spaceborne tomography of multi species indian tropical forests abstract synthetic aperture radar sar backscatter is the coherent combination of the scattering from multiple individual scatterers within the radar resolution cell which results into a 2 d radar image tomographic sar tomosar takes advantage of multiple sar acquisitions to provide 3 d vertical structure of the imaged target over forests parameters such as canopy structure canopy density leaf area and phenology contribute to different sar scattering mechanisms along the vertical dimension of the trees tomography has been demonstrated in various earlier works for forest bio physical parameter estimation using airborne data in this research work multi polarimetric space borne tandem x tomograms are examined for the first time over a multi species indian tropical forest multiple tandem x acquisitions are focused using capon beamforming at five polarimetric channels hh hv vv hh vv and hh vv four distinct forest species compartments are selected representing different canopy structure and density the tomograms obtained in different polarizations for these species are analyzed in detail to understand the scattering patterns across different forest species field surveys carried out in several forest locations provide in situ observations of forest height and vertical structure it was observed that canopy gaps and leaf density play a crucial role for x band sar signal penetration through ground for dense canopy species the backscatter contributions are spread through the canopy while in case of sparse canopy species the ground scattering is dominant vertical profiles obtained at surveyed plot locations are plotted in all polarizations and provide a good agreement with field observations further the obtained tomosar backscatter layers have a good correlation with field measured above ground biomass agb the agb is modeled from tomosar with the hh pol tomosar backscatter layer at 27 m canopy height leading to an agb estimation with correlation r 0 76 and rmse of 50 4 t ha

digital terrain model retrieval in tropical forests through p band sar tomography this paper focuses on the retrieval of terrain topography below dense tropical forests by means of synthetic aperture radar sar systems low frequency signals are needed to penetrate such a thick vegetation layer however this expedient alone does not guarantee proper retrieval it is here demonstrated that the phase center of p band backscatter may lie several meters above the ground depending on the slope and incidence angle sar tomography is shown to overcome this problem and retrieves the actual topography even in the presence of dense trees up to 50 m tall digital terrain models returned by sar tomography are here put in comparison with light detection and ranging lidar terrain models the accuracy of radar derived maps is found to be at least comparable with the one offered by lidar systems moreover the discrepancy between tomography and lidar is larger if large footprint lidar is considered thus suggesting that in this case tomographic maps should be considered the reference height analyses are carried out by processing three data sets gathered over different tropical forests in western africa the robustness of the radar estimates is assessed with respect to both ground slope and treetop height

predicting north atlantic sea surface temperature variability on the basis of the first mode baroclinic rossby wave model 1 predictability of sea surface temperature sst variations over the north atlantic ocean is studied on the basis of the first mode baroclinic rossby wave model this simple linear wave model can explain about 10 46 of the wintertime sst variability in several regions of the north atlantic basin including the tropics between 5 n and 20 n the eastern subtropics between 27 n and 34 n and the east of newfoundland it is shown that the wintertime sst anomalies can be skillfully predicted up to 3 months ahead in the tropical atlantic 18 months in the eastern subtropical atlantic and 3 years east of newfoundland on the basis of the first mode baroclinic rossby wave adjustment

north atlantic subtropical mode waters and ocean memory in hadcm3 abstract a study of the formation and propagation of volume anomalies in north atlantic mode waters is presented based on 100 yr of monthly mean fields taken from the control run of the third hadley centre coupled ocean atmosphere gcm hadcm3 analysis of the temporal and spatial variability in the thickness between pairs of isothermal surfaces bounding the central temperature of the three main north atlantic subtropical mode waters shows that large scale variability in formation occurs over time scales ranging from 5 to 20 yr the largest formation anomalies are associated with a southward shift in the mixed layer isothermal distribution possibly due to changes in the gyre dynamics and or changes in the overlying wind field and air sea heat fluxes the persistence of these anomalies is shown to result from their subduction beneath the winter mixed layer base where they recirculate around the subtropical gyre in the background geostrophic flow anomalies in the warmest mode 18 c formed on the western

single and multipolarimetric sar tomography of forested areas a parametric approach in this paper a technique is described for the tomographic characterization of forested areas through multiple synthetic aperture radar sar observations based on either single or multipolarimetric acquisitions this technique is based on the idea of characterizing the fourier spectrum of the multibaseline data as being constituted by two effective scattering centers displaced along the vertical direction plus the associated decorrelation terms as a result sar tomography will be formulated as the problem of detecting the number of scattering centers within the resolution cell estimating the parameters that describe their spatial structure and evaluating the associated backscattered powers parameter estimation is carried out through the covariance matching estimation technique which provides an asymptotically optimal solution the results of an experiment performed on a real p band multibaseline fully polarimetric data set relative to the forested site of remningstorp sweden are reported

introduction to this special section advances in seismic sensors seismic detectors have been around for centuries and seismic prospecting for many decades the variety of seismic sensors in modern surveys is dazzling they can measure particle velocity and acceleration pressure and pressure gradient strain and strain rate and multiple components z h1 h2 yaw pitch roll from near dc to hundreds or thousands of hertz in land marine borehole and extraterrestrial environments

the long term hydrographic record at bermuda abstract a long by oceanographic standards time series of hydrographic observations at bermuda was begun in 1954 and continues to the present analysis of this dataset has shown the temperature and salinity variations on interannual timescales to be largely independent in the surface layer 0 200 dbar where integral timescales for salinity are 50 longer than for temperature and surface salinity changes are correlated with decadal changes in the 18 c water production temperature salinity anomalies are highly correlated in the thermocline where the interannual variability at that level is accountable to either vertical oscillations of the thermocline with amplitudes of 50 m or meridional oscillations of the horizontal gradient set up at the southern edge of the recirculation gyre of 300 kim salinity changes in the deepest layer observed at bermuda station s 1500 2500 dbar are uncorrelated with temperature masked by measurement errors in the early years of the time series inclusion of earlier

variability of sea surface height and circulation in the north atlantic forcing mechanisms and linkages abstract simulations with a coarse resolution global ocean model during 1958 2004 are analyzed to understand the inter annual and decadal variability of the north atlantic analyses of empirical orthogonal functions eofs suggest relationships among basin scale variations of sea surface height ssh and depth integrated circulation and the winter north atlantic oscillation nao or the east atlantic pattern eap indices the linkages between the atmospheric indices and ocean variables are shown to be related to the different roles played by surface momentum and heat fluxes in driving ocean variability in the subpolar region variations of the gyre strength ssh in the central labrador sea and the nao index are highly correlated surface heat flux is important in driving variations of ssh and circulation in the upper ocean and decadal variations of the atlantic meridional overturning circulation amoc surface momentum flux drives a significant barotropic component of flow and makes a noticeable contribution to the amoc in the subtropical region momentum flux plays a dominant role in driving variations of the gyre circulation and amoc there is a strong correlation between gyre strength and ssh at bermuda

the estimation of global sea level change a problem of uniqueness an objective method of estimating regional averages of coherent sea level sl change is developed the technique is applied to a large set of sl data representative of most of the world s continental margins the results show highly coherent sl changes over many of the regions studied the method is then applied to the regional averages themselves to develop an overall estimate of the coherent pattern of sl variations existing in the historical sl data set the pattern is characterized by a coherent rise of sl in all regions except alaska scandinavia both areas of notorious crustal uplift and southeast asia where sl appears to be falling the analysis suggests little or no change in sl prior to the early 1900 s the period since that time has seen an increase in sl that is optimally fit by a linear trend of 23 cm century the study results suggest that it is not possible to uniquely determine either a global rate of change of sl or even the average rate of change associated with the existing inadequate data set indeed different analysis methods by themselves can cause 50 variations in the estimates of sl trend in the existing data set a signal noise analysis suggests it should be easy to detect small future changes in the sl trends estimated for the period 1930 1980 however detection of theoretically predicted low frequency signals e g caused by co2 warming will be difficult in view of the huge low frequency natural variability associated with glacial tectonic processes

a model study on internally generated variability in subtropical mode water formation internally generated variability in the subtropical gyre is studied as a possible mechanism for the observed interannual to decadal variability in subtropical mode water formation an isopycnic ocean model with idealized geometry and forcing which mimics the north atlantic subtropical gyre is used for this purpose the horizontal resolution is sufficiently high and the friction and diffusion sufficiently low for the flow to become barotropically and baroclinically unstable two modes of low frequency variability are found both modes consist of westward propagating thickness anomalies the anomalies have a first baroclinic modal structure with a maximum amplitude at the thermocline one mode has a timescale of 8 years and a basin wide spatial scale the other has a timescale of 4 5 years and a smaller spatial scale the modes appear to be damped when the diffusion is high in that case the 8 year mode can be excited by a spatially coherent stochastic wind stress the evolution of the modes is determined by an interaction between the mean flow and the low frequency variability itself the modes are instabilities of the mean flow determined by the basic stratification it appears that coupling to the atmosphere and a parameterization of surface mixing are necessary for the low frequency variability to appear in the mixed layer the coupling and surface mixing do not play a role in generating the modes it is concluded that these internally generated modes may play a role in the observed variability in mode water formation

buoyancy driven interannual sea level changes in the southeast tropical pacific 1 it is commonly held that interannual to decadal sea level variability patterns mainly represent the ocean s response to wind forcing this view is based in part on modeling studies of wind driven sea level changes along the tropical pacific however because buoyancy forcing and other generating mechanisms are usually ignored this paradigm may overemphasize the role of winds focusing on the southeast tropical pacific we use a data constrained ocean state estimate to demonstrate that distinct mechanisms including the ocean s response to buoyancy forcing as well as nonlinear processes can also contribute to interannual sea level variability contrary to the notion that buoyancy driven sea level changes are dynamically passive such changes exhibit a strongly nonlocal dynamically active character made manifest in westward propagating waves as similar findings apply elsewhere accurate modeling of interannual to decadal regional sea level changes requires consideration of a variety of forcing mechanisms including but not limited to the winds

seismic monitoring leveraging existing telecom infrastructure at the sdasa active passive and ambient noise analysis abstract we analyze active and passive seismic data recorded by the stanford distributed acoustic sensing array sdasa located in conduits under the stanford university campus for the active data we used low energy sources betsy gun and sledge hammer and recorded data using both the das array and 98 three component nodes deployed along a 2d line the joint analysis of shot profiles extracted from the two data sets shows that some surface waves and refracted events are consistently recorded by the das array in areas where geophone coupling was suboptimal because of surface obstructions das recordings are more coherent in contrast surface waves are more reliably recorded by the geophones than the das array because of the noisy environment and weak sources neither data set shows clear reflections we demonstrate the repeatability of das recordings of local earthquakes by comparing two weak events magnitude 0 95 and 1 34 with epicenters 100 m apart that occurred only one minute from each other an

analyzing tomographic sar data of a forest with respect to frequency polarization and focusing technique forest canopies are semitransparent to microwaves at both l and p bands thus a number of scattering sources and different types of scattering mechanisms may contribute to a single range cell of a synthetic aperture radar sar image by appropriately combining the sar data of multiple parallel flight paths a large 2 d aperture is synthesized which allows for tomographic imaging of the 3 d structure of such semitransparent media and the underlying ground a separate paper deals with the actual tomographic imaging part that leads to the 3 d data cube in particular three focusing techniques are described and analyzed multilook beamforming robust capon beamforming and multiple signal classification beamforming in this paper the resulting data products obtained by tomographically focusing two airborne multibaseline sar data sets of a partially forested area one at l band and another at p band are subject to a detailed analysis with respect to the location and the type of backscattering sources in particular the following aspects are investigated 1 the forest structure as obtained from the vertical profiles of intensities at sample plot locations within the forest is compared to the height distribution of the top of the forest canopy as derived from airborne laser scanning data and profiles are presented for all polarimetric channels and focusing techniques as well as at both frequencies 2 the type and location of scattering mechanisms are analyzed as functions of height for the two frequencies namely l and p bands and using the polarimetric channels as well as the pauli and cloudepottier decompositions thereof and 3 the accuracy of the ground elevation estimation obtained from the different focusing techniques and the two frequencies is assessed with the help of a lidar derived digital elevation model

on the observability of oceanic gyres abstractthis study examines the observability of a stratified ocean in a square flat basin on a midlatitude beta plane here observability means the ability to establish in a finite interval of time the time dependent ocean state given density observations over the same interval and with no regard for errors the dynamics is linearized and hydrostatic so that the motion can be decomposed into normal modes and the observability analysis is simplified an observability gramian a symmetric matrix is determined for the flows in an inviscid interior in frictional boundary layers and in a closed basin its properties are used to establish the condition for complete observability and to identify optimal data locations for each of these flows it is found that complete observability of an oceanic interior in time dependent sverdrup balance requires that the observations originate from the westernmost location at each considered latitude the degree of observability increases westward due to westward prop

interannual baroclinic rossby waves in the midlatitude north atlantic abstract twenty six year time sequences of upper thermocline temperature block averaged in 5 degree latitude and longitude squares reveal strong in phase vertical coherence and low to moderate horizontal coherence over 550 km least squares fitting theoretical cross spectra from a stochastic first baroclinic mode rossby wave model to cross spectra of the temperature time sequences yields several best fit wavenumber vectors that conform to the dispersion relation of first baroclinic mode rossby waves in a flat bottom ocean with no mean current the slope of the midocean ridge which is as important as midlatitude beta and the mean circulation were ignored about 25 55 of the cross spectral energy can be attributed to the best fit waves a composite spectrum of the baroclinic potential energy of all the demonstrated rossby waves is qualitatively similar to the spectrum of north pacific first baroclinic mode rossby waves showing a peak around 6 7 years but is 30 times larger in magnitude the geograph

assessment of scattering mechanism of polarimetric sar signal from mountainous forest areas this study aims to understand the effects of the topographic slope variation on the vegetation backscattering characteristics of polarimetric imaging radar most of the previous studies in modeling microwave backscattering signatures of vegetated area have been carried out over relatively flat areas in order to model vegetation scattering mechanisms of mountainous forests this paper presents an improvement of the radiative transfer model that accounts for the tilted scattering surface beneath a forest canopy an l band polarimetric synthetic aperture radar sar data set acquired by the nasa jet propulsion laboratory airborne sar system was used to test and to assess the vegetation scattering model for a sloping forest area experimental result shows the proposed model to be adequate for evaluating slope induced changes in microwave scattering mechanisms

4d das vsp as a tool for frequent seismic monitoring in deep water abstract thanks to its relatively low cost time lapse vertical seismic profiling vsp with distributed acoustic sensing das is an attractive proposition for frequent seismic monitoring around production and injection wells aimed at production optimization in complex deepwater fields we demonstrate that 4d das vsp provides sufficient data quality for reservoir monitoring in deep water with a high value to investment ratio 4d quality and image extent can be enhanced through well executed acquisition and advanced processing further cost lowering via innovations on the source side is being pursued the path to establishing 4d das vsp as a monitoring tool in deep water is through further field applications to demonstrate its ability to impact business decisions

observations inferences and mechanisms of the atlantic meridional overturning circulation a review this is a review about the atlantic meridional overturning circulation amoc its mean structure temporal variability controlling mechanisms and role in the coupled climate system the amoc plays a central role in climate through its heat and freshwater transports northward ocean heat transport achieved by the amoc is responsible for the relative warmth of the northern hemisphere compared to the southern hemisphere and is thought to play a role in setting the mean position of the intertropical convergence zone north of the equator the amoc is a key means by which heat anomalies are sequestered into the ocean s interior and thus modulates the trajectory of climate change fluctuations in the amoc have been linked to low frequency variability of atlantic sea surface temperatures with a host of implications for climate variability over surrounding landmasses on intra annual timescales variability in amoc is large and primarily reflects the response to local wind forcing meridional coherence of anomalies is limited to that of the wind field on interannual to decadal timescales amoc changes are primarily geostrophic and related to buoyancy anomalies on the western boundary a pacemaker region for decadal amoc changes is located in a western transition zone along the boundary between the subtropical and subpolar gyres decadal amoc anomalies are communicated meridionally from this region amoc observations as well as the expanded ocean observational network provided by the argo array and satellite altimetry are inspiring efforts to develop decadal predictability systems using coupled atmosphere ocean models initialized by ocean data

on too fast baroclinic planetary waves in the general circulation abstract recent altimetric observations of the ocean surface reveal signatures of long planetary waves near the annual frequency band comparisons of the observed wave speeds and those predicted by standard linear theory suggest that the latter is inadequate as it yields different westward speeds than those measured in the extratropical latitudes the predicted speeds are typically slower than the observations here the problem of long baroclinic wave propagation in a forced stratified ocean is considered theoretically with a view toward explaining these observations of too fast planetary waves from a quasigeostrophic analysis it is argued that baroclinic waves in a sheared environment are accelerated to the west via their interactions with both the mean advective field and the mean potential vorticity field conditions under which the ratio of actual to linear phase speeds matches the observed ratio are computed and found to be typical of the open ocean extensions of these ideas to continuously st

climatic warming of atlantic intermediate waters abstract interdecadal temperature variability of the atlantic ocean is investigated by differencing hydrographic sections taken from the 1920s through the 1990s a comprehensive reanalysis of north atlantic sections and the inclusion of south atlantic sections show that warming seen previously in the north atlantic extends to the south atlantic the largest statistically significant changes occur on pressure surfaces between 1000 and 2000 decibars db over this pressure range and for latitudes between 32 s and 36 n temperatures have warmed by 0 5 c century 1 at 48 n a cooling of 3 c century 1 occurred between the 1950s and 1980s these isobaric temperature trends are decomposed into ones along surfaces of constant neutral density and ones due to the vertical movement of neutral surfaces the two components are associated with different processes in the southern north atlantic 8 36 n the subthermocline warming between the 1950s and 1980s appears to be due primarily to downward displacements of n

can long term variability in the gulf stream transport be inferred from sea level recent studies by sturges and collaborators suggest a simple but powerful technique to estimate climatic changes in the transport of the gulf stream from the difference between the oceanic sea level calculated with a simple wind driven rossby wave model and the observed coastal sea level the hypothesis behind this technique is tested using 40 years of data 1950 to 1989 obtained from a three dimensional atlantic ocean model forced by observed surface data the analysis shows that variations in sea level difference between the ocean and the coast are indeed coherent with variations of the gulf stream transport for periods shorter than 1 year or longer than 4 5 years the results obtained from the three dimensional model confirm the findings of the simple rossby wave model that decadal climatic changes in the gulf stream transport vary considerably with latitude

diagnosing the annual cycle of the equatorial undercurrent in the atlantic ocean from a general circulation model abstract ten year long output series from a general circulation model forced by daily realistic winds are used to analyze the annual cycle of the equatorial undercurrent euc in the atlantic ocean two well defined transport maxima are found one present during boreal summer and autumn in the central part of the basin is generally recognized and regarded as a near equilibrium response to the equatorial easterly trades that culminate in this period another one most pronounced near the western boundary occurs in april may when the trades relax this second maximum is less patent in the observations but concomitant signals in previously published analyses of the north brazil current and surface velocity seasonal variations might be indirect manifestations of its reality because this intensification appears at periods when the boundary between the tropical and equatorial gyres nears the equator the authors relate its existence to wind stress curl variations at subequatorial latitudes a link between

the effect of topography on radar scattering from vegetated areas the ways in which radar scattering from vegetated areas is affected by the topography of the surface underneath the vegetation are discussed it is shown using a discrete scatterer model that the dominant scattering mechanism may change drastically when the ground surface is tilted relative to the horizontal for a horizontal ground surface for example the total scattering may be dominated by scattering off the tree trunks followed by a reflection off the ground surface for a relatively small tilt in the ground surface the ground trunk interaction term may be replaced by scattering from the branches alone as the dominant scattering mechanism the effect of the topography is more pronounced for scattering by longer wavelengths and the implications on algorithms designed to infer forest woody biomass and soil and vegetation moisture using polarimetric sar data are discussed the effect of the topography on the scattering behavior from forested areas is illustrated with images acquired by the nasa jpl three frequency polarimetric sar over the black forest in germany

frequency of ring separations from the loop current in the gulf of mexico a revised estimate the most energetic events in the circulation of the gulf of mexico are the separation of large anticyclonic rings from the loop current building on previous work the authors examine all the apparent rings since july 1973 this new dataset includes the satellite altimetry since 1992 providing a set of 34 consecutive ring formations the primary advantage of altimetry is that the data remain available in the summer one finding is that the ambiguity of whether or not a ring has separated is reduced but not eliminated the uncertainty with which separation events can be specified remains approximately 4 weeks even with nearly continuous data primary peaks in the distribution of separation intervals are found at 6 and 11 months with a smaller peak at 9 months if the spectrum is smoothed heavily enough a peak in the distribution can be formed nearer 12 months but this near annual peak is a result more of the smoothing than of the data

a description of coads surface meteorological fields and the implied sverdrup transports for the atlantic ocean from 30 s to 60 n abstract using coads data spanning 1947 1988 we describe the regional nature of the atlantic ocean wind driven circulation between 30 8 and 60 n and its annual and interannual variability the sverdrup streamfunction defines the circulation gyres our focus is on three central gyres the northern hemisphere anticyclonic subtropical gyre the cyclonic tropical gyre just north of the equator and the clockwise equatorial gyre straddling the equator this rendition of the sverdrup streamfunction computed with constant drag coefficient and air density compares favorably with that from other climatologies in the straits of florida analyses suggest that differences between the annual cycle in sverdrup transport and observations may be due to regional winds farther north in the tropical gyre the sverdrup circulation argues against a continuous western boundary current transporting water from the equatorial region into the caribbean in boreal winter bringing to question the mechanisms for the known interh

mechanisms of decadal north atlantic climate variability and implications for the recent cold anomaly decadal sea surface temperature sst fluctuations in the north atlantic ocean influence climate over adjacent land areas and are a major source of skill in climate predictions however the mechanisms underlying decadal sst variability remain to be fully understood this study isolates the mechanisms driving north atlantic sst variability on decadal time scales using low frequency component analysis which identifies the spatial and temporal structure of low frequency variability based on observations large ensemble historical simulations and pre industrial control simulations we identify a decadal mode of atmosphere ocean variability in the north atlantic with a dominant time scale of 13 18 years large scale atmospheric circulation anomalies drive sst anomalies both through contemporaneous air sea heat fluxes and through delayed ocean circulation changes the latter involving both the meridional overturning circulation and the horizontal gyre circulation the decadal sst anomalies alter the atmospheric meridional temperature gradient leading to a reversal of the initial atmospheric circulation anomaly the time scale of variability is consistent with westward propagation of baroclinic rossby waves across the subtropical north atlantic the temporal development and spatial pattern of observed decadal sst variability are consistent with the recent observed cooling in the subpolar north atlantic this suggests that the recent cold anomaly in the subpolar north atlantic is in part a result of decadal sst variability

role of the gulf stream and kuroshio oyashio systems in large scale atmosphere ocean interaction a review abstract ocean atmosphere interaction over the northern hemisphere western boundary current wbc regions i e the gulf stream kuroshio oyashio and their extensions is reviewed with an emphasis on their role in basin scale climate variability sst anomalies exhibit considerable variance on interannual to decadal time scales in these regions low frequency sst variability is primarily driven by basin scale wind stress curl variability via the oceanic rossby wave adjustment of the gyre scale circulation that modulates the latitude and strength of the wbc related oceanic fronts rectification of the variability by mesoscale eddies reemergence of the anomalies from the preceding winter and tropical remote forcing also play important roles in driving and maintaining the low frequency variability in these regions in the gulf stream region interaction with the deep western boundary current also likely influences the low frequency variability surface heat fluxes damp the low frequency sst anomalies ove

field testing of fiber optic distributed acoustic sensing das for subsurface seismic monitoring distributed acoustic sensing das is a relatively recent development in the use of fiber optic cable for measurement of ground motion discrete fiber optic sensors typically using a bragg diffraction grating have been in research and development and field testing for more than 15 years with geophysical applications at least 12 years old bostick 2000 and summary in keul et al 2005 however developments in recent years have sought to remove the need for point sensors by using the fiber cable itself as a sensor mestayer et al 2011 miller et al 2012

bermuda s tale of two time series hydrostation s and bats abstract this paper describes the oceanic variability at bermuda between 1989 and 1999 recorded in two overlapping hydrographic time series station s and bermuda atlantic time series study bats which are 60 km apart both show that a multidecadal trend of deep warming has reversed likely as a result of the increased production of labrador sea water since the early 1980s in addition to recording similar changes in watermass properties the two time series show similar mean vertical structure and variance as a function of pressure for temperature salinity and density above 1500 dbar the seasonal cycles of these water properties at the two sites are statistically indistinguishable the time series differ in the individual eddy events they record and in their variability below 1500 dbar the two time series are used to investigate the propagation of eddy features coherence and phase calculated from the low mode variability of density show westward propagation at 3 cm s 1 of wavelengths around 300

time lapse 3d vsp using permanent receivers in a flowing well in the deepwater gulf of mexico the vision of smart wells permanently instrumented with geophones has existed for some time such installations would enable opportunities for frequent reservoir monitoring high resolution 3d vsp imaging and illumination of difficult areas for many subsalt fields 3d vsps acquired in such wells may be the best option to illuminate and monitor reservoirs without the need to stop production or enter a well however this technology is not yet widely applied nor perhaps proven

wind forcing of the atlantic thermocline along 32 n at low frequencies abstract the bermuda tide gauge record extends back to the early 1930s that sea level fluctuations there are highly coherent with dynamic height from hydrographic data has two interesting implications first it should contain information about the low frequency circulation of the atlantic furthermore because dynamic height contains information on heat storage it might on the limited timescales accessible in the record also contain clues about climate a simple model of wind forcing of the atlantic from the african coast to bermuda uses the levitus mean density data to estimate the long rossby wave speed as a function of longitude sea level and thermocline variability estimated this way are in remarkably good agreement with observations at periods of more than a few years duration the peak to peak sea level signal is 18 cm which is nearly 25 of the slope across the gulf stream at this latitude the model results suggest that the variability is largest somewhat to the east of bermuda fluctuatio

monitoring co2 injection for carbon capture and storage using time lapse 3d vsps carbon capture and storage ccs is the process through which a nearly pure carbon dioxide co2 stream is captured separated from flue gas or other industrial processes compressed transported to an appropriate storage site and injected deep underground into a geological formation where it can be safely stored for long term geologic storage benson 2005 large sedimentary basins such as the illinois michigan and western canadian sedimentary basins are good targets for ccs as they are in close proximity to large co2 emitters and are composed of the appropriate saline formations and overlying nonpermeable formations in 2003 the u s department of energy s national energy technology laboratory doe netl created a nationwide network of federal state and private sector partnerships to determine the most suitable technologies regulations and infrastructure for future ccs in different areas of the north america office of fossil energy 2013

decadal variabilities of the upper layers of the subtropical north atlantic an ocean model study numerical simulations of the atlantic ocean during the period 1950 to 1989 using a sigma coordinate free surface numerical model show long term variabilities in the upper ocean subtropical gyre similar to those obtained from observations the simulations show how westward propagating planetary waves originated in the eastern north atlantic affect interdecadal variabilities of ocean properties such as the bermuda sea level the gulf stream position and strength and subsurface temperature anomalies in the western north atlantic special attention is given to the dramatic sea level drop at bermuda in the early 1970s which is accompanied by cooling of subsurface layers in the western north atlantic and a northward shift and weakening of the gulf stream following these events between 1970 and 1980 the cold temperature anomalies in the upper layers of the western north atlantic slowly propagated eastward and downward the strongest propagating signal in the model is found at 200 m depth suggesting that advection of anomalies downstream by the gulf stream current and changes in winter mixing are involved significant correlations were found between the sea level anomalies at bermuda and sea level anomalies in the eastern north atlantic up to eight years earlier sensitivity experiments with different atmospheric forcing fields are used to study the ocean response to observed sea surface temperature and wind stress anomalies it is shown that on decadal timescales the ocean model responds in a linear fashion to the combined effect of sst and wind stress anomalies a fact that might be exploited in future climate prediction studies

low vhf band backscatter from coniferous forests on sloping terrain low frequency synthetic aperture radar sar is a promising technique for stem volume retrieval particularly for dense forests due to the good penetration of forest canopies however it is well known that the dominant scattering mechanism the trunk ground dihedral interaction decreases rapidly on sloping terrain in this paper we use low vhf band sar data collected with carabas over dense coniferous forests in sweden to examine the effect of topography using flight passes with different headings the effect of slope and aspect angle on backscatter is characterized for tall trees spl sim 30 m on the steepest slopes in the test site up to spl sim 12 spl deg differences of up to 8 db are observed between images acquired with different look directions relative to the slope a physical model is developed to investigate the different scattering mechanisms and their sensitivity to terrain slopes the model shows that the trunk ground scattering still dominates the response for large trees on moderate slopes and a semiempirical model for the effect of topography on backscatter is proposed the model shows good agreement with measurements indicating the possibility of using it to compensate for the effects of sloping terrain when retrieving stem volume in coniferous forest

the mean and annual cycle of upper layer temperature fields in relation to sverdrup dynamics within the gyres of the atlantic ocean using 28 years of expendable bathythermograph data 1967 1994 we describe the mean and annual cycle of the upper ocean temperature fields in the atlantic from 30 s to 50 n in the context of the basin scale wind driven gyres sverdrup stream function field which provide a framework for describing the oceanographic measurements we examine the circulation field implied by the temperature distributions which are used as a proxy for the field of mass similarities between the temperature and stream function fields increase with depth in the lower to subthermocline depths of the tropical and equatorial gyres the zonal currents form a closed circulation a southeastward boundary current is suggested near and below 150 m that provides closure for the tropical gyre and the equatorial gyre axis is southward of that suggested by the stream function field higher in the water column the north equatorial countercurrent necc may be a surface manifestation of the north equatorial undercurrent neuc where the latter can be interpreted as the southern limb of the tropical gyre because there are large vertical shears in the tropics the equatorial gyre is not clearly indicated in the vertically integrated temperature field but appears below about 200 m here the south equatorial undercurrent seuc can be interpreted as the eastward flowing northern limb of the equatorial gyre and is opposite in direction to the westward flowing south equatorial current above both the neuc and seuc are analagous to currents in the pacific that are governed by non sverdrup dynamics despite the shortcomings of the data the mean annual cycle appears to be relatively stable and we have discounted the possibility that in regions where it represents a significant percentage of the total variance it is changing slowly over the 28 years of record the wind forcing fields which undergo large meridional movements 5 6 of latitude during their annual cycle with some exceptions have essentially no counterpart in gyre movements between their seasonal extremes most of the variability associated with the annual cycle is confined to the upper 300 m greatest variability where ranges exceed 6 c occurs in the northwestern atlantic in late winter and early spring during this time of year south of the gulf stream and below about 100 m water temperatures exhibit a systematic phase lag with depth the next largest area of variability where ranges can also exceed 6 c resides in the tropical western basin between the equator and 10 n just below 100 m in the eastern basin ranges decrease and shoal additionally the phase fields are consistent with the intensification and relaxation of the tropical ridge trough system where the necc disappears in march in the west but the necc neuc complex is strongest in september

solar modulation of north atlantic central water formation at multidecadal timescales during the late holocene article i nfo understanding natural climate variability in the north atlantic region is essential not only to assess the sensitivity of atmosphere ocean climate signal exchange and propagation but also to help distinguish between natural and anthropogenic climate change the north atlantic oscillation is one of the controlling modes in recent variability of atmosphere ocean linkages and ice freshwater fluxes between the polar and north atlantic ocean through these processes the nao influences water mass formation and the strength of the atlantic meridional overturning circulation and thereby variability in ocean heat transport however the impact of the nao as well as other forcing mechanisms on multidecadal timescales such as total solar irradiance on eastern north atlantic central water production central water circulation and climate signal propagation from high to low latitudes in the eastern subpolar and subtropical basins remains uncertain here we use a 1200 yr long benthic foraminiferal mg ca based temperature and oxygen isotope record from a 900 m deep sediment core off northwest africa to show that atmosphere ocean interactions in the eastern subpolar gyre are transferred at central water depth into the eastern boundary of the subtropical gyre further we link the variability of the nao over the past 165 yrs and solar irradiance late holocene and their control on subpolar mode water formation to the multidecadal variability observed at mid depth in the eastern subtropical gyre our results show that eastern north atlantic central waters cooled by up to 0 8 0 7 c and densities decreased by 0 3 0 2 during positive nao years and during minima in solar irradiance during the late holocene the presented records demonstrate the sensitivity of central water formation to enhanced atmospheric forcing and ice freshwater fluxes into the eastern subpolar gyre and the importance of central water circulation for cross gyre climate signal propagation during the late holocene 2011 elsevier b v all rights reserved

interpentadal variability of steric sea level and geopotential thickness of the north atlantic ocean 1970 1974 versus 1955 1959 we have composited and objectively analyzed historical hydrographic observations for the north atlantic ocean for two periods 1955 1959 and 1970 1974 difference fields of steric sea level and geopotential thickness for the north atlantic ocean in the 0 to 1500 m depth range between the 1955 1959 and 1970 1974 pentads were computed we find that in the central portion of the subtropical gyre steric sea level decreased by up to 17 5 dyn cm whereas in the western subarctic gyre north of the gulf stream steric sea level increased by an amount up to 7 5 dyn cm from the earlier to the later pentad a decrease in steric sea level 5 dyn cm occurred along the eastern boundary of the north atlantic

steam injection monitoring in south oman from single pattern to field scale surveillance downhole seismic monitoring has become an alternative to more conventional surface seismic in cases where the latter has low signal to noise ratio or poor repeatability or when frequent monitoring of a local target is required downhole 3d vsp monitoring has been applied to both onshore o brien et al 2004 kiyashchenko et al 2011 and offshore environments wu et al 2011 in onshore environments surface seismic repeatability often suffers from surface noise and near surface variations caused by water table changes or surface facilities construction for vsp surveys the wavefield separation into downgoing and upgoing fields presents an opportunity to discriminate between near surface and reservoir changes thus making time lapse applications more effective

a study of temperature changes in the upper north atlantic 1950 94 in this paper decadal evolution of warm and cold anomalies in the subtropical and subpolar gyres of the north atlantic in the 300 500 m and 100 250 m depth ranges is described a series of pentadally averaged objective maps of upper ocean thermal anomalies from bathythermograph data are presented warm and cold anomalies in the western subtropical gyre are succeeded by similar anomalies in the subpolar gyre and the east atlantic and subtropical return flow major warm and cold anomalies in the 1950s and 1970s respectively are similar to those described previously in ssts although there is more temporal continuity in the subsurface anomalies two very strong events in the subtropical gyre are identified a cold anomaly in 1966 72 and an intense warm anomaly in 1988 94 that show the greatest temperature anomalies in the north atlantic during the period of the study interisotherm thickness anomalies are shown for the subtropical gyre during these periods in the warm period mode waters are both warmer 188 198c and of greater volume than on average and lie in a narrow band south of the gulf stream above a depressed thermocline with warm temperature anomalies to at least 800 m depth in the cold period the predominant mode water temperature is closer to 178c but there is reduced water formation overall with a raised thermocline and cold temperature anomalies down to 600 m depth the bowl of the gyre is flat during the cold period and the implied recirculation may be weaker and extend farther to the south the changes appear to be consistent with the intensification of the subtropical gyre in the warm period and a spindown in the cold period although the relative roles of wind stress and air sea heat fluxes in these changes need to be determined

algae a fast algebraic estimation of interferogram phase offsets in space varying geometries this paper deals with the estimation of terrain topography from multipass synthetic aperture radar sar interferometry insar focusing on the case where variation of the system geometry within the imaged swath is relevant a typical case is represented by airborne multipass interferometric campaigns where due to the closeness between the radar sensor and the targets the incidence angle sensitivity undergoes a dramatic increase with respect to the spaceborne case resulting in a high spatial variability of the normal baselines the space varying nature of the system geometry gives rise to a major issue in multipass insar analyses in that it prevents from compensating for the presence of interferogram phase offsets by simply phase locking the data stack to a reference point therefore hindering the retrieval of terrain topography to cope with this issue properly we propose a novel approach that exploits the algebraic properties of the problem such an approach allows casting the problem in terms of identification of a null space component for terrain topography after which both topography and the interferogram phase offsets are quickly obtained without exploiting calibration points experimental results are shown based on a p band data set acquired by the experimental sar e sar airborne system operated by the german aerospace center dlr in the framework of the european space agency esa campaign biosar 2008

distributed acoustic sensing for reservoir monitoring with vsp 3d vsp has long been viewed as conceptually attractive for illuminating targets under complex overburden both for exploration purposes and for time lapse monitoring of reservoirs however the widespread use of 3d vsp has been hindered by the cost and risk of deploying geophones in a borehole and by the limited availability of accessible wells these hurdles are largely removed when acquiring downhole seismic with a new measurement called distributed acoustic sensing das

mechanisms of eddy driven variability of the florida current abstractin this study mechanisms causing year to year changes in the florida current seasonality are investigated using controlled realistic numerical experiments designed to isolate the western b

monitoring horizontal well hydraulic stimulations and geomechanical deformation processes in the unconventional shales of the midland basin using fiber based time lapse vsps microseismic and strain data

annual variation of the kuroshio transport in a two layer numerical model with a ridge abstract a two layer numerical model driven by the wind stress is used to explain the observed annual variation of the kuroshio transport south of japan special attention is given to the effect of a ridge representing the izu ogasawara ridge on the generation of the baroclinic activity through the coupling of the barotropic and baroclinic modes of motion for annual variation lower layer motion is found in areas surrounding the ridge because isostasy a state of no motion in the lower layer is not achieved within such a short timescale thus the lower layer flow impinges on the bottom slope this impinging process generates anomalies of the upper layer thickness especially on the eastern side of the ridge thereafter anomalies move westward with characteristic velocities composed of the vertically averaged flow and westward propagation of the long baroclinic rossby wave forced above the ridge as anomalies of the upper layer thickness move westward above the ridge isostasy is accomplished with res

modelling hydrographic changes in the labrador sea over the past five decades abstract inter annual to inter decadal changes of hydrographic structure and circulation in the subpolar north atlantic are studied using a coarse resolution ocean circulation model the study covers 1949 through 2001 inclusive a time mean state nudging method is applied to assimilate the observed hydrographic climatology into the model the method significantly reduces model biases in the long term mean distribution of temperature and salinity which commonly exist in coarse resolution ocean models by reducing the time mean biases we also significantly improve the model s representation of inter annual to inter decadal variations in the central labrador sea the model broadly reproduces the heat and salt variations of the labrador sea water lsw as revealed by hydrographic observations model sensitivity experiments confirm that the low frequency hydrographic changes in the central labrador sea are closely related to changes in the intensity and depth of deep convection changes in surface heat flux associated with the winter north atlantic oscillation nao index play a major role in driving the changes in t s and sea surface height ssh changes in wind stress play a secondary role in driving these changes but are important in driving the changes in the depth integrated circulation the total changes in both ssh and depth integrated circulation are almost a linear combination of the separate influences of variable buoyancy and momentum fluxes

distributed acoustic sensing for reservoir monitoring with vertical seismic profiling distributed acoustic sensing is a novel technology for seismic data acquisition particularly suitable for vertical seismic profiling it is a break through for low cost on demand seismic monitoring of reservoirs both onshore and offshore in this article we explain how distributed acoustic sensing works and demonstrate its usability for typical vertical seismic profiling applications such as checkshots imaging and time lapse monitoring we show numerous data examples and discuss distributed acoustic sensing as an enabler of seismic monitoring with 3d vertical seismic profiling key words borehole geophysics acquisition seismics time lapse monitoring

on the propagation of baroclinic waves in the general circulation the propagation of long first mode baroclinic planetary waves in eddy resolving quasigeostrophic general circulation models is studied recent topex poseidon observations argue oceanic first mode planetary waves move with speeds other than those predicted by simple theory these data have prompted theoretical analyses of wave propagation in a mean flow with the results suggesting mean shear can have a controlling effect on the planetary wave guide some of the predicted effects appear to be relevant to the observations while others are less obvious this coupled with other explanations for the observations motivates the calculations based on these experiments the authors suggest that the predicted effects of mean shear on wave propagation are consistent with those computed in a fully geostrophically turbulent ocean these are that a two layer model misses the dominant component of long wave interaction with a mean flow a three layer model captures this interaction qualitatively and the correction to wave propagation is in the direction opposite to the mean flow quantitative comparisons between the theory and the numerical experiments are good in the northern latitudes and questionable in the southern latitudes reasons for the southern discrepancy are offered

interaction of helically wound fibre optic cables with plane seismic waves distributed acoustic sensing is a novel technology for seismic acquisition in this technology strain changes induced by seismic waves impinging on an optical fibre are monitored due to the fact that glass is relatively rigid straight glass fibres are not sensitive to broadside waves we suggest using distributed acoustic sensing systems with fibres helically wound around cables one increases the fibre sensitivity to broadside waves by decreasing the fibre wrapping angle the angle between the fibre axis and the plane normal to the cable axis the optimal wrapping angle is chosen to minimize the impact of rayleigh waves on the signal measured this angle depends on the cable poisson ratio and it is approximately equal to 30 for cables composed of plastic for reliable detection of seismic waves one needs a good mechanical contact between the cable and the surrounding medium on the other hand the sensitivity of distributed acoustic sensing systems to primary waves can be significantly reduced if the cable is placed in a cemented borehole

observational evidence for flow between the subtropical and tropical atlantic the atlantic subtropical cells abstract this study determines the mean pathways and volume transports in the pycnocline and surface layer for water flowing between the subtropical and tropical atlantic ocean using potential vorticity salinity geostrophic flow maps on isopycnal surfaces and surface drifter velocities in both hemispheres subducted salinity maximum waters flow into the tropics in the pycnocline along both interior and western boundary pathways the north atlantic ventilating trajectories are confined to densities between about 23 2 and 26 0 and only about 2 sv sv 106 m3 s 1 of water reaches the tropics through the interior pathway whereas the western boundary contributes about 3 sv to the equatorward thermocline flow flow on shallower surfaces of this density range originates from the central atlantic near 40 w between 12 and 16 n whereas flow on the deeper surfaces originates from near 20 w just off the coast of africa at higher latitudes the pathways skirt around the potential vorticity barrier located

fiber optic network observations of earthquake wavefields author s lindsey nj martin er dreger ds freifeld b cole s james sr biondi bl ajo franklin jb abstract 2017 american geophysical union all rights reserved our understanding of subsurface processes suffers from a profound observation bias seismometers are sparse and clustered on continents a new seismic recording approach distributed acoustic sensing das transforms telecommunication fiber optic cables into sensor arrays enabling meter scale recording over tens of kilometers of linear fiber length we analyze cataloged earthquake observations from three das arrays with different horizontal geometries to demonstrate some possibilities using this technology in fairbanks alaska we find that stacking ground motion records along 20nm of fiber yield a waveform that shows a high degree of correlation in amplitude and phase with a colocated inertial seismometer record at 0 8 1 6nhz using an l shaped das array in northern california we record the nearly vertically incident arrival of an earthquake from the geysers geothermal field and estimate its backazimuth and slowness via beamforming for different phases of the seismic wavefield lastly we install a fiber in existing telecommunications conduits below stanford university and show that little cable to soil coupling is required for teleseismic p and s phase arrival detection

multibaseline polarimetric sar tomography of a boreal forest at p and l bands longer wavelength synthetic aperture radars sars are precious in the remote sensing of forested areas being sensitive to contributions from the whole vegetation layer and from the ground below the electromagnetic properties of such contributions are retrieved from multipolarimetric acquisitions whereas their vertical structure is retrieved from multibaseline acquisitions through tomographic imaging combining baseline and polarization diversity provides most information allowing the decomposition of the sar signal into ground and volume only contributions a formal treatment of this problem is provided with the algebraic synthesis technique which extends the concepts of polinsar the decomposition however is shown to be ambiguous in that different solutions are equally consistent with the data the main goal of this paper is to discuss this topic in light of the experimental results from a tomographic and polarimetric analysis of the boreal forest within the krycklan river catchment northern sweden investigated at p and l bands during the esa campaign biosar 2008 different solutions to the decomposition problem will be discussed by examining the corresponding vertical structures accessible through tomographic techniques elements are shown supporting the idea that ground volume interactions play a nonnegligible role at p band and a solution is proposed to isolate contributions from direct volume backscattering the retrieval of forest top height is discussed as well leading to the conclusion that such parameter is robust against erroneous choices in the identification of volume only contributions thus corroborating the polinsar approach for the analysis of single baseline data

sea level on the u s east coast decadal variability caused by open ocean wind curl forcing one of the puzzling features of sea level on the east coast of the united states is the decedal scale variability the fluctuations are 10 15 cm peak to peak at periods longer than a few years the authors find that this variability in the frequency band treated with the model is largely caused by a deep sea signal generated by the wind stress curl over the north atlantic a simple forced long rossby wave model of the response of the thermocline to wind forcing is used computing long wave speeds from observed hydrographic data the authors model the response of the ocean at periods longer than 3 years for the full width of the atlantic and for the north south extent of the main anticyclonic gyre 188 388n the model output in deep water shows remarkably good agreement with tide gauges both at bermuda 328n and puerto rico 188n as well as with dynamic height fluctuations of 20 cm peak to peak once these fluctuations reach the western side of the ocean the authors estimate coastal sea level by constructing a complementary coastal model the coastal model is geostrophic and conserves mass within a nearshore region that encompasses the gulf stream by extending this nearshore region as far south as 148 188n and using only the oceanic fluctuations to force the variability in the stream between 80 and 90 of the variance of sea level at coastal tide gauges can be explained sea level along the coast is used to test the model assumptions the basic results however seem important because they are constrained only by open ocean wind forcing and not by input boundary conditions

first demonstration of airborne sar tomography using multibaseline l band data in synthetic aperture radar sar interferometry the phase differences between two different sensor positions are used to estimate the terrain topography although it is possible in this way to find a three dimensional 3d surface representation the distribution of the different scatterers in the height direction at a fixed range and azimuth position remains unknown contrary to this tomographic techniques enable a real geometric resolution capability in the height direction and introduce new possibilities for many applications and inversion problems even misinterpretations in sar images caused by layover and foreshortening effects can be solved by the tomographic processing in this paper the successful experimental realization of polarimetric airborne sar tomography is demonstrated for the first time the authors present the concept of aperture synthesis for tomographic imaging for the case of a multibaseline imaging geometry and discuss the constraints arising from the limited number of flight tracks they propose a method for reduction of the height ambiguities associated to the irregular and undersampled spatial distribution of the imaging positions finally they address the experimental requirements for polarimetric airborne sar tomography and show experimental results using a multibaseline data set acquired in l band by dlr s experimental sar e sar of a test site near oberpfaffenhofen germany

pushing the limit of earthquake detection with distributed acoustic sensing and template matching a case study at the brady geothermal field template matching has been widely applied in the detection of earthquakes and other seismic events due to its power in detecting weak signals recent studies using synthetics have shown that application of template matching to large n arrays can potentially detect earthquakes substantially below the noise level here we apply template matching to the distributed acoustic sensing das data recorded in the brady hot springs geothermal field nevada using 5 catalogued events we detect 116 events and find 68 of them well below the noise level we confirm 112 events are true earthquakes by examining the patterns of their sensor to sensor cross correlation sections this demonstrates that the combination of das and template matching has capability to detect microseismicity below the noise level which is unusual for conventional seismic arrays and methods with the updated catalogue we observe a surge of earthquakes during the shutdown of a geothermal power plant nearby in addition the rapid increases in the downhole pressure record coincide with intense swarms of earthquakes these observations show a strong correlation between the seismicity frequencies and the downhole pressure changes finally we investigate several factors that may affect the detection performance and compare different strategies for spatial down sampling in order to provide helpful insights for future large n design and data processing

estimation of forest structure ground and canopy layer characteristics from multibaseline polarimetric interferometric sar data this paper concerns forest parameter retrieval from polarimetric interferometric synthetic aperture radar polinsar data considering two layers one for the ground under the vegetation and one for the volumetric canopy a model is designed to combine a physical model based polarimetric decomposition with the random volume over ground rvog polinsar parameter inversion approach the combination of a polarimetric scattering media model with a polinsar rvog vertical structure model provides the possibility to separate the ground and the volume coherency matrices based on polarimetric signatures and interferometric coherence diversity the proposed polarimetric decomposition characterizes volumetric media by the degree of polarization orientation randomness and by the particle scattering anisotropy using the full model enhances the estimation of the vertical forest structure parameters by enabling us to estimate the ground to volume ratio the temporal decorrelation and the differential extinction for forest vegetation observed at l band this model accounts for the ground topography forest and canopy layer heights wave attenuation in the canopy tree morphology in the form of the angular distribution and the effective shapes of the branches and the contributions from the ground level consisting of surface scattering and double bounce ground trunk interactions as well as volumetric understory scattering the parameter estimation performance is evaluated on real airborne l band sar data of the traunstein test site acquired by the german aerospace center dlr s e sar sensor in 2003 in both single and multibaseline configurations the retrieved forest height is compared with the ground truth measurements revealing for the given test site an average root mean square error rmse of about 5 m in the repeat pass configuration this implies an improvement in rmse by over 2 m in comparison to the pure coherence based rvog polinsar parameter inversion

sofar float observations of an intermediate depth eastern boundary current and mesoscale variability in the eastern tropical atlantic ocean two neutrally buoyant sofar floats vigorously looped and meandered at depths of 950 1150 m in the eastern tropical atlantic ocean the float trajectories illustrate a poleward flow along the tropical eastern boundary and significant intermediate depth mesoscale variability in the low latitude eastern basin one float caught within an energetic cyclonic eddy near the eastern boundary looped cyclonically 14 times while translating 600 km northward parallel to the african coastline a second float launched near the mid atlantic ridge meandered eastward with a lagrangian zonal wavelength of 400 km and meridional amplitude exceeding 200 km satellite infrared imagery indicates that horizontal shear associated with the system of near surface zonal equatorial currents may contribute to the observed intermediate depth variability

an idealized model study of the mass and heat transports between the subpolar and subtropical gyres abstract the response of an ocean model of the subtropical and subpolar gyres to idealized surface forcing anomalies that mimic the thermal and mechanical forcing associated with the north atlantic oscillation nao is analyzed emphasis is given on the subpolar gyre and the mechanisms that drive the mass and heat exchanges between the two gyres first steady anomalies are applied surface heat flux anomalies induce density gradient anomalies at depth which drive current anomalies reinforcing the north eastward mean current separating the two gyres the northward heat transport of these anomalous currents is 10 times stronger than that associated with the transport of temperature anomalies by the mean current the heat transport anomalies between the two gyres balances the prescribed surface heat flux after 6 7 yr a similar mechanism is at work when a decadal harmonic forcing is considered but the lag is shortened to 3 4 yr the model response to a wind stress curl anomaly shows a similar behavior to

water masses and circulation in the surface layers of the caribbean at 66 w a meridional hydrographic section was made in august september 1997 at 66 w from the coast of venezuela to woods hole aboard the r v knorr in this report we concentrate on near surface measurements in the caribbean the data show two distinct water masses with different origins from approximately 14 n to puerto rico caribbean surface water and subtropical under water with their source in the north atlantic are found as previously observed from venezuela to approximately 13 n a less saline water mass with its source in the tropics and south atlantic is found within the southern portion of the section two different velocity patterns are observed namely an eastward flow with a subsurface maximum near the coast of venezuela and a surface intensified westward jet with velocities of 130 cm s 1 in midbasin

thermocline forced by varying ekman pumping part ii annual and decadal ekman pumping abstract thermocline variability forced by zonally uniform ekman pumping with annual to decadal periods is investigated both analytical and numerical solutions are obtained by the method of characteristics as found in part i there is little thermocline variability in the ventilated zone or pool zone in contrast strong variability may exist in the shadow zone for annual forcings nonlinearity is negligible however the linear solution is influenced substantially by the basic state thermocline structure as a result local responses dominate for a shallow interface while remote rossby waves dominate for a deep interface under a strong decadal forcing nonlinearity may become important the time mean thermocline in the shadow zone is shallower than the steady thermocline under the mean ekman pumping particularly in the western part of a shadow zone where the mean deviation may reach the order often meters this shallower mean thermocline is caused by the nonlinear rossby wave

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

a field experiment of walkaway distributed acoustic sensing vertical seismic profile in a deep and deviated onshore well in japan using a fibre optic cable deployed inside coiled tubing abstract a two dimensional walkaway vertical seismic profiling survey using distributed acoustic sensing was conducted at an onshore site in japan the maximum depth and the deviation of the observation well were more than 4 000 m and 81 degrees respectively among the several methods for installing fibre optic cables we adopted the inside coiled tubing method in which coiled tubing containing a fibre optic cable is deployed the signal to noise ratio of the raw shot gather was low possibly due to poor coupling between the fibre optic cable and the subsurface formation resulting from the fibre optic cable deployment method and the existence of considerable tubewave noise nevertheless direct p wave arrivals p p reflections and p s converted waves exhibited acceptable signal to noise ratios after careful optimization of gauge length for distributed acoustic sensing optical processing and the application of carefully parameterized tubewave noise suppression one of the challenges in current distributed acoustic sensing vertical seismic profile data processing is the separation of p and s waves using only one component measurements hence we applied moveout correction using two dimensional ray tracing this process effectively highlights only reflected p waves which are used in subsequent subsurface imaging comparison with synthetic well seismograms and two dimensional surface seismic data confirms that the final imaging result has a sufficiently high quality for subsurface monitoring we acquired distributed acoustic sensing vertical seismic profile data under both flowing conditions and closed conditions in which the well was shut off and no fluid flow was allowed the two imaging results are comparable and suggest the possibility of subsurface imaging and time lapse monitoring using data acquired under flowing conditions the results of this study suggest that by adopting the inside coiled tubing method without drilling a new observation well more affordable distributed acoustic sensing vertical seismic profile monitoring can be achieved in fields such as co2 capture and storage and unconventional shale projects where monitoring costs have to be minimized

variability of the thermocline due to a sudden change in the ekman pumping the thermocline variability caused by a sudden variation of the ekman pumping is studied using a 2 5 layer geostrophic model that represents the ventilated and the shadow zones of a subtropical gyre and baroclinic rossby wave propagation during spinup the propagation of the first baroclinic mode induces a large deepening of the thermocline on a timescale ranging between 2 and 15 yr depending on latitude the propagation is similar throughout the basin and is not influenced by the geostrophic flow save nonlinearly through the variation in layer depth south of the subduction line the adjustment is completed by the second baroclinic mode in the ventilated zone the latter is not very active and there are only smaller by a factor of 5 variations of the thermocline depth primarily linked to a slight imbalance between ekman pumping and vertically averaged meridional advection in the shadow zone the second baroclinic mode plays a more important role since it primarily balances the ekman pumping although the variations of the second layer depth remain smaller than in the ventilated area spindown induces similarly a shoaling of the thermocline but because of nonlinearities lower rossby wave speeds and decreased advection the adjustment is everywhere slower than during spinup

impact of dielectric changes on l band 3 d sar reflectivity profiles of forest volumes synthetic aperture radar sar tomography tomosar allows the reconstruction of the vertical distribution of the power backscattered by natural volumes by combining multiple sar images acquired with slightly different incidence angles being a radar quantity the profile depends on the radar frequency polarization and acquisition geometry the 3 d distribution of the scattering elements and their dielectric properties the characterization of each one of these factors is crucial to enable the extraction of physical 3 d structure attributes from tomosar profiles the objective of this paper is to investigate how the vertical distribution of the backscattered power at l band is affected by seasonal and weather induced changes radiometric e g ground and volume powers and geometric e g center of mass of the volume only profiles and phase centers of the volume scattering layers parameters have been estimated under different weather and season conditions and compared then tomosar data sets affected by dielectric nonstationarity i e variability have been considered in order to assess the invariance degree of each radiometric and geometric parameters this analysis has been carried out by processing four l band airborne tomosar data sets acquired before and after a rainfall and in spring and autumn over the traunstein forest south of germany

on the relationship between decadal buoyancy anomalies and variability of the atlantic meridional overturning circulation abstractowing to the role of the atlantic meridional overturning circulation amoc in ocean heat transport amoc variability is thought to play a role in climate variability on a wide range of time scales this paper focuses on the potential role of the amoc in climate variability on decadal time scales coupled and ocean only general circulation models run in idealized geometries are utilized to study the relationships between decadal amoc and buoyancy variability and determine whether the amoc plays an active role in setting sea surface temperature on decadal time scales decadal amoc variability is related to changes in the buoyancy field along the western boundary according to the thermal wind relation buoyancy anomalies originate in the upper ocean of the subpolar gyre and travel westward as baroclinic rossby waves when the buoyancy anomalies strike the western boundary they are advected southward by the deep western boundary current leading to latitudinally coherent amoc variability the amoc i

the effect of bottom pressure decoupling on the speed of extratropical baroclinic rossby waves abstract in layered models of the ocean the assumption of a deep resting layer is often made motivated by the surface intensification of many phenomena the propagation speed of first mode baroclinic rossby waves in such models is always faster than in models with all the layers active the assumption of a deep resting layer is not crucial for the phase speed enhancement since the same result holds if the bottom pressure fluctuations are uncorrelated from the overlying wave dynamics in this paper the authors explore the relevance of this behavior to recent observational estimates of too fast waves by chelton and schlax the available evidence supporting this scenario is reviewed and a method that extends the idea to a continuously stratified fluid is developed it is established that the resulting amplification factor is at leading order captured by the formula where cfast is the enhanced phase speed cstandard the standard phase speed 1 z is the standard first mode for the velocity and pressur

sofar floats reveal midlatitude intermediate north atlantic general circulation part ii an eulerian statistical view abstract part i of this paper has given a descriptive view of the trajectories of 26 sofar floats drifting near 700 m depth in the central north atlantic during the mid 1980s as part of the topogulf experiment here an eulerian analysis of the 53 4 collected float years is performed by grouping data in 2 latitude 4 longitude boxes the mean circulation lacks a significant southward sverdrupian flow and shows instead zonal bands of alternating westward and eastward currents except in the canary basin west of the ridge and north of 38 n the general northeastward flow of the gulf stream system is recovered while south of 38 n the westward recirculation observed from historical float data between 70 and 55 w is shown to extend as far as 40 w a mean azores current is observed both west of the ridge near 33 n and east of 30 w near 34 n in between east of the ridge a tongue of high eddy energy indicates stronger eddy activity and local instabilities of the azores current eddy kinetic energy and e

decadal wind forcing of the north atlantic subtropical gyre abstract in the central north atlantic ocean there are large decadal scale fluctuations of sea level and of the depth of the thermocline this variability can be explained by low frequency rossby waves forced by wind the authors have used a simple model of ocean fluctuations driven by the coads wind stress curl and find that their model results and hydrographic data to the limited extent they can be compared meaningfully agree rather well the variation in wind curl over the ocean leads to surprisingly large north south variability in the computed oceanic response over the subtropical gyre the peak to peak sea level differences are as great as 20 cm and persist for many years these large variations could induce major errors in calculations of the mean ocean flow when hydrographic sections from many years are combined it appears possible however to correct for these wind induced effects to allow the lower frequency signals to be determined the westernmost edge of our oceanic calculations is at the

caribbean current and eddies as observed by surface drifters abstract recent satellite tracked surface drifter trajectories were analyzed to describe the mean currents and eddies in the caribbean sea the structure of the caribbean current and its variability were determined from high resolution 1 2 degree maps of the mean velocity and eddy kinetic energy looping drifter trajectories were used to identify discrete cyclones and anticyclones and their characteristics were described and related to the structure of the mean flow the translation rate of eddies in different areas was found to be similar to the mean velocity of the local background flow fields suggesting that the eddies were largely advected by the background flow ten energetic anticyclones translated westward at 13 cm s in the venezuela and colombia basins these anticyclones tended to lie in two bands centered near 15 n and 17 n coinciding with two jets of the caribbean current the northern weaker jet contains water primarily from the north atlantic the southern stronger jet contains water from the tropical and south atlantic the anticyclones are thought to have formed in the eastern caribbean from the anticyclonic vorticity derived from north brazil current rings the ring vorticity enters the eastern caribbean through island passages and is probably amplified by the anticyclonic shear on the northern side of the jets southwest of cuba a cyclone anticyclone pair was observed to translate slowly 2 cm s westward into the yucatan current the cyclone was tracked for 10 5 months with four drifters making it the longest tracked of the caribbean eddies

phenomenology of ground scattering in a tropical forest through polarimetric synthetic aperture radar tomography this paper aims at characterizing the scattering mechanisms occurring at the ground level in a tropical forest illuminated by a p band synthetic aperture radar sar the analysis is carried out based on the multibaseline fully polarimetric data set collected by onera over paracou french guyana in the frame of the european space agency campaign tropisar the favorable baseline distribution of this data set results in the possibility of removing most contributions from the vegetation layer by tomographic techniques thus allowing the generation of a new fully polarimetric single look complex sar image relative to scattering contributions from the ground level only such a ground layer image is then analyzed by considering the variation of its polarimetric signature with respect to terrain local slope and radar look angle two major conclusions are drawn 1 double bounce scattering from trunk ground interactions is observed to be the dominant scattering mechanism at the ground level on flat terrains whereas it rapidly tends to vanish as the topographic slope increases and 2 the characteristic parameter that rules trunk ground scattering is not the tree height but rather the available free path facing the tree as a result of the presence of nearby trees undulating topography or understory preventing double bounce scattering from taking place whenever the ground bounce occurs too far away from the considered tree the mean free path length resulting from the analysis of this data set is found to be l 7 m finally we discuss how the concept of free path length can be accounted for in simple terms by assuming an equivalent extinction model characterized by a variation along the horizontal dimension