energy flux of nonlinear internal waves in northern south china sea 1 we analyze three sets of adcp measurements taken on the dongsha plateau on the shallow continental shelf and on the steep continental slope in the northern south china sea scs the data show strong divergences of energy and energy flux of nonlinear internal waves nliw along and across waves prevailing westward propagation path the nliw energy flux is 8 5 kw m 1 on the plateau only 0 25 kw m 1 on the continental shelf 220 km westward along the propagation path and only 1 kw m 1 on the continental slope 120 km northward across the propagation path along the wave path on the plateau the average energy flux divergence of nliw is 0 04 w m 2 which corresponds to a dissipation rate of o 10 7 10 6 w kg 1 combining the present with previous observations and model results a scenario of nliw energy flux in the scs emerges nliws are generated east of the plateau propagate predominantly westward across the plateau along a beam of 100 km width that is centered at 21 n and dissipate nearly all their energy before reaching the continental shelf

the unpredictable nature of internal tides on continental shelves abstractpackets of nonlinear internal waves nliws in a small area of the mid atlantic bight were 10 times more energetic during a local neap tide than during the preceding spring tide this counterintuitive result cannot be explained if the waves are generated near the shelf break by the local barotropic tide since changes in shelfbreak stratification explain only a small fraction of the variability in barotropic to baroclinic conversion instead this study suggests that the occurrence of strong nliws was caused by the shoaling of distantly generated internal tides with amplitudes that are uncorrelated with the local spring neap cycle an extensive set of moored observations show that nliws are correlated with the internal tide but uncorrelated with barotropic tide using harmonic analysis of a 40 day record this study associates steady phase motions at the shelf break with waves generated by the local barotropic tide and variable phase motions with the shoaling of distantly generated internal tides

on the formation and propagation of nonlinear internal boluses across a shelf break high resolution two and three dimensional numerical simulations are performed of first mode internal gravity waves interacting with a shelf break in a linearly stratified fluid the interaction of nonlinear incident waves with the shelf break results in the formation of upslope surging vortex cores of dense fluid referred to here as internal boluses that propagate onto the shelf this paper primarily focuses on understanding the dynamics of the interaction process with particular emphasis on the formation structure and propagation of internal boluses onshelf a possible mechanism is identified for the excitation of vortex cores that are lifted over the shelf break from where from the simplest viewpoint they essentially propagate as gravity currents into a linearly stratified ambient fluid

nearshore internal bores and turbulent mixing in southern monterey bay 1 we observed transient stratification and mixing events associated with nearshore internal bores in southern monterey bay using an array of instruments with high spatial and temporal resolution the arrival of the bores is characterized by surging masses of dense cold water that tend to stratify the water column the bore is followed by a gradual drop in the temperature throughout the water column over several hours defined here as the bore period until a sharp warm front relaxation followed by high frequency temperature fluctuations returns the column back to nearly its original state defined here as the mixing period mixing periods revealed increased temperature variance at high frequencies n as well as a greater percentage of events where dynamic instabilities may be present ri 0 25 suggesting active mixing of the stratified water column turbulent dissipation rates in the stratified interior during the mixing period estimated using the technique of isopycnal slope spectra revealed mean values the same order of magnitude as near bed bottom generated turbulence observations indicate that local shear produced turbulent kinetic energy by the warm front relaxations dominates mixing in the stratified interior the non canonical nature of these bore and relaxation events is also investigated with a numerical model and the dynamics are shown to depend on the internal iribarren number our results suggest that nearshore internal bores interacting with local bathymetry dramatically alter local dynamics and mixing in the nearshore with important ecological implications

a barotropic inverse tidal model for the arctic ocean 1 we describe high resolution 5 km grid linear dynamics and inverse models of arctic ocean barotropic tides obtained with the osu tidal inversion software otis package the 8 constituent dynamics based model uses the latest ibcao bathymetry and open boundary forcing from the recent tpxo 6 2 global barotropic tidal solution this model performs significantly better than the present benchmark arctic tidal model 14 km grid by z kowalik and a proshutinsky as judged by comparisons with 300 coastal tide gauges the greatest improvements are found in the canadian arctic archipelago nares strait and the baffin bay and labrador sea and can be explained by the higher resolution of the new model in these topographically complex regions the new arctic inverse model assimilates coastal and benthic tide gauges and topex poseidon and ers altimetry for further improvements of the 4 dominant constituents m2 s2 k1 and o1

the modification of bottom boundary layer turbulence and mixing by internal waves shoaling on a barrier reef abstractresults are presented from an observational study of stratified turbulent flow in the bottom boundary layer on the outer southeast florida shelf measurements of momentum and heat fluxes were made using an array of acoustic doppler velocimeters and fast response temperature sensors in the bottom 3 m over a rough reef slope direct estimates of flux richardson number rf confirm previous laboratory numerical and observational work which find mixing efficiency not to be a constant but rather to vary with frt reb and rig these results depart from previous observations in that the highest levels of mixing efficiency occur for frt 1 suggesting that efficient mixing can also happen in regions of buoyancy controlled turbulence generally the authors find that turbulence in the reef bottom boundary layer is highly variable in time and modified by near bed flow shear and stratification driven by shoaling internal waves

community production modulates coral reef ph and the sensitivity of ecosystem calcification to ocean acidification coral reefs are built of calcium carbonate caco3 produced biogenically by a diversity of calcifying plants animals and microbes as the ocean warms and acidifies there is mounting concern that declining calcification rates could shift coral reef caco3 budgets from net accretion to net dissolution we quantified net ecosystem calcification nec and production nep on dongsha atoll northern south china sea over a 2 week period that included a transient bleaching event peak daytime ph on the wide shallow reef flat during the nonbleaching period was 8 5 significantly elevated above that of the surrounding open ocean 8 0 8 1 as a consequence of daytime nep up to 112 mmol c m 2 h 1 diurnal averaged nec was 390 90 mmol caco3 m 2 d 1 higher than any other coral reef studied to date despite comparable calcifier cover 25 and relatively high fleshy algal cover 19 coral bleaching linked to elevated temperatures significantly reduced daytime nep by 29 mmol c m 2 h 1 ph on the reef flat declined by 0 2 units causing a 40 reduction in nec in the absence of ph changes in the surrounding open ocean our findings highlight the interactive relationship between carbonate chemistry of coral reef ecosystems and ecosystem production and calcification rates which are in turn impacted by ocean warming as open ocean waters bathing coral reefs warm and acidify over the 21st century the health and composition of reef benthic communities will play a major role in determining on reef conditions that will in turn dictate the ecosystem response to climate change

east west asymmetry in nonlinear internal waves from luzon strait the nonhydrostatic regional ocean modeling system is applied to study the effects of thermocline shoaling deepening bathymetry and asymmetric modulated tides on the soliton growth to the west and east of luzon strait in the south china sea and western pacific ocean luzon strait comprises a shallow east ridge and a deep west ridge and its interaction with barotropic tidal currents yields strong westward internal tides that disperse into solitons satellite imagery indicates that the westward solitons are more numerous and better defined than the eastward solitons the model results show that the eastward solitons are 45 39 28 and 23 smaller than the westward solitons due to asymmetric modulated barotropic tides at the east ridge a deeper pacific ocean westward thermocline shoaling related to the kuroshio current and internal tide resonance in a double ridge configuration respectively due to the westward location of the kuroshio little thermocline deepening occurs east of the east ridge hence the influence of thermocline deepening on counteracting eastward soliton growth is small the kuroshio mainly enhances westward soliton growth the dispersion of internal tides into solitons is governed by the balance between the nonlinearity parameter on the one hand and the nonhydrostatic and coriolis dispersions on the other it is shown that this balance favors soliton growth for thermocline shoaling while it counters it for a deeper ocean a series of double ridge experiments is performed in which the distance between the ridges and the height of the west ridge are varied for a semidiurnal tidal forcing and two gaussian ridges separated by 100 km barotropic to baroclinic energy conversion is enhanced at both ridges causing larger westward internal tides and solitons the combination of coriolis forcing thermocline shoaling and a double ridge configuration enhances the distinctiveness of the so called type a and b solitons when a modulated tide occurs

nonlinear internal waves in the south china sea observation of the conversion of depression internal waves to elevation internal waves 1 the conversion of depression nonlinear internal solitons to elevation internal waves has been observed twice at the south china sea continental shelf break shipboard x band radar tow yo ctd adcp and high frequency acoustic flow visualization of the process are presented the data focuses on up slope propagation of depression internal solitons from a water depth of 264 m to a water depth of 110 m dissipation by large amplitude shear instabilities was observed the kinetic energy density was found to be a decreasing monotonic function of range with an energy dissipation rate coefficient of 0 063 km 1 the rate of energy dissipation over the 16 5 km soliton propagation path was 0 17 w m m simple numerical models of the waveform evolution are qualitatively compared to the observations the observations extracted scale parameters and dissipation rates should be useful for testing a variety of evolution equation representations of internal soliton propagation

observation of very large and steep internal waves of elevation near the massachusetts coast 1 we report on near bottom waves of elevation with amplitude nearly half the 25 m water column very steep and propagating into a sheared turbulent wave guide the waves contained trapped cores transporting parcels of water shoreward these large waves depart strongly from weakly nonlinear and weakly nonhydrostatic conditions and challenge established paradigms they can also represent an important factor in the across shore transport of plankton and contaminants

circulation and larval distribution in internal tidal bore warm fronts internal tidal bore warm fronts were observed during the summer of 1996 off the coast of southern california warm bore fronts had concentrating currents resulting from high frequency internal motions and from a larger two way flow the two way flow featured surface currents onshore and bottom currents offshore a sharp thermocline depression and high frequency large amplitude internal motions followed the leading edge of the bore with downwelling currents on the trailing side of the crest of the nonlinear internal waves and upwelling currents in front of the crest warm bores propagated onshore with a propagation speed c that ranged from 10 6 to 19 6 cm s 1 while time averaged frontal currents varied from 11 2 to 17 6 cm s 1 in the shallowest bin in one out of three cases c which implied that there were faster currents than the rate of advance of the front and which implied that the origin of surface frontal material is behind the front not in front of it three invertebrate larval taxa were found at all sites across fronts but only two intertidal barnacles pollicipes polymerus and chthamalus spp were concentrated at the front s surface while the subtidal bryozoan membranipora spp was not frontal pollicipes were more concentrated than were chthamalus the frontal downwelling currents observed suggested that concentrated larvae would have to swim upward in order to maintain depth pollicipes were abundant on the offshore warm side of the fronts but were absent or rare on the onshore colder side suggesting that the origin of frontal pollicipes was behind the front although an alternative cannot be ruled out conclusively chthamalus were more abundant at depth than at the surface at all sites except at the front where this pattern was reversed the origin of frontal chthamalus is uncertain membranipora were more abundant on the onshore colder side of the fronts and abundances were usually higher at depth than at surface lack of accumulation in this species may be due to its limited swimming capability

the oceanography of the northern south china sea shelf sea nosocs and its adjacent waters overview and highlights abstract tropical shelf seas constitute a sub set of shelf seas that has not been studied extensively the no rthern so uth c hina sea s helf sea nosocs study is a continuation of the longstanding interest in taiwan on the oceanography of the east asian shelf seas and is an attempt to provide systematic and synoptic observations on a tropical shelf sea the two basic hypotheses in the study are 1 as in the ocean interior the behaviors of the shelf seas vary with latitude and 2 the behaviors of the nosocs are representative of those of the shelf seas in the tropical zone the nosocs has been sampled bi annually in alternating seasons since 2009 the results obtained primarily in 2009 to 2012 are presented here as in the tropical ocean interior a distinguishing characteristic of the nosocs is its shallow mixed layer with depths of about 40 m in the summer and 70 m in the winter as similar mixed layer depths are found in the adjoining northern south china sea scs and they are shallower than the shelf break depth of 120 m the upper nutricline water in the northern scs extends freely into the nosocs and forms a layer of water with significant concentrations of the nutrients immediately below its mixed layer any process that can induce vertical mixing on the shelf may make the nutrients in this subsurface water available for supporting biological activities in the mixed layer in the nosocs such processes include winter convective overturn over the entire nosocs as a result of surface cooling and the strong northeast monsoonal wind winter formation of bottom water in parts of the inner and middle shelf the action of internal waves at the outer shelf and the continental slope and upwelling maintained by wind and or topography the upwelling takes place in the summer off the coasts of dongshan shantou and the northeast coasts of the hainan island but year round at the taiwan bank upwelling over the shelf break is not required for bringing the nutrients in the sub surface waters in the open scs to the nosocs and it was not observed in addition to vertical mixing terrestrial inputs especially through the outflow of the pearl river which reaches its peak in the summer also contribute to the spatial and temporal variations in the composition of the nosocs the combined effects of all these processes lead to a unique seasonal pattern in the variations of the surface concentrations of chlorophyll a in the nosocs with two distinct yearly maxima in the winter and summer

internal bores and breaking internal tides on the oregon continental slope abstractobservations of breaking internal tides on the oregon continental slope during a 40 day deployment of 5 moorings along 43 12 n are presented remotely generated internal tides shoal onto the slope steepen break and form turbulent bores that propagate upslope independently of the internal tide a high resolution snapshot of a single bore is captured from lowered acoustic doppler current profilers ladcp ctd profiles in a 25 h time series at 1200 m the bore is cold salty over 100 m tall and has a turbulent head where instantaneous dissipation rates are enhanced e 10 6 w kg 1 and sediment is resuspended at the two deepest slope moorings 1452 and 1780 m similar borelike phenomena are observed in near bottom high resolution temperature time series mean dissipation rates and diapycnal diffusivities increase by a factor of 2 when bores are present w kg 1 and m s 1 and observed internal tides are energetic enough to drive these enhanced dissipation rates globally the authors estimate

internal solitary wave reflection near dongsha atoll the south china sea internal solitary wave isw reflection is rarely observed in satellite images even in the south china sea scs where the strongest and most energetic isws in the world have been observed compared to the large number of satellite images showing shoaling isw in the scs fewer than ten satellite images have been reported showing isw reflection in this study we collect recent satellite images and implement a numerical model to analyze isw reflection near dongsha atoll in the scs satellite observations show that the reflection appears to be associated with the large amplitude isws generated by strong tidal currents in luzon strait numerical simulations show that isws break when reaching the sloping bottom part of isw energy is reflected by mode 1 waves and their trailing mode 2 waves the mode 1 waves have two types long inertial gravity waves and breaking isw induced short waves they propagate quickly but induce weak vertical velocity and surface imprints mode 2 waves induce strong vertical velocity showing visible signature in satellites horizontal distribution of the energy indicates that a maximum energy of about 2 of the incident energy is contained in a single reflected wave this could explain why the reflected waves are rarely observed because reflected waves must be sufficiently large to be detected in satellite images although individual wave s energy is small in total up to 20 of the incident wave is reflected by the groups of mode 1 and mode 2 waves this suggests that isw reflection has a significant impact on energy distribution over the continental slopes

novel monitoring of antarctic ice shelf basal melting using a fiber optic distributed temperature sensing mooring measuring basal melting of ice shelves is challenging and represents a critical component toward understanding ocean ice interactions and climate change in november 2011 moorings containing fiber optic cables for distributed temperature sensing dts were installed through the mcmurdo ice shelf antarctica 200 m and extending 600 m into the ice shelf cavity the high spatial resolution of dts allows for transient monitoring of the thermal gradient within the ice shelf the gradient near the ice ocean interface is extrapolated to the in situ freezing temperature in order to continuously track the ice ocean interface seasonal melt rates are calculated to be 1 0 mm d 1 and 8 6 mm d 1 and maximum melting corresponds to the arrival of seasonal warm surface water in the ice shelf cavity between january and april the development of continuous surface based techniques for measuring basal melting represents a significant advance in monitoring ice shelf stability and ice ocean interactions

three dimensional nonhydrostatic numerical simulation of nonlinear internal wave generation and propagation in the south china sea 1 we present the results of three dimensional nonhydrostatic simulations of internal tides and waves in the south china sea scs using the suntans model model results accurately predict the observed wave arrival times at two mooring locations in the scs internal wave amplitudes are underpredicted which causes underprediction of internal wave speeds due to a lack of amplitude dispersion we show that the well known a and b waves arise from the steepening of semidiurnal internal tides that are generated due to strong barotropic flow over ridges in the luzon strait a wave generation is stronger in the southern portion of the luzon strait because diurnal internal tidal beams augment the amplitude of the semidiurnal a waves b wave generation is stronger in the northern portion where the distance between the eastern and western ridges is approximately equal to one internal tidal wavelength and leads to semidiurnal internal tidal resonance the orientation of the ridges produces large a waves that propagate into the northern portion of the western scs basin and stronger b waves that propagate into the southern portion when traced back in time along linear characteristics a waves consistently line up close to peak ebb eastward barotropic currents while b waves consistently line up with peak flood westward barotropic currents this reinforces the notion that the lee wave mechanism and associated hydraulic or nonlinear effects are weak as demonstrated by a simple linear model relating the amplitude of the simulated waves to the excursion parameter at the ridges

solibore induced sediment resuspension in the faeroe shetland channel 1 high resolution measurements of temperature and current velocity over the seabed in the faeroe shetland channel fsc reveal an intense internal wave train referred to as a solibore propagating up the continental slope in addition to enhancing turbulent mixing a rotor formed at the leading edge of the solibore generates sediment fluxes o 102 greater than background levels the interaction of solibores which appear to evolve from baroclinic bores with the seabed and the resulting rotor provides a dominant mechanism for the upward transport of sediment over continental slopes that may counteract downward avalanching of material by gravity

two dimensional model for site effect studies of microtremors in the san fernando valley a new model is developed for the resonant response of ground motion in enclosed sedimentary basins in their study of deeply embanked sediment filled valleys bard and bouchon 1980 a b 1985 show that reflections and refractions at the valley s edges generate important conversion of incident sv waves to horizontally propagating p waves which establish lateral resonance patterns our model is related to these results through the use of two approximations reflecting edges and horizontal p waves this model allows us to calculate lateral resonances in a given sedimentary basin for any shape of its borders we apply this model to the actual shape of san fernando valley and account for the large differential amplifications reported by kagami et al 1986 in their two dimensional study of microtremors in this basin we obtain a map of amplifications in the surface of the san fernando valley that shows a remarkable coincidence with the microtremor experimental data

observations of polarity reversal in shoaling nonlinear internal waves observations off the new jersey coast document the shoaling of three groups of nonlinear internal waves of depression over 35 km across the shelf each wave group experienced changing background conditions along its shoreward transit despite different wave environments a clear pattern emerges nearly symmetric waves propagating into shallow water develop an asymmetric shape in the wave reference frame the leading edge accelerates causing the front face to broaden while the trailing face remains steep this trend continues until the front edge and face of the leading depression wave become unidentifiable and a near bottom elevation wave emerges formed from the trailing face of the initial depression wave and the leading face of the following wave the transition from depression to elevation waves is diagnosed by the integrated wave vorticity which changes sign as the wave s polarity changes sign this transition is predicted by the sign change of the coefficient of the nonlinear term in the kdv equation when evaluated using observed profiles of stratification and velocity

observation of 1 to 5 second microtremors and their application to earthquake engineering part iii a two dimensional study of site effects in the san fernando valley abstract a two dimensional study of the influence of deep sediment on seismic ground motions was conducted by recording and analyzing long period microtremors in the san fernando valley california the recordings were made at 50 regularly distributed sites in the valley three reference sites were employed at the baserock outcrop around the valley so as to observe the time dependent characteristics of the microtremors 1 amplitudes in a period range of several seconds correlate with the thicknesses of the sedimentary layers 2 a site amplification effect which was evaluated in terms of sediment to rock spectral ratios is qualitatively consistent with available geological and strong motion data 3 the practical field observation procedure designed for this study the two dimensional approach can be easily used in other surveys for estimating the spatial characteristics of earthquake ground motions in the period range of several seconds

energetics of barotropic and baroclinic tides in the monterey bay area abstracta detailed energy analysis of the barotropic and baroclinic m2 tides in the monterey bay area is performed the authors first derive a theoretical framework for analyzing internal tide energetics based on the complete form of the barotropic and baroclinic energy equations which include the full nonlinear and nonhydrostatic energy flux contributions as well as an improved evaluation of the available potential energy this approach is implemented in the stanford unstructured nonhydrostatic terrain following adaptive navier stokes simulator suntans results from three dimensional high resolution suntans simulations are analyzed to estimate the tidal energy partitioning among generation radiation and dissipation a 200 km 230 km domain including all typical topographic features in this region is used to represent the monterey bay area of the 152 mw energy lost from the barotropic tide approximately 133 mw 88 is converted into baroclinic energy through internal tide generation and 42 56

evolution of a shoaling internal solitary wavetrain 1 field observations of an internal solitary wavetrain impacting a shoaling bottom are presented measurements of the spatio temporal characteristics of the shoaling waves are given as well as estimations of the mixing they may have caused upon impact the observations are discussed in the context of numerical simulations laboratory experiments and hypotheses recently raised on the origin and evolution of internal solitary waves in coastal environments

strong motion seismology although this is the first review on this topic to appear in a quadrennial report the roots of strong motion seismology extend back to at least 1932 when far sighted engineers in the seismological field survey of the u s coast and geodetic survey installed rugged fieldworthy instruments designed to make on scale recordings of large earthquakes carder 1964 these instruments are called accelerographs for their output closely mimics ground acceleration hudson 1979 the original instruments and their offspring have provided a wealth of information about ground motions of direct use to engineers due in large part to the continued devotion of the seismological field survey now part of the branch of engineering seismology and geology at the u s geological survey the number of recordings has increased substantially particularly in the last two decades and multiple recordings of a few california earthquakes have provided the data necessary to begin to unravel the complexities of the ground motions and to predict these motions on an empirical basis although seismologists used accelerograph records in studies of earthquake energy and ground motion attenuation as long ago as 1942 gutenberg and richter 1942 1956 widespread seismological use of the records began with aki s 1968 analysis of the 1966 parkfield earthquake

variability of nonlinear internal waves in the south china sea affected by the kuroshio and mesoscale eddies long term observations of nonlinear internal waves in the south china sea reveal seasonal to interannual variability during two selected segments of inverted echo sounder observations tidal forcing in luzon strait is almost identical but the observed amplitudes of nonlinear internal waves in the south china sea are very different the effects of the kuroshio and mesoscale eddies reproduced by hybrid cooridnate ocean model hycom reanalysis simulation are then investigated the kuroshio can enhance the zonal tilt of the thermocline and induce intruding flow in luzon strait during the two selected segments different thermocline slopes did not significantly change the internal tide generation but the intruding flow may result in a 11 difference in the amplitude of generated m2 internal tides during the two selected segments mesoscale eddies appeared on the path of internal wave propagation a cold eddy in one case and a warm one in the other the eddies changed local stratification and induced additional background currents thus affecting the nonlinear evolution of internal tides in addition wave front steering due to the mesoscale eddies dramatically affected the observed amplitude changes of the nonlinear internal waves the edge rather than the center of the nonlinear internal wave front passed through the observational stations resulting in reduced amplitude in the observations

local diurnal wind driven variability and upwelling in a small coastal embayment the oceanic response to high frequency local diurnal wind forcing is examined in a small coastal embayment located along an understudied stretch of the central california coast we show that local diurnal wind forcing is the dominant control on nearshore temperature variability and circulation patterns a complex empirical orthogonal function ceof analysis of velocities in san luis obispo bay reveals that the first mode ceof amplitude time series which accounts for 47 9 of the variance is significantly coherent with the local wind signal at the diurnal frequency and aligns with periods of weak and strong wind forcing the diurnal evolution of the hydrographic structure and circulation in the bay is examined using both individual events and composite day averages during the late afternoon the local wind strengthens and results in a sheared flow with near surface warm waters directed out of the bay and a compensating flow of colder waters into the bay over the bottom portion of the water column this cold water intrusion into the bay causes isotherms to shoal toward the surface and delivers subthermocline waters to shallow reaches of the bay representing a mechanism for small scale upwelling when the local winds relax the warm water mass advects back into the bay in the form of a buoyant plume front local diurnal winds are expected to play an important role in nearshore dynamics and local upwelling in other small coastal embayments with important implications for various biological and ecological processes

connecting wind driven upwelling and offshore stratification to nearshore internal bores and oxygen variability this study utilizes field observations in southern monterey bay ca to examine how regional scale upwelling and changing offshore shelf conditions influence nearshore internal bores we show that the low frequency wind forcing e g upwelling relaxation time scales modifies the offshore stratification and thermocline depth this in turn alters the strength and structure of observed internal bores in the near shore an internal bore strength index is defined using the high pass filtered potential energy density anomaly in the nearshore during weak upwelling favorable conditions and wind relaxations the offshore thermocline deepens in this case both the amplitude of the offshore internal tide and the strength of the nearshore internal bores increase in contrast during strong upwelling conditions the offshore thermocline shoals toward the surface resulting in a decrease in the offshore internal tide amplitude as a result cold water accumulates in the nearshore nearshore pooling and the internal bore strength index decreases empirical orthogonal functions are utilized to support the claim that the bore events contribute to the majority of the variance in cross shelf exchange and transport in the nearshore observed individual bores can drive shock like drops in dissolved oxygen do with rapid onset times while extended upwelling peri ods with reduced bore activity produce longer duration low do events

the formation and fate of internal waves in the south china sea internal oceanic waves are subsurface gravity waves that can be enormous and travel thousands of kilometres before breaking but they are difficult to study here observations of such waves in the south china sea reveal their formation mechanism extreme turbulence relationship to the kuroshio current and energy budget internal waves are the underwater version of more familiar surface waves they can be enormous and travel thousands of kilometres before breaking the south china sea is known to be home to the largest internal waves in the world s oceans but their size generation mechanisms and role in the regional energy budget are unknown matthew alford and colleagues now present the results from the iwise observational campaign and reveal that internal waves more than 200 metres high break in the south china sea and create turbulence that is orders of magnitude larger than in the open ocean and that wave formation is influenced by the kuroshio current these results now allow for a complete energy budget of the south china sea and for a more accurate incorporation of internal waves into climate models internal gravity waves the subsurface analogue of the familiar surface gravity waves that break on beaches are ubiquitous in the ocean because of their strong vertical and horizontal currents and the turbulent mixing caused by their breaking they affect a panoply of ocean processes such as the supply of nutrients for photosynthesis1 sediment and pollutant transport2 and acoustic transmission3 they also pose hazards for man made structures in the ocean4 generated primarily by the wind and the tides internal waves can travel thousands of kilometres from their sources before breaking5 making it challenging to observe them and to include them in numerical climate models which are sensitive to their effects6 7 for over a decade studies8 9 10 11 have targeted the south china sea where the oceans most powerful known internal waves are generated in the luzon strait and steepen dramatically as they propagate west confusion has persisted regarding their mechanism of generation variability and energy budget however owing to the lack of in situ data from the luzon strait where extreme flow conditions make measurements difficult here we use new observations and numerical models to 1 show that the waves begin as sinusoidal disturbances rather than arising from sharp hydraulic phenomena 2 reveal the existence of 200 metre high breaking internal waves in the region of generation that give rise to turbulence levels 10 000 times that in the open ocean 3 determine that the kuroshio western boundary current noticeably refracts the internal wave field emanating from the luzon strait and 4 demonstrate a factor of two agreement between modelled and observed energy fluxes which allows us to produce an observationally supported energy budget of the region together these findings give a cradle to grave picture of internal waves on a basin scale which will support further improvements of their representation in numerical climate predictions

turbulent dissipation on the margins of the south china sea 1 measurements of turbulence along the continental slope shelfbreak and shelf of the northern south china sea are presented from a 10 day measurement program during april 2005 the shelfbreak region was characterized by a deep stratification that appears to be typical of the late winter monsoon this appears to shift the wave field at the shelfbreak from the soliton like depression anomalies observed in previous years to a more complex wave field supporting high frequency waves in both upper and lower depth intervals of the water column on average 30 of the depth integrated turbulent dissipation occurs within 10 m of the bottom where baroclinic energy is preferentially dissipated dissipation levels reaching 50 mw m2 are an order of magnitude larger than those attainable through frictional dissipation of the local barotropic tide and an order of magnitude larger than levels typical in the open ocean

sediment resuspension mechanisms associated with internal waves in coastal waters 1 large amplitude vertically trapped internal waves can induce sizable velocities and trigger hydrodynamic instabilities in the bottom boundary layer thereby contributing to the resuspension of sediments and the maintenance of sediment concentration in the water column we discuss numerical simulations of several different situations in which the boundary layer in the wave footprint undergoes hydrodynamic instability with a resultant increase in the incidence of spatiotemporal structures that could facilitate sediment resuspension for the case of internal solitary waves we provide bounds in parameter space separating regions in which internal waves can be expected to efficiently resuspend sediment from those in which the boundary layer in the wave footprint is both laminar and stable a notable finding is that the onset of instability is a strong function of the background current the lagrangian transport of passive particles due to the instability is explored and some quantitative measures of the efficiency of the particle transport process are provided we subsequently discuss the evolution of the power spectra of the bottom shear stress with time and find that while the general characteristics of the instability are robust lowering either the reynolds number or the strength of the background current leads to an increase in the typical length scales associated with the mature instability finally we discuss instabilities during the internal wave generation process and alternative instability mechanisms when the bottom is not flat

energy of nonlinear internal waves in the south china sea 1 four sets of adcp measurements were taken in the south china sea scs these results were combined with previous satellite observations and internal tide numerical model results analysis suggests that strong internal tides are generated in luzon strait propagate as a narrow tidal beam into the scs are amplified by the shoaling continental slope near tungsha island become nonlinear and evolve into high frequency nonlinear internal waves niw internal waves in the scs have geographically distinct characteristics 1 west of luzon strait the total internal wave energy eiw is 10 that predicted by garrett munk spectra egm levine 2002 there is no sign of niw 2 near tungsha island eiw 13 egm strong nonlinear and high harmonic tides are present repetitive trains of large amplitude niw appear primarily at a semidiurnal periodicity with their amplitudes modulated at a fortnightly tidal cycle the rms vertical velocity of niw shows a clear spring neap tidal cycle and is linearly proportional to the barotropic tidal height in luzon strait with a 1 85 day time lag consistent with the travel time of internal tides from luzon strait to tungsha island 3 at the northern scs shelfbreak eiw 4 egm single depression waves are found but no multiple waves packets are evident 4 on the continental shelf eiw 2 egm both depression and elevation niw exist

suspended particulate layers and internal waves over the southern monterey bay continental shelf an important control on shelf mud belts 1 physical and optical measurements taken over the mud belt on the southern continental shelf of monterey bay california documented the frequent occurrence of suspended particulate matter features the majority of which were detached from the seafloor centered 9 33 m above the bed in fall 2011 an automated profiling mooring and fixed instrumentation including a thermistor chain and upward looking acoustic doppler current profiler were deployed at 70 m depth for 5 weeks and from 12 to 16 october a long range autonomous underwater vehicle performed across shelf transects individual spm events were uncorrelated with local bed shear stress caused by surface waves and bottom currents nearly half of all observed spm layers occurred during 1 week of the study 9 16 october 2011 and were advected past the fixed profiling mooring by the onshore phase of semidiurnal internal tide bottom currents at the start of the 9 16 october period we observed intense near bed vertical velocities capable of lifting particulates into the middle of the water column this updraft event appears to have been associated with nonlinear adjustment of high amplitude internal tides over the mid and outer shelf these findings suggest that nonlinear internal tidal motions can erode material over the outer shelf and that once suspended this spm can then be transported shoreward to the middle and shallow sections of the mud belt this represents a fundamental broadening of our understanding of how shelf mud belts may be built up and sustained

internal wave reflection on shelf slopes with depth varying stratification abstractreflection of internal waves from sloping topography is simple to predict for uniform stratification and linear slope gradients however depth varying stratification presents the complication that regions of the slope may be subcritical and other regions supercritical here a numerical model is used to simulate a mode 1 m2 internal tide approaching a shelf slope with both uniform and depth varying stratifications the fractions of incident internal wave energy reflected back offshore and transmitted onto the shelf are diagnosed by calculating the energy flux at the base of slope with and without topography and at the shelf break for the stratifications topographies considered in this study the fraction of energy reflected for a given slope criticality is similar for both uniform and depth varying stratifications this suggests the fraction reflected is dependent only on maximum slope criticality and independent of the depth of the pycnocline the majority of the reflected energy flux is in

numerical investigation of solitary internal wave induced global instability in shallow water benthic boundary layers abstract the time dependent boundary layer induced by a weakly nonlinear solitary internal wave in shallow water is examined through direct numerical simulation waves of depression and elevation are both considered the mean density field corresponds to that typical of the coastal ocean and lakes where the lower fraction of the water column is subject to the stabilizing effect of a diffuse stratification sufficient resolution of the inviscid dynamics of the boundary layer is ensured through use of a legendre spectral multidomain discretization scheme in the vertical direction at higher reynolds numbers where the simulations become underresolved because of restrictions in available computational resources spectral accuracy and numerical stability at the scales of physical interest are preserved through use of a penalty scheme in the vertical and explicit spectral filtering thus a highly accurate description of the qualitative dynamics of the wave induced global instability is possible and finesca

physical and biological processes underlying the sudden surface appearance of a red tide in the nearshore the sudden appearance at the surface of an alongshore parallel band of red tide near huntington beach california is described in high spatial and temporal resolution using novel instrumentation including a global positioning system tracked jet ski the scale of the surface chlorophyll a chl a band was small 200 m crossshore and ephemeral 3 h compared with the subsurface extent of the red tide 2 km 7 d the red tide was dominated by the regionally common dinoflagellate lingulodinium polyedrum f stein and had developed as a subsurface chl a layer during the 7 d prior to the surface appearance a few hours before the surface appearance a subsurface patch of elevated chl a chl a 30 m gl 21 was observed in 13 m total depth in the trough of a shoreward propagating internal wave consistent with dinoflagellate vertical swimming interacting with the internal wave driven convergence internal wave breaking induced vertical mixing in 8 m water depth vertically spread the chl a patch to the surface creating the alongshore surface band 500 m from shore both the subsurface chl a patch and the surface chl a band were prevented from entering the surf zone by a density barrier of warm water adjacent to the beach these high resolution observations emphasize the role of nearshore physical dynamics in controlling the duration and intensity of red tide exposure to coastal habitats

prototypical solitons in the south china sea 1 surface signatures associated with non linear internal waves are often seen in satellite images of the western south china sea scs slope and shelf observation in the deep sea to the east are rare here we report on the evolution of an energetic packet as it propagated through the deep central basin of the scs toward the western slope and shelf the waves have amplitudes estimated at 170 m half widths of 3 km and phase speeds of 2 9 0 1 m s faster than the mode 1 linear phase speed of 2 6 m s the shape and observed phase speed were consistent with the korteweg devries kdv model over the 65 km path that they were tracked the intrinsic velocity shear of the waves is small compared to pre existing shears and the waves exhibit weak turbulence the kdv fit and a satellite derived estimate of horizontal wave extent imply a westward energy flux of 4 5 gw for each crest

a review of internal solitary wave dynamics in the northern south china sea abstract the current research into internal solitary waves isws and the related dynamic processes in the northern south china sea scs are reviewed in this paper this unique wave phenomenon did not draw much interest until about one decade ago and is now one of the hot topics in the field of wave dynamics three methods of investigation are summarized in the paper namely remote sensing images in situ measurements and numerical simulations previous works have primarily been based on one or two of these methods and have provided great insights into such wave phenomena the lifetime of an isw in the northern scs from its origin in the luzon strait ls through to its formation and evolution in the deep basin and its transformation near the shelf break up until its dissipation on the continental shelf is summarized with the illustration of different investigation approaches various factors that can affect the wave generation processes are summed up as well such factors as are barotropic tides in the ls kuroshio intrusion temporal and spatial variation of stratification and the modulation of the western ridge in the ls can significantly alter the wave fields and are extensively discussed

observations of nonlinear internal wave run up to the surfzone abstractthe cross shore evolution of nonlinear internal waves nliws from 8 m depth to shore was observed by a dense thermistor array and adcp isotherm oscillations spanned much of the water column at a variety of periods at times nliws propagated into the surfzone decreasing temperature by 1 c in 5 min when stratification was strong temperature variability was strong and coherent from 18 to 6 m depth at semidiurnal and harmonic periods when stratification weakened temperature variability decreased and was incoherent between 18 and 6 m depth at all frequencies at 8 m depth onshore coherently propagating nliw events had associated rapid temperature drops t up to 1 7 c front velocity between 1 4 and 7 4 cm s 1 and incidence angles between 5 and 23 front position t and two layer equivalent height ziw of four events were tracked upslope until propagation terminated front position was quadratic in time and normalized t and ziw both decreased collapsing as a linearly decaying funct

speed and evolution of nonlinear internal waves transiting the south china sea abstract in the south china sea scs 14 nonlinear internal waves are detected as they transit a synchronous array of 10 moorings spanning the waves generation site at luzon strait through the deep basin and onto the upper continental slope 560 km to the west their arrival time speed width energy amplitude and number of trailing waves are monitored waves occur twice daily in a particular pattern where larger narrower a waves alternate with wider smaller b waves waves begin as broad internal tides close to luzon strait s two ridges steepening to o 3 10 km wide in the deep basin and o 200 300 m on the upper slope nearly all waves eventually develop wave trains with larger steeper waves developing them earlier and in greater numbers the b waves in the deep basin begin at a mean speed of 5 greater than the linear mode 1 phase speed for semidiurnal internal waves computed using climatological and in situ stratification the a waves travel 5 10 faster than b waves until they reach

observation of 1 to 5 second microtremors and their application to earthquake engineering part ii evaluation of site effect upon seismic wave amplification due to extremely deep soil deposits abstract the usefulness of long period microtremor observation for earthquake engineering problems at extremely deep soil deposit site was examined in this study microtremor observations were made in the niigata plain japan and in los angeles california where depths to the basement rock are several kilometers these two locations were selected because strong motion records obtained during the niigata earthquake of 1964 and the san fernando earthquake of 1971 contain large long period amplitudes understanding why these predominate long period motions were recorded is important for the evaluation of seismic input motions for large scale structures long period microtremor observations were carried out in both areas in order to evaluate the characteristics of deep soil observations were performed simultaneously at a number of stations to distinguish the nature of deep soil deposit the result of fourier analysis showed that amplitude of microtremors in long period range increases systematically from the point of basement rock outcrop to deep deposit site with the increase corresponding to the depth to basement rock this relationship coincides with that observed in the strong motion earthquake records these analyses indicated that simultaneous observation of long period microtremors at a number of stations can provide insight to the characteristic of deep soil amplification and therefore permit estimation of seismic input motions for large scale structures

climate modulates internal wave activity in the northern south china sea 2015 the authors internal waves iws generated in the luzon strait propagate into the northern south china sea nscs enhancing biological productivity and affecting coral reefs by modulating nutrient concentrations and temperature here we use a state of the art ocean data assimilation system to reconstruct water column stratification in the luzon strait as a proxy for iw activity in the nscs and diagnose mechanisms for its variability interannual variability of stratification is driven by intrusions of the kuroshio current into the luzon strait and freshwater fluxes associated with the el nino southern oscillation warming in the upper 100m of the ocean caused a trend of increasing iw activity since 1900 consistent with global climate model experiments that show stratification in the luzon strait increases in response to radiative forcing iw activity is expected to increase in the nscs through the 21st century with implications for mitigating climate change impacts on coastal ecosystems

characterization of rockfalls from seismic signal insights from laboratory experiments the seismic signals generated by rockfalls can provide information on their dynamics and location however the lack of field observations makes it difficult to establish clear relationships between the characteristics of the signal and the source in this study scaling laws are derived from analytical impact models to relate the mass and the speed of an individual impactor to the radiated elastic energy and the frequency content of the emitted seismic signal it appears that the radiated elastic energy and frequencies decrease when the impact is viscoelastic or elasto plastic compared to the case of an elastic impact the scaling laws are validated with laboratory experiments of impacts of beads and gravels on smooth thin plates and rough thick blocks regardless of the involved materials the masses and speeds of the impactors are retrieved from seismic measurements within a factor of 3 a quantitative energy budget of the impacts is established on smooth thin plates the lost energy is either radiated in elastic waves or dissipated in viscoelasticity when the impactor is large or small with respect to the plate thickness respectively in contrast on rough thick blocks the elastic energy radiation represents less than 5 of the lost energy most of the energy is lost in plastic deformation or rotation modes of the bead owing to surface roughness finally we estimate the elastic energy radiated during field scale rockfalls experiments this energy is shown to be proportional to the boulder mass in agreement with the theoretical scaling laws

the generation and evolution of nonlinear internal waves in the deep basin of the south china sea abstracttime series observations of nonlinear internal waves in the deep basin of the south china sea are used to evaluate mechanisms for their generation and evolution internal tides are generated by tidal currents over ridges in luzon strait and steepen as they travel west subsequently generating high frequency nonlinear waves although nonlinear internal waves appear repeatedly on the western slopes of the south china sea their appearance in the deep basin is intermittent and more closely related to the amplitude of the semidiurnal than the predominant diurnal tidal current in luzon strait as the internal tide propagates westward it evolves under the influence of nonlinearity rotation and nonhydrostatic dispersion the interaction between nonlinearity and rotation transforms the internal tide into a parabolic or corner shape a fully nonlinear two layer internal wave model explains the observed characteristics of internal tide evolution in the deep basin for different representative forcing cond

residual circulation due to internal waves shoaling on a slope we describe the residual circulation induced in a two layer system when internal waves with a wave length equal to or longer than the slope length propagate over a sloping bottom and either reflect or break for the case of no wave breaking scaling is used to derive boussinesq type equations the solution of which leads to an expression for the residual circulation adjacent to the sloping bottom this residual circulation is maintained by a weak slope on the density interface for breaking waves laboratory experiments and numerical modeling were used to ascertain the details of the residual circulation arising from the formation of gravitational intrusions results from these three investigative tools were used to determine as a function of bottom slope and incident wave amplitude the internal wave reflection coefficient and the strength of the residual circulation pattern with and without wave breaking the ocean and most lakes are thermally stratified for at least part of the year in stratified fluids the density anomaly associated with the thermal stratification supports internal waves with a range of vertical modal structures antenucci et al 2000 antenucci and imberger 2001 antenucci and imberger 2003 the gravest or first vertical mode induces a large current over the lake or ocean bottom and when the bottom slopes the waves shoal causing them to break and lose energy to dissipation the associated currents and turbulence can often lead to sediment resuspension and mixing of the water column gloor et al 1994 pierson and weyhenmeyer 1994 steinman et al 1997 the gravitational motions in turn induced by the mixing may combine with secondary internal wave motions to drive a residual circulation that may transport resuspended and dissolved material to the central area of a lake hakanson 1982 ostrovsky et al 1996 inall 2009 also demonstrated mass transport due to intrusion caused by internal wave breaking in the fjord loch etive by using a fluorescent dye tracer such intrusions have been observed but their dynamics do not seem to have received any attention in this paper the processes leading to residual circulation are described when a continuous train of internal waves with an individual wavelength equal to or longer than the slope length supported by a two layer stratification impinges perpendicularly onto a sloping bottom two cases were investigated when the waves break and when they are reflected perfectly without breaking internal waves and their associated mass transport in lakes fjords and coastal oceans are reviewed in ostrovsky and stepanyants 1989 and huthnance 1989 whereas solitary internal waves are reviewed by brown and christie 1998 lamb 2002 and grue et al 2000 regarding mass transport lamb 2002 investigated shoaling of largeamplitude internal waves and demonstrated that trapped

generation and propagation of nonlinear internal waves in massachusetts bay 1 during the summer nonlinear internal waves nliws are commonly observed propagating in massachusetts bay the topography of the area is unique in the sense that the generation area over stellwagen bank is only 25 km away from the shoaling area and thus it represents an excellent natural laboratory to study the life cycle of nliws to assist in the interpretation of the data collected during the 1998 massachusetts bay internal wave experiment mbiwe98 a fully nonlinear and nonhydrostatic model covering the generation shoaling region was developed to investigate the response of the system to the range of background and driving conditions observed simplified models were also used to elucidate the role of nonlinearity and dispersion in shaping the nliw field this paper concentrates on the generation process and the subsequent evolution inthe basin themodel was foundtoreproducewell the range of propagation characteristics observed arrival time propagation speed amplitude and provided a coherent framework to interpret the observations comparison with a fully nonlinear hydrostatic model shows that during the generation and initial evolution of the waves as they move away from stellwagen bank dispersive effects play a negligible role thus the problem can be well understood considering the geometry of the characteristics along which the riemann invariants of the hydrostatic problem propagate dispersion plays a role only during the evolution of the undular bore in the middle of stellwagen basin the consequences for modeling nliws within hydrostatic models are briefly discussed at the end

the degeneration of internal waves in lakes with sloping topography in a laboratory study we quantified the temporal energy flux associated with the degeneration of basin scale internal waves in closed basins the system is two layer stratified and subjected to a single forcing event creating available potential energy at time zero a downscale energy transfer was observed from the wind forced basin scale motions to the turbulent motions where energy was lost due to high frequency internal wave breaking along sloping topography under moderate forcing conditions steepening of nonlinear basin scale wave components was found to produce a high frequency solitary wave packet that contained as much as 20 of the available potential energy introduced by the initial condition the characteristic lengthscale of a particular solitary wave was less than the characteristic slope length leading to wave breaking along the sloping boundary the ratio of the steepening timescale required for the evolution of the solitary waves to the travel time until the waves shoaled controlled their development and degeneration within the domain the energy loss along the slope the mixing efficiency and the breaker type were modeled using appropriate forms of an internal iribarren number defined as the ratio of the boundary slope to the wave slope amplitude wavelength this parameter allows generalization to the oceanographic context analysis of field data shows the portion of the internal wave spectrum for lakes between motions at the basin and buoyancy scales to be composed of progressive waves both weakly nonlinear waves sinusoidal profile with frequencies near 10 24 hz and strongly nonlinear waves hyperbolic secant squared profile with frequencies near 10 23 hz the results suggest that a periodically forced system may sustain a quasi steady flux of 20 of the potential energy introduced by the surface wind stress to the benthic boundary layer at the depth of the pycnocline

high resolution observations of subsurface fronts and alongshore bottom temperature variability over the inner shelf author posting american geophysical union 2019 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 53 3 2019 1639 1649 doi 10 1029 2018jc014454

three dimensional dense distributed temperature sensing for measuring layered thermohaline systems distributed temperature sensing has proven a useful technique for geoscientists to obtain spatially distributed temperature data when studies require high resolution temperature data in three spatial dimensions current practices to enhance the spatial resolution do not suffice for example double diffusive phenomena induce sharp and small scale temperature patterns in water bodies subject to thermohaline gradients this article presents a novel approach for a 3 d dense distributed temperature sensing setup the design of which can be customized to the required spatial resolution in each dimension temperature is measured along fiber optic cables that can be arranged as needed in this case we built a dense cage of very thin 1 6 mm cables to ensure that interference with flow patterns was minimal application in water bodies with double diffusion induced sharp temperature gradients shows that the setup is well able to capture small scale temperature patterns and even detects small unsuspected seeps and potential salt fingers however the potential effect of the setup on the flow patterns requires further study

source and propagation of internal solitary waves in the northeastern south china sea 1 large amplitude internal solitary waves isws observed near dongsha island in the south china sea originate in tide topography interactions at luzon strait their arrival times at two moorings s7 at 117 17 e 21 37 n and y at 117 13 2 e 21 2 8 n are investigated with respect to model predicted barotropic tidal currents over lan yu ridge at luzon strait each isw packet can be associated with a westward tidal current peak the time lags between the isws and the barotropic tidal currents are 57 6 0 9 hours at s7 and 55 1 1 0 hours at y consistent with the mode one internal waves propagating nondispersively through the region s bathymetry and climatological stratification larger isws usually arrive earlier than smaller ones consistent with the theoretical relation between nonlinear wave speed and wave amplitude the observation that the isws are associated with westward tidal currents with without the presence of earlier eastward tidal currents suggests that they are generated by nonlinear steepening of internal tides rather than by the lee wave mechanism an idealized nonlinearization distance over which the isws are generated in internal tide troughs is estimated to be 260 40 km from luzon strait

observations of shoaling nonlinear internal bores across the central california inner shelf abstractwe present observations of shoaling nonlinear internal bores off the coast of central california the dataset includes 15 moorings deployed during september october 2017 and cross shore shi