detailed rupture imaging of the 25 april 2015 nepal earthquake using teleseismic p waves we analyze the rupture process of the 25 april 2015 nepal earthquake with globally recorded teleseismic p waves the rupture propagated east southeast from the hypocenter for about 160 km with a duration of 55 s backprojection of both high frequency hf 0 2 to 3 hz and low frequency lf 0 05 to 0 2 hz p waves suggest a multistage rupture process from the low frequency images we resolve an initial slow downdip northward rupture near the nucleation area for the first 20 s stage 1 followed by two faster updip ruptures 20 to 40 s for stage 2 and 40 to 55 s for stage 3 which released most of the radiated energy northeast of kathmandu the centroid rupture power from lf backprojection agrees well with the global centroid moment tensor solution the spatial resolution of the backprojection images is validated by applying similar analysis to nearby aftershocks the overall rupture pattern agrees well with the aftershock distribution a multiple asperity model could explain the observed multistage rupture and aftershock distribution

scales and dynamics of submesoscale coherent vortices formed by deep convection in the northwestern mediterranean sea since 2010 an intense effort in the collection of in situ observations has been carried out in the northwestern mediterranean sea thanks to gliders profiling floats regular cruises and mooring lines this integrated observing system enabled a year to year monitoring of the deep waters formation that occurred in the gulf of lions area during four consecutive winters 2010 2013 vortical structures remnant of wintertime deep vertical mixing events were regularly sampled by the different observing platforms these are submesoscale coherent vortices scvs characterized by a small radius 5 8 km strong depth intensified orbital velocities 10 20 cm s 1 with often a weak surface signature high rossby 0 5 and burger numbers o 0 5 1 anticyclones transport convected waters resulting from intermediate 300 m to deep 2000 m vertical mixing cyclones are characterized by a 500 1000 m thick layer of weakly stratified deep waters or bottom waters that cascaded from the shelf of the gulf of lions in 2012 extending down to the bottom of the ocean at 2500 m the formation of cyclonic eddies seems to be favored by bottom reaching convection occurring during the study period or cascading events reaching the abyssal plain we confirm the prominent role of anticyclonic scvs and shed light on the important role of cyclonic scvs in the spreading of a significant amount 30 of the newly formed deep waters away from the winter mixing areas since they can survive until the following winter they can potentially have a great impact on the mixed layer deepening through a local preconditioning effect

a heton model of the spreading phase of open ocean deep convection abstract a point vortex heton model of the lateral dispersion of cold water formed in open ocean deep convection is developed and studied as an idealized representation of the sinking and spreading phase of open ocean deep convection the overturning and geostrophic adjustment of dense fluid on and below the radius of deformation scale formed by cooling on the large scale are parameterized in the model by introducing paired discrete point vortices hetons of cyclonic sense in the surface layer anticyclonic below driving a cold baroclinic vortex the convection site is imagined to be made up of many such baroclinic vortices each with a vertically homogeneous core carrying cold convectively tainted waters the point vortices are introduced at a rate that depends on the large scale cooling and the intensity assumed for each vortex the interaction of many cold baroclinic vortices making up a cloud is studied using point vortex green s function techniques the current solenoids of the individual ele

the subthermocline lens d1 part i description of water properties and velocity profiles abstract one remarkable result of the local dynamics experiment in polymode is the discovery of a large number of small energetic eddies using ctd data sofar float tracks and profiles of absolute velocity we describe one of these features the subthermocline eddy d1 the feature has an advective time scale of 1 day and its primary mode of movement is advection by the ambient flow field the eddy is resolved into a coordinate system moving with the velocity of the ambient flow which ranges from 11 16 cm s 1 its phase speed is less than 2 cm s 1 the eddy is a lens centered at 1500 db velocity profiles show the lens has no detectable signal in and above the main thermocline or below about 3000 db its subsurface velocity maximum is 28 6 cm s 1 at 1500 db 15 km from the center the radial variation of the azimuthal velocity is gaussian inside the velocity maximum but decays as e br beyond there is little evidence of the eddy beyond a radius of 25 km inside the velocity maximum the eddy is characte

restratification after deep convection abstract an important yet poorly understood aspect of the water mass transformation process in the ocean is the manner in which the convected fluid once formed is accommodated and drawn into the general circulation following violent mixing in the open ocean that creates a deep homogenous body of fluid restratification of the surface 500 m layer is observed to occur rapidly sealing over the convection patch recent hydrographic casts and tomography inversions in the gulf of lions by send et al for example show that very quickly within a week or so of the cessation of cooling a stratified near surface layer develops on top of the mixed patch this restratification occurs much more rapidly than can be accounted for by air sea fluxes by analytical and numerical study the authors argue that advection by geostrophic eddies spawned by the baroclinic instability of the mixed patch is likely to be a principal mechanism by which restratification occurs a restratification timescale restrat 56r

a simulation of thermohaline effects of a great salinity anomaly abstract model simulations of an idealistic great salinity anomaly gsa demonstrate that variability in the sea ice export from the arctic when concentrated to short pulses can have a large influence on the meridional heat transport and can lead to an altered overturning state one single freshwater disturbance resulting from excess ice export as in 1968 can disrupt the deep mixing process the critical condition for a large oceanic response is defined by the intensity duration and timing of the ice pulse in particular as it exits through the denmark strait a recovery from this event takes several years for advection and diffusion to remove the salinity anomaly concurrently the influence of the gsa propagates to the subtropics via the boundary currents and baroclinic adjustment as a result of this adjustment there are large up to 20 changes in the strength of the overturning cell and in the meridional heat transport in the subtropics and subpolar areas simulations show a temperature sali

on the characteristics of circumpolar deep water intrusions to the west antarctic peninsula continental shelf 1 hydrographic and current velocity observations collected from march 2001 to february 2003 on the west antarctic peninsula shelf as part of the southern ocean global ecosystems dynamics program are used to characterize intrusions of upper circumpolar deep water ucdw and lower circumpolar deep water lcdw onto the shelf and marguerite bay ucdw is found on the middle and outer shelf along marguerite trough which connects the shelf break to marguerite bay and at another location farther south ucdw intrudes in the form of frequent four per month and small horizontal scales 4 km warm eddy like structures with maximum vertical scales of a few hundred meters however no evidence of ucdw intrusions was found in marguerite bay lcdw was found in several deep depressions connected to the shelf break including marguerite trough forming a tongue of relatively dense water 95 m thick on average that reaches into marguerite bay through marguerite trough a steady advective diffusive balance for the lcdw intrusion is used to make an estimation of the average upwelling rate and diffusivity in the deep layer within marguerite trough which suggest the lcdw layer is renewed approximately every six weeks

distribution and circulation of labrador sea water abstract labrador sea water is the final product of the cyclonic circulation of subpolar mode water in the open northern north atlantic mccartney and talley 1982 the temperature and salinity of the convectively formed subpolar mode water decrease from 14 7 c 36 08 to 3 4 c 34 88 on account of the cumulative effects of excess precipitation and cooling the coldest mode water is labrador sea water which spreads at mid depths and is found throughout the north atlantic ocean north of 40 n and along its western boundary to 18 n a vertical minimum in potential vorticity is used as the primary tracer for labrador sea water labrador sea water is advected in three main directions out of the labrador sea 1 northeastward into the irminger sea 2 southeastward across the atlantic beneath the north atlantic current and 3 southward past newfoundland with the labrador current and thence westward into the slope water region crossing under the gulf stream off cape hatteras the labrador sea water core is

influences of time dependent precipitation on water mass transformation heat fluxes and deep convection in marginal seas abstractinfluences of time dependent precipitation on water mass transformation and heat budgets in an idealized marginal sea are examined using theoretical and numerical models the equations proposed by spall in 2012 are extended to cases with time dependent precipitation whose form is either a step function or a sinusoidal function the theory predicts the differences in temperature and salinity between the convective water and the boundary current as well as the magnitudes of heat fluxes into the marginal sea and across the sea surface moreover the theory reveals that there are three inherent time scales relaxation time scales for temperature and salinity and a precipitation time scale the relaxation time scales are determined by a steady solution of the theoretical model with steady precipitation the relaxation time scale for temperature is always smaller than that for salinity as a result of not only the difference in the form of fluxes at the surface but also the variation in the eddy transpor

the structure dynamics and origin of a small scale lens of water in the western north atlantic thermocline abstract a small scale isolated anticyclonically rotating lens of water was observed in the western north atlantic thermocline during the polymode local dynamics experiment using a combination of sofar float hydrographic nutrient and moored current and temperature data we deduce that the lens was about 20 km across with a thickness not greater than 300 m centered on 750 m that its shape was not dissimilar to that of a vertical radial gaussian eddy and that at its center the lens had strong anomalies of salinity dissolved oxygen nitrate and vortex stretching the water mass properties within the eddy are not inconsistent with an origin for the feature near 15 n 54 w several thousand kilometers from where it was observed in the western north atlantic although an unambiguous origin cannot be discerned from the data if such features are not uncommon they may be an important mechanism for large scale mixing of water properties in the ocean

a meddy off cape st vincent part i description abstract a meddy an eddy formed from mediterranean source water was surveyed in detail with two types of expendable profilers and a ctd instrument the muddy comprised two distinct vertically aligned tenses with a combined thickness of 650 m both lenses were stratification minima the upper lens was warmer fresher 12 25 c 36 5 psu and more circular the lower lens was cooler more saline 12 1 c 36 65 psu and more elliptical oriented alone a northeast by southwest line the upper lens homogeneous out to a radius of 6 km had a radius of maximum velocity of 9 km its relative vorticity was 0 85 f and its ertel potential vorticity 4 10 12 m s 1 was 17 times below ambient levels due to the combined effects of negative relative vorticity and vortex stretching the meddy contained more kinetic energy than available potential energy energy burger number of 2 5 compared with historical meddies it had a larger burger number and a more negative vorticity rossby number

coupled sea ice ocean state estimation in the labrador sea and baffin bay sea ice variability in the labrador sea is of climatic interest because of its relationship to deep convection mode water formation and the north atlantic atmospheric circulation historically quantifying the relationship between sea ice and ocean variability has been difficultbecause ofin situ observation paucity and technical challenges associated with synthesizing observations with numerical models here the relationship between ice and ocean variability is explored by analyzing new estimates of the ocean ice state in the northwest north atlantic the estimates are syntheses of in situ and satellite hydrographic and ice data with a regional 1 38 coupled ocean sea ice model the synthesis of sea ice data is achieved with an improved adjoint of a thermodynamicicemodel modelanddataaremadeconsistent inaleastsquaressense byiterativelyadjustingcontrol variables including ocean initial and lateral boundary conditions and the atmospheric state to minimize an uncertainty weighted model data misfit cost function the utility of the state estimate is demonstrated in an analysis of energy and buoyancy budgets in the marginal ice zone miz in mid march the system achieves a state of quasi equilibrium during which net ice growth and melt approaches zero newly formed ice diverges from coastal areas and converges via wind and ocean forcing in the miz the convergence of ice mass in the miz is ablated primarily by turbulent ocean ice enthalpy fluxes the primary source of the enthalpy required for sustained miz ice ablation is the sensible heat reservoir of the subtropical origin subsurface waters

dynamical characterization of a low oxygen submesoscale coherent vortex in the eastern north atlantic ocean a submesoscale coherent vortex scv with a low oxygen core is characterized from underwater glider and mooring observations from the eastern tropical north atlantic north of the cape verde islands the eddy crossed the mooring with its center and a 1 month time series of the scv s hydrographic and upper 100 m currents structure was obtained about 45 days after and 100 km west the scv frontal zone was surveyed in high temporal and spatial resolution using an underwater glider satellite altimetry showed the scv was formed about 7 months before at the mauritanian coast the scv was located at 80 100 m depth its diameter was 100 km and its maximum swirl velocity 0 4 m s 1 a burger number of 0 2 and a vortex rossby number 0 15 indicate a flat lens in geostrophic balance mooring and glider data show in general comparable dynamical and thermohaline structures the glider in high spatial resolution the mooring in high temporal resolution surface maps of chlorophyll concentration suggest high productivity inside and around the scv the low potential vorticity pv core of the scv is surrounded by filamentary structures sloping down at different angles from the mixed layer base and with typical width of 10 20 km and a vertical extent of 50 100 m

localization of deep ocean convection by a mesoscale eddy abstract observations of open ocean deep convection indicate that it is a highly localized phenomenon occurring over areas of tens of kilometers in diameter the cause of this localization has been ascribed to preconditioning the local weakening of the stable density stratification associated with upwardly domed isopycnal surfaces in a surface intensified cyclonic circulation however most numerical and laboratory studies of localized convection have prescribed the localization artificially by confining the surface buoyancy loss to a circular disk in contrast in the numerical simulations described here deep convection forced by horizontally uniform buoyancy loss is localized within a region of initially weaker stratification than its surroundings the preconditioned region is associated with a cold core cyclonic eddy in geostrophic and cyclostrophic balance as in previous studies of disk shaped cooling the localized convection region undergoes baroclinic instability at late times causing the br

the formation of labrador sea water part i large scale processes abstract data obtained in the western labrador sea during march 1976 by hudson are analysed to show that new labrador sea water was being formed at this time on the basis of hydrographic and moored current meter data it is hypothesized that a 200 km scale cyclonic gyre forms in winter in the western labrador sea and that this gyre retains the developing deep mixed layers in this general area long enough for the transformation to labrador sea water to take place using a model it is demonstrated that water columns found along the western boundary of the labrador sea can be modified by cooling evaporation and mixing to form deep mixed layers with the properties of labrador sea water approximately 105 km3 of new labrador sea water was formed in 1976 an estimate that is consistent with earlier estimates of mean annual production rates this water 2 9 c 34 84 is some 0 6 c cooler and 0 06 fresher than that defined by lazier 1973 from his data collected in 1966 the variation of labrador sea water

pressures on a rubble mound breakwater crown wall for tsunami impact abstract rubble mound breakwaters are commonly constructed with a parapet or crown wall at the crest the design of these superstructures depends on the expected storm wave load history throughout the service life cycle in tsunami prone areas this design must include tsunami actions since their loads can definitely exceed those of storm waves however tsunami loads are rarely accounted for this study aimed at incorporating tsunami actions in the design of crown walls of rubble mound breakwaters for the first time within this scope laboratory experiments on a scaled model of a typical mediterranean rubble mound breakwater typology under tsunami actions were conducted this paper is the continuation of our previous paper aniel quiroga et al 2018 1 in which experiments were presented and a stability analysis of the armor units was conducted this research paper presents the second part of the analysis focused on understanding the pressures that crown walls of rubble mound breakwaters must support due to tsunami like actions these pressures were measured and analyzed providing the horizontal and uplift pressure time series and laws the magnitude and timing of the maximum pressure peaks were identified the maximum horizontal pressure is caused by the first impact of the tsunami by contrast the maximum uplift pressure is prompted by a pressure wave generated by the overtopped water falling into the leeside this pressure wave penetrates the structure from the rear slope as a result of this analysis pressures were characterized allowing the presentation of a new complete methodology that provides for the tested structure the design procedure of the crown wall under tsunami actions a new formulation to calculate the run up of solitary waves on the tested rubble mound breakwater slope is presented here

seasonal and interannual variations of irminger ring formation and boundary interior heat exchange in flame abstractthe contribution of warm core anticyclones shed by the irminger current off west greenland known as irminger rings to the restratification of the upper layers of the labrador sea is investigated in the 1 12 family of linked atlantic models experiment flame model the model output covering the 1990 2004 period shows strong similarities to observations of the irminger current as well as ring observations at a mooring located offshore of the eddy formation region in 2007 09 an analysis of fluxes in the model shows that while the majority of heat exchange with the interior indeed occurs at the site of the irminger current instability the contribution of the coherent irminger rings is modest 18 heat is provided to the convective region mainly through noncoherent anomalies and enhanced local mixing by the rings facilitating further exchange between the boundary and interior the time variability of the eddy kinetic energy and the boundary to interior heat flux in the model are strongly corr

the formation of labrador sea water part ii mesoscale and smaller scale processes abstract in a previous paper clarke and gascard argued that the formation of labrador sea water was taking place in a cyclonic gyre set up each winter in the western labrador sea within the gyre and at its boundaries a number of different scales of organization are believed to be important in the formation processes the longest of these scales is the mesoscale 50 km which appears to be related to topographic rossby waves generated in the labrador current and propagating offshore the next smaller scale is an eddy scale 20 km believed to arise because the mesoscale is baroclinically unstable as shown by applying a two layer model of tang this instability is believed to promote mixing by generating frontal structures and vertical motions along them thus bringing subsurface t s maxima nearer the surface then within the mesoscale and eddy scale structures intense vertical convective cells take place at scales which are probably of the order of 1 km in three dimensions these events are short liv

structure of two hydrothermal megaplumes the dynamic signatures of two megaplumes above the juan de fuca ridge are analyzed the chemical properties of these two lenslike masses of water were described by baker et al 1989 and clearly indicate that they were generated by massive and rapid ventings of hot hydrothermal fluid from the ridge both are nearly circular with radii of about 6 5 km the isopycnals bow upward around these cores of anomalous water leading to an anticyclonic circulation a cyclogeostrophic balance gives maximum currents at the edge of the core of 0 11 m s 1 for the first megaplume mp1 and 0 07 m s 1 for the second megaphone mp2 currents extend beyond the core to a radius of 12 15 km the centers of the cores are in nearly solid body rotation with relative voracities of 0 5 mp1 and 0 3 mp2 and potential vorticity anomalies expressed in units of equivalent relative vorticity of 0 8 mp1 and 0 6 mp2 where is the coriolis frequency the aspect ratio of each megaplume gives a burger number of 0 22 in terms of these nondimensional numbers the megaplumes are very similar to eddies of mediterranean water found in the eastern atlantic meddies despite their very different origin

observations of water mass transformation and eddies in the lofoten basin of the nordic seas abstractthe lofoten basin of the nordic seas is recognized as a crucial component of the meridional overturning circulation in the north atlantic because of the large horizontal extent of atlantic water and winter surface buoyancy loss in this study hydrographic and current measurements collected from a mooring deployed in the lofoten basin from july 2010 to september 2012 are used to describe water mass transformation and the mesoscale eddy field winter mixed layer depths mlds are observed to reach approximately 400 m with larger mlds and denser properties resulting from the colder 2010 winter a heat budget of the upper water column requires lateral input which balances the net annual heat loss of 80 w m 2 the lateral flux is a result of mesoscale eddies which dominate the velocity variability eddy velocities are enhanced in the upper 1000 m with a barotropic component that reaches the bottom detailed examination of two eddies from april and august 2012 highlights the variability of the e

reconstructed mediterranean salt lens trajectories the existence of energetic anticyclonic mid depth vortices of mediterranean water meddies questions the validity of a conventional advective diffusive balance in the eastern atlantic subtropical gyre a mesoscale experiment in the azores madeira region reveals a link of these meddies to large scale subsurface meanders for the first time it is shown that meddies may have strong surface vorticity indicative of a generation process involving the azores current a deep reaching near surface jet

coherent eddies in the labrador sea observed from a mooring abstract during june november 1994 a mooring in the central labrador sea near the former ocean weather station bravo recorded a half dozen anomalous events that prove to be two different types of coherent eddies comparisons with simple analytical models are used to classify these events as coherent eddies on the basis of their velocity signatures the first clear examples of long lived convectively generated eddies are reported these four small radius 5 15 km eddies are exclusively anticyclonic with cold fresh middepth potential temperature and salinity s cores surrounded by azimuthal currents of 15 cm s 1 their s properties identify them unambiguously as the products of wintertime deep convection in the interior labrador sea compared with eddies in other regions these anticyclones are unusual for their strong surface expressions and composite s cores two warm cyclones are also seen these are larger radius 15 km than the anticyclones and about as energetic currents 15 cm s 1

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

comparisons of localized convection due to localized forcing and to preconditioning although observations indicate that localization of deep convection results from oceanic preconditioning and only to a lesser extent from the gradients in the atmospheric forcing most laboratory and numerical simulations of oceanic deep convection localize convection via the buoyancy forcing it is as yet unclear to what extent the localized forcing simplification is representative of realistic preconditioned convection and whether conclusions drawn from analyzing the former scenario can be applied to the latter comparison between these two localized convection scenarios is the focus of this study the analysis is conducted using a high resolution nonhydrostatic numerical model that assumes no variations in the latitudinal direction although this model cannot represent baroclinic instability it represents well the violent mixing phase of chimney formation that precedes baroclinic instability because of the inherently different initial and boundary conditions there is no single comparison to be made between the two scenarios all of the comparisons however show that a localized forcing tends to enhance the frontal structures at the edge of the convected water mass the authors explain these results by means of some simple analytical calculations that indicate that convection as a result of a localized forcing induces a continuous increase in the horizontal density gradient while convection in a surface intensified cyclonic gyre results in a decrease in the horizontal gradient the authors conclude that the two scenarios are not equivalent and discuss how some of the conclusions valid for localized forcing do not necessarily apply to the preconditioned scenario in particular the equilibrium state observed in localized forcing simulations in which the lateral fluxes due to the baroclinic eddies balance the surface buoyancy loss may not have an analog for the case of preconditioned convection

north atlantic surface circulation during the 1990 s observed with satellite tracked drifters a new compilation of lagrangian velocity observations describes the state of the north atlantic surface circulation during the 1990s gridded fields of velocity and eddy kinetic energy eke are constructed from trajectories of more than 1500 15 m drogued satellite tracked surface drifters in service between january 1990 and december 1999 this time period overlaps a coordinated field study of circulation and variability in the north atlantic completed between 1996 2000 as part of the world ocean circulation experiment we describe the construction of a self consistent drifter climatology present decadal mean quasi eulerian velocity and eke fields computed on a 1 grid and compare these results with contemporary satellite measurements detailed discussion of the inferred surface circulation is focused on three regions 1 the gulf stream and north atlantic current 2 the labrador sea and subpolar gyre and 3 the caribbean sea the swiftest drifter motions were found in the equatorial region and along the tropical subtropical and subpolar western boundaries the maximum instantaneous speed determined from a single quality controlled and filtered drifter observation was 273 cm s 1 in the gulf stream southeast of cape cod the highest eke value in the north atlantic 2790 cm2 s 2 was found in the gulf stream just downstream of the new england seamounts over most of the atlantic basin drifter derived eke values were found to be o 100 cm2 s 2 higher than corresponding values derived from satellite altimetry in the labrador sea a region of sharply elevated eke appears to be geographically related to the localized ejection of drifters and by extension mass and kinetic energy from the energetic west greenland current between 60 and 62 n when compared to drifter measurements made in the late 1970s our results suggest but do not statistically confirm an enhancement and slight northward shift of the zonal gulf stream extension such a shift is consistent in sign with expectations based on observed interdecadal variations in wind stress and subtropical gyre potential energy associated with the north atlantic oscillation

can meddies be detected by satellite altimetry geosat exact repeat mission altimeter data have been used to estimate the sea surface height anomaly relative to a 2 year mean reference surface in the eastern north atlantic ocean horizontal maps of the sea surface height anomaly for various periods were constructed by means of an objective analysis procedure the mean sea level was approximated by the dynamic topography from climatological hydrographic data results were compared to the dynamic topography calculated from hydrographic ground truth data sampled during march 1988 on an eddy resolving station network in the iberian basin despite the low signal to noise ratio of the altimeter data in this part of the ocean the agreement of the altimeter signal with hydrographic measurements is found to be significant individual cyclonic and anticyclonic eddies in the mediterranean outflow are identified in the altimetric maps the information visible in the sea surface height is significantly correlated with the dynamic topography of the layer 500 3000 dbar containing the core of the mediterranean outflow and maximum velocities of the baroclinic eddies the successive development of the identified eddies as studied from a sequence of sea surface height maps indicates a slight westward drift of the most pronounced feature with approximately 1 9 cm s propagation velocity the inferred path of that feature is consistent with additional information from moored current meter data

observations of the labrador sea eddy field this paper is an observational study of small scale coherent eddies in the labrador sea a region of dense water formation thought to be of considerable importance to the north atlantic overturning circulation numerical studies of deep convection emphasize coherent eddies as a mechanism for the lateral transport of heat yet their small size has hindered observational progress a large part of this paper is therefore devoted to developing new methods for identifying and describing coherent eddies in two observational platforms current meter moorings and satellite altimetry details of the current and water mass structure of individual eddy events as they are swept past by an advecting flow can then be extracted from the mooring data a transition is seen during mid 1997 with long lived boundary current eddies dominating the central labrador sea year round after this time and convectively formed eddies similar to those seen in deep convection modeling studies apparent prior to this time the topex poseidon altimeter covers the labrador sea with a loose net of observations through which coherent eddies can seem to appear and disappear by concentrating on locating and describing anomalous events in individual altimeter tracks a portrait of the spatial and temporal variability of the underlying eddy field can be constructed the altimeter results reveal an annual pulsation of energy and of coherent eddies originating during the late fall at a particular location in the boundary current pinpointing the time and place of the boundary current type eddy formation the interannual variability seen at the mooring is reproduced but the mooring site is found to be within a localized region of greatly enhanced eddy activity notably lacking in both the annual cycle and interannual variability is a clear relationship between the eddies or eddy energy and the intensity of wintertime cooling these eddy observations as well as hydrographic evidence suggest an active role for boundary current dynamics in shaping the energetics and water mass properties of the interior region

seasonal to interannual variability of the eddy field in the labrador sea from satellite altimetry sea level anomalies measured by the altimeters aboard the topex poseidon and ers satellites for the periods 1993 2001 and 1997 2001 respectively are used to investigate the eddy field in the subpolar north atlantic and in the labrador sea a quadratic correction of the obtained eddy kinetic energy eke with respect to significant wave height is applied that led to an increased correlation between moored and altimetric eke in the central labrador sea the mean eke field shows higher levels associated with the main currents and a strong seasonality in the labrador sea the annual cycle of the eke shows a propagation of west greenland current wgc eke into the central labrador sea with a mean southward propagation speed of about 3 cm s 1 while the eke maximum in the labrador current is well separated from the interior by local eke minima the interannual variability of the eke in the labrador sea shows distinct regional differences in the wgc region strong early winter maxima are found during 1993 and 1997 1999 in the central labrador sea maxima are found during march april 1993 1995 and 1997 variations in the annual cycle of the wgc eke are observed while there is a weak annual cycle in the wgc region during 1994 1996 with more continuous eke generation during 1997 2000 there is a strong seasonal cycle with maximum eke during january and particularly low eke during summer the propagation of wgc eke into the central labrador sea is enhanced during 1997 2000 leading to a long persistence of eke in the central labrador sea during 1993 1995 and 1997 the central labrador sea eke almost instantaneously increased during march april followed in the earlier years by a relatively fast destruction of the winterly generated eke

observations of open ocean deep convection in the northwestern mediterranean sea seasonal and interannual variability of mixing and deep water masses for the 2007 2013 period we present here a unique oceanographic and meteorological data set focus on the deep convection processes our results are essentially based on in situ data mooring research vessel glider and profiling float collected from a multiplatform and integrated monitoring system moose mediterranean ocean observing system on environment which monitored continuously the northwestern mediterranean sea since 2007 and in particular high frequency potential temperature salinity and current measurements from the mooring lion located within the convection region from 2009 to 2013 the mixed layer depth reaches the seabed at a depth of 2330m in february then the violent vertical mixing of the whole water column lasts between 9 and 12 days setting up the characteristics of the newly formed deep water each deep convection winter formed a new warmer and saltier vintage of deep water these sudden inputs of salt and heat in the deep ocean are responsible for trends in salinity 3 3 0 2 10 3 yr and potential temperature 3 2 0 5 10 3 c yr observed from 2009 to 2013 for the 600 2300 m layer for the first time the overlapping of the three phases of deep convection can be observed with secondary vertical mixing events 2 4 days after the beginning of the restratification phase and the restratification spreading phase still active at the beginning of the following deep convection event

large lenses of highly saline mediterranean water isolated compact anticyclonic eddies or salt lenses were found in the canary basin hydrographic surveys of three such lenses show large anomalies of salinity and temperature 0 8 2 5 c they are centered at 1100 m have a vertical extent of up to 900 m and radii of 50 km current meter records indicate anticyclonic velocities up to 29 cm s 1 fine structure with vertical scales of 20 m and less possibly due to intrusive decay appears at the outer edges of the lenses whereas the centers are free of such structure the probability of finding a salt lens at any station in the canary basin is fairly high 0 08

on mapping the diapycnal water mass transformation of the upper north atlantic ocean abstractdiapycnal water mass transformation is the essence behind the atlantic meridional overturning circulation amoc and the associated heat freshwater transports existing studies have mostly

evolution of a mediterranean salt lens scalar properties abstract the evolution of a mediterranean salt lens meddy over a two year period is examined several nondimensional numbers can be used to describe the overall decay in the structure of the moddy two rossby numbers one using the central relative vorticity and another using the radius and velocity of the azimuthal velocity maximum did not change over the two year period however the burger number n2h2 f2l2 increased as the meddy decayed another burger number the ratio of total kinetic energy to total available potential energy decreased from 1 1 to 0 6 over a one year period the rates at which the meddy lost salt and heat are consistent with estimates of horizontal fluxes by intrusions a horizontal diffusivity of o 5 m2 s 1 is needed if this flux by intrusions is parameterized by an eddy coefficient simple models of the evolution of an isolated eddy by horizontal and vertical mixing of mass and momentum are examined these simple attempts to explain the evolution of the meddy suggest more c

long lived vortices as a mode of deep ventilation in the greenland sea the greenland sea is one of a few sites in the world ocean where convection to great depths occurs1 2 3 4 a process that forms some of the densest waters in the ocean but the role of deep convective eddies which result from surface cooling and mixing across density surfaces followed by geostrophic adjustment5 has not been fully taken into account in the description of the initiation and growth of convection6 here we present tracer float and hydrographic observations of long lived 1 year and compact 5 km core diameter vortices that reach down to depths of 2 km the eddies form in winter near the rim of the greenland sea central gyre and rotate clockwise with periods of a few days the cores of the observed eddies are constituted from a mixture of modified atlantic water that is warm and salty with polar water that is cold and fresh we infer that these submesoscale coherent eddies contribute substantially to the input of atlantic and polar waters to depths greater than 500 m in the central greenland sea

generation of submesoscale vortices a new mechanism small scale intense vortices composed of water with anomalous values of quasi conservative tracers have been observed in many oceans they are particularly numerous in the beaufort gyre of the arctic ocean possible mechanisms responsible for the generation of these features are examined conservation of temperature salinity and nutrients requires that beaufort sea vortices be created from water that flows into the arctic ocean from the pacific ocean across the broad shallow chukchi sea much of this water passes through barrow canyon near point barrow alaska observations in the canyon show the generation of vortices of approximately the same size as those observed in the beaufort sea barrow canyon is therefore a likely site for the generation of beaufort sea vortices most observed beaufort sea vortices have a central potential vorticity near zero because of a relative vorticity close to their chukchi sea source water is typically stratified with little relative vorticity so that its potential vorticity is nonzero a key step in the generation of the vortices is therefore the reduction of the potential vorticity of chukchi sea water to nearly zero it is proposed that this occurs through the action of frictional torques occurring as the chukchi sea water flows through barrow canyon rather than througji the action of vertical mixing because this flow is driven by a downstream pressure gradient it is concentrated on the right hand wall of the canyon by the coriolis force the frictional torques thus preferentially reduce the potential vorticity of the fluid anticyclonic vortices are therefore preferentially generated it is suggested that a similar scenario may play a role in the generation of submesoscale vortices containing water from the mediterranean and labrador seas