Measuring electron density in coronal active regions

In order to study the electron density at the scale of the most encountered structures in coronal active regions a new multichannel coronagraph associated with a photoelectric spectrograph is now used at the Pic-du-Midi Observatory. In its quasi-routine mode this instrument, which is described in this paper, works with a 30 field aperture in a parallel manner with aK-polarimeter. On each observed region it obtains maps of intensities of the 3388, 10747, and 10798 Å emission lines due to Fexiii ion. Each measurement point is associated with a quasi-simultaneous image of the emission corona structures viewed in the light of the5303 Å line of Fexiv. Three examples of observations are given and the capabilities are discussed.Measuring electron density in coronal active regions. II A multichannel photoelectric coronagraph with a photo-electric spectrograph and a reflex monitor at5303 Å.LA du CNRS No. 040285.     

Export stoichiometry and migrant-mediated flux of phosphorus in the North Pacific Subtropical Gyre

Export processes play a major role in regulating global marine primary production by reducing the efficiency of nutrient cycling and turnover in surface waters. Most studies of euphotic zone export focus on passive fluxes, that is, sinking particles. However, active transport, the vertical transfer of material by migrating zooplankton, can also be an important component of carbon (C) and nitrogen (N) removal from the surface ocean. Here we demonstrate that active transport is an especially important mechanism for phosphorus (P) removal from the euphotic zone at Station ALOHA (Hawaii Ocean Time-series program; 22°45′N, 158°W), a P-stressed site in the North Pacific Subtropical Gyre. Migrant excretions in this region are P-rich (C₅₁:N₁₂:P₁) relative to sinking particles (C₂₅₀:N₃₁:P₁), and migrant-mediated P fluxes are almost equal in magnitude (82%) to P fluxes from sediment traps. Migrant zooplankton biomass and therefore the importance of this P removal pathway relative to sinking fluxes has increased significantly over the past 12 years, suggesting that active transport may be a major driving force for enhanced P-limitation of biological production in the NPSG. We further assess the C:N:P composition of zooplankton size fractions at Station ALOHA (C₈₈:N₁₈:P₁, on average) and discuss migrant-mediated P export in light of the balance between zooplankton and suspended particle stoichiometries. We conclude that, because active transport is such a large component of the total P flux and significantly impacts ecosystem stoichiometry, export processes involving migrant zooplankton must be included in large-scale efforts to understand biogeochemical cycles.     

Multi-criteria spatialization of soil organic carbon sequestration potential from agricultural intensification in Senegal

On the eve of the 15th climate negotiations conference in Copenhagen, the pressure to assess all climate mitigation options is mounting. In this study, a bio-physic model and a socio-economic model were designed and coupled to assess the carbon sequestration potential of agricultural intensification in Senegal. The biophysical model is a multiple linear regression, calibrated and tested on a dataset of long-term agricultural trials established in West Africa. The socio-economic model integrates both financial and environmental costs related to considered practice changes. Both models are spatially explicit and the resulting spatial patterns were computed and displayed over Senegal with a geographic information system. The national potential from large-scale intensification was assessed at 0.65–0.83 MtC. With regards to local-scaled intensification as local projects, the most profitable areas were identified in agricultural expansion regions (especially Casamance), while the areas that meet the current financial additionality criteria of the Clean Development Mechanism were located in the northern part of the Peanut Basin. Using the current relevant mode of carbon valuation (Certified Emission Reductions), environmental benefits are small compared to financial benefits. This picture is radically changed if “avoided deforestation”, a likely consequence of agricultural intensification, is accounted for as the greenhouse gases sink capacity of projects increases by an average of a hundred-fold over Senegal.     

First insights into the structure and environmental setting of cold-seep communities in the Marmara Sea

A brackish-water cold seep on the North Anatolian Fault (NAF) in the Marmara Sea was investigated with the Nautile submersible during the MarNaut cruise in 2007. This active zone has already been surveyed and revealed evidence of active seeping on the seafloor, such as bubble emissions, patches of reduced sediments, microbial mats and authigenic carbonate crusts. MarNaut was the first opportunity to sample benthic communities in the three most common microhabitats (bioturbated and reduced sediments, carbonate crust) and to examine their relationships with environmental conditions. To do so, faunal communities were sampled and chemical measurements were taken close to the organisms. According to diversity indices, the bioturbated microhabitat exhibited the highest taxonomic diversity and evenness despite a lower number of samples. Conversely, the reduced sediment microhabitat exhibited the lowest taxonomic diversity and evenness. The carbonate crust microhabitat was intermediate although it had the highest biomass. Multivariate analyses showed that (1) fauna were relatively similar within a single microhabitat; (2) faunal community structure varied greatly between the different microhabitats; (3) there was a link between faunal distribution and the type of substratum; and (4) chemical gradients (i.e. methane, oxygen and probably sulphides) may influence faunal distribution. The estimated fluid flow velocity (0.4–0.8 m/yr) confirmed the presence of fluid emission and provided evidence of seawater convection in the two soft-sediment microhabitats. Our results suggest that the reduced sediments may represent a harsher environment with high upward fluid flow, which restrains seawater from penetrating the sediments and inhibits sulphide production, whereas bioturbated sediments can be viewed as a bio-irrigated system with sulphide production occurring at greater depths. Therefore, the environmental conditions in reduced sediments appear to prevent the colonization of symbiont-bearing fauna, such as vesicomyid bivalves, which are more often found in bioturbated sediments. Fluid flow appears to control sulphide availability, which in turn influences the horizontal and vertical distribution patterns of fauna at small spatial scales as observed at other seep sites.     

Comparison of spectral and time domain calibration methods for precipitation‐discharge processes

Hydrological model parameter estimation is an important aspect in hydrologic modelling. Usually, parameters are estimated through an objective function minimization, quantifying the mismatch between the model results and the observations. The objective function choice has a large impact on the sensitivity analysis and calibration outcomes. In this study, it is assessed whether spectral objective functions can compete with an objective function in the time domain for optimization of the Soil and Water Assessment Tool (SWAT). Three empirical spectral objective functions were applied, based on matching (i) Fourier amplitude spectra, (ii) periodograms and (iii) Fourier series of simulated and observed discharge time series. It is shown that most sensitive parameters and their optimal values are distinct for different objective functions. The best results were found through calibration with an objective function based on the square difference between the simulated and observed discharge Fourier series coefficients. The potential strengths and weaknesses of using a spectral objective function as compared to utilising a time domain objective function are discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

What is the “sign” of the atmospheric-electric field?

Summary The sign of the vector representing the atmospheric electric field has recently been subject of debate. For the sake of clarity, it is recommended to refer only to a normal or reversed clear-weather potential gradient.

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Zusammenfassung Eine in letzter Zeit entstandene Diskussion darüber, welches Vorzeichen dem Vektor des atmosphärisch-elektrischen Feldes bzw. des Potentialgefälles zuerkannt werden soll, erscheint wenig sinnvoll. Zur Vermeidung künftiger Unklarheiten wird empfohlen, bei der atmosphärischen Elektrizität nur von normaler Schönwetterrichtung und umgekehrter Schönwetterrichtung des Feldes bzw. des Potentialgefälles zu sprechen.

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Résumé Une récente discussion a porté sur le signe qui devait être attribué au vecteur du champ électrique atmosphérique respectivement de son gradient de potentiel. On recommande, pour éviter à l'avenir toute confusion, de ne parler en électricité atmosphérique et quand il s'agit du champ ou du gradient de potentiel, que de «direction normale de beau temps» et de «direction inversée de beau temps».

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Dedicated to Dr.W. Mörikofer on the occasion of his 70th birthday.     

Author index volume 36

Using the single zircon technique, two areas which give some of the oldest ages on earth have been investigated, namely the Minnesota River Valley and West Greenland.The results on single zircons from the Minnesota River Valley and from the Amîtsoq gneisses (West Greenland) do not differ significantly from the results of Farhat (1975) and Baadsgaard (1973) at about 3.3 and 3.65 b.y., respectively.The U-Pb analyses of single zircons from acid boulders from the conglomerate unit at Isua (West Greenland) yield the oldest age so far reported for a terrestrial rock, namely 3.824_?0.009^+0.012 b.y.     

The worldwide character of the 1969–1970 impulse of the secular acceleration rate

This paper continues earlier studies to ascertain whether the distribution of the 1969–1970 jump of the secular variation rate has a worldwide character. The geometry of the jump presents some similarities with the geometry of the secular variation itself. We give a new estimation of the westward drift rate and information about spatial and temporal variations of the secular variation field.     

Kondensationskerne im Rahmen der Luftelektrizität

Zusammenfassung Die Rolle der Kondensationskerne im atmosphärischen Geschehen wird besonders deutlich, wenn man sich vorstellt, wie sich dieses Geschehen ohne Kondensationskerne abspielen würde: Es käme dann auf der ganzen Erde nur der globale Anteil der atmosphärisch-elektrischen Erscheinungen zur Geltung während die Bindungen zum Wettergeschehen fehlen würden. Somit hängt also der gestaltende Einfluß des Wetters auf die elektrischen Vorgänge ursächlich mit dem Vorhandensein von Suspensionen bezw. Kondensationskernen zusammen.Die atmosphärisch-elektrischen Ereignisse sind zu verstehen aus dem Zusammenwirken von Generatoren und veränderlichen Schaltelementen. In beiden Gruppen spielen die Kondensationskerne eine entscheidende Rolle, wie im einzelnen gezeigt wird:Die bekannten Zusammenhänge zwischen dem luftelektrischen Potentialgefälle und der atmosphärischen Leitfähigkeit einerseits und meteorologischen Elementen (Luftkörper, Turbulenz, Austausch, Inversionen u.a.) andererseits sind aus den Wiedervereinigungsbeziehungen zwischen Kleinionen und Suspensionen zu verstehen. Sie gehören in die Gruppe der veränderlichen Schaltelemente.An einem in den letzten Jahren beobachteten Effekt (Anstieg von Potentialgefälle und Vertikalstrom nach Sonnenaufgang), der seinem jahreszeitlich verschiedenen und von Ort zu Ort wechselnden Verhalten entsprechend als Austauschwirkung zu deuten ist («Austausch-Generator»), wird nach umfangreichen Untersuchungen an einigen Stationen der Schweizer Alpen die Mitwirkung der Kondensationskerne demonstriert. Diese scheint darin zu bestehen, daß Raumladungsbildungen in der Atmosphäre je nach dem Vorhandensein von Kondensationskernen in stärkerem oder geringerem Maße gewissermaßen zeitlich fixiert werden, sodaß der zur Generatorwirkung notwendige Transport dieser Ladungen durch Kräfte nicht-elektrischer Natur quantitativ durch die Kernzahl beeinflußt wird.

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Summary The role of the condensation nuclei in the atmospheric electrical processes becomes especially evident if it is imagined how this process would take place without condensation nuclei: On the entire earth only the global atmospheric electrical phenomena would become effective, while the relations to the weather processes would not exist. Thus, the influence of the weather on the electric processes is causally related with the existence of suspensions, resp. condensation nuclei.The atmospheric electrical processes are to be interpreted from the co-operation of generators and variabile circuit elements. In both groups the condensation nuclei play an important part as is shown here in detail:The known relations between the atmospheric electrical potential gradient and the atmospheric conductivity on one hand and meteorological elements [air masses, turbulence, exchange (Austausch), inversions, etc.] on the other hand must be understood by the recombination relations between small ions and suspensions. They belong to the group of variable circuit elements.As an effect observed in recent years (increase of the potential gradientand the air-earth-current after sunrise) which, corresponding to its behaviour varying at the different seasons and from place to place, must be interpreted as exchange (Austausch) effect («Austausch-Generator»), the co-operation of condensation nuclei is demonstrated on the basis of comprehensive investigations at some stations of the Swiss Alps. This seems to exist in the fact that space charge formations in the atmosphere may be transfered into a more stable, longer lasting state by the interaction of the condensation nuclei to a greater or smaller extent so that the transport of these charges by nonelectric forces necessary for the generator effect is quantitatively influenced by the number of nuclei.