bluuebunny/crossref_metadata_2025 huggingface dataset:
Phonological neighbourhood density: effects in a rhyme awareness task in five-year-old children
Authors: DE CARA BRUNO , GOSWAMI USHA
Published: August 2003

Phonological awareness skills are critical for reading acquisition, yet relatively little is known about the origins of phonological awareness. This study investigates one plausible source of the emergence of phonological awareness, phonological neighbourhood density. As vocabulary grows, the number of similar-sounding words in the child's mental lexicon increases. This could create developmental pressure to develop awareness of sub-units within words such as syllables, rhymes and phonemes. If this is the case, then neighbourhood density effects should be discernible in phonological awareness tasks. Children should be more successful in these tasks with words from dense phonological neighbourhoods, as they should show greater awareness of sub-units within these words. We investigated this hypothesis in a group of 48 five-year-old children, most of whom were pre-readers. The five-year-olds with a high vocabulary age showed neighbourhood density effects in a rhyme oddity task, but five-year-olds with lower vocabulary ages did not. This suggests that vocabulary acquisition and consequent neighbourhood density effects are indeed one source of the emergence of phonological awareness skills in pre-readers.
Input and word learning: caregivers' sensitivity to lexical category distinctions
Authors: HALL D. GEOFFREY , BURNS TRACEY C. , PAWLUSKI JODI L.
Published: August 2003

Twenty-four caregivers and their two- to four-year-old children took part in a storybook reading task in which caregivers taught children novel labels (‘DAXY’) for familiar objects. One group (N=12) received labels modelled syntactically as proper names (‘This is NAMED DAXY’), and another group (N=12) received the same labels for the same objects modelled syntactically as adjectives (‘This is VERY DAXY’). Caregivers took strikingly different approaches to teaching words from the two lexical categories. In teaching proper names, but not adjectives, caregivers flagged cases in which one word was paired with two objects; two words were paired with one object; and one word was paired with an inanimate object. In teaching adjectives, but not proper names, caregivers discussed meaning and offered translations. Caregivers' distinctive strategies for teaching proper names and adjectives are congruent with recent findings about children's word meaning assumptions, and with analyses of the semantics of these lexical categories. The findings indicate that parental speech could provide a rich source of information to children in learning how different lexical categories are expressed in their native language.
Environmental correlates of geographical variation in skull and mandible shape of the punaré rat Thrichomys apereoides (Rodentia: Echimyidae)
Authors: Monteiro Leandro R. , Duarte Luiza C. , dos Reis Sérgio F.
Published: August 2003

The pattern of correlations between geographic–environmental variables and geometric shape descriptors for the skull and mandible of Thrichomys apereoides was studied by recently developed combinations of geometry and multivariate statistical techniques. Environmental variables were obtained for each locality: altitude, mean temperature, rainfall, human population density, and vegetation type. The three views of the skull (dorsal, lateral and ventral) and the mandible were significantly associated with a latitudinal environmental gradient along the diagonal of open areas (caatinga and cerrado) throughout the range sampled. The populations from xeric environments presented relatively larger coronoid processes, larger jugals and wider snouts (related to the activity of jaw closing muscles). A correlation of patterns of shape variation from data sets of different skull views showed that lateral skull shape is the most informative view. Further studies are necessary to separate completely the contribution of genetic and environmental components to skull and mandible shape divergence among populations of T. apereoides.
Differential osmoregulatory capabilities of common spiny mice (Acomys cahirinus) from adjacent microhabitats
Authors: Shanas Uri , Afik Daniel , Scantlebury Michael , Haim Abraham
Published: August 2003

The osmoregulatory function of common spiny mice Acomys cahirinus living on opposite slopes of the lower Nahal Oren (‘Evolution Canyon’) on mount Carmel, Israel, was investigated by increasing the salinity of the water source whilst maintaining a high‐protein diet. The southern‐facing slope (SFS) of this canyon differs from the northern‐facing slope (NFS) as it receives considerably more solar radiation and consequently forms a more xeric, sparsely vegetated habitat. During the summer, mice living on the two opposite slopes significantly differed in their urine osmolality, which also increased significantly as dietary salinity increased. Offspring of wild‐captured mice, born in captivity, and examined during the winter, continued to show a difference in osmoregulatory function depending on the slope of origin. However, they differed from wild‐captured mice, as they did not respond to the increase in dietary salinity by increasing the concentration of their urine, but rather by increasing the volume of urine produced. This study shows that A. cahirinus occupying different microhabitats may exhibit differences in their ability to concentrate urine and thus in their ability to withstand xeric conditions. We suggest that they may also differ genetically, as offspring from the NFS and SFS retain physiological differences, but further studies will be needed to confirm this hypothesis.
Response of territorial males to the threat of sneaking in the three‐spined stickleback (Gasterosteus aculeatus): a field study
Authors: Le Comber Steven C. , Faulkes Chris G. , Formosinho Joana , Smith Carl
Published: August 2003

Alternative mating tactics are found in many species, and may have important implications for population genetics and speciation. The existence of such alternative mating tactics is well‐documented in the three‐spined stickleback Gasterosteus aculeatus, and sneaking and egg‐stealing may occur in a significant proportion of matings under natural conditions. Sneaking can impose high costs on territorial males, both in terms of reduced reproductive output and caring for unrelated offspring. We ask whether territorial males adjust their behaviour in response to the risk of sneaking. In a field study of three‐spined sticklebacks on the Isle of Arran, Scotland, territorial males were presented with glass bottles containing either a male, a female or neither, to address whether territorial males were more aggressive to other males in the presence of a female, and whether territorial males courted females less in the presence of another male. Behavioural observations showed that territorial males did not behave more aggressively towards rival males in the presence of a female, but did reduce their rate of courtship towards females in the presence of rival males. We conclude that territorial males adopt behavioural strategies that may reduce their risk of reproductive parasitism.
An experimental assessment of invertebrate/vertebrate predation: the interaction between wolf spiders (Gladicosa pulchra) and terrestrial salamanders (Ambystoma maculatum)
Authors: Rubbo Michael J. , Townsend Victor R. , Smyers Scott D. , Jaeger Robert G.
Published: August 2003

A series of laboratory experiments were conducted to determine if adult wolf spiders Gladicosa pulchra were capable of acting as predators of juvenile spotted salamanders Ambystoma maculatum. Spiders preyed upon salamanders in two of 20 trials and attacked salamanders in five trials. As attacks did not always kill salamanders, multiple attacks per trial were possible. A total of 11 attacks was observed: two complete attacks, and nine incomplete attacks. Attacks were considered complete if the spider inserted its chelicerae into the salamander and incomplete if the spider did not. In response to complete attacks, the salamander would flip onto its back. Salamanders occasionally responded to incomplete attacks by continuously raising and lowering their heads. To our knowledge, this behaviour is undescribed in this group of salamanders. An additional experiment investigated the influence of increased levels of salamander movement on this interaction. In this experiment, spiders preyed upon salamanders in one of eight trials and attacked salamanders in six trials (28 total attacks: four complete attacks, 24 incomplete attacks). The results of this study indicate that wolf spiders can prey upon juvenile spotted salamanders, and that the ecological relationship between wolf spiders and amphibians may be quite complex.
Structure and variability of bat social calls: implications for specificity and individual recognition
Authors: Pfalzer Guido , Kusch Jürgen
Published: August 2003

Communication sounds or ‘social calls’ of 16 European bat species (Chiroptera, Vespertilionidae) were recorded at a range of roost and foraging sites. A comparative analysis of more than 5400 individual calls for general structures and for inter‐ as well as intraspecific variability resulted in 50 types of calls, which differed by their specific structure and by the calling species. These types could be grouped into four different general types of calls, according to the kind and complexity of their structure, independent of the calling species. Distinct types of calls seem to have similar functions in different bat species. One general type may be used predominantly in female–infant interactions as an isolation or direction call, which serves as mutual recognition. This type of social call was also used in ‘tandem flights’ of pairs of bats, which might increase individual knowledge of roost sites and foraging success. A second type was used in mate attraction, and a further one in an aggressive context. The fourth one was used by hindered or distressed bats. The group of ‘aggressive’ calls is least variable, but the complex mating calls and isolation calls are very diverse. Species‐specific sound structures were identified, which allowed a computational species distinction. The measured inter‐individual variability of social calls should be significant for their functions in individual recognition. So, beyond common features concerning the frequency structure of bat social calls, interspecific differences, as well as the intraspecific variability of details of sonagraphic parameters, should elucidate the specific functions of the calls.
Social structure of the solitary slow loris Nycticebus coucang (Lorisidae)
Authors: Wiens Frank , Zitzmann Annette
Published: August 2003

The social structure and social interactions of the nocturnal slow loris Nycticebus coucang are described from locational as well as observational data on wild animals. Data were collected during 600 h of nocturnal radio‐tracking and 400h spent radio‐locating sleeping slow lorises during the day. Data are also presented on morphometrics, injuries and ectoparasites, and dispersal. The slow loris is generally described as solitary, but although close‐range encounters were rare, animals were observed to form stable social units (‘spatial groups’) characterized by home‐range overlap and friendly interactions among members and non‐overlap between units. Four spatial groups were observed, each consisting of a single adult female, a single adult male and a varying number of younger individuals. Group composition, together with relatively small testis volume and natal dispersal occurring in both sexes, hints towards a monogamous mating system. One extended family group was formed by the delayed dispersal of a primary pair's offspring. We did not find another often quoted correlate of monogamy – a weak sexual size dimorphism. Friendly interactions among members of a spatial group included allogrooming, following, alternate click‐calls, and sleeping in contact. Yet, members did not engage in any co‐operative behaviour of the types usually thought to be responsible for group formation in gregarious mammals. One important factor contributing to the sharing of space between slow lorises is probably that chances of successful dispersal are low. However, subtle benefits arising from the presence of conspecifics (allogrooming, transfer of information on food resources) may also be crucial for the formation or maintenance of slow loris spatial groups.
Gill‐cleaning mechanisms of the burrowing thalassinidean shrimps Nihonotrypaea japonica and Upogebia major (Crustacea: Decapoda)
Authors: Batang Zenon B. , Suzuki Hiroshi
Published: August 2003

The burrowing habits of thalassinidean shrimps presuppose their high susceptibility to the deleterious effects of gill fouling by particulate debris and epibionts. The structures and strategies used to prevent gill fouling were examined in Nihonotrypaea japonica and Upogebia major by morphological inference and aquarium observations. The gill complement of both species consists of 10 arthrobranchs, with flattened filaments of the phylloid trichobranch type. Nihonotrypaea japonica and U. major lack passive gill‐cleaning setal systems in the branchial chamber, but were found to actively groom gills by inserting and brushing the gill filaments with a pad of dense setae on the distal segments of their fifth pereiopods (P5 brush). Grooming setae of the P5 brush in N. japonica are of serrate and plumose types, whereas they are serrate and pappose in U. major. Serrate setae with distally curved spiniform denticules were morphologically similar in both species. Phylogenetic mapping of the gill‐cleaning mechanisms suggests that gill‐cleaning characters are homoplasic and systematically conservative among the families of the Thalassinidea.
Differential parasitaemia in the tawny owl (Strix aluco): effects of colour morph and habitat
Authors: Galeotti Paolo , Sacchi Roberto
Published: August 2003

The relationships between haematozoan parasites, cell‐mediated immune response, territory features and colour morph were investigated in tawny owls Strix aluco, in the Park of Monza in Milan, northern Italy. Rufous and grey birds were found to differ significantly in their blood parasite loads, particularly during the breeding season, when rufous birds hosted more parasites than grey birds. The increase in parasitaemia of rufous owl was not, however, owing to the breeding status of sampled individuals. Although body condition was similar between the two colour morphs, immune response was higher in grey than in rufous owls for the same level of parasites. Moreover, parasites seemed to influence breeding of rufous birds negatively, because only individuals with no or few parasites reproduced. Both these results suggested a higher susceptibility to parasites of rufous owls. Nevertheless, a habitat effect existed because parasite loads increased significantly with woodland extent and tree‐density within owl territories, and rufous birds defended more wooded territories than grey ones. Thus, the differential parasitaemia between colour morphs in tawny owls may be the result of both a differential exposure to flying vectors depending on habitat selection and a differential colour‐based susceptibility of individuals.
An insect larva with a ‘pig‐snout’: structure and function of the nasale of Hyphydrus ovatus L. (1763) (Coleoptera: Dytiscidae)
Authors: Friis Henning , Bauer Thomas , Betz Oliver
Published: August 2003

Hyphydrus ovatus beetles inhabit lakes, ponds and slow running streams. In central Europe the larvae develop at water temperatures of >10°C from May to July. All three instars live on or close to plants. The first instar prefers the upper areas of plants. Its prey are insect larvae and small stages of planktonic crustaceans. The second instar chooses deeper areas and catches larger prey, whereas the third instar prefers the root zone and feeds mainly on tubificids and chironomids that are caught in the detritus of the bottom layer. The elongated nasale of Hyphydrus ovatus is equipped with different sensilla. Despite the rather different shape of their outer parts, their ultrastructure indicates that they all have a mechanoreceptive function. Chaetiform sensilla are especially numerous and are especially long near the tip. Plate‐like mechanosensilla are positioned in a half circle at the ventral edge of the rostral tip. The assumed function of these sensilla is the location of prey. As in other Hydroporinae, the axis connecting the dorsal and ventral points of articulation of the mandibles is sloped laterally. Thereby, the closing mandibles move upwards and press the prey against the underside of the nasale, which – like the upper jaw in vertebrates – serves as the counterpart of the mandibles. On its ventral side, the nasale is equipped with various cuticular teeth that serve to hold the prey when it is pressed against them by the mandibles.
Evolutionary correlations between escape behaviour and performance ability in eight species of snow skinks (Niveoscincus: Lygosominae) from Tasmania
Authors: Melville Jane , Swain Roy
Published: August 2003

Three locomotor modes were examined (sprinting, jumping and climbing) in eight species of skinks: seven Niveoscincus spp. and Pseudemoia entrecasteauxii. These species formed four distinct ecological types: ground‐dwelling, arboreal, heath/rock dwelling, and saxicolous. Significant behavioural preferences for particular escape modes in the field were found, which reflected the performance capabilities at an animal in the laboratory. This study used both non‐phylogenetic and evolutionary based analyses to demonstrate that species occupying different microhabitats and using different escape tactics exhibit corresponding differences in performance abilities. Four Niveoscincus species are specialized in performance abilities and behavioural responses (N. greeni, N. ocellatus, N. pretiosus, N. orocryptus) by excelling in some performance abilities but having behavioural restrictions at attemping other locomotor modes. Only N. microlepidotus and N. orocryptus used escape tactics opportunistically; these species possess a suite of behavioural responses that may reflect the wide range of microhabitats they occupy. Ground‐dwelling species N. metallicus, N. coventryi and Pseudemoia entrecasteauxii performed poorly at all performance abilities and seemed to have biomechanical limitations, rather than behavioural restrictions, on locomotor mode. Thus, when making interspecific comparisons, the behaviour of an animal needs to be considered before appropriate performance measures are selected. Phylogenetic analyses demonstrate that escape tactics and performance abilities have co‐evolved in Niveoscincus, with an evolutionary trend towards behavioural and locomotor specialization.
Erectile tissue in an invertebrate animal: the Octopus copulatory organ
Authors: Thompson Joseph T. , Voight Janet R.
Published: August 2003

The most familiar examples of erectile tissue are the genitalia of mammals, notably the penis and clitoris. Among the soft‐bodied invertebrates, erectile tissue is virtually unknown, even in sex organs. Here we report that the ligula, the copulatory organ that is a modification of an arm tip of male octopuses, is erectile in Octopus bimaculoides. The normally minute ligula was observed during an unsuccessful mating attempt to be engorged. Histological sections of the ligula reveal striking structural convergences with mammalian erectile tissue: large, well‐vascularized internal cavities subdivided by networks of collagen fibres and enclosed by an array of collagen fibres. This internal structure differs markedly from the dense, three‐dimensional array of muscles and connective tissues seen in the other octopodid ligulae examined. Erectile tissue may represent an evolutionary compromise between opposing selective forces. Small ligulae may be advantageous because O. bimaculoides hunts in daylight and the white‐faced ligula may be conspicuous to predators. Large ligulae, however, may be advantageous if the intense sexual selection thought to occur among octopodids selects for large ligulae, which can transfer larger spermatophores that carry more sperm. An erectile ligula may minimize the impact of these opposing selective forces.
Temperature and salt balances on Georges Bank February–August 1995
Authors: Lentz Steven J. , Beardsley Robert C. , Irish James D. , Manning James , Smith Peter C. , Weller Robert A.
Published: August 2003

Temperature and salinity variability over the crest and southern flank of Georges Bank are investigated using moored observations obtained from February to August 1995 and historical data. There was a large seasonal variation in water temperature, which decreased 1°C–2°C in February to a minimum of 5°C due to surface cooling and wind‐forced cross‐bank advection, and then increased steadily due to surface heating, reaching 10°C (southern flank) to 17°C (crest) in August. The crest warmed more than the southern flank because it is shallower. Temperature variability at shorter timescales (days to weeks) was primarily due to surface heating on the crest and horizontal advection on the southern flank. Salinity variability over the southern flank was primarily associated with two processes. Intrusions of warm, salty, shelf‐slope‐front water in May and August were associated with Gulf Stream warm‐core rings, but did not cause longer‐term changes on the southern flank or penetrate onto the crest. Alongbank advection brought low‐salinity, cool Scotian Shelf Water to the southern flank sites in March and early May, about three weeks after crossing the Northeast Channel onto the northeastern flank of Georges Bank (≈130 km away). This low‐salinity water on the southern flank in the spring did not penetrate immediately onto the crest. Instead, the crest salinity steadily decreased from April to August due to both precipitation (evaporation was small) and, based on historical data, a tidally forced, cross‐frontal exchange flow (0.01–0.02 m s−1) that both freshens and cools the crest.
Feedbacks between oceanic redox states and marine productivity: A model perspective focused on benthic phosphorus cycling
Authors: Wallmann K.
Published: August 2003

A new model for the marine cycles of particulate organic carbon (POC), oxygen, nitrate, and phosphorus has been developed and applied to explore the controls and constraints on marine productivity and nutrient inventories. The coupled benthic‐pelagic model uses a new approach for the simulation of the reactive phosphorus turnover (Preac corresponding to the sum of organic P, authigenic P, and adsorbed phosphate) in marine sediments. The simulated POC/Preac burial ratio in shelf, slope and rise, and deep‐sea sediments increases under strongly reducing conditions in agreement with field observation. The model runs revealed that the spread of anoxia in bottom waters may enhance the productivity of the global ocean by one order of magnitude if sufficient nitrate is provided by N2‐fixation. Thus anoxic bottom waters promote eutrophic conditions and vice versa. Additional model runs showed that the productivity and nutrient inventory of the glacial ocean were probably enhanced due to the falling sea level. Marine regression induced a narrowing of the depositional areas on the continental shelves and thereby an increase in the fraction of POC exported to the deep ocean. The accelerated POC delivery, in turn, decreased the oxygen contents of the deep water and thus favored the release of phosphate from deep‐sea and rise sediments. Enhanced recycling of phosphate at the seafloor promoted further POC export in a positive feedback loop.
Planetary bow shocks: Gasdynamic analytic approach
Authors: Verigin M. , Slavin J. , Szabo A. , Gombosi T. , Kotova G. , Plochova O. , Szegö K. , Tátrallyay M. , Kabin K. , Shugaev F.
Published: August 2003

A new analytical model of the bow shock surface is suggested for reasonably accurate and fast prediction of this boundary's position near obstacles of different shape. For axially symmetric obstacles the model was verified by comparison with experiments and results of gasdynamic code application for a wide range of upstream polytropic indexes, 1.15 < γ < 2, and Mach numbers, 1 < Ms < ∞. The model can also be used for prediction of the bow shock position around nonaxially symmetric obstacles.
Slip history and dynamic implications of the 1999 Chi‐Chi, Taiwan, earthquake
Authors: Ji Chen , Helmberger Donald V. , Wald David J. , Ma Kuo‐Fong
Published: September 2003

We investigate the rupture process of the 1999 Chi‐Chi, Taiwan, earthquake using extensive near‐source observations, including three‐component velocity waveforms at 36 strong motion stations and 119 GPS measurements. A three‐plane fault geometry derived from our previous inversion using only static data [Ji et al., 2001] is applied. The slip amplitude, rake angle, rupture initiation time, and risetime function are inverted simultaneously with a recently developed finite fault inverse method that combines a wavelet transform approach with a simulated annealing algorithm [Ji et al., 2002b]. The inversion results are validated by the forward prediction of an independent data set, the teleseismic P and SH ground velocities, with notable agreement. The results show that the total seismic moment release of this earthquake is 2.7 × 1020 N m and that most of the slip occurred in a triangular‐shaped asperity involving two fault segments, which is consistent with our previous static inversion. The rupture front propagates with an average rupture velocity of ∼2.0 km s−1, and the average slip duration (risetime) is 7.2 s. Several interesting observations related to the temporal evolution of the Chi‐Chi earthquake are also investigated, including (1) the strong effect of the sinuous fault plane of the Chelungpu fault on spatial and temporal variations in slip history, (2) the intersection of fault 1 and fault 2 not being a strong impediment to the rupture propagation, and (3) the observation that the peak slip velocity near the surface is, in general, higher than on the deeper portion of the fault plane, as predicted by dynamic modeling.
Dynamic interactions between the gulf of Guinea passive margin and the Congo River drainage basin: 1. Morphology and mass balance
Authors: Leturmy Pascale , Lucazeau Francis , Brigaud Frédéric
Published: August 2003

A sediment budget between the Congo River drainage basin and the western African margin in the Gulf of Guinea is proposed on the basis of published and unpublished offshore Tertiary isopach maps, and onshore digital elevation analysis. The overall denudation of that area may be as high as 3.5 × 106 km3 with a maximum of 10% coming from Mesozoic and Cenozoic covers. The southern part of the Congo River basin, related to uplift of the South African and Kalahari shields, appears as the most immature from the morphologic standpoint but provides one third of the present‐day sediment production; it represents a maximum denudation of 150,000 km3. On the easternmost part, East African Rift drainage basins show a more mature relief and a maximum denudation of 270,000 km3, which can increase to 570,000 km3 if the Congo drainage basin had extended up to the east branch of the rift. These values are confidently established from the existence of remnant geological surfaces, and can explain the volume of Tertiary sediment in the Gulf of Guinea. During upper Cretaceous, the most important accumulations of sediments correspond to the Ogooe and Kwanza fans, which shows that the organization of continental drainage was different as was potential source of sediments. In the northern part of the present‐day Congo River drainage basin, there was a compressional episode during Santonian that may have caused significant relief and erosion along a Benue‐Chad axis.
Dynamic interactions between the Gulf of Guinea passive margin and the Congo River drainage basin: 2. Isostasy and uplift
Authors: Lucazeau Francis , Brigaud Frédéric , Leturmy Pascale
Published: August 2003

The Gulf of Guinea continental margin is paralleled by a coastal relief that isolates the Congo drainage basin and can play a subsequent role in interactions between margin deposits and continental denudation: Migration of depocenters from the Ogooe and Kwanza Rivers to the Congo fan in the Oligocene, low present‐day sediment delivery, or Pleistocene submarine channels instabilities are possible evidences for this interaction. In order to test this hypothesis, we examine successively margin isostasy, regional uplift, erosional unloading and flexural bulge created by sediment loads. Satellite free air gravity and two‐dimensional thermomechanical modeling, including depth of necking, are used to determine the structure of continental margin and strength conditions for two selected sections across South Gabon and Congo fan. Both verify similar conditions for extension geometry, depth of necking (10–20 km) and strength (equivalent elastic thickness of 20–30 km); differences in observed gravity are explained mainly by differences in sediment volumes. Regional uplift during Miocene of at least 450 m is attributed for both continent and margin, as evidenced by the elevated base level of the Congo drainage basin and the uplift of shelf break and coastal plains. Topography corrected for regional uplift, valley erosion below relics surfaces, and corresponding erosion unloading has been determined as a proxy of Oligocene topography; it shows a typical rift shoulder topography isolating Congo drainage basin from margin. In such conditions, small‐amplitude flexural uplift related to sediment loads can possibly have negative feedbacks for both Oligocene and present time.
A new three‐dimensional higher‐order thermomechanical ice sheet model: Basic sensitivity, ice stream development, and ice flow across subglacial lakes
Authors: Pattyn Frank
Published: August 2003

A new three‐dimensional thermomechanically coupled ice sheet model is developed. Contrary to the majority of three‐dimensional ice sheet models (shallow ice approximation), higher‐order stress gradients (longitudinal and transverse) are accounted for in the force balance equations. The horizontal velocity field is determined from the force balance equations in their “derivative form” (elliptical equation) using the method presented by Pattyn [2000, 2002a]. The model is solved on a regular grid in the horizontal and an irregular grid in the vertical and is numerically stable. Basic experiments include the European Ice Sheet Modeling Initiative (EISMINT) benchmarks for large‐scale ice sheet models and a comparison with the Saito‐Blatter ice sheet model including higher‐order stress gradients [Saito et al., 2003]. Detailed calculations of ice flow over three‐dimensional bedrock perturbations showed the validity of the higher‐order solution. The model is capable of simulating the evolution of an ice stream within the ice sheet and shows important aspects of observed ice stream features, such as the surface flattening and the importance of side drag. The simulation of the ice flow over a subglacial lake results in a flattening of the surface, a local velocity increase over the lake, and a deviation of the ice flow from the main flow direction, features which are also observed at Lake Vostok, Antarctica.
Vertical structure of surface gravity waves propagating over a sloping seabed: Theory and field measurements
Authors: Zou Qingping , Hay Alex E. , Bowen Anthony J.
Published: August 2003

Theoretical predictions of the vertical structure of wave motion over a sloping seabed are compared with field observations close to the bed in the nearshore zone. Of particular interest is the effect of the local slope on the magnitude and phase of the vertical velocity. Field measurements of near‐bed velocity profiles on a 2° bed slope were obtained using a coherent Doppler profiler. The surface elevation was measured by a colocated, upward looking, acoustic sounder. Results are presented from two intervals of different wave energy levels during a storm event: for wave height/water depth ratios smaller than 0.3 and for Ursell numbers smaller than 0.6. The local comparisons of magnitude and phase between the vertical velocity and surface elevation measurements are in good agreement with linear theory for a sloping bed, but differ greatly from that for a horizontal bottom, especially in the lower water column. The sloping bottom, however, has little effect on the horizontal velocity. Linear theory appears to adequately describe the transfer function between the surface elevation and the near‐bed velocities, not only at the peak frequencies but also at their harmonics. However, in relatively shallow water the local transformations of free and forced waves at the harmonic frequencies are indistinguishable in the lower water column. Therefore, given surface elevation measurements at a particular location (which reflect the integrated effects of nonlinearities associated with wave shoaling), the vertical structure of the third moments of velocity fields estimated from linear theory is in reasonable agreement with the observations. Both theory and observations show that the skewness and asymmetry of the vertical velocity are subject to significant bottom slope effects, whereas those of horizontal velocity are not.
Second and first baroclinic Kelvin modes in the equatorial Pacific at intraseasonal timescales
Authors: Cravatte Sophie , Picaut Joël , Eldin Gérard
Published: August 2003

TOPEX/Poseidon sea level and time series from the TAO (Tropical Atmosphere Ocean) array of moorings over 1992–1999 are used to investigate the spatiotemporal characteristics of equatorial Kelvin waves in the Pacific at period shorter than 180 days. Spectral analyses show high oceanic energy in two separate bands of period, around 70 days and 120 days. Signals are coherent in both bands all along the equator. Ocean General Circulation Model (OGCM) simulations forced by different wind stress fields are also analyzed and exhibit the same features. Observed and modeled sea level, dynamic height and 20°C isotherm depth, band‐pass filtered around 70 days, show an eastward propagation at phase speed of 2.4–2.9 m s−1, typical of the first baroclinic Kelvin mode. The meridional and vertical structures of the equatorial waves at the onset of the 1997 El Niño are also those expected for a first Kelvin mode. At 120‐day period, phase speeds, meridional and vertical structures are closer to those expected for a second baroclinic mode. Both modes are nevertheless present in the two frequency bands. A simple Kelvin wave model shows that the wind at 120‐day period seems to force the Kelvin waves at the same period. However, the predominance of second baroclinic mode at 120‐day period cannot be explained solely by the characteristics of the wind. OGCM simulations rather suggest the importance of internal oceanic processes such as vertical redistribution of energy from first to second baroclinic mode as the waves propagate eastward. Model outputs over 1984–1999 indicate that these equatorial Kelvin waves at 70‐ and 120‐day period may have an effect on El Niño since they seem to be stronger at its onset.
Morphology of gravity‐wave energy as observed from 4 years (1998–2001) of high vertical resolution U.S. radiosonde data
Authors: Wang Ling , Geller Marvin A.
Published: August 2003

Gravity‐wave energy densities have been derived from 4 years (1998–2001) of U.S. high vertical resolution (∼30 m) radiosonde wind and temperature data. This data set includes more than 90 stations that extend from 14°S to 71°N and 135°E to 55°W and cover such varied terrain as tropical islands, midcontinent plains, and mountainous regions, and they extend to the Arctic. This data set also includes both winds and temperatures in the troposphere and lower stratosphere for all stations. Thus analysis of this data set should be useful in distinguishing source effects from propagation effects. Some of the features found in this analysis are as follows. On the average, lower stratospheric gravity‐wave energies decrease poleward and are stronger in (Northern Hemisphere) winter than summer. Tropospheric gravity waves are also stronger in winter than summer, but they maximize at middle latitudes (35°–40°N). In the troposphere, gravity‐wave energy maxima exist over the Rocky Mountains, but in the lower stratosphere the energy maxima are mostly in the southeastern United States. Quasi‐Biennial Oscillation and El Nino–Southern Oscillation effects appear to account for much of the observed interannual variability in lower stratospheric gravity‐wave energy. The time series of tropospheric and lower stratospheric gravity‐wave energies are virtually uncorrelated with one another.
Correlations of long‐lived chemical species in a middle atmosphere general circulation model
Authors: Sankey David , Shepherd Theodore G.
Published: August 2003

Correlations between various chemical species simulated by the Canadian Middle Atmosphere Model, a general circulation model with fully interactive chemistry, are considered in order to investigate the general conditions under which compact correlations can be expected to form. At the same time, the analysis serves to validate the model. The results are compared to previous work on this subject, both from theoretical studies and from atmospheric measurements made from space and from aircraft. The results highlight the importance of having a data set with good spatial coverage when working with correlations and provide a background against which the compactness of correlations obtained from atmospheric measurements can be confirmed. It is shown that for long‐lived species, distinct correlations are found in the model in the tropics, the extratropics, and the Antarctic winter vortex. Under these conditions, sparse sampling such as arises from occultation instruments is nevertheless suitable to define a chemical correlation within each region even from a single day of measurements, provided a sufficient range of mixing ratio values is sampled. In practice, this means a large vertical extent, though the requirements are less stringent at more poleward latitudes.
Interannual variability of surface evaporative moisture sources of warm‐season precipitation in the Mississippi River basin
Authors: Sudradjat Arief , Brubaker Kaye L. , Dirmeyer Paul A.
Published: August 2003

Patterns of variability of the evaporative sources of Mississippi River basin precipitation are investigated. Time series of selected regions' evaporative contributions to warm‐season precipitation in the Mississippi and its subbasins are produced on a 15‐day basis for the years 1963 to 1998. Source region contributions are estimated by backward‐trajectory analysis, which tracks water vapor backward in time from its site of condensation to its point of evaporation. The National Centers for Environmental Prediction (NCEP) reanalyses are used for the required atmospheric dynamics and observed data from NCEP Climate Prediction Center for precipitation. Correlation and principal component analyses of the source contribution and precipitation anomaly time series reveal a spatial pattern consisting of internal (Missouri, Red/Arkansas, and Lower Mississippi) and external (Texas/Mexico and Caribbean) sources, which explains statistically much of the interannual variability in warm‐season precipitation. Further analysis of the pattern reveals that the external sources play a more important role than internal sources in the anomalies of precipitation. Examining a subset of the period, from 1979 to 1998, moisture flux analysis confirms the role of the external sources by showing the strong association between the precipitation anomalies and flux across the southern boundaries of the basin (which includes the contributions from Texas/Mexico and Caribbean). An index is introduced, based on measurable surface pressure differences between centers over the Atlantic Ocean and central United States (Mississippi watershed). The index is potentially useful in forecasting slow variations of precipitation supply in the basin.
Impact of snow conditions in spring dynamical seasonal predictions
Authors: Schlosser C. Adam , Mocko David M.
Published: August 2003

A suite of numerical simulations with the Center for Ocean Land Atmosphere (COLA) Studies' and the Goddard Earth Observing System (GEOS) general circulation models (GCMs) has been performed in conjunction with the Dynamical Seasonal Prediction (DSP) Project. These simulations aim to quantify the impact of realistic snow conditions on skill in the GCMs. In this study, ensemble climate simulations conducted for Northern Hemisphere spring (March–June) that span the years 1982–1998 are considered. For each year of these seasonal simulations, a pair of complementary runs is performed. For one of the simulations, snow conditions are allowed to evolve interactively; for the other simulation, the snow conditions are prescribed, according to a daily, global snow depth analysis, within each of the land modules of the GCMs. For this study, the impact of snow conditions on simulated near‐surface air temperature is assessed. The results indicate that the prescribed (and presumably improved) snow conditions in the GCMs play a beneficial role in skillfully capturing the observed spatial/temporal patterns of interannual variations of near‐surface air temperature, at a local scale. Through consideration of the surface energy‐budget and the effect of snow cover on surface albedo, the localized improvement of near‐surface air temperature skill (both in the spatial correlations and in the root‐mean‐square error) that results from the prescribed snowfields is found to be strongly tied to when and where the interannual variabilities of snow cover and mean incident short wave radiation coincide. This impact of prescribed snow is also most considerable during the widespread ablation of the matured winter season snow cover, which typically occurs during April over the Northern Hemisphere. Overall, the impact of the prescribed snow over all land points (i.e., local and nonlocal) shows mixed results in its effect on near‐surface air temperature skill. These mixed results most likely underscore the difficulty of the GCMs to consistently translate the localized skillful response into nonlocal/remote skill. In the end, physical parameterizations in GCMs should be improved before all seasonal prediction enhancements from improved snow conditions can be realized.
A near‐field tool for simulating the upstream influence of atmospheric observations: The Stochastic Time‐Inverted Lagrangian Transport (STILT) model
Authors: Lin J. C. , Gerbig C. , Wofsy S. C. , Andrews A. E. , Daube B. C. , Davis K. J. , Grainger C. A.
Published: August 2003

We introduce a tool to determine surface fluxes from atmospheric concentration data in the midst of distributed sources or sinks over land, the Stochastic Time‐Inverted Lagrangian Transport (STILT) model, and illustrate the use of the tool with CO2 data over North America. Anthropogenic and biogenic emissions of trace gases at the surface cause large variations of atmospheric concentrations in the planetary boundary layer (PBL) from the “near field,” where upstream sources and sinks have strong influence on observations. Transport in the near field often takes place on scales not resolved by typical grid sizes in transport models. STILT provides the capability to represent near‐field influences, transforming this noise to signal useful in diagnosing surface emissions. The model simulates transport by following the time evolution of a particle ensemble, interpolating meteorological fields to the subgrid scale location of each particle. Turbulent motions are represented by a Markov chain process. Significant computational savings are realized because the influence of upstream emissions at different times is modeled using a single particle simulation backward in time, starting at the receptor and sampling only the portion of the domain that influences the observations. We assess in detail the physical and numerical requirements of STILT and other particle models necessary to avoid inconsistencies and to preserve time symmetry (reversibility). We show that source regions derived from backward and forward time simulations in STILT are similar, and we show that deviations may be attributed to violation of mass conservation in currently available analyzed meterological fields. Using concepts from information theory, we show that the particle approach can provide significant gains in information compared to conventional gridcell models, principally during the first hours of transport backward in time, when PBL observations are strongly affected by surface sources and sinks.
A meridional scan of the stratospheric gravity wave field over the ocean in 2001 (MeSSO2001)
Authors: Sato Kaoru , Yamamori Miho , Ogino Shin‐Ya , Takahashi Noriyoshi , Tomikawa Yoshihiro , Yamanouchi Takashi
Published: August 2003

In order to examine gravity wave characteristics over the ocean, we conducted a radiosonde observation campaign to scan the stratosphere meridionally over the middle Pacific with Hakuho‐maru research vessel operated by the Ocean Research Institute, University of Tokyo. Seventy vertical profiles of temperature, winds, and humidity were successfully obtained over a wide latitude range of 28°N to 48°S with an interval of 1 degree. Gravity wave energy and vertical wavenumber spectra were examined as a function of latitude. Gravity wave energy is maximized in the tropical region where the convection is active and in the middle latitude region where the subtropical westerly jet is situated. The wave energy in the tropical region is greater than the climatology based on operational radiosonde observation over land regions. The gravity wave amplitude does not necessarily increase with altitude, in contradiction to simple vertical propagation. The latitudinal distribution of wave energy rather suggests that gravity waves propagate meridionally toward higher latitudes. An interesting feature is that a wave packet having large horizontal wind and temperature amplitudes is observed continuously over 7 days in the latitudinal region extending 26 degrees. Results of hodograph analysis indicate that the wave packet is due to an inertia‐gravity wave with horizontal and vertical wavelengths of about 1800 km and 4–5km, respectively. This inertia‐gravity wave is likely generated in association with vigorous convection in the Intertropical Convergence Zone (ITCZ) in the Northern Hemisphere and propagated southward interhemispherically. The results in this study show that there are strong nonstationary gravity wave sources over the ocean. The importance of meridionally propagating gravity waves is discussed.