heat flux through sea ice in the western weddell sea convective and conductive transfer processes the heat flux through the snow and sea ice cover and at the ice ocean interface were calculated at five sites in the western weddell sea during autumn and early winter 1992 the ocean heat flux averaged 7 2 w m2 from late february to early june and average ice air heat flux in the second year floes depended on the depth of the snow cover and ranged from 9 to 17 0 8 w m2 in late february three of the five sites had an ice surface which was depressed below sea level resulting at two of the sites in a partially flooded snow cover and a slush layer at the snow ice interface as this slush layer froze to form snow ice the dense brine which was rejected flowed out through brine drainage channels and was replaced by lower salinity nutrient rich seawater from the ocean upper layer we estimate that about half of the second year ice in the region was covered with this slush layer early in the winter as the slush layer froze over a 2 to 3 week period the convection within the ice transported salt from the ice to the upper ocean and increased total heat flux through the overlying ice and snow cover on an area wide basis approximately 10 cm of snow ice growth occurred within second year pack ice primarily during a 2 to 3 week period in february and march this ice growth near the surface of the ice provides a salt flux to the upper ocean equivalent to 5 cm of ice growth despite the thick about 1 m ice cover in addition to the ice growth in the small area less than 5 open water regions

imaging the structure of a large scale tid using isr and tec data 1 here we present north american observations of the 3 dimensional structure of large scale traveling ionospheric disturbances tids that affected the low and mid latitude ionosphere during the stormtime period of october 1 2 2002 using tec data from the american network of dual frequency gps receivers we are able to examine the effect of the tids on the background tec and thus image their horizontal scales incoherent scatter radar data from the arecibo observatory give information on the vertical structure of the disturbances the meridional and zonal structure of the tids are explored by computing the tec perturbation a method which has a resolution of a fraction of a tec unit the technique is effective in mapping the global structure of large scale disturbances as the lower latitude perturbations can be examined at the same time as the higher latitude sources the method may prove valuable in studying the formation and propagation of tids

winter snow cover on sea ice in the weddell sea measurements of snow thickness temperature salinity density and stratigraphy acquired during the 1992 winter weddell gyre study are presented results indicate that the winter snow cover on sea ice in the weddell sea is extremely variable extreme fluctuations in antarctic synoptic conditions air temperature precipitation humidity and wind speed occur during the austral winter they result in unique modifications and additions to the snow layer during the aging process and act to stabilize an otherwise easily wind redistributed shallow snow cover and develop well packed drift features the latter occur even over relatively undeformed areas of sea ice and have a significant localized effect on the snow thickness distribution significant variability in snow grain size mean 2 73 3 12 mm and density 0 32 0 09 g cm 3 is observed as a result of cyclical switches between high and low temperature gradient metamorphism multiple icy layers indicate multiple thaw freeze events one such event occurred during a 3 day station during which the air temperature rose by 22 c in 12 hours to approximately 0 c this paper also examines mechanisms for flooding of the snow ice interface including snow loading even where the latter is not a factor the layer of snow immediately above the snow ice interface is commonly damp and saline 10 limitations in the data set are discussed and comparisons are drawn with other experiments

thickness distribution of antarctic sea ice 1 ship based observations are used to describe regional and seasonal changes in the thickness distribution and characteristics of sea ice and snow cover thickness around antarctica the data set comprises 23 373 observations collected over more than 2 decades of activity and has been compiled as part of the scientific committee on antarctic research scar antarctic sea ice processes and climate aspect program the results show the seasonal progression of the ice thickness distribution for six regions around the continent together with statistics on the mean thickness surface ridging snow cover and local variability for each region and season a simple ridge model is used to calculate the total ice thickness from the observations of level ice and surface topography to provide a best estimate of the total ice mass including the ridged component the long term mean and standard deviation of total sea ice thickness including ridges is reported as 0 87 0 91 m which is 40 greater than the mean level ice thickness of 0 62 m analysis of the structure function along north south and east west transects revealed lag distances over which sea ice thickness decorrelates to be of the order of 100 300 km which we use as a basis for presenting near continuous maps of sea ice and snow cover thickness plotted on a 2 5 5 0 grid

snow depth of the weddell and bellingshausen sea ice covers from icebridge surveys in 2010 and 2011 an examination we examine the snow radar data from the weddell and bellingshausen seas acquired by eight icebridge oib flightlines in october of 2010 and 2011 in snow depth retrieval the sidelobes from the stronger scattering snow ice s i interfaces could be misidentified as returns from the weaker air snow a s interfaces in this paper we first introduce a retrieval procedure that accounts for the structure of the radar system impulse response followed by a survey of the snow depths in the weddell and bellingshausen seas limitations and potential biases in our approach are discussed differences between snow depth estimates from a repeat survey of one weddell sea track separated by 12 days without accounting for variability due to ice motion is 0 7 13 6 cm average snow depth is thicker in coastal northwestern weddell and thins toward cape norvegia a decrease of 30 cm in the bellingshausen the thickest snow is found nearshore in both octobers and is thickest next to the abbot ice shelf snow depth is linearly related to freeboard when freeboards are low but diverge as the freeboard increases especially in the thicker rougher ice of the western weddell we find correlations of 0 71 0 84 between snow depth and surface roughness suggesting preferential accumulation over deformed ice retrievals also seem to be related to radar backscatter through surface roughness snow depths reported here generally higher than those from in situ records suggest dissimilarities in sample populations implications of these differences on antarctic sea ice thickness are discussed

the percolation phase transition in sea ice sea ice exhibits a marked transition in its fluid transport properties at a critical brine volume fraction p c of about 5 percent or temperature t c of about 5 c for salinity of 5 parts per thousand for temperatures warmer than t c brine carrying heat and nutrients can move through the ice whereas for colder temperatures the ice is impermeable this transition plays a key role in the geophysics biology and remote sensing of sea ice percolation theory can be used to understand this critical behavior of transport in sea ice the similarity of sea ice microstructure to compressed powders is used to theoretically predict p c of about 5 percent

sea ice thickness distribution of the bellingshausen sea from surface measurements and icesat altimetry abstract although sea ice extent in the bellingshausen amundsen ba seas sector of the antarctic has shown significant decline over several decades there is not enough data to draw any conclusion on sea ice thickness and its change for the ba sector or for the entire southern ocean this paper presents our results of snow and ice thickness distributions from the simba 2007 experiment in the bellingshausen sea using four different methods aspect ship observations downward looking camera imaging ship based electromagnetic induction em sounding and in situ measurements using ice drills a snow freeboard and ice thickness model generated from in situ measurements was then applied to contemporaneous icesat satellite laser altimetry measured freeboard to derive ice thickness at the icesat footprint scale errors from in situ measurements and from icesat freeboard estimations were incorporated into the model so a thorough evaluation of the model and uncertainty of the ice thickness estimation from icesat are possible our results indicate that icesat derived snow freeboard and ice thickness distributions asymmetrical unimodal tailing to right for first year ice 0 29 0 14 m for mean snow freeboard and 1 06 0 40 m for mean ice thickness multi year ice 0 48 0 26 and 1 59 0 75 m respectively and all ice together 0 42 0 24 and 1 38 0 70 m respectively for the study area seem reasonable compared with those values from the in situ measurements aspect observations and em measurements the em measurements can act as an appropriate supplement for aspect observations taken hourly from the ship s bridge and provide reasonable ice and snow distributions under homogeneous ice conditions our proposed approaches 1 of using empirical equations relating snow freeboard to ice thickness based on in situ measurements and 2 of using isostatic equations that replace snow depth with snow freeboard or empirical equations that convert freeboard to snow depth are efficient and important ways to derive ice thickness from icesat altimetry at the footprint scale for antarctic sea ice spatial and temporal snow and ice thickness from satellite altimetry for the ba sector and for the entire southern ocean is therefore possible

impacts of a mushy layer thermodynamic approach in global sea ice simulations using the cice sea ice model we perform global simulations of the los alamos sea ice model cice with a new thermodynamics component that has a fully prognostic variable bulk salinity vertical profile based on mushy layer physics the processes of gravity drainage melt water flushing and snow ice formation are parameterized to allow the bulk salinity to evolve with time we analyze the seasonal and spatial variation of sea ice bulk salinity area volume and thickness and compare these quantities to simulations using the previous thermodynamic component adjusting one of the gravity drainage parameters we find good agreement between simulation results and fieldwork ice core observations of sea ice bulk salinity as expected bulk salinity is highest during periods of ice growth and lowest after periods of ice melt in the northern hemisphere the new thermodynamics component produces thicker ice than the previous thermodynamics component of the nine major differences between the two models differences in how salinities are calculated and how melt pond flushing is parameterized are the principal causes of this thickness difference thickness differences are smaller in the southern hemisphere than in the northern hemisphere since a greater fraction of ice melts and differences cannot accumulate year on year model differences in how ice thickness changes and snow ice formation are calculated are the most important causes of the different thickness between the two thermodynamic components in the southern hemisphere the melt pond area and volume are found to be highly sensitive to a parameter choice controlling drainage through macroscopic holes in the ice in both hemispheres

a one dimensional percolation model of flooding and snow ice formation on antarctic sea ice a one dimensional thermodynamic sea ice growth model is developed with emphasis on seawater flooding and snow ice formation on antarctic sea ice to examine the possibility that flooding is the result of brine percolation through a porous ice matrix and the consequences of this percolation on the salinity structure and mass balance of the ice flooding is modeled in a semiheuristic fashion by examining two possible regimes for seawater and brine infiltration through the porous ice into the snowpack a standard model assumes that the upward flow of brine is horizontally homogeneous and brine flow is modeled using a darcian scheme a simple model assumes that the infiltrating brine does not interact with the internal ice brine network but instead percolates upward through cracks or is restricted in spatial extent results of simulations are shown for the climatology in the ross sea and compared to field data from one autumn and one winter cruise aboard the r v nathaniel b palmer in 1995 sensitivity studies are performed to show the effects of variations in climate forcing the dependence of brine percolation and snow ice formation on key thermophysical parameters is investigated results indicate that the mass balance depends very strongly on the brine flow regime in the standard model ice salinities and brine volumes are greatly affected by brine percolation creating a strong feedback between flooding and future snow ice production snow ice formation for the simple model was much more predictable and depended primarily on snow load comparison of results with field data indicate that if brine percolation is the major mechanism for flooding and snow ice formation then there must be either substantial convective redistribution of salt to maintain ice porosity or the flow must be spatially inhomogeneous

first observations of intense gps l1 amplitude scintillations at midlatitude 1 first observations of intense gps l1 amplitude scintillation activity in the midlatitude ionosphere at latitudes corresponding to the northeastern united states have been made moderate to severe these scintillations result from space weather effects due to a disturbed ionosphere moderate to severe scintillations can degrade or even disrupt communication and navigation systems relying upon transionospheric radio wave propagation a modified gps receiver was used to record gps satellite signal strength at cornell university 53 2 magnetic latitude during a magnetospheric disturbance on september 25 26 2001 from 0000 0400 utc this disturbance kp 6 minimum dst 110 nt prompted the ionospheric trough to move equatorward over the northeastern u s and produced large plasma densities and gradients attributed to storm time effects this disturbance resulted in intense l band amplitude scintillations 20 db s4 0 8 which are highly uncharacteristic at this magnetic latitude concurrent measurements of tec showed steep density gradients 30 tec deg and evidence of irregularity structuring

salinity profiles of antarctic sea ice field data and model results in order to describe and compare sea ice salinity distributions which are of interest in the study of physical and biological ice characteristics as well as ice ocean interaction we have computed composite profiles and fitted third degree polynomials to salinity data of 129 cores from the weddell sea four characteristic profile shapes have been recognized and described through the polynomial coefficients c s i and type profiles the field data have been compared with ideal salinity profiles generated by a simulation scheme based on thermodynamic growth under climatological conditions representative of the weddell sea composite salinity profiles agree well with simulations irrespective of the growth mechanism i e frazil or congelation suggesting that ice properties which depend on salinity or porosity may evolve independent of ice growth conditions analysis of salinity and 18o data in conjunction with the simulations demonstrates that apart from meteorological conditions controlling growth velocity and temperature distribution within the ice flooding and upward brine expulsion are important in raising top salinities as frequently observed low top salinities are typical of ice that has undergone retexturing and differential desalination salinity decreases towards the bottom of a floe are a result of high oceanic heat fluxes and snow cover effects as a consequence of these processes the bulk salinity of weddell sea ice cannot be described by a simple linear age thickness relationship as characteristic of arctic first year ice

seasonal variations in the properties and structural composition of sea ice and snow cover in the bellingshausen and amundsen seas antarctica sixty three ice cores were collected in the bellingshausen and amundsen seas in august and september 1993 during a cruise of the r v nathaniel b palmer the structure and stable isotopic composition 18 o 16 o of the cores were investigated in order to understand the growth conditions and to identify the key growth processes particularly the contribution of snow to sea ice formation the structure and isotopic composition of a set of 12 cores that was collected for the same purpose in the bellingshausen sea in march 1992 are reassessed frazil ice and congelation ice contribute 44 and 26 respectively to the composition of both the winter and summer ice core sets evidence that the relatively calm conditions that favour congelation ice formation are neither as common nor as prolonged as the more turbulent conditions that favour frazil ice growth and pancake ice formation both frazil and congelation ice layers have an av erage thickness of 0 12 m in winter evidence that congelation ice and pancake ice thicken primarily by dynamic processes the thermodynamic development of the ice cover relies heavily on the formation of snow ice at the surface of floes after sea water has flooded the snow cover snow ice layers have a mean thickness of 0 20 and 0 28 m in the winter and summer cores respectively and the contribution of snow ice to the winter 24 and summer 16 core sets exceeds most quantities that have been reported previously in other antarctic pack ice zones the thickness and quantity of snow ice may be due to a combination of high snow accumulation rates and snow loads environmental conditions that favour a warm ice cover in which brine convection between the bottom and top of the ice introduces sea water to the snow ice interface and bottom melting losses being compensated by snow ice formation layers of superimposed ice at the top of each of the summer cores make up 4 6 of the ice that was examined and they increase by a factor of 3 the quantity of snow entrained in the ice the accumulation of superimposed ice is evidence that melting in the snow cover on antarctic sea ice floes ran reach an advanced stage and contribute a significant amount of snow to the total ice mass

response of low latitude ionospheric total electron content to the geomagnetic storm of 24 august 2005 1 response of low latitude ionosphere to the geomagnetic storm of 24 august 2005 has been studied using total electron content tec data obtained from the global positioning system gps receivers these studies were carried out using the receivers that were located 1 near the northern crest 15 n mag lat of the equatorial ionization anomaly around 56 e 74 e and 102 e longitude and 2 from the northern crest of the ionization anomaly down to the magnetic equator in the longitude belt 75 e 3 e these studies have been substantiated with the ground based magnetometer data at tirunelveli and alibag an equatorial and off equatorial station respectively the ground based ionosonde data at new delhi a low latitude station have also been used to substantiate the tec observations the storm day tec shows two well defined humps at all stations wherein enhancements of the order of 80 100 have been observed while the first of the enhancements has been attributed to the prompt penetration electric field associated with an interplanetary electric field ief ey of about 35 mv m the other one has been attributed to the second episode of the prompt penetration electric field ief ey 20 mv m and abnormal equatorial plasma fountain in late evening hours respectively during the unsteady ring current conditions when the imf bz was still southward penetration of a westward electric field has been inferred two peaks in fof2 have been observed whose time of occurrence coincides with those of the humps in the low latitude tec results from stations having nearly the same magnetic latitude show that the ionospheric response in terms of gps tec to the prompt penetration electric fields is longitudinally independent formation of the first hump in tec is progressively delayed in time from low to near equatorial latitudes for stations in different magnetic latitudes along nearly the same longitude however its time of appearance at diego garcia a station magnetically conjugate to udaipur is the same as that at udaipur the results also reveal the poleward expansion of the ionization anomaly due to the storm disturbance dynamoelectric fields have been inferred to be responsible for the suppressed plasma fountain resulting in suppressed tec values and equatorward contraction of the ionization anomaly on 25 august compared to a reference quiet day

surface properties and processes of perennial antarctic sea ice in summer ice core and snow data from the amundsen bellingshausen and weddell seas antarctica show that the formation of superimposed ice and the development of seawater filled gap layers with high algal standing stocks is typical of the perennial sea ice in summer the coarse grained and dense snow had salinities mostly below 0 1 per mil a layer of fresh superimposed ice had a mean thickness ranging from 0 04 0 12 m 0 04 to 0 08 m thick gap layers extended downwards from 0 02 to 0 14 m below the water level these gaps were populated by diatom standing stocks up to 439 g l chlorophyll a we propose a comprehensive heuristic model of summer processes where warming and the reversal of temperature gradients cause major transformations in snow and ice properties the warming also causes the re opening of incompletely frozen slush layers caused by flood freeze cycles during winter alternatively superimposed ice forms at the cold interface between snow and slush in the case of flooding with negative freeboard combined these explain the initial formation of gap layers by abiotic means alone the upward growth of superimposed ice above the water level competes with a steady submergence of floes due to bottom and internal melting and accumulation of snow

dayside midlatitude ionospheric response to storm time electric fields a case study for 7 september 2002 1 with the storm of 7 8 september 2002 as a study case we demonstrate that an ionospheric model driven by a suitable storm time convection electric field can reproduce the f region dayside density enhancements associated with the ionospheric storm positive phase the ionospheric model in this case is the utah state university time dependent ionospheric model tdim the electric field model is the university of michigan s hot electron and ion drift integrator heidi extensive ground truth is available throughout the study period from two independent sources ground based vertical tec and ionosonde stations our simulation results are in good agreement with these observations we address the question of what is the source of the high density plasma that is seen during the positive storm phase and show that in this case a magnetospheric electric field with an eastward component that penetrates to midlatitudes increases local production on the dayside to a degree that is sufficient to account for the storm time density increases that have been observed

18o concentrations in sea ice of the weddell sea antarctica we present data on ice texture salinity and delta o 18 obtained from identical sections of ice cores during the winter weddell sea project 1986 on rv polarstern from july through august 1986 in the longitude range between 5 degrees w and 7 degrees e we find no uniquely definable relationship between delta o 18 values and ice texture in a particular section however most of the snow ice as well as some sections of frazil ice ar found to have negative delta o 18 concentrations this is due to varying degrees of admixtures of meteoric ice snow and sea water during formation of snow ice in contrast to common assumptions our results seem to indicate that a snow cover contributes positively to sea ice growth rather than slowing down the overall growth rate based on a simple model we have estimated the contributions of meteoric ice mean of 3 3 and the combined meteoric ice sea water fraction a minimum of 7 6 to the total ice thickness for the majority of the sampled floes although this is only a moderate contribution to the overall mass balance in the absence of congelation growth it nevertheless enhances ice growth in general this hypothesis is dependently supported by our snow and ice thickness data wadhams and others 1987 which demonstrate that the depression of the snow ice interface below the water line i e a negative freeboard and the formation of snow ice is a common occurrence in the weddell sea therefore we hypothesize that the major part of the observed apparent increase in ice thickness between our inbound and outbound tracks of wwsp 86 may not be derived from regular thermodynamically driven congelation growth but rather from the snow ice component in floes of the weddell sea

observations of brine drainage networks and microstructure of first year sea ice brine drainage networks and the microstructure of first year sea ice have been examined at two locations near barrow northern alaska a method for obtaining full depth sections of ice sheets up to 1 8 m thick is presented and shown to provide information on the spatial distribution and geometry of brine drainage networks on a scale of meters a number of such sections from the two test sites are presented which reveal a greater variety of main channel and side branch configurations than is typically observed in ice grown in the laboratory vertical and horizontal micrographs and thin section photographs were obtained in november 1993 and march and may 1994 at a test site in the relatively protected elson lagoon the resulting time series of photographic records provide detailed information on the size shape and spatial distribution of the brine and gas filled inclusions and a means to quantify their size and shape changes with time an example of the changes with time in inclusion sizes and aspect ratios in the vertical and horizontal directions for a depth of 0 2 m with a given thermal history is also presented

east antarctic sea ice albedo thickness distribution and snow cover characteristics of springtime sea ice off east antarctica were investigated during a cruise of the australian national antarctic research expedition in october through december 1988 the fractional coverage of the ocean surface the ice thickness and the snow cover thickness for each of several ice types were estimated hourly for the region near the ship these observations were carried out continuously during the 4 weeks the ship was in the ice thin and young ice types were prevalent throughout the region and the observations show a systematic increase in the total area weighted pack ice thickness including open water area from only 0 2 m within 50 km of the ice edge to 0 45 m close to the coast ice thickness averaged over the ice covered region only is also relatively thin ranging from 0 35 m near the ice edge to 0 65 m in the interior these values are probably typical of average winter thickness for the area the average snow cover thickness on the ice increased from 0 05 m near the ice edge to 0 15 m in the interior average ice concentration increased from less than 6 10 near the ice edge to 8 10 in the interior the ship observed concentrations were in good agreement with concentrations derived from passive microwave satellite imagery except in some regions of high concentration in these regions the satellite derived concentrations were consistently lower than those estimated from the ship possibly because of the inability of the satellite sensors to discriminate the appreciable percentage of very thin ice observed within the total area spectral albedo was measured for nilas young grey ice grey white ice snow covered ice and open water at wavelengths from 420 to 1000 nm allwave albedo was computed by using the spectral measurements together with estimates of near infrared albedo and modeled spectral solar flux area averaged albedos for the east antarctic sea ice zone in spring were derived from representative allwave albedos together with the hourly observations of ice types these area averaged surface albedos increased from about 0 35 at the ice edge to about 0 5 at 350 km from the edge remaining at 0 5 to the coast of antarctica the low average albedo is in part due to the large fraction of open water within the pack but extensive fractions of almost snow free thin ice also play an important role

internal melting in antarctic sea ice development of gap layers 1 an internal gap layer of deteriorated sea ice is co located with a significant microbial biological community in late first year and second year antarctic sea ice in summer we modeled gap layer formation using a thermal flux model based on the summer reversal in thermal gradient and the thermal conductivity found in the upper ice column the conductive model gives internal sea ice melt rates gap layer formation rates between 0 1 to 0 75cm day the cumulative melted layer thicknesses during summer computed from these rates agree with field observations since the processes for forming these structures act in the vertical direction only and over a significant range of expected conditions they are commonly formed in the antarctic sea ice zone during summer supporting a significant contribution of gap layers to the ice mass balance and productivity on a circumpolar basis

storm time dependence of equatorial disturbance dynamo zonal electric fields we use jicamarca radar observations of f region vertical plasma drifts and auroral electrojet indices during 1968 1988 to study the characteristics and temporal evolution of equatorial disturbance dynamo zonal electric fields these electric fields result from the dynamo action of storm time winds and or thermospheric composition changes driven by enhanced energy deposition into the high latitude ionosphere during geomagnetically active conditions the equatorial vertical drift perturbations last for periods of up to 30 hours after large increases in the high latitude currents on the average this process can be described by two basic components with time delays of about 1 12 hours and 22 28 hours between the high latitude current enhancements and the equatorial velocity perturbations our data indicate strong coupling between dynamo processes with different timescales the short term disturbance dynamo drives upward equatorial drifts eastward electric fields at night with largest amplitudes near sunrise and small downward drifts during the day these perturbation drifts are in good agreement with results from the blanc richmond disturbance dynamo theory the dynamo process with time delays of about a day drives upward drift velocities at night with largest values near midnight and downward drifts in the sunrise noon sector in this case the amplitudes of the disturbance drifts maximize during geomagnetically quiet times preceded by strongly disturbed conditions we also present results of a new equatorial storm time dependent empirical model which illustrate the characteristics of the vertical disturbance dynamo drifts

numerical simulations of the profile properties of undeformed first year sea ice during the growth season a simulation scheme is developed that estimates salinity profiles for first year sea ice during the growth season as a function of the growth history of the ice the model considers the dependence of the initial ice salinity on ice growth velocity and sea water salinity and also the subsequent drainage of brine from the ice the equation for ice growth assumes a linear temperature profile within the ice and is driven by surface heat balance equations that are based on smoothed climatic data for the central arctic basin the estimated salinity profiles are in good agreement with natural profiles although temperature and salinity profiles depend upon the time of the year when ice growth is initiated the brine volume profiles which they specify are essentially a unique function of ice thickness a conclusion that holds even when the insulative effects of snow are considered the temperature and brine volume profiles are then utilized to calculate the ice strength and elastic modulus profiles which in turn specify the composite mechanical properties of the ice sheets through the application of a theory developed by assur 1967 significant differences which are largest for thin ice sheets are observed between ice sheet properties as calculated using composite plate theory and properties calculated from uniform plate theory and average ice properties these results provide a justification for the practice common within the ice modeling community of parameterizing the mechanical behavior of pack ice on the basis of the ice thickness distribution

modeling brine and nutrient dynamics in antarctic sea ice the case of dissolved silica sea ice ecosystems are characterized by microalgae living in brine inclusions the growth rate of ice algae depends on light and nutrient supply here the interactions between nutrients and brine dynamics under the influence of algae are investigated using a one dimensional model the model includes snow and ice thermodynamics with brine physics and an idealized sea ice biological component characterized by one nutrient namely dissolved silica dsi in the model dsi follows brine motion and is consumed by ice algae depending on physical ice characteristics the brine flow is either advective diffusive or turbulent the vertical profiles of ice salinity and dsi concentration are solutions of advection diffusion equations the model is configured to simulate the typical thermodynamic regimes of first year antarctic pack ice the simulated vertical profiles of salinity and dsi qualitatively reproduce observations analysis of results highlights the role of convection in the lowermost 5 10 cm of ice convection mixes saline nutrient poor brine with comparatively fresh nutrient rich seawater this implies a rejection of salt to the ocean and a flux of dsi to the ice in the presence of growing algae the simulated ocean to ice dsi flux increases by 0 115 compared to an abiotic situation in turn primary production and brine convection act in synergy to form a nutrient pump the other important processes are the flooding of the surface by seawater and the percolation of meltwater the former refills nutrients near the ice surface in spring the latter if present tends to expell nutrients from the ice in summer

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 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

sea level rise during past 40 years determined from satellite and in situ observations the 3 2 0 2 millimeter per year global mean sea level rise observed by the topex poseidon satellite over 1993 98 is fully explained by thermal expansion of the oceans for the period 1955 96 sea level rise derived from tide gauge data agrees well with thermal expansion computed at the same locations however we find that subsampling the thermosteric sea level at usual tide gauge positions leads to a thermosteric sea level rise twice as large as the true global mean as a possible consequence the 20th century sea level rise estimated from tide gauge records may have been overestimated

ice thickness variability isostatic balance and potential for snow ice formation on ice floes in the south polar pacific ocean spatial and temporal characteristics of snow and ice thickness were determined for data acquired during five cruises into the bellingshausen amundsen and ross seas between september 1993 and 1995 when sorted into distance classes from the ice edge snow and ice thicknesses show a pattern of spatial and temporal variability that reflects the relative regional importance of different sea ice growth mechanisms motion and deformation as well as of oceanographic processes the potential for snow ice formation was directly investigated for the drilling data flooding measured prior to drilling has a strong correspondence with negative freeboard while moist snow shows a lesser correspondence wetness and flooding are strongly correlated with the ratio of snow load and ice thickness while the relation to the amount of ridging is less conclusive using an isostatic argument the contribution of snow ice formation to the overall ice growth was shown to be considerably higher than that of congelation ice growth it was found that one length unit of snow accumulation or bottom ice melt on an ice floe leads to approximately the same amount of subsidence for the floe further rates of subsidence due to snow load and ice melt appear to be similar to uplift from congelation ice growth the degree of isostatic balance on different spatial scales was evaluated by introducing a generalized density weighted snow ice thickness ratio gsi for the drilling data the gsi includes slush densities in order to account for the suggested importance of snow ice formation deviations from isostatic balance occur locally but decrease quickly on spatial averaging scales of a few meters the closest fit to isostatic equilibrium is reached by choosing a maximum value for the slush density

the thermal conductivity of seasonal snow twenty seven studies on the thermal conductivity of snow k eff have been published since 1886 combined they comprise 354 values of k eff and have been used to derive over 13 regression equation and predicting k eff vs density due to large and largely undocumented differences in measurement methods and accuracy sample temperature and snow type it is not possible to know what part of the variability in this data set is the result of snow microstructure we present a new data set containing 488 measurements for which the temperature type and measurement accuracy are known a quadratic equation where is in g cm 3 and k eff is in w m 1 k 1 can be fit to the new data r 2 0 79 a logarithmic expression can also be used the first regression is better when estimating values beyond the limits of the data the second when estimating values for low density snow within the data set snow types resulting from kinetic growth show density independent behavior rounded grain and wind blown snow show strong density dependence the new data set has a higher mean value of density but a lower mean value of thermal conductivity than the old set this shift is attributed to differences in snow types and sample temperatures in the sets using both data sets we show that there are well defined limits to the geometric configurations that natural seasonal snow can take

natural convection in the subarctic snow cover the purpose of this study was to determine if air convects in a natural snow cover to detect convection the temperature field in the subarctic snow cover in fairbanks alaska was measured hourly during three winters 1984 1987 using an array of thermistors which were suspended on threads and allowed to be buried by snowfall the results indicate that convection occurred sporadically in 1984 1985 and almost continuously in 1985 1986 and 1986 1987 the evidence was 1 simultaneous warming and cooling at different locations in a horizontal plane in the snow and 2 horizontal temperature gradients of up to 16 c m 1 during the winter warm and cold zones developed in the snow and remained relatively fixed in space we interpret these zones to be the result of a diffuse plumelike convection pattern linked to spatial variations in the temperature of the snow soil interface air flow was inferred to have been primarily horizontal near the base of the snow and vertical elsewhere calculated flow speeds were of the order of 0 2 mm s 1 with a maximum value of 2 mm s 1 the convective circulation was time dependent with perturbations such as high wind or rapid changes in air temperature triggering periods when horizontal temperature gradients were strongest suggesting that these were also periods when the air flow was fastest the coincidence of depth hoar crystals with horizontal c axes and the horizontal flow lines at the base of the snow suggests that convection may have affected crystal growth directions

non linear thermal transport and brine convection in first year sea ice we report the first results from a programme recently set up to directly measure the thermal conductivity of young sea ice an array of thermistors frozen into first year antarctic sea ice provides temperature against depth data which is fitted directly with a partial differential equation for heat conduction temperatures are recorded every hour at twenty vertical intervals of 100mm over a period of 5 months allowing accurate and direct estimation of the thermal conductivity preliminary results indicate that the thermal conductivity is in the expected range with some evidence of nonlinear effects deeper in the ice a larger variance in data is evident at higher temperature gradients and at greater depths in the ice preliminary modelling of the impact of brine migration on heat transport through first year sea ice is presented diffusion driven brine pocket migration is school of mathematical and computing sciences victoria university of wellington po box 600 wellington new zealand yphysics dept victoria university of wellington po box 600 wellington new zealand znew zealand institute for industrial research and development po box 31310 lower hutt new zealand

thermodynamics of slush and snow ice formation in the antarctic sea ice zone snow over antarctic sea ice is often flooded by brine or seawater particularly in spring forming slush and snow ice here we evaluate the representation of the thermodynamics of slush and snow ice formation in large scale sea ice models using laboratory experiments nacl solutions poured into grated ice in an isolated container scaling analysis highlights latent heat as the main term of the energy budget the temperature of the new sea ice immediately after flooding is found very close to the saltwater freezing point whereas its bulk salinity is typically 20 g kg large scale sea ice models faithfully represent such physics yet the uncertainty on the origin of flooding saltwater impacts the calculated new ice temperature because of the different salinities of seawater and brine the laboratory experiments also suggest a potential limitation to the existing physical representations of flooding for brine fractions 60 ice crystals start floating upon saltwater natural sea ice observations suggest that the isolated system assumption holds for a few hours at most after which rapid heat and salt exchanges mostly destroy the initial flooding signature on temperature and salinity a small footprint on ice salinity remains however natural snow ice is found 3 5 g kg more saline than other forms of sea ice

ionospheric response to the geomagnetic storm of 15 may 2005 over midlatitudes in the day and night sectors simultaneously the ionospheric response to the geomagnetic storm of 15 may 2005 has been studied over midlatitude stations in the dayside and nightside simultaneously in the day side the ionospheric response has been studied using the ground based gps and ionosonde measurements from the stations pol2 and alma ata respectively the dayside total electron content tec and fof2 variations are characterized by two well separated enhancements of which the first enhancement in both the parameters is attributed to the episode of prompt penetration electric field caused by the sudden southward turning of interplanetary magnetic field imf bz around 0600 ut the second enhancement which was also superposed by wave like modulations has been attributed to the storm induced winds the maximum peak to peak amplitude of modulation in tec is found to be 5 tecu total electron content unit 1 tecu 1016 el m 2 the enhanced plasma density observed during the daytime at midlatitudes is found to be locally produced and not transported from the equatorial ionization anomaly region because the time of enhanced plasma density at midlatitude is earlier than that observed at low latitudes during the storm main phase the nightside gps observations from the midlatitude station algo algonquin park canada show moderate to large tec fluctuations and short duration depletions that occur in a narrow latitude zone these fluctuations and depletions in tec have been attributed to the combined effect of storm induced equatorward movement of the midlatitude ionospheric trough due to the expansion of auroral oval and the storm time enhanced density the maximum amplitude of the tec depletions is found to be of the order of 20 tecu rate of tec index is also found to be high with a maximum value of 2

ionospheric storm of early november 1993 in the indian equatorial region an investigation is made of the response of equatorial ionosphere in the indian 75 e sector to the major magnetic storm of november 3 1993 using data from the ionosonde and magnetometer networks spanning the region 0 3 34 5 n dip some outstanding and new aspects of the storm time ionospheric behaviour are revealed an anomalous and striking positive gradient in 0f2 from the magnetic equator to 34 5 dip developed under counter electrojet cej condition in the morning on november 4 corresponding to the early stage of the storm main phase this storm effect is attributed to plasma transport by a poleward surge in transequatorial winds due to large scale atmospheric gravity waves agws launched by auroral heating remarkable wave like variations in hpf2 and 0f2 immediately followed at locations away from dip equator till local sunset with concomitant disruptions in the development of the equatorial ionization anomaly eia rapid variations in meridional neutral winds due to large scale agws are assessed as the cause of the oscillations in hpf2 and the associated cyclic sequence of development and inhibition of eia as the outcome of the combined effects of plasma transport due to meridional winds and the plasma fountain driven by e b drift just after the onset of the storm recovery phase at 1800 lt a sudden and anomalous drop 54 57 in 0f2 prevailed throughout the anomaly region over the interval 1915 2330 lt with an apparent time delay in occurrence toward the magnetic equator this premidnight collapse of equatorial f region is interpreted in terms of horizontal transport of plasma across the equator toward the opposite hemisphere by an equatorward surge in meridional winds the case study showed that besides disturbances in the zonal electric field due to prompt penetration and ionospheric disturbance dynamo effects perturbations in neutral meridional winds played a prominent role in the ionospheric storm of november 4 1993 in the indian equatorial region

modelling antarctic fast ice growth an existing thermodynamic ice growth model semtner 1976 has been tested for its ability to predict the growth of fast ice in mcmurdo sound antarctica significant discrepancies between observed and predicted ice thicknesses were found to occur primarily due to the presence of sub ice platelets and the formation of a snow ice layer although these ice growth processes are not well enough understood to permit rigorous physical modelling it is shown that fairly simple modifications to the model greatly improve the accuracy of the thickness predictions and serve to highlight the importance of these processes in the antarctic fast ice environment surface flooding and snow ice formation are assumed to occur immediately upon the establishment of a positive hydrostatic water level and a surface temperature in excess of a critical value above which interconnecting channels in the ice matrix permit the flow of water to the surface the presence of the sub ice platelet layer is assumed to increase columnar ice growth at a rate proportional to the volume fraction of ice in the platelet layer a simple technique but one that permits estimates of platelet enhanced growth without detailed knowledge of oceanographic conditions the resulting model predictions are in close agreement with measurements of fast ice growth and decay in mcmurdo sound however data suitable for testing the model over a complete range of conditions and over multi year cycles are not available at the present time

on the extraordinary snow on the sea ice off east antarctica in late winter 2012 abstract in late winter early spring 2012 the second sea ice physics and ecosystems experiment sipex ii was conducted off wilkes land east antarctica onboard r v aurora australis the sea ice conditions were characterized by significantly thick first year ice and snow trapping the ship for about 10 days in the near coastal region the deep snow cover was particularly remarkable in that its average value of 0 45 m was almost three times that observed between 1992 and 2007 in the region to reveal factors responsible we used in situ observations and era interim reanalysis 1990 2012 to examine the relative contribution of the different components of the local regional snow mass balance equation i e snow accumulation on sea ice precipitation minus evaporation p e and loss by i snow ice formation and ii entering into leads due to drifting snow results show no evidence for significantly high p e in the winter of 2012 ice core analysis has shown that although the snow ice layer was relatively thin indicating less transformation from snow to snow ice in 2012 as compared to measurements from 2007 the difference was not enough to explain the extraordinarily deep snow based on these results we deduce that lower loss of snow into leads was probably responsible for the extraordinary snow in 2012 statistical analysis and satellite images suggest that the reduction in loss of snow into leads is attributed to rough ice surface associated with active deformation processes and larger floe size due to sea ice expansion this highlights the importance of snow sea ice interaction in determining the mean snow depth on antarctic sea ice

southern ocean winter mixed layer austral winter 1986 observations from the polarstern along the greenwich meridian from the ice edge to the antarctic margin show the mixed layer beneath the winter sea ice cover to be significantly depressed in oxygen saturation incorporation of weddell deep water wdw into the winter mixed layer responsible for this undersaturation also introduces heat and salinity into the surface layer which strongly influences the mixed layer sea air exchanges and sea ice formation processes the total wdw transfer into the mixed layer averages 45 myr 1 implying a residence time for the surface water of 2 5 years the associated winter heat flux is 41 w m 2 which limits ice thickness to about 0 55 m agreeing quite well with observations the air temperatures during the cruise are just sufficient to remove the wdw heat input in the presence of observed ice thickness and concentration this suggests that the sea ice cover and wdw heat input into the mixed layer are in approximate balance by midwinter the annual heat flux from wdw to the surface layer and hence into the atmosphere is estimated as 16 w m 2 extrapolation of the greenwich meridian wdw entrainment value to the full circumpolar 60 70 s belt yields total up welling of 24 106 m3 s 1 similar extrapolation of the heat flux value gives a circumpolar total of 2 8 1014 w as a consequence of circulation topography interaction the maud rise water column stands out as an anomaly relative to the surrounding region with a significantly more saline and dense mixed layer below the mixed layer the water column over the crest of the rise is identical to that over the flanks if the latter water column is upwelled by 400 m this uplifting is believed to be a response of the upstream flow encountering the rise increased upstream flow would be expected to increase maud rise upwelling and the dependent salinity density of the mixed layer slight increases in the mixed layer density could trigger a convective mode and generation of a polynya it is hypothesized that spin up of the weddell gyre s barotropic circulation induced by an increase of the regional wind stress curl would enhance the probability of polynya development over maud rise

a quantitative description of sea ice inclusions structurally sea ice consists of an ice matrix with inclusions of brine and air a quantitative description of the size of these inclusions is critical for both interpreting and modeling the electromagnetic properties of sea ice photomicrographs of ice thin sections were analyzed using a personal computer based image processing system to determine the number of inclusions the inclusion size distributions and statistics for brine pockets in young ice and first year ice and for air bubbles in a multiyear hummock inclusions ranging in size from thousandths of square millimeters to a few square millimeters were measured in all cases a two parameter lognormal distribution fits the cumulative inclusion size distributions well correlation coefficient greater than 0 99 this includes brine pockets in both granular and columnar ice and a range of brine volumes from 2 to 40 as ice warms and its brine volume increases the size distribution shifts toward larger brine pockets this increase in brine pocket size is particularly pronounced for brine volumes greater than 10 as individual brine pockets coalesce air bubbles are much larger than brine pockets with mean major axis lengths of the order of millimeters for air bubbles and tenths of a millimeter for brine pockets observations of inclusion shape factors indicate that in general brine pockets are more elongated than air bubbles

sea ice and snow cover characteristics during the winter spring transition in the bellingshausen sea an overview of simba 2007 abstract the sea ice mass balance in the antarctic simba experiment was conducted from the rvib n b palmer in september and october 2007 in the bellingshausen sea in an area recently experiencing considerable changes in both climate and sea ice cover snow and ice properties were observed at 3 short term stations and a 27 day drift station ice station belgica isb during the winter spring transition repeat measurements were performed on sea ice and snow cover at 5 isb sites each having different physical characteristics with mean ice snow thicknesses varying from 0 6 m 0 1 m to 2 3 m 0 7 m ice cores retrieved every five days from 2 sites and measured for physical biological and chemical properties three ice mass balance buoys imbs provided continuous records of snow and ice thickness and temperature meteorological conditions changed from warm fronts with high winds and precipitation followed by cold and calm periods through four cycles during isb the snow cover regulated temperature flux and controlled the physical regime in which sea ice morphology changed level thin ice areas had little snow accumulation and experienced greater thermal fluctuations resulting in brine salinity and volume changes and winter maximum thermodynamic growth of 0 6 m in this region flooding and snow ice formation occurred during cold spells in ice and snow of intermediate thickness in contrast little snow ice formed in flooded areas with thicker ice and snow cover instead nearly isothermal highly permeable ice persisted in spring short lived cold air episodes did not effectively penetrate the sea ice nor overcome the effect of ocean heat flux thus favoring net ice thinning from bottom melt over ice thickening from snow ice growth in all cases these warm ice conditions were consistent with regional remote sensing observations of earlier ice breakup and a shorter sea ice season more recently observed in the bellingshausen sea

insights into brine dynamics and sea ice desalination from a 1 d model study of gravity drainage 1 we study gravity drainage using a new 1 d multiphase sea ice model a parametrization of gravity drainage based on the convective nature of gravity drainage is introduced whose free parameters are determined by optimizing model output against laboratory measurements of sea ice salinity evolution optimal estimates of the free parameters as well as the parametrization performance remain stable for vertical grid resolutions from 1 to 30 mm we find a strong link between sea ice growth rate and bulk salinity for constant boundary conditions but only a weak link for more realistic boundary conditions we also demonstrate that surface warming can trigger brine convection over the whole ice layer over a growth season replacing the convective parametrization with constant initial salinities leads to an overall 3 discrepancy of stored energy thermal resistance and salt release we also derive from our convective parametrization a simplified numerically cheap and stable gravity drainage parametrization this parametrization results in an approximately 1 discrepancy of stored energy thermal resistance and salt release compared to the convective parametrization a similarly low discrepancy to our complex parametrization can be reached by simply prescribing a depth dependent salinity profile

development structure and composition of land fast sea ice in the northern baltic sea the structural and stable oxygen isotopic properties of sea ice samples collected on land fast sea ice in the northern baltic sea at 60 2 65 7 n 21 3 26 9 e were used to estimate the contribution of snow ice in the total sea ice thickness and the fraction of snow in the snow ice layers and in the total sea ice thickness the textural analysis of the sea ice cores revealed a general structure of granular surface layer and a columnar basal layer using different isotopic criteria to distinguish snow ice layers we estimate that snow ice layers contributed on average 24 32 of the total ice thickness in the study region transition ice intermediate granular columnar ice also contributed significantly to the total ice thickness the snow in the snow ice layers contributed on average 18 21 of the total sea ice thickness by mass a significant contribution when compared to other regions with sea ice cover the methods used could be improved to give more accurate estimates especially by improving knowledge of the temporal variability of the isotropic properties of the snow incorporated into the sea ice cover however our results can be regarded is plausible estimates for the contribution of snow ice and snow to sea ice growth in the study area