effects of nonlinear inertial forces on nearshore currents abstract a perturbation method is developed to investigate the effects of nonlinear inertial forces on breaking wave induced nearshore currents obliquely incident waves are considered and the bottom topography varies periodically in the shoreline direction for simplicity lateral turbulent mixing is ignored numerical examples are given for a specified bottom topography with various angles of incidence and surf zone width the nearshore currents of interest mainly belong to the meandering type when the nonlinear terms are included there appears an advective shift as well as an amplitude reduction in the current pattern

surf zone currents over irregular bathymetry drifter observations and numerical simulations 1 surf zone currents over irregular bathymetry were observed with gps tracked drifters and modeled with the depth integrated nonlinear shallow water equations trajectories of drifters released in 1 2 m depth sometimes defined rip currents and surf zone eddies features that have been difficult to resolve with fixed instruments the drifter delineated surf zone circulation evolved as the tidal level changed during each 4 6 hour deployment in one case as the tide dropped a shore normal rip current present for the first 2 hours evolved to a more shore parallel flow in a second case on a rising tide a well developed bifurcated rip current was replaced by a weak amorphous circulation rip current velocities were strongest near the surf zone edge and decayed by an order of magnitude within 2 surf zone widths from the shoreline an eddy was observed to persist over a bathymetric depression within the surf zone for at least 1 hour observed and numerically simulated drifter trajectories define similar flow features but the observed and modeled velocities differed by roughly a factor of 2 and flow evolution observed during roughly 0 5 m changes in tidal level were reproduced only if the simulated water levels varied by about 1 m the alongshore momentum balance was spatially variable with wave forcing balanced by pressure gradient friction and advective terms the cross shore momentum balance was everywhere dominated by wave forcing and pressure gradient terms of about equal magnitude in the vicinity of a simulated rip current the residual of the cross shore wave forcing and pressure gradient increased and was balanced by advection terms

boussinesq modeling of longshore currents 1 a time domain boussinesq model for nearshore hydrodynamics is improved to obtain the conservation of vertical vorticity correct to second order and extended for use on an open coast using longshore periodic boundary conditions the model is utilized to simulate surface waves and longshore currents under laboratory and field conditions satisfactory agreement is found between numerical results and measurements including root mean square wave height mean water level and longshore current one striking result of the simulations is the prediction of the strong longshore current in the trough shoreward of the bar as observed during the duck experiment on low frequency and incident band longshore and across shore hydrodynamics field campaign the model results give insight into the spatial and temporal variability of wave driven longshore currents and the associated vertical vorticity field under the phase resolving random wave forcing with wave current interaction numerical experiments are carried out to examine the response of the modeled longshore currents to the randomness of surface waves and the cross shore distributions of bed shear stress coefficient we find that both regular and irregular waves lead to very similar mean longshore currents while the input of monochromatic unidirectional waves results in much more energetic shear waves than does the input of random waves the model results favor whitford and thornton s 1996 finding that the bed shear stress coefficient for the area offshore the bar is larger than that in the trough as better agreement with the field data for both regular and irregular waves is found if such coefficients are used in the boussinesq model

investigations of fennoscandian glacial isostatic adjustment using modern sea level records we present a new method for determining the rates from a network of regional tide gauge data the method involves using a model for the sea level observations annual averages of relative sea level that explicitly includes a term for the interannual sealevel variations which are assumed to be constant for all sites in the network the resulting simultaneous analysis of all the sea level observations yields sea level rates which are biased by the unknown temporal slope of the interannual variations by differencing sea level rate estimates with respect to one site site referenced sea level rates are calculated which are free from this bias the differencing procedure also removes any signal due to a common sea level rate such as might be associated with eustatic sea level rise the resulting site referenced sea level rates therefore in principle reflect only the relative vertical crustal motions of the tide gauge sites with respect to the geoid these site referenced sea level rates represent a potentially more accurate data set than have previously been used for sea level studies we have used these rates to investigate glacial isostatic adjustment gia in fennoscandia specifically we have used the site referenced sea level rates within the baltic sea to estimate adjustments to the ice history and earth model which are used to calculate vertical rates of adjustment due to gia a method never before used for fennoscandia the parameters selected were lithospheric thickness the viscosities of assumed isoviscous upper and lower mantles and a fennoscandian ice thickness scaling parameter we present the results of this estimation procedure for a specific test ice model we also find evidence that the sea level record for the site nearest the center of uplift furuogrund may be contaminated by systematic errors of unknown origin data from this site have previously been used to determine a rate for the maximum uplift that we find is perhaps 1 mm yr 1 or 10 too large

forecasting and hindcasting waves with the swan model in the southern california bight abstract the naval research laboratory created a wave forecasting system in support of the nearshore canyon experiment ncex field program the outer nest of this prediction system encompassed the southern california bight this forecasting system is described in this paper with analysis of results via comparison to the extensive buoy network in the region there are a number of potential errors two of which are poor resolution of islands in the bight which have a strong impact on nearshore wave climate and the use of the stationary assumption for computations these two problems have straightforward solutions but the solutions are computationally expensive so an operational user must carefully consider their cost the authors study the impact of these two types of error relative to other errors such as error in boundary forcing using several hindcasts performed after the completion of ncex it is found that with buoy observations as ground truth the stationary assumption leads to a modest increase in root mean square error this is due to relatively poor prediction of the timing of swell arrivals and local sea growth decay the model results are found to be sensitive to the resolution of islands however coarse resolution does not incur an appreciable penalty in terms of error statistics computed via comparison to buoy observations suggesting that other errors dominate inaccuracy in representation of the local atmospheric forcing likely has a significant impact on wave model error perhaps most importantly the accuracy of directional distribution of wave energy at the open ocean boundaries appears to be a critical limitation on the accuracy of the model data comparisons inside the bight

modeled alongshore circulation and force balances onshore of a submarine canyon alongshore force balances including the role of nonlinear advection in the shoaling and surf zones onshore of a submarine canyon are investigated using a numerical modeling system delft3d swan the model is calibrated with waves and alongshore flows recorded over a period of 1 5 months at 26 sites along the 1 0 2 5 and 5 0 m depth contours spanning about 2 km of coast field observation based estimates of the alongshore pressure and radiation stress gradients are reproduced well by the model model simulations suggest that the alongshore momentum balance is between the sum of the pressure and radiation stress gradients and the sum of the nonlinear advective terms and bottom stress with the remaining terms e g wind stress and turbulent mixing being negligible the simulations also indicate that unexplained residuals in previous field based estimates of the momentum balance may be owing to the neglect of the nonlinear advective terms which are similar in magnitude to the sum of the forcing pressure and radiations stress gradients and to the bottom stress

implementation and modification of a three dimensional radiation stress formulation for surf zone and rip current applications regional ocean modeling system roms v 3 0 a three dimensional numerical ocean model was previously enhanced for shallow water applications by including wave induced radiation stress forcing provided through coupling to wave propagation models swan ref dif this enhancement made it suitable for surf zone applications as demonstrated using examples of obliquely incident waves on a planar beach and rip current formation in longshore bar trough morphology haas and warner 2009 in this contribution we present an update to the coupled model which implements a wave roller model and also a modified method of the radiation stress term based on mellor 2008 2011a b in press that includes a vertical distribution which better simulates non conservative i e wave breaking processes and appears to be more appropriate for sigma coordinates in very shallow waters where wave breaking conditions dominate the improvements of the modified model are shown through simulations of several cases that include a obliquely incident spectral waves on a planar beach b obliquely incident spectral waves on a natural barred beach duck 94 experiment c alongshore variable offshore wave forcing on a planar beach d alongshore varying bathymetry with constant offshore wave forcing and e nearshore barred morphology with rip channels quantitative and qualitative comparisons to previous analytical numerical laboratory studies and field measurements show that the modified model replicates surf zone recirculation patterns onshore drift at the surface and undertow at the bottom more accurately than previous formulations based on radiation stress haas and warner 2009 the results of the model and test cases are further explored for identifying the forces operating in rip current development and the potential implication for sediment transport and rip channel development also model analysis showed that rip current strength is higher when waves approach at angles of 5 to 10 in comparison to normally incident waves

understanding processes controlling sediment transports at the mouth of a highly energetic inlet system san francisco bay ca abstract san francisco bay is one of the largest estuaries along the u s west coast and is linked to the pacific ocean through the golden gate a 100 m deep bedrock inlet a coupled wave flow and sediment transport model is used to quantify the sediment linkages between san francisco bay the golden gate and the adjacent open coast flow and sediment transport processes are investigated using an ensemble average of 24 climatologically derived wave cases and a 24 8 h representative tidal cycle the model simulations show that within the inlet flow and sediment transport is tidally dominated and driven by asymmetry of the ebb and flood tides peak ebb velocities exceed the peak flood velocities in the narrow golden gate channel as a result of flow convergence and acceleration persistent flow and sediment gyres at the headland tips are formed that limit sediment transfer from the ebb tidal delta to the inlet and into the bay the residual transport pattern in the inlet is dominated by a lateral segregation with a large ebb dominant sediment transport and flow prevailing along the deeper north side of the golden gate channel and smaller flood dominant transports along the shallow southern margin the seaward edge of the ebb tidal delta largely corresponds to the seaward extent of strong tidal flows on the ebb tidal delta both waves and tidal forcing govern flow and sediment transport wave focusing by the ebb tidal delta leads to strong patterns of sediment convergence and divergence along the adjacent ocean beach

field observations of wave driven setdown and setup wave driven setdown and setup observed for 3 months on a cross shore transect between the shoreline and 5 m water depth on a barred beach are compared with a theoretical balance between cross shore gradients of the mean water level and the wave radiation stress the observed setdown the depression of the mean water level seaward of the surf zone is predicted well when radiation stress gradients are estimated from the observations using linear theory at each location along the transect the observed setdown also agrees with analytical predictions based on offshore wave observations and the assumption of linear dissipationless normally incident waves shoaling on alongshore homogeneous bathymetry the observed setup the superelevation of the mean water level owing to wave breaking is predicted accurately in the outer and middle surf zone but is increasingly underpredicted as the shoreline is approached similar to previous field studies setup at a fixed cross shore location increases with increasing offshore wave height and is sensitive to tidal fluctuations in the local water depth and to bathymetric changes numerical simulations and the observations suggest that setup near the shoreline depends on the bathymetry of the entire surf zone and increases with decreasing surf zone beach slope defined as the ratio of the surf zone averaged water depth to the surf zone width a new empirical formula for shoreline setup on nonplanar beaches incorporates this dependence

directional spreading of waves in the nearshore observations of surface gravity waves shoaling between 8 m water depth and the shoreline on a barred beach indicate that breaking results in an increase in the directional spread of wave energy in contrast to the directional narrowing with decreasing depth predicted by refraction theory snell s law during low energy wave conditions when breaking induced wave energy losses over the instrumented transect are small the observed mean propagation direction and spread about the mean both decrease with decreasing depth consistent with the expected effects of refraction nonlinearity causes high frequency components of the spectrum to become directionally aligned with the dominant incident waves during high energy wave conditions with significant wave breaking on the sand bar the observed mean directions still decrease with decreasing depth however the observed directional spreads increase sharply nominally a factor of 2 for values integrated over the swell sea frequency range between the outer edge of the surf zone and the crest of the sand bar followed by a decrease toward the shoreline observations on a nonbarred beach also show directional broadening with spreads increasing monotonically from the outer edge of the surf zone to a maximum value near the shoreline although the mechanism is not understood these spatial patterns of directional broadening suggest that wave breaking causes significant scattering of incident wave energy into obliquely propagating components

vertical flow structure during sandy duck observations and modeling abstract observations of the vertical distribution of time averaged cross shore and alongshore flows during the sandy duck field experiment are compared with model predictions to assess the parameters governing the flow behaviour the measurements were obtained with a vertical stack of eight two component current meters with the lowest and highest sensor at respectively o 0 1 and o 2 7 m above the bed observations under breaking wave conditions within the surfzone show that the maximum return flow velocities occur in the lower part of the water column consistent with laboratory observations under non breaking conditions outside the surfzone the maximum return flow velocities are observed closer to the water surface again in line with laboratory results analogous to previous observations the measured longshore current velocity profiles are logarithmic under non breaking conditions and become more depth uniform under breaking conditions the model description of the vertical structure of the flow includes the presence of wind stresses wave stresses pressure gradients turbulent eddy viscosity and a wave boundary layer the model utilizes parabolic shape functions to describe the vertical distribution of the turbulent eddy viscosity in the middle layer and within the bottom boundary layer eddy viscosity is enhanced in regions where turbulence is produced i e near the surface in the case of breaking waves and within the bottom boundary layer estimates of the wave breaking induced turbulent eddy viscosity and bottom friction are obtained by minimizing the model measurement discrepancies predictions utilizing calibrated expressions for both the turbulent eddy viscosity and bottom friction are in general agreement with the observations provided the wave transformation and associated mass flux are modeled correctly and a parabolic eddy viscosity distribution is used using a piecewise constant eddy viscosity distribution generally results in a degrading of the agreement between measurements and model results

pressure gradient driven nearshore circulation on a beach influenced by a large inlet tidal shoal system 1 the nearshore circulation induced by a focused pattern of surface gravity waves is studied at a beach adjacent to a major inlet with a large ebb tidal shoal using a coupled wave and wave averaged nearshore circulation model it is found that the nearshore circulation is significantly affected by the heterogeneous wave patterns caused by wave refraction over the ebb tidal shoal the model is used to predict waves and currents during field experiments conducted near the mouth of san francisco bay and nearby ocean beach the field measurements indicate strong spatial variations in current magnitude and direction and in wave height and direction along ocean beach and across the ebb tidal shoal numerical simulations suggest that wave refraction over the ebb tidal shoal causes wave focusing toward a narrow region at ocean beach due to the resulting spatial variation in nearshore wave height wave induced setup exhibits a strong alongshore nonuniformity resulting in a dramatic change in the pressure field compared to a simulation with only tidal forcing the analysis of momentum balances inside the surf zone shows that under wave conditions with intensive wave focusing the alongshore pressure gradient associated with alongshore nonuniform wave setup can be a dominant force driving circulation inducing heterogeneous alongshore currents pressure gradient forced alongshore currents can exhibit flow reversals and flow convergence or divergence in contrast to the uniform alongshore currents typically caused by tides or homogeneous waves

offshore controls on nearshore rip currents 1 the rip current field resulting from the transformation of surface gravity waves over offshore submarine canyons is studied employing a wave transformation model and a wave induced circulation model over observed bathymetry we find that wave height variations associated with undulations in the canyon contours cause rip current circulation cells with alongshore spacing of o 100m even though the nearshore bathymetry displays no variations at these length scales further the predicted rips correspond to observed rip currents during the nearshore canyon experiment ncex motivated by these results we study the relationship between o 100 m scale variations in offshore bathymetric contours and the resulting rip current field in the nearshore to isolate the roles of possible bathymetric features we construct a series of idealized case studies that include site characteristics found at ncex that are conducive of rip current development such as a curved shoreline an offshore submarine canyon and undulations in the canyon contours our results show that the first two components are unable to produce the observed short scale circulation systems while wave refraction over undulations in the canyon walls at length scales of o 100 m provides a sufficient disturbance to generate alongshore wave height variations that drive multiple rip currents for a variety of incident wave conditions rips are not generated when the wave period is short or when the angle of incidence is large analysis of the alongshore momentum balances further demonstrates that the rip current locations are also strongly influenced by inertial effects hence nonlinear processes are important within the rip current circulation cell and we find that nonlinear advective acceleration terms balance a large portion of the driving alongshore gradient in the mean water surface elevation in the vicinity of the rip currents with bottom friction accounting for the remainder away from the rips the balance is between the wave forcing and the pressure gradient outside the surf zone and wave forcing and bottom friction inside the surf zone as expected

a laboratory study of longshore currents over barred and non barred beaches abstract a detailed description is given of the results of laboratory experiments on wave driven longshore currents on both barred and non barred beaches the objective is to examine the cross shore distribution of the longshore current velocities for purely wave driven currents with emphasis on the position of maximum current velocity with respect to areas where wave energy is dissipated unidirectional obliquely incident waves both regular and random were used the measurements were performed in a large wave basin with a pump recirculation system to create spatially homogeneous longshore currents the experiments yielded information on wave transformation set up of the mean water level and the cross shore distribution of wave driven longshore current velocity a number of cases are presented and compared with each other the measurements show that in the case of purely wave driven longshore currents the maximum current velocities occur close to areas where wave breaking is most intense the effect of mixing bottom friction and wave rollers on the longshore current velocity profile are examined in more detail with help of numerical modelling existing model equations based on the assumption of alongshore uniformity are used the results for the mean longshore current profile on a barred beach are in close agreement with the measurements

experimental study of nearshore dynamics on a barred beach with rip channels 1 wave and current measurements are presented from a set of laboratory experiments performed on a fixed barred beach with periodically spaced rip channels using a range of incident wave conditions the data demonstrate that the presence of gaps in otherwise longshore uniform bars dominates the nearshore circulation system for the incident wave conditions considered for example nonzero cross shore flow and the presence of longshore pressure gradients both resulting from the presence of rip channels are not restricted to the immediate vicinity of the channels but instead are found to span almost the entire length of the longshore bars in addition the combination of breaker type and location is the dominant driving mechanism of the nearshore flow and both are found to be strongly influenced by the variable bathymetry and the presence of a strong rip current the depth averaged currents are calculated from the measured velocities assuming conservation of mass across the measurement grid the terms in both the cross shore and longshore momentum balances are calculated and their relative magnitudes are quantified the cross shore balance is shown to be dominated by the cross shore pressure and radiation stress gradients in general agreement with previous results however the rip current is shown to influence the wave breaking and the wave induced setup in the rip channel analysis of the longshore balance shows that the overall strength of the longshore feeder currents is governed by a balance between longshore pressure gradient forcing and an opposing radiation stress gradient in addition the longshore feeder currents show maxima in the bar trough region providing experimental evidence that longshore pressure gradients can shift longshore current maxima shoreward from the bar crest finally since the longshore radiation stress gradient in the surf zone is governed by the amount of wave dissipation on the rip current there exists a positive feedback mechanism whereby a strong rip current can weaken the radiation stress gradient opposing the feeder currents and lead to even stronger feeder currents and rips

effect of alongshore nonuniformities on longshore current predictions longshore currents have been primarily modeled by assuming alongshore uniformity in this paper we revisit the problem of nonuniform longshore currents to refocus attention on the importance of accounting for alongshore nonuniformity in longshore current predictions and to provide an analytical estimate of the importance of this nonuniformity we derive a semianalytical solution for the longshore currents that allows for weak alongshore variations in the bottom topography the solution shows that the alongshore pressure gradient induced by alongshore variations in the bottom topography could contribute substantially to the forcing for the longshore currents an example calculation shows that the longshore current could deviate by up to 30 from the mean for a 10 deviation of the bottom topography thus we suggest that in many practical cases it is important to include the alongshore pressure gradient to accurately model longshore currents

field observations of wave setup wave setup is assumed to be a balance between the cross shore convergence of the onshore flux of momentum wave radiation stress sxx in the surfzone and a cross shore pressure gradient oceanic observations between the 2 and 8 m isobaths near duck north carolina provide a test of the wave setup balance without assuming that wave height in the surfzone is proportional to water depth analysis of data from a cross shore array of 11 pressure gauges and 10 sonar altimeters deployed during the fall of 1994 indicates the wave setup balance holds to at least the accuracy of the pressure measurements a few centimeters the correlation between the two terms in the setup balance is 0 93 and the linear regression slope is 1 05 0 19 accurate estimates of the cross shore pressure gradient require density measurements to adjust pressure measurements taken at different depths to the same level the assumption that pressure and bathymetry are linear between the 2 and 8 m isobaths or the more common assumption that the height of normally incident shallow water waves is proportional to the water depth introduces errors of up to 6 cm for the conditions considered here given this assumption 3 5 years of data from pressure gauges in 2 and 8 m of water indicate that the wave setup balance is valid for a wide range of conditions correlation 0 71 and regression slope 0 98 0 08

recent ice ages on mars the role of radiatively active clouds and cloud microphysics global climate models gcms have been successfully employed to explain the origin of many glacial deposits on mars however the latitude dependent mantle ldm a dust ice mantling deposit that is thought to represent a recent ice age remains poorly explained by gcms we reexamine this question by considering the effect of radiatively active water ice clouds racs and cloud microphysics we find that when obliquity is set to 35 as often occurred in the past 2 million years warming of the atmosphere and polar caps by clouds modifies the water cycle and leads to the formation of a several centimeter thick ice mantle poleward of 30 in each hemisphere during winter this mantle can be preserved over the summer if increased atmospheric dust content obscures the surface and provides dust nuclei to low altitude clouds we outline a scenario for its deposition and preservation that compares favorably with the characteristics of the ldm

refraction and reflection of infragravity waves near submarine canyons 1 the propagation of infragravity waves ocean surface waves with periods from 20 to 200 s over complex inner shelf water depths from about 3 to 50 m bathymetry is investigated with field observations from the southern california coast a wave ray path based model is used to describe radiation from adjacent beaches refraction over slopes smooth changes in bathymetry and partial reflection from submarine canyons sharp changes in bathymetry in both the field observations and the model simulations the importance of the canyons depends on the directional spectrum of the infragravity wave field radiating from the shoreline and on the distance from the canyons averaged over the wide range of conditions observed a refraction only model has reduced skill near the abrupt bathymetry whereas a combined refraction and reflection model accurately describes the distribution of infragravity wave energy on the inner shelf including the localized effects of steep walled submarine canyons

2dh mathematical modelling of morphological evolutions in shallow water abstract a class of compound mathematical models of transient morphological evolutions in shallow water is discussed based on commonly applied horizontally two dimensional formulations of the water and sediment motion in the coastal zone three major aspects of the composition of such models are considered viz the specific adequacy of the constituent models the balance of the total model and the possibility of spurious interactions the lacunae in the knowledge and the tools needed to judge a proposed model at these points are indicated examples of spurious interactions are described in further detail and techniques to trace and avoid them are given these examples concerning morphological evolutions without the influence of waves show that the advective acceleration terms in the flow model play an essential part in the bottom evolution and its interaction with the current and that incorporation of the bottom slope effects on the sediment transport is indispensable in models with a local transport formulation

observations of surfzone alongshore pressure gradients onshore of an ebb tidal delta abstract the relative importance of radiation stress gradients and alongshore pressure gradients to surfzone dynamics is investigated using observations of water levels waves and flows measured onshore of a large ebb tidal delta incident wave heights measured along the 11 m depth contour varied about 10 over a 1 2 km alongshore transect resulting in alongshore wave setup differences on the order of 10 cm over the 600 m extent of the surfzone instrument array in 1 5 m depth despite the moderate alongshore variability in wave heights the southerly alongshore pressure gradient associated with the alongshore variability of wave driven set up was typically twice as large as the northerly radiation stress gradient forcing consistent with the observed southerly currents during the week long experiment the magnitude of the alongshore forcing and resulting alongshore velocity is reproduced by the two dimensional depth averaged numerical model of shi et al jgr oceans 2011 these observations together with the numerical results indicate that moderate alongshore wave height gradients o 10 4 outside the surfzone owing to alongshore variations in the offshore bathymetry can result in alongshore pressure gradients that are larger than radiation stress gradients

numerical modeling of an estuary a comprehensive skill assessment i numerical simulations of the hudson river estuary using a terrain following three dimensional model regional ocean modeling system roms are compared with an extensive set of time series and spatially resolved measurements over a 43 day period with large variations in tidal forcing and river discharge the model is particularly effective at reproducing the observed temporal variations in both the salinity and current structure including tidal spring neap and river discharge induced variability large observed variations in stratification between neap and spring tides are captured qualitatively and quantitatively by the model the observed structure and variations of the longitudinal salinity gradient are also well reproduced the most notable discrepancy between the model and the data is in the vertical salinity structure while the surface to bottom salinity difference is well reproduced the stratification in the model tends to extend all the way to the water surface whereas the observations indicate a distinct pycnocline and a surface mixed layer because the southern boundary condition is located near the mouth the estuary the salinity within the domain is particularly sensitive to the specification of salinity at the boundary a boundary condition for the horizontal salinity gradient based on the local value of salinity is developed to incorporate physical processes beyond the open boundary not resolved by the model model results are sensitive to the specification of the bottom roughness length and vertical stability functions insofar as they influence the intensity of vertical mixing the results only varied slightly between different turbulence closure methods of k e k and k kl