modeling of deep water renewal through cold convective plumes abstract in only a few regions in the world ocean surface water is transformed into deep water by open ocean convection in this paper small areas of vertical flow or plumes are studied using a steady state model integrated in streamline coordinates we use an entrainment hypothesis based on knowledge about in mixing of water across the shear zone from an area of low turbulence into an area of high turbulence this results in a model using conservation equations for momentum heat and salt and a nonlinear equation of state effects of earth rotation are included the depth reached by surface water when moving through stationary plumes is predicted and found strongly dependent on the properties in the surface layer this layer has to be colder but only slightly denser than the water just below it to be a source for steady state plumes the thermobaric effect the dependency of compressibility on the temperature plays a major role for the plume penetration depth in weakly stratified cold water like in the greenland sea deep convection is found to be possible and efficient through steady state plumes initial excess density of less than 5 10 3 kg m 3 caused by low temperature can give convection deeper than 1500 m through plumes with horizontal scales of a few hundred meters and vertical velocities of order a few tens of centimeters per second

the temperature of europa s subsurface water ocean a 100 km deep liquid water ocean probably underlies the icy exterior of jupiter s satellite europa the long term persistence of a liquid ocean beneat ha n ice shell presents a thermal conundrum is the temperature of the ocean equal to the freezing point of water at the bottom of the ice shell or is it equal t o the somewhat warmer temperature at which water attains its maximum density we argue that most of the ocean is at the temperature of maximum density and that the bulk of the vigorously convecting ocean is separated from the bottom of the ice shell by a thin stratosphere of stably stratified water whi ch is at the freezing point and therefore buoyant if europa s subsurface water ocean is warm it could explain the widespread geologic evidence for app arent melt through events observed on its surface and may constrain the overall age of its surface

convective modifications of a geostrophic eddy field ocean convection often occurs in regions of mesoscale eddy activity where convective mixing and geostrophic eddy dynamics interact the authors examine the interactions between a group of geostrophic eddies and convective mixing induced by surface buoyancy loss through a series of numerical simulations using a nonhydrostatic boussinesq model the eddies are initially baroclinic with a surface intensified density anomaly and sheared flow but they are stable to baroclinic instability because of their small size in the absence of buoyancy loss eddy mergers occur much as in previous studies of geostrophic turbulence with the addition of surface buoyancy loss the surface stratification is eroded by small scale convection the convective mixing is highly heterogeneous being deeper in regions of weaker initial stratification and shallower in more strongly stratified regions the deformation radius is reduced in mixing regions and the weakly stratified eddies become baroclinically unstable the barotropic component of kinetic energy increases as convection proceeds largely due to the conversion of the available potential energy of the eddies in the baroclinic instability process the convective forcing therefore provides a means of increasing the barotropic component of the eddy kinetic energy by enabling the baroclinic instability the fluid is efficiently homogenized by the energetic eddy field leading to a few isolated eddies separated by a well mixed fluid these simulations provide a possible explanation for energetic eddy fields observed during convective periods in the labrador sea

open ocean deep convection due to thermobaricity 2 numerical experiments properties of open ocean deep convection due to thermobaricity at high latitudes have been investigated by executing three dimensional nonhydrostatic numerical experiments in a rotating frame as obtained with the scaling argument by akitomo this issue the first type of deep convection which is not so affected by thermobaricity can occur in a homogeneous ocean with an intermediate water depth 2000 m while the second type in a two layer ocean can occur through pure thermobaric instability it is also confirmed that the former could occur in the greenland basin and the latter in the weddell sea which suggests the different processes of deep and bottom water mass formation between the two regions dependence of convective properties on external parameters is basically the same with the scaling argument however some important differences from the theory are found in a homogeneous ocean the convective size is determined by the product of characteristic velocity and timescale whether the ocean is shallow or deep rotating or nonrotating this is possibly a feature common to nonlinear convective phenomena the characteristic timescale is given by the shortest one of the diffusion time the inertial period and the period of any oscillatory feature accompanying convective motion reduced gravity and velocity scales depend on the ocean depth in a similar manner to the nonrotating scalings even when the rotation is effective as a result the same relation is realized in the three dimensional regime as in the two dimensional regime namely that the convective size is proportional to the rossby radius of deformation

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

assessing the roles of three eddy types in restratifying the labrador sea after deep convection abstractrestratification after deep convection is one of the key factors in determining the temporal variability of dense water formation in the labrador sea in the subsurface it is primarily governed by lateral buoyancy fluxes during early spring the roles of three different eddy types in this process are assessed using an idealized model of the labrador sea that simulates the restratification season the first eddy type warm core irminger rings is shed from the boundary current along the west coast of greenland all along the coastline the boundary current forms boundary current eddies the third type convective eddies arises directly around the convection area in the model the latter two eddy types are together responsible for replenishing 30 of the winter heat loss within 6 months irminger rings add another 45 to this number the authors results thus confirm that the presence of irminger rings is essential for a realistic amount of restratification in this area the model results are com

gravitational symmetric and baroclinic instability of the ocean mixed layer abstract a hierarchy of hydrodynamical instabilities controlling the transfer of buoyancy through the oceanic mixed layer is reviewed if a resting ocean of horizontally uniform stratification is subject to spatially uniform buoyancy loss at the sea surface then gravitational instability ensues in which buoyancy is drawn from depth by upright convection but if spatial inhomogeneities in the ambient stratification or the forcing are present as always exist in nature then horizontal density gradients will be induced and within a rotation period horizontal currents in thermal wind balance with those gradients will be set up within the mixed layer there are two important consequences on the convective process upright convection will become modified by the presence of the thermal wind shear fluid parcels are exchanged not along vertical paths but rather along slanting paths in symmetric instability theoretical considerations suggest that this slantwise convection sets the potential vorticity of th

localized convection in rotating stratified fluid we study the convective overturning of a rotating stratified fluid in the laboratory convection is induced from the surface of a salt stratified fluid by the introduction of salty fluid over a circular area the external parameters are buoyancy forcing of strength b0 applied over a circular area of radius r the rotation rate as measured by f ambient stratification n and the depth h the experiments are motivated by physical scaling arguments which attempt to predict the length and velocity scales of the convective chimney as it adjusts under gravity and rotation and breaks up through baroclinic instability the scales of interest include the number size and typical speeds of the fragments of the broken chimney the final depth of penetration of the convective mixed layer and the total volume of convectively produced water these scales are tested against the laboratory experiments and found to be appropriate in this idealized problem we have found the depth of penetration depends only on the size and strength of the forcing and the ambient stratification encountered by the convection event it does not depend explicitly on rotation the implications of the work to deep water formation in the labrador sea and elsewhere are discussed finally the study has relevance to the role and representation of baroclinic eddies in large scale circulation of the ocean

arctic ocean mixed layer eddy generation under leads in sea ice 1 convection in the arctic ocean mixed layer occurs under openings in sea ice where new sea ice is formed the process of brine rejection during ice formation creates negatively buoyant fluid at the surface of ice leads when the fluid convects downward the ocean mixed layer below the lead is stirred vertically and through planetary rotational effects along lead flows at the lead edges are induced these vertical and lateral motions have been previously studied using two dimensional numerical ocean models and observed in field programs such as leadex in this paper the generation of arctic ocean eddies through dynamic instabilities is investigated using a three dimensional nonhydrostatic ocean model results suggest that salt enriched vortices can develop at the base of the mixed layer as a consequence of brine rejection but the vortex formation requires a time period of several days a time long enough that the progenitor lead would likely have closed the scale of the eddies is found to depend on the magnitude of the buoyancy forcing the width of the lead and the duration of the buoyancy forcing the number of vortices produced depends on lead width and duration of buoyancy forcing but is less sensitive to the magnitude of the buoyancy forcing vortex sizes scaled appropriately and vortex numbers are compared with those found in recent laboratory studies of convectively driven flows from line segment sources

a note on seasonal cycles of temperature and salinity in the upper waters of the greenland sea gyre from historical data monthly climatologies of temperature and salinity for two regions in the greenland sea are created by combining historical archives of hydrographie stations with observations from recent cruises the first region corresponds to the gyre center where deepwater formation occurs and a large bay forms in the winter ice pack nordbukta and the second region lies directly to the south in the area usually covered by an ice tongue odden in february and march surface temperature responds primarily to local surface heat fluxes consistently warming in the summer to about 4 c and cooling in the fall to the freezing point interannual variability appears to be greater for salinity than for temperature this coupled with the sparse data coverage makes it more difficult to define a seasonal salinity cycle however in july and august surface salinity in both regions appears to decrease drastically with freshening being more pronounced in the southern region in the fall this mixed layer fresh anomaly is removed probably by brine rejection due to the local formation of ice and its subsequent removal by northerly winds eventually ice formation causes the surface waters to overturn and entrain the warmer water below inhibiting further ice formation the fresh anomaly is smaller in the gyre center than in the odden region so that ice formation will end there earlier resulting in the appearance of a bay to the north of an ice tongue since the disappearance of ice is a necessary precursor to mixing deeper than about 100 m this suggests that large areal changes in ice cover may be used as a proxy for identifying the strength and onset of deep convection

a numerical study of local convection in the benthic ocean induced by episodic hydrothermal discharges a nonhydrostatic primitive equation model is used to investigate motions and water column property distributions accompanying the rise of hot hydrothermal fluids into a rotating water column stratified in temperature and salinity after preliminary model experiments used to fix the level of turbulent mixing the model is applied to a megaplume event the release of a large amount of hydrothermal heat into the benthic ocean over a period of several days events of this kind have produced water masses with anomalous temperature and salinity distributions 20 km in diameter 800 m thick centered vertically 700 1000 m off the seafloor the model allows the study of the initial time development and maturation of the plume from such an event preliminary experiments demonstrate the sensitivity of plume rise to the level of turbulent mixing and to the ratio of turbulence viscosity to turbulence diffusivity i e prandtl number rise to maximum plume height occurs in 4 6 n 1 where n is buoyancy frequency consequences of a megaplume sized release of heat are examined over an initial 30 day period vertical circulation accompanying a hydrothermal event leads to a slight negative salinity anomaly below the plume s temperature anomaly core the plume s heat potential temperature anomaly is shown to be a composite of hydrothermal heat and ambient heat that has been redistributed by the same vertical circulation cell horizontal circulation is dominated by an anticyclonic flow vortex centered just above the temperature anomaly maximum at 800 m above bottom and a cyclonic flow vortex at the seafloor azimuthal flow accounts for the largest fraction of kinetic energy within 4 5 hours 1 7 1 after the start of heat release azimuthal velocities reach maximum values of 70 cm s 1 90 of which is attained within the initial 10 hours even as much as 4 weeks past cessation of heat release maximum azimuthal velocities are of the order of 10 cm s 1 the balance of vertical forces is hydrostatic by 12 hours save for near bottom frictional effects during plume formation the radial force balance is primarily cyclostrophic near axis and geostrophic at a distance

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

ice ocean processes over the continental shelf of the southern weddell sea antarctica a review 1 interactions between the southern ocean and the weddell sea ice shelves are important both to the antarctic ice sheet and to the production of globally significant water masses here we review the interaction between the filchner ronne ice shelf and the shelf sea in which it floats the continental shelf processes leading to the production of weddell sea deep and bottom waters from the original off shelf source waters are discussed and a new view is offered of the initial production of high salinity shelf water data from ship based measurements at the ice front from glaciological methods and from measurements made within the sub ice shelf cavity itself are used to describe the pattern of flows beneath the ice shelf we also consider the variability observed within the cavity from tidal to interannual time scales and finish with a discussion of future research priorities in the region

boundary current eddies and their role in the restratification of the labrador sea an idealized model is used to study the restratification of the labrador sea after deep convection with emphasis on the role of boundary current eddies shed near the west coast of greenland the boundary current eddies carry warm buoyant irminger current water into the labrador sea interior for a realistic end of winter state it is shown that these irminger current eddies are efficient in restratifying the convected water mass in the interior of the labrador sea in addition it is demonstrated that irminger current eddies can balance a significant portion of the atmospheric heat loss and thus play an important role for the watermass transformation in the labrador sea

pliocene crustal shortening on the tyrrhenian side of the northern apennines evidence from the gavorrano antiform southern tuscany italy the northern tyrrhenian sea and the inner northern apennines are classically regarded as a late miocene pleistocene back arc system developed as a consequence of slab rollback along active subduction zones we present new geological and structural data on the gavorrano antiform a key sector of the inner northern apennines lying close to the northern tyrrhenian sea it provides clear evidence of pliocene shortening deformation and magma emplacement the orientation of 1 n50 e n80 e derived by fault slip data inversion is consistent with a general ene wsw shortening direction furthermore this ene wsw trending orientation of 1 is compatible with the compressive deformation recorded in coeval sedimentary basins on this basis we suggest that the inner northern apennines were affected by crustal shortening during the pliocene this scenario matches well geophysical data suggesting that since the late messinian 6 5 ma subduction rollback and back arc extension strongly decreased in the northern tyrrhenian sea whereas they continued as active processes in the southern tyrrhenian sea

formation and circulation processes of intermediate water in the japan sea abstract the formation and circulation processes of intermediate water in the japan sea have been investigated by study of the subduction of mixed layer water to simulate realistic seasonal variations in the velocity and hydrographic structures a numerical model with a nudging method for potential temperature and salinity which reproduced the general features in the japan sea is used close investigation of the subduction process reveals two major formation areas a and b of intermediate water area a 41 43 n west of 135 e corresponds to the region reported by recent observations whereas area b 40 43 n east of 136 e has not been reported so far the mixed layer water subducted in area a is advected southwestward and eventually its upper portion above 200 m reaches the eastern part of the japan basin whereas the lower branch below 200 m reaches the tsushima basin this indicates that the east sea intermediate water originates from the mixed layer in area a and suggests that the east sea

eddy formation in the denmark strait overflow on the basis of observations along the continental slope of east greenland a primitive equation open boundary model is used to study the formation of eddies in the denmark strait overflow the eddies are produced by vortex tube stretching initiated by cross slope components of the velocity field a sequence of cyclones and anticyclones is formed the cyclones are located along the deeper part of the slope and the anticyclones are along the shallower slope the eddies are almost barotropic with horizontal and vertical velocities of 30 cm s 1 and 0 1 cm s 1 respectively the cyclones migrate along the isobaths with a slight downhill component and intensify on their path until they become influenced by the flat deep basin their translation speed is typically 20 30 cm s 1 and the local change in relative vorticity is nearly entirely determined by vortex tube stretching and vorticity advection the overflow water flows mainly between the cyclonic and anticyclonic eddy chains the overflow is strongly accelerated by the eddies the existence of anticyclonic eddies along the shallower part of the east greenland continental slope predicted by the numerical model has been confirmed by observations

ice ocean interactions during shallow convection under conditions of steady winds three dimensional numerical studies abstract a three dimensional hydrodynamic ocean model coupled to a thermohydrodynamic model for young sea ice is applied to study shallow haline convection in the central greenland sea with an emphasis on sub mesoscale ice ocean interactions two types of young sea ice are distinguished i e frazil and pancake ice both acting different on surface heat salt and momentum fluxes two scenarios are considered a continued frazil ice production during steady winds and b the same scenario but with the intermittent formation of pancake ice during a short intervening period of low winds brine release due to new ice production creates shallow convection in both cases under conditions of continued frazil ice production ice streaks develop at the sea surface finally becoming oriented roughly parallel to the wind these streaks are the result of convective plumes that induce organized patterns of convergent and divergent surface currents frazil ice is herded into convergence zones where it becomes as thick as 6 m within 24 h the studies suggest a strong relationship between streak spacing and the penetration depth of convection given by an aspect ratio in the range of 2 3 after pancake ice has been formed however the organized ice streaks vanish developing into complex patterns of pancake ice this finding is in agreement with recent field observations in the greenland sea is odden ice tongue with the existence of pancake ice moreover the surface averaged buoyancy flux decreases and is determined from the integral of local sub mesoscale ice ocean interactions

statistical parameterization of heterogeneous oceanic convection abstract a statistical convective adjustment scheme is proposed that attempts to account for the effects of mesoscale and submesoscale variability of temperature and salinity typically observed in the oceanic convective regions temperature and salinity in each model grid box are defined in terms of their mean variance and mutual correlations subgrid scale instabilities lead to partial mixing between different layers in the water column this allows for a smooth transition between the only two states convection on and convection off allowed in standard convective adjustment schemes the advantage of the statistical parameterization is that possible instabilities associated with the sharp transition between the two states which are known to occasionally affect the large scale model solution are eliminated the procedure also predicts the generation of correlations between temperature and salinity and the presence of convectively induced upgradient fluxes that have been obtained in numerical simulati

shallow brine driven free convection in polar oceans nonhydrostatic numerical process studies a three dimensional nonhydrostatic convection model which accounts for small scale ice ocean interactions is used to study convection in shallow sea coastal ice formation regions which contribute significantly to water mass formation in both the arctic and antarctic ocean for certain conditions the results presented in this paper are also transferable to shallow open ocean convection the model is applied to an initial well mixed ocean at rest with a temperature close to the freezing point the ocean initially free of ice is exposed to cold and dry polar air we consider situations in which the mean wind stress is negligible but wind fluctuations result in small sensible and latent heat fluxes corresponding to a wind speed of 2 m s 1 cellular convection patterns develop in the ocean finally occupying a mean aspect ratio of 2 convection is driven by salt release during frazil ice formation due to supercooling newly forming sea ice is collected along convergent downwelling regions at the surface thus showing also cellular structures because the area of insulating sea ice remains small new ice can be formed continuously and the surface buoyancy forcing remains large this collection of ice in small fractions of the sea surface results in a latent heat polynya type which is very effective in terms of dense water mass formation a comparison of the three dimensional model and a two dimensional slice model shows that key results can be reproduced with the slice model in summary the results of the process studies indicate that cellular features in the sea ice cover which may be detectable by remote sensing techniques are closely related to active brine driven convection

on the connection between dense water formation overturning and poleward heat transport in a convective basin an isopycnal two layer idealized model for a convective basin is proposed consisting of a convecting interior region and a surrounding boundary current buoyancy and wind driven parameterized eddy fluxes govern the exchange between the two to balance the interior buoyancy loss the boundary current becomes denser as it flows around the basin geostrophy imposes that this densification be accompanied by sinking in the boundary current and hence by an overturning circulation the poleward heat transport associated with convection in the basin can thus be viewed as a result of both an overturning and a horizontal circulation when adapted to the labrador sea the model is able to reproduce the bulk features of the mean state the seasonal cycle and even the shutdown of convection from 1969 to 1972 according to the model only 40 of the poleward heat buoyancy transport of the labrador sea is associated with the overturning circulation an exact solution is presented for the linearized equations when changes in the boundary current are small numerical solutions are calculated for variations in the amount of convection and for changes in the remotely forced circulation around the basin these results highlight how the overturning circulation is not simply related to the amount of dense water formed a speeding up of the circulation around the basin due to wind forcing for example will decrease the intensity of the overturning circulation while the dense water formation remains unvaried in general it is shown that the fraction of poleward buoyancy or heat transport carried by the overturning circulation is not an intrinsic property of the basin but can vary as a result of a number of factors

lateral heat exchange after the labrador sea deep convection in 2008 abstractthe mechanisms through which convected water restratifies in the labrador sea are still under debate the labrador sea restratification after deep convection in the 2007 08 winter is studied with an eddy resolving numerical model the modeled mixed layer depth during wintertime resembles the argo observed mixed layer very well and the lateral heat flux during the subsequent restratification is in line with observations the irminger rings irs are reproduced with fresher caps above the 300 m depths and they are identified and tracked automatically the model underestimates both the number of irs in the convection area and the heat they carry the underestimation is most likely caused by the errors in the direction of the west greenland currents in the model which causes more irs propagating westward and only the irs originating south of 61 5 n are able to propagate southward yet with speed much slower than observed speed the model still observed three eddies propagating into the convection

on the relationship between the water mass pathways and eddy variability in the western mediterranean sea the role of eddies on the formation and spreading of water masses in the western mediterranean sea is studied with an ocean general circulation model the model is forced with interannually variable surface forcing for the years from 1979 to 1999 it is found that the model reproduces the major features of the observed mesoscale variability in the gulf of lions and the large eddies evolution in the algerian basin the seasonal evolution of circulation in the gulf of lions and processes of spreading of newly formed intermediate deep waters in the postconvection period is studied for years 1987 and 1992 the model results are compared with data from observations it is shown that the instability of the transition zone between old and newly formed deep waters which takes place after the violent mixing stages of the deep convection leads to collapse of the mixed patch and formation of mesoscale eddies some of these eddies propagate out of the gulf of lions transporting deep waters into the algerian basin the rest of the mesoscale eddies filled with newly formed deep waters remain in the gulf of lions and tend to merge and enlarge after the cyclonic eddies reach the algerian basin they interact with the intense mesoscale field existing there the energy analysis shows that the winter and spring are seasons of intensified baroclinic instability of the mean flow in the two regions of interest the gulf of lions and algerian basin the kinetic energy is released by baroclinic instability in spring and summer the spring spectra in the two regions have maximums at horizontal scales of about 80 100 km which is the typical scale of the eddies in the model these eddies propagate a cyclonic circuit the resulting eddy induced mass transport in deep and intermediate layers is directed out of the gulf of lions and toward the gibraltar strait equivalently we can argue the intermediate and deep waters conveyor belt of the western mediterranean sea is eddy drive

deep convection in the labrador sea as observed by lagrangian floats abstract during the winters of 1997 and 1998 a total of 24 lagrangian floats were deployed in the labrador sea these floats were designed to match the buoyancy and compressibility of seawater they measured temperature and three dimensional position pressure for vertical position and rafos acoustic tracking for latitude and longitude as they followed water motions three dimensionally this data provides direct observation of mixed layer depth and excellent estimates of vertical velocity floats were repeatedly carried across the convecting layer by vertical velocities averaging several centimeters per second with vertical excursions of up to one kilometer in the horizontal several scales of eddy motion were resolved as was a possible float predilection toward remaining in water preconditioned for convection heat flux estimates from this data reveal entrainment and surface heat fluxes similar in magnitude the mixed layer acts as a vertical conveyor belt of temperature transporting heat from depth

variability of rhodes and ierapetra gyres during levantine intermediate water experiment observations and model results 1 this work is aimed at studying the variability of rhodes and ierapetra gyres during the levantine intermediate water experiment sea surface temperature maps derived from global area coverage advanced very high resolution radiometer avhrr data in the framework of the pathfinder project and sea level anomalies derived from topex poseidon altimeter were used to track the evolution both in terms of dimension and position of the cyclonic rhode gyre and ierapetra anticyclone the analysis was performed for the period from october 1994 to the end of april 1995 i e from the preconditioning to the spreading phase of levantine intermediate water the description of the surface fields was complemented by a temporal evolution study of the rhodes and ierapetra gyres hydrological vertical structure european centre for medium range weather forecasts avhrr derived fluxes have been used as forcing for a numerical model to study the variability of the mixed layer in both gyres the simulated upper layer dynamics remarkably matched remotely sensed and in situ observations this work shows that using a combined analysis of observational data and model simulations we were able to propose a dynamical scenario for the winter of 1995 where the levantine basin was characterized by short intense heat loss events occurring during at the beginning of december the intense air sea interaction contributed to deep instead of intermediate mixing as confirmed by remote sensing in situ data and model experiments a hypothesis on the role of the lateral contribution on the water column buoyancy content in the rhodes gyre was formulated

a three dimensional numerical model of deep ventilation in temperate lakes because of the variation in the temperature of maximum density with depth it is known that the upper above 250 m and lower water columns circulate separately in deep temperate lakes while near surface water overturns twice per year the deep waters often mix only partially during a complete annual cycle it is believed that deep convection is triggered by storm surge forcing of some of the relatively cold upper water column downward through its compensation depth so that it becomes unstable and sinks the scale and intensity of the resulting deep water forming plumes are studied numerically a high resolution model based on the nonhydrostatic boussinesq equations is used deep water formation is initiated by applying a statically unstable initial temperature profile over various regions of the domain at depths below 300 m the grid spacing is small enough to resolve individual plumes which carry surface water to the lake bottom the domain of study is also large enough that the geostrophic eady 1949 wave breakup of newly formed deep water can be observed it is found that when the initial instability is applied in midbasin remote from the solid sidewalls relatively little fresh deep water is formed and the fluid quickly reaches a geostrophic and hydrostatic balance vigorous vertical mixing ceases after 4 days and the resulting baroclinic fluid has a well defined and predictable scale in contrast when the initial instability is applied immediately adjacent to a solid boundary vigorous plume motion continues for the duration of the numerical simulations 12 days producing a much greater volume of fresh deep water a parametric study investigates the scale and intensity of this boundary mixing it is found that reduced surface water temperature coriolis acceleration or higher horizontal diffusion coefficients increase the rate of deep water renewal

buoyancy driven plumes in rotating stratified cross flows plume dependence on rotation turbulent mixing and cross flow strength a three dimensional time dependent convection model is used to describe circulation and property fields in rotating stratified and moving fluids near a point source of heat the study context and consequently model scales are those of chronically discharging hydrothermal vent fields found at submarine ridge crests hydrothermal plumes having distinctive thermal and chemical anomalies have been observed to rise several hundreds of meters above the deep sea floor before being advected away by background cross flows typically of magnitude 1 4 cm s 1 the model is used to study effects of rotation and indicate differences in plumes with respect to variation of subgrid scale turbulence intensity and cross flow strength counterrotating vorticity couplets in all three coordinate directions develop in the lower plume stem at startup and follow the plume to the level of neutral buoyancy for a nonrotational case 0 patterns resemble those previously found for jets injected into homogenous cross flow ambient fluid entrainment into the convecting column is primarily from the upstream side but deflection of background flow around both sides of the rising column is the root of the relative vorticity z couplet in the lower plume turbulence intensity within the buoyant region of the plume and or globally controls smoothness and temporal variability of distal nonbuoyant plume distributions allowing or preventing oscillations of potential temperature for example at background buoyancy frequency n over the range of turbulent mixing studied rise height of plumes did not change appreciably but breadth of plumes counterintuitively increased for decreasing turbulent mixing strength increasing cross flow strength u0 bends model plumes such that rise height u0 0 4 for the two largest values of cross flow for which r the ratio of maximum vertical velocity to u0 took values of 2 8 and 1 0 plumes showed evidence of bifurcation

convective building of a pycnocline a two dimensional nonhydrostatic numerical model abstract the convective building of a pycnocline is examined using a two dimensional nonhydrostatic numerical model forced by a balanced salinity dipole source and sink although the forcing fields are steady the model develops oscillations that renew the model s analog of deep waters only intermittently the oscillation cycle consists of a freshwater layer that advects along the surface capping off the water column under the dense source and preventing sinking after a time continuing densification forms a plume that breaks through the salinity barrier and convects beneath the dense source ventilating the deep water increasing the viscosity reduces but does not eliminate this cycle when the hydrostatic assumption is added the model evolves systematically different salinity distributions than the nonhydrostatic model due to the isolation of part of the tank by a persistent convective column the deep flow is also different in this case because of differences between the entrainment detrainment

recent changes in deep water formation and spreading in the eastern mediterranean sea a review abstract observations of the last decade testify that the characteristics of the deep thermohaline circulation in the eastern mediterranean sea have changed thoroughly the source of the most dense waters of the basin has moved from the adriatic to the aegean sea this new source has proved to be very efficient since the estimated formation rate for the period 1989 95 was more than 1 sv about three times more than the dense water formation rate of the adriatic sea these new waters with hydrological characteristics that are warmer and more saline have replaced almost 20 of the older deep waters of the basin and have uplifted the deep isopycnals by about 500 m this major event can be attributed to important meteorological anomalies in the eastern mediterranean and to changes of circulation patterns the extended dry period of 1988 93 and the exceptionally cold winters of 1987 and 1992 93 created favorable conditions for increased formation of dense water in the aegean furthermore changes in the circulation patterns in the intermediate water range levantine intermediate water liw and cretan intermediate water themselves possibly linked to meteorological anomalies appear to have played an important role in the redistribution of salt as a result of an interruption to exchanges between the ionian and levantine basin the salinities in the latter started to rise high salinity waters were diverted into the aegean malanotte rizzoli p manca b b ribera dacala m theocharis a 1998 the eastern mediterranean in the 80s and in the 90s the big transition emerged from the poem bc observational evidence rapport du commission international de la mer medittanee 35 174 175 and the westward transport of liw was reduced an additional effect of the deep water discharge from the aegean and the resulting uplifting of mid depth waters was to lower salinities in the liw layer this effect is most strongly felt in the ionian sea a 3 d primitive equation numerical model for the eastern mediterranean with a 20 km grid size is used to simulate the observed changes and understand the basic mechanisms which caused them under appropriate atmospheric forcing the model successfully reproduces the main characteristics of the transient these results indicate that the observed changes can be at least partially explained as a response of the eastern mediterranean and more specifically of the aegean to atmospheric forcing variability

mechanisms of buoyancy transport through mixed layers and statistical signatures from isobaric floats idealized nonhydrostatic numerical calculations that resolve both plumes and geostrophic eddies are used to mimic isobaric float observations taken in the labrador sea deep convection experiment and study mechanisms of buoyancy transport through mixed layers the plumes and eddies are generated in a periodic channel initialized with a vertical profile of temperature and cooled by surface heat loss varying across the channel probability density functions and time series of vertical velocity and temperature computed from the floats are interpreted in terms of the kinematics of plumes and geostrophic eddies and their role in buoyancy transport estimates from eulerian time series from the numerical model suggest that geostrophic eddies and plumes have a comparable contribution to vertical heat flux

the thermohaline circulation of the arctic ocean and the greenland sea the thermohaline circulation of the arctic ocean and the greenland sea is conditioned by the harsh high latitude climate and by bathymetry warm atlantic water loses its heat and also becomes less saline by added river run off in the arctic ocean this leads to rapid cooling of the surface water and to ice formation brine released by freezing increases the density of the surface layer but the ice cover also insulates the ocean and reduces heat loss this limits density increase and in the central arctic ocean a low salinity surface layer and a permanent ice cover are maintained only over the shallow shelves where the entire water column is cooled to freezing can dense water form and accumulate to eventually sink down the continental slope into the deep ocean the part of the atlantic water which enters the arctic ocean is thus separated into a low density surface layer and a denser deep circulation these two loops exit through fram strait the waters are partly rehomogenized in the greenland sea the main current is confined to the greenland continental slope but polar surface water and ice are injected into the central gyre and create a low density lid allowing for ice formation in winter this leads to a density increase sufficient to trigger convection upwelling and subsequent ice melt the convection maintains the weak stratification of the gyre and also reinforces the deep circulation loop as the transformed waters return to the north atlantic the low salinity upper water of the east greenland current enters the labrador sea and influences the formation of labrador sea deep water the dense loop passes through denmark strait and the faroe shetland channel and sinks to contribute to the north atlantic deep water changes in the forcing conditions might alter the relative strength of the two loops this could affect the oceanic thermohaline circulation on a global scale

large scale dynamics of circulations with open ocean convection abstractformation of the densest water masses in the north atlantic and its marginal seas involves open ocean convection the main goal of this study is to contribute to the general understanding of how such convective regions connect to the large scale ocean circulation specifically analytic and numerical versions of a variable density layer model are used to explore the processes underlying the circulation in an idealized ocean basin the models are forced by a surface buoyancy flux which generates a density maximum in the ocean interior in response to the forcing a region forms that is characterized by the closed rossby wave characteristics and where the eddy mean transport converges toward the convective site outside of that region characteristics extend from the eastern boundary and a distorted plume circulation develops linking the convection site with the western boundary the overturning strength in the model can be related to several environment variables and forcings and is constrained

open ocean deep convection due to thermobaricity 1 scaling argument properties of open ocean deep convection due to thermobaricity at high latitudes have been investigated by the scaling argument two types of open ocean deep convection are found the first type appears in a homogeneous ocean or in a deepening mixed layer the increased apparent buoyancy flux due to thermobaricity makes scales of convective properties larger than those without thermobaricity the ratio of thermobaric to nonthermobaric scales is determined only by l0 h where l0 and h are the size of nonthermobaric convection and the characteristic depth for thermobaricity to be effective respectively in a nonrotating frame then thermobaricity becomes effective when the ocean depth h is comparable with h as previous studies show in a rotating frame thermobaricity is most effective with slow rotation the coriolis parameter 10 4 s 1 and low temperatures approximately the freezing point of seawater since l0 h becomes largest in the actual situation 10 4 s 1 thus thermobaricity is not so effective because the earth rotation confines l0 to a smaller level i e l0 h 1 the second type of deep convection is driven by pure thermobaric instability in a two layer ocean where a cold fresh mixed layer overlies a warm saline deep layer as often observed in polar oceans it causes an abrupt overturning of the water column scales of convective properties are dependent on the difference of water temperature between the two layers the initial size of plume and the coriolis parameter or time but not on the surface cooling rate directly with actual parameters convective properties and the associated buoyancy flux are much larger than those of the first type observed vertical profiles of water temperature and salinity suggest that the first type of deep convection could occur in the greenland basin while the second type could occur in the weddell sea

a methodology for assessing the postconvection mesoscale dynamics in the gulf of lion from composite datasets in order to access the statistical properties of the mesoscale dynamics in the western mediterranean and its associated transport and heat fluxes during the postconvection period the authors have applied data combination methods for analyzing a wide range of in situ measurements collected during the thetis 1 and convhiv experiments ctd and xbt profiles were merged with times series at a fixed or moving point and also with integral time series obtained from acoustic tomography data estimates of temperature and currents within a box of approximately one degree square over a time period of 35 days during the postconvection period were produced during this winter convection has been only partial rarely penetrating deeper than 1200 m the analysis concentrates on the upper 1000 m where most changes occur geostrophy is used as a dynamical constraint relating the parameters the time evolution is controlled by a kalman filter using simple persistence the contribution of the different datasets to the estimation indicates their complementarity in the time and space dimensions hydrography and eulerian measurements provide a major contribution to the estimation of the baroclinic modes tomography data complement the estimate at all horizontal scales float data bring some information on the barotropic mode but the major contribution on this mode comes from the reciprocal tomography data particularly at the largest scales the period analyzed mostly covers the postconvection estimation of the kinetic energy indicates that the barotropic contribution represents 85 of the total energy horizontal advection transfers heat toward the central area at a mean rate of 50 w m 2 compensating for the heat losses through the surface the mesoscale flow field observed is characterized by strongly barotropic coherent vortices with a size o 30 40 km these barotropic eddies are present during all phases of convection

convection beneath freezing leads new observations compared with numerical model results vertical distributions of temperature salinity and horizontal and vertical current speed were measured along the edges of a number of rapidly freezing leads in the southern central beaufort sea during march april 1992 these observations were restricted to cases having sufficiently small ice water relative speeds that brine driven convection was expected based on scaling arguments to dominate shear turbulence generated by the relative ice water motion the observed salinity and current features were consistent with an existing conceptual model for sublead convection consequent to brine rejection from ice formation and with the results of a numerical model which assumes two dimensionality in the cross lead direction and uses a brine input consistent with the field observations these models predict convection of brine enriched plumes beneath the lead downward to the pycnocline where they then spread outward away from the lead volume continuity is satisfied by horizontal inflow of water to the lead at the surface observed mean downward convection speeds varied from 0 2 to 0 7 cm s 1 and had maxima up to about 2 cm s 1 consistent with the numerical model salinities associated with the convecting parcels were about 0 001 practical salinity units psu above ambient which was an order of magnitude less than predicted by the model while plumes of water flowing away from the lead on the pycnocline had salinities as high as 0 004 psu above ambient these similarities and discrepancies are discussed within the context of a steady state model versus a nonsteady field situation and it is concluded that the steady convection cell concept is probably valid if viewed as a time averaged sequence of discrete convective plumes or thermals

the subpolar front of the japan east sea part iii competing roles of frontal dynamics and atmospheric forcing in driving ageostrophic vertical circulation and subduction abstractthe effects of wind stress and surface cooling on ageostrophic vertical circulation and subduction at the subpolar front of the japan east sea are investigated using a nonhydrostatic numerical model in experiments forced by wind and or cooling ageostrophic vertical circulation is enhanced relative to the unforced case both surface cooling and wind stress intensify the circulation by enhancing frontogenesis associated with frontal meandering winds further strengthen vertical motions by generating internal gravity waves downfront winds i e oriented along the frontal jet transport surface water from the denser to lighter side of the front causing it to migrate toward the region of higher stratification and enhancing the vertical mixing at the front this induces outcropping of isopycnals from the middle of the pycnocline along which surface water is subducted hence downfront winds enhance subduction down to the middle of the pycnocline but not beneath on the other hand cooling uplifts i

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

representation of convective plumes by vertical adjustment open ocean deep water formation involves the interplay of two dynamical processes plumes 1 km wide driven by upright convection and geostrophic eddies 5 km wide driven by baroclinic instability numerical twin experiments are used to address two questions about the plumes can they be represented by a simple mixing process in large scale models if so is it important that the mixing occurs over a finite time tmix or would instantaneous mixing produce the same effect on large scale properties in numerical simulations which resolve the geostrophic eddies we represent the plumes with a slow convective adjustment algorithm which is broadly equivalent to an enhanced vertical diffusivity of density in statically unstable regions the diffusivity depends on tmix the mixing timescale the fidelity of the plume parameterization is then evaluated by comparison with plume resolving simulations of open ocean deep convection integral properties of the plumes such as the temperature census of the convected water and the strength of the rim current that encircles the convecting region are all accurately reproduced by the slow adjustment scheme the importance of choosing an appropriate finite value for tmix is explored by setting tmix 12 hours in some experiments in accordance with scaling considerations and tmix 0 in others corresponding to instantaneous adjustment the conventional assumption in the case of convection into a moderately or strongly stratified ocean the behavior does not significantly depend on tmix however in neutral conditions the slow adjustment does improve the parametric representation our experiments confirm the picture of plumes homogenizing the water column over a time tmix

a numerical study of three dimensional dense bottom plumes on a southern ocean continental slope three dimensional features of dense bottom plumes flowing over continental slopes with or without along slope topographic variations are investigated by simulating the evolution of a density front at a southern ocean continental shelf break using a three dimensional primitive equation numerical model with a second order turbulence closure scheme embedded the focus of our investigation is the role of topography in determining mixing and the offshore transport of dense shelf water during the transient adjustment process of a density front over a continental slope we compare and discuss the numerical simulations for two cases a uniform shelf and slope case and a case with a canyon that leads from the coast to the deep ocean crossing the shelf and the slope the numerical simulations indicate that baroclinic instability planetary rotation bottom friction and topography play major roles in determining the surface and bottom plume formation the growth and penetration depth of the bottom plumes and the characteristics of water mass on the slope mesoscale eddies play a fundamental role in transporting mass heat and salt from shelf to deep ocean the effects of the depth and width of the canyon are examined with two more experiments the presence of a wide and deep canyon in the continental shelf and slope enhances considerably the drainage of coastal shelf water into the deep ocean

the role of preconditioning in the evolution of open ocean deep convection large eddy simulation of open ocean deep convection shows that the evolution of convection appears in a fundamentally different pattern depending on the precondition of the ocean and the magnitude of the surface buoyancy flux as the intensity of the cyclonic gyre in the ocean under the cooling increases the pattern of convection is transformed from distributed convection to localized convection in localized convection the typical pattern of open ocean deep convection appears such as the generation of baroclinic instability and large lateral buoyancy transfer secondary circulation restratification and the breakup of the original cyclonic gyre on the other hand in distributed convection small scale convective plumes appear uniformly over the whole surface similarly to the convective boundary layer without generating the typical features of open ocean deep convection hence an enormous difference in the generated eddy kinetic energies exists between the two cases it is also found that a stronger cooling at the sea surface suppresses the transition from distributed convection to localized convection dimensional analysis provides the parameters to characterize the pattern of convection and the critical condition for the transition is estimated by analyzing the numerical results

mechanisms for lateral exchange with oceanic convection sites competing influences of baroclinic instability and ambient mean flow in the shutdown of convection in the ocean are studied using a primitive equation model a mean flow over isolated bottom topography is one way to generate convection on the horizontal scales seen in the ocean modeling of this process suggests that the convective deepening is arrested when horizontal fluxes of heat due to the mean flow balance surface cooling the topographically trapped convective chimney is not prone to baroclinic instability because the mean flow advects anomalies away from the chimney faster than they can grow locally this behavior is unlike that seen in model chimneys forced by isolated circular shaped cooling regions in which baroclinic eddies provide the horizontal fluxes of heat required to shut down convection in order to elucidate the suppression of baroclinic instability by the presence of an ambient mean flow a series of experiments is carried out with a circular cooling region used to parameterize the preconditioning effect of the topography for small mean flows the chimneys generated reproduce the robust baroclinic instability seen in previous studies in this case the final depth ventilated by the convection is determined by the horizontal fluxes due to baroclinic eddies for large mean flows instability growth is suppressed and the mean flow provides the horizontal fluxes that determine the final depth of ventilation as in topographic preconditioning experiments some possible implications for the parameterization of convection in global general circulation models are discussed

parameterization of mixed layer eddies part i theory and diagnosis ageostrophic baroclinic instabilities develop within the surface mixed layer of the ocean at horizontal fronts and efficiently restratify the upper ocean in this paper a parameterization for the restratification driven by finite amplitude baroclinic instabilities of the mixed layer is proposed in terms of an overturning streamfunction that tilts isopycnals from the vertical to the horizontal the streamfunction is proportional to the product of the horizontal density gradient the mixed layer depth squared and the inertial period hence restratification proceeds faster at strong fronts in deep mixed layers with a weak latitude dependence in this paper the parameterization is theoretically motivated confirmed to perform well for a wide range of mixed layer depths rotation rates and vertical and horizontal stratifications it is shown to be superior to alternative extant parameterizations of baroclinic instability for the problem of mixed layer restratification two companion papers discuss the numerical implementation and the climate impacts of this parameterization

on the validity of the millionshchikov quasi normality hypothesis for open ocean deep convection data from numerical simulations of free convection in the ocean with rotation are used to explore the validity of the millionshchikov quasi normality hypothesis the parameterizations of fourth order moments according to a universal model proposed by gryanik et al are found to be far more accurate than their corresponding gaussian parameterizations which are based on the millionshchikov hypothesis the universal model is marginally improved by fitting the model parameters to the data the present results extend previous results that discuss shallow convection in the planetary boundary layer to rotationally controlled deep convection

north pacific upper ocean cold temperature biases in cmip6 simulations and the role of regional vertical mixing abstractsubstantial model biases are still prominent even in the latest cmip6 simulations attributing their causes is defined as one of the three main scientific questions addressed in cmip6 in t

a four dimensional analysis of the thermal structure in the gulf of lion the theoretical and experimental tomography in the sea experiment thetis 1 took place in the gulf of lion to observe the evolution of the temperature field and the process of deep convection during the 1991 1992 winter the temperature measurements consist of moored sensors conductivity temperature depth and expendable bathythermograph surveys and acoustic tomography because of this diverse data set and since the field evolves rather fast the analysis uses a unified framework based on estimation theory and implementing a kaiman filter the resolution and the errors associated with the model are systematically estimated temperature is a good tracer of water masses the time evolving three dimensional view of the field resulting from the analysis shows the details of the three classical convection phases preconditioning vigourous convection and relaxation in all phases there is strong spatial nonuniformity with mesoscale activity short timescales and sporadic evidence of advective events surface capping intrusions of levantine intermediate water liw deep convection reaching 1500 m was observed in late february by late april the field had not yet returned to its initial conditions strong deficit of liw comparison with available atmospheric flux data shows that advection acts to delay the occurence of convection and confirms the essential role of buoyancy fluxes for this winter the deep mixing results in an injection of anomalously warm water t 0 03 to a depth of 1500 m compatible with the deep warming previously reported

stability of a cold core eddy in the presence of convection hydrostatic versus nonhydrostatic modeling geostrophic eddies in a stratified liquid are susceptible to baroclinic instabilities in this paper the authors consider these instabilities when such an eddy is simultaneously cooled homogeneously from above as a linear stability analysis shows the developing convection modifies the background stratification the stability boundaries and the patterns of the dominant modes the coupling between the effects of convection and the largescale flow development of the eddy is studied through high resolution numerical simulations using both nonhydrostatic and hydrostatic models in the latter models several forms of convective adjustment are used to model convection both types of models confirm the development of the dominant modes and indicate that their nonlinear interaction leads to localized intense convection by comparing nonhydrostatic and hydrostatic simulations of the flow development carefully it is shown that convective adjustment may lead to erroneous smallscale variability a simple alternative formulation of convective adjustment is able to give a substantial improvement

variability of the large scale general circulation of the mediterranean sea from observations and modelling a review abstract in this paper we present an overview of the most recent findings about the mediterranean sea present day circulation structure both historical observations and numerical model simulations are presented outlining the differences and agreement the model simulations are presented for both an eddy resolving and a coarse resolution numerical model and the results are intercompared the importance of the mesoscales in modifying the large scale flow field is elucidated the critical point is the discovery of the large amplitude interannual variability of the circulation and water mass structure associated with the anomalies of atmospheric forcing over the basin the seasonal variability can be strictly related to changes in heat and momentum fluxes while the interannual variability has a component which is related to the mesoscale field the latter is very intense in the algerian current region and levantine basin but different in structure in the two regions results are shown which confirm the importance of wind driving in establishing the kinetic energy of the flow field by comparing the current transport at the strait of corsica with observations in conclusion the essential characteristics of the present day circulation are associated with the atmospheric forcing and the basin topographic structure results from palaeoceanographic simulations for the last 20 000 years show that changing the atmospheric forcing can cause large changes in the circulation structure which may have affected sapropel formation

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

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

modeling the deep convection in the northwestern mediterranean sea using an eddy permitting and an eddy resolving model case study of winter 1986 1987 1 in the northwestern mediterranean sea winter 1986 1987 was particularly cold inducing a strong open ocean convection event in order to investigate the impact of numerical models spatial resolution on the convection representation and the effects of deep convection on the northwestern mediterranean circulation we perform two numerical three dimensional simulations eddy permitting versus eddy resolving models are forced at the surface by the era40 atmospheric fluxes with a simple heat flux correction to better mimic the observed value we examine the characteristics of the deep convection mixed layer water masses characteristics convection zone and mesoscale structures and perform temporal analysis of this event in terms of kinetic energy buoyancy equilibrium and deep water dw evolution the convection characteristics are similarly represented on a global scale by both models and are in good agreement with observations except for the size of the convection region however the eddy resolving model better reproduces the mesoscale structures whose role in the dw formation mixing and transport is shown to be essential the boundary circulation and the overturning are enhanced during the convection event sixty six percent of the dw spreading is due to the bleeding effect into the catalan sea during the convection event whereas 33 is due to the mesoscale structures southwestward advection after the event sixty percent of the restratification with respect of the water column initial structure occurs before july 1987 and is due to light water advection afterward restratification is due to the mixing and is not complete before next year convection

a real time oceanographic nowcast forecast system for the mediterranean sea we describe here a nowcast forecast system for the entire mediterranean sea designed for real time forecasts and closely resembling operational numerical weather prediction systems the core of the system is a high resolution 10 km three dimensional primitive equation based sigma coordinate numerical circulation model assimilating remotely sensed multi channel sea surface temperature and in situ expendable bathythermograph conductivity temperature depth observational data using an optimal interpolational scheme we present results for 1993 and 1994 from this data assimilation model focusing principally on the mesoscale features prevalent in the western and eastern mediterranean sea we show that the model exhibits considerable skill in simulating both the permanent and transient mesoscale features in the mediterranean in particular hitherto less well known and less well studied circulation features in the adriatic and aegean seas are carefully examined and presented particular care is given to discussing the circulation in the entire mediterranean with particular attention to flows through various straits and their variability

an ocean largeheddy simulation model with application to deep convection in the greenland sea a nonhydrostatic boussinesq threehdimensional model the ocean largeheddy simulation model lolemr has been developed to study deep oceanic convection the model uses a subgridhscale parameterization of turbulence developed for largeheddy simulation models and the advection of scalars is accomplished using a monotonic scheme a set of experiments was performed using olem to provide a direct comparison with laboratory results and aircraft measurements of the atmospheric convective boundary layer the results from these experiments are in excellent agreement with laboratory and atmospheric convective boundary layer measurements of the mean profiles of zonal and vertical velocity variance potential temperature variance and heat flux the horizontal wavenumber spectra of zonal and vertical velocity are also in good agreement with laboratory measurements and kolmogorov s theoretical inertial subrange spectrum a set of experiments using a potential temperaturehsalinity profile from the central greenland sea for model initialization was conducted to study the effect of the thermobaric instability and rotation on the structure and evolution of deep oceanic convection the artificial removal of the thermobaric instability suppresses penetrative convection which is responsible for rapid changes in water properties at depths much greater than occurs for convective mixedhlayer deepening the vertical velocity and diameter 0 08 m s 1 and 300 m respectively of the penetrative plumes are in good agreement with observations from the greenland sea a period of strong penetrative convection is followed by a gradual transition to convective mixedhlayer deepening during penetrative convection the values of heat flux are about 2 times greater than convective mixedhlayer deepening in the absence of rotation the evolution of penetrative convection occurs more rapidly and vertical motions are more vigorous the presence of the horizontal component of rotation forces asymmetries in the circulation around a penetrative plume these experiments clearly demonstrate the importance of thermobaric instability and rotation on deep convection to properly model largehscale flows in regions of penetrative convection it is necessary to include these effects in the vertical mixing parameterization

can eddies set ocean stratification abstract a simple theory is presented for the buoyancy anomaly and depth of penetration of a warm lens created by a surface buoyancy flux and ekman pumping in an initially homogeneous rotating fluid it is assumed that the overturning of isopycnals induced by pumping and differential heating balances the counteroverturning tendency of baroclinic instability baroclinic eddies not only develop on the stratified lens but also play a fundamental role in setting its stratification the theory is successfully tested against numerical and laboratory experiments in which the mechanically induced deepening of a buoyant lens is arrested by its baroclinic instability finally the possibility is discussed that the eddy transfer process studied here might play a role in setting the stratification and depth of the main thermocline in the ocean

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

a numerical study of dense water formation and transport on a shallow sloping continental shelf the circulation and transport of dense water generated by an idealized coastal polynya is studied using a three dimensional primitive equation model starting with a homogeneous quiescent ocean a constant negative buoyancy flux is imposed at the surface over a half elliptical region adjacent to the coastal boundary on a gently sloping continental shelf the flow response can be divided into the following three phases geostrophic adjustment instability and offshore eddy transport during geostrophic adjustment the fluid within the forcing region becomes denser and the flow at the edge of the forcing region accelerates in response to the strong density gradient there eventually the flow at the leading edge of the forcing region relative to kelvin wave propagation becomes unstable and a train of counterrotating eddies develops these eddies then form a complex three dimensional flow field and rapidly transport dense water offshore across isobaths the density within the forcing region reaches a maximum which remains fairly constant after the eddies begin to transport the dense fluid offshore the results are qualitatively insensitive to weakening of the negative buoyancy forcing and to changing the bottom slope eddy scales and velocities are consistent with observations in the arctic the results suggest that instability processes and eddy fluxes are important in transporting dense water off continental shelves and into marginal seas

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

convection with rotation in a neutral ocean a study of open ocean deep convection abstract the intensity and scale of the geostrophically adjusted end state of the convective overturning of a homogeneous rotating ocean of depth h at a latitude where the coriolis parameter is f induced by surface buoyancy loss of magnitude b0 are studied by numerical experiment the experiments are related to observations and laboratory studies of open ocean deep convection a numerical model based on the nonhydrostatic boussinesq equations is used the grid spacing of the model is small enough that gross aspects of convective plumes themselves can be resolved yet the domain of integration is sufficiently large to permit study of the influence of plumes on the large scale and geostrophic adjustment of the convected water numerical simulations suggest that cooling at the sea surface is offset by buoyancy drawn from depth through the agency of convective plumes these plumes efficiently mix the water column to generate a dense chimney of fluid which subsequently breaks up through the mechanism of bar

brine driven eddies under sea ice leads and their impact on the arctic ocean mixed layer abstract eddy generation induced by a line shaped salt flux under a sea ice lead and associated salt transport are investigated using a three dimensional numerical model the model is designed to represent a typical condition for the wintertime arctic ocean mixed layer where new ice formation within leads is known to be one of the primary sources of dense water the result shows that along lead baroclinic jets generate anticyclonic eddies at the base of the mixed layer and almost all the lead originated salt is contained inside these eddies these eddies survive for over a month after closing of the lead and transport the lead originated salt laterally consequently the lead origin salt settles only on the top of the halocline and is not used for increasing salinity of the mixed layer sensitivity experiments suggest that the horizontal scale of generated eddies depends only on the surface forcing and is proportional to the cube root of the total amount of salt input this scaling of eddy size is consi

modeled radar surface signature of deep ocean convection deep ocean convection the process by which the deep waters of the world s oceans are created and renewed plays a key role in the global thermohaline circulation and hence the world s heat balance the process of deep ocean convection involves a vigorous overturning of the ocean water column down to depths of 2000 3000 m in an area probably not larger than 50 km in diameter this paper details the results of a theoretical study to identify remotely sensible surface signatures for deep ocean convection due to the all weather capability efforts have focused on the microwave part of the spectrum particularly the high resolution imaging capability of synthetic aperture radar sar the goal of this research is to use the sar surface signature or fingerprint to identify and characterize areas of convection in the open ocean this information is then used to improve model parameterizations for deep convection used in general circulation models electromagnetic simulations of remote sensing signatures of deep ocean convection have been performed based on existing hydrodynamic models simulated surface signatures of deep convection are presented for various hydrodynamic and imaging conditions along with a discussion of applicability of these simulations to real sar data key findings are the existence of a definite identifiable radar surface signature in convective regions and a set of conditions under which one would expect to observe these signatures

effects of ambient stratification and shelfbreak topography on offshore transport of dense water on continental shelves the transport of dense water offshore from an idealized coastal polynya is examined using a primitive equation numerical model first the prior scaling of the equilibrium density of water produced within the polynya is extended to include the effects of linear bottom slope next ambient linear stratification is added the equilibrium density is modified slightly by the density at the bottom at the initial time next shelfbreak topography is included with both weak and strong ambient stratification for the case of weak stratification dense water carried to the shelfbreak within eddies moves rapidly downslope and is trapped near the bottom the along shelf scale of the dense water cascading down the slope is set by the diameter of the dense water eddies that form along the periphery of the coastal polynya for the case of strong stratification dense water is carried offshore across the shelfbreak at an intermediate depth injecting water originally within the polynya across the shelf and over the continental slope a bottom trapped current flowing near the shelfbreak in the direction of coastal trapped wave propagation also forms these results suggest that water formed within coastal polynyas over arctic shelves may be capable of ventilating the continental slope regions and possibly central basins of the arctic ocean via eddy fluxes

hydrothermal plume dynamics on europa implications for chaos formation 1 hydrothermal plumes may be responsible for transmitting radiogenic or tidally generated heat from europa s rocky interior through a liquid ocean to the base of its ice shell this process has been implicated in the formation of chaos regions and lenticulae by melting or exciting convection in the ice layer in contrast to earlier work we argue that europa s ocean should be treated as an unstratified fluid we have adapted and expanded upon existing work describing buoyant plumes in a rotating unstratified environment we discuss the scaling laws governing the flow and geometry of plumes on europa and perform a laboratory experiment to obtain scaling constants and to visualize plume behavior in a europa like parameter regime we predict that hydrothermal plumes on europa are of a lateral scale at least 25 50 km comparable to large chaos regions they are too broad to be responsible for the formation of individual lenticulae plume heat fluxes 0 1 10 w m 2 are too weak to allow complete melt through of the ice layer current speeds in the plume 3 8 mm s are much slower than indicated by previous studies the observed movement of ice blocks in the conamara chaos region is unlikely to be driven by such weak flow index terms 6218 planetology solar system objects jovian satellites 5418 planetology solid surface planets heat flow 5430 planetology solid surface planets interiors 8147 4540 oceanography physical ice mechanics and air sea ice exchange processes 4568 oceanography physical turbulence diffusion and mixing processes keywords chaos europa hydrothermal plumes

thermal evolution of the greenland sea gyre in 1988 1989 slice inverses of temperature and heat content from the 1988 1989 greenland sea tomography experiment and other observations including standard conductivity temperature depth stations moored thermistors surface meteorological variables and surface ice cover are combined to better understand the thermodynamics of the greenland sea gyre thermal evolution of the gyre center seems to divide naturally into the following three periods a preconditioning phase november january during which surface salinity is increased by brine rejection from ice formation and by entrainment but in which the mixed layer deepens only slowly to a depth of some 150 200 m a deep mixing phase february march during which the surface mixed layer deepens rapidly to approximately 1500 m in the gyre center purely under the influence of local surface cooling and a restratification phase during which the products of deep mixing are replaced by arctic intermediate water flowing in from the gyre edges the onset of the deep mixing phase occurs after ice formation in the gyre center stops resulting in an area of open water where large heat fluxes can occur in surrounding regions including the odden region to the south ice is still being formed to the north and west closer to the steep topography of the continental shelf the inverse results show significant variability due to advection and large temperature and heat content fluctuations with a period of about 50 days are seen

observation of a deep convection regime with acoustic tomography in the winter of 1991 1992 a convection experiment was conducted in the western mediterranean gulf of lions combining a variety of observational techniques an essential component was an acoustic tomography array consisting of six moorings designed to observe the time evolution of the large scale processes believed to be relevant in a convection regime here two dimensional slice inversions in three directions from the central mooring are used to estimate the volume of convected water and the mean convection depth and to observe the preconditioning and restratification processes before and after the convection the near surface layer is well sampled by the acoustics which show cooling and subsequent entrainment of the warmer levantine intermediate water liw from below in agreement with mixedlayer calculations during the 2 months prior to the main convection event the total heat loss of the large scale field is in approximate agreement with the surface heat fluxes showing that little net warm water advection takes place from outside the convection region the implied confinement of water by the local circulation should be an important factor in setting the location and extent of the deep convection patch the volume of water modified by convection in this winter is estimated to correspond to an area of order 60 km radius and 1500 m depth it is argued that the homogenized area implies an annual mean deep water replenishment of 0 3 sv the restratification by the return of less dense water in the surface and liw layers occurs first by rapid capping in the near surface region thereafter the southern and eastern parts of the region restratify in the deeper layers on a 40 day timescale while a dense core of 50 60 km diameter remains in the northwest until the end of the experiment

role of transients in the dynamics of east asian summer seasonal mean circulation anomalies a study of 1993 and 1994 abstract by using the national centers for environmental prediction reanalysis data and a nonlinear barotropic model the transient activities and the possible role of transient vorticity fluxes in the maintenance of east asian summer seasonal mean circulation anomalies associated with japan s extremely cool and wet summer of 1993 and hot and dry summer of 1994 are examined data analysis shows that the summertime atmospheric circulation and the transient activity anomalies exhibit nearly opposite patterns over east asia during these two years vorticity budget calculations indicate that the anomalies of transient activities in these two years produced strong transient vorticity flux forcing anomalies that are comparable in magnitude to the divergent forcing anomalies over east asia the nonlinear barotropic model when forced by the anomalous divergence and transient vorticity flux forcing together produces simulations that bear resemblance to the observed summertime seasonal mean circulation anomalies

overturning the mediterranean thermohaline circulation for more than five decades the mediterranean sea has been identified as a region of so called thermohaline circulation namely of basin scale overturning driven by surface heat and freshwater exchanges the commonly accepted view is that of an interaction of zonal and meridional conveyor belts that sink at intermediate or deep convection sites however the connection between convection and sinking in the overturning circulation remains unclear here we use a multidecadal eddy permitting numerical simulation and glider transport measurements to diagnose the location and physical drivers of this sinking we find that most of the net sinking occurs within 50 km of the boundary away from open sea convection sites vorticity dynamics provides the physical rationale for this sinking near topography only dissipation at the boundary is able to balance the vortex stretching induced by any net sinking which is hence prevented in the open ocean these findings corroborate previous idealized studies and conceptually replace the historical offshore conveyor belts by boundary sinking rings they challenge the respective roles of convection and sinking in shaping the oceanic overturning circulation and confirm the key role of boundary currents in ventilating the interior ocean

mesoscale eddies in the labrador sea and their contribution to convection and restratification abstract the cycle of open ocean deep convection in the labrador sea is studied in a realistic high resolution 4 km regional model embedded in a coarser north atlantic setup this configuration allows the simultaneous generation and evolution of three different eddy types that are distinguished by their source region generation mechanism and dynamics very energetic irminger rings irs are generated by barotropic instability of the west greenland and irminger currents wgc ic off cape desolation and are characterized by a warm salty subsurface core they densely populate the basin north of 58 n where their eddy kinetic energy eke matches the signal observed by satellite altimetry significant levels of eke are also found offshore of the west greenland and labrador coasts where boundary current eddies bces are spawned by weakly energetic instabilities all along the boundary current system bcs baroclinic instability of the steep isopycnal slopes that result from a deep convective over

the near surface hydrography beneath the odden ice tongue as part of the european subpolar ocean programme esop the german research icebreaker polarstern worked in the greenland sea in the late winter of 1993 whilst on passage the ship encountered a severe winter storm with winds consistently above 20 m s 1 coupled to air temperatures of below 10 degrees c the underway sensors revealed heat fluxes of greater than 700 w m 2 across most of the nordic basin peaking at greater than 1200 w m 2 when the ship crossed the cold fresh water of the jan mayen current this large heat flux coupled to the unique hydrographic conditions present in the jan mayen current allowed sea ice generation in the form of frazil ice at a rate of 28 cm d 1 this frazil ice then developed into pancake ice measurements also were made in the late winter beneath this pancake ice in two remnants of the odden in the jan mayen current hydrographic conditions are such that the ice can exist for a long period of time before eventually decaying due to short wave radiation at the surface towards the centre of the greenland sea hydrographic measurements reveal that the ice is more transient and decays four times more rapidly than ice in the jan mayen current we discuss the development of the odden ice tongue in light of these results and add evidence to the argument that the eventual fate of the water stored in the ice is important and could be a relevant factor in the formation of greenland sea deep water c 1999 elsevier science ltd all rights reserved

coincident buoy and sar derived surface fluxes in the western weddell sea during ice station weddell 1992 propagation shows lower agreement for divergence 47 4 rmse 7 46 10 8 s 1 but we find these results sufficient for integrated surface flux comparisons using a toy model we test the effects of aliasing in surface flux determination the results show that variability associated with storms ocean tides inertial oscillations and other highfrequency forcing affects integrated sea ice growth rates along this continental slope location integrated salt and new ice production rates computed from buoys are found to be two times larger than those computed from ers 1 sar motion products we show that these differences in salt and ice production rates result primarily from inadequate temporal resolution of heat flux variability and sea ice divergence comparison with other studies shows that the problem is widespread thereby impacting the modeling of sea ice mass balance and variability the small scale processes cited here have significant ramifications for larger scales and the global thermohaline circulation

observations of open ocean deep convection in the labrador sea from subsurface floats abstract the occurrence and extent of deep convection in the labrador sea in winters 1996 97 and 1997 98 is investigated from measurements of over 200 neutrally buoyant subsurface profiling autonomous lagrangian circulation explorer palace and sounding oceanographic lagrangian observer solo floats in addition to providing drift velocity data and vertical profiles of temperature and salinity 55 floats are equipped with vertical current meters vcms time series of vertical velocity derived from measured pressure and vertical flow past the float and temperature are obtained from the vcm floats mixed layer depths estimated from profile measurements indicate that convection reached depths greater than 1300 m in 1997 but no deeper than 1000 m in 1998 deep mixed layers were concentrated in the western basin although a number of deep mixed layers were observed southwest of cape farewell and also north of 60 n the highest variance in vertical velocity and the lowest mean temperatures were found in t

buoyancy and wind driven convection at mixed layer density fronts in this study the influence of a geostrophically balanced horizontal density gradient on turbulent convection in the ocean is examined using numerical simulations and a theoretical scaling analysis starting with uniform horizontal and vertical buoyancy gradients convection is driven by imposing a heat loss or a destabilizing wind stress at the upper boundary and a turbulent layer soon develops for weak lateral fronts turbulent convection results in a nearly homogeneous mixed layer ml whose depth grows in time for strong fronts a turbulent layer develops but this layer is not an ml in the traditional sense because it is characterized by persistent horizontal and vertical gradients in density the turbulent layer is however nearly homogeneous in potential vorticity pv with a value near zero using the pv budget a scaling for the depth of the turbulent low pv layer and its time dependence is derived that compares well with numerical simulations two dynamical regimes are identified in a convective layer near the surface turbulence is generated by the buoyancy loss at the surface below this layer turbulence is generated by a symmetric instability of the lateral density gradient this work extends classical scalings for the depth of turbulent boundary layers to account for the ubiquitous presence of lateral density gradients in the ocean the new results indicate that a lateral density gradient in addition to the surface forcing can affect the stratification and the rate of growth of the surface boundary layer

modeling the dispersal of levantine intermediate water and its role in mediterranean deep water formation this paper demonstrates the importance of levantine intermediate water liw in the deep water formation process in the mediterranean using the modular ocean general circulation model at 0 25 resolution 19 vertical levels over the entire mediterranean with an open gibraltar strait liw formation is strongly prescribed in the rhodes gyre region by haney 1971 relaxation while in other regions surface salinity relaxation is much reduced by applying the mixed thermohaline surface boundary conditions isopycnal diagnostics are used to trace water mass movements and volume fluxes are monitored at straits low viscosity and diffusion are used to permit baroclinic eddies to play a role in water mass dispersal the overall water budget is measured by an average flux at gibraltar of 0 8 sv of which 0 7 sv is exchanged with the eastern basin at sicily liw density around 28 95 spreads rapidly after formation throughout the entire levantine due to baroclinic eddies toward the west liw accumulates in the northern and central ionian with some entering the adriatic through otranto and some mixing southward in eddies and exiting to the western mediterranean through sicily liw is converted to deep water in the south adriatic at an average rate of 0 4 sv water exchange through the otranto strait appears to be buoyancy driven with a strong bias to the end of winter march april while at sicily the exchange has a strong symmetric seasonal cycle with maximum transport of 1 1 sv in december indicating the effects of wind driving liw pathways in the west are complex and variable in the tyrrhenian intermediate water becomes uniform on isopycnal surfaces due to eddy stirring west of sardinia two liw boundary currents are formed in the balearic basin one flows northward up the west coast of sardinia and corsica and one westward along the northern african coast the northward current is consistent with observations while the westward current is intermittent for the first 10 years often breaking up into eddies which enter the basin interior some observations of high salinity waters near the african coast may support this interpretation liw retains a subsurface salinity maximum of 38 4 38 5 practical salinity units psu when reaching the northwestern mediterranean contrasting with surface waters fresher than 38 0 psu west mediterranean deep water is formed below 1500 m depth with climatological characteristics when it is mixed and cooled during winter convection in lions gyre

impact of the spatial distribution of the atmospheric forcing on water mass formation in the mediterranean sea the impact of the atmospheric forcing on the winter ocean convection in the mediterranean sea was studied with a high resolution ocean general circulation model the major areas of focus are the levantine basin the aegean cretan sea the adriatic sea and the gulf of lion two companion simulations differing by the horizontal resolution of the atmospheric forcing were compared the first simulation med16 era40 was forced by air sea fields from era40 which is the ecmwf reanalysis the second simulation med16 ecmwf was forced by the ecmwf analyzed surface fields that have a horizontal resolution twice as high as those of era40 the analysis of the standard deviations of the atmospheric fields shows that increasing the resolution of the atmospheric forcing leads in all regions to a better channeling of the winds by mountains and to the generation of atmospheric mesoscale patterns comparing the companion ocean simulation results with available observations in the adriatic sea and in the gulf of lion shows that med16 ecmwf is more realistic than med16 era40 in the eastern mediterranean although deep water formation occurs in the two experiments the depth reached by the convection is deeper in med16 ecmwf in the gulf of lion deep water formation occurs only in med16 ecmwf this larger sensitivity of the western mediterranean convection to the forcing resolution is investigated by running a set of sensitivity experiments to analyze the impact of different time space resolutions of the forcing on the intense winter convection event in winter 1998 1999 the sensitivity to the forcing appears to be mainly related to the effect of wind channeling by the land orography which can only be reproduced in atmospheric models of sufficient resolution thus well positioned patterns of enhanced wind stress and ocean surface heat loss are able to maintain a vigorous gyre circulation favoring efficient preconditioning of the area at the beginning of winter and to drive realistic buoyancy loss and mixing responsible for strong convection at the end of winter