seasat wind and wave observations of northeast pacific hurricane iva august 13 1978 seasat wind and wave observations collected in the eye of hurricane iva on august 13 1978 in the northeast pacific are examined the seasat a scatterometer system sass and scanning multichannel microwave radiometer smmr observations indicate a maximum wind speed of 25 30 m s sass derived isotachs indicate a classic banana shaped high wind speed distribution and the synthetic aperture radar sar imagery displays a large scale mean intensity pattern that is in qualitative agreement two dimensional fourier transforms of selected sar scenes show a dominant wave field characterized by wavelengths of 166 211 m with a fanlike distribution of propagation directions a simple geometric model is proposed as an explanation of this dominant wave field in terms of prior storm intensity and location this geometric model the ross parametric hurricane wave model and the seasat wind and wave data are then employed to obtain estimates of 43 km for the radius to maximum winds and 6 4 m for the corresponding significant wave height at that radius

freakish sea state and swell windsea coupling numerical study of the suwa maru incident 1 on 23 june 2008 a fishing boat with 20 crewmembers onboard sank in reportedly moderate sea state conditions in the kuroshio extension region east of japan to determine the sea state at the time of the incident we conducted a hindcast wave simulation as realistically as possible using an improved third generation wave model driven by wind and current reanalysis products our results indicated that at the time of the accident the wave steepness increased and the spectral peakedness narrowed creating a sea state favorable for freak wave occurrence due to quasi resonance detailed analyses of the spectral evolution revealed that nonlinear coupling of swell and windsea waves was the key to generating the narrow spectrum under the influence of rising wind speed the swell system grew exponentially at the expense of the windsea energy and the bimodal crossing sea state transformed into a freakish unimodal sea

a heton model of the spreading phase of open ocean deep convection abstract a point vortex heton model of the lateral dispersion of cold water formed in open ocean deep convection is developed and studied as an idealized representation of the sinking and spreading phase of open ocean deep convection the overturning and geostrophic adjustment of dense fluid on and below the radius of deformation scale formed by cooling on the large scale are parameterized in the model by introducing paired discrete point vortices hetons of cyclonic sense in the surface layer anticyclonic below driving a cold baroclinic vortex the convection site is imagined to be made up of many such baroclinic vortices each with a vertically homogeneous core carrying cold convectively tainted waters the point vortices are introduced at a rate that depends on the large scale cooling and the intensity assumed for each vortex the interaction of many cold baroclinic vortices making up a cloud is studied using point vortex green s function techniques the current solenoids of the individual ele

an s coordinate density evolving model of the northwest european continental shelf 1 model description and density structure the proudman oceanographic laboratory three dimensional baroclinic b grid model pol3db has been developed to incorporate features suitable for the modeling of baroclinic processes on the shelf at the shelf slope and in ocean regions to allow long term coupled ocean shelf simulations we test the model on the northwest european continental shelf in the period november 1988 to october 1989 against satellite sea surface temperature measurements against ctd sections both on and off the shelf and in summary against the whole of the north sea project ctd data set the model accurately reproduces the seasonal cycle in the shelf wide spatial temperature structure seen in the observations spatial correlations range from r 0 92 in december to 0 79 in july and the overall rms errors range from 0 8 c in april to 1 6 c in july we demonstrate that the increase in the errors during the summer is due to uncertainties in modeling the vertical temperature structure compared with a climatology the large scale sea surface salinity structure is also well modeled r 0 80 but there is a tendency for the model to overestimate the salinity in the norwegian trench and underestimate it in the kattegat the s coordinates a modified sigma coordinate system allow the formation of a seasonal mixed layer across the shelf break and into the northeast atlantic with a modest vertical resolution the accuracy to which this deep water region is modeled is limited by the initial and boundary conditions and by the extent of the model domain

the spatial distribution of ocean waves in tropical cyclones the spatial structure of both the wind and wave fields within tropical cyclones is investigated using two large databases the first of these was compiled from global overpasses of tropical cyclones by satellite altimeters the second dataset consists of an extensive collection of north american buoy measurements during the passage of tropical cyclones hurricanes the combined datasets confirm the vortex structure of the tropical cyclone wind field with the strongest winds to the right northern hemisphere of the storm the wave field largely mirrors the wind field but with greater right left asymmetry that results from the extended fetch to the right of the translating tropical cyclone the extensive in situ buoy database confirms previous studies indicating that the one dimensional spectra are generally unimodal the directional spectra are however directionally skewed consisting of remotely generated waves radiating out from the center of the storm and locally generated wind sea the one dimensional wave spectra have many similarities to fetch limited cases although for a given peak frequency the spectra contain less energy than for a fetch limited case this result is consistent with the fact that much of the wave field is dominated by remotely generated waves

propagation directions of ocean surface waves inside tropical cyclones abstractsurface wave propagation inside tropical cyclones tcs is complicated and multiple wave systems are frequently observed the directional wave spectra acquired by hurricane hunters are analyzed to quantify its azimuthal and radial variations referenced to the hurricane heading the dominate feature in the front half of the tc coverage area is single wave systems propagating toward left and left front multiple wave systems are generally observed in the back and right quarters outside the radius of maximum wind rmw the directional differences and locations of occurrences of multisystem spectra are gaussian distributed the directional differences of the secondary and tertiary wave systems from the primary system are centered around 60 70 the minor systems are more likely on the left hand side of the primary system than on the right hand side by a 3 to 1 ratio the most likely azimuthal location of multisystem spectra is about 210 counterclockwise from the heading in the right front quarter

polynya dynamics a review of observations and modeling 1 polynyas are nonlinear shaped openings within the ice cover ranging in size from 10 to 105 km2 polynyas play an important climatic role first winter polynyas tend to warm the atmosphere thus affecting atmospheric mesoscale motions second ocean surface cooling and brine rejection during sea ice growth in polynyas lead to vertical mixing and convection contributing to the transformation of intermediate and deep waters in the global ocean and the maintenance of the oceanic overturning circulation since 1990 there has been an upsurge in polynya observations and theoretical models for polynya formation and their impact on the biogeochemistry of the polar seas this article reviews polynya research carried out in the last 2 decades focusing on presenting a state of the art picture of the physical interactions between polynyas and the atmosphere sea ice ocean system observational and modeling studies the surface heat budget and water mass transformation within these features are addressed

eddy shedding from a boundary current around a cape over a sloping bottom abstract the authors discuss laboratory experiments that elucidate the mechanism of formation and westward drift of anticyclonic baroclinic vortices from a buoyant surface current flowing along a lateral boundary and around a cape experiments were carried out with a sloping bottom in order to simulate the topographic effect they showed how a vortex can be generated from the current where it separates and reattaches to the cape and that under some conditions the eddy is able to detach from the cape and drift westward following isobaths two important timescales regulate the flow the time tf that the current takes to generate a vortex and the time td that the vortex takes to drift westward for a distance equal to its radius when these two timescales are either of the same order of magnitude or tf td the vortex was able to form at the cape but it did not detach and drift westward the influence of the depth of the lower layer h0 on the flo

directional spectra of hurricane generated waves in the gulf of mexico 1 hurricane induced directional wave spectra in the gulf of mexico are investigated based on the measurements collected at 12 buoys during 7 hurricane events in recent years focusing on hurricane generated wave spectra we only consider the wave measurements at the buoys within eight times the radius of the hurricane maximum wind speed rmax from the hurricane center a series of numerical experiments using a third generation spectral wave prediction model were carried out to gain insight into the mechanism controlling the directional and frequency distributions of hurricane wave energy it is found that hurricane wave spectra are almost swell dominated except for the right rear quadrant of a hurricane with respect to the forward direction where the local strong winds control the spectra despite the complexity of a hurricane wind field most of the spectra are mono modal similar to those under fetch limited unidirectional winds however bi modal spectra were also found in both measurements and model results four types of bi modal spectra have been observed type i happens far away 6 rmax from a hurricane type ii is bi modal in frequency with significant differences in direction it happens in the two left quadrants when the direction of hurricane winds deviates considerably from the swell direction type iii is bi modal in frequency in almost the same wave direction with two close peaks it occurs when the energy of locally generated wind sea is only partially transferred to the swell energy by non linear wave wave interactions type iv was observed in shallow waters owing to coastal effects

offshore transport of dense shelf water in the presence of a submarine canyon the formation and offshore transport of dense water over a uniformly sloping shelf crosscut by a submarine canyon is examined using a three dimensional primitive equation numerical model a constant negative buoyancy flux is applied in a limited region adjacent to a straight coast to represent brine rejection from ice production in an idealized coastal polynya a sharp density front forms at the edge of the forcing region with surface and bottom intensified jets along the front the flow around the head of the submarine canyon triggers a frontal instability that initially grows only on one side of the canyon the unstable waves on the other side of the canyon are blocked by a localized barotropic flow that develops near the canyon head unstable waves also grow where the forcing region intersects the coast the frontal waves grow rapidly with o 1 day e folding timescales and form eddies with horizontal scales of o 15 km which extract the densest water from the forcing region and carry it offshore directly across isobaths in this way the eddies limit the maximum water density that appears in the model despite continued negative buoyancy forcing some dense water descends into the canyon forming a bottom trapped plume that transports the dense water offshore ahead of the eddies the plume moves relatively slowly i e small froude number with little turbulent entrainment so the advancement and structure of the plume nose can be described successfully as a simple gravity current with an advective diffusive heat balance eddies may slump into the canyon from the side altering both the density anomaly and speed of the canyon plume suggesting that canyon plumes are likely to be highly variable in both space and time

sir b observations of dominant ocean waves near hurricane josephine radar images of ocean surface waves near hurricane josephine were acquired with the shuttle imaging radar b sir b system on october 12 1984 fast fourier transform analyses of the images have been performed along most of the 600 km image track these data reveal the presence of at least two dominant wave systems which undergo significant spatial variations in wavelength and direction

on the importance of surface forcing in conceptual models of the deep ocean in the major ocean basins diapycnal mixing upwells dense antarctic bottom water which returns southward and closes the deepest cell of the meridional overturning circulation moc this cell ventilates the deep ocean and regulates the partitioning of co2 between the atmosphere and the ocean the oceanographic community s conceptual understanding of the deep stratification and moc has evolved from classic abyssal recipes arguments to a more recent appreciation of along isopycnal upwelling in the southern ocean consistent with a weakly mixed ocean interior both the deep stratification and the deep moc are shown here to be sensitive to the form of the surface buoyancy forcing in a two dimensional model that includes a circumpolar channel and northern basin for a fixed surface buoyancy condition the deep stratification is essentially prescribed whereas for a fixed surface buoyancy flux the deep stratification varies by orders of magnitude over the range of diapycnal diffusivity observed in the ocean these cases also produce different scalings for the deep moc with in both weak and strong regimes in addition these scalings are shown to be sensitive not only to the type of surface boundary condition but also to the latitudinal structure of the surface fluxes this latter point is crucial as buoyancy budgets and dynamical features of the circulation are poorly constrained along the antarctic margins this study emphasizes the need for caution in the interpretation of simple conceptual models that while useful may not include all mechanisms that contribute to the moc s strength and structure

numerical simulation of the filchner overflow the plume of ice shelf water isw flowing into the weddell sea over the filchner sill contributes to the formation of antarctic bottom water the filchner overflow is simulated using a hydrostatic primitive equation three dimensional ocean model with a 0 5 2 sv isw influx above the filchner sill the best fit to mooring temperature observations is found with influxes of 0 5 and 1 sv below a previous estimate of 1 6 0 5 sv based on sparse mooring velocities the plume first moves north over the continental shelf and then turns west along slope of the continental shelf break where it breaks up into subplumes and domes some of which then move downslope other subplumes run into the eastern submarine ridge and propagate along the ridge downslope in a chaotic manner the next western ridge is crossed by the plume through several paths despite a number of discrepancies with observational data the model reproduces many attributes of the flow in particular we argue that the temporal variability shown by the observations can largely be attributed to the unstable structure of the flow where the temperature fluctuations are determined by the motion of the domes past the moorings our sensitivity studies show that while thermobaricity plays a role its effect is small for the flows considered smoothing the ridges out demonstrate that their presence strongly affects the plume shape around the ridges an increase in the bottom drag or viscosity leads to slowing down and hence thickening and widening of the plume

katabatic wind forcing of the terra nova bay polynya the terra nova bay polynya is a perennial winter feature in the western ross sea antarctica which occupies roughly 1000 km2 it is formed and maintained by the combined influence of persistent katabatic winds which advect newly formed bay ice eastward and the drygalski ice tongue which prevents northward drifting pack ice from entering terra nova bay existence of anomalously strong katabatic drainage along this coast is predicted by parish s 1982 simulation of wintertime airflow which reveals a pronounced confluence of surface winds upslope from the reeves glacier where the winds are further focused by local topography the simulation is strongly supported by regional sastrugi orientations average wintertime atmospheric conditions and ice sheet topography which control surface air drainage are stable on a climatic time scale therefore persistent wintertime katabatic winds should be an annual phenomenon further evidence comes from multi year landsat images which consistently show windswept snowfree areas on the reeves glacier in marked contrast to typical antarctic katabatic winds strong persistent winter winds are observed at sea level 25 km beyond the coastal slope break air probably descends as bora type winds and is likely to be significantly denser than the air at sea level conditions are not favorable for hydraulic jumps apparently typical of other katabatic regimes the horizontal density difference is maintained during airflow across the nansen ice sheet because relatively little air mass modification occurs there in contrast to situations where air moves over an ice laden ocean observations thus suggest that katabatic winds maintain their identity for some distance seaward of the coast qualitative trajectory calculations indicate that for representative geostrophic conditions this distance is on the order of the observed polynya width estimated ice freezing rates are 20 cm day 1 but wind generated waves and currents prevent ice from consolidating the blocking effect of the drygalski ice tongue is a consequence of its orientation with regard to western ross sea ice drift patterns ice tongue length controls polynya width absence of such blocking along other coasts experiencing strong katabatic outflow partly explains why similar polynyas do not form there

recurring polynyas over the cosmonaut sea and the maud rise two polynyas over the deep ocean were observed in the antarctic region during the winter of 1980 one near 43 e 66 s cosmonaut polynya and another near 2 e 64 s maud rise polynya the time history of these two polynyas was examined on an alternate day basis using ice concentration maps from the nimbus 7 scanning multichannel microwave radiometer smmr a quantitative analysis of a study area around it shows that the totally enclosed cosmonaut polynya attained a maximum size on july 25 1980 with an open water area of as much as 137 700 km2 this polynya lasted for a few weeks disappeared on august 16 1980 and was not observed for the rest of the winter similar polynyas in the same region have occurred for several years including 1973 1975 1979 1982 and 1986 the maud rise polynya on the other hand was observed as a reduction in ice concentration to about 37 within the smmr resolution of about 900 km2 however the open water area in the region amounted to 92 800 km2 on july 20 and the polynya recurred several times during the same winter period it is proposed that both polynyas are products of deep reaching convection which introduces warmer deep water into the surface layer in this way they are viewed as sensible heat polynyas in that they are maintained by oceanic heat the oceanographic settings of these two polynyas are similar the hydrographic data at both sites indicate the existence of localized doming of the pycnocline this brings warmer saltier deep water closer to the sea surface which has been demonstrated to be an effective preconditioner for deep reaching convection it is probable that the polynyas are terminated by invasion of sea ice from the sides which attenuates convection the capability of a polynya to survive an entire winter period may be related to its size the larger polynyas are better protected from convergence of the surrounding sea ice for example a simple model shows that a polynya with a diameter of about 100 km or greater is much more likely to survive a winter season than a smaller one

on the baroclinic instability of cold core coupled density fronts on a sloping continental shelf a theory is presented to describe the linear baroclinic instability of coupled density fronts on a sloping continental shelf the new baroclinic model equations used to study the instability process correspond to an intermediate lengthscale dynamical balance specifically the frontal dynamics while geostrophic is not quasigeostrophic because frontal height deflections are not small in comparison with the frontal scale height the evolution of the frontal height is strongly coupled to the geostrophic pressure in the surrounding slope water through the hydrostatic balance which expresses the continuity of the dynamic pressures across the frontal interface the deeper surrounding slope water evolves quasi geostrophically and is coupled to the front by baroclinic vortex tube stretching compression associated with the perturbed density front allowing the release of mean frontal potential energy and the topographic vorticity gradient associated with the sloping bottom it is shown that the baroclinic stability characteristics are principally determined by a so called non dimensional interaction parameter denoted p which physically measures the ratio of the destabilizing baroclinic vortex tube stretching compression to the stabilizing topographic vorticity gradient for a given along front mode wavenumber it is shown that a minimum p is required for instability several other general stability results are presented necessary conditions for instability growth rate and phase speed bounds the existence of a high wavenumber cutoff and a semicircle theorem for the unstable modes the linear stability equations are solved exactly for a parabolic coupled density front and a detailed description of the spatial and temporal characteristics of the instabilities is given for physically realistic parameter values the instabilities are manifested as amplifying topographic rossby waves in the slope water and on the density front the unstable perturbations take the form of amplifying anticyclones which have maximum amplitude on the offshore side

hurricane directional wave spectrum spatial variation in the open ocean abstract the sea surface directional wave spectrum was measured for the first time in all quadrants of a hurricane s inner core over open water the nasa airborne scanning radar altimeter sra carried aboard one of the noaa wp 3d hurricane research aircraft at 1 5 km height acquired the open ocean data on 24 august 1998 when bonnie a large hurricane with 1 min sustained surface winds of nearly 50 m s 1 was about 400 km east of abaco island bahamas the noaa aircraft spent more than five hours within 180 km of the eye and made five eye penetrations grayscale coded images of hurricane bonnie wave topography include individual waves as high as 19 m peak to trough the dominant waves generally propagated at significant angles to the downwind direction at some positions three different wave fields of comparable energy crossed each other partitioning the sra directional wave spectra enabled determination of the characteristics of the various components of the hurricane wave field and mapping of their sp

generation of submesoscale vortices a new mechanism small scale intense vortices composed of water with anomalous values of quasi conservative tracers have been observed in many oceans they are particularly numerous in the beaufort gyre of the arctic ocean possible mechanisms responsible for the generation of these features are examined conservation of temperature salinity and nutrients requires that beaufort sea vortices be created from water that flows into the arctic ocean from the pacific ocean across the broad shallow chukchi sea much of this water passes through barrow canyon near point barrow alaska observations in the canyon show the generation of vortices of approximately the same size as those observed in the beaufort sea barrow canyon is therefore a likely site for the generation of beaufort sea vortices most observed beaufort sea vortices have a central potential vorticity near zero because of a relative vorticity close to their chukchi sea source water is typically stratified with little relative vorticity so that its potential vorticity is nonzero a key step in the generation of the vortices is therefore the reduction of the potential vorticity of chukchi sea water to nearly zero it is proposed that this occurs through the action of frictional torques occurring as the chukchi sea water flows through barrow canyon rather than througji the action of vertical mixing because this flow is driven by a downstream pressure gradient it is concentrated on the right hand wall of the canyon by the coriolis force the frictional torques thus preferentially reduce the potential vorticity of the fluid anticyclonic vortices are therefore preferentially generated it is suggested that a similar scenario may play a role in the generation of submesoscale vortices containing water from the mediterranean and labrador seas

generation of a buoyancy driven coastal current by an antarctic polynya descent and spreading of high salinity water generated by salt rejection during sea ice formation in an antarctic coastal polynya is studied using a hydrostatic primitive equation three dimensional ocean model called the proudman oceanographic laboratory coastal ocean modeling system polcoms the shape of the polynya is assumed to be a rectangle 100 km long and 30 km wide and the salinity flux into the polynya at its surface is constant the model has been run at high horizontal spatial resolution 500 m and numerical simulations reveal a buoyancy driven coastal current the coastal current is a robust feature and appears in a range of simulations designed to investigate the influence of a sloping bottom variable bottom drag variable vertical turbulent diffusivities higher salinity flux and an offshore position of the polynya it is shown that bottom drag is the main factor determining the current width this coastal current has not been produced with other numerical models of polynyas which may be because these models were run at coarser resolutions the coastal current becomes unstable upstream of its front when the polynya is adjacent to the coast when the polynya is situated offshore an unstable current is produced from its outset owing to the capture of cyclonic eddies the effect of a coastal protrusion and a canyon on the current motion is investigated in particular due to the convex shape of the coastal protrusion the current sheds a dipolar eddy

on mertz and ninnis glaciers east antarctica two large glacier tongues which extend substantially across the coastline of king george v land in east antarctica have been studied by remote sensing synthetic aperture radar jers 1 the tongue of mertz glacier is in a state of advance while the ninnis glacier tongue is retreating some more specific points are the distinctive surface structure and the form of the glacier tongues indicates that they are floating while the tongue of ninnis glacier has lost about two thirds of its area since 1913 the mertz glacier tongue has advanced substantially and has about doubled its areal extent over the same time period the annual movement of the tongue of mertz glacier was determined as about 1 2 km this is close to the value of the advance of the tip of the tongue since 1963 which was determined as 0 9 km year 1

the surface windfield over the antarctic ice sheets the intense radiative cooling of air over the ice slopes of antarctica generates a surface wind regime that is strongly controlled by topography and plays a key role in determining the behaviour of the atmosphere and ocean in high southern latitudes1 7 resultant surface winds are intimately linked to the orientation of the ice terrain fig 1 and display the highest degree of persistence found on earth the close coupling between wind and topography allows estimation of the former if the latter is known with some precision here we report on time averaged near surface airflow over the antarctic continent during winter diagnosed from a recent accurate synthesis of terrain slopes and from estimates of the lower atmospheric temperature structure the simulated drainage pat tern exhibits strong spatial variability with the airflow concentrated into several zones near the coastal margin these confluence regions are responsible for strong persistent katabatic winds over downstream coastal stretches and are indicative of zones of greatest katabatic potential

cosmonaut polynya in the southern ocean structure and variability along the far eastern margin of the weddell gyre is a persistent feature in the middle of the ice pack which we previously reported and called the cosmonaut polynya a study of polynya occurrences from 1973 to 1993 reveals that since 1986 the polynya has become more active with an average size of about 7 2 104 km2 and an average location at 52 e and 65 s satellite observations indicate that the polynya has recurred several times during winter in recent years with intervals ranging from a few days to a few weeks the centroid of the polynya varies only slightly with each formation during the year and from one year to another suggesting a controlling influence of the ocean and bottom topography that may be initially induced by wind the daily time series indicates two primary modes of formation one that is initiated in the early winter during a storm at a site usually preceded by an embayment of the ice edge and another that occurs during midwinter often preceded by a coastal polynya event adjacent to cape ann the cosmonaut polynya region is characterized in this study by compression of the westward flowing coastal current and the eastward flowing southern edge of the antarctic circumpolar current following the principle of conservation of potential vorticity vertical stretching of the water column would ensue enhancing upwelling such a process accelerates the injection of relatively warm salty deep water into the surface layer inhibiting sea ice growth and causing the polynya formation this theory appears to explain the general behavior of the polynya in terms of frequency duration size and location

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

a latent and sensible heat polynya model for the north water northern baffin bay abstract the pease latent heat polynya model is coupled to a reduced gravity coastal upwelling model in order to simulate the formation and maintenance of the north water now the arctic s largest polynya located in northern beffin bay in this region strong northerly winds during winter and spring drive ice southward as fast as it is produced locally the pease mechanism for polynya formation and also produce upwelling of warm subsurface water along the west coast of greenland this upwelling provides an upward heat flux that melts ice near the coast a sensible host mechanism for polynya formation this combined latent and sensible heat polynya model is formulated as an initial boundary value problem with uniform winds its solution gives the tide evolution of the upper layer velocity and depth and also the polynya width as measured southward from the northern boundary of the polynya there are two fundamental time scales in the problem a fast one of the order of days that characterizes the

on the influence of coastline orientation on the steady state width of a latent heat polynya this paper investigates under what conditions the steady state shape of a coastal latent heat polynya is influenced by 1 the direction of flow of free drifting frazil ice and the consolidated offshore ice sheet and 2 coastline orientation analytical solutions are obtained for coastal polynyas when the coastline is straight and when a coastline has a single step from the solutions it is shown that the asymptotic polynya width is given by the generalized pease 1987 width l cos where l is the classical pease width and is the angle between the consolidated ice sheet velocity and the normal to the coastline an expression is also obtained for the alongshore length scale l c over which the polynya adjusts toward its asymptotic width and it is shown that l c depends upon the directions of travel of the frazil ice and the consolidated ice sheet when the frazil ice and the consolidated ice sheet both drift offshore normal to the coast l c 0 in agreement with the classical pease theory variations in the coastline which occur on a length scale much smaller than l c are not reproduced in the polynya shape two numerical simulations are presented for terra nova bay antarctica and the st lawrence island polynya in the bering sea both examples employ realistic coastline geometry and information about the direction of drift of the consolidated ice sheet in each example a realistic polynya shape is obtained the examples highlight the versatility of the model because in the former case the ice sheet drifts almost parallel to the coast while in the latter it drifts offshore

the distribution and formative processes of latent heat polynyas in east antarctica a study of polynya characteristics in east antarctica was undertaken using ice concentrations derived from special sensor microwave imager data for the period july 1987 august 1994 the areas of polynyas were defined as having an ice concentration 75 the analysis revealed a total of 28 coastal polynyas within the study region the spatial and temporal variability in areal extent was quantified the timing of mean maximum areal extent varied from june to october the bathymetry and wind regime at each polynya site was examined to gauge the relative importance of these parameters in polynya formation and maintenance in 20 locations shallow banks and shoals form grounding zones for icebergs and anchoring sites for fast ice which form barriers to the predominantly westward drift of the pack ice elsewhere north south coastal protrusions or alignments form similar barriers the subsequent removal of newly formed sea ice from the lee of such barriers by katabatic and synoptic winds maintains areas of reduced ice concentration and open water very few coastal polynyas are attributed solely to katabatic outflow the combined influence of bathymetry topography and winds is responsible for the characteristics of the majority of polynyas many were considered to be marginal characterised by occasional periods when the ice concentration falls below 75 an analysis of annual winter totals of areas with ice concentrations 75 shows no trends in total polynya areal extent over the period 1987 94 known locations of emperor penguin aptenodytes forsteri rookeries were also found to be associated with the locations of coastal polynyas

a numerical study on the successive formation of meddy like lenses 1 we present a process study on the sustaining mechanism of lens formation using a series of numerical experiments of a density current over a sloping bottom with a cape along the coastline water parcels in the bottom density current are shed into the offshore region leading to periodic formation of anticyclonic lenses as part of baroclinic dipolar vortices the cyclonic partner is more prominent at the surface and the coupled vortices are carried by the mean current established in the offshore region parameter dependence of dipole generation is examined which suggests that the background current is necessary for the detached eddies to be coherent in the downstream direction and for shedding events to repeat nof and pichevin 1996 it is also shown that the density mixing of the bottom current provides criteria for cyclogenesis at the sea surface a detailed analysis is given by a five layer model forced by a water mass source sink which reproduces the baroclinic dipolar vortices similar to those observed in the preceding z coordinate model we find that the dipole generation is due to the finite amplitude divergence convergence of the baroclinic current passing the cape stern and chassignet 2000 the overall analyses suggest three necessary conditions for successive eddy formation 1 a localized variation in the coastline causing the finite amplitude disturbance 2 mixing of mediterranean water with the surrounding fluids leading to anticyclonic rotation of meddies as well as cyclogenesis at the surface and 3 background currents that advect the detached vortices out of the source region index terms 4255 oceanography general numerical modeling 4219 oceanography general continental shelf processes 4520 oceanography physical eddies and mesoscale processes 4528 oceanography physical fronts and jets keywords eddy shedding dense water plume numerical simulation

wave current interaction between hurricane matthew wave fields and the gulf stream abstracthurricanes interact with the gulf stream in the south atlantic bight sab through a wide variety of processes which are crucial to understand for prediction of open ocean and coastal haza

wind effects on the buoyancy driven general circulation in a closed basin using a two level model abstract wind effects on buoyancy driven circulation in a two level rectangular basin are studied the ocean is driven by positive and negative buoyancy fluxes in the northern and southern portions as well as wind stress of constant curl in a model with a flat and frictionless bottom a barotropic component is determined only by wind forcing a baroclinic component of the wind driven circulation associated with horizontal density gradient is reduced by horizontal diffusion i e the wind driven circulation is more barotropic with stronger diffusion meridional overturn induced by buoyancy fluxes is modified by the wind driven circulation for example the southward upper level flow produced by positive and negative buoyancy fluxes in the northern and southern portions greatly shifts to the western eastern boundary by cyclonic anticyclonic wind driven circulation with realistic intensity relative importance of the wind driven circulation to the buoyancy driven circulation for meridional density

temperature structure and characteristics appearing on ssm i images of the cosmonaut sea antarctica water temperature structure in the cosmonaut sea at 60 68 s 35 65 e in 1987 92 shows that cold water with a temperature below 1 5 c was present in the coastal region the circumpolar deep water with a temperature higher than 1 0 c was found below about 150m depth from northeast to northwest of the cold water area the ssm i images in 1987 91 indicate that polynya activities were intensive in 1988 and the typical cosmonaut polynya was observed due to weaker activities the small and sporadic cosmonaut polynya formed in 1987 1989 1990 and 1991 a coastal polynya was frequently observed every year at about 66 s 50 60 e a train of polynyas to the east of cosmonaut polynya often appeared it is considered that the atmospheric convergence line and antarctic divergence region are responsible for polynya activities in the cosmonaut sea

factor analysis of engineering geophysical sounding data for water saturation estimation in shallow formations abstractthe engineering geophysical sounding method has been applied for in situ investigation of unconsolidated near surface formations since the 1990s in this study we offer an alternative to geophysical inversion methods for data processing factor analysis is applied to engineering geophysical sounding and cone penetration test data to extract information on water saturation of the shallow region a linear correlation is indicated between water saturation and one of the new variables derived by factor analysis we used a general formula for estimating water saturation and applied it on data measured in 12 shallow boreholes situated over a nuclear waste disposal site we extended the statistical procedure to estimate the spatial distribution of water air saturation between the boreholes we compared the statistical results to inversion estimations the study showed that factor analysis gives a quick and reliable solution for the assessment of hydrogeological conditions in shallow prospecting sites

observations of a street of cyclonic eddies in the indian ocean sector of the antarctic divergence hydrographic and drifting buoy data from japanese cruises show that the antarctic divergence in the indian ocean sector is composed of a street of cyclonic eddies these eddies measure about 500 km in the zonal direction and 200 km in the meridional part of the eastward flowing antarctic circumpolar current acc meanders southward in the regions between the eddies in the eddy regions warm saline circumpolar deep water is upwelled into the shallow layers while cold dense coastal water advects into the deep layers the advection occurs along the isobaths of ridges which extend north from the coast the combination of the advection with the upwelling produces a water column denser than the surrounding water and leads to the formation and maintenance of the cyclonic eddies presence of the northward extending ridges approximately governs the location of eddy formation the eddy formation recurs year after year although eddy locations can vary somewhat a polynya was observed to persistently occur and corresponded with one of the eddies in location size and form the oceanographic observations also suggest that the primary meridional exchanges of heat and salt in the antarctic are caused through the eddies and acc meanders within the antarctic divergence

hurricane directional wave spectrum spatial variation at landfall abstract the nasa scanning radar altimeter sra flew aboard one of the noaa wp 3d hurricane research aircraft to document the sea surface directional wave spectrum in the region between charleston south carolina and cape hatteras north carolina as hurricane bonnie was making landfall near wilmington north carolina on 26 august 1998 two days earlier the sra had documented the hurricane wave field spatial variation in open water when bonnie was 400 km east of abaco island bahamas bonnie was similar in size during the two flights the maximum wind speed was lower during the landfall flight 39 m s 1 than it had been during the first flight 46 m s 1 also bonnie was moving faster prior to landfall 9 5 m s 1 than when it was encountered in the open ocean 5 m s 1 the open ocean wave height spatial variation indicated that hurricane bonnie would have produced waves of 10 m height on the shore northeast of wilmington had it not been for the continental shelf the gradual shoaling distributed t

cascades of dense water around the world ocean dense water overflow off continental shelves cascading is one of the contributing processes of shelf deep ocean exchange and of topical interest to climate studies and nutrient fluxes dense water originating from cooling evaporation freezing and salinization on a shallow shelf spills over the shelf edge and may develop as near bottom gravity current or an intermediate depth intrusion it is difficult to observe in nature due to its intermittent character this paper provides an extensive inventory of observed cases of water cascades around the world ocean summarises their locations and individual properties and provides statistics of the identified cases the search for cascading was carried out using oceanographic databases and a literature review this study identified 61 confirmed cases world wide including 25 cases in the arctic seas 12 at mid latitudes seven in sub tropical and tropical regions and 17 off the antarctic shelves eighteen cascades had not been reported before we analyze a set of numerical parameters of dense water cascades allowing us to quantify compare and contrast the properties of water cascades the overall average density contrast between the confirmed cascades and ambient water is 0 37 kg m3 it can be as much as 2 kg m3 on some arctic shelves frequently initiated by strong cooling at the surface cascades often remain colder through the descent thus supplying the deep ocean with colder and fresher water in non dimensional variables the data from all climate zones fit well to a unique curve which represents a relationship between a cascade s internal structure and the parameters describing its forcing on average the down slope volumetric flux provided by dense water cascades is estimated as 0 05 to 0 08 sv per 100 km of shelf edge regional terms arctic antarctic north atlantic ocean barents sea mediterranean sea skagerrak tasman sea sea of okhotsk

heat flux partitioning in open ocean convection abstract cold air blowing out over a warm ocean leads to convection over an isolated region of the ocean basin this phenomenon known as open ocean convection is often simulated by convective forcing from a circular disk much smaller than the dimension of the domain an important feature of these simulations is the development of eddies at the edge of the disk that serve to transport heat horizontally this has sparked interest in the heat flux characteristics of such a system this paper deals with the thermodynamic properties of this type of convective flow using a rotating tank with bottom mounted hotplate as the experimental apparatus experiments are performed in an initially unstratified fluid for a set of values of the nondimensional forcing parameter rc b1 2 hf3 2 where b is the buoyancy flux h is the fluid depth and f is the coriolis parameter the ratio of the frontal eddy size to the hotplate radius is shown to be an important parameter the experiments reported are for the regi

a numerical investigation of the transport process of dense shelf water from a continental shelf to a slope we investigate the offshore transport process of dense shelf water using a three dimensional primitive equation model we focus on the effects of bottom a dee topography in particular inclination of a bottom slope from a continental shelf to a deep basin for the numerical domain we use an idealized bottom topography in which the bottom deepens gradually from a shallow continental shelf region to a steep slope region in the continental shelf region we use a salt flux which represents the typical brine rejection in a coastal polynya results of the numerical experiments show that dense shelf water is transported offshore by eddy flux and a dense plume the transport by eddy flux occurs mainly over a continental shelf while that by the dense plume occurs over a continental slope a boundary between the regions where the above two processes are dominant corresponds locally to a shelf break a salinity front is developed in the boundary over the shelf break separating the dense shelf water from the offshore water we also investigate the stability of the surface westward current over the shelf break front using a simple analytical model the analytical model investigation shows that shelf break topography plays an important role in determining a neutral point of the stability of the shelf break current and preventing dense shelf water from being transported farther offshore by eddy flux we suggest that eddy activity on a continental shelf contributes not only to the development of the shelf break front but also to the water exchange between a continental shelf and a slope region

three dimensional simulations of overflows on continental slopes abstract three dimensional features and instabilities of dense overflows from marginal seas onto continental slopes are investigated using a three dimensional primitive equation numerical ocean model the numerical simulations reveal important instability and three dimensional features of the overflow plumes that have not been included in previous simulations with a one dimensional streamtube model and a two dimensional plume model it is shown that the large primary plume breaks into a number of smaller subplumes on the offshore side of the plume due to instabilities manifested as growing topographic rossby waves over the slope the observed high temporal and spatial variabilities in the denmark strait overflow could be caused by the inherent dynamic instabilities as revealed by the numerical simulations the simulations indicate that the initial overflow velocity and width the properties of the source water the planetary rotation and the slope steepness play major roles in determining the scales of

effects of along shore wind on dsw formation beneath coastal polynyas application to the sea of okhotsk 1 it is known that salinity anomaly under a polynya reaches and remains an equilibrium value s after termination of its initial increase associated with brine rejection at the surface in this paper we investigate effect of along shore downwelling favorable wind on the equilibrium salinity anomaly by idealized numerical calculations and scale based estimates numerical calculations showed that high saline water beneath polynya is advected downstream by wind driven circulations over the shelf besides baroclinically developed eddies which consequently induces a decrease in s beneath polynya the downwelling favorable wind generates an offshore overturning flow through lower layers referred to as ekman compensation flow ecf which causes a great offshore salinity flux as well as an along shore current we also constructed an equation for estimation of s from the viewpoint of salinity budget over the polynya region in which lateral salinity fluxes caused by ecf along shore wind driven current and baroclinic eddies are scaled the solution s was also verified by a series of numerical calculations furthermore we investigated the effects of along shore wind on dense water generation beneath the okhotsk coastal polynyas we conducted simplified numerical experiments assuming the okhotsk situation in which fs and offshore width b of polynya are predicted by a thermodynamic polynya model with ecmwf meteorological variables the simulated salinity shows a good agreement with the direct measurements the theoretical estimates for s was also applied to two okhotsk polynyas northwestern polynya nwp and northern polynya np in conclusion we found that the along shore wind causes greater salinity decrease in np than in nwp whose variations substantially depend on the aleutian low activity

a numerical study of dense water formation and transport on a shallow sloping continental shelf the circulation and transport of dense water generated by an idealized coastal polynya is studied using a three dimensional primitive equation model starting with a homogeneous quiescent ocean a constant negative buoyancy flux is imposed at the surface over a half elliptical region adjacent to the coastal boundary on a gently sloping continental shelf the flow response can be divided into the following three phases geostrophic adjustment instability and offshore eddy transport during geostrophic adjustment the fluid within the forcing region becomes denser and the flow at the edge of the forcing region accelerates in response to the strong density gradient there eventually the flow at the leading edge of the forcing region relative to kelvin wave propagation becomes unstable and a train of counterrotating eddies develops these eddies then form a complex three dimensional flow field and rapidly transport dense water offshore across isobaths the density within the forcing region reaches a maximum which remains fairly constant after the eddies begin to transport the dense fluid offshore the results are qualitatively insensitive to weakening of the negative buoyancy forcing and to changing the bottom slope eddy scales and velocities are consistent with observations in the arctic the results suggest that instability processes and eddy fluxes are important in transporting dense water off continental shelves and into marginal seas

a freshwater jet on the east greenland shelf in august 1997 rrs discovery cruise 230 world ocean circulation experiment woce section a25 ran a hydrographic section into cape farewell on the southern tip of greenland the closest approach to the shore was 2 nm in a water depth of 160 m over the east greenland shelf analysis of the hydrographic data conductivity temperature depth ctd vessel mounted acoustic doppler current profiler and thermosalinograph has revealed a current flowing southwestward 15 km wide 100 m deep and centered 10 km offshore we believe it to be driven by meltwater runoff from greenland this feature which we call the east greenland coastal current egcc carries a little less than 1 sv 106 m3 s 1 with peak current speeds of 1 m s 1 at the surface the center of the egcc lies on a salinity front with maximum salinity contrast 4 practical salinity units psu between coast and shelf break and between surface and bottom a spot value of freshwater transport is 0 06 sv 1800 km3 yr 1 which is equivalent to 30 of the arctic freshwater gain the presence of the egcc and its continuity up the east greenland coast as far as denmark strait is confirmed in satellite sea surface temperature images and surface drifter tracks we estimate the sensitivity of its freshwater flux to changes in melt season mean surface air temperature to be 25 per 1 c

wind and waves in extreme hurricanes waves breaking at the ocean surface are important to the dynamical chemical and biological processes at the air sea interface the traditional view is that the white capping and aero dynamical surface roughness increase with wind speed up to a limiting value this view is fundamental to hurricane forecasting and climate research but it has never been verified at extreme winds here we show with observations that at high wind speeds white caps remain constant and at still higher wind speeds are joined and increasingly dominated by streaks of foam and spray at surface wind speeds of 40 m s the streaks merge into a white out the roughness begins to decrease and a high velocity surface jet begins to develop the roughness reduces to virtually zero by 80 m s wind speed rendering the surface aero dynamically extremely smooth in the most intense part of extreme or major hurricanes wind speed 50 m s a preliminary assessment shows that cross swell dominant in large regions of hurricanes allows the roughness under high wind conditions to increase considerably before it reduces to the same low values

joint inversion of seismic and geoelectric data recorded in an underground coal mine1 until the present time the rock coal rock layer sequence and offsets in coal seams in underground coal mines have been detected with the aid of seismic waves and geoelectric measurements in order to determine the geometrical and petrophysical parameters of the coal seam situation the data recorded using seismic and geoelectric methods have been inverted independently in consequence the inversion of partially inaccurate data resulted in a certain degree of ambiguity this paper presents the first results of a joint inversion scheme to process underground vertical seismic profiling data geolectric resistivity and resistance data the joint inversion algorithm makes use of the damped least squares method and its weighted version to solve the linearized set of equations for the seismic and geolectric unknowns in order to estimate the accuracy and reliability of the derived geometrical and petrophysical layer parameters both a model covariance matrix and a correlation matrix are calculated the weighted least squares algorithm is based on the method of most frequent values mfv the weight factors depend on the difference between measured data and those calculated by an iteration process the joint inversion algorithm is tested by means of synthetic data compared to the damped least squares algorithm the mfv inversion leads to smaller estimation errors as well as lower sensitivities due to the choice of the initial model it is shown that compared to an independent inversion the correlation between the model parameters is definitely reduced while the accuracy of the parameter estimation is appreciably increased by the joint inversion process thus the ambiguity is significantly reduced finally the joint inversion algorithm the mfv method is applied to underground field data the model parameters can be derived with a sufficient degree of accuracy even in the case of noisy data

most frequent value based factor analysis of direct push logging data an improved iteratively re weighted factor analysis procedure is presented to interpret engineering geophysical sounding logs in shallow unsaturated sediments we simultaneously process cone resistance electric resistivity and nuclear data acquired by direct push tools to give robust estimates of factor variables and water content in unconsolidated heterogeneous formations the statistical procedure is based on the iterative re weighting of the deviations between the measured and calculated data using the most frequent value method famous for its robustness and high statistical efficiency the iterative approach improves the result of factor analysis for not normally distributed data and extremely noisy measurements by detecting a strong regression relation between one of the extracted factors and the fractional volume of water we establish an independent method for water content estimation along the penetration hole we verify the estimated values of water volume by using a highly overdetermined quality checked interval inversion procedure the multidimensional extension of the statistical method allows the estimation of water content distribution along both the vertical and horizontal coordinates numerical tests using engineering geophysical sounding data measured in a hungarian loessy sandy formation demonstrate the feasibility of the most frequent value based factor analysis which can be efficiently used for a more reliable hydrogeophysical characterization of the unsaturated zone this article is protected by copyright all rights reserved

the dispersal of dense water formed in an idealized coastal polynya on a shallow sloping shelf abstractthis study examines the dispersal of dense water formed in an idealized coastal polynya on a sloping shelf in the absence of ambient circulation and stratification both numerical and laboratory experiments reveal two separate bottom pathways for the dense water an offshore plume moving downslope into deeper ambient water and a coastal current flowing in the direction of kelvin wave propagation scaling analysis shows that the velocity of the offshore plume is proportional not only to the reduced gravity bottom slope and inverse of the coriolis parameter but also to the ratio of the dense water depth to total water depth the dense water coastal current is generated by the along shelf baroclinic pressure gradient its dynamics can be separated into two stages i near the source region where viscous terms are negligible its speed is proportional to the reduced gravity wave speed and ii in the far field where bottom drag becomes important and balances the pressure gradient the velocity i

carbonate chemistry in the mertz polynya east antarctica biological and physical modification of dense water outflows and the export of anthropogenic co2 1 dense shelf water dsw is formed in east antarctica from enhanced sea ice production driven by air sea interaction in coastal polynyas cross shelf export and downslope mixing of this dsw produces antarctic bottom water contributing to the lower limb of the global overturning circulation we present biogeochemical observations from the mertz polynya region in summer 2007 2008 with additional observations from spring 2001 and winter 1996 the seasonal changes in mixed layer carbonate chemistry are driven by a combination of air sea co2 exchange biological activity and the formation and melt of sea ice the air sea fluxes in 2008 were 15 mmol c m 2 d 1 and net community production estimated from the summertime surface dissolved inorganic carbon dic deficit ranged from 0 9 to 1 2 mol c m 2 yr 1 we show that biological modification of carbonate chemistry over the shelf in summer preconditions the dsw outflows from the adelie depression this process appears to supply both organic material and water depleted in co2 and with enhanced carbonate saturation state relative to inflowing water to coral communities on the slope we combined model based transports of exported dsw with the natural and anthropogenic cant carbon concentrations and estimate that the annual outflows of dic and cant from the mertz polynya range from 320 to 560 tg c yr 1 and from 3 to 6 tg cant yr 1 respectively the formation and export of dense water from this region and by extension all similar polynyas around antarctica is an effective mechanism for the transfer of anthropogenic carbon into the deep ocean

effects of ambient stratification and shelfbreak topography on offshore transport of dense water on continental shelves the transport of dense water offshore from an idealized coastal polynya is examined using a primitive equation numerical model first the prior scaling of the equilibrium density of water produced within the polynya is extended to include the effects of linear bottom slope next ambient linear stratification is added the equilibrium density is modified slightly by the density at the bottom at the initial time next shelfbreak topography is included with both weak and strong ambient stratification for the case of weak stratification dense water carried to the shelfbreak within eddies moves rapidly downslope and is trapped near the bottom the along shelf scale of the dense water cascading down the slope is set by the diameter of the dense water eddies that form along the periphery of the coastal polynya for the case of strong stratification dense water is carried offshore across the shelfbreak at an intermediate depth injecting water originally within the polynya across the shelf and over the continental slope a bottom trapped current flowing near the shelfbreak in the direction of coastal trapped wave propagation also forms these results suggest that water formed within coastal polynyas over arctic shelves may be capable of ventilating the continental slope regions and possibly central basins of the arctic ocean via eddy fluxes

dynamics of isolated convective regions in the ocean abstract an initially resting ocean of stratification n is considered subject to buoyancy loss at its surface of magnitude b0 over a circular region of radius r at a latitude where the coriolis parameter is f initially the buoyancy loss gives rise to upright convection as an ensemble of plumes penetrates the stratified ocean creating a vertically mixed layer however as deepening proceeds horizontal density gradients at the edge of the forcing region support a geostrophic rim current which develops growing meanders through baroclinic instability eventually finite amplitude baroclinic eddies sweep stratified water into the convective region at the surface and transport convected water outward and away below setting up a steady state in which lateral buoyancy flux offsets buoyancy loss at the surface in this final state quasi horizontal baroclinic eddy transfer dominates upright plume convection by using parcel theory to consider the energy transformations taking place it is shown that the de

the destruction of lenses and generation of wodons abstract since midocean eddies migrate westward they eventually reach the western boundaries it is therefore of interest to find out what happens after the eddies collide with the walls an isopycnic two layer primitive equation model on a plane and a simple analytical model on an f plane are constructed to investigate the meridional migration of an oceanic eddy along a western wall on a plane three factors determine the eddy s migration along a western meridional wall first the image effect pushes an anticyclonic cyclonic eddy northward southward second the force resulting from the larger coriolis force on the northern side of the eddy pulls an anticyclonic cyclonic eddy southward northward third after an anticyclonic cyclonic eddy collides with the wall parts of the anticyclonic eddy s interior fluid leak out southward northward along the wall forming a thin jet in an analogy to a rocket this jet pushes the eddy northward southward our aim is to investigate in whi

antarctic sea ice mapping using the avhrr abstract a sea ice mapping scheme based on advanced very high resolution radiometer avhrr data from the national oceanic and atmospheric administration noaa polar orbiting satellites has been developed and applied to daylight images taken between november 1989 to january 1990 and november 1990 to january 1991 over the weddell and the ross seas after masking the continent and ice shelves sea ice is discriminated from clouds and open sea using thresholds applied to the multidimensional space formed by avhrr channel 2 3 and 4 radiances sea ice concentrations in cloud free regions are then computed using the tie point method results based on the analysis of more than 70 images show that the proposed scheme is capable of properly discriminating between sea ice open sea and clouds under most conditions thus allowing high resolution sea ice maps to be produced during the austral summer season

surface winds over the antarctic continent a review surface winds over antarctica often classified as katabatic are intimately related to the orientation and steepness of the underlying ice terrain such flows result primarily from the strong radiational cooling of the sloping ice surface which creates a downslope directed horizontal pressure gradient force it is possible to diagnose the time averaged near surface streamline patterns of cold air drainage currents using recently compiled detailed antarctic ice topography maps and appropriate estimates of the strength of the surface temperature inversion the resulting streamlines agree with available observations and illustrate the high degree of nonuniformity of gravity driven flows off the ice sheets in certain interior sections negatively buoyant air from a large catchment area drains through a restricted section of coastline such confluence zones represent regions of enhanced supplies of cold air and are shown to be related to anomalously strong katabatic winds implications for sea ice formation are discussed

a two level wind and buoyancy driven thermocline model abstract a simple two level model is designed to simulate the thermocline equations applicable for large scale steady oceanic flow the model serves two functions first it replaces problems with the interpretation of slablike dynamics e g luyten et al 1983 by using continuously horizontally varying buoyancy but at the cost of reducing the vertical resolution drastically the equations used are geostrophy plus a small linear drag to close a stommel like western boundary layer mass conservation and buoyancy conservation with a small but necessary horizontal diffusion inclusion of vertical diffusion has little effect the ocean is driven by an ekman layer whose functions are to provide a given surface input of mass through ekman pumping and buoyancy through a specified buoyancy in the ekman layer i e to maintain the same boundary conditions as in classical thermocline studies sidewall conditions are not well understood and are almost certainly over specified in this formulation s

platelet ice the southern ocean s hidden ice a review basal melt of ice shelves is not only an important part of antarctica s ice sheet mass budget but it is also the origin of one of the most peculiar types of sea ice found in the polar oceans platelet ice in many regions around coastal antarctica tiny ice crystals form and grow in supercooled plumes of ice shelf water releasing heat into the surrounding ocean they usually rise towards the surface eventually becoming trapped under an ice shelf as marine ice frequently masses of those crystals are advected out of the ice shelf cavity and accumulate below a solid sea ice cover to form a semiconsolidated layer when the overlying sea ice grows into this so called sub ice platelet layer the loose crystals are consolidated adding additional thickness to the sea ice these phenomena are generally referred to as platelet ice although confusion about the terminology is widespread in the literature the presence of platelet ice has a profound impact on sea ice properties and processes in several regions of antarctica with numerous implications for the local polar marine biosphere most notably sub ice platelet layers provide a stable sheltered nutrient and food rich habitat which usually results in a highly productive and uniquely adapted ecosystem it has also been hypothesised that platelet ice may be an indicator of the state of an ice shelf although comprehensive time series are limited to the ross sea this paper clears up the terminology by providing exact definitions of the relevant terms we review platelet ice formation observational methods as well as geographical and seasonal occurrence the physical properties and ecological implications are merged in a way understandable for physicists and biologists alike to lay the foundation for the interdisciplinary research that is necessary to tackle the current knowledge gaps

eddy driven exchange between the open ocean and a sub ice shelf cavity the exchange between the open ocean and sub ice shelf cavities is important to both water mass transformations and ice shelf melting here we use a high resolution 500 m numerical model to investigate to which degree eddies produced by frontal instability at the edge of a polynya are capable of transporting dense high salinity shelf water hssw underneath an ice shelf the applied surface buoyancy flux and ice shelf geometry is based on ronne ice shelf in the southern weddell sea an area of intense wintertime sea ice production where a flow of hssw into the cavity has been observed results show that eddies are able to enter the cavity at the southwestern corner of the polynya where an anticyclonic rim current intersects the ice shelf front the size and time scale of simulated eddies are in agreement with observations close to the ronne ice front the properties and strength of the inflow are sensitive to the prescribed total ice production flushing the ice shelf cavity at a rate of 0 2 0 4 106 m3 s 1 depending on polynya size and magnitude of surface buoyancy flux eddy driven hssw transport into the cavity is reduced by about 50 if the model grid resolution is decreased to 2 5 km and eddies are not properly resolved

baroclinic instability of density current along a sloping bottom and the associated transport process numerical experiments with a three dimensional nonhydrostatic ocean model have been carried out to investigate the dynamic processes of downslope density current and associated transport of dense water focusing on the effects of bottom slope for the range of slope inclination s from 0 to 0 04 bottom slope has two effects on baroclinic instability of the flow one is the stabilizing effect due to the topographic effect and to offshoreward increase in water depth the other is the destabilizing effect due to steepened inclination of isopycnal surface which increases available potential energy since the destabilizing effect over the upper slope overcomes the stabilizing one in the early stage unstable waves develop more rapidly with increasing s nonlinear energy conversion due to reynolds stresses also affects the flow stability and then the growth rate of instability increases linearly with s in this stage after the unstable waves have finite amplitudes in the mature stage the stabilizing effect of bottom slope becomes dominant especially over the lower slope thus vigorous unstable eddies are confined to the upper slope region in steep slope cases while they cover the whole slope region in gentle slope cases and this difference in the eddy field causes a drastic change in downslope transport of dense water in gentle slope cases efficiency of the transport becomes higher with increasing s since the destabilizing effect overcomes the stabilizing one as a whole on the contrary the efficiency becomes lower with increasing s in steep slope cases since the stabilizing effect surpasses the destabilizing one as a result the most effective transport is realized in the case with s 0 005 although the transport due to eddies in steep slope cases becomes weak over the lower slope it is still larger than that due to the bottom ekman current since the eddy transport occurs in the bottom layer with a thickness of 100 200 m which is 4 8 times the ekman layer thickness