terrestrial crustacean breeding trace fossils from the cretaceous of patagonia argentina palaeobiological and evolutionary significance abstract the breeding trace fossils described herein along with the high density of loloichnus baqueroensis in the cretaceous formations of patagonia suggest that crayfishes were soil engineers along the cretaceous in southern south america and that they had acquired many of the k breeding behaviours recorded by insects in latest and post cretaceous soils such as pelletal constructions and excavation of breeding cells the k t event was probably responsible for changes in environmental conditions in such a way that crayfishes finally became restricted to two small distributional areas in southern south america and k breeding insects replaced them as keystone organisms in cainozoic and modern soils dagnichnus titoi igen and isp nov and cellicalichnus meniscatus isp nov are created to include the new trace fossils attributable to crayfishes from the cretaceous of patagonia argentina the attribution to crayfishes is based on their association and morphological affinities with the crayfish fossil burrows l baqueroensis from the same geologic units d titoi is represented by hemispherical chambers surrounded by thick and short meniscate burrows which can be arranged in two or three tight whorls in the more regular specimens meniscate burrows are curved downwards and have no neck walls are unlined c meniscatus are necked horizontal and straight cells showing meniscate fillings attached to sub vertical shafts which are relatively much wider than the neck of cells both shafts and cells show a thin and smooth lining the presence of cells or burrows smaller than the putative parental burrows and comparisons with breeding traces of marine decapoda support the interpretation of breeding traces calichnia of terrestrial crustaceans c meniscatus is interpreted as cells excavated from parental burrows whereas d titoi are probably breeding structures completely produced in a different palaeoenvironment where the female release juveniles

how do bedform patterns arise new views on the role of bedform interactions within a set of boundary conditions one explanation for bedform patterns is self organization in which the pattern emerges because of interactions among the bedforms themselves models remote images field studies and lab experiments have identified bedform interactions that involve whole bedforms only bedform defects or that are remote interactions between bedforms it is proposed that bedform interactions form a spectrum from constructive to regenerative in pattern development constructive interactions including merging lateral linking cannibalization and remote transfer of sediment push the system toward fewer larger more widely spaced bedforms regenerative interactions including bedform splitting defect creation and calving push the system back toward a more initial state other interactions including off center collision defect migration and bedform and defect repulsion cause pattern change but may not be strongly constructive or regenerative although bedform interactions are ubiquitous to any field of bedforms their dynamics flow field modification and impact upon measurable pattern parameters are yet poorly understood most bedform interactions span bedform types and fluids supporting the hypothesis that pattern emerges from dynamics at the bedform level in a hierarchy that includes lower levels of bedform flow and grain fluid interactions bedform interactions alone however cannot account for the rich diversity of bedform patterns in nature it is proposed that field diversity arises because of boundary conditions which are the environmental variables within which a field evolves conceptually boundary conditions modify the shape of the attractor toward which a field evolves possibly by altering the type and frequency of bedform interactions boundary conditions are broadly similar within system types but are unique for each bedform field so that no two are ever exactly alike although aeolian and fluvial systems share some types of boundary conditions flow depth is a unique boundary condition in shallow fluvial systems copyright 2009 john wiley sons ltd

large scale conditions favorable for the development of heavy rainfall during tamex iop 3 abstract the large scale processes responsible for development of heavy precipitation during 20 23 may 1987 along the southeastern china coast are studied there are two distinct rainfall peaks around 0000 utc 20 may and 0000 utc 22 may prior to the heavy rain event strong low level southwesterly flow developed ahead of a 850 hpa trough and transported warm moist air from the south into southeastern china to generate the convective instability for the first rainfall period positive vorticity advection by thermal winds was observed ahead of the 850 hpa trough upper level divergence as a result of the imbalance between winds and geopotential height fields was found in the different airflow region on the northeastern quadrant of the south asian anticyclone prior to the first rainfall period for the second rainfall period an upper level trough deepened in the lee side of the tibetan plateau and moved to the southeastern china coast strong upper level frontogenesis caused by horizontal deformation wa

wood borings in premnoxylon plant animal interactions in the carboniferous cichan m a and taylor t n 1982 wood borings in premnoxylon plant animal interactions in the carboniferous palaeogeogr palaeoclimatol palaeoecol 39 123 127 a complex system of anastomosing burrows is described from structurally preserved lower middle pennsylvanian premnoxylon wood the burrows are filled with small uniformly shaped coprolites this discovery represents the oldest recorded evidence for the existence of wood boring organisms and indicates that a relatively specialized form of plant animal interaction was present during the late paleozoic it also provides additional support for the idea that premnoxylon a cordaitean root was an aerial organ

comments on the paper reconnaissance of upper jurassic morrison formation ichnofossils rocky mountain region usa paleoenvironmental stratigraphic and paleoclimatic significance of terrestrial and freshwater ichnocoenoses by stephen t hasiotis

structural characteristics of deep convective systems over tropical africa and the atlantic ocean abstract the structural properties of convective cloud clusters of tropical africa and the atlantic ocean are studied using six summers of meteosat satellite data in the atmospheric infrared window a cluster at a given brightness temperature threshold is defined as the area covered by adjacent cloud cells with brightness temperature lower than the threshold the clusters are classified according to the area they cover and the position of their center of mass results show that the convective cluster number can be approximated by a power law of the radius with an exponent around 2 this gives a nearly equal contribution of each cluster size to the mean high cloud cover for a given brightness temperature threshold using the visible channel 0 4 1 1 m of meteosat we show that the part of the clusters with reflectance larger than 0 7 also follows a power law the cluster size distributions remain similar for different subregions and seasons even if they are subject to large variations in the mean cloud

warm core vortex amplification over land abstract a convectively generated mesoscale vortex that was instrumental in initiating and organizing five successive mesoscale convective systems over a period of three days is documented two of these convective systems were especially intense and resulted in widespread heavy rain with localized flooding based upon radar and satellite data the detectable size of the vortex became much larger following the strong convective developments nearly tripling its initial diameter over its three day life cycle during nighttime when convection typically intensified within the vortex movement of the system tended to slow following dissipation of the convection in the morning the daytime movement accelerated cross sections of potential vorticity taken through the vortex center clearly show a maximum at midlevels and a well defined minimum directly above the vortex and the potential vorticity maximum were essentially colocated and the system was nearly axisymmetric in the vertical over the three day life

early growth of mesoscale convective complexes a meso β scale cycle of convective precipitation abstract the evolution of precipitation fields associated with several mesoscale convective complexes mccs has been inferred from radar reflectivity data in almost all cases examined including those described in the literature the system s convective ensemble undergoes a marked modulation in intensity on a meso time scale during the early growth stage of its meso scale life cycle this scale convective cycle is most evident in time series of volumetric precipitation rate due to convective echo and is characterized by a temporal maximum followed by a minimum 0 5 1 h later superimposed on an otherwise several hour monotonically increasing trend while the latter is due to a concurrent several hour increase in the areal extent of convective echo the scale perturbation is dominated by a modulation in intensity of the existing convective entities that the system constitutes at that stage of growth the scale cycle also marks the onset of a sustained increased growth rate of the mcc s s

early stage aeolian protodunes bedform development and sand transport dynamics early stage aeolian bedforms or protodunes are elemental in the continuum of dune development and act as essential precursors to mature dunes despite this we know very little about the processes and feedback mechanisms that shape these nascent bedforms whilst theory and conceptual models have offered some explanation for protodune existence and development until now we have lacked the technical capability to measure such small bedforms in aeolian settings here we employ terrestrial laser scanning to measure morphological change at the high frequency and spatial resolution required to gain new insights into protodune behaviour on a 0 06 m high protodune we observe vertical growth of the crest by 0 005 m in two hours our direct measurements of sand transport on the protodune account for such growth with a reduction in time averaged sediment flux of 18 observed over the crestal region detailed measurements of form also establish key points of morphological change on the protodune the position on the stoss slope where erosion switches to deposition is found at a point 0 07 m upwind of the crest this finding supports recent models that explain vertical dune growth through an upwind shift of this switching point observations also show characteristic changes in the asymmetric cross section of the protodune flow form feedbacks result in a steepening of the lee slope and a decline in lower stoss slope steepness by 3 constituting a reshaping of protodune form towards more mature dune morphology the approaches and findings applied here a demonstrate an ability to quantify processes at requisite spatial and temporal scales for monitoring early stage dune evolution b highlight the crucial role of form flow feedbacks in enabling early stage bedform growth alluding to a fluctuation in feedbacks that require better representation in dune models and c provide a new stimulus for advancing understanding of aeolian bedforms

winter monsoon convection in the vicinity of north borneo part i structure and time variation of the clouds and precipitation abstract radar and satellite observations in the vicinity of northern borneo obtained during the international winter monsoon experiment wmonex showed that the convection in that region underwent an extremely regular diurnal cycle over the sea to the north of borneo the general level of convective activity was increased during monsoon surges and during the passages of westward propagating near equatorial disturbances convective activity was decreased during monsoon lulls the diurnal cycle was well defined regardless of whether the general level of convective activity was enhanced or suppressed by synoptic scale events the cycle of convection over the sea was especially well documented it was typically initiated at about midnight when an offshore low level wind began where this wind met the monsoonal northeasterly flow usually just off the coast convective cells formed after midnight the convection continued to develop and by 0800 lst it had evolved into an organized mesoscale system with a

aeolian sand strip mobility and protodune development on a drying beach examining surface moisture and surface roughness patterns measured by terrestrial laser scanning ephemeral aeolian sand strips are commonplace on beaches their formation during high energy sand transport events often precedes the development of protodunes and their dynamics present interesting feedback mechanisms with surface moisture patterns however due to their temporary nature little is known of their formation mobility or the specifics of their interaction with beach surface characteristics similarly surface moisture has an important influence on sediment availability and transport in aeolian beach systems yet it is difficult to quantify accurately due to its inherent variability over both short spatial and temporal scales whilst soil moisture probes and remote sensing imagery techniques can quantify large changes well their resolution over mainly dry sand close to the aeolian transport threshold is not ideal particularly where moisture gradients close to the surface are large in this study we employed a terrestrial laser scanner to monitor beach surface moisture variability during a three and a half hour period after a rain event and investigated relationships between bedform development surface roughness and surface moisture our results demonstrate that as the beach surface dries sand transport increases with sediment erosion occurring at the wet dry surface boundary and deposition further downwind this dynamic structure dependent upon changing surface moisture characteristics results in the formation of a rippled sand strip and ultimately a protodune our findings highlight dynamic mobility relationships and confirm the need to consider transient bedforms and surface moisture across a variety of scales when measuring aeolian transport in beach settings the terrestrial laser scanner provides a suitable apparatus with which to accomplish this

initiation and early development of barchan dunes a case study of the moroccan atlantic sahara desert abstract this paper describes field measurements that document the formation of barchan dunes in the moroccan atlantic sahara desert the first mechanism described is the transformation of patches and proto dunes at cap juby beach to barchan dunes of elementary size this transformation is discussed in relation to the wind speed and saturation length the second mechanism is the ejection of small barchans of elementary size by other small barchans in response to the perturbation of the target barchan by two other impacting small barchans this remote initiation is discussed in relation to the bulk flux transported by the barchan dunes involved in this interaction and to their morphology other modes of barchan initiation observed in the field are also presented

topographic meteorologic and canopy controls on the scaling characteristics of the spatial distribution of snow depth fields 1 in this study lidar snow depths bare ground elevations topography and elevations filtered to the top of vegetation topography vegetation in five 1 km 2 areas are used to determine whether the spatial distribution of snow depth exhibits scale invariance and the control that vegetation topography and winds exert on such behavior the one dimensional and mean two dimensional power spectra of snow depth exhibit power law behavior in two frequency intervals separated by a scale break located between 7 m and 45 m the spectral exponents for the low frequency range vary between 0 1 and 1 2 for the one dimensional spectra and between 1 3 and 2 2 for the mean twodimensional power spectra the spectral exponents for the high frequency range vary between 3 3 and 3 6 for the one dimensional spectra and between 4 0 and 4 5 for the mean two dimensional spectra such spectral exponents indicate the existence of two distinct scaling regimes with significantly larger variations occurring in the larger scale regime similar bilinear power law spectra were obtained for the fields of vegetation height with crossover wavelengths between 7 m and 14 m further analysis of the snow depth and vegetation fields together with wind data support the conclusion that the break in the scaling behavior of snow depth is controlled by the scaling characteristics of the spatial distribution of vegetation height when snow redistribution by wind is minimal and canopy interception is dominant and by the interaction of winds with features such as surface concavities and vegetation when snow redistribution by wind is dominant

airflow up the stoss slope of sand dunes limitations of current understanding the windward stoss side of a sand dune acts as a streamlined obstacle in the path of the wind continuity principles necessitate compression of the flow field up the stoss slope of a dune and shear stress must progressively increase as the flow accelerates measurements in transverse flow over thirteen dunes at padre island texas the algodones california and white sands new mexico confirm that velocity profiles on the stoss slope are not log linear and that flow acceleration occurs very close to the surface within an internal boundary layer as a consequence in the overlying flow where measurements have historically been made an overall decrease in shear stress occurs up the slope the actual shape of the velocity profiles and the identification of the appropriate segment of the profile from which to derive the shear stress that drives saltation represent major problems not approachable by traditional means

time frequency variability of enso and stochastic simulations abstract the time frequency spectral structure of el nino southern oscillation enso time series holds much information about the physical dynamics of the enso system the authors have analyzed changes of the spectrum with time of three enso indices the conventional southern oscillation index soi nino3 sea surface temperatures and a tropical pacific rain index over the period 1871 1995 three methods of time frequency analysis windowed fourier transform wavelet analysis and windowed prony s method were used and the results are in good agreement the time frequency spectra of all the series show strong multidecadal variations over the past century in particular there was reduced activity of enso in the 2 3 yr periodicity range during the period 1920 60 compared with both the earlier and later periods the dominant frequencies in the spectra do not appear to be constrained to certain frequency bands and there is no evidence that the enso system has fixed modes of oscillation the qualitative b

scale selection in locally forced convective fields and the initiation of deep cumulus abstract deep cumulus dynamics has often been treated as an initial value problem where the long time effect of surface energy fluxes are neglected initiation is often assumed to follow from a strong localized deformation of the flow field which is elsewhere quiescent in nature however the atmosphere is rarely found in an undisturbed condition just prior to the inception of deep growth one likely cause of widespread motions is the natural modal response of the environment to surface energy fluxes which results in a field of disturbances evidence is presented in this paper for the possible existence of a class of solutions when deep convection is allowed to evolve in the context of a thermally forced field of shallow convection this class of solutions is neglected when one visualizes the growth of severe local storms in term of buoyant bubbles in an otherwise tranquil atmosphere considering deep cumulus initiation as a field problem severely limits the concept of an isolated cloud individual clou

relations between dune morphology air flow and sediment flux on reversing dunes silver peak nevada relations between wind speed sediment flux and dune morphology were measured for two reversing dunes situated in the south western part of the silver peak dunefield in clayton valley west central nevada the larger dune was 120 m in length with a height of 12ae5 m and the smaller dune 80 m long and 6 m high both dunes were sharp crested aligned approximately e w perpendicular to the dominant wind direction and had slightly concave stoss profiles twenty seven rotating cup anemometers were placed 0ae3 m elevation along n s transects on each of the dunes at each anemometer site a passive wedge shaped sediment trap was used to measure sediment flux amplification of wind speed was observed towards the crest on the stoss side of both dunes with speed up factors ucrest ubase ranging from 1ae50 3ae19 with a corresponding increase in sediment flux by 1 2 orders of magnitude in general the ratio of crest flux to base flux qc qb increased with increasing incident basal wind speed on both dunes direct measurements of the stoss slope variation in sediment flux relative to the dune crest are in good agreement with owen s transport model friction speed u was approximated from near surface 0ae3 m point wind speed although not all assumptions of the owen model are upheld the modified model performance is sufficiently robust to predict short term variation in stoss sediment flux on the study dunes improved models that adequately account for variation in sediment flux under changing air flow and transport conditions are necessary for the prediction of longterm evolution of dunes in this regard further progress in model development will require increased understanding of the spatial and temporal variability of airflow and the short term response of sediment flux to these flow conditions

re evaluation of alleged bees nests from the upper triassic of arizona published records of supposed triassic bees nests are based on trace fossils in silicified wood and in sandstone in upper triassic strata of the chinle group in petrified forest national park arizona a critical firsthand restudy of these trace fossils indicates that they lack diagnostic features of bees nests such as cells with smooth linings and spiral closure caps indeed many of the observations claimed to identify these traces as bees nests cannot be replicated instead the putative triassic bees nests can be classified as 1 clavate borings in petrified wood somewhat similar to teredolites these borings preferentially penetrate heart rot fungus polyporites and are mostly likely larval chambers of wood boring beetles 2 cylindrical vertical burrows in sandstone assignable to skolithos these are almost certainly arthropod produced the recognition that the chinle group trace fossils are not bees nests eliminates them as evidence that decouples bee origins from the cretaceous origin of angiosperms the triassic trace fossils in silicified wood are also a new and unique record of likely beetle borings in triassic wood

3d mapping efficacy of a drone and terrestrial laser scanner over a temperate beach dune zone abstract understanding dynamic earth surface processes requires various spatial and temporal information to help produce patterns of landform change recent developments in sensor technology such as structure from motion sfm camera mounted airborne unmanned aerial vehicles uavs and terrestrial laser scanning tls have provided a means of acquiring high resolution spatial data on land surface topography through repeat surveys these techniques enable much better understanding of what is termed geomorphometry where we can examine a geomorphic surface for change over space and time in coastal environments change can involve significant alteration and generation of landforms over relatively short periods and therefore we require a means of measuring surface morphology quickly and over large areas here we examine a section of a beach dune system in nw ireland using sfm uav and tls plus baseline dgps data points to assess the value of these techniques and to understand their effectiveness and limitations issues such as accuracy resolution and differences of digital elevation models dems are assessed for their efficiency associated challenges and relative performance over variations in terrain types and analytical approaches we also examine the implications for differences in areal and volume calculations of the coastal landforms using both approaches we find that sensor performance is highly dependent on the terrain being measured with undulations slope vegetation cover acquisition resolution point density and interpolation issues all having pronounced impacts on effectiveness and data quality in general the tls performed better over flatter low angled topography containing sparse non vegetated areas than in areas with complex landforms where survey shadows appear to compromise final dems the sfm uav shows good performance over different terrains with the exception of relatively flat featureless areas such as sandy beaches and densely vegetated surfaces where differences between techniques are 1 m data acquisition however is much 30 faster using a sfm uav with more extensive survey areas covered than using a tls

reconnaissance of upper jurassic morrison formation ichnofossils rocky mountain region usa paleoenvironmental stratigraphic and paleoclimatic significance of terrestrial and freshwater ichnocoenoses seventy five types of ichnofossils documented during a four year reconnaissance study in the upper jurassic morrison formation demonstrate that highly diverse and abundant plants invertebrates and vertebrates occur throughout most of the morrison or equivalent strata invertebrate ichnofossils preserving the most environmentally and climatically sensitive in situ behavior of morrison organisms are in nearly all outcrops terrestrial ichnofossils record biotic processes in soil formation indicating soil moisture and water table levels freshwater ichnofossils preserve evidence of water depth salinity and seasonality of water bodies ichnofossils categorized as epiterraphilic terraphilic hygrophilic and hydrophilic new terms reflect the moisture regime where they were constructed the ichnofossils are vertically zoned with respect to physical chemical and biological factors in the environment that controlled their distribution and abundance and are expressed as surficial shallow intermediate and deep the sedimentologic stratigraphic and geographic distribution of morrison ichnofossils reflects the environmental and climatic variations across the basin through time marginal marine tidal to brackish water ichnofossils are mainly restricted to the windy hill member very large to small termite nests dominate the salt wash member similar size ranges of ant nests dominate the brushy basin member soil bee nests dominate in the salt wash decreasing in abundance through the brushy basin deeper and larger insect nests indicate more seasonal distribution of precipitation and rainfall shallower and smaller insect nests indicate either dry or wet substrate conditions depending on the nest architecture and paleopedogenic and sedimentologic character of the substrate trace fossil indicators of flowing or standing water conditions are dominant in the tidwell member and in fluvial sandstones of the salt wash and brushy basin members large communities of perennial freshwater bivalve traces are abundant in the tidwell and brushy basin members but to a lesser extent in the salt wash member shallow crayfish burrows indicating a water table level close to the surface 1 m are restricted to channel bank and proximal alluvial deposits in the salt wash recapture and brushy basin members sauropod theropod pterosaur and other vertebrate tracks occur throughout the morrison formation associated with alluvial lacustrine and transitional marine shoreline deposits ichnofossils and co occurring paleosols in the morrison reflect the local and regional paleohydrologic settings which record the annual soil moisture budget and were largely controlled by the climate in the basin contributions to near surface biologic systems by groundwater from distant sources were minor except where the water table perennially seasonally or ephemerally intersected the ground surface the jurassic morrison formation in the southern portion of the basin experienced a mosaic of seasonal climates that varied from a drier tidwell windy hill deposition to a wetter lower and middle salt wash deposition and slightly drier upper salt wash deposition tropical wet dry climate returning to a wetter tropical wet dry climate near the end of morrison deposition brushy basin deposition the northern part of the basin experienced similar trends across a mosaic of mediterranean climate types the range and mosaic pattern of wet dry morrison climates is analogous to the range of climates and their seasonal variability that dominates the african savanna today

multifractal analysis and modeling of rainfall and river flows and scaling causal transfer functions river flows have been known to be scaling for over 40 years and scaling notions have developed rapidly since the 1980s using the framework of universal multifractals and time series of rainfall and river runoff for 30 french catchments basin sizes of 40 km 2 to 200 km 2 from 1 day to 30 years we quantify types and extent of the scaling regimes for both flow and rain series we observed a scale break at roughly 16 days which we associate with the synoptic maximum the time scale of structures of planetary spatial extent for the two scaling regimes in both series we estimate the universal multifractal parameters as well as the critical exponents associated with multifractal phase transitions using these exponents we perform causal multifractal time series simulations and show how a simple linear scaling transfer function can be used to relate the low frequency rainfall series to the corresponding river flow series the highfrequency regime requires nonlinear transforms

ichnotaxonomy and ichnostratigraphy of chambered trace fossils in palaeosols attributed to coleopterans ants and termites

grainfall processes in the lee of transverse dunes silver peak nevada grainfall deposition and associated grainflows in the lee of aeolian dunes are important in that they are preserved as cross beds in the geological record and provide a key to the interpretation of the aeolian rock record despite their recognized importance there have been very few field laboratory or numerical simulation studies of leeside depositional processes on aeolian dunes as part of an ongoing study the relationships among grainfall wind speed and direction stoss sand transport rates and dune morphometry height and aspect ratio were investigated on four relatively small straightcrested transverse dunes at silver peak nevada between 55 and 95 of the total grainfall was found to be deposited within 1 m of the crest and 84 99 within 2 m depending primarily on dune size and shape grainfall decay rates on high dunes of large aspect ratio were observed to be very consistent with a weak positive dependence on wind speed for small dunes with low aspect ratios grainfall deposition was more varied and decreased rapidly within 1 m of the dune crest whereas at increased distance from the dune crest it eventually approached the smaller decay rates observed on the large dunes no dependence of grainfall on wind speed was observed for these small dunes comparison of field data with predictions from anderson s 1988 saltation model of grainfall based on the computation of saltation path lengths indicates lack of agreement in the following areas 1 deposition rate magnitude 2 variation in decay rate with wind speed and 3 the magnitude and location of the localized lee slope depositional maxima the silver peak field results demonstrate the importance of dune aspect ratio and related wake effects in determining the rate and pattern of grainfall this work confirms earlier speculation by mcdonald anderson 1995 that temporary turbulent suspension or modified saltation of relatively large grains does occur within the dune wake so that transport distances generally are larger than predicted by numerical simulations of true saltation

variations in wind velocity and sand transport on the windward flanks of desert sand dunes the magnitudes of increases in wind velocity or speed up factors have been measured on the windward flanks of transverse and linear dunes of varying height on transverse dunes velocity speed up varied with dune shape and height for linear dunes speed up factors varied principally with wind direction relative to the dune with dune shape and dune height the main effect of velocity speed up on the windward flanks of dunes is to increase potential sand transport rates considerably in crestal areas this is greatest for large dunes with winds of moderate velocity blowing at a large angle to the dune changing ratios of base to crest sand transport rates on transverse dunes tend to reduce dune steepness as overall wind velocities increase on linear dunes the tendency for crestal lowering is counteracted by deposition in this area when winds reverse in a bi directional wind regime

attributes of the wood boring trace fossil asthenopodichnium in the late cretaceous wahweap formation utah usa abstract a common macroscopic wood boring trace fossil occurs in the upper cretaceous braided and meandering stream deposits of the upper and capping sandstone members of the wahweap formation in grand staircase escalante national monument utah upon detailed examination this trace warrants assignment to asthenopodichnium thenius 1979 asthenopodichnium is a scoop shaped pouch like trace that is preserved as iron hydroxide rind casts of wood fragments and logs the long axes of the scoops are typically aligned parallel or sub parallel to the long axis of the preserved wood in the upper and capping sandstone members asthenopodichnium characteristically occur in dense clusters in which pouches overlie one another although they are found as isolated individual traces and tight clusters of multiple individuals as well the asthenopodichnium trace maker has been purported to be the possible product of mayfly nymphs developed in moving fresh water as a fresh water trace asthenopodichnium may be used in conjunction with teredolites a marine or brackish indicator to delimit the brackish fresh water limit in estuarine deposits

a long lived mesoscale convective complex part ii evolution and structure of the mature complex abstract an eight day episode in august 1977 is described wherein 14 mesoscale convective complexes mccs developed in the central united states including one to the immediate ice of the rocky mountains on each day of the episode in part i of this article the daytime genesis of one of these systems was traced from its pre convective roots in the mountains of central colorado to its incipient mcc stage on the plains of eastern colorado in this paper its continued nocturnal development into a large mcc over kansas is followed satellite imagery shows that this system remained coherent for at least three days as it passed off the east coast and across the western atlantic ocean analysis is focused on the mature stage of this and a second mcc in the episode in order to compare their major dynamic features to those of similar midlatitude systems reported in the literature and also to previous studies of tropical mesoscale convective systems many of the important characteristics of midlatitude mccs fo

morphological and sedimentary characteristics of dome dunes in the northeastern qaidam basin china abstract oval dome dunes which lack a slipface represent a specific phase of barchan dune evolution that has undergone distinctive morphodynamic processes in the northeastern qaidam basin china we measured the morphological parameters of 60 dome dunes by means of real time kinematic gps the dome dunes had an oval plan view and an asymmetrical side view with mean lengths of 14 49 and 13 26 m for the long and short axes respectively with mean windward and leeward slopes of 4 56 and 5 07 respectively dune heights ranged between 0 12 and 0 91 m and averaged 0 52 m by examining the characteristics of the dune sediments the internal sedimentary structures and regional wind regimes we found that local alluvial and fluvial sediments appear to provide the necessary materials for the dome dunes and that the dunes evolved from sand patches under a variable gentle winter wind according to our results and the andreotti saturation length theory we estimated the lengths at which the dome dunes disperse or begin to evolve into barchan dunes this knowledge will enhance our understanding of dome dune morphodynamic processes and improve numerical simulations of dune evolution

multiscale temporal variability of warm season precipitation over north america statistical analysis of radar measurements directionally averaged time series of precipitation rates for eight warm seasons 1996 2003 over the continental united states derived from next generation weather radar nexrad measurements are analyzed using spectral decomposition methods for the latitudinally averaged data in addition to previously identified diurnal and semidiurnal cycles the temporal spectra show cross scale self similarity and periodicity this property is revealed by a power law scaling with an exponent of 4 3 for the frequency band higher than semidiurnal and 3 4 for the 1 3 day band for the longitudinally averaged series the scaling exponent for the frequency band higher than semidiurnal changes from 4 3 to 5 3 revealing anisotropic properties the dominant periods and propagation speeds display temporal variability on about 1 2 1 4 11 and 25 days composite patterns describing periods of 5 days display the eastward propagation characteristic of classical mesoscale convective organization the lower frequency 5 days patterns propagate westward suggesting the influence of large scale waves and both dominant periods and propagation speeds show marked interannual variability the implied dependence between propagation and mean flow for 5 days is consistent with the macrophysics of warm season convective organization and extends known dynamical mechanisms to a statistical framework

some eulerian and lagrangian statistical properties of rainfall at small space time scales abstract management of urban hydrological systems requires a knowledge of short term and small scale rainfall properties small catchment areas dense building structures a high degree of impermeable areas and resulting rapid runoff mean that the properties of individual rain cells are important considerations accordingly this paper characterizes mainly spatial rainfall properties on a scale suitable for urban hydrology because of the usually dominant advective velocity component of individual rain cells the eulerian view observations of the moving rain cell by a fixed rain gage network gives a distorted picture in the direction of movement of the actual rain cell the extent of distortion depends on the magnitude of the advective velocity the lagrangian approach moving along with the same speed and direction as the cell gives different information regarding cell characteristics e g size compared with the eulerian approach it is shown that the lagrangian cell size as indicated by the spatial correlation structure on average is twice the size of the eulerian cell size thus it is argued that the lagrangian approach provides a more realistic picture of the rainfall structures compared with the eulerian approach the cell properties exhibit a temporal persistence of the spatial characteristics in the direction of movement this persistence is however not strong and thus a forecasting procedure using advection only does not seem appropriate

representing convective organization in prediction models by a hybrid strategy the mesoscale organization of precipitating convection is highly relevant to next generation global numerical weather prediction models which will have an intermediate horizontal resolution grid spacing about 10 km a primary issue is how to represent dynamical mechanisms that are conspicuously absent from contemporary convective parameterizations a hybrid parameterization of mesoscale convection is developed consisting of convective parameterization and explicit convectively driven circulations this kind of problem is addressed for warm season convection over the continental united states although it is argued to have more general application a hierarchical strategy is adopted cloud systemresolving model simulations represent the mesoscale dynamics of convective organization explicitly and intermediate resolution simulations involve the hybrid approach numerically simulated systems are physically interpreted by a mechanistic dynamical model of organized propagating convection this model is a formal basis for approximating mesoscale convective organization stratiform heating and mesoscale downdraft by a first baroclinic heating couplet the hybrid strategy is implemented using a predictor corrector strategy explicit dynamics is the predictor and the first baroclinic heating couplet the corrector the corrector strengthens the systematically weak mesoscale downdrafts that occur at intermediate resolution when introduced to the betts miller janjic convective parameterization this new hybrid approach represents the propagation and dynamical structure of organized precipitating systems therefore the predictor corrector hybrid approach is an elementary practical framework for representing organized convection in models of intermediate resolution

field measurements of mean and turbulent airflow over a barchan sand dune advances in our knowledge of the aeolian processes governing sand dune dynamics have been restricted by a reliance on measures of time averaged airflow such as shear velocity u it has become clear that such measures are incapable of explaining the complete dynamics of sediment transport across dune surfaces past evidence from wind tunnel and modelling studies has suggested that in some regions on a dune s surface the sediment transport might be better explained through investigations of the turbulent nature of the airflow however to date there have been no field studies providing data on the turbulent characteristics of the airflow around dunes with which to support or refute such hypotheses the field investigation presented here provides mean and turbulent airflow measurements across the centre line of a barchan sand dune in namibia data were collected using arrays of sonic anemometers and were compared with sand flux data measured using wedge shaped traps results support previously published data derived from wind tunnels and numerical models the decline in mean wind velocity at the upwind toe of the dune is shown to coincide with a rise in turbulence whilst mean velocity acceleration on the upper slope corresponds with a general decline in measured turbulence analysis of the components of reynold shear stress u w and normal stresses u 2 and w 2 supports the notion that the development of flow turbulence along the dune centre line is likely to be associated with the interplay between streamline curvature and mean flow deceleration acceleration it is suggested that due to the nature of its calculation turbulence intensity is a measure of less practical use than direct assessments of the individual components of reynolds stress particularly the instantaneous horizontal streamwise component u 2 and shear stress u w whilst increases in reynolds shear stress and the horizontal streamwise component of stress in the toe region of the dune may effectively explain the maintenance of sand flux in a region of declining mean velocity they have much less explanatory power for sand flux on the upper windward slope and in the crestal region of the dune here it is suggested that mean flow acceleration is likely to provide the most significant driving force on sand flux possibly augmented by a rise in the horizontal streamwise component of reynolds stress u 2 in the crest brink region therefore although wind turbulence is considered to be of fundamental importance in explaining the sediment transport dynamics across the dune s surface it is recognised that the interaction between mean flow deceleration acceleration streamline curvature and individual components of reynolds stress is complex and the identification of a single element of flow that offers a panacea for accounting for sand flux and dune dynamics is difficult to find

diurnal variations and modulation by easterly waves of the size distribution of convective cloud clusters over west africa and the atlantic ocean abstract using metecosat satellite data in the atmospheric infrared window the authors study short time scale fluctuations of the size distribution of tropical convective cloud clusters for july to september 1989 a cluster at a given brightness temperature threshold tir is defined as the area covered by adjacent cloudy pixels with brightness temperature lower than the threshold the clusters are classified according to the area they cover and the position of their center of mass over land regions of west africa the size distribution undergoes a very coherent diurnal behavior with development of small cells between noon and 1500 lst that later grow or merge into larger clusters over the atlantic ocean the highest cloudiness has a weak maximum extent in early morning while cloudiness at lower levels but with infrared brightness temperature tir 100 km at tir 218 k suggesting that the

space time structure of rain rate fields information on the spatial and temporal statistics of rain rate is needed for the design of remote sensing systems for the measurement of areal rainfall accumulation and for the design of millimeter wave communication systems in this study rain gage and radar data were used to determine empirically the spatial and temporal structure of the rain process as observed using rain rate as a tracer of the atmospheric motions and to test the validity of taylor s hypothesis for relating their spatial and temporal statistics weather radar derived rain rate maps were employed to obtain one and two dimensional spatial power spectra azimuthally averaged two dimensional spectra displayed the shape predicted for a passive scalar advected by a steady state field of two dimensional turbulence driven by the input of energy over a narrow band of wave numbers one dimensional spatial spectra for a short line of rain gages had the same spectral shape as the azimuthally averaged spectra obtained from the radar data temporal spectra from the gage time series were nearly identical in shape to the one dimensional spatial spectra if less than a half hour of data were processed to generate a spectrum and a constant translation velocity was assumed to relate themore temporal and spatial scales for spectra corresponding to longer durations a match could not be made less

sediment flux and airflow on the stoss slope of a barchan dune abstract measurements of sediment flux on the windward slope of an isolated barchan using an array of 30 sand traps provide new data that can constrain models of dune dynamics the data show that at low wind incident speeds flux increases up the dune exponentially whereas at higher wind speeds the increase with distance approaches linearity wind profile measurements conducted at the same time as the flux measurements indicate that although wind speed at a given height increases by 1 2 times from dune toe to brinkline wind shear velocity derived from the profile data decreases up the dune and is in many cases below transport threshold values this demonstrates that conventional wind profiles derived from anemometry on dunes do not measure the part of the boundary layer that is significant for sediment transport

the global population of mesoscale convective complexes a global set of 714 mesoscale convective complexes is compiled and some of the common properties of the convective systems are identified and examined from a global perspective the data set includes date of occurrence time of first storms initiation maximum extent termination duration cold cloud shield areas and tracks from initiation to termination it is found that the typical convective complex is nocturnal generates a cold cloud shield area of approximately 350 000 km2 and persists for about 10 h the largest systems and most persistent systems tend to occur near the summer solstices for the globe about 400 systems occur each year primarily over land areas most systems develop in favoured zones although some activity occurs over every continent except antarctica and all major oceans the concentration of activity into favoured zones indicates that there must be special dynamic and or thermodynamic conditions necessary for convection to organize into convective complexes activity is strongly tied to the solar day and shifts from 35 s in early january to about 50 n during the boreal summer and back to 35 s by december within the northern hemisphere there is a pronounced poleward migration as the jet stream shifts northward relatively little migration occurs in the ocean dominated southern hemisphere where the subtropical jet remains quasi stationary over the convective complex regions the nocturnal life cycles copious rainfall large cloud shields and great frequency of mesoscale convective complexes suggest that they may be significant contributors to the global hydrologic cycle and earth system energy budget

1 f noise and pulse like events in the tropical atmospheric surface variabilities this study discusses the 1 f noise behaviour and its connection with pulse like events in tropical surface meteorological data the 1 f noise withf being frequency refers to the unique spectrum shape of signals that represents the same degree of variability for a whole spectrum range with very long lag correlations the pulse like events are characterized by their high localizations in time and a lack of a distinct spectrum peak approximate 1 f noise behaviour is found in tropical surface temperature moisture and wind speed for periods of 1 hour to beyond 10 days and in oceanic wind stress up to 2 year periods the origin of the 1 f noise can be closely tied to pulse like events with a highly intermittent nature in the time series examples for such pulse like events include the cumulus convection events leading to convective downdraughts and intraseasonal westerly wind events associated with the madden julian oscillations mjo a method based on the wavelet is introduced to extract individual pulse like events these events are characterized by a 1 f spectrum extending up to 1 2 decades of frequency centred around their characteristic durations their successive occurrences are mutually uncorrelated and the individual pulse like events themselves constitute a 1 f spectrum for a frequency range around their durations the superposition of these events of various durations yields the 1 f noise spectrum for much wider ranges physical implications of these findings to convective quasi equilibrium and mjo el nino southern oscillation relationship are discussed copyright 2004 royal meteorological society

circulations associated with a mature to decaying midlatitude mesoscale convective system part ii upper level features abstract the vertical structure of a midtropospheric mesovortex that developed during the decay of a midlatitude mesoscale convective system over kansas and oklahoma on 23 24 june 1985 is documented surface rawinsonde wind profiler and dual doppler data are used to define its structure as has been observed in other midlatitude and tropical cases the mesovortex occurred within the trailing stratiform precipitation region of a squall line system it was associated with a preexisting synoptic scale short wave trough and as the circulation developed it deformed the back edge of the stratiform precipitation region into a hooklike pattern the 100 200 km mesovortex was confined to the midtroposphere 3 8 km with a maximum amplitude just above the 0 c level the vortex axis sloped toward the northeast but its orientation changed hour by hour over the 2 h period of dual doppler coverage overall the mesovortex was warm core although its thermal structure was complex and apparently significantly infl

large scale meteorological conditions associated with midlatitude mesoscale convective complexes abstract objective analyses of composited meteorological conditions attending ten mesoscale couvective complexes mcc reveal a number of distinctive characteristics and important interactions with the large scale environment the systems appear to be linked to eastward progression of a weak middle tropospheric short wave trough initial thunderstorms develop within a region of mesoscale convergence and lifting that is apparently forced primarily by low level warm advection the mcc system acquires mesoscale organization while it moves eastward ahead of the short wave trough diabatic heating eventually produces a system that is warm core in the middle troposphere and cold core in upper levels the mature mcc exhibits many similarities to tropical convective systems although it occurs within a considerably different large scale setting inflow within the lower half of the troposphere feeds convection within a region characterized by significant net upward mass flux and widespread precipitation thickne

an experimental study of turbulent flow over a low angle dune 1 many large sand bed alluvial channels are dominated by dunes that possess low angle lee sides often 10 which play a critical role in the transportation of sediment and generation of significant bed form roughness despite the fact that these low angle dunes are very common in such channels many current models of dune flow dynamics are based on bed forms with an angle of repose slip face that generates a zone of permanent separated flow in the dune lee study of flow associated with low angle dunes in the field is inherently difficult since it is usually both hard to measure very near the bed and hard to quantify the nature of turbulence over these bed forms results from a detailed scale model experimental study of flow over a low angle dune which is based on a prototype dune from the fraser river canada present a necessary link between flume and field studies and document the origins of macroturbulence associated with these bed forms two dimensional laser doppler anemometer measurements over a low angle dune maximum lower lee side slope 14 show that dune morphology exerts a dominant control on the turbulent flow causing flow deceleration in the lower lee and development of an intermittent layer of shear at the interface with the higher velocity flow above the scale model confirms that permanent flow separation does not occur over low angle dunes but instead is replaced by a small region here 7 of the dune wavelength in length of intermittent flow reversal which may be present for up to 4 of the time shear layers generated along this small zone of decelerated and or separated flow in the lower lee have a much smaller velocity differential than is characteristic of shear layers generated by flow separation in the lee of angle of repose dunes turbulence production associated with low angle dunes is dominated by eddies generated along this shear layer which produce highly variable horizontal and vertical velocities and large reynolds stresses in this region these results show that macroturbulence associated with low angle dunes is generated by intermittent separation or shear layer generation due to velocity gradients established in the zone of lee side flow expansion velocity profiles and maps of turbulence structure from the scale model are in reasonable agreement with field measurements from low angle dunes in natural sand bed rivers these results highlight the need to consider the temporal evolution and intermittency of shear layer behavior often very near the bed when interpreting the generation of macroturbulence and dispersal of sediment associated with low angle dunes

high frequency sediment transport responses on a vegetated foredune wind flow and sand transport intensity were measured on the seaward slope of a vegetated foredune during a 16 h storm using an array of sonic anemometers and wenglor laser particle counters the foredune had a compound seaward slope with a wave cut scarp about 0 5 m high separating the upper vegetated portion from the lower dune ramp which was bare of vegetation wind direction veered from obliquely offshore at the start of the event to obliquely onshore during the storm peak and finally to directly onshore during the final 2 h as wind speed dropped to below threshold sand transport was initially inhibited by a brief period of rain at the start of the event but as the surface dried and wind speed increased sand transport was initiated over the entire seaward slope transport intensity was quite variable both temporally and spatially on the upper slope as a result of fluctuating wind speed and direction but overall magnitudes were similar over the whole length ten minute average transport intensity correlates strongly with mean wind speed measured at the dune crest and there is also strong correlation between instantaneous wind speed and transport intensity measured at the same locations when the data are smoothed with a 10 s running mean transport on the beach for onshore winds is decoupled from that on the seaward slope above the small scarp when the wind angle is highly oblique but for wind angles 45 from shore perpendicular some sand is transported onto the lower slope copyright 2012 john wiley sons ltd

surface moisture induced feedback in aeolian environments aeolian dune development is influenced by feedback between surface properties and sediment transport yet little is known about the larger scale temporal and spatial natures of this relationship surface moisture is particularly influential and is generally recognized in aeolian environments for its ability to increase the critical shear velocity required to entrain sediment in beach settings or alternatively to sustain vegetation and stabilize surfaces at a dune field scale however conceptual models and field work have alluded to its importance in protodune initiation while field observations infer that seasonal moisture input may contribute to residual dune ridge formation at the dune field scale this has the potential to reveal geomorphic adaptation to variations in climate and identify a recognizable signature in the rock record this article presents a simulation model that produces geomorphological features similar to field observations and is capable of examining the implications of surface and transport feedback at both scales results 1 reveal the control of surface moisture at different temporal scales 2 display complexity in the development of multiple spatial scales within a cellular automaton framework 3 highlight the importance of transient sand strips and sediment supply frequency in aeolian transport dynamics and protodune development and 4 explore the relationship and significance of feedback duration development time and bedform spatial scale in the development of incipient dunes this study illustrates the importance of considering geomorphic feedback when assessing the influence of surface moisture in aeolian process dominated systems

coupling leeside grainfall to avalanche characteristics in aeolian dune dynamics avalanche grainflow processes are fundamental drivers of dune morphodynamics and are typically initiated by grainfall accumulations in sedimentary systems however the dynamism between grainfall and grainflow remains unspecified because simple measurements are hampered by the inherent instability of lee slopes here for the first time terrestrial laser scanning is used to quantify key aspects of the grainfall process on the lee slip face of a barchan sand dune we determine grainfall zone extent and flux and show their variability under differing wind speeds the increase in the downwind distance from the brink of peak grainfall under stronger winds provides a mechanism that explains the competence of large avalanches to descend the entire lee slope these findings highlight important interactions between wind speed grainfall and subsequent grainflow that influence dune migration rates and are important for correct interpretation of dune stratigraphy

mesoscale convective complexes in the western pacific region abstract a climatological study of mesoscale convective complexes mccs during 1983 1985 over the western pacific region wpr using full disc enhanced infrared satellite imagery from the japanese geostationary meteorological satellite is presented the results indicate that mccs are common in the wpr and display many of the same characteristics as those found in the americas the systems are nocturnal and tend to form over or in the immediate vicinity of land cold cloud shields in the americas last for about 10 h while wpr shields last about 11 h the cold cloud shield size distribution is similar to that of the americas with most systems exhibiting areas between 2 105 and 3 105 km2 seasonal distributions of wpr systems are also similar to that in the americas specifically the frequency of midlatitude systems peaks in late spring and early summer while low latitude mccs are distributed uniformly throughout the warm season as with western systems wpr mccs occur in preferred zones climatolog

velocity profiles measured on the windward slope of a transverse dune velocity gradients measured on the windward slope of a transverse dune show that flow acceleration strongly affects the turbulence structure of wind wind profiles measured below a height of 1 6m are nonlogarithmic and the altered nature of velocity profiles varies over the windward slope of a dune these findings suggest that calculated values of shear velocity are largely dependent upon the height and location of wind speed measurements as well as the strength of the prevailing wind moreover if bagnold type transport equations are used to calculate rates of sand transport on a dune wind speeds must be measured within 0 2 m of the dune surface if wind speeds are measured above this height the resulting errors in calculated shear velocity will manifest themselves as errors in calculated rates of sand transport if rates of sand transport are derived from wind speeds measured above 0 2 m the calculated rates may underestimate sand transport on the windward face of a dune as a result of flow acceleration in contrast if a dune has a separate crest upwind of the brink the expansion and subsequent deceleration of flow downwind from the crest may result in an overestimation of sand transport

a composite model of mesoscale convective complexes abstract a composite analysis technique is used to investigate the evolution of mesoscale features of mesoscale convective complexes mccs the early stage of the mcc lifecycle is characterized by convergence vertical motion and heating being centered in the lower troposphere as the mcc matures the level of peak upward motion and heating shifts to the upper troposphere the system achieves and maintains its maximum divergence upward motion and anticyclonic vorticity in the upper troposphere during the latter half of the life cycle this is in contrast to gate tropical clusters where the maximum divergence upward motion and anticyclonic vorticity occurred at the mature stage of the cluster and then weakened this difference might be explained by an mcc being an inertially stable form of mesoscale convective system whose radius exceeds the rossby radius of deformation the mcc is shown to be an efficient rain producer exhibiting a precipitation efficiency exceeding 100 at the mature stage due to th

a continuous model for sand dunes review new developments and application to barchan dunes and barchan dune fields basically sand dunes are patterns resulting from the coupling of hydrodynamic and sediment transport once grains move they modify the surface topography which in turns modifies the flow this important feedback mechanism lies at the core of continuous dune modelling here we present an updated review of such a model for aeolian dunes including important modifications to improve its predicting power for instance we add a more realistic wind model and provide a self consistent set of parameters independently validated as an example we are able to simulate realistic barchan dunes which are the basic solution of the model in the condition of unidirectional flow and scarce sediments from the simulation we extract new relations describing the morphology and dynamics of barchans that compare very well with existing field data next we revisit the problem of the stability of barchan dunes and argue that they are intrinsically unstable bed forms finally we perform more complex simulations first a barchan dune under variable wind strength and second barchan dune fields under different boundary conditions the latter has important implications for the problem of the genesis of barchan dunes copyright 2010 john wiley sons ltd

skolithos in a permian braided river deposit southern victoria land antarctica abstract skolithos burrows have been found in a permian braided river deposit the lower feather conglomerate of southern victoria land antarctica they are straight vertical 1 cm in diameter and up to 30 cm deep the host sediment varies from fine to very coarse sandstone and even in places fine conglomerate they are most abundant in coarse sandstone where they form densely packed clusters and have destroyed virtually all stratification they are less common in fine and medium sandstone and fine conglomerate they appear to be identical to skolithos linearis the sedimentary facies paleocurrent measurements and especially the well developed paleosols of the lower feather conglomerate provide a clear and consistent picture of rapid but intermittent deposition in relatively small shallow river channels in a high plains setting and a temperate sub humid to humid climate it is thought that the burrows are dwelling structures of worm like organisms that responded to a fluctuating water table in the same way that polychaetes in a modern coastal setting respond to tidal changes in water level we conclude that skolithos can no longer be used as it has in the past as an unequivocal indicator of coastal deposition

the role of streamline curvature in sand dune dynamics evidence from field and wind tunnel measurements abstract field measurements on an unvegetated 10 m high barchan dune in oman are compared with measurements over a 1 200 scale fixed model in a wind tunnel both the field and wind tunnel data demonstrate similar patterns of wind and shear velocity over the dune confirming significant flow deceleration upwind of and at the toe of the dune acceleration of flow up the windward slope and deceleration between the crest and brink this pattern including the widely reported upwind reduction in shear velocity reflects observations of previous studies such a reduction in shear velocity upwind of the dune should result in a reduction in sand transport and subsequent sand deposition this is not observed in the field wind tunnel modelling using a near surface pulse wire probe suggests that the field method of shear velocity derivation is inadequate the wind tunnel results exhibit no reduction in shear velocity upwind of or at the toe of the dune evidence provided by reynolds stress profiles and turbulence intensities measured in the wind tunnel suggest that this maintenance of upwind shear stress may be a result of concave unstable streamline curvature these additional surface stresses are not recorded by the techniques used in the field measurements using the occurrence of streamline curvature as a starting point a new 2 d model of dune dynamics is deduced this model relies on the establishment of an equilibrium between windward slope morphology surface stresses induced by streamline curvature and streamwise acceleration adopting the criteria that concave streamline curvature and streamwise acceleration both increase surface shear stress whereas convex streamline curvature and deceleration have the opposite effect the relationships between form and process are investigated in each of three morphologically distinct zones the upwind interdune and concave toe region of the dune the convex portion of the windward slope and the crest brink region the applicability of the model is supported by measurements of the rate of sand transport and the change of the dune surface in the field

space time variability of the rainfall over the western mediterranean region a statistical analysis 1 this study aims at better understanding the space time statistical properties of rain over a mediterranean region to this end we analyzed temporal spatial and spatio temporal spectra of rain field maps provided by an x band radar situated in the southeast part of france the database extends from 2009 to 2012 and has a spatial and temporal resolution of 1 km2 and 5 min the analysis highlights several scaling regimes which are interpreted in terms of meteorological structures convective cells mesoscale structures and midlatitude cyclones the analysis of spectra per month confirms the dependency of the spectral signature to the underlying meteorological process nevertheless our results also reveal that for a given range of scales 20 45 min in time and 7 20 km in space spectral slope is monthly invariant it means that rain behaves identically in terms of scaling whatever the mechanism that generated it convection front moreover spectral analysis shows that the temporal decorrelation scale is 10 days which can possibly be related to the longest lifetime of a meteorological phenomenon in the region i e about 10 days an approach to compute the scaling anisotropy between space and time is proposed it reveals that over two distinct ranges of scales 7 20 km 20 45 min and 20 70 km 45 min 3 h the scaling anisotropic coefficient is equal to 2 it also reveals that the ratio of spectral slope of 2 d angle averaged spatial spectrum versus 1 d temporal spectrum is equal to 1 over these ranges of scales it suggests a similarity in the second order properties e g correlation of temporal and spatial rain field all these results are important to better understand rainfall statistical behavior and could also be used for the development of downscaling schemes and the validation of numerical weather models

trace fossils in fluvial deposits of the duchesne river formation eocene uinta basin utah abstract a diverse suite of nonmarine trace fossils is present in a late eocene sandstone siltstone mustone sequence in the duchesne river formation of northeastern utah on the basis of primary sedimentary structures and stratification sequences the beds are interpreted as deposits in meandering and braided stream environments the trace fossils include ancorichnus muensteria m palaeophycus scoyenia skolithos two unidentified ichnotaxa and rhizoliths insects and oligochaetes apparently made most of the animal traces in moistor wet cohesive stream sediment during subaerial exposure or under thin water cover

teredolites wood substrates and sea level dynamics allochthonous logs and or teredolites clavate borings produced within xylic wood substrates occur in extraordinary abundance as sedimentary components in transgressive marine shelf deposits of the lower paleocene clayton formation in western alabama it is pro posed herein that the abundance and preservational state of these components were controlled by 1 an influx pulse of xylic substrates into marine and marginal marine environments 2 hydraulic concentration of substrates during ravinement and 3 condensation associated with sediment starvation all three of which are induced by sea level rise the proposed relations among fossil wood ichnofossils produced therein and sea level dynamics may be of use in the discrimination of sequence stratigraphic packages and their bounding surfaces these relations also have implications for paleobotanical prospecting and the biological evolution and stratigraphic distribution of marine organisms that inhabit xylic substrates

crescentic dunes at schiermonnikoog the netherlands this paper describes the appearance and maintenance of crescentic dunes in high wind speed conditions on a frozen beach at schiermonnikoog the netherlands the dunes were cresentic forms with horns they were barchanoidal in plan view but had reverse morphologies to typical barchans the highest and steepest slopes were upwind and led to long low slopes downwind slipfaces were absent it is hypothesized that such crescentic dunes may be a stable aerodynamic form under high to very high c 15 20 m s 1 flow conditions 1997 by john wiley sons ltd

amazon coastal squall lines part i structure and kinematics abstract mesoscale to synoptic scale squall lines that form along the northeastern coast of south america as sea breeze induced instability lines and propagate through the amazon basin are investigated using data collected during the april may 1987 amazon boundary layer experiment able 2b these systems termed amazon coastal squall lines acsl have been noted by others but details of the structure and evolution of the acsl are limited the present paper uses geostationary operational environmental satellite radar upper air rawinsonde and surface portable automated mesonet data to describe the structure dynamics and life cycle of the acsl twelve acsl were sampled during able 2b and three cases are discussed in detail the acsl are discontinuous lines of organized mesoscale cloud clusters that propagate across the central amazon basin at speeds of 50 60 km h 1 the acsl undergo six possible life cycle stages coastal genesis intensification maturity weakening reintensification and dissip