distribution of pleuroncodes monodon larvae over the continental shelf of south central chile field and modeling evidence for partial local retention and transport abstract in situ and modeled spatial distribution of squat lobster pleuroncodes monodon larvae over the continental shelf off south central chile 35 37 s was analyzed along with currents and hydrography we aimed to identify the main larval transport retention characteristics in the study area which constitutes the southernmost p monodon fishing grounds embedded in the humboldt current system we hypothesized that the main contribution to population renewal originates in the two persistent adult aggregations close to the nursery ground that occurs over a continental shelf terrace limited by two submarine canyons two extensive bio physical field campaigns were carried out during the main 2001 2002 upwelling season field data indicated that larvae were released from late austral winter to spring from spots to the north and south of the nursery zoea i were found mainly below 50 m depth in southward flowing waters whereas older zoea dominated in northward flowing layers above 50 m larvae were circumscribed between the coast and the shelf break front and pelagic retention areas were identified over the widest shelf area megalopa and juveniles during march were only found over the nursery area individual based simulations coupled to the output of a hydrodynamic model climatological configuration for the studied area showed that the release sites close to the nursery made the largest contribution to recruitment sites further north could also contribute to recruitment if hatching occurred later in the upwelling season the contribution of vertical behavior to larval success was also important as was the former s interaction with the site and time of larval release our results support the relevance of coastal circulation affected by topography on the persistence of p monodon populations off southern chile and the modulation of temporal variability these results might apply to other abundant species in the area

modeling semidiurnal internal tide variability in the southern california bight abstractthe regional oceanic modeling system roms is applied in a nested configuration with realistic forcing to the southern california bight scb to analyze the variability in semidiurnal internal wave generation and propagation the scb has a complex topography with supercritical slopes that generate linear internal waves at the forcing frequency the model predicts the observed barotropic and baroclinic tides reasonably well although the observed baroclinic tides feature slightly larger amplitudes the strongest semidiurnal barotropic to baroclinic energy conversion occurs on a steep sill slope of the 1900 m deep santa cruz basin this causes a forced near resonant semidiurnal poincare wave that rotates clockwise in the basin and is of the first mode along the radial azimuthal and vertical directions the associated tidal mean depth integrated energy fluxes and isotherm oscillation amplitudes in the basin reach maximum values of about 5 kw m 1 and 100 m and are strongly modulated by the sprin

dual doppler lidar observation of horizontal convective rolls and near surface streaks received 4 may 2008 revised 9 june 2008 accepted 18 june 2008 published 23 july 2008 1 dual doppler lidar and heliborne sensors were used to investigate the three dimensional 3d structure of the wind field over sendai airport in june 2007 the 3d structures of several hundred meter scale horizontal convective rolls hcrs in the sea breeze layer were observed by the dual doppler lidar the scale of the hcrs determined by the heliborne sensors roughly agreed with that determined by the dual doppler lidar analysis of the dual doppler lidar data showed that the region of upward flow in the hcrs originated in near surface low speed streaks this structure is consistent with the results of large eddy simulations of the atmospheric boundary layer the aspect ratios of the hcrs were close to those predicted by linear theories citation iwai h et al 2008 dual doppler lidar observation of horizontal convective rolls and near surface streaks geophys res lett 35 l14808 doi 10 1029 2008gl034571

circulation and low frequency variability near the chilean coast remotely forced fluctuations during the 1991 92 el nino results are reported from the first long recording current meter observations over the slope off chile these observations at 308s during the 1991 92 el nino event are analyzed together with observations of currents at a local deep sea site local wind and sea level sea level from the peru and chile coasts and wind temperature and currents from the equatorial pacific mean poleward flow of 12 cm s21 was observed within the peru chile undercurrent over the slope mean flow in the depth range of antarctic intermediate water was not distinguishable from zero in the presence of strong low frequency lf variability which dominated slope currents at all depths the strongest lf fluctuations had periods of about 50 days but periods of 10 and about 5 days were also observed significant local wind forcing of slope currents was only found in the period band 6 10 days and may be related to coastal trapped waves in the atmosphere our analysis shows that free coastal trapped waves in the ocean arriving from the north dominated the lf variability over the shelf and slope off northern and central chile during the 1991 92 el nino event strong 50 day period fluctuations there started their journey about two months earlier and 15 000 km farther up the coastal equatorial waveguide near the date line in the equatorial pacific as equatorial kelvin waves forced by westerly wind events of similar period upon reaching the south american coast these waves forced coastal trapped waves which propagated along the peru coast into the study region likewise a scenario of equatorial trapped waves forcing coastal trapped waves may explain 10 day as well as 6 day and 4 5 day period coastal trapped waves off chile stemming from mixed rossby gravity and inertia gravity waves trapped at the equator since the large 50 day period coastal trapped waves may strongly modify coastal upwelling source water such remotely forced waves may have a significant influence on the pelagic ecosystem off chile at least during el nino events

the vertical partition of oceanic horizontal kinetic energy to produce an interpretation of the surface kinetic energy as measured by altimeters a survey is made of the vertical structure of kinetic energy profiles in a large number of globally distributed long current meter records although the data are geographically confined primarily to a latitude band in the north pacific to the north atlantic and to a few moorings in the south atlantic the results show generally speaking that most regions are dominated by the barotropic and first baroclinic modes because of the near surface intensification of baroclinic modes altimeters primarily reflect the first baroclinic mode and thus the motion of the main thermocline there is good quantitative agreement with a few exceptions with estimates of the surface kinetic energy obtained from the topex poseidon altimeter and from vertical extrapolations to the surface of the mooring profiles these results are consistent with previous suggestions that barotropic models have little skill in depicting variability as seen in the altimeter data an eof analysis is shown to produce fictitious mode coupling unless the dynamical modes have very different energy levels

wind induced exchange at the entrance to concepcion bay an equatorward facing embayment in central chile abstract hydrographic and underway water velocity profiles were measured at the entrance to concepcion bay an equatorward facing embayment in central chile in order to illustrate the wind induced exchange flow observations took place over a 25 h period 5 6 january 2002 during the austral summer which is characterized by upwelling winds in the region one portion of the observational transect was directly influenced by the wind and the other was protected from such influence by an island the portion of the transect influenced by wind showed a surface layer delimited by a pycnocline moving downwind owing to the direct action of wind stress this surface transport should have caused an onshore decrease of surface elevation that would drive upwind flow below the surface layer the portion of the transect protected by the island was influenced by its wake and perhaps forced by a semidiurnal tide this study is one of the few observational examples of wind induced flow that documents the wind induced exchange pattern under weak internal friction low ekman number this pattern consists of downwind flow in an upper layer delimited by the pycnocline and upwind flow below

internal tide energy over topography 1 the method used to separate surface and internal tides ultimately defines properties such as internal tide generation and the depth structure of internal tide energy flux here we provide a detailed analysis of several surface internal tide decompositions over arbitrary topography in all decompositions surface tide velocity is expressed as the depth average of total velocity analysis indicates that surface tide pressure is best expressed as the depth average of total pressure plus a new depth dependent profile of pressure which is due to isopycnal heaving by movement of the free surface internal tide velocity and pressure are defined as total variables minus the surface tide components corresponding surface and internal tide energy equations are derived that contain energy conversion solely through topographic internal tide generation the depth structure of internal tide energy flux produced by the new decomposition is unambiguous and differs from that of past decompositions numerical simulations over steep topography reveal that the decomposition is self consistent and physically relevant analysis of observations over kaena ridge hawaii and the oregon continental slope indicate o 50 w m 1 error in depth integrated energy fluxes when internal tide pressure is computed as the residual of pressure from its depth average while these errors are small at major internal tide generation sites they may be significant where surface tides are larger and depth integrated fluxes are weaker e g over continental shelves

a high resolution modeling study of the 24 may 2002 dryline case during ihop part i numerical simulation and general evolution of the dryline and convection abstract results from a high resolution numerical simulation of the 24 may 2002 dryline convective initiation ci case are presented the simulation uses a 400 km 700 km domain with a 1 km horizontal resolution grid nested inside a 3 km domain and starts from an assimilated initial condition at 1800 utc routine as well as special upper air and surface observations collected during the international h2o project ihop 2002 are assimilated into the initial condition the initiation of convective storms at around 2015 utc along a section of the dryline south of the texas panhandle is correctly predicted as is the noninitiation of convection at a cold front dryline intersection triple point located farther north the timing and location of predicted ci are accurate to within 20 min and 25 km respectively the general evolution of the predicted convective line up to 6 h of model time also verifies well mesoscale convergence associated with the confluent flow around the dryline is shown to produce an u

observations of the semidiurnal internal tide on the southern california slope and shelf 1 we give a detailed description of the semidiurnal band current and temperature variability observed during the internal waves on the continental margin iwaves field experiments of 1996 and 1997 off of mission beach california this variability was dominated by the internal tide and the structure of the internal tide on the slope and shelfbreak region was different from that on the narrow shelf on the slope and shelfbreak the internal tide was dominated by alongshore propagating coastal trapped waves in this region semidiurnal band currents were predominantly oriented in the alongshore direction in the lower half of the water column at a water depth h of 350 m current and temperature variability were consonant with a short wavelength 8 km bottom trapped wave propagating in the alongshore direction to the north in the upper 120 m of the water column above the depth of the shelfbreak slope and shelfbreak currents were highly coherent with a zero phase lag that is there was no phase propagation in the cross shore direction on the narrow 10 km shelf cross shore currents u were much more energetic than on the slope and had the structure of a mode one internal wave the alongshore currents v decreased monotonically from the surface to the bottom of the water column with a phase that did not change with depth the near bottom u signal propagated toward the coast during all mooring deployments faster in the summer than in the fall the near bottom u and mid column temperature relative phase was neither consistent with a purely progressive nor a purely standing mode one internal wave we conclude that the internal tide on the shelf was partially reflected

mixing in seasonally stratified shelf seas a shifting paradigm although continental shelf seas make up a relatively small fraction ca 7 of the world ocean s surface they are thought to contribute significantly 20 50 of the total to the open ocean carbon dioxide storage through processes collectively known as the shelf sea pump the global significance of these processes is determined by the vertical mixing which drives the net co 2 drawdown which can occur only in stratified water in this paper we focus on identifying the processes that are responsible for mixing across the thermocline in seasonally stratified shelf seas we present evidence that shear instability and internal wave breaking are largely responsible for thermocline mixing a clear development from the first order paradigm for the water column structure in continental shelf seas the levels of dissipation observed are quantitatively consistent with the observed dissipation rates of the internal tide and near inertial oscillations it is perhaps because these processes make such a small contribution to the total energy dissipated in shelf seas that they are not well represented in current state of the art numerical models of continental shelf seas the results thus present a clear challenge to oceanographic models

drowning of the mississippi delta due to insufficient sediment supply and global sea level rise global sea level rise reduced sediment supply and subsidence threaten the stability of the mississippi delta calculations of riverine sediment load and storage indicate that 10 000 13 500 km2 of the delta could be submerged by ad 2100

scattering of internal waves at finite topography in two dimensions part i theory and case studies abstract the scattering of internal gravity waves at finite topography in two dimensions is studied theoretically and numerically for a finite depth ocean a formal solution is derived using a mapping function based on ray tracing the solution satisfies radiation conditions energy is conserved the incoming energy flux is redistributed in physical and modenumber space numerical solutions are calculated for a single plane wave propagating from the ocean side onto slope shelf configurations where a flat shallow shelf is connected to a flat deep ocean by linear slopes staircases convex or concave parabolic profiles and half cosine slopes the fraction of the incoming energy flux transmitted onto the shelf and reflected back to the deep ocean and the distribution of these fluxes in modenumber space are calculated the results depend on the parameters of the incident wave and of the topography especially important is the distinction between supercritical topography where the slope of the topography exc

the shaping of continental slopes by internal tides the angles of energy propagation of semidiurnal internal tides may determine the average gradient of continental slopes in ocean basins 2 to 4 degrees intensification of near bottom water velocities and bottom shear stresses caused by reflection of semi diurnal internal tides affects sedimentation patterns and bottom gradients as indicated by recent studies of continental slopes off northern california and new jersey estimates of bottom shear velocities caused by semi diurnal internal tides are high enough to inhibit deposition of fine grained sediment onto the slopes

importance of flood plain sedimentation for river sediment budgets and terrigenous input to the oceans insights from the brahmaputra jamuna river recent authors have suggested that a significant proportion of the worldwide terrigenous sediment budget is trapped landward of the river ocean boundary in high load tectonically active basins to test this idea modern flood plain sediment accumulation rates were determined along a 110 km reach of the brahmaputra locally jamuna river using 137cs geochronology of sediment cores and geographic information system gis extrapolation to adjacent areas 137cs accumulation rates decrease exponentially away from the channel from 4 cm yr on the natural levees to 1 cm yr within a few tens of kilometers basinward important controls on sedimentation in this area include proximity to distributary channels local topography and interannual variability of the flood pulse model results indicate that an average of 23 m t yr of sediment are sequestered in this section of the flood plain extrapolated basinwide as much as 39 71 of the river sediment budget may be trapped landward of the ganges brahmaputra mouth

on the semidiurnal internal tide at a shelf break region on the australian north west shelf abstract the properties of the semidiurnal internal tide in the region of the shelf break at a location on the australian north west shelf are discussed information is derived from an analysis of thermistor chain and current meter data collected over six months at the shelf break and slope locations the work is an extension of an earlier study the internal tide is described in terms of modes finding that the firm mode dominates propagating onshore at an angle of 30 from normal to the bathymetry with a rapid decay in amplitude of nearly five times from the shelf slope to the shelf break a distance of 22 5 km or approximately one wavelength the loss of energy flux from this decay gives rise to vertical mixing with a vertical eddy viscosity of 1 4 10 4 m2 s 1 the amplitude at the m2 tidal frequency dominates over the s2 amplitude giving an s2 m2 amplitude ratio significantly smaller than for the barotropic tidal motion the internal tide appears to have a three dimensional structure at the sh

a high resolution simulation of convective roll clouds during a cold air outbreak 1 a ubiquitous feature of the high latitude ocean is the occurrence of convective clouds that are organized into two dimensional structures known as roll clouds or cloud streets in this paper we present a simulation of these structures that was performed in a domain large enough to simulate numerous roll clouds and their downstream evolution at a resolution sufficient to resolve the individual convective clouds the simulations were initialized and validated using observations of roll clouds over the labrador sea the model results indicate that the secondary flow associated with the roll clouds results in significant differences in the temperature humidity and momentum fields between the updrafts and downdrafts the model was also able to reproduce the observed downstream evolution of the clouds as the organization of the convection changed from two dimensional rolls to three dimensional closed cells

mid to inner shelf coupled roms swan model data comparison of currents and temperature diurnal and semidiurnal variability abstractaccurately representing diurnal and semidiurnal internal variability is necessary to investigate inner shelf to midshelf exchange processes here a coupled regional ocean model system roms simulating waves nearshore swan model is compared to observed diurnal and semidiurnal internal tidal variability on the mid and inner shelf 26 8 m water depth near san pedro bay california modeled mean stratification is about one half of that observed modeled and observed baroclinic velocity rotary spectra are similar in the diurnal and semidiurnal band modeled and observed temperature spectra have similar diurnal and semidiurnal band structure although the modeled is weaker the observed and modeled diurnal and semidiurnal baroclinic velocity and temperature dominant vertical structures are similar and consistent with mode one internal motions both observed and modeled diurnal baroclinic kinetic energy are strongly correlated to diurnal wind forcing and enhanced by subtidal vorticity induced reduc

tide current eddy interaction a seasonal study using high frequency radar observations along the western bay of bengal near 16 n abstract the seasonally reversing boundary currents along the western bay of bengal bob provide a background for studying the rich and complex relationship between tidally driven currents mean current structure and mesoscale eddies a year long high resolution surface current data set from high frequency radars hfr during 2015 along the andhra pradesh coast near 82 e 16 n has been utilized to investigate the interaction of tidal currents with bathymetry and eddies during three seasons january march april and november december the seasonal variability shows the reversibility of boundary currents with speeds of 1 58 1 24 m s 1 during poleward equatorward flow associated with an offshore anticyclonic inshore cyclonic eddy in this region the amplitudes of the tidal constituents from the hfr currents are highly correlated r 0 80 with those from the sea level observations from a nearby tide gauge among the semi diurnal and diurnal tidal constituents m2 5 25 6 51 cm s 1 and k1 2 36 4 32 cm s 1 are the dominant two respectively in all three seasons the tidal variance of 40 70 is observed throughout the domain with highest contribution from the m2 tidal currents the m2 tidal ellipse patterns match well with the mean circulation pattern i e cyclonic anticyclonic during november december march april in the nearshore regions the tidal currents amplify mainly through shallow water tidal constituents m4 and ms4 interacting with bathymetry whereas in the offshore regions they are dominated by m2 which co vary with the mean seasonal circulation pattern the highest amplitude of m2 tidal currents during november december is predominantly due to high stratification along the western bob in the presence of stratification the loss of tidal kinetic energy into turbulent processes is reduced resulting in the amplification of m2 tidal currents the shallow water constituents are also observed with significant amplitudes of 0 50 3 50 cm s 1 in the nearshore region the amplitudes of overtides m3 m4 and s4 associated with an offshore anti cyclonic eddy are higher during march april whereas those for the compound tides mk3 sk3 ms4 2sk5 2mn6 and 2sm6 are associated with an inshore cyclonic eddy dominate during november december

mississippi delta subsidence primarily caused by compaction of holocene strata coastal subsidence causes sea level rise shoreline erosion and wetland loss which poses a threat to coastal populations this is especially evident in the mississippi delta in the southern united states which was devastated by hurricane katrina in 2005 the loss of protective wetlands is considered a critical factor in the extensive flood damage the causes of subsidence in coastal louisiana attributed to factors as diverse as shallow compaction and deep crustal processes remain controversial current estimates of subsidence rates vary by several orders of magnitude here we use a series of radiocarbon dated sediment cores from the mississippi delta to analyse late holocene deposits and assess compaction rates we find that millennial scale compaction rates primarily associated with peat can reach 5mm per year values that exceed recent model predictions locally and on timescales of decades to centuries rates are likely to be 10 mm or more per year we conclude that compaction of holocene strata contributes significantly to the exceptionally high rates of relative sea level rise and coastal wetland loss in the mississippi delta and is likely to cause subsidence in other organic rich and often densely populated coastal plains

convectively induced secondary circulations in fine grid mesoscale numerical weather prediction models abstractmesoscale numerical weather prediction models using fine grid o 1 km meshes for weather forecasting environmental assessment and other applications capture aspects of larger than grid mesh size convectively induced secondary circulations ciscs such as cells and rolls that occur in the convective planetary boundary layer pbl however 1 km grid spacing is too large for the simulation of the interaction of ciscs with smaller scale turbulence the existence of ciscs also violates the neglect of horizontal gradients of turbulent quantities in current pbl schemes both aspects poorly resolved ciscs and a violation of the assumptions behind pbl schemes are examples of what occurs in wyngaard s terra incognita where horizontal grid spacing is comparable to the scale of the simulated motions thus model ciscs m ciscs cannot be simulated reliably this paper describes how the superadiabatic layer in the lower convective pbl together with increased horizontal resolution allow the critical ra

internal tide observations from the australian north west shelf in summer 1995 abstract observations are presented of the internal tide over the continental shelf and slope from a cross section on the australian north west shelf data collected from moored instruments and repeated profile measurements during the summer months of 1995 show an energetic large amplitude shoreward propagating semidiurnal internal tide multiple generation sites are suggested coinciding with near critical bottom slopes in water less than approximately 200 m deep the vertical structure of the internal tide is predominantly a first vertical mode whereas in deeper water over the slope the vertical structure is more complicated with currents and vertical displacements intensified in the lower part of the water column the internal tide is largely confined to a region approximately 100 km wide from water depths between 70 and 1000 m strong generation and dissipation of the internal tide energy is observed over this region and there is evidence that the dissipated energy impacts on the vertical mixing

role of surface friction on shallow nonprecipitating convection abstractthe role of surface friction on shallow nonprecipitating convection is investigated using a series of large eddy simulations with varying surface friction velocity and with a cloud identification algorithm as surface friction intensifies convective rolls dominate over convective cells and secondary overturning circulation becomes stronger in the subcloud layer thus transporting more moisture upward and more heat downward between the subcloud and cloud layers identifying individual clouds using the identification algorithm based on a three dimensional topological analysis reveals that intensified surface friction increases the number of clouds and the degree of tilting in the downstream direction highly intensified surface friction increases wind shear across the cloud base and induces cloud tilting which leads to a vertically parabolic profile of liquid water mixing ratio instead of the classical two layer structure conditionally unstable and trade inversion layers furthermore cloud ti

geomorphology flood built land the southeastern us coastline is under threat as land subsides and sea level rises measurements of the 2011 mississippi river flood suggest that the river carries enough sandy sediment to offset some of this coastal drowning

mitigating land loss in coastal louisiana by controlled diversion of mississippi river sand the bonnet carre spillway diverts floodwaters from the mississippi river to lake pontchartrain and was opened for 42 days during the 2011 flood according to measurements of the newly deposited sediments at least 31 46 of the river s sand load was diverted into the spillway at this time suggesting that such diversions can help mitigate coastal wetland loss

an approximation of the sediment budget of the lower mississippi river prior to major human modification a sediment budget is constructed for the lower mississippi river prior to the introduction of most human modifications components of the budget are derived from historical data including mississippi river commission hydrographic survey maps for the period from 1877 to 1924 a quantitative estimate of major sediment sources sinks and storage locations in the lower mississippi valley suggest that the most important sediment source was from bank caving and that at least 50 per cent more sediment was deposited in short term channel storage than in longer term overbank storage the budget indicates that the proportion of sediment transported as bedload was significantly greater than previously estimated the magnitude and variability of these sediment budget components are discussed the results of the study suggest that prior to modifications the river was aggrading over much of its length

a revised holocene geochronology for the lower mississippi valley data from two locations 1 a hydrodam site at the old river diversion structure south of the latitude of natchez ms and 2 eight water wells from the latitude of baton rouge la are the basis for a revised holocene geochronology of the lower mississippi river floodplain based on 84 radiocarbon dates analyses of 64 borehole logs and 75 grain size analyses which together provide major insight into questions concerning the complexity of meander belt movement the influence of the younger dryas on the lower valley and on the pleistocene holocene interface following the younger dryas the early holocene was characterized by periodic flooding and deposition separated by times of little or no deposition

diurnal and semidiurnal internal tide energy flux at a continental slope in the south china sea 1 barotropic surface and baroclinic internal tides were measured at four mooring sites during a field investigation of acoustic propagation characteristics and physical oceanography in the northern south china sea the mooring positions were in a line moving up the shallow portion of a continental slope at water depths between 350 and 85 m using time series of temperature and velocity at several depths 1 month series of semidiurnal and diurnal species internal tidal energy flux vectors were computed for three sites with a 14 day series computed for the fourth shallow site the internal tides had a temporal signature that was not in complete accord with the barotropic tides showing an enhancement of diurnal internal tides with respect to semidiurnal bathymetric slope barotropic tidal fluid particle trajectories and scale of generation site versus internal tide wavelength are investigated as possible causes of the differing response of the species