Radiative heating of carbonaceous near-Earth objects as a cause of thermal metamorphism for CK chondrites

Metamorphic CK carbonaceous chondrites display matrix textures that are best explained by a transient thermal event with temperatures in the 550–950 K range and durations in the order of days to years, longer than what is commonly admitted for shock events but shorter than what is required for nuclide decay. We propose that radiative heating of small carbonaceous meteoroids with perihelia close to the Sun could account for the petrological features observed in CK chondrites. Numerical thermal modeling, using favorable known NEOs orbital parameters (perihelion distances between 0.07 and 0.15 AU) and physical properties of CV and CK chondrites (albedo in the range 0.01–0.1, 25% porosity, thermal diffusivity of 0.5–1.5 W m^?1 K^?1), shows that radiative heating can heat carbonaceous meteoroids in the meter size range to core temperatures up to 1050 K, consistent with the metamorphic temperatures estimated for CK chondrites. Sizes of known CV and CK chondrites indicate that all these objects were small meteoroids (radii from a few cm to 2.5 m) prior to their atmospheric entry. Simulations of dynamic orbits for NEO objects suggest that there are numerous such bodies with suitable orbits and properties, even if they are only a small percentage of all NEOs. Radiative heating would be a secondary process (superimposed on parent-body processes) affecting meteoroids formed by the disruption of an initially homogeneous CV3-type parent body. Different petrologic types can be accounted for depending on the sizes and heliocentric distances of the objects in such a swarm.     

Contamination and Sources Identification of Polycyclic Aromatic Hydrocarbons in Water and Sediments of Annaba Bay Basin,Algeria

Water Resources - Annaba gulf is a coastal area (southwestern Mediterranean Sea) that receives large diffuse inputs from Fertial plant, Seybouse wadi and Boujemaâ wadi, which are influenced by...     

Is the soil moisture precipitation feedback enhanced by heterogeneity and dry soils? A comparative study

The interaction between the land surface and the atmosphere is a crucial driver of atmospheric processes. Soil moisture and precipitation are key components in this feedback. Both variables are intertwined in a cycle, that is, the soil moisture – precipitation feedback for which involved processes and interactions are still discussed. In this study the soil moisture – precipitation feedback is compared for the sempiternal humid Ammer catchment in Southern Germany and for the semiarid to subhumid Sissili catchment in West Africa during the warm season, using precipitation datasets from the Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS), from the German Weather Service (REGNIE) and simulation datasets from the Weather Research and Forecasting (WRF) model and the hydrologically enhanced WRF-Hydro model. WRF and WRF-Hydro differ by their representation of terrestrial water flow. With this setup we want to investigate the strength, sign and variables involved in the soil moisture – precipitation feedback for these two regions. The normalized model spread between the two simulation results shows linkages between precipitation variability and diagnostic variables surface fluxes, moisture flux convergence above the surface and convective available potential energy in both study regions. The soil moisture – precipitation feedback is evaluated with a classification of soil moisture spatial heterogeneity based on the strength of the soil moisture gradients. This allows us to assess the impact of soil moisture anomalies on surface fluxes, moisture flux convergence, convective available potential energy and precipitation. In both regions the amount of precipitation generally increases with soil moisture spatial heterogeneity. For the Ammer region the soil moisture – precipitation feedback has a weak negative sign with more rain near drier patches while it has a positive signal for the Sissili region with more rain over wetter patches. At least for the observed moderate soil moisture values and the spatial scale of the Ammer region, the spatial variability of soil moisture is more important for surface-atmosphere interactions than the actual soil moisture content. Overall, we found that soil moisture heterogeneity can greatly affect the soil moisture – precipitation feedback.     

Role of reservoir regulation and groundwater feedback in a simulated ground-soil-vegetation continuum: A long-term regional scale analysis

The regional terrestrial water cycle is strongly altered by human activities. Among them, reservoir regulation is a way to spatially and temporally allocate water resources in a basin for multi-purposes. However, it is still not sufficiently understood how reservoir regulation modifies the regional terrestrial- and subsequently, the atmospheric water cycle. To address this question, the representation of reservoir regulation into the terrestrial component of fully coupled regional Earth system models is required. In this study, an existing process-based reservoir network module is implemented into NOAH-HMS, that is, the terrestrial component of an atmospheric–hydrologic modelling system, namely, the WRF-HMS. It allows to quantitatively differentiate role of reservoir regulation and of groundwater feedback in a simulated ground-soil-vegetation continuum. Our study focuses on the Poyang Lake basin, where the largest freshwater lake of China and reservoirs of different sizes are located. As compared to streamflow observations, the newly extended NOAH-HMS slightly improves the streamflow and streamflow duration curves simulation for the Poyang Lake basin for the period 1979–1986. The inclusion of reservoir regulation leads to major changes in the simulated groundwater recharges and evaporation from reservoirs at local scale, but has minor effects on the simulated soil moisture and surface runoff at basin scale. The performed groundwater feedback sensitivity analysis shows that the strength of the groundwater feedback is not altered by the consideration of reservoir regulation. Furthermore, both reservoir regulation and groundwater feedback modify the partitioning of the simulated evapotranspiration, thus affecting the atmospheric water cycle in the Poyang Lake region. This finding motivates future research with our extended fully coupled atmospheric–hydrologic modelling system by the community.     

Molecular study of insoluble organic matter in Kainsaz CO3 carbonaceous chondrite: Comparison with CI and CM IOM

Abstract— Kainsaz CO3 insoluble organic matter (IOM) was studied using Curie point pyrolysis, electronic paramagnetic resonance (EPR), and high‐resolution transmission electron microscopy (HRTEM) to determine the effect of thermal metamorphism on molecular chondritic fingerprints. Pyrolysis released a very low amount of products that consist of one‐ and two‐ring aromatic units with methyl, dimethyl, and ethyl substituents. Moreover, Kainsaz IOM contains two orders of magnitude fewer radicals than Orgueil, Murchison, and Tagish Lake IOM. In addition, no diradicaloids were found in Kainsaz, although they are thought to constitute a specific signature for weakly organized extraterrestrial organic compounds in contrast to terrestrial ones. HRTEM reveals a very heterogeneous structure, with microporous disordered carbon, mesoporous graphitic carbons and graphite. Graphitization likely occurs and explains the differences between Kainsaz and CI or CM IOM. Heating stress experienced by Kainsaz IOM, on the parent body and/or prior its accretion, is likely responsible for the differences in molecular and structural organizations compared with those of CI and CM IOM.     

The information system of the French Peatland Observation Service: Service National d'Observation Tourbières – A valuable tool to assess the impact of global changes on the hydrology and biogeochemistry of temperate peatlands through long term monitoring

Mitigating and adapting to global changes requires a better understanding of the response of the Biosphere to these environmental variations. Human disturbances and their effects act in the long term (decades to centuries) and consequently, a similar time frame is needed to fully understand the hydrological and biogeochemical functioning of a natural system. To this end, the ‘Centre National de la Recherche Scientifique’ (CNRS) promotes and certifies long-term monitoring tools called national observation services or ‘Service National d'Observation’ (SNO) in a large range of hydrological and biogeochemical systems (e.g., cryosphere, catchments, aquifers). The SNO investigating peatlands, the SNO ‘Tourbières’, was certified in 2011 ( https://www.sno-tourbieres.cnrs.fr/ ). Peatlands are mostly found in the high latitudes of the northern hemisphere and French peatlands are located in the southern part of this area. Thus, they are located in environmental conditions that will occur in northern peatlands in coming decades or centuries and can be considered as sentinels. The SNO Tourbières is composed of four peatlands: La Guette (lowland central France), Landemarais (lowland oceanic western France), Frasne (upland continental eastern France) and Bernadouze (upland southern France). Thirty target variables are monitored to study the hydrological and biogeochemical functioning of the sites. They are grouped into four datasets: hydrology, fluvial export of organic matter, greenhouse gas fluxes and meteorology/soil physics. The data from all sites follow a common processing chain from the sensors to the public repository. The raw data are stored on an FTP server. After operator or automatic processing, data are stored in a database, from which a web application extracts the data to make them available ( https://data-snot.cnrs.fr/data-access/ ). Each year at least, an archive of each dataset is stored in Zenodo, with a digital object identifier (DOI) attribution ( https://zenodo.org/communities/sno_tourbieres_data/ ).     

Radionuclides produits par le rayonnement cosmique dans la météorite Saint-Séverin

]The activities of 18 radionuclides in 4 samples from the Saint-Séverin meteorite have been measured after chemical separation. The results show that the DI sample from the D piece has been less irradiated than the samples B₂, B₃ and B₄ from the B piece. This is based on activities of isotopes produced both by spallation as ²⁶Al, ⁵³Mn, ⁵⁴Mn, ⁵⁵Fe, ⁵⁷Co and by thermal neutron capture as ⁵⁹Ni and ⁶⁰Co.Comparison of experimental values to calculated production rates suggests that the D piece was connected to the main body of the meteorite by a small surface, and that the DI sample in this piece was opposite to the main body of the meteorite.     

Zur Entwicklung der luftelektrischen Grundanschauungen

Zusammenfassung Die luftelektrischen Grundanschauungen haben im Laufe der Entwicklung mehrfach erhebliche Wandlungen durchgemacht. Auf die Entwicklungsperiode, in der man die auffallenden Parallelen im Verhalten luftelektrischer und meteorologischer Größen aufzuklären sich bestrebte — sie findet etwa mitF. Exner ihr Ende—, folgt eine Phase bewußter Emanzipation der luftelektrischen Forschung, während der man in den meteorologischen Einflüssen nur Störungen sieht. Etwa in den zwanziger Jahren beginnt dann eine Reaktion gegen dieses Isolationsbestreben und mit der früher lange vergeblich versuchten Aufklärung des luftelektrischen Grund- und Existenzproblems leitet sich eine neue Entwicklungsphase ein, die man sinngemäß als korrelative Phase bezeichnen möchte. Nach einer eingehenden und nach den inneren gründen dieser mehrmaligen Schwenkung suchenden Darstellung wird im zweiten Teil der vorliegenden Arbeit das Problem der luftelektrischen Tagesgänge behandelt und als Beweis für die komplexe elektro-meteorologische Arbeits- und Betrachtungsweise in seinen neuesten Entwicklungen kurz dargestellt. Die enge Verbindung zwischen dem luftelektrischen Geschehen und dem vertikalen atmosphärischen Massenaustausch legt die Benutzung luftelektrischer Untersuchungen in der Austausch-und Luftkörperforschung nahe.

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Summary In the course of the development the fundamental notions about atmospheric electricity have experienced considerable changes. In a first period expiring about withF. Exner, one tried to explain the striking parallels of electrical and meteorological phenomena; then follows a period with a distinct emancipation of atmospheric electricity, where meteorological influences were admitted but as perturbations. In the twenties begins a reaction to this isolationist views and a new evolution starts which might be called correlative phase. The author analyses and explains these repeated changes, and in a second part he discusses the problem of the diurnal variation of atmospheric electricity and shows the complexity of electro-meteorological relations. The close connexion between the phenomena of atmospheric electricity and the turbulent vertical exchange urges to employ investigations of atmospheric electricity for investigations in exchange and air-mass research.

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Résumé En matière d'électricité atmosphérique les points de vue ont souvent varié considérablement. Dans une première période allant jusqu'àF. Exner environ, on a essayé d'expliquer le parallélisme évident entre les phénomènes électriques et météorologiques; puis on a envisagé les premiers pour eux-mêmes, indépendamment des influences météorologiques considérées alors comme des «perturbations». Autour des années 1920, une réaction se dessine contre cette discrimination, et une nouvelle phase commence que l'on pourrait appeler corrélative. Après une analyse approfondie de ces fluctuations de la théorie, l'auteur aborde dans la deuxième partie de son étude le problème des variations diurnes des phénomènes électriques et montre la complexité des relations les unissant à ceux de l'atmosphère ellemême. La liaison étroite entre les phénomènes de l'électricité atmosphérique et les échanges turbulents de masse dans la verticale prouve l'utilité des recherches électriques pour l'étude de cet échange et pour celle des masses d'air de l'atmosphère.

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Mit 14 Textabbildungen.

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Herrn Prof. Dr.H. Benndorf zum 80. Geburtstag gewidmet.     

Zur Entwicklung der luftelektrischen Grundanschauung

Ohne Zusammenfassung     

Luftelektrische Tagesgänge und Massenaustausch im Hochgebirge der Alpen

Zusammenfassung Es wird über die Ergebnisse luftelektrischer Untersuchungen auf dem Jungfraujoch (Schweiz) und ihre Deutung berichtet. Während zweier Meßperioden von je mehrwöchiger Dauer wurden das luftelektrische Potentialgefälle und der vertikale Leitungsstrom registriert; bearbeitet sind zunächst die Tagesgänge an klaren Tagen mit Hochdruckwetter. Die Tagesvariationen der drei luftelektrischen Elemente: Potentialgefälle, Vertikalstrom und Leitfähigkeit zeigen, daß auf dem Jungfraujoch im Sommer und im Herbst zwei ganz verschiedene Typen des luftelektrischen Verhaltens zu erkennen sind: Im Sommer herrscht auch an dieser Höhenstation der von den Tieflandstationen bekannte Typ vor, bei dem das Potentialgefälle angenähert invers zur Leitfähigkeit und zum Vertikalstrom verläuft. Im Herbst dagegen verlaufen Potentialgefälle und Vertikalstrom im wesentlichen gleichsinnig bei gegensinniger, aber schwächer ausgeprägter Tagesvariation der Leitfähigkeit. Im Sommer herrscht also auch in Jungfrauhöhe in den Alpen derkontinentale Typ, während sich im Herbst die Verhältnisse demozeanischen Typ annähern. Eine genauere Analyse ergibt, daß im Sommer die Tagesvariation desSäulenwiderstandes (columnar resistance) über dem Jungfraujoch in enger Korrelation zum örtlichen Widerstand der Luft an der Meßstelle (Reziprokwert der Leitfähigkeit) steht, während dies im Herbst nicht mehr der Fall ist.Zur Deutung dieser Feststellungen ist folgendes anzunehmen: Im Hochsommer wirkt die Tagesschwankung des vertikalen Massenaustausches aerosolverändernd bis in die Höhe des Alpenkammes, erkennbar daran, daß die Steuerung der luftelektrischen Tagesvariationen im wesentlichen von den unteren Schichten her erfolgt. Im Herbst dagegen ist dieser Einfluß in Kammhöhe der Alpen nahezu geschwunden; die Austauschvariation dringt nicht mehr bis in diese Höhen vor. Die verbleibenden Variationen der Leitfähigkeit deuten auf advektiven Luftaustausch hin. Das Verhalten des Dampfdruckes auf dem Jungfraujoch im Sommer und Herbst stützt diese Deutung.

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Summary The present paper gives an account of researches on atmospheric electricity carried out at Jungfraujoch (Switzerland). During two periods of several weeks each the potential gradient and the vertical air-earth current have been recorded. In the first place the diurnal variations on fine days at high pressure weather situation are elaborated. The daily variations of the three elements: potential gradient, vertical current, and conductivity, show that in summer and autumn two different types of the conditions of atmospheric electricity can be discerned: In summer the well-known type of the lowland stations is predominating also at this high altitude station, the type where the potential gradient is very nearly inverse to conductivity and vertical current. In autumn on the contrary the potential gradient and the vertical current are essentially parallel since the conductivity shows a slight diurnal variation in contrary sense. Thus, in summer prevails at the altitude of Jungfraujoch in the Alps thecontinental type, whilst in autumn the conditions approach to theoceanic type. It results from a rigorous analysis that in summer the diurnal variation of thecolumnar resistance on Jungfraujoch is in close correlation to the local air resistance (the reciprocal figure of conductivity) at the measuring point, whereas in autumn this is no longer the case.To explain these results we must assume as follows: In midsummer the diurnal variation of vertical mass exchange produces alterations of the aerosol up to the altitude of the crest of the Alps, which is perceptible from the fact that diurnal variations of atmospheric electricity start essentially from the lower layers. In autumn this influence has almost disappeared in the summit altitude of the Alps, as the daily variation of exchange does not advance to this altitude. The remaining variations of the conductivity point at an advective exchange of air. The behaviour of vapour pressure in summer and autumn at Jungfraujoch gives support to this interpretation.

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Résumé L'article traite des résultats de recherches d'électricité atmosphérique au Jungfraujoch (Suisse) et de leur interprétation. Deux périodes de mesures de plusieurs semaines chacune ont été consacrées à l'enregistrement du gradient de potentiel et du courant vertical. On décrit tout d'abord la variation diurne lors des jours sereins de temps anticyclonique. On distingue an Jungfraujoch en été et en automne respectivement deux types très différents de la marche diurne du gradient de potentiel, du courant vertical et de la conductibilité. En été le type bien connu des stations de plaine pour lequel le gradient de potentiel varie à peu près inversement à la conductibilité et au courant vertical s'observe aussi au Jungfraujoch. Par contre en automne le gradient de potentiel et le courant vertical varient en général dans le même sens, tandis que la conductibilité varie, elle, en sens contraire, bien que faiblement. Il y a donc à l'altitude du Jungfraujoch en été le «type continental», alors qu'en automne les conditions se rapprochent du «type océanique». Une analyse plus détaillée montre qu'en été la variation diurne de la «résistance tubulaire» (columnar resistance) au-dessus du Jungfraujoch est en liaison étroite avec la résistance locale de l'air au point de mesure (inverse de la conductibilité), tandis qu'en automne ce n'est plus le cas.Pour interpréter ces résultats il faut admettre ce qui suit: En été la variation diurne de l'échange vertical turbulent modifie les aérosols jusqu'au niveau de la crête alpine, ce que l'on reconnaît au fait que les variations diurnes des phénomènes d'électricité atmosphérique sont largement conditionnés par les couches basses. En automne par contre cet effet a disparu sur les Alpes, car la variation de l'échange turbulent n'a plus d'influence à ce niveau. La variation de la conductibilité qui subsiste suggère un échange d'air par advection. L'allure de la pression de vapeur d'eau au Jungfraujoch en été et en automne confirme cette hypothèse.

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Mit 11 Textabbildungen.