scaling and parametrization of clear sky solar radiation over complex topography 1 solar radiation at the land surface is influenced by slope aspect shadows and obstruction of the sky all of which vary over a wide range of length scales in regions of complex topography with important consequences for the surface energy balance atmospheric models however generally assume the surface to be flat on subgrid scales for four areas in north america ranging in latitude from 39 n to 69 n and in topography from rolling to mountainous we simulate spatial patterns of clear sky incoming solar radiation it is found that distributions of slope components and variations in shaded area with solar elevation can be approximated by simple functions that scale to each of the areas studied from these results parametrizations are developed for averages standard deviations and distributions of direct beam and diffuse solar radiation results from these parametrizations and from a modified form of a simpler parametrization presented previously compare well with statistics from the spatial simulations the only topographic input required by the parametrizations is the standard deviation of slope components this parameter is again found to have simple scaling relationships with the resolution and extent of the underlying elevation grid and with the standard deviation of elevation

rapid formation and degradation of barrier spits in areas with low rates of littoral drift abstract a small barrier beach exposed to low energy waves and a small tidal range 0 7 m along nantucket sound mass has experienced a remarkable growth phase followed by rapid attrition during the past century in a region of low longshore transport rates the barrier spit elongated approximately 1 5 km from 1844 to 1954 developing beyond the baymouth parallel to the adjacent nantucket sound coast degradation of the barrier spit was initiated by a succession of hurricanes in 1954 carol edna and hazel a breach opened and stabilized near the bay end of the one kilometer long inlet channel providing direct access for exchange of baywater with nantucket sound and separating the barrier beach into two nearly equal limbs the disconnected northeast limb migrated shorewards beginning near the 1954 inlet and progressing northeastward filling the relict inlet channel behind it at present about ten percent of the northeast limb is subaerial the rest of the limb has completely filled the former channel and disappeared the southwest limb of the barrier beach has migrated shoreward but otherwise has not changed significantly since the breach a new mechanism is proposed for spit elongation when the inlet thalweg parallels the beach axis in which material scoured from the lengthening inlet is the dominant source for spit accretion perhaps initially deposited as a linear channel margin bar which later becomes subaerial the lengthening spit causes the parallel inlet to elongate which in turn further lengthens the spit in a self generating fashion this mechanism provides both a source of sediment for elongating the barrier spit and a sink for material scoured from the lengthening inlet the proposed mechanism for spit growth may be applicable to other locations with low wave energy small tidal prisms and low longshore sand transport rates suggesting that estimates of directions and rates of longshore sand transport based on spit geomorphology and development be scrutinized on a case by case basis

the influence of the layered character of snow cover on the triggering of slab avalanches one of the principal aims of avalanche warning is to prevent slab avalanches triggered by skiers other than explosives the best practical tool for stability evaluation is the rutschblock test whether the slab may be triggered by a skier depends on various slab characteristics important factors seem to be depth of the weak layer slab hardness and sublayering of the slab the stress distribution induced by a skier is calculated by the finite element method for typical snow cover configurations the additional shear stress is of the same order of magnitude as the shear strength of weak layers besides the critical weak layer prerequisite for a slab avalanche hard layers seem to be important the analysis suggests that a shear failure is most probable at the transition from a hard to a soft layer this corresponds well to observations of slab avalanche profiles the results may help to improve and quantify the analysis of snow profiles

study of the snow melt freeze cycle using multi sensor data and snow modelling the melt cycle of snow is investigated by combining ground based microwave radiometric measurements with conventional and meteorological data and by using a hydrological snow model measurements at 2000 m a s l in the basin of the cor devole river in the eastern italian alps confirm the high sensitivity of microwave emission at 19 and 37 ghz to the snow melt freeze cycle while the brightness at 6 8 ghz is mostly related to underlying soil simulations of snowpack changes performed by means of hydrological and electromagnetic models driven with meteorological and snow data provide additional insight into these processes and contribute to the interpretation of the experimental data

observational analysis of a gust front to bore to solitary wave transition within an evolving nocturnal boundary layer abstract the evolution of a gust front to bore to solitary wave transition and comprehensive information on the evolving nocturnal boundary layer nbl associated with this change are described with analysis of radar and profiler measurements the observations were obtained on 21 june 2002 in the oklahoma panhandle during the international h2o project the evolution of this system from a strong bore initiated by a vigorous gust front to a solitary wave was observed over a 4 h period with doppler radar and surface measurements detailed information on the mature bore structure was obtained by a cluster of profiling instruments including two boundary layer wind profilers a lidar ceilometer and a microwave profiling radiometer a strong bore was initiated by an extensive gust front that perturbed an incipient nbl whose development prior to sunset was enhanced by shading from the parent mesoscale convective system at the time of bore formation the nbl was about 300 m deep and exhibited a surface t

response of the seabed to storm generated combined flows on a sandy arctic shoreface canadian beaufort sea abstract wave and current measurements in 3 4 and 5 0 m water depths on a sandy shoreface of the canadian beaufort sea showed that a down welling circulation accompanied by strong offshore flowing near bottom currents develops during storm surges induced by northwesterly winds because fine to medium sand prevails on the shoreface a significant sediment load is probably moved down the shoreface by such currents during major storms a sidescan sonar profile recorded in 4 4 m water depth the day after a storm with seaward directed currents with mean velocity up to 0 49 ms 1 revealed the presence of narrow bands of large ripples 0 7 0 8 m wavelength with crests almost parallel to shore on the basis of theoretical calculations relating the wavelength of wave formed ripples to w ve orbital diameter the observed ripples were probably formed or reactivated during a storm in response to bed orbital motion of surface gravity waves on the sonograph the ripple bands were separated by less reflective areas interpreted as current parallel sand patches formed by seaward flowing bottom currents cores taken on the shoreface at the end of the wave and current measurement period showed the presence of thick graded sand beds which are thought to be the products of rapid deposition of sand from suspension during the waning phase of a recent storm such beds may he the modern analogues of graded sand beds in ancient wave dominated sequences and could indicate waning storm sedimentation in shallow fetch limited environments

the morphodynamics of beach ridge formation magilligan northern ireland abstract magilligan foreland is a holocene beach ridge plain comprising three principal sets of sand ridges sets i and ii are related to the mid holocene progradation of the plain while set iii represents recent deposition at the distal margin at present two types of beach ridge are being formed in both cases as part of the general recovery sequence following storm erosion of the dune cliffs mode i beach ridge development is associated with shore normal sediment transport under dissipative wave conditions these ridges form around the high water mark of spring tides through the migration of coalescence of swash bars within 30 to 55 days of a storm mode ii formation is more complex sediment initially stored in nearshore bars is moved alongshore causing bar elongation the bar moves into the intermediate and even reflective wave domains eventually narrowing of the bar leads to severance of a downdrift portion usually at or near the major drift pulse to the north west of the foreland normally this sediment starved remnant welds progressively onto the beach face in the direction of the dominant process gradient east to west but occasionally locally generated counteractive seas move sediment onshore employing the bar as a traverse conduit mode ii beach ridges emerge onto the upper beach around 90 150 days after a storm the beach ridges have distinctive structures depending on their mode of formation and both constitute important sources for dune building sand

structure age and origin of the bay mouth shoal deposits chesapeake bay virginia abstract the mouth of chesapeake bay contains a distinctive shoal complex and related deposits that result from the complex interaction of three different processes 1 progradation of a barrier spit at the southern end of the delmarva peninsula 2 strong reversing tidal currents that transport and rework sediment brought to the bay mouth from the north and 3 landward bayward net non tidal circulation and sediment transport together these processes play a major role in changing the configuration of the estuary and filling it with sediment the deposits at the mouth of the bay hold keys both to the evolution of the bay during the holocene transgression and to the history of previous generations of the bay the deposit associated with the shoals at the mouth of the bay the bay mouth sand is a distinct stratigraphic unit composed mostly of uniform gray fine sand the position and internal structure of the unit shows that it is related to near present sea level and thus is less than a few thousand years old the processes affecting the upper surface of the deposit and the patterns of erosion and deposition at this surface are complex but the geometry and structure of the deposit indicate that it is a coherent unit that is prograding bayward and tending to fill the estuary the source of the bay mouth sand is primarily outside the bay in the nearshore zone of the delmarva peninsula and on the inner continental shelf the internal structure of the deposit its surface morphology its heavy mineral composition bottom current studies comparative bathymetry and sediment budgets all suggest that sand is brought to the bay mouth by southerly longshore drift along the delmarva peninsula and then swept into the bay in addition to building the southward and bayward prograding bay mouth sand these processes result in sand deposition tens of kilometers into the bay

impact of a climate change on avalanche hazard the safran crocus mepra software is used to assess the climatology of the avalanche hazard and its sensitivity to climate change a natural avalanche hazard index based on mepra analysis is defined and validated against natural avalanche observations triggered avalanches are not taken into account a 15 year climatology then allows a comparison of avalanche hazard in the different french massifs finally a simple climate scenario with a general increase of precipitation and temperature shows that avalanche hazard may decrease slightly in winter mainly february and more significantly in may june the relative proportion of wet snow avalanches increases

dense avalanche friction coefficients influence of physical properties of snow the values of the voellmy friction parameters of 735 historical avalanches that have occurred along 26 paths in the chamonix valley france since 1958 are back analyzed with a depth averaged hydraulic model including sub models for erosion entrainment and deposition for each path the longitudinal and crosswise topographic profiles were derived from a high resolution digital elevation model acquired by laser scanning the initial snow depth and snow cohesion as well as various physical properties of snow were computed from numerical simulations of the detailed snowpack model crocus fed by the safran meteorological analysis for each event the full ranges of the two friction parameters were scanned and the pairs of friction parameters for which the run out altitude is found close enough to the observed one with an uncertainty of 5 m were retained statistical class analysis was used to investigate the correlation between the obtained friction coefficients and the snow physical properties no evident trend with the snow parameters was found for the inertial friction coefficient for the static friction coefficient an increasing trend with temperature and density was observed as well as a decreasing trend with liquid water content and initial snow depth although modeling assumptions and limitations regarding data and the calibration procedure should be kept in mind these trends are worth noting allowing avalanche simulations to be refined to take into account prevailing weather and snow conditions

the morning glory an extraordinary atmospheric undular bore summary observations made during an expedition in october 1980 to study morning glory wind squalfs in the gulf of carpentaria region of northern australia are described during a ten day period in burketown north queensland six squalls were documented on consecutive mornings 8 1 3 october including two moving from the south an apparently unusual direction the unique data gathered from the latter confirm that these have the same character as their north easterly counterparts that is they are undular bores the origin of southerly glories remains uncertain but at least in some cases appears to be linked with the northeast advance of a frontal trough across central australia while the data are equivocal it seems possible that the motion of the front into the developing nqcturnal inversion could generate waves or hydraulic type disturbances which run along the inversion layer ahead of the front as proposed by tepper 1950 the efficacy of such a mechanism is demonstrated by a simple laboratory experiment evidence is presented which suggests that morning glory type events occur elsewhere in the world sometimes as precursors to cold fronts observations in the gulf of carpentaria region show that they are effective triggers of deep convection when they advance into air with a sufficient degree of conditional instability

spatial patterns of snow stability throughout a small mountain range this research investigates snow stability on the eastern side of a small mountain range in southwest montana u s a on one mid season day and one late season day during the 1996 97 winter although previous research has addressed snow stability at smaller spatial scales this is the first field based study to investigate snow stability as measured by stability tests over a mountain range in order to better understand its spatial distribution and the implications for predicting dry slab avalanches using helicopter access six two person sampling teams collected data from over 70 sites on each of the two sampling days variables for terrain snowpack snow strength and snow stability were generated from the field data and analyzed using descriptive statistics correlation analysis and multiple regression results from the first sampling day show stability is only weakly linked to terrain snowpack and snow strength variables due to consistently stormy weather conditions leading up to that day the second field day s results demonstrate a stronger relationship between stability and the other variables due to more variable weather conditions that ranged from periods of sunshine to storms on both days stability decreased on high elevation northerly facing slopes the data structure complexity provides insights into the difficulties faced by both scientists and conventional avalanche forecasters in predicting snow avalanches

analysis of a lower tropospheric gravity wave train using direct and remote sensing measurement systems abstracton 10 august 2014 a gravity wave complex generated by convective outflow propagated across much of oklahoma the four dimensional evolution of the wave complex was analyzed using a synthesis of near surface and vertical observations from the oklahoma mesonet and atmospheric radiation measurement arm southern great plains networks two atmospheric emitted radiance interferometers aeri one located at the arm sgp central facility in lamont oklahoma and the other in norman oklahoma were used in concert with a doppler wind lidar dwl in norman to determine the vertical characteristics of the wave complex hydraulic theory was applied to the aeri derived observations to corroborate the observationally derived wave characteristics it was determined that a bore soliton wave packet initially formed when a density current interacted with a nocturnal surface based inversion and eventually propagated independently as the density current became diffuse the soliton propagated within an elevated invers

between beds and sequences stratigraphic organization at intermediate scales in the quaternary of the virginia coast usa stratigraphy presupposes a hierarchy of scales of spatial organization supplemented at the small scale end by sedimentological concepts beds bed sets and bed cosets and at larger spatial scales by sequence stratigraphic concepts systems tracts parasequences sequences between these two end members are intermediate sclae bodies described as lithofacies or simply facies a more restricted concept granulometric facies can be described in terms of horizontal grain size gradients facies change and cvclic vertical grain size gradients stratification assemblages of facies so defined also called depositional systems are not random loot occur in a limited suite of patterns such assemblages may be linked to two classes of bounding surfaces a source diastem the immediate source of the sediment and a surface of closure if preserved between which is sandwiched a transgressive or regressive basinward fining facies succession systems bounding surfaces are notably more continuous than internal gradational facies boundaries by thus restricting the definition of a facies assemblage depositional system it is possible to describe the quaternary of the virginia coast wish as few as 12 systems depositional systems in the quaternary of the virginia coast are allometric in that any system can be derived from any other by plastic expansion of one or more facies relative to another or by simple symmetry operations self similarity prevails across this intermediate scale of stratigraphic organization facies assemblages depositional systems consist of event beds which themselves have erosional basal boundaries and internal successions of microfacies at larger spatial so ales depositional systems are repeated either autocyclic repetitions forced by processes within the basin of deposition or allocyclic repetitions as parasequences and high frequency sequences in the virginia quaternary systems architecture is compatible with sequence architecture and nests conformably within its framework but analysis of systems architecture reveals rules beyond those governing sequence architecture

evolution of a classic sand ridge field maryland sector north american inner shelf the ridge and swale topography of the middle atlantic bight is best developed on the delaware maryland inner shelf here sand ridges can be seen in all stages of formation several aspects of the ridge field are pertinent to the problem of ridge genesis the first is ridge morphology there is a systematic morphologic change from shoreface ridges through nearshore ridges to offshore ridges which reflects the changing hydraulic regime as successively more seaward ridges are examined maximum side slope decreases the ratio of maximum seaward slope to maximum landward slope decreases and the cross sectional area increases these changes in ridge morphology with depth and distance from shore appear to be equivalent to the morphologic changes experienced by a single ridge during the course of the holocene transgression a second aspect is the change in bottom sediment characteristics that accompanies these large scale morphologic changes megaripples sand waves and mud lenses appear in the troughs between nearshore and offshore ridges these changes indicate that the storm flows which maintain ridges are less frequently experienced in the deeper sector and that the role of high frequency wave surge becomes less important relative to the role of the mean flow component in shaping the sea floor a third aspect is the systematic relationship of grain size to topography grain size is 90 out of phase with topography so that the coarsest sand lies between the axis of the landward trough and the ridge crest while the finest sand lies between the ridge crest and the axis of the seaward trough this relationship is characteristic of large scale bedforms finally flow was measured and transport calculated on the same ridge during a one month period november 1976 threshold was exceeded only during storm events mean transport was southerly and a little seaward with respect to both the ridge crest and the shoreline these flow measurements are in conformity with the pattern of smaller bedforms a 43 year time series of bathymetric change for this ridge reveals a systematic pattern of landward flank erosion seaward flank deposition and seaward crest migration sand ridges are considered the consequence of constructive feedback between an initial topography and the resulting distribution of bottom shear stress the relationship between grain size and topography supports this model but does not account directly for the oblique angle of the ridge with respect to the coastline this feature may be due to a more rapid alongshore migration rate of the inshore edge of the ridge than the offshore edge and the relationship between this migration rate and the rate of shoreface retreat

late pleistocene catchment wide denudation patterns across the european alps abstract we compile detrital 10be concentrations of alpine rivers representing the denudation rates pattern for 375 catchments across the entire european alps using a homogeneized framework we employ state of the art techniques for inverting in situ 10be concentrations into denudation rates from our compilation we find that i while lithologic properties and precipitation runoff do influence erosion mechanisms and rates at the scale of individual catchments and in some specific alpine regions such controls do not directly stand for the entire alps ii as also previously suggested catchment wide denudation rates across the entire european alps closely follow first order alpine topographic metrics at the scale of individual catchments or selected alpine sub regions however in addition to previous local scale studies conducted in the european alps our large scale compilation highlights a functional relationship between catchment wide denudation and mean catchment slope angle catchment wide denudation positively correlates with mean catchment slope up to a threshold angle 25 30 above this threshold any correlation between catchment wide denudation and slope as well as other catchment metrics breaks apart we can reconcile these systematic patterns by proposing a regional erosion model based on diffusive transport laws for catchments located below the slope threshold angle in oversteepened catchments situated above threshold slopes erosion is stochastic in nature as glacial carving likely caused a partial decoupling between hillslope and fluvial domains with complex topographic relationships and sediment connectivity patterns finally we identify a first order positive relationship between modern geodetic rock uplift and catchment wide denudation for the european alps the observed spatial pattern is highly variable and possibly reflects the surface response to deep geodynamic mechanisms prevailing in the different alpine regions we conclude that today s topography and geomorphic features of the entire alps are the result of a millenial scale geomorphic response to past glacial processes and active rock uplift highlighting a link between external and internal drivers for mountain erosion

a computer based system simulating snowpack structures as a tool for regional avalanche forecasting this paper describes the current state of a complete automatic system of three numerical models that simulate snow cover stratigraphy and avalanche risks for operational avalanche forecasting the first model safran estimates relevant meteorological parameters affecting snowpack evolution the second crocus is a snow numerical model which simulates the physical processes inside the snowpack and its stratigraphy the last model mepra is an expert system based on an assessment of snowpack stability it deduces natural and accidental avalanche risks to describe the great variability of the snowpack and the associated avalanche risks this automatic system simulates snow cover evolution and its stability for many typical slopes elevations and aspects representative of the different french massifs to achieve this result different kinds of validations have been carried out since winter 1981 they are mainly based on comparisons with different sets of measurements and on the opinion of users although the routinely obtained results do not yet take into account all small scale effects such as wind transport they have been considered as valuable information by avalanche forecasters since 1992 93 and used operationally since then

monitoring of snow avalanches using a seismic array location speed estimation and relationships to meteorological variables 1 monitoring snow avalanches is necessary in order to better understand their triggering mechanisms and ultimately improve forecast performance seismic monitoring has been developed by several groups over the last 20 years and holds great potential to detect locate and characterize snow avalanches during the 2009 2010 winter a seismic antenna was installed in the french alps close to the village of saint christophe en oisans 1700 m above sea level the array of seven sensors operated during 50 days in october and november 2009 under snow free conditions and during 40 days in january and february 2010 in presence of snow it recorded different types of seismic events including snow avalanches rockfalls shots and regional and local microearthquakes eighty avalanche signals were visually identified using a beam forming method we were able to locate snow avalanches on slopes of various orientations in a radius of about 3 km and track their propagation the location technique allowed for the estimation of avalanches front speed which ranged between 12 and 32 m s 1 the method can also distinguish dry and wet snow avalanches durations of avalanches can be as long as 380 s because of the length of the slopes in the area seismic monitoring provides a catalog of avalanches with precise times which can be used to analyze the impact of meteorological forcings on the avalanche triggering snowfall is found to be the dominant forcing of avalanche activity during this period as revealed by the strongest correlation for the period of study our results suggest that the impact of precipitation on the snowpack instability lasts for about 6 days

structure of an atmospheric undular bore generated from colliding boundaries during cape abstract a case study of a sea breeze front originating from the east coast of florida colliding with a gust front moving toward the southeast is presented single and multi doppler radar analyses combined with serial balloon ascents suggest that the denser sea breeze flow undercut the cold pool behind the gust front and may have generated a westward propagating undular bore in addition another undular bore was generated by the collision and propagated eastward through the cape network the latter bore propagated upstream against the southeasterly flow behind the sea breeze front and was apparent as a narrow band 5 6 km wide of near zero radial velocities embedded within an overall flow that was positive as seen by the cp 4 doppler radar as the eastern bore propagated through the dual doppler lobe defined by the ncar cp 3 and cp 4 radars a detailed and unique wind synthesis revealed its three dimensional kinematic structure significant along bore variability was shown in the convergence and verti

across shelf benthic transports on the inner shelf of the middle atlantic bight during the halloween storm of 1991 instrumented bottom boundary layer tripods were deployed on the inner shelf at depths of 13 m and 8 m off the u s army corps of engineers field research facility at duck north carolina usa over a two week period that included the severe and prolonged halloween storm of late october 1991 the storm persisted for five days and generated waves with heights and periods of up to 6 m and 22 s although the instrumentation was destroyed current profile and suspended sediment concentration profile data were recovered from the 13 m site wind driven mean along shelf currents at 1 24 m above the bed attained speeds of nearly 0 5 m s 1 across shelf flows primarily seaward directed had speeds varying from 0 05 to 0 15 m s 1 these seaward flows intensified in association with groups of high waves total mean current and skin friction bed shear stresses were increased relative to moderate energy values by more than an order of magnitude notably the highest shear stresses occurred in association with high long period swell during the late phase of the storm after winds had turned offshore creating shoreward mean flows near the bed suspended sediment concentrations exceeded 1 g 1 1 throughout the lower meter of the water column and at elevations well above the top of the wave boundary layer net across shelf suspended sediment fluxes were strongly dominated by mean flows cospectral analyses show that important but secondary roles were also played by infragravity oscillations and by wave orbital velocities

seismic stratigraphy and coastal drainage patterns in the quaternary section of the southern delmarva peninsula virginia usa abstract seismic stratigraphic analysis of the coastal zone and inner shelf of virginia s southern delmarva peninsula has revealed three geochronologically significant surfaces of post tertiary age that impose a relative chronostratigraphic framework on quaternary marine transgressive and regressive events characteristics of these surfaces indicate that two are sequence boundaries and one is a ravinement surface lying at depths of 18 70 m msl datum the lpb surface a late pleistocene basal unconformity represents the sequence boundary separating the tertiary chesapeake group from the overlying late pleistocene nassawadox formation high relief approximately 50 m on the lpb surface is associated with large fluvial channels higher in the stratigraphic section the lpr surface is found at depths of 6 28 m and corresponds to a late pleistocene transgressive or ravinement surface the surface dips southeastward with a regional dip of 0 04 and has local relief of less than 2 m the lpr surface may represent a ravinement which extended to the west side of the chesapeake bay prior to the development of the nassawadox barrier spit however the lpr surface may steepen between the axis of the southern delmarva peninsula and the holocene lagoon to form a shoreface attached to one of several known late pleistocene shorelines lying at depths of 0 20 m the hb surface is a basal unconformity that marks the holocene sequence boundary it deepens seaward with maximum local relief of about 15 m and has a topographic expression very similar to the present day lagoonal drainage pattern maximum thicknesses of holocene and pleistocene sediments 12 and 70 m respectively are found above channels on the hb and lpb surfaces the pleistocene channels are large and limited in number and represent high order channels of a drainage system that drained the piedmont and coastal plain the greater density of low order stream channels on the hb surface suggests a relationship to much smaller drainage basins that were confined to the seaward part of the coastal plain east of the delmarva peninsula these late wisconsinan smaller hb channels do not re occupy the former drain paths of the much larger high order lpb channels

waves currents sediment flux and morphological response in a barred nearshore system abstract a shore normal array of seven bi directional electromagnetic flowmeters and nine surface piercing continuous resistance wave staffs were deployed across a multiple barred nearshore at wendake beach georgian bay canada and monitored for a complete storm cycle time integrated estimates of total itvf and net invf sediment volume flux together with bed elevation changes were determined using depth of activity rods the three bars ranging in height from 0 10 to 0 40 m accreted during the storm 0 03 m and the troughs were scoured 0 05 m sediment reactivation depths reached 0 14 m and 12 of the nearshore control volume was mobilized however the invf value for the storm was less than 1 of the control volume revealing a near balance in sediment volume in the bar system landward migration of the inner crescentic and second sinuous bars occurred in association with an alongshore migration of the bar form itself the outermost straight shore parallel bar remained fixed in location the surf zone was highly dissipative throughout the storm 3 8 10 2 192 10 2 and the wave spectrum was dominated by energy at the incident frequency spectral peaks at frequencies of the first harmonic and at one quarter that of the incident wave were associated with secondary wave generation just prior to breaking and a standing edge wave respectively the former spectral peak was within the 95 confidence band for the spectrum while the latter contributed not more than 10 to the total energy in the surface elevation spectrum even near the shoreline during the storm wave height exceeded 2 m h s and periods reached 5 s t p k orbital velocities exceeded 0 5 m s 1 u rm s and were above the threshold of motion for the medium to fine sands throughout the storm shore parallel flows in excess of 0 4 m s 1 were recorded with maxima in the troughs and minima just landward of the bar crest the rate and direction of sediment flux is best explained by the interaction of antecedent bed slopes with spatial gradients in the mean and asymmetry of the shore normal velocity field these hydrodynamic parameters represent steady flows superimposed on the dominantly oscillatory motion and assumed a characteristic spatial pattern from the storm peak through the decay period increases spatially in the magnitudes of both the mean flows and flow asymmetries cause an increasing net transport potential erosion decreases in these values spatially cause a decreasing net transport potential and thus deposition these transport potentials are increased or decreased through the gravity potential induced by the local bed slope shore parallel flow was important in explaining sediment flux and morphological change where orbital velocities mean flows and flow asymmetries were at a minimum

quaternary facies assemblages and their bounding surfaces chesapeake bay mouth an approach to mesoscale stratigraphic analysis abstract shallow marine facies assemblages in the late quaternary section of virginia s eastern shore peninsula shed new light on the relationship between mesoscale stratigraphic units facies assemblages or depositional systems and the bounding surfaces from which they have been formed these units were deposited by the coast parallel progradation of the pleistocene barrier spit eastern shore peninsula during successive highstands as a consequence each segment of the spit complex has been produced by the coast parallel translation of a relatively small growth area at the spit tip the distal end of the present holocene barrier system appears to closely resemble the pleistocene highstand growth area and this environment consequently serves as a partial analog for interpreting the depositional environment of the fossil highstand deposits the many facies patterns present in the spit complex can be reduced to four kinds of facies assemblages depositional systems adopting a process based model facies template in this scheme definitions of both facies and facies assemblage are more limited than is the case in most textbook definitions in that the facies of a given assemblage are systematically related to each other by grain size and stratal pattern and also related to a bounding surface source diastem which is the immediate source of sediment for the facies assemblage vertical transitions between individual facies are easily identified in outcrop but the horizontal gradients of facies change are too gentle to be observed over the short dimensions of the borrow pits and do not have sufficient acoustic contrast to appear on ground penetrating radar records however the facies assemblages both in the borrow pits and on radar records stand out by virtue of their sharply defined bounding surfaces source diastems the facies assemblage either buries its source diastem or is capped by it the assemblages in the spit complex are in ascending stratigraphic order 1 several tidal shoal assemblages each underlain by a channel base diastem 2 two shoreface assemblages separated by an intervening marginal shoal assemblage and its underlying channel base diastem and 3 a beach strandplain assemblage underlain by a surf diastem all of these systems prograded southward as the nose of the spit prograded and while they did so zones of erosion cut the bounding surfaces that separate them two important bounding surfaces are conjugate surfaces that nourished both the facies assemblage above and the assemblage beneath as each surface advanced erosion at their leading edge spilled sediment forward down the nose of the spit while sediment was also swept backward aiding in the burial of the surface a conjugate surface creates a sandwich structure in which two facies assemblages are separated by the generating surface proximal facies are back to back across these sediment spreading boundaries episodic progradation of the spit tip by development of successive recurved beach ridges has overprinted the horizontal first order reflectors separating facies assemblages with gently dipping second order reflectors that separate successive growth increments of the spit although less clearly defined these growth increments are essentially high frequency autocyclic sequences and constitute the next higher scale of spatial organization above the depositional systems scale the manner in which facies have been organized into depositional systems in the late pleistocene highstand deposits of the eastern shore is specific to this estuary mouth setting these assemblages are however local expressions of a facies template that can be generalized to many other settings

two dimensional numerical modelling of surface wind velocity and associated snowdrift effects over complex mountainous topography a new experimental software for blowing snow sytron2 is pre sented it takes advantage of the previous limited realization sytron1andof the entire real time operational environment of the automatic chain safran crocus mepra scm it runs presently on a rectangular grid with a mesh size of about 45m covering an area of 3 0 3 0km 2 around the observation test site col du lac blanc french alps 2700m a s l near the alpe d huez ski resort sytron2 is initialized with a realistic snowpack representation derived fromthe scmoutputs andcoupledto awind fieldcom puted by the new samver model the final aim is to build a fully embedded tool sui table for representing snowdrift effects with a better resolution at different specific locations the different tools and operators used are described as well as the field valida tion processes which are based on remote identification of the eroded and accumulated areas using digital pictures

evolution and vertical structure of an undular bore observed on 20 june 2015 during pecan abstractthis study documents the evolution of an impressive largely undular bore triggered by an mcs generated density current on 20 june 2015 observed as part of the plains elevated convection at night pecan experiment the university of wyoming king air with profiling nadir and zenith viewing lidars sampled the south bound bore from the time the first bore wave emerged from the nocturnal convective cold pool and where updrafts over 10 m s 1 and turbulence in the wave s wake were encountered through the early dissipative stage in which the leading wave began to lose amplitude and speed through most of the bore s life cycle its second wave had a higher or equal amplitude relative to the leading wave striking roll clouds formed in wave crests and wave energy was detected to about 5 km agl the upstream environment indicates a negative scorer parameter region due to flow reversal at midlevels providing a wave trapping mechanism the observed bore strength of 2 4 2 9 and speed of 15 16 m s 1 agree

linking the effective thermal conductivity of snow to its shear strength and density 1 the effective thermal conductivity of snow keff is a crucial climatic and environmental variable here we test the intuition that keff is linked to microstructural and mechanical properties by attempting to relate keff to density snow and to shear strength measured with a handheld shear vane we performed 106 combined measurements of keff snow and in the alps svalbard arctic alaska and near the north pole covering essentially all snow types we find a good correlation between keff and snow which is not significantly different from that of sturm et al 1997 the correlation between keff and a combination of and snow is stronger than with density alone we propose an equation linking keff w m 1 k 1 snow kg m 3 and pa keff 7 114 10 5 snow 0 333 2 367 10 2 this equation places constraints on the calculation of keff snow and in avalanche warning models where is a key variable for our samples we calculate from measured values of keff and snow using our equation and compare the value to that predicted by the french mepra avalanche warning model which uses density and grain type as input data mepra and the prediction of based on keff and snow agree within 8 mepra agrees with observations within 11 calculating from density only yields values 55 lower than measured showing the interest of using additional data to predict

review of wave turbulence interactions in the stable atmospheric boundary layer flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods understanding turbulence intermittency and wave turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans the stable atmospheric boundary layer sabl commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces or even daytime over snow and ice surfaces and when warm air is advected over cold surfaces intermittent turbulence intensification in the sabl impacts human activities and weather variability yet it cannot be generated in state of the art numerical forecast models this failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow in which wave turbulence interaction is a potential mechanism for turbulence intermittency a workshop on wave turbulence interactions in the sabl addressed the current understanding and challenges of wave turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory observations and numerical parameterization there have been a number of reviews on waves and a few on turbulence in stably stratified flows but not much on wave turbulence interactions this review focuses on the nocturnal sabl however the discussions here on intermittent turbulence and wave turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general

continuous snowpack monitoring using upward looking ground penetrating radar technology snow stratigraphy and water percolation are key contributing factors to avalanche formation so far only destructive methods can provide this kind of information radar technology allows continuous non destructive scanning of the snowpack so that the temporal evolution of internal properties can be followed we installed an upward looking ground penetrating radar system upgpr at the weissfluhjoch study site davos switzerland during two winter seasons 2010 11 and 2011 12 we recorded data with the aim of quantitatively determining snowpack properties and their temporal evolution we automatically derived the snow height with an accuracy of about 5 cm tracked the settlement of internal layers 7 cm and measured the amount of new snow 10 cm using external snow height measurements we determined the bulk density with a mean error of 4 3 compared to manual measurements radar derived snow water equivalent deviated from manual measurements by 5 furthermore we tracked the location of the dry to wet transition in the snowpack until water percolated to the ground based on the transition and an independent snow height measurement it was possible to estimate the volumetric liquid water content and its temporal evolution even though we need additional information to derive some of the snow properties our results show that it is possible to quantitatively derive snow properties with upgpr

the spectacular undular bore in iowa on 2 october 2007 a visually impressive undular bore moved across much of iowa on 2 october 2007 and video animations were captured by numerous webcams the bore was sampled very well by doppler radar at close range and also by the high density mesoscale network of surface stations in place over iowa and 1 min automated surface observing system asos surface data at des moines iowa radar and surface observations are presented along with a brief analysis of the structure of the bore

quaternary stratigraphic evolution of the southern delmarva peninsula coastal zone cape charles virginia the quaternary evolution of the coastal zone along the southern delmarva peninsula of virginia was investigated by means of a high resolution seismic survey and supplemental shallow core borings the seismic stratigraphic framework of the area is composed of three depositional sequences separated by two prominent unconformities in ascending order the three seismic sequences represent a late tertiary substrate pleistocene deposits of post illinoian age and holocene deposits stratigraphic analysis indicates that the evolutionary development of the area was controlled mainly by glacio eustatism and paleotopographic features the late tertiary substrate was dissected by southeasterly flowing streams of the ancestral susquehanna fluvial system resulting in a highly furrowed surface consisting of valleys and interfluves that exhibit as much as 46 m of local relief the erosional surface probably represents a mature multicyclic landscape of pre sangamonian age the unconformably overlying pleistocene deposits attain a maximum thickness of 41 m pleistocene sedimentation was closely controlled by the paleotopography with relatively thicker deposits accumulating within ancestral valleys in contrast thinner deposits accumulated over the ancestral interfluves which did not become active sites of sedimentation until after the topographic relief had been substantially subdued by valley infilling pleistocene deposits are characterized by complex fades relationships multiple generations of fluvial channeling and the presence of a variety of coastal geomorphic features fluvial channel zones largely overlie the thalwegs of major southeasterly trending ancestral valleys indicating a paleotopographic control of pleistocene drainage routes the youngest pleistocene geomorphic feature which constitutes a distinctive sand lithosome is a coastal barrier ridge that appears to have developed during a sangamonian interglacial or mid wisconsinan interstadial high stand of sea level during the late wisconsin regression pleistocene deposits were eroded resulting in the development of a relatively low gradient subdued landscape compared to the highly furrowed pre sangamonian landscape holocene deposits unconformably overlie the pleistocene sequence and attain a maximum thickness of 19 m sedimentation during the holocene transgression was primarily influenced by late wisconsinan paleotopography with relatively thicker deposits accumulating within paleochannels and along the modern shoreface holocene deposits also exhibit complex facies relationships extensive channeling and coastal geomorphic features the holocene sediments consist of two distinct lithosomes that are representative of modern barrier island and lagoon marginal lagoon subenvironments microfossil assemblages indicate paleosalinities ranging from upper estuarine to marginal marine inlet conditions vertical environmental transitions during the late holocene transgression reflect a progressive restriction of the southern delmarva coastal area by barrier island development with subsequent lagoonal infilling the modern barrier islands are retrograding and lagoonal infilling has progressed to varying degrees having been influenced by both back barrier sedimentation rates and pre holocene topography

snow avalanche formation 1 snow avalanches are a major natural hazard endangering human life and infrastructure in mountainous areas throughout the world in many countries with seasonally snow covered mountains avalanche forecasting services reliably warn the public by issuing occurrence probabilities for a certain region however at present a single avalanche event cannot be predicted in time and space much about the release process remains unknown mainly because of the highly variable layered character of the snowpack a highly porous material that exists close to its melting point the complex interaction between terrain snowpack and meteorological conditions leading to avalanche release is commonly described as avalanche formation it is relevant to hazard mapping and essential to short term forecasting which involves weighting many contributory factors alternatively the release process can be studied and modeled this approach relies heavily on snow mechanics and snow properties including texture while the effect of meteorological conditions or changes on the deformational behavior of snow is known in qualitative or semiquantitative manner the knowledge of the quantitative relation between snow texture and mechanical properties is limited but promising developments are under way fracture mechanical models have been applied to explain the fracture propagation and micromechanical models including the two competing processes damage and sintering have been applied to explain snow failure there are knowledge gaps between the sequence of processes that lead to the release of the snow slab snow deformation and failure damage accumulation fracture initiation and fracture propagation simultaneously the spatial variability that affects damage fracture initiation and fracture propagation has to be considered this review focuses on dry snow slab avalanches and shows that dealing with a highly porous media close to its melting point and processes covering several orders of scale from the size of a bond between snow grains to the size of a mountain slope will continue to be very challenging

analysis and forecast of extreme new snow avalanches a numerical study of the avalanche cycles of february 1999 in france snow and weather conditions typical of exceptional cycles of fresh snow avalanches in the northern alps are investigated using the numerical avalanche hazard forecasting procedure of meteo france sensitivity tests are performed on the events of february 1999 in the chamonix france region and resulting snowpack instability modeled at the massif scale is compared using adapted new indices and maps our results complete conclusions of earlier observation based studies by providing new insights into the snow and weather conditions of february 1999 the large avalanches mainly resulted from large and very unstable fresh snow accumulations moreover the snowpack instability was increased locally by wind transport of light and fresh snow in february the mechanical weaknesses resulting from the weather conditions prior to february were a key factor in explaining the unusual volumes of these avalanches this study suggests that the operational numerical safran crocus mepra scm chain provides reliable forecasts of extreme new snow avalanche situations at the massif scale but that local scale simulations are still needed to improve the efficiency of risk mitigation and civil protection policies

a numerical model to simulate snow cover stratigraphy for operational avalanche forecasting laws of snow metamorphism have been introduced in a numerical model which simulates the evolution of temperature density and liquid water profiles of snow cover as a function of weather conditions to establish these laws the authors have summarized previous studies on temperature gradient and on wet snow metamorphism and they have also conducted metamorphism experiments on dry or wet fresh snow samples an original formalism was developed to allow a description of snow with parameters evolving continuously throughout time the introduction of laws of metamorphism has improved significantly the derivation of the settlement of internal layers and of snow covered albedo which depend on the simulated stratigraphy i e the type and size of snow grains of different layers of the snow cover the model was tested during a whole winter season without any re initialization comparison between the simulated characteristics of the snow cover and the observations made in the field are described in detail the model proved itself to be very efficient in simulating accurately the evolution of the snow cover stratigraphy throughout the whole winter season

the influence of the rocky mountains on the 13 14 april 1986 severe weather outbreak part ii evolution of a prefrontal bore and its role in triggering a squall line abstract in this paper part ii of a series the evolution of a prefrontal bore on the leeside of the rockies and its subsequent propagation and initiation of convection farther downstream over eastern colorado and western nebraska are investigated the observational evidence for this sequence of events was obtained from combined analyses of high resolution goes satellite imagery and program for regional observing and forecasting services mesonetwork data over the colorado region for the severe weather event that occurred during 13 14 april 1986 a 2d nonhydrostatic numerical model is used to further understand the initiation of the bore and its ability to propagate farther downstream and trigger convection analysis of satellite imagery and mesonet data indicated that an internal bore ahead of a cold front a moderate downslope windstorm and a quasi stationary hydraulic jump were generated within a few hours along the iceslope as a pacific cold front and its attendant upper level jet streak advanced o

spatio temporal reconstruction of snow avalanche activity using tree rings pierres jean jeanne avalanche talus massif de l oisans france snow avalanches are a major threat in many parts of the alps where they periodically damage infrastructure disrupt transportation corridors or even cause loss of life nonetheless the spatial behavior of past avalanche activity and the analysis of areas affected during particular events remain often imprecise it was therefore the purpose of this study to reconstruct spatio temporal patterns of past avalanche activity on a forested avalanche talus in the french alps pierres jean jeanne talus massif de l oisans france a total of 232 european larches larix decidua mill with clear signs of snow wasting events was analyzed and growth disturbances gd related to avalanche activity was assessed such as tangential rows of traumatic resin ducts the onset of compression wood or abrupt growth suppression and release in total 901 gd were identified in the tree ring samples indicating that 20 high magnitude avalanches occurred between ad 1919 and 1994 the mean return period of snow avalanches was 4 years with a 26 probability that an avalanche occurs in any particular year interpolated maps allowed for explicit spatial estimates of return periods throughout the talus showing a rapid increase of return frequency from 2 5 to 50 years with increasing distance from the talus apex the distribution of avalanche years seems to be quite homogeneous in time with a gap between 1951 and 1959 snowfall from a nearby meteorological station saint christophe en oisans 10 km from the study site indicated that the five most recent high magnitude events on record occurred due to above average snowfall anomalies in december and january associated with abnormally low air temperatures findings suggest that a strong snow metamorphism under high temperature gradients in january could explain the occurrence of high magnitude snow avalanches 2010 elsevier b v all rights reserved

statistical forecasting of regional avalanche danger using simulated snow cover data in the past numerical prediction of regional avalanche danger using statistical methods with meteorological input variables has shown insufficiently accurate results possibly due to the lack of snow stratigraphy data detailed snow cover data were rarely used because they were not readily available manual observations with the development and increasing use of snow cover models this deficiency can now be rectified and model output can be used as input for forecasting models we used the output of the physically based snow cover model snowpack combined with meteorological variables to investigate and establish a link to regional avalanche danger snow stratigraphy was simulated for the location of an automatic weather station near davos switzerland over nine winters only dry snow situations were considered a variety of selection algorithms was used to identify the most important simulated snow variables data mining and statistical methods including classification trees artificial neural networks support vector machines hidden markov models and nearest neighbour methods were trained on the forecasted regional avalanche danger european avalanche danger scale the best results were achieved with a nearest neighbour method which used the avalanche danger level of the previous day as additional input a cross validated accuracy hit rate of 73 was obtained this study suggests that modelled snow stratigraphy variables as provided by snowpack are able to improve numerical avalanche forecasting

barrier island evolution middle atlantic shelf u s a part i shoreface dynamics abstract in part i of this paper near bottom fluid velocity and sediment concentration measurements from the shoreface of a middle atlantic barrier long island coast are analyzed to provide insight into the dynamics of erosional shoreface retreat in part ii these data are combined with observations of coastal stratigraphy in order to construct a model for the evolution and behavior of middle atlantic barriers wave motions on the long island shoreface tend to drive sediment onshore calculations of the onshore sediment flux driven by asymmetrical shoaling waves show that for the wave states commonly encountered on the middle atlantic shelf values become strongly positive landward of approximately 10 m water depth upper shoreface but drop to very low values shortly seaward of that isobath on the lower shoreface and inner shelf floor fair weather wave current interaction tends to cause a landward creep of sediment even though the wave orbital component of the near bottom velocity field is nearly symmetrical this movement occurs because the wave approach direction generally lies within 90 of the direction up coast or down coast of the alongshore wind driven current therefore fluid shear stress acting on the sediments tends to be reinforced during the shoreward stroke of the wave orbital motion and partially cancelled during the seaward stroke during major storms the rate of sediment transport increases by at least an order of magnitude and the role of wind driven currents becomes important much more sediment is resuspended by the wave orbital current component because storm waves are more powerful than fair weather swells but the wind driven flow component is also much stronger and is now available for transporting the resuspended sediment storm flows over the shoreface occur in distinct dynamic zones surf zone friction dominated zone transition zone geostrophic zone the zones are defined by dynamical considerations and expand or contract with the intensity of the causative wind stress during peak flow events the characteristic length scales of the friction dominated and geostrophic zones tend to correspond with the morphologic zones of the shoreface and inner shelf the storm intensified wind driven alongshore flows of the lower shoreface are frequently jet like in nature and may be upwelling or downwelling wind driven coastal flows with a strong downwelling component occur during most storms on the long island coast and are particularly important to the coastal sand budget during these events sand is entrained by the storm intensified upper shoreface circulation system of wave driven alongshore currents and rip currents and is fed into the main wind driven coastal current because of the offshore component of bottom flow sand is swept down the lower shoreface and onto the adjacent inner shelf fair weather processes may be unable to return storm deposited sand to the beach from such an offshore position the shoreface transport regime of the long island barrier coast thus consists of long periods of time months during which sand moves slowly toward the beach punctuated by short intense periods hours or days during which sand is transferred from the shoreface to the adjacent inner shelf the long term sense of movement of the shoreface whether retreating the long island case or prograding must depend on the loss or gain of sand by shoreface with respect to the inner shelf the data shows that the coastal sand budget is controlled not only by the upper shoreface cycle withdrawl of sand from the beach prism storage in the breakpoint bar and its subsequent return to the beach but by a cycle of larger spatial and temporal scale in which sand is exchanged between the shoreface as a whole and the adjacent inner shelf

structure of an internal bore and dissipating gravity current as revealed by raman lidar abstract detailed moisture observations from a ground based raman lidar and special radiosonde data of two disturbances associated with a dissipating gust front are presented a synthesis of the lidar data with conventional meteorological data in conjunction with theoretical calculations and comparison to laboratory studies leads to the conclusion that the disturbances seen in both the lidar and accompanying barograph data represent a weak gravity current and an associated undular bore the disturbances display excellent coherence over hundreds of kilometers upstream of the lidar site bore formation occurs at the leading edge of the gust front coincidentally with the rapid weakening of the gravity current analysis suggests that the bore was generated by the collapse of the gravity current into a stable nocturnal inversion layer and subsequently propagated along this wave guide at nearly twice the speed of the gravity current the raman lidar provided detailed measurements of the vertical structure o

a comparison of the finescale structures of a prefrontal wind shift line and a strong cold front in the southern plains of the united states abstractthe objectives of this study are to determine the finescale characteristics of the wind and temperature fields associated with a prefrontal wind shift line and to contrast them with those associated with a strong cold front data from a mobile polarimetric x band doppler radar and from a surveillance s band radar temperature profiles retrieved from a thermodynamic sounder and surface observations from the oklahoma mesonet are used to analyze a prefrontal wind shift line in oklahoma on 11 november 2013 data from the same mobile radar and the oklahoma mesonet are used to identify the finescale characteristics of the wind field associated with a strong surface cold front in oklahoma on 9 april 2013 it is shown that the prefrontal wind shift line has a kinematic and thermodynamic structure similar to that of an intrusion elevated density current while the cold front has a kinematic structure similar to that of a classic density current other characteristics of the prefrontal wind shift line

an energy and mass model of snow cover suitable for operational avalanche forecasting a numerical model has been developed to simulate energy and mass evolution of snow cover at a given location as a function of meteorological conditions precipitation air temperature humidity wind velocity and incoming short wave and long wave radiation this model named crocus was first tested on a well instrumented field during a whole winter showing its ability to simulate the important phenomena affecting the evolution of the snow layers high temperature gradients wetting compaction and melting freezing cycles a second test was conducted at two locations in the french network used for operational avalanche forecasting though the weather observations are made there only twice daily the snow profiles calculated by the model were very close to those obtained once a week by a pit observation crocus proved itself sufficient to be considered now as a useful objective tool for operational avalanche forecasting

late pleistocene barrier island sequence along the southern delmarva peninsula implications for middle wisconsin sea levels evidence for a middle wisconsin sea level high at or above modern limits along the east coast of the us has long been controversial most reports have been dismissed as poorly dated or lacking unequivocal documentation of a marine transgression the authors describe here a sup 14 c dated middle wisconsin transgressive sequence with an extant subaerial barrier facies along the southern delmarva peninsula this sequence indicates that sea levels were near their present position between ca 23 and 34 ka it may correlate with other inferred similar age littoral deposits of the area and it suggests that the evidence for glacioeustatic fluctuations during the wisconsin glaciation should be reconsidered

radar and profiler analysis of colliding boundaries a case study abstract the kinematics of a head on collision between two gust fronts followed by a secondary collision between a third gust front and a bore generated by the initial collision are described using analyses of weather surveillance radar 1988 doppler wsr 88d and mobile integrated profiling system mips data each gust front involved in the initial collision exhibited a nearly north south orientation and an east west movement the eastward moving boundary was 2 c colder and moved 7 m s 1 faster than the westward moving boundary two dimensional wind retrievals reveal contrasting flows within each gravity current one exhibited a typical gravity current flow structure while the other assumed the form of a gravity wave current hybrid with multiple vortices atop the outflow one of the after collision boundaries exhibited multiple radar finelines resembling a solitary wave shortly after the collision about 1 h after the initial collision a vigorous gust front intersected the eastward moving bore severa

the morning glory of the gulf of carpentaria an atmospheric undular bore abstract this paper presents the results of a field expedition mounted in late september early october 1979 to investigate the structure and origin of the morning glory of the gulf of carpentaria in northern australia the morning glory is a line wind squall accompanied by a pressure jump and often by a long roll cloud or series of such clouds it frequently occurs in the early morning especially in october in the gulf area a light aircraft fitted with a temperature and humidity probe was flown in two glories to determine their thermodynamic structure and wind fields wore obtained principally by tracking pilot balloons using the double theodolite method data also were obtained from a network of surface stations recording wind velocity and pressure installed at locations across cape york peninsula which is believed to be the area of genesis the morning glory is identified as an internal undular bore propagating on the nocturnal and or maritime inversion its origin appears to lie frequently

quaternary stratigraphy and sea level history of the u s middle atlantic coastal plain abstract middle atlantic inner continental shelf stratigraphic studies document a regional late pleistocene fossiliferous mud deposit from northern new jersey to cape lookout north carolina seismic reconnaissance and detailed stratigraphic analyses reveal the nature of the mud termed unit q2 on the maryland inner continental shelf extensive amino acid relative age determinations from the single genus mulinia combined with additional amino acid analyses from onshore deposits having radiometric dates for calibration indicate an age range for unit q2 corresponding to oxygen isotope stage 5 ostracode assemblages delineate four distinct climatic episodes in unit q2 enabling correlation of the zones in q2 to the deep sea isotopic record of climatic fluctuations substages in stage 5 late stage 5 is represented on the maryland shelf by the 6 meter thick mud of unit q2 deposited in an open shelf environment at slightly depressed sea levels relative to substage 5e late stage 5 sea levels including sea level minima can be estimated for the mid atlantic coastal plain by direct measurement of the altitudes of ostracode zone boundaries offshore and from peak transgressive facies in correlative deposits onshore late stage 5 sea levels determined from the inner shelf and adjacent nearshore facies on the atlantic coast comprise the most complete sea level history for stage 5 yet proposed some recent revisions of glacioeustatic sea level models advocate slightly higher sea levels during late stage 5 substage 5c in particular than originally estimated from uplifting reef tracts and support sea levels higher than estimates from deep sea isotopic records the sea level record from the maryland inner continental shelf confirms these recent estimates in an area of minimal tectonism and adds sea level minima estimates for substages 5d and 5b offshore a more complete record of stage 5 is preserved than in onshore deposits which are limited to peak transgressive facies discrepancies in correlation among emerged coastal plain facies therefore become resolvable within the context provided by the shelf stratigraphy

a new hierarchical bayesian approach to analyse environmental and climatic influences on debris flow occurrence abstract how can debris flow occurrences be modelled at regional scale and take both environmental and climatic conditions into account and of the two which has the most influence on debris flow activity in this paper we try to answer these questions with an innovative bayesian hierarchical probabilistic model that simultaneously accounts for how debris flows respond to environmental and climatic variables in it full decomposition of space and time effects in occurrence probabilities is assumed revealing an environmental and a climatic trend shared by all years catchments respectively clearly distinguished from residual random effects the resulting regional and annual occurrence probabilities evaluated as functions of the covariates make it possible to weight the respective contribution of the different terms and more generally to check the model performances at different spatio temporal scales after suitable validation the model can be used to make predictions at undocumented sites and could be used in further studies for predictions under future climate conditions also the bayesian paradigm easily copes with missing data thus making it possible to account for events that may have been missed during surveys as a case study we extract 124 debris flow event triggered between 1970 and 2005 in 27 catchments located in the french alps from the french national natural hazard survey and model their variability of occurrence considering environmental and climatic predictors at the same time we document the environmental characteristics of each debris flow catchment morphometry lithology land cover and the presence of permafrost we also compute 15 climate variables including mean temperature and precipitation between may and october and the number of rainy days with daily cumulative rainfall greater than 10 15 20 25 30 40 mm day 1 application of our model shows that the combination of environmental and climatic predictors explained 77 of the overall variability of debris flow occurrences in this data set occurrence probabilities depend mainly on climatic variables which explain 44 of the overall variability through the number of rainy days and maximum daily temperature this important time component in the variability of overall debris flow occurrence is shown to be responsible for a significant increase in debris flow activity between 1970 and 2005 at regional scale environmental variables which account for 33 of the overall variability includes mostly the morphometric variables of the debris flow catchments

the formation of internal bores in the atmosphere a laboratory model summary recently several atmospheric observations have been interpreted as internal undular bores or internal solitary waves evolving from internal bores that propagate along low level temperature inversions it has been speculated that such disturbances are generated by some type of gravity current such as cold fronts sea breeze fronts and thunderstorm outflows interacting with an existing temperature inversion in this paper we describe a systematic laboratory study in a water channel of internal bores and their generation by the movement of gravity currents through a two layer model of the atmosphere we compare the results of our laboratory experiments with previous theories and numerical simulations and with several detailed atmospheric observations of internal bores at different stages of development

a synthetic study to assess the applicability of full waveform inversion to infer snow stratigraphy from upward looking ground penetrating radar data snow stratigraphy and liquid water content are key contributing factors to avalanche formation upward looking groundpenetrating radar upgpr systems allow nondestructive monitoring of the snowpack but deriving density and liquid water content profiles is not yet possible based on the direct analysis of the reflection response we have investigated the feasibility of deducing these quantities using full waveform inversion fwi techniques applied to upgpr data for that purpose we have developed a frequency domain fwi algorithm in which we additionally took advantage of time domain features such as the arrival times of reflected waves our results indicated that fwi applied to upgpr data is generally feasible more specifically we could show that in the case of a dry snowpack it is possible to derive snow densities and layer thicknesses if sufficient a priori information is available in case of a wet snowpack in which it also needs to be inverted for the liquid water content the algorithm might fail even if sufficient a priori information is available particularly in the presence of realistic noise finally we have investigated the capability of fwi to resolve thin layers that play a key role in snow stability evaluation our simulations indicate that layers with thicknesses well below the gpr wavelengths can be identified but in the presence of significant liquid water the thin layer properties may be prone to inaccuracies these results are encouraging and motivate applications to field data but significant issues remain to be resolved such as the determination of the generally unknown upgpr source function and identifying the optimal number of layers in the inversion models furthermore a relatively high level of prior knowledge is required to let the algorithm converge however we feel these are not insurmountable and the new technology has significant potential to improve field data analysis