organized structures in subsurface bubble clouds langmuir circulation in the open ocean observations of the movement and distribution of subsurface bubbles reveal the structure of coherent motions near the ocean surface the measurements were obtained in the open ocean from a freely drifting self contained acoustical instrument equipped with side scan sonar dual frequency echo sounders and ambient sound recording systems the bubble clouds are organized into long narrow plumes aligned with the wind consistent with windrows caused by langmuir circulations they have widths of about 3 to 5 m and lengths up to 100 m with multiple scales coexisting their mean separation depends upon wind speed below 5 m s 1 mean spacings were about 5 m increasing to 10 m when winds exceeded 10 m s 1 the maximum depth to which the plumes were observed to penetrate depended to some extent on wind speed with the greatest penetrations of 12 m occurring at the highest wind speeds 13 m s 1 however the time averaged depth of observed bubble plume penetration bears only a weak dependence on wind speed whenever winds exceeded 5 m s 1 a mean penetration depth of 6 m was observed associated with these bubble plumes were maximum downward velocities of about 0 06 m s 1 these speeds were detected at 8 m depth in the center of the plumes magnitudes decreased to zero near the surface and horizontally toward the boundaries of the plumes

patterns of deposition from experimental turbidity currents with reversing buoyancy turbidity currents are turbulent sediment laden gravity currents which can be generated in relatively shallow shelf settings and travel downslope before spreading out across deep water abyssal plains because of the natural stratification of the oceans and or fresh water river inputs to the source area the interstitial fluid within which the particles are suspended will often be less dense than the deep water ambient fluid consequently a turbidity current may initially be denser than the ambient sea water and propagate as a ground hugging flow but later reverse in buoyancy as its bulk density decreases through sedimentation to become lower than that of the ambient sea water when this occurs all or part of the turbidity current lofts to form a buoyant sediment laden cloud from which further deposition occurs deposition from such lofting turbidity currents containing a mixture of fine and coarse sediment suspended in light interstitial fluid is explored through analogue laboratory experiments complemented by theoretical analysis using a box and cloud model particular attention is paid to the overall deposit geometry and to the distributions of fine and coarse material within the deposit a range of beds can be deposited by bimodal lofting turbidity currents lofting may encourage the formation of tabular beds with a rapid pinch out rather than the gradually tapering beds more typical of waning turbidity currents lofting may also decouple the fates of the finer and coarser sediment depending on the initial flow composition the coarse fraction can be deposited prior to or during buoyancy reversal while the fine fraction can be swept upwards and away by the lofting cloud an important feature of the results is the non uniqueness of the deposit architecture different initial current compositions can generate deposits with very similar bed profiles and grading characteristics highlighting the difficulty of reconstructing the nature of the parent flow from field data it is proposed that deposit emplacement by lofting turbidity currents is common in the geological record and may explain a range of features observed in deep water massive sands thinly bedded turbidite sequences and linked debrites depending on the parent flow and its subsequent development for example a lofting flow may lead to a well sorted largely ungraded or weakly graded bed if the fines are transported away by the cloud however a poorly sorted largely ungraded region may form if during buoyancy reversal high local concentrations and associated hindered settling effects develop at the base of the cloud

quantifying upper ocean turbulence driven by surface waves 1 nearly all operational ocean models use air sea fluxes and the ocean shear and stratification to estimate upper ocean boundary layer mixing rates this approach implicitly parameterizes surface wave effects in terms of these inputs here we test this assumption using parallel experiments in a lake with small waves and in the open ocean with much bigger waves under the same wind stress and adjusting for buoyancy flux we find the mixed layer average turbulent vertical kinetic energy in the open ocean typically twice that in the lake the increase is consistent with models of langmuir turbulence in which the wave stokes drift and not wave breaking is the dominant mechanism by which waves energize turbulence in the mixed layer applying these same theories globally we find enhanced mixing and deeper mixed layers resulting from the inclusion of langmuir turbulence in the boundary layer parameterization especially in the southern ocean

turbulent large eddy momentum flux divergence during high wind events abstractmomentum transport by energy containing turbulent eddies in the oceanic mixed layer were investigated during high wind events in the northern gulf of alaska off kayak island sixteen high wind events with magnitudes ranging from 7 to 22 m s 1 were examined winds from the southeast prevailed from one to several days with significant wave heights of 5 9 m and turbulent langmuir numbers of about 0 2 0 4 surface buoyancy forcing was much weaker than the wind stress forcing the water column was well mixed to the bottom depth of about 73 m spectral analyses indicate that a major part of the turbulent momentum flux was concentrated on 10 30 min time scales the ratio of horizontal scale to mixed layer depth was from 2 to 8 turbulent shear stresses in the mixed layer were horizontally asymmetric the downwind turbulent stress at 10 20 m below the surface was approximately 40 of the averaged wind stress and was reduced to 5 10 of the wind stress near the bottom turbulent kinetic energy in the cros

aeration due to breaking waves part i bubble populations abstract the population of bubbles produced by breaking waves in 10 m winds of up to 12 m s 1 is analyzed using calibrated images from a vertical pencil beam sonar system placed on the seabed near the dutch coast the structure in the images is parameterized and the volumetric bubble backscatter is inverted to yield bubble concentrations data were obtained at three acoustic frequencies with inversion effected by prescribing a bubble spectrum with two free variables leaving a redundant measurement to test the robustness of the model median concentrations may in this way be obtained up to the sea surface measurements are multiply regressed on wind and dominant wave variables bubbles penetrate to a depth of about a factor of 6 1 times the significant wave height hs where is the wave age or ratio of dominant wave phase speed to wind speed the measured mean bubble radius decreases weakly with depth unless waves are gently sloping at about 5 m 1 at 0 4 m the mean radius ranges from 30 to 80

velocity structure in the mixed layer during mildex abstract during october november 1983 a mixed layer dynamics experiment mildex took place off the coast of california as a part of mildex a number of sensors were deployed from the research platform flip in an effort to monitor the flow structure in the near surface mixed layer profiling current meters vmcms measured velocities down to 150 m on an hourly basis other vmvms were set at fixed depths depths of interest were examined using a package which measured three component velocities and displayed them in flip s laboratory in real time the current meters often observed sequences of downwind directed jets with maximum velocities exceeding 25 cm s 1 downwelling velocities of equal magnitude were also observed the strongest currents were found 10 to 35 m below the surface at mid depth in the mixed layer surface convergences associated with these jets were visualized by scattering tracers computer cards on the sea surface these features suggest langmuir circulation six doppler sonars wer

wind driven internal waves and langmuir circulations in a numerical ocean model of the southern baltic sea 1 a one dimensional numerical ocean model of the southern baltic sea is used to investigate suitable parameterizations of unresolved turbulence and compare with available observations the turbulence model is a k e model that includes extra source terms piw and plc of turbulent kinetic energy tke due to unresolved breaking internal waves and langmuir circulations respectively as tides are negligible in the baltic sea topographic generation of internal wave energy iwe is neglected instead the energy for deepwater mixing in the baltic sea is provided by the wind at each level the source term piw is assumed to be related to a vertically integrated pool of iwe e0 and the buoyancy frequency n at the same level according to piw z e0n z this results in vertical profiles of e the dissipation rate of tke and kh the eddy diffusivity according to e n and kh n 2 below the main pycnocline earlier observations are inconclusive as to the proper value of and here a range of values of is tested in hundreds of 10 year simulations of the southern baltic sea it is concluded that 1 0 0 3 and that a mean energy flux density to the internal wave field of about 0 9 0 3 10 3 w m 2 is needed to explain the observed salinity field in addition a simple wind dependent formulation of the energy flux to the internal wave field is tested which has some success in describing the short and long term variability of the deepwater turbulence the model suggests that 16 of the energy supplied to the surface layer by the wind is used for deepwater mixing finally it is also shown that langmuir circulations are important to include when modeling the oceanic boundary layer a simple parameterization of langmuir circulations is tuned against large eddy simulation data and verified for the baltic sea

structural style of intra plate deformation central indian ocean basin evidence for the role of fracture zones abstract the structural style of the intraplate deformation developed in the central indian ocean basin was investigated in an area 78 e 82 e 0 s 6 s to the west of the afanasy nikitin seamount using an integrated data set of seismic reflection profiles from edinburgh university and lamont doherty geological observatory the study area contains two fracture zones which strike 005 e to 010 e with oceanic lithosphere age range 65 78 ma b p younging westwards across them no evidence for recent fault activity in the oceanic basement along the fracture zones could be detected in this area although the close association between intraplate earthquakes and fracture zones elsewhere suggests reactivation of the fracture zones at upper mantle depths in a left lateral strike slip sense a statistical study was carried out into the first and second orders of deformation long wavelength basement undulations and high angle reverse faults respectivelyand the relationships between them the orientations of the axes of the undulations vary from 065 e to 085 e while the high angle faults strike consistently at 090 e to 100 e the results of this analysis suggest that the high angle faults are the result of the reactivation of two sets of pre existing spreading centre normal faults one set originally facing towards the spreading centre and the other facing away furthermore although the long wavelength undulations are not fault generated the high angle faults have modified the basement topography causing the accentuation of some of the basement highs the observation that the undulations are not fault generated is consistent with them being of flexural origin including buckling of the crust and or lithosphere basement undulations are clearly discontinuous across fracture zones and the facing direction of faulting is also offset this discontinuity the orientation of the axes of the undulations the presence of other strong oblique basement trendsand information from regional earthquake studies suggest that the deformation resulted from not only n s compression as a result of the continental collision between india and asia but also left lateral strike slip along fracture zones caused by the difference in resistance to plate motion between the continental collision to the north and subduction at the sunda arc to the northeast

the influence of crosswind tidal currents on langmuir circulation in a shallow ocean 1 langmuir circulation lc is a turbulent process driven by wind and surface waves that plays a key role in transferring momentum heat and mass in the oceanic surface layer on the coastal shelves the largest scale lc span the whole water column and thus couple the surface and bottom boundary layers and enhance turbulent mixing observations and large eddy simulations les of a shallow coastal ocean demonstrate that these relatively large scale langmuir cells are strongly influenced by crosswind tidal currents two mechanisms by which crosswind tidal shear may distort and disrupt langmuir cells are proposed the first mechanism involves cell shearing due to differential advection across the whole cell for the second mechanism middepth vertical lc currents advect sheared mean crosswind current leading to the attraction of upwelling and downwelling regions so that lc cells are unsustainable when both regions overlap scaling arguments indicate that lc cells are more susceptible to crosswind shear distortion for smaller lc surface velocity convergence and greater cell aspect ratio vertical to horizontal lc scale which is consistent with the results obtained from the observations and les these results imply that scaling of lc characteristics in a coastal ocean differs from that in the open ocean which has important practical implications for parameterizing enhanced mixing due to lc

the structure and tectonics of the intraplate deformation area in the indian ocean abstract intense tectonic deformations of sediments and basement unusual for the interior of the oceanic lithosphere plates can be seen on seismic reflection profiles from the northern central indian basin 10 000 mile long csp profiles collected by the p p shirshov institute of oceanology of the ussr academy of sciences allow delineation of a ne trending area of these deformations the intraplate deformation area has a complicated tectonic framework formed by a mosaic of crustal blocks which have been severely deformed or tilted alternating with less deformed parts of the sea floor the results of a detailed csp grid survey reveal that these uplifted faulted blocks are bounded by tectonic faults of two genetic types old nearly meridional fracture zones and young ne striking faults the seismic refraction results indicate an anomalous structure of the crust and upper mantle within these blocks seismological observations from ocean bottom seismographs have proved that there is high level intraplate seismicity in the northern central indian basin the intraplate deformation area is supposed to correspond to a large scale zone of shearing strains that formed as a result of the stress difference in the indo australian plate due to the continued collision of the continents of india and asia along with spreading in the central indian ridge and normal subduction in the sunda island arc this continental collision led to an increase in compressional stress in the northernmost part of the plate while its southern part continuously subducted beneath the sunda trench in the complicated transitional zone between these parts of the plate ne sw trending shearing stress abated apparently in the late miocene as a result of folding and faulting of the sediments and basement observed on seismic reflection profiles ne sw trending wrench fault tectonics affected the system of ancient failures in the spreading oceanic crust near meridional transform faults and perhaps near latitudinal scarps parallel to the mid oceanic ridge axis the mosaic fault fold framework of the intraplate deformation area might be partly a result of this interaction

turbulent vertical kinetic energy in the ocean mixed layer abstract vertical velocities in the ocean boundary layer were measured for two weeks at an open ocean wintertime site using neutrally buoyant floats simultaneous measurements of the surface meteorology and surface waves showed a large variability in both wind and wave properties and only weak correlations between them buoyancy forcing was weak the mean square vertical velocity in the boundary layer 2w measured from the vertical motion of the floats was proportional to the squared friction velocity u2 estimated from shipboard meteorological measurements using bulk formulas thus 2w au2 the rate of momentum transport from the atmosphere to the ocean is u2 where is the density of the water the deviations from this relation can be attributed entirely to statistical variation and measurement error the measured values of 2w were corrected for measurement biases and the nonturbulent contributions of internal waves the value of the turbulent part of a is 1 75 2 times that measured in laborato

the effect of langmuir circulation on the distribution of submerged bubbles caused by breaking wind waves clouds of bubbles are generated at the sea surface by breaking wind waves or by heavy rain rows of subsurface bubble clouds have been detected by a bottom mounted side scan sonar and are possibly formed by the effects of langmuir circulation a simple equation is devised to describe the effects of the turbulent diffusion of bubbles from the free surface bubble rise and dissolution and advection by langmuir circulation the equation is solved analytically using a series expansion in which advection is supposed small in comparison with diffusion the solution provides a quantitative measure of the principal effects produced by the circulation in particular the distortion of the bubble field and estimates of the advective flux a random walk numerical model in which changes occurring in individual bubbles are followed is tested against the analytical model in the range for which the latter is valid there is good agreement the numerical model is useful in extending the solutions to more complex cases which include a broad distribution of bubble sizes and to ranges in which the analytic solution is invalid the model is used to quantify the effect of the circulation on the acoustic scattering cross section of the bubble clouds and to explore differences between the conclusions of earlier models and observations by johnson cooke 1979 in the appendices an estimate is made of the depth to which bubbles can be carried by the vertical velocities observed below wind rows and this is found to agree reasonably well with the maximum depth to which bubbles are observed to penetrate estimates of mean vertical diffusion coefficients based on observations of bubbles are compared with some calculated solely from the advective flux in langmuir circulation the latter are as expected smaller than those representing the sum of all the contributions to the flux but are a significant fraction of the order of 0 2 0 4 a method of deriving the vertical diffusion coefficient from observations of the vertical distribution of the acoustic scattering cross section of bubbles appears not to be very sensitive to circulation and may provide estimates within about 25 of the actual values

significance of langmuir circulation in upper ocean mixing comparison of observations and simulations received 4 february 2009 revised 27 march 2009 accepted 20 april 2009 published 28 may 2009 1 representing upper ocean turbulence accurately in models remains a great challenge for improving weather and climate projections langmuir circulation lc is a turbulent process driven by wind and surface waves that plays a key role in transferring momentum heat and mass in the oceanic surface layer we present a direct comparison between observations and large eddy simulations based on the wave averaged navier stokes equation of an lc growth event the evolution of cross wind velocity variance and spatial scales as well as mixed layer deepening are only consistent with simulations if lc effects are included in the model our results offer a validation of the large eddy simulation approach to understanding lc dynamics and demonstrate the importance of lc in ocean surface layer mixing citation kukulka t a j plueddemann j h trowbridge and p p sullivan 2009 significance of langmuir circulation in upper ocean mixing comparison of observations and simulations geophys res lett 36 l10603 doi 10 1029 2009gl037620

effect of planetary rotation on oceanic surface boundary layer turbulence abstracta large eddy simulation les model is configured to investigate the effect of the horizontal northward component of earth s rotation on upper ocean turbulence the focus is on the variab

kinematic constraints on distributed lithospheric deformation in the equatorial indian ocean from present motion between the australian and indian plates from an expanded accurate and up to date data set comprising 110 spreading rates 46 transform azimuths and 151 earthquake slip vectors from the indian ocean and gulf of aden we determine a new rigid plate model describing the motion since 3 ma between india and australia the euler vector 0 313 m y about 5 s 78 e lies near the middle of the equatorial diffuse plate boundary dividing the indian from the australian plate and predicts a rate of north south shortening along 85 e of 4 3 mm yr only 30 as fast as predicted by our prior model the new model also predicts north south extension of 6 2 mm yr at 68 e along the western segment of the diffuse plate boundary where our prior model predicted north south contraction using data only along the carlsberg and central indian ridges and no other plate boundaries we show that plate motion data cannot be fit by a single euler vector however the data are well fit by two euler vectors when an east west striking india australia plate boundary is assumed to intersect the central indian ridge near the equator the best location along the central indian ridge for this triple junction is 6 s 3 s with 95 confidence limits of 9 s 4 n just west of a region of intense seismicity the sense of deformation as recorded in earthquake focal mechanisms reverse faults mapped with reflection seismic data and undulations in basement topography surface gravity and the geoid agrees well with the north south extension predicted in the western part and the north south shortening predicted in the eastern part of the india australia boundary the predicted rate of north south shortening between 79 e and 86 e is consistent with the rate of shortening inferred from observed faulting and folding shortening taken up by faulting is 6 to 100 times greater than that taken up by the spectacular basement folds little of the rapid north south shortening predicted east of 86 e is taken up by crustal thickening instead lithosphere is transported northeastward toward the sumatra trench through strike slip faulting and possible clockwise rotation the failure of the convergent segment of the diffuse plate boundary to form a subducting trench provides some new observations that must be satisfied by models for the initiation of subduction a model of separate rigid indian and australian plates divided by a diffuse plate boundary appears to be valid and useful because the predictions of the model agree with independent data and because the predicted velocity of relative motion is statistically significant and comparable with that across other plate boundaries

laurentian fan morphology sediments processes and growth pattern thick sediment accumulations in deep water provide a new target in the search for oil and require an innovative approach to hydrocarbon exploration the laurentian fan is a large deep sea 2 000 to 5 000 m fan in the western north atlantic and has been the major depocenter off nova scotia since at least the early tertiary the main development of the present depositional and erosional fan morphology in the past 2 to 3 m y was closely related to onshore glacial history the slope above the fan has been the site of rapid sedimentation and consequent slumping a network of tributaries on the upper fan appears to feed three main channel systems incised up to 800 m between broad asymmetric levees these channels meander widely across the lower fan then die out abruptly and pass into a lobate suprafan differences between the laurentian fan and typical fan models result in part from the muddy nature of the sediment and the supply system the channels contain thick coarse gravels which probably grade distally into sandy lobes both should produce good reservoir bodies with suitable source and trapping mechanisms fine grained sediments were more important in fan construction interbedded turbidites contourites and hemipelagites are present in the late quaternary holocene sequence the distribution of these sediments and in particular the recognition of structural sequences textural trends and fabric types in the fine grained turbidites can be used to characterize particular parts of the fan environment the development of this approach should prove useful in future hydrocarbon exploration

seismic reflection images of intraplate deformation central indian ocean and their tectonic significance multichannel seismic reflection profiles collected from the intraplate deformation area in the central indian ocean basin are used to describe brittle structures produced under compressive stress reflectors within oceanic basement are divided into four types north dipping and south dipping reverse faults that are interpreted as reactivations of structures formed at the spreading centre as outward and inward dipping faults respectively lower angle north dipping reflectors that probably represent new faults or faults just initiating and sub horizontal reflectors within the uppermost crust that are interpreted as hydrothermal alteration fronts within the sedimentary cover upwards fault propagation shows the faults steepening from c 40 just above basement to near vertical and is preceded by sediment folding a fractal analysis of faulting suggests two fault populations possibly reflecting different criteria for brittle failure measurements of north south crustal shortening indicate a shortening rate of 2 5 0 9 mm a 1 which is at the lower end of predictions from plate motions but significant enough to recognize this area as a diffuse plate boundary the formation of long wavelength basement undulations and the reactivation of fracture zones and ridge parallel fault fabrics are linked in a unified tectonic model driven by the high level of intraplate compressive stress in the area there is little evidence from the seismic profiles for intraplate deformation starting before the widespread unconformity dated as 7 ma

global distributions of cirrus clouds determined from sage data an analysis using sage data for the period february 1979 to april 1980 was performed to determine the spatial extent and frequency of cirrus clouds over a large portion of the earth s surface these results should be of interest to among others both the researchers concerned with global monitoring and modeling of the earth s radiation budget and climate and to reentry vehicle designers concerned about anomalous aerodynamic effects or damage due to the ice particles found in cirrus clouds a by product of the study reveals the statistics of tropospheric observational opportunities for a limb sounding satellite sensor by determining the percentage of times of successful penetration to 7 km the results of the analysis showed that optically thick cirrus clouds are found most often in the mid latitudes and over the tropics with distinct minima near the 20 to 30 latitude bands thin cirrus clouds as defined in this paper on the other hand occur much less often than the optically thick cirrus clouds a comparison of the optically thick cirrus clouds observed by sage was made zonally with surface based observations and was found to generally agree the percentage of tropospheric observational opportunities down to 7 km was as high as 60 percent in the upper latitudes but fell to about 30 percent in the tropics

horizontal transport of buoyant material by turbulent jets in the upper ocean abstractcurrents in the ocean surface boundary layer osbl determine the horizontal transport of submerged buoyant material such as pollutants plankton and bubbles commonly the mean horizonta

structure and variability of langmuir circulation during the surface waves processes program a cooperative multiplatform field experiment was conducted in the eastern north pacific during february and march of 1990 as part of the surface waves processes program swapp one of the experimental objectives was to investigate langmuir circulation so that its role in the evolution of the oceanic surface boundary layer could be better understood the concurrent use of different observational techniques ranging from simple surface drifters to complex doppler sonar systems resulted in new information about langmuir circulation structure and variability estimates of langmuir cell spacing indicated that a broad range of scales from about 2 to 200 m was excited during periods of strong surface forcing and that the energy containing scales evolved with time estimates of cell spacing based on doppler velocities from a surface scanning sonar directed crosswind showed this scale evolution but estimates based on backscattered intensity did not this was attributed to the fact that the intensity based estimates were only indirectly related to circulation strength the near surface convergent velocities from the sonar were used to form an objective quantitative measure of the temporal variations in langmuir circulation strength as expected the circulation strength increased dramatically during strong wind events however circulation strength and wind stress did not decrease simultaneously and langmuir circulation was detectable for up to a day after abrupt reductions in wind stress energy from the surface wave field which decayed more slowly than the wind was apparently responsible for maintaining the circulation the variation of circulation strength was found to be better related to u us than to u where u is the friction velocity is the wind stress and us is the surface wave stokes drift this scaling is consistent with wave current interaction theories of langmuir cell generation

fault reactivation in the central indian ocean and the rheology of oceanic lithosphere the intraplate deformation in the central indian ocean basin is a well known example of a deviation from an axiom of plate tectonics that of rigid plates with deformation concentrated at plate boundaries here we present multichannel seismic reflection profiles which show that high angle reverse faults in the sediments of the central indian ocean extend through the crust and possibly into the uppermost mantle the dip of these faults which we believe result from the reactivation of pre existing faults formed at the spreading centre is 40 in the basement which is consistent with the distribution and focal mechanisms of earthquakes on faults now forming at spreading centres this style of deformation coupled with the observation of large earthquakes in the mantle lithosphere indicates that brittle failure of the oceanic lithosphere may nucleate in the vicinity of the brittle ductile transition and propagate through the crust

sediment laden gravity currents with reversing buoyancy there are many natural occurrences of sediment laden gravity currents in which the density of the interstitial fluid is less than that of the ambient fluid although the bulk density of the current is greater such currents are driven by the excess density of suspended particles however after sufficient particles have sedimented the current will become buoyant cease its lateral motion and ascend to form a plume examples of such currents include brackish underflows in deltas turbidity currents and pyroclastic flows experimental studies are described which show that due to sedimentation sediment laden gravity currents decelerate more rapidly than saline currents of the same density there is little difference in the experiments between a sediment laden current with neutrally buoyant interstitial fluid and one with buoyant interstial fluid until sufficient sediment has been lost to cause the latter kind of current to lift off a marked deceleration is then observed and a plume is generated with lift off occurring along the length of the current the resulting buoyant plume then generates a gravity current below the upper surface of the fluid in the tank the deposit from a current with buoyant fluid shows a fairly abrupt decrease in thickness beyond the lift off distance and has a flatter profile than that from a simple sediment current a theoretical model is presented which is based on the two layer shallow water equations and incorporates a model of the sedimentation in which particles are assumed to be uniformly suspended by the turbulence of the current the model shows good agreement with the observed lengths of the experimental currents as a function of time and predicts the lift off distance reasonably well these processes have implications for the behaviour of turbidity currents the interpretation of turbidites mixing processes in the oceans and the lift off of pyroclastic flows

measurements with an automatically recording inverted echo sounder aries and the bubble clouds abstract we report here analysis of the first observations with a new instrument aries designed to record the acoustic backscatter from bubble clouds at several levels below the surface of the ocean the instrument is deployed on a subsurface mooring and records internally data has been analysed from deployments of aries for one week in the irish sea and for periods of 4 and 9 weeks near the edge of the uk continental shelf during periods in which meteorological data waves and near surface temperatures and on occasion currents were being recorded by other instruments the results while being generally similar to earlier measurements in coastal waters show that the bubble clouds are more intense having greater acoustic scattering cross per unit volume mv and extend on average deeper into the water column a simple model accounting for the shape of the clouds their advection through the sonar beam and their decay through bubbles returning to the surface or through their gas dissolving int

observed growth of langmuir circulation surface velocity patterns and upper ocean density profiles are presented from a period following a sudden increase in wind a prior wind speed of 8 m s failed to produce visible signs of langmuir circulation after the wind speed increased to 13 m s langmuir circulation developed within 15 min the initial scale observed was about 16 m streak to streak and may have been restricted by the depth scale of the measurements this spacing is about two thirds of the dominant wavelength 4 s period waves the streak spacing two cell widths increased at roughly 40 m h for the next hour the density measurements indicate a depth of mixing which increased over the same period at a rate of 20 m h thus the vertical to horizontal aspect ratio was about 1 1 prior stratification was weak buoyancy frequency of about 1 5 cph and probably did not affect the circulation initially mixing at the surface of the oceans is important to a wide variety of concerns including global climate and the health of marine life two main causes of this mixing can be identified 1 when surface water is cooled it becomes denser and sinks mixing downward either to the bottom or until limited by the preexisting stratification and 2 the wind can mechanically stir the surface layer to some depth usually limited by stratification the former can result in mixing to considerable depths but the latter occurs more often over the majority of the world oceans frequently the two driving forces occur together what are the details of this mixing for example are bubbles dragged deep into the mixed layer injecting gases at depth are there repeatable features which could lead to improved models of surface mixing and its effects when wind blows over water lines are often visible on the surface running roughly parallel to the wind in an exemplary series of experiments langmuir 1938 found these to be lines of convergence along the surface with downwelling below each line he found also that maxima in the downwind surface currents occur along these lines thus the mixing layer is organized into rolls of alternating sign aligned with the wind and water parcels follow helical paths downwind this form of circulation in surface layers of water has come to be called langmuir circulation historically this term has not implied any particular mechanism of formation and it generally has not been used in reference to other similar structures e g roll vortices in the atmosphere or in wall bounded convection langmuir 1938 p 123 expressed his belief that the helical vortices set up by wind apparently constitute the essential mechanism by which the epilimnion is produced clearly this form of helical vortices is efficient in transporting momentum energy and matter throughout the surface layer of water three mechanisms are currently considered to drive langmuir circulation 1 an interaction between surface waves and winddriven shear gives rise to this form of circulation as a linear instability a review of this theory and of observations before 1983 is given by leibovich 1983 2 even without surface waves turbulent mixing will occur due to the breakdown of the

observations of seasonal variation in the ekman layer abstract the seasonal variation in the ekman layer is examined using observations from the long term upper ocean study lotus including surface meteorology current and temperature the near surface current is found to be coherent with the wind at low frequencies periods greater than one day using a wind relative averaging method the authors find the observed near surface volume transport to be consistent with ekman transport the mean current profile has a spiral shape that is flat compared to the classic ekman spiral in that it rotates less with depth than does the ekman spiral the mean current e folds over 12 m in the summer and 25 m in the winter with a decay in amplitude that implies eddy viscosities of 60 10 4 and 250 10 4 m2 s 1 respectively diurnal cycling is the dominant mode of variability in the summer and it determines the vertical structure of the spiral in the winter diurnal cycling is almost nonexistent due to greatly reduced solar insolation and stronger winds a persisten

channels echo character mapping and tectonics from 3 5 khz profiles distal bengal fan abstract the distal parts of the bengal fan are spectacularly affected by tectonic deformation related to the diffuse plate boundary between the indian and australian plates here we use 3 5 khz and 12 khz echosounder profiles seismic reflection profiles and piston core results to examine sedimentary processes and their relationships to tectonism within an area 78 82 e 0 6 s just to the south of ocean drilling program leg 116 sites echo character mapping was completed using echosounder data in conjunction with results from piston coring and a total of five different echo types have been recognised four of these fall into the echo character classification scheme developed by damuth 1980a whilst the fifth is believed to represent hemiturbidite deposits several types of submarine channel were also identified from echosounder data and a correlation between echo type and channel location can be seen their abundance erosional and or depositional nature together with a complex meandering and bifurcation pattern across a wide region of average gradient around 1 km are all features characteristic of a broad channel termination zone on a large elongate fan it is clear therefore that the bengal fan extends beyond 6 s active faulting in the area has led to the development of an irregular topography of low rounded hillocks that interfere with incoming turbidity currents this has resulted in ponding between highs rather than lobe construction thinning and pinching out of turbidites against the flanks of local relief flow lofting and hemiturbidite drape and common small scale slumping in some cases uplifted channel segments can be seen abandoned and partially filled

langmuir turbulence in shallow water part 1 observations during extended deployment at an ocean observatory off the coast of new jersey a bottom mounted five beam acoustic doppler current profiler measured large scale velocity structures that we interpret as langmuir circulations filling the entire water column these circulations are the large eddy structures of wind wave driven turbulent flows that occur episodically when a shallow water column experiences prolonged strong wind forcing many observational characteristics agree with former descriptions of langmuir circulations in deep water the three dimensional velocity field reveals quasi organized structures consisting of pairs of surface intensified counter rotating vortices aligned approximately downwind maximum downward velocities are stronger than upward velocities and the downwelling region of each cell defined as a pair of vortices is narrower than the upwelling region maximum downward vertical velocity occurs at or above mid depth and scales approximately with wind speed the estimated crosswind scale of cells is roughly 3 6 times their vertical scale set under these conditions by water depth the long axis of the cells appears to lie at an angle 10 20 to the right of the wind a major difference from deep water observations is strong near bottom intensification of the downwind jets found typically centred over downwelling regions accessible observational features such as cell morphology and profiles of mean velocities turbulent velocity variances and shear stress components are compared with the results of associated large eddy simulations reported in part 2 of shallow water flows driven by surface stress and the craik leibovich vortex forcing generally used to represent generation of langmuir cells a particularly sensitive diagnostic for identification of langmuir circulations as the energy containing eddies of the turbulent flow is the depth trajectory of invariants of the turbulent stress tensor plotted in the lumley triangle corresponding to realizable turbulent flows when langmuir structures are present in the observations the lumley map is distinctly different from that of surface stress driven couette flow again in agreement with the large eddy simulations les unlike the les observed velocity fields contain two distinct and significant scales of variability documented by wavelet analysis of observational records of vertical velocity variability with periods of many minutes is that expected from langmuir cells drifting past the instrument at the slowly time varying crosswind velocity shorter period variability of the order of 1 2 min has roughly the observed periodicity of surface wave groups suggesting a connection with the wave groups themselves and or the wave breaking associated with them in high wind conditions

lidar observations of equatorial cirrus clouds at mahe seychelles 1 in february march 1999 nocturnal observations with a ground based backscatter depolarization lidar were conducted during the airborne platform for earth observation third european stratospheric experiment on ozone ape theseo campaign at mahe seychelles 4 4 s 55 3 e upper tropospheric cirrus clouds were a common feature in the lidar echoes they were detected for about 67 hours out of a total measurement time of 125 hours optical and geometrical characteristics of the clouds detected at altitudes above 9 km throughout the campaign are derived and discussed cirri above 14 5 km present a layered structure and appear more persistent and thinner than cirri at lower altitudes the behavior of average optical and geometrical depths integrated depolarization backscatter to extinction ratio integrated backscatter and extinction coefficient is studied as a function of midcloud temperature and is compared with results from previous measurements and models the estimated cloud backscatter to extinction ratio ranges from 0 01 to 0 2 sr 1 with an average value of 0 051 0 030 sr 1 in the temperature range between 200 and 240 k the integrated depolarization ranges between 0 27 and 0 19 and appears lower than that for midlatitude cirri in a single night very high values of the integrated depolarization for a layered cirrus at 16 km could be related to outflow from an active convective cell the two highest and coldest temperature around 188 k layers show values of optical and geometrical depth and integrated depolarization lower than for cirri at temperatures between 190 and 200 k the optical characteristics of the clouds decrease for temperatures from 190 to 200 k possibly indicating different evolution phases of the clouds

dynamics of the terra nova bay polynya the potential of multi sensor satellite observations research on processes leading to formation maintenance and disappearance of polynyas in the polar regions benefits significantly from the use of different types of remote sensing data the sentinels of the european space agency esa together with other satellite missions provide a variety of data from different parts of the electromagnetic spectrum at different spatial scales and with different temporal resolutions in a case study we demonstrate the advantage of merging data from different spaceborne instruments for analysing ice conditions and ice dynamics in and around the frequently occurring terra nova bay polynya tnbp in the ross sea in the antarctic starting with a list of polynya parameters that are typically retrieved from satellite images we assess the usefulness of different sensor types on regional scales several 100 km passive microwave radiometers provide a view on the mutual influence of the three ross sea polynyas on sea ice drift and deformation patterns optical sensors with meter scale resolution on the other hand allow very localized analyses of different polynya zones the combination of different ranges of the electromagnetic spectrum is essential for recognition and classification of ice types and structures radar images together with data from thermal infrared sensors operated at tens to hundreds of meters resolution improve the separation of the outlet zone of the polynya from the adjacent pack ice the direct comparison of radar and passive microwave images reveals the visibility of deformed ice zone in the latter a sequence of radar images was employed to retrieve ice drift around the tnb which allows analysing the temporal changes of the polynya area and the extension and structure of the outlet zone as well as ice movements and deformation that are influenced by the katabatic winds

the composite characteristics of cirrus clouds bulk properties revealed by one year of continuous cloud radar data abstract the properties of midlatitude cirrus clouds are examined using one year of continuous vertically pointing millimeter wave cloud radar data collected at the atmospheric radiation measurement program southern great plains site in oklahoma the goal of this analysis is to present the cloud characteristics in a manner that will aid in the evaluation and improvement of cirrus parameterizations in large scale models using a temperature and radar reflectivity based definition of cirrus the occurrence frequency of cirrus the vertical location and thickness of cirrus layers and other fundamental statistics are examined also the bulk microphysical properties of optically thin cirrus layers that occur in isolation from other cloud layers are examined during 1997 it is found that cirrus were present 22 of the time had a mean layer thickness of 2 0 km and were most likely to occur in the 8 5 10 km height range on average the cirrus clouds tended to be found in layers in which the synoptic scale v

evolution of langmuir circulation during a storm wind stress waves stratification velocity profiles and surface fields of radial velocity and acoustic backscatter intensity were measured along a drift track 50 to 150 km off point arguello california on march 8 1995 the wind increased from calm to 12 m s from the se opposing swell from the nw it increased to 15 m s at noon utc on march 9 remained steady over the next 12 hours briefly dropped and veered by 60 then returned a mixed layer deepened quickly to 25 m then held roughly steady through the next 2 days in spite of gusty winds continuing at 15 25 m s a phased array doppler sonar system took measurements covering 250 m by 150 m of the surface with 5 m by 10 m spatial resolution averages over 6 min removed surface waves permitting continuous assessment of strength orientation spacing and degree of organization of features associated with surface motion e g langmuir circulation even when conditions were too rough for visual assessment several results stand out 1 as found previously most wind mixing arises from inertial shear across the thermocline 2 consistent with wind wave forcing of langmuir circulation plueddemann et al 1996 suggest that surface velocity variance scales like u us where u is friction velocity and us is the surface stokes drift however the measurements here scale with us 1 alone once langmuir circulation is established 3 the velocity variance is weaker here than expected given the magnitudes of wind and waves leading to a smaller estimated mixing effect 4 large vacillations in lc strength are seen just before the brief veering of the wind it is suggested that bubble buoyancy could play a dynamic role 5 mean orientation and spacing can differ for intensity versus radial velocity features

patterns of bubble clouds organized by langmuir circulation abstract a commonly observed property of near surface bubble distributions is their collective organization into long rows aligned with the wind under the influence of langmuir circulation time series observations with sonars having fixed orientation reveal the temporal evolution of bubble distributions as they drift through the sonar measurement path here this concept is extended to provide a time sequence at 37 s intervals of two dimensional images generated by horizontally rotating sonars observations obtained during a storm in the strait of georgia show individual langmuir convergence zones as they evolve above the freely drifting sonar the resulting images are processed to generate a binary representation of the convergence zone patterns from which their orientation length spacing and other properties can be extracted although there is some angular spreading most convergence lines are aligned within 20 of the wind the spacing between convergence lines reveals a wide range of scales but