The Cloud Ice Mountain Experiment (CIME) 1998: experiment overview and modelling of the microphysical processes during the seeding by isentropic gas expansion

The second field campaign of the Cloud Ice Mountain Experiment (CIME) project took place in February 1998 on the mountain Puy de Dôme in the centre of France. The content of residual aerosol particles, of H₂O₂ and NH₃ in cloud droplets was evaluated by evaporating the drops larger than 5 μm in a Counterflow Virtual Impactor (CVI) and by measuring the residual particle concentration and the released gas content. The same trace species were studied behind a round jet impactor for the complementary interstitial aerosol particles smaller than 5 μm diameter. In a second step of experiments, the ambient supercooled cloud was converted to a mixed phase cloud by seeding the cloud with ice particles by the gas release from pressurised gas bottles. A comparison between the physical and chemical characteristics of liquid drops and ice particles allows a study of the fate of the trace constituents during the presence of ice crystals in the cloud.In the present paper, an overview is given of the CIME 98 experiment and the instrumentation deployed. The meteorological situation during the experiment was analysed with the help of a cloud scale model. The microphysics processes and the behaviour of the scavenged aerosol particles before and during seeding are analysed with the detailed microphysical model ExMix. The simulation results agreed well with the observations and confirmed the assumption that the Bergeron–Findeisen process was dominating during seeding and was influencing the partitioning of aerosol particles between drops and ice crystals. The results of the CIME 98 experiment give an insight on microphysical changes, redistribution of aerosol particles and cloud chemistry during the Bergeron–Findeisen process when acting also in natural clouds.     

Behaviour of H2O2, NH3, and black carbon in mixed-phase clouds during CIME

We investigated the partitioning of trace substances during the phase transition from supercooled to mixed-phase cloud induced by artificial seeding. Simultaneous determination of the concentrations of H₂O₂, NH₃ and black carbon (BC) in both condensed and interstitial phases with high time resolution showed that the three species undergo different behaviour in the presence of a mixture of ice crystals and supercooled droplets. Both H₂O₂ and NH₃ are efficiently scavenged by growing ice crystals, whereas BC stayed predominantly in the interstitial phase. In addition, the scavenging of H₂O₂ is driven by co-condensation with water vapour onto ice crystals while NH₃ uptake into the ice phase is more efficient than co-condensation alone. The high solubility of NH₄⁺ in the ice could explain this result. Finally, it appears that the H₂O₂–SO₂ reaction is very slow in the ice phase with respect to the liquid phase. Our results are directly applicable for clouds undergoing limited riming.     

The late Quaternary development of three ancient tarns on southwestern Cumberland Peninsula, Baffin Island, Arctic Canada: paleolimnological evidence from diatoms and sediment chemistry

Sediment diatom and chemical analyses of cores from three poorly buffered extra-glacial lakes on the northeastern margin of the Canadian Shield (Cumberland Peninsula, Baffin Island) record interactions between aquatic and terrestrial spheres that were influenced by late Quaternary climatic conditions. Although differences exist between each of the lakes, notably with regards to the intensity of pre-Holocene catchment erosion and the timing of the onset of organic sedimentation, an underlying pattern of lake ontogeny, common to all three lakes, is identified. Although intensified watershed erosion characterized the Late Wisconsinan and Neoglacial cold periods, the lakes nonetheless remained viable ecosystems at these times. Sudden catchment stabilization during the late-glacial to earliest Holocene is associated with incipient organic sedimentation. Lake-water pH increased at this time, likely in response both longer base cation residence times as lake flushing rates decreased, and enhanced alkalinity production from sediment biogeochemical reactions. Subsequently, as the catchments remained stable during the productive early Holocene (c.9–7 ka BP), then gradually received a renewed increase of minerogenic sedimentation, the breakdown of sources of lake alkalinity resulted in natural acidification. Burial of cation-rich mineral sediments and the loss of permanent sedimentary sinks for the products of microbial reduction likely impeded within-lake alkalinity production, and catchment-derived base cations appeared ineffective in curtailing pH declines. The general nature of the Holocene development of these lakes is similar to that observed elsewhere on crystalline terrains, following deglaciation. Our data therefore suggest that catchment glaciation is not a necessary precursor for models of lake development characterized by initial base cation enrichment and subsequent gradual acidification.     

On the causes of landslides: Human activities,perception, and natural processes

Conceptual equations are presented for the net benefits, total risk, and total vulnerability associated with hazard zone occupation. It is shown that, as they are polycausal phenomena, landslides require a more sophisticated approach to this form of analysis than that employed for most other forms of hazard.Three examples of landsliding are examined. At Cuyocuyo, in the Peruvian Cordillera Oriental, slope instability is virtually inevitable, but human intervention may be disturbing some very fragile natural equilibria. At Calciano, in southern Italy, deforestation has resulted in a mudflow disaster, although man-made factors are not the only causes at work. Finally, in the Valle dell'Orco (also in southern Italy) demographic and agrarian change have aided the partial metamorphosis of the catchment into a large-scale mudflow complex (although the longer-term causes are natural, tectonic ones). These examples illustrate parts of the continuum that extends from dominant natural to dominant anthropogenic causes.Human intervention has played a key role in stimulating the natural antecedents of landslides occurring in the study areas. It is concluded that risk perception has not been wide enough to promote adequate risk mitigation, in part because of a failure properly to conceive of landslides as polycausal phenomena, in which man-made causes effectively cannot—and should not—be separated from natural ones.     

The role of choke points in the ocean context

Choke points are narrow international waterways where three characteristics are present. The waterway should be narrow and capable of being closed off to both commercial and military snipping. There should be no readily available maritime route to utilize in the event of closure. Finally, the choke point should be of considerable significance to at least several States. This article identifies seven “primary” choke points which seem to satisfy these criteria. These are Gibraltar, Bab el Mandeb, Hormuz, the Danish and Turkish Straits, and the Suez and Panama Canals. It also identifies eleven “secondary” choke points, where at least one of the reouired characteristics is missing. The eleven include Dover, Bering and Magellan Straits, as well as Malacca-Singapore and a number of others in the Western Pacific. Turning to a consideration of the status of choke points in a Post-Cold War era, the article notes four basic assumptions: (1) the intense military rivalry between the United States and the Soviet Union will be reduced in coming years; (2) for many countries marine-related environmental concerns may be increasing considerably; (3) as the Cold War recedes, regional contests and confrontations will grow more intense; and (4) the overall densities of water-borne traffic will undergo change as the relative economic growth of regional centers changes. The article then considers the potential impact of these trends on the future role of choke points.     

Les coulées Rhyolitiques du Nideck (Permien — Vosges) sont- elles des Ignimbrites?

Zusammenfassung Die vulkanischen Gesteine des Rotliegenden des Niedecker Gebietes sind untersucht worden. Die petrographische Untersuchung erlaubt uns, diese Formationen als Ignimbrite zu bezeichnen. Die Anwesenheit eines Minerals der Montmorin-Gruppe, inmitten des Gesteines, ist mit der Ignimbritbildung, die durch die paleomagnetischen Messungen bestätigt wird, vereinbar. Die chemische Entwicklung wird skizziert.     

Zur Frage der Geschwindigkeit des Deckenschubes

Zusammenfassung In den folgenden Ausführungen werden Daten über die Geschwindigkeit der Bewegung von Schubdecken in der Hauptbewegungsphase geliefert. Die hierfür verwendeten Beispiele stammen aus den Ostalpen und Westkarpaten. Eine sichere Geschwindigkeits-Bestimmung ist derzeit noch nicht durchführbar. Es können aber Minimalbewegungswerte von etwa 1,5 mm/Jahr errechnet werden. Die reale Transportgeschwindigkeit könnte auch wesentlich höher liegen, vielleicht bei 10–20 mm/Jahr.

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This paper presents facts pertaining to the velocity of the overthrust of nappes during a tectonical phase by means of examples from the Eastern Alps and the Western Carpathians. An exact determination of this velocity is still not possible. One can calculate minimum values of near 1,5 mm/year. The real velocity of the overthrusts of nappes might be much higher, perhaps 10–20 mm/year.

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Résumé L'article expose des données sur la vitesse des mouvements des nappes de charriage pendant la phase principale de transport. Les exemples présentés proviennent des Alpes orientales et des Carpathes occidentales. Il n'est pas possible jusqu'à présent de faire une détermination plus exacte de cette vitesse. Mais on peut calculer un minimum de transport d'environ 1,5 mm/an. La vitesse réelle des mouvements de translation pourrait même être nettement plus élevée, et atteindre peut-être 10–20 mm/ an.

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. . . 1,5 /. , 10–20 /.

     

Results of deep seismic soundings along international profile VII in Czechoslovakia and poland

Summary The paper deals with the results of DSS measurements along international profile VII, carried out by Czechoslovak and Polish geophysicists in 1970 – 71. The profile situation is shown in Fig. 1. By 1971 part of the profile in the region of the Bohemian Massif between points 1 and 3 and in Poland between points 5 and 7 had been surveyed (Fig. 2). The seismograms were used to construct the travel-time curves of the fundamental types of waves P^K, P^M, P_n (Fig. 4). The mean velocities were computed from the travel-time curves of the reflected waves (P^M and P^K) and the refracted waves (P_g). Isolines of the mean velocities could be constructed for the region of the Bohemian Massif (Fig. 6). The velocity data found were used for the depth interpretation of the travel-time curves of the principal types of waves and to construct a seismic section (Fig. 8). In the region of the Pre-Sudeten block the thickness of the crust was found to be 34–37 km, and in the Sudeten it increased to 40 km. Towards the south the thickness of the crust gradually reduces to 30 km in the system of the Luice faults. In the Bohemian Cretaceous the thickness of the crust is about 30 km. Further to the south, in the region of the Moldanubicum, the thickness of the Earth's crust increases rapidly, and at the southern border of the Central Bohemian pluton it reaches values of about 42 km.