the confluence zone of the intense katabatic winds at terra nova bay antarctica as derived from airborne sastrugi surveys and mesoscale numerical modeling the surface wind field inland of the intense coastal kataba c wind regime at terra nova bay antarctica has been studied both observationally and numerically airborne surveys of windinduced features on the snow surface have been used to construct the time averaged winter surface airflow pattern the surface motion field has also been simulated by a mesoscale primitive equation model using terrain slopes with a horizontal resolution of 32 km both methods of analys s demonstrate that the intense katabatic airstream at terra nova bay is forced by converging air currents in the continental interior the broadscale confluence zone becomes organized into two regions within about 180 km of the coast the primary route for katabatic mass transport into the terra nova bay area is reeves glacier valley but an important secondary source is provided by airflow down david glacier the former is generated by the coriolis induced concentration of mass transport on the left side looking downwind of the broadscale confluence zone as well as by the near coastal mountain deflection of airflow into the valley head the confluence zone feeding into david glacier valley stretches over 100 km into the interior and is forced by the broadscale terrain configuration of the ice sheet source areas for the two airstreams differ with reeves glacier valley being fed by cold air formed well into the interior whereas the airflow down david glacier is sustained by radiative cooling over lower parts of the ice sheet which are much closer to the ross sea evaluation of the observational and modeling results reveals both the strengths and weaknesses of each approach airborne surveys of sastrugi orientations are a highly successful method for establishing the detailed pattern of surface airflow however a systematic examination of sastrugi dimensions suggests that such work could also be carried out using spot type satellite observations which is a more cost effective approach than aircraft surveying the double jet structure of katabatic airflow into the terra nova bay area is well represented by the primitive equation modeling but much finer grids are needed to resolve the near coastal drainage details

anisotropic behavior of grip ices and flow in central greenland abstract mechanical tests have been performed on strongly textured ice samples coming from a wide range of depths from 1328 down to 2868 m of the greenland ice core project grip for different sample orientations with respect to the prescribed stress in this way two directional viscosities corresponding to the easy glide and to the hard glide orientations were determined along the core the viscoplastic anisotropy gradually increases down to a depth of 2600 m and slightly decreases below revealing a clear correlation between rheology and texture the experimental mechanical response compares well with that predicted by the viscoplastic self consistent vpsc model the vpsc model is also applied to ice samples that exhibit an axisymmetric texture to show in more detail the sensitivity of the rheology to specific texture parameters this leads to a number of recommendations for future mechanical tests on anisotropic samples a large scale ice flow model is finally used to estimate the influence of ice anisotropy on the flow along the grip gisp2 flow line the particular mechanical behavior of deep grip ices in the stress regime corresponding to an ice divide leads to deformation rates that are highly sensitive to bedrock topography and texture pattern this feature is likely to favour the formation of stratigraphic disturbances in deep ice layers as observed in the last 300 m of both grip and gisp2 cores

relation between neighbouring grains in the upper part of the northgrip ice core implications for rotation recrystallization abstract we propose a new method to investigate the relationships between neighbouring crystals and apply it to the textures measured along the upper 900 m of the northgrip ice core this method shows unexpected correlations between neighbours in the so called normal grain growth regime questioning the classical view on the onset of rotation recrystallization in ice sheets moreover the fractionation rate associated to the rotation recrystallization appears constant through time finally grains with low angle boundaries do not present a special distribution pattern of their c axes this suggests that rotation recrystallization is an isotropic process not affected by the direction of the macroscopic strain

compositional variations in the mesoarchean chromites of the nuggihalli schist belt western dharwar craton india potential parental melts and implications for tectonic setting the chromite deposits in the archean nuggihalli schist belt are part of a layered ultramafic mafic sequence within the western dharwar craton of the indian shield the 3 1 ga ultramafic mafic units occur as sill like intrusions within the volcano sedimentary sequences of the nuggihalli greenstone belt that are surrounded by the tonalite trondhjemite granodiorite ttg suite of rocks the entire succession is exposed in the tagdur mining district the succession has been divided into the lower and the upper ultramafic units separated by a middle gabbro unit the ultramafic units comprise of deformed massive chromitite bodies that are hosted within chromite bearing serpentinites the chromitite bodies occur in the form of pods and elongated lenses 60 500 m by 15 m detailed electron microprobe studies reveal intense compositional variability of the chromite grains in silicate rich chromitite 50 modal chromite and serpentinite 2 modal chromite throughout the entire ultramafic sequence however the primary composition of chromite is preserved in the massive chromitites 60 75 modal chromite from the byrapur and the bhaktarhalli mining district of the nuggihalli schist belt these are characterized by high cr ratios cr cr al 0 78 0 86 and moderate mg ratios mg mg fe2 0 38 0 58 the compositional variability occurs due to sub solidus re equilibration in the accessory chromite in the serpentinite mg ratio 0 01 0 38 cr ratio 0 02 0 99 and in silicate rich chromitite mg ratio 0 06 0 48 cr ratio 0 60 0 99 in the massive chromitites the sub solidus re equilibration for chromite is less or absent however the re equilibration is prominent in the co existing interstitial and included olivine fo96 98 and pyroxene grains mg numbers 97 99 compositional variability on the scale of a single chromite grain occurs in the form of zoning and it is common in the accessory chromite grains in serpentinite and in the altered grains in chromitite in the zoned grains the composition of the core is modified and the rim is ferritchromit in general ferritchromit occurs as irregular patches along the grain boundaries and fractures of the zoned grains in this case ferritchromit formation is not very extensive this indicates a secondary low temperature hydrothermal origin of ferritchromit during serpentinization in some occurrences the ferritchromit rim is very well developed and only a small relict core appears to remain in the chromite grain however complete alteration of the chromite grains to ferritchromit without any remnant core is also present the regular well developed and continuous occurrence of ferritchromit rims around the chromite grain boundaries the complete alteration of the chromite grains and the modification of the core composition indicate the alteration in the nuggihalli schist belt to be intense pervasive and affected by later low grade metamorphism the primary composition of chromite has been used to compute the nature of the parental melt the parental melt calculations indicate derivation from a high mg komatiitic basalt that is similar to the composition of the komatiitic rocks reported from the greenstone sequences of the western dharwar craton tectonic discrimination diagrams using the primary composition of chromites indicate a supra subduction zone setting ssz for the archean chromitites of nuggihalli and derivation from a boninitic magma the composition of the komatiitic basalts resembles those of boninites that occur in subduction zones and back arc rift settings formation of the massive chromitites in nuggihalli may be due to magma mixing process involving hydrous high mg magmas or may be related to intrusions of chromite crystal laden magma however there is little scope to test these models because the host rocks are highly altered serpentinized and deformed the present configurations of the chromitite bodies are related to the multistage deformation processes that are common in archean greenstone belts

the inversion wind pattern over west antarctica abstract the surface windfield over the gently sloping interior ice fields of antarctica is characterized by a high degree of persistence in terms of both direction and speed the forcing of the surface wind is due primarily to the radiational cooling of the air adjacent to the sloping terrain the representativeness of a simple diagnostic equation system in inferring the surface winds from a knowledge of terrain slope and temperature inversion structure is examined results suggest at least qualitatively accurate surface drainage patterns over the antarctic continent are possible using this technique a wintertime surface wind simulation for west antarctica has been generated based on an accurate ice topography map close agreement is seen between the simulated surface windfield with field observations and sastrugi orientations implications of the simulation are discussed

impeding effect of air bubbles on normal grain growth of ice abstract normal grain growth experiments were performed using polycrystalline ice samples with and without air bubbles the bubble free polycrystalline ice was prepared by a special sample preparation technique that employed a phase change method the ice samples with air bubbles were prepared from a mixture of ice powder and pure distilled water using conventional methods the temperature dependencies of the rate of grain growth were measured in artificial polycrystalline ice samples with and without air bubbles the average grain growth exponent n of the ice with bubbles was much greater than the theoretical value of 2 while that of bubble free ice was close to 2 the activation energy for the grain boundary migration of bubble free ice was 110 120 kj mol 1 whereas that of the ice with bubbles was between 40 and 70 kj mol 1 the observation of the microscopic images of samples and analyses of the evolution of bubble size distribution and location during grain growth revealed that small air bubbles are caught and swept by moving grain boundaries and a coalescence of bubbles occurs this indicates that the slow grain boundary migration of ice with bubbles is controlled by the migration of air bubbles dragged by grain boundary migration

dynamic implications of discontinuous recrystallization in cold basal ice taylor glacier antarctica crystallographic investigations have been conducted of cold 17 c debris bearing ice from the base of an antarctic outlet glacier taylor glacier the 4 m thick sequence studied has been retrieved from a 20 m long tunnel dug from the glacier snout and has been analyzed with an automatic ice fabric analyzer aifa the top and bottom of the sequence consists of clean meteoric ice englacial facies whereas alternating debris rich and clean bubbly ice layers are found in the middle part stratified facies ice from the englacial facies displays a polygonal texture and a strong c axis clustering toward the vertical denoting recrystallization through subgrain rotation sgr in contrast clean ice from the stratified facies shows sgr fabrics which are delimited at the contact with debris rich layers by large interlocking grains organized in ribbons these two distinct textures within the stratified facies are associated with looser c axis patterns at the scale of single thin sections which is interpreted as resulting from migration recrystallization mr the change from sgr to mr trends marks a clear increase in grain boundary and nucleation kinetics hence the term discontinuous recrystallization and may be associated with strain localization at rheological interfaces during basal ice genesis analogies with bottom ice from deep polar ice sheets where temperature is commonly higher than at the studied site are highlighted two recrystallization scenarios are proposed accounting for the development of both types of fabrics it is shown that by controlling the repartition of stress and strain energy within basal ice the rheology of debris bearing ice layers plays a decisive role in recrystallization dynamics at structural interfaces we also demonstrate how the same recrystallization regimes may occur in cold glaciers and temperate ice sheets provided that strain accumulation has been high enough in the former this challenges the common belief that migration fabrics observed in bottom ice from deep ice sheets are exclusive to warm stagnant annealed ice copyright 2008 by the american geophysical union

novel shearing apparatuses in confined flow for investigating recrystallization and fabric evolution processes in mono and polycrystalline ice

crystal orientation fabrics within the antarctic ice sheet revealed by a multipolarization plane and dual frequency radar survey 1 to investigate the viscosity structure of ice sheets induced by crystal orientation fabric cof we carried out a multipolarization plane and dual frequency radar survey in east antarctica radar surveys were done along a 670 km long flow line from dome fuji toward the coast and two transverse lines of 300 km and 20 km length respectively the radar echoes were highly dependent on the polarization plane for ice depths between about 40 and 60 of the ice thickness in the lower reaches of the convergent ice flow sector approaching the outlet glacier when the polarization was perpendicular to the ice flow echoes were about 10 db stronger than when the polarization was parallel to the ice flow this feature was not clear in the upper part of this convergent flow sector farther inland where ice flow is divergent or parallel the radar echo varied by several decibels because of changes of the radar polarization and had maxima in two orientations dual frequency data showed that the cause of the reflections was changes in cof multipolarization data identified anisotropic reflectivities and birefringence as causes of the anisotropic radar echoes in the lower and upper reaches respectively with the aid of ice core based studies on cof we show that ice is composed of stacked layers of single pole and vertical girdle fabrics in the lower reaches in contrast we argue that changes of single pole clustering cause isotropic reflectivities in the upper reaches we also discuss on the development of cof along ice flow and its implication to ice sheet dynamics

mapping c axis fabrics to study physical processes in ice mapping the spatial distribution of c axis orientations in ice thin sections is not much more difficult than preparing c axis scatter plots but can reveal additional information about processes responsible for the observed fabric and texture of the ice distributions of angles between c axes of neighboring grains from the byrd station west antarctica ice core suggest that polygonization causes average grain size to stabilize below 400 m depth

textures and fabrics in the grip ice core a comprehensive study of textures and fabrics has been carried out on the greenland ice core project grip ice core crystal sizes and c axis orientations have been measured on thin sections with conventional techniques yielding new information on the growth rotation and recrystallization of ice crystals in the greenland ice sheet normal grain growth is found to persist to a depth of 700 m in the core where the onset of polygonization due to increasing strain prevents a further increase in grain size in the holocene ice smaller crystals are observed in the wisconsin ice larger crystals are found in the eemian ice and the crystal size is found to vary with climatic parameters in these periods this dependence which probably results from variable impurity content in the ice persists to a depth of 2930 m coarse grained ice probably resulting from rapid growth of crystals at comparatively high temperatures is found in the lowest 100 m of the core the data on c axis orientations reveal a steady evolution of the fabric from random near the surface to a strong single maximum in the lower part of the ice sheet a significant strengthening is not observed at the holocene wisconsin transition the fabric development indicates that vertical compression at the ice divide is the main mode of deformation down to a depth of 2850 m the evolution toward a single maximum fabric hardens the ice against vertical compression but softens it against simple shear evidence of simple shear deformation is clearly observed between 2850 m and 2950 m depth stretched fabrics in coarse grained ice in the lowest 100 m could be due to tensional stresses this ice is unlikely to be undergoing any significant horizontal deformation at the present time

ice flow relations for stress and strain rate components from combined shear and compression laboratory experiments the generalized glen flow relation for ice involving the second invariants of the stress deviator and strain rate tensors is only expected to hold for isotropic polycrystalline ice previous single stress experiments have shown that for the steady state flow which develops at large strains the tertiary strain rate is greater than the minimum secondary creep value by an enhancement factor which is larger for shear than compression previous experiments combining shear with compression normal to the shear plane have shown that enhancement of the tertiary octahedral strain rate increases monotonically from compression alone to shear alone additional experiments and analyses presented here were conducted to further investigate how the separate tertiary shear and compression strain rate components are related in combined stress situations it is found that tertiary compression rates are more strongly influenced by the addition of shear than is given by a glen type flow relation whereas shear is less influenced by additional compression a scalar function formulation of the flow relation is proposed which fits the tertiary creep data well and is readily adapted to a generalized form that can be extended to other stress configurations and applied in ice mass modelling

deformation properties of subfreezing glacier ice role of crystal size chemical impurities and rock particles inferred from in situ measurements to improve understanding of the deformation properties of subfreezing polycrystalline glacier ice and in particular the role of crystal size chemical impurities and rock particle impurities we analyze in situ strain rates of the basal layers of meserve glacier antarctica strain rates were monitored on the walls of a subglacial tunnel where down flow shear stress is relatively uniform and ice properties were measured texture fabric and impurity content we propose a simple empirical model describing strain rate variations due to variations in crystal size and impurity content and we use all relevant meserve data to constrain model parameters we conclude that there is a direct dependence of strain rate on crystal size which reflects an important role for a grain size sensitive deformation mechanism such as grain boundary sliding or diffusion chemical impurities are found to enhance the grain size sensitive deformation and are found to be an important control on strain rate variations in the very impure ices of meserve glacier however the per molar sensitivity of strain rate to chemical impurity content is shown to be very low such that in the ice age ices of the greenland ice sheet there is probably an immeasurable contribution of chemical impurities to strain rate enhancement though we cannot exclude chemical enhancements as high as 1 3 there our analyses detect no direct rheologic effect of rock particles in the meserve ices which suggests that rock content is not directly responsible for the low viscosity of dirty basal layers

alleviation of a systematic westerly bias in general circulation and numerical weather prediction models through an orographic gravity wave drag parametrization systematic westerly biases in the northern hemisphere wintertime flow of the meteorological office 15 layer operational model and 11 layer general circulation model are described evidence that the failure to parametrize subgrid scale orographic gravity wave drag may account for such biases is presented this evidence is taken from aircraft studies surface pressure drag measurements and studies of the zonally averaged momentum budget a parametrization scheme is described in which the surface stress is proportional to the near surface wind speed and static stability and to the variance of subgrid scale orography the stress is absorbed in the vertical by considering the influence of such gravity wave activity on static stability and vertical wind shear a richardson number dependent wave breaking formulation is devised and the vertical stress profile determined by a saturation hypothesis whereby the breaking waves are maintained at marginal stability it is shown that wave breaking preferentially occurs in the boundary layer and in the lower stratosphere results from a simple zonally symmetric model show how the adjustment to thermal wind balance with a wave drag in the stratosphere warms polar regions by adiabatic descent and decelerates the mean westerlies in the troposphere the influence of the parametrization scheme on integrations of the 11 layer model is described and found to be generally beneficial in a discussion of the reasons why this problem has only recently emerged it is suggested that the satisfactory northern hemisphere winter circulations of previous coarser general circulation models were due to a compensation implied by underestimating both the surface drag and the horizontal flux of momentum by explicitly resolved large scale eddies

discontinuous grain growth in recrystallised vein quartz implications for grain boundary structure grain boundary mobility crystallographic preferred orientation and stress history abstract grain growth is a process driven by the reduction of interfacial free energy leading to an increase in grain size and a reduction of the number of grains in a given volume of a single phase polycrystalline material discontinuous grain growth dcgg as opposed to normal grain growth ngg involves just a few grains blasts growing at the expense of a matrix that itself undergoes much slower modification in grain size hence producing a bimodal grain size distribution as a transient state prior to impingement of the blasts such a transient state has been found in a quartz layer in metamorphic rocks of the sesia zone western alps there large strain free quartz grains occur that reveal concave outward grain boundaries against a matrix of small grains with a pronounced crystallographic and a weak dimensional preferred orientation the misorientation of the blasts with respect to the matrix grains systematically exceeds 30 this finding suggests that the mobility of high angle grain boundaries in a natural quartzite depends on the degree of their misorientation among other factors as known for metals and alloys the width of the grain boundaries must be sufficiently small to allow for this effect dcgg is promoted by a pronounced crystallographic preferred orientation cpo that leaves only a few grain boundaries with sufficient misorientation to be mobile in contrast to ngg dcgg wipes out any pre existing cpo and information on activated glide systems or kinematics during the preceding stage of flow is lost after dcgg has gone to completion a complementary new cpo could even develop that could be difficult to interpret with respect to tectonic history interfacial free energy driven grain growth reflects a period of low stress annealing and thus constitutes a first order signal

high grade regional metamorphism of ultramafic and mafic rocks from the archaean sargur terrane karnataka south india deformed and metamorphic ultramafic to mafic rocks emplaced into the archaean sargur supracrustal series 3 0 ga in karnataka southern india represent layered igneous bodies the terrane has been affected by several episodes of deformation and metamorphism in the time span from 3 4 to 2 5 ga ago during the regional metamorphism about 2 5 ga ago the igneous bodies re equilibrated partly or completely at conditions of the upper amphibolite to granulite facies the development of sagvandites with enstatite magnesite and anthophyllite magnesite bearing assemblages and of mafic garnet pyroxene charnockites indicates the presence of co2 rich intergranular fluids xco2 greater or equal slanted 0 5 in these rocks during metamorphism the physical conditions of metamorphism have been estimated by applying methods of geothermobarometry to the recrystallized ultramafic assemblages with olivine pyroxenes and spinel and to the charnockitic assemblages with garnet pyroxenes plagioclase and quartz a best temperature estimate of 700 30 c was derived with the geothermometers of evans and frost ol spi fabries ol spi wells opx cpx powell opx cpx ellis and green gra cpx lal and raith gra opx and danckwerth and newton al2o3 content in opx a mean pressure estimate of 8 6 0 8 kbar has been obtained with the models of perkins and newton gar opx cpx plag qtz the p t data indicate a minimum crustal thickness of about 35 km at c 2 5 ga in this part of the south indian archaean craton

ice crystal properties of amber ice and strain enhancement at the base of cold antarctic glaciers to improve our understanding of the deformation properties of cold based polar glaciers we examine here some of the factors leading to the localization of strain within the amber ice facies we present a crystallographic case study of amber ice a fine grained bubbly ice containing a relatively high impurity content sampled at the base of two antarctic glaciers the crystal fabrics and textures of amber ice were computed by application of a recently developed automated method to date it was tedious and awkward to determine amber ice facies accurately because of the sub millimetric crystal size and relatively high debris content of this facies the authomatic analytical method applied in this study allows not only for improving analytical accuracy in this task but also for considerably reducing the time of analysis our investigations reveal highly homogeneous crystallographic properties for the studied amber ice the ice crystals are mainly polygonal equant and sub millimetric and show a strong lattice preferred orientation these properties beside the relatively high impurity content are likely to exert a major control on strain enhancement in amber ice when this facies is present at the base of cold glaciers

the petrological significance of misorientations between grains misorientation analysis quantifies microstructural features in tectonites metamorphic and igneous rocks and allows hypotheses on their formation to be tested the misorientation between two lattices can be expressed by a rotation axis and rotation angle for lattices with symmetry it is conventional to take the minimum angle that enables one lattice to be rotated into the other for a group of lattice measurements two types of misorientation distribution can be calculated selecting random pairs of grains gives the random pair misorientation distribution selecting neighbouring pairs gives the neighbour pair misorientation distribution the forms of both distributions are visualised using histograms or cumulative frequency diagrams they are strongly influenced by any overall crystallographic preferred orientation and by intrinsic crystal symmetry in many rocks the random pair misorientation distribution and neighbour pair misorientation distribution are statistically significantly different quantified using the kolmogorov smirnov test differences between the random pair misorientation distribution and neighbour pair misorientation distribution imply that adjacent grains have physically interacted or are inherited from a precursor microstructure interactions include 1 reduction in surface energy by lattice alignment we show this may have occurred in garnet clusters in schist and olivine in a cumulate it is well known in metals and may be a common geological process 2 nucleation where those nuclei have influenced the orientation of adjacent nuclei 3 mechanical rotations of facetted grains in compacting crystal mushes so that faces become parallel 4 growth twinning inheritance includes 1 subgrain rotation recrystallisation in tectonites deforming by crystal plastic processes 2 mechanical and transformation related twinning 3 domainal microstructures e g where grains have formed from a few large original grains may give rise to spurious correlations when the orientation data cover more than one domain with this proviso misorientation analysis can be used to investigate many important microstructural processes

genesis and evolution of the ore deposits in the early precambrian greenstone belts and adjacent high grade metamorphic terrains of peninsular india a study in similarity and contrast abstract karnataka and the adjacent areas of tamil nadu and andhra pradesh in peninsular india are characterized by sublinear greenstone belts set in a tonalite trondhjemite dominated gneissic terrain mainly 3400 3000 ma skirted by a high grade metamorphic amphibolite granulite facies belt in the south and the east the greenstone belts are divided into the sedimentary volcanic sargur holenarsipur nuggihalli type 3000 ma the volcanic dominated kolar ramagiri hutti type 3000 ma and the sediment dominated dharwar type 3000 2600 ma arranged in order of increasing areal coverage the granulite facies metamorphism of the peninsular gneiss and associated supracrustals took place 2500 2600 ma ago the first type of greenstone belt is poor in ore content these belts contain a few lean base metal deposits a few chromite deposits and ti and v bearing magnetite deposits in places locally banded magnetite deposits are also present the second type of belt is known for its au content the dharwar type of belt of course contains rich deposits of fe and mn and rare small deposits of cu ore deposition in the high grade metamorphic terrain is also poor as in the sargur type of greenstone belt whatever metallizations occur there are confined to the supracrustal enclaves differential metallization in the different segments is explained in terms of the differential development of the crust the atmosphere and the biosphere

flow law hypotheses for ice sheet modeling ice flow modeling requires a flow law relating strain rates to stresses in situ but a flow law cannot be measured directly in ice sheets microscopic processes such as dislocation glide and boundary diffusion control both the flow law for ice and the development of physical properties such as grain size and c axis fabric these microscopic processes can be inferred from observations of the physical properties and the flow law can then be estimated from the microscopic processes a review of available literature shows that this approach can be imperfectly successful interior regions of large ice sheets probably have depth varying flow law constants with the stress exponent n for power law creep less than 3 in upper regions and equal to 3 only in deep ice n probably equals 3 through most of the thickness of ice shelves and ice streams

surface airflow over east antarctica abstract surface winds over the antarctic interior occur mainly due to the strong radiational cooling of the ice slopes as a consequence such winds exhibit a high degree of persistence with a predominant direction closely related to the terrain orientation using detailed contour maps of the interior ice topography and representative values of the mean wintertime strength of the temperature inversion it is possible to infer the terrain induced accelerations a simple diagnostic equation system is formulated from which a time averaged surface airflow pattern of east antarctica is generated the results appear consistent with observations the occurrence of localized anomalously strong katabatic winds is explained as a result of typographically forced patterns of cold air convergence depicted in the airflow analysis

the shape propagation and mean flow interaction of large scale weather systems abstract for a zonal average operator the eliassen palm flux provides a diagnostic of both eddy behavior and the feedback of the eddies onto the mean flow this paper addresses the diagnosis problem for other averaging operators and in particular for time averaging which has proved in recent years such a powerful means of viewing the three dimensional tropospheric flow the horizontal velocity correlation tensor gives a measure of the characteristic horizontal eddy shape at a point it also implies the direction of the group velocity relative to the mean flow in cases where such a concept is valid however the major emphasis here is on the mean flow feedback of eddies in this respect the eddy vorticity flux is determined by derivatives of the components of the anisotropic part of the tensor making a reasonable approximation allows the eddy vorticity flux convergence to be written in terms of e v 2 u 2 u v a simple interpretation of the mean flow feedback of eddies is then possible a sligh

on the existence of storm tracks abstract given that middle latitude weather systems transport heat in a manner such as to weaken the baroclinicity that is thought to be crucial to their growth it is perhaps surprising that concentrated regions of such eddy activity i e storm tracks are found in the northern hemisphere winter the existence and possible self maintenance of storm tracks is investigated using a linear stationary wave model with storm track region forcings taken from data averaged over a number of winters it is found that the direct thermal effect of the eddies does indeed act against the existence of the storm track their vorticity fluxes lead to some reduction of this effect it is argued that the mean diabatic heating in the storm track region is an indirect eddy effect this heating is found to maintain the mean maximum in baroclinicity in the region further the mean low level flow induced by the eddy effects is such as to enhance the warm western oceanic boundary currents that are crucial to the existence of t

the influence of antarctica on the momentum budget of the southern extratropics the antarctic plateau acts as a strong heat sink for the global climate cooling the atmosphere and radiating energy to space a cold dense atmospheric boundary layer is formed strong surface winds are formed as the boundary layer drains off the plateau these drainage winds and the eddy fluxes necessary to maintain them are analysed in a general circulation model gcm the drainage flow is well represented in the gcm the associated mean meridional circulation is analysed in isentropic coordinates the momentum budget over antarctica reveals a balance between the eliassen palm flux convergence and the coriolis torque exerted by the mean meridional mass flux both vertical and horizontal components of the eliassen palm flux contribute the vertical component being the greater

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