the seasonal cycle of lower tropospheric gravity wave activity at davis antarctica 69 s 78 e abstracta vhf wind profiling radar located at davis in coastal east antarctica 69 s 78 e collected data from september 2009 to august 2011 in the lower troposphere gravity wave activity is quantified using the radar s wind velocity variances era interim and antarctic mesoscale prediction system amps forecast output are used to understand the gravity wave activity in the context of the synoptic scale meteorology and to identify the likely source of the observed gravity waves the seasonal cycle of lower tropospheric gravity wave activity 2 0 3 2 km altitude obtained from the radar data for waves with ground based periods of 16 min 12 8 h reveals a maximum in winter and a minimum in summer the largest gravity wave activity corresponds in time to the presence of a surface depression centered north of davis that directs strong northeasterly winds along the antarctic coastline case studies indicate that these winds interact with an ice ridgeline located around 60 km northeast and upwind of davis th

inertia gravity waves observed in the lower stratosphere over macquarie island abstract this study examines the properties of inertia gravity waves observed in the lower stratosphere over macquarie island how these properties vary with season and the likely source of the waves the waves are observed in high resolution upper air ozonesonde soundings of wind and temperature released from macquarie island during the 1994 ashoe maesa program the properties of the inertia gravity waves observed in the soundings are quantified using hodograph and rotary spectral analyses the analyzed waves have horizontal wavelengths between 100 and 1000 km vertical wavelengths between about 1 and 7 km intrinsic frequencies between f and 2f and horizontal trace speeds between 50 and 30 m s 1 there appears to be a seasonal cycle in the inertia gravity wave activity in the lower stratosphere the minimum being in the austral winter when the background zonal flow is strong and westerly and its vertical shear is positive in contrast the variance of the horizontal perturbation winds does not show a

lagrangian exploration of the california undercurrent 1992 95 abstract during the period 1992 95 nineteen isobaric rafos floats placed in the california undercurrent at intermediate depths 150 600 m off monterey and san francisco california reveal a region of varying width of subsurface poleward flow adjacent to the continental margin the float trajectories exhibit three patterns poleward flow in the undercurrent reversing but predominately alongshore flow adjacent to the continental margin and farther offshore anticyclonic motion accompanied by slow westward drift flow continuity of the undercurrent exists between pt reyes and at least cape mendocino with an average speed dependent on the float depth speeds were variable but common features were acceleration occurring to the south of pt arena and deceleration to the north of cape mendocino an important mechanism for floats and water to enter the ocean interior from the undercurrent is through the formation of submesoscale coherent vortices

gravity wave excitation during the coastal transition of an extreme katabatic flow in antarctica abstractthe offshore extent of antarctic katabatic winds exerts a strong control on the production of sea ice and the formation of polynyas in this study we make use of a combination of ground ba

calipso observations of wave induced pscs with near unity optical depth over antarctica in 2006 2007 1 ground based and satellite observations have hinted at the existence of polar stratospheric clouds pscs with relatively high optical depths even if optical depth values are hard to come by this study documents a type ii psc observed from spaceborne lidar with visible optical depths up to 0 8 comparisons with multiple temperature fields including reanalyses and results from mesoscale simulations suggest that intense small scale temperature fluctuations due to gravity waves play an important role in its formation while nearby observations show the presence of a potentially related type ia psc farther downstream inside the polar vortex following this first case the geographic distribution and microphysical properties of pscs with optical depths above 0 3 are explored over antarctica during the 2006 and 2007 austral winters these clouds are rare less than 1 of profiles and concentrated over areas where strong winds hit steep ground slopes in the western hemisphere especially over the peninsula such pscs are colder than the general psc population and their detection is correlated with daily temperature minima across antarctica lidar and depolarization ratios within these clouds suggest they are most likely ice based type ii similarities between the case study and other pscs suggest they might share the same formation mechanisms

energy conversion in the cape verde frontal zone mechanical energy terms are calculated from moored current meter data in the cape verde frontal zone about 20 n 25 w and compared with those derived from a mesoscale model of this frontal region the model is of the bleck and boudra 1981 type with isopycnal coordinates an initially zonal jet representing the canary current is allowed to develop under the influence of baroclinic and barotropic instability processes we find reasonable agreement in magnitudes somewhat smaller in the model and similar distributions in the vertical this leads to the conclusion that the energy transfer terms from the model can be expected to be sufficiently close to reality determination of the transfer terms confirms that the energy transfer in the zone is dominated by baroclinic instability processes while barotropic instability is of minor importance average baroclinic instability energy transfer terms reach values of 2 3 w m 3 in the pycnocline peak layer mean values are of the order 10 w m 3 it is shown that the spatial distribution of active transfer regions is closely related to the structure of the transient eddy field in the frontal zone and that strong instability processes are restricted to the pycnocline

geochronology of the pre andean metamorphism and magmatism in the andean cordillera between latitudes 30 and 36 s abstract in the 30 36 s section of the andean cordillera the pre andean basement is composed by metamorphic igneous and sedimentary rocks of precambrian paleozoic and lower triassic ages they crop out in the morphostructural units named from east to west sierras pampeanas precordillera cordillera frontal and bloque de san rafael in argentina and cordillera de la costa in chile isotopic age determinations of the metamorphic rocks indicate a migration of the metamorphic events from east to west such as precambrian to lower paleozoic ages 900 m y and 650 400 m y in the sierras pampeanas lower paleozoic ages about 500 m y in the precordillera and cordillera frontal and upper paleozoic to lower triassic ages 340 210 m y in the cordillera de la costa these metamorphic belts contain a large variety of mafic and ultramafic rocks the distribution of the pre andean granitoids show no apparent chronological zonation however the plutonic activity persisted until the lower carboniferous in the sierras pampeanas to the lower triassic in the cordillera frontal and precordillera associated with an important vulcanism which also develops in the bloque de san rafael and until the jurassic in the cordillera de la costa

north atlantic potential vorticity and its relation to the general circulation abstract maps and sections of the large scale north atlantic potential vorticity q are presented here q is fd dz where f is the coriolis frequency the potential density and z the vertical coordinate they bear on the general circulation and on geostrophic waves instability and turbulence in many ways both eulerian and lagrangian mean circulations proceed along isostrophes q constant in a zero dissipation region in a resting fluid q varies simply as the sine of the latitude but we show here that the wind driven circulation reshapes the q field creating bowls and plateaus which allow the flow to cross latitude circles the implied nature of the western boundary current is very different than in classical frictional theory the maps show a region of uniform potential vorticity in the wind gyre 26 5 27 0 which fills the ocean between 15 37 n and 20 80 w such regions were prominent features of a circulation theory of rhines and young 1982a b at deeper levels and close to surface out

the effect of orographic gravity waves on antarctic polar stratospheric cloud occurrence and composition 1 a seasonal analysis of the relationship between mesoscale orographic gravity wave activity and polar stratospheric cloud psc composition occurrence around the whole of antarctica is presented gravity wave variances are derived from temperature measurements made with the constellation observing system for meteorology ionosphere and climate cosmic global positioning system radio occultation gps ro satellites data from the cloud aerosol lidar with orthogonal polarization caliop instrument onboard the cloud aerosol lidar and infrared pathfinder satellite observations calipso satellite are used to determine the psc composition class distribution and spatial volume the results show intermittent large wave activity above the antarctic peninsula which is coincident with large volumes of h2o ice pscs these ice psc volumes advect downstream where increases in nitric acid trihydrate nat psc volumes occur supporting the mountain wave seeding hypothesis during winter 2007 in the latitude range 60 s 70 s near the edge of the vortex and where temperatures are close to psc formation thresholds 30 of all pscs are attributable to orographic gravity waves in the separate composition classes around 50 of both h2o ice pscs and a high nat number density liquid nat mixture class of pscs are due to these waves while we show that planetary waves are the major determinant of psc presence at temperatures close to the nat formation threshold we also demonstrate the important role of mesoscale intermittent orographic gravity wave activity in accounting for the composition and distribution of pscs around antarctica

a global view of stratospheric gravity wave hotspots located with atmospheric infrared sounder observations 1 the main aim of this study is to find and classify hotspots of stratospheric gravity waves on a global scale the analysis is based on a 9 year record 2003 to 2011 of radiance measurements by the atmospheric infrared sounder airs aboard nasa s aqua satellite we detect gravity waves based on 4 3 m brightness temperature variances our method focuses on peak events i e strong gravity wave events for which the local variance considerably exceeds background levels we estimate the occurrence frequencies of these peak events for different seasons and time of day and use the results to find local maxima or hotspots in addition we use airs radiances at 8 1 m to simultaneously detect convective events including deep convection in the tropics and mesoscale convective systems at middle latitudes we classify the gravity wave sources based on seasonal occurrence frequencies for convection but also by means of time series analyses and topographic data our study reproduces well known hotspots of gravity waves e g the andes and the antarctic peninsula however the high horizontal resolution of the airs observations also allows us to locate numerous mesoscale hotspots which are partly unknown or poorly studied so far most of these mesoscale hotspots are found near orographic features like mountain ranges coasts lakes deserts or isolated islands this study will help to select promising regions and seasons for future case studies of gravity waves

mass fluxes in the canary basin abstract ocean studies in the 1970s provided an improved knowledge of the coastal upwelling region off nw africa while in the 1980s and 1990s they led to a good description of the open ocean flow patterns in the canary basin it was not until the late 1990s that major research addressed the open coastal ocean coupled response here we examine the mean and seasonal circulation patterns in the canary basin with data from four hydrographic cruises carried out in the region between cape ghir madeira island and the canary islands we apply an inverse box model to an ocean divided into 14 layers with several layers representing each water mass or stratum to obtain mass fluxes consistent with the thermal wind equation an optimum flow description is obtained using conservation of mass salt and heat anomaly biologically corrected oxygen and silicate and allowing for ekman transport in the surface layer and dianeutral mixing between adjacent layers the deep waters show no predominant flow direction while the intermediate waters display localized southward flowing mediterranean water far from shore and northward flowing antarctic intermediate water near the continental slope specially in the passage between the eastern canary islands and the african slope the mean upper thermocline canary current composed of north atlantic central water flows south with an open ocean branch transporting about 3 1 sv 1 sv 10 6 m 3 s 1 10 9 kg s 1 and an upwelling related branch near the continental slope carrying 1 0 3 sv the seasonal transport by the open ocean branch intensifies and moves offshore from spring to fall 2 8 1 2 sv in spring 2 9 1 1 sv in summer and 4 5 1 2 sv in fall while it carries its lowest southward mass flux in winter 1 7 1 0 sv possibly as a result of a migration offshore the sampled region upwelling related southward flow is present in spring and summer 1 9 0 1 sv and 2 4 0 1 sv respectively while in fall and winter it merges with the offshore southward branch this westward migration allows a northward mass flux between the canary islands and the african coast 1 8 0 1 sv that by winter reaches cape ghir 0 5 0 2 sv seasonal air sea heat fluxes fit well with the climatological values the net phosphate transport in the surface layer indicates that primary production was negligible in this region during january 1997 and april 1998 though in this last month production was probably starting as a result of significant nutrient supply

comparative studies of the spreading of mediterranean water through the gulf of cadiz abstract a comparative study is made of observations and model results of the spreading of mediterranean water mw from the strait of gibraltar through the gulf of cadiz past cape st vincent into the eastern north atlantic the observations include a set of hydrographic sections from west of gibraltar to offshore of lisbon the tracking of rafos floats and current meter data the model is a very fine resolution limited area model of the region around cape st vincent and includes model floats both the observational data and the model results show the mw descending into two distinct layers around 800 and 1200 m depth in the gulf of cadiz as the mw leaves the slope meddies are generated and have been tracked by the rafos floats and can be seen in the paths of the model floats

the near surface flow in the subtropical gyre south of the azores this study presents evidence that the azores current azc is a permanent feature of the north atlantic subtropical gyre and that it feeds the north equatorial current nec the azc path is located south of the azores its velocity is mostly geostrophic and the energy level in the mesoscale range is higher than in the nec the nec velocity appears to be mostly ageostrophic and the wind driven surface velocity is at about 15 to the right of the mean wind field

microstructure observations of turbulent heat fluxes in a warm core canada basin eddy abstractan intrahalocline eddy was observed on the chukchi slope in september of 2015 using both towed ctd and microstructure temperature and shear sections the core of the eddy was 6 c significa

observations and fine scale model simulations of gravity waves over davis east antarctica 69 s 78 e large vertical velocities were observed throughout the troposphere at davis east antarctica on 18 february 2014 by a vhf wind profiling radar simulations using the met office unified model at 2 2 0 5 and 0 1 km horizontal grid spacing were able to broadly capture the location timing and magnitude of the observed velocities as well as reveal that they are due to small scale orographic gravity waves resulting from the interaction between the coastal topography and strong easterly winds associated with a synoptic scale cyclone situated to the north the simulations indicated that the gravity waves are responsible for i temperature fluctuations which coincided with satellite observed cloud variations in the vicinity of davis suggesting that they have a crucial role in the formation of cirrus clouds and ii large vertical momentum fluxes in the troposphere the waves are prevented from propagating into the stratosphere by the background winds turning from near surface easterlies to lower stratospheric northerlies as well as illuminating and quantifying the role that weather systems have in producing orographic gravity waves along the east antarctic coastline studies such as this should be exploited to improve the representation of key localized atmospheric processes in global climate models

gravity wave characteristics in the southern hemisphere revealed by a high resolution middle atmosphere general circulation model abstractgravity wave characteristics in the middle to high latitude southern hemisphere are analyzed using simulation data over 3 yr from a high resolution middle atmosphere general circulation model without using any gravity wave parameterizations gravity waves have large amplitudes in winter and are mainly distributed in the region surrounding the polar vortex in the middle and upper stratosphere while the gravity wave energy is generally weak in summer the wave energy distribution in winter is not zonally uniform but it is large leeward of the southern andes and antarctic peninsula linear theory in the three dimensional framework indicates that orographic gravity waves are advected leeward significantly by the mean wind component perpendicular to the wavenumber vector results of ray tracing and cross correlation analyses are consistent with this theoretical expectation the leeward energy propagation extends to several thousand kilometers which explains part of the gravity wave distribution aro

three dimensional circulation in the nw africa coastal transition zone abstract high resolution data collected southeast of the canary islands during late winter 2006 are analyzed to describe the hydrography and three dimensional circulation in the coastal transition zone off nw africa the data are optimally interpolated over a regular grid the geostrophic velocity field is calculated and the q vector formulation of the omega equation is used to compute the quasi geostrophic qg mesoscale vertical velocity the coastal transition zone is divided into upwelling frontal and offshore regions with distinct physical and dynamic characteristics the upwelling region is characterized by cold and weakly stratified waters flowing towards the equator with a poleward undercurrent of approximately 0 05 m s 1 over the continental slope the frontal region exhibits a southwestward baroclinic jet associated with cross shore raising isopycnals the jet transport is close to 1 sv with maximum velocities of 0 18 m s 1 at surface decreasing to 0 05 m s 1 at 300 db vertical sections across the frontal region show the presence of deep eddies probably generated by the topographic blocking of the islands to the southward current as well as much shallower eddies that likely have arisen as instabilities of the baroclinic upwelling jet the qg mesoscale vertical velocity field is patchy estimated to range from 18 to 12 m day 1 with the largest absolute values corresponding to an anticyclonic eddy located south of fuerteventura island these values are significantly larger than estimates for other vertical velocities diapycnal vertical velocities associated with mixing in the frontal region a few meters per day and wind induced vertical velocities non linear ekman pumping arising from the interaction between the wind stress and the background vorticity maximum values of a few meters per day linear ekman pumping due to the divergence of ekman transport a fraction of a meter per day or the coastal constraint in the upwelling region about 0 7 m day 1 however the patchiness in both the qg mesoscale vertical velocity and the non linear ekman pumping velocity cause their integrated vertical transports to be one order of magnitude smaller than either coastal ekman transport 0 08 sv integrated linear ekman pumping 0 05 sv or diapycnal transfer about 0 1 0 2 sv the pattern of the near surface fluorescence field is a good indicator of these different contributions with large homogeneous values in the coastal upwelling region and a patchy structure associated with the offshore mesoscale structures

interaction of mediterranean water eddies with sedlo and seine seamounts subtropical northeast atlantic abstract during years 2003 and 2004 both sedlo and seine seamounts lying in the area of influence of the mediterranean water outflow in the northeast atlantic were investigated in the framework of the eu funded project oasis analysis of ctd data shows that the levels of major variability in temperature and salinity were confined to the upper ocean layer which is subject to seasonal air sea heat exchange and to the mediterranean water mw level in this paper we concentrate on the latter case and show that the variability observed resulted from mediterranean water eddies meddies colliding with the seamounts combined data from ctd surveys current meter moorings ship mounted adcp and satellite altimetry suggest that during the period of observations there was only one meddy interacting with each of the seamounts on sedlo seamount intensive interaction resulted in the loss by the meddy of about 25 of the salt around the seamount whereas on seine the meddy or portion of it escaped the seamount after performing several rotations around the summit without any significant interaction

variability of the antarctic intermediate waters in the northern canary box abstract several chemical parameters were measured during four seasonal cruises in 1997 and 1998 within the canary islands acores gibraltar observations project along the transects within the so called northern canary box ncb this area is enclosed between the african coast latitudes 29 n and 32 n and longitude 18 w to the north of the canary islands spain the nutrient and oxygen concentration data are used in order to establish the atlantic antarctic intermediate water aaiw distribution in the area by means of an anomaly method it is established that this water mass is widely found in this zone particularly new to the african coast a volumetric budget indicates that the aaiw volume flowing into the ncb is of the same order as the mediterranean water mw inflow the results indicate that only 40 of the aaiw mass reaching the box flows northwards through the 32 n section whereas 20 returns southwards through the 29 n section

canary current and north equatorial current from an inverse box model 1 the large scale canary basin circulation is estimated from a box inverse model applied to hydrographic data from a quasi synoptic survey carried out in september 2003 the cruise consisted of 76 full depth ctd and oxygen stations circulation is required to nearly conserve mass and anomalies of salinity and heat within layers bounded by neutral surfaces it permits advective and diffusive exchange between layers and an adjustment of the ekman transport and the freshwater flux divergences the canary current at the thermocline layer transports a net mass of 4 7 0 8 sv southward north of the canary islands from the african coast to 19 w it is divided into a northward circulation at a rate of 1 1 0 5 sv between the african coast and lanzarote island and a southward transport of 5 8 0 6 sv it transports north atlantic central water and organic matters advected offshore by the filaments protruding from the upwelling system off northwest africa at 24 n the canary current feeds the north equatorial current that transports a mixture of north and south atlantic central waters westward in the intermediate layer a southwestward flow of 1 2 1 1 sv transports mediterranean water to the subtropical gyre though the highest salt flux is transported by a meddy oxygen distribution and mass transport suggest a northeastward deep flow of a water mass colder than 2 2 c consisting of diluted antarctic bottom water the heat and freshwater divergences and the average dianeutral velocity and diffusion between the sections and the african coast are negligible

synthetic modelling of acoustical propagation applied to seismic oceanography experiments recent work shows that multichannel seismic mcs systems provide detailed information on the oceans finestructure the aim of this paper is to analyze if high order numerical algorithms are suitable to accurately model the extremely weak wavefield scattered by the oceans finestructures for this purpose we generate synthetic shot records along a coincident seismic and oceanographic profile acquired across a mediterranean salt lens in the gulf of cadiz we apply a 2d finite difference time domain propagation model together with second order complex frequency shifted perfectly matched layers at the numerical boundaries using as reference a realistic sound speed map with the lateral resolution of the seismic data we show that our numerical propagator creates an acoustical image of the ocean finestructures including the salt lens that reproduces with outstanding detail the real acquired one

structure and circulation of the upper atlantic ocean northeast of the azores historical data primarily from the igy but spanning the years 1914 1983 have been re examined in an attempt to define the structure and circulation of the upper ocean 0 800 m in the eastern north atlantic 30 50 n 10 40 w the saline greater than 35 7 anticyclonic surface gyre shallows to the north like a wedge being 300 500 m deep at 36 n east of 30 w and outcropping at about 45 n it lies above the mediterranean water separated from it by a salinity minimum and by a pycnostad of subpolar mode water mccartney and talley 1982 eastward flow between 36 n and 46 n is primarily confined to the saline wedge with speeds of 2 4 cm s 1 the flow converges gradually towards the east resulting in fronts and strong meridional property gradients e g mixed layer depth robinson bauer and schroeder 1979 east of 15 w the majority of the supolar mode water is formed by deep winter convection north of the saline wedge and subducts to the south under it southward advection and ventilation rates in the northeast atlantic the main ventilation region for the north atlantic sarmiento rooth and roether 1982 are similar estimated to be 0 2 cm s 1 the freshening of the surface layer between 1967 and 1976 that has been found in widely separated regions of the north atlantic rockall trough sargasso sea labrador sea is also present northeast of the azores salinities down to 500 m have decreased by 0 1 equivalent to an addition of a 1 4 m column of fresh water at the surface the freshening on t 27 1 decreases to negligible values southwards of 40 n it is suggested that changes in the balance of evaporation and precipitation must have occured

subsurface and deeper ocean remote sensing from satellites an overview and new results satellite remote sensors cannot see far beneath the surface layers of the ocean yet many important ocean processes and features are located well below the surface and at considerable depths examples include mediterranean eddies meddies mixed layer depth internal waves and bottom topography deeper ocean remote sensing is becoming even more important because recent data seem to indicate that the deeper ocean is responding to climate variability and change many of these subsurface phenomena have surface manifestations which can be interpreted with the help of models to derive key parameters of deeper ocean processes the objective of this paper is to provide an overview of satellite remote sensing and modeling techniques which enable scientists to characterize subsurface and deeper ocean processes and features and to present some new results

isopycnal eofs in the azores current region a statistical tool fordynamical analysis and data assimilation abstract an empirical orthogonal function analysis of the vertical space time variability of the thermohaline structure of the ocean in summer and fall 1993 in the azores current region has been performed the analysis used data from ctd casts of the semaphore intensive experiment referred to as a seasonally varying climatology the relative merits of depth coordinate and isopycnal coordinate representations have been examined in regard to the quality of identification of physical processes and to the effectiveness of the extrapolation from a sea level anomaly in an attempt to improve the treatment of the vertical dimension in oceanic assimilation problems the isopycnal eofs consistently proved more efficient in capturing the vertical structure of both dominant processes in the area of investigation the variability linked to the mediterranean water and the coherent physical system made up of the azores front and the azores current the isopycnal analysis also proved more robust when meddies mediterra

the source of the canary current in fall 2009 1 the source of the canary current has been inferred from an inverse box model applied to the hydrographic data of a survey carried out in 2009 in the northeast subtropical gyre 29 37 n 9 24 w the portugal current is observed between 13 5 and 14 8 w at 37 n carrying 1 8 0 4 sv southward this current presumably merges with the eastward transport of the azores current system and partly contributes to the mediterranean inflow and partly to the northward recirculation of the azores current through the gulf of cadiz the azores current system is located in the meridional range 33 50 36 25 n at 24 50 w this system transports eastward 7 2 0 5 sv in the thermocline layers and 1 1 0 8 sv at intermediate layers the azores current intermediate water mass has the highest portion of sub arctic intermediate water saiw in the region while the azores countercurrent intermediate waters mass is mainly mediterranean water the canary current extends from 22 25 to 18 50 w at 29 n the westernmost position ever observed this current transports southward 6 2 0 6 sv in the thermocline layers and 2 0 0 8 sv in the intermediate layers this intermediate flow shows a relative maximum of oxygen and a relative minimum in nutrient concentration indicating the presence of saiw the study concludes that at least in fall 2009 the canary current extends to the intermediate waters n 27 9220 approximately 1600 dbar and that azores current feeds the canary current at surface and intermediate layers

a dynamical investigation of the may 2004 mcmurdo antarctica severe wind event using amps on 15 16 may 2004 a severe windstorm struck mcmurdo antarctica the antarctic mesoscale prediction system amps is used along with available observations to analyze the storm a synoptic scale cyclone weakens as it propagates across the ross ice shelf toward mcmurdo flow associated with the cyclone initiates a barrier jet along the transantarctic mountains forcing terms from the horizontal equations of motion are computed in the barrier wind to show that the local time tendency and momentum advection terms are key components of the force balance the barrier jet interacts with a preexisting near surface radiation inversion over the ross ice shelf to set up conditions favorable for the development of large amplitude mountain waves leading to a downslope windstorm in the ross island area hydraulic theory can explain the structure of the downslope windstorms with amplification of the mountain waves possibly caused by wave breaking events the underestimation of amps wind speed at mcmurdo is caused by the misplacement of a hydraulic jump downstream of the downslope windstorms the dynamics associated with the cyclone barrier jet and downslope windstorms are analyzed to determine the role of each in development of the severe winds

mountain waves and wakes generated by south georgia implications for drag parametrization high resolution simulations of flows over south georgia south atlantic are used to increase understanding of the likely influence of small isolated mountainous islands on the large scale flow and to ascertain the extent to which parametrization schemes can account for the missing drag in models where such islands are only partially resolved long duration 1 month austral winter forecasts with a horizontal grid spacing of 1 5 km are used to quantify the mountain wave momentum fluxes generated by the island and the low level drag associated with flow blocking dynamics the characteristics of the drag such as the occurrence of high and low drag states its dependence on wind direction and the spectral contributions to the mountain wave momentum flux are considered flow splitting and low level wave breaking are shown to be responsible for wake regions that extend for hundreds of kilometres from the island regions of deceleration are also evident in the stratosphere due to mountain wave dissipation the extent to which an orographic drag parametrization scheme can reproduce the drag is investigated by comparison with coarse resolution 15 km grid spacing simulations in which the orography is poorly resolved and a large proportion of the drag is parametrized it is demonstrated that the total of the resolved plus parametrized drag in these simulations closely resembles that at high resolution although it is underpredicted during instances of high drag simple modifications to the scheme which enhance the drag when the low level flow is approximately normal to the major axis of the subgrid orography are shown to rectify this the study demonstrates that at least for relatively simple isolated mountain ranges the drag and mountain wave momentum fluxes can be predicted in a deterministic sense by a well tuned parametrization scheme of suitable complexity although inclusion of stochastic effects might lead to yet further improvements

case studies of nonorographic gravity waves over the southern ocean emphasize the role of moisture two case studies of nonorographic gravity waves are carried out for wave events that occurred over the southern ocean in november 2005 mesoscale simulations were carried out with the weather and research forecast model the simulated waves were compared to observations from superpressure balloons of the vorcore campaign and from the high resolution dynamic limb sounder satellite satisfactory agreement is found giving confidence in the estimations of wave parameters and amplitudes for the amplitudes both the model and observations provide a lower bound for different reasons waves are found in the lower stratosphere with horizontal wavelengths of the order of 150 200 km in the horizontal 5 8 km in the vertical corresponding to intrinsic frequencies between 5 and 10 f where f is the coriolis parameter although the tropospheric flow is very different between the two cases there are features which are common and appear significant for the gravity waves these include intense localized updrafts associated with convection in the troposphere and a displaced polar vortex inducing strong winds in the stratosphere above the frontal region relative to theoretical expectations the simulations emphasize the role of moisture intrinsic frequencies are significantly higher than those expected for waves produced by dry spontaneous generation from jets to quantify the contribution of moisture dry simulations were carried out yielding momentum fluxes over oceanic regions that were 2 5 times weaker identification of the generation mechanisms in these complex flows calls for further study and these should include moisture and a realistic stratospheric jet

currents fronts and eddy fluxes in the canary basin hydrographic data from two cruises in the canary basin meteor 57 july 1981 poseidon 86 april 1982 are analysed with respect to current distribution and lateral heat flux in the azores madeira region the first part of the data base consists of long transects of xbt and g e k measurements between cape finisterre north west spain and the northern canary basin where several year long current meter records exist further information is obtained by thermosalinograph surface data and by expendable current profilers xcp geostrophic currents are derived from xbt profiles using the tight temperature salinity relationship in the depth range of the warmwassersphare the results compare well with the g e k and xcp current observations the second part consists of ctd data from an eddy resolving box shaped ctd survey 500 500 km2 centered at the mooring location 33 n 22 w the observations are supplemented by satellite buoy trajectories horizontal parameter distribution is shown in terms of objectively contoured maps bands of spatially enhanced energetic structures seen in the long transects are further resolved by the box survey as a deep jet like current system cross the canary basin in a west east direction associated with this azores current is a frontal zone with near surface temperature and salinity steps of order 2 k and 0 3 practical salinity units the dynamic topography field can be decomposed into a linear background field a rossby wave and a mesoscale eddy field we find that major contributions to the meridional eddy heat flux are confined to the vicinity of the azores current frontal zone it is shown that the principal balance in the temperature equation is between heating by the mean horizontal advection terms and cooling by the eddy flux divergence

the inference of north atlantic circulation patterns from climatological hydrographic data we present a review of spiral techniques which have recently been developed for the determination of absolute velocity profiles from hydrographic observations a specific technique is then designed and applied to the north atlantic part of levitus 1982 climatological hydrographic atlas with the aim of estimating reference velocities and diffusivities for heat salt and potential vorticity these quantities are determined on a 1 grid from the local gradients of temperature and salinity under the constraints of the thermal wind relations and the conservation of the respective tracers including diapycnic and isopycnic mixing terms the estimation procedure includes the statistical framework of inverse modeling in the weighting of the constraints by the data noise variances and the determination of the covariances of the model parameters the resulting circulation pattern bears strong resemblance to the classical view of the north atlantic circulation as put foreward by wust 1935 and defant 1941 the upper layers are dominated by the gulf stream north atlantic current system with a broad subtropical gyre recirculation in the lower layer a western boundary current is fed from norwegian sea overflow penetrating the gibbs fracture zone and partly circulating around the labrador sea as a consequence of the climatological averaging the currents appear in broad shape with much reduced velocities in particular in the upper layer the vertical structure reveals an almost horizontal level of no motion pattern much along the concepts of defant 1941 diffusion coefficients were determined for an upper layer depth of mixed layer to 800 m depth and a lower layer 800 m to 2000 m the spatial pattern of these coefficients correlates with maps of eddy activity showing higher values in the strong current regimes and low values within the subtropical and subpolar gyre average values in the lower layer of the quiet regions are 10 5 m s and 10 m s for the diapycnal and isopycnal diffusivity respectively and 10 1 m s for the vertical diffusivity of vorticity which yields 10 m s for the lateral diffusivity of potential vorticity toward the regions of strong currents and in the upper layer these values roughly increase by an order of magnitude

the ichthyoplankton assemblage of the canaries african coastal transition zone a review abstract in this paper we review information on the ichthyoplankton assemblage of the canaries african coastal transition zone c actz this ctz shows the singularity that the canary archipelago interrupts the main flow of the canary current and trade winds introducing large mesoscale variability in the form of island warm wakes and cyclonic and anticyclonic eddies downstream of the islands besides upwelling filaments stretch towards the archipelago from the african coastal upwelling transporting phytoplankton zooplankton and fish larvae they also interact with eddies shed from the islands to exchange water properties and biogenic material all these mesoscale features influence the composition structure abundance and distribution of the larval fish community lfc of the region the canary current cc and eddies shed from the islands drag larvae of island neritic fish species into the oceanic region and contribute along warm wakes to the horizontal distribution of fish larvae upwelling and upwelling filaments transport larvae of african neritic species into the oceanic region these larvae dominate the lfc and account for the relatively high average larval fish abundance found in the c actz during the summer upwelling season filaments originated in the region of cape juby cape bojador are entrained around a quasi permanent cyclonic eddy trapped between gran canaria island and the african coast forming a system through which most of the african neritic larvae may return to the african shelf however some larvae reach the eastern islands of the canary archipelago and they may be spread all over the neritic region of the archipelago by eddies shed from the islands also in summer the distribution of the lfc of the c actz is vertically stratified and fish larvae seem to carry out little or not diel vertical migration overall this study highlights the strong relationship between mesoscale oceanographic processes and the lfc in the c actz

observations of layering under a warm core ring in the gulf of mexico abstracttwo glider transects in the gulf of mexico reveal fine vertical scale thermohaline structures within a loop current eddy lce partially compensating temperature and salinity anomalies are

strong current events related to a subtropical front in the northeast atlantic long term temperature and current meter records from moorings in the northern canary basin display strong current events with time scales between one and three months and large vertical scales of several thousand meters the data are compared to hydrographic surveys in the area that show a meandering subtropical front the strong current events are found to be related to the passage of the front through the mooring positions an analysis of composite time series for selected depths indicates cases of westward and of eastward propagation of frontal meanders the frontal pattern is also found in geopotential anomalies inferred from historical xbt data sets suggesting that the front is a persistent feature of the density field in two cases strong current events appear to be related to a mediterranean water lens

a quasi synoptic survey of the thermocline circulation and water mass distribution within the canary basin shipboard hydrographic measurements and moored current meters are used to infer both the large scale and mesoscale water mass distribution and features of the general circulation in the canary basin we found a convoluted current system dominated by the time dependent meandering of the eastward flowing azores current and the formation of mesoscale eddies at middepths several distinctly different water masses are identified subpolar mode and labrador sea water are centered in the northwest subantarctic intermediate water is centered in the southeast and the saltier warmer mediterranean tongue lies between them mesoscale structures of these water masses suggest the presence of middepth meanders and detached eddies which may be caused by fluctuations of the azores current

a view of the canary basin thermocline circulation in winter during january and february 1989 the recirculation of the subtropical gyre in the eastern north atlantic was surveyed with a three ship experiment the analysis of hydrographic measurements and velocity data from a shipboard acoustic doppler current profiler reveals the synoptic scale circulation patterns and water mass distributions in the canary basin the geostrophic transport stream function estimated with a horizontally varying reference level of no motion highlights the major currents in three layers representing the vertical structure of the horizontal circulation the classical circulation scheme is shown by the stream function in the upper 200 m the azores canary and north equatorial currents unlike the deep penetrating azores current the canary current and the north equatorial current are restricted to the upper 200 m both carry north atlantic central water along the water mass boundary with south atlantic central water south atlantic central water flows through the passage between the cape verde archipelago and africa via narrow currents into the area north of 14 5 n at the southern edge of the subtropical gyre we identify an eastward flow of antarctic intermediate water between 700 and 1200 m

meddy trajectories in the canary basin measured during the semaphore experiment 1993 1995 as part of the structures des echanges mer atmosphere proprietes des heterogeneites oceaniques recherche experimentale semaphore experiment four mediterranean water eddies meddies were identified in the canary basin and tracked with freely drifting rafos floats one large and energetic meddy discovered 1700 km west of cape saint vincent portugal set a distance and speed record as it translated another 1700 km southwestward at 3 9 cm s during 1 5 years this meddy traveled 57 of the distance from cape saint vincent toward the spot mcdowell and rossby 1978 found a possible meddy north of the dominican republic two meddies were observed to interact with the azores current as they passed underneath or through it three meddies collided with tall seamounts which seemed to disrupt the normal swirl velocity perhaps fatally in two cases one meddy appeared to bifurcate when it collided with seamounts

a reply to the discussion of our paper on the structure of the precambrian and lower paleozoic basement of the central andes between 22 and 32 s lat as presented by a p willner and h miller

an overview of barrier winds off southeastern greenland during the greenland flow distortion experiment during the greenland flow distortion experiment barrier flow was observed by an instrumented aircraft on 1 2 5 and 6 march 2007 off southeastern greenland during this time period the barrier flow increased from a narrow jet 15 m s 1 to a jet filling almost the whole of the denmark strait with maximum wind speed exceeding 40 m s 1 dropsonde observations show that the barrier flow was capped by a sharp temperature inversion below mountain height below the inversion was a cold and dry jet with a larger northerly wind component than that of the flow above which was also warmer and more moist thus the observations indicate two air masses below mountain height a cold and dry barrier jet of northern origin and above this a warmer and moister air mass that was of cyclonic origin numerical simulations emphasize the non stationarity of the greenland barrier flow and its dependence on the synoptic situation in the greenland iceland region they show that the barrier jet originated north of the denmark strait and was drawn southward by a synoptic scale cyclone with the strength and location of the maximum winds highly dependent on the location of the cyclone relative to the orography of greenland experiments without greenland s orography suggest a 20 m s 1 enhancement of the low level peak wind speeds due to the presence of the barrier thus the greenland barrier flows are not classic geostrophically balanced barrier flows but have a significant ageostrophic component and are precisely controlled by synoptic scale systems copyright c 2009 royal meteorological society

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

antarctic nat psc belt of june 2003 observational validation of the mountain wave seeding hypothesis abstract satellite observations of polar stratospheric clouds pscs over antarctica in june 2003 revealed small nitric acid trihydrate nat particles forming suddenly along the vortex edge models suggest the trigger was mountain waves over the antarctic peninsula ap forming ice for nat nucleation we test this hypothesis by analyzing perturbations in stratospheric radiances from the atmospheric infrared sounder airs airs data show mountain waves over the ap on 10 14 june with no resolved wave activity before or after peak wave temperature amplitudes derived from independent 40 hpa channels all return values of 10 12 k in agreement with values used to model this nat event these observations support a nat wake from a small region of mountain wave activity over the ap as the source of this circumpolar nat outbreak

what is the source of the stratospheric gravity wave belt in austral winter abstractduring austral winter and away from orographic maxima or hot spots stratospheric gravity waves in both satellite observations and interim european centre for medium range weather forecasts ecmwf re analysis era interim data reveal enhanced amplitudes in a broad midlatitude belt extending across the southern ocean from east of the andes to south of new zealand the peak latitude of this feature slowly migrates poleward from 50 to 60 s wave amplitudes are much weaker across the midlatitude pacific ocean these features of the wave field are in striking agreement with diagnostics of baroclinic growth rates in the troposphere associated with midlatitude winter storm tracks and the climatology of the midlatitude jet this correlation suggests that these features of the stratospheric gravity wave field are controlled by geographical variations of tropospheric nonorographic gravity wave sources in winter storm tracks spontaneous adjustment emission from the midlatitude winter jet frontogenesi

meddy dynamics and interaction with neighboring eddies southwest of portugal observations and modeling 1 during the semane 2000 experiment southwest of portugal two meddies were found in near contact these meddies had hydrological radii of about 20 and 30 km thickness of 900 m maximum temperatures of 12 45 c and 13 45 c and maximum salinities of 36 52 and 36 78 the smaller meddy with more pronounced thermohaline anomalies was clearly double cored at 750 and 1300 m depths while the wider one was more diffuse and more homogeneous the associated geostrophic velocities referenced at 2000 m locally reached 0 5 m s in the smaller meddy and 0 2 m s in the wider one three rafos floats and two deep drogued surface drifters seeded in the two meddies rapidly gathered in the more intense meddy this meddy trajectory revealed by the float motion was first eastward then southward maps of sea level anomaly indicate that this motion did not correspond to the long term evolution of the initial positive sea level anomaly signature of the meddies and that neighboring cyclones must have played a role in the meddy evolution to determine the role of each eddy in the observed evolution several scenarios were studied with a three layer quasi geostrophic numerical model the interaction of two meddies in isolation did not result in the observed meddy trajectories on the long term the interaction of these two meddies with successive neighboring cyclones provided a more realistic trajectory of the meddy containing the floats

structure and effects of a long lived vortex in the greenland sea direct observations of the velocity field of a submesoscale coherent vortex in the greenland sea by a vessel mounted adcp together with a detailed and complete investigation of its hydrographic structure show that within the eddy the hydrographic structure differs from the background and indicate that the entire water column of 3 7 km depth is included in an anticyclonic rotation with maximum azimuthal speeds at roughly 2000 m depth within a radius of about 9 km the water layers rotate in a solid body fashion the lifetime of the eddy is long enough and the exchange between its interior and the background is small enough to result in a persistent and pronounced anomaly with respect to physical as well as biological parameters due to the unique possibility in the high latitudes to recharge the eddy by surface forcing during winter and a corresponding long lifetime such eddies represent key areas for future bottom water production

the azores current system from a meridional section at 24 5 w 1 high spatial resolution hydrographic data including lowered acoustic doppler current profiler ladcp measurements were acquired along a meridional section at 24 5 w in october 2009 the data are analyzed in detail with the purpose of definitively defining and quantifying the zonal azores current system the azores current and azores countercurrent are delimited each extending meridionally for 110 km the azores current is located between 33 5 n and 34 5 n flanked to the north by the azores countercurrent 35 25 36 25 n vertically both currents reach the n 27 975 kg m 3 level 2000 m depth their mass transports ranging across thermocline as well as intermediate layers the azores current transports 13 9 sv 1 sv 106 m3 s 1 109 kg s 1 eastward with its maximum associated with the azores front 33 75 n the azores countercurrent flows below the surface transporting 5 5 sv westward this contributes to a net eastward flow of 8 4 sv across the section at intermediate layers the azores countercurrent transports mixed mediterranean water to the west and the azores current transports mixed sub arctic intermediate water to the east shipboard adcp and satellite derived geostrophic velocity are used to confirm the transports revealed by the hydrographic data

gravity waves over antarctica and the southern ocean consistent momentum fluxes in mesoscale simulations and stratospheric balloon observations stratospheric balloons from the vorcore campaign have provided a unique description of the gravity wave field in the lower stratosphere above antarctica and the southern ocean during the austral spring of 2005 mesoscale simulations are carried out to analyze further the gravity wave field first the realism of the simulated waves is assessed by comparison to the observations a satisfactory overall agreement is found but different behaviour is noted for orographic waves overestimation in the simulations relative to the observations and non orographic waves underestimation second the gravity wave field is analyzed in more detail than was possible from observations alone it is necessary to distinguish and quantify orographic and non orographic waves separately orographic waves are larger and more intermittent yet affect only a limited geographical region hence although orographic sources stand out as hot spots for gravity waves their contribution to momentum fluxes entering the stratosphere is comparable to or smaller than the contribution of non orographic sources a diagnostic for intermittency the gini coefficient is proposed it clearly marks the distinction between orographic and non orographic sources intermittencies of 0 8 and 0 5 respectively sensitivity to resolution is quite small regarding the spatial structure of the gravity wave field but is significant for the amplitudes the momentum flux values increase by 2 when the horizontal resolution is doubled and possible biases of both simulations and observations are discussed nonetheless the good agreement between observations and simulations and the complementary information on the biases of each dataset promises that in the future these different estimates of gravity wave momentum fluxes may converge copyright 2012 royal meteorological society

meddy seamount interactions implications for the mediterranean salt tongue abstract a quasigeostrophic point vortex numerical model is used to explore interactions of eddies and seamounts the ultimate objective of this study is to assess the role of meddy seamount interaction as an input to mediterranean salt tongue maintenance secondary objectives are to clarify the dynamics of meddy seamount interaction the results suggest that meddies survive seamount collisions with 60 70 of their initial cores remaining intact as coherent vortices given observed formation rates it appears meddies in their interactions with seamounts inject between one quarter and one half of the salt anomaly necessary to sustain the mediterranean salt tongue other considerations suggest the anomalous mass flux by meddies is comparable to that due to the mean flow in summary meddies are important to the maintenance of the salt tongue although other mechanisms are needed coherent vortex transport of which meddies are one example is a mesoscale process not well described by the downgradient mix

coriolis effects in mesoscale flows with sharp changes in surface conditions a general linearized shallow layer perturbation model where the approximately neutral lower layer of thickness h0 is situated below a stable upper layer i e an inversion with temperature change t is developed for steady mesoscale atmospheric flows over low lying topography whose height is less than h0 with the coriolis parameter f sharp changes in surface conditions surface roughness terrain elevation heat flux are modelled as a distributed body force through the lower layer the froude number of this layer is small typical cases of mesoscale discontinuities are examined the results are compared with those of a continuously stratified model and observations and with numerical mesoscale model results for a meteorological case study over the dover straits region of the english channel the main results are i if the wind direction is parallel to the edge line separating the change in surface roughness there are marked increases and decreases in these coastal winds whose maxima can occur over the sea within a distance of order h0 1 km of a coast the strength of these wind jets which do not occur in the absence of coriolis force decrease away from the edge line gradually over transverse length scales of the order of the rossby deformation radius changes to surface roughness lead to an increase in the wind speed perturbation in the downwind direction until limited by non linear effects when the wind is at an angle to a roughness change or coast the maxima occur at the coastline ii where there are sharp changes in the orientation of contours of constant roughness length e g at capes or bays on the coastline or wakes of high drag areas detached jets are formed in the downwind direction iii changes in surface elevation at a coast produce effects different from those of roughness a positive wind jet forms parallel to the coast in the direction of the wind when the coast is on the right looking downwind and a negative jet when the coast is on the left these jets do not increase in strength along the flow and do not persist downwind iv coriolis effects also determine how the inversion height varies near coastlines and surface roughness changes for example increasing decreasing inland over a distance lr when stable airflow approaches from the sea and the coast is on the right left of an observer looking downwind opposite in the southern hemisphere this mechanism is consistent with observed increasing decreasing cloudiness inland from a coast v other effects occur where the surface elevation changes gradually over a distance of order lr e g a wide shallow valley frictional effects are comparable with buoyancy and coriolis forces and flows perpendicular to the elevation change are deflected to the left in the northern hemisphere as observed in the rhine valley vi the shallow layer model simulates the major features of the low level flow field computed using the numerical mesoscale model with a horizontal resolution of 2 km i e of order h0 broad features were captured using a coarser resolution of 12 km vii the analysis provides a method of estimating errors associated with finite grid size in numerical mesoscale models copyright 2004 royal meteorological society

observations and simulations of a large amplitude mountain wave breaking over the antarctic peninsula 1 a case study of a large amplitude orographic gravity wave occurring over the antarctic peninsula is presented based on observations from the vorcore balloon campaign and on mesoscale numerical simulations the vorcore campaign september 2005 to february 2006 consisted in the flight of 27 superpressure balloons in the core of the southern hemisphere stratospheric polar vortex at altitudes of 16 19 km from september 2005 to february 2006 on 7 october 2005 one of the balloons exploded as it was flying above the antarctic peninsula the observations collected by another balloon that was flying during the same time period above the peninsula suggest the presence of a very intense gravity wave peak to peak amplitude of the order of 25 30 m s 1 in zonal and meridional velocity disturbances the wave packet is likely undersampled in the balloon observations because of its high intrinsic frequency but the balloon data set is complemented with high resolution numerical simulations carried out with the weather research and forecast model the simulations are validated by comparison with the balloon measurements and show that the wave was breaking in the lower stratosphere at the time and height where the balloon exploded the simulations highlight several consequences of the mountain wave on the stratosphere forcing of the mean flow generation of secondary inertia gravity waves and turbulence and mixing in particular the momentum fluxes are calculated and are found to compare well with the estimates from balloon measurements the large values found are likely extreme values which raises the issue of their representativity to discuss this the balloon measurements are used in conjunction with operational analyses to estimate the frequency of such large amplitude gravity waves i e to provide an estimate of their intermittency

isopycnal empirical orthogonal functions eofs in the north and tropical atlantic and their use in estimation problems we investigated the vertical variability of the thermal dynamical structure of the north and tropical atlantic ocean from a set of historical hydrographic data reynaud et al 1998 the analysis was performed in 10 geographic bins in terms of vertical empirical orthogonal functions eofs in isopycnal coordinates as first proposed by gavart and de mey 1997 hereinafter referred to as gdm97 in the isopycnal coordinate system the state vector is made up of isopycnal displacements and the compensated potential temperature along isopycnals gdm97 showed that in the azores madeira region the isopycnal eofs consistently help to better separate physical processes in the water column and to better project the dynamic height anomaly downward in comparison with the classical eof analysis in depth coordinates in the present study we extended their work geographically and the connection with state estimation and data assimilation was more formalized from our results smooth spatial variations of isopycnal eofs were found in the north atlantic and confirmed the large scale relevance of isopycnal eofs in the ocean north of 20 n the dominant isopycnal eof was associated with a quasihomogeneous vertical displacement of the isopycnal surfaces 1 with a quasiconservation of compensated potential temperature on those surfaces 0 that mode was strongly modified by thermocline intensified baroclinic effects along the path of the gulf stream up to 40 w some physical interpretations of the vertical eofs were also suggested in several areas as far as the isopycnal formulation was concerned e g some thermal fronts the mediterranean outflow water lenses or meddies this work confirmed the validity of the ideas of gdm97 over the entire north atlantic ocean the potential use of the isopycnal eofs in state estimation problems was discussed they are possible candidates to reduce the order of state estimation problems provided that they have good observability properties these observability properties were studied in the case of satellite altimetry that is we examined how the dominant isopycnal eofs were connected to sea level anomalies in most bins it was found that the order of an estimation problem could be truncated to one primarily north of 20 n or two modes the dominant eof was found to account for most of the surface dynamic height variability with a rather normally distributed error of only a few centimeters dynamically more robust results were also presented performing a univariate isopycnal analysis in leaving coherent thermal effects out as a result the dominant character of mode 1 was further enhanced everywhere these univariate isopycnal eofs can be used for purely dynamical state estimation more generally we believe that our results can be used to set up reduced order data assimilation schemes in the north atlantic or in other regions with good historical data

thermohaline staircases in a caribbean eddy and mechanisms for staircase formation the structure of a cyclonic eddy in the eastern caribbean was observed by caribbean vorticity experiment cruise cavortex i in august 2003 prominent thermohaline staircases are evident in profiles of temperature and salinity at locations that appear to correlate with the presence of lateral property gradients and shear within the eddy although such a connection is less than definitive due to the coarseness of horizontal sampling these observations are examined in light of predictions from two theories for staircase formation aspects of the data are found to be consistent with each raising the possibility that both mechanisms are operating

case study of a barrier wind corner jet off the coast of the prince olav mountains antarctica abstractthe ross ice shelf airstream ras is a barrier parallel flow along the base of the transantarctic mountains previous research has hypothesized that a combination of katabatic flow barrier winds and mesoscale and synoptic scale cyclones drive the ras within the ras an area of maximum wind speed is located to the northwest of the protruding prince olav mountains in this region the sabrina automatic weather station aws observed a september 2009 high wind event with wind speeds in excess of 20 m s 1 for nearly 35 h the following case study uses in situ aws observations and output from the antarctic mesoscale prediction system to demonstrate that the strong wind speeds during this event were caused by a combination of various forcing mechanisms including katabatic winds barrier winds a surface mesocyclone over the ross ice shelf an upper level ridge over the southern tip of the ross ice shelf and topographic influences from the prince olav mountains these forcing mechanisms induced a b

the impact of polar mesoscale storms on northeast atlantic ocean circulation every year thousands of mesoscale storms termed polar lows cross the climatically sensitive subpolar north atlantic ocean high resolution numerical simulations of the ocean circulation taking into account the effect of these storms on deep water formation suggest that polar lows significantly affect the global ocean circulation

the nose a characteristic inversion within the salinity maximum water in the tropical northeast atlantic during leg 1 of meteor cruise 10 in march april 1989 at 18 circ n 30 circ w the high spatial and temporal resolution of hydrographic ctd stations indicated that the study site was in a hydrographically complex region in the transition zone between the canary current and the north equatorial current at the southern boundary of the subtropical gyre strong variability was found within the upper 120 m due to interleavings of warmer and saltier subtropical salinity maximum water with colder and less saline upper thermocline water the interleavings caused unexpected nose like temperature salinity nitrate and oxygen profiles yet not described in the literature a second variability source was found in the central water area because the study area was situated in the vicinity of the central water boundary dividing north and south atlantic central water hydrographic analysis of the study shows that interpretations of biological and chemical data can only be done in conjunction with high resolution ctd profiling

three dimensional structure and temporal evolution of submesoscale thermohaline intrusions in the north pacific subtropical frontal zone abstract four instances of persistent intrusive deformation of the north pacific subtropical front were tagged individually by a lagrangian float and tracked for several days each feature was mapped in three dimensions using repeat towed observations referenced to the float isohaline surface deformations in the frontal zone included sheetlike folds elongated in the alongfront direction and narrow tongues extending across the front all deformations appeared as protrusions of relatively cold and fresh water across the front no corresponding features of the opposite sign or isolated lenslike structures were observed the sheets were o 10 m thick protruded about 10 km into the warm saline side of the front and were coherent for 10 30 km along the front having about the same thickness and cross frontal extent as the sheets tongues extended less than 5 km along the front all of the intrusions persisted as long as they were followed several days to one week their structures evolved on both inertial

nonlinear equilibration of thermohaline intrusions abstract the nonlinear behavior of thermohaline intrusions on a wide front is investigated using a one dimensional numerical model the model is used to follow the evolution of a field of intrusions from infinitesimal amplitude to a large amplitude state characterized by inversions in temperature and salinity it is thus possible to extend the analytical studies of toole and georgi and others to large amplitude allowing for the effects of amplitude dependent diffusivities and for the appearance of stably stratified diffusively stratified and statically unstable regions in the water column as the intrusions grow the model runs are initialized with infinitesimal disturbances that grow exponentially in time until inversions in temperature and salinity occur after inversions appear the intrusions evolve toward an equilibrium state in which friction balances buoyancy forces for both finger and diffusive sense basic state stratifications these equilibrium states are characterized by statically unstabl

a general circulation model study of the orographic gravity waves over antarctica excited by katabatic winds 1 in this study we simulated orographic gravity waves ogws over antarctica using a t213l250 general circulation model gcm the gcm has a fine vertical resolution of 300 m throughout the middle atmosphere the simulation was run for a 1 year period results from 21 28 june were primarily considered ogws are excited by katabatic winds that travel down the surface slopes of the antarctic ice sheet a strong eastward katabatic wind blows over the west coast of the ross sea at the approach of the synoptic scale upper tropospheric westerly jets a quasi stationary ogw is then excited above the coast and propagates upward into the mesosphere an ogw appears sporadically during the antarctic winter and spring its amplitude is determined by the strength of the eastward katabatic wind dissipation of ogws within the middle atmosphere results in a localized deceleration of westerly winds greater than 30 m s 1 d 1 this in turn modifies the horizontal circulation in the polar vortex strong vertical mixing occurs within the mesosphere and is associated with wave breaking large temperature fluctuations associated with the ogws affect the formation or suppression of polar stratospheric clouds in the lower stratosphere katabatic wind excitation is the most powerful source of gravity waves over antarctica around the time of the winter solstice

a low level explanation for the recent large warming trend over the western antarctic peninsula involving blocked winds and changes in zonal circulation 1 we demonstrate a mechanism whereby the impact of stronger circumpolar westerly winds on the mountains of the antarctic peninsula contributes significantly to the enhanced warming trend observed over its western side in the last 50 years numerical and laboratory meteorological modelling demonstrate how when westerly winds impinge on this side warm air below the height 1 5 2 0 km of the peninsula is advected in a southerly direction the strength of the annual mean westerly winds has increased by about 15 20 since the 1960s while the modelling results indicate that contemporaneously the air advected to its western side originates from an increasingly northerly and warmer location this gives rise to increased northerlies and a greater transport of warm air into this region consequently there is a reduction in the sea ice extent further amplifying the local warming this low level orographic mechanism for the local climate trend is supported by observational evidence

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

observed evolution of a california undercurrent eddy abstracta california undercurrent eddy cuddy was repeatedly surveyed using multiple seagliders for over three months found and tracked off of the washington vancouver island coasts this cuddy t

on the origin of the azores current the azores current south of the azores archipelago is part of the subtropical north atlantic gyre using an international hydrographic data set we analyze mean and seasonal geostrophic transport fields in the upper 800 m of the ocean in order to determine the origin of the azores current in the western basin and seasonal changes in the related flow geostrophic currents are obtained by using the method applied by stramma 1984 in the eastern basin the azores current is found to originate in the area of the southwest newfoundland rise figure 10 in winter an almost uniform current connects this region of origin with the azores current while a branching into two current bands is observed in summer with the southern band forming a marked cyclonic loop within the upper 800 m all of the transport in the northern band and about 70 of the transport in the southern band recirculates in the eastern basin additionally expendable bathythermograph data from the azores current region indicate an increase of eddy potential energy from winter to summer

the structure of the precambrian and lower paleozoic basement of the central andes between 22 and 32 s lat three major diastrophic cycles defined by their structural style and their spatial distribution are recognized in the andean basement of this region the oldest structures are related to the panamerican orogeny 500 to 700 m a which produced in the central craton multiply deformed complexes of schists gneisses and granites that are covered discordantly by unmetamorphosed cambrian and ordovician beds west of the central craton ordovician sedimentary beds are folded with a simple structural style and intruded by granites both the sedimentry beds and the granites are covered discordantly by undeformed devonian sequences the folding of the ordovician is attributed to the ocloyic phase of the caledonian movements west of the ocloyic belt is another foldbelt consisting of strongly folded devonian beds attributed to the chanic phase hercynian the chanic belt is intruded by carboniferous and permian granites and covered discordantly by carboniferous and permian sequences

northward penetration of antarctic intermediate water off northwest africa abstract in this article historical and climatological datasets are used to investigate the seasonal northward propagation of antarctic intermediate waters aaiw along the eastern margin of the north atlantic subtropical gyre a cluster analysis for data north of 26 n shows the presence of a substantial number of hydrographic stations with aaiw characteristics that stretch northeast along the african slope this water mass extends north during fall as shown both through the comparison of actual and climatological data and by applying a mixing analysis to normal to shore seasonal sections at both 28 5 and 32 n the mixing analysis is further used with several fall cruises between 32 and 36 n and shows that at these latitudes the core of aaiw propagates along the 27 5 isoneutral with contributions that reach as much as 50 at 32 5 n an idealized sverdrup type model is used in combination with climatological hydrographic and wind data to examine what forces this eastern boundary propagation it is fo

sensitivity of resolved mountain drag to model resolution for map case studies seven mountain wave case studies from the mesoscale alpine programme map have been used to investigate the behaviour of the resolved alpine pressure drag with model horizontal resolution three independent modelling systems show that the magnitude of the resolved surface pressure drag increases monotonically as the horizontal model resolution is increased from 125 km down to a few kilometres a substantial proportion of the drag will still need to be parametrized in the next generation of mesoscale models with horizontal resolutions of 3 or 4 km this is particularly true for the most important drag cases when the jet stream directly above the mountains produces larger wind speeds near mountain crest level resulting in much larger total alpine drags copyright 2006 royal meteorological society

physical oceanography of the azores front abstract there is a considerable body of evidence for the existence of a permanent front sw of the azores surveys in the summer of 1981 show the structure to penetrate to a depth of 2 000 m and suggest that its meandering is related to the alignment of the atlantis gt meteor seamount chain the total volume transport above 2 000 m is between 10 and 12 106 m3 s 1 towards the east the main water mass contrasts across the front are confined to the upper 400 m of the water column only a small change in mediterranean water strength was seen across the front satellite tracked drogued buoys seeded into the front showed surface speeds of up to 40 cm sec 1 and revealed the formation of a closed cold core eddy some 100 115 km in diameter which propagated westward at 2 2 km day 1 over a 200 day period sea surface temperature contrasts across the frontal boundary are small and together with frequent cloud cover prevent the detection of the front and associated eddies by satellite infra red imagery the front apparently marks the eastward extension of the southern branch of the gulf stream recirculation and the northern limit of the 18 c water mass eddies formed at the front could propagate westward into the interior of the sargasso sea but have not yet been observed to cross the mid atlantic ridge

the madeira mode water quasi homogeneous layers in vertical profiles of temperature and salinity in the eastern north atlantic near madeira indicate the existence of a subtropical mode water in the eastern basin temperature sections show a maximum horizontal extent of at least 500 km the frequency distribution analysis of homogeneous layers in a historical xbt dataset shows a mode water formation region near and to the north of madeira this mode water is found at increasing depths and displaced to the west and southwest during the course of the year after its formation by wintertime convection it disappears almost completely due to mixing before the next winter volume estimates suggest that this madeira mode water in the eastern atlantic accounts for 15 20 of the total central water formation in the corresponding density range as obtained from tracer studies in the north atlantic gyre

shipboard acoustic doppler current profiling in the eastern caribbean sea 1985 1986 procedures to collect and reduce shipboard acoustic doppler current profiles adcp for application to quantitative estimates of transport variation on a synoptic scale are described transport estimates based on data from five consecutive cruises across the eastern caribbean are discussed in terms of ensemble averaging and vertical smoothing of adcp records and satellite navigation procedures comparison of smoothed adcp with pegasus dropsonde current profiles indicates an error of 4 cm s 1 for earth referenced adcp eastward velocities comparisons with geostrophic current estimates in an area of significant and irregular ageostrophic effects indicate shipboard adcp as a more accurate and reliable method for establishing seasonal and spatial variability of transport within instrument specific depth limitations

southern hemisphere extratropical gravity wave sources and intermittency revealed by a middle atmosphere general circulation model abstractsouthern hemisphere extratropical gravity wave activity is examined using simulations from a free running middle atmosphere general circulation model called kanto that contains no gravity wave parameterizations the total absolute gravity wave momentum flux mf and its intermittency diagnosed by the gini coefficient are examined during january and july the mf and intermittency results calculated from the kanto model agree well with results from satellite limb and superpressure balloon observations the analysis of the kanto model simulations indicates the following results nonorographic gravity waves are generated in kanto in the frontal regions of extratropical depressions and around tropopause level jets regions with lower higher intermittency in the july midstratosphere become more less intermittent by the mesosphere as a result of lower level wave removal the gravity wave intermittency is low and nearly homogeneous throughout the sh middle atmosphere during january this indicates t

the mediterranean water tongue and its chlorofluoromethane signal in the iberian basin in early summer 1989 hydrographic observations from the iberian basin demonstrate the variability of water masses in upper and intermediate layers the surveyed area embraces the internal front between water masses from higher latitudes and the mediterranean outflow exhibits several isolated mediterranean eddy meddy structures at middepth and displays the virtual source region for the mediterranean water mw tongue off the portuguese continental slope the description is enhanced by additional chlorofluoromethane measurements which show anomalously high concentrations at middepth due to mixing of mw with the overlying atlantic waters in the gulf of cadiz the geostrophic stream function shows several meddylike features that not only are remarkably extended in the depth range of the mw but are also correlated with surface height anomalies

temporal variability of mass transport in the canary current abstract the variability of the canary current is investigated using bimonthly expandable bathythermograph sections from gran canaria island to the african coast between november 1996 and september 1998 the geostrophic transport of the easternmost branch of the canary current is estimated by integrating the thermal wind equation using the layer of neutral density 27 3 roughly 600 m depth as the layer of no motion the yearly average geostrophic transport of this branch of the canary current is 1 8 1 4 10 9 kg s 1 southward approximately half of the transport flows through the channel between the islands of gran canaria and fuerteventura and the other half through the channel between fuerteventura and the african coast the total southward geostrophic transport shows significant seasonal variability ranging from 1 2 0 3 10 9 kg s 1 in may to 2 6 0 1 10 9 kg s 1 in january although november is the only month with considerable differences in geostrophic transport between 1996 and 1997 there is seasonal northward transport in both channels during may in the gran canaria fuerteventura channel and during november in the fuerteventura african coast channel this seasonal pattern is probably linked to autumn weakening of upwelling in the canary islands area and the offshore diversion of this flow at cape ghir

meddies and decadal changes at the azores front from 1980 to 2000 twenty years of time series observations from the deep sea mooring kiel276 are used to obtain information on the frequency and propagation of meddies mediterranean water eddies on long term changes in flow properties and on a possible relation to the north atlantic oscillation the mooring was set at the nominal position 33 n 22 w at a water depth of more than 5200 m in the northern canary basin it is located near the southern boundary of the azores current ac which is part of the north atlantic subtropical gyre and also in the large scale mediterranean water mw tongue originating from the strait of gibraltar the amplitudes of time varying vertical quasi geostrophic modes and the correlation of current and temperature changes at levels in the mw and the north atlantic central water above are used to identify meddies a total of 10 meddies passed the mooring during the period 1980 2000 half of the events can be related to earlier observations directional changes in meddy related velocities are used to estimate speeds and directions of meddy propagation directions of propagation are very homogeneous with all the 10 meddies observed propagating with a southward velocity component within a sector of 90 and typical speeds are 2 3 cm s meddy occurrence was uneven in time with six meddies found during the first four years and only four meddies during the remaining 16 years decadal changes show the annual mean and the fluctuating kinetic energy levels at the site changing from lower values in the 1980s to high values in the 1990s this change appears to be correlated with variations in the north atlantic oscillation nao index with a delay in oceanic response of about 3 years a conceptual model of ac meanders is used to identify meander signals in the upper layer time series the ac axis appears to be closer to the site during the 1990s than during the preceding decade and indicates a southward or southwestward displacement of the ac with increasingly positive values of the nao index meddy frequency is lower when the ac gets closer from the north a reduction in meddy occurrence in the region just south of the ac is possibly caused by the shear induced blocking of some meddies crossing the front from the north

met office unified model high resolution simulations of a strong wind event in antarctica during winter much of the antarctic coast is susceptible to severe and hazardous strong wind events swes associated with the enhancement of katabatic winds by synoptic weather systems in this study a swe that occurred at mawson east antarctica involving a hurricane force wind speed of 39 m s 1 is simulated by the met office unified model at high horizontal resolutions with grid lengths between 12 and 1 5 km it is shown that all the simulations capture the qualitative evolution of the swe but underestimate its peak wind speed the extent of the underestimate is dependent on horizontal resolution with the 4 and 1 5 km 12 km models underforecasting the peak wind speed by around 15 36 in addition to a strengthening of the katabatic flow the simulated low level cyclonic winds associated with the depression responsible for the swe caused the formation of a barrier type jet parallel to the coast resulting in strong wind convergence interaction at the coastline and suggesting a strong topographic influence on the dynamics responsible for swe formation moreover it suggests that mawson is influenced by small scale gravity waves that formed in response to the stronger winds and that representation of this was particularly sensitive to horizontal resolution additional experiments suggest that the met office unified model simulation of the swe is most sensitive to the representation of turbulent mixing under stable conditions this study is important to identify shortcomings in the performance of the met office unified model near antarctica s coastal regions as well as to improve understanding of the processes responsible for swes

a census of eddies observed in north atlantic sofar float data abstract sofar floats that looped in discrete eddies were studied in order to map and describe the distribution and characteristics of eddies in the north atlantic one hundred eighteen individual looping float trajectories loopers were identified each consisting of two or more consecutive loops each looper was interpreted to be in a discrete eddy and its characteristics were estimated from the float trajectory the highest percentage of loopers occured at 700m in the newfoundland basin where roughly half of the float data were in loopers mostly cyclones in the gulf stream region approximately 20 of the float data recorded at 700m were in loopers again mostly cyclones overall 21 of 700m data and 6 of 2000m data were in loopers the fastest swirl speeds 40cm s 1 were in cyclones south of the gulf stream most of which were in gulf stream rings but numerous swift 35cm s 1 anticyclones were found there too swirl velocity decreased with depth to roughly half as swift at 2000m as at 700m for three eddies in the sargasso sea measured simultaneously with floats at these two depths in the western north atlantic the average swirl velocity of cyclones and anticyclones was the same translation velocity of eddies was generally westward to southwestward at a few cm s 1 the mean translation velocity of 39 eddies in the sargasso sea was u bar 2 8 0 4 cm s 1 v bar 0 4 0 4 cm s 1 many of these were located just south of the gulf stream in the region of its recirculation and were probably advected by a westward current there near the gulf stream and along its extension in the newfoundland basin eddies were often advected downstream with speeds up to 15 20cm s 1 and eddy trajectories were often complicated south of 30 n and near the western boundary 700m eddies were advected northwestward and 1300m and 2000m eddies southeastward by boundary currents there numerous energetic anticyclones were observed south of the gulf stream one was tracked for 430 days and its properties well measured the formation of these eddies has not been documented but they are inferred to have formed near and by the gulf stream and to consist of a thick layer of 18 c water lying above a depression in the thermocline analogous anticyclones were observed in the newfoundland basin seaward of the gulf stream extension there

some effects of model resolution on simulated gravity waves generated by deep mesoscale convection abstract over the past decade numerous numerical modeling studies have shown that deep convective clouds can produce gravity waves that induce a significant vertical flux of horizontal momentum such studies used models with horizontal grid spacings of o 1 km and produced strong gravity waves with horizontal wavelengths greater than about 20 km this paper is an examination of how simulated gravity waves and their momentum flux are sensitive to model resolution it is shown that increases in horizontal resolution produce more power in waves with shorter horizontal wavelengths this change in the gravity waves spectra influences their vertical propagation in some cases gravity waves that were vertically propagating in coarse simulations become vertically trapped in fine simulations which strongly influences the vertical flux of horizontal momentum

a model of baroclinic instability and waves between the ventilated gyre and the shadow zone of the north atlantic ocean abstract distributions of eddy kinetic energy in the north atlantic ocean show that enhanced mesoscale activity exists in the cape verde frontal zone the eastern part of the central water boundary this variability and its associated length and time scales are investigated with a three dimensional numerical model that uses primitive equations in a hybrid quasi isopycnic coordinate system in which the coriolis parameter varies linearly the model has a horizontal resolution of 15 625 km in 11 isopycnic layers the domain comprises a 1000 km square centered at 20 n having idealized bottom topography and zonally periodic boundary conditions a zonal geostrophically balanced jet representing an undisturbed canary current is used for the initial conditions potential vorticity is used to distinguish between water masses that are reconstructed from a hydrographic section the growth of meanders is stimulated by an ageostrophic perturbation field consisting of white noise integration is carried out for 200

meandering of the subtropical front south east of the azores a subtropical front was observed in the area south and southeast of the azores during cruises of fs meteor and fs poseidon in early 1982 the front has a basically west east extension with considerable meandering observed meso scale eddies are found on both sides the overall flow pattern corresponds to earlier results on geopotential differences in the upper northeast atlantic but the baroclinic transport of the order of 107 m3 s 1 is found to be concentrated in a 60 km wide jet we suggest here that the current band is part of the gyre circulation resulting from a branching of the north atlantic current

two years in the life of a mediterranean salt lens abstract a lens of mediterranean water meddy was tracked in the eastern north atlantic for two years with sofar floats the meddy was first found between the canary islands and the azores in october 1984 it center moved in an irregular pattern at speeds of a few cm s 1 and translated 1100 km to the south in two years this meddy was surveyed four times by ctd and velocity profilers and once with the microstructure profiler epsonde when observed during the first two surveys the meddy had a core that was stably and smoothly stratified in both salinity and temperature nearly uniform in the horizontal and was saltier than the surrounding ocean by 0 65 psu the meddy was eroded from its edges top and bottom and lost salt and hat with an e folding time of about one year the salinity at the center remained at its original value during the first year and decreased during the second year evidence was seen for mixing by lateral intrusions double diffusion and turbulence the intrusions are thought to