poincare wave induced mixing in a large lake a 10 000 km2 hypoxic dead zone forms during most years in the central basin of lake erie to investigate the processes driving the hypoxia we conducted a 2 yr field campaign where the mixing in the lake interior during the stratification period was examined using current meters and temperature loggers data as well as 600 temperature microstructure profiles from which turbulent mixing was computed near inertial poincare waves drive shear instability generating 1 m amplitude and 10 m wavelength high frequency internal waves with 1 mdensity overturns that lead to an increase in turbulent dissipation by one order of magnitude the instabilities are associated with enhanced vertical shear at the crests and troughs of the poincare waves and may be correlated with the local gradient richardson number poincare wave induced mixing should be an important factor when the burger number 0 25 the strong diapycnal mixing induced by the poincare wave activity will also significantly modify the energy flux paths for example we estimate that in lake erie 0 85 of the wind energy is transferred to the lake interior below the surface layer of this 40 is dissipated in the interior metalimnion and 60 is dissipated at the bottom boundary in smaller lakes 0 42 of wind energy is transferred to the deeper water with 90 dissipated in the boundary and 10 in the interior metalimnion 2012 by the association for the sciences of limnology and oceanography inc

damping mechanisms of internal waves in continuously stratified rotating basins damping mechanisms damping rates and the dissipative modal structure of internal waves in stratified rotating circular basins are investigated analytically the damping is shown to be due to a combination of the internal wave cancelling where waves emitted by the oscillatory boundary layers destructively interact with the parent wave and drain energy from it and spin down modified by the periodicity where the energy is drained by the sinks and sources at the bottom corner caused by a discontinuity in the ekman transport it is shown that super inertial poincare waves and sub inertial kelvin waves are damped predominantly by the internal wave cancelling and modified spin down respectively these processes also modify the internal wave structure for super inertial waves the boundary layer generated waves intensify the interior flow in the lower part of the water column and delay the phase relative to the isopycnal displacements but for sub inertial waves the ekman pumping and the corner sinks and sources add a horizontal circular flow that slants the crest and trough backwards near the wall

observations of large amplitude mode 2 nonlinear internal waves on the australian north west shelf abstractlarge amplitude mode 2 nonlinear internal waves were observed in 250 m deep water on the australian north west shelf wave amplitudes were derived from temperature measurements using three

internal waves and the generation of turbulence in the thermocline of a large lake high resolution thermistor chain data collected between 5 and 20 m in a large stratified freshwater lake lake constance at a water depth of 60 m reveal the frequent occurrence of large amplitude 2 i m vertical density inversions that indicate overturns in the pelagic thermoc1ine velocity data collected simultaneously with the temperature measurements indicate that the density inversions are mainly produced by shear instabilities a comparison between the timing of the passage of the basin scale internal kelvin wave and the density inversions demonstrates a pronounced phase relationship implying that the processes leading to the occurrence of turbulence and mixing are connected to the passage of the kelvin wave two different processes are identified during which density inversions were particularly common an increased number of density inversions and especially high dissipation rates of turbulent kinetic energy were observed when kelvin wave induced critical shear supported the generation of large kelvin helmholtz billows a particularly large number of density inversions was also associated with the passage of nonlinear high frequency waves of large amplitudes the density inversions typically occurred at the wave troughs which indicates breaking of these waves these observations indicate that self induced shear generated by the basin scale seiche and by high frequency internal waves leads to a significant amount of turbulence and mixing in the pelagic thermoc1ine

supercycle at the ecuadorian subduction zone revealed after the 2016 pedernales earthquake large earthquakes are usually assumed to release all of the strain accumulated since the previous event implying a reduced seismic hazard after them however long records of seismic history at several subduction zones suggest supercycle behaviour where centuries long accumulated strain is released through clustered large earthquakes resulting in an extended period of enhanced seismic hazard here we combine historical seismology results present day geodesy data and dense local observations of the recent mw 7 8 2016 pedernales earthquake to reconstruct the strain budget at the ecuador subduction zone since the great 1906 earthquake we show that the pedernales earthquake involved the successive rupture of two patches on the plate interface that were locked prior to the earthquake and most probably overlaps the area already ruptured in 1942 by a similar earthquake however we find that coseismic slip in 2016 exceeds the deficit accumulated since 1942 the seismic moment of every large earthquake during the twentieth century further exceeds the moment deficit accumulated since 1906 these results together with the seismic quiescence before 1906 highlighted by historical records and marine palaeoseismology argue for an earthquake supercycle at the ecuador colombia margin this behaviour which has led to an enhanced seismic hazard for 110 years is possibly still going on and may apply to other subduction zones that recently experienced a great earthquake large earthquakes are often assumed to reset the seismic hazard of a region analysis of recent and historical seismicity in ecuador suggests that this region may experience clusters of large earthquakes and extended periods of high seismic hazard

three dimensional simulation of high frequency nonlinear internal wave dynamics in cayuga lake three dimensional 3d hydrostatic and nonhydrostatic versions of the mitgcm were applied to simulate the dynamics of the internal wave field basin scale seiches nonlinear surges and high frequency nonlinear internal waves nliws in cayuga lake ny the simulations were performed using up to 226 million computational cells with several horizontal grid resolutions varying from 450 450 m to 22 22 m vertical grid spacing was not varied and ranged from 0 5 m to 2 95 m the 22 22 m nonhydrostatic grid reproduced qualitatively the formation propagation and shoaling of observed nliws using 10 grid points along the wavelength and a grid lepticity of o 1 this ensured respectively that the waves were not aliased and physical dispersion predominated over numerical dispersion using a sensitivity analysis we generalize that correctly simulating nliws in real domains using second order discretization requires grid resolutions that are an order of magnitude smaller than the wavelength and amplitude with 2 consistent with published work on idealized domains local gyre like circulation was simulated near mid basin headlands and transverse shoaling of nliw packets on lateral boundaries was associated with topographic reflection and refraction in agreement with published field observations from estuaries which show nliw propagation in long narrow quasi 2d systems e g finger lakes lochs fjords estuaries and straits is fundamentally 3d these results therefore help fill the gap in understanding and correctly modelling the multiscale 3d dynamics of nliws in complex natural systems this article is protected by copyright all rights reserved

experimental investigation of sediment resuspension beneath internal solitary waves of depression internal solitary waves isws of depression are common features of coastal environments and believed to resuspend sediments where they shoal in this study the sediment resupension process associated with isws propagating over a flat bed was investigated in the laboratory the first ever profile measurements of the three dimensional instantaneous velocity field beneath the isws revealed that resuspension occurs during burst like vertical velocity events which lift sediments into the water column in the adverse pressure gradient region beneath the trailing part of the wave resuspension was not observed when the wave induced viscous bed stress was maximal directly beneath the isw trough prediction of wave induced resuspension was therefore unsuccessful using a traditional viscous bed stress based shields diagram a parameterization for isw induced resuspension is proposed as a function of the maximum instantaneous vertical velocity in the bursts wmax here we have replaced the viscous bed stress with isw 2wmax2 where isw is the instantaneous resuspending bed stress and 2 is the near bed fluid density from these results it is possible for field oceanographers to predict the occurrence of isw induced resuspension from the bulk wave and stratifications characteristics in a two layer stratification further research is required to extend the parameterization to larger reynolds numbers at field scale

crustal seismic imaging from multifold ocean bottom seismometer data by frequency domain full waveform tomography application to the eastern nankai trough 1 in offshore surveys the deep crust is generally investigated by traveltime tomography applied to sparse ocean bottom seismometer data the inferred velocity models are of limited resolution precluding a quantitative analysis of deep tectonic discontinuities if dense arrays of ocean bottom seismometers can be deployed the resulting data sets become amenable to full waveform processing which should lead to a significant improvement in the resolution of structures such acquisition and processing were achieved on the eastern nankai subduction zone full waveform inversion is entirely implemented in the frequency domain enabling efficient finite difference wave modeling and allowing to limit the inversion to a few discrete frequencies of increasing value such a hierarchical procedure defines a multiresolution approach to seismic imaging the data set was recorded by 93 instruments deployed along a 105 km long profile thirteen frequencies ranging from 3 to 15 hz were inverted sequentially wavelengths imaged by the full waveform inversion typically range between 0 5 and 8 km full waveform tomography reveals an intense compression in the upper prism and underlying backstop as evidenced by several thrusts the frontal ones still active corresponding to negative velocity anomalies the subducting paleo zenisu ridge is also reconstructed above which stands the decollement velocities in the upper mantle beneath the ridge are rather low 7 5 km s 1 suggesting partially serpentinized mantle beneath the ridge this paper demonstrates the feasibility of full waveform tomography based on dense ocean bottom seismometer data sets and its ability to quantitatively image the entire crust with a significantly improved resolution compared to what is usually achieved through traveltime tomography

wind shear generated high frequency internal waves as precursors to mixing in a stratified lake field data were used to estimate the wavelength phase speed direction of propagation frequency and the vertical structure of high frequency internal waves observed on the crests of basin scale waves of lake kinneret during periods of strong wind shear stability analysis indicates that these waves were generated by shear in the surface mixing layer the characteristics of the high frequency internal waves changed within a wind event as the result of the evolution of the background flow conditions following the deepening of the surface layer and the propagation of the basin scale internal waves when the background conditions were appropriate the vertical structure of the unstable mode was such that the perturbations generated visible sinuous internal waves that in turn modified the density profile in the metalimnion in such a way that secondary shear instabilities were triggered the high frequency internal waves were observed over larger distances but poor coherence in temperature records from stations 200 m apart indicated that individual high frequency internal waves were dissipated locally these waves are thus a local mechanism allowing energy to be drawn from the energized surface layer and transported to the metalimnion where it sustains turbulence part of the energy extracted from the surface layer was also returned to the mean flow in the metalimnion high frequency internal waves are therefore also a source of momentum for the metalimnetic currents the vertical excursions of the waves also indicate that they could potentially play a role in phytoplankton growth by significantly altering the light regime at relatively high frequencies

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

turbulent mixing induced by nonlinear internal waves in mono lake california describing the spatial and temporal occurrence of turbulent mixing and the mechanisms of turbulence production are fundamental problems in physical limnology and oceanography here we present results from mono lake california that illustrate pronounced steepening of the pycnocline upon cessation of strong wind forcing and the enhanced turbulence resulting from this nonlinearity three events occurred with wind speed of 10 m s21 upwind the upper pycnocline upwelled but on relaxation of the wind it downwelled 6 10 m and compressed the similarity of wave amplitude during compression to mixed layer depth and lake numbers 4 were indicative of significant nonlinearity energy in the internal wave field increased by two orders of magnitude but 50 of the energy was lost within 24 h the largest energy losses occurred at low frequencies rather than via an energy flux from low to moderate and high frequencies eddy diffusivities computed over 6 d intervals using the heat budget method averaged 1026 m2 s21 in the energized pycnocline but were five to 10 times higher during the initial upwelling and downwelling periods microstructure casts taken 1 2 d after the first event revealed that the percentage of the pycnocline that was turbulent varied with bottom slope being 80 turbulent where bottom slopes were up to 10 6 0 where bottom slopes were 3 and less than 7 where bottom slopes were 0 1 the threshold for turbulent transport was exceeded only 10 of the time and only where bottom slopes were highest

strong vertical mixing of deep water of a stratified reservoir during the maule earthquake central chile mw 8 8 1 vertical profiles of water temperature in rapel reservoir central chile 34 2 23 s 71 35 23 w 110 m a s l recorded the hydrodynamic response of the stratified water column of the reservoir produced by the 8 8 magnitude maule earthquake epicentre located in 36 15 36 s 73 14 20 w showing an intense vertical mixing of deep water the vertical mixing was characterized by changes in the potential energy of the water column and the eddy diffusivity of the mixing and these values were used to estimate the mixing efficiency of the event it is hypothesized that the turbulent flow that mixed the water column was mainly induced by the oscillation of the bed although surface gravitational waves could also have contributed to the vertical mixing so far this is the first time that the hydrodynamic response of a reservoir during a mega earthquake is measured and described

boundary mixing in lakes 1 modeling the effect of shear induced convection 1 recent studies in lakes have shown evidence for a strong influence of shear induced stratification on mixing in turbulent bottom boundary layers bbls on sloping topography these observations suggest that the periodic near bottom shear resulting from internal wave motions may lead to alternating periods of gravitationally stable and unstable stratification in the bbl with relevant implications for turbulence and mixing in the entire basin the impact of these processes for basin scale mixing is investigated here in a three dimensional processes oriented modeling study using a well investigated system lake alpnach switzerland as an example consistent with available observations our results indicate that the bbl becomes gravitationally unstable in areas with upslope flow covering a substantial fraction of the total bottom area of the lake while near bottom convection associated with the unstable stratification in these areas results in strong turbulence its contribution to net mixing is negligible since the bbl is already well mixed conversely in areas with downslope flow the near bottom shear generates stable stratification leading to a suppression of turbulence but also to larger mixing rates due to an enhanced mixing efficiency overall bbl mixing is found to dominate basin scale mixing these mechanisms are likely to be important for a large class of stratified natural waters in which boundary layer mixing is energized by periodic internal waves or basin scale motions

boundary mixing in the thermocline of a large lake 1 high resolution measurements of near bottom temperature stratification and current velocity were performed on the sloping boundary of a large lake at the depth of the seasonal thermocline the measurements cover nearly the entire stratified period and reveal the periodic occurrence of strong temperature and current velocity fluctuations which can be attributed to shoaling high frequency internal waves with periods between 5 and 20 min two different techniques are applied to obtain a long term record of dissipation rates of turbulent kinetic energy from the current velocity measurements shoaling of high frequency internal waves is associated with a strong and rapid increase of turbulent dissipation rates of up to four orders of magnitude since the occurrence of high frequency internal waves on the slope is correlated with the passage of the dominant basin scale internal kelvin wave with a period of four days energy dissipation rates on the slope vary with the same period diapycnal diffusivities estimated by combining the dissipation estimates with simultaneously measured density stratification follow a similar dynamics and a comparison with a basin scale diffusivity estimate based on tracer measurements reveal the importance of boundary mixing which at this particular site is mainly driven by the interaction of high frequency internal waves with the sloping boundary

toward a robust workflow for deep crustal imaging by fwi of obs data the eastern nankai trough revisited crustal scale imaging by the full waveform inversion fwi of long offset seismic data is inherently difficult because the large number of wavelengths propagating through the crust makes the inversion prone to cycle skipping therefore efficient crustal scale fwi requires an accurate starting model and a stable workflow minimizing the nonlinearity of the inversion here we attempt to reprocess a challenging 2d ocean bottom seismometer obs dataset from the eastern nankai trough the starting model is built by first arrival traveltime tomography fat which is fwi assisted for tracking cycle skipping we iteratively refine the picked traveltimes and then reiterate the fat until the traveltime residuals remain below the cycle skipping limit subsequently we apply laplace fourier fwi in which progressive relaxation of time damping is nested within frequency continuation to hierarchically inject more data into the inversion these two multiscale levels are complemented by a layer stripping approach implemented through offset continuation the reliability of the fwi velocity model is assessed by means of source wavelet estimation synthetic seismogram modeling ray tracing modeling dynamic warping and checkerboard tests although the visco acoustic approximation is used for wave modeling the synthetic seismograms reproduce most of the complexity of the data with a high traveltime accuracy the revised fwi scheme produces a high resolution velocity model of the entire crust that can be jointly interpreted with migrated images derived from multichannel seismic data this study opens a new perspective on the design of obs crustal scale experiments amenable to fwi however a further assessment of the optimal obs spacing is required for reliable fwi

the generation and trapping of solitary waves over topography observations of tidal flow over a sill show that upstream solitary wave generation occurred in conjunction with the downstream movement of a streamline bifurcation over the obstacle crest solitary waves appeared upstream of the bifurcation riding on the surface stratification shear flow instabilities on the plunging interface were also evident and may contribute to wave generation through subharmonic interaction nonlinear waves generated downstream of an internal control became trapped in the supercritical flow

fluid circulation and seepage in lake sediment due to propagating and trapped internal waves 1 it has long been known that surface gravity waves induce significant seepage through the porous layer found at the lake bottom away from coastal regions however the pressure signature of surface waves at the lake bottom is weak we consider fully nonlinear internal gravity waves whose long wavelength and slow motion implies a sustained and strong pressure perturbation even in the deep regions of the lake we argue that internal waves can induce significant seepage through the sediment layer in regions where surface gravity waves have negligible impact the pressure profile at the fluid porous layer interface is computed from the exact dubreil jacotin long theory giving a reliable profile even for large waves this profile is used in conjunction with darcy s law to compute the seepage within the porous region we find that the geometric distribution of seepage is strongly controlled by both the ratio of porous media thickness to the horizontal length of the pressure perturbation and the bottom topography when it is present based on work on the interaction of internal solitary waves with the bottom boundary layer we develop a model to account for the changes in permeability due to wave induced instabilities in the bottom boundary layer and enhanced benthic turbulence this turbulence acts to unplug the pores near the surface by lifting the detritus that clogs them the resulting changes in permeability significantly enhance exchange between the free fluid and the porous medium on the downstream side of the wave

high frequency internal waves in lake geneva trains of high frequency internal waves have been observed in the thermocline of lake geneva within a few hours after the passing of disturbances which cause a rapid increase or jump in the depth of the thermocline three possible mechanisms for the source of the internal waves are proposed and compared with available data i that the waves are a soliton packet following the jump ii that the waves are generated as the jump passes over or around a local region of rough topography and iii that the jump produces a moving disturbance near the shoreline with internal waves forming a wake behind it the investigation of the last possibility involves the solution of the problem of the form of an internal wave wake in the presence of mean currents which vary in depth both in their strength and direction the wave pattern of the wake in the observed current distribution and stratification of the lake is described and compared with that in the absence of shear an expression for the energy of internal waves propagating in a shear flow is also derived and it is found that the rate of energy loss from the jump to the waves is small the minimum richardson number resulting from the co existence of the mean shear and the internal waves is marginally greater than 1 4 suggesting that the waves may be limited by shear flow instability however none of the mechanisms for their generation and propagation is fully compatible with the available data

near inertial waves in lake erie near inertial poincare waves with a period t p similar to 17 h are the dominant wind induced internal wave motions in central lake erie and consequently have a substantial influence on lake circulation mixing and biogeochemistry however due to the complex three basin bathymetry in lake erie the vertical and horizontal modal structure of these waves remain poorly understood in this study we analyze field data to show wind events energize frequent vertical mode one poincare waves the horizontal modal structure was also investigated in a sensitivity analysis using a calibrated three dimensional hydrodynamic transport model forced with observed and idealized spatially uniform wind events strong horizontal mode one poincare wave cells form in both the central and eastern basins when wind events have a duration of 0 25 t p to 0 5 t p are impulsive and periodic at t p or have anticyclonic rotation with a duration of t p momentum transfer from longer wind events 0 5 tp will oppose the coriolis force rotated currents and damp poincare wave generation in agreement with theory the most efficient wind events are observed and computationally modeled to have a duration of 0 25 t p causing an excitation peak at similar to 0 4 t p and converting similar to 0 8 of the wind energy input to poincare waves the efficiency of wind work in generating poincare wave kinetic energy is given by 1 cos 2 pi f t t 1 where f is the inertial frequency and t is the wind duration therefore the efficiency peaks during each nt p period where n is a non negative integer and decreases significantly for longer wind events

dynamics of mixed bottom boundary layers and its implications for diapycnal transport in a stratified natural water basin here we report on two field experiments from lake alpnach surface area 4 8 km 2 maximum depth 34 m that were designed to study the process of boundary mixing and to estimate its efficiency the ratio between the turbulent kinetic energy converted into potential energy and dissipated into heat for diapycnal tracer transport lake alpnach is particularly suited for this purpose because it is known from earlier experiments that 1 its currents follow a regular oscillatory pattern associated with basin wide standing internal waves seiches period similar to 0 5 days and 1 day respectively and 2 diapycnal tracer transport is mainly caused by boundary mixing during one of the experiments reported here strong seiches were excited regularly and damped on a timescale of the order of 3 days during the other experiment seiching motion was comparably weak if seiching is excited regularly we find a persistent well mixed bottom layer of 4 5 m height at the deepest part of the lake in the absence of regular seiching the layer disappears within 10 20 days on the sloping bottom boundaries the well mixed layers 1 are of much more transient nature 2 exhibit different thermal structure and 3 decrease in thickness toward shallower depth inversely proportionally to the stability at the same depth in the lake interior their reduced thickness is possibly the result of repeatedly occurring intrusions of boundary mixed water masses that are observed to extend horizontally similar to 100 200 m into the lake interior as a consequence of repeated generation of intrusions mixing on the sloping boundaries is expected to be considerably more efficient compared to mixing over flat bottom boundaries the observed mixing efficiency the ratio of the rate of change of potential energy below depth z caused by turbulence to the energy loss by bottom friction below depth z increases indeed from 0 01 0 01 in the deepest well mixed layers to 0 15 0 04 in the upper pycnocline

observations of second baroclinic mode internal solitary waves on the continental slope of the northern south china sea 1 a temperature and current velocity mooring located on the upper continental slope of the northern south china sea recorded a number of second baroclinic mode mode 2 internal solitary waves isws these types of waves are seldom observed in nature the mode 2 isws typically showed upward downward displacement of isotherms in the upper lower water column and three layers of eastward westward and eastward current from the uppermost to bottommost portions of a wave in summer westward propagating mode 2 isws were observed only occasionally these waves generally appeared after mode 1 isws a feature that may relate to the diurnal tide with a period of approximately 24 hours the displacement of isotherms induced by mode 2 isws was 20 14 m at 75 m and 22 15 m at 240 m and the characteristic time scale was approximately 8 0 4 3 min in winter mode 2 isws were more active but mode 1 isws were rarely observed isotherm displacement by mode 2 isws in winter was 30 18 m at 75 m and 26 16 m at 240 m and the average characteristic time scale was 6 9 4 6 min the mode 2 isws thus had larger amplitudes and smaller time scales in winter than they did in summer the observed vertical temperature profile also showed notable seasonal change the thermocline was shallow in summer and deep in winter in winter vertical temperature profiles indicated that the main thermocline was located near middepth over the upper continental slope near the 350 m isobath mode 1 isws were more active in summer than in winter reflecting the larger ursell numbers for mode 1 isws in summer among mode 2 isws in summer 90 appeared after mode 1 isws these results suggest that mode 2 isws could be related to mode 1 isws in contrast mode 2 isws were more active in winter than in summer with larger mode 2 ursell numbers also found in winter among winter mode 2 isws 72 appeared without mode 1 isws mode 2 isws in winter could be related to the main thermocline being located near middepth these seasonal variations of mode 2 isws were correlated with the seasonal change of local stratification further study on the different generating mechanisms of mode 2 isws in summer and winter is needed

anatomy of a megathrust the 2010 m8 8 maule chile earthquake rupture zone imaged using seismic tomography abstract knowledge of seismic velocities in the seismogenic part of subduction zones can reveal how material properties may influence large ruptures observations of aftershocks that followed the 2010 m w 8 8 maule chile earthquake provide an exceptional dataset to examine the physical properties of a megathrust rupture zone we manually analysed aftershocks from onshore seismic stations and ocean bottom seismometers to derive a 3 d velocity model of the rupture zone using local earthquake tomography from the trench to the magmatic arc our velocity model illuminates the main features within the subduction zone we interpret an east dipping high p wave velocity anomaly 6 9 km s as the subducting oceanic crust and a low p wave velocity we assess the role played by physical heterogeneity in governing megathrust behaviour greatest slip during the maule earthquake occurred in areas of moderate p wave velocity 6 5 7 5 km s where the interface is structurally more uniform at shallow depths high fluid pressure likely influenced the up dip limit of seismic activity the high velocity bodies lie above portions of the plate interface where there was reduced coseismic slip and minimal postseismic activity the northern velocity anomaly may have acted as a structural discontinuity within the forearc influencing the pronounced crustal seismicity in the pichilemu region our work provides evidence for how the ancient geological structure of the forearc may influence the seismic behaviour of subduction megathrusts

the degeneration of large scale interfacial gravity waves in lakes mechanisms for the degeneration of large scale interfacial gravity waves are identified for lakes in which the effects of the earth s rotation can be neglected by assuming a simple two layer model and comparing the timescales over which each of these degeneration mechanisms act regimes are defined in which particular processes are expected to dominate the boundaries of these regimes are expressed in terms of two lengthscale ratios the ratio of the amplitude of the initial wave to the depth of the thermocline and the ratio of the depth of the thermocline to the overall depth of the lake comparison of the predictions of this timescale analysis with the results from both laboratory experiments and field observations confirms its applicability the results suggest that for small to medium sized lakes subject to a relatively uniform windstress an important mechanism for the degeneration of large scale internal waves is the generation of solitons by nonlinear steepening since solitons are likely to break at the sloping boundaries leading to localized turbulent mixing and enhanced dissipation the transfer of energy from an initial basin scale seiche to shorter solitons has important implications for the lake ecology

internal wave weather in a stratified lake thermistor chain data collected in lake biwa japan during a period of strong stratification were used to determine the nature of the water column response to wind forcing the evolution of the basin scale waves in the lake were reproduced in three dimensional numerical simulations and the time variability of the internal wave spectrum is discussed based on spectral analysis of the thermistor chain records severe winds associated with the passage of three typhoons during the sampling period excited basin scale kelvin and poincare waves which by interaction with the topography of the lake and non linear effects generate trains of high frequency internal waves time frequency analysis of the temperature signals suggests that the 2 slope of the internal wave spectrum is probably the result of the composition of groups of waves with high intermittence travelling through the wave guide the observed rapid decay of internal wave energy after severe wind events seemed to be due mostly to high dissipation at the sloping boundaries of the lake

boundary versus internal diapycnal mixing in stratified natural waters using the fluorescent dye uranin tracer release experiments to study the contribution of bottom boundary mixing to diapycnal transport in stratified natural waters were performed in lake alpnach central switzerland during 1992 1995 a first experiment involved injecting the tracer from a point source into the center of the hypolimnion that part of the lake below the surface mixed layer an in situ fluorometer was then employed to detect the horizontal and vertical spreading of the tracer cloud allowing rates of diapycnal diffusivity to be determined as long as the tracer was confined to the interior water region the diapycnal diffusivity was relatively small however after the tracer cloud had reached the lake boundary the diapycnal diffusivity increased by approximately one order of magnitude in a second experiment the tracer was released near the sediment water interface in this case the dynamics of vertical tracer spreading were opposite during the first few hours after tracer release diapycnal diffusivities were large subsequently decreasing as the tracer cloud drifted away from the lake boundary basin wide diapycnal diffusivities calculated from heat flux measurements based on temperature profiles obtained from thermistor chains or conductivity temperature depth casts agreed well with the values obtained from the vertical tracer diffusion after horizontal homogenization the results of the tracer experiments corroborate the hypothesis that diapycnal fluxes are determined predominantly by mixing in the bottom boundary region

evidence for enhanced mixing over rough topography in the abyssal ocean the overturning circulation of the ocean plays an important role in modulating the earth s climate but whereas the mechanisms for the vertical transport of water into the deep ocean deep water formation at high latitudes and horizontal transport in ocean currents have been largely identified it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise however measurements of the internal wave field the main source of energy for mixing and of turbulent dissipation rates have typically implied diffusivities across surfaces of equal density of only approximately 0 1 cm2 s 1 too small to account for the return flow here we report measurements of tracer dispersion and turbulent energy dissipation in the brazil basin that reveal diffusivities of 2 4 cm2 s 1 at a depth of 500 m above abyssal hills on the flank of the mid atlantic ridge and approximately 10 cm2 s 1 nearer the bottom this amount of mixing probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry may be large enough to close the buoyancy budget for the brazil basin and suggests a mechanism for closing the global overturning circulation

flow separation and resuspension beneath shoaling nonlinear internal waves 1 laboratory observations are presented showing the structure and dynamics of the turbulent bottom boundary layer beneath nonlinear internal waves nliws of depression shoaling upon sloping topography the adverse pressure gradient beneath the shoaling waves causes the rear face to steepen flow separation to occur and wave induced near bottom vortices to suspend bed material the resuspension is directly attributed to the near bed viscous stress and to near bed patches of elevated positive reynolds stress generated by the vortical structures these results are consistent with published field observations of resuspension events beneath shoaling nliws elevated near bed viscous stresses are found throughout the domain at locations that are not correlated to the resuspension events near bed viscous stress is thus required for incipient sediment motion but is not necessarily a precursor for resuspension resuspension is dependent on the vertical velocity field associated with positive reynolds stress and is also found to occur where the mean wave averaged vertical velocity is directed away from the bed the results are interpreted by analogy to the eddy stress and turbulent bursting resuspension models developed for turbulent channel flows

2010 maule earthquake slip correlates with pre seismic locking of andean subduction zone analysis of seismic data and global positioning system gps observations from the region around the site of the recent magnitude 8 8 maule earthquake in chile have been combined with modelling of the andean subduction zone to build up a detailed image of the event the earthquake occurred at a seismic gap part of the fault that has not experienced a major earthquake since 1835 and it seems to have released most of the stress accumulated since that time the observations suggest that coseismic slip heterogeneity at the scale of single asperities and therefore the seismic potential of future great earthquakes might be anticipated by geodetic observations these authors show evidence for a high coherence between the slip distribution inferred from the 2010 maule earthquake chile and the patchwork of interseismic locking distribution derived from global positioning system observations during the previous decade their work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future earthquakes which thus might be anticipated by geodetic observations the magnitude 8 8 maule chile earthquake of 27 february 2010 ruptured a segment of the andean subduction zone megathrust that has been suspected to be of high seismic potential1 2 3 4 5 6 it is the largest earthquake to rupture a mature seismic gap in a subduction zone that has been monitored with a dense space geodetic network before the event this provides an image of the pre seismically locked state of the plate interface of unprecedentedly high resolution allowing for an assessment of the spatial correlation of interseismic locking with coseismic slip pre seismic locking might be used to anticipate future ruptures in many seismic gaps6 7 8 9 10 11 12 given the fundamental assumption that locking and slip are similar this hypothesis however could not be tested without the occurrence of the first gap filling earthquake here we show evidence that the 2010 maule earthquake slip distribution correlates closely with the patchwork of interseismic locking distribution as derived by inversion of global positioning system gps observations during the previous decade the earthquake nucleated in a region of high locking gradient and released most of the stresses accumulated in the area since the last major event in 1835 two regions of high seismic slip asperities appeared to be nearly fully locked before the earthquake between these asperities the rupture bridged a zone that was creeping interseismically with consistently low coseismic slip the rupture stopped in areas that were highly locked before the earthquake but where pre stress had been significantly reduced by overlapping twentieth century earthquakes our work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future great earthquakes which thus might be anticipated by geodetic observations

high frequency internal waves in large stratified lakes observations are presented from lake biwa and lake kinneret showing the ubiquitous and often periodic nature of high frequency internal waves in large stratified lakes in both lakes high frequency wave events were observed within two distinct categories 1 vertical mode 1 solitary waves near a steepened kelvin wave front and vertical mode 2 solitary waves at the head of an intrusive thermocline jet were found to have wavelengths 64 670 m and 13 65 m respectively and were observed to excite a spectral energy peak near 10 23 hz 2 sinusoidal vertical mode 1 waves on the crests of kelvin waves vertically coherent in both phase and frequency and bordering the thermocline jets in the high shear region trailing the vertical mode 2 solitary waves vertically incoherent in both phase and frequency were found to have wavelengths between 28 37 and 9 35 m respectively and excited a spectral energy peak just below the local maximum buoyancy frequency near 10 22 hz the waves in wave event categories 1 and 2 were reasonably described by nonlinear wave and linear stability models respectively analysis of the energetics of these waves suggests that the waves associated with shear instability will dissipate their energy rapidly within the lake interior and are thus responsible for patchy turbulent events that have been observed within the metalimnion conversely the finite amplitude solitary waves which each contain as much as 1 of the basinscale kelvin wave energy will propagate to the lake perimeter where they can shoal thus contributing to the maintenance of the benthic boundary layer

the andean ophiolitic megastructures on the buga buenaventura transverse western cordillera valle colombia abstract a structural study of the buga buenaventura transverse in the central part of the western cordillera of colombia has shown the presence of three structural units which from bottom to top and from west to east are the rio dagua unit the rio calima unit and the loboguerrero window unit all three units comprise strata between 120 and 80 m y old overlying a basement of green rocks showing the characteristics of submarine flows the bolivar ultrabasic and basic massif is geographically linked to the rio calima unit in which green rocks predominate and is separated from it by a tectonic contact the upper part of the massif on the other hand shows high temperature metamorphic rocks formed during its emplacement the rio dagua unit shows two tectonic phases with isoclinal folding and development of schistosity the first phase is contemporaneous with low grade metamorphism equivalent to lower greenschist facies conditions the loboguerrero window unit shows a large recumbent fold oriented towards the southeast deformation in the rio calima unit is weaker and appears to correspond to a higher structural level than in the two other units as the attitudes of the s1 schistosity in the rio dagua unit and of the shear zones located at the green rocks sediments contact in this same unit are similar to that of the overthrust at the base of the rio calima unit we are led to postulate that the overthrust belongs to the first phase of deformation as also does the recumbent fold in the loboguerrero window unit we are thus led to propose a southeastward direction of emplacement for the nappes in the western cordillera of colombia in conclusion the authors extend their observations and propose a new structural interpretation of the occidente colombiano

modeling circulation in lakes spatial and temporal variations the influence of spatial and temporal variations in wind forcing on the circulation in lakes is investigated using field data and the three dimensional estuary and lake computer model elcom applied to lake kinneret lake kinneret field data from six thermistor chains and eight wind anemometers deployed during july 2001 are presented internal wave motions are well reproduced by the numerical model when forced with a spatially uniform wind taken from a station near the lake center however simulated seiche amplitudes are too large especially vertical mode 2 and lead observations by 3 10 h for a 24 h period wave at different locations around the lake consideration of the spatial variation of the wind field improves simulated wave amplitude and phase error at all stations is reduced to less than 1 5 h this improvement is attributable to a better representation of the horizontally averaged wind stress and can be reproduced with a spatially uniform wind that has the same horizontally averaged wind stress as the spatially varying wind field however a spatially varying wind field is essential for simulating mean surface circulation which is shown to be predominantly directly forced by the surface layer averaged wind stress moment

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

seismicity patterns along the ecuadorian subduction zone new constraints from earthquake location in a 3 d a priori velocity model to improve earthquake location we create a 3 d a priori p wave velocity model 3 dvm that approximates the large velocity variations of the ecuadorian subduction system the 3 dvm is constructed from the integration of geophysical and geological data that depend on the structural geometry and velocity properties of the crust and the upper mantle in addition specific station selection is carried out to compensate for the high station density on the andean chain 3 d synthetic experiments are then designed to evaluate the network capacity to recover the event position using only p arrivals and the maxi technique three synthetic earthquake location experiments are proposed 1 noise free and 2 noisy arrivals used in the 3 dvm and 3 noise free arrivals used in a 1 dvm synthetic results indicate that under the best conditions exact arrival data set and 3 dvm the spatiotemporal configuration of the ecuadorian network can accurately locate 70 per cent of events in the frontal part of the subduction zone average azimuthal gap is 289 44 noisy p arrivals up to 0 3 s can accurately located 50 per cent of earthquakes processing earthquake location within a 1 dvm almost never allows accurate hypocentre position for offshore earthquakes 15 per cent which highlights the role of using a 3 dvm in subduction zone for the application to real data the seismicity distribution from the 3 d maxi catalogue is also compared to the determinations obtained in a 1 d layered vm in addition to good quality location uncertainties the clustering and the depth distribution confirm the 3 d maxi catalogue reliability the pattern of the seismicity distribution a 13 yr record during the inter seismic period of the seismic cycle is compared to the pattern of rupture zone and asperity of the mw 7 9 1942 and the mw 7 7 1958 events the mw 8 8 1906 asperity patch is not defined we observe that the nucleation of 1942 1958 and 1906 events coincides with areas of positive simple bouguer anomalies and areas where marine terraces are still preserved on the coastal morphology from north to south 1 the 1958 rupture zone is almost aseismic and is attributed to a zone of high coupling 2 south of the galera alignment perpendicular to the trench the 1942 rupture zone presents moderate seismicity deeper on the seismogenic interplate zone and abutting on the jama cluster to the south this cluster is facing the cabo pasado cap and positive bouguer anomalies on the overriding margin we suspect that this cluster reflects a zone of local asperity partial coupling south of the jama cluster the spherical aseismic zone in the bahia area is interpreted as having a low seismic coupling steady creep motion or slow slip events we suspect that the site that generated the three m 7 events 1896 1956 and 1998 correspond to a small patch of strong coupling to the south in the manta puerto lopez zone the seismicity is mainly organized in earthquake swarms 1998 2002 2005 although slow slip events have been observed in the area vallee et al submitted we infer from the coastline shape the marine terraces and the high positive bouguer anomalies that the seismicity here might reveal a significant amount of seismic coupling

breaking of internal kelvin waves shoaling on a slope in stratified flow breaking of internal waves over slopes induces resuspension of bottom sediments and transport of mass when internal waves shoal and break flow dynamics and mass transport diff

energetics and damping of basin scale internal waves in a strongly stratified lake energetics and damping of basin scale internal waves and subsequent near bottom transport processes in lake kinneret were investigated using the modal analysis in a layer stratified irregular basin the theory was extended to include small linear damping and energy budgets and damping rates of five dominant internal waves were extracted by fitting numerically calculated internal waves to isotherm displacements measured by six thermistor chains distributed throughout the lake energy contained in the dominant internal waves 3 gj resulted from a balance between energy input from diurnal winds and dissipation within a day both of which were estimated to be 3 4g j d 21 damping was caused primarily by bottom friction and the damping rates e folding time varied from 1 to 3 d depending on the velocity structure currents induced by the internal waves caused considerable spatial variability of the bottom shear stress and near bottom transport processes such as entrainment rate at the top of the benthic boundary layer and mass transfer at the sediment water interface

physical controls on the spatial evolution of a dinoflagellate bloom in a large lake a set of satellite images of chlorophyll a concentration for lake kinneret israel from the period february to april 2007 captured the temporal evolution of horizontal patchiness that developed during the typical spring bloom of the dinoflagellate peridinium gatunense narrow bands of high concentration located adjacent to the shoreline at the start of the bloom were followed by progressive propagation of this high concentration region from the shoreline toward the center of the lake as the bloom proceeded a three dimensional 3 d hydrodynamic numerical model and an analytical model for a flat bottomed elliptical basin together explain the observed phenomenon the spatial structure of kelvin waves which were demonstrated to most likely be present in february and april due to resonance produced regions of high velocity gradient contributing to horizontal dispersion close to the shoreline this region of high dispersion was narrow and close to the shoreline at the start of the bloom when the burger number was relatively small but it widened over the course of the season as the burger number increased due to increasing stratification in addition an increase in the dispersion rate with time in the lake interior was inferred from numerical simulation due to increasing wind speeds and a thinner surface layer physical processes in this case horizontal dispersion as a result of both kelvin waves and wind can play an important role in governing the dynamics and spatial evolution of dinoflagellate blooms in lakes spatial heterogeneity of phytoplankton is a ubiquitous occurrence in lakes coastal waters and the open ocean phytoplankton patchiness can be defined by localized abruptly elevated concentrations phytoplankton patches may occur at a broad range of spatial scales and such

downscaling model resolution to illuminate the internal wave field in a small stratified lake this paper presents the application of hydrostatic and nonhydrostatic three dimensional hydrodynamic models to a stratified lake focus was given to the multiscale response of the internal wave field to strong wind gusts exceeding 20 m s 1 simulations were performed using different horizontal grid resolutions with uniform grid sizes varying from 100 100 to 10 10 m results of the hydrostatic models were used to investigate the large scale features of the internal wave motion with the intent of investigating the high frequency waves observed results of these simulations were used as initial conditions for nonhydrostatic simulations using smaller grids wavelength of the high frequency waves decreased with grid resolution however none of the uniform grids were sufficiently fine to capture the waves of the highest frequency simulations performed using a nonuniform grid produced internal waves of similar frequency of the waves observed in the field the simulations showed that these waves were shear u

near bed solibores over the continental slope in the faeroe shetland channel abstract on two occasions within a 12 day measurement period in the faeroe shetland channel strongly nonlinear wave trains were observed at the sea bed propagating up the continental slope in water depths 450 m the events were separated by a period of 4 days and whilst resembling in appearance a density current running up a slope are termed solibores displaying the properties of both turbulent internal bores and nonlinear internal solitary waves isw each solibore displays a steep leading edge followed by a train of nonlinear waves with amplitudes of o 10 m and periods of 5 20 min wave induced particle velocities are consistent with isw whilst a zone of strong horizontal convergence at the leading edge of the solibores causes the formation of a rotor with flow in the opposite sense to a forward overturning surface wave in both cases upward vertical velocities 10 cm s 1 are immediately followed by a return downward flow of equal magnitude a ctd and microstructure transect conducted during the passage of the first solibore illustrates its behaviour as an up slope intrusion of cold dense water with concurrent rates of turbulent dissipation e of o 10 7 w kg 1 and resulting in short term maximum vertical diffusivities kz of o 10 1 m2 s 1 in the long term however kz 140 days which again indicate intermittency in periods of enhanced sediment flux the solibores are consistent with the results of numerical and laboratory experiments on hydraulic jumps resulting from shoaling isw the influence of the slope is proposed to be the reason for their slightly different forms and effects on sediment transport thus the first solibore propagating directly up the slope is proposed to result from an overturning hydraulic jump caused by kinematic instabilities and which subsequently forms a horizontal density intrusion the second solibore represents a dispersive wave train due its oblique direction of propagation which reduces the effective bottom slope allowing dispersion to balance nonlinear effects and prohibiting overturning

subducted oceanic relief locks the shallow megathrust in central ecuador whether subducted oceanic reliefs such as seamounts promote seismic rupture or aseismic slip remains controversial here we use swath bathymetry pre stack depth migrated multichannel seismic reflection lines and wide angle seismic data collected across the central ecuador subduction segment to reveal a broad 55 km x 50 km 1 5 2 0 km high low height to width ratio multi peaked sediment bare shallow subducted oceanic relief owing to la plata island and the coastline being located respectively 35 km and 50 60 km from the trench gps measurements allow us to demonstrate that the subducted oceanic relief spatially correlates to a shallow 80 km x 55 km locked interplate asperity within a dominantly creeping subduction segment the oceanic relief geometrical anomaly together with its highly jagged topography the absence of a subduction channel and a stiff erosive oceanic margin are found to be long term geological characteristics associated with the shallow locking of the megathrust although the size and level of locking observed at the subducted relief scale could produce a mw 7 event no large earthquake are known to have happened for several centuries on the contrary frequent slow slip events sse have been recorded since 2010 within the locked patch and regular seismic swarms have occurred in this area during the last 40 years these transient processes together with the rough subducted oceanic topography suggest that interplate friction might actually be heterogeneous within the locked patch additionally we find that the subducted relief undergoes internal shearing and produces a permanent flexural bulge of the margin which uplifted la plata island

generalizations of the wedderburn number parameterizing upwelling in stratified lakes the effect of lake geometry on wind induced upwelling in a two layer stratified lake with a variable bottom slope and generic planar shape is investigated 1 the traditional linearized classification parameter for upwelling the wedderburn number is extended to include finite amplitude effects in a rectangular basin this extension is important when the wedderburn number is 3 2 the wedderburn number is generalized to incorporate the influence of a bottom slope and a variable width basin for both the linear large wedderburn number and nonlinear small wedderburn number assumptions laboratory and numerical experiments of a two layer stratification were performed and used to validate these extensions 3 both extensions are combined to derive a methodology to estimate the interface displacement in real lakes where both geometry effects may act together and this methodology is used to discuss the response of the thermocline to the onset of wind in lake como and mundaring weir reservoir in most cases symmetry of the basin geometry along the fetch is the key characteristic that defines tilting of the interface for real lakes asymmetries in terms of bottom slopes induce shortening or stretching of the effective internal fetch while a larger excursion of the interface results in narrower upwind areas of the lake due to horizontal redistribution of displaced water volumes this paper gives the correct definition of the length scales to define the wedderburn number for any stratified basin

seasonal evolution of the basin scale internal wave field in a large stratified lake the response of the water column to varying conditions of stratification and wind forcing was investigated in lake kinneret israel using data collected from thermistor chains and acoustic doppler current profilers during 1997 and 1998 the strong daily sea breeze was found to generate a vertical mode 1 internal kelvin wave and basin scale internal poincarewaves of vertical modes 1 2 and 3 the kelvin wave the dominant component of the internal wave field was responsible for alongshore velocities in the nearshore regions in the upwind nearshore regions velocities were dominated by the forced response to the wind and were cross shore in nature in the lake interior the kelvin wave effect on the horizontal velocity field was minor compared to the higher vertical mode poincarewaves the kelvin wave is shown to exist in resonant and nonforced states with the wind whereas the vertical mode 1 poincarewave energy remained relatively constant despite large variability in the forcing condi tions the energy in the higher mode poincarewaves varied greatly both on daily and seasonal timescales the results demonstrate that the wind energy forces multiple basin scale internal wave modes and that prior motion in the water column must be considered when determining the subsequent internal wave response in periodically forced systems lake kinneret israel has long been an important regional resource providing a substantial supply of drinking water as well as supporting a commercial fishery the monomictic lake is forced daily during the summer by a powerful sea breeze with stratification and wind patterns showing little variation from year to year these factors along with a fa vorable bathymetric pattern combine to make lake kinneret an ideal place for the field investigation of large scale inter nal waves and related phenomena such as the benthic bound ary layer horizontal transport and vertical mixing processes in addition to providing substantial insight into the local pro cesses and hence influencing local management study of the lake also provides fundamental knowledge of the dynam ics of enclosed basins on a geophysical scale during summer the internal rossby radius in lake kin neret is typically one half the basin width hence large scale motion in the lake will be affected by the earth s rotation and basin scale internal waves may be of topographic ross by kelvin or poincareform topographic rossby waves are sub inertial frequency oscillations that exist only in rotating fluids with variable bathymetry mysak et al 1985 stocker and hutter 1987 and these waves result from changes in depth affecting the relative vorticity of fluid elements in the absence of vertical boundaries wavelike solutions to the lin ear inviscid equations of motion for a flat bottomed region of homogeneous fluid with a constant rate of rotation are 1

sediment resuspension mechanisms and their contributions to high turbidity events in a large lake high resolution field data collected during april to october of 2008 2009 were analyzed to investigate the quantitative contribution of sediment resuspension to high turbidity events in central lake erie resuspension events were distinguished within high turbidity events according to turbidity fluorescence and acoustic backscatter timeseries as well as satellite images we observed 16 high turbidity events causing a total duration of 20 d out of 344 d with elevated nearbed turbidity 10 ntu of these events 64 were correlated with algal biomass with the remaining 18 5 and 4 being attributed to sediment resuspension by surface waves storm generated currents and enhanced nearbed turbulence induced by high frequency internal waves respectively this is the first time that resuspension by enhanced nearbed turbulence from high frequency linear internal wave degeneration has been observed in a large lake resuspension was parameterized as a function of the instantaneous critical bottom velocity bottom shear stress and the shields parameter from the in situ measurements we suggest an extended shields diagram for silty bed material that can be used to predict resuspension in other aquatic systems with similar sediment composition 20 cohesive sediment

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

horizontal structure and excitation of primary motions in a strongly stratified lake a modal analysis in the horizontal plane was extended to a layer stratified basin with irregular bathymetry and the theory was applied to lake biwa to investigate the horizontal structure and excitation of the basin scale internal waves and gyres the horizontal structure of the basin scale internal waves consisted of cyclonic and anticyclonic elliptic cells each of which appeared to follow the dispersion relationship of kelvin and poincare waves in elliptic basins the internal waves were preferentially excited depending on the arrangement of the cells and the wind direction but the spatial distribution of wind stress curl over the lake primarily determined the horizontal structure of the ensuing gyres decoupled evolutionary equations for the individual modes provided a good approximation for excitation of the internal waves and early stages of excitation of the gyres before nonlinear effects and damping become significant the modal decomposition of hydrodynamic simulation results also showed that the primary action of the wind was to excite the internal waves however these internal waves were damped within a few days and the dynamics during calm periods were dominated by the gyres illustrating the importance of internal waves on mixing and gyres on long term horizontal transport

spatial structure of the dominant basin scale internal waves in lake kinneret field data and numerical simulations were used to investigate the effects of basin shape continuous stratification and rotation on the three dimensional structure of the dominant natural basin scale internal wave modes in lake kinneret a stratified lake large enough so that the earth s rotation influences the wave motion the structure of the modes was inferred from power spectral density of measured and simulated isotherm vertical displacements and from rotary power spectral density of isopycnal velocities obtained from numerical simulations the shape of the lake at the level of the thermocline in conjunction with the dispersion relationship determines the horizontal configuration of the natural modes the dominant response to wind forcing was an azimuthal and vertical mode 1 kelvin wave with a natural period of 22 6 h that propagated around the entire basin the second most dominant response was a vertical mode 1 wave with a natural period close to 10 5 h and composed of two counter rotating

the sulu sea internal soliton experiment abstract we present the results of a comprehensive study of large amplitude internal solitons generated in the sulu sea in the philippines by intense tidal flow over a sharp bathymetric feature surface signatures of these waves have been observed in images from the dmsp landsat and nimbus 7 satellites and the space shuttle sir a synthetic aperture radar a two week experiment was conducted in the sulu sea in may 1980 from r v oceanograher during which a three mooring phased array of current meters and thermistors was implanted near the wave source and at 82 km and 200 km from the source seventeen soliton packets were observed whose properties underwent significant change as they propagated across the sea vertical profiles of density temperature and acoustic backscatter as well as radar and photographic surface signatures were obtained from the ship data from satellites moorings and the ship give unprecedented information on the spatial and temporal characteristics of solitary waves which ha