bluuebunny/crossref_metadata_2025 huggingface dataset:
Coexistence of competitive species with a stage‐structured life cycle
Authors: Mougi Akihiko , Nishimura Kinya
Published: July 2005

Ecological theory provides explanations for exclusion or coexistence of competing species. Most theoretical works on competition dynamics that have shaped current perspectives on coexistence assume a simple life cycle. This simplification, however, may omit important realities. We present a simple two‐stage structured competition model to investigate the effects of life‐history characteristics on coexistence. The achievement and the stability of coexistence depend not only on competition coefficients but also on a set of life‐history parameters that reflect the viability of an individual, namely, adult death rate, maturation rate, and birth rate. High individual viability is necessary for a species to persist, but it does not necessarily facilitate coexistence. Intense competition at the juvenile or adult stage may require higher or lower viability, respectively, for stable coexistence to be possible. The stability mechanism can be explained by the refuge effect of the less competitive stage, and the birth performance, which preserves the less competitive stage as a refuge. Coexistence might readily collapse if the life‐history characteristics, which together constitute individual viability, change, even though two species have an inherent competitive relation conducive to stable coexistence.
A re-examination of the Nama-type Vendian organism Rangea schneiderhoehni
Authors: GRAZHDANKIN DIMA , SEILACHER ADOLF
Published: July 2005

The need to re-examine Rangea has been motivated by two factors: first, by the recent progress in the understanding of three-dimensional mouldic preservation of Vendian fossils, and second, by discoveries of this taxon outside Gondwana albeit in the same sedimentary environment as seen in Namibia. Several important features are revealed, including the in situ posture in the sediment, the double-layered quilted structure, the tripartite stemless body and the mucous-supported sheath in the sediment. It is suggested that Rangea represents an infaunal organism, and that the similarity with other members of the Nama-type biota reflects convergence in functional and fabricational constraints in relation to infaunal life habit.
Physico-chemical determinants of helminth component community structure in whitefish (Coregonus clupeaformes) from adjacent lakes in Northern Alberta, Canada
Authors: GOATER C. P. , BALDWIN R. E. , SCRIMGEOUR G. J.
Published: July 2005

Populations of hosts vary extensively in the types and numbers of parasites that the average individual contains. Understanding the factors that lead to this variation is an important goal for parasite ecologists. We characterized patterns of helminth component community structure in whitefish collected from a cluster of 7 lakes located on an isolated plateau in northern Alberta, Canada. Component communities were species rich (5–6 species per lake), high in mean helminth intensity (approximately 80–500 individuals/host), and high in between-lake similarity (50–100%), a pattern consistent with results from studies on whitefish sampled from other localities in Northern Canada and Europe. Multivariate analyses indicated that the structure of the component communities was associated with 2 opposing environmental gradients. One was defined primarily by water colour, the second by phosphorous concentration. Thus, 4 lakes were characterized by a combination of high colour, low productivity, low parasite intensities, and the absence of larval acanthocephalans. Habitat/species associations were less clear as intensities increased, but the 3 remaining lakes tended to have the opposite characteristics. These results provide evidence that variation in helminth component community structure in fish is associated with variation in physicochemical characteristics that are linked to aquatic productivity.
The impact of light quality and leaf wetness on photosynthesis in north-west Andean tropical montane cloud forest
Authors: Letts Matthew Guy , Mulligan Mark
Published: July 2005

Photosynthesis was limited by low-intensity photosynthetically active radiation (PAR) and leaf wetness in a lower montane cloud forest (LMCF) of Cauca, Colombia. Mean PAR intensity remained below the saturation level for leaf-scale net photosynthesis (Pn) throughout the solar day during the wet season and for most of the solar day during the dry season. PAR represented a smaller fraction of total solar radiation (K↓) in LMCF than in lowland rain forest (LRF). In LMCF trees and shrubs, mean PAR-saturated Pn ranged from 4.3–10.6 μmol C m−2 s−1 at 1450 m, and from 3.5–10.2 μmol C m−2 s−1 at 2150 m. Pn was reduced by abaxial wetness in leaves of some trees and shrubs, and eliminated in others. This study indicates that persistent cloudiness and interception of cloud water by leaves limit LMCF productivity.
Above- and below-ground litter production in three tropical montane forests in southern Ecuador
Authors: Röderstein Marina , Hertel Dietrich , Leuschner Christoph
Published: July 2005

Litter production from above-ground (leaves, twigs, fruits, flowers) and below-ground (roots) plant organs is an important component of the cycling of carbon and nutrients in forests. Tropical montane forests possess comparatively large quantities of fine-root biomass, suggesting that litter production by dying fine roots may represent a major component of total litter production. In a comparative study in three tropical montane forests of southern Ecuador at 1890, 2380 and 3060 m elevation, we measured leaf-fall by litter trapping and fine-root litter production by sequential soil coring and fine-root biomass and necromass analysis for about 1 y with the objectives (1) to quantify annual above- and below-ground litter production, and (2) to investigate elevational differences in litter production. Leaf litter mass decreased to less than a third (862 to 263 g m−2 y−1) with increasing elevation (1890 m to 3060 m), whereas fine-root litter production increased by a factor of about four (506 to 2084 g m−2 y−1). Thus, the ratio of leaf to fine-root litter shifted by an order of magnitude in favour of fine-root litter production between 1890 to 3060 m. Fine-root litter production was not synchronized with leaf litterfall and was seasonal only at 3060 m with mortality peaks in the drier and the wetter periods. We conclude that dying fine roots represent a very important fraction of total litterfall in tropical montane forests that can exceed the quantity of leaf litter. At 3060 m, the largest part of the organic material on top of the soil must originate from dying fine roots but not from fallen leaves.
Population dynamics of Hyperiodrilus africanus (Oligochaeta, Eudrilidae) in Ivory Coast
Authors: Tondoh Jérôme Ebagnerin , Lavelle Patrick
Published: July 2005

The population dynamics of the exotic earthworm Hyperiodrilus africanus was investigated in a secondary forest of the Natural Reserve of Lamto (Ivory Coast) over a period of 19 mo. The objectives were to assess seasonal abundance patterns and to determine the adaptive strategies of this species. Each month, 10 soil samples of 100×100×40 cm and 20 monolith samples of 25×25×30 cm were randomly excavated in a plot of 50×95 m and earthworms were extracted by both hand-sorting and wash-sieving methods. The results show significant inter-annual and seasonal fluctuations in population size. Three factors are likely to control population dynamics: (1) rainfall, (2) soil water content and (3) seasonality. The dry season appears to be the most important environmental factor that regulates population abundance when predation, density-dependent regulation and competition phenomena are ignored. Hyperiodrilus africanus exhibited an r strategy, suggesting a high ability to recover populations affected by drought.
Germination strategy of the East African savanna tree Acacia tortilis
Authors: Loth Paul E. , de Boer Willem F. , Heitkönig Ignas M. A. , Prins Herbert H. T.
Published: July 2005

Germination of Acacia tortilis seeds strongly depends on micro-site conditions. In Lake Manyara National Park, Tanzania, Acacia tortilis occurs abundantly in recently abandoned arable fields and in elephant-mediated gaps in acacia woodland, but does not regenerate in grass swards or beneath canopies. We examined the germination of Acacia tortilis using field and laboratory experiments. Seeds placed on top of the soil rarely germinated, while seeds covered with elephant dung or buried under the soil surface had a germination success between 23–43%. On bare soil 39% of both the dung-covered and buried seeds germinated, in perennial grass swards 24–43%, and under tree canopies 10–24% respectively. In laboratory experiments, seed water absorption correlated positively with temperature up to 41 °C, while subsequent germination was optimal at lower (21–23 °C) temperatures. Seeds that had absorbed water lost their viability when kept above 35.5 °C. The absence of light did not significantly influence germination success. Acacia tortilis does not actively disperse its seeds, but regeneration outside tree canopies was substantial. The regeneration potential thus strongly depends on the physiognomy of the vegetation.
Lianas and their supporting plants in the understorey at Los Tuxtlas, Mexico
Authors: Vleut Ivar , Pérez-Salicrup Diego R.
Published: July 2005

Lianas are woody climbing plants that begin their life cycles as seedlings rooted in the ground, but eventually rely on other plants for physical support in order to reach the top of the forest canopy (Holbrook & Putz 1996, Putz & Holbrook 1991). Lianas can negatively affect plants they climb by competing with them for common resources such as light, water and nutrients, and by causing them direct physical damage (Dillenburg et al. 1995, Pérez-Salicrup & Barker 2000, Stevens 1987, Whigham 1984). Yet, there is little documentation about the size at which liana individuals of different species begin to climb on other plants in nature. This information is important because the size at which a liana begins to climb on other plants will determine when lianas potentially start physically affecting their supporting plants. Furthermore, although the growth of liana seedlings might be determined by light (Sanches & Válio 2002), the availability of support will also largely influence the rate of growth of liana stems (Peñalosa 1982, 1983, 1985). Thus, information about the size at which liana species find support in the forest understorey will be useful in understanding future growth of liana individuals.
Resilience of secondary forest regrowth after slash-and-burn agriculture in central Amazonia
Authors: Gehring Christoph , Denich Manfred , Vlek Paul L. G.
Published: July 2005

This study describes forest succession following slash-and-burn agriculture in central Amazonia, based on four chronosequences (22 sites) of 2- to 25-y-old secondary regrowth and mature forest. Biomass accumulated in the form of a saturation curve: 25 y of regrowth restored half of the mature-forest biomass, 75% would be restored after an estimated 175 y. Biomass accumulation was accompanied by a rapid decrease in woody plant density and an increase of the positive skew of plant size distribution. Liana biomass share declined from 5.0% in young to 1.9% in old regrowth, and 1.3% in mature forest, whereas the share of palms was low (0.5%) in young regrowth and high in old regrowth (1.8%) and mature forest (2.2%). 25-y-old regrowth was similar with mature forest in respect to woody plant density and growth-form composition, but both the plant size distribution and the number of stems per plant differed strongly from mature forest. A moderate increase in land use had only minor effects on biomass accumulation, but profoundly changed structural characteristics of regrowth, pointing to a high vulnerability to degradation. Thus, the sustainability of slash-and-burn in central Amazonia may be lower than the rapid initial biomass accumulation would make it seem.
Competitive interactions and distributional dynamics in two Malagasy frogs
Authors: Lehtinen Richard M.
Published: July 2005

Ecological theory predicts that interspecific interactions can affect population and community dynamics. Two experiments were conducted on Mantidactylus bicalcaratus and M. punctatus, two sympatric frog species from Madagascar that live and breed in rain-forest plants (Pandanus spp.), to test for interspecific competition. The first experiment examined larval growth rates and survivorship with and without conspecifics. While survivorship did not differ among treatments, mean growth rates for M. bicalcaratus were significantly reduced in the presence of M. punctatus larvae. The second experiment manipulated the presence and density of adults in Pandanus plants. Emigration from and immigration to experimental plants tended to be higher and lower, respectively, for M. bicalcaratus in the presence of M. punctatus, but these differences were not significant. These results demonstrate asymmetric competition (at least as larvae) and indicate that M. punctatus is the superior competitor. Field data showed that M. bicalcaratus was found significantly more frequently in the absence of M. punctatus. Also, M. bicalcaratus populations were significantly more likely to go locally extinct in the presence of M. punctatus. These data suggest that asymmetric competitive interactions are important influences on the dynamics of these populations.
The population dynamics of a non-pollinating fig wasp on Ficus auriculata at Xishuangbanna, China
Authors: Peng Yan-Qiong , Yang Da-Rong , Duang Zhu-Biao
Published: July 2005

All fig wasps are confined to figs as larvae, and their specialized diets are restricted to fig embryos, galled fig ovaries or other fig wasp larvae (Boucek 1988). Almost all of the ∼800 Ficus species (Moraceae) are involved in species-specific obligate mutualism with a pollinating fig wasp (Hymenoptera: Agaonidae), which also strictly depends on its host fig for reproduction (Berg 2003, Ramirez 1970, Wiebes 1979). More than half of all fig species are functionally dioecious, with male and female functions relegated to separate plants, called gall and seed figs (Kjellberg et al. 1987). Gall figs are functionally male because they foster the pollinator larvae that disperse the fig's pollen as adults. Seed figs are functionally female and produce only seeds. The styles are too long for pollinator ovipositors to reach the ovules, and hence they cannot lay eggs. Gall fig styles are short (Ganeshaiah et al. 1995, Weiblen et al. 1995).
Where are the decomposers? Uncovering the soil food web of a tropical montane rain forest in southern Ecuador using stable isotopes (15N)
Authors: Illig Jens , Langel Reinhard , Norton Roy A. , Scheu Stefan , Maraun Mark
Published: July 2005

Trophic relationships among animals, plants and microflora are the basis for the construction of terrestrial and aquatic food webs, but both the structure and dynamics of food webs remain contentious. Examples of issues include how the overall nutrient status of a system affects the number of trophic levels, whether trophic-level omnivory and intraguild predation are rare or important, if different animal species can be aggregated into functional groups according to their taxonomic affiliation, how large numbers of decomposer animal species can coexist and why there are so many parthenogenetic taxa in soil.
The cost of nectar replenishment in two epiphytic bromeliads
Authors: Ordano Mariano , Ornelas Juan Francisco
Published: July 2005

Animal-pollinated angiosperm plants that replenish removed nectar invest energy that can entail a reproductive cost. Here we investigated whether or not seed production is affected by replenishing nectar in hummingbird-pollinated Tillandsia multicaulis and T. deppeana (Bromeliaceae) in a montane cloud forest in eastern Mexico. These epiphytic plants respond strongly and positively to repeated nectar removal. The female reproductive cost was assessed in manually, cross-pollinated flowers with or without repeated nectar removal. Seed production from experimental flowers was then contrasted with those naturally exposed to pollination and nectar removal. Tillandsia deppeana set the same number of seeds of the same size regardless of whether or not it had to replenish nectar. Seeds were slightly smaller if the result of natural open pollination than from copious hand crossing. In contrast, T. multicaulis set about half as many seeds when it had to replenish than when it did not, indicating a substantial cost to replenishment. There was no difference in seed number of T. multicaulis between open and hand-augmented pollination. The contrasting results for plants that respond strongly and positively to repeated nectar removal suggest that the female reproductive costs of nectar replenishment can range from costly to beneficial, depending on the conditions of the plants and on the species.
Catastrophic natural origin of a species-poor tree community in the world's richest forest
Authors: Pitman Nigel C. A. , Cerón Carlos E. , Reyes Carmita I. , Thurber Mark , Arellano Jorge
Published: July 2005

Upper Amazonian tree communities are famous for their very high alpha-diversity. This paper describes an anomalous forest just 6 km south of the equator in lowland Ecuador that is structurally mature, surrounded by hyperdiverse forest, but strikingly poor in species. To investigate the anomaly, a 1-ha tree inventory and soil analysis were carried out and compared with 15 similar surveys of upland forest in the same region. The anomalous forest contains only 102 tree species ha−1, compared with a regional mean of 239±28 species ha−1. It is structurally indistinguishable from richer forests, and closest in composition to upland forest, but lacks the uplands' typically rich understorey tree community. Three hypotheses for its origin are examined: recovery from anthropogenic disturbance, unique soil conditions and recovery from a large-scale natural catastrophe. The third hypothesis is the best supported. Mineralogical, geological and remote-sensing evidence, and 14C-dating suggest that the forest grows on a vast debris plain left by a catastrophic flooding event roughly 500 y ago. The forest's low diversity today is most likely due to the failure of a full complement of the region's tree species – especially understorey taxa – to recolonize the outwash plain in the time since the disaster.
Prader–Willi syndrome: clinical genetics, cytogenetics and molecular biology
Authors: Bittel Douglas C. , Butler Merlin G.
Published: July 2005

Prader–Willi syndrome (PWS) is a neurodevelopmental disorder that arises from lack of expression of paternally inherited genes known to be imprinted and located in the chromosome 15q11-q13 region. PWS is considered the most common syndromal cause of life-threatening obesity and is estimated at 1 in 10 000 to 20 000 individuals. A de novo paternally derived chromosome 15q11-q13 deletion is the cause of PWS in about 70% of cases, and maternal disomy 15 accounts for about 25% of cases. The remaining cases of PWS result either from genomic imprinting defects (microdeletions or epimutations) of the imprinting centre in the 15q11-q13 region or from chromosome 15 translocations. Here, we describe the clinical presentation of PWS, review the current understanding of causative cytogenetic and molecular genetic mechanisms, and discuss future directions for research.
Ein praktikables Verfahren zur Bestimmung der Wissensquote und der Ratequote bei Mehrfachwahlaufgaben mit Bestantwort
Authors: Michelsen Uwe A. , Cordes Manuel
Published: July 2005

Zusammenfassung. Bei der Auswertung von Tests mit Mehrfachwahlaufgaben ist von Interesse, wie viele der vorgegebenen Fragen durch Wissen beantwortet werden; diese Größe wird auch Wissensquote genannt. Hierzu hat Garcia-Peréz 1987 ein Schätzverfahren - das sog. “Finite-State-Model“ - beschrieben, das nachfolgend mit einem Binomialmodell verglichen wird, wobei die Schätzung durch das Maximum-Likelihood-Verfahren erfolgt. Es zeigt sich, dass die Schätzung nach Garcia-Peréz Werte ergibt, die deutlich weniger von den simulierten Wissensraten abweichen. Um Personen, die mit der Auswertung von Tests befasst sind, das Schätzen der Wissens- und Ratequote der Probanden zu erleichtern, wird dieses Verfahren so aufbereitet, dass die gewünschten Schätzwerte einer Tabelle entnommen bzw. an einer Grafik abgelesen werden können.
Weak mixing in Lake Kivu: New insights indicate increasing risk of uncontrolled gas eruption
Authors: Schmid Martin , Halbwachs Michel , Wehrli Bernhard , Wüest Alfred
Published: July 2005

The deep waters of the East African Rift Lake Kivu contain large amounts of dissolved carbon dioxide and methane. The release of a fraction of these gases, which could be triggered by a magma eruption within the lake, would have catastrophic consequences for the two million people living on its shore. Up to now the safety assessment of the lake was based on the assumption that the gas concentrations in the deep waters are in a steady state with a residence time of 400 years. Turbulent transport was regarded as the main pathway of vertical exchange. Recent measurements and the analysis of the vertical transport processes in the lake radically change this evaluation. The vertical turbulent exchange is negligible, as documented by a spectacular set of several hundred double‐diffusive layers. Gases are mainly transported out of the deep zones by a slow upwelling with a residence time of 800–1000 years. Our results indicate that the methane production within the sediment has recently increased, leading to a gas accumulation in the deep waters and consequently decreasing the heat input needed to trigger a devastating gas release. With the estimated current CH4 production, the gas concentrations could approach saturation within this century.
High time resolution measurement of multiple electron precipitations with energy‐time dispersion in high‐latitude part of the cusp region
Authors: Tanaka H. , Saito Y. , Asamura K. , Ishii S. , Mukai T.
Published: July 2005

The SS‐520‐2 sounding rocket skimmed over the high‐latitude part of the cusp region and observed fine‐scale field‐aligned electron precipitations in the vicinity of the inverted‐V structures with the Low Energy Particle‐Electron Spectrum Analyzer (LEP‐ESA). There are at least two types of fine‐scale electron precipitations, namely “edge‐type electron bursts” and “multiple energy‐time dispersions.” Edge‐type electron bursts were observed only at the edge of the inverted‐V region, whereas multiple energy‐time dispersions were observed separately from the inverted‐V region as well as within or overlapping it. The latter was characterized by field‐aligned precipitations with falling energies from ∼200 eV down to ∼20 eV at a repetition rate of 1–2 Hz. Source altitudes were estimated using the energy‐time and pitch angle‐time dispersions. As a result, we found that the source altitudes were distributed along the geomagnetic field at altitudes of several thousand kilometers, depending on the accelerated energies of electrons. Higher‐energy electrons are generated at higher altitudes. The source temperature of the energy‐time dispersion was much higher than that of ionospheric cold electrons. We suggest that electrons injected from the magnetosheath were accelerated by inertial Alfvén waves at altitudes of several thousands of kilometers.
Reconstructing the long‐term aa index
Authors: Clilverd Mark A. , Clarke Ellen , Ulich Thomas , Linthe Joachim , Rishbeth Henry
Published: July 2005

The robustness of the aa geomagnetic index is of critical importance to the debate about the previously reported doubling of the solar coronal magnetic field in the last 100 years, inferred from an increasing trend in this index. To test the trend in aa, we have reconstructed the aa index using two long‐running European stations (Sodankylä from 1914 and Niemegk from 1890) to provide data for the northern component of the index that are independent of data from the UK observatories used in the “official” aa index. Both the fully “reconstructed” aa series, based on Sodankylä (67°N, L = 5.2 RE) and Niemegk (52°N, L = 2.3 RE) data in combination with the official aa Southern Hemisphere data, confirm the increasing trend in the index. The Niemegk‐based index shows little solar cycle variation in its deviation from the official index, probably because of the midlatitude location of the station. The high‐latitude station, Sodankylä, is more affected by active geomagnetic conditions during solar maximum because of the proximity of the auroral oval to the station. Nevertheless, its index also clearly confirms the increasing trend in the aa index and hence supports the idea of a long‐term increase in solar coronal magnetic field strength. As an added test, we reconstructed the aa index from a single site using data from two long‐running UK stations, Eskdalemuir and Lerwick, applying a technique known as interhourly variation (IHV) proposed by Svalgaard et al. (2004). The resulting series is designed to be primarily sensitive to solar wind conditions. Both the reconstructed aaIHV also showed an increasing trend with time and high consistency with the official aa index. Overall, we conclude that the robustness of the trend in the aa index supports the idea of a long‐term increase in solar coronal magnetic field strength.
Global distribution of equatorial plasma bubbles in the premidnight sector during solar maximum as observed by KOMPSAT‐1 and Defense Meteorological Satellite Program F15
Authors: Park Jaeheung , Min Kyoung Wook , Kim Vitaly P. , Kil Hyosub , Lee Jae‐Jin , Kim Hee‐Jun , Lee Ensang , Lee Dae Young
Published: July 2005

We investigated the global distribution of equatorial plasma bubbles (EPBs) using in situ plasma density measurements from Korea Multipurpose Satellite‐1 (KOMPSAT‐1) and Defense Meteorological Satellite Program (DMSP) F15 during the solar maximum period from June 2000 to August 2001. The results were generally consistent with those of previous studies. EPBs were observed at all longitudes around the magnetic dip equator in the equinoctial seasons with the peak occurrence in the American‐Atlantic‐African regions. During the June solstice, EPBs occurred predominantly in the African sector, with enhancements in the magnetic north in the Indian and west Pacific regions, but were totally suppressed in the American‐Atlantic sector. During the December solstice, EPBs occurred frequently in the American‐Atlantic sector but were suppressed in the other longitude sectors, especially in the Pacific sector. The EPB occurrence probability was seen to be correlated with the observed topside plasma density and the model prereversal upward drift speed of ambient plasmas (Fejer et al., 1999), with their respective dominance dependent on the seasons. However, the peak EPB occurrence in the American‐Atlantic sector during the December solstice was displaced somewhat from the region of peak density and upward drift, probably due to a strong solar terminator influence on the flux tube–integrated E region Pedersen conductivity and due to anomaly morphology. The peak EPB occurrence in the African sector during the June solstice is consistent only with the high ambient density in that region, for there was no coincidence with the maximum vertical drift or the minimum E region Pedersen conductivity.
Differential ion streaming in the solar wind as an equilibrium state
Authors: Dubinin E. , Sauer K. , McKenzie J. F.
Published: July 2005

We analyze the nonlinear evolution of differential streaming between core protons and alpha particles (or any secondary minor protons) based on the analysis of fully nonlinear multifluid MHD equations. It is shown that such an ion beam‐plasma system possesses an equilibrium state with a remnant of differential streaming. The properties of this state are studied. The system through the action of nonlinear hydromagnetic waves can attain an equilibrium state which is characterized by a “gyrating” motion of both ion populations with a phase shift of π. The waves which bring about a such transition are either the Alfven or magnetosonic modes, depending upon the beam speed. It is shown that the equilibrium differential speed between the alphas and protons Vαp lies between 0.8 and 1.5 VA but only in a certain regime of injection speeds of the alphas. A similar picture obtains for proton/proton configurations in which the number density of the secondary protons imposes a constraint on the injection speeds, 1.5 ≥ Vp,p/VA ≥ 0.3 (VA is a local Alfven speed). Nonlinear Alfven waves bring about a transition to equilibrium states with much higher differential velocities uαp(upp), proportional to the injection speeds, than magnetosonic waves.
Three‐dimensional magnetotail equilibria with prescribed boundary shapes
Authors: Birn Joachim
Published: July 2005

Three‐dimensional magnetotail equilibrium configurations are presented that are derived from a prescribed outer flux surface, equivalent to a closed magnetopause. The explicit solutions neglect the effects of field‐aligned currents, closely associated with a bending of field lines in the x, y plane, but include tail flaring in y and z. Most of the solutions are derived for an axisymmetric boundary, approximately consistent with force balance between the unperturbed solar wind and the magnetosphere at a closed magnetopause (Newtonian approximation). This force balance is used to relate the downtail variation of the tail radius to that of the total interior magnetotail pressure, equivalent to the lobe magnetic pressure. However, these properties are not sufficient to determine the tail configuration. We demonstrate this by deriving solutions with identical boundaries and identical variation of the total pressure along the tail but different amounts of field line flaring in the x, y plane. Under these conditions, stronger field line flaring is associated with a reduction of the magnetotail plasma pressure near midnight and an increase of the plasma sheet thickness from midnight toward the tail flanks. A reduction of the tail boundary flaring leads to an increase of the plasma sheet thickness near the Earth but does not significantly affect the cross‐tail variation. Nonuniform boundary flaring with a flattening of the tail, corresponding to a more significant increase of the tail radius in y, can reduce the plasma sheet thickening from midnight to the tail flanks or even reverse it to a thinning. The explicit solutions illustrate the effects on the tail structure of both the instantaneous force balance between the magnetosphere and the solar wind and the history of this interaction, which affects the plasma and magnetic flux distribution inside the magnetotail.
Heliopause stability in the presence of neutral atoms: Rayleigh‐Taylor dispersion analysis and axisymmetric MHD simulations
Authors: Florinski V. , Zank G. P. , Pogorelov N. V.
Published: July 2005

The heliopause, a surface separating the tenuous hot heliosheath flow and the dense, magnetized interstellar flow, is subject to instabilities of the Rayleigh‐Taylor and Kelvin‐Helmholtz types. The dynamic properties of this discontinuity is of considerable importance for understanding the neutral atom and cosmic ray filtration at the interface. Here we investigate the stability of the upwind segment of the heliopause in the presence of charge exchange collisions using both an analytic (dispersion relation) approach and a numerical model that includes the interstellar magnetic field. Linear analysis yields dispersion relations that admit imaginary solutions for a range of wave numbers, implying that the stagnation point on the heliopause is Rayleigh‐Taylor unstable to small perturbations propagating parallel to the discontinuity surface. Effects of interstellar and heliosheath atoms are analyzed separately. We confirm our analytic results by performing time‐dependent numerical simulations of the nonlinear development of this instability using a multifluid MHD‐neutral approach. For typical solar wind and LISM conditions we obtain cyclical evolution of the upwind heliopause with a period of about 100 years. The amplitude of these oscillations is found to be dependent on the presence of hot heliosheath neutrals. We discuss the effect of a strong LISM magnetic field on the heliopause stability and possible implications of the obtained instability on the X‐ray emission and cosmic ray transport in the outer heliosphere.
On the magnetic field fluctuations during magnetospheric tail current disruption: A statistical approach
Authors: Consolini Giuseppe , Kretzschmar Matthieu , Lui Anthony T. Y. , Zimbardo Gaetano , Macek Wieslaw M.
Published: July 2005

The objective of this study is to investigate the nature of the magnetic field relaxation process associated with tail current disruption on the basis of magnetic field measurements collected in the near‐Earth tail regions. In detail, using magnetic field data for three current disruption (CD) events as observed by AMPTEE/CCE spacecraft, we investigate the scaling features of the probability distribution functions (PDFs) of the magnetic field fluctuations at different timescales τ. The PDFs of magnetic field fluctuations in non‐MHD domain (i.e., below the proton gyroperiod) show non‐Gaussian tails and the probability of return Pτ(0) scales in this domain as τ−α with α > 1/2, which is compatible with a Lévy statistics. Conversely, the scaling of the PDFs of the CD magnetic fluctuations in the magnetohydrodynamic (MHD) regime is compatible with a classical Brownian motion α ∼ 1/2. These findings are discussed in terms of an anomalous diffusion process, involving the magnetic field relaxation during CD. Furthermore, the relevance of these results of a non‐Gaussian statistics at the shorter timescales is discussed in connection with the non‐MHD nature of the CD phenomenon.
Assessment of ERS synthetic aperture radar wave spectra retrieved from the Max‐Planck‐Institut (MPI) scheme through intercomparisons of 1 year of directional buoy measurements
Authors: Violante‐Carvalho N. , Robinson I. S. , Schulz‐Stellenfleth J.
Published: July 2005

One year of directional buoy measurements comprising the period from May 1994 to April 1995 acquired in deep ocean waters by an offshore heave‐pitch‐roll buoy are used for the assessment of the directional wave spectra retrieved from synthetic aperture radar (SAR) images using the Max‐Planck‐Institut (MPI) scheme. SAR is the only sensor so far deployed from satellites that can provide measurements of the directional wave spectrum with high spatial and temporal coverage when operating in the so‐called SAR wave mode. Millions of SAR wave mode imagettes have been and are still being acquired over all oceanic basins yielding a powerful data set for investigating wind waves. However, directional spectral information retrieved from SAR images has not yet been assessed against in situ measurements. For the first time, detailed validations of the main wave parameters, that is, significant wave height, mean direction of propagation, and mean wavelength, are performed. It is shown that in terms of these parameters the first‐guess spectra taken from the wave model WAM are in better agreement with the buoy measurements than the MPI scheme retrievals. When considering only the longer waves in the part of the spectrum observed by SAR, on the other hand, the algorithm performs at least as well as the third‐generation WAM wave model. In addition to the limitations of the MPI scheme in extending the spectral information beyond the high wave number cut‐off, an observed misinterpretation of wind sea energy as swell by the MPI scheme is shown to be caused by the use of a quasi‐linear approximation of the imaging model in the numerical iteration procedure.
Flow and sediment transport induced by tide propagation: 1. The flat bottom case
Authors: Blondeaux P. , Vittori G.
Published: July 2005

A model is formulated to describe the flow field locally induced by the propagation of a tidal wave and to evaluate the sediment transport. The three‐dimensional Reynolds averaged momentum equations are considered, and Coriolis terms are retained since they affect the tide propagation. Turbulent Reynolds stresses are described by means of the Boussinesq assumption, and the eddy viscosity is assumed to be an assigned function of the distance from the sea bed. The effects of wind waves on sediment transport are taken into account, and both the bed load and the suspended load are computed. A comparison of the obtained results with laboratory data and field measurements shows that the model provides a reliable and accurate description of both the velocity field and sediment transport and does not require high computational costs.
Calcium carbonate measurements in the surface global ocean based on Moderate‐Resolution Imaging Spectroradiometer data
Authors: Balch W. M. , Gordon Howard R. , Bowler B. C. , Drapeau D. T. , Booth E. S.
Published: July 2005

We describe a two‐band algorithm for the remote quantification of the ocean's suspended calcium carbonate (also known as particulate inorganic carbon (PIC)), based on normalized water‐leaving radiance at 440 and 550 nm. We tested this algorithm using ship‐derived and satellite‐derived results from a variety of marine environments. From this validation work we calculated the overall accuracy of the satellite‐based PIC estimates, assuming different timescales and space scales for binning. After performing the validation work we applied the two‐band algorithm to water‐leaving radiance data from 2002, sampled by Moderate‐Resolution Imaging Spectroradiometer (MODIS)/Terra (a 36‐band satellite spectrometer designed to observe land, ocean, and atmosphere), and we derived seasonal, global maps of the standing stock of pelagic PIC as well as particulate organic carbon (POC). These data, along with limited observations on the turnover time of calcium carbonate coccoliths in the euphotic zone, provide some new insights into global rates of pelagic calcite production.
Patterns of recent sea level rise in the East/Japan Sea from satellite altimetry and in situ data
Authors: Kang Sok Kuh , Cherniawsky J. Y. , Foreman M. G. G. , Min Hong Sik , Kim Cheol‐Ho , Kang Hyoun‐Woo
Published: July 2005

Patterns of recent sea level rise in the East/Japan Sea (EJS) are investigated through the analyses of TOPEX/Poseidon (T/P) sea level anomalies, thermosteric sea level (TSL), and long‐term tide gauge data. The 9‐year‐long T/P analyses reveal average trends of 5.4 ± 0.3 mm yr−1 for all of EJS and 6.6 ± 0.4 mm yr−1 for the southern EJS. These are much larger than the global rates of 3.1 ± 0.4 mm yr−1 reported by Cabanes et al. (2001) and 2.8 ± 0.4 mm yr−1 by Cazenave and Nerem (2004). This T/P rate compares relatively well with those from TSL data and tidal sea level gauges, indicating that sea level rise in the EJS is mainly due to thermal expansion. The southern EJS shows a nonuniform sea level trend pattern, with the western part of the Ulleung and Yamato Basins having values of 10 mm yr−1 and larger. This nonuniform pattern is discussed in terms of variable thermal expansions arising from a recent decadal trend in the temperature anomaly in the upper layer of the two basins. The 40‐year‐long TSL time series also reveals a decadal oscillation in the Ulleung and Yamato Basins that can be explained by interannual to decadal variations in temperature in the upper ocean layers, with weaker anomalies at most of the other EJS locations. It is hypothesized that the long‐term oscillation in the southern EJS may be related to the decadal variability of heat content anomaly in the upper 300 m of the Pacific Ocean, as reported by Levitus et al. (2000), and to the north‐south migration of the Warm Tsushima Current and eddies in the southern EJS.
A 1 year sea surface heat budget in the northeastern Atlantic basin during the POMME experiment: 1. Flux estimates
Authors: Caniaux G. , Brut A. , Bourras D. , Giordani H. , Paci A. , Prieur L. , Reverdin G.
Published: July 2005

The aim of the Programme Océan Multidisciplinaire Méso Echelle (POMME) was to study the formation and subduction of 11°–13°C waters in the northeast Atlantic (21°–15°W and 38°–45°N). An extensive oceanic and atmospheric data set was collected over 1 year during the period September 2000–October 2001. Owing to the importance of energy and water exchanges between the top layers of the ocean and the atmosphere in the subduction process, a surface heat, freshwater, and momentum budget has been computed combining the use of satellite products, in situ data, and atmospheric model outputs. This data set has been compared and validated with observations collected from a moored buoy and an instrumented mast onboard a research vessel. Each component of the net heat, freshwater, and momentum flux has been individually evaluated, and turbulent fluxes were computed with a state‐of‐the‐art bulk flux algorithm deduced from turbulence measurements made during the experiment. We have adopted a 5 km grid spacing to take into account the oceanic mesoscale variability. The annual domain‐averaged heat flux is positive (+33 W m−2), indicating a heating of the ocean, whereas model estimates (European Centre for Medium‐Range Weather Forecasts (ECMWF) and the French operational weather forecast model, ARPEGE) indicate a negative (cooling) budget (−9 W m−2 and −25 W m−2, respectively). Sensitivity tests of the parameterization used and the sea surface temperature used place the accuracy of the budget to about 10 W m−2. The freshwater budget is negative, implying a freshening of the ocean, as in the ECMWF model. Our assessment proves that sea surface temperature patterns condition the mesoscale patterns of the heat budget, a feature that is not reproduced by models.
Vertical particle flux in the northeast Atlantic Ocean (POMME experiment)
Authors: Guieu C. , Roy‐Barman M. , Leblond N. , Jeandel C. , Souhaut M. , Le Cann B. , Dufour A. , Bournot C.
Published: July 2005

In the framework of the Programme Océan Multidisciplinaire Méso Echelle (POMME) experiment, a 1.5 year record (February 2001–June 2002) of downward particle flux at 400 m and 1000 m was measured by sediment traps at four moorings located in the northeast Atlantic between 39°–43°N and 17°–19°W. Thorium‐230 was used to estimate sediment trap efficiency, revealing values ranging from 18.5 to 55%. The lowest trapping efficiency was observed for the trap having experienced the highest currents. Significant interannual variability between 2001 and 2002 was clearly linked to the differences observed in the mixed layer depth. At some sites, particulate organic carbon (POC) export was higher (up to a factor of 1.6) during summer than during the spring event. This could be related to the occurrence of short wind events that deepened the thermocline along with the presence of anticyclonic eddies, yielding an input of new nutrients. The average percentage of POC exported compared to the primary production of organic carbon in the surface waters ranged between 1.3 and 5.0%, with higher export efficiency during the spring. Finally, although the area was shown to present a relatively high mesoscale activity that might impact the geochemistry, POC export was rather homogeneous over the POMME area: 4.9 ± 1.6 gC m−2 yr−1 were exported below 1000 m between February 2001 and February 2002. Therefore a large fraction of the new production may be exported through convection and mode water circulation rather than by particle settling.
A 1 year sea surface heat budget in the northeastern Atlantic basin during the POMME experiment: 2. Flux optimization
Authors: Caniaux G. , Belamari S. , Giordani H. , Paci A. , Prieur L. , Reverdin G.
Published: July 2005

Gridded air‐sea fluxes were computed during a 1 year period by applying a synthesis approach (Caniaux et al., 2005) as part of the Programme Océan Multidisciplinaire Méso Echelle (POMME) (September 2000–October 2001 in the northeast Atlantic 21°–15°W, 38°–45°N). In the present paper we address the question of adjusting the precipitation and turbulent surface fluxes so that the corresponding heat, salt, and momentum budgets are in agreement with the evolution of the thermal and salt contents deduced from the data collected during the experiment. The proposed method is based on the one‐dimensional modeling of the whole POMME area by solving specific temperature and salinity equations (including advective terms) and on the optimization of adjustable coefficients with a genetic algorithm. Adjusted fluxes allow us to simulate the average sea surface temperature and salinity with errors less than 0.02°C and 0.02 psu, respectively, over 1 year. The corresponding new surface heat budget indicates that the adjusted annual net heat (+17 W m−2) is weaker than previously calculated (+33 W m−2) but remains positive, meaning a heat gain for the ocean. The adjusted annual salt budget reveals a net evaporation of 0.75 mm d−1 for the POMME region. In contrast with climatology we find that the zone is located southward of the null buoyancy flux area during September 2000–September 2001.
A 1 year mesoscale simulation of the northeast Atlantic: Mixed layer heat and mass budgets during the POMME experiment
Authors: Giordani H. , Caniaux G. , Prieur L. , Paci A. , Giraud S.
Published: July 2005

A simplified oceanic model is used to perform a realistic yearlong simulation to study fine‐scale mixed layer processes in an area of the northeast Atlantic (21°–15°W, 38°–45°N) during the Programme Océan Multidisciplinaire Méso Echelle (POMME) experiment (September 2000–October 2001). This simplified three‐dimensional oceanic model is obtained by degenerating the primitive equations system by prescribing continuously analysis‐derived geostrophic currents Ug (called “guide”) into the momentum equation by the substitution of the horizontal pressure gradient. The realism of the simulated mesoscale structures was validated by a comparison with in situ mesoscale and submesoscale data and results from the geostrophic adjustment to the guide. With this adjustment being applied at all scales, this model was able to simulate energetic small horizontal scales taking place around stirring eddies and frontal regions. Moreover, filamentary mixed layer depth structures were simulated and correlated to intense vertical velocities confined in the mixed layer. The circulation structure during POMME consisted of three quasi‐permanent mesoscale eddies and a front. The mixed layer heat and mass budgets were thus strongly driven by the horizontal advection and the vertical transport associated with this mesoscale circulation. Although no effective detrainment or entrainment occurred at the domain scale, three regions were found to be the site of intense detrainment (around anticyclonic and cyclonic mesoscale eddies and along an axis of strong currents), in which the lateral induction and the vertical velocity at the mixed layer base are the major components driving the detrainment, respectively.
Large‐eddy simulations of the semidirect aerosol effect in shallow cumulus regimes
Authors: Johnson B. T.
Published: July 2005

This study investigates the influence of absorbing aerosols on marine boundary layer clouds using large‐eddy simulations. The study focuses on two different shallow cumulus cloud regimes: an intermediate trade wind cumulus regime with moderate cloud fraction (0.1–0.5) and a pure trade wind cumulus regime with low cloud fraction (0.05–0.2). An absorbing aerosol mixture was used that reflected the polluted conditions observed during the Indian Ocean Experiment. The aerosol layer had a midvisible optical depth of 0.4 and single scattering albedo of 0.88. Simulations with these aerosol conditions are then compared with aerosol‐free simulations to calculate direct and semidirect forcings associated with changes in cloud fraction and liquid water path. In the intermediate trade cumulus regime the aerosol heating reduced the daytime cloud fraction by about 10%. This led to a semidirect radiative forcing of 8 W m−2, which almost canceled the negative direct radiative forcing of the aerosol (−10 W m−2). However, in the pure trade cumulus regime the daytime cloud fraction was reduced by less than 2%, and the semidirect radiative forcing was just 2 W m−2. Hence this study demonstrates that the semidirect aerosol effect is highly dependent on cloud regimes.