rapid inverse modeling of pressure interference tests using trajectory based traveltime and amplitude sensitivities 1 this paper presents an efficient trajectory based approach to integrate transient pressure data into high resolution reservoir and aquifer models the method involves alternating traveltime and peak amplitude matching of pressure response using inverse modeling and is particularly well suited for high resolution subsurface characterization using hydraulic tomography or pressure interference tests compared to traveltime inversion only our proposed approach results in a significantly improved match of the pressure response at the wells and also better estimates of subsurface properties this is accomplished with very little increase in computational cost utilizing the concept of a diffusive time of flight derived from an asymptotic solution of the diffusivity equation we develop analytical approaches to estimate the sensitivities for traveltime and peak amplitude of pressure response to subsurface properties the sensitivities are then used in an iterative least squares minimization to match the pressure data we illustrate our approach using synthetic and field examples in the field application at a fractured limestone formation the predominant fracture patterns emerging from the inversion are shown to be consistent with independent geophysical experiments and borehole data

an inversion strategy for hydraulic tomography coupling travel time and amplitude inversion summary we present a hydraulic tomographic inversion strategy with an emphasis on the reduction of ambiguity of hydraulic travel time inversion results and the separation of the estimated diffusivity values into hydraulic conductivity and specific storage our tomographic inversion strategy is tested by simulated multilevel interference slug tests in which the positions of the sources injection ports and the receivers observation ports isolated with packers are varied simulations include the delaying effect of wellbore storage on travel times which are quantified and shown to be of increasing importance for shorter travel distances for the reduction of ambiguity of travel time inversion we use the full travel time data set as well as smaller data subsets of specified source receiver angles the inversion results of data subsets show different resolution characteristics and improve the reliability of the interpretation the travel time of a pressure pulse is a function of the diffusivity of the medium between the source and receiver thus it is difficult to directly derive values for hydraulic conductivity and specific storage by inverting travel times in order to overcome this limitation we exploit the great computational efficiency of hydraulic travel time tomography to define the aquifer structure which is then input into the underlying groundwater flow model modflow 96 finally we perform a model calibration amplitude inversion using the automatic parameter estimator pest enabling us to separate diffusivity into its two components hydraulic conductivity and specific storage

3d crosshole ert for aquifer characterization and monitoring of infiltrating river water the hydrogeological properties and responses of a productive aquifer in northeastern switzerland are investigated for this purpose 3d crosshole electrical resistivity tomography ert is used to define the main lithological structures within the aquifer through static inversion and to monitor the water infiltration from an adjacent river during precipitation events and subsequent river flooding the river water resistivity increases as a consequence the electrical characteristics of the infiltrating water can be used as a natural tracer to delineate preferential flow paths and flow velocities the focus is primarily on the experiment installation data collection strategy and the structural characterization of the site and a brief overview of the ert monitoring results the monitoring system comprises 18 boreholes each equipped with 10 electrodes straddling the entire thickness of the gravel aquifer a multichannel resistivity system programmed to cycle through various four point electrode configurations of the 180 electrodes in a rolling sequence allows for the measurement of approximately 15 500 apparent resistivity values every 7 h on a continuous basis the 3d static ert inversion of data acquired under stable hydrological conditions provides a base model for future time lapse inversion studies and the means to investigate the resolving capability of our acquisition scheme in particular it enables definition of the main lithological structures within the aquifer the final ert static model delineates a relatively high resistivity low porosity intermediate depth layer throughout the investigated aquifer volume that is consistent with results from well logging and seismic and radar tomography models the next step will be to define and implement an appropriate time lapse ert inversion scheme using the river water as a natural tracer the main challenge will be to separate the superposed time varying effects of water table height temperature and salinity variations associated with the infiltrating water

joint inversion of crosshole radar and seismic traveltimes acquired at the south oyster bacterial transport site the structural approach to joint inversion entailing common boundaries or gradients offers a flexible and effective way to invert diverse types of surface based and or crosshole geophysical data the cross gradients function has been introduced as a means to construct models in which spatial changes in two distinct physical property models are parallel or antiparallel inversion methods that use such structural constraints also provide estimates of nonlinear and nonunique field scale relationships between model parameters here we jointly invert crosshole radar and seismic traveltimes for structurally similar models using an iterative nonlinear traveltime tomography algorithm application of the inversion scheme to synthetic data demonstrates that it better resolves lithologic boundaries than the individual inversions alone tests of the scheme on gpr and seismic data acquired within a shallow aquifer illustrate that the resultant models have improved correlations with flowmeter data in comparison with models based on individual inversions the highest correlation with the flowmeter data is obtained when the joint inversion is combined with a stochastic regularization operator and the vertical integral scale is estimated from the flowmeter data point spread functions show that the most significant resolution improvements offered by the joint inversion are in the horizontal direction

imaging and quantifying salt tracer transport in a riparian groundwater system by means of 3d ert monitoring abstractdetermining groundwater flow paths of infiltrated river water is necessary for studying biochemical processes in the riparian zone but their characterization is complicated by strong temporal and spatial heterogeneity we investigated to what extent repeat 3d surface electrical resistance tomography ert can be used to monitor transport of a salt tracer plume under close to natural gradient conditions the aim is to estimate groundwater flow velocities and pathways at a site located within a riparian groundwater system adjacent to the perialpine thur river in northeastern switzerland our ert time lapse images provide constraints on the plume s shape flow direction and velocity these images allow the movement of the plume to be followed for 35 m although the hydraulic gradient is only 1 43 the ert time lapse images demonstrate that the plume s center of mass and its front propagate with velocities of 2 10 4 m s and 5 10 4 m s respectively these velocities are compatible with groundwate

inversion of tracer test data using tomographic constraints 1 we have developed a methodology for inverting tracer test data using zonation information obtained from two dimensional radar tomograms to improve the typically overly smooth hydraulic conductivity fields obtained from conventional inversion of tracer test data the method simultaneously yields two dimensional estimates of hydraulic conductivity as well as petrophysical relationships that relate hydraulic conductivity to radar velocity these relationships can be assumed to be stationary throughout the area of investigation or to vary as a function of zonation using a synthetic three dimensional hydraulic conductivity field we apply the developed inversion methodology and explore the impact of the strength and stationarity of the petrophysical relationship as well as the impact of errors that are often associated with radar data acquisition such as unknown borehole deviation we find that adding radar tomographic data to tracer test data improves hydrogeological site characterization even in the presence of minor radar data errors the results are contingent on the assumption that a relationship between radar velocity and hydraulic conductivity exists therefore the applicability of the proposed method may be limited to field sites where this condition is partially or fully satisfied

on the relation between the boreal spring position of the atlantic intertropical convergence zone and atlantic zonal mode abstractprevious studies have talked about the existence of a relation between the atlantic meridional mode amm and atlantic zonal mode azm via the meridional displacement of the intertropical

environmental interpretation of fossil insect assemblages from mis 5 at ziegler reservoir snowmass village colorado abstract organic rich lake sediments from a trench exposed at the ziegler reservoir fossil site near snowmass village colorado yielded a sequence of 27 insect fossil assemblages spanning the time interval from about 125 to 77 ka the assemblages appear to represent mis 5e 5c 5b and 5a a total of 99 taxa were identified mostly beetles the fossils represent the oldest known pleistocene insect faunas from high elevation in the rocky mountains and document a series of climatic oscillations from full interglacial to stadial and interstadial environments accompanied by changes in regional biological communities the mis 5e fauna indicates summer temperatures similar to modern values with winter temperatures 5 7 c cooler than today regional climates cooled somewhat by mis 5c and during mis 5b summer temperatures were 5 6 c colder than modern values summer temperatures recovered to near modern levels during early mis 5a and cooled by 1 2 c at its end although winter temperatures were apparently above modern levels the indication of milder but wetter winters strengthened by the inclusion of species found today only in the pacific northwest region suggests conditions that may have led to increased snowpack at high elevations in this part of the rocky mountains linked with the onset of mis 4 glaciation

on the inconsistent relationship between pacific and atlantic ninos the tropical atlantic wind response to el nino forcing is robust with weakened northeast trade winds north of the equator and strengthened southeast trade winds along and south of the equator however the relationship between sea surface temperature sst anomalies in the eastern equatorial pacific and atlantic is inconsistent with el nino events followed sometimes by warm and other times by cold boreal summer anomalies in the atlantic cold tongue region using observational data and a hindcast simulation of the nucleus for european modeling of the ocean nemo global model at 0 5 resolution nemo orca05 this inconsistent sst relationship is shown to be at least partly attributable to a delayed negative feedback in the tropical atlantic that is active in years with a warm or neutral response in the eastern equatorial atlantic in these years the boreal spring warming in the northern tropical atlantic that is a typical response to el nino is pronounced setting up a strong meridional sst gradient this leads to a negative wind stress curl anomaly to the north of the equator that generates downwelling rossby waves when these waves reach the western boundary they are reflected into downwelling equatorial kelvin waves that reach the cold tongue region in late boreal summer to counteract the initial cooling that is due to the boreal winter wind stress response to el nino in contrast this initial cooling persists or is amplified in years in which the boreal spring northern tropical atlantic warming is weak or absent either because of a positive north atlantic oscillation nao phase or an early termination of the pacific el nino event

new pollen and beetle analyses at the mary jane site colorado evidence for late glacial tundra conditions analyses of fossil pollen and beetles from a late pinedale peat deposit from the upper fraser river colorado allow a reassessment of previously published paleoenvironmental evidence from the site between 13 800 and at least 12 600 yr b p the environment was an open tundra indicative of a cold dry climate scattered spruce trees were probably present at the site by the end of the record ca 12 300 yr b p

geoelectrical evidence of bicontinuum transport in groundwater bicontinuum models and rate limited mass transfer rlmt explain complex transport behavior e g long tailing and rebound in heterogeneous geologic media but experimental verification is problematic because geochemical samples represent the mobile component of the pore space here we present geophysical evidence of rlmt at the field scale during an aquifer storage and recovery experiment in a fractured limestone aquifer in charleston south carolina we observe a hysteretic relation between measurements of pore fluid conductivity and bulk electrical conductivity this hysteresis contradicts advective dispersive transport and the standard petrophysical model relating porefluid and bulk conductivity but can be explained by considering bicontinuum transport models that include first order rlmt using a simple numerical model we demonstrate that geoelectrical measurements are sensitive to bicontinuum transport and rlmt parameters which are otherwise difficult to infer from direct hydrologic measurements

estimating traveltimes and groundwater flow patterns using 3d time lapse crosshole ert imaging of electrical resistivity fluctuations induced by infiltrating river water abstractthe infiltration of river water into aquifers is of high relevance to drinking water production and is a key driver of biogeochemical processes in the hyporheic and riparian zone but the distribution and quantification of the infiltrating water are difficult to determine using conventional hydrological methods e g borehole logging and tracer tests by time lapse inverting crosshole ert electrical resistivity tomography monitoring data we imaged groundwater flow patterns driven by river water infiltrating a perialpine gravel aquifer in northeastern switzerland this was possible because the electrical resistivity of the infiltrating water changed during rainfall runoff events our time lapse resistivity models indicated rather complex flow patterns as a result of spatially heterogeneous bank filtration and aquifer heterogeneity the upper part of the aquifer was most affected by the river infiltrate and the highest groundwater velocities and possible preferential flow occurred at shallow t

structure coupled joint inversion of geophysical and hydrological data abstractin groundwater hydrology geophysical imaging holds considerable promise for improving parameter estimation due to the generally high resolution and spatial coverage of geophysical data however inversion of geophysical data alone cannot unveil the distribution of hydraulic conductivity jointly inverting geophysical and hydrological data allows us to benefit from the advantages of geophysical imaging and at the same time recover the hydrological parameters of interest we have applied a coupling strategy between geophysical and hydrological models that is based on structural similarity constraints model combinations for which the spatial gradients of the inferred parameter fields are not aligned in parallel are penalized in the inversion this structural coupling does not require introducing a potentially weak unknown and nonstationary petrophysical relation to link the models the method was first tested on synthetic data sets and then applied to two combinations of geophysical hydrolog

revisiting the cause of the eastern equatorial atlantic cold event in 2009 an extreme cold sea surface temperature event occurred in the atlantic cold tongue region in boreal summer 2009 it was preceded by a strong negative atlantic meridional mode event associated with north westerly wind anomalies along the equator from march to may although classical equatorial wave dynamics suggest that westerly wind anomalies should be followed by a warming in the eastern equatorial atlantic an abrupt cooling took place in the literature two mechanisms meridional advection of subsurface temperature anomalies and planetary wave reflection are discussed as potential causes of such an event here for the first time we use in situ measurements in addition to satellite and reanalysis products to investigate the contribution of both mechanisms to the 2009 cold event our results suggest that meridional advection is less important in cold events than in corresponding warm events and in particular did not cause the 2009 cold event argo float data confirm previous findings that planetary wave reflection contributed to the onset of the 2009 cold event additionally our analysis suggests that higher baroclinic modes were involved

differential insect and mammalian response to late quaternary climate change in the rocky mountain region of north america abstract of the 200 beetle species identified from rocky mountain late pleistocene insect faunal assemblages 23 are no longer resident in this region none of the 200 species is extinct in contrast to this only 8 of 73 identified mammal species from rocky mountain late pleistocene assemblages are no longer resident in the rockies and 12 species are now extinct since both groups of organisms are highly mobile it would appear that their responses to the large scale fluctuations of climate associated with the last 125 000 years have been considerably different most strikingly contrasting with the insects there are no mammals in the rocky mountain late pleistocene fossil record that are found exclusively today in the pacific northwest pnw region the pnw does have a distinctive modern mammalian fauna but only one of these keen s myotis has a fossil record outside the pnw region in the eastern and central united states no modern pnw vertebrate species have been found in any rocky mountain fossil assemblages based on these data it appears that there has been little or no mammalian faunal exchange between the pnw region and the rocky mountains during the late pleistocene or holocene this is in stark contrast to the fossil beetle record where pnw species are a substantial component in many faunas right through to the late holocene

remotely forced variability in the tropical atlantic ocean an ensemble of eight hindcasts has been conducted using an ocean atmosphere general circulation model fully coupled only within the atlantic basin with prescribed observational sea surface temperature sst for 1950 1998 in the global ocean outside the atlantic basin the purpose of these experiments is to understand the influence of the external sst anomalies on the interannual variability in the tropical atlantic ocean statistical methods including empirical orthogonal function analysis with maximized signal to noise ratio have been used to extract the remotely forced atlantic signals from the ensemble of simulations it is found that the leading external source on the interannual time scales is the el nino southern oscillation enso in the pacific ocean the enso signal in the tropical atlantic shows a distinct progression from season to season during the boreal winter of a maturing el nino event the model shows a major warm center in the southern subtropical atlantic together with warm anomalies in the northern subtropical atlantic the southern subtropical sst anomalies is caused by a weakening of the southeast trade winds which are partly associated with the influence of an atmospheric wave train generated in the western pacific ocean and propagating into the atlantic basin in the southern hemisphere during boreal fall in the boreal spring the northern tropical atlantic ocean is warmed up by a weakening of the northeast trade winds which is also associated with a wave train generated in the central tropical pacific during the winter season of an el nino event apart from the atmospheric planetary waves these sst anomalies are also related to the sea level pressure slp increase in the eastern tropical atlantic due to the global adjustment to the maturing el nino in the tropical pacific the tropical slp anomalies are further enhanced in boreal spring which induce anomalous easterlies on and to the south of the equator and lead to a dynamical oceanic response that causes cold sst anomalies in the eastern and equatorial atlantic from boreal spring to summer most of these sst anomalies persist into the boreal fall season

a travel time based hydraulic tomographic approach 1 hydraulic tomography is a method to identify the three dimensional spatial distribution of hydraulic properties in the subsurface we propose a tomographic approach providing the inversion of travel times of hydraulic or pneumatic tests conducted in a tomographic array the inversion is based on the relation between the peak time of a recorded transient pressure curve and the diffusivity of the investigated system the development of a transformation factor enables the inversion of further travel times besides the peak time of a transient curve as the early travel times of the curve are mainly related to preferential flow features while the inversion based on late travel times are reflecting an integral behavior it can be assumed that the different inversion results reflect the properties of the overall system by comparing the different reconstructions the system interpretation therefore becomes more comprehensive and reliable furthermore the similarity of the proposed hydraulic tomographic approach to seismic travel time tomography allows us to apply the inversion algorithms which are used for seismic tomography we therefore apply the method of staggered grids which enables to refine the grid resulting in a higher nominal resolution to data from a set of interference tests arranged in a tomographic array the tests were conducted in an unsaturated fractured sandstone cylinder in the laboratory the three dimensional reconstructions of the diffusivity distribution are found to be highly reliable and robust in particular the mapped fracture of the sandstone cylinder coincides with our reconstructed diffusivity distribution

improved hydrogeophysical characterization using joint inversion of cross hole electrical resistance and ground penetrating radar traveltime data appropriate regularizations of geophysical inverse problems and joint inversion of different data types improve geophysical models and increase their usefulness in hydrogeological studies we have developed an efficient method to calculate stochastic regularization operators for given geostatistical models the method which combines circulant embedding and the diagonalization theorem of circulant matrices is applicable for stationary geostatistical models when the grid discretization in each spatial direction is uniform in the volume of interest we also used a structural approach to jointly invert cross hole electrical resistance and ground penetrating radar traveltime data in three dimensions the two models are coupled by assuming at all points that the cross product of the gradients of the two models is zero no petrophysical relationship between electrical conductivity and relative permittivity is assumed but is instead obtained as a by product of the inversion the approach has been applied to data collected in a u k sandstone aquifer in order to improve characterization of the vadose zone hydrostratigraphy by analyzing scatterplots of electrical conductivity versus relative permittivity together with petrophysical models a zonation could be obtained with corresponding estimates of the electrical formation factor the water content and the effective grain radius of the sediments the approach provides greater insight into the hydrogeological characteristics of the subsurface than by using conventional geophysical inversion methods

hierarchical geostatistics and multifacies systems boise hydrogeophysical research site boise idaho 1 the geostatistical structure of a heterogeneous coarse fluvial aquifer is investigated with porosity data derived from neutron logs at a research well field boise hydrogeophysical research site or bhrs that was designed in part to support three dimensional geostatistical analysis of hydrologic and geophysical parameters recognizing that the coarse fluvial deposits include subdivisions units between bounding surfaces we adopt a hierarchical approach and examine the porosity geostatistics of the aquifer at three scales at the bhrs the saturated fluvial deposits as a whole maximum interwell spacing 80 m thickness 16 18 m are at hierarchical level 1 five subhorizontal units within these deposits four cobble dominated units and a channel sand can be traced across the central area of the bhrs and are at hierarchical level 2 and subunits patches or lenses in one of the level 2 units unit 4 are at hierarchical level 3 we use variography and porosity statistics to recognize nonstationarity at hierarchical level 1 and in one of the level 2 units unit 4 where the means and variances of porosity differences as a function of lag are not constant between distinct units and subunits respectively the geostatistical structure at level 1 is modeled with different horizontal and vertical structures that have different sills vertical sill greater than horizontal sill the difference in sills can be explained quantitatively by the summing of weighted sills from all individual units and combined units i e a given pair of different units where the weights are the proportions of data pairs contributing to the sills at each lag from the individual and combined units extension of this analysis leads to a weighted multistructure form of the variogram function whereby a global experimental variogram in a hierarchical system can be decomposed quantitatively into weighted component individual and combined unit or facies structures for any number of units or hierarchical levels such decomposition of the global horizontal variogram from the bhrs indicates that short range periodicity in that structure is due to both 1 combined unit structures associated with patches or lenses at hierarchical level 3 in unit 4 and 2 variations in thickness of unit 2 for hierarchical multifacies systems structure models fit to global horizontal and vertical experimental variograms may not be useful for subsequent stochastic modeling if the system on which the structure models are based is nonstationary

accelerator dating of a mixed assemblage of late pleistocene insect fossils from the lamb spring site colorado abstract fossil insects from the late glacial deposits at the lamb spring archaeological site near denver colorado are relatively abundant and diverse providing considerable paleoecological data for the site the late pleistocene insect fauna from the site comprises 72 identified taxa principally beetles however the fauna presented an interpretive problem because it contained a mixture of prairie and alpine tundra species this was initially considered to be the result of a mixing of faunal elements during the climatic transition of late glacial times a no modern analog fauna accelerator dating of insect fossil specimens from the two ecological groups helped resolve the paleoecological problem fossil specimens of the prairie associated species were dated at 17 850 550 yr b p while specimens of the tundra associated species yielded an age of 14 500 500 yr b p these dates reveal that what appeared to be an ecological mixing was probably a taphonomic problem wherein full glacial age fossils were probably reworked into latest wisconsin sediments while both faunal assemblages reflect climatic conditions substantially colder than present initial results suggest that the full glacial fauna represents a cold dry grassland or steppe environment while the younger fauna suggests moister and more tundra like conditions

zonation for 3d aquifer characterization based on joint inversions of multimethod crosshole geophysical data predictive groundwater modeling requires accurate information about aquifer characteristics geophysical imaging is a powerful tool for delineating aquifer properties at an appropriate scale and resolution but it suffers from problems of ambiguity one way to overcome such limitations is to adopt a simultaneous multitechnique inversion strategy we have developed a methodology for aquifer characterization based on structural joint inversion of multiple geophysical data sets followed by clustering to form zones and subsequent inversion for zonal parameters joint inversions based on cross gradient structural constraints require less restrictive assumptions than say applying predefined petrophysical relationships and generally yield superior results this approach has for the first time been applied to three geophysical data types in three dimensions a classification scheme using maximum likelihood estimation is used to determine theparameters of a gaussian mixture model that defines zonal geometries

estimation of field scale soil hydraulic and dielectric parameters through joint inversion of gpr and hydrological data 1 a method is described for the joint use of time lapse ground penetrating radar gpr travel times and hydrological data to estimate field scale soil hydraulic parameters we build upon previous work to take advantage of a wide range of cross borehole gpr data acquisition configurations and to accommodate uncertainty in the petrophysical function which relates soil porosity and water saturation to the effective dielectric constant we first test the inversion methodology using synthetic examples of water injection in the vadose zone realistic errors in the petrophysical function result in substantial errors in soil hydraulic parameter estimates but such errors are minimized through simultaneous estimation of petrophysical parameters in some cases the use of a simplified gpr simulator causes systematic errors in calculated travel times simultaneous estimation of a single correction parameter sufficiently reduces the impact of these errors we also apply the method to the u s department of energy doe hanford site in washington where time lapse gpr and neutron probe np data sets were collected during an infiltration experiment we find that inclusion of gpr data in the inversion procedure allows for improved predictions of water content compared to predictions made using np data alone these examples demonstrate that the complimentary information contained in geophysical and hydrological data can be successfully extracted in a joint inversion approach moreover since the generation of tomograms is not required the amount of gpr data required for analyses is relatively low and difficulties inherent to tomography methods are alleviated finally the approach provides a means to capture the properties and system state of heterogeneous soil both of which are crucial for assessing and predicting subsurface flow and contaminant transport

late quaternary loess in northeastern colorado part i age and paleoclimatic significance loess in eastern colorado covers an estimated 14 000 km 2 and is the westernmost part of the north american midcontinent loess province stratigraphic studies indicate there were two periods of loess deposition in eastern colorado during late quaternary time the first period spanned ca 20 000 to 12 000 14 c yr b p ca 20 14 ka and correlates reasonably well with the culmination and retreat of pinedale glaciers in the colorado front range during the last glacial maximum the second period of loess deposition occurred between ca 11000 and 9000 14 c yr b p this interval may be holocene or may correlate with a hypothesized younger dryas glacial advance in the colorado front range sedimentologic mineralogic and geochemical data indicate that as many as three sources could have supplied loess in eastern colorado these sources include glaciogenic silt derived from the colorado front range and two bedrock sources volcaniclastic silt from the white river group and clays from the pierre shale the sediment sources imply a generally westerly paleowind during the last glacial maximum new carbon isotope data combined with published faunal data indicate that the loess was probably deposited on a cool steppe implying a last glacial maximum july temperature depression relative to the present of at least 5 6 c overall loess deposition in eastern colorado occurred mostly toward the end of the last glacial maximum under cooler and drier conditions with generally westerly winds from more than one source

hydrogeological characterization of the south oyster bacterial transport site using geophysical data a multidisciplinary research team has conducted a field scale bacterial transport study within an uncontaminated sandy pleistocene aquifer near oyster virginia the overall goal of the project was to evaluate the importance of heterogeneities in controlling the field scale transport of bacteria that are injected into the ground for remediation purposes geochemical hydrological geological and geophysical data were collected to characterize the site prior to conducting chemical and bacterial injection experiments in this paper we focus on results of a hydrogeological characterization effort using geophysical data collected across a range of spatial scales the geophysical data employed include surface ground penetrating radar radar cross hole tomography seismic cross hole tomography cone penetrometer and borehole electromagnetic flowmeter these data were used to interpret the subregional and local stratigraphy to provide high resolution hydraulic conductivity estimates and to provide information about the log conductivity spatial correlation function the information from geophysical data was used to guide and assist the field operations and to constrain the numerical bacterial transport model although more field work of this nature is necessary to validate the usefulness and cost effectiveness of including geophysical data in the characterization effort qualitative and quantitative comparisons between tomographically obtained flow and transport parameter estimates with hydraulic well bore and bromide breakthrough measurements suggest that geophysical data can provide valuable high resolution information this information traditionally only partially obtainable by performing extensive and intrusive well bore sampling may help to reduce the ambiguity associated with hydrogeological heterogeneity that is often encountered when interpreting field scale bacterial transport data

the equatorial atlantic oscillation and its response to enso an internal equatorial atlantic oscillation has been identified by analyzing sea surface temperature sst observations the equatorial atlantic oscillation can be viewed as the atlantic analogue of the el nino southern oscillation enso phenomenon in the equatorial pacific but it is much less vigorous the equatorial atlantic oscillation is strongly influenced by the pacific enso with the equatorial atlantic sea surface temperature lagging by about six months this lag can be explained by the dynamical adjustment time of the equatorial atlantic to low frequency wind stress variations and the seasonally varying background state which favours strongest growth of perturbations in summer results of an extended range simulation with a coupled ocean atmosphere gcm support this picture

why did the 2011 2012 la nina cause a severe drought in the brazilian northeast the brazilian northeast ne is strongly affected by el nino southern oscillation enso during la nina events the precipitation over the ne is generally above average however during the last la nina event in 2011 2012 the ne went through its worst drought in the last 30 years in this study observations and numerical simulations are used to determine what made the 2011 2012 event different from other events we find that eastern pacific canonical la nina events cause a cooling of the tropical north atlantic and warming of the tropical south atlantic that lead to a southward migration of the intertropical convergence zone which in turn brings rain to the ne on the other hand la nina events with the cooling concentrated in the central pacific cause the opposite meridional sea surface temperature sst gradient in the tropical atlantic leading to droughts over the ne the 2011 2012 event was of the latter type this study also shows that it is possible to predict the sign of the ne rainfall anomaly during enso events using a simple sst index

the source of benguela ninos in the south atlantic ocean 1 the intermittent occurrence of anomalous warm events in the upwelling regions of the pacific el ninos has been intensively studied pacific ninos have striking effects on the local ecosystem hence on the fisheries and on rainfall similar dramatic events have been observed in the south atlantic off the coasts of angola and namibia and named benguela ninos they tend not to occur in unison with their pacific counterpart and may thus have unrelated forcing mechanisms using an ocean general circulation model forced by real winds and verified with satellite data it is shown that benguela ninos are generated by specific wind stress events in the west central equatorial atlantic and progress from there as subsurface temperature anomalies that eventually outcropped only at the south west african coast these results suggest that it now may be possible to predict the occurrence of these disruptive events with a lead time of 2 months

hydrogeologic facies models to delineate large scale spatial trends in glacial and glaciofluvial sediments recent interest in contaminant transport in ground water has led hydrogeologists to the conclusion that predicting the movement of solutes requires information on the distribution of spatial trends and heterogeneities in porous media description of spatial trends has long been of interest to sedimentologists who have produced a large body of geologic information on the subject in this paper facies models are used to construct conceptual models of hydrogeologic facies for glacialmeltwater stream sediment and till these hydrogeologic facies models which delineate large scale trends in heterogeneity are appropriate for use in designing hydrogeologic field tests and for estimating input to regional ground water flow and transport models this paper treats each facies as a homogeneous anisotropic hydrogeologic unit the models presented herein conceptualize the hydrogeologic relationships among facies and illustrate one method of converting the apparent chaos in nature into an orderly system that can be tested scientifically and modeled mathematically the principles used to create conceptual models of hydrogeologic facies for the types of sediment considered in this paper can be extended to other sedimentary environments it should be recognized however that such models do not address the small scale heterogeneity present within individual facies additional basic research is required to measure hydraulic conductivity variation within representative hydrogeologic facies and to develop statistical descriptions to represent the variations such detailed descriptions of hydraulic conductivity may be necessary to describe ground water flow at a local scale for analysis of contaminant transport

estimating lithologic and transport properties in three dimensions using seismic and tracer data the kesterson aquifer the identification of aquifer heterogeneities particularly flow paths and barriers has become a critical research topic in hydrology cross well seismic tomography may provide the needed resolution when used in conjunction with hydraulic head and tracer concentration measurements we demonstrate a field application and sensitivity analysis of the split inversion method sim which combines seismic hydraulic and tracer data to estimate the three dimensional zonation of aquifer properties along with the hydraulic properties for these zones for the kesterson aquifer in the san joaquin valley california we first invert seismic travel times measured between six well pairs to obtain seismic slowness 1 seismic velocity cross sections or tomograms we then use conditional simulation to provide three dimensional seismic slowness realizations next the sim is used to split several realizations into three lithologic zones and assign hydraulic properties to the zones to best match six tracer concentration histories

hydraulic tomography analog outcrop study combining travel time and steady shape inversion summary travel time and steady shape inversions are complementary methods for tomographic aquifer characterization in this work a combined procedure is presented that facilitates determination of spatial hydraulic conductivity and specific storage distributions in heterogeneous groundwater systems the procedure is applied to a highly heterogeneous sedimentary aquifer analog that is implemented as a two and three dimensional case study in a numerical flow model by interpreting the observations from multiple simulated short term pumping tests the main hydraulic features of the analog are successfully reconstructed the final results demonstrate the encouraging potential of the combined procedure for identifying the dominant structural elements and composition of sedimentary aquifers however limits derived from the test design of hydraulic travel time tomography in our synthetic case study prevented us from resolving small scale 10 cm in size variability of hydraulic conductivity with high discrepancies up to 5 orders of magnitude a better reconstruction of the aquifer hydraulic parameters is expected by utilizing a larger amount of measurements which involve more test and observation intervals although such a test design would be less feasible for field applications still this newly combined scheme is very attractive for an up scaled reconstruction on the sub meter scale for the present case study representative parameter values could be estimated in a computationally efficient way

the use of land snail shells in paleoenvironmental reconstruction fossil land snail shells constitute a valuable source of paleoenvironmental information for the quaternary they can be dated by a variety of methods including radiocarbon amino acid racemization and epimerization and perhaps also thu and esr the vast majority of paleoenvironmental studies based on land snail shells have examined the faunal composition of fossil assemblages from which a variety of paleoenvironmental characteristics such as biome temperature and moisture conditions have been reconstructed still there are a number of problems involved in using this approach and these are discussed shell morphology has occasionally been used to reconstruct such factors as rainfall and temperature stable isotope studies on quaternary land snails include analysis of 18o values of organic matter in the shells to reconstruct c4 plant distributions from which rainfall amounts can be inferred and analysis of 18o values of shell carbonate from which trends in the oxygen isotope composition of rainfall can be reconstructed stable carbon isotopes of shell carbonate have also been studied but their interpretation is not clear amino acid epimerization analysis dalloisoleucinel isoleucine ratios of land snail shells has been used for estimation of paleotemperatures some potential uses of land snail shells for paleoenvironmental reconstruction include the study of stable isotopes of h and n periodic growth lines and deposits of pedogenic carbonates on the shells

characterization of mixing and dilution in heterogeneous aquifers by means of local temporal moments breakthrough curves of a conservative tracer in a heterogeneous two dimensional aquifer are analyzed by means of their temporal moments the average velocity and the longitudinal macrodispersion coefficient of the equivalent one dimensional aquifer obtained through cross sectional averaging of concentration can be defined from the first and second central moments of a breakthrough curve integrated over the outflow boundary of the domain on the basis of an integrated breakthrough curve one cannot distinguish between actual solute dilution which involves concentration reduction and variability of arrival times among parts of the plume at different cross sectional positions analyzing the temporal moments of breakthrough curves at a point within the domain gives additional information about the dilution of the tracer from these local first and second central moments an apparent seepage velocity a and an apparent dispersivity of mixing a can be derived for short travel distances a equals the local scale longitudinal dispersivity it increases with the travel distance but much more slowly than the macrodispersivity at the large distance limit a may eventually reach the level of macrodispersivity lenses of high conductivity where groundwater flow converges are identified as regions of preferential enhanced mixing the spatial distribution of these regions causes a high degree of variability of a within a domain indicating a high degree of uncertainty in the quantification of dilution at early stages in an accompanying paper cirpka and kitanidis this issue the results of conservative tracer transport are utilized for the study of mixing controlled reactive transport

mapping permeability in heterogeneous aquifers using hydrologic and seismic data a new method is presented for identification of the permeability distribution in near surface aquifers in addition to using the usual sparsely sampled pressure and permeability data the method incorporates densely sampled seismic data as obtained from a reflection or tomography survey along with empirical relationships between seismic and hydraulic properties the procedure is to first estimate by hydrologic inversion a pressure field then the velocity permeability pressure relationship is used to map the inverted pressure and measured seismic data to multivalued estimates of the permeability of those the most probable value based on the hydrologic inversion is selected in synthetic case studies the tremendous increase in coverage offered by the seismic data leads to dramatically better results in terms of both accuracy and resolution an appealing feature is the use of relatively easy to acquire pressure data a second is the incorporation of geophysical data which can sample an entire aquifer remotely without the need for an expensive and invasive drilling program

interaction between the atlantic meridional and nino modes 1 interaction between the tropical atlantic meridional and nino modes is investigated using observations and a quasi analytical linear equatorial wave model it is found that equatorial zonal wind stress anomalies associated with the boreal spring meridional mode generate eastward propagating equatorial kelvin waves in the central and eastern atlantic ocean where variability associated with the nino mode is strongest these same wind stress anomalies force westward propagating equatorial rossby waves that reflect at the western boundary into eastward propagating kelvin waves during boreal spring and summer the boundary generated kelvin waves are of the opposite sign to those directly forced by the winds earlier in the spring so they tend to damp the nino mode during boreal summer the interaction between the boreal spring meridional mode and the summer nino is therefore mediated by directly wind forced equatorial kelvin waves and the delayed negative feedback from western boundary reflections of wind forced rossby waves

the impacts of inter el nino variability on the tropical atlantic and northeast brazil climate abstractin this study observations and numerical simulations are used to investigate how different el nino events affect the development of sst anomalies in the atlantic and how this relates to the brazilian northeast ne precipitation the results show that different types of el nino have different impacts on the sst anomalies of the equatorial and tropical south atlantic but a similar sst response in the tropical north atlantic strong and long weak and short el ninos with the main heating source located in the eastern central pacific generate cold warm anomalies in the cold tongue and benguela upwelling regions during boreal winter and spring when the sst anomalies in the eastern equatorial and tropical south atlantic are cold warm the meridional sst gradient across the equator is positive negative and the itcz is not allowed allowed to move southward during the boreal spring as a consequence the precipitation is below above the average over the ne thus strong and long weak and s

main processes of the atlantic cold tongue interannual variability the interannual variability of the atlantic cold tongue act is studied by means of a mixed layer heat budget analysis a method to classify extreme cold and warm act events is proposed and applied to ten various analysis and reanalysis products this classification allows 5 cold and 5 warm act events to be selected over the period 1982 2007 cold warm act events are defined by the presence of negative positive sea surface temperature sst anomalies at the center of the equatorial atlantic in late boreal spring preceded by negative positive zonal wind stress anomalies in the western equatorial atlantic an ocean general circulation model capable of reconstructing the interannual variability of the act correctly is used to demonstrate that cold act events develop rapidly from may to june mainly due to intense cooling by vertical mixing and horizontal advection the simulated cooling at the center of the basin is the result of the combined effects of non local and local processes the non local process is an upwelling associated with an eastward propagating kelvin wave which makes the mixed layer more shallow and preconditions the upper layers to be cooled by an intense heat loss at the base of the mixed layer which is amplified by a stronger local injection of energy from the atmosphere the early cooling by vertical mixing in march is also shown to be a good predictor of june cooling in july horizontal advection starts to warm the mixed layer abnormally and damps sst anomalies the advection anomalies which result from changes in the horizontal temperature gradient are associated in some cases with the propagation of rossby waves along the equator during warm act events processes are reversed generating positive sst anomalies a downwelling kelvin wave triggers stratification anomalies and mixed layer depth anomalies amplified by a weaker injection of energy from the atmosphere in may june in july warm act events are abnormally cooled due to negative horizontal advection anomalies resulting from processes similar to those that occur during cold act events this additional cooling process extends the period of cooling of the act reducing sst anomalies

fully coupled hydrogeophysical inversion of a laboratory salt tracer experiment monitored by electrical resistivity tomography 1 we perform a salt tracer experiment monitored by time lapse electrical resistivity tomography in a quasi two dimensional sandbox with the aim of determining the hydraulic conductivity distribution in the domain we use sodium chloride as a tracer together with cochineal red for visual monitoring the time series of observed resistance for each electrode configuration is characterized by its temporal moments we invert the mean arrival time of electrical potential perturbations and a few steady state hydraulic head measurements using the fully coupled hydrogeophysical approach recently introduced by pollock and cirpka 2010 this is the first application of the approach to experimental data the results obtained show a reasonable agreement between the estimated hydraulic conductivity field and the pattern of the actual sandbox filling using this estimation a transient simulation is performed to compute the propagation of the salt tracer plume through the sandbox the latter is compared to pictures taken during the experiment these results show an even better agreement indicating that the lenses of different sand types are not entirely homogeneous and some unexpected preferential flow paths are present we conclude that temporal moments of potential perturbations obtained during salt tracer tests provide a good basis for inferring the hydraulic conductivity distribution by fully coupled hydrogeophysical inversion

borehole flowmeters field application and data analysis abstract this paper reviews application of borehole flowmeters in granular and fractured rocks basic data obtained in the field are the ambient flow log and the pumping induced flow log these basic logs may then be used to calculate other quantities of interest the paper describes the applications of the tennessee valley authority tva electromagnetic em flowmeter in a granular medium in an attempt to ascertain the effect of formation disturbance on flowmeter readings test wells were subjected to repeated periods of development using air lifting between the development periods flowmeter tests were run the results indicated that flowmeter data are not highly sensitive to formation disturbance in the near vicinity of a test well evidence of changes in the natural ambient flow in the test well was attributed to high variable rates of pumping by nearby chemical plants in fractured media flowmeters may be used to detect flow to or from individual fractures or fracture zones in these applications additional information in the form of caliper televiewer and resistivity logs are useful further studies of the type described herein are warranted

local earthquake le tomography with joint inversion for p and s wave velocities using structural constraints local earthquake le tomography with joint inversion for p and s wave velocities using structural constraints

climate science tropical atlantic warm events sea surface temperatures in the eastern equatorial atlantic ocean are subject to year to year variations reanalysis data and model simulations suggest that advection of warm water from north of the equator can drive some of the warm events

is there evidence of changes in tropical atlantic variability modes under amo phases in the observational record abstractthe atlantic multidecadal oscillation amo is the leading mode of atlantic sea surface temperature sst variability at multidecadal time scales previous studies have shown that the amo could modulate el nino southern oscillation enso variance however the role played by the amo in the tropical atlantic variability tav is still uncertain here it is demonstrated that during negative amo phases associated with a shallower thermocline the eastern equatorial atlantic sst variability is enhanced by more than 150 in boreal summer consequently the interannual tav modes are modified during negative amo the atlantic nino displays larger amplitude and a westward extension and it is preceded by a simultaneous weakening of both subtropical highs in winter and spring in contrast a meridional seesaw slp pattern evolving into a zonal gradient leads the atlantic nino during positive amo the north tropical atlantic nta mode is related to a scandinavian blocking pattern during winter and spring

influence of the atlantic zonal mode on monsoon depressions in the bay of bengal during boreal summer the influence of the atlantic zonal mode azm or the atlantic nia o on monsoon depressions in the bay of bengal during the boreal summer june august is studied our analysis shows that there is a statistically significant difference in the number of monsoon depressions in the bay of bengal between the warm and cold phases of the azm more fewer monsoon depressions form during the cold warm phase of azm it also shows that there are differences in spatial pattern of trajectories of monsoon depressions during the cold phase of azm the tracks are relatively long and seem to cluster along the axis of core monsoon region compared to the warm phase of azm the analysis indicates an increase a reduction in low level cyclonic vorticity and midtropospheric humidity but a reduction an increase in vertical wind shear due to anomalous circulation pattern all of these changes are favorable for the enhancement suppression of monsoon depressions during the cold warm phase of the azm our analysis further shows a teleconnection pathway by which the azm can influence the remote indian ocean this could have implications for enhancing monsoon prediction skill especially during non el nia o southern oscillation years key points influence of the azm on monsoon depressions during boreal summer cold warm azm increases decreases number of monsoon depressions the difference in large scale atmospheric conditions in the bob during azm

late pleistocene dune activity in the central great plains usa abstract stabilized dunes of the central great plains especially the megabarchans and large barchanoid ridges of the nebraska sand hills provide dramatic evidence of late quaternary environmental change episodic holocene dune activity in this region is now well documented but late pleistocene dune mobility has remained poorly documented despite early interpretations of the sand hills dunes as pleistocene relicts new optically stimulated luminescence osl ages from drill cores and outcrops provide evidence of late pleistocene dune activity at sites distributed across the central great plains in addition late pleistocene eolian sands deposited at 20 25 ka are interbedded with loess south of the sand hills several of the large dunes sampled in the sand hills clearly contain a substantial core of late pleistocene sand thus they had developed by the late pleistocene and were fully mobile at that time although substantial sand deposition and extensive longitudinal dune construction occurred during the holocene many of the late pleistocene osl ages fall between 17 and 14 ka but it is likely that these ages represent only the later part of a longer period of dune construction and migration at several sites significant late pleistocene or holocene large dune migration also probably occurred after the time represented by the pleistocene osl ages sedimentary structures in late pleistocene eolian sand and the forms of large dunes potentially constructed in the late pleistocene both indicate sand transport dominated by northerly to westerly winds consistent with late pleistocene loess transport directions numerical modeling of the climate of the last glacial maximum has often yielded mean monthly surface winds southwest of the laurentide ice sheet that are consistent with this geologic evidence despite strengthened anticyclonic circulation over the ice sheet mobility of large dunes during the late pleistocene on the central great plains may have been the result of cold short growing seasons with relatively low precipitation and low atmospheric co 2 that increased plant moisture stress limiting the ability of vegetation to stabilize active dune sand the apparent coexistence of large mobile dunes with boreal forest taxa suggests a late pleistocene environment with few modern analogs

three dimensional imaging of the p and s wave velocity structure and earthquake locations beneath southwest iceland three dimensional imaging of the p and s wave velocity structure and earthquake locations beneath southwest iceland

is the boreal spring tropical atlantic variability a precursor of the equatorial mode the equatorial mode em governs the tropical atlantic inter annual variability during boreal summer it has profound impacts on the climate of adjacent and remote areas however predicting the em is one of the most challenging and intriguing issues for the scientific community recent studies have suggested a possible connection between the boreal spring meridional mode mm and the em through ocean wave propagation here we use a set of sensitivity experiments with a medium resolution ocean model to determine the precursor role of a mm to create equatorial sst variability our results demonstrate that boreal summer equatorial ssts following a mm are subject to two counteracting effects the local wind forcing and remotely excited oceanic waves for a positive mm the anomalous easterly winds blowing along the equator shallow the thermocline cooling the sea surface via vertical diffusion and meridional advection anomalous wind curl excites a downwelling rossby wave north of equator which is reflected at the western boundary becoming an equatorial kelvin wave kw this downwelling kw propagates eastward deepening the thermocline and activating the thermocline feedbacks responsible for the equatorial warming moreover the local wind forcing and rw reflected mechanism have a significant and comparable impact on the equatorial sst variability changes in the intensity and persistence of these distinct forcings will determine the equatorial sst response during boreal summer our results give a step forward to the improvement of the em predictability

late pleistocene and holocene seasonal temperatures reconstructed from fossil beetle assemblages in the rocky mountains abstract mutual climatic range mcr analysis was applied to 20 fossil beetle assemblages from 11 sites dating from 14 500 to 400 yr b p the fossil sites represent a transect of the rocky mountain region from northern montana to central colorado the analyses yielded estimates of mean july and mean january temperatures the oldest assemblage 14 500 yr b p yielded mean july values of 10 11 c colder than present and mean january values 26 30 c colder than present postglacial summer warming was rapid as indicated by an assemblage dating 13 200 yr b p with mean july values only 3 4 c cooler than modern by 10 000 yr b p several assemblages indicate warmer than modern mean summer and winter values by 9000 yr b p mcr reconstructions indicate that both summer and winter temperatures were already declining from an early holocene peak mean july values remained above modern levels and mean january values remained below modern levels until 3000 yr b p a series of small scale oscillations followed

a field assessment of high resolution aquifer characterization based on hydraulic travel time and hydraulic attenuation tomography 1 in this study the potential of an inversion approach based on hydraulic travel time and hydraulic attenuation tomography was assessed both hydraulic travel time and hydraulic attenuation tomography are based on the transformation of the transient groundwater flow equation into the eikonal equation using an asymptotic approach the eikonal equation allows the calculation of pressure propagation and attenuation along trajectories which is computationally efficient the attenuation and travel time based inversion approaches are naturally complementary hydraulic travel times are determined by the hydraulic diffusivity a combination of hydraulic conductivity and specific storage whereas the attenuation is determined solely by specific storage the potential of our hydraulic tomographical approach was investigated at a well characterized sand and gravel aquifer located in the leine river valley near gottingen germany the database for the hydraulic inversion consists of 392 cross well slug interference tests performed between five wells in which the positions of the sources injection ports and the receivers observation ports isolated with double packer systems were varied between tests the results have shown that the combination of hydraulic travel time and hydraulic attenuation tomography allows the reconstruction of the diffusivity and storage distribution in two and three dimensions with a resolution and accuracy superior to that possible with type curve analysis

three dimensional stochastic estimation of porosity distribution benefits of using ground penetrating radar velocity tomograms in simulated annealing based or bayesian sequential simulation approaches 1 estimation of the three dimensional 3 d distribution of hydrologic properties and related uncertainty is a key for improved predictions of hydrologic processes in the subsurface however it is difficult to gain high quality and high density hydrologic information from the subsurface in this regard a promising strategy is to use highresolution geophysical data that are relatively sensitive to variations of a hydrologic parameter of interest to supplement direct hydrologic information from measurements in wells e g logs vertical profiles and then generate stochastic simulations of the distribution of the hydrologic property conditioned on the hydrologic and geophysical data in this study we develop and apply this strategy for a 3 d field experiment in the heterogeneous aquifer at the boise hydrogeophysical research site and we evaluate how much benefit the geophysical data provide we run high resolution 3 d conditional simulations of porosity with both simulated annealing based and bayesian sequential approaches using information from multiple intersecting crosshole gound penetrating radar gpr velocity tomograms and neutron porosity logs the benefit of using gpr data is assessed by investigating their ability when included in conditional simulation to predict porosity log data withheld from the simulation results show that the use of crosshole gpr data can significantly improve the estimation of porosity spatial distribution and reduce associated uncertainty compared to using only well log measurements for the estimation the amount of benefit depends primarily on the strength of the petrophysical relation between the gpr and porosity data the variability of this relation throughout the investigated site and lateral structural continuity at the site

characteristics of subsurface ocean response to enso assessed from simulations with the ncep climate forecast system abstractthe subsurface ocean temperature response to el nino southern oscillation enso is examined based on 31 yr 1981 2011 simulations with the national centers for environmental prediction ncep climate forecast system cfs coupled model the model sea surface temperature sst in the tropical pacific is relaxed to observations to ensure realistic enso variability in the simulations in the tropical pacific the subsurface temperature response to the enso sst is closely related to the variability of thermocline the subsurface response is stronger and deeper in the tropical indian ocean than in the tropical atlantic the analysis at three selected locations reveals that the peak response of the subsurface temperature to enso lags the nino 3 4 sst by 3 6 and 6 months respectively in the southern tropical indian ocean the northern tropical atlantic and the north pacific where ssts are also known to be strongly influenced by enso the enso forced temperature anomalies gradually penetrate to the

decadal and interannual sst variability in the tropical atlantic ocean abstract the mechanisms regulating interannual and decadal variations of sea surface temperature sst in the tropical atlantic are examined observed variations of sea surface temperature are typically in the range of 0 3 0 5 c and are linked to fluctuations in rainfall on both the african and south american continents the authors use a numerical model to simulate the observed time series of sea surface temperature for the period 1960 1989 based on the results experiments are conducted to determine the relative importance of heat flux and momentum forcing two dominant timescales for variability of sst are identified a decadal timescale that is controlled by latent heat flux anomalies and is primarily responsible for sst anomalies off the equator and an equatorial mode with a timescale of 2 5 years that is dominated by dynamical processes the interhemispheric gradient of anomalous sst the sst dipole is primarily linked to the former process and thus results from the gradual strengthening and weak

pacific influences on tropical atlantic teleconnections to the southern hemisphere high latitudes abstractseveral recent studies have connected antarctic climate variability to tropical atlantic sea surface temperatures sst proposing a rossby wave response from the atlantic as the primary dynamical mechanism in this investigation reanalysis data and atmospheric general circulation model experiments are used to further diagnose these dynamical links focus is placed on the possible mediating role of pacific processes motivated by the similar spatial characteristics of southern hemisphere sh teleconnections associated with tropical atlantic and pacific sst variability during austral winter jja both reanalyses and model simulations reveal that atlantic teleconnections represent a two mechanism process whereby increased tropical atlantic sst promotes two conditions 1 an intensification of the local atlantic hadley circulation hc driven by enhanced interaction between sst anomalies and the itcz that increases convergence at the descending branch establishing anomalous vorticity forcing

multiple causes of interannual sea surface temperature variability in the equatorial atlantic ocean the tropical atlantic ocean shows sea surface temperature variability on interannual timescales observational and model data suggest that some of this variability can be attributed to the advection of anomalously warm northern subtropical waters toward the equator

efficient three dimensional data inversion soil characterization and moisture monitoring from cross well ground penetrating radar at a vermont test site we extend our methodology for three dimensional parameter structure and value estimation and apply it to a vermont test site ground penetrating radar gpr cross well travel times are inverted for estimation of heterogeneous gpr soil velocities before and after a controlled release of salt water in the unsaturated zone the method which is based on an approximation of the extended kaiman filter in conjunction with data driven zonation automatically estimates not only distributed zone values but also the number of zones zone geometry and zone covariance resultant gpr velocity estimates are shown to reduce travel time estimation errors and to be consistent with independent cone penetrometer measurements at all five walls at the site comparison of velocity estimates before and after forced injection of salt water is used to detect and visualize soil moisture patterns in three dimensions by varying the cluster tolerance criterion in the data driven zonation process the user can obtain a desired resolution of heterogeneity number of zones used in the resultant model

structure of interannual to decadal climate variability in the tropical atlantic sector abstract a search for coupled modes of atmosphere ocean interaction in the tropical atlantic sector is presented previous studies have provided conflicting indications of the existence of coupled modes in this region the subject is revisited through a rotated principal component analysis performed on datasets spanning the 36 yr period 1958 93 the analysis includes four variables sea surface temperature oceanic heat content wind stress and atmospheric diabatic heating the authors find that the first rotated principal component is associated with fluctuations in the subtropical wind system and correlates with the north atlantic oscillation nao while the second and third modes which are the focus of interest are related to tropical variability the second mode is the atlantic nino mode with anomalous sea surface temperature and anomalous heat content in the eastern equatorial basin wind stress weakens to the west of anomalously warm water while convection is shifted south and eastward surface

analysis of coleopterans from late holocene natural spring deposits in south central sweden abstract the usage history of a natural spring deposit in associated glacial till was investigated via analysis of coleopteran remains found in peat this material was recovered during archaeological excavations in a spring outflow in south central sweden the geographical region of southern sweden has been heavily affected by uplift following the terminal glaciation weichselian in scandinavia with the study area for this project having risen above sea level about 1200 bc the spring was found in connection to the northern part of a large settlement and religious area dating from the younger bronze age and pre roman iron age 1100 300 bc however the area has been used for agricultural land up until the present day sampling was conducted for interpretation of the usage history of the site with the insect fragments showing exceptional preservation as a result of unusual conditions in the sediments 14 c dating from the lower to upper part of the spring yielded a stratigraphic range of 670 870 to 660 810 ad respectively a half circle boulder construction provides clear evidence that the spring was used early in prehistory probably during the bronze age and potentially excavated at irregular periods the coleopteran assemblage was dominated by beetles indicative of open landscapes grazing land and forested environments this closely resembles the vegetation setting of today in which the spring is situated on the border between arable land and mixed deciduous and coniferous forest a high frequency of carabid beetles suggests that the spring may have functioned as a pitfall trap and correlated well with the relative inorganic to organic compound composition of the ground conditions the spring was probably abandoned in the late iron age 600 800 ad identification of two red listed threatened species that are not present in the current fauna implies that radical change in the agricultural landscape over the last 1200 years could be negatively affecting diversity dynamics within the local fauna

robust geophysical integration through structure coupled joint inversion and multispectral fusion of seismic reflection magnetotelluric magnetic and gravity images example from santos basin offshore brazil abstractwe have applied a crossgradient joint inversion and geospectral visualization method to marine seismic reflection magnetotelluric gravity and magnetic data sets acquired along a 162 km profile across a segment of santos basin oil province in the continental margin of southeast brazil the main exploration targets are the top of the fractured precambrian crystalline basement and any concealed basement grabens the overlying presalt and salt carbonate deposits and the postsalt cover deposits the results of joint inversion clearly mapped the various units and are a significant improvement over previous models derived from separate 2d seismic reflection processing and 2d magnetotelluric imaging additionally multispectral fusion of these models resulted in a single image that permits highly constrained geologic interpretations enabling a better understanding of basin architecture we suggest that joint inversion and image fusion is the way forward for effective geophysical integration

characterization of heterogeneous near surface materials by joint 2d inversion of dc resistivity and seismic data 1 we have developed a robust 2d joint inversion scheme incorporating the new concept of cross gradients of electrical resistivity and seismic velocity as constraints so as to investigate more precisely the resistivity velocity relationships in complex near surface environments the results of joint inversion of dc resistivity and seismic traveltime data from collocated experiments suggest that one can distinguish between different types or facies of unconsolidated and consolidated materials refining a previously proposed resistivity velocity interrelationship derived from separate inversions of the respective data sets a consistent interpretive structural model can be obtained from the joint inversion models

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

accelerator radiocarbon dating at the molecular level molecular level 14c dating is the isolation of specific classes of molecules for their 14c dating by accelerator mass spectrometry ams complex matrices such as fossil bone are difficult to date due to their extreme chemical heterogeneity by isolating individual amino acids contaminants humates are removed and crystalline amino acids result bones with 0 1 0 2 n and collagenous compositions can be dated accurately because structural collagen is present contaminants are removable with xad resin bones with 0 1 n and non collagenous compositions yield dates hundreds to thousands of years too young because most of the preserved organic matter is exogenous accelerator 14c dates on collagenous and non collagenous bones are not comparable due to intrinsic dating inaccuracies ams 14c dating of amino acids demonstrated that 1 post 10 800 year ages for north american megafauna are due to sample contamination not holocene ages on extinct fauna 2 a clovis age 10 900 years was established for a human fossil from the anzick site montana 3 holocene ages cannot be established absolutely for many north american human fossils because the bones were non collagenous 4 accurate ages are attainable on vertebrate fossils as small as passerine birds from pacific island localities 5 well preserved bones are datable without their destruction by extracting protein with water at high temperatures and 6 stratigraphic anomalies to 45 000 years in european upper paleolithic rock shelters are recognizable by dating bone directly

three dimensional high resolution fluvio glacial aquifer analog part 1 field study summary describing the complex structures that exist in many sedimentary aquifers is crucial for reliable groundwater flow and transport simulation however hardly any aquifer can be inspected in such detail that all decimeter to meter heterogeneity is resolved aquifer analogs serve as surrogates to construct models of equivalent heterogeneity and thus imitate those features relevant for flow or transport processes gravel pits found in excavation show excellent sections of the sedimentary sequence and thus offer direct insight into the structural and textural composition of the subsoil this paper describes an approach to also inspect the third dimension by mapping during the ongoing excavation it is possible to obtain a three dimensional representation of the subsurface within a short period of time a detailed description of a case study is presented and the findings from sedimentological hydrogeological and geophysical analyses are compared the gravel pit is located near the town of herten in southwest germany where relatively young unconsolidated fluvio glacial and fluvial sediments in the rhine basin are mined the excavated gravel body is built up by architectural elements typical for braided river deposits the study generated a high resolution data set of lithofacies hydrofacies and ground penetrating radar gpr profiles it represents the basis for a full three dimensional geostatistical reconstruction presented in the second part comunian et al 2011

joint two dimensional dc resistivity and seismic travel time inversion with cross gradients constraints it is now common practice to perform collocated dc resistivity and seismic refraction surveys that complement each other in the search for more accurate characterization of the subsurface although conventional separate dc resistivity and seismic models can be diagnostic we posit that better results can be derived from jointly estimated models we make the assumption that both methods must be sensing the same underlying geology and have developed an innovative resistivity velocity cross gradients relationship to evaluate the structural features common to both methods the cross gradients function is incorporated as a constraint in a nonlinear least squares problem formulation which is solved using the lagrange multiplier method the resultant iterative two dimensional 2 d joint inversion scheme is successfully applied to synthetic data serving as validation tests here and to field data from collocated dc resistivity and seismic refraction profiling experiments and also compared to conventional separate inversion results the joint inversion results are shown to be superior to those from separate 2 d inversions of the respective data sets since our algorithm leads to resistivity and velocity models with remarkable structural agreement

regional patterns of sea level change related to interannual variability and multidecadal trends in the atlantic meridional overturning circulation some studies of ocean climate model experiments suggest that regional changes in dynamic sea level could provide a valuable indicator of trends in the strength of the atlantic meridional overturning circulation moc this paper describes the use of a sequence of global ocean ice model experiments to show that the diagnosed patterns of sea surface height ssh anomalies associated with changes in the moc in the north atlantic na depend critically on the time scales of interest model hindcast simulations for 1958 2004 reproduce the observed pattern of ssh variability with extrema occurring along the gulf stream gs and in the subpolar gyre spg but they also show that the pattern is primarily related to the wind driven variability of moc and gyre circulation on interannual time scales it is reflected also in the leading eof of ssh variability over the na ocean as described in previous studies the pattern however is not useful as a fingerprint of longer term changes in the moc as shown with a companion experiment a multidecadal gradual decline in the moc of 5 sv 1 sv 106 m3 s 1 over 5 decades induces a much broader basin scale ssh rise over the mid to high latitude na with amplitudes of 20 cm the detectability of such a trend is low along the gs since low frequency ssh changes are effectively masked here by strong variability on shorter time scales more favorable signal to noise ratios are found in the spg and the eastern na where a moc trend of 0 1 sv yr 1 would leave a significant imprint in ssh already after about 20 years

on the connection between benguela and equatorial atlantic ninos and the role of the south atlantic anticyclone for the eastern tropical atlantic two recurring el nino like phenomena with high interannual sst anomalies have been described one centered in the equatorial region as part of the atlantic zonal mode and one off angola referred to as benguela nino both events are supposed to be generated not locally but by a relaxation of the trade winds in the western equatorial atlantic here the connection between sst variations in the two regions is investigated with observational data sets as well as ocean model simulations they are correlated to such an extent that joint events should rather be viewed as one atlantic nino an intriguing feature counterintuitive in view of the remote forcing mechanism is that sst anomalies off angola precede those in the equatorial atlantic we show this behavior to be related to the difference in thermocline depths and a different seasonality of interannual sst variability in the two regions while benguela ninos peak in austral fall due to the angola benguela front being located furthest to the south and high interannual variability in coastal kelvin wave activity warm events at the equator are phase locked to austral winter when the thermocline is shallow perturbation experiments confirm the importance of remote forcing from the equator for sst variability off angola and demonstrate the leading role of wind stress in the generation of sst anomalies in the eastern tropical atlantic these wind stress variations are shown to be linked to fluctuations in the strength of the south atlantic anticyclone a connection that might be important with respect to the predictability of atlantic ninos

saline tracer visualized with three dimensional electrical resistivity tomography field scale spatial moment analysis 1 cross well electrical resistivity tomography ert was used to monitor the migration of a saline tracer in a two well pumping injection experiment conducted at the massachusetts military reservation in cape cod massachusetts after injecting 2200 mg l of sodium chloride for 9 hours ert data sets were collected from four wells every 6 hours for 20 days more than 180 000 resistance measurements were collected during the tracer test each ert data set was inverted to produce a sequence of 3 d snapshot maps that track the plume in addition to the ert experiment a pumping test and an infiltration test were conducted to estimate horizontal and vertical hydraulic conductivity values using modified moment analysis of the electrical conductivity tomograms the mass center of mass and spatial variance of the imaged tracer plume were estimated although the tomograms provide valuable insights into field scale tracer migration behavior and aquifer heterogeneity standard tomographic inversion and application of archie s law to convert electrical conductivities to solute concentration results in underestimation of tracer mass such underestimation is attributed to 1 reduced measurement sensitivity to electrical conductivity values with distance from the electrodes and 2 spatial smoothing regularization from tomographic inversion the center of mass estimated from the ert inversions coincided with that given by migration of the tracer plume using 3 d advective dispersion simulation the 3 d plumes seen using ert exhibit greater apparent dispersion than the simulated plumes and greater temporal spreading than observed in field data of concentration breakthrough at the pumping well

hydrostratigraphic analysis of the made site with full resolution gpr and direct push hydraulic profiling 1 f ull resolution 3d ground penetrating radar gpr data were combined with high resolution hydraulic conductivity k data from vertical direct push dp profiles to characterize a portion of the highly heterogeneous macro dispersion experiment made site this is an important first step to better understand the influence of aquifer heterogeneities on observed anomalous transport statistical evaluation of dp data indicates non normal distributions that have much higher similarity within each gpr facies than between facies the analysis of gpr and dp data provides high resolution estimates of the 3d geometry of hydrostratigraphic zones which can then be populated with stochastic k fields the lack of such estimates has been a significant limitation for testing and parameterizing a range of novel transport theories at sites where the traditional advection dispersion model has proven inadequate citation dogan m r l van dam g c bohling j j butler jr and d w hyndman 2011 hydrostratigraphic analysis of the made site with full resolution gpr and direct push hydraulic profiling geophys res lett 38 l06405 doi 10 1029 2010gl046439

enso influence on the atlantic nino revisited multi year versus single year enso events abstractthe influence of el nino southern oscillation enso on the atlantic nino over the past 113 years is investigated by comparing multi year and single year enso events multi year enso events

variability in the south atlantic anticyclone and the atlantic nino mode sea surface temperature sst anomalies in the eastern equatorial atlantic are connected to modulations in the strength of the south atlantic subtropical high pressure system referred to as the south atlantic anticyclone saa using ocean and atmosphere reanalysis products we show here that the strength of the saa from february to may impacts the timing of the cold tongue onset and the intensity of its development in the eastern equatorial atlantic eea via anomalous tropical wind power this modulation of the timing and amplitude of the seasonal cold tongue development manifests as anomalous sst events peaking between june and august the timing and impact of this connection is not completely symmetric for warm and cold events for cold events an anomalously strong saa in february and march leads to positive wind power anomalies from february to june resulting in an early cold tongue onset and subsequent cold sst anomalies in june and july for warm events the anomalously weak saa persists until may generating negative wind power anomalies that lead to a late cold tongue onset as well as a suppression of the cold tongue development and associated warm sst anomalies mechanisms by which saa induced wind power variations south of the equator influence eea sst are discussed including ocean adjustment via rossby and kelvin wave propagation meridional advection and local intraseasonal wind variations

asymmetry in zonal phase propagation of enso sea surface temperature anomalies 1 it is often emphasized in the literature that the phase propagation of el nino sea surface temperature sst anomalies along the equator changed from westward to eastward after a mid to late 1970s climate regime shift in the pacific theories have been developed to explain this change of phase propagation in terms of changes in background state on which el nino events develop those theories also suggest that the direction of la nina anomaly phase propagation should have changed from westward to eastward as well however the direction of la nina sst anomaly phase propagation did not change after the mid to late 1970s instead la nina ssts continued to exhibit westward phase propagation along the equator a feature overlooked in both observational analyses and theories this paper highlights the asymmetry in zonal phase propagation between el nino and la nina sea surface temperature anomalies since 1980 and discusses the implications of that asymmetry for understanding el nino southern oscillation enso dynamics

influence of el nino on the upper ocean circulation in the tropical atlantic ocean abstract this study investigates the influence of el nino on the upper ocean circulation in the tropical atlantic ocean via changes in the atlantic trade winds by analyzing observed sea surface temperature sst together with an ocean general circulation model integration forced by the ncep ncar reanalysis during periods with anomalously warm cold eastern equatorial pacific sst the southern atlantic tropical cell is strengthened weakened the difference of the cell strength between el nino and la nina years is about 20 of the mean cell strength however the variability of the cell is not dominated by the remote forcing from the eastern equatorial pacific but seems to be caused by intrinsic tropical atlantic variability a strengthening weakening for periods with anomalously warm cold eastern equatorial pacific sst is also found for the zonal surface and subsurface currents topex poseidon altimetry data are used to validate the results based on the ogcm integration

phase locking of equatorial atlantic variability through the seasonal migration of the itcz the equatorial atlantic is marked by significant interannual variability in sea surface temperature sst that is phase locked to late boreal spring and early summer the role of the atmosphere in this phase locking is examined using observations reanalysis data and model output the results show that equatorial zonal surface wind anomalies which are a main driver of warm and cold events typically start decreasing in june despite sst and sea level pressure gradient anomalies being at their peak during this month this behavior is explained by the seasonal northward migration of the intertropical convergence zone itcz in early summer the north equatorial position of the atlantic itcz contributes to the decay of wind anomalies in three ways 1 horizontal advection associated with the cross equatorial winds transports air masses of comparatively low zonal momentum anomalies from the southeast toward the equator 2 the absence of deep convection leads to changes in vertical momentum transport that reduce the equatorial wind anomalies at the surface while anomalies aloft remain relatively strong 3 the cross equatorial flow is associated with increased total wind speed which increases surface drag and deposit of momentum into the ocean previous studies have shown that convection enhances the surface wind response to sst anomalies the present study indicates that convection also amplifies the surface zonal wind response to sea level pressure gradients in the western equatorial atlantic where sst anomalies are small this introduces a new element into coupled air sea interaction of the tropical atlantic

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

a comparative stability analysis of atlantic and pacific nino modes abstractel nino southern oscillation enso in the pacific and the analogous atlantic nino mode are generated by processes involving coupled ocean atmosphere interactions known as the bjerknes feedback it has been argued that the atlantic nino mode is more strongly damped than enso which is presumed to be closer to neutrally stable in this study the stability of enso and the atlantic nino mode is compared via an analysis of the bjerknes stability index this index is based on recharge oscillator theory and can be interpreted as the growth rate for coupled modes of ocean atmosphere variability using observational data an ocean reanalysis product and output from an ocean general circulation model the individual terms of the bjerknes index are calculated for the first time for the atlantic and then compared to results for the pacific positive thermocline feedbacks in response to wind stress forcing favor anomaly growth in both basins but they are twice as large in the pacific compared to the atlanti

teleconnections of the tropical atlantic and pacific oceans in a cmip5 model ensemble this study investigates the teleconnections between the tropical atlantic and pacific oceans in 15 state of the art fully coupled general circulation models and earth system models without external sst forcing in contrast to other studies the teleconnection is considered in both directions from the pacific to the atlantic and from the atlantic to the pacific the model ensemble is generally able to simulate the propagation of atmospheric and oceanic signals to the adjacent ocean basin generated by warm sea surface temperature sst anomalies in the tropical eastern oceans with atlantic summer events lagging or leading pacific boreal winter events this is investigated by means of time lagged composite analyses of different atmospheric parameters including sea level pressure wind stream function velocity potential vertical air movement and divergent wind at several levels however the modelled inter basin teleconnection and its correct frequency of occurrence depend on the strong warm sst biases in the atlantic benguela upwelling region and in the pacific ocean

crosshole gpr full waveform inversion of waveguides acting as preferential flow paths within aquifer systems high contrast layers caused by porosity or clay content changes can have a dominant effect on hydraulic processes within an aquifer these layers can act as low velocity waveguides for gpr waves we used a field example from a hydrological test site in switzerland to show that fullwaveform inversion of crosshole gpr signals could image a subwavelength thickness low velocity waveguiding layer we exploited the full information content of the data whereas ray based inversion techniques are not able to image such thin waveguide layers because they only exploit the first arrival times and first cycle amplitudes this lowvelocity waveguide layer is caused by an increase in porosity and indicates a preferential flow path within the aquifer the waveguide trapping causes anomalously high amplitudes and elongated wavetrains to be observed for a transmitter within thewaveguide and receivers straddling thewaveguide depth range the excellent fit of amplitudes and phase between the measured and modeled data confirms its presence this new method enables detailed aquifer characterization to accurately predict transport and flow and can be applied to a wide range of geologic hydrological and engineering investigations

improved extraction of hydrologic information from geophysical data through coupled hydrogeophysical inversion 1 there is increasing interest in the use of multiple measurement types including indirect geophysical methods to constrain hydrologic interpretations to date most examples integrating geophysical measurements in hydrology have followed a three step uncoupled inverse approach this approach begins with independent geophysical inversion to infer the spatial and or temporal distribution of a geophysical property e g electrical conductivity the geophysical property is then converted to a hydrologic property e g water content through a petrophysical relation the inferred hydrologic property is then used either independently or together with direct hydrologic observations to constrain a hydrologic inversion we present an alternative approach coupled inversion which relies on direct coupling of hydrologic models and geophysical models during inversion we compare the abilities of coupled and uncoupled inversion using a synthetic example where surface based electrical conductivity surveys are used to monitor one dimensional infiltration and redistribution through this illustrative example we show that the coupled approach can provide significant reductions in uncertainty for hydrologic properties and associated predictions if the underlying model is a faithful representation of the hydrologic processes however if the hydrologic model exhibits structural errors the coupled inversion may not improve the hydrologic interpretation despite this limitation our results support the use of coupled hydrogeophysical inversion both for the direct benefits of reduced errors during inversion and because of the secondary benefits that accrue because of the extensive communication and sharing of data necessary to produce a coupled model which will likely lead to more thoughtful use of geophysical data in hydrologic studies

origin of the late quaternary dune fields of northeastern colorado stabilized eolian deposits mostly parabolic dunes and sand sheets cover much of the landscape of northeastern colorado and adjacent parts of southwestern nebraska in four geographically distinct dune fields stratigraphic and soil geomorphic relations and accelerator radiocarbon dating indicate that at least three episodes of eolian sand movement occurred between 27 ka and 11 ka possibly between 11 ka and 4 ka and within the past 1 5 ka thus eolian sand deposition took place under both glacial and interglacial climatic conditions in the youngest episodes of eolian sand movement holocene parabolic dunes partially buried pleistocene sand sheet deposits late holocene sands in the fort morgan and wray dune fields to the south of the south platte river have trace element ratios that are indistinguishable from modern south platte river sands but different from ogallala formation bedrock which has previously been cited as the main source of dune sand on the great plains sands in the greeley dune field to the north of the south platte river have trace element concentrations that indicate a probable laramie formation source measurements of parabolic dunes indicate paleowinds from the northwest in all dune fields in good agreement with resultant drift directions calculated for nearby weather stations thus paleowinds were probably not significantly different from present day winds and are consistent with a south platte river source for the fort morgan and wray dune fields and a laramie formation source for the greeley dune field sand accumulated downwind of the south platte river to form the fort morgan duen field in addition sand was also transported farther downwind over the upland formed by the calcrete caprock of the ogallala formation and deposited in the lee of the upland on the southeast side because of high wind energy the upland itself served as a zone of sand transport but little or no sand accumulation took place on this surface these studies which demonstrate the importance of fluvial source sediments for dune fields in colorado may be applicable to other dune fields in north america because modern drift potentials in northeastern colorado are among the highest in the world the present stability of dunes in the region may be in part a function of the dunes being supply limited rather than solely transport limited extensive 7700 km2 late holocene dunes document that eolian sand in northeastern colorado is very sensitive to small changes in climate or fluvial source conditions