incision due to gravel mining modeling a case study from the gallego river spain abstract historical information on river degradation was used in a case study on the gallego river a tributary of the ebro river in northeastern spain the gallego drains about 4000 km 2 of the southern slopes of the pyrenees good channel surveys since the 1940s allowed a comparison of longitudinal bed profiles over time over this period about 1 million m 3 of gravel was mined according to the archival records the volume of alluvium lost due to incision in the same period was 2 million m 3 this imbalance is tentatively explained by a budget model based on a bedload equation and an algorithm to determine whether the effective bedload transport is controlled by the transport capacity or by the supply of sediment it appears that the incision process has changed the magnitude of the shear stresses on channel bed as the river became deeper the channel could accommodate higher discharges without overbank flooding the results obtained from a second model based on diffusion equation for the bed elevation compared well with the field data this model is based on the hypotheses of steady uniform flow regarding water and sediment conservation

character of hearwaters adjustment to base level drop investigated by digital modeling using a computer model written for dynamic river profile modeling snow and slingerland 1987 long term profile adjustments to constant rate base level lowering tectonic block uplift have been simulated with varied conditions of outflow discharge 10 and 100 m3 s sediment diameter 0 1 0 4 and 2 0 mm and sediment load concentrations of 1200 and 400 ppm by weight tweleve sets of initially graded profile data cover all possible combinations of the variables each modeled stream has been subjected to each of three base level drop rates 0 1 1 0 and 10 0 mm yr for 10 000 years of model time modeled histories of headwaters erosional response differ in two ways the first is length of lag time of response characterized by a period of quiescence in erosion at the headwaters prior to the channel steepening sufficiently for erosion to commence at this upstream point variations in discharge and sediment concentration affect the lag time of response in all cases the second variable aspect of response is the relative magnitude of eventual headwaters erosion the main control is the drop rate a high drop rate yields a low relative magnitude whereas a low drop rate yields a high relative magnitude of response the rate of base level drop also controls to what degree the other controlling variables of discharge sediment concentration and sediment diameter affect the eventual magnitude of headwaters erosion rates of trunk stream and headwaters erosion indicate that 21 out of 36 of the modeled stream systems attain a condition approximating parallel profile erosion after 10 000 years some examples notably those with low power to erode and high imposed drop rates exhibit headwaters erosion rates that continue to be well below rates of base level lowering creating profile steepening with no apparent time limit

role of atmospheric waves in the formation and maintenance of the northern annular mode 1 we examined the roles of stationary synoptic and medium scale atmospheric waves in the formation and maintenance of the northern annular mode nam in winter by analyses of zonal momentum and wave energy based on six hourly reanalysis data from the european centre for medium range weather forecasts ecmwf era interim medium scale waves have periods shorter than about two days and their effect has been overlooked in previous research on the nam the effect of medium scale waves on the nam is about 10 of that of total eddies although their effect on the nam is of less importance than their effect on the southern annular mode sam it is still significant in the northern hemisphere our analysis also suggests that synoptic medium scale and stationary waves provide positive feedback to the zonal mean zonal wind of the nam in particular energy transfer from synoptic and low frequency transient waves to stationary waves plays a key role in sustaining the stationary waves that drive zonal winds associated with the nam

sediment yield exceeds sediment production in arid region drainage basins we use 10 be and 26 al to determine long term sediment generation rates identify significant sediment sources and test for landscape steady state in nahal yael an extensively studied hyperarid drainage basin in southern israel comparing a 33 yr sediment budget with 33 paired 10 be and 26 al analyses indicates that short term sediment yield 113 138 t km 2 yr 1 exceeds long term sediment production 74 16 t km 2 yr 1 by 53 86 the difference suggests that the basin is not in steady state but is currently evacuating sediment accumulated during periods of more rapid sediment generation and lower sediment yield nuclide data indicate that 1 sediment leaving the basin is derived primarily from hillslope colluvium 2 bedrock weathers more rapidly beneath a cover of colluvium than when exposed and 3 long term erosion rates of granite schist and amphibolite are similar

relationship between cyclone tracks anticyclone tracks and baroclinic waveguides abstract this study presents observational results concerning the structure and evolution of high frequency fluctuations with periods shorter than 6 days in the geopotential height field the results are based on a statistical analysis of 1000 500 and 250 mb height fields derived from twice daily nmc final analyses over the northern hemisphere for the 20 winters 1964 65 through 1983 84 the disturbances assume the form of waves elongated in the meridional direction with a mean wavelength of 4000 km a westward tilt with height and a mean eastward phase propagation of 12 1 5 m s 1 these results support an interpretation in terms of finite amplitude baroclinic waves whose structure and evolution varies with geographical location over the continents and especially along the eastern slopes of the rockies and the tibetan plateau the waves show marked departures in structure and evolution from those over the oceans in particular we find evidence of a systematic influence of the terrain in steering the

tectono geomorphic study of the karewa basin of kashmir valley abstract the karewa basin nestled between the pir panjal range and the great himalayan range in northwest india has been studied to understand its tectono geomorphic evolution on the basis of geomorphic indices and morphotectonic parameters supported by the field evidences satellite data topographic maps and digital elevation model dem were used to extract various parameters at various spatial scales four watersheds representative of the entire karewa basin were chosen for detailed studies on the basis of the researchable evidence of the complete sequence of the stratigraphic record and the preservation of geomorphic landscapes the integrated analysis of the geomorphic and morphometric data provides evidence of the relative variations in the tectonic activity among the watersheds geomorphic indices suggest a relatively high degree of tectonic activity along the pir panjal side of the karewa basin this variation in the relative degree of tectonic activity is consistent with the field evidence fault lineament locations and the landscape geometry of the karewa basin based on the results from this study it is suggested that late quaternary climate changes tectonic uplift and erosion of the pir panjal range and changing geometry of the karewa lake have played a key role in the evolution of the geomorphic landscape of the kashmir valley

the 4 day wave in the antarctic mesosphere a zonal wave number one eastward propagating planetary wave observed in the high latitude winter stratosphere with a period near 4 days has been studied by a number of previous authors radar observations coupled with stratospheric analyses are here used to demonstrate that this wave known as the 4 day wave extends into the antarctic upper mesosphere previous workers have asserted that the wave is a manifestation of the observation of warm pools rotating in the polar vortex and that the pool seems to behave in a quasi nondispersive manner the observation of the 4 day wave in the upper mesosophere presented here appears to validate previous claims that the warm pools are being maintained by wavelike dynamics rather than simple advection

numerical model predictions of autogenic fluvial terraces and comparison to climate change expectations terraces eroded into sediment alluvial and bedrock strath preserve an important history of river activity river terraces are thought to form when a river switches from a period of slow vertical incision and valley widening to fast vertical incision and terrace abandonment consequently terraces are often interpreted to reflect changing external drivers including tectonics sea level and climate in contrast the intrinsic unsteadiness of lateral migration in rivers may generate terraces even under constant rates of vertical incision without external forcing to explore this mechanism we simulate landscape evolution by a vertically incising meandering river and isolate the age and geometry of autogenic river terraces modeled autogenic terraces form for a wide range of lateral and vertical incision rates and are often paired and longitudinally extensive for intermediate ratios of vertical to lateral erosion rate autogenic terraces have a characteristic reoccurrence time that scales with the time for relief generation there is a preservation bias against older terraces due to reworking of previously visited parts of the valley evolving spatial differences in bank strength between bedrock and sediment reduce terrace formation frequency and length favor pairing and can explain sublinear terrace margins at valley boundaries age differences and geometries for modeled autogenic terraces are consistent in cases with natural terraces and overlap with metrics commonly attributed to terrace formation due to climate change we suggest a new phase space of terrace properties that may allow differentiation of autogenic terraces from terraces formed by external drivers

wave packets and life cycles of troughs in the upper troposphere examples from the southern hemisphere summer season of 1984 85 abstract in this paper reanalysis data for the southern hemisphere summer season of 1984 85 produced by the european centre for medium range weather forecasts have been analyzed to examine wave packets and life cycles of baroclinic waves a semiobjective algorithm has been devised to track wave packets it is found that the perturbations in the upper troposphere are dominated by wave packets some of these wave packets can be tracked for several weeks during which they can make up to two trips around the latitude circle the energy life cycles of waves that make up several of these wave packets were analyzed and apart from the incipient waves that started the wave packets most of the subsequent wave development was found to be dominated by convergence and divergence of energy fluxes rather than due to baroclinic or barotropic conversions demonstrating that these wave packets are indeed coherent entities that propagate due to downstream development or dispersion the energy life cycle of the most

drainage basin evolution in the rainfall erosion facility dependence on initial conditions four experiments in alluvial drainage basin evolution were carried out in the rainfall erosion facility ref at colorado state university to investigate the dependence of basin evolution on initial topography basins were initially undissected each experiment began with a unique initial condition representing various end members of relief and hypsometry drainage network development hillslope processes basin denudation and basin response to base level lowering all depended strongly on the initial topography no classic model of drainage network evolution was found to be generally applicable initially planar slopes first developed subparallel channels that extended headward dendritically during an early phase of extension channel incision occurred first in the interior of the basin where saturation overland flow was greatest not at the basin outlet as assumed in most classic models of network development channels widened over time initiating lateral migration and drainage capture in the downslope portion of the watershed before transferring lateral migration upslope planar basins of larger initial gradient grew headward more quickly and become more deeply entrenched inhibiting late stage lateral migration an experiment with initial relief concentrated at a plateau edge evolved in several unique ways a high ratio of subsurface to surface flow gave rise to mass movements at the plateau edge and outlet channels deep channels were quickly cut initially but did not extend far upslope because slope instability undermined channel head migration leaving the plateau undissected and hence very slow to erode these results suggest that the distribution of relief within a basin exerts an important control on drainage network pattern and basin denudation in addition erosional basins may evolve in several distinct modes characterized by particular combinations of hypsometry hillslope processes and mean denudation rate

stream profile adjustment to crustal warping nonlinear results from a simple model three numerical experiments have been performed modeling response of a greatly simplified stream system to initiation of crustal tilting and domal uplift model results show signs of nonlinear behavior in varying degrees these signs include river profile adjustments that have forms quite different from the geometries of crustal movements cases of channel erosion following deposition at the same location and spatial transition points between opposing adjustments i e erosion and deposition that fail to coincide with boundaries or axes of crustal movement particular nonlinear effects wax or wane as the system adjusts to a new dynamic equilibrium with the continuing crustal movement the modeled features of stream adjustment are not in so extreme a class as the commonly discussed complex response of fluvial systems but they do serve to suggest some caution in studies that employ stream profile information as an indicator of crustal movement

incision of alluvial channels in response to a continuous base level fall field characterization modeling and validation along the dead sea abstract the dramatic lake level drop of the dead sea during the twentieth century 30 m provides a field scale experiment in transport limited incision of gravel bed channels in response to quasi continuous base level fall at approximately constant rate we apply a one dimensional numerical incision model based on a linear diffusion equation to seven ephemeral channels draining into the dead sea the model inputs include the measured twentieth century lake level curve annual shoreline location i e annual channel lengthening following the lake level drop reconstructed longitudinal profiles of each of the channels based on mapped and surveyed terraces and the current profiles of the active channels the model parameters included the diffusion coefficient and the upstream derived sediment flux both were first calibrated using a set of longitudinal profiles of known ages and then validated using additional sets of longitudinal profiles the maximum at station total incision observed at each of the studied channels was significantly less then the total lake level drop and varied in response to both drainage area and lake bathymetry the model applied predicted degradation rates and the pattern of degradation with high accuracy this suggests that sediment flux in the modeled channels is indeed linearly dependent on slope further support for this linear dependency is provided by a linear correlation between the diffusion coefficient and the mean annual rain volume over each basin a proxy for discharge the model presented could be a valuable tool for planning in rapid base level fall environments where incision may risk infrastructure

mathematical modeling of graded river profiles numerical modeling of the longitudinal profiles of rivers at grade is accomplished using the basic equations of open channel flow sediment transport equations and empirical relations for downstream variation in flow discharge sediment discharge sediment caliber and channel width only in some cases are the computed stream profiles fit exactly by any one of the commonly supported mathematical function analogs to graded profile form exponential logarithmic or power function but in most cases any of these functions can provide a fit with a degree of error smaller than would be noted in treating field data profiles dominated by spatial change in fluid and sediment discharge are distinctly power functions while profiles dominated by sediment size reduction are not necessarily exponential in form other important controls on profile shape are the degree of downstream width change in response to increasing discharge and the general range of sediment size a dynamic model of a river s approach to grade

a scaling approximation of equilibrium timescales for sand bed and gravel bed rivers responding to base level lowering the timescale required for a river channel to reach new equilibrium conditions following a disturbance presumably depends on channel substrate size and previous field studies have suggested that gravel bed channels should reach equilibrium more quickly than sand bed channels to estimate the relative timescale difference between sand bed and gravel bed rivers responding to base level lowering we developed a simple scaling approximation equilibrium timescales derived from these equations for sand bed rivers were found to be approximately half of those for gravel bed rivers while gravel bed channels do not need to transport as much sediment to reach equilibrium conditions as sand bed channels transport of sediment is more rapid in sand bed channels leading to quicker equilibration

trapped waves in the edge region of stratospheric polar vortices 1 a global distribution and seasonal variability of short period 2 days disturbances in the lower and middle stratosphere are investigated using 6 hourly european centre for medium range weather forecasts reanalysis data over 15 years 1979 1993 two dimensional spectral analysis and a recently developed lagrangian mean diagnostic are used for the analysis it is shown that the short period disturbances are most active around the polar night jet in each winter hemisphere they have a wavelike structure in the longitudinal direction with typical zonal wavelengths of 1 700 2 000 km i e zonal wave number 10 12 and a latitudinally evanescent structure with a half width of about 1 500 km suggesting that they are waves trapped in the edge region of the polar vortex where the latitudinal gradient of isentropic potential vorticity is maximized the trapped waves have a nearly barotropic structure over a depth greater than 10 km because the polar vortex in the northern hemisphere is much deformed and not symmetric around the pole dynamical characteristics of the trapped waves in the southern hemisphere alone are investigated by applying a lag correlation analysis to the reanalysis data the characteristics of trapped waves are fairly dependent on the state of the polar vortex such as zonal wind speed and its vertical shear they have a significant westward intrinsic phase velocity from june through october when the polar vortex is most stable this indicates that the trapped waves during this period have their own dynamics contrary to the filaments being passively advected by the large scale flow

storm tracks in the southern hemisphere abstract from 1979 to 1989 global european centre for medium range weather forecasts ecmwf analyses of many meteorological variables important in baroclinic storms have been bandpass filtered to highlight fluctuations on 2 to 8 day time scales in order to illuminate the relationships among the variables in baroclinic storm track regions because of the greater zonal symmetry in the southern hemisphere sh versus the northern hemisphere nh it is possible to examine these relationships over a zonal sector without being dominated by local effects associated with jet stream entrance and exit regions of the storm tracks the bandpassed variance of geopotential height is used to define the storm track and its meridional profile has a pronounced midlatitude maximum in the sh the locations of the jet stream and the variance maxima of meridional and zonal velocity components vorticity vertical motion specific humidity and temperature all bear a distinctive relationship to the storm track but the lat

rapid incision of a small coarse and steep fan delta in response to base level fall the case of nahal qedem the dead sea israel the dead sea has been continuously dropping 0 4 1 0 m yr 1 since the middle of the 20th century and thus provides a unique field laboratory for studying in real time the response of drainage systems to a non tectonic base level fall the aim of this work is to study the short term ongoing erosive response to a rapid base level drop in a small steep fronted erodible fan delta setting the work explores the controls of the steep qedem fan delta guided by its clinoform structure on its incision longitudinal profiles of the fan delta and of its entrenched channel were measured in the field sedimentary facies changes fluviatile shallow lacustrine and beach were followed along exposures the existence of large boulders provided an opportunity to examine the uncertain role of armouring and boulder flux on incision the field study was combined with digital elevation models dems that were extracted from pairs of overlapping aerial photos maps of erosion and deposition were prepared using a change detection algorithm the longitudinal profile of the entrenched channel was found to be steep and linear the outlet temporarily hangs elevated and ungraded above the retreating lake level indicating years without incision flow events which cause lags in response to the rapid lake level drop in spite of the large boulders the small drainage basin and precipitation volume over the basin of the qedem the recorded vertical incision rates in the unconsolidated sediments are as high as 0 8 m yr 1 i e similar to those of the largest wadis draining to the dead sea the steep front of the fan delta is suggested to be a main factor controlling the efficient incision a unique transport mechanism of rolling boulders following undercutting contributed to the entrenchment efficiency copyright 2010 john wiley sons ltd

flash flood and bedload dynamics of desert gravel bed streams comparatively little is known about the hydrology of desert flash floods despite the extent of the world s drylands there is even less known about their sedimentary behaviour and particularly about the movement of coarse material as bedload the results of an intense field monitoring programme carried out on an ephemeral gravel bed stream in the northern negev desert are presented in this semi arid setting flow duration analysis indicates that the channel is hydrologically active for 2 of the time or about seven days per year and that overbank flow can be expected for only 0 03 of the time about three hours per year multipeaked flood hydrographs are the norm reflecting many factors including the arrival of separate slugs of discharge from contributing subcatchments the passage of the initial flood bore is surprisingly slow but the rising limb of the flood hydrograph is rapid with a median time of rise of 10 minutes in keeping with expected flash flood behaviour bedload flux is high averaging 2 67 kg s 1 m 1 during the period that the channel carries flow this gives very high bedload sediment yield despite the infrequent and short duration of flood flows and matches the high yield of suspended sediment the relationship between bedload flux and boundary shear stress is simple in contrast with perennial gravel bed streams and the exponent of the log log relationship is 1 52 of great value is that the behaviour of the nahal eshtemoa corroborates a pattern established by the authors previously in a smaller tributary stream 1998 john wiley sons ltd

numerical modelling of drainage basin evolution and three dimensional alluvial fan stratigraphy abstract a forward numerical model is presented to study the effects of bedrock erodability thrust displacement rate pulsating tectonic activity and sea level fluctuations on drainage basin morphology and stratigraphy of large alluvial fan systems a low value of the bedrock erodability coefficient k b 0 5 10 4 year 2 3 vs thrust rate 2 0 m ky is associated with a time lag between cessation of tectonic activity and maximum sedimentation rates observed on the alluvial fans applying higher k b values ranging between 1 0 and 8 0 10 4 year 2 3 results in higher sediment yields due to more rapid headward catchment erosion and elaborate sideways branching of drainage networks pulsating tectonic activity is reflected in a stratigraphic alternation of prograding and retrograding alluvial fan gravels during tectonic activity fan gravel fronts and coastlines retreat because catchment yields are insufficient to fill the accommodation space created by the flexural response due to thrust loading phases of tectonic quiescence and cessation of flexural subsidence are indicated by progradation of the gravel front depending on the position in the basin the lag time for arrival of the gravel associated with tectonic cessation is several tens to hundred thousands of years a combination of pulsed tectonic activity with sinuous sea level fluctuation leads to a more complex stratigraphic pattern in that case stratigraphic response to tectonic pulses is masked by a similar but higher order frequency stacking pattern especially in the more distal parts

impact of earthquakes on agriculture during the roman byzantine period from pollen records of the dead sea laminated sediment the dead sea region holds the archives of a complex relationship between an ever changing nature and ancient civilisations regional pollen diagrams show a roman byzantine period standing out in the recent millennia by its wetter climate that allowed intensive arboriculture during that period the dead sea formed laminites that display mostly a seasonal character a multidisciplinary study focused on two earthquakes 31 bc and ad 363 recorded as seismites in the ze elim gully a unit iii which has been well dated by radiocarbon in a previous study the sampling of the sediment was done at an annual resolution starting from a few years before and finishing a decade after each earthquake a clear drop in agricultural indicators especially olea and cereals is shown these pollen indicators mostly reflect human activities in the judean hills and coastal oases agriculture was disturbed in large part of the rift valley where earthquake damage affected irrigation and access to the fields it took 4 to 5 yr to resume agriculture to previous conditions earthquakes must be seen as contributors to factors damaging societies if combined with other factors such as climatic aridification disease epidemics and political upheaval they may lead to civilisation collapse

the role of wave packets in wave mean flow interactions during southern hemisphere summer abstract in this study reanalysis data produced by the european centre for medium range weather forecasts for 14 southern hemisphere sh summer seasons have been analyzed all cases of hemispheric transient eddy kinetic energy teke maxima have been identified and the evolution of the local energetics and planetary scale flow anomalies accompanying these teke growth decay episodes are composited the longitude time evolution of the composite energetics shows the clear signature of a wave packet propagating eastward at a group velocity of about 27 longitude per day and undergoing a life cycle of growth and decay with the energetics within a volume close to the wave packet center dominating the hemispheric mean energetics when individual cases are examined 52 are found to resemble the composite and have the energetics life cycle dominated by the evolution of a single wave packet and an additional 21 are found to be dominated by the evolution of two wave packets having similar amplitudes only the

hydraulic geometry of cohesive channels undergoing base level drop abstract this study extends earlier contributions on dynamic adjustments of fluvial channels to base level changes we have investigated an in situ response of self formed cohesive channels to a base level drop conditions analogous to a gradual change in uplift and or climate empirical hydraulic geometry equations for clayey cohesive natural streams are presented using data from eight channels draining perennial brackish springs and discharge into the dead sea investigation of downstream variations in gradient and stream power relations suggests existence of three distinct reaches in which channel adjustment to base level drop is shared inequitably among hydraulic geometry variables values of the flow velocity exponent m are low 0 11 m 0 24 the mid channel reach having the lowest exponent the depth exponent f has the lowest value f 0 3 for the uppermost channel reaches the rest having higher values f 0 4 the smallest width exponent b 0 35 characterizes the upper reaches these values and their spatial distribution exhibit a regular pattern we show that the lowermost channel reach adjusts by profile steepening and channel narrowing f b the prevailing mechanism in the mid channel reaches is lateral width adjustment cross sections transiently transforming toward equilibrium the uppermost reaches have wide and shallow channel cross sections because of series of bank collapses and resultant sediment aggradation bringing rise to decreased local gradient forcing further channel widening the results of this study not only allow inference about how cohesive channels regulate their geometry but also reveal the means by which hydraulic forces overcome substrate resistance adjusting slope and channel dimensions and as such have implication for reach scale channel morphology and models of stream power

using palynology to re assess the dead sea laminated sediments indeed varves lacustrine laminated sediments are often varves representing annual rhythmic deposition the dead sea high stand laminated sections consist of mm scale alternating detrital and authigenic aragonite laminae previous studies assumed these laminae were varves deposited seasonally however this assumption has never been robustly validated here we report an examination of the seasonal deposition of detrital aragonite couplets from two well known late holocene laminated sections at the ze elim fan delta using palynology and grain size distribution analyses these analyses are complemented by the study of contemporary flash flood samples and multivariate statistical analysis because transport affects the pollen preservation state well preserved mostly air borne transported pollen was analysed separately from badly preserved pollen and fungal spores which are more indicative of water transport and reworking from soils our results indicate that i both detrital and aragonite laminae were deposited during the rainy season ii aragonite laminae have significantly lower reworked and fungal spore concentrations than detrital and flash flood samples and iii detrital laminae are composed of recycling of local and distal sources with coarser particles that were initially deposited in the dead sea watershed and later transported via run off to the lake this is in line with previous carbon balance studies that showed that aragonite precipitation occurs after the massive input of tco2 associated with run off episodes consequently at least for the holocene ze elim formation laminated sediments cannot be considered as varves older quaternary laminated sequences should be re evaluated

the age and nature of the basement of southern britain evidence from sr and pb isotopes in granites the isotopic study of granitic intrusions in southern britain provides an indication of the age and geochemical nature of the south british basement which is otherwise generally obscured from observation by sedimentary cover this paper reports pb isotopic compositions of feldspars in granites from sw england lundy mountsorrel and shap in addition to age and initial 87 sr 86 sr data on two of the granites a review of published rb sr age and isotope data for southern britain and consideration of the new pb data using the plumbotectonics model of doe zartman 1979 indicate that the basement to southern britain has an age of 800 ma with an upper limit of 1200 ma the granites studied in this work have substantial components of crustally derived sr and pb

a ubiquitous wavenumber 5 anomaly in the southern hemisphere during fgge abstract predominant wavenumber 5 patterns frequent the temperature fields of the lower stratosphere of the southern hemisphere during the summer months of fgge these pentagonal features of broad latitudinal extent appear to remain quasi stationary or propagate eastward with periods on the order or 10 days ensemble statistics over the summer season confirm the presence of large amplitude wavenumber 5 anomalies in the geopotential fields magnified height amplitudes appear in the zonal spectra at wave 5 near the tropospheric jet core 50 s and 300 mb the enhanced temperature anomalies in the lower stratosphere arise not only from the magnified geopotential amplitude of wavenumber 5 but also from its sharp evanescence above the jet time series analysis reveals that the peak in rms amplitude results primarily from the fluctuating contribution the transient component of wavenumber 5 shows a regular eastward phase progression geopotential power spectra exhibit a pronounced peak corresponding to east

using river long profiles and geomorphic indices to evaluate the geomorphological signature of continental scale drainage capture duero basin nw iberia well constrained case studies of transient landscape responses are needed to improve our understanding of erosion processes associated with drainage captures the duero basin is an excellent location for such a study because the landscape is currently undergoing pronounced geomorphological changes resulting from the opening of a former closed drainage the present day continental interior basin n50 000 km2 drains to the atlantic ocean via the duero river but during the cenozoic the basin experienced a long endorheic period marked by the formation of evaporites currently the entire continental interior is an area of relative tectonic quiescence characterised by a relict low relief upland topography meseta systematic variations in lithology and a well constrained tectonic setting throughout the basin and adjacent areas allow for the comparison of channel morphology between the cenozoic duero basin and its western fringe to explore the signal of transient geomorphic response to capture and opening of the former endorheic basin the main channel and 24 tributaries were analysed in terms of their longitudinal profiles and the application of geomorphic indices concavity index ci valley floorwidth to height ratio vf and stream length gradient index sl the analysis reveals two zones with distinctive morphologies 1 an upper reach domain consisting of broad flat valleys and low gradient streams where concave longitudinal profiles dominate and 2 a middle reach domain characterised by steep deeply incised canyons where a convex long profile dominates marking a major kinckzone the quantitative information on channel shapes and long profile geometries allows the interpretation of these patterns in terms of driving forces for fluvial landscape development large scale morphometric analysis highlights the transient response of the entire basin to a capture related base level lowering and illustrates the importance of drainage captures as potential internal drivers of landscape modification and topographic adjustments furthermore the duero basin case study also emphasises that well constrained bedrock geology and tectonic patterns are essential to avoid misinterpretation of geomorphic indexes

controls on aggradation and incision in the ne negev israel since the middle pleistocene we investigated the mid pleistocene to recent aggradation incision pattern of two drainage systems nahal peres and nahal tahmas in the hyperarid north eastern negev desert southern israel although these drainage systems drain into the tectonically active dead sea basin lake level fluctuations cannot account for the aggradation incision pattern as bedrock knickpoints disconnect the investigated parts of these drainage systems from base level influence we applied geomorphic mapping soil stratigraphy optically stimulated luminescence osl and cosmogenic in situ 10be exposure dating to reconstruct cycles of aggradation and incision of alluvial terraces and to study their temporal association with regional periods of humidity and aridity and global glacial interglacial cycles the spatial and temporal relationships between the alluvial units suggest changes in the drainage system behavior since the middle pleistocene and show a pattern in which prolonged periods of sediment aggradation alternated with short periods of rapid and intense degradation through erosion and incision into sediment and bedrock we obtain ages for several pleistocene holocene periods of incision 1 1 ma 300 ka 120 ka 20 ka 12 ka and 2 ka although broadly synchronous the nahal peres and nahal tahmas systems exhibit temporal differences in aggradation and incision hyperarid conditions have persisted in the region at least since the middle pleistocene as evidenced by gypsic salic soils that ubiquitously cap the investigated alluvial terraces this observation is consistent with other observations throughout the negev indicating prolonged aridity thus alternation between sediment aggradation and degradation cannot be correlated in a simple and straightforward way to climatic changes we explain the temporal differences in aggradation and incision between nahal peres and nahal tahmas as resulting from the differences in stream gradient basin hypsometry and drainage basin area which influences the amount of water passing through the system regardless of humidity source tropical plumes red sea trough or mediterranean fronts and the frequency and intensity of rainfall in the region our study shows that 1 unlike other climatic proxies such as speleothems the evolution of alluvial terraces which involves many stages sediment generation transport deposition and subsequent incision results in a significant time gap between the actual ages of terraces and the timing of external triggers such as climatic fluctuations and 2 such time gaps may vary even within nearby drainage systems due to differences in drainage systems specific characteristics and thus result in asynchronicity or at least poor synchronicity of alluvial terrace deposition and incision

fragmentation of stratospheric intrusions evidence is presented pointing to the existence of rich and coherent subsynoptic and mesoscale flow features at tropopause levels these features are related to and evolve from the classical v shaped intrusions of stratospheric air down to tropospheric elevations it is shown that intrusions can develop into elongated 2000 3000 km and slender 200 km streamers and that thereafter such a streamer can roll up to form a train of stalactite shaped vortex subentities with an accompanying substantial thinning of the intervening filament in addition there are indications that the vortices themselves can develop a spirallike interior structure of interleaved stratospheric and tropospheric air these inferences are based upon two independent but complementary sources analysis of the potential vorticity distribution on tropopause transcending isentropic surfaces derived from the analysis fields of the european centre for medium range weather forecasts either directly or indirectly using a contour advection technique and imagery from the water vapor channel of the european space agency meteosat 4 satellite streamers were observed to occur with a frequency of approximately one per week over central and southern europe during the winter of 1991 1992 the fragmentation is linked to the instability or self development of a filament of enhanced potential vorticity and it can modify or instigate surface weather systems moreover by inducing a substantial and rapid enlargement of the intrusion s surface area it greatly enhances the potential for local irreversible mixing of stratospheric and tropospheric air

layered structure associated with low potential vorticity near the tropopause seen in high resolution radiosondes over japan horizontal wind and temperature data obtained from operational radiosondes over japan have recently been available with high vertical resolution analyzing these data over 4 yr has indicated horizontal velocity layers with vertical scales of about 5 km lasting for a week or more the layers appear frequently in winter at several stations simultaneously and are dominant in the height range of 8 16 km an empirical orthogonal function eof analysis for the time series of layered disturbance amplitude in winter indicates that there are two dominant principal components the first component eof1 describes layered disturbances in the middle of japan 308 378n and the second one eof2 describes disturbances in the south of japan 238 308n using global analysis data the background field of the layered disturbances was examined an interesting result is that the background potential vorticity pv is approximately zero or negative for eof2 disturbances even though located in a relatively high latitude region this fact suggests that the eof2 disturbances are due to inertial instability it is also shown that negative pv occurs more than 30 of the time in winter in a zonally elongated region of 238 298n in the western pacific on an isentropic surface of 345 k 10 km altitude such a high frequency of negative pv is not observed at other longitudes in this latitude band to determine the origin of the anomalous pv backward trajectories were analyzed for eof2 disturbances air parcels having mostly negative pv are traced back to the equatorial region in the longitude band 208w 1408e within a few days this is due to a strong northward branch of the hadley circulation associated with deep convection over the maritime continent and a strong northeastward subtropical jet stream on the other hand the background pv is low but scarcely negative for eof1 disturbances air parcels at eof1 stations are traced back to the far west because they are advected mostly by a strong eastward jet stream thus it is inferred that the eof1 disturbances may be due to inertia gravity waves trapped in a duct of the westerly jet core

autogenic response of fluvial deltas to steady sea level fall implications from flume tank experiments flume tank experiments on fluvial deltas conducted with constant fall of relative sea level rate a 0 constant sediment discharge q s and constant water discharge q w reveal a built in geomorphic process that inevitably causes valley incision autoincision after the beginning of the sea level fall and forms paired stream terraces on the abandoned alluvial slope despite steady sea level fall deltas aggrade without major incision until the autoincision threshold is attained at which time the aggradational regime is replaced by a degradational one results of the experiments imply that multiple valley incision and terrace formation can occur as an autogenic response of the depositional system to steady forcing by constant sea level fall changes of a q s and q w or changes in river energy are not required to account for these geomorphic events the understanding of the autogenic response when combined with the theory of shoreline autoretreat provides an alternative view of the geomorphic development of fluviodeltaic systems during base level fall

response of the ohau river and delta to lake level lowering the response of the ohau river to a lowering of lake benmore of 4 m was monitored during a three month period when the river was carrying mean daily flows between 100 and 400 m3 s from a power station initially the river degraded by up to 0 8 m for a distance of 1 3 km upstream from the lake but during the 52 day period of minimum lake level the delta and lower channel aggraded by up to 0 4 m during that period an estimated 225 000 m3 of sediment was supplied to the delta sufficient for rapid progradation of the delta front into the shallow lake and the observed aggradation of the channel and delta surface other factors in this case receiving basin geometry and sediment yield may thus control the response of a river delta system to relative base level lowering

amino acid geochronology of raised beaches in south west britain abstract based on 1 the epimerization of l isoleucine to d alloisoleucine d l ratios in patella vulgata littorina littorea l littoralis l saxatilis littorina species and nucella lapillus from raised beaches in south west britain 2 statistical analysis of the d l ratios and 3 lithostratigraphic and geomorphic evaluation three d l stages are proposed the d l ratios for all the species measured are converted to a patella vulgata standard the three d l stages are 1 1 the minchin hole d l stage d l ratios 0 175 0 014 defined at a stratotype in minchin hole cave gower wales 2 2 a provisionally defined but as yet unamed d l stage because of the current unavailability of a suitable stratotype with d l ratios of 0 135 0 014 3 3 the pennard d l stage d l ratios 0 105 0 016 defined at a stratotype in minchin hole cave gower wales two geochronological models of the three high sea level events representing the d l stages are constrained by uranium series age determinations on stalagmite interbedded with marine beds in minchin hole and bacon hole caves gower wales a potential fixed point in model evaluation is an age determination which is equivalent to oxygen isotope sub stage 5e 122 ka the two models are oxygen isotope stage and age ka bp d l stage d l ratio model 1a model 1b model 2 pennard 0 105 0 016 5a ca 80 5e 122 5e 122 5c ca 100 unnamed 0 135 0 014 5e 122 7 194 minchin hole 0 175 0 014 7 186 245 7 186 245 7 216 the ages of the raised beaches are used to constrain the timing and extent of glaciation in the area the extent of the late devensian glaciation is fixed by reference to localities where raised beaches of the pennard d l stage outcrop as well as by using unpublished data on molluscs incorporated into glacial deposits two pre devensian glaciations antedate the minchin hole d l stage the irish sea glaciation of the bristol channel irish sea older drift of south wales fremington till of north devon is ascribed to oxygen isotope 10 or earlier while the paviland welsh glaciation is ascribed to oxygen isotope stage 8 or earlier an earlier glaciation berwyn glaciation is inferred from erratics of known welsh provenance in essex

holocene hydrological changes inferred from alluvial stream entrenchment in north tian shan northwestern china abstract we analyze the possible contribution of climate change or tectonics on fluvial incision from the study of a case example along the northern flank of tian shan the rivers that exit the high range fed large alluvial fans by the end of the last glacial period they have since deeply entrenched the piedmont by as much as 300 m we have surveyed several terraces that were cut and abandoned during river entrenchment providing information on intermediate positions of the riverbed during downcutting they suggest a gradual decline in river slope during a major phase of incision throughout the holocene tectonic uplift affects only a zone about 5 km wide corresponding to a growing anticline and is shown to account for about 10 of total incision incision was therefore most probably driven by climate change from observed fluvial incision we estimate the water discharge in excess of that needed to carry the sediments supplied by hillslope erosion in the headwaters we used a model based on a transpor

life history of mobile troughs in the upper westerlies abstract increasing evidence indicates that surface cyclogenesis is predominantly a response to the approach of a preexisting trough at upper levels a question then arises about the origin of the upper level predecessor as an initial approach to this question mobile troughs in the major band of westerlies were crudely tracked in daily northern hemispheric 500 mb analysis during nine recent cold seasons these troughs were identified only in the 552 dam height contour between 8 and 15 of them were present on a given day study of a particular cold season showed a median duration of 12 days and a mode of 5 days average zonal phase speed was 13 m s 1 locations or origin and termination of individual troughs were distributed over all longitudes but births greatly exceeded deaths over and east of the rocky mountains in north america and the highlands of central asia trough terminations dominated over the eastern portions of the oceans within the quasi steady planetary waves origins and terminations o

late holocene lake levels of the dead sea this work presents a high resolution lake level record of the late holocene dead sea a hypersaline terminal lake whose drainage basin encompasses both mediterranean and hyperarid climatic zones the lake level curve reflects the regional hydrologic variations in the drainage basin which in turn represent the levant paleoclimates the curve is based on 46 radiocarbon ages of organic remains from well exposed sedimentary sequences along the dead sea shores these sequences record fluvial and lacustrine depositional environments the paleolakeshores are marked by shore ridges coarse sand units and aragonite crusts in the modern dead sea such features indicate the exact elevation of the shore the late holocene dead sea level fluctuated within the range of 390 to 415 m below sea level mbsl for most of the time the lake was below the topographic sill 402 mbsl separating the northern and southern basins of the dead sea and was confined to the deep northern basin nevertheless short term rises in the late holocene dead sea level caused the flooding of the shallow and flat southern basin highstands occurred in the second and first centuries b c and the fourth century a d during the roman and early byzan tine periods respectively in the eleventh and twelfth centuries a d during the crusader period and at the end of the nineteenth century a d the rises mark a significant change in the annual rainfall in the region which likely exceeded the instrumentally measured modern average the curve also indicates drastic drops that exposed the sedimentary sequences to erosion the oldest and probably deepest drop in the lake level culminated during the fifteenth and fourteenth centuries b c after a retreat from a higher lake stand the longest lowstand occurred after the byzantine period and continued at least until the ninth century a d this arid period coincided with the invasion of moslem arab tribes into the area during the seventh century a d the dramatic fall of the dead sea level during the twentieth century is primarily artificial and has been caused by the diversion of runoff water for the drainage basin but the magnitude is not considered exceptional for the late holocene although the past drops in the lake never exceeded the modern artificial drop rates they do represent extreme arid conditions that occurred frequently over the past several thousand years

characteristics of the southern hemisphere winter storm track with filtered and unfiltered data abstract the structure and evolution of the fluctuations in synoptic scales in the southern hemisphere sh during winter are discussed using six years of european centre for medium range weather forecasts analyses it is shown that patterns from unfiltered meridional wind series in the sh display all the features needed to represent the synoptic scale waves typical periods and wavelengths are similar to those observed in the northern hemisphere 4 days 4000 km although over the pacific ocean they can be as high as 7 8 days and 4700 km respectively as in the northern hemisphere tilts are not geographically fixed but change with the stage of the evolution of the wave the phase speed of the waves agrees with the low level winds in extensive areas of the middle latitudes and ranges from 12 m s 1 in the indian ocean to 6 m s 1 in the pacific ocean the estimated group velocities achieve maximum values of about 38 m s 1 also in the indian ocean and agree with the upper level maximum winds in accor

role of medium scale waves on the southern annular mode 1 we examined the role of short period waves on the southern annular mode sam through analysis of 6 hourly reanalysis data of the european centre for medium range weather forecasts ecmwf era interim we focused on medium scale waves those with periods shorter than about 6 days although medium scale waves generally have much smaller amplitudes than synoptic waves they have a much higher correlation with the sam index as a result about one third of wave driven meridional circulation and zonal wind acceleration associated with the sam is generated by medium scale waves their contribution is large in spite of their climatologically smaller amplitude moreover two thirds of sam related meridional circulation and zonal wind acceleration comes from waves of periods shorter than about 3 days our analysis demonstrates a positive feedback between westerly winds around 60 s and amplification of synoptic and medium scale waves which sustains hemispheric sam variability for the feedback process between zonal wind and waves baroclinic conversion is a key process to both synoptic waves and medium scale waves our analysis also shows that wave forcings calculated from daily data explain only half of the total forcings and that the contribution from short period waves is very significant around 50 s

laboratory experiment and digital simulation of multiple fill cut terrace formation the formation mechanism of multiple erosional terraces which develop in the dissection process of sedimentary valley fills was investigated by laboratory experiments and computer simulations sequences of unpaired terraces were produced on experimental fan like deposits under conditions of constant water discharge no base level change and no sediment supply the terraces developed as a result of the repetition of lateral shifting and stillstand of the stream channel at each cross section during continuous downcutting this mode of channel migration was caused by meander growth during which amplitude and wavelength increased with time the terrace formation process was well reproduced by computer simulations using a meander model having a similar wave mode

barotropic and baroclinic annular variability in the southern hemisphere abstractthe leading patterns of large scale climate variability in the southern hemisphere are examined in the context of extratropical kinetic energy it is argued that variability in the southern hemisphere extratropical flow can be viewed in the context of two distinct and largely independent structures both of which exhibit a high degree of annularity 1 a barotropic structure that dominates the variance in the zonal mean kinetic energy and 2 a baroclinic structure that dominates the variance in the eddy kinetic energy the former structure corresponds to the southern annular mode sam and has been extensively examined in the literature the latter structure emerges as the leading principal component time series of eddy kinetic energy and has received seemingly little attention in previous work the two structures play very different roles in cycling energy through the extratropical troposphere the sam is associated primarily with variability in the meridional propagation of wave activity has a s

midwinter suppression of baroclinic wave activity in the pacific abstract seasonal variations in baroclinic wave activity and jet stream structure in the northern hemisphere are investigated based upon over 20 years of daily data baroclinic wave activity at each grid point is represented for each day by an envelope function the lowpass filtered time series of the squared highpass filtered geopotential height baroclinic wave activity over the atlantic exhibits a single maximum in january whereas in the pacific it exhibits peaks in late autumn and in early spring and a significant weakening in midwinter which is more evident at the tropopause level than near the surface this suppression occurs despite the fact that the low level baroclinity and the intensity of the jet stream are strongest in midwinter based on the analysis of 31 day running mean fields for individual winters it is shown that over both the oceans baroclinic wave activity is positively correlated with the strength of the upper tropospheric jet for wind speeds up to 45 m s 1 when the strength of t

equilibrium and time scales in geomorphology application to sand bed alluvial streams equilibrium is defined as a single valued temporally invariant functional relationship between the values of an output variable and the values of the input variable s in a geomorphic system disequilibrium occurs if the output deviates from the functional relationship by more than a consensual degree natural geomorphic variables are characterized by a relaxation time output variables are insensitive to cyclical inputs with frequencies much greater than the relaxation time but can respond completely for sufficiently low frequencies rapid trends recent step changes or pulse inputs and intermediate frequency inputs can cause disequilibrium the gradient of sand bed alluvial channels the output variable is determined by sediment and water delivery from slopes the input variables and changes in this hydraulic regime require regrading by erosion and deposition initial stages of adjustment to changed regime in a long unbranched channel with sediment and water delivery only at the upstream end propagate downstream but later stages of adjustment occur simultaneously throughout the reach in a dendritic channel network the gradient responds rather uniformly throughout the network to changes in regime during all stages of adjustment the time scale of adjustment to changed regime depends upon the size of the channel network or stream length the sediment and water discharges and to a lesser degree upon the magnitude of the change grade as defined by mackin 1948 is synonymous with equilibrium as used in this paper if a period of years is replaced by a time period commensurate with the relaxation time of the gradient the use of the term grade is best restricted to a single valued relationship between channel gradient and the hydraulic regime

quantitative models of sedimentary basin filling summary quantitative modelling of the filling of sedimentary basins was begun in earnest in the 1960s dozens of themes and variations have been proposed since then and have yielded an abundance of idealized stratigraphic patterns as functions of both imposed changes and basin properties post plate tectonic modelling began with rigid lid models which show the stratigraphic signature of subsidence variation this work introduced the connection between stratigraphy and the rheology of the lithosphere rigid lid models are the simplest type of geometric model in which the sediment surface is assigned prescribed geometries usually corresponding to different depositional environments these can reproduce many aspects of overall stratal geometry but are formally restricted to relatively long timescales for which quasi steady surface topography can be assumed so called dynamic models attempt to represent the morphodynamics of the sediment surface by abstracting and averaging short term transport processes most of the dynamic models proposed to date can be seen as special cases of a single general morpho dynamic equation the most important result of the first wave of quantitative basin filling models is that even relatively simple models can produce reasonable stratal patterns we now have a wide array of tools for exploring scenarios searching for general behaviours and effects and making initial quantitative predictions we have also learned that basin response to external forcing as recorded in stratigraphy can be as sensitive to the characteristics of the basin as to the forcing the main brake on the development of basin modelling is not computing power but lack of methods and data for testing the models we have already developed physical experiments which are only just beginning are one means of doing this experimental stratigraphy is a bridge to quantitative field tests which will require collaboration among academic researchers from a wide range of areas and between academia and industry on projects of greater scale and degree of integration than we have seen so far the advancement of quantitative sedimentary geology will also require significant changes in the way the subject is taught at all levels

a 45 kyr laminae record from the dead sea implications for basin erosion and floods recurrence abstract recording and analyzing how climate change impacts flood recurrence basin erosion and sedimentation can improve our understanding of these systems the aragonite detritus laminae couplets comprising the lacustrine formations that were deposited in the dead sea are considered as faithful monitors of the freshwater supply to the lakes we count a total of 5600 laminae couplets deposited in the last 45 kyr mis3 mis1 at the dead sea center which encompass the upper 142 m of the icdp core 5017 1 the present study shows that aragonite and detritus laminae are thinner and occur at high frequency during mis 3 2 while they are much thicker and less frequent during mis 1 by analyzing multiple climate connected factors we propose that significant lake level drops enhanced dust input and low vegetative cover in the drainage basin during the last deglaciation 22 11 6 ka have considerably increased erodible materials in the dead sea watershed we find a decoupling existed between the significant lake level drop lake size reduction and lamina thickness change during the last deglaciation we argue that during the last glacial and the holocene the variation of lamina thickness at the multiple millennium scale was not controlled directly by the lake level size change we interpret this decoupling implying the transport capacity of flash floods is low and might be saturated by the oversupply of erodible materials and indicating a transport limited regime during the time period we suggest the observed thickness and frequency distribution of aragonite detritus laminae points to the high frequency of small magnitude floods during the last glacial in contrast to low frequency but large magnitude floods during the holocene

autogenic incision and terrace formation resulting from abrupt late glacial base level fall lower chippewa river wisconsin usa abstract a paucity of research exists regarding the millennial scale response of inland alluvial streams to abrupt base level fall studies of modern systems indicate that over short time scales the response is a diffusion like process of upstream propagating incision in contrast evidence from the lower chippewa river lcr located in the upper midwest of the usa suggests that autogenic controls operating over time scales of several millennia can overwhelm diffusion resulting in incision that is prolonged and episodic during the last glacial maximum the lcr drained the chippewa lobe of the laurentide ice sheet to the glacial upper mississippi river umr as a meltwater stream it aggraded and filled its valley with glacial outwash as did its largest tributaries which were also meltwater streams its nonglacial tributaries aggraded too filling their valleys with locally derived sediment during deglaciation the umr incised at least twice abruptly lowering the lcr s base level 15 m at 16 ka or earlier and an additional 40 m at ca 13 4 ka each of these base level falls initiated incision of the lcr led by upstream migrating knickpoints the propagation of incision has however been a lengthy process the optically stimulated luminescence osl ages of terrace alluvium indicate that by 13 5 ka incision had advanced up the lcr only 15 km and by 9 ka only 55 km the process has also been episodic resulting in the formation of fill cut terraces inferred from gpr surveys and exposures of terrace alluvium that are younger and more numerous in the upstream direction autogenic increases in sediment load and autogenic bed armoring the result of periodic tributary stream rejuvenation and preferential winnowing of fines by the incising river may have periodically caused knickpoint migration and incision to slow and possibly stop allowing lateral erosion and floodplain formation to dominate a decline in sediment flux from stabilizing incised tributary stream systems would have led to renewed knickpoint migration and incision when floods of sufficient magnitude to breach the channel armor occurred minimal floodplain development along the upper section of the present day lcr along with the channel morphology of an unstable wandering gravel bed river immediately downstream from it suggest that the river is still responding to the base level falls that happened many millennia ago the autogenic controls on the lcr s response to umr incision are a direct consequence of the thick fills of noncohesive sediment that accumulated in its valley and the valleys of its tributary streams during the late wisconsinan making the lcr a prime example of a former proglacial river that remains a paraglacial fluvial system

rb sr whole rock isochron evidence for the age of the malvern hills complex the malvernian igneous complex of the malvern hills consists mainlyof plutonic rocks and their locally deformed equivalents the igneous rocks are calc alkaline and range from ultra mafic diorite to granite in composition although diorite and tonalite are the most abundant rock types a rb sr whole rock isochron plot for representative samples yields an age of 681 53 ma with an initial 87 sr 86 sr ratio of 0 7049 0 0005 2 errors this is interpreted as the age of crystallization of the igneous complex and the relatively low initial 87 sr 86 sr ratio is considered to preclude a long crustal history for the source region the malvernian complex is thus regarded as a late precambrian addition to the crust it has been compared on geological grounds with the johnston complex and the stanner hanter complex and isotopic ages between 640 and 700 ma for all these complexes indicate that they may represent the earliest phase of igneous activity in the evolution of continental crust below england and wales

the origin of granite erratics in the pleistocene patella beach gower south wales rare pebbles of granite have been discovered in the raised patella beach at butterslade gower south wales their petrography trace element geochemistry and the rb sr whole rock age of 55 5 ma confirm that they are derived from the lundy granite which is about 49 km to the southwest of gower amino acid analyses of fossil gastropods in the patella beach have provided an age of 210000 years various hypotheses of transportation of pebbles from lundy and pembrokeshire to butterslade are considered erratics from pembrokeshire were probably transported by pleistocene ice into the area while clasts of lundy granite were moved by progradation of beach deposits northeastwards towards gower during glacio eustatic marine transgressions in the pleistocene

spatial and temporal variations of channel lateral migration rates in the inner mongolian reach of the upper yellow river channel variations of the inner mongolian reach in the upper yellow river are very complicated because of diversity of channel patterns intense changes in water and sediment and enhanced human activities in the last decades it is important to examine the channel migration rates in this river reach based on channel planform changes at 236 digital channel cross sections the present study estimated the channel migration rates in terms of mid channel line shift at the digital channel cross sections during the periods 1975 1990 1990 2000 2000 2006 2006 2010 and 2010 2011 the results show that the average channel migration rate for the whole river reach is 5 0 7 9 5 9 8 6 and 1 0 m 1 in the five different periods respectively in both directions to the right and to the left the highest channel migration rate was always observed in the meandering channels while the lowest channel migration rate was in the whole inner mongolian reach except the sanhuhekou zhaojunfen s z sub reach the temporal variation of channel migration rate was mainly controlled by changing sediment concentration in river flow while the spatial variation along the straight braided and meandering channel reaches was largely affected by material differences of channel banks as reflected by different channel patterns with the highest average lateral migration rate to the left bank the meandering channel reach is extremely vulnerable to lateral migration and needs to be protected with engineering practices because a large population and wide farmland are located on its left floodplain

an observational study of medium scale wave dynamics in the southern hemisphere summer part i wave structure and energetics abstract medium scale waves zonal wavenumbers 4 7 frequently dominate southern hemisphere sh summer midlatitude circulation patterns this work is an observational study that focuses on their temporal and spatial characteristics along with detailing the forcing mechanisms responsible for their formation medium scale wave characteristics for three sh summers 1978 79 through 1980 81 are discussed it is shown that the time mean medium scale wave structure is consistent with the basic state linear wave propagation characteristics the energetics of the medium scale waves are studied using the transformed eulerian mean formalism of plumb it is found that wave zonal mean exchange is a valid concept for describing the sh summer atmospheric circulation and that the flow vacillates between periods of highly perturbed and zonally symmetric states with a time wale on the order of 10 20 days these vacillations result from nonlinear baroclinic instabilities and the medium scale waves exhibit well defined

characterization of land degradation along the receding dead sea coastal zone using airborne laser scanning abstract the dead sea the lowest place on the earth s continents was at its highest level in 1896 reaching an elevation of 388 4 m below mean sea level m b m s l and 390 m in the early 1920s since then it has almost constantly been dropping reaching the level of 426 m b m s l in 2013 since the late 1990s its level has been decreasing by approximately 1 my 1 the rapid lake retreat accelerates large scale environmental deterioration including soil erosion land degradation rapid headcut migration and widespread development of collapse sinkhole fields these geomorphic elements threaten the natural environment and anthropogenic infrastructure we provide an overview of the geomorphic processes in the form of soil erosion channel incision land degradation and the development of collapse sinkholes we take advantage of the high resolution airborne laser scanning technology for three dimensional detection of surficial changes quantification of their volumes and documentation of the present state of the terrain with utmost accuracy and precision this type of information and the identification of future trends are vital for proper planning of any rapidly changing environment

vertical structure physical properties and energy exchange of the east asian trough in boreal winter the relation between the intensity of the east asian trough and the strength of the east asian winter monsoon is documented a prominent dipole of the available potential energy of the zonal mean flow can be observed over the midlatitudes and polar regions and is related to temperature anomalies variation in the intensity of the east asian trough is caused by variation in the energy conversion from the available potential energy of the zonal mean flow to the east asian trough the in phase relation between the intensities of the east asian jet and east asian trough is illustrated by the relation between the potential energy and kinetic energy of stationary eddies the dipole of height anomalies over the midlatitude and polar regions develops in late autumn and decays in early spring we investigate the effect of both stationary and transient eddy forcing on the evolution of the dipole the combined forcing of the two types of eddy makes an important contribution to the development maintenance and decay of the dipole

the relationship between flow shear stress and stream pattern based on simple hydraulic reasoning a discharge q slope s diagram for streams is given a physical interpretation permitting the assignment of a relative shear stress value to each stream a sample of 359 streams is used ranging in mean annual discharge from 900 000 to 0 05 ft 3s 1 varying in pattern from highly sinuous p 3 1 to straight and braided sorted according to their relative shear stress values 0 avg streams of high sinuosity p 1 5 are characterized by low relative shear stress median 0 56 which is significantly lower than that characterizing braided streams median 1 70 it is concluded that for natural stream populations the passage from one pattern to another is gradual and the geomorphic thresholds defined by relative shear stress are fuzzy ones

intraseasonal variations in the southern hemisphere circulation abstract intraseasonal variations in the southern hemisphere atmospheric circulation have been examined through the application of a 10 50 day bandpass filter to daily ecmwf analyses for 1980 88 variations on this time scale contribute more than 40 of the daily variance in 500 hpa geopotential over much of the middle and high latitudes of the southern hemisphere eof analysis of the unnormalized variance for all seasons shows that 49 of this variance can be explained by zonal wave trains centered on the south pacific and southern atlantic indian oceans a high latitude mode of global extent and a wavenumber 3 pattern at midlatitudes these modes are essentially equivalent barotropic but slope westward with height so that the patterns at 100 hpa typically lag those at 1000 hpa by around 1o longitude there appears to be little interaction with the low latitude circulation all of the leading modes propagate eastward but the most consistent movement is shown by the south pacific wave train represented

post last glacial maximum fluvial incision and sediment generation in the unglaciated waipaoa catchment north island new zealand abstract small river systems contribute a significant component of sediment delivered to oceans but the temporal evolution of fluvially eroded landscapes is needed a sequence of postglacial terraces in the unglaciated waipaoa river catchment provides the opportunity to document fluvial incision and sediment flux on an 2000 year timescale since the last glacial maximum lgm which has previously only been undertaken for the entire post lgm period this study also calculates sediment mass where previously sediment volume was calculated using a 15 m dem field mapping and surveying and tephrochronology we calculate rates of fluvial incision and sediment volumes excavated during successive age constrained postglacial incision events and correlate these with a framework of inferred climatic events established for new zealand we identify seven periods of terrace formation each succeeded by a period of fluvial incision six in total although the magnitude of the response during each incision event and thus the sediment volumes generated varied through time and across subcatchments draining two contrasting lithological terrains we conclude that incision events were essentially synchronous at least within the timeframe constrained by the ca 2000 year interval between successive eruptive airfall events slope relaxation processes were simultaneous with incision thereby indicating that both processes were likely climate driven we identify a period of accelerated fluvial incision 7 mm y 1 commencing before ca 14 0 cal ka bp during the early postglacial period and ceasing ca 7 9 cal ka bp toward the end of the early holocene warming period the magnitude of this incision response was significantly higher in subcatchments draining highly erodible lithologies in the higher uplifting parts of the catchment when river bedload was at over capacity in contrast within the remainder of subcatchments draining the more resistant lithologies and in areas of lower uplift and in parts subsiding incision and sediment generation was moderated by the presence of knickpoints overall since abandonment of the lgm to present day fluvial incision in the waipaoa and the adjacent waimata catchments generated 16 7 km3 of sediment of which 10 km3 90 of the estimated 35 mt of glacial postglacial slope and shelf sediment mass was potentially available for transport offshore of this 14 08 km3 7 4 km3 derived from upper and 6 7 km3 from remainder of subcatchments was excavated from waipaoa catchment at an average of 0 6 km3 ka 1 of which 80 was generated by ca 7 9 cal ka bp this potentially validates previous accounts of high rates of offshore sediment flux before 8000 14c ybp ca 8877 cal ybp thereafter for the period mid holocene cooling and variability mhcv ca 6 5 cal ka bp until the present day the rate of incision across all subcatchments slowed to 2 mm y 1 and generated just 20 of the total sediment volume in part this reflected a depletion of available sediment as rivers in the upper subcatchments returned to a steady state and coincidental with an increase in accommodation space in the rapidly growing coastal floodplain sediment flux to the marine depocentres was thereby limited

an amplification mechanism of medium scale tropopausal waves abstract the mechanism for the amplification of medium scale tropopausal waves with horizontal wavelengths of 2000 3000 km and wave periods of 1 2 days that are basically neutral is investigated using a three dimensional wave activity flux distinctive upward wave activity fluxes are found in the midtroposphere 400 hpa upstream of the region where the medium scale waves are dominant that is where the horizontal components of the wave activity flux are large these upward fluxes converge in the upper troposphere 300 hpa this convergence is a major source of medium scale waves producing large values of the horizontal components of the wave activity flux in the active regions examination of the spatial structure of the heat flux shows that the upward fluxes are due to occasional baroclinic interactions between upper level medium scale waves and lower tropospheric disturbances with the same temporal scales the seasonal and geophysical variations of the waves depend mostly on the amount of baroclin

self accelerated development of salt karst during flash floods along the dead sea coast israel we document and analyze the rapid development of a real time karst system within the subsurface salt layers of the ze elim fan dead sea israel by a multidisciplinary study that combines interferometric synthetic aperture radar and light detection and ranging measurements sinkhole mapping time lapse camera monitoring groundwater level measurements and chemical and isotopic analyses of surface runoff and groundwater the 1 m yr drop of dead sea water level and the subsequent change in the adjacent groundwater system since the 1960s resulted in flushing of the coastal aquifer by fresh groundwater subsurface salt dissolution gradual land subsidence and formation of sinkholes since 2010 this process accelerated dramatically as flash floods at the ze elim fan were drained by newly formed sinkholes during and immediately after these flood events the dissolution rates of the subsurface salt layer increased dramatically the overlying ground surface subsided a large number of sinkholes developed over short time periods hours to days and salt saturated water resurged downstream groundwater flow velocities increased by more than 2 orders of magnitudes compared to previously measured velocities along the dead sea the process is self accelerating as salt dissolution enhances subsidence and sinkhole formation which in turn increase the ponding areas of flood water and generate additional draining conduits to the subsurface the rapid terrain response is predominantly due to the highly soluble salt it is enhanced by the shallow depth of the salt layer the low competence of the newly exposed unconsolidated overburden and the moderate topographic gradients of the ze elim fan

extreme rates of channel incision and shape evolution in response to a continuous rapid base level fall the dead sea israel abstract in nature opportunities are limited for recording the response to a rapid ongoing base level fall and for examining its effects on channel evolution during the process following a dramatic base level fall the natural laboratory area of the dead sea offers such an opportunity classical shape evolution models of incised channels describe the response to an impulse type base level drop after it became stabilized the dead sea delineates during its continuous level drop a different mode of adjustment from those previously conceptualized we have recorded the entrenchment rates of channels and their transient shape evolution at a station in real time i e during the ongoing base level fall this study represents the first attempt to apply integrated time series of high resolution dems change detection maps differential global position system measurements and field methods to monitor vertical and horizontal entrenchment rates as well as the evolution of the cross sectional shape of channels in response to a continuous and rapidly lowering base level mean vertical entrenchment rates are very high 0 4 0 8 m y and widening rates are even higher 2 1 24 m y elevation change detection maps demonstrate along banks a patchy pattern of channel entrenchment indicating the initial widening stage the incised channels have a trapezoidal gorge like cross sectional form i e they have developed beyond the initial stage of net vertical incision however neither advanced channel widening nor development of an inner floodplain has been observed we conclude that widening is yet ineffective in damping the vertical adjustment the continuous and rapid lowering of the dead sea level entraps the drainage systems in the vertical incision mode preventing the evolutionary progression toward a wide graded and stable geometry which has been conceptualized in existing models

development of longitudinal profiles of alluvial channels in response to base level lowering degradation of alluvial channels in cohesive sediments was studied in 15 m and 20 m long flumes with a slope of 0 01 cm cm degradation was initiated by lowering base level to a fixed position and the development of the longitudinal profile of the channel is analysed through a model formulated as a heat diffusion equation it is based on the equation of sediment continuity combined with an assumption regarding sediment transport namely that sediment discharge is linearly proportional to the channel slope in accordance with the boundary and initial conditions imposed by the experimental setup and procedure the basic equation is amenable to an analytical solution which defines bed elevation at any distance and time as a function of the amount of base level lowering and a diffusion coefficient additional problems arising from bank erosion and channel armouring are also treated successfully within the framework of the same model the results show that in homogeneous alluvial sediments not subject to armouring the ultimate result of base level lowering by a certain amount is degradation all along the channel by the same amount the main impact of erosion is felt in the early stages after initiation of the process and mainly near the mouth the rate of degradation at any station along the channel reaches a peak and then slowly decreases with time and the peak rate is attenuated with distance from the outlet the model permits the prediction of intermediate stages of profile development at any distance from the outlet and at different times

late holocene climates of the near east deduced from dead sea level variations and modern regional winter rainfall the dead sea is a terminal lake of one of the largest hydrological systems in the levant and may thus be viewed as a large rain gauge for the region variations of its level are indicative of the climate variations in the region here we present the decadal to centennialresolution holocene lake level curve of the dead sea then we determine the regional hydroclimatology that affected level variations to achieve this goal we compare modern natural lake level variations and instrumental rainfall records and quantify the hydrology relative to lake level rise fall or stability to quantify that relationship under natural conditions rainfall data pre dating the artificial dead sea level drop since the 1960s are used in this respect jerusalem station offers the longest uninterrupted pre 1960s rainfall record and jerusalem rains serve as an adequate proxy for the dead sea headwaters rainfall principal component analysis indicates that temporal variations of annual precipitation in all stations in israel north of the current 200 mm yr 1 average isohyet during 1940 1990 are largely synchronous and in phase 70 of the total variance explained by pc1 this station also represents well northern jordan and the area all the way to beirut lebanon especially during extreme drought and wet spells we a determine the modern and propose the past regional hydrology and eastern mediterranean em climatology that affected the severity and length of droughts wet spells associated with multiyear episodes of dead sea level falls rises and b determine that em cyclone tracks were different in average number and latitude in wet and dry years in jerusalem the mean composite sea level pressure and 500 mb height anomalies indicate that the potential causes for wet and dry episodes span the entire em and are rooted in the larger scale northern hemisphere atmospheric circulation we also identified remarkably close association within radiocarbon resolution between climatic changes in the levant reflected by level changes and culture shifts in this region

estimating drawdown magnitudes of the mediterranean sea in the levant basin during the lago mare stage of the messinian salinity crisis abstract the messinian salinity crisis 5 97 5 33 ma is one of the most dramatic sea level change events in the global geological record during this event marine connection between the atlantic ocean and the mediterranean sea was restricted and episodically blocked while division of the messinian salinity crisis to three major stages is well established and accepted the scale of sea level change at each stage is still debated the magnitudes of the mediterranean fluctuations throughout the messinian salinity crisis have implications for contemporary connectivity between the eastern and western mediterranean basins during the third stage of the messinian salinity crisis commonly known as the lago mare mediterranean sea level fluctuated repeatedly lago mare drawdowns in the eastern mediterranean were estimated earlier to vary between we propose that during the lago mare ravinement along a continuously regressing transgressing coastline abraded the upper continental margin offshore israel the mediterranean regressed to a depth of 380 550 m below present day mean sea level and the eroded strata were evacuated downslope and deposited basinward of this depth as wedge shape clastic complexes during relatively short intervals sea level receded to altitudes 100 m below the erosional surface these sea level recessions exposed a pronounced inflection in the slope gradient to sub aerial processes generating knickpoints and headward migration of incising gullies these gullies developed later into channels conduits for sediment bypass fan deltas were deposited off these channels outlets a major sea level fall towards the end of the messinian salinity crisis reached 630 900 m below present day mean sea level streams incised into the exposed tops of the clastic wedges and fan deltas additionally meteoric water dissolved evaporites within the clastic complexes and formed sinkholes and dolines during this interval the mediterranean sea level fell to below the depth of the sicily sill which separated the eastern and western mediterranean basins this finding reinforces previously proposed paradigms which suggested that the messinian salinity crisis was terminated by spillover events from the atlantic ocean to the western mediterranean basin and consequently from the western to the eastern basin

natural versus human control on subsurface salt dissolution and development of thousands of sinkholes along the dead sea coast one of the most hazardous results of the human induced dead sea ds shrinkage is the formation of more than 6000 sinkholes over the last 25 years the ds shrinkage caused eastward retreat of underground brine replaced by fresh groundwater which in turn dissolved a subsurface salt layer to generate cavities and collapse sinkholes the areal growth rate of sinkhole clusters is considered the most pertinent proxy for sinkholes development analysis of light detection and ranging lidar digital elevation models dems and interferometric synthetic aperture radar insar allows translation of the areal growth rate to a salt dissolution rate of the salt layer revealing two peaks in the history of the salt dissolution rate these peaks cannot be attributed to the decline of the ds level instead we show that they are related to long term variations of precipitation in the groundwater source region the judea mountains and the delayed response of the aquifer system between the mountains and the ds rift this response is documented by groundwater levels and salinity variations we thus conclude that while the ds level decline is the major trigger for sinkholes formation the rainfall variations more than 30 km to the west dominate their evolution rate the influence of increasing rainfall in the judea mountains reaches the ds at a typical time lag of four years and the resulting increase in the salt dissolution rate lags by a total time of 5 6 years

experimental study of knickpoint and longitudinal profile evolution in cohesive homogeneous material a series of experiments were conducted in homogeneous bedrock to study knickpoint and longitudinal profile evolution knickpoints are created by successive drops in base level which simulate intermittent uplift channel morphology and flow characteristics vary systematically along a knickpoint reach as the knickpoint lip is approached width decreases but depth velocity and bottom shear stress increase as a result knickpoints are rapidly destroyed through the process of 1 knickpoint replacement and 2 subsequent knickpoint inclination knickpoint replacement consists of two morphologically distinct erosional reaches the knickpoint face below the knickpoint lip which decreases in slope and an incising reach above the knickpoint lip which increases in slope knickpoint replacement is a significant process in the evolution of knickpoints in homogeneous bedrock within experimental limits this study supports the notion that knickpoints do not undergo parallel head ward retreat in homogeneous bedrock given intermittent uplift except in those possible cases of extensive and pervasive bedrock jointing only the erosional sediment transport discontinuity above the knickpoint is developed in cohesive sediments below the knickpoint a steep bedrock channel slope low sediment load and rapid decrease in grain size of sediment load preclude development of the aggradational sediment transport discontinuity knickpoint evolution can be characterized by three general models parallel retreat replacement and inclination these models are based on the following criteria within the knickpoint reach 1 relationship between bottom shear stress 0 and critical shear stress needed to initiate motion c 2 nature of the bed load transport discontinuities and 3 spatial variability of bedrock resistance to fluvial erosion

alluvial pedogenesis in pleistocene and holocene mississippi river deposits effects of relative sea level change comparison of pleistocene and holocene soils developed in mississippi river meander belt deposits in louisiana illustrates the influence of relative sea level change on pedogenesis holocene and pleistocene meander belts have similar landscape morphologies lithofacies and soil characteristics and probably formed under similar hydrologic regimes the pleistocene avoyelles prairie meander belt is now terraced but it was originally graded to a lower relative sea level position than the holocene flood plain holocene alluvial soils are generally weakly expressed cumulative profiles with abundant redoximorphic features and formed on an aggrading flood plain with a shallow fluctuating water table the soil morphology varies with respect to landscape position and overbank lithofacies pleistocene alluvial paleosols show evidence for two stages of pedogenesis during the first stage of pedogenesis water table fluctuations and flood plain aggradation produced profiles with color mottles iron and carbonate nodules and weak b and c horizons similar to holocene flood plain soils the second stage of pedogenesis occurred after the avoyelles prairie was terraced and the regional water table fell a minimum of 30 m improved soil drainage created oxidizing and acidic conditions removed free carbonates dehydrated iron oxides and transformed clay minerals this stage produced pleistocene profiles with brighter matrix and mottle hues lower ph values larger and harder iron nodules and greater kaolinite contents than comparable holocene flood plain soils the primary influence on regional water table lowering in the southern lower mississippi valley was relative sea level fall mississippi river flood plain lowering adjacent to the avoyelles prairie most likely occurred between the end of oxygen isotope stage 3 and the maximum period of valley entrenchment during oxygen isotope stage 2 water table fall affected pedogenic processes a minimum of 400 km upvalley of the continental shelf margin pleistocene mississippi river paleosols represent excellent analogs for interpreting ancient alluvial paleosols formed during episodes of base level fall and valley incision as fluvial entrenchment terraced the meandering avoyelles prairie a pedogenic threshold was crossed that altered the pathway of chemical weathering the complexity of a multiple step pedogenic history also highlights the fact that interpretation of relative profile development as a function of time can be problematic

results from a new model of river basin evolution this paper briefly describes a model of the erosional development of catchments and their channel networks the model differentiates between the dominant transport processes in hillslope and channels the development of channels and hillslopes occurs in an integrated manner as a function of physically observable mechanisms the growth of a river basin is qualitatively described the model concepts are used to study the basin during periods of growth transient periods as well as during dynamic equilibrium this leads to hypotheses about the relationship between slopes relief tectonic uplift erodability runoff and catchment area it is shown that the model leads to very reasonable and desirable behaviour of hillslopes during retreat and degradation

fluvial response to an historic lowstand of the great salt lake utah understanding fluvial adjustments to base level changes benefits the fields of sequence stratigraphy geomorphology and petroleum geology this investigation is a modern case study of the channel dynamics of lee creek and the goggin drain two streams that are part of the jordan river drainage into the endorheic great salt lake of northern utah a lacustrine system that has experienced multiple decadal scale base level changes since 1965 the lake level has fluctuated in elevation more than 6 m transitioning from an historic lowstand 1284 m a s l and in 2009 2010 approaching an historic lowstand this study uses detailed aerial images fieldwork and lidar data to link the modern geomorphology and channel hydraulics to specific variations in sediment transport channel form and avulsion behavior although lee creek and the goggin drain are situated only a few kilometers apart and share similar shore zone gradients substrates and vegetation patterns and have been subjected to the same changes in lake level their channel forms have evolved very differently differences in discharge patterns are likely the most influential factor causing the meandering form of lee creek and the braiding channel of the goggin drain despite the differences in discharge total sediment eroded from the two streams is comparable and can be attributed to similar stream power unit stream width in the two streams although lee creek has not recently been avulsive three major avulsions of the goggin drain have taken place since 1965 two possible styles of avulsion are interpreted an allogenic response to changing base level and an autogenic response dictated by channel morphology and hydraulics despite a wealth of available information avulsions cannot be unequivocally attributed to one style or another caution should be used when attempting to link the complex process of avulsion to causal mechanisms copyright 2011 john wiley sons ltd

a diagnostic study of waves on the tropopause the spatial structure and phase velocity of tropopause disturbances localized around the subpolar jet in the southern hemisphere are investigated using 6 hourly european centre for medium range weather forecasts reanalysis data covering 15 yr 1979 93 the phase velocity and phase structure of the tropopause disturbances are in good agreement with those of an edge wave vertically trapped at the tropopause however the vertical distribution of the ratio of potential to kinetic energy exhibits maxima above and below the tropopause and a minimum around the tropopause in contradiction to edge wave theory for which the ratio is unity throughout the troposphere and stratosphere this difference in vertical structure between the observed tropopause disturbances and edge wave theory is attributed to the effects of a finite depth tropopause together with the next order corrections in rossby number to quasigeostrophic dynamics

southern hemisphere extratropical gravity wave sources and intermittency revealed by a middle atmosphere general circulation model abstractsouthern hemisphere extratropical gravity wave activity is examined using simulations from a free running middle atmosphere general circulation model called kanto that contains no gravity wave parameterizations the total absolute gravity wave momentum flux mf and its intermittency diagnosed by the gini coefficient are examined during january and july the mf and intermittency results calculated from the kanto model agree well with results from satellite limb and superpressure balloon observations the analysis of the kanto model simulations indicates the following results nonorographic gravity waves are generated in kanto in the frontal regions of extratropical depressions and around tropopause level jets regions with lower higher intermittency in the july midstratosphere become more less intermittent by the mesosphere as a result of lower level wave removal the gravity wave intermittency is low and nearly homogeneous throughout the sh middle atmosphere during january this indicates t

global characteristics of medium scale tropopausal waves observed in ecmwf operational data global characteristics and seasonal variation of medium scale zonal wavelengths of 2000 3000 km waves observed around the midlatitude tropopause are examined using 6 hourly european centre for medium range weather forecasts operational data over four years 1990 93 covering both hemispheres medium scale waves and synoptic scale waves are extracted using time filters and their characteristics are compared hovmoller diagrams indicate the existence of medium scale waves in the southern hemisphere as well as in the northern hemisphere the zonal wavelengths of medium scale waves are slightly larger in the southern hemisphere than in the northern hemisphere medium scale waves are mostly active in three regions the north atlantic in winter dec jan feb the north pacific in spring mar apr may mam and the south indian ocean in autumn mam these regions are roughly corresponding to and slightly downstream of storm tracks where synoptic waves are dominant significant differences in seasonal variation of the intensity between the two kinds of waves are also found the maximum of wave amplitudes is seen around the tropopause at latitudes slightly higher than the jet stream axis where the meridional gradient of the quasigeostrophic potential vorticity qpv is maximized the positive large qpv gradient is attributed to the atmospheric structure around the midlatitude tropopause that is located in vertical westerly shear of the jet stream this fact suggests that the medium scale waves are waves trapped around the midlatitude tropopause

disequilibrium profile of the potomac river near washington d c a result of lowered base level or quaternary tectonics along the fall line longitudinal profiles of major rivers in maryland and virginia are generally closely adjusted to the resistance of the rocks over which they flow but they all show major discontinuities at or just above the fall line the amount of discrepancy at the fall line between the actual profiles and the projection of the profiles of the upstream reaches increases from about 27 m at the james river to about 50 m at the susquehanna river at the potomac river it is about 45 m detailed study of the terraces along the potomac in the piedmont above washington d c suggests that the discontinuity in longitudinal profile is the result of quaternary downcutting in response to a lowered base level changes in base level during sea level fluctuations in the pleistocene must have been an important factor but strong circumstantial evidence suggests that the discontinuities in river profiles may in part be due to differential uplift of the piedmont with respect to the coastal plain along a zone of flexure or distributed faulting near the fall line

holocene hydrological events and human induced environmental changes reflected in a southeastern mediterranean fluvial archive abstract the chronostratigraphy of an eastern mediterranean holocene fluvial sequence reflects global trends climate and sea level local modulations hydrological regime and storm surges and anthropogenic impact two continuous cores retrieved from the tanninim stream estuary on the carmel coast of israel are dated by optically stimulated luminescence osl to span the holocene the sedimentology and faunal assemblages are analyzed for reconstructing environmental conditions despite time gaps recognized in the fluvial successions three main depositional periods provide distinctive archives capturing natural and anthropogenic centennial to millennial changes alternations between enhanced and reduced fluvial activity associated with humid and dry climate conditions characterized the early to mid holocene fluvial record between about 7 8 and 5 7 ka and may match eastern mediterranean climate records the first humid phase from 8 to 6 ka features organic rich fine sediments and proliferating brackish ostracods foraminifera and molluscs the appearance of this biofacies indicates the initiation of seepage from the yarkon tanninim aquifer through the brackish oligohaline enot timsah springs the advancing coastline due to sea level rise starting about 5 8 ka resulted in an increasing supply of quartz sands and marine transported foraminifera relatively fast accumulation of organic rich fine grained sediments with enhanced preservation of brackish fauna during the late holocene is probably associated with maintenance of the tanninim dams during the early arab period 7th 8th centuries ce the last century has been characterized by accelerated sedimentation rates that may be associated with reduced vegetation cover due to modern human activity and by deposition by a high energy surge event this study demonstrates that the lower part of a semi arid southeastern mediterranean estuary responds to periods of climatic and sea level change on a regional scale and to human impact and abrupt past hydrological events on a local scale

bathymetry of lake lisan controls late pleistocene and holocene stream incision in response to base level fall abstract this paper examines the millennial scale evolution of the longitude profile of nahal wadi zin in the dead sea basin in the northern arava valley israel nahal zin has incised 50 m into relatively soft late pleistocene lake lisan sediments incision was forced by the regressive 10 km lake level fall of a total of 200 m of lake lisan from its highest stand at 25 ka and exposure of the lake floor sediments to fluvial and coastal processes alluvial cut terraces of the incising channel are well preserved along the 17 5 km of the lowermost reach of nahal zin at its outlet into the dead sea basin nahal zin deposited a holocene alluvial fan at the base of a 10 80 m high escarpment in unconsolidated sediments the escarpment is associated with the amazyahu fault which forms the southern structural boundary of the present dead sea basin geomorphic mapping optically stimulated luminescence osl ages and soil stratigraphy allowed correlation of terrace remnants and reconstruction of several past longitudinal profiles of nahal zin and its incision history together with the published lake level chronology these data provide an opportunity to examine stream incision related to base level lowering at a millennial scale osl ages of the terraces fit relatively well with the established lake level chronology and follow its regression and fall for a few thousands of years the longitudinal profile response to the lake level fall was downstream lengthening onto the exposed former lake bed most of the incision 40 m occurred later when the lake level reached the top of the amazyahu fault escarpment and continued to drop the incision was a relatively short episode at about 17 ka and cut through this escarpment almost to its base the fast incision its timing and the profiles of the incising channels indicate that the escarpment was an underwater feature and was not formed after the lake retreated this fairly simple scenario of regressive lake level fall and knickpoint exposure and incision is modeled here using a one dimensional numerical incision model based on a linear diffusion equation the calculated diffusion coefficient fits earlier results and data obtained from other streams in the area and confirms the upscaling of this simple model to the millennial scale

modern extreme storms and the rainfall thresholds for initiating debris flows on the hyperarid western escarpment of the dead sea israel intense rainstorms cause debris flows on escarpments in hyperarid environments in contrast with more temperate environments there have been no direct observations on rainfall intensities and durations required for initiating debris flows in hyperarid environments here we report rainfall volume and intensities acquired by gauge and radar measurements for two successive storms along the hyperarid the first of the two analyzed storms occurred on 2 november 1995 during this storm two convective cells rained sequentially within a 5 h period at the lower reaches of the nahal david and the nahal arugot that dissects the western escarpment of the dead sea israel this storm triggered debris flows in 38 small 2 and high gradient drainage basins along the escarpment total rainfall volume and spatial distribution were determined by 10 cumulative rain gauges that were also used to calibrate rainfall intensity distributions from radar data for this storm region and landscape rainfall intensities exceeding 30 mm h for a duration of 1 h were required to initiate debris flows a second storm in the same area on 17 18 october 1997 allowed the evaluation of the results determined from the 1995 storm in this second more regional storm maximum rainfall intensities were 19 27 mm h for a duration of 45 min these values lower than the 30 mm h minimal threshold defined in the previous storm are consistent with the occurrence of only three debris flows the small number of debris flows resulted from the concentration of the highest intensities of rainfall on the desert plateau and not directly on top of the canyon walls most first to third order basins draining the dead sea escarpment contain evidence of zero to three late holocene 30 mm h and durations of at least 1 h the small number of debris flows that has occurred during the late holocene indicates that such events are rare at the scale of individual drainage basins

implications of sediment flux dependent river incision models for landscape evolution 1 developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of landscape evolution and the linkages between climate erosion and tectonics current models of long term river network incision differ significantly in their treatment of the role of sediment flux we analyze the implications of various sediment flux dependent incision models for large scale topography in an attempt 1 to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and 2 to explain the apparent ubiquity of mixed bedrock alluvial channels in active orogens although certain forms of the various models can be discarded as inconsistent with morphological data we find that the relative intrinsic concavity indices of detachment and transport limited systems defined herein largely dictate whether the various models can be tied to distinctive steady state morphologies preliminary data suggest that no such diagnostic differences may exist and other methods must be developed to test models accordingly we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment versus transport limited channels as a function of rock uplift rate that may allow discrimination among various models further we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate in addition to general differences between detachment and transport limited systems our analysis identifies an interesting hysteresis in landscape evolution hybrid channels at the threshold between detachment and transport limited conditions are expected to act as detachment limited systems in response to an increase in rock uplift rate or base level fall and as transport limited systems in response to a decrease in rock uplift rate especially during postorogenic topographic decline the analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed

continuous monitoring of bedload flux in a mountain gravel bed river an automatic bedload monitoring station has been established on the perennial tordera river a mediterranean mountain gravel bed stream located in ne spain bedload fluxes were obtained automatically at 1 min intervals using two birkbeck type pit bedload samplers aligned across the width of the channel flow depth and water surface slope were both measured continuously and synchronously with bedload data for five flow events show that bedload flux varies considerably bedload flux is high when it is compared with other perennial streams for a 15 min interval maximum channel average bedload flux was 0 83 kg m 1 s 1 bedload records also show that there is no direct relationship between bedload flux and grain shear stress the low correlation between bedload flux and hydraulics arises due to the different thresholds of initiation of motion for each flow event and the variable character of the bed between events for two individual floods there is a reasonable relationship between bedload flux and grain shear stress in part as a consequence of individual particle entrainment and patch movement over a stable coarse gravel bed during moderately high discharges these results demonstrate that the birkbeck system functions well in a mediterranean mountain gravel bed stream with a longitudinal slope of 2

two types of baroclinic life cycles during the southern hemisphere summer abstract baroclinic eddy life cycles of the southern hemisphere sh summer are investigated with ncep ncar reanalysis data a composite analysis is performed for the years 1980 through 2004 individual life cycles are identified by local maxima in synoptic scale eddy energy two types of baroclinic life cycles are examined each defined by the strength of the barotropic energy conversion 2 days prior to the maximum baroclinic growth for one life cycle the barotropic conversion is anomalously weak before the maximum baroclinic growth for the other the barotropic conversion is anomalously strong these two life cycles are referred to as the weak barotropic wb and strong barotropic sb life cycles the analyses for the wb life cycle find that a poleward anomalous wave activity flux is observed within the sh tropics and subtropics just before the initial growth of the synoptic scale eddies in contrast the sb life cycle exhibits an equatorward anomalous wave activity flux prior to the initial wave de