polarimetric and dual doppler radar observations of the lipscomb county texas supercell thunderstorm on 23 may 2002 abstract polarimetric and dual doppler observations of a supercell observed by the national center for atmospheric research ncar s band polarimetric spol radar two doppler on wheels dow radars and the greek xpol radar on 23 may 2002 during the international h2o project ihop are presented the polarimetric radar observations began as the storm organized into a supercell and continued for over an hour while the storm was in its mature phase the hydrometeor distribution within the mature storm was retrieved using a fuzzy logic hydrometeor classification algorithm the dual doppler radar observations began around the time that the polarimetric radar observations concluded and they covered the end of the mature phase and much of the dissipation phase of the storm the dual doppler wind syntheses are used to evaluate the importance of the forward flank outflow in augmenting the horizontal vorticity field near the storm above 400 m in this case having a relatively weak low level mesocyclone the pa

frequency and magnitude biases in the fryberger model with implications for characterizing geomorphically effective winds abstract the fryberger model uses standardized wind data to estimate regional aeolian sediment drift potential dp which allows for interpretation and classification of aeolian dune landscapes this paper identifies systematic frequency and magnitude biases in the model that result from i variations in wind direction sector range which affects frequency bin size for determining percent occurrence of transporting winds and ii use of wind speed class mid point values over more statistically representative values e g mean median or minimally classified whole knot wind speeds in the magnitude weighting factor for dp calculations the significance of these biases is tested using unclassified data from stanhope prince edward island canada frequency bias resulting from wind data aggregation into direction sectors of varying size produces statistically significant discrepancies in dp and rdp estimates for this dataset when 36 point 10 s of degree data are reduced to 16 sectors cardinal directions receive one extra direction class and the magnitude of dp and rdp values decreases by 1 4 and 2 8 respectively compared to 16 equal 22 5 sectors derived from original data this results from under representation of intermediate direction classes for this dataset the effects on rdd less than 1 and directional variability ratio rdp dp are insignificant magnitude biases result from the use of the wind speed class mid point values instead of other statistically representative measures of wind speed in dp calculations in that wind speed distributions are often positively skewed mid point values yield an over estimate of total dp by as much as 34 and rdp by up to 22 for this dataset over those derived using mean median and whole knot minimally classified values this difference is statistically significantly at both the individual wind speed direction category level and at the aggregate directionally summed level and causes rdp vectors to shift 3 5 to the south though the impacts of these frequency magnitude biases are site specific and modest the effects on rdp estimation may be more significant in complex i e multi modal wind regimes and or in environments with more frequent high magnitude winds from the cardinal directions given the increased availability of more precise unclassified wind data most of these systematic frequency magnitude biases can be avoided recommendations on reducing inaccuracies imposed by these biases include i using to the degree wind data where available and categorizing into 16 equal 22 5 direction sectors ii using either wind speed class statistical mean values or minimally classified whole knot values in dp calculations and iii recognizing that converting 36 point 10 s of degrees data to 16 direction classes may introduce a frequency bias toward the cardinal directions and will cause inaccuracies in dp and rdp estimates of an amount that depends on the wind regime further research is needed to assess the implications of such biases in different wind regimes and into the influence of localized supply and transport limiting factors on regional scale assessments of dune morphodynamics and mobility these findings are also relevant for other applications that use categorized wind speed direction data such as dust or contaminant plume dispersion modelling

late quaternary coastal evolution and aeolian sedimentation in the tectonically active southern atacama desert chile abstract analyses of aeolianites and associated dune surficial carbonate and marine terrace sediments from north central chile 27 54 s yield a record of environmental change for the coastal southern atacama desert spanning at least the last glacial interglacial cycle optically stimulated luminescence dating indicates phases of aeolian dune construction at around 130 111 98 77 69 and 41 28 ka thin section and stable carbon and oxygen isotope analyses suggest a predominantly marine sediment source for the three oldest dune phases aeolianites appear to have accumulated mainly from tectonically uplifted interglacial marine sediments that were deflated during windier and or stormier intervals bedding orientations indicate that sand transporting winds varied in direction from s ese during mis 5e and wnw ese during mis 5c 5a winds from the southeast quadrant are unusual today in this region of the atacama suggesting either major shifts in atmospheric circulation or topographic airflow modification thin section evidence indicates that the aeolianites were cemented by two phases of vadose carbonate tentatively linked to wetter periods around 70 and 45 ka tectonic uplift in the area has proceeded at an average rate of 305 542 mm kyr 1 the study illustrates the complexity of understanding onshore offshore sediment fluxes in the context of late quaternary sea level fluctuations for an area undergoing rapid tectonic uplift

the effect of wind speed averaging time on the calculation of sand drift potential new scaling laws abstract drift potential dp is a key factor used to quantify aeolian sand transport and it is often used for predicting wind erosion and dune mobility under climate change scenarios it is proportional to the mean of the cube of the wind speed at a 10 m height when that wind speed is above 6 2 m s 12 knots a speed threshold above which sand can be transported by the wind dp depends on the temporal resolution and the averaging time of the wind velocity measurements usually either a 10 min or 1 h mean wind speed is used to calculate the dp although different studies have used different averaging periods for calculating the mean wind speed and consequently the dp here we perform a comprehensive analysis of an extensive long term wind speed database from different locations around the world and from reanalysis data sources and show that dp decreases with the averaging time of the wind speed the decrease of dp versus the averaging time interval can be approximated by a stretched exponential function in addition the relative decrease of dp as a function of the maximum dp is smaller for high wind speed sites this result is a consequence of the fact that high dp sites are characterized by longer clusters of successive wind speed events above the threshold velocity they are thus less affected by the time averaging process interestingly the clusters lengths decay exponentially with wind speed and faster for low dp sites our new results have important implications for calculating the effective dp and for better estimating the biases that result from using wind data with different averaging times which is a common problem in aeolian research we also found an approximate linear relation between dp and the wind power that is close to the analytic approximation for the relation between the two this new finding has many important applications since it will allow one to calculate dp from wind power data and vice versa in addition it implies that the same scaling laws found for dp also exist for the wind power

megaripple flattening due to strong winds abstract megaripples in nahal kasuy in the southern negev desert of israel are characterized by a mean wavelength of about 70 cm and by a bimodal distribution of coarse and fine particle sizes the latter property being a pre requisite for their formation in our three year project megaripple development was monitored using a digital elevation model dem constructed from above ground stereo digital photographs temporal dynamics of wind power drift potential dp were measured and grain size analyses were performed on samples taken from different parts of the megaripple the coarse grains that protect the crest enable the ripple to grow but when ripple height becomes too high the bed shear stress increases thus allowing the wind to move the armoring layer when this happens during strong wind storms the megaripple will flatten and even disappear as was observed in our field study we present measurements that for the first time directly show the megaripple to normal ripple transition and we suggest two possible physical processes as potential causes of this phenomenon megaripple flattening can occur either when the wind exceeds the fluid threshold for a sufficient length of time or after a sequence of storms with winds blowing from the same direction

aeolian system responses to global change challenges of scale process and temporal integration aeolian sediment systems are extensive components of the earth s surface not just in today s active desert environments but in coastal locations and as presently stable loess and peri desert ergs all these systems are subject to potentially significant 21st century changes in dynamics due to global warming impacts on atmospheric circulation sediment moisture and vegetation cover but do we know enough in the critical areas of science to allow robust models of likely future dynamics to be developed since the establishment of modern aeolian science research has largely taken two divergent routes 1 small scale investigations of the processes of wind shear sediment entrainment and transportation and 2 landform and landscape analyses with bedform systems described and relationships to circulation explained an intermediate sedimentological route has generated attempts towards a more integrated understanding of system behaviour at a range of scales four recent developments provide the potential for more robust multiscale integrations of aeolian system behaviour these are 1 advances in empirical measurement that allow wind power and sediment flux relations to be better described 2 modelling of dune and dust dynamics and interactions with key controls 3 monitoring systems that allow high resolution observations of sediment flux variations to be recognized and aeolian deposit structures to be understood and 4 chronometric advances that permit the assessment of the frequency and drivers of dune system activity in the past we explore and analyse these methodological advances and their potential contribution to the multiscale integrations that are essential for better informed predictions of future global aeolian system dynamics considering whether the integration of these advances in reductionist and holistic elements of aeolian science represent an example of the effective application of the principles of earth system science copyright 2008 john wiley sons ltd

the lagrange tornado during vortex2 part i photogrammetric analysis of the tornado combined with single doppler radar data abstractthis study presents a single doppler radar analysis combined with cloud photography of the lagrange wyoming tornado on 5 june 2009 in an attempt to relate the radar observed hook echo weak echo hole weh and rotational couplet to the visual characteristics of the tornado the tornado was rated ef2 the circulation at low levels went through two intensification periods based on azimuthal shear measurements the first intensification was followed by the appearance of a brief funnel cloud the second intensification was coincident with the appearance of a second funnel cloud that remained in contact with the ground until the tornado dissipated a deep weh rapidly formed within the hook echo after damaging wind was identified at the ground and before the appearance of a funnel cloud the echo pattern through the hook echo on 5 june undergoes a dramatic evolution initially the minimum radar reflectivities are near the surface 15 dbz and the weh does not suggest a tapered structure near the gro

spatial temporal evolution of aeolian blowout dunes at cape cod abstract this paper explores historical evolution of blowouts at cape cod national seashore ccns usa a site that hosts one of the world s highest densities of active and stabilized blowouts the spatial temporal analysis of moving polygons stamp method is applied to a multi decadal dataset of aerial photography and lidar to extract patterns of two dimensional movement and morphometric changes in erosional deflation basins and depositional lobes blowout development in ccns is characterized by several geometric overlap and movement proximity responses including i generation and disappearance ii extension and contraction iii union or division iv clustering and v divergence by stabilization other possible movement events include migration amalgamation and proximal stabilization but they were not observed in this study generation events were more frequent than disappearance events the former were highest between 1985 and 1994 while the latter were highest between 2000 and 2005 high rates of areal change in erosional basins occurred between 1998 and 2000 3932 m2 a 1 the lowest rate 333 m2 a 1 between 2005 and 2009 and the maximum rate 4589 m2 a 1 between 2009 and 2011 union events occurred mostly in recent years 2000 2012 while only one division was observed earlier 1985 1994 net areal changes of lobes showed gradual growth from a period of contraction 1119 m2 a 1 between 1998 and 2000 to rapid extension 2030 m2 a 1 by 2010 which is roughly concurrent with rapid growth of erosional basins between 2005 and 2009 blowouts extended radially in this multi modal wind regime and despite odd shapes initially they became simpler in form more circular and larger over time net extension of erosional basins was toward ese 109 while depositional lobes extended sse 147 lobes were aligned with the strongest winter sand drift vector although their magnitude of areal extension was only 33 that of the basins these differences in extension responses likely result from more complex and evolving flow form interactions inside erosional basins historical photographs and ccns documents suggest that blowout evolution may be influenced by land use changes such as revegetation campaigns in 1985 that were followed by high blowout generation high magnitude regional storm events e g hurricanes also play a role the analytical framework presented provides a systematic means for two dimensional geomorphic change detection and pattern analysis that can be applied to other landscapes

regional wind fields and dunefield migration southern brazil this paper examines a seemingly anomalous situation in southern brazil where the dunefields on santa catarina island e g joaquina beach migrate to the nnw almost completely the opposite direction c 160 to the dunefields immediately to the south e g pinheira beach and some much further to the north e g cabo frio which migrate to the ssw a variety of mechanisms are examined to explain the differences in dunefield migration including grain size variations topographic effects on local winds shoreline orientation and regional wind field changes the mean grain sizes of the two beaches pinheira and joaquina are not sufficiently different to restrict aeolian sediment transport in either place nor to account for a lack of transport from the nne to the ssw in the case of joaquina some topographic steering of the wind is likely but could not account for the long term average difference in migration trends of the island dunefields compared to the mainland dunefields while the orientation of the shoreline to prevailing winds is an important control on beach and dune sediment transport it is not the dominant controlling mechanism an analysis of the regional wind patterns demonstrates that there is a major shift in the regional wind field near the island such that the dominant island winds blow from the sw ssw while those further south blow from the ne it is concluded that this is the predominant reason for the divergence in the direction of migration of the dunefields copyright 2006 john wiley sons ltd

environmental controls morphodynamic processes and ecogeomorphic interactions of barchan to parabolic dune transformations the transformation of barchans into parabolic dunes has been observed in various dune systems around the world precise details of how environmental controls influence the dune transformation and stabilisation mechanism however remain poorly understood a horns anchoring mechanism and a nebkhas initiation mechanism have previously been proposed and selected environmental controls on the transformation have been explored by some modelling efforts but the morphodynamic processes and eco geomorphic interactions involved are unclear and comparison between different dune systems is challenging this study extends a cellular automaton model informed by empirical data from fieldwork and remote sensing to fully explore how vegetation characteristics boundary conditions and wind regime influence the transformation process and the resulting dune morphologies a dynamic growth function is introduced for clump like perennials to differentiate between growing and non growing seasons and to simulate the development of young plants into mature plants over multiple years modelling results show that environmental parameters interact with each other in a complex manner to impact the transformation process the study finds a fundamental power law relation between a non dimensional parameter group so called the dune stabilising index s and the normalised migration distance of the transforming dune which can be used to reconstruct paleo environmental conditions and monitor the impacts of changes in climate or land use on a dune system four basic eco geomorphic interaction zones are identified which bear different functionality in the barchan to parabolic dune transformation the roles of different environmental controls in changing the eco geomorphic interaction zones transforming processes and resulting dune morphologies are also clarified

dunes on planet tatooine observation of barchan migration at the star wars film set in tunisia abstract sand dune migration is documented with a readily available tool google earth near chott el gharsa just north west of tozeur tunisia as fiducial markers we employ a set of buildings used to portray the fictional city mos espa this set of 20 buildings over roughly a hectare was constructed in 1997 for the movie star wars episode 1 the phantom menace the site now lies between the arms of a large pudgy barchan dune which has been documented via satellite imaging in 2002 2004 2008 and 2009 to have moved from 140 m away to only 10 m away visits by the authors to the site in 2009 and 2011 confirm the barchan to be in a threatening position a smaller set nearby was substantially damaged by being overrun by dunes circa 2004 the migration rate of 15 m yr decreases over the observation period possibly as a result of increased local rainfall and is consistent with barchan migration rates observed at other locations worldwide the migration rate of this and two other barchans suggests sand transport of 50 m3 m yr somewhat higher than would be suggested by traditional wind rose calculations we explore possible reasons for this discrepancy because of the link to popular science fiction the site may be of pedagogical interest in teaching remote sensing and geomorphic change we also note that nearby playa surfaces and agricultural areas have a time variable appearance the site s popularity as a destination for star wars enthusiasts results in many photographs being posted on the internet providing a rich set of in situ imagery for continued monitoring in the absence of dedicated field visits

unveiling past aeolian landscapes a ground penetrating radar survey of a holocene coastal dunefield system thy denmark abstract the southern part of the hvidbjerg coastal dunefield and the adjacent part of the lodbjerg coastal dunefield system in northwestern denmark has been mapped using ground penetrating radar coastal cliff exposures and 14 c datings indicate that the presently stabilized dunefield is underlain by a 10 15 m thick succession of holocene aeolian sand deposits and interbedded peaty palaeosols this succession is superimposed on a weichselian till towards the south and a mid holocene beach ridge and swash bar complex towards the north the peaty palaeosols represent preceding periods of dunefield stabilization these palaeosols reveal ages about ad 1100 1200 700 bc and 2100 bc and act as marker horizons in the study area more than 16 km of high resolution gpr data covering an area of 6 km 2 were collected in the near coastal part of the dunefields and enabled a correlation of these marker horizons across the dunefields these data allowed the elaboration of topographic subsurface and isopach maps and enabled an interpretation of the accumulation history of the aeolian system since about 2200 bc this accumulation history tells of alternating periods with a stabilization of the dunefields and periods with high sand accumulation basically a perched ground water level and the morphology of the previous stabilized dunefield made it possible to generate an accumulation space large enough to preserve the sand during periods with stronger winds and marked aeolian activity this 3d mapping of the stabilized dunefield subsurfaces has made it possible to unveil the development of the past aeolian landscape

chevrons origin and relevance for the reconstruction of past wind regimes abstract since its first use in the late 80 s the term chevron has been employed in numerous studies to describe large u and v shaped ridges found in or near shorelines worldwide most studies have so far focused on bahamian chevrons that are exclusively of late pleistocene age and on the supposed holocene chevrons found in s madagascar and australia in the bahamas these deposits have been interpreted as the product of extreme storms at the end of the last interglacial lig warm period in contrast the extensive chevrons complex exposed in s madagascar and on the western coast of australia have been associated with a tsunami induced by a meteorite impact finally several authors have also proposed a non catastrophic i e eolian origin based on the recognized importance of wind related processes in these coastal areas and term such deposits parabolic dunes in this paper we collect and synthesize existing data on the morphology sedimentology and age of these chevrons and review the different interpretations proposed in the literature with the aim to lay out a consistent database to assist further investigations on these important coastal morphologies in addition we generated a synthesis of wind data at the three study areas which highlights the relationship between present wind regimes and chevrons morphologies the ubiquity of chevrons likely actually parabolic dunes in coastal areas around the globe and their relationship with coastal processes makes them crucial archives for reconstructing past wind regimes

owens lake dune fields composition sources of sand and transport pathways abstract in this paper we describe the mineral and grain size compositions of sand from the major dune areas adjacent to the now dry owens lake california and compare them with sand from potential sources including washes draining the inyo and coso ranges to the east and south of the basin as well as to the owens river and washes draining the sierra nevada which lies to the west of the owens valley and owens lake the semi quantitative mineral compositional data indicate that the dune sands are all very similar and are composed of approximately 47 quartz 33 plagioclase and 13 potassium feldspar with minor amounts of calcite and other minerals the relative proportions of quartz plagioclase and k feldspar indicate that the sands are derived from granodioritic source rocks it is therefore considered that the primary source of sand for dune fields in the owens lake basin is sediment derived from the sierra nevada via the owens river from the north as well as from granitic rocks in the coso range to the south sediment from fluvial and alluvial sources reached the dune fields in the northeastern sector of the basin by wind transport across the exposed bed of owens lake during periods of low lake levels the pathway by which sand reached the olancha dunes located to the south of the lake is less clear but probably involved transport from the south sand sheet via the dirty socks dunes the source of sand for the south sand sheet area is hypothesized to be the adjacent vermillion canyon wash system draining the coso range

grain size characteristics of dune sands in the central taklimakan sand sea abstract compared with the sand grain size of the other sand seas central taklimakan sand sea has some of the finest sands seen globally the dunes are composed of fine and very fine sands with a diameter between 2 00 and 4 00 0 25 0 063 mm there are differences in the grain size distributions for different dune types mean grain size of the compound complex crescent dune sands is 3 08 the compound dome dunes 3 21 the compound complex linear dune sands between 2 63 and 3 41 and the star dunes 2 81 from the northern edge of the sand sea towards southern edge the components of fine and very fine sands increase closely related to the wind regimes time scale for dune development and underlying sediments compared with the foregoing there are some differences for the compound complex linear dunes in the centre of taklimakan though the pattern of coarser crests does exist the sorting parameters indicate that the sands on the west flank of compound complex linear dunes are better sorted than that on the east flank and crest sampling on the superimposed dunes developed on the surface of the complex linear dunes suggests that the patterns of finer crest coarser crest all existed in central taklimakan under the conditions of low energy wind regime when fine sand is available the frequency of the pattern for finer crest and better sorting will increase sampling on the simple crescent dunes developed on the interdunes suggests that the simple dunes are developed originally with nearly the same grain size distributions and parameters with the development of the dunes and evolution of the dune morphology the grain size distributions of the dune sands varied under the actions of the wind regimes time scale and underlying sediments

dune sand transport as influenced by wind directions speed and frequencies in the ordos plateau china the ordos plateau in china is a region with extensive wind erosion severe desertification and various aeolian sand hazards in order to determine aeolian sand transport in this region the relationship between the sand transport rate and wind speed at 10 min frequencies was established by field observation in both the qubqi sand desert and the mu us sandy land threshold wind speeds 2 m above the ground for mobile semi fixed and fixed dune surfaces were estimated by field observations the sand transport rate increased with the increase of the bare land ratio and near bed wind speed high resolution meteorological 10 min average wind velocity data at 10 m above the ground were converted into velocity values at a height of 2 m to calculate sand transport potential based on three specific parameters decisive for sand transport wind speed duration and direction the quantity of aeolian sand transported was calculated for various wind speed levels and directions and the overall characteristics of sand transport on different dune surface types were determined by vector operation techniques sand transporting winds took place mainly in springtime the prevailing wind directions were w wnw and nw with a frequency of more than 60 in total and sand transport in these directions made up more than 70 of the total transport corresponding to a general southeastward encroachment of aeolian sand in the study area the relationship between wind frequency and speed can be expressed by a power function high magnitude strong winds had a low frequency but they played a dominant role in aeolian sand transport

three years of morphologic changes at a bowl blowout cape cod usa this study presents measurements of blowout topography obtained with annual terrestrial laser surveys carried out over a three year period at a single large bowl blowout located in the provincelands dunes section of cape cod national seashore in massachusetts the study blowout was selected because its axis is aligned with northwest winds that dominate the region and because it was seemingly interacting with a smaller saucer blowout that had recently formed on the southern rim of the primary feature assuming that blowouts enlarge both horizontally and vertically in response to the wind regime the objectives of the study were to determine both the amount of horizontal growth that the blowout experiences annually and the spatial patterns of vertical change that occur within the blowout changes to the blowout lobe surrounding the feature were also determined for areas with sparse enough vegetation cover to allow laser returns from the sand surface the results show that the blowout consistently expanded outward during the three years with the greatest expansion occurring at its southeast corner opposite the prevailing winds the most significant occurrence was the removal in the first year of the ridge that separated the two blowouts resulting in a major horizontal shift of the southern rim of the new combined blowout this displacement then continued at a lesser rate in subsequent years the rim also shifted horizontally along the northwest to northeast sections of the blowout significant vertical loss occurred along the main axis of the blowout with the greatest loss concentrated along the southeast rim on the lobe there were large areas of deposition immediately downwind of the high erosion zones inside the blowout however there were also small erosion areas on the lobe extending downwind from eroding sections of the rim this study shows that 1 blowouts can experience significant areal and volumetric changes in short periods of time 2 significant changes may occur relatively suddenly when adjacent blowouts combine into a single feature and 3 the sediment transport paths are highly controlled by the topography the joining of two blowouts not only creates a new larger feature but it also releases large amounts of sediment that are then distributed across the landscape downwind creating a potential for major changes to a landscape over the longer term

formation of aeolian dunes on anholt denmark since ad 1560 a record of deforestation and increased storminess abstract sand dunes on the island of anholt denmark in the middle of kattegat form a relatively barren temperate climate aeolian system locally termed the desert the dunes have developed on top of a raised beach ridge system under the influence of dominant winds from westerly directions they are relatively coarse grained with an average mean grain size of 480 m the last phase of aeolian activity and dune formation on anholt started after ad 1560 when the local pine forest was removed historical sources report intense sand mobilization in the 17th century and new optically stimulated luminescence osl dates indicate that dune formation continued until the end of the 19th century this period of sand drift and dune formation took place during the later part of the little ice age which is characterized by increased summer storminess in large parts of nw europe dune stabilization in the beginning of the 20th century probably records a temporary decrease in storminess ground penetrating radar mapping of the internal structures in two dunes in the western part of the desert a parabolic dune and a linear dune indicates the importance of north westerly storm winds during dune formation

formation of the highest sand dunes on earth characterization of dune morphology has historically been based on relationships between dune forms and wind regimes with dune height shown to be sensitive to atmospheric boundary layer depth sand availability and sediment properties while these parameters have been used in numerical simulations to model the occurrences of some types of dunes they cannot alone explain the great diversity in form and size seen on earth and on other solar system bodies here we present results from our studies of dune formation in the badain jaran desert in western china where earth s tallest dunes occur we measured the variability of the dune morphology in this desert on the basis of landsat etm data and we detected the bedrock landforms beneath the aeolian sands by applying gravity methods wind records from stations at the periphery of the desert and srtm topographical data were examined also to augment the interpretation our studies demonstrate that in addition to average wind parameters dune height is highly sensitive to local geology subsurface characteristics and topography and interactions between changing climate conditions and aeolian and fluvial processes these additional factors need to be considered in the interpretation and simulation of dunes on earth we anticipate that analysis of anomalous dune heights like those seen in the badain jaran may also provide critical information on subsurface characteristics and environmental conditions on earth and on other planetary bodies

wind energy environments and dunefield activity in the chinese deserts there are few detailed analyses of the wind energy environments and dunefield activity in the chinese deserts on the basis of wind data and other climatic parameters collected at meteorological stations in and around the deserts this paper considers wind environments and dunefield activity in the chinese deserts in the 1990s the results show that dunes in most of the deserts were developed and controlled by low energy wind regimes although most dunes had the morphology of transverse and linear types which is consistent with wind regimes some deserts did not show close relations between dune morphology and regional wind directional distributions due to other controls although sand transport mainly occurs in spring and early summer there is strong sand transport activity in winter in some deserts dune activity in the chinese deserts has great spatial variations the regions with low dune activity are located in the chaidm mu us hobq horqin and nenjiang deserts due to much higher annual precipitation in these regions the areas with strong dune activity are located in the eastern taklimakan and northern badain jaran deserts due to arid conditions and much stronger winds

modelling the formation of residual dune ridges behind barchan dunes in north east brazil residual dune ridges are often formed by vegetation growing along a line some distance upwind of the lower stoss slope of migrating dunes this process is common in areas where vegetation germinates along the edge of the water during the rainy period when the water level is higher and interdune areas are flooded the phenomenon occurs on a large scale in north east brazil because of the rise and fall in groundwater level at the end of the rainy season each residual dune ridge corresponds to the position of the dune during the wet period in each year therefore variations in the distance between these residual dune ridges could be used potentially to monitor climatic fluctuations in rainfall and wind to examine the potential use of these residual dune ridges for the reconstruction of past climatic fluctuations a model that simulates them under varying conditions of wind rainfall and evaporation rates was formulated the model was tested for sensitivity to climatic variability in north east brazil and validated against residual dune ridge displacements as measured in the field and from high spatial resolution satellite images based on the results it is concluded that residual dune ridges may not form in north east brazil in years which are exceptionally

constructing notches in foredunes effect on sediment dynamics in the dune hinterland measurements were carried out on the island of ameland the netherlands to determine whether notches cut into foredunes stimulated the supply of fresh calcareous beach and dune sand into the white and grey dune habitats behind the dunes increasing these habitats biological quality sediment characteristics and dynamics deposition flux and grain size properties as well as aspects of the vegetation occurrence composition and cover density were studied along six transects three behind an intact foredune and three behind a foredune with a notch cut into it compared to an intact foredune the notched foredune exhibited higher deposition and accumulation behind the dune the extra supply of sand was small however and for the notches studied limited to the zone within approximately 50 60 m of the foredune s crest farther away from the dune the effect of the notches became negligible the presence of a notch did affect the grain size composition of sediment deposited behind the foredune for intact foredunes the grain size composition behind the dune was similar to that on the dune itself when a notch had been cut the sediment was finer behind the foredune gradually coarsening away from the dune sand spray deposition of sand eroded from the dune and transported in modified saltation during heavy winds explains these granulometric results the effect of the notches on the vegetation in the grey dune habitat behind the foredune was small and for the notches studied limited to the first approximately 35 m of the grey dune area between 30 and 65 m from the foredune s crest the notches had a greater effect on the white dune habitat but in the opinion of the authors this remained disproportionately small relative to the effort required for notch excavation and maintenance

aerial damage survey of the 2013 el reno tornado combined with mobile radar data abstracta detailed damage survey of the el reno oklahoma tornado of 31 may 2013 combined with rapid scanning data recorded from two mobile radars is presented one of the radars was equipped with polarimetric capability the relationship between several suction vortices visually identified in pictures with the high resolution doppler velocity data and swath marks in fields is discussed the suction vortices were associated with small shear features in doppler velocity and a partial ringlike feature of high spectral width for the first time a suction vortex that created a swath mark in a field was visually identified in photographs and high definition video while the rotational couplet was tracked by radar a dual doppler wind synthesis of the tornadic circulation at low levels near the location of several storm chaser fatalities resolved ground relative wind speeds in excess of 90 m s 1 greater than the minimum speed for ef5 damage the vertical vorticity analysis revealed a rapid transition from a s

decadal scale evolution of a small dune field keeler dunes california 1944 2010 abstract aerial photographs and satellite images have been used to document the evolution of a small 2 dunefield over the past 60 70 years over this period the dunefield has undergone significant changes including development of well defined linear and crescentic dunes from an initial small area of partially vegetated dunes resulting in an increase in the area of the dunes by a factor of 3 since 1944 the dune field continues to expand toward the southeast but its upwind margins are now experiencing significant erosion because the sand supply is now cut off by dust control measures in the source area and transport pathway this study provides some information on the timescales of dune development in a high energy aeolian environment which formerly experienced an abundant supply of sand with rapid development of crescentic dunes over a period of 20 years the complexity of dunefield development is also highlighted even on decadal timescales and the important role of episodic sediment supply in forming new generations of dunes periods of rapid dunefield change involving lagged input of additional sand from external sources appear to be linked to episodes of high flows in the owens river which is the main sediment source for the keeler dunes

a note on the use of the fryberger method for evaluating potential sand transport by wind the fryberger method provides a useful and accessible way of evaluating potential sediment transport by wind in this method an equation is used to estimate relative rates of sand transport expressed as drift potential from measurements of wind velocity however the values of drift potential obtained through the calculations are dependent upon the units in which wind velocities are expressed this paper highlights some of the confusion this dependence can cause and aims to clarify the ways in which values of drift potential can be interpreted

characteristics of wind blown sand in the region of the crescent moon spring of dunhuang china based on the detailed wind data this paper aims to investigate wind regime drift potential and the movement of mega dunes at the crescent moon spring an important scenic spot in western china and to clarify the dominant factors that control sand transport in this region the results of this paper revealed that the dominant wind directions at the spring were nw and sw the spring region belonged to a low energy wind environment the wind regime and sand drift potential were hugely influenced by local topography and the regional atmospheric circulation intensified the complexity of their variations besides the movement of the southern and northern mega dune towards the spring greatly endangered the preservation of this scenic spot these results provide insights into the characteristics of wind blown sand at the crescent moon spring that will guide efforts to control sand damages

large scale controls on the development of sand seas in northern china abstract although sand seas are located in arid regions given that the proportions of dune areas vary greatly from region to region they are clearly influenced by other factors as well as aridity this paper discusses the distribution pattern and major features of sand seas and large fields of stabilized dunes in northern china and demonstrates the main influences on their development it appears that the availability of onsite loose sediments not wind strength is critical to the occurrence of the sand seas on a regional scale tectonic endorheic basins or areas of alluvial fans or forelands of mountain ranges are advantageous to the accumulation of fluvial sediments and thus are ideal locations of large sand seas in an arid climate the large dune fields currently stabilized by vegetation were active sand seas during the drier periods of the late pleistocene and early holocene the distribution patterns of chinese sand seas suggest that the height or size of the dunes in the sand seas are determined more by the availability of sands than any other potential factors as the sand seas in china account for a large portion of deserts in the middle latitudes of the northern hemisphere taklamakan is the second largest sand sea on earth knowledge of these sand seas past changes is important for understanding climatic changes in the terrestrial regions of mid latitudes

initiation and variation of the dune fields in semi arid china with a special reference to the hunshandake sandy land inner mongolia sedimentary sequences occurring in desert dunes reflect changes in desert systems and as such may contain signals useful for recognizing spatial and temporal changes of deserts and their response to regional or even global climate fluctuations geomorphological and palaeoenvironmental studies within the dune fields of the asian middle latitudes have provided some solid evidence for interpreting the history of these sand seas using the hunshandake otindag sandy land a sandy area covered primarily by stabilized dunes and located in the semi arid zone of eastern inner mongolia china fig 1 as an example we studied the initiation and variation in the dune landscape in the eastern portion of the desert belt in northern china on the basis of physical and biochemical indicators in the sediments and osl chronology we herein argue that this dune system in the middle latitudes of eastern asia is much younger than previously assumed and that it has responded sensitively to climate change during the late quaternary geological evidence from the sandy land suggests that most of the current dunes are of late pleistocene or even holocene age palaeosols intercalated in the aeolian sequences and their osl chronology show that the climate of the hunshandake was much wetter than today between 9 6 ka and 3 ka this resulted in stabilization of the dunes in the eastern and central portions of the sandy land epochs of reworking or stabilization of the dunes are broadly consistent with the fluctuations in northern hemisphere solar radiation although with an obvious time lag because the increase rate of annual precipitation was not sufficient to fully stabilize the dunes in more arid part of the region some active dunes persisted even during this long lasting wetter epoch we conclude that periods of holocene dune stabilization due to palaeosol formation varied along the climate gradients across the various sandy lands of northern china and in general it began earlier and lasted longer in the east than in the west the general nature of the sandy lands and their counterparts in the western portion of the desert belt during the lgm and mid holocene climate optimum is discussed in comparison with their current states

formation of danube delta beach ridge plains and signatures in morphology abstract danube delta as most of the large deltas favours complex interactions between river sediment supply and marine dispersing forces which create complex configurations with concurrent morphologies i e river versus wave influenced or processes accretion versus erosion and even distinct landscapes for the same accretionary features strandplains with low monotonous beach ridges or covered by transgressive dunefields beach ridge plains brps are a common feature of the wave influenced deltaic lobes that are created by juxtaposition of succesive berms on the prograding sandy coasts with different shapes and sizes depending on the accretionary mechanisms and the accomodation space this study reports the formation and dynamics of danube delta brps based on numerical age determination osl and ams of the paleoshorelines topographic and geophysical gpr surveys and stratigraphic records by cores a chronological framework is established for all deltaic brps which points to the importance of formation timespan and growth rate as a consequence of sediment supply on the resultant morphology varying inter site from small brp formation time

late holocene cliff top blowout activation and evolution in the cooloola sand mass south east queensland australia cliff top dunes are a locally important geomorphic features of sedimentary coasts they are traditionally interpreted as being sourced by or with sand derived from the beach below the cliff this paper presents the results of a stratigraphic and geochronological study of carlo sand blow a coastal blowout that has developed on top of a high sandy cliff in the cooloola sand mass south east queensland we use a combination of sedimentological pedological and geophysical techniques along with optically stimulated luminescence dating to determine the depositional history and evolution of the blowout we demonstrate that the blowout is dominantly nourished by sand eroded from its floor rather than the adjacent beach the original dune surface dates to the first half of the last glacial period c 40 70 ka and this dune was deflated in the late holocene dune activity is directly associated with cliff undercutting because of coastal retreat in the late holocene but coastal erosion on its own is not capable of maintaining aeolian activity blowout activity occurred between 2 6 and 2 3 ka and again at 0 3 ka with aeolian sand burying palaeosols both soil surfaces contained charcoal and tree stumps in growth position and our study suggests that fire is the immediate trigger for blowout reactivation it is likely that these fires were anthropogenic in origin because the site is somewhat protected from natural fire and the ages coincide with intensification of human use of coastal sites in the area

transverse instability of megaripples as a result of their inherent differences in stability sand ripples and megaripples exhibit variations in terms of their wavelengths and grain size distributions unimodal for sand ripples and bimodal for megaripples while sand ripples form almost straight lines megaripples have greater sinuosity due to their transverse instability a property that causes small megaripple undulations to grow with time the origin of the instability is due to variations in megaripple height variations that do not diminish over time and due to the inverse dependence of ripple drift velocity on the height thus the taller regions of ripples will move more slowly than the adjacent shorter portions an outcome that promotes further perturbation growth we show an example based on fi eld work of the transverse instability of megaripples the instability growth rate depends on the difference between the heights of the different segments of the megaripple in contrast to the underlying instability of megaripples normal sand ripples are essentially stable and are not affected by transverse perturbations instead reacting quickly to the wind which tends to smooth ripple height irregularities the transverse instability of megaripples derives from the composition of their crests which comprise coarse particles that allow initial perturbations in ripple height to grow further the results suggest a physical mechanism for the transverse instability of megaripples and new insight into the spatial patterns of sand ripples

foredune vegetation patterns and alongshore environmental gradients mocambique beach santa catarina island brazil this paper examines patterns of foredune vegetation along an embayment in southern brazil and the relationships between variations in percent cover and diversity and environmental factors such as beach surfzone type and exposure to wind and wave energy the study was conducted on mocambique beach brazil which displays significant alongshore variations in exposure to the prevailing winds and waves beach surfzone morphodynamic type type and dimensions of the dune systems and foredune vegetation cover and diversity two vegetation surveys were carried out in contiguous 1 m2 quadrats across the foredune the presence absence percent cover of the species diversity and similarity between the vegetation of the profiles surveyed and their relation with environmental conditions are examined the results show that the vegetation cover decreases from south to north possibly reflecting the increasing exposure to wind and wave energy distinct patterns of species distributions occur along mocambique beach such that different plant species are dominant on the southern middle and northern ends of the beach a cluster analysis demonstrated two associations the first one is represented by the profiles located in the lower energy zone of the beach and the second association is represented by the profiles more exposed to wind and wave energy sediment deposition and salt spray the diversity of species decreases northwards possibly influenced by the surfzone type number of breaking waves and degree of aeolian transport the presence absence of the species and the vegetation cover on the foredune reflect the varying levels of exposure of the beach and foredune to the winds and waves and also reflect the volume of sediment deposition on the foredune and the beach mobility determined by the morphodynamic beach surfzone type copyright 2008 john wiley sons ltd

the evolution of holocene coastal dunefields jutland denmark a record of climate change over the past 5000 years coastal dunefields have developed on the west coast of jutland in denmark over the past 5000 years the dunefields are situated in a temperate climate zone with frequent high energy wind events dunefield development was characterized by repeated periods of transgressive dune formation punctuated by periods of dune stabilization and soil formation the chronology of dunefield evolution is based on accelerator mass spectrometry ams radiocarbon dating of peaty palaeosols 24 samples and optically stimulated luminescence osl dating of aeolian sand deposits 19 samples these dates indicate that the completeness of the stratigraphic record varies considerably but that the timing of aeolian activity events was identical in the dunefields examined here initiation of aeolian activity occurred around 2200 bc 800 bc ad 100 ad 1050 1200 and between ad 1550 and 1650 proxy climate data from bogs in southwestern sweden suggest that these periods of dunefield activity were initiated during wet cool summers most likely these climatic situations were associated with a more frequent passage of cyclones across denmark in the summer seasons increased storminess causing aeolian sand movement and dune formation the continued removal of vegetation in jutland between 4000 bc and ad 1850 allowed the aeolian sand when first activated to move more and more easily across the coastal plains the final phase of aeolian sand movement between ad 1550 1650 and 1900 had catastrophic implications for many coastal inhabitants in the region c 2008 elsevier b v all rights reserved less

coastline orientation aeolian sediment transport and foredune and dunefield dynamics of mocambique beach southern brazil abstract this paper examines the role of coastline orientation on foredune and dunefield development at mocambique beach southern brazil the beach displays significant alongshore variations in exposure to the prevailing winds and waves grain size beach surfzone morphodynamic type foredune volume and type and dimensions of the holocene dune systems two wind analyses and calculation of aeolian drift potentials were carried out one based on 1 year of wind record and another based on a record of 34 years monthly topographic surveys of beach and foredunes on 5 profiles along mocambique beach were conducted over one year to obtain data on beach mobility and width aeolian sediment transport and foredune development southerly winds dominate and aeolian sediment supply is minimal in the south moderate in the central portion and high in the northern portion of the embayment the relationship between actual sediment supply foredune building and potential sediment supply is relatively poor over one year due to factors such as beach type and mobility beach moisture levels rainfall storm surge and wave scarping the intermediate term 34 year record indicates a strong relationship between foredune size and volume winds and shoreline orientation foredune volume is minimum in the southern part of the beach and greatest in the northern part of the beach the holocene barrier and dunefield development also reflects the long term control of shoreline orientation and increasing longshore gradient in exposure to southerly winds for the last 6000 7000 years a small foredune developed in the southern portion parabolics and small transgressive dunes in the central portion and a large scale transgressive dunefield in the northern portion

photogrammetric analysis of the 2013 el reno tornado combined with mobile x band polarimetric radar data abstractthis study presents rapid scanning x band polarimetric radar data combined with photogrammetry of the el reno tornado of 31 may 2013 the relationship between the hook echo weak echo hole weh weak echo column wec and the rotational couplet with the visual characteristics of the tornado are shown for the first time cross correlation coefficient hv and differential reflectivity zdr data are included in the photogrammetric analyses the tornado was accompanied by a large tornadic debris signature tds with a diameter 2 km wide during the analysis time the center of the tds was not collocated with the weh and the rotational couplet instead the tds was displaced 1 km to the north and within the weak echo notch of the hook echo a debris overhang was identified in vertical cross sections of the hv fields the overhang was located in a weak echo trench and a notch of high hv consistent with the position of the tornado updraft the updraft was hypothesized to be carrying small deb

doppler radar analysis of the northfield texas tornado of 25 may 1994 abstract a large tornado was observed near northfield texas on 25 may 1994 during the verification of the origins of rotation in tornadoes experiment vortex an analysis of the tornado and its parent storm is discussed doppler wind velocity spectra of the tornado and its parent circulation which were computed from data collected by a low power portable fm cw frequency modulated continuous wave 3 cm wavelength doppler radar are presented at increments in the range of 78 m the fm cw radar data from the tornado are the first ever collected of high enough quality to analyze the cw spectra computed from data collected by the portable radar a pseudo dual doppler analysis of airborne doppler radar data collected by a national oceanic and atmospheric administration p 3 aircraft photogrammetric analysis of a video of the tornado and a ground based damage survey are discussed in the context of the fm cw spectra this study is unique in that both ground based and airborne doppler radar systems probe

beach dune interactions on the dry temperate danube delta coast abstract beach dune seasonal elevation changes aeolian sand transport measurements bathymetric surveys and shoreline evolution assessments were used to investigate annual and seasonal patterns of dune development on sf ntu gheorghe beach the danube delta coast from 1997 to 2004 dune volume increased consistently 1 96 m 3 m 1 y 1 to 5 1 m 3 m 1 y 1 over this 7 year period with higher rates in the southward downdrift direction dune aggradation is periodically limited by storms each of which marks a new evolutionary phase of the beach dune system as a consequence of the variable beach morphology and vegetation density during a year foredune growth occurs during the april december interval while between december and april a slightly erosive tendency is present the pattern of erosion and deposition shown by the topographical surveys is in good agreement with the sand transport measurements and demonstrates the presence of a vigorous sand flux over the foredunes which is 20 50 smaller than on the beach this high sand flux due to low precipitation and sparse vegetation cover creates an aerodynamically efficient morphology on the seaward dune slope the seaward dune face accretes during low to medium onshore winds 5 5 12 m s 1 and erodes during high winds 12 m s 1

geomorphological analysis and classification of foredune ridges based on terrestrial laser scanning tls technology abstract along the north adriatic sea coast italy vulnerability to climate change is further aggravated by anthropogenic influences such as strong subsidence rate due to deep groundwater and gas abstraction tourism and industry impacts in this context conservation and restoration of coastal sand dunes become extremely important especially because of their importance in terms of natural coastal defense this paper proposes an innovative geomorphological approach based on terrestrial laser scanning tls which allows us to measure and monitor morphometric dune evolution with high precision and details several tls surveys were performed along the ravenna coast adriatic sea italy and the resulting digital elevation models dems were analyzed in order to classify the foredune ridges in three geomorphological sub zones the topographic areal and volumetric variations over time of geomorphological units were calculated by gis tools in order to identify seasonal trends or particular pattern meteo marine climate conditions were also analyzed and principal component analysis pca was performed to correlate changes in morphology with meteo marine forcing factors highlighting the ones that most influence dune evolution and dynamics

wind regimes and aeolian transport in the great basin u s a abstract the modern great basin of the interior western united states is characterized by surface winds with considerable spatial and temporal variabilities wind records from the second half of the 20th century for 12 great basin localities analyzed with standard aeolian sediment transport methods developed elsewhere in the world reflect this complexity the drift potential dp for aeolian deposits is generally moderate dp 200 400 in the western great basin and weak dp 300 at the eastern edge of the great basin where the dominant prevailing wind direction is south southwesterly both dp and resultant drift direction rdd are consistent with synoptic meteorological observations of the evolution of cold fronts in the great basin meteorological observations show that effective winds to produce dunes are most commonly the result of late winter early spring cyclogenesis there has been considerable temporal variability of dp in the latter half of the 20th century most of the great basin has experienced decreasing wind strength since 1973 consistent with recent studies of wind strength in north america and elsewhere dune morphology matches both localized rdd and temporal variations in dp reasonably well in the great basin the results demonstrate that local topography can have an important influence on wind directionality thus providing a cautionary note on the interpretation of dune morphology in the paleoclimatic and stratigraphic record

morphodynamics and climate controls of two aeolian blowouts on the northern great plains canada blowouts are the most regionally pervasive active aeolian landform on the northern great plains of north america this study reports a long term investigation into the morphological development of two adjacent blowouts in a continental dune field the blowouts were monitored for a decade in the bigstick sand hills of southwestern saskatchewan canada topographic changes were determined from dense arrays of erosion pins in each blowout 1 per 4 m2 n 171 and 1 per 16 m2 n 150 pin measurements were made 16 times between may 1994 and may 2004 over the decade both blowouts expanded and more than doubled in volume differences in form flow interactions have caused the larger of the two blowouts to deposit more than a metre of sediment within the deflation basin and the smaller blowout to erode by more than a metre a negative feedback effect was triggered when the larger blowout reached a critical size around 1994 60 m 36 m 8 1 m length width height when sediment was no longer eroded from the deflation basin a positive feedback in the smaller blowout continues to facilitate erosion from the deflation basin monthly observations since 2002 indicate that aspect plays an important role in the development of these blowouts by creating a spatial asymmetry in sediment availability sediment is more readily available throughout the year on south facing slopes which receive greater insolation than north facing slopes and are often drier and more frequently thawed in this cold climate environment comparisons between climate data from a remote meteorological station 45 km to the southwest and sediment transport indices developed from the erosion pin data produced very few correlations significant at the 95 per cent confidence level nevertheless the signs of the correlation coefficients indicate that sediment erosion and deposition in both blowouts respond similarly to the following climate variables recorded at the remote station i the amount of precipitation ii the transport capacity of the wind and iii transporting winds from a directional wedge between 180 and 330 taken altogether the results from this study highlight the importance of climate and feedback effects in blowout development that may be extended to other blowouts in continental and coastal settings copyright 2006 john wiley sons ltd

field measurement and analysis of climatic factors affecting dune mobility near grand falls on the navajo nation southwestern united states abstract aeolian sand covers extensive areas of the navajo nation in the southwestern united states much of this sand is currently stabilized by vegetation although many drier parts of these native lands also have active and partly active dunes current prolonged drought conditions that started in the mid 1990s are producing significant changes in dune mobility reactivation of regional aeolian deposits due to drought or increasing aridity from rising temperatures resulting from climate change could have serious consequences for human and animal populations agriculture grazing and infrastructure to understand and document the current and future potential for mobility seasonally repeated surveys were used to track the location of multiple active barchan dunes by utilizing real time kinematic gps field surveys and simultaneously collecting in situ meteorological data it is possible to examine climatic parameters and seasonal variations that affect dune mobility and their relative influences through analysis of the recorded data we examined the fit of various climate parameters and demonstrate that under the current prolonged drought wind power is the dominant factor controlling dune mobility

significance of variations in the wind energy environment over the past 50 years with respect to dune activity and desertification in arid and semiarid northern china climate data from 339 meteorological stations collected from the 1950s to the early 2000s was employed to discuss aeolian activity in arid and semiarid northern china the results show that at decadal time scales erosivity varied greatly in this region most of arid and semiarid northern china was characterised by environments with moderate to low wind energy after the 1980s the erosivity was only 20 to 50 of that beforehand and this difference had a significant impact on the environmental changes observed during the two periods the dune mobility index was consistent with the observed dune activity after the 1980s dune activity decreased and in some deserts with vegetated dune systems during the 1970s most of the dune plinths were active until the 1980s after which only the crests were active some mobile dunes that had developed at the margins of mobile deserts were replaced by semi anchored or anchored dunes because most desert areas with vegetated dune systems in arid and semiarid northern china are used for farming or grazing the results of our monitoring show that the desertification trends were consistent with the trends in erosivity and dune activity in this region desertification was controlled much more by climatic changes than has previously been acknowledged and especially by fluctuations in wind energy

painting the near surface using geology geophysics and satellites a smooth interpolation of a sparse uphole survey may be the main tool available for modeling the near surface in desert areas an uphole survey does not properly define sharp near surface velocity changes associated with lithologic and topographic variations such as cliffs canyons or outcrops which may be delineated by satellite imagery instead we present a patchy interpolation technique to build a consistent near surface model the algorithm is based on k means clustering to integrate geological geophysical and remote sensing information a somewhat arbitrary aspect of the method is the choice of how many clusters are used in segregating the data linking this parameter to surface geologic formations may be inadequate because p or s wave velocities are unlikely to have a sufficiently unique correlation with geologic age and lithology we suggest an empirical criterion improvement in the seismic stack section achieved by processing with parameters derived by various clustering choices and data t

geomorphology and dynamics of a traveling cuspate foreland authie estuary france abstract cuspate forelands or salients occur all over the world in lakes estuaries and on ocean shores yet there have been few studies conducted on traveling cuspate forelands or salients that is forelands that migrate or travel alongshore this paper presents a study of a traveling foreland in the authie estuary france termed the bec du perroquet historical shoreline changes may be traced from the 1200 s ad and the region has experienced both marked intertidal subtidal accretion extending from the south and massive erosion in the north since this period an analysis of aerial photographs from 1947 until the present shows that the original bec foreland was established at the mouth of the authie estuary but gradually disappeared by the 1960 s and a new foreland developed in the middle of the northern central portion of the bay this foreland was composed of a suite of foredune ridges which have been successively eroded on the northern margin and initiated on the southern margin as the foreland traveled or migrated southwards as the foreland traveled south from 1947 to 2009 the northern part of the bay retreated more than 350 m while mid bay the coastline retreated 215 m as the foreland evolves and migrates incipient foredunes can develop rapidly e g 18 ridges formed in an 11 week period while at other times the ridges form slowly and may be eroded and disappear two or more foredune ridges may blend into a single ridge over time depending on the initial degree of vegetation cover on the ridge and swale set aeolian processes in dune swales are much more important in this system than in typical prograding foredune plain systems due to the sometimes marked lack of vegetation colonization in the swales following foredune ridge development and aeolian deflation of the swales along with blowout development is important particularly when they become open conduits to the beach as erosion of the nw foreland proceeds the ages of each of the surviving ridges on the foreland in 2009 have been determined and the evolutionary path of the ridges ascertained formerly intact relatively stable continuous ridges evolve to erosional knobs turrets and nebkha over time foredune ridges and swales can be extremely arcuate to semi circular in form where the foreland and especially the spit extension are exposed to a wide range of wind directions and where the shoreline trends through an arc of at least 270 this study illustrates a remarkable cycling of the formation destruction and reformation travel of a cuspate foreland over a 50 year period

mobile doppler radar observations of a tornado in a supercell near bassett nebraska on 5 june 1999 part i tornadogenesis abstract this two part paper details an analysis of high resolution wind and reflectivity data collected by a mobile w band doppler radar the dataset captures the near surface life history of a tornado in a supercell in north central nebraska on 5 june 1999 the formation of the tornado vortex near the ground is described from a sequence of sector scans ranging from 30 s intervals prior to tornadogenesis to 10 15 s intervals during much of the lifetime of the tornado cyclonic vortices of 100 200 m width were found along a bow shaped line of enhanced radar reflectivity at what appears to have been the leading edge of a rear flank gust front at the time of tornadogenesis one of these vortices was located just ahead of the nose of the bow shaped radar echo and a jet which were embedded within a larger scale cyclone at other times small scale cyclonic vortices coexisted with the tornado along an arc shaped line extending to its north and northeast but did not appear to interact with the tornado the

initial insights into the age and origin of the kubuqi sand sea of northern china abstract the kubuqi desert is the only active sand sea in the semiarid regions of northern china and occurs along the southern margin of the yellow river little is known about the age and origin of this large 17 000 km2 sand sea with a present annual precipitation of 200 480 mm sand drift potentials indicated net capable winds for aeolian transport are from the northwest though winds are stronger to north beyond the dune field than within the sand sea geomorphic and stratigraphic observations indicate that holocene aeolian sand often drapes over bedrock and river terraces as a palimpsest landscape field investigations identified four stratigraphic sections with multiple aeolian sand units and palaeosols with age control by optically stimulated luminescence osl dating of quartz grains palaeosols are weakly developed mostly accumulative a horizon with organic carbon content

an unusual hailstorm on 24 june 2006 in boulder colorado part i mesoscale setting and radar features abstract an unusual isolated hailstorm descended on boulder colorado on the evening of 24 june 2006 starting with scattered large flattened disk shaped hailstones and ending with a deluge of slushy hail that was over 4 cm deep on the ground the storm lasted no more than 20 min and did surprisingly little damage except to vegetation part i of this two part paper examines the meteorological conditions preceding the storm and the signatures it exhibited on weather surveillance radar 1988 doppler wsr 88d displays there was no obvious upper tropospheric forcing for this storm vertical shear of the low level wind was minimal the boundary layer air feeding the storm was not very moist maximum dewpoint 8 5 c and convective available potential energy calculated from a modified air parcel was at most 1550 j kg 1 despite these handicaps the hail producing storm had low level reflectivity exceeding 70 dbz produced copious low density hail exhibited strong rotation and generated three extensive bo