quantifying upper ocean turbulence driven by surface waves 1 nearly all operational ocean models use air sea fluxes and the ocean shear and stratification to estimate upper ocean boundary layer mixing rates this approach implicitly parameterizes surface wave effects in terms of these inputs here we test this assumption using parallel experiments in a lake with small waves and in the open ocean with much bigger waves under the same wind stress and adjusting for buoyancy flux we find the mixed layer average turbulent vertical kinetic energy in the open ocean typically twice that in the lake the increase is consistent with models of langmuir turbulence in which the wave stokes drift and not wave breaking is the dominant mechanism by which waves energize turbulence in the mixed layer applying these same theories globally we find enhanced mixing and deeper mixed layers resulting from the inclusion of langmuir turbulence in the boundary layer parameterization especially in the southern ocean

the use of topographic scale models in predicting eolian dust erosion in hilly areas field verification of a wind tunnel experiment abstract eolian erosion of natural dust in an area of 53 ha situated in the northern negev desert is investigated in detail both in the wind tunnel erosion simulations on a topographic scale model and in the field the wind tunnel results and the field results show good agreement indicating that wind tunnel simulations of eolian dust erosion on scale models of complex topography may predict at least to an acceptable level the erosion sensitive areas in a hilly landscape of nearly uniform surface roughness the experiments also indicate that a restricted height distortion of scale models may be acceptable to determine the areas of highest erosion in addition wind tunnel blockage percentages up to 10 may be allowed to obtain acceptable erosion patterns on the model when surface roughness is more or less uniform eolian erosion of dry dusty sediments is almost entirely determined by macro topography if however surface roughness is highly variable over the field the initiation of eolian erosion is also largely a function of local micro topography

wind tunnel experiments and field measurements of aeolian dust deposition on conical hills abstract the spatial pattern of short term aeolian dust deposition on and around cone shaped hills is investigated via the simulation in a wind tunnel of dust storms over a topographic scale model of a conical hill in the negev desert israel the results are tested during a full scale dust storm in the negev the wind tunnel experiments adequately predict the field pattern although some problems may arise on steep windward slopes where the accumulation threshold is more quickly exceeded on the scale model than in the field conical hills create an elongated area of low deposition dust shadow in their lee downwind from the shadow zone a local area of more than normal compared to the undisturbed surroundings deposition occurs on the lateral flanks of the hill and also on the small convex windward slope just upstream of the top and at the top itself dust deposition remains low to very low it is the lowermost concave windward slope that receives the largest amounts of dust the pattern described above refers to short term deposition only water erosion may seriously alter the final accumulation pattern since it will clean the slopes of important amounts of dust that accumulate in the wadis

structure of a paleoproterozoic continent continent collision zone a lithoprobe seismic reflection profile across the trans hudson orogen canada abstract an 800 km reflection seismic profile across the trans hudson orogen northern saskatchewan and manitoba images crustal scale tectonic imbrication in an unprecedented picture of paleoproterozoic crustal accretion and continent continent collisional tectonism the profile is crudely symmetric about a crustal scale culmination in the western part of an accreted juvenile collage reindeer zone geologic and isotopic data suggest that this culmination is cored by microcontinental archean basement west of the culmination highly reflective juvenile crustal elements dip westward into the lower crust beneath the wathaman batholith and archean continental crust of hearne craton to the east strong reflections in the juvenile reindeer zone crust and reworked archean foreland of the thompson belt have eastward dips persisting into the middle crust and extending beneath the superior craton a continuous reflection moho well defined for 500 km in the western part of the profile shows marked relief 12 15 s including a prominent root below the crustal culmination these imaged structures give evidence of substantial crustal shortening and thickening via large scale imbrication consistent with collisional orogeny w dipping structures below the wathaman batholith and reworked hearne craton may reflect subduction polarity in this part of the orogen however geological evidence suggests that e dipping structures below superior craton are largely related to late post collisional deformation rather than to prior oceanic subduction polarity

calibration of the mdco dust collector and of four versions of the inverted frisbee dust deposition sampler abstract wind tunnel experiments were conducted to determine the efficiency of sediment samplers designed to measure the deposition of aeolian dust efficiency was ascertained relative to a water surface which was considered the best alternative for simulating a perfectly absorbent surface two types of samplers were studied the marble dust collector mdco and the inverted frisbee sampler four versions of the latter catcher were tested an empty frisbee an empty frisbee surrounded by an aerodynamic flow deflector ring a frisbee filled with glass marbles and a frisbee filled with glass marbles and surrounded by a flow deflector ring efficiency was ascertained for five wind velocities range 1 5 m s 1 and eight grain size classes range 10 89 m the efficiency of dust deposition catchers diminishes rapidly as the wind speed increases it also diminishes as the particles caught become coarser adding a flow deflector ring to a catcher substantially improves the catcher s efficiency by up to 100 in some cases the addition of glass marbles to a catcher on the other hand does not seem to increase the efficiency at least not at wind velocities inferior to the deflation threshold for higher velocities the marbles protect the settled particles from resuspension keeping them in the catcher the following five parameters determine the accumulation of aeolian dust in a catcher the horizontal dust flux the weight of the particles atmospheric turbulence resuspension and the dust shadow effect created by the catcher the final accumulation flux depends on the combination of these parameters the catchers tested in this study belong to the best catchers currently in use in earth science and have been the subject of various aerodynamic studies to improve their efficiency nevertheless the catching efficiency remains low in the order of 20 40 for wind speeds above 2 m s 1 other catchers suffer from the same low efficiencies there is thus evidence to believe that dust deposition rates published in the aeolian literature and obtained by collecting the sediment in a catcher largely underestimate the true deposition the errors are considerable of the order of 100 and more a reconsideration of the literature data on aeolian dust deposition measured by catchers is therefore required

effect of rock fragment eccentricity on eolian deposition of atmospheric dust abstract the effect of rock fragment eccentricity on the deposition of airborne dust was examined in a wind tunnel eccentricity was defined as the ratioa b wherea is the longest andb the intermediate axis of the rock fragments the effect of eccentricity on the deposition of dust on the pebbles on the deposition of dust between and underneath the pebbles and on total dust deposition pebbles interpebble space was measured separately and this for different values of pebble size pebble flattening cover density and wind speed the more pebbles are elongated the larger dust deposition on them will be this effect is more pronounced as pebbles become larger as they become less flattened and as wind speed increases but no correlation is observed with cover density it also holds that the more pebbles are elongated the less dust settles between and underneath them this effect is more pronounced as pebbles become smaller and cover density becomes larger but there is no relationship with pebble flattening whether or not there is a relationship with wind speed is unclear pebble eccentricity indirectly influences total dust deposition on a pebble field since it determines whether or not and to what extent total dust deposition will be a function of pebble size for circular pebbles total dust deposition is independent of pebble size but once pebbles become elongated total dust deposition will be smaller on pebble fields composed of small pebbles than on pebble fields composed of large pebbles it was also demonstrated that the more pebbles are elongated the more the dust will tend to settle on the pebbles rather than between or underneath them air flow separation plays a primary role in the deposition of dust on a rock fragment field since it determines the location and size of the low sedimentation areas that are connected to the air flow separation bubbles highly elongated pebbles oriented parallel to the wind catch much more dust also per unit surface than circular pebbles the surface of which is largely located in a zone of very low deposition dust deposition density on highly elongated pebbles normal to the wind on the contrary is equal to dust deposition on circular pebbles it should be noted that all data in this study refer to initial dust deposition not accumulation since only wind velocities below the dust deflation threshold were tested

impacts of surface gravity waves on summer ocean dynamics in bohai sea abstract a one way coupled pomgcs swan model is applied to study the impacts of three wave processes i e langmuir turbulence coriolis stokes forcing csf and resolved scale craik leibovich vortex forcing clvf on ocean dynamics in bohai sea in summer both csf and clvf are included in the horizontal momentum equation the level 2 5 mellor yamada turbulence closure scheme is modified to contain the parameterization of langmuir turbulence numerical results show that this improved model reproduces the sea surface temperature sst better than the original one all of these wave effects considerably contribute to temperature variability at different vertical levels with the maximum temperature change of about 0 4 c based on the diagnostic experiments the impacts of the csf and clvf are much weaker than that of langmuir turbulence those wave processes reduce the current velocity and make the current more vertically uniform the horizontal distribution of langmuir number indicates that the langmuir turbulence is prevalent in bohai sea the large vertical kinematic viscosity coefficients containing the langmuir turbulence would lead to a strong vertical mixing

the effect of surface curvature on the deposition of loess a physical model summary a physical model for the deposition of fine dusty material loess on curved surfaces is presented the model is tested in a sedimentation experiment with a symmetrical hill with length axis perpendicular to the flow direction in a wind tunnel it appears both from the model and the experiment that loess deposition will occur preferably on windward slopes and not on leeward ones in contrast to the widespread wind shadow concept below the deflation threshold loess deposition increases as wind speed increases above the deflation threshold an effective accumulation of the loess layer on the surface will occur within a well defined wind speed interval the loess layer on the surface will erode away only if wind speed has exceeded this interval for flat and dry surfaces free of roughness elements the upper limit of the interval is 7 m s free stream velocity for wet surfaces however it may be considerably higher 15 m s and more

the influence of crosswind tidal currents on langmuir circulation in a shallow ocean 1 langmuir circulation lc is a turbulent process driven by wind and surface waves that plays a key role in transferring momentum heat and mass in the oceanic surface layer on the coastal shelves the largest scale lc span the whole water column and thus couple the surface and bottom boundary layers and enhance turbulent mixing observations and large eddy simulations les of a shallow coastal ocean demonstrate that these relatively large scale langmuir cells are strongly influenced by crosswind tidal currents two mechanisms by which crosswind tidal shear may distort and disrupt langmuir cells are proposed the first mechanism involves cell shearing due to differential advection across the whole cell for the second mechanism middepth vertical lc currents advect sheared mean crosswind current leading to the attraction of upwelling and downwelling regions so that lc cells are unsustainable when both regions overlap scaling arguments indicate that lc cells are more susceptible to crosswind shear distortion for smaller lc surface velocity convergence and greater cell aspect ratio vertical to horizontal lc scale which is consistent with the results obtained from the observations and les these results imply that scaling of lc characteristics in a coastal ocean differs from that in the open ocean which has important practical implications for parameterizing enhanced mixing due to lc

biogenic soil crusts and soil depth a long term case study from the central negev desert highland wind blown soil degradation is a major problem in arid regions biogenic soil crust consists of a dense growth of many small organisms covering bare desert soil surfaces in arid regions worldwide these organisms perform essential services in the ecosystem for example soil surface stabilization and carbon and nitrogen fixation a unique service provided by biogenic crusts is the incorporation of large quantities of deposited atmospheric particles leading to a significantly enhanced rate of increase in soil depth in windy and arid environments a long term study over 42 months was conducted to investigate the contribution of a biogenic crust to the accumulation of atmospheric particles in an arid zone undisturbed and treated biogenic crusts were studied for their capacity to incorporate deposited particles atmospheric particles were found to accumulate on marble dust collectors at a rate of 120 g m 2 year 1 and on sterilized crust at a rate of 208 g m 2 year 1 while the accumulation rate on live intact crusts was 277 g m 2 year 1 suggesting a soil depth accretion rate on an undisturbed biogenic crust of 10 mm every 33 years maintenance of a healthy biogenic crust in dry land environments should therefore be a major consideration for improving soil quality and increasing soil depth in arid regions

soil formation in phobjikha valley central bhutan with special regard to the redistribution of loessic sediments abstract soil development and landscape evolution were studied in the basin shaped phobjikha valley at 2900 3200 m a s l to the west of the black mountain range west central bhutan the local environmental setting with strong along valley winds frequent freeze thaw cycles extensive dry periods and sparse vegetation cover seems to encourage the generation and short distance transport of silt sized particles the effects of this process are evidenced in the smooth valley morphology and in the nature of the examined pedons their involvement in continuing redistribution of local sediments is reflected by a homogeneous silty clayey and stone free texture varying profile depths buried topsoils and weakly developed recent a horizons in protected locations in situ weathering of metamorphic parent materials results in alu andic features with bulk densities 2 and phosphate retention 95 dominance by al hydroxy interlayered clay minerals and large amounts of well crystallised iron oxides indicate an advanced stage of weathering in areas of preferred eolian deposition argic and ferralic features emerge with clay contents of up to 60 and surface areas of 50 m2 g 1 under forest umbric horizons can develop ceceff is below 10 cmolc kg 1 at all sites cluster and factor analyses of soil chemical and physical parameters confirm the redistribution of local sediments as a dominant factor behind the measured variables no clear indication of glacial activities in the area was found whereas the massive silty sediments in the lower parts of most profiles the presence of debris slopes and the asymmetric cross sections of the side valleys suggest periglacial conditions buried topsoils dated at about 2000 conventional 14c years bp indicate a weakening or absence of sediment influx under wetter conditions towards the end of the holocene climate optimum charcoal on top of paleosols suggests that human activities of deforestation grazing and arable agriculture may have contributed to the reactivation of local sediment redistribution until today

constraints on the timing of crustal imbrication in the central trans hudson orogen from single zircon 207pb 206pb ages of granitoid rocks from the pelican thrust zone saskatchewan the pelican thrust is a major ductile high strain zone in the reindeer zone trans hudson orogen northern saskatchewan it is interpreted as the main sole thrust separating stacked juvenile paleoproterozoic allochthons and underlying archean microcontinental crust in this central part of the orogen exposed nonmylonitic rocks in the footwall of the thrust consist of the sahli monzocharnockite and the smaller more highly retrograded macmillan point granite protomylonitic to ultramylonitic gneisses in the thrust zone derive from a variety of prethrust protoliths a footwall internal suite mainly comprises quartzofeldspathic orthogneisses q gneisses and high grade migmatitic paragneisses hanging wall external suite mylonitic gneisses include feldspar porphyroclastic hornblendic grey gneisses probably derived from arc plutons and laminated amphibolites derived from volcanic rocks the overlying allochthon mainly comprises protoliths equivalent to those of the porphyroclastic orthogneisses and lam

spatial distribution of dust deposition within a small drainage basin implications for loess deposits in the negev desert loessial colluvial sediments and aeolian aprons are common deposits in the negev desert highlands in an attempt to monitor the amounts and distributional pattern of loess monthly dust measurements were carried out during 2004 to 2006 in 10 cm diameter traps located at 18 stations along four slopes north facing south facing east facing and west facing in a second order drainage basin near sede boqer negev desert highlands israel annual total dust depositions ranged between 110 g and 178 g m 2 with an average of 151 1 g m 2 the average annual dust deposition in the catchment was 23 5 higher than the average amount recorded at the hilltops 122 4 g m 2 and may be a consequence of sheltering opportunities in the hilly topography when analysed according to season and aspect significantly higher monthly amounts were received during the wet rainy season of december to march 17 0 g m 2 in comparison with the rest of the year 8 1 g m 2 as for the aspect while no significant differences characterized north facing and south facing slopes east facing slopes received significantly higher amounts by 43 3 than west facing slopes pointing to preferential dust deposition at the leeward slope concurring with the classical model that anticipates higher dust deposition at the leeside slope but in disagreement with some reports published in the literature the findings of this study were also supported by a field survey that showed preferential loess accumulation at the eastern and north eastern aspects these findings may shed light on distributional patterns of colluvial sediments and aeolian aprons in the negev on soil forming processes and on past cycles of dust deposition

origin of the archean sask craton and its extent within the trans hudson orogen evidence from pb and nd isotopic compositions of basement rocks and post orogenic intrusions u pb zircon ages from the exposed sask craton are 2450 3100 ma from the peter lake domain 2575 2640 ma and from rocks of the trans hudson orogen 1840 1880 ma u pb monazite and zircon ages of post orogenic pegmatites and aplites are 1770 1800 ma common pb and sm nd isotopic compositions of post orogenic intrusions as probes of crust beneath the orogen were compared to sask craton rocks and ca 1850 ma orogenic rocks to infer the origin and subsurface distribution of the sask craton within the internides of the trans hudson orogen results show that post orogenic intrusions within most of the glennie domain and hanson lake block were derived at least in part from archean source materials demonstrating that the sask craton lies beneath paleoproterozoic orogenic rocks present at the surface in contrast common pb and sm nd isotopic compositions from pegmatites and aplites of the la ronge domain are essentially identical with those of the paleoproterozoic orogenic rocks into which they are intruded indicating derivation by partial melting of similar rocks thus if the sask craton extended to the west beneath the la ronge domain it was beneath the zone of melting that produced the post orogenic intrusions making it unlikely that the sask craton is a detached part of the hearne craton many samples from the sask craton have elevated pb 208 pb 204 ratios unlike superior craton or hearne craton rocks suggesting that the sask craton was derived from an exotic source such as the wyoming craton which shares similar elevated pb 208 pb 204 ratios

effect of rock fragments on eolian deposition of atmospheric dust abstract the effect of rock fragments and rock fragment cover on the deposition of airborne dust was examined in a wind tunnel four parameters were studied pebble size pebble flattening cover density and wind speed the effect of these parameters on the deposition of dust on the pebbles on the deposition of dust bewween and underneath the pebbles and on total dust deposition pebbles interpebble space was measured separately deposition on the pebbles increased with pebble size pebble flattening and wind speed deposition between and underneath the pebbles increased with increasing wind speed and with decreasing pebble flattening but there was no consistent relationship with pebble size total dust deposition was not influenced by pebble size pebble flattening and cover density but it increased linearly with wind speed it was also demonstrated that the larger and the flatter the pebbles and the higher cover density the more the dust will tend to settle on the pebbles rather than between or underneath them air flow separation seems to play a primary role in the spatial distribution of dust deposition within a rock fragment field as it determines the location and size of the low sedimentation areas that are connected to the air flow separation bubbles it should be noted that all data in this study refer to dust deposition not accumulation since only wind velocities below the dust deflation threshold were used

age and origin of the jan lake complex a glimpse at the buried archean craton of the trans hudson orogen the largely buried sask craton is a continental fragment or microcontinent that collided with and underthrust the paleoproterozoic flin flon glennie protocontinent along the pelican decollement zone at 1840 1830 ma rocks of the sask craton are exposed in three tectonic windows those of the pelican window have been named the jan lake complex and comprise 2960 ma arc derived leucocratic orthogneisses migmatitic paragneisses and a tholeiitic within plate igneous suite comprising 2488 ma dioritic to gabbroic rocks and 2450 ma enderbitic and charnockitic rocks including the sahli granite ages of ca 2450 ma are also common from the other two tectonic windows to the sask craton suggesting that emplacement of the igneous suite was widespread and perhaps part of the coeval matachewan igneous event the absence of rocks in the 2960 and ca 2450 ma age ranges on both the adjacent superior and rae hearne cratonic margins makes it improbable that the sask craton was derived by simple fragmentation without large scale tectonic transport the overthrust paleoproterozoic rocks represent a high grade northwestern extension of the flin flon volcanic belt and include 1856 ma leucotonalite and 1843 ma quartz monzodiorite an 1830 ma suite of homogeneous calc alkaline enderbitic rocks which intrude burntwood semipelitic migmatites throughout the kisseynew domain has also been emplaced in mylonites of the pelican decollement zone zircon and monazite ages in the 1812 1803 ma range record a high grade metamorphic event that resulted from collision between the sask craton and flin flon glennie complex

significance of langmuir circulation in upper ocean mixing comparison of observations and simulations received 4 february 2009 revised 27 march 2009 accepted 20 april 2009 published 28 may 2009 1 representing upper ocean turbulence accurately in models remains a great challenge for improving weather and climate projections langmuir circulation lc is a turbulent process driven by wind and surface waves that plays a key role in transferring momentum heat and mass in the oceanic surface layer we present a direct comparison between observations and large eddy simulations based on the wave averaged navier stokes equation of an lc growth event the evolution of cross wind velocity variance and spatial scales as well as mixed layer deepening are only consistent with simulations if lc effects are included in the model our results offer a validation of the large eddy simulation approach to understanding lc dynamics and demonstrate the importance of lc in ocean surface layer mixing citation kukulka t a j plueddemann j h trowbridge and p p sullivan 2009 significance of langmuir circulation in upper ocean mixing comparison of observations and simulations geophys res lett 36 l10603 doi 10 1029 2009gl037620

impact of langmuir turbulence on upper ocean response to hurricane edouard model and observations tropical cyclone intensity is strongly affected by the air sea heat flux beneath the storm when strong storm winds enhance upper ocean turbulent mixing and entrainment of colder water from below the thermocline the resulting sea surface temperature cooling may reduce the heat flux to the storm and weaken the storm recent studies suggest that this upper ocean turbulence is strongly affected by different sea states langmuir turbulence which are highly complex and variable in tropical cyclone conditions in this study the upper ocean response under hurricane edouard 2014 is investigated using a coupled ocean wave model with and without an explicit sea state dependent langmuir turbulence parameterization the results are compared with in situ observations of sea surface temperature and mixed layer depth from axbts as well as satellite sea surface temperature observations overall the model results of mixed layer deepening and sea surface temperature cooling under and behind the storm are consistent with observations the model results show that the effects of sea state dependent langmuir turbulence can be significant particularly on the mixed layer depth evolution although available observations are not sufficient to confirm such effects some observed trends suggest that the sea state dependent parameterization might be more accurate than the traditional sea state independent parameterization

u pb geochronologic constraints on the crustal evolution of the long range inlier newfoundland the long range mountains of newfoundland expose the northeastern most basement inlier of the appalachian orogen u pb results for two samples of basement gneiss reveal crustal formation ages of 1466 10 ma western brook pond charnockite and 1530 8 ma cat arm road gneiss indicating an affinity with pinwarian magmatism 1510 1450 ma in labrador a third sample of basement gneiss from the cat arm road dam site yielded a minimum formation age of 1631 ma these basement gneisses were intruded by granite plutons during two periods of grenvillian magmatism group i at 1032 1022 ma and group ii at 993 985 ma group i intrusions include the 1032 0 1 5 ma lomond river granite and the 1022 0 2 0 ma lake michel igneous suite group ii intrusions include the 999 4 ma potato hill charnockite 993 7 ma horse chops granite 984 9 1 6 ma cloud river granite and may include the apsy granite the metamorphic history of the long range inlier is complex and three discrete proterozoic metamorphic events can

the wathaman batholith largest known precambrian pluton the early proterozoic wathaman batholith in northern saskatchewan and manitoba is a 900 km long megacrystic granite granodiorite intrusion that straddles the junction between ensialic miogeoclinal and probably ensimatic eugeoclinal island arc terranes of the trans hudson orogen of the western churchill province although the largest precambrian batholith known it is apart from marginal complexities remarkably homogeneous throughout and unlike comparably sized and situated phanerozoic batholiths shows no evidence of multiple intrusion nor does it have comagmatic early mafic phases however it may be considered as just one phase of a larger batholithic belt that also includes numerous smaller plutons taken as a whole the composite batholithic belt is similar in many aspects to mesozoic pacific rim batholithic belts and like them probably was emplaced during plate collision the batholith is affected by pervasive internal deformation is bounded on the northwest by major blastomylonite zones a

bottom friction and wind drag for wave models abstract waves propagating in shallow water dissipate energy in a thin turbulent boundary layer near the bottom this friction can be estimated with a simple quadratic friction law scaled with an empirical coefficient two values of this coefficient have been recommended by previous studies for sandy bottoms a high value for waves in a storm and a low value for swell we show here that in contrast to current practise the lower value should be used for both applications the reason is that the high value dating from the early 1980s was inferred from observations in a severe storm using a relatively high wind drag our review of a large number of more recent observations gives a new wind drag parameterization with lower values with this new parameterization we infer from the same storm the lower value of the bottom friction coefficient using this lower value also improves the estimates of wave growth in shallow water and of low frequency wave decay in a tidal inlet independent of the wind drag

interaction of langmuir turbulence and inertial currents in the ocean surface boundary layer under tropical cyclones abstractbased on a large eddy simulation approach this study investigates the response of the ocean surface boundary layer osbl and langmuir turbulence lt to extreme wind and complex wave forc

geodynamic evolution and thermal history of the central flin flon domain trans hudson orogen constraints from structural development 40ar 39ar and stable isotope geothermometry shear zones in the flin flon area record five episodes of development these have been studied using structural analysis and 40ar 39ar thermochronology deformation occurred as a result of collision between the archean rae hearne and archean superior plates during the trans hudson orogeny 1900 to 1700 ma the geodynamic evolution encompasses a transition from island arc supracrustal development 1900 ma to tectonic mountain building under brittleductile conditions 1860 ma two episodes of ductile lineation schistosity l s shear zones on the prograde metamorphic path 1860 1810 ma and two episodes of retrograde displacement between 1790 and 1690 ma during final suturing of the archean cratons with paleoproterozoic assemblages metamorphism evolved in three stages contact aureoles to granitoid bodies formed at 1860 1840 ma hornblende homfels facies 40ar 39ar ages indicate cooling through 500 c at 1840 ma this was followed by regional heating burial which produced regional peak thermal recrystallization at 1820 1790 ma under lower greenschist to lower amphibolite conditions lastly retrograde metamorphism took place during unroofing between 1790 and 1690 ma with a regional cooling rate of 2 c m y

early proterozoic deformation along the southern margin of the kisseynew gneiss belt trans hudson orogen a 30 ma progressive deformation cycle fold axes and lineations across the southern margin of the kisseynew gneiss belt were progressively reoriented from northwesterly to northeasterly during an early proterozoic southwest directed compressive deformation cycle partitioning of deformation resulted in a concentration of non coaxial strain along the boundary between the kisseynew gneiss belt and flin flon snow lake belt the structural evolution was complicated by streamlining of the movement vector around the comparatively rigid flin flon snow lake belt the relationship of metamorphic assemblages to kinematic fabrics indicates that deformation was coeval with a prograde retrograde metamorphic cycle progressive deformation occurred during a period of 30 ma which is consistent with phanerozoic orogenic time scales

three dimensional collisional structure of the trans hudson orogen canada abstract the three dimensional structure of the eastern trans hudson orogen tho part of a paleoproterozoic continent continent collision zone in central north america is revealed through a network of lithoprobe seismic reflection profiles the seismic images are interpreted to delineate a series of stacked thrust sheets essentially confined to the crust e w profiles show strong e dipping reflections extending throughout the crust while n s profiles record events outlining antiformal and synformal structures this allows the identification of decollements that may have localized along pre existing structures e g possible basin bounding extensional faults and at major rheological boundaries e g basement cover contact upper middle crust transition the present topographic surface displays oblique crustal sections with 10 15 km of structural relief generated during post collisional intracontinental transpression of tho as a result of crustal scale folding and faulting

aeolian deposition of dust over hills the effect of dust grain size on the deposition pattern wind tunnel experiments were conducted to investigate the effects of topography on the grain size characteristics of aeolian dust deposits experiments were performed on three isolated hills having various size and aspect ratios the longitudinal profile of the median grain diameter was investigated for each hill the longitudinal dust deposition profile was also studied for nine grain size classes of between 10 and 104 m as were wind and dust concentration profiles in the atmosphere upwind of over and downwind of a hill the wind tunnel experiments show that the grain size characteristics of aeolian dust deposits are affected by topography most apparent is the occurrence of a zone of reduced grain size on the leeside of hills which extends from just upwind of the summit to a distance of several times the height of the hill slightly coarser than normal dust is deposited on the concave windward hill slope and in a zone downwind of the area of reduced grain size but the increase in grain size in these zones remains very small although the normalized dust deposition profile for a hill does not vary substantially as a function of grain size systematic trends are observed the most important tendencies are 1 a progressive extension in the downwind direction of a zone of decreased dust deposition on the leeside of a hill the coarser the grains the further downwind the zone of reduced deposition extends 2 a progressive increase in dust deposition immediately upwind of a hill the finer the grains the higher the deposition value upwind of a hill becomes both tendencies are explained by the difference in inertia of the grains which is controlled by grain size copyright 2005 john wiley sons ltd

aeolian dust transport and deposition by foehn winds in an alpine environment lake tekapo new zealand abstract observations from an automatic weather station and anemograph network are used in conjunction with recorded dust deposition rates to identify principle sources of wind blown dust within an alpine lake basin meteorological observations made throughout the study indicate that foehn windstorms provide ideal conditions for the initiation of aeolian processes including dust storm genesis a mean wind speed during foehn windstorms of 7 5 m s 1 at 2 65 m above the surface was observed to initiate entrainment of dust particles from geomorphically active areas within the lake basin particularly from the dry braid channels of glacier fed rivers exposed lacustrine deltas and degraded tussock grasslands this threshold entrainment velocity is similar to others presented within the international literature for such surface types a diurnal modulation of meteorological parameters monitored during foehn wind events suggests that aeolian processes such as dust entrainment are most likely to occur from late morning to early evening however where topography enhances wind speeds for example by channelling airflow down river valleys favourable conditions for dust entrainment may prevail throughout the night in the absence of precipitation potential dust roses were determined for two sites within the lake basin the dust roses supported anecdotal and observational evidence of principle dust sources within the study area and appear to be an effective tool for identifying the potential hazard to a particular location from blowing dust once the physical trigger conditions for dust entrainment are known this requires detailed and concurrent monitoring of meterological variables in association with dust transportation and deposition rates especially in complex terrain where many micro climates often exist

the pelican thrust zone basal detachment between the archean sask craton and paleoproterozoic flin flon glennie complex western trans hudson orogen the pelican thrust zone is a 3 7 km wide recrystallized mylonite zone along which paleoproterozoic arc volcano plutonic and derived sedimentary rocks of the flin flon glennie complex were thrust over an archean package jan lake complex consisting of ca 3 1 ga calc alkaline orthogneisses pelitic migmatites and a ca 2 45 ga tholeiitic charnockite norite intrusive suite a regional northeast plunging stretching lineation and a variety of kinematic indicators imply southwesterly transport matching that of other coeval shallower crustal level structures observed throughout the northern flin flon domain and southern flank of the kisseynew domain e g sturgeon weir and annabel lake shear zones subsequent east side up displacement on the tabbernor fault together with domal fold interference has exposed the pelican window and mantling mylonite zone where it has been seismically profiled along lithoprobe transects tectonic windows also expose archean rocks in the glennie domain to the west where similar southwest verging recrystallized mylonite zones have been documented together these zones record collision and underplating of the flin flon glennie complex by the archean sask craton during prolonged protocontinent continent collision over a minimum 1826 1805 ma interval resume la zone de chevauchement pelican est une zone de mylonite recristallisee d une largeur de 3 7 km le long de laquelle des roches volcano plutoniques d un arc datant du paleoproterozoique et des roches sedimentaires derivees du complexe de flin flon glennie ont ete chevauchees par dessus un ensemble archeen le complexe de jan lake qui est compose d orthogneiss calco alcalins et de migmatites pelitiques gees d environ 3 1 ga ainsi que d une suite intrusive charnockite norite tholeiitique gee d environ 2 45 ga une lineation regionale d etirement a pendage nord est et divers indicateurs cinematiques correspondent a un transport vers le sud ouest rejoignant celui d autres structures contemporaines de niveaux crustaux moins profonds observees a travers tout le domaine de flin flon nord et le flanc sud du domaine kisseynew p ex les zones de cisaillement de sturgeon weir et d annabel lake un deplacement subsequent le cote est vers le haut le long de la faille de tabbernor avec une interference de plis de dome a fait affleurer la fenetre pelican et la zone mylonitique qui la recouvre elle a ete determinee par des profils sismiques le long des transects lithoprobe des fenetres tectoniques permettent aussi l affleurement de roches archeennes du do maine de glennie vers l ouest la ou ont ete documentees des zones semblables de mylonites recristallisees a pendage sud ouest ensemble ces zones enregistrent la collision et le sous placage du complexe de flin flon glennie par le craton archeen sask au cours d une collision prolongee entre le protocontinent et le continent au cours d un intervalle d au moins 1826 a 1805 ma

a global perspective on langmuir turbulence in the ocean surface boundary layer the turbulent mixing in thin ocean surface boundary layers osbl which occupy the upper 100 m or so of the ocean control the exchange of heat and trace gases between the atmosphere and ocean here we show that current parameterizations of this turbulent mixing lead to systematic and substantial errors in the depth of the osbl in global climate models which then leads to biases in sea surface temperature one reason we argue is that current parameterizations are missing key surface wave processes that force langmuir turbulence that deepens the osbl more rapidly than steady wind forcing scaling arguments are presented to identify two dimensionless parameters that measure the importance of wave forcing against wind forcing and against buoyancy forcing a global perspective on the occurrence of wave forced turbulence is developed using re analysis data to compute these parameters globally the diagnostic study developed here suggests that turbulent energy available for mixing the osbl is under estimated without forcing by surface waves wave forcing and hence langmuir turbulence could be important over wide areas of the ocean and in all seasons in the southern ocean we conclude that surface wave forced langmuir turbulence is an important process in the osbl that requires parameterization citation belcher s e et al 2012 a global perspective on langmuir turbulence in the ocean surface boundary layer geophys res lett 39 l18605 doi 10 1029 2012gl052932

scale model simulations of the deposition of loess in hilly terrain the sedimentation of loess in a 40 km2 area on the northern border of the belgian loess belt is investigated by means of wind tunnel experiments loess deposition is simulated on a relief scale model for different wind directions it appears that simulation with northeast winds produces a loess deposition pattern that coincides closely to the field pattern which may be an indication that the loess bearing winds at the end of the weichselian came from the northeast loess deposition occurs preferably on windward slopes and not on leeward ones the wind shadow concept which is important in the case of sand deposition may therefore not necessarily apply to fine materials such as fine silt and clay

crustal structure and evolution of the trans hudson orogen results from seismic reflection profiling a 400 km long deep seismic reflection transect across northeastern montana and northern north dakota reveals the crustal scale structural fabric of the early proterozoic trans hudson orogen beneath the williston basin comparison with deep seismic reflection data across the canadian portion of the same orogen 700 km to the north reveals first order similarities in crustal architecture but documents significant along strike variation in orogenic evolution both transects display a broad crustal scale antiform axial to the orogen in the north geologic data suggest that this antiform is cored by an archean microcontinent in the south west dipping reflections on the western flank of the antiform extend from the upper crust to the uppermost mantle and truncate prominent subhorizontal lower crustal reflections of the archean wyoming craton within the wyoming craton the eastern limit of east dipping midcrustal reflections coincides with the subsurface age boundary between the craton and the early proterozoic trans hudson orogen as interpreted from potential field and drill core data on the basis of subsurface geochronologic data from the crystalline basement and by analogy with the glennie domain within the exposed trans hudson orogen in canada we suggest that the southern antiform is cored by an archean crustal fragment that was caught up in the terminal collision of the wyoming and superior cratons during hudsonian orogeny the eastern side of the trans hudson orogen is characterized on both seismic transects by predominantly east dipping crustal penetrating reflections we interpret the easterly dip of these reflections as evidence that the superior province was thrust westward over the interludes of the orogen during terminal collision although juvenile early proterozoic terranes characterize the exposed segment of the trans hudson orogen in canada limited drill core information within the dakota segment of the orogen shows a predominance of granulitic archean age crust this difference in basement lithologies along strike within the orogen may indicate the following either juvenile crust comparable to that exposed in the northern trans hudson was never present in the south or it was removed by progressive over thickening erosion and or faulting postorogenic extensional collapse may be responsible for preservation of juvenile terranes in the north

kisseynew metasedimentary gneiss belt trans hudson orogen canada back arc origin and collisional inversion the kisseynew metasedimentary gneiss belt initially developed in a back arc setting the ages of detrital zircons and crosscutting plutons constrain turbidite sedimentation to 1 855 1 841 ga postdating early deformation and metamorphism associated with arc arc and arc continent collisions affecting much of the trans hudson orogen these turbidites are interpreted to have been deposited in a back arc basin behind a retreating subduction boundary the kisseynew domain and its southern flank are marked by 1 84 1 83 ga magmatic rocks that may be related to subduction of back arc basin oceanic crust collapse of the kisseynew basin by ductile fold and thrust deformation began during 1 84 1 83 ga magmatism and continued through peak metamorphism at ca 1 820 1 805 ga from authors

trans hudson orogen and williston basin in montana and north dakota new cocorp deep profiling results cocorp consortium for continental reflection profiling deep reflection profiling across the williston basin and underlying trans hudson orogen shows the following 1 there is no evidence for a precursor rift basin beneath the axis of the williston basin with the exception of small scale structures e g nesson and cedar creek anticlines the basement surface beneath the williston basin is smooth and has a dish shaped geometry 2 crustal penetrating reflections within the eastern trans hudson orogen dip eastward in apparent contradiction to the conventional view that the superior province underthrusts the eastern side of the orogen 3 basement reflections beneath the center of the orogen define a broad crustal scale antiform the axis of which coincides approximately with the depocenter of the overlying williston basin midcrustal reflections defining the crest and western flank of this antiform also coincide generally with the location and shape of the source of the north american central plains conductivity anomaly 4 crustal penetrating reflections beneath the western side of the orogen dip westward supporting the current view that subduction polarity was to the west beneath the wyoming province 5 the eastern edge of the wyoming province is marked by east dipping upper crustal reflections and subhorizontal lower crustal reflections that are truncated by the west dipping reflectivity of the trans hudson orogen

tectonic implications of new shrimp and tims u pb geochronology of rocks from the sask craton peter lake domain and hearne margin trans hudson orogen saskatchewan this study reports new sensitive high resolution ion microprobe shrimp and thermal ionization mass spectrometry tims u pb geochronological data for thirteen rocks from the archean to paleoproterozic sask craton the peter lake domain and hearne margin saskatchewan seven samples from the exposed sask craton in both the glennie domain and pelican window record zircon growth between 2425 and 2525 ma and at 1800 ma older precursor material has been identified most notably a refined crystallization age of 3117 ma for a sample of quartzofeldspatic gneiss q gneiss in the pelican window which also experienced ca 2450 ma zircon growth three samples from the peter lake domain and a sample from the linn island inlier of the wollaston domain yield ages of 2575 ma one sample from the peter lake domain is distinctly older yielding an age of 2640 ma but also displays zircon growth at 2575 ma the simplest interpretation of these data is that the peter lake domain is likely a part of the hearne margin

langmuir turbulence in shallow water part 1 observations during extended deployment at an ocean observatory off the coast of new jersey a bottom mounted five beam acoustic doppler current profiler measured large scale velocity structures that we interpret as langmuir circulations filling the entire water column these circulations are the large eddy structures of wind wave driven turbulent flows that occur episodically when a shallow water column experiences prolonged strong wind forcing many observational characteristics agree with former descriptions of langmuir circulations in deep water the three dimensional velocity field reveals quasi organized structures consisting of pairs of surface intensified counter rotating vortices aligned approximately downwind maximum downward velocities are stronger than upward velocities and the downwelling region of each cell defined as a pair of vortices is narrower than the upwelling region maximum downward vertical velocity occurs at or above mid depth and scales approximately with wind speed the estimated crosswind scale of cells is roughly 3 6 times their vertical scale set under these conditions by water depth the long axis of the cells appears to lie at an angle 10 20 to the right of the wind a major difference from deep water observations is strong near bottom intensification of the downwind jets found typically centred over downwelling regions accessible observational features such as cell morphology and profiles of mean velocities turbulent velocity variances and shear stress components are compared with the results of associated large eddy simulations reported in part 2 of shallow water flows driven by surface stress and the craik leibovich vortex forcing generally used to represent generation of langmuir cells a particularly sensitive diagnostic for identification of langmuir circulations as the energy containing eddies of the turbulent flow is the depth trajectory of invariants of the turbulent stress tensor plotted in the lumley triangle corresponding to realizable turbulent flows when langmuir structures are present in the observations the lumley map is distinctly different from that of surface stress driven couette flow again in agreement with the large eddy simulations les unlike the les observed velocity fields contain two distinct and significant scales of variability documented by wavelet analysis of observational records of vertical velocity variability with periods of many minutes is that expected from langmuir cells drifting past the instrument at the slowly time varying crosswind velocity shorter period variability of the order of 1 2 min has roughly the observed periodicity of surface wave groups suggesting a connection with the wave groups themselves and or the wave breaking associated with them in high wind conditions

wind tunnel experiments of aeolian dust deposition along ranges of hills wind tunnel experiments of aeolian dust deposition on topographic scale models of ranges of hills were conducted different hill sizes and hill spacings were used and comparisons with the deposition patterns over single isolated hills were made dust profiles over ranges of hills differ from the profiles over identical but isolated hills on isolated hills the sedimentation maximum on the windward hillslope is always single and located on the concave part of the slope in the case of ranges of hills the maximum is either single or double with the second peak on the convex part of the windward slope in the latter case the local sedimentation maximum on the convex leeslope which is rather unimportant on isolated hills is much more developed in multiple hill topography also dust deposition on the leeslopes is significantly higher in multiple hill topography than on isolated hills dust patterns on ranges of hills may be affected by the dust shadow created by the most upstream located hill if hills succeed each other quickly they are located within the shadow zone and are protected from important dust deposition the plume of high air dust concentration that is created by a hill largely determines the dust pattern on the next hill as a result of the supply of dust from above by the descending plume areas that are normally devoid of dust now experience significant dust deposition

deep seismic profile across a proterozoic collision zone surprises at depth collisions between continents generate the world s most striking mountains the deep structure of these collision zones inferred from seismic reflection profiles1 3 can be equally dramatic if less well understood improved knowledge of the structure of ancient collisional belts now known to have developed through plate tectonic processes4 5 can provide important new insights into the mechanisms of crustal growth although many such belts have been partly destroyed by severe post collisional deformation6 7 or magmatism8 some have been preserved in the stable interiors of continents9 one example is the early proterozoic trans hudson orogen9 10 in western canada here we present seismic reflection images across the entire orogen which reveal a broadly symmetric structure with reflections linked to island arc rocks dipping beneath both bounding archaean cratons the observed reflection geometries imply a doubling of crustal thickness during the collision along crust penetrating faults the presence of a significant amount of archaean crust at depth the extent of which could not have been determined from surface mapping suggests the need for caution in inferring crustal growth rate from the surface area of juvenile crust11 12

role of langmuir circulation in the deepening of the ocean surface mixed layer helical motions known as langmuir circulation are a key physical process in the upper ocean but have not yet been incorporated into ocean models here surface mixed layer deepening by langmuir circulation was added to that due to convection or velocity shear langmuir circulation is more important than shear if the velocity difference across the mixed layer base is less than about 1 percent of the wind speed in an upper ocean data set evidence was found for the deepening of the mixed layer by both mechanisms thus langmuir circulation influences upper ocean diurnal and seasonal changes in stratification

quantification of the dry aeolian deposition of dust on horizontal surfaces an experimental comparison of theory and measurements eight techniques to quantify the deposition of aeolian dust on horizontal surfaces were tested in a wind tunnel the tests included three theoretical techniques and five measurement techniques the theoretical techniques investigated were the gradient technique the inferential technique without grain shape correction and the inferential technique corrected for grain shape the measuring techniques included the following surrogate surfaces a water surface a glass surface a metal surface a vertical array of metal plates and an inverted frisbee filled with glass marbles the efficiency of the techniques was investigated for the sediment as a whole all grain sizes together as well as for a large number of grain sizes extending from 1 to 104 m the surrogate surfaces showed more or less comparable catch efficiencies although the water surface nearly always caught the highest quantities of dust and the marble filled frisbee and the vertical array of metal plates the lowest quantities of dust the dust fluxes calculated by theoretical methods were markedly different from those obtained by direct measurements the fluxes calculated by the inferential technique approximated those of the direct measurements only for grain sizes between 30 and 40 m for smaller and coarser grains deviations from the measured fluxes were high the gradient method in its turn provided extremely low calculated fluxes for grains in all size classes investigated the latter technique was not considered very reliable for the dust used in the tests

a wind tunnel simulation and field verification of desert dust deposition avdat experimental station negev desert the deposition of natural dust in an area of 53 ha situated in the northern negev desert is investigated in detail both in the wind tunnel dust storm simulations over a topographic scale model and in the field the wind tunnel results and the field results show a high degree of agreement indicating that scale model simulation may be considered an important technique for future loess and desert research more dust settles on windward slopes than on leeward slopes which is in contradistinction with the widespread wind shadow concept air flow separation zones immediately downwind of steep windward slopes have an important impact on dust deposition too in the case of dust deposition on topographic scale models a restricted height distortion of the model will not necessarily lead to serious problems in addition wind tunnel blockage percentages up to 13 may be allowed in order to obtain acceptable dust deposition patterns for the scale model a mean gross dust deposition of about 200 250 g m 2 year 1 is calculated for the northern negev desert for 1987 thus if the settled dust can be protected against erosion in the cultivated areas in the negev the dust content of the top soil will markedly increase with time however it has to be borne in mind that cultivation activities themselves may also contribute to a higher soil erosion and hence to a higher dust content in the atmosphere at any rate a higher dust content in the top soil will unquestionably have an important positive effect on agricultural yields from the air dust concentration data and the dust deposition data a deposition velocity of 4 7cms 1 can be calculated for avdat dust

the wave driven ocean circulation oceanic surface gravity waves have a mean lagrangian motion the stokes drift the dynamics of winddriven basin scale oceanic currents in the presence of stokes drift are modified by the addition of so called vortex forces and wave induced material advection as well by wave averaged effects in the surface boundary conditions for the dynamic pressure sea level and vertical velocity some theoretical analyses previously have been made for the gravity wave influences on boundary layer motions including the ekman currents the present paper extends this theory to the basin scale depth integrated circulation in a bounded domain it is shown that the sverdrup circulation relation with the meridional transport proportional to the curl of the surface wind stress applies to lagrangian transport while the associated eulerian transport is shown to have a component opposite to the stokes drift transport a wave induced correction to the relation between sea level and surface dynamic pressure is also derived preliminary assessments are made of the relative importance of these influences using a global wind climatology and an empirical relationship between the wind and wave fields recommendations are made for further development and testing of this theory and for its inclusion in general circulation models

field experiments of aeolian dust accumulation on rock fragment substrata the effect of rock fragments and rock fragment cover on the accumulation of airborne dust was examined in a long term field experiment in the negev desert of israel four parameters were studied pebble eccentricity pebble size pebble flattening and cover density the effect of these parameters on the accumulation of dust on the pebbles on the accumulation of dust between and underneath the pebbles and on total dust accumulation pebbles interpebble space was measured separately accumulation on the pebbles increased as the pebbles became larger less flattened and more elongated and as cover density increased accumulation between and underneath the pebbles increased as the pebbles became smaller more flattened and more elongated and as cover density increased although the accumulation area available became smaller total dust accumulation increased as the pebbles became smaller more flattened and more elongated and as cover density increased rock fragments act as a dust trap as dust accumulation on pebble covered surfaces is several tens of times larger than dust accumulation on similar but pebble free surfaces however less than 20 of the initially settled dust is protected from further erosion in the negev desert dust erosion by wind is of the order of 10 times larger than dust erosion by water the rate of long term dust accumulation in the negev is of the order of 15 30 g m 2 yr 1 this is considerably lower than the rates proposed elsewhere in the literature which are based upon over optimistic dust retainment percentages

uranium lead zircon and titanite ages from the northern portion of the western gneiss region south central norway abstract the geochronologic history of the northern portion of the western gneiss region south central norway has been investigated by u pb analyses of zircon and titanite from various basement units and one supracrustal gneiss a six point four zircon and two titanite discordia line from a migmatite melt pod and its host gneiss astfjord migmatite gneiss defines upper and lower intercept ages of 1659 1 1 8 ma and 393 6 3 6 ma respectively the upper intercept age is interpreted as a time of tonalite emplacement and migmatite formation in the region a seven point three zircon and four titanite discordia line from the ingdal granite gneiss has similar upper and lower intercept ages 1652 9 1 7 ma and 396 1 4 9 ma respectively and the upper intercept age is interpreted as the time of granite crystallization the lower intercept age from both theastfjord migmatite gneiss and the ingdal granite gneiss is interpreted as the time of regional metamorphic resetting and is evidence for caledonian influence in the region titanite from these two gneiss units as well as from other tonalite granite and supracrustal gneisses throughout the western gneiss region displays a remarkably uniform pattern of discordance titanite discordance is variable from 6 to 100 and in general the degree of discordance is proportional to the caledonian metamorphic grade of nearby supracrustal schists episodic diffusional lead loss from titanite during caledonian metamorphism probably caused the discordance pattern but a combined mechanism of mixing and diffusional lead loss cannot be ruled out in any case the seventeen point titanite and zircon discordia line clearly indicates that 1 the bulk of the granitoid terrane in this portion of the western gneiss region was emplaced migmatized and cooled in a short time interval about 1657 ma ago 2 a second short lived thermal event that exceeded the blocking temperature of titanite occurred about 395 ma ago and 3 titanite and zircon in the region were not isotopically disturbed by comparable geologic events in the period from 1657 to 395 ma or at any time after 395 ma

dry aeolian dust accumulation in rocky deserts a medium term field experiment based on short term wind tunnel simulations the spatial pattern of medium term a few months dry aeolian dust accumulation in rocky deserts is predicted using short term deposition and erosion experiments in a wind tunnel the predictions are tested in a field experiment set up in the northern negev desert of israel the results show that superimposing wind tunnel deposition and erosion maps usually leads to correct predictions of medium term dust accumulation the predictions are somewhat less confident near the inflection lines of windward hillslopes where small scale irregularities in the local topography make it difficult to locate the exact position of the areas of little accumulation elsewhere in the topography predictions are good and the method works satisfactorily highest accumulation occurs on concave windward slopes and to a lesser extent on slopes parallel to the wind little accumulation occurs on the convex windward slopes and in dust separation bubbles the smallest accumulation rates are observed immediately upwind of the top of pronounced hills and on leeslopes the rate of dry dust accumulation measured during the field experiment varied from 17 to 93 g m 2 a 1 depending on the topographic position of the accumulation plots for most plots it was of the order of 30 60 g m 2 a 1

geochronology at the namew lake ni cu orebody flin flon area manitoba canada thermal history of a metamorphic terrane intermediate composition orthogneisses of the southward extension of the flin flon greenstone belt surround the ultramafic host rock of the namew lake ni cu deposit in northern manitoba the gneiss

structural evolution of the eastern amisk collage trans hudson orogen manitoba deformation recorded in the amisk collage in the central part of the paleoproterozoic flin flon belt southeastern trans hudson orogen is divided into pre early late and post hudsonian orogeny distinguished by significant changes in metamorphic conditions and the orientation of structures detailed structural analysis petrography and high precision geochronology combined with previous mapping and geochemical studies indicate a structural history spanning 180 ma in the amisk collage and the database provides an excellent opportunity to study the structural evolution of precambrian greenstone belts accretion of the 1 92 1 88 ga tectono stratigraphic assemblages in the amisk collage began prior to 1 868 ga the deformational history records six generations of ductile structures f1 f6 followed by development of brittle ductile and brittle structures f7 which may have continued as late as 1 690 ga during exhumation of the collage the steep generally north northeast macroscopic structural g

air flow over a two dimensional hill studies of velocity speed up roughness effects and turbulence wind tunnel measurements have been made of the streamwise mean and turbulent velocities over a rough bell shaped two dimensional hill with height h and maximum slope 0 26 placed in a neutrally stable boundary layer of thickness 10 h and roughness length zo 0 02 h close agreement is found between the mean velocity and predictions obtained from taylor s 1977 computational model and jackson and hunt s 1975 analytical linearized model for locations at or upwind of the hill top but not in the wake examination of the models shows that the shear stresses are only important in an inner region close to the hill surface so that as suggested by jackson and hunt 1975 the perturbation to the mean flow outside this region is essentially inviscid the theory shows that over very rough surfaces such as wooded or urban terrain the height of this inner region can be of the same order as the height of the roughness elements so that in our experiments no measurements could be made in this region in a second experiment flow over a smooth hill on a rough surface was studied the additional increase of wind speed over the hill top can be estimated by assuming a linear superposition of the velocity changes produced by the changes in elevation and in surface roughness in this case rough to smooth in the lee of a hill however the change in roughness significantly alters the flow with flow separation being suppressed and here a linear superposition is not appropriate finally we consider why observed changes in turbulence structure close to the surface differ from those well above the surface calculations of these changes based on the simple theoretical arguments of equilibrium shear layers and rapidly distorted turbulent flows agree well with turbulence measurements in wind tunnels and in the field