shear induced convective mixing in bottom boundary layers on slopes field data from a stratified lake demonstrate that buoyancy driven convective mixing can be an important mechanism for the formation of well mixed bottom boundary layers bbls on slopes convective turbulence is caused by differential transport of stratified water masses along the slope of a basin because the current velocity usually decreases toward the sediment water at some distance from the bottom is transported faster than is water below during upslope flow this process leads to transport of heavier water on top of lighter water and hence to unstable stratification within the bbls analogously strong bbl stratification occurs during downslope flow high frequency acoustic doppler current profiler adcp and temperature measurements in the bbls of a lake revealed the cyclic occurrence of convective turbulence driven by periodic across slope currents of internal seiching the estimated maximum buoyancy flux within the bbls was in good agreement with the highest observed dissipation rates of turbulent kinetic energy this suggests that in our specific case classical bottom shear production and the mentioned buoyancy driven convective production contributed by similar amounts to the turbulent kinetic energy

how do ocean warm anomalies favor the aggregation of deep convective clouds abstractwe investigate the role of a warm sea surface temperature sst anomaly hot spot of typically 3 k to 5 k on the aggregation of convection using cloud resolving simulations in a non rotati

nearshore internal bores and turbulent mixing in southern monterey bay 1 we observed transient stratification and mixing events associated with nearshore internal bores in southern monterey bay using an array of instruments with high spatial and temporal resolution the arrival of the bores is characterized by surging masses of dense cold water that tend to stratify the water column the bore is followed by a gradual drop in the temperature throughout the water column over several hours defined here as the bore period until a sharp warm front relaxation followed by high frequency temperature fluctuations returns the column back to nearly its original state defined here as the mixing period mixing periods revealed increased temperature variance at high frequencies n as well as a greater percentage of events where dynamic instabilities may be present ri 0 25 suggesting active mixing of the stratified water column turbulent dissipation rates in the stratified interior during the mixing period estimated using the technique of isopycnal slope spectra revealed mean values the same order of magnitude as near bed bottom generated turbulence observations indicate that local shear produced turbulent kinetic energy by the warm front relaxations dominates mixing in the stratified interior the non canonical nature of these bore and relaxation events is also investigated with a numerical model and the dynamics are shown to depend on the internal iribarren number our results suggest that nearshore internal bores interacting with local bathymetry dramatically alter local dynamics and mixing in the nearshore with important ecological implications

modelling the generation of gravity waves by a maritime continent thunderstorm observed wind and temperature profiles are used to initialize a model calculation of a maritime continent thunderstorm and the numerical solution is used to explore the effect of tropospheric shear on the gravity wave generation the resultant convective system is qualitatively similar to that observed the modelled gravity waves propagate away from the cloud with wave fronts that are approximately circular implying that the convective clouds do not generate waves which propagate in a preferred direction the gravity wave generation is related to the oscillation of the convective updraughts about their level of neutral buoyancy while the general features of the gravity waves are similar in most respects to a previous study which used an idealized wind profile the frequency of the gravity waves is doppler shifted by the tropospheric wind shear the result is a much broader power spectrum in comparison to the idealized cases

calculation of airflow over an isolated heat source with application to the dynamics of v shaped clouds abstract the stably stratified airflow over a three dimensional elevated heat source is investigated using the linearized equations of motion a low level upward motion can be produced for airflow over a prescribed isolated heat source for a wide variety of mean wind speeds above the heating layer a v shaped region of upward displacement is formed by the action of the mean wind on the upward propagating waves the horizontal pattern of the heat source is important in determining the formation of the v shaped region of upward displacement a high pressure region is produced in the vicinity of the heat source at the top of the heating layer the response of a hydrostatic airflow to a transient heating is a v shaped region of upward displacement with an embedded region of downward displacement above the heated layer the whole system advects downstream with a slower speed than the mean wind and eventually disperses a region of strong divergence is associated with the region of upward displacement above th

laurentide cordilleran and montane glaciation in the western peace river grande prairie region alberta and british columbia canada abstract geological investigations over the last decade in the western peace river grande prairie district of northwestern alberta and northeastern british columbia have provided important chronostratigraphic information regarding laurentide cordilleran and montane quaternary glacial events numerous 14 c age determinations as well as stratigraphic and sedimentological analyses of numerous exposures indicate that this area was first glaciated by cordilleran ice sometime before the late wisconsinan during the late wisconsinan ca 22 000 14 000 bp laurentide glacier ice covered much of the area between approximately 15 000 and 10 000 bp montane ice affected only the western part of the peace region there is no evidence for synchroneity of the ice advances and therefore no evidence for ice coalescence in this region the resultant ice free corridor was most likely a laterally fluctuating zone which existed during a several thousand year period in the late pleistocene climatic conditions along the corridor during this period were probably unfavorable for human migration but adequate for some plants and small animals numerous isolated areas along the western foothills of the northern rocky mountains west of the laurentide glaciation limit were never glaciated during the late wisconsinan

a linear theory of three dimensional land sea breezes abstractland sea breezes lsbs induced by diurnal differential heating are examined using a three dimensional linear model employing fast fourier transform with emphasis on the complex coastline shape and geometry the earth s rotation and background wind effects it has been demonstrated that the low level vertical motion associated with lsb can be significantly enhanced over a bay peninsula because of convergence of perturbations induced by differential heating along a seaward concave convex coastline the dependence of surface winds and vertical motion patterns and their evolutions on the coastline geometries such as the width and the aspect ratio of the bay the earth s rotation and the background winds are investigated the lsb induced by an isolated tropical island is characterized by onshore flow and ascent over the island in the afternoon to early evening with a reversal of direction from midnight to early morning the diurnal heating induced vertical motion is greatly enhanced over the isl

efficiency of turbulent mixing in the abyssal ocean circulation turbulent mixing produced by breaking of internal waves plays an important role in setting the patterns of downwelling and upwelling of deep dense waters and thereby helps sustain the global deep ocean overturning circulation a key parameter used to characterize turbulent mixing is its efficiency defined here as the fraction of the energy available to turbulence that is invested in mixing efficiency is conventionally approximated by a constant value near one sixth here we show that efficiency varies significantly in the abyssal ocean and can be as large as approximately one third in density stratified regions near topographic features our results indicate that variations in efficiency exert a first order control over the rate of overturning of the lower branch of the meridional overturning circulation

turbulence and entrainment in a buoyant surface plume in winter tidal outflow from the leschenault estuary forms a buoyant sheared stratified plume in koombana bay on each outgoing tide the turbulence in the plume and the local entrainment into the plume are examined based on measurements collected in an intensive field program coherency measurements between horizontally separated sensors are used to examine the anisotropy of the turbulence the effects of viscosity and buoyancy on the turbulence are studied using an activity diagram which is also an indicator of the mixing efficiency and total mixing the osborne cox model is tested and found to be valid in the plume

stratospheric gravity waves generated by multiscale tropical convection abstract the generation of gravity waves by multiscale cloud systems evolving in an initially motionless and thermodynamically uniform environment is explored using a two dimensional cloud system resolving model the simulated convection has similar depth and intensity to observed tropical oceanic systems the convection self organizes into preferred horizontal and temporal scales involving weakly organized propagating cloud clusters the multiscale systems generate a broad spectrum of gravity waves with horizontal scales that range from the cloud system scale up to the cloud cluster scale the gravity waves with the largest horizontal scale play an important role in modifying layered tropospheric inflow and outflow to the cloud systems which in turn influence the multiscale convective organization slower moving short scale gravity waves make the strongest individual contribution to the vertical flux of horizontal momentum and cause a robust peak in the momentum flux spectrum that corresponds to the lif

the modification of bottom boundary layer turbulence and mixing by internal waves shoaling on a barrier reef abstractresults are presented from an observational study of stratified turbulent flow in the bottom boundary layer on the outer southeast florida shelf measurements of momentum and heat fluxes were made using an array of acoustic doppler velocimeters and fast response temperature sensors in the bottom 3 m over a rough reef slope direct estimates of flux richardson number rf confirm previous laboratory numerical and observational work which find mixing efficiency not to be a constant but rather to vary with frt reb and rig these results depart from previous observations in that the highest levels of mixing efficiency occur for frt 1 suggesting that efficient mixing can also happen in regions of buoyancy controlled turbulence generally the authors find that turbulence in the reef bottom boundary layer is highly variable in time and modified by near bed flow shear and stratification driven by shoaling internal waves

evidence for the influence of form drag on bottom boundary layer flow posed of two intersecting segments smith 1977 and smith and mclean 1977 demonstrate that multiple roughness scales can generate velocity profiles with more than two segments thus when form drag is important the constantstress assumption will not be valid in an earlier paper caldwell and chriss 1979 we demonstrated the existence of the viscous sublayer in the bottom boundary layer and found a logarithmic layer above it in examining additional data from the experiment segmented profiles were found in the logarithmic region figures 1 and 2 as expected if form drag influences the flow when the original data set was reanalyzed using thinner averaging intervals in the upper portion of the profile and also incorporating both upward and downward traverses it too shows two distinct logarithmic slopes in the original study only downward traverses were used although deviation from a single logarithmic form is not necessarily large the slope of the logarithmic regression is significantly different in the two regions implying that the turbulent stress above is significantly larger than it is nearer the bed

anatomy of turbulence in thermally stratified lakes turbulence within the thermocline of two thermally stratified lakes lake biwa japan and lake kinneret israel was investigated using a portable flux profiler this instrument provided high resolution profiles of temperature conductivity and two components of velocity within a measuring volume of approximately 8 mm 3 each data profile was segmented into statistically stationary segments a range of properties of the turbulence including direct estimates of the vertical mass flux were then calculated for each segment it was found that turbulence in the thermocline was generally patchy but within a patch dissipation levels were relatively high the turbulent motions were found to be fine grained with small thorpe scales and a large skewness of the distribution of the displacement scale this is distinct to that found in the ocean where shear instability produces large overturns the measurement showed that the net vertical mass flux in the thermocline was negligible and less than that predicted by osborn 1980 this is explained by noting that the net buoyancy flux consisted of two opposing parts a down gradient irreversible flux due to turbulent mixing and an up gradient reversible flux due to restratification that often cancel each other within a segment the low measured net buoyancy flux within the interior of the lakes suggested that other processes such as gravitational adjustments and benthic boundary layer processes should be responsible for the basin averaged vertical transport in these lakes

spatial and temporal variability of internal wave forcing on a coral reef the deployment of a dense spatial array of temperature sensors on a coral reef in the florida keys provided a unique view of the interaction of cool water incursions generated by internal waves with the three dimensional reef bathymetry water temperature on the reef surface was sampled every 5 s at 100 points on a 100 m by 150 m grid with concomitant measurements of water column velocity and temperature from mid may through mid august 2003 episodic incursions of cool subsurface water were driven by periods of strong semidiurnal internal tide and higher frequency internal wave activity for every time step in the data record the mean profile of temperature as a function of depth is calculated with a 3 m vertical averaging length scale subtracting this mean profile from the raw record yields a within depth horizontal temperature anomaly visualization through time of the anomaly mapped onto the measured reef bathymetry reveals episodic variability of thermal patchiness across the reef as well as persistent features associated with reef bathymetry variation in the nature of the cooling and resulting thermal heterogeneity among events and seasons suggests multiple modes of cool water incursion ranging from unbroken tidal period internal waves to packets of higher frequency energetic broken internal bores

the contribution of salt fingers to vertical mixing in the north atlantic tracer release experiment abstract the north atlantic tracer release experiment natre was performed in an area moderately favorable to salt fingers however the classic finger signature of a distinct thermohaline staircase caused by upgradient density flux was absent this is likely because mixing by turbulence was sufficiently strong to disrupt the formation of permanent step and layer systems despite the lack of a staircase optical shadowgraph profiles revealed that small scale tilted laminae previously observed in a salt finger staircase were abundant at the natre site using microstructure observations the strength of salt finger mixing has been diagnosed using a nondimensional parameter related to the ratio of the diffusivities for heat and buoyancy the dissipation ratio by examining the dissipation ratio in a parameter space of density ratio r and richardson number ri the signal of salt fingers was discerned even under conditions where turbulent mixing also occurred while the model for turbulence descr

multiphase flow of the late wisconsinan cordilleran ice sheet in western canada in central british columbia ice flow during the late wisconsinan fraser glaciation ca 25 10 ka occurred in three phases the ice expansion phase occurred during an extended period when glaciers flowed westward to the pacific ocean and east southeastward onto the nechako plateau from ice centers in the skeena hazelton coast and omineca mountains initially glacier flow was confined by topography along major valleys but eventually piedmont and montane glaciers coalesced to form an integrated glacier system the cordilleran ice sheet in the maximum phase a cordilleran ice divide developed over the nechako plateau to 300 km inland from the pacific coast at this time the surface of the ice sheet extended well above 2500 m above sea level and flowed westward over the skeena hazelton and coast mountains onto the continental shelf and eastward across the rocky mountains into alberta in the late glacial phase a rapid rise of the equilibrium line caused ice lobes to stagnate in valleys and restricted accumulation centers to high mountains discordant directions in ice flow are attributed to fluctuations of the ice divide representing changes in the location of accumulation centers and ice thickness ice centers probably shifted in response to climate irregular growth in the ice sheet rapid calving ice streaming and drainage of proglacial and subglacial water bodies crosscutting ice flow indicators and preservation of early valley parallel flow features in areas exposed to later cross valley glacier erosion indicate that the ice expansion phase was the most erosive and protracted event

timing of terminal pleistocene deglaciation at high elevations in southern and central british columbia constrained by 10be exposure dating abstract the cordilleran ice sheet cis covered most of british columbia and southern yukon territory at the local last glacial maximum llgm during marine oxygen isotope stage 2 however its subsequent demise is not well understood particularly at high elevations east of its ocean terminating margin we present 10be exposure ages from two high elevation sites in southern and central british columbia that help constrain the time of initial deglaciation at these sites we sampled granodiorite erratics at elevations of 2126 2230 m a s l in the marble range and 1608 1785 m a s l in the telkwa range at the western margin of the interior plateau the erratics at both sites are near ice marginal meltwater channels that delineate the local ice surface slope and thus the configuration of the ice sheet during deglaciation the locations of the erratics and their relations to meltwater channels ensure that the resulting 10be ages date cis deglaciation and not the retreat of local montane glaciers our sample sites emerged above the surface of the cis as its divide migrated westward from the interior plateau to the axis of the coast mountains two of the four samples from the summit area of the marble range yielded apparent exposure ages of 14 0 0 7 and 15 2 0 8 ka these ages are 1 8 3 0 ka younger than the well established llgm age of ca 17 ka for the puget lobe of the cis in washington state they are 1 7 ka younger than the llgm age for the puget lobe if a snow shielding correction to their uncertainty weighted mean age is applied the other two samples yielded much older apparent exposure ages 20 6 1 4 and 33 0 1 5 ka indicating the presence of inherited isotopes four samples collected from the summit area of the telkwa range in the hazelton mountains yielded well clustered apparent exposure ages of 10 1 0 6 10 2 0 7 10 4 0 5 and 11 5 1 1 ka significant present day snow cover introduces a large uncertainty in the apparent exposure ages from this site a snow shielding correction based on present day snow cover data increases the uncertainty weighted mean exposure age of the telkwa range erratics to 12 4 0 7 ka consistent with deglacial 14c ages from areas near sea level to the west our exposure ages show a thinning of the southern portion of the cis shortly after the llgm and persistence of a remnant mountain ice cap in the central coast mountains into the younger dryas chronozone our data also show that the summit area of the marble range was ice covered during the llgm the presence of an ice body of considerable dimension in north central british columbia until or possibly even after the younger dryas highlights the need for geomorphological and geochronological studies of the ice dispersal centre over the skeena mountains in northwest british columbia and the need for better understanding of the response of the cis to lateglacial climate fluctuations

on the wave and current interaction with a rippled seabed in the coastal ocean bottom boundary layer interactions of currents and waves with a rippled seabed in the inner part of the coastal ocean bottom boundary layer are studied using particle image velocimetry adv and bottom roughness measurements mean velocity profiles collapse with appropriate scaling in the log layer but vary substantially in the roughness sublayer when wave induced motions are similar or greater than the mean current the hydrodynamic roughness z0 determined from velocity profiles is substantially larger than directly measured values the roughness signature in turbulent energy spectra persists with elevation when its scale falls in the dissipation range but decays in the log layer for larger roughness elements reynolds shear stress profiles peak in the lower parts of the log layer diminishing below it and gradually decaying at higher elevations in contrast wave shear stresses are negligible within the log layer but become significant within the roughness sublayer this phenomenon is caused by an increase in the magnitude and phase lag of the vertical component of wave induced motion no single boundary layer length scale collapses the reynolds stresses but both the prandtl mixing length and eddy viscosity profiles agree well with the classical model of linear increase with elevation especially near the seabed within the log region profiles of shear production and dissipation rates of turbulence converge below it dissipation rapidly increases peaking near the seabed conversely the shear production decays near the seabed in agreement with the eddy viscosity model but in contrast to both laboratory and computational rough wall studies

vertical structure of dissipation in the nearshore abstract the vertical structure of the dissipation of turbulence kinetic energy was observed in the nearshore region 3 2 m mean water depth with a tripod of three acoustic doppler current meters off a sandy ocean beach surface and bottom boundary layer dissipation scaling concepts overlap in this region no depth limited wave breaking occurred at the tripod but wind induced whitecapping wave breaking did occur dissipation is maximum near the surface and minimum at middepth with a secondary maximum near the bed the observed dissipation does not follow a surfzone scaling nor does it follow a log layer surface or bottom boundary layer scaling at the upper two current meters dissipation follows a modified deep water breaking wave scaling vertical shear in the mean currents is negligible and shear production magnitude is much less than dissipation implying that the vertical diffusion of turbulence is important the increased near bed secondary dissipation maximum results from a decrease in the tu

nunataks and valley glaciers over the mountains and through the ice models of the first peopling of the americas characterize arrival routes either along the coast or through the ice free corridor following the last glacial maximum while the pendulum has currently swung somewhat towards the coastal route archaeological evidence for either entry is lacking in this paper we introduce a third option an icy corridors entry route we argue that the traditionally envisioned corridor is an unnecessary feature for the terrestrial arrival of clovis or clovis predecessors below the ice sheets the recent genomic data is fully compatible with a re envisioned peopling route

temporal variability in thermally driven cross shore exchange the role of semidiurnal tides abstractwe examine temporal variability of thermally driven baroclinic cross shore exchange in the context of a tropical fringing reef system focusing on the role of tidally driven alongshore flow

a modified law of the wall applied to oceanic bottom boundary layers 1 near the bottom the velocity profile in the bottom boundary layer over the continental shelf exhibits a characteristic law of the wall that is consistent with local estimates of friction velocity from near bottom turbulence measurements farther from the bottom the velocity profile exhibits a deviation from the law of the wall here the velocity gradient continues to decrease with height but at a rate greater than that predicted by the law of thewall with the local friction velocity we argue that the shape of the velocity profile is made consistent with the local friction velocity by the introduction of a new length scale that near the boundary asymptotes to a value that varies linearly from the bottom farther from the boundary this length scale is consistent with the suppression of velocity fluctuations either by stratification in the upper part of the boundary layer or by proximity to the free surface the resultant modified law of the wall provides a good representation of velocity profiles observed over the continental shelf when a local estimate of the friction velocity from coincident turbulence observations is used the modified law ofthe wall is then tested on two very different sets of observations from a shallow tidal channel and from the bottom of the mediterranean outflow plume in both cases it is argued that the observed velocity profile is consistent with the modified law of the wall implicit in the modified law of the wall is a new scaling for turbulent kinetic energy dissipation rate this new scaling diverges from the law of the wall prediction above 0 2d where d is the thickness of the bottom boundary layer and agrees with observed profiles to 0 6d

cloud trails past the lesser antilles abstractobservations and cloud resolving simulations of elongated cloud plumes or cloud trails past the lesser antilles islands in the caribbean sea are presented analysis of one year of visible satellite images reveals that each island forms cloud trails on 30 40 of days typically in the afternoon in response to diurnal island heating on around 10 of days the cloud bands are very well organized with lengths of and durations of min radiosonde analysis suggests that the well organized events are favored by moderate to strong trade winds 6 10 m s 1 and stronger trade inversions the simulated cloud trails which are consistent with observations in their morphology and diurnal cycle are organized by quasi linear bands of thermally forced convergence within the heated island wake they are sensitive to overland surface fluxes inversion strength and height terrain height and trade wind speed while surface fluxes control the strength of the wake thermal circulations the inversion controls pr

late glacial drainage systems along the northwestern margin of the laurentide ice sheet abstract the evolution of drainage systems along the retreating northwestern laurentide ice sheet was complex the interaction of ice margin configuration topography and glacioisostasy resulted in a network of meltwater rivers that variably overflowed to the arctic and pacific oceans and to the gulf of mexico glacial lakes also changed dramatically in size and location during the period of deglaciation at the last and all time glacial maximum the ice sheet extended into the eastern cordillera blocking northward and eastward drainage to the arctic ocean some meltwater and most non glacial runoff were diverted through the mountains to the yukon river basin into alaska and the pacific ocean retreat from the glacial maximum prior to 21 ka bp allowed proglacial drainage from the western margin of the ice sheet to flow into the beaufort sea arctic ocean deglaciation was rapid after about 13 ka bp with the present route of the lower mackenzie river established between 13 and 11 5 ka bp continued ice retreat led to significant southward expansion of the mackenzie beaufort drainage basin at about 11 5 ka bp through drainage capture of glacial lake peace which previously had drained southeastward into the missouri river and to the gulf of mexico very rapid ice retreat between 10 5 and 10 ka bp allowed glacial lake mcconnell to expand down slope in contact with the ice margin numerous glacial lakes occurred along the northwestern margin of the ice sheet during the maximum and retreat phases these include ice dammed glacial lake old crow which occupied unglaciated terrain of the northern yukon and glacial lake peace which utilized a number of outlets as it migrated eastward with the ice front along the peace valley the largest glacial lakes in the region were the result of glacioisostatic depression reversing the regional drainage the mackenzie phase of glacial lake mcconnell was the second largest pleistocene lake in north america 215 000 km 2 late glacial and post glacial changes in drainage systems were largely in response to isostatic rebound

understanding hector the dynamics of island thunderstorms abstract linear and nonlinear models are used to examine the development of island thunderstorms in particular the hector convective system that forms over the tiwi islands just north of australia the linear model is used to examine the flow response to an isolated elliptical heat source it is found that the low level convergence is maximized when the flow is weak and along the major axis of the heat source a dry version of the nonlinear model verifies the trends predicted by the linear model except at very low flow speeds where the convergence is bounded in the nonlinear model but increases indefinitely in the linear model deep convection develops over the heat source when a moisture profile with positive convective available potential energy cape is added to the nonlinear model the sensitivity of the convective strength defined by the accumulated rainfall and total condensate to wind speed and direction surface fluxes and low level moisture is then examined it is shown that the strength i

laurentide and montane glaciation along the rocky mountain foothills of northeastern british columbia mapping the surficial geology of the trutch map area nts 94g provides new data on the timing of continental and montane glaciations along the foothills of northeastern british columbia striated surfaces on mountain crests were dated to the late wisconsinan substage by cosmogenic dating the striations were produced by eastward flowing ice emanating from the region of the continental divide this ice was thick enough to cross the main ranges and overtop the rocky mountain foothill summits at 2000 m above sea level asl it is argued here that such a flow unhindered by topography could only have been produced by the cordilleran ice sheet and not by local cirque glaciation during this time the cordilleran ice sheet dispersed limestone and schist erratics of western provenance onto the plains beyond the mountain front conversely the laurentide ice sheet did not reach its western limit in the foothills until after cordilleran ice retreated from the area during its maximum the laurentide ice penetra

stratified turbulence and mixing efficiency in a salt wedge estuary abstracthigh resolution observations of velocity salinity and turbulence quantities were collected in a salt wedge estuary to quantify the efficiency of stratified mixing in a high energy environment during the ebb tide a midwater column layer of strong shear and stratification developed exhibiting near critical gradient richardson numbers and turbulent kinetic energy tke dissipation rates greater than 10 4 m2 s 3 based on inertial subrange spectra collocated estimates of scalar variance dissipation from microconductivity sensors were used to estimate buoyancy flux and the flux richardson number rif the majority of the samples were outside the boundary layer based on the ratio of ozmidov and boundary length scales and had a mean rif 0 23 0 01 dissipation flux coefficient 0 30 0 02 and a median gradient richardson number rig 0 25 the boundary influenced subset of the data had decreased efficiency with rif 0 17 0 02 0 20 0 03 and median rig 0 16 the relationship be

mapping quaternary paleovalleys and drift thickness using petrophysical logs northeast british columbia fontas map sheet nts 94ithis article is one of a selection of papers published in this special issue on the theme geology of northeastern british columbia and northwestern alberta diamonds shallow gas gravel and glaciers the relatively subdued topography of british columbia s northern interior plains does not reflect the irregular buried bedrock surface many areas have been deeply incised by preglacial rivers tha

boundary layer turbulence and flow structure over a fringing coral reef measurements of velocity and rates of turbulence were made across a fringing coral reef in the gulf of aqaba red sea to determine the effect that the rough topography has on boundary layer mixing and flow dynamics observations were made at two fore reef sites and a nearby sandy slope the friction velocity u and drag coefficient cd were determined directly from turbulent reynolds stresses measured using acoustic doppler velocimeters values of cd for the coral substrates ranged from 0 009 to 0 015 three to five times greater than over the sandy bottom site the turbulence dissipation rate e was determined by fitting spectra of vertical velocity to the theoretical 5 3 law expected for the inertial subrange of turbulence there was a local balance between production and dissipation of turbulent kinetic energy signifying that we could estimate u from either the mean velocity profile turbulence or dissipation rate of turbulent kinetic energy estimates from all three measures agreed well with mean u uo ranging from 0 10 6 0 03 to 0 12 6 0 03 indicating that existing turbulent boundary layer flow theory can be applied to flows over the rough topography of coral reefs the bottom topography by enhancing both reef scale and local drag and mixing levels allows reef biota to more effectively exchange dissolved and particulate matter with oceanic waters

reconstructions of mountain glacier profiles northeastern united states ice surface profiles are reconstructed for 37 proposed mountain glacier localities in the northeastern united states including sites in the catskill and adirondack mountains new york the green mountains vermont the white mountains new hampshire and the longfellow mountains and mount katahdin maine the reconstructions determined numerically from the shear stress equation gh sin show estimated ice thickness as a function of valley position and slope in general ice thickness increases from zero at the position of the glacier terminus terminal position is a required input to the model to some equilibrium slab thickness in the upper valley where the slab thickness is inversely proportional to valley slope glacier reconstructions support the empirical evidence for former local glaciation in the catskill and white mountains and in some localities in the adirondack mountains in several proposed glacier locations in the adirondack and green mountains in very shallow basins and in very gently sloping valleys however estimated ice thicknesses exceed the depth of their respective valleys or the elevation of up valley cols suggesting a re evaluation of these localities as sites of local confined ice flow confirmed localities of local glaciation are mostly in valleys with mean gradients greater than about 5 where reconstructed ice thicknesses are less than about 200 m

flow pattern evolution of the laurentide and cordilleran ice sheets across west central alberta canada implications for ice sheet growth retreat and dynamics during the last glacial cycle this paper presents a reconstruction of the geometry dynamics and flow pattern of the laurentide and cordilleran ice sheets along the albertan portion of the eastern canadian rocky mountains during the last glaciation sediment landform associations relating to the evolution of these ice sheets document their initial convergence and mutual deflection across west central alberta the continued advance of laurentide ice locally displaced cordilleran ice westward into the front ranges and deflected trunk ice emerging from the athabasca river valley south eastwards along the foothills these convergent flow patterns remained major features in the regional geometry of both ice sheets throughout the last glacial maximum the onset of deglaciation was characterized by the northward retreat of the laurentide ice sheet which progressively unblocked valleys along the mountain front the configuration of buttress removal initiated the lateglacial expansion and sequential drawdown of the eastern cordilleran ice sheet along fast flowing outlet glaciers subsequent regional retreat of laurentide and cordilleran ice was associated with the development of large proglacial lakes which amplified deglaciation by destabilizing the margins of both ice sheets triggering extensive readvances due to periodic changes in water level associated with the opening and closing of outlets by ice margin fluctuations

coalescence of late wisconsinan cordilleran and laurentide ice sheets east of the rocky mountain foothills in the dawson creek region northeast british columbia canada abstract geomorphic stratigraphic and geochronological evidence from northeast british columbia canada indicates that during the late wisconsinan approximately equivalent to marine oxygen isotope stage mis 2 a major lobe of western sourced ice coalesced with the northeastern sourced laurentide ice sheet lis high resolution digital elevation models reveal a continuous 75 km long field of streamlined landforms that indicate the ice flow direction of a major northeast flowing lobe of the cordilleran ice sheet cis or a montane glacier 200 km wide was deflected to a north northwest trajectory as it coalesced with the retreating lis the streamlined landforms are composed of till containing clasts of eastern provenance that imply that the lis reached its maximum extent before the western sourced ice flow crossed the area since the lis only reached this region in the late wisconsinan the cis montane ice responsible for the streamlined landforms must have occupied the area after the lis withdrew stratigraphy from the murray and pine river valleys supports a late wisconsinan age for the surface landforms and records two glacial events separated by a non glacial interval that was dated to be of middle wisconsinan mis 3 age

giga les of hector the convector and its two tallest updrafts up to the stratosphere abstractthe dynamics of hector the convector which overshot into the stratosphere on 30 november 2005 over the tiwi islands australia is investigated using a giga large eddy simulation with a 100 m cubic mesh individual updrafts defined as 3d objects with vertical velocity above 10 m s 1 are identified among the 20 000 updrafts formed during the most intense phase only a dozen were more than 4 km tall the two tallest updrafts accounted for more than 90 of the total vertical mass flux through the tropical tropopause layer their locations were determined by low level convergence lines first created by the sea breeze in the morning then enhanced by cold pools due to cumulus congestus they finally reinforced each other as they moved inland and intersected the two tallest updrafts that overshot the tropopause were contrasted with those occurring 1 h earlier and later they presented larger widths up to 8 km greater buoyancy up to 0 1 m s 2 stronger vertical velocities up to 50 m s 1 and l

effects of western boundary current dynamics on the internal wave field of the southeast florida shelf 1 shelf sea internal wave fields are typically highly variable and dominated by wind and tidal forces however this is not necessarily true for outer shelf regions or very narrow shelves where remote physical processes originating over the slope or deep ocean may exert a strong influence on the internal wave climate during the summers of 2003 and 2004 observational studies were conducted to examine the effects of a western boundary current the florida current tides and wind on the mean currents and internal wave field on the outer southeast florida shelf wavelet analyses of nonstationary shelf currents coupled with altimetry images of the straits of florida reveal the strong influence of florida current fluctuations on outer shelf flows local winds were found to be a small factor in flows on the outer shelf region and tidal forcing diurnal and semidiurnal accounted for less than a third of the total barotropic variance high frequency internal waves dominate the internal wave field and result in bottom intensified currents and strong shoreward mass transport we present evidence that suggests that the florida current plays as large a role in the determination of the high frequency internal wave field as tidal forces these observations and analyses show that it is necessary to include the forcing from the florida current meanders and instabilities in order to predict accurately the episodic nature of the internal wave field on the southeast florida shelf

landform assemblages produced by the laurentide ice sheet in northeastern british columbia and adjacent northwest territories constraints on glacial lakes and patterns of ice retreatthis article is one of a selection of papers published in this special issue on the theme geology of northeastern british columbia and northwestern alberta diamonds shallow gas gravel and glaciers the laurentide ice sheet reached the canadian cordillera during the last glacial maximum in northeastern british columbia and adjacent northwest territories and all regional drainage to unglaciated areas in the north was dammed by the ice converging ice flow patterns near the mountain front suggest that the laurentide ice sheet likely coalesced with the cordilleran ice sheet during the last glaciation with deglaciation the ice masses separated but earlier ice retreat in the south meant that meltwater pooled between the mountain front and the laurentide margin the level of the flooding was controlled by persistent ice cover on the southern franklin mountains glacial lake liard formed when the laurentide ice sheet retreated east of the southern liard range and at its maximum extent may have impounded water at least as far south as the fort nelson river deglaciation of the plains was marked by local variations in ice flow caused by a thin ice sheet becoming more affected by the topography and formin

near bottom turbulence measurements in a partially mixed estuary turbulent energy balance velocity structure and along channel momentum balance abstract a set of moored bottom mounted and shipboard measurements obtained in a straight section of the lower hudson estuary during late summer and early fall of 1995 determine velocity density and along channel pressure gradient throughout the 15 m water column as well as providing direct eddy correlation estimates of reynolds stress and indirect inertial range estimates of dissipation within 3 m of the bottom the analysis focuses on testing 1 a simplified turbulent kinetic energy equation in which production balances dissipation 2 the prandtl karman law of the wall which is a relationship between bottom stress and near bottom velocity gradient and 3 a simplified depth integrated along channel momentum balance involving local acceleration pressure gradient and bottom stress estimates of production and dissipation agree well throughout the entire record the relationship between bottom stress and velocity gradient is consistent with the law of the wall within approximately 1 m of the sea

quaternary stratigraphy of the prophet river northeastern british columbiathis article is one of a selection of papers published in this special issue on the theme geology of northeastern british columbia and northwestern alberta diamonds shallow gas gravel and glaciers exposures in the prophet river valley in northeast british columbia provide a unique glimpse into the quaternary history of the northwest canadian boreal plains the region shows evidence of late wisconsinan laurentide glaciation in the form of widespread till containing abundant erratic clasts derived from the canadian shield vertical sections along the prophet river expose non glacial and advance glacial sediments below this till pre late wisconsinan non glacial or interglacial floodplain sediments are interbedded with fluvial gravels at many sites macrofossils within horizontally laminated organic rich black clay and silt indicate deposition on the floodplain of the paleo prophet river within an oxbow lake the climate during deposition is interpreted to be similar to present supporting a dominantly spruce forest wood obtained from eight sites provided non finite radiocarbon ages and one sample provided an age of 49 300 2000 bp which is also considered non finite glaciolacustrine clays and s

turbulent mixing and hydraulic control of abyssal water in the samoan passage 1 we report the first direct turbulence observations in the samoan passage sp a 40 km wide notch in the south pacific bathymetry through which flows most of the water supplying the north pacific abyssal circulation the observed turbulence is 1000 to 10 000 times typical abyssal levels strong enough to completely mix away the densest water entering the passage confirming inferences from previous coarser temperature and salinity sections accompanying towed measurements of velocity and temperature with horizontal resolution of about 250 m indicate the dominant processes responsible for the turbulence specifically the flow accelerates substantially at the primary sill within the passage reaching speeds as great as 0 55 m s 1 a strong hydraulic response is seen with layers first rising to clear the sill and then plunging hundreds of meters downward turbulence results from high shear at the interface above the densest fluid as it descends and from hydraulic jumps that form downstream of the sill in addition to the primary sill other locations along the multiple interconnected channels through the samoan passage also have an effect on the mixing of the dense water in fact quite different hydraulic responses and turbulence levels are observed at seafloor features separated laterally by a few kilometers suggesting that abyssal mixing depends sensitively on bathymetric details on small scales

observations of a diapycnal shortcut to adiabatic upwelling of antarctic circumpolar deep water in the southern ocean small scale turbulence causes diapycnal mixing which influences important water mass transformations in turn impacting large scale ocean transports such as the meridional overturning circulation moc a key controller of earth s climate we present direct observations of mixing over the antarctic continental slope between water masses that are part of the southern ocean moc a 12 h time series of microstructure turbulence measurements hydrography and velocity observations off elephant island north of the antarctic peninsula reveals two concurrent bursts of elevated dissipation of o 10 6 w kg 1 resulting in heat fluxes 10 times higher than basin integrated drake passage estimates this occurs across the boundary between adjacent adiabatic upwelling and downwelling overturning cells ray tracing to nearby topography shows mixing between 300 and 400 m is consistent with the breaking of locally generated internal tidal waves since similar conditions extend to much of the antarctic continental slope where these water masses outcrop diapycnal mixing may contribute significantly to upwelling

cosmogenic 36cl dating of the foothills erratics train alberta canada the foothills erratics train of alberta was carried into place during coalescence between montane glaciers and the laurentide ice sheet its age has been controversial late wisconsinan and pre wisconsinan ages have been assigned to it cosmogenic 36 cl exposure dating was carried out on erratics over a 130 km segment of the erratics train seven of eight age determinations support emplacement during the late wisconsinan glaciation these ages eliminate the possibility of an ice free corridor during the last glacial maximum they are also consistent with the hypothesis that the laurentide ice sheet was the most extensive of all pleistocene continental ice sheets in western canada

reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the laurentide ice sheet abstract this paper reconstructs the deglaciation of the laurentide ice sheet lis including the innuitian ice sheet from the last glacial maximum lgm with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides we build on a recent inventory of laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the lis which we depict in a series of palaeogeographic maps results show that the drainage network at the lgm was similar to modern day antarctica the majority of the ice streams were marine terminating and topographically controlled and many of these continued to function late into the deglaciation until the ice sheet lost its marine margin ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build up peak phase and collapse of the cordilleran laurentide ice saddle the south eastern marine margin in atlantic canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the lgm in contrast the ice streams draining towards the north western and north eastern marine margins in the beaufort sea and in baffin bay appear to have remained stable throughout most of the late glacial and some of them continued to function until after the younger dryas yd the yd influenced the dynamics of the deglaciation but there remains uncertainty about the response of the ice sheet in several sectors we tentatively ascribe the switching on of some major ice streams during this period e g m clintock channel ice stream at the north west margin but for other large ice streams whose timing partially overlaps with the yd the drivers are less clear and ice dynamical processes rather than effects of climate and surface mass balance are viewed as more likely drivers retreat rates markedly increased after the yd and the ice sheet became limited to the canadian shield this hard bed substrate brought a change in the character of ice streaming which became less frequent but generated much broader terrestrial ice streams the final collapse of the ice sheet saw a series of small ephemeral ice streams that resulted from the rapidly changing ice sheet geometry in and around hudson bay our reconstruction indicates that the lis underwent a transition from a topographically controlled ice drainage network at the lgm to an ice drainage network characterised by less frequent broad ice streams during the later stages of deglaciation these deglacial ice streams are mostly interpreted as a reaction to localised ice dynamical forcing flotation and calving of the ice front in glacial lakes and transgressing sea basal de coupling due to large amount of meltwater reaching the bed debuttressing due to rapid changes in ice sheet geometry rather than as conveyors of excess mass from the accumulation area of the ice sheet at an ice sheet scale the ice stream drainage network became less widespread and less efficient with the decreasing size of the deglaciating ice sheet the final elimination of which was mostly driven by surface melt

transport by breaking internal gravity waves on slopes we use the results of a direct numerical simulation dns with a particle tracking model to investigate three dimensional transport by breaking internal gravity waves on slopes onshore transport occurs within an upslope surge of dense fluid after breaking offshore transport occurs due to an intrusion of mixed fluid that propagates offshore and resembles an intermediate nepheloid layer inl entrainment of particles into the inl is related to irreversible mixing of the density field during wave breaking maximum onshore and offshore transport are calculated as a function of initial particle position and can be of the order of the initial wave length scale for particles initialized within the breaking region an effective cross shore dispersion coefficient is also calculated and is roughly three orders of magnitude larger than the molecular diffusivity within the breaking region particles are transported laterally due to turbulence that develops during wave breaking and this lateral spreading is quantified with a lateral turbulent diffusivity lateral turbulent diffusivity values calculated using particles are elevated by more than one order of magnitude above the molecular diffusivity and are shown to agree well with turbulent diffusivities estimated using a generic length scale turbulence closure model based on a favourable comparison of dns results with those of a similar two dimensional case we use two dimensional simulations to extend our cross shore transport results to additional wave amplitude and bathymetric slope conditions

tropical island convection in the absence of significant topography part ii nowcasting storm evolution abstract this paper examines influences on the short range prediction of organized convection under conditions of strong diurnal forcing the analyses are based on data provided by the maritime continent thunderstorm experiment which was conducted in 1995 over the tiwi islands 11 s 50 100 km north of the australian continent organized convection over the tiwi islands is often dubbed hector by residents and researchers alike the authors purpose is to utilize results from these analyses to improve convective storm nowcast systems and their associated forecast and warning products the environmental near surface wind direction is shown to be singularly influential in statistically predicting the location of convection and its time of occurrence over the tiwi islands this finding is robust despite the fact that mean wind speeds were merely 1 4 m s 1 the island boundary layer water vapor mixing ratio derived from a morning sounding and inland surface stations is shown to be correlated with measu

reconstructing the confluence zone between laurentide and cordilleran ice sheets along the rocky mountain foothills south west alberta landform mapping near the athabasca valley was fundamental to determining whether the late wisconsinan laurentide and cordilleran ice sheets lis cis coalesced in this paper we examine the detailed landform record using new lidar digital elevation and hillshade models of the area of confluence and eventual desuturing of these ice sheets this work reveals an earlier more extensive cordilleran advance before coalescence with the lis when the ice sheets coalesced the flow pattern was dominated by ice flow along the mountain front with cordilleran ice flowing out of major trunk valleys but laurentide ice flowing into the foothills up smaller valleys this flow pattern implies that when the ice sheets coalesced the cis was already waning or at least was not at its maximum deglaciation was interrupted by several re advances probably related to the destabilizing effect of proglacial lakes along the ice margin

a new characterization of the turbulent diapycnal diffusivities of mass and momentum in the ocean the diapycnal diffusivity of mass supported by turbulent events in the ocean interior plays a fundamental role in controlling the global overturning circulation the conventional representation of this diffusivity due to osborn 1980 assumes a constant mixing efficiency we replace this methodology by a generalized osborn formula which involves a mixing efficiency that varies nonmonotonically with at least two nondimensional variables using these two variables we propose dynamic parameterizations for mixing efficiency and turbulent prandtl number the latter quantifies the ratio of momentum to mass diapycnal diffusivities based on the first synthesis of an extensive direct numerical simulation of inhomogeneously stratified shear induced turbulence data from argo floats are employed to demonstrate the extent of the spatial and statistical variability to be expected in both the diapycnal diffusivities of mass and momentum we therefore suggest that previous estimates of these important characteristics of the global ocean require reconsideration

late wisconsinan cordilleran and laurentide glaciation of the peace river valley east of the rocky mountains british columbia in the past researchers have disagreed over the maximum extent of the cordilleran ice sheet in the peace river valley during the late wisconsinan some workers argued that cordilleran ice reached beyond the rocky mountains and briefly coalesced with the laurentide ice sheet on the westernmost interior plains in contrast others asserted that cordilleran ice did not reach beyond the eastern front of the rocky mountains stratigraphic interpretation of three sections within a middle wisconsinan paleovalley and re examination of a previously published regional stratigraphic framework show that western sourced ice likely the cordilleran ice sheet extended east of the mountain front during the late wisconsinan prior to the incursion of the laurentide ice sheet into the area this conclusion has implications for cordilleran ice sheet reconstruction and modelling and provides insight into the interactions between the cordilleran and laurentide ice sheets during the last glaciation

seascape level variation in turbulence and wave generated hydrodynamic signals experienced by plankton abstract plankton exhibit diverse and dramatic responses to fluid motions and these behaviors are likely critical for survival and fitness fluid motions can be generated by organisms or by physical processes including turbulence and surface gravity waves physical processes vary geographically in their intensity and generate hydrodynamic signals experienced by plankton as fluid forces on their sensory receptors in this synthesis we review how turbulence and waves vary in space the scales and statistics of their motions and the forces exerted on plankton we then quantify the hydrodynamic signals produced by turbulence and waves in four seascape types surf zones inlets and estuaries the continental shelf and the open ocean using published dissipation rates wind and wave data from buoys and observations from two coastal sites in massachusetts usa we relate these geographic patterns in signals to the observed behaviors of example species and to the forces sensed by typical plankters with different receptor types turbulence generated shears are largest in the surf zone inlets and estuaries while wave generated accelerations are larger offshore as a result each seascape exhibits some range of combined shears and accelerations that is distinct these signals generate forces on plankton that vary among habitats and with plankton size and swimming speed spatial patterns in fluid forces create a potential mechanism for dispersing larvae to distinguish habitats by their hydrodynamic signatures however turbulence can be strong in all seascapes and may cause widespread interference in signaling among predators and prey plankton with a single receptor type could identify nearshore habitats while those with multiple receptor types potentially could distinguish inshore vs offshore seascapes or decode signals produced by physical processes and by other organisms

evidence of cordilleran late wisconsinan glaciers in the ice free corridor abstract glaciers flowing down the athabasca river valley during the last glacial period were fed both by local montane glaciers and by cordilleran ice moving easterly across the continental divide from british columbia resulting in a major eastward surge into the ice free corridor the timing of this event has been disputed for many years and has important implications for the study of paleoenvironmental conditions and the north south migration of biota in the corridor chronologic and lithostratigraphic data from the jasper region suggest that this event took place in the late wisconsinan subtill radiocarbon dates on wood in the athabasca river valley indicate that non glacial alluvial sediments began accumulating there sometime before 48 ka a finite date of 29 100 560 bp gsc 3792 on wood under till near jasper provides a maximum age for the onset of the last glaciation in the region although ice from west of the rocky mountain trench probably did not cross the continental divide until after 21 5 ka the occurrence of supraglacial metamorphic erratics as well as the distribution and nature of mapped glacial deposits and the trend of subglacial paleoflow indicators in the region east of the rockies suggests that late wisconsinan glaciers flowing from the mountains coalesced with laurentide glaciers and were deflected southeasterly along the mountain front an even more extensive glacial event may have effected the region in pre late wisconsinan times the model of late wisconsinan glaciation presented here is in agreement with all known radiocarbon data from the area and is especially attractive when supratill dates on non woody lacustrine organics are viewed in light of possible contamination by old carbon

gravity waves generated by convection in the darwin area during the darwin area wave experiment 1 we describe a model study of gravity wave generation by convection near darwin during the darwin area wave experiment dawex we focus on an 7 hour period on 17 november 2001 for our study which included a major hector event over the tiwi islands followed by a continental convective outbreak that included a squall line to the southeast of darwin our model is a dry version of a three dimensional 3 d mesoscale cloud resolving model with horizontally uniform background wind and stability fields the model is forced with a spatially and temporally varying heating field representative of the convective latent heating in the area we derive this heating field from 3 d volumetric reflectivity from the precipitation radar located just north of darwin at gunn point during dawex the conversion from radar reflectivity to a 3 d latent heating field requires numerous assumptions that do not allow a quantitative heating estimate but which do provide a very realistic measure of the spatial morphology and temporal variations of the latent heating gravity waves generated by convective heating are known to be very sensitive to these characteristics of the heating so our resulting wave field is likely to be the most realistic possible description of the waves emitted from convection in the darwin area uncertainty in the wave amplitudes is large both because the input forcing heating is uncertain and because the use of heating as the sole proxy for wave forcing leads to additional wave amplitude errors we therefore compare the results of the model to other dawex measurements and previous modeling studies both to validate the waves in our model and to calibrate the wave amplitudes our study in turn aids in the interpretation of the other gravity wave measurements during dawex

an assessment of the minimum timing of ice free conditions of the western laurentide ice sheet abstract this study presents an investigation of the minimum timing of retreat of the western laurentide ice sheet which covered parts of canada and the northern united states during the wisconsin glaciation the retreat of the ice sheet is poorly constrained due to low spatial resolution of chronological data that indicate ice free conditions a limitation of radiocarbon and luminescence dating methods is that it is only possible to determine the time when it is certain that ice is absent from a region which may differ substantially from the true date of ice margin retreat the minimum timing of ice free conditions is determined using a model of ice sheet retreat inferred from landforms that formed during the late stages of glaciation and extrapolating the calibrated probability distribution of chronological data in the opposite direction the analysis excludes radiocarbon samples from materials that have been shown to give artificially old ages such as bulk sediments the results of the analysis identify 55 dates that have the most impact on the model the retreat of the western laurentide ice sheet commenced by at least 15 000 cal yr bp while the minimum timing of ice free conditions between the laurentide ice sheet and the cordillera is after 11 000 cal yr bp a lack of data in the keewatin sector prevents the determination of a precise timing of ice free conditions in the last vestiges of the laurentide ice sheet the model provides a guide to where additional samples could improve chronological control on ice margin location

numerical simulation of the diurnal evolution of tropical island convection over the maritime continent abstract numerical simulations of the diurnal evolution of tropical island convection observed during the maritime continent thunderstorm experiment mctex are performed using the meteorological research institute nonhydrostatic model mri nhm the mri nhm is double nested within a form of the australian bureau of meteorology research centre s limited area assimilation and prediction system specially operated for the mctex period excellent agreement is found between the simulation and observed evolution of the convective clouds over the tiwi islands on 27 november 1995 a transition from horizontal convection occurring during the morning to vertical convection in afternoon is evident in the morning the sea breeze appears along the coastlines with a clear contrast evident in structure between the windward and leeward sides at the windward coast the sea breeze intrudes inland more rapidly where the larger surface heat flux modifies the lowest air mass and makes the sea breeze front sbf indistinct

buoyancy forcing by turbulence above rough topography in the abyssal brazil basin abstract observations of turbulent dissipation above rough bathymetry in the abyssal brazil basin are presented relative to regions with smooth bathymetry dissipation is markedly enhanced above rough topography of the mid atlantic ridge with levels above bathymetric slopes exceeding levels observed over crests and canyon floors furthermore mixing levels in rough areas are modulated by the spring neap tidal cycle internal waves generated by barotropic tidal flow over topography are the likely mechanism for supplying the energy needed to support the observed turbulent dissipation a model of the spatial and temporal patterns in the turbulent dissipation rate is used to constrain the diapycnal advection in an inverse calculation for the circulation in an area of rough bathymetry this inverse model uses both beta spiral and integrated forms of the advective budgets for heat mass and vorticity and contains sufficient information to resolve the full three dimensional flow the inverse model solution re

quaternary stratigraphy and glacial history of the peace river valley northeast british columbiathis article is one of a selection of papers published in this special issue on the theme geology of northeastern british columbia and northwestern alberta diamonds shallow gas gravel and glaciers two cordilleran and three laurentide glacial advances are recorded in quaternary sediments and landforms in the peace river valley northeast british columbia the advances are inferred from fluvial gravels glaciolacustrine sedi ments and tills within nested paleovalleys excavated during three interglaciations and from the distribution of granitoid clasts derived from the canadian shield till of the last late wisconsinan laurentide glaciation occurs at the surface ex cept where it is overlain by postglacial sediments the advance that deposited this till was the most extensive in the study area and the only advance definitively recognized in western alberta south of the study area late wisconsinan cordil leran till has not been found in the study area but cordilleran and laurentide ice may have coalesced briefly during the last glaciation support for this supposition is provided by the inferred deflection of laurentide flutings to the southeast by cordilleran ice the earliest laurentide advance may have been the least extensive of the three laurentide events recog nized in the study area erratics attributed to this advance occur only east of the halfway river beatton river drainage divide

breaking of internal kelvin waves shoaling on a slope in stratified flow breaking of internal waves over slopes induces resuspension of bottom sediments and transport of mass when internal waves shoal and break flow dynamics and mass transport diff

the accumulation of cosmogenic chlorine 36 in rocks a method for surface exposure dating because of the reaction of cosmic rays with elements in minerals chlorine 36 accumulates in rocks exposed at the earth s surface this suggests that the ratio of chlorine 36 to stable chloride can be used as a geochronometer reasonable agreement has been obtained between measurements of chlorine 36 in volcanic rocks of known age and calculations of chlorine 36 production based on rock composition and cosmicray flux the buildup of chlorine 36 should be a useful means for measuring the surface exposure time of young volcanic rocks and geomorphic features in the age range of 10 3 to 10 6 years

advance of alpine glaciers during final retreat of the cordilleran ice sheet in the finlay river area northern british columbia canada abstract sharp crested moraines up to 120 m high and 9 km beyond little ice age glacier limits record a late pleistocene advance of alpine glaciers in the finlay river area in northern british columbia the moraines are regional in extent and record climatic deterioration near the end of the last glaciation several lateral moraines are crosscut by meltwater channels that record downwasting of trunk valley ice of the northern cordilleran ice sheet other lateral moraines merge with ice stagnation deposits in trunk valleys these relationships confirm the interaction of advancing alpine glaciers with the regionally decaying cordilleran ice sheet and verify a late glacial age for the moraines sediment cores were collected from eight lakes dammed by the moraines two tephras occur in basal sediments of five lakes demonstrating that the moraines are the same age plant macrofossils from sediment cores provide a minimum limiting age of 10 550 10 250 cal yr bp 9230 50 14c yr bp for abandonment of the moraines the advance that left the moraines may date to the younger dryas period the finlay moraines demonstrate that the timing and style of regional deglaciation was important in determining the magnitude of late glacial glacier advances

tropical island convection in the absence of significant topography part i life cycle of diurnally forced convection abstract diurnally forced convection was observed over the tiwi islands north of the australian continent as part of the maritime continent thunderstorm experiment immature peninsula scale 5 15 km sea breezes were observed to initiate moist convection early each day principally through convergence that results from the confluence or collision of peninsula breeze fronts convection initiated by peninsula scale breezes usually fails to organize beyond a small cluster of cells and dissipates as a local event mature island scale 100 km breezes develop by late morning and subsequently play a pivotal role in the forcing and evolution of organized convection the initiation of mesoscale convective systems mcss is observed to be a direct consequence of breeze front collisions for only 20 of the days on which organized convection develops this is referred to as type a forcing and it occurs when normal convective development is delayed or otherwise suppressed type a forcing is nature s backup mech

spatial and temporal variations in rainfall over darwin and its vicinity during different large scale environments this study analyses the regional variations in rainfall over darwin and its vicinity due to different large scale circulations during the australian summer by utilizing the combination of in situ and c band polarimetric radar rainfall data at hourly resolution the eight phases of the madden julian oscillation as defined by wheeler and hendon mon weather rev 132 8 1917 1932 2004 were used as indicators of different large scale environments the analysis found that the large scale forcing starts to build up from phase 4 by the reversal of low to mid level easterly winds to moist westerly winds reaching a maximum in phase 5 and weakening through phases 6 7 during phases 4 6 most of the study domain experiences widespread rainfall but with distinct spatial and temporal structures in addition during these phases coastal areas near darwin receive more rainfall in the early morning 0200 0400 lt due to the spreading or expansion of rainfall from the beagle gulf explaining the occurrence of a secondary diurnal rainfall peak over darwin in contrast local scale mechanisms sea breezes reinvigorate from phase 8 further strengthening through phases 1 3 when low level easterly winds become established over darwin producing rainfall predominately over land and island locations during the afternoon during these phases below average rainfall is observed over most of the radar domain except over the tiwi islands in phase 2

stratification and mixing on sloping boundaries 1 in lakes as well as in the ocean vertical transport is to a large extent controlled by localized mixing along the boundaries of the respective basin direct measurements of turbulent mixing and density stratification in the bottom boundary layer of a large and deep lake reveal the importance of cross slope advection near sloping boundaries for local and basin scale vertical transport the periodic internal wave driven occurrence of up and downslope directed currents results in periodic heating and cooling of the boundary layer cooling of the boundary layer during periods of up slope flow is associated with unstable stratification and turbulent diffusivities exceed those observed during periods of down slope flow by almost one order of magnitude the periodic replacement of water in this layer with water from the interior of the basin maintains vertical density gradients and thus enhances the overall efficiency of the boundary mixing

observations of small scale secondary instabilities during the shoaling of internal bores on a deep ocean slope abstractthe rockall bank area located in the northeast atlantic ocean is a region dominated by topographically trapped diurnal tides these tides generate up and downslope displacements that can be locally described as swashing motions on the bank using high spatial and time resolution of moored temperature sensors the transition toward the upslope flow cooling phase is described as a rapid upslope propagating bore likely generated by breaking trapped internal waves buoyant anomalies are found during the bore propagation likely resulting from small scale instabilities the imbalance between the rate of disappearance of available potential energy and the dissipation rate of turbulent kinetic energy suggests that these instabilities are growing i e young and have high mixing potential

how variable is mixing efficiency in the abyss author posting american geophysical union 2020 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in geophysical research letters 47 2020 e2019gl086813 doi 10 1029 2019gl086813

severe downslope windstorm calculations in two and three spatial dimensions using anelastic interactive grid nesting a possible mechanism for gustiness abstract the clark nonhydrostatic anelastic code is extended to allow for interactive grid nesting in both two and three spatial dimensions tests are presented which investigate the accuracy of three different quadratic interpolation formulae which are used to derive boundary conditions for the fine mesh model application of the conservation condition of kurihara and others is shown to result in significant improvements in the treatment of interactive nesting a significant improvement in the solutions for interactive versus parasitic nesting is also shown in the context of forced gravity wave flow this result for the anelastic system is in agreement with the earlier results of phillips and shukla who considered the hydrostatic shallow water system of equations the interactive nesting model is applied to the simulation of the severe downslope windstorm of 11 january 1972 in boulder using both two and three spatial dimensions the three dimensional simulation results in a gustiness signature in the

geology of northeast british columbia and northwest alberta diamonds shallow gas gravel and glaciersthis article introduces a selection of papers published in this special issue on the theme geology of northeastern british columbia and northwestern alberta diamonds shallow gas gravel and glaciers this special issue reports on some of the results of a multi disciplinary research program conducted in the boreal plains of northwest alberta and northeast british columbia several innovative approaches to conducting geoscientific research in this remote drift covered region are presented including geochemical analysis of bentonites for evaluating kimberlite potential the use of electromagnetic surveys for mapping buried aggregate deposits and paleo topographic mapping techniques to define buried channels results of the program include the discovery of several large aggregate deposits the first kimberlite indicator minerals in northeast british columbia a significant sphalerite dispersal train in northwest alberta the first documented report of kimberlite sourced bentonites and numerous previously unknown interglacial sites together these papers provide a greatly enhanced understanding of the glacial history quaternary stratigraphy and kimberlite geology of northwest alberta and northeast bri

variations in apparent mixing efficiency in the north atlantic central water abstract microstructure data from the north atlantic tracer release experiment natre are presented providing detailed profiles of the thermal variance in the upper 360 m of the canary basin for the fall and spring seasons the osborn cox model is used to compute the diffusivity kt the diffusivity for the depth range 240 340 m is found to be 1 0 0 04 10 5 m2 s 1 in the fall and 2 2 0 1 10 5 m2 s 1 in the spring in good agreement with dye inferred diffusivities at similar depths measured turbulent kinetic energy tke dissipation rates were found to be contaminated by hydrodynamic noise so the osborn dissipation method was not used to compute k however data segments for which the tke dissipation rate e was large enough to be unaffected by noise were used to compute the apparent mixing efficiency d the computed d values are used to investigate variations in apparent mixing efficiency with respect to density ratio r and turbulence reynolds number e n2 in an attempt to eluci

internal tide reflection and turbulent mixing on the continental slope abstract observations of turbulence internal waves and subinertial flow were made over a steep corrugated continental slope off virginia during may june 1998 at semidiurnal frequencies a convergence of low mode onshore energy flux is approximately balanced by a divergence of high wavenumber offshore energy flux this conversion occurs in a region where the continental slope is nearly critical with respect to the semidiurnal tide it is suggested that elevated near bottom mixing k 10 3 m2 s 1 observed offshore of the supercritical continental slope arises from the reflection of a remotely generated low mode m2 internal tide based on the observed turbulent kinetic energy dissipation rate the high wavenumber internal tide decays on time scales o 1 day no evidence for internal lee wave generation by flow over the slope s corrugations or internal tide generation at the shelf break was found at this site

late tertiary to late quaternary record in the mackenzie mountains northwest territories canada stratigraphy paleosols paleomagnetism and chlorine 36 a stratigraphic sequence of unconsolidated sediments ranging in age from late pliocene to late pleistocene is recorded in the canyon ranges of the mackenzie mountains three of the sections katherine creek little bear river and inlin brook expose bedrock and tertiary gravel overlain by colluvium and a multiple till sequence of montane origin separated by paleosols and capped by a till of laurentide origin the sections are correlated on the basis of lithology paleosol development paleomagnetism and chlorine dating of surface boulder erratics a formal stratigraphic nomenclature is proposed for the deposits of this region the sequence of glacial tills separated by paleosols reflects a long record of glacial interglacial cycles soil properties from the oldest paleosol to modern soil show a general decrease in the degree of soil development suggesting a progressive deterioration of interglacial climatic conditions a normal reverse normal sequence of remanent magnetization was determined within th

ice streams of the late wisconsin cordilleran ice sheet in western north america abstract the late wisconsin cordilleran ice sheet cis of western north america is thought to have reached its maximum extent 2 5 106 km2 as late at c 14 5 ka most 80 of the ice sheet s bed consists of high mountains but its core zone sited on plateaux of the intermontane belt of british columbia and coterminous parts of the usa shows broad swaths of subglacially streamlined rock and sediment broad scale mapping from new digital imagery data identifies three subglacial bed types 1 hard beds of variably streamlined bedrock 2 drumlinized soft beds of deformation till reworked from antecedent sediment and 3 mixed beds of variably streamlined bedrock protruding through drumlinized sediment drumlins on soft beds appear to be erosional features cut into till and antecedent sediments and identify the catchment areas of paleo ice streams expressed downglacier as flow sets of megascale glacial lineations msgls grooved and cloned drumlins appear to record the transition from drumlins to msgls the location of paleo ice streams reflects topographic funneling of ice from plateau surfaces through outlet valleys and a soft bed that sustained fast flow rock cut msgls are also present locally on the floors of outlet valleys cis disintegrated in

turbulence characteristics and dissipation estimates in the coastal ocean bottom boundary layer from piv data abstract turbulence characteristics in the coastal ocean bottom boundary layer are measured using a submersible particle image velocimetry piv system with a sample area of 20 20 cm2 measurements are performed in the new york bight at elevations ranging from 10 cm to about 1 4 m above the seafloor recorded data for each elevation consists of 130 s of image pairs recorded at 1 hz after processing the data at each elevation consist of 130 instantaneous spatial velocity distributions within the sample area the vertical distribution of mean velocity indicates the presence of large scale shear even at the highest measurement station the flow also undergoes variations at timescales longer than the present data series spatial spectra of the energy and dissipation are calculated from individual vector maps the data extend well beyond the peak in the dissipation spectrum and demonstrate that the turbulence is clearly anisotropic even in the dissipation range the vector maps are also patched together to

the addition of heat to a stratified airstream with application to the dynamics of orographic rain summary the response of a stratified airstream to combined thermal and orographic forcing is investigated theoretically using the linearized hydrostatic equations of motion the magnitude of the heating aloft is computed from observed rainfall rates the elevated heating is shown to produce vertically propagating waves whose amplitude relative to the mountain waves is determined by the parameter gqb cptuanh symbols appendix i for typical wind speeds and rainfall rates the thermally generated waves will equal or exceed the orographically generated waves these waves produce large vertical variations in the wave momentum flux at the levels where heat is being added and alter or even reverse the mountain drag in hydrostatic flow the phase relationship between the heating rate and the induced vertical displacements is found unexpectedly to be negative in the vicinity of the heating air parcels are displaced downwards this result can be explained by wave propagation ideas but not by parcel arguments this helps to explain why mountain wave amplitudes are sometimes reduced in moist atmospheres the broad heat induced descent may act to limit the amount of condensation precipitation occurring in a stable middle level orographic cloud other types of orographic precipitation involving embedded convection in stratus layers low level feeder clouds or deep cumulus convection may not be adversely effected by the heat induced descent

cordilleran ice sheet mass loss preceded climate reversals near the pleistocene termination the cordilleran ice sheet cis once covered an area comparable to that of greenland previous geologic evidence and numerical models indicate that the ice sheet covered much of westernmost canada as late as 12 5 thousand years ago ka new data indicate that substantial areas throughout westernmost canada were ice free prior to 12 5 ka and some as early as 14 0 ka with implications for climate dynamics and the timing of meltwater discharge to the pacific and arctic oceans early bolling allerod warmth halved the mass of the cis in as little as 500 years causing 2 5 to 3 0 meters of sea level rise dozens of cirque and valley glaciers along with the southern margin of the cis advanced into recently deglaciated regions during the bolling allerod and younger dryas

the pattern and style of deglaciation at the late wisconsinan laurentide and cordilleran ice sheet limits in northeastern british columbia this paper reports on the landform assemblages at the northern confluence of the late wisconsinan laurentide and cordilleran ice sheets with montane and piedmont glaciers in the northern rockies and southern mackenzie mountains recent observations in northeastern british columbia refine our knowledge of the pattern and style of ice sheet retreat glacial lake formation and meltwater drainage at the onset of deglaciation confluent laurentide and cordilleran terminal ice margins lay between 59 n 124 30 w and 60 n 125 15 w from this terminal limit ice sheets retreated into north central british columbia and yukon territory with remnant cordilleran ice and montane glaciers confined to mountain valleys and the liard plateau distinctive end moraines are not associated with the retreat of cordilleran ice in these areas laurentide ice retreated northeastward from uplands and the plateaus then separated into lobes occupying the fort nelson and petitot river valleys ice retreat landforms include recessional end moraines sometimes overridden and drumlinized hill hole pairs crevasse fill deposits de geer like ribbed till ridges hummocky moraines kames meltwater features and glacial lake deposits that fall within the elevation range of glacial lake liard and glacial lake fort nelson ca 840 380 m meltwater and sediment transport into glacial lakes fort nelson liard nahanni and mackenzie was sustained by remnant ice in the liard river and fort nelson river drainage basins until the end of glaciation optical dating of sand from stabilized parabolic dunes on the liard plateau indicates that proglacial conditions lake formation and drainage began before 13 0 0 5 ka calendar years the petitot fort nelson and liard rivers all occupy spillways incised into glacial deposits and bedrock by meltwater overflow from glacial lakes peace and hay