bluuebunny/crossref_metadata_2025 huggingface dataset:
Event-related potentials in semantic memory retrieval
Authors: BRIER MATTHEW R. , MAGUIRE MANDY J. , TILLMAN GAIL D. , HART JOHN , KRAUT MICHAEL A.
Published: September 2008

The involvement of the left temporal lobe in semantics and object naming has been repeatedly demonstrated in the context of language comprehension; however, its role in the mechanisms and time course for the retrieval of an integrated object memory from its constituent features have not been well delineated. In this study, 19 young adults were presented with two features of an object (e.g., “desert” and “humps”) and asked to determine whether these two features were congruent to form a retrieval of a specific object (“camel”) or incongruent and formed no retrieval while event-related potentials (ERP) were recorded. Beginning around 750 ms the ERP retrieval and nonretrieval waveforms over the left anterior fronto-temporal region show significance differences, indicating distinct processes for retrievals and nonretrievals. In addition to providing further data implicating the left frontal-anterior temporal region in object memory/retrieval, the results provide insight into the time course of semantic processing related to object memory retrieval in this region. The likely semantic process at 750 ms in this task would be coactivation of feature representations common to the same object. The consistency of this finding suggests that the process is stable across individuals. The potential clinical applications are discussed. (JINS, 2008, 14, 815–822.)
Predictors of prospective memory in adults with traumatic brain injury
Authors: FLEMING JENNIFER , RILEY LEE , GILL HANNAH , GULLO MATTHEW J. , STRONG JENNY , SHUM DAVID
Published: September 2008

Previous studies have established that prospective memory is commonly affected following traumatic brain injury (TBI). This study examines whether demographic factors, injury severity and site, executive function, and metacognitive factors predict prospective memory performance in adults with TBI, using a cross-sectional multivariate correlational model. Prospective memory of 44 adults (mean age = 30 years) with severe TBI was measured by the Cambridge Prospective Memory Test (CAMPROMPT) time-based and event-based scores. Using stepwise multiple regression, the time-based score was predicted by the Controlled Oral Word Association Test (COWAT) Animals subtest score, length of post-traumatic amnesia (PTA) and use of note-taking on the CAMPROMPT. The event-based score was predicted by length of PTA and COWAT Animals score. Therefore, patients with longer periods of PTA and executive function impairment may be expected to display poorer prospective memory. Note-taking was associated with improved performance on time-based prospective memory tasks. (JINS, 2008,14, 823–831.)
Puppets, robots, critics, and actors within a taxonomy of attention for developmental disorders
Authors: DENNIS MAUREEN , SINOPOLI KATIA J. , FLETCHER JACK M. , SCHACHAR RUSSELL
Published: September 2008

This review proposes a new taxonomy of automatic and controlled attention. The taxonomy distinguishes among the role of the attendee (puppet and robot, critic and actor), the attention process (stimulus orienting vs. response control), and the attention operation (activation vs. inhibition vs. adjustment), and identifies cognitive phenotypes by which attention is overtly expressed. We apply the taxonomy to four childhood attention disorders: attention deficit hyperactivity disorder, spina bifida meningomyelocele, traumatic brain injury, and acute lymphoblastic leukemia. Variations in attention are related to specific brain regions that support normal attention processes when intact, and produce disordered attention when impaired. The taxonomy explains group differences in behavioral inattention, hyperactivity, and impulsiveness, as well as medication response. We also discuss issues relevant to theories of the cognitive and neural architecture of attention: functional dissociations within and between automatic and controlled attention; the relative importance of type of brain damage and developmental timing to attention profile; cognitive-energetic models of attention and white matter damage; temporal processing deficits, attention deficits and cerebellar damage; and the issue of cognitive phenotypes as candidate endophenotypes. (JINS, 2008,14, 673–690.)
Contribution of right hemisphere to visual imagery: A visual working memory impairment?
Authors: GASPARINI MARINA , HUFTY ANNE MARIE , MASCIARELLI GIOVANNI , OTTAVIANI DONATELLA , ANGELONI UGO , LENZI GIAN LUIGI , BRUNO GIUSEPPE
Published: September 2008

Visual Imagery is the ability to generate mental images in the absence of perception, that is, “seeing with the mind's eye.” We describe a patient, IM, who suffered from an acute ischemic stroke in the right anterior choroidal artery who appeared to demonstrate relatively isolated impairment in visual imagery. Her cognitive function, including her performance on tests of semantic function, was at ceiling, apart from a deficit in visual memory. IM failed in tasks involving degraded stimuli, object decision involving reality judgments on normal animals, and drawings from memory. By contrast, she was able to match objects seen from an unfamiliar viewpoint and to perform tasks of semantic and visual association. We hypothesize that IM has a visual working memory deficit that impairs her ability to generate full visual representations of objects given their names, individual feature, or partial representations. The deficit appears to be the result of damage to connections between the right thalamus and the right temporal lobe. Our findings may help to clarify the role of the thalamus in the cortical selective engagement processes that underlie working memory. (JINS, 2008, 14, 902–911.)
Cognitive and adaptive deficits in young children with Duchenne muscular dystrophy (DMD)
Authors: CYRULNIK SHANA E. , FEE ROBERT J. , BATCHELDER ABIGAIL , KIEFEL JACQUELINE , GOLDSTEIN EDWARD , HINTON VERONICA J.
Published: September 2008

The goal of the current investigation was to examine adaptive behavior and cognitive skills in young children with Duchenne muscular dystrophy (DMD), a genetic disorder that causes progressive muscular weakness and concomitant cognitive deficits. Previous studies have documented specific language deficits in older children with DMD, but there are limited data on younger children. Twenty children with DMD who were between 3 and 6 years old and 20 unaffected family control children were recruited. Parents completed questionnaires relating to development and adaptive functioning, while children completed neuropsychological testing. Results of pairedttests indicate that children with DMD are rated as delayed relative to familial controls on measures of adaptive functioning, as assessed by the Vineland Adaptive Behavior Scales. Furthermore, children with DMD exhibit impairments on multiple measures of cognition, including measures of receptive language, expressive language, visuo-spatial skills, fine-motor skills, attention, and memory skills. Across all domains examined, the young children with DMD performed more poorly than their familial controls. These deficits appear to be more generalized than those reported in older children with this disorder. Dystrophin, a missing protein product, is hypothesized to be responsible for these cognitive and behavioral impairments. (JINS, 2008,14, 853–861.)
Traumatic brain injury in young children: Postacute effects on cognitive and school readiness skills
Authors: TAYLOR H. GERRY , SWARTWOUT MAEGAN D. , YEATES KEITH OWEN , WALZ NICOLAY CHERTKOFF , STANCIN TERRY , WADE SHARI L.
Published: September 2008

Previous studies have documented weaknesses in cognitive ability and early academic readiness in young children with traumatic brain injury (TBI). However, few of these studies have rigorously controlled for demographic characteristics, examined the effects of TBI severity on a wide range of skills, or explored moderating influences of environmental factors on outcomes. To meet these objectives, each of three groups of children with TBI (20 with severe, 64 with moderate, and 15 with mild) were compared with a group of 117 children with orthopedic injuries (OI group). The children were hospitalized for their injuries between 3 and 6 years of age and were assessed an average of 1½ months post injury. Analysis revealed generalized weaknesses in cognitive and school readiness skills in the severe TBI group and less pervasive effects of moderate TBI. Indices of TBI severity predicted outcomes within the TBI sample and environmental factors moderated the effects of TBI on some measures. The findings document adverse effects of TBI in early childhood on postacute cognitive and school readiness skills and indicate that these effects are related to both injury severity and the family environment. (JINS, 2008,14, 734–745.)
Executive functioning in schizophrenia and the relationship with symptom profile and chronicity
Authors: GREENWOOD KATHRYN E. , MORRIS ROBIN , SIGMUNDSSON THORDUR , LANDAU SABINE , WYKES TIL
Published: September 2008

This study reports the executive function profile in people with schizophrenia, with a simultaneous comparison of chronicity and of those with predominately disorganizationversuspsychomotor poverty symptoms. The patients were split into one set defined according to symptoms (29 with disorganization, 29 with negative symptoms) and the other representing chronicity (22 first-episode, 35 chronic) and compared with 28 healthy controls on a broad range of executive process measures. Differences were investigated in both the severity and profile of impairments. Impairment patterns interacted with symptom groups, with disorganization and psychomotor poverty symptom groups showing different profiles of executive impairment. In contrast, across these same executive processes, impairment profiles were similar between first episode and chronic schizophrenia and became more similar, particularly for working memory, when controlling for disorganization symptoms. The executive profile, therefore, is related to symptom type rather than chronicity. (JINS, 2008,14, 782–792.)
Attenuation of GPS scintillation in Brazil due to magnetic storms
Authors: Bonelli E.
Published: September 2008

Amplitude scintillations in satellite signals can cause errors in communications, because of signal fading, but can be very useful for scientists trying to improve their understanding of the physics of the ionosphere. Usually, magnetic storms are expected to affect the ionosphere in such way as to increase ionospheric irregularities responsible for scintillations. To help change the view of scientists and engineers, in this respect, we show that amplitude scintillation on GPS signals show dramatic decrease during selected magnetic storms, at Brazilian GPS stations. These stations are located on magnetic latitudes that go from equatorial (São Luís) to low‐latitude (São José dos Campos and Cachoeira Paulista) so that a region of several thousand kilometers is represented by the data. We present 4 months of data chosen from 2003 to 2005 to represent the strongest storms during each scintillation season. Although there is lack of data for some days from the different stations, it is possible to see, especially for the Halloween Storm (October 2003), that scintillations are attenuated in this wide range of latitudes. During magnetically calm periods scintillations are strong, in this region, from August to March, during solar maxima. Although the data are clear about the attenuation of scintillations during greater magnetic storms, it is not possible to easily conclude which physical mechanism was responsible for this phenomenon, even with the aid of more detailed data like Dst and AE.
Wavelet analysis of dominant scales of heterogeneous porous media
Authors: Qi Xing , Neupauer Roseanna M.
Published: September 2008

Heterogeneity of aquifer permeability has a significant influence on the transport of solutes; therefore characterization of aquifer heterogeneity is needed to accurately predict the behavior of solutes. A critical characteristic of heterogeneity is a characteristic length scale that is a measure of the distance over which property values are correlated. We show that the characteristic length scale of a statistically homogeneous permeability field can be identified through wavelet analysis using the global wavelet energy spectrum (GWES). The relationship between the wavelet scale and the characteristic length scale of a random field is investigated for the Mexican hat and Morlet wavelets and different covariance structures. The ability of the GWES to identify multiple characteristic length scales in a random field with nested covariance structures is also investigated. We use the technique to identify the characteristic length scales of a laboratory‐collected permeability transect from Massillon sandstone.
Multimodel ensembles of streamflow forecasts: Role of predictor state in developing optimal combinations
Authors: Devineni Naresh , Sankarasubramanian A. , Ghosh Sujit
Published: September 2008

A new approach for developing multimodel streamflow forecasts is presented. The methodology combines streamflow forecasts from individual models by evaluating their skill, represented by rank probability score (RPS), contingent on the predictor state. Using average RPS estimated over the chosen neighbors in the predictor state space, the methodology assigns higher weights for a model that has better predictability under similar predictor conditions. We assess the performance of the proposed algorithm by developing multimodel streamflow forecasts for Falls Lake Reservoir in the Neuse River Basin, North Carolina (NC), by combining streamflow forecasts developed from two low‐dimensional statistical models that use sea‐surface temperature conditions as underlying predictors. To evaluate the proposed scheme thoroughly, we consider a total of seven multimodels that include existing multimodel combination techniques such as combining based on long‐term predictability of individual models and by simple pooling of ensembles. Detailed nonparametric hypothesis tests comparing the performance of seven multimodels with two individual models show that the reduced RPS from multimodel forecasts developed using the proposed algorithm is statistically significant from the RPSs of individual models and from the RPSs of existing multimodel techniques. The study also shows that adding climatological ensembles improves the multimodel performance resulting in reduced average RPS. Contingency analyses on categorical (tercile) forecasts show that the proposed multimodel combination technique reduces average Brier score and total number of false alarms, resulting in improved reliability of forecasts. However, adding multiple models with climatology also increases the number of missed targets (in comparison to individual models' forecasts) which primarily results from the reduction of increased resolution that is exhibited in the individual models' forecasts under various forecast probabilities.
Planetary period oscillations in Saturn's magnetosphere: Phase relation of equatorial magnetic field oscillations and Saturn kilometric radiation modulation
Authors: Andrews D. J. , Bunce E. J. , Cowley S. W. H. , Dougherty M. K. , Provan G. , Southwood D. J.
Published: September 2008

We examine the planetary‐period oscillations in Saturn's magnetic field observed by the Cassini spacecraft on 23 near‐equatorial periapsis passes in the inner magnetosphere spanning October 2004 to July 2006. Overall, we find that the phase of the magnetic oscillations is well organized by the long‐timescale modulation phase of Saturn kilometric radiation (SKR) determined over the same interval by Kurth et al. (2007), suggesting that the slow period variation of the latter relates to inner magnetosphere processes. The relative phases of the oscillations in the spherical polar r and ϕ magnetic field components imply the presence of a quasi‐uniform equatorial field rotating near the SKR period, while the sense of the θ component indicates that the perturbation field lines form loops with apices in the Northern Hemisphere. No consistent evidence is found for a sign reversal in any field component across the equatorial plane, within ±20° in latitude. The relative SKR phasing is such that the peak radio power occurs when the r and θ component maxima lie at ∼0200 LT ± 2 hours. However, a slow drift of the magnetic phase relative to the SKR phase is also discerned, amounting to ∼75° over the study interval. This drift lies within the envelope of scatter in the SKR phase determinations, suggesting that it represents the refinement of a common periodicity. A revised magnetic phase or longitude model is derived that should form an improved organizational system for oscillatory phenomena observed during this interval of the Cassini mission. The magnetic oscillations are also found to exhibit pass‐to‐pass phase “jitter” about the long‐term variation, of RMS amplitude ∼20°, with r and ϕ strongly correlated, but not θ. The relation with the solar wind‐modulated short‐timescale phase variations reported in SKR data by Zarka et al. (2007) remains to be investigated, though the latter are 5 times larger in magnitude.
Zemmouri earthquake rupture zone (Mw 6.8, Algeria): Aftershocks sequence relocation and 3D velocity model
Authors: Ayadi A. , Dorbath C. , Ousadou F. , Maouche S. , Chikh M. , Bounif M. A. , Meghraoui M.
Published: September 2008

We analyze the aftershocks sequence of the Zemmouri thrust faulting earthquake (21 May 2003, Mw 6.8) located east of Algiers in the Tell Atlas. The seismic sequence located during ∼2 months following the mainshock is made of more than 1500 earthquakes and extends NE–SW along a ∼60‐km fault rupture zone crossing the coastline. The earthquake relocation was performed using handpicked P and S phases located with the tomoDD in a detailed 3D velocity structure of the epicentral area. Contrasts between velocity patches seem to correlate with contacts between granitic–volcanic basement rocks and the sedimentary formation of the eastern Mitidja basin. The aftershock sequence exhibits at least three seismic clouds and a well‐defined SE‐dipping main fault geometry that reflects the complex rupture. The distribution of seismic events presents a clear contrast between a dense SW zone and a NE zone with scattered aftershocks. We observe that the mainshock locates between the SW and NE seismic zones; it also lies at the NNS–SSE contact that separates a basement block to the east and sedimentary formations to the west. The aftershock distribution also suggests fault bifurcation at the SW end of the fault rupture, with a 20‐km‐long ∼N 100° trending seismic cluster, with a vertical fault geometry parallel to the coastline juxtaposed. Another aftershock cloud may correspond to 75° SE dipping fault. The fault geometry and related SW branches may illustrate the interference between pre‐existing fault structures and the SW rupture propagation. The rupture zone, related kinematics, and velocity contrasts obtained from the aftershocks distribution are in agreement with the coastal uplift and reflect the characteristics of an active zone controlled by convergent movements at a plate boundary.
Determining North Atlantic meridional transport variability from pressure on the western boundary: A model investigation
Authors: Bingham R. J. , Hughes C. W.
Published: September 2008

In this paper, we investigate the possibility of determining North Atlantic meridional transport variability using pressure on the western boundary, focusing on the 42°N latitude of the Halifax WAVE array. We start by reviewing the theoretical foundations of this approach. Next, we present results from a model analysis, both statistical and dynamic, that demonstrate the feasibility of the approach. We consider how well we can quantify the meridional transport variability at 42°N given complete knowledge of bottom pressure across the basin and to what degree this quantification is degraded by first ignoring the effect of intervening topography and then by using only bottom pressure on the western boundary. We find that for periods of greater than 1 year, we can recover more than 90% of the variability of the main overturning cell at 42°N using only the western boundary pressure, provided that we remove the depth‐averaged boundary pressure signal. This signal arises from a basin mode of bottom pressure variability, which has power at all time scales, but that does not in truth have a meridional transport signal associated with it, and from the geostrophic depth‐independent compensation of the Ekman transport. An additional benefit of the removal of the depth‐averaged pressure is that this high‐frequency Ekman signal, which is essentially noise as far as monitoring the meridional overturning circulation for climatically important changes is concerned, is clearly separated from other modes.
Three‐dimensional reconstruction of oceanic mesoscale currents from surface information
Authors: Isern‐Fontanet Jordi , Lapeyre Guillaume , Klein Patrice , Chapron Bertrand , Hecht Matthew W.
Published: September 2008

The ability to reconstruct the three‐dimensional (3D) dynamics of the ocean by an effective version of Surface Quasi‐Geostrophy (eSQG) is examined. Using the fact that surface density plays an analogous role as interior potential vorticity (PV), the eSQG method consists in inverting the QG PV generated by sea‐surface density only. We also make the extra assumption that sea‐surface temperature (SST) anomalies fully represent surface density anomalies. This approach requires a single snapshot of SST and the setup of two parameters: the mean Brunt‐Väisälä frequency and a parameter that determines the energy level at the ocean surface. The validity of this approach is tested using an Ocean General Circulation Model simulation representing the North Atlantic in winter. It is shown that the method is quite successful in reconstructing the velocity field at the ocean surface for mesoscales (between 30 and 300 km). The eSQG framework can also be applied to reconstruct subsurface fields using surface information. Results show that the reconstruction of velocities and vorticity from surface fields is reasonably good for the upper 500 m and that the success of the method mainly depends on the quality of the SST as a proxy of the density anomaly at the base of the mixed layer. This situation happens after a mixed‐layer deepening period. Therefore the ideal situation for the application of this method would be after strong wind events.
Effects of western boundary current dynamics on the internal wave field of the Southeast Florida shelf
Authors: Davis Kristen A. , Leichter James J. , Hench James L. , Monismith Stephen G.
Published: September 2008

Shelf sea internal wave fields are typically highly variable and dominated by wind and tidal forces. However this is not necessarily true for outer shelf regions or very narrow shelves where remote physical processes originating over the slope or deep ocean may exert a strong influence on the internal wave climate. During the summers of 2003 and 2004, observational studies were conducted to examine the effects of a western boundary current (the Florida Current), tides, and wind on the mean currents and internal wave field on the outer Southeast Florida shelf. Wavelet analyses of nonstationary shelf currents coupled with altimetry images of the Straits of Florida reveal the strong influence of Florida Current fluctuations on outer shelf flows. Local winds were found to be a small factor in flows on the outer shelf region and tidal forcing (diurnal and semidiurnal) accounted for less than a third of the total barotropic variance. High‐frequency internal waves dominate the internal wave field and result in bottom‐intensified currents and strong shoreward mass transport. We present evidence that suggests that the Florida Current plays as large a role in the determination of the high‐frequency internal wave field as tidal forces. These observations and analyses show that it is necessary to include the forcing from the Florida Current meanders and instabilities in order to predict accurately the episodic nature of the internal wave field on the Southeast Florida shelf.
Regional summer precipitation events in Asia and their changes in the past decades
Authors: Yao Cai , Yang Song , Qian Weihong , Lin Zhengmin , Wen Min
Published: September 2008

A recently derived data set of daily precipitation is used to study the summer precipitation events over Asia and their changes in the decades of 1978–2002. Regional features of the precipitation over entire tropical‐subtropical Asia are investigated, exploiting the increased resolution and improved accuracy of the data set relative to other estimates. The changes in precipitation amount and precipitation days for total, extreme, heavy, and light‐moderate precipitations are examined. Although the Asian summer monsoon precipitation falls mostly in the form of light‐moderate rainfalls, regions of relatively frequent extreme precipitation events are found over South Asia and East‐Southeast Asia. These regions are separated by a narrow zone over the Indo‐China peninsula, along 100°E, where extreme precipitation rarely occurs. During the period examined, the amount of total precipitation and light‐moderate precipitation exhibits positive trends over southeastern and northwestern China, separated by negative trends over central China and southwestern and northeastern Asia. This sandwich‐like pattern, which also appears in the fields of precipitation days and soil moisture content, is associated with the enhanced water vapor supply related to the strengthened monsoon flow over southeastern China and the anomalous easterlies over northwestern China. It is also associated with the decreased water vapor supply linked to the weakened monsoon flows over southern‐southwestern Asia and central China and to the anomalous northerly flow over northeastern Asia. Over the entire tropical‐subtropical Asia, the largest changes in precipitation, atmospheric circulation, and water vapor transport occur over southern China. On the other hand, the changes over India are much smaller.
Four‐dimensional variational data assimilation for inverse modeling of atmospheric methane emissions: Analysis of SCIAMACHY observations
Authors: Meirink Jan Fokke , Bergamaschi Peter , Frankenberg Christian , d'Amelio Monica T. S. , Dlugokencky Edward J. , Gatti Luciana V. , Houweling Sander , Miller John B. , Röckmann Thomas , Villani M. Gabriella , Krol Maarten C.
Published: September 2008

Recent observations from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instrument aboard ENVISAT have brought new insights in the global distribution of atmospheric methane. In particular, the observations showed higher methane concentrations in the tropics than previously assumed. Here, we analyze the SCIAMACHY observations and their implications for emission estimates in detail using a four‐dimensional variational (4D‐Var) data assimilation system. We focus on the period September to November 2003 and on the South American continent, for which the satellite observations showed the largest deviations from model simulations. In this set‐up the advantages of the 4D‐Var approach and the zooming capability of the underlying TM5 atmospheric transport model are fully exploited. After application of a latitude‐dependent bias correction to the SCIAMACHY observations, the assimilation system is able to accurately fit those observations, while retaining consistency with a network of surface methane measurements. The main emission increments resulting from the inversion are an increase in the tropics, a decrease in South Asia, and a decrease at northern hemispheric high latitudes. The SCIAMACHY observations yield considerable additional emission uncertainty reduction, particularly in the (sub‐)tropical regions, which are poorly constrained by the surface network. For tropical South America, the inversion suggests more than a doubling of emissions compared to the a priori during the 3 months considered. Extensive sensitivity experiments, in which key assumptions of the inversion set‐up are varied, show that this finding is robust. Independent airborne observations in the Amazon basin support the presence of considerable local methane sources. However, these observations also indicate that emissions from eastern South America may be smaller than estimated from SCIAMACHY observations. In this respect it must be realized that the bias correction applied to the satellite observations does not take into account potential regional systematic errors, which – if identified in the future – will lead to shifts in the overall distribution of emission estimates.
Estimating the impact of the 2004 Alaskan forest fires on episodic particulate matter pollution over the eastern United States through assimilation of satellite‐derived aerosol optical depths in a regional air quality model
Authors: Mathur Rohit
Published: September 2008

During the summer of 2004, extensive wildfires burned in Alaska and western Canada; the fires were the largest on record for Alaska. Smoke from these fires was observed over the continental United States in satellite images, and a variety of chemical tracers associated with the fires were sampled by aircrafts deployed during the International Consortium for Atmospheric Research on Transport and Transformation field experiment. Several recent studies have quantified the impacts of the long‐range transport of pollution associated with these fires on tropospheric CO and O3 levels over the eastern United States. This study quantifies the episodic impact of this pollution transport event on surface‐level fine particulate matter (PM2.5) concentrations over the eastern United States during mid‐July 2004, through the complementary use of remotely sensed, aloft, and surface measurements, in conjunction with a comprehensive regional atmospheric chemistry‐transport model. A methodology is developed to assimilate MODIS aerosol optical depths in the model to represent the impacts of the fires. The resultant model predictions of CO and PM2.5 distributions are compared extensively with corresponding surface and aloft measurements. On the basis of the model calculations, a 0.12Tg enhancement in tropospheric PM2.5 mass loading over the eastern United States is estimated on 19 July 2004 due to the fires. This amount is significantly larger (approximately a factor of 8) than the total daily anthropogenic fine particulate matter emissions for the continental United States. Analysis of measured and modeled PM2.5 surface‐level concentrations suggests that the transport of particulate matter pollution associated with the fires resulted in a 24–42 % enhancement in median surface‐level PM2.5 concentrations across the eastern United States during 19–23 July 2004.
Traveltime‐based descriptions of transport and mixing in heterogeneous domains
Authors: Luo Jian , Cirpka Olaf A.
Published: September 2008

Modeling mixing‐controlled reactive transport using traditional spatial discretization of the domain requires identifying the spatial distributions of hydraulic and reactive parameters including mixing‐related quantities such as dispersivities and kinetic mass transfer coefficients. In most applications, breakthrough curves (BTCs) of conservative and reactive compounds are measured at only a few locations and spatially explicit models are calibrated by matching these BTCs. A common difficulty in such applications is that the individual BTCs differ too strongly to justify the assumption of spatial homogeneity, whereas the number of observation points is too small to identify the spatial distribution of the decisive parameters. The key objective of the current study is to characterize physical transport by the analysis of conservative tracer BTCs and predict the macroscopic BTCs of compounds that react upon mixing from the interpretation of conservative tracer BTCs and reactive parameters determined in the laboratory. We do this in the framework of traveltime‐based transport models which do not require spatially explicit, costly aquifer characterization. By considering BTCs of a conservative tracer measured on different scales, one can distinguish between mixing, which is a prerequisite for reactions, and spreading, which per se does not foster reactions. In the traveltime‐based framework, the BTC of a solute crossing an observation plane, or ending in a well, is interpreted as the weighted average of concentrations in an ensemble of non‐interacting streamtubes, each of which is characterized by a distinct traveltime value. Mixing is described by longitudinal dispersion and/or kinetic mass transfer along individual streamtubes, whereas spreading is characterized by the distribution of traveltimes, which also determines the weights associated with each stream tube. Key issues in using the traveltime‐based framework include the description of mixing mechanisms and the estimation of the traveltime distribution. In this work, we account for both apparent longitudinal dispersion and kinetic mass transfer as mixing mechanisms, thus generalizing the stochastic‐convective model with or without inter‐phase mass transfer and the advective‐dispersive streamtube model. We present a nonparametric approach of determining the traveltime distribution, given a BTC integrated over an observation plane and estimated mixing parameters. The latter approach is superior to fitting parametric models in cases wherein the true traveltime distribution exhibits multiple peaks or long tails. It is demonstrated that there is freedom for the combinations of mixing parameters and traveltime distributions to fit conservative BTCs and describe the tailing. A reactive transport case of a dual Michaelis‐Menten problem demonstrates that the reactive mixing introduced by local dispersion and mass transfer may be described by apparent mean mass transfer with coefficients evaluated by local BTCs.
Agricultural green and blue water consumption and its influence on the global water system
Authors: Rost Stefanie , Gerten Dieter , Bondeau Alberte , Lucht Wolfgang , Rohwer Janine , Schaphoff Sibyll
Published: September 2008

This study quantifies, spatially explicitly and in a consistent modeling framework (Lund‐Potsdam‐Jena managed Land), the global consumption of both “blue” water (withdrawn for irrigation from rivers, lakes and aquifers) and “green” water (precipitation) by rainfed and irrigated agriculture and by nonagricultural terrestrial ecosystems. In addition, the individual effects of human‐induced land cover change and irrigation were quantified to assess the overall hydrological impact of global agriculture in the past century. The contributions to irrigation of nonrenewable (fossil groundwater) and nonlocal blue water (e.g., from diverted rivers) were derived from the difference between a simulation in which these resources were implicitly considered (IPOT) and a simulation in which they were neglected (ILIM). We found that global cropland consumed >7200 km3 year−1 of green water in 1971–2000, representing 92% (ILIM) and 85% (IPOT), respectively, of total crop water consumption. Even on irrigated cropland, 35% (ILIM) and 20% (IPOT) of water consumption consisted of green water. An additional 8155 km3 year−1 of green water was consumed on grazing land; a further ∼44,700 km3 year−1 sustained the ecosystems. Blue water consumption predominated only in intensively irrigated regions and was estimated at 636 km3 year−1 (ILIM) and 1364 km3 year−1 (IPOT) globally, suggesting that presently almost half of the irrigation water stemmed from nonrenewable and nonlocal sources. Land cover conversion reduced global evapotranspiration by 2.8% and increased discharge by 5.0% (1764 km3 year−1), whereas irrigation increased evapotranspiration by up to 1.9% and decreased discharge by 0.5% at least (IPOT, 1971–2000). The diverse water fluxes displayed considerable interannual and interdecadal variability due to climatic variations and the progressive increase of the global area under cultivation and irrigation.
Improving High‐Impact Weather Forecasts
Authors: Worley Steven , Schuster Doug , Bougeault Phillipe , Raoult Baudouin , Chen De Hui , Dong Jiandong
Published: September 2008

To accelerate improvements in 1‐ to 14‐day high‐impact weather forecasts, the World Meteorological Organization's (WMO) World Weather Research Programme established the Observing System Research and Predictability Experiment (THORPEX) Interactive Grand Global Ensemble (TIGGE) in 2005. The key objectives of TIGGE are enhancing international collaboration on ensemble prediction, determining new methods for combining ensembles from different sources, gaining a deeper understanding of forecast error and the feasibility of interactive ensemble systems, and developing a prototype for a future Global Interactive Forecasting System (GIFS).
Please Support AGU
Authors: Austin James A.
Published: September 2008

At its meeting in June, the AGU Council approved increasing the contribution level that qualifies donors as supporting members from $100 to $180. This increase will be phased in over 3 years starting this fall, when you, as AGU members, will be asked to consider a contribution at the supporting level by giving $120 or more to the 2009 Voluntary Contribution Campaign.
Nonlinear Dynamics in the Geosciences
Authors: Kirtman Ben P.
Published: September 2008

In the past, “nonlinearity” has been used as the catchall phrase to describe processes in the geosciences that we could not understand, and is often used in this manner in current peer‐reviewed literature and conference presentations. My graduate students often complain that their professors (me included) use nonlinearity to avoid answering difficult questions.

However, during the course of the past 20 years there have been significant breakthroughs in our understanding of nonlinear dynamics that have been enabled by advances in high‐speed computing but that reach far beyond simply solving nonlinear equations numerically. Understanding how regime transitions are possible without a change in the governing law is perhaps one of the best examples of how nonlinear dynamics has improved our understanding of geophysical phenomena.
Human Missions to Mars: Enabling Technologies for Exploring the Red Planet
Authors: Crawford Ian
Published: September 2008

In January 2004, President George W. Bush announced the new “Vision for Space Exploration,” which has refocused U.S. human spaceflight policy away from low‐Earth orbit and toward the exploration of the Moon and Mars. While the technological requirements to return people to the Moon are well understood (after all, the Apollo program had people on the Moon almost 40 years ago), the proposed missions to Mars will be much more challenging.

In this book, Donald Rapp, a former senior research scientist at the Jet Propulsion Laboratory (JPL), sets out to provide a critical assessment of the requirements for human missions to Mars from an engineering perspective. He argues, I am sure correctly, that this will prove to be a much more difficult task than is sometimes implied by the more optimistic Mars exploration advocates at NASA and elsewhere.
Observed and simulated seasonal co‐variations of outgoing longwave radiation spectrum and surface temperature
Authors: Huang Yi , Ramaswamy V.
Published: September 2008

We analyze the seasonal variations of Outgoing Longwave Radiation (OLR) accompanying the variations in sea surface temperature (SST) from satellite observations and model simulations, focusing on the tropical oceans where the two quantities are strikingly anti‐correlated. A spectral perspective of this “super‐greenhouse effect” is provided, which demonstrates the roles of water vapor line and continuum absorptions at different altitudes and the influences due to clouds. A model‐satellite comparison indicates that the GFDL General Circulation Model can fairly well represent the total‐sky radiative response to SST in the water vapor infrared absorption band despite the significant bias in the mean state, but this comprises compensating water vapor‐ and cloud‐related errors. The analysis also reveals that the GCM significantly underestimates the cloud induced radiative responses in the window region which arises from the model bias in the mean cloud forcing in convectively active regions. Thus, spectral decomposition proves essential to understand and assess the OLR‐SST relationship and the impacts of water vapor and cloud upon this linkage.
Tempered anomalous diffusion in heterogeneous systems
Authors: Meerschaert Mark M. , Zhang Yong , Baeumer Boris
Published: September 2008

Passive tracers in heterogeneous media experience preasymptotic transport with scale‐dependent anomalous diffusion, before eventually converging to the asymptotic diffusion limit. We propose a novel tempered model to capture the slow convergence of sub‐diffusion to a diffusion limit for passive tracers in heterogeneous media. Previous research used power‐law waiting times to capture the time‐nonlocal transport process. Here those waiting times are exponentially tempered, to capture the natural cutoff of retention times. The model is validated against particle concentrations from detailed numerical simulations and field measurements, at various scales and geological environments.
A numerical study of upward‐propagating gravity waves in two different MJO phases
Authors: Horinouchi Takeshi
Published: September 2008

Convectively generated atmospheric gravity waves that propagate into the equatorial stratosphere were investigated using a cloud resolving model. Numerical simulations were conducted to study wave generation during convectively inactive and active phases in a cycle of the Madden‐Julian oscillation, which occurred during an observational campaign conducted in Sumatra. Greater convective activity during the active phase caused stronger disturbances in the troposphere at relatively low phase speeds less than about 20m/s than the inactive phase. However, the contrast was weaker at higher phase speeds. Furthermore, the vertical structure of convective forcing in the inactive phase was more suitable to excite waves with wavelength longer than twice the depth of convection. Owing to the combination of these factors, upward gravity wave propagation was significantly enhanced during the inactive phase. This study demonstrates the necessity to study convection spectrally to investigate possible links between intraseasonal variabilities in the troposphere and the middle atmosphere.
Large magnetic storm‐induced nighttime ionospheric flows at midlatitudes and their impacts on GPS‐based navigation systems
Authors: Basu Su. , Basu S. , Makela J. J. , MacKenzie E. , Doherty P. , Wright J. W. , Rich F. , Keskinen M. J. , Sheehan R. E. , Coster A. J.
Published: September 2008

Analysis of GPS phase fluctuations in conjunction with regional total electron content (TEC) maps, in situ measurements of subauroral polarization streams (SAPS) and auroral convection from several Defense Meteorological Satellite Program spacecraft, and dynasonde measurements at the Bear Lake Observatory obtained during the intense magnetic storm of 7–8 November 2004 have indicated the serious impact of large ionospheric velocities on GPS‐based navigation systems within the midlatitude region in the North American sector. The major difference between this superstorm and the others observed during the earlier October‐November 2003 events is the absence of appreciable storm‐enhanced density gradients, with the midlatitude region being enveloped by either the auroral oval or the ionospheric trough within which the SAPS were confined during the local dusk to nighttime hours. This shows that it is possible to disable GPS‐based navigation systems for many hours even in the absence of appreciable TEC gradients, provided an intense flow channel is present in the ionosphere during nighttime hours. The competing effects of irregularity amplitude ΔN/N, the background F region density, and the magnitude of SAPS or auroral convection are discussed in establishing the extent of the region of impact on such systems.
On improvement to the Shock Propagation Model (SPM) applied to interplanetary shock transit time forecasting
Authors: Li H. J. , Wei F. S. , Feng X. S. , Xie Y. Q.
Published: September 2008

This paper investigates methods to improve the predictions of Shock Arrival Time (SAT) of the original Shock Propagation Model (SPM). According to the classical blast wave theory adopted in the SPM, the shock propagating speed is determined by the total energy of the original explosion together with the background solar wind speed. Noting that there exists an intrinsic limit to the transit times computed by the SPM predictions for a specified ambient solar wind, we present a statistical analysis on the forecasting capability of the SPM using this intrinsic property. Two facts about SPM are found: (1) the error in shock energy estimation is not the only cause of the prediction errors and we should not expect that the accuracy of SPM to be improved drastically by an exact shock energy input; and (2) there are systematic differences in prediction results both for the strong shocks propagating into a slow ambient solar wind and for the weak shocks into a fast medium. Statistical analyses indicate the physical details of shock propagation and thus clearly point out directions of the future improvement of the SPM. A simple modification is presented here, which shows that there is room for improvement of SPM and thus that the original SPM is worthy of further development.
F3 layer during penetration electric field
Authors: Balan N. , Thampi S. V. , Lynn K. , Otsuka Y. , Alleyne H. , Watanabe S. , Abdu M. A. , Fejer B. G.
Published: September 2008

The occurrence of an additional layer, called F3 layer, in the equatorial ionosphere at American, Indian, and Australian longitudes during the super double geomagnetic storm of 7–11 November 2004 is presented using observations and modeling. The observations show the occurrence, reoccurrence, and quick ascent to the topside ionosphere of unusually strong F3 layer in Australian longitude during the first super storm (8 November) and in Indian longitude during the second super storm (10 November), all with large reductions in peak electron density (Nmax) and total electron content (GPS‐TEC). The unusual F3 layers can arise mainly from unusually strong fluctuations in the daytime vertical E × B drift as indicated by the observations and modeling in American longitude. The strongest upward E × B drift (or eastward prompt penetration electric field, PPEF) ever recorded (at Jicamarca) produces unusually strong F3 layer in the afternoon hours (≈1400–1600 LT) of PPEF, with large reductions in Nmax and TEC; the layer also reappears in the following evening (≈1700–1800 LT) owing to an unusually large downward drift. At night, when the drift is unusually upward and strong, the F region splits into two layers.