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

regime change of the boreal summer hadley circulation and its connection with the tropical sst the year to year variability of the boreal summer june august jja hadley circulation hc is dominated by an asymmetric mode centered in the northern hemisphere amn and a quasi symmetric mode centered at 58n qsm the regime change of the jja hc is revealed by the phase reversal of the time series of the amn showing significant weakening of the northern part of the jja hc and a reversed seesaw relationship of the zonal mean updraft over 108 208n and around the equator this transition is accompanied by the southward retreat of the hc core and is well correlated with the weakening of tropical summer monsoons the strong warming trends of the sea surface temperature over the tropical atlantic and indo west pacific warm pool play an important role in the regime change of the jja hc the high frequency interannual variability of the jja hc however is mainly featured by the qsm and is highly correlated with

mass flux and undertow in a surf zone abstract the mass of water carried shoreward by the breaking waves in a surf zone will in a two dimensional situation be compensated by a seaward return flow the undertow it is shown that the undertow is driven by the local difference between radiation stress and the set up pressure gradient which only balance each other in average over the depth turbulent shear stresses are required to maintain a steady situation comparison with measurements confirms the theoretical results

the multidecadal variability of the asymmetric mode of the boreal autumn hadley circulation and its link to the atlantic multidecadal oscillation abstractprevious studies show that the first principal mode of the variability of the seasonal mean hadley circulation hc is an equatorial asymmetric mode am with long term trend this study demonstrates that the variability of the boreal autumn september november son hc is also dominated by an am but with multidecadal variability the son am has ascending and descending branches located at approximately 20 n and 20 s respectively and explains about 40 of the total variance further analysis reveals that the am is closely linked to the atlantic multidecadal oscillation amo which is associated with a large cross equatorial sea surface temperature sst gradient and sea level pressure slp gradient the cross equatorial thermal contrast further induces an equatorial asymmetric hc anomaly numerical simulations conducted on an atmospheric general circulation model also suggest that amo associated sst anomalies can also induce a cross equatorial slp gradient and anomalous vertical shear of the

nao implicated as a predictor of northern hemisphere mean temperature multidecadal variability 1 the twentieth century northern hemisphere mean surface temperature nht is characterized by a multidecadal warming cooling warming pattern followed by a flat trend since about 2000 recent warming hiatus here we demonstrate that the north atlantic oscillation nao is implicated as a useful predictor of nht multidecadal variability observational analysis shows that the nao leads both the detrended nht and oceanic atlantic multidecadal oscillation amo by 15 20 years theoretical analysis illuminates that the nao precedes nht multidecadal variability through its delayed effect on the amo due to the large thermal inertia associated with slow oceanic processes an nao based linear model is therefore established to predict the nht which gives an excellent hindcast for nht in 1971 2011 with the recent flat trend well predicted nht in 2012 2027 is predicted to fall slightly over the next decades due to the recent nao decadal weakening that temporarily offsets the anthropogenically induced warming

on the seasonality of the hadley cell abstract the annual march of the climatological mean meridional circulations mmcs in the ncep ncar reanalyses is dominated by two components of roughly comparable mean squared amplitude 1 a seasonally invariant pair of hadley cells with rising motion centered near and just to the north of the equator and subsidence in the subtropics and 2 a seasonally reversing sinusoidally varying solsticial cell with ascent in the outer tropics of the summer hemisphere and subsidence in the outer tropics of the winter hemisphere the meridional structure and seasonal evolution of the solsticial cell are suggestive of a close association with the monsoons these results are consistent with previous analyses of the mean meridional circulation based on radiosonde data

laboratory observation of boundary layer flow under spilling breakers in surf zone using particle image velocimetry abstract a boundary layer flow under spilling breakers in a laboratory surf zone with a smooth bottom is investigated using a high resolution particle image velocimetry piv technique by cross correlating the images oscillatory velocity profiles within a viscous boundary layer of o 1 mm in thickness are resolved over ten points using piv measurements taken for an earlier study and the present study flow properties in the wave bottom boundary layer wbbl over the laboratory surf zone are obtained including the mean velocities turbulence intensity reynolds stresses and intermittency of coherent events the data are then used to estimate the boundary layer thickness phase variation and bottom shear stress it is found that while the time averaged mass transport inside the wbbl is onshore in the outer surf zone it changes to offshore in the inner surf zone the zero eulerian mass transport occurs at h hb 0 92 in the outer surf zone the maximum overshoot of the streamwise velocity and boundary layer thickness are not constant across the surf zone the bottom shear stress is mainly contributed by the viscous stress through mean velocity gradient while the reynolds stress is small and negligible the turbulence level is higher in the inner surf zone than that in the outer surf zone although only a slight increase of turbulent intensity is observed inside the wbbl from the outer surf zone to the inner surf zone the variation of phase inside and outside the wbbl was examined through the spatial velocity distribution it is found the phase lead is not constant and its value is significantly smaller than previous thought by analyzing instantaneous velocity and vorticity fields a remarkable number of intermittent turbulent eddies are observed to penetrate into the wbbl in the inner surf zone the size of the observed large eddies is about 0 11 to 0 16 times the local water depth its energy spectra follow the 5 3 slope in the inertial subrange and decay exponentially in the dissipation subrange

contrasting impacts of two types of enso on the boreal spring hadley circulation the possible influences of two types of enso i e the canonical enso and enso modoki em on hadley circulation hc during the boreal spring are investigated during 1979 2010 el ni no events are featured with a symmetric pattern in equatorial zonal mean sea surface temperature anomalies ssta with a maximum around the equator in contrast the zonal mean ssta associated with el ni modoki events shows an asymmetric structure with a maximum around 108n the contrasting underlying thermal structures corresponding with enso and em have opposite impacts on the simultaneous hc in el ni years a symmetric anomalous meridional circulation is seen with enhanced rising around the equator and anomalousdescentatabout158nand208s incontrast anasymmetricequatorialmeridionalcirculationisobserved for el ni modoki years with anomalous ascent around 108n and descent at about 108s and 208n the contrasting meridional circulation anomalies within enso and em are caused by their different meridional ssta structure this result is theoretically explained indicating that anomalous meridional circulation is subject to the meridional ssta gradient moreover the observed results are reproduced in numerical experiments driven by anomalous warming in the eastern and central pacific ocean thus the authors conclude that the anomalous hc linked to enso and em is induced by the accompanying meridional gradient in zonal mean ssta

hydrodynamics and sediment transport in the swash zone a review and perspectives the dominant hydrodynamic forcing and resulting sediment transport mechanisms in the swash zone are reviewed combined with a discussion of future measurement and modelling requirements the importance of swash zone processes in the overall behaviour of the nearshore littoral zone are identified with the paper subsequently focusing on aspects that directly relate to sediment transport on beaches the review considers analytical and numerical modelling work and both field and laboratory data the hydrodynamics of the swash zone are first discussed with reference to the surf zone boundary swash characteristics forcing mechanisms and shoreline oscillations subsequent sections consider more micro scale processes such as the internal flow kinematics turbulence the bed boundary layer and infiltration exfiltration through permeable beds the second part of the paper outlines the fundamental mechanics of sediment transport in the swash zone followed by a more detailed discussion of sediment transport modes induced by the dominant hydrodynamic conditions modelling concepts are reviewed and the strengths and weaknesses of different approaches identified a final summary and future modelling perspectives conclude the paper

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

experimental study on the hydrodynamics of regular breaking waves this paper illustrates the results of experimental research carried out in the wave flume of the water engineering and chemistry department laboratory of bari technical university italy and based on the analysis of three different regular waves breaking on a sloping bottom the investigation refers particularly to the surf zone with the aim to develop two themes the study of velocity and reynolds shear stress distributions in the shoaling zone of a regular wave field and the study of turbulence in the breaking region observing that these two aspects greatly influence many coastal processes such as undertow currents sediment transport and action on maritime structures

coupled and decoupled numerical modeling of flow and morphological evolution in alluvial rivers existing numerical river models are mostly built upon asynchronous solution of simplified governing equations the strong coupling between water flow sediment transport and morphological evolution is thus ignored to a certain extent an earlier study led to the development of a fully coupled model and identified the impacts of simplifications in the water sediment mixture and global bed material continuity equations as well as of the asynchronous solution procedure for aggradation processes this paper presents the results of an extended study along this line highlighting the impacts on both aggradation and degradation processes simplifications in the continuity equations for the water sediment mixture and bed material are found to have negligible effects on degradation this is however in contrast to aggradation processes in which the errors purely due to simplified continuity equations can be significant transiently the asynchronous solution procedure is found to entail appreciable inaccuracy for both aggradation and degradation processes further the asynchronous solution procedure can render the physical problem mathematically ill posed by invoking an extra upstream boundary condition in the supercritical flow regime finally the impacts of simplified continuity equations and an asynchronous solution procedure are shown to be comparable with those of largely tuned friction factors indicating their significance in calibrating numerical river models it is concluded that the coupled system of complete governing equations needs to be synchronously solved for refined modeling of alluvial rivers

measurements of the vertical correlation in turbulence under broken waves abstract turbulence measurements have been carried out in the surf zone of a wave flume the purpose of the measurements is to determine the length scale of the turbulence generated by the wave breaking the length scale of the turbulence is estimated on basis of the correlation between simultaneous measurements of the vertical turbulent fluctuations taken at different levels above the bed

turbulence experiments in the swash zone abstract turbulence and water surface elevation measurements were carried out in the swash zone which was induced by plunging and collapsing breakers in a wave flume three different period regular waves were generated on a 1 10 smooth impermeable concrete beach and the water surface elevations were collected by a number of wave gauges and a run up meter lying on the bottom velocity measurements were carried out by a laser doppler velocimeter system at spatial steps of 1 mm from the bottom along three vertical sections in the swash zone the data have been used to describe the wave front dynamics to derive the length and velocity macro and micro scales and the eulerian frequency spectrum in some points it shows a double structure the results add to and expand on similar results obtained by other researchers in the surf zone

long term variation of the principal mode of boreal spring hadley circulation linked to sst over the indo pacific warm pool abstractthe variability of the boreal spring march may mam hadley circulation hc is investigated focusing on the long term variation of the first principal mode for 1951 2008 which is an equatorially asymmetric mode am with the rising branch located around 10 s this mode explains about 70 of the variance of the mam hc and shows an obvious upward trend and thus contributes to the strengthening of the mam hc the robust warming trends of sea surface temperature sst over the indo pacific warm pool ipwp play an essential role in the variations of the mam hc when sst over the ipwp is warm anomalous meridional circulation is induced with descending branches located in regions 30 20 s and 5 15 n and rising motion located near 10 s the anomalous rising south of the equator is due to the inhomogeneous warming of sst over the ipwp sst within the ipwp in the southern hemisphere shows a larger warming trend than that in the northern hemisphere the position of the anomalous convergence associate

observation of undertow and turbulence in a laboratory surf zone abstract undertow and turbulence in the surf zone have been studied in a wave flume for a spilling breaker and a plunging breaker fluid velocities across a 1 on 35 sloped false bottom were measured using a fiber optic laser doppler anemometer and wave decay and set up were measured using a capacitance wave gage the characteristics of mean flow and turbulence in spilling versus plunging breakers were studied the mean flow is the organized wave induced flow defined as the phase average of the instantaneous velocity while the turbulence is taken as the deviations from the phase average it was found that under the plunging breaker turbulence levels are much higher and vertical variations of undertow and turbulence intensity are much smaller in comparison with the spilling breaker it was also found that turbulent kinetic energy is transported seaward under the spilling breaker and landward under the plunging breaker by the mean flow the study indicates that there are fundamental differences in the dynamics of turbulence between spilling and plunging breakers which can be related to the processes of wave breaking and turbulence production it is suggested that the types of beach profile produced by storm and swell waves may be the results of different relationships between mean flow and turbulence in these waves

river bed degradation due to abrupt outfall lowering lower reaches of tributaries to the missouri river were straightened in the late 19th and early 20th century channel degradation has progressed upstream as a result channel deepening and widening have caused problems at stream crossings and have resulted in gully encroachment into cultivated fields a diffusion model and an hyperbolic model each describing channel degradation are solved using a laplace transform approach a closed form solution is obtained for the diffusion model but numerical methods are necessary for evaluation of the inverse transform of the hyperbolic model a closed form asymptotic solution is found for the hyperbolic case this asymptotic solution is shown to contain the solution to the diffusion model as a special case the asymptotic solution is compared with observed degradation of west tarkio creek a small river in northwestern missouri and southwestern iowa with good results

variability of boreal spring hadley circulation over the asian monsoon domain and its relationship with tropical sst the variability of boreal spring hadley circulation hc over the asian monsoon domain over the last four decades is explored the climatological distribution of the regional hc is symmetric of the equator with the ascending branch around the equator and sinking branch around the subtropics in each hemisphere the first dominant mode eof1 of the regional hc is equatorial asymmetric with the main body in the southern hemisphere sh and the ascending branch to the north of the equator this mode is mainly characterized by interannual variation and is related to el nino southern oscillation enso significant negative sea surface temperature sst anomalies are observed over the tropical indian ocean tio along with the development of la nina events however the magnitude of sst anomalies in the southern indian ocean is greater than that in the northern counterpart contributing to eof1 formation the spatial distribution of the second dominant mode eof2 is with the main body lying in the northern hemisphere nh and the ascending branch located to the south of the equator the temporal variation of this mode is connected to the warming of the tio the warming rate of the southern tio sst is faster than that in the northern counterpart resulting in the southward migration of the rising branch the above result indicates the critical role of the meridional distribution of sst on the variability of the regional hc

wally was right predictive ability of the north atlantic conveyor belt hypothesis for abrupt climate change linked abrupt changes of north atlantic deep water formation north atlantic sea ice extent and widespread climate occurred repeatedly during the last ice age cycle and beyond in response to changing freshwater fluxes and perhaps other causes this paradigm developed and championed especially by w s broecker has repeatedly proven to be successfully predictive as well as explanatory with high confidence much work remains to fully understand what happened and to assess possible implications for the future but the foundations for this work are remarkably solid

relationship between el nino southern oscillation and the symmetry of the hadley circulation role of the sea surface temperature annual cycle abstractel nino southern oscillation enso which features an equatorial quasi symmetric sea surface temperature anomaly ssta is related to both the symmetric and asymmetric components of the h

impacts of the boreal spring indo pacific warm pool hadley circulation on tropical cyclone activity over the western north pacific abstractthis study investigated the impacts of the interannual variability in the boreal spring regional hadley circulation over the indo pacific warm pool ipwp on the tropical cyclone tc activity over the western north pacific wnp the principal modes of the interannual variability in the ipwp hadley circulation were calculated using empirical orthogonal function eof analysis the leading mode eof 1 features cross equatorial southerly wind anomalies over the indian ocean and maritime continent and has an evident impact on wnp tc activity during summer in the summer following a positive phase of the eof 1 a cyclonic circulation anomaly with upward motion positive relative vorticity anomalies and weak sea level pressure dominates the wnp and this favors increased tc genesis however large positive vertical wind shear anomalies over the south china sea and philippine sea inhibit the tc intensification a positive wind sea surface temperature sst precipitation feedback was found to facili

analysis of surf zone turbulence measurements of turbulent kinetic energy k under surf zone waves are analyzed to show how k varies over depth between breaker point and shoreline and how k depends on the beach slope it is found that the variation of k over depth is remarkably weak large values being measured a few percent of the depth above the bottom a simple model for the dissipation mechanism makes it possible to derive an empirical formula for the time averaged k that accurately describes all the data considered reliable

on the dynamics of droughts in northeast brazil observations theory and numerical experiments with a general circulation model abstract it is proposed that a possible mechanism for the occurrence of severe droughts over northeast brazil is the establishment of a thermally direct local circulation which has its ascending branch at about 10 n and its descending branch over northeast brazil and the adjoining oceanic region the driving for this anomalous circulation is provided by warming due to enhanced moist convection associated with warmer sea surface temperature anomalies over the northern tropical atlantic and cooling associated with colder sea surface temperature anomalies in the southern tropical atlantic the combined effects of thermally forced subsidence and reduced evaporation and moisture flux convergence produces severe drought conditions over northeast brazil we have examined the monthly mean sea surface temperature anomalies over the tropical atlantic and rainfall anomalies over two selected stations fortaleza 3 46 s 38 31 w and quixeramobim 5 12 s 39 18 w for 25 years 1948 72 it is found that the most sever

laboratory observations of flow and sediment transport induced by plunging regular waves 1 two parallel experiments involving the evolution and runup induced by plunging regular waves near the shoreline of a sloping bed are considered 1 a rigid bed experiment allowing direct hot film measurements of bed shear stresses and 2 a sediment bed experiment allowing for the measurement of pore water pressures as well as observation of sediment suspension and bed morphological changes both experiments utilize the same initial bed profile and wave forcing the experiments show that the mean bed shear stresses experienced onshore of incipient breaking are amplified by nearly a factor of 2 relative to prebreaking conditions whereas their corresponding turbulent fluctuations are amplified even more strongly by a factor of 5 6 the plunging processes lead to a series of vortices whose formation may be explained as the result of shear layer instability measurements show that these vortices can significantly enhance peaks in the offshore directed bed shear stresses moreover near bed pore pressure measurements indicate that these vortices cause large upward directed pressure gradients which in turn produce a corresponding series of suspended sediment plumes shoreward of the initial breaking event these findings are related to the induced morphological changes over both short and long time scales the present results are also compared and contrasted with previous experiments utilizing a similar methodology but involving plunging solitary waves

turbulence in the swash and surf zones a review this paper reviews mainly conceptual models and experimental work in the field and in the laboratory dedicated during the last decades to studying turbulence of breaking waves and bores moving in very shallow water and in the swash zone the phenomena associated with vorticity and turbulence structures measured are summarised including the measurement techniques and the laboratory generation of breaking waves or of flow fields sharing several characteristics with breaking waves the effect of air entrapment during breaking is discussed the limits of the present knowledge especially in modelling a two or three phase system with air and sediment entrapped at high turbulence level and perspectives of future research are discussed

a closer comparison of early and late winter atmospheric trends in the northern hemisphere abstract decadal trends are compared in various fields between northern hemisphere early winter november december nd and late winter february march fm months using reanalysis data it is found that in the extratropics and polar region the decadal trends display nearly opposite tendencies between nd and fm during the period from 1979 to 2003 dynamical trends in late winter fm reveal that the polar vortex has become stronger and much colder and wave fluxes from the troposphere to the stratosphere are weaker consistent with the positive trend of the arctic oscillation ao as found in earlier studies while trends in nd appear to resemble a trend toward the low index polarity of the ao in the tropics the hadley circulation shows significant intensification in both nd and fm with stronger intensification in fm unlike the hadley cell the ferrel cell shows opposite trends between nd and fm with weakening in nd and strengthening in fm comparison of the observational results with general circul

expansion of the hadley cell under global warming 1 a consistent weakening and poleward expansion of the hadley circulation is diagnosed in the climate change simulations of the ipcc ar4 project associated with this widening is a poleward expansion of the subtropical dry zone simple scaling analysis supports the notion that the poleward extent of the hadley cell is set by the location where the thermally driven jet first becomes baroclinically unstable the expansion of the hadley cell is caused by an increase in the subtropical static stability which pushes poleward the baroclinic instability zone and hence the outer boundary of the hadley cell

application of a diffusion erosion model to alluvial channels which degrade due to base level lowering the applicability of a diffusion erosion model that predicts transient longitudinal profiles of degrading alluvial channels has already been demonstrated in laboratory experiments and is here applied to some field examples by fitting simulated longitudinal profiles to measured ones for several streams with discharge 0 04 q5 680 m3s 1 diffusion erosion coefficients k were determined which are well correlated to discharge and drainage area headward knickpoint migration which results from base level lowering was also treated through the diffusion erosion model theoretically the distance of a knickpoint from the mouth of a tributary should be proportional to the square root of the time that elapsed since the base level was lowered field observations are in accordance with these theoretical considerations use of the model is discussed for prediction of erosion and for assessment of the age of alluvial fault scarps crossed by streams

the sst gradient between the southwestern pacific and the western pacific warm pool a new factor controlling the northwestern pacific tropical cyclone genesis frequency abstractthe sea surface temperature gradient sstg between the southwestern pacific ocean 40 20 s 160 e 170 w and the western pacific warm pool 0 16 n 125 165 e in boreal spring has been identified as a new factor that controls the interannual variability of tropical cyclone tc frequency over the western north pacific ocean wnp this sstg can explain 53 of the total variance of the wnp tc genesis frequency during the typhoon season for the period 1980 2011 the positive sstg anomaly produces an anomalous cross equatorial pressure gradient and thus anomalies in low level southward cross equatorial flow and tropical easterlies over the central western pacific the anomalous easterlies further produce local equatorial upwelling and seasonal cooling in the central pacific which in turn maintains the easterly anomalies throughout the typhoon season these dynamical thermodynamical effects induced by the positive sstg anomaly lead to a reduced low level cyclonic shear increased vertical wind sh

a physical mechanism for north atlantic sst influence on the indian summer monsoon a link between the atlantic multidecadal oscillation amo and multidecadal variability of the indian summer monsoon rainfall is unraveled and a long sought physical mechanism linking atlantic climate and monsoon has been identified the amo produces persistent weakening strengthening of the meridional gradient of tropospheric temperature tt by setting up negative positive tt anomaly over eurasia during northern late summer autumn resulting in early late withdrawal of the south west monsoon and persistent decrease increase of seasonal monsoon rainfall on inter annual time scales strong north atlantic oscillation nao or north annular mode nam influences the monsoon by producing similar tt anomaly over eurasia the amo achieves the interdecadal modulation of the monsoon by modulating the frequency of occurrence of strong nao nam events this mechanism also provides a basis for explaining the observed teleconnection between north atlantic temperature and the asian monsoon in paleoclimatic proxies citation goswami b n m s madhusoodanan c p neema and d sengupta 2006 a physical mechanism for north atlantic sst influence on the indian summer monsoon

contributions to the wave mean momentum balance in the surf zone abstract mean wave averaged cross shore flow in the surfzone has a strong vertical variation good understanding and prediction of this mean velocity profile is of crucial importance as it determines the advective transport of constituents such as sediment and consequently the coastal morphological evolution most modeling systems for coastal hydrodynamics and morphodynamics do no resolve the wave motion and wave current coupling is a challenging topic this paper investigates stresses and forces that control mean surfzone hydrodynamics based on detailed wave flume velocity measurements above a fixed sloping bed including two breaker bars the data show that the vertical distribution of normal stress below the wave trough level is fairly uniform at the same time the data suggest that a significant part is concentrated between the wave trough and crest level furthermore it is concluded that the horizontal radiation stress gradients and the vertical shear stress gradients can be of the same order of magnitude in the vicinity of the breaker bar although usually ignored in 3d mean flow modeling systems the wave reynolds stress makes an important contribution to the mean shear stress the normal stress below the wave trough level could be reasonably well predicted using the classical 16 expression accounting for the contribution between wave crest and trough the model of 39 reproduces the main trends in the wave reynolds stresses above the bottom boundary layer

observations of wave shear stress on a steep beach observations are presented of the wave shear stress u w on a steeply sloping beach above the wave boundary layer wbl positive values of u w were observed and are attributed to a combination of both wave shoaling due to the large scale bed slope and dissipation due to wave breaking in agreement with the wave theory of zou et al 2003 within the wbl observed vertical profiles of u w were also in good agreement with theory in cases where the wave height was small as wave heights increased however the wbl profile of u w generally did not agree with theory near simultaneous rotary sonar observations of the bed suggest the disagreement with theory was due to the presence of orbital scale ripples which the present theory does not accommodate

linear hyperbolic model for alluvial channels the exact linear solutions for the sediment transport and bed form evolution for one dimensional sediment water two phase motion have been obtained using the st venant shallow water equations with the assumption of quasi steady flow these solutions are applicable to alluvial channels of infinite length initially at equilibrium followed by an arbitrary forcing function of either sediment transport or bed elevation imposed as an upstream boundary condition the solutions have been used to predict aggradation in a channel due to constant overloading comparison of the results with available experimental data and with the solution obtained from a parabolic model is satisfactory the present theory is significant conceptually since it provides valuable insight into the physical phenomenon as well as into the mathematical behavior of the solutions

dynamical connection between the stratospheric arctic vortex and sea surface temperatures in the north atlantic we used two long term reanalysis datasets and time slice simulations to examine the decadal relationship between the stratospheric arctic vortex sav and sea surface temperature anomalies sstas in the north atlantic and the dynamic mechanisms involved in the linkage between the two our results show that there is a significant decadal linkage between sstas over the north atlantic and the sav where warmed cooled sstas over the north atlantic in association with its principal mode correspond to a weakened strengthened sav the warmed north atlantic sstas tend to result in a weakened sav via two dynamic processes 1 constructive interference at high latitudes with a ridge in the atlantic sector and a trough in the pacific accompanied by a negative north atlantic oscillation like pattern over the north atlantic and a weakened aleutian low over the north pacific and 2 more wavenumber 1 waves propagated into the arctic stratosphere by modifying the baroclinic term of the zonal mean background state and altering the propagating conditions around the tropopause over the arctic results from reanalysis and model simulations both suggest that a strengthening wave intensity in the high latitude troposphere and more upward propagation of the planetary wavenumber 1 wave in response to the warmed north atlantic sstas conjunctly contribute to the increased planetary wave flux in the arctic stratosphere facilitating a weakened sav these results provide a new understanding of what dynamic processes control the sav and will help to predict the stratosphere on decadal timescales