instability waves in the equatorial atlantic ocean abstract evidence is presented for the generation of planetary waves by barotropic instability within the cyclonic shear region of the atlantic ocean s south equatorial current sec immediately following the springtime intensification of the southeast trade wind which accelerates the sec westward a packet of waves with central periodicity of around 25 days is observed lasting for about three cycles independent wavenumber analyses on 1983 and 1984 data give newly identical zonal wavelengths and phase speed estimates of around 1100 km and 50 cm s 1 the waves are anisotropic and spatially inhomogeneous with generation confined primarily to the mixed layer an energetics analysis using 1983 data centered upon the equator at 28 w shows a rapid increase in total perturbation energy tpe reaching values of 2000 erg cm 3 within two weeks the subsequent decrease in tpe at this location is due primarily to meridional pressure work divergence baroclinic instability is negligible because both the meridional

comparison of topex sea surface heights and tide gauge sea levels topex sea surface height data from the first 300 days of the mission are compared to sea level data from 71 tide gauges the initial comparison uses sea surface height data processed according to standard procedures as defined in the users handbook it is found that the median correlations for island and for coastal tide gauges are 0 53 and 0 42 respectively the analogous rms differences between the two data sets are 7 9 and 10 4 cm the comparisons improve significantly when a 60 day harmonic is fit to the differences and removed this period captures aliased m2 and s2 tidal energy that is not removed by the tide model making this correction and smoothing the sea surface height data over 25 km along track segments results in median correlations of 0 58 and 0 46 for the islands and coastal stations and median rms differences of 5 8 and 7 7 cm respectively removing once per revolution signals from the sea surface heights results in degraded comparisons with the sea levels it is also found that a number of stations have poor comparisons due to propagating signals that introduce temporal lags between the altimeter and tide gauge time series a final comparison is made by eliminating stations where this propagation effect is large discarding two stations that are suspected to have problems with the sea level data smoothing over 10 day intervals and restricting attention to island gauges this results in a set of 552 data pairs that have a correlation of 0 66 and a rms difference of 4 3 cm the conclusion is that on timescales longer than about 10 days the rms sea surface height errors are less than or of the order of several centimeters

application of turbulence energy models to the computation of tidal currents and mixing intensities in shelf edge regions abstract the major steps in the formulation of a three dimensional shelf edge model using a sigma coordinate system in the vertical are briefly described vertical diffusion of momentum is parameterized using a range of turbulence closure models and results are compared with earlier calculations using a simple flow related viscosity the influence of the magnitude of horizontal eddy viscosity upon spatial variability at the shelf edge is examined the model is applied to the calculation of m2 and o1 tidal elevations and currents in the shelf edge region off scotland the hebrides shelf and comparisons are made with data collected in the region computed m2 tidal elevations and currents are shown to be in adequate agreement with observations with no significant differences between tidal profiles computed with the turbulence energy models or the earlier calculations using a simple viscosity model the magnitude of the horizontal eddy viscosity does not appear to affect this component of the tide tidal

a vertically averaged circulation model using boundary fitted coordinates abstract a two dimensional vertically averaged circulation model using boundary fitted coordinates has been developed for predicting sea level and currants in estuarine and shelf waters the basic idea of the approach is to use a set of coupled quasi linear elliptic transformation equations to map the physical domain to a corresponding transformed plane such that all boundaries are coincident with coordinate lines and the transformed mesh is rectangular the hydrodynamic equations are then solved by a multi operation finite difference technique in the rectangular mesh transformed grid comparisons of the circulation model predictions for tidally forced flows in a wedge section with both flat and quadratic bottom topography and in a flat channel with exponential variation in width were in excellent agreement with corresponding analytic solutions simulation of steady state wind induced setup in a closed basin formed using elliptic cylindrical coordinates also was in excellent agreement with the analytic

a three dimensional model of the m2 s2 n2 k1 and o1 tides in the celtic and irish seas abstract a three dimensional model using various parameterizations of eddy viscosity covering the celtic and irish sea region is used to examine the spatial distributions of the m2 s2 n2 k1 and o1 tidal elevations and phases computed cotidal charts and comparisons with observations from shore based and offshore gauges show good agreement comparisons are also made with a standard two dimensional model in shallow water regions the three dimensional model shows significantly less damping than the two dimensional model with an associated improvement in accuracy a detailed examination of differences between computed and observed tidal currents at over thirty locations having three or more current meters in the vertical show that the model can accurately reproduce the tidal current and its vertical profile in the eastern irish sea the region furthest from the model s open boundary good agreement with observations is obtained although in the deeper channel to the south of this the model over predicts current magnitude

salinity driven thermocline transients in a wind and thermohaline forced isopycnic coordinate model of the north atlantic abstract an isopycnic coordinate oceanic circulation model formulated with the aim of simulating thermodynamically and mechanically driven flow in realistic basins is presented special emphasis is placed on the handling of diabatic surface processes and on thermocline ventilation the model performance is illustrated by a 30 year spinup run with coarse horizontal resolution 2 mesh in a domain with north atlantic topography extending from 10 to 60 n latitude the vertical structure encompasses 10 isopycnic layers in steps of 0 2 units capped by a thermodynamically active mixed layer from an initially isohaline state with isopycnals prescribed by zonally averaged climatology the model is forced by seasonally varying wind stress radiative and freshwater fluxes and by a thermal relaxation process at the surface after a mechanical spinup time of about 15 years a quasi stationary pattern of mean circulation and annual variability ensues characterized by pronounced subtropical mode water formation

a numerical model of internal tides with application to the australian north west shelf abstract a nonlinear primitive equation finite difference numerical model is applied to the problem of the generation propagation and dissipation of internal tides over a cross section of the continental slope and shelf topography of a region on the australian north west shelf the model is forced through the specification of the offshore tidal elevation and as such the full tidal field is modeled for the m2 constituent an energetic internal tide is produced in the model with results showing sensitivity to changes in both stratification and bathymetry the ratio of the slope of the internal wave characteristics to the bathymetry is generally less than or close to one producing subcritical and approximately critical conditions model results are compared to previously reported observations and show reasonable agreement in terms of wave structure propagation direction and regions of generation and energy dissipation the model shows a high degree of spatial variability in the amplitude and phase of

mean meridional currents in the central and eastern equatorial atlantic ship based acoustic doppler current profiler adcp velocity measurements collected by several major field programs in the tropical atlantic are averaged and combined with estimates of the mean near surface velocity derived from drifters and argo float surface drifts adcp d to describe the mean cross equatorial and vertical structure of the meridional currents along 23 w and 10 w data from moored adcps and fixed depth current meters a satellite derived velocity product and a global ocean reanalysis were additionally used to evaluate the mean adcp d meridional velocity the dominant circulation features in the long term mean adcp d meridional velocity in the upper 100 m are the tropical cells tcs located approximately between 5 s and 5 n with near surface poleward flow and subsurface equatorward flow that is stronger and shallower in the northern cell compared to the southern cell the thickness of the surface limb of the tcs decreases and the northern cell is found to shift further south of the equator from the central to eastern tropical atlantic analysis of two season means estimated from the ship based adcp near surface drift and moored velocity data as well as the simulated fields indicates that the maximum poleward velocity in the surface limb of the tcs intensifies during december may along 23 w largely due to seasonal compensation between the geostrophic and ageostrophic or wind driven components of the meridional velocity whereas the maximum equatorward flow in the subsurface limb of the northern cell intensifies during june november along both 23 w and 10 w due to the seasonality of the geostrophic meridional velocity

circulation in the central equatorial atlantic mean and intraseasonal to seasonal variability 1 the zonal equatorial circulation of the upper 700 m in the central tropical atlantic is studied based on 11 cross equatorial ship sections taken at 23 29 w during 1999 to 2005 and on data from a pair of moored acoustic doppler current profilers deployed on the equator at 23 w during february 2004 to may 2005 the observations on the equator reveal the existence of two mean westward cores of the equatorial intermediate current below the equatorial undercurrent in contrast to the 2002 moored observations at the same position the intraseasonal variability during the mooring period is dominated by zonal instead of meridional velocity fluctuations

potential vorticity dynamics of tropical instability vortices abstracttropical instability vortices tivs in the equatorial pacific exhibit energetic horizontal and vertical circulation characterized by regions of high rossby number and low richardson number their strong anticyclonic vorticity and vertical shear can influence the broader scale circulation by driving lateral mixing and vertical exchange between the ocean surface and interior the authors use a set of nested high resolution simulations of the equatorial pacific with a finest grid size of 3 km to examine the vortex dynamics associated with tiv core water formation tiv cores are characterized by low values of the ertel potential vorticity pv as the relative vorticity is anticyclonic with magnitude comparable to the local coriolis parameter a study of the variation of pv and other scalars along lagrangian fluid parcel tracks entering the tivs shows that the low pv water in their cores is a mix of equatorial undercurrent euc water and north equatorial counter current necc water the euc water

barotropic rossby waves radiating from tropical instability waves in the pacific ocean abstracttropical instability waves are triggered by instabilities of the equatorial current systems and their sea level signal with peak amplitude near 5 n is one of the most prominent features of the dynamic topography of the tropics cross spectral analysis of satellite altimetry observations shows that there is sea level variability in the pacific ocean as far north as hawaii i e 20 n that is coherent with the sea level variability near 5 n associated with tropical instability waves within the uncertainty of the analysis this off equatorial variability obeys the dispersion relation for nondivergent barotropic rossby waves over a fairly broad range of periods 26 38 days and zonal wavelengths 9 23 of longitude that are associated with tropical instability waves the dispersion relation and observed wave properties further suggest that the waves are carrying energy away from the instabilities toward the north pacific subtropical gyre which together with the observed coherence of the sea

dynamics of agulhas retroflection and ring formation in a numerical model part i the vorticity balance abstract the agulhas retroflection region of the wind driven idealized south atlantic indian ocean model described by deruijter and boudra is analyzed in detail here in part i the physical mechanisms of the model retroflection are elucidated through illustration of agulhas vorticity balance among various experiments in part ii the ring formation process is described in terms of its vertical structure and the associated energy conversions a one layer model demonstration shows that both inertia and internal friction may account for a partial retroflection where a linear weakly viscous system has none in the nonlinear weakly viscous one layer model the retroflection is accomplished through a free inertial boundary layer as suggested originally by de ruijter when stratification is introduced and baroclinicity increased using the bleck and boudra quasi isopycnic coordinate model with 2 or 3 layers the stretching term exerts an increasing influence with 40 km resolution terms included so that t

a wind driven isopycnic coordinate model of the north and equatorial atlantic ocean 1 model development and supporting experiments numerical approximations to the dynamic equations are given which allow basin size ocean circulation models formulated in isopycnic coordinates to accommodate variable bottom topography and irregular coastlines emphasis is placed on computational economy through the use of a split explicit time integration scheme on the proper formulation of the advection and coriolis terms in the momentum equation in case of strongly varying layer thickness and on the correct estimation of the horizontal pressure gradient force in grid boxes truncated by steep bottom slopes the algorithms are tested in a series of two and three layer double gyre experiments in cases of steady forcing leading to a steady circulation we are able to reproduce the expected motionless final state in coordinate layers that are below the direct influence of the wind forcing this includes layers intersecting topographic obstacles a long term 25 30 year vacillation tentatively associated with the outcropping of isopycnals along the edge of the cyclonic gyre in a steadily forced model is documented the paper forms the basis for a subsequent study in which circulation features obtained in a realistic north atlantic setting will be discussed

pathways and variability of the off equatorial undercurrents in the atlantic ocean the cold upwelling waters of the eastern tropical oceans not only interact with the atmospheric circulation via changing the sea surface temperatures but also influence the biological activity via affecting the nutrient and oxygen contents of the upwelling waters while the sources of the equatorial upwelling associated with the equatorial undercurrent euc have been studied extensively the relevance of the northern and southern off equatorial undercurrents neuc seuc for the off equatorial upwelling regions has remained unclear in this study we use output from a high resolution 1 12 model flame to investigate the mean pathways and variability of the off equatorial undercurrents oeucs in the atlantic in particular a calculation of lagrangian trajectories helps to gain insight into the source waters of the oeucs and their connection to the upwelling regions in the eastern tropical atlantic in the model solution the sources of both oeucs belong almost exclusively to the southern hemisphere the pathways of the source waters are found to be governed by strong recirculations between the different eastward and westward zonal currents because of intense eddy motions associated with the tropical instability wave activity whereas the seuc is predominantly fed through the recirculation in the ocean interior the neuc is also fed by a weak inflow from the western boundary current investigation of the fate of the neuc shows only a weak direct supply to the upwelling in the guinea dome and along the african coast but a significant contribution to the equatorial upwelling

chronology of warm core ring 82b a chronology constructed from satellite derived thermal imagery is presented to describe the formation and life history of warm core ring 82b this overview provides insight into a classification of features and discrete events associated with gulf stream warm core rings and allows these events as well as our limited shipboard observations to be placed in a broader spatial and temporal context than would otherwise be possible without the satellite data events influencing the evolution of 82b include environmental factors such as meteorological influences and gulf stream interactions as well as those stimulated by encounters with changes in bottom topography the interactions of the ring with surrounding waters are especially noteworthy and the existence of vortex vortex interactions is shown to be a significant cause of local water advection through streamer activity ring events are documented by following changes in ring size shape translation and surface thermal structure our satellite observations are supported by extensive contemporaneous shipboard observations including xbt ctd bops biooptical profiling system temperature profiles and along track sea surface temperature measurements in addition acoustic velocity profiling and drifter trajectories have been used to corroborate hydrographic features of the ring and environs these ship and satellite data form a coherent space time overview of the ring and its environment and show them to be closely related and continually interacting

instability waves observed on the equator in the atlantic ocean during 1983 a packet of surface confined westward propagating waves apparently generated by barotropic instability of the surface currents was observed in the equatorial atlantic during 1983 initial wavenumber analyses and energetics calculations are presented local working by the horizontal reynolds stress was large enough and at the correct time to account for the wave packet s existence the amplitude of the waves was comparable to the mean currents implying that the waves are of primary importance in the momentum balance of the seasonally varying equatorial surface currents

long waves and eddies in the tropical atlantic ocean 1984 1990 weekly images of sea surface temperature sst have been constructed for the tropical atlantic ocean for may september 1984 1990 from national oceanic and atmospheric administration national environmental satellite data and information service satellite derived sea surface temperature data these images have been analyzed to determine weekly to seasonal changes in the position of the fronts between the cold equatorial water and the warmer waters to the north and south we have found that long waves along the northern front previously reported by legeckis and reverdin 1987 are present each year although their number strength and duration vary the year 1987 was the most atypical with only a few short lived waves seen the long waves typically appear in sst in mid june and last into september they form along the equatorial thermal front between 5 w and 30 w and propagate westward sometimes reaching 45 w wave crests travel at speeds varying between 10 and 40 cm s but variations in amplitude reveal that the group velocity of the waves is eastward at 30 cm s long wave crests are observed to be associated with mesoscale anticyclonic warm core eddies which apparently play a significant role in cross equatorial heat transport instability features are also observed along the southern front of the equatorial cold tongue although because of weaker thermal gradients they are less distinct southern waves propagate westward along the front at speeds and wavelengths similar to the long waves in the north there is no simple phase relationship between long waves and the southern waves which suggests that the southern waves are not the direct result of the northern long waves

processes influencing the internal tide its higher harmonics and tidally induced mixing on the malin hebrides shelf abstract a three dimensional prognostic hydrodynamic model with a turbulence energy submodel is used to examine the spatial distribution of the internal tide in the shelf edge region off the west coast of scotland in the initial series of calculations presented here the model is used in a cross shelf form the model contains all the non linear terms necessary to examine the generation of the higher harmonics of the tide and the generation of very short waves on the density interface near the shelf break initial calculations assuming a homogeneous sea region show a thick turbulent bottom boundary layer generated by bottom friction which reduces the tidal current in the near bed region although above this the flow is essential inviscid with no vertical variation calculations with a specified vertical stratification reduce the thickness of the bottom turbulent layer with an associated change in current profile in the case of specified stratification no internal tides are generated however when the density field is allowed to evolve a significant internal tide is generated with an associated internal shear giving rise to enhanced mixing in regions of largest shear results from the model show that higher harmonics of the internal tide and short internal waves are generated above the shelf break where horizontal mixing processes are important the magnitude of these short internal waves increases with increasing tidal forcing and also depends upon the size of the horizontal diffusion term regions of intense surface and bed turbulence associated with the internal tide are found in the shelf break area suggesting that turbulence energy measurements in this location may be a good test of turbulence closure models however the significant spatial variability associated with these regions shows that an intense measurement campaign is required to avoid significant undersampling

internal tides and baroclinicity in the southern weddell sea 1 model description near the continental shelf break in the southern weddell sea warm deep water and western shelf water meet mixing mechanisms such as internal tides have the potential to mix these water masses and form antarctic bottom water a modified version of the princeton ocean model was utilized to investigate the internal tidal fields generated by the interaction of the m 2 barotropic tide with topography for transects across the continental shelf and slope in the southern weddell sea internal tides were generated over the upper continental slope as predicted by linear internal wave theory although the essentially two dimensional domain resulted in differences between the model elevations and the observations exceeding the observational uncertainties the cross slope velocities agreed well with differences less than the uncertainties for 78 of the existing observations

hydrographic and current observations on the continental slope and shelf of the western equatorial atlantic abstract hydrographic and current profiling data from december 1980 and current meter data obtained between september 1980 and november 1981 from the continental slope and shelf of the western equatorial atlantic between 2 and 7 n are used to describe the character of the north brazil coastal current nbcc system hydrographic data and the profiling results show that the nbcc has three distinct branches during the boreal fall in the near surface a strong current flows northwestward parallel to the coast at least as far as 6 n current speed within the near surface nbcc over a one year period were between 75 and 250 cm s 1 while the transport in december 1980 was between 15 and 20 106 m3 s 1 there was a southeastward near surface flow farther offshore which appears to be the return of the nbcc the ultimate destination of which is the north equatorial countercurrent offshore of the southeastward flow was a portion of a low salinity lens of amazon water the waters within and below the thermocline

local and remote atmospheric response to tropical instability waves a global view from space a la nina took place in the equatorial pacific in 1999 and strong tropical instability waves tiws developed causing large meanders of a sea surface temperature sst front between the equator and 3 n high resolution satellite measurements are used to describe the variability of sst surface wind velocity column integrated water vapor cloud liquid water and precipitation associated with these strong tiws in 1999 coherent ocean atmosphere patterns emerge in both the pacific and atlantic revealing rich regional characteristics in the far eastern pacific southeasterly trades strengthen weaken over positive negative sst anomalies apparently due to enhanced reduced mixing with high speed winds aloft in the central pacific we find evidence that sst induced sea level pressure changes also contribute substantially to wind fluctuations similar sst wind covariability also exists in the southern hemisphere along 2 s but the wind variability induced by unit sst anomaly is much larger than that north of the equator in the central pacific where the equatorial front is broad the northern sst pattern has a large meridional scale and reaches as far north as 6 n further to the north in the intertropical convergence zone itcz where local sst anomalies are small significant variability is found in clouds and precipitation which is further correlated with surface wind convergence in the atlantic tiw signals in sst are strongly trapped near the equator but they induce significant remote response in the itcz which takes a more southern position than its pacific counterpart and thus more susceptible to tiw influence

the m2 tide and its residual on the outer banks of the gulf of maine abstract tidal computations are reported for the gulf of maine with emphasis on its seaward banks georges bank browns bank nantucket shoals and the nearshore region off cape sable the model is 3d and nonlinear with quadratic vertical viscosity stratification is ignored the objective is to establish a theoretical baseline for tidal and residual currents on detailed topography against which seasonal changes may be examined two triangular meshes are used the base case corresponds to earlier studies with roughly 6 km resolution on the banks a more refined and extended mesh provides resolution at 2 3 km in critical areas and has boundaries farther removed from the banks both meshes provide very good fits with observed m2 elevations comparison of computed and observed m2 current profiles at 76 sites reveals general agreement that improves with resolution for the refined mesh and the 48 sites with records exceeding 60 days average deviations for m2 ellipse parameters are 6 1 4 7 cm s 1 for the

seasonal cycle of velocity in the atlantic north equatorial countercurrent as measured by surface drifters current meters and ship drifts this report describes the general circulation and seasonal variation of currents in the equatorial atlantic concentrating on the north equatorial countercurrent necc using data collected as part of the seasonal response of the equatorial atlantic and programme francais ocean et climat dans l atlantique equatorial experiments plus historical ship drifts during 1983 1985 the lagrangian circulation was studied by launching and tracking 30 freely drifting drogued buoys in the north equatorial countercurrent and 23 in the south equatorial current sec in addition continuously recording current meters were moored for 20 months at depths from 20 to 300 m near the center of the necc at 6 n 28 w these measurements are the longest series ever obtained in this current and provide information about its seasonal and interannual variations and zonal meridional and vertical structure the seasonal cycle of the necc is very regular from year to year each year the necc starts up in may june it flows eastward across the atlantic with surface speeds of up to 143 cm s in the west extending down to 350 m at 28 w and flowing into both the guinea current and north equatorial current it disappears or reverses from about january june west of 18 w some near surface water of the necc is inferred to downwell and flow equatorward toward the equatorial undercurrent the sec flows into the north brazil current which during spring continues up the coast into the caribbean during fall however the whole north brazil current retroflects or turns back on itself between 45 and 50 w forming the western necc the retroflection establishes a meander pattern in the necc that slowly propagates westward during fall at a speed of 4 cm s the meanders have a displacement of about 300 km in latitude a wavelength of 900 km and meridional velocity fluctuations of up to 100 cm s the swift currents and time dependent meanders in the western necc cause a high eddy kinetic energy 2400 cm2 s2 equivalent to that of the energetic part of the gulf stream

mixed layer thermocline interaction in a three dimensional isopycnic coordinate model abstract the annual buildup and obliteration of the seasonal thermocline and the associated ventilation of the permanent thermocline in a wind and thermally driven ocean basin are simulated numerically the model developed for this purpose is a combination of a single layer model of the oceanic mixed layer based on a simple closure of the turbulence kinetic energy equation and a three dimensional isopycnic coordinate model of the stratified oceanic interior the joint model set in a rectangular ocean basin is forced by annually varying wind stress and radiative plus turbulent heal fluxes approximating zonnaly averaged conditions over the north atlantic special emphasis is placed on the description of the mixed layer detrainment process which requires distributing mixed layer water of continuously variable density among constant density interior layers the truncation errors associated with this process are found to be numerically tolerable the quasi lagrangian character of the model s vertical coo

a whirling ecosystem in the equatorial atlantic 1 the equatorial pacific and atlantic oceans exhibit remarkable meridional undulations in temperature and chlorophyll fronts visible from space over thousands of kilometers and often referred to as tropical instability waves here we present new observations of an ecosystem ranging through three trophic levels phytoplankton zooplankton and small pelagic fish whirling within a tropical vortex of the atlantic ocean and associated with such undulations cold nutrient and biologically rich equatorial waters are advected northward and downward to form sharp fronts visible in all tracers and trophic levels the equatorward recirculation experiences upwelling at depth with the pycnocline and ecosystem progressively moving toward the surface to reconnect with the equatorial water mass the observations thus indicate that it is a fully three dimensional circulation that dominates the distribution of physical and biological tracers in the presence of tropical instabilities and maintains the cusp like shapes of temperature and chlorophyll observed from space

the three dimensional structure of an upper ocean vortex in the tropical pacific ocean in the equatorial pacific ocean easterly trade winds and the earth s rotation combine to drive surface currents away from the equator thereby causing cold nutrient rich subsurface water to upwell the front1 that forms between this upwelled water and warmer waters north of the equator is sometimes visible as a spectacular line in the sea 2 between 2 and 6 n westward propagating cusp shaped disturbances observed along this front3 have been attributed to the effect of dynamical instabilities in the system of zonal equatorial currents4 11but the connection between these phenomena remains unclear here we report extensive measurements from shipboard sensors satellite and drifting buoys which reveal the three dimensional structure of an anticyclonic eddy or vortex 500 km in diameter and centred at 4 n we suggest that cusp shaped disturbances of the front are caused by trains of large amplitude vortices which are driven by instability of the mean zonal shear we show that these vortices not only play an important role in the meridional transport of heat salt and momentum but are also associated with regions of intense horizontal convergence along the front where dramatic concentrations of marine life are observed

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

a model study of tidally induced suspended sediment transport in the iberian shelf edge region abstract across shelf suspended sediment transport due to tides is investigated using a three dimensional baroclinic hydrodynamic model including a sediment transport capability and parameterizing sub grid scale diffusion using a turbulence energy model the model in cross shelf form with topography characteristic of the shelf edge off the west coast of spain is used to examine sediment movement due to both barotropic and baroclinic tides and an along shelf flow calculations showed that the bed stress due to the barotropic tide and an along shelf flow exceeded the critical bed stress for part of the tidal cycle leading to sediment suspension the across shelf residual flow due to tidal rectification and the bottom ekman transport associated with the along shelf flow was on shelf in the surface layer and off shelf near the bed and produced a net off shelf sediment transport in the bottom boundary layer when a fixed stratification representing the thermocline was imposed this inhibited the upward diffusion of sediment thereby increasing its concentration in the bottom boundary layer comparison with and without stratification allowed its influence upon sediment concentration to be quantified calculations in which the stratification evolved with the flow field produced internal tides with an associated increase in current amplitude at a number of locations leading to greater spatial variability in the tidal residual and an additional residual due to the across shelf tidally induced thermal front increased diffusion and vertical velocity associated with the internal tide produced a thickening of the sediment bottom boundary layer a detailed examination of terms in the sediment transport equation enabled the importance of each in different regions to be quantified it showed that in the near bed layer the main balance was between vertical diffusion and settling however sediment concentration in the upper part of the water column was increased by the presence of the internal tide due to enhanced vertical advection and diffusion into the region changes in vertical stratification were found to influence both the horizontal and vertical distributions of sediment due to its influence upon the internal tide

a census of north brazil current rings observed from topex poseidon altimetry 1992 1998 six years of topex poseidon altimeter data are used to investigate the formation of rings and eddies shed by the north brazil current upper layer thickness maps were used to identify 34 of these features formed in the north brazil current retroflection region an average of more than 5 rings and eddies per year the ensemble of ring trajectories closely parallels the 500 m isobath and one out of six rings penetrate into the caribbean sea through the southern lesser antilles the rest of the rings and eddies follow a northern trajectory past barbados once they reach 58w their estimated mean translation speed is 14 km day and their mean length scale is approximately 100 km our results suggest that the formation rate of nbc rings and eddies is nearly twice that previously thought and that they may account for more than 1 3 of the interhemispheric transport within the atlantic meridional overturning cell

interannual variations of atlantic tropical instability waves 1 observations are used to develop metrics for interannual tropical instability wave tiw variability in the atlantic and to relate that variability to larger scale processes the analysis is partitioned into different latitude bands to distinguish between off equatorial 5 s 2 n and 5 n and near equatorial 2 s and 0 tiws tiw metrics based on sea surface temperature sst and sea level anomaly sla fluctuations are compared against interannual anomalies of sst in the cold tongue region to examine the role of barotropic shear instabilities in modulating the intensity of a tiw season wind stress and near surface current indices are developed in regions where the shear between the equatorial undercurrent euc and the northern branch of the south equatorial current nsec and between the nsec and the north equatorial countercurrent necc are expected to be largest good agreement is found between the sst and sla tiw metrics along the off equatorial latitude bands and interannual variations of both metrics can largely be attributed to barotropic shear instabilities in particular years with low high tiw variance along the off equatorial latitude bands are associated with anomalously warm cold ssts in the cold tongue region weak strong wind stress divergence and curl in the euc nsec region and weak strong zonal current shear in the nsec necc region in contrast in the near equatorial latitude bands poor agreement is found between interannual tiw activity based on the sst and sla metrics and near equatorial tiw variability cannot be explained by the large scale sst wind stress divergence and curl and current shear indices

eddies in the north brazil current retroflection region observed by geosat altimetry mesoscale fluctuations in the western tropical atlantic are analyzed in geosat altimetry sea surface height ssh and geostrophic velocity anomalies to investigate the role of eddies in the north brazil current nbc retroflection zone the detachment of anticyclonic eddies from the nbc retroflection is observed during november through january when the nbc retroflection into the north equatorial countercurrent necc weakens and finally breaks down these eddies are traced over more than 2 months between 50 and 60 w on their way toward the caribbean at average speeds of 15 cm s 1 in one case an apparent merger of two anticyclonic eddies occurs one detached from the retroflection zone and one detached from the necc cyclonic eddies are also observed but are generally less persistent mesoscale ssh variance just west of the retroflection increases by a factor of 2 from early summer to winter mainly because of the anticyclonic eddies interhemispheric water mass transfer associated with the eddy flux out of the nbc retroflection may amount to an average transport of 3 sv

a three dimensional model of the northwest european continental shelf with application to the m4 tide abstract the solution of the fully nonlinear three dimensional hydrodynamic equations in polar coordinates for tides is developed using a finite difference grid in the horizontal and the galerkin method in the vertical using this method a three dimensional model of the northwest european continental shelf is used to investigate the spatial distribution of the m4 tidal elevations and currants over the shelf computed m4 currents are compared with observations and found to he in good agreement in the celtic sea although there are significant errors in the north sea the reasons for these discrepancies and the spatial and depth variations in the m4 currants are discussed in detail

hydrothermal fluids responsible for the formation of precious minerals in the nigerian younger granite province preliminary investigations in the younger granite province of nigeria have revealed that precious and semi precious minerals like rubies sapphires emeralds aquamarine zircon and fluorite can be found in the region the gem minerals are shown to have been produced either by direct deposition along fissures veins and greisens by hydrothermal fluids or as a result of hydrothermal fluids reacting with wall rocks these wall rocks are either biotite granites from which the hydrothermal fluids originated or basement rocks or any other rocks which the biotite granites intrude and their residual hydrothermal fluids have invaded the hydrothermal fluids appear to have been rich in alkalis na k etc rare elements be zr f ree etc and siliceous as these fluids rose through fractures and channel ways through the rocks they either deposited the gem minerals in the fractures at the appropriate stability conditions or reacted with the wall rocks producing the gem minerals at the expense of elements like ca and a1 in the minerals of these rocks

application of a three dimensional turbulence energy model to the determination of tidal currents on the northwest european shelf a three dimensional turbulence energy tidal model employing a sigma coordinate system through the vertical with a logarithmic type transformation to enhance near bed resolution is used to examine m2 tidal currents on the european continental shelf a no slip bottom boundary condition is applied in the model and vertical eddy viscosity is computed from a turbulence energy closure scheme comparisons of observed and computed current profiles determined using the present model and an earlier model employing a spectral representation davies 1986 in the vertical and a slip bottom boundary condition are made in this spectral model a simple relationship between eddy viscosity and depth mean current was employed these comparisons of current profile suggest that above the near bed layer the spectral model can reproduce tidal currents with a comparable accuracy to that of the present turbulence energy model however in the near bed region the turbulence energy model is significantly more accurate computed spatial distributions of current magnitude turbulence energy intensity and eddy viscosity show similar distributions over the model region suggesting that a relationship between eddy viscosity and current intensity the form used in the spectral model is a valid alternative to using a turbulence energy model turbulence energy intensity in particular exhibits significant spatial variations both horizontally and vertically with surface contours of turbulence corresponding to known positions of tidal fronts

non pegmatitic deposits of beryllium mineralogy geology phase equilibria and origin non pegmatitic occurrences of be minerals constitute a diverse set of geologic environments of considerable mineralogical and petrological interest they currently provide the majority of the world s be ore and emeralds and they contain the greatest resource of these commodities of the approximately 100 be minerals known see chapter 1 by grew appendix a most occur in hydrothermal deposits or non pegmatitic igneous rocks where their distribution varies systematically with the setting and origin table 1 fig 1 view this table table 1 beryllium minerals in non pegmatitic deposits formulas use and occurrence 1 figure 1 chemography of the principal solid phases in the beo al2o3 sio2 h2o f2o 1 bash system with the projected positions of helvite group and alkali be silicates also shown are generalized fields for some of the major types natural of occurrences cf table 1 fig 4 see text for discussion beryllium minerals are best known from geologic systems associated with felsic magmatism they also occur in a variety of settings that lack evident igneous associations environments range from the surface to the deep crust and host rocks range from feldspathic to carbonate to ultramafic in composition genetically related igneous rocks are felsic and share low calcium and high f contents but are diverse in composition setting and origin compositions range from strongly peraluminous to peralkaline and can be silica undersaturated beryllium minerals also occur in metamorphic and basinal environments and are redistributed by surface processes table 2 summarizes the types and significance of major groups of occurrences by their lithologic associations figure 2 shows the global distribution of some important examples and regional belts for most types at least one example has been described in some detail and can be used to help evaluate general patterns however

topex poseidon the 2 cm solution the unprecedented accuracy of topex poseidon t p altimeter data warrants a new evaluation of the methods typically used to form time series of sea level change whereas explicit removal of orbit error has always been required as a first step in altimeter data processing the t p analysis presented here is based simply on unadjusted monthly averages this approach has the advantage of retaining the large scale ocean signal which would be distorted by orbit adjustment using 16 months of data we have evaluated the t p monthly means on spatial scales ranging from mesoscale to global in the tropical pacific comparisons with 17 island tide gauge records and dynamic height derived from 36 thermistor moorings show that the altimeter data have an accuracy of approximately 2 cm when averaged over spatial scales of a few hundred kilometers on basin scales in the northern hemisphere similar agreement is found between the t p data and the dynamic height climatology of levitus 1982 these new altimeter observations are thus providing the first reliable view of global sea level changes on seasonal to interannual timescales

the influence of mixing length formulation and stratification upon tidal currents in shallow seas abstract the mathematical formulation of a three dimensional shallow sea hydro dynamic model using a slip condition at the sea bed with sigma coordinates in the vertical and a range of turbulence energy closure schemes is briefly presented in this paper the equations are solved using finite difference methods in both the horizontal and the vertical and a time splitting approach is used to reduce the computational time the influence of changes in bed friction coefficient and formulation of the turbulence energy scheme upon tidal elevations currents and mixing intensities in a homogeneous sea is examined in detail comparisons are made with observations and with previous published current profiles in the irish sea using models of identical resolution and similar closure schemes but a no slip condition at the sea bed also comparisons are made with models using simple closure schemes in terms of a flow dependent eddy viscosity and a spectral approach in the vertical the influence of an imposed and maintained idealized vertical stratification upon tidal elevations current profiles turbulence profiles and mixing lengths is also considered the resulting changes in vertical structure of tidal current profiles both in terms of amplitude and phase are explained using previously published results from an idealized point model

variability of the mixed layer heat budget in the eastern equatorial atlantic during 2005 2007 as inferred using argo floats we examine the variability of the sea surface temperatures in the eastern equatorial atlantic during 2005 2007 by using argo profiling floats prediction and research moored array in the atlantic buoys and satellite in situ and atmospheric data sets the eastern equatorial atlantic characterized by shallow mixed layers all yearlong is divided into nine boxes of nearly equal surface area with respect to the dynamics and thermodynamics in this region monthly mixed layer heat budgets are computed in each box from 10 day argo profiles in all the boxes the net surface heat flux is one of the main causes of the seasonal evolution of sea surface temperatures for the 3 studied years the amount of short wave radiation penetrating through the base of the mixed layer and horizontal heat advection may locally contribute to the temperature variability while entrainment has a weaker contribution to balance the heat budget a residual term exists which includes all processes that cannot be calculated with observations as well as the possible errors in the other terms this residual is more intense in the cold tongue and the northern region and exhibits a clear seasonal cycle with minimum negative values in boreal summer and maximum values in winter this residual compares well with available observations of vertical turbulent mixing collected during etude de la circulation oceanique et des echanges ocean atmosphere dans le golfe de guinee campaigns 2005 2007 in the eastern equatorial atlantic when assuming that the residual is mostly associated with vertical turbulent mixing it can be conjectured that turbulent mixing is a significant cooling source in the cold tongue and north of the equator

effects of density front on the generation and propagation of internal tides abstract a numerical model is developed to study the internal tidal motion on the continental margin the system includes irregular bottom topography and a horizontal density stratification maintained by a mean geostrophic current both the propagation and generation processes are examined in the propagation process the topographic effect alone will scatter a significant part of the incident wave energy into higher modes resulting in a beamlike structure for the transmitted wave for a density front over a flat bottom energy in the transmitted waves remains largely in the original wave mode though the wavelength and hence wave amplitude varies with local density stratification when the density front is located over a sloping bottom the topographic effect is reduced whereas the frontal effect is not affected thus scattering into higher modes becomes more restricted in the generation process internal tides are produced in the upper and lower parts of the slope region due to the interaction bet

tropical instability vortices in the atlantic ocean 1 this paper examines the physical characteristics and dynamics of atlantic tropical instability vortices based on observational data from 1997 to 2000 and a high resolution numerical model simulation most prominent during boreal summer the vortices are characterized by 400 km spatial scales westward translation at 0 40 cm s 1 anticyclonic circumferential velocities of 30 110 cm s 1 and sstanomalies that decrease from 2 ci n midbasin to 0 5 c or less near the western boundary in contrast the sea level anomalies grow as the vortices progress westward reaching maximum amplitudes of 14 cm near 40 w the large circumferential velocities leading to relative vorticities of 4 10 6 s 1 and rossby numbers of 0 5 indicate that centrifugal effects may play an important role in the vortices vorticity balance we address the vortices vertical structure and vorticity dynamics by examination of a high resolution numerical model there is a reasonably good agreement between the model and observations simulated vortices are confined mostly to the mixed layer which increases westward in depth from 30 to 100 m near the western boundary in the eastern basin potential vorticity within the vortices is not conserved but decreases because of wind stress forcing in contrast in the western basin decreases in potential vorticity are due mostly to the vortices acquisition of southern hemisphere water we estimate an annualized cross equatorial transport of up to 1 2 sv associated with the vortices which is eventually contributed to the north brazil current system index terms 4231 oceanography general equatorial oceanography 4520 oceanography physical eddies and mesoscale processes 4528 oceanography physical fronts and jets keywords tropics instability atlantic

water masses and currents in the upper tropical northeast atlantic off northwest africa recent current measurements in the tropical eastern north atlantic reproduce the components of the large scale flow field however the observations as well as the 1 12 flame model computations indicate that a lot of eddy scale variability is superimposed on the mean flow field despite of the disturbance by variability the signature of the guinea dome is well present in november 2002 the guinea dome transport from direct observations was about 2 8 sv above 25 8 kg m3 and 4 sv between 25 8 and 27 1 kg m3 the oxygen minimum in the shadow zone comprises the central water and the antarctic intermediate water aaiw layers and is located between the equatorial current system and the north equatorial current the north equatorial counter and undercurrents at 3 to 6 n are major oxygen sources for the central water layer of the low oxygen regions in the northeastern tropical atlantic a second northern north equatorial countercurrent nnecc band exists at 8 to 10 n the nnecc carries oxygen rich water from the southern hemisphere eastward but with an admixture of water from the northern hemisphere a float at 200 m depth was spreading eastward in the north equatorial undercurrent neuc at 28 w it shifted northward into the nnecc and then was trapped in the guinea dome region for more than 3 years the model indicates the region 22 to 32 w as the area of exchange between the necc neuc and the nnecc bands in the aaiw layer the northern intermediate countercurrent acts as oxygen source for the oxygen minimum zone

velocity and hydrographic structure of two gulf of mexico warm core rings results from an extensive survey of two gulf of mexico warm core rings are presented the data were taken during a 1 week period in december 1983 using a shipboard acoustic doppler current profiler adcp expendable current probes xcp expendable bathythermographs xbt and a ctd two rings were observed an older one in the western gulf adjacent to the west texas shelf and one just separated from the loop current the western ring was of order 200 km in diameter with peak currents of 1 m s 1 at the 100 m level water properties were uniform and characteristic of the high salinity caribbean subtropical underwater the eastern ring was of order 300 km in diameter with peak currents of near 2 m s 1 at the 100 m level water below 200 m is of caribbean origin while the surface waters show more variability suggesting some inflow of gulf of mexico common water the evolution of the rings is also described based on the cruise measurements satellite avhrr and other observations of opportunity

cross equatorial structure and temporal modulation of intraseasonal variability at the surface of the tropical atlantic ocean intraseasonal variability 10 50 days in the equatorial atlantic ocean is analyzed from multiyear 1999 2005 satellite gridded products of sea level anomalies sla and sea surface temperature sst two regions with distinct intraseasonal variability have been identified the first one west of 10 degrees w is dominated by westward propagating anomalies with maximum values in sla along 5 degrees n and in sst along 2 degrees n they occur in boreal summer with periods of 25 50 days and are known to correspond to tropical instability waves tiws we show that tiws have also a signature though weaker south of the equator especially along 5 degrees s in sla northern and southern anomalies propagate together westward being mostly out of phase suggesting that equatorial wave dynamics is involved in tiws variability an sst signature of tiws is also observed near 2 degrees s in quadrature with sst anomalies detected in the northern hemisphere the interannual modulations of the tiw signature in sla and sst are compared and discussed the second dominant intraseasonal signal is only seen east of 10 degrees w in sst and corresponds to an equatorially trapped variability confined to the gulf of guinea with periods between 10 and 20 days this signal is present in boreal summer when an intense sst front is observed just north of the equator intraseasonal variability with comparable periods is also observed in the meridional wind stress throughout the year comparison of sst and meridional wind stress anomalies suggests that the 10 to 20 day variability in sst is forced by the wind stress but seasonally modulated by the presence of the sst front

the internal tide of the gareloch a scottish fjord abstract previous observations in the gareloch a scottish silled fjord have identified yet failed to explain the baroclinic circulation pattern additional fieldwork was carried out in april 2005 showing the loch to be stratified with two distinct layers and currents in each layer 180 out of phase at the m2 frequency the currents did not display the expected sinusoidal signal that is characteristic of the tide and instead were pulsated and stronger than predicted by barotropic forcing fourier analysis showed that the flow was dominated by short period non linear oscillations that were harmonics of the semi diurnal tide two hydrostatic estuarine models were applied to the gareloch a 2d vertical model slice and a 3d model ecomsed both models were capable of reproducing the observed 2005 baroclinic circulation at the m2 time scale but failed to simulate the higher frequency non linear oscillations however each model generated higher harmonics in idealised scenarios because lateral motion was negligible and slice was an order of magnitude more efficient than ecomsed the 2d model was used to simulate the higher harmonics and showed that their generation was attributed to the non linear distortion of the internal tide when the internal froude number determined by barotropic velocity stratification and water depth was increased from a sub critical value non linear advection became more important and higher harmonics were generated the internal tide was further modified by wave reflection and interaction off steep boundaries and by flow over the sill

variability of the atlantic off equatorial eastward currents during 1993 2010 using a synthetic method 1 we have developed validated and applied a synthetic method to monitor the off equatorial eastward currents in the central tropical atlantic this method combines high density expendable bathythermograph xbt temperature data along the ax08 transect with altimetric sea level anomalies slas to estimate dynamic height fields from which the mean properties of the north equatorial countercurrent necc the north equatorial undercurrent neuc and the south equatorial undercurrent seuc and their variability can be estimated on seasonal to interannual timescales on seasonal to interannual timescales the synthetic method is well suited for reconstructions of the necc variability reproduces the variability of the neuc with considerable skill and less efficiently describes variations of the seuc which is located in a region of low sla variability a positive correlation is found between interannual variations of the necc transport and two indices based on an interhemispheric sea surface temperature sst gradient and southeasterly wind stress in the central tropical atlantic the neuc is correlated on interannual timescales with ssts and meridional wind stress in the gulf of guinea and zonal equatorial wind stress this study shows that both altimetry and xbt data can be effectively combined for near real time inference of the dynamic and thermodynamic properties of the tropical atlantic current system

internal tide generation by seamounts ridges and islands a numerical investigation is made into the generation of semidiurnal internal tides by tidal flow over steep topographic features in the deep ocean a fully three dimensional free surface nonlinear hydrostatic model the princeton ocean model is used with real stratification representative tidal forcing and gaussian shaped seamounts ridges and islands for the topography the efficiencies of the different topographies in extracting energy from the barotropic tide and in generating an internal tide are considered each topography produces an internal tide characterized by signals propagating away from the feature as beams that follow internal wave characteristic paths the strength of the signals however varies markedly for different topographies this is largely attributed to the way in which the barotropic tide interacts with the three dimensional topography internal wave generation requires a significant vertical displacement of stratified water by the barotropic tide as it flows over topography it is found that for symmetric seamounts and islands the barotropic flow tends to go around the feature producing only a weak internal tide when elongated into a ridge barotropic flow is forced across isobaths generating an energetic internal tide changing the horizontal aspect ratio of the topography from 1 1 a seamount to 3 1 a ridge increases the resulting baroclinic energy flux by nearly an order of magnitude the slope of the topography relative to that of the internal wave characteristics is also shown to be important with strongest generation occurring at regions of critical or supercritical topographic slope

eddies in the tropical atlantic ocean and their seasonal variability we study mesoscale eddy characteristics in the tropical atlantic ocean using 23 yearsof daily altimetry sea level anomalies eddies are mainly generated in the eastern boundary up wellings and in the brazil current region they have westward propagating speed reaching 20 cms 1 in equatorial area decreasing with latitudes they present typical amplitudes of around 1 5 cm the largest and most energetic eddies are observed in the equatorial region in particular in theretroflection of the north brazil current nbc the seasonal cycle of the main eddy characteristicsshows a marked seasonal cycle along the nbc retroflection and along the western part of the northequatorial countercurrent necc we propose a criterion using altimetry to analyse the mecha nism responsible for eddy generation in the necc we argue that eddy generation is mainly due tobarotropic instability of mean surface currents whereas other mechanisms must be invoked for thenbc

three agulhas rings observed during the benguela current experiment a field program to study the circulation of the benguela current and its extension into the southeastern atlantic ocean has completed the survey and instrument deployment phase we report here new observations of three agulhas rings north and west of cape town south africa three mesoscale anticyclonic rings initially identified by means of topex poseidon altimetry were surveyed with expendable bathythermographs conductivity temperature depth oxygen profiles direct current measurements from a lowered acoustic doppler current profiler a hull mounted acoustic doppler current profiler and satellite tracked surface drifters characteristics of the rings are presented and their origins are discussed two are typical agulhas rings surveyed at different times after their generation the third agulhas ring has an anomalous water mass structure whose most likely origin is the subtropical front

atmospheric events disrupting coastal upwelling in the southwestern caribbean 1 year round coastal upwelling is a prevalent phenomenon in the southwestern caribbean region driven by northeast trade winds this pattern can be disrupted during the boreal winter to spring transition by event scale departures in the pressure systems characterized by a change in wind direction to northward with the accompanying relaxation of coastal upwelling to study these poorly understood events regional atmospheric and data assimilative ocean modeling experiments were carried out for the period 4 march to 9 april 2003 and compared to shipboard observations this combined ocean atmosphere approach allowed us to study the evolution of a 3 day atmospheric disturbance affecting ocean currents and collapsing the upwelling pattern against the colombian coast along the guajira peninsula near 12 n the southward extension of the coastal upwelling which normally reaches 10 5 n was blocked by the warmer and slightly lower salinity waters of the cyclonic panama colombia gyre under typical conditions the ocean model and shipboard observations of temperature and salinity profiles were in good agreement with each other both at coastal and oceanic stations the presence of a low level westward wind jet was manifested in the atmospheric model simulation confirming that it promotes the guajira upwelling system however the jet vanishes under disturbed atmospheric conditions

a detailed comparison of a range of three dimensional models of the m2 tide in the faeroe shetland channel and northern north sea abstract a three dimensional hydrodynamic model of the faeroe shetland channel and northern north sea is used to investigate the spatial variability of m2 tidal elevations and currents in the region this area is chosen because it covers a range of water depths also there is a significant database of tidal elevations namely 41 gauges and current meters namely 89 observations with which comparisons can be made with the exception of a couple of measurements made at the shelf edge which may be influenced by the internal tide namely a 180 phase shift across the thermocline due to a first mode internal tide the observations correspond to those of a barotropic tide two different approaches are used to represent the profile of tidal currents in the vertical in the first a spectral functional method is used while in the second a finite difference grid is applied a range of parameterizations of vertical eddy viscosity suitable for deep water regions are used from ones in which viscosity is relate

on the interaction between internal tides and wind induced near inertial currents at the shelf edge 1 numerical calculations are performed at the shelf edge to examine the role of nonlinear processes in transferring energy from the m2 tide and wind induced currents close to the inertial frequency f into a wave at the sum of their frequencies termed the fm2 frequency a numerical model of the hebrides shelf edge represented by a cross section initially with idealized topography and subsequently with realistic topography is used in these calculations results show that in the near coastal ocean currents at the fm2 frequency are primarily due to coupling between wind induced inertial oscillations and the m2 internal tide a major source is associated with vertical shear in the inertial oscillations and the vertical velocity due to the internal tide a secondary source is due to the nonlinear momentum advection term in the case in which eddy viscosity is computed from a turbulence energy model shear across the thermocline is larger than when a constant viscosity is used the reduction in shear with a constant viscosity reduces the role of the nonlinear term involving vertical shear and hence the magnitude of the fm2 current in the region of the thermocline increasing the wind stress leads to a deeper thermocline and hence the location of maximum fm2 current in the water column changing the vertical stratification influences the intensity of the inertial oscillations in the surface layer and the distribution of the internal tide and hence changes the pattern of fm2 currents results with realistic topography confirm the major conclusions

subtidal energetics in the faroe shetland channel coarse grid model experiments this paper compares various forcings that contribute to the regional subtidal energetics of the ocean passageway northwest of scotland in the faroe shetland channel fsc where inflow of warm and saline north atlantic water mixes with outflow of cold and less saline nordic sea waters on the scales resolvable by the coarse grid sizes of x y 20 km and 20 vertical sigma layers changes in currents energetics caused by wind atlantic inflow doubled decreased horizontal mixing surface heat flux and open boundary density specifications were 28 43 40 16 and 5 respectively of the kinetic energy of a background quasi steady slope current the subtidal currents were not sensitive to the atmospheric pressure forcing and the surface relaxation to monthly climatology nor to the inclusion of additional apart from m2 tidal constituents k1 o1 and s2 wind induced motions resulted in transport fluctuations of about 1 5 sv in the fsc maximum in winter and minimum in summer and alongshore and cross shore current variances of 0 1 and 0 05 m s 1 respectively in fair agreement with observations spectral peaks at periods of 23 30 hours were found and were shown to correspond to resonant continental shelf waves in the channel

volcanic hosted rare metals deposit at brockman western australia rare metals mineralization at brockman western australia is the product of early pyroclastic eruption of trachytic magma enriched in volatiles and incompatible elements such as zr hf nb ta be y and ree and ga the mineralization is fine grained 20 m and is the result of alteration and re mobilization of comparatively simple magmatic precursor minerals such as columbite and zircon by f rich deuteric solutions that were retained in an ash flow tuff the niobium tuff following eruption chondrite normalized ree distributions show strong enrichment in hree gel zircon is the principal residence of the hree disseminated bastnaesite parisite and synchisite carries the lree and bertrandite in late stage calcite veins is the host for be ga occurs in k mica in the groundmass trachytic flows overlying the niobium tuff contain many of the same ore minerals but in trace amounts

stability of genthelvite zn4 besio4 3s an exercise in chalcophilicity using exchange operators phase relations involving genthelvite are studied on the basis of physical chemical principles and natural occurrences stability diagrams and exchange operators are considered as well as an extended system natural associations and solid state relations it is noted that the extremely high chalcophilicity of zn explains in part why genthelvite is such as rare mineral it is only somewhat more stable than willemite and is therefore restricted to the extremely low s environments provided by alkaline granites and syenites