wave induced sediment transport and sandbar migration onshore sediment transport and sandbar migration are important to the morphological evolution of beaches but are not well understood here a model that accounts for fluid accelerations in waves predicts the onshore sandbar migration observed on an ocean beach in both the observations and the model the location of the maximum acceleration induced transport moves shoreward with the sandbar resulting in feedback between waves and morphology that drives the bar shoreward until conditions change a model that combines the effects of transport by waves and mean currents simulated both onshore and offshore bar migration observed over a 45 day period

storm time observations of plasmasphere erosion flux in the magnetosphere and ionosphere plasmasphere erosion carries cold dense plasma of ionospheric origin in a storm enhanced density plume extending from dusk toward and through the noontime cusp and dayside magnetopause and back across polar latitudes in a polar tongue of ionization we examine dusk sector 20 mlt plasmasphere erosion during the 17 march 2013 storm dst 130 nt using simultaneous magnetically aligned direct sunward ion flux observations at high altitude by van allen probes rbsp a at 3 0 re and at ionospheric heights 840 km by dmsp f 18 plasma erosion occurs at both high and low altitudes where the subauroral polarization stream flow overlaps the outer plasmasphere at 20 ut rbsp a observed 1 2e12 m 2 s 1 erosion flux while dmsp f 18 observed 2e13 m 2 s 1 sunward flux we find close similarities at high and low altitudes between the erosion plume in both invariant latitude spatial extent and plasma characteristics

direct observations of the evolution of polar cap ionization patches patches of ionization are common in the polar ionosphere where their motion and associated density gradients give variable disturbances to high frequency hf radio communications over the horizon radar location errors and disruption and errors to satellite navigation and communication their formation and evolution are poorly understood particularly under disturbed space weather conditions we report direct observations of the full evolution of patches during a geomagnetic storm including formation polar cap entry transpolar evolution polar cap exit and sunward return flow our observations show that modulation of nightside reconnection in the substorm cycle of the magnetosphere helps form the gaps between patches where steady convection would give a tongue of ionization toi

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

a statistical study of the subauroral polarization stream over north american sector using the millstone hill incoherent scatter radar 1979 2019 measurements this work conducts a statistical study of the subauroral polarization stream saps feature in the north american sector using millstone hill incoherent scatter radar measurements from 1979 to 2019

cyclonic spirals in tidally accelerating bottom boundary layers in the zhujiang pearl river estuary abstracta velocity spiral in the tidally accelerating bottom boundary layer bbl was defined as a directional shear of the prevailing flow with the elevation and the tidal phase however so far there is no information on the spiral for the oscillatory bbl flows or a valid explanation for its origin life history and persistence to investigate this rotating current in the tidally accelerating bbl flow the authors performed instrumented tripod observations in the tidally energetic zhujiang pearl river estuary the tidal bbl flows may fall into three distinct regimes i the quasi steady phase in the peak tide ii the accelerating decelerating phase at the slack tide and iii the transition between i and ii when a cyclonic spiral occurs only in the early late ebb the subcritical spiral defined by a froude number of the oscillatory bbl flow may be analytically examined by unsteady linearized turbulent bbl equations the spiral is formed under the momentum balance between local acceleration

multiradar observations of the polar tongue of ionization 1 we present a global view of large scale ionospheric disturbances during the main phase of a major geomagnetic storm we find that the low latitude auroral and polar latitude regions are coupled by processes that redistribute thermal plasma throughout the system for the large geomagnetic storm on 20 november 2003 we examine data from the high latitude incoherent scatter radars at millstone hill sondrestrom and eiscat tromso with superdarn hf radar observations of the high latitude convection pattern and dmsp observations of in situ plasma parameters in the topside ionosphere we combine these with north polar maps of stormtime plumes of enhanced total electron content tec derived from a network of gps receivers the polar tongue of ionization toi is seen to be a continuous stream of dense cold plasma entrained in the global convection pattern the dayside source of the toi is the plume of storm enhanced density sed transported from low latitudes in the postnoon sector by the subauroral disturbance electric field convection carries this material through the dayside cusp and across the polar cap to the nightside where the auroral f region is significantly enhanced by the sed material the three incoherent scatter radars provided full altitude profiles of plasma density temperatures and vertical velocity as the toi plume crossed their different positions under the cusp in the center of the polar cap and at the midnight oval polar cap boundary greatly elevated f peak density 1 5e12 m 3 and low electron and ion temperatures 2500 k at the f peak altitude characterize the sed toi plasma observed at all points along its high latitude trajectory for this event sed toi f region tec 150 1000 km was 50 tecu both in the cusp and in the center of the polar cap large upward directed fluxes of o 1 e14 m 2 s 1 were observed in the topside ionosphere

on the generation decay of the storm enhanced density plumes role of the convection flow and field aligned ion flow storm enhanced density sed plumes are prominent ionospheric electron density increases at the dayside middle and high latitudes the generation and decay mechanisms of the plumes are still not clear we present observations of sed plumes during six storms between 2010 and 2013 and comprehensively analyze the associated ionospheric parameters within the plumes including vertical ion flow field aligned ion flow and flux plasma temperature and field aligned currents obtained from multiple instruments including gps total electron content tec poker flat incoherent scatter radar pfisr super dual auroral radar network and active magnetosphere and planetary electrodynamics response experiment the tec increase within the sed plumes at the pfisr site can be 1 4 5 5 times their quiet time value the plumes are usually associated with northwestward e b flows ranging from a couple of hundred m s 1 to 1 km s 1 upward vertical flows due to the projection of these e b drifts are mainly responsible for lifting the plasma in sunlit regions to higher altitude and thus leading to plume density enhancement the upward vertical flows near the poleward part of the plumes are more persistent while those near the equatorward part are more patchy in addition the plumes can be collocated with either upward or downward field aligned currents facs but are usually observed equatorward of the peak of the region 1 upward fac suggesting that the northwestward flows collocated with plumes can be either subauroral or auroral flows furthermore during the decay phase of the plume large downward ion flows as large as 200 m s 1 and downward fluxes as large as 1014 m 2 s 1 are often observed within the plumes in our study of six storms enhanced ambipolar diffusion due to an elevated pressure gradient is able to explain two of the four large downward flow flux cases but this mechanism is not sufficient for the other two cases where the flows are of larger magnitude for the latter two cases enhanced poleward thermospheric wind is suggested to be another mechanism for pushing the plasma downward along the field line these downward flows should be an important mechanism for the decay of the sed plumes

modeling subauroral polarization streams during the 17 march 2013 storm the subauroral polarization streams saps are one of the most important features in representing magnetosphere ionosphere coupling processes in this study we use a state of the art modeling framework that couples an inner magnetospheric ring current model ram scb with a global mhd model block adaptive tree solar wind roe upwind scheme bats r us and an ionospheric potential solver to study the saps that occurred during the 17 march 2013 storm event as well as to assess the modeling capability both ionospheric and magnetospheric signatures associated with saps are analyzed to understand the spatial and temporal evolution of the electrodynamics in the midlatitude regions results show that the model captures the saps at subauroral latitudes where region 2 field aligned currents facs flow down to the ionosphere and the conductance is lower than in the higher latitude auroral zone comparisons to observations such as facs observed by active magnetosphere and planetary electrodynamics response experiment ampere cross track ion drift from defense meteorological satellite program dmsp and in situ electric field observations from the van allen probes indicate that the model generally reproduces the global dynamics of the region 2 facs the position of saps along the dmsp and the location of the saps electric field around l of 3 0 in the inner magnetosphere near the equator the model also demonstrates double westward flow channels in the dusk sector the higher latitude auroral convection and the subauroral saps and captures the mechanism of the saps however the comparison with ion drifts along dmsp trajectories shows an underestimate of the magnitude of the saps and the sensitivity to the specific location and time the comparison of the saps electric field with that measured from the van allen probes shows that the simulated saps electric field penetrates deeper than in reality implying that the shielding from the region 2 facs in the model is not well represented possible solutions in future studies to improve the modeling capability include implementing a self consistent ionospheric conductivity module from inner magnetosphere particle precipitation coupling with the thermosphere ionosphere chemical processes and connecting the ionosphere with the inner magnetosphere by the stronger region 2 facs calculated in the inner magnetosphere model

contrasts between estuarine and river systems in near bed turbulent flows in the zhujiang pearl river estuary china a bottom mounted instrumental tripod was deployed in the tidally energetic zhujiang pearl river estuary to examine the contrasting properties of the bottom boundary layer bbl flows between estuarine and tide affected river systems three aspects of the bbl flows were investigated to understand the mechanism of the turbulence responses to the large scale ambient forcing the flow structures profile anisotropy and spectra shearing strains and stresses and the balance of turbulent kinetic energy tke single log law profiles and turbulence anisotropy predominated in the two systems but the non log regime and stronger anisotropy occurred more frequently at the slack tide in the estuary the adv based turbulence intensities and shearing strains both exceeded their low frequency counterparts frictional velocities and mean shears derived from the logarithmic law on the contrary the adv based reynolds stresses were smaller than the log profile derived bottom stresses so the hypothesis of a constant stress layer cannot be well satisfied especially in the river the bandwidth of the inertial subrange in the river was of one decade larger than in the estuary the balance between shear production and viscous dissipation was better achieved in the straight river this first order balance was significantly broken in the estuary and in the meandering river by non shear production dissipation due to wave induced fluctuations or salinity sediment stratification all these disparities between two systems in turbulence properties are essentially controlled by the anisotropy induced by the large scale processes such as secondary currents density stratification in conclusion the acceleration of unsteady flows determines the profile structure of the bbl flow and turbulence anisotropy results in the invalidation of the phenomenological relations such as the constant stress hypothesis and the first order tke balance

direct observations of the role of convection electric field in the formation of a polar tongue of ionization from storm enhanced density 1 we examine the relationship of convection electric fields to the formation of a polar cap tongue of ionization toi from midlatitude plumes of storm enhanced density sed observations from the geomagnetic storm on 26 27 september 2011 are presented for two distinct sed events during an hour long period of geomagnetic activity driven by a coronal mass ejection a channel of high density f region plasma was transported from the dayside subauroral ionosphere and into the polar cap by enhanced convection electric fields extending to middle latitudes this toi feature was associated with enhanced hf backscatter indicating that it was the seat of active formation of small scale irregularities after the solar wind interplanetary magnetic field conditions quieted and the dayside convection electric fields retreated to higher latitudes an sed plume was observed extending to but not entering the dayside cusp region this prominent feature in the distribution of total electron content tec persisted for several hours and elongated in magnetic local time with the rotation of the earth no ionospheric scatter from superdarn radars was observed within this sed region the source mechanism enhanced electric fields previously drawing the plasma from midlatitudes and into the polar cap as a toi was no longer active resulting in a fossil feature we thus demonstrate the controlling role exercised by the convection electric field in generating a toi from midlatitude sed

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

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

soil phosphorus cycling in an antarctic polar desert abstract soil phosphorus distribution and cycling in the mcmurdo dry valleys is poorly understood despite its importance for contemporary antarctic ecosystem processes we present data from sequential chemical extractions of phosphorus pools from dry valley soils and sediments on tills across a gradient of surface exposure ages and across potential weathering gradients in stream channels the geologically old but poorly weathered soils of the dry valleys have large phosphorus pools relative to in situ biological requirements these pools are dominated by unweathered p fractions comprising between 60 and 90 of total soil phosphorus among sites occurring on tills ranging in surface exposure ages of approximately 103 106 yrs variation in total phosphorus concentration and availability are related to differences in the initial p content of these tills ross sea tills contain basalts and kenyte which contribute to higher concentrations of phosphorus relative to soils developing on tills deposited by advances of the taylor glacier at local scales physicochemical gradients contribute to variation in weathering rates altering the distribution of phosphorus among chemical fractions which differ in their potential mobility and availability to microorganisms for example hyporheic stream sediments exhibit evidence of phosphorus weathering from primary minerals and loss relative to upland soils adjacent to stream channels dry valley landscapes glaciers lakes streams soils are hydrologically connected providing a mechanism for phosphorus weathering and mobilization in soils and sediments to contribute to the nutrient budgets of adjacent aquatic ecosystems we suggest that landscape history till composition and contemporary subsurface and stream hydrology are the primary controls over phosphorus cycling in the mcmurdo dry valleys

estimating bottom stress in tidal boundary layer from acoustic doppler velocimeter data bed stresses in the bottom boundary layer of the york river estuary virginia were estimated from three dimensional near bottom velocities measured by acoustic doppler velocimeters advs and also by a profiling array of electromagnetic current meters by assuming the measurements were made in a constant stress layer four methods of stress estimation were evaluated using advs direct covariance cov measurement turbulent kinetic energy inertial dissipation utilizing the kolmogorov spectrum and log profile the four methods yielded similar estimates of frictional velocity u based on adv output from both 14 cm and 44 cm above bed all eight estimates of average u were consistent with the overall mean of 1 10 cm s to within the 95 confidence interval for individual burst estimates the cov method worked slightly better nearer the bed possibly because of the sensitivity of cov to the upper limit of the constant stress layer the inertial dissipation method performed marginally well at 14 cm above bed likely because of sediment induced stratification and insufficient separation of turbulent production and dissipation scales the log profile method was the most variable and appeared most sensitive to stratification and to the thickness of the constant stress layer the turbulent kinetic energy method was the most consistent at both heights and appears most promising for further development results encourage future use of the adv in estuarine environments but also favor the simultaneous use of several methods to estimate bottom stress

plasma convection in the vicinity of the dayside cleft experiments conducted with the chatanika alaska incoherent scatter radar observed the ionospheric convection pattern equatorward of the noontime cleft there plasma transport is characterized by low speed convergence toward a meridian centered somewhat before noon and rotation of the flow into a poleward direction at higher latitudes for undisturbed conditions there is only weak convection at noon at these latitudes but the eastward electric field reaches a maximum of 15 mv m 2 4 hours before and after noon at latitudes between 70 and 74 during active conditions at the peak of the solar cycle the ionospheric cleft was located within the chatanika field of view on several occasions a longitudinally narrow region of rapid poleward convection near noon was not observed rather poleward flow occurred over a 3 4 hour spread of local time for disturbed conditions the prenoon and postnoon regions of plasma entry into the polar cap were enhanced and an eastward electric field of 25 mv m was seen across the 2 hours of local time around noon high density f region plasma was observed convecting poleward through the cleft from a source at lower latitudes in the afternoon sector such plasma seen at very high latitudes within the polar cap serves as a tracer of the convection pattern away from the cleft

storm time plasma transport at middle and high latitudes associated with the large scale enhancement of the ionospheric convection electric field during disturbed geomagnetic conditions solar produced f region plasma is transported to and through the noontime cleft from a source region at middle and low latitudes in the afternoon sector as a result of the offset between the geomagnetic and geographic poles the afternoon sector region of strong sunward convection is shifted to increasingly lower geographic latitude throughout the interval between 12 ut and 24 ut a snowplow effect occurs in which the convection cell continually encounters fresh corotating ionospheric plasma along its equatorward edge producing a latitudinally narrow region of storm enhanced plasma density sed and increased total electron content which is advected toward higher latitudes in the noon sector the millstone hill incoherent scatter radar regularly observes sed as a spatially continuous large scale feature spanning local times between noon and midnight and at latitudes between the polar cap and its mid or low latitude source region for local times away from noon the latitude of most probable sed occurrence moves equatorward by 6 for an increase of 2 in the kp index during strong disturbances the topside sed is observed to be convecting sunward at 750 m s 1 with a flux of 1014 m 2 s 1 this feature accounts for the pronounced enhancement of ionospheric density near dusk at middle latitudes observed during the early stages of magnetic storms called the dusk effect and constitutes a source for the enhanced f region plasma observed in the polar cap during disturbed conditions

sediment trapping of turbidity maxima in the changjiang estuary abstract sediment trapping in the turbidity maxima tm is highly variable in different estuaries or at different times in the same estuary how related processes influence the tm behavior and its structure has not yet been completely clear here we present moored and shipboard observations in the 2008 flood and dry seasons in the lower reaches of the changjiang estuary where the deepwater navigation channel was still under construction the excavation of the pristine mouth bar has caused the saline wedge to move upstream resulting in new tm zones the magnitude and extent of the tm are strongly seasonal under the influence of distinct sediment processes the tm appears as a high concentration undercurrent in the flood season whereas they occur as a low concentration sediment cloud over the water column in the dry season the hyperpycnal flow can be formed by flocculation settling and the sediment cloud can be caused primarily by resuspension the sediment trapping in the tm occurs more often during accelerating and decelerating ebb tides when the bed stress is small but the flow is highly accelerating and decelerating sediment resuspension and deposition at these tidal reversals can be induced by the growing and decaying flow spirals respectively therefore the diversity of the tm may be associated with density stratification accelerating flows flocculation or generally the interaction between stratified flows and cohesive sediments

ionospheric signatures of plasmaspheric tails 1 we make direct comparisons between gps maps of total electron content tec over the north american continent millstone hill radar observations of storm enhanced density and low and high altitude satellite measurements of the perturbation of the outer plasmasphere during the march 31 2001 geomagnetic storm we find that storm enhanced density sed and plumes of greatly elevated tec are associated with the erosion of the outer plasmasphere by strong sub auroral polarization electric fields the sed tec plumes identified at low altitude map closely onto the magnetospheric determination of the boundaries of the plasmapause and plasmaspheric tail determined by euv imaging from the image spacecraft characteristics of the sed tec plumes tails for the march 31 2001 event are tec 100 tecu f region sunward velocity 1000 m s sunward flux 5 1024 ions s 1 total transport to dayside magnetopause merging region 3 hr event 5 1028 ions

movable bed roughness in unsteady oscillatory flow a model to predict the roughness in unsteady oscillatory flows over movable noncohesive beds is presented the roughness over movable beds is shown to be a function of the boundary shear stress rather than a fixed geometrical scale as is the case for fully rough turbulent boundary shear flows over immobile beds the model partitions the roughness into two distinct contributions these two contributions are due to the form drag around individual bed forms and to the near bed sediment transport the form drag over the bed forms is treated explicitly as a function of the boundary geometry and shear stress the ripples are predicted as a function of the local skin friction and a semiempirical expression is derived using standard law of the wall arguments which gives the ripple or form roughness as a function of the boundary geometry the ripple roughness is found to be proportional to the product of the ripple steepness and height favorable comparison of the form drag model with the results of bagnold s 1946 fixed ripple study is found the value of z0 associated with intense sediment transport in oscillatory flow over a flat bed is determined from carstens et al s 1969 experiments this value is found to be 7 or 8 grain diameters an expression is derived for the roughness associated with the maximum thickness of a near bottom sediment transporting layer consistent with owen s 1964 roughness hypothesis for saltation of uniform grains in air at large values of the boundary shear stress relative to the critical value for initial sediment motion the derived expression is similar to the results of smith and mclean s 1977 unidirectional flow approach modified for oscillatory flow the total roughness model is found to compare favorably with carstens et al s 1969 data in contrast to smith and mclean s 1977 steady flow findings the results here show that when ripples are present they account for a significant portion of the boundary roughness

sandbars in motion nearshore surf zones are turbulent places yet despite the apparently chaotic nature of the sea surface in these areas sandbars often show complex patterns with an intricate structure in their perspective stive and reniers discuss recent efforts to understand how these patterns form they highlight the report by hoefel and elgar who consider a new transport mechanism based on flow acceleration within the waves this mechanism should help to improve the predictability of sandbar structures