simulations of nearshore particle pair dispersion in southern california knowledge of horizontal relative dispersion in nearshore oceans is important for many applications including the transport and fate of pollutants and the dynamics of nearshore ecosystems two particle dispersion statistics are calculated from millions of synthetic particle trajectories from high resolution numerical simulations of the southern california bight the model horizontal resolution of 250m allows the investigation of the two particle dispersion with an initial pair separation of 500m the relative dispersion is characterized with respect to the coastal geometry bathymetry eddy kinetic energy and the relative magnitudes of strain and vorticity dispersion is dominated by the submesoscale not by tides in general headlands are more energetic and dispersive than bays relative diffusivity estimates are smaller and more anisotropic close to shore farther from shore the relative diffusivity increases and becomes less anisotropic approaching isotropy 10km from the coast the degree of anisotropy of the relative diffusivity is qualitativelyconsistentwiththat foreddy kinetic energy thetotal relative diffusivity asa functionof pairseparation distance r is on average proportional to r 5 4 additional lagrangian experiments at higher horizontal numerical resolution confirmed the robustness of these results structures of large vorticity are preferably elongated and aligned with the coastline nearshore which may limit cross shelf dispersion the results provide useful information for the design of subgrid scale mixing parameterizations as well as quantifying the transport and dispersal of dissolved pollutants and biological propagules

a self similar scaling for cross shelf exchange driven by transient rip currents transient rip currents episodic offshore flows from the surf zone to the inner shelf present a recreational beach hazard and exchange material across the nearshore ocean the magnitude and offshore extent of transient rip current induced exchange and its relative importance to other inner shelf exchange processes are poorly understood here 120 model simulations with random normally incident directionally spread waves spanning a range of beach slopes and wave conditions show that the transient rip current exchange velocity is self similar the nondimensional exchange velocity surf zone flushing time and cross shore decay length scale are scaled by beach slope and wave properties depending strongly on wave directional spread transient rip current driven exchange can be compared to other cross shelf exchange processes for example transient rip current driven exchange is stronger than wave induced stokes drift driven exchange up to six surf zone widths from shore

heterogeneous zircon cargo in voluminous late paleozoic rhyolites hf o isotope and zr hf records of plutonic to volcanic magma evolution voluminous rhyolitic lavas and ignimbrites c 34 000 km3 were formed in the ne german basin in a post collisional setting at c 295 ma trace elements ehf and 18o have been measured in dated magmatic and inherited rhyolitic zircons from three drill cores across the basin magmatic zircons crystallized in two stages the first stage in less differentiated and isotopically heterogeneous magmas and the second stage in more differentiated and isotopically homogeneous magmas the first and second stages can be related to the crystallization of zircons within a heterogeneous pluton and in an evolved silicic magma that was later erupted some zircons crystallized entirely during the evolved magma stage and provide good resolution for identifying and characterizing processes happening shortly before eruption the isotopic compositions of the magmatic zircons constrain the proportions of juvenile and reworked materials involved in the formation of voluminous silicic magmas in a post collisional tectonic setting the advantage of studying the volcanic rocks from the ne german basin is that their petrogenesis involved a relatively simple two source interaction during magma production which permits quantitative estimation of the amount of each source component afc modelling shows that the first stage zircons crystallized from magmas containing 5 80 of the juvenile component whereas the final rhyolitic magmas contained 30 40 of this material the inherited zircons have hf model ages of 1 9 2 2 ga suggesting that much of the local basement was initially derived from the mantle at that time and that it was subsequently reworked at around 1 5 ga similar model ages are a feature of baltica derived sediments and the implication is that such sediments underlie large areas of the ne german basin the lack of any record of avalonian basement in the ne german basin may indicate that both the sedimentary cover and the underlying basement are part of baltica

nearshore chlorophyll a events and wave driven transport 1 continuous records of temperature and chlorophyll a chl a fluorescence were used to characterize phytoplankton variability at two shallow intertidal stations on the northern california coast chl a records from spring and summer 2007 and 2008 were characterized by distinct peaks persisting for 1 5 to five days these peaks represent bloom events which often coincided between the two sites even though they are separated by 150 km blooms did not appear to be directly forced by individual upwelling episodes while some events were associated with reversals of upwelling favorable winds there was a stronger relationship between chl a peaks and peaks in surface swell height this relationship was dominant in spring and early summer but no longer evident by july we suggest that these nearshore chl a peaks are an accumulation of phytoplankton caused by convergence of onshore wave transport against the impermeable coastal boundary scaling arguments show this mechanism to be consistent with observed chl a increase rates this mechanism has not been previously considered as a forcing for blooms at rocky coasts and it may have significant implications for understanding coastal productivity larval dispersal and nearshore water quality

undertow over a barred beach the spatial distribution of the mean cross shore flow undertow over a barred beach is examined with field data obtained on three energetic wave days during the duck94 experiment the vertical structure of the undertow is modeled using a turbulent eddy viscosity closure and includes the important effects of wave breaking described using the roller concept and convective acceleration of the current other than a more realistic description of observed turbulence variations a depth dependent eddy viscosity compared with a constant does not improve the agreement between predicted and observed undertow profiles the effect of using different boundary conditions is investigated by extending the formulations of stive and wind 1986 and svendsen et al 1987 to include random waves by ensemble averaging over the wave height distribution the contribution of breaking wave rollers to the surface mass flux can be of the same order or greater than the contribution associated with the organized wave motion the largest discrepancies between model predictions and observations occur over the sandbar where the mass transport of the breaking waves appears to be underestimated

rip current types circulation and hazard abstract rip currents are narrow and concentrated seaward directed flows that extend from close to the shoreline through the surf zone and varying distances beyond rip currents are ubiquitous on wave exposed coasts each year they cause hundreds of drowning deaths and tens of thousands of rescues on beaches worldwide and are therefore the leading deadly hazard to recreational beach users the broad definition above masks considerable natural variability in terms of rip current occurrence in time and space flow characteristics and behaviour in particular surf zone rip currents have long been perceived as narrow flows extending well beyond the breakers flushing out the surf zone at a high rate exit flow circulation regime while more recent studies have shown that rip flow patterns can consist of quasi steady semi enclosed vortices retaining most of the floating material within the surf zone circulatory flow circulation regime building upon a growing body of rip current literature involving numerical modelling and theory together with emergence of dense lagrangian field measurements we develop a robust rip current type classification that provides a relevant framework to understand the primary morphological and hydrodynamic parameters controlling surf zone rip current occurrence and dynamics three broad categories of rip current types are described based on the dominant controlling forcing mechanism each category is further divided into two types owing to different physical driving mechanisms for a total of six fundamentally different rip current types hydrodynamically controlled 1 shear instability rips and 2 flash rips which are transient in both time and space and occur on alongshore uniform beaches bathymetrically controlled 3 channel rips and 4 focused rips which occur at relatively fixed locations and are driven by hydrodynamic processes forced by natural alongshore variability of the morphology in both the surf zone and inner shelf zone and boundary controlled 5 deflection rips and 6 shadow rips which flow against rigid lateral boundaries such as natural headlands or anthropogenic structures for each rip current type flow response to changes in hydrodynamic and morphologic forcing magnitude is examined in regard to velocity modulation and changes in circulation regime providing key force response relationships of rip currents we also demonstrate that in the real world rip currents form through a mixture of driving mechanisms and the discrete rip types defined in fact form key elements in a wide and complex spectrum of rip currents on natural beaches it is anticipated that this rip current type classification will serve as a resource for coastal scientists and non specialists with an interest in the rip current hazard and as a platform for future rip current studies finally we suggest some important future research directions highlighting the need for coastal and beach safety communities to collaborate in order to improve rip current education and awareness

rip current circulation and surf zone retention on a double barred beach abstract rip currents have an important control on the exchange of water and advected materials such as sediment and pollutants between the surf zone and inner shelf concurrent in situ eulerian and lagrangian gps drifter data of surf zone waves and currents were combined with video data on wave breaking patterns over the inner and outer bars on a high energy double barred beach the data collectively show how the occurrence of wave breaking over the outer bar changes the behavior of a channel rip current and the exchange process on both days there was a prominent clockwise eddy in the surf zone for which the seaward heading portion formed a rip current in a well defined channel rip incised into the inner bar exit rate measured with drifters from the surf zone to inner shelf decreased significantly with increased wave breaking over the outer bar from 71 exits to 6 over the two days exit rate appears to be driven by the balance between wave breaking over the inner and outer bars and pulsing of currents within the surf zone under higher wave conditions there were stronger pulsations in surf zone currents and more surf zone exits however higher wave conditions caused wave breaking over the outer bar this breaking increases vorticity around the outside of the surf zone eddy which increases surf zone retention this is in contrast to previous studies showing that vorticity is highest at the center of surf zone eddies under such conditions drifter exits were rare and occurred due to vortex shedding during lower incident wave conditions eddy vorticity was lower and drifters could relatively freely exit the surf zone this is one of the few studies that investigate surf zone circulation on a high energy double barred beach

boussinesq modelling of transient rip currents the flow on a plane beach with a random directionally spread wave field was simulated with a boussinesq model the random wave spectra were directionally symmetric with their central direction perpendicular to the beach so no constant longshore current was generated variable wave averaged currents were generated because of the spatially variable wave field and sometimes formed offshore directed rip currents that appear in variable longshore locations the rip currents are associated with a vortex pair which is generated within the surfzone and subsequently propagates offshore analysis of the vorticity balance show that the main vorticity input occurs within the inner surfzone three different beach slopes and four different wave spectra are simulated the frequency duration and intensity of the transient rips depend on both the beach slope and the incident wave spectra the results have important engineering implications for the transport of material in the nearshore zone in particular on longshore uniform beaches

low level wind maxima and the transport of pyrogenic products over southern africa low level jets llj over various regions of southern africa are shown to occur mostly as a result of a thermal gradient established over gently sloping terrain and have been observed to overlie the nocturnal temperature inversions strong low level winds associated with plain mountain and mountain plain circulations have also been observed over the central namib desert and natal interior with the exception of the namib and natal where no temperature profiles accompanied wind profile observations the llj is seen to increase in strength as the nocturnal surface temperature inversion intensifies through the night the height of the llj above the surface also increases as the inversion deepens wind speeds in all regions exceed 10 m s 1 in the jet core which typically is located between 200 and 300 m above ground level agl over the central namib the summertime plain mountain wind reaches similar wind speeds in a jetlike core located about 200 to 600 m agl the natal mountain plain winds may exceed 10 m s 1 in a layer of up to 1000 m deep it is suggested that all these regional scale wind systems transport pyrogenic products in excess of 400 km during a single night subsequent daytime convective lifting of these ozone precursors coupled with synoptic scale anticyclonic circulation provides a transport mechanism for pyrogenic products over southern africa toward the atlantic and indian oceans

wave driven inner shelf motions on the oregon coast abstract recent work by s lentz et al documents offshore transport in the inner shelf due to a wave driven return flow associated with the hasselmann wave stress the stokes coriolis force this analysis is extended using observations from the central oregon coast to identify the wave driven return flow present and quantify the potential bias of wind driven across shelf exchange by unresolved wave driven circulation using acoustic doppler current profiler adcp measurements at six stations each in water depths of 13 15 m observed depth averaged across shelf velocities were generally correlated with theoretical estimates of the proposed return flow during times of minimal wind forcing across shelf velocity profiles were vertically sheared with stronger velocities near the top of the measured portion of the water column and increased in magnitude with increasing significant wave height consistent with circulation due to the hasselmann wave stress yet velocity magnitudes and vertical shears wer

cross shore deformation of a surfzone released dye plume by an internal tide on the inner shelf abstractan inner shelf is dye plume that formed following a 3 84 h early morning surfzone sz dye release off of imperial beach california is analyzed with in situ and aerial remotely sensed o

effect of wave frequency and directional spread on shoreline runup 1 wave breaking across the surf zone elevates the mean water level at the shoreline setup and drives fluctuations about the mean runup runup often is divided into sea swell 0 04 0 3 hz and lower frequency infragravity 0 00 0 04 hz components with energetic incident waves runup is dominated by infragravity frequencies and total water levels combined setup and runup can exceed 3 m significantly contributing to coastal flooding and erosion setup and runup observations on sandy beaches are scattered about empirical parameterizations based on near shoreline beach slope and deep water wave height and wavelength accurate parameterizations are needed to determine flooding and erosion risk to coastal ecosystems and communities here numerical simulations with the boussinesq wave model funwavec are shown to statistically reproduce typical empirical setup and runup parameterizations furthermore the model infragravity runuprs ig strongly depends on the incident wave directional and frequency spread about the mean direction and peak frequency realistic directional spread variations change rs ig equivalent to a factor of two variation in incident wave height the modeled rs ig is shown to vary systematically with a new non dimensional spreading parameter that involves peak frequency frequency spread and directional spread this suggests a new parameterization forrs ig potentially useful to predict coastal flooding and erosion

observations and a model of undertow over the inner continental shelf abstract onshore volume transport stokes drift due to surface gravity waves propagating toward the beach can result in a compensating eulerian offshore flow in the surf zone referred to as undertow observed offshore flows indicate that wave driven undertow extends well offshore of the surf zone over the inner shelves of martha s vineyard massachusetts and north carolina theoretical estimates of the wave driven offshore transport from linear wave theory and observed wave characteristics account for 50 or more of the observed offshore transport variance in water depths between 5 and 12 m and reproduce the observed dependence on wave height and water depth during weak winds wave driven cross shelf velocity profiles over the inner shelf have maximum offshore flow 1 6 cm s 1 and vertical shear near the surface and weak flow and shear in the lower half of the water column the observed offshore flow profiles do not resemble the parabolic profiles with maximum flow at middepth observed within the su

lagrangian observations of inner shelf motions in southern california can surface waves decelerate shoreward moving drifters just outside the surf zone abstractthis study explores eulerian and lagrangian circulation during weak winds at two inner shelf locations off the southern california coast where the shoreline shelf wind and wave characteristics differ from those in previous studies in agreement with recent observational studies wave driven eulerian offshore flow just outside the surf zone referred to as undertow is a substantial component of the net cross shore circulation during periods of weak winds drifter observations show onshore surface flow likely due to light onshore winds and a consistent decrease in onshore velocity of roughly 4 cm s 1 within a few hundred meters of the surf zone undertow is examined as a possible explanation for the observed lagrangian decelerations model results suggest that even when waves are small undertow can decrease the velocity of shoreward moving drifters by 2 cm s 1 roughly half the observed deceleration the coastal boundary condition also has the potential to contribute to the observed deceler

numerical simulations of larval transport into a rip channeled surf zone competent larvae of intertidal invertebrates have to migrate toward shore for settlement however their migration through the surf zone is not understood we investigated larval transport mechanisms at a ripchanneled beach because tracking larvae in the surf zone is infeasible we used a three dimensional biophysical model to simulate the processes the coupled model consists of a physical module for currents and waves and a biological module for adding larval traits and behaviors as well as stokes drift to lagrangian particles model calculations were performed with and without onshore wind forcing without wind wave driven onshore streaming occurs in the bottom boundary layer outside the surf zone with onshore wind onshore currents occur near the surface in the surf zone offshore directed rip currents and compensating onshore directed currents over shoals are formed in both no wind and wind cases in the biological module neutral negative and positive buoyant particles were released offshore additionally particles either sank in the presence of turbulence or not two scenarios achieved successful onshore migration negatively buoyant larvae without wind forcing sink in the turbulent bottom boundary layer and are carried onshore by streaming positively buoyant larvae drift toward shore in wind driven surface currents to the surf zone then sink in the turbulent surf zone and remain near the bottom while transported shoreward in both cases the larval concentration is highest in the rip channel consistent with field data this successful result is only obtained if turbulence dependent sinking behavior and stokes drift are included in the transport of larvae

modeling surf zone tracer plumes 2 transport and dispersion 1 five surf zone dye tracer releases from the hb06 experiment are simulated with a tracer advection diffusion model coupled to a boussinesq surf zone model funwavec model tracer is transported and stirred by currents and eddies and diffused with a breaking wave eddy diffusivity set equal to the breaking wave eddy viscosity and a small 0 01 m2 s 1 background diffusivity observed and modeled alongshore parallel tracer plumes transported by the wave driven alongshore current have qualitatively similar cross shore structures although the model skill for mean tracer concentration is variable from negative to 0 73 depending upon release cross shore integrated tracer moments normalized by the cross shore tracer integral have consistently high skills 0 9 modeled and observed bulk surf zone cross shore diffusivity estimates are also similar with 0 72 squared correlation and skill of 0 4 similar to the observations the model bulk absolute cross shore diffusivity is consistent with a mixing length parameterization based on low frequency 0 001 0 03 hz eddies the model absolute cross shore dispersion is dominated by stirring from surf zone eddies and does not depend upon the presence of the breaking wave eddy diffusivity given only the bathymetry and incident wave field the coupled boussinesq tracer model qualitatively reproduces the observed cross shore absolute tracer dispersion suggesting that the model can be used to study surf zone tracer dispersion mechanisms

mechanisms of mid to outer shelf transport of shoreline released tracers abstracttransport of shoreline released tracer from the surfzone across the shelf can be affected by a variety of physical processes from wind driven to submesoscale with implications for shorelin

breaking wave induced cross shore tracer dispersion in the surf zone model results and scalings 1 the dispersion of surf zone tracers including pollutants and bacteria is determined by many processes acting over a range of timescales and space scales breaking waves bores are clearly important to cross shore tracer dispersion in the surf zone but little is known about the dispersal effects of bores here a simple model for bore induced cross shore dispersion are developed based upon the diffusion equation with an eddy diffusivity that propagates with the bores depth uniform tracer and bore induced mixing along with alongshore uniformity are assumed the bores are assumed well developed and the dispersion results are for a self similar constant wave height to water depth ratio surf zone four nondimensional parameters are identified and solution space is explored the tracer center of mass is approximately constant and tracer width grows with the square root of time tracer distribution becomes initially skewed after the passage of the first bore but becomes symmetric after multiple bores have passed the nondimensional tracer patch growth and dilution rates depend strongly upon the nondimensional phase speed and wave period the simple model results are consistent with the a boussinesq wave model where the breaking wave eddy viscosity is used for the bore eddy diffusivity the scaling of the dimensional parameters regarding the bore eddy diffusivity and the ranges of the nondimensional parameters are examined covariation of the nondimensional phase speed and wave period suggest that nondimensional tracer dispersion is largely cross shore independent

transient rip currents and nearshore circulation on a swell dominated beach 1 eulerian and lagrangian measurements of nearshore circulation on a longshore uniform beach with perpendicularly incident swell waves are described both the eulerian and lagrangian data show a variable rotational part of the current field that is distinct from but coexists with that due to infragravity waves a well defined feature of the flow field includes transient rip currents which occur in varying locations and are not topographically controlled drifter trajectories show that the rips behave like a shallow plane jet consisting of a constrained neck region that flows into a spreading head region there is continuous modulation of the flow within the rip neck estimates of the length scale across the rip neck using two particle statistics are 20 30 m well defined discrete vortex features are observed at the initiation point of one of the necks and in one of the rip heads estimated dispersion values suggest that mixing is greatly enhanced outside the surf zone by the intermittent presence of the rip heads the dispersion calculated from both inside and outside the surf zone appears to show scale dependence with a power law close to 4 3 in a similar way to oceanic turbulence at much larger scales

a new offshore transport mechanism for shoreline released tracer induced by transient rip currents and stratification offshore transport from the shoreline across the inner shelf of early stage larvae and pathogens is poorly understood yet is critical for understanding larval fate and dilution of polluted shoreline water with a novel coupling of a transient rip current trc generating surf zone model and an ocean circulation model we show that transient rip currents ejected onto a stratified inner shelf induce a new previously unconsidered offshore transport pathway for incident waves and stratification typical for southern california in the fall this mechanism subducts surf zone origin tracers and transports them at least 800 m offshore at 1 2 km d analogous to subduction at ocean fronts this mechanism requires both trcs and stratification as trcs are ubiquitous and the inner shelf is often stratified this mechanism may have an important role in exporting early stage larvae pathogens or other tracers onto the shelf

field observations of surf zone inner shelf exchange on a rip channeled beach cross shore exchange between the surf zone and the inner shelf is investigated using lagrangian and eulerian field measurements of rip current flows on a rip channeled beach in sand city california surface drifters released on the inner shelf during weak wind conditions moved seaward due to rip current pulses and then returned shoreward in an arcing pattern reentering the surf zone over shoals the cross shore velocities of the seaward and shoreward moving drifters were approximately equal in magnitude and decreased as a function of distance offshore the drifters carried seaward by the rip current had maximum cross shore velocities as they exited the surf zone and then decelerated as they moved offshore the drifters moving shoreward accelerated as they approached the surfzone boundary with maximum cross shore velocities as they reentered the surf zone over shoals it was found that stokes drift was not solely responsible for the onshore transport across the surfzone boundary the cross shore diffusivity on the inner shelf was greatest during observations of locally contained cross shore exchange these field observations provide evidence that the cross shore exchange between the surf zone and inner shelf on a rip channeled beach is due to wave driven rip current circulations and results in surface material being contained within the nearshore region

the generation of surfzone eddies in a strong alongshore current abstractthe surfzone contains energetic two dimensional horizontal eddies with length scale larger than the water depth yet the dominant eddy generation mechanism is not understood the wave resolving model funwavec is used to simulate surfzone eddies in four case examples from the sandyduck field experiment that had alongshore uniform bathymetry the funwavec model is initialized with the observed bathymetry and the incident wave field in 8 m depth and reproduces the observed cross shore structure of significant wave height and mean alongshore current within the surfzone the wave resolving funwavec modeled e f ky spectra and the bulk frequency and ky integrated rotational velocities are consistent with the observations below the sea swell band 0 05 hz demonstrating that the model can be used to diagnose surfzone eddy generation mechanisms in the mean squared perturbation vorticity budget the breaking wave vorticity forcing term is orders of magnitude larger than the shear instability gene

rip current review rip currents are shore normal narrow seaward flowing currents that originate within surf zone extend seaward of the breaking region rip head and can obtain relatively high velocities within the last decade there have been a significant number of laboratory and field observations within rip current systems an overview of rip current kinematics based on these observations and the scientific advances obtained from these efforts are synthesized rip current flows are partitioned into mean infragravity very low frequency vorticity and tidal contributions and it is found that each contributes significantly to the total data from the laboratory and the field suggest that the rip current strength increases with increasing wave energy and decreasing water depths the maximum mean current occurs inside the surf zone where the maximum forcing is present owing to the dissipation of waves

mean lagrangian flow behavior on an open coast rip channeled beach a new perspective article i nfo the accepted view of rip currents is that they are an efficient mechanism for transporting material out of the surf zone previous rip current campaigns on natural beaches have focused on eulerian measurements with sparse in situ pressure and current meter arrays here for the first time spatially synoptic estimates of rip current flow patterns vorticity and lagrangian transport behavior are measured in the field using a fleet of 30 position tracking surfzone drifters during multiple rip current occurrences on an open coast beach in monterey ca contrary to the classic view shepard et al 1941 the rip current flow field consisted of semi enclosed large scale vortices that retained the drifters and resulted in a high number of lagrangian observations that are temporally and spatially repeated approximately 19 of the drifters deployed in the rip currents exited the surf zone per hour on average during the experiments the observed surf zone retention of drifters is consistent with measurements from different open coast beach rip current systems 14 at meso macrotidal truc vert france and 16 at macrotidal perranporth united kingdom the three hour average cross shore rip current velocity at monterey was 30 cm s with peak time averaged velocities of 40 60 cm s depending on wave and tidal conditions drifters that episodically exited the surf zone were transported approximately 2 surf zone widths offshore at 20 cm s published by elsevier b v

cross shore surfzone tracer dispersion in an alongshore current 1 cross shore surfzone tracer dispersion in a wave driven alongshore current is examined over a range of wave and current conditions with 6 continuous dye releases each roughly 1 2 hours in duration at huntington beach california fluorescent dye tracer released near the shoreline formed shore parallel plumes that were sampled on repeated cross shore transects with a jet ski mounted fluorometer ensemble averaged cross shore tracer concentration profiles are generally shoreline attached maximum at or near the shoreline with increasing cross shore widths and decreasing peak values with downstream distance more than a few 100 m from the source tracer is often well mixed across the surfzone i e saturated with decreasing tracer concentrations farther seaward for each release cross shore surfzone absolute diffusivities are estimated using a simple fickian diffusion solution with a no flux boundary at the shoreline and range from 0 5 2 5 m2 s 1 surfzone diffusivity scalings based on cross shore bore dispersion surfzone eddy mixing length and undertow driven shear dispersion are examined the mixing length scaling has correlation r2 0 59 and the expected best fit slope 1 indicating that horizontal rotational motions are important for cross shore tracer dispersion in the surfzone

surf zone flushing on embayed beaches 1 using a numerical model we show that the surf zone of embayed beaches systematically flushes out more floating material simulated using passive tracers than on open beaches with most exits occurring through the headland rips for obliquely incident waves a headland rip acts as a persistent conduit for transporting floating material out of the surf zone and into the inner shelf region wave angle and embayment size determine which headland rip upwave or downwave flushes out more the surf zone material for narrow embayed beaches passive drifters exit the surf zone through the upwave headland rip for wider embayed beaches the longshore current has enough room to develop and is further deflected against the downwave headland where most drifters exit the surf zone our results indicate that wave exposed rugged coasts strongly enhance exchange of floating matter e g pollutants and nutrients at the ocean continent interface

the effect of stokes drift and transient rip currents on the inner shelf part i no stratification abstractthis is part ii of a two part study focused on stokes drift and transient rip current trc effects on the unstratified part i and stratified this paper inner shelf part i focuses on funwavec coupled ocean atmosphere wave sediment transport coawst coupling and trc effects on mixing and exchange on an unstratified inner shelf here two simulations r3 and r4 are performed on a stratified inner shelf and surfzone with typical bathymetry stratification and wave conditions r3 is a coawst only simulation no trcs while r4 has funwavec coawst coupling with trcs in r4 trcs lead to patchy near surface cooling vertical isotherm displacement and increased water column mixing for both r3 and r4 the mean lagrangian circulation has two nearly isolated surfzones and inner shelf overturning circulation cells with a stronger r4 inner shelf circulation cell the r4 inner shelf vertical velocity variability is 2 3 times stronger than a simulation with trcs and no stratification relative

modeling surf zone tracer plumes 1 waves mean currents and low frequency eddies 1 a model that accurately simulates surf zone waves mean currents and low frequency eddies is required to diagnose the mechanisms of surf zone tracer transport and dispersion in this paper a wave resolving time dependent boussinesq model is compared with waves and currents observed during five surf zone dye release experiments in a companion paper clark et al 2011 compare a coupled tracer model to the dye plume observations the boussinesq model uses observed bathymetry and incident random directionally spread waves for all five releases the model generally reproduces the observed cross shore evolution of significant wave height mean wave angle bulk directional spread mean alongshore current and the frequency dependent sea surface elevation spectra and directional moments the largest errors are near the shoreline where the bathymetry is most uncertain the model also reproduces the observed cross shore structure of rotational velocities in the infragravity 0 004 f 0 03 hz and very low frequency vlf 0 001 f 0 004 hz bands although the modeled vlf energy is 2 3 times too large similar to the observations the dominant contributions to the modeled eddy induced momentum flux are in the vlf band these eddies are elliptical near the shoreline and circular in the mid surf zone the model data agreement for sea swell waves low frequency eddies and mean currents suggests that the model is appropriate for simulating surf zone tracer transport and dispersion

vertical structure of the undertow outside the surf zone the vertical structure of the undertow in the shoaling region outside the surf zone is quite different from that inside the surf zone inside the surf zone the undertow typically has a large seaward directed velocity near the bottom and either a shoreward directed or a small seaward directed velocity at trough level measurements show that outside the surf zone the undertow has a small seaward directed velocity near the bed and a large seaward directed velocity at trough level in this paper we develop theoretical expressions for the undertow outside the surf zone and show that the steady streaming from the bottom boundary layer which was earlier found to have a negligible effect in the surf zone svendsen et al 1987 does have a significant influence on the vertical structure of the undertow in that region