin finite element scheme for the rectangular free overfalls the predicted water surface profiles upstream of the overfall and the free jet trajectory agree well with the measured data the computed vertical velocity and pressure distributions at the brink and upstream of the overfall are found to be in good agreement with the measured data while the computed longitudinal velocity distributions compare well with a two dimensional potential flow model the computed results for sharp crested weirs with sloping upstream faces agree well with the measured data for an upstream weir slope of up to 27 with the horizontal for an upstream slope of 45 and steeper and for a large weir height the predicted water surface upstream of a weir shows numerical instability

hurricane induced ocean waves and stokes drift and their impacts on surface transport and dispersion in the gulf of mexico hurricane isaac induced large surface waves and a significant change in upper ocean circulation in the gulf of mexico before making landfall at the louisiana coast on 29 august 2012 isaac was observed by 194 surface drifters during the grand lagrangian deployment glad a coupled atmosphere wave ocean model was used to forecast hurricane impacts during glad the coupled model and drifter observations provide an unprecedented opportunity to study the impacts of hurricane induced stokes drift on ocean surface currents the stokes drift induced a cyclonic anticyclonic rotational flow on the left right side of the hurricane and accounted for up to 20 of the average lagrangian velocity in a significant deviation from drifter measurements prior to isaac the scale dependent relative diffusivity is estimated to be 6 times larger during the hurricane which represents a deviation from okubo s 1971 canonical results for lateral dispersion in nonhurricane conditions at the ocean surface

the ideal response of a gulf of mexico estuary plume to wind forcing its connection with salt flux and a lagrangian view 1 the plume structure of perdido bay estuary pbe a typical bay on the florida alabama coast along the gulf of mexico was simulated using an existing calibrated model to better understand plume dynamics in the pbe and similar bay systems idealized sensitivity experiments were conducted to examine the influence of wind stress on the 3 d plume signature the results indicate that wind speed and direction significantly influence plume orientation area width length and depth the plume size was reduced under the effect of wind and increased wind forcing among wind forced cases the plume is largest for northerly offshore winds and smallest for southerly onshore winds bay shelf salt flux and water flux were also investigated since they are important for the formation of a 3 d plume structure model simulations show that water outflow to the coastal ocean is strongest under northerly winds and can be stopped by southerly winds for moderately strong winds the outflow and plume size are larger for easterly downwelling favorable winds than for westerly upwelling favorable winds the opposite is true for outflow and plume size for these two wind directions under stronger winds for all wind directions the ratio of salt flux and water flux at the bay mouth increases with wind speed this ratio trend is consistent with higher outflow salinities and this decreased buoyancy signature along with more energetic vertical mixing reduces plume size a detailed understanding of this water and salt flux is essential to the plume dynamics studied here and for other plumes additional particle transport analysis using variable wind forcing was conducted to determine the influence of the plume on particle movement the results showed a consistency between the surface plume salt flux and particle transport and illustrate the strong effects that winds have on particle fate and dispersion

evaluation of trajectory modeling in different dynamic regions using normalized cumulative lagrangian separation 1 the lagrangian separation distance between the endpoints of simulated and observed drifter trajectories is often used to assess the performance of numerical particle trajectory models however the separation distance fails to indicate relative model performance in weak and strong current regions such as a continental shelf and its adjacent deep ocean a new skill score is proposed based on the cumulative lagrangian separation distances normalized by the associated cumulative trajectory lengths this skill score is used to evaluate surface trajectories implied by global hycom hindcast surface currents as gauged against actual satellite tracked drifter trajectories in the eastern gulf of mexico during the 2010 deepwater horizon oil spill it is found that the new skill score correctly indicates the relative performance of the global hycom in modeling the strong currents of the gulf of mexico loop current and the gulf stream and the weaker currents of the west florida shelf in contrast the lagrangian separation distance alone gives a misleading result the proposed dimensionless skill score is particularly useful when the number of drifter trajectories is limited and neither a conventional eulerian based velocity nor a lagrangian based probability density function may be estimated

bottom friction and wind drag for wave models abstract waves propagating in shallow water dissipate energy in a thin turbulent boundary layer near the bottom this friction can be estimated with a simple quadratic friction law scaled with an empirical coefficient two values of this coefficient have been recommended by previous studies for sandy bottoms a high value for waves in a storm and a low value for swell we show here that in contrast to current practise the lower value should be used for both applications the reason is that the high value dating from the early 1980s was inferred from observations in a severe storm using a relatively high wind drag our review of a large number of more recent observations gives a new wind drag parameterization with lower values with this new parameterization we infer from the same storm the lower value of the bottom friction coefficient using this lower value also improves the estimates of wave growth in shallow water and of low frequency wave decay in a tidal inlet independent of the wind drag

a simple model of estuarine subtidal fluctuations forced by local and remote wind stress observations of estuarine low subtidal sea level and current fluctuations have often shown domination by the remote effects of the wind acting on the adjacent coastal ocean over the local surface stress acting on the estuary itself the remote effects are transmitted to the estuary by impressment on its mouth of sea level change indtlced by the onshore component of coastal ekman transport and become increasingly dominant as the frequency decreases a simple barotropic model is developed to investigate the joint action of these two wind forcing mechanisms the relative shortness of most estuaries relative to low subtidal estuarine wavelengths explains the dominance of the remote effect for both sea level and barotropic current fluctuations in the estuary for the same reason however surface slope is dominated by local wind setup for an estuary with axis nearly parallel to the coast the two effects will operate either in concert or in opposition depending on hemisphere and orientation of the estuary axis relative to the coast for the geometries of both chesapeake bay and the delawm e estuary the model predicts opposition with the remote effect dominant at lower frequencies consistent with recent observations

local and deep ocean forcing contributions to anomalous water properties on the west florida shelf 1 material property distributions on continental shelves result from the mixing and modifications of estuarine and deep ocean source waters how this occurs depends on the momentum and buoyancy that are input either locally on the shelf or from the deep ocean at the shelf break we address this question of local versus deep ocean forcing for the west florida shelf wfs using in situ data and a numerical circulation model the spring and summer seasons of 1998 and 1999 show distinctively different water properties on the shelf and at the shelf break we account for these differences by a combination of local forcing independent of the adjacent gulf of mexico loop current and interactions of the loop current with the shelf the primary role of the deep ocean is to set the height of material isopleths along the shelf slope whether or not these material isopleths broach the shelf break is then a consequence of local shelf wide wind and buoyancy forcing the subsequent along and across shelf distributions are accomplished through a combination of local and deep ocean effects with the bottom ekman layer being the major conduit for the across shelf transport of ecologically important materials

sea state dependence of the wind stress over the ocean under hurricane winds 1 the impact of the surface wave field sea state on the wind stress over the ocean is investigated with fetch dependent seas under uniform wind and with complex seas under idealized tropical cyclone winds two different approaches are employed to calculate the wind stress and the mean wind profile the near peak frequency range of the surface wave field is simulated using the wavewatch iii model the high frequency part of the surface wave field is empirically determined using a range of different tail levels the results suggest that the drag coefficient magnitude is very sensitive to the spectral tail level but is not as sensitive to the drag coefficient calculation methods the drag coefficients at 40 m s vary from 1 10 3 to 4 10 3 depending on the saturation level the misalignment angle between the wind stress vector and the wind vector is sensitive to the stress calculation method used in particular if the cross wind swell is allowed to contribute to the wind stress it tends to increase the misalignment angle our results predict enhanced sea state dependence of the drag coefficient for a fast moving tropical cyclone than for a slow moving storm or for simple fetch dependent seas this may be attributed to swell that is significantly misaligned with local wind

modeling the 1998 2003 summer circulation and thermal structure in lake michigan 1 a three dimensional primitive equation numerical model was applied to lake michigan on a 2 km grid for 6 consecutive years to study interannual variability of summer circulation and thermal structure in 1998 2003 the model results were compared to long term observations of currents and temperature at seven moorings and two noaa buoys the accuracy of modeled currents improved considerably relative to previous summer circulation modeling done on a 5 km grid while the accuracy of temperature simulations remained the same particle trajectory model results were also compared with satellite tracked surface drifter observations large scale circulation patterns tend to be more cyclonic counterclockwise toward the end of summer as the thermocline deepens and density effects become more important circulation in southern lake michigan appears to be more variable than circulation in northern lake michigan an important new feature not previously seen in observations was found in southern lake michigan an anticyclonic gyre extending northward from the southern shore of lake michigan sometimes occupying the entire southern basin

the columbia river plume study subtidal variability in the velocity and salinity fields a comprehensive study of the strongly wind driven midlatitude buoyant plume from the columbia river located on the u s west coast demonstrates that the plume has two basic structures during the fall winter season namely a thin 5 15 m strongly stratified plume tending west to northwestward during periods of southward or light northward wind stress and a thicker 10 40 m weakly stratified plume tending northward and hugging the coast during periods of stronger northward stress the plume and its velocity field respond nearly instantaneously to changes in wind speed or direction and the wind fluctuations have timescales of 2 10 days frictional wind driven currents cause the primarily unidirectional flow down the plume axis to veer to the right or left of the axis for northward or southward winds respectively farther downstream currents turn to parallel rather than cross salinity contours consistent with a geostrophic balance in particular during periods when the plume is separated from the coast currents tend to flow around the mound of fresher water at distances exceeding about 20 km from the river mouth the along shelf depth averaged flow over the inner to midshelf is linear and depth averaged acceleration is governed to lowest order by the difference between surface and bottom stress alone in this region along shelf geostrophic buoyancy driven currents at 5 m calculated from surface density and along shelf geostrophic wind driven currents computed from a depth averaged linear model are comparable in magnitude 10 25 cm s 1

modeling circulation and thermal structure in lake michigan annual cycle and interannual variability a three dimensional primitive equation numerical model was applied to lake michigan for the periods 1982 1983 and 1994 1995 to study seasonal and interannual variability of lake wide circulation and thermal structure in the lake the model was able to reproduce all of the basic features of the thermal structure in lake michigan spring thermal bar full stratification deepening of the thermocline during the fall cooling and finally an overturn in the late fall large scale circulation patterns tend to be cyclonic counterclockwise with cyclonic circulation within each subbasin the largest currents and maximum cyclonic vorticity occur in the fall and winter when temperature gradients are low but wind stresses are strongest the smallest currents and minimum cyclonic vorticity occur in spring and summer when temperature gradients are strong but wind stresses are weakest all these facts are in agreement with observations the main shortcoming of the model was that it tended to predict a more diffuse thermocline than was indicated by observations and explained only up to half of the variance observed in horizontal currents at timescales shorter than a day

a comparison of the motions of surface drifters with offshore wind properties in the gulf of finland the baltic sea abstract we analyse the interconnections of wind forcing and trajectories of in situ surface drifters deployed in the gulf of finland in different seasons of the years 2011 and 2013 the water masses of this brackish water body are usually strongly stratified resulting in a layered system the drifters were designed to follow the uppermost layer of the sea with a thickness of about 2 m the drifter speed was 2 9 6 3 of the wind speed in 2011 when the drifters were more strongly impacted by the wind and 1 9 2 9 in 2013 after the drifters had been modified to reduce the wind impact the trajectories of drifters varied in many instances the drift was almost aligned with the direction towards which the wind was blowing in some cases the motion of drifters was systematically to the left of the wind vector apparently owing to boundary effects in the gulf while on most occasions the drift was mostly along the gulf on several occurrences rapid across gulf transport was observed on time scales of 6 12 days these observations suggest that the motions in the upper layer of the gulf of finland and in similar environments are intermittently driven by two drivers the wind impact including the accompanying ekman drift under moderate and strong winds and by underlying synoptic and basin scale circulation patterns in weak wind conditions

bedload sheets in heterogeneous sediment field observations in streams with beds of coarse sand and fine gravel have revealed that bedload moves primarily as thin migrating accumulations of sediment and coarse grains cluster at their leading edge these accumulations are one or two coarse grains high and are much longer 0 2 0 6 m long in sand 0 5 2 0 m in fine gravel than their height the authors propose the term bedload sheet for these features and the authors argue that they result from an instability inherent to bedload movement of moderately and poorly sorted sediment in essence coarse particles in the bedload slow or stop each other trap finer particles in their interstices and thus cause the coarse particles to become mobile again bedload sheets develop on the stoss side of dunes causing the dune to advance incrementally with the arrival of each sheet successive deposition of coarse sediment from the leading edge followed by fine sediment may generate the grain size sorting that distinguishes cross bedding available flume experiments and field observations indicate that bedload sheets are a common but generally unrecognized feature of heterogeneous sediment transport

quasi three dimensional modeling of rip current systems 1 the focus of the paper is the analysis of the flow in rip current systems generated by channels in longshore bars on a beach the horizontal variations of rip current systems are described through the use of the quasi three dimensional nearshore circulation model shorecirc model predictions are compared to laboratory measurements of waves and current velocities throughout the entire rip current system and show reasonable agreement the rips in the two channels are found to behave differently because of the depth variation across the basin it is found that higher bottom stress leads to more stable flow where the rip current meanders less and fewer eddies are generated the wave current interaction creates forcing which reduces the distance rip currents flow offshore and can lead to a slow pulsation of the rip current this pulsation is in addition to the instabilities of a jet which can also be present in rip currents the three dimensionality of the rip current system is found to have a significant effect on the overall circulation patterns index terms 4255 oceanography general numerical modeling 4512 oceanography physical currents 4546 oceanography physical nearshore processes keywords rip currents nearshore circulation numerical modeling waves

a steady state model of wind blown sand transport a model for steady state eolian saltation is presented in which computation of sand grain trajectories in the wind and of the wind velocity profile modified by saltating grain drag forces is combined with experimental data on grain bed collisions in an iterative simulation scheme which resembles the time development of natural saltation qualitative features of eolian saltation are reproduced in the simulations including a height in the saltating layer at which the wind velocity remains roughly constant with changing free stream friction velocity and an approximate separation of the saltating population into successively hopping grains and reptating or creeping grains the numerical solutions give rise to more general arguments in support of the conclusions that fluid entrainment of grains is unimportant in steady state saltation that the mass flux profile obeys roughly an inverse power law dependence on height and that the vertically integrated mass flux dependence on the free stream friction velocity

estimation of some aeolian saltation transport parameters a re analysis of williams data a new method for analysing observed aeolian sand transport rate profiles of the kind obtained by williams is presented the method involves a mathematical model of aeolian saltation detailed information about the saltation process can be calculated from the transport rate profile by means of this model the method is used to perform a re analysis of williams trap data among the main findings of this analysis is that the grain borne shear stress appears to be a smaller fraction of the total shear stress than assumed by bagnold owen in their theories of aeolian saltation other findings are that the probability distribution of the jump height of the grains does not depend much on the wind speed once the saltation is established and that the vertical component of the mean launch velocity decreases with the grain size it is approximately inversely proportional to the grain diameter our estimates of the landing angles indicate that estimates of the impact angles obtained from photographically recorded trajectories are too small due to biased sampling the influence of grain shape on the transport characteristics is mainly due to changes in the grains ability to jump when hitting the bed it is found that angular grains have a lower mean jump height than spherical grains

hydrodynamic and sediment transport modeling of new river inlet nc under the interaction of tides and waves the interactions between waves tidal currents and bathymetry near new river inlet nc usa are investigated to understand the effects on the resulting hydrodynamics and sediment transport a quasi 3 d nearshore community model nearcom tvd is used in this integrated observational and modeling study the model is validated with observations of waves and currents at 30 locations including in a recently dredged navigation channel and a shallower channel and on the ebb tidal delta for a range of flow and offshore wave conditions during may 2012 in the channels model skills for flow velocity and wave height are high near the ebb tidal delta the model reproduces the observed rapid onshore offshore decay of wave heights current velocities model results reveal that this sharp transition coincides with the location of the breaker zone over the ebb tidal delta which is modulated by semidiurnal tides and by wave intensity the modulation of wave heights is primarily owing to depth changes rather than direct wave current interaction the modeled tidally averaged residual flow patterns show that waves play an important role in generating vortices and landward directed currents near the inlet entrance numerical experiments suggest that these flow patterns are associated with the channel shoal bathymetry near the inlet similar to the generation of rip currents consistent with other inlet studies model results suggest that tidal currents drive sediment fluxes in the channels but that sediment fluxes on the ebb tidal delta are driven primarily by waves

coastal ocean wind fields gauged against the performance of an ocean circulation model 1 atmosphere model derived flux fields are used to force coastal ocean models coarse resolution and incomplete boundary layer dynamics limit the accuracy of these forcing fields and hence the performance of the ocean models we address this limitation for the west florida shelf using optimal interpolation to blend winds measured in situ with winds produced by model analyses by improving the coastal wind field we improve the fidelity between currents modeled and currents observed comparisons between momentum analyses performed independently from the model and the data demonstrate the fidelity to be of a correct dynamical basis we conclude that the primary limitation to coastal ocean model performance lies with the boundary conditions

classification of buoyant river plumes from large aspect ratio channels abstractthe dynamics of the grand river plume a major tributary of lake michigan was studied in the vicinity of the grand haven coast on the east side of the lake the river spread laterally from the mouth and formed a thin surface buoyant plume with various shapes that have not been previously reported to understand the influence of different driving forces primarily wind buoyancy and ambient currents extensive field experiments were carried out over four periods in august and june 2006 and june and july 2007 they included aerial photography over the plume acoustic doppler current profiler adcp deployments meteorological buoys drifters sf6 and rhodamine wt tracer releases three dimensional 3d ctd profiling over the plume and ctd casts at the river mouth the results showed more flow classes than included in previous studies a modified classification scheme based on the relative magnitude of the plume crossflow length scale and a richardson number were devised that includes longshore c