the salinity temperature and δ18o of the glacial deep ocean we use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from ocean drilling program cores to reconstruct salinity and temperature of the deep ocean during the last glacial maximum lgm our data show that the temperatures of the deep pacific southern and atlantic oceans during the lgm were relatively homogeneous and within error of the freezing point of seawater at the ocean s surface our chloride data show that the glacial stratification was dominated by salinity variations in contrast with the modern ocean for which temperature plays a primary role during the lgm the southern ocean contained the saltiest water in the deep ocean this reversal of the modern salinity contrast between the north and south atlantic implies that the freshwater budget at the poles must have been quite different a strict conversion of mean salinity at the lgm to equivalent sea level change yields a value in excess of 140 meters however the storage of fresh water in ice shelves and or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level

computation of wind wave spectra in coastal waters with swan on unstructured grids abstract an unstructured grid procedure for swan is presented it is a vertex based fully implicit finite difference method which can accommodate unstructured meshes with a high variability in geographic resolution suitable for representing complicated bottom topography in shallow areas and irregular shoreline the numerical solution is found by means of a point to point multi directional gauss seidel iteration method requiring a number of sweeps through the grid the approach is stable for any time step while permitting local mesh refinements in areas of interest a number of applications are shown to verify the correctness and numerical accuracy of the unstructured version of swan

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

a model dye comparison experiment in the tidal mixing front zone on the southern flank of georges bank 1 a process oriented model dye comparison experiment was conducted to examine the ability of a numerical ocean model to simulate the observed movement of dye across the tidal mixing front on the southern flank of georges bank during 22 26 may 1999 the experiment was made using the unstructured grid finite volume coastal ocean model fvcom with varying horizontal resolution the results indicate that the observed cross isobath movement of the dye patch was primarily controlled by meso scale temporal and spatial variability of the water temperature and salinity fields onset of vertical stratification tended to slow down an upward stretching of the dye column and trapped the dye within the bottom mixed layer to reach a convergent numerical solution that reproduced the observed lateral turbulent dispersion of dye the fvcom grid required a horizontal resolution of 500 m in the dye study region within the tidal mixing front of georges bank the movement of the center of the dye patch was mainly driven by the ensemble velocity integrated over the dye volume with a first order contribution from vertical shear of the dye s horizontal velocity

a new high resolution unstructured grid finite volume arctic ocean model ao fvcom an application for tidal studies 1 a spherical coordinate version of the unstructured grid 3 d fvcom finite volume coastal ocean model has been applied to the arctic ocean to simulate tides with a horizontal resolution ranging from 1 km in the near coastal areas to 15 km in the deep ocean by accurately resolving the irregular coastlines and bathymetry in the arctic ocean coastal regions this model reproduces the diurnal k1 and o1 and semidiurnal m2 and s2 tidal wave dynamics and captures the complex tidal structure along the coast particularly in the narrow straits of the canadian archipelago the simulated tidal parameters harmonic constituents of sea surface elevation and currents agree well with the available observational data high resolution meshes over the continental shelf and slope capture the detailed spatial structure of topographic trapped shelf waves which are quite energetic along the greenland siberia and spitsbergen continental slope and shelf break areas water stratification influences the vertical distribution of tidal currents but not the water transport and thus tidal elevation the comparison with previous finite difference models suggests that horizontal resolution and geometric fitting are two prerequisites to simulate realistically the tidal energy flux in the arctic ocean particularly in the canadian archipelago

the influence of continental ice atmospheric co2 and land albedo on the climate of the last glacial maximum the contributions of expanded continental ice reduced atm9spheric co2 and changes in land albedo to the maintenance of the climate of the last glacial maximum lgm are examined a series of experiments is perform ed using an atmosphere mixed layer ocean model in which these changes in boundary conditions are incorporated either singly or in combination the model used has been shown to produce a reasonably reajistic simulation of the reduced temperature of the lgm manabe and broccoli 1985 by comparing the results from pairs of ex periments the effects of each of these envirornnental changes can be determined expanded continental ice and reduced atmospheric co2 are found to have a substantial impact on global mean temperature the ice sheet effect is confined almost ex clusively to the northern hemisphere while lowered co2 cools both hemispheres changes in land albedo over ice free areas have only a minor thermal effect on a global basis the reduction of co2 content in the atmosphere is the primary contributor to the cooling of the southern hemisphere the model sensitivity to both the ice sheet and co2 effects is characterized by a high latitude amplification and a late autumn and early winter maximum

simulations of northern hemisphere ice sheet retreat sensitivity to physical mechanisms involved during the last deglaciation a 3 dimensional thermomechanical ice sheet model is used to simulate the evolution of the geometry of northern hemisphere ice sheets through the last deglaciation the ice sheet model is forced by a time evolving climatology provided by the linear interpolation through time of climate snapshots simulated by the lmd5 3 atmospheric general circulation model agcm at different periods of the last deglaciation 21 15 9 6 and 0 kyr bp the agcm is driven by insolation atmospheric co2 content ice sheet configuration and sea surface temperatures although our approach is able to produce the complete continental ice retreat our simulated deglaciation presents a phase lag with reconstructions based on observational evidences this suggests that physical mechanisms related to climate forcing and or ice sheet internal dynamics are not properly represented the influence of millennial scale forcing feedback mechanisms between ice sheet elevation and surface mass balance and parameterization of the ice flow is also tested through a set of sensitivity experiments the rapid variability has a strong impact on the evolution of the ice volume because of nonlinear effects in temperature mass balance relationships fennoscandia appears to be strongly sensitive to the small scale ice sheet instability both ice sheets are to some extent sensitive to an increased basal sliding

a high resolution coupled riverine flow tide wind wind wave and storm surge model for southern louisiana and mississippi part ii synoptic description and analysis of hurricanes katrina and rita abstract hurricanes katrina and rita were powerful storms that impacted southern louisiana and mississippi during the 2005 hurricane season in part i the authors describe and validate a high resolution coupled riverine flow tide wind wave and storm surge model for this region herein the model is used to examine the evolution of these hurricanes in more detail synoptic histories show how storm tracks winds and waves interacted with the topography the protruding mississippi river delta east west shorelines manmade structures and low lying marshes to develop and propagate storm surge perturbations of the model in which the waves are not included show the proportional importance of the wave radiation stress gradient induced setup

polythermal three dimensional modelling of the greenland ice sheet with varied geothermal heat flux computations over 50 000 years into steady state with greve s polythermal ice sheet model and its numerical code are performed for the greenland ice sheet with today s climatological input surface temperature and accumulation function and three values of the geothermal heat flux 42 54 6 29 4 mw m 2 it is shown that through the thermomechanical coupling the geometry as well as the thermal regime in particular that close to the bed respond surprisingly strongly to the basal thermal heat input the most sensitive variable is the basal temperature field but the maximum height of the summit also varies by more than 100m furthermore some intercomparison of the model outputs with the real ice sheet is carried out showing that the model provides reasonable results for the ice sheet geometry as well as for the englacial temperatures

to the islands born the research potential of submerged landscapes and human habitation sites from the islands of nw australia this paper focuses on the continental shelf of nw australia and on models for change in littoral and offshore environments of relevance to human occupation over the last 50 kyr major island groups occur on the shelf including the montebello and barrow islands and those of the dampier archipelago at lowest sea level around 22 ka these would have been uplands that then became progressively isolated by subsequent sea level rise by integrating archaeological and zooarchaeological records from excavations on these islands with the geology and geomorphology we interpret palaeoeconomic resource potential in relation to changing sea level and coastline morphology the preservation potential for submerged archaeological sites and features is also assessed current archaeological evidence from these offshore islands indicates that the submerged coastal landscape is likely to have been a potentially rich environment for resources and human occupation even at times of lowest sea level and regional aridity should any exploration of submerged archaeology be carried out in this region it is likely to be rewarding offering unique insights into late pleistocene coastal occupation

accuracy assessment of recent ocean tide models over 20 global ocean tide models have been developed since 1994 primarily as a consequence of analysis of the precise altimetric measurements from topex poseidon and as a result of parallel developments in numerical tidal modeling and data assimilation this paper provides an accuracy assessment of 10 such tide models and discusses their benefits in many fields including geodesy oceanography and geophysics a variety of tests indicate that all these tide models agree within 2 3 cm in the deep ocean and they represent a significant improvement over the classical schwiderski 1980 model by approximately 5 cm rms as a result two tide models were selected for the reprocessing of topex poseidon geophysical data records in late 1995 current ocean tide models allow an improved observation of deep ocean surface dynamic topography using satellite altimetry other significant contributions include theft applications in an improved orbit computation for topex poseidon and other geodetic satellites to yield accurate predictions of earth rotation excitations and improved estimates of ocean loading corrections for geodetic observatories and to allow better separation of astronomical tides from phenomena with meteorological and geophysical origins the largest differences between these tide models occur in shallow waters indicating that the current models are still problematic in these areas future improvement of global tide models is anticipated with additional high quality altimeter data and with advances in numerical techniques to assimilate data into high resolution hydrodynamic models

thermomechanical modelling of northern hemisphere ice sheets with a two level mass balance parameterization a 3 d time dependent thermomechanical ice sheet model was used together with a two level snow accumulation runoff mass balance model to investigatethe quaternary ice sheets of the northern hemisphere the model freely generates the ice sheet geometry in response to specified changes of surfacetemperature and mass balance and includes bedrock adjustment basal sliding and a full temperature calculation within the ice the mass balanceparameterisation makes a distinction between snowfall and melting yearly snow fall rates depend on the present precipitation distribution and are variedproportional to changes of surface temperature and the moisture content of the air the ablation model is based on the positive degree day method anddistinguishes between ice and snow melting this paper discusses steady state characteristics conditions for growth and retreat and response time scales ofice sheets as a function of a prescribed lowering of summer temperature most notably the modelled extents of the eurasian ice sheet for a summertemperature lowering of 6 7 k and of the laurentide ice sheet for a cooling of 9 10 k are in reasonable agreement with most reconstructions based ongeological evidence except for the presence of a large ice sheet stretching from alaska across the bering strait to most of eastern siberia in addition wetbasal conditions turned out to be always confined to the margin whereas central areas in these reconstructions remained always cold based this is ofrelevance for processes involving reduced basal traction

parameterizing tidal dissipation over rough topography the traditional model of tidal dissipation is based on a frictional bottom boundary layer in which the work done by bottom drag is proportional to a drag coefficient and the velocity cubed however away from shallow coastal regions the tidal velocities are small and the work done by the bottom boundary layer can account for only weak levels of dissipation in the deep ocean the energy flux carried by internal waves generated over rough topography dominates the energy transfer away from barotropic flow a parameterization for the internal wave drag over rough topography is included as a dissipative mechanism in a model for the barotropic tides model results suggest that the inclusion of this dissipation mechanism improves hydro dynamical models of the ocean tide it also substantially increases the amount of modeled tidal dissipation in the deep ocean bringing dissipation levels there into agreement with recent estimates from topex poseidon altimetry data

energetics of the m2 barotropic ocean tides an estimate of bottom friction dissipation from a hydrodynamic model abstract the aim of this paper is to present a detailed energy budget of the m2 ocean tides over the world ocean based on the hydrodynamic tidal solution fes94 1 which includes not only the characteristics of the sea surface tidal elevations but also of the tidal currents global and regional budgets are given the global energy input by astronomical forcing deduced from the 2 2 spherical harmonic development of the m2 sea surface elevation solution is 2 35 tw lower by 0 1 tw than for the new altimetric solutions produced recently directly from satellite observations one major feature emerging from the present analysis is that a quarter of this energy input takes place over the south atlantic ocean on the other hand ocean tides work against astronomical forcing over three areas eastern indian ocean southwest of the south american continent and around new zealand this energy is dissipated in fes94 1 by bottom friction over the main continental shelves but the outstanding feature is that 40 of the tidal energy is dissipated over the north atlantic ocean energy is thus redistributed from the areas of energy input to feed the areas of dissipation the pacific ocean the indian ocean and the south atlantic ocean receive more energy in total than they dissipate in contrast with the atlantic ocean and the arctic ocean where a large deficit must be compensated by a net influx of energy from the other basins one third of the total m2 energy input by astronomical forcing over the world ocean flows northwards through the equatorial atlantic detailed energy dissipation estimates are computed over the different areas of energy dissipation and compared to the previous estimates published in the literature

once again once again tidal friction topex poseidon t p altimetry has reopened the problem of how tidal dissipation is to be allocated there is now general agreement of a m2 dissipation by 2 5 terawatts 1 tw 1012 w based on four quite separate astronomic observational programs allowing for the bodily tide dissipation of 0 1 tw leaves 2 4 tw for ocean dissipation the traditional disposal sites since jeffreys 1920 have been in the turbulent bottom boundary layer bbl of marginal seas and the modern estimate of about 2 1 tw is in this tradition but the distribution among the shallow seas has changed radically from time to time independent estimates of energy flux into the marginal seas are not in good agreement with the bbl estimates t p altimetry has contributed to the tidal problem in two important ways the assimilation of global altimetry into laplace tidal solutions has led to accurate representations of the global tides as evidenced by the very close agreement between the astronomic measurements and the computed 2 4 tw working of the moon on the global ocean second the detection by ray and mitchum 1996 of small surface manifestation of internal tides radiating away from the hawaiian chain has led to global estimates of 0 2 to 0 4 tw of conversion of surface tides to internal tides measurements of ocean microstructure yields 0 2 tw of global dissipation by pelagic turbulence away from topography we propose that pelagic turbulence is maintained by topographic scattering of barotropic into baroclinic tidal energy via internal tides and internal waves previous estimates by baines 1974 baines 1982 of this conversion along 150 000 km of continental coastlines gave a negligible 0 02 tw evidently the important conversion takes place along mid ocean ridges the maintenance of the abyssal global stratification requires a much larger expenditure of power 2 tw versus 0 2 tw this is usually attributed to wind forcing if tidal power is to play a significant role here then the bbl estimates need to be reduced the challenge is to estimate dissipation from the energy flux divergence in the t p adjusted tidal models without prior assumptions concerning the dissipation processes

general circulation gcm modelling of palaeoclimates a critique the best method so far devised for testing the ability of a general circulation model gcm to simulate climates very different from today is to conduct snapshot experiments for specific times in the past at which the climatic forcing can be prescribed in detail this paper focuses on the period from the last glacial maximum through the holocene during this interval changes in atmospheric circulation were driven primarily by variations in the seasonality of insolation and secondarily by variations in surface boundary conditions accompanying deglaciation changes in atmospheric transparency are usually neglected apart from lower co2 at 18 ka bp palaeoclimatic simulations have yielded important insights into the dynamics of glacial interglacial climate change the results have been tested in three main ways 1 qualitative comparison of the spatial patterns of climate anomalies 2 comparison of the simulated climate at individual grid points or groups of grid points with quantitative estimates derived

an upwelling case study on florida s west coast using a combination of satellite sea surface temperature imagery in situ currents temperature and sea level data and a numerical circulation model we describe an upwelling event observed along florida s west coast although ubiquitous features of continental shelves descriptions of coastal upwellings or downwellings are generally complicated by the continuum of processes in which they occur for the case study presented the winds were light and the baroclinic background currents were steady for several days prior to the event these conditions allow the evolution of a specific winddriven upwelling event to be viewed as an initial value problem the data and the numerical model analysis show that the route of adjustment by the sea level and currents is a classical ekman geostrophic one sea level drops due to an offshore ekman transport causing a geostrophic alongshore jet and the associated onshore flow within the bottom ekman layer accounts for the appearance of cold water at the surface this surface manifestation occurs as an elongated feature centered about the 25 m isobath that spans roughly half of the florida peninsula from just north of tampa bay to key west the coldest water is observed offshore from tampa bay and we explain this region of locally maximum upwelling on the basis of the coastline and isobath geometries

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

numerical modeling of the global semidiurnal tide in the present day and in the last glacial maximum 1 a hydrodynamic model incorporating a self consistent treatment of ocean self attraction and loading sal and a physically based parameterization of internal tide it drag is used to assess how accurately barotropic tides can be modeled without benefit of data and to explore tidal energetics in the last glacial maximum lgm m2 solutions computed at high resolution with present day bathymetry agree with estimates of elevations from satellite altimetry within 5 cm rms in the open ocean this accuracy and agreement with atlimetric estimates of energy dissipation are achieved only when sal and it drag are included in the model solutions are sensitive to perturbations to bathymetry and inaccuracies in available global databases probably account for much of the remaining error in modeled elevations the 100 m drop in sea level during the lgm results in significant changes in modeled m2 tides with some amplitudes in the north atlantic increasing by factors of 2 or more dissipation is also significantly changed by the drop in sea level if it drag estimated for the modern ocean is assumed dissipation increases by about 50 globally and almost triples in the deep ocean however it drag depends on ocean stratification which is poorly known for the lgm tests with modified it drag suggest that the tendency to a global increase in dissipation is a robust result but details are sensitive to stratification significant uncertainties about paleotides thus remain even in this comparatively simple case where bathymetry is well constrained

hurricane storm surge simulations comparing three dimensional with two dimensional formulations based on an ivan like storm over the tampa bay florida region 1 we provide a dynamics based comparison on the results from three dimensional and two dimensional simulations of hurricane storm surge we begin with the question what may have occurred in the tampa bay florida vicinity had hurricane ivan made landfall there instead of at the border between alabama and florida this question is explored using a three dimensional primitive equation finite volume coastal ocean model the results show that storm surges are potentially disastrous for the tampa bay area especially for landfalls located to the north of the bay mouth the worst case among the simulations considered is for landfall at tarpon springs such that the maximum wind is positioned at the bay mouth along with such regional aspects of storm surge we then consider the dynamical balances to assess the importance of using a three dimensional model instead of the usual vertically integrated two dimensional approach to hurricane storm surge simulation with hurricane storm surge deriving from the vertically integrated pressure gradient force tending to balance the difference between the surface and bottom stresses we show that three dimensional structure is intrinsically important two dimensional models may overestimate or underestimate bottom stress necessitating physically unrealistic parameterizations of surface stress or other techniques for model calibration our examination of the dynamical balances inherent to storm surges over complex coastal topography suggests that three dimensional models are preferable over two dimensional models for simulating storm surges

a basin to channel scale unstructured grid hurricane storm surge model applied to southern louisiana abstract southern louisiana is characterized by low lying topography and an extensive network of sounds bays marshes lakes rivers and inlets that permit widespread inundation during hurricanes a basin to channel scale implementation of the advanced circulation adcirc unstructured grid hydrodynamic model has been developed that accurately simulates hurricane storm surge tides and river flow in this complex region this is accomplished by defining a domain and computational resolution appropriate for the relevant processes specifying realistic boundary conditions and implementing accurate robust and highly parallel unstructured grid numerical algorithms the model domain incorporates the western north atlantic the gulf of mexico and the caribbean sea so that interactions between basins and the shelf are explicitly modeled and the boundary condition specification of tidal and hurricane processes can be readily defined at the deep water open boundary the unstructured grid enables highly refi

forced tidal response in the gulf of mexico 1 this study investigates the characteristics of tides in the gulf of mexico gom and the response to forcing by local tidal potential and tides propagating as waves through straits connecting this semienclosed sea to the caribbean sea and atlantic ocean numerical simulations performed with the navy coastal ocean model run in a barotropic configuration with 1 60 horizontal resolution are used to analyze the tidal response to different forcing mechanisms the tidal energy budget and tidal energy fluxes in the gom are calculated from the simulations results show that diurnal tides in the gom are dominantly due to co oscillation with the western atlantic and that a substantial amount of semidiurnal tidal energy also enters the gulf through the straits model experiments suggest that adding the local tidal potential significantly modifies the propagation of the semidiurnal tidal signal within the gom and reduces the tidal power associated with the diurnal tides in the basin an interesting phenomenon of nonlinear interaction between the two forcing mechanisms local forcing and propagation through the straits is described and explained by using a mechanistic mass spring system model

estimating open ocean barotropic tidal dissipation the hawaiian ridge the generalized inverse of a regional model is used to estimate barotropic tidal dissipation along the hawaiian ridge the model based on the linear shallow water equations incorporates parameterizations for the dissipation of energy via friction in the bottom boundary layer and form drag due to internal waves generated at topographic slopes sea surface height data from 364 orbit cycles of the ocean topography experiment topex poseidon satellite mission are used to perform inversions at eight diurnal and semidiurnal tidal frequencies it is estimated that the barotropic m2 tide loses energy at a rate of 19 gw of which 88 is lost within 250 km of the ridge presumably via conversion to the internal or baroclinic tide uncertainty in the assumed model error and wave drag in the forward model suggest that m2 dissipation values from 18 to 25 gw are consistent with the altimetric observations other barotropic tidal constituents are estimated to lose a total of 5 7 gw the spatial distribution of barotropic dissipation along the ridge is similar to that inferred from three dimensional primitive equation models and it is largely insensitive to details of assumed model and data errors dissipation at semidiurnal frequencies is most intense at the french frigate shoals with lesser but significant contributions at other sites diurnal tidal dissipation is concentrated to the east of the french frigate shoals at the gardner pinnacles further work with threedimensional models will be necessary to determine the fate of the energy that is removed from the barotropic tide

dynamics of the long period tides abstract the long period tides are a tool for understanding oceanic motions at low frequencies and large scales here we review observations and theory of the fortnightly monthly and pole tide constitutents observations have been plagued by low signal to noise ratios and theory by the complex lateral geometry and great sensitivity to bottom slopes a new spectral element model is used to compute the oceanic response to tidal forcing at 2 week and monthly periods the general response is that of a heavily damped q 5 system with both the energy input from the moon and the dissipation strongly localized in space the high dissipation result is probably generally applicable to all low frequency barotropic oceanic motions over much of the ocean the response has both the character of a large scale and a superposed rossby wave like character thus vindicating two apparently conflicting earlier interpretations to the extent that free waves are excited they are consistent with their being dominated by rossby and topographic rossby wave components although gravity modes are also necessarily excited to some degree in general a modal representation is not very helpful the most active regions are the southern ocean and the western and northern north atlantic these results are stable to changes in geometry topography and tide period on a global average basis the dynamical response of mm is closer to equilibrium than is mf

the drag coefficient bottom roughness and wave breaking in the nearshore the bottom drag coefficient in the nearshore has been suggested to depend on bottom roughness bedforms or alternatively on wave breaking the hypothesis that bottom drag coefficient depends on bottom roughness is tested with 2 months of field observations collected on a sandy ocean beach during the duck94 field experiment both the drag coefficient estimated from alongshore momentum balances and bottom roughness estimated from fixed altimeters are larger within the surfzone than in the region farther seaward although the drag coefficient increases with roughness seaward of the surfzone no relationship was found between the drag coefficient and roughness related quantities within the surfzone these results suggest that breaking wave generated turbulence increases the surfzone drag coefficient

tides and tidal torques of the world ocean since the last glacial maximum peltier s 1994 paleobathymetries are used to investigate tides and corresponding balances of torques of the world ocean since the last glacial maximum 21 000 years before present simulations with a numerical tidal model point out that variable ice loads at the earth s surface and rearrangements in the interior led to considerable modifications of the resonance behavior of the oceans associated evident changes of the tidal range were not confined to the vicinity of formerly ice covered areas in contrast to the tidal oscillation system that was subject to almost uniform changes since the beginning of ice retreat the dissipation rate of the m2 tide increased distinctly during the principal melting time from 15 to 8 kyr b p and reached a local extreme eight thousand years ago though surface and volume of the world ocean were already very similar to present conditions postglacial deformations during the following two thousand years caused the decrease of tidal dissipation from the maximum value to the present day level indicating the sensibility of tidal torques and dissipation rates to comparatively small variations of ocean s geometry since the vicinity of the tidal oscillation system to a resonance situation is more decisive with respect to total dissipation than the extension of shelves where most of the tidal dissipation is expected to take place states of extreme dissipation rates do not necessarily coincide with extreme bathymetric conditions

tides and the climate some speculations abstract the important role of tides in the mixing of the pelagic oceans has been established by recent experiments and analyses the tide potential is modulated by long period orbital modulations previously loder and garrett found evidence for the 18 6 yr lunar nodal cycle in the sea surface temperatures of shallow seas in this paper the possible role of the 41 000 yr variation of the obliquity of the ecliptic is considered the obliquity modulation of tidal mixing by a few percent and the associated modulation in the meridional overturning circulation moc may play a role comparable to the obliquity modulation of the incoming solar radiation insolation a cornerstone of the milankovic theory of ice ages this speculation involves even more than the usual number of uncertainties found in climate speculations

forcing of the deep ocean circulation in simulations of the last glacial maximum 1 from the interpretation of different proxy data it is widely believed that the north atlantic thermohaline circulation during the maximum of the last ice age 21 000 years ago was considerably weaker than today recent equilibrium simulations with a coupled ocean atmosphere sea ice model successfully simulated a reduction in north atlantic deep water nadw formation consistent with reconstructions here we examine the influence of different air sea fluxes on simulated changes in the deep ocean circulation between the last glacial maximum and present day we find that changes in the oceanic surface freshwater fluxes are the dominant forcing mechanism for the reduced atlantic overturning diminished export of freshwater out of the atlantic drainage basin through the atmosphere decreases surface salinities in the north atlantic leading to less nadw formation in the colder climate changes in heat fluxes which lead to increased sea surface densities in the north atlantic and therefore to an enhanced overturning are of secondary importance wind stress variations seem to play a negligible role the degree to which the atlantic freshwater export and hence the nadw formation are reduced depends on the formulation of the atmospheric hydrological cycle and on the strength of the overturning in the present day simulation simulated changes in sea surface properties for a large variety of overturning strengths are compared with different reconstruction data sets the results depend strongly on the data set used sea surface temperature reconstructions from climate long range investigation mapping and prediction climap and earlier salinity reconstructions based on planktonic foraminifera are most consistent with a significant reduction of the circulation while recent reconstructions using dinocyst assemblages allow no unequivocal conclusion

hurricane gustav 2008 waves and storm surge hindcast synoptic analysis and validation in southern louisiana abstracthurricane gustav 2008 made landfall in southern louisiana on 1 september 2008 with its eye never closer than 75 km to new orleans but its waves and storm surge threatened to flood the city easterly tropical storm strength winds impacted the region east of the mississippi river for 12 15 h allowing for early surge to develop up to 3 5 m there and enter the river and the city s navigation canals during landfall winds shifted from easterly to southerly resulting in late surge development and propagation over more than 70 km of marshes on the river s west bank over more than 40 km of caernarvon marsh on the east bank and into lake pontchartrain to the north wind waves with estimated significant heights of 15 m developed in the deep gulf of mexico but were reduced in size once they reached the continental shelf the barrier islands further dissipated the waves and locally generated seas existed behind these effective breaking zones the hardening and innovative deployment of gauges since hur

sensitivity of a greenland ice sheet model to ice flow and ablation parameters consequences for the evolution through the last climatic cycle sensitivity experiments are conducted to test the influence of poorly known model parameters on the simulation of the greenland ice sheet by means of a three dimensional numerical model including the mechanical and thermal processes within the ice two types of experiments are performed steady state climatic conditions and simulations over the last climatic cycle with a climatic forcing derived from the grip record the experiments show that the maximum altitude of the ice sheet depends on the ice flow parameters deformation and sliding law coefficients geothermal flux and that it is low when the ice flow is fast on the other hand the maximum altitude is not sensitive to the ablation strength and consequently during the climatic cycle it is driven by changes in accumulation rate the ice sheet extension shows the opposite sensitivity it is barely affected by ice flow velocity and the ice covered area is smaller for large ablation coefficients for colder climates when there is no ablation the ice sheet extension depends on the sea level an interesting result is that the variations with time of the altitude at the ice divide summit do not depend on the parameters we tested the present modelled ice sheets resulting from the climatic cycle experiments are compared with the present measured ice sheet in order to find the set of parameters that gives the best fit between modelled and measured geometry it seems that compared to the parameter set most commonly used higher ablation rate coefficents must be used

implications from the comparisons between two and three dimensional model simulations of the hurricane ike storm surge 1 we apply the finite volume coastal ocean model to simulate the hurricane ike storm surge using two dimensional 2 d and three dimensional 3 d formulations the high resolution unstructured grid extends over the gulf of mexico with open boundaries in the straits of florida and the yucatan channel with the same wind and pressure forcing the bottom drag coefficients for the baseline 2 d and 3 d simulations are determined by spatially varying manning coefficients and constant bottom roughness respectively the baseline 2 d model simulates both the forerunner and the surge whereas the baseline 3 d model simulates the surge but underestimates the forerunner increasing the minimum manning coefficient reduces the 2 d forerunner and the surge manning coefficient and bottom roughness parameterizations produce different bottom drag coefficients using the same bottom drag coefficient the 2 d simulation yields a smaller surge than in three dimensions this is investigated for scenarios of either constant or variable bottom roughness where the bottom roughness is determined through manning coefficient transformation these sensitivity studies indicate that storm surges simulated either in two dimensions or three dimensions depend critically upon the parameterizations and the parameter values used for specifying bottom stress and similar may be said of surface stress given suitable calibration 2 d and 3 d models may adequately simulate storm surge however it is unclear that a calibration for a given storm and location may apply generally hence additional experimental guidance is required on the parameterizations and the parameter values used for both the surface and bottom stresses under severe wind conditions

climate sensitivity to continental ice sheet size and configuration abstract a version of the ncar community climate model ccm has been used to carry out a study of climate sensitivity to the size and distribution of continental ice sheets by comparing two perpetual season fixed sea surface temperature sst winter simulations of the climate at a glacial maximum the two simulations differ only in the size and configuration of the continental ice sheet boundary conditions these conditions represent minimum and maximum ice sheet extent for a glacial maximum as presently constrained by the geologic evidence all other boundary conditions are as specified by climap 1981 for winter surface conditions during the last glacial maximum lgm the ice sheets specified by climap 1981 used by many previous researchers to simulate ice age climate conditions are intermediate in size between the minimum and maximum ice sheets used for the simulations described here the maximum case simulation resulted in unexpected positive temperature anomalies over the northern hemisphere

circulation of tampa bay driven by buoyancy tides and winds as simulated using a finite volume coastal ocean model 1 the circulation of tampa bay is investigated using a high resolution three dimensional density dependent finite volume coastal ocean model fvcom that includes tampa bay the intracoastal waterway and the inner portion of the west florida continental shelf model performance over the three month interval september to november 2001 is assessed against available tide gauge and velocity profiler data before using the model to describe the circulation as driven by rivers tides and winds because of a mean wind velocity vector directed down the estuary axis we ran a parallel model experiment without winds to distinguish the estuarine circulation by gravitational convection from the mean wind effects with or without winds tampa bay exhibits a robust two layered estuarine circulation that concentrates on the deep channels the mean outflow at the surface tends to converge on the channels where the free surface elevation is locally minimum the mean inflow near the bottom also concentrates in the channels where the baroclinic pressure gradient force is largest geometry thus guides the mean circulation and salinity distributions at the tampa bay mouth mean outflows exist both in the deeper egmont channel and the shallower south pass whereas a mean inflow is limited to the egmont channel a residence time based on the egmont channel influx is estimated to be about 100 days consistent with previous studies we conclude that gravitational convection is a major contributor to the water property distributions of tampa bay and that the fvcom is suitable for estuary shelf interaction studies

coupling between two inlets observation and modeling 1 the resonance coupling between two adjacent inlets is investigated field evidence of this natural phenomenon is found for two elongated inlets in the region of ciutadella menorca island in the western mediterranean ciutadella and platja gran to illustrate the fundamental features of the problem analytical solutions for two rectangular inlets with constant depth are constructed and analyzed the theoretical results mimic well the field data and demonstrate the resonance coupling characteristics of the inlet responses the phenomenon is also examined with a numeric model so that the effects of real bathymetry can be considered numerical computations show the specific resonant features of local topography and the agreement between field data and numerical results is very good

the influence of domain size on the response characteristics of a hurricane storm surge model the influence of domain size on boundary condition specification and on computed storm surge response is investigated storm surge response along the florida shelf in the gulf of mexico due to hurricane kate is examined over three domains using two different open ocean boundary forcing functions a still water or zero elevation condition and an inverted barometer condition which accounts for the atmospheric pressure component of the meteorological forcing the first domain is relatively small and is situated primarily on the continental shelf in the region of intense storm surge generation a second domain includes the entire gulf of mexico basin the final domain covers the gulf of mexico contiguous basins and extends out into the deep atlantic ocean the computed storm surge response indicates that the small domain is inadequate since cross shelf boundaries are in regions of significant storm surge generation where surge and therefore boundary conditions are not known a priori also the behavior of resonant modes that are physically excited within the gulf of mexico due to the passage of the hurricane is unknown at the boundaries of this small domain the domain that includes the entire gulf of mexico captures the primary storm surge well but may not correctly model resonant modes in general these resonant modes are difficult to accurately set up by boundary condition specification since they may be dependent on interactions between the gulf and contiguous basins the primary storm surge response as well as resonant modes excited by the storm are best represented using a domain which encompasses the western north atlantic ocean the caribbean sea and the gulf of mexico this domain with deep atlantic ocean boundaries facilitates simple boundary condition specification and minimizes the influence of boundary conditions on storm surge generation in coastal regions basin resonant modes and basin to basin interactions are also captured

sensitivity of the thermohaline circulation to tropical and high latitude freshwater forcing during the last glacial interglacial cycle recent studies indicate that the tropical freshwater budget of the atlantic is modulated by changes in el nine southern oscillation enso if anomalies of the atlantic freshwater balance persist on the order of decades these might have a large influence on the north atlantic thermohaline circulation thc here we present a sensitivity study in which we use a model scenario for enso behavior during the last 120 kyr to force a simplified model of the thc with corresponding freshwater exchange between the tropical atlantic and pacific if the steady state strength of the north atlantic thc is similar to the present day its response to the forcing is of the order of 1 3 sv 1 sv 10 6 m 3 s 1 no mode changes of the thc are simulated for reasonable values of the coupling constant between freshwater exchange and enso if on the other hand the steady state overturning is significantly weaker a collapse of the thc occurs due to forcing from the tropics the modeled thc variation due to tropical freshwater perturbations are compared to those resulting from middle and high latitude freshwater forcing due to long term growth and decay of northern hemisphere ice sheets it is found that both forcings are of similar amplitude except during the deglaciation when high latitude forcing dominates a possible out of phase relationship between deep water formation in the north pacific and north atlantic is also explored

investigation of wave growth and decay in the swan model three regional scale applications abstract wave growth and decay characteristics in a typical wave action model simulating waves nearshore swan are investigated in this paper this study is motivated by generally poor agreement between model results and measurements for a regional scale model of a two day period during the sandyduck 97 experiment wherein there is consistent underprediction of lower frequency 0 05 0 19 hz energy two separate methods are presented for improving predictions of low frequency energy 1 by altering the weighting of the relative wavenumber term that exists in the whitecapping formulation and 2 by disallowing the breaking of swell the sandyduck 97 simulation is repeated with the proposed modifications using the first modification a slight improvement is seen and with the second modification an apparent problem with nonphysical dissipation of swell by the model is corrected the modifications are then applied to two other test cases one in lake michigan and the other in the mississippi bight both

lunar orbital evolution a synthesis of recent results the present rate of tidal dissipation in the earth moon system is known to be anomalously high in the sense that the implied age of the lunar orbit is only 1 5 109 years though other evidence suggests an age closer to 4 109 years to assess how long the anomalous dissipation has persisted we use published estimates of lunar orbital configurations derived from a fine grained sediments containing tidal laminations and b numerical ocean models averaged over varying ocean geometries the implied histories of the lunar semimajor axis are surprisingly consistent over the past 109 years the ocean models imply on average reduced dissipation in the past because of a spatial mismatch between tidal forcing and oceanic normal modes of higher frequencies webb s ocean model suggests that the anomalous oceanic dissipation began about 109 years ago and has been increasing since then

semi diurnal and diurnal tidal dissipation from topex poseidon altimetry 1 tidal energy dissipation is estimated for eight semi diurnal and diurnal constituents using a global inverse solution constrained by topex poseidon altimeter data very similar spatial patterns are obtained for all semi diurnal constituents with about one third of the total dissipation occurring in the deep ocean over rough topography maps for diurnal constituents are also similar amongst themselves but quite different from the semi diurnal results for diurnals a smaller fraction of dissipation roughly 10 occurs in the deep ocean much of the difference can be explained by the very different spatial pattern of diurnal and semi diurnal tidal currents the lack of free internal waves at frequencies poleward of 30 at diurnal frequencies also probably plays a role limiting the effectiveness of baroclinic conversion as an energy sink for barotropic diurnal tides

estimates of m2 tidal energy dissipation from topex poseidon altimeter data most of the tidal energy dissipation in the ocean occurs in shallow seas as has long been recognized however recent work has suggested that a significant fraction of the dissipation perhaps 1 tw or more occurs in the deep ocean this paper builds further evidence for that conclusion more than 6 years of data from the topex poseidon satellite altimeter are used to map the tidal dissipation rate throughout the world ocean the dissipation rate is estimated as a balance between the rate of working by tidal forces and the energy flux divergence computed using currents derived by least squares fitting of the altimeter data and the shallow water equations such calculations require dynamical assumptions in particular about the nature of dissipation to assess sensitivity of dissipation estimates to input assumptions a large suite of tidal inversions based on a wide range of drag parameterizations and employing both real and synthetic altimeter data are compared these experiments and monte carlo error fields from a generalized inverse model are used to establish error uncertainties for the dissipation estimates owing to the tight constraints on tidal elevation fields provided by the altimeter area integrals of the energy balance are remarkably insensitive to required dynamical assumptions tidal energy dissipation is estimated for all major shallow seas excluding individual polar seas and compared with previous model and data based estimates dissipation in the open ocean is significantly enhanced around major bathymetric features in a manner consistent with simple theories for the generation of baroclinic tides

causation of large amplitude coastal seiches on the caribbean coast of puerto rico abstract sea level oscillations at supertidal frequency with amplitudes of the order of the mean tidal range have been reported from the caribbean coast of puerto rico analysis of a 10 year time series of digital tide data from magueyes island puerto rico demonstrates that sea level variance at the fundamental normal mode sciche frequency of the shelf has a pronounced fortnightly distribution with a maximum occurring 6 7 days after new and full moon the sieche variance also shows a bimodal seasonal distribution with an inverse relationship to easterly wind stress it is argued that the sciches are excited by internal waves generated by strong tides in the southeastern caribbean support is provided by airborne radar imagery showing sea surface patterns suggesting the presence of internal waves near the southern aves ridge and by the results of two field experiments carried out during times when large amplitude sciches were expected to search for evidence of internal wave forcing near the shelf br

comparing simulated glacial climate and paleodata a reexamination glacial sea surface temperatures ssts simulated by an atmosphere mixed layer ocean model are compared with those reconstructed by the climate long range investigation mapping and prediction climap project using planktonic microfossils two methods of comparison are employed the first is global and uses the subjectively analyzed i e hand contoured then digitized data set published by climap the second is restricted to only those discrete locations where the climap sediment cores were taken both methods indicate that many aspects of the reconstructed glacial sst changes are simulated reasonably well by the model although there are areas of disagreement the extent of the disagreement appears smaller when the ssts are sampled at discrete locations because the largest discrepancies occur in the subtropical pacific where data are sparse when examined separately for each ocean the magnitude of the disagreement in low latitudes roughly corresponds to the magnitude of the uncertainties in sst estimation using planktonic microfossils being largest in the pacific and smallest in the atlantic because the largest discrepancies occur where uncertainties in estimation are large no clear determination of whether the climate model exaggerates or underestimates low latitude climate sensitivity appears possible nonetheless sampling at discrete locations may be the best procedure for evaluating climate model performance because errors associated with extending analyses to data void areas can be avoided and uncertainties associated with inadequate spatial sampling made more evident

secular effects of oceanic tidal dissipation on the moon s orbit and the earth s rotation the earth and moon are considered as a two body system in gravitational isolation from the sun and other planets the lunar orbit is taken as circular and the solid earth is assumed to be a rigid sphere with no tidal deformation so that there are no precessional torques other than those arising from the tidally deformed ocean numerical solutions to laplace s tidal equations with dissipation by linear bottom friction are used to obtain ocean wide distributions of tidal amplitude for two idealized continentalities a single circular continent spherical cap centered at the north pole and a single spherical cap centered on the equator calculations are made for two different values of the frictional resistance coefficient thus giving rise to four sets of solutions the computed tidal amplitudes are used to calculate the oceanic tidal torque which in turn is used to integrate the orbital equations backward in time for solution of the two body problem the coriolis parameter and the tidal frequencies change with time thus requiring that the tidal equations be solved several times during the course of each orbital integration in this manner the earth s rotational and the moon s orbital histories are determined on a geologic time scale for each of the four models the calculated position of the lunar orbit at 4 5 billion years ago is found to range from 38 to 53 earth radii in the four models and corresponds to a sidereal month of 330 to 550 hours the sidereal day would have been 12 to 18 hours with a relative inclination of 3 to 22 between the terrestrial and lunar poles these results are in sharp contrast to those from previous studies of the earth moon system most of which indicated a roche limit approach of the two bodies roughly 1 to 2 billion years ago and presented therefore a time scale difficulty in theories of lunar origin this contrast arises mainly from the fact that previous modelers avoided solution of laplace s tidal equations by prescribing a constant frictional phase lag angle between the angular position of the moon and the major axis of the second degree harmonic of the tidally deformed surface of the earth the amount of phase lag was established from the present astronomically deduced rate of tidal dissipation but this precluded dynamic variations in tidal torque over geologic time which are critical for determination of the orbital time scale the present rate of oceanic tidal dissipation is evidently anomalously high because of the near resonance of the oceanic response in both frequency and shape to the tidal forcing for the earth and moon to have evolved to their present separation from a distance of less than about 35 earth radii solely on the basis of oceanic tidal dissipation would have required the m2 response to have been near resonance for a significant portion of geologic history a rather implausible scenario the calculations reported here show that on the contrary frictional coupling between the earth and moon was much weaker than at present throughout most of the orbital history and consequently the moon s closest approach could not have been as small as 35 earth radii although idealized continentalities were used in these calculations the general conclusion of a weaker frictional coupling in the past is believed to be relatively insensitive to the continental configuration this is because at faster paleorotation the semidiurnal tidal frequencies would be resonant only with smaller scale normal modes of the ocean rather than with global scale modes as at present the time scale difficulty heretofore present in models of orbital evolution is thereby eliminated it should be noted that the orbital history developed here supports the theory of binary planetary accretion for lunar origin as opposed to fission or tidal capture

the eddy experiment gnss r speculometry for directional sea roughness retrieval from low altitude aircraft we report the retrieval of sea surface directional mean square slope from global navigation satellite system reflections gnss r delay doppler map ddm data collected during an experimental flight at 1 km altitude we emphasize the utilization of the entire ddm to more precisely infer ocean roughness directional parameters and argue that the ddm exhibits the impact of both roughness and scatterer velocity obtained estimates are analyzed and compared with jason 1 measurements ecmwf numerical weather model outputs and optical data

using ddm asymmetry metrics for wind direction retrieval from gps ocean scattered signals in airborne experiments reflectometry of signals of opportunity such as those emitted by a global navigation satellite system known as gnss r has been developed over the past years as a technique with great potential for ocean scatterometry among other applications different approaches have been proposed to use gnss r for remote sensing of ocean surface roughness one of them is based on deriving some descriptor metric from the measured delay doppler map ddm and directly relating it to a geophysical property of the scattering surface for instance different descriptors have been proposed in the literature to measure the ddm spreading caused by the increase in ocean surface mean square slopes due to surface winds in this paper a new descriptor based on the ddm is proposed for wind direction retrieval this descriptor designated as the skewness angle 1 skew measures the asymmetry in the ddm power distribution along the doppler frequency axis and it was modeled as a function of wind direction by means of a simulation study then that model was validated using real gnss r data from an airborne experiment after validation the ddm skewness model was successfully used for wind direction retrieval with a resulting rms error on the order of 20

effect of sea roughness on bistatically scattered range coded signals from the global positioning system a series of aircraft experiments was performed using a specialized gps receiver and a nadir oriented left hand circularly polarized antenna this apparatus received reflections of the gps signals from water surfaces under a variety of sea states the cross correlation between the reflected signal and a reference pseudo random noise code was recorded as a function of the relative time delay the shape of this function showed a dependence on the roughness of the reflecting surface this dependence generally followed that predicted by theory for bistatic scattering of range coded signals use of this information as a remote sensing technique for the determination of sea state is discussed

coupling of surge and waves for an ivan like hurricane impacting the tampa bay florida region 1 the interactions between waves and storm surge are investigated using an unstructured grid coupled wave surge model forced by a hypothetical ivan like hurricane impacting the tampa bay florida region the waves derived from the unstructured version of the third generation wave model simulating waves nearshore the surge derives from the unstructured finite volume coastal ocean model to which wave induced forces based on radiation stress theory are added to the traditional forces by winds and atmospheric pressure dependent upon complex bathymetry and geometry the wave induced forces result in an additional 0 3 0 5 m of surge relative to an uncoupled surge only simulation and the increase in coastal sea level by the storm surge adds some 1 0 1 5 m to the significant wave heights nearshore such strong interactions through coupling suggest that waves should not be omitted in hurricane storm surge simulations especially because the forces by waves on coastal structures are perhaps the most damaging of the hurricane related forces

modeling wave effects on storm surge and coastal inundation abstract we present a parametric study of surface wave effects on storm surge and coastal inundation hurricane wind forcing terms atmosphere pressure gradient terms and radiation open boundary conditions are implemented into an existing quasi 3d nearshore model nearcom tvd which uses a shock capturing tvd scheme and can better simulate the wetting drying process during inundation than a conventional finite difference model systematic numerical experiments are carried out in an idealized continental shelf beach land system to identify the role of waves in modeling storm surge and inundation under different storm characteristics four storm parameters including storm intensity storm size translation speed and incident angle are investigated modeling results reveal that the presence of waves can increase the maximum storm surge heights significantly through wave setup and the contribution of waves varies considerably depending on the storm characteristics in addition to direct wave forcing the wave enhanced bottom stress in the surfzone also promotes higher wave setup and hence higher surge heights waves also have a major influence on the maximum inland inundation distance however we find that waves do not always favor more inundation as expected for storms traveling at very slow translation speeds or nearly parallel to the coast waves surprisingly exert a negative effect on the maximum inundation distance we argue that wave enhanced bottom stress combined with longer forcing duration in such storms counteract the positive effect of wave setup and thus less inundation is predicted in wave current coupled simulations our results highlight the necessity of fully incorporating wave effects in storm surge and inundation modeling

origin of the hurricane ike forerunner surge 1 a large unpredicted water level increase appeared along a substantial section of the western louisiana and northern texas latex coasts 12 24 hrs in advance of the landfall of hurricane ike 2008 with water levels in some areas reaching 3 m above mean sea level during this time the cyclonic wind field was largely shore parallel throughout the region a similar early water level rise was reported for both the 1900 and the 1915 galveston hurricanes the ike forerunner anomaly occurred over a much larger area and prior to the primary coastal surge which was driven by onshore directed winds to the right of the storm track we diagnose the forerunner surge as being generated by ekman setup on the wide and shallow latex shelf the longer forerunner time scale additionally served to increase water levels significantly in narrow entranced coastal bays the forerunner surge generated a freely propagating continental shelf wave with greater than 1 4 m peak elevation that travelled coherently along the coast to southern texas and was 300 km in advance of the storm track at the time of landfall this was at some locations the largest water level increase seen throughout the storm and appears to be the largest freely propagating shelf wave ever reported ekman setup driven forerunners will be most significant on wide shallow shelves subject to large wind fields and need to be considered for planning and forecasting in these cases

scattering of gps signals from the ocean with wind remote sensing application a theoretical model that describes the power of a scattered global positioning system gps signal as a function of geometrical and environmental parameters has been developed this model is based on a bistatic radar equation derived using the geometric optics limit of the kirchhoff approximation the waveform i e the time delayed power obtained in the delay mapping technique depends on a wave slope probability density function which in turn depends on wind waveforms obtained for aircraft altitudes and velocities indicate that altitudes within the interval 5 15 km are the best for inferring wind speed in some regimes an analytical solution for the bistatic radar equation is possible this solution allows converting trailing edges of waveforms into a set of straight lines which could be convenient for wind retrieval a transition to satellite altitudes together with satellite velocities makes the peak power reduction and the doppler spreading effect a significant problem for wind retrieval based on the delay mapping technique at the same time different time delays and different doppler shifts of the scattered gps signal could form relatively small spatial cells on sea surface suggesting mapping of the wave slope probability distribution in a synthetic aperture radar sar fashion this may allow more accurate measurements of wind velocity and wind direction

the application of reflected gps signals to ocean remote sensing abstract the l band broadcast signal from the global positioning system gps reflected off of the sea surface is under study for use as a ocean coastal and wetlands remote sensing tool the reflected signal from a given gps satellite is cross correlated with the pseudorandom noise code uniquely identifying that satellite the shape of this cross correlation ordinarily a very sharp triangle when tracking a direct line of sight signal becomes wider and smoother as the mean square slope of the reflecting surface increases it is proposed that the surface wind speed can be determined by matching the recorded shape of this cross correlation to that predicted by theoretical models as a function of wind speed and direction the significance of these effects increases with altitude of the receiver experimental data have been collected using a specially modified gps receiver on aircraft and on a balloon at altitudes of up to 25 km these data compare favorably with predictions of analytical models and demonstrate the dependence of the waveform shape on surface wind speed and receiver altitude the advantages that this measurement technique has over conventional scatterometers is the small size low cost and simplicity of the receiver hardware no requirement for a transmitter and the ability to simultaneously collect data from usually 10 or more points from a low earth orbiting satellite this number could be larger if the russian global navigation satellite system satellites are also considered as additional sources of radiation furthermore the bistatic scattering geometry is complementary to the backscatter used by conventional scatterometers

indirect evidence for substantial damping of low mode internal tides in the open ocean a global high resolution ocean circulation model forced by atmospheric fields and the m2 tidal constituent is used to explore plausible scenarios for the damping of low mode internal tides the plausibility of different damping scenarios is tested by comparing the modeled barotropic tides with tpxo8 a highly accurate satellite altimetry constrained tide model and by comparing the modeled coherent baroclinic tide amplitudes against along track altimetry five scenarios are tested 1 a topographic internal wave drag argued here to represent the breaking of unresolved high vertical modes applied to the bottom flow default configuration 2 a wave drag applied to the barotropic flow 3 absence of wave drag 4 a substantial increase in quadratic bottom friction along the continental shelves with wave drag turned off and 5 application of wave drag to the barotropic flow at the same time that quadratic bottom friction is substantially increased along the shelves of the scenarios tested here the default configuration 1 yields the most accurate tides in all other scenarios 2 5 the lack of damping on open ocean baroclinic motions yields baroclinic tides that are too energetic and travel too far from their sources despite the presence of a vigorous mesoscale eddy field which can scatter and decohere internal tides in the model the barotropic tides are also less accurate in the absence of an open ocean damping on barotropic motions that is in scenarios 3 and 4 the results presented here suggest that low mode internal tides experience substantial damping in the open ocean

global tidal impacts of large scale ice sheet collapses recent studies show that the glaciers draining both the west antarctic and the greenland ice sheets are experiencing an accelerated ice loss highlighting the possibility of large scale ice sheet retreat and sea level rise in the coming centuries and millennia these sea level changes would vary spatially and could significantly alter global tides as the latter are highly dependent on bathymetry or water column thickness under ice shelves and basin shape this paper investigates how the principal semi diurnal m2 tidal amplitudes and energy dissipation respond to the non uniform sea level changes induced by complete ice sheet collapses the sea level changes are calculated using gravitationally self consistent sea level theory and the tides are simulated using an established tidal model results from the simulations show global and spatially heterogeneous changes in tidal amplitudes in addition pronounced changes in tidal energy dissipation occur in both the open ocean and in shelf seas also altering the location of tidal mixing fronts these changes have the potential to impact ocean mixing and hence large scale currents and climate patterns and the contribution of shelf sea to the global carbon cycle the new results highlight the importance of considering changes in the tides in predictions of future climate and reconstructions of past climate phases such as the last interglacial

a high resolution coupled riverine flow tide wind wind wave and storm surge model for southern louisiana and mississippi part i model development and validation abstract a coupled system of wind wind wave and coastal circulation models has been implemented for southern louisiana and mississippi to simulate riverine flows tides wind waves and hurricane storm surge in the region the system combines the noaa hurricane research division wind analysis system h wind and the interactive objective kinematic analysis ioka kinematic wind analyses the wave model wam offshore and steady state irregular wave stwave nearshore wind wave models and the advanced circulation adcirc basin to channel scale unstructured grid circulation model the system emphasizes a high resolution down to 50 m representation of the geometry bathymetry and topography nonlinear coupling of all processes including wind wave radiation stress induced set up and objective specification of frictional parameters based on land cover databases and commonly used parameters riverine flows and tides are validated for no storm conditions while winds wind waves hydrographs and high wa

significant dissipation of tidal energy in the deep ocean inferred from satellite altimeter data how and where the ocean tides dissipate their energy are long standing questions1 that have consequences ranging from the history of the moon2 to the mixing of the oceans3 historically the principal sink of tidal energy has been thought to be bottom friction in shallow seas4 5 there has long been suggestive evidence6 7 however that tidal dissipation also occurs in the open ocean through the scattering by ocean bottom topography of surface tides into internal waves but estimates of the magnitude of this possible sink have varied widely3 8 9 10 11 here we use satellite altimeter data from topex poseidon to map empirically the tidal energy dissipation we show that approximately 1012 watts that is 1 tw representing 25 30 of the total dissipation occurs in the deep ocean generally near areas of rough topography of the estimated 2 tw of mixing energy required to maintain the large scale thermohaline circulation of the ocean12 one half could therefore be provided by the tides with the other half coming from action13 on the surface of the ocean

tides on the west florida shelf the principal semidiurnal m2 and s2 and diurnal k1 and o1 tidal constituents are described on the west florida continental shelf wfs using a combination of in situ measurements and a three dimensional primitive equation numerical model the measurements are of sea level and currents along the coastline and across the shelf respectively the model extends from west of the mississippi river to the florida keys with an open boundary arcing between it is along this open boundary that the regional model is forced by a global tide model standard barotropic tidal analyses are performed for both the data and the model and quantifiable metrics are provided for comparison based on these comparisons the authors present coamplitude and cophase charts for sea level and velocity hodographs for currents the semidiurnal constituents show marked spatial variability whereas the diurnal constituents are spatially more uniform apalachicola bay is a demarcation point for the semidiurnal tides that are well developed to the southeast along the wfs but are minimal to the west the largest semidiurnal tides are in the florida big bend and florida bay regions with a relative minimum in between just to the south of tampa bay these spatial distributions may be explained on the basis of local geometry a lagrangian stokes drift coherently directed toward the northwest is identified but is of relatively small magnitude when compared with the potential for particle transport by seasonal and synoptic scale forcing bottom stressinduced tidal mixing is examined and estimates are made of the bottom logarithmic layer height by the m2 tidal currents

north american ice sheet reconstructions at the last glacial maximum abstract the areal extent of the last glacial maximum lgm ice sheets is well known in north america but there is no direct geological proxy for ice sheet thickness or volume uncertainties associated with glaciological and geophysical reconstructions give widely varying estimates of north american ice sheet nais volume at lgm in an effort to quantify the uncertainty associated with glaciological reconstructions we conducted a suite of 190 numerical simulations of the last glacial cycle in north america prescribing different climatic mass balance glaciologic and isostatic treatments for the least constrained model variables lgm ice sheet reconstructions were evaluated using the well established geologic record of ice sheet area and southern extent at lgm dyke and prest 1987 these constraints give a subset of 33 simulations that produce reasonable lgm ice cover in north america ice sheet dispositions and the associated parameter settings in this subset of tests provide insight into the plausible range of nais thickness form and mass balance regime at lgm ice volume in this subset of tests spans a range of 28 5 38 9 10 15 m 3 at lgm with a predominant cluster at 32 36 10 15 m 3 taking floating ice and displaced continental water into account this corresponds to 69 94 m eustatic sea level msl more than 75 of the accepted tests fall in the range 78 88 msl we argue that this is a plausible estimate of the volume of water locked up in the nais at lgm

u s ioos coastal and ocean modeling testbed evaluation of tide wave and hurricane surge response sensitivities to mesh resolution and friction in the gulf of mexico 1 this paper investigates model response sensitivities to mesh resolution topographical details bottom friction formulations the interaction of wind waves and circulation and nonlinear advection on tidal and hurricane surge and wave processes at the basin shelf wetland and coastal channel scales within the gulf of mexico tides in the gulf of mexico are modestly energetic processes whereas hurricane surge and waves are highly energetic the unstructured mesh coupled wind wave and circulation modeling system swan adcirc is implemented to generate modeled tidal harmonic constituents and hurricane waves and surge for a hurricane ike 2008 hindcast in the open ocean mesh resolution requirements are less stringent in achieving accurate tidal signals or matching hurricane surge and wave responses however coarser resolution or the absence of intertidal zones decreases accuracy along protected nearshore and inland coastal areas due to improper conveyance and or lateral attenuation bottom friction formulations are shown to have little impact on tidal signal accuracy but hurricane surge is much more sensitive especially in shelf waters where development of a strong shore parallel current is essential to the development of ike s geostrophic setup the spatial and temporal contributions of wave radiation stress gradients and nonlinear advection were charted for ike nonlinear advection improves model performance by capturing an additional 10 20 cm of geostrophic setup and increasing resonant cross shelf waves by 30 40 cm wave radiation stress gradients improve performance at coastal stations by adding an extra 20 40 cm to water levels

determining paleoceanographic circulations with emphasis on the last glacial maximum the inference from radiocarbon and other data that the north atlantic ocean circulation during the last glacial maximum was reduced is examined because glacial periods are thought to be windier than non glacial ones a reduced circulation is difficult to rationalize a first step is to note that the circulation of mass is unlikely to correspond simply to the circulation of heat or freshwater salt by merely permitting an enhanced input of southern hemisphere water into the north atlantic one can accommodate significantly increased radiocarbon ages such an input is equally interpretable as owing to an increased mass circulation rather than a decreased one inferred estimates from paleo shear estimates in the florida current are re interpreted as producing an indeterminate net flow there determination of the paleocirculation rates is not simpler than the problem in the modern ocean it is fully three dimensional and requires an adequate data base to determine the mass flux rates

sensitivity analysis of wind vector measurements from ocean reflected gps signals the power received by a gps receiver located on an airplane flying over the ocean and collecting the gps signal reflected off the surface is estimated for varying wind speed and wind direction platform altitude satellite elevation angle and receiver integration time by accounting for the wind induced anisotropy on the surface it is shown that the trailing edges of computed waveforms change with both wind speed and direction when the receiver integration time is properly chosen substantial differences in the waveforms at different wind directions are exhibited even at the beginning of the trailing edge particularly for reflections from high elevation satellites these differences are associated with the extent and directional properties of the scattered fields as a function of reflection angle an analysis of the interdependence of the observational geometric parameters the coherence time and the receiver integration time is presented to suggest a suitable arrangement for enhanced measurement sensitivity to the wind direction

tides of the caribbean sea analysis of tidal characteristics from 45 gauge locations indicates that the caribbean sea has a microtidal range for the most part between 10 and 20 cm the tide is primarily either mixed semidiurnal or mixed diurnal but a substantial section from puerto rico to venezuela experiences diurnal tides empirical charts of six component tides m sub 2 s sub 2 n sub 2 k sub 1 o sub 1 and p sub 1 show local detail of phase and amplitude each of the semidiurnal component tides is characterized by anticlockwise rotating amphidromes centered in the eastern caribbean there is evidence of strong radiational forcing of the s sub 2 tide in the south western caribbean the diurnal component tides are largely uniform in both phase and amplitude for most of the western and central caribbean however the diurnal phases increase rapidly towards the northwest and the yucatan channel

modelling of last glacial maximum ice sheets using different accumulation parameterizations we use a three dimensional thermomechanical ice sheet model previously tested on the greenland ice sheet to reconstruct last glacial maximum lgm ice sheets we compare the effects on the results of the ice sheet model of three different accumulation parameterization schemes in the first and second schemes lgm precipitation is computed from the present precipitation taking and not taking into account moisture transport in the third scheme lgm precipitation and surface temperatures are computed using outputs of an atmospheric global circulation model agcm treated in anomaly mode results are compared to the last reconstruction of the northern hemisphere ice sheets peltier 1994 computed using global rebound rates in a visco elastic model of the earth s crust the first two accumulation parameterizations do not give satisfactory reconstructions of the lgm ice sheets since they are unable to compute realistic lgm climatic conditions the third method gives very satisfactory results which leads us to conclude that the best way to obtain realistic lgm climatic conditions is to use agcm outputs

simulating hurricane storm surge in the lower mississippi river under varying flow conditions abstracthurricanes in southeastern louisiana develop significant surges within the lower mississippi river storms with strong sustained easterly winds push water into shallow breton sound overtop the river s east bank south of pointe a la hache louisiana penetrate into the river and are confined by levees on the west bank the main channel s width and depth allow surge to propagate rapidly and efficiently up river this work refines the high resolution unstructured mesh wave current simulating waves nearshore advanced circulation swan adcirc sl16 model to simulate river flow and hurricane driven surge within the mississippi river a river velocity regime based variation in bottom friction and a temporally variable riverine flow driven radiation boundary condition are essential to accurately model these processes for high and or time varying flows the coupled modeling system is validated for riverine flow stage relationships flow distributions within the distributary systems tides and hurric

normal modes of the world ocean part ii description of modes in the period range 8 to 80 hours abstract we have calculated normal modes with period between 8 and 80 h for a domain consisting of the arctic atlantic indian and pacific oceans in this period range the numerical model has 56 modes of which 13 are topographic vorticity waves all slower than 30 h the trapping sites for these modes are the siberian shelf the icelandic plateau the grand banks the falkland plateau and patagonian shelf the kerguelen plateau the new zealand and fiji plateaus and the hawaiian ridge predominantly planetary vorticity waves do not appear in the model at periods less than 80 h the 41 modes found between 30 and 8 h include basin modes in the north atlantic indian and equatorial pacific quarter wave resonances in the arabian sea bay of bengal and gulf of guinea and kelvin waves on the antarctic coast the pacific north american coast and the new zealand coast several vorticity and gravity modes exhibit an eastward circumglobal flow of energy that is confined to equatorial latitudes except where defl

ice sheet mass balance during the last glacial maximum in the framework of the paleoclimate modelling intercomparison project pmip simulations of the last glacial maximum lgm have been performed more than 10 different atmospheric general circulation models agcms have been used with the same boundary conditions sea surface temperatures prescribed by climap 1981 ice sheet reconstruction provided by peltier 1994 change in insolation and reduced co2 content one of the major questions is to investigate whether the simulations of the lgm are in equilibrium with the prescribed ice sheet reconstruction to answer this question we have used two different approaches first we analyze the results of a sel of lgm simulations performed with different versions of the laboratoire de meteorolo gie dynamique lmd agcm and study the hydrologic and snow budgets over the laurcntide and fennoscandian ice sheets second we use the agcm outputs to force an ice sheet model in order to investigate its ability to maintain the ice sheets as reconstructed by climap 1981 or peltier 1994

gps signal scattering from sea surface wind speed retrieval using experimental data and theoretical model abstract global positioning system gps signals reflected from the ocean surface have potential use for various remote sensing purposes some possibilities are measurements of surface roughness characteristics from which wave height wind speed and direction could be determined for this paper gps reflected signal measurements collected at aircraft altitudes of 2 km to 5 km with a delay doppler mapping gps receiver are used to explore the possibility of determining wind speed to interpret the gps data a theoretical model has been developed that describes the power of the reflected gps signals for different time delays and doppler frequencies as a function of geometrical and environmental parameters the results indicate a good agreement between the measured and the modeled normalized signal power waveforms during changing surface wind conditions the estimated wind speed using surface reflected gps data obtained by comparing actual and modeled waveforms shows good agreement within 2 m s with data obtained from a nearby buoy and independent wind speed measurements derived from the topex poseidon altimetric satellite

on the balance between growth and dissipation in an extreme depth limited wind sea in the southern north sea abstract bouwa has given a discussion of a severe storm in the southern north sea on 3 january 1976 near texel one of the friesian islands this storm was characterized by a remarkable steadiness of wind and wave parameters the steadiness of the wave parameters was apparently the result of depth limitations which prevented further wave evolution here the various terms in the energy balance equation for wave growth in shallow water are estimated the relative importance of wind input surface dissipation bottom dissipation advection and nonlinear transfer is discussed for a certain choice of dissipation parameters a good balance can be obtained this is in agreement with the steadiness of the observed wave conditions

structure of the upper water column in the northwest north atlantic modern versus last glacial maximum conditions 1 during the last glacial maximum the northwestern north atlantic constituted a major conduit for labrador and greenland ice sheet meltwaters vertical density gradients in its upper water masses have been reconstructed by combining information from transfer functions based on dinocysts and from oxygen isotope measurements 18o in planktonic foraminifera transfer functions yield temperature and salinity and thus potential density for the warmest august and coldest february months in the photic zone the 18o values in different size fractions of epipelagic globigerina bulloides and mesopelagic neogloboquadrina pachyderma left coiled npl foraminifera allow us to assess gradients through the pycnocline between surface and intermediate waters based on the calibration of a versus 18o relationship from transfer function reconstructions the size and density of npl shells provide further constraints on these gradients the results show the development of a very strong pycnocline during the lgm with a difference of about 3 summer to 1 5 winter units between surface and underlying waters they indicate conditions unfavorable for vertical convection and support the hypothesis of the spreading of a shallow low salinity buoyant layer over the northern north atlantic this layer depicted a strong e w gradient with maximum seasonal contrast and minimum absolute values westward

orbitally forced sedimentary rhythms in the stratigraphic record is there room for tidal forcing the imprint of orbital cycles which result from the varying eccentricity of the earth s orbit and changes in the orientation of its axis have been recognised throughout the phanerozoic rock record variations in insolation and their effect on climate are generally considered to be the sole transfer mechanism between the orbital variables and cyclic sedimentary successions common oceanographic principles however show that the ocean tide also responds to variations in the orbital parameters the ocean tide has not yet been considered to be a valid additional transfer mechanism for the orbital variations in geological studies of milankovitch cycles in sedimentary successions the insolation paradigm offers satisfying explanations and the role of long term variations of the ocean tide has not yet been appreciated variations in the ocean tide related to changing eccentricity at present 0 0165 theoretical maximum 0 0728 affect a variety of oceanographic and sedimentary processes in addition to the widely accepted paradigm of orbitally forced insolation changes the tidal transfer of orbital signals may explain certain less well understood aspects of orbitally induced cycles in the stratigraphic record related to ocean mixing organic productivity and tidal processes in shallow seas and deep water variations of the ocean tide in relation to the 18 6 year lunar nodal cycle which has no insolation counterpart by which they may be obscured indeed show that these relatively small variations can produce significant effects in sedimentary environments that are sensitive to variations in the strength of the ocean tide in analogy with the 18 6 year lunar nodal cycle orbital variations of the tide on milankovitch time scales are likely to have affected sedimentary systems in the past

coupling an agcm with an ism to investigate the ice sheets mass balance at the last glacial maximum the aim of this paper is to investigate the consistency between the ice sheets reconstruction at the lgm and the climate simulated by agcm in particular to investigate whether the laurentian and the fennoscandian ice sheets have an equilibrated mass balance we use two complementary approaches first we analyze the changes of snow and water budgets over the ice sheets only using the model results of lgm runs second we use a thermomechanical ice sheet model ritz et al 1997 forced with the agcm simulated climate to perform long term runs at finer spatial resolution analyzing the results obtained with both approaches we show that the ice sheet mass balance computed directly from agcm results may be biaised moreover we show using two versions of the lmd agcm that the ice sheet mass balance computed by the ism is drastically sensitive to the summer surface temperatures simulated by the agcm

mediterranean balloon experiment ocean wind speed sensing from the stratosphere using gps reflections abstract the mediterranean balloon experiment mebex conducted in august 99 from the middle up stratosphere was designed to assess the wind retrieval sensitivity of global navigation satellite systems reflections gnssr technology from high altitudes global positioning system reflected signals gpsr collected at altitudes around 37 km with a dedicated receiver have been inverted to mean square slopes mss of the sea surface and wind speeds the theoretical tool to interpret the geophysical parameters was a bistatic model which also depends on geometrical parameters the results have been analyzed in terms of internal consistency repeatability and geometry dependent performance in addition wind velocities have been compared to independent measurements by quikscat topex ers ra and a radio sonde with an agreement better than 2 m s a numerical weather prediction model nwpm the mm5 mesoscale forecast model has also been used for comparison with varying results during the experiment the conclusion of this study confirms the capability of high altitude gpsr delay map receivers with low gain antennas to infer surface winds

paleoclimatic tracers an investigation using an atmospheric general circulation model under ice age conditions 2 water isotopes the linear relationship observed between the water isotopic contents of precipitation and surface air temperatures leads to the use of the water isotopes h218o and hdo in paleoclimatology applied to the measurements of the isotopic content of paleowaters like groundwaters and deep ice cores this relationship is used to infer paleotemperatures however this interpretation of paleo isotopic contents is only valid if the isotope temperature relationship is not affected by climate change to address this problem we have developed a water isotope modeling inside an atmospheric general circulation model agcm and performed simulations of both the present day and last glacial maximum lgm climatic conditions agcms are indeed the only appropriate tools able to account the whole complexity of the atmospheric circulation for the present day climate preliminary results for january were presented by joussaume et al 1984 and are complemented by new simulations performed for both february and august climatic conditions with a higher resolution version of the model model results are well corroborated by observations they also exhibit some effects of the atmospheric circulation on the isotopic fields for the simulated lgm climate the model results compare well with paleoclimatic data of water isotopic contents except for a higher than observed spatial variability the overall patterns of the simulated 18o temperature relationship for the lgm climate are practically unchanged which tends to comfort the use of water isotopes in paleoclimatology however concerning the deuterium excess i e the relationship between oxygen 18 and deuterium the model results are not sufficiently valid to allow a discussion of the use of deuterium excess in paleoclimatology

how stationary are the internal tides in a high resolution global ocean circulation model the stationarity of the internal tides generated in a global eddy resolving ocean circulation model forced by realistic atmospheric fluxes and the luni solar gravitational potential is explored the root mean square rms variability in the m2 internal tidal amplitude is approximately 2 mm or less over most of the ocean and exceeds 2 mm in regions with larger internal tidal amplitude the m2 rms variability approaches the mean amplitude in weaker tidal areas such as the tropical pacific and eastern indian ocean but is smaller than the mean amplitude near generation regions approximately 60 of the variance in the complex m2 tidal amplitude is due to amplitude weighted phase variations using the rms tidal amplitude variations normalized by the mean tidal amplitude normalized rms variability nrms as a metric for stationarity low mode m2 internal tides with nrms 0 5 are stationary over 25 of the deep ocean particularly near the generation regions the m2 rms variability tends to increase with increasing mean amplitude however the m2 nrms variability tends to decrease with increasing mean amplitude and regions with strong low mode internal tides are more stationary the internal tide beams radiating away from generation regions become less stationary with distance similar results are obtained for other tidal constituents with the overall stationarity of the constituent decreasing as the energy in the constituent decreases seasonal variations dominate the rms variability in the arabian sea and near equatorial oceans regions of high eddy kinetic energy are regions of higher internal tide nonstationarity