enhanced diapycnal mixing in the south china sea profiles of current velocity temperature and salinity were obtained in the internal wave and mixing experiment in the south china sea scs the luzon strait and the north pacific the observations are examinedforevidenceofenhanceddiapycnalmixinginthescs whichreacheso 10 23 m 2 s 21 inmagnitude resultsfrom independent casts reveal that diapycnal diffusivity in the scs andthe luzon strait is elevatedby two orders of magnitude over that of the smooth bathymetry in the north pacific which are typical of background values in an open ocean the vertical distribution of diapycnal diffusivity is nonuniform in the scs exhibiting higher values at depths greater than about 1000 m this result compares favorably with the direct microstructure measurements at four stations in the scs velocity and density profiles are combined to estimatetheinternaltideenergyfluxgeneratedintheluzonstraitanddirectedintothescs theenergyamounts to 10 gw most of which is rationalized to be the potential energy source for enhanced mixing in the scs

observations of turbulence in a tidal beam and across a coastal ridge during a microstructure survey off california in monterey bay we found a midwater beam of strong turbulence emanating from the shelf break along the ray path of the semidiurnal m2 internal tide within the 50 m thick beam the turbulence kinetic energy dissipation rate e exceeded 10 6 w kg 1 and the diapycnal eddy diffusivity k was 0 01 m2 s 1 the beam extended 4 km off the shelf break several factors suggest that this beam of strong turbulence resulted from the breaking of semidiurnal internal tides the beam appeared to originate from the shelf break which is a potential generation site for semidiurnal internal tides the beam closely followed the ray path of the semidiurnal internal tide the average e off the shelf break varied by a factor of 100 with a semidiurnal tidal periodicity the isopycnal displacement confirmed the presence of semidiurnal internal tides processes associated with the breaking of internal tides are intermittent and sporadic at the same location we also observed equally intense turbulence in a 100 m thick layer of stratified water across the ridge of a sea fan this layer of strong turbulence was separated from the bottom and was clearly not generated by bottom friction although less well resolved in time the strong turbulence above the bottom seemed to vary with the semidiurnal tide and existed at the lee of the ridge where the isopycnal surface dipped and rebounded in a pattern resembling that of internal hydraulic jumps on the basis of the behavior of the density field we believe that the deep mixing was most likely produced by the across ridge current of internal tides the breaking of internal tides at middepth where the richardson number is close to the critical value is likely due to shear instability the presence of the coastal ridge provides an alternative pathway for converting energy from internal tides to turbulence via internal hydraulics multiplying the average e in the midwater beam by the length of the global coastline gives 31 gw only a small fraction of the estimated 360 gw dissipated globally by m2 internal tides our observations suggest that either most internal tides are generated away from shelf breaks or most internal tides generated at shelf breaks propagate away from their generation sites rather than dissipate locally and eventually contribute to pelagic mixing

flow hydrography turbulent mixing and dissipation at fieberling guyot examined with a primitive equation model 1 the extensive set of measurements previously taken at fieberling guyot provides a backdrop for model results on flow hydrography turbulent mixing and derivative variables a z level primitive equation model driven at subinertial and superinertial tidal frequencies allows the nonlinear interaction of free and topographically trapped motions to jointly determine model outcomes model residual flows mean hydrographic features topographic amplification of oscillatory currents turbulent dissipation and vertical diffusivity kv profiles are all examined in the light of the observations azimuthal residual flows are toroidal above the summit with maximum speed 20 cm s 1 diurnal flow over the summit is intensified by a factor 20 downward vertical flow as a time mean w t occurs from 150 m above the summit apex to summit rim depth with radially inward flow above the apex and radial outward flow below upward w t rings the summit at larger r the existence of the observed cold dome is shown to depend on w t in the summit circulation cell vertical current shear is concentrated in a 150 m thick cap above the summit accounting for a domed distribution of and kv with maxima of 10 7 w kg 1 and 30 cm2 s 1 respectively profiles most like the observations of kv are obtained with a subgrid scale parameterization in which the turbulent prandtl number pr depends on the shear richardson number ri

internal tide scattering at seamounts ridges and islands 1 the scattering of mode 1 internal tides from idealized gaussian topography in a nonrotating ocean with constant and realistic stratifications is examined with a primitive equation numerical model incident mode 1 energy fluxes of 20 and 2000 w m 1 are used to examine the linear regime and a more realistic situation simulations using two dimensional or infinite ridges compare well with ray tracing methods and illustrate how the size and shape of the topography influence wave scattering the height affects energy transmission and reflection while the slope and width determine the conversion of low mode internal tides into beams or higher modes three dimensional topographic scattering is considered for seamounts finite width ridges and islands scattering from finite ridges focuses wave energy directly downstream while scattering from seamounts produces azimuthal energy dispersion scattering to higher wave modes occurs in the lee of near critical and supercritical seamounts and ridges nonlinear interactions transfer energy into the mode 1 m4 internal tide the mellor yamada level 2 5 submodel parameterizes turbulent mixing for the near critical and supercritical ridges with realistic stratification elevated mixing is found over the leading edge of the topography and along a tidal beam up to the first surface bounce a transition from a beam structure near the topography to a low mode structure farther away occurs due to an increased contribution from the mode 1 internal tide as it refracts around the topography and not due to turbulent dissipation internal tide scattering at topography leads to a loss of energy to mixing and to a redistribution of energy flux in space frequency and mode number

storm track dynamics this paper reviews the current state of observational theoretical and modeling knowledge of the midlatitude storm tracks of the northern hemisphere cool season observed storm track structures and variations form the first part of the review the climatological storm track structure is described and the seasonal interannual and interdecadal storm track variations are discussed in particular the observation that the pacific storm track exhibits a marked minimum during midwinter when the background baroclinicity is strongest and a new finding that storm tracks exhibit notable variations in their intensity on decadal timescales are highlighted as challenges that any comprehensive storm track theory or model has to be able to address physical processes important to storm track dynamics make up the second part of the review the roles played by baroclinic processes linear instability downstream development barotropic modulation and diabatic heating are discussed understanding of these processes forms the core of our current theoretical knowledge of storm track dynamics and provides a context within which both observational and modeling results can be interpreted the eddy energy budget is presented to show that all of these processes are important in the maintenance of the storm tracks the final part of the review deals with the ability to model storm tracks the success as well as remaining problems in idealized storm track modeling which is based on a linearized dynamical system are discussed perhaps on a more pragmatic side it is pointed out that while the current generation of atmospheric general circulation models faithfully reproduce the climatological storm track structure and to a certain extent the seasonal and enso related interannual variations of storm tracks in depth comparisons between observed and modeled storm track variations are still lacking

case studies of high wind events in barrow alaska climatological context and development processes the beaufort chukchi cyclones of october 1963 and august 2000 produced the highest winds ever recorded in barrow alaska in both cases winds of 25 m s21 were observed with gusts unofficially reported at 33 m s 21 the october 1963 storm caused significant flooding contaminated drinking water and interrupted power supplies the august 2000 storm caused the wreck of a 6 million dredge and removed roofs from 40 buildings both storms were unusual in that they tracked eastward from the east siberian sea into the chukchi and beaufort seas rather than following a more typical northward track into the arctic ocean this paper addresses through modeling and analysis the development processes of these two storms the october 1963 system was a long lived warm core zonally elongated cyclone that traversed around the arctic basin through the canadian archipelago the august 2000 system was an open wave cyclone that dissipated rapidly into a weak cold core eddy in the alaskan sector of the beaufort sea approximating the contributions to development using terms in a quasigeostrophic omega equation it was found that both storms were characterized by the increasing importance of the convergence of the q vector representing differential vorticity advection and thermal advection in the midtroposphere at the expense of forcing by the turbulent fluxes of heat moisture and momentum in the boundary layer however the influence of surface turbulent fluxes in the early stages of development was important particularly for the august 2000 cyclone which passed over an extensive coastal lead in the east siberian sea this study concludes that the observed retreat in western arctic ice cover is unlikely to be an important contributor to increasing cyclonic activity in the region but that ice retreat north of eurasia could have an impact

experiments on the generation of internal waves over continental shelf topography experiments were performed to examine the generation of internal waves by a barotropic tide forcing a continuously stratified fluid over idealized continental shelf slope topography a range of responses was observed including the generation of both internal wave beams and boundary layer boluses primarily dependent on the values of both the reynolds number and the topographic steepness parameter the formation of beams required a critical bottom slope whilst for bolus formation a large vertical fluid excursion was necessary a bolus formed when the non dimensional vertical excursion parameter hn w 0 3 2 here h is the vertical excursion n is the buoyancy frequency and w 0 is the near bottom vertical velocity associated with the local depth averaged velocity we simplified the classification of the observed flow regimes using a generation parameter g defined as the ratio of a reynolds number to the topographic steepness parameter the estimated flow regime boundaries were for g g g g 400 there was no bolus observed we estimated that approximately 4 of the barotropic energy was converted to baroclinic energy when beams were generated

seamount statistics in the pacific ocean we apply the wide beam sampling technique of jordan et al 1983 to approximately 157 000 km of wide beam profiles to obtain seamount population statistics for eight regions in the eastern and southern pacific ocean population statistics derived from wide beam echograms are compared with seamount counts from sea beam swaths and with counts from bathymetric maps we find that the average number of seamounts with summit heights h h is well approximated by the exponential frequency size distribution h oe h the exponential model for seamount sizes characterized by the single scale parameter 1 is found to be superior to a power law self similar model which has no intrinsic scale in describing the average distribution of pacific seamounts and it appears to be valid over a size spectrum spanning 5 orders of magnitude in abundance large scale regional variations in seamount populations are documented we observe significant differences in seamount densities across the murray fracture zone in the north pacific and the eltanin fracture zone system in the south pacific the eltanin discontinuity is equally evident on both sides of the pacific antarctic ridge in the south pacific regions symmetrically disposed about the ridge axis have very similar seamount densities despite the large difference between pacific plate and antarctic plate absolute velocities evidently any differences in the shear flows at the base of the pacific and antarctic plates do not affect seamount emplacement systematic variations in o and are observed as a function of lithospheric age with the number of large seamounts increasing more rapidly than small seamounts these observations have been used to develop a simple model for seamount production under the assumptions that 1 an exponential size frequency distribution is maintained 2 production is steady state and 3 most small seamounts are formed on or near the ridge axis the limited data available from this study appear to be consistent with the model but they are insufficient to provide a rigorous test of the assumptions or determine accurately the model parameters however the data from the south pacific indicate that the off axis production of large seamounts probably accounts for the majority of seamounts with summit heights greater than 1000 m

seafloor tectonic fabric from satellite altimetry abstract ocean floor structures with horizontal scales of 10 to a few hundred kilometers and vertical scales of 100 m or more generate sea surface gravity anomalies observable with satellite altimetry prior to 1990 altimeter data resolved only tectonic lineaments some seamounts and some aspects of mid ocean ridge structure new altimeter data available since mid 1995 resolve 10 km scale structures over nearly all the world s oceans these data are the basis of new global bathymetric maps and have been interpreted as exhibiting complexities in the sea floor spreading process including ridge jumps propagating rifts and variations in magma supply this chapter reviews the satellite altimetry technique and its resolution of tectonic structures gives examples of intriguing tectonic phenomena and shows that structures as small as abyssal hills are partially resolved a new result obtained here is that the amplitude of the fine scale 10 80 km roughness of old ocean floor is spreading rate dependent i

a family of frontal cyclones over the western atlantic ocean part ii parameter studies in this study a series of sensitivity experiments is performed to study the relative influence of latent heating surface friction and surface heat fluxes on the development of a family of frontal cyclones that occurred over the western atlantic ocean using the simulation presented in part i as a control run it is shown that dry dynamics determines the initiation and track of all the frontal cyclones and it accounts for about 59 of the deepening of a major frontal cyclone vorticity budget calculations reveal that in the absence of latent heating preexisting upper level cyclonic vorticity associated with a ring of potential vorticity provides the necessary forcing for the initiation and movement of the frontal cyclones whereas the low level thermal advection is responsible for a large portion of their amplifications as well as for their shallow circulations the impact of surface sensible and latent heat fluxes on the frontal cyclogenesis depends on the cyclones location with respect to the warm water surface in the absence of latent heating the surface fluxes have very weak impact through modifying the low level baroclinicity on the evolution and final intensity of the frontal cyclones when latent heating is allowed however the surface fluxes could result in more rapid cyclogenesis as a result of reduced static stability and increased moisture content in the maritime boundary layer the impact is as pronounced as the latent heating it is found that dry frontal cyclogenesis could still occur over a vast continental surface although it is the slowest moving and deepening system among all the sensitivity tests being conducted the results reveal that i the frontal cyclones in the present case are baroclinically driven in nature although they are markedly modulated by diabatic heating and surface fluxes and ii the rapid frontal cyclogenesis phenomena tend to occur more frequently over a warm ocean surface due to its associated weak surface friction and its generated weak static stability in the maritime boundary layer

internal tides and turbulence along the 3000 m isobath of the hawaiian ridge full depth velocity and density profiles taken along the 3000 m isobath characterize the semidiurnal internal tide and bottom intensified turbulence along the hawaiian ridge observations reveal baroclinic energy fluxes of 21 5k w m 1 radiating from french frigate shoals 17 2 5 kw m 1 from kauai channel west of oahu and 13 3 5 kw m 1 from west of nihoa island weaker fluxes of 1 4 2k w m 1 radiate from the region near necker island and east of nihoa island observed off ridge energy fluxes generally agree to within a factor of 2 with those produced by a tidally forced numerical model average turbulent diapycnal diffusivity k is 0 5 1 10 4 m 2 s 1 above 2000 m increasing exponentially to 20 10 4 m 2 s 1 near the bottom microstructure values agree well with those inferred from a finescale internal wave based parameterization a linear relationship between the vertically integrated energy flux and vertically integrated turbulent dissipation rate implies that dissipative length scales for the radiating internal tide exceed 1000 km

turbulent dissipation over the continental slope off vancouver island abstract thirteen profiles of the rate of viscous dissipation of turbulent kinetic energy epsi were made over the continental slope off vancouver island between 12 and 14 may 1980 in conjunction with ctd and moored current meter observations systematic variability was observed in the vertical but not in the horizontal direction above 200 m depth numerous salt stabilized temperature inversions were seen and dissipation rates were significantly larger than below 200 m dissipation rates below 200 m are the lowest ever reported and coincide with a low level of energetics revealed by the current meter moorings comparison with the garrett munk internal wave spectrum indicates an e folding decay time of internal wave energy of 50 days at depths below 200 m

uranium and thorium isotopes in marine sediments off northeastern taiwan uranium and thorium isotopes have been determined on seven box cores collected aboard r v ocean researcher i within the lower continental slope area off northeast taiwan during may 1991 the goals are to obtain the downcore u and th concentrations and their isotopic compositions in the area and to evaluate their possible source s transport and deposition u 238 contents of the box cores are fairly uniform at about 1 3 dpm g ranging between 0 9 and 1 6 dpm g u 234 has activities between 1 2 and 2 dpm g with an average of 1 4 dpm g th 232 contents are also quite uniform at about 3 2 dpm g th 230 has values roughly between 1 5 and 2 3 dpm g averaging at 1 9 dpm g th 228 is essentially equal to th 232 in activity except for the very surface sediments where th 228 appears to be slightly higher than th 232 the u and th contents of the shale slate and black schist from taiwan are about 1 9 and 3 2 dpm g respectively with a uth ratio of 0 6 th 232 in the cored sediments has similar activities but u 238 has activities lower by about 0 6 dpm g on the average if these crustal rocks have provided their weathered debris or particles as sediments to the cored area then u 238 must have lost by about this amount or 30 in transit by dissolution into the seawater as th 230 in the cores has an average activity identical to the u 238 activity of the crustal rocks mentioned above secular equilibrium between u 238 u 234 and th 230 must have been established when the rocks were exposed to weathering and erosion and no net th 230 gain or loss occurred in transit thus both th 232 and th 230 have probably been retained by the detrital particles which form the cored sediments the excess th 230 defined as the th 230 in excess over the u 234 in activity is about 0 5 dpm g however this excess may be fictitious because it is probably caused by dissolution of uranium from the terrigenous particles in transit rather than scavenging of th 230 from the water column by these particles as the th 230 production from u 234 decay in the water column can only account for 2 12 of the calculated excess th 230 a reasonable explanation is that all the th 230 observed in the cores has been of detrital origin with little authigenic contribution from the water column the th 230th 232 activity ratios are quite constant at about 0 6 for both the cored sediments and the above mentioned crustal rocks suggesting that thorium has not been leached out in transit to final deposition this is further supported by the fact that identical activity ratio has also been observed in the settling particulates collected by traps deployed in the same area the th 228th 232 activity ratios are close to unity except for the top few centimeters where the ratios are greater than unity due to the th 228 derived from ra 228 decay in the water column under rapid deposition the penetration depth for this th 228 excess is about 4 cm which is consistent with the prediction based on the known sedimentation rates of about 0 3 0 5 cm yr

spatially heterogeneous diapycnal mixing in the abyssal ocean a comparison of two parameterizations to observations 1 the spatial distributions of the diapycnal diffusivity predicted by two abyssal mixing schemes are compared to each other and to observational estimates based on microstructure surveys and large scale hydrographic inversions the parameterizations considered are the tidal mixing scheme by jayne st laurent and co authors jsl01 and the roughness diffusivity model rdm by decloedt and luther comparison to microstructure surveys shows that both parameterizations are conservative in estimating the vertical extent to which bottom intensified mixing penetrates into the stratified water column in particular the jsl01 exponential vertical structure function with fixed scale height decays to background values much nearer topography than observed jsl01 and rdm yield dramatically different horizontal spatial distributions of diapycnal diffusivity which would lead to quite different circulations in ogcms yet they produce similar basin averaged diffusivity profiles both parameterizations are shown to yield smaller basin mean diffusivity profiles than hydrographic inverse estimates for the major ocean basins by factors ranging from 3 up to over an order of magnitude the canonical 10 4 m2 s 1abyssal diffusivity is reached by the parameterizations only at depths below 3 km power consumption by diapycnal mixing below 1 km of depth between roughly 32 s and 48 n for the rdm and jsl01 parameterizations is 0 40 tw 0 28 tw respectively the results presented here suggest that present day mixing parameterizations significantly underestimate abyssal mixing in conjunction with other recently published studies a plausible interpretation is that parameterizing the dissipation of bottom generated internal waves is not sufficient to approximate the global spatial distribution of diapycnal mixing in the abyssal ocean

observations on stratified flow over a bank at low froude numbers abstract in june 2011 a 9 day oceanographic survey was conducted over the east flower garden bank a coral reef located on the outer shelf in the northwestern gulf of mexico current temperature conductivity and microstructure measurements were collected to characterize flow evolution turbulence and mixing over the bank during the experiment the flow was highly stratified subcritical froude number below 0 4 hydrostatic and nonlinear with rotational effects being important observations showed that flow structure turbulence and mixing were highly dependent on the direction and strength of the current thus they varied spatially and temporarily responses resulting from interactions between the free stream flow and the obstacle were significantly different on the upstream and downstream sides of the bank blocking and diverging of the flow just below the bank height was observed on the upstream side on the downstream side a wake with imbedded vortices developed moreover turbulence was amplified over the bank top and on its downstream side turbulent dissipation rates were as high as 1026 w kg21 and resulted in measured rates of energy dissipation and mixing by turbulence per unit width as high as 40 w m21 mixing in the downstream side was elevated with eddy diffusivities reaching 1023 m2 s21 well above a typical value of 1025 m2 s21 commonly found in the ocean thermocline and over shelves with flat topography on the upstream side estimated eddy diffusivities were close to that for the ocean thermocline i e they were generally less than 0 531024 m2 s21

tidal conversion and turbulence at a model ridge direct and large eddy simulations direct and large eddy simulations are performed to study the internal waves generated by the oscillation of a barotropic tide over a model ridge of triangular shape the objective is to go beyond linear theory and assess the role of nonlinear interactions including turbulence in situations with low tidal excursion number the criticality parameter defined as the ratio of the topographic slope to the characteristic slope of the tidal rays is varied from subcritical to supercritical values the barotropic tidal forcing is also systematically increased numerical results of the energy conversion are compared with linear theory and in laminar flow at low forcing they agree well in subcritical and supercritical cases but not at critical slope angle in critical and supercritical cases with higher forcing there are convective overturns turbulence and significant reduction as much as 25 of the radiated wave flux with respect to laminar flow results analysis of the baroclinic energy budget and spatial modal analysis are performed to understand the reduction the near bottom velocity is intensified at critical angle slope leading to a radiated internal wave beam as well as an upslope bore of cold water with a thermal front in the critical case the entire slope has turbulence while in the supercritical case turbulence originates near the top of the topography where the slope angle transitions through the critical value the phase dependence of turbulence within a tidal cycle is examined and found to differ substantially between the ridge slope and the ridge top where the beams from the two sides cross

from tides to mixing along the hawaiian ridge the cascade from tides to turbulence has been hypothesized to serve as a major energy pathway for ocean mixing we investigated this cascade along the hawaiian ridge using observations and numerical models a divergence of internal tidal energy flux observed at the ridge agrees with the predictions of internal tide models large internal tidal waves with peak to peak amplitudes of up to 300 meters occur on the ridge internal wave energy is enhanced and turbulent dissipation in the region near the ridge is 10 times larger than open ocean values given these major elements in the tides to turbulence cascade an energy budget approaches closure

internal hydraulic jumps in a long narrow lake high resolution three dimensional numerical modeling and field observations were used to describe the nonlinear response of cayuga lake to surface wind forcing the degeneration of the basin scale internal wave field was characterized according to the composite froude number g2 wedderburn number wn and lake number ln which are measures of hydraulic control and bulk and integral wind disturbance force to the baroclinic restoring force respectively the typical cayuga lake response was a nonlinear surge when 1 1 in a lake the occurrence of the hydraulic jump was correctly predicted using scaling parameters it was also shown that topographically induced internal hydraulic jumps form when the nonlinear surges interact with a sill contraction topographic feature in contrast to published literature the observed high frequency nonlinear internal waves were preferentially associated with internal jumps as opposed to steepened internal surges computed vertical diffusivities showed mixing was enhanced by two orders of magnitude within both the surges and hydraulic jumps as they propagated through the basin and interacted with topography our results can be generalized to other lakes and fjords with similar long narrow geometry and topographically separate side basins

sensitivity of cyclogenesis to sea surface temperature in the northwestern atlantic during the intensive observation period 15 13 15 february 1997 of the fastex experiment a major cyclone crossed the atlantic ocean from the newfoundland basin to southern iceland its surface low center deepened by 17 hpa in 7 h when the perturbation crossed the north atlantic current nac from cold 38c to warm water 158c to elucidate the role of sea surface temperature sst and air sea fluxes in the dynamics of oceanic cyclones three nonhydrostatic mesoscale simulations were performed the first one is a control experiment with a realistic sst field describing in detail the oceanic front associated with the nac system the two following simulations are sensitivity experiments where the sst front is removed the first one uses a uniformly cold sst equal to 38c and the second one uses a uniformly warm sst equal to 158c the frontogenetic function and the vertical velocity sources in the lower atmospheric layers of the three simulations were diagnosed in the control simulation the surface heat fluxes were found to be negative in the perturbation warm sector and positive in the region behind the cold front as reported by numerous authors this pattern of surface heating and cooling did not intensify the cyclone except in the occlusion when the phasing with the sst front occurs this configuration enhances the horizontal gradient of surface buoyancy flux across the occlusion which increases the buoyancy flux source of vertical velocity w when the sst front is removed the surface heat fluxes are strongly affected in magnitude and in spatial variability the marine atmospheric boundary layer mabl stability the convective activity the warm advection in the core of the wave and the heating depth are strongly affected by the different surface flux fields there are several consequences i the uniform ssts tend to decrease the cold front intensity of the wave ii a weaker buoyancy flux source of vertical velocity is found above a uniform cold sst across the occlusion in comparison with the control case and iii surprisingly a weaker w buoyancy flux source is also found above a uniform warm sst because of a higher heating depth vertical velocity depends not only on the buoyancy flux forcing but also on the thermal wind the turbulent momentum and the thermal wind imbalance forcings the thermal wind forcing and the thermal wind imbalance forcing were the most sensitive to the sst compared to the turbulent momentum forcing this result means that i the feed back of the ageostrophic circulation induced by the surface is greater on the kinematic forcings than on the turbulent forcings and ii the turbulent momentum forcing does not play a crucial role in cyclogenesis above a uniform warm sst the strongest intensity of the occlusion is due to the strongest w thermal wind forcing and w thermal wind imbalance forcing in the mabl in spite of a weaker w buoyancy flux forcing than in the control case this result is explained by the convective activity that increases the low level convergence and vorticity spinup this point means that latent heat release and baroclinicity are in tight interaction in the first 12 h and at the scale of the simulation domain the three cyclones evolve similarly but at a small scale their internal structures diverge strongly and rapidly the scale at which the surface turbulent fluxes act on the dynamics of marine cyclones is therefore important finally the cyclone simulated in the warm sst case developed more rapidly than those simulated in the real and the cold sst cases this behavior is attributed to the strong positive surface heat fluxes because they preconditioned the mabl by moistening and heating the low levels during the incipient stage of the cyclone development

inferences and observations of turbulent dissipation and mixing in the upper ocean at the hawaiian ridge abstract the hawaiian ridge is one of the most energetic generators of internal tides in the pelagic ocean the density and current structure of the upper ocean at the hawaiian ridge were observed using seasoar and doppler sonar during a survey extending from oahu to brooks banks and up to 200 km from the ridge peak survey observations are used to quantify spatial changes in internal wave induced turbulent dissipation and mixing the turbulent dissipation rate of kinetic energy e and diapycnal eddy diffusivity k are inferred from an established parameterization using internal wave shear as input at the kauai channel kc and french frigate shoals brooks banks sites e and k decay away from the ridge with maxima exceeding minima by 5 times at both sites average k is everywhere greater than the canonical open ocean value of 10 5 m2 s 1 along the ridge e and k vary by up to 100 times and are largest at sites of largest numerical model internal tide energy density in the eastern kc k 10 3 m2 s

the role of internal tides in mixing the deep ocean abstract internal wave theory is used to examine the generation radiation and energy dissipation of internal tides in the deep ocean estimates of vertical energy flux based on a previously developed model are adjusted to account for the influence of finite depth varying stratification and two dimensional topography specific estimates of energy flux are made for midocean ridge topography weakly nonlinear theory is applied to the wave generation at idealized topography to examine finite amplitude corrections to the linear theory most internal tide energy is generated at low modes associated with spatial scales from roughly 20 to 100 km the richardson number of the radiated internal tide typically exceeds unity for these motions and so direct shear instability of the generated waves is not the dominant energy transfer mechanism it also seems that wave wave interactions are ineffective at transferring energy from the large wavelengths that dominate the energy flux instead it appears that most of

internal tide generation in nonuniformly stratified deep oceans we present numerical and experimental studies of the conversion of tidal motions of an exponentially stratified fluid over two dimensional knife edge gaussian and complex bottom topography to radiated internal waves in a model of the deep ocean we compare the radiated internal wave power for cases of strong stratification where the buoyancy frequency profile n z proportional to the square root of the density gradient is much larger than the tidal frequency to the power radiated for weak stratifications we consider particularly internal wave generation for topography below a turning depth ztd where n ztd for z ztd although the radiated power in these waves is much weaker than in cases without turning depths the radiated power is predicted well by prior analytical theory if the nonuniform stratification is averaged over depths spanning from the bottom boundary up to an effective height zeff in the absence of a turning depth we find zeff is approximately equal to the height of the topography indicating that only the stratification for depths spanned by the topography is relevant however in the presence of a turning depth the vertical scale of the internal tide becomes larger and zeff increases approximately linearly with the turning depth height toward values comparable to the total fluid depth

evolution of mesoscale precipitation band environments within the comma head of northeast u s cyclones abstract this paper explores the mesoscale forcing and stability evolution of intense precipitation bands in the comma head sector of extratropical cyclones using the 32 km north american regional reanalysis hourly 20 km rapid update cycle analyses and 2 km composite radar reflectivity data a statistical and composite analysis of 36 banded events occurring during the 2002 08 cool seasons reveals a common cyclone evolution and associated band life cycle a majority 61 of banded events develop along the northern portion of a hook shaped upper level potential vorticity pv anomaly during the 6 h leading up to band formation lower tropospheric frontogenesis nearly doubles and the conditional stability above the frontal zone is reduced the frontogenesis increase is primarily due to changes in the kinematic flow associated with the development of a mesoscale geopotential height trough this trough extends poleward of the 700 hpa low and is the vertical extension of the surface warm front and surface

the integral role of a diabatic rossby vortex in a heavy snowfall event abstract on 24 25 february 2005 a significant east coast cyclone deposited from 4 to nearly 12 in 10 30 cm of snow on parts of the northeastern united states the heaviest snowfall and most rapid deepening of the cyclone coincided with the favorable positioning of an upper level short wave trough immediately upstream of a preexisting surface cyclone the surface cyclone in question formed approximately 15 h before the heaviest snowfall along a coastal front in a region of frontogenesis and heavy precipitation the incipient surface cyclone subsequently intensified as it moved to the northeast consistently generating the strongest convection to the east northeast of the low level circulation center the use of potential vorticity pv inversion techniques and a suite of mesoscale model simulations illustrates that the early intensification of the incipient surface cyclone was primarily driven by diabatic effects and was not critically dependent on the upper level wave these facts taken in conjunct

influence of surface sensible heat flux on incipient marine cyclogenesis abstract incipient marine cyclogenesis is investigated as an instability process of a mean baroclinic state with a vertically nonuniform static stability under the influence of a self induced surface sensible heat flux in the context of a quasigeostrophic model framework the analytic solution of such a model is first presented the surface sensible heat flux induces strongly unstable short waves in the meso range and an e folding time of the order of one day under supposedly relevant parameter conditions those modes have a shallow vertical structure near the surface with a pronounced westward tilt with height the latter facilitates a release of enough potential energy from the basic state to overcompensate the destruction of potential energy by the surface heat exchange itself the diabatic destabilization by surface sensible heat flux is therefore an alternative mechanism for initiating small marine cyclones without upper level forcing a potential vorticity interpretation of this instability proces

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

reexamining the dynamics of short scale diabatic rossby waves and their role in midlatitude moist cyclogenesis abstract as a step toward a more comprehensive study of the physical processes that underlie explosive cyclogenesis a two dimensional semigeostrophic model with a now standard parameterization of latent heat release is used to diagnose the structure energetics and propagation characteristics of short scale diabatic normal modes in a moist baroclinic atmosphere with the eady basic state upon revisiting the inviscid problem it is found that when a thermodynamically consistent vertical profile of latent heat release is used the short wave cutoff vanishes and growth rates become independent of zonal wavelength for zonal wavelengths shorter than approximately 1900 km the destabilized short scale modes identified previously as diabatic rossby waves owe their existence to the continuous generation of potential vorticity by moist processes associated with warm air advection rising motion and latent heat release to determine if these short scale diabatic rossby wave modes continue to grow at small

cold season synoptic scale waves over subtropical south america the most active winter synoptic scale wave patterns over south america are identified using an extended empirical orthogonal function eeof technique and are physically diagnosed using composite methods results show that the leading modes of short timescale variability propagate along two main paths over the subtropical jet latitudes 308s and over the subpolar jet latitudes 608s this research focuses on the subtropical mode and its evolution over south america the observed structure of the systems associated with the subtropical mode resembles that of midlatitude baroclinic waves both cyclonic and anticyclonic perturbations display significant modifications in their threedimensional structure as they evolve over extratropical and subtropical south america while the upper level perturbations are mostly unaffected when moving eastward the lower level perturbations advance following the shape of the andes mountains and exhibit an abrupt equatorward migration at the lee side of the mountains as a result of such detachment smaller eddy heat fluxes are observed in the vicinity of the orography and consequently a weaker eddy baroclinic growth is observed once the upper level system is on the lee side the perturbations acquire a more typical baroclinic wave structure and low level intensification of the system occurs the latter is largest around 1000 km east of the orography where enhanced moisture transports from tropical latitudes along the eastern portion of the low level cyclone favor precipitation occurrence over southeastern south america those precipitation processes seem to provide a diabatic source of energy that further contributes to the strengthening of the low level cyclone in addition an intensification of the cyclone once over the ocean was found in 60 of the situations considered which is consistent with previous research suggesting an additional source of moisture and heat flux due to the warm waters of the brazil current

nutrient control of the global occurrence of isolated carbonate banks the growth and origin of the world s isolated carbonate banks are as yet not completely understood this paper presents a comparison of the areas depths and latitudinal distribution of the world s carbonate banks these are then compared with chemical parameters of seawater in the upper mixed zone of the oceans and at depth the results allow large scale inferences to be made on the interacting controls on bank growth and distribution the data support the hypothesis that nutrient rich waters commonly control bank depth and size

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

the surface expression of semidiurnal internal tides near a strong source at hawaii part i observations and numerical predictions abstract observations of semidiurnal currents from high frequency radio doppler current meters and moored acoustic doppler current profilers adcps in the kauai channel hawaii are described and compared with two primitive equation numerical models of the tides the kauai channel separating the islands of oahu and kauai is a site of strong internal tide generation by the barotropic tides flowing over kaena ridge the subsurface extension of oahu the nature and impacts of internal tide generation in the kauai channel were intensively studied during the 2002 03 near field component of the hawaii ocean mixing experiment comparisons of observed coherent i e phase locked to the astronomical forcing m2 and s2 surface currents with model predictions show good agreement for the phases indicating propagation of internal tides away from the ridge although the predicted m2 and s2 surface currents are similar except for their magnitudes as expected for internal waves at periods closer to each other 12

global abyssal mixing inferred from lowered adcp shear and ctd strain profiles abstract internal wave wave interaction theories and observations support a parameterization for the turbulent dissipation rate e and eddy diffusivity k that depends on internal wave shear vz2 and strain z2 variances its latest incarnation is applied to about 3500 lowered adcp ctd profiles from the indian pacific north atlantic and southern oceans inferred diffusivities k are functions of latitude and depth ranging from 0 03 10 4 m2 s 1 within 2 of the equator to 0 4 0 5 10 4 m2 s 1 at 50 70 diffusivities k also increase with depth in tropical and subtropical waters diffusivities below 4500 m depth exhibit a peak of 0 7 10 4 m2 s 1 between 20 and 30 latitudes where semidiurnal parametric subharmonic instability is expected to be active turbulence is highly heterogeneous though the bulk of the vertically integrated dissipation e is contributed from the main pycnocline hotspots in e show some correlation with small scale bottom roughness and near bottom flow at sites where st

internal hydraulic flows on the continental shelf high drag states over a small bank observations of currents hydrography and turbulence provide unambiguous evidence for hydraulic control of flow over an isolated three dimensional topographic feature on oregon s continental shelf the flow becomes critical at the crest of the bank forming a strong supercritical downslope flow in the lower layer farther downstream internal hydraulic jumps form as the bottom flow becomes subcritical as a consequence turbulence is greatly enhanced in the bottom boundary layer in the sheared interface above the swiftly flowing bottom current and in the internal hydraulic jump the dissipation rate of turbulent energy is consistent with the mean energy removal rate for a hydraulic jump in an idealized two layer flow this enhanced turbulence constitutes a high drag state of the flow in which the form drag introduced by the topography exerts significant influence on the flow around it and mixing is increased 102 103 times the background values

topographically induced mixing around a shallow seamount measurements of the rate of dissipation of kinetic energy around a shallow seamount in the eastern north pacific show that mixing there is 100 to 10 000 times as large as that far away from the seamount if such values are typical of other seamounts mixing across density surfaces in the ocean occurs mainly at their boundaries and topographically induced mixing may help to explain the discrepancy between the observed intensity of mixing in the interior of the oceans and that required to satisfy models of ocean circulation

on subinertial oscillations trapped by the juan de fuca ridge northeast pacific spectra of currents measured along the 2100 m deep juan de fuca ridge in the northeast pacific have prominent tidal inertial and weather band 3 7 day period spectral peaks the weather band peak in particular has a number of interesting features it is strongest in close lateral proximity to the ridge and strongest near ridge depth intensification near the ridge is characteristic of trapped motion spectral peak intensities vary seasonally with largest amplitudes occurring in autumn and winter seasonal variation suggests that surface weather is forcing flow at depth together trapping and seasonality indicate opportunistic amplification of oscillatory motion at the ridge at all frequencies forcing topography and stratification together shape current and hydrographic distributions near the ridge effects of those interactions for subinertial motion are quantified here using a primitive equation numerical model forcing period 1 10 days and friction are the principal dependencies examined results show that flow over the juan de fuca ridge can be amplified by factors of 3 4 for diurnal and up to a factor of 7 for weather band frequencies amplification is ridge trapped with effects extending many hundreds of meters upward and extending 5 10 km laterally for 5 day period flow the strength and area of amplification increase with increasing period over the 1 to 10 day period band oscillatory weather band flow leads to vertical velocities on the order of 0 3 cm s 1 on ridge flanks which in turn cause periodic temperature t and salinity s variations with amplitudes of as much as 0 05 c and 0 01 practical salinity units respectively the vertical motion and consequent vertical displacement 100 m lead to isotherms that plunge below the crest alternately each side of the ridge a distribution observed in conductivity temperature depth transect data near the ridge crest cross ridge baroclinic pressure gradients caused by cyclically plunging isopycnals are in near geostrophic balance with the coriolis force associated with along ridge flow along ridge current amplification is therefore closely tied to isopycnal movement up and down ridge flanks since weather band oscillations lead to much larger cross ridge baroclinic pressure gradients than do diurnal motions of the same amplitude weather band forcing causes greater along ridge current amplification results vary strongly with forcing period and direction of forcing with respect to the ridge but depend only moderately on friction and turbulent mixing coefficients

tidal influence on particulate organic carbon export fluxes around a tall seamount as tall seamounts may be stepping stones for dispersion and migration of deep open ocean fauna an improved understanding of the productivity at and food supply to such systems needs to be formed here the 234th 238u approach for tracing settling particulate matter was applied to senghor seamount a tall sub marine mountain near the tropical cape verde archipelago in order to elucidate the effects of topographically influenced physical flow regimes on the export flux of particulate organic carbon poc from the near surface topmost 100 m into deeper waters the comparison of a suitable reference site and the seamount sites revealed that poc export at the seamount sites was 2 4 times higher than at the reference site for three out of five seamount sites the calculated poc export fluxes are likely to be underestimates if this is taken into account it can be concluded that poc export fluxes increase while the passing waters are advected around and over the seamount with the highest export fluxes occurring on the downstream side of the seamount this supports the view that biogeochemical and biological effects of tall seamounts in surface ocean waters might be strongest at some downstream distance from rather than centred around the seamount summit based on measured vessel mounted adcp and modelled regional flow field aviso internal tides at senghor mitgcm flow dynamics it is proposed that tidally generated internal waves result in a screen of increased rates of energy dissipation that runs across the seamount and leads to a combination of two factors that caused the increased poc export above the seamount 1 sudden increased upward transport of nutrients into the euphotic zone driving brief pulses of primary production of new particulate matter followed by the particles export into deeper waters and 2 pulses of increased shear driven aggregation of smaller slower settling into larger faster settling particles this study shows that under certain conditions there can be an effect of a tall seamount on aspects of surface ocean biogeochemistry with tidal dynamics playing a prominent role it is speculated that these effects can control the spatiotemporal distribution of magnitude and nutritional quality of the flux of food particles to the benthic and benthic pelagic communities at and near tall seamounts

mixing across the arctic ocean microstructure observations during the beringia 2005 expedition 1 turbulent scale temperature and conductivity were measured during the pan arctic beringia 2005 expedition the rates of dissipation of thermal variance and diapycnal diffusivities are calculated along a section from alaska to the north pole across deep flat basins canada and makarov basins and steep ridges alpha mendeleev and lomonosov ridges the mixing rates are observed to be small relative to lower latitudes but also remarkably non uniform relatively elevated turbulence is found over deep topography confirming the dominant role of bottom generated internal waves measured patterns of mixing in the arctic are also associated with other mechanisms such as double diffusive structures and deep overflows a better knowledge of the distribution of mixing is essential to understand the dynamics of the changing arctic environment

an amplification mechanism of medium scale tropopausal waves abstract the mechanism for the amplification of medium scale tropopausal waves with horizontal wavelengths of 2000 3000 km and wave periods of 1 2 days that are basically neutral is investigated using a three dimensional wave activity flux distinctive upward wave activity fluxes are found in the midtroposphere 400 hpa upstream of the region where the medium scale waves are dominant that is where the horizontal components of the wave activity flux are large these upward fluxes converge in the upper troposphere 300 hpa this convergence is a major source of medium scale waves producing large values of the horizontal components of the wave activity flux in the active regions examination of the spatial structure of the heat flux shows that the upward fluxes are due to occasional baroclinic interactions between upper level medium scale waves and lower tropospheric disturbances with the same temporal scales the seasonal and geophysical variations of the waves depend mostly on the amount of baroclin

the relative roles of diapycnal and isopycnal mixing on subsurface water mass conversion abstract fluid motion in the sea is known to occur predominantly along quasi horizontal neutral surfaces but the very small diapycnal i e across isopycnal velocities often make a significant contribution to the conversation equations of heat salt and tracer by eliminating the diapycnal advection term between the conservation equations for i heat and ii salt an equation is derived for the rate of change lagrangian derivative of potential temperature on a neutral surface which has terms caused by a turbulent mixing along isopycnal surfaces i e isopycnal mixing b diapycnal turbulent mixing and c double diffusive convection bemuse of the nature of the isopycnal reference frame the diapycnal mixing terms do not take their expected forms for example the diapycnal turbulent mixing term is proportional to the diapycnal eddy diffusivity d multiplied by the curvature of the s curve d2s d 2 rather than the usual form d x x if the s curve is locally straight small scale turbulen

the accuracy of surface elevations in forward global barotropic and baroclinic tide models abstract this paper examines the accuracy of surface elevations in a forward global numerical model of 10 tidal constituents both one layer and two layer simulations are performed as far as the authors are aware the two layer simulations and the simulations in a companion paper deep sea research ii 51 2004 3043 represent the first published global numerical solutions for baroclinic tides self consistent forward solutions for the global tide are achieved with a convergent iteration procedure for the self attraction and loading term energies are too large and elevation accuracies are poor unless substantial abyssal drag is present reasonably accurate tidal elevations can be obtained with a spatially uniform bulk drag c d or horizontal viscosity k h but only if these are inordinately large more plausible schemes concentrate drag over rough topography the topographic drag scheme used here is based on an exact analytical solution for arbitrary small amplitude terrain and supplemented by dimensional analysis to account for drag due to flow splitting and low level turbulence as well as that due to breaking of radiating waves the scheme is augmented by a multiplicative factor tuned to minimize elevation discrepancies with respect to the topex poseidon t p constrained got99 2 model the multiplicative factor may account for undersampled small spatial scales in bathymetric datasets an optimally tuned multi constituent one layer simulation has an rms elevation discrepancy of 9 54 cm with respect to got99 2 in waters deeper than 1000 m and over latitudes covered by t p 66 n to 66 s the surface elevation discrepancy decreases to 8 90 cm 92 percent of the height variance captured in the optimally tuned two layer solution the improvement in accuracy is not due to the direct surface elevation signature of internal tides which is of small amplitude but to a shift in the barotropic tide induced by baroclinicity elevations are also more accurate in the two layer model when pelagic tide gauges are used as the benchmark and when the t p constrained tpxo6 2 model is used as a benchmark in deep waters south of 66 s for antarctic diurnal tides the improvement in forward model elevation accuracy with baroclinicity is substantial the optimal multiplicative factor in the two layer case is nearly the same as in the one layer case against initial expectations that the explicit resolution of low mode conversion would allow less parameterized drag in the optimally tuned two layer m 2 solution local values of the ratio of temporally averaged squared upper layer speed to squared lower layer speed often exceed 10

stratified tidal flow over a bump the interaction of a stratified flow with an isolated topographic feature can introduce numerous disturbances into the flow including turbulent wakes internal waves and eddies measurements made near a bump east of race rocks vancouver island reveal a wide range of phenomena associated with the variable flow speeds and directions introduced by the local tides upstream and downstream flows were observed by placing two acoustic doppler current profilers adcps on one flank of the bump simultaneous shipboard adcp surveys corroborated some of the more striking features froude number conditions varied from subcritical to supercritical as the tidal velocities varied from 0 2 to 1 5 m s 1 during the strong ebb when the moored adcps were located on the lee side a persistent full water depth lee wave was detected in one of the moored adcps and the shipboard adcp however the placement of the moorings would suggest that by the time it appears in the moored adcp beams the lee wave has been swept downstream or has separated from the bump raw adcp beam velocities suggest enhanced turbulence during various phases of the tide many of the three dimensional flow characteristics are in good agreement with laboratory studies and some characteristics such as shear in the bottom boundary layer are not

internal tides in monterey submarine canyon abstract the m2 internal tide in monterey submarine canyon is simulated using a modified version of the princeton ocean model most of the internal tide energy entering the canyon is generated to the south on sur slope and at the head of carmel canyon the internal tide is topographically steered around the large canyon meanders depth integrated baroclinic energy fluxes are up canyon and largest near the canyon axis up to 1 5 kw m 1 at the mouth of the upper canyon and increasing to over 4 kw m 1 around monterey and san gregorio meanders the up canyon energy flux is bottom intensified suggesting that topographic focusing occurs net along canyon energy flux decreases almost monotonically from 9 mw at the canyon mouth to 1 mw at gooseneck meander implying that high levels of internal tide dissipation occur the depth integrated energy flux across the 200 m isobath is order 10 w m 1 along the majority of the canyon rim but increases by over an order of magnitude near the canyon head where internal ti

an intermediate depth source of hydrothermal 3he and dissolved iron in the north pacific abstract we observed large water column anomalies in helium isotopes and trace metal concentrations above the loihi seamount the 3he 4he of the added helium was 27 3 times the atmospheric ratio clearly marking its origin to a primitive mantle plume the dissolved iron to 3he ratio dfe 3he exported to surrounding waters was 9 3 0 3 10 6 we observed the loihi 3he and dfe signal at a depth of 1100 m at several stations within 100 1000 km of loihi which exhibited a distal dfe 3he ratio of 4 10 6 about half the proximal ratio these ratios were remarkably similar to those observed over and near the southern east pacific rise sepr despite greatly contrasting geochemical and volcanic tectonic origins in contrast the proximal and distal dmn 3he ratios were both 1 10 6 less than half of that observed at the sepr dissolved methane was minimally enriched in waters above loihi seamount and was distally absent using an idealized regional scale model we replicated the historically observed regional 3he distribution requiring a hydrothermal 3he source from loihi of 10 4 4 2 mol a 1 2 of the global abyssal hydrothermal 3he flux from this we compute a corresponding dfe flux of 40 mmol a 1 global circulation model simulations suggest that the loihi influenced waters eventually upwell along the west coast of north america also extending into the shallow northwest pacific making it a possibly important determinant of marine primary production in the subpolar north pacific

low frequency modulation of turbulent diapycnal mixing by anticyclonic eddies inferred from the hot time series profiles of potential density obtained from ctd measurements during the hawaii ocean time series hot programin thevicinityoftheislandofoahu hawaii areusedtoevaluatelow frequencyvariabilityof turbulent kinetic dissipation rates based on a finescale parameterization method a distinct seasonal cycle as well asan increasingtrendofdissipationrates is foundin the upper300 600 m thetrendis mainlydueto the much weaker diapycnal mixing in the first four years of the record that is 1988 92 in the upper 300 600 m enhanced diapycnal mixing is found under anticyclonic eddies with the mean dissipation rate about 53 larger than that under eddy free conditions the modulation of dissipation rates by anticyclonic eddies becomes more evident with increasing eddy strength the role of cyclonic eddies in modulating diapycnal mixing is almost negligible compared with that of anticyclonic eddies the mean dissipation rate under cyclonic eddies is comparable to that under eddy free conditions with a difference of less than 10 seasonality of the dissipation rates is partly modulated by the seasonal variation of anticyclonic eddies

ocean currents at axial volcano a northeastern pacific seamount 1 axial volcano is a magmatically active seamount that straddles the juan de fuca ridge jdfr with a summit depth of 1400 m the volcano intercepts deep ocean flows at a height well above that of the linear ridge adjoining it to the north and south multiyear yearlong observations of currents at axial show that mean flow circles the seamount in an anticyclonic sense consistent with dynamical constraints with means as large as 6 6 cm s 1 spectra of currents indicate prominent tidal inertial and in some cases weather band period 3 to 7 day peaks as has been seen elsewhere along the jdfr ridge for k1 o1 and s2 tidal currents at the seamount amplitudes are several times larger than the corresponding background amplitudes and rotation around the tidal current ellipses is anticyclonic m2 tidal currents show none of the same properties energy at the inertial frequency decreases by more than an order of magnitude from 100 m above to 400 m below the volcano s summit in contrast weather band wb period energy increases tenfold over the same depth range with wb energy all but unobservable at summit depth the presence of wb oscillations makes axial unlike other seamounts where long observations have been made the current meter observations also provide a picture of seasonal trends as expected during the period summer 1996 to spring 1997 largest amounts of wb energy are found during autumn and winter in contrast wb motion at axial volcano during winter 2000 was summer like in intensity a linear baroclinic model of forced damped azimuthal mode one oscillatory flow around an idealized axisymmetric seamount shows that amplification of diurnal flow should occur principally at the seamount summit while amplification of the wb should occur as the observations show on the seamount flanks model and measured phase relationships for temperature and current time series pairs circumscribing axial support the view that azimuthal mode one oscillations are prominent over the 0 8 to 6 day range for forcing period tc the model indicates that the principal topographic resonance as indicated by kinetic energy ke amplification occurs for a tc greater than 1 and less than 2 days with only mild dependence in that range on background stratification and seamount shape additional but weaker topographic resonances can occur at longer periods in model results but as tc becomes slightly larger than the frictional timescale topographic resonances no longer appear high dissipation and thus short frictional timescales reported by others in regions of rough sloping topography make topographic resonances at axial at periods greater than a few days somewhat unlikely the relatively broad wb spectral peaks at some axial sites are consequently more likely the result of spectral peaks in forcing than of topographic resonance

turbulent mixing and exchange with interior waters on sloping boundaries abstractmicrostructure measurements along the axes of monterey and soquel submarine canyons reveal 200 300 m thick well stratified turbulent near bottom layers with average turbulent kinetic energy dissipation rates e 4 10 8 w kg 1 and eddy diffusivities k 16 10 4 m2 s 1 assuming mixing efficiency 0 2 to at least thalweg depths of 1200 m turbulent dissipation rates are an order of magnitude lower in overlying waters whereas buoyancy frequencies are only 25 higher well mixed bottom boundary layer thicknesses hn are an order of magnitude thinner than the stratified turbulent layer hn he because well stratified turbulent layers are commonly observed above slopes arguments that mixing efficiency should be reduced on sloping boundaries do not hold in cases of energetic internal wave generation or interaction with topography an advective diffusive balance is used to infer velocities and transports predicting horizontal upslope flows of 10 50 m day 1 extrapolating this estimate globa

internal tide reflection and turbulent mixing on the continental slope abstract observations of turbulence internal waves and subinertial flow were made over a steep corrugated continental slope off virginia during may june 1998 at semidiurnal frequencies a convergence of low mode onshore energy flux is approximately balanced by a divergence of high wavenumber offshore energy flux this conversion occurs in a region where the continental slope is nearly critical with respect to the semidiurnal tide it is suggested that elevated near bottom mixing k 10 3 m2 s 1 observed offshore of the supercritical continental slope arises from the reflection of a remotely generated low mode m2 internal tide based on the observed turbulent kinetic energy dissipation rate the high wavenumber internal tide decays on time scales o 1 day no evidence for internal lee wave generation by flow over the slope s corrugations or internal tide generation at the shelf break was found at this site

semidiurnal baroclinic wave momentum fluxes at kaena ridge hawaii abstractkaena ridge hawaii is a site of energetic conversion of the semidiurnal barotropic tide diffuse baroclinic wave beams emanate from the critical slope regions near the ridge crest directed upward and southward from the north flank of the ridge and upward and northward from the south flank here the momentum fluxes associated with generation at the ridge are estimated continuous vertical profiles of density and velocity from 80 to 800 m were obtained from the research platform floating instrument platform flip over the southern edge of the ridge as an aspect of the hawaii ocean mixing experiment data are used to estimate the reynolds stress eulerian buoyancy flux and the combined eliassen palm flux in the semidiurnal band an upward southward stress maximum of 0 5 10 4 m2 s 2 appears at depths of 300 500 m generally consistent with beam like behavior a strong off ridge buoyancy flux 0 3 10 4 m2 s 3 combines with large along ridge reynolds stresses to form an eliassen palm flux

the lifecycle of semidiurnal internal tides over the northern mid atlantic ridge abstractthe life cycle of semidiurnal internal tides over the mid atlantic ridge mar sector south of the azores is investigated using in situ a high resolution mooring and microstructure profiler and satellite data in combination with a theoretical model of barotropic to baroclinic tidal energy conversion the mooring analysis reveals that the internal tide horizontal energy flux is dominated by mode 1 and that energy density is more distributed among modes 1 10 most modes are compatible with an interpretation in terms of standing internal tides suggesting that they result from interactions between waves generated over the mar internal tide energy is thus concentrated above the ridge and is eventually available for local diapycnal mixing as endorsed by the elevated rates of turbulent energy dissipation e estimated from microstructure measurements a spring neap modulation of energy density on the mar is found to originate from the remote generation and radiation of strong mode 1 internal tides fr

an isopycnal view of near boundary mixing and associated flows abstract the effectiveness of mixing near a sloping boundary is reduced not just by the ratio of the stratification there to that in the interior but by the square of this ratio this result has previously been derived and interpreted by invoking the upgradient vertical buoyancy flux associated with secondary circulation as this opposes the downgradient vertical diffusive flux here it is shown that the result may be derived very simply by considering the diffusive flux across an isopycnal rather than a horizontal surface the reduction in the buoyancy flux comes from the increased isopycnal spacing and the reduced distance to the boundary derivation of the secondary circulation in the isopycnal diapycnal framework is more subtle however as it involves allowing for the curvilinear nature of the coordinates

a model of wind and buoyancy driven ocean circulation abstract a layered model of steady geostrophic ocean circulation driven by wind stress and buoyancy flux at the surface is derived potential vorticity or thickness of the two near surface layers is driven by ekman pumping and buoyancy pumping the latter is represented as a flow of mass proportional to the modified buoyancy flux across the first submerged layer interface this mass flux is modified by the advection of buoyancy in the wind driven ekman layer though diffusive diapycnal buoyancy flux across deeper layers is neglected at lowest order it is essential for the global balance of the buoyancy budget the global buoyancy balance requirement determines such parameters as the midocean outcrop latitudes of layers that outcrop in the subtropical gyre and the depths of interfaces at the eastern boundary of layers that do not these parameters control the mean thicknesses of the layers and with the diapycnal diffusivity the mean diffusive flux of buoyancy through each active layer in this way t

internal tide radiation from mendocino escarpment abstract strong semidiurnal internal tides are observed near mendocino escarpment in full depth profile time series of velocity temperature and salinity velocity and density profiles are combined to estimate the internal tide energy flux divergence of this flux demonstrates that its source is the barotropic tide interacting with the escarpment a baroclinic energy flux of 7 kw m 1 radiates from the escarpment corresponding to 3 of the 220 kw m 1 fluxing poleward in the surface tide energy and energy flux are concentrated in packets that emanate from the flanks of the ridge surmounting the escarpment and one site 90 km north of the escarpment coherent beamlike structure along semidiurnal ray paths remains identifiable until the first surface reflection beyond the first surface reflection north of the escarpment the energy flux drops by 2 kw m 1 and beams are no longer discernible turbulence as inferred from finescale parameterizations is elevated by over two orders of magnitude relative to th