the meandering gulf stream as seen by the geosat altimeter surface transport position and velocity variance from 73 to 46 w the surface geostrophic velocity field for the gulf stream region was analyzed for the position structure and surface transport of the gulf stream for 2 5 years of the geosat altimeter exact repeat mission synthetic data using a gaussian velocity profile were generated and fit to the sea surface residual heights to create a synthetic mean sea surface height field and profiles of absolute geostrophic currents most of cross track velocity variance was due to the meandering of the gulf stream rather than to rings or complicated velocity profiles which suggested that the simple model parameters are an efficient description of the gulf stream fluctuations an analysis of the model parameters and the actual geostrophic velocity profiles revealed two different flow regimes for the gulf stream connected by a narrow transition region coincident with the new england seamount chain the upstream region was characterized by relatively straight gulf stream paths long eulerian time scales and eastward propagating meanders the downstream region had more large meanders no consistent propagation direction and shorter eulerian time scales a 25 reduction in surface transport occurred in the transition region with a corresponding reduction in current speed and no change in gulf stream width a significant anomaly in surface transport near 69 w suggested the existence of small scale recirculation gyres there the highest variance empirical orthogonal functions of position and surface transport were significantly correlated with larger surface transports leading more northerly positions by a month

absolute transports of mass and temperature for the north atlantic current subpolar front system the flow of subtropical waters carried into the northern north atlantic ocean by the north atlantic current subpolar front system nac spf is an important component of the meridional overturning circulation these waters become colder and denser as they flow through the subpolar region both by mixing with the colder subpolar waters and by atmospheric cooling the relative roles of these two processes remain to be quantified and the mechanisms driving lateral mixing need to be better understood to address those questions a new methodology is developed to estimate the mean absolute transports of mass and heat for the top 1000 dbar in the region of the nac spf for the time period 1993 2000 the transports are obtained by combining historical hydrography with isopycnal rafos float data from the area the mean absolute transport potential field shows an nac spf pipe defined by two bounding transport potential contours this pipe transports 10 0 6 3 5 sv sv 106 m3 s 21 top 1000 dbar from the subtropics into the eastern subpolar north atlantic in contrast to earlier studies the northward flowing nac follows a distinct meandering path with no evidence of permanent branches peeling off the current before reaching the northwest corner as the current enters the northwest corner it loses its tight structure and maybe splits into two or more branches which together constitute the eastward flow along the spf the eastward flow between the northwest corner and the mid atlantic ridge is not as tightly defined because of the meandering and or eddy shedding of the branches constituing the spf as the flow approaches the mid atlantic ridge it converges to cross above the charlie gibbs and faraday fracture zones the mean absolute temperature transport top 1000 dbar by the 10 sv pipe was estimated across 10 transects crossing the nac spf because the mean mass flux is constant in the pipe variations in the mean temperature transports result from lateral exchange and mixing across the pipe s side walls and from air sea fluxes across the surface of the pipe the nac spf current loses 0 18 6 0 05 pw on its transit through the region most of the loss occuring upstream of the northwest corner the heat loss is 10 times the corresponding heat lost to the atmosphere we conclude that cross frontal exchange induced by the steep meanders of the northward flowing nac is the main mechanism by which heat is lost along the current in the region between the tail of the grand banks and the mid atlantic ridge

the structure and transport of the gulf stream at 73 w abstract between september 1980 and may 1983 16 sections of temperature and velocity were obtained with the pegasus instrument along a transect crossing the gulf stream at 73 w the mean temperature and velocity fields of the upper 2000 meters were calculated the transport above 2000 meters calculated from the sections had a mean of 87 8 17 3 106 m3 s 1 a comparison with mass flux measurements obtained by previous investigators at cape fear indicated that the addition to the transport of the stream in the region was uniform with depth above 800 meters the mean inflow measured at the pegasus line was found to be uniform above 800 meters and to decrese substantially below this depth the increase in transport at the line estimated from the mean cross stream velocity field was 15 4 5 8 106 m3 s 1 per 100 km downstream distance the temporal fluctuation of the pegasus transport measurements was consistent with an annual cycle with a maximum in april the mean eddy kinetic energy at the surface

flow characteristics of large eruption triggered debris flows at snow clad volcanoes constraints for debris flow models abstract theoretical modelling is not yet adequate to predict the behavior of debris flows which can be an extremely hazardous hydrologic process commonly associated with volcanic eruptions particularly at snow clad stratovolcanoes to provide a realistic basis for modelling the behavior of large 1000 m3 s debris flows this paper summarizes kinematic volumetric and hydraulic characteristics of ten large historic volcanic debris flows from four different volcanoes although debris flows larger than these are known to have occurred in the past the ten summarized here define a practical upper range in magnitude of more typical flows to be considered for future hazard prediction peak flow velocities of the ten debris flows studied were indirectly measured to be between about 5 and 20 m s on gradients of 0 005 to 0 25 m m but locally they were as great as 40 m s hydraulic average depths were as great as 25 m but were more commonly between 5 and 15 m in channels up to 400 m wide computed peak discharges volumetric flow rates were as high as 105 m3 s and total volumes were as much as 108 m3 total flow volumes increased by as much as four times in relatively steep channels as eroded sediment was incorporated into the debris flows flows generally achieved supercritical flow and deposited minimal volumes of sediment on gradients steeper than 0 02 m m subcritical flow and active deposition predominated on gradients less than 0 01 m m although flows travelled tens of kilometers on such low gradients while laying down deposits total distances travelled as debris flows were as far as 120 km

jet streaks in the gulf stream mesoscale alongstream speed changes of the gulf stream are diagnosed from an array of current meters at depths 400 700 and 1000 m near 688w during the development of steep ratio of amplitude to wavelength o 1 meanders speed maxima jet streaks are generally found between trough and crest axes in steep meanders with local speed minima near the trough and crest axes speed changes along streamlines can be quite dramatic speed changes along the jet axis between jet streaks and local minima in excess of 0 60 0 40 and 0 35 m s 21 are observed at depth 400 700 and 1000 m respectively this is in comparison with peak speeds in a frontal coordinates system mean of 1 22 0 67 and 0 28 m s21 at depth 400 700 and 1000 m respectively from a previous study the presence of the jet streaks can be explained kinematically as a superposition of the gulf stream and barotropic vortices the development of these jet streaks in relation to the developing steep meanders differs from the canonical picture of jet streak baroclinic wave development in the atmospheric jet stream in that the jet streaks in the gulf stream are predominantly fixed in place with respect to meanders as they steepen

a comparison between the generalized digital environmental model and levitus climatologies two ocean climatologies of temperature and salinity the generalized digital environmental model gdem and the climatological atlas of the world ocean are compared dynamic height fields are computed by season from each climatology for the north atlantic north pacific and indian oceans and are compared on a 1 latitude longitude grid large scale oceanographic features are generally found to be similarly represented in both climatologies gdem appears to render better representations of seasonal variability and regions of high current shear such as the gulf stream because of a different smoothing method and a finer grid spacing maps of dynamic heights from both climatologies are presented and their similarities and differences are discussed the methodology for the construction of gdem is also described in detail

material transport in oceanic gyres part i phenomenology abstract material spreading and mixing by oceanic mesoscale eddies are analyzed in an idealized numerical model of the wind driven midlatitude oceanic circulation the main focus is on the regime with large reynolds number re and vigorous mesoscale eddies although brief comparisons are made with less turbulent solutions at smaller re the analyses are based on ensembles of lagrangian particle trajectories the authors find that tracer transport by mesoscale eddies differs in many ways from the commonly used model of homogeneous isotropic eddy diffusion the single particle dispersion which describes the spreading process is generally anisotropic and inhomogeneous and in most places it is not diffusive i e not linear in time during intermediate time intervals after tracer release in most of the basin and especially in the deep layers subdiffusive single particle dispersion occurs due to long time trapping of material by coherent structures such as vortices near the strong currents and planeta

zonal penetration scale of midlatitude oceanic jets abstract it is shown that subtle changes in the velocity profile across the seaward extension of midlatitude jets such as the gulf stream can lead to dramatic changes in the zonal penetration scale in particular if dq d 0 where q is the absolute vorticity and is a streamfunction for the geostrophic flow then the jet tends to penetrate across to the eastern boundary conversely if 0 the jet turns back on itself creating a tight recirculation on the scale of order frac12 this behavior is demonstrated in a quasigeostrophic ocean model in which a jet profile is prescribed as an inflow condition at the western margin of a half basin and radiation conditions along the remainder of the western boundary allow the injected fluid to escape jet inflows with both vertical and horizontal structure are considered in one and one half two and three layer models finally the implications of our study for numerical simulations of ocean gyres which frequently show sensitivity of jet penetra

fluvial landsculpting and the fractal dimension of topography abstract quantitative models of landform development can help us to understand the evolution of mountains and regional topography and the effects of tectonic motions and climate on landscape including its fractal geometry this paper presents a general and powerful three dimensional model of fluvial erosion and deposition at hill to mountain range scale the model works by accumulating the effects of randomly seeded storms or floods precipitons that cause diffusional smoothing then move downslope on digital topography grids that erode portions of elevation differences that transport a slope limited amount of eroded material and that deposit alluvium when their sediment carrying capacity is exceeded the iteration of these simple and almost linear rules produce very complicated simulated landscapes demonstrating that complex landscapes do not require complex laws each process implemented in the model is affected differently by changes in horizontal scale erosion a scale free process roughens topography at all wavelengths this roughening is balanced by diffusive processes scaling as 1 l 2 at short wavelengths and deposition scaling scaling as 1 l 2 at long wavelenghts such a mixture of scale free and scale dependent processes can produce multifractal behavior in the models the fractal dimension of the model topography is much more sensitive to climatic variables than to tectonic uplift landscape evolution may be fractal but it does not seem to be chaotic analysis of topography of areas in southern arizona using variograms shows approximately fractal behavior with mean fractal dimension around 2 2 2 3 departures from an exact fractal relatioship imply that the topography is in detail multifractal the fractal dimension at short wavelengths is less than that at long wavelengths this variation could either be caused by the relative strengths of diffusive and erosional processes shaping the topography or a result of changes in climatic or tectonic conditions still preserved in the landscape

regional primitive equation studies of the gulf stream meander and ring formation region abstract primitive equation and quasi geostrophic eddy resolving open ocean models are used for hindcast studies in the gulf stream meander and ring formation region a feature model approach is used to initialize the models based on one month of observations during november to december 1984 flat bottom and topographic calculations are carried out using an initial gulf stream velocity profile based on the pegasus dataset all of the major events observed in the upper thermocline are reproduced by both numerical models the addition of bottom topography is shown to significantly alter the character of the deep velocity fields large basin scale circulations found near the bottom in both flat bottom calculations were replaced by energetic jets and eddies associated with the dominant spatial scales of the bottom topography use of the quasi geostrophic model to dynamically adjust the initial conditions for the primitive equation model is shown to reduce the growth of large scale meanders on time scales o

isotopic evidence for the sources of cretaceous and tertiary granitic rocks east central alaska implications for the tectonic evolution of the yukon tanana terrane magnetotelluric traverses across the southern yukon tanana terrane ytt reveal the presence of a thick conductive layer or layers beneath paleozoic crystalline rocks these rocks have been interpreted to be flysch of probable mesozoic age on the basis of the occurrence of jurassic cretaceous flysch in the kahiltna assemblage and gravina nutzotin belt flanking the ytt to the southwest and southeast respectively the pb nd sr and o isotopes in cretaceous and tertiary granitic rocks that crop out throughout the ytt were measured to determine if these rocks do in fact contain a component of flysch previous limited analyses indicated that the pb isotopes of the granitic rocks could be a mixture of radiogenic pb derived from paleozoic crystalline rocks of the ytt with an increasing component of relatively nonradiogenic pb with decreasing age our nd sr and o data along with additional pb isotope data eliminate flysch as a likely source and strongly suggest that the nonradiogenic end member was deri

gulf stream meander propagation past cape hatteras the propagation and growth characteristics of gulf stream meanders past the stream s separation point at cape hatteras are analyzed using yearlong time series from a mooring program sponsored by the minerals management service which included moorings imbedded in the gulf stream cyclonic flank both upstream south and downstream north of cape hatteras in the upstream region energetic meanders of 3 8 day period 180 380 km wavelength propagate downstream along the gulf stream at speeds of 40 55 km day 21 this variability decays almost completely across the gulf stream separation with growth in lower frequency variability 30 120 day in the downstream direction wavelength and phase speed in the 3 8 day band are strong functions of frequency with increasing phase speed for increasing wavenumber phase speeds upstream from cape hatteras and across the gulf stream separation point are faster for a given wavenumber than downstream from cape hatteras in keeping with prior published estimates at the upstream end of the study site both baroclinic and barotropic mechanisms contribute to the decay of 3 8 day meanders and growth of lower frequency 30 120day variability in the downstream direction at the downstream end of the study region the reverse holds with both baroclinic and barotropic mechanisms contributing to growth of 3 8 day meanders and decay of lowerfrequency 30 120 day variability

nd isotopic characterization of metamorphic rocks in the coast mountains alaskan and canadian cordillera ancient crust bounded by juvenile terranes nd isotopic data are reported for 52 samples from the crustal region between the alexander wrangellia terrane and the stikine terrane of the alaskan and canadian cordillera this region is composed of the gravina belt a jurassic cretaceous assemblage of volcanic and clastic sedimentary rocks the taku terrane a terrane of probable early permian to late triassic age and four assemblages of metamorphic rocks that occur to the west of and within the coast mountains batholith the gravina belt has end t values that range from 1 1 to 8 3 similar to values of the underlying alexander terrane and consistent with the interpretation that it is a juvenile belt that formed in a back arc or intra arc basin within the alexander terrane mid cretaceous plutons that were emplaced into the gravina belt have end t values of 4 4 to 5 7 and were probably produced by mantle derived melts that incorporated some alexander terrane crust the taku terrane has end 0 values that range from 5 5 to 3 3 with corresponding depleted mantle model tdm ages of 440 to 1430 ma a mid cretaceous pluton intruding the taku terrane has an end t value of 5 1 a value indistinguishable from those determined for cretaceous plutons intruding the gravina belt metamorphic rocks east of and structurally overlying the taku terrane are divided into the tracy arm assemblage end 0 26 to 0 tdm 800 2450 ma the endicott arm assemblage end 0 10 to 1 3 tdm 950 1500 ma the port houghton assemblage end 0 9 4 to 1 1 tdm 550 1500 ma and the ruth assemblage end 0 9 4 to 2 0 tdm 650 1300 ma these isotopic signatures indicate that a substantial component of each metamorphic assemblage was derived from precambrian continental crust the metamorphic rocks from these assemblages are lithologically very similar to rocks of the yukon tanana ytt terrane of eastern alaska and yukon territory and have such similar u pb detrital zircon ages and nd isotopic compositions to ytt rocks that they are considered part of that terrane possible tectonic scenarios that can explain the present geometry of the ytt with respect to the alexander wrangellia and stikine terranes include 1 the ytt is the upturned stratigraphic basement of the stikine terrane 2 part of the ytt was structurally emplaced beside the stikine terrane in a transpressive tectonic regime 3 the stikine terrane and other inboard terranes are huge sheets that were thrust over the margin of the ytt before the final accretion of the alexander wrangellia terrane

cellular automata as analysis and synthesis engines at the geomorphology ecology interface abstract the linkages between ecology and geomorphology can be difficult to identify because of physical complexity and the limitations of the current theoretical representations in these two fields of study deep divisions between these disciplines are manifest in the methods used to simulate process such as rigidly physical deterministic methods for many aspects of geomorphology compared with purely stochastic simulations in many models of change in landcover practical and theoretical research into ecology geomorphology linkages cannot wait for a single simulation schema which may never come as a result studies of these linkages often appear disjointed and inconsistent the grid based simulation framework for cellular automata ca allows simultaneous use of competing schemas ca use in general geographic studies has been primarily limited to urban simulations models of change for land cover both highly stochastic and or expert rule based in the last decade however methods for describing physically deterministic systems in the ca framework have become much more accurate the possibility now exists to merge separate ca simulations of different environmental systems into unified multiautomata models because cas allow transition rules that are deterministic probabilistic or expert rule based they can immediately incorporate the existing knowledge rules in ecology and geomorphology the explicitly spatial nature of ca provides a map like framework that should allow a simple and deeply rooted connection with the mapping traditions of the geosciences and ecological sciences

the effect of the new england seamounts on gulf stream meandering as observed from satellite ir imagery abstract it is commonly held belief that meandering of the gulf stream increases dramatically downstream of the new england seamount chain in fact this appears not to be the case the envelope of gulf stream northern edges derived from 30 months of satellite data remains constant from 65 to 58 w only the mean of the integrated path length normalized by the mean path length appears to increase downstream of the seamounts but at very nearly the same rate as upstream of them

local gradient and between site variability of erosion rate on badlands in the karoo south africa site average values of local gradient defined as the steepest slope angle measured at a point are a powerful predictor of long term rates of soil loss as measured by erosion pins on the non channel floor portions of ten badland study sites in the karoo area of south africa local gradient may be easily measured using a smartphone clinometer the successful use of local gradient here is in strong contrast to the previous failure of other site specific attributes including other measures of gradient and relief to explain between site variation in erosion rate on these study sites each measurement of local gradient may be thought of as a sample of the site s microtopography microrelief is a strong determinant of the emergent patterns of inter channel overland flow and hence of the patterns of inter channel erosion by flow local gradient changes most rapidly during the initial stages of channel incision when channels are established local gradient changes more slowly leading to almost parallel retreat of channel sidewalls a sensitivity analysis suggests that measurements of local gradient are not all equal with regard to prediction of long term erosion rate a greater share of predictive power is contributed by measurements made on very steep or vertical channel side wall areas and a lesser share is contributed by measurements made on interfluves

profiling the gulf stream with a current meter mooring a current meter mooring was deployed for one year at the mean position of the gulf stream at 68 w with instruments from 400 m to 4000 m it provides the first unambiguous evidence that the gulf stream extends from top to bottom of the water column using the strong cross stream temperature structure to derive a horizontal coordinate related to temperature we estimate the width and transport of the gulf stream for four individual events and we determine an average profile of the vertical and cross stream structure of the gulf stream a conservative estimate of transport for this average profile indicates that the gulf stream has a transport of 103 106 m s 1 at 68 w

reevaluating the roles of eddies in multiple barotropic wind driven gyres multiple gyre ocean models have a weaker mean subtropical circulation than single gyre calculations with the same viscosity and subtropical forcing traditionally this reduction in circulation is attributed to an intergyre eddy vorticity flux that cancels some of the wind input part of which does not require a lagrangian mass exchange theory of dissipative meandering herein the intergyre eddy vorticity flux is shown to be a controlling factor in barotropic models at high reynolds number only with exactly antisymmetric gyres and slip boundary conditions almost no intergyre flux occurs when no slip boundary conditions are used yet the subtropical gyre is still significantly weaker in multiple gyre calculations sinuous modes of instability present only in multiple gyres are shown here to vastly increase the eddy vorticity transport efficiency this increase in efficiency reduces the mean circulation necessary for equilibrium with slip boundary conditions the intergyre eddy transport is possibly much larger however with wind forcing relevant for the ocean two unequal gyres a mean flow flux of vorticity rather than an eddy flux between the regions of opposing wind forcing is increasingly important with increasing reynolds number a physical rationalization of the differing results is provided by diagnosis of the equilibrium vorticity budget and eddy transport efficiency calculations varying 1 boundary conditions 2 sources and sinks of vorticity 3 eddy transport efficiency and 4 the degree of symmetry of the gyres are discussed

gulf stream flow field and events near 68 w the synoptic ocean prediction synop experiment was designed to provide an accurate understanding of the energetic mesoscale processes in the gulf stream the central array measured velocity and temperature throughout the water column with horizontal extent large enough nearly to span the meander envelope and eulerian mean structure of the jet at 68 w the 55 to 70 km mooring spacing resolved mesoscale eddy interactions with the gulf stream and the 26 month duration allowed stable estimation of long term mean fields six steep meander troughs propagated into or developed within the array each lasting around 30 60 days thus impressing a small mean trough near 68 w in the predominantly eastward currents at jet level 1000 m and above at the deep level 3500m the mean flow was southwest at the shoreward sites shallower than 4300 m but it flowed cyclonically around a mean low pressure anomaly affecting all the deeper offshore sites the eddy kinetic energy per unit mass e k decreased by a factor of about 2 5 with each depth increment from 400 to 700 to 1000 m but was only a factor of 2 smaller at 3500 m than at 1000 m values of e k in the upper central jet 400 m were 100 to 230 mj kg 1 and were 4 13 mj kg 1 at 3500 m overall e k in the upper 1000m at 68 w was higher than previously published values at 55 w two extended case studies of meander propagation through the array demonstrate the development and intensification of deep cyclonic and anticyclonic flows beneath the gulf stream the cyclonic flow at 3500m associated with amplifying meander troughs often exceeded 0 35 ms 1 which was much larger than the typical 0 05 ms 1 deep mean velocities

eddy mean flow interaction in the kuroshio extension region abstractthe authors use data collected by a line of tall current meter moorings deployed across the axis of the kuroshio extension ke jet at the location of maximum time mean eddy kinetic energy to characterize the mean jet structure the eddy variability and the nature of eddy mean flow interactions observed during the kuroshio extension system study kess a picture of the 2 yr record mean jet structure is presented in both geographical and stream coordinates revealing important contrasts in jet strength width vertical structure and flanking recirculation structure eddy variability observed is discussed in the context of some of its various sources jet meandering rings waves and jet instability finally various scenarios for eddy mean flow interaction consistent with the observations are explored it is shown that the observed cross jet distributions of reynolds stresses at the kess location are consistent with wave radiation away from the jet with the sense of the eddy feedback effect on

meanders of the gulf stream downstream from cape hatteras 1975 1978 abstract weekly gulf stream paths within 1000 km downstream of cape hatteras were obtained for 1975 78 from the navy s weekly eofa charts based on satellite ir imagery they displayed two dominant meander modes first a standing meander energetic over periods between 4 months and at least 4 years and second down stream propagating meanders that were most energetic at periods of several weeks the long period standing meander was confined between nodes located at the separation point near cape hatteras i e where the stream s mean path turns seaward and at a point about 600 km farther downstream the rms amplitude was 36 km at the antinode the amplitude of propagating meanders increased rapidly in the first 200 km downstream of the separation point where the capture of warm core eddies was common farther down stream the predominant meanders had a wavelength averaging 330 km a period averaging 1 5 month a phase speed averaging 8 cm s 1 a downstream group speed averaging 17 cm s 1 and downstrea

zonal penetration scale of model midlatitude jets abstract all available observations indicate that the most energetic time dependent currents are located in the vicinity of intense large scale oceanic current systems this characteristic is also a basic property of eddy resolving gyre scale numerical models an initial detailed intercomparison of two layer eddy resolving numerical experiments with observation focused on the largest scales of horizontal structure in patterns of abyssal eddy kinetic energy and on time scales the numerical experiments examined generally had relevant temporal and meridional scales but not necessarily realistic zonal scales the model eddy field did not penetrate as far from the western boundary as observed distributions by a factor of 2 to 3 the present study examines the physical processes that govern the model zonal penetration scale and suggests reasons for the previous discrepancy it is demonstrated that a subtle balance exists between the complex instability processes that tend to tear the jet apart restricting

sea surface height fluctuations observed simultaneously with inverted echo sounders and geosat time series of sea surface height anomaly as measured by inverted echo sounders with pressure gauges ies pgs and geosat altimetry are compared at six locations in the northwest atlantic near 40 n 55 w three ies pg sites lay along each of two adjacent geosat exact repeat mission ground tracks better agreement was found along the westernmost ground track pressure sensor noise is the probable source of the larger errors along the easternmost ground track the overall correlation is 0 78 along the westernmost ground track it is 0 91 decorrelation scales are about 100 km along track and about 5 days uncorrelated errors dominate but along the westernmost ground track ies pg derived sea surface height variability is systematically smaller than that derived from geosat data this factor determined by regression analysis is about 0 81 however a consistent adjustment of ies calibration removes the systematic discrepancy

the three dimensional chaotic transport and the great ocean barrier the aim of this paper is to renew interest in the lagrangian view of global and basin ocean circulations and its implications in physical and biogeochemical ocean processes the paper examines the lagrangian transport mixing and chaos in a simple laminar three dimensional steady basin scale oceanic flow consisting of the gyre and the thermohaline circulation mode the lagrangian structure of this flow could not be chaotic if the steady oceanic flow consists of only either one of the two modes nor if the flow is zonally symmetric such as the antarctic circumpolar current however when both the modes are present the lagrangian structure of the flow is chaotic resulting in chaotic trajectories and providing the enhanced transport and mixing and microstructure of a tracer field the lagrangian trajectory and tracer experiments show the great complexity of the lagrangian geometric structure of the flow field and demonstrate the complicated transport and mixing processes in the world ocean the finite time lyapunov exponent analysis has successfully characterized the lagrangian nature one of the most important findings is the distinct large scale barrier which the authors term the great ocean barrier within the ocean interior with upper and lower branches as remnants of the kolmogorov arnold moser kam invariant surfaces the most fundamental reasons for such lagrangian structure are the intrinsic nature of the long time mean global and basin scale oceanic flow the three dimensionality and incompressibility giving rise to chaos and to the great ocean barrier respectively implications of these results are discussed from the great ocean conveyor hypothesis to the predictability of the quasi lagrangian drifters and floats in the climate observing system

gulf stream meanders observations on propagation and growth we present a new method for continuously tracking the location of the gulf stream using a moored array of inverted echo sounders time series of lateral displacements of the front shown accurate to 8 km have been collected along three sections spaced 100 150 and 200 km downstream ne of cape hatteras north carolina for a period of 12 months these records are highly coherent at all periodicities longer than 4 days from the observed phase lags a dispersion relationship is presented for the meanders as the period and wavelength t h increase from 4 days 180 km to 30 days 600 km the phase speed decreases smoothly from 40 to 20 km d the meanders exhibited rapid growth at periods longer than 4 days doubling in variance in each 50 km step downstream this downstream growth is most appropriately described by a spatial e folding scale k 400 km for t x 14 days 400 km from an array of seven inverted echo sounders ies and three deep current meters deployed 100 to 200 km northeast of cape hatteras in 2000 4000 m water this array continu ously monitored the path of the gulf stream and the deep currents under it on four deployment and recovery cruises to the area expendable bathythermograph traces xbt and hydrographic data were collected to survey the temperature and density structure along the stream path and on sections normal to it after a brief review of earlier studies on meanders this paper presents a discussion of the measurement techniques using ies in the gulf stream we show by direct compari sons with traditional measurement methods that 1 each ies produces a continuous record of the thermocline depth here taken to be the 15oc isotherm for subsequent comparison with standard methods of determining the position of the north wall of the stream with accuracy of 20 m in a range of variation of 800 m and 2 the array of ies s paired across the stream produces continuous estimates of the stream position with 8 km accuracy the results from the three ies sections located 100 150 and 200 km downstream of cape hatteras show very high coherence throughout the array with rapid 20 to 40 km d l translation of the meanders downstream accompanied by rapid growth of the lateral displacements doubling in variance with each 50 km step downstream in a companion paper w e johns and d r watts manuscript in preparation 1982 we discuss the current meter records and the relationship of the deep currents to gulf stream meanders 1981 they have wavelengths of 150 200 km and propagate downstream at rates of approximately 30 40 km d downstream of cape hatteras the envelope of meandering broadens greatly to 200 300 km figure 1 and the stream can shift through more than its own width in the early shipboard surveys fuglister and worthington 1951 fuglis ter 1963 the path of the stream south of nova scotia was dominated by long wavelength 400 km large amplitude meanders those which were studied in detail were found to be quasi stationary and were characterized by a slowly evolving baroclinic field indicating temporal growth far ther upstream near 72ow however significant eastward propagation was observed one meander crest moved at a rate of approximately 17 km d for 3 days fuglister and worthington 1951 hansen 1970 later conducted monthly path surveys between 75 o and 55ow for 1 year with weekly surveys over a 2 month period using a towed thermistor he found meanders on appreciably shorter scales with wave lengths ranging from 200 to 400 km mean downstream propagation rates of 5 10 cm s and spatial growth rates of 2 x 10 3 km were estimated by constructing lines of constant phase between features on successive path se quences the rapid evolution between monthly paths how ever produced considerable ambiguity in identifying and tracking events weekly paths evolved more continuously and were apparently not aliased by higher frequency wave number phenomena

mechanics of wind ripple stratigraphy stratigraphic patterns preserved under translating surface undulations or ripples in a depositional eolian environment are computed on a grain by grain basis using physically based cellular automata models the spontaneous appearance growth and motion of the simulated ripples correspond in many respects to the behavior of natural ripples the simulations show that climbing strata can be produced by impact alone direct action of fluid shear is unnecessary the model provides a means for evaluating the connection between mechanical processes occurring in the paleoenvironment during deposition and the resulting stratigraphy preserved in the geologic column vertical compression of small laminae above a planar surface indicates nascent ripple growth supercritical laminae are associated with unusually intense deposition episodes and a plane erosion surface separating sets of well developed laminae is consistent with continued migration of mature ripples during a hiatus in deposition

cyclogenesis in the deep ocean beneath the gulf stream 1 description one of the primary scientific results of the synoptic ocean prediction synop observational program was the discovery of strong cyclones in the deep ocean beneath the large amplitude gulf stream meander troughs that routinely form at about 68 w these strong well organized cyclones extend to at least 3500 m below the sea surface and are an important component of the overall dynamical variability of the gulf stream and adjacent deep waters typically a small amplitude gulf stream meander stalls near 68 w and begins to amplify as the amplitude of troughs in the gulf stream jet increases the currents at 3500 m strengthen and turn forming a cyclonic circulation pattern during synop six well defined instances of meander trough amplification and deep cyclogenesis occurred the cyclones were characterized by strong swirl speeds up to 0 5 m s 1 and were long lived typically lasting 6 9 weeks frequent occurrences present 35 of the time during the 25 month deployment period the structure of the cyclones at 3500 m is characterized by increasing velocity from the cyclone center out to some radius of maximum velocity and decreasing velocity beyond that radius this structure was robust over the lifetime of an event and from event to event cyclone radius and the radius to maximum velocity were consistently 130 km and 55 km respectively evidence of cyclones at upper measurement levels and the low vertical shear values apparent in the deep water below the thermocline indicate that the cyclones extended throughout the entire water column from the benthic boundary layer through the thermocline and to the ocean s surface

on the probability that a gulf stream meander crest detaches to form a warm core ring abstract eight years of gulf stream data were examined to determine the percentage of meander crests that give rise to warm core rings because of cloud cover in many of the satellite images it was not possible to associate a specific meander crest with each warm core ring formed nor was it possible to follow each meander crest from the point at which its amplitude was first detectable to the point at which it left the study area was absorbed by another meander or split to form two meanders despite these problems a lower bound of 0 24 could be placed on the probability that a meander crest detaches to form a warm core ring this was obtained by considering all disturbances in the path of the gulf stream that could be tracked over a several day period if consideration is restricted to disturbances with a length scale the size of warm core rings or larger the probability of formation increases to 0 40 the authors argue that this is a more interesting number in that the wavelength of the meanders obs

vertical motion in the gulf stream and its relation to meanders vertical motion at 700 m in the gulf stream main thermocline is computed using the adiabatic heat equation and a combination of data from inverted echo sounders and moored current meter measurements of t and u v at 400 700 1000 and 3500 m daily maps of all data on a regular grid were created using optimal estimation from these maps the tendency and advection terms in the heat equation were calculated the mapped vertical motions w agree well with w observed contemporaneously along isopycnal rafos float tracks strong events occur frequently within the gulf stream diagnosed vertical motions greater than 2 mm s 1 that persist for days are common occurring roughly every week within the 250 km mapped region upwelling and downwelling regions have horizontal scales of about 100 km both along and across stream case studies and animation elucidate the relationship between meander properties and the structure phasing and amplitude of the w fields typically the largest w is positioned near the steepest thermocline slope downwelling upwelling occurs entering exiting troughs strongest vertical motions occur in slowly propagating features and vertical motions are usually weaker for rapidly propagating features this observed dependence upon phase speed is opposite to predictions of recent kinematic and conceptual models the main contribution to observed w and the factor missing in those models is the existence of strong abyssal flow serving as a barotropic reference for the entire water column with a component which may flow orthogonal to the baroclinic front along sloping isopycnals the strongest vertical and cross frontal components are usually associated with slowly moving or stalled steep meanders associated with which abyssal cyclones or anticyclones have developed the vertical motion which is forced in these cases can significantly alter the vertical vorticity and or frontal strength through tilting of the strong vertical shear and of the strong vertical stratification vertical and cross frontal transports of 5 sv occur in steep meanders

the gulf stream and its frontal structure a quantitative representation abstract the structure of the gulf stream current is associated with the quasi permanent density front in the western north atlantic the lighter mass of warmer but saltier water of the sargasso sea is separated from the slope water by inclined isopycnals that form the front recent satellite altimeter measurements have also revealed a well defined sea surface height change across the front in this paper a model of the gulf stream cross sectional density and current structure is presented using the complete dynamical and mass conservation equations the model postulates a forcing at the interior ocean boundary by a cross stream ageostrophic circulation with inflow of light water in the upper ocean and a return flow at greater depths the model gulf stream is found to develop after initial geostrophic adjustment of several inertial periods in the quasi steady state the normalized structural results constitute a single representation of the structure of all gulf stream sections i e all sections ar

modelling outburst floods from moraine dammed glacial lakes in response to climatic change the size and number of moraine dammed supraglacial and proglacial lake systems have increased dramatically in recent decades given an appropriate trigger the natural moraine dams that impound these proglacial lakes are breached producing catastrophic glacial lake outburst floods glofs these floods are highly complex phenomena with flood characteristics controlled in the first instance by the style of breach formation downstream glofs typically exhibit transient often non newtonian fluid dynamics as a result of high rates of sediment entrainment from the dam structure and channel boundaries combined these characteristics introduce numerous modelling challenges in this review the historical contemporary and emerging approaches available to model the individual stages or components of a glof event are introduced and discussed a number of methods exist to model the stages of a glof event dam breach models can be categorised as being empirical analytical or numerical in nature with each method having significant advantages and shortcomings empirical relationships that produce estimates of peak discharge and time to peak are straightforward to implement but the applicability of these models is often limited by the nature of the case study data from which they are derived furthermore empirical models neglect the inclusion of basic hydraulic principles that describe the mechanics of breach formation analytical or parametric models simulate breach development using simplified versions of the physically based equations that describe breach enlargement whilst complex physically based codes represent the state of the art in numerical dam breach modelling to date few of the latter have been applied to investigate the moraine dam failure problem despite significant advances in the physical complexity and availability of higher order hydrodynamic solvers the majority of published accounts that have attempted to reconstruct or predict glof characteristics have been limited often by necessity to the use of relatively simplistic models this is in part attributable to the unavailability of terrain models of many high mountain catchments at the fine spatial resolutions required for the effective application of numerically sophisticated codes and their proprietary and often cost prohibitive nature however advanced models are experiencing increasing use in the glacial hazards literature in particular the suitability of emerging mesh free particle based methods for simulating dam breach and glof routing may represent a solution to many of the challenges associated with modelling this complex phenomenon sources of uncertainty in the glof modelling chain have been identified by various workers however to date their significance for the robustness of reconstructive and predictive modelling efforts have been largely unexplored and quantified in detail these sources include the geometric and material characterisation of moraine dam complexes including lake bathymetry and the presence and extent of buried ice initial conditions freeboard precise spillway dimensions spatial discretisation of the down valley domain hydrodynamic model dimensionality and the dynamic coupling of successive components in the glof model cascade

toward a model for the bulking and debulking of lahars 1 the incorporation and loss of material sediments or water during the advance of a lahar can significantly influence the advance rate mobility rheology and inundation limits of the flow and therefore these processes have consequences for destructive potential we have developed a theoretical treatment based on the conservation of flow volume and mass to describe the influence of such processes on the depth discharge and density during transit we apply our model to a common scenario of lahar generation and evolution the formation of an initially dilute flow by catastrophic breaching or ejection of a volcanic summit crater lake followed by bulking due to incorporation of substrate materials and later debulking due to sediment deposition the key features of our model are time dependence and the inclusion of two terms describing the influx or efflux of sediments to or from the flow for lahars triggered by crater lake water we derive the time evolution of flow behavior for comparison with the well documented 1953 lahar of mount ruapehu new zealand our model demonstrates the importance of these processes on observable quantities such as flow depth density and deposit profiles hydrograph evolution and transformations between rheologic density regimes

gulf stream surface transport and statistics at 69 w from the geosat altimeter geosat altimeter height measurements for the gulf stream for three subtracks from the exact repeat mission were processed to remove the geoid and mean gulf stream height a gaussian model for the gulf stream velocity profile was used to predict the form of the residual height profiles seen by geosat and the mean height profile using estimates of the width and position derived from the height residuals estimates of the maximum surface velocity and the surface transport were obtained by a least squares fit of the synthetic height profiles to the data location statistics from the geosat data were in good agreement with values obtained from infrared images of the gulf stream maximum surface velocities were typically between 1 2 and 2 0 m s 1 the time series showed that surface transport is correlated primarily with the magnitude of the surface velocities although an anomalously large increase in surface transport in the winter of 1987 1988 was caused by an increase in the width of the gulf stream an analysis of the average annual signal in transport showed maximum values in the late fall and minimum transport in the late spring maximum minimum surface transport generally occurred when the gulf stream was north south of its mean position

on the meridional surface profile of the gulf stream at 55 w nine month records from nine inverted echo sounders iess are analyzed to describe the mean baroclinic gulf stream at 55 w ies acoustic travel times are converted to thermocline depth which is optimally interpolated kinematic and dynamic parameters gulf stream meridional position velocity and vorticity are calculated primary gulf stream variability is attributed to meandering and changes in direction a mean stream coordinate relative to gulf stream instantaneous position and direction meridional profile is derived and compared with results presented by other investigators the mean velocity is estimated at 0 84 m s 1 directed 14 to the right of eastward and the thermocline 12 c drops 657 m north to south corresponding to a baroclinic rise of the surface of 0 87 m the effect of gulf stream curvature on temporal mean profiles is found to be unimportant and of minimal importance overall the derived downstream current profile is well represented by a gaussian function and is about 190 km wide where it crosses zero surface baroclinic transport is estimated to be 8 5 104 m2 s 1 and maximum shear flanking the maximum is 1 2 10 5 s 1 results compare well with other in situ observational results from the same time period on the other hand analyses by others of concurrent satellite altimetry geosat suggest a considerably narrower more intense mean gulf stream

potential vorticity sources and sinks in a quasi geostrophic ocean beyond western boundary currents abstract potential vorticity dynamics for a quasi geostrophic eddy resolving general circulation model egcm are studied in order to determine the effects of mesoscale variability on the potential vorticity distribution of a wind driven ocean the study employs both eulerian and lagrangian analyses in the effort to describe the potential vorticity gain loss cycle along the path of a particle while the mean wind stress curl is the dominant potential vorticity source for the interior of the upper layer a redistribution of eddy potential vorticity creates sources of potential vorticity for the multiple gyres in the lower layers this redistribution is a result of the local generation of eddies via baroclinic instabilities these eddies are advected by the western boundary current into the midlatitude jet where they are responsible for a cross gyre potential vorticity exchange this exchange is concentrated at the entrance to the eastward jets where northward and southward boundary currents converge from

the dynamics of a simple baroclinic model of the wind driven circulation the authors study the dynamics of a two layer approximation to the steadily forced baroclinic circulation in a closed ocean basin with the aim of understanding its temporal variability and the onset of low frequency variability it is found that for a range of dissipation that includes values used in a number of ocean modeling studies in the past five years if one waits a sufficient length of time the asymptotic behavior of the system is characterized by only a very small number of degrees of freedom by varying the dissipation as a control parameter the authors identify abrupt transitions in the form of the long term circulation exhibited by the model one type of transition from a time varying circulation dominated by two frequencies to a chaotic circulation is accompanied by the appearance of low frequency variability this constitutes an internal mechanism for the production of variability at climatological timescales the model used is a two layer quasigeostrophic model forced by a steady wind stress with a uniform cyclonic curl dissipation is modeled by a lateral diffusion of momentum with a uniform eddy viscosity in two sets of experiments with two internal deformation radii and layer depth ratios the eddy viscosity is varied and the types of circulation that result are reported the stable steady circulation seen in the viscous limit gives way to time dependent circulations of increasing temporal complexity spatially the circulations fall into two types those dominated by large recirculating gyres in the western part of the basin and those with a strong and strongly meandering peripheral current reminiscent of that seen in the black sea from an examination of the linear eigenmodes of the steady circulation the initial transition to time dependence may be characterized as a baroclinic instability of the western recirculation gyre

determining geostrophic velocity shear profiles with inverted echo sounders it is known that vertical acoustic travel time round trip from the seafloor to the sea surface as measured by inverted echo sounders iess can be interpreted in terms of dynamic height this relationship is generalized and quantified in this paper for dynamic height di j integrated between a variety of pressure limits pi pj which span different portions of the main thermocline the generalized form of the di j relationships is nonlinear the conventional linear relationship is valid when the limits of integration span the entire main thermocline velocity and temperature records are shown to be highly correlated vertically indicating that the variability of the gulf stream and adjacent eddy field is dominated by the lowest baroclinic mode which is called a gravest empirical mode gem a parallel isotherms model is used to approximate the gem and to develop analytic expressions for the observed di j relationships in the gulf stream the analytic expressions represent the observations well with noise to signal variance ratios that are typically 1 using these new di j relationships the baroclinic velocity structure can be determined geostrophically by measuring the horizontal gradients with laterally separated measurements from iess baroclinic velocities determined from a two dimensional array of iess in the gulf stream during 1988 1990 agree with velocity shears directly measured by current meters the rms velocity difference between these two measurements of velocity shear at 400 dbar relative to 1000 dbar was 12 cm s 1 in the presence of typical currents of 50 cm s 1 ageostrophic motions at both mesoscale and submesoscale measured by the current meters but not by the iess contribute most of the velocity differences

satellite altimetry the marine geoid and the oceanic general circulation for technical reasons the general circulation of the ocean has historically been treated as a steady laminar flow field the recent availability of extremely highaccuracy and high precision satellite altimetry has provided a graphic demonstration that the ocean is actually a rapidly time evolving turbulent flow field to render the observations quantitatively useful for oceanographic purposes has required order of magnitude improvements in a number of fields including orbit dynamics gravity field estimation and atmospheric variability with five years of very high quality data now available the nature of oceanic variability on all space and time scales is emerging including new findings about such diverse and important phenomena as mixing coefficients the frequency wavenumber spectrum and turbulent cascades because the surface elevation is both a cause and consequence of motions deep within the water column oceanographers soon will be able to provide general circulation numerical models tested against and then combined with the altimeter data these will be complete three dimensional timeevolving estimates of the ocean circulation permitting greatly improved estimates of oceanic heat carbon and other property fluxes

evaluation of aster and srtm dem data for lahar modeling a case study on lahars from popocatepetl volcano mexico abstract lahars are among the most serious and far reaching volcanic hazards in regions with potential interactions of lahars with populated areas and human structures the assessment of the related hazards is crucial for undertaking appropriate mitigating actions and reduce the associated risks modeling of lahars has become an important tool in such assessments in particular where the geologic record of past events is insufficient mass flow modeling strongly relies on digital terrain data availability of digital elevation models dems however is often limited and thus an obstacle to lahar modeling remote sensing technology has now opened new perspectives in generating dems in this study we evaluate the feasibility of dems derived from the advanced spaceborne thermal emission and reflection radiometer aster and the shuttle radar topography mission srtm for lahar modeling on popocatepetl volcano mexico two gis based models are used for lahar modeling laharz and a flow routing based debris flow model modified single flow direction model msf both predicting areas potentially affected by lahars results of the lahar modeling show that both the aster and srtm dems are basically suitable for use with laharz and msf flow path prediction is found to be more reliable with srtm data though with a coarser spatial resolution errors of the aster dem affecting the prediction of flow paths due to the sensor geometry are associated with deeply incised gorges with north facing slopes laharz is more sensitive to errors of the aster dem than the msf model lahar modeling with the aster dem results in a more finely spaced predicted inundation area but does not add any significant information in comparison with the srtm dem lahars at popocatepetl are modeled with volumes of 1 10 5 to 8 10 6 m 3 based on ice melt scenarios of the glaciers on top of the volcano and data on recent and historical lahar events as regards recently observed lahars the travel distance of lahars of corresponding volume modeled with laharz falls short by 2 to 4 km an important finding is that the travel distance of potential lahar events modeled with laharz may differ by about 2 km when using srtm or aster data because of varying lateral flow volume distribution as a consequence verification and sensitivity analysis of the dem is fundamental to deriving hazard maps from predicted modeled inundation areas because of the global coverage of this type of remote sensing data the conclusion that both srtm and aster derived dems are feasible for lahar modeling opens a wide field of application in volcanic hazards studies

eddy mean flow interaction in the gulf stream at 68 w part i eddy energetics abstract from june 1988 to august 1990 twelve tall high performance current meter moorings measured the gulf stream s velocity and temperature fields at nominal depths of 400 m 700 m 1000 m and 3500 m along three lines centered at 68 w the overall eddy variability during the 26 month experiment was dominated by six large amplitude trough formation events with each event lasting approximately one month to determine the source s of energy for this eddy variability the eddy energy budget is evaluated traditionally the baroclinic conversion of mean potential energy to eddy potential energy is defined as a downgradient heat flux however because a nondivergent heat flux can be downgradient even under conditions in which there is no barolinic conversion occurring a better more dynamically correct definition of a baroclinic conversion rate is a downgradient horizontally divergent heat flux the horizontally divergent heat flux component is estimated to be approximately half the full horizontal hea

proterozoic zircon from augen gneiss yukon tanana upland east central alaska u th pb analyses of zircons from an ortho augen gneiss body in the yukon tanana upland of east central alaska yield strong evidence for the presence of early proterozoic material in this area u pb data define a chord that intersects concordia at about 2 300 and 345 m y we consider two interpretations 1 the protolith was intruded during the proterozoic and was subsequently metamorphosed in the paleozoic or more likely 2 the protolith was intruded in the paleozoic and incorporated material of proterozoic age an sm nd model age of about 1 900 m y on a whole rock sample of augen gneiss is additional evidence for the presence of proterozoic material in the gneiss k ar and u th pb dating of mica and sphene respectively reveal that younger thermal events occurred at least as recently as 110 m y ago

the three dimensional secondary circulation in developing gulf stream meanders from june 1988 until august 1990 an array of 12 inverted echo sounders ies 12 additional ies with pressure gauges to measure the abyssal pressure signal and 12 tall current meter moorings instrumented at depths 400 m 700 m 1000 m and 3500 m was deployed in the gulf stream near 688w the current meter array spanned an area of approximately 260 km by 200 km with nominal horizontal instrument spacing of 56 km in the cross stream direction and 65 km in the downstream direction six events were observed during the two year deployment during which a steep gulf stream meander trough and an abyssal cyclone developed concurrently two of the meander troughs eventually pinched off to form cold core rings as the abyssal flows spun up they became nearly barotropic with strong o 30 cm s21 swirl speeds that advected the main thermocline and helped steepen the meanders although the geostrophic barotropic flow played a large role in the development of the system ageostrophic flow was also required in this study the three dimensional mesoscale ageostrophic flow within the main thermocline is diagnosed during two steep meander trough events and one steep meander crest event it is shown that in addition to the alongstream horizontal ageostrophic flow associated with the curvature of the main jet cyclostrophic speeds greater than 25 cm s21 are not unusual on trough axes there is significant horizontal cross stream ageostrophic flow cross stream ageostrophic flow as high as 18 cm s 21 is diagnosed vertical momentum advection is also shown to be an important contributor to cross stream ageostrophic flow with values as high as 7 cm s 21 diagnosed the patterns of the ageostrophic flow are shown to be tied to the phasing between the upper level meander and the abyssal vortex both rotational and divergent patterns in the ageostrophic flow are evident for parcels on main thermocline isopycnals the ageostrophic flow provides an asymmetric cross frontal flow relative to the symmetric cross frontal flow associated with the barotropic vortices

a simple kinematic mechanism for mixing fluid parcels across a meandering jet abstract recent observations of fluid parcel pathways in the gulf stream using isopycnal rafos floats revealed a striking pattern of cross stream and vertical motion associated with meanders bower and rossby 1989 in an attempt to explain the observed pattern a two dimensional kinematic model of a meandering jet has been developed which enables examination of the relationship between streamfunction patterns and fluid parcel trajectories the streamfunction fields are displayed in a reference frame moving with the wave pattern so motions of fluid parcels relative to the jet can be seen more easily the results suggest that the observed pattern of cross stream motion results primarily from the downstream phase propagation of meanders the model successfully reproduces several of the most distinctive features of the float observations 1 entrainment of fluid into the gulf stream occurs at the leading edges of meander extrema while detrainment takes place at the trailing edges 2 exchange between the gu

a closer look at particle exchange in the gulf stream abstract the trajectories of 95 isopycnal floats deployed in the gulf stream in the last decade have shown that a substantial amount of particle exchange takes place between the gulf stream and the surrounding fluid at the level of the main thermocline this exchange is suggestive of significant cross stream eddy mixing but in order to accurately interpret the float exchange in terms of property exchange the location of float deployment was assessed relative to the strong potential vorticity front associated with the gulf stream the basic result of this analysis is that most of the observed float exchange is not representative of cross frontal exchange at the level where a strong potential vorticity front is present some fluid particles escape from the jet but most of them stay on the same side of the front in the deep main thermocline significant particle exchange is observed between the gulf stream and fluid on both sides of the jet but this exchange is indicative of particles circulating in a r

why western boundary currents in realistic oceans are inviscid a link between form stress and bottom pressure torques it is shown that wind stress curl is balanced by bottom pressure torque in a zonal integral over any strip wide enough to smooth out the effect of nonlinear terms typically about 3 of latitude the derivation is completely general as long as the zonal wind stress is balanced by form stress at each latitude as is known to be the case in the ocean this implies that viscous torques are not important in western boundary currents their place being taken by bottom pressure torques the prediction is confirmed in the context of a global eddy permitting numerical ocean model this link between form stress and bottom pressure torques makes it easier to consider southern ocean dynamics and subtropical gyre dynamics in the same conceptual framework with topographic interactions being important in both cases

a technique for diagnosing three dimensional ageostrophic circulations in baroclinic disturbances on limited area domains abstract the methodology developed by keyser et al for representing and diagnosing three dimensional vertical circulations in baroclinic disturbances using a two dimensional vector streamfunction referred to as the psi vector is restricted to f plane channel model geometry the vertical circulation described by the psi vector consists of the irrotational or divergent part of the ageostrophic wind and the vertical velocity a key property of the psi vector is that its projections onto arbitrarily oriented orthogonal vertical planes yield independent vertical circulations allowing separation of a three dimensional vertical circulation into two two dimensional components and thus objective assessment of the extent to which a three dimensional vertical circulation is oriented in a preferred direction here the methodology for determining the psi vector is modified to be suitable for real data applications the modifications consists of reformulating the diagnostic equations to apply to conformal map pr

hydrogeochemistry of seasonal flow regimes in the chena river a subarctic watershed draining discontinuous permafrost in interior alaska usa abstract thawing of permafrost and a shift in the timing of major seasonal transitions spring melt and fall freeze up are two anticipated effects of climate warming in northern regions these fundamental changes in terrestrial ecosystems could have major ramifications for the timing and fluxes of carbon and nutrient exports from watersheds and the geochemical signatures of northern rivers discontinuous permafrost which underlies watersheds in interior alaska usa is expected to degrade rapidly in response to climate warming and this will likely alter subsurface flows and flow paths water residence times water soil and water rock interactions this study of the chena river in interior alaska was undertaken to quantify dissolved organic carbon doc total dissolved nitrogen tdn major ion strontium isotope and stable oxygen and hydrogen isotope values during two year long time series sampling periods our goal was to identify the hydrogeochemical signatures associated with the major seasonal flow regimes periods of increased discharge such as spring melt and major summer precipitation events yielded elevated doc and tdn concentrations diluted major ion concentrations and shifted stable oxygen and hydrogen isotope ratios from base flow toward precipitation values during dry summer periods nutrient concentrations decreased and strontium isotope values were indicative of a higher proportion of silicate versus carbonate mineral dissolution winter base flow had a unique geochemical signal with a slight increase in tdn concentrations compared to typical summer conditions and a lower proportion of silicate versus carbonate mineral dissolution since flow paths in subarctic watersheds can change dramatically over the course of a year we interpreted our results within the context of a schematic model for subsurface flow to identify how permafrost degradation might affect nutrient exports and hydrogeochemical patterns in these watersheds

sea surface topographic variability near the new england seamounts an intercomparison among in situ observations numerical simulations and geosat altimetry from the regional energetics experiment intercomparisons are made among three sets of results for two regions of the gulf stream upstream and downstream of the new england seamount chain nesc observational records from 12 inverted echo sounders with pressure gauges ies pgs concurrent geosat altimeter crossover point differences and results from a primitive equation model of the region standard deviations of sea surface topography show generally good agreement for the three data sources no significant difference between the upstream and downstream regions is observed in the actual data ies pg records and geosat topographic variability have values of about 30 cm on both sides of the nesc although model results show a discrepancy in the eastern region barotropic fluctuations account for about 30 of the total surface topographic variability and are only partially correlated with baroclinic fluctuations

objective delineation of lahar inundation hazard zones a new method of delineating lahar hazard zones in valleys that head on volcano flanks provides a rapid objective reproducible alternative to traditional methods the rationale for the method derives from scaling analyses of generic lahar paths and statistical analyses of 27 lahar paths documented at nine volcanoes together these analyses yield semiempirical equations that predict inundated valley cross sectional areas a and planimetric areas b as functions of lahar volume v the predictive equations a 0 05v 2 3 and b 200v 2 3 provide all information necessary to calculate and plot in

lagrangian studies of fluid exchange between the gulf stream and surrounding waters abstract between spring of 1988 and winter of 1990 75 rafos floats were released east of cape hatteras near the center of the gulf stream on the 26 8 t surface o 15 c the purpose of this sequential deployment was to investigate the spatial and temporal characteristics of the meandering stream and the lagrangian properties of fluid motion in the upper thermocline these new observations were also intended to provide a database for comparative studies of fluid motion in the upper thermocline with similar observations made earlier 1984 85 in the middle and lower thermocline sixty one of the 75 rafos float trajectories in the 13 16 c layers have been analyzed from both a lagrangian and eulerian point of view the results reconfirm the strong baroclinic structure of the gulf stream established earlier and reveal enhanced cross stream motion with increasing depth and over the new england seamounts float trajectories tend to be more convoluted east of the seamounts reflecting the large amplitude meand

observations of gulf stream meander induced disturbances abstract using moored array data collected across the gulf stream at 55 w the author has investigated the dynamic signatures of the velocity fluctuations at the thermocline 550 m and near bottom 4000 m levels the cross stream amplitude and phase structures for motions with period from 64 to 12 days in a coordinate frame aligned with the instantaneous stream have a striking resemblance to those computed from small amplitude instability theory it is the sinuous or asymmetric mode that appears to dominate the observed fluctuations as is predicted in addition the mean downstream velocity at the two levels is consistent with a two layer model for the mean flow in which the lower layer has uniform potential vorticity when fit to the data this model predicts a value for the rate of change of the coriolis parameter appropriate to this latitude but one would expect it to be augmented by a factor of 2 or so by the significant slope of the bottom in this region

interannual variability of the kuroshio frontal structure along its western boundary in the north pacific ocean associated with the 1982 enso event abstract the vertically averaged temperature tav over the upper 200 m of ocean in the western boundary of the north pacific is used to detect changes in the strength and path of the kuroshio front along the western boundary from luzon 18 n to honshu 34 n during the period 1979 82 during this time the kuroshio front experienced significant interannual changes associated both with the disappearance of the kuroshio meander in late 1980 and with the development of the 1982 enso event in early 1982 when the kuroshio meander south of honshu disappeared from the fall of 1980 until the summer of 1981 the intensity of the kuroshio front increased associated with warmer than normal temperatures all along the western boundary of the north pacific from luzon to honshu the amplitude of the kuroshio meander was also correlated with fluctuations in the path of the kuroshio front at the tokara strait 30 n and the bashi strait 20 n and with the amplitude of the east china sea meander the east china sea me

initiation and flow behavior of the 1980 pine creek and muddy river lahars mount st helens washington two large high velocity lahars volcanic debris flows were triggered by a pyroclastic surge during the first few minutes of the may 18 1980 eruption of mount st helens the initial surge cloud evolved progressively by gravity segregation from a gas mobilized highly inflated density flow to a dense water mobilized basal debris flow lahar and accompanying ash cloud as it flowed down the east flank of the volcano the main source of the water for the lahars was probably from eroded snow and ice incorporated into the flow by turbulent mixing but ground water expelled together with the rock debris by the initiating volcanic explosions also may have contributed peak lahar discharge from the pine muddy fan upper smith creek and ape canyon probably exceeded 250 000 m 3 s initially but decreased exponentially in the downstream direction total volume of the lahars was in excess of 1 4 10 7 m 3 initial peak flow velocities in excess of 30 m s also decreased markedly downstream where flow was not impeded velocity was strongly related to the depth slope term r 2 3 s 1 2 from the manning uniform flow equation as a power law function during much of the route traveled lahar flow appears to have been supercritical deposits left in channels were generally thin relative to flow depth 0 to 2 5 m particles up to small boulder size were randomly distributed in the poorly sorted nonstratified matrix indicating complete suspension in a fully developed debris flow slurry however much larger clasts were transported as bed load computed sediment concentrations of matrix slurry samples ranged from 84 to 91 solids by weight and were similar for the two lahars two indirect methods for computing peak flow velocity previously only tentatively applied to debris flows were tested for accuracy by comparing computed lahar arrival times with recorded arrival times at swift reservoir the computed velocities appear to be 15 slower than the recorded velocities which is consistent with the restriction that the velocity formulas produce only minimum values

review of radiometric data from the yukon crystalline terrane alaska and yukon territory the results of more than 20 years of geochronological studies in the yukon crystalline terrane in east central alaska and the western yukon territory suggest at least six igneous and thermal metamorphic events plutonism during mississippian early jurassic mid cretaceous late cretaceous and early tertiary times is indicated evidence also indicates that mississippian early jurassic late early cretaceous and late cretaceous thermal metamorphic events have affected parts of the terrane the western part of the terrane was affected by a significant regional metamorphic event in late early cretaceous time followed by a terrane wide mid cretaceous plutonic event the pattern of k ar ages allows division of the terrane into domains bounded by northeast trending lineaments

gulf stream path analysis near the new england seamounts as part of the naval ocean research and development activity s regional energetics experiment 12 inverted echo sounders iess were deployed from june 1985 to july 1986 in two arrays across the historical mean path of the gulf stream near 67 w and 58 w slightly upstream and downstream of the new england seamount chain gulf stream positions and directions were computed at half day intervals for adjacent ies pairs levels of variability at the two array locations were similar but the characteristics of the meanders in terms of propagation and current direction were quite different evidence was found for a quasi stationary meander near 58 w features deduced from ies measurements are compared with concurrent infrared air dropped expendable bathythermograph and geosat altimetry observations

gulf stream path and thermocline structure near 74 w and 68 w the synoptic ocean prediction synop experiment had the goal of providing a physical understanding of energetic mesoscale eddy processes in the gulf stream in the synop inlet array off cape hatteras and in the central array near 68 w modred observations were collected from october 1987 through august 1990 the inlet array measured the surface path and bottom currents where the gulf stream leaves the continental margin to enter the deep water regime small amplitude propagating and growing meanders characterized the variability there the central array measured velocity and temperature as a proxy for density at four levels in the water column as well as the upper and deep level streamfunctions all with mesoscale resolution near 70 w the path envelope exhibited a relative node confined within a 40 km band 55 of the time near 68 w the path envelope was over 3 times as wide due to several elongated steep meander troughs and relatively steep meander crests the crests typically propagated downstream without much growth the troughs often stalled near 68 w steepened and persisted for one to several months two cases evolved into s shaped paths and subsequently formed rings even the time averaged fields showed a small trough in the mean path and thermocline structure whereas meanders of 20 to 60 day periods had similar spectral levels throughout 70 67 w meanders with long periods 85 day accounted for the local minimum in variance at 70 w bottom pressure and velocity observations revealed repeated periods of intense swirl speeds 0 30 m s 1 abyssal eddies the time averaged deep currents exhibited a mean cyclone centered 30 km offshore and downstream of the upper layer mean trough the cross stream slope of the thermocline steepened linearly with path curvature consistent with gradient wind balance structures are illustrated in the mapped fields consistent with baroclinic instability wherein troughs steepen and rings form

a smoothed particle hydrodynamic automaton of landform degradation by overland flow abstract a novel model for calculating hillslope degradation by overland flow is based on a coupling of the cellular automaton and smoothed particle hydrodynamics theories simulated debris laden floods were initiated on digital elevation models dems the flows were created by solving equations for diffusion routing and erosion and deposition we separated advection and diffusion terms using operator splitting then solved the advection term via automaton and the diffusion term via smoothed particle hydrodynamics the technique was tested on geometrically simple synthetic slopes against data for erosion and deposition by debris laden flows in a gully developing on a scoria cone arizona and against data on a recent moderate sized debris laden flood generated by possible partial glacier melting at popocatepetl volcano mexico the flow and erosion deposition patterns on the simple synthetic slopes appear intuitively reasonable on the synthetic scoria cone slope the model reproduced some of the observed spatial patterns of event scale erosion and deposition reasonable flow speeds runup heights and runout lengths were produced for the debris laden flood at popocatepetl the coupled cellular automaton smoothed particle hydrodynamics technique represents some advance in the modeling of landform degradation and channel development by cellular automata ca use of the technique may aid our understanding of the link between hillslope scale and landform scale degradation patterns

a cellular model of braided rivers a broad sheet of water flowing over non cohesive sediment typically breaks up into a network of interconnected channels called a braided stream fig 1 the dynamics of such networks are complex channels migrate laterally split rejoin and develop bars with the flow shifting unpredictably from one part of the network to another many processes are known to operate in a braided river1 3 but it is unclear which of these are essential to explain the observed dynamics we describe here a simple deterministic numerical model of water flow over a cohesionless bed that captures the main spatial and temporal features of real braided rivers the patterns arise from local scour and deposition caused by a nonlinear dependence of bedload sediment flux on water discharge although the morphology of the resulting network depends in detail on the sediment transport rule used in the model our results suggest that the only factors essential for braiding are bedload sediment transport and laterally unconstrained free surface flow

tropopause undulations and the development of extratropical cyclones part ii diagnostic analysis and conceptual model abstract a case study of a developing cyclone is used to show that the three dimensional distribution of height change during development can be strongly sensitive to temperature changes which occur in the lower stratosphere in association with an evolving tropopause undulation quantitative analysis of the storm with a geopotential height tendency equation indicates that a synergistic process developed between the stratosphere and troposphere whereby the vertical motion pattern maintained and intensified the upper level temperature anomalies while the subsequent upper level temperature advection led to an enhanced vertical circulation using the results of this diagnostic study a conceptual model is constructed the conceptual model is based on the hydrostatic and wind field adjustments that occur as tropopause undulations propagate over favored regions of tropospheric warm advection and less stable air

boundary current separation in a quasigeostrophic eddy resolving ocean circulation model abstract the response of a rectangular flat bottom eddy resolving quasigeostrophic ocean to a steady double gyre wind stress is studied to assess the sensitivity of the solutions to a partial slip lateral boundary condition in which tangential stress is proportional to tangential velocity the constant of proportionality has limiting values of zero and infinity corresponding to free slip no stress and no slip conditions respectively seven numerical solutions corresponding to the values 0 0 2 0 3 5 5 0 6 5 8 0 and 100 0 are obtained which span the free slip and no slip limits significant qualitative changes in the time mean behavior of the solutions are observed to occur with increasing these changes include a gradual retreat of the separation points of the western boundary currents in the subtropical and subpolar gyres a dramatic reduction in the basin integrated reservoirs of mean and eddy kinetic energy a weakening of bottom dissipation and its replacement by lateral dissipat

depositional processes in large scale debris flow experiments this study examines the depositional process and characteristics of deposits of large scale experimental debris flows to 15 m3 composed of mixtures of gravel to 32 mm sand and mud the experiments were performed using a 95 m long 2 m wide debris flow flume that slopes 31 following release experimental debris flows invariably developed numerous shallow 10 cm deep surges sediment transported by surges accumulated abruptly on a 3 runout slope at the mouth of the flume deposits developed in a complex manner through a combination of shoving forward and shouldering aside previously deposited debris and through progressive vertical accretion progressive accretion by the experimental flows is contrary to commonly assumed en masse sedimentation by debris flows despite progressive sediment emplacement deposits were composed of unstratified accumulations of generally unsorted debris hence massively textured poorly sorted debris flow deposits are not emplaced uniquely en masse the depositional

a petrologic and rb sr isotopic study of intrusive rocks near fairbanks alaska epizonal granodiorite and granite plutons intrude the northwestern portion of the yukon crystalline terrane near fairbanks alaska mineralogic major oxide and trace element studies indicate that the plutons represent a comagmatic fractionation suite a rb sr whole rock isochron for one pluton yields an age of 90 9 0 9 ma in agreement with previous k ar dating of biotite and hornblende and an initial 87sr 86sr ratio of 0 71238 0 00014 the elevated initial 87sr 86sr ratio suggests that the plutons may have had a different source from that of the belt of subduction related mid cretaceous plutonic rocks found farther to the southeast in the yukon crystalline terrane in contrast they appear to have been formed at least in part by anatectic melting of late proterozoic or early paleozoic crustal rocks comparison of aplite dike compositions with the synthetic granite system estimates of average uplift rate and k ar cooling ages of surrounding schists all indicate that the magmas that formed the plu

determining the mean gulf stream and its recirculations through combining hydrographic and altimetric data the altimetric data from the first 2 5 year geosat exact repeat mission were used to estimate the mean sea surface height ssh field in the region of the gulf stream and its recirculation gyres assuming the instantaneous surface velocity field is composed of an eastward flowing jet and two westward recirculating flows we used the time varying surface data from the altimeter to determine the shape of the along track mean ssh profiles and the historical hydrographic data to constrain the net ssh difference across the gulf stream system the two dimensional mean ssh field was determined by objectively mapping the mean height profiles along the ascending and descending tracks the ssh jump across the mean gulf stream has a maximum of 1 15m around 65 w and drops to an almost constant 0 9m downstream of the new england seamount chain nesc while the ssh jump associated with the mean northern recirculating flow is mostly uniform we found that the gulf stream s southern recirculation has two local gyres that are separated by the nesc an attempt was then made to estimate the mean deep circulation in this region by comparing the mean ssh field derived from the altimetry data and the surface dynamic height field based on the historical hydrographic data despite the large uncertainties the mean deep flow pattern thus estimated agrees favorably with the overall circulation pattern from the long term current meter observations like the well defined northern recirculation gyre we found that a continuous southward flow exists along 57 5 w which follows closely along the deep layer potential vorticity contours to the south of the gulf stream the deep circulation consists of two separated recirculation gyres the recirculation gyre to the east of the nesc appears to be trapped around the corner rise

downstream development of the gulf stream from 68 to 55 w abstract two ctd sections across the gulf stream at 68 and 55 w were acquired in late march of 1988 within 11 days of one another as part of an effort to look at downstream changes in the current using complementary current meter measurements sections of total barotropic and geostrophic baroclinic velocity are constructed and used to calculate transport in potential density classes potential vorticity sections are presented for both locations including the effects of planetary stretching and relative vorticity the data are also used to examine the core properties of recently formed 18 water at the two sections it is found that 1 water parcels in the exposed surface layers experience downstream density and potential vorticity changes consistent with surface forcing 2 thermocline gulf stream transport is conserved downstream and below the exposed layers is conserved within individual density classes 3 subthermocline gulf stream transport increases modestly at levels above the sill depth of th

potential vorticity balances and horizontal divergence along particle trajectories in gulf stream meanders east of cape hatteras abstract trajectories of 37 isopycnal rafos floats launched in the gulf stream off cape hatteras have been analyzed to examine the dynamics of meanders from a lagrangian viewpoint using the float data in conjunction with information on the structure of horizontal velocity shear from the pegasus study halkin and rossby variations in planetary curvature and shear vorticity have been estimated along the float trajectories changes in fluid layer thickness were then inferred assuming potential vorticity is conserved following the floats this analysis shows that curvature vorticity changes are typically 10 20 of f planetary vorticity as fluid parcels travel between meander troughs and crests lateral shear changes on the order of 20 30 of f are common as parcels move laterally relative to the jet axis between meander extrema although changes in these two terms are usually of opposite sign and tend to compensate significant layer thickness changes do occur with some parcels exhibiting 30 change

five year climatological survey of the gulf stream system and its associated rings a 5 year climatological survey of the gulf stream system s landward surface edge defines the mean standard deviation extreme limits annual and interannual variabilities and frequency distributions along 0 5 longitudinal transects from 91 to 44 w the climatology covers the loop current in the gulf of mexico and the gulf stream in the northwest atlantic ocean autocorrelations and power spectra are derived for longitudinal transects between 79 5 and 57 5 w the study also investigates the observed warm core ring and cold core ring movements and their areal extent the observed data are compiled from the oceanographic analysis charts produced by the national oceanic and atmospheric administration which utilize infrared satellite imagery and in situ observations east of cape hatteras the gulf stream system landward surface edge exhibits both interannual and annual signals the interannual variability is equal to the annual variability the mean monthly gulf stream position for the longitudinal band 70 44 w shifts from farthest north in september to farthest south in february the magnitude of the annual shift is largest near the grand banks frequency distributions of the gulf stream system position are quasi normal nearly everywhere autocorrelation plots from the 5 year time series of gulf stream positions at longitudinal transects 79 5 57 5 w exhibit three well defined e folding time regimes with a maximum time of 10 weeks at 72 w power spectrums from 79 5 to 57 5 w are red spectrums having dominant peaks of 1 year period or greater the largest total spectra energies are found at 61 w the loop current sheds rings at two apparent spatial scales which are labeled major 307 km mean and minor 185 km mean warm core rings annually the loop current sheds about one major warm core ring which translates into the western basin of the gulf of mexico and one minor warm core ring which is usually reabsorbed by the loop current the major loop current warm core ring sheddings have no seasonal preference loop current warm core rings have a mean velocity of 2 4 km d west southwest an average of 22 gulf stream warm core rings are formed and absorbed annually between 75 and 44 w the largest frequency of warm core ring formations is seen near the new england seamounts while the largest frequency of warm core ring absorptions is found near cape hatteras gulf stream warm core rings can absorb each other as occurred in 14 of the absorption cases with the highest frequency just upstream of the new england seamounts the gulf stream warm core rings have a surface diameter decay rate of 0 026 per week loop current warm core rings are similar the gulf stream warm core rings have a mean velocity of 2 4 km d west southwest cold core rings have a mean cool core surface diameter of 105 km and a mean velocity of 1 km d southwest more definitive conclusions on cold core rings are not possible as ring identification and tracking by satellite infrared imagery is tentative

smoothed particle hydrodynamic modeling of volcanic debris flows application to huiloac gorge lahars popocatepetl volcano mexico abstract lahars are among the most catastrophic volcanic processes and the ability to model them is central to mitigating their effects several lahars recently generated by the popocatepetl volcano mexico moved downstream through the huiloac gorge towards the village of santiago xalitzintla the most dangerous was the 2001 lahar in which the destructive power of the debris flow was maintained throughout the extent of the flow identifying the zone of hazard can be based either on numerical or empirical models but a calibration and validation process is required to ensure hazard map quality the geoflow sph depth integrated numerical model used in this study to reproduce the 2001 lahar was derived from the velocity pressure version of the biot zienkiewicz model and was discretized using the smoothed particle hydrodynamics sph method the results of the calibrated sph model were validated by comparing the simulated deposit depth with the field depth measured at 16 cross sections distributed strategically along the gorge channel moreover the dependency of the results on topographic mesh resolution initial lahar mass shape and dimensions is also investigated the results indicate that to accurately reproduce the 2001 lahar flow dynamics the channel topography needed to be discretized using a mesh having a minimum 5 m resolution and an initial lahar mass shape that adopted the source area morphology field validation of the calibrated model showed that there was a satisfactory relationship between the simulated and field depths the error being less than 20 for 11 of the 16 cross sections this study demonstrates that the geoflow sph model was able to accurately reproduce the lahar path and the extent of the flow but also reproduced other parameters including flow velocity and deposit depth

lagrangian motion and fluid exchange in a barotropic meandering jet kinematic models predict that a coherent structure such as a jet or an eddy in an unsteady flow can exchange fluid with its surroundings the authors consider the significance of this effect for a fully nonlinear dynamically consistent barotropic model of a meandering jet the calculated volume transport associated with this fluid exchange is comparable to that of fluid crossing the gulf stream through the detachment of rings although the model is barotropic and idealized in other ways the transport calculations suggest that this exchange mechanism may be important in lateral transport or potential vorticity budget analyses for the gulf stream and other oceanic jets the numerically simulated meandering jet is obtained by allowing a small amplitude unstable meander to grow until a saturated state occurs the resulting flow is characterized by finite amplitude meanders propagating with nearly constant speed and the results clearly illustrate the stretching and stirring of fluid particles along the edges of the recirculation regions south of the meander crests and north of the troughs the fluid exchange and resulting transport across boundaries separating regions of predominantly prograde retrograde and recirculating motion is quantified using a dynamical systems analysis the geometrical structures that result from the analysis are shown to be closely correlated with regions of the flow that are susceptible to high potential vorticity dissipation moreover in a related study this analysis has been used to effectively predict the entrainment and detrainment of particles to and from the jet

a review of the structure and dynamics of upper level frontal zones abstract this article presents a review of upper level fronts with the intent of synthesizing observational and modeling studies into a conceptual and dynamical description of these fronts and their evolution relative to the life cycle of midlatitude baroclinic waves the discussion begins by tracing present day concepts concerning the structure of upper level frontal systems which are based on composite analyses of radiosonde and aircraft data from their origins in the pioneering analyses of upper air data in the 1930s perspectives from scales both smaller and larger than upper level frontal systems are provided respectively by considering the effects of turbulent processes on frontal structure and dynamics and by relating variations in frontal structure to the evolution of the baroclinic waves that provide the dynamical environment for upper level frontogenesis the dynamics of upper level fronts are shown to comprise the interactions between the primary geostrophic and secondary ageostrophic cir

gulf stream structure transport and recirculation near 68 w an analysis of the structure and transport of the gulf stream is undertaken using direct current meter observations from a 13 mooring array deployed near 68 w from june 1988 to august 1990 the analysis is based on a stream coordinate approach in which velocities are rotated into a local downstream coordinate frame and averaged according to their relative cross stream location within the current the picture so obtained represents the average synoptic structure of the gulf stream rather than the eulerian averaged structure in which the current is weakened and broadened by lateral meandering of the current and adjacent recirculations many familiar features of the gulf stream are reproduced in the analysis including an asymmetric velocity profile with larger shear on the cyclonic shoreward side of the current an offshore displacement of the velocity core with depth and a subsurface velocity maximum on the offshore side of the current westward recirculations are also seen on both sides of the gulf stream maximum downstream speeds at the axis of the gulf stream reach approximately 2 0 m s at the surface and 0 7 m s at 1000 m roughly twice the corresponding eulerian averaged values the analysis also reveals a deep extension of the gulf stream at 3500 m depth with a width of 130 km and average speeds of 3 4 cm s the transport of the gulf stream in the stream coordinate frame is 113 8 sv approximately 30 larger than the eulerian averaged transport of 88 sv on the basis of these results and other recent studies the downstream transport increase of the gulf stream and the inflow structure to the gulf stream are reconsidered it is concluded that approximately 30 sv or over half of the transport increase between cape hatteras and 68 w is fed by inflow from the northern side of the gulf stream and that this inflow is concentrated near cape hatteras and 68 w where the gulf stream flows steeply across isobaths converging from the north