relating wave attenuation to pancake ice thickness using field measurements and model results wave attenuation coefficients m a1 were calculated from in situ data transmitted by custom wave buoys deployed into the advancing pancake ice region of the weddell sea data cover a 12 day period as the buoy array was first compressed and then dilated under the influence of a passing low pressure system attenuation was found to vary over more than 2 orders of magnitude and to be far higher than that observed in broken floe marginal ice zones a clear linear relation between and ice thickness was demonstrated using ice thickness from a novel dynamic thermodynamic model a simple expression for in terms of wave period and ice thickness was derived for application in research and operational models the variation of was further investigated with a two layer viscous model and a linear relation was found between eddy viscosity in the sub ice boundary layer and ice thickness

strong and highly variable push of ocean waves on southern ocean sea ice sea ice in the southern ocean has expanded over most of the past 20 y but the decline in sea ice since 2016 has taken experts by surprise this recent evolution highlights the poor performance of numerical models for predicting extent and thickness which is due to our poor understanding of ice dynamics ocean waves are known to play an important role in ice break up and formation in addition as ocean waves decay they cause a stress that pushes the ice in the direction of wave propagation this wave stress could not previously be quantified due to insufficient observations at large scales sentinel 1 synthetic aperture radars sars provide high resolution imagery from which wave height is measured year round encompassing antarctica since 2014 our estimates give an average wave stress that is comparable to the average wind stress acting over 50 km of sea ice we further reveal highly variable half decay distances ranging from 400 m to 700 km and wave stresses from 0 01 to 1 pa we expect that this variability is related to ice properties and possibly different floe sizes and ice thicknesses a strong feedback of waves on sea ice via break up and rafting may be the cause of highly variable sea ice properties

calibrating a viscoelastic sea ice model for wave propagation in the arctic fall marginal ice zone this paper presents a wave in ice model calibration study data used were collected in the thin ice of the advancing autumn marginal ice zone of the western arctic ocean in 2015 where pancake ice was found to be prevalent multiple buoys were deployed in seven wave experiments data from four of these experiments are used in the present study wave attenuation coefficients are calculated utilizing wave energy decay between two buoys measuring simultaneously within the ice covered region wavenumbers are measured in one of these experiments forcing parameters are obtained from simultaneous in situ and remote sensing observations as well as forecast hindcast models cases from three wave experiments are used to calibrate a viscoelastic model for wave attenuation dispersion in ice cover the calibration is done by minimizing the difference between modeled and measured complex wavenumber using a multi objective genetic algorithm the calibrated results are validated using two methods one is to directly apply the calibrated viscoelastic parameters to one of the wave experiments not used in the calibration and then compare the attenuation from the model with measured data the other is to use the calibrated viscoelastic model in wavewatch iii over the entire western beaufort sea and then compare the wave spectra at two remote sites not used in the calibration both validations show reasonable agreement between the model and the measured data the completed viscoelastic model is believed to be applicable to the fall marginal ice zone dominated by pancake ice

wave propagation in the marginal ice zone model predictions and comparisons with buoy and synthetic aperture radar data in this paper the ocean wave dispersion relation and viscous attenuation by a sea ice cover are studied for waves propagating into the marginal ice zone miz the derivation of the dispersion relation and the viscous attenuation by an ice sheet are discussed for waves under flexure and pack compression in the miz the flexure effect is important for short waves for a fixed wave period the changes in wavelength and group velocity as a function of ice thickness are significant in turn the exponential wave attenuation rate shows a rollover at short wave periods whereby the rapid increase in wave attenuation rate with decreasing wave period slows down or even turns into a decrease the labrador ice margin experiment limex conducted on the miz off the east coast of newfoundland canada in march 1987 provides us with aircraft synthetic aperture radar sar imagery wave buoy and ice property data on the basis of the wave number spectrum from the sar data and the concurrent wave frequency spectrum from the ocean buoy data and accelerometer data on the ice during limex 87 the dispersion relation has been estimated and compared with a model wave energy attenuation rates are estimated from sar data and the ice motion package data which were deployed at the ice edge and into the ice pack and compared with the model the model data comparisons are reasonably good for the ice conditions observed during limex 87 some previously reported data of wave attenuation in the miz are revisited for model comparison

the development of the odden ice tongue in the greenland sea during winter 1993 from remote sensing and field observations the odden ice tongue in the central greenland sea believed to be associated with midgyre convection developed prominently during the winter of 1993 january april during this period it was studied by a succession of cruises which formed part of the european subpolar ocean programme and which included direct sampling and measurement of the frazil and pancake ice which constituted the material of the ice tongue as well as studies of the ocean structure passive microwave imagery was used to determine the evolution of odden through the winter and when combined with ers 1 synthetic aperture radar studies and the field data yielded estimates of ice extent and thickness through the winter from these studies it was possible to estimate the salt flux into the ocean originating from brine release from sea ice during the growth phases of odden

spatial variations of ocean wave directional spectra from the seasat synthetic aperture radar seasat synthetic aperture radar ocean wave spectra for a 900 km pass are analyzed and interpreted in the context of both their probable generation sources and their surface current and bathymetric modifiers systematic vector wavenumber variations of several times the standard error of determination 1 5 in magnitude and 0 9 in direction occur along the entire 900 km pass the large scale spatial variation of a 200 m swell system can be accurately accounted for as a result of dispersion from a distant storm the more local variations are qualitatively well correlated in position with known currents and bathymetry but show systematic biases that appear partly due to an environmentally dependent instrument transfer function in the regions of high current and highest sea state there is also substantial evidence that a large angular deviation in the center of the pass is the result of a mesoscale eddy just to the east

notes and correspondenceatmospheric effects on upper ocean temperature in the southeast tasman sea abstract the temperature profile in the ocean mixed layer was simulated using a turbulence closure model for a period of 18 years 1980 97 at a site in the southeast tasman sea 42 s 170 e the simulation was forced at the surface by a meteorological dataset derived from land station data sea surface temperature sst from the model was compared with the ncep 1 sst analysis beginning in 1982 the mean annual cycle and monthly anomalies in modeled sst agree with the ncep dataset in several respects modeled and observed sst anomalies are highly correlated with each other and are similar in overall magnitude timescale and phase however the model underpredicts the magnitude of sst anomalies in winter modeled and observed sst lagged correlation fields are similar with both showing a high correlation of sst anomalies in winter with anomalies in the previous spring the model has a pronounced recurrence mechanism that is anomalous temperatures in the deep mixed layer in spring remain below the sha

waves in frazil and pancake ice and their detection in seasat synthetic aperture radar imagery a theoretical model of waves propagating into an ice cover composed of frazil and pancake ice is developed and compared with measurements of wavelength and direction derived from synthetic aperture radar sar imagery obtained from seasat in october 1978 the theoretical model is based on the concept that ice of these types which consists of small crystals or cakes has only a mass loading effect on the water surface we derive the dispersion relation for phase and group velocities finding that there is an upper frequency limit for propagation into the ice from the reflection coefficient at the ice edge we derive the wave radiation pressure exerted on the ice showing that it will cause a slick of frazil ice backed by thicker floes to become more dense or thick with increasing penetration the implications for radar scattering enabling detection on sar are that the bragg resonant wavelength corresponds to waves above the frequency limit for propagation so that a frazil slick appears dark on an sar image when the frazil ice becomes transformed into pancake ice through slick compression or other means the raised edges of the pancakes cause the ice to appear bright despite the fact that there are no waves present at the bragg wavelength these results are applied to a seasat sar image obtained from the chukchi sea the appearance of the ice in the image corresponds to what we expect for frazil ice gradually transforming itself into pancake ice backed by thicker floes we derive directional wave number spectra outside and inside the ice cover by digital fourier analysis of image subscenes and we find that the change of wavelength and angle of refraction of the dominant wave entering the ice field are both characteristic of the dispersion relation derived theoretically mean ice thicknesses extracted from the theory correspond to thicknesses expected for such slicks the technique offers a possible means of extracting the thickness of fields of frazil and pancake ice from sar imagery this may be of considerable utility when ers 1 sar is used to study the advancing winter ice edge in the antarctic which consists of vast areas of these ice types

formation of a diurnal thermocline in the ocean mixed layer simulated by les the formation of a diurnal thermocline in the ocean mixed layer under a stabilizing buoyancy flux was simulated successfully by large eddy simulation reproducing various features consistent with observation the analysis of the simulation result revealed that the formation of a diurnal thermocline passes through two different phases the formation of a thermocline formation stage and increasing thickness of the thermocline thereafter growth stage turbulent kinetic energy tke flux dominates tke production within the mixed layer but turbulencemaintained by shear production at the thermoclinecausesstratification below the mixed layer in addition once the thermocline is formed both the gradient and flux richardson numbers maintain constant values at the thermocline it was also found that a diurnal thermocline cannot be formed in the absence of both wave breaking and langmuir circulation furthermore the effects of stratification on turbulencewereinvestigatedbasedonthetimeseriesofvariousphysicalvariablesofturbulenceatthediurnal thermocline and within the mixed layer and the mechanism for diurnal thermocline formation is discussed

beaufort chukchi seas summer and fall ice margin data from seasat conditions with similarities to the labrador sea the margin of the sea ice pack of the beaufort and chukchi seas is examined using the microwave data from seasat taken during the summer to early fall july 4 through october 8 1978 and the observations are compared to the analogous observations taken in limex 87 the sensors used are synthetic aperture radar sar the seasat a scatterometer system and the scanning multichannel microwave radiometer

tracking storm generated waves in the northeast pacific ocean with ers 1 synthetic aperture radar imagery and buoys this paper examines the capability of synthetic aperture radar imagery from ers 1 and buoys to track the wave field emanating from an intense storm over a several day period the first part of the study is a validation component that compares sar derived wave length and direction with buoy data from two locations over 10 different dates in late 1991 and national oceanic and atmospheric administration noaa wave model wam wave direction results when the sar is linear 8 out of 10 cases mean wavelength is within 5 of the buoy measurements and mean wave direction is within 1 of direction derived from the wave model albeit with a large standard deviation of 27 indicating close agreement the wave field generated from the intense storm in late december 1991 was measured by three separate ers 1 sar passes over a 3 day period a simple kinematic model was used for waves propagating from a storm comparing the model results with both sar and buoy data indicates that sar derived peak wavelength and direction measurements can be reliably used to predict arrival times and propagation direction over a several day period and considerable distances the measurements can also be used to derive estimated wave generation source regions about the storm as well such measurements are useful for comparing with wave model results which perform less accurately for direction than wave height for example and for predicting hazardous conditions for ship navigation and coastal regions

spaceborne synthetic aperture radar observations of ocean waves traveling into sea ice 1 damping of ocean waves by sea ice is studied using spaceborne synthetic aperture radar sar images of the marginal ice zone miz acquired by the european remote sensing satellite ers 2 sar imaging of waves damped by sea ice is analyzed theoretically the impact of sea ice on the azimuthal cutoff is studied by simulation of the azimuthal sar image autocorrelation function as well as the two dimensional sar image spectrum typical imaging artifacts like spiky wave crests and wave refraction seen on sar scenes of the miz are reproduced by simulation sensitivity studies are performed using models for wind sea and swell systems it is shown that the degradation of the azimuthal sar image resolution is dominated by the orbital velocity variance of the waves while the coherence time of the complex radar reflectivity has a minor impact a first order analysis of wave damping observed on sar scenes is carried out using a technique that was originally developed for wind estimation by kerbaol et al 1998 the method does not require a priori information and is insensitive to real aperture modulation the azimuthal sar image cutoff wavelength is estimated and related to the orbital velocity variance of the sea surface by regression the model is fitted on the basis of a global set of model ocean wave spectra the technique is applied within the sea ice and in the open water in front of the ice boundary on the basis of simple models for wind sea and swell ocean wave attenuation rates are obtained from the observed orbital velocity decrease of waves entering the ice the required wind information is derived from calibrated sar data using the cmod method two case studies showing examples from the greenland and the weddell seas are given it is shown that the estimated wave damping is consistent with damping parameters found in earlier field campaigns carried out in the weddell sea and the bering sea an inversion technique providing estimates for the two dimensional wave spectra behind and in front of the ice boundary as well as a two dimensional filter function characterizing the sea ice impact is introduced the technique is based on simultaneous inversion of the two dimensional image spectra in the open water and within the ice using a priori information from an ocean wave model it is shown that the technique gives results consistent with the first order analysis based on the cutoff estimation

structure of the surface wind field from the seasat sar an intensive analysis of the vector wind field of one seasat data set pass 1339 is described wind speed and direction signatures are found in seasat sar synthetic aperture radar images and the resulting estimates are compared with the seasat a scatterometer system sass and simultaneous noaa p 3 aircraft measurements a power law is presented to relate sar measured backscatter to sass estimated wind speed and the sar estimates are shown to agree with the sass estimates to within a standard error of 0 7 m s over a range of wind speeds from 3 m s to 13 m s the surface expressions of atmospheric roll vortices are apparent in several of the sar images and may be responsible for the wind direction signature in these cases wind field estimates averaged over regions of variable sizes are possible because of the high resolution of sar imagery a method for extracting low wave number directionality and its variability from sar spectra is described and sar direction estimates obtained from spectra of 6 4 km square images are shown to have a precision of approximately 10 although a comparison data set that could validate these higher resolution estimates is lacking averages over 40 km square regions are in good agreement with the other wind field information the sar wind direction estimates yield a more complete interpretation in a region with a turning wind field near a front that is ambiguous with only sass observations in this region the flow patterns of the high resolution estimates appear consistent with our knowledge of the overall circulation considering all the observations however in another region the small scale variability is too large and random to represent real wind variability although averages derived from these estimates are still reliable

frazil formation in water of different salinities and supercoolings les experiences de formation de frazil ont ete realisees dans des eaux de mer naturelles et artificielles on trouve que la vitesse de production du frazil est tres sensible a la surfusion initiale

oceanographic conditions in the marginal ice zone north of svalbard in early fall 1979 with an emphasis on mesoscale processes during september october 1979 the norwegian remote sensing experiment was carried out in the marginal ice zone north of svalbard convergence of the ice cover is correlated with along ice edge winds with the ice to the right while divergence occurs during office winds or calm conditions a wind driven ice edge jet is observed wind driven upwelling of the pycnocline of up to 7 m was present along the ice edge during a 10 to 15 m s easterly wind event the upwelling is due to ekman divergence at the ice edge caused by higher wind stress over ice than over open water the ice edge meanders with a scale of 20 40 km and sheds eddies with a scale of 5 to 15 km into the open water this scale is of the same order as the rossby radius of deformation eddies with the same scale are also seen in the conductivity temperature and depth observations conditions during the experiment were such that barotropic instabilities could have generated these eddies

the ice thickness distribution across the atlantic sector of the antarctic ocean in midwinter during the first leg of the winter weddell sea project antarktis v 2 cruise of f s polarstern the entire width of the antarctic sea ice zone was traversed in the vicinity of 0 longitude in the period july 18 to september 10 1986 ice thicknesses were measured by direct drilling and by helicopter profiling using an exstar 100 mhz impulse radar system in addition aerial photography of the ice cover was done from 100 to 2000 m altitude using a 70 mm aerial camera mounted in the helicopter the results of the point measurements drilling are reported in this paper together with an indication of how the radar and photography data will be used to extend them so as to yield area averaged ice thickness distributions it was found that the main ice type across the entire width of the ice cover was consolidated pancake ice occurring in vast floes this formed out of a 250 km wide band at the advancing ice edge which comprised a concentrated field of individual pancakes in a matrix of frazil ice preferred thicknesses of undeformed floes were 40 60 cm of ice covered with 5 15 cm of snow the individual pancakes attained almost all of this thickness before consolidation subsequent congelation growth was slow estimated at 0 4 cm d 1 the floes contained much small scale roughness on the upper and lower surfaces due to rafting of pancakes at the time of consolidation but pressure ridging was modest except in the far south a few very thick 8 11 m multiyear floes were observed embedded in the pack at latitudes beyond 66 s

the attenuation rates of ocean waves in the marginal ice zone during field operations in the greenland and bering seas in 1978 1979 and 1983 a number of experiments were carried out in which wave energy was measured along a line of stations running from the open sea deep into an icefield wave buoys in the water and accelerometer packages on floes were the instruments employed with airborne vertical photography to supply information on floe size distribution it was found that the decay of waves is exponential with a decay coefficient which generally increases with frequency except for a roll over at the highest frequencies the observations can be fitted reasonably well to a theory of one dimensional scattering

development of sea ice in the weddell sea we report on the development and physical properties of sea ice in the central and eastern weddell sea the investigations were part of the winter weddell sea project 1986 which extended over the months of july through december major elements of the glaciological part of this study included continuous shipborne observations of sea ice conditions and occasional helicopter reconnaissance flights extensive measurements of snow and ice thicknesses at daily ice stations and detailed analyses of sampled ice cores from each ice station textural investigations of the sampled ice revealed the dominance of frazil ice in the central weddell sea and the occurrence of an additional ice class called platelet ice together with the commonly known frazil and congelation ice in the coastal region of the eastern weddell sea these results in combination with the visual ice observations reveal two major mechanisms for sea ice generation in the antarctic which were not sufficiently well accounted for in previous investigations in the central weddell sea a cycle of pancake ice formation and its growth into consolidated floes seems to be the dominant process of the advancing sea ice edge in the coastal waters the growing sea ice cover consists to a considerable degree of ice platelets which are formed in the underlying water column in front of the ice shelf edges thus congelation ice growth which is mainly controlled by atmospheric thermodynamic forcing seems to be of less importance in the central and south eastern weddell sea than for example in the arctic basin

the use of sar to measure ocean wave dispersion in frazil pancake icefields abstract icefields composed of frazil and pancake ice play important roles in both polar regions in winter during the early to midwinter period pancake ice is a major component of the antarctic sea ice cover while in the arctic the odden ice tongue in the greenland sea associated with deep convection is composed mainly of pancake ice the retrieval of sea ice thickness by remote sensing is in general a very difficult task in this paper the change in dispersion of ocean waves as they penetrate into pancake ice is considered so as to gain insight into its possible relationship with thickness spectral analysis of subscenes from ers 2 second european remote sensing satellite synthetic aperture radar sar images yields the wavelength and direction of the principal spectral component both outside and inside the ice cover there is a decrease of wavelength at the ice edge as well as refraction toward the normal and a loss of amplitude the analysis is complex because the true wave spectrum must be re

comparison of viscoelastic type models for ocean wave attenuation in ice covered seas continuum based models that describe the propagation of ocean waves in ice infested seas are considered where the surface ocean layer including ice floes brash ice etc is modeled by a homogeneous viscoelastic material which causes waves to attenuate as they travel through the medium three ice layer models are compared namely a viscoelastic fluid layer model currently being trialed in the spectral wave model wavewatch iii and two simpler viscoelastic thin beam models all three models are two dimensional a comparative analysis shows that one of the beam models provides similar predictions for wave attenuation and wavelength to the viscoelastic fluid model the three models are calibrated using wave attenuation data recently collected in the antarctic marginal ice zone as an example although agreement with the data is obtained with all three models several important issues related to the viscoelastic fluid model are identified that raise questions about its suitability to characterize wave attenuation in ice covered seas viscoelastic beam models appear to provide a more robust parameterization of the phenomenon being modeled but still remain questionable as a valid characterization of wave ice interactions generally

comparison of shuttle imaging radar b ocean wave image spectra with linear model predictions based on aircraft measurements during october 1984 coincident shuttle imaging radar b synthetic aperture radar sar imagery and wave measurements from airborne instrumentation were acquired the two dimensional wave spectrum was measured by both a radar ocean wave spectrometer and a surface contour radar aboard the aircraft in this paper we compare two dimensional sar image intensity variance spectra with these independent measures of ocean wave spectra to verify previously proposed models of the relationship between such sar image spectra and ocean wave spectra the results illustrate both the functional relationship between sar image spectra and ocean wave spectra and the limitations imposed on the imaging of short wavelength azimuth traveling waves

overview of limex 87 ice observations ice observations results and conclusions are summarized for the march 1987 labrador ice margin experiment limex 87 an international oceanographic study conducted in the pack ice of the grand banks area off the coast of newfoundland included are the ice extent flow size and thickness ice kinematics and rheology ice microwave properties oceanic properties under the ice and penetration of swell into the ice

the consequences of sampling variability on the estimation of wave number and propagation direction from spaceborne sar image spectra even if it were true that sar synthetic aperture radar ocean surface imagery provides a perfect noiseless representation of ocean surface wave height each spectrum computed from such imagery would be but a single realization of the ensemble mean ocean spectrum there would be sampling variability associated with the parameters of dominant wave number and propagation direction extracted from such a spectrum the present study addresses two questions i what statistical distribution is applicable to the spectra of sar ocean images and ii what are the consequences of such statistics on the precision with which wave number and propagation direction can be extracted an examination is made of spectra computed from ocean imagery acquired during the sir b shuttle imaging radar b mission

simulations of temperature and turbulence structure of the oceanic boundary layer with the improved near surface process an improved model for the oceanic boundary layer is presented in view of the recent observation of the microstructure of the upper ocean including the high dissipation rate near the sea surface in the new model the surface boundary conditions for both the turbulent kinetic energy flux and the roughness length scale are modified the parameterization of stratification effects on turbulence is improved and the convective process is reformulated on the basis of the observation of uniform temperature and velocity profiles within the convective mixed layer evolutions of the profiles of both the dissipation rate and temperature of the observation data patches experiment as well as the time series of the sea surface temperature over the observation days are successfully simulated during a diurnal cycle for the first time it is also shown that the model reproduces various important features of the oceanic boundary layer for example the formation of a diurnal thermocline the profiles of buoyancy flux and the magnitudes of the buoyancy gradients both within the mixed layer and at the diurnal thermocline performance of the model is compared with that of the widely used mellor yamada model

drift and mixing under the ocean surface revisited stratified conditions and model data comparisons 1 a one dimensional model of the ocean near surface currents is presented it includes the enhanced near surface mixing due to the waves the wave induced stokes drift the stokes coriolis sc effect and the stratification near surface current shears from this model are compared with the shears of the quasi eulerian currents measured using a wave following platform during the shelf mixed layer experiment smile it is shown that the downwind current shears observed during smile are well modeled however the observed crosswind shears are in poor agreement with the model the stokes coriolis sc term could qualitatively explain this misfit but it is one order of magnitude too weak the ekman stokes spiral of the model is compared with the spiral observed during the long time series of measurements long term upper ocean study 3 the effects of stratification are taken into account the mean velocity profiles of the model closely agree with observations however there is no evidence of the sc effect on the shape of the observed current profile the observed profile is found to be a consequence of the current rectification due to the time varying stratification the sc effect calculated from a numerical wave hindcast is weak but should have been observed in fact it is estimated that the wave induced bias in the current measurements is larger than the sc effect finally it is shown that the variation of surface drift with wave age which was estimated to be small in unstratified conditions is important in the presence of shallow mixed layers

extraction of marginal ice zone thickness using gravity wave imagery synthetic aperture radar sar imagery of gravity waves in the marginal ice zone miz was acquired during 1987 and 1989 using aircraft flying over the greenland sea the dominant gravity wavelengths acquired during 1987 exhibit a systematic lengthening with penetration distance into the miz for three different regions examined the extracted dominant wavelengths were analyzed using a linear least squares fit with penetration distance and a flexure gravity wave model to estimate mean ice thickness the extracted mean thickness varies from about 1 0 4 m near the ice edge to approximately 2 0 4m near the deepest detectable penetration of the waves about 20 km these thicknesses are in agreement with 31 in situ measurements taken in the fram strait miz within 2 weeks of the sar measurements we also acquired wave imagery across a 150 km section of newly forming ice called the odden a tongue shaped region during 1989 these sar images at l c and x bands display small wave modulation signatures at the northern edge of the odden which we interpret as arising from rapidly growing new ice

sar imaging of waves in water and ice evidence for velocity bunching synthetic aperture radar sar images collected over the arctic marginal ice zone show gravity wave patterns in both the open water and the ice diffuse wave patterns are visible in the water at near range small incidence angles while more distinct wave patterns are visible in the ice across the entire swath the wave patterns in the ice appear as bright lines rather than sinusoidal intensity variations additionally the images show a periodic displacement of the ice water boundary apparently due to doppler shift effects associated with the gravity wave orbital motions these observations are interpreted as evidence for the velocity bunching effect and also illustrate the effects of random scatterer motions in the open water

seasonal influence of enso on the atlantic itcz and equatorial south america 1 in late boreal spring especially may a strong relationship exists in observations among precipitation anomalies over equatorial south america and the atlantic intertropical convergence zone itcz and eastern equatorial pacific and central equatorial atlantic sea surface temperature anomalies ssta a chain of correlations of equatorial pacific ssta western equatorial atlantic wind stress wea equatorial atlantic ssta sea surface height and precipitation supports a causal chain in which el nino southern oscillation enso induces wea stress anomalies which in turn affect atlantic equatorial ocean dynamics these correlations show strong seasonality apparently arising within the atmospheric links of the chain this pathway and the influence of equatorial atlantic ssta on south american rainfall in may appear independent of that of the northern tropical atlantic brazil s nordeste is affected by the northern tropical atlantic the equatorial influence lies further to the north over the eastern amazon and the guiana highlands

a field and laboratory study of wave damping by grease ice in a field and laboratory study we discuss the formation growth and wave absorption properties of grease ice our field observations show that grease ice formation occurs under cold windy conditions in both leads and polynyas in leads grease ice forms in the open water then is herded to the down wind edge of the lead in polynyas a langmuir circulation herds the grease ice into long plumes parallel to the wind in the laboratory we grow grease ice in a wave tank and measure its wave absorption properties for single frequency two dimensional waves on a large scale we find that the thickness of the grease ice which increases away from the paddle is determined by a balance between the wave momentum flux and the free surface tilt on a small scale our photographs show that the crystals which make up the grease ice consist of discs measuring about 1 mm in diameter and 1 10 m thick which at low rates of shear sinter together into larger clumps yielding a viscosity increase to measure this non linear viscosity we study the decay of wave amplitude between two critical distances measured inwards from the leading edge the first occurs when the depth of grease ice exceeds k 1 where k is the wave number the second further distance is a line of transition from liquid to solid behavior which we call the dead zone between these two distances the wave amplitude decays with a linear slope which increases as a 0 k 2 where a0 is the wave amplitude in open water concurrent measurements of ice concentration show that it increases from values of 18 22 at the leading edge to a local maximum of 32 44 at the dead zone while the values at the dead zone increase non linearly with a0k finally comparison of the observed to that calculated from a yield stress viscosity model shows if the yield stress coefficient is proportional to the incident wave momentum flux the model predicts the observed

the near surface hydrography beneath the odden ice tongue as part of the european subpolar ocean programme esop the german research icebreaker polarstern worked in the greenland sea in the late winter of 1993 whilst on passage the ship encountered a severe winter storm with winds consistently above 20 m s 1 coupled to air temperatures of below 10 degrees c the underway sensors revealed heat fluxes of greater than 700 w m 2 across most of the nordic basin peaking at greater than 1200 w m 2 when the ship crossed the cold fresh water of the jan mayen current this large heat flux coupled to the unique hydrographic conditions present in the jan mayen current allowed sea ice generation in the form of frazil ice at a rate of 28 cm d 1 this frazil ice then developed into pancake ice measurements also were made in the late winter beneath this pancake ice in two remnants of the odden in the jan mayen current hydrographic conditions are such that the ice can exist for a long period of time before eventually decaying due to short wave radiation at the surface towards the centre of the greenland sea hydrographic measurements reveal that the ice is more transient and decays four times more rapidly than ice in the jan mayen current we discuss the development of the odden ice tongue in light of these results and add evidence to the argument that the eventual fate of the water stored in the ice is important and could be a relevant factor in the formation of greenland sea deep water c 1999 elsevier science ltd all rights reserved

dynamics of diurnal thermocline formation in the oceanic mixed layer abstract diurnal thermocline formation in the oceanic mixed layer under a stabilizing buoyancy flux is studied by numerical simulation of a turbulence model in which the interaction between turbulence structure and density stratification is taken into consideration and the mechanism for its formation is clarified based on the results from the simulations the flux of turbulent kinetic energy is a dominant source of turbulence in the upper mixed layer and plays an indispensable role for the formation of a diurnal thermocline below the diurnal thermocline turbulence is maintained by shear production which causes the growth of diurnal thermocline thickness the flux richardson number at the diurnal thermocline maintains a constant value about unity regardless of the shear stress and buoyancy flux at the sea surface and the diurnal thermocline depth grows more slowly than predicted by the monin obukhov length scale the model results are compared with the observational data and the assumptions intro

geophysical and oceanographic information in the marginal ice zone from ocean wave measurements consequent to recent experiments in marginal ice zones miz advances in remote sensing and theoretical progress studies have been published which invoke wave ice interactions to explain or predict certain geophysical phenomena while admirable and desirable in principle these works are based on a refutable surface boundary condition intended for a sheet or plate of solid ice rather than a medium made up of individual ice floes a case is argued for prudence as derived results may originate entirely from the application of an inappropriate miz model

sar imaging of wave dispersion in antarctic pancake ice and its use in measuring ice thickness 1 a synthetic aperture radar sar image of the advancing winter marginal ice zone miz in the antarctic composed of frazil pancake ice has been analysed in a new way in order to test the predictions of a recently developed theory of wave dispersion in pancake ice which treats the ice as a viscous layer in the image obtained in april 2000 the structure of the wave spectrum in the miz and its change from the open water spectrum are consistent with a pancake layer 24 cm thick intensive in situ measurements of the pancake ice in the miz 280 km w of the image location were made from fs polarstern during a period covering the satellite imaging and also yielded a mean ice thickness of 24 cm we conclude that this technique gives realistic results for ice thickness whereas earlier work based on a different dispersion theory mass loading tended to over estimate thickness after further validation it is therefore possible that the sar wave technique can become an accepted method for monitoring ice thickness in pancake icefields

wave effects on ocean ice interaction in the marginal ice zone the effects of wave train on ice ocean interaction in the marginal ice zone are studied through numerical modeling a coupled two dimensional ice ocean model has been developed to include wave effects and wind stress for the predictions of ice edge dynamics the sea ice model is coupled to the reduced gravity ocean model through interfacial stresses the main dynamic balance in the ice momentum is between water ice stress wind stress and wave radiation stresses by considering the exchange of momentum between waves and ice pack through radiation stress for decaying waves a parametric study of the effects of wave stress and wind stress on ice edge dynamics has been performed the numerical results show significant effects from wave action the ice edge is sharper and ice edge meanders form in the marginal ice zone owing to forcing by wave action and refraction of swell system after a couple of days upwelling at the ice edge and eddy formation can be enhanced by the nonlinear effects of wave action wave action sharpens the ice edge and can produce ice meandering which enhances local ekman pumping and pycnocline anomalies the resulting ice concentration pycnocline changes and flow velocity field are shown to be consistent with previous observations

airborne sar observations of ocean surface waves penetrating floating ice the results are presented for a new and improved procedure for estimating the synthetic aperture radar sar image spectrum of ocean waves this procedure the spectral sum method involves summing individual image spectra derived from each of the looks of a multilook set an automatic registration of the per look spectral information is achieved accounting for subimage look misregistration due to the wave propagation between looks spectral sum processing is compared with traditional look sum processing as a function of the radar slant range spectral sum processing is applied to sar imagery of waves penetrating the marginal ice zone