topographic and boundary effects on steady and unsteady flow through straits an overview of topographic and boundary effects in flows through straits is presented the emphasis is on the various types of interaction of uniform and stratified flow with the topography of straits especially the interaction with sills the interaction of a single layer flow in a channel with a sill obstacle depends on the froude number of the flow and the relative height of the sill two classification schemes one steady and one pseudo steady are given for single layer flow in straits where the effects of rotation are important a further parameter the ratio of the channel width to a rossby radius is needed and a similar classification scheme as for the non rotating flows can be obtained unsteady flows often result in bores for single layer flows and internal bores in stratified flows and the behaviour of these is discussed the flow of stratified flow past sills may generate lee waves while the increased flow speeds at the sill may allow deep water to be drawn up and over the sill aspiration features of the strait topography away from the sill including slopes at the side of the channel and also downstream of the sill channel curvature and channel widening have important effects on the character of the flow and on mixing

winter cascading of cold water in lake geneva 1 during the winters of 1998 and 1999 observations were made of the cascading of cold water from the nearshore shallow shelf zones and down the sloping sides of lake geneva cascading starts on the average 10 hours after the onset of surface cooling the draining cold water descends like a gravity current and the downslope speed of the head of these slugs of cold water u has a mean value of 5 2 cm s 1 with slugs persisting on the average for 8 hours when the monin obukov length scale at the water surface l is negative implying convection occurs and d over bar lg 1 where d is the mean shelf depth the nondimensionalized speed of the front of slugs u b 1 3 is found to be 1 3 0 4 where b is the surface buoyancy flux integrated over the time period from one slug to the next each slug is unsteady the head being followed by several fronts in which the temperature of the current decreases and its thickness increases these fronts travel faster than the mean flow by a factor of r 1 38 0 3 dynamical similarities are found with roll waves observed in turbulent open channel flows the circulation induced by the cascade is found to give a positive skewness to the time derivatives of near surface temperature in shallow waters in contrast with negative values close to the slope the volume of cold water carried by a slug increases with downslope distance as a consequence of turbulent entrainment and the contribution of convectively unstable plumes from the surface the average volume carried by the slug across the 21 m depth contour is about 1 9 times the volume of water in shallower water i e that on the shelf between shore and a depth of 21 m implying that cascading is an efficient means of flushing shelf water integrated around the lake the mean total volume flux amounts to 11 5 the average winter river inflow

airborne synthetic aperture radar tracking of internal waves in the strait of gibraltar abstract as part of the international gibraltar experiment we realized on june 22 and 24 1986 two surveys of the strait of gibraltar on board an aircraft equipped with a synthetic aperture radar our objective was to observe at spring tides and during two twelve hour tidal cycles at 24 h interval the generation of internal wave trains linked to the hydraulic jump formed west of the sill during the westward phase of the tidal current and their eastward propagation in the strait the speed of propagation of these waves and the effect of the diurnal component of the tide on their generation and propagation could then be determined our results suggest that two solitary waves of equal amplitude propagated eastwards in the strait on june 22 the tidal coefficient being equal to 92 with a speed relative to the ground of 2 1 to 2 6 m s 1 24 h later during the second survey on june 24 tidal coefficient 90 we observed the propagation of a train of non linear waves the speed of the leading wave of which being about 1 9 ms 1 our data show that other waves pass over the camarinal sill after the release of the bore and secondary internal wave trains are shown to propagate eastwards from there although our sar data show the appearance of waves west of the northern sill at about 4 h after high water hw the mechanism leading to their generation is not clear these waves could propagate eastwards all along the strait and or northwestwards along the western spanish coast they could be responsible for the solitary type events observed at the eastern entrance of the strait at about 7 h after hw by ziegenbein 1969 1970 these events are noticeable in the hydrological parameters time series of armi and farmer 1988 and in the high rate current data 2 min apart from their april 1986 cruise besides these alongstrait waves our sar data show the existence of cross strait waves and give an idea of their wavelength and speed of propagation their presence leads to perturbations in the current revealed by simultaneous current data at the camarinal sill and north of cape cires

whole flow field dynamics and velocity pulsing within natural sediment laden underflows sediment laden density underflows are important agents of erosion and deposition and are especially significant in the management of human made reservoirs pollutant dispersal and sediment deposition in the world9s oceans quantification of continuous sediment laden underflows in lillooet lake british columbia shows that the underflows descend along a distinct plunge line but although the input from the source is constant adopt a distinct pulsing in their velocity structure such velocity pulsing will produce temporally and spatially varying bed shear stresses sediment erosion and or deposition and fluid mixing and represents a central property of underflows that must be incorporated into models of density current behavior

a paleogene flora from the upper bonnet plume formation of northeast yukon territory canada palaeontological exploration of the bonnet plume basin in northwestern yukon territory canada has revealed a late paleocene to early eocene macrofloral assemblage from a channel fill deposit the flora is typified by cosmopolitan taxa and dominated by deciduous angiosperms with the notable presence of zizyphoides ettingshausenia and corylites floras with a similar composition are known from late cretaceous through early eocene deposits in alaska and the canadian arctic archipelago where they have been interpreted as evidence for warm equable temperatures this collection represents the most diverse known paleogene plant macrofossil assemblage from the yukon territory and helps to expand our knowledge of ancient high latitude floras

observations of the thermal structure of a lake using a submarine this note describes how a submarine the f a forel carrying a vertical array of high resolution temperature sensors was used along with conventional measurements from a lowered conductivity temperature depth probe ctd to make novel measurements of the temperature field in lake geneva during summertime conditions of stable stratification and during winter convection the submarine speed was about 0 5 m s 1 in addition to the temperatures the pressure orientation and tilt were recorded at frequencies of at least 10 hz observations were made on a vertical scale of 0 1 to 2 5 m and on a horizontal scale from 0 5 m to 1 km examples of the data are presented during the summer evidence was found of internal waves and of extensive layers of low vertical temperature gradient with vertical and horizontal scales of 0 5 m and 0 5 km respectively within this gradient the temperature changed monotonically in the horizontal during periods favoring convection in the winter when air temperatures were about 7 c below the surface water temperature convectively unstable regions typically of 5 m horizontal scale were observed in the mixed layer these appeared to be convective plumes these winter measurements also included observations of a layer of cold water that was adjacent to the sloping boundary of the lake this was identified as being a plume of dense cold water with thickness on the order of 10 m which was driven by surface cooling and consequent more rapid temperature decrease in the shallow nearshore water on meeting the thermocline at a depth of about 100 m this plume spread horizontally and formed an intrusion some 30 m thick

internal waves in a stratified shear flow the strait of gibraltar abstract the wavelengths directions and phase speeds of internal waves propagating through the strait of gibraltar were measured from shore based marine radar images of their surface features shipborne echo sounder images identified these waves as first mode and enabled their amplitudes to be measured the moving features in the radar images were closely correlated with the waves in the echo sounder image a numerical solution of the taylor goldstein equation was used to predict the phase speed of the waves utilizing simultaneous measurements of the density and velocity structure of the water column within the bounds of experimental error there was good agreement between the theoretical and measured phase speeds of the waves on two different tidal cycles no correlation appeared to be present between amplitude and estimated wave width indicating that the waves were not behaving as korteweg devries type solitons

turbidity currents and submarine channel formation in rupert inlet british columbia 1 surge observations acoustic backscatter images obtained at 107 and 200 khz of surge type turbidity currents resulting from mine tailing discharge are presented excess densities in the head of the order of 100 kg m 3 are estimated from differences in acoustic backscatter intensity and in the amplitude of the bottom reflected signal these excess densities are comparable to estimates based on surge height and speed the speed being determined by assuming a universal head shape unlike gravity current surges from an impulsively started steady source the surge type turbidity flows consist of a high concentration slug of short duration followed by a longer lived wake in which sediment concentrations are lower by 2 3 orders of magnitude the profile of the high concentration slug resembles those for density slugs on small bottom slopes obtained in laboratory experiments discrete scatterers probably fish are observed to avoid the surges

hurricane induced storm surges currents and destratification in a semi enclosed bay 1 semi enclosed bays and estuaries are usually protected from hurricane generated storm surges when a hurricane travels on the land side however it may induce high storm surges strong currents and destratification in the water column real time observations and numerical model prediction both show a slab like sloshing in chesapeake bay when it was hit by hurricane isabel in september 2003 strong southeasterly winds in the right front quadrant of the storm forced water in chesapeake bay to move northward as a single layer producing high sea levels and flooding in the northern bay region including baltimore and annapolis furthermore the strong landward winds erased water column stratification and caused a strong intrusion of high salinity shelf water into the bay after isabel s passage the longitudinal salinity gradient produces restratification and two layer circulation in the bay

simulation of storm surge wave currents and inundation in the outer banks and chesapeake bay during hurricane isabel in 2003 the importance of waves 1 this paper investigates the effects of waves on storm surge currents and inundation in the outer banks and chesapeake bay during hurricane isabel in 2003 through detailed comparison between observed wind wave surge and inundation data and results from an integrated storm surge modeling system ch3d ssms ch3d ssms which includes coupled coastal and basin scale storm surge and wave models successfully simulated measured winds waves storm surge currents and inundation during isabel comprehensive modeling and data analysis revealed noticeable effects of waves on storm surge currents and inundation among the processes that represent wave effects radiation stress outside the estuaries and wave induced stress outside and inside the estuaries are more important than wave induced bottom stress in affecting the water level maximum surge was 3 m while maximum wave height was 20 m offshore and 2 5 m inside the chesapeake bay where the maximum wave induced water level reached 1 m significant waves reached 3 5 m and 16 s at duck pier north carolina and 1 6 m and 5 s at gloucester virginia at duck wave effects accounted for 36 cm or 20 of the peak surge elevation of 1 71 m inside the chesapeake bay wave effects account for 5 10 of observed peak surge level a two layer flow is found at kitty hawk north carolina during the peak of storm surge owing to the combined effects of wind and wave breaking higher surge elevations result when the 3 d surge model instead of the 2 d surge model is coupled with the 2 d wave model owing to its relatively lower bottom friction wave heights obtained with 3 and 2 d surge models show little difference

processes influencing storm induced currents in the irish sea abstract although the problem of predicting storm surge elevations has received significant attention the simulation of currents has suffered because of lack of current observations during surges current measurements made during surge conditions are presented here and are used in combination with three dimensional models to understand processes producing storm currents in the irish sea a coarse grid resolution of order 7 km model of the west coast of britain together with a fine grid of order 1 km model of the eastern irish sea is used to examine the processes namely open boundary forcing of the west coast model and wind fields that produced flows within the eastern irish sea during the storm surge of november 1977 simulations of the surge show that the fine grid model nested within the west coast model can reproduce observed coastal changes in surge elevation however an observed major inflow that was recorded by current meters in the region prior to a storm surge elevation peak is not repr

gravity current flow over obstacles when a gravity current meets an obstacle a proportion of the flow may continue over the obstacle while the rest is reflected back as a hydraulic jump there are many examples of this type of flow both in the natural and man made environment e g sea breezes meeting hills dense gas and liquid releases meeting containment walls two dimensional currents and obstacles where the reflected jump is in the opposite direction to the incoming current are examined by laboratory experiment and theoretical analysis the investigation concentrates on the case of no net flow so that there is a return flow in the finite depth upper layer the theoretical analysis is based on shallow water theory both a rigid lid and a free surface condition for the top of the upper layer are considered the flow may be divided into several regions the inflow conditions the region around the hydraulic jump the flow at the obstacle and the flow downstream of the obstacle both theoretical and empirical inflow conditions are examined the jump conditions are based on assuming that the energy dissipation is confined to the lower layer and the flow over the obstacle is described by hydraulic control theory

generation mechanism of internal waves by a vertically sheared tidal flow over a sill the internal response over a sill to strong tidal flow superimposed on a vertically sheared steady flow is examined with a simple two layer analytical model as in the case where the vertical shear is absent the upstream propagating internal wave is gradually formed through interference of infinitesimal amplitude internal waves elementary waves emanating from the sill at each instant of time hibiya 1986 with the composite internal froude number exceeding falling below unity in the accelerating decelerating stage of the two layer flow the upstream propagating elementary waves come close together over the sill in this case however the amplitude of the elementary wave is increased when the lower layer velocity is larger than the upper layer velocity whereas it is reduced when the upper layer velocity is larger than the lower layer velocity as a result the internal wave field over the sill differs markedly between the ebb and flood tidal phases it follows from this analytical result that in the strait of gibraltar the internal wave propagating mediterraneanward is significantly amplified during the ebb westward phase of the tidal flow whereas such amplification does not take place throughout the tidal cycle for the internal wave propagating atlanticward this is consistent with the result from satellite observation that the sea surface signatures caused by underlying large amplitude internal wave trains appear only on the mediterranean side and not on the atlantic side

analysis of gravity waves generated at the top of a drainage flow abstract drainage or katabatic flows are common mesoscale circulations established as a result of differential radiative cooling of near surface air masses in sloping terrain the initial irruption of these flows with sudden shifts in wind speed and direction may result in vertical displacements of air parcels from their equilibrium position which prove to be a common source of internal gravity waves this paper illustrates this mechanism and describes the main features of the oscillations following the study of observational data gathered throughout one night during the stable atmospheric boundary layer experiment in spain 2006 sables2006 field campaign pressure differences measured by microbarometers set at different levels of a tower help to interpret the evolution of other atmospheric variables provide a detailed picture of the irruption of a drainage current and reveal the formation of gravity waves at its top the main parameters of the waves are derived from wavelet cross correlation of p

frontogenesis in a fluid with horizontal density gradients the adjustment under gravity of a fluid containing a horizontal density gradient is described the fluid is initially at rest and the resulting motion is calculated as the flow accelerates driven by the baroclinic density field two forms of the initial density distribution are considered in the first the initial horizontal gradient is constant a purely horizontal motion develops as the isopycnals rotate towards the horizontal the vertical density gradient increases continually with time but the horizontal density gradient remains unchanged the horizontal velocity has a uniform vertical shear and the gradient richardson number is constant in space and decreases monotonically with time to the second density distribution consists of a piecewise constant gradient with a jump in the gradient along a vertical isopycnal the density is continuous in this case frontogenesis is predicted to occur on the isopycnal between the two constant density gradient regions and the timescale for the formation of a front is determined laboratory experiments are reported which confirm the results of these calculations in addition lock exchange experiments have been carried out in which the horizontal mean gradient is represented by a series of step density differences separated by vertical gates

eddy formation by dense flows on slopes in a rotating fluid properties of the flow generated by a continuous source of dense fluid on a slope in a rotating system are investigated with a variety of laboratory experiments the dense fluid may initially flow down the slope but it turns under the influence of rotation to flow along the slope and initial geostrophic adjustment gives it an anticyclonic velocity profile some of the dense fluid drains downslope in a viscous ekman layer which may become unstable to growing waves provided that the viscous draining is not too strong cyclonic vortices form periodically in the upper layer and the dense flow breaks up into a series of domes three processes may contribute to the formation of these eddies first initial downslope flow of the dense current may stretch columns of ambient fluid by the taylor column process which we term capture secondly the initial geostrophic adjustment implies lower layer collapse which may stretch the fluid column and thirdly viscous drainage will progressively stretch and spin up a captured water column overall this last process may be the most significant but viscous drainage has contradictory effects in that it progressively removes dense lower layer fluid which terminates the process when the layer thickness approaches that of the ekman layer the eddies produced propagate along the slope owing to the combined effects of buoyancy coriolis balance and beta gyres this removes fluid from the vicinity of the source and causes the cycle to repeat the vorticity of the upper layer cyclones increases linearly with l d where l is the rossby deformation radius the bottom slope and d the total depth reaching approximately 2 f in the experiments presented here the frequency at which the eddy dome structures are produced also increases with while the speed at which the structures propagate along the slope is reduced by viscous effects the flow of dense fluid on slopes is a very important part of the global ocean circulation system and the implications of the laboratory experiments for oceanographic flows are discussed

in situ measurements of saltwater flux through tidal passes of lake pontchartrain estuary by hurricanes gustav and ike in september 2008 1 storm surge induced saltwater flux through multiple inlets has never been documented this article reports in situ measurements of saltwater flux through major tidal passes by two consecutive storm surges impacting lake pontchartrain estuary in louisiana during the first two weeks in september 2008 the main peak of inward saltwater flux lasted for 1 9 days during the flood followed by more than 8 days of outward salt flux the salt flux rate reached close to 200 tons sec through the northern channel and 16 tons sec through the southern channel outward flux of salt during gustav amounted to more than 16 million tons during the receding stage more than twice of that measured for the flux into the lake apparently overland inundation which was not measured caused this biased estimate of influx of salt hurricane ike however did not cause such a dramatic difference in influx and outflux of salt

eddy formation by overflows in stratified water abstract the formation of eddies by dense overflows in stratified water is examined by laboratory experiments the dense fluid initially flows down the slope but turns under the influence of rotation to flow along the slope the inviscid alongslope flow is continuously drained by a viscous ekman layer that flows more directly downslope in some cases this ekman layer flow becomes unstable to growing waves under certain conditions strong cyclonic vortices form in the ambient fluid above the alongslope flow due to vortex stretching causing the dense fluid to break up into a series of domes there are three main mechanisms for this first the initial downslope flow of the current before it turns under the influence of rotation may take captured upper layer fluid with it out into deeper water second adjustment of the current to geostrophic balance stretches the fluid column above the current and finally the continuous viscous draining from the current and later from the domes also causes stre

antarctic boundary layer parametrization in a general circulation model 1 d simulations facing summer observations at dome c the parametrization of the atmospheric boundary layer abl is critical over the antarctic plateau for climate modelling since it affects the large scale temperature inversion and the katabatic winds this study challenges state of the art parametrizations used in general circulation models to represent the clear sky summertime diurnal cycle of the abl at dome c antarctic plateau the laboratoire de meteorologie dynamique zoom model is run in a 1d configuration on the fourth gewex atmospheric boundary layers study case simulations are analysed and compared to observations giving insights into the sensitivity of one model that participates to the intercomparison exercise snow albedo and thermal inertia are calibrated leading to better surface temperatures using the so called thermal plume model improves the momentum mixing in the diurnal abl in stable conditions four turbulence schemes are tested best simulations are those in which the turbulence cuts off above 35m in the middle of the night highlighting the contribution of the longwave radiation in the abl heat budget however the nocturnal surface layer is not stable enough to distinguish between surface fluxes computed with different stability functions the absence of subsidence in the forcings and an underestimation of downward longwave radiation are identified to be likely responsible for a cold bias in the nocturnal abl apart from model specific improvements the paper clarifies on which are the critical aspects to improve in general circulation models to correctly represent the summertime abl over the antarctic plateau

internal tides in the strait of gibraltar abstract analysis of moored current measurements in the strait of gibraltar is provided here the vertical internal displacements double amplitudes with a semidiurnal frequency are extremely large and sometimes exceed 200 m it is found that these displacements are associated with forced tidal internal waves over camarinal sill which crosses the strait the separation of tidal components showed that the amplitude of internal tide with m2 frequency is 69 m while the amplitudes of other components of the internal tide s2 k1 o1 are 3 5 times smaller the amplitudes of the waves decrease with the distance from the sill and at a distance of 50 km from the sill the amplitudes are 3 times smaller than over the sill the energy of internal tides is transferred to internal bore and turbulent mixing the wavelength of the internal tide was estimated on the basis of moored measurements the wavelength of the east propagated wave is 90 km while the west propagated wave is 60 km numerical modeling demonstr

cascading of water down the sloping sides of a deep lake in winter during winter the temperature of the water overlying the shallow typically 2 5 m deep shelf region around the edge of the 310 m deep lake geneva falls more rapidly than that over deeper areas this causes the spilling or cascading of relatively dense water from the shallows down the sloping sides of the lake in the form of gravity currents 2 15 m thick and typically 0 1 c cooler than the ambient the flow is intermittent with slugs of cold water lasting on average for 8 hrs with mean downslope speeds of 5 2 cms 1 the temperature and thickness of the slugs is however variable with pulses of colder water lasting for 1 3 hrs each preceded by a front in which thickness increases and temperature falls by about 0 01 c per min the net volume flux carried by the slugs is 18 5 times the mean winter flow into the lake from rivers

control variability and internal bore evolution in the strait of gibraltar a 2 d two layer model study a two dimensional high resolution non linear two layer free surface boundary fitted co ordinate hydrostatic model was applied to study the time space variability of hydraulic controls and the development of internal bores in the strait of gibraltar the model predicts the occurrence of four averaged over a tropical month controls located to the west of the spartel sill at the spartel and camarinal sills and in the tarifa narrows the last of these controls is apparent in the sense that it consists of discrete fragments alternating with subcritical flow regions the only control which extends over the whole width of the strait is the control at the camarinal sill but it breaks down during neap tide too this control exists concurrently with the control in the tarifa narrows for short periods while for much of the tropical month there is either just one or neither of the controls the model predicts the development of a hydraulic jump and a jump drop pair near the camarinal sill the appearance of bulges of mediterranean water to the east and west of the sill the large amplitude and small amplitude internal bores released from the camarinal sill which travel respectively eastward and westward and their transformation due to radial spreading and dissipative effects also presented here are the results illustrating the effects of earth s rotation on the internal bores in the strait of gibraltar

resonant seiche motion in the chesapeake bay chesapeake bay is a long and narrow estuary in which seiche motions are common phenomena these motions are generally driven by the longitudinal n s wind at 2 to 3 day time scales and are characterized by a node at the mouth and an antinode at the head of the bay recent observations revealed a burst of seiche activity which was however related to the lateral e w wind the amplitude of current fluctuations was about 50 cm s 1 and was not simply related to the winds the period was about 1 6 days which was less than the natural period of the whole bay since the optimum wind was aligned with only a small portion of the bay the lower reaches of the bay about 40 km long the primary wind effect may be active only at the entrance region nevertheless it appeared that the wind driven current was able to trigger a resonant seiche motion in the rest of the bay the coupled response was modeled through a two section conceptual model and the results compare well with the observations

regional and local vegetation community dynamics of the eocene okanagan highlands british columbia washington state from palynology palynofloras from the middle early to early middle eocene okanagan highlands northern washington state and southern british columbia are used to reconstruct vegetation across a broad upland eocene landscape in this preliminary report forest floristic composition is reconstructed using palynological analysis of sediments from republic washington localities of the allenby formation in the princeton region hospital hill one mile creek and summers creek road hat creek mcabee falkland horsefly and driftwood canyon british columbia wind dispersed taxa were dominant in all samples consistent with floras preserved in lacustrine and paludal depositional environments pseudolarix was dominant in five of the floras but abies falkland or ulmus republic corner lot site were dominant in individual samples for some floras betulaceae were dominant for mcabee alnus and allenby formation betula matching megafloral data for these sites some taxa common to most sites suggest cool conditions e g

stable boundary layer regimes at dome c antarctica observation and analysis investigation of meteorological measurements along a 45 m tower at dome c on the high east antarctic plateau revealed two distinct stable boundary layer sbl regimes at this location the first regime is characterized by strong winds and continuous turbulence it results in full vertical coupling of temperature wind magnitude and wind direction in the sbl the second regime is characterized by weak winds associated with weak turbulent activity and very strong temperature inversions reaching up to 25 k in the lowest 10 m vertical temperature profiles are generally exponentially shaped convex in the first regime and convex concave convex in the second the transition between the two regimes is particularly abrupt when looking at the near surface temperature inversion and it can be identified by a 10 m wind speed threshold with winds under this threshold the turbulent heat supply toward the surface becomes significantly lower than the net surface radiative cooling the threshold value including its range of uncertainty appears to agree with recent theoretical predictions from the so called minimum wind speed for sustainable turbulence mwst theory for the quasi steady clear sky winter cases the relation between the near surface inversion amplitude and the wind speed takes a characteristic s shape closer analysis suggests that this relation corresponds to a critical transition between a steady turbulent and a steady radiative regime with a dynamically unstable branch in the transition zone these fascinating characteristics of the antarctic boundary layer challenge present and future numerical models to represent this region in a physically correct manner

exceptional astronomical seeing conditions above dome c in antarctica one of the most important considerations when planning the next generation of ground based optical astronomical telescopes is to choose a site that has excellent seeing the jitter in the apparent position of a star that is caused by light bending as it passes through regions of differing refractive index in the earth s atmosphere the best mid latitude sites have a median seeing ranging from 0 5 to 1 0 arcsec refs 1 5 sites on the antarctic plateau have unique atmospheric properties that make them worth investigating as potential observatory locations previous testing at the us amundsen scott south pole station has however demonstrated poor seeing averaging 1 8 arcsec refs 6 7 here we report observations of the wintertime seeing from dome c ref 8 a high point on the antarctic plateau at a latitude of 75 s the results are remarkable the median seeing is 0 27 arcsec and below 0 15 arcsec 25 per cent of the time a telescope placed at dome c would compete with one that is 2 to 3 times larger at the best mid latitude observatories and an interferometer based at this site could work on projects that would otherwise require a space mission

dynamical response to differential rates of temperature change over sloping topography lough corrib ireland 1 an enclosed water body subjected to a uniform surface heat flux exhibits differential rates of temperature change between shallow peripheral waters and adjacent deeper waters the result is the formation of horizontal temperature gradients in regions of sloping topography referred to as topographic temperature gradients ttgs an integrated observational and numerical study has been undertaken considering the impact of ttgs on the basin scale dynamics of lough corrib ireland temperature time series recorded during the winter of 2001 revealed sustained surface temperature gradients parallel to sloping boundaries cold dense water formed in peripheral regions of the lake cascaded down slope under the influence of gravity forming density plumes that extended over horizontal scales of kilometers plumes were typically 8 12 m thick and traveled down slope at speeds in the range 4 10 cm s 1 down slope cascading of cool water was typically initiated when the daily mean surface heat flux fell below 55 w m 2 meaning cascading occurred almost persistently throughout the period of seasonal cooling from early september until early january while cascading plumes exhibited a diurnal periodicity individual cascading events were linked to the passing of weather systems persisting for between 5 hours and 3 6 days the cascading of dense water formed an important mechanism for the transport of peripheral waters to depth greatly increasing rates of lake overturning and preventing stagnation during cool calm conditions the offshore transport owing to cascading was balanced by a weaker and more diffuse onshore flow within the upper 5 m of the water column quasi geostrophic alongshore currents evident in the modeled velocity field formed a basin scale anticyclonic gyre during calm conditions

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

high resolution measurements made across a tidal intrusion front high spatial resolution current and hydrographic measurements have been made across a tidal intrusion front in the james river estuary virginia during the first few hours of flood the current measurements were made with a surface towed acoustic doppler current profiler which was used in both profile and side scan configurations the profile data show a 30 50 cm s 1 inflow of water from the chesapeake bay a time evolving across front density gradient and downward velocity beneath the front of about 15 cm s 1 the side scan observations directly measure the across front change in current and provide a view of the three dimensional character of the frontal interface the near surface horizontal strain rate a critical parameter for understanding the modulation of surface waves across the front is estimated to be about 0 04 s 1 using phillips 1984 theory as a guide fronts with such large strain rates as these should be discernible in imagery from the ers 1 c band synthetic aperture radar for wind speeds of 4 m s 1

convergence and downwelling at a river plume front abstract the small scale structure of the circulation and hydrography at the frontal boundary of the connecticut river plume in long island sound has been resolved using a novel combination of instruments a towed acoustic doppler current profiler adcp and a rigid array of current meters and conductivity temperature sensors observations were made during the latter half of the eastward ebb tide when the river plume was well established and the front was moving to the west at approximately 0 3 m s 1 two across front transects revealed a horizontal convergence rate in the across front velocity components at 0 6 m of 0 05 0 1 s 1 this was associated with a salt induced horizontal density gradient of 10 2 kg m4 observations obtained during a period in which the towed adcp was caught in the zone of maximum surface convergence showed significant downwelling with a near surface maximum of 0 2 m s 1 vertical velocities of this magnitude are consistent with observed magnitudes of the convergence rate at 0 6

transitions in the wintertime near surface temperature inversion at dome c antarctica in this work we study the dynamics of the surface based temperature inversion over the antarctic plateau during the polar winter using 6 years of observations from the french italian antarctic station concordia at dome c we investigate sudden regime transitions in the strength of the near surface temperature inversion here we define near surface as being within the domain of the 45 m measuring tower in particular we consider the strongly nonlinear relation between the 10 m inversion strength t 10m t s and the 10 m wind speed to this end all individual events for which the 10 m inversion strength increases or decreases continuously by more than 15 k in time are considered composite time series and vertical profiles of wind and temperature reveal specific characteristics of the transition from weak to very strong inversions and vice versa in contrast to midlatitudes the largest variations in temperature are not found at the surface but at a height of 10 m a similar analysis was performed on results from an atmospheric single column model scm overall the scm results reproduce the observed characteristics of the transitions in the near surface inversion remarkably well using model output the underlying mechanisms of the regime transitions are identified the nonlinear relation between inversion strength and wind speed at a given level is explained by variations in the geostrophic wind speed changes in the depth of the turbulent layer and the vertical divergence of turbulent fluxes moreover the transitions between different boundary layer regimes cannot be explained without considering the contribution of subsidence heating

the boiling water phenomena at camarinal sill the strait of gibraltar abstract a detailed description of high amplitude steady topographic internal waves recorded at camarinal sill during a survey on the r v investigador is presented these internal waves are generated during the maximum outflow westward stage of the tidal current and remain over the sill for more than 4 h until the outflow slackens then being released towards the mediterranean their amplitudes are comparable to the well known internal bore of camarinal sill occurring during maximum outflow during spring tides however they respond to a different physical origin and their spatial features are also quite different in fact the favourable hydraulic conditions for the generation of steady waves over the sill inhibit the internal bore generation and vice versa analysis of the observations suggests that steady internal waves are the result of a resonant response of the stratified fluid over the sill to the forcing of the flow on the across sill topography an important consequence of the steady internal waves with clear biological implications is the significant mixing phenomena that are induced mixing is enabled by an enhancement of the shear at the trough together with a significant induced vertical advection

bouncing internal bores of ardmucknish bay scotland propagating fronts and internal waves have been observed in the sea using bottom mounted side scan sonar1 in ardmucknish bay north of oban on the west coast of scotland the fronts between brackish water and seawater are generated when less saline and so less dense water discharges tidally into the sea from the mouth of a sea loch the fronts appear to propagate from the direction of the loch as might be expected but the internal waves were found to propagate almost at right angles to this direction a time lapse cine camera was mounted on a nearby hill and was used to investigate the phenomena which are visible on the surface because of their effect on surface waves and hence on the brightness of the sea surface the internal waves are found to be generated when the fronts reflect from the coastline on one side of the bay and this explains then direction of propagation the movement of fronts influence the horizontal transfer of say nutrients from the sea loch into the surrounding coastal water

frictional processes in straits friction and mixing can be dynamically significant in straits as in many oceanographic situations for weak time dependent homogeneous flows geostrophy friction and acceleration can all play roles in limiting the flow through a strait and the ratio of the geostrophic elevation difference across the strait to the frictional difference along the strait may be of importance in more general situations a specific question for quasi steady exchange flows through straits concerns the influences of friction and entrainment on hydraulic control within the context of layered models these effects tend to drive a flow towards hydraulic criticality in the downstream direction and to shift control points downstream however friction and entrainment also induce vertical gradients in velocity and density rendering layered models dubious in such situations the conditions for hydraulic control have been uncertain even for a homogeneous fluid there is an apparent contradiction between control conditions based on a similarity assumption for the velocity profile on the one hand and on the speed of long waves on the other the resolution of this contradiction is discussed it seems that if the frictional forces only involve local flow properties then inviscid long waves are arrested at the control section though this is shifted from its location for inviscid flow but that if flow derivatives along the channel are involved the condition changes for a homogeneous flow with shear internal friction and bottom friction the control section is shifted downstream partway to where it would be for a slab flow with bottom friction while the parameterization of bottom friction actually seems to be reasonably well established the nature and quantification of internal and lateral frictional processes are uncertain in a rotating system secondary cross strait flows are expected to be driven by the vertical gradient of the vertical reynolds stress and can provide estimates of the magnitude of bottom and internal friction

night time measurements of astronomical seeing at dome a in antarctica seeing the angular size of stellar images blurred by atmospheric turbulence is a critical parameter used to assess the quality of astronomical sites at optical infrared wavelengths median values at the best mid latitude sites are generally in the range of 0 6 0 8 arcseconds1 3 sites on the antarctic plateau are characterized by comparatively weak turbulence in the free atmosphere above a strong but thin boundary layer4 6 the median seeing at dome c is estimated to be 0 23 0 36 arcseconds7 10 above a boundary layer that has a typical height of 30 metres10 12 at domes a and f the only previous seeing measurements have been made during daytime13 14 here we report measurements of night time seeing at dome a using a differential image motion monitor15 located at a height of just 8 metres it recorded seeing as low as 0 13 arcseconds and provided seeing statistics that are comparable to those at a height of 20 metres at dome c this indicates that the boundary layer was below 8 metres for 31 per cent of the time with median seeing of 0 31 arcseconds consistent with free atmosphere seeing the seeing and boundary layer thickness are found to be strongly correlated with the near surface temperature gradient the correlation confirms a median thickness of approximately 14 metres for the boundary layer at dome a as found from a sonic radar16 the thinner boundary layer makes it less challenging to locate a telescope above it thereby giving greater access to the free atmosphere

convectively driven turbulent mixing in the upper ocean abstract two experiments were performed to study the characteristics of turbulence in convective mixed layers in the upper ocean in the first a diurnal convective mixed layer developed in the bahamas under the influence of the cycle of daytime solar heating and nighttime evaporative cooling the mixed layer reached as deep as 100 m each night and restratified each day in the second the mixed layer of a warm core gulf stream ring deepened from less than 50 m to more than 150 m in a little more than a day when subjected to rapid cooling during a cold air outbreak although individual profiles of the rate of viscous dissipation of turbulent kinetic energy had considerable spatial and temporal variability the mean dissipation profiles were similar to those in convecting atmospheric boundary layers the is established by the surface buoyancy flux jb0 jb0 0 61 and 0 72 in the bahamas and ring data respectively compared with 0 64 in convecting atmospheric mixed layers the mean profiles decre

the effects of laterally sloping upper and lower boundaries on waves and instability in stratified shear flows the dispersion relation for internal waves travelling in the horizontal direction of a two dimensional stratified shear flow is affected by the presence of topography or upper and lower boundaries which vary only in the horizontal direction normal to that of the flow this is in accordance with grimshaw s 1978 findings for long internal waves such topography however imposes boundary conditions which affect both the growth rates and orientation of the crests of unstable disturbances predictions are derived for the particular case of instability of a fluid with a thin interface separating two fluids of different densities in relative flow which are confined in a tube with horizontal generators but which has upper and lower parallel plane boundaries inclined to the horizontal at an angle these predictions are compared with laboratory experiments there is good qualitative agreement and some quantitative agreement at least when the predicted angle between the crest lines of the disturbances and the cross flow direction is small relatively small disturbances or billow amplitudes are found along the centreline of the tube at large however the disturbance crests becomes less well ordered with billows on one side of the tube centreline connecting with neighbouring pairs on the other so evolving a zigzag pattern the results have application to naturally occurring flows in estuaries and channels and to the development of instability in the stratified atmosphere

observations of mixing near the sides of a deep lake in winter the dissipation rate of turbulent kinetic energy per unit mass vertical eddy diffusivity kz and the rate of dissipation of temperature variance x are estimated over the sloping sides of lake geneva both far from and near the bed using temperature data from horizontal tracks of a submarine during periods of winter cooling the estimated values are about one order of magnitude greater near the slope than those distant from it the mean dissipation rate per unit mass averaged over the epilimnion varies between o 10 210 m 2 s 23 in calm weather to o 10 28 m 2 s 23 in winds of 8 m s 21 for surface buoyancy fluxes of 6 3 10

a fluorescein tracer release experiment in the hydrothermally active crater of vailulu u volcano samoa 1 on 3 april 2001 a 20 kg point source of fluorescein dye was released 30 m above the bottom of the active summit caldera of vailulu u submarine volcano samoa vailulu u crater is 2000 m wide and at water depths of 600 1000 m with the bottom 200 m completely enclosed it thus provides an ideal site to study the hydrodynamics of an active hydrothermal system the magmatically driven hydrothermal system in the crater is currently exporting massive amounts of particulates manganese and helium the dispersal of the dye was tracked for 4 days with a fluorimeter in tow yo mode from the u s coast guard icebreaker polar sea lateral dispersion of the dye ranged from 80 to 500 m d 1 vertical dispersion had two components a diapycnal diffusivity component averaging 21 cm2 s 1 and an advective component averaging 0 025 cm s 1 these measurements constrain the mass export of water from the crater during this period to be 8 1 3 4 6 107 m3 d 1 which leads to a turnover time for water in the crater of 3 2 days coupled with temperature data from ctd profiles and mn analyses of water samples the power output from the crater is 610 100 350 mw and the manganese export flux is 240 kg d 1 the mn heat ratio of 4 7 ng j 1 is significantly lower than ratios characteristic of hot smokers and diffuse hydrothermal flows on mid ocean ridges and points to phase separation processes in this relatively shallow hydrothermal system

the importance of aspiration and channel curvature in producing strong vertical mixing over a sill on the basis of observations of the time dependent tidally forced flow over a long sill we find that aspiration and channel curvature set the flow structure and condition the flow to allow intense vertical mixing aspiration reduces the potential energy of the water column by thinning it while maintaining its density contrast channel curvature induces a cross channel circulation that can rapidly overturn a stratified flow eighteen along channel sections of density velocity and dissipation rate of turbulent kinetic energy were collected in and around the tacoma narrows of puget sound a site suspected of driving a strong vertical circulation in adjoining main basin rapid inflow to the narrows on flood from one channel of a triple junction reduces dynamic pressure allowing dense water from below sill depth to be uplifted or aspirated into the narrows we estimate water from below 150 m 3 times the sill depth is drawn into the narrows on a 3 m flood tide once in the narrows the flow remains stratified until it passes a 50 bend where a strong secondary circulation overturns the 50 m deep water column and generates intense turbulent mixing cross channel velocities of up to 0 4 m s 1 are observed and maximum values of exceed 10 3 w kg 1 upon leaving the sill stratification is reestablished and turbulence decays a similar set of sequences occurs on ebb except that the outflow bypasses the flood inflow channel and instead discharges into colvos passage the third branch of the triple junction colvos passage ultimately discharges the ebb effluent back into main basin enhancing the impact of mixing at the narrows by discharging the mixed product far from the source scaling of the cross channel momentum equation suggests that below a threshold value of along channel velocity stratification should suppress secondary circulation for a given vertical shear radius of curvature and channel width above the threshold velocity the magnitude of the cross channel velocity is roughly consistent with predictions for unstratified flow we estimate the maximum effective eddy diffusivity that aspiration and mixing in the narrows can produce in main basin to be 10 3 m2 s 1

yes some of the mediterranean outflow does come from great depth in 1973 stommel et al predicted that the western mediterranean deep water wmdw contributes directly to the mediterranean outflow through the strait of gibraltar strommel et al 1973 hydrographic data obtained in november 1985 showed unambiguous evidence of wmdw west of the major gibraltar sill thus confirming the prediction

mixing in flows down gentle slopes into stratified environments observations of the flow of dense fluid into uniformly density stratified environments down plane slopes with small inclination to the horizontal 20 are described and a quantitative model for such flows is presented in these experiments the dense fluid is released at the top of the slope for a finite period of time the resulting downslope gravity current or downflow has uniform thickness with a distinct upper boundary until it approaches its level of neutral density where the fluid leaves the proximity of the slope turbulent transfers of mass and momentum occur across the upper boundary causing a continuous loss of fluid from the downflow in most cases and associated loss of momentum the flow may be characterized by the local values of the richardson number ri the reynolds number re generally large and of m qn 3 g 2 where q is the two dimensional volume flux n the buoyancy frequency and g the negative buoyancy of the dense fluid the model for the downflow describes the turbulent transfers in terms of entrainment detrainment and drag coefficients e e e d and k respectively and the observations enable the determination of these coefficients in terms of the local values of m and ri the model may be regarded as an extension of that ellison turner 1959 to stratified environments describing the consequent substantial changes in mixing and distribution of the inflow it permits the modelling of the bulk properties of these flows in geophysical situations including shallow and deep flows in the ocean

the early miocene onset of a ventilated circulation regime in the arctic ocean deep water formation in the northern north atlantic ocean and the arctic ocean is a key driver of the global thermohaline circulation and hence also of global climate1 deciphering the history of the circulation regime in the arctic ocean has long been prevented by the lack of data from cores of cenozoic sediments from the arctic s deep sea floor similarly the timing of the opening of a connection between the northern north atlantic and the arctic ocean permitting deep water exchange has been poorly constrained this situation changed when the first drill cores were recovered from the central arctic ocean2 here we use these cores to show that the transition from poorly oxygenated to fully oxygenated ventilated conditions in the arctic ocean occurred during the later part of early miocene times we attribute this pronounced change in ventilation regime to the opening of the fram strait a palaeo geographic and palaeo bathymetric reconstruction of the arctic ocean together with a physical oceanographic analysis of the evolving strait and sill conditions in the fram strait suggests that the arctic ocean went from an oxygen poor lake stage to a transitional estuarine sea phase with variable ventilation and finally to the fully ventilated ocean phase 17 5 myr ago the timing of this palaeo oceanographic change coincides with the onset of the middle miocene climatic optimum3 although it remains unclear if there is a causal relationship between these two events

generation of an estuarine sediment plume by a tropical storm 1 tropical storm lee 2011 caused a record flood in the susquehanna river which discharged about 6 7 million tons of suspended sediments into the bay an amount equal to the input of 6 average years the flood carried sediment produced a large sediment plume that covered one half of chesapeake bay with the maximum suspended sediment concentration exceeding 2500 mg l 1 three stages were identified in the development of the sediment plume corresponding to three dominant forcing mechanisms i e river flow estuarine circulation and sediment settling most of the flood carried sediments were deposited in the bay within 20 days sands were dumped in the susquehanna flats with a maximum thickness of 10 cm while fine grained sediments were dusted over a wide area in the upper bay with a maximum thickness of 4 cm long term simulation of the post storm period showed that a majority of the flood sediments were redistributed to accumulate in the estuarine turbidity maximum region due to flood ebb asymmetry in tidal suspension and advection by estuarine circulation and tidal flows while the rest were transported seaward and deposited in the mid bay it is estimated that the flood delivered 9 months of particulate nitrogen and over 1 year of particulate phosphorus supplies to the estuary this catastrophic event may change the geological history and exacerbate water quality decline in the american largest estuary

how entraining density currents influence the stratification in a one dimensional ocean basin abstract the sensitivity of ocean stratification to the vertical distribution of plume entrainment is analyzed a large ocean basin supplied by dense water from an adjoining marginal sea is considered the dense water flows into the ocean basin as an entraining density current and interleaves at the bottom or at the level of neutral density where it deposits a mixture of marginal sea and basin water as the basin water i e old plume water is entrained and re circulated in the plume a stratification develops in the basin the mixture deposited at the bottom hence contains an increasing fraction of marginal sea water and the basin density increases with depth as well as with time a stationary solution in which diffusion of buoyancy from above is important is approached asymptotically in time non diffusive solutions to the initial transient adjustment as well as the diffusive asymptotic state have been studied in four different parameterizations of plume entrainment it is shown that in the transient regime the basin stratification and plume density are highly sensitive to how mixing is parameterized the stationary diffusive solution that is approached asymptotically in time is less sensitive to parameterization but depends strongly on basin topography source water density and buoyancy flux at the surface

upstream separation in a rotating channel flow the question of upstream separation of a current of dense rotating fluid below a stagnant layer of lower density that is critically controlled by a weir is addressed in laboratory experiments that follow from theoretical calculations for a constant potential vorticity flow in a gradually varying channel it is shown that a range of parameters lead to upstream separation in all cases the flow reattaches before reaching the sill crest so that a closed gyre is produced in laboratory experiments separation and reattachment was observed in numerous cases where the theory predicts closed gyres although the shape and size of the gyre are in accordance with theory the circulation within the gyre differs markedly from theoretical predictions the mechanism that feeds energy into the gyre appears to be an important unsolved problem the results indicate that upstream separation is a fact and that the dynamics of the gyre is significant so the gyre dynamics may modify the volume flux of fluid over the weir

study of the generation and propagation of internal waves in the strait of gibraltar using a numerical model and synthetic aperture radar images of the european ers 1 satellite a weakly nonhydrostatic two layer numerical model based on the boussinesq equations is presented which is capable of describing among others the generation and propagation of nonlinear weakly dispersive internal waves in the strait of gibraltar the model depends on one space coordinate only but it retains several features of a fully three dimensional model by including a realistic bottom profile a variable channel width and a trapezoidal channel cross section the nonlinear primitive boussinesq equations include horizontal diffusion bottom friction and friction between the two water layers the model is driven by a height difference of the mean interface depth between the atlantic and the mediterranean boundaries and by semidiurnal tidal oscillations of the barotropic transport the model presented in this paper describes 1 the mean and tidal flow in the strait of gibraltar 2 the variation of the depth of the interface during a tidal cycle 3 the generation of strong depressions of the interface at the western sides of the spartel sill and the camarinal sill 4 the generation of strong eastward propagating internal bores and 5 their disintegration into trains of internal solitary waves the surface convergence patterns associated with depressions of the interface at the camarinal sill internal bores and internal solitary waves are calculated and compared with roughness patterns visible on synthetic aperture radar sar images of the first european remote sensing satellite ers 1 in total 155 ers 1 sar scenes from 94 satellite overflights over the strait of gibraltar which were acquired in the period from january 1992 to march 1995 have been analyzed it is shown that the proposed model is capable of explaining the observed temporal and spatial evolution of surface roughness patterns associated with eastward propagating internal waves inside the strait of gibraltar as well as the observed east west asymmetry of the internal wave field

similarity structure in the convective boundary layer of a lake natural convection influences a variety of geophysical phenomena including daily mixing cycles in the atmosphere and in surface waters the seasonal overturn of lakes and global climate variability conceptual models of convection in water are primitive and based on very limited data particularly at small dissipative scales here i present an analysis of microscale data from the convective boundary layer of a lake indicating a complex depth dependence in the rate at which temperature fluctuations are dissipated suitably scaled this vertical structure is remarkably similar to that found in the atmospheric convective boundary layer1 2 stirred by rising thermals of buoyant air heated at the earth s surface this comparison consistent with recent documentation of similarity in the more uniform vertical structure of energy dissipation3 5 suggests another unifying link in the structure and dynamics of convection in boundary layers of lakes oceans and the atmosphere6

estuarine sedimentary response to atlantic tropical cyclones abstract in late summer 2011 hurricane irene and tropical storm lee impacted virtually every coastal river and estuary along the u s north atlantic seaboard we investigated the sedimentary response of the delaware estuary to these tropical cyclones through coordinated observations of flow and suspended sediment transport from moored instrumentation hydrographic surveys and sediment coring on 27 28 august hurricane irene tracked offshore of the estuary and generated strong northwesterly winds and intense short lived rainfall and river runoff on 7 8 september the remnants of tropical storm lee tracked inland along the drainage basin and produced weaker winds but more widely distributed and longer lived rainfall and river runoff an estimated 1 4 0 6 10 6 metric tons of fluvial suspended sediment was delivered to the estuary in association with these storms record setting freshwater discharges generated by lee displaced the salt front 50 km seaward of its pre storm position yet the front and associated estuarine turbidity maximum were not flushed beyond the mouth convergent gravitational and tidal circulations effectively trapped suspended sediment delivered to and produced within the estuary during the storm period normal conditions of estuarine circulation and sediment flux rebounded about five days after the passage of irene but did not fully recover before the approach of lee and it was not until two weeks thereafter that the estuary recovered bed sedimentology and inventories of the radionuclide 7 be t 1 2 53 days revealed that the upper estuary floor scoured in places under storm enhanced bottom currents whereas the lower estuary remained depositional throughout the storm period sediment flux and coring observations indicate that estuary bed resuspension was the main source of suspended sediment transported in the estuary during irene and was a major source during lee along with fluvial sediment delivered from the drainage basin regardless of the source our observations make clear that the estuary is capable of trapping suspended sediment and preventing its escape to the coastal ocean during extreme oceanic storms

the sea breeze and gravity current frontogenesis the development of a sea breeze circulation into a sea breeze front in often observed late in the afternoon measurements of horizontal temperature and humidity profiles in a number of sea breeze circulation made using an instrumented light aircraft are presented on each of the four days for which data are presented an initial weak horizontal temperature gradient extending over a distance of 5 to 10 kilometres developed later in the into a sharp front only a few hundred metres across the data are discussed in terms of simple gravity current frontogenesis models applied to the development of sharp sea breeze front from an initial diffuse transition between the air over the land sea examination of the equations for frontogenesis and the result of some previous laboratory experiments on gravity current frontogenesis lead to the proposal that given sufficient contrast between land and sea temperatures the formation of a sea breeze front depends on the balance between convergent horizontal winds which act to generate a front and turbulent convective mixing over the land which tends to prevent its formation the differences in driving force wind convergence and turbulent intensity are discussed for each day on which data are available and are shown to be consistent with the theory proposed

age and depositional environment of the rock river coal basin yukon territory canada poorly exposed late eocene strata in the rock river basin 115 km northeast of watson lake accumulated in an intermontane valley with a geometry and history controlled by subsidence associated with the rock river fault the sequence as seen in one outcrop and five borehole sections is dominated by drab mudrocks with minor sandstones and some thick lenses of coal the mudrocks accumulated in floodplain marsh and pond settings associated with a low gradient possibly anastomosed fluvial system river banks were stable owing to the abundance of plant roots in the channel walls although channel sandstone and conglomerate were not identified in the core the abundance of coarsening and fining upwards sets of sandstone of splay origin indicates pronounced levee development woody coals accumulated in areas well away from the main channel in a series of elongate forested swamps which were periodically inundated by flood water the overall palynological assemblage is typical of the eocene and early oligoce

frontogenesis in gravity driven flows with non uniform density gradients a horizontal density gradient may be steepened to form a front if the horizontal flow which it drives is convergent this convergence may be caused by an initial nonlinearity in the density gradient as described by simpson linden 1989 a quadratic density profile is analysed to illustrate the mechanism and it is shown how the flow and the density profile interact to intensify and concentrate the front near a horizontal boundary linear and curved density profiles in a container of finite length are also studied the most favourable location for frontogenesis is found to be where the flow emerges into a region of significant curvature after passing through a maximum of the density gradient

three dimensional nature of flow near a sill velocity and density sections across knight inlet british columbia demonstrate that lateral recirculations are a first order feature of the flow in the lee of the sill the flow over this sill has been used as a typical example of two dimensional hydraulics with a lower layer that thins and accelerates as it moves downstream below an almost stagnant layer that widens downstream creating a distinctive wedge shape however we find that rather than being stagnant the velocity in this wedge shaped layer is actually quite large consisting of a swiftly recirculating dipole vortex during flood tide and a monopole vortex during ebb tide though we may have missed the matching half of a dipole with our sampling during ebb the recirculations during flood tide carry an amount of water equal to 25 of the tidal flux while the monopole during ebb tide carries 20 of the tidal flux these recirculations bias along channel estimates of volume flux especially in the middle wedge shaped layer and demonstrate that accurate volume fluxes in the lee wave are only possible if three dimensional surveys are made our three dimensional survey shows that there is a net isopycnal convergence of water in the middle layer at a rate adequate to close the volume budget of the flow without recourse to diapycnal fluxes we also calculate the strength of the vorticity in the recirculations observed during flood tide and attribute their formation to boundary layer separation

impact of lake level change on deep water renewal and oxic conditions in deep saline lake van turkey 1 changes in the hydrological regime of the saline closed basin lake van a large deep lake in eastern turkey resulted in a lake level increase by about 2 m between 1988 and 1995 followed by a 1 5 m decrease until 2003 and a relatively constant lake level thereafter based on measurements of transient tracers sulfur hexafluoride cfc 12 3h 3he 4he ne dissolved oxygen light transmission conductivity temperature depth profiles and thermistor data we investigate the implications associated with lake level fluctuations for deep water renewal and oxygenation our data suggest that deep water renewal was significantly reduced in lake van between 1990 and 2005 this change in mixing conditions resulted in the formation of a more than 100 m thick anoxic deep water body below 325 m depth apparently the freshwater inflows responsible for the lake level rise between 1988 and 1995 decreased the salinity of the surface water sufficiently that the generation of density plumes during winter cooling was substantially reduced compared to that in the years before the lake level rise significant renewal and oxygenation of the deep water did not occur until at least 2005 although by 2003 the lake level was back to almost the same level as in 1988 this study suggests that short term changes in the hydrological regime resulting in lake level changes of a couple of meters can lead to significant and long lasting changes in deep water renewal and oxic conditions in deep saline lakes

mesoscale variability in denmark strait the pv outflow hypothesis abstract the outflow through denmark strait shows remarkable mesoscale variability characterized by the continuous formation of intense mesoscale cyclones just south of the sill these cyclones have a diameter of about 30 km and clear signatures at the sea surface and in currents measured near the bottom they have a remnant of arctic intermediate water aiw in their core the authors hypothesis is that these cyclones are formed by stretching of the high potential vorticity pv water column that outflows through denmark strait the light upper layer of the outflow the east greenland current remains on the surface in the irminger sea while the dense overflow water descends the east greenland continental slope the midlevel waters mostly aiw could thus be stretched by more than 100 which would induce very strong cyclonic relative vorticity the main test of this new hypothesis is by way of numerical experiments carried out with an isopycnal coordinate ocean model configured to have a marginal sea

the generation of the morning glory abstract a high resolution cloud model is used to explore in detail the generation of the morning glory a low level nonlinear atmospheric internal wave observed on the southwestern side of cape york peninsula australia the model is two dimensional and nonhydrostatic and simulates an east west cross section of the southern part of cape york peninsula at a horizontal resolution of 200 m most of the numerical experiments are initialized at sunrise with a 5 m s 1 easterly flow and a sounding taken upstream from the peninsula the sea breezes that develop over cape york peninsula are highly asymmetric with the east coast sea breeze being both deeper and warmer than its western counterpart when the sea breezes meet the east coast sea breeze rides over that from the west coast and in the process produces a series of waves that propagate on the west coast sea breeze the model calculations show that when the phase speed of these waves matches the westward propagation speed of the east coast sea breeze the

multi layer hydraulic exchange flows flows between ocean basins are often controlled by narrow channels and shallow sills a multi layer hydraulic control theory is developed for exchange flow through such constrictions the theory is based on the inviscid shallow water equations and extends the functional approach introduced by gill 1977 and developed by dalziel 1991 the flows considered are those in rectangular cross section channels connecting two large reservoirs with a single constriction sill and or narrows the exchange flow depends on the stratification in the two reservoirs represented as a finite number of immiscible layers of different uniform density for most cases the flow is controlled at the constriction and often at other points along the channel virtual controls too as with one and two layer hydraulics controls are locations at which the flow passes from one solution branch to another and at which at least one internal wave mode is stationary the theory is applied to three layer flows which have two internal wave modes predicting interface heights and layer fluxes from the given reservoir conditions the theoretical results for three layer flows are compared to a comprehensive set of laboratory experiments and found to give good agreement the laboratory experiments also show other features of the flow such as the formation of waves on the interfaces the implications of the results for oceanographic flows and ocean modelling are discussed

dynamics of dense water cascades at the shelf edge abstract plumes of dense shelf water cascade down continental slopes in many parts of the world s oceans and provide a mechanism for shelf ocean exchange in this paper a nonlinear process orientated theory is developed and used to examine the dynamics of cascading the theory is formulated in terms of a 1 layer model and incorporates bottom topography earth rotation internal and bottom friction and entrainment as well as externally imposed pressure gradients the theory occupies a niche between the stream tube class of model which considers only bulk properties of a plume and the full three dimensional primitive equation approach the model provides useful insights into the complex interplay between the controlling forces and it allows one to recover the shape and trajectory of dense plumes as well as the three dimensional flow field inside the bottom layer asymptotic limits are investigated and lead to several basic results a typical thickness of a fully developed plume is found to be twice t

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

response of sediment dynamics in the york river estuary usa to tropical cyclone isabel of 2003 tropical cyclone isabel of 2003 generated large storm surge strong waves and subsequent river flooding in the york river estuary usa during its passage across the chesapeake bay region a 3d model was used to investigate the changes of sediment concentration sediment flux and the recovery time of the york river estuary to its naturally evolved condition without the storm the results showed that two sediment concentration peaks appeared during the storm event the first one was induced by the large upstream flow and waves during the storm surge rising period and the later one was caused by the strong downstream flow during the descent of the storm surge the advection which was induced by the barotropic gradient dominated the sediment flux during the storm event the sediment fluxes increased by a factor of 100 during the rise and descent of the storm surge a large amount of sediment that was transported into the estuary and eroded from the seabed during the rising of the storm surge was quickly transported out of the estuary during the descent of the storm surge waves played a key role in stirring the seabed and increasing the sediment concentration during the storm subsequent high freshwater inflow changed the sediment loading and hydrodynamics in the estuary and thus influenced the estuarine turbidity maximum etm dynamics profoundly the etm moved downstream with the river flooding initially and returned upstream with the waning of river flooding and the re establishment of gravitational circulation the effect of river flooding on sediment concentration varied spatially and depended on the changes of etm locations and vertical mixing the model results suggest that a large amount of sediment was transported out of the estuary during the storm event and the subsequent river flooding had a larger impact on recovery time of the estuary

non normal growth of kelvin helmholtz eddies in a sea breeze the generalized stability of a sea breeze front is analyzed using a two dimensional model the objective is to understand the mechanisms leading to the shedding of eddies behind the sea breeze front as seen in observations laboratory experiments and numerical models regions with ri 1 4 the energy source for optimal growth is the vertical shear of the mean horizontal wind the vertical shear in the upper part of the front and the horizontal shear in the lower part the growth begins with vertical advection by the perturbation velocity of the mean flow momentum located in the upper part of the front perturbations eventually propagate away from the localized shear area and a feedback mechanism is needed for this growth to be sustained this feedback occurs through temperature anomalies in the upper part of the front inducing pressure gradient anomalies in the lower part these gradients lead to a growing vertical wind component and this vertical wind component then enters the upper part of the front which reinforces the extraction of energy thereby closing the feedback loop and leading to both normal mode instability and in the stable regime large non normal growth we find that both the instability and the non normal growth are vulnerable to parameter changes that weaken this feedback loop

occurrence and palaeoenvironmental significance of aromatic hydrocarbon biomarkers in oligocene sediments from the mallik 5l 38 gas hydrate production research well canada abstract the aromatic hydrocarbon biomarker distributions of thirty oligocene sediment samples with different lithology lignite clay and sand from the japex jnoc gsc et al mallik 5l 38 gas hydrate production research well canada were analyzed using gas chromatography mass spectrometry gc ms the compositions vary with lithology indicating a change in palaeoenvironmental conditions at the time of deposition aromatic diterpenoids of the abietane type are more abundant in the lignite samples than in the clay samples and represent a gymnosperm e g conifer dominated palaeovegetation in contrast in the clay samples aromatic triterpenoids are generally preserved as major constituents indicating angiosperm dominated vegetation the sand samples contain only minor amounts of aromatic terpenoids but show a preference for diterpenoid gymnosperm markers to recognise gymnosperm versus angiosperm dominated palaeoenvironments a new ratio termed the angiosperm gymnosperm aromatic ratio agar has been developed thus the terpenoid distribution in the deltaic sediments provides information on the compositional changes in the plant community at the mallik site lignites and the hinterland clays over time concomitantly the changing dominance in the plant communities allows an insight into varying climatic conditions during the late oligocene in the area additionally the aromatic biomarker composition has been used to assess the level of thermal maturity of the organic matter in the mallik samples and indicates a prevailing immature character

observations and modeling of a pulsating density current 1 we investigate density current formation and flow in the northern gulf of eilat red sea using in situ observations and a high resolution nonhydrostatic general circulation model these density currents occur in relatively warm water 20 c and are probably the warmest in the world ocean we demonstrate the intrinsic nonlinearity of density currents by comparing two high resolution simulations forced by different heat flux this nonlinearity which is poorly represented in global models is shown here to affect the properties of simulated density currents such a bias in simulating density currents in global models may lead to significant biases on the larger scale global ocean circulation and water mass distribution