diagnosis of the downstream ridging associated with extratropical transition using short term ensemble forecasts abstract the dynamical mechanisms that led to downstream ridging during the extratropical transition et of typhoons tokage and nabi are evaluated using data drawn from a cycling ensemble kalman filter coupled with the weather research and forecasting model wrf during both transitions the ensemble covariances indicate that the 350 k potential vorticity pv at the apex of the ridge which is used to define the ridge structure is proportional to the amount of precipitation along the baroclinic zone to the northeast of the tropical cyclone tc and at some times to the upper tropospheric divergence above the tropical cyclone multivariate regression calculations indicate that the frontal precipitation has the largest impact on the ridge amplitude and area during tokage s transition while the tc divergence has roughly equal impact during some times of nabi s transition the amount of precipitation along the baroclinic zone is modulated by the lower tropospheric frontogenesis and moisture flux on the

holocene floodplain soils along the rio mamore northern bolivia and their implications for understanding inundation and depositional patterns in seasonal wetland settings abstract the llanos de moxos lm in the bolivian amazon basin host one of the largest seasonally inundated savannah landscapes on earth very little is known of this area with regard to sedimentary dynamics soil formation or their relationship to longer term climatic and hydrological variability in this setting here we present a detailed study of three floodplain depositional sequences building up the inundation savannah along the mamore river in the central lm pleistocene sands and silts unit 1 are overlain by thick overbank deposits of mostly holocene age unit 2 on both sides of the mamore river and underline the importance of extensive flooding processes for the late quaternary sedimentary and geomorphic evolution of the lm the fine grained distal overbank sediments show signs of strong modification by hydromorphic processes and reflect spatial and temporal variations in flood inundation patterns in addition widespread dark gray to blackish soil and paleosol horizons are intercalated with the overbank sediments but lack evidence for significant weathering these horizons are likely the result of cumulative incorporation of organic material under conditions of particularly low sedimentation rates therefore their formation should be linked to processes such as channel migration longer term meanderbelt evolution avulsive drainage reorganization changes in sediment supply or climatically induced variations in flooding type frequency or magnitude the common occurrence of these floodplain soils in the early to mid holocene may thus reflect the combined effects of hydrological geomorphic and sedimentary changes during a drier mid holocene

geomorphology and evolution of the late pleistocene to holocene fluvial system in the south eastern llanos de moxos bolivian amazon in the bolivian amazon several paleochannel generations are preserved their wide spectrum of morphologies clearly provides crucial information on the type and magnitude of geomorphic and hydrological changes within the drainage network of the andean foreland therefore in this study we mapped geomorphological characteristics of paleochannels and applied radiocarbon and optically stimulated luminescence dating seven paleochannel generations are identified significant changes in sinuosity channel widths and river pattern are observed for the successive paleochannel generations our results clearly reflect at least three different geomorphic and hydrological periods in the evolution of the fluvial system since the late pleistocene changes in discharge and sediment load may be controlled by combinations of two interrelated mechanisms i spatial changes and re organizations of the drainage network in the upper catchment and or ii climate changes with their associated local to catchment scale modifications in vegetation cover and changes in discharge inundation frequencies and magnitudes which have likely affected the evolution of the fluvial system in the llanos de moxos in summary our study has revealed the enormous potential which geomorphic mapping and analysis combined with luminescence based chronologies hold for the reconstruction of the late pleistocene to recent fluvial system in a large portion of amazonia

potential vorticity in hurricane gloria abstract potential vorticity pv analysts for hurricane gloria of 1985 are derived from nested objective wind analyses of omega dropwindsonde and airborne doppler radar data the analyses resolve eyewall scale features in the inner vortex core and embed analyses of these features within the larger scale environment since three dimensional geopotential height fields required for evaluation of pv are not available in the core they are derived using the balance equation in the process of deriving the heights the degree of gradient balance is evaluated the 500 mb tangential winds in the core averaged azimuthally on the four cardinal points are close to gradient balance outside the radius of maximum wind the resulting depiction of pv is the first presented for a real hurricane due to data deficiencies immediately outside the doppler region as well as inside the eye smoothing of the wind data using a filter with a minimum 25 km spatial scale is required to derive a balanced geopotential height distr

an analysis of hurricane opal s forecast track errors using quasigeostrophic potential vorticity inversion abstract hurricane opal s landfall in october 1995 forms the basis of a serious hurricane forecast problem the potential for hurricane conditions over land with insufficient warning time official national hurricane center nhc a division of the tropical prediction center forecasts predicted landfall and passage inland over the eastern united states at a later time than observed because of underestimation of the northward component of the steering flow by the national centers for environmental prediction s ncep operational models and other hurricane track models the goal of this paper is to isolate the cause of the poor forecast of meridional storm motion in ncep s early eta model by using quasigeostrophic potential vorticity qgpv inversion qgpv inversion permits decomposition of the steering flow into contributions from different synoptic scale features the inversion procedure is applied to the eta analysis and 48 h eta forecast valid at 1200 utc 5 october 1995 analyses from the european centre

measuring flow velocity and sediment transport with an acoustic doppler current profiler an acoustic doppler current profiler adcp measures three dimensional velocity profiles within the water column using the doppler shift principle whilst the bottom tracking function and acoustic backscatter can be used to measure bed load velocity and estimate suspended sediment concentration the adcp offers many advantages over traditional single point current meters and sediment samplers including deployment from a moving launch a single instrument for both velocity and sediment transport measurements profiles of three dimensional velocity and suspended sediment and the ability to map an entire flow field limitations of adcps include a large sampling diameter close to the bed coarse measurement of vertical velocity fragmented bottom track records a poor understanding of the relation between bottom tracking and the mechanisms of sediment transport and sensitivity of the acoustic backscatter to particle size

the integrated effect of condensation in numerical simulations of extratropical cyclogenesis abstract by combining traditional sensitivity studies with techniques that focus on the conservation and invertibility properties of ertel s potential vorticity pv we illustrate the effect of latent heating on the structure and evolution of three simulated extratropical cyclones the cases include one continental cyclone development 15 december 1987 which we examine extensively and two cyclones over the western atlantic ocean 6 january 1983 and 5 january 1985 of somewhat greater intensity which are diagnosed to assess the generality of our findings for the continental case each storm featured a weaker cyclonic low level circulation when latent heating was removed from the simulation but the magnitude of the effect varied greatly in all cases the difference in intensity was attributed to velocities associated with a positive condensation produced pv anomaly above the warm front the amplification of the surface thermal perturbations was not strongly altered in even the case most affected by

interannual and decadal cycles in river flows of southeastern south america abstract the time series of annual streamflow of four rivers in southeastern and south central south america the negro paraguay parana and uruguay rivers for the period 1911 93 are analyzed application of the multitaper method shows that the following features are significant at the 95 level 1 a nonlinear trend 2 a near decadal component and 3 interannual peaks with enso timescales the trend and near decadal components are most marked in the two more central rivers the paraguay and parana with enso timescale variability most pronounced in the negro and uruguay rivers in the southeast composites of sst are made for each of the statistically significant oscillatory components of river flow by reconstructing each component using singular spectrum analysis these composites confirm the influence of enso on the streamflow variability of the negro and uruguay rivers with el nino associated with enhanced streamflow on the decadal timescale high river runoff is associated with anomalously coo

the impact of extratropical transition on the downstream flow an idealized modelling study with a straight jet the interaction of a tropical cyclone undergoing extratropical transition et with the midlatitude synoptic scale flow is investigated using full physics numerical experiments with idealized initial conditions the emphasis is on the impact on the midlatitude flow downstream of the et event the midlatitude flow is represented by a balanced straight jet stream as the tropical cyclone approaches the jet a ridge trough couplet and a distinct jet streak form in the upper level flow a midlatitude cyclone develops rapidly downstream of the et system and the further evolution is characterized by downstream baroclinic development based on hovmoller diagrams the upper level development is interpreted as the excitation and subsequent dispersion of a rossby wave train on the potential vorticity gradient associated with the jet the characteristics of this wave train are sensitive to the structure of the jet and to moist processes in the midlatitudes the tropical cyclone undergoing et acts as a sustained forcing for the wave train and the structure of the et system impacts the development most significantly one to two wavelengths downstream of et piecewise inversion of potential vorticity complemented by the partitioning of the flow into its rotational and divergent parts is applied to assess the impact of the et system quantitatively both the cyclonic circulation and the outflow of the tropical cyclone are important contributors to the formation and amplification of the ridge trough couplet the outflow anomaly reduces the eastward motion of the ridge trough couplet significantly and thus promotes phase locking between the tropical cyclone and the upper level pattern copyright 2008 royal meteorological society

the resonant interaction of a tropical cyclone and a tropopause front in a barotropic model part ii frontal waves abstract the influence of frontal waves on the interaction of a tropical cyclone and a tropopause front is investigated in an idealized framework in a nondivergent barotropic model the front is represented by a vorticity step with a superimposed sinusoidal perturbation this gives rise to a jet that meanders to the north and south and can be viewed as a sequence of upper level troughs and ridges the model evolution depends sensitively on the position of the cyclone relative to the troughs and ridges here a bifurcation point is identified that is located on the trough axis at a distance where the zonal speed of the background flow equals the phase speed of the wave arbitrarily small displacements from this position determine whether a cyclone is advected toward the front or repelled only a limited range of wavelengths can lead to track bifurcations the largest effects are obtained for resonant frontal waves propagating with a phase speed matching the initial zonal translation speed of the cyclone we

a new geophone device for understanding environmental impacts caused by gravel bedload during artificial floods here to assess the contribution of gravel bedload on the removal of attached algae and aquatic plants from a cobble bed river during small floods we propose a geophone type method for measuring the local bedload of non uniform sized gravel due to limited peak discharge for focused events during our study a large fraction of bed material here cobbles was immobile and only a small fraction of bed material sand and gravel was expected to be transported during the flushing flows we analyzed the device we developed has a size equivalent to immobile bed material and a shape similar to bed material rounded cobbles at the site the instrument s design allows avoidance of disturbances in river bed micro topography during installation and local bedload transport during floods a flume experiment was conducted in order to establish an empirical algorithm for estimating the diameter of impacted gravel and here discuss uncertainty related to diameter estimations the proposed method was utilized to quantify gravel bedload in a cobble bed river during flushing flows in the text we also discuss the contribution of measured gravel bedload during flushing flows on the removal of attached algae up to a 37 reduction in chlorophyll a density and aquatic plants a reduction of 38 in dry mass per area based on time variation for the measured gravel bedload we also suggest the propagation of a bed form composed of the fine sediment fraction migrating on immobile larger sediment and implications for the propagation of the fine sediment wave for attached algae removal this article is protected by copyright all rights reserved

the ohio valley wave merger cyclogenesis event of 25 26 january 1978 part ii diagnosis using quasigeostrophic potential vorticity inversion abstract the dynamical interactions between precursor disturbances during the wave merger cyclogenesis event of 25 26 january 1978 over eastern north america are diagnosed using quasigeostrophic potential vorticity qgpv inversion this case is characterized by two prominent preexisting upper level disturbances that induce rapid surface cyclogenesis as they come into close proximity static qgpv inversion is used to attribute a particular geopotential height field to the qgpv associated with each precursor disturbance the full flow is partitioned into the following components the northern upper precursor the southern upper precursor and the background flow prognostic qgpv inversion is used to quantify the instantaneous geopotential height tendencies attributable to each of these flow components the static inversion results for the upper precursors exhibit the structure of baroclinic vortices with maximum amplitude near the tropopause during the 48 h period spanning the period of study of this even

interaction of a baroclinic vortex with background shear application to hurricane movement abstract most extant studies of tropical cyclone movement consider a barotropic vortex on a plane however observations have shown that real tropical cyclones are strongly baroclinic with broad anticyclones aloft also the distribution of the large scale potential vorticity gradient in the tropical atmosphere is very nonuniform these properties may substantially influence the movement of such storms note that the anticyclone above a hurricane will interact with the lower hurricane vortex and induce storm motion such interaction can be caused by both the direct effect of ambient vertical shear and the effect of vertical variation of the background potential vorticity gradient in this paper an attempt to isolate the effect of background vertical shear is made the hurricane is represented in a two layer quasigeostrophic model as a point source of mass and zero potential vorticity air in the upper layer collocated with a point cyclone in the lower layer the model is integrated by the method of co

external influences on hurricane intensity part iii potential vorticity structure abstract the interaction of hurricane elena 1985 with a baroclinic wave was reexamined using both potential vorticity pv and a formulation for eliassen palm fluxes in cylindrical coordinates the hurricane began to deepen rapidly as a narrow upper level positive pv anomaly became nearly superposed over the low level center the intensification appeared to represent an evaporation wind feedback activated by constructive interference of the pv anomalies enhanced convection associated with this process eroded the upper pv anomaly and prevented it from crossing the hurricane and reversing the intensification the eliassen palm flux divergence showed that maximum eddy activity remained in the upper troposphere prior to the reintensification this activity was produced in part because the action of the outflow anticyclone of the hurricane contributed to synoptic scale wave breaking the upper level pv anomaly that approached the center was much narrower in extent than the original synoptic scale trough th

quantification of variability in bedform geometry we analyze the variability in bedform geometry in laboratory and field studies even under controlled steady flow conditions in laboratory flumes bedforms are irregular in size shape and spacing also in case of well sorted sediment our purpose is to quantify the variability in bedform geometry we use a bedform tracking tool to determine the geometric variables of the bedforms from measured bed elevation profiles for each flume and field data set we analyze variability in 1 bedform height 2 bedform length 3 crest elevation 4 trough elevation and 5 slope of the bedform lee face each of these stochastic variables is best described by a positively skewed probability density function such as the weibull distribution we find that except for the lee face slope the standard deviation of the geometric variable scales with its mean value as long as the ratio of width to hydraulic radius is sufficiently large if the ratio of width to hydraulic radius is smaller than about ten variability in bedform geometry is reduced an exponential function is then proposed for the coefficients of variation of the five variables to get an estimate of variability in bedform geometry we show that mean lee face slopes in flumes are significantly steeper than those in the field the 95 and 98 values of the geometric variables appear to scale with their standard deviation the above described simple relationships enable us to integrate variability in bedform geometry into engineering studies and models in a convenient way

postlandfall tropical cyclone reintensification in a weakly baroclinic environment a case study of hurricane david september 1979 abstract an analysis is conducted from a potential vorticity pv perspective of the reintensification of tropical storm david over the northeastern united states in september 1979 david a major long lived hurricane originated near the cape verde islands in late august 1979 it made final landfall in georgia on 4 september 1979 and weakened rapidly thereafter the noteworthy aspect of david was its subsequent reintensification approximately 27 h after landfall as a warm core disturbance in a weakly baroclinic environment in this regard the redevelopment of david is unlike the classical extratropical transformation of a tropical storm in a strongly baroclinic environment that has been documented in the literature the authors analysis of the evolution of the dynamical tropopause subsequent to storm landfall revealed that david reintensified in response to tropopause lifting upward displacement of the dynamic tropopause ahead of a nondeepening and otherwise very weak upper tropospheric disturbance

bedform movement recorded by sequential single beam surveys in tidal rivers abstract a portable system for bedform mapping was evaluated in the delta of the lower sacramento and san joaquin rivers california from 1998 to 2000 bedform profiles were surveyed with a two person crew using an array of four single beam transducers on boats about 6 m in length methods for processing the bedform profiles into maps with geographic coordinates were developed for spreadsheet programs and surface contouring software straight reaches were surveyed every few days or weeks to determine locations of sand deposition net transport directions flow thresholds for bedform regimes and bedform transport rates in one channel of unidirectional flow the portable system was used to record changes in bedform regime through minor fluctuations of low discharge and through high discharges near channel capacity in another channel with reversing flows from tides the portable system recorded directions of net bedload transport that would be undetectable by standard bedload sampling alone

bed load discharge coefficient using dimensional analysis the bed load discharge coefficient for the case of two dimensional flow over dunes is expressed in terms of bed form geometry and the sand size of the bed material experiments are conducted in a rectangular flume using artifical dunes and a flow visualization method to measure the flow separation length from which the bed load coefficients were determined the results show that the bed load coefficient is affected significantly by sand grain size only when the dunes are flat when dunes are steep the value of the bed load coefficient is affected mainly by the dune steepness application of the bed load coefficient results in some improvement of estimating bed load

nature of deformation of sandy bed forms 1 we explore a stochastic component of topographic evolution of sandy river beds and its relationship to bed material flux the behavior of trains of mobile bed forms can be decomposed into two independent constituents translation and deformation translation is the mean downstream migration of the bed at velocity that defines the lagrangian reference frame of the bed deformation is the sum of all changes to the bed s topographic profile measured from within the bed s moving reference frame the occurrence of deformation leads to exponential decorrelation of bed topography that is in dynamic equilibrium with flow conditions for the field and laboratory data sets used correlation decays to 0 5 by the time the bed translates 40 and 360 of the mean bed form length respectively proportions of bed material flux responsible for translation and deformation can be straightforwardly calculated translation flux is measured using the traditional bed form bed load equation deformation flux is determined by excess topographic change scaled by the ratio of horizontal sediment velocity to fall velocity deformation represents the sediment exchanged between bed load and suspended load because deformation is a stochastic process with zero mean the apparent rate of deformation decreases as a function of time interval between bed surveys for the field case deformation accounts for 40 of bed material flux while it is only 1 of the flux in the laboratory

evolution of the upper tropospheric outflow in hurricanes iselle and julio 2014 in the navy global environmental model navgem analyses and in satellite and dropsonde observations upper tropospheric outflow was examined during the life cycles of two hurricanes in the eastern and central pacific ocean the outflow from hurricanes iselle and julio was evaluated using analyses from the navy global environmental model navgem which were very highly correlated with satellite atmospheric motion vector amv and noaa g iv dropsonde observations a synoptic overview provided the environmental context for the lifecycles of both tropical cyclones tcs then the outflow magnitude and direction within 6 radial degrees of each tc center were analyzed in relation to tc intensity the synoptic environment and inertial stability with the following results in both iselle and julio the azimuthally averaged outflow magnitude was maximized initially more than 4 radial degrees from the center and that maximum moved steadily inward during a 4 day intensification period and reached a position radially inward of 2 degrees within 6 h of the time of maximum surface winds furthermore the direction of the outflow in both tcs was related to the evolution of the large scale upper tropospheric flow pattern particularly the phasing of subtropical jet ridges and troughs moving eastward north of both tcs finally outflow channels were consistently bounded by regions of lowest highest values of inertial stability counterclockwise clockwise from the maximum outflow azimuth a pattern that persisted throughout the life cycles of both storms regardless of intensity environmental flow and the number and direction of outflow channels present

a potential vorticity based study of the role of diabatic heating and friction in a numerically simulated baroclinic cyclone abstract a particularly intense case of western atlantic baroclinic cyclogenesis was investigated in this study specifically the roles of latent heat of condensation and surface friction were examined from the potential vorticity or pv thinking perspective the methodology used for this study involves three key components 1 a full physics mesoscale model which provides a continuous and dynamically consistent dataset and provides full user control over physical processes 2 a partitioned pv integration which temporally integrates the accumulation of pv due to various physical processes in the model s eulerian framework and 3 the piecewise inversion method of davis and emanuel which calculates the balanced wind and mass field associated with particular pv anomalies potential vorticity features obtained through the partitioned integration technique were inverted to yield their direct contributions to the total circulation in addition sensitivity studies were carried out to determine the overal

tropical storm formation in a baroclinic environment abstract an analysis is presented of the large scale conditions associated with the initial development of tropical storm diana september 1984 in a baroclinic environment ordinary extratropical wave cyclogenesis began along an old frontal boundary east of florida after 0000 utc 7 september and culminated in tropical cyclogenesis 48 h later water vapor satellite imagery showed that the initial cyclogenesis and incipient tropical storm formation was nearly indistinguishable from a classical midlatitude development cyclogenesis occurred in three stages a large scale cold trough and associated frontal system crossed the atlantic coast while a small potential vorticity maximum aloft fractured off the main trough and stalled over central florida in the first stage as the main trough sheared off eastward cyclogenesis began along the southwestern end of the stalled frontal zone east of florida anticyclogenesis to the north in the wake of the shearing trough allowed a surge of cooler and drier air to flo

tropical cyclone track sensitivity in deformation steering flow abstractprevious studies have suggested that tropical cyclones tcs in deformation steering flows can be associated with large position errors and uncertainty the goal of this study is to evaluat

tropical cyclone movement and surrounding flow relationships abstract this paper presents results of a comprehensive study of the relationship between the movement of tropical cyclones and the large scale circulation which surrounds them cyclones have been stratified by direction and speed of movement latitude intensity change and size as determined by the radius of the outermost closed surface isobar in three ocean basins the northwest pacific the west atlantic and the australian south pacific region twenty one different stratifications are available in the northwest pacific 13 in the west atlantic and 6 in the australian south pacific area cyclone movement and surrounding flow relationships were studied at different pressure levels and a variety of radii pressure weighted layer averages were also analyzed in search of such relationships results show an important relationship between surrounding large scale flow and tropical cyclone movement for all stratifications the winds in the mid troposphere 500 700 mb at 5 7 latitude radius from the cyclone

rossby wave packets on the midlatitude waveguide a review abstractrossby wave packets rwps are rossby waves for which the amplitude has a local maximum and decays to smaller values at larger distances this review focuses on upper tropospheric transient rwps along the midlatitude jet stream their central characteristic is the propagation in the zonal direction as well as the transfer of wave energy from one individual trough or ridge to its downstream neighbor a process called downstream development these rwps sometimes act as long range precursors to extreme weather and presumably have an influence on the predictability of midlatitude weather systems the paper reviews research progress in this area with an emphasis on developments during the last 15 years the current state of knowledge is summarized including a discussion of the rwp life cycle as well as rossby waveguides recent progress in the dynamical understanding of rwps has been based in part on the development of diagnostic methods these methods include algorithms to identify and track rwps

improved estimation of adcp apparent bed load velocity using a real time kalman filter an estimate of apparent bed load velocity v can be derived from the difference between differential global positioning system dgpss and acoustic doppler current profiler adcp bottom track bt measurements when bt is biased by a moving bottom a kalman filter has been developed to integrate gps and bottom track data to improve estimation of boat velocity during adcp measurements under moving bed conditions rennie and rainville 2008 j hydraulic eng in review the boat velocity estimated using the kalman filter is superior to boat velocity from raw gps data in this paper we assess the improvement in estimation of v using the kalman filter as opposed to raw gps data specifically a synthetic moving bed bias was generated for 22 repeat transects of the gatineau river quebec the synthetic moving bed bias had mean variance and distribution across the section as typically observed during bed load transport conditions and had the advantage that it was known explicitly the errors in estimated

probability distributions of particle hop distance and travel time over equilibrium mobile bedforms the joint probability distribution of streamwise particle hop distance lateral particle hop distance and travel time constrains the relationships between topographic change and sediment transport

a three dimensional analysis of the outflow layer of supertyphoon flo 1990 abstract isentropic coordinate analyses of rawinsondes and cloud motion wind vectors derived from geostationary satellite imagery are employed to describe the three dimensional upper tropospheric and lower stratospheric circulation attending western north pacific supertyphoon flo during september 1990 outflow from the storm is concentrated in several evolving channels in the horizontal in terms of vertical structure net outflow evaluated at 6 latitude 666 km radius is found to occur at higher levels and over an increasing range of potential temperature as the tropical cyclone intensifies outflow on the equatorward side of the tropical cyclone tends to occur at greater values higher altitudes than poleward outflow potential vorticity also decreases within the corresponding isentropic layers associated with the outflow the implications of the vertical variability of outflow structure in terms of the interactions between storm and environment and effects on storm structural changes are consi

diagnosis of the source of gfs medium range track errors in hurricane sandy 2012 abstractmedium range forecasts of hurricane sandy s track were characterized by widely diverging solutions with some suggesting that sandy would make landfall over the mid atlantic region of the united states while others forecast the storm to move due east to the north of bermuda here dynamical processes responsible for the eastward tracking forecasts are diagnosed using an 80 member ensemble of experimental global forecast system gfs forecasts initialized five days prior to landfall comparing the ensemble members with tracks to the east against those with tracks to the west indicates that the eastern members were characterized by a lower amplitude upper tropospheric anticyclone on the poleward side of sandy during the first 24 h of the forecast which in turn was associated with a westerly perturbation steering wind the amplification of this ridge in each set of members was modulated by differences in the advection of potential vorticity pv by the irrotational wind associated with sandy s seco

passive acoustic monitoring of bed load discharge in a large gravel bed river surrogate technologies to monitor bed load discharge have been developed to supplement and ultimately take over traditional direct methods our research deals with passive acoustic monitoring of bed load flux using a hydrophone continuously deployed near a river bed this passive acoustic technology senses any acoustic waves propagated in the river environment and particularly the sound due to interparticle collisions emitted during bed load movement a data set has been acquired in the large alpine gravel bedded drau river analysis of the short term frequency response of acoustic signals allows us to determine the origin of recorded noises and to consider their frequency variations results are compared with ancillary field data of water depth and bed load transport inferred from the signals of a geophone array hydrophone and geophone signals are well correlated thanks to the large network of deployed geophones analysis of the spatial resolution of hydrophone measurements shows that the sensor is sensitive to bed load motion not only locally but over distances of 5 10 m 10 20 of river width our results are promising in terms of the potential use of hydrophones for monitoring bed load transport in large gravel bed rivers acoustic signals represent a large river bed area rather than being local hydrophones can be installed in large floods they can be deployed at a low cost and provide continuous monitoring at high temporal resolution

the extratropical transition and precipitation distribution of hurricane floyd 1999 abstract several recent landfalling tropical cyclones e g dennis floyd and irene 1999 have highlighted a need for a refinement in the forecasting paradigms and techniques in the area of quantitative precipitation forecasting floyd proved to be a particularly challenging forecast problem as it was accompanied by catastrophic flooding over large regions of the east coast in spite of its relatively quick northward movement the extent and intensity of the precipitation distribution was strongly modulated by the storm s interaction with a midlatitude trough in an attempt to better understand and quantify the relevant dynamics during this interaction potential vorticity pv and quasigeostrophic perspectives are utilized as floyd approached the east coast precipitation shifted to the left of the storm track due to the presence of a deep midlatitude trough in the ohio valley the juxtaposition of a cold core pv anomaly associated with the midlatitude trough and a warm core pv anomaly associated with

the ohio valley wave merger cyclogenesis event of 25 26 january 1978 part i multiscale case study abstract the long standing observational view of cyclogenesis involves an interaction between tropopause and surface based finite amplitude disturbances there are however instances where more than one upper level disturbance contributes to low level development a subset of these events involves wave or trough merger which has been defined as the amalgamation of two or more distinct 500 hpa vorticity maxima an example of this phenomenon involving a case of very intense continental cyclogenesis 25 26 january 1978 over the eastern united states is selected to elucidate the origin and evolution of precursor disturbances from the planetary scale to the mesoscale the analysis of this event reveals that the two well defined tropopause based disturbances that contribute to cyclogenesis have distinctly different origins and are brought together by confluent planetary scale flow one of these disturbances originates over the western north pacific ocean 10 days prior to cyclogenesis and tracks eastward

the march 1993 superstorm cyclogenesis incipient phase synoptic and convective scale flow interaction and model performance abstract the incipient stages of the 12 14 march 1993 superstorm ss93 cyclogenesis over the gulf of mexico are examined noteworthy aspects of ss93 include 1 it is the deepest extratropical cyclone ever observed over the gulf of mexico during the 1957 96 period and 2 existing operational prediction models performed poorly in simulating the incipient cyclogenesis over the northwestern gulf of mexico a dynamic tropopause dt analysis shows that ss93 is triggered by a potent potential vorticity pv anomaly as it crosses extreme northern mexico and approaches the gulf of mexico the low level environment over the western gulf of mexico is warmed moistened and destabilized by a persistent southerly flow ahead of the approaching pv anomaly ascent and a lowering of the dt associated with a lowering of the potential temperature ahead of the pv anomaly contributes to further destabilization that is realized in the form of a massive convective outbreak an examination of the national centers for envi

acoustic mapping velocimetry knowledge of sediment dynamics in rivers is of great importance for various practical purposes despite its high relevance in riverine environment processes the monitoring of sediment rates remains a major and challenging task for both suspended and bed load estimation while the measurement of suspended load is currently an active area of testing with nonintrusive technologies optical and acoustic bed load measurement does not mark a similar progress this paper describes an innovative combination of measurement techniques and analysis protocols that establishes the proof of concept for a promising technique labeled herein acoustic mapping velocimetry amv the technique estimates bed load rates in rivers developing bed forms using a nonintrusive measurements approach the raw information for amv is collected with acoustic multibeam technology that in turn provides maps of the bathymetry over longitudinal swaths as long as the acoustic maps can be acquired relatively quickly and the repetition rate for the mapping is commensurate with the movement of the bed forms successive acoustic maps capture the progression of the bed form movement two dimensional velocity maps associated with the bed form migration are obtained by implementing algorithms typically used in particle image velocimetry to acoustic maps converted in gray level images furthermore use of the obtained acoustic and velocity maps in conjunction with analytical formulations e g exner equation enables estimation of multidirectional bed load rates over the whole imaged area this paper presents a validation study of the amv technique using a set of laboratory experiments

precipitation anomalies in southern brazil associated with el nino and la nina events the impact of el nino and la nina events warm and cold phases of the southern oscillation on rainfall over southern brazil is investigated through the use of a large dataset of monthly precipitation from 250 stations this region is partly dominated by rough orography and presents different climatic regimes of rainfall as previous global studies on southern oscillation precipitation relationships used data from only two stations in southern brazil this region was not included in the area of consistent southern oscillation related precipitation in southeastern south america the present analysis is based on the method by ropelewski and halpert the sensitivity of which is assessed for this region the spatial structure of the rainfall anomalies associated with warm cold events is analyzed and subregions with coherent anomalies are determined their distribution indicates the influence of relief latitude and proximity to the ocean these areas are subjected to further analysis to determine the seasons of largest anomalies and assess their consistency during warm cold events the whole of southern brazil was found to have strong and consistent precipitation anomalies associated with those events their magnitude is even larger than in argentina and uruguay all of the subregions have consistent wet anomalies during the austral spring of the warm event year with a pronounced peak in november the southeastern part also shows a consistent tendency to higher than average rainfall during the austral winter of the following year there is also a consistent tendency to dryness in the year before a warm event during the spring of cold event years strong consistent dry anomalies prevail over the whole region also with maximum magnitude in november they are even stronger and more consistent than the wet anomalies in warm event years consistent anomalies do not occur over large areas in the years before and after cold events the wet anomalies during the austral spring of the warm event year weaken and even reverse during the following january the same tendency though not so clear is observable in the dry anomalies of cold events the seasons of largest anomalies disclosed by this study differ from those found by previous global studies for other regions in southeastern south america this study expands the area of consistent warm cold event related precipitation defined by previous studies in southeastern south america by including a region of larger anomalies and provides a spatial and temporal refinement to the warm cold event precipitation relationship

concentric eye walls secondary wind maxima and the evolution of the hurricane vortex abstract research aircraft observations in recent hurricanes support the model of shapiro and willoughby 1982 for the tropical cyclone s response to circularly symmetric convective heat sources convective rings in both nature and the numerical model the tangential wind commonly increases rapidly just inside the radius of maximum wind and decreases inside the eye near the central axis of the vortex thus both secondary outer wind maxima and eyewall wind maxima often contract as they intensify this response is independent of the horizontal spatial scale of the maximum an outer maximum is frequently observed to constrict about a pre existing eye and replace it this chain of events often coincides with a weakening or at least a pause in intensification of the vortex as a whole the concentric eye phenomenon is a common but by no means universal feature of tropical cyclones it is most frequently observed in intense highly symmetric systems

midsummer low level circulation and precipitation in subtropical south america and related sea surface temperature anomalies in the south atlantic abstract the midsummer interannual variability of the low level tropospheric circulation and of the precipitation field in subtropical south america sa associated to the sea surface temperature sst anomalies in the western subtropical south atlantic ocean wssa is investigated using reanalyses regional precipitation datasets and monthly ssts the region of the wssa where sst has the strongest relation with precipitation in subtropical sa was identified using canonical correlation analysis this region extends from 20 to 30 s and from 30 to 50 w composites corresponding to extreme ssts in this area show two well differentiated patterns in the low level circulation and in the precipitation fields in the composite corresponding to the more positive sst anomalies in this area the mainstream of the low level flow and of the moisture transport from the continental low latitudes starts to follow a southeastward direction at 10 s and converges with the west flow at 35 s over the atlantic ocean on t

an empirical model of subcritical bedform migration the ability to predict bedform migration in rivers is critical for estimating bed material load yet there is no relation for predicting bedform migration downstream translation that covers the full range of conditions under which subcritical bedforms develop here the relation between bedform migration rates and transport stage is explored using a field and several flume data sets transport stage is defined as the non dimensional shields stress divided by its value at the threshold for sediment entrainment statistically significant positive correlations between both ripple and dune migration rates and transport stage are found stratification of the data by the flow depth to grain size ratio improved the amount of variability in migration rates that was explained by transport stage to ca 70 as transport stage increases for a given depth to grain size ratio migration rates increase for a given transport stage the migration rate increases as the flow depth to grainsize ratio gets smaller in coarser sediment bedforms move faster than in finer sediment at the same transport stage normalization of dune migration rates by the settling velocity of bed sediment partially collapses the data given the large amount of variability that arises from combining data sets from different sources using different equipment the partial collapse is remarkable and warrants further testing in the laboratory and field

spectral variations of underwater river sounds passive acoustic monitoring of the self generated noise of particle impacts has been shown to be correlated to bedload flux and bedload size however few studies have concentrated on the role of acoustic wave propagation in a river for the first time the river environment is modeled as a pekeris waveguide where a wave number integration technique is used to predict the transformation of sounds through their propagation paths focusing on the distance of a hydrophone from the channel bed and cutting off the low frequencies produced by impacts between gravel particles we demonstrate that acoustic propagation modifies the spectral content of bedload generated sound acoustic signals analyzed with the proposed model are interpreted by comparison to helley smith bedload data obtained during flood conditions on the large gravel bedded arc en maurienne river france this study shows that careful attention to acoustic propagation effects is required when estimating bedload grain size distribution with hydrophones in rivers especially for rivers with slopes higher than 1 bedload monitoring with a hydrophone is particularly appropriate for large gravel bed rivers especially so during large floods when in situ sampling is difficult or impractical and the impact of acoustic propagation is weaker relative to the self generated noise of bedload impacts

the motion of hurricane gloria a potential vorticity diagnosis abstract multilevel multinested analyses of hurricane gloria of 1985 are the most comprehensive kinematic dataset yet developed for a single hurricane a piecewise inversion technique is used with these analyses and the nonlinear balance equation to deduce the three dimensional distribution of potential vorticity pv that contributed to the deep layer mean dlm flow that steered gloria toward the northwest the background state is taken to be the azimuthally averaged winds in balance with a geopotential distribution on an f plane advantage is taken of the near linearity of the weak asymmetries near the hurricane s core and of pv in the environment thus ad hoc aspects of the linearization required by other investigators are effectively eliminated removal of the hurricane vortex and the use of a climatological mean background state are avoided as well the insensitivity of the results to the imposed lateral boundary conditions is also demonstrated wind anomalies attributable to pieces of anomalous p

evaluation of adcp apparent bed load velocity in a large sand bed river moving versus stationary boat conditions detailed mapping of bathymetry and apparent bed load velocity using a boat mounted acoustic doppler current profiler adcp was carried out along a 388 m section of the lower missouri river near columbia missouri sampling transects moving boat were completed at 5 and 20 m spacing along the study section stationary fixed boat measurements were made by maintaining constant boat position over a target point where the position of the boat did not deviate more than 3 m in any direction for each transect and stationary measurement apparent bed load velocity vb was estimated using adcp bottom tracking data and high precision real time kinematic rtk global positioning system gps the principal objectives of this research are to 1 determine whether boat motion introduces a bias in apparent bed load velocity measurements and 2 evaluate the reliability of adcp bed velocity measurements for a range of sediment transport environments results indicate that both high transport v b 0 6 m s and mo

validation of bed load transport measurements with time sequenced bathymetric data advances in bathymetric data acquisition have made it possible to explore alternative methods for measuring bed load transport in rivers the method validated herein consists of measuring rates of bed scour by using time sequenced bathymetric data the validation is performed in a laboratory flume by comparing the measured rates of bed scour with direct measurements of bed load transport the bed forms in the flume are dunes traveling at nearly constant speed the shape of the dunes remains nearly constant no suspended load is present the ranges for froude and rouse numbers are 0 24 0 50 and 4 6 10 4 respectively the study shows that under the given conditions bed load transport determined from time sequenced bathymetric data is equally accurate to that determined from measurements of bed form amplitude and speed obtaining bed load transport from time sequenced bathymetric data is often more expedient than traditional methods

a multiscale numerical study of hurricane andrew 1992 part i explicit simulation and verification abstract in this study the inner core structures of hurricane andrew 1992 are explicitly simulated using an improved version of the penn state ncar nonhydrostatic two way interactive movable triply nested grid mesoscale model mm5 a modified betts miller cumulus parameterization scheme and an explicit microphysics scheme were used simultaneously to simulate the evolution of the larger scale flows over the coarser mesh domains the intense storm itself is explicitly resolved over the finest mesh domain using a grid size of 6 km and an explicit microphysics package containing prognostic equations for cloud water ice rainwater snow and graupel the model is initialized with the national centers for environmental prediction analysis enhanced by a modified moisture field a model generated tropical storm like vortex was also incorporated a 72 h integration was made which covers the stages from the storm s initial deepening to a near category 5 hurricane intensity and the landfall over florida as

the step mountain coordinate model description and performance for cases of alpine lee cyclogenesis and for a case of an appalachian redevelopment abstract the problem of the pressure gradient force error in the case of the terrain following sigma coordinate does not appear to have a solution the problem is not one of truncation error in the calculation of space derivatives involved thus with temperature profiles resulting in large errors an increase in vertical resolution may not reduce and is even likely to increase the error therefore an approach abandoning the sigma system has been proposed it involves the use of step mountains with coordinate surfaces prescribed to remain at fixed elevations at places where they touch and define or intersect the ground surface thus the coordinate surfaces are quasi horizontal and the sigma system problem is not present at the same time the simplicity of the sigma system is maintained in this paper design of the model silhouette averaged mountains properties of the wall boundary condition and the scheme for calculation of the potential to kinetic energy conversion are presented for an

inundations in the mamore basin south western amazon bolivia and sea surface temperature in the pacific and atlantic oceans abstract extensive inundations have been observed in the llanos de mojos mamore basin south western amazon causing social and economic disasters since the beginning of the seventies precipitations have increased in the bolivian lowlands llanos and in the over rainy eastern cordillera and andean foothills yungas and inundations have become more frequent as a result inundations have been investigated in relation to rainfall over the mamore basin in trinidad puerto varador and in order to determine whether they are predictable in relation to sea surface temperature sst in the atlantic and the equatorial pacific oceans the methods are correlation and composite techniques as expected during the 1945 1946 1998 1999 period inundations have been associated with abundant rainfall in the mamore basin mainly in the llanos and yungas the role of rainfall in the inner dry andes and downstream from trinidad is more limited when consecutive floods are observed the ground water storage contributes to the occurrence of the second or third inundation event and rainfall anomaly is generally weaker rainfall in the mamore basin is hardly associated with sea surface temperature anomalies ssta in the pacific and atlantic oceans during the 1952 1953 1998 1999 period however during the nineties the southern atlantic ssta account for 50 percent of rainfall variability inundations are also related to negative ssta differences between the tropical and subtropical southern atlantic two thirds of the 22 inundation events occurred in association with this oceanic anomaly that features a weak ssta gradient in the southern atlantic during the 1988 1989 1998 1999 period a particularly significant relation can be observed between ssta and inundations events despite being associated with major el nino events 1982 1983 1991 1992 inundations are not significantly related to the equatorial pacific ssta

numerical simulations of the genesis of hurricane diana 1984 part ii sensitivity of track and intensity prediction abstract the authors examine numerous simulations that probe the dynamics governing the intensification and track of tropical cyclone diana 1984 simulated in part i the development process is fundamentally dependent on a preexisting upper tropospheric trough ridge couplet this couplet focuses mesoscale vertical motion that in turn produces lower tropospheric potential vorticity pv anomalies which form the seed for the tropical storm removal of this trough ridge couplet from the initial conditions eliminates cyclogenesis the simulated rate of development of diana in the prehurricane phase depends principally on choices of cumulus parameterization boundary layer treatment sea surface temperature and grid spacing simulations with cumulus schemes that allow more grid scale precipitation on the 9 km grid exhibit unrealistic grid scale overturning and slower intensification primarily due to production of cyclonic vorticity anomalies at large radii use of an innermost nest with 3 km grid spacing

wave formed sand ripples at duck north carolina a recently developed acoustic multiple transducer array was utilized to measure small scale bed forms in the nearshore and inner shelf regions at duck north carolina two populations of wave formed ripples were observed short wave ripples swr with heights ranging from 3 mm to 2 cm and lengths ranging from 4 to 25 cm and long wave ripples lwr with heights ranging from 3 mm to 6 cm and lengths ranging from 35 to 200 cm the swr were only present sometimes and their presence or absence was determined by a critical value of the near bed mobility number the swr were highly dynamic sometimes flattening during wave groups and reforming over several incident wave periods the lwr in contrast were almost always present they were longer and lower relief than predicted by models or generally observed previously both swr and lwr were often observed to migrate shoreward but were rarely observed to migrate seaward the dimensions of the swr when they were present were predictable by the nielsen 1981 model or the wiberg and harris 1994 model to within approximately a factor of 2

episodic sediment accumulation on amazonian flood plains influenced by el nino southern oscillation continental scale rivers with a sandy bed sequester a significant proportion of their sediment load in flood plains the spatial extent and depths of such deposits have been described and flood plain accumulation has been determined at decadal timescales but it has not been possible to identify discrete events or to resolve deposition on near annual timescales here we analyse 210 pb activity profiles from sediment cores taken in the pristine beni and mamore river basins which together comprise 720 000 km2 of the amazon basin to investigate sediment accumulation patterns in the andean amazonian foreland we find that in most locations sediment stratigraphy is dominated by discrete packages of sediments of uniform age which are typically 20 80 cm thick with system wide recurrence intervals of about 8 yr indicating relatively rare episodic deposition events ocean temperature and stream flow records link these episodic events to rapidly rising floods associated with la nina events which debouch extraordinary volumes of sediments from the andes we conclude that transient processes driven by the el nino southern oscillation cycle control the formation of the bolivian flood plains and modulate downstream delivery of sediments as well as associated carbon nutrients and pollutants to the amazon main stem

on the functioning of the southern oscillation in the south american sector part i surface climate abstract the functioning of the southern oscillation so over south america and the surrounding tropical atlantic and eastern pacific oceans is studied through analyses of bimonthly patterns of correlation between an so index and the fields of pressure wind temperature and rainfall hydrometeorological anomalies being further ascertained from river discharge and lake level records and measurements of outgoing longwave radiation most pronounced is the anomalously low pressure over the eastern pacific during the negative so phase defined by anomalously low high pressure at tahiti darwin consistently positive so pressure correlations over the eastern tropical pacific extend eastward into the north atlantic region and southern south america during the respective winter semester during the austral winter the tendency for anomalously abundant rainfall in central chile during the negative so phase appears related to an anomalously weak and northward displaced south pacific subtropical high while relativ