formation of coastline features by large scale instabilities induced by high angle waves along shore sediment transport that is driven by waves is generally assumed to smooth a coastline this assumption is valid for small angles between the wave crest lines and the shore as has been demonstrated in shoreline models but when the angle between the waves and the shoreline is sufficiently large small perturbations to a straight shoreline will grow here we use a numerical model to investigate the implications of this instability mechanism for large scale morphology over long timescales our simulations show growth of coastline perturbations that interact with each other to produce large scale features that resemble various kinds of natural landforms including the capes and cuspate forelands observed along the carolina coast of southeastern north america wind and wave data from this area support our hypothesis that such an instability mechanism could be responsible for the formation of shoreline features at spatial scales up to hundreds of kilometres and temporal scales up to millennia

on the coupling between the harang reversal evolution and substorm dynamics a synthesis of superdarn dmsp and image observations 1 the harang reversal is a prominent feature frequently observed in the electric and magnetic field patterns in the high latitude auroral zone and plays an important role in substorm dynamics a comprehensive set of instruments including super dual auroral radar network superdarn defense meteorological satellite program dmsp and imager for magnetopause to aurora global exploration image is used to investigate the relationship between the harang reversal and substorms on the basis of nine events that have been analyzed we find that the harang reversal forms and becomes well defined during the growth phase azimuthal flows equatorward of the harang reversal a majority of which are in the subauroral region enhance during the growth phase the observations indicate that subauroral polarization streams saps and the harang reversal evolve together as part of the growth phase development of the region 2 current system furthermore the substorm auroral onset is seen to occur quite near the center of the harang flow shear which suggests that the substorm upward field aligned current develops there after onset the evolution of convection flows in the vicinity of the harang region depends strongly on their location relative to that of the onset saps flows equatorward of the harang reversal suddenly increase at the substorm onset flow shear east of the auroral onset relaxes after the onset and poleward flows part of a clockwise vortex are observed west of the auroral onset after the onset these observations demonstrate the strong coupling between the harang reversal evolution and substorm dynamics and suggest that the nightside region 2 physics is closely related to substorm dynamics

field observations of swash zone infragravity motions and beach cusp evolution 1 fluid flows consistent with low mode edge waves were evident in video observations of swash motions during a field experiment in which beach cusps developed on an initially smooth beach as beach cusps grew energy lying along low mode dispersion curves increased the most energetic edge wave propagation direction changed from upcoast to downcoast as the orientation of the cusp horns rotated these observations suggest a coupling between morphodynamics and hydrodynamics and are evidence that beach cusp evolution might control low mode edge wave dynamics

observations of beach cusp evolution at melbourne beach florida usa abstract morphological observations terrestrial laser scanning and sediment analysis are used to study beach cusp morphodynamics at melbourne beach florida usa a moderately sloped beach characterized by fine sand the study couples rapid high resolution surveying with surficial sediment sampling over multiple tidal cycles surveys were run 500 m alongshore and sediment samples were collected intertidally over a period of 5 days beach cusp location within larger scale beach morphology is shown to directly influence cusp growth as either gross erosional or gross accretional sediment characteristics within the beach cusp morphology are reported coincident with cusp evolution variations in particle size distribution kurtosis are exhibited as the cusps evolve however no significant correlation is seen between grain size and position between horn and embayment during the end of the study a storm resulted in beach cusp destruction and increased sediment sorting

a case study of relationship between substorm expansion and global plasma convection 1 this letter reports observations of large scale ionospheric plasma flows from the superdarn radar network and global auroral images from the polar ultraviolet imager during two large and rare substorm events the substorm events were characterized by predominantly westward expansion for one and predominantly eastward expansion or lack of westward expansion for the other the westward expansion case was associated with a positive y component of interplanetary magnetic field imf whereas the eastward expansion case was associated with a negative y component of imf the concurrent plasma flow measurements from the superdarn radar network suggest that the westward eastward expansion is embedded in the large round dusk dawn convection cell a simple explanation is offered for the observed preponderance of westward expansions namely that the pre midnight onset location favors the westward plasma flow that is associated with the dusk cell eastward expansion occurs only when a large imf by negative condition causes the midnight sector to be dominated by eastward plasma flows

beach cusp morphodynamics detailed measurements of three dimensional beach cusp morphology were made on a steep gradient low energy microtidal beach in perth western australia during the field campaign a variety of wave conditions and tidal ranges were experienced and these differing hydrodynamic conditions were reflected in a consistent pattern of morphological changes to the beach cusp system a useful parameter to delineate between trends of cusp destruction and re formation appeared to be the surf similarity parameter tan i0 l0 where h0 is offshore wave height l0 is deep water wave length and tan is beach gradient for 1 2 a small storm was experienced at the start of the field campaign period and resulted in considerable erosion of the beach face the cusp morphology across the lower beachface was destroyed but a subtle remnant of the pre storm cusp morphology was preserved on the upper beachface when cusps reformed after the storm under the influence of declining wave conditions they appeared at the same location and with the same dimensions as the pre storm cusp morphology hence it is considered that the cusp re formation was controlled more by the antecedent morphology than the hydrodynamic conditions this indicates that positive feedback between swash hydrodynamics and beachface morphology necessary to form beach cusps does not require a large variation in relief 1997 john wiley sons ltd

identification of substorm onset location and preonset sequence using reimei themis gbo pfisr and geotail 1 we present state of the art multiple instrument observations of an isolated substorm on october 12 2007 the auroral breakup was observed simultaneously by reimei themis asi and pfisr the footprint of geotail was also near the breakup these observations allow for detailed study of the breakup location in terms of large and small scale auroral morphology particle precipitation and ionospheric convection which has not previously been achieved it also allows for detailed identification of the sequence leading to the breakup we report the first spaceborne high spatial and temporal resolution images of part of a breakup arc and a wave like auroral enhancement captured by reimei observations suggest a sudden plasma sheet thinning initiated 10 min before the onset wave like auroral enhancements were observed twice at the most equatorward arc 3 min and 1 min before the breakup these enhancements are likely due to some near earth instability such as ballooning instability unlike the usual substorm sequence this most equatorward arc did not develop into the breakup arc but remained almost stable until being engulfed by the auroral equatorward expansion from higher latitude after onset the wave like auroral enhancement was associated with three fine inverted v arcs and embedded within energetic ion precipitation following this enhancement an arc likely a poleward boundary intensification formed at higher latitude just adjacent to the plasma sheet boundary layer psbl this arc then extended southwestward and led to the breakup arc which was located poleward of the wavy structures assuming longitudinal homogeneity of ion precipitation over 1 this breakup arc was located in a region without ion precipitation just poleward of the energetic ion precipitation these observations suggest the possible existence of a low entropy flow channel associated with the arc adjacent to the psbl which might be associated with instability in the near earth plasma sheet responsible for the auroral breakup

the origin of swash cusps on beaches abstract genetically there are two types of beach cusps those formed in the surfzone by the nearshore circulation system and those formed on the beachface by the swash and backwash the latter are here called swash cusps and a simple model relating the physical dimensions of swash cusps to the properties of the incident wave field and the mean beach slope is developed as in some previous models the cusp wavelength is controlled by the longshore wavelength of edge waves but the edge waves are now required only to provide small periodic perturbations on an originally uniform beach further cusp growth occurs because of the interactions between the incident waves and the perturbed topography the maximum cusp height apex to valley is hypothesized to be proportional to the significant vertical excursion of swash motions it follows from the above assumptions that the maximum possible cusp steepness cusp height cusp longshore wavelength is proportional to the mean on offshore beach slope this result agrees with field data and the value of the ratio of maximum cusp height to beach slope differs from that obtained theoretically by guza and bowen 1981 using a complicated non linear model with rather different physics the present model implies that edge waves although necessary for initiating the initial bedform perturbation need not persist for the development of mature cusp topography

fracture networks in frozen ground fractures in frozen ground self organize into networks through interactions between sequentially emplaced fractures tensile stress and the developing fracture pattern from this viewpoint we model the development of networks on a lattice representing the ground surface on which fractures initiate propagate and arrest under a combination of uniform thermally induced tensile stress stress reduction near existing fractures and stochastic parameterization of heterogeneity in frozen ground and in insulating snow tensile stress from cooling tensile strength propagation threshold fracture depth and elastic properties are chosen to approximate properties of frozen ground using these parameters model networks assemble with properties similar to natural ice wedge networks including 1 individual fracture paths have lengths ranging from tens to hundreds of meters 2 fractures intersect to enclose regions with characteristic spacing between fractures of approximately 22 m 3 intersections between fractures are predominantly orthogonal with less common three way approximately equiangular intersections joint distributions of relative orientation and spacing between fractures from modeled networks and ice wedge networks at espenberg alaska are comparable at the level of variability in natural examples this similarity is consistent with the hypotheses that networks self organize by stress interactions between sequentially placed fractures in frozen ground and that networks are insensitive to the many details of fracture dynamics omitted from the model spacing between fractures in modeled networks is influenced by sub optimal placement of fractures during network development and increases nonlinearly with the length scale of stress reduction around a fracture three way approximately equiangular intersections form where modeled fractures arrest on the outside of bends in earlier fractures

morphological evolution of beach cusps and associated swash circulation patterns abstract a numerical model capable of simulating the motion of water particles on beach cusp morphology under the influence of an initial velocity and gravity is presented the model indicates that the typical swash pattern on beach cusps is three dimensional with wave uprush diverging at the cusp horns resulting in concentrated backwash streams in the embayment the degree of horn divergence is an increasing function of the parameter e s 2 where e quantifies the prominence of the beach cusps s is the horizontal swash excursion length and is the cusp spacing the numerical experiments are supplemented with detailed field measurements of beach cusp morphological change the field data include three types of morphological response each characterised by a particular pattern of swash circulation that can be delineated using e s 2 when e s 2 beach cusp morphology is large and or subdued in relation to the swash length swash circulation is essentially two dimensional oscillatory flow and results in steepening of the beachface and infilling of the cusp embayments for e s 2 0 015 to 0 15 wave uprush is deflected from the cusp horns and flows into the embayments where it exits in a concentrated backwash stream horn divergent flow the ensuing swash backwash inequality reinforces cusp development and maintains existing cusp morphology when e s 2 0 15 beach cusps are small and or pronounced in relation to the length of the swash overtopping and ponding of the cusp horn takes place and swash circulation is from the embayment to the horn horn convergent flow as a result cusp horns are eroded and accretion occurs in the embayments

recent advances in modeling swash zone dynamics influence of surf swash interaction on nearshore hydrodynamics and morphodynamics the role of the swash zone in influencing the whole nearshore dynamics is reviewed with a focus on the interaction between surf and swash zone processes local and global hydromorphodynamic phenomena are discussed in detail and a description of the overall swash zone operation is given the effects of swash zone boundary conditions are highlighted together with the importance of surf zone boundary conditions major emphasis is placed on illustrating the interactions of various hydrodynamic modes which in turn control the swash and surf zone morphology finally methods to account for swash zone processes in coastal models with different temporal and spatial resolutions are proposed

field observations of beach cusps and swash motions abstract we tested the hypothesis of cusp formation by the longshore structure of synchronous or subharmonic mode zero edge waves using detailed field measurements of foreshore topography incident waves and swash motions two distinct intervals of cusp formation were observed alongshore separated swash measurements were analyzed to detect structures at wavelengths and frequencies consistent with the measured cusp spacings for both events no statistical support for cusp generation by the traditional subharmonic or synchronous edge wave mechanisms was found however once cusps became well developed there was evidence of interaction between fluids and topography at a wavelength equal to the cusp spacing but at the period of the incident swash we propose that this interaction could have been responsible for the generation of the second set of cusps with a spacing of half the pre existing cusp wavelength

a new technique for determining substorm onsets and phases from indices of the electrojet sophie we present a new quantitative technique that determines the times and durations of substorm expansion and recovery phases and possible growth phases based on percentiles of the rate of change of auroral electrojet indices by being able to prescribe different percentile values we can determine the onset and duration of substorm phases for smaller or larger variations of the auroral index or indeed any auroral zone ground based magnetometer data we apply this technique to the supermag al sml index and compare our expansion phase onset times with previous lists of substorm onsets we find that more than 50 of events in previous lists occur within 20 min of our identified onsets we also present a comparison of superposed epoch analyses of sml based on our onsets identified by our technique and existing onset lists and find that the general characteristics of the substorm bay are comparable by prescribing user defined thresholds this automated quantitative technique represents an improvement over any visual identification of substorm onsets or indeed any fixed threshold method

nightside ionospheric convection asymmetries during the early substorm expansion phase relationship to onset local time we present superdarn radar observations of ionospheric convection during substorms substorms were grouped according to their onset latitude onset magnetic local time and the prevailing sense of imf by the radar observations were then sorted according to substorm group and average convection patterns produced here we discuss the patterns corresponding to substorms with onsets occurring in the 65 67 onset latitude range at either early 20 22h or late 01 03h magnetic local times during intervals of either dominant positive or negative imf by we show that the morphology of the convection patterns differs from that predicted by existing empirical models with the location of the nightside convection throat being largely consistent with the location of substorm onset the expected imf by induced dawn dusk convection asymmetry can be enhanced on the nightside when the substorm onset occurs at a fortuitous location but can equally be removed or even reversed from this expected state thus the nightside convection asymmetries are seemingly unrelated to the instantaneous sense of imf by

sorted bed forms as self organized patterns 1 model development 1 here we present a modified version of the exploratory numerical model originally presented by murray and thieler 2004 and use it to further investigate the development of sorted bed forms on the inner continental shelf the new version of the model is based on widely accepted parameterizations for hydrodynamics and sediment transport that are more detailed and empirically tested than the parameterizations used in the original model the shallow water wave equations are replaced by the general equations and changes in water depth related to morphological development are accounted for this model reproduces the main results of the previous one supporting the hypothesis that sorted bed forms are a self organized pattern and develop as a result of a coupling between bed composition and sediment flux the sensitivity of the model predictions evaluated in terms of the geometry of the sorted bed forms and their growth rate with respect to external forcing variables and internal model parameterizations shows increasing decreasing sorted bed form spacing height with increasing wave height and period the opposite occurs for increasing water depths more complicated behavior is observed when the ratio fine to coarse sediment diameter or the percentage of fine and coarse material is varied the shape of the suspended sediment and current profiles and the formulation used to predict the geometry of wave generated ripples can significantly affect or even inhibit growth rates of sorted bed forms results from a sensitivity analysis show that there are deficiencies in the description of small scale processes that limit the ability to quantitatively predict sorted bed form evolution highlighting gaps in our knowledge of sediment transport over mixed grain beds that need to be filled

trends in research on beaches and dunes on sandy shores 1969 2019 abstract trends in research on morphologic changes on beaches and foredunes on sandy shores are identified from the 1960s to the present research during this period evolved from early descriptive explanation and classification of profile change to instrumented field investigations to modelling of landform change at larger scales research efforts have become increasingly more collaborative with increasing use of field instrumentation data acquisition systems and remote sensing rich datasets are resulting in more comprehensive computational models human altered systems are of increasing interest but knowledge of these systems lags far behind knowledge of natural systems research is becoming more relevant to societal needs as the vulnerability of coastal populations increases the need for investigation of understudied or unexplored environments including human altered ones is ongoing many basic research issues remain but future studies would profit from the development of new models rather than validating or reconfiguring old models collaboration between geomorphologists and engineers may open up research opportunities particularly in modifying beaches and dunes built for shore protection to provide natural values in restricted space application of models to enhance knowledge of effects of sea level rise and coastal storms would be useful to managers developing resiliency plans

beach cusp destruction formation and evolution during and subsequent to an extratropical storm duck north carolina many studies have debated whether beach cusps are erosional or depositional features the april 12 14 1988 extratropical storm provided an opportunity to view the direct effects of one of the largest storms of the past decade upon beach sedimentology and morphology on barrier islands near duck north carolina prior to the storm the beach at duck was characterized by a well defined pattern of beach cusps with horn to horn spacings averaging 35 m storm induced alterations were dominated by an initial period of beach erosion that remobilized the upper 30 to 50 cm of beach sediment followed by aggradation net aggradation was most prominent along the middle beachface and within the pre storm cusp bays these morphologic adjustments resulted in the destruction of cusps which were replaced with a post storm planar beachface composed of horizontally bedded fine to coarse grained sediments within 24 hrs of storm subsidence new beach cusps formed sequentially along the coast in the direction of longshore

the role of tides in beach cusp development 1 field measurements of morphology and swash flow during three episodes of beach cusp development indicate that tides modulate the height and cross shore position of beach cusps during rising tide beach cusp height decreases as embayments accrete more than horns and the cross shore extent of beach cusps decreases during falling tide beach cusp height increases as embayments erode more than horns and cross shore extent increases a numerical model for beach cusp formation based on self organization extended to include the effects of morphological smoothing seaward of the swash front and infiltration into the beach reproduces the observed spacing position and tidal modulation during rising tide water particles simulating swash infiltrate preferentially in embayments causing enhanced deposition during falling tide exfiltration of water particles combined with diversion of swash from horns causes enhanced erosion in embayments smoothing of beach morphology in the swash zone seaward of the swash front and in the shallow surf zone accounts for most of the observed tidal modulation even in the absence of infiltration and exfiltration despite the qualitative and in some cases quantitative agreement of the model and measurements the model fails to reproduce observed large deviations of horn orientation from shore normal some aspects of beach cusp shape and deviations from the basic tidal modulation possibly because of the simplified parameterization of cross shore sediment transport and the neglect of the effects of sea surface gradients on flow index terms 4546 oceanography physical nearshore processes 4255 oceanography general numerical modeling 3220 mathematical geophysics nonlinear dynamics keywords beach cusp tides infiltration exfiltration erosion

directional spreading of waves in the nearshore observations of surface gravity waves shoaling between 8 m water depth and the shoreline on a barred beach indicate that breaking results in an increase in the directional spread of wave energy in contrast to the directional narrowing with decreasing depth predicted by refraction theory snell s law during low energy wave conditions when breaking induced wave energy losses over the instrumented transect are small the observed mean propagation direction and spread about the mean both decrease with decreasing depth consistent with the expected effects of refraction nonlinearity causes high frequency components of the spectrum to become directionally aligned with the dominant incident waves during high energy wave conditions with significant wave breaking on the sand bar the observed mean directions still decrease with decreasing depth however the observed directional spreads increase sharply nominally a factor of 2 for values integrated over the swell sea frequency range between the outer edge of the surf zone and the crest of the sand bar followed by a decrease toward the shoreline observations on a nonbarred beach also show directional broadening with spreads increasing monotonically from the outer edge of the surf zone to a maximum value near the shoreline although the mechanism is not understood these spatial patterns of directional broadening suggest that wave breaking causes significant scattering of incident wave energy into obliquely propagating components

fossil cryogenic features in paleosols of southern italy characteristics and paleoclimatic significance the work presents the results of a study of two paleosols located at 1350 m a s l on the sila massif in southern italy the purpose of this research is to examine paleoenvironmental conditions during the last glaciation based mainly on soil morphological micromorphological and sedimentological data these two paleosols contain climatically sensitive cryogenic features including a sand wedge an ice wedge cast silt veins silt lenses reticulate silt veins and matrix lenses these features are interpreted to indicate that during the last glacial maximum this area in southern italy experienced conditions characterized by very low temperature little snow cover and great aridity

low frequency swash motion induced by wave grouping abstract this paper concerns the low frequency motion of swash directly induced by wave grouping on a steep beach a new experimental investigation is presented which considers the hydrodynamics of the inner surf zone and swash zone using vertical wave gauges and a run up wire results for regular waves wave groups and random waves are discussed with particular reference to low frequency motions the inner surf zone and swash zone are found to be unsaturated at incident short wave frequencies and as a result significant wave grouping is apparent at the shoreline the low frequency motion in the surf zone is found to be in phase with the incident wave grouping and may therefore be regarded as a time varying set up watson and peregrine 1992 the low frequency motion of the swash is shown to be an order of magnitude greater than that in the inner surf zone inconsistent with cross shore standing long waves for which no evidence is found we demonstrate that the low frequency motion of the shoreline provides an excellent approximation to the run up of individual bores and therefore describes the run up envelope spectral analysis shows that the low frequency motion of the swash is directly linked to the modulations in offshore wave height i e the low frequency energy in the incident wave envelope in addition the random wave run up spectra show an f 4 high frequency roll off as found by huntley et al 1977 the accumulated data show that unless the surf zone is totally saturated a significant proportion of the low frequency swash motion may be directly due to incident wave grouping and not standing long waves

morphodynamics of nearshore rhythmic sandbars in a mixed energy environment sw france i mapping beach changes using visible satellite imagery abstract this paper presents a new method to analyze the morphology and migration of shallow water sandbanks based on the retrieval of maps from high resolution spot satellite imagery this approach was applied to the study of intertidal ridge and runnel systems and subtidal crescents that border the southwest coast of france maps were obtained from 16 spot images recorded between 1986 and 2000 ridge and runnel shapes with regard to a reference level were delineated using a watercolor reflectance code parameterized and validated with field data crescent plan shapes which appear on the images due to water transparency or breaking induced foam were directly extracted the spatial maps show that in conformity with field surveys the mean alongshore spacing of intertidal systems and crescents range from 370 146 m variability is indicated by standard deviation to 462 188 m and from 579 200 to 818 214 m respectively several couples of images also show that ridge and runnel systems and crescents move in the longshore drift direction southward by about 2 4 3 1 and 1 m day 1 respectively alongshore migration rates of intertidal systems are confirmed by field surveys whilst crescent dynamics cannot be validated because there is no in situ data available to complete these measurements an analysis of the influence of wave climate on both the shape and movements of these rhythmic sedimentary patterns is proposed in a companion paper

erosion accretion patterns and multiple beach cusp systems on a meso tidal steeply sloping beach abstract this study examines daily variations in intertidal topography and beach cusps on a meso tidal steeply sloping beach during a five month period the observations are based on coastal imagery and frequent topographic surveys and are extracted from patterns of contours positioned 1 and 3 m above msl lower higher beach face respectively the intertidal topography was very sensitive to variations in the wave regime triggering rapid transitions from erosive to accretive states and vice versa as well as transformations of the cusp systems often involving severe horn erosion and beach face scarping distinct beach cusp systems were observed at different levels of the beach with their evolution being controlled by i wave forcing ii tidal modulation of the wave power at different levels of the beach and iii interactions between the existing beach cusp systems the lower beach face rhythmical patterns changed constantly and merged with the upper beach face cuspate features typically when the significant wave height exceeded h o 1 5 m the upper beach face pattern was persistent during the monitoring period re emerging with similar spacing and alignment despite being eroded during energetic events this persistence is also maintained by the interactions between swash and irregularities e g embayments in the dune backshore morphology the spacing of the observed beach cusps ranged from c min 8 m to c max 67 m these values were underestimated by the edge wave and self organization theories and were better predicted by the sunamura 2004 formula beach cusp growth was linked to breaker angles of near normal incidence and narrow banded frequency wave conditions bay infilling was found to be the most dominant cusp reduction mechanism for larger features c 30 m while smaller features vanished during erosive conditions the most intense cusp growth episodes were linked to accretive conditions while larger features were shown to emerge during more energetic erosion events these findings highlight the need for more longer term observations of diverse beach morphologies to formulate a global theory regarding beach cusp formation and evolution

test of edge wave forcing during formation of rhythmic beach morphology 1 this paper reports on concurrent measurements of evolving rhythmic beach morphology and the associated water motion on a macrotidal coarse sandy beach beach cusps with a spacing of 19 m developed over a 3 day period of low energy swell after which they were destroyed by energetic wind waves the beach cusps were clearly accretionary features and developed mainly during the rising tide detailed hydrodynamic measurements were conducted at three locations in the swash and inner surf zone in the vicinity of a developing cusp horn and revealed that energetic standing mode zero subharmonic edge waves were not present during the initiation of the beach cusps specifically analysis of the hydrodynamic data indicated that 1 the amount of subharmonic energy was limited 10 of the total energy 2 none of the computed energy spectra exhibited a significant peak at the subharmonic frequency 3 the cross shore velocity amplitude at the subharmonic frequency was 2 3 times larger than the longshore velocity amplitude 4 the longshore current motion at the subharmonic frequency was barely coherent between adjacent locations in the surf zone and 5 the time series of pressure and cross shore current were in phase at either side of the developing cusp horn it is concluded that at least during this event of beach cusp formation energetic standing edge waves are not a prerequisite to initiate the development of rhythmic beach morphology

average characteristics and activity dependence of the subauroral polarization stream 1 data from the millstone hill incoherent scatter radar taken over two solar cycles 1979 2000 are examined to determine the average characteristics of the disturbance convection electric field in the midlatitude ionosphere radar azimuth scans provide a regular database of ionospheric plasma convection observations spanning auroral and subauroral latitudes and these scans have been examined for all local times and activity conditions we examine the occurrence and characteristics of a persistent secondary westward convection peak which lies equatorward of the auroral two cell convection individual scans and average patterns of plasma flow identify and characterize this latitudinally broad and persistent subauroral polarization stream saps which spans the nightside from dusk to the early morning sector for all kp greater than 4 premidnight the saps westward convection lies equatorward of l 4 60 invariant latitude spans 3 5 of latitude and has an average peak amplitude of 900 m s in the predawn sector saps is seen as a region of antisunward convection equatorward of l 3 55 spanning 3 of latitude with an average peak amplitude of 400 m s

relation between beachface morphology and wave climate at trafalgar beach cadiz spain abstract two years of offshore wave data and daily time exposure images from trafalgar beach a 2 km long sandy beach located on the southwest coast of spain that frequently exhibits rhythmic features were used to 1 explore the variability of the beachface morphology and 2 determine environmental conditions associated with the different morphological states the beachface morphology at three distinct alongshore sectors was analyzed and classified and five different morphological states were found that are related with the presence or absence of beach cusps and a berm 1 large beach cusps 2 small beach cusps 3 low tide terrace 4 plane beach berm and 5 plane beach the predominant beachface morphology is characterized by the presence of large beach cusps and the main wave climate consisted of offshore significant wave heights ranging from 0 5 1 m and wave periods between 4 and 12 s an alongshore variation of the morphology is found which might be related to the nearshore wave variability swan wave model results the morphologies are in some cases well correlated with the daily offshore incident wave climate described by the daily maximum significant wave height and the corresponding period particularly for the moderate to high energy wave conditions small beach cusps appear under short period waves whereas when the wave periods are longer the morphology tends to change to large beach cusps this transition only occurs if the forcing is maintained as constant for a certain duration which depends itself on the wave energy it is concluded that correlations over 90 are only found for the highest wave energy conditions or under long wave periods for the remainder it is not possible to generally correlate the beachface morphology based only on the wave forcing because the previous morphological state cannot be ignored

dependencies of high latitude plasma convection consideration of interplanetary magnetic field seasonal and universal time factors in statistical patterns 1 the database of the nine radars of the super dual auroral radar network superdarn in the northern hemisphere has been analyzed for information on factors that influence the convection of plasma in the high latitude ionosphere the velocity measurements were collected over the period 1998 2002 the data were first used to derive a new statistical model of convection that improves upon the earlier one radar model of ruohoniemi and greenwald 1996 in its specification of the dependence of the convection pattern on the magnitude and direction of the imf in the gsm y z plane we then derived average patterns for secondary sortings by season year and radar such dependencies as emerged were most clearly seen by contrasting the results for by and by the seasonal effect in the convection pattern is found to have similarities to that of the sign of by in particular the combination of by summer by winter reinforces the tendency of the by sign factor to sculpt the dusk and dawn cells into more round crescent crescent round shapes and to shift the crescent cell across the midnight mlt meridian however these combinations are associated with lower estimates of the total cross polar cap potential drop pc while the nonreinforcing combinations produce elevated pc especially by summer there is an overall tendency for pc to increase from winter to summer although the pure seasonal effect on the potential drop is weaker than that of the by sign season factor we did not find pronounced differences among the patterns derived for the 5 individual years which spanned the most recent interval of solar cycle maximum sorting by radar we found few differences among the patterns for by but for by variations emerged that are consistent with a possible dependence on universal time ut the impacts of season and ut on convection in the high latitude ionosphere thus depends on the imf especially the sign of by we speculate that variability in the ionospheric conductivity has a greater effect on magnetosphere ionosphere coupling under by conditions

understanding coastal morphodynamic patterns from depth averaged sediment concentration this review highlights the important role of the depth averaged sediment concentration dasc to understand the formation of a number of coastal morphodynamic features that have an alongshore rhythmic pattern beach cusps surf zone transverse and crescentic bars and shoreface connected sand ridges we present a formulation and methodology based on the knowledge of the dasc which equals the sediment load divided by the water depth that has been successfully used to understand the characteristics of these features these sand bodies relevant for coastal engineering and other disciplines are located in different parts of the coastal zone and are characterized by different spatial and temporal scales but the same technique can be used to understand them since the sand bodies occur in the presence of depth averaged currents the sediment transport approximately equals a sediment load times the current moreover it is assumed that waves essentially mobilize the sediment and the current increases this mobilization and advects the sediment in such conditions knowing the spatial distribution of the dasc and the depth averaged currents induced by the forcing waves wind and pressure gradients over the patterns allows inferring the convergence divergence of sediment transport deposition erosion occurs where the current flows from areas of high to low low to high values of dasc the formulation and methodology are especially useful to understand the positive feedback mechanisms between flow and morphology leading to the formation of those morphological features but the physical mechanisms for their migration their finite amplitude behavior and their decay can also be explored

on beach cusp formation a system of shallow water equations and a bed evolution equation are used to examine the evolution of perturbations on an erodible initially plane beach subject to normal wave incidence both a permeable under darcy s law and an impermeable beach are considered it is found that alongshore periodic morphological features reminiscent of swash beach cusps form after a number of incident wave periods on both beaches on the permeable impermeable beach these patterns are accretional erosional in both cases flow is horn divergent spacings of the cusps are consistent with observations and are close to those provided by a standing synchronous linear edge wave an analysis of the processes leading to bed change is presented two physical mechanisms are identified concentration gradient and flow divergence which are dominant in the lower and upper swash respectively and their difference over a wave cycle leads to erosion or deposition on an impermeable beach infiltration enters this balance in the upper swash a bed wave of elevation is shown to advance up the beach at the tip of the uprush with a smaller wave of depression on the backwash it is found that cusp horns can grow by a positive feedback mechanism stemming from decreased increased backwash on positive negative bed perturbations

numerical solutions of the sediment conservation law a review and improved formulation for coastal morphological modelling numerical solutions of the sediment conservation law are reviewed in terms of their application to bed update schemes in coastal morphological models it is demonstrated that inadequately formulated numerical techniques lead to the introduction of diffusion dispersion and the bed elevation oscillations previously reported in the literature four different bed update schemes are then reviewed and tested against benchmark analytical solutions these include a first order upwind scheme two lax wendroff schemes and a non oscillating centred scheme nocs recently applied to morphological modelling by saint cast saint cast f 2002 modelisation de la morphodynamique des corps sableux en milieu littoral modelling of coastal sand banks morphodynamics university bordeaux 1 bordeaux 245 pp it is shown that nocs limits and controls numerical errors while including all the sediment flux gradients that control morphological change further no post solution filtering is required which avoids difficulties with selecting filter strength finally nocs is compared to a recent lax wendroff scheme with post solution filtering for a longer term simulation of the morphological evolution around a trained river entrance c 2006 elsevier b v all rights reserved

substorm onset observations by image fuv 1 over the first 2 5 years of operation the fuv instrument on the image spacecraft observed more than 2400 substorm onsets in the northern hemisphere the observations confirm earlier results of statistical studies in terms of a median substorm onset location at 2300 hours mlt and 66 4 degrees magnetic latitude the purpose of this report is to publish the list to allow for further investigation the list can easily be searched for onsets close to certain ground stations or at specific magnetic latitudes or local times as one example of such use we demonstrate how the probability of onset observation was determined for the ground based automatic observatories of the themis time history of events and macroscale interactions during substorms project

a predictive relationship for the spacing of beach cusps in nature abstract modeling is carried out to obtain a relationship that enables the prediction of the spacing of beach cusps using wave and sediment parameters the modeling is based on the concepts that 1 the path of wave uprush flow diverging at a cusp horn has a close connection with the cusp spacing and 2 the flow path is affected by the grain size of beach sediment the following equation is derived a t g h in which is the cusp spacing h is the nearshore wave height t is the wave period is a dimensionless quantity representing the effect of sediment grain size exp 0 23d0 55 where d is the grain size in mm units g is the gravitational acceleration and a 1 35 the value of a is determined using a large amount of existing field data applicability of the predictive equation is examined by using the data from an embayed beach in new south wales australia the result indicates that this equation is capable of reasonably explaining a general trend of the alongshore variation in cusp spacings

relationship between substorm onset locations and nightside convection pattern features 1 this paper presents a study using the super dual auroral radar network superdarn convection database in conjunction with a list of substorm onsets determined from the image satellite to examine the relationship between substorm onset locations and features of the convection pattern particular attention is devoted to the latitude of onset locations compared to the latitude of the near midnight convection reversal boundary crb and the latitude at which the highest flow velocity the flow peak was observed equatorward of the crb because of this focus the set of observations examined is limited to cases where superdarn provided sufficient observations in the midnight sector to determine the latitude of the crb distributions of the latitude difference between the onset location and the crb and flow peak were examined for different times leading up to substorm onset and for a few different conditions it was found that the onsets occurred equatorward of the crb in more than 95 of the cases and that the distribution was approximately centered on the flow velocity peak

a model for sorted circles as self organized patterns sorted circles emerge as self organized patterns from a laterally uniform active layer that becomes laterally sorted as frost heave deforms the interface between a stone layer and an underlying soil layer in a three dimensional cellular model of the active layer cyclic freezing and thawing drives transport of stone and soil particles by 1 addition of ice particles representing soil expansion by frost heave 2 removal of ice particles representing soil consolidation during thawing 3 addition of void particles a discrete abstraction of soil compressibility representing soil expansion by water absorption 4 removal of void particles representing compaction and desiccation of underlying soil by frost heave 5 relaxation of surface morphology by soil creep and stone avalanche and 6 vertical sorting of stones and soil by illuviation these transport processes give rise to sorted circles which are characterized by a mean spacing of 3 6 m a 2 4 m wide soil domain surrounded by a 1 0 m wide 0 3 m high annulus of stones and a 750 year period of circulation in the soil domain all consistent with measured characteristics of sorted circles in western spitsbergen in the model instabilities on the stonesoil interface grow upward as soil plugs by drawing in soil from the surrounding subsurface soil layer soil plugs develop into sorted circles as they contact the ground surface simultaneously elevating an encircling annulus of stones sorted circles are dynamically maintained by circulation within the stone and soil domains initiation of soil plugs is driven by a positive feedback in which frost heave near the stone soil interface pushes soil toward more compressible soil regions where the soil layer is thicker the lateral component of these frost heave induced displacements is not reversed during thaw because soil consolidation as ice rich soil melts and drains and soil expansion as desiccated and compacted soil hydrates displace soil vertically further development of soil plugs and sorted circles is determined by an interplay between this positive feedback and amplitude dependent negative feedbacks that result from decoupling of the freezing front from the stone soil interface parameters outside the range in which sorted circles form can result for example in stone islands and labyrinthine patterns the initial wavelength of perturbations on the stone soil interface is accurately predicted using a linear stability analysis but increase in this wavelength through time reflects the nonlinearities that control the spacing of soil plugs and sorted circles namely interactions and mergers between neighboring forms

a superposed epoch study of superdarn convection observations during substorms 1 case studies of flow patterns during substorms have revealed characteristic patterns in the period leading to expansion onset velocities in the premidnight region have been observed to become strongly sheared and the premidnight convection reversal has been observed to extend across the midnight meridian at expansion onset the shear decreases and flow at midnight becomes meridional out of the polar cap the study presented here superposes flow patterns from 10 substorm intervals to determine the average flow patterns the study confirms the findings of the case studies and extends them to additional local time sectors in addition changes to the flow pattern after expansion onset are examined

beach cusps as self organized patterns computer simulations of flow and sediment transport in the swash zone on a beach demonstrate that a model that couples local flow acceleration and alongshore surface gradient is sufficient to produce uniformly spaced beach cusps the characteristics of the simulated cusps and the conditions under which they form are in reasonable agreement with observations of natural cusps the self organization mechanism in the model is incompatible with an accepted model in which standing alongshore waves drive the regular pattern of erosion and deposition that gives rise to beach cusps because the models make similar predictions it is concluded that currently available observational data are insufficient for discrimination between them

investigation of a self organization model for beach cusp formation and development a recent numerical investigation of self organization werner and fink 1993 suggests that the feedback process between currents and sediment response can result in self organized patterns and can be used to predict beach cusp formation and spacing a similar model based on self organization is tested here in order to understand the processes occurring during beach cusp formation and development to evaluate the sensitivity toward the parameters used and to examine how the model might relate to field observations results obtained confirm the validity of the self organization approach and its capacity to predict beach cusp spacing with values in fair agreement with the available field measurements with most of the input parameters primarily affecting the rate of the process rather than the final spacing however changes in the random seed and runs for large numbers of swash cycles reveal a dynamical system with significant unpredictable behavior cusp spacing tends to change with time and cusp regularity shows large long term variations cusps are found to be accretionary in the swash zone and in agreement with most observations mean flows are horn divergent over developed topography simulations over nonplanar slopes characterized by the presence of preexisting nonrhythmic or cuspate features have been performed results indicate that preexisting large amplitude cusps are destroyed if their spacing is substantially different from that expected under self organization and that the final spacing is consistent with that predicted by the model for an equivalent plane beach these findings support the hypothesis that self organization is a robust mechanism for beach cusp formation

substorm convection patterns observed by the super dual auroral radar network a study of convection patterns during substorms observed by the super dual auroral radar network superdarn radar network is presented specific attention is given to the growth phase and the time immediately following expansion onset it is found that the growth phase is characterized by the enhancement of the velocity shear near midnight and its extension to low latitudes and to local times across the midnight meridian the velocity shear was observed to diminish at expansion onset in addition the ionospheric flow velocity magnitude was observed to be enhanced for some period of time prior to expansion onset and to decrease at expansion onset possible explanations for the establishment of the midnight velocity shear during growth phase and its subsequent disappearance at expansion onset are presented also arguments are presented regarding the decrease of ionospheric flow velocity at expansion onset

morphometric and sediment analysis of beach cusp in correlation to rip currents a case study from tropical coast west coast of india the presence of rhythmic beach cusps in foreshore regions are of persistent research interest to coastal researchers engineers with respect to their formation in beaches morphometric and sediment analysis were used to study beach cusp morphology at vengurla beach a gentle slope beach characterized by medium sand the cusp dimensions such as spacing elevation amplitude and depth were measured for detailed analysis the distinctive sediment characteristics between the horn and the bays of the cusp are different and cusp measurements show a high level of irregularity horns and bays have medium sand but sorting is varying sorting variations clearly demonstrated the difference in energy condition between horns and bay negative skewness of few horn samples has been correlated with erosional trend based on the grain size analysis result it was observed that vengurla beach cusps follow the regular grain size distribution pattern additionally the low intensity rip currents were also noticed in the study area the rate of occurrence and strength of rip currents are decided by the nearshore bathymetry and play an imperative role in rip current formation the present study is based upon the field measurements along vengurla coast and contributes to morphometric analysis of beach cusps regarding beach cusps there are no documented databases along the indian coast understanding the beach cusp formation and its seasonal changes along the beaches will be useful for effective coastal management

a cellular model of braided rivers a broad sheet of water flowing over non cohesive sediment typically breaks up into a network of interconnected channels called a braided stream fig 1 the dynamics of such networks are complex channels migrate laterally split rejoin and develop bars with the flow shifting unpredictably from one part of the network to another many processes are known to operate in a braided river1 3 but it is unclear which of these are essential to explain the observed dynamics we describe here a simple deterministic numerical model of water flow over a cohesionless bed that captures the main spatial and temporal features of real braided rivers the patterns arise from local scour and deposition caused by a nonlinear dependence of bedload sediment flux on water discharge although the morphology of the resulting network depends in detail on the sediment transport rule used in the model our results suggest that the only factors essential for braiding are bedload sediment transport and laterally unconstrained free surface flow

morphodynamics of nearshore rhythmic sandbars in a mixed energy environment sw france 2 physical forcing analysis abstract the morphology and migration of rhythmic intertidal ridge and runnel systems and subtidal crescentic bars that border the southwest coast of france were characterized using in situ surveys and maps obtained by remote sensing methods the period from 1986 to 2000 was investigated a total of 35 km of coast was mapped this data set shows several specificities the origin of which are examined in the present report using hydrodynamic data a complete analysis of the influence of wave climate on both the shape and the movements of these rhythmic sedimentary patterns was performed in addition swan and morphodyn coupled numerical models were used to provide quantification of both wave breaking and longshore currents for wave parameters that were representative of the mean values and of the energetic conditions this study demonstrated the short time response of intertidal systems to the wave forcing when the offshore significant wave height h s was lower than 2 5 m regular coastal ridge and runnel systems developed in the intertidal zone and migrated in the longshore drift direction at a rate of 1 7 3 1 m day 1 by contrast the ridge and runnel system morphology abruptly changed when the h s exceeded 2 5 m and after the storm the typical ridge and runnel rhythmic topography was recovered within 5 9 days the crescentic bars which had a convex seaward shape were affected by waves with h s values greater than 3 m slightly less for short waves depending on the wave orientation the crescentic bars moved in the longshore drift direction at a rate that reached 1 m day 1 the data suggested a slight negative correlation between the mean alongshore length of the crescentic bar and the mean h s finally it seemed that increasing the wave obliquity with respect to the coast resulted in the flattening of the crescentic bars thus coupling spot and in situ mapping to hydrodynamic records allow the characterization of coastal morphology and dynamics with time and space samplings that are particularly well adapted to the little studied alongshore morphodynamics this approach should improve the difficult parameterization of morphodynamic models in high energy environments

large scale imaging of high latitude convection with super dual auroral radar network hf radar observations the hf radars of the super dual auroral radar network superdarn provide measurements of the e b drift of ionospheric plasma over extended regions of the high latitude ionosphere with the recent augmentation of the northern hemisphere component to six radars a sizable fraction of the entire convection zone approximately one third can be imaged nearly instantaneously 2 min to date the two dimensional convection velocity has been mapped by combining line of sight velocity measurements obtained from pairs of radars within common volume areas we describe a new method of deriving large scale convection maps based on all the available velocity data the measurements are used to determine a solution for the distribution of electrostatic potential expressed as a series expansion in spherical harmonics the addition of data from a statistical model constrains the solution in regions of no data coverage for low order expansions the results provide a gross characterization of the global convection we discuss the processing of the radar velocity data the factors that condition the fitting and the reliability of the results we present examples of imaging that demonstrate the response of the global convection to variations in the interplanetary magnetic field imf in the case of a sudden polarity change from northward to southward imf the convection is seen to reconfigure globally on very short 6 min timescales

cumulative versus transient shoreline change dependencies on temporal and spatial scale using shoreline change measurements of two oceanside reaches of the north carolina outer banks usa we explore an existing premise that shoreline change on a sandy coast is a self affine signal wherein patterns of change are scale invariant wavelet analysis confirms that the mean variance spectral power of shoreline change can be approximated by a power law at alongshore scales from tens of meters up to 4 8 km however the possibility of a power law relationship does not necessarily reveal a unifying scale free dominant process and deviations from power law scaling at scales of kilometers to tens of kilometers may suggest further insights into shoreline change processes specifically the maximum of the variance in shoreline change and the scale at which that maximum occurs both increase when shoreline change is measured over longer time scales this suggests a temporal control on the magnitude of change possible at a given spatial scale and by extension that aggregation of shoreline change over time is an important component of large scale shifts in shoreline position we also find a consistent difference in variance magnitude between the two survey reaches at large spatial scales which may be related to differences in oceanographic forcing conditions or may involve hydrodynamic interactions with nearshore geologic bathymetric structures overall the findings suggest that shoreline change at small spatial scales less than kilometers does not represent a peak in the shoreline change signal and that change at larger spatial scales dominates the signal emphasizing the need for studies that target long term large scale shoreline change

superposed epoch analysis of the ionospheric convection evolution during substorms imf by dependence we present superposed epoch analyses of the average ionospheric convection response in the northern and southern hemispheres to magnetospheric substorms occurring under different orientations of the interplanetary magnetic field imf observations of the ionospheric convection were provided by the super dual auroral radar network superdarn and substorms were identified using the far ultraviolet fuv instrument on board the imager for magnetopause to aurora global exploration image spacecraft we find that during the substorm growth phase the expected imf by dependent dawn dusk asymmetry is observed over the entire convection pattern but that during the expansion phase this asymmetry is retained only in the polar cap and dayside auroral zone in the nightside auroral zone the convection is reordered according to the local substorm electrodynamics with any remaining dusk dawn asymmetry being more closely related to the magnetic local time of substorm onset itself only weakly governed by imf by owing to the preponderance of substorms occurring just prior to magnetic midnight the substorm asymmetry tends to be an azimuthal extension of the dusk convection cell across the midnight sector a manifestation of the so called harang discontinuity this results in the northern southern hemisphere nightside auroral convection during substorms generally resembling the expected pattern for negative positive imf by when the preexisting convection pattern in the northern southern hemisphere is driven by positive negative imf by the nightside auroral convection changes markedly over the course of the substorm to establish this same harang configuration

eolian dunes computer simulations and attractor interpretation a simple computer simulation algorithm for the transport of sand by wind produces forms resembling barchan crescentic ridge linear and star natural dune classes sand is moved as slabs composed of many grains that are picked up at random transported in a specified direction and deposited 1 with a probability that depends on the local presence or absence of sand or 2 in shadow zones in the lee of dunes the simulated dune fields are interpreted as complex systems with sand dune classes being dynamical attractors of these systems the evolution of dunes once formed becomes decoupled from the details of eolian sand transport

test of self organization in beach cusp formation 1 field observations of swash flow patterns and morphology change are consistent with the hypothesis that beach cusps form by self organization wherein positive feedback between swash flow and developing morphology causes initial development of the pattern and negative feedback owing to circulation of flow within beach cusp bays causes pattern stabilization the self organization hypothesis is tested using measurements from three experiments on a barrier island beach in north carolina beach cusps developed after the beach was smoothed by a storm and after existing beach cusps were smoothed by a bulldozer swash front motions were recorded on video during daylight hours and morphology was measured by surveying at 3 4 hour intervals three signatures of self organization were observed in all experiments first time lags between swash front motions in beach cusp bays and horns increase with increasing relief representing the effect of morphology on flow second differential erosion between bays and horns initially increases with increasing time lag representing the effect of flow on morphology change because positive feedback causes growth of beach cusps third after initial growth differential erosion decreases with increasing time lag representing the onset of negative feedback that stabilizes beach cusps a numerical model based on self organization initialized with measured morphology and alongshore uniform distributions of initial velocities and positions of the swash front at the beginning of a swash cycle reproduces the measurements except for parts of one experiment where limited surveys and a significant low frequency component to swash motions might have caused errors in model initialization