propagation of the great salinity anomaly of the 1990s around the northern north atlantic 1 time series of t and s extending through 2001 are used to describe propagation of the great salinity anomaly of the 1990s gsa 90s comparison of the distance time relations for the gsa 70s 80s and 90s reveals a substantial intensification of the large scale circulation in the northern north atlantic especially in the subarctic gyre between newfoundland and the faroes the advection rate of the gsa 70s 80s and 90s between newfoundland and the faroe shetland channel is conservatively estimated to have been 3 5 10 and 10 cm s respectively the circulation intensification apparently occurred within a decade between the gsa 70s and 80s during the next decade the advection rate increased from 10 to 13 cm s between newfoundland and iceland basin the gsa 90s was advected towards the faroe shetland channel by the northern iceland basin s branch of the north atlantic current whereas the contribution of the southern branch via the rockall trough was minimal

on the deep western boundary current south of cape cod abstract using ctd oxygen data from eight cruises in the decade from 1994 2003 we have constructed a mean section of properties across the deep western boundary current dwbc south of cape cod near 70 w since all sections included direct velocity measurements our composite section enables us to portray the flow field as well as the mean water mass structure inshore of the gulf stream between the 2500 and 4000 m isobaths the flow is to the southwest along the bathymetry and is remarkably barotropic the equatorward flowing labrador sea water is shown to have high dissolved oxygen low salinity and low potential vorticity while the underlying overflow water is high in oxygen transport estimates for the cold limb of the thermohaline circulation give a range of 14 to 19 sv for the n atlantic deep water found on the section the greatest uncertainty is due to the presence of a warm core ring on one of the sections which apparently completely reversed the flow in the dwbc offshore of the dwbc some of the deep source waters are returned to the north in the deep gulf stream the section is compared to two other widely separated locations abaco and 55 w that have markedly different dwbc characteristics

the use of multifrequency and polarimetric sir c x sar data in geologic studies of bir safsaf egypt abstract bir safsaf within the hyperarid core of the sahara in the western desert of egypt was recognized following the sir a and sir b missions in the 1980s as one of the key localities in northeast africa where penetration of dry sand by radar signals delineates previously unknown sand buried paleodrainage valleys radar rivers of middle tertiary to quaternary age the bir safsaf area was targeted as a focal point for further research in sand penetration and geologic mapping using the multifrequency and polarimetric sir c x sar sensors analysis of the sir c x sar data from bir safsaf provides important new information on the roles of multiple sar frequency and polarimetry in portraying specific types of geologic units materials and structures mostly hidden from view on the ground and on landsat tm images by a relatively thin but extensive blanket of blow sand basement rock units granitoids and gneisses and the fractures associated with them at bir safsaf are shown here for the first time to be clearly delineated using c and l band sar images the detectability of most geologic features is dependent primarily on radar frequency as shown for wind erosion patterns in bedrock at x band 3 cm wavelength and for geologic units and sand and clay filled fractures in weathered crystalline basement rocks at c band 6 cm and l band 24 cm by contrast quaternary paleodrainage channels are detectable at all three radar frequencies owing among other things to an usually thin cover of blow sand the sir c x sar data investigated to date enable us to make specific recommendations about the utility of certain radar sensor configurations for geologic and paleoenvironmental reconnaissance in desert regions

microwave remote sensing of physically buried objects in the negev desert implications for subsurface martian exploration 1 we report the remote detection of a physically buried specular reflecting object using microwave radar at ashalim in the northern region of the negev desert israel such detection provides an important terrestrial analogy for the potential detection of specularly reflecting subsurfaces under the desiccated regolith on mars such as ground ice and liquid water at ashalim a scatterometer operating in the p band 441 mhz 68 cm was mounted on a cherry picker truck at a height of 8 m and used to detect two triangular aluminum mesh reflectors forming a one meter square area reflector buried down to a depth of 8 cm in dry sand the decrease in measured backscattered power with increasing burial depth of the reflector is clearly evident the experimental results compare well with a theoretical model that incorporates radar absorption effects arising in the sandy subsurface layer and radar interference effects arising from phase differences between reflections from the surface and buried reflector this experiment and the associated modeling approach is the first of a series of planned experiments which we outline for the detection and the theoretical evaluation of buried reflectors using remote microwave and vhf radar we identify many potential subject areas for subsurface remote sensing in the martian domain particularly groundwater ground ice

wind driven atlantic water flow as a direct mode for reduced barents sea ice cover abstractvariability in the barents sea ice cover on interannual and longer time scales has previously been shown to be governed by oceanic heat transport based on analysis of observations and results from an ocean circulation model during an event of reduced sea ice cover in the northeastern barents sea in winter 1993 it is shown that the ocean also plays a direct role within seasons positive wind stress curl and associated ekman divergence causes a coherent increase in the atlantic water transport along the negative thermal gradient through the barents sea the immediate response connected to the associated local winds in the northeastern barents sea is a decrease in the sea ice cover due to advection despite a subsequent anomalous ocean to air heat loss on the order of 100 w m 2 due to the open water the increase in the ocean heat content caused by the circulation anomaly reduced refreezing on a time scale of order one month furthermore it is found that coherent ocean heat transport anomalies occ

moored observations of western boundary current variability and thermohaline circulation at 26 5 n in the subtropical north atlantic abstract a 5 8 year time series of moored current meter observations is used with hydrographic section data cme model results and gridded wind fields over the north atlantic to describe the mean structure and variability of circulation and volume transports east of abaco bahamas at 26 5 n a mean antilles current with 5 sv of northward transport is confined against the bahamas boundary in the upper 800 m and combines with approximately 19 sv of florida current transport to balance the sverdrup interior circulation and does not contribute to interhemispheric exchange the mean transport of the deep western boundary current dwbc off the bahamas is approximately 40 sv of which 13 sv compensates the upper branch of the thermohaline circulation requiring a 27 sv deep recirculation robust annual and semiannual cycles of meridional are found in both moored observations and model results with remarkable agreement in amplitude 13 sv and phase maximum northward transports occur in winter and summer

spreading of red sea overflow waters in the indian ocean as a result of its remarkably high salinity and despite its small volume input remnants of red sea water rsw have been identified in the agulhas current over 6000 km distant of their source this provided the motivation to investigate the long term mean spreading of rsw throughout the indian ocean using a comprehensive set of observations taken from the national oceanographic data center archives and from the world ocean circulation experiment hydrographic program for the indian ocean after emerging from the gulf of aden into the arabian sea rsw spreads predominantly southwestward along the african continental slope as indicated by strongly inclined isohalines across the arabian sea there is some monsoon variability so that during the winter monsoon there is more rsw present in the gulf of aden and an intensification of southward spreading along the western boundary between 12 and 5 n elsewhere the intermediate depth salinity field of the indian ocean appears relatively stationary between 5 and 10 s in the region of the south equatorial current isohalines of the rsw layer become quasi zonal across the width of the indian ocean only dipping southward toward the western boundary west of 50 e south of here there is a strong tongue of rsw spreading southward through the mozambique channel and into the agulhas current these conclusions concur with previous localized investigations of intermediate water properties using a simple mixing model the percentage of rsw throughout the indian ocean was quantified it was found that the flux of salt into the gulf of aden from the red sea is similar to that estimated to cross 32 s in the agulhas current this result implies that all the rsw which is mixed into the interior of the indian ocean may eventually be exported at the western boundary furthermore it implies that rsw is the dominant component of the salt budget for the intermediate layer and that input from the indonesian seas and via diapycnic processes are small

modelling the long term mass balance and firn evolution of glaciers around kongsfjorden svalbard we analyse the long term 1961 2012 distributed surface mass balance and firn evolution of the kongsvegen and holtedahlfonna glacier systems in northwestern svalbard we couple a surface energy balance model to a firn model with forcing provided from regional climate model output in situ observational data are used to calibrate model parameters and validate the output the simulated area averaged surface mass balance for 1961 2012 is slightly positive 0 08 m w e a 1 which only fractionally compensates for mass loss by calving refreezing of percolating water in spring summer 0 13 m w e a 1 and stored water in fall winter 0 18 m w e a 1 provides a buffer for runoff internal accumulation i e refreezing below the previous year s summer surface in the accumulation zone peaks up to 0 22 m w e a 1 and is unaccounted for by stake observations superimposed ice formation in the lower accumulation zone ranges as high as 0 25 m w e a 1 a comparison of the periods 1961 99 and 2000 12 reveals 21 higher annual melt rates since 2000 and a 31 increase in runoff which can only in part be ascribed to recent warmer and drier conditions in response to firn line retreat both albedo lowering snow ice albedo feedback and lower refreezing rates refreezing feedback further amplified runoff

closing the mass budget of a tidewater glacier the example of kronebreen svalbard in this study we combine remote sensing in situ and model derived datasets from 1966 to 2014 to calculate the mass balance components of kronebreen a fast flowing tidewater glacier in svalbard

transformation of the labrador sea water in the subpolar north atlantic development spreading and decay of the thermohaline properties of two labrador sea water lsw classes are described during the development phase a specific lsw class repeatedly mixed by winter convection in the labrador sea becomes colder denser thicker and deeper once convection weakens the lsw class becomes isolated from the upper layer and starts to decay rapidly losing its volume while retaining the same density due to isopycnal mixing with the neighbouring warm saline intermediate waters a similar pattern in temperature salinity and density is seen in the other basins with different time lags from about two years in the irminger sea to ten years in the northern iceland basin and rockall trough regions the influence of lsw on the thermohaline properties of other north atlantic water masses is also discussed

direct observations of the current structure east of the bahamas quasisynoptic absolute velocity sections were obtained in the western north atlantic to the east of the bahamas on five cruises from 1992 to 1994 showing complex spatial and temporal variability of the currents throughout the water column lowered acoustic doppler current profilers were used on all cruises for comparison an acoustically tracked free fall profiler was used on the august 1992 and june 1993 cruises where simultaneous profiles from both methods are available depth averaged differences are less than 0 01 m s 1 in the ensemble mean and standard deviation though small the mean difference appears to be statistically non zero for one of the two doppler profilers used no cause has been found the individual velocity sections show a banded structure of currents in the offshore direction with strong baroclinic and depth averaged components extending over the full sampling domain two sections show a picture of the southward flowing deep western boundary current dwbc differing from previous observations during august 1992 and june 1993 the mean dwbc core was located more than 100 km offshore in observations prior to 1990 it was usually near 50 km offshore net southward transport below 800 m integrated from the coast to 400 km offshore varied from 15 to 50 sv with a mean of about 40 sv 1 sv 1 106 m s 1 our mean is consistent with previous estimates our sections add new evidence that the transport is highly variable to at least 400 km offshore

detection of subsurface features in seasat radar images of means valley mojave desert california igneous dikes buried beneath as much as 2 m of alluvium in the mojave desert of california were detected by the seasat l band 23 5 cm wavelength synthetic aperture radar sar in 1978 the roughness and dihedral configuration of the dikes are favorable to generation of strong radar echos the soil moisture levels in 1978 were likely below the critical 1 level the other permissive conditions for radar penetration of a fine grained and thin alluvial cover are present our findings suggest that subsurface features with potential tectonic or geomorphic significance may be revealed in other orbital radar images of semiarid terrains

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

modeling waves and wind stress 1 a model for wave and wind stress prediction is constructed the source functions that drive the space time evolution of the energy spectra are developed in form based on theory and laboratory and field experiments the calibration factors proportionality constants of the source functions are determined from a comparison of modeled and observed significant height and mean period the observations are for the month of january 2005 and are derived from an array of laser range finders mounted on a bridge between two platforms in the ekofisk oil field in the north sea the model calculates the form stress on the waves and adds it vectorially to the sheltering modified skin stress the resulting drag coefficient versus wind speed is shown to have the observed structure low in light winds increasing in moderate winds and increasing more slowly in very strong winds modeled spectral shapes in the four quadrants of hurricane bonnie 1998 match the scanning radar altimeter measurements modeled spectral properties in hurricane ike 2008 are compared against ndbc buoy estimates with good results drag coefficients in the mixed seas produced by hurricanes show dependence on wave age of the wind sea swell propagation direction and water depth the need for wave and stress modeling for atmosphere ocean coupling is emphasized the new wave model has all the necessary attributes to be the basis for such a coupler

the importance of sar wavelength in penetrating blow sand in northern arizona abstract multifrequency and polarimetric air borne s ynthetic a perture r adar airsar images of a sand streak in northern arizona demonstrate the ability of c 6 cm wavelength l 24 cm and p band 68 cm radar signals to backscatter respectively from increasingly greater depths reaching 2 m or more in active blow sand the studied sand streak located on a salient of ward terrace at lat 35 48 4 n and long 111 15 0 w is sourced in the normally dry little colorado river channel and migrates northeastward toward the moenkopi plateau scarp the sand streak is radar dark compared to the radar bright surface of ward terrace on all c band images it is however penetrated completely at p band and is invisible on these images the sand streak is recognizable on the lhh image but is poorly defined on the lhv image high resolution airsar images constitute the primary data set analyzed in addition a c band radar image acquired by the european remote sensing ers satellite is also presented the spaceborne image data confirms the results of the aircraft data at c band

detection of sand covered geologic features in the arabian peninsula using sir c x sar data eolian sand covers a large part of the arabian peninsula the flow of eolian sand is ongoing and sand covers bedrock as well as fluvial features of the peninsula consequently there is a gap in the understanding of the geological processes shaping the region the extensive coverage of shuttle imaging radar sir c x sar data over the arabian peninsula has provided a new means of mapping sand obscured features the preliminary interpretation of the data has identified several sites where l band reveals sand covered geological structures and drainage channels that are not shown on published maps and are not traceable with more conventional methods the indications are that these radar data may lead to improving the geological and fluvial geomorphic understanding of the region

subsurface valleys and geoarcheology of the eastern sahara revealed by shuttle radar the shuttle imaging radar sir a carried on the space shuttle columbia in november 1981 penetrated the extremely dry selima sand sheet dunes and drift sand of the eastern sahara revealing previously unknown buried valleys geologic structures and possible stone age occupation sites radar responses from bedrock and gravel surfaces beneath windblown sand several centimeters to possibly meters thick delineate sand and alluvium filled valleys some nearly as wide as the nile valley and perhaps as old as middle tertiary the now vanished major river systems that carved these large valleys probably accomplished most of the erosional stripping of this extraordinarily flat hyperarid region underfit and incised dry wadis many superimposed on the large valleys represent erosion by intermittent running water probably during quaternary pluvials stone age artifacts associated with soils in the alluvium suggest that areas near the wadis may have been sites of early human occupation the presence of old drainage networks beneath the sand sheet provides a geologic explanation for the locations of many playas and present day oases which have been centers of episodic human habitation radar penetration of dry sand and soils varies with the wavelength of the incident signals 24 centimeters for the sir a system incidence angle and the electrical properties of the materials which are largely determined by moisture content the calculated depth of radar penetration of dry sand and granules based on laboratory measurements of the electrical properties of samples from the selima sand sheet is at least 5 meters recent september 1982 field studies in egypt verified sir a signal penetration depths of at least 1 meter in the selima sand sheet and in drift sand and 2 or more meters in sand dunes

latitudinal dependence of atlantic meridional overturning circulation amoc variations 1 amoc variations are often thought to propagate with the kelvin wave speed resulting in a short time lead between high and low latitudes amoc variations however as shown in this paper using a coupled climate model gfdl cm2 1 with the existence of interior pathways of north atlantic deep water nadw from flemish cap to cape hatteras as that observed recently amoc variations estimated in density space propagate with the advection speed in this region resulting in a much longer time lead several years between subpolar and subtropical amoc variations and providing a more useful predictability the results suggest that amoc variations have significant meridional coherence in density space and monitoring amoc variations in density space at higher latitudes might reveal a stronger signal with a several year time lead

microwave remote sensing of physically buried objects in the negev desert implications for environmental research we report remote detections of physically buried specularly reflecting objects using microwave radar at two sites ashalim and tseelim in the northern region of the negev desert israel these detections provide confirmation that microwave subsurface remote sensing is a genuine phenomenon at ashalim a scatterometer operating in the p band 441 mhz 68 cm was mounted on a cherry picker truck at a height of 8 m and used to detect two triangular aluminum mesh reflectors forming a 1 m square area reflector buried down to a depth of 8 cm in dry sand at tseelim the same scatterometer was mounted on an airplane flying at an altitude of 70 m and used to detect 1 m square aluminum reflectors each one submerged at a different location along the airplane flight path buried down to a depth of 20 cm the experimental results compare favorably with a theoretical model that incorporates radar absorption effects arising in the sandy subsurface layer and radar interference effects arising from phase differences between reflections from the surface and buried reflector the theoretical modeling also predicts the detection of a subsurface reflector down to a depth of about 4 4 m this experiment and the associated modeling approach is the first of a series of planned experiments which we outline for the detection and the theoretical evaluation of buried reflectors using remote microwave and vhf radar we identify potential subject areas for environmental research

signatures of the mediterranean outflow from a north atlantic climatology 2 diagnostic velocity fields part 1 of this study is a descriptive analysis of the spreading of mediterranean water based on high resolution maps of salinity and density in the eastern basin in this second part of our study velocity fields for two representative isopycnal surfaces of the mediterranean outflow o 0 s 29 70 and o 0 s 29 90 are estimated from a diagnostic model that combines climatological hydrographic data from the national oceanic data center with long term direct measurements of water exchange through the strait of gibraltar the model is constrained by geostrophic dynamics conservation of mass no flux conditions at the continental shelf and specified flow through the strait of gibraltar our principal data source is a recently assembled database of the north atlantic that consists of climatological mean property fields averaged on isopycnal surfaces the mean fields are based on more than 80 years 1909 1990 of data and have a nominal horizontal resolution of 0 5 o to provide boundary conditions at the strait of gibraltar we use the results of a model developed from data collected during the gibraltar experiment in 1985 the estimated velocity fields show mediterranean water exiting the strait of gibraltar following the southern iberian coast and then entering the tagus basin where it turns anticyclonically to create a reservoir of this water mass the flow continues northward along the eastern boundary penetrating into the rockall channel finally the model flow fields do not show a significant westward advection of mediterranean waters into the subtropical gyre

wind and wave extremes from atmosphere and wave model ensembles abstractthe present work develops an innovative approach to wind speed and significant wave height extreme value analysis the approach is based on global atmosphere wave model ensembles the membe

global ocean mean wave period data validation and description a global comparison of altimeter and era 40 mean wave period data is performed for the first time altimeter and era 40 mean wave period are shown to compare well in non swell dominated conditions triply collocated altimeter buoy and era 40 data show that the variance of the random errors is bigger for the era 40 data and smaller for the buoy data a new expression is given to relate altimeter data to wave period in wind dominated conditions provided this correction is applied altimeter data are adequate for the most needed validation of global model mean wave period data in non swell dominated conditions triply collocated altimeter buoy and era 40 also reveal that altimeter mean wave period is reliable even in swell conditions for moderate to high winds in contrast to previous suggestions which limited its validity to wind dominated seas

recent changes in the greenland scotland overflow derived water transport inferred from hydrographic observations in the southern irminger sea recent decadal changes 1955 2007 in the baroclinic transport tbc of the deep western boundary current dwbc carrying the greenland scotland overflow derived waters along the east greenland slope are quantified from a set of hydrographic sections in vicinity of cape farewell the updated historical record of tbc shows clear decadal variability 2 2 5 sv with the transport minima in the 1950s and mid 1990s maximum in the early 1980s and moderate to high transport in the 2000s since the mid 1990s the dwbc tbc has increased by 2 sv significant at the 99 9 level which constitute 20 of the mean absolute transport 9 0 sv as obtained from three cruises in 2002 2006 the dwbc tbc anomalies negatively correlate r 0 80 with thickness anomalies of the labrador sea water lsw at its origin implying a close association albeit not necessarily causative between the dwbc transport east of greenland and the lsw production

spaceborne radar subsurface imaging in hyperarid regions imaging data acquired with the shuttle imaging radar sir a over the hyperarid region of egypt sudan clearly show surface penetration through the sand cover even though absorption does occur in the sand layer surface refraction leads to a steeper incidence angle at the sand bedrock interface resulting in a stronger backscatter a simple backscatter model shows that for a low loss thin sand layer the presence of the covering layer enhances the capability to image the subsurface interface particularly at large incidence angles and hh polarization

shuttle imaging radar physical controls on signal penetration and subsurface scattenng in the eastern sahara sir a signal penetration and subsurface backscatter within the upper meter or so of the sediment blanket in the eastern sahara of southern egypt and northern sudan are enhanced both by radar sensor parameters and by the physical and chemical characteristics of eolian and alluvial materials interpretation of sir a images by mccauley et al 1 2 dramatically changed previous concepts of the role that fluvial processes have played over the past 10000 to 30000000 years in shaping this now extremely flat featureless and hyperarid landscape in the present paper we summarize the near surface stratigraphy the electrical properties of materials and the types of radar interfaces found to be responsible for different classes of sir a tonal response the dominant factors related to efficient microwave signal penetration into the sediment blanket include a favorable distribution of particle sizes b extremely low moisture content and c reduced geometric scattering at the sir a frequency 1 3 ghz the depth of signal penetration that results in a recorded backscatter here called radar imaging depth was documented in the field to be a maximum of 1 5 m or 0 25 of the calculated skin depth for the sediment blanket radar imaging depth is estimated to be between 2 and 3 m for active sand dune materials diverse permittivity interfaces and volume scatterers within the shallow subsurface are responsible for most of the observed backscatter not directly attributable to grazing outcrops

effects of glacier runoff and wind on surface layer dynamics and atlantic water exchange in kongsfjorden svalbard a model study abstract a high resolution numerical ocean circulation model has been used to investigate exchange mechanisms and transport of thermal energy towards the inner part of kongsfjorden svalbard a location where tidewater glaciers expose large calving fronts to the ocean water and sea ice has been a regular winter feature until recently comparison of model simulations against a large set of observational data shows that the model captures the main features of seasonality and geographical distribution of hydrography the model is able to simulate inflow of atlantic water although the timing strength and depth of inflow events are not always the same in the model as in mooring records the model shows water entering via the shelf consistently penetrating deep into the fjord and volume transport toward the interior parts are large even under winter conditions heat transports are smaller in winter than in summer due to generally lower winter temperatures results indicate that glacial freshwater discharge in the surface layer is not a necessary factor for driving sub surface exchange rather along fjord winds stand out as important for the circulation and hence water exchange in the inner part of the fjord the combination of inflow of atlantic water from the outer shelf into the central part of the fjord and further transport of mixed water masses with intermediate heat content toward the inner part constitutes a significant transfer of thermal energy from the outer shelf and deep into the fjord the potential for glacier front melting is larger in summer than in winter as heat transports are larger this time of year while even modest heat transports in the upper part of the water column may influence the sea ice cover in winter

a high resolution hindcast of wind and waves for the north sea the norwegian sea and the barents sea 1 a combined high resolution atmospheric downscaling and wave hindcast based on the era 40 reanalysis covering the norwegian sea the north sea and the barents sea is presented the period covered is from september 1957 to august 2002 the dynamic atmospheric downscaling is performed as a series of short prognostic runs initialized from a blend of era 40 and the previous prognostic run to preserve the fine scale surface features from the high resolution model while maintaining the large scale synoptic field from era 40 the nested wam wave model hindcast consists of a coarse 50 km model covering the north atlantic forced with era 40 winds and a nested 10 11 km resolution model forced with downscaled winds a comparison against in situ and satellite observations of wind and sea state reveals significant improvement in mean values and upper percentiles of wind vectors and the significant wave height over era 40 improvement is also found in the mean wave period era 40 is biased low in wind speed and significant wave height a bias which is not reproduced by the downscaling the atmospheric downscaling also reproduces polar lows which cannot be resolved by era 40 but the lows are too weak and short lived as the downscaling is not capable of capturing their full life cycle

mapping exposed and buried drainage systems using remote sensing in the negev desert israel abstract this paper examines the use of optical visible and infrared ir data synthetic aperture radar data sar and ground penetrating radar gpr for detection identification and mapping of exposed and buried channels under sands in the western negev israel and northern sinai egypt field observations and shallow geophysical methods corroborated the observations the halutza agur and shunra sand dunes are the continuation of the northern sinai dunes playa type sediments from the late quaternary are found in upper reaches of dry river channels between the dunes of the northwest negev and represent a deterioration of the drainage system caused by shifting sand dunes a dual polarimetric radar sir c image from srl 1 having two frequencies and two polarizations exhibits meaningful differences in reflectance between the buried and abandoned channels and their surroundings the buried continuation of wadi mobra and the larger nahal nizzana channels under the western shunra sand dunes can be observed in l band radar data these channels are not clearly observed either in the landsat thematic mapper tm visible nor in the near infrared nir images the radar wavelengths and polarizations that improve the contrast between the buried river beds and the surrounding sand mantle are in descending order l hv l hh and c hh however in places where the sand mantle is very thick or where channels cut through bedrock the visible and near infrared data from landsat tm are easier to interpret and tend to be more useful for mapping fluvial patterns

deciphering the pathways for the deep limb of the meridional overturning circulation for the past 50 years it has been assumed that the principal pathway for the deep limb of the atlantic meridional overturning circulation amoc is the deep western boundary current dwbc however recent observations of lagrangian floats have shown that the dwbc is not necessarily a unique dominant or continuous pathway for these deep waters a significant portion of the deep water export from the subpolar to the subtropical gyres follows a pathway through the interior of the newfoundland and subtropical basins which is constrained by the western boundary and the western flank of the mid atlantic ridge the hypothesis that deep eddy driven recirculation gyres are a mechanism for partitioning the deep limb of the amoc into the dwbc and this interior pathway is investigated here eulerian and lagrangian analyses of the output of ocean general circulation models at eddy resolving eddy permitting and non eddy permitting resolutions are used to test this hypothesis eddy driven recirculation gyres simulated in the eddy resolving and eddy permitting models and similar to recirculations inferred from hydrographic data are shown to shape the export pathways of deep water from the subpolar to the subtropical gyres

transit time distributions in a global ocean model abstract results from a simulation of the ocean transit time distribution ttd for global and regional ocean surface boundary conditions are presented based on a 5000 yr integration using the parallel ocean program ocean general circulation model the ttd describes the probability that water at a given interior point in the ocean was at some point on the ocean surface a given amount of time ago it is shown that the spatial distribution of ocean ttds can be understood in terms of conventional wisdom regarding time scales and pathways of the ventilated thermocline and the thermohaline circulation driven deep ocean circulation the true mean age from the model the first moment of the ttd is demonstrated to be very large everywhere because of very long tailed distributions regional ttd distributions are presented for distinct surface boundary subregions and it is shown how these can help in the interpretation of the global ttd the spatial structure of each regional ttd is shown to become essential

decadal wave power variability in the north east atlantic and north sea 2015 american geophysical union all rights reserved estimation of the long term behavior of wave climate is crucial for harnessing wave energy in a cost effective way previous studies have linked wave heights to the north south atmospheric pressure anomalies in the north atlantic suggesting that the wave climate fluctuates as a response to changes in zonal circulation in the atmosphere we identify changes in wave power in the north east atlantic that are strongly correlated to the dominant pressure anomalies the north atlantic oscillation nao and other modes we present a reconstructed wave power climate for 1665 2005 using a combination of known and proxy indices for the nao and other modes our reconstruction shows high interannual and multidecadal variability which makes wave energy prediction challenging this variability should be considered in any long term reliability analysis for wave energy devices and in power scheme economics

a twenty year reversal in water mass trends in the subtropical north atlantic temperature and salinity changes have been compared along three repeat sections at 36 n in the north atlantic the principal changes cooling of the upper waters and warming of the intermediate waters observed between 1959 and 1981 were reversed between 1981 and 2005 the controlling mechanisms for the changes over the two time periods differed through the water column neutral density surfaces over the upper 800 m were firstly uplifted and secondly depressed by typically 50 m which is broadly consistent with the changes in thermocline thickness implied by the temporal changes in ekman pumping in contrast the intermediate waters 800 2500 m firstly became warmer and saltier and secondly became cooler and fresher this change in the intermediate waters was controlled by water mass changes along neutral density surfaces suggesting a change in the source waters principally labrador sea water and mediterranean outflow water

the arrival of recently formed labrador sea water in the deep western boundary current at 26 5 n the deep western boundary current dwbc of the north atlantic is a principal conduit between the formation region for labrador sea water lsw and the oceanic interior to the south time series 1985 1997 of hydrographic properties obtained in the dwbc at 26 5 n show that prior to 1994 temperature salinity and transient tracer properties within the lsw density range showed little indication of recently formed parcels properties characteristic of a newer version of lsw cooler fresher and higher tracer concentrations were observed beginning in 1994 and continuing through 1997 longer time series of temperature and salinity developed from a regional data base show both the 1994 and a 1980 1981 event in the abaco region both events are consistent with anomalies in the labrador sea that occurred some 10 years earlier the 10 year transit time from the labrador sea to 26 5 n is less than the 18 year transit time inferred from earlier studies

buoy observations from the windiest location in the world ocean cape farewell greenland 1 cape farewell greenland s southernmost point is a region of significant interest in the meteorological and oceanographic communities in that atmospheric flow distortion associated with the high topography of the region leads to a number of high wind speed jets the resulting large air sea fluxes of momentum and buoyancy have a dramatic impact on the region s weather and ocean circulation here the first in situ observations of the surface meteorology in the region collected from an instrumented buoy are presented the buoy wind speeds are compared to 10 m wind speeds from the quikscat satellite and the north american regional reanalysis narr we show that the quikscat retrievals have a high wind speed bias that is absent from the narr winds the spatial characteristics of the high wind speed events are also presented

propagation pathways of classical labrador sea water from its source region to 26 n 1 more than two decades of hydrography on the abaco line east of the bahamas at 26 n reveals decadal variability in the salinity of classical labrador sea water clsw despite the long distance from its source region in the north atlantic ocean hydrographic time series from the labrador sea and from the abaco line show a pronounced step like decrease in salinity between 1985 and 1995 in the labrador sea and between 1995 and 2010 at the abaco line suggesting a time lag between the two locations of approximately 9 years the amplitude of the anomaly at the abaco line is 50 of the amplitude in the labrador sea a similar time lag and reduction of amplitude is found in the high resolution ofes model in which salinity anomalies can be observed propagating through the deep western boundary current as well as through a broad interior pathway on its way south to the abaco line the clsw becomes 8 standard deviations saltier due to isopycnal mixing with mediterranean outflow water mow climatological data in the north atlantic suggests that the mixing ratio of mow to clsw at the abaco line is 1 4 and that no variability in mow is required to explain the observed variability at the abaco line the data studied here suggest that decadal clsw anomalies stay relatively coherent while getting advected despite the important role of interior pathways

trends of atlantic wave extremes as simulated in a 40 yr wave hindcast using kinematically reanalyzed wind fields abstract in this study seasonal extremes of wave height in the north atlantic are analyzed the analysis is based on a 40 yr 1958 97 numerical wave hindcast using an intensive kinematic reanalysis of wind fields changes in the ocean wave extremes are identified by performing the mann kendall test and are further related to changes in the atmospheric circulation sea level pressure by means of redundancy analysis the relationship between sea level pressure and ocean wave extremes is also used to reconstruct the seasonal wave statistics for the last century back to 1899 consistent with previous studies this high resolution atlantic wave hindcast also shows that the northeast north atlantic ocean has experienced significant multidecadal variations in the last century and it has indeed roughened in winters of the last four decades the winter wave height increases are closely related to changes in the north atlantic oscillation during the last four decades while showing trend patterns similar to

export of labrador sea water from the subpolar north atlantic a lagrangian perspective abstract results from 59 acoustically tracked rafos floats obtained during 2003 2008 are analyzed here to study the spreading pathways of labrador sea water lsw from the subpolar to subtropical north atlantic an earlier paper based on a subset of these float data presented evidence of a potentially important interior pathway for the southward spreading of lsw here those results are reinforced with the full data set and new information on lsw pathways around the grand banks is presented about 70 of the rafos floats were expelled into the ocean interior east of the grand banks and meandered slowly eastward toward the mid atlantic ridge a pathway observed previously with profiling floats less than 10 was advected continuously around the grand banks by the deep western boundary current dwbc a larger fraction 17 drifted into the subtropical interior from the tail of the grand banks suggesting that this pathway is at least if not more important than the dwbc pathway for the export of lsw to the subtropics rafos floats released closest to the continental slope at 700 m depth were more likely to rapidly reach subtropical latitudes mainly because they drifted through flemish pass a 1100 m deep channel between the grand banks and the flemish cap which protects fluid parcels from being swept off the continental slope by meanders of the north atlantic current a statistical comparison of the rafos trajectories with more than 5000 simulated floats obtained from the family of linked atlantic models experiment flame high resolution ocean general circulation model reveals a similar pattern of lsw spreading the rafos and simulated floats are also used to show that contrary to a previous modeling study the isobaric rafos floats do not underestimate the amount of lsw that continuously follows the dwbc around the grand banks compared to isopycnal floats these results have implications for the connectivity of the deep limb of the atlantic meridional overturning circulation between the subpolar and the subtropical north atlantic

drift in the uppermost part of the ocean lagrangian drift velocities within the uppermost meter of the ocean mostly depend on the local wind forcing turbulent mixing and waves while the interior part of the ekman layer has been extensively studied using drogued drifters the drift at or very close to the surface is less investigated the wind response of surface currents on time scales from 1 h to 10 days is analyzed using two types of satellite tracked drifters i spherical floats on the surface and ii drifters with a drogue centered at 70 cm depth the response of drifting objects to wind and wave forcing is highly dependent on the vertical position even within the upper meter of the ocean the surface drifters are wind coherent for both cyclonic and anticyclonic subinertial frequencies in contrast the subsurface drift responds primarily to anticyclonic forcing that resonates with the intrinsic ocean dynamics

signatures of the mediterranean outflow from a north atlantic climatology 1 salinity and density fields using historical data from the national oceanic data center the climatology of the eastern north atlantic basin has been investigated for the purpose of detailing the mediterranean outflow water in terms of its salinity density and flow patterns part 1 of this work is a descriptive analysis of the fate of the mediterranean water once it flows out of the strait of gibraltar tracing the salinity and density signatures high resolution maps of the climatological outflow are presented with an emphasis on the continuity of the water from its source from the climatological fields a continuous signal of mediterranean water is tracked northward to 50 20 n yet its westward advection is limited to the tagus basin recirculations of mediterranean water in the gulf of cadiz and in the bay of biscay deduced from property signals are also detailed iorga and lozier this issue present absolute velocity fields from a diagnostic model constrained by geostrophic dynamics conservation of mass and no flux boundary conditions

thinning of arctic sea ice observed in fram strait 1990 2011 1 time series 1990 2011 of sea ice thickness observed by moored sonars in the transpolar drift in fram strait are examined contrasting the post 2007 years against the 1990s three remarkable changes in the monthly ice thickness distributions are highlighted 1 the thickness of old level ice modal thickness is reduced by 32 2 the old ice modal peak width is reduced by 25 and 3 the fraction of ridged ice thicker than 5 m is reduced by 50 the combined effect on the mean ice thickness is a reduction from an annual average of 3 0 m during the 1990s to 2 2 m during 2008 2011 most of the thinning took place after 2005 2006 while the old ice modal thickness and peak width show signs of recovery after 2008 the decreasing trend in fraction of ridged ice and mean ice thickness persists until the end of the record in 2011 the ice observed in fram strait carries an integrated signal of arctic change due to the advection of ice from many sites in the arctic based on concurrence in timing we conclude that much of the thinning quantified here is reflecting recent change in the age composition of the arctic ice cover toward younger ice the old level ice remains thin and as such the ice cover remains preconditioned for new summers of very low sea ice extent

zonal circulation across 52 w in the north atlantic 1 in july august 1997 a hydrographic acoustic doppler current profiler adcp tracer section was occupied along 52 w in the north atlantic as part of the world ocean circulation experiment hydrographic program underway and lowered adcp ladcp data have been used to reference geostrophic velocities calculated from the hydrographic data additional small velocity adjustments provided by an inverse model constraining mass and silicate transports in 17 neutral density layers yield the absolute zonal velocity field for 52 w we find a vigorous circulation throughout the entire section with an unusually strong gulf stream 169 sv and southern deep western boundary current dwbc 64 sv at the time of the cruise at the northern boundary on the west side of the grand banks of newfoundland we find the westward flowing labrador current 8 6 sv whose continuity from the labrador sea east of our section has been disputed directly to the south we identify the slopewater current 12 5 sv eastward and northern dwbc 12 5 sv westward strong departures from strictly zonal flow in the interior which are found in the ladcp data make it difficult to diagnose the circulation there isolated deep property extrema in the southern portion associated with alternating bands of eastward and westward flow are consistent with the idea that the rough topography of the mid atlantic ridge directly east of our section causes enhanced mixing of antarctic bottom water properties into overlying waters with distinctly different properties we calculate heat and freshwater fluxes crossing 52 w that exceed estimates based on air sea exchanges by a factor of 1 7

spreading of labrador sea water in the eastern north atlantic the spreading of labrador sea water lsw in the eastern north atlantic south of 55 n is described on the basis of recent high resolution hydrographic lines and using an inverse model of that basin general circulation the isopycnic salinity anomaly relative to a standard s curve is used to detect the main branches and limits of dominant influence of the intermediate water masses the lsw crosses the mid atlantic ridge at latitudes around 50 n with parts spreading farther eastward and southward one southward pathway along the eastern side of the mid atlantic ridge stands out as an eastern basin counterpart of the western atlantic deep western boundary current an entry into the bay of biscay in its northern part is also evidenced with striking similitudes between two data sets from 1974 and 1989 1990 at the southern limit of the lsw extension in the vicinity of the azores biscay rise a marked front exists basinwide around 1800 m with the more saline deep mediterranean water dmw the inverse model velocity field is consistent with most features of the tracer distributions and allows estimation of lsw transports 6 3 1 2 sv of lsw with salinities lower than 34 94 cross the 35 w meridian eastward between 44 n and 54 n one fourth of which recirculates southwestward in the western basin while another fourth turns northward across 54 n and the remaining half proceeds southward in the eastern basin the model circulation suggests that dmw results from mixing between eastern basin lsw and the overlying mediterranean outflow water most probably through double diffusion we finally describe several mesoscale structures of anomalously high lsw influence south of the lsw dmw front notably one sampled by a rafos float the velocity and potential vorticity fields suggest that these lsw eddies are formed through baroclinic instability at the lsw dmw front

secondary microseisms of north atlantic windstorms in central eurasia an understanding of an anomalously big bulge of seismic noise before the 2001 november 14 mw 7 8 kunlun earthquake

great salinity anomalies in the north atlantic abstract we revisited the great salinity anomaly of the 1970s gsa 70s dickson et al 1988 and documented the newly identified great salinity anomaly of the 1980s hence termed gsa 80s both propagated around the north atlantic in a similar fashion the advective mechanism initially proposed to explain the observed sequence of low salinity low temperature events during the gsa 70s apparently holds also for the gsa 80s the latter was successively observed in the west greenland current 1982 the labrador current 1983 the flemish pass 1984 near the charlie gibbs fracture zone 1984 1985 in the rockall channel 1985 south of iceland 1985 1988 in the north sea 1986 1987 norwegian sea 1987 1988 barents sea 1988 1989 and iceland sea 1989 1990 the advection speed of the gsa 80s seems to be greater than the one of the gsa 70s the 1980s anomaly reached the barents sea 6 to 7 years after peaking in the west greenland current while the 1970s anomaly traveled the same route in 8 to 10 years these anomalies however seem to be of different origin the gsa 70s was apparently boosted remotely by a freshwater sea ice pulse from the arctic via fram strait consequently the gsa 70s was accompanied by a large sea ice extent anomaly in the greenland and iceland seas which propagated into the labrador sea in contrast the gsa 80s was likely formed locally in the labrador sea baffin bay mainly because of the extremely severe winters of the early 1980s but supplemented with a possible contribution of the arctic freshwater outflow via the canadian archipelago facilitated by strong northerly winds which would have enhanced stability and ice formation this anomaly was also associated with a positive sea ice extent anomaly in the labrador sea baffin bay which however had no upstream precursor in the greenland sea thus the gsas are not necessarily caused solely by an increased export of freshwater and sea ice from the arctic via fram strait these results are corroborated by the early 1990s data when a new fresh cold anomaly was formed in the labrador sea and accompanied by a large positive sea ice extent anomaly the harsh winters of the early 1990s were however confined to the labrador sea baffin bay area while the atmospheric and oceanic conditions in the greenland iceland and irminger seas were normal the labrador sea baffin bay area appears therefore to play a key role in formation of gsas as well as in propagation of the gsas formed upstream a likely contribution of the enhanced canadian archipelago freshwater outflow to the gsa formation also seems to be significant two major modes of the gsa origin are thus identified remote generated by an enhanced arctic ocean freshwater export via either fram strait or the canadian archipelago and local resulting from severe winters in the labrador sea baffin bay both modes should be taken into account to model decadal variability of the coupled ocean ice atmosphere system in the north atlantic arctic basin

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

44 year wave hindcast for the north east atlantic european coast this paper describes a 44 year from 1958 to 2001 wave hindcast conducted for the north atlantic using a fine grid in the north east atlantic coastal areas of europe the wind fields were obtained by a local area model that was applied in the areas adjacent to the european coasts which was forced by the results of the ncep reanalysis while the ncep results have a spatial distribution of 2 and a time step of 6 h the wind fields produced by the local area model have a spatial resolution of 0 5 and a time step of 1 h which is important for accurate descriptions of the conditions in coastal areas and in rapidly changing storms a version of the wam model that allowed two way nesting was adopted and calculations were made with nested grids allowing a fine resolution in the coastal areas of europe this paper includes the description of the set up of the wave model and the validation performed vs in situ measurements so as to allow assessments of the quality of the data produced in this study

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

recirculating components to the deep boundary current of the northern north atlantic abstract the meridional overturning system of the north atlantic is conventionally thought of as transporting warm water 4 c to high latitudes and covd water to low latitudes the northern cold water sources for this system are dense overflow from the nordic seas and less dense water from the labrador sea lsw the overflow components are carried westward by a deep northern boundary current dnbc that is shown here actually to begin southeast of the overflow regions the dnbc lies along the southern side of a system of islands and submarine ridges that divides the nordic seas from the subpolar basins the overflows act to increase the transport of the dnbc and this transport is further increased through the entrainment of warm waters once inside the labrador sea the dnbc is joined by lsw before continuing south to low latitudes as a cold deep western boundary current dwbc however published transport estimates are larger than can be explained by warm water entrainment alone thus indicating entrainment also of recirculating cold components the subject of this paper their sources are shown to be the lsw and cold abyssal waters originating from the southern hemisphere the lsw is entrained downward into the denser part of the dnbc and laterally into the upper part of the dwbc whereas the cold abyssal waters are supplied by an eastern intensified northward flow in the eastern atlantic that serves as the initial source of the dnbc and by a similar northward flow in the western atlantic the meridional overturning system described includes recirculations and poleward transport of cold water in addition tothe components described by the conventional system the cold abyssal waters in both the eastern and western basins have relatively low levels of oxygen and high concentrations of silicate reflecting their southern origin but their influence in the northwestern atlantic is somewhat obscurred by strong recirculating cyclonic gyres in the newfoundland and labrador basins this influence is detected by a deep silicate maximum extending poleward from the mid latitude western atlantic through the two gyres with eastern concentration and recirculating back diluted toward the south in the dwbc within the respective basins such a maximum also extends northward through the irminger basin into the dnbc but there is an ambiguity as to whether this is a direct extension of the signal from the south in the western basin or if it comes from the mid latitude eastern basin by way of westward flow through the charlie gibbs fracture zone it is perhaps consequence of both estimates of the volume transports of the various recirculating cold components indicate that they supply about as much water to the deep boundary currents as do the combined cold water sources in the north

paleodrainages of the eastern sahara the radar rivers revisited sir a b implications for a mid tertiary trans afnrcan drainage system a complex history of cenozoic fluvial activity in the presently hyperarid eastern sahara is inferred from sir data and postflight field investigations in southwest egypt and northwest sudan sir images were coregistered with landsat and existing maps as a guide to exploration of the buried paleodrainages radar rivers first discovered by sir a field observations explain the radar responses of three types of radar rivers rr 1 rr 2 and rr 3 rr 1 broad aggraded valleys or basins filled with alluvium generally give a dark response relative to the surrounding radar bright tone of the wind roughened discontinuously sand covered bedrock of the remnant interfluves the alluvial fill in some of the rr 1 valleys gives a locally intermediate to bright response where cemented by diagenetic caco3 caliche the rr 2 type braided channels inset in the rr 1 valleys are filled with noncalichified loose sediment and are visible on sir because of the caliche effect the dark response of unconsolidated alluvium in the inset channels contrasts with the brighter response of calichified alluvium in the broad valleys the third type rr 3 narrow long bedrock incised channels which are partly visible on the ground and on landsat in areas where the sand sheet is patchy are conspicuous on sir because the dark response of their unconsolidated channel fill contrasts with the brighter response of the surrounding bedrock disconformably overlying and concealing the rr 1 valleys the rr 2 channels and parts of the rr 3 channels are eolian sand sheet sheet de deposits which in turn are locally overridden by trains of barchan dunes

sar studies in the yuma desert arizona sand penetration geology and the detection of military ordnance debris abstract synthetic aperture radar sar images acquired over part of the yuma desert in southwestern arizona demonstrate the ability of c band 5 7 cm wavelength l band 24 5 cm and p band 68 cm airsar signals to backscatter from increasingly greater depths reaching several meters in blow sand and sandy alluvium airsar images obtained within the barry m goldwater bombing and gunnery range near yuma arizona show a total reversal of c and p band backscatter contrast image tone for three distinct geologic units this phenomenon results from an increasingly greater depth of radar imaging with increasing radar wavelength in the case of sandy and small pebble alluvium surfaces mantled by up to several meters of blow sand backscatter increases directly with sar wavelength as a result of volume scattering from a calcic soil horizon at shallow depth and by volume scattering from the root mounds of healthy desert vegetation that locally stabilize blow sand airsar images obtained within the military range are also shown to be useful for detecting metallic military ordnance debris that is located either at the surface or covered by tens of centimeters to several meters of blow sand the degree of detectability of this ordnance increases with sar wavelength and is clearly maximized on p band images that are processed in the cross polarized mode hv this effect is attributed to maximum signal penetration at p band and the enhanced phv image contrast between the radar bright ordnance debris and the radar dark sandy desert this article focuses on the interpretation of high resolution airsar images but also compares these airborne sar images with those acquired from spacecraft sensors such as ers sar and space radar laboratory sir c x sar

sir b subsurface imaging of a sand buried landscape al labbah plateau saudi arabia despite a diminution in the transmit and receive power of the sir b system a striking l band radar image was produced for a portion of the southern al labbah plateau saudi arabia a landscape dominated by eolian sand features distinct tonal and digital number dn signatures uniquely define 1 areas where the sir b beam penetrated a relatively thin sand sheet to be diffusely reflected from the buried carbonate rocks of the aruma formation and 2 a thick sand hill and associative sand shadow where sir b subsurface imaging did not occur computer analysis of the digital sir b image data indicates there is about a 26 dn difference between the sand buried aruma formation and the unpenetrated sand hill and shadow depth measurements from more than 80 test holes show that subsurface imaging occurred through a sand layer whose maximum measured thickness is 1 24 m the penetrated medium is a fine to medium grained low density quartz sand that had a very low moisture content average of about 0 2 weight percent on the day of the space shuttle overpass the minimum thickness of sand features where subsurface imaging did not occur is thought to be about 3 1 m

spreading of the labrador sea water to the irminger and iceland basins 1 labrador sea water lsw is a principal convectively formed water mass of the subpolar north atlantic spna using extensive oceanographic archives we demonstrate striking changes in spna caused by massive lsw production during 1987 1994 and document recent salinification and warming imminently bringing spna to the state last time seen in the 1960s two prominent lsw classes are spreading across spna since the 1980s the first record dense deep and voluminous class has been progressively built by intense winter convection through 1987 1994 even though most of this lsw has left spna its remnants are still present there the second shallower class strengthens in 2000 over subsequent years its core becomes slightly thicker and deepens the anomalous signals acquired by these lsw classes in their formation region arrive in the irminger and iceland basins with the characteristic delays of two and five years for deeper lsw and a year and four years for shallower lsw

variability in deep western boundary current transports preliminary results from 26 5 n in the atlantic 1 transport fluctuations of the deep limb of the meridional overturning circulation moc near the western boundary are presented from a line of inverted echo sounders bottom pressure sensors and a deep current meter east of abaco island bahamas at 26 5 n from september 2004 through september 2005 the mean southward flow between 800 dbar and 4800 dbar was 39 106 m3 s 1 with a northward recirculation of 28 106 m3 s 1 leaving a net southward flow of 11 106 m3 s 1 as the through flow of the deep western boundary current dwbc the mean southward dwbc flow essentially equals previous values that were measured at the same location by arrays of current meters deployed from 1986 to 1992 dwbc transport spectra indicate that barotropic and baroclinic changes have very similar energy levels at most periods less than 10 days and that barotropic changes dominate at periods of 10 80 days

hydrographic changes in the labrador sea 1960 2005 abstract the labrador sea has exhibited significant temperature and salinity variations over the past five decades the whole basin was extremely warm and salty between the mid 1960s and early 1970s and fresh and cold between the late 1980s and mid 1990s the full column salinity change observed between these periods is equivalent to mixing a 6 m thick freshwater layer into the water column of the early 1970s the freshening and cooling trends reversed in 1994 starting a new phase of heat and salt accumulation in the labrador sea sustained throughout the subsequent years it took only a decade for the whole water column to lose most of its excessive freshwater reinstate stratification and accumulate enough salt and heat to approach its record high salt and heat contents observed between the late 1960s and the early 1970s if the recent tendencies persist the basin s storages of salt and heat will fairly soon likely by 2008 exceed their historic highs the main process responsible for the net cooling and freshening of the labrador sea between 1987 and 1994 was deep winter convection which during this period progressively developed to its record depths it was caused by the recurrence of severe winters during these years and in its turn produced the deepest densest and most voluminous labrador sea water lsw1987 1994 ever observed the estimated annual production of this water during the period of 1987 1994 is equivalent to the average volume flux of about 4 5 sv with some individual annual rates exceeding 7 0 sv once winter convection had lost its strength in the winter of 1994 1995 the deep lsw1987 1994 layer lost communication with the mixed layer above consequently losing its volume while gaining heat and salt from the intermediate waters outside the labrador sea while the 1000 2000 m layer was steadily becoming warmer and saltier between 1994 and 2005 the upper 1000 m layer experienced another episode of cooling caused by an abrupt increase in the air sea heat fluxes in the winter of 1999 2000 this change in the atmospheric forcing resulted in fairly intense convective mixing sufficient to produce a new prominent lsw class lsw2000 penetrating deeper than 1300 m this layer was steadily sinking or deepening over the years following its production and is presently overlain by even warmer and apparently less dense water mass implying that lsw2000 is likely to follow the fate of its deeper precursor lsw1987 1994 the increasing stratification of the intermediate layer implies intensification in the baroclinic component of the boundary currents around the mid depth perimeter of the labrador sea the near bottom waters originating from the denmark strait overflow exhibit strong interannual variability featuring distinct short term basin scale events or pulses of anomalously cold and fresh water separated by warm and salty overflow modifications regardless of their sign these anomalies pass through the abyss of the labrador sea first appearing at the greenland side and then about a year later at the labrador side and in the central labrador basin the northeast atlantic deep water 2500 3200 m originating from the iceland scotland overflow water reached its historically freshest state in the 2000 2001 period and has been steadily becoming saltier since then it is argued that lsw1987 1994 significantly contributed to the freshening density decrease and volume loss experienced by this water mass between the late 1960s and the mid 1990s via the increased entrainment of freshening lsw the hydrostatic adjustment to expanding lsw or both

ocean gyre circulation changes associated with the north atlantic oscillation abstract observational evidence is presented for interannual to interdecadal variability in the intensity of the north atlantic gyre circulation related to the atmospheric north atlantic oscillation nao patterns a two point baroclinic pressure difference between the subtropical and subpolar gyre centers an oceanic analogue to the much used sea level pressure slp based atmospheric nao indices is constructed from time series of potential energy anomaly pea derived from hydrographic measurements in the labrador basin and at station s near bermuda representing the upper 2000 db eastward baroclinic mass transport between the two centers the transport index indicates a gulf stream and north atlantic current that gradually weakened during the low nao period of the 1960s and then intensified in the subsequent 25 years of persistently high nao to a record peak in the 1990s the peak to peak amplitude difference was 15 20 megatons per second mt s 1 with a 43 yr mean of about 60 mt s 1 a change of 25 33

interannual to decadal variability of outflow from the labrador sea a decade of weak convection in the labrador sea associated with decreasing water mass transformation in combination with advective and eddy fluxes into the convection area caused significant warming of the deep waters in both the central labrador sea and boundary current system along the labrador shelf break the connection to the export of deep water was studied based on moored current meter stations between 1997 and 2009 at the exit of the labrador sea near the shelf break at 5 3n more than 100 year long current meter records spanning the full water column have been analyzed with respect to high frequency variability decaying from the surface to the bottom layer and for the annual mean flow showing intra to interannual variability but no detectable decadal trend in the strength of the deep and near bottom flow out of the labrador sea

propagation of tracer signals in boundary currents abstract the propagation of a range of tracer signals in a simple model of the deep western boundary current is examined analytical expressions are derived in certain limits for the transit time distributions and the propagation times tracer ages of tracers with exponentially growing or periodic concentration histories at the boundary current s origin if mixing between the boundary current and the surrounding ocean is either very slow or very rapid then all tracer signals propagate at the same rate in contrast for intermediate mixing rates tracer ages generally depend on the history of the tracer variations at the origin and range from the advective time along the current to the much larger mean age close agreement of the model with chlorofluorocarbon cfc and tritium observations in the north atlantic deep western boundary current dwbc is obtained when the model is in the intermediate mixing regime with current speed around 5 cm s 1 and mixing time scale around 1 yr in this regime anomalies

temporal variability of the atlantic meridional overturning circulation at 26 5 n the vigor of atlantic meridional overturning circulation moc is thought to be vulnerable to global warming but its short term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain we combine continuous measurements of the moc beginning in 2004 using the purposefully designed transatlantic rapid climate change array of moored instruments deployed along 26 5 n with time series of gulf stream transport and surface layer ekman transport to quantify its intra annual variability the year long average overturning is 18 7 5 6 sverdrups sv range 4 0 to 34 9 sv where 1 sv a flow of ocean water of 106 cubic meters per second interannual changes in the overturning can be monitored with a resolution of 1 5 sv

the production of north atlantic deep water sources rates and pathways updating an earlier account by dickson et al 1990 this paper reviews the initial development phase of north atlantic deep water nadw production from the points where the dense inflows from nordic seas cross the greenland scotland ridge to the point off south greenland where the buildup of new production appears almost complete in particular three long term current meter arrays totaling 91 instruments and set at 160 km intervals south from the denmark strait sill are used to validate earlier short term arrays by others and in combination with these earlier arrays to describe the downstream evolution of mean speed depth and entrainment the variability of the overflow current in space and time and the likely contribution of the other three main constituents of nadw production at densities greater than 27 8 from the points of overflow 5 6 sv the transport within this range increases by entrainment and confluence with other contributory streams to around 13 3 sv at cape farewell while recirculating elements prevent us from determining the net southgoing transport a nadw transport of this order appears consistent with recent estimates of net abyssal flow passing south through the north and south atlantic