seasonal mesoscale and submesoscale eddy variability along the north pacific subtropical countercurrent abstractlocated at the center of the western north pacific subtropical gyre the subtropical countercurrent stcc is not only abundant in mesoscale eddies but also exhibits prominent submesoscale eddy features output from a high resolution ogcm simulation and a gridded satellite altimetry product are analyzed to contrast the seasonal stcc variability in the mesoscale versus submesoscale ranges resolving the eddy scales of 150 km the altimetry product reveals that the stcc eddy kinetic energy and rms vorticity have a seasonal maximum in may and april respectively a weak positive vorticity skewness without seasonal dependence and an inverse forward kinetic energy cascade for wavelengths larger shorter than 250 km in contrast the submesoscale resolving ogcm simulation detects that the stcc eddy kinetic energy and rms vorticity both appear in march a large positive vorticity skewness with strong seasonality and an intense inverse kinetic energy cascade whose short wave cutoff migrates seaso

redistribution of energy available for ocean mixing by long range propagation of internal waves ocean mixing which affects pollutant dispersal marine productivity and global climate1 largely results from the breaking of internal gravity waves disturbances propagating along the ocean s internal stratification a global map of internal wave dissipation would be useful in improving climate models but would require knowledge of the sources of internal gravity waves and their propagation towards this goal i present here computations of horizontal internal wave propagation from 60 historical moorings and relate them to the source terms of internal waves as computed previously2 3 analysis of the two most energetic frequency ranges near inertial frequencies and semidiurnal tidal frequencies reveals that the fluxes in both frequency bands are of the order of 1 kw m 1 that is 15 50 of the energy input and are directed away from their respective source regions however the energy flux due to near inertial waves is stronger in winter whereas the tidal fluxes are uniform throughout the year both varieties of internal waves can thus significantly affect the space time distribution of energy available for global mixing

characterizing the transition from balanced to unbalanced motions in the southern california current author s chereskin teresa k rocha cesar b gille sarah t menemenlis dimitris passaro marcello

late neogene and quaternary evolution of the northern albemarle embayment mid atlantic continental margin usa seismic surveys in the eastern albemarle sound adjacent tributaries and the inner continental shelf define the regional geologic framework and provide insight into the sedimentary evolution of the northern north carolina coastal system lithoand chronostratigraphic data are derived from eight drill sites on the outer banks barrier islands and the mobil 1 well in eastern albemarle sound within the study area parallel bedded gently dipping miocene beds occur at 95 to n160 m below sea level m bsl and are overlain by a southward thickening pliocene unit characterized by steeply inclined southward prograding beds the lower pliocene unit consists of three seismic sequences the 55 60 m thick quaternary section unconformably overlies the pliocene unit and consists of 18 seismic sequences exhibiting numerous incised channel fill facies shallow stratigraphy b40 m bsl is dominated by complex fill patterns within the incised paleo roanoke river valley radiocarbon and amino acid racemization aar ages indicate that the valley fill is latest pleistocene to holocene in age at least six distinct valley fill units are identified in the seismic data cores in the valley fill contain a 3 6 m thick basal fluvial channel deposit that is overlain by a 15 m thick unit of interlaminated muds and sands of brackish water origin that exhibit increasing marine influence upwards organic materials within the interlaminated deposits have ages of 13 11 cal ka the interlaminated deposits within the valley are overlain by several units that comprise shallow marine sediments bay mouth and shoreface environments that consist of silty fine to medium grained sands containing open neritic foraminifera suggesting that this area lacked a fronting barrier island system and was an open embayment from 10 ka to 4 5 ka seismic data show that initial infilling of the paleo roanoke river valley occurred from the north and west during the late pleistocene and early holocene later infilling

the role of mixed layer instabilities in submesoscale turbulence upper ocean turbulence at scales smaller than the mesoscale is believed to exchange surface and thermocline waters which plays an important role in both physical and biogeochemical budgets but what energizes this submesoscale turbulence remains a topic of debate two mechanisms have been proposed mesoscale driven surface frontogenesis and baroclinic mixed layer instabilities the goal here is to understand the differences between the dynamics of these two mechanisms using a simple quasi geostrophic model the essence of mesoscale driven surface frontogenesis is captured by the well known surface quasi geostrophic model which describes the sharpening of surface buoyancy gradients and the subsequent breakup in secondary roll up instabilities we formulate a similarly archetypical eady like model of submesoscale turbulence induced by mixed layer instabilities the model captures the scale and structure of this baroclinic instability in the mixed layer a wide range of scales are energized through a turbulent inverse cascade of kinetic energy that is fuelled by the submesoscale mixed layer instability major differences to mesoscale driven surface frontogenesis are that mixed layer instabilities energize the entire depth of the mixed layer and produce larger vertical velocities the distribution of energy across scales and in the vertical produced by our simple model of mixed layer instabilities compares favourably to observations of energetic wintertime submesoscale flows suggesting that it captures the leading order balanced dynamics of these flows the dynamics described here in an oceanographic context have potential applications to other geophysical fluids with layers of different stratifications

low mode internal tides and balanced dynamics disentanglement in altimetric observations synergy with surface density observations the performance of a tentative method that disentangles the contributions of a low mode internal tide on sea level from that of the balanced mesoscale eddies is examined using an idealized high resolution numerical simulation this disentanglement is essential for proper estimation from sea level of the ocean circulation related to balanced motions the method relies on an independent observation of the sea surface water density whose variations are 1 dominated by the balanced dynamics and 2 correlate with variations of potential vorticity at depth for the chosen regime of surface intensified turbulence the surface density therefore leads via potential vorticity inversion to an estimate of the balanced contribution to sea level fluctuations the difference between instantaneous sea level presumably observed with altimetry and the balanced estimate compares moderately well with the contribution from the low mode tide application to realistic configurations remains to be tested these results aim at motivating further developments of reconstruction methods of the ocean dynamics based on potential vorticity dynamics arguments in that context they are particularly relevant for the upcoming wide swath high resolution altimetric missions swot

reconstructing upper ocean vertical velocity field from sea surface height in the presence of unbalanced motion abstractreconstructability of upper ocean vertical velocity w and vorticity fields from high resolution sea surface height ssh data is explored using the global 1 48 horizontal resolution mitg

seasonality of submesoscale flows in the ocean surface boundary layer a signature of submesoscale flows in the upper ocean is skewness in the distribution of relative vorticity expected to result for high rossby number flows such skewness has implications for mixing dissipation and stratification within the upper ocean an array of moorings deployed in the northeast atlantic for one year as part of the osmosis experiment reveals that relative vorticity is positively skewed during winter even though the scale of the rossby number is less than 0 5 furthermore this skewness is reduced to zero during spring and autumn there is also evidence of modest seasonal variations in the gradient rossby number the proposed mechanism by which relative vorticity is skewed is that the ratio of lateral to vertical buoyancy gradients as summarized by the inverse gradient richardson number restricts its range during winter but less so at other times of the year these results support recent observations and model simulations suggesting the upper ocean is host to a seasonal cycle in submesoscale turbulence

incoherent signature of internal tides on sea level in idealized numerical simulations the nonpersistent phase relationship between internal tides and astronomical forcings also known as incoherence has been identified as a major question in the context of future wide swath satellite altimetry this study addresses this issue using a novel set of numerical experiments where a plane wave low mode internal tide propagates through a turbulent mesoscale eddy field these experiments demonstrate the emergence of internal tide incoherence as the eddy turbulence is strengthened in strongly turbulent situations the internal tide signature on sea level forms complex interference patterns with large amplifications of the initial internal wave these patterns evolve more rapidly than the signature of the turbulent eddy field on sea level the implications of such idealized numerical simulations for wide swath altimetry are discussed

impact of horizontal resolution 1 12 to 1 50 on gulf stream separation penetration and variability abstractthe impact of horizontal resolution 1 12 to 1 50 6 to 1 5 km at midlatitudes on gulf stream separation penetration and variability is quantified in a series of identical north atlantic experiments the questions the authors seek to address are twofold 1 is the realism of the modeled solution increased as resolution is increased 2 how robust is the modeled mesoscale and submesoscale eddy activity as a function of grid spacing and how representative is it of interior quasigeostrophic qg or surface quasigeostrophic sqg turbulence this study shows that i the representation of gulf stream penetration and associated recirculating gyres shifts from unrealistic to realistic when the resolution is increased to 1 50 and when the nonlinear effects of the submesoscale eddies intensifies the midlatitude jet and increases its penetration eastward ii the penetration into the deep ocean drastically increases with resolution and closely resembles the observations and iii surface power spec

spatial and temporal variability of the north atlantic eddy field from two kilometric resolution ocean models ocean circulation is dominated by turbulent geostrophic eddy fields with typical scales ranging from 10 to 300 km at mesoscales 50 km the size of eddy structures varies regionally following the rossby radius of deformation the variability of the scale of smaller eddies is not well known due to the limitations in existing numerical simulations and satellite capability nevertheless it is well established that oceanic flows 50 km generally exhibit strong seasonality in this study we present a basin scale analysis of coherent structures down to 10 km in the north atlantic ocean using two submesoscale permitting ocean models a nemo based north atlantic simulation with a horizontal resolution of 1 60 natl60 and an hycom based atlantic simulation with a horizontal resolution of 1 50 hycom50 we investigate the spatial and temporal variability of the scale of eddy structures with a particular focus on eddies with scales of 10 to 100 km and examine the impact of the seasonality of submesoscale energy on the seasonality and distribution of coherent structures in the north atlantic our results show an overall good agreement between the two models in terms of surface wave number spectra and seasonal variability the key findings of the paper are that i the mean size of ocean eddies show strong seasonality ii this seasonality is associated with an increased population of submesoscale eddies 10 50 km in winter and iii the net release of available potential energy associated with mixed layer instability is responsible for the emergence of the increased population of submesoscale eddies in wintertime

scaling properties of arctic sea ice deformation in a high resolution viscous plastic sea ice model and in satellite observations sea ice models with the traditional viscous plastic vp rheology and very small horizontal grid spacing can resolve leads and deformation rates localized along linear kinematic features lkf in a 1 km pan arctic sea ice ocean simulation the small scale sea ice deformations are evaluated with a scaling analysis in relation to satellite observations of the envisat geophysical processor system egps in the central arctic a new coupled scaling analysis for data on eulerian grids is used to determine the spatial and temporal scaling and the coupling between temporal and spatial scales the spatial scaling of the modeled sea ice deformation implies multifractality it is also coupled to temporal scales and varies realistically by region and season the agreement of the spatial scaling with satellite observations challenges previous results with vp models at coarser resolution which did not reproduce the observed scaling the temporal scaling analysis shows that the vp model as configured in this 1 km simulation does not fully resolve the intermittency of sea ice deformation that is observed in satellite data

seasonality in transition scale from balanced to unbalanced motions in the world ocean abstractthe transition scale lt from balanced geostrophic motions to unbalanced wave motions including near inertial flows internal tides and inertia gravity wave continuum is explored using the output from a global 1 48 horizontal resolution massachusetts institute of technology general circulation model mitgcm simulation defined as the wavelength with equal balanced and unbalanced motion kinetic energy ke spectral density lt is detected to be geographically highly inhomogeneous it falls below 40 km in the western boundary current and antarctic circumpolar current regions increases to 40 100 km in the interior subtropical and subpolar gyres and exceeds in general 200 km in the tropical oceans with the exception of the pacific and indian sectors of the southern ocean the seasonal ke fluctuations of the surface balanced and unbalanced motions are out of phase because of the occurrence of mixed layer instability in winter and trapping of unbalanced motion ke in shallow mixed layer in summe

open ocean submesoscale motions a full seasonal cycle of mixed layer instabilities from gliders abstractthe importance of submesoscale instabilities particularly mixed layer baroclinic instability and symmetric instability on upper ocean mixing and energetics is well documented in regions of strong persistent fronts such as the kuroshio and the gulf stream less attention has been devoted to studying submesoscale flows in the open ocean far from long term mean geostrophic fronts characteristic of a large proportion of the global ocean this study presents a year long submesoscale resolving time series of near surface buoyancy gradients potential vorticity and instability characteristics collected by ocean gliders that provides insight into open ocean submesoscale dynamics over a full annual cycle the gliders continuously sampled a 225 km2 region in the subtropical northeast atlantic measuring temperature salinity and pressure along 292 short 20 km hydrographic sections glider observations show a seasonal cycle in near surface stratification throughout the fall september november

submesoscale eddy vertical covariances and dynamical constraints from high resolution numerical simulations abstractwe analyze high resolution 1 km simulations of the western pacific gulf of mexico and arabian sea to understand submesoscale eddy dynamics a mask based on the okubo weiss parameter iso

characterizing meso to submesoscale features in the south china sea abstract in this study the mesoscale and submesoscale features in the south china sea scs are characterized based on a submesoscale permitting numerical simulation mitgcm llc4320 with nominal horizontal grid spacing of 1 48 2 2 km in the scs the simulation includes tidal forcing which is particularly crucial in the scs where tides play a key role in many aspects of regional dynamics evaluation against observations demonstrates that the simulation is capable of reproducing a wide spectrum of dynamical features in the scs the simulation is then used to characterize meso to submesoscale features in the scs and the key findings are summarized as follows i the scs is rich in submesoscale features e g vortices filaments which undergo significant seasonal variations in many regions ii there is a clear dominance of positive surface relative vorticity in most regions of the scs presumably due to the centrifugal instability but large negative also emerges in areas with strong flow topography interactions iii the vertical motions in the upper scs are dominated by tidal modulations with strong vertical velocities up to 0 01 m s 1 about an order of magnitude larger than those due to the quasi balanced sub inertial motions and iv both the wintertime and summertime horizontal wavenumber spectra of kinetic energy scale roughly as k 2 with k being the horizontal wavenumber for wavelengths below 100 km in addition four key regions are highlighted with distinctive characteristics of submesoscale turbulence including the northern scs luzon strait the scs western boundary current region in winter and east of vietnam in summer a number of model deficiencies are noted along with suggestions for improving model accuracy in order to better characterize the local submesoscale features as well as the underlying dynamics

pacific abyssal transport and mixing through the samoan passage versus around the manihiki plateau abstractthe main source feeding the abyssal circulation of the north pacific is the deep northward flow of 5 6 sverdrups sv 1 sv 106 m3 s 1 through the samoan passage a recent field campaign

observations of submesoscale variability and frontal subduction within the mesoscale eddy field of the tasman sea abstractsubmesoscale lenses of water with anomalous hydrographic properties have previously been observed in the east australian current eac system embedded within the thermocline of mesoscale a

subtropical catastrophe significant loss of low mode tidal energy at 28 9 1 an idealized numerical study of a northward propagating internal tide reveals a dramatic loss of energy to small scale subharmonic instabilities near 28 9 n inspired by observations of the internal tide radiating northward from the hawaiian ridge a three dimensional numerical model is initialized with a northward baroclinic tidal flux of approximately 1 7 kw m after an initial spinup period energy is quickly transferred from the baroclinic tide to subharmonic motions with half the horizontal tidal wavenumber and small vertical scales through nonlinear advection of horizontal tidal velocity gradients potential oceanic implications are twofold first once a steady state has been reached the instability acts as a partial filter of northward tidal flux between 27 5 and 29 5 n in rough agreement with some altimetric tidal observations second elevated shear of the subharmonic motions suggests the potential for elevated near surface dissipation rates near the critical latitude that may be important for upper ocean mixing

preconditioning of antarctic maximum sea ice extent by upper ocean stratification on a seasonal timescale this study uses an observationally constrained and dynamically consistent ocean and sea ice state estimate the author presents a remarkable agreement between the location of the edge of antarctic maximum sea ice extent reached in september and the narrow transition band for the upper ocean 0 100 m depths stratification as early as april to june to the south of this edge the upper ocean has high stratification which forbids convective fluxes to cross through consequently the ocean heat loss to the atmosphere is an efficient way to cool the surface ocean to the freezing point during april to september to the north the upper ocean has low stratification such that the ocean heat loss to the atmosphere is not efficient to cool the upper ocean the upper ocean is instead cooled mainly through mixing with the colder inflow carried by northward ekman transport but cannot reach the freezing point due to the nature of mixing therefore upper ocean stratification dominated by salinity here provides an important constraint on the northward expansion of antarctic sea ice to its maximum

some expectations for submesoscale sea surface height variance spectra abstractin anticipation of the surface water and ocean topography swot wide swath altimetry mission this study reviews expectations for sea surface height ssh variance spectra at wavelengths o

spectral decomposition of internal gravity wave sea surface height in global models two global ocean models ranging in horizontal resolution from 1 12 to 1 48 are used to study the space and time scales of sea surface height ssh signals associated with internal gravity waves igws frequency horizontal wavenumber ssh spectral densities are computed over seven regions of the world ocean from three simulations of the hybrid coordinate ocean model hycom and two simulations of the massachusetts institute of technology general circulation model mitgcm high wavenumber high frequency ssh variance follows the predicted igw linear dispersion curves the realism of high frequency motions 0 87cpd in the models is tested through comparison of the frequency spectral density of dynamic height variance computed from the highest resolution runs of each model 1 25 hycom and 1 48 mitgcm with dynamic height variance frequency spectral density computed from 9 in situ profiling instruments these high frequency motions are of particular interest because of their contributions to the small scale ssh variability that will be observed on a global scale in the upcoming surface water and ocean topography swot satellite altimetry mission the variance at supertidal frequencies can be comparable to the tidal and low frequency variance for high wavenumbers length scales smaller than 50km especially in the higher resolution simulations in the highest resolution simulations the high frequency variance can be greater than the low frequency variance at these scales

inferring dynamics from the wavenumber spectra of an eddying global ocean model with embedded tides 1 the slopes of the wavenumber spectra of sea surface height ssh and kinetic energy ke have been used to infer interior or surface quasi geostrophic qg or sqg dynamics of the ocean however inspection of spectral slopes for altimeter ssh in the mesoscale band of 70 to 250 km shows much flatter slopes than the qg or sqg predictions over most of the ocean comparison of altimeter wavenumber spectra with spectra from an eddy resolving global ocean circulation model the hybrid coordinate ocean model hycom at 1 12 5 equatorial resolution which has embedded tides suggests that the flatter slopes of the altimeter ssh may arise from three possible sources 1 presence of strong internal tides 2 shift of the inertial sub range to smaller scales and 3 altimeter noise artificially adding noise to the model tends to flatten the spectra for low ke regions near internal tide generating regions spectral slopes in the presence of internal waves are much flatter than qg or sqg predictions separating the variability into high and low frequency around periods of 2 days then a different pattern emerges with a flat high frequency wavenumber spectrum and a steeper low frequency wavenumber spectrum for low mesoscale ke the inertial sub range defined by the nearly flat enstrophy band moves to smaller scales and the mesoscale band of 70 to 250 km no longer represents the inertial sub range the model wavenumber spectra are consistent with qg and sqg theory when internal waves and inertial sub range shifts are taken into consideration

do split and displacement sudden stratospheric warmings have different annular mode signatures sudden stratospheric warmings ssws contribute to intraseasonal tropospheric forecasting skill due to their surface impacts recent studies suggest these impacts depend upon whether the polar vortex splits or is displaced during the ssw we analyse the annular mode signatures of ssws in a 1000 year ipsl cm5a lr simulation although small differences in the mean surface northern annular mode nam index following splits and displacements are found the sign is not consistent for two independent ssw algorithms and over 50 events are required to distinguish the responses we use the winter time correlation between extratropical lower stratospheric wind anomalies and the surface nam index as a metric for two way stratosphere troposphere coupling and find that the differences between splits and displacements and between classification methodologies can be simply understood in terms of their mean stratospheric wind anomalies predictability studies should therefore focus on understanding the factors that determine the persistence of these anomalies following ssws

diagnosing ocean wave turbulence interactions from space numerical studies indicate that interactions between ocean internal gravity waves especially those textless100 km and geostrophic or balanced motions associated with mesoscale eddy turbulence involving eddies of 100 300 km impact the ocean s kinetic energy budget and therefore its circulation results from these studies have never been confirmed by observations in regional or basin scale domains here we show that internal gravity waves have a spectral signature on sea surface height during summer that significantly differs from that of balanced motions these spectral differences lead us to propose a new dynamical framework that quantifies the interactions between internal gravity waves and balanced motions in physical space from sea surface height snapshots and in particular the energy exchanges between them our results using this dynamical framework highlight the strong potential of future satellite altimeter missions to make critical advances in assessing the ocean s kinetic energy budget from observations in large domains