sea ice models for climate study retrospective and new directions scientific observations of sea ice began more than a century ago but detailed sea ice models appeared only in the latter half of the last century the high albedo of sea ice is critical for the earth s heat balance and ice motion across the ocean s surface transports fresh water and salt the basic components in a complete sea ice model must include vertical thermodynamics and horizontal dynamics including a constitutive relation for the ice advection and deformational processes this overview surveys topics in sea ice modeling from the global climate modeling perspective emphasizing work that significantly advanced the state of the art and highlighting promising new developments

thickness distribution texture and stratigraphy and a simple probabilistic model for dynamical thickening of sea ice in the southern sea of okhotsk 1 sea ice thickness data and sea ice samples were analyzed to examine the characteristics of the ice thickness distribution and ice texture and to understand ice growth processes in the southern sea of okhotsk ice thickness data and samples were obtained aboard the icebreaker soya in early february the ice growth season ice thickness data which were obtained with a video monitoring system installed on the side deck of the ship each winter from 1991 to 2000 except 1995 show that the average thickness ranges from 19 7 to 55 23 cm and that it matches the characteristics of a poisson distribution ice structure analysis reveals that granular texture occupies about three quarters of the total ice thickness and that the ice exhibits a layered structure with unit thickness averaging 5 to 10 cm stratigraphy and stable isotopic composition of the ice indicate that snow ice accounts for 10 and frazil ice accounts for 64 of the total ice thickness this suggests that dynamic ice thickening processes such as frazil ice growth and piling up are more significant than congelation growth on the basis of these characteristics which resemble more those of antarctic than arctic sea ice we propose a conceptual model for the ice thickening process in this region it is shown that this model can explain the shape of the ice thickness distribution well and is analogous with the concept of the pancake cycle and multiple rafting of antarctic sea ice growth and thickening

large scale sea ice drift and deformation comparison between models and observations in the western weddell sea during 1992 statistical comparisons between numerical sea ice models and an observed large scale strain array in the western weddell sea during 1992 are used to evaluate the performance of three of the more generally utilized sea ice rheology formulations results show that sea ice velocity is reproduced with relatively high accuracy 90 coherence 80 normalized cross correlation in models having high quality atmospheric forcing fields e g the european centre for medium range weather forecasts on the other hand temporal and spatial variability of the velocity field as exemplified by progressive vector plots and ice deformation respectively are reproduced less accurately coherence and normalized cross correlation 50 in terms of model sensitivity this means that deformation and temporal variability are more discriminating in terms of elucidating specifics about the constitutive relation and mechanical properties of sea ice on a large scale for example inclusion of both compressive and shear stresses is important in attaining a proper probability distribution of deformation relative to observations additional analysis shows that adjustments to specific model parameters improve the model results for either drift or select deformation components but no best solution could be found given the models examined here results suggest that inclusion of more physically based processes such as subdaily tidal and inertial oscillations reconsideration of the boundary layer formulation and consideration of anisotropy may be necessary to include in next generation sea ice models especially those that are intended for coupling with high resolution eddy resolving ocean models

fram strait satellite image derived ice motions in order to develop an operational method for the u s navy noaa joint ice center to extract ice velocity vectors from sequential advanced very high resolution radiometer avhrr imagery we have combined the maximum cross correlation mcc method with a spatial filtering technique on the image inferred ice motion vectors we compute the cross correlations between images directly from the image brightness values rather than computing ffts the direct method allows greater flexibility in computational parameter settings and allows one to compute motion vectors near coastlines where irregular windows are required by using a combination of statistical and spatial filters we can then retrieve coherent ice motion vectors in the presence of cloud contaminated imagery a series of six satellite images of the fram strait region from april 1986 was used to compute sea ice motion from pairs of sequential images the resulting ice motion vectors were taken as a representation of the surface flow field derived objectively from the satellite imagery resulting vector motion fields were found to match well with manually tracked vectors for the same images thus verifying the validity of the objective mcc method of computing ice motion these techniques were applied to both the visible and infrared avhrr channels and to images with different spatial resolutions yielding an overall bias accuracy of about 0 5 cm s and standard deviations of about 0 9 cm s the mcc ice motion results were also compared with wind driven numerical model simulations of the region marked differences between the mcc image derived velocities and those from the numerical model were thought to be primarily due to a stronger ocean current than was present in the model

anorthite rich chondrules in cr and ch carbonaceous chondrites genetic link between ca al rich inclusions and ferromagnesian chondrules anorthite rich chondrules in cr and ch carbonaceous chondrites consist of magnesian low ca pyroxene and forsterite phenocrysts feni metal nodules interstitial anorthite al ti cr rich low ca and high ca pyroxenes and crystalline mesostasis composed of silica anorthite and high ca pyroxene three anorthite rich chondrules contain relic ca al rich inclusions composed of anorthite spinel al diopside and forsterite a few chondrules contain regions which are texturally and mineralogically similar to magnesian type i chondrules and consist of forsterite low ca pyroxene and abundant feni metal nodules anorthite rich chondrules in cr and ch chondrites are mineralogically similar to those in cv and co carbonaceous chondrites but contain no secondary nepheline sodalite or ferrosilite relatively high abundances of moderately volatile elements such as cr mn and si in the anorthite rich chondrules suggest that these chondrules could not have been produced by volatilization of the ferromagnesian chondrule precursors or by melting of the refractory materials only we infer instead that anorthite rich chondrules in carbonaceous chondrites formed by melting of the reduced chondrule precursors olivine pyroxenes feni metal mixed with the refractory materials including relic cais composed of anorthite spinel high ca pyroxene and forsterite the observed mineralogical and textural similarities of the anorthite rich chondrules in several carbonaceous chondrite groups cv co ch cr may indicate that these chondrules formed in the region s intermediate between the regions where cais and ferromagnesian chondrules originated this may explain the relative enrichment of anorthite rich chondrules in 16o compared to typical ferromagnesian chondrules russell et al 2000

results of the sea ice model intercomparison project evaluation of sea ice rheology schemes for use in climate simulations a hierarchy of sea ice rheologies is evaluated on the basis of a comprehensive set of observational data the investigations are part of the sea ice model intercomparison project simip four different sea ice rheology schemes are compared a viscous plastic rheology a cavitating fluid model a compressible newtonian fluid and a simple free drift approach with velocity correction the same grid land boundaries and forcing fields are applied to all models as verification data there are 1 ice thickness data from upward looking sonars uls 2 ice concentration data from the passive microwave radiometers smmr and ssm i 3 daily buoy drift data obtained by the international arctic buoy program iabp and 4 satellite derived ice drift fields based on the 85 ghz channel of ssm i all models are optimized individually with respect to mean drift speed and daily drift speed statistics the impact of ice strength on the ice cover is best revealed by the spatial pattern of ice thickness ice drift on different timescales daily drift speed statistics and the drift velocities in fram strait overall the viscous plastic rheology yields the most realistic simulation in contrast the results of the very simple free drift model with velocity correction clearly show large errors in simulated ice drift as well as in ice thicknesses and ice export through fram strait compared to observation the compressible newtonian fluid cannot prevent excessive ice thickness buildup in the central arctic and overestimates the internal forces in fram strait because of the lack of shear strength the cavitating fluid model shows marked differences to the statistics of observed ice drift and the observed spatial pattern of ice thickness comparison of required computer resources demonstrates that the additional cost for the viscous plastic sea ice rheology is minor compared with the atmospheric and oceanic model components in global climate simulations

sea ice motion from satellite passive microwave imagery assessed with ers sar and buoy motions observing the motion of sea ice from space is analogous to observing wind stress over the wet oceans both provide surface forcing for modeling ocean dynamics ice motion also directly provides the advective component of the equations governing the mass balance of the sea ice cover thus its routine observation from space would be of great value to understanding ice and ocean behavior to demonstrate the feasibility of creating a global multidecadal ice motion record from satellite passive microwave imagery and to quantitatively assess the errors in the estimated ice motions we have tracked ice every 3 days in the arctic ocean and daily in the fram strait and baffin bay during the 8 winter months from october 1992 to may 1993 and daily in the weddell sea during the 8 winter months from march to october 1992 the method which has been well used previously involves finding the spatial offset that maximizes the cross correlation of the brightness temperature fields over 100 km patches in two images separated in time by from 1 to 3 days the resulting ice motions are compared with contemporaneous buoyand sar derived ice motions the uncertainties in the displacement vectors between 5 and 12 km are better than the spatial resolution of the data both 85 ghz data with 12 km spatial resolution and 37 ghz data with 25 km resolution are tracked these trials with the 37 ghz data are new and show quite surprisingly that the error is only about 1 km larger with these data than with the 12 km 85 ghz data errors are typically larger than average in areas of lower ice concentration in the most dynamic regions particularly near the ice edge in the barents and greenland seas and in zones of high shear these passive microwave ice motions show a large increase in spatial detail over motion fields optimally interpolated from buoy and wind observations especially where buoy data are virtually absent such as near coasts and in some passages between the arctic ocean and its peripheral seas the feasibility of obtaining ice motion from the 37 ghz data in addition to the 85 ghz data should allow an important record of ice motion to be established for the duration of the scanning multichannel microwave radiometer smmr special sensor microwave imager ssm i and future microwave sensors that is from 1978 into the next millenium

characteristics of sea ice floe size distribution in the seasonal ice zone 1 the size distribution of sea ice floes was observed by coordinated landsat imagery and video monitoring conducted from an icebreaker and a helicopter for an area 38 km 26 km in seasonal sea ice in the southern sea of okhotsk in february 2003 the combination of imagery on several scales allowed measurements of ice floes over three orders of magnitude from 1 m to 1 5 km two different regimes were observed floes larger than about 40 m have a power law number density with an exponent of 1 87 in the lower range of earlier results below 40 m the power law exponent is 1 15 the cause of these two different regimes is hypothesized to lie in the effects of swell on floes of different sizes and thicknesses the importance of the floe size distribution for lateral melting is elucidated

open water production in arctic sea ice satellite measurements and model parameterizations sequential synthetic aperture radar sar images from the ers 1 spacecraft were routinely used as input to the geophysical processor system at the alaska sar facility from 1992 through 1994 to produce sea ice displacement vectors on a 5 km grid we have combined some 5000 of these products consisting of nearly 700 000 displacement vectors into a set of 914 strips or mosaics of ice motion that span mostly 3 day intervals for each strip we compute the opening and closing of leads based on the change in area of the 5 km grid cells we also compute the area averaged deformation or strain invariants of the motion the small scale several kilometer lead activity can be parameterized fairly well in terms of the large scale several hundred kilometer strain invariants sea ice models implicitly contain such a parameterization through their constitutive equations the well known model of hibler 1979 that uses a viscous plastic rheology and an elliptical yield curve is in good agreement with our data the variance in the data about this theoretical relationship is less than that suggested by a random model of sea ice motion the data also indicate that shearing deformation contributes to the opening and closing of leads models with two categories or levels of ice thickness generally do not take shearing deformation into account in the evolution of the ice concentration nor do they redistribute ice as a result of ridging we show how to add these features to two level models however we argue that three level models consisting of open water thin ice and thick ice are much better suited to the proper treatment of open water production and we present such a model

a three component mixing model for ridge crest hydrothermal fluids the hydrothermal fluid chemistry data set for sediment starved ridge axes is used to estimate endmember compositions and to constrain a three component mixing model based on that of von damm using numerical methods to estimate the endmember compositions the data set includes fe cl h2s na k ca and sr at 11 13 n and 21 n east pacific rise north and south cleft segment southern juan de fuca ridge tag and mark q mode factor analysis shows that the data can be explained 99 9 by 3 factors a constrained optimization of a weighted least squares algorithm assuming conservative mixing and with the constraints that all endmember concentrations and contributions are non negative and that fractional contributions sum to one is used to partition the data set into endmembers mixing of the calculated endmembers consistently found to be phase separated brine vapor and hydrothermally altered seawater reproduces the composition of the vent fluids the model is consistent with the presence of a convecting brine layer in the primary reaction zone at depth as suggested by bischoff and rosenbauer that transfers properties to the overlying circulating seawater by release of a vapor and by diffusion we suggest that future experimental work examine solubility controls in conjunction with and subsequent to phase separation and work with a wider range of fluid salinities

automated extraction of pack ice motion from advanced very high resolution radiometer imagery multiple subarea cross correlations have been computed from visible advanced very high resolution radiometer images of the beaufort sea in an automated technique to detect pack ice motion the computational method is an application of the well known matched filter and consists of subdividing the first image into a set of subareas and correlating each reference subarea against the appropriate region of the second image the correlation functions are processed to determine a set of local maxima which define end point vectors of ice displacements from the subarea centers resulting velocities agree well with estimates of ice movement obtained by manually measuring invariant ice feature displacements the velocity fields show the spatial structures of ice motion over scales of 100 500 km with a high degree of pattern consistency and agreement with simple surface wind driving

relationship between sea ice motion and geostrophic wind in the northern hemisphere this paper presents maps showing the relationship between sea ice motion derived from defense meteorological satellite program dmsp special sensor microwave imager ssm i imagery and the geostrophic wind in the northern hemisphere for seven winters 1991 92 1997 98 the sea ice motion is highly correlated with the geostrophic wind except for some coastal regions overall the direction of the ice motion is nearly parallel to the wind an obvious contrast between seasonal ice zones and the interior of the arctic is observed in the speed reduction factor ratio of ice speed to wind speed which is probably caused by the spatial variation of internal ice stress surface ocean currents are also derived by subtracting the wind effect from the ice motion

effect of sea ice rheology in numerical investigations of climate 1 plastic sea ice rheologies that employ teardrop and parabolic lens yield curves and allow varying biaxial tensile stresses have been developed these rheologies together with the previously developed ellipse and mohr coulomb ellipse rheologies are implemented in a thickness and enthalpy distribution sea ice model to examine the rheological effect in numerical investigations of arctic climate the teardrop lens and ellipse rheologies obey a normal flow rule and result in a two peak shear stress distribution the first peak is at the zero shear stress the second is near 16 000 n m 1 for the ellipse and two lens rheologies and near 30 000 n m 1 for the two teardrop rheologies the location of the second peak depends on the fatness of the yield curve and the amount of biaxial tensile stress allowed in contrast the mohr coulomb ellipse rheology based on coulombic friction failure does not tend to create the second peak the incorporation of biaxial tensile stress tends to increase ice thickness in most of the arctic a fatter yield curve tends to increase the frequency of large shear stresses an increased frequency of large shear stresses in conjunction with the inclusion of biaxial tensile stress tends to reduce ice speed and ice export to enhance ice ridging in the arctic interior and to reduce ice ridging in the coastal areas which has a significant impact on arctic spatial ice mass distribution and the total ice budget the teardrop rheologies reduce spatial bias of modeled ice draft against submarine observations more than others by changing ice motion deformation and thickness the choice of plastic rheology also considerably affects the simulated surface energy exchanges particularly in the arctic marginal seas

improving the spatial distribution of modeled arctic sea ice thickness 1 the spatial distribution of ice thickness draft in the arctic ocean is examined using a sea ice model a comparison of model predictions with submarine observations of sea ice draft made during cruises between 1987 and 1997 reveals that the model has the same deficiencies found in previous studies namely ice that is too thick in the beaufort sea and too thin near the north pole we find that increasing the large scale shear strength of the sea ice leads to substantial improvements in the model s spatial distribution of sea ice thickness and simultaneously improves the agreement between modeled and ers derived 1993 2001 mean winter ice thickness

the thickness distribution of sea ice and snow cover during late winter in the bellingshausen and amundsen seas antarctica data collected from a voyage of rv nathaniel b palmer to the bellingshausen and amundsen seas during august september 1993 are used to investigate the thickness distribution of sea ice and snow cover and the processes that influence the development of the first year pack ice the data are a combination of in situ and ship based measurements and show that the process of floe thickening is highly dependent on ice deformation in particular rafting and ridging play important roles at different stages of floe development rafting is the major mechanism in the early stages of development and core structure data show the mean thickness of individual layers of crystals to be only 0 12 m most ice 0 6 m having some surface deformation blocks within ridge sails are typically in the range 0 3 0 6 m thick and ship based observations estimate approximately 25 of the pack exhibits surface ridging when corrected for biases in the observational methods the data show that the dominant ice and snow thickness categories are 0 7 m and 0 2 0 5 m respectively and account for 40 and 36 of the surface area of the pack ice approximately 8 of the pack is open water an estimate of the effects of ridging on the distribution of ice mass within the pack suggests that between 50 and 75 of the total mass is contained within the 25 of the pack that exhibits surface ridging

opening and closing of sea ice leads digital measurements from synthetic aperture radar the coming opportunity to extract quantitative sea ice data from routine synthetic aperture radar imagery requires the development of automated image processing techniques an algorithm is described for measuring the opening and the closing of leads by comparing two sequential synthetic aperture radar sar digital images the pair of images is classified into leads and ice correcting for variation in brightness with range displacements are determined automatically on a regular 2 km grid on a 100 km square scene by cross correlation an algorithm groups together cells which cover a lead event the lead area change is estimated for each cell group by counting lead pixels before and after deformation all positive changes are summed to obtain the amount of opening and all negative changes give closing errors are estimated by comparison with area changes determined from manually digitized lead boundaries and are about 0 2 of the area of the scene for comparison the measured opening and closing are in the range of 1 to 3 of the scene area in ice models the openings and closings of leads are parameterized in terms of the large scale deformation sar allows us to study these parametric relations by giving us access both to direct observations of opening and closing and to detailed kinematic data from which to estimate the mean deformation in this image pair for which the deformation is nearly pure shear we find relatively small amounts of opening and closing consistent with previous observations and with parameterizations in most models the large values of opening and closing predicted by the poisson gauss kinematic model are not in evidence

dependence of sea ice yield curve shape on ice thickness in this note the authors discuss the contribution that frictional sliding of ice floes or floe aggregates past each other and pressure ridging make to the plastic yield curve of sea ice using results from a previous study that explicitly modeled the amount of sliding and ridging that occurs for a given global strain rate it is noted that the relative contribution of sliding and ridging to ice stress depends upon ice thickness the implication is that the shape and size of the plastic yield curve is dependent upon ice thickness the yield curve shape dependence is in addition to plastic hardening weakening that relates the size of the yield curve to ice thickness in most sea ice dynamics models the yield curve shape is taken to be independent of ice thickness the authors show that the change of the yield curve due to a change in the ice thickness can be taken into account by a weighted sum of two thickness independent rheologies describing ridging and sliding effects separately it would be straightforward to implement the thickness dependent yield curve shape described here into sea ice models used for global or regional ice prediction

sea ice tracking by nested correlations spatial differences in sea ice displacement affect ice stress ice production and the mass balance of the ice cover our concepts about the spatial structure of this field have been undernourished because of a paucity of data with high spatial detail and because of the tedium of extracting such measurements from images manually a method is described that measures displacements from synthetic aperture radar digital imagery with fine spatial resolution and does so fully automatically many small areas of ice common to two images are identified by correlating the two images the strategy is to acquire a crude displacement field first from highly averaged images and to refine this field with images of successively higher resolution the median discrepancy between automatically and manually measured displacements is three pixels 0 075 km the algorithm operates successfully on compact ice with large floes and modest rotation rates we believe it will prove applicable to most of the arctic ice cover throughout the year

on modeling the anisotropic failure and flow of flawed sea ice the failure and flow of sea ice on scales small and large is characterized by the propagation of oriented leads and cracks in this paper a theory for the dynamical treatment of anisotropic oriented flaws in sea ice is developed and used to examine the interaction of these oriented flaws under idealized stress forcing the essential idea of the theory is to take one or more oriented weak leads imbedded in thick ice a constitutive law for both the thin and thick ice is taken to be similar to laboratory observations which are consistent with mohr coulomb like failure application of normal continuum mechanics boundary conditions leads to anisotropic flow and failure characteristics of this anisotropic composite under both near and far field forcing the local failure characteristics show that there is a preferred orientation for failure with the intersection between leads increasing as confinement increases for spatially separated interacting flaws the theory predicts a preference for the weakening of flaws in a narrow range of angles of 10 20 relative to the principal far field stress imbedding isolated flaws leads to simulated damage directions consistent with local failure characteristics in the case where the ice is considered to have available flaws in all directions fracture propagation is found to proceed by picking out oriented flaws alternating in direction along large scale damage strikes with individual flaw alignments of 20 relative to far field principal stresses the mechanisms responsible for these results and how this anisotropic sea ice rheology might be implemented in current dynamic thermodynamic sea ice models are discussed