anthropogenic influence on sedimentation and intertidal mudflat change in san pablo bay california 1856 1983 analysis of a series of historical bathymetric surveys has revealed large changes in morphology and sedimentation from 1856 to 1983 in san pablo bay california in 1856 the morphology of the bay was complex with a broad main channel a major side channel connecting to the petaluma river and an ebb tidal delta crossing shallow parts of the bay in 1983 its morphology was simpler because all channels except the main channel had filled with sediment and erosion had planed the shallows creating a uniform gently sloping surface the timing and patterns of geomorphic change and deposition and erosion of sediment were influenced by human activities that altered sediment delivery from rivers from 1856 to 1887 high sediment delivery 14 1 10 6 m 3 yr to san francisco bay during the hydraulic gold mining period in the sierra nevada resulted in net deposition of 259 14 10 6 m 3 in san pablo bay this rapid deposition filled channels and increased intertidal mudflat area by 60 37 4 3 4 to 60 6 6 2 km 2 from 1951 to 1983 23 3 10 6 m 3 of sediment was eroded from san pablo bay as sediment delivery from the sacramento and san joaquin rivers decreased to 2 8 10 6 m 3 yr because of damming of rivers riverbank protection and altered land use intertidal mudflat area in 1983 was 31 8 3 9 km 2 similar to that in 1856 intertidal mudflat distribution in 1983 however was fairly uniform whereas most of the intertidal mudflats were in the western part of san pablo bay in 1856 sediment delivery through its affect on shallow parts of the bay was determined to be a primary control on intertidal mudflat area san pablo bay has been greatly affected by human activities and will likely continue to erode in the near term in response to a diminished sediment delivery from rivers 2007 elsevier ltd all rights reserved

exploring links between arctic amplification and mid latitude weather 1 this study examines observed changes 1979 2011 in atmospheric planetary wave amplitude over northern mid latitudes which have been proposed as a possible mechanism linking arctic amplification and mid latitude weather extremes we use two distinct but equally valid definitions of planetary wave amplitude termed meridional amplitude a measure of north south meandering and zonal amplitude a measure of the intensity of atmospheric ridges and troughs at 45 n statistically significant changes in either metric are limited to few seasons wavelengths and longitudinal sectors however in summer we identify significant increases in meridional amplitude over europe but significant decreases in zonal amplitude hemispherically and also individually over europe and asia therefore we argue that possible connections between arctic amplification and planetary waves and implications of these are sensitive to how waves are conceptualized the contrasting meridional and zonal amplitude trends have different and complex possible implications for midlatitude weather and we encourage further work to better understand these

a blocking view of the stratosphere troposphere coupling dynamical influence from the stratosphere is known to play a role in shaping the wintertime tropospheric circulation patterns observations suggest that this influence is strongest following weak and strong polar vortex events termed sudden stratospheric warmings ssws and vortex intensification vi events respectively in this work stratosphere troposphere coupling is studied through the modulation by extreme vortex events of the northern hemispheric tropospheric blocking frequency and eddy driven jet displacements this is done using three reanalysis data sets and the centro euro mediterraneo sui cambiamenti climatici climate model with a resolved stratosphere cmcc cms coupled model control run reanalysis results suggest the existence of distinct patterns of blocking activity following extreme vortex events over the atlantic basin ssws are shown to lead by about 20 50 days the occurrence of increased reduced blocking frequency on the poleward equatorward side of the atlantic jet stream anomalies of the opposite sense with poleward reduction and equatorward enhancement of the blocking frequency occur following vi events the response over the pacific sector is less clear compared to reanalyses cmcc cms shows a similar but weaker response especially over the atlantic a possible explanation is identified in the different structure of the polar vortex and weaker wind shear anomalies with respect to reanalysis we finally highlight that patterns identified following vortex extremes show similarities with the northern annular mode over the atlantic but not over the pacific this suggests that the stratosphere troposphere coupling is more a regional than annular feature

the use of modeling and suspended sediment concentration measurements for quantifying net suspended sediment transport through a large tidally dominated inlet abstract sediment exchange at large energetic inlets is often difficult to quantify due complex flows massive amounts of water and sediment exchange and environmental conditions limiting long term data collection in an effort to better quantify such exchange this study investigated the use of suspended sediment concentrations ssc measured at an offsite location as a surrogate for sediment exchange at the tidally dominated golden gate inlet in san francisco ca a numerical model was calibrated and validated against water and suspended sediment flux measured during a spring neap tide cycle across the golden gate the model was then run for five months and net exchange was calculated on a tidal time scale and compared to ssc measurements at the alcatraz monitoring site located in central san francisco bay 5 km from the golden gate numerically modeled tide averaged flux across the golden gate compared well r 2 0 86 p value mckee et al 2013 this issue there was little variation from year to year exports were computed to be greatest during the wettest water year analyzed but only marginally so

sediment transport patterns in the san francisco bay coastal system from cross validation of bedform asymmetry and modeled residual flux abstract the morphology of 45 000 bedforms from 13 multibeam bathymetry surveys was used as a proxy for identifying net bedload sediment transport directions and pathways throughout the san francisco bay estuary and adjacent outer coast the spatially averaged shape asymmetry of the bedforms reveals distinct pathways of ebb and flood transport additionally the region wide ebb oriented asymmetry of 5 suggests net seaward directed transport within the estuarine coastal system with significant seaward asymmetry at the mouth of san francisco bay 11 through the northern reaches of the bay 7 8 and among the largest bedforms 21 for 50 m this general indication for the net transport of sand to the open coast strongly suggests that anthropogenic removal of sediment from the estuary particularly along clearly defined seaward transport pathways will limit the supply of sand to chronically eroding open coast beaches the bedform asymmetry measurements significantly agree up to 76 with modeled annual residual transport directions derived from a hydrodynamically calibrated numerical model and the orientation of adjacent flow sculpted seafloor features such as mega flute structures providing a comprehensive validation of the technique the methods described in this paper to determine well defined cross validated sediment transport pathways can be applied to estuarine coastal systems globally where bedforms are present the results can inform and improve regional sediment management practices to more efficiently utilize often limited sediment resources and mitigate current and future sediment supply related impacts

reversed sediment wave migration in the irish sea nw europe a reappraisal of the validity of geometry based predictive modelling and assumptions abstract the observation and prediction of the mobility of the seabed are in high demand with rapidly expanding offshore engineering developments and the increasing urgency to start mitigation against changing coastlines from repeatedly surveyed sediment wave fields in the irish sea average sediment wave migrations have been mapped from which broad scale net sediment transport directions can be derived the proximity of bathymetric highs and lows seems to redirect sediment migration pathways and increases migration rates by a factor 5 on average via current deflection and amplification a few hundred sediment waves were analysed geometrically in this study and compared to their migration behaviour revealing a lack of statistical correlation sediment wave lee slope directions asymmetry indices and other geometrical parameters appear poorly indicative of their degree of mobility in the irish sea a considerable amount of sediment waves counter intuitively migrate in the direction of their gentle stoss slope i e opposite to the expected sense of migration even when considering the limitations of the predominantly 2 dimensional sampling method these results fundamentally challenge established assumptions on the indicative meaning of sediment wave geometry they question the validity and robustness of sediment wave migratory predictions based on single geometrical readings that fail to represent the complexity of local hydrodynamics and partial sediment wave modifications until predictive tools for sediment wave migration are developed that can pass the test in all aquatic environments repeat surveying with sonar systems provides the only reliable way to record true natural variability

storm track dynamics this paper reviews the current state of observational theoretical and modeling knowledge of the midlatitude storm tracks of the northern hemisphere cool season observed storm track structures and variations form the first part of the review the climatological storm track structure is described and the seasonal interannual and interdecadal storm track variations are discussed in particular the observation that the pacific storm track exhibits a marked minimum during midwinter when the background baroclinicity is strongest and a new finding that storm tracks exhibit notable variations in their intensity on decadal timescales are highlighted as challenges that any comprehensive storm track theory or model has to be able to address physical processes important to storm track dynamics make up the second part of the review the roles played by baroclinic processes linear instability downstream development barotropic modulation and diabatic heating are discussed understanding of these processes forms the core of our current theoretical knowledge of storm track dynamics and provides a context within which both observational and modeling results can be interpreted the eddy energy budget is presented to show that all of these processes are important in the maintenance of the storm tracks the final part of the review deals with the ability to model storm tracks the success as well as remaining problems in idealized storm track modeling which is based on a linearized dynamical system are discussed perhaps on a more pragmatic side it is pointed out that while the current generation of atmospheric general circulation models faithfully reproduce the climatological storm track structure and to a certain extent the seasonal and enso related interannual variations of storm tracks in depth comparisons between observed and modeled storm track variations are still lacking

role of the east asian trough on the eastern mediterranean temperature variability in early spring and the extreme case of 2004 warm spell this study investigates the potential influence of the east asian trough eat on the eastern mediterranean temperature variability in early spring in connection with this it also examines the extreme case of the year 2004 when anomalous warming of the eastern anatolia resulted in unprecedented snowmelt runoff amounts in the euphrates and tigris basins in early march in the analyses we used reanalysis data gridded products of surface temperature and snow cover river discharge data and satellite imagery we employed an intensity index for the eat and a trough displacement index for the mediterranean trough medt to explore the relationship between the strength of the eat and the displacement of the medt at pentad resolution our analysis shows that there are statistically significant correlations at 99 confidence level between the strength of the eat and the zonal shift of the medt on some pentads e g 3rd 13th 37th and 59th but that the highest correlation occurs on the 13th pentad of the year corresponding to the early days of march it seems that on this pentad when the eat is strong the medt tends to be located in the west of its climatological position about 30 hbox 35 circ hbox e which causes warmer conditions over the eastern mediterranean in 2004 which appears to be an extreme year for this phenomenon the medt is positioned and deepened in the central mediterranean about 10 hbox 15 circ hbox e and extended towards central africa during the early days of march this synoptic pattern provided favorable conditions for the development of a tropical plume atmospheric river with a southwest northeast orientation carrying warm tropical african air towards the eastern mediterranean and anatolian highlands resulting in rapid melting of the snowpack as well as severe precipitation and thus flooding events in the eastern anatolia a key finding in our analysis is that the strengthening of the eat was instrumental to the increased amplitude of the ridge trough system over the euro mediterranean region in the early days of 2004 spring we highlight that the response of surface and upper level meteorological conditions to the amplitude of the ridge trough system enhanced by the strength of the eat might be crucial in the understanding of some of the extreme hydrometeorological events in the eastern mediterranean region

the influence of oceanic swell on flows over an estuarine intertidal mudflat in san francisco bay in this study we examine the role that remotely forced ocean waves play in the hydrodynamics of an intertidal estuarine mudflat the observations indicate that long period 10 20 s ocean waves are a potentially important source of near bed energy and shear stress in this environment over a two week period in february 2001 we deployed an autonomous sontek hydra system on a mudflat in central san francisco bay and measured velocity and sediment concentration approximately 10 cm from the bed using an acoustic doppler velocimeter adv and an optical backscatter sensor obs the experiment continued through wet high tide and dry low tide periods over an entire spring neap cycle and thus included the variation of near bed velocity over a range of timescales results show that during large ebb tides tidally forced flows dominate the near bed dynamics during calm conditions wind waves dominate whenever the wind direction exposes the mudflat to wind coming off the bay from the south and southwest as occurs during winter storms during periods when tidal forcing is limited and wind waves are small remotely forced ocean swells become an important energy source these motions appear in the burst samples at frequencies between 0 1 and 0 04 hz and their energy correlates well q 0 8 with ocean swell measured from a buoy offshore of san francisco spectral analysis of data shows that the average energy of ocean waves per tide varied between 2 and 15 of total energy load moreover extreme values in the distribution of ocean waves bring episodic bursts of greater energy onto the estuarine mudflat which may influence local suspension of sediments 2003 elsevier ltd all rights reserved

sedimentary geology of the columbia river estuary abstract a multiyear study of the sedimentary geology of the columbia river estuary has provided valuable data regarding sediment distribution bedform distribution and suspended sediment distribution on spatial and temporal scales that permit delineation of sedimentary environments and insight into the sedimentary processes that have shaped the estuary in comparison to other more intensively studied estuaries in north america the columbia river estuary has relatively larger tidal range maximum semidiurnal range of 3 6m and large riverflow 6 700m3s 1 variations in riverflow sediment supply and tidal flow occur over a range of time scales making the study of modern processes as they relate to long term effects particularly challenging analyses of more than 2000 bottom sediment grab samples indicate that the bed material of the estuary varies in a relatively narrow range between 0 and 8 phi 1 0 and 0 0039mm with an overall mean size of 2 5 phi 0 177mm sediment size decreases generally in the downstream direction sediments from the upriver channels are coarse 1 5 2 0phi 0 25 0 35mm and moderately sorted sediments in the central estuary show wider range and variation in grain size and sorting 1 75 6 0phi 0 016 0 3mm sediment from the entrance region has a mean size of 2 75phi 0 149mm and is well sorted seasonal changes in sediment size distributions occur and are best delineated by those samples containing more than 10 mud silt plus clay sediments containing a significant fine fraction generally occur only in the peripheral bays and in channels isolated from strong currents thin deposits of fine sediments are occasionally found in main channels and the ephemeral nature of these sediments suggest that they may erode and produce the silty rip up clasts that appear intermittently in the same regions the distribution of bedforms of various size and shape has been mapped with side scan sonar during three seasons and at various tidal stages the presence of bedforms with wavelengths of 6 8m and alternating slip faces about 40cm high indicates that the deeper portion of the entrance region is dominated by tidally reversing lower flow regime sediment transport bedforms in the upper reaches of the estuary are much larger with heights of up to 3m and wavelengths of up to 100m these bedforms and the smaller superimposed bedforms imply downstream transport under fluvial conditions in the central estuary bedforms in the deep portion of the main channels are oriented upriver while those on the shallow flanks of the channels are oriented seaward the landward limit of upriver bedform transport varies seasonally in response to riverflow fluctuations a complex array of sedimentary environments exists in the columbia river estuary each environment is influenced by the relative importance of waves fluvial currents and tidal currents as modified by the presence or absence of estuarine circulation vegetation or human activity the importance of these enviroments to the ecosystem of the estuary is discussed in subsequent papers in this volume

application of spatial cross correlation to detection of migration of submarine sand dunes knowledge of migration rates of bedforms provides an indirect indication of thebehavior of tidally averaged bottom currents enables optimization of hydrographic surveyfrequency and may enable calculation of bedload transport rate to measure bedformmigration rate we test the use of spatial correlation as a measurement method whichquantifies and locates a region of maximum similarity between two spatial variables forthe latter we use consecutive eight bit images of spatial gradient derived frombathymetric digital terrain models carrying out the correlation over this representation ofthe shape of the seabed rather than the bathymetric surface the digital terrain modelswere compiled from six repeat multibeam surveys of a headland associated bank nearsaint john new brunswick with a roughly 30 day interval vectors are drawn depictingthe movement of a sand dune at time t

wave breaking characteristics of northern hemisphere winter blocking a two dimensional approach abstractthis paper generalizes and applies recently developed blocking diagnostics in a two dimensional 2d latitude longitude context which takes into consideration both mid and high latitude blocking these diagnostics identify characteristics of the associated wave breaking as seen in the potential temperature on the dynamical tropopause particularly the cyclonic or anticyclonic direction of wave breaking db index and the relative intensity ri index of the air masses that contribute to blocking formation the methodology is extended to a 2d domain and a cluster technique is deployed to classify mid and high latitude blocking according to the wave breaking characteristics midlatitude blocking is observed over europe and asia where the meridional gradient of is generally weak whereas high latitude blocking is mainly present over the oceans to the north of the jet stream where the meridional gradient of is much stronger they occur on the equatorward and poleward flank of the jet s

on the modeling of sand wave migration 1 we describe a simple mathematical model capable of reproducing the main features of sand wave inception and growth in particular we focus on the prediction of the migration rates that sand waves undergo because of tidal and residual currents the model adequately predicts migration rates even for the cases of upstream propagating sand waves i e for sand waves which migrate in the direction opposite to that of the residual current we show that upstream downstream propagation is mainly controlled by the relative strength of the residual current with respect to the amplitude of the quarter diurnal tide constituent and by the phase shift between the semi diurnal and quarter diurnal tide constituents therefore to accurately predict field cases a detailed knowledge of the direction strength and phase of the different tide constituents is required

tropospheric precursors of anomalous northern hemisphere stratospheric polar vortices regional extratropical tropospheric variability in the north pacific and eastern europe is well correlated with variability in the northern hemisphere wintertime stratospheric polar vortex in both the ecmwf reanalysis record and in the whole atmosphere community climate model to explain this correlation the link between stratospheric vertical eliassen palm flux variability and tropospheric variability is analyzed simple reasoning shows that variability in the north pacific and eastern europe can deepen or flatten the wintertime tropospheric stationary waves and in particular its wavenumber 1 and 2 components thus providing a physical explanation for the correlation between these regions and vortex weakening these two pathways begin to weaken the upper stratospheric vortex nearly immediately with a peak influence apparent after a lag of some 20 days the influence then appears to propagate downward in time as expected from wave mean flow interaction theory these patterns are influenced by enso and october eurasian snow cover perturbations in the vortex induced by the two regions add linearly these two patterns and the quasi biennial oscillation qbo are linearly related to 40 of polar vortex variability during winter in the reanalysis record

wave breaking characteristics of midlatitude blocking in this article northern hemisphere winter midlatitude blocking is analysed through its wave breaking characteristics rossby wave breaking is identified as a key process in blocking occurrence as it provides the mechanism for the meridional reversal pattern typical of blocking two indices are designed to detect the major properties of wave breaking i e the orientation cyclonic anticyclonic direction of breaking or db index and the relative contribution of air masses warm cold relative intensity or ri index the use of the db index differentiates between the anticyclonic cases over europe and asia and the cyclonic events over the oceanic basins one of the three regions displaying cyclonic type was found over the atlantic ocean the other two being over the pacific ocean the first of these is located over the western side of the pacific and is dominated by warm air extrusions whereas the second is placed northward of the exit region of the jet stream where the meridional gradient is much weaker two european blocking types have been detected using the ri index which separates out the cases dominated by warm and cold air masses the latter cases in particular exhibited a well structured dipole with associated strong anomalies in both temperature and precipitation copyright 2011 royal meteorological society

use of swath bathymetry in the investigation of sand dune geometry and migration around a near shore banner tidal sandbank banner tidal sandbanks in the bristol channel have been repeatedly surveyed with a multibeam sonar to study the geometry and migration patterns of superimposed dunes the data presented in this paper constitute one of the first studies concerned with sediment transport around a banner sandbank helwick sands in the bristol channel using repeated swathbathymetry the data reveal that the dunes maintain their shapes over a period of 11 months and that they migrate in opposite directions on the alternate sides of the bank curiously dunes connect over the crest of the bank despite opposing sediment transport directions on the flanks dune height increases with water depth as found in similar environments we suggest how the morphology of the dunes results from the complex interaction between surface waves and tidal currents that occurs within the proximity of the headland 1995 furthermore repeated full bathymetric coverage of sub tidal sedimentary structures using swath sonar technology will provide information of their dynamics and threedimensional characteristics which are of interest for the understanding of coastal and shelf sedimentary transport this paper describes the morphology and dynamical characteristics of sand dunes at the eastern end of the helwick sandbank lying near a headland in the bristol channel fig 1 the analysis is based on two sets of swathbathymetry data collected on 26 september 2001 and 20 august 2002 the main objective of this paper is to demonstrate the potential for tracking dune migration and dune geometry changes from repeated bathymetric multibeam surveys this paper is therefore intended to a describe the morphological characteristics of the dunes and their spatiotemporal evolution b estimate dune migration rate and from that infer sediment transport flux and c relate these data to the work elsewhere of sediment transport around sandbanks and their maintenance in describing the sand dunes in this paper we follow the terminology developed by ashley 1990

understanding processes controlling sediment transports at the mouth of a highly energetic inlet system san francisco bay ca abstract san francisco bay is one of the largest estuaries along the u s west coast and is linked to the pacific ocean through the golden gate a 100 m deep bedrock inlet a coupled wave flow and sediment transport model is used to quantify the sediment linkages between san francisco bay the golden gate and the adjacent open coast flow and sediment transport processes are investigated using an ensemble average of 24 climatologically derived wave cases and a 24 8 h representative tidal cycle the model simulations show that within the inlet flow and sediment transport is tidally dominated and driven by asymmetry of the ebb and flood tides peak ebb velocities exceed the peak flood velocities in the narrow golden gate channel as a result of flow convergence and acceleration persistent flow and sediment gyres at the headland tips are formed that limit sediment transfer from the ebb tidal delta to the inlet and into the bay the residual transport pattern in the inlet is dominated by a lateral segregation with a large ebb dominant sediment transport and flow prevailing along the deeper north side of the golden gate channel and smaller flood dominant transports along the shallow southern margin the seaward edge of the ebb tidal delta largely corresponds to the seaward extent of strong tidal flows on the ebb tidal delta both waves and tidal forcing govern flow and sediment transport wave focusing by the ebb tidal delta leads to strong patterns of sediment convergence and divergence along the adjacent ocean beach

the role of transient eddies in north pacific blocking formation and its seasonality abstractthe mechanism of north pacific np blocking formation is investigated by conducting a reanalysis based budget analysis of the quasi geostrophic geopotential tendency equation it is confir

bidimensional diagnostics variability and trends of northern hemisphere blocking abstractin this paper northern hemisphere winter blocking is analyzed through the introduction of a set of new bidimensional diagnostics based on geopotential height that provide information about the occurrence the duration the intensity and the wave breaking associated with the blocking this analysis is performed with different reanalysis datasets in order to evaluate the sensitivity of the index and the diagnostics adopted in this way the authors are able to define a new category of blocking placed at low latitudes that is similar to midlatitude blocking in terms of the introduced diagnostics but is unable to divert or block the flow furthermore over the euro atlantic sector it is shown that it is possible to phenomenologically distinguish between high latitude blocking occurring over greenland north of the jet stream and dominated by cyclonic wave breaking and the traditional midlatitude blocking localized over europe and driven by anticyclonic wave breaking these latter events are uniform

blocking and rossby wave breaking on the dynamical tropopause in the southern hemisphere abstract rossby wave breaking on the dynamical tropopause in the southern hemisphere the 2 pvu surface is investigated using the era 40 dataset the indication of wave breaking is based on reversal in the meridional gradient of potential temperature and persistent large scale wave breaking is taken as a strong indication that blocking may be present blocking in the midlatitudes is found to occur predominantly during wintertime in the pacific and is most vigorous in the east pacific while during summertime the frequency of blocking weakens and its extent becomes confined to the west pacific the interannual variability of blocking is found to be high wave breaking occurs most frequently on the poleward side of the polar jet and has some but not all of the signatures of blocking so it is referred to as high latitude blocking in general cyclonic wave breaking occurs on the poleward side of the polar jet otherwise anticyclonic breaking occurs however at least in wintertime wave breaking in th

quaternary geology and surficial sediment processes browns bank scotian shelf based on multibeam bathymetry abstract browns bank is located on the glaciated continental shelf off southern nova scotia geological mapping of browns bank is based on interpretation of multibeam bathymetric and backscatter data in conjunction with 220 line km of seismic reflection profiles and sidescan sonograms sea floor sediment samples and bottom photographs the fundian moraine part of the previously identified end moraine system on the continental shelf off nova scotia is a prominent west east flat topped multi lobate ridge identifiable in the multibeam bathymetric data and in geophysical records the fundian moraine was subjected to erosion in the surf zone during sea level rise in depths less than 100 m a series of north south roughly parallel till ridges continuous in the subsurface with the fundian moraine is interpreted as interlobate moraines suggesting formation by a tidewater glacier the browns bank moraine connected to the fundian moraine is evidence of a newly identified grounded ice position farther seaward than the latter bedforms including obstacle marks comet marks sand waves and megaripples are evidence of a vigorous anticyclonic current pattern on browns bank the combination of multibeam bathymetric imagery with high resolution geoscientific information represents a powerful technique for sea floor geological investigations

observations of sand waves megaripples and hummocks in the dutch coastal area and their relation to currents and combined flow conditions 1 this paper aims to investigate the distribution and stability of large scale bed forms in response to storm and fair weather conditions in a shallow marine environment multibeam and side scan sonar data off the dutch coast median grain size 0 25 0 35 mm were collected to monitor sand waves 100 800 m and superimposed megaripples 1 40 m through multiple storm and fair weather events box cores were used to observe the vertical bed structure and grain size in the dutch coastal area two dimensional 2 d megaripples x 1 15 m are the dominant bed forms in current dominated 0 4 m s tidal flow regimes with oscillatory flows 0 4 m s undulating bed topography of mound like 3 d bed forms 20 40 m is observed immediately after storms these bed forms are covered by smaller 3 d megaripples which are related to sets of low angle converging laminae in box cores interpreted as hummocky cross stratification hcs the sand waves form compound bed forms of sets of 2 d and 3 d megaripples the morphology of the sand waves is a function of the general wind wave climate of the marine environmental setting with flat topped 3 d sand waves occurring in shallow wave dominated settings and 2 d sand waves occurring in the tide dominated environment farther offshore copyright 2005 by the american geophysical union

the role of high and low frequency dynamics in blocking formation time evolutions of prominent blocking flow configurations over the north pacific and europe are compared based upon composites for the 30 strongest events observed during 27 recent winter seasons fluctuations associated with synoptic scale migratory eddies have been filtered out before the compositing a quasi stationary wave train across the atlantic is evident during the blocking amplification over europe while no counterpart is found to the west of the amplifying blocking over the north pacific correlation between the tropopause level potential vorticity pv and meridional wind velocity associated with the amplifying blocking is found to be negative over europe in association with the anticyclonic evolution of the low pv center but it is almost zero over the north pacific feedback from the synoptic scale eddies as evaluated in the form of 250 mb geopotential height tendency due to the eddy vorticity flux convergence accounts for more than 75 of the observed amplification for the pacific blocking and less than 45 for the european blocking this difference is highlighted in two types of contour advection with surgery experiments in one of them pv contours observed four days before the peak blocking time were advected by composite time series of the low pass filtered observational wind and in the other experiment they were advected by the low pass filtered wind from which the transient eddy feedback evaluated as above had been removed at every time step hence the latter data should be dominated by low frequency dynamics for the european blocking both experiments can reproduce the anticyclonic evolution of low pv air within a blocking ridge as observed for the pacific blocking in contrast the observed intrusion of low pv air into the higher latitudes cannot be reproduced without the transient feedback furthermore in a barotropic model initialized with the composite 250 mb flow observed three days before the peak time a simulated blocking development over the north pacific is more sensitive to the insertion of the observed transient feedback than that over europe these results suggest that the incoming wave activity flux associated with a quasi stationary rossby wave train is of primary importance in the blocking formation over europe whereas the forcing by the synoptic scale transients is indispensable to that over the north pacific

the seasonal evolution of planetary waves in the southern hemisphere stratosphere and troposphere seasonality in planetary wave structure in the southern hemisphere stratosphere and troposphere 1000 1 mb is studied based on eight years 1979 1986 of daily geopotential data emphasis is placed on the distinctive seasonality in the stratosphere along with tracing the stratospheric fluctuations into the troposphere time filtering is used to separate stationary and transient components maximum geopotential height variance is observed in the middle to upper stratosphere in late winter spring with a distinct secondary smaller maximum in late fall early winter these maxima sandwich the strongest mid winter zonal winds this sequence occurs approximately one month earlier in the upper stratosphere two corresponding peaks are observed in stratospheric zonal mean wind and temperature fluctuations the two maxima in stratospheric wave variance are not in agreement with observed seasonal changes in quasi geostrophic refractive index of the zonal mean flow the stratospheric geopotential variance maxima result from nearly equal amounts of stationary and transient zonal wave 1 fluctuations with transient wave 2 also contributing during late winter stationary wave 1 shows intriguing seasonal evolution the early winter maximum is predominantly equivalent barotropic whereas that of late winter spring is highly baroclinic in the stratosphere stratospheric poleward fluxes of heat and momentum both exhibit pronounced maxima during september october these result primarily from the stationary wave 1 contributions and the transients assume a secondary role although not as pronounced as the stationary wave seasonality seasonal differences in transient wave behaviour are also documented including three dimensional propagation characteristics and wave mean flow interaction diagnostics

patterns of bottom current flow deduced from dune asymmetries over the gulf of cadiz shelf southwest spain abstract the analysis of dune like morphologies on the gulf of cadiz continental shelf using high resolution seismic reflection profiles and sediment samples reveals a well defined distribution pattern controlled by the area s hydrodynamics these bedforms are considered to be modern features from the holocene and therefore they provide information about the bottom circulatory patterns established over the continental shelf most of the submarine dunes have been identified over a shallow physiographic feature named the barbate high the current flows that generate the bedform fields can be attributed to a complex interaction of several hydrodynamic agents in which the process of current direction reversal related to the tidal cycle in the straits of gibraltar seems to be involved eastward oriented submarine dunes located on the onshore zones of the inner shelf are generated by the atlantic inflow which over these shallow zones is mainly orientated towards the east during high tide conditions in the straits of gibraltar bedforms oriented westwards and west northwestwards in the offshore zones indicate that a previously undescribed flow occurs on the gulf of cadiz continental shelf this flow is attributed to the influence of ebb tidal currents which move preferentially towards the west over these zones as a result of this complex bottom flow pattern a clockwise sand transport pattern over the barbate high is established

sub weekly to interannual variability of a high energy shoreline abstract sixty one global positioning system gps sub aerial beach surveys were completed at 7 km long ocean beach san francisco ca usa between april 2004 and march 2009 the five year time series contains over 1 million beach elevation measurements and documents detailed changes in beach morphology over a variety of spatial temporal and physical forcing scales results show that seasonal processes dominate at ocean beach with the seasonal increase and decrease in wave height being the primary driver of shoreline change storm events while capable of causing large short term changes in the shoreline did not singularly account for a large percentage of the overall observed change empirical orthogonal function eof analysis shows that the first two modes account for approximately three quarters of the variance in the data set and are represented by the seasonal onshore offshore movement of sediment 60 and the multi year trend of shoreline rotation 14 the longer term trend of shoreline rotation appears to be related to larger scale bathymetric change an eof based decomposition technique is developed that is capable of estimating the shoreline position to within one standard deviation of the range of shoreline positions observed at most locations along the beach the foundation of the model is the observed relationship between the temporal amplitudes of the first eof mode and seasonally averaged offshore wave height as well as the linear trend of shoreline rotation this technique while not truly predictive because of the requirement of real time wave data is useful because it can predict shoreline position to within reasonable confidence given the absence of field data once the model is developed at a particular site

wave events climatology trends and relationship to northern hemisphere winter blocking and weather extremes abstractdiagnostics of finite amplitude local wave activity lwa are applied to the 500 hpa geopotential height field to diagnose persistent synoptic weather events of anomalously large wave activity in the northern hemisphere by considering the cyclonic and anticyclonic components of lwa separately persistent weather systems associated with large amplitude troughs and ridges are detected while anticyclonic wave events are predominantly found over europe and alaska cyclonic wave events usually occur over east asia and northeastern canada those preferred regions correspond to the location of planetary scale ridges and troughs which contribute together with transient anomalies to the formation of wave events although wave events are not blocking events per definition they are typically associated with increased blocking in their vicinity their spatial relationship to blocking however varies depending on their cyclonic or anticyclonic nature and the type of wave breaking signatures wave events

atmospheric blocking space time links to the nao and pna in the northern hemisphere regions characterized by an enhanced frequency of atmospheric blocking overlap significantly with those associated with the major extra tropical patterns of large scale climate variability namely the north atlantic oscillation nao and the pacific north american pna pattern there is likewise an overlap in the temporal band width of blocks and these climate patterns here the nature of the linkage between blocks and the climate patterns is explored by using the era 40 re analysis data set to examine 1 their temporal and spatial correlation and 2 the interrelationship between blocks and the nao pna it is shown that a strong anti correlation exists between blocking occurrence and the phase of the nao pna in the north atlantic western north pacific and that there are distinctive inter basin differences with a clear geographical over north atlantic and quantitative over north pacific separation of typical blocking genesis lysis regions during the opposing phases of the climate patterns an empirical orthogonal function eof analysis points to a significant influence of blocking upon the nao pattern identifiable as the leading eof in the euro atlantic and a temporal analysis indicates that long lasting blocks are associated with the development of negative nao pna index values throughout their life time in addition an indication of a cause and effect relationship is set out for the north atlantic linkage

a new rossby wave breaking interpretation of the north atlantic oscillation this paper proposes the hypothesis that the low frequency variability of the north atlantic oscillation nao arises as a result of variations in the occurrence of upper level rossby wave breaking events over the north atlantic these events lead to synoptic situations similar to midlatitude blocking that are referred to as high latitude blocking episodes a positive nao is envisaged as being a description of periods in which these episodes are infrequent and can be considered as a basic unblocked situation a negative nao is a description of periods in which episodes occur frequently a similar but weaker relationship exists between wave breaking over the pacific and the west pacific pattern evidence is given to support this hypothesis by using a two dimensional potential vorticity based index to identify wave breaking at various latitudes this is applied to northern hemisphere winter data from the 40 yr ecmwf re analysis era 40 and the events identified are then related to the nao certain dynamical precursors are identified that appear to increase the likelihood of wave breaking these suggest mechanisms by which variability in the tropical pacific and in the stratosphere could affect the nao

the non gaussianity and spatial asymmetry of temperature extremes relative to the storm track the role of horizontal advection abstractthe distribution of near surface and tropospheric temperature variability in midlatitudes is distinguishable from a gaussian in meteorological reanalysis data consistent with this warm extremes occur preferentially poleward of the location of cold extremes to understand the factors that drive this non gaussianity a dry general circulation model and a simple model of lagrangian temperature advection are used to investigate the connections between dynamical processes and the occurrence of extreme temperature events near the surface the non gaussianity evident in reanalysis data is evident in the dry model experiments and the location of extremes is influenced by the location of the jet stream and storm track the cause of this in the model can be traced back to the synoptic evolution within the storm track leading up to cold and warm extreme events negative temperature extremes occur when an equatorward propagating high low couplet high to the west strongly advects isotherms equatorward ove

morphology internal structure and reversal of asymmetry of large subtidal dunes in the entrance to gironde estuary france abstract the gironde is a macrotidal estuary characterized by important changes in tidal current velocity and river discharge two surveys were made in the lower estuary in june 1987 and october 1989 in an area with large dunes the symmetry of these dunes 1 5 6 7 m high changes from flood dominated in upstream areas to ebb dominated in downstream areas a transition zone consists of symmetrical dunes with a very low vertical form index the internal structure of the dunes revealed by seismic records shows a hierarchy of bounding surfaces related to fluctuations in movement speed and asymmetry of the dunes the lowest part of symmetrical dunes consists of ebb oriented reflectors while the upper part has flood oriented reflectors the same profile lines run in 1989 show that each large dune can be identified despite an upstream shift of the transition zone of about 1000 m comparison of seismic records shows that some lower reflectors are preserved between the two surveys and that the dunes moved downstream a mean distance of 30 m in 1989 the internal structure of symmetrical dunes was reversed with flood oriented reflectors in the lower part overlain by ebb oriented reflectors both seasonal changes in river discharge and fortnightly oscillations of the tidal range control the magnitude and orientation of the net bed load transport in the study area because the response time of the large dunes is longer than that of the superimposed small dunes the reversal of asymmetry of the large dunes requires a long period process while fortnightly oscillation or even semi iurnal reversal of the tidal current during spring tides could cause reversal of small dunes

anthropogenic influences on shoreline and nearshore evolution in the san francisco bay coastal system abstract analysis of four historical bathymetric surveys over a 132 year period has revealed significant changes to the morphology of the san francisco bar an ebb tidal delta at the mouth of san francisco bay estuary from 1873 to 2005 the san francisco bar vertically eroded an average of 80 cm over a 125 km 2 area which equates to a total volume loss of 100 52 million m 3 of fine to coarse grained sand comparison of the surveys indicates the entire ebb tidal delta contracted radially with the crest moving landward an average of 1 km long term erosion of the ebb tidal delta is hypothesized to be due to a reduction in the tidal prism of san francisco bay and a decrease in coastal sediment supply both as a result of anthropogenic activities prior research indicates that the tidal prism of the estuary was reduced by 9 from filling diking and sedimentation compilation of historical records dating back to 1900 reveals that a minimum of 200 million m 3 of sediment has been permanently removed from the san francisco bay coastal system through dredging aggregate mining and borrow pit mining of this total 54 million m 3 of sand sized or coarser sediment was removed from central san francisco bay with grain sizes comparable to the ebb tidal delta and its direct connection to the bay mouth removal of sediments from central san francisco bay may limit the sand supply to the delta and open coast beaches swan wave modeling illustrates that changes to the morphology of the san francisco bar have altered the alongshore wave energy distribution at adjacent ocean beach and thus may be a significant factor in a persistent beach erosion hot spot occurring in the area shoreline change analyses show that the sandy shoreline in the shadow of the ebb tidal delta experienced long term 1850s 1890s to 2002 and short term 1960s 1980s to 2002 accretion while the adjacent sandy shoreline exposed to open ocean waves experienced long term and short term erosion therefore the recently observed accelerating rates of bay sediment removal ebb tidal delta erosion and open coast beach erosion are all correlated temporally

development of subaqueous barchanoid shaped dunes due to lateral grain size variability in a tidal inlet channel of the danish wadden sea 1 high resolution bathymetry at centimeter scale accuracy acquired with a multibeam echo sounder system revealed the existence of barchanoid shaped large i e length 10 100 m to very large i e length 100 m dunes in the gradyb tidal inlet channel in the danish wadden sea the development of these dunes is due to an increase in dune celerity from 12 m yr in the center of the channel to around 30 m yr at the sides this increase in dune celerity can be explained by the fact that dune heights decrease from 3 1 m in the center of the channel to 1 4 m at the sides as a smaller sediment volume has to be moved per unit time for equal dune celerity water depth is uniform across the channel likewise high resolution acoustic doppler current profiler measurements across the channel showed a uniform distribution of both ebb and flood flow thus no correlation between dune dimensions and water depth or flow velocity was established instead high accuracy bed sampling along the crests of the dunes showed a decrease in mean grain size from 0 63 mm in the center to 0 36 mm at the sides of the channel the decrease in dune height is ascribed to this decrease in grain size given that flow depth and flow velocity are uniform across the channel the lateral decrease in grain size is suggested to result from sorting effects by secondary currents directed from the center toward the sides of the channel in the trough lee side region of the barchanoid shaped dunes

rates and mechanisms of shoreface progradation and retreat downdrift of the amazon river mouth field surveys of the 350 km shoreline adjacent to the amazon river mouth reveal three distinct types erosional mud accretionary sand and accretionary mud formation of these zones is controlled by the delivery of amazon suspended sediment mediated by the hydrodynamic regime erosional mud shorelines extend from rio araguari near the amazon river mouth northwestward 280 km to 3 5 n near cabo cassipore shoreface 5 m water depth retreat annually yields 1 4 106 tons of fine grained sediment deposited during an earlier phase of shoreface progradation sandbodies up to 5 m thick overlie erosional mud shorefaces for 10 30 km downdrift of small rivers the sand is supplied from these rivers and released by shoreline retreat of the river mouth areas amazon river sand is restricted in the coastal zone from its mouth north to the cabo norte shoal area where it mixes with sand carried by rio araguari from the guiana highlands north of 3 5 n mud aggradation and progradation is taking place on underconsolidated low gradient tidal flats backed by mangrove swamps 210pb and 14c geochronology of vibracores from the mudflats indicate that sediment accumulation is rapid 0 24 2 0 cm yr landward of the 2 m isobath supplied from a thick 50 150 cm seasonal surface layer shoreface progradation is episodic separated by decadal hiatuses fine grained suspended sediment flux from the amazon and minor amounts of sand and mud from the local rivers supply sediment to the mudflats shore normal tidal currents and solitary waves rework the surface mud layer preferentially transporting available sand landward into the mangrove fringe and producing very fine grained accumulation on the tidal flat 10 12 mean grain size lateral accretion of features 10 100 km long termed mudcapes produces tens of kilometers of seaward coastal plain addition along the northern coast similar features are identified downdrift along the guianas coast as far as the orinoco river 1600 km the northern amapa shoreface deposits are a locus of modern sediment accumulation which progrades over subaqueous deltaic strata

integration of bed characteristics geochemical tracers current measurements and numerical modeling for assessing the provenance of beach sand in the san francisco bay coastal system abstract over 150 million m3 of sand sized sediment has disappeared from the central region of the san francisco bay coastal system during the last half century this enormous loss may reflect numerous anthropogenic influences such as watershed damming bay fill development aggregate mining and dredging the reduction in bay sediment also appears to be linked to a reduction in sediment supply and recent widespread erosion of adjacent beaches wetlands and submarine environments a unique multi faceted provenance study was performed to definitively establish the primary sources sinks and transport pathways of beach sized sand in the region thereby identifying the activities and processes that directly limit supply to the outer coast this integrative program is based on comprehensive surficial sediment sampling of the san francisco bay coastal system including the seabed bay floor area beaches adjacent rock units and major drainages analyses of sample morphometrics and biological composition e g foraminifera were then integrated with a suite of tracers including 87sr 86sr and 143nd 144nd isotopes rare earth elements semi quantitative x ray diffraction mineralogy and heavy minerals and with process based numerical modeling in situ current measurements and bedform asymmetry to robustly determine the provenance of beach sized sand in the region

a study of the dynamics of a marine sandwave the movement of the crest of a sandwave was studied using cross sectional profiles obtained from lines of sea bed reference stakes measurements were made over a six month period before and after flood and ebb tides in relation to both spring and neap tides and surface wave conditions additional observations were obtained on a daily basis over an equinoctial neap to spring to neap tidal period in conjunction with boundary layer flow measurements tracer experiments were conducted to study the dispersion of sediment from the sandwave crest the results showed that the sandwave was relatively stable at neap tides whilst at higher tidal ranges the crest position oscillated with successive flood and ebb tides net flank erosion occurred on the less steep upstream slope during the dominant ebb tide this together with increased deposition on the lee slope caused the crest to advance it was not possible to extrapolate sandwave migration over long periods as the tidal dynamic trends were interrupted by wind stress and surface wave activity high particle orbital velocities generated at the sea bed by storm waves caused major reductions in crestal heights calculated volumes of sediment eroded and accreted were used with boundary layer flow measurements to calculate threshold velocities for the movement of the sediment and sediment transport rates

the genesis of an inter field marine sandwave and the associated anti asymmetry migration of neighboring crests 1 a series of high resolution multibeam echo sounding surveys near san francisco ca suggests the occasional migration of marine sandwave crests in the direction opposite to that indicated by the shape asymmetry of the individual sandwaves in contrast to all previous observations of the relationship between bedform shape asymmetry and migration the anti asymmetry migration occurs over approximately the same time period that a new sand wave crest is formed within the large and relatively stable field the new sandwave crest appears approximately midway between two larger crests in the vicinity of structural defects in a nearly two dimensional portion of the field the sandwaves in the vicinity of the new crest are found to have migrated away from the new crest regardless of their shape asymmetry later a large section of the new crest disappears and the neighboring sandwaves migrated back toward the vacated crest location this migration occurs for sandwaves up to at least ten wavelengths away from the new crest

multibeam bathymetric investigations of the morphology of sand ridges and associated bedforms and their relation to storm processes sable island bank scotian shelf abstract storm formed sand ridges are important morphologic features occurring on many continental shelves of the world our understanding of the morphology migration and the controlling processes over this type of sand ridges under different environmental settings is still limited in the present study an integrated approach of combining multibeam bathymetry survey seabed sampling sidescan seismic surveys and seabed instrumentation measurements was used to characterize the surficial geology and morphology of offshore sand ridges on sable island bank scotian shelf and to evaluate the relationship between sand ridge morphology migration and the storm processes on this storm dominated outer shelf bank multibeam data obtained at selected sites demonstrated the series of ne sw oriented sand ridges with an average height of 4 3 m and wavelength of 1 5 km sand ridges attain maximum spacing height and steepness in the intermediate depths sand ridge size and steepness also decrease from west to east and this decrease is correlated with decreasing dynamic condition sediment grain size and depth sand ridge profiles show weak easterly asymmetry this morphological asymmetry augments the sediment texture and grain size asymmetry to suggest eastward long term sand ridge migration and net sediment transport in the study area sand ridge asymmetry also shows strong local variation and the number of sand ridges asymmetric to the west is nearly equal to that asymmetric to the east the likely cause is the nearly equal number of major storms passing to the south versus to the north of the island so that the westerly and easterly peak storm driven currents associated with these storm path scenarios affect equally the sand ridges on sable island bank a suite of smaller bedforms were found superimposed on the sand ridges sand waves widely superimposed on both flanks of sand ridges mixed 2d and 3d megaripples commonly occurring in the sand ridge troughs and on the lower western flanks and large wave ripples ubiquitously found in the troughs of all megaripples surficial sediment is coarsest coarse sand with shell fragments in the sand ridge trough and becomes progressively finer eastward toward the sand ridge crest and down the eastern flank while best sorting occurs near the sand ridge crest box cores collected across sand ridges reveal characteristic storm event bed structure that reflects the development and migration of bedforms with the evolution of storms

simple models for the shape and symmetry of tidal sand waves 1 statically stable equilibrium forms abstract tidal sand waves are divisible between dynamically and statically stable equilibrium types statically stable equilibrium forms take that cross sectional shape in relation to prevailing tidal currents such that bedload transport just fails to occur at every point on the surface given that the bed material entrainment threshold is a function of bed slope this shape is calculated to be 1 symmetrical and convex up under a symmetrical tidal current and 2 asymmetrical and locally concave up under an asymmetrical flow the longer side of the bedform facing in the direction of the residual current sand waves similar to theoretical statically stable forms occur near the edge of the continental shelf off the eastern u s a knebel and folger 1976 the bedforms are today found in a substantial water depth and are being affected by only weak currents the structures containing sediment dating from the early flandrian appear to be relict and could represent a modification of originally dynamically stable forms brought about as the sea deepened and currents weakened during the post glacial sea level rise

sand wave migration predictor based on shape information 1 migration of offshore seabed waves which endangers the stability of pipelines and communication cables is hard to measure the migration rates are small compared to the measurement errors here sandwave migration rates are determined from the change in the crest position deduced from long time series of bathymetric echo sounding data the crests are identified as local extremes in a bathymetric profile after low pass filtering this approach is applied to both two dimensional data and to profiles along pipelines a consistent migration rate of several meters per year is found a strong correlation between the sandwave shape and the migration rate is translated in a migration predictor the predictor assumes that the sandwaves migrate in the direction of the steepest slope following a quadratic relation with the asymmetry furthermore it is included that longer waves travel faster but higher waves travel slower the predictor is calibrated against data from nine areas and validated using three additional areas an error analysis using markers shows that the error of the predictor is small compared to the noise in the individual crest position observations

new stratospheric dust belt due to the chelyabinsk bolide 1 the ozone mapping profiler suite omps limb profiler lp on the recently launched nasa noaa npp suomi satellite detected aerosol excess in the mid stratosphere 25 45 km altitude between 50 n and 70 n latitudes omps lp observations trace this aerosol plume to the meteor that struck near chelyabinsk russia on 15 february 2013 this new dust layer located above the junge aerosol layer has persisted over at least a 3 month period material collected on the ground following the bolide explosion showed that the meteor was mostly composed of olivine and pyroxenes simulations using lagrangian and eulerian atmospheric models trace the plume back to chelyabinsk and confirm that the plume altitude was at altitudes between 25 and 45 km the models also confirm the plume circumpolar longitudinal spreading observed by omps lp with propagation speeds up to 85 m s

sand waves and sediment transport around the end of a tidal sand bank two detailed surveys have been made of the north western end of the haisborough sand off the norfolk coast using echosounder 3 5 khz reflection profiler and side scan sonar asymmetrical sand waves indicate north westerly sand movement on the southern side and south easterly sand movement on the steeper northern side of the bank secondary superimposed megaripples which are probably better indicators of sediment movement give evidence of a cross bank component between the north westerly and south easterly facing sand waves on the tip of the bank there is a zone of symmetrical sand waves these are usually taken to indicate zero net transport but in this case the oblique orientation of megaripples in their troughs indicates transport parallel to the sand wave crests this suggests the route by which sand travels around the end of the bank to form a roughly closed circulation sediment textural parameters support the notion that sand is winnowed from the foot of the bank on both sides and is transported to the middle with an overall net transport from the south to the north analysis of charts dating back to 1886 shows that the bank is stable within the error limits of position fixing though that could allow more than 0 25 km shift to the north east in 100 years to pass undetected a box model is drawn up for the estimated sediment fluxes around the end of the bank and implications for residence times and circulation rates are drawn from it