stalling of near inertial waves in a cyclone 1 observations at the edge of the loop current after hurricane katrina show inertial energy amplified at a depth of approximately 600 700 m ray analysis using the eddy field obtained from a numerical simulation with data assimilation suggests that the amplification is due to inertial motions stalled in a deep cyclone

near inertial internal wave interactions with mesoscale fronts observations and models moored observations of near inertial currents and buoyancy fluctuations from the frontal air sea interaction experiment fasinex may be understood as nearinertial internal waves reflecting off sheared background currents the fasinex moored array measured upper ocean currents temperature and conductivity between january and june 1986 in a region of the sargasso sea heavily populated by strong upper ocean fronts the background jets associated with these features have typical cross front scales of 20km maximum currents of 0 5 m s 1 and relative vorticities of 0 3 in the vicinity of fronts observed near inertial currents have short horizontal scales show no clear horizontal phase structure and trace out elongated current ellipses with elevated across front over along front variance during these periods inertial band pass buoyancy fluctuations often correlate with major axis currents wkb ray tracing models of propagating monochromatic plane waves exhibit horizontal phase propagation and correlations between minor axis currents and buoyancy and thus cannot explain these results models of near inertial internal waves reflected or trapped by a barotropic frontal jet produce mode like structures with short horizontal scales little horizontal phase propagation and anisotropic current ellipses aligned primarily cross front model buoyancy may correlate with one or both current ellipse components depending on the incidence angle of the wave and the degree to which it reflects completely reflected waves with horizontal scales similar to those of the front and near normal incidence angle produce current ellipses and correlation patterns consistent with the observations

an assessment of a ka band radar interferometer mission accuracy over eurasian rivers the water elevation recovery satellite mission is dedicated to the determination of land surface water extent elevation and slope using a ka band radar interferometer karin as its primary instrument determining these parameters to the accuracy desired for hydrologic applications is challenging the scientific objectives of the mission have been set up to 10 cm for the height budget and 10 murad 1 cm 1 km for the slope budget in this paper we implement a virtual mission simulation and use it to examine the measurement performances for three case studies in europe a relatively small river such as the meuse in northern western europe the lena river in russia one of the major siberian rivers and lake leman in western europe we simulate karin data with the associated instrument and geophysical error sources and implement ground processing techniques to go from the original raw data to science data we examine the impact of external errors in detail and implement calibration techniques that rely on the use of ancillary topographic data such as the shuttle radar topography mission digital elevation model dem we find that the impact of external errors can be reduced to a few centimeters the random error budget can also be reduced below 10 cm by means of appropriate processing the scientific requirements of the mission are shown to be met for all cases

spectral analysis of highly aliased sea level signals observing high wavenumber ocean phenomena with a satellite altimeter generally calls for along track analyses of the data measurements along a repeating satellite ground track are analyzed in a point by point fashion as opposed to spatially averaging data over multiple tracks the sea level aliasing problems encountered in such analyses can be especially challenging for topex poseidon all signals with frequency greater than 18 cycles per year cpy including both tidal and subdiurnal signals are folded into the 0 18 cpy band because the tidal bands are wider than 18 cpy residual tidal cusp energy plus any subdiurnal energy is capable of corrupting any low frequency signal of interest the practical consequences of this are explored here by using real sea level measurements from conventional tide gauges for which the true oceanographic spectrum is known and to which a simulated satellite measured spectrum based on coarsely subsampled data may be compared at many locations the spectrum is sufficently red that interannual frequencies remain unaffected intra annual frequencies however must be interpreted with greater caution and even interannual frequencies can be corrupted if the spectrum is flat the results also suggest that whenever tides must be estimated directly from the altimetry response methods of analysis are preferable to harmonic methods even in nonlinear regimes this will remain so for the foreseeable future we concentrate on three example tide gauges two coastal stations on the malay peninsula where the closely aliased k1 and ssa tides are strong and at canton island where trapped equatorial waves are aliased

waveform retracking for improving level estimations from topex poseidon jason 1 and jason 2 altimetry observations over african lakes estimating accurate water heights from complex radar return waveforms as observed by satellite altimeters over inland water bodies requires the application of postprocessing algorithms known as retrackers this study introduces a new retracking algorithm the institute for theoretical geodesy retracker itgr which is applied to topex poseidon t p jason 1 and jason 2 waveforms over african lakes the itgr algorithm first analyzes the pattern of returned waveforms to identify retrackable waveforms to provide range corrections it then applies a maximum likelihood estimator to a flexible waveform model which is constructed based on the number of identified peaks and their position in the waveform itgr also adopts an adjustable peak model to deal with both symmetric and asymmetric shaped peaks as a result the introduced method exhibits some skill in mitigating the impact of peaks in the waveform pattern we validated our retracked lake level heights llhs over lake volta by comparing them to daily tide gauge and llhs derived from various retracking algorithms as well as to llhs from the global reservoir and lake monitoring database our results over lake volta indicate that itgr llhs can be obtained with a standard deviation of 33 cm from t p 10 cm from jason 1 and 8 cm from the jason 2 altimeter this represents an improved performance when compared to existing retrackers investigations over a land contaminated region of lake victoria confirm the superior performance of subwaveform retrackers such as itgr over lake naivasha where mostly specular peak waveform patterns were observed the performance of these retrackers was found similar to that of conventional threshold retrackers

geodetic corrections to amazon river water level gauges using icesat altimetry 1 gauge stations are vital for monitoring water levels worldwide however many remote basins suffer from having gauges that are not tied to a common datum making it impossible to know absolute water elevations and therefore slope this problem is known to exist on the river amazon for example where water flux modeling efforts have been hampered by inconsistently leveled gauge data that serve as boundary conditions for these models this paper presents a methodology for using ice cloud and land elevation satellite icesat laser altimetry observations to geodetically level gauge stations a proof of concept study was carried out to ascertain the feasibility and accuracy of the approach and a mean absolute error of 19 cm was found once this was established gauges within the amazon basin were geodetically leveled this produced offsets for six gauges using a method that can be transferred to other locations and allows slope and discharge estimates to be calculated the results are significant with offsets as large as 13 37 m being added the approach could provide improvements in modeling floodplain flow processes and fluxes in the amazon basin and worldwide

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

on the mid depth circulation in the labrador and irminger seas a numerical circulation model with 1 6 resolution and an accurate topography formulation explains details of the observed circulation in the irminger and labrador seas that were recently revealed by lavender et al 2000 we show that the recirculation pattern is established through a locally wind induced flow controlled by the bottom topography and enhanced through remote baroclinic forcing by the dense plume of denmark strait overflow water the basic circulation is a robust feature in a hierarchy of model setups it exists in the purely barotropic case driven by steady winds and is even maintained when realistic daily forcing is added the narrow recirculation zone is manifested by a sea level depression spanning from the denmark strait across the irminger into the labrador sea

trapped near inertial waves and enhanced chlorophyll distributions waves with near inertial frequencies were observed along a front associated with a large mesoscale feature in the sargasso sea during the late summer of 1987 high subsurface chlorophyll concentrations occurred on the edge of this front coincident with the wave packets the amplitude of the waves increased with time and kinetic energy propagated downward reducing 20 m richardson numbers in the thermocline to 1 or less chlorophyll levels were episodic showing no periodicity coincident with wave dynamics however on two occasions chlorophyll concentration increased from 1 mg chl m 3 several hours after the waves penetrated the thermocline it was hypothesized that mixing associated with shear instabilities stimulated new production a diffusivity model combined with nutrient data produced a phytoplankton bloom that accounted for only one of the maxima the other increase in chlorophyll may have been the result of horizontal advection of the wave packets near the front

icesat derived inland water surface spot heights accurate measurement of water surface height is key to many fields in hydrology and limnology satellite radar and laser altimetry have been shown to be useful means of obtaining such data where no ground gauging stations exist and the accuracy of different satellite instruments is now reasonably well understood past validation studies have shown water surface height data from the icesat instrument to have the highest vertical accuracy mean absolute errors of 10 cm for icesat compared for example with 28 cm from envisat yet no freely available source of processed icesat data currently exists for inland water bodies here we present a database of processed and quality checked icesat derived inland water surface heights iwsh for water bodies greater than 3 arc sec 92 m at the equator in width four automated methods for removing spurious observations or outliers were investigated along with the impact of using different water masks we find that the best performing method ensures that observations used are completely surrounded by water in the srtm water body data using this method for removing spurious observations we estimate transect averaged water surface heights at 587 292 unique locations from 2003 to 2009 with the number of locations proportional to the size of the river

near real time flood wave approximation on large rivers from space application to the river po italy 1 this paper investigates the potential of low cost spaceborne data to approximate longitudinal surface profiles during flood events on large rivers in february 2000 the shuttle radar topography mission srtm measured the elevation of most of the earth s surface with spatially continuous sampling and an absolute vertical accuracy between 5 6 and 9 m the vertical error has been shown to change with topographic complexity being less important over flat terrain this allows water surface slopes to be measured and associated discharge volumes to be estimated for open channels in large basins such as the amazon building on these capabilities this paper demonstrates that near real time coarse resolution radar imagery of a recent flood event on a 98 km reach of the river po italy combined with srtm terrain height data leads to a water slope remarkably similar to that derived by combining the radar image with highly accurate airborne laser altimetry moreover it is shown that this spaceborne flood wave approximation compares well to a hydraulic model and thus allows the performance of the latter calibrated on a previous event to be assessed when applied to an event of different magnitude in near real time these results are not only of great importance to real time flood management and flood forecasting but also support the upcoming surface water and ocean topography mission that will routinely provide water levels and slopes with higher precision around the globe

north atlantic climate and deep ocean flow speed changes during the last 230 years variations in the near bottom flow speed of iceland scotland overflow water isow are documented in a 230 year long deep sea sediment record from the eastern flank of reykjanes ridge in the subpolar north atlantic at sub decadal time scales for recent decades the isow palaeocurrent reconstructions show similarities with observational hydrographic data furthermore recent isow flow changes fall mostly within the range of its variability of the past 230 years the record also reveals a hitherto unrecognized coupling of deep flow speeds in the subpolar north atlantic with the north atlantic oscillation nao index with more less vigorous isow flow during negative positive phases of the nao our results suggest that the changes in isow vigor are largely controlled by the transport and characteristics of labrador sea water rather than variations in the overflow itself with implications for the meridional overturning of the atlantic ocean and climate

circulation characteristics in three eddy permitting models of the north atlantic a systematic intercomparison of three realistic eddy permitting models of the north atlantic circulation has been performed the models use different concepts for the discretization of the vertical coordinate namely geopotential levels isopycnal layers terrain following sigma coordinates respectively although these models were integrated under nearly identical conditions the resulting large scale model circulations show substantial differences the results demonstrate that the large scale thermohaline circulation is very sensitive to the model representation of certain localised processes in particular to the amount and water mass properties of the overflow across the greenland scotland region to the amount of mixing within a few hundred kilometers south of the sills and to several other processes at small or sub grid scales the different behaviour of the three models can to a large extent be explained as a consequence of the different model representation of these processes

the improved retrieval of coastal sea surface heights by retracking modified radar altimetry waveforms measuring sea surface height ssh using satellite altimetry in coastal from coasts and shallow water region has long been a challenge since the radar altimeter waveforms are often contaminated by complex coastal topography and do not conform to theoretical brown waveform shapes the land contamination or surface variation due to ocean dynamics induce spurious peaks in altimeter waveforms that deviate from brown s theoretical model as the altimeter footprint approaches or leaves the shoreline these spurious peaks should be mitigated to minimize the error in the determination of the leading edge and associated track offset in the waveform retracking process here we introduce a novel algorithm to modify coastal waveforms 0 5 7 km from coasts using 20 hz altimetry data thus improving coastal data coverage and accuracy we apply our processing algorithm and use various retrackers to compare retrieved coastal sshs in four study regions in north america using both envisat and jason 2 altimetry the retrieved altimetry data in the 1 7 km coastal zone indicate that the 20 threshold retracker with modified waveform has a rmse of 21 cm as compared with in situ tide gauge data which corresponds to a 63 improvement in accuracy compared to the use of the original deep ocean waveform retracker

internal inertial waves in a surgasso sea front abstract this work examines the presence of internal inertial waves in a front in the north atlantic subtropical convergence zone results of doppler shear profiler and towed thermistor chain surveys are displayed to document the position and magnitude of the front objective maps of the total measured velocity are computed and subtracted from the observed velocity fields the remaining wave signal is processed to yield horizontal towed and vertical dropped kinetic energy spectra across the front from these rotary spectra are also computed along the line of tow and in the vertical to determine the horizontal and vertical anisotropy it is found that several nearly monochromatic waves are propagating northward and southward from the front with horizontal length scales of 32 50 km it was also discovered that the region of anticyclonic frontal vorticity exhibits an excess of downgoing energy at the longest vertical wavelength thus sampled 50 m while the region of cyclonic vorticity possesses more

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

fine scale temperature variability the influence of near inertial waves measurements made with a towed thermistor chain and acoustic doppler current profiler in the seasonal thermocline of the sargasso sea are examined for relationships among small scale temperature activity shear and internal wave variability patches of intense activity measuring 5 10 m high and several kilometers in length are found to persist within a near inertial wave packet the packet was tagged with a drogue and followed for about 16 hours as it was advected along an edge of a cold core ring the patches occur along surfaces of high vertical shear where the richardson number 7 m vertical resolution falls to values less than one within the patches are groups of small scale internal waves and fluid overturns the overturns are 1 3 m high and are associated with wave breaking events away from the wave packet activity levels are less and the active fraction of the water column appears to be linked to variability in the internal wave field it is conjectured that the near inertial wave patches are the same species as persistent mixing patches observed by gregg et al 1986 which were also associated with a near inertial wave

some dynamical constraints on upstream pathways of the denmark strait overflow abstractthe east greenland current egc had long been considered the main pathway for the denmark strait overflow dso recent observations however indicate that the north icelandic jet nij which flows westward along the north coast of iceland is a major separate pathway for the dso in this study a two layer numerical model and complementary integral constraints are used to examine various pathways that lead to the dso and to explore plausible mechanisms for the nij s existence in these simulations a westward and nij like current emerges as a robust feature and a main pathway for the denmark strait overflow its existence can be explained through circulation integrals around advantageous contours one such constraint spells out the consequences of overflow water as a source of low potential vorticity a stronger constraint can be added when the outflow occurs through two outlets it takes the form of a circulation integral around the iceland faroe ridge in either case the direction of overall

the sensitivity of the greenland scotland ridge overflow to forcing changes processes that influence the volume and heat transport across the greenland scotland ridge system are investigated in a numerical model with horizontal resolution the focus is on the sensitivity of cross ridge transports and the reaction of the subpolar north atlantic ocean circulation to changes in wind stress and buoyancy forcing on seasonal to interannual timescales a general relation between changes in wind stress or cross ridge density contrasts and the overturning transport of greenland iceland norwegian seas source water is established from a series of idealized experiments the relation is used subsequently to interpret changes in an experiment over the years 1992 97 with realistic forcing on seasonal and interannual timescales there is a clear correlation between heat flux and wind stress curl variability the realistic model suggests a steady decrease in the strength of the cyclonic subpolar gyre of the north atlantic with a corresponding decrease in heat transport during the 1990s

the joint gravity model 3 an improved earth geopotential model complete to spherical harmonic degree and order 70 has been determined by combining the joint gravity model 1 jgm 1 geopotential coefficients and their associated error covariance with new information from slr doris and gps tracking of topex poseidon laser tracking of lageos 1 lageos 2 and stella and additional doris tracking of spot 2 the resulting field jgm 3 which has been adopted for the topex poseidon altimeter data rerelease yields improved orbit accuracies as demonstrated by better fits to withheld tracking data and substantially reduced geographically correlated orbit error methods for analyzing the performance of the gravity field using high precision tracking station positioning were applied geodetic results including station coordinates and earth orientation parameters are significantly improved with the jgm 3 model sea surface topography solutions from topex poseidon altimetry indicate that the ocean geoid has been improved subset solutions performed by withholding either the gps data or the slr doris data were computed to demonstrate the effect of these particular data sets on the gravity model used for topex poseidon orbit determination

characterization of complex fluvial systems using remote sensing of spatial and temporal water level variations in the amazon congo and brahmaputra rivers the surface water and ocean topography swot satellite mission will provide global space based estimates of water elevation its temporal change and its spatial slope in fluvial environments as well as across lakes reservoirs wetlands and floodplains this paper illustrates the utility of existing remote sensing measurements of water temporal changes and spatial slope to characterize two complex fluvial environments first repeat pass interferometric sar measurements from the japanese earth resources satellite are used to compare and contrast floodplain processes in the amazon and congo river basins measurements of temporal water level changes over the two areas reveal clearly different hydraulic processes at work the amazon is highly interconnected by floodplain channels resulting in complex flow patterns in contrast the congo does not show similar floodplain channels and the flow patterns are not well defined and have diffuse boundaries during inundation the amazon floodplain often shows sharp hydraulic changes across floodplain channels the congo however does not show similar sharp changes during either infilling or evacuation second shuttle radar topography mission measurements of water elevation are used to derive water slope over the braided brahmaputra river system in combination with in situ bathymetry measurements water elevation and slope allow one to calculate discharge estimates within 2 3 accuracy these two studies illustrate the utility of satellite based measurements of water elevation for characterizing complex fluvial environments and highlight the potential of swot measurements for fluvial hydrology copyright 2010 john wiley sons ltd

statistics of mixing patches observed in the sargasso sea temperature measurements made with a towed thermistor chain in the seasonal thermocline of the sargasso sea have been converted to sections of fine structure activity by normalizing values of meter scale horizontal fluctuations by the local vertical gradient individual patches of high activity are then separated from background and examined for length l height h aspect ratio l h and signal intensity over the range 0 5m h 20m and 30 m l 2 km the aspect ratio tends to be about 100 similar to reports of turbulent patches measured with velocity microstructure profilers numbers of patches decrease with increasing patch height and length and large patches tend to have higher activity levels

interannual changes in the overflow from the nordic seas into the atlantic ocean through denmark strait the global thermohaline circulation is an important part of earth s climate system cold dense water formed in the nordic seas enters the atlantic ocean as overflows across the sills of the greenland scotland ridge the denmark strait overflow dso is one of the main sources of north atlantic deep water until now the dso has been believed to be stable on interannual timescales here for the first time evidence is presented from a 4 year program of observations showing that overflow transports in 1999 2000 were approximately 30 higher than previous estimates later transports decreased remarkably during the observation period coincident with a temporary temperature increase of about 0 5 c

improving hydrological information acquisition from dem processing in floodplains extraction of hydrological information from digital elevation models dems is a required step when conducting any spatially distributed hydrological modelling in particular automated methods are proposed to extract the drainage structure from the dem however a realistic river network is not always derived from conventional dem processing methods indeed inaccuracy occurs in flat areas corresponding to floodplains in these areas additional sources of information are required to extract the correct drainage direction from the dem in this study it is demonstrated that traditional approaches of dem preprocessing such as the commonly known stream burning fail to provide correct maps of drainage directions and catchment areas when the extension of flat areas is large a new method is proposed to take advantage of available imagery data this method is based on a double dem burning process dem is first burned in the main rivers using the channel network and then in the floodplain using the spatial distribution of floodplains provided by classified satellite images in this sense the method has been referred to as the floodplain burning approach or simply fb approach spatial distribution of floodplains is derived from a multitemporal sar image classification a system of equations is used to vary the elevation offset required to be burnt in each cell representing the floodplain according to the minimal distance from the channel network which is calculated by a distance transformation the fb approach was applied to a sub basin located within the larger amazon river basin the region is characterized by large floodplain extensions basin delineation maps derived from the new method were compared with those obtained from the traditional stream burning method and highlighted more realistic results copyright 2008 john wiley sons ltd

using altimetry waveform data and ancillary information from srtm landsat and modis to retrieve river characteristics in this paper spaceborne radar altimeters are shown to have the potential for monitoring the height of large rivers with accuracies of approximately 1 m however the need for a better height accuracy and the observations of smaller continental basins have led to studies on how to improve and extend the use of nadir altimeter data conventional retracking techniques over land are limited to the examination of altimeter waveforms on a case by case basis due to the arbitrary geometry which may be present at altimeter river crossings this approach may be limited to large rivers which approximate ocean crossings to overcome this limitation we introduce a waveform fitting method which uses the entire set of waveforms associated with a water crossing rather than individual waveforms by using ancillary data such as digital elevation model obtained from shuttle radar topography mission and gtopo30 and classification maps obtained from landsat and modis it is possible to recast the retracking problems as a maximum likelihood estimation problem theoretical power returns based on the a priori knowledge of the observed scenes are generated resulting in a parametric library of waveform histories which is then used to constrain the estimation for demonstration we concentrate on the river meuse in northern western europe and on the river lena in russia the meuse has important social impact since it has flooded in the past and better real time predictions of its changing stage may improve flood forecasting skill furthermore it presents a challenge to conventional nadir altimeter waveform retracking we will present both theoretical performance results and demonstrate the feasibility based on real altimeter data

remote sensing of volumetric storage changes in lakes three dimensional remote sensing promises a giant leap forward for surface water hydrology in much the same way that radar altimetry transformed physical oceanography however the complex geometries of small terrestrial water bodies introduce difficulties particularly with respect to trade offs between changing water depth and inundation area we use in situ measurements of water surface stage h dt and remotely sensed area a to compute time varying storage changes s in nine lakes of the peace athabasca delta canada despite their identical geomorphic setting regression slopes between h and a vary significantly between lakes primarily from a predictable area effect but also small bathymetric variations between basins on average lateral contraction expansion versus stage adjustment contributes as little as 7 versus 93 to as much as 76 versus 24 of overall storage change s we conclude that both surface area and h dt rather than just either alone must be measured to confidently estimate s from space copyright 2009 john wiley sons ltd

surface water dynamics in the amazon basin application of satellite radar altimetry 1 satellite radar altimetry has the ability to monitor variations in surface water height stage for large wetlands rivers and associated floodplains a clear advantage is the provision of data where traditional gauges are absent as part of an international program a complete altimetric analysis of the amazon basin is being undertaken here an updated and more rigorous evaluation of the topex poseidon t p data set is presented for the first 7 5 years of the mission with an initial study group of 230 targets height variability at many ungauged locations can be observed for 30 50 the range reflecting the clarity of the variations in lieu of instrument limitations an assessment of the instrument performance confirms that the minimum river width attainable is 1 km in the presence of some inundated floodplain this constraint does allow observation of the main stem solimoes amazon and the larger tributaries but rugged terrain in the vicinity of the target additionally places severe limitations on data retrieval first order validation exercises with the deduced 1992 1999 time series of stage fluctuations reveal accuracies ranging from tens of centimeters to several meters mean 1 1 m rms altimetric water levels in the solimoes and amazon are particularly well defined with amplitudes 13 m and variations in peak level timing from may to july the water surface gradient of the main stem is found to vary both spatially and temporally with values ranging from 1 5 cm km downstream to 4 0 cm km for more upstream reaches in agreement with ground based estimates the seasonal variability of the gradients reveals that the hysteresis characteristic of the flood wave varies along the main stem and the derived altimetric velocity of this flood wave is estimated to be 0 35 m s overall the altimetric results demonstrate that the t p mission is successfully monitoring the transient flood waves of this continental scale river basin

seasonal fluctuations in the mass of the amazon river system and earth s elastic response 1 a gps station in manaus near the center of the amazon basin manifests an annual cycle of vertical displacement with a peak to peak amplitude of 50 75 mm this is by far the largest crustal oscillation observed to date and nearly 2 3 times larger than the amplitude predicted for this region vertical ground displacement is strongly anti correlated with the local stage height of the amazon river with no detectable time lag between the two time series this suggests that we are observing for the first time a purely elastic response to changes in the weight of a flowing river system we use a simple hydrological model to relate stage height to the regional pattern of flooding and argue that the elastic oscillations observed in manaus are dominated by changes in water loading developed within 200 km of the gps station

spreading of near inertial energy in a 1 12 model of the north atlantic ocean near inertial energy in the ocean is thought to be redistributed by s dispersion whereby near inertial waves generated at the surface by wind forcing propagate downward and equatorward in this letter we examine the spreading of near inertial energy in a realistic 1 12 model of the north atlantic driven by synoptically varying wind forcing we find that 1 near inertial energy is strongly influenced by the mesoscale eddy field and appears to be locally drained to the deep ocean largely by the chimney effect associated with anticyclonic eddies and 2 the interior of the subtropical gyre shows very low levels of near inertial energy contrary to expectations based on the s dispersion effect

origin transport and deposition of leaf wax biomarkers in the amazon basin and the adjacent atlantic paleoenvironmental studies based on terrigenous biomarker proxies from sediment cores collected close to the mouth of large river systems rely on a proper understanding of the processes controlling origin transport and deposition of biomarkers here we contribute to the understanding of these processes by analyzing long chain n alkanes from the amazon river system we use the dd composition of long chain n alkanes from river bed sediments from the amazon river and its major tributaries as well as marine core top samples collected off northeastern south america as tracers for different source areas the d13c composition of the same compounds is used to differentiate between long chain n alkanes from modern forest vegetation and petrogenic organic matter our d13c results show depleted d13c values 33 to 36 in most samples indicating a modern forest source for most of the samples enriched values 31 to 33 are only found in a few samples poor in organic carbon indicating minor contributions from a fossil petrogenic source long chain n alkane dd analyses show more depleted values for the western tributaries the madeira and solimoes rivers 152 to 168 while n alkanes from the lowland tributaries the negro xingu and tocantins rivers 142 to 154 yield more enriched values the n alkane dd values thus reflect the mean annual isotopic composition of precipitation which is most deuterium depleted in the western amazon basin and more enriched in the eastern sector of the basin samples from the amazon estuary show a mixed long chain n alkane dd signal from both eastern lowland and western tributaries marine core top samples underlying the amazon freshwater plume yield dd values similar to those from the amazon estuary while core top samples from outside the plume showed more enriched values although the variability in the river bed data precludes quantitative assessment of relative contributions our results indicate that long chain n alkanes from the amazon estuary and plume represent an integrated signal of different regions of the onshore basin our results also imply that n alkanes are not extensively remineralized during transport and that the signal at the amazon estuary and plume includes refractory compounds derived from the western sector of the basin these findings will aid in the interpretation of plant wax based records of marine sediment cores collected from the adjacent ocean

channel floodplain geomorphology along the solimoes amazon river brazil across the cratonic landscape of brazil the solimoes amazon river transports to its delta plain 1240 mt of suspended sediment derived from andean erosion and reworks another 3200 mt of floodplain sediments distribution of these sediments has resulted in a variable along stream pattern of geomorphology the upstream reaches are characterized by sediment erosion in the main channel and deposition in floodplain channels that are an order of magnitude smaller in discharge than the main channel sediment deposition in and migration of the floodplain channels erases oxbow lakes of the main channel and yields an intricate scroll bar topography that forms the boundaries of hundreds of long narrow lakes in contrast downstream reaches are characterized by channels restricted by stabilizing long term levee building and floodplain construction dominated by overbank deposition overbank deposition buries the scroll bar topography resulting in a flat floodplain covered by a patchwork of large more equant shallow lakes on the basis of estimated rates of recycling of floodplain sediments the modern floodplain of the brazilian amazon could have been recycled in 5000 yr and is recycled more rapidly in the upstream than the downstream reaches the cratonic interior is interrupted by structural arches that bound intracratonic basins four of these arches cross the valley of the main river system at intervals of several hundred kilometres and impart a tectonic imprint on the channel floodplain geomorphology at this spatial scale structural arches appear to exert a primary influence by promoting entrenchment of the river as it passes through zones of deformation thus restricting channel movement for example as the river crosses the purus arch the valley narrows to 20 km compared to an average of 45 km the water surface gradient decreases sediment is deposited and yet the rate of channel migration is negligible hence the effect of the arches is to create a landscape where on the spatial scale of hundreds of kilometres the river is confined and entrenched in its valley is straight and is relatively immobile local valley tilting apparently unrelated to the arch structures also imprints the geomorphology in particular a tilted valley in the upstream reaches appears to have caused avulsions which have left behind the only large scale oxbow type features on the brazilian amazon river floodplain

dynamics of north atlantic deep water masses during the holocene high resolution flow speed reconstructions of two core sites located on gardar drift in the northeast atlantic basin and orphan knoll in the northwest atlantic basin reveal a long term decrease in flow speed of northeast atlantic deep water neadw after 6 500 years benthic foraminiferal oxygen isotopes of sites currently bathed in neadw show a 0 2 depletion after 6 500 years shortly after the start of the development of a carbon isotope gradient between neadw and norwegian sea deep water we consider these changes in near bottom flow vigor and benthic foraminiferal isotope records to mark a significant reorganization of the holocene deep ocean circulation and attribute the changes to a weakening of neadw flow during the mid to late holocene that allowed the shoaling of lower deep water and deeper eastward advection of labrador sea water into the northeast atlantic basin

synoptic sections of the denmark strait overflow we report on a rapid high resolution survey of the denmark strait overflow dso as it crosses the sill the first such program to incorporate full water column velocity profiles in addition to conventional hydrographic measurements seven transects with expendable profilers over the course of one week are used to estimate volume transport as a function of density our observations reveal the presence of a strongly barotropic flow associated with the nearly vertical front dividing the arctic and atlantic waters the seven section mean transport of water denser than 27 8 is 2 7 0 6sv while the mean transport of water colder than 2 0 c is 3 8 0 8 sv although this is larger than the 2 9 sv of 2 c water measured by a 1973 current meter array we find that a sampling of our sections equivalent to the extent of that array also measures 2 9sv of cold water both the structure and magnitude of the measured flow are reproduced well by a high resolution numerical model of buoyancy driven exchange with realistic topography

the m2 tide on the amazon shelf as part of a multidisciplinary amazon shelf sediment study amasseds moored and shipboard current measurements made over the amazon shelf during 1990 1991 have been analyzed to determine the dominant semidiurnal tidal constituent the m2 these results have been combined with coastal sea level data from within the amazon and para rivers the adjacent shelf and with satellite derived tidal elevation data from off the shelf to provide a more complete description of the m2 tide in this complex river shelf system near the amazon river mouth the m2 tide propagates across the shelf and through the mouth as a damped progressive wave with its amplitude decreasing and phase increasing upriver over the adjacent shelf north of cabo norte the m2 tide approaches a damped standing wave with large amplitudes greater than 1 5 m near the coast due to near resonance within the coastal embayment formed by the cabo norte shoal to the south and cabo cassipore to the north the observed m2 tidal currents are nearly rectilinear and oriented primarily across the local isobaths comparisons between tidal observations in both the north channel and the cabo norte cabo cassipore embayment and a simple variable width channel tidal model indicate that 1 most of the m2 tidal energy dissipation occurs over the mid and inner shelf in water depths less than 20 m and 2 fluid muds found there cause a significant reduction of order 50 in the effective bottom friction felt by the m2 tide the approximate resonant period of the cabo norte cabo cassipore embayment is 11 9 hours and at resonance the average energy dissipation per forcing period is roughly 2 2 times the average mechanical energy in the embayment this damping rate is large enough that the tidal amplification is rather insensitive to forcing frequency so that the response of the embayment to forcing over the semidiurnal band should be essentially the same the vertical structure of the m2 tidal current is examined at one outer shelf site located in 65 m water depth the observed semimajor axis increases logarithmically with height above bottom within the lowest 1 2 m and reaches a maximum in excess of 0 5 m s at approximately 11 m above bottom the mean ellipticity is small less than 0 1 and positive indicating clockwise rotation of a nearly rectilinear current and the semimajor axis is oriented within 10 of the local cross isobath direction the m2 phase increases with height above bottom with flood at the bottom leading flood at the surface by about 1 hour a simple local homogeneous tidal model with time and space dependent eddy viscosity simulates the observed near bottom velocity reasonably well however the model suggests that stratification above the lowest few meters may significantly affect the tidal boundary layer structure at this site the m2 energy flux onto the amazon shelf and into the amazon and para rivers has been estimated using current and surface elevation data and the best fit variable width channel model results the net m2 energy flux into the mouths of the amazon and para rivers is 0 47 1010w and 0 19 1010w respectively a net m2 energy flux of about 3 3 1010w occurs onto the shelf between the north channel of the amazon river and cabo cassipore this stretch of the amazon shelf accounts for about 1 3 of the global dissipation of the m2 tide

exchanges of sediment between the flood plain and channel of the amazon river in brazil sediment transport through the brazilian sector of the amazon river valley a distance of 2010 km involves exchanges between the channel and the flood plain that in each direction exceed the annual flux of sediment out of the river at obidos 1200 mt yr 1 the exchanges occur through bank erosion bar deposition settling from diffuse overbank flow and sedimentation in flood plain channels we estimated the magnitude of these exchanges for each of 10 reaches of the valley and combined them with calculations of sediment transport into and out of the reaches based on sediment sampling and flow records to define a sediment budget for each reach residuals in the sediment budget of a reach include errors of estimation and erosion or deposition within the channel the annual supply of sediment entering the channel from bank erosion was estimated to average 1570 mt yr 1 1 3 the obidos flux and the amount transferred from channel transport to the bars 380 mt yr 1 and the flood plain 460 mt yr 1 in channelized flow 1230 mt yr 1 in diffuse overbank flow totaled 2070 mt yr 1 1 7 the obidos flux thus deposition on the bars and flood plain exceeded bank erosion by 500 mt yr 1 over a 10 16 yr period sampling and calculation of sediment loads in the channel indicate a net accumulation in the valley floor of approximately 200 mt yr 1 over 16 yr crudely validating the process based calculations of the sediment budget which in turn illuminate the physical controls on each exchange process another 300 400 mt yr 1 are deposited in a delta plain downstream of obidos the components of the sediment budget reflect hydrologic characteristics of the valley floor and geomorphic characteristics of the channel and flood plain which in turn are influenced by tectonic features of the amazon structural trough

the inertial chimney the near inertial energy drainage from the ocean surface to the deep layer a three dimensional primitive equation numerical model is used to study the behavior of near inertial waves generated by surface wind stress on an plane the model is fixed depth with a rigid lid on the surface and is horizontally periodic this study shows the behaviors of the wind generated near inertial waves for four different eddies 1 a subtropical cold core eddy 2 a subtropical warm core eddy 3 a california subsurface warm core eddy and 4 the gulf stream warm core ring the mean secondary circulation generated by the wind eddy interaction has magnitude to comparable to that of the ekman current and its characteristics are determined by the relative angle between wind and current the propagation characteristics of near inertial waves are quite different depending upon the sign of the relative vorticity in a cyclonic eddy near inertial wave propagation is outward from the core of the eddy the propagation direction in an anticyclonic eddy is downward and toward the core vertically propagating waves inside the eddy are trapped above a critical layer and slowly dissipated by parameterized viscous effects the model shows that anticyclones efficiently drain near inertial energy from the surface to the deep layer below the thermocline

simulating the surface waters of the amazon river basin impacts of new river geomorphic and flow parameterizations this paper describes the impacts of new river geomorphic and flow parameterizations on the simulated surface waters dynamics of the amazon river basin three major improvements to a hydrologic model are presented 1 the river flow velocity equation is expanded to be dependent on river sinuosity and friction in addition to gradient forces 2 equations defining the morphological characteristics of the river such as river height width and bankfull volume are derived from 31 622 measurements of river morphology and applied within the model 3 1 km resolution topographic data from the shuttle radar topography mission srtm are used to provide physically based fractional flooding of grid cells from a statistical representation of sub grid scale floodplain morphology the discharge and floodplain inundation of the amazon river is simulated for the period 1968 1998 validated against observations and compared with results from a previous version of the model these modifications result in considerable improvement in the simulations of the hydrological features of the amazon river system the major impact is that the average wet season flooded area on the amazon mainstem for the period 1983 1988 is now within 5 of satellite derived estimates of flooded area whereas the previous model overestimates the flooded area by about 80 the improvements are a consequence of the new empirical river geomorphologic functions and the srtm topography the new formulation of the flow velocity equation results in increased river velocity on the mainstem and major tributaries and a better correlation between the mean monthly simulated and observed discharge copyright 2007 john wiley sons ltd

improved gravity anomaly fields from retracked multimission satellite radar altimetry observations over the persian gulf and the caspian sea satellite radar altimetry observations are used to derive short wavelength gravity anomaly fields over the persian gulf and the caspian sea where in situ and ship borne gravity measurements have limited spatial coverage in this study the retracking algorithm extrema retracking extr was employed to improve sea surface height ssh measurements that are highly biased in the study regions due to land contaminations in the footprints of the satellite altimetry observations extr was applied to the waveforms sampled by the five satellite radar altimetry missions topex poseidon jason 1 jason 2 gfo and ers 1 along track slopes have been estimated from the improved ssh measurements and used in an iterative process to estimate deflections of the vertical and subsequently the desired gravity anomalies the main steps of the gravity anomaly computations involve estimating improved ssh using the extr technique computing deflections of the vertical from interpolated sshs on a regular grid using a biharmonic spline interpolation and finally estimating gridded gravity anomalies a remove compute restore algorithm based on the fast fourier transform has been applied to convert deflections of the vertical into gravity anomalies finally spline interpolation has been used to estimate regular gravity anomaly grids over the two study regions results were evaluated by comparing the estimated altimetry derived gravity anomalies with and without implementing the extr algorithm with ship borne free air gravity anomaly observations and free air gravity anomalies from the earth gravitational model 2008 egm2008 the comparison indicates a range of 3 5 mgal in the residuals which were computed by taking the differences between the retracked altimetry derived gravity anomaly and the ship borne data the comparison of retracked data with ship borne data indicates a range in the root mean square error rmse between approximately 1 8 and 4 4 mgal and a bias between 0 4062 and 2 1413 mgal over different areas also a maximum rmse of 4 4069 mgal with a mean value of 0 7615 mgal was obtained in the residuals an average improvement of 5 2746 mgal in the rmse of the altimetry derived gravity anomalies corresponding to 89 9 per cent was obtained after applying the extr post processing

inertial wave dynamics in the north atlantic subtropical zone doppler current profiler observations of an inertial wave packet are presented from a region where a cold core ring impinges on a front in this intense current a drogue is deployed to mark one region of the fluid as the drogue is advected by the current the ship follows it zigzagging across the drogue s trajectory along this ship track vertical rotary velocity spectra indicate the presence of a downgoing intertial wave with a vertical wavelength which slowly changes from 50 to 100 m as time progresses the wave s intrinsic frequency was measured for the first time ever a horizontally synoptic data set is obtained at the drogue depth by correcting for frontal advection and the temporal rotation of the wave velocity examination of these synoptic data indicates the presence of a southgoing near inertial wave with horizontal wavelength 20 km the wave is confined to a 25 km region supplementary ray tracing calculations through objective maps of the ring flow field indicate that the wave is strongly influenced by doppler shifting this is accompanied by a slow counterclockwise turning of the horizontal wave number vector a decrease in the intrinsic frequency and an increase in the vertical wavelength in qualitative agreement with the data a companion paper marmorino et al this issue details the effect of this inertial wave upon the small scale temperature activity with horizontal length scales of 1 3 m

water slope and discharge in the amazon river estimated using the shuttle radar topography mission digital elevation model 1 we find that the standard deviation hence error of the water surface elevation data from the shuttle radar topography mission srtm is 5 51 m for basin wide regional and local amazon mainstem reaches this error implies a minimum reach length of 733km in order to calculate a reliable water surface slope resulting slopes are 1 92 0 19 cm km for manacapuru 2 86 0 24 cm km for itapeua and 3 20 0 34 cm km for tupe manning s equation is applied with these slopes and with channel width measurements from the global rain forest mapping project synthetic aperture radar mosaics grfm sar channel depths averaged from nautical charts and reasonable estimates of manning s n resulting discharge values are 84 800 m3 s at manacapuru 79 800 m3 s at itapeua and 62 900 m3 s at tupe averaged over the srtm mission period these values are within 6 2 at manacapuru 7 6 at itapeua and 0 3 at tupe of the in situ gage based estimates for the same or similar time period

the impact of polar mesoscale storms on northeast atlantic ocean circulation every year thousands of mesoscale storms termed polar lows cross the climatically sensitive subpolar north atlantic ocean high resolution numerical simulations of the ocean circulation taking into account the effect of these storms on deep water formation suggest that polar lows significantly affect the global ocean circulation

magnitude frequency distributions of boundary shear stress along a rapidly eroding bedrock river 1 the magnitude frequency distribution of boundary shear stress frames erosion rates in bedrock rivers but empirical constraints are rare particularly for extreme floods here we present measurements of mean stress b and its frequency distribution along a fast eroding river in taiwan we construct rating functions of discharge and hydraulic geometry using high resolution satellite images of flood patterns river stage time series topographic profiles and post flood field surveys the method allows us to assess the spatiotemporal variation in b along the channel the boundary shear stress pdf p b has a steep power law tail and includes semiannual floods generating b 100 200 pa and 50 year 3000 m3 s 1 events driving b 300 pa all such floods contribute to modification of the coarse alluvial cover and erosion of the bedrock bed given the steep tail decay in p b the rapid channel incision probably owes more to the exceptional frequency of moderate shear stresses than to the magnitude of the extremes

estimation of river discharge propagation speed and hydraulic geometry from space lena river siberia 1 moderate resolution imaging spectroradiometer modis derived measurements of lena river effective width we display a high predictive capacity r2 0 81 mean absolute error 60 90 km 2 3 time valley width satellite derived we q rating curves and hydraulic geometry b exponents converge upon stable values b 0 48 indicating transferability of the discharge retrieval method between different locations put another way at length scales exceeding 60 90 km all subreaches display similar behavior everywhere at finer reach length scales e g 0 25 1 km longitudinal extraction of b exponents represents the first continuous mapping of a classical hydraulic geometry parameter from space while at least one gauging station is required for calibration results suggest that multitemporal satellite data can powerfully enhance our understanding of water discharge and flow conveyance in remote river systems

decreasing overflow from the nordic seas into the atlantic ocean through the faroe bank channel since 1950 the overflow of cold dense water from the nordic seas across the greenland scotland ridge and into the atlantic ocean is the main source for the deep water of the north atlantic ocean this flow also helps drive the inflow of warm saline surface water into the nordic seas the faroe bank channel is the deepest path across the ridge and the deep flow through this channel accounts for about one third of the total overflow previous work has demonstrated that the overflow has become warmer and less saline over time here we show using direct measurements and historical hydrographic data that the volume flux of the faroe bank channel overflow has also decreased estimating the volume flux conservatively we find a decrease by at least 20 per cent relative to 1950 if this reduction in deep flow from the nordic seas is not compensated by increased flow from other sources it implies a weakened global thermohaline circulation and reduced inflow of atlantic water to the nordic seas

structure and variability of the denmark strait overflow model and observations we report on a combined modeling and observational effort to understand the denmark strait overflow dso four cruises over the course of 3 years mapped hydrographic properties and velocity fields with high spatial resolution the observations reveal the mean path of the dense water as well as the presence of strong barotropic flows energetic variability and strong bottom friction and entrainment a regional sigma coordinate numerical model of interbasin exchange using realistic bottom topography and an overflow forced only by an upstream reservoir of dense fluid is compared with the observations and used to further investigate these processes the model successfully reproduces the volume transport of dense water at the sill as well as the 1000 m descent of the dense water in the first 200 km from the sill and the intense eddies generated at 1 3 day intervals hydraulic control of the mean flow is indicated by a region supercritical to long gravity waves in the dense layer located approximately 100 km downstream of the sill in both model and observations in addition despite the differences in surface forcing both model and observations exhibit similar transitions from mostly barotropic flow at the sill to a bottom trapped baroclinic flow downstream indicating the dominant role of the overflow in determining the full water column dynamics

water levels in the amazon basin derived from the ers 2 and envisat radar altimetry missions article i nfo this study sets out to analyze the stages of water bodies in the amazon basin derived from the processing of ers 2 and envisat satellite altimetry data for envisat gdr measurements for both ice 1 and ice 2 tracking algorithms were tested for ers 2 the ice 2 data produced by the oscar project was used water level time series over river segments of very different width from several kilometers to less than a hundred of meters were studied the water level time series that can be derived from narrow riverbeds are enhanced by off nadir detections conversely the off nadir effect may degrade the series over large bodies if not properly accounted for comparison at crossovers and with in situ gauges shows that the quality of the series can be highly variable from 12 cm in the best cases and 40 cm in most cases to several meters in the worse cases cautious data selection is clearly a key point to achieve high quality series indeed low quality series mostly result from inclusion of outliers in the data set finally retained for the computation of the series ice 2 and ice 1 tracking algorithms in the envisat data perform almost equally well envisat altimetry is clearly an improvement on ers 2 altimetry

investigating the spatial distribution of water levels in the mackenzie delta using airborne lidar airborne light detection and ranging lidar data were used to map water level wl and hydraulic gradients h x in the mackenzie delta the lidar wl data were validated against eight independent hydrometric gauge measurements and demonstrated mean offsets from 0 22 to 0 04 m 0 1 m was observed at a channel constriction entering a meander bend suggesting a localized modification of the channel hydraulics furthermore water levels in the anabranch channels of the peel river were almost 1 m higher than in middle channel of the mackenzie river this suggests i the channels are elevated and have shallower bank heights in this part of the delta leading to increased cross delta and along channel hydraulic gradients and or ii a proportion of the peel river flow is lost to middle channel due to drainage across the delta through anastamosing channels this study has demonstrated that airborne lidar data contain valuable information describing arctic river delta water surface and hydraulic attributes that would be challenging to acquire by other means copyright 2011 john wiley sons ltd

patterns of anabranching channels the ultimate end member adjustment of mega rivers abstract large fluvial systems adjust to a combination of controls to form distinctive channels which represent a dominant factor in the evolution of floodplain geomorphology and sedimentology fluvial geomorphology has commonly classified river channels into meandering straight and braiding patterns which are seen to represent a continuum of channel geometry anabranching patterns rivers with multiple channels however are characteristic of many rivers the identification of a combination of variables that discriminates specific channel patterns has been a significant focus of research in fluvial geomorphology the development of this body of knowledge however has been established from medium and small rivers and laboratory flume studies very few of these research ideas developed from analysis of large fluvial systems this paper assesses the pattern of channel adjustment of large fluvial systems by employing hydraulic geometry discharge w d slope grain size stream power specific stream power and froude number q mean 1000 m 3 s the study demonstrates that methods currently used to discriminate channel patterns are not useful when applied to very large rivers further with the exception of the lower mississippi alluvial rivers with mean annual discharges greater than 17 000 m 3 s here classified as mega rivers do not generate single thread meandering or typical braided patterns these mega rivers develop anabranching patterns

planform evolution of two anabranching structures in the upper peruvian amazon river we present a study to relate the sinuosity of the main channel and its effect on the dynamics of the secondary channels of anabranching structures for this purpose two locations of the peruvian amazon river were selected 1 a site with a medium to high sinuosity main channel ms site muyuy peru and 2 a site with a low sinuosity main channel ls site at the triple boundary between brazil colombia and peru the main channels for both the ms and ls anabranching structures have freedom to migrate in the lateral direction while at least one of their secondary channels is adjacent to the geological valley for ms and ls sites temporal analysis of planform evolution was carried out using 30 years of satellite imagery from which metrics such as width sinuosity and annual maximum migration rates of main and secondary channels were calculated additionally detailed hydrodynamic and bed morphology field measurements were carried out and a two dimensional shallow water numerical model was developed for a medium to high sinuosity main channel anabranching structure the secondary channels present a dominant mechanism for reworking the floodplain while for the low sinuosity anabranching structure the main channel planform dynamics is dominant flow velocities along the main and secondary channels for low transition and high flow discharges describe that for ms ls site the velocities are much higher along the secondary main channels

turbulent mixing induced by upgoing near inertial waves in the seasonal thermocline of the norwegian sea acoustic doppler current profiler and towed thermistor chain measurements made in the seasonal thermocline in the norwegian sea are examined for evidence that near inertial shear leads to small scale turbulent mixing as inferred from meter scale temperature fluctuations for the 1 day of data examined here spatial variability in shear is dominated by near inertial waves having upward energy propagation 30 m vertical wavelength and 5 to 10 km horizontal extent 20 km wavelength repeated samples of one of these waves had high froude number and enhanced small scale variability dominated by 20 m long waveforms which we conjecture are kelvin helmholtz instabilities arising from the near inertial shear

wind driven recirculations and exchange in the labrador and irminger seas it is demonstrated that recently observed cyclonic recirculation gyres in the irminger and labrador seas may be forced by the strong cyclonic wind stress curl that develops each winter seaward of the east coast of greenland idealized analytical and numerical models forced with such variable winds over a sloping bottom reproduce the essential aspects of the observed gyres strength location and horizontal and vertical length scales the communication between the forcing region in the irminger sea and the recirculation to the west is achieved by baroclinic topographic rossby wave propagation along potential vorticity contours the circulation is characterized as a time dependent stratified topographic beta plume for weak stratification as found in the subpolar north atlantic the recirculation strength exhibits only weak seasonal variability consistent with the observations even though the forcing is active only during the winter baroclinic rossby waves that develop when the wind forcing ceases in springtime interact with the bottom to provide a source of cyclonic vorticity that maintains the circulation until the wind strengthens again in the following winter

observations of near inertial waves in acoustic doppler current profiler measurements made during the mixed layer dynamics experiment measurements of upper ocean shear made during the mixed layer dynamics experiment mildex provide evidence of large horizontal scale motion at near inertial frequency the measurements consist of shipboard acoustic doppler current profiles four large scale spatial surveys of 2 4 days duration were made by the r v wecoma as a set of boxes approximately 60 km per side around a drifting current meter buoy velocity time series from the drifting buoy and from sonar measurements made from flip also indicated the presence of motions at near inertial frequency horizontal length and time scales of the motion are estimated from the phase of the shear vector measured during the spatial surveys estimates of the length scale of the waves range from 500 to 1000 km and the frequency is approximately 1 1f the behavior of the phase is found to be consistent with a model of narrow band inertial waves with vertical structure such that there is a zero crossing in velocity at the base of the mixed layer 40 60 m

near surface frontal zone trapping and deep upward propagation of internal wave energy in the japan east sea the full depth current structure in the japan east sea was investigated using direct velocity measurements performed with lowered and shipboard acoustic current doppler profilers rotary spectral analysis was used to investigate the three dimensional energy distribution as well as wave polarization with respect to vertical wavenumbers yielding information about the net energy propagation direction highly energetic near inertial downward propagating waves were found in localized patches along the southern edge of the subpolar front between 500 and 2500 m depth the basin average energy propagation was found to be upward with the maximum of relative difference between upward and downward propagating energy lying at about 1500 m depth this difference was most pronounced in the southeastern part of the basin

near inertial wave wake of hurricanes katrina and rita over mesoscale oceanic eddies abstract tropical cyclones tcs katrina and rita moved as major hurricanes over energetic geostrophic ocean features in the gulf of mexico increased and reduced oceanic mixed layer oml cooling was measured following the passage of both storms over cyclonic and anticyclonic geostrophic relative vorticity g respectively this contrasting thermal response is investigated here in terms of the evolution of the storms near inertial wave wake in geostrophic eddies observational data and ray tracing techniques in realistic geostrophic flow indicate that tc forced oml near inertial waves are trapped in regions of negative g where they rapidly propagate into the thermocline these anticyclonic rotating regimes coincided with the distribution of reduced oml cooling because rapid downward dispersion of near inertial energy reduced the amount of kinetic energy available to increase vertical shears at the oml base by contrast tc forced oml near inertial waves were stalled in upper layers of cyclonic circula

rating curves and estimation of average water depth at the upper negro river based on satellite altimeter data and modeled discharges summary the objective of this study is to derive the stage discharge relationship for 21 virtual gauge stations located at the upper negro river amazon basin brazil a virtual station can be defined as any crossing of water body surface i e large rivers by radar altimeter satellite tracks rating curve parameters are estimated by fitting with a power law the temporal series of water surface altitude derived from satellite measurements and the discharge discharges are calculated using progum a flow routing model based on the muskingum cunge m c approach considering a diffusion cum dynamic wave propagation leon j g bonnet m p cauhope m calmant s seyler f submitted for publication distributed water flow estimates of the upper negro river using a muskingum cunge routing model based on altimetric spatial data j hydrol among these parameters is the height of effective zero flow measured from the wgs84 ellipsoid used as reference it is shown that the height of effective zero flow is a good proxy of the mean water depth from which bottom slope of the reaches can be computed and manning roughness coefficients can be evaluated mean absolute difference lower than 1 1 m between estimated equivalent water depth and measured water depth indicates the good reliability of the method employed we computed the free surface water slope from envisat altimetry data for dry and rainy seasons these profiles are in good agreement with the bottom profile derived from the aforementioned water depths also the corresponding manning coefficients are consistent with the admitted ranges for natural channels with important flows superficial width 30 5 m chow v t 1959 open channel hydraulics mcgraw hill new york and irregular section

response of the greenland scotland overflow to changing deep water supply from the arctic mediterranean 1 a simple two layer channel model with a topographic barrier is used to study the response of the overflows across the greenland scotland ridge to changes in the available volume of deep and intermediate waters in the nordic seas hydraulic control determines the deep exchange through the different gaps in the ridge while a geostrophic balance in the north provides the respective upstream conditions in the model the overflow through denmark strait is more sensitive to changes in the deep water supply than that of the faeroe bank channel but no sudden breakdown of the exchanges across the ridge is seen when the supply decreases transport variations in the east greenland current have only minor influence on the total overflow

global ocean circulation during 1992 1997 estimated from ocean observations and a general circulation model 1 a three dimensional oceanic state is estimated for the period 1992 1997 as it results from combining large scale ocean data sets with a general circulation model at the cost of increased computational load the estimation assimilation method is chosen specifically so that the resulting state estimate is consistent with the model equations having no artificial sources or sinks to bring the model into close agreement with observations its initial temperature and salinity conditions are permitted to change as are the time dependent surface fluxes of momentum heat and freshwater resulting changes of these control vectors are largely consistent with accepted uncertainties in the hydrographic climatology and meteorological analyses the assimilation procedure is able to correct for many of the traditional shortcomings of the flow field by changing the surface boundary conditions changes in the resulting flow field are predominantly on the gyre scale and affect many features that are often poorly simulated in traditional numerical simulations such as the strengths of the gulf stream and its extension the azores current and the anticyclonic circulation associated with the labrador sea tests of the results and their consistency with prior error assumptions show that the constrained model has moved considerably closer to the observations imposed as constraints but has also moved closer to independent data from the world ocean circulation experiment not used in the assimilation procedure in some regions where the comparisons remain indeterminate not enough ocean observations are available and it is difficult to ascribe the residuals to either the model or the observations although problems remain a useful first solution to the global time dependent ocean state estimation problem has been found the estimates will continue to improve through the evolution of numerical models computer power increases more data and more efficient estimation methods

the production of north atlantic deep water sources rates and pathways updating an earlier account by dickson et al 1990 this paper reviews the initial development phase of north atlantic deep water nadw production from the points where the dense inflows from nordic seas cross the greenland scotland ridge to the point off south greenland where the buildup of new production appears almost complete in particular three long term current meter arrays totaling 91 instruments and set at 160 km intervals south from the denmark strait sill are used to validate earlier short term arrays by others and in combination with these earlier arrays to describe the downstream evolution of mean speed depth and entrainment the variability of the overflow current in space and time and the likely contribution of the other three main constituents of nadw production at densities greater than 27 8 from the points of overflow 5 6 sv the transport within this range increases by entrainment and confluence with other contributory streams to around 13 3 sv at cape farewell while recirculating elements prevent us from determining the net southgoing transport a nadw transport of this order appears consistent with recent estimates of net abyssal flow passing south through the north and south atlantic

amazon flood wave hydraulics summary a bathymetric survey of 575 km of the central amazon river and one of its tributaries the purus are combined with gauged data to characterise the amazon flood wave and for hydraulic modelling of the main channel for the period june 1995 march 1997 with the lisflood fp and hec ras hydraulic models our investigations show that the amazon flood wave is subcritical and diffusive in character and due to shallow bed slopes backwater conditions control significant reach lengths and are present for low and high water states comparison of the different models shows that it is necessary to include at least the diffusion term in any model and the rmse error in predicted water elevation at all cross sections introduced by ignoring the acceleration and advection terms is of the order of 0 02 0 03 m the use of a wide rectangular channel approximation introduces an error of 0 10 0 15 m on the predicted water levels reducing the bathymetry to a simple bed slope and with mean cross section only introduces an error in the order of 0 5 m these results show that when compared to the mean annual amplitude of the amazon flood wave of 11 12 m water levels are relatively insensitive to the bathymetry of the channel model the implication for remote sensing studies of the central amazon channel such as those proposed with the surface water and ocean topography mission swot is that even relatively crude assumptions regarding the channel bathymetry will be valid in order to derive discharge from water surface slope of the main channel as long as the mean channel area is approximately correct

hydrographic observations in denmark strait in fall 1997 and their implications for the entrainment into the overflow plume denmark strait is the most important exit for water masses formed in the arctic mediterranean sea and supplies a substantial fraction of the north atlantic deep water observations obtained from rv aranda in august september 1997 indicate that the water crossing the 620m deep sill is mainly drawn from the intermediate waters of the east greenland current the overflow plume was stratified and capped by a less saline layer as it descended beyond 2000m the presence of a low salinity lid implies that entrainment of ambient water is small and that the downstream evolution of the plume characteristics is due to mixing within the plume between the initial overflow waters low salinity but dense water from the east greenland current flowing over the shelf may cross the shelf break south of the sill and add a less dense fraction to the overflow

variability of the meridional overturning in the north atlantic from the 50 year gecco state estimation abstract the german partner of the consortium for estimating the circulation and climate of the ocean gecco provided a dynamically consistent estimate of the time varying ocean circulation over the 50 yr period 1952 2001 the gecco synthesis combines most of the data available during the entire estimation period with the ecco massachusetts institute of technology mit ocean circulation model using its adjoint this gecco estimate is analyzed here for the period 1962 2001 with respect to decadal and longer term changes of the meridional overturning circulation moc of the north atlantic a special focus is on the maximum moc values at 25 n over this period the dynamically self consistent synthesis stays within the error bars of h l bryden et al but reveals a general increase of the moc strength the variability on decadal and longer time scales is decomposed into contributions from different processes changes in the model s moc strength are strongly influenced by the southward communication of d

mapping wetland water depths over the central congo basin using palsar scansar envisat altimetry and modis vcf data abstract we have for the first time developed a simple linear regression model based on palsar scansar backscattering coefficients 0 water levels from envisat altimetry and modis vegetation continuous field vcf product to generate water depth maps over flooded forest in the central congo basin the water depth maps we generated are relative to the lowest water level from envisat altimetry which is assumed to be a base level with essentially zero depth the predicted and observed water depths along the envisat pass showed excellent agreements with rms differences of 12 8 cm to 17 8 cm the water depth maps were also independently validated with h t obtained from palsar interferometry and storage anomalies estimated by multiplying inundation extents from palsar scansar with spatially averaged water level anomalies from envisat altimetry the water storage volumes calculated from our water depth maps were calculated to be 11 3 2 0 km 3 10 3 2 3 km 3 and 9 3 1 8 km 3 for 12 05 2006 12 08 2007 and 12 10 2008 respectively it is expected that our method can be applied to other river basins that have flooded forest with satellite radar altimeter over passes the water depth maps can be directly used to calibrate and validate the spatial and temporal variation of inundation extent and water depth in the wetland derived from a 2 d hydrodynamic model furthermore our water depth maps can be used as a true dataset to perform a pre launch virtual mission study of the surface water ocean topography swot mission to be launched in 2020