new evidence of a herd of titanosauriform sauropods from the lower berriasian of the iberian range spain abstract a study of the undescribed part of the las cerradicas tracksite in galve teruel spain has revealed 6 trackways made by small sauropods showing gregarious behaviour parallel trackways las cerradicas is located towards the top of the villar del arzobispo formation early berriasian the wide gauge condition the manus pes distance the kidney shaped morphology of the manus and the subtriangular morphology of the pes with a big digit i that swells medially and a narrow heel oriented posterolaterally suggest that the sauropods in question are more similar to sauropodichnus giganteus than to any other sauropod ichnotaxa some of the features point to the titanosauriforms as the best candidates to be the trackmakers recent work in bone histology the differences with respect to other iberian tracksites of similar age and the differences with respect to other sauropod herds of the track record do not allow us to establish whether the sauropods were juvenile or dwarfs the sauropod skeletal record and other large sauropod footprints in the villar del arzobispo formation could tip the scales in favour of the first hypothesis

large scale dam removal on the elwha river washington usa river channel and floodplain geomorphic change abstract a substantial increase in fluvial sediment supply relative to transport capacity causes complex large magnitude changes in river and floodplain morphology downstream although sedimentary and geomorphic responses to sediment pulses are a fundamental part of landscape evolution few opportunities exist to quantify those processes over field scales we investigated the downstream effects of sediment released during the largest dam removal in history on the elwha river washington usa by measuring changes in riverbed elevation and topography bed sediment grain size and channel planform as two dams were removed in stages over two years as 10 5 million t 7 1 million m3 of sediment was released from two former reservoirs downstream dispersion of a sediment wave caused widespread bed aggradation of 1 m greater where pools filled changed the river from pool riffle to braided morphology and decreased the slope of the lowermost river the newly deposited sediment which was finer than most of the pre dam removal bed formed new bars largely pebble granule and sand material prompting aggradational channel avulsion that increased the channel braiding index by almost 50 as a result of mainstem bed aggradation floodplain channels received flow and accumulated new sediment even during low to moderate flow conditions the river system showed a two to tenfold greater geomorphic response to dam removal in terms of bed elevation change magnitude than it had to a 40 year flood event four years before dam removal two years after dam removal began as the river had started to incise through deposits of the initial sediment wave 1 2 million t of new sediment 10 of the amount released from the two reservoirs was stored along 18 river km of the mainstem channel and 25 km of floodplain channels the elwha river thus was able to transport most of the released sediment to the river mouth the geomorphic alterations and changing bed sediment grain size along the elwha river have important ecological implications affecting aquatic habitat structure benthic fauna salmonid fish spawning and rearing potential and riparian vegetation the response of the river to dam removal represents a unique opportunity to observe and quantify fundamental geomorphic processes associated with a massive sediment influx and also provides important lessons for future river restoration endeavors

deconstructing atlantic intertropical convergence zone variability influence of the local cross equatorial sea surface temperature gradient and remote forcing from the eastern equatorial pacific 1 we investigate causes of interannual variability in atlantic intertropical convergence zone itcz convection using a monthly mean global precipitation data set spanning 1979 1999 starting from the hypothesis of two dominant influences on the itcz namely the cross equatorial gradient in tropical atlantic sea surface temperature sst and the anomalous walker circulation due to the rearrangement of tropical pacific convection associated with the el nino southern oscillation we analyze anomaly composites over the 1979 1999 period that best isolate the effects of each mechanism our results suggest that to first order a strong anomalous walker circulation suppresses precipitation over the tropical atlantic whereas an anomalous warm north cool south sst gradient shifts the meridional location of maximum itcz convection anomalously north we examined the processes underlying each of the two mechanisms for the anomalous walker circulation we find consistency with the idea of suppression of convection through warming of the tropical troposphere brought about by anomalous convective heating in the eastern equatorial pacific for the sst gradient mechanism our results confirm previous studies that link convection to cross equatorial winds forced by meridional sst gradients we find that positive surface flux feedback brought about through the cross equatorial winds is weak and confined to the deep tropics on the basis of the results of this and other studies we propose an expanded physical picture that explains key features of atlantic itcz variability including its seasonal preference its sensitivity to small anomalous sst gradients and its role in the context of tropical atlantic sst gradient variability index terms 4215 oceanography general climate and interannual variability 3309 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 3354 meteorology and atmospheric dynamics precipitation 1854 3374 meteorology and atmospheric dynamics tropical meteorology 4522 oceanography physical ocean optics keywords tropical atlantic precipitation climate variability el nino southern oscillation ocean atmosphere interaction

a comparison of past small dam removals in highly sediment impacted systems in the u s abstract the ability to predict the effects of dam removal in highly sediment filled systems is increasingly important as the number of such dam removal cases continues to grow the cost and potential impacts of dam removal are site specific and can vary substantially depending on local conditions of specific concern in sediment impacted removals is the volume and rate of reservoir deposit erosion the complexity and potential accuracy of modeling methods used to forecast the effects of such dam removals vary substantially current methods range from predictions based on simple analysis of pre dam channel geometry to sophisticated data intensive three dimensional numerical models in the work presented here we utilize data collected from past dam removals to develop an additional tool for predicting the rate and volume of sediment deposit erosion through the analysis of sediment discharge deposit removal timeline channel and watershed data in conjunction with post removal monitoring data from a wide range of dam removal projects some significant trends in the evolution of reservoir deposits following dam removal can be seen results indicate that parameters such as median grain size level of cohesion spatial variability of the deposit and removal timeline are among the most influential factors in determining the rate and volume of sediment erosion by comparing local conditions of dams and reservoirs slated for removal with those of past removals we hope that predictions of the rate and volume of sediment deposit erosion can be usefully constrained

the evolution of gravel bed channels after dam removal case study of the anaconda and union city dam removals the anaconda and union city dams on the naugatuck river in connecticut were removed in february and october 1999 a detailed study of the sites prior to removal was undertaken including sediment testing and predictions of upstream channel formation post dam removal the 3 35 m high timber crib rock fill spillway of the anaconda dam partially breached during a storm prior to the dam s scheduled removal allowing a portion of the impounded sediment to move down through the river system this event changed the removal plans and the remainder of the spillway was removed under an emergency order in the course of 4 days the union city dam a 2 44 m high timber crib rock fill dam capped with concrete and stone was removed on schedule a portion of the impounded sediment was removed by mechanical means during the deconstruction of the structure the evolution of the two upstream channels post project provided unique challenges and valuable insights as to what kind of channel transition can be expected in gravel bed river systems after a low head dam has been removed this paper describes the initial engineering analysis and design the subsequent removal of the two dams and compares observations on the transition of the upstream channels following dam removal to the initial engineering predictions and other models the relatively steep gravel bed channels evolved in a predictable manner except where anthropogenic barriers sanitary sewer rock weir interrupted

channel adjustments following two dam removals in wisconsin 1 we examined channel response following the removal of low head dams on two lowgradient fine to coarse grained rivers in southern wisconsin following removal channels eroded large quantities of fine sediment resulting in deposition 3 5 km downstream at one site baraboo river upstream changes were rapid and included bed degradation minimal bank erosion and sediment deposition on channel margins and new floodplain sand was transported through the former impoundment and temporarily deposited downstream at the second site koshkonong river head cut migration governed channel adjustments a deep narrow channel formed downstream of the headcut with negligible changes upstream of the head cut fluvial changes were summarized in a conceptual channel evolution model that highlighted 1 similarities between adjustments associated with dam removal and other events that lower channel base level and 2 the role of reservoir sediment characteristics particle size cohesion in controlling the rates and mechanisms of sediment movement and channel adjustment index terms 1815 hydrology erosion and sedimentation 1824 hydrology geomorphology 1625 1857 hydrology reservoirs surface keywords dams dam removal channel evolution model

sampling surficial fluvial gravels the precision of size distribution percentile sediments abstract grid by number wolman sampling is commonly used to characterize the texture of surficial fluvial sediments assessments of sampling precision have concentrated on the median grain size but adequate representation of other grain size percentiles is paramount in a number of sedimentological contexts the field effort required to construct percentile sampling distributions by replication is prohibitive and the absence of any general size distribution for fluvial sediments precludes theoretical calculation of percentile standard errors bootstrapping is used in this paper to determine percentile standard errors for large samples from two gravel bar surfaces the improvement of percentile precision with sample size follows the theoretical expectation hence improvement in percentile recision is achieved only at the expense of much greater sampling effort once sample sizes reach about 400 stones however absolute percentile standard errors differ significantly from theoretically derived values of particular interest is the stability of coarser percentile estimates in coarse skewed distributions d95 estimates may be as precise as d50 estimates for a given sample size the sensitivity of the precision of estimated percentiles to distribution shape is examined using synthetic skewed and bimodal grain size distributions the absolute precision of percentile estimates is shown to vary with the grain size distribution of a particular sediment our field results provide a reference for further work

a model of channel response in disturbed alluvial channels dredging and straightening of alluvial channels between 1959 and 1978 in west tennessee caused a series of morphologic changes along modified reaches and tributary streams degradation occurred for 10 to 15 years at sites upstream of the area of maximum disturbance and lowered bed levels by as much as 6 1 m following degradation reaches upstream of the area of maximum disturbance experienced a secondary aggradation phase in response to excessive incision and gradient reduction aggradation downstream of the area of maximum disturbance reached 0 12 m per year with the greatest rates occurring near the stream mouths the adjustment of channel geometry and phases of channel evolution are characterized by six process oriented stages of morphologic development premodified constructed degradation threshold aggradation and restabilization down cutting and toe removal during the degradation stage causes bank failure by mass wasting when the critical height and angle of the bank material is exceeded threshold stage channel widening continues through the aggradation stage as the slough line develops as an initial site of lower bank stability the bank profile develops three dynamic elements 1 vertical face 70 to 90 2 upper bank 25 to 50 and 3 slough line 20 to 25 alternate channel bars form during the restabilization stage and represent incipient meandering of the channel

immediate changes in stream channel geomorphology aquatic habitat and fish assemblages following dam removal in a small upland catchment abstract dam removal is becoming an increasingly important component of river restoration with 1100 dams having been removed nationwide over the past three decades despite this recent progression of removals the lack of pre to post removal monitoring and assessment limits our understanding of the magnitude rate and sequence of geomorphic and or ecological recovery to dam removal taking advantage of the november 2012 removal of an old 190 year old 6 m high run of river industrial dam on amethyst brook 26 km2 in central massachusetts we identify the immediate eco geomorphic responses to removal to capture the geomorphic responses to dam removal we collected baseline data at multiple scales both upstream 300 m and downstream 750 m of the dam including monumented cross sections detailed channel bed longitudinal profiles embeddedness surveys and channel bed grain size measurements which were repeated during the summer of 2013 these geomorphic assessments were combined with detailed quantitative electrofishing surveys of stream fish richness and abundance above and below the dam site and throughout the watershed and visual surveys of native anadromous sea lamprey petromyzon marinus nest sites post removal assessments were complicated by two events 1 upstream knickpoint migration exhumed an older ca late eighteenth century intact wooden crib dam 120 m upstream of the former stone dam and 2 the occurrence of a 10 20 year ri flood 6 months after removal that caused further upstream incision and downstream aggradation now that the downstream reach has been reconnected to upstream sediment supply the predominant geomorphic response was bed aggradation and associated fining 30 60 reduction at dam proximal locations aggradation ranged from 0 3 to 1 m where a large woody debris jam enhanced aggradation although less pronounced distal locations still showed aggradation with a mean depth of deposition of 0 20 m over the 750 m downstream reach post removal but pre flood bed surveys indicate 2 m of incision had migrated 25 m upstream of the former reservoir before encountering the exhumed dam which now acts as the new grade control limiting progressive headcutting approximately 1000 m3 of sediment was evacuated in the first year with 67 of the volume occurring by pre flood process driven e g changes in base level controls the combination of changes in channel bed sedimentology the occurrence of a large magnitude flood and the emergence of the new crib dam that is a likely barrier to fish movement was associated with major reductions in abundance and richness in sites downstream and immediately upstream adjacent to the former dam in post removal sampling at the same time we documented the presence of four species of fish including sea lamprey which were not present above the dam prior to removal indicating that upstream passage has been achieved and we also documented lamprey spawning activity at sites immediately below the dam which had previously been unsuitable owing to an excessively coarse and armored riverbed our results point to the importance of interactions between dam removal and flood disturbance effects with important implications for short and long term monitoring and assessment of dam impacts to river systems

stream channel changes as a result of sudden sediment release due to check dam lowering polish carpathians channel response to dam removal is still poorly understood as there is a lack of monitoring data a small dam in the gravel bed krzczonowka stream was lowered in 2014 as the first in the polish carpathians the paper describes the direction and magnitude of channel changes after the check dam lowering against the backdrop of slow changes in the riverbed occurring over a period of several decades geomorphologic mapping and geodetic measurements started in 2013 and were repeated in 2014 archived cartographic sources were used to identify channel morphology in the past after the studied check dam had been partially lowered a flood occurred and caused movement of sediment from the reservoir into the channel downstream debris filled pools and artificial riffles were created in 2013 the largest deposition occurred just below the dam the channel width also increased in this area the channel reach upstream from the dam was incised additional gravel supply is limited because of a sequence of drop structures just upstream of the studied reach long term channel evolution after dam lowering depends on flood events and the availability of material for fluvial transport

north south variations of tropical storm genesis locations in the western hemisphere in the western hemisphere tropical storms or hurricanes form in the north atlantic and eastern north pacific previous studies have focused on storm variability in the frequency duration and intensity in each basin here we find that the tropical storm genesis location in one ocean basin ties to the other one on both interannual and multidecadal timescales a northward southward shift of the tropical storm genesis location is associated with a southward northward variation in the other ocean basin the change of cross central america wind in the upper troposphere which induces an out of phase relation of vertical wind shear bridges storm activity in the two ocean basins sea surface temperatures in both the tropical pacific and north atlantic can induce the zonal wind change across central america it implies that hurricane outlooks can be improved by considering the two ocean basins together and thus helping reduce the damage caused by hurricane landfall

air photo based change in channel width in the minnesota river basin modes of adjustment and implications for sediment budget abstract the minnesota river and major tributaries have experienced large increases in discharge over the past century aerial photograph based measurements of channel width were made for the 1938 2015 period at 16 multibend subreaches by digitizing the area between vegetation lines and dividing by centerline length results show considerable increases in width for the main stem 0 62 0 10 y and major tributaries 0 31 0 08 y but are inconclusive for smaller channels width

effects of vertical wind shear on the intensity and structure of numerically simulated hurricanes a series of numerical simulations of tropical cyclones in idealized large scale environments is performed to examine the effects of vertical wind shear on the structure and intensity of hurricanes the simulations are performed using the nonhydrostatic pennsylvania state university national center for atmospheric research fifth generation mesoscale model using a 5 km fine mesh and fully explicit representation of moist processes when large scale vertical shears are applied to mature tropical cyclones the storms quickly develop wavenumber one asymmetries with upward motion and rainfall concentrated on the left side of the shear vector looking downshear in agreement with earlier studies the asymmetries develop due to the storm s response to imbalances caused by the shear the storms in shear weaken with time and eventually reach an approximate steady state intensity that is well below their theoretical maximum potential intensity as expected the magnitude of the weakening increases with increasing shear all of the storms experience time lags between the imposition of the large scale shear and the resulting rise in the minimum central pressure while the lag is at most a few hours when the storm is placed in very strong 15 m s21 shear storms in weaker shears experience much longer lag times with th e5ms 21 shear case showing no signs of weakening until more than 36 h after the shear is applied these lags suggest that the storm intensity is to some degree predictable from observations of largescale shear changes in all cases both the development of the asymmetries in core structure and the subsequent weakening of the storm occur before any resolvable tilt of the storm s vertical axis occurs it is hypothesized that the weakening of the storm occurs via the following sequence of events first the shear causes the structure of the eyewall region to become highly asymmetric throughout the depth of the storm second the asymmetries in the upper troposphere where the storm circulation is weaker become sufficiently strong that air with high values of potential vorticity and equivalent potential temperature are mixed outward rather than into the eye this allows the shear to ventilate the eye resulting in a loss of the warm core at upper levels which causes the central pressure to rise weakening the entire storm the maximum potential vorticity becomes concentrated in saturated portions of the eyewall cloud aloft rather than in the eye third the asymmetric features at upper levels are advected by the shear causing the upper portions of the vortex to tilt approximately downshear the storm weakens from the top down reaching an approximate steady state intensity when the ventilated layer can descend no farther due to the increasing strength and stability of the vortex at lower levels

strong seasonality in sand loading and resulting feedbacks on sediment transport bed texture and channel planform at mount pinatubo philippines declining sand inputs to a channel with bimodal bed sediment can lead to degradation armoring and reduced bedload transport rates where sand loading is episodic channels may alternate between high sand and low sand conditions with ensuing responses in bed texture and bedload transport rates the effects of episodic sand loading are explored through flow grain size and bedload transport measurements on the pasig potrero river a sediment rich channel draining mount pinatubo philippines sand loading on the pasig potrero river is highly seasonal and channel adjustments between seasons are dramatic in the rainy season inputs from sand rich 1991 eruption deposits lead to active sand bedded braided channels in the dry season many precipitation driven sand sources are cut off leading to incision armoring and significantly lower bedload transport rates this seasonal transition offers an excellent opportunity to examine models of degradation incision and armoring as well as the effectiveness of sediment transport models that explicitly encapsulate the importance of sand on transport rates during the fall 2009 seasonal transition 7 6 km of channel incised and armored carving a 2 3 m deep channel on the upper alluvial fan bedload transport rates measured in the august 2009 rainy season were over four orders of magnitude greater than gravel bedded dry season channels surveyed in january 2010 despite having similar shear stress and unit discharge conditions within dry season incised channels bed armoring is rapid leading to an abrupt gravel sand transition bedload transport rates adjust more slowly creating a lag between armoring and commensurate reductions in transport seasonal channel incision occurred in steps aided by lateral migration into sand rich banks these lateral sand inputs may increase armor layer mobility renewing incision and forming terraces within the incised seasonal channel the seasonal incised channel is currently being reset by precipitation driven sand loading during the next rainy season and the cycle begins again copyright 2012 john wiley sons ltd

sediment deposition and transport patterns following a reservoir sediment release a reservoir sediment release on the north fork poudre river supplied 7000 m3 of silt to pebble sized sediment to an originally boulder bed channel deposition along the 12 km of channel downstream from the reservoir occurred primarily in pools during the subsequent snowmelt hydrograph sediment was progressively scoured from the upstream and then the downstream pools initial sediment reworking in the pools created a deep narrow thalweg scoured to the original pool bed with additional sediment deposition in lateral eddies continued reworking reduced but did not completely remove these eddy deposits the channel became supply limited with respect to finer grain sized fractions clay to medium sand first at upstream and then at downstream sites and eventually became supply limited with respect to coarser grain sized fractions coarse sand to pebbles bedload transport rates at a site were strongly linked to the depletion of sediment stored in upstream pools magnitude duration and sequence of flows were all important controls on bedload transport and return of the channel to its prerelease state

westward shift of western north pacific tropical cyclogenesis tropical cyclones tcs in the western north pacific or typhoons account for one third of all tcs in the world and the change of the mean tc genesis location can affect billions of people in pacific islands and asian countries the annual mean tc genesis longitude is generally controlled by the east west shift of the tropical upper tropospheric trough tutt a pronounced westward shift in the tutt is found in all of the available reanalysis data sets during 1979 2012 suppressing tc genesis in the eastern portion east of 145 e of the western north pacific basin due to the enhanced vertical wind shear associated with the tutt shift as a result the annual mean tc genesis longitude has significantly shifted westward since 1979 the westward shifting trends in the tutt and tc genesis are associated with the enhanced tropical tropospheric warming which is consistent with the response of the tropospheric temperature to global warming

adjustment of the atmospheric circulation to tropical pacific sst anomalies variability of transient eddy propagation in the pacific north america sector nas a pattern that is shifted southward northward compared with climatology paths of coherent phase propagation of transient eddies and of the propagation of wave packets are analyzed a coherent path of propagation across the pacific towards north america is identified that is more zonal during el niwinters and during la nihas a dominant path heading northeastward to the pacific northwest a second path heading southeastward from the central pacific to the tropical east pacific is more accentuated during la ni nas than el ni nos these changes in wave propagation are reproduced in an ensemble of seasonal integrations of a general circulation model forced by a tropical pacific sea surface temperature pattern confirming that the changes are forced by changes in the mean atmospheric state arising from changes in tropical sea surface temperature a simplified model with a specified basic state is used to model the storm tracks for el ni no and la ni na winters the results suggest that the changes in transient eddy propagation and the eddy statistics can be understood in terms of the refraction of transient eddies within different basic states copyright c 2010 royal meteorological society

the anthropogenic nature of present day low energy rivers in western france and implications for current restoration projects abstract as in other european countries western france has seen an increase in river restoration projects in this paper we examine the restoration goals methods and objectives with respect to the long term trajectory and understanding of the contemporary dynamics of the small low energy rivers typical of the lowlands of western europe the exhaustive geomorphological paleoenvironmental and historical research conducted in the seulles river basin normandy provides very accurate documentation of the nature and place of the different legacies in the fluvial systems we have inherited the sedimentation rate in the seulles valley bottom has multiplied by a factor of 20 since the end of the bronze age and has generated dramatic changes in fluvial forms hydraulic control of the rivers and valley bottoms drainage throughout the last millennium has channelized rivers within these deposits the single meandering channel which characterizes this river today is the legacy of the delayed and complex effects of long term exploitation of the river basin and the fluvial system bring to light that the naturalness of the restored rivers might be questioned our research emphasizes the gap between the poor knowledge of the functioning of these rivers and the concrete objectives of the restoration works undertaken including dam and weir removal account of the long term history of fluvial systems is required not only to produce a pedagogic history of the river degradation but more fundamentally i to situate the current functioning of the fluvial system in a trajectory to try to identify thresholds and anticipate the potential turning points in a context of climate and land use change ii to understand the role of morphosedimentary legacies on the current dynamics iii to open the discussion on reference functioning or expected states and iv to open discussion on the sustainability of ecological restoration to conclude we point out the necessity to take into account the hybrid nature of low energy rivers in rural environments and to develop specific evaluation protocols which would include both biophysical processes and usual human activities which could be a way to share the evaluation and overcome conflicts between socioeconomic needs and environmental issues

large scale dam removal on the elwha river washington usa erosion of reservoir sediment abstract base level lowering of reservoirs impounding upstream sediment supply triggers a series of channel evolution steps such as degradation lateral erosion and redeposition that can dramatically alter the reservoir landscape and decouple the relationship between stream power and sediment supply many case studies exist for small dam removals with a few years of sediment storage or dam breaches triggering instantaneous large sediment releases however quantitative information for a controlled drawdown initiating erosion of a large sediment deposit is rare we investigate reservoir sediment response to the phased and concurrent drawdown of two reservoirs on the elwha river washington usa during the largest dam removal in history by measuring changes in reservoir topography and channel morphology as a function of base level lowering river discharge and cohesion after two years the elwha dam was completely removed and three quarters of glines canyon dam were removed reservoir drawdown increments of 3 to 5 m were sufficient to initiate channel degradation and delta progradation across the width of the receding reservoir redistributing decades of accumulated delta sediment throughout the reservoir while the lake still remained the first year of dam removal resulted in up to 5 m of incision through the lake aldwell delta down to the predam surface and in just over 20 m of incision through the lake mills delta in contrast delta progradation resulted in a few meters of deposition in lake aldwell and 2 to 10 m in lake mills on top of prodelta and lakebed deposits in coarse noncohesive sediment a braided channel developed and widened up to tenfold across the entire width of the reservoir the most extensive lateral erosion occurred in noncohesive deposits during multiweek hold periods coinciding with flows greater than the mean annual flow but less than a 2 year flood peak channel widening in more cohesive fine sediments of the prodelta and lakebed was less than half of that in the coarse noncohesive delta sediments dam removal resulted in the erosion and downstream release of 23 of the sediment in lake aldwell 1 12 0 07 million m3 and 37 of the sediment in lake mills 5 95 0 12 million m3 representing nearly four decades of sediment supply from the upstream watershed within a two year time frame a significant portion of the reservoir sediment is expected to remain as sediment terraces within the reservoir landscape but additional erosion is expected after the remainder of the glines canyon dam is removed and during future floods until the river reaches quasi equilibrium after phased dam removal the reservoir landscape consists of a series of sediment terraces of varying heights composed of prograded coarse sediment overlying fine lakebed deposits the predam surface is exposed along the river corridor and abundant 1 to 3 m stumps from pre removal forests create unique morphology where the river interacts with the predam landscape

estimating the fluvial sediment input to the coastal sediment budget a case study of ghana knowledge of fluvial sediment supply to the coastal sediment budget is important for the assessment of the impacts on coastal stability such knowledge is valuable for designing coastal engineering schemes and the development of shoreline management planning policies it also facilitates understanding of the connection between rivers in the hinterland and adjoining coastal systems ghana s coast has many fluvial sediment sources and this paper provides the first quantitative assessments of their contributions to the coastal sediment budget the methods use largely existing data and attempt to cover all of ghana s significant coastal rivers initially work was hindered by insufficient direct measured data however the problem was overcome by the application of a regression approach which provides an estimated sediment yield for non gauged rivers based on data from gauged rivers with similar characteristics the regression approach was effective because a regional coherence in behaviour was determined between those rivers where direct measured data were available the results of the assessment revealed that ghana s coast is dissected by many south draining rivers stream and lagoons these rivers streams and lagoons supply significant amounts of sediment to coastal lowlands and therefore contribute importantly to beaches anthropogenic impoundment of fluvial sediment especially the akosombo dam on the volta river has reduced the total fluvial sediment input to the coast from about 71 106 m3 a before 1964 pre akosombo dam to about 7 106 m3 a at present post akosombo dam this sharp reduction threatened the stability of the east coast and prompted an expensive 83 million defence scheme to be implemented to protect 8 4 km long coastline at keta sections of ghana s coast are closely connected to the hinterland through the fluvial sediment input from local rivers therefore development in the hinterland that alters the fluvial sediment input from those local rivers could have significant effects on the coast there is the need therefore to ensure that catchment management plans and coastal management plans are integrated or interconnected

baroclinic eddies and the extent of the hadley circulation an idealized gcm study thehadleycirculationhaswidenedoverthepast30years thiswideninghasbeenqualitativelyreproduced in general circulation model gcm simulations of a warming climate comprehensive gcm studies suggest this widening may be caused by a poleward shift in baroclinic eddy activity yet the limited amplitude of the climate change signals analyzed so far precludes a quantitative comparison with theories this study uses two idealized gcms one with and one without an active hydrologic cycle to investigate changes in the extent of the hadley circulation over a wide range of climates the climates span global mean temperatures from 243 to 385k and equator to pole temperature contrasts from 12 to 100k baroclinic eddies control the extent of the hadley circulation across most of these climates a supercriticality criterion that quantifies the depth of baroclinic eddies relative to that of the troposphere turns out to be a good indicator of where baroclinic eddies become deep enough to terminate the hadley circulation the supercriticality depends on meridional temperature gradients and an effective stability that accounts for the effect of convective heating on baroclinic eddies astheequator to poletemperaturecontrastweakensortheconvectivestaticstabilityincreases convective heating increasingly influences the thermal stratification of the troposphere and the supercriticality consistent with the supercriticality criterion the hadley circulation contracts as meridional temperature gradients increase and it widens as the effective static stability increases the former occurs during el nino and may account for the observed hadley circulation contraction then the latter occurs during global warming

the impact of single natural vegetation elements on flow characteristics in this experimental study measurements were conducted to explore the impacts of different forms of individual natural vegetative elements within the flow domain on velocity and turbulence characteristics all the experiments were performed in a flume measuring 26 m in length 0 98 m in width and 0 85 m in depth and real tree saplings were utilized to represent the vegetation element in order to analyse this commonly observed nature phenomenon in floodplains trees with wide trunks were classified into three groups on the basis of their volume versus height relation throughout the velocity measurements three acoustic doppler velocimeters were employed time averaged velocity streamwise and vertical turbulence intensities and turbulent kinetic energy parameters were examined additionally a formulation that gives the velocity profile at a certain distance downstream of vegetation was introduced and the validity of the proposed formulation was checked with experimental data it is seen that despite their porous structures the presence of vegetation considerably disturbs the flow field and dissipates a remarkable amount of energy by turbulence copyright 2008 john wiley sons ltd

channel evolution after dam removal in a poorly sorted sediment mixture experiments and numerical model dam removal is commonly used for river restoration however there are still some uncertainties associated with dam removal mainly related to the sediment transport rates released downstream from the deposit that had previously filled the impoundment this research studies the physical response to dam removal in the antecedent deposit by answering the following questions a how does an initial channel excavated into the deposit evolve and b what is the time distribution of the material released during the early stages of the process these goals are achieved by an experimental campaign using a poorly sorted mixture of sediment in the antecedent deposit the research shows that for the given conditions of our experiments the rate at which the sediment is released depends on the height of the removed dam the water discharge and the maximum potential volume of sediment to be eroded this investigation provides new insights of the width evolution when the sediment is composed of a poorly sorted mixture this evolution is linked to the bed degradation rates channel narrows during a rapid incisional phase and subsequently widens when bed degradation rates decrease channel width changes propagate upstream as a convection like perturbation associated with a kinematic wave starting at the location of the antecedent dam these features are modeled through a new numerical model accounting for mixtures more specifically a set of equations has been derived for the variation of bed elevation channel bottom width and bed grain size distribution which when solved numerically describe the observed channel processes

classifying north atlantic tropical cyclone tracks by mass moments a new method for classifying tropical cyclones or similar features is introduced the cyclone track is considered as an open spatial curve with the wind speed or power information along the curve considered to be a mass attribute the first and second moments of the resulting object are computed and then used to classify the historical tracks using standard clustering algorithms mass moments allow the whole track shape length and location to be incorporated into the clustering methodology tropical cyclones in the north atlantic basin are clustered with k means by mass moments producing an optimum of six clusters with differing genesis locations track shapes intensities life spans landfalls seasonal patterns and trends even variables that are not directly clustered show distinct separation between clusters a trend analysis confirms recent conclusions of increasing tropical cyclones in the basin over the past two decades however the trends vary across clusters

middle triassic archosaur population structure interpretation based on isochirotherium delicatum fossil footprints southern alps italy abstract well preserved archosaur footprints have recently been found on a single bedding plane in the italian alps the tracks are referable to isochirotherium delicatum courel and demathieu 1976 a form that was identified for the first time at the anisian ladinian boundary in the area of argentiere ardeche france the isochirotherium delicatum footprints and trackways from gampenpass represent a possible social group or herd estimating the age of the trackmakers from the examination of the footprints is difficult and complicated by the fact that the sample can be divided into two groups of tracks distinguishable by the l w cross axis and interdigital angle the diversity of the tracks is here interpreted as an indication of sexual dimorphism

dinosaur footprints with skin impressions from the cretaceous of alberta and colorado cretaceous dinosaur footprints discovered in the j sandstone of the south platte formation dakota group in colorado and the st mary river formation of southwestern alberta exhibit the first repo

climatic and volcanic forcing of tropical belt northern boundary over the past 800 years the position of the northern boundary of the tropical belt affects the hydroclimate of many arid and semi arid regions in the northern hemisphere widening of the tropical belt since the 1970s has largely been attributed to anthropogenic forcing however the relative influence of natural drivers of tropical belt expansion and contraction before this time is poorly understood here we use data on tree ring widths from five mid latitude regions in the northern hemisphere to reconstruct the movement of the northern boundary of the early spring tropical belt over the past 800 years ad 1203 2003 our reconstruction explains 45 of the interannual variance in the latitudinal extent of the hadley circulation a metric of the position of the tropical belt boundary we find that the tropical belt contracted expanded during positive negative phases of the el nino southern oscillation and pacific north american teleconnection patterns the tropical belt also contracted significantly following major volcanic events that injected sulfur into the stratosphere the longest period of persistent tropical belt expansion occurred in the late sixteenth century during one of the coldest periods of the little ice age our results warn of potential socio economic consequences of future variations in tropical belt width driven by natural climate variability or stratospheric aerosol injections whether volcanic or artificial climate variability and volcanic forcing both influenced the latitudinal migration of the tropical belt over the past 800 years according to an analysis of tree ring widths in the northern hemisphere

channel adjustment of an unstable coarse grained stream opposing trends of boundary and critical shear stress and the applicability of extremal hypotheses channel adjustments in the north fork toutle river and the toutle river main stem were initiated by deposition of a 2 5 km3 debris avalanche and associated lahars that accompanied the catastrophic eruption of mount st helens washington on 18 may 1980 channel widening was the dominant process in combination adjustments caused average boundary shear stress to decrease non linearly with time and critical shear stress to increase non linearly with time at the discharge that is equalled or exceeded 1 per cent of the time these trends converged by 1991 1992 so that excess shear stress approached minimum values extremal hypotheses such as minimization of unit stream power and minimization of the rate of energy dissipation minimum stream power are shown to be applicable to dynamic adjustments of the toutle river system maximization of the darcy weisbach friction factor did not occur but increases in relative bed roughness caused by the concomitant reduction in hydraulic depths and bed material coarsening were documented predictions of stable channel geometries using the minimum stream power approach were unsuccessful when compared to the 1991 1992 geometries and bed material characteristics measured in the field it is concluded that the predictions are not applicable because the study reaches are not truly stable and cannot become so until a new floodplain has been formed by renewed channel incision retreat of stream side hummocks and establishment of riparian vegetation to limit the destabilizing effects of large floods further prediction of energy slope and consequently stream power by the sediment transport equations is inaccurate because of the inability of the equations to account for significant contributions of finer grained sand and gravel bank materials relative to the coarsened channel bed from bank retreat and from upstream terrace erosion

recent channel adjustments in alluvial rivers of tuscany central italy drastic channel adjustments have affected the main alluvial rivers of tuscany central italy during the 20th century bed level adjustments were identified both by comparing available topographic longitudinal profiles of different years and through field observations changes in channel width were investigated by comparing available aerial photographs 1954 and 1993 98 bed incision represents the dominant type of vertical adjustment and is generalized along all the fluvial systems investigated the arno river system is the most affected by bed level lowering up to 9 m whereas lower incision generally less than 2 m is observed along the rivers of the southern part of the region human disturbances appear to be the dominant factors of adjustments the main phase of vertical change occurred during the period 1945 80 in concomitance with the phase of maximum sediment mining activity at the regional scale the second dominant type of adjustment that involved most of the rivers in the region consists of a narrowing of the active channel based on measurements of channel width conducted on aerial photographs 38 of the reaches analysed experienced a narrowing greater than 50 of the initial channel width the largest values of channel narrowing were observed along initially braided or sinuous with alternate bars morphologies in the southern portion of the region a regional scheme of channel adjustments is derived based on initial channel morphology and on the amounts of incision and narrowing different styles of channel adjustments are described rivers that were originally sinuous with alternate bars to braided generally became adjusted by a moderate incision and a moderate to intense narrowing in contrast sinuous meandering channels mainly adjusted vertically with a minor amount of narrowing copyright 2003 john wiley sons ltd

convective self aggregation and tropical cyclogenesis under the hypohydrostatic rescaling abstractthe behavior of rotating and nonrotating aggregated convection is examined at various horizontal resolutions using the hypohydrostatic or reduced acceleration in the vertical rave rescaling this modification of the equations of motion reduces the scale separation between convective and larger scale motions enabling the simultaneous and explicit representation of both types of flow in a single model without convective parameterization without the rave rescaling a dry bias develops when simulations of nonrotating radiative convective equilibrium are integrated at coarse resolution in domains large enough to permit convective self aggregation the rescaling reduces this dry bias and here it is suggested that the rescaling moistens the troposphere by weakening the amplitude and slowing the group velocity of gravity waves thus reducing the subsidence drying around aggregated convection separate simulations of rotating radiative convective equilibrium exhibit tropical cyclogenesis as horizo

tropical sea surface temperature vertical wind shear and hurricane development 1 the anomalously strong hurricane activity in the atlantic sector during the recent years led to a controversy about the impact of global warming on hurricane activity in the atlantic sector here we show that the temperature difference between the tropical north atlantic and the tropical indian and pacific oceans indo pacific is a key parameter in controlling the vertical wind shear over the atlantic an important quantity for hurricane activity the stronger warming of the tropical north atlantic relative to that of the indo pacific during the most recent years drove reduced vertical wind shear over the atlantic and is thus responsible for the strong hurricane activity observed in 2006 however the temperature difference between the tropical north atlantic and the tropical indian and pacific oceans is much reduced which explains the relatively weak hurricane season

nature s complex flume using a diagnostic state and transition framework to understand post restoration channel adjustment of the clark fork river montana abstract there is an imperfect symmetry between the patterns of channel evolution observed during laboratory flume experiments and those which materialize in rivers exposed to ambient environmental conditions that produce hydrogeomorphic fluxes which are more complex contingent and unpredictable one strategy to improve our understanding of short to medium term channel evolution is to study landscapes that have undergone significant disturbance and have had their biogeomorphic templates reset to a known condition in effect creating a flume in nature this study adopts a diagnostic state and transition framework to narrate and document baseline hypotheses for the potential evolutionary trajectories clark fork river near milltown montana following dam removal and remediation a 5 km stretch of the clark fork river and its adjoining floodplain were reconstructed since flow was introduced to the newly constructed channel in december 2010 complex evolutionary trajectories have been observed on the clark fork s mainstem its secondary channels and floodplain focusing particularly on the river s secondary channels this paper develops a typology of channel states that have been observed and demonstrates that multiple adjustment trajectories have materialized sometimes within the same channel a diagnostic state and transition framework offers a parsimonious strategy to quantitatively or qualitatively anticipate the influence of water sediment and ecological fluxes on channel evolution at the basin reach or segment scale it provides environmental agencies with a robust method to devise spatially explicit scenario based management plans for rivers in a variety of geomorphic settings

probabilistic clustering of extratropical cyclones using regression mixture models a probabilistic clustering technique is developed for classification of wintertime extratropical cyclone etc tracks over the north atlantic we use a regression mixture model to describe the longitude time and latitude time propagation of the etcs a simple tracking algorithm is applied to 6 hourly mean sea level pressure fields to obtain the tracks from either a general circulation model gcm or a reanalysis data set quadratic curves are found to provide the best description of the data we select a three cluster classification for both data sets based on a mix of objective and subjective criteria the track orientations in each of the clusters are broadly similar for the gcm and reanalyzed data they are characterized by predominantly south to north s n west to east w e and southwest to northeast sw ne tracking cyclones respectively the reanalysis cyclone tracks however are found to be much more tightly clustered geographically than those of the gcm for the reanalysis data a link is found between the occurrence of cyclones belonging to different clusters of trajectory shape and the phase of the north atlantic oscillation nao the positive phase of the nao is associated with the sw ne oriented cluster whose tracks are relatively straight and smooth with cyclones that are typically faster more intense and of longer duration the negative nao phase is associated with more erratic w e tracks with typically weaker and slower moving cyclones the s n cluster is accompanied by a more transient geopotential trough over the western north atlantic no clear associations are found in the case of the gcm composites the gcm is able to capture cyclone tracks of quite realistic orientation as well as subtle associated features of cyclone intensity speed and lifetimes the clustering clearly highlights though the presence of serious systematic errors in the gcm s simulation of etc behavior

tropical cyclone recurvature an intrinsic property the typical track of a tropical cyclone tc in the northern hemisphere is an initial northwestward movement followed by an eventual turning toward the east such turning is referred to as recurvature and often explained by the change of the environmental flow that steers the tc here we show that even in the absence of background flow a tc initiated at a high enough latitude can recurve itself differential horizontal advection of the planetary vorticity by the tc circulation at different vertical levels leads to the development of vertical wind shear upper tropospheric anticyclone and asymmetric distribution of convection the flow associated with the upper tropospheric anticyclone on the equatorward side of the tc and the diabatic heating associated with the asymmetric convection combine to cause the tc to recurve such knowledge an intrinsic recurvature property of the tc is important in forecasting the tc track when the environmental flow is weak

large scale dam removal on the elwha river washington usa fluvial sediment load abstract the elwha river restoration project in washington state includes the largest dam removal project in united states history to date starting september 2011 two nearly century old dams that collectively contained 21 3 million m3 of sediment were removed over the course of three years with a top down deconstruction strategy designed to meter the release of a portion of the dam trapped sediment gauging with sediment surrogate technologies during the first two years downstream from the project measured 8 200 000 3 400 000 tonnes of transported sediment with 1 100 000 and 7 100 000 t moving in years 1 and 2 respectively representing 3 and 20 times the elwha river annual sediment load of 340 000 80 000 t y during the study period the discharge in the elwha river was greater than normal 107 in year 1 and 108 in year 2 however the magnitudes of the peak flow events during the study period were relatively benign with the largest discharge of 292 m3 s 73 of the 2 year annual peak flow event early in the project when both extant reservoirs still retained sediment despite the muted peak flows sediment transport was large with measured suspended sediment concentrations during the study period ranging from 44 to 16 300 mg l and gauged bedload transport as large as 24 700 t d five distinct sediment release periods were identified when sediment loads were notably increased when lateral erosion in the former reservoirs was active or reduced when reservoir retention or seasonal low flows and cessation of lateral erosion reduced sediment transport total suspended sediment load was 930 000 t in year 1 and 5 400 000 t in year 2 of the total 6 300 000 3 200 000 t of suspended sediment load 3 400 000 t consisted of silt and clay and 2 900 000 t was sand gauged bedload on the lower elwha river in year 2 of the project was 450 000 360 000 t bedload was not quantified in year 1 but qualitative observations using bedload surrogate instruments indicated detectable bedload starting just after full removal of the downstream dam using comparative studies from other sediment laden rivers the total ungauged fraction of

the role of vegetation and bed level fluctuations in the process of channel narrowing abstract a catastrophic flood ire 1965 on plum creek a perennial sandbed stream in the western great plains removed most of the bottomland vegetation and transformed the single thalweg stream into a wider braided channel following eight years of further widening associated with minor high flows a process of channel narrowing began in 1973 narrowing continues today the history of channel narrowing was reconstructed by counting the annual rings of 129 trees and shrubs along a 5 km reach of plum creek near louviers colorado sixty three of these plants were excavated in order to determine the age and elevation of the germination point the reconstructed record of channel change was verified from historical aerial photographs and then compared to sediment stratigraphy and records of discharge and bed elevation from a streamflow gaging station in the study reach channel narrowing at plum creel occurs in two ways first during periods of high flow sand and fine gravel are delivered to the channel temporarily raising the general bed level subsequently several years of uninterrupted low flows incise a narrower channel second during years of low flow vegetation becomes established on the subaerial part of the present channel bed in both cases surfaces stabilize as a result of vegetation growth and vertical accretion of sediment

is the poleward migration of tropical cyclone maximum intensity associated with a poleward migration of tropical cyclone genesis a recent study showed that the global average latitude where tropical cyclones achieve their lifetime maximum intensity has been migrating poleward at a rate of about one half degree of latitude per decade over the last 30 years in each hemisphere however it does not answer a critical question is the poleward migration of tropical cyclone lifetime maximum intensity associated with a poleward migration of tropical cyclone genesis in this study we will examine this question first we analyze changes in the environmental variables associated with tropical cyclone genesis namely entropy deficit potential intensity vertical wind shear vorticity skin temperature and specific humidity at 500 hpa in reanalysis datasets between 1980 and 2013 then a selection of these variables is combined into two tropical cyclone genesis indices that empirically relate tropical cyclone genesis to large scale variables we find a shift toward greater smaller average potential number of genesis at higher lower latitudes over most regions of the pacific ocean which is consistent with a migration of tropical cyclone genesis towards higher latitudes we then examine the global best track archive and find coherent and significant poleward shifts in mean genesis position over the pacific ocean basins

a physically based climatology of the occurrence and intensification of australian east coast lows abstractthe subtropical part of the eastern australian seaboard experiences intense cyclonic activity the severe damage caused by the intense storms in the region known as east coast lows ecls

causes of 20th century channel narrowing in mountain and piedmont rivers of southeastern france extensive channel narrowing in southeastern france provides an illustration of geomorphic response to land use changes the study region comprises a range of environments from large piedmont and intramountain gravel bed rivers to small mountain streams field measurements and analysis of historical data demonstrate two distinct periods of channel change from 1850 to 1950 channel narrowing is interpreted to be the result of a recovery process in response to widespread channel destabilization induced by major floods during the second half of the 19th century at the time the largely deforested basins were highly responsive to flooding whereas the recovery process was accelerated by floodplain and basin scale land use changes afforestation and torrential control works which in turn reduced sediment delivery and enabled vegetation development in channels from 1950 to 1970 channel narrowing accelerated in most of the studied rivers this recent phenomenon is considered as a human induced fluvial adjustment directly related to forest development on river margins and human abandonment of intensive floodplain land uses at the same time long profile degradation occurred as a result of long term bedload supply decrease in small mountain streams channel narrowing is mainly explained by channel incision which seems to progress from upstream where sediment sources are progressively stabilized by afforestation copyright 2002 john wiley sons ltd

the impact of beaver dams on the morphology of a river in the eastern united states with implications for river restoration restoration projects in the united states typically have among the stated goals those of increasing channel stability and sediment storage within the reach increased interest in ecologically based restoration techniques has led to the consideration of introducing beavers to degraded channels with the hope that the construction of beaver dams will aggrade the channel most research on beaver dam modification to channels has focused on the long term effects of beavers on the landscape with data primarily from rivers in the western united states this study illustrated that a role exists for beavers in the restoration of fine grained low gradient channels a channel on the atlantic coastal plain was analyzed before during and after beaver dams were constructed to evaluate the lasting impact of the beaver on channel morphology the channel was actively evolving in a former reservoir area upstream of a dam break colonization by the beaver focused the flow into the channel allowed for deposition along the channel banks and reduced the channel width such that when the beaver dams were destroyed in a flood there was no channel migration and net sediment storage in the reach had increased however the majority of the deposition occurred at the channel banks narrowing the channel width while the channel incised between sequential beaver dams the study indicated that where channels are unstable laterally and bank erosion is a concern the introduction of beavers can be a useful restoration tool however because of the likelihood of increased channel bed erosion in a reach with multiple beaver dams they may not be the best solution where aggradation of an incised channel bed is the desired result copyright 2014 john wiley sons ltd

probable palaeogeographic influences of the lower cretaceous iberian rifting phase in the eastern cameros basin spain on dinosaur trackway orientations abstract the cameros basin sedimentary infill comprises a large essentially continental megasequence ranging from the tithonian upper jurassic to the albian lower cretaceous it occupies an area of some 5500 km2 and is home to around 300 dinosaur tracksites most of these tracksites are found in either the huerteles formation which is part of the oncala group berriasian or the enciso group lower aptian both of which represent early cretaceous lacustrine episodes dinosaur trackways n 1170 from both episodes were analysed in order to establish the preferred direction of dinosaur movement and to determine whether these movements were influenced by the palaeogeographic and palaeoenvironmental conditions of the area the huerteles formation is interpreted as a complex record of alluvial plain systems distally connected with a playa lake its dinosaur tracksites are distributed throughout its alluvial plain facies and trackways show two preferential unidirectional orientations 1 nw more or less parallel to the distribution of the facies belt and 2 nne the enciso group is represented by a wide and shallow lacustrine system connected with marine environments towards the se iberian basin realm and in close proximity to marine settings to the nw basque cantabrian basin realm rendering the cameros basin as the only continental connection between the ebro and iberian massifs the fluctuating but always shallow water level of the system with frequent desiccations probably allowed dinosaurs to pass through the lake basin as a consequence of these paleogeographic restrictions the dinosaur trackways generally show a bidirectional ne sw orientation despite the temporal and geographical differences between the huerteles formation and enciso group the ichnocenoses of both are dominated by theropod dinosaur trackways 85 as a mean value this is probably explained by these dinosaurs being more active than others a consequence of their searching hunting behaviour

climate modulation of north atlantic hurricane tracks the variability of north atlantic tropical storm and hurricane tracks and its relationship to climate variability is explored tracks from the north atlantic hurricane database for the period 1950 2007 are objectively separated into four groups using a cluster technique that has been previously applied to tropical cyclones in other ocean basins the four clusters form zonal and meridional separations of the tracks the meridional separation largely captures the separation between tropical and more baroclinic systems while the zonal separation segregates gulf of mexico and cape verde storms general climatologies of the seasonality intensity landfall probability and historical destructiveness of each cluster are documented and relationships between cluster membership and climate variability across a broad spectrum of time scales are identified composites with respect to cluster membership of sea surface temperature and other environmental fields show that regional and remote modes of climate variability modulate the cluster members in substantially

mechanisms of enso forcing of hemispherically symmetric precipitation variability summary the patterns of precipitation anomalies forced by the el nino southern oscillation during northern hemisphere winter and spring are remarkably hemispherically symmetric and in the mid latitudes have a prominent zonally symmetric component observations of global precipitation variability and the moisture budget within atmospheric reanalyses are examined to argue that the zonally symmetric component is caused by interactions between transient eddies and tropically forced changes in the subtropical jets during el nino events the jets strengthen in each hemisphere and shift equatorward changes in the subtropical jet influence the transient eddy momentum fluxes and the eddy driven mean meridional circulation during el nino events eddy driven ascent in the mid latitudes of each hemisphere is accompanied by low level convergence and brings increased precipitation this changes in the transient eddy and stationary eddy moisture fluxes almost exactly cancel each other and in sum do not contribute to the zonal mean precipitation anomalies propagation of anomalous stationary waves disrupts the zonal symmetry flow around the deeper aleutian low and the eastward extension of the pacific jet stream supply the moisture for increased precipitation over the eastern north pacific and the western seaboard of the united states while transient eddy moisture convergence supplies the moisture for increased precipitation over the southern united states in each case increased precipitation is fundamentally caused by anomalous ascent forced by anomalous heat and vorticity fluxes

effects of stronach dam removal on fluvial geomorphology in the pine river michigan united states abstract although dam removal has been increasingly used as an option in dam management and as a river restoration tool few studies provide detailed quantitative assessment of the geomorphological response of rivers to dam removal in this study we document the response of the pine river michigan to the gradual removal of stronach dam in 1996 prior to the initiation of removal 31 permanent cross sectional transects were established in the 10 km study area these transects were surveyed annually during the course of the removal 1996 2003 and for the three years following removal 2004 2006 dam removal resulted in progressive headcutting of sediments in the former impoundment extending upstream 3 89 km of the dam over the course of the 10 years since dam removal was initiated a net total of 92 000 m 3 of sediment erosion occurred the majority of sediments stored in the former reservoir remained in place with only 12 of the estimated reservoir sediment fill being eroded approximately 14 of the net erosion was deposited within the stream channel 1 km downstream of the dam location with the remainder being transported further downstream or deposited in the floodplain sediment fill incision resulted in a narrower and deeper channel upstream with higher mean water velocity and somewhat coarser substrates downstream deposition resulted in a wider and shallower channel with little change in substrate size composition counter intuitively water velocity also increased downstream because of the increased slope that developed prior to removal bedforms in the former impoundment were dominated by runs but are showing signs of restoration toward reference conditions continuing changes in river geomorphology are evident even three years following removal and are likely to occur for years to come

sediment transfer and transformation of an alluvial valley floor the river south tyne northumbria u k the amounts of alluvial storage and the mechanisms responsible for the dispersal of sediment associated with historic metal mining are examined for a 115 year timespan on a 22 km reach of the river south tyne northern england analysis of lateral and vertical channel change over this period the extent of actively reworked gravels and identification of metals in alluvial units show five sedimentation zones separated by more stable reaches aggradation in the late nineteenth century was followed by a period of storage and local reworking and then incision some reaches show short term storage of sediment injected from tributaries which may be dispersed by floods there is some evidence of transfer of sediment bodies downvalley within sedimentation zones and of a sediment wave movement between zones in lower parts of the south tyne investigated present day incision the variation in the area of actively reworked gravel spreads and the widespread dispersal of fine grained toxic metal mining wastes all have practical implications the intricate response of the channel system to historic changes in sediment supply is not readily described by either a complex response model or a simple translatory wave

the extratropical transition of tropical cyclones part i cyclone evolution and direct impacts abstractextratropical transition et is the process by which a tropical cyclone upon encountering a baroclinic environment and reduced sea surface temperature at higher latitudes transforms into an extratropical cyclone this process is influenced by and influences phenomena from the tropics to the midlatitudes and from the meso to the planetary scales to extents that vary between individual events motivated in part by recent high impact and or extensively observed events such as north atlantic hurricane sandy in 2012 and western north pacific typhoon sinlaku in 2008 this review details advances in understanding and predicting et since the publication of an earlier review in 2003 methods for diagnosing et in reanalysis observational and model forecast datasets are discussed new climatologies for the eastern north pacific and southwest indian oceans are presented alongside updates to western north pacific and north atlantic ocean climatologies advances in understanding and in some cases mode

interdecadal changes in eastern pacific itcz variability and its influence on the atlantic itcz the eastern pacific and atlantic intertropical convergence zones itcz exhibit the largest year to year variations in boreal spring we show evidence suggesting that atlantic itcz april may variability is linked to that for the eastern pacific through the walker circulation as it respond to changes in equatorial pacific convection analysis of itcz proxy indices shows the link appears to be strong in the 1980 90 s and 1920 30 s but virtually nonexistent in the 1950 60 s we argue that this apparent nonstationarity results from the nonlinear relationship between sea surface temperature sst and convection in the eastern equatorial pacific and its consequent effect on the walker circulation and the atlantic itcz this mechanism was modulated over 1856 1998 by interdecadal changes in peak sst attained in the eastern equatorial pacific during boreal spring

channel evolution on the dammed elwha river washington usa abstract like many rivers in the western u s the elwha river washington has changed substantially over the past century in response to natural and human forcing the lower river is affected by two upstream dams that are slated for removal as part of a major river restoration effort in preparation for studying the effects of dam removal we present a comprehensive field and aerial photographic analysis of dam influence on an anabranching gravel bed river over the past century with the dams in place loss of the upstream sediment supply has caused spatial variations in the sedimentary and geomorphic character of the lower elwha river channel bed sediment is armored and better sorted than on the naturally evolving bed upstream of the dams on time scales of flood seasons the channel immediately below the lower dam is fairly stable but progresses toward greater mobility downstream such that the lowermost portion of the river responded to a recent 40 year flood with bank erosion and bed elevation changes on a scale approaching that of the natural channel above the dams in general channel mobility in the lowest 4 km of the elwha river has not decreased substantially with time enough fine sediment remains in the floodplain that given sufficient flood forcing the channel position sinuosity and braiding index change substantially the processes by which this river accesses new fine sediment below the dams rapid migration into noncohesive banks and avulsion of new channels allow it to compensate for loss of upstream sediment supply more readily than would a dammed river with cohesive banks or a more limited supply of alluvium the planned dam removal will provide a valuable opportunity to evaluate channel response to the future restoration of natural upstream sediment supply

depositional history of lower cretaceous strata in northeastern new mexico implications for regional tectonics and depositional sequences lower cretaceous strata in northeastern new mexico reflect deposition during marine transgression and regression associated with the kiowa skull creek cycle development of regionally significant unconformities can be directly related to shoreline shifts during this cycle topography related to early cretaceous tectonic activity on crystalline basement structures including the dalhart basin tucumcari basin and the intervening bravo dome also had a direct effect on early cretaceous deposition and is reflected by thickness trends in marine strata the kiowa skull creek transgression was preceded by infilling of paleovalleys represented by the long canyon and campana sandstone beds of the glencairn formation and tucumcari shale respectively the long canyon and campana sandstone beds are equivalent to the plainview formation of central colorado and together they represent an extensive drainage network developed over a correlative unconformity that is preserved throughout most of the southern western interior glencairn and tucumcari marine shales represent clastic deposition during kiowa skull creek transgression and early regression base level drop associated with kiowa skull creek regression resulted in dramatic shoreline regression and deposition of fluvial channel sandstone in the dalhart basin which maintained a low offshore gradient this produced an erosional unconformity at the base of mesa rica channel sandstone that correlates with the well documented erosional surface at the base of the muddy sandstone in central colorado the tucumcari basin which maintained a steeper offshore gradient accumulated marine deltaic mesa rica sandstone at this time marine strata in both the tucumcari and dalhart basins thin toward the bravo dome mesa rica and upper tucumcari strata represent the only extensive marginal marine lowstand deposits found on the high plains to date associated with the southern arm of the kiowa skull creek sea major mesa rica deposition was followed by transgression that infilled only those mesa rica fluvial channels that were active at that time and also that deposited marine influenced strata of the basal pajarito formation this event most likely represents onset of the greenhorn cycle in northeastern new mexico other crystalline basement structures in the northern part of the united states western interior basin were active during early cretaceous time tectonism in these areas may be related to structures in northeastern new mexico and thus may be expressions of broad scale crustal strain in the early cretaceous western interior that is undocumented by present tectonic models

the 1995 and 1996 north atlantic hurricane seasons a return of the tropical only hurricane hurricane activity over the north atlantic basin during 1995 and 1996 is compared to the combined hurricane activity over the previous four years 1991 94 the earlier period produced a total of 15 hurricanes compared to a total of 20 hurricanes over the latter period despite this similarity in numbers the hurricanes of 1995 and 1996 were generally of the tropical only variety which marks a substantial departure from activity during the early 1990s the return of tropical only hurricanes to the atlantic basin is likely the result of several global and local factors including cool sst conditions in the equatorial central and eastern pacific and warm ssts in the tropical atlantic the hurricane activity of 1995 and 1996 is more reminiscent of activity of some seasons during the early and mid 1950s

local partitioning of the overturning circulation in the tropics and the connection to the hadley and walker circulations conceptually it is useful to partition the three dimensional tropical circulation into meridional and zonal components namely the hadley and walker circulations the averaging involved in their definitions can introduce ambiguities these problems can be circumvented by first partitioning the total vertical mass flux into components associated with overturning in the meridional and zonal directions respectively called here the local hadley and local walker circulations defining the local hadley and local walker circulations this way ensures the pair of two dimensional overturning circulations can be added to give the original three dimensional circulation even when the averages are taken over limited domains the method is applied to the vertical motion from the era interim reanalysis for the period 1979 to 2009 one important result is that the local hadley circulation responds much more strongly to enso than the local walker circulation even though the local walker circulation in the central pacific weakens during el nino years and strengthens and widens during la nina years

three age groups of ornithopods inferred from footprints in the mid cretaceous dakota group eastern colorado north america abstract ornithopod population structure is inferred from a large sample of footprints from the mid cretaceous dakota group of colorado new mexico and oklahoma allometric analyses and size frequency distributions suggest size age classes or recruitments for tracks identified as caririchnium leonardii ornithopoda from sequence 3 of the mid cretaceous dakota group of the rocky mountain front range high plains region five hundred ninety eight footprints from 284 trackways were used in the statistical analysis tests were conducted that revealed no significant difference between analyses of right and left footprints or between casts and molds allometric analysis suggests a growth curve that can be subdivided into three segments corresponding to foot lengths of 16 5 21 7 21 7 29 3 and 29 3 55 0 cm respectively these are interpreted as juvenile possibly yearlings subadults and adults the former two categories may correspond to animal recruitments n n 1 whereas the latter category may represent several recruitments n 2 n 3 n 4 etc once ornithopod growth curves of the type proposed for maiasaura are established there is considerable potential for estimating dinosaur age from footprints in the meantime however large track samples can be analyzed for the size class information they contain

some atmospheric processes governing the large scale tropical circulation in idealized aquaplanet simulations abstract the large scale tropical atmospheric circulation is analyzed in idealized aquaplanet simulations using an atmospheric general circulation model idealized sea surface temperatures ssts are used as lower boundary conditions to provoke modifications of the atmospheric general circulation results show that 1 an increase in the meridional sst gradients of the tropical region drastically strengthens the hadley circulation intensity 2 the presence of equatorial zonal sst anomalies weakens the hadley cells and reinforces the walker circulation and 3 a uniform sst warming causes small and nonsystematic changes of the hadley and walker circulations in all simulations the jet streams strengthen and move equatorward as the hadley cells strengthen and become narrower some relevant mechanisms are then proposed to interpret the large range of behaviors obtained from the simulations first the zonal momentum transport by transient and stationary eddies is shown to modulate the eddy driven jets whic

rates and processes of channel response to dam removal with a sand filled impoundment 1 dam removal projects are playing an increasingly important role in stream restoration and offer unparalleled opportunities to study sediment dynamics following disturbance we used the removal of the 4 m high merrimack village dam mvd on the souhegan river in southern new hampshire to measure processes and rates of channel evolution in a sand filled impoundment from 2007 to 2010 we repeatedly surveyed 11 cross sections and the longitudinal profile and collected sediment samples to measure changes in channel morphology and bed texture the dam removal in august 2008 resulted in a nearly instantaneous base level drop of 3 9 m and caused a two phased channel response the initial process driven phase 2 months was characterized by rapid incision and removal of the impounded sand up to 1013 t d 1 followed by channel widening once incised to base level the rate of sediment removal slowed 30 7 t d 1 and adjustments became event driven and the former impoundment segmented into a nonalluvial section and an alluvial section with erosion and deposition influenced by vegetation on the channel banks two years after the dam removal and two high magnitude floods the river has excavated 79 of the original sediment continued response will be substantially influenced by the establishment of bank vegetation within the former impoundment and the magnitude and frequency of high discharge events initial channel development and sediment erosion occurs rapidly weeks to months in sand filled impoundments but excavation of the remaining sediment occurs more slowly depending on vegetation feedbacks and flood events

cluster analysis of typhoon tracks part ii large scale circulation and enso abstract a new probabilistic clustering method based on a regression mixture model is used to describe tropical cyclone tc propagation in the western north pacific wnp seven clusters were obtained and described in part i of this two part study in part ii the present paper the large scale patterns of atmospheric circulation and sea surface temperature associated with each of the clusters are investigated as well as associations with the phase of the el nino southern oscillation enso composite wind field maps over the wnp provide a physically consistent picture of each tc type and of its seasonality anomalous vorticity and outgoing longwave radiation indicate changes in the monsoon trough associated with different types of tc genesis and trajectory the steering winds at 500 hpa are more zonal in the straight moving clusters with larger meridional components in the recurving ones higher values of vertical wind shear in the midlatitudes also accompany the straight moving tracks compared to

concurrent changes to hadley circulation and the meridional distribution of tropical cyclones abstractpoleward trends in seasonal mean latitudes of tropical cyclones tcs have been identified in direct observations from 1980 to the present paleoclimate reconstructions also indicate poleward equatorward migrations over centennial millennial time scales hadley circulation hc is often both implicitly and explicitly invoked to provide dynamical linkages to these shifts although no direct analysis of concurrent changes in the recent period has been presented here the observational tc record 1981 2016 and era interim jra 55 and merra 2 are studied to examine potential relationships between the two a zonally asymmetric hc is defined by employing helmholtz theory for vector decomposition and this permits the derivation of novel hc diagnostics local to tc basins coherent variations in both long term linear trends and detrended interannual variability are found tc genesis and lifetime maximum intensity latitudes share trend sign and magnitude with shifts in local hc extent with rates being a

cluster analysis of downscaled and explicitly simulated north atlantic tropical cyclone tracks abstracta realistic representation of the north atlantic tropical cyclone tracks is crucial as it allows for example explaining potential changes in u s landfalling systems here the authors present a tentative study that examines the ability of recent climate models to represent north atlantic tropical cyclone tracks tracks from two types of climate models are evaluated explicit tracks are obtained from tropical cyclones simulated in regional or global climate models with moderate to high horizontal resolution 1 0 25 and downscaled tracks are obtained using a downscaling technique with large scale environmental fields from a subset of these models for both configurations tracks are objectively separated into four groups using a cluster technique leading to a zonal and a meridional separation of the tracks the meridional separation largely captures the separation between deep tropical and subtropical hybrid or baroclinic cyclones while the zonal separation segregates gulf of mexico and ca

natural streams and the legacy of water powered mills gravel bedded streams are thought to have a characteristic meandering form bordered by a self formed fine grained floodplain this ideal guides a multibillion dollar stream restoration industry we have mapped and dated many of the deposits along mid atlantic streams that formed the basis for this widely accepted model these data as well as historical maps and records show instead that before european settlement the streams were small anabranching channels within extensive vegetated wetlands that accumulated little sediment but stored substantial organic carbon subsequently 1 to 5 meters of slackwater sedimentation behind tens of thousands of 17th to 19th century milldams buried the presettlement wetlands with fine sediment these findings show that most floodplains along mid atlantic streams are actually fill terraces and historically incised channels are not natural archetypes for meandering streams

stream ecosystem response to small dam removal lessons from the heartland in this paper we synthesize a series of small dam removal studies to examine how changes in channel form can affect riparian vegetation fish macroinvertebrates mussels and nutrient dynamics each of the ecosystem attributes responded to the disturbance of dam removal in different ways and recovered at very different rates ranging from months to decades riparian vegetation appeared to require the greatest time for recovery while macroinvertebrates had the least mussel communities were the most adversely affected group of species and showed no signs of recovery during the time period of the study based on these and other studies we suggest that ecosystems may follow two trajectories of recovery following dam removal first ecosystems may fully recover to pre dam conditions although this may be unlikely in many cases even if full recovery occurs the timescales over which different attributes recover will vary greatly and may be perceived by the public or management agencies as not recovering at all second ecosystems may only partially recover to pre dam conditions as the legacy of environmental damage of long term dam presence may not be reversible or because other watershed changes inhibit full recovery the potential for full or partial recovery is likely driven by the sensitivity of particular organisms the characteristics of the dam removed and the local geomorphic conditions of the watershed scientists and management agencies should assess the potential for full or partial recovery prior to dam removal and in particular should identify those species or groups of species that are likely to not recover to pre dam conditions such information is critical in the decision of whether or how to remove a dam

importance of hydrology on channel evolution following dam removal case study and conceptual model abstracta slow draining reservoir on the u s east coast was monitored to identify the processes governing channel evolution upstream of a dam removal channel evolution was documented through cross section surveys sediment size analysis discharge measurements and visual assessments of vegetative growth the reservoir drained slowly allowing for an analysis of channel evolution and identification of the morphometric parameters defining the path and time required for a channel to reach dynamic equilibrium channel evolution was a multidirectional process and evolving channel reaches actively migrated laterally while alternating between aggradation and degradation channel formation was dominated primarily by the hydrologic regime at the time of dam removal and secondarily by the ability of vegetation to establish and stabilize the channel form the importance of seasonal site hydrology over the minimum time required for channel evolution and the process through which the channel evolves indicates the

rapid channelization and incision into soft bedrock induced by human activity implications from the bachang river in taiwan abstract many taiwanese river channels have been affected by human activity such as engineering works and gravel mining environmental conditions such as high seasonal precipitation and young sedimentary bedrock exaggerate the narrowing and incising of river channels the bachang river is located in southwestern taiwan and the 11 km long channel at its midstream reach has been incised to a maximum depth of approximately 30 m within several decades therefore the morphologic evolution of the bachang river in southwestern taiwan provides an illustration of channel changes in response to human activity the historical data used for this analysis of morphology change include one set of topographic maps and six sets of aerial photographs from the past 100 years the channel changes are analyzed qualitatively and quantitatively and include the channel planform longitudinal profiles channel incision channel width and channel cross sections the results indicate that remarkable channel changes have occurred since the 1980s as a result of human influence the 11 km long study reach transformed from an alluvial type channel to a gorge type channel within several decades the maximum accumulated depth of the channel incision is approximately 30 m with a meter scale annual average incision rate the maximum width has been decreased to approximately one sixth of the original width 448 m the process of channel evolution is divided into four stages and we have concluded that the causes of channel change include six factors from two categories natural factors that include geological conditions hydrological conditions and the process of bedrock erosion and human factors that include gravel mining lateral structures and levees the initiation of channel evolution is triggered by human factors finally we discuss the potential future channel evolution and lessons learned from the case study

first report of sauropod tracks from the upper jurassic tianchihe formation of guxian county shanxi province china abstract this paper presents the first report of sauropod tracks from the upper jurassic of shanxi province china dinosaur tracks appear concentrated in five trackways in different stratigraphic levels of the late jurassic tianchihe formation tracks are dominantly small and medium size sauropod tracks and are tentatively assigned to brontopodus based on preserved track morphology trackway pattern and statistical analysis the tianchihe formation in which the tracks appear shows a gradual change from meandering fluvial to sandy braided fluvial depositional systems developed in a seasonally arid environment comparisons of the evaluated speed of bipedal to quadruped trackways indicate that the slower walk more easily produces pes dominated overprints trackways in the guxian tracksite appear following different orientations suggesting that these trackways were produced by different sauropods at different times an unusual trackway following a curved pattern has been identified in the site and could represent a special locomotion character or a social behavior the presence of eolian deposits in central shanxi province could have acted as a paleogeographic and paleoenvironmental barrier for the dispersion of the yanliao biota that survived in northern hebei western liaoning and northestern shanxi province to the ordos basin during the late jurassic

estimating the probability of river channel adjustment river channels respond not only to natural external controls and natural controls internal to individual drainage basins but also to the influence of human activity although many site specific instances of change have been documented the complexity of the process interactions means that very little is known about the general nature of different styles of adjustment or their relative sensitivity to drainage basin controls data obtained from the thames basin southeast england are used in a probabilistic approach to differentiate between four styles of river channel adjustment and a variety of drainage basin characteristics adopting a probabilistic approach quantifies the degree of confidence attributable to any prediction of river channel adjustment while acknowledging that certainties are difficult to obtain in studies of the natural environment this approach could thus allow environmental planning decisions to be made with a quantified degree of uncertainty four multivariate logistic regression models are described which use a combination of continuous and categorical variables to associate drainage basin characteristics with four styles of river channel adjustment derived from a reconnaissance evaluation survey in comparison it is shown that laterally migrating river channels are the most common natural channel type in the thames basin and their probability of occurrence rises to 71 per cent in sand gravel environments in channels regulated by low weirs deposition is the most likely channel activity where gradients are lower than 0 0040 whilst above this threshold the majority of channels are morphologically inactive in urban channels many of which are also lined by concrete the likelihood of obtaining a stable channel is mostly in excess of 80 per cent in channels straightened during this century deposition is most likely in gradients below 0 0050 whereas erosional enlargement is most probable above this value in channels which were initially channelized prior to this century deposition gives way to stability at a threshold gradient of 0 0080

the measurement of river bank erosion and lateral channel change a review a detailed review and chronological survey is presented of the various techniques which have been used for the measurement of river bank erosion and channel change the techniques are classified according to the time scales involved long intermediate and short and each is discussed with respect to accuracy and repeatability the methods covered include sedimentological evidence botanical evidence historical sources planimetric resurvey repeated cross profiling erosion pins and terrestrial photogrammetry prospects for future developments are also discussed

influence of track changes on the poleward shift of lmi location of western north pacific tropical cyclones abstractthe annual mean latitude at which tropical cyclones tcs reach their lifetime maximum intensity lmi over the western north pacific ocean basin has shifted northward since the early 1980s

yeosu dinosaur track sites of korea the youngest dinosaur track records in asia abstract eighty two dinosaur trackways were newly discovered in upper cretaceous lacustrine deposits on islands in the vicinity of yeosu korea most dinosaur tracks occur in marginal lake deposits with polygonal desiccation cracks the dinosaur tracks at the yeosu site include 65 ornithopod trackways 16 theropod trackways and one sauropod trackway the prevalence of ornithopod tracks and the limited occurrence of sauropod tracks at the yeosu site evidently reflect decreased sauropod diversity in the upper cretaceous all ornithopod trackways represent bipeds and most of the ornithopod tracks are similar to caririchnium from other sites of the korean peninsula all fossil wood specimens collected in the study area represent conifers three species of cupressaceous and two species of taxodiaceous conifers and a new species except for one which is a discotyledon it is thus inferred that the southwestern part of the korean peninsula was primarily covered with mesic forests with taxodiaceous trees during the late cretaceous the k ar age of the yeosu tracksite is determined as 81 65 ma camapnian to maastrichtian it indicates that the yeosu track site contains the last records of dinosaurs living in asia consequently semi arid palaeoclimatic conditions together with a large lake as a persistent water source and rich vegetation of gymnosperm trees as food resulted in the preservation of abundant dinosaur tracks in the upper cretaceous on the korean peninsula

rapid reservoir erosion hyperconcentrated flow and downstream deposition triggered by breaching of 38 m tall condit dam white salmon river washington condit dam on the white salmon river washington a 38 m high dam impounding a large volume 1 8 million m3 of fine grained sediment 60 sand 35 silt and clay and 5 gravel was rapidly breached in october 2011 this unique dam decommissioning produced dramatic upstream and downstream geomorphic responses in the hours and weeks following breaching blasting a 5 m wide hole into the base of the dam resulted in rapid reservoir drawdown abruptly releasing 1 6 million m3 of reservoir water exposing reservoir sediment to erosion and triggering mass failures of the thickly accumulated reservoir sediment within 90 min of breaching the reservoir s water and 10 of its sediment had evacuated at a gauging station 2 3 km downstream flow increased briefly by 400 m3 s 1 during passage of the initial pulse of released reservoir water followed by a highly concentrated flow phase up to 32 sediment by volume as landslide generated slurries from the reservoir moved downstream this hyperconcentrated flow analogous to those following volcanic eruptions or large landslides draped the downstream river with predominantly fine sand during the ensuing weeks suspended sediment concentration declined and sand and gravel bed load derived from continued reservoir erosion aggraded the channel by 1 m at the gauging station after which the river incised back to near its initial elevation at this site within 15 weeks after breaching over 1 million m3 of suspended load is estimated to have passed the gauging station consistent with estimates that 60 of the reservoir s sediment had eroded this dam removal highlights the influence of interactions among reservoir erosion processes sediment composition and style of decommissioning on rate of reservoir erosion and consequent downstream behavior of released sediment

seasonal to multidecadal variability of the width of the tropical belt 1 an expansion of the tropical belt has been extensively reported in observations reanalyses and climate model simulations but there is a great deal of uncertainty in estimates of the rate of widening as different diagnostics give a wide range of results this study critically examines robust diagnostics for the width of the tropical belt to explore their seasonality interannual variability and multidecadal trends the width based on the latitudes of the maximum tropospheric dry bulk static stability measuring the difference in potential temperature between the tropopause and the surface is found to be closely coupled to the width based on the subtropical jet cores on all time scales in contrast the tropical belt width and northern hemisphere edge latitudes based on the latitudes at which the vertically averaged stream function vanishes a measure of the hadley circulation s poleward edges lag those of the other diagnostics by approximately 1month the tropical belt width varies by up to 10 latitude among the diagnostics with trends in the tropical belt width ranging from 0 5 to 2 0 per decade over the 1979 2012 period nevertheless in agreement with previous studies nearly all diagnostics exhibit a widening trend although the stream function diagnostic exhibits a significantly stronger widening than either the jet or dry bulk stability diagnostics finally gps radio occultation observations are used to assess the ability of the reanalyses to reproduce the tropical belt width finding that they better situate the latitudes of maximum bulk stability versus those of the subtropical jets

trends in the local hadley and local walker circulations the linear trend in the local hadley and walker circulations from 1979 to 2009 is calculated these local circulations are defined through a decomposition of the vertical mass flux into its zonal and meridional components defining the local circulation this way ensures that the two orthogonal circulations the local hadley and walker circulations sum to the original circulation even after averaging the circulations regionally large regional differences in changes in the local hadley and walker circulations over a 31 year period are found for example the local hadley circulation has shifted southward over africa the maritime continent and the western and central pacific by about 1 over the americas and the atlantic the local hadley circulation has strengthened by about 1 5 the zonal component of the vertical mass flux has increased by about 10 20 in the tropics over all continents and decreased over the adjacent oceans by about 10 20 although the local walker circulations in the indian ocean and the atlantic have weakened the circulation in the pacific has changed little about 1 2 the local walker circulations in all ocean basins have shifted westward by about 1 2 on average