a subtropical oceanic ring of magnitude storm in the eastern north atlantic physical chemical and biological properties a subtropical oceanic ring of magnitude storm that budded from the azores current was studied in the eastern north atlantic ocean in april 1999 the cyclonic eddy called leticia was centred at 32 4 n 28 7 w and extended across more than 200 km in an east west direction leticia had been previously detected by means of topex poseidon altimetry data and further intensively investigated using expendable bathythermograph and conductivity temperature depth stations the altimeter surface signature of the eddy revealed a 20 cm sea level depression an upward displacement of the 16 c isotherm of 125 m was linked to the eddy centre and geostrophic transport of the amount of water swirling cyclonically was 7 sv the temperature nitrate and oxygen anomalies on the 0 26 5 isopycnal surface inside leticia were 0 4 c 1 mol l 1 and 0 3 ml l 1 respectively with respect to surrounding waters shallowing 50 m of the deep chlorophyll maximum 0 3 mg m 3 was observed at the eddy centre associated with vertical displacements of the isotherms 100 m within the photic layer vertical excursions of the isopycnals and the deep chlorophyll maximum of more than 30 m were observed over temporal scales of a few 3 6 h integrated nitrate concentration over the photic layer was 4 fold higher inside leticia than outside however primary production rates were only slightly higher eddy diffusive fluxes across the nitracline located 30 m below the deep chlorophyll maximum ranged from 0 02 to 0 10 mmol no3 m 2 d 1 and explained 25 of the nitrate required to sustain the estimated new production 0 24 0 48 mmol no3 m 2 d 1

generation and propagation of near inertial waves in a baroclinic current on the tasmanian shelf abstractnear inertial waves niws are often an energetic component of the internal wave field on windy continental shelves the effect of baroclinic geostrophic currents which introduce both rela

plate generation in a simple model of lithosphere mantle flow with dynamic self lubrication one of the more enigmatic features of the earth s style of mantle convection is plate tectonics itself in particular the existence of strike slip or toroidal motion toroidal motion is uncharacteristic of basic thermal convection but necessarily forms through the interaction of convective flow and nonlinear rheological mechanisms recent studies have implied that the empirically determined power law rheologies of mantle silicates are not sufficient to generate the requisite toroidal motion a simple source sink model of mantle or lithospheric flow shows that dynamic self lubrication which arises through the coupling of viscous heating and temperature dependent viscosity is highly successful at generating strike slip motion in particular as the viscosity of the fluid system becomes more temperature dependent the toroidal flow field makes an abrupt transition from a state of weak unplate like motion to a state with intense and extremely focused structure in essence the fluid dynamical model develops strike slip faults

breaking of internal waves and turbulent dissipation in an anticyclonic mode water eddy abstracta four month glider mission was analyzed to assess turbulent dissipation in an anticyclonic eddy at the western boundary of the subtropical north atlantic the eddy radius 60 km had a c

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

seasonal heat and freshwater budgets of the upper ocean in the north east atlantic heat and freshwater content changes were calculated from two repeated sections at 48 n 18 w and 48 n 26 w surveyed during the vivaldi cruise of the research ship rrs charles darwin in may 1991 best estimates of the air sea heat fluxes agreed within error with the observed heat content changes suggesting that diabatic forcing dominated the heat budget this was confirmed by a numerical model which showed that ekman and geostrophic advection and eddy diffusion together contributed less than 20 w m 2 to the heat budget however the model also showed that near the oceanic polar front under westerly winds ekman advection of cold fresh water southwards over the front can cause 40 w m 2 and 4 mm d 1 heat and freshwater content changes in the upper 53 m compared to air sea fluxes of typically 67 w m 2 and less than 1 mm d 1 the ekman advection contributed little to the model s density budget as the advective cooling and freshening had opposing effects however an air sea interaction model showed that the advective surface cooling may be reduced because it triggers an extra air sea heat flux and the remaining advective freshening then makes an important contribution to the density budget

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

forced ocean response during the frontal air sea interaction experiment a central hypothesis of the frontal air sea interaction experiment fasinex was that the strong gradients in the upper ocean associated with ocean fronts would spatially modulate the response of the ocean to local atmospheric forcing to test this hypothesis measurements of near surface meteorology and upper ocean variability were made for 5 months from an array of moorings and for one of those 5 months from two ships a number of fronts passed through the moored array and the moored meteorological and current meter data were used to examine the response of the upper ocean to atmospheric forcing at subinertial and near inertial frequencies at low frequencies an ekmanlike frictionally driven component in the mixed layer and a more deeply penetrating component thought to be forced by ekman pumping were found strong near inertial response was found in the mixed layer the near inertial motion showed considerable spatial variability in the seasonal thermocline here it was evident that the structure of the front influenced the downward propagating near inertial internal waves data were also obtained by profiling instruments deployed along cross frontal sections these data were used to examine the spatial and temporal variability of the internal waves microstructure and dissipation and the relation of that variability to oceanic fronts and atmospheric events the spectral densities of the components of the internal waves that rotated clockwise with increasing depth were higher in regions of negative relative vorticity than those predicted by garrett and munk munk 1981 and estimates of clockwise and total shear were highest in regions of negative relative vorticity in the strong shear of the ocean front significant anisotropy of the internal wave field was observed and kinetic energy dissipation levels relative to the rate of work by the wind were higher than previously reported

compressible convection with constant and variable viscosity the effect on slab formation geoid and topography two dimensional cartesian finite difference models of compressible convection with constant and variable viscosity and fixed bottom temperature are presented density variations according to the adams williamson equation of state are included in the case of constant viscosity convection viscous and adiabatic heating damp the flow compressible density variations hardly influence geoid undulations however the lower thermal boundary layer becomes thinner and the mean cell temperature increases in the case of variable viscosity the nonlinear coupling between compression adiabatic and viscous heating and a temperature pressure and stress dependent rheology leads to important consequences the upwelling flow broadens and plumes are retarded the flow strongly concentrates toward the downwelling region and becomes mechanically decoupled from the interior of the cell by a low viscosity region this mechanism seems to be important for the formation of subducting slabs extrapolated to mantle conditions two low viscosity regions are predicted flanking the slab on either side and inhibiting an early dispersal and mixing of slab material into the mantle this process might be aided by an increase of negative buoyancy forces with depth as observed in the models further results are as follows increasing the dissipation number in variable viscosity convection may either damp or speed up convection depending on the rheology models with internal heating and a fixed bottom temperature show that the threshold to time dependent variable viscosity convection is drastically reduced if the anelastic liquid approximation is applied instead of the extended boussinesq approximation

the effect of a bottom shelf front upon the generation and propagation of near inertial internal waves in the coastal ocean abstract a three dimensional nonlinear baroclinic model in cross sectional form is used to study the generation and propagation of wind forced near inertial internal waves in a coastal region in the presence of a bottom front initially calculations are performed with the front in an infinite domain region by this means coastal effects are removed the initial response is in terms of inertial oscillations in the surface layer however in the frontal area these are modified by interaction through the nonlinear momentum terms with regions of positive and negative vorticity associated with the alongfront flow this leads to a change in amplitude phase and frequency of the inertial current and a resulting ekman pumping that drives near inertial internal waves in the frontal region on the positive vorticity side of the front these waves are at the superinertial frequency and rapidly propagate away on the negative side they are at the subinertial frequency and are trapped and inertial energy leaks to dep

the relation of near inertial motions observed in the mixed layer during the jasin 1978 experiment to the local wind stress and to the quasi geostrophic flow field abstract oscillations with near inertial frequencies were an energetic component of the upper ocean velocity field observed at each of two moorings separated by 44 km during the joint air sea interaction jasin experiment during the late summer of 1978 at each mooring the amplitude of the inertial motion was highest in the mixed layer where it was nearly depth independent previous work pollard and millard 1970 pollard 1980 had found that the amplitude and phase of inertial motion in the mixed layer was related to the local wind stress in this case the loacal winds measured at each mooring were coherent but the time series of mixed layer near inertial motion at one mooring bore little resemblance to that at the other mooring during jasin 1978 the differences in the inertial response at the two moorings coincided with differences in the quasi geostrophic flow field in the vicinity of the two moorings inclusion of the horizontal gradients of the quasi geostrophic flow in model equations prov

a fine resolution numerical model of the iceland farœ front with open boundary conditions an eddy resolving limited area primitive equation model of the iceland far frontal region is developed the spatial and temporal evolution of the front is examined on time scales of up to 2 months experiments are performed changing the open boundary conditions at the lateral boundaries using passive and active open boundary conditions the experiment with the passive open boundary conditions reproduces many observed features of the iceland far frontal region discrepancies between these results and observations in the area are noted in particular the western end of the front drifts too far north the model is then forced at the lateral boundaries using two contrasting barotropic velocity fields improvements in the results are noted comparison of the results illustrate to what extent and how far field currents can affect the dynamics of this frontal region the east icelandic current is found to have the following important effect on the front maintaining its vertical structure and confining the western end of the front to more southerly latitudes

interaction of superinertial waves with submesoscale cyclonic filaments in the north wall of the gulf stream abstracthigh resolution nearly lagrangian observations of velocity and density made in the north wall of the gulf stream reveal banded shear structures characteristic of near inertial waves niws here the current follows submesoscale dynamics with rossby and richardson numbers near one and the vertical vorticity is positive this allows for a unique analysis of the interaction of niws with a submesoscale current dominated by cyclonic as opposed to anticyclonic vorticity rotary spectra reveal that the vertical shear vector rotates primarily clockwise with depth and with time at frequencies near and above the local coriolis frequency f at some depths more than half of the measured shear variance is explained by clockwise rotary motions with frequencies between f and 1 7f the dominant superinertial frequencies are consistent with those inferred from a dispersion relation for niws in submesoscale currents that depends on the observed aspect ratio of the wave shear as well as the vertical vorticity

intense local toroidal motion generated by variable viscosity compressible convection in 3 d spherical shell strong dynamical effects arising from lateral viscosity variations are found near the heads of fast upwelling plumes approaching the top boundary for unsteady 3 d compressible convection in a spherical geometry at an average rayleigh number of o 106 the temperatures at the center of fast upwelling plume are very hot due to the positive feedback interaction between viscous dissipation and temperature dependence of the viscosity although the laterally averaged ratio of toroidal to poloidal energy varies only around 10 the local toroidal velocities can reach about 40 of the poloidal velocities the strongest toroidal motions always take place right above or close to the fast upwelling plume heads and behave as vortical flows with time this finding may explain the origins of microplate rotation in regions with hotspot activity e g easter island which shows no direct relation to the transform faulting system near the mid ocean ridge

wind induced motion in the vicinity of a bottom density front response to forcing frequency 1 a numerical model is used to examine the influence of nonlinear processes in the vicinity of a shallow sea bottom density front upon the depth of penetration of the wind s momentum at both superinertial and subinertial frequencies calculations show that nonlinear effects associated with differences in vorticity across the frontal jet significantly influence the depth of penetration of the wind s momentum and internal wave propagation differences in wind induced current amplitude and phase at depth due to nonlinear effects give rise to substantial vertical velocity in the frontal region which drives near bed currents and forces internal waves at superinertial frequencies internal waves propagate away from the positive vorticity side of the front however at depth internal waves are generated and current amplitude increases in the region of sloping density surfaces associated with the front on the negative vorticity side due to an effective inertial frequency below inertial the wind s energy can propagate deeper into the water column wind forcing at subinertial frequencies does not lead to internal wave propagation on the positive vorticity side of the front the wind s momentum cannot diffuse to depth due to turbulence suppression by stable stratification the ability of the wind s momentum to penetrate to a greater depth in a frontal region through nonlinear effects suggests that these may be important processes influencing wind mixing in frontal regions

space time scales of shear in the north pacific abstractthe spatial temporal and directional characteristics of shear are examined in the upper 1400 m of the north pacific during late spring with an array of five profiling moorings deployed from 25 to 37 n 1330 km and simultaneous shipboard transects past them the array extended from a regime of moderate wind generation at the north to south of the critical latitude 28 8 n where parametric subharmonic instability psi can transfer energy from semidiurnal tides to near inertial motions analyses are done in an isopycnal following frame to minimize contamination by doppler shifting approximately 60 of rms shear at vertical scales 20m and 80 for vertical scales 80 m is contained in near inertial motions an inertial back rotation technique is used to index shipboard observations to a common time and to compute integral time scales of the shear layers persistence times are o 7 days at most moorings but o 25 days at the critical latitude simultaneous shipboard transects show that these sh

observation of tropical cyclone induced shallow water currents in taiwan strait the data from three stations equipped with acoustic doppler current profilers adcps deployed in the shallow water of the taiwan strait tws were used to study the shallow coastal ocean response to five quasi continuous tropical cyclone tc events in the late summer 2006 we revealed that in the forced stage when the large and strong tc bilis transited the geostrophic currents were formed which dominated the whole event while the strong but relatively small one saomai or the weak one bopha primarily leaded to the generation of ekman currents in the relaxation stage the barotropic subinertial waves and or the baroclinic near inertial oscillations nios were triggered typically during the transit of the saomai subinertial waves were induced which demonstrated a period of 2 8 4 1 days and a mean alongshore phase velocity of 14 9 3 2 m s in the form of free barotropic continental shelf waves however the nios are only notable in the area in which the water column is stably stratified and also where the wind stress is dominated by the clockwise component and accompanied by high frequency near inertial variations we also demonstrated that due to the damping effects the nonlinear wave wave interaction e g between nio and semidiurnal tide in our case together with the well known bottom friction led to the rapid decay of the observed tc induced near inertial currents giving a typical e folding time scale of 1 3 inertial periods moreover such nonlinear wave wave interaction was even found to play a major role during the spring tide in tws

melting instabilities in the transition zone abstract melting in the transition zone could result from the rapid passage of hot upwelling through the perovskite spinel phase transition a large temperature increase could be produced above the perovskite to spinel transition by both viscous heating and a nonlinear positive feedback between temperature dependent viscosity and latent heat release the rise times for these instabilities have been estimated to be about 10 ma these instabilities were triggered by the episodic downwelling instabilities which preceded the flush events of cold material in layered mantle convection with phase transitions these results would suggest that melting in the transition zone would have had a greater tendency to occur in the past and might have caused the generation of komatiites in the archean

the velocity structure of the upper ocean in the presence of surface forcing and mesoscale oceanic eddies one goal of the joint air sea interaction experiment jasin was to investigate the structure of the near surface velocity field and to attempt to quantify what fraction of that field was related to the local wind toward that end in the late summer of 1978 two moorings were deployed in the northern rockall trough with oceanographic instrumentation concentrated in the upper 100m of the ocean simultaneous observations were made of the surface winds at each mooring and adjacent to one of the moorings of the velocity field at depths from 79 to 1000m energetic eddy like circulation dominated the velocity field in the jasin area at depths shallower than approximately 800m however both the velocity and the vertical shear of horizontal velocity showed variability that increased with proximity to the surface empirical orthogonal functions computed to separate the velocity data into uncorrelated modes of variability showed that over 97 of the variability in the upper 300m was distributed among only three vertical modes the first function had little depth dependence the second had strong depth independent flow in the depth range of the mixed layer and weak flow in the opposite direction at all depths below and the third had strong flow near the surface strong flow in the opposite direction just below the base of the mixed layer and weaker flow at all other depths function 1 alone provided a near complete description of the velocity variability below 85m where the flows associated with the eddy like circulation and the barotropic semidiurnal tide were the dominant components at 85m and above all three functions were necessary to provide a complete description temporal variability of function 2 was coherent with the local wind stress at the inertial frequency but at lower frequencies resulted in transport in the mixed layer to the southeast that was not coherent with the local wind low frequency temporal variability of function 3 was coherent with the local wind stress at these frequencies the velocity vector of function 3 nearest the surface was directed to the right of the wind stress vector and the velocity vector just below the base of the mixed layer was directed to the left of the wind stress thus forcing by the local wind can account for some but not all of the increased variability found near the surface

mesoscale 50 100 km circulations revealed by inverse and classical analysis of the jasin hydrographic data abstract inverse analysis wunsch 1978 has been applied to two 10 day surveys of an area 15 km consisting of nearly 100 ctd stations in order to determine the velocity field with a horizontal resolution of 45 km reference levels above the main thermocline 1100 m lead to physically implausible circulations below the thermocline the preferred solution conserves mass with bottom velocities not significantly different from zero all casts were repeated after 6 h and the surveys were 20 days apart allowing errors in the reference velocities due to internal waves tides and changes of mass between surveys to be estimated at less than 1 cm s 1 further spatial resolution is obtainable by classical geostrophic analysis contouring dynamic heights with an assumed bottom level of no motion from casts 15 km apart forming triangles 45 km apart two regions of anticyclonic circulation are revealed one a meander the other an eddy the meander and eddy have different water properties and interact as the eddy

dynamical consequences on fast subducting slabs from a self regulating mechanism due to viscous heating in variable viscosity convection the authors have studied 2 d time dependent convection for a rheology which is both non newtonian and temperature dependent strong effects associated with viscous heating are found in the downwelling sheets which are heated on both sides with an intensity around o 10 sup 2 times the chondritic value the magnitude of viscous heating increases strongly with the subduction speed the slab interior is weakened by viscous heating and slab breakoff then takes place this process provides a self regulating mechanism for governing the speed of intact slabs able to reach the deep mantle timescales associated with viscous heating are quite short a few million years internal heating by radioactivity decreases the amount of shear heating 13 refs 5 figs

layered convection induced by phase transitions we report a systematic study on the conditions under which an endothermic phase transition can enforce layered convection two dimensional numerical calculations of convection in a domain containing a divariant phase change were performed in the framework of the extended boussinesq approximation i e considering the effects of adiabatic gradient latent heat and frictional heating in the energy equation we find that the critical value of the negative clapeyron slope which must be surpassed in order to induce layered convection decreases in magnitude with increasing rayleigh number ra in the range 104 ra 2 106 near the critical clapeyron slope vacillations between double and single layer convection or strongly leaking double layer convection are possible the breakdown into layers is influenced very little by the latent heat release but depends solely on the phase boundary deflection caused by lateral temperature differences the value of the critical clapeyron slope also seems little affected by the width of the transition zone or by its depth a possible superplastic rheology within the transition zone would tend to favor layered convection scaling the model results to the 670 km discontinuity in the earth s mantle as a possible endothermic phase boundary we estimate the critical clapeyron slope to be in the range of 4 to 8 mpa k 40 to 80 bar k the possibility that the spinel perovskite periclase transition is within this range appears to be remote but certainly cannot be neglected

the development of slabs in the upper mantle insights from numerical and laboratory experiments we have performed numerical and laboratory experiments to model subduction of oceanic lithosphere in the upper mantle from its beginnings as a gravitational instability to the fully developed slab a two dimensional finite element code is applied to model newtonian creep in the numerical experiments scaled analog media are used in the laboratory a sand mixture models the brittle crust silicone putty simulates creep in the lower crust and mantle lithosphere and glucose syrup is the asthenosphere analog both model approaches show similar results and reproduce first order observations of the subduction process in nature based on density and viscosity heterogeneities in a stokes flow model subduction nucleates slowly and a pronounced slab forms only when the viscosity contrast between oceanic plate and mantle is below a threshold we find that the subduction velocity and angle are time dependent and increase roughly exponentially over tens of millions of years before the slab reaches the 670 km discontinuity the style of subduction is controlled by the prescribed velocity of convergence the density contrast between the plates and the viscosity contrast between the oceanic plate and the mantle these factors can be combined in the buoyancy number f which expresses the ratio between driving slab pull and resisting viscous dissipation in the oceanic plate variations in f control the stress in the plates the speed and the dip of subduction and the rate of trench retreat reproducing the contrasting styles of subduction observed in nature the subduction rate is strongly influenced by the work of bending the lithosphere as it subducts

rapid conversion of elastic energy into plastic shear heating during incipient necking of the lithosphere an important and novel mechanism for ductile failure of the lithosphere is identified here which is intrinsic to the thermal mechanical feedback in a temperature dependent plastic body with coupled elastic fields both a temperature dependent power law visco elasto plastic rheology and a temperature dependent elasto plastic rheology are employed to study in a self consistent fashion the deformation of the lithosphere subject to extension by means of a two dimensional finite element code a structural perturbation initially localizes elasto plastic deformation only in its immediate vicinity however after 800 000 years have elapsed the localized zone of deformation takes off in a crack like fashion and travels to the bottom of the lithosphere in about 50 000 years time when the plate is severed thermal runaway is caused by mechanical heating triggered by the rapid energy transfer of the globally stored elastic energy into localized plastic dissipation in the ductile fault

thermomechanical modeling of pulsation tectonics and consequences on lithospheric dynamics pulsating phenomena can control continental breakup and the formation and closing of oceanic basins using a two dimensional time dependent convection model with a non linear temperature and depth dependent rheology we have obtained self consistently such types of pulsating behavior very hot mantle plumes ascend to the surface where they can quickly thin the lithosphere down to a few kilometers an episode of intense shear heating then ensues which is comparable to the length of the main episode for flood volcanism lasting a couple of myrs the highest plate velocities occur during this period when both the lithosphere and slab are profusely lubricated by the impingement of the hot plume

orographic signature on multiscale statistics of extreme rainfall a storm scale study 1 rainfall intensity and spatiotemporal patterns often show a strong dependence on the underlying terrain the main objective of this work is to study the statistical signature imprinted by orography on the spatial structure of rainfall and its temporal evolution at multiple scales with the aim of developing a consistent theoretical basis for conditional downscaling of precipitation given the topographic information of the underlying terrain the results of an extensive analysis of the high resolution stage ii doppler radar data of the rapidan storm june 1995 over the appalachian mountains is reported in this study the orographic signature on the elementary statistical structure of the precipitation fields is studied via a variable intensity thresholding scheme this signature is further explored at multiple scales via analysis of the dependence of precipitation fields on the underlying terrain both in fourier and wavelet domains the generalized normal distribution is found to be a suitable probability model to explain the variability of the rainfall wavelet coefficients and its dependence on the underlying elevations these results provide a new perspective for more accurate statistical downscaling of orographic precipitation over complex terrain with emphasis on preservation of extremes

a simple and effective method for quantifying spatial anisotropy of time series of precipitation fields the spatial shape of a precipitation event has an important role in determining the catchment s hydrological response to a storm to be able to generate stochastic design storms with a realistic spatial structure the anisotropy of the storm has to be quantified in this paper a method is proposed to estimate the anisotropy of precipitation fields using the concept of linear generalized scale invariance gsi the proposed method is based on identifying the values of gsi parameters that best describe isolines of constant power on the two dimensional power spectrum of the fields the method is evaluated using two sets of simulated fields with known anisotropy and a measured precipitation event with an unknown anisotropy from brisbane australia it is capable of accurately estimating the anisotropy parameters of simulated nonzero fields whereas introducing the rain no rain intermittency alters the power spectra of the fields and slightly reduces the accuracy of the parameter estimates the parameters estimated for the measured event correspond well with the visual observations on the spatial structure of the fields the method requires minimum amount of decision making and user interaction making it suitable for analyzing anisotropy of storm events consisting of long time series of fields with a changing spatial structure

role of spatial anisotropy in design storm generation experiment and interpretation rainfall accumulation depths over a given area are strongly dependent on the shape of the storm together with its direction of advection a method to produce design storms exhibiting anisotropic spatial scaling is presented by combining a state of the art stochastic rainfall generator steps with the linear generalized scale invariance gsi notation the enhanced model is used to create ensembles of design storms based on an extreme storm with a distinct rainband shape observed in melbourne australia design storms are generated both with and without accounting for anisotropy effect of anisotropy on precipitation characteristics is studied using the entire region covered by the radar radar scale and at a significantly smaller catchment scale a rainfall runoff model is applied to route the rainfall through the catchment into streamflow accounting for anisotropy allows for a more realistic description of precipitation features at the radar scale at the catchment scale anisotropy increases the probability of high rainfall accumulations which translates into greater flood volumes no discernible difference was observed in streamflow characteristics after controlling for the accumulation over the catchment this could be explained by a lower importance of anisotropy relative to other factors affecting streamflow generation and by the difficulties in creating representative rainfall temporal properties at the catchment scale when the radar scale is used for model calibration the proposed method provides a tool to create ensembles of design storms when the anisotropic shape of the fields is of importance

tidally driven vorticity diurnal shear and turbulence atop fieberling seamount abstract fine and microstructure profiles collected over fieberling seamount at 32 26 n in the eastern north pacific reveal a variety of intensified baroclinic motions driven by astronomical diurnal tides the forced response consists of three phenomena coexisting in a layer 200 m thick above the summit plain i an anticyclonic vortex cap of core relative vorticity 0 5f ii diurnal fluctuations of 15 cm s 1 amplitude and 200 m vertical wavelength and iii turbulence levels corresponding to an eddy diffusivity e 10 10 4 m2 s 1 the vortex cannot be explained by taylor proudman dynamics because of its 0 3fn2 negative potential vorticity anomaly the 0 3f fortnightly cycle in the vortex s strength suggests that it is at least partially maintained against dissipative erosion by tidal rectification the diurnal motions are slightly subinertial turning clockwise in time and counterclockwise with depth over the summit plain they also exhibit a fortnightly cycle in their amplitude pointing to

model studies of near inertial motion on the continental shelf off northeast spain a three dimensional two dimensional one dimensional model comparison study 1 a three dimensional nonlinear model of the balearic sea region is used to examine the spatial distribution of wind induced near inertial internal waves results from the model are compared with those from two dimensional cross section and single point models in the case of motion induced by a wind pulse there is no significant along shelf flow and comparable solutions are obtained from the three and two dimensional models however when forced with a realistic wind a significant along shelf flow is produced that is larger in the cross section model than in the three dimensional model because of the absence of an along shelf pressure gradient associated with this change in flow are important differences in across shelf currents and temperature fields that influence the distribution of near inertial motion since the point model cannot take account of internal pressure gradients near inertial internal waves are absent however when some account of barotropic pressure gradients related to local wind stress are included currents and inertial oscillations were in better agreement with the three dimensional model than with the cross section model although the major features of the wind induced deepening of the thermocline could be reproduced by the single point model the absence of internal waves and mixing associated with them lead to a sharper thermocline than in the three dimensional model comparison of two and one dimensional models with the full three dimensional model shows some severe limitations in the simpler models

new chemical bio optical and physical observations of upper ocean response to the passage of a mesoscale eddy off bermuda a mesoscale eddy advected across the bermuda testbed mooring site over a 30 day period centered on july 14 1995 temperature and current measurements along with biogeochemical measurements were used to characterize the biological response of the upper ocean associated with the introduction of nitrate into the euphotic layer due to the doming of isotherms associated with the eddy complementary shipboard data showed an anomalous water mass which extended from a depth of 50 to 1000 m manifesting as a cold surface expression and warm anomaly at depth although mesoscale eddies are frequently observed in the sargasso sea the present observations are particularly unique because of the high temporal resolution measurements of the new instrumentation deployed on the mooring analyzers that measure nitrate plus nitrite were placed at depths of 80 and 200 m and bio optical sensors were located at depths of 20 35 45 71 and 86 m peak nitrate values of nearly 3 0 mm at 80 m and chlorophyll a values of 1 4 mg m 23 at 71 m were observed as well as a 25 to 30 meter shoaling of the 1 light level depth a doppler shift from the inertial period 22 8 hours to 25 2 hours was observed in several time series records due to the movement of the eddy across the mooring inertial pumping brought cold nutrient rich waters farther into the euphotic zone than would occur solely by isothermal lifting silicic acid was depleted to undetectable levels owing to the growth of diatoms within the eddy the chlorophyll a values associated with the eddy appear to be the largest recorded during the 8 years of the ongoing u s jgofs bermuda atlantic time series study bats program

vorticity balance off the south shore of oahu hawaii derived by high frequency radio doppler current observations abstracthigh frequency radio doppler surface current observations off the south shore of oahu hawaii are used to calculate the vorticity equation at a 2 km spatial resolution in terms of a time

tidal currents in the northwestern adriatic high frequency radio observations and numerical model predictions the results of a two year long deployment of high frequency radars along the italian coast of the northern adriatic are analyzed to characterize the surface tidal currents m2 and k1 ellipses are aligned with the basin axis and exhibit large eccentricities in the middle of the basin decreasing toward the italian coast comparisons are made with a 3d finite element non linear numerical model of the tides complex correlations between modeled and observed tidal currents show a remarkable agreement in the middle of the basin with magnitudes reaching 0 985 and average phases of 6 4 deg however the magnitudes drop to 0 5 within 20 30 km from the italian coast where the modeled currents amplitudes are underestimated by 2cm s and the phases lag the observed phases by 60 deg this shallow region less than 30 m deep is characterized by low salinity water originating at the po river and laterally sheared coastal flows the radars may have captured the influence of stratification or mean sheared flows both absent from the model the model parameterization of bottom friction may also inadequately represent the effects of real bottom friction on the vertical current shear

development of the temperature and salinity structure of the upper ocean over two months in an area 150 times 150 km and discussion during the two months of the jasin experiment a regular conductivity temperature depth station pattern was worked by hr neth ms tydeman giving a total of eight surveys of temperature and salinity structure in an area 100 km times 150 km the data are averaged to obtain hourly and spatial mean profiles it is shown that this averaging conserves heat and salt content the spatial mean profiles are compared with heat budget computations and it is found that on average surface heat fluxes dominate the time history of the oceanic heat content on the scale of the whole survey area on smaller scales advection due to mesoscale structures dominates masking any differences in heating in different water masses comparison with results from a one dimensional mixed layer model indicates that this type of model satisfactorily simulates the development of the temperature profile as a spatial average for the survey area in this paper we have shown that it is possible to obtain average profiles of temperature and salinity that can be considered representative for an ocean area of about 100 km times 150 km covering several meoscale features total removal of the eddy signal from temperature profiles is found to be impossible owing to the eddy signal s varying with depth we have shown that on average the surface heat fluxes 50 w m 2 balance the changes in the oceanic heat budget advective terms being generally smaller by an order of magnitude 10 w m 2 during most of the jasin field experiment though measured currents were high up to 26 cm s 1 most of the flow was associated with the eddies and was contained within the 100 km times 150 km area and did not lead to large transport of heat in or out of the area on scales less than an eddy diameter 90 km eddy advection 400 300 w m 2 dominated local changes in heat content a one dimensional model is presented capable of simulating the observed changes in the temperature profile

inertial oscillations in the korea strait inertial oscillations io are examined in the korea strait based on measurements from 13 acoustic doppler current profilers covering the time period may 1999 through march 2000 strong io responses to wind stress occur during summer a simple linear model predicts that winter wind stress is expected to generate inertial responses of the same order of magnitude as those in summer however the observed winter io response is much weaker than predicted during summer the currents within the mixed layer and below the mixed layer are of comparable amplitude but in opposite directions the depth at which the currents reverse directions varies throughout the year as the mixed layer deepens from about 40 m during summer to the bottom of the water column in november during winter the velocity structure is more uniform in depth with currents in the same direction throughout the water column one possible explanation for these phenomena is related to the combined effect of the strait boundaries and the strong summer stratification the stratification prevents the wind stress momentum flux from mixing downward below the thermocline and thus allows the development of a bottom current separate from the surface current such a velocity structure is necessary to satisfy the no flow condition through the land boundaries

drifting buoy in the field of flow of two eddies on east thulean rise northeast atlantic the track of an argos buoy drogued at a depth of 70 m over a year s deployment from april 18 1989 to april 18 1990 in the ne atlantic is described the mean speed of the buoy over a year s period was 1 4 cm s 1 to the ne for 320 days there was little net movement and during this time the buoy spent 66 days in a cyclonic eddy and 130 days in an anticyclonic eddy the anticyclonic eddy diameter was about 200 km and the buoy completed 21 complete revolutions around the eddy center at a radius of 55 km the rotation rate was 10 days in the eye of the anticyclonic eddy the rotation rate was 36 hours the inertial period for the latitude 51 5 n was 15 3 hours and inertial motions were occasionally marked in the anticyclonic eddy the observed inertial period was about half an hour longer than the inertial period corresponding to the latitude both eddies appeared to be partially trapped to east thulean rise water depth 3000 m and moved at a mean speed of about 1 cm s 1 to the nw along the rise following water depth contours though the anticyclonic eddy was stationary for about 50 days over the more central region of the rise the track of an imperfectly drogued buoy in a circular eddy field is then examined analytically a simple balance of stress forces on the drogued assembly is assumed and commonly adopted assumptions for the stress forces are made with assumptions the idealized study shows that under conditions of a steady surface stress a surface wind or current for example a buoy can remain trapped within an eddy field and show no tendency for steady translation in the direction of the surface stress for a clockwise eddy the displacement of the buoy s track is to the right of the surface stress direction for larger surface stresses or time varying winds the buoy may be blown out of an eddy of limited extent

a shallow subtropical subducting westward propagating eddy swesty swesty is a shallow subtropical subducting westward propagating eddy that was observed to move across the eastern basin of the north atlantic at a latitude near 25 n the eddy was first detected by the movement and temperature of a drogued argos buoy near 23 w 26 n in february 1993 by december 1993 the drogued buoy had moved 1000 km westward to 33 w and a winter eddy survey was made from rrs charles darwin the eddy was about 100 km in diameter and had a centre water mass core at a depth of 190 m with characteristic temperature 19 9 c and salinity 37 06 psu but was best resolved by properties related to vertical gradient structure e g brunt vaisala frequency temperature perturbation structure the eddy was particularly flat with a height to width aspect ratio of only ca 0 14 and a vertical decay scale of ca 250 m for temperature displacements maximum azimuthal currents were ca 16 cm s 1 at a depth of 175 m and the eddy azimuthal transport was only 3 sv however the potential vorticity in the eddy core was 1 5 x 10 11 rad ms 1 comparable with other deep anticyclonic lenses and lower than background values by a factor of ten the eddy appeared slightly elliptical with a detectable sea surface cooling ca 0 2 c over its centre three argos buoys with drogues set at a depth of 200 m were deployed near the centre of the eddy and one buoy continued looping westward for a further ca 800 km the drogued argos buoy results showed that the eddy moved westward at ca 100 km month 1 and about half this westward rate was attributed to self propagation during this ca 1650 km continuously drogued journey the eddy only slipped southward by about one degree of latitude and so was perhaps resisting the southward component of flow of the subtropical gyre the buoy results suggested that the central rotation rate increased with time but the eddy became smaller the initial rotation period of the central core was ca 8 d giving a corresponding normalized relative vorticity of 0 3 about 400 d later the period of core rotation was ca 5 d with normalized relative vorticity of 0 5 some of the increase in central rotation rate was attributed to subduction effects variance spectra and filtered components of velocity were derived from the buoy positions kinetic energy levels in the eddy ca 73 cm 2 s 2 were markedly elevated with respect to background levels ca 29 cm 2 s 2 the core properties of the eddy indicated a winter formation near 27 n 22 w and hydrographic sections showed that the eddy would be sinking at a rate of about 40 m a 1 by the second year the subducted water parcel the eddy core was sufficiently deep below the surface of the ocean to escape further effects of winter mixing

modelling planetary dynamics by using the temperature at the core mantle boundary as a control variable effects of rheological layering on mantle heat transport abstract in planetary convection there has been a great emphasis laid on the usage of the rayleigh number as a control parameter for describing the vigor of convection however realistic mantle rheology not only depends on temperature pressure strain rate and composition but also on the nature of the dominant creep mechanism which varies with pressure and also with temperature it is difficult to study the effects of varying influences from the convective strength without also changing the mantle flow law in the process we have adopted the approach of using as the sole control parameter the temperature at the core mantle boundary t cmb in modelling planetary dynamics with a composite non newtonian and newtonian rheology which is temperature dependent in the upper mantle and both temperature and pressure dependent in the lower mantle increasing the t cmb strengthens convective vigor and leads to a non linear increase of averaged temperature heat flow and root mean squared velocity the interior viscosity decreases strongly with t cmb and internal heating due to radioactivity a viscosity maximum is found in the horizontally averaged viscosity profile at a depth around 2000 km this viscosity hill moves downward with diminishing amplitude in the face of increasing dissipation number and internal heating the bottom third of the lower mantle appears to be superadiabatic as a consequence of the stiff lower mantle rheology the scaling relationship between the nusselt nu number and t cmb shows a relatively insensitive increase of nu with t cmb in terms of an effective rayleigh number of the whole system ra e the power law exponent of the nu ra e relationship is very low around 0 12 strong pressure dependence of lower mantle rheology and its large volume relative to the entire mantle would induce a much lower cooling rate of the planet than previous models based on parameterized convection with a temperature dependent viscosity

the near surface dynamics of coastal upwelling abstract an attempt is made to examine some observational and theoretical aspects of upper ocean dynamics in regions of strong coastal upwelling upper ocean is roughly defined as about the upper 10 30 m of the water column for most systems first the basic surface ekman and mixed layers are discussed including some of the modifications due to upwelling next coastal upwelling fronts and their associated circulation are treated finally areas of strongly three dimensional upwelling are classified and discussed horizontal advection of heat and momentum appear to be generally important for the near surface dynamics of coastal upwelling and these phenomena make realistic theoretical treatments especially difficult

mesoscale eddy internal wave coupling part i symmetry wave capture and results from the mid ocean dynamics experiment abstract vertical profiles of horizontal velocity obtained during the mid ocean dynamics experiment mode provided the first published estimates of the high vertical wavenumber structure of horizontal velocity the data were interpreted as being representative of the background internal wave field and thus despite some evidence of excess downward energy propagation associated with coherent near inertial features that was interpreted in terms of atmospheric generation these data provided the basis for a revision to the garrett and munk spectral model these data are reinterpreted through the lens of 30 years of research rather than representing the background wave field atmospheric generation or even near inertial wave trapping the coherent high wavenumber features are characteristic of internal wave capture in a mesoscale strain field wave capture represents a generalization of critical layer events for flows lacking the spatial symmetry inherent in a parallel shear flow or isolated vortex

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

is the lower mantle rheology newtonian today the issue concerning the dominant creep mechanism in mantle convection has been studied numerically with a rheology incorporating both linear and non linear elements we have employed a rheology suggested by the recently obtained melting temperature of lower mantle constituents for an effective rayleigh number between 105 and 106 this type of strongly temperature and pressure dependent rheology induces a circulation in the earth s mantle which is characterized by a sluggish type of flow in the lower mantle with a prevailing newtonian character while in the upper mantle much more vigorous flows are developed in a predominantly non newtonian rheology

internal wave trapping and mixing in a cold water dome 1 a cross sectional nonlinear numerical model of a shallow sea basin containing a cold water dome is used to examine the influence of wind frequency and dome characteristics upon internal waves and mixing at superinertial forcing frequencies nonlinear effects in the frontal regions of the dome give rise to propagating internal waves which are reflected by the dome s fronts this reflection gives a standing internal wave trapped within the dome the spatial variability of the wave is determined by forcing frequency stratification and dome length the magnitude of the internal wave and the length of the dome are related to the horizontal distribution of density in the frontal region at the inertial frequency there is little internal wave propagation while at subinertial forcing frequencies the internal wave is trapped in the frontal region and energy cannot radiate away consequently vertical mixing is enhanced in the frontal regions while in the center of the dome the mixed layer increases due to the vertical diffusion of the wind s momentum to depth as in a single point model in the case of wind forcing at a superinertial frequency there is less mixing in the frontal region with internal wave propagation leading to mixing in the center of the dome these calculations suggest that the breakdown of cold water domes in response to winter wind events may be due to a number of mixing processes depending upon wind frequency

shear instability in a viscoelastic material as the cause of deep focus earthquakes the mechanism of deep focus earthquakes has been examined by numerical and linear analysis of shear instability in subducting slabs we assume subducting slabs deform such that the spatially averaged strain rate becomes time independent furthermore we assume that rheology depends on temperature in the manner of an activation process using this model we investigate quantitatively the conditions under which shear instability takes place i e the deformation in the material concentrates in a thin layer whose temperature increases explosively until melting occurs first we study instability in a material whose rheological properties are spatially homogeneous shear instability takes place in a homogeneous material when exceeds a certain critical level e c which depends strongly on the stress in the slabs but does not depend on the detail of the creep law the value of the activation energy next we study instability in a material that contains shear zones similar to those often observed by field geologists i e a thin layer made of material with lower vicosity than the surrounding region we find that shear zones trigger shear instability even for the case of provided that g the ratio of characteristic time of thermal diffusion to that of shear heating in shear zones exceeds 1 and that f the ratio of stiffness of elastic deformation in the surrounding region to that of ductile deformation in shear zones becomes lower than 1 applying this condition to subducting slabs with shear zones we find that shear zones trigger shear instability even when the average strain rate is lower than by an order of magnitude from these results and from an estimate of in subducting slabs we conclude that shear instability is a mechanism likely to induce deep focus earthquakes

the role of shear heating in lubricating mantle flow abstract the role of viscous heating in mantle flows has been studied within the framework of a steady state two dimensional cartesian model with a composite non newtonian and newtonian rheology there is temperature dependence in the upper mantle rheology and temperature and pressure dependent rheology in the lower mantle we have considered adiabatic and viscous heating using the extended boussinesq approximation we have selected as the only control variable the temperature at the core mantle boundary cmb we have compared systematically both the boussinesq and extended boussinesq solutions for the same rheology and same amount of internal heating by varying the temperature at the cmb from 2000 k to around 10 000 k viscosity contrasts in the system increase with the vigor of convection and reach up to five orders in magnitude both the vigor of convection and the global viscous heating increases systematically with the temperature at the cmb the rms velocity shows a power law type dependence on the temperature at the cmb with a power law exponent of 1 5 for high cmb temperatures greater then 3500 k a focused concentration of shear heating promotes the development of high strain rate and low viscosity zones next to descending flows which is primarily non newtonian in character in the high cmb temperature regime much more pronounced shear zones are developed along the downwelling for models with viscous heating present than for the boussinesq flows illustrating the important role played by mechanical heating on lubricating limbs in mantle circulation